渭河地堑盆地新构造运动及其基本特征

渭河地堑盆地新构造运动表现繁多,运动类型齐全。本文侧重从多层地形、切割地形、沉积厚度、岩相变化、地形变、活动断裂、地裂缝、黄土节理与切沟等方面,结合建造与改造,讨论该区的垂直升降运动和断裂运动两大类型,并从中总结归纳了区内的构造应力场、运动的阶段性、间歇性、继承性与新生性、运动幅度与速度、运动时期、块体运动、以及区域地壳稳定性和活动性等基本特征,提出了不少新认识,从而加深了该区的研究深度和广度。

THE NEOTECTONIC MOVEMENT AND ITS BASIC CHARACTERISTICS IN THE WEIHE GRABEN BASIN

The neotectonic movement in the Weihe graben basin has experienced a period of about 50 million years since the Late Eocene, leaving behind numerous features of activities such as geomorphic sedimentary, structure, seismic, volcanic geothermal and ground deformational. In the light of the Cenozoic geomorphology and structural geology, through the studies of layered topography, dissected landforms, thickness of sediments, iithofacies changes, ground deformational features, active faults, ground fissures, and joints in loess deposits, two major types of the neotectonic movement, i. e. the elevation- subsidence movement and the faulting movement have been recognized and expounded in the paper. On this basis, the main characteristic features of the neotectonic movement have been analyzed and are summarized as follows: 1. Development by stages: Based on contact relations, geomorphic types and tectonic features three development stages of the Weihe graben basin, namely E2- N21 (tensile), N22 (compressional) and Q (tensile) have been distinguished. 2. Inheritance and neogenesis: The tectonic intensity and deep downwarping on the southern edge of the basin during the Cenozoic as well as the inheritance of frequent elevation-subsidence fluctuations and similar sedimentary features in various atages of the Tertiary are mainly discussed. On this basis, it is considered that the variations in tectonic intensity of the faults of different trends and the blocks controlled by these faults caused the repeated shifting nd directional variation of the depocenters in the three subsidence areas of the basin. 3. Amplitude and velocity: It is indicated by the features of the Tertiary sediments that the Qinling orogeny was a wavy movement of rapid and frequent fluctuations with a small aggregate amplitude of elevation. At the beginning of the Quaternary, this orogeny was transformed to a lineol movement of slow, stable and relatively continuous elevation, resulting in a substantial elevation of the Qinling mountain mass. This was the principal mountain-making stage of the Qinling mountains. The Cenozoic period saw a total elevation amplitude of over 10000 m, with an increasing elevation-subsidence spead at various stages from the older to the younger. 4. Intermittence: blelands and river terraces that the tectonic movement showed a repeated alternation of "stabilization" and "activization". 5. Block movement: It is a movement of the crisscross network of faults and the blocks sandwiched in between within the basin under the joint action of the fault movement and elevation-subsidence movement. As a result, there appeared uplifted and depressed blocks as independent tectonic elements in an alternating arrangement from east to west and from south to north.