Teses em Geologia e Geoquímica (Doutorado) - PPGG/IG

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/6341

O Doutorado Acadêmico pertence ao Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).

Navegar

Agora exibindo 1 - 16 de 16

Acesso aberto (Open Access)
O Cambriano no Sudeste do Cráton Amazônico: paleoambiente, proveniência e implicações evolutivas para o Gondwana Oeste
(Universidade Federal do Pará, 2018-06-15) SANTOS, Hudson Pereira; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Transgressive events recorded in many cratonic regions marked the Cambrian period, hypothetically related to the glacioeustasy and/or the progressive opening of the Iapetus ocean (~600 Ma). Such events influenced the paleoceanography of this period, including the progressive biota evolution – the ‘Cambrian Revolution’. Although the Gondwana Supercontinent margins, entirely amalgamated in the Lower Cambrian (540 Ma), were flooded, the inner part of this supercontinent was emergent, probably triggered by postcollisional epirogenic uplifts. Epeiric seas covered subsiding areas with projections towards the interior of the Western Gondwana, developing shallow platforms that covered ancient colisional suture zones. In the southeastern Amazon Craton, the recurrence of platform environments dates from Upper Cryogenian (~635 Ma) until the Cambrian with the installation of glacial deposits, overlaid by carbonatic and siliciclastic successions. Despite the previous insertion in the context of a foreland type basin related to the evolution of North Paraguai Belt (650-640 Ma), these deposits have been included in an inverted intracratonic basin in the Ordovician. The bottommost deposits of the Cambrian sequences, here presented, are comprised dominantly by siliciclastic rocks. These consist in the Upper and Lower members of the Raizama Formation and the base of Lower Member of the Sepotuba Formation, Alto Paraguai Group, exposed in the central and northeast portions of the inverted intracratonic basin, Mato Grosso state. Two depositional sequences (DS1 and DS2) characterize the Cambrian successions of the base of Alto Paraguai Group. The DS1 presents as a sequence boundary (SB1) an erosional hiatus previously interpreted in the southwestern basin. This stratigraphic surface becomes a correlative conformity towards the central and northern portions, where this covers the Araras carbonates and Cryogenian glacial deposits from Puga diamictites. The SB1 represents an erosional or non-depositional period of approximately 80 Ma developed over the carbonates of the Lower Ediacaran Araras Group, related to the epeirogenic uplifts of the basin. A second thermal subsidence phase would have led to the installation of a siliciclastic platform during the Cambrian, characterized by DS1 composed by two facies associations denominated FA1 and FA2. FA1 consists of subarkoses, quartz-wackes and pelites dominated by wave and storm processes, inserted in the offshoretransition, lower-middle shoreface and upper shoreface zones. The presence of infaunal vertical trace fossils belonging to the Skolithos Ichnofacies (Skolithos linearis; Diplocraterion parallelum; and Arenicolites isp.) at the base of the lower-middle shoreface deposits indicated a Lower Cambrian age, or younger, to the Raizama Formation, previously considered as Ediacaran. The FA2 comprehends subarkoses, quartzarenites, sublitarenites, quartz-wackes and sandstone/pelite rhythmites interpreted as complex tidal plain deposits, unconformably overlaid (SB2) by braided fluvial channel deposits of (FA3), which belong to the DS2. The DS1 would have been deposited during lowstand to transgressive system tract, organized in progradational parasequences. This stacking pattern is not compatible with the traditional stratigraphy sequence for TST, which is attributed to a slow subsidence rate concomitantly to a high sediment supply indicated by the Skolithos Ichnofacies. Subsequently, a less expressive drop in the sea level promoted a progradation of distal braided deposits (FA3) over the DS1, related to the lowstand system tract (LST) characterized by an abrupt change of the tidal heterolitic deposits to medium and coarse-grained quartzarenites from fluvial deposits. Paleoflow data oriented preferentially to NE and SE obtained in coastal beds from FA2 and FA3 allied to the Paleo- to Mesoproterozoic U-Pb detrital zircon ages have indicated provenance exclusively from SW and NW sources from Amazon Craton. Besides that, the detrital quartz grains analysis of sandstones of the bottommost Cambrian deposits indicate mainly igneous and metamorphic sources. Previous works indicated that the fluvial deposits of DS2 were succeeded by a transgressive system tract, marking this as the last transgressive event that influenced the Cambrian deposits of the intracratonic basin. Slowly, the ocean connection was interrupted as a consequence of the closing of Iapetus Ocean (~500 Ma) as a result of basin uplift. In this way, Cambrian epeiric seas were confined and consequently started the lacustrine phase of the basin in the Ordoviacian, represented by the Diamatino Formation deposits. Posteriorly, the intracratonic basin of the southeast Amazon Craton would have been inverted by the transtensional tectonics which propitiated the implantation of post-Cambrian intracontinental basins of the Western Gondwana.
Acesso aberto (Open Access)
Evolução geológica das seqüências do embasamento na porção sul do Cinturão Araguaia - Região de Paraíso do Tocantins
(Universidade Federal do Pará, 2002-09-12) ARCANJO, Silvia Helena de Souza; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626
The basement rocks in the south segment of the Araguaia Belt, due to the scarcity of geochronological information, were firstly considered as of Archean age. This interpretation began to be reviewed after the geochronological investigations were carried out during the last decade, which showed an important contribution of geological processes of the Paleoproterozoic in the formation of those basement rocks. In this work an isotopic study was carried out on the basement sequences of the southern segments of the Araguaia Belt and its results were based on the single zircon Pb-evaporation technique (Pb-Pb in zircon) and the Sm-Nd (whole rock) systematic. These techniques were used in order to improve and reconstruct the geological evolution of this crustal segment where Rio do Coco Group, Rio dos Mangues Complex, and Serrote Granite occur, as well as Monte Santo Suite that also appear in this context. The geological processes identified for the region took place from the Archean through the Neoproterozoic Era. The first evidences from the archean source were obtained in some restricted orthoderivated bodies in the east sector of the mapped area in which the TDM ages varied between 3.25 and 2.78 Ga. In a clear way, the Archean occurs in the northwest portion of the studied area being represented by a metabasic rock belonged to the Rio do Coco Group (greenstone belt sequence), with 2.618 ± 14 Ma. This age is interpreted as the age of the extrusion of the volcanic protolith. They would represent the two crustal preterit segments found in the region. During the Paleoproterozoic the Rio dos Mangues Complex was constituted, representing the most expressive unit of the basement. Ortogneisses of the Rio dos Mangues Complex were dated and their Pb-Pb in zircon ages varied between 2.054 ± 4 Ma and 2.086 ± 16 Ma. They were formed from a mantelic and juvenile source, with a small crustal contribution and their TDM ages are between 2.35 e 2.21 Ga. The geological processes that marked this period, involved crustal shortening with the participation of collision and thrusting that induced partial fusion of some parts of the thickened crust. The results were the generation of some igneous bodies (1.85 and 1.82 Ga) and of the Serrote Granite (1.86 Ga). Although the emplacement of the Serrote Granite took place at the end of the Paleoproterozoic, it was developed from older sources (2.50 e 2.43 Ga) than those of the Rio dos Mangues Complex. So, The continental crust established, with rocks from different ages and sources may be projected to the east, far from the studied area, inside the context of the architecture from the Atlantic Super Continent, formed definitively at the end of the Paleoproterozoic. At the end of a period without tectonic registers (end of Mesoproterozoic) a new phase took place in the region marked by tafrogenetic processes as the appearing of alkaline and basic magmatism as well as depositional basins that show an extensive context along the whole area. One of these basins received the sediments that originated the Araguaia Belt Supracrustals, which, during its evaluative process, reach the proto-rifte stage. Far from here, at the north portion of Goiás Massif, this rifting process seemed to permit the constitution of an oceanic domain, that, by evolution and recycling, may have be formed the rocks of the Magmatic Arc of Goiás. At the worked area, this arc terrain could be only be predicted by the appearing of one tonalitic gneiss with the age of 840 Ma and TDM model ages of 1.83 Ga. The effects of this tafrogenetic processes, from which the most important evidences are sienitic gneisses, found at Monte Santo Suit, with 1.051 ± 17 Ma, are related to the fission processes in the whole world which made the break up of the Rodinia Super Continent possible. The protolith of this suit were also been formed during the Mesoproterozoic as they can be seen in the TDM model age between 1.49 e 1.70 Ga. Finally, passing to the Neoproterozoic, through the inversion in the geodinamic conditions, processes of horizontal shortening again took place in the region, with the participation of crustal thickening as well as distinct volumetric and spatial fusions that may have generated the Matança and Santa Luzia Granites. The last one found inside the domain of Araguaia Belt. The Araguaia Belt was built from this tectonic motion, and has registers of past structural formations, also present in the older litostructural groups. The mass tectonic transport in the Amazonian Craton way might have occurred, resulting in the actual architecture found nowadays in the form of imbricated slices.
