Collaborative Research: The Rosario Segment of the Cretaceous Alisitos Oceanic Arc (Baja California, Mexico): An Outstanding Field Analog to the Izu Bonin Arc

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This collaborative research project will interface closely with the IODP projects in the Izu-Bonin-Mariana (IBM) arc by fully characterizing what is probably its best field analog on Earth: the Rosario segment of the Alisitos arc. DeBari has been deeply involved in the IBM proposals, and Busby is co-chief scientist on IODP Expedition 350. Exhumed rocks from arc crustal sections have the unique ability to inform studies of active subduction zones by "ground-truthing" the assumptions that go into models, experiments, and interpretive geophysics and geochemistry. Some of the questions we will ask, highly complementary to the IBM work, are: How is arc middle crust constructed? What is the relationship and proportion between volcanic and plutonic rocks in juvenile arc crust? What is the tempo of constructing arc crust? How does arc crust composition change with time? Is there any older crust that makes up significant parts of the Alisitos arc? What can we learn about convergent margin mineralization by comparing the Alsitos arc to the Izu Bonin arc? How does the crustal structure of the Alisitos arc compare with seismic velocity profiles in modern arcs? Can surface and borehole heat flow measurements in modern arcs be related to features preserved in the geologic record of ancient arcs?This research furthers the careers of two female scientists (DeBari at WWU and Busby at UCSB) and their respective graduate students. Training of these graduate students is collaborative so that both students will become skilled at the integration of field geology, petrology and geochronology. Scientific interaction between US scientists at WWU and UCSB and international colleagues at UNAM in Mexico will broaden the perspectives of all participants, and enhance research and training outcomes. The proposed project is of interest to the broader science community, as it addresses some of the foremost questions in the NSF GeoPRISMS science plan on the growth and evolution of continental crust through study of island arcs (http://www.geoprisms.org/science-plan.html#science-plan), as well as research envisioned by the GeoPRISMS ExTerra initiative (http://www.geoprisms.org/scd/exterra.html). One of the main products, a web-based 'Island Arc Crust Virtual Field Model', will be used by scientists as a reference model for IBM drilling outcomes, and in curriculum for both undergraduate and graduate students. A field workshop in the Alisitos arc, ideally held in conjunction with Expeditions 350-352 post-expedition meetings and before IBM-4 drilling begins, will provide invaluable context for IBM drilling participants.The Rosario segment of the Cretaceous Alisitos arc in Baja California is an outstanding field analog for the Izu-Bonin-Mariana (IBM) volcanic arc. The IBM arc is under intense study by the International Ocean Drilling Program (IODP) as an in-situ example of present-day formation of nascent continental crust. Earth is the only planet in the solar system with extensive felsic (Si-rich, Mg-poor) continental crust. The rocky planets and the Moon have basaltic (Mg-rich) crusts formed early in the history of the solar system. The volume of continental crust on Earth has grown over time due to plate tectonic processes, dominantly because of accretion of felsic to intermediate volcanic arcs at convergent margins. However, the processes that produce this felsic to intermediate crust are not well characterized in situ. The Rosario segment has superior three-dimensional exposures of an upper- to middle-crustal section through an extensional oceanic arc. Previous mapping of this 60-km-long segment of the Alisitos arc, done in the 1990?s (Busby et al., 2006), will provide a framework for the proposed study; however, that study focused mainly on field descriptions of the volcanic rocks, with limited geochronology, and no geochemistry. The proposed study will determine in detail the relationships between rock types at all stratigraphic levels in the arc, using field, geochemical, and geochronological data. This collaborative research project will interface closely with IODP Expeditions 350-352 (in 2014) and a fourth ambitious proposal to drill to the arc middle crust (IODP Proposal 698 at site IBM-4, awaiting scheduling. These data will be used to construct an 'Island Arc Crust Virtual Field Model' to be used by scientists as a reference model for IBM drilling outcomes.