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机构地区:[1]新疆自然资源与生态环境研究中心,乌鲁木齐830000 [2]北京大学地球与空间科学学院造山带与地壳演化教育部重点实验室,北京100871
出 处:《岩石学报》2007年第7期1603-1610,共8页Acta Petrologica Sinica
基 金:国家科技支撑计划重点项目(2006BAB07B08);国家自然科学基金(批准号:40572033)资助.
摘 要:东准噶尔卡姆斯特蛇绿岩剖面由玄武岩、变辉长岩、辉石岩、蛇纹石片岩、硅质岩和火山碎屑岩等组成。辉石不发育出溶结构,说明地幔岩侵位过程相对缓慢(从上地幔到下地壳迁移过程中没有发生突然抬升或者 PT 条件的巨大改变)。辉石岩中存在三类角闪石:具有出溶结构的角闪石(Amp Ⅰ,镁绿钙闪石),与 Amp Ⅰ共生的均匀角闪石(Amp Ⅱ,镁质普通角闪石),以及交代单斜辉石边部的角闪石(Amp Ⅲ,钙镁闪石质普通角闪石)。基于对辉石岩和变辉长岩中角闪石的化学组成及其结构的仔细研究,获得该蛇绿岩侵位的基本演化特征如下:地幔岩在中下地壳环境被快速抬升,导致辉石岩中的角闪石分解而形成铬磁铁矿出溶结构,当蛇绿岩侵位到中地壳环境后,岩石经受角闪岩相退变质改造,继续上升到上地壳环境后,岩石发生绿片岩相的退变质。A newly discovered ophiolite outcrop in Kamste region, locating in the west part of the Kelameili ophiolite belt in east Junggar, consists of basalt, metagabbro, pyroxenite, serpentite schists, siltstone, and volcanic breccia. No exsolution texture occurs in pyroxene in the pyroxenite samples, which implies that the mantle rocks gradually exhumated at least in the upper mantle. Three kinds of amphiboles were identified in pyroxenite: amphibole with exsolution of Cr-magnetite lamellae (Amp Ⅰ, Mg-Hastingsite ), homogeneous amphibole coexisting with Amp Ⅰ (Amp Ⅱ, Mg-Hastingsite hornblende), and amphibole replaced clinopyroxene margins (Amp Ⅲ, Tschmakite Hornblende). Based on the characteristics of the studied amphibole, we suggest that the mantle rocks were elevated to shallow levels ( probably at the lower crust), which caused the decomposition of amphibole and formed the exsolution texture. When the ophiolite mélange was elevated to the middle crust level, these rocks undergone retrograde metamorphism at amphibolite phase. Afterwards, these rocks have undergone retrograde metamorphism at greenschist phase when they reached the shallow level of the continental crust.
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