provenance and tectonic setting of the paleoproterozoic metasedimentary rocks from the liaohe group jiao liao ji belt north china craton insights from detrital zircon u pb geochronology whole rock sm nd isotopes and geochemistry abstract geochronological geochemical and isotopic studies were carried out on the paleoproterozoic metasedimentary rocks from the jiao liao ji belt north china craton to constrain their provenance and tectonic setting as well as to evaluate the effects of weathering and sedimentary processes on the source rock signature u pb isotopic dating using the la icp ms method on zircons from the paleoproterozoic metasedimentary rocks reveals that the depositional age can be constrained in the period between 1 98 and 1 9 ga geochemical data reveal low intermediate degrees of weathering of the source compositionally immature and poorly sorted detailed analysis of detrital zircon u pb geochronology whole rock sm nd isotope and geochemistry show that these metasedimentary rocks are derived from a mixed provenance the predominant derivation is from metavolcanic rocks of the liaohe group and paleoproterozoic gneissic granitoids there is also an input of archean continental crust the metasedimentary rocks were probably deposited in a back arc basin within an arc system thus supporting the paleoproterozoic arc continent collision model as already proposed by some authors

slope failure characteristics and stabilization methods this paper presents numerical and laboratory experiments to investigate slope failure characteristics and commonly used slope stabilization methods using an improved distinct element method the i

extent of oceanic crust in the labrador sea1 this paper examines the mode of formation of the northern margins of the labrador sea observations of faulted and rotated crustal blocks across the northwest margin of greenland had led to the suggestion that this region is underlain by extended continental crust a detailed analysis of all geophysical data from this region presented here suggests on the contrary the possibility that it could have been formed by an excessively slow seafloor spreading process and ridge axis propagation this gave rise to rotated fault blocks at a time when spreading was mainly confined to the greenland side prior to its shift to the west supporting evidence for such a reconfiguration of the spreading axis comes from gravity and magnetic observations of this and neighbouring regions modelling of magnetic anomalies in the area based on the average rate of spreading for the entire labrador sea shows that a gradual shift of the ridge axis to the west started after the formation of anomaly 32 because the earliest seafloor spreading anomalies are highly attenuated in amplitudes other models like extended and intruded continental crust are possible if one only considers the magnetic anomalies however an extended continental crustal model poses problems in accounting for other geophysical observations based on a slow spreading model it is shown that oceanic crust extends fairly close to the foot of the slope with a narrow belt of extended continental crust along the west greenland margin while a much wider zone of perhaps attenuated continental crust extends off labrador breakup of the continental landmass occurred much closer to the west greenland coast than to labrador the applicability of a slow spreading model to other passive margins where similar geophysical observations have been reported is discussed

structure of palaeogene sediments in east ellesmere island constraints on eurekan tectonic evolution and implications for the nares strait problem abstract the nares strait problem represents a debate about the existence and magnitude of left lateral movements along the proposed wegener fault within this seaway study of palaeogene eurekan tectonics at its shorelines could shed light on the kinematics of this fault palaeogene late paleocene to early eocene sediments are exposed at the northeastern coast of ellesmere island in the judge daly promontory they are preserved as elongate sw ne striking fault bounded basins cutting folded early paleozoic strata the structures of the palaeogene exposures are characterized by broad open synclines cut and displaced by steeply dipping strike slip faults their fold axes strike ne sw at an acute angle to the border faults indicating left lateral transpression weak deformation in the interior of the outliers contrasts with intense shearing and fracturing adjacent to border faults the degree of deformation of the palaeogene strata varies markedly between the northwestern and southeastern border faults with the first being more intense structural geometry orientation of subordinate folds and faults the kinematics of faults and fault slip data suggest a multiple stage structural evolution during the palaeogene eurekan deformation 1 the fault pattern on judge daly promontory is result of left lateral strike slip faulting starting in mid to late paleocene times the palaeogene judge daly basin formed in transtensional segments by pull apart mechanism transpression during progressive strike slip shearing gave rise to open folding of the palaeogene deposits 2 the faults were reactivated during se directed thrust tectonics in mid eocene times chron 21 a strike slip component during thrusting on the reactivated faults depends on the steepness of the fault segments and on their obliquity to the regional stress axes strike slip displacement was partitioned to a number of sub parallel faults on shore and off shore hence large scale lateral movements in the sum of 80 100 km or more could have been accommodated by a set of faults each with displacements in the order of 10 30 km the wegener fault as discrete plate boundary in nares strait is replaced by a bundle of faults located mainly onshore on the judge daly promontory

genesis of the neoproterozoic early cambrian banded iron ore bearing sedimentary rocks in the jiertieke zankan iron ore belt west kunlun orogenic belt xinjiang nw china abstract the jiertieke zankan area lies in the taxkorgan region west kunlun mountains of xinjiang province northwestern china the area contains the largest commercial iron ore belt in the region furthermore this iron ore belt hosts the youngest banded iron formation identified to date the jiertieke iron deposit which was deposited during the early cambrian previous studies have mainly provided evidence regarding the depositional environment and formational age of this area but the tectonic setting and geochronology of the ore deposits remains poorly studied here we provide an integrated examination of high precision sims zircon u pb dating along with the major and trace element geochemistry of the metasedimentary rock a biotite quartz schist that host the iron ores the jiertieke area is characterized by bedded metapelites that contain detrital zircons as young as 546 ma whereas the zankan area contains metapsammites in addition to the metapelites as young as 541 ma multiple detrital zircons age groups ranging from 700 1100 ma 1600 1850 ma and 2250 2500 ma indicate the input of ancient clastic material to the basin based on provenance indicators and nd isotopic data they suggest that the metasedimentary rocks are the product of an undifferentiated felsic terrain likely ancient upper continental crust being eroded given the geochronological and geochemical features of the metasedimentary rocks and previously identified bimodal volcanics within the region we suggest that the tectonic setting of the zankan jiertieke area was a back arc rift basin during the late neoproterozoic to early cambrian

two dimensional water flood and mudflow simulation flo 2d is a two dimensional finite difference model that simulates clear water flood hazards mudflows and debris flows on alluvial fans and urban floodplains interactive flood or mudflow routing between channel street and floodplain flow is performed using a uniform grid system to describe complex floodplain topography a quadratic rheological model developed from field and laboratory mudflow data enables appropriate simulations of flooding conditions ranging from clear water to hyperconcentrated sediment flows computer aided design cad graphics of predicted time sequenced flood depths automates the delineation of flood hazards replication of the 1983 rudd creek mudflow in utah demonstrates the capability of the model

an empirical statistical model for debris flow travel distance an empirical model is presented for analysis of debris flows based on field observations of landslides from clear cuts in the queen charlotte islands british columbia given an initial failure volume changes in event magnitude arising from entrainment and deposition along the path of movement are used to establish the point at which the cumulative flow volume diminishes to zero and therefore the total travel distance hillslope morphology is used to assign three types of flow behaviour unconfined confined and transition flow flow behaviour and slope angle determine the occurrence of entrainment or deposition in the model for every reach of the event path volume change in a reach is calculated from regression analysis of the queen charlotte islands field observations predictor variables are reach length width of entrainment and or deposition and slope angle together with a bend angle function and the incoming flow volume key words slope stability debris flow travel distance runout ris

volume loss model for trace element enrichments in mylonites mylonites from three widely separated localities along the fries ductile deformation zone in the blue ridge province show substantial enrichments in trace and minor elements tio sub 2 p sub 2 o sub 5 zr y and v and depletions in rb and sr relative to the protolith two end member hypotheses can explain the enrichments one involves partitioning to and from an infiltrating fluid and assumes that all the elements were mobile the second hypothesis assumes the high field strength cations were largely immobile and that their enrichment is due to large volume losses in the mylonites modeling indicates that ti is immobile for fluid rock ratios as high as 10 sup 4 and petrographic and modal data support a volume loss mechanism volume loss was accommodated by loss of sio sub 2 and alkalies during feldspar dissolution calculated fluid rock volume ratios required to produce the observed sio sub 2 losses assuming ti mobility range from 70 to 600 variable enrichments in p zr y and v are attributed to selective mobility of these elements during fluid infiltration

