mineral parageneses in metamorphic rocks exposed along tailuko gorge central mountain range taiwan field petrographic and microprobe investigations of metaclastic rocks calcareous schists marbles chloritic calcareous meta volcanic units and schists paragneisses which crop out along the eastern portion of the central east west cross island highway in taiwan demonstrate that metamorphic intensity gradually increases eastward the lower greenschist facies slate formation on the w contains completely recrystallized pure albitic plagioclase but at least some of the white micas chlorites probably represent relict detrital flakes neo blastic biotite and epidote occur sporadically in the pihou formation and increase dramatically eastward concomitantly the abundance of carbonaceous matter decreases to zero in the eastern tailuko zone and the amount of chlorite white mica diminishes somewhat epidote becomes more aluminous at higher metamorphic grade eastward phengites change progressively to more muscovitic compositions as the proportion of biotite increases a close approach to chemical equilibrium for the pre cenozoic complexly deformed metamorphic basement assemblages is suggested by regular systematic major and minor element partitioning between analysed coexisting phases fractionation is less pronounced on the e reflecting higher temperatures estimated physical conditions of recrystallization with h2o and co2 moderate are t 325 75 c p 3 kbar w t 425 75 c p 4kbar e the gradual eastward increase in metamorphic intensity from the slate formation through the pihou formation and the three tailuko zones as well as the relict precursor textures in the pre cenozoic layered basement rocks indicate that the observed paragenetic sequence could represent a synchronous neogene recrystallization event probably accompanying the plio pleistocene collision of the asiatic continental margin and the luzon coastal range andesitic arc

grading opening and shearing deformation of deep outward dip shear belts inside high slope a case study abstract tectonic shear belts with their low mechanical strengths large spatial extents and obvious shearing damage present challenges for the excavation of high slopes in this study we described the basic unloading performances of shear belts induced by excavation through observational data and numerical back analysis the unloading deformation and failure processes of deep outward dipping shear belts exposed on a hydraulic slope nearly 300 m tall were investigated first the field observation and monitoring data indicated that the excavation induced deformation pattern of the outward dipping shear belt can be divided into two stages primarily opening deformation normal to the shear belt during the first stage and primarily shear deformation along the shear belt during the second stage manifested as opening and shear cracks along the active shear belt then the numerical and analytical analysis were performed to expose the displacement evolution of the shear belt during the multistep excavation of the slope from the top down the back analysis showed that the grading deformation mechanism of the shear belt was primarily related to the reduction of normal compressive stress on the shear belt s plane due to slope excavation the reinforcement schemes including a prestressed anchor cable to limit deep unloading deformation and a prestressed rock bolt to restrain the surface relaxation of the rock mass of the slope were also discussed in practice actual excavation and corresponding monitoring data indicated that the unloading mechanism and supporting measures for the shear belt presented in this study were reasonable and effective these presented experiences can also enrich the stability analysis and support design for similar high slopes

active continental subduction and crustal exhumation the taiwan orogeny a tectonic model of active continental subduction followed by crustal exhumation is proposed to explain the orogeny in taiwan the subducted crust is represented by a low velocity zone dipping eastwards beneath the major part of taiwan while the exhumed crust is marked by a high velocity bulge high heat flow and absence of seismicity beneath the eastern central range the boundary between the subducted and exhumed crust has been identified from surface geology and analyses of thermal history across the central range the dynamic force that has been driving the exhumed crust is identified by results from focal mechanisms structural geology and geodetic survey in the eastern central range such a tectonic model may provide a good explanation for the evolution of the taiwan orogeny as well as an active case for studying other long extinct systems of continental subduction and exhumation

high pressure metamorphism in the chinshuichi area yuli belt eastern taiwan abstract tectonic blocks and slabs of mafic ultramafic rocks are distributed discontinuously in the yuli metamorphic belt of taiwan the blocks include rare omphacite metagabbros and garnet epidote blueschists in the wanjung and juisui tamayen areas respectively such high pressure hp mineral assemblages have been attributed to a mid miocene subduction event however the surrounding psammitic pelitic and chloritic schists are the dominant greenschist facies lithologies of the yuli belt in the chinshuichi area tectonic blocks are enclosed in garnet bearing metapelites suggesting elevated pressures in this area we recently discovered meta plagiogranite containing the assemblage glaucophane omphacite xjd up to 0 39 rutile quartz indicating p t conditions near 13 kbar 550 c new equilibrium phase modeling of a garnet paragonite mica schist and compositional isopleths for peak assemblage minerals garnet and phengite si 3 33 3 37 pfu indicate metamorphic conditions of 15 5 17 kbar 530 550 c these p t estimates are higher than previously reported in the yuli belt and suggest that both tectonic blocks and host metapelites underwent hp metamorphism the juxtaposition of tectonic blocks and metapelites apparently occurred during the formation of a subduction accretionary complex followed by exhumation facilitated by a collisional event these new findings imply that hp metamorphism was not limited to tectonic blocks and instead played a significant role attending orogenesis in eastern taiwan

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

mountain building in taiwan a thermokinematic model the taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening however a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge we propose here a new thermokinematic model of the taiwan mountain belt reconciling existing kinematic thermometric and thermochronological constraints in this model shortening across the orogen is absorbed by slip on the most frontal faults of the foothills crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge tananao complex tc where the uplift rate is estimated to 6 3 mm a 1 and beneath the westernmost internal region of the orogen hsueshan range units hr where the uplift rate is estimated to 4 2 mm a 1 our model suggests that the tc units experienced a synchronous evolution along strike despite the southward propagation of the collision it also indicates that they have reached a steady state in terms of cooling ages but not in terms of peak metamorphic temperatures exhumation of the hr units increases northward but has not yet reached an exhumational steady state presently frontal accretion accounts for less than 10 of the incoming flux of material into the orogen although there is indication that it was contributing substantially more 80 before 4 ma the incoming flux of material accreted beneath the tc significantly increased 1 5 ma ago our results also suggest that the flux of material accreted to the orogen corresponds to the top 7 km of the upper crust of the underthrust chinese margin this indicates that a significant amount 76 of the underthrust material has been subducted into the mantle probably because of the increase in density associated with metamorphism we also show that the density distribution resulting from metamorphism within the orogenic wedge explains well the topography and the gravity field by combining available geological data on the thermal and kinematic evolution of the wedge our study sheds new light onto mountain building processes in taiwan and allows for reappraising the initial structural architecture of the passive margin

