Near-ultrahigh pressure processing of continental crust: Miocene crustal xenoliths from the Pamir
Near-ultrahigh pressure processing of continental crust: Miocene crustal xenoliths from the Pamir
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DOI：
10.1093/petrology/egi030
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发表时间：
2005-08-01
影响因子：
3.9
通讯作者：
Metcalf, J
中科院分区：
文献类型：
--
作者：
Hacker, B;Luffi, P;Metcalf, J
帕米尔南部中新世超钾质火成岩中的俯冲壳源捕虏体为印度-欧亚碰撞期间伴随构造运动的地质过程提供了重要的新信息。研究了四种类型：透长石榴辉岩（绿辉石、石榴石、透长石、石英、黑云母、蓝晶石）、长英质麻粒岩（石榴石、石英、透长石和蓝晶石）、玄武质榴辉岩（绿辉石和石榴石）和玄武质榴辉岩（黑云母、单斜辉石和透长石）。磷灰石、金红石和碳酸盐是最丰富的次要相。含水相（长英质麻粒岩和玄武质榴辉岩中的黑云母和多硅白云母，基性榴辉岩和透长石榴辉岩中的角闪石）和斜长石在石榴石或蓝晶石中形成少量包裹体。固相热压法揭示了在1000-1100摄氏度的高温和2.5-2.8 GPa的近高温压力下的再结晶。岩石的结构、共生关系和矿物组成表明，包体来自俯冲的玄武质、英云闪长质和泥质地壳，经历了高压脱水熔融、富钾交代和固态再平衡过程。这些过程的时间被来自捕虏体的锆石年龄和寄主火山岩的40 Ar/39 Ar年龄限制在57-11 Ma。这些捕虏体表明，深俯冲地壳可能经历了广泛的脱水驱动的部分熔融，密度驱动的分化和解聚，并封存在地幔。这些过程也可能有助于在大陆碰撞带观察到的碱性火山作用。
Xenoliths of subducted crustal origin hosted by Miocene ultrapotassic igneous rocks in the southern Pamir provide important new information regarding the geological processes accompanying tectonism during the Indo-Eurasian collision. Four types have been studied: sanidine eclogites (omphacite, garnet, sanidine, quartz, biotite, kyanite), felsic granulites (garnet, quartz, sanidine and kyanite), basaltic eclogites (omphacite and garnet), and a glimmerite (biotite, clinopyroxene and sanidine). Apatite, rutile and carbonate are the most abundant minor phases. Hydrous phases (biotite and phengite in felsic granulites and basaltic eclogites, amphiboles in mafic and sanidine eclogites) and plagioclase form minor inclusions in garnet or kyanite. Solid-phase thermobarometry reveals recrystallization at mainly ultrahigh temperatures of 1000-1100 degrees C and near-ultrahigh pressures of 2.5-2.8 GPa. Textures, parageneses and mineral compositions suggest derivation of the xenoliths from subducted basaltic, tonalitic and pelitic crust that experienced high-pressure dehydration melting, K-rich metasomatism, and solid-state re-equilibration. The timing of these processes is constrained by zircon ages from the xenoliths and 40Ar/39Ar ages of the host volcanic rocks to 57-11 Ma. These xenoliths reveal that deeply subducted crust may undergo extensive dehydration-driven partial melting, density-driven differentiation and disaggregation, and sequestration within the mantle. These processes may also contribute to the alkaline volcanism observed in continent-collision zones.