the angle of reach as a mobility index for small and large landslides the relations between the angle of reach fahrboschung and other indexes expressing the mobility of landslides and vertical drop horizontal reach and volume of landslide mass have been analyzed by means of simplified plots and regression equations results for 204 landslides of all sizes show that whatever the mechanism of motion all kinds of landslides experience a continuous reduction of the angle of reach with volume increase this reduction starts from the smallest sizes scattering in this relation is mostly due to mechanisms of motion and to both obstacles and topographic constraints on the path this synthesis indicates that small landslides less than 0 5 106 m3 in relative terms display excesses of travel distance similar to large landslides since most small landslides are not expected to develop any change in the mechanism of progression while moving the decrease in the reach angle with volume suggests that scale effects should be taken into account the angle of reach is found to be

scandinavia s north atlantic passive margin 1 the tectonics of the eastern passive margin of the north atlantic are reexamined the scandinavian north atlantic passive margin includes not only the offshore exploration and basin domain but also large portions of the onshore domains of the scandinavian caledonides combined information from structural geology potential field data regional geology basin development and geomorphology made it possible to propose a new definition of the passive margin the rift shoulder is formed by linked faults defining the present rift flank these faults are the extensional structures located furthest to the east onshore norway sweden that can be linked to the rifting that led to the formation of the north atlantic this innermost boundary fault system ibf is formed by a set of normal west dipping crustal faults it extends over a distance exceeding 2000 km from the north sea across the caledonian mountain belt to the barents sea the passive margin width between the continent ocean boundary and the ibf ranges from 550 km in the south to over 700 km in mid norway to 165 km north of lofoten rifting and faulting on the ibf started in permo carboniferous and a succession of rift phases eventually culminated in continental breakup and the formation of the north atlantic basin development between permian and cretaceous was toward the future breakaway fault but faulting was also active on land from mesozoic to present onshore offshore crustal scale cross sections show the geometry of the passive margin the dip orientation of the major faults and the changes in crustal thickness

geochronological and geochemical constraints on the origin of clastic meta sedimentary rocks associated with the yuanjiacun bif from the luliang complex north china abstract the luliang complex is situated in the central part of the western margin of the trans north china orogen tnco in the north china craton ncc and consists of metamorphic volcanic and sedimentary rocks and granitoid intrusions the yuanjiacun formation metasediments occupy roughly the lowest part of the luliang group and are mainly represented by well bedded meta pelites chlorite schists and sericite chlorite phyllites banded iron formations bifs and meta arenites sericite schists which have undergone greenschist facies metamorphism the youngest group of detrital zircons from the meta arenite samples constrains their maximum depositional age at 2350 ma in combination with previous geochronological studies on meta volcanic rocks in the overlying jinzhouyu formation the depositional age of the yuanjiacun formation can be constrained between 2350 and 2215 ma the metasediments have suffered varying degrees of source weathering measured using widely employed weathering indices e g cia ciw pia and th u ratios source rocks of the low al meta pelites have undergone severe chemical weathering whereas those of the meta arenites and high al meta pelites have suffered relatively moderate chemical weathering significant secondary k addition is recognized in the a cn k diagram for most of the studied samples diagnostic geochemical features like the al 2 o 3 tio 2 values trace element ratios e g th sc and ree patterns suggest that the meta arenites and high al meta pelites are predominantly derived from felsic igneous sources whereas the low al meta pelites are sourced mainly from mafic rocks coupled with nd isotopic data it is proposed that the meta arenites and high al meta pelites were sedimentary erosion products of the less differential felsic terrain likely the old upper continental crust the low al meta pelites however have geochemical affinities with both pelite and bif like components suggesting that they were mixtures of these two sediments moreover the u pb ages of detrital zircons from the yuanjiacun metasediments yield three age populations of 2 8 2 65 ga 2 6 2 5 ga and 2 5 2 35 ga the dominant archean detrital zircons were most likely sourced from both the archean igneous rocks in the hengshan wutai fuping belt and old hidden archean basement rocks in the western block whereas the subordinate paleoproterozoic detrital zircons were probably derived from the granitoid plutons within this age range in the luliang complex taking the geochemical and geochronological data together the yuanjiacun formation is interpreted as having been deposited in a passive margin setting likely the eastern margin of the western block most probably on a stable continental shelf

a perturbation solution for bingham plastic mudflows an analytical solution is proposed for laminar mudflows and debris flows that can be modeled by a bingham plastic law two dimensional unsteady nonuniform bingham flows released from a point source or a source of finite size dam break problem or mudslide problem on a steep slope are considered the method of matched asymptotic expansions was implemented to get a first order solution for the dam break problem the proposed model is found to be valid when the shock wave has advanced three reservoir lengths downstream also it is found that the bingham flow only propagates a finite distance downstream with the shock depth asymptotically approaching the yield depth and the shock velocity asymptotically falling to zero the hydrograph produced by a bingham flow is seen to have a slower and lower flood peak and a longer and higher flow tail than that produced by newtonian flow having the same dynamic viscosity comparison of the model predictions with laboratory observations shows reasonable agreement

geochemistry of metasedimentary rocks of the proterozoic xingxingxia complex implications for provenance and tectonic setting of the eastern segment of the central tianshan tectonic zone northwestern china the eastern segment of the central tianshan tectonic zone in northwestern china includes the proterozoic metasedimentary xingxingxia complex because these rocks have been extensively deformed and metamorphosed to greenschist or amphibolite facies a geochemical and nd isotopic study was undertaken to constrain their provenance and tectonic setting as well as to evaluate the effects of weathering and sedimentary processes on the source rock signature major and trace element data indicate that these samples are characterized by negative eu anomalies low chemical index of alteration values and high index of compositional variability values chemical index of alteration values and the plot of molecular proportions al2o3 cao na2o k2o suggest low degrees of weathering of the source they are compositionally immature and poorly sorted geochemical data and immobile elemental ratios for example al2o3 tio2 cr th eu eu and la yb n indicate that the clastic materials were derived predominantly from

presenting regional shallow landslide movement on three dimensional digital terrain abstract a storm can trigger numerous shallow landslides on hilly terrains this paper presents a distributed cell model for presenting regional shallow landslide movement on a three dimensional digital terrain the model consists of five components namely a digital terrain module a spatial rainfall distribution module an infiltration analysis module a slope stability evaluation module and a movement prediction module the locations and volumes of landslides are analyzed first through rainfall infiltration and slope stability analyses the detached material is assumed to move along the steepest path from one cell to a lower cell empirical equations that are developed based on local landslide inventories are adopted as a landslide movement cessation criterion the effect of landslide size on travel distance is considered by grouping unstable cells that are bounded at least at one side or corner the uncertainties in soil shear strength parameters and the landslide movement process are considered in determining the possible bounds of travel distance the movement analysis method is applied to a 164 5 km 2 hilly terrain in the wenchuan earthquake zone to test its performance in presenting regional shallow landslide movement the method predicts the volume of landslides reasonably well the observed and computed movement traces and deposition locations of the detached material also agree reasonably well the volume of individual landslide and travel distance may be substantially underestimated if the size effect is not considered

