Early Cretaceous overprinting of the Mesozoic Daqing Shan fold-and-thrust belt by the Hohhot metamorphic core complex,Inner Mongolia,China

The Early Cretaceous Hohhot metamorphic core complex （mcc） of the Daqing Shan （Mtns.） of central Inner Mongolia is among the best exposed and most spectacular of the spatially isolated mcc＇s that developed within the northern edge of the North China ＂craton＂. All of these mcc＇s were formed within the basement of a Late Paleozoic Andean-style arc and across older Mesozoic fold-and-thrust belts of variable age and tectonic vergence. The master Hohhot detachment fault roots southwards within the southem margin of the Daqing Shan for an along-strike distance of at least 120 km. Its geometry in the range to the north is complicated by interference patterns between （1） primary, large-scale NW-SE-trend- ing convex and concave fault corrugations and （2） secondary ENE-WSW-trending antiforms and syn- forms that folded the detachment in its late kinematic history. As in the Whipple Mtns. of California, the Hohhot master detachment is not of the Wernicke （1981） simple rooted type; instead, it was spawned from a mid-crustal shear zone, the top of which is preserved as a mylonitic front within Carboniferous metasedimentary rocks in its exhumed lower plate. 4~Ar-39Ar dating of siliceous volcanic rocks in basal sections of now isolated supradetachment basins suggest that crustal extension began at ca. 127 Ma, although lower-plate mylonitic rocks were not exposed to erosion until after ca. 119 Ma. Essentially synchronous cooling of bornblende, biotite, and muscovite in footwall mylonitic gneisses indicates very rapid exhumation and at ca. 122--120 Ma. Contrary to several recent reports, the master detachment clearly cuts across and dismembers older, north-directed thrust sheets of the Daqing Shah foreland fold-and-thrust belt. Folded and thrust-faulted basalts within its foredeep strata are as young as 132.6 ± 2.4 Ma, thus defining within 5--6 Ma the regional tectonic transition between crustal contraction and profound crustal extension.

Cretaceous-Neogene Exhumation of the Daqing Shan,North China Constrained by Apatite Fission Track Thermochronology

The Daqing Shan(DQS)located in the Yinshan-Yanshan Orogenic Belt plays an important role in the Mesozoic to Cenozoic evolution of the North China Craton.However,the cooling and exhumation history since the Cretaceous is still controversial.Integrating the apatite fission track(AFT)data in both this study and previous works,a three-stage exhumation history from Cretaceous to Neogene of the DQS is proposed.(1)The first stage is composed of the early exhumation during Early Cretaceous driven by the collision between the North China and Siberia cratons(ca.148-132 Ma)and the far-field effect of the subduction of the Pacific Plate(ca.132-114 Ma).(2)Due to the subsidence of the Hetao Basin and the subsequent compensation between the DQS and the Hetao Basin,the DQS experienced the second rapid exhumation from Early Eocene to Early Oligocene(ca.54-29 Ma).(3)Since the Late Miocene(ca.13.5 Ma),the third rapid cooling and exhumation of the DQS occurred due to the far-field effect of the uplift of the Tibetan Plateau and the subduction of the Pacific Plate.