南祁连党河南山地区奥陶纪沉积盆地性质分析

There is always been a controversy that Danghenanshan-Lajishan tectonic belt had been rift valley or ocean from Cambrian to Ordovician period in center of Qilian moutain. Ordovician volcanic-sedimentary rocks are widespread in the Danghenanshan, South Qilian. They are the most derect carrier in the study of Ordovician structural environment and the type of basin between South Qilian and Center Qilian area Preliminary study shows that Ordovician sedimentary strata are Early Ordovician wuligou formation, Middle Ordovician yanchiwan formation and Late Ordovician duosuoqu formation. From the bottom up to top are Continental slope facies, deep-water facies, lake delta facies. They are indicating the sequence from progradation to retrogradation. Spatially the Middle Ordovician yanchiwan formation as a pivot, two sides distribute Early Ordovician wuligou formation and Late Ordovician duosuoqu formation. That show the characteristic of rift basin. This project intends to focus on sedimentary sequence in Danghenanshan and make use of the results of sedimentary filling sequence, sedimentary facies and provenance analysis, and combined with the research on petrology and geochemistry of the volcanic strata, which could finally find out the type of sedimentary basin and its forming environment and reveal the Ordovician sedimentary evolution in Danghenanshan. Furthermore, establishing typical sedimentary filling sequence and discuss the relationship between regional tectonic evolution and sedimentary basin.

祁连山中部党河南山—拉脊山地区在寒武纪—奥陶纪时期为裂谷还是大洋一直存在争议。南祁连党河南山地区出露奥陶纪火山—沉积岩系，是研究中、南祁连接合带奥陶纪沉积盆地性质及其构造环境最为直接的载体。初步研究表明，南祁连党河南山地区奥陶纪地层由下向上分别为早奥陶世吾力沟组、中奥陶世盐池湾组与晚奥陶世多索曲组，依次发育被动陆缘斜坡相、盆地深水相以及河湖三角洲相，总体表现为裂谷盆地由进积—退积的发展过程。空间分布上，该区以中奥陶世盐池湾组为轴，两侧分布早奥陶世吾力沟组与晚奥陶世多索曲组，具有裂谷盆地的对称分布特征。本申请拟以党河南山地区奥陶纪沉积序列为研究重点，通过开展充填序列、沉积相和物源的研究，结合与沉积岩伴生火山岩的岩石学和地球化学研究成果，查明沉积盆地类型及其形成环境，揭示党河南山地区奥陶纪沉积演化过程，建立典型沉积序列组合，探讨沉积盆地与构造环境之间的联系。

青海南祁连党河南山地区的奥陶—志留系为该地区的地质演化提供了精细的沉积记录。此次通过层序地层、年代地层以及岩石地球化学的研究，查明了奥陶系地层的充填序列、沉积环境与形成时代，探讨了沉积盆地性质；厘清了志留系地层的岩石组合、变质变形与形成时代，并从中解体出新元古代拐杖山岩群，为完善南祁连地区早古生代的构造演化历史提供了重要依据。.研究表明，吾力沟组显示多个周期性的火山旋回特征，顶部出露较厚的灰岩，属浅海陆棚沉积环境，从中获得基性火山熔岩与花岗闪长岩的锆石U-Pb年龄分别为483±3.5Ma和464±2.2Ma，指示其形成时代为早奥陶世，物源主要来自华北板块、中祁连与全吉地块；盐池湾组以巨厚的碎屑岩为特征，属次深海—深海相浊流沉积，时代厘定为中—晚奥陶世，物源来自中祁连与全吉地块；多索曲组岩石主要为中性与中酸性火山碎屑岩夹少量火山熔岩与板岩，属半深海-浅海沉积环境，获得中基性火山岩锆石U-Pb年龄451±2.3Ma，时代厘定为晚奥陶世晚期，物源主要来自中、南祁连与华北板块。综合奥陶系地层的沉积充填序列与岩石地球化学研究，认为其形成于南祁连洋扩张—俯冲时期的弧后盆地之中。本次研究还查明了南祁连地区志留系巴龙贡噶尔组的物质组成、形成时代与物源特征。巴龙贡噶尔组具有复理石式的沉积建造，物源主要来自邻近的全吉，柴达木和中祁连地块。此外，在巴龙贡噶尔组中解体出了一套浅变质、强变形的火山—碎屑岩地层，获得该地层中基性火山岩的锆石U-Pb年龄为734±8.5Ma和786.6±5.8Ma，将其厘定为新元古代拐杖山岩群，其物源主要来自全吉地块与中祁连地块，响应了Rodinia超大陆裂解事件。