what controlled mid late miocene long term aridification in central asia global cooling or tibetan plateau uplift a review abstract debate continues over whether global cooling or uplift of the tibetan plateau provided the first order driver for the aridification moisture levels of central asia throughout the mid late miocene between about 17 and 5 ma this review attempts to throw new light on the relations between the aridification and these two key factors this paper examines the evolution of miocene climate both moisture and temperature within five separate regions of eurasia to help understand the large scale controls of long term moisture in central asia the five regions include 1 europe 2 high latitude asia 3 the east asian monsoon region 4 the south asian monsoon region and 5 central asia itself because moisture reaching central asia has to firstly cross at least one of the other four regions temperature proxy data compiled from these five regions correlate with ocean temperatures from the global deep sea oxygen isotope records furthermore compiled moisture proxy data from the four regions surrounding central asia co vary and correlate with each other this can be explained by positive feedbacks between drying and cooling and supports the assumption that global cooling provides a dominant driving factor for the drying of eurasia global cooling reduces the amount of water vapor held in the atmosphere and thereby can cause terrestrial drying however in central asia the moisture evolution shows less similarity with its surroundings the uplift of the tibetan plateau including the tianshan mountains could provide a possible explanation for this difference the changing topography resulting from uplift events over time and space strongly influenced the moisture patterns in central asia during miocene times future research on the spatial timing and amplitude of tibetan plateau uplift should be useful to understand the moisture processes in central asia during the miocene

validation of models and empirical equations to estimate deformations in jointed rock through the monitoring of a 40 storey tower foundation abstract there is a pressing need in rock mechanics for the calculation of deformations and stresses of structures in rock with this aim the rock mass modulus must be estimated and a model chosen to perform the calculations monitoring the foundation of twin towers in tenerife island has allowed validating both the rock mass modulus estimated from empirical equations and the model in this paper only the second tower tower n with a structural height of 137 4 m above foundation has been studied because the first tower had been previously presented by justo et al int j rock mech min sci 2006 43 267 81 the foundations of both towers are supported by jointed vesicular and weathered basalt and scoria the parameters have been deduced from the simple empirical equations proposed by several authors as a function of geological strength index gsi or rock mass rating rmr three dimensional elastic and advanced elasto plastic finite element fe programs have permitted calculation of the displacements of tower n the stresses in the slab and the factor of safety fos of the excavation the installation of rod extensometers at different depths below the slab has permitted comparison between measured and calculated displacements good fit has been obtained in this type of rock these results increase our confidence in the use of classification schemes to estimate the deformations in jointed rock in construction processes that involve unloading reloading it is important to use a material model that considers these processes the use of advanced elasto plastic methods increases the calculated settlements even if there are no failure points as the pre consolidation stress and the mobilized angle reached during the excavation phase are exceeded at many points during the loading phase tension cut off points also increase deformations with respect to linear elastic behaviour the hardening soil model improves fit between measured and calculated settlements as well

regional variations in fluid formation and metal sources in mvt mineralization in the pennine orefield uk implications from rare earth element and yttrium distribution sr nd isotopes and fluid inclusion compositions of hydrothermal vein fluorites abstract the pennine orefield is one of the most important ore fields for pb zn ba f mineralization in great britain it is subdivided into the northern pennine orefield npo consisting of the alston and askrigg blocks and the southern pennine orefield spo the alston block is underlain by the early devonian weardale granite and the askrigg block by the coeval wensleydale granite the potential relationship between the batholiths and the mineralization is a matter of debate we here studied the rare earth elements and y rey geochemistry sr nd isotopes and fluid inclusion fi compositions of fluorites from the two structural blocks in the npo and found that the fluorite mineralization in these blocks differ substantially the rey in askrigg fluorites show features that are characteristic for leaching of adjacent lower carboniferous limestones in contrast alston fluorites have significantly higher rey concentrations lack reysn limestone signatures and show a decoupling of redox sensitive eu from its trivalent rey neighbours neodymium isotopes indicate a similar crustal source of rey in both blocks but higher rey concentrations and lower y ho ratios suggest lower carboniferous shales as potential rey source in the alston block the fluids that precipitated the alston fluorites experienced temperatures 250 c prior to mineral formation as evidenced by eu geothermometry fluorite formation however occurred at much lower temperatures as suggested by homogenization temperatures in fi that fall within ranges of 105 159 c in alston and 99 160 c in askrigg fluorites mineralization of the mississippi valley type usually lack association with igneous activity we show that some of the fluids responsible for the npo mineralization were influenced by magmatic sources the rey systematics in alston fluorites may be linked to an interaction of the permian age whin sill dolerite with the basement granite which heated fluids and focussed fluid flow into the overlying sedimentary rocks in the askrigg block where such a dolerite intrusion was not described fluorites lack any positive eusn anomalies indicating that these fluids had never been subjected to temperatures exceeding 200 250 c

predicting the deformation moduli of rock masses abstract predictive empirical models for the mechanical properties of rock masses have been used in rock engineering because direct measurement of the properties is difficult due to the presence of discontinuities such empirical models are open to improvement because they are based on collected data the purposes of the present study are to assess the existing empirical equations and to develop a new empirical approach for this reason in the first stage of the study the prediction performance of the existing models proposed for predicting the deformation modulus of rock masses were evaluated statistically by using a database including 115 data values obtained from in situ plate loading and dilatometer tests a new empirical approach with higher prediction capacity than the existing empirical models was developed in the subsequent stage of the study the new empirical model considers the modulus ratio of intact rock e i ucs rock quality designation rqd and weathering degree wd although data obtained from very weak and weak rock masses were included in the development of the new empirical equation the type of rocks employed in the study were limited therefore a crosscheck between the new empirical equation and previous empirical approaches should be performed in the design stage

chronology and paleoenvironmental records of a drill core in the central tengger desert of china abstract the desertification history of inland asia provides most direct evidence for asian drying history but the formation ages of the most asian deserts are not clear due to the lack of outcrops the tengger desert one of the main proximal deserts of the chinese loess plateau clp is of special paleoclimatic significances for its dust emission and environmental affection here we report lithofacies paleomagnetic ages and paleoenvironmental proxy indexes of the first drill core wedp01 from the central tengger desert paleomagnetism measurements reveal that the core spans from 3 55 ma to present consistent with the electron spin resonance esr dating results the strata of the central desert consist of alluvial fluvial deposits lacustrine fluvial deposits mixed with dust and eolian sand from bottom to top sedimentary analysis reveals that continuous eolian sand started by 0 9 ma marking the initial formation of the tengger desert and the domination of eolian sand in the strata with similar characters of the modern desert appeared by 0 68 ma indicating expansion of the tengger desert the proximal deserts formation and simultaneous increase of dust accumulation in the clp and the north pacific ocean in mid pleistocene demonstrate the role of proximal deserts for the dust loading of northern china and even northern hemisphere our analysis suggests the uplift of tibetan plateau in the mid pleistocene probably played the main role for this drying event and desert formation while global cooling may strength the arid environment of the proximal deserts

trace element and sr nd isotope geochemistry of fluorite from the xiangshan uranium deposit southeast china the trace element and sr nd isotope geochemistry of fluorite have been investigated in the xiangshan volcanic rock hosted uranium deposit in southeast china detailed sr nd isotope data of the hydrothermal fluorite closely associated with the uranium mineralization suggest that ore forming fluids were a combination of mantle derived fluid and fluids equilibrated with basement metamorphic rocks this model is consistent with previously published h o isotope data and is incompatible with meteoric water as the only ore forming fluid trace element geochemical profiles across the uranium orebody can be interpreted to reflect reaction between the host rocks and a mantle derived fluid containing high u and th with low th u ratios the mantle derived fluid is considered to have been u f and carbonate rich mixing with shallowly circulated meteoric water within the fractures of the host volcanic rocks caused dilution and cooling of the ore forming fluid and subsequent precipitation of fluorite and uranium ore

