WorldWideScience

Sample records for surrounding metamorphic rocks

  1. Metamorphic Rocks in West Irian

    NARCIS (Netherlands)

    Wegen, van der G.

    1971-01-01

    Low-grade metamorphics of West Irian occur to the east of Geelvink Bay associated with two narrow belts of basic and ultrabasic igneous rocks which represent ophiolitic suites of an eugeosynclinical development beginning in Early Mesozoic time. In both of these belts there are indications of regiona

  2. Low grade metamorphism of mafic rocks

    Science.gov (United States)

    Schiffman, Peter

    1995-07-01

    Through most of this past century, metamorphic petrologists in the United States have paid their greatest attention to high grade rocks, especially those which constitute the core zones of exhumed, mountain belts. The pioneering studies of the 50's through the 80's, those which applied the principles of thermodynamics to metamorphic rocks, focused almost exclusively on high temperature systems, for which equilibrium processes could be demonstrated. By the 1980's, metamorphic petrologists had developed the methodologies for deciphering the thermal and baric histories of mountain belts through the study of high grade rocks. Of course, low grade metamorphic rocks - here defined as those which form at pressures and temperatures up to and including the greenschist facies - had been well known and described as well, initially through the efforts of Alpine and Circum-Pacific geologists who recognized that they constituted an integral and contiguous portion of mountain belts, and that they underlay large portions of accreted terranes, many of oceanic origins. But until the mid 80's, much of the effort in studying low grade rocks - for a comprehensive review of the literature to that point see Frey (1987) - had been concentrated on mudstones, volcanoclastic rocks, and associated lithologies common to continental mountain belts and arcs. In the mid 80's, results of the Deep Sea Drilling Project (DSDP) rather dramatically mitigated a shift in the study of low grade metamorphic rocks.

  3. Petrology of blueschist facies metamorphic rocks of the Meliata Unit

    Directory of Open Access Journals (Sweden)

    Faryad Shah Wali

    1997-06-01

    Full Text Available Meliata blueschists originated from basalts, limestones, pelites, psammitic and amphibolite facies basement rocks. Compositionally, the metabasalts have a geochemical signature mostly indicative of a transitional arc-MORB origin, but some mafic rocks having affinity with within plate basalts also present. The mafic blueschists consist of blue amphibole, epidote and albite, rarely also garnet, Na-pyroxene and chloritoid. Apart from phengite and quartz the metapelites and metapsammites contain one or more of the minerals: chloritoid, paragonite, glaucophane, albite, chlorite, occasionally also Na-pyroxene and garnet. Amphibolite facies rocks contain relic garnet, plagioclase and hornblende, the latter two replaced by albite and blue amphibole, respectively. The zoning patterns of blue amphibole, garnet and chloritoid suggest their formation during prograde stage of metamorphism. P-T conditions of meta-morphism are estimated to be about 350-460 oC and 10-12 kbar.

  4. Chlorine isotope behavior during prograde metamorphism of sedimentary rocks

    Science.gov (United States)

    Selverstone, Jane; Sharp, Zachary D.

    2015-05-01

    Chlorine stable isotope compositions of two sedimentary sequences and their metamorphic equivalents were measured in order to study fractionation effects during prograde metamorphism and devolatilization. Protoliths (n = 25) were collected from a 50 m section of Triassic fluvial and playa-lake strata and Jurassic (Liassic) marine black shales in a well-characterized quarry. Low greenschist to middle amphibolite facies equivalents (n > 80) were collected from the Glarus Alps, Urseren Zone, and Lucomagno region. Bulk δ37Cl values are constant within individual sedimentary layers, but vary from -2.0 to + 2.4 ‰ in Triassic rocks and from -3.0 to 0‰ in the black shales. Dolomitic and gypsiferous samples have positive δ37Cl values, but marls and shales are isotopically negative. Bulk Cl contents show only small declines during the earliest stages of metamorphism. Metamorphic equivalents of the Triassic and Liassic protoliths record the same overall ranges in δ37Cl as their protoliths. Samples with highly correlated bulk compositions but different metamorphic grade show no statistically significant difference in δ37Cl. These data lead to the following conclusions: (1) Terrestrial and marine sedimentary rocks display large primary heterogeneities in chlorine isotope composition. As a result, an unambiguous "sedimentary signature" does not exist in the chlorine stable isotope system. (2) No isotopic fractionation is discernable during metamorphic devolatilization, even at low temperatures. Alpine-style metamorphism thus has little to no effect on bulk chlorine isotopic compositions, despite significant devolatilization. (3) Cl is largely retained in the rocks during devolatilization, contrary to the normally assumed hydrophilic behavior of chlorine. Continuous release of mixed-volatile C-O-H fluids likely affected Cl partitioning between fluid and minerals and allowed chlorine to remain in the rocks. (4) There is no evidence for fluid communication across (meta

  5. Burial metamorphism in rocks of the Western Andes of Peru

    Science.gov (United States)

    Offler, R.; Aguirre, L.; Levi, B.; Child, S.

    1980-01-01

    An unconformity bound, episodic pattern of burial metamorphism is preserved in marine and terrestrial volcanic and sedimentary rocks which were deposited in the West Peruvian Trough during the Mesozoic and Cenozoic Eras. A particular metamorphic facies series is developed in each of the stratigraphic-structural units bounded by unconformities. In each unit, grade increases with stratigraphic depth and covers part or all of the range from zeolite to greenschist facies. At every unconformity a mineralogic break occurs where higher grade assemblages on top of the unconformity plane overlie lower grade assemblages. The presence of wairakite and the development of a wide range of metamorphic facies in thin sequences suggest high geothermal gradients, possibly related to generation of magma at depth.

  6. Metamorphic rocks in the deep boreholes near Maribor

    Directory of Open Access Journals (Sweden)

    Mirka Trajanova

    2002-12-01

    Full Text Available Six research-captive boreholes for thermal water passed through a pile of metamorphic rocks near Maribor (Eastern Slovenia that is on average about 1000 m thick. The succession of metamorphic rocks is characteristic for the Pohorje Mt. and eastern Kobansko region. In the area of the boreholes two tectonic zones are more pronounced: the upper one, at a depth of about 510 to 550 m at the contact of the Štelenska Gora and Phyllite formations and the deeper one at a depth of about 460 to 590 m, indicating the reverse fault junction of the Phyllite and Kobansko formations. They belong to the second andthe third thrust unit of the accretionary wedge formed at the collision of the European and African plates. Four Alpine nappe units are proven in the Slovenian part of the Eastern Alps.

  7. Nitrogen determination in micas of metamorphic rocks

    Energy Technology Data Exchange (ETDEWEB)

    Ager, F.J. [Depto. Fisica Aplicada I, Escuela Universitaria Politecnica, Universidad de Sevilla, C. Virgen de Africa 7, E-41011 Sevilla (Spain) and Centro Nacional de Aceleradores, Av. Thomas A. Edison, E-41092 Sevilla (Spain)]. E-mail: fjager@us.es; Mata, M.P. [Depto. Geologia, Fac. Ciencias del Mar y Ambientales, Campus Rio San Pedro, s/n, E-11510 Puerto Real, Cadiz (Spain); Ynsa, M.D. [Centre d' Etudes Nucleaires de Bordeaux-Gradignan, IN2P3-CNRS, BP 120, 33175 Gradignan Cedex (France); Respaldiza, M.A. [Centro Nacional de Aceleradores, Av. Thomas A. Edison, E-41092 Sevilla (Spain); Goffe, B. [UMR 8538, Lb. Geologie, ENS, 24, Rue Lhomond, F-75231 Paris Cedex 05 (France); Nieto, F. [Dpto. Mineralogia y Petrologia, Fac. Ciencias, Av. Fuentenueva s/n, E-18002 Granada (Spain)

    2006-08-15

    Micas are minerals that provide large amounts of information regarding geological processes, because of the sensitivity of their chemical composition to temperature, pressure and deformation of rocks in which they form. Rocks under analysis are formed of different minerals with variable grain size. Mica grain size may vary between 5 and 10 {mu}m and approximately correspond to the chemical formula (Si{sub 3.2}Al{sub 0.8})O{sub 10}(Al{sub 1.9}Fe{sub 0.05}Mg{sub 0.1})(OH){sub 2}(K{sub 0.75}Na{sub 0.05}), being distinguishable from other minerals because of their composition and their morphology in secondary electron images and specially backscattered electron (BSE) images. NH{sub 4}, when present, would partially substitute K in the previous formula. In some cases NH{sub 4}-rich micas (tobelites) have been described coexisting with the corresponding K-rich micas, but the actual NH{sub 4} content of normal K-rich micas is still unknown. Low N content makes necessary to use nuclear reactions such as {sup 14}N(d, p{gamma}){sup 15}N at 1.4 MeV and its cascade of intense {gamma}-rays. For the quantification and localization of nitrogen on the surface of the samples, PIGE analysis was carried out in the vacuum microprobe line of the CNA, together with simultaneous micro-RBS and micro-PIXE analyses, giving a more comprehensive picture of sample structure and composition.

  8. REE Geochemistry of Precambrian Metamorphic Rocks in Wutaishan Region

    Institute of Scientific and Technical Information of China (English)

    吴素珍

    1989-01-01

    The metasedimentary-volcanic series of the Wutai and Hutuo groups experienced regional metamorphism and thus turned into moderate-to low-grade metamorphic rocks.REE abundances and REE distribution patterns in the Shizui and Taihuai Subgroup metasedimentary-volcanic rocks are typical of the Archean,whereas the Gaofan Subgroup and the Hutuo Group show post-Archean REE geochemical char-acteristics.Five types of REE distribution pattern are distinguished:(1)rightward inclined smooth curves with little REE anomaly(Eu/Eu*=0.73-0.95) and heavy REE depletion (e.g.the Late Archean metasedimentary rocks);(2)rightward inclined V-shaped curves with sharp Eu anoma-ly (Eu/Eu*=0.48-0.76) and slightly higher ∑REE (e.g.the post-Archean metasedimentary rocks);(3) rightward inclined steep curves with negative Eu anomaly(Eu/Eu*=0.73-0.76) and the lowest ∑REE (e.g.the post-Archean dolomites);(4)rightward inclined,nearly smooth curves with both positive Eu anomaly and unremarkable positive Eu anomaly(Eu/Eu*=0.95-1.25)(e.g.the meta-basic volcanic rocks);and (5) rightward inclined curves with Eu anomaly(Eu/Eu*=1.09-1.19)and heavy REE depletion(e.g.the meta-acid volcanic rocks).Strata of the two groups are considered to have been formed in an island-arc belt-an instable continental petrogenetic environment.

  9. Morphological preservation of carbonaceous plant fossils in blueschist metamorphic rocks from New Zealand.

    Science.gov (United States)

    Galvez, M E; Beyssac, O; Benzerara, K; Bernard, S; Menguy, N; Cox, S C; Martinez, I; Johnston, M R; Brown, G E

    2012-03-01

    Morphological and chemical evidence of ancient life is widespread in sedimentary rocks retrieved from shallow depths in the Earth's crust. Metamorphism is highly detrimental to the preservation of biological information in rocks, thus limiting the geological record in which traces of life might be found. Deformation and increasing pressure/temperature during deep burial may alter the morphology as well as the composition and structure of both the organic and mineral constituents of fossils. However, microspore fossils have been previously observed in intensely metamorphosed rocks. It has been suggested that their small size, and/or the nature of the polymer composing their wall, and/or the mineralogy of their surrounding matrix were key parameters explaining their exceptional preservation. Here, we describe the remarkable morphological preservation of plant macrofossils in blueschist metamorphic rocks from New Zealand containing lawsonite. Leaves and stems can be easily identified at the macroscale. At the microscale, polygonal structures with walls mineralized by micas within the leaf midribs and blades may derive from the original cellular ultrastructure or, alternatively, from the shrinkage during burial of the gelified remnants of the leaves in an abiotic process. Processes and important parameters involved in the remarkable preservation of these fossils during metamorphism are discussed. Despite the excellent morphological preservation, the initial biological polymers have been completely transformed to graphitic carbonaceous matter down to the nanometer scale. This occurrence demonstrates that plant macrofossils may experience major geodynamic processes such as metamorphism and exhumation involving deep changes and homogenization of their carbon chemistry and structure but still retain their morphology with remarkable integrity even if they are not shielded by any hard-mineralized concretion.

  10. Survey yields data on unique metamorphic rock complex in China

    Science.gov (United States)

    Schulze, A.; Jiang, M.; Ryberg, T.; Gao, R.

    Seismic data from survey work last year in Dabie Shan, China, are giving scientists their first view of the subsurface structure of a unique metamorphic rock complex. The work, in which a joint Chinese-German research team surveyed possible sites for a super deep borehole, set the stage for more intensive petrological and seismic investigations this year and next.Data were collected by near-vertical seismic imaging at Dabie Shan, the Earth's largest outcrop of ultra-high pressure metamorphic (UHM) rocks, some exhumed from depths of 100 km. Processing so far has revealed unexpectedly strong mid-and lower-crustal reflections, predominantly dipping west to east, indicating the involved tectonic history of the region. Upcoming research will look more closely at the three-dimensional structure of the rock and other matters. Scientific deep drilling is essential in addressing a wide range of major geoscientific problems of global importance. The International Continental Scientific Drilling Programme (ICDP) coordinates such, and one key target of ICDP is the Dabie Shan. To find the most appropriate location for a drill site and to extend the findings of the drilling beyond the drill hole, geophysical methods, especially seismic investigations, play an important role. Integrated interpretation of seismic and drill results in the Dabie Shan will lead to a better understanding of the structure and dynamic processes of the collisional history of the Yangtze and Sino-Korean Cratons. The Dabie Shan is located in the eastern part of the Qinling orogen in Anhui province, central China. The rocks there contain microdiamonds and coesite within a 20-km-thick eclogite zone representing a part of the lower lithosphere of the Yangtze Craton [Okay, 1993]. Such rocks suggest that continental crust had been subducted to depths greater than 100 km and exhumed afterwards [Hackeretal, 1995].

  11. Formation Mechanism and Exhumation Processes for HP-UHP Metamorphic Rocks in Dabie Mountains

    Institute of Scientific and Technical Information of China (English)

    Hou Mingjin; Tang Jiafu

    2004-01-01

    The high, ultrahigh pressure metamorphic rocks, widely distributed in Dabie Mountains, were described in terms of the geological setting, the marks of the petrology and the mineralogy of the ultrahigh pressure (UHP) metamorphic rocks. According to the estimated uplifting and denudation of the Dabie Mountains, and to the thermodynamics theory, were assessed the depth and pressure (high pressure autoclave) of the formation setting of the UHP metamorphic rocks. Based on all the information mentioned above, a new explanation is derived from the mechanism of formation and the processes of exhumation of the UHP metamorphic rocks.

  12. Possible polyphase metamorphic evolution of high grade metabasic rocks from the Songshugou ophiolite, Qinling orogen, China

    Science.gov (United States)

    Belic, Maximilian; Hauzenberger, Christoph; Dong, Yunpeng; Chen, Danling

    2014-05-01

    The Proterozoic Songshugou ophiolite consists of a series of ultrabasic and tholeitic metabasic rocks. They were emplaced as a lense shaped body into the southern margin of the Qinling Group. Isotope composition and trace element geochemistry display an E-MORB and T-MORB signature for the mafic rocks (Dong et al., 2008). Within the ophiolite sequence some rudimental fresh peridotites (dunites and harzburgites) within serpentines display low CaO (non-fertile mantle rocks. The metabasic rocks comprise the mineral assemblage garnet, amphibole, symplectitic pyroxenes, ilmenite, apatite, ±zoisite, ±sphene and show a strong retrograde metamorphic overprint. Garnet typically contains many inclusions within the core but are nearly inclusion free at the rim. The cores have sometimes snowball textures indicating initially syndeformative growth. Albite and prehnite were found in central parts of garnet. In the outer portions, pargasitic amphibole, rutile and a bluish amphibole, probably glaukophane were found. Garnet zoning pattern clearly show a discontinous growth seen in an sudden increase in grossular and decrease in almandine components. The symplectitic pyroxenes are of diopsidic composition which enclose typically prehnite and not albite, as common in retrograde eclogitic rocks. Different stages of garnet breakdown to plagioclase and amphibole, from thin plagioclase rims surrounding the garnets to plagioclase rich pseudomorphs, can be observed in different samples. Based on symplectitic pyroxenes a high pressure metamorphic event can be concluded (Zhang, 1999). The garnet breakdown to plagioclase and the symplectites clearly indicate a rapid exhumation phase. The age of the metamorphic event is probably related to the closure of the Shangdan ocean during the early Paleozoic. It is unclear if the garnet rims grew during a later stage of the metamorphic cycle or developed during a separate event. The financial support by Eurasia-Pacific Uninet is gratefully

  13. Nano-texture of penetrative foliation in metamorphic rocks

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    By observing four samples obtained from Jiangxi Province, China, under the scanning electron mi-croscope (SEM), we discovered that nano-particle layers were commonly formed on sliding planes of the penetrative foliation in metamorphic rocks. We also successfully reproduced this phenomenon with a tri-axial pressure experiment. Having gone through the granulitization-alienation-partition in the shear sliding process, the nano-particles (40-95 nm in diameter) display different individual shapes and dis-tinct layered textures. This nano-confinement layer is essentially a frictional-viscous stripe with vis-cous-elastic deformation. In the micro-domain stripe, activities in structural stress field-rheological physical field-geochemical field are very dynamic, corresponding to the three stages (i.e., shear sliding strengthening-weakening-exfoliating) of the foliation development in metamorphism rocks. As such, the viscous-elastic deformation behavior helps shed light on the understanding of the micro-dynamic mechanism of the structural shearing.

  14. Rheologic Transitions During Exhumation of High-Pressure Metamorphic Rocks

    Science.gov (United States)

    Whitney, D. L.; Teyssier, C. P.; Rey, P. F.

    2015-12-01

    The exhumation of deeply buried rocks typically involves dynamic feedbacks between deformation and metamorphic reactions (+ fluid and/or melt) that influence rheology and facilitate or drive large-magnitude exhumation. The evolution of grain-scale to terrane-scale processes during decompression can be seen in rocks exhumed from oceanic and continental subduction and from orogenic crust. In the Sivrihisar (Turkey) high-P/low-T (oceanic subduction) complex, microstructures record deformation and syn-kinematic reactions during decompression from eclogite to blueschist facies conditions; this transformation resulted in dramatic strength reduction that promoted strain localization along the subduction interface. In quartz-rich rocks, qz was deformed in the dislocation creep regime and records transitions in microstructure and slip systems during near-isothermal decompression from 2.5 to 1.5 GPa; these transitions may be related to decreasing water fugacity over tens of km of decompression. High-to ultrahigh-P eclogite in exhumed continental subduction zones such as the Western Gneiss Region (Norway) record decompression from >2.5 GPa to crust, upper crustal extension/transtension drives rapid ascent of the deep crust to form migmatite-cored domes. The exhuming deep crust entrains HP relics such as eclogite (e.g. Montagne Noire dome, France) as it traverses much of the orogenic crust, from >1.2 GPa to (in some cases) crust reaches the near-surface. In summary, decompression of subducted or deeply buried crust systematically leads to rheologic transitions and feedbacks between deformation and metamorphism in the presence of aqueous fluid and/or melt.

  15. Thermal evolution of high-pressure metamorphic rocks in the Alps

    NARCIS (Netherlands)

    Brouwer, F.M.

    2000-01-01

    There are two major and currently unresolved issues in Alpine geology concerning the metamorphic evolution of the rocks in the internal zones of the Alps. First, rocks showing evidence for geologically young, high-pressure to very high-pressure metamorphism are now exposed at the Earth's surface, im

  16. Thermal evolution of high-pressure metamorphic rocks in the Alps

    NARCIS (Netherlands)

    Brouwer, F.M.

    2000-01-01

    There are two major and currently unresolved issues in Alpine geology concerning the metamorphic evolution of the rocks in the internal zones of the Alps. First, rocks showing evidence for geologically young, high-pressure to very high-pressure metamorphism are now exposed at the Earth's surface, im

  17. Formation history and protolith characteristics of granulite facies metamorphic rock in Central Cathaysia deduced from U-Pb and Lu-Hf isotopic studies of single zircon grains

    Institute of Scientific and Technical Information of China (English)

    YU Jinhai; ZHOU Xinmin; Y. S. O'Reilly; ZHAO Lei; W. L. Griffin; WANG Rucheng; WANG Lijuan; CHEN Xiaomin

    2005-01-01

    The petrochemical as well as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Taoxi Group in eastern Nanling Range, Central Cathaysia indicate that its protolith is the sedimentary rock with low maturation index. The clastic materials are mostly from middle Neoproterozoic (~736 Ma) granitoid rocks with minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement with the second period of magmatism widespread surrounding the Yangtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recycled Paleoproterozoic mantle-derived crustal materials. The sedimentary rock was deposited in Late Neoproterozoic Era, and carried into low crust in Early Paleozoic. The partial melting of the meta-sedimentary rock took place at about 480 Ma and subsequently granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval (Early Paleozoic) show large Hf isotope variations, and their -Hf(t) values increase from -13.2 to +2.36 with decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early Paleozoic. Calculation results show that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby Mesozoic high Si peraluminous granites, implying that this kind of granulite facies metamorphic rock is probably the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range.

  18. [Myanmar jadeitite low-temperature metamorphic water-rock reaction: eveidence from microscopic fourier transform infrared spectroscopy].

    Science.gov (United States)

    Yan, Ruo-Gu; Qiu, Zhi-Li; Feng, Ming; Jin, Chun-Mei; Li, Liu-Fen; Shi, Gui-Yong; Wang, Ping

    2014-09-01

    Weathering & transporting and depositing processes may improve the quality of some natural low-quality jadeite through reaction with surrounding water fluids. But the mechanism of such water-rock reaction has not been known clearly to date. Applying microscopic Fourier transform infrared spectroscopy (Micro-FTIR), this paper carried out comparatively in-situ research of jadeites' mineral composition before and after water-rock reaction. The results show that water-rock reaction cannot impact jadeites in their major and minor element composition, but greatly change their water content. Jadeites became richer, with even several times increase, in water content, after experiencing water-rock reaction, and hence show a shift of absorption peak at 3 550 cm(-1) to higher frequency. The mineral crystals of these jadeites showed reglar variation in water content from core to edge, and these jadeites have more water in marginal area than in center area, being opposite to the change in water content in jadeite during high temperature and pressure metamorphic process, hence implying that there are different mechanism and shift direction for H+/OH of jadeite between high pressure metamorphic process and low temperature water-rock reaction. We think that this finding may contribute to understanding the behavior of water in jadeite during metamorphic process and the mechanism of jadeite quality improvement.

  19. Catastrophe mechanism and disaster countermeasure for soft rock roadway surrounding rock in Meihe mine

    Institute of Scientific and Technical Information of China (English)

    Yu Yang⇑; Zhu Caikun; Chong Deyu; Liu Yang; Li Sichao

    2015-01-01

    The soft rock’s heterogeneity and nonlinear mechanical behavior cause extremely difficult maintenance on the soft rock roadway. Aiming at the asymmetric deformation and destruction phenomenon appearing after excavating and supporting the 7101 air return way in Meihe mine, this paper comprehensively adopted a variety of methods to analyze the roadway surrounding rock deformation rule, obtaining the roadway surrounding rock stress and plastic zone distribution rule under no supporting condition and the roadway surrounding rock deformation features under original symmetric supporting condition. Furthermore, this paper revealed the catastrophe mechanism, and proposed the concept of‘weak struc-ture’ and the disaster countermeasure of‘overall stabilizing the roadway and strengthening the support of weak structure’ . The industrial test shows that the disaster control technology can realize the coordination deformation of the supporting structure and roadway surrounding rock, thus significantly controlling the deformation of roadway surrounding rock.

  20. Rock relationships in the Mogok metamorphic belt, Tatkon to Mandalay, central Myanmar

    Science.gov (United States)

    Mitchell, A. H. G.; Htay, Myint Thein; Htun, Kyaw Min; Win, Myint Naing; Oo, Thura; Hlaing, Tin

    2007-03-01

    The Mogok metamorphic belt (MMB), over 1450 km long and up to 40 km wide, consists of regionally metamorphosed rocks including kyanite and sillimanite schists and granites lying along the Western margin of the Shan Plateau in central Myanmar and continuing northwards to the eastern Himalayan syntaxis. Exposures in quarries allow correlation of Palaeozoic meta-sedimentary, early Mesozoic meta-igneous and late Mesozoic intrusive rocks within a 230 km long northerly-trending segment of the MMB, from Tatkon to Kyanigan north of Mandalay, and with the Mogok gemstone district 100 km to the northeast. Relationships among the metamorphic and intrusive rocks, with sparse published radiometric age controls, indicate at least two metamorphic events, one before and one after the intrusion of Late Jurassic to early Cretaceous calc-alkaline rocks. These relationships can be explained by either of two possible tectonic histories. One, constrained by correlation of mid-Permian limestones across Myanmar, requires early Permian and early Jurassic regional metamorphic events, prior to an early Tertiary metamorphism, in the western part of but within a Shan-Thai - western Myanmar block. The second, not compatible with a single laterally continuous Permian limestone, requires pre-Upper Jurassic regional metamorphism and orogenic gold mineralization in the Mergui Group and western Myanmar, early Cretaceous collision of an east-facing Mergui-western Myanmar island arc with the Shan Plateau, and early Tertiary metamorphism in the MMB related to reversal in tectonic polarity following the arc-Plateau collision.

  1. Different origins of garnet in high pressure to ultrahigh pressure metamorphic rocks

    Science.gov (United States)

    Xia, Qiong-Xia; Zhou, Li-Gang

    2017-09-01

    Garnet in high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in subduction zone commonly shows considerable zonation in major and trace elements as well as mineral inclusions, which bears information on its growth mechanism via metamorphic or peritectic reactions in coexistence with relic minerals and metamorphic fluids or anatectic melts at subduction-zone conditions. It provides an important target to retrieve physicochemical changes in subduction-zone processes, including those not only in pressure and temperature but also in the durations of metamorphism and anatexis. Garnet from different compositions of HP to UHP metamorphic rocks may show different types of major and trace element zonation, as well as mineral inclusions. Discrimination between the different origins of garnet provides important constraints on pressure and temperature and the evolution history for the HP to UHP metamorphic rocks. Magmatic garnet may occur as relics in granitic gneisses despite metamorphic modification at subduction-zone conditions, with spessartine-increasing or flat major element profiles from inner to outer core and exceptionally higher contents of trace elements than metamorphic mantle and rim. Metamorphic garnet can grow at different metamorphic stages during prograde subduction and retrograde exhumation, with spessartine-decreasing from core to rim if the intracrystalline diffusion is not too fast. The compositional profiles of metamorphic garnet in the abundances of grossular, almandine and pyrope are variable depending on the composition of host rocks and co-existing minerals. Peritectic garnet grows through peritectic reactions during partial melting of HP to UHP rocks, with the composition of major elements to be controlled by anatectic P-T conditions and the compositions of parental rocks and anatectic melts. Trace element profiles in garnet with different origins are also variable depending on the coexisting mineral assemblages, the garnet

  2. Experimental Study of Deformation of Surrounding Rock with Infrared Radiation

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yong-jun; AN Li-qian; REN Run-hou; FAN Shi-min; MA Nian-jie; LI Jian-hui; JI Yuan-ming

    2005-01-01

    According to the practical conditions of coal roadway in Changcun Coal Mine of Lu'an Mining Group, the deformation of rock surrounding roadway was experimentally studied by means of thermal infrared (TIR) imaging system in the process of confined compressions. It is found that the model surface TIR temperature (TIRT) changes with the increase of load. Furthermore, TIRT changes non-synchronously in different ranges such as the roof, floor, wall, corners and bolted ranges. The TIRT is higher in the location of stress concentration and bolted ranges than that in the location of stress relaxation and broken ranges. The interaction ranges of bolt and rock are determined preliminarily according to the corresponding relationship of TIRT fields and the strain fields of the surrounding rock. The new method of TIR image processing has been proved to be effective for the study of bolt support and observation of roadway stability under mine pressure.

  3. Contact metamorphism in Middle Ordovician arc rocks (SW Sardinia, Italy): New paleogeographic constraints

    Science.gov (United States)

    Costamagna, Luca Giacomo; Elter, Franco Marco; Gaggero, Laura; Mantovani, Federico

    2016-11-01

    In the early Cambrian Bithia Formation in the Variscan foreland of Sardinia, a Middle Ordovician granitic intrusion (478-457 Ma) is hosted by marly metasedimentary rocks that were affected by high-temperature (HT) metamorphism. A detailed structural-petrographical transect was conducted through the granitic intrusion and its host rocks. Field data and relationships between HT/low-pressure (LP) mineral assemblages in the metasedimentary rocks (Grt + Wo + Ves in carbonate lenses and And in pelite) demonstrate that the study area was affected by a polyphase HT overprint (I: T = 520-620 °C at XCO2 = 0.1, P: 0.2-0.4 GPa; and II: T = 600-670 °C at XCO2 = 0.1, P = 0.2-0.4 GPa) that pre-dates the Variscan tectonic, metamorphic, and igneous phases. In the Canigò or Canigou Massif (Eastern Pyrenees), the Somail Massif (Montagne Noire), and the Ruitor Massif (Internal Massifs, NW Alps), Middle Ordovician orthogneiss with relict igneous textures are deciphered despite being overprinted by Variscan amphibolite-to-granulite-facies metamorphism and subsequent Alpine low-grade metamorphism. Comparisons of associated igneous and metasedimentary rocks in the Sardinia foreland with the High-Grade Metamorphic Complex in the Variscan Axial Zone and the Canigou Massif indicate a convergent Middle Ordovician evolution that was overprinted by HT Variscan metamorphism.

  4. Petrographic analysis of igneous and metamorphic rocks from the Fishguard 1:50000 sheet, south Wales

    OpenAIRE

    McKervey, J.A.

    2005-01-01

    This report presents the results of petrographic analysis of samples of igneous and metamorphic rocks collected as part of a mapping survey of the Fishguard 1:50000 sheet, south Wales. The objective of the report is to provide petrographic descriptions of the rocks and to discuss the origin of the fabrics present.

  5. Zonal disintegration phenomenon in rock mass surrounding deep tunnels

    Institute of Scientific and Technical Information of China (English)

    WU Hao; FANG Qin; GUO Zhi-kun

    2008-01-01

    Zonal disintegration is a typical static phenomenon of deep rock masses. It has been defined as alternating regions of fractured and relatively intact rock mass that appear around or in front of the working stope during excavation of a deep tunnel. Zonal disintegration phenomenon was successfully demonstrated in the laboratory with 3D tests on analogous gypsum models, two circular cracked zones were observed in the test. The linear Mohr-Coulomb yield criterion was used with a constitutive model that showed linear softening and ideal residual plastic to analyze the elasto-plastic field of the enclosing rock mass around a deep tunnel. The results show that tunneling causes a maximum stress zone to appear between an elastic and plastic zone in the surrounding rock. The zonal disintegration phenomenon is analyzed by considering the stress-strain state of the rock mass in the vicinity of the maximum stress zone. Creep instability failure of the rock due to the development of the plastic zone, and transfer of the maximum stress zone into the rock mass, are the cause of zonal disintegration. An analytical criterion for the critical depth at which zonal disintegration can occur is derived. This depth depends mainly on the character and stress concentration coefficient of the rock mass.

  6. Metamorphic fluid flow - a question of scale, crustal depth and bulk rock composition

    Energy Technology Data Exchange (ETDEWEB)

    Tracy, R.J.; Rye, D.M.

    1985-01-01

    Recent studies have indicated that certain metamorphic rocks interacted with significant volumes of aqueous fluid during their time-integrated mineral reaction history. Rather than demonstrating that pervasive fluid flow is general in metamorphic rocks, these documented cases instead suggest the likelihood of pronounced to extreme channelization of through-going in fluids in deep-seated metamorphic terranes (P>3 kbar). In rocks more shallowly buried, and therefore under low lithostatic stress, pervasive flow along grain boundaries and open microfractures probably occurred, as at Skye and the Skaergaard Complex. In higher pressure metamorphic environments, documented cases of high fluid/rock ratio make a strong case for flow channelized in veins or in impure marble aquifers where pore space and permeability were created by decarbonation reactions driven by infiltration of aqueous fluid. The source of this fluid may commonly be traced to a nearby wet granitic intrusion or quartz vein. As long as the pressurized source of aqueous fluid continued, outward flow was possible as fluid held open the intergranular pore space which was created only at the infiltration/reaction front where a reduction in solid volume accompanied reaction. Cessation or interruption of fluid flow would allow the pore space to close due to porous-rock strength being exceeded by lithostatic stress. Pervasive flow or aqueous fluid in deepseated metamorphic terranes is therefore probably limited to carbonate-bearing lithologies adjacent to sources of major volumes of fluid; otherwise, fluid flow is likely to be localized in fractures or veins.

  7. Mechanism of zonal disintegration in surrounding rock mass around deep rock engineering and its application

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The mechanical behaviors of deep rock mass are different from those of shallow rock mass.Through cases of Jinping II Hydropower Station,the special phenomenon of zonal disintegration in the surrounding rock mass around the diversion tunnels,is analyzed.On the basis of fracture mechanics,a new strength criterion for deep rock mass is derived.The new nonlinear strength criterion that is relative to the rock mass rating classification can be applied to the study of the tensile failure of deep rock mass.Subsequently,zonal disintegration model is established,and the radius of fractured zone and none-fractured zone of deep surrounding rock mass around cylindrical tunnel are obtained,their exact positions and the evolution law of zonal disintegration of surrounding rock mass is determined.To validate the present model,comparison between calculation results and the experiment observation on facture and failure around underground openings is carried out.It is found that the numerical simulation result is in good agreement with the experimental one on failure modes around the hole.Through sensitivity analysis,the effects of stress condition,cohesion and the angle of internal friction on the phenomenon of zonal disintegration are determined.Finally,the present model is adopted in the analysis of the zonal disintegration in the surrounding rock mass around the diversion tunnels in Jinping II Hydropower Station.Meanwhile,the magnitude and distributions of fractured zones are determined by numerical simulation.

  8. Study on Temperature Fieldof Surrounding Rock with BEM

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The authors analyzed the characteristic of surrounding rock temperature field around a drifting face, setup its mathematic model, and got its numerical result with the boundary element method(BEM). To calculate in-tra-domain integral, it was transformed into boundary integration with the DRM method. Using the similitude the-ory, the dimensionless differential equation was educed. Finally, the authors calculated two drifting faces of San-hejian Coal Mine using the computer software developed by authors based on the above principium, and got the dis-tribution characteristic of surrounding rock temperature field around a drifting face and the periodic variation intemperature with its periodic moving forward. Comparing the calculated heat dissipating-capacity of surroundingrock with the measured data shows that the computer software is proper.

  9. Deformation characteristics of surrounding rock of broken and soft rock roadway

    Energy Technology Data Exchange (ETDEWEB)

    Jin-xi Wang; Ming-yue Lin; Duan-xin Tian; Cun-liang Zhao [Hebei University of Engineering, Handan (China)

    2009-03-15

    A similar material model and a numerical simulation were constructed and are described. The deformation and failure of surrounding rock of broken and soft roadway are studied by using these models. The deformation of the roof and floor, the relative deformation of the two sides and the deformation of the deep surrounding rock are predicted using the model. Measurements in a working mine are compared to the results of the models. The results show that the surrounding rock shows clear rheological features under high stress conditions. Deformation is unequally distributed across the whole section. The surrounding rock exhibited three deformation stages: displacement caused by stress concentration, rheological displacement after the digging effects had stabilized and displacement caused by supporting pressure of the roadway. Floor heave was serious, accounting for 65% of the total deformation of the roof and floor. Floor heave is the main reason for failure of the surrounding rock. The reasons for deformation of the surrounding rock are discussed based on the similar material and numerical simulations. 12 refs., 4 figs., 3 tabs.

  10. Grain coarsening in polymineralic contact metamorphic carbonate rocks: The role of different physical interactions during coarsening

    DEFF Research Database (Denmark)

    Brodhag, Sabine; Herwegh, Marco; Berger, Alfons

    2011-01-01

    ) and microstructures with considerable second-phase volume fractions of up to 0.5. The variations might be of general validity for any polymineralic rock, which undergoes grain coarsening during metamorphism. The new findings are important for a better understanding of the initiation of strain localization based...... on the activation of grain size dependent deformation mechanisms....

  11. Arrested development - a comparative analysis of multilayer corona textures in high-grade metamorphic rocks

    Science.gov (United States)

    Ogilvie, Paula; Gibson, Roger L.

    2017-02-01

    Coronas, including symplectites, provide vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include prevailing pressure (P), temperature (T) and water activity (aH2O) during formation, reaction duration (t) single-stage or sequential corona layer growth; reactant bulk compositions (X) and the extent of metasomatic exchange with the surrounding rock; relative diffusion rates for major components; and/or contemporaneous deformation and strain. High-variance local equilibria in a corona and disequilibrium across the corona as a whole preclude the application of conventional thermobarometry when determining P-T conditions of corona formation, and zonation in phase composition across a corona should not be interpreted as a record of discrete P-T conditions during successive layer growth along the P-T path. Rather, the local equilibria between mineral pairs in corona layers more likely reflect compositional partitioning of the corona domain during steady-state growth at constant P and T. Corona formation in pelitic and mafic rocks requires relatively dry, residual bulk rock compositions. Since most melt is lost along the high-T prograde to peak segment of the P-T path, only a small fraction of melt is generally retained in the residual post-peak assemblage. Reduced melt volumes with cooling limit length scales of diffusion to the extent that diffusion-controlled corona growth occurs. On the prograde path, the low melt (or melt-absent) volumes required for diffusion-controlled corona growth are only commonly realized in mafic igneous rocks, owing to their intrinsic anhydrous bulk composition, and in dry, residual pelitic compositions that have lost melt in an earlier metamorphic event. Experimental work characterizing rate

  12. Fluid inclusions evidence for differential exhumation of ultrahigh pressure metamorphic rocks in the Sulu terrane

    Institute of Scientific and Technical Information of China (English)

    FAN Hongrui; GUO Jinghui; HU Fangfang; CHU Xuelei; CHEN Fukun; JIN Chengwei

    2005-01-01

    Differential exhumation was petrologically recognized in ultrahigh pressure metamorphic rocks from the southern and northern parts of the Sulu terrane. While a normal exhumation occurred for eclogites and gneisses in south Sulu, granulite-facies overprinting of ultrahigh pressure metamorphic rocks took place with high retrograde temperatures in north Sulu. A study of fluid inclusions reveals trapping of five type fluid inclusions in high and ultrahigh pressure eclogite minerals and vein quartz in the Sulu terrane. These are A-type N2±CO2 inclusion trapped at high and ultra-high pressure eclogite-facies metamorphic condition, B-type pure-CO2 liquid phase inclusion with higher density trapped during granulite-facies overprinting metamorphism of eclogites, C-type CO2-H2O inclusion and D-type hypersaline inclusion trapped in high pressure eclogite-facies re-crystallization stage, and E-type low salinity H2O inclusion trapped in the latest stage of ultrahigh pressure exhumation (amphibolite-facies retrogression). Identification of crowded-distributing pure-CO2 liquid inclusions with higher density trapped in garnet of eclogites provides an evidence for granulite-facies overprinting metamorphism in the north Sulu terrane.

  13. Rheological properties of surrounding rock in deep hard rock tunnels and its reasonable support form

    Institute of Scientific and Technical Information of China (English)

    王辉; 陈卫忠; 王清标; 郑朋强

    2016-01-01

    Second lining stability, which is the last protection in tunnel engineering, is critically important. The rheological properties of the surrounding rock heavily affect second lining stability. In this work, we used laboratory triaxial compressive rheological limestone tests to study nonlinear creep damage characteristics of surrounding rock mass in construction projects. We established a nonlinear creep damage constitutive model for the rock mass, as well as a constitutive model numerical implementation made by programming. Second, we introduced a new foam concrete with higher compression performance and good ductility and studied its mechanical properties through uniaxial and triaxial tests. This concrete was used as the filling material for the reserved deformation layer between the primary support and second lining. Finally, we proposed a high efficiency and accuracy staged optimization method. The minimum reserved deformation layer thickness was established as the optimization goal, and the presence of plastic strain in the second lining after 100 years of surrounding rock creep was used as an evaluation index. Reserved deformation layer thickness optimization analysis reveals no plastic strain in the second lining when the reserved deformation minimum thickness layer is 28.50 cm. The results show that the new foam concrete used as a reserved deformation layer filling material can absorb creep deformation of surrounding rock mass, reduce second lining deformation that leads to plastic strain, and ensure long-term second lining stability.

  14. Source and location mechanism for lode gold deposits hosted in metamorphic rocks in northeastern Hunan, China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    For understanding the source and location mechanism of lode gold deposits hosted in metamorphic rocks in northeastern Hunan, the authors analyzed the REE (rare earth elements) in ores and their host rocks, metallogenic elements in host rocks near and distant from the ore-bodies, and characteristics of ore-controlling structures, and deduced their genetic implication. Their geochemical features of REE and metallogenic elements suggest that they are formed by mobilization of dispersed metallogenic materials in Lengjiaxi Group of Middle Proterozoic during deformation and metamorphism process, mainly in Wulingian period. From the attributes of ore-controlling structures and regularity of location of gold metallization, it is concluded that the location of gold deposits is closely related to reverse shearing. Ore-forming fluids are focused on the secondary faults and extension fractures of reverse shear zones of nearly EW strike by stress-driven diffusion and seismic pumping.

  15. Complex Dielectric Properties of Several Igneous and Metamorphic Rocks

    Science.gov (United States)

    1980-10-01

    Padovani et al. (1980). 2383 New York (eastern Garnet granulite Adirondacks) 2390 New York (eastern Garnet granulite Adirondacks) 2422 Central Maine...File Report 79-993, 1979. Padovani, E.R., S.B. Shirey, and G. Simons, Microcracks in amphibolite and granulite facies grade rocks from southeastern...hypersthene (pyroxene)-plagioclase granulite with lesser amounts of clinopyroxene, K-feldspar, and pyrite. Garnet, hornblende, and clinopyroxene occur as

  16. The discovery and significance of the northeastern Jiangxi Province ophiolite (NEJXO), its metamorphic peridotite and associated high temperature-high pressure metamorphic rocks

    Science.gov (United States)

    Guoqing, Zhou

    The NEJXO with a N.E.-S.W. elongation occurs in the mid-Lower Qigong Group, under which lies the Jiuling Group (1401 Ma) and above which lies the Shangshu Group (817 ± 87 Ma), so that the age of NEJXO is defined to be Proterozoic between 1401 Ma and 817 ± 87 Ma. The sediments of the Jiuling Group show evidence of continental derivation, but the Qigong Group and Shangshu Group are characterised by CA volcanic rocks and probably represent a gradually growing island-arc. Thus, we regard the NEJXO as occurring in a back-island-arc basin between the ancient continent and the island-arc. On the whole, the main members of dismembered ophiolite are all present. The metamorphic periodotite present in them, is considered to be especially important, because it may be the sole representative of the older mantle present and it differs from those younger. The high-T metamorphic rocks associated with the NEJXO are various hornstones and melilite marble, whereas the high-P metamorphic rocks are aragonite-jadeite-glaucophane schist and schistose lawsonite marble. From the fact that high-P metamorphism was superimposed on the high-T metamorphic rocks, it may be suggested that early tension (at opening stage) and late compression (at closing stage) occurred during the development of the basin.

  17. Reliability analysis of tunnel surrounding rock stability by Monte-Carlo method

    Institute of Scientific and Technical Information of China (English)

    XI Jia-mi; YANG Geng-she

    2008-01-01

    Discussed advantages of improved Monte-Carlo method and feasibility aboutproposed approach applying in reliability analysis for tunnel surrounding rock stability. Onthe basis of deterministic parsing for tunnel surrounding rock, reliability computing methodof surrounding rock stability was derived from improved Monte-Carlo method. The com-puting method considered random of related parameters, and therefore satisfies relativityamong parameters. The proposed method can reasonably determine reliability of sur-rounding rock stability. Calculation results show that this method is a scientific method indiscriminating and checking surrounding rock stability.

  18. Failure mechanism of Mesozoic soft rock roadway in Shajihai coal mine and its surrounding rock control

    Institute of Scientific and Technical Information of China (English)

    Yuan Yue; Zhu Yongjian; Wang Weijun; Yu Weijian

    2014-01-01

    In view of the buckling failure caused by large deformation of Mesozoic soft rock roadway in Shajihai mining area, such as serious roof fall, rib spalling, floor heave, etc., based on the detail site investigation, theoretical analysis, mineral composition test, microstructure test, water-physical property test and field experiments were carried out. And we revealed the compound failure mechanism of Mesozoic soft rock roadway in Shajihai mining area, namely the molecule expansion-shear slip of weak structural plane-construction disturbance. On this basis, the coupling support technology whose core is constant resistance with large deformation bolt was proposed. The feature of this supporting technology is that a new type of structural composite material was used, which makes the supporting system not only has the ideal deformation characteristics, but also has high supporting resistance. Thus the fully release of plastic energy within surrounding rock and reasonable control of the thickness of the plastic ring were realized. Then the differential deformation between the surrounding rock and support was eliminated by the secondary coupling support of bolt–mesh–cable, and the bolt with high strength was applied in the base angle to control floor. Eventually the collaborative bearing system of surrounding rock–support was formed. Through field tests the validity and rationality of support was also verified.

  19. Extensional deformation of post ultrahigh-pressure metamorphism and exhumation process of ultrahigh-pressure metamorphic rocks in the Dabie massif, China

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A detailed tectonic analysis demonstrates that the present observed regional tectonic configuration of the ultrahigh-pressure metamorphic terrane in the Dabie massif was mainly formed by the extension processes of the post-Indosinian continent-continent oblique collision between the Sino-Korean and Yangtze cratons and ultrahigh-pressure metamorphism (UHPM). The configuration is characterized by a regional tectonic pattern similar to metamorphic core complexes and by the development of multi-layered detachment zones. On the basis of the identification of compressional and extensional fabrics, it is indicated that the exhumation and uplift of ultrahigh-pressure (UHP) metamorphic rocks from the mantle depth to the surface can be divided into at least three different decompression retrogressive metamorphism and tectonic deformation stages, in which the subhorizontal crustal-scale extensional flow in the middle-lower crust under amphibolite facies conditions is an important geodynamic process in the exhumation of UHP metamorphic rocks. Moreover, the extensional flow is probably driven by delamination and magmatic underplating of thickened lithospheric mantle following the continental oblique collision.

  20. Extensional deformation of post ultrahigh-pressure metamorphism and exhumation process of ultrahigh-pressure metamorphic rocks in the Dabie massif,China

    Institute of Scientific and Technical Information of China (English)

    索书田; 钟增球; 游振东

    2000-01-01

    A detailed tectonic analysis demonstrates that the present ob served regional tectonic configuration of the ultrahigh-pressure metamorphic terrane in the Da bie massif was mainly formed by the extension processes of the post-lndosinian continent-continent oblique collision between the Sino-Korean and V’angtze cratons and ultrahigh-pressure metamorphism (UHPM). The configuration is characterized by a regional tectonic pattern similar to metamorphic core complexes and by the development of multi-layered detachment zones. On the basis of the identification of compressional and extensional fabrics, it is indicated that the exhumation and uplift of ultrahigh-pressure (UHP) metamorphic rocks from the mantle depth to the surface can be divided into at least three different decompression retrogressive metamo rphism and tectonic deformation stages, in which the subhorizontal crustal-scale extensional flow in the middle-lower crust under amphibolite facies conditions is an important geodynamic process in the exhu

  1. Multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks

    Science.gov (United States)

    Bernard, Sylvain; Benzerara, Karim; Beyssac, Olivier; Brown, Gordon E., Jr.

    2010-09-01

    Pyritized plant tissues with well-preserved morphology were studied in rocks from Vanoise (western Alps, France) that experienced high-pressure, low-temperature metamorphic conditions in the blueschist facies during the Alpine orogeny. Organic and inorganic phases composing these fossils were characterized down to the nanometer scale by Raman microspectroscopy, scanning transmission X-ray microscopy and transmission electron microscopy. The graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups. Its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and/or thermal degradation during metamorphism. Various mineral phases are closely associated with this organic matter, including sulphides such as pyrite and pyrrhotite, carbonates such as ankerite and calcite, and iron oxides. A tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed. The absence of traces of organic matter sulphurization, the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional/diagenetic environment of these metasediments was likely rich in reactive iron. Fe-sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism. In contrast, iron oxides which form rims of 100-nm in thickness at the interface between organic matter and Fe-sulphides may result from metamorphic processes. This study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism.

  2. Macro mechanical parameters' size effect of surrounding rock of Shuibuya project's underground power station

    Institute of Scientific and Technical Information of China (English)

    GUO Zhi-hua; ZHOU Chuang-bing; ZHOU Huo-ming; SHENG Qian; LENG Xian-lun

    2005-01-01

    Scale effect is one of the important aspects in the macro mechanical parameters' research of rock mass, from a new point of view, by means of lab and field rock mechanics test, establishment of E~Vp relation, classification of engineering rock mass, numerical simulation test and back analysis based on surrounding rock's displacement monitoring results of Shuibuya Project's underground power station, rock mass deformation module's size effect of surrounding rock of Shuibuya Project's undegroud power station was studied. It's shown that rock mass deformation module's scale effect of surrounding rock of Shuibuya Project's undeground power station is obvious, the rock mass deformation module to tranquilization is 20% of intact rock's. Finally the relation between rock mass deformation modules and the scale of research was established.

  3. The principle of stability control of surrounding rock-bearing struc-tures in high stress soft rock roadways

    Institute of Scientific and Technical Information of China (English)

    WANG Wei-jun; ZHU Yong-jian; LI Shu-qing; ZHANG Peng

    2009-01-01

    Through the description of the deformational features of the surrounding rock around high stress engineering soft rock roadways,the coupling stabilization principle of inner and outer structures in surrounding rock was put forward.The supporting principles of high stress engineering soft rock roadway (high resistance and yielding support,timely support,high strength and high stiffness supports) were proposed,which were applied in engineering practices,and obtained better achievements.

  4. The principle of stability control of surrounding rock-bearing structures in high stress soft rock roadways

    Energy Technology Data Exchange (ETDEWEB)

    Wei-jun Wang; Yong-jian Zhu; Shu-qing Li; Peng Zhang [Hunan Key Laboratory of Safe Mining Techniques of Coal Mines, Xiangtan (China)

    2009-03-15

    Through the description of the deformational features of the surrounding rock around high stress engineering soft rock roadways, the coupling stabilization principle of inner and outer structures in surrounding rock was put forward. The supporting principles of high stress engineering soft rock roadway (high resistance and yielding support, timely support, high strength and high stiffness supports) were proposed, which were applied in engineering practices in Shuijingtou colliery, and obtained better achievements. 5 refs., 4 figs.

  5. Traces of H2O in Ultrahigh-Pressure Metamorphic Rocks

    Science.gov (United States)

    Dobrzhinetskaya, L. F.

    2007-05-01

    Ultrahigh-pressure (UHP) metamorphic rocks accommodate a significant amount of H2O at high pressures and temperatures during their deep subduction. Fluid-driven processes are responsible for mineral reactions; they may trigger phase transformations and provide a decisive weakening effect on the rheological behavior of the rocks during deep subduction, or they may lead to brittle failure and earthquakes. Dehydration reactions, producing fluid (i.e., H2O, CO2) during regional metamorphism at low-to-mid crustal levels (P ~ 0.1 - 1 GPa), are reasonably pressure insensitive. At these levels, the maximum dehydration occurs at the greatest temperatures experienced by buried rocks. In the deep subduction zone (> 120 - 150 km), where both high pressures and temperatures operate, the situation is different. There, on the one hand, the water becomes chemically bonded and incorporated into the structure of both nominally hydrous and anhydrous minerals. On the other hand, the aqueous fluid (a supercritical fluid) dissolves a considerable amount of mineral components at high pressures and temperatures, and a solute concentration increases as pressure is increased. Microstructural observations on ultrahigh-pressure minerals from eclogites and metasediments provide convincing evidence of fluid involvement as deep as the upper mantle and possibly, the mantle transition zone. Diamond is one of the minerals of great importance because it unambiguously records the high pressure (minimum 4 GPa and possibly > 4GPa) at which the host rocks were recrystallized. We present here the results of studies of nano-inclusions associated with dislocations of growth and/or with interstitial defects of carbon in diamond structure obtained with transmission electron microscopy, microRaman, and microInfrared synchrotron assisted spectroscopy. A diverse composition of multicomponent fluid and crystalline inclusions and characteristic of nitrogen aggregations, provide evidence that the diamonds were

  6. Hydrogen and oxygen isotope studies of metamorphic fluid-rock interactions in the Dabie Mountains

    Institute of Scientific and Technical Information of China (English)

    傅斌; 郑永飞; 李一良; 肖益林; 龚冰

    1999-01-01

    Hydrogen and oxygen isotope studies were carried out on mineral separates from high to ultrahigh pressure metamorphic rocks at Huangzhen and Shuanghe in the eastern Dabie Mountains, East China. The δ 18O values of eelogites cover a wide range of-5‰ to+9‰, but the δD values of micas fall within a narrow range of -85‰ to -70‰. Both equilibrium and disequilibrium oxygen isotope fractionations were observed between quartz and the other minerals, with reversed fractionations between omphacite and garnet in some eclogite samples. The δ 18O values of -5‰ to -1‰ for some of the eclogites represent the oxygen isotope compositions of their protoliths which underwent meteoric water-rock interaction prior to plate subduction. The preservation of oxygen isotope heterogeneity in the eclogites implies a channelized flow of fluids during progressive metamorphism caused by rapid subduetion. Retrograde metamorphism has caused oxygen and hydrogen isotope disequilibria between some of the minerals, but the f

  7. Petrology and Geochronology of High-Grade Metamorphic Rocks from Cedros Island, Baja California, Mexico

    Science.gov (United States)

    Gonzales, D.; Leech, M. L.

    2014-12-01

    High-grade metamorphic rocks exposed on Cedros Island, Baja California, Mexico, record the Mesozoic subduction history of western North America. Blocks of amphibolite, blueschist, and eclogite crop out in a serpentinite-matrix mélange on the southeast and southwestern parts of Cedros Island. Amphibolite blocks contain Amp + Ep + Ab + Chl ± Ms ± Grt ± Ttn ± Qz; blueschist blocks have the assemblage Na-Amp + Ms + Lw + Qz ± Ttn ± Grt ± Jd ± Chl; and eclogite blocks are comprised primarily of Omp + Grt with retrograde Na-Amp + Ms + Lw. Blueschists from Cedros have been dated using 40Ar/39Ar step-heating of white mica and sodic amphiboles that yield ages from 103 ± 4 Ma to 94.9 ± 1.1 Ma, respectively, that represent cooling during exhumation. Apatite fission-track dating gives ages from 32 ± 4 Ma to 22 ± 3 Ma that record exhumation through the upper crust. Related Mesozoic subduction zone rocks of the Franciscan Complex crop out in a serpentinite-matrix mélange along coastal northern California. The Franciscan rocks are older, yielding 40Ar/39Ar step-heating ages of hornblende from amphibolite ranging from 159 to 156 Ma and represent an older part of the subduction history of the oceanic Farallon plate along western North America. I will determine the prograde and peak metamorphic P-T conditions for these high-grade rocks using petrography, mineral chemistries, and isochemical phase diagram modeling with Perple_X to generate complete P-T paths. I will then supplement these data with Sm-Nd and Lu-Hf geochronology for these high-grade Cedros rocks to evaluate their subduction/exhumation history, and develop a tectonic model for these southernmost Franciscan-type rocks. Ultimately, I will compare my results to Franciscan rocks in northern California to better understand the Mesozoic subduction margin of western North America.

  8. Geochemistry and Petrogenesis of Neoarchean Metamorphic Mafic Rocks in the Wutai Complex

    Institute of Scientific and Technical Information of China (English)

    L(U) Yongjun; LIU Shuwen; Guochun ZHAO; LI Qiugen; Jian ZHANG; LIU Chaohui; K. H. PARK; Y. S. SONG

    2006-01-01

    Neoarchean metamorphic mafic rocks in the lower and the middle Wutai Complex mainly comprise metamorphic gabbros, amphibolites and chlorite schists. They can be subdivided into three groups according to chondrite normalized REE patterns. Rocks in Group #1 are characterized by nearly flat REE patterns (Lan/Ybn=0.86-1.3), the lowest total REEs (29-52 ppm), and weak negative to positive Eu anomalies (Eun/Eun*=0.84-1.02), nearly flat primitive mantle normalized patterns and strong negative Zr(Hf) anomalies. Their geochemical characteristics in REEs and trace elements are similar to those of ocean plateau tholeiite, which imply that this group of rocks can represent remnants of Archean oceanic crust derived from a mantle plume. Rocks in Group #2 are characterized by moderate total REEs (34-116 ppm), LREE-enriched (Lan/Ybn=1.76-4.34) chondrite normalized REE patterns with weak Eu anomalies (Eun/Eun*=0.76-1.16), and negative Nb, Ta, Zr(Hf), Ti anomalies in the primitive mantle normalized spider diagram. The REE and trace element characteristics indicate that they represent arc magmas originating from a sub-arc mantle wedge metasomatized by slabderived fluids. Rocks in Group #3 are characterized by the highest total REEs (61-192 ppm), the strongest LREEs enrichment (Lan/Ybn=7.12-16) with slightly negative Eu anomalies (Eun/Eun*=0.81-0.95) in the chondrite normalized diagram. In the primitive mantle normalized diagram,these rocks are characterized by large negative anomalies in Nb, Ta, Ti, negative to no Zr anomalies.They represent arc magmas originating from a sub-arc mantle wedge enriched in slab-derived melts.The three groups of rocks imply that the formation of the Neoarchean Wutai Complex is related to mantle plumes and island-arc interaction.

  9. Numerical analysis of tunnel reinforcing influences on failure process of surrounding rock under explosive stress waves

    Institute of Scientific and Technical Information of China (English)

    ZUO Yu-jun; TANG Chun-an; ZHU Wan-cheng; LI Di-yuan; LI Shu-cai

    2008-01-01

    Based on mesoscopic damage mechanics, numerical code RFPA2D (dynamic edition) was developed to analyze the influence of tunnel reinforcing on failure process of surrounding rock under explosive stress waves. The results show that the propagation phenomenon of stress wave in the surrounding rock of tunnel and the failure process of surrounding rock under explosive stress waves are reproduced realistically by using numerical code RFPAED; from the failure process of surrounding rock,the place at which surrounding rock fractures is transferred because of tunnel reinforcing, and the rockfall and collapse caused by failure of surrounding rock are restrained by tunnel reinforcing; furthermore, the absolute values of peak values of major principal stress, and the minimal principal stress and shear stress at center point of tunnel roof are reduced because of tunnel reinforcing, and the displacement at center point of tunnel roof is reduced as well, consequently the stability of tunnel increases.

  10. Analysis of lineament swarms in a Precambrian metamorphic rocks in India

    Indian Academy of Sciences (India)

    Tapas Acharya; Sukumar Basu Mallik

    2012-04-01

    Addressing the geologic significance of lineaments and their correlation with joints/fractures is still unclear. The present study attempts to analyse the lineament swarms developed in a Precambrian metamorphic terrain in India using both unfiltered and filtered techniques. The unfiltered analysis technique shows that the major lineament and fracture trends are oriented along EW and NS directions respectively, thus failing to provide any correlation between them. The application of domain-based filtering techniques identifies a highly predominant fracture-correlated lineaments in mica schist constituting the EW trending shear zone in the area. This correlation is not evident in the areas north and south of the shear zone, where the lineaments are consistently oriented along the foliation planes of the rocks and are designated as ‘foliation correlated’. The present analysis indicates that the fracture frequency and the strain history may have played significant roles for the formation of fracture-correlated lineaments in the metamorphic terrain.

  11. Shock metamorphism of Bosumtwi impact crater rocks, shock attenuation, and uplift formation.

    Science.gov (United States)

    Ferrière, Ludovic; Koeberl, Christian; Ivanov, Boris A; Reimold, Wolf Uwe

    2008-12-12

    Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by approximately 5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure.

  12. Thermal contraints on high-pressure granulite metamorphism of supracrustal rocks

    Science.gov (United States)

    Ashwal, L. D.; Morgan, P.; Leslie, W. W.

    1983-01-01

    The circumstances leading to the formation and exposure at the Earth's surface of supracrustal granulites are examined. These are defined as sediments, volcanics, and other rock units which originally formed at the surface of the Earth, were metamorphosed to high-pressure granulite facies (T = 700-900 C, P = 5-10 kbar), and reexposed at the Earth's surface, in many cases underlain by normal thicknesses of continental crust (30-40 km). Five possible heating mechanisms to account for granulite metamorphism of supracrustal rocks are discussed: magnetic heating, thermal relaxation of perturbed temperature profiles following underthrusting of the continental crust, thermal relaxation after underthrusting of thin slivers of supracrustal rocks below continental crust of normal thickness, major preheating of the upper plate, and shear heating caused by frictional stress along the thrust plane.

  13. Numerical simulation study of the failure evolution process and failure mode of surrounding rock in deep soft rock roadways

    Institute of Scientific and Technical Information of China (English)

    Meng Qingbin; Han Lijun; Xiao Yu; Li Hao; Wen Shengyong; Zhang Jian

    2016-01-01

    Based on the safety coefficient method, which assigns rock failure criteria to calculate the rock mass unit, the safety coefficient contour of surrounding rock is plotted to judge the distribution form of the frac-tured zone in the roadway. This will provide the basis numerical simulation to calculate the surrounding rock fractured zone in a roadway. Using the single factor and multi-factor orthogonal test method, the evolution law of roadway surrounding rock displacements, plastic zone and stress distribution under different conditions is studied. It reveals the roadway surrounding rock burst evolution process, and obtains five kinds of failure modes in deep soft rock roadway. Using the fuzzy mathematics clustering analysis method, the deep soft surrounding rock failure model in Zhujixi mine can be classified and pat-terns recognized. Compared to the identification results and the results detected by geological radar of surrounding rock loose circle, the reliability of the results of the pattern recognition is verified and lays the foundations for the support design of deep soft rock roadways.

  14. In search of early life: Carbonate veins in Archean metamorphic rocks as potential hosts of biomarkers

    Science.gov (United States)

    Peters, Carl A.; Piazolo, Sandra; Webb, Gregory E.; Dutkiewicz, Adriana; George, Simon C.

    2016-11-01

    The detection of early life signatures using hydrocarbon biomarkers in Precambrian rocks struggles with contamination issues, unspecific biomarkers and the lack of suitable sedimentary rocks due to extensive thermal overprints. Importantly, host rocks must not have been exposed to temperatures above 250 °C as at these temperatures biomarkers are destroyed. Here we show that Archean sedimentary rocks from the Jeerinah Formation (2.63 billion yrs) and Carawine Dolomite (2.55 billion yrs) of the Pilbara Craton (Western Australia) drilled by the Agouron Institute in 2012, which previously were suggested to be suitable for biomarker studies, were metamorphosed to the greenschist facies. This is higher than previously reported. Both the mineral assemblages (carbonate, quartz, Fe-chlorite, muscovite, microcline, rutile, and pyrite with absence of illite) and chlorite geothermometry suggest that the rocks were exposed to temperatures higher than 300 °C and probably ∼400 °C, consistent with greenschist-facies metamorphism. This facies leads to the destruction of any biomarkers and explains why the extraction of hydrocarbon biomarkers from pristine drill cores has not been successful. However, we show that the rocks are cut by younger formation-specific carbonate veins containing primary oil-bearing fluid inclusions and solid bitumens. Type 1 veins in the Carawine Dolomite consist of dolomite, quartz and solid bitumen, whereas type 2 veins in the Jeerinah Formation consist of calcite. Within the veins fluid inclusion homogenisation temperatures and calcite twinning geothermometry indicate maximum temperatures of ∼200 °C for type 1 veins and ∼180 °C for type 2 veins. Type 1 veins have typical isotopic values for reprecipitated Archean sea-water carbonates, with δ13CVPDB ranging from - 3 ‰ to 0‰ and δ18OVPDB ranging from - 13 ‰ to - 7 ‰, while type 2 veins have isotopic values that are similar to hydrothermal carbonates, with δ13CVPDB ranging from - 18

  15. Microprobe monazite dating and the ages of some granitic and metamorphic rocks from southeastern Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Vlach, Silvio Roberto Farias; Gualda, Guilherme Augusto Rosa [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias]. E-mail: srfvlach@usp.br

    2000-03-01

    Electron microprobe monazite crystallization ages are presented for selected granite and metamorphic rock samples from the Socorro and Guaxupe Nappes and the Alto Rio grande and Ribeira Belts, southeastern Brazil. Results are consistent with ages close to 625 Myr of the main metamorphic episode in the nappe structures. Anatetic granite magmatic events in these terranes and in the Alto Rio Grande Belt were roughly coeval, most samples sharing ages between 610-625 ({+-} 15) Myr. A crust-derived granite and a granite contact aureole from the Ribeira Belt have ages of 600-608 ({+-} 15) Myr., suggesting that the main granite magmatism in this belt was somewhat younger, probably contemporaneous with the late orogenic phase in the nappe domains. Some regional and granite samples from all these terranes point to possible inheritance or incompletely monazite grains and intra-grain domains giving older ages, up to 690 Myr. The microprobe age results agree very well with independent isotopic data, reinforcing the applicability of the method to highlight an overall picture of main geochronological trends within the continental crust. The high spatial resolution of the probe should play an important role in understanding geochronological patterns of metasedimentary rocks and related migmatites and granites, as these rocks and their minerals often present chemical and isotopic domains related to contrasting geological events, not always recognized by conventional dating schemes. (author)

  16. Stability classification model of mine-lane surrounding rock based on distance discriminant analysis method

    Institute of Scientific and Technical Information of China (English)

    ZHANG Wei; LI Xi-bing; GONG Feng-qiang

    2008-01-01

    Based on the principle of Mahalanobis distance discriminant analysis (DDA) theory, a stability classification model for mine-lane surrounding rock was established, including six indexes of discriminant factors that reflect the engineering quality of surrounding rock: lane depth below surface, span of lane, ratio of directly top layer thickness to coal thickness, uniaxial comprehensive strength of surrounding rock, development degree coefficient of surrounding rock joint and range of broken surrounding rock zone. A DDA model was obtained through training 15 practical measuring samples. The re-substitution method was introduced to verify the stability of DDA model and the ratio of mis-discrimination is zero. The DDA model was used to discriminate3 new samples and the results are identical with actual rock kind. Compared with the artificial neural network method and support vector mechanic method, the results show that this model has high prediction accuracy and can be used in practical engineering.

  17. 大别-苏鲁超高压变质带内部的浅变质岩%On low-grade metamorphic rock within Dabie-Sulu ultrahigh pressure metamorphic belt.

    Institute of Scientific and Technical Information of China (English)

    周建波; 郑永飞; 李龙; 谢智

    2001-01-01

    There are sparotic occurrences of low-grade metamorphic rocks as tectonic relict flakes within the Dabie-Sulu ultrahigh pressure (UHP) orogen. They are mainly composed of metaclastics, phyllites and marbles. They having, suffered from dynamic metamorphism at low greenschist-facies and fold-and-fault deformation, are in tectonic contacts with the surrounding UHP rocks. Micro-paleontologic fossils from the low-grade metamorphic rocks suggest that their sedimentary protoliths were deposited in a shallow marine environment at Sinian in the northern margin of Yangze plate. Isotopic datings indicate that their igneous protoliths are of Late Proterozoic ages and experienced tectonic events at Caledonian and Indosinian like the surrounding UHP eclogites and gneisses. Oxygen isotope analysis shows that the low-grade metamorphic rocks within the Dabie orogen are depleted in 18O like the surrounding UHP rocks and thus their protoliths underwent hydrothermal alteration by ancient meteoric water at high temperatures. It appears that the low-grade metamorphic rocks were originally the Sinian sedimentary rocks and enclosed volcaniclastic rocks in the northern margin of the Yangtze plate, and have the geological occurrence and formation mechanism similar to accretionary wedge that was scraped from the subducting Yangtze plate and accumulated in the subduction zone. Therefore, they may be a part of the tectonic accretionary wedge of continental plate subduction.%大别苏鲁超高压变质带内部零星出露有若干呈构造残片状产出的浅变质岩,主要以变质碎屑岩-千枚岩-大理岩组合为代表,遭受过低绿片岩相变质和脆-韧性变形作用的改造,与围岩均为构造接触(断层或韧性剪切带)。微古生物化石研究表明,其原岩为震旦纪前后扬子板块北缘的浅海相沉积。同位素年代学研究指示,它们经历过加里东期和印支期构造热事件的影响,与区域超高压岩石经受

  18. Reconstruction of protoliths of metamorphic rocks and tectonic setting of Wolegen Group

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Parametamorphic rocks from Arong County in southeastern Inner Mongolia-Daxinganling district are regarded as Proterozoic in age,belonging to the Wolegen Group and composed of volcanoclastic and sandstone in origin,and have been disputed in tectonic setting.Because of the stability in metamorphism,the rare earth dements indicate the features of their protoliths.The authors integrated the petrologic methods with the geochemical parameters which include ∑REE,∑LREE/∑HREE,δCe,δEu,La/Yb,Sm/Nd,Th/Sc and the standard values of chondrite.The results show that the protoliths of Wolengen Group may be a group of voleanoclastic and continental margin elastic rocks,and their tectonic setting is the continent island arc.

  19. Effect of longwall length on mechanical characteristics of surrounding rock stress shell in mining face

    Energy Technology Data Exchange (ETDEWEB)

    Guang-Xiang Xie; Lei Wang [Anhui University of Science and Technology, Huainan (China)

    2008-12-15

    The mechanical characteristics of surrounding rock stress shell in longwall mining face were studied, based on the results of in-situ measurement combined with numerical simulation, and the effect of longwall length on mechanical characteristics of surrounding rock stress shell was discovered. The results show that the mechanical characteristics of surrounding rock stress shell are influenced by the length of the face. With an increase of mining face length, the level of concentration of shell stress located in the front face and surrounding rock of roadway is amplified and the three- dimensional stress is focused in the working face. The damage lies in the head entry corner of face and the vertical displacement is reduced but horizontal displacement is enlarged. The dynamic balance of surrounding rock stress shell is improved with rational adjustment of face length. It is effective in protecting the working face and controlling strata behavior. 5 refs., 7 figs.

  20. Analysis of nonlinear dynamic character in the surrounding rock system for deep buried underground engineering

    Institute of Scientific and Technical Information of China (English)

    ZHAO Yu; PENG Hai-you

    2010-01-01

    Combining the field monitoring results of a deep-buried tunnel in Chongqing,the dynamic characteristics of the surrounding rock system under high in situ stress was analyzed by phase space reconstruction, calculating correlation dimension, Kolmogorov entropy and largest Lyapunov exponents. Both the Kolmogorov entropy and largest Lyapunov exponents show that the surrounding rock system is a chaotic one. Based on this, a local model was applied to predict surrounding rock displacement, and a nonlinear dynamic model was derived to forecast the interaction of the surrounding rock and support structure. The local method was found to have an extremely small total error. Also, the nonlinear dynamic model forecasting curves agree with the monitoring ones very well. It is proved that the nonlinear dynamic characteristic study is very important in analyzing rock stability and predicting the evolution of rock systems.

  1. Review of roadway control in soft surrounding rock under dynamic pressure

    Institute of Scientific and Technical Information of China (English)

    侯朝炯

    2003-01-01

    The basic characteristics of the soft rock roadway under the dynamic pressure are analyzed. At the same time, the three fundamental approaches for controlling the surrounding rock are proposed, which are improving the surrounding rock strength, lowering the rock mass stress and selecting the reasonable supporting technology. The research results are elucidated, including the distribution of the surrounding rock plastic zone, the movement and damage of the surrounding rock under the dynamic pressure, controlling the floor heave through reinforcing the roadway walls and corners, the new route to develop the roadway metal supporting technique, the key theory and technique for the bolt supporting in the coal roadway, the performance and prospect of the ZKD high-water-content quick-setting material, and so on. Finally, some personally views are put forward about the roadway metal supporting, bolt supporting, new material and the stress-relief under the high stress condition.

  2. On the role of horizontal displacements in the exhumation of high pressure metamorphic rocks

    Science.gov (United States)

    Brun, J.-P.; Tirel, C.; Philippon, M.; Burov, E.; Faccenna, C.; Gueydan, F.; Lebedev, S.

    2012-04-01

    High pressure metamorphic rocks exposed in the core of many mountain belts correspond to various types of upper crustal materials that have been buried to mantle depths and, soon after, brought back to surface at mean displacement rates up to few cm/y, comparable to those of plate boundaries. The vertical component of HP rock exhumation velocity back to surface is commonly well constrained by pressure estimates from petrology and geochronological data whereas the horizontal component remains generally difficult or impossible to estimate. Consequently, most available models, if not all, attempt to simulate exhumation with a minimal horizontal component of displacement. Such models, require that the viscosity of HP rocks is low and/or the erosion rate large -i.e. at least equal to the rate of exhumation. However, in some regions like the Aegean, where the exhumation of blueschists and eclogites is driven by slab rollback, it can be shown that the horizontal component of exhumation related displacement, obtained from map view restoration, is 5 to 7 times larger than the vertical one, deduced from metamorphic pressure estimates. Using finite element models performed with FLAMAR, we show that such a situation simply results from the subduction of small continental blocks (walk, with the block's tail slipping along a basal décollement, approaching the head and making a large buckle, which then unrolls at surface as soon as the entire block is delaminated. Finally, the crustal block emplaces at surface in the space created by trench retreat. This process of exhumation requires neither rheological weakening of HP rocks nor high rates of erosion.

  3. Why are Q-Ratios High in the Sulu UHP Metamorphic Rocks?

    Institute of Scientific and Technical Information of China (English)

    Liu Qingsheng

    2011-01-01

    I found high Q values (Q-ratio=Jn/Ji, Jn, Ji are remanent magnetization and induced magnetization) in the Sulu ultrahigh pressure (UHP) metamorphic rocks, eastern China which is the world's largest UHP metamorphic belt (Fig. 1 in Liu et al., 2009). Q values of 320 core samples with variable lithologies in the 100-2 000 m interval from the Chinese Continental Scientific Drilling (CCSD) main hole are as follows: values between 0.06 and 608.24, with an average of 15.56 for 171 eclogite samples; values between 0.11 and 23.83, with an average of 1.93 for 61 orthogneiss samples; values between 0.13 and 1 746.00, with an average of 63.63 for 74 paragneiss samples; and values from 8.07 to 28.23, with an average of 16.59 for 14 serpentinized peridotite (Liu et al., 2010, 2009). However, continental lower crustal rocks generally have low Q values. For example, several thousand samples from the Ukranian shield show a mean Q of about 1.0 (Krutikhovskaya and Pashkevich, 1977).

