automatic conversion of magnetic data to depth dip and susceptibility contrast using the spi tm method the source parameter imaging spi method computes source parameters from gridded magnetic data the method assumes either a 2 d sloping contact or a 2 d dipping thin sheet model and is based on the complex analytic signal solution grids show the edge locations depths dips and susceptibility contrasts the estimate of the depth is independent of the magnetic inclination declination dip strike and any remanent magnetization however the dip and the susceptibility estimates do assume that there is no remanent magnetization image processing of the source parameter grids enhances detail and provides maps that facilitate interpretation by nonspecialists the spi method tests successfully on synthetic profile and gridded data spi maps derived from aeromagnetic data acquired over the peace river arch area of northwestern canada correlate well with known basement structure and furthermore show that the ksituan magmatic arc can be divided into several susceptibility subdomains

an equivalent discontinuous modeling method of jointed rock masses for dem simulation of mining induced rock movements abstract the discrete element method dem is of obvious and inherent advantages in simulating large displacements and discontinuous deformations of rock masses and thus is suitable to simulate the mining induced rock movements however when the region of the dem calculation model is large for example when both the length and width of the research area are larger than several hundreds of meters the rock mass in the model range often contains a large number of actual joints if the calculation model is built according to the distribution of the actual joints the calculation model of dem will consist of a large number of blocks which would lead to the impossibility of numerical calculations to address this problem an equivalent discontinuous modeling method edmm of jointed rock masses for dem simulation of mining induced rock movements is proposed in this paper in this method an actual geological body with a complex joint system will be simplified into an equivalent discontinuous model edm which is a dem calculation model with a simple hypothesis joint system the approach for determining the mechanical parameters i e the cohesive strength c the internal friction angle the joint normal stiffness jkn and the joint shear stiffness jks of the hypothetical joints of the edm is the core of the proposed edmm the main procedure of the proposed edmm is composed of 1 for each subarea of an edm building a group of equivalent discontinuous cube models edcms that are of different joint spacings 2 determining the joint mechanical parameters of each edcm based on the mechanical properties of the actual rock masses of the subarea 3 establishing the relationships between the joint spacings and joint mechanical parameters for each subarea of edm and 4 determining the mechanical parameters of the hypothesis joints in each subarea of the edm according to these relationships by exploiting the edm the dem numerical simulation is performed to simulate the mining induced rock movements and failures to demonstrate the applicability the proposed edmm was employed to simulate the rock movements and failures triggered by mining under the western open pit final slope of yanqianshan iron mine

historical development of the gravity method in exploration the gravity method was the first geophysical technique to be used in oil and gas exploration despite being eclipsed by seismology it has continued to be an important and sometimes crucial constraint in a number of exploration areas in oil exploration the gravity method is particularly applicable in salt provinces overthrust and foothills belts underexplored basins and targets of interest that underlie high velocity zones the gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies there is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets gravimeters have undergone continuous improvement during the past 25 years particularly in their ability to function in a dynamic environment this and the advent of

the tectonic frame of the variscan alleghanian orogen in southern europe and northern africa abstract by confronting different geological and geophysical data we attempt to reconstruct the variscan alleghanian orogenic belt with especial emphasis on the links between iberia northwest africa and northeast america the northern iberia transect corresponds to the rifted margin of gondwana inverted during the variscan orogeny and overthrust in its westernmost sector by a pile of allochthonous units some of them with oceanic affinity and witnessing an orogenic suture the southern iberia section reveals two sutures at both boundaries of a terrane closely tied to gondwana namely the ossa morena zone the southern boundary of this zone i e the contact with the south portuguese zone is enhanced by amphibolites with oceanic affinity and probably represents the suture of the rheic ocean the moroccan variscides can be divided into i a western external zone namely the coastal block and the central massif ii an internal zone namely the eastern meseta iii an eastern external zone represented in the anti atlas region and iv the african cratonic foreland since neither ophiolites nor eclogites crop out along this transect of the orogen we consider it to be an incomplete transect lacking the main suture zone rheic ocean stratigraphic and faunal affinities between the moroccan meseta on the one hand and the central iberian western asturian leonese and cantabrian zones of iberia on the other hand suggest that they may well have been part of a common pre orogenic domain at the margin of gondwana on the contrary there are no counterparts in morocco for the ossa morena zone thus the northern iberia palaeogeographic zones would prolong in the moroccan meseta through an eastward arcuate structure while the suture of the rheic ocean would do so offshore morocco in our reconstruction an avalonian spur grand banks indentor which included the caledonian sehoul block in northern morocco and the crust of the south portuguese zone in sw iberia played an important role on the kinematic evolution of the orogen as well as on the final configuration of the suture of the rheic ocean this suture would mould around the avalonian spur being laterally translated to southeastern nova scotia newfoundland

evidence for ancient lithospheric deformation in the east european craton based on mantle seismic anisotropy and crustal magnetics abstract we present new shear wave splitting measurements performed at 16 stations on the east european craton and discuss their implications in terms of upper mantle anisotropy for this geophysically poorly known region previous investigations of mantle anisotropy in central europe have shown fast directions aligning smoothly with the craton s margin and various suggestions have been proposed to explain their origin such as asthenospheric flow or lithospheric frozen in deformation here we aim at investigating the continuation of this shear wave splitting pattern further to the east into the east european craton for the craton the interpretation appears to be less ambiguous than for central europe since several arguments support lithospheric anisotropy in this region 1 the large scale coherence within either of the four constituting blocks and the significant variations between the blocks on a small scale 2 the weak correlation with absolute plate motion vectors and 3 the good correlation between anisotropy and crustal features for which we use magnetic field alignments as a proxy rather good correlation of these magnetic features with seismic fast orientations strongly supports the idea of vertically coherent deformation throughout upper mantle and crust the observed splitting orientations thus reflect the last tectonic events of each block frozen in into the lithosphere for hundreds of millions of years

continental transform tectonics great slave lake shear zone ca 1 9 ga northwest canada great slave lake shear zone gslsz is a northeast trending dextral mylonite zone across which the coeval north trending thelon and taltson magmatic zones on the west margin of the churchill province are offset 300 700 km it is proposed that the gslsz is a continental transform structure related to oblique collisional indentation of the active margin of the churchill province by the microcontinental slave province this accounts for geologic and geophysical differences between the thelon and taltson zones and explains the localization of a tibetan type queen maud uplift north of the gslsz and the abrupt loss of slip on the gslsz east of the uplift it also provides a new model for the athapuscow aulacogen analogous to the modern bay of bengal indo burman ranges sagaing transform andaman sea situation

automatic lineament extraction from potential field images using the radon transform and gradient calculation linear anomalies are critical in the interpretation of gravity and magnetic data visual identification of lineaments is usually done by experienced interpreters and identification results then have to undergo a digitization or import procedure the traditional identification method has unavoidable subjectivity and inefficiency to overcome these limitations we fuse the radon transform rt with gradient calculation to process gravity or magnetic data and to realize automatic detection and extraction of lineaments as part of the detection procedure we define the rt based mean gradient mg effective mean gradient emg and residual mean gradient rmg in order to highlight long linear segments or to enhance short linear ones in the transform domain the gradient forms are applied self adaptively and self selectively to gravity or magnetic images according to specific conditions gradient directions are also taken into account in the transformation procedure to emphasize the characteristics of linear anomalies to extract the position and length of the detected lineaments from the transform domain a constraint inverse searching method cism is given and used to locate the starting and end points of the lineaments the method can deal with the condition that there is at least one linear section in a specific direction or that separate linear sections may belong to one lineament through tests with synthetic images and with real data from the haijiao upheaval area in the east china sea basin the detection and extraction methods are shown to be more effective and robust than the conventional rt applications the results from the real data roughly coincide with major geologic faults that are visually identified these results show that the methods constitute a useful tool to aid fault interpretation

lateral variation of crustal properties from aerogeophysical data in northern brazil abstracta new method is proposed for the study of crustal azimuthal anisotropy and the lateral variation of other crustal aerogeophysical parameters using a quantitative approach the processing of a large newly acquired high resolution set of aerogeophysical data is considered using the existing radon transform and the geostatistical analysis approaches the data set includes an area of the guyana shield in northern brazil which was not included in previous surveys the area is covered by dense rain forest vegetation and thick soil layers parameterization was performed considering the possible anisotropic character of the geophysical 2d data application of the newly proposed geostatistical data processing yielded high resolution images of the lateral variation of quantitative geophysical parameters which indicate good correlation with previously determined seismic anisotropy in the area average anisotropy as measured by the radon transform and variogram analysis is scale dependent at scales gr

