Paleomagnetism indicates no Neogene rotation of the Qaidam Basin in northern Tibet during Indo-Asian collision
- 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA
- 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA
- 3Institute of Geomechanics, Beijing, 10081, People's Republic of China
Abstract
Paleomagnetic data were obtained from Tertiary red sedimentary rocks at two locations separated by several hundred kilometers within the Qaidam Basin. In the east-central part of the basin, 30 sites from the lower Pliocene Youshashan Formation yielded characteristic remanent magnetization (ChRM) directions with intermediate unblocking temperatures (100–600 °C); ChRM with high unblocking temperatures (to 680 °C) was isolated from 14 sites. In the same area, ChRM directions were obtained from six sites within the Oligocene Lower Gancaigou Formation. Characteristic magnetization was also determined from 16 sites within the Lower Gancaigou Formation exposed in the E Bo Liang range of the north-central Qaidam Basin. When compared with equivalent- age expected directions for Eurasia, the mean paleomagnetic directions indicate no Neogene vertical-axis rotation of the Qaidam Basin or the Altyn Tagh fault. The Qaidam Basin may act as an indentor translating without rotation toward the North China block and driving clockwise vertical-axis rotations by differential shortening within the Nan Shan fold-and-thrust belt.
Footnotes
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↵GSA Data Repository item 2002023, Table 1, Site-mean paleomagnetic directions, Table 2, Paleomagnetic results from eastern Tibetan Plateau, and Figure DR1, Vector-component diagrams of thermal-demagnetization behavior, is available on request from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, editinggeosociety.org, or at www.geosociety.org/pubs/ ft2002.htm.
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- Accepted November 20, 2001.
- Received August 8, 2001.
- Revision received November 16, 2001.
- Geological Society of America
