苏皖下扬子区晚白垩世以来的构造-热历史:浦口组砂岩磷灰石裂变径迹证据

Thermo-tectonic history of the Lower Yangtze area since Late Cretaceous: evidence from apatite fission track analysis of sandstones from Pukou Formation

张沛 周祖翼 许长海

Zhang Pei Zhou Zuyi Xu Changhai

同济大学海洋地质国家重点实验室, 上海 200092

State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092

对苏皖下扬子区上白垩统浦口组(K2p)的三个砂岩样品进行了磷灰石裂变径迹(AFT)研究。结果显示:2个样品的AFT合并年龄为(88.8±4.4)Ma(径迹长度为(12.0±0.3)μm)和(82.1±6.8)Ma(径迹长度为(14.4±0.3)μm)与浦口组沉积年龄相近,说明它们沉降的幅度达到但没有超过AFT部分退火区间,1个样品的AFT合并年龄(117.3±5.9)Ma(径迹长度为(13.3±0.3)μm)大于浦口组沉积年龄,代表物源区抬升、剥露的冷却年龄。根据热历史模拟结果,识别出黄桥事件(110~90 Ma)、仪征事件(70~60 Ma)和三垛事件(35~22 Ma)三期重要的构造事件,并将下扬子区晚白垩世以来的盆地演化划分为四个阶段:110~70 Ma断坳复合型伸展盆地、70~35 Ma拉张断陷盆地、35~22 Ma挤压抬升阶段和22 Ma至今坳陷盆地。

Apatite fission track(AFT) ages are determined on three sandstones of Pukou formation(K2p) collected from Lower Yangtze area(Anhui and Jiangsu Province). Pooled ages of two samples are (88.8±4.4) Ma(track length is (12.0±0.3) μm) and (82.1±6.8) Ma(track length is (14.4±0.3) μm) respectively, and both are close to the sedimentary age of Pukou formation, which indicates they have been buried into but not exceed AFT partial annealing zone. Pooled age of the other sample is (117.3±5.9) Ma (track length is (13.3±0.3) μm), older than its host rock formation, which is the cooling age related to the source rock uplift and exhumation. AFT thermal-history modeling identifies three important tectonic events (Huangqiao, Yizheng and Sanduo) occurred in 110~90 Ma, 70~60 Ma and 35~22 Ma respectively, and regional evolution for Lower Yangtze area are classified into 4 stages since Late Cretaceous: 110~70 Ma fault sag basin, 70~35 Ma faulted basin, 35~22 Ma compressional uplift stage and down-warped basin since 22 Ma.

https://doi.org/10.3969/j.issn.1008-2336.2009.04.026