geochemical identification of episodes of gold mineralisation in the barberton greenstone belt south africa abstract the morphology and mineral chemistry of gold and associated sulphides at sheba fairview and new consort gold mines in the barberton greenstone belt bgb identify two main types of mineralization the first type occurs associated with sulphides mainly pyrite either as inclusions 10 30 m or as sub microscopic gold the second gold type consists of large gold grains 100 m within the silicates mostly quartz la icp ms studies reveal that some gold and associated sulphide grains contain high values of cl br na and i the elemental relationships reflect the different chemistry and precipitation processes of possible source fluids and identify several episodes of mineralisation in the study area one of them formed due to a boiling process in a supercritical hydrothermal environment this paper reports on the compositional characteristics of these gold grains the significance of the halogen contents and the implications for possible sources of the gold and associated sulphides

fold related faults in the syrian arc belt of northern egypt abstract late cretaceous early tertiary syrian arc folds in northern egypt include both inversion and non inversion folds these folds are well exposed in northern sinai and the northern eastern desert but exist in the subsurface in the northern western desert in northern sinai the maghara yelleg and halal inversion folds are 45 50 km long similar size inversion folds with opposite vergence exist in the subsurface in the northern western desert and include the kattaniya mubarak alamein razzak and matruh basin folds smaller non inversion compressional folds include the falig and meneidret el etheili folds in northern sinai as well as the abu gharadig anticline in the subsurface in the northern western desert among others detailed surface and subsurface structural mapping made use of the excellent exposures and good 2d and 3d seismic data and led to the identification of the fault patterns of the inversion and non inversion syrian arc folds inversion folds have fault patterns that differ from the backlimb to the forelimb the backlimbs are pervasively dissected by long nw se oriented normal faults that were formed by the regional stress field on the contrary the forelimbs of inversion folds as well as the two limbs of non inversion folds are affected by the local stress in the folded areas and are dissected by three shorter fault sets a set of hinge transverse normal faults and two conjugate sets of hinge oblique faults that have oblique slip the hinge oblique faults dominate the steeper limbs of asymmetric non inversion folds

formation age and metamorphic history of the nuvvuagittuq greenstone belt abstract the nuvvuagittuq greenstone belt ngb in northern quebec canada is dominated by mafic and ultramafic rocks metamorphosed to at least upper amphibolite facies rare felsic intrusive rocks provide zircon ages of up to 3 8 ga david et al 2009 cates and mojzsis 2007 establishing the minimum formation age of the ngb as eoarchean primary u rich minerals that may provide reliable formation ages for the dominant mafic lithology called the ujaraaluk unit have yet to be found metamorphic zircons rutiles and monazites are present in the unit and give variably discordant results with 207pb 206pb ages ranging from 2 8 ga to 2 5 ga the younger ages overlap 2686 4 ma zircon ages for intruding pegmatites david et al 2009 and sm nd ages for garnet formation in the ujaraaluk rocks suggesting this era as the time of peak metamorphism and metasomatism in the ngb coeval with regional metamorphism of the superior craton sm nd data for ujaraaluk whole rocks scatter about a sm nd vs 143nd 144nd correlation mswd 134 whose slope would correspond to 3 6 0 2 ga if interpreted as an isochron this isochron is seen to consist of a series of younger 3 2 2 5 ga slopes for the different geochemical groups within the ujaraaluk emanating from a baseline distribution older than 4 ga the 146sm 142nd chronometer is less affected by metamorphism at 2 7 ga because of 146sm extinction prior to 4 ga expansion of the 142nd dataset for the ujaraaluk and associated ultramafic rocks continues to show a good correlation between sm nd ratio and 142nd 144nd that corresponds to an age of 4388 15 17 ma the dataset now includes samples with superchondritic sm nd ratios that extend the correlation to 142nd excesses of up to 8 ppm compared to the terrestrial standard with a total range in 142nd 144nd of 26 ppm the upper sm nd ratio end of the ujaraaluk correlation is defined by rocks that are interpreted to be cumulates to compositionally related extrusive rocks indicating that this crystal fractionation had to occur while 146sm decay was active i e well before 4 ga intruding gabbros give 143nd and 142nd isochron ages of respectively 4115 100 ma and 4313 41 69 ma also supporting an hadean age for the gabbros and providing a minimum age for the intruded ujaraaluk unit 3 6 ga tonalites surrounding the ngb 3 8 ga trondhjemitic intrusive veins and a 2 7 ga pegmatite show a deficit in 142nd compared to the terrestrial standard these felsic rocks plot to the low sm nd ratio side of the ujaraaluk isochron and do not show a correlation between their sm nd and 142nd 144nd ratios which can be explained if they are melts of ancient lree enriched mafic rocks such as the ujaraaluk with the melting occurring after 146sm was extinct a subset of least disturbed ujaraaluk samples has coherent isotopic compositions for both short lived and long lived nd isotopic systems giving 143nd and 142nd isochron ages overlapping within error of 4321 160 ma mswd 6 3 and 4406 14 17 ma mswd 1 0 respectively this age represents our best age estimate for the ujaraaluk unit the ngb thus preserves over 1 6 billion years of early earth history including an expanse of mafic crust formed in the hadean

