Deep Structure of the Northeast Tibetan Collision Zone:
INDEPTH IV
Summary
The northeastern boundary of the Tibetan Plateau is a new focus of contemporary
debate concerning continental plateau formation as an intracontinental response to
collisional orogeny. Recent geological studies and limited geophysical measurements in
this region have been cited to argue that a) uplift is due to internal imbricate “stacking” of
Asian crust while b) Asian continental lithospherie is being detached and “subducted”
into the underlying mantle. Such models contrast with a competing paradigm, derived
primarily from observations in southern and eastern portions of the Plateau, that attributes
plateau formation ductile flow in the deep crust. Complicating both views is the overprint
of major strike slip faulting, which may – or may not—penetrate the entire lithosphere.
Critical to any model of the surface tectonics are the mantle dynamics beneath the
plateau, with gross variations in mantle geophysical properties various attributed to
delimination, mantle lid detachment and subduction and/or counterflow of the
asthenosphere. We propose to test key elements in these hypotheses with an integrated,
focused program of geophysical surveys across three key segments of the NE Plateau
boundary zone: 1) the Jiansha Suture, which separates the Qiangtang from the terranes
within the high Plateau, 2) the Kunlun strike-slip and thrust systems which form the
boundary between the Songpan-Ganzi-Hoh Xil terrane and the Qaidam Basin, and 3) the
Altyn Tagh strike slip fault, which forms the northwest boundary of the thrust system
which characterizes the NE collision zone. The geophysical survey will consist of a)
integrated seismic reflection, refraction and high resolution passive profiles, b) detailed
magnetotelluric surveys, and c) a regional broadband seismic array to image in 3D the
mantle beneath these crustal elements. The geophysical surveys will be complemented by
a suite of geological studies focused establishing the timing of the key events represented
by these structures.
Specific features to be addressed by the proposed surveys include: a) the existence
and nature of proposed Moho offsets (strike slip overprint or roots of crustal thrusts?), (b)
the deep geometry of the major thrust faults at NE plateau boundary (decollements vs
crustal “stacking”), c) the relationship between major thrusts and strike slip faults (which
decapitates which?), and d) direct evidence of lower crustal flow (or absence thereof)
from structural disruption of crustal markers (e.g. thrust and strike slip faults).
Intellectual Merit: Continent-continental collision is a cornerstone of plate tectonics,
and a central process in continental evolution. The intra-continental response to such
collision, especially as it relates to plateau formation, is perhaps its least understand
aspect. Our study will delineate the 3D geometry of those structures which have recorded
this process as it relates to the Tibetan Plateau, and directly test existing geodynamic
hypotheses for the evolution of the distal portions of collision zones.
Broader Impact: The structural evolution of the intracontinental portions of the
southern Asian collision zone have implications for a range of phenomena with direct
societal implications, including earthquake hazards, geothermal energy, and climate
history. The technology transfer featured in the seismic component of this proposal also
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represents development of observational facilities, which should bear important scientific
return well after the proposed activities are complete.
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