辽东半岛河栏镇火山-沉积岩构造研究——对古元古代弧后盆地张裂与闭合的启示

前寒武纪盆地演化及造山作用一直是造山带研究中的热点和难点，通过对华北克拉通东部陆块胶-辽-吉构造带中辽东半岛河栏镇火山-沉积岩进行深入的野外及室内研究，反演该地区古元古代大地构造演化过程.通过对辽河群里尔峪组火山岩、高家峪组钙质泥岩以及大石桥组碳酸盐岩野外的详细构造解析，识别出各类岩石单元中发育同沉积伸展构造（D_1-0），包括同沉积不对称褶皱、层间平卧褶皱和滑脱面理及线理，指示辽吉弧后盆地早期伸展张裂过程.通过对河栏镇蒲石河地区基性侵入岩及喷出枕状熔岩进行详细的野外构造填图及解析，提出伴随基性枕状熔岩的喷发，辽吉弧后盆地张裂到最大程度.此外，在各组相关岩石中观察到大量逆冲推覆构造及不对称断展褶皱，构造归为D_1-1或者D_1-2，指示辽吉弧后盆地受挤压应力影响发生收缩.锆石年代学研究指示高家峪组沉积物物源主要来自于~2.5 Ga基底，少量来自古元古代（2 172 Ma）火山弧.综合区域内已有岩石地球化学及年代学资料，研究表明辽吉弧后盆地的拉张及闭合过程伴随着古元古代增生造山作用，并暗示板块构造在古元古代已经开启. 

Paleoproterozoic Back-Arc Basin Opening and Closure: Evidence from the Structural Research of the Volcanic-Sedimentary Rocks in the Helan Town,Liaodong Peninsula

Precambrian orogenesis has always been a hot and challenging issue in the study of accretionary and collisional orogenic belts. In this paper, we study the volcanic-sedimentary rocks in the Paleoproterozoic Jiao-Liao-Ji orogenic belt at the Helan Town in the Liaodong Peninsula using methods of detailed mapping in the field and age dating indoors, and finally decipher the Paleoproterozoic evolution of this area in the eastern China Block of the North China Craton. Many syn-depositional structures such as asymmetric folds, isoclinal folds, and inter-bedding slip lineations were recognized and classified as syn-depositional structures based on our detailed field structural analysis of the volcanic rocks from the Li'eryu Formation, calcareous mudstones from the Gaojiayu Formation, and carbonates from the Dashiqiao Formation. We further classified these structures as D_1-0, which formed in an extensional process at the early opening stage of the Liaoji back-arc basin. Based on detailed field mapping of the intrusive mafic rocks and its related eruption "pillow lava" in the Pushihe area of Helan Town, it was proposed that the eruption of the basic "pillow lava" indicates that the Liaoji back-arc basin turned into the maximum extension stage. Besides, a large number of thrust nappe structures and asymmetric fault-propagation folds were observed in the volcanic rocks of the Li'eryu Formation, the calcareous mudstones of the Gaojiayu Formation, and the carbonates of the Dashiqiao Formation in the Liaohe Group, and were defined as D_1-1 or D_1-2. These structures indicate the contraction of the Liaoji back-arc basin, also imply the beginning of the Paleoproterozoic orogenesis. Detrital zircon study of the Gaojiayu Formation indicates that the predominated provenance of the clastics was from a 2.5 Ga basement, and few of them were from the 2.17 Ga volcanic rocks. Combined with petro-geochemistry and geochronology data in our study area, it is concluded that the opening and closure of the Liaoji back-arc basin recorded a complete Paleoproterozoic orogenesis process and also indicated the plate tectonic initiation at the time.