Acesso aberto (Open Access)
Geocronologia 207Pb/206Pb, Sm-Nd, U-Th-Pb E 40Ar-39Ar do segmento sudeste do Escudo das Guianas: evolução crustal e termocronologia do evento transamazônico
(Universidade Federal do Pará, 2006-07-06) ROSA-COSTA, Lúcia Travassos da; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645
The southeastern portion of the Guiana Shield is part of a large Paleoproterozoic orogenic belt, with evolution related to the Transamazonian Orogenic Cycle (2.26 – 1.95 Ga). In this area, previous works defined distinct tectonic domains, named Jari, Carecuru and Paru, which present outstanding differences in terms of age, lithological content, structural pattern and geophysical signature. The Jari Domain is constituted of a granulite-gneiss-migmatite basement assemblage derived from Archean protoliths, and the Carecuru Domain is composed mainly of calc-alkaline rocks and metavolcano-sedimentary sequences, developed during the Transamazonian Event. The Paru Domain is an oval-shaped granulitic nucleous, located within the Carecuru Domain, formed by granulitic gneisses with Archean precursors and Paleoproterozoic charnockitic plutons. In this study, distinct geochonological methods were employed in rocks from the distinct domains, in order to define their tectonic meaning and crustal evolution processes during Archean and Paleoproterozoic times. Pb-evaporation on zircon and Sm-Nd on whole rock dating were provided on magmatic and metamorphic units from the Jari Domain, defining its long-lived evolution, marked by several stages of crustal accretion and crustal reworking. Magmatic activity occurred mainly at the Meso-Neoarchean transition (2.80-2.79 Ga) and during the Neoarchean (2.66-2.60 Ga). The main period of crust formation occurred during a protracted episode at the end of Paleoarchean and along the whole Mesoarchean (3.26-2.83 Ga). Conversely, crustal reworking processes have dominated in Neoarchean times. During the Transamazonian Event, the main geodynamic processes were related to reworking of older Archean crust, with minor juvenile accretion at about 2.3 Ga, during an early orogenic phase. Transamazonian magmatism consisted of syn- to late-orogenic granitic pulses, which were dated between 2.22 and 2.03 Ga. Most of the εNd values and TDM model ages (2.52-2.45 Ga) indicate an origin of the Paleoproterozoic granites by mixing of juvenile Paleoproterozoic magmas with Archean components. The new geochronological results, added to data from previous studies, revealed that the Jari Domain represents the southwestern part of the most expressive Archean continental landmass of the Guiana Shield, here defined and named Amapá Block. The recognition of an extended Archean block precludes previous statements that the Archean in the southeast of the Guiana Shield, was restricted to isolated remnants or inliers within Paleoproterozoic terrains. In the Carecuru Domain the widespread calc-alkaline magmatism occurred at 2.19-2.18 Ga and at 2.15-2.14 Ga, and granitic magmatism was dated at 2.10 Ga. Crustal accretion was recognized at about 2.28 Ga, in agreement with the predominantly Rhyacian crust-forming pattern of the Guiana Shield. Nevertheless, TDM model ages (2.50-2.38 Ga), preferentially interpreted as mixed ages, and εNd < 0, point to some participation of Archean components in the source of the Paleoproterozoic rocks. The lithological association and the available isotopic data registered in the Carecuru Domain, suggests a geodynamic evolution model based on the development of a magmatic arc system during the Transamazonian Orogenic Cycle, which was accreted to the southwest border of the Archean Amapá Block. In the Paru Domain, Neoarchean magmatism at about 2.60 Ga was produced by reworking of Mesoarchean crust, as registered in the Amapá Block. Crustal accretion events and calc-alkaline magmatism were recognized at 2.32 Ga and at 2.15 Ga, respectively, as well as charnockitic magmatism at 2.07 Ga. U-Th-Pb chemical ages in monazites from high-grade rocks of the southwestern part of Amapá Block, dated two main tectono-thermal events. The first one was revealed by the monazite ages of about 2.09 Ga and marks the age of the granulite-facies metamorphism. These data, added to petro-structural information, indicate that the granulite-facies metamorphism was contemporaneous to the development of a thrusting system associated to the collisional stage of the Transamazonian Orogeny. The later event was testified by monazite ages at about 2.06 Ga and 2.04 Ga, and is consistent with a late-orogenic stage marked by granitic emplacement and coeval migmatization of the Archean basement along strike-slip zones. Finally, 40Ar/39Ar geochronological study on amphibole and biotite from representative units of the Amapá Block and of the Carecuru Domain delineated contrasting cooling and exhumation stories. In the former amphibole vary from 2.13 to 2.09 Ga, and biotite ages range mainly between 2.10 and 2.05 Ga. In the later, amphibole and biotite ages are between 2.16 and 2.06 Ga, and 1.97 and 1.85 Ga, respectively. In the Amapá Block, fast cooling rates around 67 °C/m.y. and 40 °C/m.y indicate a tectonically controlled exhumation, related to collisional stages of the Transamazonian Event. Conversely, in the Carecuru Domain, regional cooling rates in the order of 3-2.3 °C/m.y. suggest slow cooling and gradual uplift, which is consistent with the magmatic arc model, where continental growth results mainly from lateral magmatic accretion, precluding significant tectonic crustal thickening.
Acesso aberto (Open Access)
Geocronologia em zircão, monazita e granada e isótopos de Nd das associações litológicas da porção oeste do domínio Bacajá: evolução crustal da porção meridional da província Maroni-Itacaiúnas - sudeste do Cráton Amazônico
(Universidade Federal do Pará, 2006-11-16) VASQUEZ, Marcelo Lacerda; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The Bacajá domain is located in the southeastern Amazonian craton and represents the southern part of the Maroni-Itacaiúnas province, which comprises Paleoproterozoic orogens and Archean blocks reworked during the Transamazonian cycle (2.2–1.95 Ga). This domain is composed of granitoids, charnockitic and supracrustal rocks, orthogneisses, migmatites, metaigneous granulites and high-grade metasedimentary rocks. The previous geochronological data denote reworking of Archean crust and formation of juvenile crust during the Transamazonian cycle. The present study was based on field work, petrography, isotope geochemistry and geochronology in order to identify the igneous and high-grade metamorphic events in the western part of the Bacajá domain and to discuss its crustal evolution. The previous geochronological data, plus new data on zircon (U-Pb SHRIMP and Pbevaporation) and Nd isotope data for the igneous and meta-igneous rocks of the lithologic associations from the study area allowed the identification and dating of magmatic events from Neoarchean to Orosirian times, with a climax of crust formation during the Rhyacian. The 2.67- 2.44 Ga orthogneisses and 2.45 Ga metavolcanoclastic rock remnants are related to the first event of crust formation in the western Bacajá domain marked by an accretion at ca. 2.7 Ga and contamination by Mesoarchean crust (ca. 3.0 Ga). A second event of accretion at ca. 2.5 Ga and reworking of Mesoarchean crust were identified in 2.36 Ga metavolcanic rocks and associated 2.34 Ga granitoids, respectively. They are probably related to the amalgamation of a late Siderian island arc to an Archean microcontinent. The 2.21-2.18 Ga granitoids with Neoarchean crustal sources (ca. 2.8 Ga) and 2.16-2.13 Ga granitoids formed by mixture of a 2.3 Ga juvenile component with Archean crustal sources are related to Rhyacian magmatic arcs that collided against an Archean-Siderian continent. This collision was marked by the formation of 2.10 Ga granitoids (syncollisional rocks ?), probably originated from sources related to late magmatic arc rocks, and of charnockitic rocks and granitoids of 2.09-2.07 Ga (post-collisional rocks) formed respectively by mixture of Ryacian crustal sources and the 2.3 Ga juvenile component and by melting of Archean crust (3.0-2.7 Ga). There are Orosirian magmatic events identified in 1.99 Ga granitoids, whose correlation with the Transamazonian cycle is controversial, and by the extensional magmatism of ca. 1.88 Ga. Both events have Neoarchean crustal sources (ca. 2.8 Ga), probably derived from the Bacajá domain. The high-grade metamorphic events and associated anatexis were identified in the metaigneous and metasedimentary rocks from the western Bacajá domain. However, the petrologic and geochronological studies focused only on the high-grade metasedimentary rocks. These rocks have dominantly Archean detrital sources (3.1-2.5 Ga) and were affected by Rhyacian metamorphic events preliminary constrained by Sm-Nd whole rock-garnet isochrones (2208- 2025 Ma), but there is little evidence suggesting the existence of a high-grade metamorphic event at 2.3 Ga, that could be related to the collage of the late Siderian island arc. High-grade Transamazonian metamorphism commenced with a 2147-2123 Ma migmatization event that took place under upper amphibolite facies P-T conditions and was preserved in zircon overgrowths and in the cores of monazite grains. This event could be related to the collision of the early Rhyacian magmatic arc against to a Neoarchean-late Siderian continent. An anatectic event at 2109 Ma was recorded on unzoned rims of zircon crystals, which is probably it related to the continental collision at 2.1 Ga that has been identified in the Transamazonian orogens of the French Guiana shield. Despite the formation of synchronous granitoids and charnockitic rocks during this collision, in the studied metapelites it was a modest anatexis. After that, a low pressure granulite facies metamorphism (4-6 kbar / 700-800 ºC) at ca. 2070 Ma was registered on monazite and zircon grains, followed by a possible Pb-loss event at 2057 Ma. The existence of coeval quartz diorite and charnockitic intrusions suggests underplating of mafic magma and crustal thinning during the post-collisional period. The igneous and metamorphic events of the western Bacajá domain are analogue to those identified in other Transamazonian domains of the Amazonian craton and South America. In global scale, the 2.1 Ga collage has been correlated to the collision of the paleoplates of eastern South America and western Africa that triggered the formation of a Paleoproterozoic supercontinent.
