Constraints on metasomatized mantle under Central South America: evidence from Jurassic alkaline lamprophyre dykes from the Eastern Cordillera, NW Argentina.

HAUSER, N. MATTEINII MM OMARINI I, R.H. PIMENTELL MMMM

CONTRIBUTIONS TO MINERALOGY AND PETROLOGY

SPRINGER

Lugar: New York; Año: 2010 vol. 100 p. 153 - 184

0010-7999

Abstract In the Río Grande Valley, NW Argentina, several porphyritic panidiomorphic, ocelli-bearing dykes and sills intrude the Neoproterozoic to lower Paleozoic basement of the Eastern Cordillera. New petrographical and geochemical data permit us to classify these rocks as ocellar-analcime monchiquites, a feldspar-free variety of alkaline lamprophyre composed of Ti-rich-diopside/augite, Ti-rich biotite/phlogopite, forsteritic olivine, titanianpargasite and analcime, with abundant ocelli filled with analcime/carbonate. In terms of geochemical compositions they are characterized by LILE and LREE enrichment and lack of Nb-Ta and Eu anomalies. The 87Sr/86Sr and 143Nd/144Nd initial ratios range between 0.70377 to 0.70781 and 0.512506 and 0.512716 respectively, and TDM model ages vary between 0.25–0.64 Ga. A K-Ar age of 163±9 Ma suggests that these rocks are related to the pre-rifting stage of the Mesozoic-Cenozoic continental Salta Rift in NW Argentina. Partial melting of a heterogeneous enriched metasomatized lithospheric mantle, magma mixing and fractionation are envisaged to explain the petrographic, geochemical and isotope characteristics of these magmas.