塔西北地区早寒武世玉尔吐斯组热液作用及沉积模式

埃迪卡拉纪-寒武纪之交全球沉积了一套黑色泥页岩和硅质岩组合,塔里木盆地早寒武世玉尔吐斯组即包含这样一套组合,并被认为是塔里木古生界主力烃源岩之一,然而目前对这套岩石组合的成因及沉积过程的研究还相对薄弱。在野外研究的基础上,将玉尔吐斯组分为5段,分为两个海进-海退旋回,认为其总体沉积于缓坡背景之上。对第一段硅质岩进行主量元素及稀土元素分析,结果显示其含有较低的Al/(Al+Fe+Mn)和较高的Fe/Ti值(均值分别为0.29和108.24)。在Al-Fe-Mn和Fe/Ti-Al(Al+Fe+Mn)图解上,多数样品落入热液作用范围,表明硅质岩主要受热液作用控制。硅质岩REE配分模式显示其不具有Eu的正异常和LREE富集的特征,这显示了海水对热液的稀释作用。靠近热液盆内口的库勒和什艾日克剖面发育较厚的硅质岩和一系列滑移变形构造。早寒武世时期,南天山洋已经打开,硅质热液广泛发育于整个塔北的深水和浅水区,这些迹象表明该区早寒武世仍然有很强的伸展构造活动。

Hydrothermal activity and depositional model of the Yurtus Formation in the Early Cambrian,NW Tarim,China

Black shale and chert suites were deposited during the Edicarian-Cambrian transition all around the world. The Early Cambrian Yurtus Formation in the Tarim Basin contains this rock suites and was considered to be one of the major Paleozoic source rocks in Tarim. However, the origin and depositional process of the rock suites are poorly understood. In this contribution, our field study shows that the Yurtus Formation can be divided into five stages and comprises two transgression-regression cycles. The cherts of stage 1 are characterized by low Al/(Al+Fe+Mn) (average 0.29) and high Fe/Ti (average 108.24) ratios. In AlFeMn and Fe/TiAl/(Al+Fe+Mn) diagrams, most of the samples show strong hydrothermal influence. Lacking pronounced positive Eu anomaly (average 0.84) and no LREE enrichment in the cherts REE pattern suggests seawater involvement to the sediment. Kule and Shiairike profiles near the hydrothermal vent are characterized by thicker chert and related deformation. In the Early Cambrian, the South Tianshan Ocean evolved into a mature ocean with silica-rich hydrothermal fluid spreading widely in the shallow and deep environment across northern Tarim Basin, reflecting strong extensional tectonic activities in this area.