Pliocene Kinematic History of the Northern Gulf of California

北加利福尼亚湾的上新世运动史

• 批准号: 0610011
• 负责人: Joann Stock
• 金额: $ 10万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0610011&HistoricalAwards=false
• 关键词: Pliocene; Kinematic; History; Northern; Gulf; Pliocene; Kinematic; History; Northern; Gulf

We are studying how a very large crustal block (the Isla Angel de la Guarda crustal block) separated from the adjacent land in the northern Gulf of California in the past 3 to 6 million years and became an island. The Isla Angel de la Guarda crustal block was originally part of the Baja California Peninsula. It split away from Tiburon Island (Sonora) when the northern Gulf of California started to open about 6 million years ago along the Pacific-North America plate boundary. About 2-3 million years ago, the position of the plate boundary changed, and a fault developed between IAG and the rest of the peninsula, transferring IAG back onto the North America plate as an island. Since then, the Isla Angel de la Guarda crustal block should have moved approximately 100 kilometers relative to the Baja California Peninsula due to slip on the faults in the Ballenas channel (west of the Isla Angel de la Guarda crustal block), which are part of the Pacific-North America plate boundary and connect northwards to the San Andreas fault. The total displacement between the Isla Angel de la Guarda crustal block and the peninsula is important for constraining the evolution of the Pacific-North America plate boundary, the history of the San Andreas fault system, and for understanding how much sunken continental crust is present under water in the northern Gulf of California, between Baja California and the island, in the Lower Delfin Basin. The key to solving this problem is the correlation of volcanic rocks that were erupted at various times in the past, as well as correlation of the older basement rocks. When the Isla Angel de la Guarda crustal block was attached to the Baja California peninsula, the basement rocks were continuous. Volcanic eruptions in the region deposited lava and tuffs (pyroclastic flow deposits) on both the island and on the adjacent peninsula. The volcanic rocks on the Baja California Peninsula are relatively well studied, so their stratigraphy and distribution is known. However, Isla Angel de la Guarda is uninhabited and its volcanic rocks have not been studied in detail. We are studying these rocks first using satellite imagery and air photos to identify the outcrops we need to visit. Subsequent field work on the island will allow us to sample rocks in the most important locations and to map their distribution. We are using the techniques of volcanic stratigraphy, paleomagnetics, geochemistry, and geochronology (age dating) of rock samples, in order to characterize them and determine which ones match the rocks exposed in the surrounding regions. The thickness and number of the different volcanic units vary from place to place. We will be able to use these variations to determine the likely original position of the island when it broke away from Baja California, and to know how far back in time it became an isolated island separated from the rest of the peninsula. We will also compare Isla Angel de la Guarda crustal block rocks to the rocks on Tiburon Island to see if we can determine how the two were related initially, before the rifting started.This study complements an existing Mexican government research project that is evaluating correlations of volcanic rocks across the Gulf of California. The Mexican project will provide geochemical analyses and argon dates, reducing the costs to this project. Field work on the island is being conducted by scientists and students from Caltech and Mexico. The paleomagnetic and other laboratory studies at are being done using laboratories at Caltech. The results of the ages and geochemical analyses are being archived in the community data base on volcanic rocks of North America (NAVDAT). The results are being disseminated in scientific publications and presented at professional meetings in the USA and Mexico. The results are also being used for outreach talks to students or the general public, in both English and Spanish. Finally, our results are helping biologists studying the animals and plants of the island, because they constrain how long the biological communities on the island have been isolated from those of the adjacent regions of Mexico. The research is being supported by funds from the Tectonics Program, Division of Earth Sciences, and the Americas Program of the Office of International Science and Engineering.

我们正在研究过去3至600万年的一个非常大的地壳块（Isla Angel de La Guarda Crustal块）与加利福尼亚北部北部的邻近土地分开并成为一个岛屿。 Isla Angel de La Guarda地壳块最初是Baja California Peninsula的一部分。 当加利福尼亚北部海湾大约600万年前沿太平洋北美板块边界开始开放时，它远离了Tiburon岛（Sonora）。 大约200至300万年前，板边界的位置发生了变化，IAG和半岛其他地区之间出现了断层，将IAG转移回北美板块，作为一个岛屿。 从那时起，由于在Ballenas频道（Isla Angel de La Guarda Crustal Block街区以西）的断层，这是Pacific-North America Plate边界的一部分，并连接到Sandrereas的故障，因此相对于Baja California Peninsula的Isla Angel de La Guarda地壳块应移动约100公里。 Isla Angel de la Guarda地壳块与半岛之间的总位移对于约束太平洋北美板块边界的演变，圣安德烈亚斯断层系统的历史以及了解加利福尼亚北部海湾的水下有多少沉没的大陆壳，在Bajaa California和下岛底层之间，在加利福尼亚州北部的北部，在北部湾的北部，在北部的Delfeldeldeldeldeldeldelfins之间，存在多少沉没。 解决此问题的关键是过去在不同时间爆发的火山岩的相关性以及较旧的地下岩石的相关性。 当伊斯拉天使德拉·瓜达（Isla Angel de La Guarda）地壳附在巴哈加州半岛时，地下室岩石是连续的。 该地区的火山喷发沉积在岛上和邻近半岛上的熔岩和凝灰岩（火山碎屑矿床）。 巴哈加利福尼亚半岛上的火山岩进行了相对良好的研究，因此它们的地层和分布是已知的。 但是，Isla Angel de la Guarda无人居住，其火山岩尚未详细研究。 我们首先使用卫星图像和空气照片研究这些岩石，以识别我们需要参观的露头。 随后在岛上进行的现场工作将使我们能够在最重要的位置采样岩石并绘制其分布。 我们使用的是火山地层，古磁学，地球化学和地质学（年龄约会）的技术，以表征它们并确定哪些岩石与周围地区暴露的岩石相匹配。 不同火山单元的厚度和数量随着地点而异。 我们将能够利用这些变体从巴哈加利福尼亚州的巴贾（Baja California）脱离时，确定岛上可能的原始位置，并知道它在时间上变成了一个与半岛其他地区分离的孤立岛屿。 我们还将将Isla Angel de la Guarda地壳岩石与Tiburon岛上的岩石进行比较，以查看我们是否可以在裂谷开始之前确定两者最初的关系。这项研究补充了一项现有的墨西哥政府研究项目，该项目正在评估加利福尼亚湾的火山岩石的相关性。 墨西哥项目将提供地球化学分析和氩气约会，从而降低该项目的成本。 来自加州理工学院和墨西哥的科学家和学生正在岛上进行现场工作。 正在使用加州理工学院的实验室进行古磁和其他实验室研究。 年龄和地球化学分析的结果已在北美火山岩（NAVDAT）的社区数据基础上存档。 结果正在科学出版物中传播，并在美国和墨西哥的专业会议上介绍。 这些结果也用于用英语和西班牙语与学生或公众进行宣传对话。 最后，我们的结果是帮助研究岛上动物和植物的生物学家，因为它们限制了岛上的生物群落与墨西哥邻近地区的生物群落隔离了多长时间。这项研究得到了构造计划，地球科学部和国际科学与工程办公室的美洲计划的资金。