some aspects of mining under aquifers in china abstract a number of case studies of mining induced permeability enhancement are documented the extent of strata failure around active underground mines is determined through use of a borehole discharge test the test delimits zones and the severity of extraction induced fracturing from these data empirical relationships are developed to determine the vertical and horizontal extents of the caving and fracture zones induced by mining these relationships are developed for a variety of strata types and strengths and give quantitative recommendations applicable to similar mining conditions elsewhere these recommendations are particularly important for sub sea or sub aquifer mining to ensure hazard free operation

removing varying directional trends in aeromagnetic data both qualitative and quantitative interpretations of aeromagnetic data can be hindered by the presence of magnetic anomalies caused by mafic dykes such anomalies obscure the magnetic signatures due to basement lithology and structure and their effects will often dominate when automated interpretation methods are applied to gridded data sets since dyke swarms are often nonparallel simple frequency domain strike sensitive filtering based on a single directional trend is not a viable method for removing their signatures we use a coordinate transformation to project anomalies of various strikes onto one direction which is then suppressed using a standard decorrugation method the resulting grid is subsequently transformed back to the original projection this approach is illustrated by the removal of the magnetic signature of the proterozoic mackenzie dyke swarm occurring in the slave structural province northwest territories canada

the aguablanca cu ni ore deposit extremadura spain a case of synorogenic orthomagmatic mineralization age and isotope composition of magmas sr nd and ore s abstract the aguablanca cu ni orthomagmatic ore deposit is hosted by mafic and ultramafic rocks of the aguablanca stock which is part of the larger high k calc alkaline santa olalla plutonic complex this intrusive complex ca 338 ma in age is located in the ossa morena zone omz of the iberian variscan belt mineralization consists mainly of pyrrhotite pentlandite and chalcopyrite resulting from the crystallization of an immiscible sulphide rich liquid isotope work on the host igneous rocks sr nd and the ore s suggests that contamination with an upper crustal component took place at some depth before final emplacement of the plutons end338 6 to 7 5 sr 338 0 7082 to 0 7100 34s sulphides near 7 4 assimilation fractional crystallization afc processes are invoked to explain early cumulates and immiscible sulphide magma formation intrusion took place at the beginning of the type a oblique subduction of the south portuguese zone under the ossa morena zone and was probably driven by transpressive structures strike slip faults the mineralization is thus synorogenic aguablanca is probably the first case referred to in the literature of a magmatic cu ni ore deposit hosted by calc alkaline igneous rocks

deformation characteristics of a roadway in steeply inclined formations and its improved support abstract mining roadways in steeply inclined rock layers commonly experience severe deformation in form of large asymmetric deformation roof subsidence and floor heave which significantly threaten the stability of a roadway using a coal exploration roadway in anhui province china as a case study the deformation characteristics of a roadway in steeply inclined rock formations and the corresponding improved support scheme is analysed by numerical simulation the simulation is performed using a cohesive element to consider the influence of geologic bedding plane around the roadway the results show that due to the spatial relationship of the roadway and the two bedding planes i e interfaces rocks above the roadway move downward along the interface while rocks below the roadway move upward along the interface the maximum deformation occurs along the upper left and lower right sides of the roadway surface which accounts for the large leaning asymmetric deformation of the roadway right inclination an improved support scheme for the roadway is proposed using long cables to restrain severe deformation short cables and enclosed u shaped steel sets to improve the ground stress state the proposed scheme can effectively restrain floor heave manage large asymmetrical deformation compared to the original scheme

geotechnical sedimentology its use in underground coal mining from a geotechnical perspective bedding is a discontinuity in a rock mass sedimentology is concerned in part with the origin of bedding there is much to be gained by a melding of the two disciplines in the underground coal mining sector bedding controls the strength of rock units in coal measures by defining beams that may or may not span openings voussoir beam theory can be used to explain how massive sandstone conglomerate units can span longwall panels and what thickness of roof beam is required to span a coal mine roadway bedding also controls the way in which stresses are distributed about coal mine openings by utilizing transverse isotropic elastic properties the effect of bedding can be readily implemented in continuum numerical codes geologists logging core need to discriminate between bedding as a textural element in the rock and bedding as a geotechnical discontinuity geotechnical engineers need to explicitly consider bedding when formulating their design models

variscan accretionary complex of northwest iberia terrane correlation and succession of tectonothermal events the allochthonous terranes of northwest iberia can be correlated with specific paleogeographic realms of the continental masses and intervening oceans involved in the variscan collision assuming that the existing ophiolites represent the suture formed by the closure of the rheic ocean the units in the footwall to the suture correspond to the outer edge of the gondwana continental margin and the units in the hanging wall are interpreted as fragments of the conjugate margin represented by the meguma terrane this correlation establishes a precise link between circum atlantic terranes and makes it possible to draw a relatively simple scenario of the successive tectonothermal events recorded following the amalgamation of avalon to laurentia the remaining outboard terranes underwent a progressive accretion to this continent that ended with the collision between laurentia and gondwana

subduction and eduction of continental crust major mechanisms during continent continent collision and orogenic extensional collapse a model based on the south norwegian caledonides during continental collision in the middle silurian the thickness of the lithosphere under the caledonides of s norway was doubled by subduction of the western margin of baltica including the western gneiss region under laurentia crustal rocks of the baltic plate reached sub moho depths of near 100 km or more as inferred from the presence of coesite in eclogites isostatic calculations indicate an average elevation of the mountain chain of about 3 km at this stage the subducted lithosphere experienced vertical constrictional strains as a result of slab pull by its heavy and cold root eduction of the deeply buried crustal material was initiated by decoupling of the thermal boundary layer in the subducted lithosphere isostatic rebound resulted in very rapid uplift 1 2 mm yr 1 and the deep crust was exhumed mainly by tectonic extensional stripping over a period of 30 40 myr the eduction was probably related to a rolling hinge footwall uplift mechanism and the early high pressure coaxial fabrics were overprinted by extensional simple shear as the deep crust reached middle and upper crustal levels the model explains the present day normal crustal thickness under the exhumed deep rocks without necessarily invoking large scale lateral flow of material in the lower crust or igneous underplating

effect of rock mass and discontinuity mechanical properties and delayed rock supporting on tunnel stability in an underground mine abstract in this paper the rock mass stability around the tunnels in an underground mine is investigated using the distinct element method a three dimensional model was developed based on the available geological geotechnical and mine construction information it incorporates the inclined lithologies including a weak interlayer the persistent and non persistent faults and a complex tunnel system the strain softening constitutive model was prescribed for the rock masses in the numerical model the continuously yielding joint model was used to describe the non linear behavior of the faults to account for the deformations occurred between the excavations and rock supporting the delayed installation of supports was implemented by using the stress relaxation method numerical analyses were performed to study the effects of the post failure constitutive parameters of the rock masses the mechanical properties of faults and the delayed supporting on tunnel stability the following results are presented a the rock mass deformations and failure zones around the excavations b the joint shear displacements of the major fault and c the failure conditions of the applied supports satisfactory comparisons are obtained between the predictions based on numerical modeling and the field deformation measurements the analysis procedures presented in this study are applicable for stability assessment of various underground rock excavation projects located in different parts of the world having different geological settings and complex engineering situations

