Collaborative Research: Recent Kinematic Evolution of the Northern Eastern California Shear Zone from Geologic Data

板块电路计算表明，在~8 Ma时，太平洋板块相对于北美板块的运动由西风向西北方向转变。这一观测结果与地质资料非常吻合，地质资料表明，在~8-10 Ma期间，相对于科罗拉多高原，喜马拉雅-大峡谷地块的运动由西风向西北方向转变。地质研究表明，加洛克断层以北的东加利福尼亚剪切带约8 Ma左右的右侧剪切速率为约15 mm/yr，占相对板块运动的约30%。大地测量学研究表明，现今的右向剪切速率为10-12毫米/年，这为东加利福尼亚剪切带仍然是太平洋-北美板块边界带内变形的重要组成部分提供了明确的证据。尽管它在构造上很重要，但人们对东加利福尼亚剪切带的时空演化只是大致了解。本提案要求使用野外测绘、构造地貌学、古地震学和地质年代学的综合方法，对东加利福尼亚剪切带北部的板内右旋断层系统的运动学进行研究。提出的研究的动机是正在进行的大地测量调查的应变积累和空间分布的大小横跨加州东部剪切带。鉴于这些大地测量对应变积累的限制，对新近纪晚期和第四纪应变释放的时空格局的认识是及时的。这两个数据集将为东加利福尼亚剪切带演化的地球动力学假设提供重要的约束。准确描述东加利福尼亚剪切带应变释放的时空模式对于理解与太平洋和北美板块相互作用相关的更广泛的板内变形区域的构造过程至关重要。

Plate circuit calculations indicate that motion of the Pacific plate relative to North American plate changed from westerly to NW at ~8 Ma. This observation corresponds extremely well with geologic data which indicates that motion of the Sierran-Great Valley block relative to the Colorado Plateau changed from westerly to NW at ~8-10 Ma. Geologic studies indicate that the rate of right lateral shear at ~8 Ma within the Eastern California Shear Zone north of the Garlock fault was ~15 mm/yr accounting for ~30%of relative plate motion. Geodetic studies indicate a present-day dextral shear rate of 10-12 mm/yr, providing clear evidence that the Eastern California Shear Zone is still an important component of deformation within the Pacific-North America plate boundary zone. In spite of its tectonic importance, the space-time evolution of much of the Eastern California Shear Zone is only broadly understood. This proposal requests support for investigating the kinematics of a system of intraplate dextral faults in the northern part of the Eastern California Shear Zone using an integrated approach of field mapping, tectonic geomorphology, paleoseismology, and geochronology. The proposed research is motivated by ongoing geodetic investigations on present-day magnitude of strain accumulation and spatial distribution across the Eastern California Shear Zone. In light of these geodetic constraints on strain accumulation, it is timely to improve the understanding of the spatial and temporal patterns of strain release during the late Neogene and Quaternary. The two data sets will provide important constraints on geodynamic hypotheses proposed for the evolution of the Eastern California Shear Zone. An accurate characterization of the spatial and temporal patterns of strain release within the Eastern California Shear Zone is crucial for understanding tectonic processes over a much broader area of intraplate deformation associated with the interaction of the Pacific and North American plates.