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

当一块大陆裂开形成一个新的洋盆时，有时它会分裂成两大块和几个小块，称为微大陆。微大陆在裂谷历史的早期形成，之后它们停留在裂谷的一侧，沉没到海平面以下，并被更年轻的海洋沉积所掩埋。了解微大陆边界的发展是很重要的，因为这些边界可能含有矿藏和碳氢化合物。我们将对一个年轻的微大陆进行野外地质研究，该大陆在海平面以上，仍在积极形成，两侧都有活动断裂。我们将测试不同的模型，以确定断层模式和导致其发展的隆起时间。我们需要收集的现场数据包括：活动断裂的地质测绘；详细研究被断裂错开的阶地的海拔和年龄；以及对附近的火山岩进行测绘和采样，以确定火山作用在年龄或成分方面是否与裂谷有关。我们的研究将帮助科学家了解其他更古老的微大陆，这些大陆在资源勘探中很重要，但现在被沉积物埋藏，只能通过钻探才能到达。我们的调查团队包括两名来自美国的女教授和她们的学生，以及来自墨西哥一家研究机构的合作者。在这项研究中，我们将培训两名研究生掌握最先进的地质技术，包括运动构造、发光和/或宇宙成因放射性核素测年。该项目将加强三所院校之间的国际合作，培养从事国际实地工作的研究生。研究成果将纳入推广活动，包括西班牙语电视新闻采访、一年一度的教师培训讲习班、加州理工学院的信息公开展示以及加州大学洛杉矶分校的公共推广活动。已经提出了多种模型来解释走滑环境中的微大陆隔离。为了测试这些模型，我们将检查加利福尼亚州海湾北部的天使岛(Isla Angel De La Guarda，IAG)一个新隔离的空中微大陆的结构。IAG位于太平洋-北美板块交界处，其南端包含密集的年轻大陆断层。这些切割了一组海洋阶地，沿着一个新生的扩张中心走向，距离一个发育良好的转换断层不到20公里。我们将评估IAG上的断层如何在几何上与巴列纳斯变换系统中目前活动的板块边界断层以及提伯隆盆地到岛的东南方向的以前的板块边界断层相联系。我们将通过详细的地质和构造制图、使用高分辨率数字高程制图的地形分析以及地貌表面的测年来约束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、断层几何和构造以及地貌表面变形图，并收集样品用于基岩、海相阶地、冲积扇和断裂带的测年。地质野外工作和图像处理将由加州理工大学、加州大学洛杉矶分校和墨西哥恩塞纳达CICESE的研究人员和学生共同进行。加州大学洛杉矶分校将使用发光和/或宇宙成因放射性核素测年技术对第一年和第二年收集的地貌表面测年样品进行处理。基岩样本将在加州理工大学进行地球化学分析，并由CICESE确定日期。这项研究的结果可以改变我们对微大陆早期发展的理解，我们的方法也可以适用于大西洋、印度洋和北冰洋的其他微大陆，这些微大陆是资源勘探的目标。

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.