petrology and thermal maturity of coals in the jharia basin implications for oil and gas origins abstract coals from the karharbari formation early permian the barakar formation early permian and the raniganj formation late permian of the jharia basin have distinctive petrographic characteristics the karharbari formation coals are dominated by inertinite whereas the barakar formation and the raniganj formation coals are vitrinite dominated the vitrinite and exinite content of the jharia basin coals generally increases towards the upper parts of the sequence coal facies analyses based on petrographic composition that the jharia coals were formed from woody peat facies in a fluvial environment the karharbari coals were formed in a predominantly forest swamp condition whereas the lower barakar coals were formed in mixed facies wet dry conditions the middle and upper barakar and the raniganj coals were formed under wet forest swamp conditions high rank permian coals r v max 0 93 1 27 occur near the surface in the jharia basin comparisons of the vitrinite reflectance versus depth profiles from the jharia basin samples with some known reflectance profiles indicate that 2 5 3 5 km of cover was lost in the jharia basin cover loss values extrapolated from a profile matching method show good correlation with those calculated from model temperatures the thermal history of the jharia basin suggests that the permian sections of the basin suffered a major permian triassic thermal event during this time a tensional tectonic regime probably prevailed in india possibly centred in the jharia basin this probably caused extensive subsidence and consequently a thicker sedimentary sequence was deposited in the jharia basin than in the other gondwana basins of india the early permian barakar formation is late mature to overmature this section has a high potential for oil condensate and gas generation although only condensate and gas are likely to be preserved the late permian raniganj formation is mature and the source potential for hydrocarbon generation of this section is assessed as very good however most structures within the jharia basin are probably fractured

dynamic modelling of stress accumulation in central italy we develop a viscoelastic dynamic model to calculate the stress distribution in central italy induced by different geodynamic processes likely active in the region africa eurasia convergence adriatic underthrusting subduction and asthenospheric upwelling underneath tuscany model results are compared with the hypocentral distribution of earthquakes and with the orientation of p and t axes available for the region the first order characteristics of the seismotectonic observations in central italy are subcrustal seismicity the pair extension compression in tuscany and in the outer apennines and the flexural behaviour evident in long wavelength orientation of t axes these features are reproduced by the combination of two processes underthrusting of the adriatic plate under the apennines and asthenospheric upwelling underneath tuscany the comparison with available data does not give insights about slab pull as an ongoing process

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

influences of igneous intrusions on coal rank coal quality and adsorption capacity in hongyang handan and huaibei coalfields north china article i nfo localized igneous intrusions with varying types of intrusion patterns were found in the pennsylvanian permian coals in north china five typical patterns including dike cut through pattern i dike cut in pattern ii floor intru sion by sill pattern iii roof intrusion by sill pattern iv and dual intrusions of roof and floor by sills pattern v were investigated at five different underground profiles it was found that the influence of localized intrusions on rank petrology and coal quality characteristics are mainly related to the emplacement temperature the style of heat transfer convection or conduction the intrusion forms dike or sill and size the distance from the contact and the thermal properties of the surrounding rocks at the contact of the intrusion among the five patterns only pattern v was found to have two distinct contact metamorphic aureoles within a distance of 1 2timesofthethick ness of the intrusion whereas patterns i through iv show wave like profiles of vitrinite reflectance ash and volatile matter this resulted from the typical characteristics of multiphasic and superimposed thermal metamorphic evo lution of north china coals except for the heat conduction by intrusion contact the hydrothermal convection and tectonic heat played important roles in heat transfer away from dike sill intrusion induced coal changes including coal rank organic inorganic composition and pore properties work together to influence the adsorption capacity of coals the effect of intrusion upon the adsorption capacity of altered coals is related to the values of their altered coal ranks adsorption capacity is elevated from the langmuir volume vl of 7 6 pre intrusion to 17 5 m 3 t post intrusion for altered bituminous coals and semi anthracites with vrrb2 1 in contrast the adsorption ca pacity is moderately reduced from background levels of about 27 2 m

the lower permian coal seams from singrauli coalfield m p india petrochemical nature rank age and sedimentation abstract biopetrographic and chemical investigations carried out on the lower permian barakar formation coal seams encountered in two bore holes ncsm 3 and cmsa 111 from the singrauli coalfield son valley reveal that they are in general rich in inertinite and mineral matter towards the eastern part whereas towards the western part they are rich in vitrinite with subordinate amounts of inertinite and mineral matter the turra and purewa top seams in the eastern part consist chiefly of mixed and fusic coal types and the turra and purewa merged seams in the western part of the basin are characterized dominantly by vitric and mixed coal types the basin of deposition was shallower in its major part but deepened towards west consequently frequent oxic fluctuations are most common in the coal seams of the eastern part the rank of these coal seams ranges between subbituminous a to high volatile bituminous c stages they show normal increase in rank with depth the coal seams in the western part of the area are higher in rank than their counterparts in the east the purewa bottom seam ncsm 3 is petro palynologically correlatable with the turra seam cmsa 111 of the western part it has been presumed that glossopteridophyta a complex group of gymnospermous plants arthrophytes and ferns were the vegetal source for the formation of barakar coal seams these plants during the early permian grew as thick forests along river valleys and as upland and subaquatic vegetation and experienced a warm humid and windy temperate climate the coal seams were presumably deposited in backwater and lacustrine swamps in fluvial environment from hypoauchthonous source material an attempt has been made to explain reasons for the high incidence of mineral matter and its apparent relationship with inertinite content in the coal seams while also discussing the depositional history

petrographic characteristics of the solid fuels of india with particular reference to the coking coals abstract a summary is given of the available petrographic data on indian lignites and coals the latter categorised into coking semi caking and non coking fuels as delimited by vitrinite oil reflectances the coking coals form one fifth of the total solid fuel reserves in tertiary mesozoic and gondwana rock formations an attempt is made to establish the geological factors responsible for their genesis the tertiary lignites occur in the nichahom upper siwaliks neyveli miocene panandhro eocene kalol eocene and palana paleocene lignite fields they are of meso lignitous rank and composed mainly of huminite r m only the panandhro lignite being mainly of inertinite the tertiary coals of the jammu coalfields eocene are of hypoanthracitous rank and composed essentially of vitrinite r m 2 3 and fusinite the mesozoic coal deposit at ghuneri cretaceous mainly comprises vitrinite and subordinate inertinite and is of meta lignitous rank r m 0 52 the gondwana permian coals are composed of variable proportions of vitrinite and inertinite in the main and exinite in very minor amounts showing marginal variations from one coalfield to another and significant variations from one depositional basin to another the rank of the coals varies between meta lignitous and meso bituminous r m 0 42 1 45 evaluation of the permian coals indicates that the vitrinite oil reflectance determined in vitrinite rich coal is the main parameter for delineating predicting and assigning the coking properties many of the non coking coals have a maceral microlithotype composition which prevents the formation of good quality coke even from coal of suitable rank the proportion of vitrite and clarite together is higher than that of durite and fusite in the coking coals in the non coking coals the proportion of durite and fusite together exceeds that of vitrite and clarite and of the intermediates the semi caking coals are intermediate between the coking and non coking coals the vitrinite oil reflectance ranges from 0 85 to 1 50 in the coking coals from 0 70 to 0 85 in the semi caking coals and is less than 0 70 in the non coking coals the coking coals were formed at paleodepths exceeding 3 km other factors such as geological time being equal it is assumed that the petrographic composition of the coal is a function of the rate of subsidence of the basin thus the coking potential can be predicted from the knowledge of the geological history of the gondwana coal basins