  4. Numerical Analysis of Advanced Displacement in Construction Progress of Tunnel Excavation with Weak Surrounding Rock

    Directory of Open Access Journals (Sweden)

    Qian Zhang

    2013-07-01

    Full Text Available Analysis of advanced displacement in construction progress of tunnel excavation with weak surrounding rock is carried out by numerical method and comparison of model test result. In allusion to the problems of regional landslides and extruded large-deformation seriously impacting the stability of rock mass in construction process of large-section tunnel with weak surrounding rock, the elastic-plastic numerical simulation relying on Liangshui tunnel of Lan-Yu railroad is conducted on mechanical behaviors and deformation steric effect of tunnel construction and the calculation results are compared with the modeling data. The research results show that: the steric effect of excavation face is the dominant factor in the incidence of working face and the stress of surrounding rocks gradually releases from excavation face; the range of 0.5~1 times the cave diameter around rock mass in front of working face is the disturbance range and the key area of stabilization and reinforcement for wake surrounding rock. According to the analysis and construction practice, the supporting structure of large-section tunnel with weak surrounding rock should be established as soon as possible to control the displacement change of surrounding rock in the range of load-bearing ring, reduce disturbance and improve the self-bearing capability of surrounding rock. Because of the distinct excavation steric effect of weak surrounding rock, the secondary lining structure must be established in time to bear the later pressure and restrict the large displacement of surrounding rock. The research results can provide reliable basis for engineering stability control of analogous tunnels.

  5. Comparison of laboratory, in situ, and rock mass measurements of the hydraulic conductivity of metamorphic rock at the Savannah River Plant near Aiken, South Carolina

    Energy Technology Data Exchange (ETDEWEB)

    Marine, I W

    1980-01-01

    In situ testing of exploratory wells in metamorphic rock indicates that two types of fracturing occur in the rock mass. Rock containing small openings that permit only extremely slow movement of water is termed virtually impermeable rock. Rock containing openings of sufficient size to permit transmission of water at a significantly faster rate is termed hydraulically transmissive rock. Laboratory methods are unsuitable for measuring hydraulic conductivity in hydraulically transmissive rock; however, for the virtually impermeable rock, values comparable to the in situ tests are obtained. The hydraulic conductivity of the rock mass over a large region is calculated by using the hydraulic gradient, porosity, and regional velocity. This velocity is determined by dividing the inferred travel distance by the age of water which is determined by the helium content of the water. This rock mass hydraulic conductivity value is between the values measured for the two types of fractures, but is closer to the measured value for the virtually impermeable rock. This relationship is attributed to the control of the regional flow rate by the virtually impermeable rock where the discrete fractures do not form a continuous open connection through the entire rock mass. Thus, laboratory methods of measuring permeability in metamorphic rock are of value if they are properly applied.

  6. Comparison of Laboratory, in Situ, and Rock Mass Measurements of the Hydraulic Conductivity of Metamorphic Rock at the Savannah River Plant Near Aiken, South Carolina

    Science.gov (United States)

    Marine, I. Wendell

    1981-06-01

    In situ testing of exploratory wells in metamorphic rock indicates that two types of fracturing occur in the rock mass. Rock containing small openings that permit only extremely slow movement of water is termed virtually impermeable rock. Rock containing openings of sufficient size to permit transmission of water at a significantly faster rate is termed hydraulically transmissive rock. Laboratory methods are unsuitable for measuring hydraulic conductivity in hydraulically transmissive rock; however, for the virtually impermeable rock, values comparable to those of the in situ tests are obtained. The hydraulic conductivity of the rock mass over a large region is calculated by using the hydraulic gradient, porosity, and regional velocity. This velocity is determined by dividing the inferred travel distance by the age of water, which is determined by the helium content of the water. This rock mass hydraulic conductivity value is between the values measured for the two types of fractures but is closer to the measured value for the virtually impermeable rock. This relationship is attributed to the control of the regional flow rate by the virtually impermeable rock where the discrete fractures do not form a continuous open connection through the entire rock mass. Thus laboratory methods of measuring permeability in metamorphic rock are of value if they are properly applied.

  7. Tethyan and Indian subduction viewed from the Himalayan high- to ultrahigh-pressure metamorphic rocks

    Science.gov (United States)

    Guillot, S.; Mahéo, G.; de Sigoyer, J.; Hattori, K. H.; Pêcher, A.

    2008-04-01

    The Himalayan range is one of the best documented continent-collisional belts and provides a natural laboratory for studying subduction processes. High-pressure and ultrahigh-pressure rocks with origins in a variety of protoliths occur in various settings: accretionary wedge, oceanic subduction zone, subducted continental margin and continental collisional zone. Ages and locations of these high-pressure and ultrahigh-pressure rocks along the Himalayan belt allow us to evaluate the evolution of this major convergent zone. (1) Cretaceous (80-100 Ma) blueschists and possibly amphibolites in the Indus Tsangpo Suture zone represent an accretionary wedge developed during the northward subduction of the Tethys Ocean beneath the Asian margin. Their exhumation occurred during the subduction of the Tethys prior to the collision between the Indian and Asian continents. (2) Eclogitic rocks with unknown age are reported at one location in the Indus Tsangpo Suture zone, east of the Nanga Parbat syntaxis. They may represent subducted Tethyan oceanic lithosphere. (3) Ultrahigh-pressure rocks on both sides of the western syntaxis (Kaghan and Tso Morari massifs) formed during the early stage of subduction/exhumation of the Indian northern margin at the time of the Paleocene-Eocene boundary. (4) Granulitized eclogites in the Lesser Himalaya Sequence in southern Tibet formed during the Paleogene underthrusting of the Indian margin beneath southern Tibet, and were exhumed in the Miocene. These metamorphic rocks provide important constraints on the geometry and evolution of the India-Asia convergent zone during the closure of the Tethys Ocean. The timing of the ultrahigh-pressure metamorphism in the Tso Morari massif indicates that the initial contact between the Indian and Asian continents likely occurred in the western syntaxis at 57 ± 1 Ma. West of the western syntaxis, the Higher Himalayan Crystallines were thinned. Rocks equivalent to the Lesser Himalayan Sequence are present

  8. Partial melting of ultrahigh-pressure metamorphic rocks during continental collision: Evidence, time, mechanism, and effect

    Science.gov (United States)

    Chen, Yi-Xiang; Zhou, Kun; Gao, Xiao-Ying

    2017-09-01

    Partial melting of ultrahigh-pressure (UHP) metamorphic rocks during continental collision has been increasingly found in nature. More and more studies have devoted to the evidence, time, mechanism and effect of crustal anataxis at mantle to lower crust depths. This is particularly so for UHP rocks from the Dabie-Sulu orogenic belt, whereas similar studies on these issues are relatively minor for other UHP terranes. The petrological evidence, especially microstructural observations and multiphase solid inclusion analyses, have been accumulated for the partial melting of UHP metamorphic rocks in collisional orogens. The results indicate that this is a kind of low-degree crustal anataxis at convergent plate margins due to decompressional dehydration of the UHP rocks themselves. Thus it has great bearing on intracrustal differentiation and crust-mantle interaction in continental subduction channels. Zircon may grow through peritectic reactions due to the breakdown of hydrous minerals. By dating of the peritectic zircons that contain coesite or diamond inclusions, the time of crustal anatexis under UHP conditions can be directly determined. In general, the partial melting of UHP rocks mainly took place at the stage of their early exhumation, partly still in the UHP regime and partly in the subsequent high-pressure (HP) regime. The crustal anatexis still at mantle depths is common in many UHP terranes, possibly facilitating exhumation of deeply subducted continental slices toward shallower levels. Petrological and geochemical studies indicate that phengite dehydration-driven melting during exhumation is the common mechanism for the anatexis of UHP rocks, though the other hydrous minerals were also involved in this process. The resulted HP to UHP melts may occur at different spatial scales and show significant fractionation in melt-mobile incompatible trace elements such as LILE and LREE. These melts are enriched in LILE to large extent and LREE and Th to small extent

  9. Mineral chemistry of garnet in pegmatite and metamorphic rocks in the Hamedan area

    Directory of Open Access Journals (Sweden)

    Ahmad Ahmadi Khalaji

    2015-10-01

    Full Text Available Introduction The area of this study is located near Hamadan within the Sanandaj - Sirjan tectonic zone. In the Hamadan area, consisting mainly of Mesozoic plutonic and metamorphic rocks, aplites and pegmatites locally contain garnets.(Baharifar et al., 2004, Amidi and Majidi, 1977; Torkian, 1995. Garnet-bearing schists and hornfelses in the area are products of regional metamorphism shown by slate and phyllite (Baharifar, 2004. In this investigation the distribution of elements in garnet in different rock type was studied to determine their mineral types and conditions of formation. Garnet samples from igneous and metamorphic rocks were analyzed by electron microprobe (EMPA, the results of which are presented in this article. Materials and methods Thirty-five samples were selected for thin section preparation and twenty thin-polished sections were prepared for mineralogical and microprobe analysis. Thin sections of garnet-bearing igneous (pegmatite and metamorphic rocks (schist and hornfels were studied by polarizing microscope. Chemical analysis was performed on the garnets (38 points using a Caimeca SX100 electron microprobe at an acceleration voltage of 15 kV and electric current of 15 nA in the Mineral Processing Research Center, Iran. Separation of iron (II and Fe (III was calculated by Droop’s method (1987 and the structural formulas of the garnets were calculated using 24 oxygens to determine the relative proportions of the end-members using the mineral spreadsheet software of Preston and Still (2001. Results Based on the analyses, almandine (Fe - Al garnet and spessartine (Mn - Al garnet are the principal types of the (Kamari metamorphic and (Abaro pegmatitic garnets, that belong to the well-known pyralspite garnet group. Chemical zoning patterns of the garnets in the metamorphic rocks (schists differ from those in the igneous rocks (pegmatite, showing different compositions from core to rim. Petrographic evidence such as: co

  10. Li and B Isotope Systematics of Ultrahigh-pressure Metamorphic Rocks from the Chinese Continental Scientific Drilling Program

    Institute of Scientific and Technical Information of China (English)

    Yilin Xiao; Rolf L. Romer; Jochen Hoefs; Anette Meixner; Zeming Zhang

    2007-01-01

    @@ 1 Introduction Recent improvements in the precision of Li and B isotope measurements have demonstrated the potential of these elements in tracing a wide range of geological processes. The Li and B isotope systematics of ultrahigh-pressure (UHP) metamorphic rocks provides a unique opportunity to investigate the behaviour of Li and B during fluid-rock interaction at high temperatures and very high pressures and to constrain the fluid budget and the recycling of subducted crustal materials into the mantle during UHP metamorphism.

  11. "Fossil" bright layer recorded in the low-P/T metamorphic rocks

    Science.gov (United States)

    Terabayashi, M.; Yamamoto, H.; Kitajima, K.

    2004-12-01

    The "fossil" (geological time) bright layer was recognized in the Cretaceous low-P/T Ryoke metamorphic rocks in the Iwakuni-Yanai area, southwest Japan. Silicified pelitic schists distribute as layers or lenticular bodies several to fifteen meters in thickness, and they are restricted in the greenschist facies conditions within structurally vertical thickness about one kilometer. Silicified pelitic schist is mainly composed of fine-grained quartz and minor muscovite and biotite, and some of colored minerals are decolored by alteration more or less. The boundary between silicified layer and underlying pelitic schist is fairly distinct but that between the overlying pelitic schist is rather gradual. Quartz veins crossing high angles with schistosity were preferentially developed in the silicified rocks, while schistosity-parallel quartz veins, which underwent ductile flow, were observed in the pelitic schist. En echelon quartz vein and fishnet-like quartz veins are characteristic of silicified rocks. The mode of occurrences of quartz veins indicates that silicified rocks are competent relative to underlying pelitic schist. Fluid inclusion studies were conducted from two kinds of quartz-filled veins: crosscutting foliation in silicified pelitic schist and foliation-parallel in pelitic schist. Fluid inclusions in quartz from a vein crosscutting foliation in silicidied pelitic schist occur as isolated individual inclusions or clusters with preferred spatial arrangement. The isolated inclusions display negative crystal geometries, and are generally range in size from 5 to 10 μ m, with some inclusions up to 20 μ m across. Fluid inclusions in quartz from a foliation-parallel vein are rounded and usually small about a few μ m. Homogenization of the vapour and liquid phases to a single liquid phase occurred at temperatures (Th) between 275 and 330 ° C except in rare instances. The value is considered to be close to the condition of vein formation. Importantly, the

  12. Stress and deformation analysis on deep surrounding rock at different time stages and its application

    Institute of Scientific and Technical Information of China (English)

    Li Ming; Mao Xianbiao; Yu Yuanlin; Li Kai; Ma Chao; Peng Yan

    2012-01-01

    Based on the characteristics of the deep circular tunnel,the surrounding rock was divided into three regions:the cracked region,the plastic region and the viscoelastic region.The process of rock stress deformation and change was divided into three stages after the roadway excavation.By using the elastic-plastic mechanics theory,the analytical solutions of the surrounding stress and displacement at different stages and the radii of cracked and plastic regions were formulated.We additionally explained the surrounding rock stress and displacement which appeared in practical project.Simultaneously,based on the problem which emerged from a mine in Xuzhou during the excavating process of rock roadway's transport,we got the theoretical solutions for the stress and displacement in the process of rock roadway's excavation and considered that the broken area of rock roadway was largely loosing circle.The results indicate that according to the rheological characteristics of surrounding rock,in the primeval excavation of rock roadway,we should increase the length of anchor bolt and cooperate it with anchor nets cable-U steel supporting frame.In addition,when the deformation rate of the surrounding rock is descending after the 15 days' excavation,we should use the "three anchor" supporting method (anchor bolt spray,anchor note and anchor rope) and set aside about 20 cm as the reserved deformation layer.

  13. Chemical Variations in a Granitic Pluton and Its Surrounding Rocks.

    Science.gov (United States)

    Baird, A K; McIntyre, D B; Welday, E E; Madlem, K W

    1964-10-09

    New techniques of x-ray fluorescence spectrography have provided, for the first time, abundant data regarding chemical variability of granitic rocks on different scales. The results suggest that current designs of sampling plans for trend surface analysis should be modified; in particular several specimens, preferably drillcores, may be required at each locality.

  14. Rock-magnetic studies on hematite, maghemite and combustion-metamorphic rocks

    NARCIS (Netherlands)

    de Boer, C.B.

    1999-01-01

    This thesis is structured in three parts. Part I and II comprise fundamental research of the magnetic properties of hematite and maghemite, respectively, essential to improve the quality of paleomagnetic interpretations of sedimentary rocks in particular. The main purpose is to develop diagnostic ro

  15. Zircon U-Pb geochronology of basement metamorphic rocks in the Songliao Basin

    Institute of Scientific and Technical Information of China (English)

    PEI FuPing; XU WenLiang; YANG DeBin; ZHAO QuanGuo; LIU XiaoMing; HU ZhaoChu

    2007-01-01

    Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphic rocks in the Songliao Basin mainly consist of metagabbro (L45-1), amphibolite (SN117), metarhyolitical tuff (G190), sericite (Ser) schist (N103), chlorite (Chi) schist (T5-1), biotite (Bi)-actinolite (Act)-quartz (Q) schist (Y205), and metagranite (L44-1). The cathodoluminesence (CL)images of the zircons from metagabbro (L45-1) and metagranite (L44-1) indicate that they have cores of magmatic origin and rims of metamorphic overgrowths. Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively. The zircons with oscillatory zoning from amphibolite (SN117) and Chi schist (T5-1), being similar to those of mafic igneous rocks, yield ages of 274 ± 3.4 Ma and 264 ± 3.2 Ma, respectively. The zircons from metarhyolitical tuff (G190) and Ser schist (N103) display typical magmatic growth zoning and yield ages of 424 ± 4.5 Ma and 287 ± 5.1Ma, respectively. Most of zircons from Bi-Act-Q schist (Y2O5) are round in shape and different in absorption degree in the CL images, implying their sedimentary detritals. U-Pb dating yield concordant ages of 427 ± 3.1Ma, 455 ± 12 Ma, 696 ± 13 Ma,1384±62 Ma, 1649±36 Ma, 1778±18 Ma, 2450±9 Ma, 2579±10 Ma, 2793±4 Ma and 2953±14 Ma. The above-mentioned results indicate that the Precambrian crystalline basement (1808-1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424-490 Ma) and Late Paleozoic magmatisms (264-292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.

  16. Preliminary study of microscale zircon oxygen isotopes for Dabie-Sulu metamorphic rocks: Ion probe in situ analyses

    Institute of Scientific and Technical Information of China (English)

    CHEN Daogong; Deloule Etienne; CHENG Hao; XIA Qunke; WU Yuanbao

    2003-01-01

    151 in situ analyses of oxygen isotopes were carried out by ion micro-probe for zircons from 8 localities of HP-UHP metamorphic rocks including eclogites in the Dabie-Sulu terrane. The results show significant heterogeneity inδ18O values, with variation in different rocks from -8.5‰ to +9.7‰ and within one sample from 2‰ to 12‰. No measurable difference inδ18O was observed between protolith magmatic (detrital) zircons and metamorphic recrystallized zircons within analytical uncertainties from the ion micro-probe measurements. This indicates that the metamorphic zircons have inherited the oxygen isotopic compositions of protolith zircons despite the HP to UHP metamorphism. According to their protolith ages from zircon U-Pb in situ dating by the same ion micro-probe, two groups of oxygen isotope composition are recognized, with one having δ18O values of 6‰-7‰ for old protolith of 1.9-2.5 Ga ages and the other 0‰-2‰ for young protolith of 0.7-0.8 Ga ages. The latter anomalously lowδ18O values of zircons indicate that the magma has had the obvious involvement of meteoric water when forming the young protolith of high-grade metamorphic rocks. This may be correlated with the snowball Earth event occurring in South China and the world elsewhere during the Neoproterozoic.

  17. Simulating the metamorphic evolution of rocks in the laboratory: experimental modelling of orogenic metamorphism of metapelites using a piston cylinder apparatus

    Science.gov (United States)

    Tropper, Peter; Mair, Philipp

    2017-04-01

    Metamorphic rocks contain a more or less complex mineral assemblage reflecting their metamorphic evolution. If the complex mineral assemblage is of multi-stage origin how do we know which mineral grew at which stage during the P-T evolution? To answer this question one needs to put constraints on the geological evolution of a given rock. The metamorphic evolution of a rock can be deciphered using three approaches: 1.) the practical geothermobarometric approach (inverse modelling), 2.) the theoretical pseudosection approach (forward modelling) and 3.) the experimental approach. Whereas with the first two approaches it is possible to constrain several stages of the P-T-X evolution but how do we know what assemblage is actually present at the desired P-T conditions? This question leads to the experimental approach, which allows a detailed mineralogical investigation of a given rock at distinct P-T conditions. Therefore, experimental investigations should be viewed as a forward modelling technique, which allow putting additional constraints on the evolution of a rock under defined P and T conditions and hence represents a snap-shot of a P-T point of the evolution of a given rock! For this purpose, simple experiments using natural rocks as starting materials can easily be conducted. The disadvantage of this method lies in the complex chemical composition of natural rocks and the deviation from chemical end-member systems. Therefore these experiments need to be evaluated not only 1.) in terms of their ability to reproduce the natural observations but also 2.) in their ability to reproduce theoretical calculations. In this study experimental investigations of orogenic metamorphism of metapelites (quartzphyllites with Grt1 + Ms1 + Ch1 + Bt1 + Rt) was investigated. Four different P-T conditions were chosen to represent an orogenic clockwise P-T loop: 400°C, 0.8 GPa, 600°C, 1.2 GPa, 700°C, 1 GPa and 500°C, 0.4 GPa. Two experiments with a duration of 16 and 33 days were

  18. Reconstruction of P-T-t metamorphic conditions from symplectites: insights from Pouso Alegre mafic rocks (Brasília Belt, Brazil)

    Science.gov (United States)

    Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Hermann, Jörg; Pedrosa-Soares, Antônio Carlos; Dussin, Ivo; Aurélio Pinheiro, Marco; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2017-04-01

    Reconstructing the metamorphic history of polycyclic tectono-metamorphic mafic rocks that preserve potential relicts of high-pressure metamorphism is challenging because such rocks are commonly retrogressed and rare in supercrustal sequences. However, pressure-temperature-time (P-T-t) information is required to obtain the paleo-geothermal gradients and thus to define those units as markers for suture zones. The mafic rocks from Pouso Alegre in the Meridional Brasília Orogen (SW-Brazil) outcrop as rare lenses within Sil-Grt gneisses, Amp-Grt orthogneisses and Bt granites. They are heavily weathered. They have previously been defined as "retro-eclogites", based on the characteristic symplectite texture and some mineralogical observations. They have been intepreted to mark the suture zone between the Paranapanema and São Francisco cratons, although no quantitative estimates of the pressure is available to support this conclusion. In this study we investigated in detail these samples to refine their P-T-t history. As commonly observed in retrogressed eclogites, the studied mafic rock shows symplectite and corona textures overprinting the former paragenesis of Garnet (Grt) - Clinopyroxene (Cpx) 1 - Amphibole (Amp) 1 - Rutile (Rt). Phase equilibrium modelling shows that this assemblage is stable at 690°C and 13.5 kbar, in line with Zr-in-rutile thermometry (720 ±30° C). Local compositions of the symplectite domains were used to retrieve the jadeite content of Cpx1. This low-Jd cpx is in line with the predictions of the model and confirms a maximum pressure of 14 kbar. The symplectite formed from the reaction Cpx1+Qz+H2O→Cpx2+Amp+Pl+Qz taking place at conditions of 600-750°C and <7 kbar. Zircon and monazite U-Th-Pb geochronology was performed for the mafic and surrounding rocks. Zircon core dates from the mafic rock spread along concordia from ca. 1.7 to 1.0 Ga with a cluster at 1520±17 Ma, which is interpreted as the protolith crystallization age. Zircon rim

  19. Mass wasting process at the surface of the Sangun metamorphic rocks in Kaminishigawa area, Asahi-machi, Okayama Prefecture.

    OpenAIRE

    新宮原, 秀和; 平山, 恭之; 津島, 淳; 於保, 幸正

    1999-01-01

    The relation among microstructures, weathering and mass wasting of the Sangun metamorphic rocks in the Kaminishigawa area, Asahi-machi, Okayama Prefecture, was studied. Three stages of penetrative planar structures are recognized; S1 schistosity, S2 crenulation cleavage and S3 crenulation cleavage. The S2 cleavage is the most commonly observed structure. The deree of weathering is divided into two classes on the base of appearance; slightly weathered and highly weathered rock. The three types...

  20. Stresses and Shear Fracture Zone of Jinshazhou Tunnel Surrounding Rock in Rich Water Region

    Institute of Scientific and Technical Information of China (English)

    ZHENG Jun-jie; LOU Xiao-ming

    2008-01-01

    Field evidence has shown that large-scale and unstable discontinuous planes in the rock mass surrounding tunnels in rich water region are probably generated after excavation. The tunnel surrounding rock was divided into three zones, including elastic zone, plastic damage zone and shear fracture zone fof assessing the stability of the tunnel surrounding rock. By local hydrogeology, the stresses of surrounding rock of Jinshazhou circular tunnel was analyzed and the stress solutions on the elastic and plastic damage zones were obtained by applying the theories of fluid-solid coupling and elasto-plastic damage mechanics. The shear fracture zone generated by joints was studied and its range was determined by using Mohr-Coulomb strength criterion. Finally, the correctness of the theoretical results was validated by comparing the scopes of shear fracture zones calculated in this paper with those from literature.

  1. Thermodynamic modeling using BINGO-ANTIDOTE: A new strategy to investigate metamorphic rocks

    Science.gov (United States)

    Lanari, Pierre; Duesterhoeft, Erik

    2016-04-01

    BINGO-ANTIDOTE is a new program, combing the achievements of the two petrological software packages XMAPTOOLS[1] and THERIAK-DOMINO[2]. XMAPTOOLS affords information about compositional zoning in mineral and local bulk composition of domains at the thin sections scale. THERIAK-DOMINO calculates equilibrium phase assemblages from given bulk rock composition, temperature T and pressure P. Primarily BINGO-ANTIDOTE can be described as an inverse THERIAK-DOMINO, because it uses the information provided by XMAPTOOLS to calculate the probable P-T equilibrium conditions of metamorphic rocks. Consequently, the introduced program combines the strengths of forward Gibbs free energy minimization models with the intuitive output of inverse thermobarometry models. In order to get "best" P-T equilibrium conditions of a metamorphic rock sample and thus estimating the degree of agreement between the observed and calculated mineral assemblage, it is critical to define a reliable scoring strategy. BINGO uses the THERIAKD ADD-ON[3] (Duesterhoeft and de Capitani, 2013) and is a flexible model scorer with 3+1 evaluation criteria. These criteria are the statistical agreement between the observed and calculated mineral-assemblage, -proportions (vol%) and -composition (mol). Additionally, a total likelihood, consisting of the first three criteria, allows the user an evaluation of the most probable equilibrium P-T condition. ANTIDOTE is an interactive user interface, displaying the 3+1 evaluation criteria as probability P-T-maps. It can be used with and without XMAPTOOLS. As a stand-alone program, the user is able to give the program macroscopic observations (i.e., mineral names and proportions), which ANTIDOTE converts to a readable BINGO input. In this manner, the use of BINGO-ANTIDOTE opens up thermodynamics to students and people with only a basic knowledge of phase diagrams and thermodynamic modeling techniques. This presentation introduces BINGO-ANTIDOTE and includes typical examples

  2. The petrological evidence for the uplift of ultrahigh-pressure met-amorphic rocks in root zone of the Qinling-Dabie orogenic belt

    Institute of Scientific and Technical Information of China (English)

    游振东; 韩郁菁; 张泽明

    1996-01-01

    Petrographic evidence indicates that some of the ultrahigh-pressure (UHP) eclogites in Dabie Mountains area may be evolved from epidote amphibolite fades rocks recrystallized under ultrahigh pressure conditions. The evolution of the erogenic belt had eventually resulted in the uplift of the metamorphic terrane soon after the peak metamorphic ultrahigh pressure stage of collision. During the uplift the ultrahigh-pressure metamorphic rocks were superimposed by nearly isothermal decompressive retrograde metamorphism through high-pressure (HP) edogite fades to amphibolite fades. Some of them were followed by epidote amphibolite fades and greenschist fades of metamorphism, while others were followed by epidote blueschist fades and then lowered to greenschist fades. Accompanying the retrogressive metamorphism. the rocks underwent at least 6 stages of deformation ranging from plastic to brittle character. The decompressive P-T path is also shown in the evolution of fluid inclusions: the entrapment pressure is

  3. Study on visualization simulation of temperature distributions in surrounding rock of tunnels in a deep mine

    Institute of Scientific and Technical Information of China (English)

    SUN Pei-de

    2006-01-01

    Based on the mathematical model for rock temperature distribution in a geothermal field, the properties of rock temperature distribution in geothermal field for four kinds of surrounding rock cross-sections of tunnels in a deep mine were simulated by using finite element method. It is shown that the relationship for rock temperature distribution varied with the geothermal parameters, time and space. Namely, 2-dimensional time-dependent isograms clearly showed the process for rock temperature variation and distribution in a geothermal field which has been redisplayed with visualization numerical simulation.

  4. Geochronology of source materials from high-pressure and ultrahigh-pressure metamorphic rocks in Jurassic sedimentary rocks of Hefei Basin

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    In this report, it is proven through stable isotopic geochronological study that for the Jurassic sedimentary rocks in the Dushan area of Anhui Province, the source materials derived from high-pressure and ultrahigh-pressure metamorphic rocks are the products of subduction and exhumation of the Yangtze plate under the North China plate during the Triassic period. The cobble of high-pressure or ultrahigh-pressure metamorphic rock in the Fenghuangtai Formation of Hefei Basin has Rb-Sr isotopic isochron age of phengite, apatite and whole rock, 232.1±2.1 Ma (MSWD = 0.59). Plateau ages of 40Ar/39Ar age spectra of detrital phengites in the Sanjianpu and Fenghuangtai formations are concordant, and they are 216.5±0.6 Ma and 217.4±1.3 Ma, respectively.

  5. Research on characters of surrounding rock in complex geology conditions and supporting time

    Institute of Scientific and Technical Information of China (English)

    Yu Weijian; Gao Qian; Zhai Shuhua; Zhang Meihua

    2008-01-01

    The methods combined by test, field monitoring and theoretical analysis were adopted to do the systemic re- search on the rock mass from micro-structure to macro-deformation, and rheological model of Jinchuan rock mass was es-tablished to discuss the reasonable supporting time. Results show that supporting after suitable stress and displacement release can benefit for the long-term stability of surrounding rock.

  6. Settlement behavior of coal mine waste in different surrounding rock conditions

    Institute of Scientific and Technical Information of China (English)

    MA Chun-de; LI Xi-bing; HU Bing-nan; CHEN Feng; XU Ji-cheng; LI Di-yuan

    2008-01-01

    In order to investigate the influence of complex conditions of in-situ surrounding rocks on the settlement behavior of nubbly coal mine waste subjected to high gravity pressure, four kinds of loading chambers made of different similar materials with different elastic moduli in experiments were used to simulate the deformation features of in-site rocks, including soft, moderate hardness, hard and extra-hard rocks. The results show that all the settlement-axial load (or axial strain-stress) curves obtained under four different surrounding rock conditions present power-exponential function feature. The final settlement of coal mine waste under the same axial load is closely related to the lumpiness gradations and the deformation behavior of chamber materials used to simulate behaviors of different in-situ surrounding rocks. In the same surrounding rock condition, the final settlement under the same maximum axial load decreases with the decrease of the proportion of larger gradation of coal mine waste. While for the same lumpiness gradation case, the settlement increases with the decrease of elastic modulus of simulated surrounding rocks and the lateral pressure induced by axial load increases with the increase of elastic modulus of loading chambers that are used to simulate different surrounding rocks. The test results also reveal that both the compaction curve and lateral pressure curve show a three-stage behavior, and the duration of each stage, which is closely related to gradations and the deformation feature of loading chamber materials, decreases with the increase of the proportion of the small size of coal mine waste and elastic modulus of the simulated rock materials.

  7. Radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico with annotated bibliography. [Over 600 citations

    Energy Technology Data Exchange (ETDEWEB)

    McLemore, V. T.

    1982-01-01

    From an extensive literature search and field examination of 96 nonsandstone radioactive occurrences, the author compiled an annotated bibliography of over 600 citations and a list of 327 radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico. The citations are indexed by individual radioactive occurrence, geographic area, county, fluorspar deposits and occurrences, geochemical analyses, and geologic maps. In addition, the geology, mineralization, and uranium and thorium potential of 41 geographic areas in New Mexico containing known radioactive occurrences in veins and igneous and metamorphic rocks or that contain host rocks considered favorable for uranium or thorium mineralization are summarized. A list of aerial-radiometric, magnetic, hydrogeochemical, and stream-sediment survey reports is included.

  8. Metamorphic conditions and CHIME monazite ages of Late Eocene to Late Oligocene high-temperature Mogok metamorphic rocks in central Myanmar

    Science.gov (United States)

    Maw Maw Win; Enami, Masaki; Kato, Takenori

    2016-03-01

    The high temperature (T)/pressure (P) regional Mogok metamorphic belt is situated in central Myanmar, and is mainly composed of pelitic gneisses, amphibolites, marbles, and calc-silicate rocks. The garnet-biotite-plagioclase-sillimanite-quartz assemblage and its partial system suggest equilibrium P/T conditions of 0.6-1.0 GPa/780-850 °C for the peak metamorphic stage, and 0.3-0.5 GPa/600-680 °C for the exhumation and hydration stage. Monazite grains show complex compositional zoning consisting of three segments-I, II, and III. Taking into consideration the monazite zoning and relative misfit curves, the calculated chemical Th-U-total Pb isochron method (CHIME) monazite age data (284 spot analyses) indicated four age components: 49.3 ± 2.6-49.9 ± 7.9, 37.8 ± 1.0-38.1 ± 1.7, 28.0 ± 0.8-28.8 ± 1.6, and 23.7 ± 1.3 Ma (2σ level). The ages of the Late Eocene and Late Oligocene epochs were interpreted as the peak metamorphic stage of upper-amphibolite and/or granulite facies and the postdated hydration stage, respectively.

  9. Damage Characteristics of Surrounding Rock Subjected to VCR Mining Blasting Shock

    Directory of Open Access Journals (Sweden)

    Nan Jiang

    2015-01-01

    Full Text Available For limiting the damage range caused by explosive shock loads in vertical crater retreat (VCR mining, the blasting damage characteristics of surrounding rock were studied by two methods: numerical simulation and ultrasonic testing. Combined with the mining blasting in Dongguashan Copper Mine of China, the VCR blasting shock characteristics under different conditions are obtained by using LSDYNA. Based on statistical fracture mechanics and damage mechanics theories, a damage constitutive model for rock mass subjected to blasting shock load was established. Then by using the fast Lagrange analysis codes (FLAC3D, the blasting damage characteristics of surrounding rock were analyzed by applying the blasting shock loads obtained from the VCR mining and the damage zone is obtained. At last, the relationship between the amount of explosives and the radius of damaged surrounding rock mass was discussed, and its formula was also derived. The research provides a theoretical basis for rationally controlling stope boundaries and optimizing mining blasting parameters.

  10. Development of fractures in soft rock surrounding a roadway and their control

    Institute of Scientific and Technical Information of China (English)

    Li Xuehua; Yao Qiangling; Man Jiankang; Chen Chaoqun; He Lihui

    2011-01-01

    As the excavation of roadway,new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks.Eventually,fracture zone and bed separation are formed in rocks because of the developed fractures.Therefore,mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway.The surrounding rocks of main haulage roadway in a certain coal mine is so broken and loose that the supporting is very difficult.Based on comprehensive analysis of the engineering geological conditions,a sight instrument was used to observe the fractures of internal surrounding rocks.Four indices,i.e.,the width of fracture zone W,the number of fractures n,the width of fractures d and rock fracture designation RFD,are put forward to evaluate the fracture development.According to the evolution rules of the soft rock roadway from this paper,control principles by stages and by regions are presented through the research.At the same time,the best time of grouting reinforcement is determined on the basis of fracture saturation.Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.

  11. Control over Surrounding Rocks Deformation of Soft Floor and Whole-Coal Gateways with Trapezoidal Supports

    Institute of Scientific and Technical Information of China (English)

    ZHAI Xin-xian; LI De-Quan; SHAO Qiang; SUN Yu-feng

    2005-01-01

    In Gengcun Colliery, Yima Coal Group Co. Ltd.the characteristics of the gateways of thick coal seam and the coal seam is with fully mechanized sublevel caving mining are that the thickness of roof coal seam of gateways is larger, their surrounding rocks are the whole-coal mass and the coal seam is prone to Spontaneous Combustion. With the natural equilibrium arch theory, the reasonable adjacent distance of No.11 mine-type metal supports was calculated in trapezoidal gateways based on these characteristics. Then, in-situ supporting experiments were carried out. The results indicate that under the action of virgin rock stress, the width of broken rocks zone of surrounding rocks is 1.7-2.0 m in return heading and 1.1-1.3 m in going headway. And their surrounding rocks belong to the Ⅳ-type soften rock and the Ⅲ-type common surrounding rock respectively. Therefore, under the movable abutment pressure, the gateways deformation is serious. It is suggested that the designed gateways have to use pre-broadened cross section to suit their deformation. At the same time, the accumulated water on gateway floor must be drained in time. These measures were taken in the 1302 and 1304 coal faces in Gengcun Colliery, and the satisfactory results have been obtained.

  12. Study on calculation of rock pressure for ultra-shallow tunnel in poor surrounding rock and its tunneling procedure

    Institute of Scientific and Technical Information of China (English)

    Xiaojun Zhou; Jinghe Wang; Bentao Lin

    2014-01-01

    A computational method of rock pressure applied to an ultra-shallow tunnel is presented by key block theory, and its mathematical formula is proposed according to a mechanical tunnel model with super-shallow depth. Theoretical analysis shows that the tunnel is subject to asymmetric rock pressure due to oblique topography. The rock pressure applied to the tunnel crown and sidewall is closely related to the surrounding rock bulk density, tunnel size, depth and angle of oblique ground slope. The rock pressure applied to the tunnel crown is much greater than that to the sidewalls, and the load applied to the left side-wall is also greater than that to the right sidewall. Mean-while, the safety of the lining for an ultra-shallow tunnel in strata with inclined surface is affected by rock pressure and tunnel support parameters. Steel pipe grouting from ground surface is used to consolidate the unfavorable surrounding rock before tunnel excavation, and the reinforcing scope is proposed according to the analysis of the asymmetric load induced by tunnel excavation in weak rock with inclined ground surface. The tunneling procedure of bench cut method with pipe roof protection is still discussed and carried out in this paper according to the special geological condition. The method and tunneling procedure have been successfully utilized to design and drive a real expressway tunnel. The practice in building the super-shallow tunnel has proved the feasibility of the calculation method and tunneling procedure presented in this paper.

  13. Provenance of the Late Neogene Siwalik sandstone, Kumaun Himalayan Foreland Basin: Constraints from the metamorphic rank and index of detrital rock fragments

    Indian Academy of Sciences (India)

    Poonam Jalal; Sumit K Ghosh

    2012-06-01

    An understanding about lithology, tectonics and unroofing history of provenance is mostly drawn from the compositional and textural parameters of the detrital fragments. We here use different metamorphic ranks (Rm) and metamorphic index (MI) values of rock fragments present in Late Neogene Siwalik sandstone of the Ramganga sub-basin to infer the provenance history. The study indicates maximum contribution from metamorphic ranks 1 and 2 (Rm1 and Rm2; meta-sedimentary and very low grade metamorphic rocks) and minimum from metamorphic rank 4 (Rm4; high metamorphic grade rocks). The metamorphic index (MI) values range from 118 to 224, with an average of 186. The meta-sedimentary and very low-grade metamorphic rock fragments are derived from the Lesser Himalayan domain. The medium-to-high grade metamorphic fragments are derived from the Lesser Himalayan Crystalline bodies. The abundance of Rm2 and Rm3 detrital modes suggest the exhumation of crystalline bodies of the Ramgarh and Almora most likely occurred prior to 7 Ma and subsequently the source area shifted and resulted abundant supply of Rm1 fragments due to the upliftment along Main Boundary Thrust around 5.55 Ma.

  14. Petrology, geochemistry, and metamorphic evolution of meta-sedimentary rocks in the Diancang Shan-Ailao Shan metamorphic complex, Southeastern Tibetan Plateau

    Science.gov (United States)

    Wang, Fang; Liu, Fulai; Liu, Pinghua; Shi, Jianrong; Cai, Jia

    2016-07-01

    Meta-sedimentary rocks are widely distributed within the Diancang Shan-Ailao Shan metamorphic complex in the Southeastern Tibetan Plateau. Detailed geochemical analyses show that all of them have similar geochemical features. They are enriched in light rare-earth elements (LREEs) and depleted in heavy rare-earth elements (HREEs), with moderately negative Eu anomalies (Eu/Eu∗ = 0.55-0.75). Major and trace element compositions for the meta-sedimentary rocks suggest that the protoliths were probably claystone, siltstone, and greywacke and deposited in an active continental margin. Garnet porphyroblasts in meta-sedimentary rocks have distinct compositional zonation from core to rim. The zonation of garnet in St-Ky-Grt-Bt-Ms schist indicates an increasing P-T trend during garnet growth. In contrast, garnets from (Sil)-Grt-Bt paragneiss show diffusion zoning, implying a decreasing P-T trend. Based on mineral transformations and P-T estimates using conventional geothermobarometers and pseudosection calculations, four metamorphic stages have been determined, including an early prograde metamorphic stage (M1), a peak amphibolite-granulite facies metamorphic stage (M2), a near-isothermal decompression stage (M3), and a late amphibolites-facies retrograde stage (M4). The relic assemblage of Ms + St ± Ky ± Bt ± Kfs + Qz preserved as inclusions in garnet porphyroblasts of the meta-sedimentary rocks belongs to prograde (M1) stage and records P-T conditions of 560-590 °C and 5.5-6.3 kb. Matrix mineral assemblages of Grt + Bt + Ky/Sil + Pl + Qz and Grt + Bt ± Sil + Pl ± Kfs + Qz formed at peak (M2) stage yield P-T conditions of 720-760 °C and 8.0-9.3 kb. M3 is characterized by decompression reactions, dehydration melting of assemblages that include hydrous minerals (e.g., biotite), and partial melting of felsic minerals. The retrograde assemblages is Grt + Bt + Sil + Pl + Qz formed at 650-760 °C and 5.0-7.3 kb. At the amphibolites-facies retrograde (M4) stage, fine

  15. The fate of carbon and CO2 - fluid-rock interaction during subduction metamorphism of serpentinites

    Science.gov (United States)

    Menzel, Manuel D.; Garrido, Carlos J.; López Sánchez-Vizcaíno, Vicente; Marchesi, Claudio; Hidas, Károly

    2016-04-01

    Given to its large relevance for present and past climate studies, the deep carbon cycle received increasing attention recently. However, there are still many open questions concerning total mass fluxes and transport processes between the different carbon reservoirs in the Earth's interior. One key issue is the carbon transfer from the subducting slab into fluids and rocks in the slab and mantle wedge. This transfer is controlled by the amount and speciation of stable carbon-bearing phases, which have a strong impact on the pH, redox conditions and trace-element budget of slab fluids. As recent experiments and thermodynamic modeling have shown, water released from dehydrating serpentinites has a great potential to produce CO2-enriched slab fluids by dissolution of carbonate minerals. To constrain the fate of carbon and CO2-fluid-rock interactions during subduction metamorphism of serpentinites, we have studied carbonate-bearing serpentinites recording different prograde evolutions from antigorite schists to Chl-harzburgites in high-P massifs of the Nevado-Filabride Complex (Betic Cordillera, S. Spain). Our results indicate that dissolution of dolomite in marbles in contact with dehydrating serpentinites is spatially limited during prograde metamorphism of carbonate-bearing serpentinites, but it can lead to the formation of silicate-rich zones in marbles close to the contacts. In lower grade serpentinite massifs (1.0-1.5 GPa / 550 °C), the presence of marble lenses in contact with antigorite schists appears to promote local dehydration of serpentinite coupled with carbonation of antigorite, forming Cpx-Tr-Chl-bearing high grade ophicarbonate zones. At the Cerro del Almirez ultramafic massif, where a dehydration front from antigorite-serpentinite to prograde Chl-harzburgite is preserved (1.9 GPa / 680 °C), a significant amount of carbon is retained in prograde Chl-harzburgites and Tr-Dol-marble lenses. This observation is at odds with thermodynamic models that

  16. X-ray color maps of the zoned garnets from Silgará Formation metamorphic rocks,SantanderMassif, Eastern Cordillera (Colombia

    Directory of Open Access Journals (Sweden)

    Takasu Akira

    2010-12-01

    Full Text Available

    The metamorphic rocks of the Lower Paleozoic Silgará Formation of the Santander Massif, Eastern Cordillera (Colombia, were affected by a Barrovian-type metamorphism under low to high temperature and medium pressure conditions. These rocks contain garnet porphyroblasts, which show several kinds of chemical zoning patterns. The garnet grains behave as closed systems with respect to the rock matrix. Most of the observed zoning patterns are due to gradual changes in physicochemical conditions during growth. However, some garnet grains show complex zoning patterns during multiple deformation and metamorphic events.

  17. Signature of Cenozoic orogenic movements in combustion metamorphic rocks: mineralogy and geochronology (example of the Salair-Kuznetsk Basin transition)

    Energy Technology Data Exchange (ETDEWEB)

    Novikov, I.S.; Sokol, E.V.; Travin, A.V.; Novikova, S.A. [RAS, Novosibirsk (Russian Federation)

    2008-06-15

    Cenozoic combustion metamorphic (CM) complexes produced by fossil natural coal fires are widespread at range-basin junctions worldwide. Large-scale fires accompany the initial orogenic phases as fresh coal-bearing strata become drawn into the aeration zone as a result of crustal deformation. In combustion metamorphism, the protolith melts to different degrees either into ferrous basic paralava or in glassy clinker. The melt rocks have a phase composition favorable for Ar-40/Ar-39 dating of ignition coeval with the onset of each episode in Late Cenozoic orogenic events. We suggest an algorithm providing correct Ar-40/Ar-39 age determination of CM rocks followed by well-grounded geological interpretation and test the new approach on melt rocks from the Kuznetsk Coal Basin. Paralava samples were dated by Ar-40/Ar-39 incremental heating and the isotope ratios were corrected for Ca-, Cl-, and K-derived Ar isotopic interferences. The interpretation of age-spectrum results was checked against internal and external criteria. The former were plateau and isochrone ages and the latter included the so-called 'couple criterion' and conventional relative ages inferred from geological and stratigraphic evidence. As a result, we distinguished two groups of dates for combustion metamorphic events bracketed between 1.2 {+-} 0.4 and 0.2 {+-} 0.3 Ma. The older ages represent rocks in the western edge of the Prokopievsk-Kiselevsk block of the Salair zone and the younger dates correspond to those in its eastern edge. The reported dates record the time when the fault boundaries of the blocks were rejuvenated during recent activity and the block accreted to the Salair orogenic area as a submontane step. The suggested approach to the choice of objects, classification of rocks, and interpretation of Ar-40/Ar-39 spectra is universal and can be practiced in any area of combustion metamorphism.

  18. The Metamorphic Rocks-Hosted Gold Mineralization At Rumbia Mountains Prospect Area In The Southeastern Arm of Sulawesi Island, Indonesia

    Directory of Open Access Journals (Sweden)

    Hasria Hasria

    2017-09-01

    Full Text Available Recently, in Indonesia gold exploration activities  are not only focused along volcanic-magmatic belts, but also starting to shift along metamorphic and sedimentary terrains. The study area is located in Rumbia mountains, Bombana Regency, Southeast Sulawesi Province. This paper is aimed to describe characteristics of alteration and ore mineralization associated  with metamorphic rock-related gold deposits.  The study area is found the placer and  primary gold hosted by metamorphic rocks. The gold is evidently derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC. These quartz veins are currently recognized in metamorphic rocks at Rumbia Mountains. The quartz veins are mostly sheared/deformed, brecciated, irregular vein, segmented and  relatively massive and crystalline texture with thickness from 1 cm to 15.7 cm. The wallrock are generally weakly altered. Hydrothermal alteration types include sericitization, argillic, inner propylitic, propylitic, carbonization and carbonatization. There some precious metal identified consist of native gold and ore mineralization including pyrite (FeS2, chalcopyrite (CuFeS2, hematite (Fe2O3, cinnabar (HgS, stibnite (Sb2S3 and goethite (FeHO2. The veins contain erratic gold in various grades from below detection limit <0.0002 ppm to 18.4 ppm. Based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposit type. The orogenic gold deposit is one of the new targets for exploration in Indonesia

  19. ANALYSIS ON INCREMENTAL COHESION OF SURROUNDING ROCK DUE TO PRESTRESSED CABLE ANCHOR

    Institute of Scientific and Technical Information of China (English)

    夏建中; 闫莫明; 滕年保; 李方政

    1998-01-01

    A new method for determining the incremental cohesion △Cm of surrounding rock due toprestressed cable anchor is presented, and the formulas for △Cm are deduced and ACredistributions also are discussed, based on the two anchorage effects, one is the effect with theprestressed value △Q3 of cable anchor improving the stress state of surrounding rock andincreasing the surrounding rock strength, the other is the fully encapsulated effect. Thedetermined incremental cohesion △Cm is subjected to the model test and field measurement in thereferences, and coincides well with those tested results. The formulas for △Cm can be used indesigning supoport parameters and related numerical analyses of prestressed cable anchor.

  20. Research on the stability analysis and design of soil tunnel surrounding rock

    Institute of Scientific and Technical Information of China (English)

    Zheng Yingren; Qiu Chenyu; Xiao Qiang

    2010-01-01

    The paper first analyzes the failure mechanism and mode of tunnel according to model experiments and mechanical calculation and then discusses the deficiency of taking the limit value of displacement around the tunnel and the size of the plastic zone of surrounding rock as the criterion of stability.So the writers put forward the idea that the safety factor of surrounding rock calculated through strength reduction FEM(finit element method)should be regarded as the criterion of stability,which has strict mechanical basis and unified standard and would not be influenced by other factors.The paper also studies the safety factors of tunnel surrounding rock(safety factors of shear and tension failure)and lining and some methods of designing and calculating tunnels.At last,the writers take the loess tunnel for instance and show the design and calculation results of two-lane railway tunnel.

  1. Tectono-geochemistry analyses of fault rocks in shear zone of metamorphic core complex in north Jiangxi, China

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Through a systematic sampling test and mass equilibrium analysis of the three sorts of complex assemblages (intrusive complex, tectonic complex and metamorphic complex) penetrating the metamorphic core complex (MCC) in the Xingzi area of north Jiangxi, the authors find that, like major elements, the trace elements of small ion radius, big specific gravity and high potential form the accumulative series in fault rocks, instead of divergence series. In rare earth elements, ΣREE and HREE are relatively centralized, characteristic of rising and Eu loss in the distribution pattern. Only on the upside of the ductile fault, there exist some phenomena contrary to the general rules, most of which are restricted by the rock rheologic differentiation, coupling of mechanics and chemistry, and inversion of tectonic regime.

  2. Experimental study on stability control technology of surrounding rock of deep roadways in coal mine

    Institute of Scientific and Technical Information of China (English)

    Luo Yong; Yuan Liang; Yang Yang

    2014-01-01

    In order to solve effectively the problems of deep mining with safety and high efficiency,the multi-ple factors influencing the stability of deep rock roadway and technical problems are analyzed in the light of the severe situation of effective mining for deep coal resource,and the stability control methods for deep rock road-way are provided,which are based on the idea of combined support with separated steps and integral control of surrounding rock of deep rock roadway. The suggested methods were applied to a deep rock roadway with-648 m depth in Gubei coal mine of Huainan area. The field test was carried out and the in-situ monitoring was imple-mented,and the support scheme was optimized and adjusted to improve the stability of the surrounding rock of the roadway based on the feedback analysis. The results showed that the stability can be improved greatly by the provided control methods for deep roadway. The present methods for stability control of deep rock roadway can be used to other deep rock roadways with the similar conditions.

  3. Surrounding rock deformation regularity of roadway under extremely complicated geological conditions in deep mine and its control

    Institute of Scientific and Technical Information of China (English)

    刘长友; 何卓军; 万志军

    2003-01-01

    By combining the practices of deep mine mining in Changguang Mine field and using the Universal Distinct Element Code 3.0(UDEC3.0) numerical computing method, the distribution characteristics of deformation field and stress field as well as the surrounding rock deformation regularity of soft rock roadway are analyzed under extremely complicated geological conditions, a technical principle of bolting to control the surrounding rock of roadway is put forward. And also using a dynamic control for surrounding rocks designing method, the supporting parameters and implement plan are rationally determined. The experimental tests have obtained a good controlling result of surrounding rock.

  4. Analysis for interaction of supports and surrounding rock of gateways in Iongwall minging

    Institute of Scientific and Technical Information of China (English)

    伍永平

    2001-01-01

    Gateway supporting in long-wall mining has been a problem that restricts the mine production and safety, the paper sets up an interaction model between support and surrounding rock ( rock mass structure) and probes the elementary t.heory about ground pressure behaviors of gateway. Based on the analysis of supporting theories, some new viewpoints about gateways supporting and ground pressure controlling are put forward.

  5. Analysis for interaction of supports and surrounding rock of gateways in longwall minging

    Institute of Scientific and Technical Information of China (English)

    WU Yong-ping

    2001-01-01

    Gateway supporting in long-wall mining has been a problem that restri cts the mine production and safety, the paper sets up an interaction model betwe en support and surrounding rock (rock mass structure) and probes the elementary theory about ground pressure behaviors of gateway. Based on the analysis of supp orting theories, some new viewpoints about gateways supporting and ground pressu re controlling are put forward.

  6. Study on mechanism and practice of surrounding rock control of high stress coal roadway

    Institute of Scientific and Technical Information of China (English)

    WANG Wei-jun; YANG Lei; OUYANG Guang-bin

    2006-01-01

    The mechanical principle and surrounding rock deformation feature of high stress coal roadway was analyzed. The condition of stress balance of the kind of the roadway was put forward. The surrounding rock control principle and supporting technique of high stress coal roadway were discussed. It was very important to control early days deformation of coal sides. The supporting strength is should increased, so the strength loss of coal sides is decreased. The range of plastic fluid zone is reduced. The above mention-ned principle is applied in industrial test, and the new supporting technique is applied successfully.

  7. Control over surrounding rocks deformation of soft floor and whole-coal gateways with trapezoidal supports

    Energy Technology Data Exchange (ETDEWEB)

    Zhai, X.; Li, D.; Shao, Q.; Sun, Y. [Henan Polytechnic University, Jaozuo (China). Dept. of Resource and Material Engineering

    2005-06-01

    The coal seams of Guengcun Coal mine of Yima Coal Group Co. Ltd. are prone to spontaneous combustion. Fully mechanized longwall mining with sublevel caving is used as the mining method. Based on the characteristics of the gateways of the 1301 coal face and of the roof coal seams, the natural equilibrium arch theory was used to design the parameters of 11 mine-type metal supports. Then, in-situ supporting experiments were carried out. The results indicate that under the action of virgin rock stress, the width of broken rocks zone of surrounding rocks is 1.7-2.0 m in the return heading and 1.1-1.3 m in the outgoing headway and their surrounding rocks belong to the IV-type soft rock and the III-type common surrounding rock respectively. Therefore, under the movable abutment pressure, the gateway deformation is serious. At the same time, the accumulated water on gateway floor must be drained in time. These measures were taken in the 1302 and 1304 coal faces in Gengcun colliery, and satisfactory results have been obtained. 8 refs., 3 figs.

  8. Petrographic study on the high-grade metamorphic rocks from the Highland and Kadugannawa Complexes, central Sri Lanka

    OpenAIRE

    Malaviarachchi, Sanjeewa; 高須, 晃

    2005-01-01

    This study focused on texture of the metamorphic rocks from the central region of Sri Lanka,representing both the Highland Complex and the Kadugannawa Complex.Petrographical investigation of some pelitic and intermediate to basic granulites from the central Highland Complex and some pelitic and mafic rocks from the Kadugannawa Complex of Sri Lanka was carried out.13; Among the metapelites,garnet-absent and garnet-bearing as well as spinel-absent and spinel-bearing lithologies were studied.Gar...

  9. Petrogenetic relationships between jadeitite and associated high-pressure and low-temperature metamorphic rocks in worldwide jadeitite localities

    Science.gov (United States)

    Tsujimori, T.; Harlow, G. E.

    2011-12-01

    Jadeitite-bearing serpentinite-matrix mélange is distributed in the Caledonian (Russia), Alps-Himalayan (Italy, Iran, Greece, and Myanmar), Caribbean (Guatemala, and Cuba), and circum-Pacific (Japan, and Western USA) orogenic belts, and always contains high-pressure, low-temperature (HP-LT) metamorphic rocks. There are also jadeitite xenoliths in kimberlitic pipes. Major occurrences consist principally of primary fluid precipitates (P-type) that infiltrated the mantle wedge, fewer occurrences document metasomatic replacement (R-type) of plagiogranite, metagabbro and eclogite, and both types may be possible in the same occurrence or system. Conditions of crystallization are difficult to constrain because of high-variance assemblages (few phases containing many components). Blueschist correlations are abundant, largely on textural grounds with respect to coexisting eclogites, however without adequate phase-assemblage constraints, jadeitite formation at eclogite conditions cannot be ruled out. Available geochronological data of both jadeitite and associated HP-LT rock show temporal discrepancies between jadeitite-formation and HT-LP metamorphism at some localities. The close association between older jadeitite and younger HP-LT rock in a single mélange complex implies different histories for the subduction channel and mélange. Jadeitite can stay at the wedge mantle for a considerable time and, as a result, experience multiple fluid-infiltration events. The subduction channel can occasionally incorporate overlying serpentinized mantle wedge material due to tectonic erosion. With time the disrupted wedge mantle containing jadeitite veins is mixed with younger blueschists, exhumed eclogites and various fragments of suprasubduction zone lithologies. Consequently, recrystallization and re-precipitation of jadeitite are reactivated along a slab-wedge mantle interface. All these possible scenarios and their combinations yield a complicated petrologic record in jadeitite

  10. ALTERNATING METHOD STUDY ON STRESS ANALYSIS OF SURROUNDING ROCK FOR TWO RANDOM GEOMETRY TUNNELS

    Institute of Scientific and Technical Information of China (English)

    吕爱钟; 张路青

    1997-01-01

    The stress analysis of surrounding rock for two random geometry tunnels is studied inthis paper by using Schwarz's alternating method. The simple and effective alternating algorithm is found, in which the surplus surface force is approximated by Fourier series, thus the iteration derivation can be conducted according to the precision required, finally, the stress results with high precision are obtained.

  11. Plastic zone distribution laws and its types of surrounding rock in large-span roadway

    Institute of Scientific and Technical Information of China (English)

    Li Chong; Xu Jinhai; Pan Jianzhong; Ma Chao

    2012-01-01

    In order to study the distribution laws and types of plastic zone of surrounding rock in large-span roadway,we analyzed the distribution laws with different spans and lateral pressures using FLAC3D numerical calculation software.Based on the roadway support difficulty and distribution laws of the plastic zone of surrounding rock,we defined the large-span roadway and classified the types of large-span rectangular roadways.As a result,the distribution laws of the plastic zone on surrounding rock in a rectangular roadway with different spans and lateral pressures were obtained.The results show that the area of the plastic zone on surrounding rock increased with the increase of the spans and lateral pressures,and the plastic zone was symmetrical to the center line of roadway.At λ =0.5,1.0,1.5,and 2.0,the plastic zone presented "addleshape" distribution,"ellipse" distribution."thin and high" distribution and "inverse trapezium" distribution,respectively.In addition,we classified the roadways into four types according to the different lateral pressures and spans,including small-span,moderate-span,large-span and extreme-large-span roadways.

  12. Simulation of coupled THM process in surrounding rock mass of nuclear waste repository in argillaceous formation

    Institute of Scientific and Technical Information of China (English)

    蒋中明; 陈永贵

    2015-01-01

    To investigate and analyze the thermo-hydro-mechanical (THM) coupling phenomena of a surrounding rock mass in an argillaceous formation, a nuclear waste disposal concept in drifts was represented physically in an in-situ test way. A transversely isotropic model was employed to reproduce the whole test process numerically. Parameters of the rock mass were determined by laboratory and in-situ experiments. Based on the numerical simulation results and in-situ test data, the variation processes of pore water pressure, temperature and deformation of surrounding rock were analyzed. Both the measured data and numerical results reveal that the thermal perturbation is the principal driving force which leads to the variation of pore water pressure and deformations in the surrounding rock. The temperature, pore pressure and deformation of rock mass change rapidly at each initial heating stage with a constant heating power. The temperature field near the heater borehole is relatively steady in the subsequent stages of the heating phase. However, the pore pressure and deformation fields decrease gradually with temperature remaining unchanged condition. It also shows that a transversely isotropic model can reproduce the THM coupling effects generating in the near-field of a nuclear waste repository in an argillaceous formation.

  13. U-Pb zircon and CHIME monazite dating of granitoids and high-grade metamorphic rocks from the Eastern and Peninsular Thailand - A new report of Early Paleozoic granite

    Science.gov (United States)

    Kawakami, T.; Nakano, N.; Higashino, F.; Hokada, T.; Osanai, Y.; Yuhara, M.; Charusiri, P.; Kamikubo, H.; Yonemura, K.; Hirata, T.

    2014-07-01

    In order to understand the age and tectonic framework of Eastern to Peninsular Thailand from the viewpoint of basement (metamorphic and plutonic) geology, the LA-ICP-MS U-Pb zircon dating and the chemical Th-U-total Pb isochron method (CHIME) monazite dating were performed in the Khao Chao, Hub-Kapong to Pran Buri, and Khanom areas in Eastern to Peninsular Thailand. The LA-ICP-MS U-Pb zircon dating of the garnet-hornblende gneiss from the Khao Chao area gave 229 ± 3 Ma representing the crystallization age of the gabbro, and that of the garnet-biotite gneisses gave 193 ± 4 Ma representing the timing of an upper amphibolite facies metamorphism. The CHIME monazite dating of pelitic gneiss from the Khao Chao gneiss gave scattered result of 68 ± 22 Ma, due to low PbO content and rejuvenation of older monazite grains during another metamorphism in the Late Cretaceous to Tertiary time. The U-Pb ages of zircon from the Hua Hin gneissic granite in the Hub-Kapong to Pran Buri area scatter from 250 Ma to 170 Ma on the concordia. Granite crystallization was at 219 ± 2 Ma, followed by the sillimanite-grade regional metamorphism at 185 ± 2 Ma. Monazite in the pelitic gneiss from this area also preserves Early to Middle Jurassic metamorphism and rejuvenation by later contact metamorphism by non-foliated granite or by another fluid infiltration event in the Late Cretaceous to Tertiary time. The Khao Dat Fa granite from the Khanom area of Peninsular Thailand gave a U-Pb zircon age of 477 ± 7 Ma. This is the second oldest granite pluton ever reported from Thailand, and is a clear evidence for the Sibumasu block having a crystalline basement that was formed during the Pan-African Orogeny. The Khao Pret granite gives U-Pb zircon concordia age of 67.5 ± 1.3 Ma, which represents the timing of zircon crystallization from the granitic melt and accompanied sillimanite-grade contact metamorphism against surrounding metapelites and gneisses. Metamorphic rocks in the Doi Inthanon area

  14. Field investigations of high stress soft surrounding rocks and deformation control

    Directory of Open Access Journals (Sweden)

    Weijian Yu

    2015-08-01

    Full Text Available Field investigations of high stress soft rock deformations show that the high stress soft rock roadway can slide with large deformation. Severe extrusion and floor heave can also be subsequently observed. The supported roadway can be locally damaged or completely fail, where the floor has a large deformation and/or is seriously damaged. The factors inducing large deformation of surrounding rocks in deep roadway are rock strengths, structure face cutting types, stress states, stress release, support patterns, and construction methods. Based on the deformation characteristics of high stress soft rock roadway, a comprehensive support scheme is proposed. The overall support technology of “step-by-step and joint, hierarchical reinforcement” for roadway is presented, and the anchor cable and bolt parameters to check the design methods are also given. Finally, the proposed comprehensive support method “bolt + metal mesh + U-steel arch + shortcrete + grouting and cable” is used in the extension section of east main haulage roadway at −850 m level of Qujiang coal mine. The 173-day monitoring results show that the average convergence of sidewalls reaches 208 mm, and the average relative convergence of roof and floor reaches 448 mm, suggesting that this kind of support technology for controlling large deformation of high stress soft surrounding rock roadway is effective.

  15. Determination and distribution of diesel components in igneous rock surrounding underground diesel storage facilities in Sweden.

    Science.gov (United States)

    Loren, A; Hallbeck, L; Pedersen, K; Abrahamsson, K

    2001-01-15

    In Sweden, a preliminary investigation of the contamination situation of igneous rock surrounding underground storage facilities of diesel showed that the situation was severe. The diesel was believed to have penetrated into the rock as far as 50 m from the walls of the vaults. Consequently, the risk for contamination of groundwater and recipients could not be neglected. To be able to assess the fate of diesel components in rock, both a suitable drilling method and a method for the determination of a wide range of diesel components were needed. The analytical method presented made it possible to quantify a number of hydrocarbons in rock samples collected with triple-tube core drilling. The samples were dissolved in hydrofluoric acid (HF) with hexane in Teflon centrifuge tubes. After digestion of the rock, extraction of the analytes with hexane was performed. Determination of the individual hydrocarbons present was done with gas chromatography-mass spectrometry (GC-MS). The method was used to study the environmental impact of the underground storage of diesel. The drilling method enabled sampling without contamination risks. Our data show that the major transport of diesel components in rock occurs through fracture systems and that diffusion of diesel through the rock is of minor importance. The results have drastically changed the view of the contamination situation of diesel in the vicinity of storage facilities in hard rock in Sweden.

  16. Hydro-mechanically coupled modelling of deep-seated rock slides in the surroundings of reservoirs

    Science.gov (United States)

    Lechner, Heidrun; Preh, Alexander; Zangerl, Christian

    2016-04-01

    In order to enhance the understanding of the behaviour of deep-seated rock slides in the surroundings of large dam reservoirs, this study concentrates on failure mechanisms, deformation processes and the ability of self-stabilisation of rock slides influenced by reservoirs. Particular focus is put on internal rock mass deformations, progressive topographical slope changes due to reservoir impoundment and shear displacements along the basal shear zone in relation to its shear strength properties. In this study, a two-dimensional numerical rock slide model is designed by means of the Universal Distinct Element Code UDEC and investigated concerning different groundwater flow scenarios. These include: (i) a completely drained rock slide model, (ii) a model with fully saturated rock mass below an inclined groundwater table and (iii) a saturated groundwater model with a reservoir at the slope toe. Slope displacements initiate when the shear strength properties of the basal shear zone are at or below the critical parameters for the limit-equilibrium state and continue until a numerical equilibrium is reached due to deformation- and displacement-based geometrical changes. The study focuses on the influence of a reservoir at the toe of a rock slide and tries to evaluate the degree of displacement which is needed for a re-stabilisation in relation to the geometrical characteristics of the rock slide. Besides, challenges and limitations of applied distinct element methods to simulate large strain and displacements of deep-seated rock slides are discussed. The ongoing study will help to understand the deformation behaviour of deep-seated pre-existing rock slides in fractured rock mass during initial impounding and will be part of a hazard assessment for large reservoirs.

  17. Multiphase solid inclusions in ultrahigh-pressure metamorphic rocks: A snapshot of anatectic melts during continental collision

    Science.gov (United States)

    Gao, Xiao-Ying; Chen, Yi-Xiang; Zhang, Qiang-Qiang

    2017-09-01

    Partial melting of crustal rocks may take place during continental collision, giving rise to anatectic melts. Their composition and evolution are major concerns in the chemical geodynamics of continental subduction zones. They are often recorded by multiphase solid (MS) inclusions enclosed by peritectic minerals in ultrahigh-pressure (UHP) metamorphic terranes inside collisional orogens. These MS inclusions generally show negative crystal shapes with the wedge-shaped off-shoot structure in garnet, omphacite and kyanite. They contain a number of silicate, carbonate and sulfate minerals such as K-feldspar, plagioclase, quartz, epidote, calcite and barite, with occasional occurrences of magnetite, zircon and pyrite. An integrated study of petrology, mineralogy and geochemistry indicates that the MS inclusions are the primary crystallization product of former silicate and carbonate melts. The silicate melts were derived from dehydration melting of hydrous minerals such as phengite and paragonite in UHP metamorphic rocks, and the carbonate melts were produced by partial melting of subducted carbonate minerals. Some MS inclusions show remarkably high Na contents, suggesting their derivation from dehydration melting of paragonite. In contrast, K-bearing MS inclusions are produced by dehydration melting of K-bearing hydrous minerals like phengite. Many studies have been devoted to the mineralogical and geochemical compositions of MS inclusions in UHP metamorphic rocks, with the aim to determine the time and mechanism of crustal anataxis during collisional orogeny. Various analytical methods were used to characterize the morphology, texture, mineral chemistry and trace element composition of MS inclusions. The results provide insights into the physicochemical properties of anatectic melts in continental subduction zones. The partial melting of deeply subducted crustal rocks would lead to their significant differentiation in lithochemistry and geochemistry. This process has

  18. MINING INDUCED INFLUENCE ON THE ROADWAYS IN WEAK SURROUNDING ROCK AND ITS CONTROLLING MEASURES

    Institute of Scientific and Technical Information of China (English)

    陆士良; 王悦汉

    1991-01-01

    The application of destressing method can change the distribution patterns of the stress field in the weak rock surrounding openings, locate the openings in the zone of low stress level, thus improve their loading and maintaining conditions. Such method is considered as a new way of opening maintenance in weak rock and has caused extensive interests in mining industry both at home and abroad. The results of theoretic research and lab experiments of utilizing topdestresslng trough to maintain the opening affected by mining activities in weak rock, as well as its practical application in a coal mine are introduced in this paper. The research results indicate that the deformation and floor heaving of the opening in weak rock can be effectively controlled, and long-term stability of the opening can be realized by applying destressing method as long as the destressing plan and concerned parameters are carefully determined.

  19. A Novel Model of Set Pair Analysis Coupled with Extenics for Evaluation of Surrounding Rock Stability

    Directory of Open Access Journals (Sweden)

    Mingwu Wang

    2015-01-01

    Full Text Available The evaluation of surrounding rock stability is a complex problem involving numerous uncertainty factors. Here, based on set pair analysis (SPA coupled with extenics, a novel model, considering incompatibility, certainty, and uncertainty of evaluation indicators, was presented to analyze the surrounding rock stability. In this model, extension set was first utilized to describe the actual problem of surrounding rock stability. Then, the connectional membership degree of the set pair was introduced to compare the measured values with classification standards from three aspects embracing identity, discrepancy, and contrary. Also, according to identity-discrepancy-contrary (IDC analysis in the universe of the extension set, the connection numbers were proposed to specify the connectional membership degree of an evaluation indicator to each class. Combined with the weights of evaluation indicators, integrated connectional membership degrees were calculated to determine their classes of rock stability. Finally, a case study and comparison with variable fuzzy set method, triangular fuzzy number method, and basic quality (BQ grading method were performed to confirm the validity and reliability of the proposed model. The results show that this model can effectively and quantitatively express the differences within a group, transformation of different groups, and uncertainty of complex indicators as a whole.

  20. Petrography and Metamorphism of the Metasedimentary Country-Rocks of the Jacurici Valley Chromitite-Hosting Mafic-Ultramafic Complexes, Bahia, Northeastern Brazil

    Directory of Open Access Journals (Sweden)

    Eliane A. Del Lama

    2001-11-01

    Full Text Available This paper deal with on the metasedimentary country-rocks of the chromite-bearing ultramafic rocks that occur in the “Jacurici River Valley Chromium District” northeastern Bahia, Brazil. This region presents a complex geologic-petrologic framework of rocks that were intensely deformed, metamorphosed and transformed by metasomatic processes, making it difficult to interpret their volutionary/metamorphic record. Although the metasedimentary country rocks have also been affected by such processes, it is possible to distinguish evidence of a previous high-grade metamorphism that affected them. Thermobarometric data for the observed mineralogical associations indicate P-T conditions around 750-800ºC and 7-8 kb for the metamorphic peak, based mainly on the presence of olivine in marbles and the cordierite-garnet-sillimanitespinel association in aluminous gneisses.

  1. Stability Evaluation on Surrounding Rocks of Underground Powerhouse Based on Microseismic Monitoring

    Directory of Open Access Journals (Sweden)

    Feng Dai

    2015-01-01

    Full Text Available To study the stability of underground powerhouse at Houziyan hydropower station during excavation, a microseismic monitoring system is adopted. Based on the space-time distribution characteristics of microseismic events during excavation of the main powerhouse, the correlation between microseismic events and blasting construction is established; and the microseismic clustering areas of the underground powerhouse are identified and delineated. The FLAC3D code is used to simulate the deformation of main powerhouse. The simulated deformation characteristics are consistent with that recorded by microseismic monitoring. Finally, the correlation between the macroscopic deformation of surrounding rock mass and microseismic activities is also revealed. The results show that multiple faults between 1# and 3# bus tunnels are activated during excavation of floors V and VI of the main powerhouse. The comprehensive method combining microseismic monitoring with numerical simulation as well as routine monitoring can provide an effective way to evaluate the surrounding rock mass stability of underground caverns.

  2. Failure mechanism and stability control technology of rock surrounding a roadway in complex stress conditions

    Institute of Scientific and Technical Information of China (English)

    Yu Yang; Bai Jianbiao; Chen Ke; Wang Xiangyu; Xiao Tongqiang; Chen Yong

    2011-01-01

    To solve the problem of supporting three downhill coal structures in the Yongan Coal Mine of Shanxi Jincheng,we studied the regular development of stress and plastic zones and characteristics of deformation of rock surrounding roadway groups after a period of roadway driving,mining one side as well as mining both sides,we used FLAC3D for our numerical and theoretical analyses.Field test were carried out,where we revealed the deformation mechanism of roadways and its coal pillars in complex stress conditions.We proposed a roadway stability control technology using backwall grouting with high-water rapid hardening material and combined support with bolt and cable anchoring after mining both sides.Our field practices showed that deformation of rock surrounding roadways can be controlled with this technology.

  3. Modification of rock mass permeability in the zone surrounding a shaft in fractured, welded tuff

    Energy Technology Data Exchange (ETDEWEB)

    Case, J.B.; Kelsall, P.C.

    1987-03-01

    The excavation of a nuclear waste repository at Yucca Mountain, Nevada requires access through shafts and ramps from the ground surface to the repository horizon. To evaluate the need and performance of the sealing subsystem, it is necessary to predict the modifications in the rock immediately surrounding the shaft. The purpose of this study is to develop a model of permeability changes as a function of radial distance from a shaft. The model is based upon analyses which consider modification in rock mass permeability resulting from stress redistribution and blast damage due to excavation around a shaft. Elastic and elastoplastic stress analyses are performed to estimate the stress distribution for a wide range of rock properties and in situ stress conditions. Changes in stress are related to changes in rock mass permeability using stress-permeability relations for fractures obtained from laboratory and field testing. The effects of blast damage are estimated from case histories. The analyses indicate that rock mass permeability is expected to decline rapidly to the undisturbed value with greater permeability changes occurring at or near the shaft wall. For several conditions evaluated, the equivalent permeability of the modified permeability zone, averaged over an annulus one radius wide around the shaft, ranges from 15 to 80 times the undisturbed rock mass permeability. 61 refs., 24 figs., 6 tabs.

  4. Domino instability effect of surrounding rock-coal pillars in a room-and-pillar gob

    Institute of Scientific and Technical Information of China (English)

    Li Chong; Xu Jinhai; Wang Zhongliang; Qin Shuai

    2013-01-01

    To discuss the domino instability effect and large area roof falling and roof accidents of surrounding rock-coal pillars in a room-and-pillar gob, the equilibrium equation for a roof-coal pillar-floor system with the influence of mining floor was developed based on the engineering conditions of the surrounding rock in a room-and-pillar gob in the 3-2 coal seam of Tanggonggou mine. The conditions of system instability and the relationship between system stability and system stiffness were analyzed from an energetic point of view. Numerical simulation using the discrete element software UDEC was also carried out to simulate conditions causing the domino effect on surrounding rock-coal pillars in a 3-2 room-and-pillar gob. The results show that:if we want the system to destabilize, the collective energy in roof-and-floor must be larger than that in the coal pillar. When the stiffness of the coal pillars and the roof-and-floor are both greater than zero, the system is stable. When the stiffness of the coal pillars is negative but the summed stiffness of the coal pillars and roof-and-floor is larger than or equal to zero, the system is statically destroyed. When the sum of the coal pillars and the roof-floor stiffness is negative, the system suffers from severe damages. For equal advance distances of the coal mining face, the wider coal pillars can reduce the probability of domino type instability. Conversely, the smaller width pillars can increase the instability probability. Domino type instability of surrounding rock-coal pillars is predicted to be unli-kely when the width of coal pillars is not less than 8 m.

  5. Damage Characteristics of Surrounding Rock Subjected to VCR Mining Blasting Shock

    OpenAIRE

    Nan Jiang; Chuanbo Zhou; Xuedong Luo; Shiwei Lu

    2015-01-01

    For limiting the damage range caused by explosive shock loads in vertical crater retreat (VCR) mining, the blasting damage characteristics of surrounding rock were studied by two methods: numerical simulation and ultrasonic testing. Combined with the mining blasting in Dongguashan Copper Mine of China, the VCR blasting shock characteristics under different conditions are obtained by using LSDYNA. Based on statistical fracture mechanics and damage mechanics theories, a damage constitutive mode...

