temporal evolution of the magmatic system at tungurahua volcano ecuador detected by geodetic observations abstract changes in the pathway and timescale of magma ascent can be responsible for variations in eruptive style during long lived eruptions but are only documented at a small number of well instrumented systems here we integrate ps insar from high resolution terrasar x radar imagery with continuous gps data from 4 sites at tungurahua volcano ecuador our results show long term uplift between 2011 and 2014 associated with a continuously inflating prolate spheroid reservoir at a depth of 10 km beneath the summit comparisons with eruptive flux taking compressibility into account suggest that during this time period slightly over half the magma supplied to the system was erupted the observations span three distinct phases of eruption and in 2012 2013 an increase in eruptive activity was accompanied by uplift on the volcano s western flank similar episodes have previously been observed during large vulcanian eruptions and we attribute them to intrusions into an area of mechanical weakness a localised patch of subsidence mid way up the tungurahua s western flank is co located with a swarm of shallow long period seismicity and may represent a potential site for a development of a lateral vent this study demonstrates that satellite geodetic techniques are capable of characterising the geodetic signature of transitions in eruptive style during long lived andesitic eruptions even where deformation is low magnitude and measurements are challenging

control actions of sedimentary environments and sedimentation rates on lacustrine oil shale distribution an example of the oil shale in the upper triassic yanchang formation southeastern ordos basin nw china abstract oil shale is an important form of unconventional resources it is significant to determine the control factors on oil shale distribution abundant oil shale resources are hosted in the member chang 7 3 ch7 3 triassic yanchang formation in southeastern ordos basin nw china this study was conducted to investigate the sedimentary environment distribution and organic matter source of the ch7 3 oil shale by a combined study of outcrops core data organic and element geochemical indices the controlling factors of the oil shale distribution were determined by an analysis of sedimentary environments and geochemical features of the oil shale sedimentary facies analysis based on outcrops and core data indicated that the ch7 3 oil shale was deposited in lacustrine delta environments warm and moist climates and reducing conditions indicated by major and trace elements were favorable to organic matter production and preservation rock eval pyrolysis showed that the organic matter of the ch7 3 oil shale is from both lacustrine phytoplankton and terrigenous higher plants the organic matter from terrigenous higher plants was probably transported into the deep lake by gravity flows sedimentary facies and la yb n values show that the spatial distribution of oil shale was controlled by sedimentary environments and sedimentation rates in the deep lake area near to delta turbidite fan deposition systems terrestial organic matter input was bounteous and sedimentation rates were moderate which were beneficial to organic matter accumulation and preservation providing favorable conditions for oil shale formation in delta turbidite fan deposition systems high sedimentation rates led to organic matter dilution in the deep lake area far from delta turbidite fan deposition systems sedimentation rates were relatively low and organic matter was easily degraded in addition only lacustrine organic matter input with no terrestial organic matter input inhibited organic matter enrichment

persistent scatterer interferometric synthetic aperture radar for crustal deformation analysis with application to volcan alcedo galapagos 1 while conventional interferometric synthetic aperture radar insar is a very effective technique for measuring crustal deformation almost any interferogram includes large areas where the signals decorrelate and no measurement is possible persistent scatterer ps insar overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms existing ps methods have been very successful in analysis of urban areas where stable angular structures produce efficient reflectors that dominate background scattering however man made structures are absent from most of the earth s surface furthermore existing methods identify ps pixels based on the similarity of their phase history to an assumed model for how deformation varies with time whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study we describe here a method for ps analysis stamps that uses spatial correlation of interferogram phase to find pixels with low phase variance in all terrains with or without buildings prior knowledge of temporal variations in the deformation rate is not required for their identification we apply stamps to volcan alcedo where conventional insar fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time we detect two sources of deformation the first we model as a contracting pipe like body which we interpret to be a crystallizing magma chamber the second is downward and lateral motion on the inner slopes of the caldera which we interpret as landsliding

petrology and geochemistry of mafic rocks in the acasta gneiss complex implications for the oldest mafic rocks and their origin abstract the acasta gneiss complex located in the western part of the slave province canada is widely recognized as the oldest eoarchean terrane in addition to felsic gneisses with the ages of 3 6 4 0 ga minor mafic rocks occur as rounded to elliptical enclaves and inclusions within the felsic gneisses despite serving as potential sources of geochemical information on the hadean mantle the mafic rocks have received less attention in previous studies thus we conducted a comprehensive geological petrological and geochemical investigation on the acasta mafic rocks to constrain their petrogenesis and geodynamic setting the mafic rocks comprise massive to weakly foliated amphibolite garnet amphibolite and hornblendite with variable abundances of hornblende plagioclase chlorite and quartz and subordinate clinopyroxene garnet and cummingtonite they commonly underwent high grade metamorphic recrystallization under amphibolite to upper amphibolite facies conditions the observed variations in mineral assemblages abundances and compositions reflect large differences in whole rock compositions likely caused by crustal anatexis during the eoarchean thermal events responsible for the generation of the surrounding felsic gneisses infiltration or extraction of felsic melts formed due to partial melting of precursor rocks can account for an overall negative correlation between al 2 o 3 and mgo contents and variable enrichments in the incompatible elements despite the widespread influence of anatexis on the geochemistry of acasta mafic rocks we identified the precursor compositions of the least modified amphibolites as basaltic magmas they are characterized by intermediate al 2 o 3 and mgo contents on the observed array and by near chondritic patterns for incompatible trace elements except for slightly negative nb and ta anomalies we considered two scenarios to explain the origin of eoarchean basaltic rocks with nb ta anomalies 1 generation of nb ta deficient basaltic magma in a suprasubduction setting analogous to modern arcs derived magmas and 2 generation of nb ta deficient basaltic magma from the melting of a nb ta deficient primitive mantle possible if the core contains significant proportions of the earth s nb and ta budget although the operation of plate tectonics and the presence of subduction zones at the end of hadean may be an attractive explanation for the observed nb ta depletions the chondritic relative proportions of other immobile trace elements for acasta mafic rocks leave open the possibility of their formation from an nb ta deficient primitive mantle

sequential porphyroblast growth during deformation in a low pressure metamorphic terrain orrs island harpswell neck maine poikiloblastic index minerals in pelitic rocks from the orrs island harpswell neck area of coastal maine contain inclusion textures that indicate sequential growth of progressively higher grade metamorphic minerals during development of a near vertical crenulation foliation the sequence of zones in the field is garnet staurolite staurolite andalusite staurolite sillimanite and sillimanite inclusion fabrics characteristic of different stages in crenulation cleavage development indicate that index minerals nucleated and grew sequentially biotite began to grow before deformation garnet began to grow during early stages of crenulation cleavage development staurolite grew during intermediate stages and andalusite grew relatively late when transposition of the foliation was nearly complete muscovite pseudomorphs and sillimanite were mainly post kinematic the fact that metamorphic index minerals grew sequentially in individual rocks in the same order in which they appear across the field area indicates that the high temperature part of the pressure temperature path was similar to the metamorphic field gradient metamorphism in the orrs island harpswell neck area is consistent with the magmatic heating model that has been proposed for western maine sequential development of index minerals in pelitic rocks in the orrs island harpswell neck area apparently resulted from sequential nucleation after substantial overstepping of mineral forming reactions once nucleation of an index mineral had taken place initial growth was rapid and poikiloblasts preserved inclusion trails characteristic of the prevailing stage of crenulation cleavage development because nucleation of sillimanite may have required more overstepping of the andalusite sillimanite reaction than nucleation at dehydration reactions determination of metamorphic conditions for rapidly heated rocks such as these by comparison with a petrogenetic grid is problematic garnet zoning patterns in these rocks should reflect the fact that growth of garnet interiors occurred early during metamorphism in equilibrium with a low grade assemblage only garnet rims would be expected to record the subsequent pressure temperature path

