regional variations in deformation mechanisms and structural styles in the central appalachian orogenic belt orogenic belts such as the central appalachian fold and thrust belt consist of distinct tectonic provinces characterized by different structural styles as a result of deformation under different physical conditions a quantitative study of deformation mechanisms was undertaken for quartzites and sandstones of the central appalachian orogenic belt in order to understand the controls of different physical parameters on the relative importance of these mechanisms and on the geometry and mechanics of formation of structures in the different provinces in the blue ridge province the dominant deformation mechanisms are pressure solution dislocation creep and extension fracturing with some accompanying grain boundary sliding and recrystallization the proportion of dislocation creep to pressure solution strain increases both with temperature and deviatoric stress an axial plane slaty cleavage which contains the maximum and intermediate principal directions of the strain ellipsoid maintains a uniform orientation in both the blue ridge and the great valley provinces folds in the blue ridge province have a similar geometry formed by progressive flattening of parallel folds due to internal deformation ductile deformation zones on the overturned limbs of folds acted as precursors for the propagation of thrust faults in the late stages of folding in the valley and ridge and massanutten synclinorium important deformation mechanisms in the sandstone units include pressure solution plastic deformation cataclasis brecciation extension fracturing and slip along minor faults and bedding planes major folds are strongly disharmonic and show variations between concentric and angular geometries they are associated with thrust ramps that propagated through progressively developing folds in the late stages of folding brittle deformation zones characterized by high intensities of extension fractures and cataclastic bands formed on the steep forelimbs these features are interpreted to be the result of layer parallel extension and the propagation of splay faults through these limbs cleavage developed during layer parallel shortening prior to the onset of folding and was rotated to its present fanned geometry during folding on the basis of the results of this study the central appalachian orogenic belt can be subdivided into two deformational provinces dominated by different deformation mechanisms and characterized by different geometries and mechanics of formation of the structures for orthoquartzites the tectonite front which separates the tectonites of the hinterland from the non tectonites of the foreland is located along the blue ridge front for carbonates and argillaceous sandstones the tectonite front is located along the north mountain fault

de glauconiarum origine the glauconitic facies is widespread on present day continental shelves from 50 s to 65 n and at water depths between 50 and 500 m and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m it is also common in many ancient rocks of post late precambrian age it occurs as sand to pebble sized essentially green particles granular facies but also as a surface coating on particles and hardgrounds and as a diffuse impregnation film and diffuse facies we suggest the replacement of the term glauconite which has been interchangeably used to designate a morphological form and a specific mineral by glaucony facies and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family the widely accepted model of burst and hower for glauconitization requires a degraded micaceous 2 1 layer lattice structure parent clay mineral however detailed analysis of numerous samples of recent glaucony reveals that such a parent substrate is exceptional the model therefore requires modification generally the parent material is carbonate particles argillaceous kaolinitic faecal pellets infillings of foraminiferal tests various mineral grains and rock fragments that pass gradually into the commonly occurring green grains we show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate accompanied by progressive alteration and replacement of the substrate it is this two fold evolution that causes the verdissement of granular substrates macrofossils and hardgrounds the authigenic mineral is an iron rich and potassium poor glauconitic smectite while new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium producing decreasingly expandable minerals with a non expandable glauconitic mica as the end member this mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony four categories nascent little evolved evolved and highly evolved glaucony are distinguished glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro environment and ambient open marine sea water the optimum conditions for glauconitization are those of semi confinement as a result the interior of a grain is more glauconitized than its less confined periphery similarly for identical substrate types large grains 500 m provide more favourable substrates for glauconitization than lesser confined small grains on a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing low accumulation rates expose grains to the open marine environment for sufficiently long times 105 106 years for highly evolved glaucony