  6. Caving thickness effects of surrounding rocks macro stress shell evolving characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Guang-xiang Xie; Ke Yang [Anhui University of Science and Technology, Huainan (China). Key Laboratory of Coal Mine Safety and Efficiently Caving of Ministry of Education

    2009-06-15

    In order to explore the influence of different caving thicknesses on the macro stress shell, (MSS) distribution and evolving characteristics of surrounding rocks in unsymmetrical disposal and fully mechanized top-coal caving (FMTC), based on unsymmetrical disposal characteristics, the analyses of numerical simulation, material simulation and in-situ observation were synthetically applied according to the geological and technical conditions of the 1151(3) working face in Xieqiao Mine. The results show that the stress peak value of the MSS-base and the ratio of MSS-body height to caving thickness are nonlinear and inversely proportional to the caving thickness. The MSS-base width, the MSS-body height, the MSS-base distance to working face wall and the rise distance of MSS-base beside coal pillar are nonlinear and directly proportional to the caving thickness. The characteristics of MSS distribution and its evolving rules of surrounding rocks and the integrated caving thickness effects are obtained. The investigations will provide theoretic references to the surrounding rocks stability control of the working face and roadway, roadway layout, gas extraction and exploitation, and efficiency of caving, etc. 13 refs., 5 figs., 5 tabs.

  7. Caving thickness effects of surrounding rocks macro stress shell evolving characteristics

    Institute of Scientific and Technical Information of China (English)

    XIE Guang-xiang; YANG Ke

    2009-01-01

    In order to explore the influence of different caving thicknesses on the MSS dis-tribution and evolving characteristics of surrounding rocks in unsymmetrical disposal and fully mechanized top-coal caving (FMTC), based on unsymmetrical disposal characteris-tics, the analyses of numerical simulation, material simulation and in-situ observation were synthetically applied according to the geological and technical conditions of the 1151(3) working face in Xieqiao Mine. The results show that the stress peak value of the MSS-base and the ratio of MSS-body height to caving thickness are nonlinear and inversely proportional to the caving thickness. The MSS-base width, the MSS-body height, the MSS-base distance to working face wall and the rise distance of MSS-base beside coal pillar are nonlinear and directly proportional to the caving thickness. The characteristics of MSS distribution and its evolving rules of surrounding rocks and the integrated caving thickness effects are obtained. The investigations will provide lots of theoretic references to the surrounding rocks' stability control of the working face and roadway, roadway layout, gas extraction and exploitation, and efficiency of caving, etc.

  8. Numerical analysis and field monitoring tests on shallow tunnels under weak surrounding rock

    Institute of Scientific and Technical Information of China (English)

    刘建华; 刘晓明; 张永杰; 肖庭

    2015-01-01

    The Jianpudong No. 4 tunnel is a shallow tunnel, which belongs to Shaoshan County scenic highway in Hunan province, China and whose surrounding rock is weak. According to its characteristics, the field monitoring tests and numerical analysis were done. The mechanical characteristics of shallow tunnels under weak surrounding rock and the stress−strain rule of surrounding rock and support were analyzed. The numerical analysis results show that the settlement caused by upper bench excavating accounts for 44% of the total settlement, and the settlement caused by tunnel upper bench supporting accounts for 56% of the total settlement. The maximum axial force of shotcrete lining is 177.2 kN, which locates in hance under the secondary lining. The maximum moment of shotcrete lining is 5.08 kN·m, which locates in the arch foot. The stress curve of steel arch has three obvious stages during the tunnel construction. The maximum axial force of steel arch is 297.4 kN, which locates in tunnel vault. The axial forces of steel arch are respectively 23.5 kN and−21.8 kN, which is influenced by eccentric compression of shallow tunnel and locates in hance. The results show that there is larger earth pressure in tunnel vault which is most unfavorable position of steel arch. Therefore, the advance support should be strengthened in tunnel vault during construction process.

  9. Upper bound analytical solution for surrounding rock pressure of shallow unsymmetrical loading tunnels

    Institute of Scientific and Technical Information of China (English)

    雷明锋; 彭立敏; 施成华; 谢友均; 谭立新

    2015-01-01

    By combining the results of laboratory model tests with relevant flow rules, the failure mode of shallow unsymmetrical loading tunnels and the corresponding velocity field were established. According to the principle of virtual power, the upper bound solution for surrounding rock pressure of shallow unsymmetrical loading tunnel was derived and verified by an example. The results indicate that the calculated results of the derived upper bound method for surrounding rock pressure of shallow unsymmetrical loading tunnels are relatively close to those of the existing “code method” and test results, which means that the proposed method is feasible. The current code method underestimates the unsymmetrical loading feature of surrounding rock pressure of shallow unsymmetrical loading tunnels, so it is unsafe; when the burial depth is less or greater than two times of the tunnel span and the unsymmetrical loading angle is less than 45°, the upper bound method or the average value of the results calculated by the upper bound method and code method respectively, is comparatively reasonable. When the burial depth is greater than two times of the tunnel span and the unsymmetrical loading angle is greater than 45°, the code method is more suitable.

  10. Fi Investigations On Hp-Rocks From The Lower Engadine Window New Insights On Its Late Tectono-Metamorphic Evolution

    Science.gov (United States)

    Bertle, R. J.; Götzinger, M. A.; Koller, F.

    2003-04-01

    Fluid inclusions studies in metamorphic rocks allow to reconstruct not only the chemistry of the fluids enabling and/or supporting metamorphic reactions but also the late metamorphic evolution of orogenesis. Therefore late, discordant quarz-calcite veins were investigated using FI-techniques. The Engadine Window which is exposed at the Swiss-Austrian-border exposes the penninic units of the Western Alps as a tectonic window within the Austroalpine nappes of the Eastern Alps. The nappes of the Engadine window underwent metamorphism and deformation during Tertiary times (THÖNI 1981, BERTLE 2000). The highest unit (Fimber unit) and the core of the window (= Zone of Pfunds) suffered HP-LT-metamorphism. P-T-conditions for parts of the Zone of Pfunds at the region of Piz Mundin are at 13-15 kbar at 380^oC (BOUSQUET et al. 2002) indicated by the occurrence of carpholite and glaucophane. The late metamorphic history is not very well constrained. There exist only a few FI-data published in an abstract by STÖCKHERT et al. 1990 and some unpublished data in RING 1989. During the ongoing mapping campaign of the first author samples from the Fimber unit and the Zone of Pfunds were collected and investigated using a LINKHAM freezing-cooling-stage. The investigated veins are discordant in respect to the main-foliation of the rocks and show nice cristalls of quarz, calcite and sometimes feldspar (adularia). Structural data implie that the investigated veins correspond to a set of ac-joints that correlate to the late updoming of the large "Engadiner Gewölbe" (Engadin anticlinal structure, MATTMÜLLER 1996). All investigated veins (from all tectonic units) show the same relationship to the anticlinal structure. FI-investigations show, that a large amount of the primary FI are decrepitated, however it was possible to find enough to provide a serious statistical data set. FI from Piz Mundin in the core of the Engadine window exhibit at the base of the vein quarz at the contact to

  11. Nonlinear Progressive Failure Analysis of Surrounding Rock System Based on Similarity Theory

    Directory of Open Access Journals (Sweden)

    Zhao Y.

    2016-01-01

    Full Text Available Nonlinear progressive failure study of surrounding rock is important for the stability analysis of underground engineering projects. Taking a deep-buried tunnel in Chongqing as an example, a three dimensional(3-D physical model was established based on similarity theory. To satisfy similarity requirement of physical–mechanical properties, such as elastic modulus, compressive strength and Poisson ratio, physical model materials were developed. Using full inner-spy photograph technology, the deformation and failure process of rock were studied under the situation of independent and combined action of anchor, shotcrete and reinforcing mesh. Based on experimental results, the interaction mechanism between rock and support structure under high stress was investigated.

  12. METAMORPHIC PETROLOGY

    Institute of Scientific and Technical Information of China (English)

    2016-01-01

    20160203 Ji Genyuan(Cores and Samples Center of Land Resources,Sanhe 065201,China);Dai Tagen Petrological Characteristics and Original Rocks for Metamorphic Rocks from the Jinmo Sb Deposit,in Quang Ninh Province,Vietnam(Acta Geologica Sichuan,ISSN1006-0995,CN51-1273/P,35(1),2015,p.43-46,6illus.,1table,6refs.)

  13. Deformation and Metasomatic Evolution at the Subduction Plate Interface As Viewed from Study of HP/UHP Metamorphic Rocks

    Science.gov (United States)

    Bebout, G. E.; Penniston-Dorland, S.

    2014-12-01

    We provide a view of lithologic makeup, deformation, and fluid-rock interaction along the deep forearc to subarc plate interface, based on insights gained from study of HP/UHP metamorphic rocks. Exposures of plate-boundary shear zones on which we base our perspective represent 30-80 km depths and are on Catalina Island and at Monviso, Syros, and New Caledonia. Each contains highly deformed zones with schistose matrix, commonly with a large ultramafic component, containing bodies of less deformed mafic, sedimentary, and ultramafic rocks. These "blocks" have varying geometries, are up to km-scale, and can preserve disparate P-T histories reflecting dynamics of incorporation and entrainment. Sheared matrices contain high-variance, hydrous mineral assemblages in some cases resembling metasomatic zones ("rinds") at block-matrix contacts, and rinds and matrices have homogenized isotopic compositions reflecting extensive fluid-rock interaction. Shearing and related physical juxtaposition of disparate metasomatic rocks can result in mixed or 'hybrid' chemical compositions. The chlorite-, talc-, and amphibole-rich schists developed by these processes can stabilize H2O to great depth and influence its cycling. Fluids (hydrous fluids, silicate melts) released within slabs necessarily interact with highly deformed, lithologically hybridized zones at the plate interface as they ascend to potentially enter mantle wedges. Fluids bearing chemical/isotopic signatures of hybrid rocks appear capable of producing arc magma compositions interpreted as reflecting multiple, chemically distinct fluids sources. Geophysical signatures of these rheologically weak zones are equivocal but many recognize the presence of zones of low seismic velocity at/near the top of slabs and attribute them to hydrated rocks. Whether rocks from this interface buoyantly ascend into mantle wedges, indicated in some theoretical models, remains largely untested by field and geophysical observations.

  14. Petrologic and geochemical characterization and mineralization of the metavolcanic rocks of the Heib Formation, Kid Metamorphic Complex, Sinai, Egypt

    Directory of Open Access Journals (Sweden)

    Ibrahim H. Khalifa

    2011-07-01

    Full Text Available Metavolcanic rocks hosting base metal sulphide mineralization, and belonging to the Kid Metamorphic Complex, are exposed in the Samra-Tarr area, Southern Sinai. The rocks consist of slightly metamorphosed varicolored porphyritic lavas of rhyolite-to-andesite composition, and their equivalent pyroclastics. Geochemically, these metavolcanics are classified as high-K calc-alkaline, metaluminous andesites, trachyandesites, dacites, and rhyolites. The geochemical characteristics of these metavolcanics strongly point to their derivation from continental crust in an active continental margin. The sulphide mineralization in these metavolcanics occurs in two major ore zones, and is represented by four distinct styles of mineralization. The mineralization occurs either as low-grade disseminations or as small massive pockets. The associated hydrothermal alterations include carbonatization, silicification, sericitization and argillic alterations. The base metal sulphide mineralization is epigenetic and was formed by hydrothermal solutions associated with subduction-related volcanic activity.

  15. Different stages of chemical alteration on metabasaltic rocks in the subduction channel: Evidence from the Western Tianshan metamorphic belt, NW China

    Science.gov (United States)

    Xiao, Yuanyuan; Niu, Yaoling; Wang, Kuo-Lung; Iizuka, Yoshiyuki; Lin, Jinyan; Wang, Dong; Tan, Yulong; Wang, Guodong

    2017-09-01

    To understand the geochemistry of subduction zone metamorphism, especially the large-scale mass transfer at forearc to subarc depths, we carried out a detailed study of a ∼1.5 m size metabasaltic block with well-preserved pillow structures from the Chinese Western Tianshan high- to ultrahigh-pressure metamorphic belt. This metabasaltic block is characterized by omphacite-rich interiors gradually surrounded by abundant channelized (veins) glaucophane-rich patches toward the rims. The glaucophane-rich rims share the same peak metamorphic conditions with omphacite-rich interiors, but have experienced stronger blueschist-facies overprinting during exhumation. Representative samples from the glaucophane-rich rims and omphacite-rich interiors yield a well-defined Rb-Sr isochron age of 307 ± 23 Ma, likely representing this overprinting event. Both glaucophane-rich rims and omphacite-rich interiors show elevated K-Rb-Cs-Ba-Pb-Sr contents relative to their protolith, reflecting a large-scale enrichment of these elements and formation of abundant phengite during subduction. Compared with the omphacite-rich interiors, the glaucophane-rich rims have gained rare earth elements (REEs, >25%), U-Th (∼75%), Pb-Sr (>100%) and some transition metals like Co and Ni (25-50%), but lost P (∼75%), Na (>25%), Li and Be (∼50%); K-Rb-Cs-Ba show only 10% loss. These chemical changes would be caused by serpentinite-derived fluids during the exhumation in the subduction channel. Therefore, there are two stages of fluid action in the subduction channel. As the formation of phengite stabilizes K-Rb-Cs-Ba at the first stage, the residual fluids released from the phengite-rich metabasaltic rocks would be depleted in these elements, which are unlikely to contribute to elevated contents of these elements in arc magmas if phengite remains stable at subarc depths. In addition, the decrease of U/Pb ratios as the preferred enrichment of Pb over U in the eclogitic rocks during the first stage

  16. Theoretical analysis of a new segmented anchoring style in weakly cemented soft surrounding rock

    Institute of Scientific and Technical Information of China (English)

    Zhao Zenghui; Wang Weiming; Wang Lihua

    2016-01-01

    According to the tensile failure of rock bolt in weakly cemented soft rock, this paper presents a new seg-mented anchoring style in order to weaken the cumulative effect of anchoring force associated with the large deformation. Firstly, a segmented mechanical model was established in which free and anchoring section of rock bolt were respectively arranged in different deformation zones. Then, stress and displace-ment in elastic non-anchoring zone, elastic anchoring zone, elastic sticking zone, softening sticking zone and broken zone were derived respectively based on neural theory and tri-linear strain softening constitutive model of soft rock. Results show that the anchoring effect can be characterized by a supporting parameter β. With its increase, the peak value of tangential stress gradually moves to the roadway wall, and the radial stress significantly increases, which means the decrease of equivalent plastic zone and improvement of confining effect provided by anchorage body. When β increases to 0.72, the equivalent plastic zone disappears, and stresses tend to be the elastic solutions. In addition, the anchoring effect on the displacement of surrounding rock can be quantified by a normalization factorδ.

  17. Fluid inclusions hidden in coesite-bearing zircons in ultrahigh-pressure metamorphic rocks from southwestern Sulu terrane in eastern China

    Institute of Scientific and Technical Information of China (English)

    LIU Fulai; XU Zhiqin

    2004-01-01

    Primary fluid inclusions, together with coesite mineral inclusions, are identified in the same zircon domains by laser Raman spectroscopy, cathodoluminescence (CL) image and micro-texture analysis in paragneiss and eclogite from the main drilling hole of Chinese Continental Scientific Drilling Project in southwestern Sulu terrane. Most fluid inclusions are characterized by CO2 (gas)-H2O (liquid) two-phase, a few by H2O one-phase liquid inclusions. These features indicate that the eclogite and its country-rocks may be located in the "wet system" rather than in the "dry system" during UHP metamorphism. SHRIMP U-Pb dating indicates that the timing of trapping the fluid and coesite inclusions in metamorphic zircon domains is about 233.7 ± 4.3 Ma, which may represent the age of zircon growth in the stage of pressure decrease but temperature increase during the retrograde period of UHP metamorphism thus indicating the fluid activity still under the UHP conditions. The zircons further overgrew at about 213.2 ± 5.2 Ma in response to amphibolite-facies retrogression. Therefore, fluid activity in the Sulu UHP metamorphic rocks principally occurred during the exhumation of UHP slab in the Middle to Late Triassic. The present results not only provide insight into the fluid property and fluid-rock interaction mechanism in the Sulu-Dabie UHP terrane, but also present a new means to exactly identify the primary fluid inclusions preserved in zircons from the UHP metamorphic rocks.

  18. THE GEOCHEMISTRY AND AGES OF ROCKS IN THE FOOTWALL OF THE BUTULIYN-NUR AND ZAGAN METAMORPHIC CORE COMPLEXES (NORTH MONGOLIA – WESTERN TRANSBAIKALIA)

    OpenAIRE

    T. V. Donskaya; A.M. MAZUKABZOV

    2015-01-01

    This article reviews data on ages of rocks in the footwall of the Butuliyn-Nur and Zagan metamorphic core complexes (MCC) and provides new data on the geochemistry of the rock complexes. It is noted that the oldest rocks are mylonitized gneisses on rhyolites (554 Ma) in the footwall of the Butuliyn-Nur MCC. The Late Permian – Triassic (249–211 Ma) igneous rocks are ubiquitous in the footwall of the Butuliyn-Nur and Zagan MCC. The youngest rocks in the studied MCC are the Jurassic granitoids (...

  19. An Index for Estimating the Stability of Brittle Surrounding Rock Mass: FAI and its Engineering Application

    Science.gov (United States)

    Zhang, C. Q.; Zhou, H.; Feng, X. T.

    2011-07-01

    Based on the geometric analysis of the relationship between the stress state at a point and the yield surface defined in the principal stress space, a coefficient ω is set up as an estimation index to describe the stress-induced yield risk. After yield, the equivalent plastic shear strains is usually used to characterize the failure degree (FD) of the material and adopted here as an index of the damage degree for the surrounding rock masses. Then, a unified variable combining ω and FD, named failure approaching index (FAI), is constructed to estimate the stability of rock mass which may be at different deformation stages. The formulas of FAI are derived for some popular yield criteria in geomechanics. Details for such development are addressed in the paper. Its rationality is verified by numerical simulation and comparative analysis of the conventional triaxial compression tests and typical tunnel projects. In addition, the method for applying FAI to the stability estimation of surrounding rock mass is proposed. As examples, the stability of the underground powerhouse, access tunnels and headrace tunnels at the Jinping II hydropower station are estimated by making use of the method we presented. The results indicate that not only is the index rational in mechanics, but the theory also has good expansibility, and the estimation methods are simple and practical as well. It is easier for field engineers to analyze and understand the numerical results.

  20. Detachment within subducted continental crust and multi-slice successive exhumation of ultrahigh-pressure metamorphic rocks: Evidence from the Dabie-Sulu orogenic belt

    Institute of Scientific and Technical Information of China (English)

    LIU YiCan; LI ShuGuang

    2008-01-01

    Although tectonic models were presented for exhumation of ultrahigh-pressure (UHP) metamorphic rocks during the continental collision, there is increasing evidence for the decoupling between crustal slices at various depths within deeply subducted continental crust. This lends support to the multi-slice successive exhumation model of the UHP metamorphic rocks in the Dabie-Sulu orogen. The available evidence is summarized as follows: (1) the low-grade metamorphic slices, which have geotectonic af-finity to the South China Block and part of them records the Triassic metamorphism, occur in the northern margin of the Dabie-Sulu UHP metamorphic zone, suggesting decoupling of the upper crust from the underlying basement during the initial stages of continental subduction; (2) the Dabie and Sulu HP to UHP metamorphic zones comprise several HP to UHP slices, which have an increased trend of metamorphic grade from south to north but a decreased trend of peak metamorphic ages corre-spondingly; and (3) the Chinese Continental Science Drilling (CCSD) project at Donghai in the Sulu orogen reveals that the UHP metamorphic zone is composed of several stacked slices, which display distinctive high and low radiogenic Pb from upper to lower parts in the profile, suggesting that these UHP crustal slices were derived from the subducted upper and middle crusts, respectively. Detachment surfaces within the deeply subducted crust may occur either along an ancient fault as a channel of fluid flow, which resulted in weakening of mechanic strength of the rocks adjacent to the fault due to fluid-rock interaction, or along the low-viscosity zones which resulted from variations of geotherms and lithospheric compositions at different depths. The multi-slice successive exhumation model is different from the traditional exhumation model of the UHP metamorphic rocks in that the latter as-sumes the detachment of the entire subducted continental crust from the underlying mantle lithosphere and its

  1. Fluorian garnets from the host rocks of the Skaergaard intrusion: implications for metamorphic fluid composition

    Science.gov (United States)

    Manning, C.E.; Bird, D.K.

    1990-01-01

    Zoned, silica-deficient, calcic garnets containing up to 5 mol% F substitution for O formed during contact metamorphism of basalts by the Skaergaard intrusion in East Greenland. Fluorian calcic garnets occur as a retrograde alteration of prograde wollastonite and clinopyroxene that fills vesicles and vugs in lavas 30-70 m from the intrusion. The F content of garnet is extremely sensitive to minor changes in fluid composition. The calculations show that a decrease in pH or an increase in log aF- of 0.3 at constant pressure and temperature will decrease the F concentration in garnet from 5 to 0 mol%. The results of this study show that fluorian hydrous grandites provide a mineralogical record of the activities of F species in coexisting metamorphic and hydrothermal fluids. -from Authors

  2. Elemental geochemistry and Nd isotopic characteristics of the metasedimentary rocks from the metamorphic belt in central Jiangxi: Provenance and tectonically environmental constraints

    Institute of Scientific and Technical Information of China (English)

    HU Gongren; LIU Congqiang; ZHANG Bangtong; TANG Hongfeng; YU Ruilian

    2005-01-01

    The metamorphic belt in central Jiangxi, located in the compound terrain within the Cathaysia, Yangtze Block and Caledonian fold zone of South China, is composed dominantly of meta-argillo-arenaceous rocks, with minor amphibolite. These rocks underwent amphibolite-facies metamorphism. The meta-argillo-arenaceous rocks show large variations in major element composition, but have similar REE patterns and trace element composition, incompatible element and LIE enrichments [ high Th/Sc (0.57-3.59) , La/Sc ( 1.46 - 12.4), La/Yb (5.84 - 19.0) ] and variable Th/U ratios, with ∑REE = 129-296μg/g, δEu =0.51 -0.86, and (La/Yb)N = 3.95 -12.9. The Nd isotopic model ages tDM of these rocks vary from 1597 to 2124 Ma. Their 143 Nd/144 Nd values are low [εNd (0) = - 11.4 to -- 15.8]. Some conclusions have been drawn as follows: (1) The metamorphic rocks in central Jiangxi Province are likely formed in a tectonic environment at the passive continental margin of the Cathaysia massif. (2) The metamorphosed argillo-arenaceous rocks are composed dominantly of upper crustal-source rocks (Al- and Krich granitic or/and sedimentary rocks of Early Proterozoic), which experienced good sorting, slow deposition and more intense chemical weathering. (3) According to the whole-rock Sm-Nd isochron ages (1113±49 to 1199 ± 26 Ma) of plagioclase-amphibole (schist) and Nd isotopic model age tDM ( 1597 - 2124Ma) of meta-argillo-arenaceous rocks, the metamorphic belt in central Jiangxi Province was formed during the Middle Proterozoic ( 1100 - 1600 Ma).

  3. Elastic-plastic model identification for rock surrounding an underground excavation based on immunized genetic algorithm.

    Science.gov (United States)

    Gao, Wei; Chen, Dongliang; Wang, Xu

    2016-01-01

    To compute the stability of underground engineering, a constitutive model of surrounding rock must be identified. Many constitutive models for rock mass have been proposed. In this model identification study, a generalized constitutive law for an elastic-plastic constitutive model is applied. Using the generalized constitutive law, the problem of model identification is transformed to a problem of parameter identification, which is a typical and complicated optimization. To improve the efficiency of the traditional optimization method, an immunized genetic algorithm that is proposed by the author is applied in this study. In this new algorithm, the principle of artificial immune algorithm is combined with the genetic algorithm. Therefore, the entire computation efficiency of model identification will be improved. Using this new model identification method, a numerical example and an engineering example are used to verify the computing ability of the algorithm. The results show that this new model identification algorithm can significantly improve the computation efficiency and the computation effect.

  4. Mineralogical and microstructural investigations of fractures in Permian z2 potash seam and surrounding salt rocks

    Science.gov (United States)

    Mertineit, Michael; Grewe, Wiebke; Schramm, Michael; Hammer, Jörg; Blanke, Hartmut; Patzschke, Mario

    2017-04-01

    Fractures occur locally in the z2 potash seam (Kaliflöz Staßfurt). Most of them extend several centimeter to meter into the surrounding salt rocks. The fractures are distributed on all levels in an extremely deformed area of the Morsleben salt mine, Northern Germany. The sampling site is located within a NW-SE trending synclinal structure, which was reverse folded (Behlau & Mingerzahn 2001). The samples were taken between the -195 m and - 305 m level at the field of Marie shaft. In this area, more than 200 healed fractures were mapped. Most of them show opening widths of only a few millimeters to rarely 10 cm. The fractures in rock salt are filled with basically polyhalite, halite and carnallite. In the potash seam, the fractures are filled with kainite, halite and minor amounts of carnallite and polyhalite. In some cases the fracture infill changes depending on the type of surrounding rocks. There are two dominant orientations of the fractures, which can be interpreted as a conjugated system. The main orientation is NE-SW trending, the dip angles are steep (ca. 70°, dip direction NW and SE, respectively). Subsequent deformation of the filled fractures is documented by a strong grain shape fabric of kainite, undulatory extinction and subgrain formation in kainite, and several mineral transformations. Subgrain formation in halite occurred in both, the fracture infill and the surrounding salt rocks. The results correlate in parts with investigations which were carried out at the close-by rock salt mine Braunschweig-Lüneburg (Horn et al. 2016). The development of the fractures occurred during compression of clayey salt rocks. However, the results are only partly comparable due to different properties (composition, impurities) of the investigated stratigraphic units. Further investigations will focus on detailed microstructural and geochemical analyses of the fracture infill and surrounding salt rocks. Age dating of suitable minerals, e.g. polyhalite (Leitner et al

  5. Stability assessment of rock surrounding an I-beam supported retreating roadway

    Institute of Scientific and Technical Information of China (English)

    严红; 张吉雄; 李林玥; 冯锐敏

    2015-01-01

    The installation of a back-wall guard-board is the key to successfully supporting underground retreating roadways in coal mines. Based on the coordinate support principle, and using an I-shaped steel support for the surrounding rock, a mechanical model was developed for the stability of the roadway support and surrounding rock. Analysis of the bearing capacity of the roof back-wall guard-board and modelling of the equations for the maximum deflection and the maximum compressive stress of the top and side beams of the I-shaped steel support were undertaken. Simultaneously, the model was used to calculate and analyse the stability of the top and side beams of the I-shaped steel support structure and analyse the criteria for their stability. The results provide a reliable theoretical basis for the judgment of the stability of the surrounding rock and support structure. The theoretical evaluation results are consistent with field data. Finally, the key support parameters of the top and side beams of the I-shaped steel support structure and the variation of the maximum deflection and the maximum compressive stress as affected by the influence of the guard-board length were investigated. It is concluded that, as the back-board length increases, the maximum compressive stress in the top beam of the I-shaped steel support increases while the compressive stress in the side beam decreases. The results show that the accuracy of judgment of the stability of a supported retreating roadway is improved, providing guidance for the design of such typical I-shaped steel support and back-board structures.

  6. Determining age of Pan African metamorphism using Sm-Nd garnet-whole rock geochronology and phase equilibria modeling in the Tasriwine ophiolite, Sirwa, Anti-Atlas Morocco

    Science.gov (United States)

    Inglis, Jeremy D.; Hefferan, Kevin; Samson, Scott D.; Admou, Hassan; Saquaque, Ali

    2017-03-01

    Sm-Nd garnet-whole rock geochronology and phase equilibria modeling have been used to determine the age and conditions of regional metamorphism within the Tasriwine ophiolite complex, Sirwa, Morocco. Pressure and temperature estimates obtained using a NaCaKFMASHT phase diagram (pseudosection) and garnet core and rim compositions predict that garnet growth began at ∼0.72 GPa and ∼615 °C and ended at ∼0.8 GPa and ∼640 °C. A bulk garnet Sm-Nd age of 647.2 ± 1.7 Ma, calculated from a four point isochron that combines whole rock, garnet full dissolution and two successively more aggressive partial dissolutions, provides a precise date for garnet formation and regional metamorphism. The age is over 15 million years younger than a previous age estimate of regional metamorphism of 663 ± 13 Ma based upon a SHRIMP U-Pb date from rims on zircon from the Iriri migmatite. The new data provide further constraints on the age and nature of regional metamorphism in the Anti-Atlas mountains and emphasizes that garnet growth during regional metamorphism may not necessarily coincide with magmatism/anatexis which predominate the signature witnessed by previous U-Pb studies. The ability to couple PT estimates for garnet formation with high precision Sm-Nd geochronology highlights the utility of garnet studies for uncovering the detailed metamorphic history of the Anti-Atlas mountain belt.

  7. Application of phase space reconstruction and v-SVR algorithm in predicting displacement of underground engineering surrounding rock

    Institute of Scientific and Technical Information of China (English)

    SHI Chao; CHEN Yi-feng; YU Zhi-xiong; YANG Kun

    2006-01-01

    A new method for predicting the trend of displacement evolution of surrounding rock was presented in this paper. According to the nonlinear characteristics of displacement time series of underground engineering surrounding rock, based on phase space reconstruction theory and the powerful nonlinear mapping ability of support vector machines, the information offered by the time series datum sets was fully exploited and the non-linearity of the displacement evolution system of surrounding rock was well described.The example suggests that the methods based on phase space reconstruction and modified v-SVR algorithm are very accurate, and the study can help to build the displacement forecast system to analyze the stability of underground engineering surrounding rock.

  8. Elasto-plastic analysis of the surrounding rock mass in circular tunnel based on the generalized nonlinear unified strength theory

    Institute of Scientific and Technical Information of China (English)

    Huang Xiujie; Zhang Jixun; Yang Ling; Yang Shikou; Wang Xingli

    2016-01-01

    The present paper aims to establish a versatile strength theory suitable for elasto-plastic analysis of underground tunnel surrounding rock. In order to analyze the effects of intermediate principal stress and the rock properties on its deformation and failure of rock mass, the generalized nonlinear unified strength theory and elasto-plastic mechanics are used to deduce analytic solution of the radius and stress of tunnel plastic zone and the periphery displacement of tunnel under uniform ground stress field. The results show that: intermediate principal stress coefficient b has significant effect on the plastic range, the magnitude of stress and surrounding rock pressure. Then, the results are compared with the unified strength criterion solution and Mohr–Coulomb criterion solution, and concluded that the generalized nonlinear unified strength criterion is more applicable to elasto-plastic analysis of underground tunnel surrounding rock.

  9. U-Pb zircon dating constraints on formation time of Qilian high-grade metamorphic rock and its tectonic implications

    Institute of Scientific and Technical Information of China (English)

    XU WangChun; ZHANG HongFei; LIU XiaoMing

    2007-01-01

    In order to constrain the formation time of high-grade metamorphic rocks in the Qilian Mountains, U-Pb zircon dating was carried out by using LA-ICPMS technique for a paragneiss of the Hualong Group in the Qilian Mountains basement series and a weakly foliated granite that intruds into the Hualong Group. Zircons from the paragneiss consist dominantly of detrital magma zircons with round or sub-round shape. They have 207Pb/206Pb ages mostly ranging from 880 to 900 Ma, with a weighted mean age of 891±9 Ma, which is interpreted as the magma crystallization age of its igneous provenance and can be taken as a lower age limit for the Hualong Group. Magma crystallization age for the weak-foliated granite is 875±8 Ma, which can be taken as an upper age limit for the Hualong Group. Accordingly, the formation time of the Hualong Group is constrained at sometime between 875 and 891 Ma. A few zircons from both paragneiss and weak-foliated granite display old inherited ages of 1000 to 1700 Ma and young metamorphic ages of Early Paleozoic. The zircon age distribution pattern confirms that the Qilian Mountains and the northern margin of Qaidam Basin had a united basement, with geotectonic affinity to the Yangtze Block. The results also reveal that sediments of the Hualong Group formed by rapid accumulation due to rapid crustal uplift-erosion. This process may result from intensive Neoproterozoic orogenesis due to assembly of the suppercontinent Rodinia.

  10. Mechanical Behavior of the Near-field Host Rock Surrounding Excavations

    Energy Technology Data Exchange (ETDEWEB)

    Kelkar, Sharad M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Stauffer, Philip H. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Robinson, Bruce Alan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-01-09

    This report is being prepared under the FY14 activity FT-14LA0818069, Mechanical and Hydrological Behavior of the Near-Field Host Rock Surrounding Excavations, and fulfills the Los Alamos National Laboratory deliverable M4FT-14LA08180610, which in PICS:NE is titled “Draft report, Test Plan for Mechanical and Hydrological Behavior of the Near-field Host Rock Surrounding Excavations.” Since the report is an intermediate deliverable intended as input to the eventual test plan for this test, rather than being an actual test plan, the activity title is used as the title of this document to avoid confusion as to the contents in the report. This report summarizes efforts to simulate mechanical processes occurring within a hypothetical high-level waste (HLW) repository in bedded salt. The report summarizes work completed since the last project deliverable, “Coupled model for heat and water transport in a high level waste repository in salt “, a Level 2 milestone submitted to DOE in September 2013 (Stauffer et al., 2013).

  11. Improved response surface method and its application in stability reliability degree analysis of tunnel surrounding rock

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    An approach of limit state equation for surrounding rock was put forward based on deformation criterion. A method of symmetrical sampling of basic random variables adopted by classical response surface method was mended, and peak value and deflection degree of basic random variables distribution curve were took into account in the mended sampling method. A calculation way of probability moment, based on mended Rosenbluth method, suitable for non-explicit performance function was put forward.The first, second, third and fourth order moments of functional function value were calculated by mended Rosenbluth method through the first, second, third and fourth order moments of basic random variable. A probability density the function(PDF) of functional function was deduced through its first, second, third and fourth moments, the PDF in the new method took the place of the method of quadratic polynomial to approximate real functional function and reliability probability was calculated through integral by the PDF for random variable of functional function value in the new method. The result shows that the improved response surface method can adapt to various statistic distribution types of basic random variables, its calculation process is legible and need not iterative circulation. In addition, a stability probability of surrounding rock for a tunnel was calculated by the improved method,whose workload is only 30% of classical method and its accuracy is comparative.

  12. The Kenna ureilite - An ultramafic rock with evidence for igneous, metamorphic, and shock origin

    Science.gov (United States)

    Berkley, J. L.; Brown, H. G.; Keil, K.; Carter, N. L.; Mercier, J.-C. C.; Huss, G.

    1976-01-01

    Ureilites are a rare group of achondrites. They are composed mainly of olivine and pigeonite in a matrix of carbonaceous material, including graphite, lonsdaleite, diamond, and metal. In most respects Kenna is a typical ureilite with the requisite mineralogical and chemical properties of the group. Differences of the Kenna ureilite from previously studied ureilites are related to a greater density, the occurrence of exceedingly minute quantities of feldspar, and a very strong elongation lineation of the silicate minerals. A description is presented of a study which indicates a complex history for Kenna, including igneous, mild metamorphic, and shock processes.

  13. Evidence of microstructures and fluid inclusions for the origin of polycrystalline quartz ribbons in high-grade metamorphic rocks in Daqingshan resion

    Institute of Scientific and Technical Information of China (English)

    LIU ZhengHong; XU ZhongYuan; WANG KeYong

    2007-01-01

    Polycrystalline quartz ribbons in high-grade metamorphic rocks from the Daqingshan region, are typical microfabrics of, and provide information for, deep crust deformation and metamorphism. The quartz ribbons have straight boundaries and extend stably along gneissosity. They truncate other mineral grains in the rocks and may contain inclusions of such minerals that are lens-shaped and oriented. They frequently end into branching termination. Analysis fluid inclusions in polycrystalline quartz ribbons reveal that the complex types of fluid inclusions are inhomogeneously distributed. They are obviously different from inclusions captured at granulite facies, in both fluid compositions and T-P estimations. Based on microfabric and fluid inclusion analysis, the polycrystalline quartz ribbons are suggested to be formed by SO2-rich fluids filling micro-fractures that are parallel to early gneissosity. The SO2 composition is derived from the deformed host rocks. The fluid phase has significant effects on the rheological characteristics, fracturing of rocks, and formation of quartz ribbons.

  14. Possibility of the misidentification of contaminated microdiamonds in UHP metamorphic rocks: An example of diamond grains in Dabie garnet clinopyroxenite

    Science.gov (United States)

    Ogasawara, Y.; Igarashi, M.; Tsai, C.; Iwasaki, I.; Liou, J. G.

    2011-12-01

    Extracted diamonds from crushed UHP metamorphic rocks always have some possibilities of misidentification by the contamination during crushing. In-situ Raman spectroscopy using polished thin sections or polished sections is necessary for the identification of microdiamonds in UHP metamorphic rocks. Even in in-situ observation that we use thin sections for the microdiamond identification by laser Raman spectroscopy, we have to pay attentions to the risk of the contamination during cutting with diamond blades, polishing with diamond paste/spray because most metamorphic diamonds are μm size and extremely rare, except for those from the Kokchetav Massif. Particularly, on the microdiamond grains which are not entirely included in the host crystals (e.g., garnet, zircon), we should carefully observe those occurrences, the positions and the coexisting materials in the host crystal under an optical microscope. If host crystals have holes or pits, the contamination of abrasive diamond and other shavings is highly probable. When acquired Raman spectra of microdiamonds are not clear (e.g., weak intensity, broad bands, low P/B ratio, mixture with other materials near diamond band), we have to keep in mind that several organic materials used in polished thin section making will make "noise" to Raman spectra of diamonds. During our study of lamellae and inclusions in clinopyroxene of Grt clinopyroxenite (no. 95-9A) from Raobazhai, North Dabie of central China, we found that several microdiamond grains in three holes of one clinopyroxene crystal. Microdiamond grains were positively identified by laser Raman spectrometry; Ar+ laser: 514.5 cm-1, 10 mW laser power, and 1 μm Φ laser beam. Typical diamond Raman band at about 1332 cm-1 (strong intensity and small FWHM) was detected. These microdiamond grains were not completely included in the host, and occurred as captured in a "hole" of clinopyroxene. On the basis of the observation with a reflected light microscope and the multi

  15. Zonal disintegration phenomenon in enclosing rock mass surrounding deep tunnels Elasto-plastic analysis of stress field of enclosing rock mass

    Institute of Scientific and Technical Information of China (English)

    WU Hao; FANG Qin; ZHANG Ya-dong; GONG Zi-ming

    2009-01-01

    The zonal disintegration phenomenon (ZDP) is a typical phenomenon in deep block rock masses. In order to investigate the mechanism of ZDP, an improved non-linear Hock-Brown strength criterion and a bi-linear constitutive model of rock mass were used to analyze the elasto-plastic stress field of the enclosing rock mass around a deep round tunnel. The radius of the plastic region and stress of the enclosing rock mass were obtained by introducing dimensionless parameters of radial distance. The results show that tunneling in deep rock mass causes a maximum stress zone to appear in the vicinity of the boundary of the elastic and the plas-tic zone in the surrounding rock mass. Under the compression of a large tangential force and a small radial force, the rock mass in the maximum stress zone was in an approximate uniaxial loading state, which could lead to a split failure in the rock mass.

  16. Model test of anchoring effect on zonal disintegration in deep surrounding rock masses.

    Science.gov (United States)

    Chen, Xu-Guang; Zhang, Qiang-Yong; Wang, Yuan; Liu, De-Jun; Zhang, Ning

    2013-01-01

    The deep rock masses show a different mechanical behavior compared with the shallow rock masses. They are classified into alternating fractured and intact zones during the excavation, which is known as zonal disintegration. Such phenomenon is a great disaster and will induce the different excavation and anchoring methodology. In this study, a 3D geomechanics model test was conducted to research the anchoring effect of zonal disintegration. The model was constructed with anchoring in a half and nonanchoring in the other half, to compare with each other. The optical extensometer and optical sensor were adopted to measure the displacement and strain changing law in the model test. The displacement laws of the deep surrounding rocks were obtained and found to be nonmonotonic versus the distance to the periphery. Zonal disintegration occurs in the area without anchoring and did not occur in the model under anchoring condition. By contrasting the phenomenon, the anchor effect of restraining zonal disintegration was revealed. And the formation condition of zonal disintegration was decided. In the procedure of tunnel excavation, the anchor strain was found to be alternation in tension and compression. It indicates that anchor will show the nonmonotonic law during suppressing the zonal disintegration.

  17. Model Test of Anchoring Effect on Zonal Disintegration in Deep Surrounding Rock Masses

    Directory of Open Access Journals (Sweden)

    Xu-Guang Chen

    2013-01-01

    Full Text Available The deep rock masses show a different mechanical behavior compared with the shallow rock masses. They are classified into alternating fractured and intact zones during the excavation, which is known as zonal disintegration. Such phenomenon is a great disaster and will induce the different excavation and anchoring methodology. In this study, a 3D geomechanics model test was conducted to research the anchoring effect of zonal disintegration. The model was constructed with anchoring in a half and nonanchoring in the other half, to compare with each other. The optical extensometer and optical sensor were adopted to measure the displacement and strain changing law in the model test. The displacement laws of the deep surrounding rocks were obtained and found to be nonmonotonic versus the distance to the periphery. Zonal disintegration occurs in the area without anchoring and did not occur in the model under anchoring condition. By contrasting the phenomenon, the anchor effect of restraining zonal disintegration was revealed. And the formation condition of zonal disintegration was decided. In the procedure of tunnel excavation, the anchor strain was found to be alternation in tension and compression. It indicates that anchor will show the nonmonotonic law during suppressing the zonal disintegration.

  18. Felsic granulite with layers of eclogite facies rocks in the Bohemian Massif; did they share a common metamorphic history?

    Science.gov (United States)

    Jedlicka, Radim; Faryad, Shah Wali

    2017-08-01

    High pressure granulite and granulite gneiss from the Rychleby Mountains in the East Sudetes form an approximately 7 km long and 0.8 km wide body, which is enclosed by amphibolite facies orthogneiss with a steep foliation. Well preserved felsic granulite is located in the central part of the body, where several small bodies of mafic granulite are also present. In comparison to other high pressure granulites in the Bohemian Massif, which show strong mineral and textural re-equilibration under granulite facies conditions, the mafic granulite samples preserve eclogite facies minerals (garnet, omphacite, kyanite, rutile and phengite) and their field and textural relations indicate that both mafic and felsic granulites shared common metamorphic history during prograde eclogite facies and subsequent granulite facies events. Garnet from both granulite varieties shows prograde compositional zoning and contains inclusions of phengite. Yttrium and REEs in garnet show typical bell-shaped distributions with no annular peaks near the grain rims. Investigation of major and trace elements zoning, including REEs distribution in garnet, was combined with thermodynamic modelling to constrain the early eclogite facies metamorphism and to estimate pressure-temperature conditions of the subsequent granulite facies overprint. The first (U)HP metamorphism occurred along a low geothermal gradient in a subduction-related environment from its initial stage at 0.8 GPa/460 °C and reached pressures up to 2.5 GPa at 550 °C. The subsequent granulite facies overprint (1.6-1.8 GPa/800-880 °C) affected the rocks only partially; by replacement of omphacite into diopside + plagioclase symplectite and by compositional modification of garnet rims. The mineral textures and the preservation of the eclogite facies prograde compositional zoning in garnet cores confirm that the granulite facies overprint was either too short or too faint to cause recrystallisation and homogenisation of the eclogite

  19. The Rock Elm meteorite impact structure, Wisconsin: Geology and shock-metamorphic effects in quartz

    Science.gov (United States)

    French, B.M.; Cordua, W.S.; Plescia, J.B.

    2004-01-01

    The Rock Elm structure in southwest Wisconsin is an anomalous circular area of highly deformed rocks, ???6.5 km in diameter, located in a region of virtually horizontal undeformed sedimentary rocks. Shock-produced planar microstructures (PMs) have been identified in quartz grains in several lithologies associated with the structure: sandstones, quartzite pebbles, and breccia. Two distinct types of PMs are present: P1 features, which appear identical to planar fractures (PFs or cleavage), and P2 features, which are interpreted as possible incipient planar deformation features (PDFs). The latter are uniquely produced by the shock waves associated with meteorite impact events. Both types of PMs are oriented parallel to specific crystallographic planes in the quartz, most commonly to c(0001), ??112??2, and r/z101??1. The association of unusual, structurally deformed strata with distinct shock-produced microdeformation features in their quartz-bearing rocks establishes Rock Elm as a meteorite impact structure and supports the view that the presence of multiple parallel cleavages in quartz may be used independently as a criterion for meteorite impact. Preliminary paleontological studies indicate a minimum age of Middle Ordovician for the Rock Elm structure. A similar age estimate (450-400 Ma) is obtained independently by combining the results of studies of the general morphology of complex impact structures with estimated rates of sedimentation for the region. Such methods may be applicable to dating other old and deeply eroded impact structures formed in sedimentary target rocks.

  20. Some aspects of the role of intergranular fluids in the compositional evolution of metamorphic rocks

    Indian Academy of Sciences (India)

    Sumit Chakraborty; Ralf Dohmen

    2001-12-01

    Minerals that react with each other during the progressive evolution of metamorphic terranes are not always in physical contact. As such, an "intergranular fluid" could play a major role in element transfer and chemical evolution. However, the nature of this uid and its specific role remains somewhat elusive. Recent experiments in our laboratory shed some light on the behavior of such a uid. Here we present a simple mathematical model which accounts for diffusion within crystals and fluid, solubility in the fluid and mass balance between the various reservoirs. The model elucidates the nature of element exchange between two minerals via the mediation of an intergranular fluid. It is shown that a coupling of thermodynamics and kinetics controls the evolution of the system and the concentration of an element in the intergranular fluid is a key parameter of interest. The results have important implications for standard tools of metamorphic petrology such as geothermometers and barometers, geospeedometry and the closure of isotopic systems. For example, homogeneity of mineral grains may be a poor criterion for equilibrium and the rim compositions of minerals showing diffusion zoning may be out of equilibrium with distant exchange partners, even in the presence of a uid in which transport is fast.

  1. Crustal uplift of the Precambrian cratons due to metamorphism in crustal rocks under infiltration of mantle fluids

    Science.gov (United States)

    Artyushkov, Eugene; Chekhovich, Peter; Korikovsky, Sergey; Massonne, Hans-Joachim

    2017-04-01

    Precambrian cratons cover about 70% of the total area of the continents. During the last several million years cratonic areas underwent rapid uplift, from 100-200 m in East Europe to 1000-1500 m Southern Africa. Shortening of the Precambrian crust terminated half a billion years ago or earlier and this popular mechanism cannot be applied to its recent uplift. Large thickness of cratonic mantle lithosphere, 100-200 km in most regions, together with its low density precludes delamination of this layer and magmatic underplating as possible causes of recent uplift. It cannot be precluded that in some cratonic regions recent uplift occurred due to delamination of the lower part of mantle lithosphere with the density increased by metasomatism. Even a small uplift of ≥ 100-200 m would require delamination of a thick layer of mantle lithosphere. As a result a temperature drop of > 200 C would arise at the base of the lithosphere producing a shear wave velocities drop of > 2%. According to the seismic tomography data such a drop in VS is observed only in some regions with the Precambrian lithosphere, e.g., in Northeastern Africa. Spatial distribution of the Precambrian cratons is quite different from that predicted by the main models of dynamic topography in the mantle. Moreover, many uplifted blocks are bounded by steep slopes hundreds of meters to one kilometer high and only tens of kilometers wide. Such slopes could not have been formed by bending of thick cratonic lithosphere under the forces acting from below. Their recent formation indicates rock expansion within the crust at shallow depth comparable with the slope width. Rocks formed at the pressure P ˜ 0.5-1.0 GPa are widespread on the Precambrian cratons. This indicates that during their lifetime a layer of rocks ˜ 15-30 km thick has been removed from the crustal surface by denudation. As a result rocks which were initially located in the lower crust emerged to the middle or upper crust. Due to metamorphic

  2. Metamorphism of the Oddanchatram anorthosite, Tamil Nadu, South India

    Science.gov (United States)

    Wiebe, R. A.; Janardhan, A. S.

    1988-01-01

    The Oddanchatram anorthosite is located in the Madurai District of Tamil Nadu, near the town of Palni. It is emplaced into a granulite facies terrain commonly presumed to have undergone its last regional metamorphism in the late Archean about 2600 m.y. The surrounding country rock consists of basic granulites, charnockites and metasedimentary rocks including quartzites, pelites and calc-silicates. The anorthosite is clearly intrusive into the country rock and contains many large inclusions of previously deformed basic granulite and quartzite within 100 meters of its contact. Both this intrusion and the nearby Kaduvar anorthosite show evidence of having been affected by later metamorphism and deformation.

  3. Dissipation of Impact Stress Waves within the Artificial Blasting Damage Zone in the Surrounding Rocks of Deep Roadway

    Directory of Open Access Journals (Sweden)

    Jianguo Ning

    2016-01-01

    Full Text Available Artificial explosions are commonly used to prevent rockburst in deep roadways. However, the dissipation of the impact stress wave within the artificial blasting damage zone (ABDZ of the rocks surrounding a deep roadway has not yet been clarified. The surrounding rocks were divided into the elastic zone, blasting damage zone, plastic zone, and anchorage zone in this research. Meanwhile, the ABDZ was divided into the pulverizing area, fractured area, and cracked area from the inside out. Besides, the model of the normal incidence of the impact stress waves in the ABDZ was established; the attenuation coefficient of the amplitude of the impact stress waves was obtained after it passed through the intact rock mass, and ABDZ, to the anchorage zone. In addition, a numerical simulation was used to study the dynamic response of the vertical stress and impact-induced vibration energy in the surrounding rocks. By doing so, the dissipation of the impact stress waves within the ABDZ of the surrounding rocks was revealed. As demonstrated in the field application, the establishment of the ABDZ in the surrounding rocks reduced the effect of the impact-induced vibration energy on the anchorage support system of the roadway.

  4. Test studies of gas flow in rock and coal surrounding a mined coal seam

    Institute of Scientific and Technical Information of China (English)

    Lv Youchang

    2012-01-01

    An analysis of the variation rule of abutment pressure at the mining working face in a single coal seam and the mechanical behavior of surrounding rock during stoping is presented.Consideration of the elastic and plastic deformation zones that develop during the mining process allowed the determination of a relationship between horizontal stress and vertical stress.Based on this,a confined pressure unloading test was conducted by the use of the "gas-containing coal thermo-fluid-solid coupling 3-axis servo seepage" experimental apparatus.Thus,gas flow patterns in the elastic and plastic zones were derived from an experimental point of view.Darcy's law and the Klinkenberg effect were used to derive a gas flow equation for the elastic and plastic stress fields.The study of gas flow phenomena at the working face during coal mining is of great importance for the study of gas migration and enrichment oatterns.

  5. Stability control of surrounding rocks for a coal roadway in a deep tectonic region

    Institute of Scientific and Technical Information of China (English)

    Xiao Tongqiang; Wang Xiangyu; Zhang Zhigao

    2014-01-01

    In order to effectively control the deformation and failure of surrounding rocks in a coal roadway in a deep tectonic region, the deformation and failure mechanism and stability control mechanism were stud-ied. With such methods as numerical simulation and field testing, the distribution law of the displace-ment, stress and plastic zone in the surrounding rocks was analyzed. The deformation and failure mechanisms of coal roadways in deep tectonic areas were revealed:under high tectonic stress, two sides will slide along the roof or floor;while the plastic zone of the two sides will extend along the roof or floor, leading to more serious deformation and failure in the corner of two sides and the bolt supporting the corners is readily cut off by the shear force or tension force. Aimed at controlling the large slippage defor-mation of the two sides, serious deformation and failure in the corners of the two sides and massive bolt breakage, a ‘controlling and yielding coupling support’ control technology is proposed. Firstly, bolts which do not pass through the bedding plane should be used in the corners of the roadway, allowing the two sides to have some degree of sliding to achieve the purpose of ‘yielding’ support, and which avoid breakage of the bolts in the corner. After yielding support, bolts in the corner of the roadway and which pass through the bedding plane should be used to control the deformation and failure of the coal in the corner. ‘Controlling and yielding coupling support’ technology has been successfully applied in engineering practice, and the stability of deep coal roadway has been greatly improved.

  6. A 100 km-long paleomagnetic traverse radial to the Sudbury Structure, Canada and its bearing on Proterozoic deformation and metamorphism of the surrounding basement

    Science.gov (United States)

    Halls, Henry C.

    2009-09-01

    The 1850 Ma Sudbury Igneous Complex (SIC), considered to be a composite melt sheet of a major meteorite impact, has been deformed into an oval-shaped basin known as the Sudbury Structure. This paper explores to what extent this deformation has been communicated to the surrounding Archean basement around the northern margin of the SIC. Paleomagnetism of 2450 Ma Matachewan dykes and 1850 Ma impact breccia along a traverse, about 100 km-long and normal to strike of the contact between the SIC and the basement, suggests that the basement beneath the NW corner of the Sudbury Structure has been tilted to the SE within about 10 km of the contact. At this distance a possible fault separates the tilted region from one that shows no evidence of tilting. Petrographically the dykes out to a distance of about 50 km distant from the SIC are altered to upper greenschist facies of metamorphism with a fibrous amphibole replacing pyroxene and with loss of primary texture that characterizes less altered Matachewan dykes at distances greater than 50 km. The direction of magnetization found in the altered Matachewan dykes is an overprint which is probably associated with regional metamorphism related to orogenesis, or possibly with thermo-chemical alteration associated with SIC emplacement. The direction of the component is compatible with an age of about 1.8 to 1.9 Ga suggesting that the Penokean orogen is the most likely cause, if not the impact event. The paleomagnetism of the breccias, together with shatter cone orientation data, suggests that within 10 km of the SIC/basement contact, basement tilting to the southeast increases towards the SIC.

  7. Borehole camera technology for measuring the relaxation zone of surrounding rock: mechanism and application

    Energy Technology Data Exchange (ETDEWEB)

    Jing Hong-wen; Li Yuan-hai; Liang Jun-qi; Yu De-cheng [China University of Mining & Technology, Xuzhou (China). State Key Laboratory for Geomechanics & Deep Underground Engineering

    2009-05-15

    A panoramic borehole camera technology (BCT) and digital image processing method was developed by constructing a system composed of hardware and software. The technology was used for measuring the relaxation zone of surrounding rock with the borehole camera. The hardware consists of a mini CCD camera and a high-pressure sealed magnetic compass that is used for camera positioning. The software includes real-time image monitoring and a processing program that includes the procedure for analysis of the relaxation zone. The roundness of cracks in the boreholes is taken as the index for identifying the relaxation zone. The system was used to measure the relaxation zone of a deep roadway in the Qiwu coal mine of Shandong province. The distribution of the relaxation zone around the roadway was obtained. The results show that the thickness of the broken rock zone varies with the measuring position within a cross section of the roadway. The reliability of the measuring method was tested and verified by comparing the data from BCT with those measured by an ultrasonic method; the difference is less than 3.5%. The system provides a new method for the measurement of the relaxation zone when engineering deep underground. 6 refs., 11 figs., 2 tabs.

  8. High-grade metamorphic rocks of the Mellid area, Galicia, NW Spain

    NARCIS (Netherlands)

    Hubregtse, J.J.M.W.

    1973-01-01

    This study concerns the petrology of the Mellid area, the SE portion of the outer zone of the Ordenes Complex which is one of the upthrusted Precambrian complexes in the axial zone of the Hercynian orogen in Galicia, NW Spain. An eugeosynclinal rock sequence is found containing units with different

  9. The catazonal poly-metamorphic rocks of Cabo Ortegal (NW Spain), a structural and petrofabric study

    NARCIS (Netherlands)

    Engels, J.P.

    1972-01-01

    The petrological study of the southern part of the Cabo Ortegal area is a complement of Vogel’s (1967) investigation of the northern half. The present investigations include a structural as well as a petrofabric study. The rocks belong to an eugeosynclinal sequence which during the Precambrian under

  10. The catazonal poly-metamorphic rocks of Cabo Ortegal (NW Spain), a structural and petrofabric study

    NARCIS (Netherlands)

    Engels, J.P.

    1972-01-01

    The petrological study of the southern part of the Cabo Ortegal area is a complement of Vogel’s (1967) investigation of the northern half. The present investigations include a structural as well as a petrofabric study. The rocks belong to an eugeosynclinal sequence which during the Precambrian

  11. Microscopic Effects of Shock Metamorphism in Crystalline Rocks Correlated With Shock Induced Changes in Density, Haughton Impact Structure

    Science.gov (United States)

    Singleton, A. C.; Osinski, G.; Moser, D.

    2009-05-01

    Asteroid and comet impacts are an important geological process on all solid planetary bodies, including Earth, and involve pressures and temperatures that may reach several hundred GPa and several thousand K [1] over very limited spatial and temporal scales. This results in shock metamorphism and alters the target material on both megascopic and microscopic scales [2]. Many shock metamorphic features are unique to hypervelocity impact environments and are, therefore, diagnostic of such an event [1,2]. Of particular interest for this study is the effect of hypervelocity impact on the density of the target material. In the case of crystalline target rocks, shock metamorphism results in an increase of pore space and impact induced fractures which act to decrease the density. The Haughton impact structure is a well-preserved late Eocene (39 ± 2 Ma) complex impact structure, situated near the western end of Devon Island (75°22'N, 89°41'W) [3]. The geology of the area consists of a sedimentary sequence unconformably overlying crystalline Precambrian gneisses of the Canadian Shield. Since the impact, Devon Island has remained tectonically stable and Haughton remains well-preserved despite being subjected to several glaciations. The excellent preservation of the structure is largely due to the primarily cold and relatively dry environment that has existed in the Arctic since the Eocene [3]. Samples of crystalline material were collected from 36 sites within the impact breccia unit of the Haughton impact structure. These samples display a wide range of density and physical appearance. The type of shock effect(s) created depends upon the pressures and temperatures involved as well as the composition, density and material's location in the target. The samples found in the Haughton impact structure show a wide range of shock effects and thus were exposed to a variety of different conditions likely due to their in-situ positions relative to the impact. Polished thin sections

  12. Discontinuity characterisation in metamorphic rock based on scanline and photogrammetric methods

    Science.gov (United States)

    Koppensteiner, Matthias; Zangerl, Christian

    2016-04-01

    The Ötztal-Stubai crystalline basement (Tyrol, Austria) is characterised by several ductile and brittle deformation phases. Concerning slope stability, landslide formation as well as engineering projects e.g. dam and tunnel construction brittle deformation phases forming brittle fault zones and fractures are highly relevant. These are the structures, which control failure processes, deformation behaviour and groundwater flow in fractured rock masses. A high alpine area of about two square kilometres in size, and located mostly in fractured granodioritic rock was selected to study the discontinuity pattern of faults and joints. Within this area, brittle fault zones are mapped by field survey and analyses of remote sensing data i.e. aerial views and high resolution digital elevation models based on airborne laser scanning. Concerning the joint pattern, sampling points for investigating the geometrical properties are distributed evenly over the area covered with granodioritic gneiss. Whereas most of the collected data is gathered through conventional scanline mapping, at some selected outcrops photogrammetric mapping methods (window mapping) are applied. Among the recorded and analysed parameters of the discontinuities are: orientation, number of joint sets, spacing, frequency, trace length, size, termination, roughness and waviness, block size and GSI. A systematic pattern of recurring discontinuity sets can be observed in the outcrops throughout the whole investigation area. Thus, spatial uniformity is assumed for the whole granodioritic gneiss lithology. Based on this the orientation of the discontinuities and their respective estimated sets are compared between scanline and photogrammetric measurements. For certain representative joint sets, calculated spacing data (mean and probability distribution) as well as joint trace lengths are compared between the scanline surveys and computed parameters from the photogrammetric models. This will help to understand the

  13. Petrology and physical conditions of metamorphism of calcsilicate rocks from low- to high-grade transition area, Dharmapuri District, Tamil Nadu

    Science.gov (United States)

    Narayana, B. L.; Natarajan, R.; Govil, P. K.

    1988-01-01

    Calc-silicate rocks comprising quartz, plagioclase, diopside, sphene, scapolite, grossularite-andradite and wollastonite occur as lensoid enclaves within the greasy migmatitic and charnockitic gneisses of the Archaean amphibolite- to granulite-facies transition zone in Dharmapuri district, Tamil Nadu. The calc-silicate rocks are characterized by the absence of K-feldspar and primary calcite, presence of large modal quartz and plagioclase and formation of secondary garnet and zoisite rims around scapolite and wollastonite. The mineral distributions suggest compositional layering. The chemical composition and mineralogy of the calc-silicate rocks indicate that they were derived from impure silica-rich calcareous sediments whose composition is similar to that of pelite-limestone mixtures. From the mineral assemblages the temperature, pressure and fluid composition during metamorphism were estimated. The observed mineral reaction sequences require a range of X sub CO2 values demonstrating that an initially CO2-rich metamorphic fluid evolved with time towards considerably more H2O-rich compositions. These variations in fluid composition suggest that there were sources of water-rich fluids external to the calc-silicate rocks and that mixing of these fluids with those of calc-silicate rocks was important in controlling fluid composition in calc-silicate rocks and some adjacent rock types as well.

  14. Analysis on mechanism and key factors of surrounding rock instability in deeply inclined roadway affected by argillation and water seepage

    Institute of Scientific and Technical Information of China (English)

    Ma Rui; Li Guichen; Zhang Nong; Liu Cong; Wei Yinghao; Zhang Ming

    2015-01-01

    Based on the characteristics of surrounding rocks for deeply inclined roadway affected by argillation and water seepage, a structure model of layer crack plate was established to analyze the shear sliding insta-bility mechanism. Through solid mechanics analysis of anchored surrounding rock with defect from water seepage, combined with numerical analysis for instability mechanism under water seepage in deeply inclined roadway, key factors were proposed. Results show that with increasing height of layer crack plate, lateral buckling critical load value for high wall of the roadway decreases;there is a multi-stage distribution for tensile stress along the anchor bolt with defect under pulling state condition;groundwater seepage seriously affects the strength of surrounding rock of the roadway, to some extent the plastic zone of the high side rises up to 8 m. Finally some support strategies were proposed for the inclined roadway and successfully applied to Haoyuan coal mine in Tiela mining area, western China.

  15. The Classifications of Metamorphic Rocks and Their Applications to Air Photo Interpretation Procedures,

    Science.gov (United States)

    1983-09-01

    minerals and the facies "". to which that assemblage belongs, such as orthopyroxene-plagioclase granulite . -.., Q 6 -. . . . . . . . . . . . . . 717...prehnite or green- ." schist); whereas, high-grade rocks were assumed to be of higher facies (amphibolite or granulite ). Specific facies names were then...350/400 3-8 .. - Greenschist,. - Upper 350-400/500 3-8 ’-" Lower 450/500-550 3--8 ~Amphibolite 2 ~Upper 550-650/700 3-8 ." Granulite Above 650 3--I12 l

  16. Magnetic fabric of the rocks from the Klodzko Metamorphic Complex (West Sudetes, Poland) and relation to tectonics

    Science.gov (United States)

    Kadzialko-Hofmokl, M.; Werner, T.; Kruczyk, J.; Mazur, S.

    2003-04-01

    The Klodzko Metamorphic Complex KMC consists of metaigneous and metasedimentary rocks of Early Paleozoic and Precambrian age occurring as fragments of a nappe pile lying between the weakly metamorphosed Givetian sediments and Frasnian-Fammenian limestones and shales. At the basis of the Givetian sediments lies a fragment of the Silurian Sudetic ophiolite from which some pillow lavas were sampled. The study concerns the 5 KMC units, Silurian pillow lavas and both Devonian sets of sediments. According to Mazur the rocks under study underwent 6 deformational episodes out of which four D1-D4 took place at the Middle/Late Devonian and two other D5 and D6 - after the Namurian A. The D1 episode was connected with the WNW thrusting, the D2 and subsequent episodes - to dextral transpression or NNE-SSW compression. The mesoscopic mineral lineations L1 and L3 have an azimuth 90-135°E with dip ranging between 15° and 45°. This direction is common in the Sudetes and compatible with the direction of the Intrasudetic and Boundary Sudetic faults. The results of the AMS study agree with the structural conclusions. The Kmax directions calculated in situ for metaigneous rocks, part of metasediments, pillow lavas and Givetian limestones agree well with the mineral lineations. In metasediments from the passive continental margin where the diamagnetics prevail inversion of the anisotropy axes was observed in the fresh specimens. After heating them to 650°C, directions of Kmax became similar to the lineation. Directions of maximum axes of anisotropy of remanence were similar to magnetic lineation in the unheated specimens supporting the conclusion about the inversion of the AMS axes. In the Frasnian-Fammenian limestones the directions of Kmax axes are similar to the results from other units only after correction .for bedding. The results obtained lead to the following conclusions: the magnetic fabric of all studied rock units reflects one or more deformational episodes described by

  17. Orogenesis, high-T thermal events, and gold vein formation within metamorphic rocks of the Alaskan Cordillera

    Science.gov (United States)

    Goldfarb, R.J.; Snee, L.W.; Pickthorn, W.J.

    1993-01-01

    Mesothermal, gold-bearing quartz veins are widespread within allochthonous terranes of Alaska that are composed dominantly of greenschist-facies metasedimentary rocks. The most productive lode deposits are concentrated in south-central and southeastern Alaska; small and generally nonproductive gold-bearing veins occur upstream from major placer deposits in interior and northern Alaska. Ore-forming fluids in all areas are consistent with derivation from metamorphic devolatilisation reactions, and a close temporal relationship exists between high-T tectonic deformation, igneous activity, and gold mineralization. Ore fluids were of consistently low salinity, CO2-rich, and had ??18O values of 7 ???-12??? and ??D values between -15??? and -35???. Upper-crustal temperatures within the metamorphosed terranes reached at least 450-500??C before onset of significant gold-forming hydrothermal activity. In southern Alaska, gold deposits formed during latter stages of Tertiary, subduction-related, collisional orogenesis and were often temporally coeval with calc-alkaline magmatism. -from Authors

  18. Influence of underground water seepage flow on surrounding rock deformation of multi-arch tunnel

    Institute of Scientific and Technical Information of China (English)

    LI Xi-bing; ZHANG Wei; LI Di-yuan; WANG Qi-sheng

    2008-01-01

    Based on a typical multi-arch tunnel in a freeway, the fast Lagrangian analysis of continua in 3 dimensions(FLAC3D) was used to calculate the surrounding rock deformation of the tunnel under which the effect of underground water seepage flow was taken into account or not. The distribution of displacement field around the multi-arch tunnel, which is influenced by the seepage field, was gained. The result indicates that the settlement values of the vault derived from coupling analysis are bigger when considering the seepage flow effect than that not considering. Through the contrast of arch subsidence quantities calculated by two kinds of computation situations, and the comparison between the calculated and measured value of tunnel vault settlement, it is found that the calculated value(5.7-6.0 mm) derived from considering the seepage effect is more close to the measured value(5.8-6.8 mm).Therefore, it is quite necessary to consider the seepage flow effect of the underground water in aquiferous stratum for multi-arch tunnel design.

  19. Epithermal neutron activation, radiometric, correlation and principal component analysis applied to the distribution of major and trace elements in some igneous and metamorphic rocks from Romania

    Energy Technology Data Exchange (ETDEWEB)

    Cristache, C.I. [National Institute of Research and Development for Physics and Nuclear Engineering Horia-Hulubei, P.O. Box MG-6, 077125 Magurele, Ilfov (Romania); Duliu, O.G. [University of Bucharest, Department of Atomic and Nuclear Physics, P.O. Box MG-11, 077125 Magurele, Ilfov (Romania)], E-mail: duliu@b.astral.ro; Culicov, O.A.; Frontasyeva, M.V. [Joint Institute of Nuclear Research, 6, Joliot Curie str. 141980, Dubna (Russian Federation); Ricman, C. [Geological Institute of Romania, 1 Caransebes Street, 012271 Bucharest (Romania); Toma, M. [National Institute of Research and Development for Physics and Nuclear Engineering Horia-Hulubei, P.O. Box MG-6, 077125 Magurele, Ilfov (Romania)

    2009-05-15

    Six major (Na, Al, K, Ca, Ti, Fe) and 28 trace (Sc, Cr, V, Mn, Co, Zn, Cu, As, Br, Sr, Rb, Zr, Mo, Sn, Sb, Ba, Cs, La, Ce, Nd, Eu, Sm, Tb, Hf, Ta, W, Th and U) elements were determined by epithermal neutron activation analysis (ENAA) in nine Meridional Carpathian and Macin Mountains samples of igneous and metamorphic rocks. Correlation and principal factor analysis were used to interpret data while natural radionuclides radiometry shows a good correlation with ENAA results.

  20. Epithermal neutron activation, radiometric, correlation and principal component analysis applied to the distribution of major and trace elements in some igneous and metamorphic rocks from Romania.

    Science.gov (United States)

    Cristache, C I; Duliu, O G; Culicov, O A; Frontasyeva, M V; Ricman, C; Toma, M

    2009-05-01

    Six major (Na, Al, K, Ca, Ti, Fe) and 28 trace (Sc, Cr, V, Mn, Co, Zn, Cu, As, Br, Sr, Rb, Zr, Mo, Sn, Sb, Ba, Cs, La, Ce, Nd, Eu, Sm, Tb, Hf, Ta, W, Th and U) elements were determined by epithermal neutron activation analysis (ENAA) in nine Meridional Carpathian and Macin Mountains samples of igneous and metamorphic rocks. Correlation and principal factor analysis were used to interpret data while natural radionuclides radiometry shows a good correlation with ENAA results.

  1. Short-lived subduction and exhumation in Western Papua (Wandamen peninsula): Co-existence of HP and HT metamorphic rocks in a young geodynamic setting

    Science.gov (United States)

    François, Camille; de Sigoyer, Julia; Pubellier, Manuel; Bailly, Vivien; Cocherie, Alain; Ringenbach, Jean-Claude

    2016-12-01

    Understanding processes of formation of accretionary wedges requires studying young and well preserved examples. The Lengguru wedge (West Papua) is younger than 10 Myr and is a result of oblique and fast subduction (11 cm/yr) of the Bird's Head (a part of the Australian margin beneath the Melanesian Arc). Thus, the rapid formation of this wedge (actually a Fold and Thrust Belt) may be attributed to a single tectonic event. High pressure (HP) metabasic and metasedimentary rocks have been discovered in the core of the wedge in the Wandamen peninsula. Locally, these rocks are overprinted by migmatization during the decompression. Field relationships indicate that migmatites and anatectic leucogranite crosscut the HP metamorphic rocks. This paper reports characterization of petrology and thermobarometry of metasediments and metabasic samples, all included in a former mélange-type rock association, as well as geochronology of metasediments. Pressure-Temperature (P-T) conditions highlight two stages of metamorphism within a small time bracket. In metasediments, a first stage of relatively HP ( 13-17 kbar) is observed as attested by a first paragenesis of garnet-kyanite-phengite. Garnet, kyanite and phengite are then destabilized in favor of biotite during the decompression (5-12 kbar and > 550 °C). Late fractures filled with chlorite and a second generation of white mica crosscut the foliation (< 7 kbar and 500-600 °C). In metabasic rocks, the peak of pressure is reached from 17 to 23 kbar and from 700 to 800 °C. Geochronological study was conducted using U-Pb dating (LA-MC-ICPMS) on zircons from the metasedimentary and migmatitic rocks. Some zircon cores often present high Th/U ratio typical for magmatic origin, as confirmed by trace element signature of metasediments, and recorded ages older than 300 Ma, witness of the activity of a volcanic arc on the former margin of the Australian craton. Most other zircons present a low Th/U ratio attesting their metamorphic

  2. Mechanical analysis on deformation of surrounding rock with road-in packing of gob-side entry retaining in fully-mechanized sub-level caving face

    Institute of Scientific and Technical Information of China (English)

    ZHU Chuan-qu; MIAO Xie-xing; LIU Ze

    2008-01-01

    Based on the movement regularity of surrounding rock with road-in packing of gob-side entry retaining in fully-mechanized sub-level caving face (RPGERFCF), the me-chanical model of its surrounding rock was established and the calculating formulas of the deformation of the roof, coal wall and filling body were attained. By the mechanical analy-sis to the deformation of the surrounding rock of RPGERFCF, the major factors influencing the deformation of the surrounding rock were found out and the technologic approaches reduced the deformation and enhanced the stability of the surrounding rock were put for-ward. Consequently, the scientific bases were provided for the stability control of the sur-rounding rock of RPGERFCF.

  3. The instability mechanics of surrounding rock-coal mass system in longwall face and the prevention of pressure bumps

    Institute of Scientific and Technical Information of China (English)

    李新元; 李英明

    2003-01-01

    According to the movement and change rules of mechanical structure of surrounding rock-coal mass system during coal excavation, the mechanism of sudden instability and damage was found out. The criterions that distinguishing the occurring of the pressure bump were put forward. This criteria have been applied successfully in the comprehensive prevent of pressure bumps in Tangshan colliery.

  4. Natural radioactivity content in groundwater of Mt. Etna’s eastern flank and gamma background of surrounding rocks.

    Directory of Open Access Journals (Sweden)

    Beata Kozłowska

    2016-02-01

    Full Text Available Waters of Mt. Etna are the main source of drinking water for the local population and are also distributed in municipal supply systems to neighbouring areas. Radioactivity in underground waters and surrounding rocks from the eastern flank of Mt.Etnawas investigated on the basis of 9 water and 8 rocks samples from 12 localities altogether. Three samples were from water drainage galleries and six from water wells. All water intakes are used for consumption. Activity concentration of uranium isotopes 234,238U, radium isotopes 226,228Ra and radon 222Rn were determined with the use different nuclear spectrometry techniques. The determination of uranium isotopes was carried out with the use of alpha spectrometry. The measurements of radium and radon activity concentration in water were performed with the use of a liquid scintillation technique. Additionally, rocks surrounding the intakes were examined with gamma spectrometry. All water samples showed uranium concentration above Minimum Detectable Activity (MDA, with the highest total uranium (234U + 238U activity concentration equal to 149.2±6 mBq/L. Conversely, all samples showed radium isotopes activity concentrations below MDA. Radon activity concentration was within the range from 2.91±0.36 to 21.21±1.10 Bq/L, hence these waters can be classified as low – radon waters. Gamma natural background of the rocks surrounding the water sampling sites was found on the same levels as other volcanic rocks of Italy.

  5. Deciphering igneous and metamorphic events in high-grade rocks of the Wilmington complex, Delaware: Morphology, cathodoluminescence and backscattered electron zoning, and SHRIMP U-Pb geochronology of zircon and monazite

    Science.gov (United States)

    Aleinikoff, J.N.; Schenck, W.S.; Plank, M.O.; Srogi, L.A.; Fanning, C.M.; Kamo, S.L.; Bosbyshell, H.

