摘要:变质底板是俯冲下插板片发生变质作用而形成，一般与俯冲带之上热的地幔橄榄岩直接接触。主要包括石榴子石角闪岩等高温和变质泥岩等低温变质底板。全球范围内，变质底板一般以岩块形式出露在蛇绿混杂岩中。但是阿曼蛇绿岩中出现了相对完整的变质底板序列，由顶至底依次出露高温变质底板和低温变质底板，它们位于条带状橄榄岩之下。由于变质底板中包含的高温变质底板部分只能形成于板块初始俯冲阶段，因此变质底板能很好记录板块初始俯冲过程。初始俯冲是指俯冲带在转变为成熟俯冲体系之前的一个相对短暂的过程。变质底板形成时间的约束方法主要包括：1）40Ar/39Ar定年，定年矿物包括角闪石和白云母等；2）U-Pb定年，定年矿物包括榍石、锆石和独居石等；3）Lu-Hf定年，定年矿物包括石榴子石等。而变质底板侵位机制主要有：1）俯冲角度变缓模型，2）浮力驱动模型，3）局部应变增生模型。为了探讨变质底板对初始俯冲过程的约束，本文收集了大量新特提斯中蛇绿岩和变质底板的年龄数据。结果表明每期变质底板形成时都会有对应的俯冲带之上型蛇绿岩形成，而且它们在不同的测年体系下有近乎相同的定年结果，这可能反映变质底板和蛇绿岩在后期经历了快速的剥露作用。通过研究发现，仅仅依靠蛇绿岩和变质底板之间的年龄对比无法约束初始俯冲机制。只有在确定变质底板原岩、变质底板和蛇绿岩三者的年龄关系并重建变质底板的P-T-t轨迹等条件下，才能有效约束初始俯冲机制及蛇绿岩的形成背景。
关键词: 初始俯冲/
变质底板/
侵位机制/
新特提斯洋
Abstract:Metamorphic sole is formed by metamorphism of subducting slab, and it mainly consists of the high temperature metamorphic sole including garnet amphibolite and the low temperature metamorphic sole including meta-sedimentary rock. Generally, the metamorphic sole is in fault contact with its overlying ophiolite. The metamorphic sole generally occurred within the ophiolitic mélange as blocks. However, a relatively integrated sequence was preserved within the Oman ophiolite, of which includes high temperature and low temperature metamorphic soles from top to bottom. Since high temperature metamorphic sole can only be generated during the subduction initiation, the metamorphic sole can potentially well record the initial subduction process. The subduction initiation refers to a relatively transient process between the transformation of a nascent subduction zone into a mature subduction system. At least the following three main methods for dating the metamorphic sole：1） 40Ar/39Ar, the major minerals are hornblende and muscovite; 2） U-Pb, the most commonly used minerals are titanite, zircon and monazite; 3） Lu-Hf, the employed mineral is garnet. Three emplacement mechanisms have been proposed：1） slab flattening model, 2） buoyancy-driven model and 3） local strain accretion model. In order to reveal the possible constraints on subduction initiation through the metamorphic sole, the ages of the Neo-Tethyan ophiolites and the metamorphic soles have been compiled. Results show that each metamorphic sole in the Neo-Tethyan ophiolite has a corresponding supra-subduction zone ophiolite. Furthermore, ages of the metamorphic sole and ophiolite with different dating methods are basically contemporary, which may reflect that they might have experienced fast exhumation. To provide new insights into the subduction initiation process and its mechanism, it requires to determine ages of the metamorphic sole protolith, the metamorphic sole and the ophiolite and to reconstruct the P-T-t trajectories of the metamorphic sole.
Key words:Subduction initiation/
Metamorphic sole/
Emplacement mechanism/
Neo-Tethyan ocean
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