provenance of cenozoic sedimentary rocks from the sulaiman fold and thrust belt pakistan implications for the palaeogeography of the indus drainage system abstract the provenance of middle eocene to early miocene sedimentary rocks cropping out in the sulaiman fold and thrust belt has been determined examining the mineralogy bulk rock major and trace elements and nd sr isotopes the older 50 30 ma deposits are characterized by a mixed orogenic provenance with a major contribution from the karakorum and the tethyan belt c 80 as the 50 30 ma deposits have a provenance distinct from that of coeval subathu khojak and ghazij shallow marine formations of india and pakistan we propose that they were deposited as a distinct delta system that once fed the palaeo indus fan we document a major change in provenance that occurred before the early late oligocene transition at c 30 ma this change in provenance is marked by the appearance of chlorite and monazite and a shift toward more radiogenic nd sr isotopic compositions we interpret this change as the result of the exhumation and erosion of the proto higher himalaya the 30 15 ma sampled rocks are characterized by a major contribution from the tethyan belt and the higher himalayan crystallines 70 90 and a subordinate contribution 10 30 from the karakorum ophiolitic suture and trans himalaya as the end 0 values of our 30 15 ma samples are similar to those of the palaeo indus fan deposits we suggest that the 30 15 ma sedimentary rocks of the sulaiman fold and thrust belt were the fluvial onshore record of the indus fan other coeval deposits of india and pakistan recorded similar increasing exhumation of the higher himalaya range so that we postulate that these sedimentary rocks all derived from the palaeo indus drainage basin this would suggest that the modern indus drainage basin is no younger than 30 ma

seismic data geometry evolution and shortening in the active sulaiman fold and thrust belt of pakistan southwest of the himalayas surface and subsurface data from the sulaiman fold and thrust belt are integrated to analyze the deep structure tectonic shortening and kinematics of the sulaiman fold and thrust belt at the western margin of the indian subcontinent seismic reflection data show that nearly all the 10 km thick sequence of dominantly platform 7 km and molasse strata is detached at the deformation front these strata thicken tectonically to about 20 km in the hinterland without significant thrust faults in the foreland a balanced structural cross section suggests that structural uplift in the sulaiman fold and thrust belt is a result of a thin skinned passive roof duplex style of deformation the duplex sequence consists of jurassic and older strata it is separated from the roof equence by a passive roof thrust in thick cretaceous shales that has a backthrust sense of displacement over foreland propagating duplexes the roof sequence with incipient out of sequence thrusting is intact for about 150 km northwards where it emerges along a passive backthrust sequential restoration of the balanced section reveals a series of structural and geometrical features including 1 development of low amplitude broad concentric detachment folds sui and loti at the tip of the decollement 2 increase in amplitude of a detachment fold to a critical level for development of ramp and duplex structures and 3 out of sequence thrusting to create required critical taper for an outward translation of the foreland fold and thrust belt a balanced structural cross section 349 km long from the sulaiman fold and thrust belt restores to an original length of 727 km suggesting a maximum of 378 km of shortening since 21 ma in the cover strata of the indian subcontinent calculation of displacement rates over the sulaiman fold and thrust belt 18 mm yr added to the resolved rate of the chaman fault vector for the component parallel to the plate convergence direction 15 mm yr are close to the current india asia plate convergence rate 37 mm yr

the assessment of ree patterns and 143nd 144nd ratios in fish remains abstract the ree content and isotopic composition of sr and nd have been determined in fish teeth ranging in age from the trias to the present and from various localities mostly around the atlantic these measurements have been carried out on selachian and teleost remains from the same locality in togo and show no appreciable difference which suggests with the help of a mass balance calculation of the ce anomaly that diagenetic effects are not responsible for the ree enrichment of biogenic phosphates one group of fossil teeth has about 3 times the ree abundances of shale and a shale normalized pattern with a minimum at sm it is thought to reflect deposition in the open sea environment a second group has ree concentration about 10 times higher than the first group with either a regular light ree enrichment or more frequently a maximum in the middle ree both being probably indicative of deposition in estuarine or near shore conditions the shape of the ree spectra and the size of the ce anomaly can be used semi quantitatively to determine the depth of deposition the results presented here on late cretaceous eocene fish teeth samples from morocco reflect an increasing influx of deep waters with a lowla yb ratio and strong negative ce anomaly which agrees well with the evolution of sediment chemistry and microfauna associations in contrast nd is typical of the water mass in which the fish debris decayed examples of nearly isolated basins identified with nd isotopes include the south atlantic prior to the lutetian nd 13 5 the miocene persian gulf nd 3 1 and bolivia during the late cretaceous nd 12 8 togo and guinea bissau results suggest that in the south atlantic the meridional oceanic circulation had not started before 45 ma ago combination of ree and nd data suggests that the assignment of jurassic cretaceous samples measured so far to open sea water masses is still ambiguous

limitations of rupture forecasting exposed by instantaneously triggered earthquake doublet assessments of earthquake risk often assume rupture of a single fault analysis of a 1997 pakistan earthquake reveals that not one but two separate ruptures caused the shaking implying that cascading events should be factored into forecasts