the jura mountains an active foreland fold and thrust belt abstract recently completed in situ stress measurements using the borehole slotter at 33 new test sites within the swiss and french jura mountains combined with previously published stress data allow a detailed description of the contemporary state of stress in this fold and thrust belt and the adjacent foreland five stress provinces can be recognized with two different general orientations of maximum horizontal stress sh 1 the central and southwest provinces with a nnw sse to nne ssw orientation 2 the east northwest and southeast provinces with an e w to nw se orientation stress magnitudes are in general higher in the southern than in the northern jura mountains characteristic of the northern jura is an e w trending zone of low stress magnitudes which can be traced from the bresse depression south of besancon to the eastern end of the jura northwest of zurich boundaries of stress provinces show poor agreement with boundaries of tectonic units in the jura in addition stress provinces extend beyond the boundaries of the jura mountains into their foreland furthermore palaeo stress orientations show large discrepancies with respect to the contemporary stress orientation these findings are considered to indicate a termination of jura thin skinned foreland tectonics which probably took place some time between 9 and 4 ma according to palaeontological and tectonic evidence it is suggested that a new style of tectonics has commenced in the jura mountains deforming both the basement directly below the jura fold and thrust belt and the cover rocks in a similar mode

mechanical model for subduction collision tectonics of alpine type compressional orogens alpine type orogens are characterized by three distinct convergent tectonic phases subduction with deformation that has primarily single vergence a transition from subduction to collision and continental collision with double vergence although the cenozoic history of the european alps has additional complexities a mechanical explanation for these three phases would provide the necessary crustal scale framework in which to develop an understanding of the smaller scale processes we present results from a simple numerical model which explain the mechanics of these three phases as a consequence of the changing buoyancy of the lithosphere subducted beneath the orogen the development and exhumation of a subduction complex suture zone and basement nappe stack piemont suture penninic nappes the presence of a crustal scale back fold and thrust insubric line and uplift of basement on the pro european side of the orogen external basement massifs may be explained as a simple consequence of changing dynamics during the transition from subduction to collision

microseismic signals of double layer hard and thick igneous strata separation and fracturing abstract in order to analyze the microseismic ms effects of hard and thick igneous strata separation and fracturing and the corresponding evaluation index of fracturing intensity the temporal spatial evolution of the ms sources generated by igneous strata fracturing in the 10416 working face of the yangliu coal mine ycm was dynamically recurred and the waveform and frequency spectrum distribution characteristics of primary and igneous strata fracturing were clearly investigated respectively in addition the relationship between the ms dominant frequency the energy ratio in low frequency band and the intensity of igneous strata fracturing was revealed and the energy ratio of ms event in low frequency band can be verified as an effective index for evaluating roof fracturing intensity the work may put forward a certain reference for early warning and evaluating hard and thick roof fracturing and the induced coal rock dynamic disasters based on in situ ms observation

deformation and motion in the western alpine arc we attempt to reconstruct the kinematics deformation and motion of the western alpine arc between the mercantour and aar massifs first we compile a map showing principal extension x direction within three major structural units in the external zone x directions are broadly radial to the alpine arc in the internal zone they are uniform or smoothly varying in some domains whereas in the intermediate zone they often show much scatter next we use geochronological data and p t conditions estimated from metamorphic mineral reactions to time the deformation on each of a series of interval maps we show x directions for strain accumulated during a chosen time interval we argue that these incremental x directions are approximately equivalent to segments of particle paths showing displacements relative to stable europe for 120 100 ma the displacement direction was about n150 and coeval with eclogite facies metamorphism it is interpreted as a direction of overthrusting by the african plate around 40 ma the displacement in the south part of the arc became westerly finally between 25 and 15 ma displacement directions were generally radial to the arc

petrological chemical and depositional aspects of eastern himalayan coals from elephant flat area kameng district arunachal pradesh india abstract the eastern himalayan coals of india associated with permian lower gondwana sediments in the kameng district of arunachal pradesh have petrographic and chemical properties differing from peninsular permian coals the coals are moderately to highly crushed and have reached a semianthracitic stage macerals are highly reflecting and homogenized vitrinite and inertinite exhibit a crushing effect in the form of criss cross fissures and cracks exinite is unidentifiable and has attained an inertinitic reflectivity the kameng coals are of high rank with average fixed carbon 88 75 and volatile matter 13 75 on d a f basis the reflectance values ro max 2 02 2 31 in oil of these coals are quite high with marked anisotropy it is inferred that these peculiar coal properties have been attained due to prolonged tectonic disturbance in the area during the later himalayan orogeny the coal characteristics suggest that these coals were formed in a humid tropical climate within a deltaic regime the depositional site experienced occasional marine influx due to tectonically controlled subsidence during peat accumulation

geodetic measurements of crustal deformation in the western mediterranean and europe geodetic measurements of crustal deformation over large areas deforming at slow rates 5 mm yr over more than 1000 km such as the western mediterranean and western europe are still a challenge because 1 these rates are close to the current resolution of the geodetic techniques 2 inaccuracies in the reference frame implementation may be on the same order as the tectonic velocities we present a new velocity field for western europe and the western mediterranean derived from a rigorous combination of 1 a selection of sites from the itrf2000 solution 2 a subset of sites from the european permanent gps network solution 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy on the order of 1 mm yr or better its analysis shows that central europe behaves rigidly at a 0 4 mm yr level and can therefore be used to define a stable europe reference frame in that reference frame we find that most of europe including areas west of the rhine graben the iberian peninsula the ligurian basin and the corsica sardinian block behaves rigidly at a 0 5 mm yr level in a second step we map recently published geodetic results in the reference frame previously defined geodetic data confirm a counterclockwise rotation of the adriatic microplate with respect to stable europe that appears to control the strain pattern along its boundaries active deformation in the alps apennines and dinarides is probably driven by the independent motion of the adriatic plate rather than by the africa eurasia convergence the analysis of a global gps solution and recently published new estimates for the african plate kinematics indicate that the africa eurasia plate motion may be significantly different from the nuvel1a values in particular geodetic solutions show that the convergence rate between africa and stable europe may be 30 60 slower than the nuvelia prediction and rotated 10 30 counterclockwise in the mediterranean