fossil fluid reservoir beneath a duplex fault structure within the central range of taiwan implications for fluid leakage and lubrication during earthquake rupturing process in order to understand the kinematics which likely facilitated the speedy rupturing process of the 1999 mw 7 6 taiwan chichi earthquake we examined exposed rocks in the taiwan slate belt where the pressure and temperature conditions most resembled the hypocentre of the chi chi earthquake i e subgreenschist facies field observations and composition analyses of the silicified vein rich zones beneath the duplex structure suggest that impermeable slate layers may serve as cap rocks for confining deep seated fluids these fluids most likely come from the taiwan metamorphic complex at deeper depths by the dehydration and decarbonation reactions or partial melting in addition the gouge zone of a link fault above the detachment also indicates the presence of overpressured fluids during faulting it is probable that episodic leakage of the confined fluid reservoirs may provide essential fluids for fault lubrication during earthquake ruptures

collapse of the luzon volcanic arc during onset of arc continent collision evidence from a miocene pliocene unconformity eastern taiwan a regional miocene pliocene unconformity in the coastal range of eastern taiwan provides information about vertical motions that affected the colliding volcanic arc during initiation of arc continent collision the unconformity separates precollisional volcanic and volcaniclastic rocks of the miocene luzon arc and forearc basin from an overlying thick sequence of syncollisional pliocene pleistocene sedimentary rocks derived from the metasedimentary accretionary wedge of taiwan the duration of time represented by the unconformity averages 1 2 m y and locally ranges up to 4 m y the basal unit of the younger syncollisional sequence consists of bathyal mega slump folded mudstone pebbly mudstone and thin bedded turbidites sharp stratigraphic juxtaposition of these deep marine deposits directly above shallow marine limestone and epiclastic rocks upper part of the older arc sequence requires extremely rapid subsidence during initiation of the collisional basin the coastal range unconformity is interpreted to represent a period of latest miocene nondeposition and or erosion in the luzon arc that was related to initial subduction of the eurasian continental margin along the manila trench this period was followed in pliocene time by very rapid subsidence or collapse of the arc platform to 1 2 km water depth there are two dissimilar mechanisms of basin subsidence that may have controlled initiation of the collisional basin 1 extension rifting and crustal thinning in the luzon arc massif to form a series of small rift or pull apart subbasins or 2 flexural subsidence of oceanic lithosphere in a foreland style basin due to crustal loading in the expanding accretionary wedge of proto taiwan although data are insufficient to provide a unique solution the flexural subsidence model is supported by systematic younging of the initial subsidence event from west to east which may record eastward migration of an outer flexural bulge notable differences between the unconformity and paleogeography of the early collisional basin and analogous present day basins in the offshore region to the south suggest that arc continent collision and basin development in eastern taiwan have experienced secular change since late pliocene time

a systematic engineering geological evaluation of diabase dikes exposed at the underground caverns of dagangshan hydropower station southwest china dagangshan hydropower station is located in the middle of dadu river southwest china many diabase dikes were exposed in the adamellite granite body during excavation of the underground caverns the dikes are highly directional have crushed interiors exhibit strong alteration and have poor contact relationships with surrounding rocks all of which is inconsistent with the characteristics of typical diabase this paper describes systematic research that focused on the dikes spatial distribution macroscopic characteristics physical and mechanical properties and common instability modes factors influencing their stability and their corresponding control measurements are discussed in the context of the site and its conditions results show that most of the dikes located in the underground caverns are the branches of the main dike 9 which produced from a strong basic magma extrusion overflow event happened in between the permian and triassic due to multiple strong tectonic activities the chlorite alignment of these dikes generally tended to be significant and leaded the physical and mechanical properties to be poor then excavation and repetitive blasts resulted in strong disturbances to the original dikes and even caused rock unloading collapse rock block fall and groundwater runoff system water inflow change according to the common instability modes and reasons of diabase dikes some specific control measures including solidified rubbles reinforcement methods pre grouting and small ducts are implemented in order to keep the surrounding of diabase safety and the results show that the control methods perform a proper effect on these engineering problems

the structure of southwest taiwan the development of a fold and thrust belt on a margins outer shelf and slope d b j a m and c b acknowledge funding provided by the spanish ministerio de economia y competividad grant cgl2013 43877 p h k c acknowledges funding by most 104 2628 m 008 005 my3

magmatic like fluid source of the chingshui geothermal field ne taiwan evidenced by carbonate clumped isotope paleothermometry abstract the chingshui geothermal field a moderate temperature and water dominated hydrothermal system was the site of the first geothermal power plant in taiwan many geological geophysical and geochemical studies using more than 21 drilled wells have been performed since the 1960s however there are still controversies regarding the heat and fluid sources due to the tectonically complicated geological setting to clarify the heat and fluid sources we analyzed clumped isotopes with carbon and oxygen isotopic compositions of calcite scaling in geothermal wells and veins on outcrops and calculated the 18 o values of the source fluids two populations of 18 o values were calculated 5 8 0 8 vsmow from scaling in the well and 1 0 1 6 to 10 0 1 3 vsmow from outcropping calcite veins indicative of meteoric and magmatic fluid sources respectively meanwhile two hydrothermal reservoirs at different depths have been identified by magnetotelluric mt imaging with micro seismicity underneath this area as a result we propose a two reservoir model the shallow reservoir provides fluids from meteoric water for the scaling sampled from wells whereas the deep reservoir provides magmatic fluids from deep marble decarbonization recorded in outcropping calcite veins

