郯庐断裂带南段造山期变形格局、演化规律与形成机制

发布时间：2018-07-04 13:28

本文选题：郯庐断裂带 + 张八岭群　；参考：《合肥工业大学》2016年博士论文

【摘要】：中国东部巨型的郯庐断裂带左行错开大别-苏鲁造山带达400 km,但是其南端又截然中止在大别造山带东南角,显示其具有特殊的起源方式,但这方面长期以来存在着不同的认识。本次工作通过LA-ICP-MS锆石U-Pb定年,分别获得张八岭隆起北段、庐江地区和大别造山带东缘张八岭群原岩年龄分别为754-753Ma、751-749Ma和751-748 Ma,而肥东杂岩原岩时代为802-754 Ma。这些定年结果表明,郯庐断裂带南段沿线张八岭群与肥东杂岩内的正变质岩原岩是扬子板块新元古代中期岩浆活动的产物,张八岭群属于扬子板块早阶段盖层,而不是过去认为的变质基底。通过本次详细的研究发现,郯庐断裂带南段造山期构造目前保存在大别造山带东缘至庐江地区的张八岭群内,以韧性走滑剪切带形式存在。大别造山带东缘郯庐韧性剪切带经历了两期变形事件。早期变形(D1)表现为北东走向左行走滑韧性剪切带。显微观察显示,这些剪切带糜棱岩内石英呈现为嵌入式或亚颗粒旋转型重结晶,而长石表现为显微破裂或塑性拉长。石英C轴组构显示以底面＜a＞滑移为主,含少量柱面＜a滑移组分。这些显微构造特征指示早期韧性剪切带的变形温度为350-400-C。该走滑韧性剪切带被广泛叠加了晚期变形(D2),呈现为NE-SW向的紧闭褶皱及上盘向南东的逆冲断层。本次白云母40Ar/39Ar定年获得大别东缘早期(D1)韧性剪切带变形年龄为236-230 Ma(中-晚三叠世),而晚期变形(D2)时间为225-217 Ma(晚三叠世中晚期)。通过对宿松杂岩与襄樊-广济剪切带白云母40Ar/39Ar定年,表明大别造山带折返时间为230-209 Ma(晚三叠世中晚期)。因此,大别造山带东缘郯庐左行走滑活动(D1)发生在造山带深俯冲阶段,而其所叠加的缩短变形(D2)是大别造山带向南东折返的推挤结果。庐江地区郯庐韧性剪切带也呈NE-SW走向,具有向南东陡倾的剪切带面理,而矿物拉伸线理近水平,显示为左旋剪切运动。剪切带糜棱岩石英以嵌入式(BLG)及亚颗粒旋转型(SR)重结晶为主,长石表现为显微破裂或塑性拉长。石英C轴组显示以底面＜a滑移为主,含极少量柱面＜a滑移组分。这些显微构造特征指示剪切带的变形温度为350-400℃。前人白云母40Ar/39Ar定年结果为239 Ma,因此,庐江地区郯庐剪切带左行走滑时代也为中三叠世。张八岭隆起北段张八岭群及上覆下震旦统表现为上盘向南南西运动的、平缓的韧性滑脱变形带。其中的剪切带糜棱岩内,石英以嵌入式及亚颗粒旋转型重结晶为主,长石表现为显微破裂或塑性拉长,也指示了低绿片岩变形环境。前人白云母40Ar/39Ar定年结果表明变形时间为245-236 Ma(中三叠世),与造山期郯庐剪切带走滑活动同时。张八岭隆起南段肥东杂岩被广泛叠加了晚侏罗世郯庐剪切带左行走滑变形,但其南部仍可识别出早期变形构造,现今表现为NEE-NE向的宽缓褶皱。推测其印支期变形组构与北部张八岭群一致,也为平缓的韧性滑脱带。扬子板块前陆褶断带受郯庐断裂带造山期左行走滑的影响发生了显著的牵引弯曲,其褶皱枢纽及逆冲断层走向在远离郯庐断裂带的区域呈NEE-SWW走向,而在靠近郯庐断裂带的区域表现为向郯庐断裂带方向的明显偏转。华北板块前陆构造在郯庐断裂带旁并没有发生明显的牵引弯曲,显示华北板块较扬子板块更为刚硬,具有较强的抵抗变形能力。基于以上分析,我们提出了郯庐断裂带起源的板片撕裂模式。我们认为现今华北板块南缘的边界轮廓应代表了其印支期原始的边缘形状,在大别造山带区域呈现向南的突出。在华北与扬子板块之间大洋岩石圈俯冲过程中,沿华北板块嵌入体东缘形成大洋撕裂断层。当印支期华北与扬子两大陆首先沿大别造山带发生陆—陆碰撞时,大洋撕裂断层扩展到被动的扬子大陆内部。在此嵌入式碰撞与扬子板块撕裂过程中,大别造山带之下的扬子板块以低角度向北长距离俯冲,同时嵌入体东侧扬子板块沿撕裂断层继续向北水平运动,出现了郯庐断裂带同造山期的左行走滑活动,直至苏鲁造山带处与华北板块碰撞。随后至晚三叠世中晚期,随着大洋板片的断离,大别造山带内部深俯冲陆壳发生了向南东的折返,造成了大别造山带东缘郯庐走滑韧性剪切带强烈的挤压褶皱作用。
[Abstract]:The giant Tan Lu fault zone in eastern China has left the Dabie Su Lu orogenic belt up to 400 km, but the southern end of the Tanlu fault zone was suspended in the southeastern corner of the Dabie orogenic belt, showing its special origin, but it has been different in this respect for a long time. This work obtained the north of the Zhang eight ridge uplift through the LA-ICP-MS zircon U-Pb dating. The original rock age of the Zhang eight Ling group in the eastern margin of the Lujiang and Dabie orogenic belts is 754-753Ma, 751-749Ma and 751-748 Ma, while the original rock age of the Feidong complex is 802-754 Ma., which indicates that the normal metamorphic rocks in the Zhang eight Ling group and the Feidong complex along the southern Tan Lu fault zone are the middle Neoproterozoic magmatism of the Yangzi plate. The Zhang eight Ling group belongs to the early stage of the Yangtze plate, not the metamorphic basement that was considered in the past. Through this detailed study, it is found that the southern segment of the Tanlu fault zone is currently preserved in the Zhang eight ridge group of the Dabie orogenic belt to the Lujiang area, and exists in the form of the ductile strike slip shear zone. The sexual shear zone has undergone two phases of deformation. The early deformation (D1) is shown as the north-east strike slip ductile shear zone. The microscopic observation shows that the quartz in the mylonite of these shear bands is characterized by embedded or subgranular rotating recrystallization, while the feldspar is characterized by microrupture or plastic elongating. The quartz C axis fabric shows the bottom surface < a > slip These microstructural characteristics indicate that the deformation temperature of the early ductile shear zone is 350-400-C., and the early ductile shear zone is widely superimposed on the late deformation (D2), which presents the closed fold of NE-SW direction and the reverse thrust fault of the South East of the South East. This Muscovite 40Ar/39Ar has obtained the early Dabie early Eastern Margin (D1) for this time. The deformation age of the ductile shear zone is 236-230 Ma (mid - late three fold), while late deformation (D2) time is 225-217 Ma (late late