摘要
摘要:中国阿尔泰造山带发育了一套被认为是早古生代的变质岩系，保留了原始成分层理S₀。岩石在下-中地壳层次经历了塑性变形及最深达到角闪岩相变质作用的改造。通过对岩石构造层次及变形序列分析，在造山带南缘识别出由深至浅、由早到晚发育的4个构造层次的变形样式，分别为流变构造、韧性剪切构造、褶皱劈理构造和断裂节理构造。流变构造以轴面NW走向、枢纽近直立的流动褶曲和NW走向近直立片麻岩面理为特征，局部发育长英质和镁铁质矿物分异条带，相当于下构造层次变形（约15～18 km）。韧性剪切构造以NW-NNW向和NNE-NEE向近直立的糜棱岩面理和片理面为特征，相当于下-中构造层次变形（约8～12 km）。褶皱劈理构造对应轴向NW、枢纽近水平的等厚褶皱、NWW和NNW向近直立劈理的产出，为中-上构造层次变形（约5～8 km）。上构造层次的断裂、节理构造在造山带南缘广泛发育，变形深度约浅于3～ 4 km。根据变形几何学、运动学关系及变形次序，确认它们是3期构造应力场作用的结果。在二叠—三叠纪，阿尔泰经历NE向（47°～55°）挤压应力场，在下-中构造层次发育317°～325°走向的流动褶皱、片麻理构造S_1-1，306°～308°走向左行和328°～332°走向右行近直立韧性剪切面理S_1-2，290°～295°走向左行和350°～355°走向右行、近直立片理面S_1-3。在古近纪NW向挤压应力场下，中-上构造层次发育20°～22°走向左行和78°走向右行片理面S_2-1，10°～20°和70°～78°近直立脆—韧性剪切面S_2-2和5°～8°压扭性断裂构造S_2-3。新近纪近N-S向应力场下，在浅地壳层次产出320°～325°和340°～345°走向右行走滑断裂，NWW向破劈理和NE向节理构造S₃。下构造层次变形被中-上构造层次变形叠加改造，体现变形深度层次与变形序列的一致性，反映了同构造挤压期的地壳抬升现象。
关键词: 中国阿尔泰/
构造层次/
变形序列/
变形深度

Abstract:There is a set of metamorphic rocks in Chinese Altai Orogen, which is considered to be Early Paleozoic and still retains the original bedding S₀. The rocks have experienced ductile deformation and amphibolite facies metamorphism in the mid-low crustal. During the subsequent uplifting and exhumation, they are modified by late ductile or brittle deformation. Based on the analysis of tectonic level and deformation sequence, we recognize four tectonic levels for deformation units, flow deformation, ductile shear structure, fold-cleavage structure and brittle fractures, developed from deep to shallow and early to late. Flow deformation is characterized by the near-vertical, NW trending flow fold and gneissosity, with felsic and mafic mineral ribbons locally, which are developed at middle and lower tectonic level(15~18 km). Ductile shear deformation is featured with near-vertical NW-NNW and NNE-NEE-direction mylonite foliation and schistosity, which developed at mid-upper tectonic level(8~12 km). The NW-trending isopach fold, and the NWW and NNW-trending cleavage developed at middle-shallow tectonic level(5~8 km). Brittle faults and fractures of upper tectonic level, which formed at the depth shallower than 3~4 km, are widely developed in the southern margin of Altai. According to the sequence, geometry and kinematics of deformation structures, three phases of tectonic stress field are confirmed. During Permian to Triassic, Altai experienced NE-direction(47°~55°) compressive stress field, developing the S_1-1 of 317°~325° trending flow fold and gneissosity, S_1-2 of 306°~308° trending sinistral and 328°~332° trending dextral ductile shear deformation, S_1-3 of 290°~295° trending sinistral and 350°~355° trending dextral near-vertical schistosity, at the low-middle tectonic level. Under NW-direction compressive stress field during Paleogene, there developed the S_2-1 of 20°~22° trending sinistral and 78° dextral schistosity, S_2-2 of 10°~20° and 70°~78° trending brittle-ductile shear surface and S_2-3 of 5°~8° trending trans-pressive fault. In Neogene, the S₃ of 320°~325° and 340°~345° trending dextral faults, NWW-trending cleavage and NE-direction fractures were developed under the near N-S-direction stress field. The deformation of lower tectonic level is superimposed by the structure of upper tectonic level, which reflects the consistency of the deformation depth and deformation sequence, and revels the crustal uplift during tectonic compression.
Key words:Chinese Altai/
Tectonic levels/
Deformation sequence/
Deformation depth



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