Belt In South China Research Articles

Constraints on the depth, geometry and kinematics of blind detachment faults provided by fault-propagation folds: An example from the Mesozoic fold belt of South China

The Mesozoic multi-layered thin-skinned, fault-related fold belt in South China is characterized by propagation chevron folding and thrust faulting. We examine the geometry and depth of blind detachment faults in this belt using faults and folds that crop out along a well-defined cross-section. A combination of parameters such as backlimb dip angle (2 θ), interlimb angle ( γ), height of anticline ( h), thickness of the referenced layer ( h 0), width of the anticline ( AB) and thickness-change ratio of layering within the forelimb ( t f / t) are used to develop new equations to estimate the geometry and depth of the detachment faults. In the cross-section, the Huangdushan chevron anticline has parameters revealing a blind fault with a ramp angle of 42° and a flattened segment at a depth of 4.9 km. Based on existing seismic data, we interpret this blind fault as a backthrust developed over an in-sequence imbricated duplex of Cambrian to Ordovician strata. A chevron anticline at Qiyueshan also reveals a backthrust fault. However, a broad anticline in Lengzhuba and a small cylindrical, sinusoidal anticline in Yupize reveal a flat-ramp-flat detachment fault with flat segments at depths of 7.4 and 3.4 km, respectively, suggesting that the Sinian strata were thickened probably by an out-of-sequence imbricated duplex. Our results indicate that the flat-ramp-flat detachment fault along the bottom of the Sinian strata produced the out-of-sequence imbricated duplex and cylindrical sinusoidal folds. The in-sequence imbricated duplex produced backthrusts and related chevron anticlines. We consider that this fault-related fold belt was produced by collision between the Yangtze Block and North China Blocks.

Sensitive High‐Resolution Ion Microprobe U‐Pb Zircon and 40Ar‐39Ar Muscovite Ages of the Yinshan Deposit in the Northeast Jiangxi Province, South China

AbstractThe Yinshan deposit in the Jiangnan tectonic belt in South China consists of Pb‐Zn‐Ag and Cu‐Au ore bodies. This deposit contains approximately 83 Mt of the Cu‐Au ores at 0.52% Cu and 0.8 g/t Au, and 84 Mt of the Pb‐Zn‐Ag ores at 1.25% Pb, 1.02% Zn and 33.3 g/t Ag. It is hosted by low‐grade metamorphosed sedimentary rocks and mafic volcanic rocks of the lower Mesoproterozoic Shuangqiaoshan Group, and continental volcanic rocks of the Jurassic Erhuling Group and dacitic subvolcanic rocks. The ore bodies mainly consist of veinlets of sulfide minerals and sulfide‐disseminated rocks, which are divided into Cu‐Au and Pb‐Zn‐Ag ore bodies. The Cu‐Au ore bodies occur in the area close to a dacite porphyry stock (No. 3 stock), whereas Pb‐Zn‐Ag bodies occur in areas distal from the No. 3 stock. Muscovite is the main alteration mineral associated with the Cu‐Au ore bodies, and muscovite and chlorite are associated with the Pb‐Zn‐Ag ores. A zircon sensitive high‐resolution ion microprobe U‐Pb age from the No. 3 dacite stock suggests it was emplaced in Early Jurassic. Three 40Ar‐39Ar incremental‐heating mineral ages from muscovite, which are related to Cu‐Au and Pb‐Zn‐Ag mineralization, yielded 179–175 Ma. These muscovite ages indicate that Cu‐Au mineralization occurred at 178.2±1.4 Ma (2σ), and Pb‐Zn‐Ag mineralization at 175.4±1.2 Ma (2σ) and 175.3±1.1 Ma (2σ), which supports a restricted period for the mineralization. The Early Jurassic ages for the mineralization at Yinshan are similar to that of the porphyry Cu mineralization at Dexing in Jiangnan tectonic belt, and suggest that the polymetallic mineralization occurred in a regional transcompressional tectonic regime.

Mirror-image thrusting in the South China Orogenic Belt: tectonic evidence from western Fujian, southeastern China

The Mesozoic orogenic belt in south China is readily divided into two fold and thrust belts and a central multiply-deformed zone of ductile deformation dominated by folds with steeply dipping axial planes. Southeast-directed thrusting in the eastern belt and northwest-directed thrusting in the western belt resulted in a mirror image of one another during the Mesozoic. The eastern fold and thrust belt can be further divided into three domains that overlap one another and exhibit a southeast-verging wedge-like geometry and kinematics. Deviatoric stress has been calculated from quartz dislocation density at 91.5 MPa, 74.5 MPa and 73.8 MPa, decreasing toward the southeast. Upper Devonian and Lower Carboniferous sandstones have been used to constrain bed length for cross-section balancing to estimate crustal shortening from three typical areas. These indicate 45%, 41.6% and 37.3% shortening and suggest that 110 km of contraction has been achieved as a result of thrusting. This orogen correlates with the Ogcheon Belt in South Korea to the northeast. To the southwest it appears to correlate with a thrust belt in western Guangdong. This southeast-verging thrusting may be at least partially controlled by Cathaysia to the east.