some observational constraints on the global scale wind systems of mars wind direction measurements from a variety of indicators taken over several mars years and covering the entire planet have been collected these include observations of lee wave clouds not previously studied the data exhibit a high degree of consistency and seasonal reproducibility making it possible to interpret most of the observations in terms of the zonally symmetric circulation of mars we examine these data in the context of the constraints the observed wind directions place upon the thermal and polar cap mass flux fields which force the flows within the limitations of the data set mid and high latitude winds appear to be controlled by the thermal field during mid and late summer and winter and in the northern hemisphere during early spring and early summer at other times the cap flows dominate at high latitudes the strongest yearly winds are probably generated by cap formation in the north and cap recession in the south the hemispheric asymmetry seems to result primarily from the effects of global dust storms on the north polar cap turning of the prograde wind from poleward to equatorward in midautumn is observed consistent with reduced poleward mass flux and increased meridional temperature gradient at that time the latitudinal extent of the equatorial hadley cell when observed is probably larger than that predicted by nearly inviscid models of low latitude circulation the cross equational hadley cell and high latitude poleward flows which occur in both hemispheres during the summer seasons may set additional constraints on the thermal forcing mechanisms at these times

sediment compositions in offshore southern taiwan and their relations to the source rocks in modern arc continent collision zone modal analyses of 31 sand samples collected by piston coring document variations in sediment composition along and across the developing collision zone off southern taiwan and help constrain sediment transport paths and by inference of sediment sources overall sand composition from this region is dominated by lithic fragment populations with a qtfl average of qt27f21l52 three geographic domains are based on morphotectonics and variations in sand composition 1 south china sea and the adjacent slope of the accretionary prism 2 suture zone south of southern taiwan and north of the luzon forearc and 3 the luzon forearc basin north luzon trough and immediate adjacent slopes sands from the accretionary prism and the suture zone contain subequal amounts of sedimentary and metamorphic lithic fragments ls51lv5lm45 and ls47lv5lm48 respectively whereas sands from the forearc basin are dominated by volcanic lithic fragments ls29lv49lm22 in addition compositions of individual sand beds vary dramatically in the forearc basin this heterogeneity indicates that sediments from different sources have been deposited sequentially but do not typically mix during transport and deposition similar but less dramatic within core variations occur over the accretionary prism the major sediment input for the accretionary prism is from western taiwan and is dominated by sedimentary and low grade metamorphic lithic fragments there appears to be a second sediment source however from southeastern china this implies that a significant amount of sediment is the input from china to this region the major component of sands in the suture zone is derived from taiwan but medium grade metamorphic lithic fragments are rather sparse in these sands considering the extensive and highrelief exposures of metamorphic rocks on the island of taiwan the major source of sands in the forearc basin is the active volcanoes of the batan islands episodically minor components appear to be fed to the forearc basin from the arcward slope of the accretionary prism presumably by submarine mass wasting this observation provides support for the hypothesized olistostromal

earth fissures triggered by groundwater withdrawal and coupled by geological structures in jiangsu province china earth fissures in jiangsu province china have caused serious damages to properties farmlands and infrastructures and adversely affected the local or regional economic development under the geological and environmental background in jiangsu province this paper presents the earth fissures caused by excessive groundwater withdrawal and coupled by distinctive geological structures such as ancient yellow river fault in xuzhou karst area and ancient yangtze river course and bedrock hills in suzhou wuxi and changzhou area although all the earth fissures are triggered by groundwater exploitation the characteristics are strongly affected by the specific geological and hydrogeological settings in particular in the water thirsty xuzhou city the cone of depression caused by groundwater extraction enlarged nearly 20 times and the piezometric head of groundwater declined 17 m over a decade as groundwater is extracted from the shallowly buried karst strata in the ancient yellow river fault zone the development of earth fissures is highly associated with the development of karstic cavities and sinkholes and their distribution is controlled by the ancient yellow river fault with all the 17 sinkholes on the fault on the other hand in the rapidly developing southern jiangsu province groundwater is mainly pumped from the second confined aquifer in the quaternary which is distributed neither homogeneously nor isotropically the second confined aquifer comprises more than 50 m thick sand over the ancient yangtze river course but this layer may completely miss on the riverbank and bedrock hills with a typical drawdown rate of 4 6 m per annum the piezometric head of groundwater in the second confined aquifer has declined 76 m at maocunyuan since 1970s and 40 m at changjing since mid 1980s and a large land subsidence e g 1 100 mm at maocunyuan is triggered coupled with the dramatic change of the bedrock topography that was revealed through traditional geological drilling and modern seismic reflection methods the geological structure controlled differential settlement and earth fissures are phenomenal in this area

a new method for assessing slope unloading zones based on unloading strain unloading zones are formed in shallow slopes after rock mass relaxation and crack extension generally slope unloading assessment depends on the traditional methods mainly related to the phenomena however unloading is a process of energy release based on the fracture mechanics and the statistical theory of rock mass structure a theoretical analysis was performed to establish the relationship between the accumulative opening displacement of unloading cracks and unloading strain and a new method was proposed to quantify the extent and damage degree of unloading zones according to unloading strain the new method was applied to assess the slope unloading zones at a hydropower station dam site in northwest china results showed that the accumulative opening displacement curve of unloading cracks regularly varied and could be easily divided into three parts the strong and weak unloading zones could be recognized from the slope of the first two parts while their extent was limited by the two inflexions on each curve by comparison with the traditional method the new method confirmed the reasonability in the slope unloading zone assessment however with an increase in the unloading degree the difference in the zonation results obtained from the two methods may increase

overturned marble layers evidence for upward extrusion of the backbone range of taiwan abstract the backbone range is part of the taiwan mountain belt which was formed due to the oblique collision between the luzon arc and the eurasian passive continental margin from plio pleistocene to the present stable isotope compositional profiles of thin marble layers from this mountain range show that marble layers from rock sections with an inverted metamorphic zonation were all overturned after the peak metamorphism and that marble layers from rock sections with a normal metamorphic zonation were not overturned exhumation folding seems to be the responsible process an upward extrusion exhumation model is therefore postulated as the probable mechanism for the mountain building process this model can well explain the fanning orientation of rock cleavage s dipping in a regional scale as well as the metamorphic characteristics across the mountain range the model also shows that the recorded stretching lineation is secondary in nature meaning the exact direction of rock movement during the initial exhumation stage in response to the oblique collision cannot be deduced