neoarchean granitoid gneisses in eastern hebei north china craton revisited abstract neoarchean granitoid gneisses are widely distributed throughout eastern hebei eastern north china craton which are dominated by deformed and metamorphosed tonalite trondhjemite granodiorite ttg diorite and granite this study presents the results of systematic zircon u pb geochronological whole rock geochemical and sm nd isotopic analyses of the neoarchean granitoid gneisses in eastern hebei these data provide insights into the archean paleoproterozoic multiple tectonothermal events as well as the petrogenesis of these gneisses zircon u pb isotopic dating indicate that the granitoid gneisses were contemporaneously emplaced between 2546 10 and 2510 10 ma reflecting a giant neoarchean igneous event throughout eastern hebei subsequently these rocks were subjected to regional amphibolite facies metamorphism at 2 48 2 45 ga the close spatial and temporal relationships in terms of magmatism and metamorphism at ca 2 5 ga suggest a uniform tectonothermal evolution of eastern hebei the granitic gneisses have mainly originated from the partial melting of juvenile metamorphosed greywackes with minor involvement of basalts the large geochemical and isotopic variations within the dioritic and ttg gneisses both provide evidence for the mixing of mafic and felsic magmas coupled with fractional crystallization however the chemical differences between the dioritic and ttg gneisses might result from individual mafic magma sources viz basaltic and high mg melts the mafic magma may also form the basalt or komatiite within the greenstone belt or evolve via fractional crystallization prior to the magma mixing large scale granitoid activities were possibly related to mafic magma underplating the combined geochronological geochemical and geological data support an archean proto mantle plume model for a geodynamic interpretation of the eastern north china craton during the neoarchean

tectonic and economic implications of trace element 40ar 39ar and sm nd data from mafic dykes associated with orogenic gold mineralisation in central victoria australia abstract mafic to intermediate dykes are spatially and temporally closely associated with major post tectonic granitic complexes in the western lachlan orogen of se australia these dykes which range petrographically from basaltic to andesitic are concentrated within several north to northwest trending zones and were emplaced during two broad intervals of extensive magmatic activity during the silurian devonian period geochemical and sm nd isotopic characteristics of these mafic intrusives are consistent with their formation in a complex subduction related tectonic setting interaction between mantle wedge material sinking oceanic crust and input from the overlying continental crust resulted in the petrological and geochemical variations displayed by these and more felsic dykes throughout the study region field evidence and 40 ar 39 ar data show that in the eastern part of the stawell zone and in the northwest portion of the bendigo zone mafic dyke were intruded between 410 and 400 ma late silurian early devonian further emplacement in the bendigo zone and the eastern part of the melbourne zone took place at between 375 and 365 ma middle to late devonian episodic mantle derived magmatism was possibly related to step wise rollback slab detachment or changes in the angle and rate of westward subduction in response to periodically occurring accretionary pulses a close spatial and temporal relationship also exists between the dykes and orogenic gold mineralisation in the central victorian gold province mafic to intermediate dykes both crosscut and are host to mineralisation in a number of goldfields although there is little evidence for a direct genetic association the two processes are linked by the common utilisation of translithospheric structures which facilitated the rapid ascent into shallow crustal levels of both mantle derived magma and crustal scale ore forming fluid systems previous studies have suggested that transfer of heat into the crust via ascending mafic mantle magmas can provide a thermal engine which triggers and sustains extensive crustal melting thus explaining the commonly observed close association of mafic to intermediate and felsic intrusive suites this study supports the viability of this mechanism and in addition indicates that a causal link exists between the formation of mantle magmas in collisional zones and the generation of orogenic gold deposits

nd sr and pb isotopic characteristics of cretaceous intrusive rocks from deep levels of the sierra nevada batholith tehachapi mountains california the cretaceous gabbroic to granitic intrusive rocks of the tehachapi mountains were emplaced at depths of 25 30 km and thus afford a view of deep processes in the sierra nevada batholith they consist of the 115 ma tehachapi suite and the 100 ma bear valley suite new zircon u pb age data reveal the presence of the latter as far west as grapevine canyon the nd sr pb and o isotopic whole rock data and zircon pb inheritance patterns for the bulk of the suites suggest an origin by mixing between depleted mantle derived magmas and metasedimentary material with a substantial component of old continental material however this mixing is not evident in variations between isotopic ratios and chemical and lithologic parameters this implies that isotopic hybridization of magmas took place deeper than 30 km and that fractionation processes are likely responsible for the bulk of the chemical variation in this part of the sierra nevada batholith consideration of the isotopic data in the context of the sierra nevada batholith as a whole suggests that the well known east to west isotopic gradients in the batholith may reflect a change in the average isotopic character of the preintrusive framework rather than a change in amount of crustal component on the other hand the lack of areal gradients in sr and nd isotopic ratios in the main study area may indicate a lack of pronounced gradation at deep levels at least within the western batholith

evidence for late paleozoic and mesozoic non dipole fields provides an explanation for the pangea reconstruction problems abstract paleomagnetic pole positions have long been calculated with the assumption that the ancient geomagnetic field was purely that of a geocentric dipole but in recent years it has become a concern that this assumption is not always valid because of long term contributions from non dipole fields in particular octupole fields we tested for the presence of a zonal octupole field in the late carboniferous permian mesozoic and early tertiary by comparing the observed paleomagnetic paleolatitude distributions for the laurentian north america and greenland and european landmasses with those predicted from the mean paleopoles such a test is possible for a good sized continent not subsequently deformed when numerous and reliable paleomagnetic results exist from sites that cover a wide range of paleolatitudes if the field were purely dipolar coeval results should form a coherent dataset such that a regression line through the individual points in an observed versus predicted paleolatitude plot has a slope of 1 if the slopes of regression lines are systematically different from 1 0 for successive time intervals and granted that the earth s radius stayed the same then it is likely that non dipole fields can be held responsible regression line slopes standard errors for three intervals analyzed are 0 78 0 04 200 300 ma 0 93 0 11 120 200 ma and 0 82 0 06 40 120 ma as might be expected with a non dipole contribution to the total geomagnetic field paleomagnetic results from the most northerly areas of laurentia and europe i e ellesmere greenland and svalbard show clearly anomalous paleolatitudes because of the agreement between the equatorial locations determined independently by paleomagnetism and equatorial rain forest occurrences d v kent p e olsen earth planet sci lett 179 2000 311 324 we argue that long term quadrupole fields are less likely than octupole fields to be the cause of the paleolatitude discrepancies estimates of the magnitude of the octupole dipole field ratio are not very precise but center around 0 1 which could cause errors in conventional paleopole determinations using the dipole formula of 7 5 because of the antisymmetry of octupole fields a comparison of paleomagnetic poles from mid northern and mid southern hemisphere locations could thus be off by as much as 15 the well known misfit between the paleomagnetic results from the laurentia european and gondwana continents in a classical pangea a configuration could be explained by such errors due to octupole fields this explanation would negate the need to seek tectonic pangea b type solutions for the misfit these solutions have generally remained unacceptable in terms of the geology of the gondwana laurussia borderzone

numerical simulation of debris flows a key requirement in the assessment of landslide risk in such densely populated urban areas as hong kong consists of the prediction of potential runout distance or the extent of the subsequent debris flow this paper presents a three dimensional dynamic model of unsteady gravity driven debris flow the lagrangian galerkin finite element method is used to determine the nodal velocity and depth of soil column elements within the sliding mass with the momentum and mass conservation mathematically closed within the soil column elements the numerical solution also features a lumped mass matrix and a volume weighted procedure the method of least squares approximation plays a smoothing role which enhances stability and efficiency of the numerical solution scheme the nodal elevation during sliding is obtained via a dynamic bilinear interpolation of the elevation function for the base of the sliding mass furthermore the accuracy robustness and generality of this method are validated by experimental results

