羌塘盆地性质及构造演化

羌塘盆地位于班公湖-怒江缝合带和西金乌兰-金沙江缝合带之间,是一沉积盆地,分为羌南坳陷、中央隆起、羌北坳陷。盆地形成演化受特提斯构造带地球动力学控制。对盆地地层格架和区内碎屑岩的主要矿物成分、化学成分、微量元素以及火成岩化学成分的分析表明,羌塘盆地系不同类型盆地叠置而成的多旋回叠合盆地。晚古生代至中生代初为克拉通裂谷盆地、晚三叠世-侏罗纪为前陆盆地、白垩纪-第四纪为挤压抬升阶段,形成山间断陷盆地。      

博茨瓦纳三级成矿区带划分

博茨瓦纳以盛产金刚石闻名于世,但其基础地质和矿产地质研究的程度并不高。文章依据地质构造单元、主要矿种和主要成矿类型的成矿单元划分原则,将博茨瓦纳划分为太古宙津巴布韦克拉通铜-镍-钴-金多金属成矿带、太古宙卡普瓦尔克拉通铁-锰-金多金属成矿带、古元古代林波波铜-镍成矿带、太古宙刚果克拉通(铜)成矿带、新元古代达马拉铜-锡成矿区、卡拉哈里盆地煤-金刚石-铀成矿区等6个Ⅲ级成矿区带,并对这些成矿区带的主要特征进行了阐述。     

南北地震带大地形变监测与大震预测问题思考

本文以南北地震带及其附近地区大地形变监测与地震预测实践为基础,简要总结回顾了利用大地形变进行强震预测研究的工作思路、方法和一些进展;进而结合2001年昆仑山口西8．1级、2008年四川汶川8．0级特大地震前区域地壳运动变形背景和已有的研究结果,分析和探讨了基于大地形变监测,并考虑地震构造的差异性来进一步提高大震预测的科...     

中国东南部中生代基性岩脉时空分布与形成机理

中国东南部发育的基性岩脉见于中生代各个时期,其年龄从内陆至沿海逐渐变新,与区内花岗岩年龄有相同的变化趋势,但两者活动高峰期不重合。基性岩脉主要发育于花岗岩体内部的拉裂带,鲜见穿过花岗岩上方或周围的沉积变质盖层。中生代各时期的基性岩脉与相应时期的中酸性和基性火山岩浆活动具有清晰的分带现象。进一步研究表明,基性岩脉与同期基性火山岩应是同源不同相的产物,而中酸性喷发的岩浆与基性喷发(侵入)的岩浆,则可能分别来自壳内熔融层和壳下(地幔)熔融层或壳内岩浆层的上部和下部。中酸性与基性岩浆活动的"错峰"现象和基性岩脉带的"迁移"现象,均与本区中生代陆壳系统的内能变化有关。     

秦、祁、昆三大造山带的结合特征

秦、祁、昆三大造山带结合地区的物质组成及结构特征显示,其间存在不同时期发育起来的陆缘、陆内转换断层,受其制约,造山带内曾发生大规模侧向运动和由此引起的岩心活动及复杂的构造变形。据此,结合演化可分三阶段,并且秦、祁、昆三大造山带间并不存在东西向贯通的单一结合带,而是在转换断层作用下,分阶段逐步完成了转换结合的结合方式。     

辽宁四道沟金矿地球化学基本特征研究

四道沟金矿床的矿脉群规模较大且复杂，单个矿体较零碎，连续性不好。各矿体及矿化体的成晕相互干扰较大。通过对典型矿脉群中的矿体、蚀变带、围岩及构造带、预测点系统取样分析，据热液成矿成晕原理对矿区基本地球化学参数进行了多元统计分析的若干方法处理得出并分析了元素组合规律；确定了成矿指示元素并解释了指示元素的地质地球化学意义；总结了矿脉群中矿体原生晕中元素的轴向组合分带序列。     

山东平邑铜石金矿田成矿系列及成矿模式

铜石金矿田主要由隐爆角砾岩型(归来庄式)、碳酸盐岩层状微细浸染型(磨坊沟式)、夕卡岩叠加型、斑岩型和蚀变岩型等多种类型的矿床(点)组成,矿种以金为主,伴有银、铜、铁矿化,构成一个较完整的成矿亚系列.成矿作用与铜石富钾碱性次火山杂岩关系密切,岩浆活动为矿床的形成提供了热液和热源.泰山岩群为主要矿源层;寒武纪朱砂洞组上灰岩段之白云质灰岩、灰质白云岩为磨坊沟式金矿的有利含矿层位;寒武系上部-奥陶系下部的白云质灰岩、白云岩等是归来庄式金矿的有利围岩.杂岩体构成的次火山穹窿及伴生的环形放射状构造,控制着矿体的分布.     

