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郯庐断裂带肥东段走滑运动的^(40)Ar/^(39)Ar法定年 被引量:77

^(40)Ar/^(39)Ar Dating for the Strike-Slip Movement on the Feidong Part of the Tan-Lu Fault Belt
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摘要 郯庐断裂带在华北与华南板块碰撞之后是否发生过大规模左行平移及其准确的时间,仍然是存在着争议的重要问题。郯庐断裂肥东段地表出露了大规模的、北北东走向的韧性剪切带。野外构造、显微构造与石英C轴组构分析皆指示为左旋走滑韧性剪切带。糜棱岩中变形矿物组合与矿物变形行为指示该韧性剪切带形成于中—高绿片岩相环境。通过对该段走滑糜棱岩中角闪石与黑云母的40Ar/39Ar年代学研究,本次工作中获得了一个角闪石(N14)的40Ar/39Ar坪年龄为143.3±1.3Ma(早白垩世初),据变形温度判断其代表了该断裂带左行平移中的变形年龄。该糜棱岩(N14)中新生的黑云母40Ar/39Ar坪年龄为134.1±0.6Ma,而同一采场中另一糜棱岩(N13)中新生黑云母40Ar/39Ar坪年龄为130.3±0.6Ma,皆指示了左行平移活动的冷却年龄。另外4处走滑糜棱岩中黑云母的40Ar/39Ar坪年龄分别为137.2±0.8Ma(N47)、135.6±0.6Ma(N17)、124.8±0.7Ma(N21)和125.9±0.4Ma(N22),也都属于冷却年龄,反映了该走滑韧性剪带内的不均匀冷却现象。由此变形年龄与冷却年龄可以判断该断裂带的左行平移持续时间不超过6Ma左右。由N14糜棱岩中的角闪石与黑云母坪年龄得到该处的平均冷却速率为21.7℃/Ma,属于较快速的冷却。本次40Ar/39Ar测年结果。 It is still debatable whether or not large-scale left-lateral displacement took place along the Tan-Lu fault belt after collision of the North and South China plates and when the displacement happened. A large-scale NNE-striking ductile shear belt is found in the Feidong part of the Tan-Lu fault belt. Field structure, microstructures and quartz C-axis analysis all indicate sinistral shear sense of the ductile shear belt. Newly-formed mineral assemblages and mineral deformation behaviors demonstrate that the ductile shear belt was developed under a condition of mid-high-grade greenschist facies. 40Ar/ 39Ar chronological study was undertaken on hornblende and biotite from the mylonite in this work. A plateau age of 143.3±1.3 Ma, Early Cretaceous, was obtained from the hornblende sample N14. Deformation temperature estimation suggests that this hornblende age represents deformation time related to the sinistral movement. Matrix biotite N14 from the same mylonite sample gives a plateau age of 134.1±0.6 Ma, while another matrix biotite N13 from the same quarry yields a plateau age of 130.3±0.6 Ma. These two biotite ages are interpreted as cooling ages related to the sinistral faulting. Biotite samples from other 3 localities gave plateau ages of 137.2±0.8 Ma (N47), 135.6±0.6 Ma (N17), 124.8±0.7 Ma (N21) and 125.9±0.4 Ma (N22) respectively. They all represent cooling ages and show inhomogeneous cooling. The deformation age and cooling ages suggest that the duration of the sinistral displacement was less than 6 Ma. From the plateau ages of hornblende and biotite N14, a cooling rate of 21.7℃/Ma was calculated for the locality, showing faster cooling. These 40Ar/ 39Ar dating results prove with reliable data that the Tan-Lu fault belt experienced large-scale left-lateral displacement in the earliest Early Cretaceous, and give an accurate displacement time of 143.3 Ma along the Feidong part. This sinistral faulting resulted from high-speed NNW-oblique subduction of the Izanagi plate in the Pacific region, and represents the typical Peri-Pacific tectonic regime and the turning point of the tectonic framework in East China.
出处 《地质学报》 EI CAS CSCD 北大核心 2005年第3期303-316,共14页 Acta Geologica Sinica
基金 国家自然科学基金项目(编号49872074 40272094)资助的成果。
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