reply to comment on geochronologic evidence for a cold arc continent collision the taiwan orogeny by chin ho tsai tzen fu yui wen shan chen and sun lin chung

how the structural architecture of the eurasian continental margin affects the structure seismicity and topography of the south central taiwan fold and thrust belt studies of mountain belts worldwide show that along strike changes are common in their foreland fold and thrust belts these are typically caused by processes related to fault reactivation and or fault focusing along changes in sedimentary sequences the study of active orogens like taiwan can also provide insights into how these processes influence transient features such as seismicity and topography in this paper we trace regional scale features from the eurasian continental margin in the taiwan strait into the south central taiwan fold and thrust belt we then present newly mapped surface geology p wave velocity maps and sections seismicity and topography data to test the hypothesis of whether or not these regional scale features of the margin are contributing to along strike changes in structural style and the distribution of seismicity and topography in this part of the taiwan fold and thrust belt these data show that the most important along strike change takes place at the eastward prolongation of the upper part of the margins necking zone where there is a causal link between fault reactivation involvement of basement in the thrusting concentration of seismicity and the formation of high topography on the area correlated with the necking zone the strike slip reactivation of east northeast striking extensional faults is causing sigmoidal offset of structures and topography along two main zones here basement is not involved in the thrusting there is weak focusing of seismicity and localized development of topography we also show that there are important differences in structure seismicity and topography between the margins shelf and its necking zone

global imaging of mars by hubble space telescope during the 1995 opposition hubble space telescope hst imaging of mars near the 1995 opposition resulted in excellent synoptic scale images of the planet during the spring season in the northern hemisphere because this season coincides with the aphelion position of mars in its orbit it is therefore the most difficult for ground based observation because of the relatively small angular size of mars this is the first sequence of images fully utilizing the capability of the new planetary camera to produce global synoptic images of the planet the images reveal bright discrete clouds associated with topographic features superimposed on a zonal band of condensate clouds between latitudes 10 and 30 the maximum violet optical depth of the cloud band is about 0 3 in a few instances the appearance of clouds beyond the morning terminator can be used to infer cloud heights of roughly 8 km a large dark albedo feature in the cerberus region observed for many years by ground based observers has almost disappeared in the 1995 hst images other aspects of mars such as the north polar cap appear much as they did during previous oppositions although cloudy regions were observed by spacecraft during this season the hst images uniquely reveal the global extent of significant optical depth clouds

provenance evolution during arc continent collision sedimentary petrography of miocene to pleistocene sediments in the western foreland basin of taiwan taiwan is an example of an orogen involving a doubly vergent critical wedge critical wedge theory predicts asymmetrical tectonic development of the pro and retro sides of an orogen whereas the consequences for exhumation peak metamorphism and erosion have been extensively investigated the implications for sandstone petrography preserved on either side of an orogen have not been adequately documented plio pleistocene sandstones from the western foothills of taiwan were deposited in a rapidly subsiding foreland basin recording the collision between a volcanic arc and the asian passive margin new data on the evolution of sedimentary petrography and clay minerals preserved in miocene to pleistocene sandstone of the western pro foreland basin record the history of taiwan s orogenesis sandstone petrography of the eastern basin on the retro side of taiwan s orogenic wedge had been studied previously comparison of the provenance record from the western and eastern basins illustrates the opposing signature of unroofing and recycling held to be characteristic of an asymmetric orogenic wedge sandstone petrography can be used in ancient sedimentary basins to complement other indications of the polarity of subduction

cloud formation under mars pathfinder conditions temperature data taken during the mars pathfinder entry are applied to a time dependent microphysical model of cloud formation our goal is to reproduce the characteristics of clouds observed at the pathfinder site we assume that the total water column abundance is 11 percipitable microns we also assume that the atmospheric dust initially has a lognormal size distribution with a modal radius of 0 6 m r eff 1 5 m and an optical depth of 0 5 three temperature profiles are used in the model calculations the first is the pathfinder entry observation the second is this same profile but with the inversion at 10 km removed the third simulation uses the temperature profiles calculated by the ames mars general circulation model for mars pathfinder conditions in all cases clouds form at altitudes of 35 45 km in addition lower thicker clouds form within the 10 km inversion of the unaltered profile while peak cloud formation occurred near local noon at 20 km for the gcm calculated profiles given a combination of all three temperature scenarios cloud optical depths particle sizes and colors are consistent with imp observations

characteristics of a deep seated flexural toppling fracture and its relations with downcutting by the lancang river a case study on a steeply dipping layered rock slope southwest china abstract a deep seated flexural toppling fracture situated on the left bank of the lancang river southwest china was used as a case study of the fracture mechanism and relations with the rapid and continuous downcutting of the lancang river the toppling fracture body has a maximum horizontal distance to the slope surface exceeding 150 m and a volume of approximately 6 106 m3 based on surface and adit surveys the toppled rock mass was divided into three zones highly toppled moderately toppled and weakly toppled zones the formation of the deep seated toppling failure in the steeply dipping layered rock mass was the result of the intense unloading of rock mass caused by the continuous and rapid downcutting of the lancang river the intense unloading caused the rock mass to be relaxed and cataclastic and formed a deep stress relaxation zone in rock mass on both banks the toppling failure of the steeply dipping layered rock mass occurred in the stress relaxation zone under the action of gravity and developed inwards and downwards to the lower parts of the slope with the river further downcutting the horizontal distance to the slope surface of highly toppled and moderately toppled rock mass was limited by the boundary of strongly unloaded rock mass