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

trace element and sr nd isotopic evidence for the origin of the sardinian fluorite mineralization italy abstract the fluorite bearing hydrothermal mineralization in sardinia mainly occurs within paleozoic volcanic and metasedimentary rocks only 3 occurrences are located in volcanic and siliciclastic cenozoic rocks most sardinian fluorites exhibit relatively high rare earth and y rey contents strong positive y anomalies slightly negative ce and generally positive eu anomalies these features indicate that the rey were mobilized mainly from non carbonate rocks neither sr nor nd isotopes can be used to date radiometrically the sardinian fluorites however the measured sr isotope ratios of the fluorites hosted by paleozoic rocks fit mixing lines in the 1000 sr versus 87sr 86sr plot once recalculated at 280 ma suggesting that the age inferred for the correction probably represents that of the formation of the fluorite mineralization mixing likely occurred between diluted surficial waters and brines circulating mainly through the lower paleozoic metasedimentary basement the cenozoic fluorites exhibit chemical and isotopic features similar to those of the paleozoic fluorites except the nuraghe onigu fluorite displaying a possible contribution of sr from cenozoic magmatic rocks the initial end values of the paleozoic fluorites fit the age proposed for the formation of the deposits moreover the values suggest that radiogenic nd was provided to the fluids from the ordovician siliciclastic basement except for 3 deposits where the potential source rocks of nd were mainly ordovician acidic magmatic rocks the initial end values of the cenozoic fluorites suggest a provenance of nd essentially from the leaching of variscan granitoids

an example of estimating rock mass deformation around an underground opening using numerical modeling abstract in rock engineering rock strength is regarded as an important rock mass parameter and it is widely estimated using the uniaxial compressive strength ucs test a ucs test in laboratory requires sampling and preparation of core samples which necessitates time consuming and expensive studies furthermore preparation of cores is almost impossible for a weak rock material taken from foliated laminated or thinly bedded rock masses of low rock quality designation rqd values 0 20 in this case determination of ucs by laboratory test may be impossible in compliance with isrm or astm standards to overcome this difficulty indirect tests such as point load index pli schmidt hammer sh rebound number tests are often employed to predict the ucs however indirect tests are likely to yield ucs values with large standard deviations depending on the geological origin of the rock mass the block punch index bpi has recently been developed to overcome the drawbacks of ucs and indirect tests and to minimize the errors arisen from the structural deficiencies and large standard deviations in this study determination of rock mass behavior in laminated foliated bornova melange yellowish brown flysch and grayish black flysch and well jointed yamanlar volcanics altindag formation where the second phase of the izmir metro tunnels was excavated is aimed the bpi ratings were directly used in rmr calculations and indirectly used to estimate the ucs values of rock materials then the obtained results were input into numerical models along with the rock mass strength ucs rm and deformation modulus of rock mass e rm the results obtained from the numerical models agreed with that obtained results from inner tunnel convergence and ground settlement measurements

stable isotope composition of f pb zn mineralization in the valle de tena spanish central pyrenees this study dealing with the stable isotope c o and s geochemistry of f pb zn deposits is part of an integrated metallogenetic study of the valle de tena central pyrenees the objective of this work is to place constraints on the origin of the mineralizing solutions and sources of sulphur and metals two types of mineralization have been identified 1 stratabound ores linked to an emersion episode that occurred during the namurian to westfalian transition portalet mines and 2 low temperature hydrothermal veins related to post hercynian extensional tectonics yenefrito and lanuza mines and tebarray occurrences stable isotopic study indicates that the source of mineralizing components was the local upper palaeozoic country rocks in the case of the stratabound portalet deposit biogenic sulphides and connate waters modified by some meteoric input through a karst surface in the case of vein deposits stable isotopes point toward either modified connate water or marine water as the mineralizing fluid with sulphur and metals derived from a mixture in different proportions of regional igneous and meta sedimentary country rocks

impacts of uplift of northern tibetan plateau and formation of asian inland deserts on regional climate and environment abstract based on the geological evidence that the northern tibetan plateau ntp had an uplift of a finite magnitude since the miocene and the major asian inland deserts formed in the early pliocene a regional climate model regcm4 1 with a horizontal resolution of 50 km was used to explore the effects of the ntp uplift and the related aridification of inland asia on regional climate we designed three numerical experiments including the control experiment representing the present day condition the high mountain experiment representing the early pliocene condition with uplifted ntp but absence of the asian inland deserts and the low mountain experiment representing the mid miocene condition with reduced topography in the ntp by as much as 2400 m and also absence of the deserts our simulation results indicated that the ntp uplift caused significant reductions in annual precipitation in a broad region of inland asia north of the tibetan plateau tp mainly due to the enhanced rain shadow effect of the mountains and changes in the regional circulations however four mountainous regions located in the uplift showed significant increases in precipitation stretching from the pamir plateau in the west to the qilian mountains in the east these mountainous areas also experienced different changes in the rainfall seasonality with the greatest increases occurring during the respective rainy seasons predominantly resulted from the enhanced orographically forced upwind ascents the appearance of the major deserts in the inland asia further reduced precipitation in the region and led to increased dust emission and deposition fluxes while the spatial patterns of dust deposition were also changed not only in the regions of uplift impacted topography but also in the downwind regions one major contribution from this study is the comparison of the simulation results with 11 existing geological records representing the moisture conditions from miocene to pliocene the comparisons revealed good matches between the simulation results and the published geological records therefore we conclude that the ntp uplift and the related formation of the major deserts played a controlling role in the evolution of regional climatic conditions in a broad region in inland asia since the miocene

an empirical method for determining the mechanical properties of jointed rock mass using drilling energy abstract characterization of jointed rock masses and evaluation of their mechanical properties are challenging tasks in rock engineering this paper presents an experimental investigation of the response characteristics of drilling energy to the discontinuity of rock mass using a drilling method the linear relationship between the drilling energy and discontinuity frequency is revealed which only depends on the rock type and is independent of calculation units a new empirical method for determining the rock quality designation rqd versus the variation of drilling energy is proposed based on the discontinuity frequency comparison between the prediction and in situ investigation results demonstrates that the rqd can be estimated from this empirical method the em er modulus ratio and cm c strength ratio versus rqd relations are modified for the determination of rock mass strength and deformation modulus in order to consider the continuous variation of em er and cm c with the model parameter which is related to the drilling energy and modulus of elasticity of intact rock and the variation of drilling energy for rock mass the results show that the modified em er cm c versus rqd relations can give proper values compared with the field test results as well as compared with the various proposed relations from rmr q and gsi the modified relations can provide a practical fast and easy to use method for the estimated rock mass strength and deformation modulus but they are only a first approximation

