Detrital zircon U–Pb-Hf isotopes-based reconstruction of the depositional history of (ultra)high-temperature metamorphic rocks from the Socorro-Guaxupé Nappe (southern Brasília orogen, Brazil)

Abstract

Deciphering the provenance of paraderived rocks that underwent high-to ultrahigh (HT-UHT) temperature metamorphism is a challenging task. Such metamorphic conditions can generate protracted zircon U–Pb age records of unclear meaning. However, the combination of U–Pb and Lu–Hf in zircon geochronology might be used as a powerful tool in order to retrieve the geological significance of geochronological data and track the signature of possible protosources. Six samples of ortho- and paraderived rocks from the São João da Mata complex in the Socorro-Guaxupé Nappe (SE Brazil), a section mainly containing a continental magmatic arc built at the margins of the Paranapanema paleocontinent affected by HT-UHT metamorphism have been investigated. U–Pb and Lu–Hf isotopic analyses were carried out to evaluate disturbances in the U–Pb system, identify minimum crystallization ages and the Lu–Hf signatures of protosources and protoliths. Five protosources were identified, being four showing crustal Hf signatures (εHf(804-776) = −16 to −2) and minimum U–Pb ages between ca. 804 Ma and ca. 776 Ma, and one with a moderately juvenile Hf signature (εHf(816) = +3 to +9) and a minimum U–Pb age of ca. 816 Ma. The moderately juvenile signature suggests contribution of an island or continental arc-related source. The remaining protosources exhibit similar Lu–Hf signatures to those of orthoderived rocks found within the Socorro-Guaxupé Nappe. We propose that the analyzed paraderived rocks were deposited in a restricted, arc-related setting, that evolved through the following stages: i) an island to early-continental arc stage, with a maximum depositional age of ca. 816 Ma; ii) a continental arc setting, recorded by the protosources with crustal signatures and exhibiting a maximum depositional age of ca. 776 Ma; iii) HT-UHT metamorphism between ca. 690–630 Ma, with high temperature conditions lasting until the end collisional stage of the Orogen (ca. 630–610).