scholarly journals Applications of Vitrinite Anisotropy in the Tectonics: A Case Study of Huaibei Coalfield, Southern North China

2012 ◽  
Vol 2012 ◽  
pp. 1-16
Author(s):  
Yudong Wu ◽  
Quanlin Hou ◽  
Yiwen Ju ◽  
Daiyong Cao ◽  
Junjia Fan ◽  
...  
Keyword(s):  
North China ◽  
Vitrinite Reflectance ◽  
Eastern China ◽  
Tectonic Stress ◽  
Deformation Mechanisms ◽  
Thermal Metamorphism ◽  
Regional Tectonic ◽  
Projection Analysis ◽  
Huaibei Coalfield

29 oriented and 10 nonoriented coal samples are collected in the study from three different regions of the Huaibei coalfield, eastern China, and their vitrinite reflectance indicating surface (RIS) parameters are systematically calculated and analyzed. Using the available methods, Kilby’s transformations and RIS triaxial orientations are obtained. The magnitudes and orientations of the RIS axes of the three regions were respectively projected on the horizontal planes and vertical sections. The results show that the samples in high deformed region have significant anisotropy magnitudes (higher Bw/Rmax and Ram values) with a biaxial negative style, whereas the samples in the slightly deformed area have unimpressive anisotropy magnitudes with a biaxial negative style. Thermal metamorphism superposed might enhance the complication and variation of RIS style. RIS projection analysis deduced that the RIS orientation is mainly controlled by regional tectonic stress, and likely influenced by deformation mechanisms of coal.

scholarly journals Genesis of High-Mg Adakites in the Southeastern Margin of North China Craton: Geochemical and U-Pb Geochronological Perspectives

2021 ◽  
Vol 9 ◽  
Author(s):  
Shuo Zheng ◽  
Yanfei An ◽  
Chunkit Lai ◽  
Hongzhi Wang ◽  
Yunfeng Li
Keyword(s):  
Early Cretaceous ◽  
North China Craton ◽  
North China ◽  
Eastern China ◽  
Parental Magma ◽  
Quartz Diorite ◽  
Underground Mines ◽  
Geodynamic Setting ◽  
Southeastern Margin ◽  
Regional Tectonic

In the eastern North China Craton (NCC), Mesozoic tectonics was dominated by the Paleo-Pacific subduction rollback and the Tanlu crustal-scale fault movement. The regional transtension had generated extensive adakitic magmatism, some Cu-Au ore-forming but others not. To establish the geodynamic setting and any metallogenic link for the adakites from the southeastern NCC margin, we analyzed the ore-barren adakitic rocks from underground mines in the Huaibei-Linhuan coalfield (where surface igneous outcrops are scarce), and compared their ages and geochemistry with other mineralized and ore-barren adakites across Eastern China. Zircon U-Pb dating reveals two magmatic episodes in the Huaibei-Linhuan coalfield: 1) early-Early Cretaceous (ca. 130–129 Ma) (quartz-)diorite and granodiorite, and 2) late-Early Cretaceous (ca. 115.8 and 105.8 Ma) microgabbro and dolerite. Whole-rock geochemistry indicates that the (quartz-)diorite and granodiorite are high-Mg adakitic, featured by low K2O/Na2O (avg. 0.33), high Sr/La (avg. 44.3), and lack of correlation between SiO2 (fractionation index) and Sr/Y (avg. 56.55) and MREE/HREE (avg. 1.09), resembling typical adakites derived from oceanic-slab partial melting. Geochronological correlation with the regional tectonic events suggests that the slab-melting may have been caused by the Paleo-Pacific subduction rollback. Further extension and crustal thinning in the late-Early Cretaceous along the southern Tanlu fault may have formed the gabbro-dolerite in the coalfield. Geochemical comparison suggests that parental magma of the Huaibei-Linhuan adakites may have had similar water content [similar zircon 10,000*(Eu/Eu*)/Y and Eu/Eu* ratios] to typical porphyry Cu-Au ore-forming magmas, yet the former may have been considerably more reduced (lower zircon Ce/Nd and whole-rock V/Sc ratios). We considered that the assimilation of Carboniferous-Permian coal seams in the area may have further lowered the magma fO2 and thus its potential to form Cu-Au mineralization.

