Sub-solidus dehydration of amphiboles in an andesitic magma |
| |
Authors: | Peter Mazzone Dion C Stewart John M Hughes |
| |
Institution: | (1) Department of Geology, Miami University, 45056 Oxford, OH, USA;(2) Department of Geology, Bowling Green State University, 43403 Bowling Green, OH, USA;(3) Department of Geology, Miami University, 45056 Oxford, OH, USA;(4) Present address: Department of Geology and Geography, University of Massachusetts, 01003 Amherst, MA, USA |
| |
Abstract: | Several petrologic experiments have demonstrated that in igneous and metamorphic reactions amphibole minerals can break down by a subsolidus dehydration reaction, but evidence for the reaction in natural rocks has been lacking. Evidence for the breakdown of an edenite-pargasite amphibole by a subsolidus dehydration reaction has now been found in an andesite flow from Garner Mountain, southern Cascase Range. The andesite contains one modal percent of crystal clots formed of crystallites of opx, cpx, plag, K-spar, opaque and quartz. The crystal clots retain the original amphibole morphology and intra-clot pyroxenes are aligned with crystallographic c parallel to c in the amphibole precursor; these conditions would not be duplicated by a melting reaction.Microprobe analyses of the bulk clot and the intra-clot minerals suggest the solid-state reaction: 100 amph+10 SiO2=>55 cpx+33 plag+22 opx+ 1 opq+1 ksparPyroxene thermometry of the andesite groundmass pyroxenes and the intra-clot pyroxenes demonstrates that the amphibole dehydration reaction occurred in the xenocrystic amphiboles as a result of heating by the near-solidus andesite magma. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|