U–Pb geochronology, Nd–Hf isotopes, and geochemistry of Rhyacian granitoids from the Paleoproterozoic Lourenço domain (Brazil), southeastern Guiana Shield

Abstract

Listen

Translate article

The southern sector of the Paleoproterozoic Lourenço domain in the central-eastern region of the Amapá state, northern Brazil, consists mainly of Rhyacian granite-greenstone terranes with some Archean fragments. It is located at the transition with the Archean Amapá block, a Meso-Neoarchean continental landmass (2.85–2.60 Ga), strongly reworked during the Transamazonian orogeny (2.26–1.95 Ga). Geochemical and petrographic data together with combined zircon U–Pb and Lu–Hf (LA-ICP-MS) as well as whole-rock Sm–Nd (TIMS) dating, establish the chronology and petrogenesis of the granitoids and record the crustal growth and reworking at the transition between the Archean and Paleoproterozoic domains in the southeastern Guiana Shield. Two episodes, dated at ~2.18–2.16 Ga and 2.14–2.13 Ga, respectively, include medium-to high-K calc-alkaline and metaluminous to peraluminous rocks of the Flexal and Papa-Vento intrusive suites, emplaced in a magmatic arc environment. A third episode, dated at ~2.08 Ga, encompasses mostly peraluminous granites with a medium-to high-K calc-alkaline signature, of the syn-to late-collisional Vila Bom Jesus Suite. The zircon ƐHf (−3.5 to −4.3) and whole-rock ƐNd (−2.7 to −4.3) signatures with respective Hf-TDMC (2.9–3.1 Ga) and Nd-TDM (2.6–2.7 Ga) model ages indicate a mixture of Rhyacian juvenile material with a Mesoarchean crustal component for the magma sources of the Flexal and Papa-Vento intrusive suites. The geochemical characteristics, zircon ƐHf (−6.6 to −12.5) and whole rock ƐNd (−3.7 to −5.4) signatures, and Hf-TDMC (2.9–3.6 Ga) and Nd-TDM (2.7–2.9 Ga) model ages, together with the presence of Rhyacian (2.19 Ga) and Mesoarchean (2.82 Ga) inherited zircon crystals in the Vila Bom Jesus Suite, indicate dominant crustal reworking of Rhyacian magmatic arc rocks and Archean rocks from the adjacent Amapá Block during the arc-continent collision. The geochemical and isotopic signatures of the magmatic arc granitoids (Flexal and Papa-Vento intrusive suites) may be attributed to the incorporation in the juvenile magmatic sources of Archean continental sediments or hidden crustal fragments from the Amapá Block during the subduction processes. Geochemical affinities with continental magmatic arc and subchrondritic Hf–Nd isotopic signatures are consistent with a scenario of a long-lived Mesorhyacian (~2.20–2.13 Ga), Cordilleran-type magmatic arc setting, which evolved to a collisional setting with the amalgamation of the Archean Amapá block and the Rhyacian Lourenço domain during the Neorhyacian (2.11–2.08 Ga).