Acesso aberto (Open Access)
Geologia e petrogênese do “Greenstone Belt” identidade: implicações sobre a evolução geodinâmica do terreno granito - “Greenstone” de Rio Maria, SE do Pará
(Universidade Federal do Pará, 1994-10-07) SOUZA, Zorano Sérgio de; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
This thesis deals to the geology and petrogenesis of the Identidade greenstone belt, located between Xinguara and Rio Maria towns, SE of Pará state. The data of this area permitted the discussion of the tectonic evolution of the gravite greenstone terrain of the Rio Maria region in the context of the Província Mineral de Carajás, SE of the Amazonian craton. The greenstone studied compose a synformal belt in the WNW-ESE direction, corresponding to one metavolcanic pile, formed predominantly by ultramafic schists (UM), basalts (BAS) and gabbros (GB) at the base, and hypabyssal dacitic rocks (DAC - ca. 2.94 Ga, Pb/Pb) at the top. The whole was intruded by metaplutonic rocks of Mesoarchean ages, the older one being quartz diorites, followed successively by granodiorites, trondhjemites / tonalites and leucogranites. The gneissic basement (GN - outcroping toward north and recognized for having an older fabric Sn-1/D1), the greenstone and the metagranitoids were intruded by hypabyssal rhyolitic (ca. 1.60 Ga, Rb/Sr) and basic dykes at the end of the Paleoproterozoic. The greenstone presents igneous structures and textures still recognized, although obliterated near the contacts with the metagranitoids and shear zones. The ultramafics occur as tremolitites, tremolite - talc schists and talc schists; the amphibole is very elongated and thin, commonly in parallel arrays, interpreted as ghosts of spinifex textures. The basalts are massive or pillowed and frequently variolitic. They show different degrees of recrystallization, with some relicts of hyalophitic, pilotaxitic and traquitoid textures. Clinoamphibole (actinolitic hornblende), epidotes and plagioclase (albite - andesine) are the most abundant minerais. The gabbros may be massives to porphyritics (plagioclase phenocrysts), still with some relicts of subophitic and granophyric textures. The dacites are porphyritic, with phenocrysts of quartz and plagioclase (oligoclase), besides hornblende and mafic clots (biotite, chlorite, opaque minerais, epidotes, sphene, apatite) in the less evolved samples. Concerning the metagranitoids, the leucogranites and trondhjemites have chloritized biotite, whereas the granodiorites and some tonalites comprise biotite or biotite + hornblende (also in quartz diorites). The greenstone and the metagranitoids were affected by one event of heterogeneous, ductile deformation, that evolved to mylonitic zones. The structural framework of the area is marked by a planar fabric (Sn//Sm/D2) in the WNW-ESE to E-W direction, with moderate to strong dips in a divergent fan. E-W, WNW-ESE or NW-SE stretching lineations, meso and asymmetric S-C microstructures, mica and clinoamphibole fishes, and rotation of o and i porphyroclasts indicated one megastructure resulting from a binary system with NW-SE shortening direction. The actual geometry of the greenstone would be derived from a dextral transpression, with the greenstone forming a positive flower structure. The transpressional regime favored the grow of transtensional cites and subsequent emplacement of granitic plutons on the NW contact, and extensional crenulation cleavage (Sn+1/D2) on the SW of the greenstone. Strain measurements displayed a ca. 60% shortening, subhorizontal extension of ca. 60 to 500% parallel to the greenstone trend, and vertical extension of ca. 101 to 280%. The strain ellipsoid may be oblate to prolate, with changes in density and rotation of the axis of maximum stretching (X) toward the mylonitic zones. The inversion of the deformation permitted the reconstruction of the original shape of the greenstone, that would be also elongated WNW-ESE, but with lesser eccentricity than today. These data, together with the quartz petrofabric, suggested that the deformation has been accommodated by pure and simple shear mechanisms, the final framework resulting essentially from the later. The last event (D3) are represented by faults and fractures which also affected the felsic and basic dykes. The paragenesis of the main metamorphic event (Mn/M2) is represented by static recrystallization, which modified some textures and almost ali minerais within the greenstone. The minerais formed phases were bluish green amphibole (actinolitic hornblende), epidotes, sphene and quartz in BAS and GB; tremolite, talc and chlorite in UM. The metagranitoids show transformations of plagioclase (saussurite, fine white mica), amphibole (to biotite and/or sphene) and biotite (to chlorite). The coexistence of hornblende + plagioclase (An>17) and/or actinolitic hornblende + chlorite in metabasic rocks shows that this event was of low pressures and temperatures in the transitional field of the greenschist and amphibolite facies. This episode should reflect a regional crustal heating produced by the plutonism at the end of the Mesoarchean, that obliterated the previous associations of ocean floor metamorphism. Slightly coeval to subsequently, it occurred one event of extensive dynamic recrystallization (Mm/M2) in the greenschist facies, specially within shear zones and lithological contacts. In these places, there are evidences of fluid incoming (schistose blastomylonites and abundant quartz veins) and remobilization of chemical elements (Al, Fe, Ca, K, Na, Rb, Sr, Zr). Finally, under lower PT conditions, it occurred a less expressive event related to crenulation cleavages and forming chlorite, epidotes and quartz (Mn+1/M2). The M2 event, as well as the one detected only in GN (M1 under amphibolite facies), was of ductile nature and cleary distinguished from the last one (D3/M3). The later was placed at the end of the Paleoproterozoic, being of hydrothermal character and associated to high crustal structures. The progressive evolution of the M2 metamorphism with its thermal peak predating the deformation suggested a counterclockwise P-T-t path, corresponding to the metamorphic evolution of Phanerozoic marginal basins. Some chemical analysis of the metavolcanic rocks permitted the definition of magmatic series and a discussion of petrogenetical modeling. It was possible to recognize three geochemical series, that is, from the older to the younger, komatiitic (UM), tholeiitic (BAS and GB) and calc-alkaline (DAC). The first one corresponds to peridotitic komatiites with MgO>18 weight % (volatile-free basis), with an enrichment trend in Al, such as in Geluk and Munro, and less calcic than the Barberton one. The light rare earth element patterns are irregular with (La/Sm)N ratios between 0.42 and 4.2 and negative Eu anomalies. The heavy rare earth elements seem less affected by post-eruptive processes, being plate or slightly fractionated (1.0<(Gd/Yb)N<2.3). The quantitative models were of hard execution due to the remobilization of several elements. It was possible estimate cumulates rich in olivine and orthopyroxene. With regarding to tholeiites, the BAS and GB showed very similar geochemical signatures, both being low potassium tholeiites comparable to depleted Archean tholeiites. The rare earth elements are almost plate, with values 10X the chondrite, and slight or no Eu anomaly. Preliminary modeling suggested similar cumulates for BAS and GB, composed essentially by clinopyroxene and plagioclase. The magma sources that originated the komatiites and tholeiites would be a garnet lherzolite. The DAC presented geochemical characteristics of modern and Archean metavolcanics and metaplutonics of trondhjemitic nature. The magmatic differentiation would be achieved by fractionation of plagioclase>quartz>hornblende>K-feldspar, with subordinated amount of biotite, magnetite, sphene, allanite and zircon. The source of the dacitic magma would be a tholeiite metamorphosed to the garnet amphibolite facies and somewhat enriched in light rare earth elements. The geodynamical model proposed admit the existence of a gneissic basement prior to 2.96 Ga. Between 2.96 and 2.90 Ga, the interplay of high geothermal gradients and lithospheric extension was responsible for extensive rifting, forming marginal basin systems, where extruded the komatiitic and tholeiitic rocks. At 2.94(?)-2.90 Ga, the DAC were generated from partia' melting of oceanic crust in subduction zone settings, and evolved by low pressure fractional crystallization. The same mechanisms that generated the DAC are extended also to the calc-alkaline plutonism, this one being responsible for the structural inversion of the greenstone, crustal thickening and final shape of the granite - greenstone terrain (dextral transpression ca. 2.88-2.86 Ga). The region still suffered a late episode (end of Eoarchean, 2.69-2.50 Ga) of (re)heating, registered only in sorne mineral, without any evidente of deformation and/or metamorphism. Finally, it occurred the intrusion of felsic (1.60 Ga, Rb/r) and basic dykes at the end of the Paleoproterozoic. The correlation with the actual understanding of the Província Mineral de Carajás permitted envisage that the Rio Maria granite - greenstone terrain was then configured at the moment of implantation of the Itacaiúnas Supergroup (ca. 2.76 Ga) and alkaline granitic plutonism at the Serra dos Carajás. So the sinistrai transpression that inverted that supergroup would correspond to a newer event, very distinct as regards as the dextral transpression of the Rio Maria region.
Acesso aberto (Open Access)
Geologia, geoquímica e geocronologia do magmatismo paleoproterozóico da região de Vila Riozinho, Província Aurífera do Tapajós, Cráton Amazônico
(Universidade Federal do Pará, 2001-09-27) LAMARÃO, Cláudio Nery; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Several Paleoproteroic granitoids and two volcanic sequences were studied in the Vila Riozinho region. This region is located in the eastern area of the Tapajós Gold Province, near the border between the Tapajós and Central Amazonian tectonic provinces in the south-central part of the Amazonian craton. In the southern part of the region, it was identified the Vila Riozinho volcanic sequence composed of basaltic andesite, basaltic trachyandesite, trachyte and rhyolite, with a high-K calc-alkaline to shoshonitic geochemical signature. Pb-Pb zircon dating indicate ages of 2000 + 4 Ma and 1998 + 3 Ma for this sequence. The São Jorge granite pluton is spatially associated with this volcanic sequence. Two granitoids were distinguished in the pluton, the Old São Jorge granite, with Pb-Pb zircon ages of 1981 + 2 Ma and 1983 + 8 Ma, and the Younger São Jorge granite with an age of 1891 + 3 Ma. The Older São Jorge granite, largely dominant in the pluton, is composed of an expanded magmatic series including biotite-amphibole monzodiorite/quartz monzodiorite, amphibole-biotite monzogranite/quartz monzonite, biotite leucomonzogranite/syenogranite and granite porphyry. It has a metaluminous to mildly peraluminous character, and high-K cale-alkaline signature, similar to that of volcanic arc granitoids. The Younger São Jorge granite was initially identified in drill cores obtained in the gold mineralized area of the pluton. In that area, it corresponds to a hornblende-biotite monzogranite, but biotite leucogranites occur in the southern part of the pluton. This granite also has a high-K calc-alkaline signature, but it differs from the Older São Jorge granite in some geochemical and mineralogical aspects and it is comparatively younger. In the northern part of the Vila Riozinho region, it was identified the Moraes Almeida volcanic sequence, the Maloquinha and Jardim do Ouro granites and a granite porphyry distinct from that associated with the Older São Jorge granite. The Moraes Almeida Formation is composed of ignimbrite and rhyolite with subordinate trachyte, with Pb-Pb zircon ages of 1875 + 4 Ma, 1890 + 6 Ma and 1881 + 4 Ma, respectively. The 1880 + 9 Ma old Maloquinha granite is composed of leucosyenogranite and subordinate leucomonzogranite. This granite and the rhyolite and ignimbrite of the Moraes Almeida Formation show affinities with aluminous, A-type series. The strong petrographic and geochemical similarities between these rocks suggest that they are cogenetic. An age of 1880 + 3 Ma, similar to that of the Maloquinha grafite, was obtained for the Jardim do Ouro hornblende-biotite monzogranite. However, preliminary data indicate that it differs from the former, as well as from the Older São Jorge and Younger São Jorge granites, in petrographic and geochemical aspects. Geochemical and mineralogical data allow the distinction of two different types of grafite porphyries. The first one is spatially associated and similar to the Older São Jorge granite. The second occurs along the contact between the Maloquinha granite and the ignimbrite of the Moraes Almeida Formation and is geochemically similar to the Jardim do Ouro granite and trachyte of the Moraes Almeida Formation. The magmatic activity in the Vila Riozinho region is concentrated into two distinct periods, near the end of the Paleoproterozoic. The Vila Riozinho Formation and the Older São Jorge granite formed during the first period between 2010 and 1970 Ma. At the second period, between 1900 and 1870 Ma, the Moraes Almeida Formation, Maloquinha, Younger São Jorge and Jardim do Ouro granites were formed. The high-K calc-alkaline magmatism that was formed during the first period is probably related to subduction processes. Two hypotheses are considered to explain the diversified magmatic activity registered during the second period: (1) the different magmas could result from late tectonic activity related to the subduction processes; (2) these magmas are related to taphrogenetic processes that affected the Amazonian craton at 1.88 Ga and lasted the entire Mesoproterozoic. It implies to admit a crustal source for the magmas originated during the second period. The second hypothesis is assumed as the more plausible at this stage, but the need for additional isotopic information is emphasized.
