in situ gasification of coal a natural example history petrology and mechanics of combustion a 6 m thick coal seam of the upper jurassic and lower cretaceous mist mountain formation in the southeastern canadian cordillera has been burning since 1936 the upper 3 m of coal is being consumed to an estimated depth of 20 m temperatures in excess of 1100 c are locally reached resulting in the melting of overlying sandstones and shales the melted and vitrified rocks contain a new suite of minerals including diopside anorthite cristobalite and tridymite underlying the burnt coal ash is a zone of coke averaging about 10 cm thick which is in turn underlain by unaltered coal within the area of combustion three zones can be distinguished an advance zone where open cracks are developed at the ground surface a zone of active combustion where volatiles driven off the coal bum en route to the surface and at the mouth of vents and an abandoned zone marked by vents some of which act as air intakes approximately 1000 tlyear of coal is consumed giving an energy release of about 1 mw the heat generated is carried both forward and upward by convecting gas thereby coking the coal and baking the roof rock little heat is carried downward as evident from a sharp decrease in vitrinite reflectance below the zone of combustion the baked roof rocks are brittle and extensively fractured providing little roof support the completely fused and scoriaceous rock and welded associated breccias on the other hand have greater coherence this welding hinders roof collapse and thereby assists the passage of gases

impact of underground coal fire on coal petrographic properties of high volatile bituminous coals a case study from coal fire zone no 3 2 in the wuda coalfield inner mongolia autonomous region north china abstract the wuda coalfield located in the inner mongolia autonomous region north china is known as one of china s major source of prime coking coals and a site of well researched and well documented underground coal fires the underground coal fire at the coal fire zone no 3 2 is situated in the active coal mine of suhai tu located in the north westerly part of the wuda coalfield the present paper investigates the impact of the underground coal fire on the coal seam no 10 by application of coal petrographic methods including detailed characteristic of macerals and other coal components maceral analysis microstructural analysis and vitrinite reflectances performed on 1 coal grains lacking impurities microfractures dark oxidation rims 2 on dark rimmed vitrinite as well as 3 on low temperature semi coke the investigated coal seam no 10 represents a high volatile a bituminous coal and is dominated by vitrinite followed by inertinite with minor amounts of liptinite and by non isotropic low temperature semi coke the microstructure of the oxidatively and thermally altered coals is represented by 1 extensive non tectonic microfissures and non tectonic microfractures i e shrinkage microfractures leading to defragmentation of coal grains 2 dark oxidation rims observed at grain margins non tectonic microfissures and microfractures and by 3 devolatilisation micropores random vitrinite reflectances measured in 1 coal grains lacking impurities microfractures and dark oxidation rims and in 2 dark rimmed vitrinite at non tectonic microfissures and fractures reveal significant lateral variations the presence of low temperature semi coke and its marked lower reflectance values are indicative of thermal alteration induced by the underground coal fire in the coal fire zone no 3 2 the results obtained from the performed analyses of organic matter point to both low temperature oxidation and low temperature pyrolysis processes the applied coal petrological approach revealed characteristic changes to the coal s microstructure its petrographic composition as well as to optical properties induced by the underground coal fire

the lateral and vertical reflectance and petrological variation of a heat affected bituminous coal seam from southeastern british columbia canada abstract thermally altered pods of coal of very high rank have been observed in a high volatile bituminous coal seam in the eastern side of eagle mountain elk valley coalfield british columbia rank changes have been measured over a strike distance of 7 5 m from 1 24 to 7 1 r o max corresponding to a rank gradient of 0 78 r o m 1 petrologically unaltered to extremely altered vitrinite showing nongranular basic anisotropy mosaic textured liptinite and pyrolytic carbon are the most abundant components the limited presence of mosaic on vitrinite is an indication that the coal seam may have been weathered prior to being heat affected evidence points to localized temperatures as high as 1 000 c which could have been caused by a lightning strike the eastern side of eagle mountain has experienced higher temperatures than the western side and it appears that the heat front and zone of alteration have an irregular pattern pointing to saturation of parts of the coal seam by water four types of pyrolytic carbon having distinct morphology anisotrophy and optical path with increasing temperature were observed reflectance of pyrolytic carbon falls within the zone of heat affected coals whereas the optical path of heat affected seam 15 samples is different from that of fresh coal with increasing rank finally the reflectance of vitrinite in heat affected coal is higher than the reflectance of vitrinite in carbonaceous shale in the seam 15 section

detection of natural weathering of upper mcalester coal and woodford shale oklahoma u s a abstract natural weathering refers to the natural oxidation of organic and inorganic matter in rocks at the surface and in the shallow subsurface the objective of this study is to apply routine geochemical analyses including organic petrography to coal and shale samples extending from the weathered to unaltered zones to illustrate the effects of weathering on organic matter in coal and shale some significant observations from the upper mcalester coal and the woodford shale are 1 a sulfate index si using sulfur form analysis data that reveals the transformation of pyrite to sulfate minerals is a very sensitive weathering indicator it increased in weathered samples 2 rock eval pyrolysis data such as hydrogen index hi and oxygen index oi are very sensitive to weathering oi hi increased in weathered samples 3 vitrinite reflectance decreased in weathered samples and 4 petrographic signs of weathering include microfractures pitted surface dark reaction rims and high relief sulfate index and petrographic signs of weathering should be used on surface and shallow subsurface rock samples as an indication of the extent of weathering the validity of other analyses can then be evaluated accordingly

detrital zircon reference for the north china block abstract u pb analyses of 250 single detrital zircons from upper proterozoic to ordovician strata collected from the zhuozi shan in north central china provide a detrital zircon reference for the north china block a major crustal entity in the asian tectonic collage the results which range in age from 1 72 to 2 97 ga shed new light on the age of the crystalline basement in north china much of which is covered by younger sedimentary units in addition this detrital zircon reference can be used to help determine the provenance of clastic sedimentary units and for assessing validity of paleogeographic and regional tectonic models that include the complex history of asian continental amalgamation terrane accretion and subsequent translation that is ongoing today

