paleoseismology along the 1980 surface rupture of the irpinia fault implications for earthquake recurrence in the southern apennines italy the irpinia fault was the source of the ms 6 9 1980 irpinia earthquake and produced the first unequivocal historical surface faulting in italy trenching of the 1980 fault scarp at piano di pecore a flat intermontane basin about 5 km south of the 1980 instrumental epicenter provides the first data on earthquake recurrence intervals slip per event and slip rate on a major normal fault in the southern apennines fault zone the trenches exposed evidence of four pre 1980 paleoearthquakes that occurred during the past 8600 years a best estimate average recurrence interval is 2150 years although the time interval between individual events varies by as much as a factor of 2 each paleo earthquake is similar to the 1980 surface rupture in amount of slip and style of deformation which suggests that the 1980 event is characteristic for the irpinia fault slip per event values average 61 cm the net vertical displacement of 2 12 2 36 m since 8600 cal year b p observed in the trenches gives a vertical slip rate of 0 25 0 35 mm yr a dip slip rate of 0 29 0 40 mm yr and an extension rate of 0 14 0 20 mm yr although fault behavior data are only available for the irpinia fault they provide a starting point for evaluating earthquake recurrence and rates of deformation in southern apennines they suggest that 1 fault specific earthquake recurrence intervals based on the historical seismic record overestimates the occurrence of large magnitude m7 earthquakes and 2 the holocene rate of extension across the apennines is 1 mm yr the 1980 earthquake and the paleoseismologic observations show that repeated and localized surface faulting occurs in southern apennines and leaves subtle but distinct geomorphic evidence that can be detected with detailed and careful investigation

superplastic nanofibrous slip zones control seismogenic fault friction understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults displacement in such fault zones is frequently localized on highly reflective mirrorlike slip surfaces coated with thin films of nanogranular fault rock we show that mirror slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions these microstructures and associated frictional data suggest a fault slip mechanism resembling classical ashby verrall superplasticity capable of producing unstable fault slip diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains with nanogranular fault surfaces becoming increasingly recognized in crustal faults the proposed mechanism may be generally relevant to crustal seismogenesis

comparison of smectite and illite rich gouge frictional properties application to the updip limit of the seismogenic zone along subduction megathrusts along plate boundary subduction thrusts the transformation of smectite to illite within fault gouge at temperatures of 150 c is one of the key mineralogical changes thought to control the updip limit of seismicity if correct this hypothesis requires illite rich gouges to exhibit frictionally unstable velocity weakening behavior here we report on laboratory experiments designed to investigate the frictional behavior of natural and synthetic clay rich gouges we sheared 5 mm thick layers of commercially obtained pure ca smectite a suite of smectite quartz mixtures and natural illite shale grain size ranging from 2 to 500 m in the double direct shear geometry to shear strains of 7 30 at room humidity and temperature xrd analyses show that the illite shale contains dominantly clay minerals and quartz within the clay sized fraction 40 mpa our data specifically the velocity strengthening behavior of illite shale under a wide range of conditions do not support the hypothesis that the smectite illite transition is responsible for the seismic aseismic transition in subduction zones we suggest that other depth and temperature dependent processes such as cementation consolidation and slip localization with increased shearing may play an important role in changing the frictional properties of subduction zone faults and that these processes in addition to clay mineralogy should be the focus of future investigation

use of fracture filling mineral assemblages for characterizing water rock interactions during exhumation of an accretionary complex an example from the shimanto belt southern kyushu japan abstract various fracture filling minerals and secondary minerals in fracture walls were formed by fluid rock interaction during the exhumation of the palaeogene shimanto belt of kyushu japan which is located in an accretionary complex each mineral formed under favourable geological conditions and can be used to estimate the conditions of accretion and formation of the related rock sequences petrographic observations mineralogical and geochemical analyses were made on fracture filling minerals and secondary minerals from boreholes of ca 140 m depth drilled in the shimanto belt results reveal that the secondary minerals were formed in three major stages distinguished by the sequential textural relationships of the minerals and the interpreted environment of mineral formation filling mineral assemblages show that the studied rock formation has been subducted to a depth of several km and the temperature reached was ca 200 300 c after the subduction the rock formation was uplifted and surface acidic water penetrated up to 80 m beneath the present ground surface the acid water dissolved calcite fracture filling minerals to form the present groundwater flow paths which allowed recent wall rock alteration to occur the results shown here imply that filling mineral assemblages can be an effective tool to evaluate the environmental changes during exhumation of an accretionary complex

frictional viscous flow of phyllosilicate bearing fault rock microphysical model and implications for crustal strength profiles it is widely believed that around the brittle ductile transition crustal faults can be significantly weaker than predicted by conventional two mechanism brittle ductile strength envelopes factors contributing to this weakness include the polyphase nature of natural rocks foliation development and the action of fluid assisted processes such as pressure solution recently ring shear experiments using halite kaolinite mixtures as an analogue for phyllosilicaterich rocks for the first time showed frictional viscous behavior i e both normal stress and strain rate sensitive behavior involving the combined effects of pressure solution and phyllosilicates this behavior was accompanied by the development of a mylonitic microstructure a quantitative assessment of the implications of this for the strength of natural faults has hitherto been hampered by the absence of a microphysical model in this paper a microphysical model for shear deformation of foliated phyllosilicate bearing fault rock by pressure solution accommodated sliding along phyllosilicate foliae is developed the model predicts purely frictional behavior at low and high shear strain rates and frictional viscous behavior at intermediate shear strain rates the mechanical data on wet halite kaolinite gouge compare favorably with the model when applied to crustal materials the model predicts major weakening with respect to conventional brittle ductile strength envelopes in particular around the brittle ductile transition the predicted strength profiles suggest that in numerical models of crustal deformation the strength of high strain regions could be approximated by an apparent friction coefficient of 0 25 0 35 down to depths of 15 20 km

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

frictional sliding of dolomite a variation in constitutive behavior fault slip occurs via earthquakes or stable creep depending on the manner in which frictional resistance varies with sliding velocity and displacement if the form of this dependence is a function of rock type observed spatial variations in slip behavior along faults could be explained by lithologic variation we have used a rotary shear apparatus to investigate the frictional response of dolomite marble to changes in sliding velocity we have modeled the results using a state variable constitutive law for rock friction and a numerical method to solve for the interaction between the friction law and the compliance of our machine dolomite marble displays steady state velocity strengthening as contrasted with granite and quartzite which show velocity weakening at the same conditions to model the dolomite results it is necessary to use two state variables and surprisingly the parameters specifying the decay magnitudes associated with these state variables differ in sign from each other the magnitude of the parameter associated with the longer decay is negative leading to a downward decay of frictional strength associated with a decrease in velocity if the shorter decay is of sufficient magnitude as we observe at low velocity it is possible for the machine rock system to exhibit instability and oscillatory behavior even though the steady state response is velocity strengthening another way in which dolomite contrasts with granite and quartzite is that the friction parameters vary strongly with velocity a transition from unstable to stable sliding with increasing velocity has been observed previously and our observed variation of the constitutive parameters with velocity can explain this behavior there is some indication that the evolution of the state variables for dolomite occurs as a function of time rather than displacement in contrast with granite and quartzite the frictional behavior of dolomite shows that the constitutive laws that have been developed based on results from granite and quartzite are inadequate to describe all rock types and that more general laws are required

effects of temperature and co2 on the frictional behavior of simulated anhydrite fault rock the frictional behavior of anhydrite bearing faults is of interest to a the safety and effectiveness of co2 storage in anhydrite capped reservoirs b seismicity induced by hydrocarbon production and c natural seismicity nucleated in evaporite formations we performed direct shear experiments on simulated anhydrite fault gouges at a range of temperatures 80 150 c and sliding velocities 0 2 10 ms 1 under a fixed effective normal stress of 25 mpa four types of experiments were conducted 1 dry experiments 2 experiments pressurized with water 3 dry experiments pressurized with co2 and 4 wet experiments pressurized with co2 fluid pressures of 15 mpa were used when applied over the temperature range investigated water saturated samples were found to be up to 15 frictionally weaker than dry equivalents wet samples containing co2 were also up to 15 weaker than co2 free equivalents dry sample strength without co2 was independent of temperature whereas wet samples without co2 strengthened 10 from 80 to 150 c samples containing co2 weakened by 4 dry and 10 wet from 80 to 150 c under the p t conditions investigated only dry anhydrite fault gouge showed velocity weakening behavior above 120 c required for faults to potentially generate earthquakes assuming natural fault gouges are wet in situ seismicity is unlikely to nucleate in anhydrite rich faults though the presence of dolomite or reaction produced calcite may change seismic potential co2 penetration into wet anhydrite rich faults may trigger slip on critically stressed faults due to the observed short term co2 weakening effects excluding possible formation of secondary minerals but is not expected to influence slip stability

detection of hydrothermal mineralized zones associated with listwaenites in central oman using aster data abstract listwaenites are highly altered ultramafic rocks that are potentially associated with economic mineralization and research on these is extremely important worldwide in the present study the classification of mineralized listwaenites developed along the serpentinite amphibolite interface of the semail ophiolite its associated lithology and the zones of alteration and mineralization in the fanjah saddle of the central oman mountains region of the sultanate of oman are carried out using advanced spaceborne thermal emission and reflection radiometer aster satellite data the developed band ratioing principal component analysis pca and the spectral angle mapper sam supervised classification and image processing techniques applied on the aster data set have proved their capability for better interpretation and identification of hydrothermally altered rocks and associated mineralization the hyperspectral tools minimum noise fraction mnf pixel purity index ppi and nd visualizer extracted end member spectra and sam classification clearly show the occurrence of minerals and their spatial distributions the promising results are verified and confirmed in the field by identification of alteration and mineralization such as listwaenites silicification serpentinization and talc alteration and are validated further through laboratory analysis the confirmation of the occurrence of base metal mineralization along the serpentinite amphibolite interface in listwaenites suggests that detailed investigation in this and other arid regions which have similar geological conditions may locate mineral deposits the hyperspectral tools applied on aster satellite data show that these can be used as a powerful tool to explore the listwaenites and the potential associated mineralization in other arid geographical regions worldwide

