Collaborative Research: Uplift and Exhumation Along the San Andreas Fault Zone; An Empirical Study of Transpression

扭压沿圣安德烈亚斯断层系统的42%发生。因此，它对转换断层行为的影响具有一级重要性，可能是全面理解走滑断层和板块边界行为的最重要的复杂因素之一。考虑到这一点，PI提出了一项合作研究，该研究将系统地和定量地整合在圣安德烈亚斯断层沿线的几个地点对挤压变形的适应方式的地质约束。对扭压的功能理解将使垂直变形模式很容易预测在已知主要边界条件的地方，例如板块运动的倾斜度和主要转换断层的力学。然而，圣安德烈亚斯断层的物质性质仍存在争议，大量证据表明，次级因素(构造和岩性非均质性、侵蚀力)在形成对扭压作用的地质响应方面起着重要作用。因此，对于板块如何在地壳变形时表现出跨压运动的一般理解还没有发展起来。PI的目标之一是定量评估外部因素对变形划分的影响，以便我们最终可以评估基于圣安德烈亚斯断层力学性质假设的扭压变形模型。他们的方法将是利用基岩抬升(地表抬升+折返)所表现的垂直运动的时空分布作为转压的表示。他们将结合对折返年龄和大小的热年代学约束((U-Th)/He测年)，以及对地表抬升、侵蚀和驱动基岩抬升的变形结构的地貌和构造约束。他们将使用这些互补技术来确定垂直运动模式是如何相对于圣安德烈亚斯断层(即近场和远场)及其与板块运动的倾角在空间上分布的。因此，PI的目标是建立横向变形与这些关键变量之间的函数关系。这将需要制定关于垂直运动的年表如何与每个地点的扭压的出现有关的控制，以及对沿走向的独立边界条件(例如地质、构造、气候)的影响的控制。他们将重点关注四个地点(卡里佐平原/地震山脉、圣埃米吉迪奥山脉、圣加布里埃尔山脉北部和科切拉山谷)，每个地点都代表着对圣安德烈亚斯断层沿线的挤压作用的理解存在重大差距。这些场地的综合结果，当与以前的研究相结合时，将提供所需的全范围的边界条件和平移参数，以创建不同模型的扭压变形的具体测试。这项提议的一个关键方面是将在实现我们的目标方面所采用的合作。少年派对南加州的地质学和将要采用的分析技术有广泛的了解。Spotila是第一批应用这种综合方法来理解横向范围的部分的人之一。豪斯积极寻求将在这项研究中使用的热年代学技术的新应用。布雷迪在构造地质学和地球物理学方面提供了坚实的基础，将把隆起估计与个别构造联系起来。博士后助理Niemi将增加新生代地层学、构造地质学和野外测绘方面的额外专业知识。这一数目的PI还将使我们能够同时在所有现场开始工作，并代表着一支足够强大的科学团队来解决这一重大问题。

Transpression occurs along 42% of the San Andreas fault system. Its influence onthe behavior of the transform fault is thus of first-order importance and may represent oneof the most important complications in developing a comprehensive understanding ofhow strike-slip faults and plate boundaries behave. With this in mind, the PI's propose acollaborative study that will systematically and quantitatively integrate geologicalconstraints on the manner in which transpressional deformation is accommodated atseveral sites along the San Andreas fault. A functional understanding of transpression would make patterns of vertical deformation easy to predict where primary boundary conditions, such as the degree of plate motion obliquity and the mechanics of the main transform fault, are known. However, the material properties of the San Andreas fault are debated, and considerable evidence suggests that secondary factors (structural and lithologic heterogeneity, erosivity) play a significant role in shaping the geologic response to transpression. As a result, a general understanding of how transpressional plate motion becomes manifest as deformation in the crust has not been developed. One of the PI's objectives is to quantitatively evaluate the effects of external factors on deformation partitioning, so that we may ultimately evaluate models of transpressional deformation that are predicated on assumptions of the mechanical properties of the San Andreas fault. Their approach will be to use the spatial and temporal distribution of vertical motion, manifested in bedrock uplift (surface uplift + exhumation), as a representation of transpression. They will combine thermochronologic constraints ((U-Th)/He dating) on the age and magnitude of exhumation with geomorphic and structural constraints on surface uplift, erosion, and the architecture of deformation that drives this bedrock uplift. They will use these complementary techniques to determine how patterns of vertical motion are spatially distributed with respect to the San Andreas fault (i.e. near vs. far field) and its obliquity to plate motion. The PI's objective is thus to develop a functional relationship between transpressive deformation and these key variables. This will require developing controls on how the chronology of vertical motion relates to the emergence of transpression at each site as well as controls on the effects of independent boundary conditions (e.g. geological, structural, climatic) along strike. They will focus on four sites (Carrizo Plain/Temblor Range, San Emigdio Mountains, northern San GabrielMountains, and Coachella Valley), each of which represents a major gap in understanding of transpression along the San Andreas fault. The integrated results fromthese sites, when synthesized with previous studies, will provide the full range inboundary conditions and transpressive parameters needed to create specific tests ofdifferent models of transpressional deformation. A key aspect of this proposal is the collaboration that will be employed in attaining our goal. The PI's have extensive knowledge of southern California geology and the analytical techniques to be employed. Spotila was among the first to apply this type of integrated approach to understanding portions of the Transverse Ranges. House has actively pursued new applications of the thermochronologic technique that will be employed in this study. Brady provides a robust foundation in structural geology and geophysics that will link uplift estimates with individual structures. Post-doctoral associate Niemi will add an additional expertise in Cenozoic stratigraphy, structural geology, and field mapping. This number of PI's will also enable us to begin work at all field sites concurrently and represents a science team strong enough to tackle this significant problem.