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

the 3 d crustal structure in the manicouagan region new seismic and gravity constraints lithoprobe line 55 represents an oblique seismic crossing of tectonic domains in the manicouagan region of the grenville province in eastern quebec that has provided a basis for construction of a 3 d model of crustal structure reprocessing of the seismic profile presented here has enhanced the imaging of prominent out of the plane reflection zones that originate from high pressure metamorphic rocks northwest of the line we show that after conventional migration the apparent dips of out of plane reflections can be compared with regional foliation trends but the reflection orientations in themselves provide only weak constraints on the orientation of out of plane of reflectors we describe and implement several graphical techniques to estimate reflector orientation near large bends in the profile using a prestack processing technique we find poorly resolved but shallow dips and approximately eastward strike directions for reflections from berthe hart jaune and tshenukutish terranes near relais gab

statistical analysis of spatial point patterns on deep seismic reflection data a preliminary test summary spatial point patterns generated from bitmaps of images of processed reflection seismic profiles are analysed to quantify the reflectivity patterns the point process characteristics for two different regions of a deep seismic reflection profile in northwestern canada demonstrate that in both cases the points are not randomly distributed and that the point pattern distribution is different between the regions the cluster effects for small point pair distances are stronger for the region of data where there is strong sedimentary layering than for the region where the layering is less distinct as a result it appears that future developments in point pattern analysis may provide a new tool for analysing spatial variations in reflection data

numerical investigation of the effects of coal seam dip angle on coal wall stability abstract instability and failure mechanism of coal wall at coalface is one of the hot button and difficult issues in the study of coal mine ground control research to date has mainly focused on the macro characteristics of coal face failure whereas few efforts have been devoted to the micro aspects or to the mechanisms behind these failures the work described here takes coal face 8102 in the wolonghu mine china as an example and employs distinct element numerical software udec to investigate the distribution of abutment stress in front of the coal face at different mining dip angles from micro and macro perspectives and reveal the main failure form and location of coal rib the numerical results indicate the following six points 1 the distance between the location of the peak abutment stress and the coal face increases with greater mining dip angles 2 the rank by angle of abutment stress concentration factors is horizontal up dip down dip coal faces 3 tensile fractures dominate the failure of horizontal and up dip coal faces and the only difference between the two is the form of the failure 4 shear fractures are the dominant failure components of down dip coal faces 5 the coal face failure forms include integral rib spall and a combination of upper rib shear failure and roof caving 6 tensile fractures are mainly responsible for roof failures the difference in roof movement between up dip and down dip coal faces is reflected in the forms of failure of their coal faces and of their roofs moreover the effect of coalface depth mining height panel advance velocity and coal strength on the stability of coal rib is studied the conclusions obtained from numerical simulation are consistent with engineering result which verifies the reasonability of simulation analysis by udec finally we propose measures to avoid coal face failure in the wolonghu mine considering the numerical outcomes the monitored strata behavior and the recorded setting support resistance

pattern analysis of seismic records the three steps in automated analysis of seismic records are trace matching event detection and seismic zoning our algorithm matches traces by comparing sequences of peaks on neighboring traces and edits pairs of peaks identified as similar for consistency in trend across and down the record by combining connected pairs we obtain laterally coherent events of varying quality which divide a record into zones that may have lithologic significance these zones can be obtained automatically by applying cluster analysis to seismic attributes and other discriminating properties of these events on common shot gathers from a four fold survey in saskatchewan canada the coherent events which we detected this way are consistent with those recognized visually and are associated with clear formation boundaries strong reflections correspond to events detected with high confidence and the seismic zones show good correlation among shot records high detection confidence and good correlation indicate that the app

sm nd isotopic systematics as tectonic tracers an example from west avalonia in the canadian appalachians abstract the tectonothermal evolution of west avalonia in mainland nova scotia appalachian orogen provides an excellent example of the application of sm nd isotopic analyses to tectonic studies regional syntheses indicate that west avalonia originated in the neoproterozoic as one of a number of terranes collectively known as peri gondwanan terranes along the gondwanan margin these terranes are characterized by late neoproterozoic voluminous arc related magmatism west avalonia became detached from gondwana in the early ordovician was accreted to laurentia by the silurian and was deformed by post accretionary strike slip tectonics in the late devonian and carboniferous associated with the amalgamation of pangea all stages of this evolution can be recognized in the sm nd isotopic signature in various neoproterozoic and paleozoic volcanic and sedimentary successions in mainland nova scotia crustally derived felsic volcanic rocks of late neoproterozoic ca 615 ma early cambrian and early silurian ages define an envelope that provides gross constraints on the sm nd isotopic composition of the underlying basement source e nd values range from 0 78 to 2 92 in the neoproterozoic rocks from 2 0 to 5 0 in the cambrian rocks and from 0 1 to 2 5 in the silurian rocks t dm model ages for each of these suites are remarkably similar they typically range from 0 9 to 1 2 ga suggesting that the sm nd isotopic composition of these suites was profoundly influenced by repeated melting of the same basement source this sm nd envelope provides a reference by which other suites may be compared and interpreted for example turbidites in a late neoproterozoic volcanic arc basin have sm nd compositions that lie within this envelope suggesting that they are derived from the coeval volcanic rocks that flank the basin the genetic significance of the model ages can be investigated by the analysis of felsic and metasedimentary rocks that pre date the main arc phase two felsic complexes have compositions that lie within the envelope and have similar model ages the presence of this signature in early avalonian rocks suggests that the model ages represent a genuine tectonothermal event at ca 1 0 to 1 2 ga that formed juvenile proto avalonian crust by implication the main arc phase in avalonia recycled this crust sm nd isotopic analyses of the metasedimentary sequences are incompatible with previous interpretations of deposition in a passive margin setting that pre dated avalonian arc activity instead the data indicate derivation from two distinct sources ancient gondwanan basement and juvenile avalonian arc suggesting deposition in a western pacific type back arc environment this re interpretation has important implications for neoproterozoic reconstructions the sm nd isotopic composition of west avalonian basement contrasts with that of other peri gondwanan terranes for example similarly aged felsic rocks in the cadomian terrane of nw france are characterized by more negative e nd values and older t dm model ages 1 0 1 9 ga these data together with detrital u pb data suggest that west avalonia was developed along the amazonian margin whereas cadomia was developed along the west african margin of gondwana sm nd isotopic analyses of early silurian clastic rocks in mainland nova scotia show fundamental differences with unconformably underlying neoproterozoic and early paleozoic avalonian successions these data have e nd values ranging from 5 7 to 6 1 with t dm model ages of about 1 4 to 1 7 ga indicating that the clastic rocks cannot have been derived from underlying successions a variety of geologic data and regional constraints suggests that they may have been derived from the caledonide orogen of western europe thereby providing a minimum age for the accretion of west avalonia to laurentia baltica sm nd isotopic analyses from late devonian early carboniferous continental clastic rocks deposited along the southern flank of avalonia in mainland nova scotia also show little influence from avalonian rocks and are compatible with derivation from the meguma terrane immediately to the south these data are consistent with regional synthesis which indicate uplift of the meguma terrane relative to west avalonia during dextral transpression

fdm predictive methodology for subsidence due to flat and inclined coal seam mining abstract a subsidence estimation methodology to predict subsidence troughs due to flat and inclined coal seam exploitation is described the foundations of the procedure are the correct definition of the rock mass behaviour model its adequate characterization and its implementation in the code flac fast lagrangian analysis of continua was written by p a cundall and is marketed by itasca cons group inc of minneapolis mn usa which is based on the finite difference method or fdm numerical modelling technique the method is first validated for flat coal seam longwall mining with caving in british basins because of the large number of data from this area which includes subsidence measurements and characterization parameters the method is then applied to gently inclined seams and the results are seen to fit empirical observations finally for steeply inclined and sub vertical seams the proposed methodology allows observation of two different movement trends in the overlying strata the former is perpendicular to the strata direction in the same way as the one observed in flat seam subsidence and the latter which becomes the most important one in seams dipping by more than 75 is parallel to the strata these two different trends produce subsidence troughs presenting two relative subsidence maxima and extending along large surface areas thus it would be unlikely to predict and assess these troughs this may be a possible reason why so little coherent data about this kind of subsidence exists these numerical observations of steeply inclined coal seams need to be validated empirically

new method for determining the elastic parameters of rock mass layers in the region of underground mining influence abstract the primary objective of the following paper is to determine the value of strata elastic parameters in a selected polish mining area using a new method based on finite element analysis gsi geotechnical classification and back analysis the individual rock layer strain parameters were estimated by means of comparing the measured subsidence trough with the result of numerical analysis carried out for the same geological and mining conditions as a result of such an analysis the values of the elastic modulus of the anisotropic model of strata were obtained in the region of underground mining influence

use of the slant stack for geologic or geophysical map lineament analysis the slant stack technique also known as radon transform p transform and plane wave decomposition used in seismic data processing for discriminating between and separating seismic events of differing dips or moveout is applied here to the problem of geologic or geophysical map lineament analysis the latter problem is analogous to the seismic coherent noise problem in the sense that lineaments associated with one geologic event or episode are often underprinted by the lineaments of preceding geologic disturbances and overprinted by the lineaments of subsequent disturbances consequently it can be difficult to distinguish between the individual lineament sets

