Tectonic deformations of the cover in the southern limb and western plunging crown of the Malanyu anticlinorium, eastern Hebei, and its tectonic implications.

The large-scale E-W-trending tectonic deformation terrane cored by the Archean high-grade metamorphic crystalline basement rocks in Zunhua, Qianxi and Qinglong, eastern Hebei, central part of the intraplate Yanshan orogenic belt has long been regarded as an anticlinorium. In recent years, some researchers have suggested that it is a late Mesozoic metamorphic core complex. The two different views concern the Mesozoic tectonic evolution in the northern North China craton and the mechanism for the exhumation of the basement crystalline rocks in the interior of the stable craton. Detailed mapping was conducted in the southern limb and the western plunging crown of the Malanyu anticlinorium. It is revealed that: deformation is generally manifested by continuous folding and associated thrust; structural style is by coexistence of basement-involved thick-skinned structures and thin-skinned controlled by rock series of weakness within covers; the deformation mechanism by longitudinal flexure resulting from bedding-parallel compression and related faults; nearly N-S shortening rates range between 16 and 27%. No high-angle or listric normal faults as are expected by the metamorphic core complex model have been identified so far in the covers. Although the unconformity between the cover and basement has undergone local differential slide during late-stage structural deformation, it is not a detachment fault causing large-scale tectonic erosion and crustal column excisement. Therefore the Malnayu anticlinorium in eastern Hebei is not a late Mesozoic metamorphic core complex but a both basement- and cover-involved thick-skinned fold formed in the setting of lateral compression.