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

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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.