苏皖下扬子区构造热演化史的裂变径迹证据

Evidence of Fission Track Data for Thermotectonic Evolution History of the Lower Yangtze Area

王丹萍 湛祥惠 王剑

WANG Danping ZHAN Xianghui WANG Jian

中国石油化工股份有限公司上海海洋油气分公司研究院, 上海 200120; 同济大学海洋地质国家重点实验室, 上海 200092; 中国石油化工股份有限公司上海海洋油气分公司工程院, 上海 200120

Institute of SINOPEC Shanghai Offshore Oil & Gas Company, Shanghai 200120, China; National Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China; Engineering Institute of SINOPEC Shanghai Offshore Oil & Gas Company, Shanghai 200120, China

为了揭示下扬子苏皖南露头区中、古生界的构造热演化特点及其控制环境,应用磷灰石裂变径迹技术(AFT),对苏皖下扬子7个中、古生界碎屑岩进行热演化分析。研究结果表明:中、古生界碎屑岩表现出105.7~50.9 Ma的AFT年龄特点,均远小于其相应的地层年龄,平均径迹长度在13.19~13.70μm之间,呈单峰分布,分析结果反映了下扬子苏皖南露头区中、古生界经历燕山期岩浆事件热改造完全退火后晚白垩世以来差异抬升剥露的冷却历史。FT热史模拟结果反映了研究区三阶段的热演化特点:快速冷却抬升(1.7~15℃/Ma)、缓慢剥露冷却(0.27~0.81℃/Ma)和再次快速冷却抬升(2.8~5.6℃/Ma)。通过对样品热历史的分析:发生在113~100Ma的构造转折与黄桥事件相对应,代表了由挤压体制转变为拉张断陷盆地阶段;发生在75~68 Ma的构造转折与仪征事件相对应;发生在18~10 Ma的构造转折代表喜山晚期区域遭受整体抬升剥蚀过程。

In order to reveal characteristics of the tectono-thermal evolution of the outcrops of south Lower Yangtze area and its regional controls, detailed apatite fission track analysis (AFT) on seven Palaeo-Mesozoic clastic rocks has been carried out. The results show that the Palaeo-Mesozoic clastic rocks have apatite fission-track ages ranging from 105.7 to 50.9 Ma, much younger than corresponding strata ages. Mean fission track length ranges from 13.19 μm to 13.70 μm, with a single-peak distribution. The AFT heat history modeling curves show that the cooling history since Late Cretaceous can be divided into three phases. The first phase was rapid basin uplifting and cooling (1.7 to 15℃/Ma), the second phase was stable basin uplifting and cooling (0.27 to 0.81℃/Ma) and the third phase was rapid basin uplifting and cooling (2.8 to 5.6℃/Ma).The 113 Ma to 100 Ma transformation corresponding to Huangqiao transform event (110 Ma to 90 Ma) was related with the tectono-thermal change from the Yanshan magmatism to extensional faulting. The 75 Ma to 68 Ma transformation corresponds to Yizheng tectonic event(70 Ma to 60 Ma).The 18 Ma to 10 Ma transformation represents the uplifting and erosion process during the late Himalayan period.

https://doi.org/10.3969/j.issn.1008-2336.2014.03.055