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

逆压发生在圣安德烈亚斯断层系统的42%。因此，它对转换断层行为的影响是一级重要的，并且可能是全面了解走滑断层和板块边界行为的最重要的复杂问题之一。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圣安地列斯断层沿线几个地点的挤压变形方式的地质限制。在已知主要边界条件（如板块运动倾斜度和主转换断层的机制）的情况下，对逆压作用的功能性理解将使垂直变形模式易于预测。然而，圣安德烈亚斯断层的物质性质仍有争议，大量证据表明，次要因素（结构和岩性非均质性、侵蚀性）在形成对逆压的地质反应中起着重要作用。因此，对于地壳的变形是如何表现出向外板块运动的，还没有一个普遍的认识。PI的目标之一是定量评估外部因素对变形分配的影响，这样我们就可以最终评估基于圣安德烈亚斯断层力学特性假设的跨震变形模型。他们的方法是使用垂直运动的时空分布，表现在基岩隆起（地表隆起+掘出），作为压迫的代表。他们将结合热年代学限制（(U-Th)/He定年）和地表隆起、侵蚀以及驱动基岩隆起的变形结构的地貌和结构限制。他们将使用这些互补的技术来确定相对于圣安德烈亚斯断层的垂直运动模式的空间分布（即近场与远场）及其对板块运动的倾斜度。因此，PI的目标是发展压迫变形和这些关键变量之间的函数关系。这将需要对垂直运动的年代学如何与每个地点的逆压发生相关进行控制，以及对沿走向的独立边界条件（例如地质、构造、气候）的影响进行控制。他们将重点关注四个地点（Carrizo平原/Temblor山脉，San Emigdio山脉，San GabrielMountains北部和Coachella山谷），每个地点都代表了对圣安德烈亚斯断层的逆压理解的主要空白。这些站点的综合结果，当与先前的研究相结合时，将提供创建不同的跨移变形模型的具体测试所需的全方位的边界条件和跨移参数。这项建议的一个关键方面是将用于实现我们目标的合作。PI对南加州的地质和分析技术有广泛的了解。Spotila是最早应用这种综合方法来理解横向山脉部分地区的人之一。House一直在积极探索热年代学技术的新应用，这些技术将用于本研究。Brady为构造地质学和地球物理学提供了坚实的基础，将隆起估计与单个构造联系起来。博士后助理Niemi将在新生代地层学、构造地质学和野外测绘方面增加额外的专业知识。PI的数量也将使我们能够同时在所有现场开始工作，并代表一个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.