汉诺坝玄武岩中熔体-捕虏体相互作用初步研究  

A preliminary study of the melt-xenolith interaction in Hannuoba basalt

作　　者：杜星星[1] 樊祺诚[1] 

机构地区：[1]中国地震局地质研究所,北京100029

出　　处：《岩石矿物学杂志》2010年第4期377-386,共10页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目(40772038)

摘　　要：汉诺坝新生代玄武岩捕获的地幔橄榄岩及其解体矿物橄榄石、单斜辉石、斜方辉石捕虏晶,普遍发育反应边结构,提供了玄武岩浆在上升穿越岩石圈地幔过程中橄榄岩-熔体相互作用的重要信息。橄榄石和单斜辉石捕虏晶反应边的成分变化一致,由核部富镁向边部富铁变化,趋同于玄武岩中相应斑晶的成分。斜方辉石捕虏晶反应边一般由橄榄石+单斜辉石+玻璃构成,多为双层结构,反应边矿物橄榄石、单斜辉石较相应的地幔矿物富铁,其富硅、碱的中酸性玻璃成分,为中国东部地幔矿物包裹体中存在的富硅、碱熔体的来源提供了重要信息。同时发现橄榄岩捕虏体中尖晶石颜色、成分的变化与温度的关系。地幔矿物捕虏晶反应边结构(非平衡结构)得以保存,暗示了玄武岩浆的快速上升。而大规模的熔体-捕虏体相互作用,改变着岩石圈地幔的性质。During the migration of basaltic magma through the lithosphere mantle, the interaction between melt and peridotite inevitably took place and led to the compositional variation of the lithosphere mantle. Mantle peridotite and its disaggregated minerals such as olivine （Ol）, clinopyroxene （Cpx） and orthorpyroxene （Opx） xenocrysts were captured by the Cenozoic basalt in Hannuoba. The xenocrysts usually have the reaction rim structure, which provides important information about the melt-xenolith interaction during the migration of basaltic magma through the lithosphere mantle. The xenocrysts in basalt are on the whole perfectly round, embayed or serrated in shape and have characteristic reaction rim structure which distinguishes them from relatively euhedral and small phenocrysts in basalt. Based on microscopic petrographic observations and electron microprobe analyses of xenocrysts and their reaction rims, this paper deals tentatively with the melt-xenolith interaction. The rims of Ol and Cpx xenocrysts show similar compositional variations from the Mg-rich core to the Ferich rim. The composition of the outer part of the reaction rim tends to be close to the composition of the phenocryst in basalt. Olivine composition changes from the core （Fo 88～90） to the rim （Fo 68～72）. Clinopyroxene composition changes from Mg^#90 to Mg^#74, with the corresponding variation of diopside in the core to salite in the rim. Usually, the reaction rim of Opx with double-layered structure consists of Ol＋Cpx＋Glass. The composition of Ol and Cpx in the Opx reaction rim is rich in Fe relative to its mantle counterpart. Meanwhile, the reaction rim minerals will become richer in Fe and poorer in Mg with the Opx xenocrysts approaching the host basalt. The glass constituent rich in silicon and alkali （the content of SiO2, Al2O3, Na2O and K2O is respectively 64%～67%, 18%～19%, 5%～7% and 6%～9%） in the Opx reaction rim offers important information concerning the origin of Si- and alkali-rich melt inclusions

关 键 词：熔体-捕虏体相互作用 捕虏晶 反应边 岩石圈地幔 玄武岩 汉诺坝 

分 类 号：P588.145[天文地球—岩石学] P574.2[天文地球—地质学]