displacement efficiency of faults and fractures abstract faults and fractures evolve kinematically as somigliana dislocations as a result displacement gradients are always present with displacements reducing to zero at fault fracture tips we present a graphical method for the comparison of displacement gradients from fractures of various magnitudes and types displacement efficiency of a fault fracture is defined as its ability to maximise displacement across its surface

using physical volcanology chemical stratigraphy and pyrite geochemistry for volcanogenic massive sulfide exploration an example from the blake river group abitibi greenstone belt an innovative approach to enhance volcanogenic massive sulfide vms exploration in regions outside of mining camps is to first use physical volcanology with litho and chemostratigraphy to establish the location of effusive centers in the volcanic units and use pyrite geochemistry in sulfide bearing stratified intervals with whole rock geochemistry in the underlying volcanic units to identify hydrothermal upflow zones this methodology is illustrated by this study in the archean blake river group within the abitibi greenstone belt of quebec and ontario the blake river group contains numerous vms deposits yet large segments remain underexplored including the hebecourt formation which contains four tholeiitic units that range from basalt to rhyolite in composition effusive centers are located for three felsic units and subunits 1 low ti porphyritic subunit of the main rhyolite 2 high ti aphyric subunit of the main rhyolite and 3 the upper rhyolite and for a basaltic andesite unit stringer and disseminated zn cu mineralization occurs within the flank breccia of the low ti rhyolite dome an inferred vent area for an overlying basaltic andesitic unit has also been identified in this area illustrating the coincidence of hydrothermal upflow zones with volcanic vents la icp ms analysis of pyrite grains from several sulfide bearing stratified intervals indicates two broad areas of higher cu zn au and ag contents the eastern region corresponds to known volcanic vents and mineralization the western region also indicates upflow of cu bearing hydrothermal fluids and corresponds to a possible effusive center for the high ti subunit the western region does not contain known mineralization at lower stratigraphic positions but it has not been thoroughly explored

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

two distinct origins for archean greenstone belts abstract applying the th yb nb yb plot of pearce 2008 to the well studied archean greenstone sequences of western australia shows that individual volcanic sequences evolved through one of two distinct processes reflecting different modes of crust mantle interaction in the yilgarn craton the volcanic stratigraphy of the 2 99 2 71 ga youanmi terrane mainly evolved through processes leading to th yb nb yb trends with a narrow range of th nb constant th nb greenstones in contrast the 2 71 2 66 ga volcanic stratigraphy of the eastern goldfields superterrane evolved through processes leading to th yb nb yb trends showing a continuous range in th nb variable th nb greenstones greenstone sequences of the pilbara craton show a similar evolution with constant th nb greenstone evolution between 3 13 and 2 95 ga and variable th nb greenstone evolution between 3 49 and 3 23 ga and between 2 77 and 2 68 ga the variable th nb trends dominate greenstone sequences in australia and worldwide and are temporally associated with peaks in granite magmatism which promoted crustal preservation the increasing th nb in basalts correlates with decreasing end reflecting variable amounts of crustal assimilation during emplacement of mantle derived magmas these greenstones are typically accompanied in the early stages by komatiite and can probably be linked to mantle plume activity thus regions such as the eastern goldfields superterrane simply developed as plume related rifts over existing granite greenstone crust in this case the youanmi terrane their th nb trends are difficult to reconcile with modern style subduction processes the constant th nb trends may reflect derivation from a mantle source already with a high and constant th nb ratio this and a lithological association including boninite like lavas basalts and calc alkaline andesites all within a narrow th nb range resembles compositions typical of modern style subduction settings these greenstones are very rare and were probably only preserved when fortuitously stabilised by granitic magmatism related to the evolution of later variable th nb greenstones the rarity of constant th nb trends suggests that either processes forming them never dominated archean greenstone evolution or that such greenstones simply were rarely preserved metamorphic mobility of th renders the th yb nb yb plot inappropriate for interpreting eoarchean greenstone units worldwide nevertheless such sequences appear dominated by volcanic rocks that in modern settings reflect only the embryonic or initiation stages of subduction they probably record subduction failure rather than anything resembling modern style subduction

