吉林省南部荒沟山地区老岭群珍珠门组构造样式及其控矿

吉林省南部荒沟山地区的珍珠门组可以分为:(1) 条带状大理岩;(2) 厚层状大理岩两个岩性段。变形分析表明它至少经历了三期变形,其中第二期变形对本区构造格架影响甚小。第三期北北东向直立褶皱叠加在第一期北北西向平卧褶皱之上形成的异轴异面褶皱叠加型式是本区的特征性构造样式。荒沟山铅锌矿与朝鲜检德铅锌矿类似,并且处于同一早元古代活动带内。朝鲜检德铅锌矿主要控矿构造是第一期褶皱转折端,因此荒沟山地区第一期褶皱转折端也应是寻找检德型大型铅锌矿的有利部位,本文提出了第一期褶皱转折端的可能部位,即寻找大型铅锌矿的有利部位。     

WRITING FOR NONGEOGRAPHERS: LESSONS FROM THE J. B. JACKSON PRIZE

ABSTRACT. Recent presidents of the Association of American Geographers have made it clear that as a discipline we need to do more to reach outside the confines of academia. Since 1985, the J. B. Jackson Award has recognized individuals whose books provide examples of how to share professional geographical knowledge with the educated lay public. Through correspondence with these individuals, recommendations for improving geographers' outreach are presented.     

Main crustal discontinuities of Morocco derived from gravity data

Sharp linear gradients in maps of potential field data are generally assumed to result from sharp discontinuities or boundaries between rocks having different densities or magnetic susceptibilities and are usually associated with faults or other geological contacts. The computation of the horizontal gradients of the gravity field permits us to localize the limits of such blocks and then the fault locations. The horizontal derivative maxima of the Bouguer anomaly and its upward continuation at several heights show lineaments that could reflect the layout of faults and/or contacts and their dip directions. The application of this method to the Bouguer anomaly map of Morocco (with 19,571 points, using an average crustal density ρ = 2.67 g/cm³) allowed us to perform a multiscale analysis of the gravimetric lineaments of the country. The obtained structural map is consistent with several faults already identified in previous studies, and highlights five new major subsurface faults systems with location and dip: the Saghro fault system; Bou-Arfa Midelt fault system; Sidi Slimane Mezquitem fault; Ksar El Kebir–Chefchaouen fault and the Rifan West Mediterranean fault. In addition, this study suggests a new shape and localization for the Agadir-Oujda trans-Moroccan major fault with a NE-SW direction and 900 km length, subdividing Morocco into two main domains. The results of this study contribute to the improvement of the regional structural map of the north western part of Africa, which is situated within the convergence zone between Africa and Eurasia.     

岩体结构研究中统计区间长度的确定

岩体结构研究日益得到工程地质界的重视,而岩体结构面现场测量数据是获得岩体结构特征的必需资料。在目前常用的2种结构面测量方法中对如何选择合理的统计区间长度缺乏充分的论证。利用我国西南某大型水电工程丰富的结构面测量资料,研究统计区间长度对岩体结构类型的影响,取得了一定的成果。即最小有效测线长度与结构面间距大小及概率密度分布形式有关,研究岩体结构特征时,必须根据工程实际情况选择满足要求的统计区间长度。     

试论柴达木盆地北缘构造样式与古、今层间氧化带的形成

柴达木盆地北缘是中新生代以来发育的块断带,中新生代盆地受逆冲推覆构造作用形成的构造岩席呈不同的展布形式.本文通过对不同构造部位构造样式的分析、中下侏罗统层间氧化带发育特征的阐述,认为在与盆地蚀源区相向的目的层,即对冲构造样式是古层间氧化带的发育部位,而相一致的单冲构造与斜坡带构造样式是现代层间氧化带发育的有利部位.     

Role of fluid mixing and wallrock sulfidation in gold mineralization at the Semna mine area, central Eastern Desert of Egypt: Evidence from hydrothermal alteration, fluid inclusions and stable isotope data

