埃达克岩研究的进展存在问题及思考.pdfVIP

西北大学研究生课程报告 高级岩石学 埃达克质岩研究进展、存在争论及思考 秦江锋,2006 埃达克质岩研究进展、存在争论及思考 秦江锋 （西北大学大陆动力学国家重点实验室，西北大学地质学系西安 710069 ） Abstract According to the primary definition of adakite proposed by Defant and Drummond in 1990，adakite was commonly considered as such a kind of rock ：They are volcanic or intrusive rocks in Cenozoic arcs associated with subduction of young （≤25Ma ）oceanic lithosphere. Meanwhile，Adakites are characterized by SiO ≥56% ，Al O ≥15%（rarely lower ），usually MgO ＜3%（rarely above 6% ）， 2 2 3 low Y and HREE relatively to island-arc ADRs （for example Y and Yb≤18 and 1.9ppm，respectively ）， high Sr relative to island-arc ADRs （rarely ＜400ppm ，low high-field strength elements （HFSEs ）， 87 86 as most island-arc ADRs，and Sr/ Sr usually ＜0.7040. The petrography of adakites is somewhat variable. Plagioclase is ubiquitous phase ，and amphibole is common in all samples but the more MgO-rich varieties. Clinopyroxene and orthoprroxene are also common constituents with biotite and opaques occurring frequently. A common assemblage is plagioclase and amphibole （with or without biotite ，pyroxene and opaques ）.Adakites are rarely associated with parental basalt or basaltic andesite. Recent research suggests that adakitic rocks are not derived from partial melting of young ，warm subducting oceanic slab，but also generated from partial melting of old ，cold flat subducting oceanic slab and thickened lower continental crust. Domestic scholars propose that the Miocene high K adakites from east China are utmost attributed to the effects of thicken