strain variation in the henaux basse normandie duplex northern france abstract a completely exposed section through a miniature duplex developed in carboniferous limestones exists in a disused quarry and an adjacent railway cutting in the boulonnais region of northern france the structure is unique in that the propagating tip of the duplex where the shortening dies to zero is exposed a balanced restored section reveals an overall contraction of 38 7 increasing from zero at the duplex tip to over 70 at the distal end the limestone beds above the roof thrust of the duplex have shortened by 24 5 in a complex of foreland and orogen dipping thrusts which are typically developed above decollements

pre 2 8 ga crust in the opatica gneiss belt a potential source of detrital zircons in the abitibi and pontiac subprovinces superior province canada ages of detrital zircons in post 2 7 ga metasedimentary rocks of the southern abitibi and northern pontiac subprovinces require that pre 2 8 ga crust was exposed during or following deformation of the 2 70 and 2 68 ga and the belt forms a high grade crystalline core to a south vergent mountain belt along the northern margin of the abitibi subprovince erosion of the opatica and northern abitibi during thrusting would shed detritus southward in advance of a south vergent thrust system the lac rodayer complex may be the enigmatic source of 2 8 ga detrital zircons within turbidites of the southern abitibi and northern pontiac subprovinces

lateral and vertical changes of deformation style in the osen roa thrust sheet oslo region abstract changes in deformation style and amounts of shortening in the osen roa thrust sheet of the oslo region occur vertically and laterally approaching the thrust front in the south deformation in the cambromiddle ordovician sequence passes laterally from closely spaced imbricates in the north 50 60 shortening through triangle pop up and imbricate zones toward the south 20 37 shortening to widely spaced zones of deformation up to 20 shortening approaching the thrust front changes in deformation style are attributed to changing boundary conditions across the klekken thrust declining end of orogenic forces and an increase in thickness of competent units in the ordovician rocks to the south vertical changes in deformation style are attributed to the increasing percentage of competent units upward in the cambro silurian sedimentary rocks in the north the accompanying decrease in shortening upwards requires a structurally necessary upper detachment horizon to separate folded late middle ordovician silurian sediments from imbricated early cambro middle ordovician sediments below while southward in the oslo area the upper detachment needs to be placed between silurian and cambro ordovician units finally in eiker with less than 20 shortening the whole cambrosilurian sequence appears to have deformed as a single unit in the northern oslo region the upper detachment probably has a backthrust sense of motion above an imbricate stack passive roof duplex further south the upper detachment is probably directed toward the foreland

