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Title: Petrologia e geotermobarometria das rochas metamórficas do Cinturão Araguaia: região de Xambioá-Araguanã (TO)
metadata.dc.creator: PINHEIRO, Bruno Luis Silva
metadata.dc.contributor.advisor1: GORAYEB, Paulo Sérgio de Sousa
Keywords: Petrologia
Metamorfismo (Geologia)
Cinturao-Araguaia – Xambioa (TO)
Issue Date: 16-Dec-2016
Publisher: Universidade Federal do Pará
Citation: PINHEIRO, Bruno Luis Silva. Petrologia e geotermobarometria das rochas metamórficas do Cinturão Araguaia: região de Xambioá-Araguanã (TO). Orientador: Paulo Sérgio de Sousa Gorayeb. 2016. 258 f. Tese (Doutorado em Geologia e Geoquímica) – Instituto de Geologia, Universidade Federal do Pará, Belém, 2016. Disponível em: Acesso em:.
Abstract: In order to contribute to the understanding of the metamorphic processes of the metamorphic rocks of the Araguaia Belt (CA), this thesis presents field data and metamorphic modeling, used as tools to obtain the maximum conditions of P-T reached by the units located in the Xambioá-Araguanã (TO) region of the rocks studied are five samples of Staurolite-garnetbiotite- muscovite-schist with Kyanite and a sample of Garnet amphibolite, belonging to the Xambioá Formation and Xambica Suite, respectively. The study of the metamorphism occurred through petrographic, chemical analyzes of rocks and minerals of the main associations of pelitic rocks, semipelitic and mafic rocks that comprise the zone of greater metamorphic degree of CA, for later analysis by metamorphic modeling in the NCKFMASH system and optimized geothermobarometry, In the avPT mode, in the THERMOCALC program, as well as the Hb-Pl software, which made it possible to identify PT metamorphic peak conditions. In addition to defining an approximate age of metamorphism using the Ar-Ar method in biotite and amphibole. The petrographic-mineralogical study identified the main mineral parageneses in the studied micaxists, such as St + Grt + Bt + Ms + Qtz ± Pl (An12-31) + Ky, and in the amphibolites Hb + Grt + Bt + Pl (An12-25). The mineral chemistry results showed that the pomegranate composition of the six samples is dominated by the almandide molecule, which is followed by pyropo, thickenstock, and andradite, increasing Fe2 + and Mg from the nuclei to the edges, with a concomitant decrease of Mn and Ca. The higher Fe and Mg contents towards the edges indicate an increase in the temperature conditions during mineral development. The composition of the biotite is in the transition of the biotite with phlogopite, becoming more ferromagnesian mica. Staurolite from the core to the border is enriched in Fe2 + and depleted in Mg, which may suggest reactions in contact with the matrix and / or with micas or grenades. Metamorphic modeling in the NCKFMASH system resulted in pseudosections with similar topologies for samples BP002, BP149 and BP299, suggesting that the maximum metamorphic conditions they were subjected to are similar, being situated within a PT window with pressure approximately between 7 and 9 kbar and temperature between 630 and 665 ° C. The models of composite isopleths of the minerals calculated in the pseudosections indicate a higher participation of Mg and a lower participation of Ca in the composition of the main minerals according to the increase of the metamorphic P-T conditions in the region, compatible with the mineral chemistry results of the studied rocks. In addition to the plagioclase and the pomegranate of the sample BP002 presenting as good indicators of metamorphism conditions, with values of 8 kbar and 660 °C, in which the coreedge variation of Ca and Na in plagioclase crystals and the variation Core-edge in the iron content of the grenades show a progressive barometric-type metamorphic trajectory, represented by a small slope curve, coming from the trivariant field Chl + Grt + Bt + Ms. PT estimates obtained in the avPT mode of THERMOCALC in all the selected samples (BP002, BP005, BP149, BP149, BP299, BP006), as well as in the Hb-Plag software in the amphibolites (BP006), presented enough Consistent and consistent with calculations of metamorphic peak conditions via THERMOCALC for rocks in the Xambioá-Araguanã region, although there are discrepancies in the calculated results. All calculated P-T results are compatible with the field of the amphibolite facies of the mean P-T series, typical of continental orogenic belt environments and therefore characteristic of continental collisions. Metamorphic conditions are reinforced with the mineral chemistry results of calcium amphiboles suggesting the same average pressure conditions of the Dalradian terrain of Scotland. The air-air ages in minerals obtained in the metapelites and amphibolites in this thesis were similar, around 504 Ma, and they show that the peak of the metamorphism of the amphibolite facies in the region under study has an older age and they suggest that it was next to the Neoproterozoic-Paleozoic interface, because these Ar-Ar ages obtained are younger ages than the K-Ar ages of 520-560 Ma, interpreted as relating the metamorphism of the CA with the Brasilian thermo-tectonic event, and because it is within the error of the U-Th-Pb monazites chemical age in feldspathic schist biotite from an area near the city of Presidente Kennedy (TO), 513 ± 14 Ma interpreted only at a younger age than the mean age evaluated for the metamorphism of the Araguaia Belt (550 - 530 Ma).
Appears in Collections:Teses em Geologia e Geoquímica (Doutorado) - PPGG/IG

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