pop up structure in massive carbonate hosted fold and thrust belt insight from field mapping and 2d kinematic model in the central apennines abstract fold and thrust belts are characterized by the occurrence of foreland verging thrusts and antithetic backthrust which develop in the hangingwall of thrust sheets both thrust and backthrust bound the so called pop up structure which is a deformed zone characterized by thrust and backthrust related anticlines pop up structures mainly develop in fold and thrust belts characterized by a multilayered sedimentary sequence consisting of limestones marls and shales deformed above a weak decollement such as evaporites however in this work we combine field mapping stratigraphic constrains and structural analysis with 2d kinematic forward modeling to document a pop up structure developed within limestones dolostones deformed above a strong decollement consisting of dolostones in the central apennines italy in particular we describe a sw verging anticline and a ne verging anticline in the sw and ne margin of the serra lunga ridge respectively such folds were generated by a ne dipping backthrust and by sw dipping forethrust respectively therefore we suggest that the serra lunga ridge represents a pop up structure showing geometries similar to other pop up structures observed within fold and thrust belts characterized by a multilayered sedimentary sequence in addition backlimb tilting of backthrust related anticlines generates the forelandward dipping monoclines observed within thrust sheets in the central apennines and in several fold and thrust belts worldwide

hydrocarbon possibilities of concealed mesozoic paleogene sediments below himalayan nappes reappraisal hydrocarbon exploration of the ganga ganges and sub himalayan basins indicates the presence of upper neogene quaternary continental molasse and the absence of paleogene sediments regarded as hydrocarbon source beds marine to brackish water paleogene lower neogene sediments closely fringing the sub himalayan foothills increase in thickness northward their presence and facies in the frontal schuppen zone and in the lesser himalayan windows commonly in close association with upper mesozoic shelf sediments indicate a formerly greater width for the late mesozoic early neogene shelf miogeosynclinal basin the pre tertiary rocks of the lesser himalayas are in nappes floored by the flat lying sole thrust redesignated the main boundary thrust mbt schuppen structure and ateral shortening complicate the geometry of the mbt downfaulted klippen and decken also are present in grabens of pre tertiary rocks in the sub himalayan schuppen zone pre tertiary tectonic grain and metamorphism ubiquitously developed within the lesser himalayan cover rocks are typically absent in the subjacent paleogene lower neogene window zone sediments deformations within the latter are much less than in pre tertiary cover rocks with which they are commonly intersliced owing to the development of schuppen structure tertiary deformations are unlikely to affect adversely the possible hydrocarbon resource within the thick mesozoic lower neogene autochthonous sediments or those which have migrated to the lesser himalayan cover rocks this opinion is corroborated by a few oil and gas shows from the eocene limestone outcrops close to the mbt and also from the lesser himalayan pre tertiary metamorphic cover rocks

secular variation in the isotopic composition of nd in tethys seawater abstract this preliminary nd isotopic study of authigenic glauconites that are mineralogically chemically isotopically rb sr k ar and stratigraphically well characterized suggests that these minerals can be used to determine the nd isotopic evolution of ancient ocean water generally glauconites indicate the same evolutionary history of nd in tethys seawater as published data for marine phosphates e g fish remains mn ores and fossil debris the initial nd values define a smooth curve with lowest values of 9 to 10 for the cretaceous and lower tertiary highest nd values have been found for 150 200 ma tethys seawater that was influenced by both a nonradiogenic continental component and a greater input of young mantle derived material

structural interpretation of the eastern sulaiman foldbelt and foredeep pakistan the sulaiman foldbelt is an active tectonic feature on the northwestern margin of the indian plate seismic reflection data have been combined with surface geological mapping and drill hole data to interpret the structural style and tectonic shortening of the eastern sulaiman foldbelt and its adjacent foredeep the data show that the basement is more than 8 km deep near the deformation front and that it deepens towards the west the foredeep adjacent to the eastern sulaiman foldbelt is a broad synclinal structure with a steep western limb the more gentle eastern limb has monoclinal dips from near zero to 2 5 several salt cored anticlines are observed on the eastern part of the monocline but the salt structures are lacking in the western foredeep and in the frontal part of the sulaiman foldbelt the basal decollement under the sulaiman lobe lies either in ductile eocambrian salt or within a deep zone of other material that undergoes ductile behavior near the deformation front ramps from the basal detachment become flats in lower triassic and lower cretaceous shales a steep and highly elevated zone immediately to the west of the frontal folds is interpreted to be underlain by a passive roof duplex the culmination wall of this oblique duplex is separated from the overlying roof sequence by a passive roof thrust in lower cretaceous shales the roof thrust has a backthrust sense of movement relative to the forelandward propagating duplex and may extend obliquely 100 km into the interior of the foldbelt fault propagation and fault bend folds are present in the frontal portion of the eastern sulaiman foldbelt palinspastic restoration of a balanced cross section shows 108 km of shortening in the eastern sulaiman foldbelt east of the kingri strike slip fault the presence of more than 11 km of pre neogene strata on top of basement suggests that the mesozoic rifted margin of the indian subcontinent may lie beneath the sulaiman foldbelt this interpretation is also favored by the presence of ophiolites and flysch deposits overthrusted on late cretaceous shelf strata