influence of pore fluid salinity on pressure solution creep in gypsum abstract the uniaxial compaction creep behaviour of wet granular gypsum is investigated under chemically closed drained conditions known to favour pressure solution the experiments were performed using applied stresses of 1 to 4 mpa and grain sizes in the range 50 to 280 m at room temperature the tests were carried out using saline pore fluids with a nacl concentration of 0 01 to 6 m saturated with respect to the unstressed gypsum starting material since gypsum is almost always associated with other evaporite minerals such as halite pore fluid compositions in gypsum will generally be highly saline data on the effect of pore fluid salinity on pressure solution in gypsum are thus directly relevant to the behaviour of gypsum in geological situations the results obtained in terms of mechanical behaviour and microstructures developed are in good agreement with the results obtained in previous experiments performed using nacl free pore fluids however the absolute creep rates obtained here are up to 50 times faster than in the nacl free tests comparison with theoretical models for pressure solution creep and crystal growth data reveals that diffusion is unlikely to be the rate controlling mechanism of pressure solution in the present experiments since the growth rate of gypsum increases with nutrient salinity the observed effect of nacl on pressure solution is consistent with the possibility of rate control by the precipitation reaction however the absolute creep rates observed are one to two orders of magnitude slower than creep rates predicted by a precipitation rate limited model so that the detailed mechanism remains unclear

fluid inclusion technique for determining maximum temperature in calcite and its comparison to the vitrinite reflectance geothermometer theory laboratory experiments and empirical observation suggest that many aqueous fluid inclusions in calcite reequilibrate during overheating and therefore some homogenization temperatures t h record a temperature close to the maximum reached by the rock this characteristic suggests that aqueous fluid inclusions in calcite can be used to establish maximum temperature t peak to test this hypothesis we have compiled fluid inclusion t peak mean random vitrinite reflectance r m and present day t peak from 46 diverse geologic systems that have been at t peak from 10 4 to 10 6 yr present t peak ranged from 65 to 345 c t h modes and means ranged from 59 to 350 c and r m data ranged from 0 4 to 4 6 spanning the temperature and thermal maturity range associated with burial diagenesis hydrothermal alteration and low grade metamorphism plots of t h and t peak data for systems thought to be currently at maximum temperature demonstrate close agreement between t h and present t peak in sedimentary basins although caution should be applied the relation suggests that t h of aqueous fluid inclusions in calcite may be a useful measure of maximum temperature this study also compares t h to mean random vitrinite reflectance r m to offer further support for the use of t h as a measure of t peak and to provide a better understanding of r m t h correlates well with r m and results in a curve similar to r m vs t peak calibrations determined by other workers the strong correlation correlation coefficient r 0 93 between t peak and r m in these systems suggests that maximum temperature is the major control on thermal maturation

spaceborne mapping of hydrothermal alteration zones associated with the mundiyawas khera copper deposit rajasthan india using swir bands of aster implications for exploration targeting abstract this paper discusses the effectiveness of spectroscopic techniques for identifying hydrothermal alteration zones associated with the mundiyawas khera copper deposit alwar basin western india and assesses implications for mineral exploration targeting in the greater alwar basin mineral specific swir bands of aster were spectrally enhanced to highlight areas of anomalous al oh and mg oh responses representing key mappable expressions of the mundiyawas khera copper deposit the hydroxyl bearing mineral zones were identified at 98 and 95 threshold pixels respectively kaolinite scapolite sericite muscovite tremolite and dolomite contained in the felsic volcanic and dolomitic copper host rocks were identified from spectroscopic data and corroborated with petrographic and xrd data on this basis distinct argillic phyllic and propylitic hydrothermal alteration zones could be identified at mundiyawas khera the integrated approach presented here i identified a well defined phyllic alteration pattern in the felsic volcanic rocks ii resulted in a comprehensive remotely sensed hydrothermal alteration map illustrating the spatial distribution of the copper related hydrothermal alteration zones i e an eastern argillic a central phyllic and a western propylitic zone iii helped to delineate potential copper rich zones coincident with a known lithostructural trend and iv has implications for copper exploration in the greater alwar basin

velocity dependence of strength and healing behaviour in simulated phyllosilicate bearing fault gouge abstract despite the fact that phyllosilicates are widespread in fault zones little is known about the strength of phyllosilicate bearing fault rocks under brittle ductile transitional conditions in this study we explored the steady state strength and healing behaviour of a simulated phyllosilicate bearing fault rock i e muscovite plus halite and brine at room temperature normal stresses of 1 9 mpa atmospheric fluid pressure and sliding velocities of 0 001 13 m s using a rotary shear apparatus while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behaviour the strength of mixtures containing 10 50 muscovite is both normal stress and sliding velocity dependent at low velocities 1 m s velocity weakening frictional behaviour occurs along with the development of a structureless intermixed cataclastic microstructure the steady state porosity of samples deformed in this regime increases with increasing sliding velocity we propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution towards higher sliding velocities dilatation increasingly dominates over pressure solution compaction so that porosity increases and frictional strength decreases during periods of zero slip pressure solution compaction occurs causing a significant strength increase on reshearing our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions but can simply result from oscillating fault motion rates our healing data suggest that foliated aseismically creeping fault segments will remain weak and aseismic whereas segments that have slipped seismically will rapidly re strengthen and remain in the unstable velocity weakening regime

structurally controlled hydrothermal alteration of carbonate reservoirs introduction langhorne taury smith heads the reservoir characterization group at the new york state museum he holds a b s degree from temple university a ph d from virginia tech and did postdoctoral work at the university of miami he also worked for chevron as a development geologist and current research interests are focused on carbonate reservoir characterization and hydrothermal alteration of carbonate reservoirs graham davies received his b sc honors degree and ph d from the university of western australia his doctoral thesis was on modern carbonates in shark bay western australia published in aapg memoir 13 after a postdoctoral fellowship with james lee wilson at rice university he joined the geological survey of canada gsc in calgary after 7 years with the gsc graham co founded and became principal owner of agat applied geoscience and technology consultants laboratories since 1983 he has operated through gdgc ltd he has published about 70 papers on the geology of australia and canada and has authored or coauthored more than 600 consulting reports graham received the cspg douglas medal in 2002 for his work on arctic paleozoic carbonates and evaporites and on the triassic and other aspects of western canadian geology his principal current interest is in hydrothermal dolomites this issue of the aapg bulletin is dedicated to structurally controlled hydrothermal alteration of carbonate rocks and reservoirs this type of alteration covers the spectrum of carbonate hosted sulfide ore deposits to hydrothermal dolomite to leached limestones and in many cases has a major impact on reservoir type geometry quality and distribution hydrothermal dolomite htd reservoirs have a long history of exploration and development in north america extending from the earliest discoveries in the ordovician lima indiana and other trends of the northeastern united states hurley and budros 1990 wickstrom et al 1992 and continuing today with the trenton black river play

mapping of serpentinites in the eastern desert of egypt by using landsat thematic mapper data serpentinites in the eastern desert of egypt were mapped from landsat thematic mapper tm data by using procedures that take advantage of the distinctive spectral reflectance of these rocks caused by the abundance of antigorite lizardite clinochrysotile and magnetite the method employs a threshold classifier based on three reflectance ratios 1 band 5 7 for estimating the abundance of hydroxyl bearing phases 2 band 5 1 for magnetite content and 3 the calculated value of reflectance for band 4 based on a linear interpolation between bands 3 and 5 divided by the observed band 4 reflectance the third ratio was used to identify rocks in iron bearing aluminosilicates and thereby to distinguish mafic rocks containing substantial amounts of magnetite and hydroxyl bearing phases from serpentinites the method was first successfully tested over the meatiq dome and wadi ghadir areas where serpentinites and ophiolitic melanges dominated by serpentinites have been mapped during the course of field work a tm based map was then generated the map covered about 60 000 km sup 2 in the eastern desert results demonstrate that tm data can be used with reliability to distinguish serpentinites from surrounding rocks in arid regions and to generate detailed maps over wide regions by using quantitative reproducible mapping criteria more possibilities for locating suture zones over the less well known parts of arid continents are clear less

genetic and temporal relations between formation waters and biogenic methane upper devonian antrim shale michigan basin usa abstract controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane natural gas in most conventional deposits has migrated from a source rock to a reservoir rarely remaining associated with the original or cogenetic formation waters we investigated an unusual gas reservoir the late devonian antrim shale in which large volumes of variably saline water are coproduced with gas the antrim shale is organic rich of relatively low thermal maturity extensively fractured and is both source and reservoir for methane that is generated dominantly by microbial activity this hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas providing a unique opportunity to characterize methane generating mechanisms the well developed fracture network provides a conduit for gas and water mass transport within the antrim shale and allows invasion of meteoric water from overlying aquifers in the glacial drift steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases dilute waters grade into dense brines 300 000 ppm over lateral distances of less than 30 km radiogenic 14c and 3h and stable isotope 18o and d analyses of shallow antrim shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20 000 yr bp carbon isotope compositions of methane from antrim shale wells are typical of the established range for thermogenic or mixed gas 13c 47 to 56 however the unusually high 13c values of co2 coproduced with methane 22 and dissolved inorganic carbon dic in formation waters 28 require bacterial mediation the d values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis methane ethane propane ratios and 13c values for ethane indicate 1 the presence of a thermogenic gas component that increases basinward and 2 progressive bacterial oxidation of ethane as the antrim shale subcrop is approached multiple episodes of pleistocene glaciation over northern michigan appear critical to the development of these gas deposits loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water the physical erosion cycle of repeated glacial advances and retreats exhumed the antrim shale around the northern margin of the michigan basin subjecting it to near surface physiochemical and biochemical processes the chemical and hydrologic relations demonstrated in the antrim shale reservoir suggest a dynamic connection between pleistocene glacial history of the midcontinent region and development of recoverable microbially generated natural gas reserves

carbon dioxide earth degassing and seismogenesis in central and southern italy 1 we present the first regional map of co2 earth degassing from a large area most of central and south italy derived from the carbon of deep provenance dissolved in the main springs of the region the investigation shows that a globally significant amount of deeply derived co2 10 of the estimated global co2 emitted from subaerial volcanoes is released by two large areas located in western italy the anomalous flux of co2 suddenly disappears in the apennine in correspondence to a narrow band where most of seismicity concentrates here at depth the gas accumulates in crustal traps generating co2 overpressurized reservoirs which induce seismicity