the challenging retrieval of the displacement field from insar data for andesitic stratovolcanoes case study of popocatepetl and colima volcano mexico abstract despite the ability of synthetic aperture radar sar interferometry to measure ground motion with high resolution application of this remote sensing technique to monitor andesitic stratovolcanoes remains limited specific acquisition conditions characterizing andesitic stratovolcanoes mainly vegetated areas with large elevation ranges induce low signal coherence as well as strong tropospheric artefacts that result in small signal to noise ratio we propose here a way to mitigate these difficulties and improve the sar measurements we derive ground motions for two of the most active mexican stratovolcanoes popocatepetl and colima volcano from the time series of sar data acquired from december 2002 to august 2006 the sar data are processed using a method that combines both persistent scatterers and small baseline approaches stratified tropospheric delays are estimated for each interferogram using inputs from the global atmospheric model narr up to a maximum of 10 rad km these delays are validated using spectrometer data as well as the correlation between the wrapped phase and the elevation the tropospheric effect is removed from the wrapped phase in order to improve the unwrapping process on popocatepetl we observe no significant deformation the colima summit area exhibits a constant subsidence rate of more than 1 cm year centered on the summit but enhanced reaching more than 2 cm year around the 1998 lava flow we model this subsidence considering both a deflating magma source at depth and the effect of the eruptive deposits load

deep lacustrine sandy debrites and turbidites in the lower triassic yanchang formation southeast ordos basin central china facies distribution and reservoir quality abstract the deep lacustrine gravity flow deposits are widely developed in the lower triassic yanchang formation southeast ordos basin central china three lithofacies include massive fine grained sandstone banded sandstone and massive oil shale and mudstone the massive fine grained sandstones have sharp upper contacts mud clasts boxed shaped gamma ray gr log but no grading and bouma sequences in contrast the banded sandstones display different bedding characteristics gradational upper contacts and fine upward the massive fine grained sandstones recognized in this study are sandy debrites deposited by sandy debris flows while the banded sandstones are turbidites deposited by turbidity currents not bottom currents the sediment source for these deep gravity flow sediments is a sand rich delta system prograding at the basin margin fabric of the debrites in the sandy debris fields indicates initial formation from slope failure caused by the tectonic movement as the sandy debris flows became diluted by water and clay they became turbidity currents the deep lacustrine depositional model is different from the traditional marine fan or turbidite fan models there are no channels or wide lobate sand bodies in the lower triassic yanchang formation layers within the sandy debrites have higher porosity 8 14 and permeability 0 1 4 md than the turbidites with lower porosity 3 8 and permeability 0 04 1 md consequently only the sandy debrites constitute potential petroleum reservoir intervals results of this study may serve as a model for hydrocarbon exploration and production for deep lacustrine reservoirs from gravity flow systems in similar lacustrine depositional environments

controls on organic matter accumulation in the triassic chang 7 lacustrine shale of the ordos basin central china abstract the triassic chang 7 formation is a rich lacustrine source rock in the ordos basin central china petrographic and geochemical analyses were performed in order to research the mechanism of organic matter om enrichment in the chang 7 shales bulk geochemical data indicate that the om rich shales were formed in a fresh and brackish water which is not usually the case for high toc total organic carbon content sediments therefore there must be some special conditions favorable for om enrichment in chang 7 shales petrography and element geochemistry show that the chang 7 om rich shales are abundant in om enriched laminae framboidal pyrites collophanes and some elements including iron fe diphosphorus pentoxide p2o5 copper cu vanadium v molybdenum mo and uranium u high bio productivity algae blooming and anoxic depositional environments are critical for om enrichment as the organic carbon contents increase the fe p2o5 cu v mo and u element contents increase as well and the ratios of u th and v v ni are growing many geochemical data demonstrate that the water was oxic while the environment under the sediment water interface was anoxic as a result of a high organic supply that sufficiently consumed oxygen taking into account the geological settings and our previous studies we propose that the frequent volcanic events and hydrothermal activity caused by the collision of the north china landmass with the yangtze landmass and consequential formation of the qingling mountains had a significant role in the om enrichment in the fresh and brackish lacustrine shales deposition of volcanic ash into aqueous environments might lead to the increase of some key nutrients such as fe and p2o5 which might enhance primary bio productivity new evidence for hydrothermal activity the reddingite was demonstrated in this study not only can the hydrothermal activity provide elements necessary for life but is also favorable for formation of anoxic settings the deposition of the chang 7 lacustrine om rich shales can be explained using the high bio productivity driven model which is related to volcanic events and hydrothermal activity as a consequence of regional tectonic movements an anoxic depositional setting is beneficial for om preservation and slow sedimentation rates in the deep lacustrine environments are favorable for om enrichment

formation distribution and resource potential of the sweet areas sections of continental shale oil in china abstract shale oil refers to oil stored in organic rich shale it is an important part of unconventional oil and provides a large amount of resources based on the systematic study of the geological characteristics of shale oil in china s major continental basins the geological connotation of the sweet area section in shale oil is proposed in this paper and it refers to areas sections that can be preferentially explored and developed in oil bearing shale formations under current economic and technical conditions the formation conditions and distribution characteristics of continental shale oil in china are analyzed with a focus on the geological properties of the triassic yanchang formation in the ordos basin the cretaceous qingshankou formation in the songliao basin and the permian lucaogou formation of the jimusar sag in the junggar basin it is found that the sweet areas of shale oil with medium high maturation are mainly located in thick shales with a ro greater than 0 9 and the sweet sections are mainly located in the middle and lower parts of the shale formation the geological resources of continental shale oil in the major continental basins in china are estimated to be approximately 3700 108 tons the in situ conversion process icp may be a key technology for the effective development of medium to low mature shale oil the scale maximum burial depth and present depth of the organic rich shale are proposed as the three key parameters for the optimization of pilot sites by taking the triassic yanchang formation in the ordos basin as an example using icp it is expected that the recoverable resources of china s continental shale oil will be approximately 400 500 108 tons the terminology of man made reservoir is proposed in this paper in an man made reservoir the overall industrial output of the sweet areas sections is formed by artificial intervention and the construction of an underground fracture network system with man made permeability continental shale oil may be another revolutionary source of unconventional oil and is expected to be first successfully produced in china

tungurahua volcano ecuador structure eruptive history and hazards abstract tungurahua one of ecuador s most active volcanoes is made up of three volcanic edifices tungurahua i was a 14 km wide andesitic stratocone which experienced at least one sector collapse followed by the extrusion of a dacite lava series tungurahua ii mainly composed of acid andesite lava flows younger than 14 000 years bp was partly destroyed by the last collapse event 2955 90 years ago which left a large amphitheater and produced a 8 km3 debris deposit the avalanche collided with the high ridge immediately to the west of the cone and was diverted to the northwest and southwest for 15 km a large lahar formed during this event which was followed in turn by dacite extrusion southwestward the damming of the chambo valley by the avalanche deposit resulted in a 10 km long lake which was subsequently breached generating another catastrophic debris flow the eruptive activity of the present volcano tungurahua iii has rebuilt the cone to about 50 of its pre collapse size by the emission of 3 km3 of volcanic products two periods of construction are recognized in tungurahua s iii history from 2300 to 1400 years bp high rates of lava extrusion and pyroclastic flows occurred during this period the magma composition did not evolve significantly remaining essentially basic andesite during the last 1300 years eruptive episodes take place roughly once per century and generally begin with lapilli fall and pyroclastic flow activity of varied composition andesite dacite and end with more basic andesite lava flows or crater plugs this pattern is observed in the three historic eruptions of 1773 1886 and 1916 1918 given good age control and volumetric considerations tungurahua iii growth s rate is estimated at 1 5 106 m3 year over the last 2300 years although an infrequent event a sector collapse and associated lahars constitute a strong hazard of this volcano given the 3000 m relief and steep slopes of the present cone a future collapse even of small volume could cover an area similar to that affected by the 3000 year old avalanche the more frequent eruptive episodes of each century characterized by pyroclastic flows lavas lahars as well as tephra falls directly threaten 25 000 people and the agoyan hydroelectric dam located at the foot of the volcano