Acesso aberto (Open Access)
Geologia, geoquímica e isótopos (U-Pb, Lu-Hf e Sm-Nd) de granitos orosirianos do Domínio Iriri-Xingu setentrional, Província Amazônia Central
(Universidade Federal do Pará, 2023-03-29) ALCÂNTARA, Davi da Costa Bezerra Gobira; VASQUEZ, Marcelo Lacerda; http://lattes.cnpq.br/4703483544858128; https://orcid.org/0000-0003-2729-9404; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The Orosirian of SE Amazonian Craton is mainly characterized by igneous associations from I, A and rare S types outcropping from west to eastward, in the Tapajós, Iriri-Xingu and Carajás domains. The Carajás domain represents the oldest crustal region, stabilized during the Neoarchean. The Tapajós domain represents, at least to some extent, the proximal region of a continental margin actived during the Orosirian. The Iriri-Xingu domain (IXD), at the center, still holds an uncertain tectonic role. These igneous associations were formed in multiple magmatic episodes through this geological period, which can be temporally divided in three intervals. The first interval, from 2030 to 2000 Ma, is marked by a juvenile, I-type, calc-alkaline volcano-plutonism in the Tapajós domain. The second interval, from 2000 to 1960 Ma, is marked by a series of I type, high K calc-alkaline to shoshonitic rocks that expands from Tapajós domain to the east, in the IXD. The rocks of the third interval (1900 to 1860 Ma) are represented by an I type calc-alkaline magmatism and an A type magmatism, the later associated to mafic rocks. The A type rocks, typically from A 2 sub-type, belong to a broader geographical context than the I type magmatism, and outcrop in an expressive area through the Amazonian Craton (ca. 1,500,000 km 2 ). These rocks are generically attributed to the Silicic LIP Uatumã. In this thesis, we concentrate on the plutonic part of these associations and present new geological, lithochemical and isotopic (U-Pb, Lu-Hf in zircon and whole rock Sm-Nd) data for granites of the second and third magmatic episodes from central-eastern and northern IXD. In central-eastern IXD, the granites São Pedro do Iriri, Vila Primavera, Caboclo and Jabá present an alkaline to subalkaline, metaluminous to slightly peraluminous, ferroan to slightly magnesian character. The first three granites are akin to the reduced tin-specialized A type granites of Velho Guilherme Suite, from Carajás Domain. U-Pb and Lu-Hf data provided a crystallization age of 1897 ± 8 Ma for the São Pedro do Iriri Granite, and εHf (t) values (from -8.22 to -17.44) that point to a mixing of meso and paleoarchean crustal sources. The Jabá Granite exhibits geochemical affinity to the oxidized A type granites from Iriri-Xingu and Carajás domains. This granite yielded a U-Pb in zircon crystallization age of 1887 ± 14 Ma and εHf (t) values of -6.43 to -10.21, indicating a more radiogenic, homogeneous and predominantly mesoarchean crustal source. The classic I type calc-alkaline rocks studied in this work comprise the Rio Bala, Porto Estrela and other sparse granitic samples from Iriri river that represent, among others plutons, the Serra do Chavito and Pedra do O granites. They are amphibole and biotite bearing rocks that show magnesian, metaluminous, high K calc-alkaline to slightly shoshonitic character. The Porto Estrela Granite exhibits tonalitic to granitic facies and yielded a U-Pb age of 1972 ± 6.6 Ma. The samples of the calc-alkaline granites from Iriri river are quartz-monzonitic to granitic in composition. Samples from the Serra do Chavito and Pedra do O granites yielded ages of 1987 ± 6.6 and 1988 ± 8 Ma, respectively. The ages yielded by the Porto Estrela and the Iriri river’s granites correlate these rocks to the second interval volcano-plutonic association of Iriri-Xingu and Tapajós domains. The Rio Bala Granite is quartz-monzonitic and granitic in composition, exhibits a chemical trend typical of subalkaline rocks and yielded a U-Pb in zircon age of 1877 ± 8.2 Ma. This granite represents the first record of a high K calc-alcalic plutonism coeval to the volcanic rocks of the Iriri Group (1.88-1.87 Ga calc-alkaline rhyolite and dacite) in IXD. Chemically, it presents a more evolved character and affinity to the granitic facies of Parauari Suite. The remaining studied rocks of the central and northern IXD comprise two atypical samples of A type and I type granites, that represents respectively the Cachoeira do Julião and Igarapé Limão plutons. The A type granite sample is a cpx-hb-bt quartz-syenite. Its petrographical, chemical and previous geochronological data (1889 ± 3 Ma) allow a correlation with the plutonic rocks of the Uatumã SLIP. The other sample constitutes a biotite monzogranite of magnesian, slightly peraluminous, medium to high K calc-alkaline character, similar to the I type adakitic rocks. The REE curved upwards pattern and the relatively low Dy/Yb ratio (1.04) suggest residual amphibole or its fractioning in relatively high P in presence of garnet. The low contents of MgO, #Mg, Yb and Ni, and high FeO t /MgO ratio indicate an affinity to the adakites of thickened lower crust melting. The necessary conditions to this rock genesis are satisfied if we consider the IXD crust to be deformed and thickened in the Transamazonian Cycle and latter thinned in the Orosirian. The data related to the I type magmatism with ages of 2.00 to 1.96 Ga suggest an extensive but brief event, with a minimum area of 190,000 km 2 and lifespan of 40 M.y. Extrapolating modern geodynamical conditions for subduction to the Paleoproterozoic, it is concluded that the space-temporal pattern of this magmatism cannot be uniquely explained by subduction process. Therefore, it is inferred that at least part of this magmatism should be generated in a convergent margin by other process than subduction or, alternatively, a post-orogenic event. The same reasoning can be adequately projected to the 100 M.y. younger calc-alkaline rocks of the third time interval (1.90–1.86 Ga). The Nd isotopic data for the studied rocks present moderately to highly negative εNd (t) values and siderian to mesoarchean Nd-T DM model ages. The available data, presented in this work and from literature, reveal a heterogeneous crust, partly composed by a crust similar to the Carajás’. The neoarchean and siderian isotopic signatures could represent, in a non-mutually exclusive way: the presence of juvenile crustal segments; mixture of ancient archean crust and mantellic input (probably from Ryacian and/or Orosirian); or mixture of diverse crustal components. This crust could be interpreted as paleo to mesoarchean preserved nuclei bordered by reworked crust that probably underwent juvenile inputs on Ryacian and/or Eo-Orosirian, besides presenting isolated blocks/segments of juvenile Neoarchean and Ryacian rocks. Concerning the IXD lithostratigraphy, we suggest the Iriri Group to be composed by the Santa Rosa – acid A type volcanics - and Confresa – acid I type calc-alkaline volcanics – formations, both with crystallization ages within 1.90 and 1.86 Ga. We propose the 2.00 to 1.96 Ga calc-alcalic volcanic rocks, formerly related to the Iriri Group, to be grouped in the Jarinã Formation. We also recommend the adoption of the term Vila Rica Suite to refer the I type granites coeval to the Jarinã Formation. We also endorse grouping the A type granites akin to the oxidized granites of Carajás in the Rio Dourado suite. In respect to the potentially tin-specialized reduced A type granites, we recommend this group of rocks to be assembled in the proposed São Pedro do Iriri Suite.
Acesso aberto (Open Access)
Geologia, geoquímica, geocronologia e petrogênese das suítes TTG e dos leucogranitos arqueanos do Terreno Granito-Greenstone de Rio Maria, sudeste do Cráton Amazônico
(Universidade Federal do Pará, 2010-03-23) ALMEIDA, José de Arimatéia Costa de; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675; 2158196443144675
TTG and granite suites are exposed in large domains of the Mesoarchean Rio Maria granitegreenstone terrane (RMGGT), southeastern Amazonian craton. Extensive field work in key areas of the RMGGT, integrated with petrographic, geochemical, and geochronological studies, the latter employing the Pb-Pb evaporation and U-Pb LA-ICP-MS on zircon techniques, indicates that the TTG magmatism record in the RMGGT can be divided into three episodes: (I) A first event at 2.96±0.2 Ga (the older rocks of the Arco Verde tonalite and the Mogno trondhjemite), (II) a second one at 2.93±0.1 Ga (Caracol tonalitic complex, Mariazinha tonalite, and the younger rocks of the Arco Verde tonalite), and (III) a restricted event at 2.86±0.1 Ga (Agua Fria trondhjemite). The new data demonstrate that the Mogno trondhjemite is significantly older than previously admitted, reveal the existence of a new TTG suite (Mariazinha tonalite) and indicate that the volume of TTG suites formed during the 2.87 event was limited. The Arco Verde tonalite yielded significant age variations (2.98 to 2.93 Ga) but domains with different ages could not be individualized so far. The tonalitic-trondhjemitic suites of the RMGGT derived from sources geochemically similar to the metabasalts of the Andorinhas supergroup, which were extracted from the mantle during the Mesoarchean (3.0 to 2.9 Ga) and had a short time of crustal residence. Three groups of TTG granitoids were distinguished in Rio Maria: 1) high-La/Yb group, with high Sr/Y and Nb/Ta ratios, derived from magmas generated at relatively high pressures (≥1.5 GPa) from sources leaving garnet and amphibole as residual phases; 2) medium-La/Yb group which magmas formed at intermediate pressure conditions (~1.0-1.5 GPa), but still in the garnet stability field; and 3) low-La/Yb group, with low Sr/Y and Nb/Ta ratios, crystallized from magmas generated at lower pressures (≤1.0 GPa), from an amphibolitic source that left plagioclase as a residual phase. These three geochemical groups do not have a direct correspondence with the three episodes of TTGs generation and a same TTG unit can be composed of rocks of different groups. The geochronological data indicate that the emplacement of the Archean granites of the RMGGT occurred during Mesoarchean (2.87 and 2.86 Ga) being coeval with the sanukitoid suite (~ 2.87 Ga) and post-dating the main timing of TTG suites formation (2.98 - 2.92 Ga). Three main types of Archean granites were distinguished in the RMGGT on the basis of petrographic and geochemical data: (1) Potassic leucogranites (Xinguara and Mata Surrão granites), that are composed dominantly of biotite-monzogranites with high SiO2, K2O, and Rb contents and fractionated REE patterns with moderate to pronounced negative Eu anomalies. These granites are similar to the low-Ca granites of the Yilgarn craton and to the CA2 Archean granites. Their magmas resulted from the partial melting of sources similar to the older TTG suites of the RMGGT; (2) Amphibole-biotite monzogranites (Rancho de Deus granite) generated by fractional crystallization and differentiation of sanukitoid magmas; (3) leucogranodiorite-granite suites (Guarantã suite and Grotão granodiorite), which are Ba- and Sr-rich rocks with strongly fractionated REE patterns without significant Eu anomalies. These granites have affinity with the high-Ca granites of the Yilgarn craton and the CA1-type Archean granites. On the basis of modeling and geochemical data we suggest that the leucogranodiorite-granite suites were derived from mixing between a granite, similar to the Ba- and Sr-enriched samples of the Guarantã suite, and trondhjemitic liquids. The granite magmas participating in the mixture were originated by fractional cystallization of 35% of a sanukitoid magma of granodioritic composition. The fractionated mineral phases were: plagioclase (46.72%), hornblende (39.05%), clinopyroxene (10.36%), magnetite (3.12%), ilmenite (0.7%) and allanite (0.06%). The large compositional variations observed in the Guarantã suite can be apparently explained by mixing in different proportions between the granite and trondhjemitic liquids. A model involving a subducting slab underneath a thick oceanic plateau was envisaged to explain the tectonic evolution of the RMGGT. In this context, the low-La/Yb group was formed from magmas originated by the melting of the base of a thickened basaltic oceanic crust at comparatively lower pressures (≤ 1.0 GPa), whereas the medium- and high-La/Yb groups were derived from the slab melting at increasing different pressures (1.0-1.5 and > 1.5 GPa, respectively). Part of these TTG magmas react during their ascent with the mantle wedge being totally consumed and leaving a metassomatized mantle. 50 m. y. later, at ca. 2870 Ma, thermal events, possibly related to the slab-break-off, causing asthenosphere mantle upwelling, or to the action of a mantle plume, may have induced the melting of the metassomatized mantle and the generation of sanukitoid magmas. These magmas may have heated the base of the Archean continental crust during their rising to the surface and could have lead to the local melting of the basaltic crust forming the Água Fria trondhjemite magma. This was accompanied by partial melting (at shallower crustal levels) of the Rio Maria tonalitic-thondhjemitic crust and generation of the potassic leucogranite.
