A relação entre o domínio bacajá e o domínio carajás, sudeste do cratón amazônico, com base em geologia isotópica e química mineral

Abstract

The Amazonian Craton represents a large continental plate, composed of several crustal provinces of Archean to Mesoproterozoic ages, with boundaries between provinces based on geological and, mainly, geochronological data. Although these boundaries are well established, doubts about how this might have happened are raised, such as the contact between the Carajás Domain (Central Amazonian Province) and the Bacajá Domain (Maroni- Itacaiúnas Province), southeastern of the craton. The study region is located in this boundary and is characterized by the occurrence of several lithotypes, among them amphibolites, granulites, granites, gneisses and charnockites. Mineral chemistry analyses on amphiboles of the amphibolites showed magnesium-hornblende and ferropargasite composition, with medium to high amphibolite facies metamorphism and temperature between 676 to 730º C, with pressure 3,7 to 8,8 kbar. Amphiboles from charnockites were classified as magnesiumhornblende and magnesium-hastingsite, biotite as annita, plagioclase with andesine composition and pyroxenes as augite and ferrosilite. The magmatic temperature for the charnockites ranges from 853 to 910 ºC, with pressure from 3,3 to 6,6 kbar. The generation environment is proposed as a magmatic arc, since it presented a metaluminous and magnesian composition. Biotite from granulites was classified as phlogopite, plagioclase has an andesine composition and pyroxenes classified as augite and ferrosilite. The temperature of 650º C indicates a low granulite facies, recording the minimum temperature imposed on the rock. The Igarapé Gelado granite-related metagranite was 2854 ± 11 Ma old, weakening the idea of a relationship between them. Two crystallization ages were found for orthognaisses protoliths, one of 2848 ±8 Ma and other of 2882 ± 25 Ma; and two ages that indicates a metamorphic event, 2763 ± 16 Ma and 2748 ± 47 Ma. For the model-ages a range between 3,12 and 3,48 Ga was determined, with εHf (t) -3,68 to 2,12. The other model-age ranges from 3,00 to 3,16 Ga, εHf (t) from 1,99 to 4,45. Three distinct events were described for the study area: (1) a magmatic event during the Mesoarchean, around 2.8 Ga, with possible contribution of magmatic arc environment, generating metamonzogranite and monzogranitic orthognaisses protoliths; (2) subsequently a dynamic metamorphic event acting in the study area, recorded in Carajás Domain lithotypes; (3) the union between the Bacajá Domain and the Carajás Domain, at the end of the Transamazonic Cycle.