structural and litho tectonic controls on neoproterozoic base metal sulfide and gold mineralization in north hamisana shear zone south eastern desert egypt the integrated field structural landsat 7 etm and aster data approach abstract the hamisana shear zone hsz is an excellent example of high strain shear belt of the neoproterozoic arabian nubian shield ans situated in a position between three major pan african terranes se desert gabgaba and gebeit terranes the north hamisana shear zone area nhsz cuts across sequences of island arc related metasediment metavolcanic which are structurally overlain by ophiolitic nappes and intruded by a number of granitoids and gabbroic rocks although it is interesting geological tectonic setting for base metal sulfide and gold ores there is a lack of detailed studies on structure geology and mineralization in this area which considered as poorly mapped remote region not only in egypt but also in sudan for these reasons we integrated image transformation methods include principal components analysis pca band ratios br false color composite fcc and filtering on the spectral bands of two distinct datasets etm and aster for detailed mapping of the nhsz area spectral data fusion with structural data analysis and field observations provide a better understand of the temporal and spatial relationships between the litho tectonic units and regional tectonic setting in the course of controls on base metal sulfide and associated gold mineralization merging these different data sources in the study area suggests that the base metal sulfide and associated gold mineralization are restricted to quartzites member of island arc related metasediments and mostly controlled by d3 deformational event main hsz deformational event this event characterized by transpressional stress regime with 1 trending e w and 3 trending n s activated conjugate nnw sinistral and nne ssw dextral strike slip faulting likely during syn tectonic granodiorite emplacement

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

review of late proterozoic sutures ophiolitic melanges and tectonics of eastern egypt and north east sudan the distribution structural relations and ages of ophiolites and ophiolitic melanges in the eastern deserts of egypt and north east sudan and their relation to arc and post arc magmatism are used to infer the probable positions of sutures and the directions of obduction and subduction the ages of the successive tectonic stages in the terranes decrease northwards by about 100 ma in the region discussed obduction was north westwards the obducted sheets of ophiolite and ophiolitic melange extending about 500 km north from the onib sol flamed suture may all represent a single back arc basin the direction of subduction is still not clearly proved more geochemical evidence of arc magmatic polarity is needed the late tectonic north westward thrusting the nw se stretching lineation the transpressional north south hamisama shear zone and the nw se sinistral najd faults are all attributed to north westward movement present coordinates of terranes towards the older craton west of the nile the najd faults are interpreted as intracontinental transform faults

spectral mapping of alaskan ophiolites using landsat thematic mapper data abstract ophiolites are sections of oceanic lithosphere that have been exposed by thrusting in mountain belts thematic mapper three band color composites have been used to differentiate the main rock types of the ophiolites of the western brooks range alaska and to map mineralogic variations produced by processes that affect oceanic lithosphere such as mantle partial melting hydration of ultramafic rock formation of cumulate layers and hydrothermal alteration and metamorphism of basalt scaled composites of tm bands 7 3 1 and 5 4 2 and 3 2 1 displayed in red green and blue are most useful for visually differentiating rocks of the ophiolites ternary diagrams of digital number valves are used to evaluate color variations observed in the three band composites geologic maps interpreted from tm images and reconnaissance field studies are presented for the asik mountain maiyumerak mountains avan hills and misheguk mountain ophiolites the mapping results are being used to guide additional studies of the tectonics of the brooks range ophiolites

cohesive strengthening of fault zones during the interseismic period an experimental study 1 there is widespread evidence indicating that faults regain a portion of their strength during the interseismic period here we present experiments designed to understand and quantify the interseismic cohesive strengthening resulting from fluid rock reactions in fault zones the triaxial experiments consisted of fracturing cores of fontainebleau sandstone under dry conditions forming a localized shear failure zone stage 1 the specimens were then reacted hydrothermally under isostatic conditions allowing the fault damage zone to compact consolidate and strengthen stage 2 following reaction the specimens were then reloaded to failure under nominally dry conditions so that the increase in cohesive strength of the fault could be measured stage 3 experiments show that cohesion increase is positively correlated to temperature and pore pressure during reaction after 6 hours of reaction at the highest temperatures 927 c and pore pressures 200 mpa cohesion increases by as much as 35 mpa microstructural examination of the specimens showed that the gouge particles within the fault compacted and cemented together exhibiting textures typical of pressure solution and that fractures in the surrounding damage zone had healed a theoretical treatment of the data was conducted using these experiments in combination with results on time dependent changes in fault cohesion presented by tenthorey et al 2003 we find that the rate controlling process in our experiments has an activation energy q of approximately 70 kj mol 1 we use this information to develop a model for time dependent cohesive strengthening in fault zones within the continental seismogenic regime we conclude that significant cohesive strengthening of fault zones can occur during the interseismic period of medium to large earthquakes given the presence of reactive pore fluids

fractured hydrothermal dolomite reservoirs in the devonian dundee formation of the central michigan basin the middle devonian dundee formation is the most prolific oil producing unit in the michigan basin with more than 375 million bbl of oil produced to date reservoir types in the dundee formation can be fracture controlled or facies controlled and each type may have been diagenetically modified although fracture controlled reservoirs produce more oil than facies controlled reservoirs little is known about the process by which they were formed and diagenetically modified in parts of the dundee preexisting sedimentary fabrics have been strongly overprinted by medium to coarse grained dolomite dolomitized intervals contain planar and saddle dolomite with minor calcite anhydrite pyrite and uncommon fluorite fluid inclusion analyses of two phase aqueous inclusions in dolomite and calcite suggest that some water rock interaction in these rocks occurred at temperatures as high as 120 150c in the presence of dense na ca mg cl brines these data in conjunction with published organic maturity data and burial reconstructions are not easily explained by a long term burial model and have important implications for the thermal history of the michigan basin the data are best explained by a model involving short duration transport of fluids and heat from deeper parts of the basin along major fault and fracture zones connected to structures in the precambrian basement these data give new insight into the hydrothermal processes responsible for the formation of these reservoirs

structural control on overprinting high sulfidation epithermal on porphyry mineralization in the chodarchay deposit northwestern iran abstract the chodarchay high sulfidation epithermal porphyry deposit is located in the tarom volcano plutonic subzone of western alborz structural zone in nw iran in addition to chodarchay the tarom subzone hosts several other epithermal deposits lithologic units in chodarchay consist of volcanic pyroclastic rocks and intrusive bodies petrographical studies have identified different rocks which host the mineralization mineralization has taken place in both volcanic pyroclastic units and intrusions detailed mineralogical and alteration data gathered from drill cores and thin sections provides support for the hypothesis that the high sulfidation epithermal mineralization is underlain by a porphyry copper system this deposit is the first reported porphyry epithermal mineralization in this subzone the main structure of the chodarchay area is a fault zone that formed parallel to the general tarom nw se direction based on remote sensing studies on a wider scale lineaments generally show ne sw trends but the chodarchay fault zone has a nw se strike and is associated with another w e trending fault zone these fault zones are correlated with argillic alteration there are two sets of reverse fault fractures with a strike slip component based on slickenlines in the field and core observations a normal sense of fault movement remains in the nw part of the structural system these new data sets indicate two main extensional and compressional mechanisms for the fault the evolution of the fault system from normal to reverse in the deposit characterizes the present day structural system of the chodarchay area plutonism and porphyry mineralization are related to the extensional stage whereas the epithermal part of the deposit is associated with the compressional stage of fault activation

hydrothermal dolomite reservoir in the precambrian dengying formation of central sichuan basin southwestern china abstract the precambrian dengying formation is maximum buried carbonate reservoir in the sichuan basin reservoir types are thought to be dominated by sedimentary facies or karst controlled precursory sedimentary fabrics have been intensively superimposed by medium to coarse grained dolomite in most areas dolomitized intervals contain planar and saddle dolomite quartz and few hydrothermal replacive minerals fluid inclusion analyses of dolomite suggests that rocks are formed at temperatures ranging from 132 6 c to 218 7 c in the presence of dense brines while the dolomite phases are demonstrated by negative 18 o and 13 c vpdb values strontium isotopes enriched in 87 sr and the fluid source could support the conclusion the dolomites of the dengying formation in central sichuan basin that formed around basement rooted wrench faults in turn mainly oriented towards the north south and east west strike slip faults are detectable lastly the grabens take the form of negative flower structures the result of an intra cratonic rift that took place during the sinian and early cambrian period through tensional faulting our primary contention is that basement fault which resulted in the magmatic or deep clastic fluids migration was key for the formation of the obvious high temperature coarse dolomite and saddle dolomite replacement subsequently hot fluids that circulated within the matrix dolomite were aided by fractures or vugs and 1 leached into the dolomite producing vugs and pores 2 precipitated saddle dolomite and 3 led to hydrofracturing fractures enlargement and further brecciation the dolomite eventually formed porous hydrocarbon reservoirs through diagenesis this model better illustrates how fluids that originated from deep basin migration along strike slip transfer faults and fractures flowed out to structures in precambrian basement rooted faults inheriting the rift in the cambrian the data involved offers a fresh perspective pertinent to deep hydrocarbon exploration of dolomite reservoirs in southwestern china

a low angle normal fault in the umbria region central italy a mechanical model for the related microseismicity abstract in the northern apennines the upper crust is thinned by a set of east dipping low angle normal faults lanfs the easternmost and more recent of these lanfs is the altotiberina fault atf located in northern umbria the geometry of the atf has been reconstructed matching surface geology with seismic reflection profiles and borehole data the fault whose average dip is 20 borders the upper pliocene quaternary tiber basin and has a displacement of about 8 km the deeper portion of the atf is located below the axial zone of the northern apennines where the strongest instrumental and historical seismicity is recorded the microseismicity of the region m 1 to evaluate the boundary conditions for the brittle activity of the atf the fault can be reactivated for low values of differential stress 1 3 t 10 mpa and tensile fluid overpressure p f 3 e g v 0 93 in the peculiar situation of the northern apennines the deep emissions of large amounts of co 2 documented in the area can be entrapped in their ascent by structural seals e g atf favouring localised fluid overpressures the impossibility of sustaining p f 3 for wide fault portions counteracted by hydraulic fracturing increased permeability under low effective stress and load weakening behaviour for normal faulting would prevent the nucleation of moderate ruptures along the fault the short lived attainment of p f 3 along small fault portions can account for the microseismic activity located along the atf which occurs on rupture surfaces in the range of 10 1 10 3 km 2

