weathering and morphogenesis in a mediterranean climate calabria italy abstract deeply weathered plutonic rocks occur widely in the sila massif calabria southern italy three representative weathering profiles developed on the hilltops indicate that sand represents more than 50 by weight throughout most of the weathering profile and silt and clay size fractions are also well represented filling the interstices among corestones both sand and finer fractions of grus and soil horizons are thought to be derived from a combination of granular disintegration and chemical decomposition developed on relatively flat terrains of the sila massif these slopes are now experiencing transport limited morphodynamics under a montane modified mediterranean climate the depth of the weathered layers that have suffered little erosional truncation typically exceed 15 m and may reach 50 60 m or more major isolated or grouped exfoliation boulders are the most common minor landform feature developed on the sila massif granite boulders have developed as a result of spheroidal weathering and by removal of the sandy textured granite the schmidt hammer sh test on boulders and corestones suggests three distinctive degree of weathering from moderately to completely weathered rock and that biotite content is the major controlling factor of the granite mechanical behaviour understanding of the dynamics of this weathering system is crucial to the interpretation of the complex suite of variables that control landscape evolution of granitoid terrains

lewisian crustal history from in situ sims mineral chronometry and related metamorphic textures abstract a combination of detailed petrography and in situ sims 207 pb 206 pb micro chronometry of monazite has been carried out on samples from the lewisian high grade metamorphic terrain northwest scotland two episodes of granulite facies metamorphism have been recognized the thermal maxima of which are estimated at or before 2760 12 ma 2 and at 2526 8 ma respectively pegmatites at scourie crystallised at 2480 ma the amphibolite facies metamorphism of the main laxfordian event is estimated at 1752 12 ma and the formation of kyanite and staurolite is associated with this event the oldest ages of 2760 ma have been obtained from micro inclusions of monazite in garnet it appears that garnet which has a high closure temperature for the u pb system plays an important role in the behaviour of the monazite u pb system it serves to shield monazite from reaction with the other phases and to armour monazine from diffusive pb loss or from resetting

experimental resetting of the u th pb systems in monazite abraded fragments 200 400 m of a large chemically homogeneous and non metamict brazilian monazite crystal characterised by a concordant u pb ages of 474 1 ma 208pb 206pb 19 5 were hydrothermally treated at varying temperatures with solutions of different compositions product monazites were analysed with scanning electron microscope sem electron microprobe emp secondary ion mass spectrometer sims and isotope dilution thermal ionisation mass spectrometer id tims experiments with pure water over a temperature range of 800 1200 c at 700 mpa and durations ranging from 5 to 60 days showed that even at 1200 c any dissolution and recrystallization of new monazite is confined to the outermost surface of the grain neither pb diffusion at the emp scale nor significant discordancy were observed we performed experiments at 800 and 1000 c for different durations using different fluid compositions at quartz saturation a 10 wt cacl2 fluid a 10 wt srcl2 fluid a 10 wt nacl fluid and a fluid containing nbs 982 pb standard 208pb 206pb 1 for all runs emp traverses revealed no pb diffusion profiles significant overgrowths of newly formed monazite are documented by sem analyses they occurred only in the 1000 c experiments when either cacl2 or pb bearing fluids were present in the cacl2 experiment two zones could be distinguished within the crystal a core possessing the initial monazite composition and a rim consisting of newly formed monazite produced by dissolution precipitation which was enriched in ca and pb free id tims dating of single grains treated with srcl2 and cacl2 solutions at 1000 c are significantly discordant experiments employing the nbs pb standard produced sub concordant monazite for which the 207pb 206pb apparent age has become older than prior to the experiment 544 ma at 800 c and 495 ma at 1000 c the newly grown monazite rim had obviously incorporated pb from the fluid none of our reaction products contained a detectable diffusion profile the only resetting mechanism we detected involved dissolution precipitation the extent of the dissolution precipitation process depends on fluid composition and is a more efficient mechanism than diffusion for controlling the resetting of monazite in natural rocks

late paleoproterozoic magmatism in delhi fold belt nw india and its implication evidence from epma chemical ages of zircons abstract zircons from six granitoid plutons occurring in the northern part of the delhi fold belt nw india have been chemically dated using an electron microprobe most of the zircons occurring in the granites are chronologically unzoned and gave ages around 1 78 1 71 ga but younger ages of 1 1 0 9 ga have also been obtained from the rim of some grains monazite and zircons from the metasediments of delhi supergroup adjacent to the granitoids were also analyzed the older age of 1 9 1 7 ga obtained for monazites could possibly indicate their provenance age detrital zircon grains mostly rounded in the delhi metasediments which gave older ages of 1 9 ga could possibly have been derived from the archaean basement rocks exposed in this aravalli delhi fold belt the geochemical signatures of these granitoids are consistent with an extensional tectonic regime it is quite likely that contrary to the prevailing assumption of the granitoids being intrusive our geochronologic data suggests them to be the basement for sedimentation the new geochronologic information on these granitoids in the northern part of the delhi fold belt and their comparison with other correlative events establishes a widespread thermal event during late paleoproterozoic

geological and isotopic geochemical constraints on the evolution of the fuping complex north china craton abstract the neoarchean to paleoproterozoic fuping complex together with the adjacent hengshan and wutaishan complexes form the middle part of the central zone that separates the north china craton into the eastern and western archean continental blocks the fuping complex comprises three major lithological assemblages the 2 50 ga fuping trondhjemite tonalite granodiorite ttg gneisses the wanzi paragneisses and the 2 08 and 2 02 ga nanying granitic gneisses the ttg gneisses contain abundant enclaves of highly metamorphosed supracrustal rocks including 2 70 ga mafic granulites and amphibolites with endt of 3 29 to 3 96 and tdm of 2 72 2 82 ga and are characterized by tdm of 2 76 3 04 ga and a linear correlation between endt 1 64 to 0 96 and 1 nd indicative of mixing of melts derived from the 2 70 ga metabasic rocks and 3 0 ga crustal materials mafic dikes along the chengnanzhuang shear zone were most likely emplaced at 2 31 ga and have endt of 2 24 to 4 78 and tdm of 2 34 2 59 ga the nanying granitic gneisses with endt of 4 04 to 5 24 were most likely related to partial melting of the 2 70 ga supracrustal rocks and or the 2 50 ga ttg gneisses these geological relationships and isotopic data suggest that the fuping complex probably formed from the following five major tectonomagmatic events 1 mafic magmatism and early crustal growth at 2 7 ga with the possible existence of older 3 0 ga crust s 2 collision related crustal thickening underplating of basaltic magma high grade metamorphism crustal anatexis and ttg magmatism at 2 5 ga 3 extensional deformation and emplacement of the mafic dikes and the nanying granitic plutons along the chengnanzhuang shear zone 2 5 to 2 0 ga 4 s type granitic magmatism and associated amphibolite facies metamorphism 2 0 to 1 80 ga and 5 emplacement of granitic pegmatite dikes at 1 80 ga

terrestrial laser scanning of rock slope instabilities this manuscript presents a review on the application of a remote sensing technique terrestrial laser scanning tls to a well known topic rock slope characterization and monitoring although the number of publications on the use of tls in rock slope studies has rapidly increased in the last 5 10 years little effort has been made to review the key developments establish a code of best practice and unify future research approaches the acquisition of dense 3d terrain information with high accuracy high data acquisition speed and increasingly efficient post processing workflows is helping to better quantify key parameters of rock slope instabilities across spatial and temporal scales ranging from cubic decimetres to millions of cubic metres and from hours to years respectively key insights into the use of tls in rock slope investigations include a the capability of remotely obtaining the orientation of slope discontinuities which constitutes a great step forward in rock mechanics b the possibility to monitor rock slopes which allows not only the accurate quantification of rockfall rates across wide areas but also the spatio temporal modelling of rock slope deformation with an unprecedented level of detail studying rock slopes using tls presents a series of key challenges from accounting for the fractal character of rock surface to detecting the precursory deformation that may help in the future prediction of rock failures further investigation on the development of new algorithms for point cloud filtering segmentation feature extraction deformation tracking and change detection will significantly improve our understanding on how rock slopes behave and evolve perspectives include the use of new 3d sensing devices and the adaptation of techniques and methods recently developed in other disciplines as robotics and 3d computer vision to rock slope instabilities research

landslide susceptibility revealed by lidar imagery and historical records seattle washington abstract light detection and ranging lidar data were used to visually map landslides headscarps and denuded slopes in seattle washington four times more landslides were mapped than by previous efforts that used aerial photographs the mapped landforms landslides headscarps and denuded slopes were created by many individual landslides the spatial distribution of mapped landforms and 1308 historical landslides show that historical landslide activity has been concentrated on the mapped landforms and that most of the landslide activity that created the landforms was prehistoric thus the spatial densities of historical landslides on the landforms provide approximations of the landforms relative susceptibilities to future landsliding historical landslide characteristics appear to be closely related to landform type so relative susceptibilities were determined for landslides with various characteristics no strong relations were identified between stratigraphy and landslide occurrence however landslide characteristics and slope morphology appear to be related to stratigraphic conditions human activity is responsible for causing about 80 of historical seattle landslides the distribution of mapped landforms and human caused landslides suggests the probable characteristics of future human caused landslides on each of the landforms the distribution of mapped landforms and historical landslides suggests that erosion of slope toes by surface water has been a necessary condition for causing seattle landslides human activity has largely arrested this erosion which implies that landslide activity will decrease with time as hillsides naturally stabilize however evaluation of glacial age analogs of areas of recent slope toe erosion suggests that landslide activity in seattle will continue for the foreseeable future

dating low grade metamorphic events by shrimp u pb analysis of monazite in shales although the u pb isotopic system is widely used to date magmatism and medium to high grade metamorphism dating low grade metamorphic events has been hampered by a scarcity of suitable minerals we show that monazite forms in shales during low grade metamorphism and can be dated by in situ u pb analysis providing precise ages for low temperature thermal events in proterozoic shales from the pine creek inlier of northern australia monazite and xenotime crystals that formed in a contact aureole yield ages synchronous with granite intrusion ca 1830 ma in the pilbara craton of northwestern australia monazite growth 2192 5 m y ago coincided with basaltic volcanism and rifting an event apparently responsible for hydrothermal iron oxide mineralization in a nearby giant iron ore deposit the mineralizing environment was highly oxic and bathed by meteoric fluids thus our results imply the existence of an oxygen rich atmosphere by 2200 ma given the abundance of shales in the stratigraphic record and the likely widespread distribution of monazite in such rocks in situ u pb dating of monazite may become an important chronometer for low grade metamorphic events