    2006-01-01

    High-grade rocks of the Wilmington Complex, northern Delaware and adjacent Maryland and Pennsylvania, contain morphologically complex zircons that formed through both igneous and metamorphic processes during the development of an island-arc complex and suturing of the arc to Laurentia. The arc complex has been divided into several members, the protoliths of which include both intrusive and extrusive rocks. Metasedimentary rocks are interlayered with the complex and are believed to be the infrastructure upon which the arc was built. In the Wilmingto n Complex rocks, both igneous and metamorphic zircons occur as elongate and equant forms. Chemical zoning, shown by cathodoluminescence (CL), includes both concentric, oscillatory patterns, indicative of igneous origin, and patchwork and sector patterns, suggestive of metamorphic growth. Metamorphic monazites are chemically homogeneous, or show oscillatory or spotted chemical zoning in backscattered electron images. U-Pb geochronology by sensitive high resolution ion microprobe (SHRIMP) was used to date complexly zoned zircon and monazite. All but one member of the Wilmington Complex crystallized in the Ordovician between ca. 475 and 485 Ma; these rocks were intruded by a suite of gabbro-to-granite plutonic rocks at 434 ?? Ma. Detrital zircons in metavolcanic and metasedimentary units were derived predominantly from 0.9 to 1.4 Ga (Grenvillian) basement, presumably of Laurentian origin. Amphibolite to granulite facies metamorphism of the Wilmington Complex, recorded by ages of metamorphic zircon (428 ?? 4 and 432 ?? 6 Ma) and monazite (429 ?? 2 and 426 ?? 3 Ma), occurred contemporaneously with emplacement of the younger plutonic rocks. On the basis of varying CL zoning patterns and external morphologies, metamorphic zircons formed by different processes (presumably controlled by rock chemistry) at slightly different times and temperatures during prograde metamorphism. In addition, at least three other thermal episodes are

  6. Numerical simulation on deformation character of surrounding rock masses of Changjiashan tunnel through the gob of coalmine

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhi-pei

    2006-01-01

    Based on the construction project of the Changjiashan tunnel of the freeway,the variety rule of surrounding rock masses of the tunnel through the gob of coalmine was studied by using of finite element methed(FEM). The status of the stress and strain, the variety of the plastic area were simulated in the whole rock mass before and after the tunnel was excavated. The characters of stress and deformation of surrounding rock masses were analyzed when the tunnel was built. It concluded from the numerical simulation that the influence on the tunneling is great when the tunnel passing through the gob of coalmine is excavated, and the relative measures should be taken.

  7. Amphiboles and their host rocks in the high-grade metamorphic Precambrin of Rogaland/Vest-Agder, Sw. Norway

    NARCIS (Netherlands)

    Dekker, A.G.C.

    1978-01-01

    In the high-grade metamorphic Precambrian of the Sirdal-¢rsdal area, Rogaland/Vest-Agder,south-west Norway, the Ca-amphiboles show a change in pleochroic colours, not only with changes in metamorphic grade, but also to some extend in bulk composition. A regional study was performed on the amphiboles

  8. Effect of Stresses and Strains of Roadway Surrounding Rocks on Borehole Airtightness

    Directory of Open Access Journals (Sweden)

    WU Wei

    2016-02-01

    Full Text Available At present, many high gas and outburst mines have poor gas drainage effects. An important reason influencing the gas drainage effect is a poor hole-sealing effect. Most studies on gas drainage borehole sealing focus on local and foreign borehole sealing methods, borehole sealing equipment, and borehole sealing materials. Numerical simulations of initial drilling sealing depth are insufficient because studies on this subject are few. However, when the initial sealing depth of the borehole is not chosen reasonably, air can enter the gas drainage drill hole through the circumferential crack of roadway surrounding rocks under the influence of suction pressure of the drainage system. This phenomenon ultimately affects the hole-sealing effect. To improve the drilling hole sealing of gas drainage boring, we deduced the expression formulas of the crushing zone, plastic zone, and elastic zone around the coal-seam floor stone drift and conducted a stress–strain analysis of the coal-seam floor stone drift of the 2145 working surfaces of the Sixth Coal Mine of Hebi Coal Mine Group Company by using theoretical analysis, numerical simulation, and on-scene verification. Finally, we obtain the initial drilling sealing depth, which is a main contribution of this study. The results prove the following. The performed hole-sealing process with an initial drilling sealing depth of 8 m has a gas drainage efficiency of 55%. Compared with the previous 6.8 m initial drilling sealing depth with a gas drainage efficiency of less than 30%, which was adopted by the mine, the initial sealing depth of 8 m chosen in the numerical simulation is reasonable and conforms to the actual situation on the spot. Therefore, the initial drilling sealing depth chosen in the numerical simulation will produce practical and effective guidance to study the field hole-sealing depth.

  9. [Characterization of dinosaur fossils and their surrounding rocks by atomic emission spectrometry and X-ray powder diffractometry].

    Science.gov (United States)

    Yang, Qun; Wang, Yi-lin; Li, Chao-zhen; Yuan, Bo

    2005-02-01

    More dinosaur fossils have been found in the Laochangqing valley, Lufeng county than anywhere else in the world, and the dinosaur fossils found here cover the longest time span (including the early and middle Jurassic ages). This excavation offers an ideal experimental base for prehistoric biology studies. This paper presents an elementary analysis of the components and structure of the dinosaur fossils in three different geologic-layers and their surrounding rocks in the above mentioned area. Atomic emission spectrum shows that the fossils are rich in the contents of calcium (>5%) and phosphor, but low in the content of silicon (3%-8%), while the surrounding rocks are high in the content of silicon (>10%). Furthermore, XRD results show that the major compound of the fossils is CaCO3 (66%), followed by SiO2 (17%); while that of the surrounding rocks is SiO2 (>80%), followed by CaCO3 (dinosaur fossils from other rocks. This paper provides valuable data for further zoological studies on the living conditions and evolution of the dinosaurs in the Laochangqing valley, Lufeng county.

  10. Evidence of microstructures and fluid inclusions for the origin of polycrystalline quartz ribbons in high-grade metamorphic rocks in Daqingshan region

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Polycrystalline quartz ribbons in high-grade metamorphic rocks from the Daqingshan region, are typi- cal microfabrics of, and provide information for, deep crust deformation and metamorphism. The quartz ribbons have straight boundaries and extend stably along gneissosity. They truncate other mineral grains in the rocks and may contain inclusions of such minerals that are lens-shaped and oriented. They frequently end into branching termination. Analysis fluid inclusions in polycrystalline quartz rib- bons reveal that the complex types of fluid inclusions are inhomogeneously distributed. They are ob- viously different from inclusions captured at granulite facies, in both fluid compositions and T-P esti- mations. Based on microfabric and fluid inclusion analysis, the polycrystalline quartz ribbons are suggested to be formed by SO2-rich fluids filling micro-fractures that are parallel to early gneissosity. The SO2 composition is derived from the deformed host rocks. The fluid phase has significant effects on the rheological characteristics, fracturing of rocks, and formation of quartz ribbons.

  11. Monazite Growth from the Eocene to the Miocene: New Interpretations of the Metamorphic History of Greater Himalayan Rocks in the Eastern Himalaya

    Science.gov (United States)

    Gordon, S. M.; Kauffman, R.; Gonzales-Clayton, B.; Long, S. P.; Kylander-Clark, A. R.

    2015-12-01

    Across the Himalaya, mid- to lower-crustal Greater-Himalayan (GH) rocks have been exhumed during active continent-continent collision. In the eastern Himalaya within Bhutan, GH rocks are divided into an upper and lower level by an intra-GH shear zone, the Kakthang thrust (KT). To decipher the metamorphic, melt-crystallization and exhumation history of the GH rocks exposed above and below the KT, monazite from metapelites and migmatites was dated and trace elements were analyzed by laser-ablation, split-stream ICPMS. The trace elements from the monazite were used to track when the rocks were at near-peak conditions (based on the depletion of HREE and the likely presence of garnet during monazite growth) versus likely undergoing initial exhumation and garnet breakdown (based on an increase in HREE). Samples were collected from two N-S transects that cross the KT in central and eastern Bhutan. The eastern transect reveals a progressive younging of near-peak metamorphism within the GH, with dates of ca. 23-20 Ma for the structurally-highest sample versus ca. 18-16 Ma in the structurally-lowest sample. The youngest dates from all structural levels of the eastern Bhutan metapelites are 13-15 Ma; the same analyses yield higher HREE abundances, suggesting garnet breakdown during their (re)crystallization. The migmatites yield ca. 14-16 Ma melt-crystallization ages, consistent with the GH having undergone cooling and initial exhumation to cause garnet breakdown by ca. 15 Ma. In comparison, the central Bhutan transect reveals older near-peak metamorphic ages, with garnet-stable monazite populations at ca. 48­-46 Ma within the KT zone, ca. 38-30 Ma for rocks in the middle of the upper-GH, and ca. 25-22 Ma for the structurally-highest sample. Youngest monazites from the central Bhutan transect that yield growth or recrystallization at garnet-unstable conditions range from ca. 17-26 Ma. These results suggest earlier metamorphism and exhumation of GH rocks in central Bhutan

  12. Raman spectra of carbonaceous materials in a fault zone in the Longmenshan thrust belt, China; comparisons with those of sedimentary and metamorphic rocks

    Science.gov (United States)

    Kouketsu, Yui; Shimizu, Ichiko; Wang, Yu; Yao, Lu; Ma, Shengli; Shimamoto, Toshihiko

    2017-03-01

    We analyzed micro-Raman spectra of carbonaceous materials (CM) in natural and experimentally deformed fault rocks from Longmenshan fault zone that caused the 2008 Wenchuan earthquake, to characterize degree of disordering of CM in a fault zone. Raman spectral parameters for 12 samples from a fault zone in Shenxigou, Sichuan, China, all show low-grade structures with no graphite. Low crystallinity and δ13C values (-24‰ to -25‰) suggest that CM in fault zone originated from host rocks (Late Triassic Xujiahe Formation). Full width at half maximum values of main spectral bands (D1 and D2), and relative intensities of two subbands (D3 and D4) of CM were variable with sample locations. However, Raman parameters of measured fault rocks fall on established trends of graphitization in sedimentary and metamorphic rocks. An empirical geothermometer gives temperatures of 160-230 °C for fault rocks in Shenxigou, and these temperatures were lower for highly sheared gouge than those for less deformed fault breccia at inner parts of the fault zone. The lower temperature and less crystallinity of CM in gouge might have been caused by the mechanical destruction of CM by severe shearing deformation, or may be due to mixing of host rocks on the footwall. CM in gouge deformed in high-velocity experiments exhibits slight changes towards graphitization characterized by reduction of D3 and D4 intensities. Thus low crystallinity of CM in natural gouge cannot be explained by our experimental results. Graphite formation during seismic fault motion is extremely local or did not occur in the study area, and the CM crystallinity from shallow to deep fault zones may be predicted as a first approximation from the graphitization trend in sedimentary and metamorphic rocks. If that case, graphite may lower the friction of shear zones at temperatures above 300 °C, deeper than the lower part of seismogenic zone.

  13. Acoustic and physiological effects of the surroundings in rock cutting process

    Directory of Open Access Journals (Sweden)

    Lucia Ivaničová

    2010-03-01

    Full Text Available A noise effect arising in the rock cutting process is gaining a large attention as to the identification and optimization of the cuttingprocess. The sense experience acquired during the experiments in the process of rotary rock drilling related to the determination of rock typeor to the optimal drilling regime determination is formed due to sense perception, mainly hearing, and its further evaluation by the humanbrain from the information exempted from the environment.

  14. Deep-derived enclaves (belonging to middle-lower crust metamorphic rocks) in the Liuhe-Xiangduo area,eastern Tibet: Evidence from petrogeochemistry

    Institute of Scientific and Technical Information of China (English)

    WEI Qirong; LI Dewei; ZHENG Jianping; WANG Jianghai

    2006-01-01

    Petrological and geochemical studies of deep-derived enclaves from the Liuhe-Xiangduo area, eastern Tibet, showed that the enclaves involve five types of rocks, i. e. , garnet diopsidite, garnet amphibolite, garnet hornblendite, amphibolite and hornblendite, whose main mineral assemblages are Grt+Di + Hbl, Grt+ Pl + Hbl + Di, Grt + Hbl + Pl, Pl + Hbl, and Hbl + Bt, respectively. The enclaves exhibit typical crystalloblastic texture, and growth zones are well developed in garnet (Grt) in the enclaves. In view of major element geochemistry, the deep-derived enclaves are characterized by high MgO and FeO * ,ranging from 12.00% to 12.30% and 8.15% to 10.94%, respectively. The protolith restoration of metamorphic rocks revealed that the enclaves belong to ortho-metamorphic rocks. The REE abundances vary over a wide range, and ∑ REE ranges from 53.39 to 129.04 μg/g. The REE patterns slightly incline toward the HREE side with weak LREE enrichment. The contents of Rb, Sr, and Ba range from 8.34 to 101μg/g, 165 to 1485 μg/g, and 105 to 721 μg/g, respectively. The primitive mantle-normalized spider diagrams of trace elements show obvious negative Nb, Ta, Zr and Hf anomalies. Sr-Nd isotopic compositions of the enclaves indicated that the potential source of deep-derived enclaves is similar to the depletedmantle, and their (87Sr/86Sr) i ratios vary from 0.706314 to 0.707198, (147Nd/144Nd)i ratios from 0.512947 to 0.513046, and εNd(T) values from + 7.0 to +9.0, respectively. The potential source of the enclaves is obviously different from the EM2-type mantle from which high-K igneous rocks stemmed(the host rocks), i.e. , there is no direct genetic relationship between the enclaves and the host rocks.Deep-derived enclaves in the host rocks belong to mafic xenoliths, and those in the Liuhe-Xiangduo area,eastern Tibet, are some middle-lower crust ortho-metamorphic rocks which were accidentally captured at20-50 km level by rapidly entrained high-temperature high-K magma

  15. Microtectonic-assisted P-T determination on low-grade Alpine metamorphic rocks from the "Tisia Mega-Unit" of the Slavonian Mountains in Croatia

    Science.gov (United States)

    Balen, Dražen; Lihter, Iva; Massonne, Hans-Joachim

    2016-04-01

    The internal structure of the Tisia (Tisza) Mega-Unit in the Alpine-Carpathian-Dinaridic orogenic system encompasses large Alpine nappe systems brought to its present-day position by complex regional-scale movements. The Slavonian Mountains are part of the Bihor nappe system which is below the Codru and above the Mecsek nappe systems. The low-grade metamorphic schist unit of the Slavonian Mountains includes numerous rocks which were previously related to Precambrian and/or Lower Paleozoic orogeneses. However, recent studies (e.g. Balen, 2014, European Geosciences Union General Assembly, EGU 2014-6122) show that the metapelites of this unit should be attributed to the Alpine orogeny and the poorly known P-T conditions, which they experienced, should be refined. Although metapelites can be sensitive to changes of metamorphic conditions and, therefore, be suitable for the P-T estimation of metamorphic event(s), the extraction of mineral assemblages, being in equilibrium, and associated microtectonic data for particular low-grade metamorphic rocks is not straightforward. On the contrary, due to lack of suitable minerals and complex mictotectonic features, one can be faced with a severe problem concerning (dis)equilibrium. To avoid this, the observation scale in the research was set to the sub-mm level taking into account microtectonic positions of minerals. The investigated samples from the Slavonian Mountains are fine-grained schists consisting of chlorite (15-30 vol. %), white mica (15-25 vol. %), quartz (10-25 vol. %), feldspars (albite 10-15 vol. %; some K-feldspar), biotite (ages (113±20 and 82±23 Ma; Balen, 2014) has a significance in clarifying details of the geodynamic evolution during the Alpine orogeny. Financial support by the Croatian Science Foundation (IP-2014-09-9541) and T. Theye's help during microprobe work is greatly acknowledged.

  16. Deciphering P-T-t Paths from Reaction Microstructures in Metamorphic Rocks: a New Approach by Means of Three-Dimensional Finite Element Modelling

    Science.gov (United States)

    Sassi, R.; Marcuzzi, F.; Mazzoli, C.

    2008-12-01

    One of the main goals of metamorphic petrology is to obtain information on the variations of metamorphic P-T conditions during orogenesis (P-T-t paths). For this purpose petrologists are aware of the potentiality of studying reaction microstructures, although results are not always satisfactory as in most cases qualitative approaches, failing on the real meaning of specific microstructral relationships, are often adopted. Thus, the present research aimed to study the petrogenetic meaning of reaction microstructure in metamorphic rocks through the formulation of a new true three-dimensional finite-element model. For this purpose, different petrologically well studied metamorphic microstructural situations have been selected, in order to identify information, variables and constraints fundamental for the development of the model. A generalised finite-elements model (FEM) has been developed, applicable to any microstructural situation, independently on grain-size and distribution of minerals in the matrix, and able to also consider growth anisotropies, intracrystalline diffusion, pressure solution, and possibly anisotropy of the strain field. This model is based on a combination of the usual diffusion linear equations used in current irreversible thermodynamic models, providing constraints on absolute values of diffusion coefficients of chemical components, chemical potential gradients and time of reactions during metamorphism, starting from information on textural anisotropies observed in metamorphic rocks. In the model, parameterization is given by diffusion, convection and reaction coefficients of each chemical species within each finite element, which dimension is equal to the spatial resolution of the experimentally measured input data (i.e. SEM elemental maps). Thus, parameterization is able to describe locally heterogeneous reaction phenomena although based on a basically linear partial derivative differential model. Such a discretization of the continuum model

  17. A Novel Model of the Ideal Point Method Coupled with Objective and Subjective Weighting Method for Evaluation of Surrounding Rock Stability

    Directory of Open Access Journals (Sweden)

    Yingchao Wang

    2016-01-01

    Full Text Available The classification of surrounding rock stability is the critical problem in tunneling engineering. In order to decrease engineering disasters, the surrounding rock stability should be accurately evaluated. The ideal point method is applied to the classification of surrounding rock stability. Considering the complexity of surrounding rock classification, some factors such as rock uniaxial compressive strengthen, integrality coefficient of rock mass, the angle between tunnel axis and the main joint, joints condition, and seepage measurement of groundwater are selected as evaluation indices. The weight coefficients of these evaluation indices are determined by the objective and subjective weighting method, consisting with the delphi method and the information entropy theory. The objective and subjective weighting method is exact and reliable to determine the weights of evaluation indices, considering not only the expert’s experiences, but also objectivity of the field test data. A new composite model is established for evaluating the surrounding rock stability based on the ideal point method and the objective and subjective weighting method. The present model is applied to Beigu mountain tunnel in Jiangsu province, China. The result is in good agreement with practical situation of surrounding rock, which proves that the ideal point method used to classify the surrounding rock in tunnels is reasonable and effective. The present model is simple and has very strong operability, which possesses a good prospect of engineering application.

  18. Fluxed-melting of shallow and hot high-grade metamorphic rocks in the Namcha Barwa Massif: A new mechanism for the generation of adakitic melts

    Science.gov (United States)

    Zeng, L.; Liu, J.; Hou, Z.; Gao, L.; Xie, K.

    2008-12-01

    Extremely rapid exhumation has been a major factor leading to rapid advection of relatively hot crustal rocks into shallow crustal levels in the Namcha Barwa massif. In such a hot tectonic regime, it is conceivable that hot crustal material can undergo partial melting assisted by excessive water. Previous studies indeed have documented extremely young Na-rich granitic rocks (63.5 and up to 237.1), consistent with garnet either as a non-reactant phase or as a residue phase; (2) these leucosomes have similar Sr isotope compositions to their host rocks, but some of them have Nd isotope compositions significantly deviated from their host by ~4-5 epsilon units. Since high-grade metamorphic rocks in the Namcha Barwa were already shallower than 10 km in the past 5 million years, these data is best explained by water- fluxed melting of granitic components in the source rocks. This interpretation is also consistent with at water- present and relatively lower temperature conditions, both apatite and garnet behaves as non-reactant phases during a partial melting event, which could lead to depletion of garnet-compatible elements as well as negative shift in Nd isotope compositions in the amphibolite- or metapelite-derived melts. Our data emphasize that at rapidly exhumed and relatively hot tectonic regimes (e.g. the Nanga Parbat and Namcha Barwa areas), fluxed-melting of high-graded metamorphic rocks at relatively shallower crustal levels could be another important mechanism to produced adakitic magma and associated porphyritic Cu-Au deposits.

  19. Numerical Analysis of Effect of Water on Explosive Wave Propagation in Tunnels and Surrounding Rock

    Institute of Scientific and Technical Information of China (English)

    XIA Chang-jing; SONG Zhen-duo; TIAN Lu-lu; LIU Hong-bin; WANG Lu; WU Xiao-fang

    2007-01-01

    Based on the application of practical engineering, propagation processes of explosive waves in rock with water well and tunnel are simulated by ANSYS/LS-DYNA software. The evolution of damage in rock is presented. The effect of water on the damage of the concrete slab in a tunnel is compared with damage inflicted without water. The numerical simulation illustrates that water plays an important role in the evolution of damage of the concrete slab in a mine tunnel. In the presence of water in the rock the concrete slab is damaged more severely than without water in rock. The effect of water location in the rock is also considered. It is found that the concrete slab in the tunnel shows various degrees of damage as a function of the different locations of water. Attenuation laws of stress waves over time-space in rock with water are also obtained. Numerical results indicate that, under blast loading, there are three zones in the rock: a crushed zone nearby the explosive charge, a damaged zone and an elastic zone. The conclusions of numerical analysis may provide references for blasting designs and structure protection.

  20. Treatment measures for underground water leakage during construction of tunnel in metamorphic soft rock%变质软岩隧道施工中地下水渗漏处治措施

    Institute of Scientific and Technical Information of China (English)

    李皓晖; 左昌群; 唐霞; 丁少林; 刘代国

    2015-01-01

    Due to the metamorphic soft rock characteristics of water softening and disintegration,there is the phenomenon such as groundwater seepage and water inflow in tunnel construction,which could bring huge hidden danger to the tunnel construction safety. T aking the typical groundwater seepage zone of W udang group schist tunnel in Shiyan-fangxian expressway as research object,in this paper,the groundwater seepage effect in metamorphic soft rock tunnel construction w as analyzed from the aspects including groundw ater seepage characteristics of disaster section,water rationality of surrounding rock,physical mechanics function of groundwater,and put forward the specific control measures of groundwater. T he practice showed that the measures presented in this paper has good control effect on groundw ater leakage of soft rock tunnel,w hich could provide a reference for w atery section safe construction of similar soft rock tunnel.%由于变质软岩具有遇水软化、崩解的特征,在隧道施工过程中易出现地下水渗漏、涌水等,给隧道施工安全带来巨大隐患。以十堰至房县高速公路武当群片岩隧道中典型地下水渗漏区段为主要研究对象,从灾害段地下水渗漏特征、围岩的水理性、地下水的物理力学作用等方面阐述了变质软岩隧道施工中地下水渗漏的影响,并提出了有针对性的地下水控制措施。实践证明,该措施对软岩隧道地下水渗漏具有较好的控制作用,可为类似软岩隧道富水段安全施工提供参考。

  1. Comparison of Rock Varnish Bacterial Communities with Surrounding Non-Varnished Rock Surfaces: Taxon-Specific Analysis and Morphological Description.

    Science.gov (United States)

    Esposito, Alfonso; Ahmed, Engy; Ciccazzo, Sonia; Sikorski, Johannes; Overmann, Jörg; Holmström, Sara J M; Brusetti, Lorenzo

    2015-10-01

    Rock varnish is a thin layer of Fe and Mn oxyhydroxides with embedded clay minerals that contain an increased Mn/Fe ratio compared to that of the Earth's crust. Even if the study of rock varnish has important implications in several fields, the composition of epilithic bacterial communities and the distribution of taxa on varnish surfaces are still not wholly described. The aim of this study was (i) to identify the bacterial taxa which show the greatest variation between varnish and non-varnish environments, collected from the same rock, and (ii) to describe the morphology of epilithic communities through scanning electron microscopy (SEM). Triplicate samples of rock surfaces with varnish and triplicate samples without varnish were collected from five sites in Matsch Valley (South Tyrol, Italy). The V4 region of 16S rRNA gene was analyzed by Illumina sequencing. Fifty-five ubiquitous taxa have been examined to assess variation between varnish and non-varnish. Cyanobacteria, Chloroflexi, Proteobacteria along with minor taxa such as Solirubrobacterales, Conexibaxter, and Rhodopila showed significant variations of abundance, diversity, or both responding to the ecology (presence/absence of varnish). Other taxa, such as the genus Edaphobacter, showed a more marked spatial variation responding to the sampling site. SEM images showed a multitude of bacterial morphologies and structures involved in the process of attachment and creation of a suitable environment for growth. The features emerging from this analysis suggest that the highly oxidative Fe and Mn-rich varnish environment favors anoxigenic autotrophy and establishment of highly specialized bacteria.

  2. Experiments on Graphitization of Diamond in the Presence of Water: Implications for Exhumation of Ultrahigh Pressure Metamorphic Rocks

    Science.gov (United States)

    O'Bannon, E. F.; Xia, G.; Green, H. W.; Wirth, R.; Dobrzhinetskaya, L.

    2012-12-01

    Diamond and graphite occur in the mantle, and crustal ultrahigh pressure metamorphic (UHPM) rocks. The stability fields of carbon are well studied experimentally, but the mechanisms of phase transformation are not well understood. Observations on natural samples from UHPM terranes show that graphitization of diamond is accompanied by the formation of disordered graphite containing nanometric fluid inclusions. Since the structures of diamond and graphite are very dissimilar, it is unlikely that a direct phase transformation would occur during the graphitization process. Such an assumption is also supported by higher enthalpy (1.897) and lower entropy (2.38) of C-diamond with respect of those of C-graphite (enthalpy = 0, entropy=5.74). At least three different mechanisms of diamond-to-graphite transformation have been proposed. To constrain this process we conducted a series of anhydrous and hydrous experiments in a piston-cylinder apparatus and a hydrous experiment in a multianvil apparatus using 20-40 micron size virgin diamonds as the starting material. The piston-cylinder experiments were conducted at P=1 GPa and T=1300oC. In the hydrous experiments 1.15 wt.%. Mg(OH)2 was added to the starting material as the H2O supply according to the breakdown reaction: Mg(OH)2 = MgO + H2O. The multianvil experiment was conducted at P=6GPa and T=1300oC with 1 wt.%. distilled water added to the starting diamonds. Run products were studied with SEM, FIB assisted TEM, and SEM-Raman. The anhydrous experiments show that diamond crystals are "integrated" together producing deformed polycrystallites with complicated textural patterns occurring at the grain boundaries. The hydrous experiments show the formation of metastable nanometric spheroidal carbon particles which were distributed on the surface and between the corners of the diamonds. The metastable phase existed for ~6 months before it decomposed into graphite flakes. The graphite flakes have a disordered structure which was

  3. SHRIMP U–Pb and REE data pertaining to the origins of xenotime in Belt Supergroup rocks: evidence for ages of deposition, hydrothermal alteration, and metamorphism

    Science.gov (United States)

    Aleinikoff, John N.; Lund, Karen; Fanning, C. Mark

    2015-01-01

    The Belt–Purcell Supergroup, northern Idaho, western Montana, and southern British Columbia, is a thick succession of Mesoproterozoic sedimentary rocks with an age range of about 1470–1400 Ma. Stratigraphic layers within several sedimentary units were sampled to apply the new technique of U–Pb dating of xenotime that sometimes forms as rims on detrital zircon during burial diagenesis; xenotime also can form epitaxial overgrowths on zircon during hydrothermal and metamorphic events. Belt Supergroup units sampled are the Prichard and Revett Formations in the lower Belt, and the McNamara and Garnet Range Formations and Pilcher Quartzite in the upper Belt. Additionally, all samples that yielded xenotime were also processed for detrital zircon to provide maximum age constraints for the time of deposition and information about provenances; the sample of Prichard Formation yielded monazite that was also analyzed. Ten xenotime overgrowths from the Prichard Formation yielded a U–Pb age of 1458 ± 4 Ma. However, because scanning electron microscope – backscattered electrons (SEM–BSE) imagery suggests complications due to possible analysis of multiple age zones, we prefer a slightly older age of 1462 ± 6 Ma derived from the three oldest samples, within error of a previous U–Pb zircon age on the syn-sedimentary Plains sill. We interpret the Prichard xenotime as diagenetic in origin. Monazite from the Prichard Formation, originally thought to be detrital, yielded Cretaceous metamorphic ages. Xenotime from the McNamara and Garnet Range Formations and Pilcher Quartzite formed at about 1160– 1050 Ma, several hundred million years after deposition, and probably also experienced Early Cretaceous growth. These xenotime overgrowths are interpreted as metamorphic–diagenetic in origin (i.e., derived during greenschist facies metamorphism elsewhere in the basin, but deposited in sub-greenschist facies rocks). Several xenotime grains are older detrital grains of igneous

  4. Displacement Forecasting Method in Brittle Crack Surrounding Rock Under Excavation Unloading Incorporating Opening Deformation

    Science.gov (United States)

    Li, X. J.; Yang, W. M.; Wang, L. G.; Butler, I. B.

    2014-11-01

    Splitting failure, which is recognized as a special engineering geology phenomenon, occurs continually in the brittle rock mass of caverns during underground excavation. In this paper, a splitting model of linear slippage crack groups is built with fracture mechanics, energy analysis, and crack extension theories. Considering intrinsic cracks in rock mass and change of outer stress, intrinsic cracks propagate into macroscopical splitting cracks that are approximately parallel to the side wall of caverns. The splitting criterion of cavern rock mass and the method for predicting displacement in view of splitting opening displacement are proposed. In the end, the forecasting method is applied to the Jinping-I Hydropower Station, underground caverns engineering in China, the splitting failure zone and forecasting displacement are accordant with the monitoring data. The new forecasting displacement method is proven to contribute to the construction of similar underground caverns.

  5. Rock glaciers of the Karakoram Himalaya and surrounding mountains, Inner Asia

    Science.gov (United States)

    Hewitt, Kenneth

    2013-04-01

    The transHimalayan upper Indus Basin contains thousands of rock glaciers. An exceptional diversity of forms and sizes exist, hitherto largely unresearched. They are in a well-defined elevation band across the mountains, usually less than 1400 m vertically, although total relief exceeds 7000 m. The zone varies from north to south, west to east, and with slope orientation. Interfluve elevations are primary constraints. Rock glaciers are absent below the lowest and the highest interfluves. They are uncommon in the highest Mustagh Karakoram, Nanga Parbat, and Hindu Kush where glacier ice blankets the elevations where they could develop. The heaviest concentrations occur in sub-ranges of intermediate elevation. A full spectrum of generative conditions is found; related to periglacial, talus, glacial, avalanche, wind-blown snow, and rock avalanche processes. Forms vary between north and south slopes; arid, rainshadowed and more snowy, humid valleys. Rock glacier complexes, where two or more join to create extensive lobes, may have tributaries with different source conditions. The larger examples are several kilometres in length,usually glacier-derived, evidently affected by Holocene glacial history, trans-glacial processes, and paraglacial instabilities. In lesser ranges, many smaller rock glaciers are associated with glacier-free cirques, glacially sculpted valley walls, and floors with abundant glacial deposits. In general, they are transitional in genesis, process, and spatially relative to glacierization, to the vertical cascade of moisture and debris, and climate change in the vertical. Their landscape roles include extensive fragmentation of drainage systems. Countless inactive rock glaciers occur, typically continuing below active ones.

  6. THE GEOCHEMISTRY AND AGES OF ROCKS IN THE FOOTWALL OF THE BUTULIYN-NUR AND ZAGAN METAMORPHIC CORE COMPLEXES (NORTH MONGOLIA – WESTERN TRANSBAIKALIA

    Directory of Open Access Journals (Sweden)

    T. V. Donskaya

    2015-09-01

    Full Text Available This article reviews data on ages of rocks in the footwall of the Butuliyn-Nur and Zagan metamorphic core complexes (MCC and provides new data on the geochemistry of the rock complexes. It is noted that the oldest rocks are mylonitized gneisses on rhyolites (554 Ma in the footwall of the Butuliyn-Nur MCC. The Late Permian – Triassic (249–211 Ma igneous rocks are ubiquitous in the footwall of the Butuliyn-Nur and Zagan MCC. The youngest rocks in the studied MCC are the Jurassic granitoids (178–152 Ma of the Naushki and Verhnemangirtui massifs. In the footwall of the Butuliyn-Nur and Zagan MCC, the most common are granitoids and felsic volcanic rocks (249–211 Ma with many similar geochemical characteristics, such as high alkalinity, high contents of Sr and Ba, moderate and low concentrations of Nb and Y. Considering the contents of trace elements and REE, the granitoids and the felsic volcanic rocks are similar to I-type granites. Specific compositions of these rocks suggest that they might have formed in conditions of the active continental margin of the Siberian continent over the subducting oceanic plate of the Mongol-Okhotsk Ocean. The granitoids of the Naushki and Verhnemangirtui massifs, which are the youngest of the studied rocks (178–152 Ma, also have similar geochemical characteristics. In both massif, granitoids are ferriferous, mostly alkaline rocks. By contents of both major and trace elements, they are comparable to A-type granites. Such granitoids formed in conditions of intracontinental extension while subduction was replaced by collision. Based on ages and geochemical characteristics of the rocks in the footwall of the Butuliyn-Nur and Zagan MCC, a good correlation is revealed between the studied rocks  and the rock complexes of the Transbaikalian and North-Mongolian segments of the Central Asian fold belt (CAFB, and it can thus be suggested that the regions under study may have a common evolutionary history.

  7. Dual sources of water overprinting on the low zircon δ18O metamorphic country rocks: Disequilibrium constrained through inverse modelling of partial reequilibration

    Science.gov (United States)

    Wei, Chun-Sheng; Zhao, Zi-Fu

    2017-01-01

    Since water is only composed of oxygen and hydrogen, δ18O and δ2H values are thus utilized to trace the origin of water(s) and quantify the water-rock interactions. While Triassic high pressure (HP) and ultrahigh pressure (UHP) metamorphic rocks across the Dabie-Sulu orogen in central-eastern China have been well documented, postcollisional magmatism driven hydrothermal systems are little known. Here we show that two sources of externally derived water interactions were revealed by oxygen isotopes for the gneissic country rocks intruded by the early Cretaceous postcollisional granitoids. Inverse modellings indicate that the degree of disequilibrium (doD) of meteoric water interactions was more evident than that of magmatic one (-65 ± 1o vs. -20 ± 2°) the partial reequilibration between quartz and alkali feldspar oxygen isotopes with magmatic water was achieved at 340 °C with a water/rock (W/R) ratio of about 1.2 for an open-hydrothermal system; two-stage meteoric water interactions were unraveled with reequilibration temperatures less than 300 °C and W/R ratios around 0.4. The lifetime of fossil magmatic hydrothermal system overprinted on the low zircon δ18O orthogneissic country rocks was estimated to maintain up to 50 thousand years (Kyr) through oxygen exchange modellings. Four-stage isotopic evolutions were proposed for the magmatic water interacted gneiss.

  8. Dual sources of water overprinting on the low zircon δ18O metamorphic country rocks: Disequilibrium constrained through inverse modelling of partial reequilibration

    Science.gov (United States)

    Wei, Chun-Sheng; Zhao, Zi-Fu

    2017-01-01

    Since water is only composed of oxygen and hydrogen, δ18O and δ2H values are thus utilized to trace the origin of water(s) and quantify the water-rock interactions. While Triassic high pressure (HP) and ultrahigh pressure (UHP) metamorphic rocks across the Dabie-Sulu orogen in central-eastern China have been well documented, postcollisional magmatism driven hydrothermal systems are little known. Here we show that two sources of externally derived water interactions were revealed by oxygen isotopes for the gneissic country rocks intruded by the early Cretaceous postcollisional granitoids. Inverse modellings indicate that the degree of disequilibrium (doD) of meteoric water interactions was more evident than that of magmatic one (−65 ± 1o vs. −20 ± 2°); the partial reequilibration between quartz and alkali feldspar oxygen isotopes with magmatic water was achieved at 340 °C with a water/rock (W/R) ratio of about 1.2 for an open-hydrothermal system; two-stage meteoric water interactions were unraveled with reequilibration temperatures less than 300 °C and W/R ratios around 0.4. The lifetime of fossil magmatic hydrothermal system overprinted on the low zircon δ18O orthogneissic country rocks was estimated to maintain up to 50 thousand years (Kyr) through oxygen exchange modellings. Four-stage isotopic evolutions were proposed for the magmatic water interacted gneiss. PMID:28091552

  9. Habitat surrounding patch reefs influences the diet and nutrition of the western rock lobster

    Science.gov (United States)

    In this study the influence of habitat on the diet and nutrition of a common reef-associated generalist consumer, the western rock lobster Panulirus cygnus, was tested. Stable isotopes (13C/12C and 15N/14N) and gut contents were used to assess the diet of lobsters collected from ...

  10. Correlation of metabasic rocks from metamorphic soles of the Dinaridic and the Western Vardar zone ophiolites (Serbia: Three contrasting pressure-temperature-time paths

    Directory of Open Access Journals (Sweden)

    Srećković-Batoćanin Danica

    2012-01-01

    Full Text Available The field, petrological-mineralogical, geochemical and geochronological data of the metamorphic sole rocks recorded beneath the Fruška Gora, Povlen (Tejići, Stolovi and Banjska ophiolites in the Western Vardar Zone (WVZ and beneath the Zlatibor, Bistrica, Sjenički Ozren and Brezovica ophiolites in the Dinaridic ophiolite belt (DOB in Serbia are compared. The focus has been made on metabasic rocks formed in contact with the oceanic crust members: cumulate gabbro and basalts of SSZ-type with E-MORB and OIB-signature and more evolved tholeiitic basalts of MOR-affinity. Amphibole, the major phase formed from the mafic sole components, depending on pressure-temperature conditions exhibits compositional variations. According to mineral assemblages, estimated P-T conditions and ages, the potential P-T paths are given: high pressure - low temperature blueschist facies assemblage (7-9 kbar and ~400°C and <300-350°C and 4-8 kbar, recorded only in the metamorphic sole at the Fruška Gora (WVZ; high pressure - high temperature amphibolite to granulite facies (8-10 kbar and >700-850°C, recorded in both domains, the WVZ (Banjska and the DOB (Bistrica, Sjenički Ozren, Brezovica and medium pressure - medium temperature amphibolite facies assemblages (~3.5-7 kbar and >350-650°C recognized in the WZV (Tejići, Devovići and the DOB (Zlatibor. The peak metamorphic conditions point to depths of the oceanic lithosphere detachment and its initial cooling at 10-30 km, but the ages and tectonic setting of ophiolites remain poorly constrained. The summarized data may be used as an important key in geodynamic evolution of the Mesozoic Tethyan ophiolites. [Projekat Ministarstva nauke Republike Srbije, br. 176019 and br. 176016

  11. New insights into the history and origin of the southern Maya block, SE Mexico: U-Pb-SHRIMP zircon geochronology from metamorphic rocks of the Chiapas massif

    Science.gov (United States)

    Weber, Bodo; Iriondo, Alexander; Premo, Wayne R.; Hecht, Lutz; Schaaf, Peter

    2007-01-01

    The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás and Rondonian-San Ignacio provinces.

  12. Factor analysis of rock, soil and water geochemical data from Salem magnesite mines and surrounding area, Salem, southern India

    Science.gov (United States)

    Satyanarayanan, M.; Eswaramoorthi, S.; Subramanian, S.; Periakali, P.

    2017-09-01

    Geochemical analytical data of 15 representative rock samples, 34 soil samples and 55 groundwater samples collected from Salem magnesite mines and surrounding area in Salem, southern India, were subjected to R-mode factor analysis. A maximum of three factors account for 93.8 % variance in rock data, six factors for 84 % variance in soil data, five factors for 71.2 % in groundwater data during summer and six factors for 73.7 % during winter. Total dissolved solids are predominantly contributed by Mg, Na, Cl and SO4 ions in both seasons and are derived from the country rock and mining waste by dissolution of minerals like magnesite, gypsum, halite. The results also show that groundwater is enriched in considerable amount of minor and trace elements (Fe, Mn, Ni, Cr and Co). Nickel, chromium and cobalt in groundwater and soil are derived from leaching of huge mine dumps deposited by selective magnesite mining activity. The factor analysis on trivalent, hexavalent and total Cr in groundwater indicates that most of the Cr in summer is trivalent and in winter hexavalent. The gradational decrease in topographical elevation from northern mine area to the southern residential area, combined regional hydrogeological factors and distribution of ultramafic rocks in the northern part of the study area indicate that these toxic trace elements in water were derived from mine dumps.

  13. Factor analysis of rock, soil and water geochemical data from Salem magnesite mines and surrounding area, Salem, southern India

    Science.gov (United States)

    Satyanarayanan, M.; Eswaramoorthi, S.; Subramanian, S.; Periakali, P.

    2016-04-01

    Geochemical analytical data of 15 representative rock samples, 34 soil samples and 55 groundwater samples collected from Salem magnesite mines and surrounding area in Salem, southern India, were subjected to R-mode factor analysis. A maximum of three factors account for 93.8 % variance in rock data, six factors for 84 % variance in soil data, five factors for 71.2 % in groundwater data during summer and six factors for 73.7 % during winter. Total dissolved solids are predominantly contributed by Mg, Na, Cl and SO4 ions in both seasons and are derived from the country rock and mining waste by dissolution of minerals like magnesite, gypsum, halite. The results also show that groundwater is enriched in considerable amount of minor and trace elements (Fe, Mn, Ni, Cr and Co). Nickel, chromium and cobalt in groundwater and soil are derived from leaching of huge mine dumps deposited by selective magnesite mining activity. The factor analysis on trivalent, hexavalent and total Cr in groundwater indicates that most of the Cr in summer is trivalent and in winter hexavalent. The gradational decrease in topographical elevation from northern mine area to the southern residential area, combined regional hydrogeological factors and distribution of ultramafic rocks in the northern part of the study area indicate that these toxic trace elements in water were derived from mine dumps.

  14. Theoretical relation between water flow rate in a vertical fracture and rock temperature in the surrounding massif

    CERN Document Server

    Maréchal, Jean-Christophe

    2010-01-01

    A steady-state analytical solution is given describing the temperature distribution in a homogeneous massif perturbed by cold water flow through a discrete vertical fracture. A relation is derived to express the flow rate in the fracture as a function of the temperature measured in the surrounding rock. These mathematical results can be useful for tunnel drilling as it approaches a vertical cold water bearing structure that induces a thermal anomaly in the surrounding massif. During the tunnel drilling, by monitoring this anomaly along the tunnel axis one can quantify the flow rate in the discontinuity ahead before intersecting the fracture. The cases of the Simplon, Mont Blanc and Gotthard tunnels (Alps) are handled with this approach which shows very good agreement between observed temperatures and the theoretical trend. The flow rates before drilling of the tunnel predicted with the theoretical solution are similar in the Mont Blanc and Simplon cases, as well as the flow rates observed during the drilling....

  15. Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)

    Science.gov (United States)

    Trincal, Vincent; Buatier, Martine; Charpentier, Delphine; Lacroix, Brice; Lanari, Pierre; Labaume, Pierre; Lahfid, Abdeltif; Vennemann, Torsten

    2017-09-01

    In orogens, shortening is mainly accommodated by thrusts, which constitute preferential zones for fluid-rock interactions. Fluid flow, mass transfer, and mineralogical reactions taking place along thrusts have been intensely investigated, especially in sedimentary basins for petroleum and uranium research. This study combines petrological investigations, mineralogical quantifications, and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties (nature, origin, temperature, and redox) and fluid-host rock interactions (mass transfers, recrystallization mechanisms, and newly formed synkinematic mineralization) in the Pic-de-Port-Vieux thrust fault zone (Pyrenees, Spain). We demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low-grade metamorphism conditions during thrusting. The hanging-wall Triassic red pelite was locally bleached, while the footwall Cretaceous dolomitic limestone was mylonitized. The results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite. Geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior (tectonic and hydraulic), and improve our knowledge of fluid-rock interactions in open fluid systems in the crust.

  16. Deformation mechanism of surrounding rocks and key control technology for a roadway driven along goaf in fully mechanized top-coal caving face

    Institute of Scientific and Technical Information of China (English)

    李学华

    2003-01-01

    The variation of the stress in the bolted surrounding rocks structure of the roadway driven along goaf in a fully mechanized top-coal caving face with moderate stable conditions are studied by using numerical calculation. The essential deformation characteristics of the surrounding rocks in this kind of roadway are obtained and the key technology of bolting support used under these conditions is put forward.

  17. Deformation mechanism of surrounding rocks and key control technology for a roadway driven along goaf in fully mechanized top-coal caving face

    Energy Technology Data Exchange (ETDEWEB)

    Li, X. [China University of Mining and Technology, Xuzhou (China). School of Energy Science and Engineering

    2003-06-01

    The variation of the stress in the bolted surrounding rocks structure of the roadway driven along the goaf in a fully mechanized top-coal caving face with moderate stable conditions are studied by using numerical calculation. The essential deformation characteristics of the surrounding rocks in this kind of roadway are obtained and the key technology of bolting support used under these conditions is put forward. 3 refs., 2 figs., 1 tab.

  18. Intelligent direct analysis of physical and mechanical parameters of tunnel surrounding rock based on adaptive immunity algorithm and BP neural network

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Because of complexity and non-predictability of the tunnel surrounding rock, the problem with the determination of the physical and mechanical parameters of the surrounding rock has become a main obstacle to theoretical research and numerical analysis in tunnel engineering. During design, it is a frequent practice, therefore, to give recommended values by analog based on experience. It is a key point in current research to make use of the displacement back analytic method to comparatively accurately determi...

  19. Study of Block Stability of Surrounding Rock Mass of Main Transformer Chamber Based on VATS Program

    Directory of Open Access Journals (Sweden)

    Zhongchang Wang

    2012-11-01

    Full Text Available The fracture of rock mass for main transformer chamber in HuangGou hydropower station is very developed. The blocks slide along the discontinuous face or free face with the excavation of cavern. It leads to the failure of normal construction. In the study, according to geology of disclosed discontinuous face in detecting cavern and local three-dimensional coordinate of underground caverns, the vector analysis program for tunnel stability VATS is compiled by using the method of vector analysis of the block theory which is applicable to analyze the discontinuous rock mass and numerical software MATLAB. The occurrence of joints, the coordinate of measuring point, the radius and vertical wall height of underground caverns and other relevant engineering datum is required to input the program. The combination of discontinuous face, boundary condition, geometric parameter, the mode of failure and stability factor of existent unstable blocks is obtained. The geometry distributing characteristic of block and key discontinuous faces in different position is figured by the AUTOCAD software. The guidance for construction of underground caverns is provided.

  20. Isotopic evidence for the infiltration of mantle and metamorphic CO2-H2O fluids from below in faulted rocks from the San Andreas Fault System

    Energy Technology Data Exchange (ETDEWEB)

    Pili, E.; Kennedy, B.M.; Conrad, M.E.; Gratier, J.-P.

    2010-12-15

    To characterize the origin of the fluids involved in the San Andreas Fault (SAF) system, we carried out an isotope study of exhumed faulted rocks from deformation zones, vein fillings and their hosts and the fluid inclusions associated with these materials. Samples were collected from segments along the SAF system selected to provide a depth profile from upper to lower crust. In all, 75 samples from various structures and lithologies from 13 localities were analyzed for noble gas, carbon, and oxygen isotope compositions. Fluid inclusions exhibit helium isotope ratios ({sup 3}He/{sup 4}He) of 0.1-2.5 times the ratio in air, indicating that past fluids percolating through the SAF system contained mantle helium contributions of at least 35%, similar to what has been measured in present-day ground waters associated with the fault (Kennedy et al., 1997). Calcite is the predominant vein mineral and is a common accessory mineral in deformation zones. A systematic variation of C- and O-isotope compositions of carbonates from veins, deformation zones and their hosts suggests percolation by external fluids of similar compositions and origin with the amount of fluid infiltration increasing from host rocks to vein to deformation zones. The isotopic trend observed for carbonates in veins and deformation zones follows that shown by carbonates in host limestones, marbles, and other host rocks, increasing with increasing contribution of deep metamorphic crustal volatiles. At each crustal level, the composition of the infiltrating fluids is thus buffered by deeper metamorphic sources. A negative correlation between calcite {delta}{sup 13}C and fluid inclusion {sup 3}He/{sup 4}He is consistent with a mantle origin for a fraction of the infiltrating CO{sub 2}. Noble gas and stable isotope systematics show consistent evidence for the involvement of mantle-derived fluids combined with infiltration of deep metamorphic H{sub 2}O and CO{sub 2} in faulting, supporting the involvement of

  1. "High-grade burial metamorphism of sedimentary mélange, Shoo Fly Complex, central Sierra Nevada, California"

    Science.gov (United States)

    Mendoza, Y.; Wakabayashi, J.

    2013-12-01

    The Shoo Fly Complex, California is a subduction complex metamorphosed at lower greenschist facies in much of the northern Sierra Nevada. Central Sierra Nevada exposures include higher grade assemblages. Previous studies have interpreted the higher grade rocks as gneissic granitoids representing the roots of a Paleozoic arc. Recent field work in the North Fork Mokelumne River drainage, shows that high-grade and low-grade metamorphic rocks were derived from similar subduction complex protoliths. The Shoo Fly in this region consists of mostly phyllite (metasiltstone, metasandstone, metachert), with some metabasite, and metaultramafic blocks. There is a metamorphic gradient from west to east in the field area, transitioning from sub to lower greenschist facies (white mica only) to middle and upper green schist facies (biotite) within the phyllites to amphibolite/upper amphibolite/granulite grade mica schists, gneisses, and amphibolites This gradient occurs across a zone about 1.5 km wide and this gradient is about 5 km west of the contact between the Shoo Fly Complex and plutons of the Sierra Nevada batholith. The higher-grade rocks do not have an apparent west-east metamorphic gradient. Accordingly the high-grade metamorphism does not appear to be a consequence of either contact metamorphism or raised regional geothermal gradients connected with the batholith. This conclusion is consistent with the fact that published metamorphic ages from probable correlative rocks within the central Sierra are much older than the Sierra Nevada batholith. Protoliths for the higher grade rocks appear identical to the lower grade rocks, for metaclastic rocks dominate with subordinate metacherts, metabasites, and metaultramafic rocks. The latter are represented by tremolite-talc schists. In the lower grade rocks some of the metabasite and metaultramafic blocks exhibit a higher grade of metamorphism than the surrounding metaclastic rocks and metacherts. Amphibolite and tremolite schist

  2. Analysis of Metamorphic Rock Tunnel Deformation Influencing Factors and Mechanism by Monitoring Measurement%基于监控测量的石英片岩区变质岩隧道变形影响因素及机理分析

    Institute of Scientific and Technical Information of China (English)

    于卫云; 李伟

    2016-01-01

    为研究石英片岩区隧道变形破坏机理及影响因素,本文以油坊坪隧道作为研究对象,在对隧道围岩物理力学特性及工程地质条件进行调查分析的基础上,结合隧道变形监测方案,总结归纳了石英片岩隧道的变形破坏过程。研究发现:该变质岩隧道变形破坏多发生在节理裂隙发育,含有地下水,且含有蒙脱石、伊利石、高岭土等膨胀性矿物的围岩之中,且隧道变形破坏具有滞后性、多样性、变形速率快、变形时间长等特点;隧道围岩变形量均超过其对应围岩级别的预留变形量,油坊坪隧道进出口段及拱顶部位沉降变形速率范围为10~35 mm /d。在监测过程中,底板最终沉降最大值为130.5 mm,最小值为15.3 mm,拱顶沉降最大值为131.1 mm,最小值为27.8 mm;隧道变形破坏主要由重力驱动型、应力驱动型和应力-结构驱动型3种。%For the study of metamorphic rock tunnel deformation failure mechanism and influence factors,this paper takes oil mill ping metamorphic rock tunnel as the research object,on the surrounding rock physical and mechanical properties and engineering geological conditions on the basis of investigation and analysis,combined with the tunnel deformation monitoring,sums up the deformation and failure process of the metamorphic rock tunnel.Study found:metamorphic rock tunnel surrounding rock is mainly affected by ground stress,rock mass characteristics and groundwater three factors;Tunnel surrounding rock deformation than its corresponding reserve level of surrounding rock deformation,Oil Mill Flat tunnel section and arch parts import and export settlement rate range for 10 ~35 mm /d.In the process of monito-ring,the maximum floor final settlement is 130.5 mm,minimum value is 15.3 mm,a maximum of 131.1 mm,vault subsidence minimum value is 27.8 mm.;Tunnel deformation damage mainly driven by the gravity driven,stress and stress and

  3. Field Monitoring of Deformations and Internal Forces of Surrounding Rocks and Lining Structures in the Construction of the Gangkou Double-Arched Tunnel—A Case Study

    Directory of Open Access Journals (Sweden)

    Qixiang Yan

    2017-02-01

    Full Text Available Double-arched tunnel is a special and complex underground structure which needs to be monitored carefully during construction. Taking the Gangkou tunnel as the engineering background, this paper presents a case study of field monitoring of a representative double-arched tunnel. Typical cross sections were chosen in each class of surrounding rock masses in the tunnel area and different types of sensors were embedded in designed locations, and the deformations and forces of both surrounding rocks and lining structures were monitored systematically. The dynamic evolution as well as the spatial distribution characteristics of the monitoring data including the internal displacements of surrounding rocks and the contact pressures between surrounding rocks and primary linings, the axial forces in rock bolts and the internal forces in both steel arches and secondary linings were analyzed. The monitoring and analysis results show that the deformations and forces of both surrounding rocks and lining structures are directly related to the construction procedures, geological conditions and locations in the double-arched tunnel. According to the results, some reasonable suggestions were provided for the improvement of the tunnel construction. This study will provide useful reference and guidance for the design, construction and monitoring of similar engineering projects in future.

  4. Fluid-mediated slab-mantle interaction during (U)HP and HT metamorphism of garnet peridotites and their hosting crustal rocks (Monte Duria, Central Alps, N Italy)

    Science.gov (United States)

    Pellegrino, Luca; Malaspina, Nadia; Zanchetta, Stefano; Tumiati, Simone

    2017-04-01

    The Adula-Cima Lunga nappe represents the highest of the Lower Penninic units of the Central Alps. It consists of orthogneiss and paragneiss of pre-Mesozoic origin hosting lenses of metacarbonates, partly retrogressed eclogites and garnet/chlorite peridotites. The garnet peridotite bodies cropping out in the southern area of the nappe complex (Alpe Arami, Cima di Gagnone and Monte Duria) record the highest metamorphic conditions (P>3.0 GPa, T=800-850°C. In the study area garnet peridotite lenses are in contact with biotite-bearing migmatites or hosted in amphibole-bearing migmatites and K-feldspar gneisses. Petrographic and minerochemical data indicate a previously unknown HT stage during peridotite and eclogite exhumation. Peridotites show orthopyroxene with symplectites of tiny crystals of baddeleyte (ZrO2) and srilankite (ZrTi2O6), whereas only zircon was found in the symplectites after garnet. Bulk rock analyses of peridotites show REE content 3 to 5 times lower than PM but with a clear selective enrichment in LREE (spoon-like pattern), and with a Eu positive anomaly. The same "spoon like" pattern in the LREE field is displayed also by eclogites, shifted to values 2 to 5 times higher than PM. Due to the similarities of the REE patterns of peridotite and eclogite and the occurrence of the Eu positive anomaly in most of the peridotite analyses that points to a contamination by a "basaltic" source, we suggest that eclogites are the source of the metasomatic agent that enriched the original garnet peridotite. The Monte Duria area thus represents a natural laboratory where is possible to study "in situ" the mantle-crust interaction. Metasomatic agents and processes, relationships between UHP-UHT metamorphism and metasomatism, and mechanisms of emplacement of mantle rocks into crustal slab can be here addressed and framed in the context of the well known geological background of the Alps.

  5. Tectonic and regional metamorphic implications of the discovery of Middle Ordovician conodonts in cover rocks east of the Green Mountain massif, Vermont

    Science.gov (United States)

    Ratcliffe, N.M.; Harris, A.G.; Walsh, G.J.

    1999-01-01

    Middle Ordovician (late Arenigian - early Caradocian) conodonts were recovered from a dolostone lens in carbonaceous schist 30 m below the base of the Pinney Hollow Formation in the Eastern Cover sequence near West Bridgewater, Vermont. These are the first reported fossils from the metamorphic cover sequence rocks east of the Green Mountain, Berkshire, and Housatonic massifs of western New England. The conodonts are recrystallized, coated with graphitic matter, thermally altered to a color alteration index (CAI) of at least 5, and tectonically deformed. The faunule is nearly monospecific, consisting of abundant Periodon aculeatus Hadding? and rare Protopanderodus. The preponderance of Periodon and the absence of warm, shallow-water species characteristic of the North American Midcontinent Conodont Province suggest a slope or basin depositional setting. The conodont-bearing carbonaceous schist is traceable 3 km southeast to the Plymouth area, where it had been designated the uppermost member of the Plymouth Formation, previously regarded as Early Cambrian in age. The age and structural position of the carbonaceous schist above dolostones of the Plymouth Formation but below the Pinney Hollow Formation (upper Proterozoic and Lower Cambrian?) suggest that this unit may be correlative or time transgressive with the Ira Formation, which underlies the Taconic allochthons in the Vermont Valley. Such a correlation supports the concept of placing the western limit of the root zone of the Taconic allochthons beneath the Pinney Hollow Formation. An approximate absolute age assignment for the conodont-bearing rock is between 470 and 454 Ma. This suggests that dynamothermal metamorphism during the Taconian orogeny on the east flank of the Green Mountains was younger than early Caradocian, which is in accord with the middle Caradocian age of the Ira Formation west of the Green Mountain massif.

  6. Extensional Tectonic Framework of Post High and Ultrahigh Pressure Metamorphism in Dabieshan, China

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    The most prominent feature of the extensional tectonic framework of post high-pressure (HP) and ultrahigh-pressure (UHP) metamorphism in Dabieshan is the development of the multi-layered extension detachment zones surrounding the core of the Luotian dome, and the separation of the UHP, HP and epidote blueschist units by the detachment zones, which form the vertically stacking sheet-like slices of the HP and UHP metamorphic rocks. From the core outwards, exist the HP and UHP rock-barren Dabie complex, UHP unit, HP unit and epidote blueschist unit. The extension tectonics of post HP and UHP metamorphic event constrain the distribution and present configuration of the HP and UHP metamorphic rocks, and the extensional tectonic framework bears some similarities to the Cordillera metamorphic core complex. It is suggested that partial melting happened in the Dabie gneiss complex (DGC) and UHP unit contemporaneously with the extrusion of UHP metamorphic rocks into the lower-middle crust. The formation and emplacement of the migmatite and granites are the response to the change in thermal state, facilitating the transfer from the compressive regime to extensional regime in the crust. The large-scale crustal extension and uplift and the accompanying anatexis in Dabieshan are probably related to the delamination and magmatic underplating in the mantle and the lower crust.

  7. Effects of the metamorphic changes on the subducting processes

    Science.gov (United States)

    Bousquet, R.; de Capitani, C.; Arcay, D.

    2005-12-01

    During the subduction-collision processes, the Earth's crust is squeezed, thickened and uplifted. Therefore rocks will be exposed to changing temperature, pressures and stress regimes and they may undergo metamorphism or partial melting. Meanwhile less attention has been paid to other important aspects of the metamorphic processes. The formation of different kind of rocks (amphibolites, eclogites, granulites) can lead to dramatic changes in petrophysical properties. When reacting rocks expand and contract, the volume changes will set up in the surrounding material. Modeling several cases of subduction for different types of rocks (granites, sediments, mafic and ultramafic rocks), we explore implications 1) on the dynamic of the subduction. Hence computing changes of physical properties of rocks as well quantity of released fluids by dynamic modeling of metamorphic reactions, we will show that some subductions are more propitious to exhume (U)HP rocks and thus to obstruct the subduction dynamic the while others are more propitious to produce heavier rocks and self-sustained subduction. 2) on the localization of earthquakes into the subducting slab. As shown by several authors, intermediate-depth earthquakes mainly occur where hydrous minerals are predicted to be present, implying a causal link between dehydration reactions and seismicity. We investigate petrophysical changes related to dehydration and their implications for generating an earthquake? 3) on the dynamic of the mantle wedge. In many subductions, the upper plate thinning seems to be controlled by the dehydration reactions. We test influence of bulk composition of the lithosphere to estimate the back-arc dynamic. Preliminary results suggest that the appearance of amphiboles within the lithosphere favors local convection and formation of back-arc basin. We conclude that changes associated with metamorphism as an alternative to changes attributed solely to compositional differences.

  8. 40Ar/39Ar Dating of Deformation Events and Reconstruction of Exhumation of Ultrahigh-Pressure Metamorphic Rocks in Donghai,East China

    Institute of Scientific and Technical Information of China (English)

    LI Jinyi; YANG Tiannan; CHEN Wen; ZHANG Sihong

    2003-01-01

    Recent investigations reveal that the ultrahigh-pressure metamorphic (UHPM) rocks in the Donghai regionof East China underwent ductile and transitional ductile-brittle structural events during their exhumation. The earlierductile deformation took place under the condition of amphibolite facies and the later transitional ductile-brittledeformation under the condition of greenschist facies. The hanging walls moved southeastward during both of these twoevents. The 40Ar/39Ar dating of muscovites from muscovite-plagioclase schists in the Haizhou phosphorous mine, whichare structurally overlain by UHPM rocks, yields a plateau age of 218.0±2.9 Ma and isochron age of 219.8Ma, indicatingthat the earlier event of the ampibolite-facies deformation probably took place about 220 Ma ago. The 40Ar/39Ar dating oforiented amphiboles parallel to the movement direction of the hanging wall on a decollement plane yields a plateau age of213.1 ±0.3 Ma and isochron age of 213.4±4.1 Ma, probably representing the age of the later event. The dating of pegmatiticbiotites and K-feldspars near the decollement plane from the eastern Fangshan area yield plateau ages of 203.4±0.3 Ma,203.6±0.4 Ma and 204.8±2.2 Ma, and isochron ages of 204.0±2.0 Ma, 200.6±3.1 Ma and 204.0±5.0 Ma, respectively,implying that the rocks in the studied area had not been cooled down to closing temperature of the dated biotites and K-feldspars until the beginning of the Jurassic (about 204 Ma). The integration of these data with previous chronological ageson the ultrahigh-pressure metamorphism lead to a new inference on the exhumation of the UHPM rocks. The UHPM rocksin the area were exhumed at the rate of 3-4 km/Ma from the mantle (about 80-100 km below the earth's surface at about240 Ma) to the lower crust (at the depth of about 20-30km at 220 Ma), and at the rate of 1-2 km/Ma to the middle crust (atthe depth of about 15 km at 213 Ma), and then at the rate of less than 1 km/Ma to the upper crust about 10 km deep

  9. 公路隧道围岩变形破坏理论研究%Deformation Damage Theory of Highway Tunnel Surrounding Rock

    Institute of Scientific and Technical Information of China (English)

    尚峰利

    2014-01-01

    this paper uses the methods of theoretic analysis, simulation, field monitoring and measuring to deeply study deformation damage theory of highway tunnel surrounding rock. This paper gets the relation-ship between damage variable and surrounding material parameter by analyzing the evolution of surround-ing damage in the course of excavation and proposes the method of predicting mechanical parameters of surrounding rocks;by studying rock damage mechanism, the influence scope of surrounding rock damage stress and all of the factors influencing surrounding rock stability, this paper establishes constitutive rela-tionship of surrounding rock damage in unloading condition and damage constitutive model based on ener-gy dissipation. Based on the elastoplastic numerical analysis mechanism, this paper establishes the analy-sis method of tunnel surrounding rock damage evolution in consideration of deterioration course of sur-rounding rock parameters and analyzes the elastoplastic damage evolution mechanism of tunnel surround-ing rock in excavation stress condition;establishes the model of highway tunnel surrounding rock pressure evolution trend and prediction based on experience formula and progressive surrounding rock damage the-ory, and proposes the predicting method of highway tunnel surrounding rock pressure evolution trend.%采用理论分析、数值模拟以及现场监控量测等手段对公路隧道围岩变形破坏理论进行较深入的研究。通过分析开挖过程中围岩损伤演化,获得了损伤变量与围岩材料参数之间的关系,提出了围岩力学参数的预测方法。通过岩体破坏机理、围岩损伤应力影响范围以及影响围岩稳定性的各个因素综合研究,建立了卸荷状态下的围岩损伤本构关系和基于能量耗散的损伤本构模型。基于一般弹塑性数值分析原理,建立了考虑围岩参数劣化过程的隧道围岩损伤演化分析方法,分析了开挖应力状态下隧道围

  10. Xenoliths in ultrapotassic volcanic rocks in the Lhasa block: direct evidence for crust-mantle mixing and metamorphism in the deep crust

    Science.gov (United States)

    Wang, Rui; Collins, William J.; Weinberg, Roberto F.; Li, Jin-xiang; Li, Qiu-yun; He, Wen-yan; Richards, Jeremy P.; Hou, Zengqian; Zhou, Li-min; Stern, Richard A.

    2016-07-01

    Felsic granulite xenoliths entrained in Miocene (~13 Ma) isotopically evolved, mantle-derived ultrapotassic volcanic (UPV) dykes in southern Tibet are refractory meta-granitoids with garnet and rutile in a near-anhydrous quartzo-feldspathic assemblage. High F-Ti (~4 wt.% TiO2 and ~3 wt.% F) phlogopite occurs as small inclusions in garnet, except for one sample where it occurs as flakes in a quartz-plagioclase-rich rock. High Si (~3.45) phengite is found as flakes in another xenolith sample. The refractory mineralogy suggests that the xenoliths underwent high-T and high-P metamorphism (800-850 °C, >15 kbar). Zircons show four main age groupings: 1.0-0.5 Ga, 50-45, 35-20, and 16-13 Ma. The oldest group is similar to common inherited zircons in the Gangdese belt, whereas the 50-45 Ma zircons match the crystallization age and juvenile character (ɛHf i +0.5 to +6.5) of Eocene Gangdese arc magmas. Together these two age groups indicate that a component of the xenolith was sourced from Gangdese arc rocks. The 35-20 Ma Miocene ages are derived from zircons with similar Hf-O isotopic composition as the Eocene Gangdese magmatic zircons. They also have similar steep REE curves, suggesting they grew in the absence of garnet. These zircons mark a period of early Miocene remelting of the Eocene Gangdese arc. By contrast, the youngest zircons (13.0 ± 4.9 Ma, MSWD = 1.3) are not zoned, have much lower HREE contents than the previous group, and flat HREE patterns. They also have distinctive high Th/U ratios, high zircon δ18O (+8.73-8.97 ‰) values, and extremely low ɛHf i (-12.7 to -9.4) values. Such evolved Hf-O isotopic compositions are similar to values of zircons from the UPV lavas that host the xenolith, and the flat REE pattern suggests that the 13 Ma zircons formed in equilibrium with garnet. Garnets from a strongly peraluminous meta-tonalite xenolith are weakly zoned or unzoned and fall into four groups, three of which are almandine-pyrope solid solutions and have low

  11. Mid-Late Triassic metamorphic event for Changhai meta-sedimentary rocks from the SE Jiao-Liao-Ji Belt, North China Craton: Evidence from monazite U-Th-Pb and muscovite Ar-Ar dating

    Science.gov (United States)

    Liu, Fulai; Wang, Fang; Liou, J. G.; Meng, En; Liu, Jianhui; Yang, Hong; Xiao, Lingling; Cai, Jia; Shi, Jianrong

    2014-11-01

    The precise constraints on the timing of metamorphism of the Changhai metamorphic complex is of great importance considering the prolonged controversial issue of the north margin and the extension of the Sulu-Dabie HP-UHP Belt. While the monazite U-Th-Pb and muscovite 40Ar/39Ar techniques are widely accepted as two of the most powerful dating tools for revealing the thermal histories of medium-low grade metamorphic rocks and precisely constraining the timing of metamorphism. The Changhai metamorphic complex at the SE Jiao-Liao-Ji Belt, North China Craton consists of a variety of pelitic schist and Grt-Ky-bearing paragneiss, and minor quartzite and marble. Analyses of mineral inclusions and back-scattered electric (BSE) images of monazites, combined with LA-ICP-MS U-Th-Pb ages for monazites and 40Ar/39Ar ages for muscovites, provide evidence of the origin and metamorphic age of the Changhai metamorphic complex. Monazites separates from various Grt-Mus schists and Grt-Ky-St-Mus paragneisses exhibit homogeneous BSE images from cores to rims, and contain inclusion assemblages of Grt + Mus + Qtz ± Ctd ± Ky in schist, and Grt + Ky + St + Mus + Pl + Kfs + Qtz inclusions in paragneiss. These inclusion assemblages are very similar to matrix minerals of host rocks, indicating they are metamorphic rather than inherited or detrital in origin. LA-ICP-MS U-Th-Pb dating reveals that monazites of schist and paragneiss have consistent 206Pb/238U ages ranging from 228.1 ± 3.8 to 218.2 ± 3.7 Ma. In contrast, muscovites from various schists show slightly older 40Ar/39Ar plateau ages of 236.1 ± 1.5 to 230.2 ± 1.2 Ma. These geochronological and petrological data conclude that the pelitic sediments have experienced a metamorphic event at the Mid-Late Triassic (236.1-218.2 Ma) rather than the Paleoproterozoic (1950-1850 Ma), commonly regarded as the Precambrian basement for the Jiao-Liao-Ji Belt. Hence, the Changhai metamorphic complex should be considered as a discrete

  12. Preliminary Assessment of the Hydrogeology and Groundwater Availability in the Metamorphic and Siliciclastic Fractured-Rock Aquifer Systems of Warren County, Virginia

    Science.gov (United States)

    Nelms, David L.; Moberg, Roger M.

    2010-01-01

    Expanding development and the prolonged drought from 1999 to 2002 drew attention to the quantity and sustainability of the groundwater resources in Warren County, Virginia. The groundwater flow systems of the county are complex and are controlled by the extremely folded and faulted geology that underlies the county. A study was conducted between May 2002 and October 2008 by the U.S. Geological Survey, in cooperation with Warren County, Virginia, to describe the hydrogeology of the metamorphic and siliciclastic fractured-rock aquifers and groundwater availability in the county and to establish a long-term water monitoring network. The study area encompasses approximately 170 square miles and includes the metamorphic rocks of the Blue Ridge Physiographic Province and siliciclastic rocks of the Great Valley section of the Valley and Ridge Physiographic Province. Well depths tend to be shallowest in the siliciclastic rock unit (predominantly in the Martinsburg Formation) where 75 percent of the wells are less than 200 feet deep. Median depths to bedrock are generally less than 40 feet across the county and vary in response to the presence of surficial deposits, faults, siliciclastic rock type, and topographic setting. Water-bearing zones are generally within 200 feet of land surface; median depths, however, are slightly deeper for the hydrogeologic units of the Blue Ridge Province than for those of the Great Valley section of the county. Median well yields for the different rock units generally range from 10 to 20 gallons per minute. High-yielding wells tend to cluster along faults, along the eastern contact of the Martinsburg Formation, and within potential lineament zones. Specific capacity is relatively low and ranges from 0.003 to 1.43 gallons per minute per foot with median values from 0.12 to 0.24 gallon per minute per foot. Transmissivity values derived from specific capacity data range over four orders of magnitude from 0.6 to 380 feet squared per day

  13. Amphibolites and other metamorphic mafic rocks of the blastomylonitic graben in Western Galicia, NW Spain: field relations and petrography

    NARCIS (Netherlands)

    Arps, C.E.S.

    1981-01-01

    Within the strongly migmatized axial zone of the Hesperian massif in western Galicia a graben-like structure has been distinguished, characterized essentially by the presence of non-migmatic rocks that comprise orthogneisses with blastomylonitic textures, leucocratic gneisses, plagioclase-blastbeari

  14. Deep Fracturing of the Hard Rock Surrounding a Large Underground Cavern Subjected to High Geostress: In Situ Observation and Mechanism Analysis

    Science.gov (United States)

    Feng, Xia-Ting; Pei, Shu-Feng; Jiang, Quan; Zhou, Yang-Yi; Li, Shao-Jun; Yao, Zhi-Bin

    2017-08-01

    Rocks that are far removed from caverns or tunnels peripheries and subjected to high geostress may undergo `deep fracturing'. Deep fracturing of hard rock can cause serious hazards that cause delays and increase the cost of construction of underground caverns with high sidewalls and large spans (especially when subjected to high geostress). To extensively investigate the mechanism responsible for deep fracturing, and the relationship between fracturing and the excavation & support of caverns, this paper presents a basic procedure for making in situ observations on the deep fracturing process in hard rock. The basic procedure involves predicting the stress concentration zones in the surrounding rocks of caverns induced by excavation using geomechanical techniques. Boreholes are then drilled through these stress concentration zones from pre-existing tunnels (such as auxiliary galleries) toward the caverns before its excavation. Continuous observations of the fracturing of the surrounding rocks are performed during excavation using a borehole camera in the boreholes in order to analyze the evolution of the fracturing process. The deep fracturing observed in a large underground cavern (high sidewalls and large span) in southwest China excavated in basalt under high geostress is also discussed. By continuously observing the hard rock surrounding the arch on the upstream side of the cavern during the excavation of the first three layers, it was observed that the fracturing developed into the surrounding rocks with downward excavation of the cavern. Fracturing was found at distances up to 8-9 m from the cavern periphery during the excavation of Layer III. Also, the cracks propagated along pre-existing joints or at the interfaces between quartz porphyry and the rock matrix. The relationship between deep fracturing of the surrounding rocks and the advance of the cavern working faces was analyzed during excavation of Layer Ib. The results indicate that the extent of the

  15. Mineral inclusions in zircons of S-type granite: implications for high pressure metamorphism history of meta-sedimentary rocks in the Huai'an terrain, North China Craton

    Science.gov (United States)

    Wang, Haozheng; Zhang, Huafeng; Zhai, Mingguo; Cui, Xiahong

    2016-04-01

    The Paleoproterozoic evolution of North China Craton (NCC) arises many argument as geologists have different viewpoints on the distribution and metamorphic history of mafic granulites and granulite facies meta-sedimentary rocks. To provide more evidence of constraining the metamorphic history of granulite facies meta-sedimentary rocks, we select granulite facies meta-sedimentary rocks and co-existing S-type granite in the Huai'an terrain to make a deep research. Magmatic zircons derived from the S-type granite reveal the magmatic age of ˜1.95 Ga and metamorphic age of ˜1.85 Ga with ɛHf(t) value of -4.5 - -0.5. The ɛHf(t) value of S-type granite and relict of garnet-sillimanite gneiss suggest that the S-type granite is generated by melting of meta-sedimentary rocks. Zircons with ages of ˜1.95 Ga and ˜1.85 Ga have the mineral inclusions of Ky + Qz + Ru + Pl and these mineral inclusions are determined by method of Laser-Raman. The ˜1.95 Ga magmatic zircons with inclusions of Ky + Qz + Ru + Pl suggest that meta-sedimentary rocks have mineral assemblages Ky + Qz + Ru + Pl. However, previous studies in the Huai'an terrain showed that almost granulite facies metamorphic condition of meta-sedimentary rocks were regarded as medium pressure by considering the Sill + Grt + Bt + Pl + Qz + Ru + Kf. Presence of kyanite instructs that meta-sedimentary rocks may experience high pressure granulite facies metamorphism. According to pseudosection calculation by using effective bulk composition of garnet-sillimanite gneiss, mineral assemblage of Grt + Ky + Pl + Bt + Qz + Ru + Kf is regarded as the peak stage of high pressure metamorphism. This mineral assemblage is occurred at field of 1033 - 1123 K and 9 - 15 Kbar and the peak pressure is around 11 - 13 Kbar, determined by the XMg and XCa isopleths of garnet. This P-T result is consistent with peak condition of high pressure mafic granulite. Considering the ˜1.95 Ga magmatic age of S-type granite generated by decompression

  16. Petrological Characteristics and Original Rocks for Metamorphic Rocks from the Jinmo Sb Deposit, in Quang Ninh Province, Vietnam%越南广宁晋磨锑矿床变质岩石特征及原岩恢复

    Institute of Scientific and Technical Information of China (English)

    季根源; 戴塔根; 孔令湖; 姜爱玲

    2015-01-01

    The Jinmo Sb deposit lies in the collision boundary between the Indo-Chinese block and the South China block, and is close to the east side of the Honghe strike-slip fault and belongs to the South China block. The study of petrology and geochemistry of metamorphic rocks in this region indicates that the original rocks are greywacke, carbonaceous argillaceous sandstone, argillaceous sandstone and clay rock.%晋磨锑矿床位于印支地块和华南地块碰撞界限的边缘,紧靠红河走滑大断裂的东侧,属于华南地块。对研究区变质岩的岩石学、地球化学研究表明,该矿床变质岩均为浅变质的副变质岩,其原岩主要为杂砂岩,其次为泥质砂岩、含炭泥质砂岩,粘土岩。

  17. THE PETROLOGY CHARACTERISTIC OF GRANITOID ROCK BASED ON GEOCHEMICAL ANALYSIS OF BAJAU CAPE COAST AND ITS SURROUNDING, WEST KALIMANTAN

    Directory of Open Access Journals (Sweden)

    Noor C.D. Aryanto

    2017-07-01

    Full Text Available The aim of this study is to identify of petrology characteristic based on geochemical analysis in order to know the granitoid rock type. Administratively, the study area is in the City and District of Singkawang, West Kalimantan Province, at coordinate 108°48'30” - 109°1'30” E and 0°40'30” - 0°54'30” N and, situated ± 145 km to the north of Pontianak City. The outcrop of granitoid along Bajau Cape coast and its surrounding, had been analyzed petrographically and geochemically using AAS method. Based on analysis of five samples show that the ratio mole of Al2O3/(CaO+Na2O +K2O > 1 ranged between 1.12 and 1.7, while the rest of three samples are moderately aluminous, with a ratio value between 0.5 and 1.0. The ratio between K2O and (K2O+Na2O+CaO ranges 0.07 to 0.55 (moderate that forms alkali feldspar normative ranges from 3.8 to 15.89 wt%. This ratio shows that granite alkali feldspar is classified to be calc-alkaline series. Petrographically, this rock is porfiritic texture, hollocrystalline, granular hypodiomorphic and biotite present as phenocryst, yellowish brown, euhedral, thin and platy. The content of oxides element (Na2O and MgO tend to decrease, whereas of other oxides elements, namely Al2O3, TiO2, K2O, FeO and CaO increased, parallel with the raising of SiO2. Therefore, the Singkawang Granitoid can be grouped as alkali feldspar granite, syeno-granite and quartz monzonite.

