Dados da Submissão

Título

RHYACIAN MAGMATISM OF THE SOUTHERN BACAJÁ DOMAIN NEAR THE CARAJÁS PROVINCE BOUNDARY, SE AMAZONIAN CRATON

Texto do resumo

The Bacajá domain is in the Maroni-Itacaiúnas Province, SE Amazonian Craton. It is related to a Rhyacian collisional event developed during the Transamazonian Orogeny (ca. 2.2-1.95 Ga), which reworked the Archean and Siderian crust and provided significant crustal growth during the Paleoproterozoic. The southern portion of the domain is situated near the proposed boundary between it and the Carajás Province and has not been heavily studied so far. Detailed geological mapping, petrography, whole-rock geochemistry, U-Pb geochronology, and Nd isotopes undertaken in that portion of the Bacajá domain allow us to identify new distinct Paleoproterozoic granitic and charnockitic units previously encompassed in the Mesoarchean Cajazeiras Complex. The granitic units encompass calc-alkaline amphibole-biotite and biotite monzogranites to syenogranites and rare biotite granodiorites and tonalites (Rio Preto granitic complex), calc-alkaline amphibole monzogranites to leucogranites (Bandeirante granite) and calc-alkaline and strongly peraluminous garnet-bearing granites to granodiorites (Bernardino granite). The charnockitic units consist of calc-alkaline orthopyroxene-bearing and orthopyroxene-free tonalites and granodiorites with rare monzogranites (Serra Azul charnockite) and shoshonitic to high-K calc-alkaline fayalite-bearing granites, orthopyroxene-bearing granodiorites, with rare gabbros, monzonites, quartz-monzonites (Maravilha charnockite). Three major periods of magmatism at 2.12-2.10 Ga, 2.09-2.06 Ga, and 2.05 Ga were recognized. The crystallization of the amphibole-bearing varieties of the Rio Preto granitic complex and Bandeirante granite marks the older event. It is followed by the crystallization of the biotite-bearing varieties of the Rio Preto Complex and Maravilha and Serra Azul charnockites. The crystallization of the Bernardino granite marks the younger event. The Nd isotopes of the different units reveal moderate to highly negative εNd(t) (from -1.91 to -8.96) with Mesoarchean to early Siderian (2.90 to 2.48 Ga) TDM ages. The εNd(t) indicates that the Paleoproterozoic crust from southern Bacajá is neither juvenile nor heavily influenced by mantle sources in its origin. The gap between crystallization ages and TDM ages (400 to 830 Ma) suggests long periods of crustal residence. The Paleoproterozoic magmatic units that are dominant in the studied area are not akin in geochemistry, age, and isotopic behavior to the Archean units present in northern Carajás, which implies that the southern region of the Bacajá domain does not represent an exhumated crust from Carajás but rather an extension of the Paleoproterozoic crust from northern Bacajá.

Palavras Chave

Geochemistry; Nd isotopes; Crustal evolution; Rhyacian granitoids