aster spectral analysis for alteration minerals associated with gold mineralization abstract this study presents classifications of advanced spaceborne thermal emission and reflection radiometer aster imagery based on spectral analysis of alteration minerals associated with gold mineralization in abo marawat area which is located in the central eastern desert of egypt spectral analysis of continuum removed reference spectra of alteration minerals alunite kaolinite sericite and calcite from usgs and jpl spectral libraries show shifts in position shape and strength most probably related to changes in sample purity and particle size of analyzed samples spectral information divergence sid classification method proved successful for mapping sericite calcite and clay minerals spectral angle mapper sam classification identified only sericite and calcite alteration minerals the identified alteration zones are coincidence with the field sampling and geological map of the study area the microscopic examination of samples collected from the quartz veins and hydrothermally altered wall rocks from near surface and subsurface at abu marawat gold mine shows sericitization argillaceous and carbonatization alteration zones gold occurs as very fine inclusions in pyrite chalcopyrite and sphalerite and also found filling the fractures between chalcopyrite grains this study concludes that aster image classifications using reference spectra are a stable and reproducible technique for mapping gold related hydrothermal alteration zones in areas with no dominant vegetation cover

geology of the devonian dundee reservoir west branch field michigan 1 west branch field located near the center of the michigan basin is a low relief asymmetric northwest southeast trending anticline since 1934 the dundee reservoir middle devonian dundee and rogers city limestones has produced more than 12 million bbl 2 million m 3 of oil from this field dundee sediments were deposited on a carbonate ramp that dipped gently to the northwest core studies and log correlations show that the reservoir is dominated by normal marine somewhat lenticular beds of skeletal peloidal grainstones and packstones crinoids are very abundant comprising nearly 100 of the grains in some intervals the uppermost dundee consists of micritic carbonates with a restricted faunal assemblage the dundee rogers city contact is a disconformity that ppears to be a pyritized extensively bioeroded hardground the overlying rogers city limestone is a dark nodular wackestone with rare packstone interbeds trace amounts of dolomite are common throughout the field however pervasive dolomite is common only in the top 10 15 ft 3 4 5 m of the dundee this dolomite generally has high porosity 5 15 but very low permeability 0 1 0 md primary interparticle porosity in limestones accounts for most of the reservoir porosity although previous workers have concluded that fracture controlled dolomites are responsible for porosity and permeability in this field we conclude that such dolomites are not important we also conclude that at west branch field there is no evidence for reefal growth over a pre existing fold as has been reported in other dundee rogers city reservoirs

thermal subsidence and generation of hydrocarbons in michigan basin temperature histories for selected stratigraphic horizons in the michigan basin are computed from three dimensional continually filled subsidence models mechanical evolution of the michigan basin is modeled as flexure of the lithosphere caused by thermal contraction results are compatible with the subsidence record of the sediments and free air gravity anomalies paleotemperature is determined from excess temperature due to the thermal anomaly plus burial temperature predicted from subsidence curves for an equilibrium temperature gradient of 22 c km 1 2 f 100 ft surface temperature of 20 c 68 f and an equilibrium surface heat flow of 1 1 hfu excess temperature paleotemperature and surface heat flow do not exceed 15 c 27 f 110 76 c 230 f and 2 5 hfu respectively these estimates are consistent with upper limits set by paleomagnetic studies the low value for excess temperature is caused by concentration of the thermal anomaly below 15 km 9 mi in agreement with gravity results the great depth of the thermal anomaly can explain the lack of evidence for an initial heating event prior to subsidence once the thermal history of the sediments is specified the oil potential of the basin can be determined from laboratory derived kinetic equations for degradation of kerogen to petroleum for the michigan basin predicted temperature conditions are sufficient for source rock 25 conversion of type i and type ii kerogen only in ordovician and older rocks in the southern peninsula of michigan by this model petroleum found in rocks younger than ordovician would have had to migrate upward from the older rocks geochemical studies of dundee devonian and trenton ordovician crude oils in michigan are compatible with this interpretation niagaran silurian crude oils appear to come from a different source than the dundee and trenton oils if their source is silurian rocks on the flanks of the basin either the scheme used to calculate maturity is not applicable to these oils or the temperature of the source rocks was significantly higher in the past than today more likely the model underestimates the depth of burial of silurian source rocks near the center of the basin especially in local regions of downfaulting

active tectonics in the central apennines and possible implications for seismic hazard analysis in peninsular italy abstract the central apennines fault system cafs of peninsular italy overprints earlier structures of a neogene fold and thrust belt and includes segments characterized by diffuse seismicity distributed within a nnw sse trending zone 50 60 km wide the system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments the resulting fault structure consists of an interconnecting network of roughly n s trending left lateral strike slip segments and mostly nw se oriented transtensional to normal faults evidence for recent activity of cafs structures is provided by faulted middle pleistocene holocene deposits including 30 40 ka old pyroclastites and 40 ka old palustrine sediments fresh scarps in both bedrock and late quaternary continental deposits and decametric lateral offsets locally affecting the post wurmian drainage pattern of the area the regional stress field responsible for the development and evolution of the cafs as inferred from fault slip data is characterized by a nw se compression and by a ne sw extension the cafs pattern and its present day kinematics have been related to left lateral strike slip motion on north south trending crustal faults the existence of deep seated strike slip faults in the central apennines has implications for seismic hazard analysis motion along these structures suggests in fact that coseismic surface faulting is distributed and that cumulative displacements include normal transtensional and strike slip components the seismogenic potential of cafs structures can therefore be best described by multiple rupture models and be better analysed in terms of partial contributions of lower rank features constituting congruent structural associations within the system

frictional properties of a low angle normal fault under in situ conditions thermally activated velocity weakening the zuccale fault is a regional low angle normal fault exposed on the isle of elba in central italy that accommodated a total shear displacement of 6 8 km the fault zone structure and fault rocks formed at 8 km crustal depth the present day fault structure is the final product of several deformation processes superposed during the fault history in this study we report results from a series of rotary shear experiments performed on 1 mm thick powdered gouges made from several fault rock types obtained from the zuccale fault the tests were done under conditions ranging from room temperature to in situ conditions i e at temperatures up to 300 c applied normal stresses up to 150 mpa and fluid saturated the ratio of fluid pressure to normal stress was held constant at either 0 4 or 0 8 to simulate an overpressurized fault the samples were sheared at a constant sliding velocity of 10 m s for at least 5 mm after which a velocity stepping sequence from 1 to 300 m s was started to determine the velocity dependence of friction this can be represented by the rate and state parameter a b which was determined by an inversion of the data to the rate and state equations friction of the various fault rocks varies between 0 3 and 0 8 similar to values obtained in previous studies and decreases with increasing phyllosilicate content friction decreases mildly with temperature whereas normal stress and fluid pressure do not affect friction values systematically all samples exhibited velocity strengthening conditionally stable behavior under room temperature conditions and a b increased with increasing sliding velocity in contrast velocity weakening accompanied by stick slips was observed for the strongest samples at 300 c and sliding velocities below 10 m s an increase in fluid pressure under these conditions led to a further reduction in a b for all samples so that they exhibited unstable stick slip behavior at low sliding velocity the results suggest that phyllosilicate bearing fault rocks can deform by stable aseismic creep at low resolved shear stress and low shear rate conditions an increase in fluid pressure or loading of stronger portions could lead to a runaway instability the runaway instability might be limited in size because of 1 the fault heterogeneity 2 the observed strengthening at higher sliding velocities and 3 a co seismic drop in pore fluid pressure

structural interpretation and tectonic evolution of a part of the najd shear zone saudi arabia using landsat thematic mapper data abstract digital landsat thematic mapper data were used to extrapolate structural features associated with the ajjaj shear zone from well characterized to less well known areas the satellite images were enhanced using a linear mixing model with the spectra of known rock types measured from the images as endmember components the approach uses information for all six spectral bands the effects of desert varnish coating in modulating the spectral response of rock exposures are specifically accounted by using of an empirically derived coat component comparison between the lithologic component images produced from the unmixing procedure and published geologic maps demonstrate that these images can be effectively used to map brittle faults ductile shear zones and certain spectrally distinct lithologies by combining interpretation of the enhanced images with available geologic data it has been shown in this study that the ajjaj shear zone is dominantly a ductile structure characterized by the continuity of rotated layers across the shear zone with a minimum sinistral displacement of 25 to 30 km the northern boundary of this shear zone is dominantly ductile whereas the southern boundary consists of a continuous brittle displacement surface which juxtaposes contrasting lithologies several brittle faults within and crosscutting the ductile shear zone had previously been mapped as najd faults these faults are not strike slip in character and clearly postdate najd deformation in the middle of the area studied the ajjaj shear zone changes orientation from wnw to nnw this change corresponds spatially to the intersection of the shear zone with a n s oriented structure here named the hanabiq shear zone the hanabiq shear zone is one of a set of broadly n s trending dextral shear zones which crosscut the arabian shield proponents of the rigid indentor model for the origin of the najd fault system have suggested that these faults form a conjugate set to the nw trending sinistral najd faults our study presents clear evidence that the ajjaj shear zone postdates the hanabiq shear zone this supports recent criticisms of the rigid indentor model as applied to the najd the tectonic significance of the najd fault system remains as intriguing problem