胶北地区内生金矿成矿规律

胶北内生金矿是壳幔混源岩浆期后热液成矿,受复合基底EW向构造的早新华夏系和郭家岭超单元控制,蚀变、矿化分阶段连续进行,分为焦家式、灵山式、玲珑式及上庄式四个亚类型.金矿床区域上东西成行、南北成列、汇集成片呈棋盘格局;矿带内矿床沿走向等距分布、沿横向对应出现,矿床类型横向具分带、走向有变化、倾向相对稳定.矿体在控矿构造引张扩容段和构造叠加段赋存,并具斜立、侧伏、尖灭再现、斜列、瓦叠等产出规律.     

Kinematic model for out-of-sequence thrusting: Motion of two ramp-flat faults and the production of upper plate duplex systems

Kinematic models developed here suggest a bewildering array of structural styles can be generated during out-of-sequence thrusting. Many of these structures would be difficult to distinguish from a normally stacked thrust sequence and the process can produce younger-on-older faults that could easily be misinterpreted as normal faults. This paper considers a small subset of this problem within a large model space by considering structures that develop along a pair of ramp-flat faults that are moving simultaneously, or sequentially. Motion on the lower ramp warps the structurally higher fault due to fault-bend folding and when the fault ruptures through the warp it transfers a horse to the upper hanging wall. Continuity of the process generates what is referred to here as an “upper plate duplex” to distinguish the structure from a conventional duplex. Kinematic parameters are developed for two models within this general problem: 1) a system with a fixed ramp in the lower thrust, overridden by an upper thrust; and 2) a double-duplex system where a conventional duplex develops along the lower fault at the same time as an upper plate duplex is formed along the upper fault. The theory is tested with forward models using 2D Move software and these tests indicate different families of structural styles form in association with relative scaling of ramp systems, slip-ratio between faults, and aspect ratios of horse blocks formed in the upper-plate duplex. A first-order result of the analysis is that an upper plate duplex can be virtually indistinguishable from a conventional duplex unless the trailing branch lines of the horses are exposed or imaged; a condition seldom met in natural exposures. Restoration of an upper-plate duplex produces counterintuitive fault geometry in the restored state, and thus, restorations of upper plate duplexes that erroneously assume a conventional duplex model would produce restored states that are seriously in error. In addition, in most of the models some fault segments place younger rocks on older rocks which could be easily misinterpreted as normal fault systems. In some models younger-on-older juxtapositions are significant and if scaled to crustal scale would produce core-complex style structures that would be difficult to recognize as contractional features. Collectively, these observations imply that many areas where simultaneous contraction and extension are inferred may be entirely contractional with younger-on-older relationships generated by out-of-sequence thrust systems. Examples where this process may have occurred are in southwestern North America and the Moine thrust system and future studies should evaluate these systems in light of these models. Distinguishing upper plate duplex from conventional duplex is potentially important in economic evaluations of thrust systems because fluid migration paths would be very different in the two alternatives. The process may also be important in seismogenic mechanisms, particularly in subduction megathrusts, because faults warping faults could produce fault irregularities that would form transient asperities along the fault.     

Geometries of frontal fold and thrust belts: Insights from discrete element simulations

This study investigated the evolution of frontal structures of fold and thrust belts with 2D numerical simulations using the discrete element method (DEM). Of specific interest is the occurrence of triangle zones, and how mechanical stratigraphy affects the formation of the triangle zones. In our simulations, we varied the strength of a two unit stratigraphy, as well as the décollement horizons, to determine the controlling parameters of different types of frontal structures. For models with homogenous stratigraphy, deformation was concentrated along forethrusts, which involved both the upper and lower units. With the addition of a mechanically weak upper unit, deformation along forethrusts and popup structures largely occurred in the upper unit with relatively little deformation of the lower unit. With thicker décollement surfaces and strong upper and lower units, decoupling was enhanced and allowed for the formation of triangle zones in front of the deforming wedge. The triangle zones were uplifted along lower forethrusts, until a new frontal triangle zone formed. Results compared favorably with triangle zones found in the Canadian Cordillera in southern Alberta.