palaeomagnetic and palaeoenvironmental study of two parallel sections of late cenozoic strata in the central taklimakan desert implications for the desertification of the tarim basin abstract due to marine recession and stepwise uplift of the tibetan plateau during the cenozoic era an extremely arid environment and large deserts developed progressively in the interior of asia the tarim basin is a typical region that experienced this type of palaeoenvironmental evolution in this study we apply high resolution palaeomagnetic dating esr dating and palaeoenvironmental reconstruction to two parallel sections from an almost 1000 m thick sequence of terrestrial sediments in the central tarim basin in order to characterize and date the process of drying and desertification our results indicate that the western tarim basin started to accumulate terrestrial sediments in a dry land environment at the latest by 4 2 ma and that the initial desert was formed by 3 4 ma from fluvial sands originating from the tibetan plateau when the climate became particularly dry in the interior of asia due to the uplift of the tibetan plateau variations of the stratum properties including colour index and magnetic susceptibility indicate that the aridification trend was significantly intensified at 2 6 ma coincident with the onset of the northern hemisphere glaciations and consequently forming the present desert regime

a sr isotope study on fluorite and siderite from post orogenic mineral veins in the eastern harz mountains germany rb sr isotope data for siderite and fluorite from sediment hosted epithermal mineral veins in the eastern harz mountains germany are presented several fluorite and siderite bearing paragenetic stages have been proposed for these veins with the most important mineralization being related to a quartz sulfide and a subsequent calcite fluorite quartz stage which occurred at 226 1 and 209 2 ma respectively our rb sr data do not permit the identification of distinct generations of siderite and fluorite but rather reveal straight internal mixing relations reflecting mixing of fluids or differential fluid rock interaction processes this indicates merely two significant phases of mineral deposition related to the quartz sulfide and calcite fluorite quartz stages it is shown that the paleozoic sedimentary host rocks of the veins are the most likely source for the siderite sr whereas fluorite displays a two component mixture between sedimentary sr and radiogenic sr derived from locally occurring permian metavolcanic rocks

northeastward growth of the tibet plateau deduced from balanced reconstruction of two depositional areas the qaidam and hexi corridor basins china we address the problem of late cenozoic uplift erosion and growth of northeastern tibet by reconstructing from isopach maps and drill holes the volumes and masses of sediments deposited in the qaidam and hexi corridor basins since 35 myr ago the mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages in the qaidam where our record extends back to the oligocene the budget shows a huge rise of the accumulation rates after the beginning of the pliocene 5 3 ma the early pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr 1 2 7 kg m 2 yr 1 of compacted rocks throughout the basin there also seems to be a southeastward shift of the largest depocenters between the upper pliocene 3 4 1 6 ma and the quaternary in the hexi corridor sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the qilian shan and occurs at an average rate one order of magnitude smaller than in the qaidam basin the accumulation rate is maximum in the quaternary the sedimentation history appears to support a plateau building mechanism resulting from the combination of two geologicallly common processes crustal scale thrusting and sedimentary basin infilling the time needed to completely fill the qaidam basin and make its catchment a plateau closely resembling that of the highest part of tibet qangtang is of the order of 9 myr the mechanism now at work north of the kunlun which involves rapid infilling of broad flat areas separated by relatively narrow mountain ranges has thus probably been important in producing the high smooth topography that characterizes much of central tibet

sensitivity of eurasian climate to surface uplift of the tibetan plateau experiments with climate models are used to illustrate how earth s climate could be expected to change if surface uplift occurred the experiments contrast two climate simulations one with all continents at sea level and one with present day mountains and plateaus the simulations in the eurasia sector show that surface uplift increased elevation produces marked increases in the intensity of summer and winter monsoons of asia with development of wetter climates to the south and east of the tibetan plateau and drier climates to the north and west of the plateau there is a general cooling in northern polar latitudes comparison of simulations from two different models shows that the magnitude of the simulated changes depends upon how the models calculate the land surface hydrology and the ocean temperature the simulated changes produced by surface uplift agree in a general way with many geologic indicators of late cenozoic climate change the results suggest that surface uplift of mountains and platea

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

genesis of the banxi sb deposit south china constraints from wall rock geochemistry fluid inclusion microthermometry rb sr geochronology and h o s isotopes abstract the banxi sb deposit is located in the world class central western hunan sb belt in south china with quartz vein type sb only mineralization hosted by neoproterozoic epimetamorphic clastic sedimentary rocks in this contribution microthermometric rb sr geochronological and h o isotopic analyses on fluid inclusions trapped in quartz s isotopic studies on stibnite and major trace elemental measurements on fluid altered and unaltered wall rocks are presented to constrain the genesis of the deposit the fluid inclusions are characterized by low homogenization temperature 170 260 c and low salinity 3 7 wt nacl equiv with a low fluid density of 0 72 0 93 g cm3 and a ph of 5 59 the low dw fluid 2h 140 to 107 whereas positive 18ov smow 15 9 17 2 and 18ow fluid 18o 5 9 8 4 values in quartz indicate that the mineralizing fluid was generated from the low grade metamorphic basement rocks and received a certain input of meteoric water the rb sr isotopic compositions of quartz samples yielded an isochron age of 196 4 ma 1 mswd 0 70 for quartz stibnite ores a highly radiogenic 87sr 86sr value 0 72663 0 74002 initial 87sr 86sr 0 72640 indicates that ore forming materials are derived mainly from basement rocks and a direct material contribution from local granitic rocks can be ruled out the 34sv cdt values of stibnite range narrowly from 4 81 to 6 72 and are in the 34sv cdt range of the metamorphic rocks indicating that the sulfur was sourced from the basement rocks by sulfate reduction compositional differences between fluid altered decolorized and unaltered wall rocks are obvious the migrated sio2 so3 lree hf nb zr ta th u mo sn w into altered wall rocks suggests a deep basement metamorphic rocks derived si rich alkaline brine for the fluid rock interaction while the leached fe2o3 mgo mno tio2 ba cs rb as co v ni sb sc cu pb and zn from the altered rocks imply a material contribution of banxi group wall rocks during the sb mineralization process consequently we conclude that the quartz stibnite stage of the banxi sb deposit was formed during the late triassic orogeny in the xuefeng mountain region heated by granitic magmatism sb and s were leached from the basement rocks forming an initial si rich and alkaline ore bearing fluid precipitation of stibnite from the fluid resulted from interacting with wall rocks and mixing of meteoric water coupled by releasing of stress decreasing of temperature and lowering of the ph at higher crustal levels

