Crustal structure: A key constraint on the mechanism of ultra-high-pressure rock exhumation
Crustal structure: A key constraint on the mechanism of ultra-high-pressure rock exhumation
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DOI：
10.1016/j.epsl.2009.08.001
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发表时间：
2009-09-30
影响因子：
5.3
通讯作者：
Warren, C. J.
中科院分区：
文献类型：
--
作者：
Beaumont, C.;Jamieson, R. A.;Warren, C. J.
超高压变质岩的分布表明，陆壳的埋藏（> 100 km）和快速折返（> 1cm a（-1））是早期（约10 Ma）大陆碰撞的正常部分。目前，还没有一个全面的模型，这一基本的构造过程，也令人满意地解释了上地壳结构所造成的早期碰撞超高压岩石折返。需要解释的特征包括：以超高压推覆体为核心的构造穹丘;显示出明显“压力间隙”的相关中高压推覆体;上覆低品位岩石，包括缝合带蛇绿岩;以及同时代的前陆定向逆冲断层和同折返正断层。我们提出了一个地球动力学模型，包括在一个俯冲通道下面的增生楔地壳埋藏和折返。下游通道剪切牵引力和上游通道浮力之间的竞争（表示为折返数E）控制着埋藏和折返，当E > 1时，导致快速的上游通道流动。当超高压物质穿透并破坏上覆楔体的稳定性时，超高压物质的出露形成了推覆体和构造穹丘，从而推动了逆冲推覆和拉张作用。这个解决方案是令人信服的，因为它解释了Tso Morari和其他超高压复合体的地质和岩石学，因为它表明，来自俯冲通道深处的脉冲式浮力折返产生了观察到的上地壳结构。这对挖掘机制造成了限制，并提供了对替代模式的测试。其他提出的机制，如在岩石圈规模的楔或超压俯冲通道的连续循环，预测不同类型的上地壳结构，因此不能令人满意的解释早期碰撞折返的超高压岩石。(C)2009 Elsevier B. V.保留所有权利。
The distribution of ultra-high-pressure (UHP) metamorphic rocks demonstrates that burial (to > 100 km) and rapid exhumation (> 1 cm a(-1)) of continental crust is a normal part of early (similar to 10 Ma) continental collision. Currently, there is no comprehensive model for this fundamental tectonic process that also satisfactorily explains the upper-crustal structures resulting from early collisional UHP rock exhumation. Characteristic features requiring explanation include: structural domes that are cored by UHP nappes; associated medium- to high-pressure nappes displaying a distinct "pressure gap"; overlying lower-grade rocks, including suture zone ophiolites; and, coeval foreland-directed thrust-faults and syn-exhumation normal faults. We present a geodynamical model involving crustal burial and exhumation in a subduction channel below an accretionary wedge. Competition between down-channel shear traction and up-channel buoyancy forces, expressed as the exhumation number, E, controls burial and exhumation, leading to rapid up-channel flow when E > 1. Exhuming UHP material forms a nappe stack and structural dome as it penetrates and destabilises the overlying wedge, driving thrusting and extension. This solution is compelling because it explains both the geology and the petrology of the Tso Morari and other UHP complexes, and because it demonstrates that pulse-like buoyant exhumation from deep in the subduction channel creates observed upper crustal structures. This places constraints on the exhumation mechanism and provides a test of alternative models. Other proposed mechanisms, such as continuous circulation in a lithospheric-scale wedge or overpressured subduction channel, predict different types of upper-crustal structures and are therefore unsatisfactory explanations for early collisional exhumation of UHP terranes. (C) 2009 Elsevier B.V. All rights reserved.