  18. Coupled Chemical and Thermal Processes During Contact Metamorphism: Constraining Rates and Duration with Time-Dependent 3-D Heat and Mass Transport Modeling of Fluid-Rock Systems

    Science.gov (United States)

    Dutrow, B. L.; Henry, D.; Gable, C. W.; Heydari, E.; Travis, B. J.

    2016-12-01

    Hydrothermal, metamorphic and metasomatic rocks develop through a complex set of coupled thermal, chemical and mechanical processes that contain non-linear feedbacks. The integrated outcome results in a mineral assemblage with a specific texture that records the rates, magnitude and duration of the controlling processes. However, it is often difficult to extract this coupled information from the rock record due to the competing and time-integrated nature of the final product. A particularly problematic case arises when advective metasomatism accompanies thermal energy transport. Advective transport of reactive components by thermally driven flowing fluids can dramatically alter the original bulk rock chemistry. In some instances, these chemical transformations are slow but in others, these alterations can occur over short time scales (yrs). To facilitate investigations of coupled, complex systems and to constrain the rates, duration and relative importance of governing processes during a thermal event, high-resolution 3-D time dependent computational modeling is used. An example of the integrated effects of thermal and chemical transport is found in subsurface Louisiana. Here, an 11m alkali igneous dike intruded Late Jurassic sandy limestones transforming these into new mineral assemblages rich in alkali, alkaline earth elements and F; hydrogrossular, diopside, pectolite (pct), apophyllite, fluorite, and feldspars. Increased temperatures (Ts) and significant mass transport of components from the dike into the host rocks are required. A series of coupled heat and mass transport calculations constrain the rates and duration of the thermal pulse and provide insights into the time-scale of mass transport within this system. For example, calculations incorporating silica transport indicate that at the pct zone (1.5m), thermal conditions remained above 150oC for 2.8 yrs assuming anisotropic permeability (K) and 4.2 yrs (layered K) reaching Tmax at 0.36 (aniso) or 0.53 yr

  19. Impact of weathering on the geomechanical properties of rocks along thermal metamorphic contact belts and morpho-evolutionary processes: The deep-seated gravitational slope deformations of Mt. Granieri Salincriti (Calabria Italy)

    Science.gov (United States)

    Pellegrino, A.; Prestininzi, A.

    2007-06-01

    Numerous Deep-Seated Gravitational Slope Deformations (DSGSDs) occur throughout Italy, that originate from particular tectono-stratigraphic settings, relief, seismicity, deglaciation, as well as from intense and deep processes of chemico-physical weathering of crystalline-metamorphic rocks. These DSGSDs are particularly widespread in the Calabrian mountains. This study is focused on the Mt. Granieri-Salincriti slope, on the Ionian side of the Serre Massif, where granites and granodiorites (Stilo Unit, Palaeozoic) are in contact with metamorphites through a thermal-metamorphic aureole. This setting generates deep geochemical processes, inducing intense chemical weathering. These processes are mainly due to the interaction between groundwater and the sulphides that are contained in the local pegmatitic-hydrothermal intrusions, especially along the thermal-metamorphic contact belt. The Mt. Granieri-Salincriti slope has an important DSGSD, which is associated with many active and/or quiescent landslides. Among these landslides, the Salincriti rock avalanche-debris flow (about 2 M m 3) represents the paroxysmal and terminal stage of the deep creep deformations of Mt. Granieri, typifying a geological setting that is common in the Calabrian Arc. This multi-disciplinary study assessed the weathering susceptibility of the local crystalline-metamorphic rocks, especially those lying along thermal-metamorphic contact belts, by characterising the weathering horizons and the spatial distribution of weathering in the rock mass. The study was also aimed at identifying the relations between weathering, above all deep geochemical processes, effects on rocks and slope morphodynamics. The methodology was based on detailed geological data, geological-engineering surveys, geomorphology and surface hydrogeology analyses, as well as physico-mechanical laboratory tests. These investigations, supported by a monitoring program, led to the development of an engineering-geological model of the

  20. Erosion of the Alps: use of Rb-Sr isotopic data from molassic sediments to identify the ages of the metamorphism recorded by the eroded rocks; Erosion des Alpes: histoire metamorphique des roches erodees par l`analyse du couple Rb-Sr des sediments molassiques

    Energy Technology Data Exchange (ETDEWEB)

    Henry, P.; Deloule, E. [Centre National de la Recherche Scientifique (CNRS), 54 - Nancy (France). Centre de Recherches Petrographiques et Geochimiques; Michard, A. [Aix-Marseille-3 Univ., 13 - Marseille (France)

    1994-06-01

    Rb-Sr isotopic data from Oligocene and Miocene peri-alpine molassic sediments allow us to identify the different periods for which the eroded rocks have or have not recorded an alpine metamorphism. The Chattian and the Burdigalian sediments result from the erosion of rocks for which the latest metamorphic event was variscan, while the Stampian, Aquitanian and ``Helvetian`` sediments show evidence for the erosion of rocks which have recorded alpine metamorphic events. The application of this method to old detrital sediments could permit determination of the ages of the tectonic events which occurred in the sediment source regions. (authors). 18 refs., 6 figs.

  1. Very low-temperature metamorphism in Ordovician metasedimentary rocks above and below the Sardic unconformity, SW Sardinia, Italy

    Science.gov (United States)

    Franceschelli, M.; Battaglia, S.; Cruciani, G.; Pasci, S.; Puxeddu, M.

    2017-03-01

    In the Iglesiente region, the Cabitza and Monte Argentu Formations are separated by an angular unconformity known as the Sardic unconformity. This is related to an early Ordovician mild compressional phase, known as the "Sardic phase". The pelitic samples from the structurally lower Cabitza Formation consist of alternating reddish phyllosilicate-rich and whitish phyllosilicate-poor, sialic layers, whose S0 bedding plane is parallel to a pre-Variscan S1P schistosity overprinted by the Variscan S1V schistosity. Pelitic samples from the Monte Argentu Formation are characterized by a Variscan S1V axial plane schistosity. Samples from the two formations consist of quartz and phyllosilicates. The latter are potassic white mica, chlorite, paragonite, locally kaolinite, and pyrophyllite. The illite crystallinity values determined for the Cabitza samples are 0.25-0.31, with an average of 0.29; meanwhile, the Monte Argentu samples produce values of 0.33-0.38, with an average of 0.35. The chlorite crystallinity and b0 of potassic white mica values show greater heterogeneity in the Cabitza than the Monte Argentu samples. The b0 values and P-T pseudosections allow us to confirm that there is no significant difference in the P-T metamorphism conditions between the Cabitza and Monte Argentu samples. The Iglesiente region, which is considered to be the rift zone behind the Middle Ordovician Sarcidano-Barbagia volcanic arc, underwent the "Sardic phase", giving rise to E-W folds. These were first overprinted by weak E-W, and then by stronger N-S-oriented Variscan deformation events.

  2. Rheological Heterogeneity Along the Deep Subduction Interface: Insights from Exhumed HP Metamorphic Rocks Exposed on Syros Island, Greece

    Science.gov (United States)

    Kotowski, A. J.; Behr, W. M.; Stockli, D. F.; Ashley, K. T.

    2015-12-01

    Rheological properties of subduction interface shear zones control several aspects of subduction zone dynamics, including shear tractions along the plate interface, rates and amounts of exhumation, and depths and styles of seismicity. We document the rheological properties of a deep subduction interface using exhumed eclogite and blueschist-facies rocks from Syros Island, Greece. These rocks were subducted to ~60 km depth during the Eocene, were exhumed part way along the top of the subducting slab, and were then exhumed to upper-crustal levels beneath Miocene detachment faults. Localization of strain during exhumation allowed prograde fabrics to be preserved. The PT conditions (400-550°C, 12-16kb) of these fabrics are comparable to conditions of episodic tremor and slow slip (ETS) observed in some modern subduction zones, including Cascadia. Two types of prograde fabrics were distinguished after analyzing macro-scale distributions of strain and microphysical mechanisms of creep in metamafic rocks. Type 1 fabrics contain eclogite pods boudinaged within a blueschist matrix. The eclogites show brittle deformation with cross-cutting veins containing high-pressure minerals. Deformation in matrix blueschists is accommodated by rigid rotation of amphibole and diffusion creep in plagioclase. Type 2 fabrics contain blueschists and eclogites that are isoclinally folded at similar wavelengths, thus are approximately isoviscous. Deformation is again accommodated by diffusion creep in blueschists, but by dislocation creep of omphacite in eclogites. These deformation types characterizing boudin-matrix and isoviscous rheologies of blueschist-eclogite assemblages appear to reflect varying amounts of finite strain, but work is in progress to determine whether they also record different PT conditions. The transition from Type 1 to 2 fabrics represents a significant change in bulk viscosity and seismic anisotropy, and may correspond to a transition from ETS-type behavior

  3. Eduction, extension, and exhumation of ultrahigh-pressure rocks in metamorphic core complexes due to subduction initiation

    Science.gov (United States)

    Petersen, Kenni Dinesen; Buck, W. Roger

    2015-09-01

    The controversy over the exhumation of ultrahigh-pressure (UHP) rocks centers on whether it involves rising of pieces of crust detached from subducted continental lithosphere or an entire subducted plate that undergoes "eduction," i.e., reverse subduction. We present a new thermomechanical model of continental subduction showing that these apparently contrasting mechanisms can occur together: crust subducted deep enough is heated and weakened, causing limited diapiric rise, while crust subducted to shallower depths retains strength and is exhumed only by eduction. The model also shows for the first time how eduction followed by seafloor spreading can occur in a zone of regional convergence. This occurs spontaneously when subduction of buoyant crust causes a subduction zone to "lock up" in one place causing a new subduction zone to form in another. The model is consistent with many features of the youngest region of UHP rock exhumation on earth: the D'Entrecasteaux Islands. UHP exhumation and the amount of regional extension, as well as the seismic structure around the islands, can be explained by eduction. Ductile flow fabrics, seen on the islands, would result from exhumation of the most deeply subducted crust heated enough to undergo partial melting. Reversal of motion on the north-dipping continental subduction zone, required by this model, was likely triggered by initiation of the New Britain Trench, as suggested previously. Our model implies that the crust of Goodenough Basin, south of the islands, was exhumed by eduction in the last 5 Ma and this hypothesis can be tested by drilling.

  4. Stability principle of big and small structures of rock surrounding roadway driven along goaf in fully mechanized top coal caving face

    Energy Technology Data Exchange (ETDEWEB)

    Hou, C.; Li, X. [China University of Mining and Technology, Xuzhou (China)

    2001-02-01

    Based on the characteristics of the surrounding rock of roadway driven along the goaf in a fully mechanised top coal caving face, the stability principle of big and small structures is put forward, which provides the theoretical basis to the application of bolting. The mechanical characteristics of the arc-triangle key block in the main roof and the stability of the roadway during drivage and extraction and the effect on the roadway driven along the next goaf are analysed. The main factors which affect the stability of the small structure of the surrounding rock are discussed. The bolting surrounding strength reinforcement theory is applied to study the important significance of improving the pre-tension of bolting and the support strength. 4 refs., 7 figs., 2 tabs.

  5. 地下水封储油库围岩稳定性数值分析%Numerical analysis on the stability of surrounding rock for underground water-sealing oil storage in rock caverns

    Institute of Scientific and Technical Information of China (English)

    胡谋鹏; 粱久正; 许杰

    2013-01-01

    An underground water-sealing oil storage in rock caverns in Liaoning Province follows a low level of ground stress in the low-stress area. After its excavation, surrounding rock deformation and fracture are controlled under the combination between single structure plane and multi-group structure plane. Therefore, it is required to first analyze whether the surrounding rock suffer stress problems or structure plane problems and equivalent to value selection of surrounding rock parameters on the importance. Geological strength index (GSI) proposed by Hoek and Brown are based on rock quality evaluation. It can reduce subjectivity in determining the shear strength indicator to define rock mass mechanics parameters by the empirical formula. The underground water-sealed oil storage in rock caverns in Liaoning Province is taken as the object of study. Using the surrounding rock parameter value selection method based on GSI system as well as FLAC3D software, numerical analysis on the surrounding rock stability is conducted and its results are interpreted based on displacement criteria and stress criterion to determine the surrounding rock stability, thus having a guiding significance in engineering practice.%辽宁某地下水封储油硐库地应力水平不高,属于低应力区,开挖后围岩变形破坏受单一结构面和多组结构面的组合控制,因此首先需要分析围岩属于应力型问题还是属于结构面型问题,其重要性等同于围岩参数取值的重要性.Hoek和Brown提出的地质强度指标(GSI)法基于岩体质量评价,应用经验公式确定岩体力学参数,可以一定程度上减少确定抗剪强度指标过程中的主观成分.以辽宁某地下水封储油库工程储油硐室为研究对象,采用基于GSI系统的围岩参数取值方法,借助FLAC3D软件对围岩稳定性进行数值分析,利用位移判据和应力判据对数值分析结果进行解释,进而判断围岩的稳定性,对工程实践具有一定的指导意义.

  6. Chevkinite-group minerals from granulite-facies metamorphic rocks and associated pegmatites of East Antarctica and South India

    Science.gov (United States)

    Belkin, H.E.; Macdonald, R.; Grew, E.S.

    2009-01-01

    Electron microprobe data are presented for chevkinite-group minerals from granulite-facies rocks and associated pegmatites of the Napier Complex and Mawson Station charnockite in East Antarctica and from the Eastern Ghats, South India. Their compositions conform to the general formula for this group, viz. A4BC2D2Si4O22 where, in the analysed specimens A = (rare-earth elements (REE), Ca, Y, Th), B = Fe2+, Mg, C = (Al, Mg, Ti, Fe2+, Fe3+, Zr) and D = Ti and plot within the perrierite field of the total Fe (as FeO) (wt.%) vs. CaO (wt.%) discriminator diagram of Macdonald and Belkin (2002). In contrast to most chevkinite-group minerals, the A site shows unusual enrichment in the MREE and HREE relative to the LREE and Ca. In one sample from the Napier Complex, Y is the dominant cation among the total REE + Y in the A site, the first reported case of Y-dominance in the chevkinite group. The minerals include the most Al-rich yet reported in the chevkinite group (49.15 wt.% Al2O3), sufficient to fill the C site in two samples. Conversely, the amount of Ti in these samples does not fill the D site, and, thus, some of the Al could be making up the deficiency at D, a situation not previously reported in the chevkinite group. Fe abundances are low, requiring Mg to occupy up to 45% of the B site. The chevkinite-group minerals analysed originated from three distinct parageneses: (1) pegmatites containing hornblende and orthopyroxene or garnet; (2) orthopyroxene-bearing gneiss and granulite; (3) highly aluminous paragneisses in which the associated minerals are relatively magnesian or aluminous. Chevkinite-group minerals from the first two parageneses have relatively high FeO content and low MgO and Al2O3 contents; their compositions plot in the field for mafic and intermediate igneous rocks. In contrast, chevkinite-group minerals from the third paragenesis are notably more aluminous and have greater Mg/Fe ratios. ?? 2009 The Mineralogical Society.

  7. Genesis of the metamorphic rock from southeastern Lhasa terrane and the Mesozoic-Cenozoic orogenesis%拉萨地体东南部变质岩的成因与中-新生代造山作用

    Institute of Scientific and Technical Information of China (English)

    董昕; 张泽明; 刘峰; 王伟; 于飞; 林彦蒿; 姜洪颖; 贺振宇

    2012-01-01

    本文对青藏高原拉萨地体东南部林芝地区分布的变质岩进行了岩石学和年代学研究,结果表明这套岩石在中-新生代经历三期变质作用,形成了三个变质带,它们是:(1)米林变质带,经历了高温中压麻粒岩相峰期变质作用和角闪岩相退变质作用,峰期麻粒岩相的变质作用温、压条件为830~900℃和0.9~1.3GPa,变质时代为90 ~80Ma的晚白垩世;(2)八一变质带,经历了低压角闪岩相变质作用,变质作用温、压条件为625 ~ 679℃,0.4~0.55GPa,变质作用时间为55 ~ 50Ma的始新世;(3)布久变质带,经历中压角闪岩相变质作用,变质作用温、压条件为615 ~ 663℃和0.5~0.8GPa,变质作用时间为32~26Ma的渐新世.研究表明,拉萨地体东南部的中高级变质岩系的原岩主要由形成在晚古生代的沉积岩和古生代-新生代的岩浆岩组成,变质沉积岩的物质源区具有格林威尔和泛非造山作用的构造热事件记录,表明拉萨地体具有冈瓦纳大陆的构造亲缘性.我们认为,拉萨地体东南部的晚白垩世高温中压变质作用发生在新特提斯大洋岩石圈向拉萨地体之下俯冲所导致的安第斯型造山作用过程中,始新世的低压角闪岩相变质作用发生在印度与欧亚碰撞和深俯冲的新特提斯洋壳断离过程中,而渐新世的中压角闪岩相变质作用发生在印度大陆向欧亚大陆之下的持续俯冲,地壳加厚过程中.因此,拉萨地体东南部的高级变质岩揭示了俯冲/碰撞复合造山带上盘中、下地壳的组成与构造演化历史.%This work researched the petrology and chronology of the metamorphic rocks distributed in the Xyingchi region from the southeastern segment of Lhasa terrane, Qinghai-Tibet Plateau. Our study indicates this suit of metamorphic rocks experienced three-stage metamorphism during Mesozoic-Cenozoic, and formed three metamorphic belts. Firstly, Mainling belt experienced peak high

  8. SEM observation of grain boundary structures in quartz-iron oxide rocks deformed at intermediate metamorphic conditions

    Directory of Open Access Journals (Sweden)

    Leonardo Lagoeiro

    2011-09-01

    Full Text Available Several studies have demonstrated the effect of a second phase on the distribution of fluid phase and dissolution of quartz grains. However, as most observations came from aggregates deformed under hydrostatic stress conditions and mica-bearing quartz rocks, 3-D distribution of pores on quartz-quartz (QQB and quartz-hematite boundaries (QHB has been studied. Several fracture surfaces oriented according to finite strain ellipsoid were analyzed. The pore distribution characterizes the porosity and grain shape as highly anisotropic, which results from the nature and orientation of boundaries. QHB have physical/chemical properties very different from QQB, once the hematite plates have strong effect on wetting behavior of fluid, likewise micas in quartzites. They are pore-free flat surfaces, normal to compression direction, suggesting that they were once wetted with a continuous fluid film acting as faster diffusion pathway. At QQB, the pores are faceted, isolated, close to its edges reflecting the crystallographic control and an interconnected network of fluid along grain junctions. The QQB facing the extension direction are sites of fluid concentration. As consequence, the anisotropic dissolution and grain growth were responsible for the formation of hematite plates and tabular quartz grains significantly contributing for the generation of the foliation observed in the studied rocks.Muitos estudos têm demonstrado o efeito de uma segunda fase sobre a distribuição de fase fluida e dissolução de grãos de quartzo. Entretanto, como a maioria das observações vêm de agregados deformados sob condições de tensão hidrostática e em rochas quartzosas ricas em mica, a distribuição 3D de poros e bordas quartzo-quartzo (BQQ e quartzo-hematita (BQH tem sido estudada. Várias superfícies de fraturas orientadas segundo o elipsóide de deformação finita foram analisadas. A distribuição dos poros caracteriza a porosidade e a forma dos grãos como

  9. A thermo-mechanical numerical scenario aiming at reproducing the metamorphic record of high-P rocks in the Palaeoproterozoic Eburnean orogeny.

    Science.gov (United States)

    Gerbault, Muriel; Ganne, Jerome; Baratoux, Lenka; Dioh, Edmond; de Andrade, Vincent; Block, Sylvain; Perrouty, Stephane; Jessell, Marc

    2013-04-01

    We test a scenario of the evolution of the Palaeoproterozoic Eburnean event characterising the Birimian Province (2.2-2.0 Ga, Western African Craton). A compilation of field data and petrological modeling indicates that an early thermal regime (M1, =20 km), and which would have formed above an original Birimian oceanic crust (possibly preaccreted forearc-backarcs systems). These assemblages record elevated pressures (P> 6-8 Kb) and are found in the thermal aureoles of CaO-poor granitoids. A second warmer, dominant geothermal gradient M2a (20-30°C/km) is found superimposed on M1, associated to greenschist-amphibolite metamorphic assemblages of moderate- to high-pressure rocks. We suggest that these rocks underwent exhumation processes in close association with continued regional shortening and granitoid intrusions. A thermo-mechanical model is proposed here for the Birimian crust, in which we choose an initial setting of oceanic arc resistant layer underlain by a layer of buoyant granitoids (CaO-rich TTGs). At the center of the model, this layer is itself overlain by a tectonically paired, mechanically weak basin several hundreds of kilometers wide (forearc-backarc system ?). Under applied compression, the model reproduces a mechanism of burial and distributed large-scale folding of this juvenile crust. As the oceanic arc and TTGs layers fold below the overlying hydrated sediments, their hinges deepen and they reach appropriate PT conditions to start melting and transform into a dominantly buoyant (CaO-poor) melt product, of lower viscosity and density (by ~5%). This newly formed material ascends and migrate laterally towards the upper parts of the buckle folds, and then pursues its ascension through the weak overlying sediments, within about 50 Myrs. This spatially periodical and "diapiric" mode of exhumation is capable to entrain preserved lower crustal material as well as re-heated sediments, upwards to about 10-15 km depth. A significant recycling of TTGs in

  10. Unraveling an antique subduction process from metamorphic basement around Medellín city, Central Cordillera of Colombian Andes

    Science.gov (United States)

    Bustamante, Andres; Juliani, Caetano

    2011-10-01

    In the surroundings of Caldas and El Retiro cities (Colombia) metamorphic rocks derived from basic and pelitic protoliths comprise the Caldas amphibole schist and the Ancón schist respectively. Subordinated metamorphosed granite bodies (La Miel gneiss) are associated to these units, and The El Retiro amphibolites, migmatites and granulites crops out eastwards of these units, separated by shear zones. The Caldas amphibole schist and the Ancón schist protoliths could have been formed in a distal marine reduced environment and amalgamated to the South American continent in an apparent Triassic subduction event. The El Retiro rocks are akin to a continental basement and possible include impure metasediments of continental margin, whose metamorphism originated granulite facies rocks and migmatites as a result of the anatexis of quartz-feldspathic rocks. The metamorphism was accompanied by intense deformation, which has juxtaposed both migmatites and granulite blocks. Afterward, heat and fluid circulation associated with the emplacement of minor igneous intrusions resulted in intense fluid-rock interaction, variations in the grain size of the minerals and, especially, intense retrograde metamorphic re-equilibrium. Thermobarometric estimations for the Caldas amphibole schist indicate metamorphism in the Barrovian amphibolite facies. The metamorphic path is counter-clockwise, but retrograde evolution could not be precisely defined. The pressures of the metamorphism in these rocks range from 6.3 to 13.5 kbar, with narrow temperature ranging from 550 to 630 °C. For the Ancón schist metapelites the P- T path is also counter-clockwise, with a temperature increase evidenced by the occurrence of sillimanite and the cooling by later kyanite. The progressive metamorphism event occurred at pressures of 7.6-7.2 kbar and temperatures of 645-635 °C for one sample and temperature between 500 and 600 °C under constant pressure of 6 kbar. The temperature estimated for these rocks

  11. SHRIMP U-Pb Dating of Zircons of a Dark Eclogite and a Garnet-bearing Gneissic Granitic Rock from Bixiling, EasternDabie Area, Anhui Province: Isotope Chronological Evidence of Neoproterozoic UHP Metamorphism

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite, which is metamorphosed basic tuff, contains very scarce zircons in omphacite or garnet, but more zircons in quartz. They usually exhibit a double-layered texture, as shown clearly in cathodoluminescence images. Their inner main parts give a206 Pb/238U age of 757±7Ma, representing the approximate age of the high-pressure (HP)-ultrahighpressure (UHP) metamorphic event duing which the eclogite was formed. The outer peripheral parts of the zircons,which have been modified by late-stage fluids, give an age of 223±3 Ma. The granitic rock contains more zircons of anatectic origin found mostly in feldspar and quartz and usually also showing a similar composite texture. The inner main parts of the anatectic zircons with oscillatory zoning give a 206Pb/238U age of 727±15Ma for the approximate age of the emplacement of the granitic rock, and their outer parts, an age of 219±3 Ma for a similar or even the same fluid event. It is thus suggested that the HP-UHP metamorphism of the Bixiling eclogite facies rocks took place during the Neoproterozoic Jinningian,and the Indosinian age values may only represent a late event in the nature of fluid activity.

  12. Intelligent direct analysis of physical and mechanical parameters of tunnel surrounding rock based on adaptive immunity algorithm and BP neural network

    Institute of Scientific and Technical Information of China (English)

    Xiao-rui Wang; Yuan-han Wang; Xiao-feng Jia

    2009-01-01

    Because of complexity and non-predictability of the tunnel surrounding rock, the problem with the determination of the physical and, mechanical parameters of the surrounding rock has become a main obstacle to theoretical research and numerical analysis in tunnel engineering. During design, it is a frequent practice, therefore, to give recommended values by analog based on experience. It is a key point in current research to make use of the displacement back analytic method to comparatively accurately determine the parameters of the surrounding rock whereas artificial intelligence possesses an exceptionally strong capability of identifying, expressing and coping with such complex non-linear relationships. The parameters can be verified by searching the optimal network structure, using back analysis on measured data to search optimal parameters and performing direct computation of the obtained results. In the current paper, the direct analysis is performed with the biological emulation system and the software of Fast Lagrangian Analysis of Continua (FLAC3D. The high non-linearity, network reasoning and coupling ability of the neural network are employed. The output vector required of the training of the neural network is obtained with the numerical analysis software. And the overall space search is conducted by employing the Adaptive Immunity Algorithm. As a result, we are able to avoid the shortcoming that multiple parameters and optimized parameters are easy to fall into a local extremum. At the same time, the computing speed and efficiency are increased as well. Further, in the paper satisfactory conclusions are arrived at through the intelligent direct-back analysis on the monitored and measured data at the Erdaoya tunneling project. The results show that the physical and mechanical parameters obtained by the intelligent direct-back analysis proposed in the current paper have effectively unproved the recommended values in the original prospecting data. This is of

  13. Study on the Reinforcement Measures and Control Effect of the Surrounding Rock Stability Based on the Shield Tunneling Under Overpass Structure

    Directory of Open Access Journals (Sweden)

    Qian-cheng Fang

    2016-04-01

    Full Text Available To study the stability of surrounding rocks for shield tunneling under overpass structures and the safety of existing bridge structures, a practical example of the method was cited through a shield tunneling project under the overpass structure between K1+110 and K1+700 on Line 2 of Shenyang Subway, China. The sub-area reinforcement was proposed according to surrounding rock deformation characteristics during shield tunnel excavation. The bridge foundation (i.e., the clear spacing to the shield tunnel is less than 2 m was reinforced by steel support, the bridge foundation (the clear spacing is about 2~7m used “jet grouting pile” reinforcement, whereas the bridge foundation (the clear spacing is greater than 7 m did not adopt any reinforcement measures for the moment. For this study, the mean value and material heterogeneity models were established to evaluate the reinforcement effect from several aspects, such as surrounding rock deformation, plastic zone development, and safety factor. The simulation results were consistent with those of field monitoring. After reinforcement, the maximum deformation values of the surrounding rock were reduced by 4.9%, 12.2%, and 48.46%, and the maximum values of surface subsidence were decreased by 5.6%, 72.2%, and 88.64%. By contrast, the overall safety factor was increased by 4.1%, 55.46%, and 55.46%. This study posited that this reinforcement method can be adopted to solve tunnel construction problems in engineering-geological conditions effectively. References for evaluating similar projects are provided.

  14. Application of AOSVR on Surrounding Rock Displacement Forecasting of Underground Powerhouse%AOSVR在地下厂房围岩变形预测中的应用

    Institute of Scientific and Technical Information of China (English)

    金长宇; 马震岳; 张运良

    2006-01-01

    针对目前广泛使用的模糊系统和神经网络预测方法在地下结构围岩变形预测中的缺陷,提出一种精确在线支持向量机(AOSVR)并将其应用到水电站地下厂房开挖过程中顶拱围岩的变形预测.通过与其他预测方法的比较,可以发现精确在线支持向量机有很强的学习能力和很高的预测精度.%Because the prediction accuracy of ANN and Fuzzy system algorithm is insufficient for underground powerhouse rock surrounding stability, the method of Accurate Online Support Vector Regression(AOSVR) was applied to study the evolution law for underground powerhouse rock surrounding displacement. Comparison of the forecasting results of ANN and Fuzzy System with the monitoring result for rock surrounding displacement of underground powerhouse show that the learning efficiency and prediction accuracy of AOSVR is superior to ANN and Fuzzy System obviously.

  15. System dynamics model of the support-surrounding rock system in fully mechanized mining with large mining height face and its application

    Institute of Scientific and Technical Information of China (English)

    Yuan Yong; Tu Shihao; Zhang Xiaogang; Li Bo

    2013-01-01

    Fully mechanized mining with large mining height (FMMLMH) is widely used in thick coal seam mining face for its higher recovery ratio, especially where the thickness is less than 7.0 m. However, because of the great mining height and intense rock pressure, the coal wall rib spalling, roof falling and the instabil-ity of support occur more likely in FMMLMH working face, and the above three types of disasters interact with each other with complicated relationships. In order to get the relationship between each two of coal wall, roof, floor and support, and reduce the occurrence probability of the three types of disasters, we established the system dynamics (SD) model of the support-surrounding rock system which is composed of‘coal wall-roof-floor-support’ (CW-R-F-S) in a FMMLMH working face based on the condition of No. 15104 working face in Sijiazhuang coal mine. With the software of Vensim, we also simulated the inter-action process between each two factors of roof, floor, coal wall and the support. The results show that the SD model of ‘CW-R-F-S’ system can reveal the complicated and interactive relationship clearly between the support and surrounding rock in the FMMLMH working face. By increasing the advancing speed of working face, the support resistance or the length of support guard, or by decreasing the tip-to-face distance, the stability of ‘CW-R-F-S’ system will be higher and the happening probability of the disasters such as coal wall rib spalling, roof falling or the instability of support will be lower. These research findings have been testified in field application in No. 15104 working face, which can provide a new approach for researching the interaction relationship of support and surrounding rock.

  16. Solution of Strain-Softening Surrounding Rock in Deep Tunnel Incorporating 3D Hoek-Brown Failure Criterion and Flow Rule

    Directory of Open Access Journals (Sweden)

    Jin-feng Zou

    2016-01-01

    Full Text Available In order to investigate the influence of the intermediate principal stress on the stress and displacement of surrounding rock, a novel approach based on 3D Hoek-Brown (H-B failure criterion was proposed. Taking the strain-softening characteristic of rock mass into account, the potential plastic zone is subdivided into a finite number of concentric annulus and a numerical procedure for calculating the stress and displacement of each annulus was presented. Strains were obtained based on the nonassociated and associated flow rule and 3D plastic potential function. Stresses were achieved by the stress equilibrium equation and generalized Hoek-Brown failure criterion. Using the proposed approach, we can get the solutions of the stress and displacement of the surrounding rock considering the intermediate principal stress. Moreover, the proposed approach was validated with the published results. Compared with the results based on generalized Hoek-Brown failure criterion, it is shown that the plastic radius calculated by 3D Hoek-Brown failure criterion is smaller than those solved by generalized H-B failure criterion, and the influences of dilatancy effect on the results based on the generalized H-B failure criterion are greater than those based on 3D H-B failure criterion. The displacements considering the nonassociated flow rule are smaller than those considering associated flow rules.

  17. Tectono-metamorphic evolution of high-P/T and low-P/T metamorphic rocks in the Tia Complex, southern New England Fold Belt, eastern Australia: Insights from K-Ar chronology

    Science.gov (United States)

    Fukui, Shiro; Tsujimori, Tatsuki; Watanabe, Teruo; Itaya, Tetsumaru

    2012-10-01

    The Tia Complex in the southern New England Fold Belt is a poly-metamorphosed Late Paleozoic accretionary complex. It consists mainly of high-P/low-T type pumpellyite-actinolite facies (rare blueschist facies) schists, phyllite and serpentinite (T = 300 °C and P = 5 kbar), and low-P/high-T type amphibolite facies schist and gneiss (T = 600 °C and P high-Mg andesite and adakite might explain formation of S-type granitoids (Hillgrove suite) and coeval low-P/high-T type metamorphism in the Tia Complex.

  18. Metamorphic geology: Why should we care?

    Science.gov (United States)

    Tajcmanova, Lucie; Moulas, Evangelos; Vrijmoed, Johannes

    2016-04-01

    Estimation of pressure-temperature (P-T) from petrographic observations in metamorphic rocks has become a common practice in petrology studies during the last 50 years. This data then often serves as a key input in geodynamic reconstructions and thus directly influences our understanding of lithospheric processes. Such an approach might have led the metamorphic geology field to a certain level of quiescence. Obtaining high-quality analytical data from metamorphic rocks has become a standard part of geology studies. The numerical tools for geodynamic reconstructions have evolved to a great extend as well. Furthermore, the increasing demand on using the Earth's interior for sustainable energy or nuclear waste disposal requires a better understanding of the physical processes involved in fluid-rock interaction. However, nowadays, metamorphic data have apparently lost their importance in the "bigger picture" of the Earth sciences. Interestingly, the suppression of the metamorphic geology discipline limits the potential for understanding the aforementioned physical processes that could have been exploited. In fact, those phenomena must be considered in the development of new generations of fully coupled numerical codes that involve reacting materials with changing porosity while obeying conservation of mass, momentum and energy. In our contribution, we would like to discuss the current role of metamorphic geology. We will bring food for thoughts and specifically touch upon the following questions: How can we revitalize metamorphic geology? How can we increase the importance of it? How can metamorphic geology contribute to societal issues?

  19. Zircon U-Pb dating of metabasic rocks in the Zanhuang metamorphic complex and its geological significance%赞皇变基性岩中锆石的U-Pb定年及其地质意义

    Institute of Scientific and Technical Information of China (English)

    肖玲玲; 王国栋

    2011-01-01

    赞皇变质杂岩区位于阜平杂岩南部,地处华北克拉通中部造山带的中段,和中部带北段杂岩一样,是洞悉华北克拉通前寒武纪基底构造演化历史的一个重要窗口.研究区变基性岩可分为斜长角闪岩和角闪斜长片麻岩两种,二者均以似层状方式产于黑云斜长片麻岩或长英质片麻岩中,斜长角闪岩亦可呈透镜状,二者后期与围岩一起共同经历了高角闪岩相变质作用.斜长角闪岩和角闪斜长片麻岩中普遍存在变质锆石,锆石SIMS U-Pb原位定年获得的207Pb/206Pb谐和年龄表明,赞皇变基性岩记录了约18.5亿年(1842±21 Ma、1868±29 Ma)的一次较为广泛的变质作用事件,结合赞皇变质杂岩的构造背景和变质演化特征,推测该期变质作用事件与古元古代末期华北克拉通东部陆块和西部陆块间的俯冲碰撞作用有关.%The Zanhuang metamorphic complex is significant for understanding the Precambrian tectonics and evolution of the North China Craton. Metabasic rocks composed of amphibolite and amphibole-bearing plagio-clase gneiss as thin layers or lenses are widely distributed within felsic gneisses and biotite-plagioclase gneisses. These metabasic rocks together with country rocks underwent high-amphibolite facies metamorphism, and abundant metamorphic zircons were formed during this thermal event. SIMS U-Pb chronological analysis indicates that metamorphic zircons record peak high-amphibolite facies metamorphism at 1 868~1 842 Ma. These Paleo-proterozoic metamorphic ages are largely in accordance with metamorphic ages of ~ 1 850 Ma produced from high-pressure granulites in the northern segment of the Trans-North China Orogen, indicating that a significant subduction-collision event did occur in the Trans-North China Orogen between the eastern block and the western block during Paleoproterozoic ( ~ 1 850 Ma).

  20. 2D DEM analyses for T-M coupling effects of extreme temperatures on surrounding rock-supporting system of a tunnel in cold region

    Institute of Scientific and Technical Information of China (English)

    张玉军; 杨朝帅; 王永刚

    2013-01-01

    Taking the Kunlunshan Tunnel on Qinghai Tibet Railway as an engineering background, the curved wall-inverted arch lining of the tunnel was simplified into the straight wall-umbrella arch one, and the fractured rock mass with developed joints was treated as a discrete medium in the calculation. Using the UDEC code, the numerical simulations for thermo-mechanical coupling processes in the surrounding rock mass-supporting system were carried out aiming at the conditions of mean temperature, extreme highest temperature and extreme lowest temperature in one year. The distributions and changes of stresses, displacements, plastic zones, temperatures in the rock mass of near field, as well as the loading states in the model-building concrete and bolting were investigated and compared for these three computation cases. The results show that compared with the case of mean temperature, the ranges, where the temperatures of surrounding rock mass change obviously, are 6.0 m and 6.5 m, respectively, for the cases of extreme highest temperature and extreme lowest temperature; the displacements of tunnel are raised by 3.2 9.3 and 5.7 12.7 times, and the thicknesses of plastic zones reach 1.5 2.5 m and 2.0 4.5 m for case 2 and 3, respectively; the extreme temperatures of air have strong effects on the stress, deformation and failure states of supporting structure of tunnel in cold region, and the influence degree of extreme lowest temperature is the highest.

  1. Heterogeneity in friction strength of an active fault by incorporation of fragments of the surrounding host rock

    Science.gov (United States)

    Kato, Naoki; Hirono, Tetsuro

    2016-07-01

    To understand the correlation between the mesoscale structure and the frictional strength of an active fault, we performed a field investigation of the Atera fault at Tase, central Japan, and made laboratory-based determinations of its mineral assemblages and friction coefficients. The fault zone contains a light gray fault gouge, a brown fault gouge, and a black fault breccia. Samples of the two gouges contained large amounts of clay minerals such as smectite and had low friction coefficients of approximately 0.2-0.4 under the condition of 0.01 m s-1 slip velocity and 0.5-2.5 MP confining pressure, whereas the breccia contained large amounts of angular quartz and feldspar and had a friction coefficient of 0.7 under the same condition. Because the fault breccia closely resembles the granitic rock of the hangingwall in composition, texture, and friction coefficient, we interpret the breccia as having originated from this protolith. If the mechanical incorporation of wall rocks of high friction coefficient into fault zones is widespread at the mesoscale, it causes the heterogeneity in friction strength of fault zones and might contribute to the evolution of fault-zone architectures.

  2. Attempts of whole-rock K/Ar dating of mesozoic volcanic and hypabissal igneous rocks from the Central Subbetic (Southern Spain: A case of differential Argon loss related to very low-grade metamorphism

    Directory of Open Access Journals (Sweden)

    Sanz de Galdeano, C.

    1988-04-01

    Full Text Available 12 samples of basic intrusives within Triassic rocks «ophites» and 11 samples of volcanic and associated intrusives within Jurassic to Early Cretaceous sequences of the Subbetic Zone were subjected to whole-rock K/Ar dating in combination with chemical/petrological analysis. Satisfactory results were obtained only from a number of samples of volcanic rocks, however, analytical ages commonly agree, within about 10 relative percent, with those deduced from stratigraphic location. «Ophite» samples, on the other hand, may reveal considerably lower analytic ages than the volcanics and show much stronger scattering, even among samples collected within a small area. It is argued that the inferred loss of Ar results from very-low-grade alpine metamorphic alteration, which affected the «ophites» more intensely than the higher volcanic rocks. Other post-emplacement chemical changes, such as the degree of secondary oxidation of Fe, are also distintive among the two groups of samples, and are to some extent consistent with the above view in that the alteration environment of the ophites should have produced conditions for more penetrative fluid-rock interactions and homogeneous recrystallization. Overall, the magmatic activity from which the ophitic rocks originated might have started in the Late Triassic and continued in the Lower Jurassic. 80th, the «ophites» and the volcanics are though to be the result of magmatic events Collowing tensional to transtensive crustal movements affecting the external basins of the Betic Cordilleras Crom Late Triassic to Early Cretaceous times.Doce muestras de cuerpos básicos intrusivos en rocas triásicas («ofitas» y 11 muestras de volcanitas y rocas intrusivas asociadas en secuencias jurásico-cretáceas de la zona Subbética han sido objeto de datación radiométrica K/Ar (roca total en combinación con análisis químico-petrográfico. Las edades analíticas obtenidas son 's

  3. High-grade contact metamorphism in the Reykjanes geothermal system: Implications for fluid-rock interactions at mid-oceanic ridge spreading centers

    Science.gov (United States)

    Marks, Naomi; Schiffman, Peter; Zierenberg, Robert A.

    2011-08-01

    Granoblastic hornfels identified in cuttings from the Reykjanes seawater-dominated hydrothermal system contains secondary pyroxene, anorthite, and hornblendic amphibole in locally equilibrated assemblages. Granoblastic assemblages containing secondary orthopyroxene, olivine, and, locally, cordierite and spinel occur within groups of cuttings that show dominantly greenschist facies hydrothermal alteration. Granoblastic plagioclase ranges continuously in composition from An54 to An96, in contrast with relict igneous plagioclase that ranges from An42 to An80. Typical hydrothermal clinopyroxene compositions range from Wo49En3Fs48 to Wo53En30Fo17; clinopyroxene from the granoblastic grains is less calcic with an average composition of Wo48En27Fs25. The hornfels is interpreted to form during contact metamorphism in response to dike emplacement, resulting in local recrystallization of previously hydrothermally altered basalts. Temperatures of granoblastic recrystallization estimated from the 2-pyroxene geothermometer range from 927°C to 967°C. Redox estimates based on the 2-oxide oxybarometer range from log fO2 of -13.4 to -15.9. Granoblastic hornfels comprised of clinopyroxene, orthopyroxene, and calcic plagioclase have been described in a number of ancient hydrothermal systems from the conductive boundary layer between the hydrothermal system and the underlying magma source, most notably in Integrated Ocean Drilling Program Hole 1256D, Ocean Drilling Program Hole 504B, and in the Troodos and Oman ophiolites. To our knowledge, this is the first evidence of high-grade contact metamorphism from an active geothermal system and the first description of equilibrated amphibole-absent pyroxene hornfels facies contact metamorphism in any mid-ocean ridge (MOR) hydrothermal system. This contribution describes how these assemblages develop through metamorphic reactions and allows us to predict that higher-temperature assemblages may also be present in MOR systems.

  4. A multi-isotope approach to understanding the evolution of Cenozoic magmatism in the northeastern Basin and Range: Results from igneous rocks in the Albion-Raft River-Grouse Creek metamorphic core complex

    Science.gov (United States)

    Konstantinou, A.; Strickland, A.; Miller, E. L.

    2012-12-01

    Deep crustal rocks exposed by extensional processes in metamorphic core complexes provide a unique opportunity to address the magmatic and isotopic evolution of the crust and assess the relative crust versus mantle contributions in Cenozoic igneous rocks exposed in the complexes. The Albion-Raft River-Grouse Creek metamorphic core complex exposes mid-crustal rocks that resided at depths of ~15-20 km before the onset of Cenozoic extension. Three major Cenozoic magmatic events are represented in the complex and have been studied using multiple isotopic systems (whole rock Sr and Nd coupled with the Oxygen isotopes in zircon). These three major events are: (1) 42-31 Ma intrusion of a composite plutonic complex of calc-alkaline composition that intrudes both upper crustal rocks (~5-10 km depth) and deeper rocks. (2) A 32-25 Ma plutonic complex, with evolved calc-alkaline composition that intruded in the middle crust (~12-15 km depth), and (3) A 10-8 Ma bimodal (basalt-rhyolite) suite of volcanic rocks that contain high-T anhydrous mineral assemblages erupted across the complex. The pre-extensional crust consisted of an upper crust composed primarily of Neoproterozoic through Triassic metasedimentary rocks (schist and quartzite at its base and limestone at its top). The middle crust consists of late Archean orthogneiss with evolved composition (metamorphosed peraluminous granite) with average 87Sr/86Sr40~0.800, ɛNd40~ -43.4 and δ18Ozirc ~5.7‰. The lower crust is inferred to have been composed of Precambrian intermediate composition igneous rocks with average 87Sr/86Sr40~0.750, ɛNd40~ -37.5 and δ18Ozirc ~5.9‰, and Precambrian mafic rocks with average 87Sr/86Sr40~0.717, ɛNd40~ -25 and δ18Ozirc ~7.0‰. Existing and new data indicate that the 42-31 Ma upper crustal plutonic complex ranges in isotopic composition from 87Sr/86Sri=0.709-0.712, ɛNdi=-15 to -25 and δ18Ozirc 4.7-6.5‰. The composition of the 32-25 Ma middle crustal plutonic complex ranges from 87Sr

  5. METAMORPHIC PETROLOGY

    Institute of Scientific and Technical Information of China (English)

    2013-01-01

    <正>20132334 Chai Fengmei(Key Laboratory of Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt,Xinjiang University,Urumqi 830049,China);Yang Fuquan Geochronology and Genesis of Meta-Felsic Volcanic Rocks from the Kangbutiebao Formation in Chonghuer Basin on Southern Margin of Altay,Xinjiang(Geological

  6. On Continent-Continent Point-Collision and Ultrahigh-Pressure Metamorphism

    Institute of Scientific and Technical Information of China (English)

    董树文; 武红岭; 刘晓春; 薛怀民

    2002-01-01

    Up to now it is known that almost all ultrahigh-pressure (UHP) metamorphism of non-impact origin occurred in continent-continent collisional orogenic belt, as has been evidenced by many outcrops in the eastern hemisphere. UHP metamorphic rocks are represented by coesite- and diamond-bearing eclogites and eclogite facies metamorphic rocks formed at 650–800°C and 2.6–3.5 Gpa, and most of the protoliths of UHP rocks are volcanic-sedimentary sequences of continental crust. From these it may be deduced that deep subduction of continental crust may have occurred. However, UHP rocks are exposed on the surface or occur near the surface now, which implies that they have been exhumed from great depths. The mechanism of deep subduction of continental crust and subsequent exhumation has been a hot topic of the research on continental dynamics, but there are divergent views. The focus of the dispute is how deep continental crust is subducted so that UHP rocks can be formed and what mechanism causes it to be subducted to great depths and again exhumed to the shallow surface. Through an analysis of the continental process and mechanical boundary conditions of the Dabie collisional belt—an UHP metamorphic belt where the largest area of UHP rocks in the world is exposed, this paper discusses the variations of viscous stresses and average pressure in the viscous fluid caused by tectonism with rock physical properties and the contribution of the tectonic stresses to production of UHP. Calculation indicates that the anomalous stress state on the irregular boundary of a continental block may give rise to stress concentration and accumulation at local places (where the compressional stress may be 5–9 times higher than those in their surroundings). The tectonic stresses may account for 20–35% of the total UHP. So we may infer that the HP (high-pressure)-UHP rocks in the Dabie Mountains were formed at depths of 60–80 km. Thus the authors propose a new genetic model of UHP

  7. 天然缅甸硬玉岩低温变质水岩反应作用:显微红外光谱的证据%Myanmar Jadeitite Low-Temperature Metamorphic Water-Rock Reaction:Eveidence from Microscopic Fourier Transform Infrared Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    严若谷; 丘志力; 冯敏; 金春梅; 李榴芬; 石贵勇; 王萍

    2014-01-01

    Weathering & transporting and depositing processes may improve the quality of some natural low-quality jadeite through reaction with surrounding water fluids .But the mechanism of such water-rock reaction has not been known clearly to date .Applying microscopic Fourier transform infrared spectroscopy (Micro-FTIR) ,this paper carried out comparatively in-situ research of jadeites’ mineral composition before and after water-rock reaction .The results show that water-rock reaction cannot impact jadeites in their major and minor element composition ,but greatly change their water content .Jadeites became richer , with even several times increase ,in water content ,after experiencing water-rock reaction ,and hence show a shift of absorption peak at 3 550 cm -1 to higher frequency .The mineral crystals of these jadeites showed reglar variation in water content from core to edge ,and these jadeites have more water in marginal area than in center area ,being opposite to the change in water content in jadeite during high temperature and pressure metamorphic process ,hence implying that there are different mechanism and shift direction for H+ /OH - of jadeite between high pressure metamorphic process and low temperature water-rock reaction .We think that this finding may contribute to understanding the behavior of water in jadeite during metamorphic process and the mechanism of jadeite quality improvement .%水岩反应是天然低质量硬玉岩(翡翠)在风化搬运和埋藏过程中获得品质改善的重要机理,这种反应一般被认为是在低温还原条件下完成的,目前,科学界对这种低温变质水岩反应机理的了解知之甚少。利用显微红外光谱对水岩反应前后翡翠矿物集合体及晶体进行了精细原位(in-situ)测试。结果显示,水岩反应后硬玉集合体矿物组成及单晶矿物主量元素的成分均没有明显的改变,但含水量明显增大,和水岩反应前相比

  8. Degradation of potassium rock by earthworms and responses of bacterial communities in its gut and surrounding substrates after being fed with mineral.

    Directory of Open Access Journals (Sweden)

    Dianfeng Liu

    Full Text Available BACKGROUND: Earthworms are an ecosystem's engineers, contributing to a wide range of nutrient cycling and geochemical processes in the ecosystem. Their activities can increase rates of silicate mineral weathering. Their intestinal microbes usually are thought to be one of the key drivers of mineral degradation mediated by earthworms,but the diversities of the intestinal microorganisms which were relevant with mineral weathering are unclear. METHODOLOGY/PRINCIPAL FINDINGS: In this report, we show earthworms' effect on silicate mineral weathering and the responses of bacterial communities in their gut and surrounding substrates after being fed with potassium-bearing rock powder (PBRP. Determination of water-soluble and HNO(3-extractable elements indicated some elements such as Al, Fe and Ca were significantly released from mineral upon the digestion of earthworms. The microbial communities in earthworms' gut and the surrounding substrates were investigated by amplified ribosomal DNA restriction analysis (ARDRA and the results showed a higher bacterial diversity in the guts of the earthworms fed with PBRP and the PBRP after being fed to earthworms. UPGMA dendrogram with unweighted UniFrac analysis, considering only taxa that are present, revealed that earthworms' gut and their surrounding substrate shared similar microbiota. UPGMA dendrogram with weighted UniFrac, considering the relative abundance of microbial lineages, showed the two samples from surrounding substrate and the two samples from earthworms' gut had similarity in microbial community, respectively. CONCLUSIONS/SIGNIFICANCE: Our results indicated earthworms can accelerate degradation of silicate mineral. Earthworms play an important role in ecosystem processe since they not only have some positive effects on soil structure, but also promote nutrient cycling of ecosystem by enhancing the weathering of minerals.

  9. Early Jurassic tectonism occurred within the Basu metamorphic complex, eastern central Tibet: Implications for an archipelago-accretion orogenic model

    Science.gov (United States)

    Li, Hua-Qi; Xu, Zhi-Qin; Webb, A. Alexander G.; Li, Tian-Fu; Ma, Shi-Wei; Huang, Xue-Meng

    2017-04-01

    The Basu metamorphic complex, surrounded by ophiolitic melanges and intruded by a large volume of undeformed granitoid rocks along the eastern segment of the Bangong-Nujiang suture, holds one of the keys to understanding the pre-Cenozoic tectonic evolution of central Tibet. Zircon U-Pb dating of rocks from the Basu metamorphic complex reveals that meta-igneous rocks yield Early Paleozoic crystallization ages of 500-492 Ma and an Early Jurassic metamorphic age of 173 Ma, and that undeformed granitoid rocks yield crystallization ages of approximately 186-174 Ma. Whole rock geochemical and zircon Lu-Hf isotopic data indicate that the undeformed granitoid rocks originated mainly from partial melting of ancient crustal sources, which may reflect a collisional orogenic setting. 40Ar/39Ar dating of biotite from a sillimanite-garnet-biotite paragneiss shows cooling to 300 ± 50 °C at 165 Ma. These data indicate significant Early Jurassic tectonism, during which most of the Basu metamorphic complex was formed. Furthermore, the age data resemble those of the Amdo metamorphic complex located approximately 500 km to the west along the Bangong-Nujiang suture. Together, these complexes may represent a ;destroyed or unrecognized; block, i.e., the Amdo-Tongka block, which may be the eastern extension of the South Qiangtang terrane. Based on the tectonic outlines of the multiple ophiolitic zones and magmatic belts, we suggest a new archipelago-accretion model that attributes the Early Jurassic tectonism to an arc-continent/micro-continent collision. This model further enables the reconstruction of the eastern Tethyan Ocean and the orogenic processes of central Tibet during the Mesozoic.

  10. METAMORPHIC PETROLOGY

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    <正>20091533 Gao Changgui(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China);Liu Yongsheng Distributions and Geodynamic Implications of High Field Strength Elements in Rutile from Ultrahigh Pressure Eclogites(Earth Science,ISSN1000-2383,CN42-1233/P,33(4),2008,p.487-503,8 illus.,3 tables,80 refs.)Key words:eclogite,Su-Lu orogenic beltsTrace element compositions of rutiles in eclogites from the Chinese Continental Scientific Drilling(CCSD)main hole were analyzed using LA-ICP-MS.The results indicate that Nb and Ta contents of rutiles are significantly controlled by whole rock compositions,while Zr and Hf show no obvious dependence on the whole rock compositions.Coupled with enrichments of Pb and Sr at the rim of the interstitial rutiles,Zr contents decrease from the core to the rim.

  11. Onset of Grain Boundary Migration and Drastic Weakening of Quartzite during increasing grade of Metamorphism in the Contact Aureole surrounding the Eureka Valley-Joshua Flat-Beer Creek pluton, California, USA

    Science.gov (United States)

    Morgan, S. S.; Student, J. J.; Jakeway, J.

    2015-12-01

    The Eureka Valley-Joshua Flat-Beer Creek (EJB) pluton in eastern California is surrounded by a ~1.3 km wide intensely deformed concordant aureole of metasedimentary rocks. South of the pluton, the Harkless Quartzite can be mapped from where it is located outside the aureole, with its regional strike through the transition into the aureole and concordancy with the pluton. The transition into concordancy, which is fairly abrupt, occurs over a distance of less than 100 m. Across this transition the bedding rotates close to 90° to become subvertical. Here the metasedimentary formations in the aureole have undergone 65% shortening. A suite of Harkless Quartzite samples was collected starting at 2.3 km south of the pluton, across the transition into concordancy at 1.3 km, and to within 450m from the pluton contact. Microstructurally, the transition is defined by changes in the dominant recrystallization mechanisms. At 2.3 km from the pluton, subgrain rotation recrystallization (SGR) plus grain boundary migration (GBM) operate together and many sedimentary grains (rounded grain boundaries) exist. As the pluton is approached, SGR decreases, GBM increases, and rounded grain boundaries slowly disappear. The abrupt transition into concordancy is marked by the final disappearance of SGR and rounded grain boundaries and extensive GBM. The transition is not completely smooth, and other variables such as pinning and amount of fluid inclusions seem to have a strong local affect on the dominant recrystallization mechanism. We suspect that the onset of extensive GBM allows for the diffusion of water into the crystal lattice which results in the drastic weakening and rotation of metasedimentary formations into concordancy.

  12. Timing and conditions of metamorphism and melt crystallization in Greater Himalayan rocks, eastern and central Bhutan: insight from U-Pb zircon and monazite geochronology and trace-element analyses

    Science.gov (United States)

    Zeiger, K.; Gordon, S. M.; Long, S. P.; Kylander-Clark, A. R. C.; Agustsson, K.; Penfold, M.

    2015-05-01

    Within the eastern Himalaya in central and eastern Bhutan, Greater Himalayan (GH) rocks are interpreted to have been thickened by the Kakhtang thrust (KT). In order to understand the metamorphic and exhumation history of the GH and to evaluate the structural significance of the KT, zircon and monazite from twenty samples were analyzed by laser-ablation split-stream ICPMS. In eastern Bhutan, zircon and monazite from samples collected in the KT hanging wall revealed ca. 36-28 Ma metamorphism. Subsequently, the initiation of melt crystallization shows a trend with structural distance above the KT, with early melt crystallization (ca. 27 Ma) in the structurally highest samples and younger melt crystallization (ca. 16 Ma) for leucosomes within the KT zone. Melt crystallization was protracted and continued until ca. 14-13 Ma in both the KT hanging wall and the footwall. In comparison, in central Bhutan, two leucosomes revealed extended melt crystallization from ca. 31 to 19 Ma. The youngest zircon dates from samples exposed structurally above and below the KT are similar, indicating that the KT was not as significant of a structure as other fault systems to which it has been correlated. However, the younging trend in the initiation of melt crystallization with decreasing structural distance above the KT argues that progressive underplating of ductile material assisted in the initial emplacement of the GH unit in central and eastern Bhutan. The KT likely represents a minor shear zone that aided in this underplating process.

  13. U-Th-Pb zircon geochronology on igneous rocks in the Toija and Salittu Formations, Orijärvi area, southwestern Finland: constraints on the age of volcanism and metamorphism

    Directory of Open Access Journals (Sweden)

    Christopher L. Kirkland

    2008-01-01

    Full Text Available Zircons from a felsic volcanic rock in the Toija Formation and a synvolcanic gabbro intrusion in the Salittu Formation within the Orijärvi area were dated by U-Th-Pb SIMS in order to provide depositional constraints on these formations. Zircon crystals from the felsic rock preserve a two-stage crystallisation history with zoned core domains and homogeneous rim domains. Inner domains yield a 1878±4 Ma concordia age, interpreted to determine the crystallisation of this rock. Rims yield a 1815±3 Ma concordia age interpretedto determine the regional metamorphism. Small rounded zircon grains from the Salittu gabbro, located within the Jyly shear zone, yield a concordia age of 1792±5 Ma. We interpret the grain textures to suggest that they recrystallised from inherited zircon seeds during the heat and fluid flow into the shear zone. Although no direct ages for the Salittu Formation have been recovered, field relationships imply that it was deposited between 1878−1875 Ma.

  14. Unusual high-density and saline aqueous inclusions in ultrahigh pressure metamor-phic rocks from Sulu terrane in eastern China

    Institute of Scientific and Technical Information of China (English)

    SHEN Kun; ZHANG Zeming; A. M. van den Kerkhof; XIAO Yilin; XU Zhiqin; J. Hoefs

    2003-01-01

    Primary high-density fluid inclusions were identified in garnet from ultrahigh pressure eclogite in the southern part of the Sulu terrane. They occur isolatedly or in cluster together with relatively low-density two-phase inclusions. The eutectic temperature of the inclusions is as low as ≤ -52℃. A bubble was nucleated in a liquid inclusion during the specific stage of cyclic cooling-heating runs, and the liquid-gas homogenization temperature was measured to be ≤-12.5℃. The composition of the inclusions modeled by the system CaCl2-NaCl-H2O, yields the fluid density of 1.27 g/cm3 that corresponds to a pressure of ca. 2.4 Gpa at the temperature of peak eclogite-facies metamorphism, close to the ultrahigh pressure metamorphic conditions. During the exhumation of the eclogite the inclusions reacted with the host mineral, forming hydrous silicate minerals that resulted in lowering of the fluid density and its transformation to multi-phase inclusions.

  15. Early carboniferous wrenching, exhumation of high-grade metamorphic rocks and basin instability in SW Iberia: Constraints derived from structural geology and U-Pb and 40Ar-39Ar geochronology

    Science.gov (United States)

    Pereira, M. Francisco; Chichorro, Martim; Silva, J. Brandão; Ordóñez-Casado, Berta; Lee, James K. W.; Williams, Ian S.

    2012-08-01

    New U-Pb and 40Ar-39Ar geochronology and structural data from high- to medium grade metamorphic shear zones of the Ossa-Morena Zone, and structural data from Early Carboniferous basins (Ossa-Morena Zone and South-Portuguese Zone), place additional constraints on the Variscan tectonics in SW Iberia. A zircon U-Pb age of 465 ± 14 Ma (Middle Ordovician) measured on migmatite from the Coimbra-Cordoba shear zone is interpreted as the age of protolith crystallization. This age determination revises the information contained in the geological map of Portugal, in which these rocks were considered to be Proterozoic in age. This paper describes the evolution of Variscan wrench tectonics related to the development of shear zones, exhumation of deep crustal rocks and emplacement of magma in the Ossa-Morena Zone basement. In the Coimbra-Cordoba shear zone (transpressional), migmatites were rapidly exhumed from a depth of 42.5 km to 16.6 km over a period of ca. 10 Ma in the Viséan (ca. 340-330 Ma), indicating oblique slip exhumation rates of 8.5 to 10.6 mm/yr (Campo Maior migmatites) and 3.2 mm/yr (Ouguela gneisses) respectively. In the Évora Massif, the gneisses of the Boa Fé shear zone (transtensional) were exhumed from 18.5 to 7.4 km depth in the period ca. 344-334 Ma (Viséan), with exhumation oblique slip rates of 2.8 to 4.2 mm/yr. At the same time, the Early Carboniferous basins of SW Iberia were filled by turbidites and olistoliths, composed mostly of Devonian rocks. The presence of olistoliths indicates significant tectonic instability during sedimentation with large-scale mass movement, probably in the form of gravity slides. Deformation and metamorphism dated at 356 ± 12 Ma, 321 ± 13 Ma and 322 ± 29 Ma respectively suggests that Variscan wrench movements were active in SW Iberia during the Early Carboniferous for a period of at least 35 Ma.

  16. Age of metamorphic events : petrochronology and hygrochronology

    Science.gov (United States)

    Bosse, Valerie; Villa, Igor M.

    2017-04-01

    , reflect the interaction with the surrounding mineral assemblages. An often neglected observation is that the K-Ar chronometer minerals show similar patterns of isotopic inheritance closely tied to relict patches and heterochemical retrogression phases (Villa and Williams 2013). Isotopic closure in the U-Pb and K-Ar systems follows the same principle: thermal diffusion is very slow, dissolution and reprecipitation are several orders of magnitude faster. This means that both U-Pb and K-Ar mineral chronometers are hygrochronometers. The interpretation of the ages of the different domains cannot be decoupled from the geochemical and petrological context. The focus on petrology also requires, following Villa (1998, 2016), that the ages measured in metamorphic rocks no longer can be used in geodynamic models according to the "closure temperature" concept as originally defined by Dodson (1973). Bosse et al. (2009) Chem Geol 261: 286 Didier et al. (2014) Chem Geol 381: 206 Didier et al. (2015) Contrib Mineral Petrol 170: 45 Dodson (1973) Contrib Mineral Petrol 40: 259 Muller (2003) EPSL, 206: 237 Villa (1998) Terra Nova 10: 42 Villa (2016) Chem Geol 420: 1 Villa & Williams (2013) In: Harlov & Austrheim (eds.), Metasomatism and the Chemical Transformation of Rock. Springer, p171

  17. Measured versus calculated thermal conductivity of high-grade metamorphic rocks – inferences on the thermal properties of the lower crust at ambient and in-situ conditions

    DEFF Research Database (Denmark)

    Ray, Labani; Förster, Hans-Jürgen; Förster, Andrea

    The bulk thermal conductivity (TC) of 26 rock samples representing felsic, intermediate and mafic granulites, from the Southern Granulite Province, India, is measured at dry and saturated conditions with the optical-scanning method. Thermal conductivity is also calculated from modal mineralogy (d...

  18. U–Pb zircon and biostratigraphic data of high‐pressure/ low‐temperature metamorphic rocks of the Talea Ori : tracking the Paleotethys suture in central Crete, Greece

    NARCIS (Netherlands)

    Zulauf, G.; Dörr, W.; Krahl, J.; Lahaye, Y.; Chatzaras, V.; Xypolias, P.

    2016-01-01

    Inherited deformation microfabrics of detrital quartz grains and U–Pb (Laser ablation (LA)-ICPMS and ID TIMS) ages of detrital zircons separated from the Phyllite–Quartzite Unit s.l. of the Talea Ori, central Crete, suggest strikingly different source rocks. Albite gneiss of the lower Rogdia Beds in

  19. Palaeoproterozoic continental arc magmatism, and Neoproterozoic metamorphism in the Aravalli-Delhi orogenic belt, NW India: New constraints from in situ zircon U-Pb-Hf isotope systematics, monazite dating and whole-rock geochemistry

    Science.gov (United States)

    Kaur, Parampreet; Zeh, Armin; Chaudhri, Naveen

    2017-04-01

    Presently, the extent, origin and petrogenesis of late Palaeoproterozoic (ca. 1.85 Ga) magmatism in the north-central Aravalli-Delhi orogenic belt, NW India and subsequent metamorphic overprints are poorly constrained. Results of new in situ zircon U-Pb-Hf isotope analyses in combination with whole-rock elemental and isotopic data provide the first hard evidence that granitoid magmatism occurred in a continental magmatic arc setting between 1.86 and 1.81 Ga. The Hf-Nd model ages of 3.0-2.6 Ga and inherited zircon grains of 3.3-2.5 Ga indicate abundant reworking of Archaean crust. Flat HREE patterns with negative Eu anomalies furthermore reveal that the granitoids were generated from garnet-free and plagioclase-rich sources at shallow depths. Significant isotope variation among granitoid samples (εHft = -3.7 to -9.0; εNdt = -4.8 to -7.9) indicate that the reworked Archaean crust was not completely homogenised during the Palaeoproterozoic. This is best reflected by zircon Hf-isotope variation of ca. 9.5 epsilon units within the oldest granitoid sample. Zircon grains from this sample define three discrete Hf-isotope groups at εHf1.86Ga = -8.9, -4.8 and -1.6. These are interpreted to result from mixing of zircon-saturated magmas derived from three distinct sources within the crust prior to solidification. A monazite U-Pb isochron age of 868 ± 4 Ma from one of the granitoid samples furthermore indicates that the Aravalli fold belt was affected by an important post-magmatic overprint, perhaps related to the widespread metasomatic, granulite metamorphic and/or magmatic events during the same time span.

  20. De-stressed mining of multi-seams: Surrounding rock control during the mining of a roadway in the overlying protected seam

    Institute of Scientific and Technical Information of China (English)

    Wang Cheng; Zhang Nong; Li Guichen; Zhang Nianchao

    2011-01-01

    Surrounding rock control in the overlying protective coal seam is a challenging topic for de-stressed mining of multi-seamed coal. Current research findings on roadway control were used in the design of a physical model of a complex textured roof having a varying thickness. The model was used to study roadway instability and collapse caused by dynamic pressure. The results show that when the thickness of the roof exceeds the bolted depth the roadway security is least and the roof has the greatest possibility for collapse. Numerical simulations were also carried out to study stress redistribution before and after roadway excavation during underlying protective seam mining. The evolution of roadway displacement and fracture, as affected by support methods, has been well studied. A series of support principles and technologies for mining affected roadways has been proposed after demonstration of successful practical application in the Huainan Mines. These principles and technologies are of extended value to deep coal mining support in China.

  1. The test research on partial relieving pressure for the entry in the deep mine under high stress and friable surrounding rock

    Institute of Scientific and Technical Information of China (English)

    DU Ji-ping; HOU Chao-jiong; ZHU Ya-ping; HAO Ming-kui

    2007-01-01

    Based on the geological condition of Zhangxiaolou deep mine in Xuzhou mining area, under 986 m in depth, 20.6~31.6 MPa in maximum horizontal principal stress, and friable and fractured surrounding rock, test researches on partial relieving pressure were completed for the entry with U-steel arched yielding support. The relieving pressure parameters, technology process and results of springing blasting by boreholes and excavating pockets in the two sides of entry were introduced. It is demonstrated that springing will not be shaped under the condition of single borehole arrangement after exploded, the arrangement by a group, it will make borehole bottom form springing in 0.6~0.8 m in diameter, that convergence of two sides and roof to floor have some increments by using springing blasting for reliving pressure. This kind of method for reliving pressure is not suitable to use in the deep mine, and that the convergence of two sides obviously declined by excavating pocket in two sides, it can be still used in the entry with metal support, while maintenance of entry in deep mines is difficult, and can not be supported by bolt or bolt with wire mesh.

  2. 铁路松散破碎围岩隧道防塌控制技术%Collapse Control Technology in Incompact and Fractured Surrounding Rock Railway Tunnel

    Institute of Scientific and Technical Information of China (English)

    柴跃进

    2013-01-01

    隧道施工中经常遇到破碎围岩而发生塌方及掌子面涌出、坍塌的事故.一旦塌方灾害发生,不仅影响工程进度,而且影响施工企业形象;若处理不当,将遭受更大损失,如塌方频繁发生,或留下隐患.提出一种新型隧道防塌控制技术-“双曲拱”耦合支护技术,支护效果表明该技术可靠性强,能有效控制隧道顶板坍塌,具有很好的经济效益和社会效益.%Often fractured surrounding rock in tunnel construction and face the collapse and gushing, collapse accident.Once the landslide disaster, not only the project, but construction corporate image;If not handled properly, will suffer more losses, such as landslides are frequent, hidden or left.Made a new tunnel collapse prevention control technologies - "double -curved arch" coupling supporting technology, supporting effect indicates that the technical reliability, can effectively control the tunnel roof collapsed, with good economic and social benefits.

  3. From oceanic subduction to continental collision: An overview of HP-UHP metamorphic rocks in the North Qaidam UHP belt, NW China

    Science.gov (United States)

    Zhang, Guibin; Zhang, Lifei; Christy, Andrew G.

    2013-02-01

    The North Qaidam UHPM belt is unique among "continental type" subduction zones in showing well-preserved subducted oceanic relics that predate continental subduction and collision. We review petrologic, thermobarometric, geochemical and geochronological studies for the Yuka, Luliang Shan, Xitieshan and Dulan terranes in this belt. UHP conditions are demonstrated by coesite inclusions in eclogite and country gneiss, and diamond inclusions from garnet peridotite. The relict subducted oceanic lithology crops out in the Shaliuhe cross-section in Dulan terrane; it originated as the floor of a Paleo-Qilian Ocean that existed between Qaidam and Qilian blocks before the early Ordovician. Whereas most eclogites of this belt are derived from mafic rocks of either a Neoproterozoic continental rift or incipient oceanic basin setting, which were subducted along with continental rocks in the early Paleozoic. The data, especially the two protolith sources for eclogites, demonstrate tectonic evolution of the North Qaidam UHPM belt from oceanic subduction to continental collision.

  4. Boninitic metavolcanic rocks and island arc tholeiites from the Older Metamorphic Group (OMG) of Singhbhum Craton, eastern India: Geochemical evidence for Archean subduction processes

    Digital Repository Service at National Institute of Oceanography (India)

    Manikyamba, C.; Ray, J.; Ganguly, S.; Singh, M.R.; Santosh, M.; Saha, A.; Satyanarayanan, M.

    . Major, trace and rare earth element compositions of these rocks are characterized by high Mg# (80–82), MgO (30.6–32.9 wt.%), Ni (490–1262 ppm) and Cr (2404–4385 ppm) contents, high Al2O3/TiO2 (49–67), Zr/Hf (10...

  5. Structural and metamorphic evolution of the Orocopia Schist and related rocks, southern California: Evidence for late movement on the Orocopia fault

    Science.gov (United States)

    Jacobson, Carl E.; Dawson, M. Robert

    1995-08-01

    The Pelona, Orocopia, and Rand Schists (POR schists) of southern California and southwesternmost Arizona are late Mesozoic or early Tertiary subduction complexes that underlie Precambrian to Mesozoic continental basement along the low-angle Vincent-Chocolate Mountains (VCM) fault system. The VCM faults are often considered to be remnants of the original subduction zone, but recent work indicates that many have undergone substantial postsubduction reactivation. In the Orocopia Mountains, for example, the Orocopia Schist exhibits an exceptionally complex structural and metamorphic history due to multiple periods of movement along the Orocopia fault. Structures in the schist include isoclinal folds with axial-planar schistosity, open-to-tight folds that fold schistosity, penetrative stretching lineations, and crenulation lineations, all of which show a nearly 360° range in trend. Folds and lineations that trend approximately NE-SW occur throughout the schist and are thought to be part of an early phase of deformation related to subduction. Folds of this orientation show no consistent vergence. Folds and lineations that trend approximately NW-SE are concentrated near the Orocopia fault and are interpreted to have formed during exhumation of the schist. The NW-SE trending folds, and shear indicators in late-stage mylonite at the top of the schist, consistently verge NE. The exhumation event culminated in emplacement of the schist against brittlely deformed upper plate. Exhumation of the Orocopia Schist was accompanied by retrograde replacement of garnet, biotite, epidote, and calcic amphibole by chlorite, calcite, and sericite. Matrix amphibole has a lower Na/Al ratio than amphibole inclusions in albite, consistent with a late-stage decrease in pressure. As NE vergence in the Orocopia Mountains is associated with exhumation of the schist, the NE movement along other segments of the VCM fault may also be late and therefore have no bearing on the facing direction of the

  6. P-T-t Path of Mafic Granulite Metamorphism in Northern Tibet and Its Geodynamical Implications

    Institute of Scientific and Technical Information of China (English)

    HU Daogong; WU Zhenhan; JIANG Wan; YE Peisheng

    2004-01-01

    Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early metamorphic assemblage (Mi) is preserved only in the granulites and represented by plagioclase+homblende inclusions within the cores of garnet porphyroblasts. The peak assemblage (M2) consists of gamet+clinopyroxene+hornblende+plagioclase in the mafic granulites. The peak metamorphism was followed by near-isothermal decompression (M3), which resulted in the development of horublende+plagioclase symplectites surrounding embayed garnet porphyroblasts, and decompression-cooling (M4) is represented by minerals of homblende+plagioclase recrystallized during mylonization. The peak (M2) P-T conditions of gamet+clinopyroxene+plagioclase+homblende were estimated at 769-905°C and 0.86-1.02 GPa based on the geothermometers and geobarometers. The P-T conditions of plagioclase+hornblende symplectites (M3) were estimated at 720-800°C and 0.55-0.68 GPa, and recrystallized hornblende+plagioclase (M4) at 594-708°C and 0.26-0.47 GPa. It is impossible to estimate the P-T conditions of the early metamorphic assemblage (M1) because of the absence of modal minerals. The combination of petrographic textures, metamorphic reaction history, thermobarometric data and corresponding isotopic ages defines a clockwise near-isothermal decompression metamorphic path, suggesting that the mafic granulites had undergone initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record two major phases of collision which resulted in both the assemblage of Gondwanaland during the Pan-African orogeny at 531 Ma and the collision of the Qiangtang and Lhasa Terranes at 174 Ma, respectively.