alteration of monazite and zircon and lead migration as geochemical tracers of fluid paleocirculations around the oklo okelobondo and bangombe natural nuclear reaction zones franceville basin gabon abstract large scale light rare earth element lree uranium lead and phosphorus migration has been evidenced in the fa lower proterozoic sandstones of the franceville basin gabon hosting oklo natural nuclear reaction zones rz in relation with extensive accessory mineral alteration by highly saline diagenetic brines 28 7 wt nacl eq to 30 wt cacl2 eq at about 140 c and 1 kbar monazite is the most severely altered accessory mineral in the coarse grained sandstones of the basal fa formation detrital monazite crystals are altered to th oh silicate microcrystalline phase with very low concentrations of u and lree the th la ratio increase from non altered th la 0 27 to altered sandstones th la 1 14 shows that about 76 of the lree was leached this corresponds to the leaching of 2 01 109 metric tons at the scale of the fa formation in the franceville basin similarly the th u increase from monazite th u 18 6 to the th silicate phase th u 88 7 is interpreted as a result of an alteration by oxidizing brines with leaching of u together with lree and p it corresponds to the leaching of 9 06 106 metric tons of uranium this amount of uranium largely exceeds the known uranium reserves from the franceville basin in zircon crystals the cores are generally homogeneous weakly fractured and well preserved as attested by the archean ages 2867 24 and 2865 51 ma obtained by ionic microprobe analysis on zircon of the fa formation respectively from the marginal and central parts of the basin their composition corresponds to the pure end member zr hf sio4 poor in th and u th u 1 at the contrary their rims which present several growth zones with cracks fillings are enriched in ree p th and u with higher th u ratios 5 10 both altered monazite and altered zircon contain galena as numerous inclusions in the outer growth zones and as crack fillings for example in zircon the pb of galena crystals 3 23 wt largely exceeds the amount of pb maximum 0 1 wt that would have been produced in situ by radioactive decay in this mineral nearly all the lead were introduced into altered zones of accessories dissolution of accessory minerals occurred at 2000 ma producing a porous and distorted crystal structure which has allowed a later incorporation of pb galena inclusions in altered zircons located in the vicinity of reactor zones have radiogenic lead compositions altered zircon rims and galena inclusions in altered zircon located far from reactor zones have non radiogenic pb isotopic compositions confirming the external origin of lead pb isotopic evolution models indicate a crystallization age sometime after 1000 ma both for galena located close to and far from u mineralizations and reactor zones which may be synchronous with a regional extension event contemporaneous with intrusion of dolerite dyke swarms between 1000 and 750 ma at the scale of the franceville basin the present study also illustrates the different retention capacities of accessory mineral for elements representing analogs of the radiotoxic nuclides in the relatively extreme natural conditions created by the circulation of moderately hot and chloride rich fluids during the diagenesis of a sedimentary basin

failure mechanisms and stability analyses of granitic boulders focusing a case study in galicia spain abstract granitic boulders are widespread geomorphological elements particularly found in humid granitic areas although they seldom represent a hazard for people or infrastructures sometimes their location in steep or natural slopes may jeopardise their stability and potentially affect people or infrastructures in addition their complex geometry makes the instability mechanisms difficult to identify so it is even more difficult to compute factors of safety regarding their stability in this paper the authors analyse potential failure mechanisms of granite boulders based on analytical mechanic calculations and physical tilt tests permitting understanding the phenomena under scrutiny then they study the stability of one of these boulders the pena do equilibrio or equilibrium rock to do that they resort to standard geotechnical characterization and advanced geometrical characterization derived from uav photogrammetric and 3d laser scanning of the boulder the presented results exemplify how the application of these recently available topographic technologies in combination with rock mechanics approaches enable a rigorous analysis of the stability of granite boulders

shrimp u pb zircon geochronology of the fuping complex implications for formation and assembly of the north china craton abstract the fuping complex located within the central zone of the north china craton is composed of amphibolite to granulite facies orthogneisses interleaved with minor supracrustal rocks at similar metamorphic grade the oldest components recognised are hornblende gneiss enclaves within the predominant biotite orthogneiss which have a shrimp u pb zircon age of 2708 8 ma we consider these enclaves to represent fragments of 2 7 ga continental materials incorporated in the biotite gneiss the biotite gneiss has a shrimp u pb zircon age of 2513 12 ma interpreted to be time of magmatic crystallisation of the igneous precursor based on the igneous characteristics of the zircons this indicates a major magmatic episode at 2 52 ga in the fuping complex identical to the age of felsic volcanism within the low grade wutai complex which crops out immediately to the west a gneissic granite that intrudes the biotite gneisses has a poorly defined 207pb 206pb age of 2045 64 ma this is within error of the age of 2097 46 ma obtained from a fine grained gneiss interlayered with amphibolite of the wanzi supracrustal suite wss interpreted to be volcanic in origin zircons from both these samples have strong oscillatory zoning and provide the first indication of a palaeoproterozoic magmatic event in the area again similar in age to magmatic events recently recognised in the adjacent wutai complex these data indicate a comparable history for the fuping and wutai complexes and support geochemical evidence that they had a common origin and formed part of a late archaean arc affected by later palaeoproterozoic re activation low uranium zircons without oscillatory zoning separated from a sample of biotite gneiss yield data clustered at 1817 26 ma which is interpreted to reflect a period of new zircon growth during a major metamorphic event these data support the recently proposed tectonic model that amalgamation of the north china craton occurred due to collision of the eastern and western blocks along the central zone at 1 8 ga ago

use of digital terrestrial photogrammetry in rocky slope stability analysis by distinct elements numerical methods abstract current approaches to rocky slope stability analysis require knowledge of the geometrical structural setting as well as the physical mechanical properties of the intact material and its discontinuities the physical mechanical properties are derived from in situ and laboratory tests whereas the geometrical characteristics come from field attitude measurements frequently the inaccessibility of walls does not allow direct measurement of discontinuity surfaces by traditional geological methods in such cases data can only be obtained by statistical methods although this approach is significant and provides spatial meaning it is ineffective for deterministic analysis this paper provides a solution to this problem by applying digital terrestrial photogrammetric techniques employing a reamed bar an aerostatic balloon and a helicopter results demonstrate that the accuracy and the quantity of geometrical and engineering geological data coming from the photogrammetric survey allow for numerical simulation of the relationship between rock elements as a function of their physical mechanical properties and load conditions the 3dec code was chosen among the different methods available to model the discontinuous media through distinct elements the proposed methodology was applied to a quarry located in the carrara marble district the apuan alps italy the largest and most exploited mining region in europe the economic value of the area required a detailed study of the presence of instability phenomena so that marble extraction could continue in safe conditions

development of the north china craton during the late archaean and its final amalgamation at 1 8 ga some speculations on its position within a global palaeoproterozoic supercontinent abstract new data obtained over the past few years indicate that by the end of the archaean the north china craton consisted of two major crustal entities identified as the eastern and western blocks the formation of island and magmatic arcs along the western margin of the eastern block record the latest archaean events so far identified the location of the western block at this time is unknown however the occurrence of palaeoproterozoic passive margin sediments similar in age to those occurring in the eastern block indicates essentially similar conditions and possible separation by an ocean of unknown dimensions re initiation of east dipping subduction beneath the western margin of the eastern block resulted in closure of this palaeoproterozoic ocean bringing the western block into close proximity continued subduction resulted in a major continental continental collision and the western margin of the eastern block was again reactivated leading to extensive thrusting high pressure metamorphism and the generation of crustal melts this occurred between 1 88 and 1 79 ga ago resulting in the formation of the trans north china orogen and final amalgamation of the north china craton although information is sparse to non existent we have reviewed the possible location of the north china craton at the time of collision and note a similarity in terms of age lithology and distribution of major crustal components between the north china craton and baltica although speculative we present this model in the hope that it will stimulate debate and lead to further research in these areas

fusion of multi resolution surface terrestrial laser scanning and subsurface geodata ert srt for karst landform investigation and geomorphometric quantification a multi method research design based on terrestrial laser scanning gis geophysical prospecting electrical resistivity tomography refraction seismics and sedimentology is applied for the first time to investigate enclosed karst depressions in an integrated way fusing multi resolution surface and subsurface geodata provides profound insights into the formation geometry and geomorphologic processes of dolines the studied landforms which are located in the dikti mountains of east crete are shown to be filled by loose sediments of thicknesses of up to 30 m that mainly consist of fine grained material overlying solid bedrock at depths below 35 to 45 m by combining subsurface observations with geomorphometric calculations local doline genesis can be traced back to initial collapse of fractured bedrock followed by subsequent infilling with colluvials in order to define crucial methodological requirements and guidelines for data fusion both the impact of different elevation models and the influence of data resolution are assessed surface volumes of depressions derived by the digital surface model are 7 21 higher than the results obtained from the terrain model due to vegetation similarly estimates of infill volume calculated on the basis of geophysical outcomes and elevation data differ by up to 13 calculations of the landforms current volumes i e total surface and subsurface volume however are fairly insensitive to raster resolution hence the distinct geomorphologic properties of landforms e g shape terrain roughness slope inclination substantially determine the geomorphometric analysis of both surface and subsurface data as shown by the findings data fusion to integrate digital terrain geophysical and sedimentological datasets of varied resolutions benefits geomorphologic studies and helps provide a comprehensive image of landforms copyright 2013 john wiley sons ltd

