青藏高原造山带的某些特征

Some Characteristics of Orogenic Belts in the Qinghai-Tibet Plateau

以昆仑中央断裂为界，青藏高原可分为南、北两部分￣［１］。北部的造山带是在刚性基底地壳上发育起来的。造山前期是裂陷槽发展阶段，并经简单的碰合褶皱成山。造山期后构造变形也简单，以逆冲、叠覆构造为主。南部的造山带是在柔性基底地壳上发育起来的。它的特点是活动性强，经多旋回开、合，造山前期出现有连贯性较好的洋盆及两侧广阔的陆缘沉积，造山期后变形复杂，除逆冲、叠覆构造外，出现大量平移断层。这一总的构造格局形成了青藏高原造山带一系列独有的特征。

There are many orogenic belts developed in the Qinghai-Tibet plateau. Various information on the whole proress of formation and evolution of the Qinghai- Tibet plateaulithosphere is preserved in them. 1.Orogenic belts in the northern rigid basement crust Some regions of Qinghai,Gansu and Xinjiang,north the central Kunlun fault,werepartly consolidated during early Proterozoic and were fully consolidated in middle Proterozoic,and then became relatively stable tectonic units. Becase of the long evolution of theircrystallized basemet and their high consolidation,they demonstrated rigidity.The Qilianshan,Altun Mts northern Qaidam,and northern Kunlun(even northern West Qinling)are just theorogenic belts developed from the break-up of these rigid blocks.The rift of the rigid blocksstarted at the beginning of Paleozoic or slightly earlier.The rifting continued and ocean basinsemerged afterward,the ocean basins shrank and had been folded by the end of Silurian. 2.Orogenic belts in southern soft basements In Hoh Xll- Bayan Xar and Tanggula regions,south of the central Kunlun fault,themetamorphic basement below the orogenic belts are generally regarded as westward extensionof the basement of the Yangtze platform,but softer than the Yangtze basement as a whole. There are some small blocks,c. g. ,Songpan block,Shuiluohe-Zhongza block and Qamdo-Simao blork. Like those rigid parts of Yangtze platform,farther southward,in the lake areaof northem Tibet and Himalayas area the basement rocks were consolidated in 500- 600 Ma(Pan-African age).They have medium grade metamorphism and crystallization,youngerhistory.Orogenic belts in soft basement crust have features as follows:1)More active,theyexperience complex polycyclic opening- closing.2)During the pre- orogeny rifting stage,extended huge ocean basins,their continental margins and sea-mount sedimentaryenvironment came out,and assembly of block accompaniened trench-arc systems and terraneaccretiOns. 3)Post- orogeny defomation was comple. Besides simple thrusting,nappe anddetachment structures were also developed.A large amount of strike slipping achieved due torotation of rigid blocks between them. 3.Notable thickening of the crust of Qinghai- Tibet plateau and unlifting of the Plateauinlate Pliocene The orogenic blets in the northern rigid blocks show simple compression in bothsouthward and northward directions. The huge nountains thrusted toward the adjacent basins(rigid frament)in opposite directions which forms fan symmetric patterns and rejuvenate theorogenic belt.The orogenic belts in the southern soft crust demonstrated notable strike slipfaulting,beside compression in north-south direction,In view of this,the characteristics of theorogenic belts are controlled by the nature of the crustal basement and have distinctinheritance.