Recent tectonic stress field research in Shanxi graben system

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Arc–arc collision in the Izu collision zone, central Japan, deduced from the Ashigara Basin and adjacent Tanzawa Mountains

The Pleistocene Ashigara Basin and adjacent Tanzawa Mountains, Izu collision zone, central Japan, are examined to better understand the development of an arc–arc orogeny, where the Izu–Bonin – Mariana (IBM) arc collides with the Honshu Arc. Three tectonic phases were identified based on the geohistory of the Ashigara Basin and the denudation history of the Tanzawa Mountains. In phase I, the IBM arc collided with the Honshu Arc along the Kannawa Fault. The Ashigara Basin formed as a trench basin, filled mainly by thin-bedded turbidites derived from the Tanzawa Mountains together with pyroclastics. The Ashigara Basin subsided at a rate of 1.7 mm/year, and the denudation rate of the Tanzawa Mountains was 1.1 mm/year. The onset of Ashigara Basin Formation is likely to be older than 2.2 Ma, interpreted as the onset of collision along the Kannawa Fault. Significant tectonic disruption due to the arc–arc collision took place in phase II, ranging from 1.1 to 0.7 Ma in age. The Ashigara Basin subsided abruptly (4.6 mm/year) and the accumulation rate increased to approximately 10 times that of phase I. Simultaneously, the Tanzawa Mountains were abruptly uplifted. A tremendous volume of coarse-grained detritus was provided from the Tanzawa Mountains and deposited in the Ashigara Basin as a slope-type fan delta. In phase III, 0.7–0.5 Ma, the entire Ashigara Basin was uplifted at a rate of 3.6 mm/year. This uplift was most likely caused by isostatic rebound resulting from stacking of IBM arc crust along the Kannawa Fault which is not active as the decollement fault by this time. The evolution of the Ashigara Basin and adjacent Tanzawa Mountains shows a series of the development of the arc–arc collision; from the subduction of the IBM arc beneath the Honshu Arc to the accretion of IBM arc crust onto Honshu. Arc–arc collision is not the collision between the hard crusts (massif) like a continent–continent collision, but crustal stacking of the subducting IBM arc beneath the Honshu Arc intercalated with very thick trench fill deposits.     

豫北地区地震活动性及其与区域地壳运动的关系

本根据地震地质和地震分布条带,把豫北地区从西至东分为弱,中,强三个区段。由于区域地壳深部主断裂和大震活动的牵动作用,是造成本地震活动的重要原因,因而从区域地壳块体活动背景上探讨了本区及邻近地区地震活动趋势,中还指出,豫北西部太行山区的林县－薄壁地震带,虽不具有强震构造背景,但小震年月频率多寡和震群活动,却能反映了大区域地壳应力场强弱,亦可作为判断区域性地震活动的指标。     

On Palaeozoic Tectonics in the Alxa Region, Inner Mongolia, China

Two ophiolitic melange belts in the Late Carboniferous formations have been discovered recently in the Alxa region. One is in the Engger Us fault and possesses properties of oceanic crust. The other is in the Badain Jaran fault and shows properties of a back-arc basin. These two faults, together with the Yagan fault, constitute the important boundaries of tectonic units in the Alax region. The four tectonic units delimited by these faults are different in rock assemblages, metamorphism and geochemistry. They reflect the nature of tectonic environments in which they are found. The tectonic units may be traced and correlated to the eastern and western neighbouring areas. The formation and evolution process of the units and their interaction in the Alxa region may be described in terms of the evolution of the Palaeo-Mongolian Ocean and its continental margins.     

构造地球化学测量在找金中的应用

通过马庄山地区构造地球化学测量找金试验和在特克斯县１５号水系沉积物异常区开展构造地球化学测量的推广应用证明：构造地球化学测量工作,以遥感地质构造解译为先导,民裂裂构造裂隙充填物及蚀变岩石为采样介质,较岩石地球化学测量更具有矿直接性。     

断裂构造控矿的数学和力学分析：以山东新城——河西金矿区为例

以山东新城－河西金矿区为例,通过新城、河西和候西矿床容矿断裂的形态、断裂活动、构造因素、构造应力场和变形场的数学、力学半定量及定量分析,探计断裂构造控矿规律以及成矿的力学机理。提出了金矿成矿受主断裂面形态、次级小断裂、节理的发育强度,断裂构造的力学特征、变形强度等控制。矿体多位于波状起伏的主断裂面凸峰的下盘、凹谷的上盘。矿化强度与次级断裂、节理的发育强度正相关。断裂构造带和次级构造裂隙带是内应力低     

