Collaborative Research: Structural Constraints on Microcontinent Formation, Gulf of California

当一个大陆裂开形成一个新的海洋盆地时，有时它会分裂成两大块和几个较小的块，称为微大陆。 微大陆在裂谷作用的早期形成，之后它们停留在裂谷的一侧，沉入海平面以下，并被较年轻的海洋沉积物所掩埋。了解微大陆边界的发展是很重要的，因为这些边界可能是矿床和碳氢化合物的所在。我们将对一个年轻的微大陆进行野外地质研究，该大陆位于海平面以上，仍在活跃地形成，两侧以活动断层为界。我们将测试不同的模型，以了解断层模式和导致其发展的隆起时间。我们需要收集的实地数据包括：活动断层的地质测绘;断层偏移阶地的海拔和年龄的详细研究;以及附近火山岩的测绘和采样，以确定火山活动是否与裂谷的年龄或成分有关。我们的研究将帮助科学家了解其他更古老的微大陆，这些微大陆在资源勘探中很重要，但现在被沉积物掩埋，只能通过钻探才能进入。我们的调查团队包括来自美国的两位女教授及其学生，以及来自墨西哥研究所的合作者。 在这项研究中，我们将培养两名研究生在国家的最先进的地质技术，包括结构从运动，发光和/或宇宙成因放射性核素测年。该项目将加强三个机构之间的国际合作，培养国际实地工作的研究生。研究结果将纳入外展活动，包括西班牙语电视新闻采访，年度教师培训研讨会，在加州理工学院的信息公开展示，并在加州大学洛杉矶分校的公共外展活动。已经提出了多种模型来解释走滑环境中的微大陆隔离。为了检验这些模型，我们将研究一个新的孤立的，陆上微大陆的天使岛（IAG）在北方海湾的加州。IAG位于沿着太平洋-北美板块边界，其南端包含一系列密集的年轻大陆断层。这些切割一套海洋阶地20公里内的一个发育良好的转换断层，沿着走向从一个新生的扩张中心。我们将评估IAG上的断层如何与Ballenas转换系统中当前活动的板块边界断层以及Tiburon盆地至该岛东南部的前板块边界断层几何连接。我们将通过详细的地质和构造测绘、使用高分辨率数字高程测绘的地形分析以及地貌表面的测年来限制IAG断层的时间和运动学。在每年的实地考察中，我们将绘制基岩类型，断层几何形状和结构，地貌表面变形，并收集样品用于基岩，海洋阶地，冲积扇和断层带的测年。地质野外工作和图像处理将由加州理工学院、加州大学洛杉矶分校和CICESE（墨西哥恩塞纳达）的研究人员和学生共同进行。在第1年和第2年收集的用于测定地貌表面年龄的样品将在加州大学洛杉矶分校使用发光和/或宇宙成因放射性核素测年技术进行处理。基岩样本将在加州理工学院进行地球化学分析，并由CICESE进行日期测定。这项研究的结果可以改变我们对微大陆早期发展的理解，我们的方法可以适用于大西洋，印度洋和北冰洋的其他微大陆，这些微大陆已成为资源勘探的目标。

When a continent rifts apart to form a new ocean basin, sometimes it breaks into two big pieces and a few smaller pieces called microcontinents. Microcontinents form early in the history of rifting, and afterwards they stay on one side of the rift, sink below sea level, and are buried by younger oceanic sedimentation. It is important to understand the development of microcontinent boundaries because these boundaries may host mineral deposits and hydrocarbons. We will do a field geology study of a young microcontinent that is above sea level, still actively forming, and bordered on two sides by active faults. We will test different models for the fault patterns and the timing of the uplift that caused its development. The field data we need to collect include: geological mapping of active faults; detailed study of elevations and ages of terraces that are offset by the faults; and mapping and sampling of nearby volcanic rocks to see if the volcanism was related to the rifting in terms of age or composition. Our study will help scientists to understand other, older microcontinents that are important in resource exploration, but are now buried by sediments and accessible only by drilling. Our team of investigators includes two female professors from the USA with their students, and collaborators from a Mexican research institute. During this study, we will train two graduate students in state-of-the art geological techniques including structure-from-motion, luminescence and/or cosmogenic radionuclide dating. This project will strengthen the international collaboration among the three institutions and train the graduate students in international field work. Research results will be incorporated into outreach activities including Spanish-language TV news interviews, annual teacher training workshops, an informational public display at Caltech, and public outreach events at UCLA. Multiple models have been proposed to explain microcontinent isolation in strike-slip settings. To test these models, we will examine the structures of a newly isolated, subaerial microcontinent of Isla Angel de la Guarda (IAG) in the northern Gulf of California. The IAG lies along the Pacific-North America plate boundary, and its southern tip contains a dense array of young continental faults. These cut a set of marine terraces within 20 km of a well-developed transform fault, along strike from a nascent spreading center. We will evaluate how the faults on IAG may be geometrically connected to the currently active plate boundary faults in the Ballenas Transform system as well as to former plate boundary faults in the Tiburon Basin to the SE of the island. We will constrain the timing and kinematics of the IAG faults through detailed geologic and structural mapping, topographic analysis using high resolution digital elevation mapping, and dating of geomorphic surfaces. During yearly field trips we will map bedrock types, fault geometry and structures, and geomorphic surface deformation, and collect samples for dating of bedrock, marine terraces, alluvial fans, and fault zones. Geological field work and image processing will be conducted jointly by researchers and students from Caltech, UCLA, and CICESE (Ensenada, Mexico). Samples collected in years 1 and 2 for dating geomorphic surfaces will be processed at UCLA using luminescence and/or cosmogenic radionuclide dating techniques. Bedrock samples will be geochemically analyzed at Caltech and dated by CICESE. The results of this study can transform our understanding of the early development of microcontinents, and our approach can be applicable to other microcontinents in the Atlantic, Indian, and Arctic oceans that have been targeted for resource exploration.