determination of deformation modulus in a weak rock mass by using menard pressuremeter abstract the deformation modulus of heavily jointed andesitic rock mass was investigated by using 41 menard pressuremeter test results and geotechnical information obtained from seven geotechnical boreholes the geotechnical borehole logs and laboratory test results provided by a mining company were used for the assessment of rock mass characterization the log and the test results were taken into account in the rock mass classification work the well known empirical equations were employed to predict the deformation modulus of the rock mass the predictions and the pressuremeter test results were compared and their performance indicators were presented non linear multiple regression methods were used for predictive modelling of the deformation modulus of the rock mass by considering the available data rock quality designation rqd discontinuity condition rating dc of the rock mass rating rmr system and uniaxial compressive strength of the intact rock ci were taken into consideration as input parameters in four new prediction equations to be used for determination of deformation modulus one more equation was proposed by the addition of the depth as a predictive parameter the influence of the depth and vertical to horizontal stress ratio k on the deformation modulus was preliminarily examined by using finite element modelling initially the rock mass was assumed to be an isotropic elastic brittle plastic medium later on the rock mass was modelled as a discontinuum by imposing a discrete fracture network dfn keeping all of the mechanical properties constant different depth and k parameters were applied to the pressuremeter models no influence of the depth and k on the deformation modulus was observed for the isotropic medium while the depth contributed to an increase in the modulus in the anisotropic discontinuum analysis the numerical modelling findings constituted a basis for the inclusion of the depth parameter into the new predictions

isotopic composition of strontium in the valle de tena spanish central pyrenees fluorite deposits relevance for the source of elements and genetic significance the fluorite deposits of the valle de tena central pyrenees include stratabound portalet and vein lanuza and tebarray deposits the formation of which are linked to a namurian westfalian emersion episode and to post hercynian hydrothermal systems similar to those occurring elsewhere in hercynian europe in this study strontium isotopes were used to determine the source s of strontium and by inference calcium of the fluorite mineralizations as well as the nature of the ore forming fluids fluorite and calcite from each deposit have similar 87sr 86sr ratios portalet 0 7085 0 7108 lanuza 0 7086 0 7104 and tebarray 0 7086 0 7101 in all deposits the sr isotope composition of most of the ca minerals is more radiogenic than that of the host limestones this indicates that the ca minerals contain a mixture of sr derived locally from the host limestones and 87 sr enriched sr leached from silicate minerals in the siliciclastic portion of the basement sequence and in granites from the study area volcanic rocks are ruled out as a significant sr source for the fluorite deposits the observed trend in 87sr 86sr versus 1 sr support a fluid rock interaction model which satisfactorily reproduces the marked 87sr enrichment in the fluorites and calcites from the deposits

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

indirect determination of the modulus of deformation of rock masses based on the gsi system today as a result of the increase in the number of large tunnel constructions and underground excavations required for civil engineering and waste disposal and the operation of deep open pit mines determination of rock mass properties has become one of the most important stages in design and construction for rock engineering when rocks and rock masses are classified for geotechnical purposes this needs to be on the basis of strength or static modulus of deformation to give an indication of their stability or deformational response in addition the strength and modulus of deformation are the necessary input parameters of the rock masses to be utilized by numerical methods the modulus of elasticity of the rock material is undoubtly the geomechanical parameter that best represents the mechanical behaviour of rock material a similar conclusion can also be made for rock masses however the modulus of deformation of rock masses should be determined in situ by carrying out special tests which normally implies considerable costs and operational difficulties because of such difficulties the determination of the modulus of deformation of the rock masses continues to attract the attention of rock engineers and engineering geologists given the importance of having the value of the modulus of deformation available and at the same time the operational and economical difficulties mentioned above many researchers mentioned below were led to consider several cost effective and not too time consuming indirect procedures that can provide information on the modulus of deformation these attempts

geochemistry and geochronology of the banxi sb deposit implications for fluid origin and the evolution of sb mineralization in central western hunan south china abstract central western hunan in south china hosts the largest antimony belt in the world with two types of sb deposits identified sb au woxi type and sb only xikuangshan type banxi is the most representative deposit in the region with vein type sb mineralization hosted in neoproterozoic clastic rocks stibnite developing in ores and arsenopyrite mainly occurring in altered country rocks trace element contents including rare earth elements ree and isotopic ratios s pb sr nd he and ar in stibnite and or arsenopyrite were analyzed to determine the timing of ore formation and to elucidate fluid origin and evolution processes most sulfides have high ree contents 45 103 ppm moderate fractionation between lree and hree lree hree 6 38 11 56 and slightly negative eu anomalies eu eu 0 53 0 72 the 34 s values are 3 88 5 81 for stibnite and 9 25 11 82 for arsenopyrite the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios range from 18 617 to 18 635 15 695 to 15 739 and 38 965 to 38 981 for stibnite and from 18 594 to 18 609 from 15 587 to 15 698 and from 38 893 to 38 926 for arsenopyrite the 87 rb 86 sr and 87 sr 86 sr ratios are 0 3016 3 538 and 0 711463 0 717591 respectively for stibnite and 0 2251 2 214 and 0 711244 0 711565 respectively for arsenopyrite the 147 sm 144 nd and 143 nd 144 nd ratios are 0 1174 0 9816 and 0 511942 0 512768 for stibnite with end t values t 130 ma ranging from 12 4 to 6 6 and two stage model ages t 2dm ranging from 1457 to 1932 ma the 40 ar 36 ar and r ra ratios where ra is the atmospheric 3 he 4 he ratio of 1 4 10 6 are 409 545 and 0 0088 0 0348 respectively for stibnite the rb sr and sm nd isotopic analyses of the sulfides yield isochron ages of 129 4 2 4 ma 2 mswd 1 3 and 130 4 1 9 ma 2 mswd 1 6 respectively the combined trace element and isotopic data set indicates that the ore forming fluids were a mixture of dominantly deep basement derived solute rich parent water and a small amount of dilute heated meteoric water the decreases in ree 34 s 206 pb 204 pb 207 pb 204 pb 208 pb 204 pb 87 rb 86 sr 87 sr 86 sr 147 sm 144 nd and 143 nd 144 nd and increases in 40 ar 36 ar and 4 he contents in the stibnite from the earlier quartz stibnite mineralization stage stage ii through to the later stibnite mineralization stage stage iii indicate that the influx of meteoric water increased during sb mineralization the deep sourced relatively high temperature rock reacted fluid mixed with increasing amounts of more oxidized low temperature meteoric fluids causing the precipitation of arsenopyrite and stibnite sequentially at the banxi deposit a two period genetic model has been proposed for the world class sb mineralization in the central western hunan region the woxi type sb au deposits were derived from orogenic fluids generated from folding and shearing during the caledonian and indosinian orogeny whereas the xikuangshan type sb deposits were formed by mixing heated basement derived hydrothermal fluid circulating during the flare up of magmatism in south china with lower temperature meteoric water