potential of small baseline sar interferometry for monitoring land subsidence related to underground coal fires wuda northern china case study uncontrolled coal fires can result in massive surface displacements due to the change in volume of burning coal and thermal effects in the adjacent rock mass simultaneously the resultant surface breakings provide greater access to air and water that in turn can aggravate the problem of underground coal seam burning in this case study we have investigated the feasibility and potential of detecting the land subsidence accompanying coal fires by means of satellite insar observations three groups of small baseline insar approaches psi stacking and 2 passdinsar were applied to the wuda coalfield northern china to reveal the spatial and temporal signals of the land subsidence in the areas affected by the coal fires the interferometric results agree well with gps observations and coal fire data obtained by field investigation which demonstrates that the small baseline insar techniques have remarkable potential to detect this land subsidence of interest in particular our results show that the development of coal fires can lead to new subsiding areas and also accelerate the ongoing surface subsidence typically within the areas of mature coal fires through a comparison of the interferometric observations and the multi temporal coal fire maps this timely and reliable information on land subsidence will be useful for the detection and mapping of the coal fire affected regions and thereby assist in fighting and controlling coal seam burning

heterogeneous deformation recorded by magnetic fabrics in the pyrenean axial zone abstract magnetic fabrics studies ams are a useful tool in order to describe the distribution of deformation in orogenic areas where conventional techniques are difficult to apply especially due to the lack of proper strain markers in the present study ams and structural analysis are used to define the distribution of deformation in the central axial and nogueres zones an area of strong structural changes i in the geometry of the antiformal stack defining the pyrenean axial zone and ii the distribution of alpine cleavage the studied rocks are lower middle triassic red beds that crop out in three different stacked thrust units bielsa nogueres and orri primary sedimentary fabrics are preserved in the uppermost thrust units nogueres zone but a high percentage of the sampling sites shows an overprint of alpine compression on magnetic fabrics with the magnetic lineation mostly parallel to the tectonic grain defined by compressional structures and the magnetic foliation showing different orientations between the poles to cleavage and bedding the development of compressional fabrics strongly depends on the structural position of the sites and two deformation gradients can be inferred the southern margin of the axial zone orri and bielsa units shows strong internal deformation increasing towards the north farther north in the restored cross section deformation is in general terms lower but increases towards the basal thrust of the nogueres zone the heterogeneous distribution of alpine internal deformation indicates a preferred development of cleavage in the variscan basement and overlying units of the southern margin of the axial zone mainly in the orri unit that could be partly controlled by the tectonic load resulting from the stacking of thrust sheets

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

u pb age and lead isotopic characterization of au bearing skarn related to the andorra granite central pyrenees spain auriferous skarns are associated with post and late kinematic hercynian granites that intruded into cambro ordovician to devonian sediments of the central pyrenees we determined the age of the andorra granite and the associated skarn at 305 3 ma by u pb dating titanite from the endo skarn the sulfur isotopic composition from sulfides in the skarn cardellach et al 1992 shows a significant variation with isotopically light sulfur 34s 3 in the barren skarns and heavy sulfur 34s 11 in the gold bearing skarns outwards it increasingly resembles sulfur from arsenopyrite disseminations in the cambro ordovician sediments the lead isotopic composition from sulfides of the skarns is very homogeneous 206pb 204pb 18 410 207pb 204pb 15 699 208pb 204pb 38 574 in contrast to the one in gold bearing arsenopyrite veins and in arsenopyrite disseminations in the sediments e g 206pb 204pb varies from 18 54 to 30 36 combined sulfur and lead isotope data indicate that the lead in the skarn is dominantly derived from the granite whereas the sulfur is derived at variable portions from both the granite and the sediments

development law of air leakage fractures in shallow coal seams a case study in the shendong coalfield of china continuous air leakage from ground mining induced cracks is a significant cause of coal spontaneous combustion low oxygen at the working face and other disasters in shallow coal seams this paper studies mining induced cracks and air leakage caused by the repeated mining of shallow coal seams at the bulianta coal mine shendong coalfield china a similar simulation experiment was carried out in the laboratory and then the ground mining induced cracks were observed and the crack air leakage was detected the results showed that the surface air flowed into the composite goaf before the fractures redeveloped to the surface during the process of lower coal seam mining due to the different development processes of vertical fractures in various regions the width of the vertical fractures in the boundary area of the overlying goaf increases significantly after the repeated mining of coal seams while the vertical fractures in the central area of the overlying goaf experience almost no change the distribution of the surface air leakage cracks is in the shape of graben type cracks and half graben type cracks are surface air leakage cracks which are the focus of surface air leakage problems especially the half graben type cracks the results are important in engineering for reducing air leakage from surface mining induced cracks

late orogenic doming in the eastern betic cordilleras final exhumation of the nevado filabride complex and its relation to basin genesis the geometry timing and kinematics of late orogenic extension in the betic cordilleras pose the problem of a decoupling of upper crustal and lower crustal deformation regimes perpendicular directions of extension in metamorphic domes and nearby sedimentary basins remain unexplained this paper puts kinematic constraints on the final exhumation of the nevado filabride complex focusing on the formation of metamorphic domes and their relations with the adjacent basins structural fabrics and kinematic indicators below the main shear zones as well as their relations with both published changing metamorphic p t conditions and geochronological data were studied our approach describes 1 a consistent top to the west shear parallel to dome axes of during d2 i e during decompression with distributed ductile flow and the onset of strain localization along major shear zones 2 further strain localization along the major shear zones under greenschist facies conditions during d3 leading to s c mylonites formation accompanied with a rock strong thickness reduction 3 the divergence of shear direction on either limbs of domes during d3 showing the appearance of the dome geometry and 4 a local evolution toward n s brittle extension d4 in the upper plate and formation of sedimentary basins continuous ductile to brittle top to the west shear is compatible with the slab retreat hypothesis from the miocene the formation of domes which adds gravitational forces responsible for the final stages of exhumation is thus characterized by important kinematics changes necessary to explain coeval n s opened basins later from the upper tortonian a contractional event d5 amplified the earlier domal structures forming the present north vergent folds