  7. 复杂围岩条件下开切眼全锚支护%Full-bolt supporting in open-off cut under complex surrounding rock condition

    Institute of Scientific and Technical Information of China (English)

    刘惠德; 尹根成; 栗兴仁; 李志强

    2001-01-01

    The mine open-off cut should be very safety because it is a wide-spanned place where the mining facilities are located. In the past, the supporting of open-off cut used to be log shed. Since the space is limited, the facilities fixing efficiency and safety are influenced greatly. The rock layer above coal bed of Malan mine 2th coal bed is composed of multiple layers of different rock beds or thin coal beds. So if using log shed to support open-off cut, the deformation of surrounding would be large and the space would be limited, then the facilities fixing efficiency would be low and the log consume would be huge. The method of bolt + stay rope is an effective way. It can improve the facilities fixing environment greatly as well as efficiency and safety reliability. At the same time, the cost and working intensity are lowed geratly.%采煤工作面的开切眼不仅跨度大,而且是采煤设备安装的场所,对于空间的安全有较高的要求。以往开切眼的支护一般为木棚,使开切眼的空间狭小,对于安装设备的效率和安全有很大影响。马兰矿2#煤层的顶板为多层不同性质的岩层和薄煤层组成,属于复杂性顶板,用木棚支护,开切眼围岩变形大,安装空间狭小,使安装效率低下,而且木材消耗量大。用锚杆+锚索支护获得成功,从根本上改善了综采设备安装的环境,提高了安装的效率和安全可靠性,降低了开切眼的支护成本和劳动强度。

  8. Teaching the Rock Cycle with Ease.

    Science.gov (United States)

    Bereki, Debra

    2000-01-01

    Describes a hands-on lesson for teaching high school students the concept of the rock cycle using sedimentary, metamorphic, and igneous rocks. Students use a rock cycle diagram to identify pairs of rocks. From the rock cycle, students explain on paper how their first rock became the second rock and vice versa. (PVD)

  9. Seawater-like trace element signatures (REE + Y) of Eoarchaean chemical sedimentary rocks from southern West Greenland, and their corruption during high-grade metamorphism

    Science.gov (United States)

    Friend, C. R. L.; Nutman, A. P.; Bennett, V. C.; Norman, M. D.

    2008-02-01

    Modern chemical sediments display a distinctive rare earth element + yttrium (REE + Y) pattern involving depleted LREE, positive La/La*SN, Eu/Eu*SN, and YSN anomalies (SN = shale normalised) that is related to precipitation from circumneutral to high pH waters with solution complexation of the REEs dominated by carbonate ions. This is often interpreted as reflecting precipitation from surface waters (usually marine). The oldest broadly accepted chemical sediments are c. 3,700 Ma amphibolite facies banded iron-formation (BIF) units in the Isua supracrustal belt, Greenland. Isua BIFs, including the BIF international reference material IF-G are generally considered to be seawater precipitates, and display these REE + Y patterns (Bolhar et al. in Earth Planet Sci Lett 222:43 60, 2004). Greenland Eoarchaean BIF metamorphosed up to granulite facies from several localities in the vicinity of Akilia (island), display REE + Y patterns identical to Isua BIF, consistent with an origin by chemical sedimentation from seawater and a paucity of clastic input. Furthermore, the much-debated magnetite-bearing siliceous unit of “earliest life” rocks (sample G91/26) from Akilia has the same REE + Y pattern. This suggests that sample G91/26 is also a chemical sediment, contrary to previous assertions (Bolhar et al. in Earth Planet Sci Lett 222:43 60, 2004), and including suggestions that the Akilia unit containing G91/26 consists entirely of silica-penetrated, metasomatised, mafic rock (Fedo and Whitehouse 2002a). Integration of our trace element data with those of Bolhar et al. (Earth Planet Sci Lett 222:43 60, 2004) demonstrates that Eoarchaean siliceous rocks in Greenland, with ages from 3.6 to 3.85 Ga, have diverse trace element signatures. There are now geographically-dispersed, widespread examples with Isua BIF-like REE + Y signatures, that are interpreted as chemically unaltered, albeit metamorphosed, chemical sediments. Other samples retain remnants of LREE depletion but

  10. 激发极化法在早前寒武纪变质岩系找水中的应用%Application of Induced Polarization Method for Groundwater Exploration in Metamorphic Rock Areas of Taishan Group

    Institute of Scientific and Technical Information of China (English)

    刘洪波; 于林松; 刘伟; 魏印涛; 王强; 于在利

    2012-01-01

    通过对在早前寒武纪变质岩系进行抗旱找水中利用地球物理勘探定井的实例分析,阐述了利用激发极化法在早前寒武纪变质岩分布区辨认含水层,确定含水层埋深,最终确定较好井位的方法。该方法对解决早前寒武纪变质岩系的干旱缺水现状有广泛深远的意义。%Through analysis on successful examples for groundwater exploration,by using geophysical prospecting method in metamorphic rock areas of Taishan group,it is regarded that the induced polarization method is very useful for identifying aquifer,determining the depth of aquifer,and determining the position of wells finally.It will play an important role in solving the needs of water in the arid region.

  11. U-Pb zircon and biostratigraphic data of high-pressure/low-temperature metamorphic rocks of the Talea Ori: tracking the Paleotethys suture in central Crete, Greece

    Science.gov (United States)

    Zulauf, G.; Dörr, W.; Krahl, J.; Lahaye, Y.; Chatzaras, V.; Xypolias, P.

    2016-10-01

    Inherited deformation microfabrics of detrital quartz grains and U-Pb (Laser ablation (LA)-ICPMS and ID TIMS) ages of detrital zircons separated from the Phyllite-Quartzite Unit s.l. of the Talea Ori, central Crete, suggest strikingly different source rocks. Albite gneiss of the lower Rogdia Beds includes Cambrian and Neoproterozoic rounded zircons with main U-Pb age peaks at 628 and 988 Ma. These and minor Paleoproterozoic and Archean peaks, together with the lack of Variscan-aged and Mesoproterozoic zircons, are similar to the age spectra obtained from the Phyllite-Quartzite Unit s.str. of the Peloponnesus and eastern Crete and from the Taurides. All of these zircons should be derived from the northeastern passive margin of Gondwana (Cimmeria). Metatuffites of the uppermost Rogdia Beds and metasandstone of Bali beach, on the other hand, include euhedral detrital zircons displaying a Variscan U-Pb age spectra at ca. 300 Ma with concordia ages at 291 ± 3, 300 ± 1 Ma (Rogdia) and 286 ± 3, 300 ± 3, 313 ± 2 Ma (Bali). Both types of metasediments and their zircons are similar to those of the pre-Alpine basement and overlying Tyros Beds of eastern Crete, revealing a provenance at the southern active margin of Laurasia. Thus, in central Crete the Paleotethys suture should be situated inside the Rogdia Beds. Magmatic zircons separated from a rhyolite boulder of the lower Achlada Beds yielded a concordant U-Pb zircon age at 242 ± 2 Ma placing a maximum age for the deposition of the (meta)conglomerate from which the boulder was collected. This age is compatible with an Olenekian-early Anisian age of the underlying Vasilikon marble suggested by new findings of the foraminifera Meandrospira aff. pusilla. Both the Achlada Beds and the Vasilikon marble can be attributed to the lower Tyros Beds of eastern Crete. The Alpine deformation led to a pervasive mylonitic foliation, which is affecting most of the studied rocks. This foliation results from D2 top

  12. Coincidence of gabbro and granulite formation and their implication for Variscan HT metamorphism in the Moldanubian Zone (Bohemian Massif), example from the Kutná Hora Complex

    Science.gov (United States)

    Faryad, Shah Wali; Kachlík, Václav; Sláma, Jiří; Jedlicka, Radim

    2016-11-01

    Leucocratic metagabbro and amphibolite from a mafic-ultramafic body within migmatite and granulite in the Kutná Hora Complex were investigated. The mafic-ultramafic rocks show amphibolite facies metamorphism, but in the central part of the body some metagabbro preserves cumulus and intercumulus plagioclase, clinopyroxene and spinel. Spinel forms inclusions in both clinopyroxene and plagioclase and shows various degree of embayment structure, that was probably a result of reaction with melt during magmatic crystallization. In the metagabbro, garnet forms coronae around clinopyroxene at the contacts with plagioclase. Amphibolite contains garnet with prograde zoning and plagioclase. Phase relations of igneous and metamorphic minerals indicate that magmatic crystallization and subsequent metamorphism occurred as a result of isobaric cooling at a depth of 30-35 km. U-Pb dating on zircon from leucogabbro yielded a Variscan age (337.7 ± 2 Ma) that is similar or close to the age of granulite facies metamorphism (ca 340 Ma) in the Moldanubian Zone. Based on the calculated PT conditions and age data, both the mafic-ultramafic body and surrounding granulite shared the same exhumation path from their middle-lower crustal position at the end of Variscan orogeny. The coincidence of mafic-ultramafic intrusives and granulite-amphibolite facies metamorphism is explained by lithospheric upwelling beneath the Moldanubian Zone that occurred due to slab break-off during the final stages of subduction of the Moldanubian plate beneath the Teplá Barrandian Block. The model also addresses questions about the preservation of minerals and/or their compositions from the early metamorphic history of the rocks subjected to ultradeep subduction and subsequent granulite facies metamorphism.

  13. The effect of CO2 and N2 on phase relations, fluid composition, and quartz solubility in amphibolite facies metamorphic rocks

    Science.gov (United States)

    Artimenko, Margaret V.

    2016-12-01

    Phase equilibria in the system SiO2-TiO2-Al2O3-Fe2O3-MnO-MgO-CaO-Na2O-K2O-P2O5-H2O-CO2-N2 are calculated to illustrate phase relations in amphibolite facies metasediments over a wide range of X[H2O-CO2-N2] conditions at 600 °C and 4.4 kb. Calculations are performed using the Gibbs free energy minimization technique. Results are presented in plots showing stable mineral assemblages as a function of total carbon in the system at varying water (a_{{{{H}}2 {{O}}}} = 1) content in the presence/absence of N2 in the fluid. The calculations indicate that the typical assemblage plagioclase—quartz—biotite—ilmenite—garnet—apatite is restricted to the rocks with CO2 saturation and X_{{{{H}}_{ 2} {{O}}}} higher than 60% in the fluid. Significant decrease in X_{{{{CO}}2 }} favors the stability of muscovite rather than garnet, whereas the decrease in X_{{{{H}}_{ 2} {{O}}}} leads to the stability of microcline over all range of X_{{{{CO}}2 }}. This paper also presents the composition and parameters (pH, Eh) of the fluid equilibrated with mineral assemblage. It is shown that the presence of low concentrations of N2 causes the fluid to consist of two phases when an aqueous supercritical solution (AS) coexists with a supercritical fluid with gas-like properties (SF). At high concentration of N2, the fluid consists of SF alone; in the absence of nitrogen, the fluid consists of AS alone. The solubility of monomer SiO 2 0 and dimer Si2O 4 0 decreases with increasing CO2 and after CO2 saturation point is held constant. The magnitude of the silica solubility at CO2 saturation depends upon the water content in AS. The effect of nitrogen on quartz solubility has been demonstrated to be negligible.

  14. 高应力松软围岩煤仓失稳分析及联合支护技术%High Stress Soft Surrounding Rock Coal Bunker Instability Analysis and Combined Support Technology

    Institute of Scientific and Technical Information of China (English)

    张鹏

    2015-01-01

    Aiming at the supporting problem of coal bunker instability under high stress soft surrounding rock, studies the mechanism of coal bunker damage under complicated conditions through theory analysis,puts forward the combined supporting technology,which includes first high -strength anchor net spray support and secondary structure reinforcement,and carries out the engineering application and surrounding rock deformation monitoring.The results show that by adopting the recovery technique for support,the surrounding rock deformation of coal bunker is effective-ly controlled,the supporting result is well,and safety and normal use of coal bunker is ensured.It provides an effec-tive support method for coal bunker soft surrounding rock supporting under the similar condition.%针对高应力松软围岩煤仓失稳破坏面临的支护难题,通过理论分析,研究了复杂条件下煤仓破坏的机理,提出了“一次高强锚网喷支护+二次结构补强”的联合支护技术,并进行了工程应用和围岩变形量监测。结果表明,采用该支护修复技术后,煤仓围岩变形得到有效控制,支护效果良好,保障了煤仓正常安全使用。为类似条件下煤仓软弱围岩支护提供了一种有效的支护方法。

  15. 等效数值法在围岩稳定性评价中的应用%Evaluation on Stability of Surrounding Rock Mass Based on Equivalent Numerical Method

    Institute of Scientific and Technical Information of China (English)

    高科; 李夕兵

    2009-01-01

    提出了一种新的围岩的稳定性评价方法--等效数值法,建立了基于等效数值方法的围岩稳定性评价新模型.该方法将样本指标值与围岩稳定性各指标分类标准对比来确定权重,客观性强,计算简捷.对5个典型的围岩作为评价样本进行了评价研究,并将得到的评价结果与模糊识别法、可拓方法与模糊可变集合工程方法结果进行比较.研究结果表明,等效数值法成功率高、客观性强,为围岩稳定性的评价研究提供了一条新思路.%In this paper,a new stability evaluation method on surrounding rock mass by using equivalent numerical method is presented.The stability assessment model for the Surrounding Rock Mass based on an equivalent numerical method is established.5 actual samples were used to verify the effectiveness of this method.Compared with Furry Pattern Reeoginition,extension method and engineering method of variable fuzzy set,equivalent numerical method has a practical performance in evaluating the stability of surrounding rock mass.This paper provides a new way for evaluation on stability of surrounding rock mass.

  16. HP metamorphic belt of the western Alps

    Institute of Scientific and Technical Information of China (English)

    RobertoCompagnoni

    2003-01-01

    The understanding of the subduction-related processes benefited by the studies of the high-pressure (HP) meta-morphic rocks from the western Alps. The most stimu-lating information was obtained from the inner part of the western Alpine belt, where most tectonic units show an early Alpine eclogite-facies recrystallisation. This is especially true for the Austroalpine Sesia Zone and the Penninic Dora-Maira massif. From the Sesia zone,which consists of a wide spectrum of continental crust lithologies recrystallised to quartz-eclogite-facies min-eral assemblages, the first finding of a jadeite-bearingmeta-granitoid has been described, supporting evidencethat even continental crust may subduct into the mantle.From the Dora-Maira massif the first occurrence of regional metamorphic coesite has been reported, open-ing the new fertile field of the ultrahigh-pressure meta-morphism (UHPM), which is now becoming the rule in the collisional orogenic belts.

  17. Metamorphism, Plate Tectonics, and the Supercontinent Cycle

    Science.gov (United States)

    Brown, Michael

    Granulite facies ultrahigh temperature metamorphism (G-UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian; G-UHTM facies series rocks may be inferred at depth in younger, particularly Cenozoic orogenic systems. The first occurrence of G-UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G-UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the cyclic formation of supercontinents and their breakup, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those associated with the modern Pacific rim. Medium-temperature eclogite, high-pressure granulite metamorphism (E-HPGM), is also first recognized in the Neoarchean rock record and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E-HPGM belts are complementary to G-UHTM belts and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; they record the low thermal gradients associated with modern subduction. Lawsonite blueschists and eclogites (high-pressure metamorphism, HPM) and ultrahigh pressure metamorphism (UHPM) characterized by coesite (±lawsonite) or diamond are predominantly Phanerozoic phenomena. HPM-UHPM registers the low thermal gradients and deep subduction of continental crust during the early stage of the collision process in Phanerozoic subduction-to-collision orogens. Although perhaps counterintuitive, many HPM-UHPM belts appear to have developed by closure of small ocean basins in the process of accretion of a continental terrane during a period of supercontinent introversion (Wilson cycle ocean basin opening and closing). A duality of metamorphic belts—reflecting a duality of thermal regimes—appears in the record only since the Neoarchean Era. A

  18. 不衬砌水工隧洞围岩稳定性数值模拟分析%Numerical simulation analysis for surrounding rock stability of unlined high pressure hydraulic tunnels

    Institute of Scientific and Technical Information of China (English)

    刘新颖; 曹平; 刘涛影; 梅慧浩; 宁果果

    2012-01-01

    Aiming at the phenomena that hyperosmolar role will not only change the stress state of rock and soil, but also cause the rock splitting , destroy the original structure of the rock. Based on the coupled fluid - solid theorem, numerical analysis for the stability of tunnel surrounding rock was done with fast Lagrangian analysis of continua in three - dimension (FLAC3D). Based on the surrounding rock stability considering percolation and the surrounding rock characteristics with the internal water fluid as main research aspects, the stress field and displacement field feature after rock excavation, feedback of excavation on seepage field, evolution trend of failure characteristics and hydraulic characteristics of the tunnel under the role of internal water was achieved. The research results can provide a theoretical basis for corresponding safety measurement in construction process and waterproofing of tunnel in aquifer condition.%针对高渗压作用不仅会改变岩土体的应力状态,同时可能会使岩体劈裂、破坏岩体的原有结构的现象,基于流固耦合分析理论,利用快速拉格朗日有限差分法对隧洞围岩稳定性进行分析.从考虑渗流效应时围岩开挖稳定性、内水作用下围岩力学特性方面开展研究,得到围岩开挖后应力场、位移场分布特征,开挖卸载对渗流场的反馈,内水作用下隧洞的破坏特征和水力特性演变趋势.研究结果表明:对隧洞施工过程中采取安全措施,富水条件下的隧洞工程防排水提供一定的理论参考.

  19. Geochemistry and spatial distribution of late-Paleozoic mafic volcanic rocks in the surrounding areas of the Gonghe Basin: Implications for Majixueshan triple-junction and east Paleotethyan archipelagic ocean

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The late-Paleozoic mafic volcanic rocks occurring in the surrounding areas of the Gonghe basin are distributed in the A'nyêmaqên ophiolite zone, Zongwulong tectonic zone and Kuhai-Saishitang volcanic zone. The mafic volcanics in the A'nyêmaqên zone formed an ancient ridge-centered hotspot around the Majixueshan OIB, the Kuhai-Saishitang mafic rocks consist of E-MORB and continental rift basalts and the Zongwulong volcanic rocks are enriched N-MORB. The regionally low Nb/U and Ce/Pb ratios reflect the influence of the OIB material on the mafic magma source. From geochemistry, spatial distribution and tectonic relationship of the mafic rocks, an ancient triple-junction centered at the Majixueshan can be inferred. The existence of the Kuhai-Saishitang aulacogen may have provided a tectonic channel for the Majixueshan OIB materials metasomatizing the magma source for the Zongwulong rocks. The formation of the triple-junction and the rifting of the Zongwulong zone have separated the orogens and massifs in the region.

  20. Cristobalite-pyroxene in an L6 chondrite - Implications for metamorphism

    Science.gov (United States)

    Olsen, E. J.; Mayeda, T. K.; Clayton, R. N.

    1981-01-01

    CRISPY is a cristobalite-pyroxene assemblage in the L6 chondrite ALHA 76003. It was formed by reaction of a very siliceous inclusion with the surrounding olivine-rich rock. Oxygen isotopes show that the inclusion was derived from a source with non-chondritic isotopic composition. The isotopes also show that the oxygen of the pyroxene reaction product was derived by simple mixing of oxygen from the inclusion and its immediately adjacent surroundings, with exchange with the bulk meteorite limited to a distance of about a millimeter. The persistence of cristobalite in close proximity to olivine, and the lack of isotopic equilibration, show that the metamorphic processes that form petrographic grade 6 chondrites involve transport of major elements over distances only on the order of millimeters.

  1. Indicators of coal metamorphism

    Energy Technology Data Exchange (ETDEWEB)

    Proskuryakov, A.E.

    1982-06-01

    Important in determining metamorphism of coal is the reliability of indicators of coalification. Both the reflection of vitrinite and emission of volatile matter have been used for this purpose. To determine which indicator more accurately characterizes metamorphism of coal, their conformity to the following demands was established: 1. uniformity in direction of change of parameters with degree of metamorphism; 2. independence of the indicator of the genetic characteristics of coal (petrographic composition, reduction and oxidation of coal); 3. sensitivity of indicator. Both indicators conform to the first requirement. Emission of volatile substance decreases and reflective capacity of vitrinite increases uniformly with degree of metamorphism. However, the reflectivity of vitrinite is not influenced by petrographic composition of coals and is less dependent on the oxidation and reduction of coal than emission of volatile matter. It is also a more sensitive indicator distinguishing more degrees of metamorphism than emission of volatile matter. Reflectivity of vitrinite is a more reliable indicator of metamorphism than emission of volatile matter. However, in many laboratories this indicator is not measured with sufficient accuracy. To correct this, measuring equipment must be standardized.

  2. 某水工隧洞围岩稳定及支护结构分析%ANALYSIS ON SURROUNDING ROCK STABILITY AND SUPPORTING STRUCTURE OF DIVERSION SPILLWAY TUNNEL

    Institute of Scientific and Technical Information of China (English)

    秦雷; 郭德发; 王庆

    2012-01-01

    隧洞的围岩稳定及支护结构安全是保证隧洞安全、实现隧洞功能的关键因素.由围岩加固圈承担主要的外水压力是优化支护结构设计、保证围岩稳定的一种有效方法.建立肯斯瓦特导流泄洪洞三维有限元模型,并进行非线性有限元分析.分析结果表明,设计的支护措施能明显减少围岩变形、改善应力分布,为类似工程设计提供参考.%The stability of surrounding rock tunnel and the safe of support structure is the key factor to ensure tunnels safe and to achieve tunnel function. It is a optimized design to exert major external water pressure at reinforce circle also it is an effective method for the stability of surrounding rock. The author did the nonlinear finite element analysis by creating three-dimensional finite element model of Kensi-wate diversion spillway tunnel. The results show that the designed support measures can significantly reduce the rock deformation and improve the stress distribution,and it can provide a reference for the design of similar projects.

  3. 围岩松动圈锚注联合支护技术研究与应用%Research and Application of Surrounding Rock Loosen Zone Bolting Grouting United Support Technology

    Institute of Scientific and Technical Information of China (English)

    李飞鹏; 郜建明

    2014-01-01

    为解决赵庄煤业西翼胶带巷极破碎软岩的变形控制技术问题,对西翼胶带巷两帮和底板进行了探地雷达松动圈测试,得出了巷道围岩松动圈范围和破碎情况,基于松动圈测试及分析,提出了由预留变形量让压、初次全锚索网喷支护、深浅孔注浆加固、底角锚注加固组成的锚注联合支护体系,并在西翼胶带巷进行了应用。数值模拟和现场围岩变形监测结果表明,全锚索及深浅孔注浆加固下,巷道围岩强度提高,整体性较好,围岩破坏范围大幅减小,巷道表面变形得到有效控制,能够较好地满足巷道的使用,成功地解决了胶带巷大松动圈极破碎软岩条件下的巷道稳定控制问题。%In order to solve the problem of the deformation control technology in the Zhao Zhuang coal mine west wing belt roadway with bro-ken soft surrounding rock , the GPR loose circle testing was carried on two sides wall and bottom of the roadway surrounding rock and got the loose circle range and broken rock conditions. Based on the analysis of the loose circle testing , a combined support system was proposed with a reserved deformation pressure first, the anchor net spray support, deep-shallow hole grouting reinforcement and bottom anchor grouting re-inforcement, which were applied in the West Wing belt roadway. Deformation monitoring and the numerical simulation results show that under the deep-shallow hole grouting reinforcement, the surrounding rock strength is improved, integrity is better, rock damage range is greatly re-duced, the roadway surface deformation is effectively controlled, which means the scheme can better meet the roadway operating requirement, successfully resolved the conveyor broken roadway stability control problem of soft rock conditions.

  4. Geology and geochronology of the metamorphic suite Colorado and his rock assemblages, southeastern Rondonia, Brazil: implications for the mesoproterozoic evolution of the southwestern Amazon Craton; Geologia e geocronologia da suite metamorfica Colorado e suas encaixantes, SE de Rondonia: implicacoes para evolucao mesoproterozoica do SW do Craton Amazonico

    Energy Technology Data Exchange (ETDEWEB)

    Rizzotto, Gilmar Jose [Centro de Pesquisas de Recursos Minerais (CPRM), Rio de Janeiro, RJ (Brazil). Servico Geologico do Brasil; Bettencourt, Jorge Silva; Teixeira, Wilson; Basei, Miguel Angelo Stipp [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Pacca, Igor Ivory Gil; D' Agrella Filho, Manoel Sousa [Sao Paulo Univ., SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas; Vasconcelos, Paulo [Queensland Univ., Brisbane, (Australia); Onoe, Artur Takashi [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Centro de Pesquisas Geocronologicas; Passarelli, Claudia Regina [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Programa de Pos-graduacao em Geoquimica e Geotectonica

    2002-12-15

    Combined geochronological (U-Pb, 40 Ar/ 39 Ar, and RB-Sr) geological data help define an important tectonomagmatic event in the Colorado do Oeste and Cabixi regions, southeastern Rondonia, Brazil, and characterize the Colorado Metamorphic Suite (CMS), well represented by rock assemblages which experienced deformation and metamorphic recrystallization (upper-amphibolite facies). The suite is composed of: porphyritic monzogranite associated with amphibolite (bimodal magmatism); interlayered clastic and chemical metasedimentary rocks (sillimanite schists and iron formation); muscovite-garnet leucogranite; and mafic-ultramafic intrusive rocks. The CMS mafic rocks occur as underformed isolated bodies of layered coarse-grained metagabbro, still preserving typical cumulate igneous texture. U-Pb zircon isotopic data for three fractions of sample RO-10 define a discordia with an upper intercept (crystallization) age of 1352 + 4/-3 Ma (MSWD = 0,18). The porphyritic orthogneisses (RO-15; monzogranite and amphibolite) yielded a Rb-Sr whole rock isochron age of 1360 {+-} 45 Ma, and 87 Sr/86 Sr, = 0.7040 {+-} 0.0012 (MSWD = 9.2). One sample of aplite that is subparallel to the main regional foliation has furnished an age 1360 {+-}13 Ma. The 40 Ar/39 Ar data for muscovite from a anatectic leucogranite (RO-14) yielded plateau ages of 1312 {+-} 3 Ma (grain 1), and 1303 {+-} 2 Ma/1305 {+-} 2 Ma (grain 2). Grain 3 presented an heterogeneous isotopic spectrum, the integrated age being 1289 {+-} 2 Ma. Hornblende from two amphibolite samples yielded 40 Ar/39 Ar plateau ages of 1313 {+-} 4 Ma; 1313 {+-} 6 Ma and 1312 {+-} 3 Ma (RO-18), and 1325 {+-} 3 Ma; 1326 {+-} 2 Ma; 1330 {+-} 3 Ma (RO-19). The weighted-mean age 1319 {+-} 10 Ma, and is interpreted as the best estimated age for regional metamorphic cooling. These data suggest that southeastern Rondonia was affected by a tectonomagmatic event at ca. 1.36 - 1.32 Ga, predating the evolution of the Nova Brasilandia Terrane (1215 - 1110 Ma

  5. FAST CLASSIFICATION METHOD FOR ROCK MASS SURROUNDING HIGHWAY TUNNEL DURING CONSTRUCTION%公路隧道施工期围岩快速分级的一种新方法

    Institute of Scientific and Technical Information of China (English)

    方昱; 刘开云; 刘保国

    2013-01-01

    施工期围岩快速分级是保证隧道施工安全和工程质量的关键措施.结合绩黄、宁绩高速公路隧道群施工期围岩分级实践,在大量现场测试和室内试验的基础上,提出了一种基于国标BQ分级的新分级体系,并给出了每个分级指标的现场快速测试方法.用新分级体系进行隧道施工期围岩的快速分级工作,并以分级结果作为进化支持向量回归算法分级的训练样本,建立了隧道围岩分级的进化支持向量回归智能模型.为了方便现场使用,依据支持向量回归理论,将智能模型进一步转化为初等函数数学模型,经隧道围岩分级实例验证了该初等函数数学模型的准确性,为隧道施工期围岩快速分级提供了一种简便的新方法.%Fast classification of surrounding rock mass during construction period is the key measure for construction security and engineering quality. This paper combines the surrounding rock mass classification work during tunnel group construction in Jihuang and Ningji expressway. It proposes a new classification system as a kind of improved national standard BQ classification method. The system is based on many field tests and indoor experiments. The quick field testing method of each classification index is presented. Furthermore, the new classification system is used to cope with the surrounding rock classification in-situ. The classification results are served as the training samples of the evolutionary support vector regression ( SVR) algorithm in order to establish the intelligent classification model. Finally, the intelligent model is transferred to an elementary function mathematical model according to SVR theory for the purpose of convenience application. The accuracy of this mathematical classification model is verified by classification examples of tunnel group. Thus, the system offers a new simple fast classification method for surrounding rock mass during tunnel construction period.

  6. 大松动圈破碎围岩二次注浆加固试验研究%Experiment Study on Secondary Grouting Reinforcement of Broken Surrounding Rock in Large Loose Circle

    Institute of Scientific and Technical Information of China (English)

    李云; 韩立军; 孙昌兴; 董叶茂

    2012-01-01

    为解决赵庄煤矿高地应力条件下松软破碎围岩巷道持续变形的问题,通过理论分析、试验模拟和现场观测的手段对二次注浆加固进行研究,基于松动圈理论,采用地质雷达探测技术、深浅孔原位复注浆技术及锚注加固技术,在西翼南回风巷原有的锚网索支护基础上进行了全断面二次注浆加固试验。采用数值模拟以及巷道变形量观测的方法对支护效果进行检验。结果表明:二次注浆加固提高了围岩的整体强度,塑性区大幅减小,形成了复合承载结构,实现了锚固体与破碎围岩共同承载和自承载,可有效解决破碎围岩的持续变形问题。%In order to solve the continued deformation problem of the gateway with broken surrounding rock under the high geostress conditions in Zhaozhuang Mine, a study was conducted on the secondary grouting reinforcement with the theoretical analysis, test simulation and site observation means. Based on the loose circle theory, the geological radar detection technology, the in-situ re-grouting technology with shallow borehole and the boh and grouting reinforcement technology were applied to the full section secondary grouting reinforcement test based on the previous bolt/steel mesh/anchor support of the south air returning gateway in the west wing of the mine. The numerical software similar simulation and the gateway deformation observation were applied to the inspection of the support effect. The results showed that the secondary grouting reinforcement had improved the integrated strength of the surrounding rock, high reduced the plastic zone, formed a complex loading structure, released the joint loading and self loading of the anchoring mass and the broken surrounding rock and could effectively solve the continued deformation problem of the broken surrounding rock.

  7. Revisiting the high temperature metamorphic field gradient of the Ryoke Belt (SW Japan): New constraints from the Iwakuni-Yanai area

    Science.gov (United States)

    Skrzypek, Etienne; Kawakami, Tetsuo; Hirajima, Takao; Sakata, Shuhei; Hirata, Takafumi; Ikeda, Takeshi

    2016-09-01

    We revisit the origin of the metamorphic field gradient exposed in the Ryoke Belt (SW Japan) - the type locality for low pressure/high temperature (LP/HT) conditions - based on combined structural, petrological and geochronological data from the Iwakuni-Yanai area (W Ryoke). In this area metasedimentary rocks pass from schist in the north to partly migmatitic paragneiss in the south, and are surrounded by numerous granitoid bodies. Three deformation phases are emphasized; an accretionary-stage or burial deformation of weak intensity (D0), a vertical shortening (D1) which generated a subhorizontal, locally extensional foliation in the southern gneiss zone, and E-W upright folding (D2) which reworked both the northern schist and southern gneiss zones. Crystallization-deformation relationships indicate that, in the schist zone, most andalusite, cordierite and mica porphyroblasts formed after D0 and before D1. Syn-D1 mineral assemblages define E-W trending metamorphic zones with increasing grade from north to south, and rare syn-D2 parageneses reveal a similar pattern. Continuous magmatic activity lasted from ca. 105 to 94 Ma. The oldest granitoids (Shimokuhara, Soo, Namera), found in the western part of the belt, were emplaced below schistose rocks at 105-100 Ma. Subsequently, syn- to post-D1 granodiorite (Gamano) intruded concordantly with the foliation of southern, high-grade gneissic rocks from 100 to 94 Ma. A large, syn-D1 pluton (Kibe) intruded the center of the belt at 98 Ma, whereas a younger granite (Iwakuni) and its satellite dykes were emplaced to the northeast at 96-94 Ma. Constraints on the timing of D1 (103-99 Ma) and the likely diachronous D2 phase (100-94 Ma) suggest a deformation continuum during magma intrusion and metamorphism. We conclude that the exposed metamorphic field gradient is an apparent, but fortuitous, alignment of P-T data resulting from spatially and temporally distinct thermal events. Peak temperature conditions in the relatively

  8. 越南西北部大象山超高温变质岩的发现及其区域构造意义%The discovery and tectonic implication of ultrahigh-temperature metamorphic rocks in the Day Nui Con Voi, northwestern Vietnam

    Institute of Scientific and Technical Information of China (English)

    吴虎峻; 刘俊来; TRANMy Dung; NGUYEN QuangLuat; PHAMBinh; 吴文彬; 陈文; 张招崇

    2011-01-01

    越南西北部大象山群孔兹岩系中发育一套含刚玉+尖晶石+石榴石+夕线石组合的富铝岩石块体,它们呈透镜状包体形式赋存于孔兹岩系内.岩石中刚玉+尖晶石+石榴石+夕线石组合的发育指示岩石经历了超高温变质作用的改造.其中尖晶石和石英的共生组合表明了变质温度高于900℃,而利用岩石退变质矿物组合中的黑云母-石榴石温度计,黑云母-斜长石-石榴石-石英组合温度-压力计估算的变质温度压力条件分别为879 ~917℃、0.90 ~0.94GPa.岩石中的早期刚玉+夕线石的组合的存在说明岩石变质作用已经从高角闪岩相进入到了麻粒岩相;而峰期变质矿物组合尖晶石+石英的出现,指示了变质温度高于900℃的超高温变质作用.另一方面,退变质过程中钛铁矿的发育表明岩石经历了快速抬升降压的过程.变质作用的P-T轨迹分析揭示出岩石经历了早期同步升温增压后的快速增温达到峰期条件,后经历快速等温减压过程.这种温压条件的变化与板块会聚过程中由于俯冲板片的断离而使软流圈上涌造成热异常的温压条件变化基本一致.通过对超高温变质岩石进行锆石SIMS U-Pb测年获得的结果大于58Ma,推测这次超高温变质与喜马拉雅运动中印度与欧亚大陆的初期会聚-碰撞作用相关.%There is a pile of rock blocks which contain corundum + spinel + garnet + fibrolite association in the form of lenticular enclaves in khondalite series along the Day Nui Con Voi, northwestern Vietnam. The mineral association is resulted from ultrahigh-temperature metamorphism. The coexistence of spinel and quartz indicates that the metamorphic temperature is higher than 900℃. Meanwhile, the biotite-garnet thermometer and biotite-plagioclase-garnet-quartz association thermobarometer for the mineral associations during retrogressive metamorphism gave temperature and pressure ranges of 879 ~917℃ and 0

  9. 大断面破碎硐室围岩蠕变模拟及控制技术%Creep simulation on fractured surrounding rock of large section chamber and its control technology

    Institute of Scientific and Technical Information of China (English)

    2013-01-01

      对大断面破碎围岩多次返修巷硐,锚网索支护方式难以有效控制其强流变。结合焦煤公司中马村矿39#泵房多次返修的状况,认为高应力作用下的不稳定强流变岩层,支架受力不均等因素是硐室围岩失稳的主因,提出了主动支护与被动支护联合修复方案:一次锚网索支护,二次封闭刚性支架联合支护,三次围岩注浆加固。采用蠕变数值模拟方法对原支护和返修加固方案进行了分析,结果表明:原方案在360 d时的断面收缩率达到92.2%,顶板最大下沉量达到2792 mm,围岩处在加速蠕变失稳阶段;返修加固方案在1000 d时的顶板最大下沉量仅56.8 mm,围岩处在蠕变稳定阶段;锚索作用在完整岩体范围内,锚杆大部分作用在塑性圈范围内,注浆范围外应力等值线密集,其峰值随时间的延长而增大,且逐渐内移。工业性试验表明:224 d时,硐室表面最大位移为18 mm,变形速率小于0.5 mm/d,修复加固取得了成功。%To large section chamber with fractured surrounding rock and repeatedly repairing, strong rheology cannot be controlled effectively with bolt-wire-cable support style. According to the repeatedly repairing 39# pump house of Zhongmacun Colliery, Jiaozuo Coal Company, the main factors on insta-bility of surrounding rock include strong rheology strata influenced by high stress, uneven loading on steel timbers. Repair scheme combined initiative and passive support is proposed, which includes pri-mary bolt-wire mesh-cable, secondary closed steel timber and third grouting reinforcement. Original and repairing support is analyzed with creep numerical simulation. The results indicate that shrinkage percentage of chamber section is 92.2% within 360 days, and the maximum roof subsidence is 2 792 mm, and accelerated creep phase of surrounding rock appears. The maximum roof subsidence is 56.8 mm within 1 000 days, and stable creep

  10. A study on the relationships between metamorphic anatexis and petrogenesis and mineralization

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Metamorphic processes are closely associated with the formation and evolution of the crust and highly related to petrogenesis and mineralization processes. Dynamic systematic analysis indicates that regional metamorphism-migmatization-metamorphic anatexis process is a temperature-pressure progressive process. Metamorphic anatexis process is a critical part with its unique pressure/temperature and thermodynamic, dynamic and geochemical characteristics. The concept of metamorphic anatexis system (MAS) introduced by the author includes the essential factors of material resources, energy resources, process format, material transportation and concentration, occurring time and location. Based on the essential factors of MAS, metamorphic anatexis process-related granitic rocks and deposit cases are discussed on their petrogenesis and/or mineralizaion mechanisms. The discussion points out that granites in the Ailaoshan and Yunkai metamorphic zones are of metamorphic anatexis origin. The genesis of pegmatite ore deposits in metamorphic zones and shear zone gold deposits in shear zones are highly related to metamorphic anatexis process. The study of metamorphism process involved in ore formation and material transport is a hot subject concerned by the international geological circles. Thorough investigations into the relationships between metamorphic anatexis and petrogenesis-meneralization processes are of great importance not only in geological theory, but also in industrial practice.

  11. Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures

    Science.gov (United States)

    French, Bevan M.

    1998-01-01

    This handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures emphasizes terrestrial impact structures, field geology, and particularly the recognition and petrographic study of shock-metamorphic effects in terrestrial rocks. Individual chapters include: 1) Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System; 2) Target Earth: Present, Past and Future; 3) Formation of Impact Craters; 4) Shock-Metamorphic Effects in Rocks and Minerals; 5) Shock-Metamorphosed Rocks (Impactities) in Impact Structures; 6) Impact Melts; 7) How to Find Impact Structures; and 8) What Next? Current Problems and Future Investigations.

  12. Kanfenggou UHP Metamorphic Fragment in Eastern Qinling Orogen and Its Relationship to Dabie-Sulu UHP and HP Metamorphic Belts, Central China

    Institute of Scientific and Technical Information of China (English)

    Suo Shutian; Zhong Zengqiu; Zhou Hanwen; You Zhendong

    2003-01-01

    In the Central Orogenic Belt, China, two UHP metamorphic belts are discriminated mainly based on a detailed structural analysis of the Kanfenggou UHP metamorphic fragment exposed in the eastern Qinling orogen, and together with previous regional structural, petrological and geochronological data at the scale of the orogenic domain. The first one corresponds to the South Altun-North QaidamNorth Qinling UHP metamorphic belt. The other is the Dabie-Sulu UHP and HP metamorphic belts. The two UHP metamorphic belts are separated by a series of tectonic slices composed by the Qinling rock group, Danfeng rock group and Liuling or Foziling rock group etc. respectively, and are different in age of the peak UHP metamorphism and geodynamic implications for continental deep subduction and collision. Regional field and petrological relationships suggest that the Kanfenggou UHP metamorphic fragment that contains a large volume of the coesite- and microdiamond-bearing eclogite lenses is compatible with the structures recognized in the South Altun and North Qaidam UHP metamorphic fragments exposed in the western part of China, thereby forming a large UHP metamorphic belt up to 1 000 km long along the orogen strike. This UHP metamorphic belt represents an intercontinental deep subduction and collision belt between the Yangtze and Sino-Korean cratons, occurred during the Paleozoic. On the other hand, the well-constrained Dabie-Sulu UHP and HP metamorphic belts occurred mainly during Triassic time (250-220 Ma), and were produced by the intrucontinental deep subduction and collision within the Yangtze craton. The Kanfenggou UHP metamorphic fragment does not appear to link with the Dabie-Sulu UHP and HP metamorphic belts along the orogen. There is no reason to assume the two UHP metamorphic belts us a single giant deep subduction and collision zone in the Central Orogenic Belt situated between the Yangtze and Sino-Korean cratons. Therefore, any dynamic model for the orogen must account

  13. Evaluation of models for estimating changes in fracture permeability due to thermo-mechanical stresses in host rock surrounding a potential repository

    Energy Technology Data Exchange (ETDEWEB)

    Berge, P A; Blair, S C; Shaffer, R J; Wang, H F

    1997-02-18

    We provide in this report a methodology to estimate bounds on the changes in fracture permeability due to thermal-mechanical processes associated with excavation of drifts and emplacement of waste. This report is the first milestone associated with Task A of the LLNL initiative to evaluate available methods for estimating chamges in fracture permeability surrounding drifts in the Exploratory Studies Facility (ESF) and the potential repository at Yucca Mountain in response to (1) construction-induced stress changes and (2) subsequent thermal pulse effects due to waste emplacement. These results are needed for modeling changes in repository-level moisture movement and seepage.

  14. Determination of Stability and Reinforcement Range of Horse-head under Condition of Weak Surrounding Rock%软弱围岩条件下马头门稳定性及加固范围确定

    Institute of Scientific and Technical Information of China (English)

    张兆军

    2012-01-01

    以国内某大型矿井副井马头门的高埋深、高应力、高破碎、大断面等复杂条件为工程背景,采用理论分析,研究了马头门附近围岩破坏区分布规律及应力场分布规律,并通过建立三维立体数值计算模型予以验证。据此确定了马头门围岩的不稳定区域,提出了支护建议。%Taking complex conditions of auxiliary shaft horse-head of high burial depth, high stress, high crushing and large section, the author researched distribution law of breakdown area of surrounding rock and stress field by using theoretical analysis. Through verification of building three-dimensional numeric calculation model, the author determined unstable area of surrounding rock of horse-head, and put forward suggestions of support.

  15. Research on The Surrounding Rock Deformation Law of Carbon Shale Small Interval Tunnel%炭质页岩小净距隧道围岩变形规律研究

    Institute of Scientific and Technical Information of China (English)

    段宝福; 翁现合

    2012-01-01

    以湖北宴家隧道工程为例,结合现场施工监测,采用有限元程序对节理围岩隧道施工进行模拟,对节理围岩隧道的开挖对地层扰动的范围进行定量确定.对小间距双线隧道在炭质页岩条件下节理面上游隧道先行施工进行数值模拟,将实测数据与数值模拟进行对比,总结出炭质页岩小间距隧道左右洞有施工差别时围岩变形规律.%Taking the Hubei Yanjia tunnel project as an example, the construction of jointed surrounding rock tunnels was simulated using finite element software and the range of disturbance caused by the excavation was quantatively determined. Numerical simulations were also performed for the upper tunnel under carbonaceous shale in small interval tunnel and simulation results were compared against site measurement.Conclusions were drawn regarding the principles of tunnel surrounding rock deformation when the two holes are constructed differently.

  16. Stability Analysis on Recovery Goaf Surrounding Rock of the Pillar-9 in Dongshengmiao Mine%东升庙矿9号矿柱回收采空区围岩稳定性分析

    Institute of Scientific and Technical Information of China (English)

    张飞; 王滨; 菅玉荣; 刘文刚; 冀杰

    2012-01-01

    This topic is based on the project of Pillar recovery and goaf processing at Dongshengmiao mine#2 and #11 ore deposit, with the purpose that in the goaf processing field to form a relatively perfect key technical model for empty area processing, by means of the treatment of goaf and the indoor test, using the new version of FLAC3D 4. 0 numerical simulation software to simulate and analyse the stability of surrounding rock after goaf processing, combined with the natural equilibrium arch theory to forecast scope of the surrounding rock of goaf which may inbreak, so as to effectively control groud pressure and to prevent the roof rock burst which may cause a major accident. We mainly study the Pillar-9 recovery process at above the midpiece of 900 m, in Pillar-9 recovery process, the major damage form of the surrounding rocks of the goafs upper plate was plastic damage due to that the tensile stress and shear stress exceeded the yield limit, the plastic damage area was mainly distributed in the surrounding areas of the plate under angle, footwall upper corner of surrounding rock and in the Pillar-32 position within the area of the strata.%以东升庙矿2#和11#矿床矿柱回收及空区处理项目为基石展开,目的是想在空区处理研究领域形成一套相对完善的空区处理关键性技术模式,通过开展东矿现场和室内试验研究,采用FLAC3D 4.0新版本数值模拟软件对空区围岩稳定性进行模拟分析,结合极限自然平衡拱理论对空区围岩可能冒落的范围进行预测,以便有效地控制地压,预防空区顶板围岩突然冒落造成矿山重大安全事故.我们对900 m中段以上9号矿柱回收过程进行了详尽的模拟研究,在9号矿柱回收过程中,空区上盘围岩的主要破坏形式主要为拉应力及剪应力超过屈服极限引发的塑性破坏,塑性破坏区域主要分布在空区上、下盘围岩隅角及32号矿柱上覆岩层内的部分区域.

  17. Study of dynamic damage of surrounding rocks for tunnels under high in-situ stress%高地应力下隧道围岩动力损伤分析

    Institute of Scientific and Technical Information of China (English)

    杨栋; 李海波; 夏祥; 罗超文; 李卫兵

    2013-01-01

    为预估和控制爆破荷载作用下围岩损伤范围,在赣龙铁路梅花山隧道工程现场进行岩体声波测试,得到围岩的损伤范围。根据爆破荷载作用下岩体损伤发展规律,采用基于概率形式的损伤变量定义,运用三维有限差分软件对不同地应力状态下爆破产生的围岩损伤范围进行数值模拟,并与现场岩体声波测试结果进行比较。计算结果表明,数值计算与实测结果有较好的一致性,随着地应力大小增大,围岩损伤范围呈现先减小后增大的趋势,且增大幅度较大,地应力较高时,局部部位如顶板、底板损伤更为明显,说明地应力大小对围岩损伤分布有着显著影响;随着侧压力系数增大,损伤范围先减小后增大,但增速逐渐减小。所得到的结论可为高地应力下隧道稳定性分析和支护设计提供依据。%In order to forecast and control the damage zone of surrounding rock under blasting load, sound wave tests have been conducted in the construction site of Meihuashan Tunnel in Jiangxi province dragon railway. Based on the change rate of sound wave speed, damage zone size of surrounding rock are obtained. On this basis, a statistics-based damage variable of rockmass has been proposed based on micromechanics. Damage zone size of surrounding rock under blasting load at different in-situ stresses is thus studied by using three-dimensional finite difference software. Calculations show that the numerical simulation results agree well with the site monitoring results. With the in-situ stress increasing, the size of damage zone decreases first, then increases, and increases by a large margin;when the in-situ stress is high, local parts such as tunnel roof, floor damage is more obvious; it is shown that the in-situ stress has significant impact on surrounding rock damage distribution. With the lateral pressure coefficient increasing, the size of damage zone decreases first

  18. Reactions to define the biotite isograd in the Ryoke metamorphic belt, Kii Peninsula, Japan

    Science.gov (United States)

    Wang, Ge-Fan; Banno, Shohei; Takeuchi, Keiji

    1986-03-01

    Two types of biotite isograd are defined in the low-grade metamorphism of the Wazuka area, a Ryoke metamorphic terrain in the Kii Peninsula, Japan. The first, BI1, is defined by the reaction of chlorite+K-feldspar= biotite+muscovite+quartz+H2O that took place in psammitic rocks, and the second, BI2, by the continuous reaction between muscovite, chlorite, biotite and quartz in pelitic rocks. The Fe/Mg ratios of the host rocks do not significantly affect the reactions. From the paragenesis of pelitic and psammitic metamorphic rocks, the following mineral zones were established for this low-pressure regional metamorphic terrain: chlorite, transitional, chlorite-biotite, biotite, and sillimanite. The celadonite content of muscovite solid solution in pelitic rocks decreases systematically with the grade of metamorphism from 38% in the chlorite zone to 11% in the biotite zone. Low pressure does not prohibit muscovite from showing the progressive change of composition, if only rocks with appropriate paragenesis are chosen. A qualitative phase diagram of the AKF system relevant to biotite formation suggests that the higher the pressure of metamorphism, the higher the celadonite content of muscovite at BI1, which is confirmed by comparing the muscovites from the Barrovian and Ryoke metamorphism.

  19. Natural radioactivity levels in soils, rocks and water at a mining concession of Perseus gold mine and surrounding towns in Central Region of Ghana.

    Science.gov (United States)

    Faanu, A; Adukpo, O K; Tettey-Larbi, L; Lawluvi, H; Kpeglo, D O; Darko, E O; Emi-Reynolds, G; Awudu, R A; Kansaana, C; Amoah, P A; Efa, A O; Ibrahim, A D; Agyeman, B; Kpodzro, R; Agyeman, L

    2016-01-01

    Levels of naturally occurring radioactive materials prior to processing of gold ore within and around the new eastern concession area of Perseus Mining (Ghana) Limited were carried out to ascertain the baseline radioactivity levels. The study was based on situ measurements of external gamma dose rate at 1 m above ground level as well as laboratory analysis by direct gamma spectrometry to quantify the radionuclides of interest namely; (238)U, (232)Th and (40)K in soil, rock, ore samples and gross alpha/beta analysis in water samples. The average absorbed dose rate in air at 1 m above sampling point using a radiation survey metre was determined to be 0.08 ± 0.02 μGyh(-1) with a corresponding average annual effective dose calculated to be 0.093 ± 0.028 mSv. The average activity concentrations of (238)U, (232)Th, and (40)K in the soil, rock, and ore samples were 65.1 ± 2.2, 71.8 ± 2.2 and 1168.3 Bqkg(-1) respectively resulting in an average annual effective dose of 0.91 ± 0.32 mSv. The average Radium equivalent activity value was 257.8 ± 62.4 Bqkg(-1) in the range of 136.6-340.2 Bqkg(-1). The average values of external and internal indices were 0.7 ± 0.2 and 0.9 ± 0.2 respectively. The average gross alpha and gross beta activity concentrations in the water samples were determined to be 0.0032 ± 0.0024 and 0.0338 ± 0.0083 Bql(-1) respectively. The total annual effective dose from the pathways considered for this study (gamma ray from the soil, rock and ore samples as well as doses determined from the gross alpha/beta activity concentration in water samples) was calculated to be 0.918 mSv. The results obtained in this study shows that the radiation levels are within the natural background radiation levels found in literature and compare well with similar studies for other countries and the total annual effective dose is below the ICRP recommended level of 1 mSv for public exposure control.

  20. Measurement of activity concentration of {sup 222}Rn in ground waters drawn from two wells drilled in the Amparo Complex metamorphic rocks, municipio de Amparo, SP; Medida da atividade do {sup 222}Rn em aguas subterraneas extraidas de dois pocos perfurados em rochas metamorficas do Complexo Amparo, municipio de Amparo, SP

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Igor Jose Chaves de

    2008-07-01

    A sampling system was assembled for field {sup 222}Rn activity concentration measurements in ground waters. The system consists of a sampling flask that prevents the contact between the water sample and the atmosphere and a closed line for radon extraction from water. The system, its operation and calibration, are described in full detail, as well as, the conversion of the measured alpha counting rates in activity concentrations. The assembled system was used in {sup 222}Rn activity concentrations measurements in ground waters drawn from two wells drilled in the Amparo Complex metamorphic rocks. The wells are located at the urban area of the city of Amparo and are exploited for public use water. One well, named Vale Verde, is 56 meters deep and crosses 18 meters of soil, 26 meters of quartz rich gneiss and 12 meters of biotite-gneiss. The other well, named Seabra, is 117 meters deep, crosses 28 meters of soil and weathered rocks and ends in granite-gneiss. The mean activity concentrations for the year long observation were (377 +- 25) Bq/dm{sup 3}, for Seabra well, and (1282 +- 57) Bq/dm3, for the Vale Verde well. The {sup 222}Rn activity concentrations fall in the activity concentration range reported in the literature for similar geology areas and are larger than the concentrations found neighboring areas of the same metamorphic Complex. The seasonal activity concentration variations seem to correlate with rain fall variations in the study area. (author)

  1. 考虑围岩蠕变特性的轴对称有限元非线性分析%The nonlinear axisymmetric finite element method for anlaysis of surrounding rock in consideration of creeping

    Institute of Scientific and Technical Information of China (English)

    杜丽惠; 黄丽清

    2001-01-01

    本文采用轴对称非线性有限元方法分析竖洞开挖与混凝土的衬砌施工过程中围岩的应力应变,计算中引入破坏接近度的概念以判定材料的非线性及其破坏问题,分析了围岩的软化及其破坏形态,并进行了实际竖洞的蠕变分析.%In this paper, the nonlinear axisymmetric finite element method is adopted to analyze the stree-strain of surrounding rock of vertical tunnel in the process of excavation and lining. The failure approach concept is introduced in the discrimination of the non-linearity and failure of the rock. The softening of the rock and the types of failure are simulated and the creeping of the tunnel is analyzed.

  2. Phanerozoic magmatism and associated metamorphism in the Bird's Head, New Guinea

    Science.gov (United States)

    Jost, Benjamin; White, Lloyd; Webb, Max

    2017-04-01

    The Bird's Head is the north-westernmost peninsula of New Guinea. It is characterised by a mountain range exposing a basement of metamorphosed Silurian-Devonian turbidites cross-cut by various granitoid bodies. This area offers a unique window to study pre-Cenozoic tectono-thermal events at the north-eastern margin of eastern Gondwana. We present new field, geochemical, and U-Pb zircon data from this remote, relatively unstudied region. We show that the granitoids intruded the basement rocks in two distinct phases in the Devonian-Carboniferous and the Permian-Triassic. Both events produced highly evolved peraluminous granite and granodiorite, supplemented by fewer metaluminous diorite and gabbro. Abundant country rock xenoliths, associated migmatites, as well as mineralogical and geochemical data suggest that the granitoids were generated by partial melting of the continental crust (S-type). The Permian-Triassic event is further characterised by structures indicating syn-intrusive extension. We propose that Permian-Triassic magmatism in the Bird's Head occurred in an evolved continental-arc environment. Mantle-wedge-derived melts underplated and intruded the lower crust, providing the necessary heat to induce partial melting of the overlying metasedimentary crust. These melts were emplaced during a phase of crustal extension and are the likely cause of high-T/low-P regional metamorphism in the surrounding country rocks. Partial melting in a continental arc setting has been proposed for the generation of S-type granitoids of the Andes and along the western Pacific. The paired metamorphic and igneous rocks that we observe also show similarities to the Buchan type area in NE Scotland and the Cooma Complex in SE Australia, the latter of which is considered to have formed in an Andean-type margin.

  3. Charnockite microstructures: From magmatic to metamorphic

    Directory of Open Access Journals (Sweden)

    Jacques L.R. Touret

    2012-11-01

    Full Text Available Charnockites sensu lato (charnockite-enderbite series are lower crustal felsic rocks typically characterised by the presence of anhydrous minerals including orthopyroxene and garnet. They either represent dry (H2O-poor felsic magmas that are emplaced in the lower crust or granitic intrusions that have been dehydrated during a subsequent granulite facies metamorphic event. In the first case, post-magmatic high-temperature recrystallisation may result in widespread metamorphic granulite microstructures, superimposed or replacing the magmatic microstructures. Despite recrystallisation, magmatic remnants may still be found, notably in the form of melt-related microstructures such as melt inclusions. For both magmatic charnockites and dehydrated granites, subsequent fluid-mineral interaction at intergrain boundaries during retrogradation are documented by microstructures including K-feldspar microveins and myrmekites. They indicate that a large quantity of low-H2O activity salt-rich brines, were present (together with CO2 under immiscible conditions in the lower crust.

  4. Experimental research of gas injection displacement mechanism and efficiency in the fractured metamorphic rock reservoir%裂缝型变质岩油藏注气驱机理及驱替效率实验研究

    Institute of Scientific and Technical Information of China (English)

    林仁义; 孙雷; 梁宇; 黄堃

    2015-01-01

    采用物理模拟实验的方法,做注气膨胀实验,评价天然气在原油中的溶解性。通过数模和细管实验,确定目前地层压力和温度下的最小混相压力。开展双重介质变质岩油藏顶部注天然气,底部注水长岩心驱替实验(岩心夹持器呈30°倾斜),得出了裂缝和基质分别对采收率的贡献。驱替压力25.6 MPa和38.6 MPa,均小于最小混相压力,实验中天然气驱替过程为非混相驱。由于裂缝的收缩性远大于基质,衰竭采出的原油可以看作是裂缝的贡献。同时,由于基质与裂缝之间的渗透率相差极大,因此在初期的驱替过程中,裂缝中的原油可以被完全驱出。结合以上分析,可以由最终实验结果得出基质与裂缝系统各自对采收率的贡献。%The swelling test is conducted under physical simulation to analyze the natural gas solvency in the crude oil. MMP is cal⁃culated by simulation and slim tube experiment under the current pressure and temperature situation. The long core displacement experiment on the double medium metamorphic reservoir rock cores is conducted to get the recovery of the contribution from the matrix and fractures respectively, including natural gas injection on the top and water injection at the bottom of the long core(the core holder is 30° to the horizontal direction). The displacement pressure is 25.6 MPa and 38.6 MPa, lower than the MMP, meaning that the whole procedure is immiscible displacement. Contractility of fractures is much larger than matrix, thus the oil recovery from the depletion can be treated as the contribution of fractures. And the assumption can be made that the oil are completely out of the fractures in the initial displacement process because of the great permeability difference between fractures and matrix. Based on the analysis above, the contribution to the final recovery of the fractures and matrix respectively can be obtained from the experi

  5. A convection-conduction model for analysis of the freeze-thaw conditions in the surrounding rock wall of a tunnel in permafrost regions

    Institute of Scientific and Technical Information of China (English)

    何春雄; 吴紫汪; 朱林楠

    1999-01-01

    Based on the analyses of fundamental meteorological and hydrogeological conditions at the site of a tunnel in the cold regions, a combined convection-conduction model for air flow in the tunnel and temperature field in the surrounding has been constructed. Using the model, the air temperature distribution in the Xiluoqi No. 2 Tunnel has been simulated numerically. The simulated results are in agreement with the data observed. Then, based on the in situ conditions of air temperature, atmospheric pressure, wind force, hydrogeology and engineering geology, the air-temperature relationship between the temperature on the surface of the tunnel wall and the air temperature at the entry and exit of the tunnel has been obtained, and the freeze-thaw conditions at the Dabanshan Tunnel which is now under construction is predicted.

  6. DYNAMIC MODELING OF METAMORPHIC MECHANISM

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The concept of metamorphic mechanism is put forward according to the change of configurations from one state to another. Different configurations of metamorphic mechanism are described through the method of Huston lower body arrays. Kinematics analyses for metamorphic mechanism with generalized topological structure, including the velocity, angular velocity, acceleration and angular acceleration, are given. Dynamic equations for an arbitrary configuration, including close-loop constraints, are formed by using Kane's equations. For an arbitrary metamorphic mechanism, the transformation matrix of generalized speeds between configuration (*)and(*)+1 is obtained for the first time. Furthermore, configuration-complete dynamic modeling of metamorphic mechanism including all configurations is completely established.

  7. 强采动下近距离硐室群围岩应力演化及加固对策%Stress Development and Reinforcement Countermeasure of Surrounding Rock of Close-distance Caverns Influenced by Strong Mining

    Institute of Scientific and Technical Information of China (English)

    姜鹏飞; 郭相平

    2014-01-01

    Stress development rule of close-distance caverns influenced by 2322 face's strong mining was researched with FLAC3D , and the mechanism of grouting reinforcement for close-distance caverns was researched by applying UDEC software. Corresponding reinforce-ment countermeasure was put forward. Results showed that after close-distance caverns including water sumps and substation were exca-vated, superimposition effect of vertical stress of surrounding rock between caverns was more obvious than that of horizontal stress, but horizontal stress concentration degree was larger. Mining of 2322 face result into abutment pressure of coal-pillar moving to floor. Influenced by high stress superimposition of coal and floor, strong floor heave occurred in caverns. Under the condition of the same grouting pressure and ratio of water-to-ash, slurry diffusion radius along tangential direction of hole was larger than that along radial di-rection. Bearing capacity of caverns' shallow surrounding rock largely increased by reinforcing with grouting anchored-cable. High mining stress was transferred from deep to shallow location, which prevented further failure of deep rock. Underground test showed that after ap-plying grouting anchored-cable, surrounding rock of every cavern could keep stability and deformation of surrounding rock of close-dis-tance caverns influenced by strong mining was effectively controlled.%以成庄煤矿井下甲、乙水仓及变电所等近距离硐室群为背景,采用FLAC3D 有限差分程序计算分析了2322工作面强采动下近距离硐室群围岩应力演化规律,采用UDEC离散元软件研究了近距离硐室群注浆加固机理,并提出了相应的加固对策。研究结果表明:成庄煤矿甲、乙水仓及变电所等近距离硐室群开挖后,围岩间垂直应力叠加效应较水平应力更为明显,但水平应力集中程度更高;2322工作面回采引起煤柱支承压力向底板传递,受煤柱高应力与底

  8. Metamorphic crystallization kinetics quantified through space and time

    Science.gov (United States)

    Kelly, E. D.; Carlson, W. D.; Ketcham, R. A.

    2012-12-01

    Numerical simulations of diffusion-controlled nucleation and growth of garnet porphyroblasts in regionally metamorphosed rocks constrain values for interfacial energy and rates of nucleation and Al intergranular diffusion, quantities that exert a strong control on the sizes and disposition of porphyroblasts in most metamorphic rocks. During simulation of a reaction, product crystals consume a rate-limiting component (Al) and gradients in Al concentration in the intergranular fluid develop between the product and reactant crystals. Low Al concentrations surrounding product crystals (low reaction affinity) reduce nucleation probability, creating a tendency toward spatial ordering of crystal centers in homogeneous portions of a rock. Also, as Al depletion zones impinge, crystals compete for Al, resulting in a tendency toward smaller sizes for neighboring crystals and larger sizes for those that grow in isolation. These phenomena produce distinctive textural effects that allow the simulations to be constrained by measurements of the sizes and locations of porphyroblasts in natural samples. The 13 rocks analyzed in this study were collected from 7 localities exhibiting a diverse range of crystallization conditions. In the simulations, unknown kinetic parameters governing nucleation and intergranular diffusion were adjusted iteratively to achieve fits between simulated and natural porphyroblastic textures. Model fits were assessed primarily from textural characteristics precisely measured by high-resolution X-ray computed tomography. The range of interfacial energies obtained for heterogeneous nucleation is 0.007-0.118 J/m2 for the sample suite, assuming shape factors in the range 0.1-1.0. Nucleation rates change through space and time due to growth and impingement of Al depletion zones. In some modeled rocks, the actual (whole-rock) rate rises steeply, achieves a steady state, and then falls rapidly as reactants are consumed; in others, the steady-state is not achieved

  9. Stability and Control Technology of Surrounding Rock under Permanent Coal Pillar%永久煤柱下巷道围岩稳定性及控制技术分析

    Institute of Scientific and Technical Information of China (English)

    孙明磊; 李佳丽

    2016-01-01

    Broken influence elements and mechanism of special return air entry of Daihe coal mine were analyzed, which included supporting pressure of coal pillar, surrounding rock strength and supporting way. Detailed numerical modeling of FLAC2D was conducted to evaluate surrounding rock stress distribution that influence by horizontal distance of roadway to coal pillar edge and supporting way. These papers studied the characters of roadway moment distribution and surrounding rock displacement that influenced by three different supporting way, which included U style steel supporting, grouting reinforcement and compensate supporting with cable, put forward grouting and compensate supporting with cable should be used on the basis of U style steel supporting in roadway under the per-manent coal pillar, then stability supporting body would formed, and roadway deformation could be controlled effectively.%以岱河煤矿Ⅳ1专用回风巷变形破坏为研究对象,从煤柱支承压力、围岩强度、现有支护措施3个方面分析了其破坏影响因素和机理,通过建立FLAC2D 模拟模型明确了巷道与煤柱边缘水平距离、巷道支护方式对围岩应力分布的影响。研究了U型钢、注浆及锚索结构补偿支护3种作用下的巷道弯矩分布、围岩位移等特点,提出了永久煤柱下的巷道在U型钢基础上应进行注浆加固,再用锚索进行针对性支护结构补偿,形成稳定的共同承载体,有效地控制巷道变形。

  10. 黄土连拱隧道动态施工围岩损伤局部化研究%Study of damage localization of loess multi-arch tunnel's surrounding rock under dynamic construction

    Institute of Scientific and Technical Information of China (English)

    钟祖良; 刘新荣; 刘元雪; 李鹏; 王吉明

    2012-01-01

    In order to study the damage distribution of tunnel's surrounding rock, firstly, an elastoplastic damage constitutive model of Q2 loess is deduced based on triaxial shear tests and compiled as a user-defined damage model( UDM ) of FLAC3D. Then the conception of surrounding rock damage degree (SRDD) is put forward and compiled into a post-processing module. Based on the first loess multi-arch tunnel of road-Lishi tunnel, the damage position of tunnel's surrounding rock of two construction schemes is numerically simulated. The research results show that the SRDD and damage localization rules can be simulated well at every excavation step; and it also provides reference for the optimization of tunnel construction scheme. The research results provide a new method for the optimization of tunnel construction scheme and choice of construction scheme.%为了研究黄土连拱隧道动态施工时围岩的损伤情况和损伤分布规律,在室内试验的基础上推导了Q2黄土的弹塑性损伤本构模型,并基于FLAC3D平台编制了自定义本构模型,提出了损伤度概念并编制了损伤度后处理模块.以国内首条高速公路黄土连拱隧道-离石隧道为依托工程,对两种开挖方案施工时围岩损伤情况进行数值分析.研究表明,该成果可以较好地掌握隧道每一开挖步后围岩损伤度的分布情况和损伤区的演化规律,为施工方案优化选择提供依据.该研究成果为地下工程支护参数优化和方案的选择开辟了一个新的方向.

  11. Displacement Monitoring and Analysis Platform for Highway Tunnel Surrounding Rock Based on Internet Technology%基于互联网技术的公路隧道围岩常规位移监测分析平台

    Institute of Scientific and Technical Information of China (English)

    姜锡宸; 孟陆波; 李天斌; 刘家民

    2015-01-01

    Informationization of tunnel construction management is a trend nowadays.A displacement monitoring and analysis platform for highway tunnel surrounding rocks based on internet technology is developed by using PHP (Personal Home Page)programming language and in conjunction with Mysql data storage function and analysis principles of the least square method and regression model,so as to meet the informationization requirement of highway tunnel monitoring.By using the mentioned platform,the recording and regression analysis of the monitoring data of the highway tunnel,the assessment of the stability of the surrounding rock and the estimation of the final displacement of the surrounding rock and the secondary lining time can be realized.Furthermore,by using the mentioned platform,the technical staffs that are not at the site can obtain the monitoring data and analysis results of the tunnel so that they can make timely adjustment on the lining structure.%信息化是当前隧道施工管理的必然趋势,针对公路隧道监控量测信息化建设要求,采用 PHP 编程语言,结合 Mysql 的数据存储功能、最小二乘法及回归模型的分析原理,研发基于互联网技术的公路隧道围岩常规位移监测分析平台。该平台实现了在网络上对公路隧道监测断面数据的录入存储、回归分析、围岩稳定性判别及隧道围岩最终位移变形量与二次衬砌时间预估等功能。通过网络访问该平台,可使不在现场的参建人员及时掌握隧道监测数据及分析结果,可为支护结构的调整和变更提供更有效率的依据,进而提高公路隧道的管理效率。

  12. 基于广义粒子动力学的巷道围岩弹塑性分析%Elastoplastic analysis of surrounding rock masses around tunnels using general particle dynamics method

    Institute of Scientific and Technical Information of China (English)

    赵毅; 周小平; 钱七虎

    2016-01-01

    提出了广义粒子动力学数值分析方法,该方法是一种无网格数值分析方法,可以考虑关联塑性流动法则和非关联塑性流动法则对岩石材料塑性变形的影响。将广义粒子动力学数值分析方法应用于巷道围岩的弹塑性分析,确定了巷道围岩的应力场、位移场和塑性区。该数值模拟结果与有限元结果吻合较好,表明将考虑岩石材料剪胀特性的弹塑性本构理论引入到广义粒子动力学数值分析方法,不失为模拟岩石类材料弹塑性破坏的一种有效数值手段,研究结果为更好地理解岩石材料的屈服破坏过程提供重要的参考。%The novel meshless numerical method, which is known as general particle dynamics (GPD) method, is proposed. The non-associated flow law and the associated flow law can be employed to analyze the plastic deformation of the surrounding rock masses around tunnels using the GPD method. The stability of the surrounding rock masses around tunnels are also determined using the GPD method as well as the stress fields, displacement fields and plastic zone. The numerical results by the proposed method are in good agreement with the FEM results. It is proved that the GPD method is efficient to predict the elastic-plastic properties of the surrounding rock masses around tunnels.

  13. The Attenuation Law of Vibrations in Highway Tunnel Surrounding Rocks Caused by Smooth Blasting%公路隧道光面爆破围岩振动衰减规律

    Institute of Scientific and Technical Information of China (English)

    陆瑜; 李超

    2014-01-01

    为了获得隧道围岩在爆破荷载作用下的振动效应,运用有限元软件 ADINA 建立隧道计算模型,通过加载简化的三角形等效爆破荷载,模拟了青山隧道Ⅲ类围岩段在单循环进尺为2 m 、2.5 m 和3 m 三种情况下的爆破振动效应,得到了隧道拱顶、拱脚和边墙部位围岩的振动衰减规律。计算结果表明:围岩质点的峰值振速随着与开挖轮廓面距离的增大先急剧衰减后平缓衰减,开挖进尺越大,围岩受到的扰动越大。最后通过满足规范的安全质点振动速度来确定三种开挖进尺条件下的最大段药量大小,为类似隧道钻爆设计的合理性提供参考。%In order to obtain vibration effect of tunnel surrounding rocks under blasting load ,the tunnel calculation model was established by using the finite element software ADINA .Under simplified triangle equivalent blast loading ,the blast-ing vibration effect of class Ⅲ surrounding rock section of Qingshan tunnel with the single footage driving cycle being 2 m ,2 .5 m and 3 m was simulated .And then the vibration attenuation law for adjacent rocks at the arch vault ,spring and side walls of the tunnel under blasting load action was obtained .As shown by the calculation results ,the peak particle velocity showed abrupt attenuation first and then flat attenuation with the increase of excavation profile distance .The larg-er the footage ,the more vibrations the rock was subject to .Lastly ,safety particle vibration velocity in compliance with specifications was used to determine the maximum charge under these three excavation footage conditions .This study will provide reference to the rationality of blasting and drilling design of similar tunnels .

  14. 渗水泥化巷道锚杆支护围岩稳定性控制研究%Surrounding rock stability control with bolt support in seepage argillaceous roadway

    Institute of Scientific and Technical Information of China (English)

    王成; 韩亚峰; 张念超; 钱德雨

    2014-01-01

    Because of the poor reliability of bolt support in seepage argillaceous roadway, roof fall accidents occur frequently. In this paper, typical rock disintegration and weathering experiments, field tests of roadway deformation rules and bolt anchorage performance in water seepage roadways were studied. The results indicate that once the clay mineral in roadway surrounding rock meet water, the rock will become sliming and weathering embrittlement, which will cause a sharply decrease in the load bearing capability. In addition, the deformation of seepage argillaceous roadway has obvious stage cha-racteristics, which shows whole process of “decelerated deformation-weak argillization-accelerated deformation-strong argillization-instability”. Thus, the key point of stability control in such roadway is to control the argillaceous process effectively. Meanwhile, the surrounding rock control technology in seepage argillaceous roadway was proposed, which is composed of “there-high” bolt enhancement technology and lag grouting strengthening technology. Moreover, the best grouting time which is 10 to 30 days after the roadway drivage was given, engineering practice was then conducted, and good results were obtained.%渗水泥化巷道锚杆支护可靠性差,导致此类巷道冒顶事故频发。通过典型岩样崩解和风化实验、渗水泥质巷道变形规律及锚杆锚固性能实测开展研究。结果表明:煤系地层含有黏土类矿物,使得巷道围岩遇水崩解,发生泥化现象,且风化脆裂,导致自身承载力急剧降低;渗水泥质巷道围岩变形破坏具有明显阶段性,演绎“减速变形-弱泥化-加速变形-强泥化-失稳”全过程,有效控制泥化进程是该类巷道稳定性控制的关键;提出了渗水泥化巷道围岩的控制技术,即新型“三高”锚杆强化控制技术和滞后注浆加固技术,给出巷道掘进后10~30 d最佳注浆时机,开展了典型的工程实践

  15. Thermal, Mechanical and Thermo-Mechanical Assessment of the Rock Mass Surrounding SKB's Prototype Repository at Äspö HRL

    Science.gov (United States)

    Lönnqvist, Margareta; Hökmark, Harald

    2016-04-01

    The Prototype Repository (PR) was a field test of six, electrically heated, full-scale waste containers resembling the key component of a KBS-3 nuclear waste repository. The design and heat load was similar to the proposed repository at Forsmark, Sweden. In this paper, the thermal, mechanical and thermo-mechanical response of the PR host rock to excavation and to the subsequent heating is assessed. The assessment is carried out using three-dimensional models (numerical and analytical) in combination with monitoring data and visual observations from the excavations. Certain measurements and observations agree well with results from the models. These include temperature measurements during the heating phase. Additional measurements include patterns of low-magnitude acoustic emission events around the deposition holes tracked during the excavation. The spatial distribution of these events coincide with regions of modelled high compressive stresses. Models with a simple fracture network, consisting of planar disks with laboratory-scale properties, appear to give upper bound estimates of the stress disturbances caused by a real fracture network. The magnitude of the modelled stresses around the deposition hole is typically below the spalling strength. The lack of any significant or systematic occurrence of spalling in the deposition hole walls supports the modelling results. Several instruments installed at different positions to monitor stress change, strain and deformation malfunctioned during the nearly 8-year-long monitoring period. Despite this, there is ample evidence to support the overall conclusion that the modelling results and observations are in sufficient agreement to strengthen the confidence in the modelling approach.

