滇西澜沧江构造带及邻区几何学、运动学和构造年代学分析

滇西澜沧江构造带自北向南沿碧螺雪山和崇山连续延伸； 按照构造几何学特点和运动学特征我们把该构造带分为3段：北段、中段和南段； 本文对各段的构造、组构、运动学及构造年代学进行了翔实研究，得到以下认识：构造带呈双变质岩带，核部为强变形高级变质岩带，两侧为强变形低级变质岩带，部分剖面几何形态似“花状”构造； 宏观和微观组构特征均指示构造带北段和中?南段存在明显的运动学差异，北段为右旋走滑剪切，中、南段为左旋走滑剪切； 同构造浅色花岗质糜棱岩中分选出白云母(北段)和黑云母(中段)，进行单颗粒矿物的激光熔化40Ar?39Ar定年，结果显示，糜棱岩化造成了花岗质岩石同位素时钟的重置和部分重置； 表面年龄指示了该构造带中新世的构造变形事件； 其中，北段右旋韧性剪切作用年龄为17.8～13.4 Ma或更早，至少持续到13.4 Ma，构造带中段记录了17.9～13.1 Ma的左行韧性剪切事件； 构造变形时代表现出同时代和同期次特点。综合分析认为，位于印度与欧亚大陆斜向汇聚带东缘的澜沧江构造带，是调节印支块体陆内变形的重要变形区域，为典型的新生代剪压应变区； 与区内哀牢山-红河构造带新生代左旋走滑相对应； 剪压应变和应变分解过程中，构造带东-西向减薄作用通过韧性物质垂向挤出和沿剪切方向的挤出平衡，垂向挤出导致地壳增厚和高应变体的抬升，形成现今的地貌高位，统一的陡立面理和亚水平拉伸线理是韧性物质沿剪切方向挤出的流变学响应； 构造带南段和北段运动学差异是澜沧江构造带新生代左旋剪压应变分解的必然产物和运动学要求。

Architecture, kinematics and thermochronology analysis in Lancangjiang Structural Zone,in western Yunnan

Lancangjiang Structural Zone extends continuously between Lanping?Simao terrane and Baoshan Block，along Biluoxueshan and Chongshan. The zone is separated into three segments according to the architecture and kinematics. The conclusions obtained are as the following：The zone shows a “metamorphic pair” with a strip of intensively?deformed/high?grade gneiss in the crest and intensively?deformed/low?grade rocks along the two sides; and some cross?sections display a flower like structure. Opposite shear senses develop in different segments of the Lancangjiang Structural Zone，i.e.，right?lateral slip in the northern segment but left?lateral slip in the middle and southern segments. The syntectonic leucogranitic mylonite samples collected from shear zones are broken to successively finer biotite and muscovite for single?grain laser fusion 40Ar/39Ar dating. Data show that mylonitization has caused complete and part isotope resetting of the micas. Spectrum and isochron ages of micas indicate Miocene deformation along the zone，i.e. ages of dextral shear in the north ranging from 17.7 Ma to 13.4 Ma，while the sinistral slip of the middle and southern segments from 17.9 Ma to 13.1 Ma. Deformation is homochronous in the north and middle segments. The Lancangjiang Structural Zone，eastern part of Indo?Asian continental oblique convergence，is a classical Tertiary sinistral transpressional region. The transpressional deformation occurred along the Zone，as an intra?continental tectonic event，can be correlated to the sinistral slip along the Ailao Shan?Red River Structural Zone. During the transpressional strain and strain partitioning，E?W thinning is balanced by vertical and lateral extrusions that occurred synchronously. Vertical extrusion resulted in the crustal thickening and the uplift of the high?grade terrain. Consistent vertical foliation and horizontal lineation are a rheological response to the extrusion along the strike?slip direction(the shear direction). The contrary shear sense between the southern and northern Lancangjiang zone is a kinematic requirement for the strain?partitioning along the shear direction during Tertiary sinistral transpression.