| Full text | |
| Author(s): |
Motta, Rafael G.
[1, 2, 3]
;
Fitzsimons, Ian C. W.
[3]
;
Moraes, Renato
[1]
;
Johnson, Tim E.
[3]
;
Schuindt, Sheila
[4]
;
Benetti, Beatriz Y.
[5]
Total Authors: 6
|
| Affiliation: | [1] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo, SP - Brazil
[2] Univ Fed Rio Grande do Norte, Ctr Ciencias Exatas & Terra, Dept Geol, BR-59078970 Natal, RN - Brazil
[3] Curtin Univ, Sch Earth & Planetary Sci, Inst Geosci Res TIGeR, GPO Box U1987, Perth, WA 6845 - Australia
[4] Univ Portsmouth, Sch Environm, Portsmouth PO1 3QL, Hants - England
[5] Univ Torino, Dipartimento Sci Terra, Via Valperga Caluso 35, I-10125 Turin - Italy
Total Affiliations: 5
|
| Document type: | Journal article |
| Source: | Precambrian Research; v. 359, JUL 1 2021. |
| Web of Science Citations: | 2 |
| Abstract | |
Mineral assemblages that are diagnostic of ultrahigh-temperature (>900 degrees C) metamorphism are generally restricted to Mg- and Al-rich rocks. However, in many metamorphic terrains such compositions do not occur, and the rocks are dominated by orthogneisses that typically contain high-variance mineral assemblages that are not diagnostic of particular pressure-temperature (P-T) conditions. Here we use whole-rock and mineral chemistry, thermodynamic phase equilibrium modelling, and zircon U-Pb-Hf isotopic data to constrain the P-T-time history of granulites from the Socorro-Guaxupe Nappe of the Southern Brasilia Orogen. These rocks occur as part of a stack of Neoproterozoic nappes that were assembled during the formation of West Gondwana. Based on phase equilibrium modelling, the peak assemblage in a garnet-bearing felsic granulite (ortho- and clinopyroxene, garnet, K-feldspar, plagioclase, quartz, ilmenite, and silicate melt) records pressures of around 11.5 kbar and temperatures of similar to 1000 degrees C, consistent with the high-Al content of orthopyroxene. The retrograde path records a small decrease in pressure to 9 kbar marked by orthopyroxene replacing garnet and the exsolution of magnetite from ilmenite followed by near-isobaric cooling that led to the development of coronas of hornblende around pyroxene due to crystallization of the last vestiges of melt. Zircon cores yielding U-Pb ages of ca. 625 Ma are interpreted as dating close-to-peak conditions during high-temperature metamorphism. In one sample, zircon rims and `soccer ball' zircon neoblasts both have high U contents and yield ages of ca. 615 Ma, interpreted to mark the onset of melt crystallization. In two other samples, low-U rims and `soccer ball' zircons grains yield ages of ca. 600-595 Ma, interpreted to date the end of melt crystallization. These data reveal a protracted regional metamorphic event in which the lower crust remained at granulite-facies conditions for at least 30 Myr during collision and assembly of West Gondwana. (AU) | |
| FAPESP's process: | 16/22627-3 - Metamorphism and partial melting in ancient orogens II |
| Grantee: | Renato de Moraes |
| Support Opportunities: | Regular Research Grants |
| FAPESP's process: | 13/04007-0 - Metamorphism and partial melting in ancient orogens |
| Grantee: | Renato de Moraes |
| Support Opportunities: | Regular Research Grants |
| FAPESP's process: | 15/22355-0 - FORMATION, TRANSFORMATION AND EVOLUTION OF LOWER CONTINENTAL CRUST: INVESTIGATING THE SOUTHERN BRASÍLIA OROGEN |
| Grantee: | Rafael Gonçalves da Motta |
| Support Opportunities: | Scholarships in Brazil - Doctorate |
| FAPESP's process: | 16/10276-1 - Formation, Transformation and Evolution of Lower Continental Crust: Investigating the Southern Brasília Orogen |
| Grantee: | Rafael Gonçalves da Motta |
| Support Opportunities: | Scholarships abroad - Research Internship - Doctorate |