anomalous porosity and permeability preservation in deeply buried tertiary and mesozoic sandstones in the cusiana field llanos foothills colombia reply abstract porosity in deeply buried 14000 ft 4200 m sandstones of the lower tertiary mirador formation in the cusiana field llanos foothills colombia is less than 10 porosity units p u however permeability is as much as 1000 md which is believed to be due to the simple quartzose detrital grain composition and large grain size the low porosity has resulted from pervasive quartz cement 10 15 fluid inclusion microthermometry and intergranular grain volumes indicate that the quartz cement precipitated at a temperature of around 100 c during deep burial surprisingly thick 400 ft 120 m sandstones of the underlying upper cretaceous guadalupe group in the cusiana field have porosity as high as 20 p u these sandstones are lithic sandstones composed of quartz and a variety of phosphate grain types and are poorly cemented quartz cement is not abundant and occurs as rims of microcrystalline quartz on quartz and phosphate grains in contrast interbedded quartz arenites within the guadalupe group are heavily cemented by quartz cement and have porosity similar to the overlying mirador formation the major control on porosity in these sandstones appears to be the presence of quartz cement the quartz cement is controlled by grain composition the reasons for the lack of quartz cement in the lithic sandstones of the guadalupe group are uncertain but phosphate poisoning inhibiting quartz cement growth is a possibility the presence of high porosity sweet spots in deeply buried sandstones may be linked to the occurrence of phosphate beds a primary depositional control

strains developed in the hangingwalls of thrusts due to their slip propagation rate a dislocation model reply abstract fault planes propagate radially from a point source and this failure propagation process is very similar to the movement of a dislocation through a crystal lattice an elastic strain represented by an extra half plane is necessarily imparted to the lattice at an edge dislocation and this is equivalent to the ductile bead which accompanies the propagating tip of a thrust fault this ductile bead migrates with the fault tip and imparts a characteristic internal strain to the thrust sheet a two dimensional model is presented to illustrate the inter relationship between fault plane slip fault tip propagation and internal strain in multilayered sequences internal strain is usually represented by asymmetric folds verging in the thrust transport direction a simple technique the displacement distance plot utilizes the fact that displacement dies out towards the fault tip this plot can be used to quantify the relative stretch measured parallel to the fault movement which is dependent on the slip propagation rate and it may be used to define exactly the position of the fault tip on a cross section examples of fold thrust structures from devon england and pembrokeshire wales are used to illustrate the technique

origin of a thrust related fold geometric vs kinematic tests abstract geometric tests to determine the origin of fault related folds are common but as is typical in structural geology more than one fold origin may yield the final natural geometry thus the results of geometric tests are usually non unique in contrast kinematic tests of origin which employ both geometry and data about deformation commonly yield more constrained if not unique results unfortunately the necessary data collection requires much more work than for a geometric test in this study the thrust related barclay anticline is analyzed both geometrically and kinematically to determine which test is more effective geometric tests using angular relationships indicate three possible origins fault bend fault arrest and break thrust for the kinematic test predicted deformations for interlayer and flexural slip flexural flow simple shear and bending strains are compared to micro and mesostructural distributions solution strain and finite strain from the anticline strain measurements indicate that microscale deformation is uniformly distributed through the structure and is lithification dominated the microscale deformation does not match kinematic predictions and did not accommodate fold formation fold growth was achieved primarily through layer parallel slip restricted mostly to the forelimb and absent in the hinge which eliminates fault bend and fault arrest origins that require material transport from forelimb to backlimb the barclay anticline is therefore interpreted to be a break thrust structure interestingly a suite of contraction faults in the forelimb and hinge indicates material transport from forelimb to backlimb such transport has been discounted for break thrust folds the most important result of this study is that a kinematic test was a necessary step for distinguishing fold origin geometric testing alone was insufficient given that the barclay anticline has geometric characteristics typical of many thrust related folds kinematic testing appears necessary to determine their structural origin

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

subduction influence of philippine sea plate on the mantle beneath northern kyushu sw japan an examination of boron contents in basaltic rocks abstract northern kyushu characterized by the subduction of two oceanic slabs a hot shikoku basin and a cold philippine sea plate beneath the eurasian plate forms a complex portion of southwestern japan arc in order to evaluate the effect of slab derived fluids from these two contrasting oceanic plates we determined the boron b contents in basaltic rocks from ten volcanoes and three old volcanic fields which erupted since 11 ma since b is distinctly concentrated into slab derived fluids among the earth s materials we attempted to estimate the influences of subduction on the sub arc mantle composition from the interpretation of the b data in basaltic rocks old 11 6 ma basaltic rocks contain low ratios of b sm 0 5 1 3 b zr 0 02 0 05 and b nb 0 2 0 5 suggesting little influence of subduction similarly backarc basaltic rocks occurring throughout the observed period show little influence of subduction in contrast volcanic products from young aso volcano located at the volcanic front show a strong influence of subduction as indicated by the high b sm 1 6 4 3 b zr 0 07 0 16 and b nb 1 4 3 7 ratios after 6 ma the volcanic arc segment containing aso volcano is associated with the subduction of the cold philippine sea plate hence a b rich fluid was probably added to the sub arc mantle however yufu tsurumi and kuju volcanoes which are located at the same volcanic front show small b sm 0 9 1 9 b zr 0 04 0 07 and b nb 0 5 0 9 ratios this implies that the subduction of the hot shikoku basin released fluids from the slab at shallow depths therefore it is depleted of b and other subduction components by the time it reaches the volcanic front