Acesso aberto (Open Access)
Geoquímica, petrogênese e evolução estrutural dos granitóides arqueanos da região de Xinguara, SE do Cráton amazônico
(Universidade Federal do Pará, 2001-05-25) LEITE, Albano Antônio da Silva; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Xinguara region is situated in the northern sector of the Rio Maria Granite-Greenstone Terrain (RMGGT), southeastern Amazonian craton. The RMGGT is composed by greenstone belts and diversified granitoid plutons. Granitoids and gneisses, formeriy included indistinctly in the Xingu Complex, have been individualized in two new stratigraphic units: The Caracol tonalitic complex (CTc), which shows enclaves of the greenstone belts and the Água Fria trondhjemite (THaf). The Iatter is intrusive in the Sapucaia greenstone belt and in the CTc, and coeval with the Xinguara granite (Gxg). Some granodioritic bodies exposed in the Xinguara region are correlated with the Rio Maria granodiorite (GDrm). They are younger than the CTc and older than the THaf and Gxg. The dominant regional structures follow a WNW-ESE trend, observed in the south portion of the CTc and also in the comparatively younger granitoid plutons. The CTc preserves a N-S banding in its NW sector, but this structure is transposed to the WNW-ESE regional trend. The GDrm shows strongly flattened mafic enclaves, which defines a foliation; The THaf displays a magmatic banding; The Gxg pluton has an elongated shape; ali these structures follow the regional trend. The Gxg displays a weak foliation, subhorizontal at the center and dipping at high angles along the borders of the intrusion. The G1 axis of the regional stress during the intrusion of the granitoids was horizontal and trending N40E. The regional stress remained active during the submagmatic stage of the CTc evolution, as indicated by the presence of folds or boudins affecting its banding. It was responsible by the transposition to WNW-ESE of N-S structures. The stress field orientation was similar during the two phases of the Archean evolution of the region. This is suggested by the main submagmatic to subsolidus deformation structures in the GDrm, THaf, and Gxg. The changing trends of the CTc foliation suggest that the CTc was formed by domic plutons, intruded and sectionated by the younger granitic intrusions. Al-in amphibole geobarometer data suggest that the GDrm crystallized under a lithostatic pressure of —3 kbar, equivalent to a —10 km depth. The contact metamorphic effects of the Rio Maria granodiorite in the metabasaltic rocks of the Identidade greenstone belt are coherent with this data and suggest also that its emplacement was not diapiric-controlled. The variation in the intensity and orientation of the foliation in the Xinguara pluton and the deformation imprinted on its country rocks suggest its emplacement by bailooning. The emplacement of the THaf was probably controlled by diapiric processes. The CTc is a typical TTG, similar to those of the Archean trondhjemite series. Two different geochemical signatures have been identified in this granitoid on the basis of accentuated contrasts in LaN/YbN ratios. The GDrm is different of the TTG series. It follows the calc-alkaline trend and is similar to the Mg-rich granodiorites of the Sanukite Series. The THaf is geochemically similar to the CTc and by extension to the Archean TTG, but it is comparatively enriched in K2O. The Gxg is a high-K2O, strongly fractionated, calc-alkaline Archean leucogranite. Its REE pattern is indicative of a crustal origin. The dominant, high LaN/YbN ratio CTc group crystallized from a liquid probably originated from the partial melting of garnet amphibolites derived from 'normal' tholeiites. The latter should be similar in composition to the Archean metabasalts or to the metabasalts from the Identidade greenstone belt and the degree of partial fusion required would be, respectively, 25-30% and 10-15. On the other hand, the tonalites with Iow LaN/YbN ratios crystallized from a liquid derived from a garnet-free similar source. Nd isotopic data indicate a mantle source and a juvenile character for the tonalites of the first group. A tonalite sample of the second group and an enclave in the Gxg yielded negative ONd values and >3.2 Ga TDM ages. These data suggest that the tonalites of this group could derive from an older source with a longer crustal residence time. The THaf may have been generated by 5-10% partial melting of garnet amphibolites derived from metabasalts, chemically similar to the metabasalts from Identidade. The liquids of the Gxg were originated by variable degrees of partial melting of a source similar to the oldest TTG granitoids. The Archean geologic evolution of the Xinguara region occurs in two stages. The first starts in the interval of <2.95 to 2.91 Ga and is apparently similar to those of the Pilbara and Darwhar cratons. The second stage starts at 2.88 Ga and it is coincident with a sharp change in crustal behavior. At this time, the increasing thickening and stabilization of this Archean crustal segment, turned more effective the processes of plate subduction and convergence. In this tectonic context, the partial melting of an enriched mantie wedge would generate the parental magma of the GDrm and the partial fusion of garnet amphibolites derived from the subducted ocean crust would generate the THaf magma. Finally, the upward movement of the THaf and GDrm magmas would induce the melting of the TTGs in the lower crust, thus generating the granitic magmas of the Xinguara pluton.
Acesso aberto (Open Access)
Greisens e Epi-sienitos potássicos associados ao granito água boa, Pitanga (AM): um estudo dos processos hidrotermais geradores de mineralizações estaníferas
(Universidade Federal do Pará, 2002-10-23) BORGES, Régis Munhoz Krás; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Three stanniferous greisen types were characterized in the western border of Água Boa pluton, Pitinga mine (AM), associated with the rapakivi granite facies: greisen 1 (Gsl), composed mainly by quartz, topaz, brown siderophyllite and sphalerite; greisen 2 (Gs2), composed essentially by quartz, phengite and chlorite; greisen 3 (Gs3), composed of quartz, fluorite and phengite, with minor green siderophyllite. Besides these rocks, a potassic episyenite (EpSK) was identified associated with the Gs2. In spite of the compositional and petrographic differences, all of these hydrothermal rocks derived from a same protholith, a hornblende biotite aikali feldspar granite to syenogranite. The Gsl shows an inner mineralogical zoning defined by topaz or siderophyllite predominance. Along drill cores, the siderophyllite-rich zone occurs near the contact with the greisenized grafite and the topaz-rich zone is situated far from the grafite contact. The brown siderophyllite displays moderated Al contents, and its compositional changes can be explained by Fe+2 substitution for A1+3 and Li in octahedral sites, with a coupled Al+3 substitution for Si+4 in tetrahedral sites. The mineralogical zones in the Gs2 are physicaliy separated in leveis with phengite or chlorite predominance. The mica of Gs2 is a phengite, whose chemical variation is due to substitution of viAl for Fe+2, coupled with Si+4 enrichment. The calculated Li contents in phengites are lesser than those estimated in siderophyllite. The green siderophyllite from Gs3 is VIAl richer and F poorer than Gs1 brown siderophyllite, and the phengite displays two compositional types: an early Fe+2-poor aluminous phengite and a later Fe+2- F-rich one whose chemical variation is similar to that of Gs2 phengite. The chlorite from the three greisen is a Fe-rich daphnite, and its compositional range is due to VIAl substitution for R+2 cations, coupled with Si+2 enrichment. The aluminous chlorite displays higher temperature formation than ferrous one, according to the geothermeter proposed in the literature. The Pitinga greisens were formed by different processes of interaction among three main fluids: (1) low salinity, F-rich, aquo-carbonic fluid, with initial temperatures between 400° -350°C, present during Gsl and Gs3 formation; (2) low salinity aqueous fluid, with a temperature around 300°C, which during a progressive salinity increasing process, originates a moderate to high salinity residual fluid, with temperatures between 200° - 100°C, present during the Gs2 formation and silicification stage of EpSK; (3) low salinity aqueous fluid, with temperatures between 200° - 150°C, which interplayed with the others two fluids in differents grades, contributing to the formation of ali the hydrothermal rocks. The first two fluids has seemingly an orthomagmatic origin while the latter has a surface characteristic (meteoric water?). Moreover, the data suggests that the fluid responsible by the initial stage of the episyenitization process was not registered in the studied samples. These fluids were trapped in pressure conditions around 1 Kbar, representing high crustal levels conditions, similar to that of the stanniferous granites from Pitinga. Both episyenitization and greisenization processes occurred without volume changes in the granitic protholith, and the density differences of the altered rocks were caused by the mass variations along the alteration processes. The greisenization process caused a extensive loss of Na2O and K2O, while SiO2 showed a immobile behaviour in Gsl but was parcially removed in Gs2. The Al2O3 was depleted during the Gs2 formation but added in Gsl. The Fe2O3 (Fe total), Sn, S, volatiles LOl and F were the responsible by the mass increase at greisenization. In the Gsl, the chemical changes in the fiuids were caused by F activity decrease and fO2 increase during cooling. These changes also originated the differentiation between the ZT, in the inner portions of the fratures/conducts, and the ZS, nearest to surrounding gravite. The Gs3 was formed in more oxidizing conditions by F-poorer fiuids than those trapped in the ZS. The dissolution cavities generated during the episyenitization process increased the permeability of the altered rocks, providing an increase of fluid/rock ratios in the EpSK and Gs2 sites. The interaction between aqueous fluid and EpSK feldspar, during the Gs2 formation, caused a continuous salinity increase. The ZF was formed in the early stages of this interaction, at higher temperatures, while the ZC was originated by the more cold and saline, residual fluid. The latter was also trapped in the quartz filling cavities in the EpSK during the later silicification stage. In this way, the greisens and the potassic episyenites were generated from interactions among, at least, three fluids of seemingly independent origin, from a same protholith, in shallow crust conditions. The fO2, F activity and salinity variations, during the hydrothermal system cooling, and the contrast in fluid/rock ratios caused by permeability differences, were very important factors to greisen differentiation. These factors controlled greatly the fluids compositional changes, and caused the cassiterite and sulphides precipitation in the greisens and the Sn- S-enrichment during later greisenization of EpSK.