reliability based design for allowable bearing capacity of footings on rock masses by considering angle of distortion abstract this study addresses the impact of spatial variability on the angle of distortion between two footings in rock masses a simple elasto perfectly plastic model based on the hoek brown criterion is taken to simulate the spatial variation of rock mass properties in the finite element analyses this model is calibrated by a large rock mass database with monte carlo simulations stochastic samples of angle of distortion between two footings are obtained which are further used to derive reliability based allowable bearing stresses the analysis results show that the geological strength index gsi of rock masses and uniaxial compressive strength of intact rock are the two dominate factors that affect the reliability based design comparisons to the existing codes show that these codes are appropriate for poor to fair rock masses conservative for good to very good rock masses and un conservative for very poor rock masses

a comparative study of the determination of rock mass deformation modulus by using different empirical approaches abstract the increase in rock engineering projects over the last decade has made an increase in the importance of the determination of the rock mass parameters although properties of rock material are usually determined at laboratory it can also be determined by special in situ tests these in situ tests are both expensive and time consuming therefore empirical equations are developed to estimate rock mass properties by several researchers in numerical modelling rock mass properties are important furthermore controlling the results of models making back analysis and taking the feedback are very important comparison of different empirical equations of deformation modulus of rock mass suggested by different researchers by using field displacement measurements and numerical modelling results is aimed in this study

middle miocene to earliest pliocene sedimentological and geochemical records of climate change in the western qaidam basin on the ne tibetan plateau global cooling tibetan plateau uplift and the retreat of the para tethys sea have long been thought to be the key controls of the cenozoic climate change in the asian inland however due to the scarcity of long term palaeoclimate records it is not entirely clear which of these factors plays the major role here we present new sedimentological and geochemical proxy records toc carbonate so42 and cl from a 1040 m late cenozoic sedimentary sequence ca 17 to 5 0 ma from the western part of the qaidam basin the largest inland basin on the ne tibetan plateau geochemical records reveal an evident two stage change from ca 17 ma to 11 1 ma phase i the proxies show an upward decrease of carbonate content and toc concentration and a persistent increase in the concentration of the soluble anions so42 and cl even though superimposed high frequency fluctuations are evident from ca 11 1 ma to 5 0 ma phase ii the average concentrations of so42 and cl are higher than those from phase i and a sharp decrease in the carbonate content occurred the sedimentological and geochemical proxy records demonstrate that the qaidam basin has experienced increased aridity since ca 11 1 ma we suggest that the miocene global cooling exerted a significant influence on the drying of the qaidam basin by decreasing evaporation rates and water vapour concentrations in the atmosphere the mio pliocene episodic and persistent uplift of the ne tibetan plateau exerted an important influence superimposed upon this driving force while during ca 11 1 to 8 ma the rapid uplift of the altun shan might have played a key role in climate change of the qaidam basin c 2013 elsevier b v all rights reserved

what triggers the transition of palaeoenvironmental patterns in china the tibetan plateau uplift or the paratethys sea retreat abstract geological research has illustrated the transition of palaeoenvironmental patterns by the earliest miocene from a planetary wind dominant type to a monsoon dominant type indicating that the east asian monsoon became markedly intensified and played a leading role in the east asian climate from a modeling point of view the pioneering research using the reduced number of scenarios had demonstrated that both the tibetan plateau uplift and the paratethys sea retreat were important for understanding the asian monsoon evolution however the sensitivity of the paratethys retreat to the east asian climate still needs further studies based on the more detailed scenarios thirty numerical experiments under the six paratethys sea and the five tibetan plateau conditions illustrate the shifts from zonal climate to the monsoon climate in east asia the results confirm again that both the paratethys retreat and the tibetan plateau uplift play important roles in the formation of the monsoon dominant environmental pattern and show that the paratethys retreat can strengthen the east asian monsoon and greatly increase humidity and aridity respectively in the monsoon areas and northwest china which is similar to the impact of the tibetan plateau uplift on the east asian climate furthermore the fact that the paratethys sea retreats to the turan plate is found to be the key criterion for the palaeoenvironmental patterns transition in china the shrinkage of paratethys sea leads to the reconstructions of the pressure system and the atmospheric circulations which result in the variations of precipitation and the transition of palaeoenvironmental patterns

the foundation of a 40 storey tower in jointed basalt abstract a 132 70 m high tower above foundation has been successfully completed at tenerife island the foundation of the tower a 2 m thick reinforced concrete slab is supported by jointed vesicular and weathered basalt and scoria a three dimensional elastic finite element program has permitted to calculate the displacements of the tower and the stresses in the slab the installation of rod extensometers at different depths below the slab and clinometers at the lower basement has provided comparison between measured and calculated displacements and the estimation of in situ deformation moduli a first stage prediction before construction has allowed establishment of an upper limit based upon pressuremeter modulus and a lower limit based upon bieniawski s equation the geomechanics classification in rock engineering applications in proceedings of the fourth cong isrm congress montreux vol 2 1979 p 41 48 of the settlements of the tower slab the geometric mean of these values comes close to the measured settlement the moduli deduced from the simple empirical equation proposed by gokceoglu et al predicting the deformation modulus of rock masses a comparative study int j rock mech min sci 2003 40 701 10 and hoek and brown practical estimates of rock mass strength int j rock mech min sci 1997 40 701 10 as a function of gsi provide a good fit with the measured settlements in this type of rock a good correlation is also obtained with the empirical equation presented by verman et al effect of tunnel depth on modulus of deformation of rock mass rock mech rock eng 1997 30 3 121 7 that incorporates the influence of the confining stress in the deformation modulus

hypogene and supergene alteration of the late palaeozoic ratburi limestone during the mesozoic and cenozoic thailand surat thani province implications for the concentration of mineral commodities and hydrocarbons an interdisciplinary study of the upper carboniferous to middle permian ratburi group peninsular thailand is presented the investigation involved sedimentary petrography inorganic geochemistry sr c o isotope analyses micropalaeontology as well as radio carbon age dating emphasis was placed on the post depositional evolution of the ratburi limestone in the surat thani province the holocene chemical residues and the various calcite and dolomite minerals which have formed since the late palaeozoic in the ratburi limestone are the product of a complex multistage alteration which is called supergene and hypogene karstifications respectively sedimentation took place in a shelf environment with some reefs evolving during the late murgabian at the shelf margin there was no pre concentration of elements except for ca and f during sedimentation diagenetic neomorphism and cementation under marine and freshwater conditions caused the ratburi limestone to convert into a marble like rock fabric selective dolomitization is of local scale and has impacted only on part of the ratburi limestone during the lower to upper permian a significant enhancement of pore space and better conduits were generated during the late cretaceous epithermal alteration the most favorable conditions for the accumulation of metals were provided during the high temperature stage of epithermal alteration when a low metal concentration with as zn sb u co and pb existed unlike the other elements sb was subject to a multiphase concentration giving rise to a considerable sb deposit in the region the most recent stage of karstification produced numerous caves dripstones tufa terraces and encrustations around brine pools in the study area this alteration originated from per descensum and per ascensum processes which may be traced back to 15 000 years before present the alteration of the ratburi limestone may be subdivided into two parts the prograde post depositional alteration beginning with diagenesis reached its temperature climax during epithermal subsurface alteration i the retrograde branch of alteration lasted until the most recent times the initial stages deposition and diagenesis took place under more or less closed system conditions relative to the succeeding stages of the prograde alteration which saw the strongest influx of metal bearing brine during the epithermal stage i the retrograde branch of alteration is element conservative