magmatic affinity of modern and ancient subalkaline volcanic rocks determined from trace element discriminant diagrams when dealing with ancient subalkaline volcanic rocks the alkali total iron magnesium afm diagram is of limited use in assigning a tholeiitic versus calc alkaline affinity because these eleme

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

insights into the damage zones in fault bend folds from geomechanical models and field data abstract understanding the rock mass deformation and stress states the fracture development and distribution are critical to a range of endeavors including oil and gas exploration and development and geothermal reservoir characterization and management geomechanical modeling can be used to simulate the forming processes of faults and folds and predict the onset of failure and the type and abundance of deformation features along with the orientations and magnitudes of stresses this approach enables the development of forward models that incorporate realistic mechanical stratigraphy e g the bed thickness bedding planes and competence contrasts include faults and bedding slip surfaces as frictional sliding interfaces reproduce the geometry of the fold structures and allow tracking strain and stress through the whole deformation process in this present study we combine field observations and finite element models to calibrate the development and distribution of fractures in the fault bend folds and discuss the mechanical controls e g the slip displacement ramp cutoff angle frictional coefficient of interlayers and faults that are able to influence the development and distribution of fractures during fault bend folding a linear relationship between the slip displacement and the fracture damage zone the ramp cutoff angle and the fracture damage zone and the frictional coefficient of interlayers and faults and the fracture damage zone was established respectively based on the geomechanical modeling results these mechanical controls mentioned above altogether contribute to influence and control the development and distribution of fractures in the fault bend folds

contemporaneously erupted tholeiitic and calc alkaline magmas in the archean colomb chaboullie greenstone belt james bay quebec petrologic implications abstract archean greenstone terranes are key to understanding the geological processes active during early earth history these areas are also of economic interest due to their association with volcanogenic massive sulphide vms deposits and several other types of mineral deposits the archean colomb chaboullie greenstone belt is located between the nemiscau and opatica subprovinces of the superior province quebec canada this belt comprises three submarine volcanic units pillowed to massive basaltic lavas variably porphyritic massive to pillowed intermediate lavas intrusions and intermediate to felsic volcaniclastic rocks the calc alkaline intermediate lavas and volcaniclastic assemblages are intercalated with the tholeiitic to transitional basaltic lavas this implies that these volcanic rocks were contemporaneously formed within a limited geographical area the major element trends of the basalts are explained by crystal fractionation while the trace elements are influenced by independently occurring minor degrees of crustal contamination the major and trace element geochemistry of the calc alkaline rocks share many geochemical characteristics with pre existing crustal contaminants we therefore propose that the intermediate and felsic assemblages were produced via crustal contamination and mixing processes within a pre existing magma chamber the basalts spent less time in the crust and had a more direct passage to the surface massive to semi massive au ag cu showings along with associated paleo hydrothermal manifestations are dominantly associated with the basaltic lavas and show evidence of a syn volcanic origin chemo stratigraphy in conjunction with detailed mapping of the gold bearing lac marcaut vms showing allows a basalt basalt contact to be identified which may be favourable for exploration elsewhere in the colomb chaboullie belt