Acesso aberto (Open Access)
Mapeamento geoquímico da bacia do rio Itacaiúnas, Província Mineral de Carajás: Assinatura geoquímica dos blocos crustais e implicações para recursos minerais e meio ambiente
(Universidade Federal do Pará, 2020-10-26) SALOMÃO, Gabriel Negreiros; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607; https://orcid.org/0000-0002-3026-5523
Multielement geochemical surveys (MGS) when combined with advanced data processing techniques and robust statistical analysis, are important tools for understanding the environment. In the last decades, its application in mineral exploration is well established and, in the last decades, it has shown remarkable relevance for environmental studies linked to sustainable territorial management, particularly in the establishment of geochemical background concentration values. The definition of background values has been widely used to demonstrate the inconsistencies of laws and regulations, which establish concentration limits for potentially toxic elements in the environment, often without taking into account the complex spatio-temporal heterogeneity of each region. In Brazil, many MGS were, and continue to be carried out mostly by the Companhia de Pesquisa de Recursos Minerais (CPRM, Geological Survey of Brazil) in different parts of the national territory, although they are still scarce in the Amazon region. The present study is associated with a large geochemical mapping project called the Geochemical Background of the Itacaiúnas River Basin (GBI) carried out by the Instituto Tecnológico Vale (ITV). The Itacaiúnas River Watershed (IRW) is located in the largest mineral province of Brazil, the Carajás Mineral Province, and it is particularly relevant for geochemical studies, because the distribution of chemical elements in this region and the influence of the great geological domains on that distribution are not known. The purpose of this research is to investigate the influence of large geological domains in the chemical composition and geochemical signature of stream sediments of the IRW. In addition, it is intended to generate geochemical maps, identify the associations and geochemical processes in stream sediments, define geochemical compartments for the whole watershed, and determine background concentrations for the analyzed elements, taking into account the geochemical compartments and/or geological domains of the study area. In order to achieve these objectives, the stream sediment geochemical data from the GBI-ITV project obtained in the whole IRW in 2017, and those from two CPRM projects in the center-south portion of the BHRI with sampling in the years 2011-2012 were used. These projects were conceptualized at different scales and sample density; however, the sampling techniques and analytical procedures are similar. Stream sediment sample collections were carried out in active water stream, at surface levels from 0 to 10 cm deep, and preferably in the middle of the channel. Sample preparation included the following steps: drying, disaggregation, quartering and sieving. Approximately 50 g of the fraction <0.177 mm was sent to accredited laboratory for chemical analysis. In the laboratory, the samples were submitted to digestion with aqua regia, and then 51 elements were analyzed (Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Ge, Hf, Hg, In, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Rb, Re, S, Sb, Sc, Se, Sn, Sr, Ta, Te, Th, Ti, Tl, U, V, W, Y, Zn and Zr) via Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The geochemical data was submitted to descriptive statistical analysis and some non-parametric statistical tests. Several graphs (e.g., boxplots, histograms, probability and dispersion) were generated for the main chemical elements. Multivariate statistics (e.g., correlation matrices, cluster analysis and factor analysis) were used to investigate the main existing multi-element associations. To determine geochemical background values, modern methods widely used in the specialized literature were employed. Geospatial information was processed and managed in an environment of geographic information systems, in which different cartographic and geoprocessing techniques were used to generate geochemical distribution maps. In general, it was found that, on the scale of geochemical surveys conducted by ITV and CPRM, there is no conclusive evidence of contamination related to human activity, but very strong evidence of a marked geological contribution in the geochemistry of the stream sediments of the IRW. A consistent and replicable methodology was used to identify the main multi-element associations and to define IRW’s surface geochemical compartments. The geochemical associations identified are controlled by the geological domains, by specific lithologies in restricted areas and/or by biogeochemical factors acting in the study area. The delimitation of geochemical compartments revealed a strong similarity with the simplified geological domains of the basin. Geochemical background concentrations were determined for the IRW and its geological domains. Among the methods suggested for determining the background, the Median ± 2*Median Absolute Deviation showed the most consistent and realistic results. In addition, it is considered essential to define reference values based on geochemical compartments, or even a simple geological setting. The assumption of a single uniform reference value for a wide area is inappropriate. The background values proposed in this research may assist environmental impact studies by monitoring anomalous concentrations of potentially toxic elements, which exceed background concentrations. In addition to its scientific interest, the results presented here can be useful to assist local surveys of geochemical prospecting and in the formulation of environmental policies in the Brazilian territory.
Acesso aberto (Open Access)
Petrogênese dos granitos Manda Saia e Marajoara: contribuições para a definição da natureza do magmatismo paleoproterozóico da Província Carajás.
(Universidade Federal do Pará, 2024-12-13) SANTOS, Rodrigo Fabiano Silva; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
The Marajoara (MJG) and Manda Saia (MSG) granites are located in southeastern Pará State, Brazil, and represent circular intrusions with stock dimensions embedded in Mesoarchean rocks of the Rio Maria Domain, in the central-southern portion of the Carajás Province. These rocks outcrop as extensive pavements, exhibiting no solid-state deformation features (isotropic aspect) and frequently containing angular enclaves of the surrounding host rocks. The MJG comprises equigranular biotite monzogranite (eBMzG) and heterogranular (hBMzG) varieties, as well as porphyritic (pME) and microgranular enclaves (ME) restricted to the hBMzG facies. Quartz content and plagioclase/microcline ratios vary significantly, allowing these rocks to be classified from syenogranitic to monzogranitic, and even granodioritic in the case of microgranular enclaves. They are peraluminous granites, similar to ferroan granites with high K2O+Na2O/CaO and FeOt/(FeOt+MgO) ratios, enriched in Rb, Zr, Y, Nb, F, and heavy REEs, with more evolved facies displaying low Sr and Ba contents. In REE patterns, negative Eu anomalies are prominent, and heavy REEs show a gradual increase with magmatic differentiation. These granites fall within the intraplate granite field and exhibit geochemical affinities with A-type granites. Their FeOt/(FeOt+MgO) ratios align with typical oxidized (hBMzG and pME) and reduced (eBMzG) A-type granites, while the MSG displays a moderately reduced character. The ME, however, show affinity with magnesian and calcalkaline series granites. According to biotite mineral chemistry, MSG and the hBMzG facies of MJG fall within the magnetite series field, while eBMzG rocks are similar to ilmenite series rocks. SHRIMP zircon U–Pb analyses provide crystallization ages of 1884 ± 11 Ma for MJG and 1866 ± 10 Ma for MSG (LA–SF–ICP–MS). Lu–Hf isotopic data indicate ƐHf(t) between - 11 and -18 and Hf-TDMC from 3.2 to 3.6 Ga for MJG; and ƐHf(t) between -13 and -19 and Hf-TDMC from 3.3 to 3.6 Ga for MSG. The compositional gaps among the various MJG varieties suggest that their magmas are not cogenetic. Geochemical modeling suggests that MJG and MSG were generated by partial melting of tonalitic rocks, with occasional metasedimentary contributions, at a melting rate ranging from 16 to 18%, with a residual assemblage of plagioclase, quartz, biotite, magnetite, and ilmenite. Felsic and mafic magma mixing played an important role in the emplacement. The enclaves represent enriched lithospheric mantle-derived magmatism injected into the magma chamber during the subduction process, interacting to varying degrees with the magma forming the Marajoara granite. This hypothesis may be reinforced by the occurrence of a 1.88 Ga diabase-porphyritic granite composite dyke in the Rio Maria region. The proposed model suggests that the granitic magma initially formed a magma chamber, followed by repeated mafic magma injections, resulting in small-scale convection. Subsequently, large volumes of hot mafic magma entered the chamber, leading to mixing processes. Microgranular and porphyritic enclaves were formed due to magma mixing in areas where there were temperature contrasts between felsic and mafic magmas. The results presented in this study highlight the importance of the Archean crust in the origin of Paleoproterozoic granites, which were emplaced in shallow crustal levels through a dyke feeder system as a result of extensional tectonics.
