科研之友
微信
新浪微博
Facebook
分享链接
摘要
the pay迆n matr迆 volcanic field is located in the payenia basaltic province of the recent back-arc of western argentina (35～s-38～s). this province is younger than 5 ma, and most of its volcanic activity took place since 2 ma. the pay迆n matr迆 volcanic field contains two composite volcanoes, pay迆n matr迆 and pay迆n liso, and two basaltic fields in an e-w oriented zone, located east and west of the pay迆n matr迆 volcano. pay迆n matr迆 is the largest volcano of this volcanic field, and consists of a shield-shaped edifice with a circular summit caldera of 8 km in diameter. the composition of both composite volcanoes is alkaline and predominantly trachytic, having also minor intermediate lavas. the basaltic fields consist of basalts and trachybasalts, with clinopyroxene and abundant olivine as phenocrysts and also in the groundmass. textures indicating mixing and mingling processes, such as dusty plagioclases along with clear ones, biotite replaced by anhydrous minerals and two groundmasses with a fluid-fluid relationship, are common in the early pre-caldera stage of pay迆n matr迆 and some post-caldera lavas. the latest post-caldera lavas are trachytic, with clean sanidine phenocrysts without disequilibrium textures. a remarkable characteristic of the pay迆n matr迆 volcanic field is the fact that the pay迆n matr迆 caldera is surrounded by basaltic fields at its base, while no basalts were erupted in the caldera region. we propose that the absence of basaltic lavas in the pay迆n matr迆 volcano is due to the presence of a magmatic chamber below it, and that the mafic magmas rising from deeper levels were unable to erupt without interaction with more evolved melts. intermediate hybrid magmas produced as a consequence of magma mixing and mingling between basaltic and trachytic magmas, are present in the early and mid-history of pay迆n matr迆 volcano. we present here new information about the quaternary pay迆n matr迆 volcanic field derived from field work, petrography, and major element geochemi