zonation of monazite in metamorphic rocks and its implications for high temperature thermochronology a case study from the lewisian terrain abstract monazite is a valuable chronometer for many geological processes and a proper interpretation for the age derived from monazite requires an adequate understanding of the behaviour of this phase and its chemical and isotopic systems during geological processes this contribution reports the results of a detailed study on chemical and isotopic zonation of monazite in lewisian granulites which is of general significance for monazite geochronology in high grade metamorphic rocks detailed investigations on two lewisian granulite samples using sem epma and sims have revealed that lewisian monazites frequently show petrographic chemical and age zonation the petrographical zonation which reflects the chemical compositional variation can be characterised as follows on the basis of the bse images 1 concentric zoning 2 patchy zoning and 3 intergrowth like zoning the chondrite normalised ree distribution patterns are remarkably similar between different zones of single monazite grains this rules out the possibility that any portion of a zoned monazite in these two samples is detrital in origin some possible mechanisms are proposed for the formation of monazite zonation these include 1 intergrowth of monazite crystals with different composition 2 episodic growth or regrowth of monazite in response to the change of environment conditions during thermal event s which may involve recrystallisation or replacement of the original crystals in short the diversity of zoning patterns in monazites observed in this study cannot be explained assuming a single mechanism accordingly interpretation of the chemical and age information from any zoned monazite requires an adequate understanding of its formation mechanism line scans of th u pb la ce nd sm ca and si across monazite zones have been performed on two monazite grains which experienced granulite facies metamorphism the very sharp boundaries in these line scans indicate that the diffusive transport of these elements in monazite is low even at the temperature of granulite facies metamorphism the effective closure of monazite grains may also depend upon other factors such as the armouring effects of the host phase and recrystallisation of the mineral itself thus great care needs to be taken for geological application of the closure temperature concept

determining precambrian crustal evolution in china a case study from wutaishan shanxi province demonstrating the application of precise shrimp u pb geochronology

a morb arc basalt adakite association in the 2 5 ga wutai greenstone belt late archean magmatism and crustal growth in the north china craton abstract the wutai fuping and hengshan complexes form part of a major 2 5 ga late archean arc system in the northern part of the north china craton the wutai complex is a well preserved greenstone belt dominated by mafic intermediate and felsic volcanic rocks with a mid ocean ridge basalt morb arc back arc basalt adakite association multi element plots for morb type mafic volcanic rocks are characterised by depletion of th nb ta and la nearly flat or lree depleted ree patterns and nb u and nb th ratios greater than primitive mantle values back arc basin basalt babb type rocks have nearly flat trace element patterns with nb ti and y troughs and lree depleted or near flat ree patterns island arc basalt iab type rocks are characterized by negative anomalies of nb ta zr hf ti and y and by lree enrichment the felsic volcanic rocks conform to most compositional criteria for cenozoic adakites including low y and yb high la smn la yb and zr sm ratios and similar trace element and ree patterns trends defined by the association are consistent with magma mixing between morb like melts and subduction slab related melts intra oceanic subduction coupled with contemporary morb type mantle upwelling related to back arc basin extension can account for the interaction between the two components subduction accretion or back arc basin collapse led to accretion of the wutai intra oceanic arc back arc complexes with the magmatic arcs of the fuping and hengshan terranes that are dominated by high grade tonalite trondhjemite granodiorite ttg gneisses this geodynamic interpretation is different from many tectonic models for archean greenstone belts in which magmatism and crustal growth were dominated by mantle plumes or interaction between subduction zones and mantle plumes the final disposition of the arc complexes was controlled by the collision of the eastern and western blocks of the north china craton during the paleoproterozoic resulting in extensive tectonic interleaving within a major orogenic belt that extended throughout the central portion of the north china craton

rb sr and sm nd isotopic dating of an early precambrian spilite keratophyre sequence in the wutaishan area north china preliminary evidence for nd isotopic homogenization in the mafic and felsic lavas during low grade metamorphism the spilite keratophyre sequence in the wutaishan area north china has been dated by zircon from the quartzkeratophyre and a volcanic crystallization age of 2522 ma liu dunyi et al 1985 was obtained this volcanic rock sequence experienced a low grade metamorphism of greenschist facies during 1800 2000 ma however combined sm nd whole rock data from the volcanic rock sequence if interpreted in terms of an isochron gives a younger age of 2250 182 ma if separately calculated sm nd isochrons for quartz keratophyre and spilite yield two consistently younger ages of 1977 385 ma and 1981 178 ma these sm nd isochron ages are consistent with a rb sr age of 1871 98 ma and with the time of regional greenschist facies metamorphism consequently we interpret the 2250 ma alignment on the sm nd diagram as an errorchron the two sm nd metamorphic ages suggest that partial homogenization of nd isotopic composition in water rich spilite keratophyric meta volcanics can be achieved during low grade metamorphism as a result of ree mobility using the nd values at the time of metamorphism and the average 147sm 144nd ratios of the spilite and the quartzkeratophyre initial nd values of 2 6 3 5 and 3 0 6 1 respectively are estimated at the time of volcanic eruption 2522 ma similar positive initial nd values for the spilites and quartz keratophyres suggest that they might have been derived from the same depleted mantle source or that the quartz keratophyres are derived from a short lived mafic source

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

electron microprobe dating of monazites from high grade gneisses and pegmatites of the kerala khondalite belt southern india monazites of five samples one leptynitic garnet biotite gneiss one khondalite one augen gneiss and two pegmatites from the central and northern part ponmudi unit of the kerala khondalite belt kkb in southern india were analyzed with the electron microprobe dating technique monazites in the augen gneiss and the pegmatites yield grain sizes between 200 800 m th abundances are rather low 10 wt and the distribution of th u and pb within single grains is fairly homogeneous contrasting to this monazites in the leptynitic gneiss and the khondalite are small 150 m they often display very complex th u pb patterns and contain high th concentrations up to 20 wt the statistical treatment of individual ages from the investigated samples revealed three populations of lower proterozoic 1 9 ga upper proterozoic 580 ma and ordovician age 470 ma as well as mid proterozoic ages between 0 8 1 7 ga which are not regarded to be of geological significance lower proterozoic ages are preserved in the cores of monazites from leptynitic gneisses and khondalites they fairly agree with sm nd model ages for similar rocks of the kkb and give a minimum age for first monazite growth or complete homogenization the prominent pan african population with mean values between 540 and 580 ma is present in the leptynitic gneiss the khondalite and the augen gneiss and in line with published isotope ages for the kkb the ordovician population finally marks the emplacement of granitic pegmatites subsequent to the pan african high grade metamorphic event there is an obvious discrepancy between khondalites and leptynitic gneisses on the one hand and augen gneisses on the other concerning the presence of lower proterozoic ages while these are abundant in the former often rimmed by upper proterozoic ages they are completely absent in the latter it appears unlikely that lower proterozoic ages were completely reset during a pan african event exclusively in the augen gneisses while they were preserved in leptynitic gneisses and khondalites it is further concluded that the augen gneisses are of magmatic origin and were derived from porphyritic granites thus the upper proterozoic age of 605 37 ma calculated for the investigated sample approximates the time of magma emplacement which slightly precedes the peak stage of pan african high grade metamorphism in the kkb and of monazite crystallization from the granitic melt a characteristic feature of the investigated monazites is the resetting of lower proterozoic and pan african ages to significantly younger values due to partial pb loss monazites not shielded by other minerals e g garnet suffered selective mobilization of pb along fractures or at their rims while th and u concentrations remained almost unchanged the results presented in this study indicate that this was mainly due to fluid rock interaction it is concluded that thermal diffusion of pb even at the suggested temperatures of 900 c only had minor influence on the th u pb composition in monazite and that the closure temperature for this system must be significantly higher than previously assumed 750 c

sm nd and shrimp u pb zircon geochronology of high pressure granulites in the sanggan area north china craton timing of paleoproterozoic continental collision abstract high pressure hp mafic granulites are widely distributed as sheet like and lenticular bodies within highly deformed tonalitic gneisses in the sanggan area north china craton they have clockwise isothermal decompression and isobaric cooling p t paths implying continental collision tectonics whole rock analyses of 15 samples define a sm nd isochron yielding an age of 2547 87 ma with e nd t 2 7 corresponding nd depleted mantle model ages show a similar range and are interpreted as the age of the magmatic protolith to the high pressure granulites a combined sm nd mineral whole rock isochron from one of these samples yields an age of 1813 23 ma taken to represent the metamorphic age at an early stage on the cooling path shrimp u pb zircon analyses of three hp mafic granulite samples give uniform weighted mean 207 pb 206 pb ages of 1817 12 1817 12 and 1819 16 ma these ages are interpreted to date metamorphism of the hp granulites and with the sm nd mineral whole rock result strongly suggest that the time of continental collision was at ca 1 82 ga an additional sample records two age populations one at 1803 9 ma and an older one at 1872 16 ma the latter may indicate the timing of either an earlier metamorphic event or possibly the earliest stage of a single prolonged metamorphic episode that peaked at 1 82 ga these results confirm the paleoproterozoic age for assembly of the north china craton

an improved u th pb age calculation for electron microprobe dating of monazite abstract determination of u th pb ages using the electron probe microanalyser epma is an inexpensive alternative method for dating monazite the method is rapid and reliable both for simple monogenenetic monazite and for complex polygenetic monazite having undergone metamorphic events involving fluid interaction and recrystallization the main limitation of the method is its rather poor precision i e 45 to 120 ma for ages ranging from 300 to 3000 ma calculated on each spot the precision is limited by pb content and by counting statistics which cannot give precision better than 2 for individual determinations on u th and pb even at high levels a procedure that uses the new th pb vs u pb diagram to improve the calculated precision on u th pb ages gives results to within 5 to 15 ma for ages ranging from 300 to 3000 ma with complex polygenetic monazite in which either the points show large scattering indicated by a large mswd or the regression line exhibits a slope very different from neighbour theoretical isochrons the procedure must be applied separately on homogeneous domains only this makes it possible to distinguish between events separated by a gap of 20 to 60 ma according to the range of ages concerned i e 300 to 3000 ma several examples are given to illustrate these systematics