microseismic monitoring and stability analysis of the left bank slope in jinping first stage hydropower station in southwestern china risks associated with the left bank slope of jinping first hydropower station in southwestern china are growing as a result of excavation of the dam foundation ditch and various tunnels as well as grouting to soft strata to improve our understanding of the slope instability and resolve the complex subsurface conditions of the highly fractured rock mass a microseismic monitoring system was installed in june 2009 which is the first time such a technique has been introduced into stability analysis of a high steep rock slope in china the microseismic monitoring system consists of a data acquisition unit a data processing unit and a three dimensional array of uniaxial accelerometers in order to analyze the correlation between seismicity and potential slip surface of the slope a numerical model was implemented to analyze the failure processes and stability of the slope the monitoring results illustrate that microseismic events mainly occur as a strip along the spandrel groove of the dam which coincides with the potential slip surface obtained from numerical analysis especially at the bottom of the slope therefore the comprehensive method incorporating microseismic monitoring and numerical analysis has been proven to be very promising in instability prediction of rock slope subject to identification and delineation of potential slip surface and failure regions

numerical simulations of the formation and evolution of water ice clouds in the martian atmosphere abstract a one dimensional aerosol model was used to study the microphysics of water ice cloud formation and evolution on mars the time dependent nature of the model permits realistic simulations of diurnal cycles the results are sensitive to the choice of the temperature profile the eddy diffusion coefficient the efficiency of nucleation of the condensation nuclei and the condensation history of the cloud simulations having a large diurnal temperature variation yield condensed water total optical depths of a few tenths in good agreement with the viking lander opacity data ice clouds are typically simulated at 25 30 km altitude with mean particle radii of 0 2 5 0 m we also obtain good agreement with the particle extinction observed in the viking orbiter limb data for a temperature profile constrained by the infrared thermal mapper data in order for repeated cloud formation to occur each day we need to include a vertical and or horizontal resupply of water and dust to the higher altitudes where the condensation occurs because of loss by sedimentation this can take the form of a micrometeoritic influx of particles at the top of the atmosphere or a latitudinal transport of material the efficiency of the nucleation process is determined by the contact angle changing this angle from 0 945 to 0 999 can have the effect of doubling the total ice optical depth of the cloud the time evolution of the cloud is important for comparison with the observations if a diurnal temperature change exists under these conditions the optical thickness of the cloud is dependent on the number of condensation cycles having previously occurred and the time of day this time dependence and the need for a resupply of material into the condensing region show that the cloud formation process cannot be considered a steady state phenomenon we have shown that the eddy diffusion coefficient and particle radii cannot be constrained by the available data even if a detailed model is used for the interpretation of the observations in our simulations there is an extensive vertical redistribution of water by clouds however water is only lost to the surface when the temperature is at the frost point near the ground precipitation across subsaturated layers is not significant

the rb sr isotopic record in taiwan gneisses and its tectonic implication abstract a rb sr isotopic study of six taiwan gneiss bodies has revealed three thermal events at ca 90 ma ca 40 ma and

topographic characteristics of the submarine taiwan orogen a complete digital elevation and bathymetry model of taiwan provides the opportunity to characterize the topography of an emerging mountain belt the orogen appears to form a continuous wedge of constant slope extending from the subaerial peaks to the submarine basin we compare submarine channel systems from the east coast of taiwan with their subaerial counterparts and document a number of fundamental similarities between the two environments the submarine channel systems form a dendritic network with distinct hillslopes and channels there is minimal sediment input from the subaerial landscape and sea level changes are insignificant suggesting that the submarine topography is sculpted by offshore processes alone we implement a range of geomorphic criteria widely applied to subaerial digital elevation models and explore the erosional processes responsible for sculpting the submarine and subaerial environments the headwaters of the submarine channels have steep straight slopes and a low slope area scaling exponent reminiscent of subaerial headwaters that are dominated by bedrock landslides the main trunk streams offshore have concave up longitudinal profiles extensive knickpoints and a slope area scaling exponent similar in form to the onshore fluvial domain we compare the driving mechanisms of the likely offshore erosional processes primarily debris flows and turbidity currents with subaerial fluvial incision the results have important implications for reading the geomorphic signals of the submarine and subaerial landscapes for understanding the links between the onshore and offshore environments and more widely for focusing the future research of the submarine slope

mechanism of deep cracks in the left bank slope of jinping first stage hydropower station abstract the proposed jinping first stage hydropower station is located on the middle reach of the yalongjiang river sichuan province pr china it consists of a double curvature arch dam with a maximum height of 305 m which will be the highest in the world cracks are well developed in the left bank slope of the pusiluogou the dam site of jinping first stage hydropower station some cracks are even developed at the horizontal distance into rock face in this paper the term horizontal depth was used to describe the horizontal distance into face of the slope beyond 200 m and these cracks are here referred to as deep cracks the distribution of these deep cracks is far beyond people s experiences in common unloading zones so the mechanism of the deep cracks is put forward as a new subject since these cracks are significant for the stability of the slope their mechanism becomes one of the key engineering geology problems a comprehensive study is made in this paper on the distribution characteristics of the cracks as well as their deformation features the factors that influence their distribution and deformation feature are also analyzed by means of geology mechanics and numerical simulation an important conclusion is consequently reached that deep cracks occurred as a result of release of high ground stress including gravitational stress and tectonic stress the formation of the deep cracks in the slope is a result of unloading process under favorable geology conditions fast crust uplift and quick river cutting and high tectonic stress are indispensable regional geological condition steep and high geometry condition provides favorable geometry condition hard at the lower part and soft at the upper part of the slope offers suitable rock combination condition and back facing bending planes and consequent discontinuities supply suitable structure of the slope

