INSIGHTS INTO THE SOURCE OF CONTINENTAL ARC MAGMATISM: A STUDY OF MAFIC MINERAL CLUSTERS FROM THE CENTRAL ANDES
Lavas from the Quillacas volcanic center form the basis of this study. Samples have been investigated via polarized light microscopy and SEM EDS. Future work will include in situ analyses of mineral grains via EPMA and LA-ICP-MS.
Studied lavas are fine-grained, with a bulk andesitic composition and porphyritic texture. The crystal population is dominated by hornblende and plagioclase. Biotite, quartz, and oxides are present in minor amounts with rarer apatite. The groundmass consists of plagioclase microlites and microphenocrysts of hornblende, oxides, and glass. Within these studied lava samples are rare mafic mineral clusters. These consist of olivine, orthopyroxene and Cr-spinel. Olivine ranges from ~250μm - ~800 μm and is often rimmed with amphibole. Orthopyroxenes are ~1800 μm and Cr-spinels range from <5μm to 34μm in diameter. Cr-spinels occur within the interior of both olivine and orthopyroxene. Preliminary EPMA data revealed olivine have high mg# (87). Future study of these rare mafic mineral clusters aims to provide new insights into the nature of primitive magmas in the Central Andes.