focal mechanisms and depths of earthquakes in central pakistan a tectonic interpretation focal mechanisms and depths for seven earthquakes in central pakistan were determined from an analysis of rayleigh waves of 20 to 50 s periods in east central pakistan the nodal planes for some solutions strike obliquely to the grain of surface structures this observation supports the contention of other workers that a thin surficial unit decoupled from the basement along a surface of decollement characterizes this region in west central pakistan relative movement between the indian and eurasian plates is at least partially accommodated by seismic slip along the chaman fault other faults which are situated to the east of and lie subparallel to the chaman fault may also take up some of the relative plate motion observed activity within the zone of convergent type structure in central pakistan may be a result of the greater component of convergence across the indian eurasian plate boundary north of quetta pakistan appendix is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 010 2 50 payment must accompany order

comparison of rb sr and k ar dates of middle eocene bentonite and glauconite southeastern atlantic coastal plain rb sr and k ar dates for euhedral biotite from high mg chetotype smectitic bentonite in glaucony bearing beds of the middle eocene lutetian castle hayne limestone indicate deposition of volcanic ash in the north carolina coastal plain at 46 ma five evolved high potassium glauconitic micas from 30 35 cm below the bentonite yield a rb sr isochron date of 45 3 0 3 ma and an initial 87 sr 86 sr ratio of 0 70764 0 00015 a single split yields a conventional k ar date of 46 7 1 8 ma six evolved high potassium glauconitic micas from 25 30 cm above the bentonite yield a rb sr date of 43 1 1 2 ma and an initial 87 sr 86 sr ratio of 0 7079 0 00011 a single split yields a conventional k ar date of 44 5 1 7 ma agreement of rb sr and k ar biotite dates in the bentonite with rb sr and k ar glauconitic mica dates in the underlying and overlying carbonate suggests that carefully selected evolved glauconitic mica that has neither been deeply buried nor experienced cation exchange with ground water can provide reliable isotopic ages and constraints for the standard geologic time scale

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

changes in paleocurrents during the development of an obliquely convergent plate boundary sulaiman fold belt southwestern himalayas west central pakistan abstract pre orogenic cretaceous shelf sandstones at the northern and southern ends of the sulaiman range in west central pakistan show basically westward dispersal which is off the craton however paleocene marine sandstones in the south spread east southeast and early eocene deltaic sandstones in the north spread southeast and north these are mostly onto the craton and indicate slope reversal of the cretaceous shelf post oligocene fluvial molasse shows mostly southward drainage a 3852 m section of molasse in the northern sulaiman range comprises a lower 2378 m of claystones and upwardly fining sandstones that represent meandering rivers and an upper 1474 m that are dominated by conglomerates that represent gravelly braided rivers paleocurrents in the lower meandering part of the section were generally southward but very variable whereas those in the upper braided part were more uniform and show eastward flow a 3146 m section of molasse in the southern sulaiman range comprises 1 a basal 1160 m sequence of claystones and sandstones meandering streams with very diverse flow directions overall to the southwest 2 a middle 1603 m sequence dominated by pebbly sandstone with large bedforms big sandy braided rivers with less diverse flow to the southwest and 3 an upper 383 m conglomeratic sequence gravelly braided streams that still flow uniformly southwest rivers in the early molasse paralleled the modern sulaiman range in the north and flowed obliquely into it in the south which suggests no uplift of the modern front of the range until the onset of modern transverse eastward drainage and the associated influx of conglomerates in present and admittedly uncertain lithostratigraphic terms uplift of the modern front of the range apparently began about 700 m lower in the north than in the south the northern and southern molasse sections otherwise show broadly similar histories of river development