petrogenesis of the highly potassic 1 42 ga barrel spring pluton southeastern california with implications for mid proterozoic magma genesis in the southwestern usa syenites from the barrel spring pluton were emplaced in the early proterozoic mojave crustal provine of southeastern california at 1 42 ga all rocks even the most mafic are highly enriched in incompatible elements e g k2o 4 12 wt rb 170 370 ppm th 12 120 ppm la 350 1500xchondrite la ybn 35 100 elemental compositions require an incompatible element rich but mafic or ultramafic source trace element models establish two plausible sources for barrel spring magmas 1 lree enriched garnet websterite with accessory apatite rutile enriched lithospheric mantle and 2 garnet amphibolite or garnet hornblende granulite with enriched alkali basalt composition also with accessory apatite rutile mafic lower crust nd and pb isotopic ratios do not distinguish a crust vs mantle source but eliminate local mojave province crust as the principal one and indicate that generation of the enriched source occurred several hundred million years before emplacement of the barrel spring pluton 1 40 1 44 ga potassic granites are common in southeastern california suggesting a genetic link between the barrel spring pluton and the granites however although the same thermal regime was probably responsible for producing both the granitic and syentic magmas elemental and isotopic compositions preclude a close relationship isotopic similarity of the barrel spring pluton to 1 40 1 44 ga granites emplaced in the central arizona crustal province to the east may imply that a common component was present in the lithosphere of these generally distinct regions

the theoretical effect of metasomatism on sm nd isotopic systems abstract if sm and nd are mobilized during fluid rock interaction fractionation of the ratio between sm and nd in geological units may take place the fractionation can be characterized by a fractionation factor f which can attain any value between d sm d nd and 1 d sm d nd depending on the fluid rock ratio during ree transfer if such fractionations are not recognized this will induce errors in sm nd isotopic interpretations of age and provenance of the affected geological units the apparent ages and nd values are functions of the true values f and the time lapse between petrogenesis and secondary disturbance the functional relationships can be closely approximated by direct proportionalities

the liaohe group an insight into the paleoproterozoic tectonic evolution of the jiao liao ji belt north china craton abstract the jiao liao ji belt represents one of the largest exposed regions of paleoproterozoic rocks along the eastern margin of the north china craton paleoproterozoic basement material in this area is dominated by deformed and metamorphosed volcano sedimentary successions with minor amounts of granitic and mafic intrusions this study presents the results of a systematic zircon u pb geochronological whole rock geochemical and sm nd isotopic analysis of the volcano sedimentary successions within the liaohe group of the jiao liao ji belt these data provide insights into the multiple paleoproterozoic tectonothermal events that have affected the belt as well as the petrogenesis of the paleoproterozoic meta volcanics and metasedimentary rocks on the liaodong peninsula accurate u pb age and trace element determinations of zircons from the meta volcanics in this region using laser ablation inductively coupled plasma mass spectrometry indicate that these units formed at ca 2 2 ga and were metamorphosed at ca 1 9 ga respectively these data indicate that the paleoproterozoic geochronological framework of this region is dominated by 2 2 2 0 ga magmatic 1 98 1 90 ga sedimentary ca 1 90 ga metamorphic and 1 87 1 82 ga post tectonic magmatic events the meta volcanics can be split into basalt basaltic andesite andesite dacite and rhyolite units that define a continuous calc alkaline dominated magmatic sequence that is similar to the sequences commonly found within phanerozoic magmatic arcs the meta basalts are enriched in the light rare earth elements cr co and ni and are depleted in the heavy rare earth elements and the high field strength elements e g nb ta and ti indicating that they formed from magmas generated by the partial melting of lithospheric mantle material that was previously metasomatized by subduction zone derived fluids melts the large geochemical and isotopic variations within the metamorphosed andesite dacite and rhyolite units all provide evidence of magma mixing between felsic melts generated by the partial melting of paleoarchean neoarchean basement material and the mafic melts that may also formed the meta basalts within the liaohe group or evolve via fractional crystallization prior to mixing the geochemistry of the metasedimentary rocks indicate that the pre metamorphism sedimentary units ranged from being compositionally mature to being immature and poorly sorted and were weakly to moderately weathered these sediments were derived primarily from metamorphosed felsic volcanics within the liaohe group as well as the paleoproterozoic liaoji granites they also contain archean continental crustal material that is derived mainly from ancient intermediate mafic basement units the combined geochronological geochemical and geological data indicate that a paleoproterozoic arc continent collision model can well explain the nature and formation of the jiao liao ji belt

the rotations opening the central and northern atlantic ocean compilation drift lines and flow lines we provide an up to date compilation of euler rotations that model the evolution of the central and northern atlantic ocean table 1 the data basis forms seafloor spreading magnetic anomalies of the atlantic we checked the published rotations and selected those that form a consistent model the increments of the euler rotations going back in time from magnetic anomaly to magnetic anomaly can be illustrated by chains of points on drift lines that are paths of motions from continent to continent along these paths the continents bordering the atlantic ocean can be moved back to their mesozoic position within pangea other figures exhibit the early rifting of the north atlantic the drift of iberia and the evolution of the greenland ellesmere region the points on the drift lines do not correspond directly to the lines of magnetic anomalies or their picks displayed today symmetrically in the atlantic ocean to acquire correspondence symmetric flow lines are constructed analogous to the spreading procedure but points on the flow lines constructed by half of the increments partially also deviate from the expected symmetric position and in this way quantify displacements or jumps of the axis of rifting or spreading most of the selected rotations are from the excellent analyses of previous work essential deviations from published rotations are the m 0 rotations of eurasia and of the porcupine unit with respect to north america eur nam and por nam they lead to a better coincidence between the back rotated m 0 magnetic anomalies in the bay of biscay on the one side and a change of the first transform motions between greenland and svalbard on the other side through this explanation an overlap in pangea sw of svalbard is avoided and transform motions instead of strong extension are predicted some additional data are needed to complete the model the earliest part of the path of iberia to north america iba nam up to m 4 is calculated assuming that iberia moved parallel to the african plate though with slower spreading rates the evolution of the central and north atlantic ocean system is described in short this model of the central and north atlantic was produced with the primary intention of clearing and fixing the positions of africa iberia and eurasia as a framework for an improved reconstruction of the western tethys evolution

hillslope infiltration divergent and convergent slopes this perturbation analysis of divergence convergence effects on hillslope infiltration and downslope unsaturated flow indicates that in general these effects are unimportant for usual hillslope topography only where the radius of the contour is less than about 10 times the characteristic infiltration length lgrav or 10 times the sorptive length need the perturbation be taken into account this result opens up a considerable extension of applicability of the analysis of infiltration on planar hillslopes to embrace slopes with curved contours such as ridge noses and hollows

sm nd data for granitoids across the namaqua sector of the namaqua natal province south africa sm nd data for rocks of granitic composition in an east west traverse across the namaqua sector of the mesoproterozoic c 1 2 ga namaqua natal province of southern africa provide new evidence about the timing of crustal extraction from the mantle recent ion probe zircon dating has shown that contrary to previous indications that pre namaqua basement had been preserved in parts of the namaqua sector the majority of the magmatic rocks were emplaced during the 1 4 1 0 ga namaqua tectogenesis and very little u pb evidence of older precursors remains sm nd model ages show that mesoproterozoic crustal extraction did occur but was also strong in the palaeoproterozoic with local evidence for the existence of archaean crust the distribution of model ages generally corresponds with the established terranes subdivided using lithostratigraphic and structural criteria the northern part of the bushmanland terrane shows early palaeoproterozoic to archaean model ages and is clearly different from the southern part which has mesoproterozoic model ages this supports the previously published results of a north south traverse and justifies the separation of the garies terrane from the bushmanland terrane though further subdivisions are not supported the continuation of the richtersveld province east of pofadder is supported by one sample and the terrane boundary between the bushmanland and kakamas terranes is marked by an abrupt change from palaeoproterozoic to mesoproterozoic model ages model ages for the kakamas and areachap terranes do not distinguish them well they suggest a mesoproterozoic to late palaeoproterozoic origin for both terranes neither of which has a purely juvenile character the influence of palaeoproterozoic crust forming events is clear in the kaaien terrane to the east possibly reflecting reworking of the kaapvaal craton the namaqua sector of the province thus has a history of crustal extraction and evolution which reaches back locally to the archaean with major palaeoproterozoic and mesoproterozoic crust forming events this differs from the natal sector which has a largely juvenile character related to a mesoproterozoic wilson cycle attempts to reconstruct the mesoproterozoic supercontinent rodinia will have to take into account the extensive nd isotopic evidence for older crustal events in the namaqua sector