a petrologic method of analysis of nonmaceral microstructures in coal abstract the petrographic maceral composition and vitrinoid reflectance of bituminous coals have been correlated with their carbonization characteristics and are widely used to predict how coals will perform in the coking process and to calculate the strength of the resulting coke as a result there is a growing dependence on coal petrographic data in characterizing coals for cokemaking in addition there is a growing awareness that there are other nonmaceral microstructures in coal such as material size shape association fracturing and weathering which should permit better characterization of coals when properly interpreted these nonmaceral microstructures also give an insight into the metamorphic history and changes due to burial and exhumanation to expand the use of coal petrologic and petrographic data a new analytical procedure has been developed that requires the microscopic determination of such nonmaceral microstructures as normal coal coal fines pseudovitrinoids microbrecciation oxidation coarse mineral matter miscellaneous materials and contamination the occurrence of one or more of these microstructures in coal depending on their kind and abundance may have a significant effect on the coal performance in various processes this work has resulted in formulation of a technique for determining the nonmaceral microstructures in coal and if applied as a supplement to the routine maceral analysis of coals should help in explaining the anomalous behavior of some coals

numerical modeling for analyzing thermal surface anomalies induced by underground coal fires abstract coal seams burning underneath the surface are recognized all over the world and have drawn increasing public attention in the past years frequently such fires are analyzed by detecting anomalies like increased exhaust gas concentrations and soil temperatures at the surface a proper analysis presumes the understanding of involved processes which determine the spatial distribution and dynamic behavior of the anomalies in this paper we explain the relevance of mechanical and energy transport processes with respect to the occurrence of temperature anomalies at the surface two approaches are presented aiming to obtain insight into the underground coal fire situation in situ temperature mapping and numerical simulation in 2000 to 2005 annual temperature mapping in the wuda inner mongolia pr china coal fire area showed that most thermal anomalies on the surface are closely related to fractures where hot exhaust gases from the coal fire are released those fractures develop due to rock mechanical failure after volume reduction in the seams the measured signals at the surface are therefore strongly affected by mechanical processes more insight into causes and effects of involved energy transport processes is obtained by numerical simulation of the dynamic behavior of coal fires simulations show the inter relation between release and transport of thermal energy in and around underground coal fires our simulation results show a time delay between the coal fire propagation and the observed appearance of the surface temperature signal additionally the overall energy flux away from the burning coal seam into the surrounding bedrock is about 30 times higher than the flux through the surface this is of particular importance for an estimation of the energy released based on surface temperature measurements finally the simulation results also prove that a fire propagation rate estimated from the interpretation of surface anomalies can differ from the actual rate in the seam

surface analysis of pyrite in the no 9 coal seam wuda coalfield inner mongolia china using high resolution time of flight secondary ion mass spectrometry abstract the chemical composition of pyrite in coal can be used to investigate its geological and mineralogical origin in this paper high resolution time of flight secondary ion mass spectrometry tof sims was used to study the chemical composition of various pyrite forms in the no 9 coal seam st d 3 46 from the wuda coalfield inner mongolia northern china these include bacteriogenic framboidal massive cell filling fracture filling and nodular pyrites in addition to fe 54fe 56fe 57fe other fragment ions were detected in bacteriogenic pyrites such as 27al si 28si 29si 30si 40ca cu 63cu 65cu zn 64zn 66zn 67zn 68zn ni 58ni 60ni 62ni and c3h7 tof sims images show bacteriogenic pyrites are relatively rich in cu zn and ni suggesting that bacteria probably play an important role in the enrichment of cu zn and ni during their formation intense positive secondary ion fragments from framboidal aggregates such as 27al 28si 29si alo ch2 c3h3 c3h5 and c4h7 indicate that formation of the framboidal aggregates may have occurred together with clay mineral and organic matter which probably serve as the binding substance the intense ions of 28si and 27al from massive pyrites also suggest that their pores incorporated clay minerals during crystallization together with the lowest 28si 23na value the intense organic positive secondary ion peaks from cell filling pyrites such as c3h3 c3h5 c3h7 and c4h7 indicate that pyrite formation may have accompanied dissolution or disintegration of the cell the intense p peak was observed only in the fracture filling pyrite and the highest 28si 23na value of fracture filling pyrite reflects its epigenetic origin together with xrd and rees data the stronger 40ca in nodular pyrite than other pyrite forms shows seawater influence during its formation

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

fissure formation and subsurface subsidence in a coalbed fire abstract coalbed fires are uncontrolled subsurface fires that occur around the world these fires are believed to be significant contributors to annual co 2 emissions although many of these fires have been burning for decades researchers have only recently begun to investigate physical mechanisms that control fire behavior one aspect of fire behavior that is poorly characterized is the relationship between subsurface combustion and surface fissures at the surface above many fires long wide fissures are observed at a coalbed fire near durango colorado these fissures form systematic orthogonal patterns that align with regional joints in the upper cretaceous fruitland formation understanding the mechanisms that form these fissures is important as the fissures are believed to play vital roles in sustaining the combustion in the subsurface in some of the coalbed fire simulation models available today these fissures are treated as fixed boundary conditions we argue using data collected field observations and simulation result that there exists a relationship between the location and magnitude of subsidence caused by the fire and the opening of fissures the results presented suggest that fissures are believed to open when subsurface subsidence gives rise to tensile stresses around pre existing joints

the abnormal condition analysis used to characterize weathered discard coals coal by its nature is unstable and weathers when exposed to moisture and oxygen weathering can result in a general decline on the commercial value and technological properties of coal coals of similar chemical properties have been shown to combust differently and the differences can be attributed to petrographic composition variations poor combustion environments and weathered particles stockpiled and dumped discard coals have been targeted for use by a lower power utility and a novel technique was developed to quantify and qualify the degree of weathering in these coals the petrographic based abnormal condition analysis previously referred to as the weathering index analysis considers features not typically characterized during routine petrographic analyses but which may have an impact on the technological properties of coals discard coals ranging in age from 5 to 40 years where characterized to determine the extent of secondary weathering eight secondary weathering features clearly different from inherent weathering were qualified and quantified margin effect appears to be an early microscopic indicator of weathering followed by discoloration alteration minerals have only been observed in stockpiled and dumped coals and hence could be a useful feature to benchmark when considering whether or not a coal has been stored long term stored coals have microcrack and fissure patterns clearly different from fresh coals the length of exposure to weathering processes was determined to be proportional to the extent of weathering as determined petrographically the abnormal condition analysis should be used as a supplement to routine coal petrography as it can assist with the determination of anomalous behavior of coals