geometric tests and their application to fault related folds in kuqa abstract for brittle rock deformation there are two main types of fault related folds found in foreland thrust belts i e fault bend folds and fault propagation folds the predicted angular function for the quantitative geometric relationships between fault shapes and fold shapes in fault bend folds and fault propagation folds have been tested in seismic profiles i e deep bashijiqike tugeerming kashangtokai east qiulitage deep east qiulitage and yakelike fault bend anticlines and bashijiqike yiqikelike and south yiqikelike fault propagation anticlines in the kuqa rejuvenated foreland thrust belt test results for the transformation from seismic time section into seismic depth section using the seismic velocity spectrum can be used to identify whether the interpreted structures are reasonable with geometric analysis and testing of the subsurface structures it is possible to predict the existence of the fault bend folds and fault propagation folds in the kuqa area this study provides convincing proof that the kuqa basin is a rejuvenated foreland basin

mobile hinge kinking in layered rocks and models abstract an unresolved question in structural geology is whether kink folds grow by the gradual rotation of the fold limbs about a fixed hinge by the nucleation of kink bands that grow by fold hinge migration or by some combination of these mechanisms the importance of mobile hinge kinking has previously been recognized in experimentally deformed slate and phyllite as well as decks of paper cards but its importance in the folding of multilayers consisting of alternating competent and incompetent layers has been uncertain this study shows that mobile hinge kinking can be an important folding mechanism in both natural and experimental multilayers the natural folds are in pelagic limestones from the umbria marche apennines of italy the geometrical properties of these folds as well as the small scale structures in the rocks indicate that these folds formed by the nucleation and expansion of kink bands with mobile hinges not by a fixed hinge folding mechanism the experimental folds were produced by the deformation of multilayered models consisting of layers of lead separated by layers of wax impregnated cloth the progressive growth of these folds by the nucleation and expansion of kink bands was directly observable a rough estimate of the rate at which fold hinges migrated through the apennine limestones was obtained indirectly using the displacement history recorded by calcite fibers on a fault which cuts a kink fold and was active during the formation of the fold it appears that the rate at which fold hinges migrated was approximately 100 times greater than the displacement rate along a fault that was moving by pressure solution slip

late brittle deformation in a caledonian ductile thrust wedge new evidence for gravitational collapse in the moine thrust sheet sutherland scotland abstract in the ductile regions of orogenic wedges late brittle structures formed at shallow crustal depths have received little attention however they are important as they of ten record the final stages in deformational history during uplift and erosion of the orogen in the moine rocks of sutherland late caledonian brittle folds and low angle faults post date ductile structures formed during wnw nw directed thrust movements earlier in the same orogenic event in the western moine nappe the late structures display geometries which indicate that they formed during regionally ese directed extensional movements down the dip of the pre existing regional foliation these late structures are correlated with similar wnw directed extensional low angle faults recognised in the moine thrust zone south of the assynt culmination both are thought to have formed in response to late caledonian gravity induced thinning of the moine thrust wedge and both pre date devonian extension associated with the formation of the west orkney basin along strike changes in the location and sense of extensional movements north and south of the assynt culmination are explained by changes in the pre existing structural geometry of the caledonian ductile thrust nappes within the moine hence earlier deformation patterns are thought to exert important controls over later events in an evolving orogenic wedge

impacts of the tectonic stress field on natural gas migration and accumulation a case study of the kuqa depression in the tarim basin china stress fluid and temperature are three of the major factors that impact natural gas migration and accumulation in order to study the influences of tectonic stress field on natural gas migration and accumulation in low permeability rocks we take the kuqa depression as an example and analyze the evolution of the structure and tectonic stress field at first then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the kl2 gas field we summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation firstly under the effects of the tectonic stress field the rock dilation increases with the added stress and strain and when the shear stress of rock exceeds its shear strength the shear fractures are well developed on one hand the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration on the other hand these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation secondly because fluid potentials decrease in these places near the faults where fractures are well developed natural gas can migrate rapidly along the faults and accumulates the impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low permeability rocks in an active tectonic compressive setting

