Cataclastic rheology of carbonate rocks     

LU Xiancai  SUN Yan  SHU Liangshu  GU Lianxing  GUO Jichun & ZHU Wenbin State Key Laboratory of Mineral Deposits Research  Department of Earth Sciences  Nanjing University  Nanjing  China 《中国科学D辑(英文版)》2005,48(8):1227-1233

  相似文献   

The secular variation of inner zone high energy proton environment in the SAA     

XIE Lun  PU Zuyin  JIAO Weixin & FU suiyan Department of Geophysics  Peking University  Beijing  China 《中国科学D辑(英文版)》2005,48(12):2123-2130

The main portion of the inner radiation belt en-countered by spacecraft in low-Earth orbits (LEOs) is concentrated over the South Atlantic Anomaly (SAA) where satellites observed the highest particle flux. The anomaly arises from the Earth’s magnetic field being less intense in the region centered near the east of the Atlantic coast of South America. The trapped radiation belt particles therefore have their lowest mirroring altitudes over the center region of the SAA. Drift shells in t…  相似文献   

Spatial Distribution of Fractures in the Asmari Formation of Iran in Subsurface Environment: Effect of Lithology and Petrophysical Properties     

Nemati  Masoud  Pezeshk  Hamid 《Natural Resources Research》2005,14(4):305-316

The distribution of fractures and its dependence on lithology and petrophysical properties of rock in the Asmari Formation were examined using three wells data of one of the largest oil fields of southwestern Iran. Fractures were measured on cut cores. Mineral content and petrophysical data were obtained through thin section study and core plug measurement respectively. Influence of mineral composition and petrophysical property of rocks on fracture density was explored statistically. Increasing quartz (sand) and anhydrite content of rocks decrease and dolomite increases the threshold of fracture densities, however no significant relation was observed between calcite content of rock and fracture density. Increasing porosity and permeability of rock decrease the threshold of fracture density in some of the defined lithology groups. There are significant differences between the lithology groups in terms of fracture density, although the results in the three wells are not the same. In whole data, the highest fracture density can be observed in dolostone. Limestone and impure carbonates hold broader spaced fractures and sandstones display the least fracture density. The average fracture densities in the wells are strictly different. These differences are the result of the structural position of the wells and also the trend of the well and fractures. The distribution of fractures in most lithology groups can be explained by the function: , where F is relative frequency, D is fracture density and a, b, and c are constants.  相似文献   

Dehydration melting, fluid buffering and decompressional P–T path in a granulite complex from the Eastern Ghats, India     

S. DASGUPTA  P. SENGUPTA  M. FUKUOKA  S. CHAKRABORTI 《Journal of Metamorphic Geology》1992,10(6):777-788

A suite of metapelites, charnockites, calc-silicate rocks, quartzo-feldspathic gneisses and mafic granulites is exposed at Garbham, a part of the Eastern Ghats granulite belt of India. Reaction textures and mineral compositional data have been used to determine the P–T–X evolutionary history of the granulites. In metapelites and charnockites, dehydration melting reactions involving biotite produced quartzofeldspathic segregations during peak metamorphism. However, migration of melt from the site of generation was limited. Subsequent to peak metamorphism at c . 860° C and 8 kbar, the complex evolved through nearly isothermal decompression to 530–650° C and 4–5 kbar. During this phase, coronal garnet grew in the calc-silicates, while garnet in the presence of quartz broke down in charnockite and mafic granulite. Fluid activities during metamorphism were internally buffered in different lithologies in the presence of a melt phase. The P–T path of the granulites at Garbham contrasts sharply with the other parts of the Eastern Ghats granulite belt where the rocks show dominantly near-isobaric cooling subsequent to peak metamorphism.  相似文献   

The Alpine Rif Belt (Morocco): A Case of Mountain Building in a Subduction-Subduction-Transform Fault Triple Junction     

A.?Chalouan  A.?MichardEmail author 《Pure and Applied Geophysics》2004,161(3):489-519