scaling of rock friction constitutive parameters the effects of surface roughness and cumulative offset on friction of gabbro we describe experiments in which large 14 40 cm nominal contact area blocks of gabbro were sheared in a direct shear apparatus at room temperature 5 mpa normal stress and slip velocities from 0 1 to 10 m s the apparatus was servocontrolled using a displacement feedback measurement made directly between the gabbro blocks two surface roughnesses were studied rough produced by sandblasting and smooth produced by lapping with 60 grit and accumulated displacements reached 60 mm measurements of surface topography were used to characterize roughness and asperity dimensions step changes in loading velocity were used to interrogate friction constitutive properties both rough and smooth surfaces showed appreciable displacement hardening the coefficient of friction for rough surfaces was about 0 45 for initial slip and 0 7 after sliding 50 mm smooth surfaces exhibited higher and a greater tendency for unstable slip the velocity dependence of frictiona b and the characteristic friction distanced c show systematic variations with accumulated displacement for rough surfacesa b started out positive and became negative after about 50 mm displacement andd c increased from 1 to 4 m over the same interval for smooth surfaces a b began negative and decreased slightly with displacement andd c was about 2 m independent of displacement for displacements 30 mm rough surfaces exhibit a second state variable with characteristic distance about 20 m the decrease ina b with displacement is associated with disappearance of the second state variable our data indicate thatd c is controlled by surface roughness in a complex way including but not limited to the effect of roughness on contact junction dimensions for bare rock surfaces the data show that simple descriptions of roughness such as rms and peak to trough are not sufficient to inferd c our observations are consistent with a model in whichd c scales with gouge thickness

thermal history of michigan basin and southern canadian shield from apatite fission track analysis apatite fission track ages and confined length distributions were collected from 38 basement outcrop and 5 basement drillcore samples in order to reconstruct the phanerozoic thermal history of the michigan basin and southern canadian shield the apatite data indicate two periods of thermal activity in the region triassic heating cooling that affected the basin and adjacent shield and cretaceous or post cretaceous heating cooling that primarily affected the basin the magnitude timing and cause of cretaceous thermal activity cannot be identified with the present data model calculations suggest that some of the shield samples and probably all of the basin samples were heated to temperatures of at least 90c just prior to relatively rapid cooling in the triassic available stratigraphic and geochemical constraints suggest that these elevated temperatures were the result of burial by an additional 2 5 km of late paleozoic probably pennsylvanian and permian sediments it is likely that the basin was buried during the alleghenian orogeny as observed for the adjacent appalachian basin

healing and sliding stability of simulated anhydrite fault gouge effects of water temperature and co2 abstract anhydrite bearing faults are currently of interest to 1 co2 storage sites capped by anhydrite caprocks such as those found in the north sea and 2 seismically active faults in evaporite formations such as the italian apennines in order to assess the likelihood of fault reactivation the mode of fault slip and or fault leakage it is important to understand the evolution of frictional strength during periods of no slip and upon reloading healing and relaxation behavior and of the velocity dependence of friction of anhydrite fault gouge therefore we performed slide hold slide experiments combined with a velocity stepping sequence using simulated anhydrite fault gouge 95 wt caso4 vacuum dry and water wet experiments were performed at temperatures ranging from 20 to 150 c and at an effective normal stress of 25 mpa we also performed tests using dry co2 water wetted co2 and co2 saturated water as pore fluid but only at 120 c if pore fluid was present a fluid pressure of 15 mpa was present vacuum dry samples exhibit similar frictional healing to samples containing lab air but healing is significantly enhanced in wet samples dry samples exhibit velocity weakening behavior at t 120 c and wet samples exhibit velocity strengthening behavior over the full temperature range the presence of co2 does not influence the healing behavior or the velocity dependence of friction samples containing water wetted co2 exhibit behavior similar to wet samples we infer that the healing in dry samples is controlled by plastic asperity creep dieterich type possibly through dislocation creep and or twinning in wet samples healing is inferred to be controlled by increases in contact area and cohesion by pressure solution using a pressure solution rate model to extrapolate healing by contact area growth indicates that the maximum re strengthening through such a mechanism will only take days to tens of days

temporal merging of remote sensing data to enhance spectral regolith lithological and alteration patterns for regional mineral exploration abstract remote sensing has been widely used to map geological structure regolith materials and hydrothermal alteration minerals in different regions of the world based largely on the spectral characteristics of clay carbonate and iron oxide minerals given that features related to minerals may form very subtle patterns in landsat imagery finding suitable methods for enhancing the spectral information due to alteration minerals has been the subject of much research since the satellites were launched although multispectral sensors such as landsat do not have enough spectral resolution to distinguish between specific minerals effective processing of the data does yield useful images for regional exploration and targeting when combined with a good understanding of the associated landforms aster and various airborne systems can now provide useful high resolution mineral information however the cost and time taken to acquire and process good resolution spectral data should now be balanced against the enhanced spectral discrimination possible using temporal merging or data stacking from the existing landsat data archive dating back to 1972 one critical characteristic of the spectra related to surface mineral composition is its persistence over time this study proposes a further enhancement to the data using temporal merging to create images that are both easier to interpret and more reliable indicators of lithology and alteration the new approach is to select a large number of scenes typically separated by two or more years and to merge the data for each band to give a cumulative spectral signature the technique of stacking landsat data to create a new dataset with much greater spectral depth is termed landsat tm3 or landsat tm temporal merge for terrain mapping this emphasises not only the process used to create the dataset but also the dominant use to which these data are ideally suited namely mapping geological and mineral related terrains

evolution of strength recovery and permeability during fluid rock reaction in experimental fault zones abstract physical and chemical fluid rock interactions are implicated in controlling earthquake nucleation and recurrence in particular interseismic compaction sealing and healing of fractured fault rocks can lead to strength recovery and stabilisation of fault zones in contrast these same processes can also assist increases in pore fluid pressures and consequent destabilisation of faults here we present high temperature hydrothermal experiments designed to assess the evolution of strength of fault zones in previously intact rock and also characterise the associated changes to porosity and permeability cores of fontainebleau sandstone were initially loaded to failure in a high pressure gas medium apparatus the failed specimens were then hydrothermally reacted at 927 c for variable duration under isostatic conditions and subsequently re fractured to determine the interseismic strength recovery in the most extreme case hydrothermally induced gouge compaction cementation and crack healing resulted in 75 strength recovery after reaction for 6 h isostatic hydrothermal treatment also resulted in dramatic reduction in porosity and permeability strength of the fault zone following hydrothermal reaction appears to be closely correlated to porosity consistent with previous studies on brittle failure of porous aggregates the experimental results show how hydrothermal reactions in fault zones may lead to two competing time dependent effects fault strengthening due to increased cohesion in the fault zone and fault weakening arising from elevated pore pressures within a well cemented low permeability gouge layer

deep burial hydrothermal alteration of the pre salt carbonate reservoirs from northern campos basin offshore brazil evidence from petrography fluid inclusions sr c and o isotopes abstract petrographic mineralogical elemental isotopic and fluid inclusion analyses were integrated to unravel the diagenetic evolution of brazilian pre salt lacustrine carbonate reservoirs of northern campos basin southeast brazilian margin detailed thin section and cathodoluminescence petrography scanning electron microscopy and electron microprobe analyses established a paragenetic evolution of diagenetic processes and products comprising extensive dolomitization silicification and dissolution a paragenesis including saddle dolomite macrocrystalline calcite mega quartz sr barite celestine fluorite dickite sphalerite galena and other metallic sulfides filling fractures and dissolution porosity and aqueous fluid inclusions with homogenization temperatures of 92 152 c and salinities between 13 and 26 wt eq nacl characterized a hydrothermal system with some analogy to carbonate hosted pb zn mississippi valley mvt and irish type deposits petroleum inclusions and solid bitumen testify atypical oil generation and migration associated with the hydrothermal flow the host pre salt spherulitic and fascicular carbonates present highly radiogenic 87sr 86sr ratios indicating strong interaction with continental crust materials hydrothermal phases show 18o values more negative than syngenetic and diagenetic carbonates the 13c values are interpreted as result of interaction between the hydrothermal fluids and the host rocks the combined data set provides clear evidence of intense hydrothermal alteration of northern campos basin pre salt reservoirs at deep burial conditions 2 km possibly related to late cretaceous or more probably paleogene magmatic activity mixed sourced fluids bearing a basinal signature fed the hydrothermal system and promoted dissolution of the host rocks the hydrothermal alterations had strong impact on the porosity permeability and heterogeneity contributing together with the associated fracturing to the excellent production performance of the pre salt reservoirs

significance of primary hilltop loess in reconstructing dust chronology accretion rates and sources an example from the negev desert israel 1 although high latitude loess sequences have been studied extensively for reconstructing past climates loess in desert margins has been mostly overlooked moreover many low latitude loess studies have focused on secondary reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control in this respect the spatial distribution of the loess and its different types are crucial in this study we differentiate primary and secondary loess using remote sensing and field criteria we present remote sensing and geographic information system procedures for mapping loess distribution in general and for identifying pristine hilltop loess sequences in particular then we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary hilltop loess sequence in the negev desert that show that the late pleistocene negev loess started accumulating at 95 ka much earlier than previously proposed 70 ka it was preceded by a previously unknown middle pleistocene period of loess formation at 180 130 ka the ages also suggest that the threshold of dust accretion rate needed for loess formation is 0 02 mm a 1 30 g m 2 a 1 a factor of 2 or more lower than previously thought 0 04 to 1 0 mm a 1 our results also provide insights into causes of late pleistocene loess accretion and its close association with regional dune field activity the methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other more remote desert areas

devonian dundee formation crystal field michigan basin recovery of bypassed oil through horizontal drilling carbonate reservoirs of the devonian dundee formation represent the most productive interval in the michigan basin yet have suffered widespread abandonment due to improper early reservoir management and completion practices dundee carbonate reservoirs deposited in marginal marine and shallow marine environments have produced over 351 mmbbl oil from 137 fields most of which were discovered in the 1930s and 1940s initial potentials for many dundee wells ranged from 2000 to 9000 bbl day presumably due to high permeability fractures and solution enhanced porosity in some areas and excellent primary interparticle porosity in other areas crystal field discovered in 1935 at a depth of less than 3500 ft 1060 m was aggressively developed and produced at high rates causing widespread water coning such that 95 of the field was drilled and abandoned in less than 5 yr leaving considerable interwell reserves in the ground no cores or wireline logs existed for the field prior to 1995 when the field became the subject of a multiyear study aimed at determining the feasibility of employing horizontal drilling to recover bypassed reserves a vertical test portion of the tow 1 3 horizontal well located in a structurally elevated portion of the field cored and logged the entire reservoir interval yielding crucial new information on the basis of relevant data a horizontal leg was drilled resulting in an excellent producer with estimated recoverable reserves of 200 000 bbl two subsequent horizontal tests with poor results were drilled in downdip locations and oriented perpendicular to the tow well suggesting the importance of both structural position and azimuth selective use of horizontal drilling is considered an appropriate cost effective means for recovering bypassed reserves in dundee fields where sufficient geologic data exist to adequately characterize the reservoir and oil occurrence for some fields this may require new coring and logging operations