Acesso aberto (Open Access)
Petrogênese e evolução magmática da Suíte Sanukitóide Rio Maria, Terreno Granito – Greenstone de Rio Maria, Cráton Amazônico
(Universidade Federal do Pará, 2009-08-25) OLIVEIRA, Marcelo Augusto de; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675; 2158196443144675
The Archean sanukitoid Rio Maria suite yielded zircon ages of ~2.87 Ga and is exposed in large domains of the Rio Maria Granite-Greenstone Terrane, southeastern Amazonian craton. It is intrusive in the greenstone belts of the Andorinhas Supergroup, in the Arco Verde, Mariazinha, and Caracol tonalite, and Mogno trondhjemite. Archean potassic leucogranites, Água Fria trondhjemite, and the Paleoproterozoic granites of Jamon Suite are intrusive in the rocks of the Rio Maria suite. The dominant rocks have granodiorite to subordinate monzogranitic compositions, with minor proportions of intermediate quartz-diorites or quartz-monzodiorites rocks, in addition to mafic end members occurring as layered rocks or as enclaves. The Rio Maria suite has clear geochemical characteristics of Sanukitoids rocks (high Mg#, elevated Cr and Ni contents, LREE enrichment, and high Ba and Sr contents relative to typical calc-alkaline series). The significant geochemical contrasts between the occurrences of the granodiorites in different areas suggest that this unit corresponds in fact to a granodioritic suite of rocks derived from similar but distinct magmas. In spite of their broad geochemical similarities, granodiorites, intermediate rocks, and mafic enclaves show some significant differences in their REE patterns and in the behavior of Rb, Ba, Sr, and Y. The granodiorites and intermediate rocks are not related by fractional crystallization and the internal evolution of intermediate rocks were leaded by fractionation of amphibole + biotite ± apatite, whereas granodiorites evolved by fractionation of plagioclase + amphibole ± biotite. The layered rocks should have been derived from the granodiorite magma by accumulation of 50% of amphibole (dark layer) and 30% of amphibole ± plagioclase accumulation (gray layer). Modeling and geochemical data suggest that mafic enclave and granodiorite magmas were originated at different depths and should have mingled during their ascent and final emplacement and a limited interaction would explain the relatively uniform geochemical behavior of each rock variety and the distinct trends displayed by their rocks in different modal and geochemical diagrams. These contrasts between granodiorites and mafic enclaves are reflected in the behavior of the Sr and Y, which are generally seen as good indicators of the pressure of melt formation. The behavior of these elements, observed in different sanukitoid rocks from Archean terranes worldwide, indicates that the geochemical and modal contrasts observed between the granodioritic (granodiorites) and monzonitic (mafic enclaves) sanukitoid series are a general feature of these rocks and their origin is strongly dependent of the pressure of magma generation and, as a consequence, that the nature of the series could indicate the approximate depth of formation of its magma. The petrogenesis of the Rio Maria suite requires melting of a modified mantle extensively metasomatized by addition of about 30% TTG-like melt to generate the granodiorite (21% of melt) and intermediate magmas (24% of melt), and ~20% TTG-like melt in the case of mafic enclave magma (9% of melt). Our modeling results indicate that an active subduction tectonic setting was present in the Rio Maria terrane in between 2.98 to 2.92 Ga to generate the TTG magmas and the proposed metasomatism of the mantle by these magmas, before the melting process responsible for the origin of the sanukitoid magmas. A tectonothermal event at ~2.87 Ga, possibly related to a mantle plume, causing the partial melting of the metasomatized mantle and generating the Rio Maria sanukitoid magmas. In the rocks of the Rio Maria suite, the mineral assemblage is dominated by amphiboleplagioclase-biotite and epidote minerals, all of inferred magmatic origin, pyroxenes being notably absent. Textural and compositional criteria indicate that amphibole is a principal mineral on the liquidus of all the Rio Maria rocks. To derive crystallisation conditions, the phase assemblages, proportions and compositions of the natural rocks were compared with experimental works carried out on similar magma compositions. The comparison shows that the parental magmas were water-rich, with more than 7 wt% dissolved H2O near liquidus, with crystallisation temperature in the range 950-680°C. The Mg/(Mg+Fe) ratios of both amphibole and biotite indicate fO2 conditions in the range NNO + 0.5 up to NNO + 2.5, therefore pointing to both water-rich and oxidizing conditions for sanukitoid magmas. Analyses of amphibole aluminium content in cumulate rocks, indicate in addition a high pressure crystallisation stage, around 700-1000 MPa, prior to emplacement in the upper crust at around 200 MPa. Sanukitoid magmas share therefore two of the principal characteristics of modern arc magmas, elevated redox sate and volatile contents, which suggest that they may have formed in a geodynamic environment broadly similar to present-day subduction zones.
Acesso aberto (Open Access)
Petrologia de granitos alcalinos com alto flúor mineralizados em metais raros: o exemplo do Albita-granito da mina Pitinga, Amazonas, Brasil
(Universidade Federal do Pará, 2000-11-23) COSTI, Hilton Túlio; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The mineral deposits of the Pitinga mine are related to the Proterozoic Água Boa and Madeira granites. Both are intrusive in the 1888 ± 3 Ma old acid volcanic rocks of the lricoumé Group. The Madeira Granite is composed by four facies, which emplacement sequence was inferred from its field relationships. The early facies is an 1824 ± 2 Ma old, porphyritic, metaluminous amphibole biotite syenogranite, which locally shows rapakivi texture. This facies is followed by an 1822 ± 1 Ma old, equigranular, peraluminous alkali feldspar biotite gravite. The two late facies are an 1818 ± 2 Ma old porphyritic, hypersolvus, alkali feldspar grafite and subsolvus albite gravite. Contact relationships indicate that the liquids forming these two late phases coexisted during the magmatic stage. This implies that they were emplaced almost simultaneously and also that the albite gravite and the hypersolvus grafite have a similar age. The albite gravite is composed by two facies. The dominant is a gray, peralkaline core facies (CAbG), which is composed essentially by albite, quartz and K-feldspar, accompanied by cryolite, zircon, polylithionite, riebeckite, Li-Fe mica, cassiterite, pyrochlore and magnetite. The modal proportions of the essential phases are similar, suggesting a magmatic origin for the CAbG and a cotectic or near minimum composition for its melt. Other features indicating a magmatic origin for the CAbG are: (1) the common occurrence of microscopic snowball textures; (2) it's petrographic and geochemical homogeneous character; (3) local presence of associated rocks with fluidal or pegmatitic textures. The CAbG is transitional to a reddish, peraluminous border facies (BAbG), found along the contacts of the albite with the early facies of the Madeira Granite. The BAbG is composed by albite, quartz and K-feldspar, with subordinate amounts of fluorite, zircon, chlorite, cassiterite, hematite, and columbite. The BAbG modal proportions of the essential phases are more variable and it has higher quartz and lower albite modal contents compared with the CAbG. The BAbG was originated by the autometasomatic alteration of the CAbG. The fluids involved in this process had a strongly oxidizing character and associated chemical changes destabilized the peralkaline mineralogy of the CAbG as evidenced by the replacement of cryolite, micas, pyrochlore and riebeckite. EMPA analyses indicate that the feldspars of the CAbG have near end-member compositions. The K-feldspars (Or —98%) are not perthitic and show high contents of Rb20 (-2%) and Fe2O3 (-0.6%), while the albites (Ab —99%) show anomalously high Fe2O3 (-1%) and relatively low Al2O3. These compositional characteristics indicate: a final crystallization temperature around 500°C or lower for the CAbG; the Al2O3 depleted character of the CAbG melt. Two micas were identified in the CAbG, both showing extremely low K/Rb ratios and high contents of Fe, Zn e Li. The more abundant is a Zn-Rb-polylithionite and the other is dark, Fe-Li mica with high Zn, F and Rb contents. The latter is relatively impoverished in Al2O3 and has Fe in tetrahedral positions, being tentatively classified as a tetra-ferri-Li mica. The unusual chemical compositions of micas and feldspars, as weli as the associated Sn, Nb, Zr, F, mineralization indicate that the CAbG derived from a melt that was geochemically similar to those forming fractionated, rare metal NYF pegmatites. The high Fe2O3 in feldspars and high Fe2O3/FeO in the dark mica, besides the presence of magnetite in the CAbG, suggests that it crystallized under relatively oxidizing conditions (-NINO). The CAbG shows very high contents of F, Na2O, Sn, Nb, Zr, U, Th, Zn, Li and Rb, and low CaO, MgO, TiO2, P2O5, Ba, and Sr. K/Rb and Rb/Sr ratios display extreme values, demonstrating the advanced fractionation of the liquid that originates the CAbG. The gullwing-shaped REE patterns and very low LaN/YbN ratios indicate the strong influence of F during magmatic evolution. The REE are distributed as M-type tetrads, showing that the fractionation mechanisms and the distribution of the REE's were controlled by processes similar to those observed in rare metal-bearing, evolved granitic systems. The Nd isotopes indicate crustal Paleoproterozoic protholiths for the two early facies of the Madeira Granite, which shows slightly negative εNd values. The CAbG and one sample of the hypersolvus grafite show low, positive εNd values. These data can be interpreted as indicating that: (1) the albite granite and the hypersolvus grafite have a protholith which is distinct from that of the earlier facies of the Madeira Granite; (2) both group of rocks derived from a same protholith but the Sm-Nd isotopic system of the albite granite and hypersolvus grafite was disturbed. Ali analyzed samples of the BAbG and an oxidized sample of the hypersolvus grafite shows strongly negative and scattered εNd values. This suggests that the hydrothermal processes that affected these rocks were able to strongly disturb their Nd isotopic system. The adopted petrogenetic nnodel, based on experiments on the system albite grafite -H20 - HF at 1 Kbar, suggests that the albite granite was originated from residual liquids derived from pristine F-rich, MgO-, TiO2--, CaO-depleted magmas. The very high F contents of the residual liquids strongly depressed the viscosity, density and the solidus of the system. This permitted a extreme fractionation of the melt, which evolved in a temperature interval coincident with those of pegmatitic processes. Due to the increase of the H2O contents in the residual liquid in the inner portions of the albite grafite, water saturation was attained and an aqueous fluids was segregated allowing the formation of pegmatitic rocks, while the F-rich residual melt phase generated the veins and pods of massive cryolite.
Acesso aberto (Open Access)
Sedimentação siliciclástica e proveniência do grupo Alto Paraguai (neoproterozóico-cambriano), borda Sul do Cráton Amazônico e faixa Paraguai Norte, estado do Mato Grosso.
(Universidade Federal do Pará, 2011-09-02) SILVA JÚNIOR, José Bandeira Cavalcante da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; 8867836268820998
The Neoproterozoic-Cambrian Alto Paraguai Group exposed in the southern Amazon Craton and the northern Paraguay Belt, western-central Brazil, represents a 2,400m thick siliciclastic succession that succeed the carbonate platform sedimentation deposited after the last Cryogenian glaciation (635 Ma). The Alto Paraguai Group consists of Raizama (fine to coarse grained sandstones, conglomerates, mudstones, pebbly mudstones and secondary chert), Sepotuba (dolomites, stromatolites, mudstones and fine to medium grained sandstones) and Diamantino (mudstones and fine to medium grained sandstones) formations. Outcropbased facies and stratigraphic analysis in combination with provenance studies using detrital zircon U-Pb dating, allowed understanding the lithostratigraphy and the depositional history of the Alto Paraguai Basin. The depositional model include the progradation of a fluvialwave-tide- and storm-dominated coastal region (upper member of the Raizama Formation) onto a shallow to moderately deep storm-influenced marine platform, locally influenced by debris flow (lower member of the Raizama Formation). Afterwards, the last transgressive event in the Paraguai Basin generated tidal flat-sabkha setting in the shallower portions of the basin to the west (lower member of the Sepotuba Formation) and a storm-dominated marine platform in the central and eastern portion of the basin (upper member of the Sepotuba Formation). The progression of the Pan-African-Brasilian orogenesis resulted in the confinement of the Sepotuba Sea as a foredeep sub-basin, against the edge of the Amazon Craton. These restricted lake/sea was filled with turbidites deposits (lower member of Diamantino Formation), lacustrine sediments (middle member of the Diamantino Formation) and progradational deltaic front deposits (upper member of the Diamantino Formation). This sedimentation was supplied by source areas of 600 to 500 Ma, located in the southeast and east of the basin, related to the Brasilia Belt and the Paraguay orogen. This stage represents the final amalgamation of Western Gondwana, marked by the closure of the Neoproterozoic Clymene Ocean between the Amazon Craton and Central Gondwana, generating the northern Paraguay Belt.