structural evolution and 40ar 39ar dating of the zanhuang metamorphic domain in the north china craton constraints on paleoproterozoic tectonothermal overprinting abstract the zanhuang domain in the hinterland of the north china craton consists of archaean paleoproterozoic mesoproterozoic and palaeozoic rocks and was previously considered a mesozoic metamorphic core complex our reappraisal of regional structural history and mineral 40 ar 39 ar geochronology shows that the domain was subjected to a number of deformation events and had a heterogeneous uplift cooling history during the paleoproterozoic four primary deformation events have been recognized in the domain the first event reflects the earliest deformation in the region however only closed and rootless folds are preserved d2 was dominated by wnw ese shortening and top to ese thrusting in a collisional environment d3 was a divergent extensional and ductile shearing event driven by the post collisional extensional collapse and exhumation of the thickened crust in the domain d4 was characterized by localized ductile shearing with the development of three nne trending ductile shear zones the 40 ar 39 ar plateau ages derived from the thermochronology analyses of the biotite concentrates from the metamorphic rocks are interpreted as cooling ages through biotite 40 ar 39 ar closure temperature 300 c and this allows us to constrain the timing of deformation events in conjunction with the evidence from structural analyses and previous geochronological data we conclude that 1870 and 1870 1826 ma define the timing of d1 and d2 events respectively while 1826 1793 ma represents the age of d3 the last event d4 occurred at 1689 1633 ma as constrained by 40 ar 39 ar plateau ages of biotite concentrates from the mylonites within the ductile shear zones these data together with k feldspar 40 ar 39 ar geochronology allows us to depict the cooling history of the region during the paleoproterozoic and mesoproterozoic it appears that the uplift cooling rate varies temporally and spatially in the region

interpretation of monazite ages obtained via in situ analysis abstract monazite grains from nepal and vietnam were compositionally analyzed with an electron microprobe and dated th pb with an ion microprobe five sources of uncertainty explain age distributions from single samples that appear inconsistent with a single population 1 pb loss due to diffusion 2 dissolution reprecipitation reactions along a retrograde path 3 analytical uncertainties 4 analyses of overlapping age domains and 5 episodic monazite growth the influence of these factors is sample dependent but can be evaluated 1 using peak metamorphic conditions and x ray element maps to assess potential polymetamorphism or retrogression 2 obtaining other geochronologic data including previous work or dating other minerals in the sample 3 evaluating any method related uncertainty including counting statistics for electron microprobe analyses or calibration reproducibility for ion microprobe analyses and 4 ascertaining the potential growth mechanism of the monazite grain including dissolution of detrital grains or production from rare earth element ree oxide or allanite chemical contents of monazite grains analyzed in this study fail to reflect timing information or mineral growth mechanisms instead of relying on monazite chemical composition major mn fe mg ca and minor y element garnet zoning patterns and peak p t conditions should be used to facilitate age interpretation this thermobarometric data records the sample s thermal history changes in garnet growth rate and mechanisms and accessory mineral breakdown

a three dimensional method for calculating independent chemical u pb and th pb ages of accessory minerals abstract previous theoretical considerations on the chemical u th total pb dating method failed to distinguish between thorogenic and uranogenic lead however it can be shown that the data points are located on a plane in the three dimensional tho2 pbo uo2 space the calculation of the best fit plane yields a slope in the tho2 pbo and uo2 pbo coordinate projections and an initial pbo value from the two slopes th pb and u pb ages can be calculated independently the method described in this paper is applied to monazites from the hercynian g4 granite of the fichtelgebirge germany th pb and u pb ages were calculated at 323 20 ma and 304 15 ma respectively the intercept value close to zero indicates that no significant amounts of common lead are present in the monazites studied

shrimp u pb zircon ages of the fuping complex implications for late archean to paleoproterozoic accretion and assembly of the north china craton the fuping complex is situated in the central part of the north china craton and consists of four major lithological assemblages fuping tonalitic trondhjemitic granodioritic gneisses longquanguan augen gneisses wanzi supracrustal assemblage and nanying granitic gneisses shrimp u pb geochronology combined with u th and cathodoluminescence cl imaging of zircon enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the fuping complex cl images reveal the coexistence of magmatic and metamorphic zircons in nearly all rock types of the fuping complex the metamorphic zircons occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores and are all characterized by nebulous zoning or being structureless with extremely high luminescence and very low th contents these features make them distinct from magmatic zircons that are characterized by concentric oscillatory zoning comparatively low luminescence and high th and u contents shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic plutons of the fuping gneisses were emplaced at 2523 14 ma 2499 10 ma and 2486 8 ma respectively whereas the monzogranitic and granitic plutons of the longquanguan augen gneisses were intruded respectively at 2510 22 ma and 2507 11 ma prismatic and oscillatory zoned zircons dominate in the pelitic rocks of the wanzi supracrustal assemblage and are interpreted as detritus from igneous source rocks the concordant and discordant u pb ages of 2502 5 ma and 2507 14 ma obtained from two pelitic rock samples indicate these rocks must have been deposited no earlier than 2507 ma ago in addition a zoned zircon grain in one pelitic rock sample has a near concordant age of 2109 5 1 ma which may provide a maximum depositional age for the wanzi supracrustal rocks shrimp results also reveal that granitic magmatism assigned to the nanying granitic gneisses occurred over a protracted interval from 2077 13 ma to 2024 21 ma the nebulously zoned zircon grains and overgrowth recrystallization zircon rims from different rocks yielded similar concordant 207pb 206pb ages in the range 1875 to 1802 ma interpreted as approximating the age of regional metamorphism of the fuping complex timing of primary zircon crystallization and regional metamorphism of the fuping complex is in general agreement with recent u pb zircon ion probe results for the wutai and hengshan complexes that bound the fuping complex to the northwest these areas are characterized by the emplacement of major granitoid bodies at around 2 50 ga to 2 48 ga ago deposition of supracrustal rocks in the paleoproterozoic intrusion of paleoproterozoic granitic bodies at 2 1 to 2 0 ga and regional metamorphism at 1 875 to 1 802 ga these data indicate that the fuping and hengshan complexes do not represent an older crystalline basement to the wutai complex as suggested in previous tectonic models but together with the wutai complex represent elements of a single late archean to paleoproterozoic magmatic arc system that has been subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western north china blocks at 1 85 ga which resulted in the final assembly of the north china craton

comparative isotopic and chemical geochronometry of monazite with implications for u th pb dating by electron microprobe an example from metamorphic rocks of the eastern wyoming craton u s a polygenetic monazite grains in diverse precambrian crystalline rocks from the black hills south dakota have been analyzed in situ by ion and electron microprobe methods shrimp and emp to evaluate the accuracy and precision of emp ages determined using a new analytical protocol that incorporates improved background acquisition and interference corrections parallel evaluations were conducted by comparing emp chemical and shrimp isotopic ages at regional rock and grainscales the monazite data set includes 354 emp chemical analyses from 26 grains in six metamorphic rocks which resolve into 54 age composition domains and 31 shrimp isotopic ages from 13 grains in one of the rocks with six grains microanalyzed in common by the two methods the data set also includes monazite bearing garnets in two of the rocks whose isotopic compositions were analyzed using pb stepwise leaching pbsl methods both the emp and shrimp data sets reveal a continuum of apparent monazite ages spanning a 1790 1680 ma timeframe with a relatively high probability of ages at 1755 and 1715 ma that correspond spatially to core and rim domains pbsl ages of 1742 and 1734 ma obtained from monazite bearing garnet in two rocks are intermediate compared to the corresponding emp ages and are thereby interpreted as mixed ages emp data for two grains in the structurally deepest of the six rocks record 1785 and 1755 ma ages in the cores and higher y and lower th rims respectively and these results are duplicated by shrimp ages in these and or other grains from the same rock overall the emp shrimp and pbsl ages are internally consistent at the various scales of observation which serves to validate emp chemical dating as an accurate and precise method of discerning monazite age populations in polymetamorphic terrains the emp data set is interpreted geologically as res ecting multiple episodes of monazite growth that are provisionally related to known metamorphic events in the black hills taking the most precise emp data at face value it is possible to resolve the timing of the two older events at 1784 4 ma or 1786 6 ma and 1756 3 ma or 1753 4 ma with 95 con dence these events are considered to be related to sequential episodes of n directed thrusting and e w compression associated with paleoproterozoic crustal assembly in the mid continent a younger metamorphism related to granite intrusion known to have occurred at 1715 3 ma is dated independently at 1717 2 ma from the emp monazite ages

archean geodynamics in the central zone north china craton constraints from geochemistry of two contrasting series of granitoids in the fuping and wutai complexes abstract the archean to paleoproterozoic central zone of the north china craton is situated between the eastern and western archean continental blocks and contains two contrasting series of neoarchean granitoids the 2523 2486 ma tonalite trondhjemite granodiorite ttg gneisses in the fuping complex and the 2555 2525 ma calc alkaline granitoids tonalite granodiorite granite and monzogranite in the wutai complex the fuping ttg gneisses most likely formed from partial melting of 2 7 ga basalts at 50 km with an involvement of 3 0 ga crustal material the wutai granitoids have higher k 2 o lile and rb sr but lower sr y and la n yb n than the fuping ttg gneisses are characterized by nd t dm from 2 5 to 2 8 ga and e nd t from 0 49 to 3 34 and are derived from partial melting of a juvenile source at the geochemistry of these two contrasting series of neoarchean granitoids provides further evidence that the wutai complex originated and evolved separately from the fuping complex the wutai complex most likely formed as an oceanic island arc with volcanism and synvolcanic granitoid intrusions at 2555 2525 ma the wutai complex was subsequently accreted onto the eastern archean continental block and was probably responsible for crustal thickening and ttg magmatism at 2523 2486 ma in the fuping complex as part of the taihangshan hengshan block at the western margin of the eastern archean continental block

terrestrial laser scanning used to determine the geometry of a granite boulder for stability analysis purposes abstract in this paper we analyze the use of terrestrial laser scanning tls technologies to determine the geometric features of a granite boulder accurate determination of these features is a key to performing a reliable stability analysis of the boulder tls has been demonstrated to have important advantages over traditional measurement techniques such as for example direct methods based on the use of tapes or indirect methods such as topography or close range photogrammetry tls equipment enables thousands of points to be accurately measured in minutes in our study tls measured points were used to model the surface of a boulder geometric parameters were then calculated namely centre of gravity volume of the boulder and dimensions of the boulder contact area with the ground taking into account mechanical and environmental factors these parameters were used to calculate the safety factor of the boulder against toppling and sliding our results show that when seismic activity in the region is taken into consideration the boulder is borderline stable unstable