hydrothermal events in the valle de tena spanish western pyrenees as evidenced by fluid inclusions and trace element distribution from fluorite deposits abstract this paper provides further evidences from fluorite and calcite geochemistry and from fluid inclusion studies for the origin of the valle de tena fluorite deposits the valle de tena spanish western pyrenees contains two kinds of fluorite mineralizations 1 vein type deposits located in the vicinity of the panticosa granite and enclosed by devonian carbonate facies and 2 carbonate hosted mineralizations on highly silicified lower carboniferous limestones based on geological evidences the latter deposits can be referred to as permo triassic microthermometrical measurements on two phase water rich inclusions with high liquid to vapor ratios yield homogenization temperatures ranging from 100 to 200 c for the two deposit types salinities range from 4 0 to 11 6 eq wt nacl for carbonate hosted deposits and from 12 5 to 21 3 eq wt nacl for vein mineralizations ree contents are variable and highest abundances are found in the fluorite from lanuza and tebarray green flurite these later fluorite mineralizations have primary ree patterns with positive eu anomalies which possibly reflect the alteration of feldspar the ree distribution patterns of fluorites and calcites from the carbonate hosted mineralizations are different from those occurring as veins the decrease of lree in the former resulted in roof shaped ree patterns the negative eu anomalies as well as the trace element distribution allow us to deduce that the fluid from which these later ca minerals were formed was probably equilibrated with the sedimentary country rocks the fluid inclusion geochemical geologic and preliminary stable isotope data support two temporally distinct hydrothermal systems accounting for the fluorite formation and suggest a sedimentary basin source for the ore fluids high salinity fluids basement brines are involved in the formation of the vein type deposits whereas the subsequent carbonate hosted mineralizations were formed by mobilization of the fluorite veins by formation waters the most likely fluorite deposition mechanism is cooling with minor contribution of fluid rock interaction in such context magmatic activity is considered as heat source the above mineralization events possibly span a time from permian to triassic which is in close agreement with the timing of hydrothermal processes documented throughout the hercynian europe

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

late miocene pliocene deceleration of dextral slip between pamir and tarim implications for pamir orogenesis abstract the timing of the late cenozoic collision between the pamir salient and the tien shan as well as changes in the relative motion between the pamir and tarim are poorly constrained the northern margin of the pamir salient indented northward by 300 km during the late cenozoic accommodated by south dipping intracontinental subduction along the main pamir thrust mpt coupled to strike slip faults on the eastern flank of the orogen and both strike slip and thrust faults on the western margin the kashgar yecheng transfer system kyts is the main dextral slip shear zone separating tarim from the eastern pamir with an estimated cumulative offset of 280 km at an average late cenozoic dextral slip rate of 11 15 mm a cowgill 2010 in order to better constrain the slip history of the kyts we collected thermochronologic samples along the eastward flowing deeply incised antecedent tashkorgan yarkand river which crosses the fault system on the eastern flank of the orogen we present 29 new biotite 40 ar 39 ar ages apatite and zircon u th sm he ages and apatite fission track aft analysis combined with published muscovite and biotite 40 ar 39 ar and aft data to create a unique thermochronologic dataset in this poorly studied and remote region we constrain the timing of four major n trending faults the latter three are strands of the kyts the westernmost the kuke fault experienced significant dip slip west side up displacement between 12 and 6 ma to the east within the kyts our new thermochronologic data and geomorphic observations suggest that the kumtag and kusilaf dextral slip faults have been inactive since at least 3 5 ma long term incision rates across the aertashi dextral slip fault the easternmost strand of the kyts are compatible with slow horizontal slip rates of 1 7 5 3 mm a over the past 3 to 5 ma in summary these data show that the slip rate of the kyts decreased substantially during the late miocene or pliocene furthermore miocene present regional kinematic reconstructions suggest that this deceleration reflects the substantial increase of northward motion of tarim rather than a significant decrease of the northward velocity of the pamir

the grid work texture of authigenic microcrystalline quartz in siliceous crust type sct mineralized horizons siliceous crust type sct formations are pervasive silicified horizons associated with fluoritebarite polymetallic sulfide mineralization in carbonate rocks they almost invariably show a peculiar grid work texture formed by microcrystalline quartz the mineralogical and textural features of several sct samples from italy spain france china and brazil were investigated by optical and electron microscopy and x ray and neutron powder diffraction the resulting 001 pole figures exhibit two main components of orientation of the crystallographic c axis with respect to the normal to the sample surface one located at about 35 and the other in the range 60 85 the observed textural features are seen in all samples and they appear to be independent of the age and geographical location of the sct formation the observed grid work texture is tentatively interpreted as forming by nucleation of quartz seeds on specific faces of surrounding crystals the observed morphology and the regularly oriented populations of crystals are consistent with simultaneous growth of quartz crystals having well defined reciprocal orientations the grid work texture of quartz in sct horizons is similar to the type reported for magadi type cherts which are commonly interpreted as formed by magadiite mediated silica precipitation processes since the genesis of sct deposits is totally unrelated to alkaline lake genetic processes it is concluded that cherts showing strongly textured patterns of microcrystalline quartz may have a different origin than magadi type deposits

estimating the deformation modulus of rock masses a comparative study although the modulus of deformation of rock masses has crucial importance for geotechnical projects such as tunnels and dams the determination of this parameter by in situ tests requires considerable costs and involves difficult operational processes for this reason empirical equations for the indirect estimation of the modulus of deformation are an interesting issue for rock engineers and engineering geologists this study includes assessment of the prediction performances of some existing empirical equations using in situ plate loading test data and rock mass properties producing an empirical equation depending on the new data construction of a fuzzy inference system for the estimation of modulus of deformation and making a comparison between results obtained from the empirical equations and fuzzy inference system a series of calculations and statistical analyses were undertaken it is concluded that the performance of the empirical equations and fuzzy inference system obtained in this study is satisfactory however the prediction models developed in this study are limited by the number of the data used and the rock types employed for these reasons a cross check should be performed before using these prediction models for design purposes

timing of the tianshan mountains uplift constrained by magnetostratigraphic analysis of molasse deposits abstract the tianshan mountains lie in the actively deforming part of the india asia collision zone the thrust faulting and folding of the neogene and quaternary sediments forming linear roughly east west anticlines at the northern and southern borders of the orogenic belts indicate crustal shortening and thickening in late cenozoic time detailed magnetostratigraphic studies of the molasse deposits of the folded neogene and quaternary strata in the northern edge of the tianshan mountains indicate that the onset of uplift occurred at 7 ma deposition of the thick conglomerates between 7 and 2 58 ma in the studied region was mainly in response to the tectonic uplift while the accumulation of the early pleistocene conglomerates xiyu formation was mostly controlled by both tectonics and climatic cooling our results indicate that the present high relief of the tianshan mountains is the result of two dominant phases of uplift occurring at about 7 2 58 ma and the early pleistocene

