Characteristics And Geochronology Of The Tectonic Deformations In Huludao-jianchang Area, Western Liaoning Province And Its Significance

At least five different kinds of structures–roughly WE striking fold-thrusts, NWstriking fold-thrusts, NE-NNE striking fold-thrusts, NNE striking normal faults, NNEstriking sinistral faults–have been identified in the Huludao-Jianchang area, westernLiaoning Province. In terms of cross-cutting relationships between different fault setsand independent geochronologic constraints on some of the fault sets and related folds,five important tectonic events during Paleozoic-Mesozoic in western Liaoningprovince have been clarified in this research.D1, forming Pre-Caboniferous west-east extending, southvergened asymmetricfolds and thrusts within Cambrian and overlying Ordvician carbonate rocks. TheseJura-style fold and fault system is floored by1mud décollement layers, andcharacterized by tight anticlines with steep to overturned south limbs and wide spacedsynclines and south-directed thrusts. These deformations might be interpreted asfar-field responses to either late Early Paleozoic or early Late Paleozoic subduction ofpaleo-Asian oceanic plate along the northern boundary of the North China plate;D2, forming Late Triassic (227-221Ma) or late Triassic to early Jurassic(227-190Ma) WE striking, top-to-south thrust faults and basement-cored, faultbounded asymmetric folds and Jura-type folds and thrusts controlled by incompetentlayers (Jxy, likely) within cover sequences locally. Some of the major thrusts might bereactivated paleo-synsedimentary faults formed during Proterozoic as profoundthickness contrasts of the same sequences are found across the faults. This generationis inferred to be corresponded to late Indosian or late Indosian to early Yashanian;D3, forming Early Creataceous (140~132Ma) NE-NNE striking, SE-directedthrusts and folds. NE-NNE striking thrust faults placed Tiaojishan Formation (J2-3t)volcanic rock and its underneath sequences on top of Late Jurassic TuchengziFormation (J3tch), and was then unconformably overlaid by Early CretaceousZhangjiakou Formation (K1z). These faults and folds overprinted on the former WEstriking folds and crosscut the WE striking thrusts. Nearly at the same time or fromlate Jurassic, the WE-NEE striking, south-directed, ancient major thrust faults reactivated again with a significant dextral-slip along it;D4and D5forming NNE oriented normal faults and the later NNE left-lateralstrike-slip faults respectively. These faults cut through the WE-, NW-, NNE-strikingfold-thrusts formed during D1~D3, especially the NNE oriented normal faults, theyreformed the morphology of the former WE-striking anticline profoundly.Moreover, NW striking fold-thrusts formed both before NNE strikingfold-thrusts and after NNE striking normal faults.