Constraints on Large-Magnitude Extension Coupled to Subduction Channel Flow Above a Flat Slab Segment - Southern Sierra Nevada Region, California

海洋岩石圈和大陆岩石圈之间的浮力对比可能导致俯冲作用，即大洋板块在大陆板块下方的驱动作用。这种俯冲过程在我们的星球上很常见，例如，它被表达为环太平洋火山带。之所以叫这个名字，是因为它的边缘有一连串的火山。俯冲的另一个后果是广泛的地震活动或地震能量释放。为了了解俯冲机制的演化，继续开展大陆地壳几何演化的基础研究至关重要。这项研究处于构造学领域的前沿，对火山作用、地震减灾、金属矿石成因以及地壳中的热流体分布具有间接意义。除非我们了解地球深处的几何演化，否则我们永远无法完全理解控制这些问题的过程。海洋岩石圈沿着各种轨迹俯冲到大陆岩石圈之下，这些轨迹通常以陡峭、浅或平坦为特征。地球上大约10%的俯冲带由广泛的浅倾斜或平坦的俯冲板块组成，这表明形成大陆底部的地幔岩石圈的构造移动。在这种情况下，覆盖大陆板块造山带具有地壳缩短加剧的带和弧岩浆活动的空隙。众所周知，浅层俯冲带段也会随着时间的推移而变陡，但人们对这种变陡的地质后果知之甚少。在古代造山带中很少发现浅层和平坦俯冲带的残余物，这一事实表明，在造山带的完整生命周期中，伴随的构造过程将地壳破坏到这样一种状态，以致于其决定性的特征丧失了。在内华达山脉-莫哈韦沙漠南部，白垩纪活动边缘约500公里长的一段已被证明经历了法拉隆板块浅层板块的完整生命周期。有证据表明，在这一浅板段的消亡过程中，上覆板块发生了大幅度的伸展变形。此外，沿着浅层轨迹俯冲的物质迅速上升回到俯冲带的上层，将伸展应变耦合到上覆板块。本研究采用地质填图和构造分析、岩石学、微组构分析、热气压测量和地质年代学等方法，量化了上覆板块的伸展量，确定了下伏俯冲组合的应变、位移和热史。

Buoyancy contrasts between oceanic lithosphere and continental lithosphere may lead to subduction, the driving of the oceanic plate below the continental plate. This process of subduction is common around our planet and it is expressed as, for example, the Pacific Rim of Fire. It is called this due to the chains of volcanoes that outline the Rim. Another consequence of subduction is extensive seismicity or earthquake energy release. In order to understand the evolution of subduction regimes it is critical for basic research into the geometric evolution of the continental crust to continue. This research is at the cutting edge of the field of tectonics, with indirect implications for volcanism, earthquake hazard mitigation, genesis of metallic ores, and thermal and fluid distribution in the crust. Unless we understand the geometric evolution of the Earth at depth we will never fully understand the processes that control these issues.Oceanic lithosphere subducts beneath continental lithosphere along a variety of trajectories, generally characterized as steep, shallow, or flat. About ten percent of Earth's subduction zones consist of extensive shallowly dipping or flat subducted slabs, indicating the tectonic removal of mantle lithosphere forming the base of the continent. Overriding continental plate orogens in such cases possess zones of intensified crustal shortening and gaps in arc magmatism. Shallow subduction zone segments are also known to steepen with time, but the geological consequences of such steepening are poorly understood. The fact that the remnants of shallow and flat subduction zones are so rarely recognized in ancient orogens suggests that the tectonic processes attendant in their complete life cycle disrupt the crust to such a state that the defining characteristics are lost. In the southern Sierra Nevada-Mojave Desert an ~500 km long segment of the Cretaceous active margin has been shown to have experienced the complete life cycle of a shallow slab segment in the Farallon plate. There is evidence indicating that during the demise of this shallow slab segment large magnitude extension deformed the overriding plate. It also appears that material subducted along that shallow trajectory rapidly ascended back out the upper levels of the subduction zone, coupling extensional strain into the overriding plate. This study employs geologic mapping and structural analysis, petrography, microfabric analysis, thermobarometry, and geochronology to quantify the amount of overriding plate extension, and to determine the strain, displacement and thermal history of the underlying subduction assemblage.