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 lithosphere is being detached and “subducted” into
the Tibetan mantle. Such models contrast with a competing paradigm, derived primarily
from observations in the southern and eastern portions of the Plateau, that attribute
plateau formation to 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 surface tectonics are the mantle dynamics beneath
the plateau and adjacent regions. Upper mantle geophysical properties beneath the
northern plateau have been variously attributed to delamination triggered by instability of
a thickened lithosphere, mantle lid detachment and/or asthenospheric counterflow
associated with subduction of Indian continental lithosphere. 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 Jinsha Suture, which
separates the Qiangtang from the Songpan-Ganzi- Hoh Xil 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 Qilian Shan-Nan Shan thrust
system which characterizes deformation of this foreland zone. The geophysical surveys
will consist of a) integrated seismic reflection, refraction and densely spaced passive
profiles, b) detailed magnetotelluric surveys, and c) a regional broadband seismic array.
Specific features to be addressed by the proposed surveys include: a) the existence
and nature of proposed Moho offsets, (b) the deep geometry of major thrust faults at the
plateau boundary (decollements vs crustal “stacking”), c) the relationship between major
thrusts and strike slip faults (which decapitates which?), d) constraints on lower crustal
flow from structural continuity (or lack thereof) of crustal markers, e) the existence and
nature of subducting Asian lithosphere, and f) the mode of lithospheric thickening
beneath the plateau foreland.
Intellectual Merit: Continent-continent 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 INDEPTH collaboration between Chinese and western scientists has already
stimulated geoscience research within China and will continue to lead to valuable spinoff investigations.
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