| Full text | |
| Author(s): |
Almeida, Vidya Vieira
;
Janasi, Valdecir de Assis
;
Faleiros, Frederico Meira
;
Simonetti, Antonio
;
Moraes, Renato
Total Authors: 5
|
| 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 |