tectonothermal history of the basement rocks in the western zone of the north china craton and its tectonic implications the basement of the north china craton can be divided into the eastern central and western zones based on lithological structural metamorphic and geochronological data the western zone comprises two different petrotectonic units archaean tonalitic trondhjemitic granodioritic ttg grey gneisses and metamorphic mafic rocks and palaeoproterozoic khondalite series the former is characterized by isobaric cooling ibc type anticlockwise p t paths in the north northwestern part of the zone and near isothermal decompression itd type clockwise p t paths in the eastern part adjacent to the central zone on the other hand the tectonothermal evolution of palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling defining clockwise p t paths the archaean ttg gneisses and associated mafic rocks with anticlockwise metamorphic p t paths reflects an origin related to underplating and intrusion of mantle derived magmas which may be derived from mantle plumes they represent a late archaean continental block in the western part of the north china craton the palaeoproterozoic khondalite series rocks represent passive continental margin deposits they were metamorphosed and deformed in the late palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the north china craton the itd type clockwise p t t paths of the palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the north china craton at c 1800 ma

time constraints on deformation and metamorphism from epma dating of monazite in the proterozoic robertson river metamorphics ne australia epma dating of monazite confirms the relative timing of a succession of foliation intersection axis trends in porphyroblasts fias and two periods of progressive metamorphism intervened by retrogression in the robertson river metamorphics ne australia a complete pressure temperature deformation time p t d t path has been deciphered involving an early clockwise p t loop followed by high temperature low pressure metamorphism successive generations of monazite were identified using microstructure and fia trends and then dated the succession of four fias trending ene wsw fia1 e w fia2 n s fia3 ne sw fia4 plus four matrix foliations s1 s4 were accompanied by three periods of garnet and two periods of staurolite growth monazite grew in response to most of these events isopleth thermobarometery using p t pseudosections in the mnnckfmash system for garnet porphyroblasts selected based on fia trends in their core reveal that pressure increased progressively from 3 4 kb at 530 550 c to 6 7 kb at 600 620 c during medium pressure temperature metamorphism this was accompanied by changing bulk shortening directions from nnw sse to n s to e w perpendicular to fias 1 2 and 3 the development of fia1 and fia2 occurred between 1655 2 2 ma and 1625 15 ma fia3 developed over 30 50 ma periods from 1625 15 ma to 1586 6 ma retrogressive metamorphism decompression and exhumation occurred over a not vert similar45 ma period further metamorphism accompanied regional granite intrusion and generated lower pressure higher temperature metamorphism during the development of fia4 nw se bulk shortening at 1542 8 ma this period possibly extended for another 30 50 ma based on the monazite ages obtained from the youngest foliations in the matrix correlation of these data with other ne australian proterozoic inliers suggests that they were all once part of a single orogen that developed from ca 1650 to 1500 ma

origin chemistry and flow of formation waters in the mississippian jurassic sedimentary succession in the west central part of the alberta basin canada abstract the flow and chemistry of formation waters was analyzed in the mississippian jurassic succession in the west central part of the alberta basin using publicly available standard chemical analyses of formation waters and drillstem test data collected by the petroleum industry in alberta the interpretation of the thoroughly culled hydrogeological data show that a transition between a southern and a northern basin scale flow system takes place in the study area in the southeastern half of the study area the mississippian jurassic hydrostratigraphic group represents a single continuous carbonate sandstone aquifer system consisting of the lower jurassic nordegg member the triassic montney formation the permian belloy formation and the mississippian stoddart and rundle groups the confining units are the competent fernie and exshaw banff aquitards at the top and base respectively the salinity of formation waters increases northwestwards from 50 to 150 g l while the bicarbonate content decreases in similar fashion from 3 to 0 5 g l the flow pattern based on hydraulic heads and chemical composition of formation waters indicate decreasing mixing of meteoric water carried northward in the southern basin scale long range system with heavier connate water present in the northern part of the study area in the center and in the northeast the permian and mississippian carbonates and the triassic montney and charlie lake halfway sandstones form individual aquifers separated by the intervening doig montney aquitard the flow in the charlie lake halfway and the permo mississippian aquifers is directed east northeastward from the deformation front into the overlying aquitards or discharging into the southern basin scale flow system respectively only in the montney aquifer the flow is directed inward south southwestward drawn into a local hydrocarbon saturated sink which is created by a higher rate of gas escape than of gas generation through a low permeability and capillary seal region the high salinity in the 130 150 g l range and low bicarbonate content 0 5 g l of formation waters in the northern part of the study area indicate a connate origin the relation of na ca cl br concentrations in the formation waters suggest that these waters initially originated as seawater that was altered to some degree by subaerial evaporation and dolomitization but halite dissolution probably is the main source of salinity the driving mechanism for the flow of these waters could be either tectonic expulsion from deep strata in the deformed part of the basin as suggested by the high salinity of these waters or topography driven meteoric recharge in the rocky mountains through a tortuous path unidentified as yet the integrated interpretation of flow and chemistry of formation water shows that mississippian jurassic formation waters in the deep west central parts of the alberta basin have been influenced less by mixing with meteoric water than was identified previously in the central southern and northern parts of the basin the main reasons for the isolation of relict mississippian jurassic formation waters in the deep alberta basin are effective confining aquitards and the fact that this area is influenced only marginally by mixing with meteoric water carried by a gravity driven flow system

age and evolution of a late archean to paleoproterozoic upper to lower crustal section in the wutaishan hengshan fuping terrain of northern china abstract the taihangshan wutaishan area forms part of the central north china craton and consists of three main components the hengshan and fuping complexes containing predominantly ductilely deformed late archean to paleoproterozoic high grade granitoid orthogneisses intruded by mafic dykes of gabbroic composition and the low grade late archean wutai greenstone belt developed between the high grade terrains and consisting of bimodal volcanic rocks and metasediments associated with coeval granitoids zircon dating shows that both the hengshan and fuping complexes were intruded by major granitoid bodies between 2 52 and 2 48 ga with rare occurrences of 2 7 ga gneisses wutai granitoids adjacent to the fuping complex also contain 2 7 ga xenocrysts all possibly reflecting the same older basement rare granitic gneisses in the hengshan have emplacement ages of 2 35 ga and show the same structural features as the older rocks indicating that the main deformation occurred after 2 3 ga deposition of supracrustal rocks and emplacement of mafic dykes occurred in the paleoproterozoic together with intrusion of granitic bodies at 2 1 2 0 ga and all underwent regional metamorphism at 1 88 1 85 ga we interpret the hengshan and fuping granitoid gneisses as the lower plutonic part of a late archean to early paleoproterozoic japan type magmatic arc with the upper volcanic part represented by the wutai complex components of this arc may have evolved at a continental margin as indicated by the 2 7 ga zircons virtually all magmatic events are recorded in all three complexes however the 1 85 ga metamorphic event is only recorded in the higher grade portions of the wutai since low grade and presumably high crustal level precluded metamorphic zircon growth shear zones in the hengshan are interpreted as major lower crustal discontinuities post dating the peak of high pressure granulite metamorphism we suggest that they formed during orogenic collapse and uplift of the hengshan complex in the late paleoproterozoic 1800 ma

quantitative assessment for the rockfall hazard in a post earthquake high rock slope using terrestrial laser scanning abstract geometric information and discontinuity characterization of rock masses are the key aspects of the analysis of the evolution and failure mechanisms of rockfalls with the advantageous use of terrestrial laser scanning tls the accurate three dimensional 3d spatial information of rock slopes can be obtained without contact by conducting a fuzzy k means algorithm in this study the automatic identification of discontinuity sets is achieved and dominant occurrences of rock mass discontinuities in each local region can be acquired in great detail this automatic identification method permits the user to visually identify the discontinuity sets and acquire their spacial distribution features e g occurrences spacings trace lengths and their geometric compounding relationships at the same time based on the shortest distance sd algorithm and the surface to plane volume calculation algorithm the distributions shapes volumes and scars of the rockfalls can be accurately detected over the monitored time interval these methods are able to provide adequate investigations and quantitative assessment for the rockfall failure mechanisms and evolutions of the hongshiyan post failure rock slope after the 2014 ludian earthquake the topography of the landslide surface mechanical properties scales and the structural features of the discontinuities have a significant effect on the failure mechanisms distributions and volumes of rockfalls the main failure mechanisms of the rockfall investigated in this rock slope can be divided into plane failure wedge failure and toppling failure the plane and wedge failures mainly occurred in the landslide surface while the toppling failures are mainly observed along the edge of the post failure slope which is obviously responded by preferred discontinuities the reverse dip stratified structure characteristics and the excavation disturbances during the recovering and slope treatment stage induce numerous progressive and continuous failures of rockfalls the results are beneficial for the design and optimization of rockfall treatments

high pressure granulites in the sanggan area north china craton metamorphic evolution p t paths and geotectonic significance high pressure basic granulites are widely distributed as enclaves and sheet like blocks in the huaian ttg gneiss terrane in the sanggan area of the central zone of the north china craton four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles the p t conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers the low ca core of growth zoned garnet along with inclusion minerals defines a prograde assemblage m1 of garnet clinopyroxene plagioclase quartz yielding 700 c and 10 kbar the peak of metamorphism at about 750 870 c and 11 14 5 kbar m2 is defined by high ca domains in garnet interiors and inclusion minerals of clinopyroxene plagioclase and quartz kelyphites or coronas of orthopyroxene plagioclase magnetite around garnet porphyroblasts indicate garnet breakdown reactions m3 at conditions around 770 830 c and 8 5 10 5 kbar garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole plagioclase around garnet formed during the cooling process at about 500 650 c and 5 5 8 kbar m4 these results help define a sequential p t path containing prograde near isothermal decompression itd and near isobaric cooling ibc stages the clockwise hybrid itd and ibc p t paths of the hp granulites in the sanggan area imply a model of thickening followed by extension in a collisional environment furthermore the relatively high pressures 6 14 5 kbar of the four metamorphic stages and the geometry of the p t paths suggest that the hp granulites together with their host huaian ttg gneisses represent the lower plate in a crust thickened during collision the corresponding upper plate might be the tectonically overlying khondalite series which was subjected to medium to low pressure mp lp 7 4 kbar granulite facies metamorphism with a clockwise p t path including an itd segment both the hp and the mp lp granulite facies events occurred contemporaneously at c 1 90 1 85 ga in a collisional environment created by the assembly process of the north china craton

