中国阿尔泰山后造山伸展垮塌的地质证据

Geological Evidences for Post-Orogenic Extensional Collapse in Altaides,NW China

继大规模海西期深层次逆冲推覆之后,阿尔泰造山带南缘发生了后造山伸展,形成了克兰、库尔提、麦兹、阿热勒托别和苏鲁巴依变质核杂岩.变质核由中泥盆统浅变质岩及同构造侵入的碱性花岗岩组成,盖层由逆冲推覆过来的前寒武系中-深变质岩或弱变质的上泥盆世、下石炭世地层组成,在变质核的上部发育有绿片岩相顺层韧性剪切带,其变质变形从下往上逐渐增强.剪切带中石英棒拉伸线理的产状集中在110°～125°∠5°～20°,表明伸展平行于造山带方向.剥离断层切削了早期的逆冲推覆构造的部分推覆断层及部分滑动系统,但又与推覆体系一起受到了晚期褶皱与断裂的强烈改造.上述变质核杂岩不仅是阿尔泰造山带后造山伸展垮塌的直接构造证据,而且也是造山带南缘出露的后造山幔源花岗岩、基性-超基性杂岩活动的地质响应.

After largescale deep-level thrust nappe in Hercynian, the post-orogenic extension occurred in the southern boundary of Ahaides, and formed Kelan, Kuerti, Maizi, Areletuobie and Sulubayi metamorphic core complexes. The cores consist of the epimetamorphic rocks of middle Devonian system and systectonic alkali granites. The covers are composed of the meso-and hypometa-morphic rocks in Precambrian which are foreign geological bodies formed by thrusting, or of the slight metamorphic upper Devonian and lower Carboniferous formations. At the top of the cores, the bedded greenschist faces ductile shear zones are formed and their metamorphism and deformation gradually become strong from bottom to top. The occurrences of quartz-rod stretching lincations are 110°- 125°∠5°- 20°, indicating parallel extensional direction of the orogenic belt. The detachment faults partly cut away the parts of the thrust nappe faults and the sliding systems of thrust nappe tectonics, and, together with thrust -nappe system, are strongly superimposed by the late folds and fractures. The metamorphic core complexes are not only a direct evidence for the post-orogenic extension in the Ahaides, but also a reflection for the activity of post-orogenic mantle-resource granites, basic - ultrabasic complexes in the southern boundary of Altaides.