Fracture patterns and their relations to mountain building in a fold-thrust belt: A case study in NW Taiwan

2013 ◽  
Vol 184 (4-5) ◽  
pp. 485-500 ◽  
Author(s):  
Hao-Tsu Chu ◽  
Jian-Cheng Lee ◽  
Françoise Bergerat ◽  
Jyr-Ching Hu ◽  
Shen-Hsiung Liang ◽  
...  
Keyword(s):  
Principal Stress ◽  
Bedding Plane ◽  
Tectonic Stress ◽  
Maximum Principal Stress ◽  
Thrust Belt ◽  
Mountain Building ◽  
Fracture Patterns ◽  
Building Process ◽  
Regional Tectonic

Abstract The main purpose of this study is to analyse striated micro-faults and other types of fractures (including tensile and shear joints, and veins), in order to elucidate their relationships with regional folds and thrusts and regional tectonic stress. We take the fold-thrust belt (i.e., the foothills and the Hsuehshan range) in NW Taiwan as a case study, which is a product of the Plio-Pleistocene arc-continent collision. A total of about 760 and 1700 faults and other fractures, respectively, were collected at 41 sites in the field. We have identified four sets of bed-perpendicular joints in the study area. The observation of joints and bedding at each site indicates that most of the penetrative joint sets developed in the earlier tectonic stage of the pre-folding/pre-tilting event, illustrating the fact that the intersection of joint sets lies along the line perpendicular to the bedding plane. We thus interpret these sets as tectonic fractures under deep-seated tectonic stress. We used the regional fold axes as reference to define the four fracture sets. However, we found that complexity in the study area makes this rather tentative. Principal stress axes σ1, σ2, σ3, were calculated by means of inversion of fault slip data at each site. The ratio Φ that defines the shape of stress ellipsoid is generally small, indicating that the value of the maximum principal stress axe σ1 is much larger compared to that of σ2 and σ3, which are approximately equal. The paleostress regime was characterized by a combination of thrust and strike-slip tectonic regimes. Based on their geometric relationships with tilted bedding, we found most of striated micro-faults were strongly related to the regional folding and can be categorized as early-, during, and late-folding stages. We characterized two major directions for the compressive event, oriented N110–120°E and N150–160°E respectively, which provide additional evidence to delineate the debates about paleostress changes in the Taiwan mountain building process.

scholarly journals Multisource stress data constraints on Cretaceous—present regional tectonic stress field evolution in the southern Jinzhou area, North China Craton

2021 ◽  
Vol 18 (6) ◽  
pp. 1007-1021
Author(s):  
Chengwei Yang ◽  
Chenghu Wang ◽  
Mingruo Jiao ◽  
Yujiang Li ◽  
Pu Wang
Keyword(s):  
Stress Field ◽  
Hydraulic Fracturing ◽  
Focal Mechanism ◽  
North China Craton ◽  
North China ◽  
Tectonic Stress ◽  
Strike Slip ◽  
Stress Fields ◽  
Focal Mechanism Solutions ◽  
Regional Tectonic

Abstract Regional tectonic stress fields are key crustal stress elements that drive tectonic movements and are associated with regional tectonics and geological resources. Regional tectonic stress field evolution of the Jinzhou area, located in the eastern block of the North China Craton (NCC), may provide a deeper understanding of tectonics of western Liaoning and the NCC. This work conducted borehole television, hydraulic fracturing and focal mechanism solutions to invert the paleo and present regional tectonic stress fields. Four groups of tensile fracture in the southern Jinzhou area were identified via borehole television, and their azimuths were NNW–SSE, NWW–SEE, nearly W–E and NE–SW in temporal order representing four stages of extensional tectonic events. Hydraulic fracturing and focal mechanism solutions showed that the stress status was normal fault and strike-slip, revealing that the southern Jinzhou area is undergoing NEE–SWW-oriented compression and nearly N–S-oriented extension in accordance with the strike-slip mechanism. From the Early Cretaceous to the present, the direction of the regional extensional stress in the southern Jinzhou area has evolved counterclockwise and sequentially from NNW–SSE to NWW–SEE, W–E, NE–SW and nearly N–S, and the regional tectonic mechanism has transited from extension to extension-strike-slip to strike-slip, leading to the current tectonic framework.

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