detection and spatial prediction of rockfalls by means of terrestrial laser scanner monitoring abstract a rock face affected by small rockfalls has been monitored using a ground based remote sensing apparatus terrestrial laser scanner tls the pilot study area corresponds to the main scarp of the 1881 puigcercos landslide pallars jussa catalonia spain four datasets of the slope were acquired from september 2007 to july 2008 in an ongoing project the geomorphological evolution of the rock face in terms of volume and frequency of rockfall was studied by the comparison of sequential datasets in addition to the detection of past events this study deals with the spatial prediction of rockfalls through the detection of pre failure deformation as a precursory indicator the high resolution and accuracy and the maximum range of the tls offer interesting prospects for both spatial location and prediction of rockfall

electron microprobe age mapping of monazite high resolution x ray maps of th u pb and y in monazite can be used to construct age maps which reveal the continuous spatial distribution of ages in a single grain of monazite the age mapping algorithm and three examples are presented to illustrate the capabilities and applications of this mapping technique the insights it can provide into monazite geochronology in general and its limitations compared to electron microprobe emp quantitative dating and other in situ geochronologic techniques age maps offer critical information for unraveling metamorphic and tectonic histories and for interpreting results from other geochronologic techniques and they are a valuable aid for rigorously locating in situ analytical points age mapping also can be used to better understand the behavior of the u th pb system in monazite during metamorphism deformation and s uid circulation events age maps presented in this paper reveal unsuspected age heterogeneities on the micrometer scale like a now healed fracture not visible in back scattered electron bse images or young domains less than 5 m in width located inside an older core in both cases using age maps as a template for locating in situ analysis points will minimize the peril of age mixing and erroneous geological interpretations in addition to providing critical information for illustrating and interpreting the history of complex polygenetic monazite age mapping may ultimately lead to a better understanding of the processes involved with monazite growth and recrystallization and thus even more powerful applications of the monazite geochronometer the agemap program is available in a windows version and can be downloaded from the internet at the following address http www geo umass edu probe agemap

application of a long range terrestrial laser scanner to a detailed rockfall study at vall de nuria eastern pyrenees spain abstract in this study we show the application of a long range terrestrial laser scanner tls to a detailed rockfall study in a test zone at vall de nuria located in the eastern pyrenees data acquisition was carried out using tls ilris3d the new generation of reflector less laser scanners with a high range accuracy and velocity of measurements eight scans were performed at 3 stations to acquire coordinates of almost 4 million points the results from the acquired data are a high accuracy digital elevation model dem and the reconstruction of the joint geometry the former is used for inventory of rockfalls and for more accurate rockfall simulation trajectories and velocities the latter allows us to model the geometry and volume of the source area in recent rockfalls our findings suggest that tls technology could be a tool of reference in rockfall studies in the near future

geochemical ar 40 ar 39 geochronological and sr nd isotopic constraints on the origin of paleoproterozoic mafic dikes from the southern taihang mountains and implications for the ca 1800 ma event of the north china craton abstract the wide occurrence of paleoproterozoic mafic dikes in the basement of the trans north china orogen provides important constraints on the major 1800 ma tectonothermal event of the north china craton these mafic dikes form a tholeiitic series dominated by basalts and basaltic andesites and can be geochemically classified into three groups the groups 1 and 2 rocks are characterized by high total feo contents 12 69 15 61 of which the group 1 rocks are more enriched in lile and lree contents and depleted in hfse th nb n 2 5 3 8 la yb cn 3 0 5 8 nb la n 0 27 0 38 and have more radiogenic nd isotopic ratios nd t 3 40 to 5 14 than the group 2 rocks th nb n 0 8 1 2 la yb cn 1 5 2 1 nb la n 0 65 0 87 nd t 0 60 to 1 67 in contrast the group 3 rocks are typified by low feot 7 86 11 04 and high mgo 5 62 9 56 contents higher la yb cn 4 22 7 13 ratios less radiogenic nd isotopic ratios nd t 2 75 to 5 52 and more significant th u and nb ta depletion are also apparent features 40ar 39ar geochronology of three representative samples from each group yielded plateau ages of 1780 7 0 5 ma 1765 3 1 1 ma and 1774 7 0 7 ma respectively these elemental and isotopic data suggest that the geochemical variations of these rocks cannot be simply explained by crystallization from a common parental magma involving crustal contamination during emplacement instead they most likely originated from variable sources under different degrees of partial melting the group 1 rocks were derived from relatively low degrees of partial melting of a refractory lithospheric mantle previously metasomatised by subduction related fluids whereas the group 2 rocks originated from a hybridized source involving ca 40 subduction modified lithospheric mantle similar to the group 1 and ca 60 n morb component in contrast the group 3 rocks show significant th u depletion that may mark the involvement of portions of gabbroic lower crust trapped in the source region during subduction based on all the available data we propose a tectonic model of a full subduction syncollision postcollision rifting cycle for the evolution of the ncc between 1870 and 1765 ma a variety of source regions beneath the southern taihang mountains initially developed during the period of subduction collision and subsequent extension rifting resulted in the melting of the subduction modified lithospheric mantle which produced widespread paleoproterozoic mafic dikes on the trans north china orogen in response to upwelling of convective mantle

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

palaeoproterozoic assembly of the north china craton the basement of the north china craton consists of the eastern and western blocks separated by the central zone both the eastern and western blocks are dominated by late archaean tonalitic trondhjemitic granodioritic gneiss complexes interdigitated with minor supracrustal rocks metamorphosed at 2 5 ga with anticlockwise p t paths the central zone is composed of reworked late archaean components and palaeoproterozoic juvenile crustal materials that underwent regional metamorphism at 1 85 ga with clockwise p t paths involving isothermal decompression as a result of collision between the eastern and western blocks which resulted in the final assembly of the north china craton

denudation history of the high t p ryoke metamorphic belt southwest japan constraints from chime monazite ages of gneisses and granitoids chime chemical th u total pb isochron method monazite ages were determined for gneisses and granitoids from the eastern and western parts of the ryoke belt separated by about 500 km the monazite ages for the gneisses are concentrated between 102 and 98 ma and are interpreted as the time of monazite formation under lower amphibolite facies conditions the peak metamorphism seems to be contemporaneous with the emplacement of the geologically oldest plutons that are dated at c 95 ma in both the eastern and western parts in the eastern part plutonism continued from c 95 ma to c 68 ma at intervals of 2 10 ma whereas in the western part it ceased at c 85 ma the chime monazite ages agree well with the relative age of granitoids derived from intrusive relationships of granitoids in both parts these lines of evidence are incompatible with a current view that the plutonometamorphism in the ryoke belt becomes younger towards the east the chime monazite ages coupled with available data on the depth at which the ryoke metamorphism took place and the emplacement of individual plutons show that the western part was eroded more rapidly about 1 5 mm year 1 than the eastern part about 0 8 mm year 1 over the time span from 91 to 85 ma the denudation rates agree well with those in active orogenic belts like the alps and himalayas

further evidence for 1 85 ga metamorphism in the central zone of the north china craton shrimp u pb dating of zircon from metamorphic rocks in the lushan area henan province abstract this paper reports shrimp zircon u pb dating of precambrian supracrustal and granitic rocks from the lushan area henan province in the southern portion of the central zone also referred to as the trans north china orogen of the north china craton a graphite garnet sillimanite gneiss sample tw0006 1 of the shangtaihua group gives a range of inherited zircon ages from 2 73 to 2 26 ga and a metamorphic zircon age of 1 84 0 07 ga a garnet bearing gneissic granitoid sample twj358 1 which is considered to intrude the shangtaihua group gives a magmatic zircon age of 2 14 0 02 ga and a metamorphic zircon age of 1 87 ga the metamorphic zircon ages of 1 87 1 84 ga obtained in this study indicate that an important tectonothermal event occurred at the end of the paleoproterozoic in the lushan area this supports the southern continuation of a central zone in the north china craton that workers have recently considered to result from continent continent collision it is also evident that the shangtaihua group was formed during the paleoproterozoic between 2 26 and 2 14 ga and not during the archean as previously considered

zircon geochronology and metamorphic evolution of mafic dykes in the hengshan complex of northern china evidence for late palaeoproterozoic extension and subsequent high pressure metamorphism in the north china craton abstract magmatic and metamorphic zircons have been dated from ductilely deformed gabbroic dykes defining a dyke swarm and signifying crustal extension in the northern part of the hengshan complex of the north china craton these dykes now occur as boudins and deformed sheets within migmatitic tonalitic trondhjemitic granodioritic and granitic gneisses and are conspicuous due to relics of high pressure granulite or even former eclogite facies garnet pyroxene bearing assemblages shrimp ages for magmatic zircons from two dykes reflect the time of dyke emplacement at 1915 ma whereas metamorphic zircons dated by both shrimp and evaporation techniques are consistently in the range 1848 1888 ma the youngest granitoid gneiss yet dated in the hengshan has an emplacement age of 1872 17 ma these results complement recent geochronological studies from the neighbouring wutai and fuping complexes to the se of the hengshan showing that a crustal extension event occurred in the late palaeoproterozoic this preceded a major high pressure collision type metamorphic event in the central part of the north china craton that occurred in the palaeoproterozoic and not in the late archaean as previously thought our data support recent suggestions that the north china craton experienced a major craton wide orogenic event in the late palaeoproterozoic after which it became cratonized and acted as a stable block