effect of igneous intrusive on coal microconstituents study from an indian gondwana coalfield abstract petrological and palynological analyses of coals from two bore holes intruded by an igneous body dolerite dyke reveal characteristic changes due to thermal alteration the unaffected coals are high volatile bituminous rr 0 50 0 61 the coals recovered from samples located close to the dyke had vitrinite with devolatization microvacuoles higher reflectance ranging from 0 9 to 3 0 and liptinite with none to very low fluorescence there is an increasing trend in reflectance and a decreasing trend in fluorescence in the samples occurring closer to the dyke presence of injected mineral matter and pyrite in the macerals further indicate the impact of thermal metamorphism on the coals occurring near the igneous body the palynological investigation of unaffected coals shows the presence of a number of well identified spores and pollen however very few palynomorphs could be recovered from coals located close to the intrusive as the pollen spores were found to be charred beyond recognition

present day vertical isostatic readjustment of the western alps revealed by numerical modelling and geodetic and seismotectonic data the active tectonics of the western alps reveals contrasting regimes ongoing extension at the heart of the chain and transpression compression at its external sectors the active processes currently affecting this region are still a matter of debate the classical models proposed in the literature invoke eurasia adria plate collision counterclockwise motion of the adria micro plate slab retreat of the subducted continental lithosphere and slab detachment more recently several authors prefer the hypothesis of tectonics driven by isostasy buoyancy forces to better understand the influence of these processes on the velocity strain and stress fields at the surface and in the crust we developed 2d viscoelastic numerical models along a vertical cross section perpendicular to the western alps we run our models with different driving forces in order to investigate one by one the geodynamic processes proposed in the literature results are compared with available geodetic geological and seismotectonic data in order to bring into coincidence model predictions and observations an important vertical isostatic readjustment must be included in the modelling together with a slight horizontal compression 0 5 mm year 1 probably due to africa eurasia convergence we show that the subduction process in this alpine region is likely to be dead and that buoyancy forces may be dominating the present day tectonics the geological society of london 2010

continental plate collision p t t z conditions and unstable vs stable plate dynamics insights from thermo mechanical modelling there was much debate recently on the mechanisms of continental convergence and related pressure temperature p t conditions both in modeling and petrologic community depending on the mechanisms of convergence subduction collision folding or rt instability one can argue about the possibility of large scale deviations of pressure and temperature in the accretion prism and below it from reference i e lithostatic conditions commonly used for petrologic reconstructions of evolution of exhumed metamorphic rocks these deviations can be caused for example by tectonic overpressure that as suggested in some studies may be responsible for formation of uhp ultra high pressure rocks however overpressure in exhumation zones can be built only in specific collision scenarios associated with plate coupling pure shear folding in this study we analyze conditions that define various mechanisms of convergence and consequently of exhumation these mechanisms can be represented as a superposition of 1 simple shear subduction 2 pure shear collision 3 folding and 4 rayleigh taylor instability we study these scenarios using a thermo mechanical model that accounts for brittle elastic ductile rheology surface processes and metamorphic changes it appears that stable oceanic type subduction may occur in the case of cold lithospheres tmohob550 c and relatively high convergence rates n3 5 cm yr depending on the lower crustal rheology strong or weak either the whole upper and lower crust or only the lower crust can be involved in subduction in case of weak metamorphic rheologies phase changes improve chances for stable subduction pure shear becomes a dominant mechanism when tmohon550 c or convergence rates are lower than 3 cm yr large scale folding is favored in case of tmoho 500 650 c and is more effective in the case of mechanical coupling between crust and mantle e g strong lower crust gravitational rayleigh taylor instabilities overcome other mechanisms for very high values of tmoho n800 c and may lead to development of subvertical cold spots however it is reasonable to assume that in most cases continental collision is initiated at oceanic subduction rate which is rarely slower than 5 cm yr this rate is sufficient to drive continental subduction during the first several myr of collision in this case the subduction channel is characterized by nearly lithostatic pressure conditions large scale zones of tectonic overpressure may be built outside the channel but do not affect the exhumed rocks overpressure may be built inside the channel in the short moment of its closure we suggest that most continental orogenic belts could have started their formation from continental subduction this evokes small tectonic overpressures and thus deep origin of the uhp rocks that may be brought to the surface via the suggested multi level mechanism of exhumation

subduction of continental crust in the western alps as a result of recent deep reflection and refraction seismology the crustal structure of the western alps is now quite well defined however this raises the question of what is present below the moho such as a crustal eclogitic root this study attempts to estimate the volume of this eclogitic root on the basis of palinspastic reconstructions even with a minimum estimate of the crustal material involved in the subduction processes which took place during the alpine orogeny a significant eclogitized crustal root must be present down to depths of around 100 km below the po plain a maximum estimate suggests that a large part of this root could now be recycled in the asthenosphere

are systematic variations in thrust belt style related to plate boundary processes the western alps versus the carpathians within the mediterranean region cenozoic deformation of the western alps and the west to east carpathians has resulted in two different styles of foreland fold and thrust belt the most prominent difference between the two belts is the presence carpathians or absence western alps of contemporaneous back arc extension but other important differences in structure topography and metamorphism also exist these differences in thrust belt style developed mainly during the final stages of thrust belt evolution and appear to reflect fundamental differences in the tectonic settings of the western alps and the carpathians in middle and late cenozoic time in particular they appear to be the result of convergence that is in the first case driven primarily by major plate motions and in the second case only by local motions of small lithospheric flakes or fragments we suggest that the structural styles developed in these two mountain belts may be useful in identifying mountain belts that have evolved in similar tectonic settings elsewhere in the world in this respect the western alps and the carpathians can be regarded as typical examples of two different styles of foreland fold and thrust belt or more properly as end member examples within a broad spectrum of foreland fold and thrust belt styles we propose that continental subduction zones and orogenic belts can be loosely divided into segments that show no major back arc extensional deformation adjacent to the belt the western alps and segments that exhibit back arc extension contemporaneously with thrusting the carpathians the former are found in areas where the rate of overall plate convergence exceeds the rate of subduction and are commonly typified by extensive involvement of crystalline basement in thrusting exposure of high grade metamorphic rocks at the surface high topographic elevation and large amounts of erosion tens of kilometers the latter are found in areas where the rate of subduction exceeds the rate of overall plate convergence and are commonly typified by thrust belts with little to no involvement of crystalline basement in thrusting low grade to no metamorphism low topographic elevation little erosion and in some instances an anomalously deep foredeep basin system