comparative behavior of sr nd and hf isotopic systems during fluid related deformation at middle crust levels abstract we have carried out a comparative rb sr sm nd and lu hf isotopic study of a progressively deformed hercynian leucogranite from the french massif central belonging to the la marche ductile shear zone in order to investigate the respective perturbation of these geochronometers with fluid induced deformation the one meter wide outcrop presents a strongly deformed and mylonitized zone at the center and an asymmetric deformation pattern with a higher deformation gradient on the northern side of the zone ten samples have been carefully collected every 10 cm north and south away from the strongest deformed mylonitic zone they have been analyzed for a complete major trace element data set oxygen isotopes rb sr sm nd and lu hf isotopic systematics we show that most of major and trace elements except sio2 alkaline elements k2o rb and some metal transition elements cu are progressively depleted with increasing deformation this depletion includes ree y but also hfs elements ti hf zr nb which are commonly considered as immobile elements during upper level processes variations in elemental ratios with deformation e g decrease in lree mree hree nd hf th sr increase in rb sr u th and constant sr nd lead to propose the following order of element mobility u th sr nd hf hree we conclude in agreement with previous tectonic and metallogenic studies that trace element patterns across the shear zone result from circulation of oxidizing f rich hydrothermal fluids associated with deformation a temperature of the fluid of 470 480 c can be deduced from the 18o equilibrium between quartz muscovite pairs elemental fractionation induces perturbation of the rb sr geochronometer the well defined 87rb 86sr 87sr 86sr correlation gives an apparent age of 294 19 ma slightly younger than the 323 4 ma age of leucogranites in this area this apparent age is interpreted as dating event of intense deformation and fluid circulation associated with mass transfer and exhumation of the ductile crust shortly after the leucogranite emplacement sm nd and lu hf isochron type diagrams do not define any correlation because of the low fractionated sm nd and lu hf ratios isotopic data demonstrate that only the lu hf geochronometer system is not affected by fluid circulation and gives reliable tdm age 1 29 0 03 ga and ehf signatures by contrast the sm nd geochronometer system gives erroneous old tdm ages of 2 84 4 ga there is no positive end ehf correlation because of decreasing end values with deformation at constant ehf values however end ehf values remain in the broad end ehf terrestrial array which strongly indicates that fluid induced fractionation can contribute to the width of the terrestrial array the strong ehf negative values of the leucogranite are similar to metasedimentary granulitic xenoliths from the french massif central and confirm the generation of the leucogranite by several episodes of reworking of the lower crust

newtonian fluid mechanics treatment of debris flows and avalanches calculations are carried out first for steady fully developed laminar flow on a slope application of this result to field data published in a previous paper by another author suggests that many debris flows are laminar then singular perturbation techniques are used to obtain first order solutions for unsteady non uniform flow from a point source on a steep slope solutions are obtained for both laminar and turbulent flows and it is found that the laminar flow model gives the best description of laboratory data obtained by a previous investigator a number of differences are observed in the behavior of the outer kinematic wave solutions for laminar and turbulent flow and it is suggested that it is probably not possible to describe all debris flows and avalanches with laminar flow models it is also suggested that more comparisons need to be made between theoretical results and field data measurements

nd and sr isotope study of hydrothermally altered granite at san manuel arizona implications for element migration paths during the formation of porphyry copper ore deposits a study of the nd and sr isotope composition of the late cretaceous monzogranite stock at san manuel arizona and its mineralized alteration halo was undertaken in order to assess the transport of nd and sr that accompanied the hydrothermal alteration sampling was along a 1 km transect perpendicular to the alteration zones extending from the potassically altered core to the propylitically altered fringe of the system large isotopic differences between the stock and the enclosing 1 4 b y old granitic wall rock coupled with the original homogeneity of the latter provide optimal conditions for detecting evidence of chemical transport the mineralizing porphyry stock has a lower 87 sr 86 sr ratios 0 708 and a higher epsilon nd 6 than the precambrian granite wall rock 0 782 11 the 87 sr 86 sr ratios of the altered wall rock decrease regularly from 0 782 to 0 715 from the propylitic alteration zone to the stock contact indicating that material flow was primarily from the stock into the wall rock consistent with an orthomagmatic model for porphyry copper ore genesis the sr in the ore zone is 75 percent stock derived and evidence of stock derived sr is found up to 700 m into the wall rock the sr and rb concentration variations are mainly controlled by the alteration mineralogy and do not correlate with the isotopic variations the epsilon nd values and the sm and nd concentrations of the altered wall rock show subtle changes that are mostly confined to the potassically altered zone only one wall rock sample located 0 5 m from the stock contact is strongly disturbed the results suggest that sr isotopes may provide a useful tool for studying or locating fossil hydrothermal systems whereas the relatively immobile nd isotopes are reliable indicators of the magmatic provenance of altered intrusions

the rotations opening the central and northern atlantic ocean compilation drift lines and flow lines int j earth sci 102 1357 1376 strait and marked the wegener fault figure 1b depicts the present day geography and geology of the region modified from dawes 2009 fig 9 the mismatch between ellesmere island and greenland in fig 1a is immediately apparent from the disruption of the two sedimentary basins the mesoproterozoic thule and paleozoic franklinian that straddle nares strait the component of the thule basin on greenland is displaced from that on ellesmere island the regional architecture of the franklinian basin depicted in fig 1b by cambrian to devonian markers in ellesmere island and greenland is destroyed and the cambro silurian folded deep water trough of the franklinian basin on greenland strikes into paleoproterozoic gneiss on ellesmere island other misfits on a more detailed scale are listed by dawes 2009 in addition closure of the major seaways flanking devon island lancaster and jones sounds likewise results in gross mismatches within canadian geology similar problems arising from the undoing of harmonious geology mar greiner and neugebauer s reconstructions at 84 and 52 65 ma saalmann et al 2005 described a paleogene netrending strike slip fault zone and later se directed thrusting on land in a 100 km long stretch of the ne ellesmere island coastline they considered this deformation to be a manifestation of the wegener transform fault and plate boundary but admitted that the fault could not be traced farther south through southern nares strait into baffin bay greiner and neugebauer have used saalmann et al s findings to support their case for convergence of greenland and ellesmere island and large scale displacement along the wegener fault but fail to acknowledge that these paleogene tectonic features are of limited regional significance and that in any event the amount of strike slip recorded on land is insufficient to account for the separation of greenland from north america by spreading in baffin bay greiner and neugebauer 2013 have modeled the opening of the central and northern atlantic ocean using a computer program that generates paleogeographic reconstructions based on euler rotational data which in turn are derived from magnetic anomalies flanking oceanic spreading ridges here we confine ourselves to a critique of greiner and neugebauer s results for the nares strait northern baffin bay region bordered by greenland and the eastern canadian high arctic reconstructions at or before 175 84 and 52 65 ma are shown in greiner and neugebauer s figures 5 6 9 and 10 all these are strictly paleogeographic representations none shows any surface geological feature greiner and neugebauer a priori consider greenland to be an independent tectonic plate separated from ellesmere island part of the north american plate by a transform fault the wegener fault running through nares strait they accept the wegener fault as a proven structure and overlook abundant evidence that it is hypothetical oakey and damaske 2006 harrison 2006 dawes 2009 hansen et al 2011 rasmussen and dawes 2011 they cite only one reference to geology relevant to their reconstructions viz saalmann et al 2005 to which we will return below figure 1a is a reproduction of part of greiner and neugebauer s fig 9 reconstruction before 175 ma with four geological provinces shown as well as their postulated north american plate boundary coinciding with nares