iranshahr blueschist subduction of the inner makran oceanic crust the makran accretionary prism in se iran and sw pakistan is one of the most extensive subduction accretions on earth it is characterized by intense folding thrust faulting and dislocation of the cenozoic units that consist of sedimentary igneous and metamorphic rocks rock units forming the northern makran ophiolites are amalgamated as a melange metamorphic rocks including greenschist amphibolite and blueschist resulted from metamorphism of mafic rocks and serpentinites in spite of geodynamic significance of blueschist in this area it has been rarely studied peak metamorphic phases of the northern makran mafic blueschist in the iranshahr area are glaucophane phengite quartz omphacite epidote post peak minerals are chlorite albite and calcic amphibole blueschist facies metasedimentary rocks contain garnet phengite albite and epidote in the matrix and as inclusions in glaucophane the calculated p t pseudosection for a representative metabasic glaucophane schist yields peak pressure and temperature of 11 5 15 kbar at 400 510 c these rocks experienced retrograde metamorphism from blueschist to greenschist facies 350 450 c and 7 8 kbar during exhumation a back arc basin was formed due to northward subduction of neotethys under eurasia lut block exhumation of the high pressure metamorphic rocks in northern makran occurred contemporarily with subduction several reverse faults played an important role in exhumation of the ophiolitic and hp lt rocks the presence of serpentinite shows the possible role of a serpentinite diapir for exhumation of the blueschist a tectonic model is proposed here for metamorphism and exhumation of oceanic crust and accretionary sedimentary rocks of the makran area vast accretion of subducted materials caused southward migration of the shore this article is protected by copyright all rights reserved

winter clouds over the north martian polar cap the mars orbiter laser altimeter mola experiment carried on the mars global surveyor spacecraft has observed echoes from cloud tops on roughly 2 5 of the total data taken above 70 n over the northern winter martian polar hood from march to june 1998 sloping wavefronts are commonly seen at latitudes above 70 n implying the presence of propagating buoyancy waves since these wavefronts frequently extend from the surface up to 10 km at a time when co2 is known to be condensing on the polar surface it seems likely that the laser scattering particles consist primarily of co2 ice and that the near surface temperature lapse rate is 0 85 k km 1 set by the vapor pressure of dry ice from the observed wavelengths where available we have calculated the corresponding phase velocities some of these waves appear to be correlated with surface discontinuities and may represent lee waves

detection and monitoring of h2o and co2 ice clouds on mars we have developed an observational scheme for the detection and discrimination of mars atmospheric h2o and co2 clouds using ground based instruments in the near infrared we report the results of our cloud detection and characterization study using mars near ir images obtained during the 1990 and 1993 oppositions we focused on specific wavelengths that have the potential based on previous laboratory studies of h2o and co2 ices of yielding the greatest degree of cloud detectability and compositional discriminability we have detected and mapped absorption features at some of these wavelengths in both the northern and southern polar regions of mars compositional information on the nature of these absorption features was derived from comparisons with laboratory ice spectra and with a simplified radiative transfer model of a co2 ice cloud overlying a bright surface our results indicate that both h2o and co2 ices can be detected and distinguished in the polar hood clouds the region near 3 00 m is most useful for the detection of water ice clouds because there is a strong h2o ice absorption at this wavelength but only a weak co2 ice band the region near 3 33 m is most useful for the detection of co2 ice clouds because there is a strong relatively narrow co2 ice band at this wavelength but only broad continuum h2o ice absorption weaker features near 2 30 m could arise from co2 ice at coarse grain sizes or surface dust minerals narrow features near 2 00 m which could potentially be very diagnostic of co2 ice clouds suffer from contamination by mars atmospheric co2 absorptions and are difficult to interpret because of the rather poor knowledge of surface elevation at high latitudes these results indicate that future ground based earth orbital and spacecraft studies over a more extended span of the seasonal cycle should yield substantial information on the style and timing of volatile transport on mars as well as a more detailed understanding of the role of co2 condensation in the polar heat budget

geomorphic constraints on the active tectonics of southern taiwan summary taiwan is a region of rapid active tectonics yet the study of the tectonic processes that shape the interior of the island is difficult due to the high rates of erosion and dense vegetation we use digital topography to look for indications of active deformation preserved in the local geomorphology in particular anomalies in the regional pattern of drainage are used to infer zones of enhanced tectonic activity the apparent anticlockwise rotation of major river systems in plan view indicates the presence of a diffuse zone of left lateral shear running down the southeastern side of taiwan asymmetries in the catchments of individual drainage basins show the influence of varying rates of uplift across southern taiwan with the most rapid uplift close to taitung at the indentation point of the luzon arc with the chinese continental margin our interpretations though based predominantly on remote sensing observations are consistent with the available field evidence this study demonstrates the usefulness of drainage basins as tectonic markers in the quantification of regional strain and uplift which may have wider applicability in other deforming parts of the world

upb zircon geochronology constraints on the ages of the tananao schist belt and timing of orogenic events in taiwan implications for a new tectonic evolution of the south china block during the mesozoic abstract the tananao schist belt is a low pressure metamorphic complex comprised of three lithological units of marble schist formation and granite in ascending order of proportion previous studies have found that the schist formation was formed during the mesozoic however there is a lack of geochronological data to corroborate the schist protolith and metamorphic ages in this study we have used u pb zircon geochronology to provide a time frame for the creation of the schist formation and metamorphism as well as a new tectonic model twenty three schist and eleven meta magmatic samples were used for u pb dating by la icp ms results from the youngest peak age of detrital zircon indicate that the schist formed in a new depositional age of 120 110 ma and therefore is different from the previously estimated age of the paleozoic mesozoic additionally the block in matrix schist indicates an age that ranges from 270 to 80 ma and was inferred from the chaotic deposits to be a metamorphic melange the tananao schist belt appears to represent an arc trench system that formed during the cretaceous in the south china block margin moreover the youngest u pb age of 80 ma from the leucogranite dike and schist constrains the upper age limit for a metamorphism that is younger than the previously accepted age of 100 90 ma the contact layer between permian triassic marble and the overlying early cretaceous schists remains a chloritoid bed that is therefore considered to be a paleosol at the unconformity which formed over an extended duration of 60 30 ma the stratigraphic contact indicates a long period of erosion during the jurassic and suggests that a tectonic event occurred however we propose that two important metamorphic events took place prior to and following the schist formation during the jurassic and late cretaceous orogenic events