Acesso aberto (Open Access)
Soleiras e enxames de diques máficos do Sul-Sudoeste do Cráton Amazônico
(Universidade Federal do Pará, 2016-08-19) LIMA, Gabrielle Aparecida de; SOUSA, Maria Zélia Aguiar de; http://lattes.cnpq.br/3596566506872372; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
Sills and mafic dyke swarms are an important tool for understanding geodynamic processes once they mark the beginning of large extensional tectonic events, but also they are fundamental indicators of nature and evolution of mantle sources through geological time. In the S-SW Amazon Craton, Proterozoic sills and dyke swarms are reported in Eastern Bolivia, and in the Brazilian states of Mato Grosso and Mato Grosso do Sul. There are examples, such as the dyke swarms of the Huanchaca, Rancho de Prata, and Rio Perdido intrusive suites as well as mafic sills of the Huanchaca, and Salto do Céu suites, and Rincón del Tigre Complex. This work aims to characterize the nature, petrological evolution and tectonics of the mafic magmatic event related to tafrogenetic events that are responsible for the break-up or attempted break-up of continental crust. Several tools were used in order to clarify this issue, such as geological mapping, petrographic, lithogeochemical and geochronological (U-Pb IDTIMS and Ar-Ar) analysis. The studied units are sited in the municipalities of Vila Bela da Santíssima Trindade, Nova Lacerda, Conquista D‟Oeste, and Salto do Céu in Mato Grosso, and in Porto Murtinho and Caracol in Mato Grosso do Sul. Rocks of the Salto do Céu suite occur in the municipalities of Salto do Céu and Rio Branco (MT), and outcrop as sills and lava flows. Sills are emplaced into pelitic rocks of the Aguapeí Group usually with shallow dips towards WSW. Lava flows overly the same sedimentary unit and show internal vertical structures and flow-top structures that are typical of thin basaltic flows. Vesicles and amygdales are commonly observed along with flow-folds and breccias. Petrographically, these rocks are mesocratic to melanocratic, greenish-gray to black, and equigranular varying from very fine- to medium-grained. Sills consist of diabases and massif gabbros that under the microscope show ophitic, sub-ophitic, intergranular, and coronitic textures. They are essentially composed of plagioclase and pyroxene having its accessory assemblage represented by opaques, acicular apatite and subhedral sphene. Lava flows, in turn, consist of basalts and diabases that commonly displays ophitic, sub-ophitic, hyalophitic, porphyritic or amygdaloidal textures in a pseudo-trachytic groundmass; some samples exhibit vitrophyric texture. The main components are plagioclase, pyroxene, and relict glass. Amygdales are rounded to ellipsoidal filled with fibrous to fibro-radiated material which is composed of zeolites, chlorite, fluorite, and opaques. Sills and lava flows have tholeiitic affinity, and are classified as intraplate basalts. This suite shows a U-Pb (ID-TIMS) baddeleyite age of 1439 ± 4 Ma. 40Ar-39Ar analysis of plagioclase and amphibole provided a plateau age of 1021 ± 5 Ma, and an integrated age of 1385 ± 9 Ma, respectively. Numerous mafic dykes of the Rancho de Prata Intrusive Suite occur in the surroundings of Nova Lacerda and Conquista D‟Oeste (MT) along an array about 30 km-wide and 150 km-long trending NNW. They occurs as parallel dyke swarms striking N30°–40°W with steep dips. There are no records of deformation or metamorphism on these rocks which occur in intrusive contact with gneissic, granitic and metavulcanossedimentary rocks of the basement. These mafic dykes consist of gabbros, diabases, and basalts, very fine to medium-grained, which exhibits phaneritic, aphanitic to porphyritic textures. They are melanocratic dark-gray to black, with massif structure, in places with discrete foliation parallel to the dyke walls. Microscopically, these rocks are holo- to hypocrystalline, and show porphyritic, intergranular, and subophitic to ophitic textures, and are essentially composed of plagioclase, clinopyroxene and orthopyroxene, olivine and amphibole. Dark-brown intergranular glass is seldom observed in basalts. Lithogeochemical studies allow us to classify these rocks as basalts and andesiticbasalts. The magmatism is sub-alkaline to tholeiitic whose chemical affinity is compatible with continental basalts. Two groups are observed in rare earth elements distribution patterns: one strongly fractionated and enriched in light ETR, and another one weakly fractionated with medium La/Yb ratios, respectively, 3.22 and 1.26. A U-Pb (ID-TIMS) baddeleyite age of 1387 ± 17 Ma was obtained for the dyke swarms. 40Ar-39Ar analysis of plagioclase provided plateau ages of 967 ± 5 Ma and 980 ± 7 Ma. However, 40Ar-39Ar age-spectrum data for amphibole is heterogeneous, therefore provide integrated ages of 1495 ± 8 Ma and 1509 ± 7 Ma. Sills and mafic dykes of the Huanchaca Intrusive Suite are sited in the portion of the Paraguá Terrane which is not affected by the Sunsás Orogeny (1.1 to 0.9). Dykes occur emplaced into the basement rocks underlying the Aguapeí Group that are represented by the Mesoproterozoic granites Guaporeí and Passagem that form part of the Pensamiento Granitoid Complex, as well as by the Paleoproterozoic orthogneisses Shangri-lá and Turvo that occur within the Chiquitania Metamorphic Complex; sills, in turn, are emplaced into the pelites and sandstones of the Vale da Promissão Formation (Aguapeí Group). Sills outcrop as blocks and low-lying outcrops in abrupt and parallel contacts to the layering of sedimentary rocks. On the other hand, dykes outcrop as small and discontinuous trending-ENE crests, or as single, rounded and angular blocks in the granitic-gnaissic terrane whose main orientation varies between N70°-90°E. Sills consist of gabbros and diabases, are greenish-gray to black in colour, and fine- to medium-grained. Optically, these are holocrystalline with sub-ophitic to ophitic texture, and rare intergranular texture. Cumulate rocks of restricted occurrence were identified with paragenesis and textures similar to each other whose difference is the presence of olivine and high content of mafic minerals. These rocks are essentially composed of plagioclase, pyroxene, amphibole, opaques, and in a few of them, alkali-feldspar and quartz displaying graphic intergrowth are also observed. Dykes are dark-gray to greenish-gray with grain size decreasing from the rock wall towards the center of the body from very fine-grained or glassy to medium-grained, respectively. They are classified as diabases and basalts, respectively, holo to hypocrystalline, and have an essential composition of plagioclase, pyroxene and olivine. Under the microscope, diabases show inequigranular, sub-ophitic, and subordinate ophitic textures, and are fine- to medium-grained, while basalts display porphyritic, glomeroporphyritic, and textures vitrophyric, and rarely intersertal to hyalophitic textures. Chemically, dykes and sills are classified into sub-alkaline andesitic basalts (tholeiitic) formed in intraplate settings. REE patterns show that sills are richer in total REE relative to the dykes, as well as show significant vertical variation with respect to the REE pattern envelope, yet parallel to it. Ar-Ar plateau ages were obtained for the sills both from plagioclase (948 ± 5 Ma), and amphibole (1113 ± 11 Ma). A U-Pb (ID-TIMS) baddeleyite age of 1111.5 ± 1.9 Ma was also obtained for sills. The dyke swarms that form part of the Rio Perdido Intrusive Suite occur emplaced into Paleoproterozoic rocks sited in the Rio Apa Terrane (SW of Mato Grosso do Sul), and Paraguay. Dykes are tabular to lenticular, 1 to 30 m thick, generally striking N70°-90°E and N70º-90ºW. They exhibit abrupt and discordant contact with respect to the general NS trend. Dykes consist of very fine- to fine-grained diabases, and fine- to medium-grained microgabbros, both with no evidence of ductile deformation and metamorphism. Under the microscope, they are holocrystalline with ophitic to sub-ophitic, intergranular, and, in places, porphyritic textures, as well as quench textures in which they display swallow-tail shape. They contain essential plagioclase, pyroxenes and olivine, and show a tholeiitic trend with FeOt enrichment relative to MgO for relatively constant alkali contents. They are classified as basalts and andesitic basalts that are similar to Phanerozoic intraplate basalts. REE patterns show strong fractionation of light REE relative to the heavy, with La/Yb ratios varying between 2.8 and 6.2 and Eu anomalies subtly negative or absent. Recent U-Pb (ID-TIMS) data on baddeleyite provided an age of 1110 Ma. The Rincón del Tigre Igneous Complex is a thick layered intrusion that intrudes into the Sunsás Group (below), and into the Vibosi Group (above). Its name is due to the region of Rincón del Tigre in Bolivia, and is characterized as an igneous event related to the Sunsás Orogeny. It is divided into three units: Ultramafic (basal), Mafic (intermediate), and Felsic (superior). The Ultramafic Unit is composed of serpentinized dunite, harzburgite, olivine bronzite, bronzite picrite, and melanorite, while the Mafic Unit is composed of norite and gabbro. The Felsic Unit is represented by granophyres. A U-Pb (ID-TIMS) baddeleyite age of 1110.4 ± 1.8 Ma was obtained from the Felsic Unit, and show chronological similarity to the syn- and postorogenic granitic suites that occur in the Sunsás-Aguapeí province sited in Bolivia, and Brazil. Based on K-Ar ages varying between 1006 and 875 Ma, the units above were attributed to a single magmatic event and interpreted as a LIP that formed during an attempted breakup of Rodinia. Now, based on new precise geochronologic data (U-Pb TIMS on baddeleyite, and Ar-Ar on amphibole and plagioclase), and field and petrological data, this hypothesis is not supported anymore. There were two fissural magmatic events prior to the agglutination of this supercontinent: the older one with ages of 1439 and 1387 Ma, and the younger one around 1110 Ma old. By taking into account the evolution of the Amazon Craton, the older episode is marked by dyke swarms of the Rancho de Prata suite as well as lava flows and sills of the Salto do Céu suite, likely associated with post-orogenic stages of the Santa Helena Magmatic Arc in the Jauru Terrane; the younger event, which have occurrence restricted to the Paraguá and Rio Apa Terranes, is represented by the Huanchaca, and Rio Perdido suites and Rincón del Tigre Complex, and form part of a Stenian LIP sited in the south-southwestern Amazon Craton. This LIP evolved from an attempted break-up of continental crust that resulted in the formation of the Aguapeí Aulacogen. The Sunsás and Aguapeí Belts mark the period of agglutination of Rodinia, and are responsible for the metamorphism and deformation observed in part of this Stenian LIP.

Navegar

Navegando Teses em Geologia e Geoquímica (Doutorado) - PPGG/IG por Assunto "Cráton Amazônico"