—The Rif belt forms with the Betic Cordilleras an asymmetric arcuate mountain belt (Gibraltar Arc) around the Alboran Sea, at the western tip of the Alpine orogen. The Gibraltar Arc consists of an exotic terrane (Alboran Terrane) thrust over the African and Iberian margins. The Alboran Terrane itself includes stacked nappes which originate from an easterly, Alboran-Kabylias-Peloritani-Calabria (Alkapeca) continental domain, and displays Variscan low-grade and high-grade schists (Ghomarides-Malaguides and Sebtides-Alpujarrides, respectively), shallow water Mesozoic sediments (mainly in the Dorsale Calcaire passive margin units), and infracontinental peridotite slices (Beni Bousera, Ronda). During the Late Cretaceous?-Eocene, the Alboran Terrane was likely located south of a SE-dipping Alpine-Betic subduction (cf. Nevado-Filabride HP-LT metamorphism of central-eastern Betics). An incipient collision against Iberia triggered back-thrust tectonics south of the deformed terrane during the Late Eocene-Oligocene, and the onset of the NW-dipping Apenninic-Maghrebian subduction. The early, HP-LT phase of the Sebtide-Alpujarride metamorphism could be hypothetically referred to the Alpine-Betic subduction, or alternatively to the Apenninic-Maghrebian subduction, depending on the interpretation of the geochronologic data set. Both subduction zones merged during the Early Miocene west of the Alboran Terrane and formed a triple junction with the Azores-Gibraltar transform fault. A westward roll back of the N-trending subduction segment was responsible for the Neogene rifting of the internal Alboran Terrane, and for its coeval, oblique docking onto the African and Iberian margins. Seismic evidence of active E-dipping subduction, and opposite paleomagnetic rotations in the Rif and Betic limbs of the Gibraltar Arc support this structurally-based scenario.  相似文献   

Criteria for defining and recognizing the various orders of sequences in outcrop sequence stratigraphy     

WANG Xunlian Faculty of Earth Sciences  Mineral Resources  China University of Geosciences  Beijing  China  State Key Laboratory of Palaeobiology  Stratigraphy  Nanjing Institute of Geology  Palaeontology  Chinese Academy of Sciences  Nanjing  China 《中国科学D辑(英文版)》2004,47(7):618-629

Sequence stratigraphy which began in the late seventies of the previous century has not only enriched and widened the scope of stratigraphy, but also has been widely used in sedimentary geology, basin analy-sis, exploration of oil and gas, and other fields of ge-ology. In the last two decades and more, sequence stratigraphy, as a new branch of stratigraphical disci-pline, has become a cornerstone of modern stratigra-phy, and has produced more profound influences than all others. The currently …  相似文献   

The granite hosted gold deposit of Moulin de Chéni (Saint-Yrieix district,Massif Central,France): petrographic,structural, fluid inclusion and oxygen isotope constraints     

Jean?VallanceEmail author  Marie-Christine?Boiron  Michel?Cathelineau  Serge?Fourcade  Michel?Varlet  Christian?Marignac 《Mineralium Deposita》2004,39(3):265-281

The Moulin de Chéni orogenic gold deposit is the only granite-hosted deposit of the Saint-Yrieix district, French Massif Central. It occurs in 338±1.5 Ma-old peraluminous leucogranites and is characterized by intense microfracturing and bleaching of the granite in relation to pervasive sulfide crystallization. Formation of quartz veins and gold deposition occurred in two successive stages: an early mesozonal stage of quartz-sulfide (Fe-As-S) deposition, usually devoid of gold and a late epizonal stage of base metal and gold deposition. Both stages postdate peak metamorphism and granite intrusion. The genesis of the deposit is the result of four successive fluid events: (1) Percolation of aqueous-carbonic metamorphic fluids under an assumed lithostatic regime of 400–450 °C, at a maximum depth of 13 km; (2) Formation of the main quartz lodes with coeval K-alteration and introduction of As and S from aqueous-carbonic fluids percolating along regional faults. Arsenopyrite and pyrite deposition was linked to the alteration of Fe-silicates into K-feldspar and phengite at near-constant iron content in the bulk granite. Temperature was similar to that of the preceding stage, but pressure decreased to 100–50 MPa, suggesting rapid uplift of the basement up to 7.5 km depth; (3) The resulting extensional tectonic leads to the deposition of gold, boulangerite, galena and sphalerite in brecciated arsenopyrite and pyrite from aqueous fluids during a mixing process. Temperature and salinity decrease from 280 to 140 °C and 8.1 wt% eq. NaCl to 1.6 wt% eq. NaCl, respectively; (4) Sealing of the late fault system by barren comb quartz which precipitated from dilute meteoric aqueous fluids (1.6 wt% eq. NaCl to 0.9 wt% eq. NaCl) under hydrostatic conditions at 200–150 °C.Editorial handling: B. Lehmann  相似文献   

Neoproterozoic and Cambro-Ordovician magmatism in the Variscan Kłodzko Metamorphic Complex (West Sudetes,Poland): new insights from U/Pb zircon dating     

Stanis?aw?MazurEmail author  Krzysztof?Turniak  Michael?Br?cker 《International Journal of Earth Sciences》2004,93(5):758-772

