扬子陆块和华夏陆块拼合带的几何学、运动学、年代学特征及其构造演化研究

Under the theoretical guidance of modern plate tectonics and continental dynamics, using advanced techniques and analysis means, this program will principally focus on the Shaoxing-Jiangshan and NE-Jiangxi suture zones between the Yangtze and Cathaysia blocks, and carry out a systematic study for the following five geological problems. The studying contents are mainly (1) the SE boundary of the Yangtze block, the NW boundary of the Cathaysia block and the western segment of the Shaoxing-Jiangshan fault zone during Neoproterozoic-Early Paleozoic, (2) the comparison of the Shaoxing-Jiangshan zone with the Qinzhou-Hangzhou zone, including kinematics, geochronology, tectonic setting and evolution, (3) the timing of amalgamation and the tectonic evolutionary process of the Shaoxing-Jiangshan suture zone between the Yangtze and Cathaysia blocks, (4) the geometric, structural kinematic, geochemical, geochronological features and polyphase evolution of the Shaoxing-Jiangshan zone, and (5) the tectonic and magmatic rewoking on the pre-Devonian South China framework during the Late Paleozoic-Late Mesozoic period. We will interpret and answer the following problems: (1) the westward extrending and tectonic settings of the Shaoxing-Jiangshan zone, (2) the kinematic and geochronological conclusions of polyphase ductile deformation that took place in the Shaoxing-Jiangshan zone, (3) the spatial-temporal relation of the Shaoxing-Jiangshan and the Qinzhou-Hangzhou fault zones, (4) re-constructing tectonic framework of South China in various periods. Furthermore, this program will analysis and confirm the Late Paleozoic-Mesozoic tectono-magmatic features and reworking to pre-Devonian framework. By aforementioned researches, a tentative continental geodynamic model of South China during Neoproterozoic-Mesozoic will be constructed.

以当代板块构造理论为指导，运用先进的测试技术和方法，以扬子和华夏两大陆块的拼合带为重点研究对象，兼及赣东北断裂带，开展扬子块体的南东边界、华夏块体的北西边界、拼合带的西延位置的调查与构造几何学特征研究，分析块体拼合前的地质背景，开展拼合带运动学、地球化学、年代学特征以及东西两段对比研究，弄清江绍断裂带与钦杭构造带的关系，阐明扬子与华夏两大块体拼合过程与大陆边缘演化历史，确定拼合期的运动学动向，了解拼合后地质背景变迁与多期构造-岩浆活动特征，恢复不同时期构造格架和变质变形时序，探索华南大陆在不同地质时期的构造变形过程、构造属性及其动力学原因，为建立华南新元古代以来板块-大陆动力学演化模型提供科学依据。

扬子与华夏两个陆块的新元古代拼合带位置及其构造演化是华南地质研究的瓶颈问题。围绕此问题，开展了构造背景、拼合带西延位置、拼合带几何学与运动学特征、岩石组合的地球化学与年代学、显生宙构造再造、研究区构造演化等内容的全面调查与研究。通过研究，在江南造山带西段桂北地区确定了新元古代沟-弧构造体系，其蛇绿岩具有MORB特征，岛弧为大陆岩浆弧，形成于890-860 Ma，被830-820 Ma的同碰撞S型花岗岩所侵入，其上被丹洲群角度不整合覆盖；江南东段的诸暨石角和弋阳登山地区情况与此相似。通过区域调查和综合研究，初步确定了两个块体拼合带的位置，为诸暨-龙游-东乡-新余-萍乡-祁东-全州-桂林-南宁一线；查明了此拼合带的几何学与运动学基本特征，基本弄清了其拼合过程，是一种NW盘向SE方向的韧性变形动向，对应华夏陆块朝NW方向下冲、扬子陆块朝SE逆冲的拼合过程；在440-400 Ma, 华夏陆块遭受了强烈的陆内造山和花岗岩浆以及变质作用的叠加；在240-220 Ma，两个块体的拼合带被一次强烈的左旋韧性走滑变形作用所改造。通过一千多颗碎屑锆石的年龄谱研究，查明了华夏与扬子陆块前寒武纪不同程度经受了其峰值为2.46Ga、1.76Ga、0.97Ga、0.78Ga的四期构造-岩浆事件的作用，两个块体演化既有区别又有密切联系，能与全球陆核生长、Columbia大陆聚合、Rodinia大陆聚合与裂解等重大事件相联系，可与全球各陆块对比。查明华夏陆块继新元古代块体碰撞拼合之后，从震旦纪到三叠纪的漫长时代里，研究区均处于板内稳定沉积环境中，在早古生代晚期和早中生代早期分别遭受了短时间但大范围强烈陆内构造事件的再造，破坏了新元古代板块构造格局与拼合带构造。在上述基础上，我们重建了研究区的构造演化历史，恢复了不同时期构造格架和变质变形时序，探索了华南大陆在不同地质时期的构造变形过程、构造属性及其动力学原因。