observations of martian ice clouds by the mars global surveyor thermal emission spectrometer the first martian year successful operation of the mars global surveyor spacecraft beginning in september 1997 ls 184 has permitted extensive observations over more than a martian year initially thin normal optical depth 0 06 at 825 cm 1 ice clouds and hazes were widespread showing a distinct latitudinal gradient with the onset of a regional dust storm at ls 224 ice clouds vanished in the southern hemisphere to reappear gradually after the decay of the storm the zonally averaged cloud opacities show little difference between the beginning and end of the first martian year a broad low latitude cloud belt with considerable longitudinal structure was present in early northern summer apparently characteristic of the northern summer season it vanished between ls 140 and 150 the latitudinal extent of this feature is apparently controlled by the ascending branch of the hadley circulation the most opaque clouds optical depth 0 6 were found above the summits of major volcanic features these showed spatial structure possibly associated with wave activity variety among low lying late morning clouds suggests localized differences in circulation and microclimates limb observations showed extensive optically thin optical depth 0 04 stratiform clouds at altitudes up to 55 km considerable latitude and altitude variations were evident in ice clouds in early northern spring ls 25 near 30 km thin clouds extended from just north of the equator to 45 n nearly to the north polar vortex a water ice haze was present in the north polar night ls 30 at altitudes up to 40 km because little dust was present this probably provided heterogeneous nucleation sites for the formation of co2 clouds and snowfall at altitudes below 20 km where atmospheric temperatures dropped to the co2 condensation point the relatively invariant spectral shape of the water ice cloud feature over space and time indicates that ice particle radii are generally between 1 and 4 m

layered deformation in the taiwan orogen the underthrusting of continental crust during mountain building is an issue of debate for orogens at convergent continental margins we report three dimensional seismic anisotropic tomography of taiwan that shows a nearly 90 rotation of anisotropic fabrics across a 10 to 20 kilometer depth consistent with the presence of two layers of deformation the upper crust is dominated by collision related compressional deformation whereas the lower crust of taiwan mostly the crust of the subducted eurasian plate is dominated by convergence parallel shear deformation we interpret this lower crustal shearing as driven by the continuous sinking of the eurasian mantle lithosphere when the surface of the subducted plate is coupled with the orogen the two layer deformation clearly defines the role of subduction in the formation of the taiwan mountain belt

three dimensional elastic wave velocity structure of the hualien region of taiwan evidence of active crustal exhumation the hualien region of taiwan is located at a complex transition of the boundary between the eurasian and philippine sea plates to the southwest the mountains of taiwan are uplifting rapidly as a consequence of an ongoing arc continent collision while to the east the oceanic philippine sea plate is subducting northward beneath eurasia we investigated the structure and dynamics of this region by analyzing seismograms of local earthquakes recorded during a deployment of the portable array for numerical data acquisition ii network p and s wave velocity structures deduced from travel time tomography analysis show that the collisional suture to the south of hualien is characterized by a narrow 10 km width near vertically dipping zone of low velocities that extends to depths in excess of 20 km velocities in the eastern central range west of the suture zone are significantly higher and define a feature 10 15 km wide that appears to be continuous from the near surface to depths as great as 40 km farther to the west beneath the western central range the velocities again decrease focal mechanisms of local earthquakes show that while thrust faulting is the predominate mode of deformation throughout the region normal faulting occurs as well beneath the eastern central range thus the rapid uplift of the mountains of taiwan may be a result not only of compressional shortening but also of an excess of positive buoyancy we suggest that the higher velocities and extensional mechanisms in the eastern central range are caused by the ongoing exhumation of previously subducted continental crust while the lower velocities to the west reflect continued underthrusting of the crust beneath the eastern central range

late cenozoic metamorphism and mountain building in taiwan a review abstract the orogenic wedge of taiwan results from the late miocene collision of the chinese passive margin and the luzon volcanic arc because of the southward propagation of the collision over time and because of its extreme rates of deformation and erosion it has appeared as an ideal place to investigate mountain building processes here we review existing metamorphic and thermochronological data on late cenozoic burial and exhumation most of the island has been extensively investigated in particular in terms of zircon or apatite fission track and u th he thermochronology peak metamorphic temperatures have also been quantified from the raman spectroscopy of carbonaceous material along three transects in central taiwan the different datasets appear consistent and indicate that cooling rates and exhumation are more intense within the hsueshan range and within the tananao complex lateral variations from south to north are also observed and they can be interpreted in terms of different stages of exhumation and mountain building existing models provide a framework to analyze the data and discuss the limits of some previous interpretations in particular in terms of exhumational steady state or of recent acceleration of uplift and exhumation these models are also discussed in light of available data it appears that all of them fit thermochronological data within the tananao complex whatever the kinematics the depth of the wedge or the mechanism responsible for exhumation and that exhumation of the hsueshan range has been ignored in most models future models need therefore to consider the taiwan wedge as a whole additional constraints on peak metamorphic conditions on kinematics of shortening and exhumation or on the geometry of the wedge at depth need to be gathered to further unravel mountain building processes at the scale of the whole orogen

pb pb dating of young marbles from taiwan direct determination of the depositional age of a sedimentary sequence usually relies on isotopic analyses of authigenic minerals such as glauconite1 and fine grained clay minerals2 4 moorbath et al 5 recently reported the first direct dating of sedimentary carbonates using the whole rock pb pb method the success of this method depends on the chemical fractionation of u from pb and the consequent variation in 206pb 204pb and 207pb 204pb ratios the high values and large variation of u pb ratios in sedimentary carbonates long known to marine geochemists have however not been exploited by geochronologists until recently5 6 here i report a pb pb isochron age for a relatively young carbonate sequence in taiwan and demonstrate that the long lived u pb decay scheme can be used to determine events as young as mesozoic age the new results also lead to the identification of an early jurassic 170 myr bp thermal event which has never before been recognized in the polymetamorphic schist belt the tananao schist of taiwan but is widespread in southeastern continental china and other parts of eastern asia7 10