petrology of some permian coals of india abstract in india permian coal deposits constitute approximately 99 of the total coal reserves of the country and occur in the early permian karharbari formation early permian barakar formation and the late permian raniganj formation in the present study petrographic analyses were carried out on coals from the pench kanhan valley son mahanadi valley and damodar valley basins the permian coals of india show a remarkable range in vitrinite content 13 79 seams with low vitrinite content are common the raniganj formation coals contain more vitrinite than the coals of the barakar and karharbari formation exinite liptinite content of many indian coals varies from 2 to 23 sporinite is generally dominant over cutinite and resinite exinite tends to be associated with vitrinite rich coal and most inertiniterich coals have relatively low exinite content inertinite is relatively abundant 10 67 in many permian coals of india and consists mainly of semifusinite inertodetrinite and fusinite coal facies analysis based on petrographic parameters indicate that the indian peats coals were deposited in dry and wet forest swamps a comparison of indian coals with some other coals of permian age from australia and south africa shows broad similarities even though the coals are from different basinal settings this suggests that palaeoclimate and floral assemblages outweighed basinal setting in determining the coal type being deposited in india outcrops of high rank coals r o max 0 85 1 30 are largely restricted to the damodar valley basin in this basin vertical rank gradients are higher and uplift and erosion have occurred to a greater extent than in other gondwana basins of india coals of other gondwana basins occur at shallow depth and are generally subituminous in rank r o max 0 40 0 65 the oil potential of the coals of the barakar and raniganj formations is very good except in the jharia basin in this basin the oil may have been released due to breaching of the structures

a three dimensional crustal velocity model of the southwestern alps from local earthquake tomography a temporary network of 65 short period seismological stations was installed in the southwestern alps during the second half of 1996 it complemented the permanent monitoring networks obtaining an average interstation distance of 10 km travel time data from 446 local earthquakes and 104 quarry blasts were inverted simultaneously for hypocenter parameters and three dimensional velocity structure the p wave velocity model displays strong lateral contrasts both at shallow and deeper levels a low velocity anomaly stands out at shallow depths beneath the digne and castellane nappes in the southwestern part of the investigated area farther east the monviso ophiolitic massif appears to have a much larger extension at depth than previously assumed the largest and strongest anomaly is located under the dora maira massif and the westernmost po plain it correlates with the well known ivrea body which is classically interpreted as a wedge of adriatic upper mantle at the best resolved depths 10 and 15 km it appears as a rather thin 10 to 15 km north south elongated high velocity 7 4 to 7 7 km s 1 anomaly with very sharp edges extending to the south as far as 10 km north of the surface trace of the frontal penninic thrust special care was taken with regard to the quantitative estimation of the resolution for the main anomalies using the inversion of synthetic travel time data

widespread extension in the core of the western alps revealed by earthquake analysis the western alps are an active collision belt whose current stress field is inhomogeneous muller et al 1992 we report new seismological data which significantly improve our knowledge of this stress field about 1600 earthquakes which occurred in the western alps during the last 10 years were precisely located and 79 new focal solutions were computed the analysis of this database shows that widespread extension affects all the internal zones of the belt to better constrain the associated stress regime six stress tensors were computed using the gephart and forsyth 1984 method they show that the current tectonics of the western alps are contrasted with close variation in the stress regime transpression to the front of the belt contrasting with extension in the core of the belt the extensional direction is radial to the arcuate geometry of the belt and bounded outboard by the former thrust of the internal zones onto the external zone suggesting extensional reactivation of this inherited crustal discontinuity such widespread extension within the inner part of an actually ongoing collision belt cannot be explained by simple collision related tectonics we propose that intrabelt buoyancy forces such as those produced by a slab retreat or slab break off interfere with the boundary forces driven by the ongoing europe africa convergence

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

properties of thermally metamorphosed coal from tanjung enim area south sumatra basin indonesia with special reference to the coalification path of macerals abstract thermally metamorphosed tertiary age coals from tanjung enim in south sumatra basin have been investigated by means of petrographic mineralogical and chemical analyses these coals were influenced by heat from an andesitic igneous intrusion the original coal outside the metamorphosed zone is characterized by high moisture content 4 13 11 25 wt and volatile matter content 40 wt daf as well as less than 80 wt daf carbon and low vitrinite reflectance vr max 0 52 0 76 those coals are of subbituminous and high volatile bituminous rank in contrast the thermally metamorphosed coals are of medium volatile bituminous to meta anthracite rank and characterized by low moisture content only 80 wt daf and vitrinite reflectance vr max 1 87 6 20 all the studied coals have a low mineral matter content except for those which are highly metamorphosed due to the formation of new minerals the coalification path of each maceral shows that vitrinite liptinite and inertinite reflectance converge in a transition zone at vr max of around 1 5 significant decrease of volatile matter occurs in the zone between 0 5 and 2 0 vr max a sharp bend occurs at vr max between 2 0 and 2 5 above 2 5 the volatile matter decreases only very slightly between vr r 0 5 and 2 0 the carbon content of the coals is ascending drastically above 2 5 vr r the carbon content becomes relatively stable around 95 wt daf vitrinite is the most abundant maceral in low rank coal 69 6 86 2 vol liptinite and inertinite are minor constituents in the high rank coal the thermally altered vitrinite composes 82 4 93 8 vol mosaic structures can be recognized as groundmasss and crack fillings the most common minerals found are carbonates pyrite or marcasite and clay minerals the latter consist of kaolinite in low rank coal and illite and rectorite in high rank coal change of functional groups with rank increase is reflected most of all by the increase of the ratio of aromatic c h to aliphatic c h absorbances based on ftir analysis the oxygen index values of all studied coals are low oi 2 g toc and the high rank coals have a lower hydrogen index t max increases with maturity 420 440 c for low rank coals and 475 551 c for high rank coals based on the above data it was calculated that the temperature of contact metamorphism reached 700 750 c in the most metamorphosed coal

plio quaternary vertical motion of the northern apennines insights from dynamic modeling we test the effects of different geodynamic mechanisms on the pliocene to present day dynamics and in particular on the vertical motions of the northern apennines system by means of two dimensional finite element models we show that the pliocene features of the northern apennines exhumation of deep rocks in western italy and fast subsidence rates in the adriatic foredeep can be adequately reproduced by a model slab characterized by the passive sinking of a negatively buoyant adriatic slab and by the upwelling of buoyant asthenosphere beneath western italy model slab is however not able to account for the quaternary and present day pattern of vertical motion of eastern italy and of the adriatic basin a deep configuration of the system characterized by a detached slab model detach may explain the vertical motions of these areas constrained by uplift of the eastern portions of the apenninic chain by an eastward shift of the foredeep depocenter and by lower subsidence rates in the adriatic basin the tectonic and stratigraphic data showing major differences between the tertiary and the quaternary evolution of the northern apennines are discussed

dynamics of retreating slabs 1 insights from two dimensional numerical experiments from the effects of mantle flux part 2 therefore in this paper we apply forces to the slab using simple analytical functions related to buoyancy and viscous forces in order to isolate the role of rheology on slab dynamics we analyze parameters for simplified elastic viscous and nonlinear viscoelastoplastic single layer models of slabs and compare them with a stratified thermomechanical viscoelastoplastic slab embedded in a thermal solution the near surface behavior of slabs is summarized by assessing the amplitude and wavelength of forebulge uplift for each rheology in the complete thermomechanical solutions vastly contrasting styles of slab dynamics and force balance are observed at top and bottom bends however we find that slab subduction can be modeled using simplified rheologies characterized by a narrow range of selected benchmark parameters the best fit linear viscosity ranges between 5 10 22 pa s and 5 10 23 pa s the closeness of the numerical solution to nature can be characterized by a deborah number 0 5 indicating that elasticity is an important ingredient in subduction index terms 8120 tectonophysics dynamics of lithosphere and mantle general 8159 tectonophysics rheology crust and lithosphere 8160 tectonophysics rheology general keywords subduction numerical models lithospheric rheology