a study of surface subsidence and coal pillar safety for strip mining in a deep mine some villages and bridges are located on the ground surface of the working district no 7 in the wanglou coal mine if longwall mining is adopted the maximum deformation of the ground surface will exceed the safety value strip mining is employed for the working district no 7 which is widely used to reduce surface subsidence and the consequent damage of buildings on the ground surface to ensure the safety of coal pillars and improve the recovery coefficient theoretical analysis and numerical simulation flac 3d were adopted to determine the coal pillar and mining widths and to discuss the coal pillar stress distribution and surface subsidence for different mining scenarios the results revealed that the width of coal pillars should be larger than 162 m and the optimized mining width varies from 150 to 260 m as the coal seam is exploited vertical stress is mainly applied on the coal pillar inducing stress changes on its ribs the coefficient of mining induced stress varies from 2 02 to 2 62 for different mining scenarios the maximum surface subsidence and horizontal movement increase as the mining width increases however when the mining width increases to a certain value increasing the pillar width cannot significantly decrease the maximum subsidence to ensure the surface subsidence less than 500 mm the mining width should not be larger than 200 m considering the recovery coefficient and safety of the coal pillar a pillar width of 165 m is suggested

collision between the north and south china blocks a crustal detachment model for suturing in the region east of the tanlu fault a crustal detachment model based on the interpretation of linear aeromagnetic anomalies surface geological observations and deep seismic profiles is proposed for the continent continent collision between the north and south china blocks east of the tanlu fault the model suggests that during the mid mesozoic collision between the two continental blocks the upper crust of the south china block in the subei yellow sea region was detached from the lower crust and thrust over the north china block for 400 km whereas the lower part of the lithosphere was subducted under the north china block along a subsurface suture running east from nanjing the sinistral offset of the qinling suture by the tanlu fault is only 110 120 km in the deep crust much less than previously suggested

u pb geochronology and petrology of the late paleozoic gil marquez pluton magmatism in the variscan suture zone southern iberia during continental collision and the amalgamation of pangea the origin of plutonic complexes that stitch suture zones developed during collision is not well understood in southern iberia the pulo du lobo suture zone pdlz is intruded by the syn to postcollisional gil marquez pluton gmp thought to be part of the sierra norte batholith u pb la icpms zircon data on various phases of the gmp yield from oldest to youngest 1 a 354 4 7 6 ma unfoliated gabbro 2 a 345 6 2 5 ma foliated intermediate phase 3 a 346 5 5 4 ma unfoliated porphyritic granite 4 a 335 1 2 8 ma unfoliated biotite granite this sequence is consistent with cross cutting relationships observed in the field the range in ages is consistent with interpretations that the gmp is part of the composite ca 350 308 ma snb inherited ages preserved in the gmp intermediate and felsic phases indicate that its magmas traversed through south portuguese zone and pdlz crust during emplacement the ca 345 ma emplacement of the late kinematic foliated intermediate phase constrains the age of late stage strike slip deformation within the pdlz and the lack of a foliation in the older gabbro indicates that is was not proximal to a shear zone neither at the time of emplacement nor during its subsequent history the unfoliated porphyritic granite and unfoliated biotite granite cut the foliation of the intermediate phase indicating emplacement during the waning stages of collision while the ca 335 ma biotite granite intrudes the santa ira flysch thereby providing a tight constraint for the latest stage of deformation in the pdlz

lateral ramps as an aid to the unroofing of deep crustal rocks seismic evidence from the grenville province we suggest that lateral ramps in the basement to orogenic wedges may be important agents in the rapid unroofing of deeply buried continental crust our suggestion is based on a study of the distribution of high pressure metamorphosed continental rocks in the mesoproterozoic grenvillian orogen in eastern quebec these rocks were buried to depths of more than 50 km through crustal thickening during a continental collision and were then rapidly unroofed they are currently exposed in a 100 km 60 km lobate embayment north of the manicouagan reservoir using a combination of surface structural data and seismic reflection data from lithoprobe line 55 we reconstruct the three dimensional form of the high pressure rocks our reconstruct ion methods are based on demonstrable correlations between the attitudes of gneissic layering at the surface and the attitudes of reflectors on the seismic profile they make extensive use of the fact that much of the seismic reflectivity on line 55 comes from outside the vertical plane of the seismic line because of the sinuous nature of the line and its obliquity to tectonic strike the validity of the reconstructions is demonstrated by the generation of a synthetic seismogram from the interpreted geometry that is very similar to the observed seismogram our reconstruction shows that a steep lateral ramp extends to the base of the crust immediately behind the broad lobe of high pressure rocks at the surface the lateral ramp probably provided a favorable pathway for the extrusion of deep seated rocks from the deep crust and their transport onto the foreland

structural analysis of an accretionary prism in a continental collisional setting the late paleozoic pulo do lobo zone southern iberia abstract models concerning the tectonic evolution of accretionary complexes typically relate outcrop scale to plate scale multiphase deformation as a smooth variation of strain on all scales however at oblique convergent margins regional scale brittle faults in the shallow crust are commonly parallel to the main orogenic grain these faults impose a strong structural anisotropy and can subsequently control deformation at subordinate scales as a result finite strain in each domain may not record local kinematics consistent with the overall orogenic scale motion implying that structural data must be analyzed selectively from a large area in order to relate outcrop scale kinematics to global plate scale dynamics field mapping and preliminary structural analysis of the late devonian pulo do lobo pdl formation and suspect exotic south portuguese zone spz in southern iberia indicate tectonic juxtaposition of diverse deposits such as foreland basin flysch sedimentary and tectonic melange and passive margin sediments showing an overall geometry consistent with an accretionary wedge setting variations in finite strain lithology and regional structure were used as proxies for defining tectonic domains for structural analysis numerous local kinematic indicators within the pdl suggest a complex regional deformation with several enigmatic features that can be explained by sequential compartmentalization of strain during the development of the imbricate stack followed by late stage bulk strain imposed across the entire complex structural data produced by local strain partitioning reveals kinematic indicators which contradict the overall regional structural style e g spatial juxtaposition of sinistral and dextral fabrics when viewed at larger scales i e regional scale however these data indicate that significant sinistral strike slip movement occurred in conjunction with both an extension and shortening outcrop scale deformation in polydeformed domains is controlled by local conditions resulting from brittle deformation coeval with orogenic scale bulk strain the entire pulo do lobo zone is dominated by a pervasive late stage vertical to sub vertical e w cleavage axial planar to chevron folds which overprint earlier deformation in the older passive margin units this overprinting suggests that in the late stages of the evolution of the accretionary complex bulk strain was imposed over the entire complex as a result of internal locking of the accretionary complex and reduced strain rates during the waning stages of collision between gondwana and laurussia stereographic analysis of fabric elements from each distinct tectonic domain together with regional geological constraints support this hypothesis and are indicative of progressive deformation imposed on the pdl during the variscan orogeny

physical modelling of subsidence from sequential extraction of partially overlapping longwall panels and study of substrata movement characteristics field examples of subsidence from sequential extraction of overlapping coal longwall panels have shown that complex and unexpected subsidence effects can occur physical models comprising sand and plaster obeying relevant similarity rules were used to investigate the subsidence mechanisms displacements within the models were measured using a combination of optical transducers photogrammetry and laser scanning the observed results were compared with finite element models the models demonstrate that the incremental subsidence and substrata movement profiles after lower seam extraction can be separated into three different zones these zones undergo different horizontal and vertical movement characteristics the zone of overlap of the two longwall panels undergoes greater total subsidence compared to a single seam of equivalent thickness the limit angle of the subsidence also differs at the two ends of the lower extraction as a result of the effects of the previously mined out area above