electron microprobe dating as a tool for determining the closure of th u pb systems in migmatitic monazites high spatial resolution dating of monazite by the electron probe microanalyzer epma enables systematic and detailed studies of small minerals like zircon monazite records the complex history undergone by the host rocks recent improvements in the statistical treatment of many in situ data now make it possible to decipher the related thermal events and so obtain reliable and precise ages our work shows that a significant number of individual spot analyses is required to reach such precise information i e more than 30 40 data using the examples of monazites from three migmatites and one granite we show how to select the most efficient method of age calculation according to the u and th geochemistry of the grains or grain domains that we are trying to date three situations may be met 1 monazites exhibiting significant th u ratio variation 2 monazites exhibiting a fairly constant th u ratio but significant u th heterogeneity and 3 monazites of constant u and th concentrations for the first case a precise mean age can be calculated using a method of data reduction in the th pb f u pb diagram whereby a precision of 5 10 ma 2 is commonly achieved for the second case an isochron age can be calculated according to the pb f th method with a common precision of around 20 ma 2 whereas for the third case a simple weighted average age can be calculated using these approaches coupled with a back scattered electron image study we demonstrate that inheritance is probably as common for monazite as for zircon in addition the combination of high spatial resolution and precise age determination show the limited extent of pb diffusion in monazite finally an example from a migmatite from southern french guiana demonstrates the especially robust behavior of the th u pb system in monazite this system remains closed during late migmatization and during the subsequent zircon crystallization and zircon overgrowth of protolith zircons the monazite yielded exactly the same age as the protolith zircons

photogrammetry and laser scanning for analyzing slope stability and rock fall runout along the domodossola iselle railway the italian alps abstract in italy railways crossing the alpine valleys are a vital means of civil and commercial communications with the rest of europe the geomorphologic configuration and the climatic conditions especially in winter and spring can cause rock fall events resulting in railway service interruptions and damage to infrastructure and in the worst case to people there were rock fall events at a slope adjacent to the domodossola iselle railway most recently in 2004 this paper evaluates the stability of a mountain slope and maps rock fall hazards through the modeling of potential runout trajectories traditional geological geomorphological and geo engineering surveys were combined with data derived from digital terrestrial photogrammetry stereo photographic pairs of rocky outcrops in inaccessible areas were acquired from a helicopter data from photogrammetry topographic measurements and laser scanning were then integrated to build a digital model of the slope to characterize the rock mass and block geometry and to define possible runout trajectories the geomatic methods used have yielded oriented stereo images orthophotos and precise digital models of rocky wedges geometrical and structural characteristics of slopes such as joint attitude spacing and persistence and block volumes were also derived the results were used together with a deterministic limit equilibrium method to evaluate slope stability we assessed the probabilistic distribution of rock fall end points and kinetic energy along the rock falling paths and existing barriers and created a hazard map based on the spatial distribution of trajectories rock fall transit density and kinetic energy

two linear granite belts in the central western north china craton and their implication for late neoarchaean palaeoproterozoic continental evolution abstract precambrian granitoid rocks are widely distributed in the north china craton ncc the dominant granitic rocks in the central western ncc are trondhjemitic tonalitic and granodioritic ttg gneisses as well as some calc alkaline granitic gneisses and minor charnockites two linear granite belts in this area are different from other early precambrian granitic rocks in the ncc in terms of their occurrence and chemistry the liang tu lt garnet granite belt and the sanggan sg granite belt the lt belt occurs along two large scale ductile shear zones in metamorphosed al rich sedimentary country rocks khondalitic series in the central part of the lt belt are metagabbroic granulite lenses that were originally mafic dykes in the outer part of the belt garnet granites grade into khondalitic rocks lt belt granites have geochemical characteristics of s type granites the sg granite belt is 400 km long and composed of many deformed gneissic granitic bodies and granitic sills and veins with without gneissosity they contain various lenses including high pressure granulites and retrograded eclogites the sg granite belt trends east northeast parallel to the regional gneissosity of the country rocks major and trace element geochemistry of these granites shows characteristics of syn collisional and post collisional granite the country rocks beside the sanggan granite belt are different including the huai an fengzhen terrain hft to the northwest and the wutai fuping terrain wft to the southeast the lt and sg granite belts formed within an old continental craton and an old orogenic zone between two blocks respectively

geological and morphological study of the jiufengershan landslide triggered by the chi chi taiwan earthquake the jiufengershan rock and soil avalanche is one of the largest landslides triggered by the chi chi earthquake taiwan 1999 the landslide destabilized the western limb of the taanshan syncline along a weak stratigraphic layer it involved a flatiron remnant which was almost entirely mobilized during the earthquake the avalanche was slowed down by ns trending ridges located downstream along the jiutsaihu creek the landslide affected a 60 m thick and 1 5 km long sedimentary pile composed of shales and sandstones which dip 228se toward a transverse valley the triggering mechanism and the sliding process were analyzed by means of geological and morphological data from aerial photographs and observed in the field a high resolution airborne light detection and ranging lidar image taken 2 5 years after the landslide allows the identification of morphological structures along the sliding surface and the landslide accumulation the sliding surface shows several deformation structures such as fault scarps and folds these structures are interpreted in terms of basal shear stresses created during the avalanche three major joint sets were identified at the sliding surface the isopach map of the landslide was calculated from the comparison between elevation models before and after the earthquake the coseismic volume of mobilized material and landslide deposit data are 4210 6 m 3 and 5010 6 m 3 respectively the geometry of the landslide accumulation in the field has an irregular star shape the morphology of the deposit area shows a sequence of smooth reliefs and depressions that contrast with the neighboring ridges d 2005 elsevier b v all rights reserved

geochronology of polygenetic monazites constrained by in situ electron microprobe th u total lead determination implications for lead behaviour in monazite abstract monazite grains are generally concordant and with an electron microprobe give th u total pb isochron ages in agreement with conventional u pb data monazites from four samples of post archean migmatite from the ivory coast record two main ages an archean age at 2 80 ga partly overprinted by a late migmatization event at 2 03 ga the in situ electron microprobe determination has also shown a third event that systematically appears at 2 72 ga for all the monazites from two of the four studied rocks the three events at 2 80 2 72 and 2 03 ga recorded by the th u total pb system in monazite were each obtained on independent homogeneous parts of a single grain with no sign of pb diffusion thus the oldest monazite remained closed during a high grade resetting migmatization at a temperature estimated at around 700 c and also remained closed during the growth of secondary monazite conventional u pb data isotope dilution on monazite from the same rocks did not allow precise age determinations because the representative points were highly up to 83 discordant and did not fit well along a chord in the concordia diagram the u pb isotope dilution method gave a lower intercept age of 2029 25 ma in agreement with the electron microprobe age although with an unusually high uncertainty due to a poor fit of the data the pb evaporation method gave an old archean age at 2830 7 ma and proterozoic ages ranging from 2417 10 to 2074 7 ma thus although the oldest archean age obtained with the pb evaporation and electron microprobe methods is similar within the analytical error the proterozoic ages obtained by the pb evaporation method are significantly older than the th u total pb proterozoic age obtained with the electron microprobe this discrepancy is presumed to be due to the influence in the pb evaporation method of radiogenic lead contained within archean zones of the monazite grains in other words it means that migmatization took place later than 2074 7 ma and probably around 2030 ma the second archean event at 2 72 ga revealed by high spatial resolution of the electron microprobe could not be determined by other methods the th u total pb method appears to be an inexpensive alternative method for dating simple monazites with a precision close to 20 ma even if the u pb isotopic dilution technique remains the reference method moreover owing to the very high spatial resolution 1 m of the electron microprobe it appears to have no competitor for dating complex polygenetic monazites especially when more than two events are recorded homogeneous zones of different ages coexist in a single grain with no major indication of lead diffusion a procedure for age and error calculations is defined

improved u th total pb dating of zircons by electron microprobe using a simple new background modeling procedure and ca as a chemical criterion of fluid induced u th pb discordance in zircon abstract we present a simple new background modeling method particularly for the determination of trace concentrations of pb u and th to date zircons chemically by electron microprobe this method reduces the acquisition time considerably and at the same time increases the precision of a single pb u and th analysis depending on the analytical conditions theoretical detection limits down to 45 ppm 99 confidence level for u th and pb could be obtained the final precision on age for a single measurement was between 8 and 35 l at pb concentrations between 100 and 200 ppm in proterozoic zircons precise u th and pb analyses however do not necessarily facilitate a straightforward chemical age calculation u th total pb data of zircons from four granites could not be objectively interpreted because of a severe disturbance of the u th pb system however it is shown that chemical ages derived only from zircon areas containing less than 0 2 wt cao agree very well with published conventional radiometric ages of these rocks we propose a model which explains the ca gain and pb loss of zircons which have not undergone any metamorphism after emplacement to be the result of a hydration of radiation damaged zircon domains through low temperature aqueous solutions it is suggested that the ca content can be used independently from u th and pb analyses as a chemical criterion to discriminate between altered zircon domains having suffered a low temperature fluid induced pb loss and non altered zircon domains for which there is a high probability that they will give concordant u th pb ages 2000 elsevier science b v all rights reserved

partial resetting of the upb isotope system in monazite through hydrothermal experiments an sem and upb isotope study abstract natural monazites of different grain sizes were treated experimentally under hydrothermal conditions and their u pb isotope systematics measured before and after the runs runs were carried out with monazite grain size fractions ranging from 40 to 125 m in diameter and on 207 pb 206 pb ages close to 380 ma u concentrations remained always unchanged all recrystallized monazites from the powdered starting material define a discordia with intercept ages of 379 3 2 3 and 7 18 ma the latter indicating the hydrothermally induced pb loss at the time of the experiment sem observations of monazite grains from hydrothermally treated grain size fractions exhibited only minor dissolution features confined to the grain surfaces run products from monazite powders showed recrystallization and grain growth induced by a dissolution precipitation mechanism increasing temperature resulted in a distinct enlargement of grain sizes at 650 and 750 c a dissolution precipitation process in presence of a fluid phase rather than pb volume diffusion acts as a very efficient mechanism for the resetting of the u pb isotope system of monazites even at low temperatures this process is most important in shear zones where channelized fluid flow may occur

high resolution 3 d mapping using terrestrial laser scanning as a tool for geomorphological and speleogenetical studies in caves an example from the lessini mountains north italy abstract terrestrial laser scanning tls is increasingly used in geomorphology for the study of medium to small scale landforms a light weight compact and portable tls device has been used in the grotta a cave mt lessini n italy to make a detailed 3d model of the underground environment a total of 16 scans were used to survey the about 150 m long cave in

