The system of extensional structures developed in the late Yanshanian orogeny in the west of Shandong Province, China

Abstract

The system of extensional structures in the west of Shandong Province is located on the east margin of the China continental block and on the west side of the Tangcheng-Lujiang fault. Complex crustal movements occurred in the region after the Late Triassic. The system of extensional structures is composed of a linked system of faults, formed under biaxial horizontal extensions after the Yanshanian orogenic contraction. The structure consists of three groups of faults: (1) listric normal faults with NW-SE, approximately E-W and approximately N-S trends; (2) transfer faults that are perpendicular to the normal faults; gently dipping detachments in several layers. The NW-SE-trending Late Jurassic and Early Cretaceous basins have an extension of about 11–16 km (about 6.7%). The Eogene basins have NW-SE and E-W trends, and an extension of about 13–19 km (about 8%). Adding the extensional value of the top of the Archaean metamorphic basement, the total N-S extension is about 25–30 km (about 14%). The total extension of N-S-trending grabens formed during the Late Eogene is about 9.8 km (about 6.6%). The amount of extension in this system was not large enough to produce a typical metamorphic core complex. The Taishan-Lushan-Yishan mountains are uplifted bodies of Precambrian basement which have approximately E-W trends and which were formed by N-S extension. Similarly, the Nishan mountain is an uplifted body by E-W extension. These structures represent a late-orogenic extensional system, characterised by multiple glide surfaces and by faults with different orientations causing extension in all horizontal directions.