delamination in collisional orogens thermomechanical modeling 1 modes of mantle delamination in collision zones are discussed in the light of 2d numerical modeling freely evolving thermomechanical models take into account phase changes in the mantle and melting in the crust distinct modes are identified in which orogens undergo mantle delamination concurrently or after collision delamination propagates along the moho of the subducted plate together with the retreating trench provided that slab pull is sufficient and that the meta stability of the crust lithospheric mantle interface is overcome topography is an instantaneous response to delamination and migrates with the focused and localized separation between crust and lithospheric mantle delamination front early exhumation of high pressure rocks is followed by exhumation of high temperature partially molten rocks convective stabilization of delamination outlasts slab break offs and impedes renewed build up of mechanically strong lithospheric mantle by static cooling parameter studies investigate the sensitivity of delamination to the age of the subducted oceanic plate the collision rate the mantle rheology and explore the effects of melting and sedimentation mantle flow patterns that form around delamination and subduction are sensitive to and often limited by the semi permeable 670 km spinel perovskite transition demonstrating that phase changes are essential factors delamination may account for the formation of complex boundary zones between continents such as between africa and europe in the mediterranean where transient compression and extension the lack of mantle lithosphere and the exhumation of high grade metamorphic core complexes are features also obtained in our modeling results

continental mafic magmatism of different ages in the same terrane constraints on the evolution of an enriched mantle source the antigonish highlands nova scotia are within the avalon terrane of the northern appalachians and contain four distinct episodes of rift related magmatism neoproterozoic cambrian middle ordovician and late devonian all four magmatic suites are composed of basalts and subordinate crustally derived felsic rocks the mafic rocks of these suites which do not appear to be significantly contaminated by continental crust display similar geochemical and sm nd isotopic characteristics consistent with an enriched mantle source that was metasomatically enriched prior to the oldest rifting event probably between 0 8 and 1 1 ga these data also imply that the avalonian crust and its subcontinental lithospheric mantle remained coupled during four magmatic events because the earliest phases of magmatism occurred when avalonia was located along the gondwanan margin and the latest phases after avalonia accreted to laurentia the coupling of crust and mantle in the antigonish highlands suggests that the migration of avalonia did not completely detach its lithospheric mantle from its crustal cover this study demonstrates the importance of comparing magmatism of different ages in the same terrane

directional filtering for linear feature enhancement in geophysical maps geophysical maps of data acquired in ground and airborne surveys are extensively used for mineral groundwater and petroleum exploration lineaments in these maps are often indicative of contacts basement faulting and other tectonic features of interest to aid the interpretation of these maps a versatile processing technique of directional filtering based on the 2 d normal radon transform is used to enhance or suppress specific lineaments synthetic data and field examples using electromagnetic and radiometric data are used to demonstrate the superiority of the radon transform method over conventional fourier transform filtering the radon transform technique is shown to be more versatile and less susceptible to processing artefacts than the fourier transform methods

determination of actual limit angles to the surface and their comparison with the empirical values in the upper silesian basin czech republic abstract this study deals with the determination of the actual limit angles in the long term formed subsidence basin in the czech part of the upper silesian basin the remaining part lays in poland here there was the most extensive underground exploitation of black coal in the north east of the czech republic a limit angle is absolutely decisive in the determination of deep mining influences in relation to the current and future utilisation of this territory the two csm and paskov mine localities on the edge of the subsidence basin were selected for this study since they could not have been affected by mining in neighbouring mines on the grounds of the long term levelling monitoring of points on the surface which started prior to mining the horizontal distance between the mined out area and the undisturbed ground surface was identified the impact of limit angle on the surface was calculated by means of the horizontal distance and the established mining depth such identified actual limit angles reached the values of 36 at the csm mine and 25 for the paskov mine the calculated values are significantly lower when compared with the currently applied empirical values of 57 for the csm mine and 56 for the paskov mine this means that the extent of the undermining effects is unambiguously wider by 611 m at the csm mine and by 883 m at the paskov mine this study thus establishes the existence of a significantly vaster area influenced by coal deep mining than previously expected the identified facts lead to the conclusion that regular revisions and follow up updates of the empirically determined parameters are recommended

automatic interpretation of magnetic dike parameters using the analytical signal technique the analytical signal of the magnetic field is used to automatically determine the source parameters of dikelike structures the method is particularly useful for interpreting large amounts of data collected during airborne surveys because it makes full use of the high density of data along the flight lines while simultaneously checking for two dimensionality and strike directions by searching for coherent signals in neighboring profiles the maximum horizontal curvature of the amplitude of the analytical signal is used to locate the dikes along a given profile tests with synthetic data show that the dike s horizontal position is resolved accurately magnetic data from the siljan impact structure in sweden show that the estimated strikes are reliable and that dip depth and width estimates are coherent especially for well isolated dikelike structures

comparing crustal and mantle fabric from the north american craton using magnetics and seismic anisotropy a central target in earth sciences is the study of deformation at various depth levels within the earth seismology has offered a remarkable tool for doing this via seismic anisotropy it is however not always clear how to interpret those observations a question of interest is to understand the relation between the deformation of the mantle and the crust and in studying the relation between the two mantle deformation is expressed in seismic anisotropy in this paper we seek an objective way of extracting information about crustal fabric as well to be able to compare with seismic anisotropy the magnetization of crustal rocks offers an attractive possibility for doing this we thus explore the use of magnetic data and we compare magnetic crustal fabric orientation with mantle fabric observations from seismic anisotropy we apply our technique to the north american craton for which we have an excellent magnetic dataset and we show that there is a clear relation between crustal and mantle fabric for the cratonic region this has important implications for crustal formation and for interpreting seismic anisotropy observations

a meta analysis of coal mining induced subsidence data and implications for their use in the carbon industry abstract many empricial subsidence estimation tools exist worldwide but are designed and calibrated for specific coalfields this paper presents an universal tool for the estimation of maximum subsidence smax the subsidence tool is based on pooling and meta analysis of empirical data from a number of different countries and coalfields the key factors influencing smax are the void dimensions and the mechanical competency of the overburden these factors are used to estimate subsidence using the empirical equation smax c 1 10 a w d b m where w is the width of the void d the depth m the effective void thickness and a b c are parameters related to the mechanical competency of the overburden this universial empirical method was validated against historical data from united kingdom and australia the method also provided smax estimations for underground coal gasification ucg projects that were inline with those from numerical modelling under certain conditions this tool would likely be most useful when investigating areas where there are little or no historical data of subsidence and mining such areas are most likely to be targeted by ucg schemes

subsurface ground strain and fracture development associated with longwall mining abstract experiments employing physical modelling to study ground behaviour above longwall faces in different geological conditions are reported the development of subsurface fractures from longwall mining extractions and the resulting principal strain patterns are described the significance of the strain patterns in relation to the mining dimensions and the geological setting in terms of rock strength is discussed the effect of faulting on subsidence behaviour is also considered

structure and evolution of the magnitogorsk forearc basin identifying upper crustal processes during arc continent collision in the southern urals the southern urals of russia contain a well preserved example of a paleozoic arc continent collision in which the intraoceanic magnitogorsk volcanic arc and its forearc basin sediments accreted to the east european craton during the devonian the magnitogorsk arc records the evolution from incipient intraoceanic subduction to a mature arc and by comparing its surface geological features with those in active arc continent collision settings it is possible to identify upper crustal processes that were active in the southern urals the arc edifice can be divided into western and eastern volcanic fronts that were active during different stages of arc evolution and for which two distinct phases of forearc basin development can be recognized the late lower to middle devonian aktau formation represents a remnant of the intraoceanic to collisional forearc basin to the irendyk volcanic front whereas the middle devonian to lower carboniferous ulutau koltubanian and zilair formations were deposited in a suture forearc basin to the east magnitogorsk volcanic front it was not until the late devonian that these two basins were joined structural mapping combined with reflection seismic profiling shows these basins to be affected by open nonlinear volcanic basement cored synsedimentary folds the karamalytash anticline appears to have the geometry of a growth fold that formed during deposition of sediments in the suture forearc basin the forearc region is affected by minor thrusting that involves the volcanic basement although it is not clear if these thrusts reactivate preexisting trench parallel faults synsedimentary deformation slumping and olistostrome development were common throughout the suture forearc basin history but were especially widespread during the late devonian when the full thickness of the continental crust is interpreted as having arrived at the subduction zone

unstable flow magma mixing and magma rock deformation in a deep seated conduit the gil marquez complex south west spain the gil marquez complex is an exceptional outcrop of plutonic rocks ranging in composition from diorites to granites emplaced into devonian terrigenous metasediments of the southernmost part of the hercynian basement of iberia a combined study of this complex including field geology petrology structural geology and geochemistry reveals that it represents an ancient conduit of magma transport through the continental crust this conduit allowed the intrusion of magmas of contrasted compositions two end members and several hybrids are identified the first end member is a biotite granite and the second is a basaltic magma generated by partial melting of a depletedmantle source both magmas rose through a common channel in which favorable conditions for unstable flow and magma mixing occurred the observed relations in the gil marquez complex show that mixing in conduits may be an important mechanism for producing homogeneous hybrid magmas