early variscan visean granites in the core of central pyrenean gneiss domes implications from laser ablation u pb and th pb studies abstract laser ablation u pb and th pb single zircon and monazite geochronology was applied to seven samples from two variscan gneiss domes in the central pyrenean axial zone detrital zircon ages obtained from a paragneiss in the western aston dome range from neoarchean ca 2 57 ga to late neoproterozoic ca 560 ma suggesting that late ediacaran sediments were deposited along the northern margin of gondwana cadomian magmatism is recorded for the first time in the central pyrenees from a biotite metagranite ca 545 ma in the central aston dome a second sample of an orthogneiss from the aston dome yields a middle ordovician protolith age ca 467 ma similar in age to other dated orthogneisses of the axial zone three samples from granite stocks situated in the core of the aston and bossost domes have crystallization ages of ca 339 337 ma providing the first evidence of visean igneous activity in the axial zone in contrast to the larger and significantly younger ca 312 305 ma granite plutons along the margins of the gneiss domes visean magmatism caused lp ht contact metamorphism m 2 migmatization throughout the aston dome though less well constrained by overgrowth ages on zircon ca 331 ma and monazite ages ca 340 320 ma is likely to be related to visean intrusions the main s 2 schistosity in the aston and bossost domes is coeval with the visean intrusions inclusion trails in porphyroblasts nucleating in the contact aureoles document the continuous development of s 2 related to local extension crystal plastic deformation of the granites indicates that the d 2 deformation event continued after their crystallization visean magmatism played a crucial role in early stages of dome formation by thermally weakening the metasedimentary mantle and to a certain degree the orthogneiss as well enhancing the development of orogen parallel shear zones in an overall n s compressive setting

in situ u pb zircon ages for early ordovician magmatism in the eastern pyrenees france the canigou orthogneisses u pb age determinations with an ion probe on zircons within orthogneisses from the canigou massif eastern pyrenees give an emplacement age for their granitic protolith of 475 10 ma arenigian this invalidates the previous interpretation of basement cover relationships between the orthogneisses and the overlying lower cambrian canaveilles metasedimentary series and corroborates the intrusive character of the orthogneisses which is further supported by field evidence the data also define two groups of inherited zircons paleo meso proterozoic and cadomian in addition to partial lead loss during the hercynian late carboniferous high temperature low pressure metamorphic event these results are in agreement with ages reported from other orthogneissic bodies across the entire variscan chain of western europe and indicate the existence of a widespread cambro ordovician magmatic event

petrological arguments for high temperature extensional deformation in the pyrenean variscan crust saint barthelemy massif ariege france abstract the saint barthelemy massif is one of the variscan massifs of the north pyrenean zone thermobarometric analysis has been completed across a sequence comprising from bottom to top basal granulitic gneisses the main mylonite band and migmatites pt estimates are correlated with textures which represent progressive stages of gneissification and mylonitization the main foliation and the mylonitic textures were developed during the retrogressive evolution of the lp ht granulitic metamorphism retrogressive conditions are characterized by high heat flow associated with a pressure reduction the main penetrative deformation of the saint barthelemy massif is interpreted as resulting from a continuous extensional event

organic petrology of hat creek coal deposit no 1 british columbia abstract the upper eocene hat creek coal deposits of british columbia canada are one of the thickest lignite to subbituminous coal deposits of the world and comprise 350 550 m of coal samples of sedimentary organic material were taken from a 560 m interval of interbedded shale siltstone and carbonate that was penetrated by corehole 75 106 in the centre of the coal basin and the reflectances of huminite eu ulminite from coal and kerogen from the organic material were determined and petrographical analyses were made the coal deposit contains many leaf and resinite rich horizons and the reflectance of huminite in these horizons in lower than in corresponding horizons containing less liptinite when compared with huminite in adjacent coal beds the reflectance of huminite in shale is lower that in siltstone is similar and huminite associated with carbonate rocks has slightly higher reflectance values the petrological variation in the coal is mainly within the huminite group of macerals the coal at the top of the deposits is lignite r o 0 38 and becomes subbituminous c r o 0 50 at the base the inertinite content is very low indicating a low level of peat fire or oxidation the early stages of transformation of gelinite to macrinite are described the paleoenvironment appeared to be lacustrine as determined by organic petrological analysis of coals and interbedded sediments four major zones each containing many subzones were found paleoenvironments were similar for the a and c zones and also for the b and d zones

mercury emissions from dynamic monitoring holes of underground coal fires in the wuda coalfield inner mongolia china abstract the wuda coalfield inner mongolia china is one of the largest coalfields suffering from coal fires in china and has experienced fires for 50 years with the aim of observing the active state of underground coal seam fires to protect the main roadways of the coal mine 44 drill holes were drilled in five fire areas of the suhaitu coal mine to monitor gas emissions a lumexra 915 portable mercury analyzer was used to measure mercury concentrations in the exhaust gas the drill holes exhibited high gaseous mercury concentrations with an average of 4165 ng m 3 34 62 513 ng m 3 n 1584 which was 45 times higher than that measured in the near surface atmosphere around the drill holes this finding indicates that the mercury emissions originate from underground coal fires furthermore mercury concentration has a positive correlation with co content and gas temperature implying that mercury has the potential to act as a supplementary coal fire index gases to monitor the prevailing underground coal fire in north china on the basis of traditional indicators whether it can perform satisfactorily in practical applications requires further comprehensive study

