Detrital zircon U-Pb-Hf isotopes-based reconstruction of the depositional history of (ultra)high-temperature metamorphic rocks from the Socorro-Guaxup′e Nappe (southern Brasilia orogen, Brazil)

Author(s)

Rossi-Vieira, P. L. N. C. ; Tedeschi, M. ; Rocha, B. C. ; Lana, C. C. ; Barrote, V. ; Pedrosa-Soares, A. C. ; Dussin, I. A. ; Alkmim, A.

• Document type: Journal article
• Source: Journal of South American Earth Sciences; v. 128, p. 25-pg., 2023-08-01.

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 Sa & SIM;o Joa & SIM;o da Mata complex in the Socorro-Guaxupe & PRIME; 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 (& epsilon;Hf(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 (& epsilon;Hf(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-Guaxupe & PRIME; 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 earlycontinental 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) HTUHT metamorphism between ca. 690-630 Ma, with high temperature conditions lasting until the end collisional stage of the Orogen (ca. 630-610). (AU)

• FAPESP's process: 21/09437-9 - Dating metamorphic processes in the deep continental crust: petrochronology of key UHT and HP units from orogens in Brazil
• Grantee: Brenda Chung da Rocha
• Support Opportunities: Regular Research Grants