【作者】 王勇生；

【导师】 朱光；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2005， 博士

【摘要】 郯庐断裂带是中国东部呈NNE走向的一条巨型断裂带,在中国境内延伸长度约2400 km。长期的研究已表明,这一巨型断裂带中生代以来经历了长期、复杂的演化历史,也记录了中国东部地球动力学的演变。该断裂带晚白垩世至老第三纪的伸展活动及随后的挤压历史,由于构造保存较好,因而基本上得了人们的肯定。然而,关于该断裂带的早期平移历史及起源,特别是它与大别-苏鲁造山带之间的关系,虽然在国际地学界受到了广泛的重视,但在认识上却存在着很大的分歧与争论。一些学者主张郯庐断裂带属于同造山构造,并分别提出了转换断层模式、斜向板块边界模式、旋转的缝合线模式、撕裂断裂模式。另一些学者则认为郯庐断裂带源于晚侏罗-早白垩世期间,属于滨太平洋构造。之所以对郯庐断裂带的平移时间还存在如此大的分歧,主要是因为缺乏该断裂带系统的年代学工作,尤其是没有针对郯庐断裂带出露的中-深层次韧性剪切带进行系统的年代学工作。大量的野外工作发现,郯庐断裂带存在早、晚两期韧性剪切带。早期剪切带糜棱面理走向NE-NNE,倾向NW或SE,面理倾角较陡,矿物拉伸线理水平或近水平;晚期剪切带糜棱面理优势走向为NE-NNE,面理倾角较陡,以向SE倾为主,拉伸线理一致向SSW缓倾,倾角最大不超过20°。显微构造(S-C构造、残斑拖尾、“云母鱼”构造等)和石英C轴组构都指示这些糜棱岩形成于断裂带的左旋剪切过程中。为了能够获得郯庐早、晚两期剪切带左行平移的准确活动时间以及确定郯庐断裂带与大别-苏鲁造山带之间的关系,本次研究在郯庐断裂带中-南段糜棱岩中选取了角闪石、白云母、黑云母、斜长石、钾长石等一系列单矿物进行40Ar/39Ar年代学研究。在大别山东缘和苏鲁造山带西缘的郯庐早期韧性剪切带内分别获得了181 Ma左右和209. 9-214. 3 Ma的白云母年龄值。所有这些样品的形成温度均高于白云母的封闭温度,因而均记录了郯庐断裂带早期剪切活动的冷却时间。由于一系列冷却年龄的最大值更接近于变形年龄,因而可以认为郯庐断裂带形成的最晚时间为214. 3 Ma前的晚三叠世。通过糜棱岩中新生矿物组合、长石和石英的变形特征的估算和白云母-绿泥石地质温度计的计算获得了郯庐早期剪切带的变形温度分别为400-500℃(大别山东缘)、600-700℃(苏鲁造山带西缘)。利用白云母Si原子数地质压力计获得了郯庐早期剪切带的变形压力主要为0. 25-0. 42 GPa(大别山东缘)、1. 02-1. 45 GPa(苏鲁造山带西缘)。可以看出,郯庐早期韧性剪切带的变形温压环境明显低于造山带峰期变质的温压条件,因而郯庐断裂带应形成于大别-苏鲁造山带峰期变质之后的折返过程中。再结合该断裂带在大别造山带南端突然中止的地质事实,本次研究推断郯庐断裂带为形成于造山带折返过程中的转换断层。本次研究在郯庐断裂带中-南段晚期剪切带的糜棱岩中获得了131. 5-143. 3 Ma的角闪石年龄、121. 2-138. 8 Ma的白云母年龄和109. 8-137. 2 Ma的黑云母年龄。其中来自张八岭隆起的N14含角闪石糜棱岩的变形温度与K-Ar体系中角闪石的封闭温度一致,因而该角闪石样品记更多还原

【Abstract】 The Tan-Lu fault zone is a major fault zone trending NNE in east China and extends about 2400 km. Long-term studies suggest that the large fault zone experienced complicated evolution history and recorded geodynamic processes of eastern China. Because extensional structures from late Cretaceous to Paleogene and compressional structures since Neogene are conserved well, most geologists agreed on that the Tan-Lu fault zone experienced extension and following compression since late Cretaceous. However, though lots of international geologists paid more attention to the early strike-slip history and origin of the Tan-Lu fault zone, especially the relation between it and the Dabie-Sulu orogenic belt, but their viewpoints about that were different. Some workers considered the fault zone as a syn-orogenic tectonics, and proposed different models for it, such as transform fault model, oblique plate boundary model, rotated suture line model and tear fault model. Other workers suggest that the fault zone originated as a result of circum-Pacific tectonic movement in Late Jurassic to Early Cretaceous. The reason of the debates about strike-slip time of the fault zone mostly is lack of systematic chronology work, especially lack of systematic chronological work on ductile shear zone formed at middle-deep levels.According to lots of field works, two phases of sinistral strike-slip ductile shear belts were found in the Tan-Lu fault zone. Steep mylonite foliation in the earlier shear belts strikes NE-NNE, and dips NW or SE; its stretching lineation is gentle. Steep mylonite foliation in the later shear belts strikes NE-NNE, and mostly dips SE. Its stretching lineation is gentle and dips SSW, the maximum dip angle is less than 20°. Such microstructures as S-C fabrics, rotated feldspar porphyroblasts, and mica fish and quartz c-axis fabrics all indicate sinistral shear sense.For the sake of getting exact time of the Tan-Lu strike-slip movement and understanding relation between the fault zone and the Dabie-Sulu orogenic belt, this work selected a series of mineral separates, such as hornblende, muscovite, biotite, plagioclase and K-feldspar from mylonites in middle- southern segment of Tan-Lu fault zone, for ⁴⁰Ar/³⁹Ar dating.In this study, muscovite ⁴⁰Ar/³⁹Ar ages of 181 Ma and 209.9-214.3 Ma were obtained from earlier Tan- Lu ductile shear zone respectively on the eastern margin of the Dabie belt and the western margin of the Sulu belt. The formation temperatures of all these mylonite are more than the closure temperature of muscovite, so these ages are cooling ages of the earlier Tan-Lu faulting. A maximum cooling age is closest to deformation age, so the latest formation time of Tan-Lu fault zone is 214.3 Ma （late Triassic）. Based on newly-formed mineral assembles and deformation behaviors of feldspar and quartz in mylonites, and using muscovite-chlorite geothermometry, this work shows that deformation temperatures of earlier Tan-Lu faulting are separately 400-500℃ and 600-700 ℃ respectively on the eastern margin of Dabie belt and the western margin of the Sulu belt.Confining pressures are 0.25-0.42 GPa and 1.02-1.45 GPa respectively for the earlier shear zones on the eastern margin of the Dabie belt and the western margin of the Sulu belt according to geobarometry of Si-in-phengite. Therefore, the deformation temperatures and pressure ars less than that of peak metamorphism of the Dabie-Sulu orogenic belt, which suggests that the Tan-Lu fault zone was formed during exhumation of the Dabie-Sulu orogenic belt. Considering the fault zone terminates in the southern end of the Dabie belt, it is concludes that the Tan-Lu fault zone is a transfer fault formed during exhumation of the Dabie-Sulu orogenic belt.In this study, hornblende Ar/Ar ages of 131.5-143.3 Ma, muscovite 40Ar/"Ar ages of 121.2-138.8 Ma and biotite 40Ar/39Ar ages of 108.9-137.0 Ma were obtained from later ductile shear zone in the middle-southern segment of the Tan-Lu fault zone. The deformation temperature of N14 mylonite from the Zhangbaling uplift is equa更多还原