Time-dependent stress change during failure of rocks     

V.T. Belikov  A.F. Shestakov 《Russian Geology and Geophysics》2008,49(5):350-356

The energy balance of a solid subject to fracture has been explored using heat and mass transfer equations with regard to the volumetric and superficial components. In the suggested model, brittle fracture of a cracked solid considered as a heterogeneous two-phase medium is described by an equation analogous to the Griffith’s criterion for propagation of a single crack. The derived equation is used, together with estimates of relative change in specific interface area, to study the respective change of free strain energy and pressure in rocks associated with failure.  相似文献   

湖南香花岭花岗岩岩石化学特征及其构造环境   总被引：3，自引：0，他引：3  

赵龙辉  邹宾微  柏道远 《华南地质与矿产》2008,(1):1-6

湖南南部燕山早期香花岭岩体主要由铁锂云母二长花岗岩组成。岩石SiO：和K2O平均含量分别为73．72％和4．78％,Na2O＋KO平均8．47％,K2O／Na2O比值平均为1．40,A1：03平均为13．81％。总体属强过饱和铝质钙碱性一碱性花岗岩类。氧化物构造环境判别图解及区域构造演化背景反映香花岭岩体形成于后造山构造环境。  相似文献   

Geochemistry of the Mian-Lue ophiolites in the Qinling Mountains, central China: Constraints on the evolution of the Qinling orogenic belt and collision of the North and South China Cratons   总被引：3，自引：0，他引：3  

Ji-feng Xu  Ben-ren Zhang  Yin-wen Han 《Journal of Asian Earth Sciences》2008,32(5-6):336

The Anzishan ophiolite, a typical ophiolitic block of early Carboniferous age in the Mian-Lue suture zone of the Qinling Mountains, central China, consists of amphibolites/metabasalts, gabbros and gabbroic cumulates. All of these rocks, as well as those in the Hunshuiguan-Zhuangke (HZ) block, have compositions similar to normal MORB and back-arc basin basalts (BABB) with high ε_Nd(t) values, indicating that they were derived from a depleted mantle source. The Mian-Lue suture zone also contains blocks of other lithologies, e.g., rift volcanic rocks in the Heigouxia block and arc volcanic rocks in the Sanchazi block. Although they are in fault contact with each other, the presence of these different blocks in the Mian-Lue suture zone may represent a complete Wilson cycle, from initial rifting to open ocean basin to final subduction and continent-continent collision, during the late Paleozoic-early Triassic. In this region, the North and South China Cratons were separated by Paleo-Tethys at least until the early Carboniferous, and final amalgamation of both cratons along the Qinling orogenic belt took place in the Triassic.  相似文献   

Provenance of late Palaeozoic metasediments of the Patagonian proto-Pacific margin (southernmost Chile and Argentina)     

Carita Augustsson  Heinrich Bahlburg 《International Journal of Earth Sciences》2008,97(1):71-88

In this provenance study of late Palaeozoic metasediments of the Eastern Andean Metamorphic Complex (EAMC) along the south Patagonian proto-Pacific margin of Gondwana, the palaeogeological setting of the continental margin in Devonian–Carboniferous and Permian times is reconstructed. The study is based on detrital heavy mineral contents, chemical compositions of tourmaline grains, and whole rock element and Nd-Sr isotopic compositions. Element and isotopic compositions reveal that Devonian–Carboniferous metaturbidites deposited before the development of a Late Carboniferous–Permian magmatic arc along the margin were mainly fed from felsic, recycled, old continental rocks. The last recycling phase involved erosion of metasediments that were exposed in Patagonia. Feeder systems to the basin cut either through epidote-rich or garnet-rich metasediments. In Permian time, EAMC metaturbidites were deposited next to the evolving magmatic arc and were derived from felsic, crustal rocks. Two provenance domains are recognised. The metasediments of the northern one are chemically similar to those of the Devonian–Carboniferous metasediments. This domain was fed from the metasedimentary host rocks of the magmatic arc. The southern domain probably was fed from the arc proper, as indicated mainly by the dominance of metaplutonic lithic fragments, abundant detrital biotite, and the major element composition of the metasediments.  相似文献   

An implementation of rock engineering system for ranking the instability potential of natural slopes in Greek territory. An application in Karditsa County   总被引：1，自引：0，他引：1  