influence of flow resistance stresses on debris flow runout the hydrodynamic modeling of debris flows is challenged by the complicated mechanism of debris flow and the large variability of material composition therefore in the dynamic continuum modeling of debris flows it is essential to select suitable rheological and associated friction parameters the quadratic rheological model is the most comprehensive approach because it considers the effects of viscous behavior solid particle resistance turbulent properties and friction characteristics of debris flow therefore this study adopted the quadratic model as the governing flow resistance stress and analyzed the influence of various flow resistance stresses to evaluate the runout performance the shallow water equations with modified bottom friction were discretized and the developed model was validated against a dam break flow and a spreading of circular cone problem then to investigate the relationship between the flow resistance relations and the bottom shear stresses exerted by the cones and dry bed the model was applied to runout in a rectangular domain with three cone shaped obstacles an actual field runout event that occurred in korea in 2011 was replicated and the runout paths and flow patterns were analyzed according to the various resistance stresses by considering both the extremely rapid runout velocity and the striking run up height the results obtained by the quadratic stress relation achieved the best performance however for the successful application of the quadratic approach three parameters had to be adjusted with consideration to locality

1d modeling of mud debris unsteady flows the national weather service 1d dynamic flood routing model fldwav is enhanced to include capability of modeling mud debris unsteady flows by including an additional friction slope term in the momentum equation of the saint venant equations three techniques are incorporated into the model to determine the mud debris related friction slope term due to the internal viscous dissipation of non newtonian fluids and granular sliding friction of coarse grained debris surges these techniques are tested and some computational results are compared with observed field data and experimental data

stretching and subsidence rifting of conjugate margins in the north atlantic region subsidence on rifted conjugate continental margins around the north atlantic is analyzed to derive the amount and areal distribution of stretching in the crust and in the lower lithosphere during continental rifting study areas are the grand banks and orphan basin regions of the eastern canadian continental margin and the goban spur and galicia bank regions off western europe in all areas maps of synrift and postrift sediment thickness and bathymetry were used to derive maps of post and synrift subsidence a two layer lithospheric stretching model with independent amounts of stretching in the crust and in the lower lithosphere was assumed to be applicable with the rifting history approximated by several instantaneous episodes of extension this model was used to derive estimates of stretching at all points on a 0 05 geographical grid where subsidence values were available within the study regions the models are constrained with seismic measurements of crustal thickness the results imply that pure shear stretching predominates at a lithospheric scale while simple shear is more localized laterally and confined to the crust in places there is significant decoupling between crustal and mantle stretching near the continent ocean boundary final continental breakup may be localized on one side of the rift between conjugate margin pairs rather than symmetrically located total extension of the margins is compatible with that estimated from normal fault geometries and indicates that the continent ocean boundary has been extended up to 350 km seaward of its original position which should be considered in plate kinematic reconstructions

predicting deposition of debris flows in mountain channels an empirical model for predicting deposition of coarse textured debris flows in confined mountain channels is developed based on field measurements of 14 debris flows in the pacific northwest u s a the model uses two criteria for deposition channel slope less than 3 5 and tributary junction angle greater than 70 the model is tested by predicting travel distances of 15 debris flows in the oregon coast range and six debris flows in the washington cascades u s a the model is further tested on 44 debris flows in two lithological types in the oregon coast range using aerial photos and topographic maps on these flows only the approximate travel distance is known the model can be used by resource professionals to identify the potential for impacts from debris flows key words debris flow deposition travel erosion

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

upb geochronology of the sri lankan basement abstract u pb ages of zircons and monazites from ortho and paragneisses representing the major crystalline basement units of sri lanka establish a new geochronological framework which is consistent with previously published work on sm nd model ages rb sr whole rock ages and u pb mineral ages in the highland complex three newly dated orthogneisses one previously dated by baur et al 1991 and one dated by kroner and williams 1992 all intruded 1 85 to 1 9 ga ago this widespread intrusion event occurred soon after the end of sediment deposition which is estimated at 1 9 to 2 0 ga using upper intercept ages of zircons from metapelites in the highland complex within the boundaries of this complex established by sm nd model age mapping milisenda et al 1994 only one orthogneiss has been found which is substantially younger than 1 8 ga this is the metatonalite from polonnaruwa which intruded 670 ma ago baur et al 1991 three orthogneisses from the vijayan complex which lies to the east of the highland complex yield similarly consistent crystallization ages of 1023 8 1016 28 and 1033 121 ma in the wanni complex which lies to the west of the highland complex a sillimanite bearing gneiss which is apparently of metasedimentary origin but contains zircons of igneous appearance yields a primary crystallization age of 793 4 ma consistent with a previously dated orthogneiss from kurunegala of 770 ma baur et al 1991 in addition single zircon data by kroner et al 1994 indicate primary crystallization ages of 1 0 to 1 1 ga for orthogneisses from the vavuniya charnockite province which is considered to be part of the wanni complex these results confirm the age contrast between the highland complex on the one hand and the vijayan complex and wanni complex on the other as previously inferred from sm nd model ages milisenda et al 1988 1994 post tectonic granitoids and pegmatites intruded throughout all three complexes 550 ma ago the age of regional high grade metamorphism mostly granulite facies in the highland complex mostly amphibolite facies in the vijayan complex and both granulite and amphibolite facies in the wanni complex is constrained to be less than 670 ma the primary crystallization age of the polonnaruwa metatonalite it is more closely defined by lower intercept zircon ages which include one concordant age of 608 4 ma and one discordant but well defined age of 611 23 ma and by a nearly concordant monazite age of 592 2 ma this indicates that peak metamorphic conditions occurred 610 ma ago numerous other lower intercept ages between 590 and 550 ma and post tectonic intrusion ages of 550 ma set a lower age limit for high grade conditions and deformation the temperature history between 610 and 550 ma is not yet well resolved and it is not clear whether there was a separate thermal event 550 ma ago previously published whole rock rb sr and sm nd isochrons for gneisses from the highland complex yielding ages of 2 ga and greater and previously interpreted to date the time of granulite grade metamorphism must be reinterpreted in the light of the new data presented here as well as other recently published results e g burton and o nions 1990b baur et al 1991 and in view of the accumulated evidence for very limited element mobility during high grade metamorphism these whole rock ages are in fact identical or close to the ages of primary granitoid emplacement rather than the age of granulite facies metamorphism

geohazards of slope mass movement and its prevention in hong kong rapid urban development in hilly terrain coupled with tropical storms with heavy rainfall has led to the frequent occurrence of disastrous landslides in hong kong this paper outlines several case histories of such disastrous landslides in hong kong and the major efforts that have been made to mitigate landslide hazards in hong kong since the mid 1970s factors that contributed to such landslides and their causative mechanisms are analyzed methods of predicting the runout distance and lateral extent of rainfall induced slope failures are summarized slope maintenance requirements and stabilization measures are delineated including the stabilization of loose fill slopes

behavior of a loosely compacted unsaturated volcanic soil in this paper the stress strain relationsihp and volumetric behavior of a loosely compacted unsaturated decomposed volcanic soil fill were studied by conducting three series of triaxial stress path tests 1 consolidated undrained on the saturated fill 2 constant water content and 3 a reducing suction under constant deviator stress on the unsaturated fill the last two series of tests were designed to simulate the effects of undrained response and rainfall infiltration in initially unsaturated slopes respectively it was found that the saturated loose volcanic soil behaves like clay under isotropic compression but it resembles sand behavior when it was subjected to undrained shear for isotropically consolidated unsaturated specimens sheared under a constant water content a hardening stress strain and a nonlinear shear strength suction relationship are observed at relatively high suctions both angle of friction and apparent cohesion appear to be independent of suction volumetric contraction during shear is observed in this series of tests on the other hand anisotropically consolidated loose unsaturated specimens subjected to a reducing suction change from contractive to dilative behavior as the net mean stress increases this observed volumetric behavior unlike the shear strength is stress path dependent and cannot be explained by using the existing elastoplastic critical state theoretical framework extended for unsaturated soils