thermodynamic projection and extrapolation of high variance mineral assemblages a procedure is described whereby the effect of extra components on the plotting positions of minerals in projected phase diagrams may be accounted for rigorously the method employs the equilibrium constraints of the mineral assemblage to extrapolate the compositions of the minerals to where the values of the extra components approach 0 the same procedure may also be used to extrapolate the compositions of natural assemblages over isothermal isobaric composition diagrams or polythermal polybaric diagrams

continuous hydrocarbon accumulation over a large area as a distinguishing characteristic of unconventional petroleum the ordos basin north central china abstract global petroleum exploration is currently undergoing a strategic shift from conventional to unconventional hydrocarbon resources unconventional hydrocarbons in tight reservoirs show characteristics distinct from those of conventional hydrocarbon sources hosted in structural and stratigraphic traps the characteristic features include the following a hydrocarbon source and reservoir coexist porosity and permeability are ultra low nano pore throats are widely distributed hydrocarbon bearing reservoir bodies are continuously distributed there is no obvious trap boundary buoyancy and hydrodynamics have only a minor effect and darcy s law does not apply phase separation is poor there is no uniform oil gas water interface or pressure system and oil or gas saturation varies examples of unconventional hydrocarbon accumulations are the mesozoic tight sandstone oil province and the upper paleozoic tight sandstone gas province in the ordos basin north central china generally continuous hydrocarbon accumulation over a large area is a distinguishing characteristic of unconventional hydrocarbon sources because of the great potential of unconventional petroleum resources it is believed that research on such resources will be at the forefront of the future development of petroleum geology

sedimentary and diagenetic controls on reservoir quality of low porosity and low permeability sandstone reservoirs in chang101 upper triassic yanchang formation in the shanbei area ordos basin china abstract there are many reservoirs with low porosity and low permeability in the world and many large oilfields have been found in these reservoirs unlike conventional reservoirs the genesis of low porosity and low permeability reservoirs and the controls of relatively high porosity and high permeability zones are still unclear this study takes the chang101 reservoir sandstones of the shanbei area in the ordos basin china a typical low porosity and low permeability as an example chang101 sandstones are fine grained to medium grained moderately to well sorted arkose and lithic arkose deposited in a delta plain environment it is a typical low porosity and low permeability reservoir with an average porosity of 10 21 and an average permeability of 2 88 md pore types mainly include primary intergranular pores and secondary dissolved pores the main controls on the reservoirs are the sedimentary environment and diagenesis the sedimentary environment determines the initial properties of the reservoir sandstones including the material composition and texture that determine the primary porosity and permeability diagenesis further transforms the reservoir quality to develop heterogeneity in the porosity and permeability the reservoir sandstones have undergone complex diagenetic processes and are currently in stage a of mesodiagenesis compaction accounts for the major reduction of the primary porosity of the sandstones different types of cementation have both positive and negative influences on reservoir quality carbonate cementation quartz overgrowths and some authigenic clay cementation i e i s and illite are major pore filling components that reduce the reservoir quality an appropriate amount of chlorite resists compaction and prevents quartz overgrowth but excessive chlorite coatings fill the pores and block the pore throats the laumontite cement is not only resistant to compaction but also easily dissolved to form a large number of effective secondary pores the dissolution of feldspar and rock fragments plays a role in contributing to connecting the isolated intergranular pores and increasing the secondary pores relatively high porosity and high permeability zones are deposited in high energy environment mainly delta plain distributary channel sandstones with more detrital quartz fewer rock fragments and coarser grains than other sandstones were deposited in high energy environment there is weaker compaction and less or no carbonate cement with the preservation of the primary pores by chlorite coatings and an increase in the pores by the dissolution of laumontite cement

effects of diffusional modification of garnet growth zoning on p t path calculations the effect of intragranular diffusion on chemical zoning in garnet and on p t paths calculated from that zoning was evaluated using a numerical model of multicomponent diffusion in combination with simulations of garnet growth syn and post growth diffusion of mg fe mn ca species in garnet was calculated for a model pelitic assemblage over a range of temperatures from 485 to 635 c compositions from zoned garnet as modified by diffusion hypothetical inclusions of plagioclase within garnet and matrix phases were used to reconstruct pressure temperature p t paths from isobaric and polybaric model histories p t path calculations based on numerical simulations conducted over an input isobaric heating path that reached peak temperatures between 585 and 635 c show that relaxation of garnet compositional gradients by diffusion can induce modest to appreciable curvature in the inferred paths retrieved paths also indicated somewhat smaller overall temperature changes relative to the actual temperature difference of the input path the magnitude of these distortions is shown to depend upon the heating and cooling rate and garnet crystal size as well as the actual peak temperature condition the effect of diffusion on path trajectories in simulations with thermal histories that also included cooling were comparable to heating only models that reached peak temperatures approximately 15 30 c higher compositions of garnets with radii less than 1 mm that reached actual peak temperatures of 605 c along temperature time histories characteristic of regional metamorphism experienced sufficient diffusional relaxation to introduce errors of hundreds of bars to in excess of one kilobar in path trajectories path distortions were significant at heating cooling rates less than 10 c ma but rapidly diminished for rates faster than this in polybaric simulations diffusion effects were least noticeable when the actual pressure temperature conditions changed in a clockwise sense i e convex to higher p and higher t but apprecciable modification was seen in path models that underwent counterclockwise changes in p and t reequilibration of garnet rim compositions occurred during cooling on all paths and temperature maxima obtained from garnet biotite geothermometry underestimated actual peak conditions by 40 to 70 c calculations suggest that p t path trajectories calculated from garnets of at least 1 mm size and that experienced actual thermal maxima below 585 c are not likely to be distorted by diffusional effects during regional metamorphism however p t path reconstructions based on garnet zonation with smaller grains or higher temperatures may lead to misinterpretation of crystallization history the partitioning record of peak metamorphic temperatures may be destroyed by diffusional reequilibration of garnet rim compositions during cooling seriously complicating the task of quantitatively estimating diffusion effects on path calculations

detrital zircon provenance of the late triassic songpan ganzi complex sedimentary record of collision of the north and south china blocks the majority of the songpan ganzi triassic flysch sequence is believed to have derived from denudation of the dabie and sulu ultrahigh pressure uhp metamorphic belt in eastern china e g nie et al 1994 1 zhou and graham 1996 2 however intense debate still exists on the sources of

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

tectonic and stratigraphic controls of hydrocarbon systems in the ordos basin a multicycle cratonic basin in central china the ordos basin is the oldest and still an important hydrocarbon province in central china it is a typical cratonic basin developed on the archean granulites and lower proterozoic greenschists of the north china block the development of the ordos basin during the paleozoic mesozoic can be divided into three evolutionary stages cambrian early ordovician cratonic basin with divergent margins middle ordovician middle triassic cratonic basin with convergent margins and late triassic early cretaceous intraplate remnant cratonic basin two hydrocarbon systems are present in the basin the paleozoic gas and mesozoic oil systems in the paleozoic gas system the lower ordovician marine carbonates and pennsylvanian lower permian coal measures serve as source rocks the lower ordovician karst modified dolomites and pennsylvanian bauxitic mudstones form a significant reservoir seal association and the pennsylvanian lower permian deltaic sandstones and upper permian lacustrine mudstones form another effective reservoir seal association in the mesozoic oil system the upper triassic lacustrine mudstones are mature source rocks the upper triassic deltaic sandstones and overlying shallow lacustrine and swamp mudstones form a reservoir seal association and the lower jurassic fluvial sandstones and overlying shallow lacustrine and swamp mudstones form another reservoir seal association in both hydrocarbon systems the stratigraphic variations provide the principal traps the ordos basin is characterized by a stable tectonic setting that controlled the distribution of depositional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types

