南太行山中新生代隆升过程：磷灰石裂变径迹证据

摘要

南太行山地区地处华北陆块中部,是研究华北岩石圈减薄、克拉通活化期间山脉隆升与剥露机制的理想场所。本文对太行山南麓的中生代岩浆岩和元古宙变质岩开展了磷灰石裂变径迹低温热年代学研究,获得了相关样品的磷灰石径迹年龄和径迹长度。研究表明,南太行山地区磷灰石裂变径迹表观年龄集中在75~32 Ma 之间,峰值径迹长度在11μm以上,为宽带单峰分布。综合考虑裂变径迹反演,南太行山地区初始隆升始于100 Ma 前,晚白垩世以来的剥蚀去顶量在3 km 以上。100~50 Ma 的构造抬升相对平静,50~40 Ma 及10 Ma 左右以来隆升速度加快,是太行山地区的主要隆升期。南太行山区域上表现为北早南晚的倾伏式差异隆升格局,其新生代隆升与华北东部同期的快速沉降相耦合。以上资料有利于更好认知华北陆块中–新生代冷却史及岩石圈减薄地表响应。%The South Taihang Mountains, tectonically located in the center of the North China Craton, was a stable tectonic zone during Paleoproterozoic and Early Mesozoic, but significantly reactivated since Late Triassic. It is an ideal area for better understanding of the mountain uplifting and unroofing during the Mesozoic lithospheric thinning of the North China Craton. This paper presents the results of our field investigations, apatite fission track dating, track length analysis and tectonothermal modeling of the Paleoproterozoic gneisses and Cretaceous diorite samples. The apatite fission track apparent ages of our samples range from 32 Ma to 75 Ma, significant younger than their corresponding ages of formation. The lengths of the fission tracks for each sample show a broad and unimodal pattern with the peak value of 11 μm. In combination with thermal simulation results and other geological observations, it is inferred that at least 3 km thick superficial materials of the South Taihang Mountains have been unroofed since the Late Cretaceous. The uplift of the mountains initiated before 100 Ma. Similar to the Weibei uplift of the Ordos basin, two episodic uplifts of the Taihang Mountains occurred at about 50–40 Ma and 10 Ma to present. The apatite fission track data also indicate that the uplift-cooling event of the South Taihang Mountains took place earlier in the north than in the south. Such an unroofing and uplift-cooling pattern temporally couples with the form of the Beitai planation surface and the rapid depression in the eastern North China (e.g. Bohaiwan basin). Our data provide important constraints on the shallow-level processes in response to the lithospheric thinning of the North China Craton.