摘要:蛇绿岩是刻画造山带洋—陆演化格局的标志性证据，由具有成因联系的超基性—基性岩和上覆远洋—深海沉积物组成，是一种理想剖面，非实际的野外露头表现。蛇绿岩分为MOR型和SSZ型两类，前者形成于洋中脊、洋盆宽度足够的弧前/弧后盆地扩张脊环境，后者形成于洋壳初始俯冲阶段的弧前环境。蛇绿岩的形成年龄可以通过古生物和同位素测年方法获得，同位素年龄与最老古生物化石（如放射虫、牙形刺等）年龄相近；洋壳运移过程中，有岩浆击穿洋壳而发育二元结构，由早期洋壳和叠覆的晚期岩浆岩构成；晚期岩浆岩比最老古生物年龄更为年轻。蛇绿岩通过俯冲铲刮、深部底垫和仰冲作用就位，发育褶皱和叠瓦状—双冲构造、及构造肢解为“基质夹岩块”结构成为蛇绿混杂带；蛇绿岩的形成年龄和就位年龄之间可从无年龄差到数十、甚至上百个百万年的时间跨度。蛇绿岩就位后继续经历俯冲带上盘和陆内活化等阶段的演化：蛇绿岩就位时的滑脱断层切穿俯冲带上盘，为后期岩浆提供通道，可侵入多期次的、非蛇绿岩套组份的中基性—酸性岩脉和岩体，包括SSZ型特征的岩浆岩，如新疆扎河坝—和布克赛尔蛇绿混杂带和美国Klamath山蛇绿混杂带。蛇绿混杂带在变质变形强烈的俯冲带上盘和活化的陆内环境中，受到构造改造，造成单一露头区不能够完整地出露有蛇绿岩套的岩石组份，而侵入在蛇绿混杂带中的岩浆岩被构造肢解、形成岩块并使得混杂带内岩石组份复杂化。现今露头的蛇绿混杂带是经历过多阶段演化的、一种现时状态的“四维时空”信息的综合体，即多个时期的物质叠置在同一个露头的三维空间内，一些岩石可能与蛇绿岩套并无成因联系。
关键词: 蛇绿岩/
基性—超基性岩/
蛇绿混杂带/
“基质夹岩块”结构/
侵入岩
Abstract:Ophiolite is a key to constrain orogenic evolution, and consists of genesis related ultramafic-mafic rocks and overlaying pelagic sediments. It contains MOR- and SSZ-type ophiolites, which formed in mid-oceanic ridge and spreading ridge of fore-arc and back-arc basin, and initial subduction zone, respectively. It contrasts with other tectonic settings that generate ultramafic-mafic rocks, including intra-oceanic arc, slab window, oceanic plateau/seamount and large igneous province/rifting environment, in the aspect of rock assemblages, geochemical features and contact relations with host sediments. The generation age of ophiolite can be constrained by coeval isotopic and fossil ages; however, some magmas upwells across through migrating oceanic crust before entering trench, and has younger isotopic age than the oldest fossil age. Ophiolite emplaces through off-scraping and underplating from down-going slab, and obduction, and develops folds, imbricated thrust, duplex, and block-in-matrix textures by tectonic dismembering to ophiolitic mélange. The gap between formation and emplacement ages of ophiolite can range from zero to several tens of or more than one hundred Ma. The megathrust, emplacing the ophiolitic mélange, would act as a channel to upwell magmas to generate multiple stages of non-ophiolitic intermediate-mafic and felsic dikes and plutons, such as SSZ-type dikes inside of the ophiolitic mélanges in the Zheheba-Hebukesair area （Xinjiang） and Mt. Klamath area （western U.S.A）. Continuous tectonic overprint in supra-subduction zone or intra-continental environment would change rock assemblages making some outcrops exposing incomplete components of ophiolitic suit, and dismember intrusive rocks to blocks involving into mélange with more complicated components. Therefore, the present ophiolitic mélange is a snapshot of four-dimensional juxtaposition of ophiolite and other rocks, such as younger intrusions, since their formation and following tectonic modification.
Key words:Ophiolite/
Mafic-ultramafic rock/
Ophiolitic mélange/
Block-in-matrix texture/
Magmatic intrusions
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