T41F-06
The effects of thick sediment upon continental breakup: seismic imaging and thermal modeling of the Salton Trough, southern California

Thursday, 17 December 2015: 09:15
304 (Moscone South)
Liang Han1, John A Hole1, Robert P Lowell2, Joann M Stock3, Gary S Fuis4, Neal W Driscoll5, Annie M Kell6, Graham M Kent7, Alistair J Harding8, Antonio Gonzalez-Fernandez9 and Octavio Lázaro-Mancilla10, (1)Virginia Polytechnic Institute and State University, Blacksburg, VA, United States, (2)Virginia Polytechnic Institute and State University, Geosciences, Blacksburg, VA, United States, (3)California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States, (4)USGS California Water Science Center Menlo Park, Menlo Park, CA, United States, (5)Scripps Institution of Oceanog, La Jolla, CA, United States, (6)University of Nevada Reno, Incline Village, NV, United States, (7)University of Nevada Reno, Nevada Seismological Laboratory, Reno, NV, United States, (8)University of California San Diego, La Jolla, CA, United States, (9)CICESE National Center for Scientific Research and Higher Education of Mexico, Geology, Ensenada, Mexico, (10)Organization Not Listed, Washington, DC, United States
Abstract:
Continental rifting ultimately creates a deep accommodation space for sediment. When a major river flows into a late-stage rift, thick deltaic sediment can change the thermal regime and alter the mechanisms of extension and continental breakup. The Salton Trough, the northernmost rift segment of the Gulf of California plate boundary, has experienced the same extension as the rest of the Gulf, but is filled to sea level by sediment from the Colorado River. Unlike the southern Gulf, seafloor spreading has not initiated. Instead, seismicity, high heat flow, and minor volcanoes attest to ongoing rifting of thin, transitional crust.

Recently acquired controlled-source seismic refraction and wide-angle reflection data in the Salton Trough provide constraints upon crustal architecture and active rift processes. The crust in the central Salton Trough is only 17-18 km thick, with a strongly layered but relatively one-dimensional structure for ~100 km in the direction of plate motion. The upper crust includes 2-4 km of Colorado River sediment. Crystalline rock below the sediment is interpreted to be similar sediment metamorphosed by the high heat flow and geothermal activity. Meta-sediment extends to at least 9 km depth. A 4-5 km thick layer in the middle crust is either additional meta-sediment or stretched pre-existing continental crust. The lowermost 4-5 km of the crust is rift-related mafic magmatic intrusion or underplating from partial melting in the hot upper mantle.

North American lithosphere in the Salton Trough has been almost or completely rifted apart. The gap has been filled by ~100 km of new transitional crust created by magmatism from below and sedimentation from above. These processes create strong lithologic, thermal, and rheologic layering. While heat flow in the rift is very high, rapid sedimentation cools the upper crust as compared to a linear geotherm. Brittle extension occurs within new meta-sedimentary rock. The lower crust, in comparison, is maintained hot and weak by the overlying sedimentary thermal blanket. The lower crust stretches by ductile flow and magmatism is not localized. In this passive rift driven by distant plate motions, rapid sedimentation and its thermal effects delay final breakup of the crust and the onset of seafloor spreading.

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