Insights on the origin of the Graciosa A-type granites and syenites (Southern Brazil) from zircon U-Pb geochronology, chemistry, and Hf and O isotope compositions
Abstract
The Neoproterozoic, post-collisional, Graciosa Province (southern Brazil) comprises several A-type intrusions and related volcanics of alkaline and subalkaline (or aluminous) petrographic associations. U-Pb age determinations, trace element, and Hf and O isotopic compositions were obtained for zircons from six distinct A-type granitic and syenitic plutons from both alkaline and subalkaline associations from the province. Geochronological results indicate that their emplacement, petrogenetic evolution and crystallization spanned over a 9 million years interval, with peak magmatism at 580 Ma. Plutons were emplaced in a post-collisional extensional regime related to the geodynamic evolution of the south-southeastern part of the Gondwana supercontinent. Hf isotopic compositions are highly variable, with ɛHf(t) values between +1.4 to -31, whereas δ18O signatures are mainly between +4.7 and +6.0‰. These features, along with trace element signatures, especially for Hf, U, Nb, and rare-earth elements, suggest that generation of the Graciosa rocks occurred via partial melting of a lithospheric mantle previously metasomatized by slab-derived fluids, followed by variable degrees of crustal contamination at depth.
- Publication:
-
Lithos
- Pub Date:
- September 2019
- DOI:
- 10.1016/j.lithos.2019.05.001
- Bibcode:
- 2019Litho.340...20V
- Keywords:
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- Zircon;
- Trace element composition;
- U-Pb dating;
- Hf and O isotope geochemistry;
- A-type magmatism;
- Graciosa Province