Origin and evolution of melting in the migmatites and granulites of the Socorro-Guaxupé Nappe, in the Alfenas region (MG)

• Grant number: 12/22380-7
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: March 01, 2013
• End date: June 22, 2016
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Renato de Moraes
• Grantee: Brenda Chung da Rocha
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated scholarship(s): 14/05563-6 - Linking in-situ U-Pb dating in accessory minerals using LA-ICP-MS with P-T data in high-grade metamorphic rocks of the Socorro-Guaxupé nappe, BE.EP.DR

Abstract

The Socorro-Guaxupé Nappe represents a magmatic arc domain with granulites and migmatites which record the collision of the Paranapanema plate with the Sanfranciscana plate, in the Neoproterozoic. The Socorro-Guaxupé Nappe is characterized by an allochthonous pile of three distinct units of lower continental crust: Unidade Granulítica Basal, Unidade Diatexítica Intermediária and Unidade Migmatítica Superior. In Alfenas region (MG) there are good exposures of granulites and migmatites of the Socorro-Guaxupé Nappe, providing excellent conditions for the study of partial melting processes in deep continental crust. The best exposure of Unidade Granulítica Basal within the study area is located in Santa Terezinha Quarry, located in the south of Alfenas, where mafic and felsic granulites outcrop, being cut by veins of charnockite and hornblende granite. The Unidade Diatexítica Intermediária is well exposed in an out of work quarry on the road connecting Alfenas to Machado (MG-179). In this quarry occur both stromatic metatexite with intercalated mafic granulite lenses, which can represent restites, and nebulitic diatexites with large volumes of felsic leucosome of pink color, which represents the product of partial melting of a distinct rock than the stromatic metatexite. The analysis of petrological and structural aspects in the two quarries indicates that both sets underwent partial melting, although with the melting controlled primarily by the fertility of protolith or, secondarily, by the conditions of T, P and XH2O of melt. These exposures provide notice of the partial melting process, the formation of leucosome and thick veins of charnockites and granites formed in situ or mobilized, but still in the source area. The aim of this work is to investigate the processes of partial melting and metamorphism through detailed mapping of the two quarries to establish the structural relationships between rock types, together with petrographic studies to determine the main textural relations. The partial melting process will be investigated with further whole rock chemistry, minor and trace elements and mineral chemistry analysis, as well as retrograde reactions commonly observed in theses rocks. The mineral chemistry will be investigated by electron microprobe and ICP-MS with laser ablation. Different thermodynamic methods will be used to determine the attained conditions related to the metamorphic peak, ranging from classical geothermobarometry to PT calculations using accessory minerals such as Zr in rutile, Ti in zircon, Ti in quartz and the garnet-monazite pair. In situ dating techniques, such as LA-ICP-MS and/or SHRIMP, will be applied in some of the minerals used in the P-T calculations, which aim determination of the time intervals involved in the processes of partial melting and metamorphism, in addition to establishing P-T-t paths.

Scientific publications

(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)

ROCHA, B. C.; MORAES, R.; MOLLER, A.; CIOFFI, C. R.; JERCINOVIC, M. J.. Timing of anatexis and melt crystallization in the Socorro-Guaxupe Nappe, SE Brazil: Insights from trace element composition of zircon, monazite and garnet coupled to U-Pb geochronology. LITHOS, v. 277, n. SI, p. 337-355, APR 15 2017. (13/04007-0, 12/22380-7, 10/11152-8, 14/05563-6)

ROCHA, BRENDA CHUNG; MORAES, RENATO; MOLLER, ANDREAS; CIOFFI, CAUE RODRIGUES. Magmatic inheritance vs. UHT metamorphism: Zircon petrochronology of granulites and petrogenesis of charnockitic leucosomes of the Socorro-Guaxupe nappe, SE Brazil. LITHOS, v. 314, p. 16-39, AUG 2018. (16/22627-3, 13/04007-0, 12/22380-7, 14/05563-6)

ROCHA, B. C.; MORAES, R.; MOLLER, A.; CIOFFI, C. R.; JERCINOVIC, M. J.. Timing of anatexis and melt crystallization in the Socorro-Guaxupe Nappe, SE Brazil: Insights from trace element composition of zircon, monazite and garnet coupled to U-Pb geochronology. LITHOS, v. 277, p. 19-pg., 2017-04-15. (13/04007-0, 10/11152-8, 14/05563-6, 12/22380-7)

Academic Publications

(References retrieved automatically from State of São Paulo Research Institutions)

ROCHA, Brenda Chung da. Idade, duração e condições P-T do metamorfismo de temperatura ultra-alta, anatexia e cristalização de fundido na nappe Socorro-Guaxupé. 2016. Doctoral Thesis - Universidade de São Paulo (USP). Instituto de Geociências (IG/BT) São Paulo.