neoproterozoic early devonian magmatism in the antigonish highlands avalon terrane nova scotia tracking the evolution of the mantle and crustal sources during the evolution of the rheic ocean abstract the antigonish highlands lies in the avalon terrane avalonia in the canadian appalachians and records four episodes of continental rift related bimodal magmatism ranging in age from late neoproterozoic to middle devonian the oldest episode ca 615 ma clydesdale formation was emplaced in a local rift setting in an andean style arc when avalonia resided along the northern gondwanan margin early cambrian magmatism arbuckle brook formation occurred in a local transtensional setting after arc magmatism had given way to a san andreas type transform environment middle ordovician dunn point and bears brook formations magmatism occurred in a local rift in an ensialic island arc setting analogous to the modern taupo volcanic zone in northern new zealand after avalonia had separated from gondwana middle devonian mcarras brook formation and correlatives occurred after avalonia had collided with laurentia in each episode mafic rocks are characterized by high feot feot mgo tio2 zr y and ti y typical of differentiated within plate mafic magmas multi element spider diagrams indicate that all four episodes were generated in an enriched sub continental lithospheric mantle lil hfs and ree patterns indicate that the clydesdale dunn point bears brook and mcarras brook formations were sourced in the shallow spinel lherzolite mantle and that the arbuckle brook formation was generated in the deeper garnet lherzolite mantle in each episode coeval felsic rocks were generated by crustal anatexis taken together the sm nd isotopic data for the mafic rocks form an envelope that defines the evolution of the mantle source beneath the antigonish highlands that was enriched between 0 8 and 1 1 ga and has an average sm nd ratio of ca 0 24 a value that is typical of an enriched mantle source sm nd isotopic data for the felsic rocks are characterized by a recurrence of tdm ages between 0 95 and 1 0 ga interpreted to reflect repeated melting of the lower crust that was itself derived from a depleted mantle source between 0 95 and 1 1 ga the remarkable geochemical and isotopic similarity of the neoproterozoic to middle devonian mafic and felsic magmas indicate that the crust and sub continental lithospheric mantle beneath the antigonish highlands were coupled during the rift and drift of avalonia from the gondwanan margin during the formation of the rheic ocean in the ordovician its accretion to baltica and to laurentia in the silurian and post accretionary strike slip movement of avalon along the laurentian margin although the sm nd isotopic data suggest that avalonian basement and lithospheric mantle formed over the same time interval 0 8 to 1 1 ga the divergence of their respective envelopes with time reflects their differing end values and sm nd ratios we suggest that avalonian crustal basement and its enriched mantle were both formed between 0 8 and 1 1 ga in a panthalassa type ocean that surrounded the supercontinent rodinia and were accreted to the northern gondwanan margin at about 650 ma prior to the oldest magmatic event in the antigonish highlands

probabilistic analysis of subsidence induced strains at the surface above steep seam mining abstract using profile functions to predict subsidence induced by mining activities has two major advantages quick calculations and easy writing of computer programs capable of undertaking such calculations the possibility of quickly obtaining many subsidence profiles by slightly changing the initial data allows for a statistical approach which does not consider the value of the strain at a given point but the likelihood of finding a certain strain at such point the study of subsidence effects is more realistic with this approach and also eliminates the errors that could arise either from the estimation of the initial data or from the calculation of the strains starting from a given subsidence profile in this paper the authors present a work methodology applied to the case of a profile function developed for steep coal seams

changing mantle sources in a suture zone in the heart of pangea implications for collisional tectonics during the waning stages of ocean closure the formation and emplacement of syn collisional mafic dykes that intrude suture zones and their association with orogenic processes are enigmatic southern iberia records the late paleozoic amalgamation of pangea and exposes today a fragment of laurussia south portuguese zone which is spatially juxtaposed with autochthonous gondwana fault bounded oceanic metasedimentary rocks melanges and ophiolite complexes characterize the suture zone and are in turn crosscut by intrusive granitoid rocks and mafic dykes the generation and emplacement of these mafic dykes and their relationship to the suture zone are undetermined field evidence shows the dykes were emplaced at high angles to pre existing orogenic fabrics in the melange granitoid and metasedimentary rocks geochemical analyses major trace rare earth elements indicate the dykes exhibit a mid ocean ridge basalt signature u pb zircon geochronology reveals the crystallization age of the dykes is ca 316 ma and sm nd isotopic analysis suggests a deep mantle source taken together these data support existing temporal constraints on events leading up to the amalgamation of pangea and suggest progressive lower crustal delamination during the waning stages of continent continent collision

slab in the wrong place lower lithospheric mantle delamination in the last stage of the eastern carpathian subduction retreat a model with a new type of delamination of the lower lithospheric mantle is proposed to explain the pliocene to recent tectonic evolution of the eastern carpathians we suggest that after the continental collision in middle miocene time break off of the west dipping subducting slab occurred at a depth of 70 km slab break off propagated horizontally toward the east inducing lithospheric delamination and movement of the vrancea slab into its present position delamination was followed by rapid asthenospheric rise resulting in magma generation and the explosive alkaline basaltic magmatism of the persani mountains contamination of the former subduction related magmatic reservoirs with the alkalic basaltic material and differentiation processes produced the harghita calc alkaline and shoshonitic rocks the asthenospheric rise induced crustal uplift which is the triggering mechanism for extension and formation of the brasov gheorghieni hinterland basins the extension was accommodated by shortening and folding in the foreland the vertical vrancea slab appears in our model as a segment of delaminated lower lithospheric mantle that is seismically active due to the ongoing pull of the eclogitized oceanic crust the model explains the displaced and shallow position of the slab relative to the eastern carpathian suture zone

a reappraisal of the structure of the spanish segment of the iberian pyrite belt the major structural features of the iberian pyrite belt are described in terms of geometry deformation mechanisms scale timing kinematics and the mutual relationships among the various architectural elements the result of such an analysis allows this zone to be considered as a s verging thin skinned fold and thrust belt propagating southwards over a mid crustal basal detachment this was the response in the footwall of the suture to the major phase of hercynian oblique collision between the south portuguese plate and the ossa morena zone of the iberian autochthon this thin skinned event inverted a previous extensional structure acquired during the initial stages of the collisional process and intimately linked to the formation of the ore deposits that make this region a world class metallogenic province

geological constraints on the paleozoic tectonic evolution of tectonostratigraphic terranes in the iberian massif abstract the presence of oceanic paleozoic sequences in the iberian variscan fold belt is used to identify and separate suspected exotic terranes from a reference iberian autochthon terrane which constitutes the greater part of it in this paper the relevant data characterizing the pre accretionary evolution of the paleozoic iberian terranes are presented as well as the available evidence concerning the accretionary process itself emphasis is placed on the analysis of the sedimentary igneous and structural expression of the major events which affected the iberian terranes before during and after their amalgamation the main conclusions of such an analysis may be summarized as follows 1 a recognition of rift and passive margin stages in all the iberian massif terranes during the early paleozoic 2 b late paleozoic accretion of the exotic terranes to the iberian autochthon via a long and complex process variscan orogeny which involved initial subduction underneath the latter and eventual obduction followed by oblique collision of a promontory the iberian autochthon northwestern margin with a northwestern continental block this latter process could account for the large scale crustal imbrication shown by the northern branch of the orogen coeval with predominant strike slip faulting in the southern branch as well as with the formation of the typical arcuate shape of this orogenic belt major present uncertainties relate to the palinspastic provenance of continental suspect terranes and their correlation with similar units in other circum atlantic paleozoic orogens a discussion and speculations on this subject are dealt with in the final section of this paper

space and time in the tectonic evolution of the northwestern iberian massif implications for the variscan belt recent advances in geochemical studies of igneous rocks isotopic age data for magmatism and metamorphism quantitative pressure temperature p t estimates of metamorphic evolution and structural geology in the northwestern iberian massif are integrated into a synthesis of the tectonic evolution that places the autochthonous