engineering characteristics of ankara greywacke under the foundation of the beytepe open air theatre ankara turkey the construction of a large open air theatre having with an audience capacity of 7 000 is planned at the beytepe campus of hacettepe university located near ankara turkey in the heart of anatolia the foundation of the open air theatre is composed of weak and heavily jointed ankara greywacke an estimation of the strength and deformation of the ankara greywacke was required for assessments of short and long term stability accordingly rock mass characterization of the ankara greywacke was investigated in detail by scan line surveys and back analyses of in situ tests performed on the excavated surface of the rock mass the final version of the hoek and brown criterion hoek et al in proceedings of the north american rock mechanics society meeting toronto canada pp 1 6 2002 together with and improvements proposed by sonmez and gokceoglu int j rock mech min sci 43 671 676 2006 were considered together for the back analyses of small slope benches subjected to plate loading test loaded to failure in addition the plate loading test data were used with some well known empirical equations for predicting of deformation modulus of rock masses to calculate ranges of values of the geological strength index gsi the static and pseudostatic slope stabilities of the audience seating structures to be supported by benches excavated into the rock were also analyzed the stability assessments revealed the unlikelihood of large rock mass failures for the short term construction stages or for the long term as constructed conditions under static or pseudo static conditions additionally the analyses showed that there was no need for anchors between the concrete seating structures and greywacke rock mass

asynchronous responses of east asian and indian summer monsoons to mountain uplift shown by regional climate modelling experiments it has been demonstrated in climate models that both the indian and east asian summer monsoons ism and easm are strengthened by the uplift of the entire asian orography or tibetan plateau tp i e bulk mountain uplift such an effect is widely perceived as the major mechanism contributing to the evolution of asian summer monsoons in the neogene however geological evidence suggests more diachronous growth of the asian orography i e regional mountain uplift than bulk mountain uplift this demands a re evaluation of the relation between mountain uplift and the asian monsoon in the geological periods in this study sensitivity experiments considering the diachronous growth of different parts of the asian orography are performed using the regional climate model cosmo clm to investigate their effects on the asian summer monsoons the results show that different from the bulk mountain uplift the regional mountain uplift can lead to an asynchronous development of the ism and easm while the ism is primarily intensified by the thermal insulation mechanical blocking effect of the southern tp zagros mountains the easm is mainly enhanced by the surface sensible heating of the central northern and eastern tp such elevated surface heating can induce a low level cyclonic anomaly around the tp that reduces the ism by suppressing the lower tropospheric monsoon vorticity but promotes the easm by strengthening the warm advection from the south of the tp that sustains the monsoon convection our findings provide new insights to the evolution of the asian summer monsoons and their interaction with the tectonic changes in the neogene

late miocene quaternary rapid stepwise uplift of the ne tibetan plateau and its effects on climatic and environmental changes abstract the way in which the ne tibetan plateau uplifted and its impact on climatic change are crucial to understanding the evolution of the tibetan plateau and the development of the present geomorphology and climate of central and east asia this paper is not a comprehensive review of current thinking but instead synthesises our past decades of work together with a number of new findings the dating of late cenozoic basin sediments and the tectonic geomorphology of the ne tibetan plateau demonstrates that the rapid persistent rise of this plateau began 8 1 ma followed by stepwise accelerated rise at 3 6 ma 2 6 ma 1 8 1 7 ma 1 2 0 6 ma and 0 15 ma the yellow river basin developed at 1 7 ma and evolved to its present pattern through stepwise backward expansion toward its source area in response to the stepwise uplift of the plateau high resolution multi climatic proxy records from the basins and terrace sediments indicate a persistent stepwise accelerated enhancement of the east asian winter monsoon and drying of the asian interior coupled with the episodic tectonic uplift since 8 ma and later also with the global cooling since 3 2 ma suggesting a major role for tectonic forcing of the cooling

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

transforming the miocene altyn tagh fault slip into shortening of the north western qilian shan insights from the drainage basin geometry although it has long been proposed that active crustal shortening within the qilian shan accommodates slip along the altyn tagh fault questions regarding the temporal and spatial amount of slip transfer remain debated traditional shortening calculations cannot yet be made accurately because the geology is not known well enough following the view that long linear drainage basins in the north western qilian shan developed in response to internal shortening associated with slip transfer along the altyn tagh fault we targeted this special irregular drainage basin geometry to develop an alternative way to estimate shortening we infer a total of 66 km of shortening in the western qilian shan with a north eastward decrease in the magnitude of shortening this 39 shortening strain is comparable to previous estimates estimates of dates of initiation support the view that significant shortening and topographical growth within the north western qilian shan occurred in post middle miocene time

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

the development of a coal measure classification cmc and its use for prediction of geomechanical parameters abstract many studies have been performed to predict the strength and deformation moduli for both rock masses and discontinuities however in most empirical equations in the literature that have been proposed for the estimation of the strengths and deformation moduli the rock mass is assumed isotropic although it is known that the strength and deformation of a stratified rock mass varies depending on the loading direction in relation to the orientation of the lamination planes there exists at present no commonly accepted method for characterising this anisotropy this paper outlines the development of a rock mass rating system for coal measure rock masses that can be used to empirically predict the engineering properties of stratified rock masses the output from the classification system is two numerical ratings representing the different engineering properties of the strata in directions parallel and perpendicular to stratification a detailed description on the methodology used to develop the classification system has been given and the derivation and rating of the various rock mass parameters is outlined the methodology of deriving the in situ stratified rock mass input parameters and geomechanical computational analysis is illustrated for the case of two rock bolted roadways within a representative deep uk coal mine the model predictions were validated against the actual in situ monitoring data of displacements within the immediate roof of the roadway

estimation of rock mass deformation modulus and strength of jointed hard rock masses using the gsi system abstract rock mass characterization is required for many applications in rock engineering practice including excavation design support design stope design amongst others for these purposes it is necessary to obtain design input parameters such as deformation moduli and strength parameters for numerical modeling although such parameters can ultimately be determined from in situ tests at the preliminary design stage where access to underground is limited the practical way to obtain these parameters is to apply a rock mass classification system to characterize the rock mass and estimate the rock mass properties over the years many classification systems such as rqd rock mass rating q and geological strength index gsi systems have been developed amongst them the q system is widely used for rock support system design and the gsi system is used for estimating design parameters the gsi system is the only rock mass classification system that is directly linked to engineering parameters such as mohr coulomb hoek brown strength parameters or rock mass modulus however the application of the existing gsi system is hindered by the facts that the use of the system is to some extent subjective and requires long term experience in the present study a quantitative approach to assist in the use of the gsi system is presented it employs the block volume and a joint condition factor as quantitative characterization factors the approach is built on the linkage between descriptive geological terms and measurable field parameters such as joint spacing and joint roughness the newly developed approach adds quantitative means to facilitate use of the system especially by inexperienced engineers the gsi system is applied to characterize the jointed rock masses at two underground powerhouse cavern sites in japan gsi values are obtained from block volume and joint condition factor which in turn are determined from site construction documents and field mapping data based on gsi values and intact rock strength properties equivalent mohr coulomb strength parameters and elastic modulus of the jointed rock mass are calculated and compared to in situ test results the point estimate method is implemented to approximate the mean and variance of the mechanical properties of the jointed rock masses it is seen that both the means and variances of strength and deformation parameters predicted from the gsi system are in good agreement with field test data

