Titanite petrochronology of the southern Brasilia Orogen basement: Effects of retrograde net-transfer reactions on titanite trace element compositions

Author(s)

Cioffi, Caue Rodrigues ^{[1, 2, 3]} ; Campos Neto, Mario da Costa ^[1] ; Moller, Andreas ^[3] ; Rocha, Brenda Chung ^{[1, 3]}

Affiliation

^[1] Univ Sao Paulo, Inst Geociencias, Rua Lago 562, BR-05508080 Sao Paulo, SP - Brazil

^[2] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Rua Matao 1226, BR-05508090 Sao Paulo, SP - Brazil

^[3] Univ Kansas, Dept Geol, 1420 Naismith Dr, Slawson Hall, Lawrence, KS 66045 - USA

• Document type: Journal article
• Source: LITHOS; v. 344, p. 393-408, NOV 2019.
• Web of Science Citations: 0

Abstract

Combining U-Pb geochronology and trace element characteristics of accessory minerals more reactive during metamorphism and deformation than zircon, such as titanite (CaTiSiO5), is a powerful tool for elucidating pressure-temperature-time (P-T-t) evolution of orogenic basement complexes. This study reports in-situ titanite U-Pb and trace element data from upper-amphibolite facies metatexitic orthogneisses of the Pouso Alegre Complex in the basement of the Neoproterozoic southern Brasilia Orogen, SE Brazil. The titanite data is combined with thermodynamic modeling, major phase compositions and U-Pb zircon dating and used to constrain the P-T-t path of the complex during the Neoproterozoic orogenesis. The investigated garnet amphibole gneisses record peak metamorphic conditions of 750-775 degrees C and 10.5-12.5 kbar, associated with partial melting and dated at ca. 630-620 Ma based on U-Pb analyses of HREE+Y depleted titanite cores, inferred to have crystallized in the presence of garnet near the peak P-T conditions. Extensive melt crystallization at ca. 616 Ma is constrained by U-Pb dating of leucosome zircons. The exhumation of the complex and re-equilibration to ca. 550-625 degrees C at 6-9 kbar led to widespread generation of biotite + epidote/clinozoisite, partially replacing amphibole + garnet along the main foliation. Trace element signatures of these retrograde net-transfer reactions are recorded in the titanite rims which are HREE+Y enriched, strontium depleted and were dated at 605.7 +/- 62 Ma. The average zirconium contents of the titanite rims are higher than cores suggesting disequilibrium partitioning of zirconium into titanite during the retrograde path resulting in overestimated Zr-in-titanite temperatures for the rims. The exhumation of the complex was concomitant with the intrusion of folded and recrystallized leucogranite dykes dated at 607.0 +/- 5.7 Ma, attesting the persistence of deformation after their intrusion. Assuming that the Pouso Alegre Complex is part of the Sao Francisco paleocontinent reworked during the Brasilia orogeny, the data constrain the minimum age for the collision between the Sao Francisco paleocontinent and the Paranapanema block at ca. 620-630 Ma and agree with the idea of long-lived metamorphism and deformation in the southern Brasilia Orogen. (C) 2019 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 13/13530-8 - The orogenic margins of the Paranapanema and São Francisco blocks: from Rodinia to Gondwana
• Grantee: Mario da Costa Campos Neto
• Support Opportunities: Regular Research Grants
• FAPESP's process: 14/05881-8 - Zircon and titanite LA-ICP-MS U-Pb dating of Archean to Paleoproterozoic crust-forming events and Neoproterozoic reworking processes of the basement rocks of the Southern Brasília orogen
• Grantee: Caue Rodrigues Cioffi
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 16/25987-0 - Application of petrochronology in the reconstruction of P-T-t (pressure-temperature-time) paths of the northern Borborema Province during the Neoproterozoic
• Grantee: Caue Rodrigues Cioffi
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 16/23266-4 - Age and duration of acid magmatism in the Paraná Magmatic Province from 40Ar-39Ar sanidine and U-Pb zircon and baddeleyite dating
• Grantee: Brenda Chung da Rocha
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 12/24933-3 - GEOLOGICAL EVOLUTION OF MIGMATITES FROM THE INFRASTRUCTURE OF SOUTHERN BRASÍLIA BELT NAPPE SYSTEM
• Grantee: Caue Rodrigues Cioffi
• Support Opportunities: Scholarships in Brazil - Doctorate