crustal structure beneath the western canada sedimentary basin constraints from gravity and magnetic modelling regional gravity and magnetic anomalies that originate from crystalline basement rocks extend over many parts of the western canada sedimentary basin although these potential field anomalies provide a basis for tectonic subdivisions of the basement crust most previous interpretations of these features have been largely qualitative in nature this study focuses on numerical simulation and quantitative interpretation of five regional potential field anomalies in alberta canada for which independent constraints on crustal structure are available from lithoprobe seismic and electromagnetic studies the kimiwan high 55 n 116 w is a roughly 250 km long linear magnetic high seismic profiles across this anomaly provide evidence for a crustal scale extensional fault system that offsets the winagami reflection sequence a series of mid crustal sills we find that the magnetic anomaly can be modelled as either a 15 40 km wide zone of moderate positive susceptibility 4 5 10 3 si units in the hanging wall

skeletons and fractals a statistical approach to deep crustal seismic data processing and interpretation abstract coherent seismic reflection events are identified using seismic skeletonization an automatic pattern recognition technique in which waveforms are parameterized such that the attributes of each event are identified and stored in a relational database or event file this new approach to seismic interpretation allows statistical analyses of the attributes including estimation of scaling laws for reflectivity observed on deep seismic data and development of new filtering techniques based on characteristics such as dip and reflection event length applications of the technique to deep crustal reflection data sets from the alberta basement transect of the lithoprobe project assist interpretation in areas that lack surface outcrop or other means of relating reflections from the deep crust to the surface

probing the composition of unexposed basement south portuguese zone southern iberia implications for the connections between the appalachian and variscan orogens geochemistry and sm nd and u pb magmatic zircon isotope data from a postcollisional batholith that crosscuts the allochthonous south portuguese zone spz of southern iberia suggest that the base

an automated method for the interpretation of magnetic vertical gradient anomalies the use of airborne magnetic vertical gradient surveys is increasing interpretation however is mostly used qualitatively as an aid to geologic mapping presently quantitative interpretation techniques are based on the analysis of isolated anomalies in this paper we develop a numerical method for interpreting the magnetic vertical gradient anomalies of dipping dikes and planar geologic contacts the method is based on a linearization of the equations describing these anomalies the solution can be used to interpret isolated anomalies or whole profiles in a werner style deconvolution using data from the val d or mining area canada we have calculated magnetic models to test the interpretation technique magnetic vertical gradient profiles calculated from the interpreted models closely match the observed data

insar based model parameter estimation of probability integral method and its application for predicting mining induced horizontal and vertical displacements this paper presents a novel method for estimating the model parameters of the probability integral method pim based on the line of sight deformation derived from the interferometric synthetic aperture radar then it applies the settled pim to forward predict the horizontal and vertical displacements induced by the extraction of a new working panel the proposed method first constructed the functional relationship between the insar derived los deformation and the model parameters of pim subsequently an improved genetic algorithm ga in which gross error elimination was imposed was proposed and used to estimate the model parameters of pim with a large number of los deformation measurements the estimated model parameters and pim were then employed to forward predict the horizontal and vertical displacements induced by the extraction of a working panel simulated experiments show that the rmses of the predicted displacements along the up down west east and north south directions are 1 5 0 9 and 2 5 mm respectively real data experiments over the qianyingzi coal mining area of china indicate that the predicted displacements are highly consistent with those by field surveys with rmses of 4 1 and 3 cm for the vertical and horizontal directions respectively these imply that the proposed approach can be a very promising tool for predicting the mining induced displacements and will potentially contribute to the assessing and forecasting of possible geological hazards in the mining area

approximating edges of source bodies from magnetic or gravity anomalies cordell and grauch 1982 1985 discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks the final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes we attempt to automate their final step our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources the method applies to both local surveys and to continent wide compilations of magnetic and gravity data e g zietz 1982 simpson et al 1983a kane et al 1982

geochemistry of the peramora melange and pulo do lobo schist geochemical investigation and tectonic interpretation of mafic melange in the pangean suture zone southern iberia the peramora melange is part of an accretionary complex between the south portuguese zone a fragment of laurussia and the ossa morena zone para autochthonous gondwana and is an expression of the pangean suture zone in southwestern iberia the suture zone is characterized by fault bounded units of metasedimentary rocks melanges and mafic complexes detailed geologic mapping of the peramora melange reveals a complex pattern of imbricated schists and mafic block in matrix melanges geochemical signatures of the pulo do lobo schist pdl are consistent with derivation from both mafic and continental sources the mafic block in matrix melange displays normal mid ocean ridge basalt nmorb geochemical signature juvenile sm nd isotopic compositions and a range of zircon ages similar to those observed in the pdl suggesting a sedimentary component taken together these data suggest a complex tectonic history characterized by erosion of a nmorb source melange formation and imbrication during underplating occurring during the final stages of continent continent collision

deformation forecasting and stability analysis of large scale underground powerhouse caverns from microseismic monitoring abstract to assess the stability of the underground powerhouse caverns and analyse the failure mechanism of the surrounding rock mass at the baihetan hydropower station in southwest china a high resolution microseismic ms monitoring system was implemented in the left bank underground powerhouse caverns based on the temporal and spatial distribution of ms events the correlation between ms activities and construction was established and three damage regions for the surrounding rock mass during excavation were identified ms clusters were found to occur most often in stress concentration regions of the underground powerhouse caverns and to result from various factors including excavation induced unloading and geological structure activation the seismic source parameters i e moment magnitudes and s wave to p wave energy ratios e s e p of the three ms clusters demonstrate the different failure modes and risks of the surrounding rock mass the temporospatial evolution of the ms activities apparent stress and cumulative apparent volume in localized rock mass during the period of a typical large deformation were used to develop a comprehensive analytical method for forecasting the deformation of the surrounding rock mass thus this comprehensive analytical method which incorporates ms monitoring conventional monitoring geological survey and construction is promising for identifying the damage zones and forecasting the macro deformation of the surrounding rock mass in underground powerhouse caverns subjected to excavation

skeletonization of aeromagnetic data skeletonization is a syntactic pattern recognition method that is applied to gridded data to produce an automatic line drawing with an associated event catalog previous implementations of skeletonization have been tailored for seismic data here we modify that technique to render it more suitable for other types of gridded data with particular emphasis on aeromagnetic maps a modification from previous schemes is the use of a two pass approach to reduce the effects of an otherwise problematic directional bias that discriminates against events oriented parallel to columns of the grid the method can be used effectively for filtering aeromagnetic data on the basis of strike direction event linearity event amplitude and polarity it is based on the delineation of peak trough pairs cycles which are traced throughout the grid to form contiguous events cycles and events are characterized by attributes that include amplitude polarity and pulse width events are further characterized by length average strike direction and linearity the event attributes are stored in a catalog thus enabling one to perform attribute based analysis and data filtering we illustrate our algorithm using two regional aeromagnetic examples from different parts of the canadian shield the first from the great slave lake shear zone is dominated by linear anomaly trends produced by faults and mafic dikes the second from the manicouagan region of northeastern quebec contains abundant subcircular and arcuate anomaly patterns caused by large intrusive complexes and a meteorite impact structure

crustal melting and recycling geochronology and sources of variscan syn kinematic anatectic granitoids of the tormes dome central iberian zone a u pb la icp ms study in this study we report u pb laser ablation icp ms zircon and id tims monazite ages for peraluminous granitoid plutons biotite muscovite cordierite sillimanite in the tormes dome one of the gneiss cored domes located in the central iberian zone of the variscan belt of northern spain textural domains in zircon interpreted to represent the magmatic crystallization of the granitoids and one monazite fraction in the ledesma pluton yielded ages around 320 ma in agreement with other geochronological studies in the region this age is interpreted to date the timing of decompression crustal melting driven by the extensional collapse of the orogenic belt in this domain of the variscan chain of western europe in addition there are several populations of inherited xenocrystic zircon 1 carboniferous zircon crystals ca 345 ma as well as one of the monazite fractions in the coarse grained facies of the ledesma pluton that also yielded an age of ca 343 ma 2 devonian silurian zircon xenocrysts with scattered ages between ca 390 and 432 ma 3 middle cambrian ordovician ca 450 511 ma 4 ediacaran cryogenian zircon ages ca 540 840 ma 5 mesoproterozoic to archaean zircon 900 2700 ma the abundance of carboniferous inherited zircon shows that crustal recycling cannibalization may often happen at a fast pace in orogenic scenarios with only short lapses of quiescence in our case study it seems plausible that a crustal layer of ca 340 ma granitoids migmatites was recycled partially or totally only 15 20 my after its emplacement

