摘要
经过在塔里木盆地内701个大地电磁测站的数据采集、资料处理和三维反演,取得测点分布比较均匀的岩石圈三维电阻率模型,从电性结构角度刻划了塔里木地体三维岩石圈构造。反演取得的电阻率模型表明电性岩石圈厚度为138km,沉积盆地内部的电阻率大都反映为低阻,电阻率小于10Ωm。上地壳结晶基底为高阻,深度12~24km;中下地壳为中低阻层,深度约24~47km。岩石圈地幔上层为低阻,深度约47~88km,电阻率为10Ωm。岩石圈地幔下层高阻,深度约88~138km。软流圈极低阻,电阻率仅为4Ωm。塔里木地体中上地壳高导层不发育(满加尔除外),地壳平均电阻率值偏高,电性莫霍面不清晰,下方有一个厚的高电阻率"根",说明塔里木盆地具有克拉通盆地的属性。同时塔里木地体的四周为高角度岩石圈断裂包围,四缘有高电阻率区存在,深度从15km到90km基本不变,这又说明塔里木盆地为处于造山带之间的大型断陷盆地。塔里木地体为早古生代古特提斯洋中漂移的大陆克拉通地体,以后由于大陆碰撞挤压发生地壳断陷成盆;因此,把它称为断陷型克拉通盆地更为准确。盆地内满加尔和罗布泊低阻区深度从上地壳15km到约90km地幔一直存在,到下地壳之后在北缘打开缺口冲过南天山。推测这一低阻带形成于晚古生代古亚洲洋封闭阶段,是塔里木和哈萨克斯坦地体、西伯利亚克拉通发生碰撞的产物。满加尔坳陷、塔西南的和田坳陷、叶城-莎车坳陷和于田-民丰坳陷、以及唐古孜巴斯坳陷地壳呈现低电阻率,说明这里流体活跃,有利于大型特大型油气成藏。
This paper presents the results of magnetotelluric investigation in Tarim Basin.We completed the survey at 701 stations and performed data processing and 3Dinversion,obtaining 3Dlithospheric electrical resistivity model of the Tarim terrane,which reflects lithospheric structures from viewpoint of electrical properties.Interpretation of the results determines that the electrical thickness of the asthenosphere in the terrane is 138 km,sedimentary basin has low electrical resistivity less than 10 Ωm.The crystalline basement is of high-resistivity with depth from 12~24km.The middle and lower crust is of more or less low-resistivity with depth from 12~24km.The crystalline basement is of high-resistivity with depth from24~47km.The upper part of the lithospheric mantle is of low-resistivity of about 10Ωm with depth from47~88km.The lower part of the lithospheric mantle has higher resistivity with depth from 88~138km.The asthenosphere has very low resistivity of 4Ωm.Except the Manjar depression,its upper and middle crust do not contain any developed low-resistivity layers,crustal average resistivity turns to a slight high,the Moho discontinuity is not clear,and there is a high-resistivity root supporting the basin reaching depth of 80 km.These facts show that the Tarim basin should belong to the craton type.However,the terrane is surrounded by steep lithospheric faults,contains high-resistivity blocks all around without movement from depth 15 kmto 90km.These facts also show that the Tarim basin should belong to the fault-sunken type.As a matter of fact,the Tarim terrane was a continental craton terrane drifting along a ocean in the Paleozoic,and then faulted and sunken becoming a basin owing to continental collision and compression afterwards.Thus we may call it as a large fault-sunken craton basin.The Manjar depression within the basin is a low resistivity block from depth 15 km down to 90 km,and develops a low resistivity loophole in its northern boundary into Tien Shan。 We infer that this low resistivity block was created during the closure of the Paleo-Asian ocean in the late Paleozoic,caused by collision between the Tarim,Kazakhstanterranes and Siberia craton.The Manjar, Hetain,Yecheng-Sache,Yutain-Mingfeng and Tangguzibasdepressions are all crustal low resistivity blocks,showing active fluid movement.They can be potential areas for oil/gas exploration.