estimating present day displacement fields and tectonic deformation in active mountain belts an example from the chartreuse massif and the southern jura mountains western alps abstract determination of relative movements between the alpine foreland and the external crystalline massif is a key point for the understanding of the present day tectonics of the western alps in this study we try to test the continuity of the present day tectonics with the mio pliocene deformation in particular we will test if the present day displacements are localized along the thrusts of the jura mountains or along a blind thrust in the bas dauphine molasse basin definition of relative movements is achieved by several methods including a comparison of two high precision leveling networks to estimate vertical displacements horizontal deformation measurements performed by triangulation triangulation and triangulation gps comparison in situ stress measurements performed in the different tectonic units and geomorphologic observations that constrain the location and the magnitude of the quaternary deformation comparison of leveling data demonstrates 1 an uplift of the southern bas dauphine molasse basin relative to its northern part 0 8 mm year also revealed by geomorphologic analysis 2 a significant uplift of the most external jurassian anticlines 0 8 to 2 mm year also recorded by the deformation of a paleo river bed and 3 an important uplift up to 2 mm year of the subalpine massifs the horizontal strain estimated from comparison of horizontal geodetic data triangulation gps shows 1 a nw se directed shortening between the eastern chartreuse massif and the bas dauphine molasses basin approximately 3 mm year 2 an e w directed shortening in the jura mountains approximately 4 3 mm year and 3 a dextral strike slip motion consistent with focal mechanisms along a nne ssw direction between the eastern chartreuse massif and the eastern belledonne massif these data reveal a present day strain partitioning between the belledonne external crystalline massif and the bas dauphine molasses basin the westward motion of the subalpine massifs is partitioned along two southern jurassian thrust folds and a dextral nne ssw strike slip shear zone between the chartreuse massif and the belledonne massif this strain partitioning is also accompanied by a stress partitioning between the alpine foreland and the external crystalline massifs

a numerical model of the hellenic subduction zone active stress field and sea level changes a 2 d viscoelastic finite element model for subduction in the southern aegean sea allows us to study the distribution of stress and surface velocities in a vertical cross section through the island of crete recent tomographic results constrain the geometry of the slab and the structure of the crust lithosphere and mantle two models are considered the first for passive subduction driven solely by slab pull and the second one where active convergence between the african and aegean plates is also included both models predict subsidence of the hellenic trench and of cretan trough uplift of crete and of the aegean volcanic arc the island of crete is subject to differential uplift highest in the southern part with maximum rates of 1 5 and of 3 2 mm yr for the two models respectively these results agree with the tectonic uplift inferred from holocene sea level changes in the island the style of stress within the modeled african and aegean plates is in general agreement with the focal mechanisms of the largest earthquakes along the subduction zone

effects of igneous intrusions on coal petrology pore fracture and coalbed methane characteristics in hongyang handan and huaibei coalfields north china article i nfo the effects of igneous intrusions have proved to be important for the exploration and development of coalbed methane in many coal basins however the studies of the influences of localized intrusions on coalbed meth ane reservoirs are still insufficient in the context of five typical dike sill intrusion patterns i e dike cut through dike cut in floor intrusion by sill roof intrusion by sill and dual intrusions of roof and floor by sills this study investigates the changes of coal organic composition and pores fractures resulting from igneous intrusions the influences of igneous intrusions on coal composition mainly include the decrease of vitrinites especially telocollinite and the increase of inertinites contents as well as the formation of secondary devolatilization vacuoles and of exogenous desiccation microfractures the vacuoles have size of 0 1 10 m and the microfractures are commonly developed with a wide space and a significantly short length the microfractures typically have irregular dendritic filamentous and turtleback textures and densi ties of hundreds per 9 cm 2 the influences of igneous intrusions on coal pores and fractures vary significantly depending on the intrusion patterns the coal ranks after the intrusion and the nature of the adjacent forma tion surrounding the intrusion for the coals with a vrr 4 2 the intrusion significantly reduced the coal pore development for the coals with a vrr from 2 1 4 2 the development of the coal pores improved with decreasing distance to the contact for the coals with a vrr b2 1 the intrusion resulted in a slight improvement of the coal pore development a possible explanation for the increasing gas content near the intrusion is that the secondary vacuoles and microfractures induced an increase in the gas storage capacity and in the permeability of the coal reservoir the detailed intrusion patterns of sills and dikes contribute to the formations of the coalbed methane accumulation in coal seams and to the coal generated gas accumula tion in the reservoir of the highly permeable surrounding rocks

thermomechanical modelling of slab detachment abstract slab detachment or breakoff is appreciated as an important geological process as shown by recent tomographic imaging using a 2 d upper mantle model 660 km deep and 2000 km wide we have investigated with a 2 d finite difference and marker in cell numerical technique the multi resolutional character of the thermomechanical phenomena related to this complex geological process our experiments show that this process can be initiated in form of slab necking by a prolonged 8 30 my period of slab weakening due to thermal diffusion 60 c my due to strong positive thermal feedback from shear heating detached slab fragments sink rapidly with a tendency for coherent rotation the influence of temperature and pressure dependent thermal conductivity on the process of thermal weakening of the slab is quite significant this supports the idea that the breakoff process is triggered by thermal diffusion on a time scale linearly dependent on heat conductivity rapid topographic changes and increasing volcanic activities due to the melting of subducted oceanic crust are possible scenarios of this vigorously driven geodynamic process

neogene lateral extension during convergence in the central alps evidence from interrelated faulting and backfolding around the simplonpass switzerland abstract the simplon fault zone occurs at the western end of the lepontine metamorphic dome in the central alps and represents a major low angle 25 dip normal fault associated with wsw ene directed lateral extension movement began in the early miocene and continued until at least 3 ma accumulating a total vertical throw of around 10 km corresponding to 24 km displacement parallel to the fault this displacement is partitioned between a broad zone of ductile mylonites in the footwall and a more discrete cataclastic detachment fault the simplon line in the central region simplon village to zwischbergen some 3 km of the total vertical displacement is accommodated by the discrete cataclastic zone due to the higher exposed structural level the importance of the cataclastic component increases towards the northwest in the northern steep belt around the simplonpass retrograde greenschist facies mylonite formation and younger cataclastic faulting associated with lateral extension occurred contemporaneously with sse vergent large scale backfolding representing nnw sse shortening and crustal thickening the combined effect was an overall shortening across the orogen accommodated by an extension parallel to the orogen allowing lateral escape of continental material normal faulting and the resultant lateral escape was not just superficial it extended to depths of at least 15 km and probably to depths exceeding 25 km the overall geometry and kinematics of the simplon fault zone and in particular the interplay between folding and faulting is very similar to that described from the metamorphic core complexes and detachment faults of the cordillera of the southwestern usa within the central alps extension was associated with rapid exhumation of the lepontine metamorphic dome as evidenced by very rapid cooling rates determined from mineral ages in the footwall similar to the cenozoic tectonics of the himalayas and tibet orogen parallel extension in the mountain belt may have been promoted by an overall reduction in the horizontal compressive stress in this direction more limited extension of the same age and orientation is known from a large area of the european foreland greater extension in the mountain belt compared with the foreland was accommodated by major strike slip transfer fault systems and was linked to coeval overthrusting of the lowlands towards the southwest in the external southwestern alps of haute provence france coeval folding and orogen parallel extension such as at the simplonpass were developed in a dextral transpressive regime due to oblique wnw ese convergence across the alps during the neogene