D. Rozos  L. Pyrgiotis  S. Skias  P. Tsagaratos 《Landslides》2008,5(3):261-270

This paper presents an application of rock engineering system (RES) in an attempt to reveal and assess the inherent instability potential of 388 sites where equivalent landslides have been manifested and recorded in the region of Karditsa County, Greece. The main objective has been defining the principal causative and triggering factors responsible for the manifestation of landslide phenomena, quantify their interactions, obtain their weighted coefficients, and calculate the instability index, which refers to the inherent potential instability of each natural slope of the examined region. From the statistical interpretation of the data reported in a well-documented database and concerning the examined failure sites, a clear correlation between the instability index and the area affected by a single landslide event has been revealed. Almost the entire failure sites, 98% of the examined slope sites, exhibit an instability index value over 55, a value which is thought to be a critical threshold for landslide manifestation concerning natural slopes in Karditsa County. It is argued that the presented RES methodology, engaging the selected set of parameters, could be considered as an effective expert's tool for ranking, in an objectively optimal and simple way, the instability potential of natural slopes in Karditsa County, and thus providing a tool for sound zoning landslide hazard.  相似文献   

Upper Cretaceous carbonate hosted zinc–lead–barite deposits in Northern Thrust Zone, northern Iraq: petrography and geochemistry     

Salih M. Awadh  Habib R. Habib  Khaldoon S. Al-Bassam 《Arabian Journal of Geosciences》2008,1(1):75-85

Zinc–lead–barite deposits located in Lefan and Lower Banik localities of about 25 km northeast of Zakho City, Northern Iraq consist of a group of strata-bound sulfides hosted in Upper Cretaceous (Upper Campanian–Maastrichtian) dolomitic limestone. Carbonate-hosted ores contain 3.77% Zn, 2% Pb, and 5% Fe, while in lower Banik, they contain 1.5% Zn, 0.37% Pb, and 1.4% Fe. Diagenetic processes, such as dolomitization and recrystalization in addition to the type of microfacies, provided appropriate physical and chemical conditions that permitted the passage of ore-bearing fluids and participated in precipitation and ore localization. These deposits are precipitated in a platform and developed within the Foreland Thrust Belt. Ore precipitated as infill of intergranular dolomite porosity with replaced dolomite and rudist shells forming disseminated crystals that occupy intergranular pore spaces around dolomite and calcite and as infill of dissolution spaces and fractures.  相似文献   

Environmental geochemistry of the River Gomti: A tributary of the Ganges River     

L. P. Gupta  V. Subramanian 《Environmental Geology》1994,24(4):235-243

Water and sediment samples collected from the Gomti River, a tributary of the Ganges River system, during the postmonsoon season have been analyzed to estimate major elemental chemistry. Water chemistry of the River Gomti shows almost monotonous spatial distribution of various chemical species, especially because of uniform presence of alluvium Dun gravels throughout the basin. The river annually transports 0.34×10⁶ tonnes of total suspended material (TSM) and 3.0×10⁶ tonnes of total dissolved solids (TDS), 69 percent of which is accounted for by bicarbonate ions only. Samples collected downstream of the city of Lucknow show the influence of anthropogenic loadings for a considerable distance in the river water. Na⁺, Cl^–, and SO₄ ^2– concentrations build up downstream. The bed sediment chemistry is dominated by Si (36 percent), reflecting a high percentage of detrital quartz, which makes up about 74 percent of the mineralogy of the bed sediments in the River Gomti. The average Kjeldahl nitrogen concentration (234 g/g) indicates indirectly the amount of organic matter in the sediments. The Hg concentration in sediments has been found to be higher (average 904 ppb) than the background value. The suspended sediments are well sorted, very finely skewed, and extremely leptokurtic, indicating a low energy condition of flow in the Gomti River. The influence of chemical loads in the Gomti has been found to be small or nonexistent on the Ganges River, perhaps because the water discharge of the Gomti (1.57 percent) to the Ganges is quite low.  相似文献   