fracture responses of conventional logs in tight oil sandstones a case study of the upper triassic yanchang formation in southwest ordos basin china fractures are the main fluid flow pathways in tight oil sandstones and they have a significant influence on tight oil distribution exploration and development cores and image logs are commonly unavailable because of their high costs so employing conventional logs for fracture detection is imperative for tight oil sandstones we compared the fracture response characteristics of conventional logs based on two data sets one from 8 cored wells with fracture intensities greater than 1 m 1 3 3 ft 1 and the other from 11 cored wells with fracture intensities less than 0 5 m 1 1 6 ft 1 with a case study of the upper triassic yanchang formation in southwest ordos basin china the results indicate that when tight oil sandstones are more intensely fractured the caliper log acoustic log compensated neutron log density log dual induction logs and laterolog 8 present fracture responses to some extent however it is difficult to make a distinction between fractured and nonfractured zones using conventional logs in sandstones with smaller fracture intensities the fracture response intensities of conventional logs are weak and they are influenced by fracture abundance fracture occurrence fracture scale and mineral filling degree moreover lithology fluids and rock physical properties can cause fracturelike responses hence some ambiguity exists when using conventional logs to directly identify fractures accompanying fracture sensitive conventional logs with some methods to enhance fracture response intensity and eliminate nonfracture influence could enable fracture identification in tight oil sandstones

metamorphic fractional crystallization and internal metasomatism by diffusional homogenization of zoned garnets metamorphic fractional crystallization involves fractionation of material into the interior of a crystallizing mineral such as garnet with consequent change in the effective bulk composition in assemblages with thermodynamic variance of 3 or greater the mineral assemblage compositions of coexisting phases and the zoning profile preserved in the garnet are a function of the amount of material that is fractionated homogenization of zoned garnet by intracrystalline diffusion at elevated temperatures operates on a time scale of millions to tens of millions of years depending on the temperature time path and radius of the garnet one effect of homogenization is to drive chemical reactions by a metasomatic mechanism internal metasomatism even in the absence of changes in pressure or temperature this process may affect the appearance or disappearance of minerals and may in some rocks be responsible for the first appearance of kyanite or the disappearance of staurolite in barrovian terranes

long period seismicity in the shallow volcanic edifice formed from slow rupture earthquakes volcanic eruptions are often preceded by long period seismic events that were thought to be generated by the resonance of cracks filled with magmatic fluid analysis and modelling of long period seismicity at volcanoes in italy costa rica and peru shows that it could instead be caused by slow rupture along faults in the upper volcanic edifice

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

controls on hydrocarbon accumulation by facies and fluid potential in large scale lacustrine petroliferous basins in compressional settings a case study of the mesozoic ordos basin china abstract large scale lacustrine basins in compressional settings are an important type of petroliferous basin and the study of the characteristics of hydrocarbon accumulation in such basins is of great significance this synthesis paper takes the mesozoic ordos basin central china as a case study to establish lateral and vertical hydrocarbon accumulation patterns in this basin type and highlights how facies and fluid potential control hydrocarbon accumulation in such basins based on systematic analyses of the mesozoic source rocks sedimentary facies migration and accumulation patterns and characteristics of the oil reservoirs the hydrocarbon accumulation characteristics in the mesozoic ordos basin are discussed the analysis indicates that sedimentary facies controlled the characteristics and distribution of hydrocarbon source rocks and reservoirs while diagenetic facies controlled the quality and distribution of the reservoirs excess pressure and fluid potential controlled hydrocarbon migration directions and paths whereas facies and potential controlled the locations of oil accumulations and traps it is concluded that source rocks controlled oil bearing regions sedimentary facies controlled oil bearing plays and fluid potential controlled the locations of accumulations for shallow intervals because fluid migration is mainly controlled by buoyancy paleotopographic highs played an important role in controlling hydrocarbon accumulations for deep layers chang 7 to chang 10 members since buoyancy is less than the capillary pressure excess pressure caused by the undercompaction of mudstone and hydrocarbon generation at depth provides the driving force for lateral and vertical migration of oil and becomes the main migration force the reservoir accumulation characteristics differ laterally between regions of the basin at the periphery of the basin reservoir units are stacked in a step wise manner whereas at the center of the basin multiple reservoir intervals are vertically stacked in the form of multistorey accumulations vertically layers with different burial depths have different accumulation characteristics the paleotopography controlled hydrocarbon accumulation in shallow intervals instead excess pressure fluid potential and paleotopography controlled accumulation in deep intervals this understanding could be used to inform prospecting in other large scale lacustrine petroliferous basins in compressional settings such as the eocene green river basin in the u s a and the middle triassic gunnedah basin in australia

triassic diorites and granitoids in the foping area constraints on the conversion from subduction to collision in the qinling orogen china abstract the western qinling is characterized by triassic granitic plutons which are keys to constrain the timing of subduction and collisional processes between the north china and south china blocks this paper presents a set of new la icpms u pb zircon geochronology major and trace element geochemistry for several representative diorite and granitoid plutons in the foping area the diorites are characterized by high mgo al2o3 y and yb contents but low sio2 sr y and la yb ratios as well as depletion of nb ta p and ti suggesting derived from a subduction related setting la icpms zircon u pb age of 216 9 1 5 ma mswd 0 69 from the diorite constrains the time of the subduction event the medium and fine grained monzogranites as well as the biotite granites exhibit relative high sio2 mgo and rb low y and yb contents and low sr y and la yb ratios as well as various depletions of nb ta p and ti these features indicate a derivation from lower continental crust but had been influenced by slab released fluids in a syn collisional setting the medium grained monzogranite and biotite granite yield la icpms zircon u pb ages of 207 3 2 1 ma mswd 1 8 and 201 6 1 2 ma mswd 1 04 respectively proposing the syn collision during ca 207 201 ma geochemical and geological evidences suggest that the granodiorites intruding in the syn collisional monzogranites were related to the post orogenic collapse after the collision between the north china and south china blocks the la icpms u pb zircon age of 189 3 2 9 ma mswd 5 6 for the granodiorite constrains the time of the post orogenic collapse our geochronological and geochemical data provide important constraints on the triassic evolution from subduction to collision then up to post collisional collapse along the qinling orogen

diagenesis of tight sandstone reservoirs in the upper triassic yanchang formation southwestern ordos basin china abstract in order to better predict the petrophysical properties of the tight sandstone reservoirs in the upper triassic yanchang formation ordos basin china the nature of the diagenetic system involved was investigated using a suite of petrographic and geochemical techniques including thin section and x ray diffraction analysis scanning electron microscopy maps mineralogy cathodeluminescence electron probe microanalysis and fluid inclusion analysis on a set of selected tight sandstone samples the sandstones investigated are texturally mature but compositionally immature with an average framework grain composition of q32f41l27 authigenic quartz calcite and chlorite coatings are the major cements while feldspars are partially dissolved two groups of quartz cement are present in the tight sandstone reservoirs smectite to illite conversion provided silica source for the first group of quartz overgrowth qo i while the silica source for the second quartz overgrowth qo ii was mainly originated from feldspar dissolution calcite cements consist of two types namely ca i and ca ii the ca i calcite cement contains no chlorite coatings and have higher concentrations of fe2 and mg2 whereas the ca ii calcite cement developed over the chlorite coatings plagioclase dissolution appears to be always accompanied by calcite cementation while k feldspar albitization forms euhedral albite locally the burial diagenesis processes were in most cases not episodic but occurred as slow adjustments in response to increased burial depths and temperatures in all the studied diagenetic minerals elemental distributions appear to be strictly constrained by the interaction of authigenic minerals involved indicating that the chemical reactions during the diagenesis comply well with the general principle of mass balance the diagenesis in the upper triassic yanchang formation tight sandstones was thus mainly developed in a closed geochemical system where mineral dissolution and precipitation are approximately balanced and diagenetic fluids were not affected by external sources significantly mechanical compaction has played a more important role in destroying the primary porosities of the upper triassic yanchang formation than the cementation

