Discrete VS.Continious Continental Deformation and the Role of the Lower Crust in the Tien Shan (Project in progress)(GeoScience)
Organizations who response for the project from Russian/Kirgizian side: Research Station in
Bishkek, Russian Ac.Sci; International Research Center – Geodynamic Proving Ground in Bishkek
Principals (leaders) (Russia): Dr. G.G.Schelochkov- responsible executor; Dr.V.D. Bragin , N.N. Orlenko,
A.I.Matix- leading specialists
Organizations who response for the project from US side: Rensselaer Polytechnic Institute;
University of South Carolina
Principal Investigator USA: Prof. Steve Roecker, Prof. James Knapp
Description:
Reasonable constraints on the type, amount, and onset of shortening in the Kyrgyz Tien Shan, and some idea about flow and stratification in the mantle are available now due to recent years studies. What remains very poorly defined is the role of the lower crust, which acts as the crucial link between processes documented at the surface and those imaged in the mantle. The principal objective of the project is to collect observations that will allow us to address some key questions on the role of the lower crust in intraplate shortening, and in the larger picture of discrete vs. continuous deformation.
The following are the main scientific objectives of this project:
- trace the deep geometry of active structures identified at the surface, thus linking upper crustal kinematics directly to lower crustal and upper mantle dynamics. Relevant questions are: Do major thrust faults penetrate the Moho? Does strain on the Chinese (Tarim) side occur by slip on more than one major fault, or is the deformation at shallow depths merely that associated with fold-and-thrust belts and hence due only to thick sediment?
- Correlate historic seismicity with major structures in the subsurface, especially in the Seismically active Jiashi region, along the southern margin of the orogen,
- evaluate the hypothesis that intracontinental subduction of the Tarim basin crust has played a dominant role in development of the Tien Shan,
- assess the role, on a crustal scale, of Cenozoic reactivation of Paleozoic and Mesozoic structures in localization of intracontinental strain,
- provide high-resolution control on crustal thickness and structural architecture across the entire orogen to quantify mass balance of the thickened plate,
- test alternative geodynamic models for the relative movement (strike-normal vs. strikeparallel) of crust and mantle during orogeny, and
- document the reflection signatures of lower crust and Moho as they relate to processes of mass transfer (subduction vs. magmatism) between crust and mantle during intraplate orogenesis.
The seismic experiments shall offer the chance to trace structures laterally from the surface (at resolutions of a few meters) to the base of the lithosphere, and perhaps deeper, by the use of a tightly integrated, mutually supportive set of independent seismic observations. GPS is added to provided rheological constraints on what would otherwise be a strictly static picture. The high rate of deformation along the strike of the transect (roughly north-south) makes the deduction of lower crustal rheology from a few years of GPS monitoring feasible.
The Project proposes an integrated experiment in the Tien Shan, combining GPS with two seismological investigations:(1) an active source experiment with multichannel CMP reflection profiling and (2) broadband recording of mostly teleseismic events. In order to assess crustal structure and its relationship to the upper mantle in the context of intracontinental shortening, an ~450 km transect is required. This transect will image the entire orogen, from the Kazak Shield in the North to the Tarim Basin in the South
