Results
Title

Pb isotope geochemistry and reappraisal of Sr-Nd isotopes of the Cerro Morado basic magmatism (Ischigualasto-Villa Union Triassic basin, NW Argentina): Implications for the mantle sources.

Authors

Sommer, Carlos Augusto; Barreto, Carla Joana S.; Lafon, Jean Michel; de Lima, Evandro Fernandes; Alexandre, Felipe Marcelo; Chemale Jr., Farid; Koester, Edinei

Abstract

Sr-Nd-Pb isotopic signatures were determined for silica-undersaturated hypabyssal alkaline basic rocks of the Los Baldecitos Formation in the Cerro Morado area, situated in the Ischigualasto -- Vale de la Luna Provincial Park (northernmost San Juan Province, Argentina). The basic rocks show slight variations of the Sr-Nd-Pb isotopes and similar behavior of whole-rock geochemistry, which suggest a single source for the Cerro Morado volcanic rocks. The present-day Pb isotopic data show moderately radiogenic Pb compositions (206Pb/204Pb = 18.31 - 18.35), in addition to low values of 87Sr/86Sr initial ratios of 0.70314 - 0.70386 and highly radiogenic Nd initial isotopic compositions ( 7.1 Nd(228 Ma) < 9.3), which point to a PREMA mantle reservoir signature for the alkaline basalts with little evidence of crustal contamination. The involvement of a HIMU component in the source, previously suggested for the Cerro Morado volcanics, should be disregarded in the light of the Pb isotopic signature. The Sr-Nd signature together with Nd-TDM model ages not older than 295 Ma does not support the involvement of an ancient crust.

Subjects

LEAD isotopes; GEOCHEMISTRY; STRONTIUM isotopes

Publication

Brazilian Journal of Geology, 2018, Vol 48, Issue 1, p115

ISSN

2317-4889

Publication type

Academic Journal

DOI

10.1590/2317-4889201820170106