Five-Stage Model of the Palaeozoic Crustal Evolution in Xinjiang

The great majority of the Palaeozoic orogenjc belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang.     

地壳的拆离作用与华北克拉通破坏:晚中生代伸展构造约束

伸展条件下的地壳拆离作用是岩石圈减薄的重要浅部构造响应。晚中生代时期的伸展构造(包括拆离断层、变质核杂岩构造和断陷盆地)在华北、华南、东北和东蒙古及贝加尔地区普遍发育,它们切过上部地壳(断陷盆地)、中、上地壳(拆离断层)或中部地壳(变质核杂岩)。地壳拆离作用具有运动学极性(NWW或SEE)、几何学宏观(区域)对称与微观(局部)不对称性、遍布全区但不均匀性,以及形成时间的跨越性(140~60Ma)等特点,并使得地壳和岩石圈发生显著的减薄。本文研究揭示出现今岩石圈厚度变化与晚中生代伸展构造的发育程度和分布之间并没有必然的联系。其变化的基本规律是,除新生代裂陷发育区岩石圈厚度明显较小且厚度有迅速变化外,从华北向贝加尔地区总体的变化趋势是逐渐加厚,也即东亚地区岩石圈具有楔形形态。晚中生代时期的地壳(或地幔)拆离作用伴随着广泛的岩石圈减薄作用,区域岩石圈同时遭受到一定程度的减薄和破坏,华北克拉通在这一时期的破坏仅仅是区域岩石圈减薄在华北的具体体现。     

阿尔金山东段恰什坎萨依沟的地层新发现

出露于阿尔金山北坡的这套厚度巨大、基本不变质的海相沉积地层,岩性以火山岩、碎屑岩、碳酸盐岩为主,在恰什坎萨依沟的实测剖面中发现该套地层不整合于一套中深变质的长城系之上,不整合以上的硅质岩中发现放射虫、海绵骨针等化石,放射虫化石经鉴定,年代为奥陶纪中晚期,根据以上新发现对本地区的该套地层进行了重新划分与厘定。     

含有不整合面的钻井剖面中酸解烃的垂向分布规律

系统测量了不同时代、不同埋深的不整合面钻井剖面中酸解烃的分布,发现不整合面之下发育有总烃、甲烷浓度低而大分子烃类相对富集的烃类异常带,分析认为此异常带是风化脱气作用形成的脱气带,其厚度与下伏地层成岩程度有关。该发现对评价含油气盆地剥蚀与气藏保存、破坏的关系,不整合面对油气运聚的影响等有重要意义,也为解决剥蚀量恢复问题提供了新的科学线索。     

辽西地区晚侏罗世张家口组及其地质意义

辽宁省西部地区张家口组是在近几年来1:5万、1:25万区域地质调查的基础上发现和建立的,主要分布于金岭寺-羊山盆地的东缘、北票盆地西缘、四家子-铁营子盆地及凌源三十家子盆地东缘,呈北东向沿断裂带分布.岩性为一套偏酸、偏碱性的火山岩,以爆发相的火山角砾岩、集块岩及凝灰岩为主,呈角度不整合覆于晚侏罗世土城子组之上,其上被早白垩世义县组角度不整合覆盖.形成于挤压造山与伸展构造的过渡环境,是古亚洲构造域压性体制与滨太平洋活动带张性体制构造转换阶段的产物.地层时代为晚侏罗世.     

冀中坳陷古近纪的伸展构造

冀中坳陷的构造格架是新生代的伸展构造系统。该系统以大兴、保定－石家庄拆离滑脱断层为主体,与牛东－河东、马西、宁晋、新河等伸展断层以及徐水－安新变换带和衡水、宝坻－桐柏镇变换断层等组合而成。据平衡剖面和基底沉降曲线分析,冀中坳陷古近纪伸展作用过程持续发育,具幕式特点,以沙三期伸展作用最为强烈。地壳的快速伸展作用与火山活动强度之间缺乏耦合关系。冀中坳陷的动力学成因与伸展背景下的剪切作用有关。     

鄂西娄山关组顶部古岩溶不整合面的发现及层序地层学意义

鄂西娄山关组顶部存在古岩溶不整合面，有众多陆上暴露和溶蚀标志，表明其产生受寒武纪末海平面下降事件的控制。它不仅形成了碳酸盐台地上典型的Ⅱ型层序界面，而且恰与寒武—奥陶纪年代地层界线相重合，体现了层序界面、年代界线和事件界线三位一体的有机结合     

Geology and Genesis of Barite Deposits of Lasbela and Khuzdar Districts, Balochistan, Pakistan

Abstract: Geology and genesis of the sediment-hosted barite deposits in the Lasbela and Khuzdar districts of Balochistan, Pakistan have been studied and described. Hot solutions generated in rifting environments during the initial stage of separation of the continental crustal block related to the Gondwanaland fragmentation subsequently reposed in Jurassic rocks, most probably played an important role on barite formation.
Paragenetic relationships indicate that the period of barite mineralization was distinctly later than that of zinc-lead sulphide mineralization in the Lasbela and Khuzdar districts. The barite deposits occur on top and in peripheral to the zinc-lead sulphides. The earliest barite mineralization took place in the clastic rock sequence of the lower Spingwar Formation as cross cutting veins. Younger mineralization as stratabound-replacement type occurred within the platform limestones of Loralai Formation, just above the Spingwar Formation. The youngest mineralization as stratiform is hosted within black shales, mudstones and argillaceous limestones of Anjira Formation at the top of Loralai Formation. In the light of the evidences gathered from field and laboratory investigations a genetic model has been deduced.     

加拿大McArthur River铀矿床成矿特点及在我国寻找相同类型铀矿床的几点认识

加拿大萨斯喀彻温省西北部阿萨巴斯卡盆地McArthur River铀矿床是世界上最大、最富的不整合面型铀矿床。笔者通过对该矿床的剖析，从宏观上对这类铀矿床的一些形成规律进行了初步探讨，并对在我国寻找不整合面型或相似类型的铀矿床提出了一些认识。     

准噶尔永进地区深部储层的保存与发育机理

随着油气勘探向深部发展,在深部寻找优质储层是一个亟待深入研究的问题。永进地区位于准噶尔腹部中石化中部3区块,勘探目的层埋藏深,大于5000m,储层多为低孔-特低孔低渗-特低渗储层,因此,在该地区深部寻找相对优质储层具有重要的理论意义和勘探意义。该地区发育区域性不整合,即J/K不整合。在不整合形成期间,大气淡水具有高的流速和相对开放的流体环境,可以溶蚀易溶矿物并将溶蚀产物带离出溶蚀区;颗粒包壳可以抑制石英加大和碳酸盐矿物沉淀,保存原生孔隙和形成的次生孔隙;永进地区油气充注早,早期的油气充注改善了流体成岩环境,抑制胶结作用,同时,其携带的有机酸溶蚀易溶矿物,产生次生孔隙,油气早期充注从两个方面改善储层。