Lead isotope constraints on the mantle sources involved in the genesis of Mesozoic high-Ti tholeiite dykes (Urubici type) from the São Francisco Craton (Southern Espinhaço, Brazil)

Leila Soares Marques,Marly Babinski,Liliane Aparecida Petronilho,Eduardo Reis Viana Rocha-Júnior,Karine Zuccolan Carvas,Angelo De Min

doi:10.1590/2317-4889201620150010

Abstract

ABSTRACT: The first results of Pb isotope compositions of the high-Ti Mesozoic dykes of the Southern Espinhaço are presented. The results do not show large variations and are significantly more radiogenic than the Pb isotope compositions of the high-Ti tholeiites from the Paraná Continental Flood Basalts. The data combined with published geochemical and Sr-Nd isotope results rule out crustal contamination processes in the genesis of the dykes, requiring magma generation in metasomatized subcontinental lithospheric mantle with the involvement of HIMU-type and carbonatite components. The magmas may have been also derived from a mantle source containing ~4 - 5% of pyroxenite and ~1% of carbonatite melts, agreeing with published Os isotope compositions of high-Ti rocks from the Paraná Continental Flood Basalts. These metasomatizing agents could be responsible for mantle source refertilization, as was also proposed in the literature to explain the characteristics of xenoliths of the Goiás Alkaline Province, which also occurs in the border of the São Francisco Craton. Additionally, to evaluate the risks of Pb contamination during sample preparation for analysis, several experimental tests were accomplished, which indicate the need of sawed surface removal and a careful washing of small-sized rock fragments before powdering, especially for rocks with [Pb] < 7 µg/g.

Highlights

Large igneous provinces (LIP) have been intensively studied all around the world, occurring in both oceanic and continental environments, where vast volumes of volcanic and intrusive rocks are produced in an interval of few million years (Coffin & Eldholm 1994; Bryan & Ernst 2008; Ernst 2014)
In order to contribute to the understanding of the mantle sources involved in Paraná Continental Flood Basalts (PCFB), this study presents the first Pb isotope data and a review of published major, minor and incompatible trace element abundances, as well as Sr-Nd isotope data (Rosset et al 2007) for tholeiitic Mesozoic dykes from the Southern Espinhaço
The dykes have significant radiogenic Pb compositions in comparison to the high-Ti basalts (Pitanga and Urubici types) from the Paraná Continental Flood Basalts, the Sr-Nd-Pb isotope compositions rule out crustal contamination processes in their genesis

Summary

INTRODUCTION

Large igneous provinces (LIP) have been intensively studied all around the world, occurring in both oceanic and continental environments, where vast volumes of volcanic and intrusive rocks are produced in an interval of few million years (Coffin & Eldholm 1994; Bryan & Ernst 2008; Ernst 2014). In order to contribute to the understanding of the mantle sources involved in PCFB, this study presents the first Pb isotope data and a review of published major, minor and incompatible trace element abundances, as well as Sr-Nd isotope data (Rosset et al 2007) for tholeiitic Mesozoic dykes from the Southern Espinhaço. These rocks crop out beyond the north-northwestern limits of the Paraná Basin, located at southeastern border of São Francisco Craton (Minas Gerais State, Brazil). For the present investigation, some samples studied by Rosset et al (2007) were analyzed for Pb isotope compositions, in order to better constrain the mantle sources involved in the MSED genesis

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

LEAD ISOTOPE RESULTS OF THE MESOZOIC SOUTHERN ESPINHAÇO

15.56 Tristan da

CONCLUDING REMARKS