塔里木北缘库鲁克塔格南华系阿勒通沟组沉积环境及构造背景分析

The depositional environment and tectonic setting of Nanhuan Altungol Formation in the Quruqtagh area, northern margin of Tarim

关于塔里木北缘南华-震旦纪的构造演化存在争议，本文研究了其东北缘库鲁克塔格地区南华系阿勒通沟组的沉积环境、地球化学特征等方面，揭示其源区风化、物源类型和构造背景等信息，以期为塔北同期构造演化及古地理环境恢复提供更多证据。阿勒通沟组由底部的冰碛砾岩和之上发育细密纹层的细砂-粉砂-泥岩组成，砂岩中发育丘状交错层理、渠模等典型风暴沉积构造，可识别出3种风暴沉积序列，为风暴浪控浅海陆棚沉积，是阿勒通沟组冰期和特瑞艾肯组冰期分属两个冰期的有力证据。该组宽广陆棚相的沉积环境，砂岩较高的结构成熟度及V-Cr—Ni—Sc负异常、Ti—Hf-Zr-Y正异常等地球化学特征皆显示其处于被动大陆边缘。物源判别图解、过渡族元素含量和稀土配分特征显示该组砂岩主要碎屑物质为来自南部塔里木克拉通的长英质岩类，另有古老沉积岩的加入。砂岩样品CIA值、A—CN—K图解和Th／u比值等显示其源区经历了微弱-中等的化学风化，碎屑物质具沉积分选、沉积物再旋回特征，且在成岩过程中钾交代明显，这些特征也与被动大陆边缘一致。在此基础上，结合前人研究成果认为库鲁克塔格自贝义西组裂解至阿勒通沟组演化为被动大陆边缘，且至少持续到震旦系扎摩克提组。

Recently, the controversies arisen from the tectonic evolution of northern margin of the Tarim Basin during the Nanhua-Sinian are still heated. This article draws up from the sedimentary environment and geochemical characteristics of Nanhuan Altungol Formation in Quruqtagh, and the authors attempt to reveal its source areas weathering, source-rocks composition and tectonic setting that provides more evidences on tectonic evolution and paleogeographic environment reconstruction of northern margin of the Tarim Basin over that period. Altungol Formation consisted of diamictite and a suit of fine sandstone-silty-mudstones with thin horizontal bedding. The sedimentary structures developed characteristically in storm deposits, includes hummocky cross stratifications and gutter casts. Three types of storm deposits are recognized, indicating that it＇s a storm-dominated shallow clastic sea depositional environment. The well textural maturity of sandstones and the shallow clastic sea depositional environment and the geochemical characteristics with V-Cr-Ni-Sc negative anomaly, Ti-Hf-Zr-Y positive anomaly all indicate a passive margin tectonic setting. Provenance discrimination diagrams, the transition elements and REE patterns all show that the detrital materials of Altungol Formation were derived from felsic rocks and old recycled sediments which mainly came from southern Tarim craton. The CIA, A-CN-K diagram and Th/U ratio all suggest that the source area underwent a lower-moderate weathering and sediment recycling and K mobility are significant, whose characteristics were in accordance with the passive margin environment. Combining previous research results, it can be summarized that the continental rifting began on Nanhua Beiyisi Formation, then Altungol Formation evolved into a passive margin and last until Sinian System Zhamoketi Formation in the Quruqtagh area.