  16. Tunnel large deformation of surrounding rock research based on radar information and monitoring warning%基于雷达信息与监测预警的隧道围岩大变形研究

    Institute of Scientific and Technical Information of China (English)

    董辉; 陈家博; 杨珺博; 侯俊敏

    2012-01-01

    针对公路隧道溶洞和孔洞的存在给围岩的稳定性控制带来不同程度的困难且围岩大变形极易发生而造成工程事故,采用探地雷达超前探测和监控量测,归纳分析隧道围岩大变形的异常特征,并进一步通过贵州省晴兴高速公路登攀隧道出口围岩大变形预警的工程实例进行验算,获得黔西南区强风化多孔玄武岩及下伏灰岩溶洞雷达图像特征:有充填物时反射波振幅在洞腔范围内衰减强烈,强弱相间;无充填物时反射波基本无衰减,存在中断、起伏和错动现象。围岩大变形监测以拱顶下沉为主,21d最大累计沉降值达到89.40mm,变形速率最大波动范围为14.66~0.64mm/d。应用此结论可以在围岩出现大变形时及时预警并采取控制措施,更好地为后续工程服务。%Aiming at the existence of caves and holes in high.way tunnel will cause difficulty for surrounding rock' s stability in varying degrees and it is prone to result in large deformation of surrounding rock, cause accident, the paper summarizes and analyzes the abnormal characteristics of tunnel large deformation of surrounding rock by advanced detection of ground penetrating radar and monitoring. Meanwhile, with the project of Qingxing highway Dengpan tunnel exit surrounding rock' s large deformation and warning, we obtain radar images' characteristics to highly weathered porous basalt and underlying limestone caves in southwest of Guizhou province: reflection amplitude attenuates strongly and strength of the white in filling caves and there is almost no attenuation but with the phenomenon of disruption, ups and downs and dislocation in inanition. On the other side, when large deformation of surrounding rock is mainly vault sedimentation, its maximum cumulative settlement is 89.40mm during 21 days and deformation rate fluctuates from 14.66mm to 0.64mm per day. With the conclusion, it should be warned and take control measures timely

  17. The anisotropic properties analysis of the rock mass surrounding the roadway' s in seepage and stress field%巷道围岩渗流场和应力场各向异性特征分析及应用

    Institute of Scientific and Technical Information of China (English)

    杨天鸿; 师文豪; 于庆磊; 李海洲; 郑超; 夏冬

    2012-01-01

    依托范各庄煤矿12号煤层底板的砂岩巷道工程实际,应用岩体结构面非接触测量(Sha-peMetriX3D)系统,对巷道开挖面进行岩体结构面数字摄影测量及识别,得到岩体结构面的几何分布参数;在此基础上,利用Mont-Carlo方法生成裂隙网络,分别利用离散介质渗流方法和几何损伤理论计算岩体的渗透张量和弹性张量,研究了岩体力学参数各向异性和尺度效应;最后,建立了平面应变情况下的巷道围岩各向异性渗流力学模型,采用COMSOL Multiphysics多物理场分析软件,计算得到了可以考虑节理分布特征的巷道围岩应力场和渗流场,并讨论了岩体力学性质主方向对围岩应力场、渗流场及损伤区的影响。研究表明,岩体的各向异性对数值模拟结果影响显著,等效连续介质的各向异性模型能考虑岩体结构面的影响,更符合工程实际。%Depending on the sandstone roadway on the floor of No. 12 coal seam in Fangezhuang Coal Mine,a 3D con- tact-free measuring system, named as ShapeMetriX3D, was employed to capture discontinuities on the face of the road- way and obtain statistical parameters for each set of discontinuities. And then, fracture network was generated by Mont- Carlo method. Permeability tensor of rock mass was calculated by the discrete medium seepage method, and the elastic- ity tensor of rock mass was obtained by geometrical damage theory. Then, scale effect and anisotropic behaviors of rock mass were studied. Finally, an anisotropic percolation mechanics model of surrounding rock mass of the roadway was built under plane strain condition. Using COMSOL multiphysics code, the stress field and seepage field surrounding the roadway were obtained, which can take into account the influence of orientation of discontinuities. Furthermore, the in- fluences of principal direction of rock mass properties on stress, seepage and damage zone were discussed. The results show that the

  18. Cause Analysis on the Phase Transition of the Tectonic Facies of the Metamorphic Rock Series in the Wutai Mountain-Heng Mountain Areas%五台山—恒山地区变质岩系构造相相变成因分析

    Institute of Scientific and Technical Information of China (English)

    郭景林; 米广尧; 范林森

    2011-01-01

    Areas in the Wutai mountain-Heng mountain are considered to be one of the most popular places for the tectonic facies researches owing to the various structural characters at different crust levels. In the present study, the structural characteristics of the Early Precambrian were analyzed. On the basis of the different geological characters of fold, fracture, pudding of the rock and syntectonic crystallization, some references were provided for analyzing the tectonic facies and the structural phase transition in the areas. Combined with the information of the geological characteristics, petrology, deformation,and metamorphic characteristics,and isotope chronology of the geological unit,the preliminary studies were conducted on the tectonic environment of the the Early Precambrian in the areas, and discussions were made on the crustal evolution andthe cause of the tectonic facies phase transition. The phenomena occurring commonly in the Metamorphic rock areas was explained reasonably,that is, the alienation between the same rocks and the convergence between the different rocks,or the same thing with different phases and the same phase with different faces. All of these provided the new research thinking and the working methods for the metamorphic rock areas.The high-grade regions of the Hornblende granulite phase in the Heng mountain areas represent the mid-lower crust's transitional zone and detachment zone. Their and it's typical structural styles, material composition, metamorphism and the effects of the deep melting have important significance on the researches of the mid-lower crust's rheological behavior, crustal differentiation and the cracking events for early continent.%五台山—恒山地区出露有不同层次的地壳,是研究构造相最理想的地区之一.作者对该区早前寒武纪构造特征进行了分析.根据不同层次的褶皱、断裂、布丁化岩石及同构造分泌结晶脉的宏观地质特征和与其相关的微组构特

  19. Coupled gas flow/solid dynamics model for predicting the formation of fracture patterns in gas well simulation experiments. [Propellant mixture used instead of explosives to fracture rock surrounding borehole

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, L.M.; Swenson, D.V.; Cooper, P.W.

    1984-07-01

    A two-dimensional finite element model for predicting fracture patterns obtained in high energy gas fracture experiments is presented. In these experiments, a mixture of propellants is used instead of explosives to fracture the rock surrounding the borehole. The propellant mixture is chosen to tailor the pressure pulse so that multiple fractures emanate from the borehole. The model allows the fracture pattern and pressure pulse to be calculated for different combinations of propellant mixture, in situ stress conditions, and rock properties. The model calculates the amount of gas generated by the burning propellants using a burn rate given by a power law in pressure. By assuming that the gas behaves as a perfect gas and that the flow down the fractures is isothermal, the loss of gas from the borehole due to flow down the cracks is accounted for. The flow of gas down the cracks is included in an approximate manner by assuming self-similar pressure profiles along the fractures. Numerical examples are presented and compared to three different full-scale experiments. Results show a good correlation with the experimental data over a wide variety of test parameters. 9 reference, 10 figures, 3 tables.

  20. MetPetDB: New Directions for Metamorphic Studies

    Science.gov (United States)

    Spear, F. S.; Adali, S.; Szymanski, B. K.; Hallett, B. K.; Waters, A. J.; Linder, Z. J.; Fyffe, M. E.; Goldfarb, D.; Barlett, K.

    2008-12-01

    It is estimated that less than 1% of the data collected on metamorphic rocks is published, and MetPetDB (database for metamorphic geochemistry) is being developed and populated to preserve these data and to foster new and innovative directions for scientific research and education. The data model is based on a sample of metamorphic rock and includes information about location, rock type, mineral assemblage, fabric, plus images of all types and mineral composition data. Mineral analyses are linked to locations on appropriate images so the spatial integrity of the data is preserved. Tools will be available for mineral recalculation, plotting, and thermobarometric applications. Derivative data such as peak P-T conditions, metamorphic P-T path, and cooling rate will also be stored. The database will be searchable based on any number of data fields, permitting rapid location of samples that can be used to test hypotheses and discover new relationships. For example: A student is designing a thesis project and MetPetDB will be a first resource to determine the types of rocks present in a region, the work that has been done on them, and links to the published findings. The Fe/Mg zoning in migmatitic garnets has been used to infer cooling rates. What is the range of cooling rates recorded by migmatitic garnets, and is there a correlation between peak metamorphic temperature and cooling rate? Is it possible that melting triggers rapid thrusting that causes the rapid cooling? A search on: rock type = migmatite plus Fe and Mg X-ray maps of garnet would reveal all samples that could be used in this study. A new geobarometer based on a specific mineral assemblage is proposed that permits pressures to be estimated to within 50 MPa. A search of the database for all samples with this assemblage plus analyses of the necessary minerals would provide a set of samples to which this new barometer can be applied. Recalculating pressures and temperatures for an entire region using new

  1. Geochemical Characteristics of the Basic and Magnesian Metamorphic Rocks in Longyou Area,Zhejiang Province and Their Tectonic Setting%浙江龙游地区基性及镁质变质岩的地球化学特征及其构造环境

    Institute of Scientific and Technical Information of China (English)

    董学发; 唐增才; 陈忠大; 余盛强; 赵旭东; 周宗尧; 吴小勇; 肖庆辉

    2016-01-01

    位于扬子陆块东南缘与华夏地块之间的龙游地区出露一套中深变质岩系,其对华南前泥盆纪地质构造格局问题的解释至关重要,但目前人们对其形成时的大地构造背景了解不多。通过对其中的基性及镁质变质岩进行系统的岩石地球化学研究,可将这些岩石可以分为3种类型:“N-MORB”型、“T-MORB”型和“E-MORB”型。其中“N-MORB”型岩石原岩可能主要形成于洋内弧环境,“T-MORB”型岩石原岩主要形成于过渡型大洋中脊及火山弧环境,而“E-MORB”型岩石的原岩则主要形成于富集型大洋中脊、陆缘弧和板内环境。岩石成岩环境的多样性表明龙游地区的变质岩实属一套构造混杂岩,形成过程与古大洋地壳的俯冲、消减有关,这也为龙游榴闪岩的产出、定位提供了合理的解释。%A medium and high grade metamorphic rock series is exposed in Longyou area located in the southeast margin of Yan-gtze block and Cathaysia block,which is important for the interpretation of South China Predevonian tectonic pattern.But the tectonic setting of its formation remains unknown presently.It is found out these rocks can be divided into three types:“N-MORB”,“T-MORB”and “E-MORB”type rock by a basic and magnesian metamorphic rock geochemical study in this paper The protoliths of the “N-MORB”is mainly formed in the intra-oceanic arc,the “T-MORB”is mainly formed in the transition of mid-oceanic ridge and the volcanic arc,and the “E-MORB”type rock is formed in the enrichment of mid-oceanic ridge,epiconti-nental arc and intraplate environment.Rock diagenesis environment diversity shows that the metamorphic rock of Longyou area is a tectonic mélange and its forming process is related with the ancient oceanic crust subduction,which also provides a reasona-ble explanation for the output,positioning of the pomegranate amphibolite in Longyou area.

  2. 砂性地层中盾构隧道掘进围岩变形特性%Deformation characteristics of the shield tunnelling surrounding rock in sandy stratum

    Institute of Scientific and Technical Information of China (English)

    张业炜; 杨新安

    2011-01-01

    Based on the geological conditions and construction data in the sandy stratum of Shiziyang tunnel, the numerical model was established. By the comparison on the displacement of monitoring points in different sections during the excavation, it concluded that; the surrounding rock of the antecedence tunnel shrink to the centre, and the deformation of the top & bottom rock is obviously larger than that of the two sides. The antecedence tunnel has applied external force on the later tunnel; however, it has applied little longitudinal force. By the comparison on the two conditions with seepage and without seepage, it concluded that the early effects of the seepage are limited, but the deformation of the surrounding rock is aggravated to a large extent eventually. The method was put forward to determine the cumulative effects and cumulative effect curves of the soil disturbance in front of the excavation face, and the disturbance scope and extent were determined by the cumulative effects curves. Finally two factors affect the soil displacement rate were obtained, there were the distance between the soil and the excavation face and shield thrust.%以狮子洋隧道砂性地层段地质条件和施工资料为基础,建立有限差分数值计算模型.通过比较不同断面监测点随开挖进程的位移值,结果表明:先掘隧道围岩向中心收缩,上下部围岩变形明显大于两侧;后掘隧道对先掘隧道有横向外挤的作用,但对纵向几乎没有影响.对有、无渗流作用的2种工况的比较分析说明,起初渗流对围岩变形影响不大,但最终加剧了围岩的变形程度.提出了开挖面前方土体扰动的累积效应和累积效应曲线的确定方法,通过该曲线可确定土体扰动范围和程度,经过理论分析,认为影响土体位移速率的2个因素是土体与开挖面间距和盾构推力.

  3. 基于Hoek-Brown准则的隧洞围岩变形研究%Study of deformations of surrounding rock of tunnel based on Hoek-Brown criterion

    Institute of Scientific and Technical Information of China (English)

    温森; 杨圣奇

    2011-01-01

    In many practical situations, for instance, in jointed rock mass, linear M-C yield criterion may not be justified and a nonlinear Hoek-Brown yield criterion would be more appropriate, so it is necessary to attempt to calculate deformation of tunnel by the criterion.The surrounding rock is divided into three zones: elastic zone, strain softening zone and plastic flow zone.Theoretical derivation on deformation is carried out by Hoek-Brown criterion and non-associated flow rule.Parameters of surrounding rock in strain softening zone are variable and they depend on the plastic deformation of this zone, so it's difficult to derive the analytical solution for stress in this zone.Runge-Kutta method is used to carry out numerical calculation and the radiuses of strain softening zone and plastic flow zone are calculated.Finally, the deformations of tunnel are calculated.It is demonstrated by an example that the results calculated by the method in this paper and Carranza-Torres's method are almost the same when strain softening zone and plastic flow zone are not be considered.Furthermore, it is demonstrated by the other example that dilation angle affects deformation more severely when in-situ stress becomes greater.%由于在许多实际条件下,比如节理岩体中,线性的M-C准则不太适用,非线性的Hoek-Brown比较适用,因此,可以尝试使用这一非线性屈服准则对洞室变形进行研究.研究隧洞变形时,将围岩分为弹性区、应变软化区、塑性流动区.采用Hoek-Brown准则和非关联流动法则对洞室变形进行了理论推导:软化区域围岩参数随着塑性变形增加而变化,解析法难以求得应力,采用龙格一库塔方法进行数值计算,求解得到塑性软化区和流动区半径,并最终求得洞室变形.通过算例计算表明,在不考虑软化区和流动区时,方法和Carranza-Torres计算结果相差甚小;随着原岩应力的增加,膨胀角对洞室变形的影响增大.

  4. SHRIMP Dating and Recrystallization of Metamorphic Zircons from a Granitic Gneiss in the Sulu UHP Terrane

    Institute of Scientific and Technical Information of China (English)

    LI Hongyan

    2004-01-01

    An unusual zircon SHRIMP dating result of a granitic gneiss from the Qinglongshan eclogite-gneiss roadcut section is presented in this paper. The very peculiar and complicated internal structures, as well as the very low Th/U ratios (0.01-0.08) of the zircons indicate that they were formed by metamorphic recrystallization. Strongly in contrast with previously published zircon U-Pb ages of the Dabie-Sulu UHP metamorphic rocks where protolith ages of 600-800 Ma are commonly recorded, only metamorphic age of 218+5 Ma, defined by 18 analytical spots either in rim or in core of zircons, are recorded in this granitic gneiss. This age represents the time of the complete metamorphic recrystallization overprint on primary magmatic zircons. The recrystallization was derived by the UHP metamorphism,and was strengthened by the early stage of retrograde metamorphic fluid activity.

  5. Garnet peridotites from Pohorje: Petrography, geothermobarometry and metamorphic evolution

    Directory of Open Access Journals (Sweden)

    Mirijam Vrabec

    2010-06-01

    Full Text Available Ultrahigh-pressure (UHP metamorphism has been recorded in Eo-Alpine garnet peridotites from the PohorjeMts., Slovenia, belonging to the Eastern Alps. The garnet peridotite bodies are found within serpentinized metaultrabasitesin the SE edge of Pohorje and are closely associated with UHP kyanite eclogites. These rocks belongto the Lower Central Austroalpine basement unit of the Eastern Alps, exposed in the proximity of the Periadriaticfault system.Garnet peridotites show signs of a complex four-stage metamorphic history. The protolith stage is represented bya low-P high-T assemblage of olivine + Al-rich orthopyroxene + Al-rich clinopyroxene + Cr-spinel. Due to metamorphism,primary clinopyroxene shows exsolutions of garnet, orthopyroxene, amphibole, Cr-spinel and ilmenite. TheUHP metamorphic stage is defined by the assemblage garnet + olivine + Al-poor orthopyroxene + clinopyroxene +Cr-spinel. Subsequent decompression and final retrogression stage resulted in formation of kelyphitic rims aroundgarnet and crystallization of tremolite, chlorite, serpentine and talc.Pressure and temperature estimates indicate that garnet peridotites reached the peak of metamorphism at 4 GPaand 900 °C, that is well within the UHP stability field. Garnet peridotites in the Pohorje Mountains experiencedUHP metamorphism during the Cretaceous orogeny and thus record the highest-pressure conditions of all Eo-Alpinemetamorphism in the Alps.

  6. RESEARCH ON MECHANISM OF LARGE DEFORMATION AND COUNTERMEASURES OF SURROUNDING ROCKS OF TUNNEL THROUGH COAL STRATA%穿越煤系地层隧道围岩大变形机制及处治研究

    Institute of Scientific and Technical Information of China (English)

    李生杰; 谢永利; 吴丹泽; 朱小明

    2013-01-01

    Surrounding rock of Anyuan highway tunnel through coal strata is made of carbonaceous shale,coal line and mudstone weak interlayer. The uniaxial compressive strength of the carbonaceous shale specimens are 3.9-4.8 MPa. The geostress measurement is carried out,and the results show that the maximum horizontal principal stress is 8-10 MPa,and the horizontal principal stress is dominant in the area of tunnel. Based on the on-site monitoring and numerical simulation,the characteristics of surrounding rock deformation are analyzed. The reasons for large deformation are summarized as follows:(1) The strength of surrounding rock is low and the rock swells easily;(2) The level of geostress is high as to the low strength of rockmass;(3) Water effect;(4) Improper construction. The mechanism of large deformation is discussed also. The countermeasures are proposed as follows:the tunnel face should be closed quickly after excavation,then the temporary support is set up,long bolts and grouting pipe are used to control the deformation,the arch is replaced after deformation become stable,the spacing of steel arch is reduced,and finally,invert and inner lining are applied timely. According to the measurement results,it is shown that the treatment measures are effective.%高速公路安远隧道穿越煤系地层,围岩主要由炭质页岩、煤线、泥岩夹层组成,炭质页岩试件单轴抗压强度为3.9~4.8 MPa。开展地应力测量,测量结果表明隧址区最大水平主应力为8~10 MPa,水平应力作用占主导。通过现场监测以及数值模拟分析,分析围岩大变形的特征,总结围岩大变形产生的原因,主要有:(1)围岩强度低且易膨胀;(2)相对岩体强度,地应力较高;(3)水理作用;(4)施工不当。在此基础上探讨变形机制。提出相应的处治措施:开挖后迅速封闭掌子面,设置临时支撑,施作长锚杆和注浆小导管控制变形,待变形稳定后适时进行拱圈

  7. PETROLOGY METAMORPHIC PETROLOGY

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    <正>20070226 Chen Nengsong (Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China); Liu Rong LA-ICP-MS U-Pb Zircon Dating for Felsic Granulite, Huangtuling Area, North Dabieshan: Constraints on Timing of Its Protolith and Granulite-Facies Metamorphism, and Thermal Events in Its Provenance (Journal of China University of Geosciences, ISSN1002-0705, CN42-1279/P, 16(4), 2005, p.317-323, 4 illus., 2 tables, 32 refs.) Key words: granulites, Dabie Mountains

  8. Metamorphic Testing for Cybersecurity.

    Science.gov (United States)

    Chen, Tsong Yueh; Kuo, Fei-Ching; Ma, Wenjuan; Susilo, Willy; Towey, Dave; Voas, Jeffrey; Zhou, Zhi Quan

    2016-06-01

    Testing is a major approach for the detection of software defects, including vulnerabilities in security features. This article introduces metamorphic testing (MT), a relatively new testing method, and discusses how the new perspective of MT can help to conduct negative testing as well as to alleviate the oracle problem in the testing of security-related functionality and behavior. As demonstrated by the effectiveness of MT in detecting previously unknown bugs in real-world critical applications such as compilers and code obfuscators, we conclude that software testing of security-related features should be conducted from diverse perspectives in order to achieve greater cybersecurity.

  9. 隧道石膏质围岩溶蚀及溶出特性试验研究%Experimental Research on Corrosion and Leaching Characteristics of Gypsum Rock Surrounding Tunnels

    Institute of Scientific and Technical Information of China (English)

    祝艳波; 吴银亮; 余宏明

    2016-01-01

    石膏质岩的溶蚀对隧道工程的建设及运营极为不利,研究其溶蚀机理及其影响因素,可为此类隧道的建设提供参考。宜巴高速公路部分隧道通过的地层含有石膏质岩,为了研究其溶蚀及溶出特性,利用X-衍射试验仪、自制简易溶蚀装置、离子色谱分析仪从宏观角度研究其溶蚀、溶出现象及其规律,利用环境扫描电镜从微观上观察其溶蚀机理。结果表明,研究区石膏质岩在地下水的作用下易溶蚀,溶蚀后强度性质变差,同时溶出大量的硫酸根离子于环境水中。影响石膏质岩溶蚀的因素多而复杂,动态水环境将使其溶蚀作用更强烈,并且水流流速越大,溶蚀特征越明显。弱酸性环境的水溶液也会促进溶蚀作用的进行。温度通过影响石膏质岩在水中的溶解度,从而影响其溶蚀量及溶蚀速率。石膏质岩溶蚀后会降低隧道围岩的稳定性,溶出的酸根离子对混凝土衬砌结构产生中等腐蚀,在隧道建设中应注意采取相应防治措施,避免工程病害的发生。%Since the corrosion of gypsum rock has detrimental effects on tunnel construction and operation, the cor⁃rosion mechanism and its influencing factors were studied, providing a reference for tunnel construction in these con⁃ditions. In this paper, the gypsum rock surrounding tunnels on the Yichang-Badong expressway is studied, and a se⁃ries of experiments on the corrosion and leaching characteristics of gypsum rock are carried out to macroscopically study and analyze the law of corrosion and leaching phenomena by using X-ray diffraction tester, self-made corro⁃sion equipment and ion-chromatography analyzer. Additionally, the corrosion mechanism is microscopically ob⁃served with an environmental scanning electron microscope. The research results indicate that the corrosion of gyp⁃sum rock is obvious under the action of underground water and the gypsum

  10. Study of thermo-mechano-damage coupling behavior of surrounding rock of deep tunnel%热-应力-损伤耦合作用下深埋隧洞围岩稳定性分析

    Institute of Scientific and Technical Information of China (English)

    贾善坡; 吴渤; 陈卫忠; 伍国军; 高敏; 龚俊

    2014-01-01

    以热力学和弹塑性力学理论为基础,分析岩石热-力完全耦合作用及其对力学参数和热特性参数的影响,建立了岩石热-力-损伤耦合模型及其参数演化方程,以ABAQUS软件为平台对其进行二次开发,并通过典型算例验证了岩石热-力完全耦合的重要性。然后以某深埋软岩隧洞为例,研究温度和开挖卸载共同作用下的隧洞围岩力学行为和损伤过程。计算结果表明:温度对岩石的力学性质和损伤演化过程影响显著,开挖损伤和热应力诱发的损伤对围岩热力学参数的影响不可忽略;所提出的力学模型可以有效反映围岩损伤演化、调热圈演化以及热力学参数演化,具有一定的借鉴作用。%Based on the theories of thermo-mechanics and elastoplastic mechanics, the thermo-mechanical coupling effects of rock and their effects on mechanical and thermal parameters are analyzed. By defining the evolution equations of thermo-mechanical coupling parameters under the damage of temperature effects and mechanics, a new coupled thermo-mechanical damage model with improved Mohr-Coulomb criterion is established, and the numerical implementation in ABAQUS is given. Using finite element method, a typical example was given to verify the importance of the thermo-mechanical fully coupling of rock. Taking a deep tunnel of clay stone as background, the evolution and distribution of damage, temperature and coupling parameters of the surrounding rock are simulated in detail. The results show that the temperature has a great influence on rock properties and damage evolution. Also, the damage by excavation and thermal stress has a great influence on conducting and diffusing of heat. The proposed model can depict the excavation damage, control heat circle and coupling parameters evolution, and may provide a new tool for associated applications.

  11. Rockin' around the Rock Cycle

    Science.gov (United States)

    Frack, Susan; Blanchard, Scott Alan

    2005-01-01

    In this activity students will simulate how sedimentary rocks can be changed into metamorphic rocks by intense pressure. The materials needed are two small pieces of white bread, one piece of wheat bread, and one piece of a dark bread (such as pumpernickel or dark rye) per student, two pieces of waxed paper, scissors, a ruler, and heavy books.…

  12. Site Measurement of Surrounding Rock Pressure and Analysis of Structure Stress of Large-span Bias-pressured Shallow Tunnels%大跨浅埋偏压隧道围压实测及结构受力分析

    Institute of Scientific and Technical Information of China (English)

    江磊; 侯哲生; 吴海卫

    2015-01-01

    大跨浅埋偏压隧道由于其非对称的受力条件,易引发结构变形与开裂等突出问题,近年来越来越受工程技术界的重视。以邢汾高速公路邢台段后偏梁大跨度隧道浅埋偏压段为例,通过实测围岩压力,根据荷载结构法的基本原理,利用 ANSYS 软件对其结构受力特性进行数值分析,得到结论:实测的围岩压力分布和偏压的地形之间具有较为一致的对应性,即围岩压力受地形的影响显著;二衬总应力受轴力引起的应力影响较小,主要受弯矩引起的应力控制,整个拱圈范围内最危险的部位是在受围岩压力最大的左侧拱肩处;随着二衬厚度的变化,二衬总应力在不同的部位均发生相应变化,但变化幅度均不大。相关研究结论为后续类似大跨浅埋偏压隧道的合理设计与施工提供参考依据。%The asymmetrical stress condition of the Large-span bias-pressured shallow tunnels can cause many problems easily ,such as structural deformation and cracking .These problems have attracted more and more attentions from engi-neering and technology research field in recent years .The Houpianliang large-span bias-pressured shallow tunnel in Xing-tai section of Xingtai - Fenyang highway was taken as an example to numerically analyze the mechanical characteristics of the structure by adopting ANSYS ,according to the data of site measurement of surrounding rock pressure and the princi -ple of load structure method .The results indicate that :the actual measured surrounding rock pressure is consistent with the bias terrain ,which means the surrounding rock pressure is influenced by topography significantly ;the total stress of the second lining is mainly controlled by the stress from bending moment and is less influenced by the stress from axial force ,the weakest part within the scope of the arch ring is the left spandrel which is subject to maximum pressure ;with the change of the

  13. Geochemistry of Carboniferous low metamorphic grade sedimentary and tholeiitic igneous rocks in the western Acatlán complex, southern Mexico: deposition along the active western margin of Pangea

    National Research Council Canada - National Science Library

    Ortega Obregón, Carlos; Duncan Keppie, J; Brendan Murphy, J

    2010-01-01

    Low grade metasedimentary rocks in the western Acatlán complex (Olinalá area) of southern Mexico occur in two units termed here the Progreso and Zumpango units of Lower and middle Carboniferous ages, respectively...

  14. Elastic-plastic analytical solutions for surrounding rocks of tunnels and its engineering applications%巷道围岩弹塑性解析解及工程应用

    Institute of Scientific and Technical Information of China (English)

    曾开华; 鞠海燕; 盛国君; 张常光

    2011-01-01

    Based on the unified strength theory and a non-associated flow rule, the elastic-plastic analytical solutions of stress and displacement for surrounding rocks of tunnels were presented. The effects of intermediate principal stress,elastic strains in the plastic zone and dilatancy properties were taken into account in the analytical solutions. The resuits show that the influences of intermediate principal stress and dilatancy properties on the ground reaction curve and support pressure are significant. The strength potentials of rock mass are better achieved due to considering the intermediate principal stress effect. The tunnel design with ignoring volume changes in the plastic zone is in danger, in that the corresponding support pressure is smaller. The effect of dilatancy is important for the tunnel support design.%基于统一强度理论和非关联流动法则,合理考虑中间主应力、围岩塑性区弹性应变和剪胀特性等影响,建立了巷道围岩弹塑性应力和位移解析解.研究结果表明:中间主应力和围岩剪胀特性对围岩特征曲线和支护压力的影响显著,考虑中间主应力的影响能充分发挥围岩的强度潜能;不考虑塑性区体积变化所得支护压力较小,设计偏危险;巷道支护设计应考虑围岩剪胀特性的重要影响.

  15. Research on Impact on Plastic Zone of Roadway Surrounding Rock Based on Different Yield Criteria%不同屈服条件对巷道围岩塑性区的影响研究

    Institute of Scientific and Technical Information of China (English)

    王洪涛; 尤春安; 王绪勇

    2011-01-01

    基于Drucker-Prager 准则,推导了巷道围岩塑性区的解析解,以某工程为例分析比较了基于不同屈服准则的巷道围岩塑性区的解答,并结合数值软件分析的计算结果,探究了不同屈服条件对巷道围岩塑性区的影响规律.结果表明,Drucker-Prager系列准则考虑了中间主应力的影响,计算结果更符合实际,外交点圆DP1准则用于工程设计计算稍显危险,内切圆DP5准则用于工程设计计算偏于安全,而MC等面积圆DP3准则与MC准则计算结果较接近,为巷道围岩支护设计计算屈服准则的选取与应用提供了依据.%The analytic solution of plastic zone of roadway surrounding rock is deduced from the Drucker-Prager criterion. Taking a practical project for an example, the solutions are compared and analyzed in terms of the different yield criteria. Then, combination of results with numerical analysis software, the impact rules of plastic zone of roadway surrounding rock is studied in this paper. The results show that the it is more realistic for considering the influence of intermediate principal stress in DP series criteria; the result with DP1 criterion is a little dangerous in project design, DP5 criterion is the most conservative and a little safe in project design; while the result with MC criterion is close to it under its equivalent area circle criterion. Thus, it provides basis for selection and application of yield criteria in supporting design of roadway.

  16. 充填采煤面收作眼围岩变形控制技术研究%Study on surrounding rock deformation control of finishing cut in backfilling mining face

    Institute of Scientific and Technical Information of China (English)

    李猛; 张吉雄; 巨峰; 刘世伟; 曹远威

    2016-01-01

    To solve support dismantling problems caused by big cross-section finishing cut and to con-trol strata movement in solid backfilling mining face,this paper has adopted the theoretical analysis and FLAC3D numerical simulation method to study laws of surrounding rock deformation and failure mechanism of finishing cut. Then the comprehensive support technology of anchor (rope) mesh rein-forcement, temporary support of“#” type wooden cogs filled with grouting and permanent support of finishing cut grouting have been put forward. In addition,the supporting parameters of concrete pier consisting of wooden cogs has been optimized. The results have shown that when the reasonable spac-ing of concrete pier is 2 000 mm, the pier bearing capacity can satisfy the requirement of temporary support. The technology has been applied in Yangzhuang coal mine of Huaibei Coal Mining Group, and the accumulated sink value about 80 m above the working face has been only 60 mm, which has indi-cated that surrounding rock deformation control of finishing cut is well controlled.%为解决充填采煤面收作眼断面大、难支护及撤架困难等难题,采用理论分析和FLAC3D数值模拟方法研究了收作眼围岩变形破坏规律,提出了滑架通道锚(索)网加强支护、“井”字型木垛封闭灌浆的临时支护和收作眼空间注浆永久支护相结合的围岩控制技术方法,优化设计了“井”字型木垛形成的混凝土墩柱支护参数。结果表明:混凝土墩柱间排距均为2000 mm时,墩柱承载能力可满足临时支护的要求。该技术在淮北矿业集团杨庄煤矿进行了应用,通过监测工作面上方垂距约为80 m的巷道变形,其巷道累积下沉量仅为60 mm,表明收作眼围岩变形控制效果显著。

  17. Origin of eclogite-bearing, domed, layered metamorphic complexes ("core complexes") in the D'entrecasteaux Islands, Papua New Guinea

    Science.gov (United States)

    Davies, Hugh L.; Warren, R. G.

    1988-02-01

    Compositionally layered metamorphic rocks of the D'Entrecasteaux Islands, Papua New Guinea, are folded into domes and antiforms bounded by faults parallel to metamorphic layering and foliation. The structures are broadly similar to the metamorphic "core complexes" of western North America. Lenses of ultramafic rock lie on the bounding faults, and the same faults have served as loci for Quaternary andesitic volcanic activity. Metamorphic grade in the northern islands (Goodenough and Fergusson) is amphibolite facies, with pockets of eclogite (Fergusson Island only) and granulite, and is greenschist facies in the southern island (Normanby). In all three islands there is a characteristic tectonostratigraphic sequence (FMU sequence) from felsic metamorphic rocks at base, or internally, through mafic metamorphic rocks to ultramafic rocks at top, or externally. The association of metamorphic and ultramafic rocks apparently developed in a north dipping Paleogene subduction system and was exhumed to upper crustal level in the Oligocene--Early Miocene, possibly by reversal of movement on faults in the former subduction system. Vigorous uplift and development of domes and antiforms in the Pliocene was triggered by westward propagation of the Woodlark Basin spreading ridge and was accompanied by rifting, rift-related magmatism, rapid erosion, and deposition of coarse sediment in the adjacent Trobriand Basin.

  18. Submarine hydrothermal metamorphism of the Del Puerto ophiolite, California.

    Science.gov (United States)

    Evarts, R.C.; Schiffman, P.

    1983-01-01

    Metamorphic zonation overprinted on the volcanic member and overlying volcanogenic sediments of the ophiolite complex increases downward in grade and is characterized by the sequential appearance with depth of zeolites, ferric pumpellyite and pistacitic epidote. Metamorphic assemblages of the plutonic member of the complex are characterized by the presence of calcic amphibole. The overprinting represents the effects of hydrothermal metamorphism resulting from the massive interaction between hot igneous rocks and convecting sea-water in a submarine environment. A thermal gradient of 100oC/km is postulated to account for the zonal recrystallization effects in the volcanic member. The diversity and sporadic distribution of mineral assemblages in the amphibole zone are considered due to the limited availability of H2O in the deeper part of the complex. Details of the zonation and representative microprobe analyses are tabulated.-M.S.

  19. Hf Isotope Composition and REE Pattern of Zircons from Early Precambrian Metamorphic Rocks in the Daqing Mountains, Inner Mongolia%内蒙古大青山地区早前寒武纪变质岩的锆石Hf同位素组成和稀土模式

    Institute of Scientific and Technical Information of China (English)

    董春艳; 刘敦一; 万渝生; 徐仲元; 王伟; 颉颃强

    2009-01-01

    This paper reports Hf isotope and REE composition of zircons from metamorphic rocks in the Daqing Mountains, Inner Mongolia. Detrital zircons from two meta - sedimentary rock samples have [n(176Hf)/n(177Hf)]c, tDM1(Hf) and tDM2(Hf) ranging from 0. 281079~0. 281502, 2548~3000 Ma and 2612 ~ 3153 Ma and from 0. 280916 ~0. 281451, 2533 ~ 2717 Ma and 2600 ~ 3404 Ma, respectively. The eHf (t) and tym (Hf) of magmatic zircon from one meta-gabbro sample range from-5. 45 -6.68 and 2319-2647 Ma, respectively. These indicate that late Neoarhcaean - early Palaeoproterozoic tectono-magmatic events occurred in the Daqing Mountains and adjacent areas, with both mantle addition and crustal recycling. Metamorphic zircon rims commonly show young tDM2 (Hf) when comparing with detrital and magmatic zircon cores, suggesting that Lu-Hf compositions of the rocks and minerals were changed during metamorphic processes. Metamorphic zircon rims are similar in REE pattern to adjacent detrital and magmatic cores, but commonly being lower in total REE content. Most of the metamorphic rims are smaller than 0. 1 in Th/U ratio, being quite different from the cores which Th/U ratios are generally higher than 0. 5. It is speculated that metamorphic fluid was high in w(176Hf)/w(177Hf) ratio and U and low in Th and REE and played an important role in metamorphic zircon formation.%本文报道了内蒙古大青山地区早前寒武纪变质岩石的锆石Hf同位素和稀土组成.两个古元古代晚期(1.9~2.1 Ga)变质碎屑沉积岩样品中碎屑锆石的[n(176Hf)/n(177Hf)]c、tDM1(Hf)和tDM2(Hf)分别为0.281079~0.281502、2548~3000 Ma、2612~3153 Ma和0.280g16~0.281451、2533~2717 Ma、2600~3404 Ma;一个古元古代早期(2.37 Ga)变质辉长岩样品中岩浆锆石的εHf(t)和tDM1(Hf)分别为1.50~6.68和2449~2647 Ma,表明大青山及邻区在新太古代晚期-古元古代早期存在强烈的构造岩浆热事件,既有地幔添加又有壳内再循环作用.三个样

  20. 深部高应力煤巷围岩变形与控制技术研究%Research on Surrounding Rock Deformation of Deep Coal Roadway under High Stress and Its Control Technology

    Institute of Scientific and Technical Information of China (English)

    翟金腾

    2012-01-01

    Using methods of theoretical analysis, physical simulation,industrial test and in - situ measurement, the deformation laws of coal roadway along gob in different depth were researched in Chensilou Coal Mine. The results showed that when the depth is up to 950 m over the deformation velocity of surrounding rock for roadway drivage along goaf increases rapidly, and the deformation of 6 m coal pillar is small er than that of 4 m coal pillar. The researched results provide a theoretical basis for the design of mining roadway support in working face.%采用理论分析、物理模拟、工业性试验与实测方法,对陈四楼煤矿沿空煤巷不同深度的变形规律进行了研究,结果表明,当采深达到950m以上时,沿采空区掘巷的围岩变形速度将会迅速增加,此时6m煤柱比4m煤柱的围岩变形要小,研究结果为工作面回采巷道支护设计等提供了理论依据。

  1. 隧道爆破开挖围岩动力损伤效应数值模拟%Numerical simulation of dynamic damage effect of surrounding rocks for tunnels by blasting excavation

    Institute of Scientific and Technical Information of China (English)

    左双英; 肖明; 续建科; 史文兵

    2011-01-01

    采用数值模拟技术预估岩体开裂深度及爆破损伤影响范围对工程设计可以起到事先指导作用,对施工安全具有重大意义,其中科学的、合理的损伤模型及迭代计算方法是关键.基于FLAC3D程序的用户自定义本构模块,将考虑累积应变和荷载作用时间的Yang-Liu率相关动力损伤模型与Mohr-Coulomb弹塑性本构进行耦合,将围岩破坏过程中的损伤特性反映在荷载增量迭代计算中,形成了弹塑性动力损伤本构模型,详细推导了损伤应力修正迭代计算方法.对一圆形隧道爆破开挖进行模拟,探讨了爆破诱发的质点振动衰减特征及围岩损伤分布规律.分析结果表明,爆破产生的质点振动速度峰值与其所造成的损伤具有很好的相关性.该爆破损伤模型及模拟方法可以为类似工程提供一定参考.%It can not only play a guiding role in engineering design in advance predicting the cracking depth and damaged range of surrounding rocks by blasting excavation in use of numerical simulation method, but also is of great significance to construction safety; in which, a scientific and reasonable damage model and iterative calculation method are most important key technique. Based on the user-defined constitutive modules of the fast Lagrangian analysis of continua in three dimensions (FLAC3D) procedure, Yang-Liu dynamic damage model dependent on strain rate considering cumulative strain and load time is embedded in Mohr-Coulomb elastoplastic model. The rock damage characteristic is reflected in the iteration calculation process of a incremental load; thus an elastoplastic dynamic damage constitutive model is formed. Subsequently, iterative format of damaged and modified stresses is derived in detail. In simulating a circular tunnel by blasting excavation, a discussion and analysis for characteristics of vibration attenuation and distribution rules of damage in surrounding rock mass induced by blasting are carried

  2. Geochronological constraints on the metamorphic sole of the Semail ophiolite in the United Arab Emirates

    Directory of Open Access Journals (Sweden)

    Nick M.W. Roberts

    2016-07-01

    Full Text Available The Semail ophiolite of Oman and the United Arab Emirates (UAE provides the best preserved large slice of oceanic lithosphere exposed on the continental crust, and offers unique opportunities to study processes of ocean crust formation, subduction initiation and obduction. Metamorphic rocks exposed in the eastern UAE have traditionally been interpreted as a metamorphic sole to the Semail ophiolite. However, there has been some debate over the possibility that the exposures contain components of older Arabian continental crust. To help answer this question, presented here are new zircon and rutile U-Pb geochronological data from various units of the metamorphic rocks. Zircon was absent in most samples. Those that yielded zircon and rutile provide dominant single age populations that are 95–93 Ma, partially overlapping with the known age of oceanic crust formation (96.5–94.5 Ma, and partially overlapping with cooling ages of the metamorphic rocks (95–90 Ma. The data are interpreted as dating high-grade metamorphism during subduction burial of the sediments into hot mantle lithosphere, and rapid cooling during their subsequent exhumation. A few discordant zircon ages, interpreted as late Neoproterozoic and younger, represent minor detrital input from the continent. No evidence is found in favour of the existence of older Arabian continental crust within the metamorphic rocks of the UAE.

  3. Permo-Carboniferous granitoids with Jurassic high temperature metamorphism in Central Pontides, Northern Turkey

    Science.gov (United States)

    Gücer, Mehmet Ali; Arslan, Mehmet; Sherlock, Sarah; Heaman, Larry M.

    2016-12-01

    In the northern part of the Central Pontides (N Turkey) there are different metamorphic rocks exposed, notably the Devrekani metamorphic rocks. Here, upper amphibolite-lower granulite facies metamorphic rocks contain predominantly paragneiss, orthogneiss and metacarbonate, and to a lesser extent, amphibolite and quartzite, with cross-cutting aplite, pegmatite and granite veins. This is the first report of these rocks and includes new data on the petrochemistry, geochronology and metamorphic evolution of the Devrekani orthogneisses from the Central Pontides. The orthogneisses show five different mineral parageneses with the characteristic mineral assemblage quartz + K-feldspar + plagioclase + biotite ± hornblende ± opaque (± ilmenite and ± magnetite), and accessory minerals (zircon, sphene and apatite). These metamorphic rocks exhibit generally granoblastic, lepidogranoblastic and nematolepidogranoblastic with locally migmatitic and relic micrographic textures. They have well-developed centimeter-spaced gneissic banding and display gneissose structure with symmetric, asymmetric and irregular folds. The petrographic features, mineralogical assemblages and weak migmatization reflect high temperature conditions. Thermometric calculations in the orthogneisses indicate metamorphic temperatures reached 744 ± 33 °C. Field relations, petrography and petrochemistry suggest that the orthogneisses have predominantly granodioritic and some granitic protoliths, that show features of I-type, medium to high-potassic calc-alkaline volcanic arc granitoids. The orthogneisses have high contents of LILEs and low contents of HFSEs with negative Nb and Ti anomalies, which are typical of subduction-related magmas. The orthogneisses also show significant LREE enrichment relative to HREE with negative Eu anomalies (EuN/Eu* = 0.33-1.07) with LaN/LuN = 6.98-20.47 values. Based on U-Pb zircon dating data, the protoliths are related to Permo-Carboniferous (316-252 Ma) magmatism. It is

  4. Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins

    Science.gov (United States)

    Zheng, Yong-Fei; Chen, Ren-Xu

    2017-09-01

    Regional metamorphism at extreme conditions refers either to Alpine-type metamorphism at low geothermal gradients of 30 °C/km. Extreme pressures refer to those above the polymorphic transition of quartz to coesite, so that ultrahigh-pressure (UHP) eclogite-facies metamorphism occurs at mantle depths of >80 km. Extreme temperatures refer to those higher than 900 °C at crustal depths of ≤80 km, so that ultrahigh-temperature (UHT) granulite-facies metamorphism occurs at medium to high pressures. While crustal subduction at the low geothermal gradients results in blueschist-eclogite facies series without arc volcanism, heating of the thinned orogenic lithosphere brings about the high geothermal gradients for amphibolite-granulite facies series with abundant magmatism. Therefore, UHP metamorphic rocks result from cold lithospheric subduction to the mantle depths, whereas UHT metamorphic rocks are produced by hot underplating of the asthenospheric mantle at the crustal depths. Active continental rifting is developed on the thinned lithosphere in response to asthenospheric upwelling, and this tectonism is suggested as a feasible mechanism for regional granulite-facies metamorphism, with the maximum temperature depending on the extent to which the mantle lithosphere is thinned prior to the rifting. While lithospheric compression is associated with subduction metamorphism in accretionary and collisional orogens, the thinned orogenic lithosphere undergoes extension due to the asthenospheric upwelling to result in orogen-parallel rifting metamorphism and magmatism. Thus, the rifting metamorphism provides a complement to the subduction metamorphism and its operation marks the asthenospheric heating of the orogenic lithosphere. Because of the partial melting and melt extraction of the lower continental crust, contemporaneous granite-migmatite-granulite associations may serve as a petrological indicator of rifting orogeny that is superimposed on precedingly accretionary and

  5. Contrasting metamorphism across Cauvery Shear Zone, south India

    Indian Academy of Sciences (India)

    Manish M John; S Balakrishnan; B K Bhadra

    2005-04-01

    The Palghat Cauvery Shear Zone (CSZ) is a major shear zone that possibly extends into different fragments of Gondwanaland. In the present study mafic granulites occurring on either side of the CSZ in Namakkal area, southern India are examined. Textural features recorded in the mafic granulites are crucial in elucidating the metamorphic history of the southern granulite terrane (SGT). In the mafic granulites occurring to the south of CSZ, evidence of garnet breaking down during near isothermal decompression (ITD) is indicated by the development of orthopyroxene + plagioclase moats in between quartz and garnet. The presence of comparatively small elongated second generation garnet embedded in pyroxenes from the mafic granulites occurring to the north of CSZ is indicative of the garnet formation via reaction between pyroxenes and plagioclase, which occurred during isobaric cooling (IBC). Rocks occurring to the south of CSZ have recorded comparatively higher temperature and pressure (849°C and 9.6 kbar) than those occurring to the north of the CSZ (731°C and 8.6 kbar) using conventional geothermobarometry. The rocks occurring to the north of CSZ have suffered more complex metamorphic histories in comparison to the southern part. Integrating the results of the present field and metamorphic studies with the earlier investigations and available geochronological data we suggest that the CSZ could represent a suture zone between two different continental blocks that underwent distinct metamorphic evolution.

  6. 大别—苏鲁区超高压(UHP)变质岩的多阶段构造折返过程%Multi-Stage Tectonic Exhumation Processes of Ultrahigh-Pressure (UHP) Metamorphic Rocks in the Dabie-Sulu Area, East-Central China

    Institute of Scientific and Technical Information of China (English)

    索书田; 钟增球; 周汉文; 张利; 游振东

    2012-01-01

    Exhumation processes of ultrahigh-pressure (UHP) metamorphic rocks, by which these deep-seated rocks were rapidly returned from mantle depths of more than 100 km within deep subduction zones into the upper crust and to the surface, are of paramount importance for the understanding of the kinematics and dynamics of convergent plate margins and continental collision belts. At least four large successive stages of the exhumation process of UHP metamorphic rocks in the Dabie-Sulu area, east-central China, mainly based on structural, petrological, geochemical data and available geochronological data, combined with previously regional polyphased deformation analyses, can be distinguished. Massive eclogites recorded the deep continental subduction/collision between the Sino-Korean and Yangtze cratons during the Triassic (~250-230 Ma). The early exhumation occurred after the peak of UHP metamorphism at conditions of up to >3. 1-4. 0 Gpa and 800±50 ℃ , which may correspond to the Dz regional deformation phase and took place at mantle depths, displaying the model of vertical ductile extrusion, within the coesite stability field. The subsequent exhumation stages, corresponding with D3, D4 and D5 regional deformation phase, respectively, and two intermediate tectono-thermal events, I. E. , the formation of the granulite/amphibolite facies symplectite or corona and the generation of extensive partial melting, occurred in crustal levels. Shear zones of an anastomosing rheological type were developed at diffterent stages and depths, indicating that the partitioning of deformation and metamorphism within the UHP metamorphic belt repeated. These imply that the exhumation of the UHP rocks is a complex tectonic process, in response to subduction/collision or extension of the continental crust, and is strongly constrained by a number of internal and external factors of the belt. In particular, fluids play important roles in the exhumation process of UHP rocks in the Dabie

  7. 榴辉岩相高压-超高压变质岩的He同位素地球化学研究现状与问题%Helium isotopic geochemistry of HP-UHP eclogite facies metamorphic rocks: a review

    Institute of Scientific and Technical Information of China (English)

    李兆丽; 李天福

    2011-01-01

    The helium isotopic composition of each sphere of the Earth has its characteristic isotopic ratios. These ratios show significant differences. Therefore, helium isotopes, as a tracer, are more sensitive than other isotopes to distinguishing crust from mantle materials. Up till now, geochemical behaviors of helium isotopes during the HP-UHP metamorphism have not been well studied, it led to the limited application of helium isotope in eclogites. Many HP-UHP eclogite belts have been discovered in China. These eclogites can be genetically classified into two types: one is associated with subduction of the continental slab, and the other is formed by the subduction of the oceanic slab. This paper reviewed the progresses therefore of HP-UHP eclogite fades metamorphic rocks well studied and some problems and future work of the application of helium isotope in eclogites are also discussed.%He同位素是区分地壳、地幔物质,研究壳-幔相互作用最灵敏的示踪剂之一,但其在高压-超高压变质作用过程中的地球化学行为目前仍不清楚,因而制约其在榴辉岩研究中的应用.中国作为高压-超高压榴辉岩带分布的重要地区,榴辉岩产出得天独厚,大洋、大陆两种俯冲成因榴辉岩均有分布.本文在归纳榴辉岩相高压-超高压变质岩研究进展的基础上,分析了He同位素示踪在榴辉岩研究中的应用现状.

  8. Restoration of the Western Himalaya:implications for metamorphic protoliths,thrust and normal faulting,and channel flow models

    Institute of Scientific and Technical Information of China (English)

    Michael P.Searle; Ben Stephenson; James Walker; Christian Walker

    2007-01-01

    @@ The Greater Himalayan Sequence(GHS)is composed of a sequence of Barrovian facies metamorphic rocks up to kyanite or sillimanite+K-feldspar grade,migrmatites,layered stromatic migmatites and leucogranite sheets.

  9. Intelligent Displacement Back Analysis of Surrounding Rock Parameters of the Mined Subway Tunnel in Changchun%长春地铁暗挖隧道围岩参数智能位移反分析

    Institute of Scientific and Technical Information of China (English)

    王志斌; 麻凤海; 张碧雪

    2015-01-01

    为了更加真实的反映岩土体整体特性主要力学参数的取值,以长春地铁某暗挖区间现场监测位移值为依据,通过敏感性分析,确定了该地区对地表变形影响最大的力学参数为弹性模量 E和内摩擦角φ,运用Madis GTS三维正算模型、BP神经网络模型组成的智能位移反分析系统对其进行了反分析。运用反分析得到的参数值进行数值模拟,将得到的监测断面位移值与实测值进行了对比,并根据断面的位移云图对隧道围岩的稳定性进行了评价,验证了反分析结果的合理性和准确性。%In order to determine the value of the main mechanical parameters that could truely reflect the global property of rock and soil ,the mining section of Changchun subway was taken as the engineering background ,and it was confirmed that the mechanical parameters with the greatest impact on the surface deformation were the elasticity modulus E and in-ternal friction angle φ,based on the sensitivity analysis of the field monitoring displacement data .And then the intelli-gent displacement back analysis system formed by the Midas GTS 3D forward solution model and BP neural network was applied for the back analysis of these parameters .The new parameters obtained from the back analysis were used in the simulation analysis ,and the displacement value was calculated and then compared with the monitoring data .According to the displacement cloud picture of the section ,the stability of the tunnel surrounding rock was evaluated ,and the rational-ity and accuracy of the back analysis result was verified .

  10. Self-induced nanofluidic transport enables crustal-scale metamorphism

    Science.gov (United States)

    Plümper, Oliver; Botan, Alexandru; Los, Catharina; Liu, Yang; Malthe-Sørenssen, Anders; Jamtveit, Bjørn

    2017-04-01

    The reaction of fluids with rocks is fundamental for Earth's dynamics as they facilitate heat/mass transfer and induce volume changes, weaknesses and instabilities in rock masses that localize deformation enabling tectonic responses to plate motion. During these fluid-rock interactions it is the ability of a rock to transmit fluid, its permeability, that controls the rates of metamorphic reactions. However, although some geological environments (e.g., sediments) are open to fluids, the majority of solid rocks (e.g., granites, elcogites, peridotites, etc.) are nearly impermeable. Surprisingly though, even in rocks that are nominally impermeable widespread fluid-rock interactions are observed leading to the question: How can fluids migrate through vast amounts of nominally impermeable rocks? Here we investigate one of the most wide-spread fluid-mediated metamorphic processes in the Earth's crust, the albitization of feldspatic rocks. We show that fluid flow and element mobilization during albitization is controlled by an interaction between grain boundary diffusion and reaction front migration through an interface-coupled dissolution-precipitation process. Using a combination of focused ion beam scanning electron microscopy (FIB-SEM)-assisted nanotomography combined with transmission electron microscopy (TEM) we show that the porosity is dictated by pore channels with a pore diameter ranging between 10 to 100 nm. Three-dimensional visualization of the feldspar pore network reveals that the pore channels must have been connected during the replacement reaction. Analysis of the pore aspect ratios suggests that a Rayleigh-Taylor-type instability associated to surface energy minimization caused the disconnection of the pore channels. Fluid transport in nanometer-sized objects with at least one characteristic dimension below 100 nm enables the occurrence of physical phenomena that are impossible at bigger length scales. Thus, on the basis of our microstructural

  11. Coupling of Oceanic and Continental Crust During Eocene Eclogite-Facies Metamorphism: Evidence From the Monte Rosa Nappe, Western Alps, Italy

    Science.gov (United States)

    Lapen, T. J.; Johnson, C. M.; Baumgartner, L. P.; Skora, S.; Mahlen, N. J.; Beard, B. L.

    2006-12-01

    Subduction of continental crust to HP-UHP metamorphic conditions requires overcoming density contrasts that are unfavorable to deep burial, whereas exhumation of these rocks can be reasonably explained through buoyancy-assisted transport in the subduction channel to more shallow depths. In the western Alps, both continental and oceanic lithosphere has been subducted to eclogite-facies metamorphic conditions. The burial and exhumation histories of these sections of lithosphere bear directly on the dynamics of subduction and the stacking of units within the subduction channel. We address the burial history of the continental crust with high precision U-Pb rutile and Lu-Hf garnet geochronology of the eclogite-facies Monte Rosa nappe (MR), western Alps, Italy. U-Pb rutile ages from quartz-carbonate-white mica-rutile veins that are hosted within eclogite and schist of the MR, Gressoney Valley, Italy, indicate that it was at eclogite-facies metamorphic conditions at 42.6 +/- 0.6 Ma. The sample area (Indren glacier, Furgg zone; Dal Piaz, 2001) consists of eclogite boudins that are surrounded by micaceous schist. Associated with the eclogite and schist are quartz-carbonate-white mica-rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist. Intrusion of the veins occurred at eclogite-facies metamorphic conditions (480-570°C, >1.3-1.4 GPa) based on textural relations, oxygen isotope thermometry, and geothermobarometry. Lu-Hf geochronology of garnet from a chloritoid-talc-garnet-phengite-quartz-calcite-pyrite - chalcopyrite bearing boudin within talc-chloritoid whiteschists of the MR, Val d'Ayas, Italy (Chopin and Monie, 1984; Pawlig, 2001) yields an age of 40.54 +/- 0.36 Ma. The talc-chloritoid whiteschists from the area record pressures and temperatures of 1.6-2.4 GPa and 500-530°C (Chopin and Monie, 1984; Le Bayon et al., 2006) indicating near UHP metamorphic conditions. Based on the age, P-T, and textural

  12. Facies metamórficas y edades relativas de las rocas del extremo oriental del Brazo Huemul, provincia de Neuquén Metamorphic facies and relative ages of rocks on the eastern part of Brazo Huemul, Neuquén province

    Directory of Open Access Journals (Sweden)

    M.F. Gargiulo

    2006-06-01

    Full Text Available El estudio de las asociaciones minerales y facies metamórficas presentes en las rocas del extremo oriental del Brazo Huemul del lago Nahuel Huapi permitió establecer la sucesión temporal de aquellas unidades cuyos afloramientos son saltuarios, principalmente debido a la exuberante cubierta vegetal que caracteriza a este sector situado en el extremo sur de la provincia de Neuquén. En el área de estudio afloran rocas de composición principalmente tonalítica, que en este trabajo se correlaciona con el batolito patagónico Subcordillerano debido a que están atravesadas por dos tipos de diques básicos. Un grupo de estos diques está caracterizado por la asociación albita - clorita - epidoto - cummingtonita/grunerita - hornblenda, que indica condiciones de metamorfismo térmico transicional entre la facies de hornfels de albita - epidoto hacia la facies de hornfels de hornblenda, metamorfismo originado por la intrusión del Batolito Patagónico Cordillerano de edad cretácica. Motivo por lo cual estos diques han sido correlacionados con la Formación Montes de Oca. Los diques básicos correspondientes al otro tipo no están hornfelizados pero muestran asociaciones de metamorfismo de muy bajo grado en facies zeolita de alta temperatura (clorita + pumpellyita + laumontita + clorita/esmectita + óxidos de hierro y/o poseen alteración propilítica, por lo cual fueron asignados a la F. Ventana. La distinción entre estos dos tipos de diques permite poner en discusión la edad relativa del cuerpo tonalítico que los hospeda, proponiéndose en este trabajo una edad relativa jurásica inferior a media para el mismo.The study of mineral assemblages and metamorphic facies in rocks exposed on the eastern margin of Brazo Huemul, Nahuel Huapi Lake, allowed the reconsideration of the temporal succession of units whose outcrops are isolated and difficult to locate due to the exuberant forest that covers the southestern part of Neuquén province. The rocks

  13. Paleoproterozoic, High-Metamorphic, Metasedimentary Units of Siberian Craton

    Institute of Scientific and Technical Information of China (English)

    Lena URMANTSEVA; Olga TURKINA

    2009-01-01

    Sensitive, high-resointion ion microprobe zircon U-Pb ages of Paleoproterozoic, high-grade,metasedimentary rocks from the south-western part of the Siberian Craton are reported. Early Precambrian, high-grade complexes, including garnet-biotite, hypersthene-biotite, and cordierite-bearing gneisses compose the Irkut terrane of the Sharyzhalgay Uplift. Protoliths of studied gneisses correspond to terrigenous sediments, ranging from greywacke to shale. The paragneiss model Nd ages of 2.4-3.1 Ga indicate Archean-to-Paleoproterozoic source provinces. Zircons from gneisses show core-rim textures in cathodoluminescence (CL) image. Round or irregular shaped cores indicate detrital origin. Structureless rims with low Th/U are metamorphic in origin. The three age groups of detrital cores are: ≥2.7, -2.3, and 1.95-2 Ga. The ages of metamorphic rims range from 1.86 to 1.85 Ga;therefore, the sediments were deposited between 1.95 and 1.86 Ga and derived from Archean and Paleoproterozoic source rocks. It should be noted that Paleoproterozoic metasedimentary rocks of the Irkut Block are not unique. High-grade metaterrigenons sediments, with model Nd ages ranging from 2.3 to 2.5 Ga, are widely distributed within the AIdan and Anabar Shields of the Siberian Craton. The same situation is observed in the North China Craton, where metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 to 2.1 Ga (Wan et al., 2006). All of these sedimentary units were subjected to Late Paleoproterozoic metamorphism. In the Siberian Craton, the Paleoproterozoic sedimentary deposits are possibly marked passive margins of the Early Precambrian crustal blocks, and their high-grade metamorphism was related to the consolidation of the Siberian Craton.

  14. 大连地下石油储备库洞室群围岩稳定性及渗流场分析%ANALYSES OF SURROUNDING ROCK STABILITY OF CAVERN GROUP AND SEEPAGE FIELD AT DALIAN UNDERGROUND OIL STORAGE

    Institute of Scientific and Technical Information of China (English)

    于崇; 李海波; 周庆生

    2012-01-01

    为分析水封式大连地下石油储备库洞室群围岩稳定性及渗流场特征,首先基于现场地应力实测结果的回归分析,利用Fish语言编写函数,反演初始地应力场.其次,采用三维离散元程序3DEC生成三维节理网络模型,反演库区初始渗流场的各向异性特征.最后,利用应力与渗流耦合模块实施开挖仿真计算,获取围岩应力场、位移场变化特征.考虑平行、垂直层理面不同材料特性,基于带有抗拉的Mohr-Coulomb强度储备型点安全系数,定量评价洞室群的稳定性.借鉴国外水封效果评价标准,分别从地下水位线和垂直水力坡降2个方面,分析渗流场变化特征.研究表明:在洞室周边平行层理面点安全系数为1.02~1.25,垂直层理面点安全系数为1.95~2.00.在补水隧道及注水孔组成的人工水幕系统作用下,建设期内地下水位下降3~5 m,地下水位距洞室顶55 m.开挖洞室附近平均垂直水力坡降大于1.0,满足设计规范及密封性要求.%Aiming at analyses of surrounding rock stability of cavern group and seepage field characteristics at Dalian water-tight underground oil storage, firstly, based on regression analysis of in-situ stress testing data, initial in-situ stress field inversion is conducted with functions defined with program language Fish. Secondly, after three-dimensional random joint networks with different sizes are generated with 3DEC. a new method of calculating the anisotropy permeability is proposed. Finally, stress field and displacement field of surrounding rocks are gained using coupled fluid and mechanical excavation calculations. Based on point safety factor, whose criterion is the Mohr-Coulomb one with the tensile strength, cavern group stability is quantitatively evaluated considering parallel and vertical bedding planes owing to different materials characteristics. Referring to ideas from abroad, seepage field is analyzed by groundwater table and vertical

  15. Thermal history of a metamorphic core complex

    Science.gov (United States)

    Dokka, R. K.; Mahaffie, M. J.; Snoke, A. W.

    1985-01-01

    Fission track (FT) thermochronology studies of lower plate rocks of the Ruby Mountains-East Humbolt Range metamorphic core complex provide important constraints on the timing an nature of major middle Tertiary extension of northeast Nevada. Rocks analyzed include several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison Pass pluton was also studied. The minerals dated include apatite, zircon, and sphene and were obtained from the same rocks that have been previously studied. FT ages are concordant and range in age from 26.4 Ma to 23.8 Ma, with all showing overlap at 1 sigma between 25.4 to 23.4 Ma. Concordancy of all FT ages from all structural levels indicates that the lower plate cooled rapidly from temperatures above approx. 285 C (assumed sphene closure temperature (2)) to below approx. 150 C (assumed apatite closure temperature) near the beginning of the Miocene. This suggests that the lower plate cooled at a rate of at least approx. 36 deg C/Ma during this event. Rapid cooling of the region is considered to reflect large-scale tectonic denudation (intracrustal thinning), the vertical complement to intense crustal extension. FT data firmly establish the upper limit on the timing of mylonitization during detachment faulting and also coincide with the age of extensive landscape disruption.

  16. Thermal effects of metamorphic reactions in a three-component slab

    DEFF Research Database (Denmark)

    Chemia, Zurab; Dolejš, David; Steinle-Neumann, Gerd

    2010-01-01

    or consumption can occur due to metamorphic reactions, including endothermic devolatilization. We investigate enthalpy budget in a subducting slab using a self-consistent thermodynamic model. Petrological model of a subducting slab consists of three layers: oceanic subducting sediment (GLOSS), oceanic basalt (OB......), and moderately serpentinized harzburgite (SHB). These layers are examined over the range of pressure-temperature conditions of interest by computing metamorphic phase diagrams and retrieving whole-rock thermodynamic properties. Our results suggest that metamorphic reactions consume a significant amount of slab...

  17. Thermal effects of metamorphic reactions in a three-component slab

    DEFF Research Database (Denmark)

    Chemia, Zurab; Dolejš, David; Steinle-Neumann, Gerd

    2010-01-01

    or consumption can occur due to metamorphic reactions, including endothermic devolatilization. We investigate enthalpy budget in a subducting slab using a self-consistent thermodynamic model. Petrological model of a subducting slab consists of three layers: oceanic subducting sediment (GLOSS), oceanic basalt (OB......), and moderately serpentinized harzburgite (SHB). These layers are examined over the range of pressure-temperature conditions of interest by computing metamorphic phase diagrams and retrieving whole-rock thermodynamic properties. Our results suggest that metamorphic reactions consume a significant amount of slab...

  18. Thermal effects of magmatic sills on coal seam metamorphism and gas occurrence

    Science.gov (United States)

    Wang, Liang; Cheng, Long-biao; Cheng, Yuan-ping; Yin, Guang-zhi; Cai, Chun-cheng; Xu, Chao; Jin, Kan

    2014-04-01

    Igneous intrusions in coal seams are found in 80 % of coal mines in the Huaibei coalfield, China, and coal and gas outburst accidents have occurred 11 times under a 120-m-thick sill in the Haizi mining field. The magma's heat had a significant controlling effect on coal seam gas occurrence. Based on theoretical analysis, experimental tests and site validation, we analyzed the temperature distribution following magma intrusion into coal measure strata and the variations in multiple physical parameters and adsorption/desorption characteristics between the underlying coal seams beneath the sill in the Haizi mining field and coal seams uninfluenced by magma intrusion in the adjacent Linhuan mining field. The research results show that the main factors controlling the temperature distribution of the magma and surrounding rocks in the cooling process include the cooling time and the thickness and initial temperature of the magmatic rock. As the distance from sill increases, the critical effective temperature and the duration of sustained high temperatures decrease. The sill in the Haizi mining field significantly promoted coal seam secondary hydrocarbon generation in the thermally affected area, which generated approximately 340 m3/t of hydrocarbon. In the magma-affected area, the metamorphic grade, micropore volume, amount of gas adsorption, initial speed of gas desorption, and amount of desorption all increase. Fluid entrapment by sills usually causes the gas pressure and gas content of the underlying coal seams to increase. As a result, the outburst risks from coal seams increases as well.

  19. Peak metamorphic temperatures from cation diffusion zoning in garnet

    DEFF Research Database (Denmark)

    Smit, Matthijs Arjen; Scherer, Erik; Mezger, Klaus

    2013-01-01

    A model that relates the characteristic diffusion length and average cooling rate to peak temperature was developed for chemical diffusion in spherical geometries on the basis of geospeedometry principles and diffusion theory. The model is quantitatively evaluated for cation diffusion profiles in...... is robust and provides a reliable means of estimating peak temperatures for different types of high-grade metamorphic rock. The tool could be of particular advantage in rocks where critical assemblages for conventional thermometry do not occur or have been replaced during retrogression....

  20. Quantifying the impact of metamorphic reactions on strain localization in the mantle

    Science.gov (United States)

    Huet, Benjamin; Yamato, Philippe

    2014-05-01

    Metamorphic reactions are most often considered as a passive record of changes in pressure, temperature and fluid conditions that rocks experience. In that way, they provide key constraints on the tectonic evolution of the crust and the mantle. However, natural examples show that metamorphism can also modify the strength of rocks and affect the strain localization in ductile shear zones. Hence, metamorphic reactions have an active role in tectonics by inducing softening and/or hardening depending on the involved reactions. Quantifying the mechanical effect of such metamorphic reactions is, therefore, a crucial task for determining both the strength distribution in the lithosphere and its evolution. However, the estimate of the effective strength of such polyphase rocks remains still an open issue. Some flow laws (determined experimentally) already exist for monophase aggregates and polyphase rocks for rheologically important materials. They provide good constraints on lithology-controlled lithospheric strength variations. Unfortunately, since the whole range of mineralogical and chemical rock compositions cannot be experimentally tested, the variations of strength due to in metamorphism reaction cannot be systematically and fully characterized. In order to tackle this issue, we here present the results of a study coupling thermodynamical and mechanical modeling that allows us to predict the mechanical impact of metamorphic reactions on the strength of the mantle. Thermodynamic modeling (using Theriak-Domino) is used for calculating the mineralogical composition of a typical peridotite as a function of pressure, temperature and water content. The calculated modes and flow laws parameters for monophase aggregates are then used as input of the Minimized Power Geometric model for predicting the polyphase aggregate strength. Our results are then used to quantify the strength evolution of the mantle as a function of pressure, temperature and water content in two

  1. Ultrahigh Pressure Metamorphic Terrane Evolution; Norwegian Caledonides

    Science.gov (United States)

    Rodda, C. I.; Koons, P. O.; Terry, M.; Robinson, P.

    2007-12-01

    Rocks in Norway's Western Gneiss Region (WGR) experienced high pressure and ultrahigh pressure (UHPM) (4GPa., 800C) peak metamorphic conditions during the Scandian orogeny at 410Ma. Thermobarometric studies of exhumed ultramafic eclogite pods from the Nordfjord, Soroyane and Nordoyane areas place tight time constraints on subduction, UHP metamorphism and exhumation, with all but the final phase of exhumation occurring in ca. 12 million years. However, few structures apparently related to the descent phase of terrane evolution were observed during field studies. Rather, ubiquitous quartz-rod lineation and pervasive minor folding indicate top-to-the-west, relatively shallow unroofing of the subducted margin as indicated in a new bedrock map of a portion of the Norwegian coast. Many of the mapped units have been redescribed, with emphasis put on those features that are of interest to the geophysical community.. To address the ambiguous kinematics of UHPM evolution, numerical models are employed in this study to consider the trajectory of crustal materials during continental collision that concentrate on the delicate balance of forces driving and resisting the subduction of buoyant continental materials as a function of kinetically-controlled equilibration.. In the WGR, past stability of coesite and rarely, of diamond, is preserved in robust mafic eclogites as inclusions within zircon and garnet grains. However, the extent of UHPM equilibration of the volumetrically dominant quartzo-feldspathic gneisses and consequently the contribution of these lithologies to the overall subduction suystemare unclear. . As such, simple equilibrium- defined strength and density parameters are insufficient to define natural model behavior. (Meaning of this next sentence escapes me. How does the following sound?) Rather, numerical solutions involving end member and intermediate states between equilibrium and non-equilibrium assemblages are explored While UHP metamorphic reactions in the

  2. Mesoproterozoic syntectonic garnet within Belt Supergroup metamorphic tectonites: Evidence of Grenville-age metamorphism and deformation along northwest Laurentia

    Science.gov (United States)

    Nesheim, T.O.; Vervoort, J.D.; McClelland, W.C.; Gilotti, J.A.; Lang, H.M.

    2012-01-01

    Northern Idaho contains Belt-Purcell Supergroup equivalent metamorphic tectonites that underwent two regional deformational and metamorphic events during the Mesoproterozoic. Garnet-bearing pelitic schists from the Snow Peak area of northern Idaho yield Lu-Hf garnet-whole rock ages of 1085??2. Ma, 1198??79. Ma, 1207??8. Ma, 1255??28. Ma, and 1314??2. Ma. Garnet from one sample, collected from the Clarkia area, was micro-drilled to obtain separate core and rim material that produced ages of 1347??10. Ma and 1102??47. Ma. The core versus rim ages from the micro-drilled sample along with the textural and spatial evidence of the other Lu-Hf garnet ages indicate two metamorphic garnet growth events at ~. 1330. Ma (M1) and ~. 1080. Ma (M2) with the intermediate ages representing mixed ages. Some garnet likely nucleated and grew M1 garnet cores that were later overgrown by younger M2 garnet rims. Most garnet throughout the Clarkia and Snow Peak areas are syntectonic with a regional penetrative deformational fabric, preserved as a strong preferred orientation of metamorphic matrix minerals (e.g., muscovite and biotite). The syntectonic garnets are interpreted to represent one regional, coeval metamorphic and deformation event at ~. 1080. Ma, which overlaps in time with the Grenville Orogeny. The older ~. 1330. Ma ages may represent an extension of the East Kootenay Orogeny described in western Canada. These deformational and metamorphic events indicate that western Laurentia (North America) was tectonically active in the Mesoproterozoic and during the assembly of the supercontinent Rodinia. ?? 2011 Elsevier B.V.

  3. Dating of Mesoproterozoic metamorphism in the Mount Isa and George Fisher Zn-Pb-Cu-Ag deposits, Australia, by paleomagnetism

    Science.gov (United States)

    Kawasaki, K.; Symons, D. T.

    2010-12-01

    The Mount Isa Zn-Pb-Cu-Ag and George Fisher Zn-Pb-Ag black-shale-hosted deposits in Queensland, Australia, are in carbonaceous and dolomitic shales of the ~1655 Ma Urquhart Formation of the Mount Isa Group that exhibit greenschist facies metamorphism. Both deposits give lead model ages of ~1655 Ma. Ar-Ar biotite and Re-Os ages for the Mount Isa copper ore are 1523±3 and 1372±4 Ma, respectively. Excluding modern hematite, paleomagnetic and rock magnetic analyses of 333 specimens (28 sites) isolate a stable characteristic remanent magnetization (ChRM) in single- and pseudosingle-domain pyrrhotite for the Zn-Pb-Ag ore specimens and in pyrrhotite and/or titanomagnetite for the Cu ore. A negative paleomagnetic fold test shows that the ChRM postdates D3 deformation of the ~1595 to 1500 Ma Isan orogeny, yielding a Mesoproterozoic paleopole at ~1505 Ma on the northern Australian apparent polar wander path. The ~1505 Ma age is similar to the ~1523 Ma Ar-Ar age and it provides a minimum age for ore genesis of both deposits, as well as the age for peak greenschist metamorphism during the Isan orogeny in the surrounding Mount Isa inlier.

  4. Petrographic (thin section) notes on selected samples from hornblende-rich metamorphic terranes in the southernmost Sierra Nevada, California

    Science.gov (United States)

    Ross, Donald Clarence

    1983-01-01

    Medium- to high-grade metamorphic rocks that are commonly hornblende-rich, and probably largely of 'oceanic' affinity, are widespread in the southernmost Sierra Nevada, California. These metamorphic rocks are largely amphibolite, mafic and felsic gneiss, granofels, and hypersthene granulite The mineral assemblages suggest that these rocks are at least in part of granulite grade, represent relatively deep crustal levels, and may be exposed parts of the root zone of the Sierra Nevada batholith. Access to the largest area of these rocks is relatively limited and for this reason petrographic data (textures and mineral content based on thin section study) are summarized here. Directions to readily accessible localities are presented, however, where the major metamorphic rock types can be examined and sampled.

