Tao Wang, Chinese Academy of Geological Sciences (China)
Yadong Zheng, Peking University (China)
Jinjiang Zhang, Peking University (China)
Lingsen Zeng, Chinese Academy of Geological Sciences (China)
Xinshe Wang, Chinese Academy of Geological Sciences (China)
Late Mesozoic crustal extension, represented by well-development of various extensional structures (including MCCs, metamorphic domes and normal faults) and graben or half-graben basins as well as alkalic A-type magmatism and associated mafic intrusions, widely occurs in the northeastern (NE) Asian continent and resulted in the largest extensional province in the world. Metamorphic core complexes (MCCs) are typical representatives of the extensional structures.
This paper summarizes major characteristics of the MCCs and obtains an insight into the pattern and kinematics of this extension event. These MCCs have similar biotite and hornblende 40Ar/39Ar cooling ages ranging predominately from 130 to 110 Ma. This suggests that the early Cretaceous extension across the northeastern Asian is nearly synchronous. Most MCCs in the Trans-Baikal region, Sino-Mongolia tract, and northwest-central North China craton (NCC) have a top-to-southeast tangential shear, whereas those in the eastern and southern NCC have undergone locally top-to-northwest shear. The transitional zone lies where the three largest basins in the North China are located. The late Mesozoic crustal extension in NE Asian therefore seems to have a kinematical polarity. A dynamic scenario in terms of late-orogenic collapse is proposed to interpret the kinematic pattern and mechanics of the crustal extension. The crustal extension in the Trans Baikal, Sino-Mongolia tract and northwestern part of NE China is reasonable to attribute to the Middle-Late Jurassic to Early Cretaceous late-orogenic collapse of the thickened crust related to the middle-Late Jurassic Okhotsk suturing. The southward extension is probably controlled by a crustal-scale top-to-SES tangential shear.
The transition from contraction to extension is marked by extensional detachment faults that nucleated as extension crenulation cleavage (ecc) in sub-horizontal ductile shear zones during the orogeny. The combinational effect of gravitational loading and thermal-uplifting is considered to be responsible for the late-orogenic collapse. The top-to-NNW extension in locale NE north China craton might be anti sub-extensional zones or be derived from far-field effect of the Pacific plate subduction.