geochemistry of meta sedimentary rocks associated with the neoarchean dagushan bif in the anshan benxi area north china craton implications for their provenance and tectonic setting abstract the anshan benxi area is situated in the northeastern part of the north china craton ncc and consists predominantly of neoarchean supracrustal rocks and plutons with minor eoarchean to mesoarchean rocks these supracrustal rocks were originally considered to be formed synchronously 2 5 ga at different localities on an active continental margin recently more detailed petrographic geochemical and geochronological analyses showed that the supracrustal strata in the benxi area 2 56 2 53 ga were slightly older than those in the anshan area 2 53 2 51 ga which further indicates that they were formed during opening and closure of the back arc basin respectively however the dagushan banded iron formation bif and associated supracrustal rocks in the anshan area were interpreted to be deposited in mesoarchean 3 10 ga which constructs a clear contrast with other supracrustal rocks in the anshan benxi area and renders previous tectonic models controversial on the basis of detailed field investigations in the dagushan area we present in situ zircon u pb hf isotopic whole rock geochemical and sm nd isotopic data of a suite of meta sedimentary rocks i e meta arenites meta shales and high fe meta shales in order to provide constraints on their depositional age provenance and tectonic setting the weighted mean u pb ages of the youngest group of detrital zircons for the meta arenite in the dagushan area coupled with the maximum metamorphic age of 2 51 ga in the anshan benxi area suggest that the dagushan bif was deposited between 2 53 and 2 51 ga geochemical features such as the al2o3 tio2 and th zr values and ree patterns suggest that the meta arenites and meta shales were mainly derived from felsic igneous sources whereas the high fe meta shales were predominantly sourced from mafic rocks the u pb age spectrum diagram of detrital zircons within meta arenites further indicates that the dominant source rocks may be the coeval volcanic rocks in the benxi area our zircon hf isotopes coupled with other previously published zircon hf isotopic data from neoarchean supracrustal rocks in the anshan benxi area suggest that major juvenile crustal growth and reworking events occurred at 2 9 2 7 ga and 2 5 ga respectively in all the dagushan meta sedimentary rocks were probably deposited in a back arc basin on the ancient continental margin

behavior of isotopic systematics during deformation and metamorphism a hf nd and sr isotopic study of mylonitized granite a combined compositional and hf nd and sr isotopic study was performed on a suite of samples of progressively deformed granite from a mylonite zone in the harquahala mountains western arizona to evaluate the effects of deformation and metamorphism on the isotopic systematics of typical continental crustal rocks the 1 4 ga harquahala granite was deformed during mesozoic thrusting along the harquahala thrust granite in the resulting 60 m wide shear zone ranges from protomylonite to ultramylonite in most of these mylonites the protolith is not megascopically recognizable and can be discerned only by the progressive transition to undeformed granite isotopic analyses of hf nd and sr from the shear zone document the immobility of the hf and nd isotopic systems relative to that of the sr isotopic system during deformation the rb sr isotopic data show considerable scatter on an isochron plot exhibiting both gains and losses of rb and sr from the whole rock systems in contrast the sm nd and lu hf isotopic systematics are mostly well behaved on isochron diagrams plotting mostly in tight clusters or along 1 4 ga isochrons these results show that while the sr isotopic system in crustal rocks is quite susceptible to later tectonic disturbance both hf and nd isotopic systems can provide reliable model age information in continental crustal terranes even when the rocks have been subjected to low to medium grades of deformation and metamorphism

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

unsteady nonuniform landslide motion 1 theoretical dynamics and the steady datum state unsteady nonuniform motion of persistently active landslides is a process of widespread importance a general three dimensional theory aimed at elucidating this process is developed from physical principles and field measurements of landslide behavior the theory employs a versatile constitutive model that represents landslides as deformable bodies composed of frictional nonlinear viscoplastic material the three dimensional theory is reduced to a mathematically tractable form by defining an ideal landslide datum state that consists of steady unidirectional shear flow driven by ground water seepage and gravitational forces solution of the datum state equation of motion yields vertical landslide velocity profiles that can represent deformation styles ranging from shear thickening viscoplastic flow to perfectly plastic frictional slip this range of theoretical profiles encompasses the range of profiles measured in four persistently active northern california landslides also obtained from the datum st

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

fracture zones in the north atlantic from combined geosat and seasat data we present a new tectonic fabric map of the northern and central north atlantic ocean floor from 10 s to 66 n based on combined geosat and seasat altimetry data short wavelength vertical gravity along track was derived by hilbert transforming and high pass filtering geosat and seasat deflection of the vertical profiles the along track gravity data were used in conjunction with magnetic anomaly data to locate a large number of fracture zones as well as extinct spreading ridges and v shaped structures we traced many fracture zones more continuously and closer to adjacent continental margins than was previously possible we also mapped a number of unnamed fracture zones and fracture zone segments many of which were previously uncharted we have evaluated the agreement between the mapped fracture zones and synthetic flow lines as predicted from recent plate models for the opening of the north central north and south atlantic most fracture zones in this area correlate quite well with synthetic flow lines supporting the proposition that geosat seasat altimetry data serve as a useful tool to map fracture zones where insufficient bathymetric data are available many fracture zones including some small offset fracture zones in the central north atlantic have been stable and follow tectonic flow lines for tens of millions of years however many other fracture zones do not reflect a railroad track pattern of plate motions the geometry of many small and medium offset fracture zones indicates that the ridge axis discontinuities that produce them can migrate along the ridge causing off axis traces that deviate from tectonic flow lines velocity space diagrams constructed using a recent relative and absolute present day plate motion model indicate that some low angle v shaped troughs and ridges are likely formed by migration of the plate boundary relative to a mesospheric reference frame other low angle v shaped structures reflect slow migrations oscillations of small offset ridge axis discontinuities that are distinct from both tectonic flow lines and v shapes reflecting absolute plate motions high angle v shaped structures are the result of fast migrating ridge axis discontinuities propagating rifts

a fission track transect across nares strait canada greenland further evidence that the wegener fault is a myth many workers continue to model nares strait between greenland and ellesmere island canada as a plate boundary and locus of major cenozoic compression and strike slip marked by the postulated wegener transform fault this despite continuity of precambrian paleozoic provinces across the seaway including an undeformed neoproterozoic mafic dyke swarm that crosses at a high angle as a test of the speculative plate kinematic modelling apatite fission track aft dating was undertaken along a transect across the paleoproterozoic shield of smith sound at the south end of nares strait running from sea level to ca 600 m elevation and as much as 70 km inland on both sides the shield is overlain by three sedimentary basins separated by major hiatuses the aft ages fall into two groups 282 34 and 650 51 ma they indicate maximum depth was 4 km in the lower paleozoic from both coasts to 50 km inland and at 50 km inland temperatures were below the annealing interval throughout phanerozoic time durin

age origin and cooling history of the coronel joao sa pluton bahia brazil received april 2 2002 accepted august 8 2004advance access publication october 22 2004in north east brazil archean and paleoproterozoic cratonic blocksare enclosed within a network of brasiliano age 0 7 0 55ga metasedimentary foldbelts the unfoliated coronel joa o sa grano diorite pluton which contains magmatic epidote and stronglyresorbed clinopyroxene intrudes the sergipano foldbelt zirconsyield a concordant u pb crystallization age of 625 2ma titanite ages are approximately 621ma discordant zircons suggestinheritance from at least two magma sources of ages 2 2ga model calculations based on diffusion parameters andrb sr isotope data from separated minerals indicate that the plutoncooled ata rate of 36 c myr whole rock element compositionsandinitialsr ndisotopic compositionsthat areheterogeneous onalllength scales suggest magma mixing trace element concentrationsand nd isotope data argue against a contribution from a contem poraneous mantle derived magma values of magmatic e

