Collaborative Research: Dating Submerged Continental Crust Beneath the Southern Gulf of California, and a Synthesis of the Magmatic and Tectonic History of This MARGINS Focus Site

PIs计划测量和解释从300-3500米深的水下数百个地点采集的各种火山岩和深部岩石的U-Pb结晶年龄，这些地点位于加利福尼亚湾南部大部分地区的水下和以前未取样的裂谷大陆地壳上。许多样本是通过远程操作的车辆沿着断层陡坡和火山特征的穿越收集的；50艘挖泥船也回收了火成岩。所有相关样品都进行了岩石学描述和地球化学分析。这些样品记录了该地区漫长而复杂的岩浆历史，在过去的20 Myr中，该地区从火山弧转变为陆上大陆内裂谷，受到海洋入侵的淹没，并形成了海底扩张生长的轴向盆地链。要确定这段历史，并检验到目前为止仅从裂谷边缘仍在地面上的露头中得出的假设，需要放射性测定的日期。现有的年代测定显示，年龄估计之间存在着惊人的不一致，暗示着有趣的冷却历史可能与构造有关。目标锆石(U-Th)/He和k -长石40Ar/39Ar热年代学分析和建模将约束热历史，从而有助于理解裂谷构造，包括海湾裂谷的大陆隆起和沉降。这项工作很可能加深我们对加利福尼亚湾南部裂谷历史的理解。资金还将为研究生提供研究机会，促进与墨西哥科学家的合作，研究结果将用于正在进行的教育和推广项目，如SDSU的K-8项目。

The PIs propose to measure and interpret U-Pb crystallization ages of a varied suite of volcanic and plutonic rocks recovered from water depths of 300-3500m at several hundred sites on the submerged and previously unsampled rifted continental crust that underlies most of the southern Gulf of California. Many samples were collected along traverses up fault scarps and across volcanic features by a remotely operated vehicle; 50 dredge hauls also recovered igneous rock. All relevant samples have been petrographically described and geochemically analyzed. These samples record a long and complex magmatic history in this region, which in the past 20 Myr has changed from a volcanic arc to a subaerial intra-continental rift, been flooded by a marine incursion, and developed a chain of axial basins growing by seafloor spreading. Radiometric dates are needed to define this history, and to test hypotheses that up till now have been solely derived from still-subaerial outcrops at the margins of the rift. Existing dating show striking discordance between the age estimates, hinting at interesting cooling histories with likely tectonic implications. Targeted zircon (U-Th)/He and K-feldspar 40Ar/39Ar thermochronologic analyses and modeling will constrain thermal histories, thereby contributing to understanding rift tectonics including continental uplift and subsidence in the gulf rift.The work will very likely deepen our understanding of rifting history of the southern Gulf of California. Funding will also provide research opportunities for graduate students, foster collaboration with Mexican scientists and the results will be used in ongoing education and outreach programs, such as SDSU's K-8 project.