giant granulite terranes of northeastern superior province the ashuanipi complex and minto block the ashuanipi complex and minto block of the superior province are large regions that have been classified as high grade gneiss terranes on the basis of the presence of orthopyroxene bearing units like the granite greenstone and metasedimentary subprovinces of the southern superior province the two terranes consist predominantly of intrusive rocks but are distinguished by their primary magmatic orthopyroxene both high grade and gneiss are misnomers because granulite facies gneisses are only sparingly present and the regions consist dominantly of massive unmetamorphosed plutonic rock the ashuanipi complex consists of a deformed metamorphosed package of metasedimentary rocks and primitive early tonalite cut by widespread orthopyroxene garnet granodiorite diatexite as well as plutons of tonalite granite and syenite based on its lithological and chronological similarity and on strike position the complex appears to be the continuation of metasedimentary subprovinces such as the quetico its evolution involved deposition of immature greywacke in an accretionary prism early arc tonalitic magmatism and deformation followed by widespread intracrustal magmatism in the period 2700 2670 ma both metamorphic and igneous rocks record equilibration under granulite facies conditions 700 835 c 0 35 0 65 gpa a 0 3 and indicate exposure levels of 20 km the minto block at the latitude of leaf river consists of several north northwest trending domains of similar scale and diversity to the east trending subprovinces of the southern superior province the central goudalie domain is dominantly amphibolite facies tonalitic rocks including some with ages 3 ga with small belts of volcanic and sedimentary origin lake minto domain contains poorly preserved supracrustal remnants in a plutonic complex comprising hornblende granodiorite clinopyroxene orthopyroxene granodiorite orthopyroxene biotite diatexite and granite the hornblende granodiorite suite constitutes most of the utsalik and tikkerutuk domains and is thought to represent continental arc magmatism on the basis of their distinct aeromagnetic and lithological character two additional domains are evident north of the leaf river area the inukjuak domain in the west and the douglas harbour domain in the east the northerly grain of the minto block appears to have been established in situ with respect to the easterly belts of the southern superior province i e no large scale block rotation during the same interval of time 3 0 2 7 ga modification of the tectonic framework for the superior province is required to explain minto arc magmatism in the interval 2730 2690 ma ago a continental magmatic arc built the berens river and bienville subprovinces and minto block on the southern and eastern edges respectively of a northern protocratonic foundation in the same period primitive volcanic arcs and accretionary prisms developed outboard on oceanic crust and were accreted to form a southern tectonic regime

displacement transfer at thrust terminations the saltville thrust and sinking creek anticline virginia u s a abstract the saltville thrust terminates in the core of the sinking creek anticline changes in the amplitude of the anticline may preserve profile shortening as the thrust displacement decreases towards the fault termination consequently thrust displacement would be transferred into the fold we combine newly published maps and new strain and mesostructural data from the tuscarora sandstone to argue that the sinking creek anticline did perform this kinematic role we propose that the anticline developed as a fault propagation fold that experienced both decollement and anticlinal breakthrough by the saltville thrust thrust displacement was accommodated by the development of the modified fault propagation fold and by transfer to a roof flat from the decollement breakthrough new strain and mesostructural data indicate no fixed pin lines in either the hinge or backlimb throughout folding consequently layer slip occurred through the hinge during folding and the forelimb deformed internally during breakthrough towards the plungeout of the sinking creek anticline the displacement on the saltville thrust is transferred to a floor thrust we apply this interpretation to the termination of the st clair thrust which has a similar surface geometry where the thrust terminates into an anticline a testable implication of this proposed interpretation for the st clair thrust is that the appalachian plateau must absorb over 20 km of thrust displacement as horizontal shortening

conditions and timing of metamorphism in the southern abitibi greenstone belt quebec regional metamorphism ranging in grade from the subgreenschist facies to the greenschist amphibolite facies transition affects all archean supracrustal rocks 2677 ma in the rouyn noranda area contact metamorphic minerals associated with the posttectonic preissac lacorne batholith 2643 ma show no evidence of a regional retrograde event accordingly the age of regional metamorphism can be bracketed between 2677 and 2643 ma three reaction isograds were mapped in subgreenschist facies metabasites dividing the low grade rocks into three metamorphic zones the pumpellyite actinolite zone the prehnite pumpellyite zone and the prehnite epidote zone in addition the pumpellyite actinolite epidote quartz bathograd corresponding to a pressure of approximately 200 mpa occurs on both sides of the porcupine destor fault low pressure regional metamorphism is also indicated both by the occurrence of an actinolite oligoclase zone and the persistence of pre regional metamorphic andalusite the coincidence