reconciliation of the excess 176 hf conundrum in meteorites recent disturbances of the lu hf and sm nd isotope systematics abstract the long lived 176 lu 176 hf and 147 sm 143 nd radioisotope systems are commonly used chronometers but when applied to meteorites they can reveal disturbances specifically lu hf isochrons commonly yield dates up to 300 myr older than the solar system and varying initial 176 hf 177 hf values we investigated this problem by attempting to construct mineral and whole rock isochrons for eucrites and angrites meteorites from different parent bodies exhibit similar disturbance features suggesting that a common process is responsible minerals scatter away from isochron regressions for both meteorite classes with low hf phases such as plagioclase and olivine typically being most displaced above or left of reference isochrons relatively hf rich pyroxene is less disturbed but still to the point of steepening lu hf errorchrons using our lu hf and sm nd data we tested various hf and lu redistribution scenarios and found that decoupling of lu hf from 176 hf 177 hf must postdate the accumulation of significant radiogenic 176 hf therefore early irradiation or diffusion cannot explain the excess 176 hf instead disturbed meteorite isochrons are more likely caused by terrestrial weathering contamination or common laboratory procedures the partial dissolution of phosphate minerals may predominantly remove rare earth elements including lu leaving relatively immobile and radiogenic hf behind robust lu hf and improved sm nd meteorite geochronology will require the development of chemical or physical methods for removing unsupported radiogenic hf and silicate hosted terrestrial contaminants without disturbing parent daughter ratios

characteristics and formation mechanism of the july 25 2013 tianshui group occurring geohazards a field investigation was conducted for the group occurring mountain torrent geohazards that took place on july 25 2013 in tianshui city china the formation causes range development characteristics and distribution laws of these geohazards were systematically revealed in addition a three dimensional dynamic numerical continuum model was established to simulate the motion characteristics of the typical landslides in tianshui city the field investigation and simulation results show that the mountain torrent geohazards that occurred on july 25 2013 had five major characteristics universality and evident group occurrence local outbreak strong concealment considerable potential damage and a significant hazard chain mode the hazards intensity was aggravated by the superposition effects of intense rainfall and earthquakes most of the landslide prone slopes in these geohazards had a concave geometry the landslides occurred mainly within a slope gradient range of 35 45 the most common slope angle was 40 the loess landslides had a narrow strip shape and ranged in width from several meters to 10 m and in length from 10 s of meters to 100 s of meters these landslides were relatively small scale with volumes from 10 to 100 s of cubic meters the mean velocity frontal velocity total kinetic energy and total potential energy of the typical landslide masses all increased sharply during the downslope motion and decreased gradually in the deposition zone entrainment was a very important factor in these landslide events as it caused the mass of the hazard bodies to increase the increased mass together with a high motion velocity 30 m s enhanced the destructiveness of the hazard bodies

a sliding consolidation model for flow slides a model is proposed for the behaviour of flow slides in loose cohesionless materials in which the debris spreads out as a uniform sheet excess pore fluid pressures are assumed to be generated for example by undrained loading arising from the collapse of metastable structure in the source area of the flow slide under the influence of these the leading element of the debris moves downslope by basal sliding consolidating as it does so by single upward drainage as a result the pore pressure at the base of the element eventually decays to a value that brings the element to rest hence defining the run out of the flow slide the model is applicable in principle to subaqueous and subaerial flow slides and to pore fluids consisting of water gas or both of these the predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at aberfan south wales the results show that a sliding consolidation model provides a possible mechanism for that event

a sliding block model for the runout prediction of high speed landslides a sliding block model is developed for predicting the runout of high speed slide like landslides based on the analysis of the dynamic mechanism of high speed landslides this model adopts the limit equilibrium analysis approach and incorporates mass dynamics and soil deformation into the calculation of soil movements the critical state is considered as the initial stress state and the interslice forces are obtained considering the equivalence of deformation energy it is possible applying this model to simulate the whole travel process of the soil mass from the onset of the landslide and to predict the travel speed of the soil mass and the hazard area of the landslide application of the model to the sale mountain landslide and the tianshui forging machine factory landslide in china gives reasonable results in comparison to the field observations the calculated results illustrate that i the fundamental causes of the high speed are the decline of the resultant friction force during sliding and the

nd isotope and geochemical constraints on the depositional setting of paleoproterozoic metasedimentary rocks along the margin of the archean hearne craton saskatchewan canada abstract the cree lake zone in the southwestern part of the hearne craton reworked during the paleoproterozoic trans hudson orogeny includes the wollaston group a sequence of paleoproterozoic metasedimentary rocks as these rocks have been multiply deformed and metamorphosed to high grade a geochemical and isotopic study was initiated to see through the overprinting events to better constrain the provenance and evolution of the wollaston group the wollaston group consists of thick sedimentary successions representing different depositional and tectonic environments that can be subdivided into two subgroups the lower subgroup is represented by deep water turbidite to shallow water marine deposits the upper subgroup separated from the lower one by a regional unconformity comprises molasse type assemblages ranging from talus to shallow marine lacustrine with subordinate volcanogenic rocks major and trace element data obtained from 31 psammopelitic rocks indicate that the clastic material was derived from sources consisting of both felsic and mafic material although felsic sources are more important in the samples from the lower subgroup sedimentary tectonic discrimination diagrams demonstrate that most of the wollaston group was deposited on an active continental margin rather than a passive margin the e nd values for the wollaston group psammopelites calculated at 1 92 ga the approximate age of the boundary between the lower and upper subgroups vary from 3 4 to 6 8 which yields an approximate 70 30 mixture between juvenile paleoproterozoic detritus and archean detritus from the hearne craton a secondary source of detritus may be 1 95 2 0 ga rocks of the taltson orogen which is exposed to the west of the archean rae hearne craton the wollaston group records the complete evolution of the western margin of the trans hudson orogen during the paleoproterozoic the rifting of an archean continent at ca 2 1 ga led to the deposition of the passive margin siliciclastic sediments comprising the lowermost but poorly preserved part of wollaston group the formation of a continental arc rottenstone along the hearne margin at ca 1 92 ga resulted in a change in tectonic environment from a passive margin to a back arc basin and detritus in most of the lower subgroup was then derived from both basement and newly formed magmatic arc collision with the juvenile la ronge arc led to uplift along the hearne margin which transformed the back arc basin into a retroarc foreland basin at ca 1 88 ga sedimentary starvation and shallowing of the basin led to widespread accumulation of carbonate and evaporite deposits in the west whereas rapidly uplifted orogenic belts in the east provided sources of coarse grained clastic detritus forming the wollaston upper subgroup closure and inversion of the sedimentary basin occurred by ca 1 86 ga coincident with the emplacement of mafic to felsic intrusive rocks in the cree lake zone and the emplacement of the voluminous ca 1860 ma andean type wathaman batholith into the continental margin closure was manifested by the onset of foreland directed thrusting of the wollaston group

element mobility associated with syn metamorphic shear zones near scotchport nw mayo ireland three major blastomylonitic synmetamorphic epidote amphibolite to mid amphibolite facies shear zones are seen on the nw coast of the mullet peninsula in nw mayo these shear zones occur at the contacts of major structural units and in an imbricated slice where rocks of the erris complex are deformed and chemically modified chemical changes associated with individual shear zones have been deduced by comparing the compositions of various gneisses both within and adjacent to the shear zones compositional changes are different in the constituent rock types within each unit and many elements normally considered immobile have been selectively mobilized within the shear zones little evidence of wholesale metasomatic introduction of components into these shear zones was found to accompany the selective mobilization