山西南部燕山期类隔挡式褶皱构造特征

晋南地区自西向东发育一系列NNE向背斜与向斜。背斜地区主要出露太古代结晶基底或早古生代地层,向斜核部出露的最新地层则是三叠系。在宁武-静乐盆地、太原西南水浴贯等地可见零星或成片分布的侏罗系残存,部分地区可见残留的白垩系,与侏罗系呈不整合接触。根据卷入地层时代分析,这些褶皱应为燕山期变形产物。背斜区域地层相对较陡,核部或翼部发育大量NNE向逆冲断裂,太古代结晶基底同样卷入变形;而向斜核部地层非常平缓,产状近于水平。山西南部整体构造表现为一种类隔挡式褶皱构造特征。在吕梁山区、霍山背斜带及太行山沿晋获断裂一带均可见燕山期岩浆岩体分布。根据这些岩体的同位素年龄及前人节理统计结果,可知该区在晚侏罗世至早白垩世于NW-SE向的挤压应力场下发生了剧烈的构造运动。同时期,华北地区及整个中国东部都表现出相似的构造特征,而古太平洋板块正NW向往亚洲板块下俯冲,因此,晋南地区的类隔挡式褶皱的形成可能与太平洋板块俯冲有关。

Characteristics of the Yanshanian Chevron Anticline-like Folds in the Southern Part of Shanxi Province

A series of NNE-trending folds developed in the southern part of Shanxi province.The Archean crystalline basement or Paleozoic strata are exposed in the anticline cores,and the newest strata exposed in the core of the chevron syncline are of Triassic.The Middle Jurassic strata locally cropped out in the Ningwu-Jingle basin such as at the Shuiyuguan area.The Middle Jurrasic strata have a flat occurrence.In the anticlines area,the occurrences of the strata are rather sharp,and many thrust faults developed in the area.In contrast,the occurrences of the strata in the syncline area are gentle.The structures in the southern part of Shanxi province exhibit as three chevron anticlines.The Late Jurassic-Early Cretaceous plutons are cropped out in the Lvliang Mountain,the Huoshan anticline or along the Jin-Huo fault in the Taihang Mountains.Based on the statistics of the joints which cut through the Jurassic and Cretaceous strata in the Taihang Mountains,the Yanshanian stress field in this area is NW-SE compression.It is deduced that the Pacific Plate subducted northwestwards underneath the Eurasian Plate.Therefore,the formation of the folds in the southern part of Shanxi province was possibly related to the subduction of the Pacific Plate.