The Semna gold deposit is one of several vein-type gold occurrences in the central Eastern Desert of Egypt, where gold-bearing quartz veins are confined to shear zones close to the boundaries of small granitoid stocks. The Semna gold deposit is related to a series of sub-parallel quartz veins along steeply dipping WNW-trending shear zones, which cut through tectonized metagabbro and granodiorite rocks. The orebodies exhibit a complex structure of massive and brecciated quartz consistent with a change of the paleostress field from tensional to simple shear regimes along the pre-existing fault segments. Textural, structural and mineralogical evidence, including open space structures, quartz stockwork and alteration assemblages, constrain on vein development during an active fault system. The ore mineral assemblage includes pyrite, chalcopyrite, subordinate arsenopyrite, galena, sphalerite and gold. Hydrothermal chlorite, carbonate, pyrite, chalcopyrite and kaolinite are dominant in the altered metaggabro; whereas, quartz, sericite, pyrite, kaolinite and alunite characterize the granodiorite rocks in the alteration zones. Mixtures of alunite, vuggy silica and disseminated sulfides occupy the interstitial open spaces, common at fracture intersections. Partial recrystallization has rendered the brecciation and open space textures suggesting that the auriferous quartz veins were formed at moderately shallow depths in the transition zone between mesothermal and epithermal veins.Petrographic and microthermometric studies aided recognition of CO₂-rich, H₂O-rich and mixed H₂O–CO₂ fluid inclusions in the gold-bearing quartz veins. The H₂O–CO₂ inclusions are dominant over the other two types and are characterized by variable vapor: liquid ratios. These inclusions are interpreted as products of partial mixing of two immiscible carbonic and aqueous fluids. The generally light δ³⁴S of pyrite and chalcopyrite may suggest a magmatic source of sulfur. Spread in the final homogenization temperatures and bulk inclusion densities are likely due to trapping under pressure fluctuation through repeated fracture opening and sealing. Conditions of gold deposition are estimated on basis of the fluid inclusions and sulfur isotope data as 226–267 °C and 350–1100 bar, under conditions transitional between mesothermal and epithermal systems.The Semna gold deposit can be attributed to interplay of protracted volcanic activity (Dokhan Volcanics?), fluid mixing, wallrock sulfidation and a structural setting favoring gold deposition. Gold was transported as Au-bisulfide complexes under weak acid conditions concomitant with quartz–sericite–pyrite alteration, and precipitated through a decrease in gold solubility due to fluid cooling, mixing with meteoric waters and variations in pH and fO₂.     

板块俯冲起始与大陆地壳演化

组成大陆地壳的物质主要来自两个地质过程:地幔柱活动和板块俯冲。目前大多数研究认为板块俯冲起始于30多亿年前。在板块俯冲起始之前,基性的初始地壳物质受热重熔是大陆地壳生长的主要方式,其中,地幔柱活动是关键。地幔柱不仅向地壳输送玄武质岩浆,同时导致已有玄武质岩石和沉积岩通过部分熔融向中酸性岩石转化。当原始岩石圈强度足够大时,地幔柱会导致岩石圈倾斜、破裂,产生下滑力,诱发板块俯冲。板块俯冲引发岩浆活动,产生大量的岩浆岩,如岛弧安山岩、弧后盆玄武岩等。这些岩浆岩通过喷发、侵位,再经由块体拼贴、增生等过程加入到大陆地壳,是大陆地壳生长的主要途径。同时,板内岩浆活动乃至地幔柱活动等也与板块俯冲有直接或者间接的联系。俯冲再循环物质促进地幔柱发育,也为大陆地壳的生长提供物源和热能。与此同时,大陆地壳不断风化剥蚀,其中一部分沉积物随俯冲板块再循环到地幔,而板块俯冲过程也通过俯冲剥蚀等过程,将仰冲盘岩石圈物质刮削带入地幔。这些是大陆地壳消减的主要途径。目前大陆地壳增生和消减基本处于动态平衡。     

Brittle rotational faults and the associated shear heating

Brittle faulting-related shear heating is important in petroleum geosciences, tectonics and seismic studies. Temporal variation of shear heat related temperature rise for rotational and roto-translational faults are investigated in this work. For planar fault planes, devoid of gouge and any secondary faulting, temperature rise is proportional to the coefficient of friction, and rate of (angular) slip. Tectonically realistic physical parameters for rotational faults, especially prolonged faulting, can significantly increase temperature by shear heating at shallow crustal depth, capable of thermal maturity of hydrocarbons.     

江西湖口隧道工程地质条件评价

论述了江西湖口隧道场区的地层岩性条件。根据断层、层面、节理结构面的组合赤平投影图,判定了隧道西洞口与东洞口自然斜坡的稳定性,以及隧道西洞口、东洞口SW、东洞口NE路堑坡的稳定性。F2、F2′、F3断层横切洞体,断层与洞体交汇处及软岩分布区,围岩不稳定,易出现掉块及小塌方。提出了短开挖、弱爆破、强支护、先排水隧道的施工方案。     

Application of lithospheric rheology in structural metallogenesis: taking BIF-type iron-rich ore deposits as an exampleEI北大核心CSCD

Based on the basic theory and recent progresses of rock rheology, this paper addresses the critical role of rock rheological properties in the structural metallogenesis. The worldwide, metamorphic banded iron formation-type (BIF) iron-ore deposits are referred as example to delineate and evaluate the influences of structural deformation and rock rheological properties on the formation of this type of ore deposit. It is concluded that due to rheological differentiation, folding induced by ductile shearing and high-temperature plastic flow played a particularly key role in the formation of the high-grade, BIF-type Fe-rich ore deposits. Therefore, we propose that a combination between structural metallogenesis and rock rheology may be of help to our understanding of the tectono-physicochemical characteristics of large to super-large ore deposits. ©, 2015, Science Press. All right reserved.