dynamics and structural development of metamorphic core complexes the development of metamorphic core complexes mccs in a thickened continental lithosphere is studied using fully coupled thermomechanical numerical code accounting for elastic brittle ductile properties of constituent rocks for mccs to develop the middle lower crust and the sub moho mantle are required to be weak enough to flow laterally so as to simultaneously feed the exhuming dome and enable the moho to keep a flat geometry the conditions are satisfied with initial moho temperatures of 800 c or higher with crustal thicknesses of 45 km or greater and with initial effective viscosities lower than 1020 pa s and 1022 pa s in the lower crust and the underlying mantle respectively a compositional mainly density anomaly with the properties of granite is placed centrally in the crust to localize strain at the onset of deformation during a first stage of upper crust necking the deformation pattern is relatively symmetrical and dominated by graben formation in the upper crust when the first ductile layers reach the surface a second stage of dome amplification and widening occurs dome amplification is accommodated by horizontal flow in the ductile crust giving an early symmetrical pattern of conjugate shear zones with no obvious detachment zone the system then rapidly becomes asymmetric with the localization of a detachment zone along one dome limb further accommodating dome widening thus the exhumation process of a metamorphic dome results in the progressive development of a detachment zone depending on initial moho temperature the detachment zone can migrate in space or die out and be replaced by a new one with an opposite dip

oxidatively and thermally altered high volatile bituminous coals in high temperature coal fire zone no 8 of the wuda coalfield north china abstract coal fires have received increasing attention due to their environmental economic and social impacts their significant influence on coal properties is widely documented by geophysical and geochemical methods the present paper demonstrates by means of coal petrological methods significant changes of microstructure optical appearance and optical properties of medium rank bituminous coals affected by an underground coal fire the studied changes are suggested to result from distinct oxidative and thermal alterations induced by a high temperature regime temperatures over 800 c encountered in the coal fire zone no 8 wuda coalfield the investigated coal seam no 9 represents a high volatile a bituminous coal and is dominated by vitrinite followed by inertinite with minor amounts of liptinite the microstructure of the coal fire affected coals facilitate a broad spectrum of characteristic features the microscopic analyses revealed development of 1 non tectonic fissures and non tectonic fractures 2 distinct micropores 3 dark oxidations rims and 4 bright spots interpreted as incipient mesophases optical properties were characterised for megasporinite and vitrinite in the examined megasporinite a noticeable anisotropy and distinct granular appearance was observed in the investigated coals both a dominant increase as well as a minor decrease in both random and maximum vitrinite reflectances were documented for 1 coal grains and 2 dark rimmed vitrinite at non tectonic fissures and non tectonic fractures in addition also a characteristic bimodal vitrinite population was measured the increase in bireflectance was clearly documented for two sub zones within the coal fire zone no 8 the applied kilby s cross plots suggested a large overlapping of the data sets of r max and r min indicating marked changes in vitrinite structure the applied coal petrological approach revealed distinct changes to the coal s microstructure appearance as well as to optical properties induced by the underground coal fire the presented coal petrographic approach may help determine the extent of coal fires in coal mines and the direction of propagation of coal fire front

permo carboniferous paleogeography and coal accumulation and their tectonic control in the north and south china continental plates abstract permo carboniferous strata in north china and south china were essentially controlled by paleogeography paleoclimate and plate tectonics during that time north china and south china were separate microcontinents located on opposite sides of the equator thus the characteristics of their coal deposits differ substantially in north china the coal seams were initially deposited on a north sloping epicontinental basin during the middle carboniferous by the middle of the late permian the locus of coal formation had shifted from the north to the south as a result of the uplift of the northern margin due to continental collision with the siberian plate as the paleoplate was situated in the low northern latitudes moist tropical climate and favorable geographic setting allowed the extensive development of late carboniferous and earliest permian peat swamps on the northern alluvial fluvial plain and central paralic regimes more significantly two thick coal sequences were formed in the transition belt between the alluvial apron and fluvial plain and the shoreline area where high groundwatertable fed by both rainwater and groundwater favored the formation of thick peat in swamps with northward drift the paleoplate entered the subtropic semiarid and arid climatic belt between the late early permian and early late permian coal formation was restricted to the paralic delta plain where locally oceanic wet climate and high groundwatertable prevailed following this the subduction of the paleo tethys beneath the southern margin of north china led to the upwarp of the southern margin and kept the delta system growing vertically for a considerable period so that it kept pace with shoreline fluctuations on the southern area the result was that multicycle deltaic coals were well developed at this stage in south china coal was formed in the coastal zone of an epeiric and shelf sea which connected the marinal basins the basins were frequently influenced by plate marginal tectonic movements and continental rifting related to back arc extension as a result coal formation was often interrupted by sea level fluctuations early carboniferous coal was deposited during the short regressions during the widespread transgression mainly on the restricted marine paralic plain where clastic deposition was active in the middle and late carboniferous no coal was formed because the paleoplate had drifted into a subtropic arid belt early permian coal accumulated at first in the northeast and later in the southwest due to tectonic influences in the late permian relatively thick and extensive coal was formed even though it was during a transgressive period in both the western and eastern margins under the equatorial hot humid conditions in general the seam geometry and quality particularly ash and sulfur of the coal was directly controlled by the geography and the changes in the depositional environments however the fluctuation in coal formation and the migration of thicker coal zones was indirectly controlled by paleoclimate and the sea level fluctuations in response to plate tectonic influences

cold water corals are they hydrocarbon seep related numerous cold water ahermatypic coral reefs so called lophelia reefs up to 30m high 150m wide and 400m long occur at waterdepths from 100 to 350 m off mid norway after the discovery of relatively high interstitial methane concentrations 204 ppb in sediments collected at the base of one of these reef structures a causative link between the presence of the reefs and local micro seepage through seabed of light hydrocarbons is here suggested shallow seismic records gathered across this and other reef colonies off mid norway also indicate the existence of gas charged sediments below the reefs