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

gravity and tectonic model across the sulaiman fold belt and the chaman fault zone in western pakistan and eastern afghanistan abstract gravity data from the western boundary of the indian subcontinent have been analysed to infer the gross crustal structure across the indian afghan collision zone seismic reflection profiles reveal the gross structural duplex geometry of the sulaiman fold belt these data show that the wedge which is 10 km thick at the deformation front thickens northwestward to attain a tectonic thickness thickness due to deformation of about 20 km in the hinterland gravity modeling depicts the depth of the moho between 33 and 35 km at the deformation front of the sulaiman fold belt the moho depth shows an upward convexity along an e w profile it decreases northward with a gentle gradient of 1 1 20 m km below the sulaiman fold belt and then deepens abruptly with a gradient of about 7 8 136 m km across the chaman fault zone attaining a depth of about 57 km in eastern afghanistan the model suggests that the sulaiman fold belt is underlain by transitional crust 15 27 km thick in contrast to the continental crust 38 km thick underneath the fold belt of the himalayan collision zone in northern pakistan the about 57 km thick crystalline crust in eastern afghanistan may be due to 1 underplating by crust of the indian subcontinent and 2 structural thickening within the afghan block

the effects of spall on regional seismograms the effects of spall on regional signals are investigated using synthetic seismograms to frequencies of 20 hz depending on the scaling relationships used it is found that spall may have an important effect on regional body waves and especially surface waves the frequency range in which the spall effect dominates is dependent upon the characteristic times of the spallation process but generally occurs in the frequency range of about 0 2 to 2 hz because of the peaked nature of the radiated spall spectra effects at frequencies outside the 0 2 to 2 hz frequency range will be dominated by the explosion source the frequency range and strength of the spall effect depend in a complicated manner upon the yield depth of burial near source structure and material strength uncertainties in the spall scaling relationships need to be better understood before the effects of spall on regional discrimination and yield estimation can be properly quantified copyright american geophysical union 1989

geometry and development of zindapir anticlinorium sulaiman range pakistan abstract surface geological field and landsat images and subsurface geophysical seismic reflection and borehole data were analyzed for geometry and development of n s oriented frontal zindapir anticlinorium in the sulaiman range pakistan the anticlinorium with its four segments of structural relief salients north to south as dhodak rodho affiband and zindapir extends over about 130 km with east vergence of the fold axis of general ns trend highly oblique to the plate convergence vector based on seismic and well data correlation sedimentary strata are interpreted with an east to west increase in thickness over the basement along the western passive margin of the indian plate the basement is modelled to have ns trend with gentle 2 5 westward dip ns well correlation along the fold axis and seismic reflection interpretation depict structural relief of 2 4 km along different salient s based on seismic reflection profiles shallow rooted pop ups in tertiary and cretaceous strata are interpreted contrary to their earlier interpretation as thick skinned structures the core of the anticlinorium is occupied with duplication of jurassic and older triassic strata of flat ramp flat geometry as a fault bend fold and an anticlinal stack due to variable shortening from edges to the centre across strike of the anticline it is interpreted to develop along lateral ramps oblique to the direction of tectonic transport along the eastern edge of the sulaiman fold belt sfb shortening along the zindapir anticlinorium reflects a fraction of 37 mm yr convergence along thrust faults of flat and ramp geometry the zindapir anticlinorium serves an example for better understanding of oblique mountain fronts active tectonics and hydrocarbon exploration in the region

genesis and evolution of hydrocarbons entrapped in the fluorite deposit of koh i maran north kirthar range pakistan abstract the exceptional development of coeval hydrocarbon and aqueous fluid inclusions fi in fluorite from the mvt type ore deposit of koh i maran baluchistan north kirthar range pakistan provides samples which are representative of the ore forming fluid and which support the hypothesis of petroleum migration in the province primary brines at 125 c 10 wt equ nacl and secondary ch 4 rich brines at 135 c 7 wt equ nacl are recognised to be associated with oil migration in the fluid inclusions they support the model of a per ascensum mvt mississippi valley type stratabound hydrothermal deposit a pressure temperature path of 120 125 c to 165 200 bars is calculated from microthermometric data and pvt modelling of hydrocarbon fi using the modified peng robinson equation of state ifp software from primary cogenetic inclusions oil and brines the composition of gas and oil fractions is obtained by a combination of synchrotron ftir microanalysis and gas chromatography performed on individual fluid inclusions the oil entrapped as a coeval primary fluid phase is a light aliphatic normal oil in the range c 8 c 35 with a high co 2 content the brown solid phase found systematically in the oil is probably asphaltene resulting from precipitation after trapping of the heavy fraction which commonly occurs by decreasing pressure and temperature and or by co 2 injection later ch 4 rich brine influx probably modified part of the oil in the primary fluid inclusions because degraded oil is observed within such inclusions biomarkers obtained by gc ms analysis indicate a terpane distribution quite similar to the nearest oil seepage in the gokurt area this result and the high co 2 content of organic fluid inclusions indicate a restricted confined sedimentary environment for the source rock which could correspond to the eocene carbonate formation with type ii organic matter a possible additional input of gas from the sambar formation is suggested as feasible the link between the fluid inclusion data and the geodynamic evolution lead us to propose a circulation of basinal fluids driven mainly by the fault system during dewatering in the foredeep in pakistan they are coeval to major compressional nw se oligocene episode in the thrust belt the origin of the fluorine may be found in the basin sediments as well as near the basement the brines originated in salt structures recognized in eocambrian at the decollement level the source rock was already mature