The Kodzko Metamorphic Complex (KMC) in the Central Sudetes consists of meta-sedimentary and meta-igneous rocks metamorphosed under greenschist to amphibolite facies conditions. They are comprised in a number of separate tectonic units interpreted as thrust sheets. In contrast to other Lower Palaeozoic volcano-sedimentary successions in the Sudetes, the two uppermost units (the Orla-Googowy unit and the Kodzko Fortress unit) of the KMC contain meta-igneous rocks with supra-subduction zone affinities. The age of the KMC was previously assumed to be Early Palaeozoic–Devonian, based on biostratigraphic findings in the lowermost tectonic unit. Our geochronological study focused on the magmatic rocks from the two uppermost tectonic units, exposed in the SW part of the KMC. Two orthogneiss samples from the Orla-Googowy unit yielded ages of 500.4±3.1 and 500.2±4.9 Ma, interpreted to indicate the crystallization age of the granitic precursors. A plagioclase gneiss from the same tectonic unit, intimately interlayered with metagabbro, provided an upper intercept age of 590.1±7.2 Ma, which is interpreted as the time of igneous crystallization. From the topmost Kodzko Fortress unit, a metatuffite was studied, which contains a mixture of genetically different zircon grains. The youngest ²⁰⁷Pb/²⁰⁶Pb ages, which cluster at ca. 590-600 Ma, are interpreted to indicate the maximum depositional age for this metasediment. The results of this study are in accord with a model that suggests a nappe structure for the KMC, with a Middle Devonian succession at the base and Upper Proterozoic units at structurally higher levels. It is suggested here that the KMC represents a composite tectonic suture that juxtaposes elements of pre-Variscan basement, intruded by the Lower Ordovician granite, against a Middle Palaeozoic passive margin succession. The new ages, combined with the overall geochemical variation in the KMC, indicate the existence of rock assemblages representing a Gondwana active margin. The recognition of Neoproterozoic subduction-related magmatism provides additional arguments for the hypothesis that equivalents of the Teplá-Barrandian domain are exposed in the Central Sudetes.  相似文献   

Événements panafricains dans l'Adrar Souttouf (Sahara marocain)     

Michel Villeneuve  Hervé Bellon  Abdelkrim El Archi  Mohamed Sahabi  Jean-Pierre Rehault  Jean-Louis Olivet  Abdel M. Aghzer 《Comptes Rendus Geoscience》2006,338(5):359-367

The Adrar Souttouf belt (Western Sahara) lies in the northern part of the Mauritanide belt and was considered as a part of the Hercynian Mauritanian-Appalachian belt. Recently the presence of a Panafrican protolith (595 Ma) was evidenced by the age of inherited zircons from an eclogitic unit and led to consider complex Panafrican events included in the Hercynian belt, as in the central and southern Mauritanide belt. Our new field survey completed by ten KAr dating (whole rocks and separate minerals) confirmed that multiphased Panafrican formations outcrop within the center of the Adrar Souttouf massif. Diverse events ranged from ca. 1000 to 500 Ma, some of them being indicative of an oceanic type environment and metamorphism. The 1000 Ma metamorphic event is recorded for the first time in the West African craton. A large Hercynian remobilisation is also evidenced. To cite this article: M. Villeneuve et al., C. R. Geoscience 338 (2006).  相似文献   

辽宁沿海经济带工业环境效率分析   总被引：10，自引：3，他引：7  

佟连军  宋亚楠  韩瑞玲  李名升 《地理科学》2012,(3):294-300

环境效率是生态效率的重要组成部分。基于环境效率对于指导区域经济与环境协调发展的重要意义,以重工业基地辽宁沿海经济带为例作环境效率研究,应用数据包络分析(DEA)和随机前沿分析(SFA)测算辽宁沿海经济带2001~2009年工业环境效率和产出弹性。在此基础上利用Tobit模型构建多元线性回归,分析工业环境效率的关键影响因素。结果表明:2001~2009年辽宁沿海经济带工业环境效率有大幅提高,但与理想状况仍有一定差距。其中大连的工业经济增长主要依靠劳动力推动,对环境成本的依赖正在减小,丹东、营口和葫芦岛3市的工业增长需要牺牲更多的环境成本。重工业化、资本密集化和高新技术化不利于工业环境效率提高,经济发展水平的提高则极大地促进了工业环境效率的提高。所有制结构、生产规模、外商投资和环境管理力度等因素因其作用的两面性,对工业环境效率无有效影响。  相似文献