辽西—大兴安岭晚侏罗世—早白垩世火山岩形成动力学背景的新认识

New Viewpoints on the Dynamic Background of the J_3—K_1 Volcanic Rocks in Da Hinggan Mts.and Western Liaoning Province

大兴安岭及附近地区中生代火山岩是两种动力学背景下形成的。晚侏罗世早期,即相当于辽西—冀北的土城子期(156～145 Ma),是大兴安岭地区的强挤压造山时期。大兴安岭地区晚侏罗世—早白垩世火山岩(150～100 Ma)是后造山期挤压背景下"减压—剪切"环境中形成的,该时期火山岩与地幔柱火山岩有较大差异。

The Mesozoic volcanic rocks in the Da Hinggan Mts. and its adjacent areas were formed in two backgrounds,divided by an important geological event, i. e. the Tuchengzi orogenic movement (156～145 Ma) therefore the volcanic rocks, which were formedbefore and after the movement, could not be compared in characteristics of evolution or space distribution. According to the study in tectonics,tectono-stratigraphy, palaeo-magnetism and geophysics,the early stage of the late Jurassic (156～145 Ma)is the strong orogenic period of the Da Hinggan Mts. ,i. e. the Da Hinggan Mts. were in the backgroung of strong compression. It was in this period that the Da Hinggan orogenic belt was formed,which is so-called the Tuchengzi orogenic movement(156～ 145 Ma). According to the result of geochemical analysis the volcanic rocks of the late Jurussic to early Cretacous(150～100 Ma)were formed in the compressional background. Comprehensive study shows that the volcanic rocks of the late Jurussic to early Cretacous(150～100 Ma)were formed in the compressional background of post-orogeny with a 'reduced pressure-shearing' process. Besides the volcanic rocks of this age are very different from those of mantle plume.