development and testing of a 3d velocity model for improved event location a case study for the india pakistan region 3d velocity models will play an important role in improving location accuracies of small events within the context of a comprehensive nuclear test monitoring treaty commonly such models are developed using tomographic methods that require the initial velocity model to be a reasonable approximation of the true earth structure in this article we present a method for the development of an a priori model for the crust and upper mantle in the india pakistan region and techniques for evaluating its suitability for use as an initial model in tomographic studies we developed the weston india pakistan 3d velocity model winpak3d by integrating the results of more than 60 previous studies related to crustal velocity structure in the region a well located event that occurred near nilore pakistan on 14 february 1977 provided a basis for testing the model via several different approaches evaluation of the 3d model included 1 cross validation analysis 2 comparison of model determined hypocenters with a known event location and 3 comparison of model based and empirically derived travel time correction surfaces generated for an event within 5 km of the seismic station at nilore the 3d model is demonstrated to improve the regional location of the 1977 event as compared to 1d models the epicenter mislocation using the first arrival phase at 23 regional stations determined by the 3d model was only 6 2 km compared to 13 1 km and 15 4 km for a regional 1d model and the iasp91 model respectively results of extensive testing demonstrate that winpak3d will be a particularly good initial model for tomographic studies as it improves regional location accuracy specifically for sparse networks these results demonstrate that 3d velocity models are essential for improving location accuracy in regions that have complicated crustal geology and structures such 3d models may be a prerequisite for achieving location accuracies as called for by the comprehensive nuclear test ban treaty particularly for small events that are not recorded teleseismically

structural interpretation of frontal folds and hydrocarbon exploration western sulaiman fold belt pakistan abstract seismic reflection profiles and borehole data combined with geological mapping was used to analyze foreland structures with 3 d structural variation estimates of shortening and kinematic evolution of western sulaiman fold belt sfb pakistan the western sfb is interpreted with passive roof duplex geometry the floor thrust decollement is interpreted in triassic strata rather than its inference in precambrian cambrian evaporites whereas the roof thrust upper detachment of hinterland vergence is located in eocene ghazij shale based on seismic data the folds in the frontal duplex are interpreted as fault propagation and fault bend type they are located over curved and staircase geometry of blind back thrusts the folds and thrusts of ew trend show right hand en echelon stepping along nw se oriented mountain front due to drag along the western margin of the fold belt the blind thrusts cut across the hanging wall flat of the duplex horse with roots in base triassic at depth of 4 4 5 km 3d surfaces of reservoir strata show three areas of closed elliptical contours as potential prospects over blind thrusts with maximum structural relief of 2200 m shortening of 2100 22 and 9950 m 47 is calculated along with thrusts in the frontal duplex with the interpretation of out of sequence structures passive roof duplex structures between foreland and hinterland vergent back thrusts are reported from mountain belts around the world we have identified out of sequence deformation in the frontal duplex with stacked structures identification of these features adds to our understanding of the development of mountain fronts in the context of anderson s theory of faulting with the presence of a conjugate set of faults and foreland propagation of mountain fronts with secondary out of sequence deformation subsurface seismic data appears to be critical in their recognition for analysis of active foreland deformation and assessment of hydrocarbon plays in the fold belts

interpretation of the eastern sulaiman fold and thrust belt pakistan a passive roof duplex abstract surface geology seismic reflection and well data from the eastern sulaiman fold and thrust belt sftb were integrated to analyze its structural geometry deformation style foreland structure development and tectonic shortening the n s oriented fold belt s deformation front has a monoclinal expression over 350 km along the eastern edge of the sftb the cross section shows a 9 km thickness of platform sequences that are detached from the basement by an inferred decollement in paleozoic strata the base of cretaceous strata is 6 km deep in the foredeep syncline rising 7 km in the foreland in the absence of a major thrust and is interpreted as a thin skinned passive roof duplex style of deformation the duplex sequence of jurassic and older strata are separated from the cretaceous and younger roof sequence which is intact over foreland structures for 60 km a balanced structural cross section of this area restores to an original length of 172 km implying 112 km 65 of shortening since 6 2 ma with rates of 18 mm yr this is greater than the 50 shortening along a 359 km long n s balanced cross section across the sftb but is likely to occur along stacked duplexes with high relief along the eastern sftb

