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

• Main Authors: Carlos Augusto Sommer, Carla Joana S. Barreto, Jean Michel Lafon, Evandro Fernandes de Lima, Felipe Marcelo Alexandre, Farid Chemale Jr., Edinei Koester
• Format: Article
• Language: English
• Published: Sociedade Brasileira de Geologia
• Series: Brazilian Journal of Geology
• Subjects: Ischigualasto-Villa Unión Triassic Basin; Silica Undersaturated Rocks; Northwestern Argentina; Sr-Nd-Pb Isotopes
• Online Access: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892018000100115&lng=en&tlng=en
• ISSN: 2317-4692

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 < εNd (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.