glacier shrinkage and modeled uplift of the alps 1 present day glacier reduction in the alps estimated from glacier inventories and induced viscoelastic response of a stratified earth s model is responsible for sizable uplift rates patches of 0 4 0 5 mm yr due to ice mass loss of largest ice complexes overprint a characteristic area of slower uplift of 0 1 0 2 mm yr signature of the phenomenon in the whole alpine chain viscous stress relaxation in the lower crust due to glacier mass loss after the end of the little ice age is expected to produce uplift rates of 0 32 mm yr leading to a total viscoelastic response up to 0 8 mm yr our predictions in the western alps show that viscoelastic response to present day glacier shrinkage forms a substantial fraction half of the observed uplift data attempts to constrain the contributions arising from active alpine tectonics and drainage must account for this uplift signal citation barletta v r c ferrari g diolaiuti t carnielli r sabadini and c smiraglia 2006 glacier shrinkage and modeled uplift of the alps geophys res lett 33 l14307 doi 10 1029 2006gl026490

present day geodynamics in the bend of the western and central alps as constrained by earthquake analysis summary the contrasted tectonics of the western central alps is examined using a synthesis of 389 reliable focal mechanisms the present day strain regime is mapped and interpolated for the entire alpine belt based on a newly developed method of regionalization the most striking feature is a continuous area of extension which closely follows the large scale topographic crest line of the alpine arc thrusting is observed locally limited to areas near the border of the alpine chain a majority of earthquakes within the alps and its forelands are in strike slip mode stress inversion methods have been applied to homogenous subsets of focal plane mechanisms in order to map regional variations in stress orientation the stress state is confirmed to be orogen perpendicular both for 3 in the inner extensional zones and 1 in the outer transcurrent transpressional zones extensional areas are well correlated with the part of the belt which presents the thickest crust as shown by the comparison with the bouguer anomaly and the average topography of the belt in the northwestern swiss alps extension is also correlated with currently uplifting zones these observations and our strain stress analyses support a geodynamic model for the western alps in which the current activity is mostly a result of gravitational body forces earthquakes do not provide any direct evidence for ongoing convergence in the alpine system but a relationship with ongoing activity of complex block rotations of the apulian microplate cannot be ruled out

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

the interplay between global tectonic processes and the seismic cycle in the umbria marche seismogenic region summary for the central apennines peninsular italy a series of tectonic mechanisms are reproduced by means of finite element models in order to study the effects of active tectonics on the seismic cycle in the umbria marche seismogenic zone continental extension and rift push effects induced by small scale convection are modelled within 2 d viscoelastic models of the crust lithosphere system in vertical cross sections perpendicular to the strike of the major tectonic structures under study namely the apennines and the colfiorito fault zone where the 1997 seismic sequence took place with the aim of constraining the active tectonic mechanisms at the regional scale and the behaviour of the fault in the seismogenic zone at the local scale modelled baseline rate of change are compared with newly acquired gps data retrieved from the two permanent gps receivers of camerino came and elba elba deliberately installed along the modelled transect these receivers are located at both edges of the continental extension in the front of the apennines close to the adriatic plate in the east and in the rear of the chain in the tyrrhenian domain the deformation pattern inferred from seismicity and from the geodetic data is consistent with small scale convection in the tyrrhenian domain which reproduces extension in the rear of the apennines and compression in the front of the chain a convective mechanism associated with backarc opening and doming of the asthenosphere provides an extensional rate along a baseline connecting two sites in the front of the chain camerino and in its rear elba comparable to the observed baseline rate of change the viscosity of the lower crust plays a fundamental role in determining the style of stress in the crust lithosphere system once constrained by means of the extensional baseline rate inferred from gps the modelled slip across the colfiorito fault and the modelled earthquake recurrence time are consistent with the 1997 normal fault event and with palaeoseismicity respectively

quaternary erosion induced isostatic rebound in the western alps the high elevation and deep incision of the alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates normal faulting and horizontal extension however dominate current tectonic activity and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations here we test the idea that enhanced quaternary erosion of the alps and isostatic compensation of the mass removed can account for the distribution of present day geodetically measured rates of vertical movement in the western alps using geophysical relief and kuhlemann s estimated average erosion rate for the alps we quantify the spatial distribution of erosion and the volume of eroded rock respectively from these we obtain a map of rock eroded within a given time span the calculated isostatic response of the alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the alpine lithosphere reaches a maximum of 500 m since 1 ma in the inner swiss alps and vertical movement extends across the entire belt including peri alpine basins assuming a steady erosion rate since 1 ma this rebound accounts for half of the measured vertical motion of 1 1 mm yr in the southern valais thus a significant fraction 50 of the present day vertical movement results from the isostatic response to enhanced erosion during plio quaternary time

assessment of nature and distribution of inertinite in indian coals for burning characteristics maceral composition and mean reflectance rr of coal are considered to be important parameters which influence the coal combustion characteristics vitrinite and liptinite are traditionally considered to be reactive components towards combustion numerous studies on gondwana coals suggest that some inertinites low in reflectance having mean reflectance up to 1 30 show good burning behaviour and they can even be more reactive than vitrinite thermogravimetric analysis tga technique has been used to assess combustion characteristics of the coal samples the traditional parameters such as fuel ratio and rank as reflected by vitrinite reflectance did not correlate well with the tga parameters rather tga parameters were found to show good correlation with the petrofactor which combines the effect of the rank and the total reactive macerals content which includes the reactive macerals vitrinite semivitrinite liptinite and low reflecting reactive inertinites the study indicates the necessity of considering the role of low rank inertinites while assessing the combustion behaviour of inertinite rich non coking non caking coals

