SHOSHONITIC LAMPROPHYRES (MINETTES) FROM THE SIERRA DE SAN LUIS (ARGENTINA)- THE OLDER EVIDENCE FOR AN ENRICHED MANTLE SOURCE DURING THE ACHALIAN OROGENY

MARTÍNEZ DOPICO, C. I.; LÓPEZ DE LUCHI, M. G.; RIBACKI, E.; ALTENBERGER, U; TRUMBULL, R.; MONTENEGRO, T.

Pto Madryn, Chubut

Congreso; XXI Congreso Geologico Argentino; 2022

Asociacion Geologica Argentina

In the Sierra de San Luis, lamprophyric rocks occur as dykes that crosscut the Cambrian Conlara Metamorphic Complex and as part of the monzonite suite (Lopez de Luchi et al. 2017) of the Devonian batholiths. Lamprophyric minette dykes exhibit phlogopite and apatite phenocrysts (50% modal) immersed in a fine-grained groundmass of K-feldspar, phlogopite, quartz, scarce oligoclase and accessories (titanite, allanite and Fe-Ti oxides). A Lower Devonian phlogopite 40K/39Ar age of a lamprophyre dyke (408 ± 6 Ma; Montenegro et al. 2010) indicates that this magmatism predates the Devonian batholiths (López de Luchi et al. 2017, Dahlquist et al. 2019 among others) and hence, it could be the first evidence of a subcontinental enriched lithospheric mantle in the Sierras Pampeanas