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

paleomagnetic chronology fluvial processes and tectonic implications of the siwalik deposits near chinji village pakistan a 2800 m section of siwalik strata containing the stratotypes for both the chinji and nagri formations has been dated by magnetic polarity stratigraphy and the observed polarity zonation has securely been correlated with the chron 17 7 segment of the time scale the base of the section is the base of the kamlial formation which occurs near the top of chron 17 18 3 m y the kamlial chinji formation boundary occurs in the middle of chron 15 14 3 m y the chinji nagri boundary near the bottom of chron 10 10 8 m y and the nagri dhok pathan boundary at the chron 8 9 boundary 8 5 m y the siwalik deposits near chinji village consist of four distinct classes of fluvial cycles each with a characteristic periodicity a first order of 10 7 years a second order of 10 6 years a third order of 10 4 10 5 years and a fourth order of 10 0 10 4 years the river system responsible for siwalik sedimentation flowed from west to east and had properties much like the modern ganges river syste

thrust kinematics in the kohat plateau trans indus range pakistan abstract the kohat plateau consists of a heavily deformed and structurally elevated thrust sheet pop ups broad synclines and narrow fault and evaporite cored anticlines record high level translation of a large thrust mass along eocene evaporites a lower detachment level is also inferred located at the base of the mesozoic palaeozoic section this lower detachment is common to both the kohat and the adjacent potwar plateaux whereas the upper level is restricted to the kohat beneath the kohat a blind imbricate stack of pre tertiary rocks is developed above their roof thrust the foreland basin fill of kohat records greater internal deformation compared to that of the adjacent potwar plateau in contrast the potwar thrust belt displays a greater amount of overthrusting on its basal surface this displacement emerging in the salt range total shortening across the two plateaux is comparable but is accommodated in an areally smaller thrust belt with a higher structural relief in the kohat as compared to the potwar structural province the resultant geographical offset of the thrust front is denoted by the hukni kalabagh lateral ramp the differences in the thrust kinematics are tentatively suggested to be caused by the mechanical response of the orogenic wedge to different imposed geometries of the wedge laterally within the basin the kohat plateau appears to have a lower basal dip than does the western potwar and thus shows greater internal deformation

roof sequence response to emplacement of the wills mountain duplex the roles of forethrusting and scales of deformation abstract this paper focuses on the behavior of a roof sequence in the appalachian plateau of west virginia u s a and emplacement of the wills mountain duplex with 17 5 km of displacement unlike the plateau along strike in pennsylvania and new york where forethrusting was previously documented this roof sequence lacks an underlying salt dominated roof decollement kinematic analyses reveal that the roof sequence in the west virginian plateau accommodated about two thirds of the 17 5 km of shortening by the adjacent wills mountain duplex as a forethrusting kinematic response the remaining shortening imbalance of about 5 km between the duplexes and younger roof sequence rocks is accommodated by additional forethrusting further into the foreland and local compensation this kinematic response matches that along strike in the central appalachians despite the loss of the salt decollement we interpret that an ordovician shale dominated formation was sufficiently weak to substitute for the salt horizon thus a weak mechanical unit rather than specifically a salt decollement is a necessary prerequisite for forethrusting a contributing factor to forethrusting may be the subvertical front of the wills mountain duplex which inhibited other responses by the roof sequence mesoscale and smaller processes including grain to grain pressure solution twinning and cleavage formation account for over 75 of the shortening in the roof sequence and if ignored would result in an erroneous interpretation of backthrusting or local compensation this result suggests that failure to consider all deformation scales could lead to incorrect kinematic conclusions in other tectonic systems

