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作 者:王勇生[1] 向必伟[2] 朱光[1] 陈文[3] 魏鑫[1]
机构地区:[1]合肥工业大学资源与环境工程学院,安徽合肥230009 [2]中国地质大学地球科学学院,湖北武汉430074 [3]中国地质科学院地质研究所,北京100037
出 处:《地球化学》2009年第5期458-471,共14页Geochimica
基 金:国家自然科学基金(40602025)
摘 要:晓天-磨子潭断裂是北大别杂岩带的北部边界,其早白垩世构造活动型式可以为北大别带穹隆演化过程提供制约。为了获得晓天-磨子潭断裂的活动时间,本次工作在详细的野外研究基础上,采集了一系列含黑云母、角闪石、白云母糜棱岩样品进行40Ar-39Ar年代学测试。采自佛子岭地区的XM31-2糜棱岩中角闪石获得了141.9Ma的坪年龄,该样品变形温度接近于角闪石K-Ar体系的封闭温度,表明该年龄结果为最接近于变形年龄的冷却年龄,指示断裂带形成于141.9Ma之前的晚侏罗世末或早白垩世初。断裂带糜棱岩中所记录的年龄结果表现出明显的东早西晚的规律,这指示北大别带内罗田穹隆的启动时间要晚于岳西穹隆。断裂带内东、西两段运动学上的差异指示其现今的几何学形态是经过后期构造运动改造而形成的。断裂带东段130Ma的快速冷却事件的存在指示改造断裂带几何学形态的构造事件发生于130Ma之后。As the northern boundary of the North Dabie complex unit, the motion of the Xiaotian-Mozitan fault (XMF) in the Early Cretaceous can be used to understand evolution of the North Dabie complex unit during doming. To obtain deformation age of the XMF, this paper used 40Ar-39Ar geochronology to study a series of mylonites including biotite, hornblende, and muscovite from Xiaotian-Mozitan ductile shear zone based on detailed field survey. Hornblende separate from XM31-2 mylonite gives a plateau age of 141.9 Ma. Deformation temperature of XM31-2 mylonite is close to the closure temperature of K-Ar system in hornblende, which suggests that the plateau age of 141.9 Ma is the cooling age proximal deformation time of the XMF. Therefore, the XMF formed in the terminal Late Jurassic or the beginning of the Early Cretaceous before 141.9 Ma. Older ages exist in east segment of the XMF and younger ages in the west segment indicate that the Luotian Dome started later than Yuexi Dome. Differences in kinematics of different segment of the XMF supports the conclusion that the present shape of the XMF was rebuilt by later event. The fast cooling of 130 Ma exists in the east segment of the XMF suggests that the event shaped the XMF occurred after 130 Ma.
关 键 词:40Ar-39Ar定年 后造山伸展 晓天.磨子潭断裂 北大别杂岩带
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