automatic boundary extraction from magnetic field data using triangular meshes boundary extraction is a collective term that we use for the process of extracting the locations of faults lineaments and lateral boundaries between geologic units using geophysical observations such as measurements of the magnetic field the process typically begins with a preprocessing stage where the data are transformed to enhance the visual clarity of pertinent features and hence improve the interpretability of the data the majority of the existing methods are based on raster grid enhancement techniques and the boundaries are extracted as a series of points or line segments in contrast we set out a methodology for boundary extraction from magnetic data in which we represent the transformed data as a surface in 3d using a mesh of triangular facets after initializing the mesh we modify the node locations such that the mesh smoothly represents the transformed data and that facet edges are aligned with features in the data that approximate the horizontal locations of subsurface boundaries to illustrate our boundary extraction algorithm we first apply it to a synthetic data set we then apply it to identify boundaries in a magnetic data set from the mcfaulds lake area in ontario canada the extracted boundaries are in agreement with known boundaries and several of the regions that are completely enclosed by extracted boundaries coincide with regions of known mineralization

fractals in deep crustal seismic reflection profiles application of a syntactic pattern recognition technique seismic skeletonization to deep crustal seismic reflection data allows attributes such as energies lengths and dips to be associated with individual reflection events some of these attributes exhibit fractal properties e g the relationship between seismic event lengths and their spatial distribution throughout the crust this approach provides a new technique to analyse complex geometry on seismic reflection data

analysis of the evolution of ground movements in a low densely urban area by means of dinsar technique abstract this paper presents an application example of the use of the differential interferometry synthetic aperture radar technique dinsar for monitoring ground movements in a geologically complex area around the village of suria ebro basin catalonia ne spain associated to underground mining activities and to the presence of a salt dome the analysis has been mostly performed in a rural environment affected by ground movements with different patterns magnitudes and causes a total of fifty sar images recorded between 1995 and 2007 were processed to generate the interferograms in order to study the non linear trends or changes of the ground surface behavior the dinsar technique was applied in two sets of images the interferometric results in the form of vertical displacement rate maps were checked against conventional surveying and gps measurements the results present a significant discrepancy in some location due to the wrapping of the phase when both fast and significant deformations occur in order to avoid the latter effect and improve the accuracy of the results all sar images were reprocessed using topographic leveling and gps data of different monitored points to support the dinsar interpretation a detailed geological reconnaissance of the study area was carried out as well as an inventory of ground movement indicators four different patterns of ground movement have been identified active shifting subsidence associated to the progression of the mining exploitation fronts residual subsidence on abandoned galleries with a decreasing rate of closure uplifting due to the intrusion of the salt dome and sudden ground collapses sinkholes caused by the dissolution of soluble materials laying close to the ground surface

the historical development of the magnetic method in exploration the magnetic method perhaps the oldest of geophysical exploration techniques blossomed after the advent of airborne surveys in world war ii with improvements in instrumentation navigation and platform compensation it is now possible to map the entire crustal section at a variety of scales from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale methods of data filtering display and interpretation have also advanced especially with the availability of low cost high performance personal computers and color raster graphics the magnetic method is the primary exploration tool in the search for minerals in other arenas the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications such as locating intrasedimentary faults defining subtle lithologic contacts mapping salt domes in weakly magnetic sediments and better defining targets through 3d inversion these new applications have increased the method s utility in all realms of exploration in the search for minerals oil and gas geothermal resources and groundwater and for a variety of other purposes such as natural hazards assessment mapping impact structures and engineering and environmental studies

highly depleted oceanic lithosphere in the rheic ocean implications for paleozoic plate reconstructions the rheic ocean formed at ca 500 ma when several peri gondwanan terranes e g avalonia and carolinia drifted from the northern margin of gondwana and were consumed during the late carboniferous collision between laurussia and gondwana a key event in the formation of pangea several mafic complexes ranging in age from ca 400 330 ma preserve many of the lithotectonic and or chemical characteristics of ophiolites they are characterized by anomalously high end values that are typically either between or above the widely accepted model depleted mantle curves these data indicate derivation from a highly depleted hd mantle and imply that i the mantle source of these complexes displays time integrated depletion in nd relative to sm and ii depletion is the result of an earlier melting event in the mantle from which basalt was extracted the extent of mantle depletion indicates that this melting event occurred in the neoproterozoic possibly up to 500 million years before the rheic ocean formed if so the mantle lithosphere that gave rise to the rheic ocean mafic complexes must have been captured from an adjacent older oceanic tract the transfer of this captured lithosphere to the upper plate enabled it to become preferentially preserved possible mesozoic cenozoic analogues include the capture of the caribbean plate or the scotia plate from the pacific to the atlantic oceanic realm our model implies that virtually all of the oceanic lithosphere generated during the opening phase of the rheic ocean was consumed by subduction during laurentia gondwana convergence

progressive magmatism and evolution of the variscan suture in southern iberia magmatic activity is an integral component of orogenic processes from arc magmatism during convergence to post collisional crustal melting southern iberia exposes a late paleozoic suture zone within pangea and where a crustal fragment of laurussia south portuguese zone is juxtaposed with parautochthonous gondwana ossa morena zone fault bounded oceanic metasedimentary rocks melanges and ophiolite complexes characterize the suture zone and are intruded by plutonic rocks and mafic dykes the generation and emplacement of these intrusive rocks and their relationship to development of the suture zone and the orogen are undetermined field evidence combined with u pb zircon geochronology reveals three main phases of plutonism a pre collisional unfoliated gabbroic phase emplaced at ca 354 ma crosscut by a syn tectonic ca 345 ma foliated granodiorite phase followed by a ca 335 ma granitic phase geochemical analyses major trace rare earth elements indicate that the gabbro exhibits a calc alkaline arc signature whereas the granodiorite and granite are typical of post collisional slab break off taken together these data demonstrate a protracted development of the orogen and support a complex late stage evolution broadly similar to the tectonics of the modern eastern mediterranean in this scenario the highly oblique closure of a small tract of oceanic lithosphere postdates the main collision event resulting in escape of parautochthonous and allochthonous terranes toward the re entrant

comparative evolution of the iapetus and rheic oceans a north america perspective abstract differences in the origin and evolution of the iapetan and rheic oceans profoundly affected the development of the ouachitan appalachian variscan orogen the iapetus ocean was initiated in the late neoproterozoic early cambrian by the separation of large continental landmasses laurentia baltica gondwana whereas the rheic ocean originated in the late cambrian early ordovician as the result of the separation of several ribbon continents collectively termed peri gondwanan terranes from the northern margin of gondwana compared to the classic passive margin developed along the laurentian margin of iapetus passive margin successions to the rheic ocean are more limited in extent during convergence both margins of the iapetus ocean developed western pacific type arc back arc systems whereas subduction of the rheic ocean was primarily directed beneath laurentia and was andean in style closure of iapetus involved a number of arc back arc accretionary events and had occurred by the middle silurian as a result of laurentia baltica collision to form laurussia and the accretion of the peri gondwanan terranes rheic ocean closure occurred in the carboniferous by way of continent continent collision between laurussia and gondwana with gondwana on the lower plate within iapetus the formation of ophiolites occurred early in the orogenic cycle and was followed soon after by obduction hp lt metamorphism and foreland directed thrusting that is intimately related to accretionary events these features dominate the northern appalachian orogen where ht lp metamorphism is attributed to post accretionary slab break off events in contrast hp lt metamorphism within the rheic ocean reflects a type subduction during laurussia gondwana collision and is rapidly succeeded by ht lp metamorphism attributed to orogenic collapse ophiolites are rare and were formed either very early early ordovician or very late devonian carboniferous in the evolution of the ocean the early ordovician ophiolites were not obducted until the carboniferous at least 100 million years after their protoliths were formed rheic ocean closure resulted in the formation of large scale bivergent structures within the orogen with symmetry changing on either side of the rheic suture comparison of the evolution of the iapetus and rheic oceans suggests that differences in rift configuration passive margin development and subduction zone geometry within the two oceans profoundly influenced the subsequent style of orogenesis within the ouachita appalachian variscan orogen