广东从化石岭碱性杂岩的岩石学特征及其地质意义

对广东从化石岭碱性杂岩体进行了１：１万地质调查和填图,并进行了详细的岩石力学研究。其结果表明：杂岩体由霞石角闪石正长岩、角闪石正长岩、墨云母正长岩等岩性组成,为Ａ－型花岗岩的分异结晶作用所形成,产于板内引张构造环境,与深大断裂有关。岩体本身已构成霞石正长岩矿床,具有较高的工业利用和经济价值。     

内蒙古温都尔庙地区温都尔庙群的形成环境和构造意义

内蒙古温都尔庙地区有一套统称为温都尔庙群的变质岩系,该岩系主要由两种不同的岩石组合组成：一套是出露于乌兰沟一带的浅变质岩系,主要由变玄武岩、硅质岩、火山碎屑岩、碎屑岩组成的基性火山岩－碎屑岩组合;另一套是出露于德言其庙一带的深变质岩系,主要由斜长角并岩、斜长片麻岩组成。这两套岩石组合在变形变质、岩石化学和形成环境等方面都有很大的差异,前者主要表面出弧后盆地的特征,后者则是拉张过程中板底垫托的产物,它们分别代表了华北板块北缘中元古代不同构造演化阶段的产物。     

Intrusion–Related Vein Gold Deposits: Types, Tectono-Magmatic Settings and Difficulties of Distinction from Orogenic Gold Deposits

Abstract: A spectrum of intrusion-related vein gold deposits is recognized. Representative examples are described of the following geochemical associations: Au-Fe oxide–Cu, Au–Cu–Mo–Zn, Au–As–Pb–Zn–Cu, Au–Te–Pb–Zn–Cu and Au–As–Bi–Sb. The associated intrusions range from small outcropping stocks to complex batholiths. The different vein associations are believed to reflect the compositions of related intrusions, which themselves characterize distinct tectonic settings. The Au-Fe oxide–Cu and Au–Cu–Mo–Zn associations belong to two broad groups of deposits, Fe oxide–Cu–Au and porphyry Cu–Au, both of which are related to highly oxidized calc-alkaline intrusions emplaced in sub–duction–related arcs. The Au–As–Pb–Zn–Cu association seems to be linked to somewhat less oxidized intrusions emplaced in a similar setting. The Au–Te–Pb–Zn–Cu association, which possesses well-known epithermal counterparts, is also found with highly oxidized intrusions, but of alkaline composition and back-arc location. In contrast, the Au–As–Bi–Sb association, part of a newly recognized class of intrusion-hosted Au–Bi–W–As deposits, is related to relatively reduced intrusions, spanning the boundary between the magnetite– and ilmenite–series. Such intrusions, which may host major bulk-mineable gold deposits, were emplaced along the landward sides of arcs, possibly during lulls in subduction, as well as in continental collision settings. Therefore, a variety of geological environments is prospective for vein and, by extrapolation, other styles of gold mineralization, not all of them fully appreciated in the past. Several features of vein gold deposits, including imprecise relationships to individual intrusive phases, poorly developed mineral and metal zoning, apparent time gaps between intrusion and mineralization and presence of low–salinity, CO₂–rich fluid inclusions, are commonly taken to indicate a non-igneous origin and to be more typical of orogenic (mesothermal) gold deposits generated during accretionary tectonic events. However, several or all of these features apply equally to some intrusion– related vein gold deposits and, therefore, do not constitute distinguishing criteria. The currently popular assignment of most gold-rich veins to the orogenic category requires caution, because of the geological convergence that they show with some intrusion-related deposits. A proper distinction between intrusion-related and orogenic gold deposits is crucial for exploration planning.     

赣东北地区构造演化的新认识

根据近几年来赣东北地区的区域地质调查及科研工作所获的地质资料、化石资料和实测数据,论述了该区晋宁期以来的构造演化,提出了以下看法：①该区是一个多期造山作用的复合体,它经历了褶皱基底形成、洋陆转化和陆内发展三大阶段和晋宁期、加里东期、印支期、燕山期四个构造旋回;②早古生代该区存在一小洋盆;③加里东期构造旋回在赣东北地区是明显的,其造山作用是存在的,并由此奠定了该区构造分区的总体格局。