microstructures and microtextures of natural cokes a case study of heat affected coking coals from the jharia coalfield india abstract in jharia coalfield nearly 1250 mt of coking coal has been devolatilized due to igneous intrusives and 1900 mt due to mine fires this paper is an effort to investigate the effect of carbonization in two intrusive affected coal seams of ena seam xiii and alkusa seam xiv collieries of this coalfield through petrographic studies by microscopy characterization of normal and heat affected coals was carried out the microstructures and microtextures produced due to extraneous heat have been related to nature and extent of heat location of heating source and quality and quantity of natural coke produced based on the results of this study and earlier studies an effort has been made to study the classification scheme for microtextures of natural cokes generated through in situ carbonization of the coal seams it has been observed that in case of such heat effects under overburden pressure the anisotropy is much more pronounced as compared to laboratory carbonized cokes in the mildly carbonized coals pre plastic phase 500 c the identified microtextures were mesophase spheres different shapes and sizes of natural cokes graphitic sphaeroliths pyrolytic carbons inerts with morpho structural changes and slightly higher reflectance values and altered and unaltered mineral matters a gradual change in the heat affected coals with increasing temperature was observed with respect to location of intrusive body it has been concluded that barring the effect of pressure the changes due to heat effect on coking coals whether in situ or laboratory carbonization are almost similar organic and inorganic constituents undergoing changes at a particular temperature are nearly similar in both conditions in case of pronounced overburden pressure flow structures develop in the natural coke groundmass higher reflectance and very strong anisotropy as evidenced in completely baked coking coals with fine to very coarse mosaic structures may be a good criterion to explore these heat altered coals for the carbon artifact industry and further efforts are required to be made in this line

evidence for a post 3 16 ma change in nubia eurasia north america plate motions we combine updated gps velocities from the nubian nu eurasian eu and north american na plates with 500 new 3 16 myr average seafloor spreading rates and nine transform fault azimuths from the northern atlantic and arctic basin seafloor spreading centers to estimate and test for changes in the relative motion between these plates the numerous new seafloor spreading rates and gps velocities improve our ability to detect recent changes in the relative motions of these plates the angular velocity vector that best fits the eu na gps velocities lies significantly north of the 3 ma average pole in accord with previously published geologic evidence that the eu na pole has migrated northward since v3 ma although we also find evidence for a significant post 3 ma change in nu na motion it is less compelling because the nubian plate gps velocity field is sparse and nu na seafloor spreading rates appear to have remained steady within the 1 mm yr 31 uncertainties if we systematically decrease the seafloor spreading rates to correct for outward displacement of seafloor spreading magnetic lineations the nu eu pole derived from gps site velocities lies more than 30 angular degrees south of the tightly constrained 3 ma average estimate and predicts significantly slower and more oblique present day nu eu convergence in the mediterranean both models for nu eu motion pass a key test for their accuracy namely they correctly predict strike slip motion along the well mapped gloria fault east of the azores the change to more oblique nu eu motion may reflect increasing difficulty in maintaining margin normal convergence within this continent continent collision zone 8 2003 published by elsevier b v

the arc of the western alps in the light of geophysical data on deep crustal structure recently two international deep seismic campaigns in the western and central alps etude continentale et oceanique par reflexion et refraction sismique progetto strategico crosta profonda ecors crop roure et al 1996b and national research program 20 nrp 20 pfiffner et al 1997 have been completed here we present a synoptic interpretation of the wealth of geophysical data about deep crustal structure of the alps collected during the past 40 years including the two above mentioned geophysical projects the tectonic reinterpretation of the ecors crop high resolution seismic transect is based on an evaluation of the deep crustal structure by integrating new and literature data on surface geology combined with previously published interpretations regarding the central alps schmid et al 1996 this study reveals substantial differences in geometry and kinematics between transects across the western and central alps respectively at depth the transition between the central and western alps is marked by the western limits of an adriatic lower crustal wedge shaped structure and the northeastern limits of a similar structure made of european lower crustal material at the surface it coincides with a corridor of dextral strike slip along the tonale and simplon lines in addition the thickness of the seismogenic zone shows a remarkable variation from over 40 km beneath the penninic realm of the western alps to less than 20 km in the central alps the formation of the western alpine arc was initiated during convergence and collision before 35 myr ago when the adriatic micro plate moving northward with respect to the european foreland caused sinistral transpression in the western alps while the central and eastern alps underwent head on convergence and collision during the post collisional stage i e after 35 myr ago the arcuate shape of the western alps was accentuated by wnw directed movement and anticlockwise rotation of the adriatic microplate decoupled from the central and eastern alps along the tonale simplon dextral shear zone this led to wedging of lower crustal slices both in the western alps and in the central alps the new tectonic interpretation of the ecors crop transect allows a kinematic model to be established for crustal shortening in the western alps during the past 35 myr the ivrea mantle plays the role of a backstop in our tectonic model we distinguish three episodes of post collisional crustal shortening along the ecors crop transect from 35 to 30 ma the brianconnais basement was back thrusted over the gran paradiso units leading to 30 km of crustal shortening first episode in the early miocene movements concentrated mainly along the penninic frontal thrust and resulted in about 60 km shortening second episode post 12 ma shortening within the external massifs is associated with folding in the jura mountains when the crust was shortened by an additional 30 km third episode

mantle unrooting in collisional settings abstract we present a two dimensional numerical model to study the thermo mechanical evolution of the lithosphere under a convergence regime in order to define the conditions that lead to lithospheric mantle break up and consequent unrooting a newtonian rheology with a temperature dependent viscosity is considered the system is not closed and horizontal flow through lateral boundaries is permitted a horizontal velocity is imposed at the top of the model to simulate compression whereas velocity vanishes at the bottom of the model the initial conditions correspond to a homogeneous lithosphere with a constant heat production in the crust the analysis of variations of maximum shear stress strain rate and total kinetic energy allowed us to define four major stages during the mantle unrooting process orogenic growth initiation of gravitational instability until lithospheric failure sinking of the detached lithosphere and relaxation of the system numerical results also show that the conditions for lithospheric unrooting strongly depend on the convergence velocity the wideness of the deformation zone and the imposed rheology

petrographic and geochemical effects of sill intrusions on coal and their implications for gas outbursts in the wolonghu mine huaibei coalfield china abstract since the early 1980s fifteen outbursts have occurred in the huaibei coalfield of china these outbursts were reported to be associated with sills to study the effect of sill intrusions on coal seam and their relationship to methane outbursts eleven samples from the no 10 coal seam were taken from the wolonghu mine at various distances from a diorite sill comparisons were made between unaltered and heat affected coals using petrographic and chemical data micropore characteristics adsorption properties of coal and gas outburst indexes from field approaching the intrusion vitrinite reflectance levels increased from 2 74 to 5 03 and the thermal aureole of the sill 60 m from the sill boundary to sample 9 three zones along this gradient were identified as corresponding to 1 thermal evolution zone no 1 0 5 m from sill 2 thermal evolution zone no 2 5 60 m from sill and 3 unaltered zone the methane adsorption capacity of coal samples in the thermal evolution zone no 2 was generally higher than in the two other zones and the unaltered zone higher than the thermal evolution zone no 1 it is concluded that the contact metamorphism decreased the adsorption capacity of coal and the thermal evolution of sill increased it the trap effect of sill combined with the mudstone and siltstone roof and floor of the no 10 coal seam provided a seal for the formation of a gas pocket abnormally high formation pressures at the no 10 coal seam led to two outbursts

