白云岩成因探讨:新疆三塘湖盆地发现二叠系湖相喷流型热水白云岩

晚石炭世—早二叠世是新疆北部地区构造转换、海陆变迁的重要变革时期，包括三塘湖盆地在内的北疆地区该时期发育多个呈近东西向分布的陆内裂谷，其中存在大量基性、酸性及中性火山岩，它们以裂隙式喷发为特征。中二叠世芦草沟期，北疆地区发育裂谷期后半深湖沉积，沉积了厚层暗色泥岩、凝灰质泥岩、白云质泥岩夹白云质泥晶灰岩、凝灰岩、白云岩及火山岩的岩石组合，在暗色泥岩、凝灰质泥岩中普遍发育吐鲁番鳕鱼、双壳、叶肢介、介形虫等化石。其中的白云岩具如下特征:以铁白云石为主，多呈泥晶和粉晶状，与泥晶石英和有机质（含藻类）构成纹层；与方沸石岩互层，并作为方沸石的胶结物同时交代方沸石；伴生纳长石、伊利石、硬石膏、黄铁矿等多种热液矿物。此类白云岩及其热液矿物为本研究区首次发现，其分布与上石炭统火山岩的分布范围一致，表现出裂隙式、点式分布特点；火山岩中发育丰富的网状、树枝状裂缝并被热液矿物充填，可见火山岩具角砾状构造，可能反映了热液喷流口的沉积特征。初步分析认为该白云岩是一种与岩浆作用、深部热液作用相关的喷流型湖相热水沉积白云岩。

Permian Lacustrine Eruptive Hydrothermal Dolomites, Santanghu Basin, Xinjiang Province

Late Carboniferous to Early Permian was an important period of tectonic changes and ocean continent transformation in northern Xinjiang area. Several approximately east west intracontinental rifts occurred,such as Santanghu basin, where abundant basic, intermediate, and acidic volcanic rocks are present. Deposition of moderately deep lacustrine sediments of the Lucaogou Formation occurred during Middle Permian in Northern Xinjiang. The sediments include thick dark colored shale, tuffaceous shale, and dolomite shale, intercalated with dolomitic micritic limestone, tuff, dolomite, and volcanic rocks. They contain Turfania, bivalve, conchostracans, and ostracoda. The dolomite is composed of interlaminated ankerite,cryptocrystalline quartz and organic matter including algae, and analcime laminae as annalcite.The analcites were cenmented and replaced by ankerite. In addition, hydrothermal minerals like albite, illite, anhydrite,and pyrite are present. These hydrothermal minerals were firstly recognized in the Lucaogou,and the distribution of dolomite is consistent with that of the underlying Upper Carboniferous volcanic rocks, which occur in fractures and point sources. The network like and branch like fractures in volcanic rocks with a brecciated structure are filled with hydrothermal minerals indicating deposition around a hydrothermal vent. Preliminary analysis indicateds that dolomites were related to magmatism and mantle hydrothermal fluid, and formed as lacustrine eruptive hydrothermal dolomites.