| Abstract: | There are two extensional systems in the Xiaoqinling
metamorphic core complex (XMCC). One is the detachment fault system developed along the
peripheries of the XMCC, which extended in an ESE-WNW direction and whose upper plate
moved towards the WNW. The other extensional system includes the retrograde shear zones
and normal faults developed within the XMCC, which represent the collapse of the XMCC.
Ar-Ar and K-Ar dating shows that the extension of the detachment fault system continued
from 135 to 123 Ma, i.e. in the late stage of its evolution at about 127 Ma. The collapse
represented by the extensional system within the XMCC was operative during 120(106 Ma, and
its main activity occurred about 116 Ma ago. These suggest that the XMCC experienced two
extensional stages in its evolution, i.e., the syn-orogenic regional extension and
post-orogenic collapse extension. |