  5. 新城金矿深部热环境分析及围岩温度测试%Analysis on Deep Thermal Environment and Temperature Measurement of Surrounding Rock in Xincheng Gold Mine

    Institute of Scientific and Technical Information of China (English)

    刘凯; 朱兆文; 朱万成; 刘洪磊; 侯晨

    2016-01-01

    随着开采深度的增加,新城金矿已经进入深部开采阶段,逐步面临高温热害问题。鉴于此,开展地下深部热环境分析,分析矿区主要热源及其形成机理,应用工程热力学手段量测不同开采深度下巷道风流温度、湿度以及风速等环境因素。采用深孔测量法测定不同深度的围岩温度,研究地温梯度变化规律。测试结果表明,巷道风温、水温均随着开采深度的增加而增大,主要生产中段相对湿度在80% RH以上,矿区恒温带温度为23℃,正常地温梯度为0.018℃/m,调热圈半径为17~18 m。该结果为有效控制井下作业场所的热环境状况以及热害防治研究提供了基础数据。%With the increase of mining depth,Xincheng Gold Mine has entered the stage of deep mining,and is gradually facing with the problem of high temperature stress. In this regard,an analysis of deep underground thermal environment was conducted,the main heat sources and the formation mechanism in the mining area were analyzed,environmental factors such as air temperature,humidity and wind speed of different mining depths of roadways were measured by means of Engineering Ther-modynamics. The temperature of surrounding rock in different depths was determined by Deep Hole Measurement Method and the variation regularity of geothermal gradient was studied. Test results show that the air temperature and water temperature of the roadways increase with the increasing of mining depth,the relative humidity of main mining levels are above 80% RH,the temperature of underground constant temperature zone in the mine area is 23 ℃, the normal geothermal gradient is 0. 018 ℃/m,and the radius of heat adjustment circle is 17~18 m,all these will provide basic data for the effective control of thermal environment conditions in underground workplaces and the prevention and treatment of thermal hazard.

  6. Thermal modeling of pluton emplacement and associated contact metamorphism:Parashi stock emplacement in the Serranía de Jarara (Alta Guajira, Colombia

    Directory of Open Access Journals (Sweden)

    Zuluaga C. Carlos A.

    2010-12-01

    Full Text Available

    In the northernmost portion of the Serrania de Jarara (Alta Guajira, Colombia, low - medium grade metamorphic rocks from the Etpana Metamorphic Suite were thermally affected by emplacement of a small calc-alkaline intrusion (Parashi Stock. Detailed petrographic analysis in collected rock samples across the NE and NW plutonic contacts show occurrences of textural and mineralogical changes in the country rock fabric that evidence contact metamorphism overprinting regional metamorphism of the Etpana Suite. These changes include growth of andalusite (chiastolite, calcic clinopyroxeneand amphibole porphyroblast crosscutting Sn+1 metamorphicfoliation. Hornblende-plagioclase barometry (ca. 3.1 kbar and cooling models for the stock show maximum time temperature evolution in the country rock at the interpreted depth of intrusion (ca. 11 km and help to evaluate the behavior of the country rock with the changing local geotherm.

  7. 随机介质理论下隧道围岩渐进破坏过程数值实验研究%Numerical Experiment Research on the Progressive Failure Process of the Surrounding Rock of the Tunnel under the Stochastic Medium Theory

    Institute of Scientific and Technical Information of China (English)

    商拥辉; 李航; 张波; 方前程

    2015-01-01

    The strength subtraction is introduced to safety evaluation of tunnel surrounding rock,combining with “the shallow tunnel rapid construction double small spacing tunnels,wear interchange structure under the shield tunnel and the surface of the structure containing joint,irregular fissure of mountain highway tunnel”engi-neering examples,using real damage of material analysis software RFPA -2D ,the finite element model of each strength reduction factor is set up.Viscoelastic artificial boundary is adopted to eliminate the influence of boundary conditions on the calculation precision in model,and the model achieves the mesoscopic structure unit of surround-ing rock of the mean and the defects of random distribution by means of random medium theory,it also reveals the dynamic gradual damage process of surrounding rock,the primitive phase change damage evolution mechanism and characteristics of rock mass structural plane under different working conditions,the mesoscopic damage of surround-ing rock is thought to be caused by non average of rock nonlinear material macroscopic unit,the calculation results judged in failure of tunnel surrounding rock with different step reduction in crack development trends and the num-ber of cell damage,and calculates safety factor in the sense of the safety reserve.At the same time,combining ABAQUS with RFPA -2D two different finite element models,comparatively analyzing the random medium theory and continuum theory combining strength subtraction in differences of the evaluation of surrounding rock stability.%将强度折减法引入到隧道围岩安全评价中,结合“浅埋暗挖快速施工双线小间距隧道、盾构下穿立交结构隧道和结构面含有节理、不规则裂隙的山体公路隧道”等工程实例,借助材料真实破坏分析软件 RFPA-2D,建立每个强度折减系数下的有限元模型。模型采用了黏弹性人工边界来消除边界条件对计算精度的影响,并借助随机介

  8. Cataclastic rheology of carbonate rocks

    Institute of Scientific and Technical Information of China (English)

    LU Xiancai; SUN Yan; SHU Liangshu; GU Lianxing; GUO Jichun; ZHU Wenbin

    2005-01-01

    Based on the knowledge of the shallow-level mylonitization of detrital rocks and intrusive rocks, the poorly-known cataclastic rheology of carbonate rocks is discussed comprehensively in this paper. The cases taken from eastern China are analyzed in various aspects including ductile-brittle fault zone, rock texture and structure, clastomylonite layer, leucocratic stress minerals, and frictional dynamometamorphism. It is proposed that the cataclastic flow structure represented by clastomylonite texture is a cooling pattern of flow assemblage characterized by cooling metamorphism, cooling mylonite and cooling stress minerals. Such a pattern is formed generally in mildly reducing physicochemical environments, and is commonly related to regional tectonism and mesothermal and epithermal mineralization.

  9. Metamorphic P-T-t path retrieved from metapelites in the southeastern Taihua metamorphic complex, and the Paleoproterozoic tectonic evolution of the southern North China Craton

    Science.gov (United States)

    Lu, Jun-Sheng; Zhai, Ming-Guo; Lu, Lin-Sheng; Wang, Hao Y. C.; Chen, Hong-Xu; Peng, Tao; Wu, Chun-Ming; Zhao, Tai-Ping

    2017-02-01

    The Taihua metamorphic complex in the southern part of the North China Craton is composed of tonalite-trondhjemite-granodiorite (TTG) gneisses, amphibolites, metapelitic gneisses, marbles, quartzites, and banded iron formations (BIFs). The protoliths of the complex have ages ranging from ∼2.1 to ∼2.9 Ga and was metamorphosed under the upper amphibolite to granulite facies conditions with NWW-SEE-striking gneissosity. Metapelitites from the Wugang area have three stages of metamorphic mineral assemblages. The prograde metamorphic mineral assemblage (M1) includes biotite + plagioclase + quartz + ilmenite preserved as inclusions in garnet porphyroblasts. The peak mineral assemblage (M2) consists of garnet porphyroblasts and matrix minerals of sillimanite + biotite + plagioclase + quartz + K-feldspar + ilmenite + rutile + pyrite. The retrograde mineral assemblage (M3), biotite + plagioclase + quartz, occurs as symplectic assemblages surrounding embayed garnet porphyroblasts. Garnet porphyroblasts are chemically zoned. Pseudosection calculated in the NCKFMASHTO model system suggests that mantles of garnet porphyroblasts define high-pressure granulites facies P-T conditions of 12.2 kbar and 830 °C, whereas garnet rims record P-T conditions of 10.2 kbar and 840 °C. Integrating the prograde mineral assemblages, zoning of garnet porphyroblasts with symplectic assemblages, a clockwise metamorphic P-T path can be retrieved. High resolution SIMS U-Pb dating and LA-ICP-MS trace element measurements of the metamorphic zircons demonstrate that metapelites in Wugang possibly record the peak or near peak metamorphic ages of ∼1.92 Ga. Furthermore, 40Ar/39Ar dating of biotite in metapelites suggests that the cooling of the Taihua complex may have lasted until ∼1.83 Ga. Therefore, a long-lived Palaeoproterozoic metamorphic event may define a slow exhumation process. Field relationship and new metamorphic data for the Taihua metamorphic complex does not support the previous

  10. Linking monazite geochronology with fluid infiltration and metamorphic histories: Nature and experiment

    Science.gov (United States)

    Shazia, J. R.; Harlov, D. E.; Suzuki, K.; Kim, S. W.; Girish-Kumar, M.; Hayasaka, Y.; Ishwar-Kumar, C.; Windley, B. F.; Sajeev, K.

    2015-11-01

    Migmatised metapelites from the Kodaikanal region, central Madurai Block, southern India have undergone ultrahigh-temperature metamorphism (950-1000 °C; 7-8 kbar). In-situ electron microprobe Th-U-Pb isochron (CHIME) dating of monazites in a leucosome and surrounding silica-saturated and silica-poor restites from the same outcrop indicates three principal ages that can be linked to the evolutionary history of these rocks. Monazite grains from the silica-saturated restite have well-defined, inherited cores with thick rims that yield an age of ca. 1684 Ma. This either dates the metamorphism of the original metapelite or is a detrital age of inherited monazite. Monazite grains from the silica-poor restite, thick rims from the silica-saturated restite, and monazite cores from the leucosome have ages ranging from 520 to 540 Ma suggesting a mean age of 530 Ma within the error bars. In the leucosome the altered rim of the monazite gives an age of ca. 502 Ma. Alteration takes the form of Th-depleted lobes of monazite with sharp curvilinear boundaries extending from the monazite grain rim into the core. We have replicated experimentally these altered rims in a monazite-leucosome experiment at 800 °C and 2 kbar. This experiment, coupled with earlier published monazite-fluid experiments involving high pH alkali-bearing fluids at high P-T, helps to confirm the idea that alkali-bearing fluids, in the melt and along grain boundaries during crystallization, were responsible for the formation of the altered monazite grain rims via the process of coupled dissolution-reprecipitation.

  11. Hydrothermal alteration of a seamount complex on La Palma, Canary Islands: Implications for metamorphism in accreted terranes

    Science.gov (United States)

    Schiffman, P.; Staudigel, H.

    1994-02-01

    The hydrothermal metamorphism of a sequence of Pliocene-age seamount extrusive and volcaniclastic rocks on La Palma, Canary Islands, is characterized by a relatively complete low-pressure-high-temperature facies series encompassing the zeolite, prehnite-pumpellyite, and greenschist facies. The observed mineral zonations imply metamorphic gradients of 200-300 °C/km. The metamorphism of the seamount, at least in its core region, is distinct from ocean-floor metamorphism: the former is characterized by a serially continuous facies series encompassing zeolite, prehnite-pumpellyite, and greenschist assemblages, and the latter by a discontinuous metamorphic gradient in which prehnite-pumpellyite assemblages are absent. These metamorphic features, presumably reflecting fundamental thermal-tectonic differences between extending oceanic crust at mid- oceanic ridges vs. the more static crust underlying seamount volcanoes, should aid in the recognition of incoherent fragments of seamount metamorphic rocks within accreted terranes which typically have undergone subsequent higher pressure-temperature regional metamorphism, albeit to comparable grades.

  12. High-temperature carbidization of carboniferous rocks

    Science.gov (United States)

    Goldin, B. A.; Grass, V. E.; Nadutkin, A. V.; Nazarova, L. Yu.

    2009-08-01

    Processes of thermal metamorphism of carboniferous rocks have been studied experimentally. The conditions of high-temperature interaction of shungite carbon with components of the contained rocks, leading to formation of carbide compounds, have been determined. The results of this investigation contribute to the works on searching for new raw material for prospective material production.

  13. Age, temperature and pressure of metamorphism in the Tasriwine Ophiolite Complex, Sirwa, Morocco

    Science.gov (United States)

    Samson, S. D.; Inglis, J.; Hefferan, K. P.; Admou, H.; Saquaque, A.

    2013-12-01

    Sm-Nd garnet-whole rock geochronology and phase equilbria modeling have been used to determine the age and conditions of regional metamorphism within the Tasriwine ophiolite complex,Sirwa, Morocco. Pressure and temperature estimates obtained using a NaCaKFMASHT phase diagram (pseudosection) and garnet core and rim compositions predict that garnet growth began at ~0.72GPa and ~615°C and ended at ~0.8GPa and ~640°C. A bulk garnet Sm-Nd age of 645.6 × 1.6 Ma, calculated from a four point isochron that combines whole rock, garnet full dissolution and two successively more aggressive partial dissolutions, provides a precise date for garnet formation and regional metamorphism. The age is nearly 20 million years younger than a previous age estimate of regional metamorphism of 663 × 14 Ma based upon a SHRIMP U-Pb date from rims on zircon from the Irri migmatite. The new data provide further constraints on the age and nature of regional metamorphism in the Anti-Atlas mountains and emphasizes that garnet growth during regional metamorphism may not necessarily coincide with magmatism/anatexis which predominate the signature witnessed by previous U-Pb studies. The ability to couple PT estimates for garnet formation with high precision Sm- Nd geochronology highlights the utility of garnet studies for uncovering the detailed metamorphic history of the Anti-Atlas mountain belt.

  14. The role of boron and fluids in high temperature, shallow level metamorphism of the Chugach Metamorphic Complex, Alaska

    Science.gov (United States)

    Sisson, V. B.; Leeman, W. P.

    1988-01-01

    The possible role of boron (B) involvement in granite equilibria and generation of melts during crustal metamorphism has been a focus of speculation in recent literature. Most of the evidence for such involvement derives from experimental data which implies that the addition of B will lower the temperature of the granite solidus. Also the presence of tourmaline has a minor effect on the temperature of the solidus. Further indirect evidence that B may be involved in partial melting processes is the observation that granulites are commonly depleted in B, whereas the B content of low grade metapelites can be high (up to 2000 ppm). Researchers' measurements of the whole-rock B contents of granulites from the Madras region, India are low, ranging from 0.4 to 2.6 ppm. Ahmad and Wilson suggest that B was mobilized in the fluid phase during granulite facies metamorphism of the Broken Hill Complex, Australia. Thus, it appears that during the amphibolite to granulite transition, B is systematically lost from metasediments. The B that is released will probably partition into the vapor phase and/or melt phase. Preliminary measurements imply that the boron content of rocks in the Chugach Metamorphic Complex is not sufficient to influence the processes of partial melting at low pressures.

  15. 辽东地区新太古代变质深成岩岩石化学特征及构造背景%LITHOCHEMISTRY AND TECTONIC SETTING OF THE NEOARCHEAN METAMORPHIC PLUTONIC ROCKS IN EASTERN LIAONING REGION

    Institute of Scientific and Technical Information of China (English)

    赵丽君; 吕晓瑜; 王岐

    2012-01-01

    The Neoarchean rocks in Eastern Liaoning form the basement of North China landmass, which is divided by the Paleoproterozoic Liaoning-Jilin rift into two micro-landmasses in north and south. The northern micro-]andmass is composed of Fujiapuzi gneiss complex (U-Pb 2730 Ma), Huzhuang gneiss (U-Pb 2524.85 Ma) and Lianshanguan granite (U-Pb 2563 Ma). The southern micro-landmass consists of Desheng gneiss complex (U-Pb 2591 Ma). The northern micro-landmass geochemically presents the characteristics of shoshonite series-sodic calc-alkaline series, belonging to LREE enriched type with positive to negative Eu anomalies. The magma evolved from sodic calc-alkaline to potassic calc-alkaline series. The tectonic setting is active continental margin, with crustal evolution from extension in early orogenic period to compression in major orogenic period. The geochemistry of the rocks in the southern micro-landmass is characterized by high Al and Mg, which is similar to that of adakite, with low total REE, belonging to LREE enriched type with negative Eu anomaly. The magmatic evolution shows sodic trend. The existence of adakite in the southern micro-landmass suggests that the southern micro-landmass subducted northward around 2500 Ma, forming the united Archean continent in Eastern Liaoning region.%辽东地区新太古代构成了华北陆块重要结晶基底.以辽吉古元古代裂谷为界,分为南北两个微陆块.北部微陆块由新太古代付家堡子片麻杂岩(U-Pb法2730 Ma)、虎庄片麻岩(U-Pb法2524.85 Ma)、连山关花岗岩(U-Pb法2563 Ma)组成,南部微陆块由得胜片麻杂岩(U-Pb法2519 Ma)组成.北部微陆块岩石地球化学显示钾玄岩系列-钠质钙碱系列,正铕异常-负铕异常轻稀土富集型特征.岩浆演化由钠质钙碱系列→钾质钙碱系列.源区性质为地壳深熔,相当于变质泥岩、变质杂砂岩部分熔融.构造背景为活动大陆边缘,由造山早期构造拉张环境上侵就位(付家堡子片

  16. Migmatites and migmatite-like rocks of Olkiluoto

    Energy Technology Data Exchange (ETDEWEB)

    Kaerki, A. [Kivitieto Oy, Oulu (Finland)

    2015-02-15

    Bedrock of the Olkiluoto Island in the western end of the Palaeoproterozoic Svecofennian Accretionary Arc Complex, SW Finland is composed of high-grade metamorphic pelites, arenites and intermediate, arc type metavolcanic rocks intruded by granodioritic to tonalitic plutonic rocks. Regional metamorphism culminated with voluminous migmatization in the temperature of 660 - 700 deg C and relatively low pressure of about 3.5 - 4 kbar. The end result of polyphase metamorphism and deformation is a metamorphic rock succession composed of diverse migmatite rocks, metatexites and diatexites. Metatexites are migmatites in which several, discrete components can be detected, and in which the paleosome with some pre-partial-melting textures is identifiable. Diatexites are more advanced migmatites in which the pre-migmatization structures are often totally destroyed and the rock is dominated by different neosome components meaning leucosome, melanosome or mesosome. Based on the migmatite structures the metatexites of Olkiluoto have been classified into six subgroups. Dike-structured metatexites are composed of well preserved paleosome intruded by one single set of narrow, subparallel leucosome dikes which cover ca. 5 - 10 % of the whole rock volume. Net-structure is composed of a network of narrow leucosome dikes which show a reticulated structure in a plane section and cover less than 30 % of the whole rock volume. Breccia-structure is composed of angular or rounded paleosome blocks surrounded by moderate amount of leucosome. Patch-structure is composed of irregular leucosome patches which intruded the well preserved paleosome and compose typically 20 - 70 % of the rock volume. Layer-structure is characterized by more or less regular leucosome dikes sub-parallel to the foliation of the well preserved paleosome. Vein-structured metatexites and also diatexites include a set of pipe-like, longish leucosome veins most probably generated by synchronous melting and deformation

  17. Initiation of continental accretion: metamorphic conditions

    Science.gov (United States)

    Clement, Conand; Frederic, Mouthereau; Gianreto, Manatschal; Adbeltif, Lahfid

    2017-04-01

    The physical processes involved at the beginning of the continental collision are largely unknown because they are transient and therefore hardly identifiable from the rock record. Despite the importance of key parameters for understanding mountain building processes, especially the formation of deep mountain roots and their impacts on earthquakes nucleation, rock/fluid transfers and oil/gas resources in the continental crust, observations from the earliest collision stages remain fragmentary. Here, we focus on the example of Taiwan, a young and active mountain belt where the transition from oceanic subduction, accretion of the first continental margin to mature collision can be followed in space and time. We present preliminary results and provide key questions regarding the reconstruction of time-pressure-temperature paths of rocks & fluids to allow discriminating between rift-related thermal/rheological inheritance and burial/heating phases during convergence. Previous studies have focused on peak temperatures analyzed by Raman Spectrometry of Carbonaceous Matter from the deeper structural layers exposed in the Central Range of Taiwan. In the pre-rift sediments, these studies reported a positive gradient from West to Est, and values from units. Cross sections and maps with high resolution peak temperatures are in process as well as pressure estimations to determine how the sediments were metamorphosed. In addition to this work, we report a few inherited temperatures in the 390-570 °C range, indicating recycling of organic matter from metasediments that recorded HT events, likely originated from higher grade metamorphic units of mainland China, which have been eroded and deposited in the post-rift sediments.

  18. The structural evolution of carbonaceous material during metamorphism : a geothermometer

    Science.gov (United States)

    Beyssac, O.; Goffe, B.; Brunet, F.; Bollinger, L.; Avouac, J.; Rouzaud, J.

    2003-12-01

    With increasing metamorphic temperature, the organic matter present in sedimentary rocks is progressively transformed into graphite (graphitization). The degree of organization of this carbonaceous material (CM) as characterized by Raman spectroscopy (RSCM), can be used as a geothermometer which yields the maximum temperature reached during the metamorphic cycle (Beyssac et al., 2002). We used this RSCM geothermometer to map the maximum metamorphic temperatures through the Lesser Himalaya (LH) in Nepal. This study provides a large dataset (80 samples) to estimate uncertainty of this method and to ascertain its reliability by comparison with conventional petrological investigations. We show that the RSCM geothermometer might be used to detect inter-samples temperature variations as small as 10° C or so, but absolute temperatures are only loosely determined to +/- 50° C due to the uncertainty on the calibration. This successful application of the RSCM geothermometer confirms that, at the timescale of regional metamorphism (several My), the transformation of CM is mainly controlled by temperature. However, laboratory investigations suggest that, in addition to temperature, pressure should also play a role (Beyssac et al. 2003). As a matter of fact, high degree of organizations encountered in natural CM cannot be reproduced in laboratory without pressure, even at temperatures as high as 3000° C. In addition to the data acquired on natural CM, we will discuss laboratory experiments performed up to 8 GPa which show that (1) a few kbar of hydrostatic pressure are required to initiate microtextural and subsequent structural transformations within CM and (2) the overall effect of increasing pressure is to speed up graphitization process. Beyssac, O., Goffe, B., Chopin, C., and Rouzaud, J.N., 2002, Raman spectra of carbonaceous material in metasediments: a new geothermometer. Journal of Metamorphic Geology, 20, 859-871. Beyssac, O., Brunet, F., Petitet, J.P., Goffe, B

  19. Oman metamorphic sole formation reveals early subduction dynamics

    Science.gov (United States)

    Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Plunder, Alexis; Ildefonse, Benoît; Yamato, Philippe; Prigent, Cécile

    2016-04-01

    Metamorphic soles correspond to m to ~500m thick tectonic slices welded beneath most of the large-scale ophiolites. They typically show a steep inverted metamorphic structure where the pressure and temperature conditions of crystallization increase upward (from 500±100°C at 0.5±0.2 GPa to 800±100°C at 1.0±0.2 GPa), with isograds subparallel to the contact with the overlying ophiolitic peridotite. The proportion of mafic rocks in metamorphic soles also increases from the bottom (meta-sediments rich) to the top (approaching the ophiolite peridotites). These soles are interpreted as the result of heat transfer from the incipient mantle wedge toward the nascent slab (associated with large-scale fluid transfer and possible shear heating) during the first My of intra-oceanic subduction (as indicated by radiometric ages). Metamorphic soles provide therefore major constraints on early subduction dynamics (i.e., thermal structure, fluid migration and rheology along the nascent slab interface). We present a detailed structural and petrological study of the metamorphic sole from 4 major cross-sections along the Oman ophiolite. We show precise pressure-temperature estimates obtained by pseudosection modelling and EBSD measurements performed on both the garnet-bearing and garnet-free high-grade sole. Results allow quantification of the micro-scale deformation and highlight differences in pressure-temperature-deformation conditions between the 4 different locations, showing that the inverted metamorphic gradient through the sole is not continuous in all locations. Based on these new constraints, we suggest a new tectonic-petrological model for the formation of metamorphic soles below ophiolites. This model involves the stacking of several homogeneous slivers of oceanic crust leading to the present-day structure of the sole. In this view, these thrusts are the result of rheological contrasts between the sole and the peridotite as the plate interface progressively cools down

  20. Oxyvanite, V3O5, a new mineral species and the oxyvanite-berdesinskiite V2TiO5 series from metamorphic rocks of the Slyudyanka Complex, southern Baikal region

    Science.gov (United States)

    Reznitsky, L. Z.; Sklyarov, E. V.; Armbruster, T.; Ushchapovskaya, Z. F.; Galuskin, E. V.; Polekhovsky, Yu. S.; Barash, I. G.

    2010-12-01

    Oxyvanite has been identified as an accessory mineral in Cr-V-bearing quartz-diopside meta- morphic rocks of the Slyudyanka Complex in the southern Baikal region, Russia. The new mineral was named after constituents of its ideal formula (oxygen and vanadium). Quartz, Cr-V-bearing tremolite and micas, calcite, clinopyroxenes of the diopside-kosmochlor-natalyite series, Cr-bearing goldmanite, eskolaite-karelianite dravite-vanadiumdravite, V-bearing titanite, ilmenite, and rutile, berdesinskiite, schreyerite, plagioclase, scapolite, barite, zircon, and unnamed U-Ti-V-Cr phases are associated minerals. Oxyvanite occurs as anhedral grains up to 0.1-0.15 mm in size, without visible cleavage and parting. The new mineral is brittle, with conchoidal fracture. Observed by the naked eye, the mineral is black, with black streak and resinous luster. The microhardness (VHN) is 1064-1266 kg/mm2 (load 30 g), and the mean value is 1180 kg/mm2. The Mohs hardness is about 7.0-7.5. The calculated density is 4.66(2) g/cm3. The color of oxyvanite is pale cream in reflected light, without internal reflections. The measured reflectance in air is as follows (λ, nm- R, %): 440-17.8; 460-18; 480-18.2; 520-18.6; 520-18.6; 540-18.8; 560-18.9; 580-19; 600-19.1; 620-19.2; 640-19.3; 660-19.4; 680-19.5; 700-19.7. Oxyvanite is monoclinic, space group C2/ c; the unit-cell dimensions are a = 10.03(2), b = 5.050(1), c = 7.000(1) Å, β = 111.14(1)°, V = 330.76(5)Å3, Z = 4. The strongest reflections in the X-ray powder pattern [ d, Å, ( I in 5-number scale)( hkl)] are 3.28 (5) (20 bar 2 ); 2.88 (5) (11 bar 2 ); 2.65, (5) (310); 2.44 (5) (112); 1.717 (5) (42 bar 2 ); 1.633 (5) (31 bar 4 ); 1.446 (4) (33 bar 2 ); 1.379 (5) (422). The chemical composition (electron microprobe, average of six point analyses, wt %): 14.04 TiO2, 73.13 V2O3 (53.97 V2O3calc, 21.25 VO2calc), 10.76 Cr2O3, 0.04 Fe2O3, 0.01 Al2O3, 0.02 MgO, total is 100.03. The empirical formula is (V{1.70/3+} Cr0.30)2.0(V{0.59/4+} Ti0.41)1.0O

  1. On the compositional variability of metamorphic chlorites as an effect of the micro-site chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Sassi, Raffaele; Zane, Antonella [Padua, Univ. (Italy). Dipt. di Mineralogia e Petrologia

    1997-12-31

    Chlorite is a widespread mineral in all metamorphic rock sequence with the exception of the upper part of the amphibolite facies and granulite. Its stability field is well known but the petrologic meaning of its compositional variability is still poorly understood. In this paper, the chemical variability of low grade metamorphic chlorites as an effect of the micro-site chemistry has been tested by means of 2169 microprobe analyses of selected chlorite flakes. The chemistry of studied chlorites turns out to be significantly scattered, as a function of the micro-site chemistry. As a general conclusion, the possible existence in the same thin section, of chlorite flakes having different composition is a serious drawback for geothermobarometry, at least in low grade metamorphic rocks.

  2. Accessories after the facts: Constraining the timing, duration and conditions of high-temperature metamorphic processes

    Science.gov (United States)

    Taylor, Richard J. M.; Kirkland, Christopher L.; Clark, Chris

    2016-11-01

    High-temperature metamorphic rocks are the result of numerous chemical and physical processes that occur during a potentially long-lived thermal evolution. These rocks chart the sequence of events during an orogenic episode including heating, cooling, exhumation and melt interaction, all of which may be interpreted through the elemental and isotopic characteristics of accessory minerals such as zircon, monazite and rutile. Developments in imaging and in situ chemical analysis have resulted in an increasing amount of information being extracted from these accessory phases. The refractory nature of these minerals, combined with both their use as geochronometers and tracers of metamorphic mineral reactions, has made them the focus of many studies of granulite-facies terrains. In such studies the primary aim is often to determine the timing and conditions of the peak of metamorphism, and high-temperature metasedimentary rocks may seem ideal for this purpose. For example pelites typically contain an abundance of accessory minerals in a variety of bulk compositions, are melt-bearing, and may have endured extreme conditions that facilitate diffusion and chemical equilibrium. However complexities arise due to the heterogeneous nature of these rocks on all scales, driven by both the composition of the protolith and metamorphic differentiation. In additional to lithological heterogeneity, the closure temperatures for both radiogenic isotopes and chemical thermometers vary between different accessory minerals. This apparent complexity can be useful as it permits a wide range of temperature and time (T-t) information to be recovered from a single rock sample. In this review we cover: 1) characteristic internal textures of accessory minerals in high temperature rocks; 2) the interpretation of zircon and monazite age data in relation to high temperature processes; 3) rare earth element partitioning; 4) trace element thermometry; 5) the incorporation of accessory mineral growth

  3. Petrology of metabasic and peridotitic rocks of the Songshugou ophiolite, Qinling orogen, China

    Science.gov (United States)

    Belic, Maximilian; Hauzenberger, Christoph; Dong, Yunpeng

    2013-04-01

    The Proterozoic Songshugou ophiolite outcrops as a rootless nappe which was emplaced into the southern margin of the Qinling Group. It consists mainly of amphibolite facies metamafic and -ultramafic rocks. Trace element geochemistry and isotope composition show that the mafic rocks are mainly E-MORB and T-MORB metabasalts (Dong et al., 2008b). Within the ophiolite sequence, ultramafic rocks consist mainly of peridotites and serpentinites. Particularly, extremely fresh dunites and harzburgites, are found which do not display a conspicuous metamorphic overprint. The low CaO (non-fertile mantle rocks. Chromite is found as disseminated phase but can sometimes form massive chromite bands. The platinumgroup mineral Laurite (RuS2) could be identified as inclusion in chromites. Usually part of Ru is substituted by Os and Ir. The metamafic rocks consist of garnet, amphibole, symplectitic pyroxenes, ilmenite, apatite, ±zoisite, ±sphene and show a strong metamorphic overprint. Garnet contains numerous inclusions in the core but are nearly inclusion free at the rim. The cores have sometimes snowball textures indicating initially syndeformative growth. Pure albite and prehnite were found in the central parts of the garnets. In the outer portions, pargasitic amphibole, rutile and rarely glaukophane were found. The symplectitic pyroxenes are of diopsidic composition which enclose prehnite and not albite, as common in retrograde eclogitic rocks. Different stages of garnet breakdown to plagioclase and amphibole, from thin plagioclase rims surrounding the garnets to plagioclase rich pseudomorphs, can be observed in different samples. Based on the glaukophane inclusions and symplectitic pyroxenes a high pressure metamorphic event can be concluded. The garnet breakdown to plagioclase and the symplectites clearly indicate a rapid exhumation phase. The age of the metamorphic event is unclear but probably related to the closure of the Shangdan ocean during the early Paleozoic. The

  4. Effects of thermal metamorphism on compositions of lunar spinels

    Science.gov (United States)

    Misra, K. C.; Taylor, L. A.

    1977-01-01

    The reported study represents an attempt to evaluate experimentally the compositional and textural changes that are likely to be observed in the Fe-Ti-Cr spinels of lunar igneous rocks by subsequent thermal metamorphism. The Apollo 12 igneous rock, 12018,43, was chosen for this investigation because an earlier study of another fraction of this rock by El Goresy et al. (1971) has reported an almost continuous trend of spinel compositions between Cr-Ulvoespinel and Ti-chromite. The nature of the compositional changes in the heated spinels (and ilmenites) is found to be such that the changes cannot be explained by intragranular adjustments alone. In the heated sample, pyroxene grains adjacent to the high-Ti spinels show a decrease in FeO, and an increase in MgO and Al2O3 at the interface. This may account for the MgO depletion and a part of the FeO enrichment in the high-Ti spinels. It is believed that the heating experiment demonstrates that thermal metamorphism of lunar basalts is likely to modify the compositions of their preexisting spinels (and ilmenites).

  5. Can the Metamorphic Basement of Northwestern Guatemala be Correlated with the Chuacús Complex?

    Science.gov (United States)

    Cacao, N.; Martens, U.

    2007-05-01

    The Chuacús complex constitutes a northward concave metamorphic belt that stretches ca. 150 km south of the Cuilco-Chixoy-Polochic (CCP) fault system in central and central-eastern Guatemala. It represents the basement of the southern edge of the Maya block, being well exposed in the sierra de Chuacús and the sierra de Las Minas. It is composed of high-Al metapelites, amphibolites, quartzofeldspathic gneisses, and migmatites. In central Guatemala the Chuacús complex contains ubiquitous epidote-amphibolite mineral associations, and local relics of eclogite reveal a previous high-pressure metamorphic event. North of the CCP, in the Sierra de Los Cuchumatanes area of western Guatemala, metamorphic rocks have been considered the equivalent of the Chuacús complex and hence been given the name Western Chuacús group, These rocks, which were intruded by granitic rocks and later mylonitized, include chloritic schist and gneiss, biotite-garnet schist, migmatites, and amphibolites. No eclogitic relics have been found within metamorphic rocks in northwestern Guatemala. Petrographic analyses of garnet-biotite schist reveal abundant retrogression and the formation of abundant zeolite-bearing veins associated with intrusion. Although metamorphic conditions in the greenschist and amphibolite facies are similar to those in the sierra de Chuacús, the association with deformed intrusive granites is unique for western Guatemala. Hence a correlation with metasediments intruded by the Rabinal granite in the San Gabriel area of Baja Verapaz seems more feasible than a correlation with the Chuacús complex. This idea is supported by reintegration of the Cenozoic left-lateral displacement along the CCP, which would place the metamorphic basement of western Guatemala north of Baja Verapaz, adjacent to metasediments intruded by granites in the San Gabriel-Rabinal area.

  6. Research on Mechanism of Rock Burst Generation and Development for High Stress Rock Tunnels

    Institute of Scientific and Technical Information of China (English)

    高全臣; 赫建明; 王代华

    2001-01-01

    Through the investigation and analysis of high stress distribution in surrounding rock during the excavation of rock tunnels,the key factors to cause rock burst and the mechanism of rock burst generation and development are researched. The result shows that the scale and range of rock burst are related with elastic deformation energy storied in rock mass and the characteristics of unloading stress waves. The measures of preventing from rock burst for high stress rock tunnels are put forward.

  7. Assessment of fire-damaged concrete. Combining metamorphic petrology and concrete petrography

    NARCIS (Netherlands)

    Larbi, J.A.; Nijland, T.G.

    2001-01-01

    Metamorphic petrology is a branch of geology that deals with the study of changes in rocks due changing physio-chemical conditions. As conditions shift in or out of the thermodynamic stability field of phases, new phases may appear whereas others disappear. A basic approach is mapping of so-called

  8. Research on the Application of Energy Conservative Principal in Lining Design of Tunnel with V-class Surrounding Rock%能量守恒原理在吁级围岩隧道衬砌设计中的应用研究

    Institute of Scientific and Technical Information of China (English)

    胡磊; 王志杰; 许瑞宁; 马安震; 何晟亚

    2014-01-01

    There exists energy delivery and transformation in the closed surrounding rock - tunnel lining system during the process of tunnel construction. When thermal energy transformation is left out of consideration and the surrounding rock is treated as an elastic body, the release of static energy of surrounding rock equals the increase in the elastic strain energy of tunnel lining. According to this energy conservative principle, Liu Hongyan and other researchers[1 2] calculated the thickness of lining of single track tunnel subject to Ⅲ-class surrounding rock. Based on these research findings, this paper further studies the application of energy conservative principle in V-class tunnel lining design. V-class surrounding rock of the three-dimensional FLAC3D model is established, dynamically simulating the process of tunnel excavation. With MATLAB language to the program of elastic strain energy density function, elastic strain energy of each unit of solid model is obtained, thus, static energy curves of surrounding rock associated with excavation depth within the specific scope of monitoring surrounding rock are finally obtained. According to the above curves, we are able to obtain the release value of static energy of surrounding rock. Additionally, toughness tests of steel fiber reinforced concrete ( SFRC) members are conducted, which leads to the finding of the relationship between energy expenditure of SFRC trisection beam under critical conditions and that of SFRC tunnel lining. Thus, theoretical tunnel lining thickness can be defined by solving the energy equation deduced from the energy expenditure relationship, and proved to satisfy the safety requirements. The research results show that, the tunnel lining design method with energy conservative principles is no longer limited by the conditions of II,Ⅲ-class surrounding rock in small section tunnels, and it is also applicable to the lining design of large section tunnels with Ⅴ-class surrounding rock.%在

  9. Nitrogen isotope and content record of Mesozoic orogenic gold deposits surrounding the North China craton

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    As an effective tracer, nitrogen isotopes have been used to determine the source of ore materials in recent years. In this study, the nitrogen isotopes and contents were measured on K- feldspar and sericite of gold deposits and some related granitic intrusions in Jiaodong, Xiaoqinling-Xiong'ershan, west Qinling, the west part of North Qilian and the Zhangjiakou-Xuanhua district around the North China craton (NCC). Although the gold deposits around the NCC are hosted in Precambrian metamorphic rocks, Phanerozoic sedimentary rocks, mafic volcanic rocks or granite, comparison of which with the nitrogen contents and isotope data of previous studies on mantle-derived rocks, granites, metamorphic rocks and gold deposits indicates that those deposits are closely related to granitic rocks. In addition, mantle-derived materials may have been involved in the ore-forming processes to a certain degree. This conclusion is consistent with the result of previous hydrogen, oxygen and carbon isotopic studies of those gold deposits.

  10. Evidence and implications of shock metamorphism in lunar samples.

    Science.gov (United States)

    Short, N M

    1970-01-30

    Lunar microbreccias and loose regolith materials contain abundant evidence of shock metamorphism related to crater-forming meteorite impacts. Diagnostic shock effects include (i) planar features in a silica phase and feldspars, and lamellae in clinopyroxene, (ii) thetomorphic feldspar glass, (iii) heterogeneous glasses of rock and mineral composition, (iv) distinctive recrystallization textures, and (v) characteristic changes in crystal structure as indicated by x-ray diffraction analysis and measurements of refractive index. The microbreccias are produced from regolith materials (ejected fromz craters) by shock lithification. Some feldsparrich fragments may represent ejecta introduced from nonlocal sources, such as the lunar highlands.

  11. Lichenometric age measured on rock-falls related to historic seismicity affecting Lorca and its surroundings (Murcia, SE Spain); Datacion mediante liquenometria de los desprendimientos rocosos asociados a la sismicidad historica en Lorca (Murcia, SE de Espana)

    Energy Technology Data Exchange (ETDEWEB)

    Perez-Lopez, R.; Martin-Gonzalez, F.; Martinez-Diaz, J. J.; Rodriguez-Pascua, M. A.

    2012-11-01

    During the earthquake at Lorca (Murcia, SE Spain) in 2011 (5.2 Mw, 4km depth) several rock-falls occurred, mobilizing an estimated volume of close to 2,000 m3. All these rock-falls took place within the Estancias and La Tercia mountain ranges, the topography of which is composed of Tortonian calcarenitic sandstones with steep scarps more than 30 m in height. We have conducted a lichenometric study to obtain the age of the ancient rock-falls within the Las Estancias Range. We have assumed an annual growth rate of 0.24 mm for lichen species classified as calcicolous and related to warm climatic conditions. Our aim was to corroborate the hypothesis that seismic events triggered these massive rock-falls. The city of Lorca had experienced two nearfield historic earthquakes (1674 EMS VIII and 1818 EMS VI) and one far-field tremor during the great Lisbon earthquake in 1755 (EMS VI). Results obtained here indicate that the earthquakes of 1674 and 2011 were quite similar, except that the 1674 one mobilised a greater quantity and twenty times the volume of blocks mobilised during the 2011 earthquake. Therefore, we conclude that the size of the earthquake of 1674 was possibly between 6.0 < M < 6.8, assuming similar focal and seismotectonic conditions to those of the instrumentally measured earthquake of 2011. (Author) 34 refs.

  12. Geology of crystalline rocks of northern Fiordland: details of the granulite facies Western Fiordland Orthogneiss and associated rock units

    Science.gov (United States)

    Bradshaw, J.Y.

    1990-01-01

    A c. 700 km2 area of northern Fiordland (South Island, New Zealand) is described in which Early Cretaceous high-pressure metamorphic rocks and virtually unmetamorphosed plutonic rocks occur. The dominant rocks are orthogneisses developed from synmetamorphic basic-intermediate intrusive complexes, the youngest and most widespread of which is the Early Cretaceous Western Fiordland Orthogneiss (WFO). The latter has undergone granulite facies metamorphism and occurs throughout much of western Fiordland. WFO was emplaced synkinematically in a subduction-related magmatic arc. A collisional event during or immediately following magma emplacement resulted in crustal thickening equivalent to onloading of a 20 km thick section over rocks already buried at mid-crustal depths. This event was responsible for peak load pressures of c. 12-13 kbar. The steeply dipping Surprise Creek Fault juxtaposes high-pressure metamorphic rocks of western and central Fiordland against virtually unmetamorphosed gabbroic rocks of the Early Cretaceous Darran Complex. -from Author

  13. Alkali control of high-grade metamorphism and granitization

    Directory of Open Access Journals (Sweden)

    Oleg G. Safonov

    2014-09-01

    Full Text Available We review petrologic observations of reaction textures from high-grade rocks that suggest the passage of fluids with variable alkali activities. Development of these reaction textures is accompanied by regular compositional variations in plagioclase, pyroxenes, biotite, amphibole and garnet. The textures are interpreted in terms of exchange and net-transfer reactions controlled by the K and Na activities in the fluids. On the regional scale, these reactions operate in granitized, charnockitized, syenitized etc. shear zones within high-grade complexes. Thermodynamic calculations in simple chemical systems show that changes in mineral assemblages, including the transition from the hydrous to the anhydrous ones, may occur at constant pressure and temperature due only to variations in the H2O and the alkali activities. A simple procedure for estimating the activity of the two major alkali oxides, K2O and Na2O, is implemented in the TWQ software. Examples of calculations are presented for well-documented dehydration zones from South Africa, southern India, and Sri Lanka. The calculations have revealed two end-member regimes of alkalis during specific metamorphic processes: rock buffered, which is characteristic for the precursor rocks containing two feldspars, and fluid-buffered for the precursor rocks without K-feldspar. The observed reaction textures and the results of thermodynamic modeling are compared with the results of available experimental studies on the interaction of the alkali chloride and carbonate-bearing fluids with metamorphic rocks at mid-crustal conditions. The experiments show the complex effect of alkali activities in the fluid phase on the mineral assemblages. Both thermodynamic calculations and experiments closely reproduce paragenetic relations theoretically predicted by D.S. Korzhinskii in the 1940s.

  14. Hornblende-rich, high grade metamorphic terranes in the southernmost Sierra Nevada, California, and implications for crustal depths and batholith roots

    Science.gov (United States)

    Ross, Donald Clarence

    1983-01-01

    The southernmost Sierra Nevaaa widely exposes hornblende-rich, gneissic to granoblastic, amphibolite- to granulite-grade, metamorphic rocks and associated magmatic rocks, all of mid-Cretaceous age. Locally, red garnet, in part in euhedral crystals as large as 10 cm, as well as strongly pleochroic hyperstnene, characterize these rocks. These hornblende-rich rocks dominate the north slopes of the southern tail of the Sierra Nevada, but are also present as inclusion masses of various sizes in the dominantly granitic terrane to She northeast. The mafic, hornblende-rich rocks reflect a deeper crustal level than the dominantly granitic terrane to the northeast based on: 1) 'index' minerals (presence of hypersthene, coarse garnet, and brown hornblende; 2) textures (considerable ambivalence of whether individual samples are metamorphic or magmatic, 3) metamorphic grade (at least local granulite facies); and 4) the presence of migmatite, and the eviaence of local melting and mobilization. These rocks may be exposures of the upper part of the root zone and metamorphic substrate of the Sierra Nevada batholith. Xenoliths of gneiss, amphibolite, and granulite from sub-batholithic levels, that have been transported upward and preserved in volcanic rocks in the central Sierra Nevada, are similar to some exposed rocks of the southernmost Sierra Nevada. Hypersthene-bearing granulite and tonalite, as well as distinctive granofels of mid-Cretaceous age, are exposed in the western part of the Santa Lucia Range (some 300 km to the northwest across the San Andreas fault). These rocks have much in common with some of the metamorphic and magmatic rocks in the southernmost Sierra Nevada, suggesting that the two areas record similar metamorphic conditions and crustal depth. Mid-Cretaceous hypersthene granulite is rare, which makes correlation of the Santa Lucia Range and the southernmost Sierra Nevada seem attractive. Nevertheless, possibly significant petrographic anm rock distribution

  15. Deviatoric stress transfer and stability of surrounding rock in large-section open-off cut roof%大断面切眼顶板偏应力运移及围岩稳定

    Institute of Scientific and Technical Information of China (English)

    何富连; 许磊; 吴焕凯; 李通达

    2014-01-01

    To study the control mechanism of large-section open-off cut roof, No. 5205 open-off cut in a coal mine is selected as an engineering case. The deviatoric stress of roof, fracture field and deformation law are investigated by UDEC4.0 in the change process of width from 6 to 10 m. The results show that:(1) The deviatoric stress of roof gradually increases in shallow part and decreases in deep part. The wider the open-off cut, the lower the deviatoric stress in shallow part and the higher in deep part and the same time the peak of deviatoric stress is moving to the deeper part;(2) The fracture fild in surrounding rock were divided into three areas:fracture transfixion area, fracture area and microfracture area, which distributed as semi-ellipse;(3) With the width of open-off cut increasing, The trend of microfracture area transformed to fracture area and fracture area transformed to fracture transfixion area are strengthed in the roof. Besides, the roof subsidence is aggravated. It believed that:(1) The stability of unstable triangle block is the more important to keep roof safe;(2) High-performance bolt can control fracture slip preferably;(3) Double-truss and anchor rope can be anchored in the shoulder non-fracture area and deep roof pre-stressed superimposed area, which can control the expansion and deformation of fracture transfixion area in the middle part of the roof. Based on this, the combined support technology of high-strength and high pre-tension bolt&net &bar and double-truss and anchor rope is proposed. The observed results of mining pressures show that the open-off cut is self-stabilized after it is dug out for 10 days; the relative convergence of roof-to-floor is 128 mm; the relative convergence of both sides is 96 mm; and the separation of roof is 4 mm.%为了探究大断面切眼顶板控制机理,以某煤矿5205切眼为工程背景,采用UDEC4.0模拟了切眼宽度6~10 m过程中,顶板偏应力、裂隙场、变形规律等响应特征

  16. Fluid heterogeneity during granulite facies metamorphism in the Adirondacks: stable isotope evidence

    Science.gov (United States)

    Valley, J.W.; O'Neil, J.R.

    1984-01-01

    The preservation of premetamorphic, whole-rock oxygen isotope ratios in Adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived, hot CO2-H2O fluids during granulite facies metamorphism. This conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations. The data suggest that these rocks were not an open system during metamorphism; that fluid/rock ratios were in many instances between 0.0 and 0.1; that externally derived fluids, as well as fluids derived by metamorphic volatilization, rose along localized channels and were not pervasive; and thus that no single generalization can be applied to metamorphic fluid conditions in the Adirondacks. Analyses of 3 to 4 coexisting minerals from Adirondack marbles show that isotopic equilibrium was attained at the peak of granulite and upper amphibolite facies metamorphism. Thus the isotopic compositions of metamorphic fluids can be inferred from analyses of carbonates and fluid budgets can be constructed. Carbonates from the granulite facies are on average, isotopically similar to those from lower grade or unmetamorphosed limestones of the same age showing that no large isotopic shifts accompanied high grade metamorphism. Equilibrium calculations indicate that small decreases in ??18O, averaging 1 permil, result from volatilization reactions for Adirondack rock compositions. Additional small differences between amphibolite and granulite facies marbles are due to systematic lithologie differences. The range of Adirondack carbonate ??18O values (12.3 to 27.2) can be explained by the highly variable isotopic compositions of unmetamorphosed limestones in conjunction with minor 18O and 13C depletions caused by metamorphic volatilization suggesting that many (and possibly most) marbles have closely preserved their

  17. Soft rocks in Argentina

    Institute of Scientific and Technical Information of China (English)

    Giambastiani; Mauricio

    2014-01-01

    Soft rocks are a still fairly unexplored chapter in rock mechanics. Within this category are the clastic sedimentary rocks and pyroclastic volcanic rocks, of low to moderate lithification (consolidation, cemen-tation, new formed minerals), chemical sedimentary rocks and metamorphic rocks formed by minerals with Mohs hardness less than 3.5, such as limestone, gypsum, halite, sylvite, between the first and phyllites, graphitic schist, chloritic shale, talc, etc., among the latter. They also include any type of rock that suffered alteration processes (hydrothermal or weathering). In Argentina the study of low-strength rocks has not received much attention despite having extensive outcrops in the Andes and great impact in the design criteria. Correlation between geomechanical properties (UCS, deformability) to physical index (porosity, density, etc.) has shown promising results to be better studied. There are many studies and engineering projects in Argentina in soft rock geological environments, some cited in the text (Chihuído dam, N. Kirchner dam, J. Cepernic Dam, etc.) and others such as International Tunnel in the Province of Mendoza (Corredor Bioceánico), which will require the valuable contribution from rock mechanics. The lack of consistency between some of the physical and mechanical parameters explored from studies in the country may be due to an insufficient amount of information and/or non-standardization of criteria for testing materials. It is understood that more and better academic and professional efforts in improv-ing techniques will result in benefits to the better understanding of the geomechanics of weak rocks.

  18. Metamorphic pattern of the Cretaceous Celica Formation, SW Ecuador, and its geodynamic implications

    Science.gov (United States)

    Aguirre, Luis

    1992-04-01

    The volcanic rocks of the Cretaceous Celica Formation of southern Ecuador are affected by a weak although widespread alteration. The chemical study of the secondary chemical phases present in andesitic and basaltic lava flows reveals that this alteration corresponds to very low-grade metamorphism comprising the zeolite and the prehnite-pumpellyite facies. Main features of this metamorphism are: weak lithostatic pressure, moderate to steep thermal gradient, high ƒ O2, low value of the seawater/rock ratio and total absence of deformation. These characteristics are typically present in other volcanic suites of similar age and composition along the Andes and correspond to the pattern of metamorphism developed in extensional settings (diastathermal metamorphism) linked to various degrees of thinning of the continental crust. Based on this metamorphic pattern, a geodynamic model is proposed in which the Celica Formation is interpreted as an ensialic, aborted, marginal basin developed on strongly attenuated continental crust at the border of the South American plate. The relationship between the Ecuadorian and Colombian volcanic suites of Cretaceous age present along the Western Cordillera is discussed in the light of the model suggested.

  19. Metamorfismo de muy bajo grado asociado a un sistema geotermal en rocas volcánicas básicas del Jurásico Medio, Formación Lonco Trapial, Paso Berwin, Chubut extra-andino Very low grade metamorphism associated with a geothermal system in basic volcanic rocks of the Middle Jurassic, Lonco Trapial Formation, Paso Berwin, Extra-Andean Chubut

    Directory of Open Access Journals (Sweden)

    P. Montecinos

    2004-12-01

    Full Text Available Las rocas volcánicas básicas de la Formación Lonco Trapial, poseen una mineralogía primaria compuesta principalmente por olivino, plagioclasa cálcica y piroxeno, presentando además gran cantidad de amígdalas. La mineralogía metamórfica de muy bajo grado en estas rocas está caracterizada por ceolitas, minerales arcillosos y micáceos. La asociación mineral más característica está compuesta por celadonita, montmorillonita, heulandita, analcima, gonnardita y, además, por levyna y minerales de la serie analcima-wairakita en forma subordinada. Esta asociación pertenece a la facies ceolita y tuvo un origen asociado a un sistema geotermal. La analogía establecida con las zonas de ceolitas conocidas para sistemas geotermales equivalentes y el uso de la grilla petrogénetica para paragénesis ceolíticas, en el sistema An-Ab-SiO2-H2O, permiten establecer un rango de temperatura entre 80°-180°C. En este contexto habría ocurrido un único evento metamórfico hidrotermal en presencia de una fase fluida, muy pobre en CO2, cuya composición química habría cambiado desde un carácter neutro con baja a(SiO2 y a(K2O moderada (permitiendo la precipitación de esmectitas y celadonita a un carácter neutro-alcalino con a(SiO2 que posibilita la estabilidad de la heulandita.The basic volcanic rocks of the Lonco Trapial Formation, have a primary mineralogy mainly composed of olivine, calcic plagioclase and pyroxene, and present a large quantity of amygdales. Their metamorphic mineralogy is characterized by zeolites, clay and micaceous minerals. The main mineral association includes celadonite, montmorillonite, heulandite, analcime, gonnardite and subordinate levyne and minerals of the wairakite-analcime series. This association belongs to the zeolite facies and its origin was associated with a geothermal system. The analogy with known zeolite zones in equivalent geothermal systems and the use of the petrogenetic grid for zeolite parageneses, in

  20. The timing of tertiary metamorphism and deformation in the Albion-Raft River-Grouse Creek metamorphic core complex, Utah and Idaho

    Science.gov (United States)

    Strickland, A.; Miller, E.L.; Wooden, J.L.

    2011-01-01

    The Albion-Raft River-Grouse Creek metamorphic core complex of southern Idaho and northern Utah exposes 2.56-Ga orthogneisses and Neoproterozoic metasedimentary rocks that were intruded by 32-25-Ma granitic plutons. Pluton emplacement was contemporaneous with peak metamorphism, ductile thinning of the country rocks, and top-to-thewest, normal-sense shear along the Middle Mountain shear zone. Monazite and zircon from an attenuated stratigraphic section in the Middle Mountain were dated with U-Pb, using a SHRIMP-RG (reverse geometry) ion microprobe. Zircons from the deformed Archean gneiss preserve a crystallization age of 2532 ?? 33 Ma, while monazites range from 32.6 ?? 0.6 to 27.1 ?? 0.6 Ma. In the schist of the Upper Narrows, detrital zircons lack metamorphic overgrowths, and monazites produced discordant U-Pb ages that range from 52.8 ?? 0.6 to 37.5 ?? 0.3 Ma. From the structurally and stratigraphically highest unit sampled, the schist of Stevens Spring, narrow metamorphic rims on detrital zircons yield ages from 140-110 Ma, and monazite grains contained cores that yield an age of 141 ??2 Ma, whereas rims and some whole grains ranged from 35.5 ?? 0.5 to 30.0 ?? 0.4 Ma. A boudinaged pegmatite exposed in Basin Creek is deformed by the Middle Mountains shear zone and yields a monazite age of 27.6 ?? 0.2 Ma. We interpret these data to indicate two periods of monazite and metamorphic zircon growth: a poorly preserved Early Cretaceous period (???140 Ma) that is strongly overprinted by Oligocene metamorphism (???32-27 Ma) related to regional plutonism and extension. ?? 2011 by The University of Chicago.

  1. Ga/Mg ratio as a new geochemical tool to differentiate magmatic from metamorphic blue sapphires

    Science.gov (United States)

    Peucat, J. J.; Ruffault, P.; Fritsch, E.; Bouhnik-Le Coz, M.; Simonet, C.; Lasnier, B.

    2007-10-01

    Using ICP-MS-LA analyses, we demonstrate that the use of the Ga/Mg ratio, in conjunction with the Fe concentration, is an efficient tool in discriminating between "metamorphic" and "magmatic" blue sapphires. Magmatic blue sapphires found in alkali basalts (e.g. southeastern Asia, China, Africa) are commonly medium-rich to rich in Fe (with average contents between 2000 and 11000 ppm), high in Ga (> 140 ppm), and low in Mg (generally 10). Conversely, metamorphic blue sapphires found in basalts (e.g. Pailin pastel) and in metamorphic terrains (e.g. Mogok, Sri Lanka, Ilakaka) are characterized by low average iron contents ( 60 ppm) with low average Ga/Mg ratios (< 10). Basaltic magmatic sapphires have Fe, Ga and Mg contents similar to those obtained for primary magmatic sapphires found in the Garba Tula syenite. This suggests that these both sets of sapphires have a possible common "syenitic" origin, as previously proposed from other criteria. In addition, plumasite-related sapphires and metamorphic sapphires also exhibit similar composition in trace elements. Based on results from the present study, we suggest that fluid circulations during a metamorphic stage produced metasomatic exchanges between mafic and acidic rocks (plumasite model), thus explaining the high Mg contents and converging Ga/Mg ratios observed in metamorphic sapphires.

  2. CARBONACEOUS MATTER PRECURSORS AND METAMORPHIC CONDITIONS IN THERMALLY PROCESSED CHONDRITES

    Science.gov (United States)

    Quirico, E.; Montagnac, G.; Rouzaud, J.; Bonal, L.; Bourot-Denise, M.; Duber, S.; Reynard, B.

    2009-12-01

    Unravelling the origin of carbonaceous matter in pristine chondrites requires the understanding of the effect of post-accretion processes. In chondrites of petrologic type 3, thermal metamorphism modified to various extents the composition and structure of carbonaceous matter. Interestingly, this process controls the degree of structural order of carbonaceous matter, and clues on the thermal history of the parent body may be recovered from the physico-chemical study of carbonaceous matter. Following this framework, geothermometers based on Raman spectrometry of carbonaceous matter and covering a wide range of temperatures (100-650 °C) have been developed over recent years, both on terrestrial rocks and chondrites. While Raman data have been largely interpreted in terms of temperature, they are also the fingerprint of certain metamorphic conditions, especially in the low temperature range relevant to poorly ordered carbonaceous matter. This study investigates the Raman spectra of two series of chondritic carbonaceous matter and coal samples formed from different precursors and under different metamorphic conditions. The Raman spectra of Polyaromatic Carbonaceous Matter (PCM) from 42 chondrites and 27 coal samples, measured with visible (514 nm) and ultra-violet (244 nm) excitation wavelengths, are analyzed. The Raman spectra of low rank coals and chondrites of petrologic types 1 and 2, which contain the more disordered PCM, reflect the distinct carbon structures of their precursors. The 514 nm Raman spectra of high rank coals and chondrites of petrologic type 3 exhibit continuous and systematic spectral differences reflecting different carbon structures present during the metamorphism event. They result from differences in the chemical structures of the precursors concerning for instance the reticulation of polyaromatic units or an abundance of ether functional groups, or possibly from a lack of carbonization processes to efficiently expel oxygen heteroatoms, due

  3. Rock softening due to ultrasonic acoustical energy

    Science.gov (United States)

    Freund, F. T.; Freund, M. M.; Hedberg, C. M.; Haller, K. C.; Dahlgren, R.; Williams, C.; Agrawal, P.

    2011-12-01

    When igneous or high-grade metamorphic rocks are subjected to deviatoric stresses, dormant defects existing in the matrix of common rock-forming minerals become activated releasing mobile positive hole charge carriers. These defects consist of pairs of oxygen anions in the 1- valence state, e.g. peroxy links such as O3Si-OO-SiO3. When the peroxy bond breaks, O3Si-O:O-SiO3, an electron is transferred from a neighboring O2- creating a trapped electron defect, O3Si-O.O-SiO3, while the donor oxygen, now O-, turns into a defect electron or hole that can propagate as a highly mobile positive charge traveling along the upper edge of the valence band. There is evidence that the wave function associated with these positive hole charge carriers is highly delocalized. The delocalization lowers the electron density at the surrounding O2-, hence the bond energy, thereby affecting fundamental properties including the mechanical strength. To demonstrate the rock softening effect we mounted a rectangular bar of fine-grained gabbro about 30 cm long in a horizontal position clamping it at one end. A piezoelectric transducer (PZT) was epoxied to the fixed end of the rock bar to send ultrasonic energy at 57 KHz toward the cantilevered end. The downward deflection of the free end of the beam was measured with an interferometer to a high degree of precision. With ultrasonic energy present, the free end of the beam sagged near-instantaneously by about 0.2 μm and continued to sag slowly by about 0.4 μm over 120 sec. Upon turning off the PZT the rock bar returned slowly to the baseline deflection value. The ultrasound waves generated by the PZT activate positive holes, changing the apparent stiffness of the beam and causing its cantilevered end to bend downward. We also conducted experiments using an Instron 5569 Dual Column Testing System to subject rectangular plates (15.2 x 3.8 x 0.5 cm) of the same gabbro to dynamic three-point flexural tests. Using electrostatic fields of different

  4. Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan

    Science.gov (United States)

    Collett, Stephen; Faryad, Shah Wali

    2015-11-01

    The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

  5. Metamorphic complexes in accretionary orogens: Insights from the Beishan collage, southern Central Asian Orogenic Belt

    Science.gov (United States)

    Song, Dongfang; Xiao, Wenjiao; Windley, Brian F.; Han, Chunming; Yang, Lei

    2016-10-01

    The sources of ancient zircons and the tectonic attributions and origins of metamorphic complexes in Phanerozoic accretionary orogens have long been difficult issues. Situated between the Tianshan and Inner Mongolia orogens, the Beishan orogenic collage (BOC) plays a pivotal role in understanding the accretionary processes of the southern Central Asian Orogenic Belt (CAOB), particularly the extensive metamorphic and high-strained complexes on the southern margin. Despite their importance in understanding the basic architecture of the southern CAOB, little consensus has been reached on their ages and origins. Our new structural, LA-ICP-MS zircon U-Pb and Hf isotopic data from the Baidunzi, Shibandun, Qiaowan and Wutongjing metamorphic complexes resolve current controversial relations. The metamorphic complexes have varied lithologies and structures. Detrital zircons from five para-metamorphic rocks yield predominantly Phanerozoic ages with single major peaks at ca. 276 Ma, 286 Ma, 427 Ma, 428 Ma and 461 Ma. Two orthogneisses have weighted mean ages of 294 ± 2 Ma and 304 ± 2 Ma with no Precambrian inherited zircons. Most Phanerozoic zircons show positive εHf(t) values indicating significant crustal growth in the Ordovician, Silurian and Permian. The imbricated fold-thrust deformation style combined with diagnostic zircon U-Pb-Hf isotopic data demonstrate that the metamorphic rocks developed in a subduction-accretion setting on an arc or active continental margin. This setting and conclusion are supported by the nearby occurrence of Ordovician-Silurian adakites, Nb-rich basalts, Carboniferous-Permian ophiolitic mélanges, and trench-type turbidites. Current data do not support the presence of a widespread Precambrian basement in the evolution of the BOC; the accretionary processes may have continued to the early Permian in this part of the CAOB. These relationships have meaningful implications for the interpretation of the tectonic attributions and origins of other

  6. Syn-extensional plutonism and peak metamorphism in the albion-raft river-grouse creek metamorphic core complex

    Science.gov (United States)

    Strickland, A.; Miller, E.L.; Wooden, J.L.; Kozdon, R.; Valley, J.W.

    2011-01-01

    The Cassia plutonic complex (CPC) is a group of variably deformed, Oligocene granitic plutons exposed in the lower plate of the Albion-Raft River- Grouse Creek (ARG) metamorphic core complex of Idaho and Utah. The plutons range from granodiorite to garnet-bearing, leucogranite, and during intrusion, sillimanite- grade peak metamorphism and ductile attenuation occurred in the country rocks and normal-sense, amphibolite-grade deformation took place along the Middle Mountain shear zone. U-Pb zircon geochronology from three variably deformed plutons exposed in the lower plate of the ARG metamorphic core complex revealed that each zircon is comprised of inherited cores (dominantly late Archean) and Oligocene igneous overgrowths. Within each pluton, a spread of concordant ages from the Oligocene zircon overgrowths is interpreted as zircon recycling within a long-lived magmatic system. The plutons of the CPC have very low negative whole rock ??Nd values of -26 to -35, and initial Sr values of 0.714 to 0.718, consistent with an ancient, crustal source. Oxygen isotope ratios of the Oligocene zircon overgrowths from the CPC have an average ??18O value of 5.40 ?? 0.63 permil (2SD, n = 65) with a slight trend towards higher ??18O values through time. The ??18O values of the inherited cores of the zircons are more variable at 5.93 ?? 1.51 permil (2SD, n = 29). Therefore, we interpret the plutons of the CPC as derived, at least in part, from melting Archean crust based on the isotope geochemistry. In situ partial melting of the exposed Archean basement that was intruded by the Oligocene plutons of the CPC is excluded as the source for the CPC based on field relationships, age and geochemistry. Correlations between Ti and Hf concentrations in zircons from the CPC suggest that the magmatic system may have become hotter (higher Ti concentration in zircon) and less evolved (lower Hf in zircon concentration) through time. Therefore, the CPC represents prolonged or episodic magmatism

  7. Clumped isotope thermometry of calcite and dolomite in a contact metamorphic environment

    Science.gov (United States)

    Lloyd, Max K.; Eiler, John M.; Nabelek, Peter I.

    2017-01-01

    Clumped isotope compositions of slowly-cooled calcite and dolomite marbles record apparent equilibrium temperatures of roughly 150-200 °C and 300-350 °C, respectively. Because clumped isotope compositions are sensitive to the details of T-t path within these intervals, measurements of the Δ47 values of coexisting calcite and dolomite can place new constraints on thermal history of low-grade metamorphic rocks over a large portion of the upper crust (from ∼5 to ∼15 km depth). We studied the clumped isotope geochemistry of coexisting calcite and dolomite in marbles from the Notch Peak contact metamorphic aureole, Utah. Here, flat-lying limestones were intruded by a pluton, producing a regular, zoned metamorphic aureole. Calcite Δ47 temperatures are uniform, 156 ± 12 °C (2σ s.e.), across rocks varying from high-grade marbles that exceeded 500 °C to nominally unmetamorphosed limestones >5 km from the intrusion. This result appears to require that the temperature far from the pluton was close to this value; an ambient temperature just 20 °C lower would not have permitted substantial re-equilibration, and should have preserved depositional or early diagenetic Δ47 values several km from the pluton. Combining this result with depth constraints from overlying strata suggests the country rock here had an average regional geotherm of 22.3-27.4 °C/km from the late Jurassic Period until at least the middle Paleogene Period. Dolomite Δ47 in all samples above the talc + tremolite-in isograd record apparent equilibrium temperatures of 328-12+13 °C (1σ s.e.), consistent with the apparent equilibrium blocking temperature we expect for cooling from peak metamorphic conditions. At greater distances, dolomite Δ47 records temperatures of peak (anchi)metamorphism or pre-metamorphic diagenetic conditions. The interface between these domains is the location of the 330 °C isotherm associated with intrusion. Multiple-phase clumped isotope measurements are complemented by

  8. Jurassic to Miocene magmatism and metamorphism in the Mogok metamorphic belt and the India-Eurasia collision in Myanmar

    Science.gov (United States)

    Barley, M. E.; Pickard, A. L.; Zaw, Khin; Rak, P.; Doyle, M. G.

    2003-06-01

    Situated south of the eastern Himalayan syntaxis at the western margin of the Shan-Thai terrane the high-grade Mogok metamorphic belt (MMB) in Myanmar occupies a key position in the tectonic evolution of Southeast Asia. The first sensitive high-resolution ion microprobe U-Pb in zircon geochronology for the MMB shows that strongly deformed granitic orthogneisses near Mandalay contain Jurassic (˜170 Ma) zircons that have partly recrystallized during ˜43 Ma high-grade metamorphism. A hornblende syenite from Mandalay Hill also contains Jurassic zircons with evidence of Eocene metamorphic recrystallization rimmed by thin zones of 30.9 ± 0.7 Ma magmatic zircon. The relative abundance of Jurassic zircons in these rocks is consistent with suggestions that southern Eurasia had an Andean-type margin at that time. Mid-Cretaceous to earliest Eocene (120 to 50 Ma) I-type granitoids in the MMB, Myeik Archipelago, and Western Myanmar confirm that prior to the collision of India, an up to 200 km wide magmatic belt extended along the Eurasian margin from Pakistan to Sumatra. Metamorphic overgrowths to zircons in the orthogneiss near Mandalay date a period of Eocene (˜43 Ma) high-grade metamorphism possibly during crustal thickening related to the initial collision between India and Eurasia (at 65 to 55 Ma). This was followed by emplacement of syntectonic hornblende syenites and leucogranites between 35 and 23 Ma. Similar syntectonic syenites and leucogranites intruded the Ailao Shan-Red River shear belt in southern China and Vietnam during the Eocene-Oligocene to Miocene, and the Wang Chao and Three Pagodas faults in northern Thailand (that most likely link with the MMB) were also active at this time. The complex history of Eocene to early Miocene metamorphism, deformation, and magmatism in the MMB provides evidence that it may have played a key role in the network of deformation zones that accommodated strain during the northwards movement of India and resulting extrusion or

  9. A perspective view on ultrahigh-pressure metamorphism and continental collision in the Dabie-Sulu orogenic belt

    Institute of Scientific and Technical Information of China (English)

    ZHENG YongFei

    2008-01-01

    The study of continental deep-subduction has been one of the forefront and core subjects to advance the plate tectonics theory in the twenty-first century. The babie-Sulu orogenic belt in China crops out the largest lithotectonic unit containing ultrahigh-pressure metamorphic rocks in the world. Much of our understanding of the world's most enigmatic processes in continental deep-subduction zones has been deduced from various records in the Dabie-Sulu rocks. By taking these rocks as the natural laboratory, earth scientists have made seminal contributions to understanding of ultrahigh-pressure metamorphism and continental collision. This paper outlines twelve aspects of outstanding progress, including spatial distribution of the UHP metamorphic rocks, timing of the UHP metamorphism, time-scale of the UHP metamorphism, the protolith nature of deeply subducted continental crust, subduction erosion and crustal detachment during continental collision, the possible depths of continental sub-duction, fluid activity in the continental deep-subduction zone, partial melting during continental colli-sion, element mobility in continental deep-subduction zone, recycling of subducted continental crust, geodynamic mechanism of postcollisional magmatism, and lithospheric architecture of collision oro-gen. Some intriguing questions and directions are also proposed for future studies.

  10. Combustion metamorphic events as age markers of orogenic movements, in Central Asia

    Energy Technology Data Exchange (ETDEWEB)

    Novikov, I.S.; Sokol, E.V. [Russian Academy of Science, Novosibirsk (Russian Federation)

    2007-07-15

    Combustion metamorphic (pyrometamorphic) complexes produced by prehistoric natural coal fires are widespread in Central Asia, namely at the interfaces between mountain systems and the flanking sedimentary basins. Large-scale and prolonged fires accompanied the initial orogenic stages as unweathered coal-bearing formations became exposed into the aeration zone. Pyrometamorphic rocks are comparable to sanidinite facies rocks in formation conditions and in alteration of sedimentary material but, unlike these, their protolith underwent different melting degrees to produce either ferrous basic paralavas or glazed clinkers. The phase composition of the newly-formed melted rocks are favorable for Ar-40/Ar-39 dating of combustion metamorphic events which are coeval to the onset of the main stage of recent orogenic events. We suggest a new algorithm providing correct Ar-40/Ar-39 dating of pyrometamorphic rocks followed by well-grounded geological interpretation. We applied it to pyrometamorphic rocks in the western Salair zone of the Kuznetsk coal basin where combustion metamorphism under temperatures above 1000 degrees C acted upon large volumes of coal-bearing sediments.

  11. Formation and metamorphic evolution of the Douling Complex from the East Qinling Mountains

    Institute of Scientific and Technical Information of China (English)

    张寿广; 魏春景; 赵子然; 沈洁

    1996-01-01

    The Douling Complex occurs as a Precambrian tectonic block distributed between the North China and Yangtze plates and has a protracted evolutional history. It is composed of various metamorpnic intrusives and supracrustal rocks. According to the studies on geology and geochronology, it can be concluded that the complex may have been formed in the early Proterozoic, about 2000 Ma ago and experienced two phases of regional metamorphism during the Jinningian and late Caledonian-early Hercynian. It can be correlated with the Qinling Complex from the North Qinling Mountains in lithic assemblage, formation age, tectonic setting and metamorphism, and is probably a thrust nappe split from the Qinling Complex.

  12. CRITERIA FOR ROCK ENGINEERING FAILURE

    Institute of Scientific and Technical Information of China (English)

    ZHUDeren; ZHANGYuzhuo

    1995-01-01

    A great number of underground rock projects are maintained in the rock mass which is subject to rock damage and failure development. In many cases, the rock. engineering is still under normal working conditions even though rock is already fails to some extent. This paper introduces two different concepts: rock failure and rock engineering failure. Rock failure is defined as a mechanical state under which an applicable characteristic is changed or lost.However, the rock engineering failure is an engineering state under which an applicable function is changed or lost. The failure of surrounding rocks is the major reason of rock engineering failure. The criterion of rock engineering failure depends on the limit of applicable functions. The rock engineering failure state possesses a corresponding point in rock failure state. In this paper, a description of rock engineering failure criterion is given by simply using a mechanical equation or expression. It is expected that the study of rock engineering failure criterion will be an optimal approach that combines research of rock mechanics with rock engineering problems.

  13. Caracterización y evolución metamórfica de las rocas ultramáficas de la faja del río de las Tunas, Cordillera Frontal de Mendoza Characteristics and metamorphic evolution of the ultramafic rocks from Río de Las Tunas Belt, Frontal Cordillera of Mendoza.

    Directory of Open Access Journals (Sweden)

    M. Florencia Gargiulo

    2011-12-01

    penetrativa de los cuerpos ultramáficos, dando lugar a verdaderas serpentinitas. El posterior aumento en la proporción de CO2 del fluido mineralizante, inhibe la cristalización de Srp y da lugar a la cristalización conspicua de Tlc concentrado en estas zonas de cizalla, acompañado localmente por la presencia de carbonato.The goal of this contribution is to present the petro-mineralogical and chemical study of metaperidotites and serpentinites from the río de Las Tunas belt in Frontal Cordillera, Mendoza province. The metaperidotites preserve relictic magmatic minerals Ol, Cpx, (brownish-redSpls.l., scarce Opx with different modal proportions allowing to define the ultramafic protoliths: dunites, spinel-dunites, clinopyroxenitic-dunites, wehrlites, olivine-clinopyroxenites and clinopyroxenites. The crystallization sequence Srp+Mgt(±Brc±Chl→Tr±Tlc→�}Athà±(greenSpls.s./Ple±Opx evidence the metamorphic evolution of the ultramafic rocks. The initial serpentinization with pseudomorphic textures is followed by prograde metamorphism reaching the transition between the upper amphibolite facies and the granulite facies conditions. A second serpentinization process is evidenced by pseudomorphic textures after Amp and Chl and non-pseudomorphic and recrystallization textures, in agreement with the sequence a FeChrà→CrMgt→àMgt and b Spls.s./Ple(greenàMgt, which altogether indicate the low grade conditions during the retrogressive stage. During this stage reaction zones at metaperidotite-schist, -gneiss or -orthoamphibolite interfaces also were developed due to metasomatism between these lithologies. At the same time, local but pervasive carbonatization of the ultramafics near carbonatic levels of the Guarguaráz Complex took place. The emplacement of gondwanic igneous bodies in the study area occurred during the final stage of the metamorphic cycle. This magmatic event provides the physic-chemical conditions to allow elements mobilization, minerals concentration

  14. Metamorphism of bauxites on Naxos, Greece

    NARCIS (Netherlands)

    Feenstra, A.

    1985-01-01

    This thesis presents the results of a petrological-mineralogical and geochemical study of the metamorphosed karstbauxites on the island of Naxos, Greece. The bauxites have been subject to an Eocene highpressure metamorphism (M1), followed by a Late Oligocene-Miocene medium-pressure metamorphism (M2)

  15. Petrology of HP metamorphic veins in coesite-bearing eclogite from western Tianshan, China: Fluid processes and elemental mobility during exhumation in a cold subduction zone