Leloup, P. H., T. M. Harrison, F. J. Ryerson, W. Chen, Q. Li, P. Tapponnier, et R. Lacassin
Journal of Geophysical Research, vol 98, n°B4, p 6715-6743, 1993.
Abstract
The Diancang Shan, a horst bounded massif within the Red River
fault zone in Yunnan, P.R.C., preserves a structural, petrological
and thermal record of two distinct phases of tectonic activity;
a left-lateral ductile shear that terminated between 20 and 17
Ma, and a ductile-to-brittle phase of normal faulting which began
at 4.7 Ma and remains active. Mylonitic rocks in the core of the
range contain an early, steep, high temperature (HT), schistosity
and a horizontal stretching lineation that are both parallel to
the trend of the belt. Kinematics indicators indicate that shear
was left-lateral. The complex shape of the high temperature schistosity
at the southern termination of the massif likely corresponds to
a large scale, oblique, left-lateral shear plane that dismembered
the shear zone and separated the Ailao Shan and the Diancang Shan
at the end of the left-lateral deformation. Thermochronological
and thermobarometric results suggest that the gneisses were partially
unroofed during this event. Along the eastern edge of the Diancang
Shan, the high temperature fabrics were overprinted by low temperature
structures during activation of east-dipping normal faults. Cooling
associated with this normal/right-lateral faulting along the Diancang
Shan (and perhaps, activation of the right-lateral/normal movement
on the Range Front fault further south along the Ailao Shan) began
at 4.7+-0.1 Ma. These results tend to support the view that extrusion
of Indochina occurred along the left-lateral Red River shear zone
between about 32 and 19-17 Ma. Initiation of right-lateral/normal
slip during the late Miocene may relate to eastward extensional
collapse of the thickened Tibetan crust, or more probably to initiation
of a second phase of extrusion .
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Insigths from Tertiary deformation of SE Asia. |