Settlement distribution in Xing 'an

Xing' an is located in the southeast edge of the western segment of Jiangnan ancient land and in the north of the Hunan-Guangxi fold belt. Geological development has experienced three stages: pre-Devonian geosyncline (about 250-400 million years ago), late Paleozoic platform (about 400-230 million years ago) and Mesozoic-Cenozoic continental margin active belt (about 200-300 million years ago). In the history of geological and mineral research, it is an important area in northeast Guangxi, and the naming of some local stratigraphic units also comes from this.

floor

Xing 'an stratum is widely distributed, covering an area of 2 126 square kilometers, accounting for 90.5% of the county area. From old to new, there are Sinian, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Cretaceous and Quaternary. Among them, Devonian is unique and widely distributed, accounting for 50% of the county's area.

The Sinian system is only distributed in Dongshang Village of Huajiang Yao Township, Zhongdong Village of Jinshi Township and Yong 'an Village, with an area of 10 square kilometer. The lower part is light gray, gray-green gravelly sandstone and gravelly feldspathic sandstone. The middle and upper parts are dark gray shale and carbonaceous siliceous shale. The upper part is gray-white siliceous rock with hard texture, which constitutes a steep cliff landform. The thickness in the county is unknown.

Cambrian is distributed in the north and northwest of the county, starting from Sujia Village in Jieshou Town in the east, along Ruiwei, Shuibu, Tongren and Cave in Huajiang Yao Township, and reaching You 'an, Middle East and Yong 'an Village in Jinshi Township in the west. Area 190 km2. The lower part is gray-black argillaceous shale and carbonaceous shale. The upper part is gray-green massive sandstone and feldspar timely sandstone. The bottom is siliceous rock with a small amount of limestone in the middle. Thickness1589 ~1619m.

The Ordovician is mainly distributed in the west and east of the northwest, and is divided into two parts. From west to northwest, it includes Jinshi Township, villages in Huajiang Yao Township except Gaozhai and Yangque Village, Chayuan Village in Rongjiang Town, Qingshui Village in Yan Guan Township, the eastern border of Hucheng Town, Hongwei Village and Shimen Village in Jieshou Town. There are oriental films in Xiexing, Lin Bao and Linyan Village in Mo Chuan Township. The total area is 375 square kilometers. It consists of grayish green, grayish black sandstone and shale. The bottom is gray limestone and dolomite. It is 2784 ~ 3332 meters thick.

Silurian only has the lower series. It is distributed in Shengping Village, Huajiang Yao Township, with an area of 10 square kilometer. Lithology is grayish green and grayish black sandstone mixed with shale. It is 370 meters thick.

Devonian is widely distributed. Except Carboniferous and Quaternary distributed sporadically on both sides of Xiangjiang River and Lijiang River, the above two Ordovician outcrops belong to this stratum. There is also a small distribution in Zhongdong Village of Jinshi Township. Total area 1 153 square kilometers. The lower part is purplish red sandstone containing hematite. The middle and upper parts are light gray, gray limestone, dolomite, shale and a small amount of siliceous rocks. 326 ~ 2956 meters thick.

Carboniferous only has the lower series. Mainly distributed in the north-central part, it can be found in Cuijia and Gaoze villages in Cui hometown, Putou, Li Tou and Maiyuan villages in Li Xiang township, Yuan Zhe, Shikeng, Guancheng, Autonomous, Nanyuan, Tang Shi and Hongwei villages in urban and rural areas, and Shimen, Jieshou and Xingtian villages in Jieshou town. Secondly, the aristocratic villages in Jizhong, Renhe, Bao Li and Tian Ming in the south and the Qianjia and Liaojia villages in Rongjiang Town have small areas exposed. Total area 150 km2. The lithology is mainly gray limestone, hard limestone and dolomite, mixed with gray-black carbonaceous shale, coal seam and gray-yellow argillaceous siltstone. Thickness 1085 ~ 2 168m. It is distributed in Li Xiang, Shang Gao, Rongjiang and other townships (towns), with a thickness of 328 ~ 408 meters, excluding coal.

Cretaceous is only distributed in Dadong and Baili Village of Jieshou Town, covering an area of 13 square kilometers. The lower part is purplish red conglomerate, sandstone, siltstone and limestone. The exposure is incomplete, and the visible thickness is 356 meters.

The Quaternary is mainly distributed along the Xiangjiang River (Yanghe) and Lijiang River (Lingqu and Darong River), especially at the intersection of water system, villages and plains. The total area is 225 square kilometers. It is mainly composed of gravel, sand, clayey silt, clay and loam formed by alluvial flood, and most of them have been reclaimed as cultivated land. The thickness is 1 ~ 27.6 meters.

magmatite

Magmatic rocks are not widely distributed in the county, covering an area of 222 square kilometers. Single species, mainly Caledonian acid intrusive rocks, belonging to Maoershan, Yuechengling and Haiyang Mountain.