nanocrystalline slip zones in calcite fault gouge show intense crystallographic preferred orientation crystal plasticity at sub seismic slip rates at 18 150 c a central aim in fault mechanics is to understand the microphysical mechanisms controlling aseismic seismic transitions in fault gouges and to identify microstructural indicators for such transitions we present new data on the slip stability of calcite fault gouges and on microstructural development down to the nanometer scale our experiments consisted of direct shear tests performed dry at slip rates of 0 1 10 m s at a constant normal stress of 50 mpa at 18 150 c the results show a transition from stable to potentially unstable slip above 80 c all samples recovered showed an optical microstructure characterized by narrow 30 40 m wide riedel and boundary shear bands marked by extreme grain comminution and a crystallographic preferred orientation cpo boundary shear bands sectioned using fib sem focused ion beam scanning electron microscopy revealed angular grain fragments decreasing from 10 to 20 m at the outer margins to 0 3 m in the shear band core where dense aggregates of nanograins also occurred transmission electron microscopy applied to foils extracted from boundary shears using fib sem combined with the optical cpo showed that these aggregates consist of calcite nanocrystals 5 20 nm in size with the 104 201 dislocation glide system oriented parallel to the shear plane and direction our results suggest that the mechanisms controlling slip include cataclasis and localized crystal plasticity because crystal plasticity is strongly thermally activated we infer that the transition to velocity weakening slip is likely due to enhanced crystal plasticity at 80 c this implies that tectonically active limestone terrains will tend to be particularly prone to shallow focus seismicity

frictional properties and microstructure of calcite rich fault gouges sheared at sub seismic sliding velocities we report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone 96 caco3 and pure calcite our experiments consisted of direct shear tests performed under dry and wet conditions at an effective normal stress of 50 mpa at 18 150 c and sliding velocities of 0 1 10 m s wet experiments used a pore water pressure of 10 mpa wet gouges typically showed a lower steady state frictional strength 0 6 than dry gouges 0 7 0 8 particularly in the case of the pure calcite samples all runs showed a transition from stable velocity strengthening to potentially unstable velocity weakening slip above 80 100 c all recovered samples showed patchy mirror like surfaces marking boundary shear planes optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands characterized by extreme grain comminution and a crystallographic preferred orientation cross sections of boundary shears cut normal to the shear direction using focused ion beam sem from pure calcite gouges sheared at 18 and 150 c revealed dense arrays of rounded 0 3 m sized particles in the shear band core transmission electron microscopy showed that these particles consist of 5 20 nm sized calcite nanocrystals all samples showed evidence for cataclasis and crystal plasticity comparing our results with previous models for gouge friction we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands with water facilitating pressure solution subcritical cracking and intergranular lubrication our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains contrary to recent claims our data also demonstrate that nanocrystalline mirror like slip surfaces in calcite rich faults are not necessarily indicative of seismic slip rates

the 1997 98 umbria marche earthquake sequence geological vs seismological faults abstract the 1997 98 umbria marche earthquake provided a huge amount of good quality seismological data the geology of the region has been extensively mapped for over a century by geologists from all over the world the subsurface geology is constrained by a set of seismic reflection profiles and deep boreholes acquired for oil exploration the earthquake stimulated the acquisition of many other geological and geophysical data sets surface ruptures structural analysis geodetic data geoeletrical data etc as a consequence the 1997 98 earthquake is one of the best case studies in the world for extensional earthquakes driving the possibility of building up an integrated model of an extensional system we use this favourable test site to discuss the possibility of integrating and connecting the seismological faults i e the short term instantaneous ruptures generated during the earthquakes representing the effect of a single event and the geological faults i e the long term active faults exposed at the surface that are the effects of multiple repeated events of faulting the review of this complex data set points to an integrated model where the moderate seismicity of the region is driven by sw dipping normal faults whose dip changes with depth from 60 70 the fault surfaces mapped at the surface to 35 45 the fault segments ruptured during the earthquake at depths of 2 8 km to less than 20 at depth 8 km these normal faults are not inherited from previous tectonic events however the pre existing arc shaped compressional structures act as barriers segmenting the extensional fault system the depth and thickness of the seismogenic layer is lithologically controlled since the seismicity is confined within the sedimentary cover and do not penetrate the underlying basement the mainshocks are located close to the bottom of the seismogenic layer within the triassic evaporites

formation of saddle dolomites in upper cambrian carbonates western tarim basin northwest china implications for fault related fluid flow abstract the saddle dolomites occur more intensely in cores closely to fault than that in cores far away from the fault in upper cambrian carbonate of western tarim basin suggesting that formation of the saddle dolomites is likely related to fault controlled fluid flow they partially fill in fractures and vugs of replacement dolomite the saddle dolomites exhibit complex internal textures commonly consisting of core and cortex in comparison with the matrix dolomites the saddle dolomites show lower sr content and 87 sr 86 sr ratios higher fe and mn content and more negative 18 o values combined with high th 100 130 c of primary fluid inclusions it is suggested that the saddle dolomites precipitated from hydrothermal fluid derived from the deep evaporite bearing middle cambrian strata and the magnesium source may be due to dissolution of host dolomite during hydrothermal fluid migration fault activity resulted in petrographic and geochemical difference of the core and cortex of the saddle dolomites the cores precipitated from the formation water mixed by deep brines at the early stage of fault activity and the cortexes precipitated from the deep fluid with higher temperatures through the middle cambrian later in summary the formation of the saddle dolomites implies a hydrothermal fluid event related to fault activity which also resulted in high porosity in upper cambrian carbonate in western tarim basin

aster detection of chromite bearing mineralized zones in semail ophiolite massifs of the northern oman mountains exploration strategy abstract economically viable chromite deposit occurrences are widespread in the ultramafic rocks of semail ophiolite massifs of the northern oman mountains particularly in the basal dunite and harzburgite unit of the mantle section geological mapping of this region is challenging primarily due to difficult access complexity of structures and lack of resolution and areal integrity of lithological differentiation using conventional mapping techniques the present research study evaluates the discrimination and occurrence of chromites bearing mineralized zones within ophiolites by analyzing the capabilities of landsat tm and advanced spaceborne thermal emission and reflection radiometer aster satellite data using a number of selected methods including decorrelated stretching different band rationing and principal component analysis image processing techniques exist in the scientific literature the study results show that the processed vnir and swir spectral wavelength regions are promising in detecting the areas of potential chromite bearing mineralized zones within the ophiolite region and proved to be successful for mapping of serpentinized harzburgite containing chromites exploration geologists industrialists and mine owners are advised to adopt this technique and avoid the limits in filed data alone for more exploration and exploitation of areas having chromite deposits in arid region elsewhere

frictional heterogeneities on carbonate bearing normal faults insights from the monte maggio fault italy observations of heterogeneous and complex fault slip are often attributed to the complexity of fault structure and or spatial heterogeneity of fault frictional behavior such complex slip patterns have been observed for earthquakes on normal faults throughout central italy where many of the mw 6 to 7 earthquakes in the apennines nucleate at depths where the lithology is dominated by carbonate rocks to explore the relationship between fault structure and heterogeneous frictional properties we studied the exhumed monte maggio fault located in the northern apennines we collected intact specimens of the fault zone including the principal slip surface and hanging wall cataclasite and performed experiments at a normal stress of 10 mpa under saturated conditions experiments designed to reactivate slip between the cemented principal slip surface and cataclasite show a 3 mpa stress drop as the fault surface fails then velocity neutral frictional behavior and significant frictional healing overall our results suggest that 1 earthquakes may readily nucleate in areas of the fault where the slip surface separates massive limestone and are likely to propagate in areas where fault gouge is in contact with the slip surface 2 postseismic slip is more likely to occur in areas of the fault where gouge is present and 3 high rates of frictional healing and low creep relaxation observed between solid fault surfaces could lead to significant aftershocks in areas of low stress drop

a microphysical model for strong velocity weakening in phyllosilicate bearing fault gouges 1 previous rotary shear experiments performed on a halite muscovite fault gouge analogue system have shown that the presence of phyllosilicates under conditions favoring the operation of cataclasis and pressure solution in the matrix phase can have major effects on the frictional behavior of gouges while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behavior the strength of mixtures containing 10 30 muscovite is both normal stress and sliding velocity dependent at high sliding velocities 1 m s 1 such mixtures show unusually marked velocity weakening along with the development of a structureless cataclastic microstructure in the present paper a micromechanical model is developed in an attempt to explain this behavior the model assumes a granular flow process involving competition between intergranular dilatation and compaction by pressure solution the predictions of the model agree favorably with the experimental results extension of the model to quartz mica systems implies that the presence of phyllosilicates plus the operation of pressure solution can strongly promote unstable velocity weakening behavior at rapid slip rates on natural faults under midcrustal conditions static stress drop predictions based on the model agree reasonably well with estimates from seismic observations our results may help explain the discrepancy between laboratory derived rate and state friction parameter values obtained for dry low strain and or single phase rock systems and the values for natural fault rocks inferred from seismological data

thermal history of michigan basin the elevated organic maturity observed in shallowly buried units from the michigan basin implies that higher temperatures and thicker overburdens once existed in the basin evidence from sediment accumulation rates regional dips and maturity of pennsylvanian age coals suggests that up to 1 000 m 3 280 ft of sediment were removed by erosion prior to the late jurassic when the basin became stable geothermal gradients during paleozoic basin subsidence probably ranged from 35 to 45 c km 19 to 25 f 1 000 ft in contrast to the average present value of 25 c km 14 f 1 000 ft depths to the top of the oil window ranged from 1 900 to 2 300 m 6 230 to 7 540 ft during the paleozoic post pennsylvanian erosional uplift and further thermal m turation of the basin have combined to raise the top of the oil window to its present level of 500 m 1 640 ft

