Intellectual merit. Clastic sedimentary sequences shed from orogenic belts provide a fertile, and arguably unique, record of crustal exhumation. However, in spite of recent analytical advances, interpretive methods for detrital thermochronology have remained relatively basic. There is a clear need for numerical approaches for interpreting detrital thermochronology that are capable of dealing with transient heat flow related to intrusion and faulting and, at the same time, are constructed to appropriately and comprehensively accept input from a variety of thermochronologic constraints. Similarly, there is a need to move beyond simple interpretation of detrital age distributions and employ more informative thermochonometers that can reduce ambiguities in data interpretation for environments with complex thermal histories (such as shallow arc crust).
The proposed research will: [1] Produce a general thermo-kinetic model capable of describing rifted arc crust and an optimization scheme based upon FORTRAN Feasible Sequential Quadratic Programming to constrain the initiation time, slip history, and erosion history related to normal faulting by simultaneously fitting detrital and basement thermochronologic data collected within a continental rift setting (Baja California margin of the southern Gulf of California). [2] Further develop and employ higher resolution detrital thermochronometric methods that include multi-diffusion domain 40Ar/39Ar thermal history analysis of single detrital Kfeldspar crystals and coupled U-Pb & (U-Th)/He analyses of zircon to better understand the effects of transient heating and obtain continuous thermal history data between 350-150 C. Self-consistent integration of lower temperature apatite FT and (U-Th)/He data will further improve ability to constrain crustal evolution with detrital thermochronology.
Broader Impacts. Parameters for Testing Controls of Oblique Rifting in the Southern Gulf. This study will provide basic data regarding the magnitude and timing of continental rifting affecting the SE Baja margin of the southern Gulf of California. This information, considered within the context of ongoing and proposed projects in the NSF-MARGINS program, is required to comprehensively evaluate the controls on how and where the plate boundary of the southern Gulf of California formed.
Educational and Societal Benefits of Research. There will be direct benefit to a UCLA graduate student working on a MS thesis directly related to the project. Benefits will also be realized by students working with our collaborators (Dave Kimbrough, SDSU; John Fletcher, CICESE; Paul Umhoeffer, NAU; Tobias Schwennicke, UABCSur; and Barry Kohn, Melbourne). Furthermore, in their role at UCLA, Lovera and Grove interact with many graduate students at UCLA and other institutions. The direct products of this research (i.e., numerical code and optimization routines) will be made available to these students for their thesis research (as well as the community at large via our website as has been done for MDD modeling code). Finally, this project will enhance international collaboration with the groups at the Mexican institutions CICESE and UABCS. These collaborations offer opportunities for American students to work in Mexico and for Mexican students to attend universities in the United States. Finally, in his role as manager of UCLA's NSF-sponsored national ion probe facility, Grove is involved in an education and outreach program for grade 5 thru 9 students in the Los Angeles area. Grove will work with collaborators at SDSU, NAU, CICESE, and UABCS and Tanya Atwater at UCSB's visualization center to add a supplementary exercise concerned with the opening of the Gulf of California that incorporates the results of this study and other ongoing investigations.