three). Through the year of 40Ar/39Ar dating of the Susong complex and the Xiangfan Guangji shear zone, the reentry time of the Dabie orogenic belt is 230-209 Ma (late three late superposition). Therefore, the Tanlu left of the Dabie orogenic belt is in the eastern margin of the Dabie orogenic belt. The movement of D1 occurs in the deep subduction stage of the orogenic belt, and its superimposed shortening deformation (D2) is the result of the reentry of the Dabie orogenic belt to the South East. The Tan Lu ductile shear zone in the Lujiang area also shows the direction of the shear zone with a steep dip in the South and the East, while the mineral extension line is near the horizontal, showing a left-handed shear movement. Prism quartz is dominated by embedded (BLG) and subgranular rotating (SR) recrystallization, and feldspar is characterized by microrupture or plastic elongating. The quartz C axis group shows the main bottom surface < a slip and a very small number of cylinder a slip components. These microstructure features indicate that the deformation temperature of the shear zone is 350-400 C. The 40Ar/39Ar dating results of the former Muscovite 239 Ma, therefore, the Tan Lu shear zone in the Lujiang area is also the middle three fold era. The Zhang eight Ling group and the overlying Sinian in the northern part of the Zhang eight ridge uplift are shown to the South and South West movement of the upper plate and the gentle ductile deformable belt. The deformation environment of the low green schist is indicated by the microscopic rupture or plastic elongating. The 40Ar/39Ar dating results of the former Muscovite showed that the deformation time was 245-236 Ma (middle three fold), and the Tanlu shear belt slipping in the orogenic period. The Feidong complex in the southern part of the Zhang eight ridge uplift was widely superimposed on the left walking and sliding deformation of the Tan Lu shear zone in the late Jurassic. The early deformation structure in the South still can be identified as a wide and gentle fold of NEE-NE direction. It is presumed that the Indosinian deformation fabric is the same as the northern Zhang eight Ling group, and also a gentle ductile detachment zone. The thrust fault trend is NEE-SWW in the area far away from the Tanlu fault zone, while the area near the Tan Lu fault zone shows a clear deflection to the direction of the Tanlu fault zone. The North China plate foreland structure has no obvious traction bending beside the Tanlu fault zone, showing that the North China plate is more rigid than the Yangtze plate and has strong resistance. Based on the above analysis, we put forward a plate tear model of the origin of the Tanlu fault zone. We think that the boundary outline of the southern margin of the North China plate should represent the original edge shape of its Indosinian period and present a southward protruding in the Dabie orogenic zone. The eastern margin of the North China plate formed an oceanic tearing fault. When the two continent of North China and the Yangtze were first collided along the Dabie orogenic belt, the ocean tear fault extended to the passive Yangtze continent. In this embedded collision and the tearing of the Yangtze plate, the Yangtze plate under the Dabie orogenic belt was northward to the north. Long distance subduction, at the same time, the Yangtze plate on the east side of the embedded body continues to move northward along the tearing fault, and the Tan Lu fault zone has the same left strike slip movement with the orogenic period until the Su Lu orogenic belt collided with the North China plate. Then, at the end of the late three fold, the deep subducted continental crust of the Dabie orogenic belt occurred along with the breakage of the oceanic plates. The exhumation to South East resulted in a strong compression fold in the Tan Lu strike slip ductile shear zone along the eastern margin of the Dabie orogenic belt.
【学位授予单位】：合肥工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542

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