Marginal basins preserve a detailed record of the spatial and temporal evolution of orogenic systems along continental margins. This investigation focuses on the fundamental question of how the exhumation history of orogenic systems is preserved in the ancient stratigraphic record, and with what fidelity this history can be extracted from derivative sedimentary successions. It integrates complementary isotopic detrital provenance techniques to constrain source area heterogeneity, exhumation patterns and rates, sediment dispersal characteristics, and basin subsidence mechanisms. Specifically, the study is testing the utility of integrating multiple isotopic techniques (detrital zircon U-Pb geochronology, whole rock Nd analyses, and detrital K-feldspar & muscovite 40Ar/39Ar thermochronology) with traditional sedimentologic analyses (biostratigraphic, lithostratigraphic and petrologic studies) to assess the dynamic linkage between orogenesis, basin subsidence and resultant sediment dispersal and accumulation in continental margin arc systems. A key aspect of this investigation is development and application of new analytical and modeling approaches associated with 40Ar/39Ar closure age distributions of detrital minerals. Preliminary results utilizing total fusion 40Ar/39Ar analysis of K-feldspar from sediments derived from the northern Peninsular Ranges of California indicate that indicate this method can provide a sensitive, high-resolution record of deep basement exhumation. Meaningful application of the method to batholithic source regions requires characterization of intrusion history, necessitating detrital U-Pb zircon geochronology to provide basement crystallization ages. Source area heterogeneity and temporal and spatial variations in sediment dispersal and accumulation patterns are constrained using whole rock neodymium isotopic analyses of fine-grained clastic rocks.
Two basins that share broad first-order similarities in age, provenance and depositional setting, but have strongly constrasting syn-sedimentary crustal exhumation records in their respective batholithic source regions are being examined The Vizcaino basin of Baja California is exposed adjacent to the relatively shallowly exhumed (5-10 km) Peninsular Ranges batholith where a distinct episode of accelerated arc denudation appears to have been triggered by large-volume batholith emplacement. The Nanaimo basin of southern British Columbia is exposed adjacent to deeply eroded (20-30 km) magmatic arc rocks of the Coast Plutonic Complex that were exhumed in response to a more complex interplay of plutonism and regional deformation. Both basins have well-dated stratigraphically coherent successions that span the exhumation events in their respective source regions areas. This provides the necessary interpretive framework to interpret details of basement exhumation histories recorded in the derivative sedimentary record. Undergraduate student research collaborators are heavily involved in all aspects of field and laboratory analyses conducted during this investigation.
Student collaborators (n~12) are participating in stratigraphic analysis, sedimentary petrology, geochemistry, and isotopic analysis at both the University of Wisconsin-Eau Claire and San Diego State University.
