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

与平板段上方俯冲通道流耦合的大范围伸展的约束 - 加利福尼亚州内华达山脉南部地区

• 批准号: 0739071
• 负责人: Jason Saleeby
• 金额: $ 20.83万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-15 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0739071&HistoricalAwards=false
• 关键词: Constraints; Large; Magnitude; Extension; Coupled

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.

大洋岩石圈和大陆岩石圈之间的浮力差异可能导致俯冲，即大洋板块在大陆板块下方的驱动。这种俯冲过程在我们的星球上很常见，例如，它被表示为环太平洋火圈。它之所以叫这个名字，是因为勾勒出边缘的一连串火山链。俯冲的另一个后果是广泛的地震活动或地震能量释放。为了了解俯冲体制的演化，继续进行陆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、减轻地震灾害、金属矿石的成因以及地壳中的热和流体分布具有间接影响。除非我们了解地球深部的几何演化，否则我们永远不会完全了解控制这些问题的过程。大洋岩石圈沿着各种轨迹俯冲到大陆岩石圈之下，通常表现为陡峭、浅或平坦的轨迹。地球上约10%的俯冲带由广泛的浅倾角或平坦的俯冲板块组成，表明构成大陆底部的地幔岩石圈的构造搬运。在这种情况下，俯冲的大陆板块造山带具有加强的地壳缩短带和弧岩浆活动的缝隙。浅俯冲带段也已知会随着时间的推移变陡，但这种变陡的地质后果却知之甚少。浅水和平坦俯冲带的残留物在古代造山带中很少被识别，这一事实表明，伴随着整个生命周期的构造过程破坏了地壳，以至于失去了定义特征。在内华达山脉-莫哈韦沙漠南部，白垩纪活动边缘长约500公里的一段已被证明经历了法拉隆板块中浅板片段的完整生命周期。有证据表明，在这个浅板段消亡期间，巨大的震级伸展使上覆板块变形。沿着浅层轨迹俯冲的物质似乎也迅速上升回到俯冲带的上层，将伸展应变耦合到俯冲板块中。这项研究利用地质填图和构造分析、岩石学、显微组构分析、温压测量和地质年代学的方法，量化了俯冲板块伸展的数量，并确定了下伏俯冲组合的应变、位移和热史。