柴北缘滩间山群构造对南祁连加里东造山及超高压变质岩折返的启示

柴北缘原滩间山群依构造与岩性可肢解为3部分：下岩组为岛弧中-基性火山岩系，已部分变形变质为绿片岩相糜棱岩；中岩组为弧后盆地喷流-沉积岩系，为锡铁山式铅锌矿床赋矿层位，已产生绿片岩相变形分解；上岩组为弱变形变质的紫红色含砾砂岩。构造解析表明：应将原滩间山群下岩组置于上寒武统-下奥陶统，为洋-陆碰撞体制下产物；中岩组置于中-上奥陶统，为弧后盆地产物；上岩组置于下志留统，为陆-陆碰撞体制下前陆盆地产物。下岩组或中岩组与早元古界达肯大坂群以基底剥离断层接触，上岩组或达肯大坂群逆冲岩席与中岩组以上剥离断层接触，二剥离断层组成双重构造。在造山带伸展垮塌前，未含榴辉岩的达肯大坂群逆冲堆垛于滩间山群之上，且在后造山伸展中被上剥离断层挫失，仅局部可残存。造山带伸展之后，柴北缘叠加了板内造山，原滩间山群、推覆岩席、推覆断层、剥离断层一并转入豆荚状倒转向斜，并上叠晚泥盆世磨拉石盆地。在造山带伸展期，阿尔金走滑断裂调节了柴北缘与南阿尔金超高压变质岩的早期折返，并在造山带后续多期次挤压与伸展体制下调节了超高压变质带的剥蚀出露。

Structure Implication in Tanjianshan Group on Southern Qilian Caledonian Orogeny and Exhumation of UHP Metamorphic Rocks in Northern Qaidam

The original Tanjianshan Group in Northern Qaidam can be decomposed into three parts by its stuc-ture and lithology.The lower rock formation is island-arc intermediate-basic volcanic rock series deformed and metamorphosed to greenschist facies mylonite .The middle rock formation is back-arc basin jet-sedimentary rock series in which deformational partitioning of greenschist facies occurred , belonging to the ore-bearing layer of Xitieshan-type Pb-Zn ore deposit.The upper rock formation is purple-red pebbled sandstone with slight de-formation and metamorphism .Structural analysis suggests that the lower rock formation of the original Tanjians-han Group belongs to Upper Cambrian-lower Ordovician,which is the product of ocean -continent collision sys-tem .The middle rock formation belongs to the middle-late Ordovician, the product of the Back-arc basin.The upper rock formation belongs to the early Silurian , the product of the foreland basin in the continent-continent collision system.The lower or middle rock formation and the gneiss of early Proterozoic Dakendaba Group are contacted with the base Detachment fault, while the upper rock formation or the thrust sheet of the Dakendaba Group and the middle rock formation are contacted with the upper detachment fault .The two detachment faults are characteristed by duplex thrust structure.Before the extensional collapse of the orogenic belt, the Dakenda-ba Group without eclogite was thrusted and stacked on the Tanjianshan Group , subsequently setback loss by the upper detachment fault during the Post-orogenic extensional, only partialy remaining relics.After the extension of orogenic belt, the Northern Qaidam was superimposed by intracontinental orogeny, the original Tanjianshan Group, thrust sheets.Nappe faults and detachment faults are transferred into the podiform inverted syncline to-gether, and superimposed on the late Devonian molasse basin .In Caledonian orogenic extensional period, the Altyn strike-slip fault was adjusted by early exhumation between north Qaidam and South Altyn UHP metamor-phic rocks, and the tectonic erosion of the UHP metamorphic belt at the follow-up of the extrusion and exten-sional system.