Initiation of the Pacific-North America Plate Boundary in NW Mexico

该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。该项目正在研究墨西哥西北部太平洋和北美板块之间地质分界线的早期历史。下加利福尼亚州半岛位于太平洋板块，墨西哥其余地区属于北美板块。1200万年前，在圣安德烈亚斯断层和加利福尼亚州海湾形成之前，下加利福尼亚半岛和加利福尼亚州海湾的岛屿都作为一个陆地连接在一起。该地区的一次大规模火山喷发产生了火山碎屑流，将火山岩从不同方向沉积到距离喷口至少150公里的地方。由于板块边界断裂，这些岩石现在已经断裂，并被分成两个板块上的不同山脉。来自加州理工学院的学生和教职员工将与墨西哥科学家合作，在从下加利福尼亚州中部半岛到加利福尼亚州海湾海岸的横断面上绘制这些岩石的地图，从索诺兰海岸向东150公里进入墨西哥，以及Tiburon岛和Angel de La Guarda岛上的目标位置。目的是验证这些1200万年前的火山岩的相关性，检查它们是起源于一次大喷发还是几次喷发，并研究它们下面的岩石，以了解它们沉积的地貌。根据这些数据，可以重建这些火山岩的原始范围和沉积模式。这使得可以通过断层来测量偏移量，并确定它们是否仅位移300公里(圣安德烈亚斯断层上的位移量)或多达600公里(这是加利福尼亚州南部海湾的一些断层滑动模型所暗示的位移量)。将使用的技术包括野外地质填图和取样，以及实验室中岩石的磁学研究(古地磁学和磁化率的各向异性)。该项目将更好地了解影响北美西侧的主要板块边界-太平洋和北美板块之间的边界。1200万年前到600万年前沿这条边界的运动历史，并解决了关于该地区发生了多少板块边界断层的争议。这项研究的结果将有助于理解大陆上新的板块边界是如何形成的，以及广泛的断裂带需要多长时间才能转变为大洋中脊系统，例如目前存在于加利福尼亚州海湾盆地之下的海脊系统。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project is studying the early history of the geological boundary zone between the Pacific and North America plates in northwestern Mexico. The peninsula of Baja California lies on the Pacific plate, and the rest of Mexico belongs to the North America plate. Twelve million years ago, before the San Andreas Fault and the Gulf of California formed, the Baja California peninsula and the islands in the Gulf of California were all connected together as a single land mass. A large volcanic eruption in this region produced pyroclastic flows that deposited volcanic rocks up to at least 150 kilometers from the vent in different directions. These rocks have now been faulted and separated into different mountain ranges on the two plates, due to plate boundary faulting. Students and faculty from the California Institute of Technology will work in collaboration with Mexican scientists to map these rocks in a transect from the Central Baja California peninsula to the Coast of the Gulf of California, and from the Sonoran coast a distance 150 kilometers eastward into Mexico, as well as targeted locations on Isla Tiburon and Isla Angel de la Guarda. The objective is to verify the correlation of these 12-million-year-old volcanic rocks, to check whether they originated in one mega-eruption or in several eruptions, and to study the rocks underneath them in order to understand the landscape upon which they were deposited. From these data, the original extent and depositional pattern of these volcanic rocks can be reconstructed. This allows measurement of the amount of offset by faulting and determination if they are only displaced 300 km (the amount of displacement on the San Andreas fault) or as much as 600 km (which is the amount of displacement implied by some models of fault slip in the southern Gulf of California). The techniques to be used include geological mapping and sampling in the field, and magnetic studies (paleomagnetics and anisotropy of magnetic susceptibility) of the rocks in the laboratory.This project will give a better understanding of the initiation of a major plate boundary that affects the western side of North America - the boundary between the Pacific and North America plates. The history of motion along this boundary between twelve million years ago and six million years ago and solve a controversy regarding how much plate boundary faulting took place in this region. The results of this study will help understand how new plate boundaries form in continents, and how long it can take for a broad zone of faulting to turn into a mid-ocean ridge system, such as the one that is now present beneath the basins of the Gulf of California.