mari bugti pop up zone in the central sulaiman fold belt pakistan abstract the sulaiman fold and thrust belt is an active tectonic feature of the himalayan mountain system in pakistan seismic reflection profiles borehole surface geology data and bouguer gravity modeling suggested a passive roof duplex geometry over a transitional crust related to the former passive margin of the indian subcontinent in the frontal part of the sulaiman fold belt a passive roof sequence of cretaceous and younger rocks is structurally uplifted at the surface the roof sequence displays a coherent stratigraphy over the underlying duplex sequence of jurassic and older strata the folds in the roof sequence reflect blind faults in the duplex sequence the duplex style of deformation persists throughout the central sulaiman fold belt however unlike the frontal sulaiman fold belt stratigraphy at the surface in the central sulaiman is disrupted by e w and ne trending faults with apparent map lengths of tens of kilometers these foreland and hinterland verging high angle faults juxtapose cretaceous rocks in the cores of tight symmetrical anticlines against eocene ghazij shale and kirthar limestone according to seismic reflection data they have only minor vertical offsets of 1 2 km and are mostly restricted to the roof sequence as a result cretaceous rocks bounded between reverse faults are exposed at the surface in the cores of tight anticlines as pop up structures this implies that 1 the exposed faults in the central sulaiman fold belt are not primary structures with major shortening and 2 recognition of these faults in the roof sequence may reflect an early stage of development of overstep back thrusts from the upper decollement passive roof thrust

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

mechanisms of thrust propagation some examples and implications for the analysis of overthrust terranes abstract evidence is presented for the existence of three fundamental mechanisms by which thrust sheets move the mechanisms are 1 failure of a stiff layer to form ramp flat geometry imbricated thrust sheets 2 detachment of a layer by folding decollement thrust sheets 3 differential layer parallel shortening lps thrust sheets the mechanisms are independent but may operate interactively to form families of hybrid thrust sheets since lps thrust sheets have not been previously described or documented data from the new york plateau deformed almost exclusively by differential lps is presented to demonstrate the physical characteristics of this thrust mechanism information from the plateau indicates that finite strain behavior closely reflects the geometric boundary conditions and is independent of temperature and depth of burial finite strain data are used to construct a set of iso strain maps in both the deformed and undeformed states the iso strain maps are in turn used to determine the displacement field for the thrust sheet the displacement field allows visualization of the effects of both lagrangian and eulerian transformations on an initially orthogonal grid utilizing sections from a number of overthrust belts it is shown that the three mechanisms occur universally although in various proportions lps is regionally developed throughout the central and northern appalachians the presence of the lps thrust sheets probably accounts for the failure of structural cross sections to bed length balance in these blind thrust terranes finally a series of examples drawn from the field as well as the literature are used to illustrate both the characteristics of hybrid thrust sheet families as well as to indicate how knowledge of their behavior can be utilized in developing strategies for the construction and balancing of structural cross sections

tectonic patterns of shortening landforms in mercury s northern smooth plains abstract mercury s northern smooth plains are volcanically emplaced units characterized by ghost craters volcanically buried impact basins and thrust fault related landforms we analyzed the thrust fault related landforms traditionally categorized as lobate scarps and wrinkle ridges within the northern plains in order to describe trends in how these landforms are organized and oriented and what style of deformation either thin or thick skinned their map patterns represent our analysis also establishes geologic constraints for which global processes may have produced stresses contributing to these tectonic patterns we mapped 4853 thrust fault related landforms in the northern plains at a map scale of 1 1 000 000 using three mercury surface space environment geochemistry and ranging messenger global monochrome mosaics these landforms described as curvi linear asymmetric ridges frequently occur in complex geometrical arrangements that are interpreted to share similar structural characteristics we called these arrangements compound landforms like prior studies we observed thrust faults to follow rims of buried craters we also observed 1 sigmoidal rises bounded by fault related landforms 2 v shaped rises composed of two landforms terminating at a single sharp point 3 broad arcuate rises of nearly equal width 4 parallel evenly spaced ridges and 5 landforms showing alternation in direction of tectonic transport along strike respectively we interpreted these landforms as transpressional uplifts faults with sharply juxtaposing ramps pop up structures fold and thrust belts and antithetic fault intersections by comparison with earth analogues and patterns produced in numerical and physical models our results suggest that deformation in the nsps is thin skinned orientation analysis showed that the northernmost landforms 90 70 n were predominantly oriented east west while most of the landforms between 50 and 30 n were oriented north south variations in orientation with latitude indicate that the growth of thrust fault related landforms was influenced by sources of stress other than global contraction if reorientation of the pole due to the formation of the caloris basin impact did occur the pattern of fault orientations indicates that geologic processes producing the pattern operated after reorientation

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex