karst systems analyzed using borehole logs devonian carbonates of the świetokrzyskie holy cross mountains central poland abstract the methodological assessment of the quality and the usefulness of borehole logs for karst analysis versus the use of data obtained via direct observation is the first objective of this paper the second objective of the paper is to present in the form of a case study regional analysis of karst in devonian carbonates of the wietokrzyskie holy cross mountains south central poland the subjects of the discussion are karst evolution stages karst horizons and their relationship to relief development the analyzed examples sites presented herein where the reliability of borehole data has often been verified by field observations prove that descriptions of borehole logs can be used for karst analysis however borehole log data analysis is subject to many limitations and requires extensive validation the basic condition that has to be met is the explicitness of the descriptions of karst forms in borehole logs the number and the length of logs macro records as well as the number and the size of karst forms micro records are other important factors that affect log interpretation quality nevertheless the principal general advantage of borehole log analysis is the representative nature of the obtained information the formation of karst horizons independent of the lithology and the stratigraphy of the kowala fm in the wietokrzyskie mountains but controlled by external morphological factors suggests an isotropic character of this formation two general vertical types of karst systems are distinguished in this formation 1 karst horizons and 2 extensive karst development without distinct differentiation the former could have been connected with fluvial base levels whereas the latter represents systems formed within the vadose zone

breccias and ores part 1 history organization and petrography of breccias abstract although the term breccia is one of the oldest rock names still in use and proliferating in its application a satisfactory definition remains problematic and an overall classification of breccias is non existent the names of breccia varieties several hundred please the heart rather than the computer and there is little interdisciplinary correlation among the more than fifty specialized schools of breccia study this contribution reviews briefly the history of breccia research and provides a list of the present study trends complete with references with emphasis on ore associated breccias wherever possible conventional breccia definitions and their shortcomings are discussed and a case is made for the introduction of the petrographic category of coarse fragmentites of which the typical sedimentary breccias and conglomerates as well as volcanic tectonic hydrothermal impact and other fragmental materials are members whether designated or not as breccia in the conventional literature this is followed by a proposed rational organization classification of coarse fragmentites and breccias based on the regime of formation and architecture fabric gefuge two fundamental end member sequences a b and a transitional suite c can be recognized a disaggregation fragmentites d breccias produced from a solid progenitor by increasing rate of fracturing expansion rotation mixing and attrition the transitional sequence is crackle mosaic rubble melange milled breccia b aggregation fragmentites a breccias generated by gathering aggregation and accumulation of originally dispersed fragments at the site of deposition these materials form a sequence ranging from tightly packed fragment supported matrix free fragmentites through matrix infilled matrix supported fragmentites to lonestone rocks c in transport fragmentites t breccias formed by redeposition of an aggregate gathered in an earlier phase of development as an a fragmentite or by transportation and redeposition of an advanced member i e rubble melange or milled fragmental aggregate of a d fragmentite examples of metallic mineralizations coeval with or superimposed on the fragmentite sequences are reviewed

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

pervasive dolomitization with subsequent hydrothermal alteration in the clarke lake gas field middle devonian slave point formation british columbia canada the clarke lake gas field in british columbia canada is hosted in pervasively dolomitized middle devonian carbonates of the slave point formation the clarke lake field consists mostly of pervasive matrix dolomite and some saddle dolomite the latter varying in volume from about zero in limestones to normally 20 40 locally up to 80 in dolostones over any given 10 m 33 ft core interval some of the saddle dolomite is replacive some is cement and both varieties are associated with dissolution porosity and recrystallized matrix dolomite the major objective of this study is to identify the causes and timing of matrix and saddle dolomite formation specifically whether these dolomites are hydrothermal a comprehensive petrographic and geochemical examination indicates that pervasive matrix dolomitization was accomplished by long distance migration of halite saturated brines during the late devonian to mississippian fluid inclusion homogenization temperatures suggest about 150 uncorrected to 190c corrected at the time of matrix dolomitization these temperatures differ markedly from most published work on the dolomitized devonian reefs in the alberta basin south of the peace river arch where pervasive matrix dolomitization was accomplished by advection of slightly modified seawater at temperatures of about 60 80c and where no hydrothermal influence was ever present the saddle dolomites at clarke lake are not cogenetic with matrix dolomite and are not the product of hydrothermal dolomitization sensu stricto instead they formed through the hydrothermal alteration of matrix dolomite by way of invasion of a gypsum saturated brine during periods of extremely high heat flow and regional plate margin tectonics in the late devonian to mississippian fluid inclusion homogenization temperatures suggest that hydrothermal alteration occurred between 230 uncorrected and 267c corrected which is significantly higher than the maximum temperature of about 190c attained by the slave point formation during burial the sources of the halite and gypsum saturated brines are middle devonian evaporite depositional environments roughly 200 km 124 mi south and or east of clarke lake near the peace river arch

lead and zinc in formation waters alberta basin canada their relation to the pine point ore fluid abstract the source of the ore fluid for the pine point zn pb deposit has been controversial for decades both formation waters from deep in the basin and geothermal fluids from the precambrian basement have been considered as sources of the ore in this carbonate hosted deposit a database of 694 analyses of pb and zn in formation waters from the alberta basin bears on this controversy these waters have a mean content of 4 66 mg l 1 pb and 6 88 mg l 1 zn for each of these metals the maximum content is 360 mg l 1 and the median content is 0 9 mg l 1 in 71 of the samples pb zn with a mean ratio of 2 3 1 this is in contrast to the pb zn ratio of formation waters in other sedimentary basins and geothermal waters but is consistent with that in brines from the canadian shield geochemical modelling using solmineq 88 shows that pb and zn occur mainly as the mecl 4 2 complex it is not possible to produce a sulphide precipitate with zn pb such as the ore at pine point from a formation water with pb zn even when the formation water carries the metals in the absence of h2s and the metals are precipitated by h2s rich brines therefore the present formation waters are a poor candidate for the source of the metals at pine point it is more likely that geothermal fluids rising along the great slave lake shear zone were the source of the metals additional evidence for this alternate source includes 1 the very homogeneous non radiogenic character of the pb isotopes in galena 2 the absence of a thermal anomaly along the great slave lake shear zone 3 a famennian time of deposition based on rb sr dating of sphalerite when overburden was thin and reservoir temperature low and 4 the distribution of sphalerite and galena in the subsurface of the alberta basin in relation to major crustal discontinuities and normal faults cutting the crystalline basement exploration for other zn pb deposits should therefore focus on the location of suitable shear zones and faults up which geothermal fluids might have migrated rather than the flow and composition of formation waters

compression of oceanic lithosphere an analysis of intraplate deformation in the central indian basin intraplate compressional deformation in the central indian basin is expressed as linear e w trending topographic undulations and geoid anomlies with characteristic spacings of approximately 200 km to elucidate the nature of this deformation we develop models of an oceanic lithosphere in a state of horizontal compression the lithosphere is treated as a viscous or plastic layer of uniform strength which overlies a viscous half space in which strength decreases exponentially with depth we compare models in which deformation with a dominant wavelength develops in response to flexural buckling and the hydrodynamic growth of instabilities for the viscous flexural buckling model deformation is constrained to occur in the antisymmetric mode by flexural folding which is characterized by uniform bending of the layer in the hydrodynamic flow model a range of deformational styles are possible in a strong viscous lithosphere deformation of the layer occurs by flexural folding at a wavelength which agrees with that predicted from flexural buckling theory in a lithosphere of intermediate strength the layer deforms by folding characterized by thickening which localizes beneath topographic highs in a relatively weak lithosphere the layer incurs an even greater amount of localized thickening and deforms in the symmetric or pinch and swell mode by inverse boudinage if the layer has a plastic rheology deformation occurs by inverse boudinage independent of the yield stress results from models in which the layer folds either flexurally or with periodic thickening are consistent with the observed depth distribution of seismicity in the central indian basin and with experimental rock rheological data because of the trade off between buoyancy forces and layer strength in determining the dominant wavelength a lithosphere which was overlain by weak sediments when intraplate deformation initiated can be characterized by a compressive layer strength almost a factor of 3 less than a lithosphere which was initially sediment free for a range of plausible models which consider both a sediment covered and sediment free lithosphere the observed wavelength requires deviatoric stresses in the indian plate of several hundreds of mpa

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

seismic hazard assessment for mymensingh bangladesh mymensingh municipality lies in one of the most earthquake prone areas of bangladesh the town was completely destroyed during the great indian earthquake of 12 june 1897 for which the surface wave magnitude was 8 1 in this study the 1897 great indian earthquake was used as a scenario event for developing seismic microzonation maps for mymensingh for microzonation purposes spt data from 87 boreholes were collected from different relevant organizations to verify those data ten boreholes of depth up to 30 m were drilled intensity values obtained for different events were calibrated against attenuation laws to check applicability to the study area vibration characteristics at diverse points of the study area were estimated by employing the one dimensional wave propagation software shake shake discretizes the soil profile into several layers and uses an iterative technique to represent the non linear behavior of the soil by adjusting the material properties at each iteration step the required input information includes depth shear wave velocity damping factor and unit weight of each soil layer the liquefaction resistance factor and the resulting liquefaction potential were estimated to quantify the severity of liquefaction quantification of secondary site effects and the weighting scheme for combining the various seismic hazards were heuristic based on judgment and expert opinion

rare earth element geochemistry of dolomites in the middle devonian presqu ile barrier western canada sedimentary basin implications for fluid rock ratios during dolomitization rare earth elements ree were determined in fine medium and coarse crystalline replacement dolomites and for saddle dolomite cements from the middle devonian presqu ile barrier from pine point and the subsurface of the northwest territories and north eastern british columbia ree patterns of the fine crystalline dolomite are similar to those of middle devonian limestones from the presqu ile barrier fine crystalline dolomite occurs in the back barrier facies and may represent penecontemporaneous dolomitization at or just below the sea floor medium crystalline dolomite is widespread in the lower southern and lower central barrier medium crystalline dolomite is slightly depleted in heavy ree compared with devonian marine limestones and fine crystalline dolomite and has negative ce and eu anomalies medium crystalline dolomites replaced pre existing limestones or were recrystallized from earlier fine crystalline dolomites during these processes the ree patterns of their precursors were modified late stage coarse crystalline replacement dolomite and saddle dolomite cements occur together in the upper barrier and have similar geochemical signatures coarse crystalline dolomites have negative eu anomalies and those from the pine point area also have positive la anomalies saddle dolomites are enriched in light ree and have positive la anomalies the ree patterns of coarse crystalline dolomite and saddle dolomite differ from those of marine limestones and fine and medium crystalline dolomites suggesting that different diagenetic fluids were responsible for these later dolomites although massive dolomitization requires relatively large volumes of fluids in order to provide the necessary amounts of mg2 dolomitization and subsequent recrystallization may not necessarily modify the ree signatures of the precursor limestones because of the low concentrations of ree in most natural fluids thus relative fluid rock ratios during diagenesis may be estimated from ree patterns in the diagenetic and precursor minerals fine crystalline dolomites retain the ree patterns of their limestone precursors in the medium and coarse crystalline dolomites the precursor ree patterns were apparently altered by large volumes of fluids involved during dolomitization this study suggests that ree compositions of dolomites and their limestone precursors may provide important information about the relative amounts of fluids involved during diagenetic processes such as dolomitization

stromatoporoid growth forms and devonian reef fabrics in the upper devonian alexandra reef system canada insight on the challenges of applying devonian reef facies models

examples of structural control of hydrothermal mineralization fault zones in epicontinental sedimentary basins a review by compiling data available from progressive geoscientific research and by complementary studies it seems possible for an increasing number of mineral districts to find indications of the regional structural control of hydrothermal ore deposits the relationship between hydrothermal mineralization faulting or fault reactivation and related processes can of course best be examined at the less deformed sedimentary record of ancient epicontinental sedimentary basins there is increasing evidence that the sediment hosted submarine hydrothermal zn pb ba mineralizations such as meggen rammelsberg howards pass and mcarthur river are spatially and genetically related to deep synsedimentarily active fault systems of intracontinental basins or stretched passive continental margins for long periods of basin development the faults provided favorable conduits for episodically released basin dewatering brines which precipitated the leached metals into third order basins situated next to these faults there are many similarities to epigenetic mineralizations which formed either pre syn or postorogenetically from brines leaching the meta sediments and associated magmatites and migrating along fault zones to their near surface trap structures

the saqisan mine a paleokarst uranium deposit south china abstract the saqisan uranium deposit located in guangxi province south china is hosted mainly by a dark gray limestone solution breccia unit and paleocavern fill sedimentary rocks the deposit is the largest known breccia hosted uranium deposit in china and was initially described as of synsedimentary shallow marine origin however recent open pit operations at the saqisan mine have uncovered new exposures that necessitate a thorough change in the genetic interpretation of the deposit the new exposures suggest that the occurrence of saqisan ores in sediment filled solution breccia and paleokarst cavities of limestone is in part similar to that of solution collapse breccia pipe type uranium deposits in arizona united states the interconnected paleokarst passages and caverns were filled with consolidated mineralized clastic sedimentary rocks most of the orebodies were deposited in the interconnected paleokarst passages and caverns two stages of primary uranium mineralization are recognized the early stage i mineralization is the most important for uranium as it accounts for 60 of saqisan s total uranium tonnage stage i mineralization formed low grade ore the late stage ii mineralization which accounts for the remaining 40 of saqisan s total uranium tonnage is hosted by strongly silicified foliated and mylonitized host limestones the uranium in stage i ores predominantly occurs as micro sized pitchblende in the clay rich breccia matrix the uranium in stage ii ores mainly occurs as pitchblende veinlets 0 1 2 mm wide and as disseminated pitchblende grains ranging from less than 0 1 to 1 mm in size sulfur isotope data indicate that biogenic pyrite in the host carbonate may have been the major source of sulfur in the mineralizing fluids oxygen and carbon isotope data show that most of the participated co 2 and hco 3 during stage i mineralization was derived from bicarbonate dissolved out of the marine host carbonate oxygen and hydrogen isotope data combined with determinations of temperature and salinity for the inclusion fluids of stage ii veinlet quartz show that the ore bearing fluids of stage ii mineralization are apparently devoid of co 2 and ch 4 and were originally saline meteoric ground water these basinal brines which were from connate waters trapped in the paleozoic carbonates are believed to have flowed along aquifers of the basinal sequence and up preexisting subvertical faults to produce the observed style of mineralization by chemical interaction with host carbonates it is postulated that the high grade uranium ore of stage ii is the product of multiple superimposed reconcentration of uranium from the early synpaleokarstic ore stage i by low to middle temperature 110 251 c uranium enriched hydrothermal brines driven by a regional heating event such as the late yanshanian tectonism the heat source for the saqisan hydrothermal system could have been related to conversion of mechanical energy into heat during the late yanshanian regional tectonic deformation

geoelectric structure of the proterozoic wopmay orogen and adjacent terranes northwest territories canada magnetotelluric mt soundings were made along a transect in northern canada crossing the proterozoic wopmay orogen fort simpson basin and adjacent parts of the slave craton and the nahanni terrane the results are used to define the geoelectric structure and constrain the crustal and lithospheric structure and evolution across the wopmay orogen geoelectric strikes at crustal depths average n34 e and are interpreted to be related to transcurrent faulting that occurred during late distal collisions at the western margin of the orogen weak two dimensionality in the fort simpson basin is interpreted to be due to the sedimentary rocks in the basin at longer periods geoelectric strikes across the wopmay orogen rotate from n43 e at uppermost mantle penetration to n62 e at a depth of 100 km the uppermost mantle strikes are interpreted to be due to ductile shearing linked to the transcurrent faulting in the overlying crust the deeper strikes may be caused by shearing at the base of the present day lith

continental lithosphere folding in central asia part i constraints from geological observations abstract geological observations support the occurrence of long wavelength surface undulations in central asia which can be treated in terms of folding of the whole lithospheric plate the characteristic wavelength of the whole lithosphere folding is 360 km in the western part of the gobi sub plate superimposed on the long wavelength deformation two shorter wavelength scales of spatially periodical deformation are also observed an intermediate wavelength of 30 50 km of the intraplate deformation reflects the response of the mechanically strong upper crustal part of the central asian lithosphere small wavelength 4 9 km deformation corresponds to faulting in the uppermost crustal layer and folding and faulting in the sedimentary cover folding of the lithosphere controls the location and geometry of compressional basin formation in the western part of the gobi sub plate a number of folding and faulting characteristics of continental intraplate deformation in central asia presented in this study are strikingly similar to observed styles of intraplate deformation in oceanic lithosphere in the northeastern indian ocean

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

horizontal lithosphere compression and subduction constraints provided by physical modeling physical modeling of the subduction is performed with a two layered mantle model elastico plastic lithosphere and low viscosity asthenosphere and is governed by the criteria of similarity compression of the lithosphere in the area of a passive continental margin has been shown to produce a buckling instability in the oceanic plate with wavelengths of 200 km on the average later a localization of deformation occurs in sagging at some distance from the margin where a strongly dislocated linear ridge is formed due to the thrusting the plate then experiences a failure along the inclined zone and subduction starts the inner trench slope which forms therefore has a scraped structure and include a block of crushed and dislocated oceanic crust and sediments in the lower section if there is an old inclined fault striking across the compression of an oceanic lithosphere it is on that fault that a subduction zone is initiated the inner trench slope has then a different structure and forms due to normal faulting in the frontal part of the overriding plate the formation of a subduction zone requires a compression that is smaller than that in the preceding case by a factor of 2 or 3 the subducting plate experiences an elastico plastic bending and under specific conditions thrusting along the zone dipping from under the overriding plate oceanward and crossing the entire lithosphere the best agreement between generalized relief in subduction zone in the model and nature is achieved when a shear yield limit s 1 3 108 pa modulus of elasticity e about a few times 1011 pa and a thickness h 60 km are adopted for the real lithosphere

a basement interacted fluid in the n81 deposit pine point pb zn district canada sr isotopic analyses of single dolomite crystals the mississippi valley type pb zn deposits of the pine point district northwest territories canada are located close to the eastern edge of the present day western canadian sedimentary basin the deposits are thought to have formed as the result of basin wide fluid flow in the presqu ile barrier the host to the ore deposits a laser ablation multi collector inductively coupled plasma mass spectrometric study of 87sr 86sr ratios of ore related dolomites from the n81 deposit at pine point indicates that at least two sources of sr were present in the mineralizing system one fluid has a range in sr isotopic values from 0 07073 to 0 71200 and is interpreted to be derived from middle devonian seawater that interacted with clastic units in the basin the second fluid has higher sr isotopic values up to 0 71520 similar to those found in some canadian shield brines and is interpreted to represent an evaporated seawater derived brine which has interacted with crystalline basement rocks reactivation of old structures in the basement may have provided a pathway for cross formation fluid flow to the site of mineralization the data suggest that the stratigraphic location of the pine point district near the interface between the western canadian sedimentary basin and its basement may have exerted a fundamental control on the formation of these deposits

characterization and dispersal of indicator minerals associated with the pine point mississippi valley type mvt district northwest territories canada1 a glacial dispersal study was conducted around a subcropping pb zn deposit o28 in the pine point mississippi valley type mvt district northwest territories canada with the intent of characte

manetoe facies a gas bearing megacrystalline devonian dolomite yukon and northwest territories canada the manetoe facies is a broadly stratiform and regionally developed 38 000 km2 or 15 000 mi2 body of white sparry dolomite hosted in lower and middle devonian strata and is the northwestward continuation of the similar but better known presqu ile facies dolomite several large gas fields have been discovered within anomalously thick developments of the manetoe dolomite close to the northwest limit of the devonian elk point basin of alberta the external geometry of the manetoe facies indicates that it may have been a cavern or karst system excavated in the late middle devonian by a large vertically confined coastal aquifer the local regions of anomalously thick manetoe facies may have developed where the aquifer stoped upward into strata above the confining aquiclude of the headless formation shale dolomite cementation may have occurred during any of three possible episodes of large scale fluid movement fluid inclusion and strontium isotope data favor the hypothesis that manetoe dolomites precipitated from heated 150 210 c or 300 410 f hypersaline evaporitic brines that have interacted with the underlying precambrian crust probably in the late devonian lead isotope data support the general concept of pre mesozoic dolomite cementation and largely preclude a late early tertiary deep burial setting spectacular zones of detrital dolomite cement within the manetoe are most readily accommodated by a near surface very early middle devonian aquifer mixing model origin but the presence of these zones does not preclude the other possible origins carbon and xygen isotope data from the manetoe facies support the concept that the presqu ile and manetoe facies are physically continuous and had a common origin

pine point orebodies and their relationship to the stratigraphy structure dolomitization and karstification of the middle devonian barrier complex mississippi valley type ore field on the south side of great slave lake pine point has produced 58 2 million tons of 3 0 percent pb and 6 7 percent zn with present reserves of 25 7 million tons of 2 7 percent pb and 6 3 percent zn most pine point orebodies were deposited in interconnected paleokarst networks that developed at the lower limits of coarse dolomite alteration of upper barrier limestones karstic structures which exhibit the largest cavity development and consequently the greatest amounts of infilling internal sediments host the best grades of mineralization the following conclusions are suggested the barrier developed due to subtle epeirogenic crustal movements and or eustatic sea level changes affecting normal sedimentary processes deformation of the barrier is possibly due to differential sediment compaction or warping of underlying evaporites coarse dolomitization and paleokarstification metals introduced by chloride rich brines brines expelled by overburden pressures migrated eastward along the barrier and precipitated metals in paleokarst structures upon encountering reduced sulfur species modified journal abstract

geophysical evidence for thick skinned crustal deformation in central australia until now there has been no clear evidence from deep seismic reflection profiles of crustal faults that displace the moho new data from central australia show such a structure in a region characterized by large thrust structures large gravity anomalies and abrupt changes in teleseismic travel times here the principal thrust the redbank deformed zone cuts through the crust and the moho is significantly displaced across it the geological and geophysical evidence leads to a model of thick skinned crustal deformation which occurred in an intra cratonic environment in late devonian time

strontium isotopic composition of devonian dolomites western canada sedimentary basin significance of sources of dolomitizing fluids abstract dolomites from the middle and upper devonian of five regions in the western canada sedimentary basin wwere studied middle devonian winnipegosis formation outcrop keg river formation reefs in the rainbow field and presqu ile barrier and the upper devonian miette buildup and the wabamun group of northern alberta data from the upper middle devonian swan hills formation in the rosevear field and nisku formation reefs were also included in these areas of western canada there are at least three dolomitizing events 1 early dolomites in winnipegosis reefs and the subsurface part of the presqu ile barrier have 87sr 86sr values near 0 7080 wabamun sabkha dolomites have 87sr 86sr values near 0 7083 and all fall on their respective parts of the seawater curve thus the sources of dolomitizing fluids were devonian seawaters 2 secondary matrix dolomites from the presqu ile barrier rainbow rosevear miette nisku and wabamun all have slightly higher 87sr 86sr values 0 7081 0 7094 than the correspnding devonian seawater dolomitizing fluids were probably modified from devonian seawater with small amounts of radiogenic 87sr being added during early compaction from adjacent or underlying clastics or older carbonates 3 late stage saddle dolomites from presqu ile rainbow rosevear miette nisku and wabamum are all highly radiogenic 0 7100 up to 0 7151 except for most pine point saddle dolomites indicating significant input of radiogenic 87sr with likely sources from the underlying cambrian and precambrian clastics and or the precambrian basement at pine point some presqu ile saddle dolomites have sr isotopic values similar to matrix dolomites suggesting a different fluid source possibly from subsurface brines that may have evolved from pressure solution of devonian strata alternatively formation waters derived from the deeper part of the basin may have been progressively diluted with low 87sr 86sr shallow formation waters as they moved updip along the presu ile barrier the 87sr 86sr values support and refine earlier conclusions based on textual evidence c and o isotopes geochemistry and fluid inclusions they considerably limit the sources of the dolomitizing fluids in open diagenetic systems however the timing of the widespread secondary matrix dolomites can only be broadly constrained to sometime during the late paleozoic the similarity of the o and sr isotopes in the replacement dolomites from widely separated locations geographically and stratigraphically tentatively suggests that these dolomites may have precipitated from similar formation waters on a basin wide scale the late stage saddle dolomites and probably the coarsely crystalline dolomites could only have formed near maximum burial conditions in the late cretaceous to early tertiary from warm hydrothermal brines that moved updip from more deeply buried portions of the basin later coarse crystalline calcites precipitated from highly saline brines and are generally more radiogenic than saddle dolomites they apparently formed from more radiogenic formation waters than have curretly been reported from the basin

effects of glaciations and permafrost upon the development of karst in canada canadian examples suggest that karst landforms may be divided into eight types in terms of their temporal relationships to the record of repeated quaternary glaciations two types are postglacial two are subglacial one type occurs where glacial features are adapted to karstic drainage and three types display sequences of karstic and glacial action glacier effects upon karst landforms and their underlying aquifers display the gamut of possibilities they may destroy inhibit preserve or stimulate karst development where continuous permafrost is maintained when covered by glacier ice postglacial karst is limited to the active layer epikarst where permafrost is thawed beneath ice or during deglaciation there are a variety of postglacial karst developments depending in part upon climate and in part upon local lithologic and relief conditions

formation of coarsely crystalline hydrothermal dolomite reservoirs in the presqu ile barrier western canada sedimentary basin late stage coarsely crystalline replacement dolomite and associated saddle dolomite cement form a widespread diagenetic facies in the middle devonian presqu ile barrier that extends southwestward from pine point to the subsurface of the foothills in northeastern british columbia these dolomites create hydrocarbon reservoirs in otherwise tight limestones in the subsurface of the northwest territories and northeastern british columbia and host mississippi valley type deposits at pine point the coarsely crystalline replacement dolomite and saddle dolomite cement are interpreted to have formed during burial because they replace blocky sparry calcite cements occur continuously across the sub watt mountain unconformity postdate stylolites and earlier replacement dolomites and overlap sulfide mineralization the dgr18o values of both replacement and saddle dolomites increase eastward updip along the presqu ile barrier from 16 pmil pdb in the deeper subsurface of northeastern british columbia to 7 pmil pdb at pine point whereas the corresponding homogenization temperatures of saddle dolomite fluid inclusions decrease from 178 to 92 c the 87sr 86sr ratios of coarsely crystalline and saddle dolomites decrease eastward along the pres u ile barrier from about 0 7106 in the subsurface of northeastern british columbia to 0 7081 at pine point these geochemical trends suggest a possible basin scale migration of hot radiogenic dolomitizing fluids updip eastward along the presqu ile barrier such large scale fluid movements probably were related to western canada sedimentary basin tectonic compression and sedimentary loading which occurred at least twice during early burial between the late devonian and early carboniferous and during deep burial between the late jurassic and early tertiary

shortening of analogue models of the continental lithosphere new hypothesis for the formation of the tibetan plateau initial stages of compression produce periodic buckling of models analogous to a four layer continental lithosphere with further shortening amplification of the buckles occurs by thrust faulting at inflection points in both brittle layers of the upper crust and upper mantle the rescaled results suggest that a continental lithosphere under compression will buckle with a first order wavelength of about 200 km and a second order wavelength of 20 30 km continued shortening results in the amplification of undulations troughs sink and become compressional basins while deformation keeps going on major thrusts within the upper mantle thus giving rise to an irregular topography of the moho fifty percent shortening results in a 60 km thick continental crust we argue that this model history may explain the elevation and deep crustal structure of the tibetan plateau

fluid inclusion chemistry in the exploration for mississippi valley type deposits an example from east tennessee u s a scanning electron microscopy and energy dispersive analysis of fluid inclusion decrepitates in sparry dolomite cements associated with sphalerite mineralization in the mascot jefferson city missis sippi valley type district of east tennessee show a markedly lower najca ratio than those in dolomites unassociated with ore the exploration potential of this variation in fluid inclusion chemistry has been evaluated by analyzing inclusion decrepitates from white sparry dolomite along a 150 m traverse in the new market west mine area the traverse extends from the central portion of a large domal collapse breccia orebody with greater than 3 zn into the dolomite veined but unmineralized knox group limestones ratios of na ca as low as 0 8 1 2 were common in dolomite hosted decrepitates from the high grade collapse ores this anomalous decrepitate chemistry was not observed in sparry dolomites less than 12 m from the margins of the breccia bodies where na ca ratios ranged from 1 8 to 3 6 dolomite cements in idly grade 1 0 zn parts of the collapse bodies showed the greatest variation in na ca ratio with values ranging from 0 9 to 3 5 no systematic trends were observed in k na and s c1 ratios from the same samples

thermal comparison of mississippi valley type lead zinc deposits and their host rocks using fluid inclusion and conodont color alteration index data fifteen north american mississippi valley type districts distributed from the arctic archipelago to arkansas and in host rocks ranging in age from late cambrian to early carboniferous were selected for abroad test survey of mississippi valley type district thermal histories for each district in which data were collected histograms of homogenization temperatures for the ore minerals were compared with the temperature range of the corresponding host rocks as indicated by color alteration index cai determinations on conodonts in the host rock carbonates although a special effort was made to collect conodonts from the upper cambrian bonneterre formation host rock to the southeast missouri district all samples were devoid of conodonts thus only 14 districts were used in the final analysis comparison of fluid inclusion homogenization temperatures in main stage ore minerals with color alteration index determined host rock temperatures reveals that a majority of mississippi valley type districts pine point newfoundland zinc mascot jefferson city copper ridge sweetwater central missouri northern arkansas and tri state are representative of group 1 i e they are in thermal equilibrium with their host rocks insofar as could be determined by the color alteration index method ore minerals in group 2 districts upper mississippi valley polaris and central tennessee are significantly hotter than surrounding host rocks and as such define a positive thermal anomaly host rocks to the austinville ivanhoe northern newfoundland and robb lake deposits group 3 revealed the highest color alteration index values of north american mississippi valley type districts with host rock temperatures greatly exceeding ore mineral fluid inclusion temperatures negative thermal anomaly with respect to major tectonic elements of north america group 3 deposits cool ore in hot rocks are positioned within orogenic belts but on the continental side some group 1 deposits ore temperature host rock temperature are well within the continental interior but others are adjacent to orogenic belts on the continental side group 2 deposits hot ore in cool rocks are all within the continental interior current hypotheses regarding the formation of mississippi valley type deposits and simultaneous heating of their host rocks invoke the migration of hot brines set into motion craton ward by the hydraulic gradient produced by orogenic uplift at the craton edge once the ore bearing fluids entered the foreland carbonate platforms they traveled through sedimentary aquifers of the continental interior raising the temperature of the thinly covered carbonate rocks the fluids left as evidence of their passage elevated color alteration index values and group 1 mississippi valley type deposits distributed with decreasing homogenization temperatures away from the orogenic front the correspondence between host rock and ore temperatures suggests that group 1 deposits were deposited essentially within their own aquifers group 2 deposits were formed when the same or genetically similar fluids rose from the regional aquifer s into structurally controlled conduits in the continental interior possibly developed as a result of synorogenic doming and arching this upward channeling of the fluids resulted in rapid and localized fluid flow which precluded or at least inhibited wide spread heating of the host rocks by ore fluids consequently color alteration index values in group 2 districts record only maximum burial depths of the host rocks and bear little relation to temperatures of the ore fluids although the cause of the unusually high color alteration index values 4 5 of group 3 districts is not fully understood it is noted that these districts occur near the extreme outward edge of foreland platforms near or within the leading margins of orogenic belts whether these group 3 host rocks were heated by simple tectonic burial or by passage of heated fluids under shallower conditions is not known

the relief canyon gold deposit nevada a mineralized solution breccia the relief canyon gold deposit in the humboldt range of western nevada is a low grade high tonnage orebody of tertiary or younger age the host rocks include limestones of the triassic cane spring formation which are overlain by shales of the triassic grass valley formation the rocks were folded and metamorphosed to greenschist grade during jurassic and cretaceous regional tectonic activity mesozoic thrusting may have occurred along the shale limestone contact but evidence has been obscured by later hydrothermal activity the sedimentary rocks were nominally offset along several late tertiary normal faults related to uplift of the range the upper part of the cane spring formation is composed of a poorly sorted breccia composed of limestone clasts with a clay matrix irregular pockets within this zone are filled with clay to pebble sized fragments derived from the grass valley shale the enclosing limestone beds were tilted moderately to the southwest during mesozoic deformation whereas bedding within these pockets is generally horizontal indicating post tilting deposition of the sediments the sediments show graded bedding and other sedimentary features that indicate deposition from flowing water thermally mature carbon derived from the limestone is also concentrated in small pockets in the matrix the breccia unit is likely the product of low temperature solution brecciation ground water dissolved much of the limestone directly beneath the shales progressively creating irregular cavities and the breccia sediments derived from the overlying grass valley shale were fiuvially deposited as a matrix to the developing solution breccia episodic pulses of hydrothermal fluids were introduced along faults and possibly mixed with the ground water in the breccia zone initially jasperoids formed along the faults but later hydrothermal pulses introduced gold silica and fluorine into both the early jasperoids and the unconsolidated cave fill sediments to form the orebody continued solution related brecciation chaotically disrupted the gold deposit gold fluorite pyrite silver calcite and fine grained silica are the principal hydrothermal minerals in the deposit gold was deposited as micron sized flakes of native gold and rarely as electrum during a relatively late stage of silicification of the jasperoids the carbon rich zones and the clay rich matrix of the breccia fluorite was deposited with and later than the gold in the jasperoids and it in part replaced the clay rich breccia matrix antimony arsenic mercury and thallium are directly associated with gold in the orebody the deposit formed at a relatively shallow depth on the basis of fluid inclusion data late stage hydrothermal fluids related to gold and fluorite deposition were extremely dilute and had temperatures near 200 degrees c the fluid inclusions in fluorite show no evidence for boiling but porous crackle breccias in the jasperoids suggest that hydrobrecciation took place

geochemical constraints on the origin of the kicking horse and monarch mississippi valley type lead zinc ore deposits southeast british columbia canada two mississippi valley type mvt ore deposits kicking horse and monarch have been studied with the aim of comparing the ores at the two localities and to characterize the origin of the mineralizing fluids and the ore formation process es both deposits are hosted by the middle cambrian cathedral formation carbonate host rocks kicking horse on the north and monarch on the south flank of the kicking horse valley near field se british columbia the ore bodies are situated at the transition of western basinal to eastern shallow water strata of the paleo pacific passive margin succession in the cordilleran foreland province of the western canada sedimentary basin both deposits are related spatially to normal faults in both localities the ore minerals are dominated by pyrite sphalerite and galena dolomite minor quartz and calcite are also present in close association with the ores the salinity 21 30 wt nacl eq and homogenization temperatures 63 182 c measured in fluid inclusions in carbonate quartz and sphalerite lie within the typical range of mvt fluid conditions the good stoichiometry 50 53 mol caco3 low 18o values 21 to 14 vienna peedee belemnite and relatively high homogenization temperatures 95 c of the dolomite suggest the dolomites were formed under burial diagenesis the ore forming fluids probably interacted with siliciclastic units based on elevated li contents and 87sr 86sr ratios which are highest in the dolomite type after the main ore stage we propose that the ores formed from the mixing of a downward infiltrating sulfur bearing halite dissolution fluid with an upward migrating metal rich evaporated seawater fluid which had already undergone minor mixing with a dilute fluid

rheological modelling and deformation instability of lithosphere under extension summary continental break up which precedes oceanic accretion probably results from an unstable extension of the lithosphere analogous to necking of metals when they are submitted to tension by reason of complexity of the rheology no conclusion about lithospheric extension stability may be reached by an a priori analysis we thus examine directly the evolution when the lithosphere is stretched of lateral inhomogeneities represented in our example by small scale variations of thickness the rheological model is derived from the hypotheses of brace kohlstedt 1980 and is consistent with the results of rock mechanics the lithosphere consists of three or four layers of varying thicknesses and mechanical properties the brittle upper crust and eventually the brittle part of the mantle are assimilated to perfectly plastic media and are described in a state of uniform extension by a constant viscosity in the lower crust and ductile mantle lithosphere the effective viscosity is supposed to be exponential the mechanical model relies on a perturbation method developed by fletcher hallet 1983 among others contrary to previous published results no unstable behaviour of the lithosphere is observed unless the latter is more dense than the asthenosphere in which case a gravitational instability may develop this discrepancy can be explained by differences in assumptions concerning the variation of strength in the lithosphere as yet poorly constrained by the data we observe a great sensitivity of the results to the strength stratification and to the artificial discontinuities of density or viscosity implied by the models

structure of the crust and upper mantle of the great slave lake shear zone northwestern canada from teleseismic analysis and gravity modelling the great slave lake shear zone gslsz exposes lower crustal rocks analogous to deep seated segments of modern strike slip fault zones such as the san andreas fault extending for 1300 km beneath the western canada sedimentary basin to the southern margin of the slave province the gslsz produces one of the most prominent linear magnetic anomalies in canada from may to october 1999 13 three component portable broadband seismograph stations were deployed in a 150 km profile across a buried segment of the shear zone to investigate its lithospheric structure splitting analysis of core refracted teleseismic shear waves reveals an average fast polarization direction n49 e 19 that is approximately parallel to the shear zone individual stations near the axis of the shear zone show more northerly splitting directions which we attribute to interference between regional anisotropy in the upper mantle fast axis n60 e and crustal anisotropy within the shear zone fast axis n30 e at the location of o

fault reactivation in the central indian ocean and the rheology of oceanic lithosphere the intraplate deformation in the central indian ocean basin is a well known example of a deviation from an axiom of plate tectonics that of rigid plates with deformation concentrated at plate boundaries here we present multichannel seismic reflection profiles which show that high angle reverse faults in the sediments of the central indian ocean extend through the crust and possibly into the uppermost mantle the dip of these faults which we believe result from the reactivation of pre existing faults formed at the spreading centre is 40 in the basement which is consistent with the distribution and focal mechanisms of earthquakes on faults now forming at spreading centres this style of deformation coupled with the observation of large earthquakes in the mantle lithosphere indicates that brittle failure of the oceanic lithosphere may nucleate in the vicinity of the brittle ductile transition and propagate through the crust

fluid inclusion and isotopic evidence on dolomitization devonian of western canada the presqu ile and manetoe facies are diagenetic features developed in lower and middle devonian formations of the elk point basin presqu ile and the mackenzie shelf manetoe both facies contain coarsely crystalline dolomite and white sparry dolomite cement less extensive diagenetic phases in order of paragenesis include fluorite anhydrite barite calcite quartz sphalerite and galena conditions of dolomitization are outlined from core and outcrop examination thin section and cathodoluminescent petrography fluid inclusion analyses and c and o isotopic data fluid inclusion and stable isotope analyses from dolomite are combined to determine the isotopic composition of the dolomitizing fluids chemical analyses of fluid inclusion waters are compared with formation water analyses to derive a proposed origin for the diagenetic fluids dolomite formed from hot high salinity fluids early in the diagenetic history of the basin limestone was dolomitized as a result of the same process that created white sparry dolomite cement in the manetoe facies remnants of the dolomitizing fluids are present as formation waters in some devonian formations in alberta subsequent invasion of meteoric waters produced more dilute diagenetic fluids which resulted in the precipitation of calcite and quartz cement in the manetoe facies these fluids are present in fluid inclusionsmore and are responsible for the low sup 18 o content of the calcite cement the temperatures of calcite and quartz formation differ as a function of burial depth within the manetoe facies during the mesozoic and cenozoic while the temperature of formation for dolomite does not less

karst controlled reservoir heterogeneity in ellenburger group carbonates of west texas petroleum production from restricted shelf carbonates of the lower ordovician ellenburger group is commonly considered to have been a result of a pervasive relatively homogeneous tectonic fracture system within the reservoir rock however regional facies and diagenetic paleokarst studies of ellenburger strata based on cores and wireline logs have demonstrated that significant reservoir compartmentalization was caused by karst modification in the upper part of the unit ellenburger group carbonates which attain a thickness of over 1 700 ft 520 m record sedimentation on a shallow water restricted shelf occupying most of west texas logging of over 10 000 ft 3 050 m of core from 63 wells has allowed recognition of six facies assemblages 1 lithic arenite 2 mixed siliciclastic carbonate packstone grainstone 3 ooid peloid grainstone 4 mottled mudstone 5 laminated mudstone and 6 gastropod intraclast packstone grainstone these facies assemblages record initial transgression and subsequent progradation and aggradation paleoslope was generally south and east from the texas arch toward the ouachita and marathon orogenic belts all facies assemblages with the local exception of the ooid peloid grainstone assemblage are characterized y very low intergranular and intercrystalline porosity porosity development in ellenburger group carbonates is directly related to a prolonged period of subaerial exposure that coincided with a middle ordovician eustatic lowstand prior to transgression of simpson group siliciclastics during this episode a widespread system of caves sinkholes joint controlled solution features and collapse breccias developed of particular importance to reservoir development was the formation of a regionally extensive cave system between 100 and 300 ft 30 and 90 m beneath the exposed ellenburger surface infill of this cave system by simpson group sand and clay segmented the upper ellenburger into three karst facies which are in descending order 1 cave roof dolomites fracture and mosaic breccias 2 laterally persistent cave fill facies siliciclastic matrix supported and carbonate matrix supported breccias and 3 lower collapse facies chaotic clast supported breccias of the cave floor pronounced vertical segregation of permeable zones defined by the three karst facies is evident in the emma andector martin block 13 and several other major ellenburger reservoirs lateral reservoir heterogeneities formed by localized laterally extensive collapse structures such as in the shafter lake reservoir also contribute to compartmentalization of producing zones within the upper ellenburger group secondary and tertiary recovery programs in these ellenburger reservoirs can be optimized by integrating concepts of lateral and vertical heterogeneity predicted by the karst model

magnetotelluric response and geoelectric structure of the great slave lake shear zone the great slave lake shear zone gslsz is a northeast trending 25 km wide dextral continental transform fault from the foothills of the rocky mountains in northeast british columbia to the southeast side of great slave lake based on its magnetic expression the gslsz can be correlated for at least 1300 km mostly in the subsurface magnetotelluric mt soundings were made at 60 sites in the southwest part of the northwest territories canada along the lithoprobe slave northern cordillera lithospheric evolution snorcle transect corridors 1 and 1a in the summer and autumn of 1996 of these 15 sites were along corridor 1a which crossed the gslsz the great bear magmatic arc and hay river terrane to the northwest of the shear zone and the buffalo head terrane to the southeast the primary objective of the corridor 1a deployments was to image the structure of the gslsz analysis of mt data indicates that along the corridor 1a the resistivity structure is approximately 1d at shallow depth 6 1 km corresponding to phanerozoic sedimentary rocks 2d in the upper to mid crust with a strike vn30 e and approximately 2d in the lower crust to lithospheric mantle with a strike of vn60 e the direction in the upper crust is interpreted to represent the local scale 6 50 km horizontal strike of the gslsz whereas the direction in the mantle is parallel to the larger scale strike of the gslsz 2d inversions of the mt data reveal that the gslsz forms a crustal scale resistive zone s 5000 6m that is spatially correlated with a magnetic low the gslsz comprises greenschist to granulite facies mylonites its high resistivity is interpreted to be due to the resistive nature of the granitic protolith of the mylonites and that mylonites are dominated by rocks deformed in the ductile regime to the northwest of gslsz the mt profile reveals crustal conductors beneath the great bear magmatic arc and hay river terrane the enhanced conductivity occurring beneath the great bear magmatic arc is interpreted to be caused by electronic conduction within deformed and metamorphosed rocks of the hottah terrane or the coronation supergroup the mt results also reveal a mantle conductor beneath the margin of the hottah terrane and great bear magmatic arc that is interpreted to be associated with the subduction of oceanic lithosphere a second mantle conductor to the southeast is truncated at the gslsz suggesting an older source for the enhanced conductivity and that the gslsz includes significant strike slip motion of sub crustal lithosphere fl 2002 elsevier science b v all rights reserved

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

buckling of the oceanic lithosphere from geophysical data and experiments two major hypotheses have been advanced for the formation of the long wavelength 100 300 km undulations of oceanic basement and overlying sediments developed in the central indian ocean basin whole layer folding buckling and local thickening inverse boudinage using appropriately scaled two layer analogue models for the oceanic lithosphere comprising a brittle layer above a ductile layer we show that buckling of the entire brittle layer is likely to be the mode of deformation however the lithosphere asthenosphere boundary remains undisturbed we find a relationship between the thickness of the brittle layer and the wavelength of folding such that the wavelength is 7 times the brittle layer thickness

dolomite fronts and associated zinc lead mineralization usa this paper provides previously unpublished drill core and mapping evidence of the spatial relationship between regional dolomitization and mississippi valley type mvt mineralization in the midcontinent of the united states dolomitization is discussed for several key carbonate units and their contained mvt mineralization this more complete picture of the relationship between regional dolomitization and mineralization provides constraints on models for mvt mineralization and serves as an exploration guide for new deposits

optical compositional character of six bitumen species from middle devonian rocks of the pine point pbzn property northwest territories canada abstract pine point lead zinc property northwest territories canada is unique in that it contains within a limited area a number of different types of naturally occuring bitumens normally much more widely separated in occurrence in nature the most abundant forms of bitumen are asphaltic varieties with more mature bitumen species present on a more limited scale pine point bitumens were examined using reflected white and fluorescence light microscopy for determination of optical properties optical dispersion based on reflectance was determined and results were compared with those for coal macerals and graptolites pine point bitumen species include gilsonite glance pitch grahamite wurtzilite albertite and epi impsonite optical dispersion of these bitumens falls from short blue toward longer red wavelengths indicating that these bitumens are immature to mature comparison of the atomic h c ratios with atomic h c ratios of liptinite rich coals and normal coals indicates that the bitumens follow a maturation trend close to that of immature to mature liptinite rich coals bituminous shales from pine point the source rocks for the bitumens have a similar liptinite composition to other bituminous shales found in the middle devonian of the northwest territories including the normal wells area

periodic instabilities during compression of the lithosphere 2 analogue experiments we have modeled the behavior of the continental and oceanic lithospheres under compression using materials with analogous properties in laboratory experiments to study the development of lithospheric buckling periodic instabilities which are a major deformation process during the compression of the lithosphere have already been described by several authors using an analytical perturbation method at small strains analogue experiments corroborate most of the results obtained by the perturbation method 1 the deformation modes geometrical relationships of interfaces and related wavelengths are mainly dependent on the spatial distribution of the brittle layer s and 2 the amplitude of buckling is an exponential function of the horizontal strain some departure from the perturbation method occurs when there are two instabilities growing concurrently the breakdown of the exponential growth occurs for strains of about 5 and is concomitant with the appearance of thrust faults in experiments including one brittle layer which model the compression of the oceanic lithosphere faults are regularly located at the inflection points of the folds in experiments including two brittle layers which model continental lithosphere faults form more complicated patterns with an asymmetrical deep thrust overlain by a fan shaped symmetrical thrust system in the upper brittle layer such fault geometries give some new highlights on typical compressive geological structures such as those encountered in central asia

zebra and boxwork fabrics in hydrothermal dolomites of northern canada indicators for dilational fracturing dissolution or in situ replacement zebra and boxwork fabrics in manetoe and presqu ile hydrothermal dolomites provide critical data for discrimination between hypotheses for their origin in a unique occurrence sets of weakly imbricated decimetre sized curvilinear lenticles of white dolospar are developed within sub metre sized tongues of greyish white dolomitized crinoidal packstone and grainstone this nascent zebra fabric has developed along wavy to nodular intra bed sedimentary partings primary bedding can be traced through dolomitized masses containing these fabrics into the surrounding undolomitized limestone all zebra and boxwork fabrics are confined within single beds consistent with an early burial time of origin no change in bed thickness occurs across zebra or boxwork fabrics within beds this indicates a dissolutional rather than a dilational origin for the creation of pore space partly cemented with white dolospar the dolomitized groundmass displays an abruptly gradational or sharp transition to centripetal saddle dolomite cement which partially to nearly completely occludes vugs circulation of geothermally heated hypersaline devonian elk point basinal sea water brines led to dissolution and replacive dolomitization of limestone adjacent to vugs and near contemporaneous precipitation of white dolospar within dissolutional vugs consistent with geochemical simulations the presence of downward extending galleries of white dolospar cemented solution collapse breccia provides further support for an interpretation of regional thermally driven convection of hydrothermal evaporative sea water brines across a broad area of northern canada the absence of gases under pressure in vacuoles within fluid inclusions from manetoe and presqu ile dolospars is also more consistent with a dissolutional and contemporaneous dolomitization origin for these fabrics rather than an origin involving dilational fracturing for space creation and dolospar precipitation the ubiquitous presence of zebra and boxwork fabrics in hydrothermal dolomite reservoirs indicates that they are not confined fault zones and instead occur wherever precursor limestones had relatively greater porosity and permeability prior to dolomitization