migration features of crude oil in fluvial deposits of maling oilfield in ordos basin china abstract oils in the maling oil field ordos basin are produced from fluvial deposits within the yan 9 and yan 10 subsections of the yanan formation through the analysis of pyrrolic nitrogen compounds and fluid inclusions the oil charging site migration direction and pathway and timing were interpreted in relationship with the sedimentary features and the high pressure observed in the mesozoic sequence the spatial distribution pattern of the fractionation of neutral nitrogen compounds in the crude oils suggested two possible charging positions in the studied area the ratios of the isomeric nitrogen compounds increase toward the center of the study area from both northwest and southeast directions of the region indicating that the lateral charging directions were likely from both the southeast and the northwest toward the center of the oil field the isomeric ratios of pyrrolic nitrogen compounds in the oils from different area of the maling oilfield increase with the decrease of depth from yan 10 to yan 4 5 subsections showing vertical migration of oil to the reservoirs the homogenization temperature of fluid inclusions in the reservoir rocks exhibited two peaks reflecting the two stages of oil migration and accumulation the migration pathways include fluvial sand bodies and unconformity surfaces the migration driving force was likely the capillary pressure and the abnormally high strata pressure in the mesozoic sequences

the effects of thermomechanical heterogeneities in island arc crust on time dependent preeruptive stresses and the failure of an andesitic reservoir using ground deformation data from soufriere hills volcano shv we present results from numerical modeling of the temperature and time dependent stress evolution in a mechanically heterogeneous crust prior to reservoir failure and renewed eruptive activity the best fit models do not allow us to discriminate between a magmatic plumbing system consisting of either a single vertically elongated reservoir or a series of stacked reservoirs a prolate reservoir geometry with volumes between 50 and 100 km3 reservoir pressure changes between 4 and 7 mpa and reservoir volume changes between 0 03 and 0 04 km3 with magma compressibility between 4 10 11 and 1 10 9 pa 1 provide plausible thermomechanical model parameters to explain the deformation time series around an order of magnitude less overpressure than is generally inferred from homogeneous elastic crustal models reservoir failure is predicted to occur at the crest of the reservoir except for reservoirs with highly compressible magma 4 10 9 pa for which subhorizontal sill formation is predicted upon reservoir failure introducing a deep crustal hot zone modulates the partitioning of strains into the hotter underlying crust and results in a further reduction in overpressure estimates to values of around 1 2 mpa upon reservoir failure deduced volume fluxes are consistent with constraints from thermal modeling of active subvolcanic systems and imply dynamic failure of a compressible magma mush column feeding eruptions at shv our interpretation of the results is that the combined thermomechanical effects of a deep crustal hot zone and hot encasing rocks around a midcrustal andesitic reservoir fundamentally alter the time dependent subsurface stress and strain partitioning upon reservoir priming these effects substantially influence surface strains recorded by volcano geodetic monitoring

fractal analysis of tight shaly sandstones using nuclear magnetic resonance measurements assessing quantitatively the microscopic pore structures of porous rocks including irregularities of pore shapes and pore size distributions is becoming one of the most challenging efforts nuclear magnetic resonance nmr measurements were used to provide insights into the pore geometry pore size and shape and pore connectivity of the chang 7 tight shaly sandstones in situ permeability 0 1 md in ordos basin the incremental transverse relaxation time t2 distributions for the 100 brine saturated samples display unimodal and bimodal behaviors presenting a geometrical arrangement composed of small to large pore size domains the nmr parameters such as bulk volume irreducible bvi capillary and clay bound water free fluid index ffi movable water the value of t2 separating the bvi from ffi the amplitude weighted mean on a logarithmic scale t2gm and the value of t2 that shows the highest frequency on the t2 spectrum t2peak for each sample were determined then the fractal theory was adopted to quantitatively express the complexity and heterogeneity of the sandstones the results show that only minor primary intergranular porosity remains and variable amounts of micropores and secondary intragranular porosity with poor connectivity occur in the chang 7 tight shaly sandstones assuming spherical pores a new model to calculate the fractal dimension of pore structure from the nmr t2 distributions is proposed the fractal dimensions of all the samples are calculated and the accuracy of the proposed model is verified by the regression coefficients the microscopic pore structures are heterogeneous in these tight sandstones according to the high value of fractal dimensions micropores are the primary causes of heterogeneity in tight sandstones and samples with unimodal t2 distribution behaviors and high content of short components have the highest fractal dimension and heterogeneity the calculated fractal dimension is strongly correlated with t2peak and t2gm therefore the fractal model proposed in this study can be used to calculate the fractal dimensions and evaluate the heterogeneities of the porous rocks satisfactorily the fractal model proposed in this study helps to quantitatively assess the pore structures of tight sandstones using nmr measurements

dynamic basis of volcanic spreading the established models of the structure and dynamics of a typical hawaiian volcano lead inevitably to a paradox finite element viscoelastic calculations using tecton melosh and raefsky 1980 1981 predict that a compressional stress field should characterize their upper flanks instead extension is observed the paradox is solved by postulating that volcanic evolution is determined by feedback processes related to growth and spreading of the volcanic edifice many examples of the process of spreading are documented in the geologic literature on volcanoes of a very broad size range and very different geologic settings the process is similar across many orders of magnitude in size the deformation of the substratum related to magma intrusion during lava dome building events is at the lower end of the scale the spreading of seafloor at oceanic ridges is at the higher end of the scale volcanoes may evolve from small constructs into huge shield volcanoes and perhaps into ocean plates key elements for volcanic spreading are 1 the existence of a weak basal layer and 2 a sufficiently high mass and magma influx to drive the process as the mass of a volcano grows it passes through five phases which may overlap repeat or be omitted building compressing thrusting intruding and spreading during the building phase the mass of a volcano does not significantly affect the stress field of the substratum primitive magmas are likely to be erupted as the mass increases the volcano subsides and becomes characterized by a compressional stress field which inhibits any further intrusion of magma into the volcanic edifice magma may differentiate in the crust allowing for large caldera forming eruptions to occur in the next phase thrusting begins on a decollement usually located at the foot of the edifice while the stress field on the upper slopes of the volcano remains compressional the stress at the base close to the center becomes extensional allowing the magma to intrude and differentiate at the base of the edifice a basal intrusive complex begins to grow explosive eruptions may be expected finally spreading of this complex creates an extensional stress field on the upper flanks of the volcano confining compression to the lower slopes of the edifice the extension allows primitive magma to erupt again at the summit the process of spreading seems to have a fundamental influence on the structural and magmatic evolution of volcanoes at every scale this process results from coupling and feedback between the gravitational and thermal fields thus studying this process may improve our understanding of the relation between structural dynamics and magma evolution and of the origin and evolution of volcanic seismicity and eruptions

tectonic features of oil and gas basins in eastern part of china during the mesozoic cenozoic eastern china underwent two stages of structural development sedimentary basins in eastern china have certain characteristics basement faults are well developed in these basins there was rapid sedimentation during the mesozoic cenozoic the basins are located on either side of the songliao depression the amount of subsidence in these basins is limited with a maximum depth of sedimentation of 4 000 to 6 000 m 13 000 to 20 000 ft during the mesozoic the most intense tectonic movements occurred in the songliao basin where there was much faulting accompanied by volcanic activity the bohai bay basin was the center of major tertiary tectonic activity there are more than 50 major basement faults in this basin basin formation was controlled primarily by movement of the pacific plate and related volcanic activity these basins are epicontinental basins along the margin of continental crust hydrocarbons were generated during the time of basin formation and much of the oil and gas discovered has been in rocks where it was generated or where migration was over short distances