geochronologic evidence for a cold arc continent collision the taiwan orogeny abstract in order to constrain the tectonic consequences of the collision of the luzon arc with the se chinese continental margin during the neogene taiwan orogeny we assess the thermal history of the poly metamorphic para autochtthonous rocks of the continental margin in taiwan to accomplish this we report a new sims u pb age of prograde metamorphic zircons and interpret this age in the context of existing geochronology and thermochronology zircons extracted from the fenniaolin amphibolite near nanao taiwan in the contact aureole of a granodiorite are interpreted to have crystallized during the first lower amphibolite facies prograde metamorphism based on 1 their equant shape rather than the prismatic shape typical of magmatic zircon 2 their microcrystalline or micro saccharoidal aggregate structure and patchy and sector zoning rather than oscillatory zoning visible in cathodoluminescent imaging 3 their low concentrations of u most 206 pb 238 u age of 86 1 ma analytically indistinguishable from the age of the adjacent pluton that caused the contact metamorphism we thus conclude that the contact metamorphism of this intrusion caused the first lower amphibolite facies metamorphism of these rocks in the mid cretaceous existing 40 ar 39 ar and rb sr cooling ages of both amphibole and muscovite at 80 ma e g lan 1990 lo and onstott 1995 show that the granodiorite and its contact aureole cooled rapidly from 700 to the crustal history reconstructed from these data shows that the regional gneissic terrane of the northern tananao complex may have been caused by coalescing contact aureoles of multiple mid cretaceous intrusions the nanao intrusive event and not by the neogene taiwan orogeny on the contrary the tananao rocks probably achieved middle greenschist conditions and 15 20 km depth in a forearc setting in the early cretaceous this intrusive event caused regional contact metamorphism at about 85 ma after which the passive margin setting preserved these rocks at mid crustal depths until the beginning of the taiwan orogeny 5 ma these depths 10 12 km and temperatures 200 250 c were high enough to account for the late miocene lower greenschist facies cleavages and the pliocene pleistocene fission track cooling ages without additional loading and heating from the taiwan orogeny

sequential thrusting model for mountain building constraints from geology and heat flow of taiwan in this study we analyze the thermal evolution of the taiwan fold and thrust belt based on the available geological information a finite element program is used to simulate the complex kinematics of the observed sequential thrusting and the interplay of uplift erosion and sedimentation processes the discrete sequential thrusting model successfully reproduces the observed decrease in heat flow at the deformation front in northern taiwan this reveals that the heat flow drop may be due to the recent stacking of cold thrust sheets at the deformation front this inference is consistent with the high seismicity and dense quaternary fault distribution in western taiwan the model also successfully reproduces the observed high heat flow in the central ranges suggesting that the observed high heat flow may be a result of tectonic unroofing due to active underplating uplift and erosion these conclusions are insensitive to uncertainties in the frictional coefficient on the thrust plane

stability investigation and stabilization of a heavily fractured and loosened rock slope during construction of a strategic hydropower station in china abstract this paper presents a case history of the 205 m high intake slope at the huangjinping hjp hydropower station on the dadu river deformation and cracks developed on the cut slope during excavation and the deformation extended onto the natural slope above the cut giving rise to serious safety concerns research was conducted to study the engineering geological conditions and the deformation characteristics of the slope during excavation in situ monitoring data and possible causes of cracking were analyzed the results show that the zone of loosened rock mass extended much deeper into the rock mass than it did at other sites in the region because of the tectonic history of the site and cutting the empirically designed cable anchors with lengths of 40 m or 45 m were insufficient to stabilize the slope while the remedial cable anchors as long as 100 m successfully stabilized the slope the analytic method and procedure used in this paper could be useful to similar projects

a method for assessment of excavation damaged zone edz of a rock mass and its application to a dam foundation case abstract excavation of slope is an unloading process and also an energy releasing process when the stress in the rock mass is unloaded leading to the rebounding deformation towards the free face and then a zone namely excavation damaged zone edz will be formed near the excavation boundary where the rock is damaged or disturbed and its physical mechanical and hydraulic properties are greatly changed this paper is to put forward a new method to quantify the extent and damage degree of the edz according to the unloading strain energy which is released in the process of excavation a simple relationship between unloading strain e and accumulative opening displacement t of cracks d t d h is proposed to describe the damage degree of rock mass in the edz where h is the depth variable in normal direction of the open cracks this method is used to assess the edz of the dam foundation at xiaowan hydropower station in southwestern china by the accumulative opening displacement curves of cracks along boreholes based on boreholes camera photos we find that the edz can be naturally divided into two sub zones i e the excavation heavily disturbed sub zone ehdz and excavation slightly disturbed sub zone esdz according to the variation of unloading strain e two inflexions of the accumulative opening displacement curve indicate the lower limits of ehdz and esdz respectively

titanite inclusions in altered biotite from granitoids of taiwan microstructures and origins biotites with three sets of titanite inclusions i e sagenitic biotites have been reported from both igneous and metamorphic rocks two formation mechanisms have been postulated the precipitation model for the sagenitic biotite of igneous origin shau y h yang h y peacor d r 1991 on oriented titanite and rutile inclusions in sagenitic biotite am mineral 76 1205 1217 and the percussion figure model for the sagenitic biotite of metamorphic origin xu s ji s 1991 biotite percussion figures in naturally deformed mylonites tectonophysics 190 373 380 sagenitic biotites in granitoids of the tananao metamorphic complex of taiwan were studied especially with regard to the variable degrees of superimposed collision induced deformation metamorphism mass balance considerations transmission electron microscopic observations and regional geological relations exclude the simple intra biotite precipitation model as the possible mechanism instead the formation of titanite inclusions in these igneous biotites is suggested more likely to be facilitated by inward diffusion of ca and outward diffusion of ti along the basal cleavage planes and the fracture surfaces induced by shear deformation i e the percussion figure in biotites under greenschist facies temperature conditions interdiffusion may also account for the formation of rutile particles with varied size and varied crystallographic orientation in some titanite laths q 2001 elsevier science ltd all rights reserved