Química mineral de las lavas de la Formación Somuncurá del sector noroeste de la meseta de Somuncurá, provincia de Río Negro

Abstract

Mineral chemistry of Somuncurá Formation lava flows from the northwestern part of Meseta de Somuncurá, Río Negro province. In the northwestern part of the Meseta de Somuncurá, basaltic and basaltic andesite lava flows of the Somuncurá Formation with petrographic and geochemical disequilibrium evidences are studied. According to the chemical features of the mineral phases from these lavas, it is recognized that mainly the alkaline lavas show plagioclase and orthopyroxene microphenocrysts and crystals of the groundmass, with normal and inverse variations of CaO and MgO, respectively. However, such variations are not always directly related to the disequilibrium textures observed. Nonetheless, the chemical variations documented in this contribution are also considered as cryptic evidences of the chemical disequilibrium in these lavas. All the characteristics of instability recognized in the studied lavas of the Somuncurá Formation indicate that these basalts and basaltic andesites must have been affected by some magmatic process that would give rise to such disequilibrium. Two possibilities are: 1) magma mixing; 2) Somuncurá lava flows belong to different mantle sources.