内蒙古中西部宝音图群石榴角闪岩的地球化学、变质作用及年代学特征     

姜灵  张晋瑞  唐爽  魏春景  初航 《岩石学报》2021,37(12):3759-3780

宝音图群分布于内蒙古中西部狼山、图古日格和达茂旗一带，主要由云母片岩、石英片岩、石英岩、角闪岩和大理岩组成。在狼山格尔敖包沟和图古日格西南地区发育十分典型的石榴角闪岩，均以似层状或透镜状产自云母片岩中，但两地具有不同的矿物组合，前者主要以石榴石+角闪石+斜长石+含钛矿物（金红石和钛铁矿）为特征，后者主要以石榴石+角闪石+绿帘石+含钛矿物（金红石和钛铁矿）为特征。地球化学研究显示两个地区的石榴角闪岩原岩具有相似的化学组成，均为亚碱性玄武岩的拉斑系列。宝音图群的石榴角闪岩具有右倾的稀土配分模式，REE总量为83.31×10^-6~125.9×10^-6，（La/Yb）_N比值为2.17~6.48，δEu=0.87~0.98。Ta、Nb、Ti没有明显的负异常，其配分型式类似E-MORB特点。微量元素构造判别图解表明这些石榴角闪岩的原岩产于板内拉张环境中。本文通过模拟格尔敖包沟样品LS01和图古日格西南地区样品LS35的P-T视剖面图研究其变质作用及矿物演化过程，结果显示这两个样品均经历了早期进变质，峰期以及峰后近等温减压的顺时针型P-T轨迹。样品LS01的峰期温压条件为~11kbar/~735℃，模拟得到的峰期矿物组合可能为石榴石+角闪石+斜长石+黑云母+透辉石+金红石+熔体，P-M（H₂O）视剖面图显示，由于峰后演化过程中存在饱和流体渗透，导致峰期透辉石无法保留。样品LS35的峰期温度压力条件为~8kbar/675℃，其峰期组合为石榴石+角闪石+绿帘石+金红石。两个地区的石榴角闪岩的温度压力条件明显不同，推测宝音图群中呈透镜体或似层状产出的变质基性岩，存在着递增型的变质作用。锆石LA-ICP-MS U-Pb年代学的研究结果显示石榴角闪岩样品LS01的变质锆石年龄为394±8Ma。由此推测这些石榴角闪岩的原岩可能形成于华北北缘在新元古代发育的裂陷盆地，在泥盆纪中期，宝音图群作为华北克拉通的一部分，被卷入到与古亚洲洋闭合有关的造山过程，发育中压型递增变质作用。  相似文献   

重视和加强岩矿物性的测量研究     

蒋宏耀  张立敏 《地球物理学进展》1995,10(3):118-123

本文从物探科学技术的进步,勘查任务的发展变化、物探方法应用范畴的扩大和物性勘探等几个方面,论述了岩石和矿物物理性质测量、研究的重要性,指出：物性工作不可能毕其功于一役,并提出了五点建议：１．深入研究各类矿藏及其围岩（直至地面）物性的空间变化规律,为选择、研究合适的物探方法,提高物探效果,进一步探讨“直接”找矿问题,提供依据;２．这项工作可专门进行,但最好尽可能利用为其他目的而设计的钻井进行;３．物  相似文献   

Granitoids in the Rozvadov Pluton,Western Bohemia and Oberpfalz     

Karel Breiter  Wolfgang Siebel 《International Journal of Earth Sciences》1995,84(3):506-519

The Rozvadov Pluton is a complex of mainly Variscan granitoid rocks situated near the Bohemian-Bavarian border between Bärnau, Tachov, Rozvadov and Waidhaus, 25 km ESE of the KTB site. Five mappable units can be distinguished, which intruded as folows: (1) slightly deformed leucocratic meta-aplite/metapegmatite dykes with garnet and tourmaline; (2) a complex of cordierite-bearing granitoids, which have been divided into three facies (a) biotite granite with cordierite (at the margin of the complex), (b) biotite-cordierite granite and (c) cordierite tonalite (in the centre of the complex; (3) fine-grained biotite granite of the Rozvadov type with associated pegmatite bodies; (4) two-mica Bärnau granite; and (5) geochemically specialized albite-zinnwaldite-topaz granite (Kríový kámen/Kreuzstein granite) with indications of Sn-Nb-Ta mineralization and associated phosphorus-rich pegmatite cupolas. Rare earth element data suggest that meta-aplite/pegmatite dykes are the result of a batch partial melting process, whereas the compositional variation of the other rock types was mainly controlled by fractional crystallization. The genesis of the cordierite granitoid suite is best explained in terms of a batch melting of metapelitic source followed by crystallization of a cordierite-rich cumulate and K-feldspar enriched melt. The leucocratic pluton constituents — the meta-aplites and the Bärnau and Kíový kámen granites are rich in phosphorus (0.5–0.8%). The main carriers of phosphorus are alkali feldspars, especially K-feldspar (up to 0.8% P₂O₅). The presence of P-rich leucocratic granites is one of the features distinguishing the Variscan granitoids within the Moldanubian zone from the nearly contemporaneous granitoids in the Saxothuringian zone.  相似文献