the role of an intracrustal asthenosphere on the behavior of major strike slip faults measurements of strain accumulation adjacent to the san andreas fault indicate that the zone of strain accumulation extends only a few tens of kilometers away from the fault such a narrow zone of cyclic strain accumulation and release is consistent with the measured coseismic strain and inferred stress drop during the 1906 earthquake the restricted zone of cyclic accumulation and release of elastic energy adjacent to major strike slip faults has been attributed to the damping effect of a viscoelastic asthenosphere however to explain the narrowness of the zone on the san andreas fault it is necessary to conclude that the thickness of the lithosphere is 10 20 km this does not appear to be consistent with the relatively low surface heat flow measurements in this paper an alternative four layer model is proposed to explain the behavior of the san andreas fault an upper elastic plate extends to a depth of about 15 km the depth of the deepest seismicity on and adjacent to the fault beneath this upper elastic plate is a soft intracrustal asthenosphere that exhibits a viscoelastic behavior the viscous behavior of these crustal rocks at relatively low temperatures is attributed to either the presence of quartz which is known to have a very soft rheology or the presence of water that can lead to pressure solution creep or to both effects beneath this soft layer is a second elastic layer made up of the tough lower crustal and upper mantle rocks and beneath this second elastic layer is the asthenosphere there is extensive geological and geophysical evidence for the existence of an intracrustal asthenosphere both in california and elsewhere we show that the damping due to the intracrustal asthenosphere can explain the observed narrow zone of cyclic strain accumulation and release on the san andreas fault

stretching instabilities and lithospheric boudinage a competent layer with a nonlinear rheology can under extension exhibit pinch and swell instabilities such instabilities can explain small scale regular deformations of rock recently they have also been invoked in relation to the distribution of basins and ranges fletcher and hallet 1983 and the undulation of the bouguer map froidevaux 1986 in the western part of north america for the case of a simple stratified structure different authors have expressed mathematical solutions describing these instabilities in this paper we elucidate the general physical meaning of these nonhomogeneous deformations in the simplest case where the competent layer is fully embedded in a softer material a fundamental mode develops with a preferred wavelength equal to 4 times the thickness of a competent layer the novelty is the occurrence of overtones with alternate symmetrical and antisymmetrical deflections of the interfaces between layers these modes have a large amplitude when the rheology tends to perfect plasticity the presence of a free surface like the earth s surface for the upper crust is shown to double the preferred wavelength of the fundamental mode and to forbid one overtone out of two this new effect is caused by gravity which inhibits the growth of surface topography another shift is of opposite sign to that caused by a free surface numerical solutions for multilayer structures can elucidate the nature of couplings between various layers the case of a three layer lithosphere having a soft lower crust and overlying a mantle asthenosphere has been analyzed in some detail it shows that in the range of wavelengths larger than 30 km up to five preferred modes may be superimposed this should encourage further analysis of the western u s topography and gravity pattern which is known to contain at least two wavelengths about 40 km for the individual basins and ranges and about 200 km for the bouguer troughs in nevada and their associated broad topographies

some examples and mechanical aspects of continental lithospheric folding abstract recent theoretical and observational advances in understanding the dynamics of lithosphere processes have yielded strong evidence in favour of the existence of large scale lithosphere folds intraplate compressional stresses generated by plate tectonic forces can reach magnitudes that approach the plastic buckling strength of mechanical models of lithosphere with brittle ductile rheological stratification the models predict lower plastic buckling stresses for continental lithosphere than for oceanic lithosphere intraplate folding of relatively strong oceanic lithosphere documented extensively in the northeastern indian ocean occurs where stresses are concentrated by restricted geometric and dynamic conditions resulting in unusually high stress levels several hundreds mpa on continents where geophysical data suggest that lithosphere folding may have occurred during the development of sedimentary basins in northern canada and central australia buckling stresses can have magnitudes that are of a similar order to those thought typically to occur in the lithosphere several tens mpa folding of continental lithosphere although more difficult to document is likely to be an important mechanism of large scale continental deformation in particular thinned continental lithosphere with a history of superposition of thick sedimentary successions might be the preferential locus of such folding lithosphere folding could also be a controlling factor in the near surface deformation of rifted basins as reflected by tectonic basin inversion

extension of continental lithosphere a model for two scales of basin and range deformation we develop a model for deformation in an extending continental lithosphere that is stratified in density and strength assuming a rheology consistent with seismic focal depths and experimental flow laws the model demonstrates that necking instabilities at two wavelengths will arise due to the presence of a strong upper crust and upper mantle separated by a weak lower crust the magnitudes of the instabilities are directly related to strength contrasts within the lithosphere while the dominant wavelengths of necking are controlled mainly by the thicknesses of the strong layers the results are applied to the basin and range province of the western united states where two scales of deformation can be recognized one corresponding to the spacing of ranges and the other to the width of tilt domains a bouguer gravity anomaly and associated regional topography with a wavelength comparable to the width of tilt domains has also been recognized for plausible density and strength stratifications our results show that the horizontal scale of short wavelength necking is consistent with the spacing of individual basins and ranges while that of the longer wavelength necking is consistent with the width of tilt domains we thus suggest that basin and range deformation may be controlled by two scales of extensional instability extension in the weak lower crust in this model is laterally displaced from regions of upper crustal extension the resultant horizontal shearing in the lower crust may be a mechanism for the initiation of low angle extensional detachments

petrography and geochemistry of early stage fine and medium crystalline dolomites in the middle devonian presqu ile barrier at pine point canada the petrography and geochemistry of fine and medium crystalline dolomites of the middle devonian presqu ile barrier at pine point western canada sedimentary basin are different from those of previously published coarse crystalline and saddle dolomites that are associated with late stage hydrothermal fluids fine crystalline dolomite consists of subhedral to euhedral crystals ranging from 5 to 25 m mean 8 m the dolomite interbedded with evaporitic anhydrites that occur in the back barrier facies in the elk point basin fine crystalline dolomite has 18 values between 1 6 to 3 8 pdb and 87sr 86sr ratios from 0 7079 0 7081 consistent with derivation from middle devonian seawater its sr concentrations 55 225 p p m mean 105 p p m follow a similar trend to modern little bahama seawater dolomites its rare earth element ree patterns are similar to those of the limestone precursors these data suggest that this fine crystalline dolomite formed from middle devonian seawater at or just below the sea floor medium crystalline dolomite in the presqu ile barrier is composed of anhedral to subhedral crystals 150 250 m mean 200 m some of which have clear rims toward the pore centres this dolomite occurs mostly in the southern lower part of the barrier medium crystalline dolomite has 18o values between 3 7 to 9 4 pdb mean 5 9 pdb and 87sr 86sr ratios from 0 7081 0 7087 mean 0 7084 sr concentrations from 30 to 79 p p m mean 50 p p m and mn content from 50 to 253 p p m mean 161 p p m and negative ce anomalies compared with those of marine limestones the medium crystalline dolomite may have formed either 1 during shallow burial at slightly elevated temperatures 35 40 c from fluids derived from burial compaction or more likely 2 soon after deposition of the precursor sediments by middle devonian seawater derived from the elk point basin these results indicate that dolomitization in the middle devonian presqu ile barrier occurred in at least two stages during evolution of the western canada sedimentary basin the geochemistry of earlier formed dolomites may have been modified if the earlier formed dolomites were porous and permeable and water rock ratios were large during neomorphism