构造叠加弱应变沉积岩地区的磁组构研究——以川西北盆地为例  

Magnetic Fabric of Weak Deformed Sediments under the Tectonic Superposition:A Case of the Northwest Sichuan Basin

作　　者：罗良[1] 贾东[1] 李一泉[1] 邓飞[1] 孙圣思[1] 

机构地区：[1]南京大学地球科学系,南京210093

出　　处：《地质学报》2008年第6期850-856,共7页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40372091和40672132);中国石油天然气集团公司创新基金;南京大学地质学研究生创新基金联合资助成果

摘　　要：磁组构是一种灵敏的应变指示计。单一方向应力作用下,在平行层缩短的初始阶段,磁线理与地层走向是一致的。然而,在构造叠加背景下弱变形的沉积岩地区,另一个(多个)不同方向的应力使得已经产生定向排列的磁性矿物发生旋转,表现为磁线理和与地层走向斜交。川西北盆地在新生代是一个典型的构造叠加区域,来自龙门山和米仓山的变形在此相互作用。本文在川西北盆地分3条剖面在18个采样点中采集了172个样品进行了磁组构研究。研究区内观察到3种弱变形的磁组构类型:沉积磁组构、初始变形磁组构和铅笔状磁组构。由于应变的叠加,由盆地内部向造山带前缘没有出现应变由弱到强的变化趋势,同时磁线理的方向也不一致。由盆地向造山带,来自米仓山的变形逐渐增强,磁线理从与地层走向一致转变成与地层走向斜交。Magnetic fabric is a sensitive strain indicator. Under the function of single stress, the direction of magnetic lineation is consistent with the bedding strike at the early stage of layer parallel shortening. However, in the low deformed sedimentary region under tectonic superposition, another different directed stress would rotate the arranged magnetic minerals, which will induce that magnetic lineation is oblique to the bedding strike. The Northwest Sichuan Basin is a typical tectonic superposition region in Cenozoic, where the deformations transferred from the Longmenshan and Micangshan affected together. Investigation of magnetic fabric was carried out in the Northwest Sichuan Basin, 172 samples were drilled in 18 sites in 3 cross-sections. Three low deformed magnetic fabrics were observed in the study area： sedimentary magnetic fabric, initial de,formation magnetic fabric and pencil structure magnetic fabric. Because of deformation superposition, deformation intensity from basin to orogen is not increasing, and the magnetic lineations are not in the same direction. From basin to orogen, the deformation transferred from Micangshan becomes more intensive, the magnetic lineation fits bedding strike at the interior of basin, and magnetic lineation is oblique to the bedding strike in the region adjacent to the orogen.

关 键 词：构造叠加 弱变形 磁组构 川西北盆地 

分 类 号：P512.2[天文地球—地质学]