petrological constraints on the eclogite and blueschistfacies metamorphism and p t t paths in the western alps phase relationships in the model mafic system and geothermobarometry allow discrimination of four main groups of high p rocks in the nappes of the western alps very high p eclogite facies including kyanite eclogites and coesite pyrope assemblages eclogite facies paragonite zoisite eclogites high t blueschist facies glaucophane garnet lawsonite assemblages and low t blueschist facies glaucophane lawsonite pumpellyite assemblages the blueschist facies eclogite facies transition is promoted chiefly by increasing t low bulk xmg and relatively low h2o the variety of assemblages and the heterogeneous approach to equilibrium observed in the alpine rocks are not only constrained by the intersection of the reaction surfaces in p t x space but also by the effect and timing of the processes which control kinetics i e pervasive deformation and fluid infiltration the faster rate of dehydration reactions relative to hydration reactions along with the fact that different bulk compositions crossed the reaction curves at different temperatures and times all may have induced h2o gradients and contributed to the heterogeneous distribution of deformation through a process of reaction enhanced ductility also mass transfer may have been an effective process in determining the type of high p assemblage in particular rock volumes as regards the p t t paths only the post climax histories are recorded well in the alpine nappes post eclogitic exhumation paths at decreasing temperatures characterize structurally higher nappes which were first subducted during the early alpine cretaceous event in contrast more or less isothermal decompression paths characterize structurally deeper nappes formed by westward propagation of the underthrust surfaces during the early alpine event and the subsequent meso alpine palaeogene collision between the european and african plates in the western alps prevalent eclogite facies conditions were attained during the metamorphic climax of the early alpine subduction while blueschist facies recrystallization characterizes the early alpine exhumation of the eclogitized units and the subsequent intracontinental underthrusts linked to the meso alpine continental collision

styles of post subduction collisional orogeny influence of convergence velocity crustal rheology and radiogenic heat production abstract a number of models of continental collision already exist but the role of foregoing oceanic plate subduction or variable coupling between plates still remains to be explored in addition heat generation by radioactive decay may be quite variable for example our geochemical data from low to high grade metamorphic rocks of the lesser and higher himalayan sequences reveal measured heat production values on the order 4 5 w m 3 which is considerably higher than normal inferred upper crustal values 3 therefore we performed 2d numerical experiments of oceanic continental subduction followed by continental collision for varying continental lower crustal strength convergence velocity and radiogenic heating rate oceanic subduction produces thinning and upwarping of the overriding lithospheric wedge such as is observed in andean type collisional settings cascadia and central andes after collision two main orogenic styles develop depending on the values of key parameters either a slow convergence rates weak shear heating and consequently strong rheological coupling between plates and or a weak lower crust generate a two sided thick and narrow symmetrical collisional zone or b high convergence rates strong shear heating and therefore weak rheological coupling between plates and a strong lower crust produce a one sided thin and broad asymmetrical collisional zone in this case a vertical lithospheric body divides two upper crustal wedges that develop distinct deformation patterns in both cases enhanced radiogenic heating favors the formation of midcrustal partially melted channels that propagate toward the surface and the pro foreland partial melting triggers lateral extrusion of metamorphic rocks from different depths 15 23 kbar 700 c on top of coherent lp lt units the geometry of metamorphic isograds inverted shapes of p t paths at different grades and exhumation rates are similar to those observed in parts of the himalayan chain indicating that the models capture the essence of real systems the model results demonstrate that internal heat production rate is a crucial parameter in determining the timing of slab breakoff polarity reversal and exhumation of the inverted metamorphic sequence with respect to the timing of partial melting late stages of some numerical experiments showed interesting geodynamical evolution of the collisional zone with the appearance of polarity reversal roll over of both plates and roll back of the subducting slab irrespective of these details hundreds of km of continental lithosphere are recycled into the mantle in all models supporting the idea that continental crustal consumption is indeed a common and considerable process during collision this affects inferences about extents of convergence and or shortening during orogenesis moreover crustal recycling into the deep mantle during collisional orogeny needs to be considered in models of crustal growth and evolution

genesis of natural cokes some indian examples abstract in indian coalfields huge amounts of natural coke have been produced due to magmatic intrusions jharia coalfield in eastern part of india alone contains approximately 2000 mt of baked coking coal as a consequence of these intrusions in the form of discordant and concordant bodies this paper is an effort to investigate the effect of carbonization in two intrusion affected coal seams of ena seam xiii and alkusa seam xiv collieries of jharia coalfield natural coke is derived from coking coal under in situ conditions due to intense magmatic induced heat and overburden pressure natural coke is characterized by the presence of low volatile matter and high ash contents and organic constituents showing isotropy and anisotropy through physical petrographic and chemical properties of natural coke or jhama as determined by various methods it has been established that the reactives in the unaltered coals vitrinite liptinite pseudovitrinite reactive semifusinite etc are

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

hydrogeological interpretation and potential of the new magnetic resonance sounding mrs method abstract this study reviews the up to date hydrogeological contribution of the new geophysical magnetic resonance sounding mrs method and presents new interpretation ideas and potential regarding various hydrogeological applications the main advantage of the mrs method as compared to other geophysical methods is in its water selectivity mrs is commercially available but is also the subject of r d to minimize a number of limitations related not only to data acquisition but also to hydrogeological data interpretation the two main mrs output data types are free water content mrs and decay time constant t d relations between mrs and effective porosity specific yield and specific storage are discussed in the framework of an original groundwater storage concept t d is correlated empirically with hydraulic conductivity however such correlation is not yet quantified for various rock types so t d has to be calibrated by borehole data as an improvement of the data interpretation a proposal of a new multi decay approach is presented the advantage of such analysis is that it combines storage and flow property characteristics in assessing water content at various pore size fractions and the disadvantage is that it is applicable only at large signal to noise ratios five case examples are used to show that combined interpretation of mrs and t d can be used to evaluate subsurface hydrostratigraphy although such analysis is vulnerable to equivalence error and its resolution decreases with depth mrs with large volume averaging schema and current limitation to 1d approach is already suitable for groundwater modelling applications and for evaluation of groundwater potential in the mrs measurement scale 100 100 m 2 but is not yet optimized for well siting mrs can detect water in the unsaturated zone which can be potentially used in real time subsurface flux monitoring field experiments indicate that mrs is not appropriate for groundwater salinity detection no field experiments have yet been made to detect hydrogenated compounds like hydrocarbons and tracers in the subsurface

petrography and metamorphism of the lower gondwana permian coal of rangit valley eastern himalays india abstract a triangular outlier of coal bearing lower gondwana rocks comprises a tectonic window within the precambrian metamorphic terrain of the rangit valley in the eastern himalays of india due to a series of tectonic events which took place during the mesozoic and tertiary the succession has become reversed and the coal has undergone severe physical chemical microstructural and optical changes studies reveal that 1 the rank of the coal prior to tectonism was low 2 the coal underwent oxidation in the peat forming stage and during subsequent orogenic stages but effect of oxidation on the properties of coal was insignificant 3 the coal reached its present abnormally high rank mainly due to heating under tectonic pressure and 4 the heat which was generated due to tectonic pressure affected all the coal seams of this belt