two stage deformation of the mont louis andorra granite pluton variscan pyrenees inferred from magnetic susceptibility anisotropy the mont louis andorra granodiorite pluton eastern pyrenees france andorra and spain was the subject of a thorough study of its internal structures principally the measurement of the anisotropy of its magnetic susceptibility and the classification of its microstructures regularly spaced sampling 281 sites allowed the precise mapping of the susceptibility magnitudes consistent with mapped rock types the magnetic structures fall into two distinct families which occur in separate parts of the pluton and have different microstructures family i is observed almost everywhere and has close to horizontal lineations remarkably constant in ne sw azimuth magmatic to submagmatic microstructures characterize these rocks in contrast family ii is confined within nw se trending corridors where moderate to steep nw plunges of the lineations are recorded and subsolidus microstructures are observed magnetic structures of family i are argued to equate with the kinematic framework of the deforming magma during its emplacement family ii structures represent a late to post consolidation reworking and therefore record a second stage of deformation in the pluton it is concluded that magma emplacement was related to a ne sw trending strike slip and or thrust fault system coeval with the sw verging thrust episode documented in the pyrenees the second stage corresponds to dextral shear movements with a thrust component on nw se striking planes corridors containing family ii structures are shear zones responsible for dissection of the massif into three blocks the eastern block representing the former base and the western block the top of the pluton restoration of the pluton9s shape along these corridors demonstrates the importance of the early variscan ne sw kinematic direction because the family ii structures that form shear zones affecting the pluton have similar orientation and kinematics as the compressive steep main phase of deformation ubiquitous in the pyrenees the pluton of mont louis andorra was probably emplaced before this main phase of deformation

sedimentary record of triassic intraplate extension in north china evidence from the nonmarine nw ordos basin helan shan and zhuozi shan abstract the helan shan and zhuozi shan of the nw ordos basin china contain thick up to 4 km sequences of nonmarine triassic strata these rocks represent a major intraplate sedimentary basin the paleogeography tectonic setting and provenance of which are poorly understood and controversial studies of the sedimentary geology of the basin supported by new palinspastic reconstruction of younger deformation demonstrate that the basin filled from three sides by fluvial lacustrine deltaic and alluvial fan depositional systems the basin forms a westward thickening wedge that reaches its maximum thickness along the western margin of the helan shan and thins to a relatively constant 600 800 m east of the zhuozi shan the stratigraphy of the basin is strongly asymmetric alluvial fan strata are restricted to the extreme western margin of the basin and interfinger with axial fluvial deposits low in the section and deep lacustrine facies high in the section much of the eastern part of the basin is dominated by west flowing meandering river and deltaic systems large structures of triassic age have not been identified in the helan shan or zhuozi shan but small triassic normal faults have been documented in the western and central helan shan these characteristics most strongly support an extensional origin for the triassic basin in nw ordos the basin is interpreted to have been a north trending half graben bound along its western margin by an east dipping normal fault presently concealed beneath quaternary cover west of the helan shan the eastern margin now found in the zhuozi shan has simple ramp margin geometry driving mechanisms for this extension are not obvious due to limited documentation of triassic structure throughout the region but probably relate to far field stresses from the qinling or jinsha active margins interacting with the stable ordos block

mineralogy and geochemistry of the no 6 coal pennsylvanian in the junger coalfield ordos basin china abstract this paper discusses the mineralogy and geochemistry of the no 6 coal pennsylvanian in the junger coalfield ordos basin china the results show that the vitrinite reflectance 0 58 is lowest and the proportions of inertinite and liptinite 37 4 and 7 1 respectively in the no 6 coal of the junger coalfield are highest among all of the late paleozoic coals in the ordos basin the no 6 coal may be divided vertically into four sections based on their mineral compositions and elemental concentrations a high boehmite content mean 6 1 was identified in the no 6 coal the minerals associated with the boehmite in the coal include goyazite rutile zircon and pb bearing minerals galena clausthalite and selenio galena the boehmite is derived from weathered and oxidized bauxite in the weathered crust of the underlying benxi formation pennsylvanian a high pb bearing mineral content of samples zg6 2 and zg6 3 is likely of hydrothermal origin the no 6 coal is enriched in ga 44 8 g g se 8 2 g g sr 423 g g zr 234 g g rees 193 3 g g hg 0 35 g g pb 35 7 g g and th 17 8 g g gallium and th in the no 6 coal mainly occur in boehmite and the pb bearing selenide and sulfide minerals contribute not only to se and pb contents in the coal but also probably to hg content a high zr content is attributed to the presence of zircon and sr is related to goyazite the rees in the coal are supplied from the sediment source region and the rees leached from the adjacent partings by groundwater

coalbed methane characteristics of gates formation coals northeastern british columbia effect of maceral composition the majority of research reported on methane adsorption characteristics of coal seams has focused on vitrinite rich coals however western canadian coals are more inertinite rich than those of the western united states and are shown to differ in gas adsorption characteristics the influence of maceral composition upon gas adsorption characteristics of medium volatile coal samples from the middle cretaceous gates formation of northeastern british columbia was investigated lithotype coal facies samples were analyzed for surface area maceral and mineral composition and methane adsorption standard coal analyses were also performed proximate low temperature ash and equilibrium moisture the vitrinite content of the samples analyzed ranges from 18 to 95 vol min ral matter free the ash yield varies from 4 4 to 33 7 wt both maceral composition and mineral matter content have an important influence on adsorption characteristics as indicated by carbon dioxide surface areas and methane adsorption isotherms on a mineral matter free basis the amount of methane adsorbed generally increases with vitrinite enrichment the lowest methane adsorption occurs in the sample with the highest inertinite content carbon dioxide surface areas of the lithotypes range from 87 to 176 m2 g on a raw coal basis and from 99 to 184 m2 g on a mineral matter free basis surface area generally decreases with increased mineral matter content and increases with increased vitrinite content the increase in adsorption of both methane and carbon dioxide with increased vitrinite concentration is interpreted a resulting from differences in the pore size distribution of vitrinite and inertinite vitrinite is predominantly microporous whereas inertinite is meso to macroporous the monolayer volumes of carbon dioxide as calculated from the dubininradushkevich equation are higher than those of methane as determined from the langmuir equation but are correlated the methane adsorption isotherms and surface area data indicate that the maceral compositional variations in coal are at least as significant as coal rank in determining the potential volume of adsorbed methane and thus the coalbed methane potential of a deposit

the detection of weathering in coal by petrographic rheologic and chemical methods abstract this study examines petrographic rheologic proximate and ultimate analyses techniques to investigate the effects of natural weathering on coal the applicability of such tests to both the detection of weathering and to the prediction of the properties of a fresh coal based upon analyses of a weathered sample is discussed rheologic parameters and a petrographic staining technique showed the most sensitive response to weathering the latter test is considered the most suitable of these for the detection of weathering as it is independent of prior knowledge of the properties of the fresh coal and of the petrographic composition a petrographic approach is also considered most suitable for estimation of fresh coal characteristics from weathered samples rank may be closely approximated and petrographic type determined microscopically even on highly weathered samples and these two parameters may be used to estimate properties such as volatile matter calorific value and dilatation minor modification should be made to vitrinite reflectance measurements according to the degree of weathering as revealed by selective staining

