S33D-07:
3D Lithospheric Structure in an Arc-Continent Collisional Setting: Results from the EarthScope IDOR Passive Seismic Receiver Functions
Wednesday, 17 December 2014: 3:10 PM
Adrian C Stanciu1, Raymond M Russo2, Victor I Mocanu3, David A Foster1, Paul M Bremner4, Megan E Torpey1, Sutatcha Hongsresawat1, John C VanDecar5, John A Hole6 and Basil Tikoff7, (1)University of Florida, Gainesville, FL, United States, (2)Univ of FL-Geological Sciences, Gainesville, FL, United States, (3)University of Bucharest, Dept. of Geophysics, Bucharest, Romania, (4)University of Florida, Ft Walton Beach, FL, United States, (5)Carnegie Inst Washington, DTM, Washington, DC, United States, (6)Virginia Polytechnic Institute and State University, Blacksburg, VA, United States, (7)Univ Wisconsin, Madison, WI, United States
Abstract:
We present new images of lithospheric structure obtained from P-to-S receiver functions at 86 broadband seismic stations we deployed as part of the EarthScope IDOR experiment. The high-quality data of the IDOR survey allowed us to image in detail the crustal thickness, and the structure of the lithospheric mantle beneath the Blue Mountains accreted terranes and the Paleozoic margin of North America. At the surface, the ~110 Ma suture between the arc terranes and the North American Craton is marked by the dextral transpressional system of the Western Idaho Shear Zone (WISZ), which closely follows the Sr 0.706 isopleth. Long-lived magmatism (108 – 50 Ma) of the Idaho Batholith occurred during and after the WISZ deformation. We constructed more than 7000 P-to-S teleseismic receiver functions using iterative time domain deconvolution, and we used H-k grid search, inversion, and common conversion point stacking (CCP) to image the lithospheric structure. Moho depths vary from 35-40 km beneath the Blue Mountain terranes and the extended regions of central Idaho, and shallow to ~30 km in the central part of the IDOR network. We see a clear break in the continuity of the Moho across the WISZ, with depths increasing from 30 to 40 km east of the WISZ. We also see a strong mid-crustal converting interface at 15-20 km depth beneath the Idaho Batholith on the east side of the WISZ. To the east, beneath the Lost River Range and Pahsimeroi valley, we see an offset in Moho depth possibly related to Basin-and-Range extension. A strong shallow contrast in crustal velocities beneath the West Snake River Plain is probably due to Columbia River Basalts and sedimentary cover. We observe a horizontal, continuous positive amplitude phase at ~90 km across the entire network that we interpret as the Mid-Lithospheric Discontinuity. A second positive amplitude phase varies from ~120 km beneath the accreted terranes to ~140 km beneath the western margin of the North American Craton. The increase in depth in this phase occurs over a horizontal distance of ~160 km and is most likely related to the contact between the accreted Blue Mountain lithosphere and Precambrian North America. This structure lies at depths consistent with the regional lithosphere boundary resolved by Yuan and Romanowicz (2010).
