Geodynamics of Intracontinental Mountain Building in the Tien Shan, Central Asia

Department of Geological Sciences Research

Bradford H. Hager (MIT), Douglas Burbank (Penn State), Thomas A. Herring (MIT), Marcia McNutt (MIT), M. Meghan Miller (CWU), Peter Molnar (MIT), Stephen K. Park (UCR), Gary Pavlis (IU), Steven W. Roecker (RPI), Charles Rubin (CWU), Ray J. Weldon (UO), and Frank Vernon (Scripps).

Images

Click on each image for a high-resolution jpg image

	Digital elevation model (DEM)
	Geologic map
	Active fault map
	Digital elevation model of Eurasia
	Kyrgyz boy on horeback
	Sunset over the Tien Shan
	Thrust fault & CMR
	Tilted Cenozoic erosion surface
	Ray in Kochkorka
	North-dipping thrust fault in Naryn Valley

Posters (PDF)

 Our 1997 poster at the American Geophysical Union Annual Meeting [1.3MB Adobe PDF document]

 Our 1997 poster at the Geological Society of America Annual Meeting [2.4 MB Adobe PDF document]

Project Summary

We propose a multidisciplinary investigation of the deep structure and kinematics of deformation of the Tien Shan, the largest and most active intracontinental range in the world. Our objective is to understand the dynamic processes responsible for intracontinental mountain building, using the Tien Shan as a natural laboratory to ask: Why and how does such deformation occur where it does within continental regions? How does such deformation evolve with time? What bounds does the deep structure place on flow in the mantle? and, How do such possible flow and possible pre-existing geological heterogeneity relate to the observed deformation of the upper crust.

To determine the kinematics, we plan to use: (1) Quaternary geology to define late Quaternary slip rates and styles of deformation on thrust faults and rates of folding across the range, (2) an assortment of other geologic approaches to determine the growth and long-term history of the range, including balanced geologic cross sections, magnetostratigraphy, fission-track dating, and remote sensing coupled to a synthesis of existing regional geologic mapping, (3) GPS geodesy to determine present-day relative movements of 120 benchmarks, and (4) seismicity and focal mechanisms of earthquakes to define both locations and dips of major active faults, as well as the depths in the crust to which these faults reach. In addition, we will study the reconstructed distribution of pre-orogenic rock types, including isotopic and chemical compositions of Late Cretaceous and early Cenozoic basalt and intrusive rock, to place bounds on possible pre-existing weakness in the crust and mantle beneath the Tien Shan.

To determine the deep structure, we plan to use seismology, magnetotellurics, and gravity anomalies to define and quantify lateral heterogeneity in order to test various hypotheses for dynamic processes in the crust and mantle responsible for the lateral heterogeneity.

Finally, we plan a series of numerical experiments to examine how elastic and inelastic deformation and rheological parameters can be extracted from geologically and geodetically determined rates of deformation, how a continental interior is likely to deform in response to plausible forces and stresses applied to it, and how convection is likely to develop within a deforming continental region. This project is multidisciplinary, with 6 separate disciplines of the earth sciences; multi-institutional, with 9 institutions in the USA participating; and multinational, with involvement of scientists from 6 nations (China, France, Kazakhstan, Kyrgyzstan, Russia, and the USA).