the late palaeozoic early mesozoic from the catalan pyrenees spain 60 myr of environmental evolution in the frame of the western peri tethyan palaeogeography the eastern catalan pyrenees form the southernmost segment of the pyrenean axial zone they experienced complex multistage process as the result of both the variscan and the pyrenean orogenic cycles after the late palaeozoic several small extensional sub basins were filled by continental successions as a response to the changing tectonic setting within the frame of the southwestern europe this stratigraphic record perfectly exposed in the studied eastern pyrenean areas preserves the signatures of the late palaeozoic pangea break up during the progressive dismantling of the variscan chain up to the triassic diffused extension despite structural network being severely affected by cenozoic reworking the stratigraphic framework can be unravelled by the detailed sedimentological and stratigraphical analysis of the well exposed sequences in short this paper addresses facies patterns and architectural elements of late carboniferous permian triassic continental sections studied in the catalan pyrenees and aims to use these signatures for correlation not only at a regional scale but also within the broader picture of the southwestern europe our stratigraphical reconstruction clearly demonstrates that the thick studied succession consists of fluvial lacustrine basal units affected by intense volcanic activity and overlaying predominantly fluvial fining upwards units for each unit several lithofacies architectural elements and bounding surfaces of different order have been identified and their lateral and vertical staking characterized deposition and erosion processes are controlled by alternating periods of tectonic activity producing different stages of high and low subsidence the uplift of the sub basin margins and subsequent extended erosive events marked by angular unconformities on the strength of the major rank bounding surfaces analysis the studied sedimentary packages have been grouped into different tectono stratigraphic units and then correlated they have been contextualized within the latest palaeogeographic reconstructions of the studied sector contributing to detail the role of the study area within the frame of the s european palaeogeography

anatomy of an extensional shear zone leading to the exhumation of the middle crust within the canigou dome eastern pyrenees axial zone abstract to investigate the mechanism of exhumation of deep crustal rocks in hot orogens we focus on the southwestern part of the variscan canigou gneiss dome pyrenees where the transition between the middle and upper crust can be observed on the basis of new structural data geological mapping cross sections microstructural analyses and petrologic observations we propose that flat lying foliation within the gneiss dome and steep cleavage developed above it formed coevally we note the presence of regional scale shear zones at the boundary between the middle crust nuria canigou unit and upper crust puigmal unit at this boundary the e w south canigou shear zone is an extensional shear zone showing top to the southwest kinematics deformation which is localized within the andalusite biotite transition zone occurred under retrogressive conditions from high grade ductile to brittle conditions during the main deformation stage d2 the tectonic contact was folded during a later stage d3 we propose that the shape of the canigou dome resulted from the activation of extensional shear zones at the top of the orthogneiss leading to partial exhumation of high grade rocks the canigou gneiss dome can be considered an extensional dome that formed during late variscan ca 310 290ma transpression

binderless briquetting of some selected south african prime coking blend coking and weathered bituminous coals and the effect of coal properties on binderless briquetting abstract the binderless briquetting of some selected south african prime coking and blend coking coals as well as the effects of weathering on the binderless briquetting of some inertinite rich bituminous coals were investigated in the laboratory selected properties of these coals were determined and the coals were briquetted at various moisture contents and pressures based on the results obtained in this study binderless briquetting was found to be most successful in the cases of the fresh vitrinite rich coking and blend coking coals and satisfactory in the fresh inertinite rich witbank coals however the bonding process seemed to be adversely affected by weathering the negative impact on bonding could be ameliorated to some extent by the presence of a significant kaolinite content when the percentage ash reports in the order of more than 15 air dry basis it should however be noted that kaolinite may reduce the water resistance of the briquettes

thermobarometric constraints on the conditions of metamorphism in the canigou massif pyrenees implications for hercynian geothermal gradients quantitative thermobarometry of garnet biotite sillimanite f cordierite pelitic assemblages from the canigou massif and constraints based on consideration of high grade metapelitic reaction equilibria indicate that peak temperatures during hercynian metamorphism reached 725 25 c at depths of 16 2 km 4 5 0 5 kbar this corresponds to an average peak geothermal gradient of 45 50 c km 1 which is in broad agreement with results from studies of granulite facies assemblages in the pyrenees but is significantly lower than gradients proposed for some other amphibolite facies areas in the terrane it is suggested that the claims by numerous authors for peak hereynian geothermal gradients in the pyrenees in excess of 70 100 c km 1 fail to consider the effects of post metamorphic attenuation of metamorphic sequences and the unreliable nature of p estimates made in the absence of suitable assemblages for quantitative thermobarometry

variations in vitrinite reflectance with organic facies examples from pennsylvanian cyclothems of the midcontinent u s a abstract significant variations in vitrinite reflectance r0 with organic facies have been demonstrated from pennsylvanian aged cyclothems of the midcontinent u s a thermal alteration index tai and rock eval tmax values remain relatively constant through these thin lithologic successions irregardless of facies and are in reasonable agreement with r0 measurements on interbedded coal organic rich black and phosphatic black shales which contain a significant component of liptinitic organic matter of presumed marine algal derivation display r0 values which are suppressed relative to the coal benchmark a distinct correlation between increased hydrogen index hi and liptinite content with suppressed reflectivities is apparent more oxic facies e g calcareous and fosiliferous gray shales and limestones often display r0 s that are considerably higher than for coal soxhlet extraction prior to maceration yielded no variation in reflectance compared to non extracted kerogens suggesting bitumen adsorption was not the cause of the apparent suppression in the organic rich black shales lower total organic carbon toc normalized bitumen contents and rock eval transformations ratios in liptinite rich facies suggest different reaction kinetics for kerogen types with terrestrial organic matter maturing at an earlier stage than hydrogen rich marine derived organic matter

