太行山中段羊角玄武岩形态特征及其地质意义

太行山中段左权羊角镇发育新生代玄武岩, 记录了太行山新生代以来的构造隆升事件。在详细的野外调查和研究的基础上, 通过与玄武岩发育相关的地貌面及其上的地层特征分析, 初步确定该玄武岩是上新世末期到早更新世初期的喷发产物, 初步揭示了太行山中段区域上晚上新世以来地貌发育历史, 主要存在6次构造隆升与剥蚀期: 在唐县期宽谷面形成的基础上, 于上新世晚期存在一次隆升和一次稳定侵蚀期, 并侵蚀形成“U”形谷; 早更新世初, 玄武岩开始间歇性喷发, 同时发生以西武家坪为中心的地区上拱, “U”形谷为玄武岩充填, 之后经剥蚀堆积形成第四级阶地面; 早更新世末, 该区再次发生隆升, 并形成第四级阶地; 中更新世末, 该区发生隆升, 形成第三级阶地; 晚更新世以来, 太行山中段又连续发生两次抬升, 从而在玄武岩体上形成了4级阶地, 形成太行山现今地貌。研究同时表明, 太行山中段上新世晚期以来的隆升主要发生于上新世末到早更新世时期。这一认识为探讨太行山中段晚上新世以来的构造隆升提供了具体证据。

Morphologic Characteristics of Yangjiao Basalt in the Middle Taihang Mountains and Their Geological Significance

The uplift events have been recorded by the basalt around Yangjiao Town of Zuoquan County in middle Taihang Mountains since the end of Pliocene. Based on field investigation, the authors studied the morphologic characteristics of the basalt and the related topographic surface, and detected that the basalt was formed between the end of Pliocene and the beginning of Early Pleistocene. The geomorphic evolution of the middle Taihang Mountains since Late Pliocene is as follows: in Late Pliocene, this area underwent two phases of geomorphic evolution, i.e., uplift and erosion, and this led to the formation of the "U" valley; at the end of Pliocene, because of the repeated and intermittent eruption of the basalt and the uplift of the geomorphic surface of the middle Taihang Mountains centered at Wujiaping Village, the basalt filled the "U" valley, and then the geomorphic surface of the fourth terrace was formed through erosion and accumulation; in Early Pleistocene, the geomorphic surface of the middle Taihang Mountains was uplifted so that the fourth step terrace was formed. At the end of Middle Pleistocene, the third terrace was formed; Since Late Pleistocene, two times of uplifting of the geomorphic surface took place, and hence all of the four steps of terraces came into being on the basalt. It is shown that the uplift of the middle Taihang Mountains occurred mainly between the end of Pliocene and Early Pleistocene. This cognition offers material evidence for the uplift of the middle Taihang Mountains since Late Pliocene.