HR: 1340h
AN: S33A-1076    [Abstracts]
TI: Multi-Band Images from CD-ROM: Paleo-Subduction and Modern Basalt Extraction Structures in the Southern Rocky Mountains
AU: * Levander, A
EM: alan@rice.edu
AF: Earth Science, Rice University MS-126 6100 Main St., Houston, TX 77005 United States
AU: Zelt, C A
EM: czelt@rice.edu
AF: Earth Science, Rice University MS-126 6100 Main St., Houston, TX 77005 United States
AU: Magnani, M B
EM: beatrice@rice.edu
AF: Earth Science, Rice University MS-126 6100 Main St., Houston, TX 77005 United States
AU: Dueker, K G
EM: dueker@uwyo.edu
AF: Dept. of Geology and Geophysics, Dept. 3006 1000 University Ave. University of Wyoming, Laramie, WY 82071-3006 United States
AU: Yuan, H
EM: yuan@uwyo.edu
AF: Dept. of Geology and Geophysics, Dept. 3006 1000 University Ave. University of Wyoming, Laramie, WY 82071-3006 United States
AB: The CD-ROM (Continental Dynamics of the Rocky Mountains) seismic experiments targeted two Paleoproterozoic suture zones in the western U.S. along a north-south study corridor that extends from central New Mexico to central Wyoming. Seismic reflection, refraction, and teleseismic measurements were made across the Cheyenne Belt in southern Wyoming, and across the Jemez Lineament in northern New Mexico. The Cheyenne Belt is a profound geologic boundary separating the Archean Wyoming craton from island arc terranes accreted to the proto-continent in the Paleoproterozoic. The Jemez Lineament is a linear trend of modern volcanics extending SW from southern Colorado to Arizona, and also coincides with the southern edge of the suture between Yavapai and Mazatzal Paleoproterozoic island arc terranes. Karlstrom and Humphreys (1998) have speculated that the ancient accretionary boundaries influence Cenozoic tectonism in the western U.S., noting the correlation of NE-SW low velocity upper mantle tomography anomalies with geochemical boundaries and mapped suture zones in the Southern Rocky Mountains. At the Cheyenne Belt, the reflection, refraction, P and S tomograms, and pre-stack depth-migrated receiver function images show crust and upper mantle subduction-collision structures that are inferred to have formed during Paleoproterozic island arc collision with the southern margin of the Wyoming craton. Of particular note are a north dipping, high velocity (+3$%$ in P, +5$%$ in S), slab-like structure and a fragment of imbricated crust imaged with both the P and S tomography and the depth-migrated receiver functions. At the Jemez Lineament the reflection data image a bi-vergent orogen marking the Yavapai-Mazatzal suture in the crust. Refraction data show that under the suture zone the crust thins; upper mantle velocity ($\sim$7.7-7.8 km/s) determined from P{_${n}$ suggests that the upper mantle contains 1$%$ partial melt. In the same upper mantle region P and S tomograms show large magnitude low velocity anomalies (-2.5$%$, -5$%$) that correspond to a series of moderately bright but complicated upper mantle events that extend over a distance of $\sim$200 km and to depths of $\sim$100km in the receiver function images. We have modeled this complex series of events using a stochastic description of the velocity field, and generated finite-difference seismograms that match the observations. We interpret the upper mantle low velocity zone as the source region for the recently erupted basaltic magmas found at the Jemez Lineament along the CD-ROM corridor. We speculate that the paleo-suture zone left from continental accretion acts as a crustal conduit for basaltic magmas to pass through the crust, form sills, and erupt.
DE: 7260 Theory and modeling
DE: 7294 Instruments and techniques
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
DE: 3260 Inverse theory
SC: Seismology [S]
MN: 2004 AGU Fall Meeting