a field and theoretical analysis of garnet chlorite chloritoid biotite assemblages from the tri state ma ct ny area usa the prograde evolution of minerals in metapelites of a barrovian sequence from the tri state area massachusetts connecticut new york of the taconic range involves assemblages with garnet ga chlorite ch chloritoid ct biotite bi and staurolite st detailed petrologic observations mineral compositions and chemical zoning in garnet show 1 garnet high in mn and fe but low in mg is stable with chlorite at grades below those where chloritoid biotite is found 2 early formed garnet reacted partially to form ct bi at intermediate grades 3 at higher grades garnet with low mn chlorite is again produced at the expense of chloritoid biotite suggesting a reversal in the continuous reaction involving the phases ga ch ct and bi thermodynamic modeling of the assemblage ga ch ct bi st in the mnkfmash system reveals 1 in the mnkfash system the prograde reaction is ga ch ct bi whereas in the kfmash system the prograde reaction is the opposite ct bi ga ch 2 the ga ch ct bi st invariant point in the kfmash system occurs twice at approximately 6 5 kbar 545 c and 14 8 kbar 580 c although one of them may be metastable in a complex phase system the appearance of the petrogenetic grid is markedly different from that of albee but similar to that of spear and cheney 3 as a consequence in the kfmash system chloritoid biotite are stable over a wide range of p t conditions whereas garnet chlorite assemblages are restricted to a narrow band of p t conditions 4 mno increases the stability field of ga ch relative to both ct bi at low temperatures and st bi at high temperatures 5 in natural samples the occurrence of ct bi is controlled more by bulk mg fe mn composition than p t conditions specifically ct bi is restricted to bulk compositions with fe mg fe mn 0 6 rocks with fe mg fe mn 0 5 are likely to display only chlorite biotite at low grade these observations are consistent with wang and spear and spear and cheney

lacustrine basin unconventional resource plays key differences abstract there has been a revival in hydrocarbon source rock characterization and development associated with growing interest in unconventional resources where these fine grained organic rich rocks act as both source and reservoir to date the exploration focus on shale reservoirs has been largely on marine systems lacustrine source rocks for conventional resources are geographically important dominating regions such as china indonesia and brazil s resource base however they have been generally untested for unconventional resources there are a number of key differences in the nature of these hydrocarbon systems that should be considered when assessing whether lacustrine systems may represent future unconventional opportunities in areas where the conventional resource base is dominated by lacustrine sourced oil among the key differences between these depositional systems is the greater sensitivity to high frequency climatic variability within lacustrine systems lacustrine systems are highly sensitive to changes in the balance between precipitation and evaporation which may lead to rapid changes in lake level potentially exceeding 600 m these changes in depositional conditions are geologically rapid and may occur over periods of thousands of years such changes can reduce the areal extent of potentially thick source rock intervals to only those portions of a basin where a permanent deep lake was present thus the core unconventional target area may be geographically limited compared with their marine counterpart although potentially areally limited a review of many lacustrine source rocks suggests that their thicknesses are often significantly greater than marine source rocks an examination of the more distal portions of lacustrine systems where better source rock potential is present reveals that there is generally limited connectivity between source and conventional reservoir in these settings such as the wind river basin waltman shale the hydrocarbons remain trapped within the shales potentially leading to over pressured hydrocarbon charged systems such conditions suggest that although areally limited viable unconventional targets may exist if suitable reservoir conditions are present finally the character of the oils produced is different in these settings with lacustrine oils being waxy and displaying different hydrocarbon generation and cracking kinetics high wax oils display distinct flow characteristics being more viscous and may offer different production challenges than their non waxy marine equivalents additionally differences in their cracking kinetics may indicate that the timing of gas generation for shale gas plays may differ significantly from marine systems

crust mantle relationships in the french variscan chain the example of the southern monts du lyonnais unit eastern french massif central garnet lherzolite from the lyonnais area eastern french massif central occurs as several lenses elongated within the regional foliation of garnet biotite sillimanite gneisses within the peridotites a mylonitic foliation can be observed which clearly is oblique to the regional foliation of the surrounding gneisses petrological and thermobarometric studies emphasize a tectonometamorphic re equilibration for both crustal and mantle rocks characterized by a prograde metamorphic stage followed by retrograde evolution during the burial stage interpreted as lithospheric subduction the peridotites underwent their mylonitic deformation under high pressure conditions 23 30 kbar in contrast the paragneisses have suffered their deformation during the retromorphic evolution under mesozonal conditions 6 8 kbar 700 c our thermobarometric investigations allow us to interpret the granulitic ultramafic association from the monts du lyonnais area as a lithospheric section buried into a palaeozoic subduction zone laminated during continental collision and uplifted by erosion processes

models for dynamic evaluation of mudstone shale cap rocks and their applications in the lower paleozoic sequences sichuan basin sw china abstract the estimation of the sealing capability of cap rocks dynamically is one of the fundamental geological problems that must be resolved in petroleum exploration in this paper a porosity capillary pressure p c method was used to estimate the sealing capacity during cap rock burial and a permeability capillary pressure k p c plus over consolidation ratio ocr method to estimate the sealing capacity during uplift based on 120 capillary pressure porosity measurements a p c mathematical model has been established for the burial phase by analyzing the permeability data measured from 12 mudstone shale samples from different stratigraphic intervals under step loading conditions a permeability confining pressure k p mathematical model has been constructed moreover capillary pressure permeability data measured from 141 mudstone or shale cap rocks have been used to establish a k p c mathematical model for seal capacity evaluation during uplift additionally the ocr of mudstone or shale was calculated from the results of reconstructed burial and uplift histories these mathematical models were used in case studies in the sichuan basin south china the results indicate that capillary pressure p c is inadequate in evaluating sealing capacity of cap rocks but the combination of parameters p c and ocr works well the agreement between calculated and measured values shows the effectiveness and reliability of the models for dynamic estimation of the sealing capacity of mudstone shale cap rocks established in this study

upper paleozoic petroleum system ordos basin china abstract the ordos basin is a typical lapped basin including three sequences of strata early paleozoic late paleozoic and mesozoic with a total thickness of 4000 6000 m impermeable sealing beds are well developed at the top and base of the upper paleozoic sequence separating it from the mesozoic and the lower paleozoic strata to form an independent petroleum system in this petroleum system the source rocks are widely distributed coals and dark mudstones occurring in the carboniferous lower permian coal measures with a thickness of 10 15 and 40 60 m respectively the reservoirs are mainly early permian tight sandstones mostly with a porosity of 4 8 and a permeability of 0 1 1 0 10 3 m2 the regional cap rock is a 100 150 m thick mudstone in the upper permian strata the structural framework of the basin is a huge asymmetric syncline dipping gently toward the east and north and steeply toward the south and west well data show that gas saturated gas water transition and water saturated zones are developed from the depositional center to the basin edges the gas saturated zone mainly lies in the gently dipping slope area of the shanbei slope toward eastern and northern up dip directions the water gas transitional zone occurs and finally the water saturated zone presenting a reverse relation of water on top of gas an abnormal negative strata pressure is developed in the gas bearing area with a pressure coefficient cp ranging from 0 83 to 0 95 fluid inclusion data indicate that the upper paleozoic gas pool began to develop around the wuqi area at about 150 ma and it extended toward the north and was largely formed at about 120 ma showing there was a regional migration of the gas water interface from south to north during the gas pool formation these characteristics appear to show that the northern and eastern margins of the petroleum system are defined by a regional hydrodynamic regime the critical moment of the petroleum system occurred during the early cretaceous the basin experienced a rapid subsidence and a significant geothermal event resulting in the source rocks being matured into the main stage of gas generation to form a huge amount of gas the gas migrated into the tight sandstone reservoirs and displaced the rock pore water to form the gas pools and developing the regional hydrodynamic trap