discrimination of iron ore deposits of granulite terrain of southern peninsular india using aster data abstract this work describes a new image processing technique for discriminating iron ores magnetite quartzite deposits and associated lithology in high grade granulite region of salem southern peninsular india using visible near infrared and short wave infrared reflectance data of advanced spaceborne thermal emission and reflection radiometer aster image spectra show that the magnetite quartzite and associated lithology of garnetiferrous pyroxene granulite hornblende biotite gneiss amphibolite dunite and pegmatite have absorption features around spectral bands 1 3 5 and 7 aster band ratios 1 3 2 3 5 4 5 7 6 in rgb are constructed by summing the bands representing the shoulders of absorption features as a numerator and the band located nearest the absorption feature as a denominator to map iron ores and band ratios 2 4 3 5 7 6 7 9 8 in rgb for associated lithology the results show that aster band ratios 1 3 2 3 5 4 5 7 6 in a red green blue rgb color combination identifies the iron ores much better than previously published aster band ratios analysis a principal component analysis pca is applied to reduce redundant information in highly correlated bands pca 3 2 and 1 for iron ores and 5 4 2 for granulite rock in rgb enabled the discrimination between the iron ores and garnetiferrous pyroxene granulite rock thus this image processing technique is very much suitable for discriminating the different types of rocks of granulite region as outcome of the present work the geology map of salem region is provided based on the interpretation of aster image results and field verification work it is recommended that the proposed methods have great potential for mapping of iron ores and associated lithology of granulite region with similar rock units of granulite regions of southern peninsular india this work also demonstrates the ability of aster s to provide information on iron ores which is valuable for mineral prospecting and exploration activities

evidence from the northern red sea on the transition from continental to oceanic rifting abstract the northern red sea is an active rift in the last stages of continental rifting which is beginning to undergo the transition to oceanic seafloor spreading the rift can be divided into two distinct regions the marginal areas consist of a series of bathymetric terraces and as indicated by geophysical data are underlain by a series of rotated fault blocks the axial depression which forms the axis of deep water is a continuous region 10 to 25 km wide near the center of the sea which is characterized by high heat flow a large gravity minimum and very deformed sediments both regions are divided along strike into segments roughly 60 km long by cross trending transfer zones the presently active tectonics are characterized by the concentration of extension and deformation in the axial depression and by the emplacement of a number of large intrusions the intrusions occur at distinct sites located at the intersection of transfer zones with the faults bounding the rotated blocks in the marginal areas and at deeps located in the axial depression halfway between transfer zones although extension is becoming concentrated in the axial depression geophysical data imply that at least the upper few kilometers of the crust in that region consists of non magnetic continental type material and that this ca apace has been ruptured by large intrusions only at the deeps a wide range of crustal seismic velocities has been observed in the northern red sea including velocities normally associated with oceanic crust the velocity variations appear spatially related to corresponding large variations in basement rock type observed on shore in the eastern desert of egypt the northern red sea is in an intermediate stage between a continental rift valley and a young ocean basin and delineation of its structure and tectonics allows a model to be developed for the evolution of a rifted continental margin rifting starts in a series of linked half grabens 50 60 km long and formed over detachment surfaces which probably penetrate no deeper than the mid or lower crust this style of rifting can accommodate at least the amcunt of extension represented by the gulf of suez 35 km at some greater amount of extension the rift acquires a more symmetric shape probably through the development of antithetically faulted blocks in the hanging wall extension in this stage is still distributed throughout the rift and is accommodated in the upper crust by rotation of fault blocks at the stage represented by the northern red sea extension becomes concentrated in an axial depression and begins to be partially accommodated by large intrusions which form deeps the position of the deeps is controlled by the transfer zones established in the earliest stages of rifting with further extension the deeps serve as nucleation points that develop into small discrete cells of seafloor spreading these cells grow and coalesce to form a continuous mid ocean ridge spreading center such as is found in the southern red sea

the effect of loading rate on static friction and the rate of fault healing during the earthquake cycle the seismic cycle requires that faults strengthen heal between earthquakes and the rate of this healing process plays a key role in determining earthquake stress drop1 2 3 4 rupture characteristics5 6 and seismic scaling relations2 3 4 7 frictional healing as evidenced by increasing static friction during quasi stationary contact between two surfaces1 8 9 10 11 12 is considered the mechanism most likely to be responsible for fault strengthening2 3 13 14 previous studies however have shown a large discrepancy between laboratory and seismic field estimates of the healing rate2 3 4 14 15 in the laboratory rock friction changes by only a few per cent per order of magnitude change in slip rate whereas seismic stress drop increases by a factor of 2 to 5 per order of magnitude increase in earthquake recurrence interval but in such comparisons it is assumed that healing and static friction are independent of loading rate here i summarize laboratory measurements showing that static friction and healing vary with loading rate and time as expected from friction theory16 17 18 applying these results to seismic faulting and accounting for differences in laboratory seismic and tectonic slip rates i demonstrate that post seismic healing is expected to be retardedfor a period of several hundred days following an earthquake in agreement with recent findings from repeating earthquakes13 14 19 20

compaction creep of wet granular calcite by pressure solution at 28 c to 150 c 1 uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone analytical grade calcite and superpure calcite the tests were performed at 28 c 150 c effective stresses of 20 47 mpa and a pore pressure of 20 mpa using presaturated caco3 solution as the pore fluid sample grain sizes ranged from 12 to 86 m the aim was to determine if creep occurs by intergranular pressure solution ips under these conditions and to identify the rate controlling process the wet samples showed significant creep while dry and oil flooded samples did not wet samples were also characterized by microstructures such as sutured grain contacts grain indentations and overgrowths suggesting the operation of ips the behavior of the wet samples at low strains 4 5 agreed well with the predictions of standard models for diffusion controlled pressure solution however at higher strains 5 10 creep slowed down compared with the model predictions transient flow through tests performed in this regime led to an acceleration of creep consistent with models for precipitation controlled ips and demonstrated an increase in the impurity content of the pore fluid toward higher strains since some of these impurities notably mg2 retard precipitation in calcite we suggest that creep occurred by diffusion controlled ips at low strain giving way to precipitation control at larger strains as impurities accumulated fitting of the diffusion controlled ips model to the low strain data yielded values of the grain boundary diffusion product ds in calcite of 10 19 m3 s 1 at 150 c

evidence against the dorag mixing zone model for dolomitization along the wisconsin arch a case for hydrothermal diagenesis ordovician carbonates near the wisconsin arch represent the type locality in ancient rocks for the dorag or mixing zone model for dolomitization field petrographic and geochemical evidence suggests a genetic link between the pervasive dolomite trace mississippi valley type mvt minerals and potassium k silicate minerals in these rocks which preserve a regional hydrothermal signature constraints were placed on the conditions of water rock interaction using fluid inclusion methods cathodoluminescence and plane light petrography stable isotopic analyses and organic maturity data homogenization temperatures of two phase aqueous fluid inclusions in dolomite sphalerite and quartz range between 65 and 120c freezing data suggest a na ca mg cl h2o fluid with salinities between 13 and 28 wt nacl equivalent the pervasive dolomitization of paleozoic rocks on and adjacent to the wisconsin arch was the result of water rock interaction with dense brines at elevated temperatures and it was coeval with regional trace mvt mineralization and k silicate diagenesis a reevaluation of the dorag mixing zone model for dolomitization in conjunction with convincing new petrographic and geochemical evidence has ruled out the dorag model as the process responsible for pervasive dolomitization along the wisconsin arch and adds to the abundant body of literature that casts serious doubt about the viability of the dorag model in general

early history of the michigan basin subsidence and appalachian tectonics geometries of cambrian to silurian stratigraphc sequences in the michigan basin record discrete episodes of basin centered subsidence separated by periods of regional tilting backstripping reveals irregular subsidence rates that argue against a simple thermal contraction model depositional facies architecture also reflects episodic subsidence patterns basin centered facies tracts dominating during subsidence reactivations these three lines of evidence indicate that subsidence cessations and reactivations characterize the early history of the michigan basin periods of episodic subsidence correlate temporally with orogenic events in the appalachians suggesting that reactivation of basin subsidence is related to tectonic activity we propose that appalachian orogenic activity caused the episodic subsidence of the michigan basin possibly through weakening of the lower crust and reactivation of a preexisting upper crustal isostatic imbalance

remote sensing based approach for mapping of co2 sequestered regions in samail ophiolite massifs of the sultanate of oman abstract documentation of chemical weathering and co 2 sequestration in the samail ophiolite massifs of the sultanate of oman represents an important case study for geological carbon capture and storage system gccss the present research study demonstrates the capability of remote sensing technique for mapping of weathered zones and potential co 2 sequestration area abundances at different scales within peridotites in the northern mountain region of the samail ophiolite massifs the carbonate mineral index ci applied with other mineral indices to the tir wavelength region of advanced spaceborne thermal emission and reflection radiometer aster tir spectral bands 13 and 14 mapped co 2 sequestered minerals along the structural and wadi controlled co 2 flowing regions peridotites the source rocks of co 2 sequestration in the study area were mapped using an aster 8 3 and 1 band combinations the decorrelated landsat tm image discriminated the rock types associated with peridotites of ophiolite sequences and delineated the region of weathered and altered serpentinized peridotites in the zone of co 2 sequestration co 2 sequestration mapping was carried out using landsat tm satellite data that span 20 years 1986 1998 2000 2003 and 2006 to assess the present status of co 2 sequestration in this region the image interpretations are verified with existing geological maps and through field and laboratory studies the spectral measurements of carbonate minerals at 1300 to 2500 nm with the spectral resolution of 7 nm using a pima sp infrared spectrometer in the field and laboratory show the presence of hydroxyl bearing minerals and carbonates that have spectral absorption features around 1 4 m 1 9 m and 2 35 m the strong absorptions around 2 35 m are mainly due to c o bonds in carbonate minerals such as calcite caco 3 dolomite camg co 3 2 magnesite mgco 3 aragonite caco 3 and siderite feco 3 which form 15 to 57 12 to 53 9 to 38 11 to 21 and 3 to 8 respectively in the samples the absorptions around 1 4 m and 1 9 m are caused by hydration effects of hydroxyl minerals including antigorite and montmorillonite present at 10 to 21 and 37 to 81 respectively in the samples the alterations of serpentinite are evidenced by the presence of antigorite and lizardite minerals x ray powder diffraction analyses further confirms the occurrence of co 2 sequestered major carbonate minerals such as aragonite calcite and dolomite in the samples the study demonstrates that the aster and landsat tm satellite multispectral sensors are useful to detect the carbonate minerals to delineate the peridotites and to discriminate the areal abundance of potential co 2 sequestration this technique is a useful tool to map and monitor the region of co 2 sequestration in well exposed arid and semi arid regions and to analyze and understand this aspect of the world geological carbon capture and storage system

