东大别地区磷灰石裂变径迹年龄的构造意义初析

PRIMARY ANALYSIS ON TECTONIC IMPLICATION OF APATITE FISSION TRACK AGES FROM EASTERN DABIE AREA, CHINA

东大别山地区磷灰石裂变径迹年龄值为 5 9 4± 3 4～ 1 0 5 6± 9 8Ma ,具跨度较大 ,空间分布不均匀 ,沿主要断裂走向及倾向均不连续的特点。磷灰石裂变径迹年龄的这些特点暗示的构造意义可能是 :自燕山运动以来研究区的构造抬升为缓慢且不均匀格局 ;晓天—磨子潭断裂中段在第三纪时可能有逆冲活动 ;由磷灰石封闭径迹长度及单颗粒磷灰石年龄进行的初步热历史模拟分析显示 ,距今约 45～ 5 5Ma,郯庐断裂和晓天—磨子潭断裂曾再次活动 ,前者活动规模较后者大 ;断裂活动可能是该区不均匀构造抬升的主要控制因素之一。

The apatite fission track ages are 59.4±3.4 ～105.6±9.8 Ma in eastern Dabie area, which show the characteristics of wide range, inhomogeneous distribution and asymmetric pattern, and discontinuity along main faults' striking and dipping. These characteristics would suggest some implications on tectonics in eastern Dabie area: 1) the tectonic uplift being quite slow and the pattern being inhomogeneous and asymmetric after the Yangshanian orogeny; 2)the apatite fission track ages from two sides of central sector of the Xiaotian Mozitan fault showing that the fault might be a thrust in the Tertiary; 3) according to the primary thermal history modeling analysis based on the lengths of confined tracks and the ages of single grains, it being suggested that the Tan Lu and Xiaotian Mozitan faults might react during 45～55 Ma ago and the former might be more active than the latter. The authors thought that the faulting should be one of main controlling elements for the inhomogeneous uplift in eastern Dabie area.