华北克拉通南部前寒武纪重大地质事件构造响应的GIS统计分析——以中条-豫西地区为例

位于华北克拉通南部的中条-豫西地区记录了华北克拉通复杂、多阶段构造演化历史。其中,前寒武纪时期经历了新太古代末期(2550~2350Ma)地壳增生、古元古代(2350~1850Ma)活动带和早中元古代(1800~1600Ma)多期裂解活动,是研究区构造-岩浆活动最为剧烈的阶段。丰富的构造事件形成多层构造层,并发育大量构造形迹。本文依据GIS数据统计分析断裂切穿地层单元年代新老关系的规律,即构造运动的发生时间晚于构造形迹切穿的所有地层单元时代;如果构造形迹的发育被某一地层单元所限制,则表明构造运动的发生早于该地层的结束时间,并结合构造形迹的样式、规模、方位、强度和构造建造特征来解析构造作用性质,探讨构造演化,挖掘前寒武纪不同构造演化阶段形成的主体构造形迹的数字特征。在本项研究中,首先提取研究区内切穿Ar构造单元并限制在Pt地层单元内的构造形迹,代表前寒武纪时期的主体构造形迹特征。其次,运用GIS技术提取Pt1-Pt2期间不整合面,删去切穿不整合面的构造形迹,进一步筛选出Ar-Pt2期间主体构造形迹并统计其走向和长度,进而初步确定了Ar-Pt2期间的主要构造方位特征是NEE/NWW/近SN向。最后,依据构造形态、构造建造特征和地球物理场特征,结合区域构造演化史确定不同构造层主体构造方位特征,代表了不同构造演化阶段形成的主体构造形迹。其中,新太古代末期形成的主体构造形迹的方位特征是NE/NW向;古元古代构造层主体构造形迹的方位特征是NEE/NWW向;早中元古代构造层主体构造形迹的方位特征是近EW向。

GIS-based approach to extract structure features of different structure layers during the Precambrian: A case study of the Zhongtiao-Yuxi area, southern North China Craton

The Zhongtiao-Yuxi area is located in the southern part of the North China Craton. The area experienced the most intensely multi-stage tectono-magmatic events during the Precambrian, including Neoarchean-Early Paleoproterozoic (2550~2350Ma) crustal growth, Paleoproterozoic (2350~1850Ma) rifting-subduction-accretion-collision, and Early Mesoproterozoic (1800~1600Ma) extension. The geological events caused tectonic stress field varied and contributed to numerous structure faults in different structure layers. It is believed that the development of structural faults was younger than the stratigraphic units which were cut through by the structural faults, and the development of structural faults was older than the stratigraphic units which were not cut through by the structural faults. Here we make a analysis of tectonic evolution to extract structure features of different structure layers using GIS-based approach, combined with faults of style, size, orientation and strength and the features of structure construction. A three-step process has been proposed in this study as follows: (1) Extracting the structure faults confined in Neoarchean-Early Mesoproterozoic stratigraphic units. They represented the main structure features during the Precambrian. (2) Translating the unconformities into mappable features using Geographic Information System (GIS) to determine the main structure features during Ar-Pt₂. Statistics on strike and length of fault structures had been selected, it is confirmed that the NEE, sub-SN and NWW-trending structures were the main structural orientation. (3) Extracting the main structure faults of different structure layers based on the structural formations characteristics, and the region tectonic evolution. The main structural orientations of Neoarchean-Early Paleoproterozoic, Paleoproterozoic and Mesoproterozoic structure layers were the NE/NW, NEE/NWW, and sub-EW-strending, respectively.