evolution of optical properties of vitrinite sporinite and semifusinite in response to heating under inert conditions abstract the objective of the study was to characterize changes of reflectance reflectance anisotropy and reflectance indicating surface ris shape of vitrinite sporinite and semifusinite subjected to thermal treatment under inert conditions examination was performed on vitrinite liptinite and inertinite concentrates prepared from channel samples of steam coal r r 0 70 and coking coal r r 1 25 collected from seam 405 of the upper silesian coal basin the concentrates were heated at temperatures of 400 1200 c for 1 h time in an argon atmosphere all components examined in this study vitrinite sporinite and semifusinite as well as matrix of vitrinite and liptinite cokes despite of rank of their parent coal show in general the most important changes of reflectance value and optical anisotropy when heated at 500 c 800 c with the exception of bireflectance value of sporinite and 1200 c after heating the steam coal at 1200 c the vitrinite and the semifusinite reveal similar reflectances whereas the latter a slightly stronger anisotropy sporinite and matrix of liptinite coke have lower reflectances but anisotropy r bi and r am values similar to those observed for vitrinite and semifusinite however at 1000 c sporinite and matrix of liptinite coke have the highest reflectivity of the studied components the ris at 1200 c is the same for all components the optical properties of the three macerals in the coking coal become similar after heating at 1000 c coke obtained at 1200 c did not contain distinguishable vitrinite grains at 1200 c semifusinite and vitrinite coke matrix have highest r r values among the examined components maximum reflectance r max reach similar values for vitrinite and sporinite slightly lower for semifusinite matrix of liptinite coke and matrix of vitrinite coke have considerably stronger anisotropy r bi and r am values than other components ris at 1200 c is also similar for all components

early permian coal forming floras preserved as compressions from the wuda district inner mongolia china four different compression impression floras are preserved in only 4 32 m of the geologic section in the early permian shanxi formation of the wuda district of inner mongolia northwestern china these floras represent four different plant communities and landscapes that followed each other in time the oldest flora was rooted in sandy clay and initiated peat accumulation that lead to the formation of the lower coal seam this seam is 230 cm thick and overlain by a 66 cm thick volcanic tuff that preserves a second different flora that grew on the peat at the time of the ash fall standing stems and large plant parts are present the upper part of the tuff is rooted by a single species of lycopsid the third flora again initiating peat accumulation on top of this second seam of 120 cm thickness rests a roof shale deposited as mud in a shallow lake the formation of which was responsible for the cessation of peat deposition this fourth flora represents the plants growing around the lake on clastic substrate four different environments followed each other in this locality over a geologically short time span and each time conditions prevailed to preserve plant macrofossils three of these floras represent peat forming plant communities of essentially the same time interval this demonstrates the great variability of vegetation and landscapes in the tropical cathaysian realm of the late paleozoic

hercynian tectonometamorphic evolution of the bosost dome french spanish central pyrenees metamorphic and structural studies show that the bosost dome central pyrenees is a metamorphic as well as a structural dome developed in cambro ordovician to devonian metasediments around a migmatitic core during the hercynian orogeny the structural metamorphic dome occurs in epizonal terranes and is twice as large as originally described the structural dome shows a concentric zoning of d2 and d3 local deformations developed around the migmatites and superimposed on the d1 regional hercynian deformation the structural data suggest that migmatites were emplaced diapirically into palaeozoic metasediments during d1 and are responsible for the local d2 and d3 deformations an early medium pressure high temperature metamorphism occurred during d1 leading to anatexis under water rich conditions then evolved progressively to a high temperature low pressure metamorphism during the d2 and d3 deformations the corresponding p t time path is a clockwise loop representing the evolution of the metamorphism from migmatiza tion to the diapiric emplacement of migmatites in a compressional setting pressure values obtained from geobarometry are three times as high as expected from sedimentological data this suggests that the hercynian metamorphism developed in a thickened crust during the n s shortening responsible for the large scale e w folding observed throughout the pyrenean axial zone

mesozoic contractional deformation in the middle of the asian tectonic collage the intraplate western ordos fold thrust belt china abstract intraplate deformation can occur at great distances from synchronous plate boundaries and is most likely the result of strain concentrations into weak zones these weak zones may be pre existing crustal heterogeneities such as faults thermally weakened zones due to magmatism and or the effects of a thick sedimentary cover or mechanical contrasts between adjacent crustal blocks intraplate deformation is not exclusively related to continent continent collision it can be the result of a change in subduction dynamics or the interaction of two convergent plate boundaries asia has many examples of active intraplate deformation that are thought to be related to the cenozoic indo asian collision although much attention is placed on active examples discerning controls on pre cenozoic asian intraplate deformation will lead to not only a better understanding of the processes involved in intraplate orogens but also the tectonic evolution of asia situated on either side of the yellow river along the western margin of the ordos plateau the intraplate western ordos fold thrust belt involves units as old as archean basement and as young as late jurassic the fold thrust belt is spectacularly exposed in two ranges the helan shan and the zhuozi shan cross sections drawn through the north trending fold thrust belt suggest 30 minimum shortening a paleocurrent reversal within the lower middle jurassic section is interpreted to mark the onset of contraction and mountain building a late jurassic synorogenic boulder conglomerate records the final deformation in the fold thrust belt synchronous with contraction and cutting across the fold thrust belt is an e w striking strike slip fault that displays right lateral drag and sub horizontal striae we interpret this fault as an accommodation structure in the thrust belt following e w contraction the thrust belt was dismembered by an n15 w trending left lateral strike slip fault the left lateral fault displaces the frontal portion of the thrust belt the zhuozi shan 62 km to the north relative to a more internal portion the helan shan we propose that the anomalous orientation and intraplate location of the western ordos fold thrust belt is a function of mechanical contrasts between a previously deformed area and a stable crustal block ordos to the east pre existing crustal weakness or anisotropy along the western margin of the ordos block is most likely related to either a late proterozoic early paleozoic aulacogen a triassic fault system or to both although its intraplate location and the complexities of mesozoic asian plate interactions make it difficult to relate deformation in the western ordos fold thrust belt to a specific contemporaneous plate boundary its n s trend may suggest a link with paleo pacific subduction along the eastern margin of asia