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

Author(s)

Rocha, B. C. ; Moraes, R. ; Moller, A. ; Cioffi, C. R. ; Jercinovic, M. J.

• Document type: Journal article
• Source: LITHOS; v. 277, p. 19-pg., 2017-04-15.

Abstract

The timing of partial melting and melt crystallization in granulite fades rocks of the Socorro-Guaxupe Nappe (SGN), Brazil is constrained using a combination of imaging techniques, LA-ICP-MS and EPMA dating, trace element geochemistry and thermobarometry. (Orthopyroxene)-garnet-bearing migmatite that records extensive biotite dehydration melting shows evidence for a clockwise P-T-t path. UHT peak conditions were attained at 1030 +/- 110 degrees C, 11.7 +/- 1.4 kbar, with post-peak cooling to 865 +/- 38 degrees C, 8.9 +/- 0.8 kbar. Cryogenian igneous inheritance of ca. 720-640 Ma is identified in oscillatory zoned zircon cores (n = 167) with steep HREE patterns. Resorbed, Y-rich monazite cores preserve a prograde growth stage at 631 +/- 4 Ma prior to the partial melting event, providing an upper age limit for the granulite facies metamorphism in the SGN. REE-rich, Th-depleted monazite related to apatite records the initial stages of decompression at 628 +/- 4 Ma. Multiple monazite growth episodes record melt crystallization events at 624 +/- 3 Ma, 612 +/- 5 Ma and 608 +/- 6 Ma. Stubby, equant "soccer ball" zircon provide evidence for melt crystallization at 613 +/- 2 Ma and 607 +/- 4 Ma. The excess scatter in zircon and monazite age populations between 629 +/- 4 and 601 +/- 3 Ma is interpreted as discontinuous and episodic growth within this age range, characterizing a prolonged metamorphic event in the SGN lasting ca. 30 m.y. The development of Y + HREE-rich monazite rims at ca. 600 Ma documents retrograde garnet breakdown, extensive biotite growth and the final stages of melt crystallization. Th-rich, Y + HREE-poor monazite rims at ca. 590 Ma record monazite recrystallization. (C) 2016 Elsevier B.V. All rights reserved. (AU)

• 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: 10/11152-8 - Tectonics of Brasília orogen at Southern margin of São Francisco Craton: a paleogeographic, metamorphic and structural perspective
• Grantee: Mario da Costa Campos Neto
• Support Opportunities: Regular Research Grants
• FAPESP's process: 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
• Grantee: Brenda Chung da Rocha
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 12/22380-7 - Origin and evolution of melting in the migmatites and granulites of the Socorro-Guaxupé Nappe, in the Alfenas region (MG)
• Grantee: Brenda Chung da Rocha
• Support Opportunities: Scholarships in Brazil - Doctorate