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Underplating in the Himalaya-Tibet Collision Zone Revealed by the Hi-CLIMB Experiment

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Science  11 Sep 2009:
Vol. 325, Issue 5946, pp. 1371-1374
DOI: 10.1126/science.1167719

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  1. Fig. 1

    The layout of the Hi-CLIMB experiment in Nepal and on the Tibetan Plateau. Red circles indicate the positions of broadband seismological stations. The white vertical line is the location of the projected cross section shown in Fig. 2. Barbed and dashed black lines mark major fault zones and sutures separating main tectonic blocks: the Main Boundary thrust (MBT), YTS, and BNS. The yellow line shows the inferred northern limit of the underplated lower crust of the Indian plate. Blue dashed lines show locations of lower crust duplexes observed in other receiver function studies (9, 26).

  2. Fig. 2

    (A) Receiver function image along the main profile showing the principal contrasts within the lithosphere (red and blue colors represent interfaces with increasing and decreasing impedance with depth, respectively). The horizontal distances are referenced to the MFT. All depths are relative to sea level. The top of the figure shows the station altitude (blue dashes), average topography (black line), and Moho depth (red line). To determine the crustal thickness, one must add topography to the observed Moho depth. (B) Image of the Moho using northward illumination by the PS phases. (C) Same as in (B) but illuminated from the south. (D) Interpretative cross section of the India-Eurasia collision zone. The lower part of the Indian lithosphere underplates the Himalayas and Tibet up to 31°N. The eclogitized lower crust is shown in green. Moho conversion is shown by a black line when it is strong and a gray line when it is weak. The approximate dip of the inferred opposing lower crustal fabric is indicated by thin lines. Focal mechanisms mark mantle earthquakes (32). The MHT, which becomes a broader mid-crustal LVZ (blue wavy pattern) in the southern Lhasa Block, accommodates the simple shear of the plate motions and acts as a conduit for the transfer of the Indian upper crust into the Himalayan orogenic prism (red arrows). The prominent lineations of the upper mantle fabric are shown in gray. The average P-wave velocity depth profile for the southern Lhasa Block determined by receiver function waveform inversion is also shown (black line).

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