Crustal Detachment and Destruction of the Keel of North China Craton: Constraints from Late Mesozoic Extensional Structures

Extensional crustal detachment is one of the most important tectonic responses of lithosphere thinning. Late Mesozoic extensional structures, i.e., detachment faults, metamorphic core complexes (mcc's) and fault depression basins, are commonly found in North, South and Northeast China, eastern Mongolia and the Baikal region. The detachment faults associated with these extensional structures may root into either the upper crust (detachment faults of fault depression basins), upper to middle crust (detachment faults), or middle crust (detachment faults in mcc's). Crustal detachments in North China have features, such as kinematic polarity, geometrically regional symmetry and local asymmetry, and are widely and inhomogeneously distributed. These usually take place during the period between 140 and 60 Ma, and lead to thinning of both the crust and the lithosphere. This study reveals that there is no definite correlation between variation of thickness of the present lithosphere and the development and distribution of Late Mesozoic extensional structures in the North China Craton (NCC). The general tendency is that thickness of lithosphere increases from Northeast China to the Baikal region, which means that the present lithosphere is wedge-shaped and the abrupt changes in lithosphere thickness in East Asia are closely related to Cenozoic rifting. It is also found that there is extensive lithosphere thinning in Late Mesozoic detachment (or coeval mantle detachment), and the lithosphere in a vast area from Baikal to Northeast China is thinned in a unified regional extensional stress field. All of the above indicates that destruction of the NCC's keel in the Late Mesozoic was a response of regional crustal detachment and lithospheric thinning in East Asia.