Geological map of the lower crust in the Early Cretaceous of Shanxi Province: Based on vitrinite reflectance evidence

doi:10.13745/j.esf.sf.2024.10.20

Abstract

Abstract:

A geological map of the Early Cretaceous lower crust in Shanxi Province has been compiled based on granite data, which has added vitrinite reflectance data and recompiled the geological map of the Early Cretaceous lower crust in Shanxi Province. Many new insights have been obtained through comparison,which indicates that vitrinite reflectance is a very useful dataset for lower crustal mapping. Vitrinite reflectance can record the maximum temperature reached after its formation and is one of the widely used and reliable methods for maturity measurement in coalfield and petroleum geology departments. The vitrinite reflectance method is also very useful in petrology and mineral deposit studies. Therefore, it is possible to infer the presence, distribution, and scale of concealed rock mass in deeper layers, as well as the presence and distribution of mantle upwelling at the base of the lower crust based on vitrinite reflectance data. A new method for mineral exploration involves using vitrinite reflectance distribution to locate concealed rock masses and subsequently prospecting for mineral deposits based on these features.

This paper infers that concealed rock mass may exist in the deeper layers of several areas where R_o>3.0% based on the distribution of vitrinite reflectance in Shanxi Province. Among these, the concealed rock mass in Qixian has already been confirmed through drilling verification. There are many coal mines in Shanxi Province, and all anthracite distribution areas are favorable regions for locating concealed rock mass. The paper also revises the geological map of the Early Cretaceous lower crust in Shanxi Province based on vitrinite reflectance data, pointing out that the deeper layers in the central and southern parts of Shanxi Province are extensive regions of Mesozoic (mainly Early Cretaceous) granite distribution, which were also areas of mantle upwelling during the Early Cretaceous.It is inferred based on stratigraphic and granite data that the northern part of Shanxi Province (north of Datong) represents a region with normal crustal thickness, while the southern part represents a region of crustal thickening (part of the eastern China plateau). The southern part is a mantle upwelling region, while the northern part shows no signs of mantle upwelling. Therefore, the lower crust in the southern part is a high-temperature eclogite facies region, while the lower crust in the northern part is a low-temperature eclogite facies region. The lower crust is a fluid-bearing eclogite facies region in areas with surface mineral deposits. The lower crust in the central and western parts of Shanxi Province may represent a transitional zone between eclogite facies and granulite facies, suggesting that the eastern China plateau in Shanxi Province may exhibit a gradual westward subsidence trend.

Key words: Shanxi Province, vitrinite reflectance, anthracite, lower crust geological map, concealed rock mass, plateau, Early Cretaceous

CLC Number:

P56
P584

JIAO Shoutao, LIU Dongna, ZHANG Qi, JIN Zhibin, ZHANG Yusheng, YUAN Jie, ZHOU Ligang, LIU Tieyi, XIE Tuanjie, FAN Zongsheng, YAN Tongtong, ZHOU Xinpeng, ZHANG Shuangkui, WEI Qianqian, YAN Tao, ZHANG Kun, YIN Bihan. Geological map of the lower crust in the Early Cretaceous of Shanxi Province: Based on vitrinite reflectance evidence[J]. Earth Science Frontiers, 2025, 32(1): 418-431.

Figures/Tables 20

Fig.1 The relationship between vitrinite reflectance and metamorphic grade, temperature, coal rank, organic carbon, and organic nitrogen. Adapted from [5].

Fig.2 Isothermal contour map of geothermal temperature in the vertical cross-section of the magma chamber center. Adapted from [6].

Fig.3 Diagram illustrating the temperature field changes caused by an igneous intrusion. Adapted from [3].

Fig.4 Schematic diagram of deep magmatic metamorphism in southern Shanxi and Henan. Adapted from [12,16].

Fig.5 Schematic diagram of thermal metamorphism by hypabyssal magmatism in the Taozao Coalfield. Adapted from [12].

Fig.6 The distribution patterns of different types of mineral deposits around rock mass

Fig.7 Distribution map of deposits surrounding concealed rock mass. Adapted from [17].

Fig.8 Distribution map of concealed rock mass and contact metamorphic zone in Mangchang, Guangxi. Adapted from [18].

Fig.9 Isoline map of vitrinite reflectance for coal seam no.2 in the Shanxi Formation, southern north China region. Adapted from [19].

Fig.10 Inferred concealed rock mass conditions based on fig.9. Adapted from [1].

Fig.11 Schematic diagram of the relationship between magmatic thermal fields and mineralization. Adapted from [3].

Fig.12 Shanxi Province vitrinite reflectance distribution map

Fig.13 Distribution map of coal types in no.2 coal seam of Shanxi Formation, Xishan Coalfield, Taiyuan. Adapted from [2].

Fig.14 Reflectance distribution map of vitrinite in the Xishan Coalfield. Adapted from [20].

Fig.15 Coalification evolution map of the eastern margin of the Ordos Basin. Adapted from [22].

Fig.16 Coal rank and Ro distribution map of no.3 coal seam in the Qinshui Basin

Fig.17 Distribution map of vitrinite reflectance in Shanxi Province and the associated concealed rock mass distribution map

Fig.18 Reflectance distribution map of vitrinite in the carboniferous-permian coal seams of the North China Paleozoic basin. Adapted from [2].

Fig.19 Geological map of the lower crust from the Early Cretaceous period in Shanxi Province

Fig.20 Distribution map of mesozoic igneous rocks in Shanxi Province. Adapted from [2].

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