HR: 0800h
AN: T11B-0581    [Abstracts]
TI: Evidence for rapid recycling of subduction erosion forearc material into Cordilleran TTG batholiths: insight from the Peninsular Ranges of southern and Baja California
AU: * Kimbrough, D L
EM: dkimbrough@geology.sdsu.edu
AF: San Diego State University, Dept of Geological Sciences, San Diego, CA 92182-1020, United States
AU: Grove, M
EM: marty@oro.ess.ucla.edu
AF: UCLA, Dept of Earth & Space Sciences, Los Angeles, CA 90095-1567, United States
AB: Studies at oceanic convergent margins show unambiguously that large volumes of continental material are recycled into the mantle by sediment subduction and forearc subduction erosion. The fate of this subducted continental material is poorly known; mass balance consideration suggest that at least 95 percent of this material is recycled to deep mantle circulation. The Late Cretaceous La Posta-type TTG suite of the eastern Peninsular Ranges batholith however displays evidence that accretionary prism sediments were subducted and magmatically recycled into the Late Cretaceous the on a very short (<10 Ma) timescale. The La Posta suite represents a tremendous flare-up of deep (garnet-involved) partial melting preceded by an episode of crustal shortening and presumed crustal thickening from ca. 98-92 Ma. Evidence from the Catalina Schist subduction complex terrane directly outboard of the PRB demonstrates that these rocks were being underthrust and metamorphosed synchronously with La Posta magma generation. Elevated δ18O values from La Posta plutons indicate substantial contributions of isotopically unevolved (initial Sr < 0.706) intermediate to mafic composition supracrustal materials into the melt souce regions consistent with contributions from the Catalina Schist accretionary complex. Further, inherited zircon in the La Posta rocks are dominated by a 120-100 Ma component that closely matches the age of the western PRB as well as the dominant detrital zircon component in Catalina Schist. These results are consistent with "conveyor belt-type" recycling of western PRB material into the forearc and then downward via underthrusting into the magma source region of La Posta melts.
DE: 3619 Magma genesis and partial melting (1037)
DE: 8104 Continental margins: convergent
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 9350 North America
DE: 9610 Cretaceous
SC: Tectonophysics [T]
MN: 2007 Fall Meeting