Supercontinent cycles, extreme metamorphic processes, and changing fluid regimes
Supercontinent cycles, extreme metamorphic processes, and changing fluid regimes
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DOI：
10.1080/00206814.2010.527682
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发表时间：
2011-02
影响因子：
2.6
通讯作者：
M. Santosh;T. Kusky;Lu Wang
中科院分区：
文献类型：
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作者：
M. Santosh;T. Kusky;Lu Wang
固体地球超大陆旋回与流体旋回密切相关，流体旋回在地球历史上经历了长期的变化。讨论了超大陆旋回与超高压(UHP) +超高温（UHT）变质作用的时间和过程以及旋回内流体释放的关系。确定了两大流体特征截然不同的区域——以水为主和以CO2为主，并评价了它们与超大陆组合和分散的关系。汇聚边缘俯冲带在超大陆旋回的所有阶段都存在，但它们的相对长度和位置在整个旋回过程中发生变化。俯冲作用的主要作用之一是将海洋岩石圈、未被刮掉和积聚的上覆沉积物以及含水矿物带入地幔深处；这些原岩代表了地幔深处许多流体的源物质。我们提出了一个完整的山脊俯冲模型来解释超高压造山带和超高压造山带的动力学。在脊状俯冲过程中，板块窗打开并被上涌的地幔物质填满。在中等水平，靠近地壳底部和较低的区域，板块窗口将热软流圈放置在上覆板块底部的一个区域，该区域通常会被板块冷却，导致在弧和弧前的深层形成一个超高温变质岩带，在那里没有含水流体，二氧化碳占主导地位。在这部分之下，板块窗的几何结构使得板块窗的热软流层与上覆板块的热软流层相对放置，因此最大的影响可能与板块下降的冷却损失有关，并且（暂时）剥夺了板块产生的沉积物和流体。脊状俯冲还与增生楔的大量断裂、海沟中较高的沉积速率以及俯冲方式的变化有关，这些变化导致楔的更大增长和沉积物向更深的深度俯冲。这些沉积物中的许多最终被俯冲，并在地幔深处形成薄的造山楔，使地幔水化，并将唾液物质带到深处。深俯冲物质经历高、超高压变质作用；由于俯冲带内的水提供了润滑通道，它们的挤压和返回地表在显生宙变得更加普遍。
The solid Earth supercontinent cycle is intimately related to a fluid cycle, and the fluid cycle has undergone secular changes throughout Earth history. We discuss the relationships between the supercontinental cycle with the timing and processes of ultrahigh-pressure (UHP) + ultrahigh-temperature (UHT) metamorphism and the release of fluids within the cycle. Two broad regions of contrasting fluid characteristics – water dominated and CO2 dominated – are identified, and their relation to the assembly and dispersal of supercontinents is evaluated. Subduction zones at convergent margins are present at all stages of the supercontinent cycle, but their relative length and locations change throughout the cycle. One of the main effects of subduction is to bring oceanic lithosphere, overlying sediments that are not scraped off and accreted, and hydrous minerals deep into the mantle; these protoliths represent the source material for many of the fluids deep in the mantle. We propose an integrated model of ridge subduction to explain the dynamics of UHP and UHT orogens. During ridge subduction, a slab window opens and is filled by upwelling mantle material. At moderate levels, near the base of the crust and in the lower domain, the slab window places hot asthenosphere against the base of the overlying plate in a region that would normally be cooled by the slab, leading to a belt of UHT metamorphic rocks at deep levels of the arc and forearc where hydrous fluids are absent and CO2 dominates. Below this part, the geometry of the slab window is such that hot asthenosphere from the slab window is placed against hot asthenosphere of the overriding plate, so the largest effects are probably related to the loss of cooling by the descending slab, and the deprivation (temporarily) of slab-derived sediments and fluids. Ridge subduction is also associated with considerable disruption of the accretionary wedge, higher sedimentation rates in the trench, and changes in the style of subduction that lead to both greater growth of the wedge and subduction of sediments to greater depths. Many of these sediments ultimately are subducted, and form thin orogenic wedges deep in the mantle, hydrating the mantle and bringing sialic material to depth. Deeply subducted material undergoes high and UHP metamorphism; their extrusion and return to the surface became more common in the Phanerozoic Earth due to the lubricated channels provided by water within the subduction zone.