Composition and thermal evolution of the lithospheric mantle beneath the Ribeira Belt, SE Brazil: evidence from spinel peridotite xenoliths

Author(s)

Almeida, Vidya Vieira ; Janasi, Valdecir de Assis ; Faleiros, Frederico Meira ; Simonetti, Antonio ; Moraes, Renato

• Document type: Journal article
• Source: INTERNATIONAL JOURNAL OF EARTH SCIENCES; v. 111, n. 3, p. 21-pg., 2022-02-18.

Abstract

This study reports the first geochemical and Pb isotopic data for mantle xenoliths from beneath the Neoproterozoic Ribeira Belt, southeastern Brazil. The cm-sized spinel peridotite xenoliths are hosted by a Cretaceous lamprophyre dike that intruded high-grade metamorphic rocks. Major- and trace-element compositions of the main minerals indicate that the xenoliths derive from a shallow fertile mantle that has undergone a low degree of melt extraction (2-9% partial melting). On the basis of modeled isochemical phase diagrams for lherzolites, pressure and temperature conditions are inferred to vary from 1300-1350 degrees C and 17-19 kbar (fertile composition) to 1330-1430 degrees C and 17-23 kbar (relatively depleted composition), which correspond to high geothermal gradients of 65-80 mW/m(2). Temperatures of last equilibration calculated based on the average REE content of pyroxenes for the same lherzolite samples vary from 1233 +/- 56 degrees C to 1085 +/- 42 degrees C, while conventional thermometry (T-BKN) yields average values of 807 and 755 degrees C, indicating re-equilibration at lower temperatures. Pb isotope ratios of clinopyroxene define a mixing line that intercepts the Stacey-Kramers two-stage terrestrial Pb evolution curve at ca. 200 Ma. Linear regressions yield two errorchrons of 56 +/- 75 Ma and 571 +/- 99 Ma (95% confidence level). These results combined with the ages and tectonic settings of host rocks are suggestive of an overprint of a younger tectono-thermal event, most likely related to the opening of the South Atlantic Ocean, over a mantle previously equilibrated during the Precambrian development of the Ribeira Belt. (AU)

• FAPESP's process: 19/22084-8 - The Paraná Magmatic Province: petrogenesis, chronology and environmental impact of Cretaceous tholeiitic, alkaline and silicic magmatism in the Brazilian Platform
• Grantee: Valdecir de Assis Janasi
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 07/00635-5 - Contributions from the mantle and different crust reservoirs to the Neoproterozoic granitic magmatism in SE Brazil
• Grantee: Valdecir de Assis Janasi
• Support Opportunities: Regular Research Grants
• FAPESP's process: 06/01925-4 - Mineralogy and petrology of mantle xenoliths from Ubatuba (SP) and Coromandel (MG) regions
• Grantee: Vidya Vieira de Almeida
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 18/10012-0 - Fluid flow, deformation and tectonic significance of regional shear zones from the southern Ribeira Belt
• Grantee: Frederico Meira Faleiros
• Support Opportunities: Regular Research Grants