late quaternary environmental changes in the taklamakan desert western china inferred from osl dated lacustrine and aeolian deposits sediment records from the tarim basin of western china are of great importance for understanding late quaternary climatic variability in central asia a chronology of aeolian and lacustrine deposits from the centre and southern margin of the taklamakan desert central tarim basin has been established using optical dating methods distinct variations in humidity during the last 40 000 a in this extremely arid inland basin have been identified lacustrine sediments were deposited in the centre of the taklamakan during two periods of wetter than present day conditions at around 2000 and 30 000 a ago another humid period is recorded between 40 000 and 30 000 a ago aeolian processes the development of large migrating dune fields dominated during periods of more arid conditions sand wedges at the southern margin of the taklamakan are dated at ca 40 000 a and ca 18 000 a and imply a significant temperature decrease in that area sedimentological evidence for a late holocene humid period are consistent with records in ancient chinese literature wetter environmental conditions in the past within the taklamakan as indicated by the presence of lacustrine deposits are also supported by data from adjacent regions it is assumed that changes of global westerlies and of the mobile polar high triggered the fluctuations of precipitation in the study area however variations in temperature in the taklamakan desert are presumed to be mainly controlled by the intensity of the winter monsoon

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

increasing nd isotopic ratio of asian dust indicates progressive uplift of the north tibetan plateau since the middle miocene the time and rate of tibetan uplift is critical in understanding both the geodynamics of plateau growth and the influence of mountain building on climate change models predict that the uplift of the north tibetan plateau ntp occurred later than uplift of the south and central tibetan plateau uplift of the ntp is believed to have initiated the aridity in the interior of asia and to have critically affected the evolution of asian monsoon and ultimately global climate the history of ntp uplift has remained uncertain however scenarios range from early miocene to the past million years this work provides new evidence by relating the nd isotopic evolution of asian dust to ntp uplift the sources of the asian dust are located in the arid lands between the ntp and the central asia orogen mass balance calculations indicate that the decreasing e nd values from 8 2 to 10 4 for pacific dust since 15 ma reflects increasing relative contribution of ntp materials 40 to 70 to the dust source as paleoelevation in the central asia orogen has largely remained constant the increasing relative ntp detritus contribution is interpreted to reflect the progressive surface uplift of the ntp at a rate of at least 0 12 mm yr 1 since 15 ma

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

the evolution of dry lands in northern china and in the republic of mongolia since the last glacial maximum abstract the dry lands in china and mongolia include sand seas gravel deserts stable sand dunes desert steppe steppe and scrub woodlands environments distributed in a wide range of geomorphological and tectonic settings from 155 m below sea level to more than 5000 m asl in china the sandy deserts and gravel deserts are located in the arid regions mainly west of the helan mountains 106 e whereas the stable dune regions are distributed in the semi arid areas east of the helan mountains in mongolia deserts cover more than 40 of the country they are mainly distributed in the southern and southwestern part of the country in inter mountain valleys and basins of the altai mountains and in the uvs nuur basin in northwestern mongolia the desert regions enclose mainly gravel desert gobi and comprise some areas with sand fields and dune fields especially in western mongolia relict frost wedges and moraines in the chaidamu and tarim basins of china indicate that the coldest time of the last glaciation occurred at 30 25 ka in these two areas the stratigraphy of the dunes in the badain jaran desert high lake levels in the areas near and within the large deserts in china and in mongolia suggest a much more humid climate in western china and in mongolia during marine isotope stage three however the period after 24 ka to the end of the pleistocene was mostly characterised by increased temperature and reduced precipitation in the chaidamu and tarim basins paleoenvironmental conditions in the eastern part of the chinese desert belt were marked by an extensive widening of dune formation at 21 13 ka reflecting a weaker intensity of east asian summer monsoon during the holocene higher lake levels stratigraphy of dunes and results of palynological isotopical and sedimentological analyses of lacustrine sediments in the western china and mongolia suggest a few wetter periods especially in the earlier part of the holocene the holocene climatic conditions in the eastern part of the chinese deserts have enabled stabilisation of dunes and formation of soils the presently active dunes in this region are a result of desertification due to human influences recent investigations in the dry lands of china and mongolia demonstrate broad regional differences that must be given attention for the understanding of palaeoclimates

metallogenesis at the terramonte pb zn ag quartz vein portugal geological mineralogical and geochemical evidences abstract the pb zn ag quartz vein from terramonte cuts the neoproterozoic cambrian schist greywacke complex this orebody was partially exploited the paragenetic sequence consists of four stages containing quartz accompanied mainly by arsenopyrite and pyrite in the first stage sphalerite in the second stage galena showing many inclusions of several sulphosalts in the third stage and carbonates in the fourth remobilization stage several sulphide and sulphosalt grains are oscillatory zoned the chemical distinction between lighter and darker zones in backscattered images of arsenopyrite pyrite sphalerite and freibergite is due to substitutions in the mineral lattices but the distinction between these zones in semseyite is due to a higher pb content and a lower sb content in the lighter zone than in the darker zone and the metal and metalloid are the main constituents in the solid solution but are not correlated the sb ag and bi substitute for pb in galena but did not cause any zoning ore deposition was possible due to mixing of a hypersaline fluid with up to 26 wt nacl equivalent and occasionally with cacl2 up to 17 wt which carried the metallic content of the fluid with an extremely low salinity fluid of presumed meteoric origin that percolated down into the basement the metals could have been leached from a mixture of mainly metasediments and also previous sb au deposits by fluids that acquire high salinity in one of two probable ways leaching of salt beds or following seawater evaporation the entire mineralizing event probably occurred at a relatively low temperature possibly between 120 and 230 c remobilization of pb zn ag as sb and cu will be due to the tectonic evolution of the opening of the atlantic ocean this vein is probably of alpine age

empirical estimation of rock mass modulus the deformation modulus of a rock mass is an important input parameter in any analysis of rock mass behaviour that includes deformations field tests to determine this parameter directly are time consuming expensive and the reliability of the results of these tests is sometimes questionable consequently several authors have proposed empirical relationships for estimating the value of rock mass deformation modulus on the basis of classification schemes these relationships are reviewed and their limitations are discussed based on data from a large number of in situ measurements from china and taiwan a new relationship based upon a sigmoid function is proposed the properties of the intact rock as well as the effects of disturbance due to blast damage and or stress relaxation are also included in this new relationship