Abstract

The mechanisms of thinning of the lithosphere and destruction of the North China Craton have been debated in recent decades. Their causal link with regional tectonic extension is well exemplified by the exhumation of the Wulian metamorphic core complex (mcc), along the Sulu orogenic belt to the SE of the North China Craton. The Wulian mcc is a Cordilleran type mcc with a northwestward dipping low-angle master detachment fault zone (the Wulian detachment fault zone), an Early Cretaceous supradetachment basin (the Zhucheng Basin) and a lower plate of ultrahigh-pressure metamorphic rocks in the Sulu orogenic belt. Synthetic structural, fabric and thermochronological data suggest that tectonic extension is responsible for the exhumation of the lower plate and triggered syn- and post-tectonic magmatisms. A new cooling path for the lower plate rocks indicates that the lower plate was exhumed at a high rate of 2.0 km Ma−1 from before c. 128 Ma to 123 Ma and at a moderate rate of 0.35 km Ma−1 from 81 to 61 Ma. The rapid exhumation is consistent temporally with the sedimentation of terrestrial deposits of the Laiyang Group in the Zhucheng supradetachment basin. The post-kinematic granitic intrusions are dated as c. 122 Ma, which marks the cessation of rapid exhumation of the lower plate. Vast amount of andesitic volcanic rocks from 120 to 105 Ma in the Qingshan Group in the Zhucheng Basin may be related to the peak of lithospheric thinning in the Wulian area. These data highlight the importance of regional tectonic extension in the formation of the detachment fault zone and the exhumation of the Wulian mcc, and in triggering syn- and post-kinematic magmatisms. The scenario is consistent with the parallel extension tectonics model in which tectonic extension of the lithosphere led to detachment faulting in both the crust and mantle, resulted in the loss of some of the subcontinental roots, gave rise to the exhumation of the mccs, and triggered plutonic emplacement and volcanic eruptions of hybrid magmas.

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