用深浅地震反射资料研究郯庐断裂带南段的岩石圈精细结构和浅部构造响应

Tan-Lu Fault Zone is the largest active tectonic belt in eastern China, and it has a complicated history of formation and evolution. It is proved that it has been playing an important control role on regional tectonic, magmatic activity, formation and distribution of mineral resource, as well as present-day earthquake activities. For many years, centered on the problems of Tan-Lu Fault Zone's formation, evolution, and activity mechanism, a lot of geological, geochemical, and geophysical research works have been carried out, and a series of important results have been obtained. But these results mainly revealed the Tan-Lu Fault Zone's macro-characteristics. The complicated structures and the faults' patterns cannot be meticulously depicted yet, that thereby influences our understanding on the evolution process and the relationship between deep and shallow structures of Tan-Lu Fault Zone. Therefore, we propose imaging the fine structures beneath the southern segment of Tan-Lu Fault Zone and its complex patterns in the lithosphere scale using the deep seismic reflection profile data acquired in the Southern segment of the Tan-lu Fault Zone, and implementing high-resolution shallow seismic exploration across the fault zone. The structural variations and coupling relationship between the fault zone and its adjacent blocks, the tectonic features and the influence depth of the fault zone will be analyzed. Meanwhile, the composition of strike-skip, extrusion and extension structure systems, the deep process, the shallow tectonic response, and the geodynamic implication in the southern segment of the Tan-Lu Fault Zone will also be discussed.

郯庐断裂带是中国东部规模最大的构造活动带，有着复杂的形成和演化历史，对中国东部的区域构造、岩浆活动、矿产资源的形成和分布以及现代地震活动都有重要控制作用。多年来，围绕郯庐断裂带的形成、演化和活动机制等问题，地球科学家做了大量的地质、地球化学和地球物理等研究工作，并取得了一系列重要成果。但这些成果主要揭示了断裂带的宏观特征，对断裂带内部的复杂结构、断裂构造样式还难以做到精细刻画，从而影响了对郯庐断裂带演化过程及其深浅构造关系的认识。为此我们提出，利用在郯庐断裂带南段完成的深地震反射剖面资料，并通过实施跨断裂带的高精度浅层地震探测，对郯庐断裂带南段近地表至岩石圈尺度的复杂结构和构造样式进行精细解剖，分析研究郯庐断裂带南段与两侧地块的结构差异和耦合关系、断裂带内不同力学性质的断裂构造形态及其影响深度，探讨郯庐断裂带走滑、挤压和伸展的构造体系组成、深部过程、浅部响应以及所包含的地球动力学含义。

郯庐断裂带是中国东部规模最大的构造活动带，有着复杂的形成演化历史，对中国东部的区域构造、岩浆活动、矿产资源的形成和分布以及现代地震活动都有重要控制作用。为了研究郯庐断裂带的岩石圈精细结构，我们在郯庐断裂带中南段的江苏宿迁市附近，采用深地震反射和高分辨率浅层地震勘探方法对郯庐断裂带及其两侧地块的岩石圈结构进行了解剖。研究结果表明，该区莫霍面和岩石圈底界均向西倾，地壳厚度约31～36km，岩石圈厚度约为75～86km，在郯庐断裂带下方，莫霍面出现约4～6km的拱起，且岩石圈厚度出现约10km的厚度变化。深地震反射剖面揭示的郯庐断裂带不是简单的铲形正断层或低角度逆断层，而是一个构造面形态随深度变化、断层面倾角近于直立、由多条断裂组成的大型“花状”构造，且组成郯庐断裂带的各条主干断裂还表现出了张、压、扭结构面共存的复杂结构。表明郯庐断裂带是一个以走滑为主的、并兼有逆冲和正断运动分量的复杂断裂构造带。该断裂带由浅到深依次切割了近地表沉积层、壳内分界面、莫霍面和岩石圈地幔，其变形方式有规律地从脆性、脆-韧性和韧性逐渐转换过渡，属于岩石圈尺度的深大断裂带。近地表的郯庐断裂带主要由5条主干断裂F1-F5组成，在浅层地震反射剖面上，这5条主干断裂以正断层方式错断了近地表沉积层，控制了白垩纪盆地的发育和堑-垒构造的形成，断裂的最新活动可追踪至晚更新世末期或全新世，是构造继承性活动的结果。项目成果不但可为分析研究和了解郯庐断裂带复杂的深部结构和深浅构造关系提供新的地震学证据，而且还可为研究区城市规划中避让活动断层提供科学依据。