petrochemistry and sr pb and nd isotopic geochemistry of early precambrian rocks wutaishan and taihangshan areas china abstract in the wutaishan and taihangshan region china the lowermost high grade metamorphic complex of grey gneiss and amphibolite the fuping complex gives a 2 2 0 2 ga pb pb isochron age with a first stage growth 7 73 and a 2 37 0 07 ga sm nd isochron age with 143nd 144nd 0 0 50963 0 00005 or nd t 1 50 nd depleted mantle model dates tdm of amhibolites 2 48 to 2 60 ga those of gneisses are 2 43 to 2 46 ga the unconformably overlying medium to low grade metavolcanic complex the wutai complex gives a 2 0 0 1 ga rb sr isochron age with 87 86sr 0 0 7025 2 a 2 27 0 02 ga pb pb isochron date with afirst stage growth 7 73 and a 2 26 0 06 ga sm nd isochron first stage 143nd 144nd 0 0 5097 2 or nd t 1 08 individual sample nd depleted mantle model date are 2 5 ga metavolcanic samples from low grade metasedimentary rocks of the hutuo group all lie close to a 2 3 ga reference line on a rb sr isochron plot have nd tdm 2 32 2 34 and 2 62 ga from previous geological work published u pb zircon dating and ourisotopic and geochemical results we infer that the fuping rocks formed 2 6 ga ago in an environment like a modern island arc the wutai complex formed by 2 5 ga ago mostly formed in a tectonic setting similar to that of the fuping complex with the exception that one volcanic cycle formed in an environment like a modern mor and one unit formed in an environment transitional between modern within plate and plate margin settings the hutuo group formed 2 4 ga ago in a within plate tectonic environment there is no evidence for continental crust before 2 6 ga in the wutaishan and taihangshan region this contradicts previous assignment of the fuping complex to 2 8 ga ol older the fuping complex is not an early nucleus of the sino korean craton the new data also confirm that the wutai complex is older than its original assignment as early proterozoic the sm nd systems for metabasaltic rocks in the region either in amphibolite facies or in greenschist facies are all significantly disturbed in contrast with the undisturbed sm nd reported in previous studies of the sino korea craton this study provides further evidence that the archean igneous rocks in china formed at different times from heterogeneous and depleted mantle sources

granitoid evolution in the late archean wutai complex north china craton abstract two temporally discrete episodes of granite magmatism have been identified in the wutai complex of the north china craton based on shrimp u pb zircon dating of all major granitoid bodies in the area the older period is latest archean and ranges in age from 2560 to 2515 ma whereas the younger episode is paleoproterozoic with magmatism at 2170 and 2120 ma archean magmatism can be further separated into two pulses based on geochemistry and the association of the younger plutons with extensive coeval volcanic activity in the wutai complex the early phase of archean activity is represented by the lanzhishan ekou and portions of the chechang betai granites with ages ranging from 2560 to 2540 ma the lanzhishan granite is the only one at wutaishan that contains inherited zircon with a number of cores and individual grains giving ages in excess of 2700 ma these are relatively evolved granitoids interpreted to be derived from older basement of the eastern block of the north china craton the shifo guangmingshi the main grey phase of the wangjiahui granite and the major components of the chechang betai granite have ages of 2540 2515 ma and are coeval with felsic volcanism in the wutai complex which is a consequence of subduction and related arc magmatism the dawaliang granite and pink phase of the wangjiahui granite are considerably younger with paleoproterozoic ages of 2170 and 2120 ma respectively these are also evolved granitoids most likely derived by partial melting of the older basement although we have found no evidence of inheritance the petrogenesis of the granitoids reflects the precambrian amalgamation history of the north china craton indicating derivation along the western edge of the eastern block during development and amalgamation of the wutai arc and prior to collision with the western block of the craton 1 8 ga ago

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

automatic identification and characterization of discontinuities in rock masses from 3d point clouds abstract the routine application of remote surveying techniques which can quickly acquire 3d digital data with high resolution in particular digital photogrammetry light detection and ranging lidar and unmanned aerial vehicle uav for rock mass characterization has rapidly grown over the past decade in this paper a new method for automatic identification and interpretation of rock mass discontinuities clustering of discontinuity sets and characterization of discontinuity orientation persistence and spacing using 3d point clouds is presented the proposed method is based on a four stage procedure consisting of 1 normal vector calculation using the iterative reweighted plane fitting irpf method 2 discontinuity sets clustering by fast search and find of density peaks cfsfdp algorithm and fisher s k value iterative calculation to eliminate noise points 3 discontinuity segmentation using density ratio based method and discontinuity plane fitting using the random sample consensus ransac algorithm 4 persistence and spacing calculation using the theory of analytic geometry the method is applied to two case studies i e rock slopes and compared with the results from previous studies and from manual survey it is concluded that the proposed method is reliable and yields a great accuracy for automatic identification of discontinuities in rock masses

age constraints on terrane scale shear zones in the gawler craton southern australia abstract electron probe micro analysis epma chemical dating of monazite from crustal scale shear zones in the late archaean to mesoproterozoic gawler craton southern australia highlights a long history of shear zone development associated with assembly and reworking of the craton in the southeast gawler craton dextral transpression was focussed into the 250 km long kalinjala shear zone which dominates the structural character of that part of the craton monazite in upper amphibolite facies shear fabrics within the kalinjala shear zone give a mean age of 1682 10 ma this is indistinguishable from an age of 1693 16 ma obtained from monazite inclusions within garnet porphyroclasts within the shear fabric in the western gawler craton monazite populations from two separate locations along the 400 km long tallacootra shear zone give ages of 1680 37 and 1679 39 ma respectively suggesting that both the kalinjala and tallacootra shear zone systems record regional scale strain partitioning toward the end of the ca 1730 1700 ma kimban orogeny in the northwest gawler craton the karari fault zone can be traced for 700 km and separates late archaean rocks from an assembly of tectonic terranes that comprise the northern and northwest gawler craton monazites from amphibolite grade mylonites associated with the karari fault zone have a mean age of 1631 12 ma this age is identical to the timing of regional arc like magmatism represented by the st peter suite in the central gawler craton and suggests that exhumation of the ca 1650 1640 ma ultra high grade granulites of the nawa domain in the northwest gawler craton was linked to the development of the st peter suite magmatic margin in the central gawler craton monazite in the 200 km long yerda shear zone which sheared granites belonging to the ca 1580 ma hiltaba suite have a mean age of 1503 16 ma similar ages of 1516 18 and 1508 14 ma are obtained from monazite inclusions in garnet porphyroclasts within mylonites along the 300 km long coorabie fault zone in the western gawler craton younger ages of 1468 12 and 1457 22 ma from the amphibolite grade mylonitic fabrics in the coorabie fault zone are similar to 40ar 39ar ages from the western gawler craton and suggest that reactivation of the coorabie shear zone in part was associated with regional cooling and stabilisation of the gawler craton at ca 1450 ma the history of deformation on the terrane scale shear zones in the gawler craton therefore does not reflect a single period of terrane assembly or reworking rather it points to a complex pattern of strain partitioning during tectonic events in the late palaeoproterozoic to early mesoproterozoic

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

study of a rockfall in a limy conglomerate canyon covarrubias burgos n spain in this paper a rockfall of some tenths of cubic metres of rock occurred in a conglomerate canyon in the northern castilian plateau n central spain is described in detail this includes the basic data geology mapping meteorological data and rock involved the mechanical mechanism of the instability the propagation and reach of the fallen rock boulders and the final location of the pieces the study is based on detailed geological aerial photography and geotechnical studies and advance topographical measurements geological engineering techniques are used to analyze the instability initiation and rockfall propagation this study contributes to a better understanding of the geological processes leading to the occurrence of calcareous canyons and cliffs in the drainage network of the upper castilian plateau it is also helpful to improve our knowledge on natural rockfall phenomena for risk engineering purposes aiming to quantify control and mitigate associated hazards

geochemistry of the paleoproterozonic nanying granitic gneisses in the fuping complex implications for the tectonic evolution of the central zone north china craton abstract the nanying granitic gneisses represent a major 2 0 ga magmatic event in the fuping complex of the central zone of the north china craton they occur in the chengnanzhuang shear zone which is chiefly developed along the contact between the neoarchean fuping tonalite trondhjemite granodiorite ttg gneisses and the wanzi paragneisses the nanying granitic gneisses were derived from monzogranite and syenogranite with minor amounts of quartz diorite and granodiorite and belong to the metaluminous to peraluminous high potassium calc alkaline series correlations between major and trace elements and similarities in chondrite normalized rare earth element ree patterns support field relationships e g gradational contacts indicating that the nanying granitic gneisses originated from similar magmas the granodioritic monzogranitic and syenogranitic gneisses have similar ranges of initial 87sr 86sr values 0 7030 0 7093 0 7021 0 7193 and 0 7049 0 7111 respectively although these variations are partly attributable to local resetting of the isotopic system during late deformation hydrothermal alteration the whole rock 208pb 204pb 206pb 204pb and 207pb 204pb values of the nanying granitic gneisses are 37 32 76 8 15 24 23 82 and 14 92 17 92 respectively these sr pb isotope systematics together with previously published nd isotope compositions suggest that the nanying granitic gneisses were derived from partal melting of the 2 50 ga fuping ttg gneisses with local assimilation involving the wanzi paragneisses the nanying granitic gneisses are geochemically similar to the cca and ccl groups of granitoids except for a few samples which plot in the hlo group the nanying granitic gneisses exhibit depletion in rb sr ba ti and u and enrichment in th nb zr hf and ree similar to those of syn shear high potassium calc alkaline granitoids and late shear alkaline granitoids they therefore represent the product of a syn collisional to post collisional magmatic event this collisional event which is significantly older than the 1 84 1 80 ga event that has been proposed for the juxtaposition of the eastern and western archean continental blocks in the final stabilization of the north china craton supports a tectonic model involving multiple collisional events for the amalgamation of the internal lithotectonic domains within the central zone and the assembly of the north china craton as a whole