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

resource potential and core area prediction of lacustrine tight oil the triassic yanchang formation in ordos basin china unlike liquid rich hydrocarbons in marine shale systems in north america the triassic yanchang oil is preserved in tight sandstone reservoirs deposited in a lacustrine setting the tight reservoir covers an area of 30 000 km2 11 600 mi2 and is characterized by ultralow permeability 0 001 1 00 md 0 001 10 3 1 00 10 3 m2 a low subsurface pressure coefficient 0 6 0 8 and low single well yield several tons 10 40 bbl to 10 tons 70 bbl per day the reservoir also features a high content of quartz feldspar and carbonate averaging 70 80 and low crude oil density of 0 84 g cm3 36 5 api with an oil saturation of approximately 60 80 for the first time this study employs the assessment of petroleum in place resources based on the genesis and statistics predicting method gspm and estimated ultimate recovery method for the tight oil in the ordos basin the advantage of gspm over previously reported methodologies is the suitable combination of genetic and statistical methods to estimate proximally sourced tight oil the results show that the total in place resource potential of the investigated tight oil is approximately 42 26 108 t 295 82 108 bbl with an average abundance of 15 104 t km2 99 104 bbl mi2 the recoverable resources for the 50 probability of the chang 7 tight oil accumulation is 3 11 108 t 21 77 108 bbl in the ordos basin the top two grades of the chang 7 tight oil core area cover the total area of three layers comprising 12 745 km2 4921 mi2 with 22 51 108 t 157 57 108 bbl of in situ resources furthermore the four most promising zones have been identified

mineral zoning p t x m phase relations and metamorphic evolution of some adirondack granulites new york detailed petrologic analysis of ten meta anorthosites and related introduction rocks from the adirondack highlands new york has been used to the adirondack highlands of new york are one of constrain the p t history of the region metamorphic orthopyroxene the best studied granulite facies terranes of the world and clinopyroxene occur in aggregates of 1 mm diameter grains e g bohlen et al 1985 valley et al 1990 and that are zoned concentrically with decreasing al and fe fe mg references therein based on this considerable volume and increasing ca towards the rim moreover zoning is not related of work the peak metamorphic conditions in the to the presence of garnet zoning is interpreted to have been produced adirondack highlands have been fairly well constrained during growth by the reaction igneous pyroxene plagioclase at pressures of 7 8 kbar crustal depths of 25 30 metamorphic opx metamorphic cpx along a cooling path with a km and temperatures that range from 775 c in slope of 6 bars c starting at 850 c and 6 5 8 kbar garnet the central highlands to t 675 c in the southern occurs as isolated clusters of 5 25 grains of 1 mm diameter adirondacks e g bohlen et al 1985 p t paths have crystals and as necklaces of 1 mm diameter crystals surrounding been shown to follow nearly isobaric cooling trajectories metamorphic pyroxenes or oxides plagioclase quartz typically e g bohlen 1987 because of this wealth of inseparates garnet from pyroxene but locally garnet embays metaformation some fundamental questions about the origin morphic pyroxene suggesting that garnet grew at the expense of of the adirondack granulite facies terrane have emerged pyroxene garnet clusters have slightly lower fe fe mg than e g bohlen et al 1985 how did the crust achieve garnet in necklaces fe fe mg 0 73 and 0 75 0 78 rethe relatively high temperature conditions necessary to spectively and slightly higher grossular xgrs 0 20 vs 0 19 produce granulite facies rocks at depths of 25 30 km neither is zoned in mn and zoning towards increasing fe and what is the relative importance of magmatic fe mg is restricted to contacts with biotite and locally clinoheating vs continental burial in this process pyroxene biotite adjacent to garnet is zoned towards decreasing this study will present new data on mineral comfe fe mg production of garnet in necklaces is interpreted position and element zoning in garnet pyroxene to be the result of the continuous fe mg reaction opx pl biotite amphibole and plagioclase from adirondack grt cpx qtz p t x m modeling of this reaction reveals a meta anorthosite and related rocks with the goal of p t path with a slope of 6 bars c no evidence for early prefurther constraining the metamorphic evolution of this metamorphic peak garnet is observed which rules out any possibility terrane mineral compositions will be used to construct of early higher pressure metamorphism the p t path is therefore phase diagrams in an attempt to evaluate approach to inferred to be counterclockwise with loading to 6 5 8 kbar at a chemical equilibrium theoretical analysis will be used maximum temperature of 850 c occurring during or immediately to construct p t x m phase diagrams depicting how following an influx of heat presumably from early orogenic plutons mineral composition and modes change with p and t this theoretical analysis will then be applied to the mineral zoning to constrain the p t path and the results will be discussed in the context of a tectonic

three dimensional p wave velocity structure of tungurahua volcano ecuador abstract tungurahua volcano in the ecuadorian andes is a large andesitic stratovolcano 5023 m that has been erupting mildly since 1999 we studied the three dimensional 3 d p wave velocity vp structure beneath the volcano down to 5 km below the summit we inverted 1708 p wave first arrival times from 263 volcano tectonic vt earthquakes recorded by 5 to 10 short period vertical seismic stations on the volcano from august 1999 to may 2003 a tomographic inversion method was used to image the velocity structure in which first arrival times were calculated with a finite difference method the root mean square of the arrival time residuals rms was reduced by 43 after running 10 iterations from the initial rms of 0 15 s the relocated hypocenters in our model are tightly clustered along a vertical structure at depths between sea level and the summit crater a high velocity zone exists above the central base of the volcano under the vertically aligned hypocenters and may be interpreted as the source zone for recharge of the shallow magmatic system high velocity zones are also identified under the lower northeastern and southern flanks of the edifice the southern high velocity anomaly lies close to the surface and is connected to the high velocity zone in the central base of the volcano a feature suggesting an old lateral dike system except for these high velocity zones in the central northern and southern flanks the volcanic edifice is composed of low velocity materials down to a depth of 2 km above sea level these low velocity zones correlate with young unconsolidated deposits and older highly fractured and or altered volcanic materials

analysis of satellite and in situ ground deformation data integrated by the sistem approach the april 3 2010 earthquake along the pernicana fault mt etna italy case study abstract etna is known worldwide as one of the most studied and monitored active volcanoes flank instability along the eastern and southern portions of mt etna has been observed and measured thanks to geodetic networks and insar data analysis the spreading area is bordered to the north by the east west pernicana fault system pfs whose dynamics is often linked with the eruptive activity as recently observed during the 2002 2003 eruption a seismic sequence occurred from april 2 3 2010 along the pfs with very shallow a few hundred meters mainshocks of magnitude 4 3 and 3 6 explosions and ash emissions at the summit craters followed this swarm culminating a few days later april 7 8 despite their small magnitude the earthquakes caused damage and significant surface fracturing along the pfs in order to investigate and measure the deformations in the near field of the earthquakes the sistem integration approach has been exploited the sistem enabled integrating geodetic in situ ground deformation measurements gps and leveling with satellite interferometric measurements envisat and alos in order to obtain high resolution 3d displacement maps allowing to overcome the limitations of each technique and take advantage of the particular features of each of them the integrated ground deformation field evidenced that the medium behave elastically we inverted the sistem results using an optimization algorithm based on the genetic algorithm ga in order to model the kinematics of the pfs associated to seismic swarm the results are in good agreement with the field evidence and improved the knowledge on the kinematics of the pfs and mt etna s unstable flank

diffusion control of garnet growth harpswell neck maine usa a detailed analysis of chemical zoning in two garnet crystals from harpswell neck maine forms the basis of an interpretation of garnet nucleation and growth mechanisms garnet apparently nucleates initially on crenulations of mica and chlorite and quickly overgrows the entire crenulation giving rise to complex two dimensional zoning patterns depending on the orientation of the thin section cut contours of ca zoning cross those of mn fe and mg indicating a lack of equilibrium among these major garnet constituents zoning of fe mg and mn is interpreted to reflect equilibrium with the rock matrix whereas ca zoning is interpreted to be controlled by diffusive transport between the matrix and the growing crystal image analysis reveals that the growth of garnet is more rapid along triple grain intersections than along double grain boundaries moreover different minerals are replaced by garnet at different rates the relative rate of replacement by garnet along double grain boundaries is ordered as muscovite chlorite plagioclase quartz flux calculations reveal that replacement is limited by diffusion of si along double grain boundaries to or from the local reaction site it is concluded that multiple diffusive pathways control the bulk replacement of the rock matrix by garnet with si and al transport being rate limiting in these samples