an integrated approach for identification of potential aquifer zones in structurally controlled terrain wadi qena basin egypt abstract wadi qena basin represents one of the most promising regions for future development in egypt fresh water supplies are crucial for such plans we provide an integrated remote sensing landsat aster dem geoeye 1 geophysical aeromagnetic isotopic 18 o 2 h field stratigraphic and structural interpretation and geochemical major dissolved ions approach to delineate zones of potential groundwater resources in wadi qena basin four water bearing horizons were sampled fractured crystalline aquifer nubian aquifer system nas post nubian aquifer system pnas and the quaternary aquifer findings include 1 spatial analysis of remote sensing data in a gis environment indicates extensive structural deformation by dextral faults trending ne sw i e qena safaga shear zone qs and sinistral faults trending nw se i e najd shear zone and sufficient surface water supply from the east through wadi fattera sub basin 2 analysis of geophysical data indicates that these faults control the water bearing horizons in the subsurface 3 isotopic analysis reveals four isotopic groups including two end members one mixed group and one mixed and evaporated group group i highly depleted fossil nubian waters range 18 o from 6 39 to 6 74 and 2 h from 48 21 to 52 46 group ii modern waters in fractured basement range 18 o from 1 41 to 1 51 and 2 h from 5 46 to 6 04 group iii a mixed cluster between nas and modern waters range 18 o from 4 82 to 5 05 and 2 h from 33 28 to 38 54 and group iv samples which have both mixing between the nubian and meteoric waters and also have a considerable deviation from the global meteoric water line gmwl range 18 o from 0 58 to 4 69 and 2 h from 19 59 to 38 68 4 samples with a mixed isotopic signature in group iii which tap the nas and are located along the main channel of wadi fattera area 3600 km 2 provide evidence for modern recharge along surface exposures of the nas and enhanced infiltration along deep seated faults 5 samples with a mixed isotopic signature in group iv which tap the quaternary and pnas aquifers and are located along deep seated faults provide evidence of artesian upward leakage from the deep nas into the shallower quaternary and pnas aquifers the present study improves our understanding of the role of structural control and modern recharge in exploration for aquifer potential in arid environments

petrographic and geochemical characteristics of dolomite types and the origin of ferroan dolomite in the trenton formation ordovician michigan basin u s a three major types of dolomite occur in the trenton formation mid ordovician of the michigan basin these are 1 regional dolomite which is confined to the extreme western edge of the basin 2 cap dolomite which occurs in the upper portion of the trenton and is confined to the basin s southern margin and 3 fracture related dolomite which occurs in association with both large and small scale faults and fractures these three dolomite types can be distinguished from one another by their major element chemistry oxygen isotope ratios and rock texture the regional dolomite is fine grained has 0 34 mol feco3 and mean 18o of 6 8 opbd the cap dolomite is texturally similar to regional dolomite but contains 3 13 0 mol feco3 and has a mean 18o of 7 7 fracture related dolomites are coarse grained low in iron and have the most depleted 18o ratios x 9 0 pdb petrographic relationships imply that the regional dolomite formed prior to the cap dolomite probably during early diagenesis the cap dolomite formed at relatively shallow depths as a result of the interaction of the overlying utica shale and the trenton limestone fracture related dolomites post date the cap dolomite and formed during deeper burial a temperature of precipitation of approximately 80 c was calculated for fracture related dolomites using oxygen isotope data the distribution of the cap dolomite was controlled by the availability of fe2 which was in turn controlled by the availability of s2 in the centre of the basin trenton utica deposition was continuous the upper trenton contained relatively high concentrations of organic matter which was used by sulphate reducing bacteria to produce h2s from seawater sulphate the precipitation of iron sulphides pyrite iron monosulphide followed and used up most of the available fe2 as a result only small amounts of ferroan dolomite formed on the periphery of the basin subaerial exposure resulted in the oxidation of most of the available organic matter sulphate reducing bacteria were therefore limited and produced limited amounts of h2s as a result only a minor amount of iron sulphide iron monosulphide formed the remaining fe2 was then available for the formation of the ferroan cap dolomite this model is supported by the following 1 in the southern margin of the basin the contact between trenton cap dolomite and the overlying utica shale is sharp and probably unconformable in the centre of the basin the contact is gradational 2 in the centre of the basin the total organic carbon content in the upper trenton is an order of magnitude higher than in the cap dolomite 3 the whole rock concentration of iron is high in both the cap dolomite and in slightly dolomitized equivalent beds in the basin centre 4 iron sulphides are abundant in the centre of the basin and mostly in the form of pyrite in the cap dolomite iron sulphide is minor and primarily in the form of iron monosulphide

extension of the najd shear system from saudi arabia to the central eastern desert of egypt based on integrated field and landsat observations the najd shear system in saudi arabia extends over 1200 km in a nw se direction and has a width of approximately 300 km a digital color mosaic compiled from seven landsat thematic mapper scenes was used to delineate characteristic structural features of the najd system in the midyan region of saudi arabia and to search for similar features in the egyptian eastern desert the digital mosaic was generated using ratios of landsat thematic mapper bands bands 5 4 3 4 5 1 5 7 that are sensitive to the rock content of fe bearing aluminosilicates spectrally opaque phases and hydroxyl bearing or carbonate minerals respectively the mosaic covers approximately 130 000 km of late proterozoic exposures of the arabian nubian shield and has the eastern desert and the midyan region placed in their approximate pre red sea locations the ajjaj shear zone ajz marks the termination of the najd system against the eastern margin of the red sea in the midyan region the ajz aligns with the central eastern desert based on analysis of pre red sea locations analyses of landsat data and field observations show that the ajjaj shear zone and the central eastern desert exhibit the following features in common 1 outcrops that are generally elongate in a nw se direction as a result of folding with fine scale lithologic heterogeneity at the outcrop scale related to deformation associated with faulting 2 nw trending left lateral faults and ductile shear zones 3 subhorizontal nw trending mineral lineations and variably dipping nw trending foliations with local changes in attitude around large competent e g granitic bodies and 4 lithologic contacts that are generally tectonic in nature and related to faulting these features are less common to the north and south of both the ajjaj shear zone and the central eastern desert results are consistent with the najd shear system extending into the eastern desert and dominating the structural patterns within the central part of the eastern desert

fluid assisted healing processes in gouge bearing faults insights from experiments on a rock analogue system on the basis of both experimental and field studies solution transfer processes are expected to be important in contributing to fault strength recovery healing under the hydrothermal conditions prevailing in large parts of the seismogenic zone however most experimental work on healing effects in faults has been done using quartzo feldspathic sliding surfaces or fault gouges under conditions in which solution transfer processes are very slow mechanisms of fluid assisted fault healing are accordingly rather poorly understood we have performed slide hold slide fault healing experiments on simulated faults containing brine saturated granular halite as a fault rock analogue halite was used because solution transfer processes are known to be rapid in this system under easily accessible conditions we studied the effects of hold time duration shear stress during hold pre hold sliding velocity and pore fluid composition on strength evolution the results show rapid fluid assisted compaction and stress relaxation during hold periods and a significant hold time dependent strengthening upon re shear the data reveal that healing resulted from both a packing density increase and a contact area strength increase during hold periods the general type of behaviour observed is similar to that observed in quartzo feldspathic gouges at room temperature although important differences were observed as well notably the time dependence of healing deviates from the log linear trend observed in gouges where solution transfer processes are absent this means that if pressure solution is an important healing mechanism in natural faults applying a log linear trend will underestimate natural fault healing rates

the effect of shear load on frictional healing in simulated fault gouge we report on frictional strengthening healing in granular quartz gouge as a function of time of true stationary contact to distinguish between the slip dependent ruina 1983 and time dependent dieterich 1979 friction constitutive laws we designed tests similar to conventional slide hold slide shs tests except that shear load was completely removed prior to holds we find large healing values 0 033 0 054 for holds of 101 102 s compared with quasi static shs experiments and our data indicate time dependent weakening in contrast with strengthening observed from shs tests gouge layer compaction increases with increasing hold time comparable to observations from conventional shs tests our data indicate that purely time dependent processes have a minor influence on healing under the conditions studied and or that such effects are efficiently erased by particle rearrangement during removal reapplication of shear load the data are not adequately described by either the time dieterich or slip ruina dependent state evolution laws

hydrothermal origin of early permian saddle dolomites in the junggar basin nw china abstract hydrothermal related saddle dolomites widely exist in the lower permian fengcheng formation in the northwestern junggar basin and this formation is a set of carbonate rich deposits in an alkaline saline basin core and thin section observations cathodoluminescence cl imaging and carbon and oxygen isotope composition analyses have been used to study the origins of saddle dolomites with various occurrences hydrothermal fluids include si rich and si poor fluids and saddle dolomites occur along with siliceous bands as debris and assemblages in fragmented rocks and as cements filling pores and microfractures different types of dolomites in the fengcheng formation have similar 13c values while the 18o values differed from each other which demonstrated that the dolomites originated from the same primary carbonates and underwent multiple stages of recrystallization the 18o values were extremely negative which was caused by fractionation at high temperatures from hydrothermal fluids dolomites are directly or indirectly affected by hydrothermal diagenetic fluids according to the diagenetic stages the types of migration paths for hydrothermal fluids and the patterns of hydrothermal fluids acting on the dolomites a model was proposed to illustrate the origins and evolution of the dolomites and three paths were utilized path i occurred during the contemporaneous diagenetic stage when the carbonate particles were still free and could be captured by high density bottom hydrothermal flows and distorted path ii occurred during the long diagenetic history after the carbonate bearing sediments had consolidated saddle dolomite assemblages and saddle dolomite debris occurred with the aid of compressive tectonic forces path iii also occurred in the long diagenetic history and the host rocks were not fragmented the saddle dolomites reprecipitated as cements in the pores stylolites fractures microfractures or laminated seams