高校地质学报2012，Vol.18Issue(1)：74-87,14.
辉石岩:高压结晶还是再循环洋壳?
Pyroxenites: High-Pressure Segregates or Recycled Oceanic Crust?
摘要
Abstract
There are three petrogenetically different pyroxenites, namely cumulate pyroxenite, metamorphosed oceanic crust, and metasomatic pyroxenite. Type I pyroxenites formed as crystallization segregates from mantle-derived melts under pressure of 1.5～2.5 Gpa. They commonly show cumulated or igneous textures and do not form perfect linear correlations in a CaO/MgO-SiO2/MgO plot. Type I pyroxenits show no Eu anomaly and their Sr-Nd-0 isotopes are similar to those of mantle rocks. Type II pyroxenites are metamorphic products of recycled oceanic crust. They commonly show a deformed texture, forming a linear correlation in a CaO/MgO-SiO2/MgO plot and show a positive Eu anomaly. While their εNd values are identical to those of the MORB, their Sr-0 isotopes show distinct features. Metasomatic pyroxenites result from interactions between melts and peridotite. They are commonly surrounded by harzburgite or dunite. Minerals in metasomatic pyroxenites are less variable than other two types of pyroxenites. Dispersed in the CaO/MgO-SiO2/MgO plot, their εNd values are lower than those of the Type II pyroxenites,and their Sr isotopic ratios show a restricted range. The δ18 O values of metasomatic pyroxenites are variable, either lower than, higher than, or similar to the mantle value. To explain the co-existence of pyroxenites of different origins within a single ultramafic massif, the following model is conceived: the oceanic upper crust, including basalts and sediments, produces considerable elementally variable fluids and magmas, which react with surrounding peridotites and convert it to pyroxenites and also form type I pyroxenites by high-pressure crystal segregation along magma conduits in the peridotites. The oceanic lower crust consisting of troctolite and gabbroic rocks retained their original compositions and translated to type II pyroxenites without partial melting or other significant metasomatic reaction during subduction and exhumation at subsolidus conditions.关键词
辉石岩/高压结晶/循环洋壳/交代作用/鉴别标Key words
pyroxenites/ high-pressure crystallization/ recycling oceanic crust/ metasomatism/ discrimination分类
天文与地球科学引用本文复制引用
张亚玲,徐义刚..辉石岩:高压结晶还是再循环洋壳?[J].高校地质学报,2012,18(1):74-87,14.基金项目
国家自然科学基金项目(70914001 （）
91014007) （）