Maoershan rock mass occurs as a banded bedrock, and its long axis is northeast. Exposed area 1623 km2, county area 190 km2. It is the southernmost tip of the rock mass, located in the west of Huajiang Yao Township and the northeast edge of Jinshi Township, and is composed of gray-white medium-grained porphyritic biotite granite (commonly known as granite). There are many tungsten-bearing time pulses in the inner contact zone west of Youmaling, Dongshangcun, southern tip.

Yuechengling rock mass is parallel to Maoershan rock mass in the form of bedrock, with an area of 1.450 square kilometers. The county covers an area of only 4 square kilometers, which is the southwest corner of the rock mass and located in the northeast of Ruiwei Village, Huajiang Yao Township. The lithology is gray coarse-medium grained porphyritic biotite granite.

Haiyangshan rock mass is produced in the form of bedrock, with an oval plane, covering an area of about 400 square kilometers, and the county seat covers an area of 28 square kilometers. It is located in the east of Xiexing Village and Lin Bao Village in Mo Chuan Township, and is a small part of the western rock mass. It consists of medium-fine grained porphyritic biotite granite.

structure

Xing 'an area experienced three strong fold and fault movements in Caledonian, Indosinian and Yanshan periods. Caledonian movement is dominated by the formation of fold structures, followed by faults, accompanied by the intrusion of granite basement. After tectonic movement, the geosyncline returned, and the development stage of geosyncline ended here. The Indosinian movement was dominated by folds and faults, which formed the platform cap structure and ended the marine deposition. Yanshan movement is dominated by fault tectonic activity, followed by fold activity. After this tectonic movement, the geological structure of this area was finally determined. The folds and faults formed by the three tectonic movements are regularly distributed along the northeast. The similarity of the structural development directions in different periods reflects that the caprock structure inherits the direction of the basement structure and the control of the basement structure on the caprock structure, and also reflects the relationship between geological and tectonic mechanical properties, that is, the formation of folds and faults in the area is mainly the result of NW-SE structural compression, forming fold structures and solutions such as Maoershan anticline, Xing 'an syncline and Haiyangshan dome.

Maoershan anticline is more than 50 kilometers long and 30 kilometers wide. The county is the southern end of the anticline, located in Huajiang Yao Township and Jinshi Township. The axis of anticline is 30 ~ 40 degrees northeast and inclined to the south. The core stratum is Precambrian, which was destroyed and replaced by Caledonian granite. The strata in the two wings are Cambrian, Ordovician and Silurian.

Haiyangshan Dome (short axis anticline) is located in Haiyangshan area in the east of Mo Chuan Town. Its long axis is 30 degrees northeast, 40 kilometers long and 20 kilometers wide, and it is inclined to the surrounding edges, almost oval. The dome nucleus is composed of Ordovician and was invaded and destroyed by Caledonian granite. The wing is composed of Devonian system, and the county seat is only a part of the west wing.

Xing 'an syncline is located between Maoershan anticline and Haiyangshan dome, which crosses the border in the north and is too noble in the south. It is more than 50 kilometers long, 20-30 kilometers wide and 40-50 degrees northeast. The core strata are Carboniferous and Cretaceous, and the wing strata are Devonian. Syncline is broad and gentle, with secondary folds developed, and it is an open short-axis compound syncline. Due to the destruction of Rongjiang and Baishi regional faults, the shape of syncline is more complicated.

Rongjiang fault strikes 40 ~ 50 degrees, inclines to the northwest, and the dip angle is 30 ~ 60 degrees. From south to north, the county passes through Rongjiang Town, Yan Guan Township, Nanyuan Village, which protects urban and rural areas, and Shimen Village, Jieshou Town, and passes through the west side of Xing 'an syncline, with both ends extending out of the county. It is more than 40 kilometers long and the crushing bandwidth is tens to hundreds of meters. The northwest plate rises and the south plate falls. The staggered strata are Ordovician, Devonian, Carboniferous and Cretaceous. Affected by this fault, the footwall limestone was altered and recrystallized, forming discontinuous marble bands with a width of tens to hundreds of meters. The fault is still active in Cenozoic, and there have been two earthquakes with magnitude above 4 near Rongjiang Town.

Baishi fault strike is 30 ~ 40 degrees, inclined to the northwest, and the dip angle is 37 ~ 45 degrees. From north to south, the county passes through Baishi Township and Baimian Village in Mo Chuan Township. It is more than 30 kilometers long and the crushing bandwidth is 30 ~ 200 meters. The northwest plate rises and the south plate falls. The regional staggered strata are Devonian, Carboniferous and Cretaceous.