widespread uplift and trapdoor faulting on galapagos volcanoes observed with radar interferometry volcanic uplift caused by the accumulation of magma in subsurface reservoirs is a common precursor to eruptions1 2 but for some volcanoes uplift of metres or more has not yet led to an eruption3 here we present displacement maps of volcanoes in the galapagos islands constructed using satellite radar interferometry that might help explain this dichotomy we show that all but one of the seven volcanoes on the islands of isabela and fernandina deformed during 1992 99 cerro azul and fernandina erupted4 5 6 during the observation period and show evidence of inflation co eruptive deflation and shallow dyke intrusion in contrast the largest volcano sierra negra has not erupted yet exhibits spatially and temporally variable deformation with a maximum uplift of 2 7 m between 1992 and 1999 which can be modelled by a shallow inflating sill inflation during 1997 98 however was accompanied by trapdoor faulting on a steeply dipping fracture system within the caldera repeated trapdoor faulting over geological time has formed an arcuate intra caldera ridge within sierra negra and may have acted to relax stresses above the magma chamber inhibiting summit eruptions similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes

large scale inflation of tungurahua volcano ecuador revealed by persistent scatterers sar interferometry the tungurahua volcano in ecuador has been experiencing a substantial activity period since 1999 with several eruptions including those of 2006 and 2008 we use a persistent scatterers approach to analyze a time series of envisat synthetic aperture radar sar data over the period 2003 2009 to investigate surface deformation in the region of the volcano we measure a continuous large scale uplift with a maximum line of sight displacement rate of about 8 mm yr which is the first evidence of a sustained inflation in the andes for an active volcano encompassing several eruptions we model this signal as magma emplacement in a permanent storage zone at 11 5 km below sea level with a net inflow rate of 7 million m3 yr the paroxysmal eruptions in 2006 and 2008 did not seem to disrupt this long term signal however we observe significant deformation during the 2006 eruption consistent with an additional intrusion of 4 5 million m3 of magma

outcrop architecture of a fluvio lacustrine succession upper triassic yanchang formation ordos basin china abstract although several studies have considered the sedimentary facies of the upper triassic yanchang formation in terms of their hydrocarbon potential in the petroliferous ordos basin such studies have mostly interpreted subsurface data and few have systematically examined the detailed outcrop based anatomy of this succession this study characterizes a series of well exposed outcrop sections along an 80 km long e w oriented series of road cuttings in the southeast ordos basin to reconstruct the sedimentary architecture of a fluvio lacustrine succession and determine the principal controls that governed the style of accumulation and preservation the yanchang formation is divided into 10 depositional units chang 10 base to chang 1 top that record the sedimentary evolution of a series of large scale fluvial systems that constructed delta front and pro delta bodies as they entered a large interior draining lake detailed analysis of the internal architectures of the delta front bodies records the mechanism of growth of a large scale shallow water delta succession lacustrine subaqueous distributary channels are composed of 3 15 m thick sandstone fills such channelized bodies are highly elongate and many can be traced several kilometres such bodies can be shown to be commonly associated with thin bedded mouth bar and subaqueous interdistributary bay deposition the progradational architecture of the delta front elements is difficult to recognize on outcrop scale deposits of the chang 10 to 1 units record 4 major lacustrine transgressive regressive cycles during the late triassic transgressive events are signified by the widespread occurrence of 10 20 m thick oil shale prone intervals regressive events are signified by the progradational stacking towards the basin centre of sandstone prone facies associations mainly accumulated in fluvial channel delta plain and upper delta front environments the uppermost chang 1 interval records late stage filling of the lacustrine basin the transgressive regressive cycles equate to sequences that can be correlated across the region development of which was controlled by a combination of changes in the rate of tectonic subsidence the rate of sediment delivery from the basin margin hinterland and climate factors that were themselves influenced by intracontinental growth of the neighbouring qinling orogen

metamorphic and structural evolution of the early proterozoic puolankajrvi formation finland ii the pressure temperature deformation composition path the paragenetic relationships between sillimanite andalusite kyanite chlorite cordierite biotite garnet and staurolite in the early proterozoic puolankajarvi formation pjf together with mineral compositions are used to construct a partial petrogenetic grid for metapelites with significant mn content mno 0 1 0 5 by adding a six phase invariant point over the garnet absent invariant point for mn free amf phases the grid and textural relations of the pjf are used to construct part of the p t deformation path for the pjf relatively short deformation pulses and associated flow of oxidizing fluid along shear zones were responsible for the paragenetic and compositional changes during cooling and decompression at 600 500 c and 6 0 2 5 kbar oxidation led to decreased fe2 and further stressed the importance of mn increased mn divalent cations a tectonothermal evolution of the kainuu schist belt is presented which includes crustal thinning and steepening of a previously established thermal gradient this was followed by thrusting and folding of the isotherms into a thermal antiform on the western side of the belt

detachment depth revealed by rollover deformation an integrated approach at mount etna this work was partially funded by ingv and the dpc ingv project flank and partially by the asi srv project

effects of topography on the interpretation of the deformation field of prominent volcanoes application to etna we have investigated the effects of topography on the surface deformation field of volcanoes our study provides limits to the use of classical half space models considering axisymmetrical volcanoes we show that interpreting ground surface displacements with half space models can lead to erroneous estimations of the shape of the deformation source when the average slope of the flanks of a volcano exceeds 20 tilting in the summit area is reversed to that expected for a flat surface thus neglecting topography may lead to misinterpreting an inflation of the source as a deflation comparisons of mogi s model with a three dimensional model shows that ignoring topography may lead to an overestimate of the source volume change by as much as 50 for a slope of 30 this comparison also shows that the depths calculated by using mogi s solution for prominent volcanoes should be considered as depths from the summit of the edifices finally we illustrate these topographic effects by analyzing the deformation field measured by radar interferometry at mount etna during its 1991 1993 eruption a three dimensional modeling calculation shows that the flattening of the deflation field near the volcano s summit is probably a topographic effect

stratovolcano growth by co eruptive intrusion the 2008 eruption of tungurahua ecuador 1 volcanic edifices are constructed by a combination of erupted material and internal growth we use the l band satellite alos to produce insar measurements at tungurahua volcano ecuador we find a maximum of 17 5 cm of uplift on the upper western flank between december 2007 and march 2008 coincident with an eruption in february 2008 the deformation can be modeled using an ellipsoidal or sill like source within the edifice the models require an elongated aspect ratio with a length of 4 6 km the intruded volume of 1 2 106 m3 is roughly equivalent to the bulk erupted volume of 1 5 106 m3 and together the values are roughly equal to the long term magma flux the question remains whether this uplift is permanent thus contributing to the internal growth of the edifice or temporary in which case the magma will be released in a future eruption

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

characteristics and controlling factors of lacustrine tight oil reservoirs of the triassic yanchang formation chang 7 in the ordos basin china abstract tight sandstone oil reservoirs have received increasing attention in petroleum exploration and exploitation previous research concerning tight oil reservoirs has predominantly focused on marine basins however in china tight oil reservoirs are mostly distributed in lacustrine basins taking the tight oil sandstones of the yanchang formation chang 7 oil reservoir interval the chang 7 for short in the ordos basin as an example five factors are identified that control their formation and occurrence firstly three episodes of oil charging took place during the early cretaceous which were 142 139 ma 128 122 ma and 114 106 ma respectively continuous generation and episodic expulsion led to multiple episodes of oil accumulation secondly widely distributed source rocks toc 1 0 provide hydrocarbons to the chang 7 the distribution of tight oil was controlled by the outer boundary of the source rock distribution while the transition areas between generation expulsion centers were the accumulation and enrichment zones in the chang 7 thirdly with the favorable conditions for retained hydrocarbons massive continuous tight reservoir beds average porosity 7 6 and average permeability 0 15 md developed in the chang 7 capable of forming large scale successive tight oil reservoirs fourthly different source reservoir assemblages have different expulsion patterns and amounts which led to different charging degrees and sizes of tight oil accumulations type iii source reservoir interbeds will be the most favorable target for exploration and exploitation in the chang 7 ordos basin finally under the driving mechanism of non buoyancy migration and accumulation pressure differences between source and reservoir rocks pdbsr serve as the primary expulsion and migration force for crude oil during the main accumulation periods in the chang 7