structural trend analysis by axial surface mapping we present a new method of structural trend analysis in which axial surfaces fold hinges are mapped through grids of seismic reflection profiles and balanced forward models axial surface maps 1 define fold trends lateral terminations and closure in structure 2 constrain underlying fault geometry and slip and 3 highlight and connect regions that can be interpreted by a series of balanced models or cross sections maps of folds in southern california and northeastern pennsylvania are compared with forward model solutions and used to construct balanced three dimensional structural interpretations using fault bend fold theory axial surface maps generated from balanced fault bend fold models define theoretical relationships between map patterns and structural geo etry and fault slip kink band widths between paired axial surfaces in map view are related to underlying fault slip lateral variations in fault slip which can be identified on axial surface maps may cause fold plunge and provide lateral closure lateral changes in subsurface fault geometry which include lateral and oblique ramps are also reflected by terminations bends or offsets of axial surfaces in map view based on these relationships between folding and faulting we develop map view interpretations and balanced cross sections across structures that are consistent with the geology along trend

reservoir performance of late eocene incised valley fills cusiana field llanos foothills eastern colombia the cusiana field is located in the llanos foothills of eastern colombia the principal reservoir is the late eocene mirador formation which comprises 50 of reserves currently the mirador reservoir is providing nearly all of the 150 00bopd of production from the cusiana field the mirador reservoir comprises a stack of incised valley deposits the fills of the valleys are dominated by quartz arenite sandstones the average porosity of the valley sandstones is 8 which reflects abundant quartz cement approximately 14 and significant compaction during deep burial approximately 20 000feet single valleys are up to 70 feet thick and exhibit a distinctive bipartite fill that reflects changing energy conditions during filling bases of valleys have the coarsest grain size and have sedimentological and trace fossil evidence for deposition in highly stressed brackish water environments the upper parts of the valleys are typically finer grained and were deposited in more saline settings despite the low porosity of the mirador valleys drill stem tests and production log data show that they have phenomenal performance characteristics rates of ge 10 000bopd are achieved from single valleys bases of the valley fills are the key contributors to flow integration of detailed core and pore system analysis with the reservoir performancemore data shows that the permeability fabric of the mirador can be explained by original depositional architecture and simple loss of primary porosity comparison of cusiana with other quartz rich sandstones from around the world suggests that it s low porosity high performance is predictable less

effect of basement structure and salt tectonics on deformation styles along strike an example from the kuqa fold thrust belt west china abstract the kuqa fold thrust belt kftb has a complex thrust system geometry and comprises basement involved thrusts decollement thrusts triangle zones strike slip faults transpressional faults and pop up structures these structures combined with the effects of paleogene salt tectonics and paleozoic basement uplift form a complex structural zone trending e w interpretation and comprehensive analysis of recent high quality seismic data field observations boreholes and gravity data covering the kftb has been performed to understand the characteristics and mechanisms of the deformation styles along strike regional sections fold thrust system maps of the surface and the sub salt layer salt and basement structure distribution maps have been created and a comprehensive analysis of thrust systems performed the results indicate that the thrust fold system in paleogene salt range can be divided into five segments from east to west the kela 3 keshen dabei bozi and awate segments in the easternmost and westernmost parts of the paleogene salt range strike slip faulting and basement involved thrusting are the dominant deformation styles as basement uplift and the limits of the cenozoic evaporite deposit are the main controls on deformation salt core detachment fold thrust systems coincide with areas of salt tectonics and pop up imbricate and duplex structures are associated with the main thrust faults in the sub salt layer distribution maps of thrust systems basement structures and salt tectonics show that paleozoic basement uplift controlled the paleozoic foreland basin morphology and the distribution of cenozoic salt in the kftb and thus had a strong influence on the segmented structural deformation and evolution of the fold thrust belt three types of transfer zone are identified based on the characteristics of the salt layer and basement uplift and the effects of these zones on the fault systems are evaluated basement uplift and the boundary of the salt deposit generated strike slip faults in the sub salt layer and supra salt layers at the basin boundary model a when changes in the basement occurred within the salt basin strike slip faults controlled the deformation styles in the sub salt layer and shear zone dominated in the supra salt layer model b a homogeneous basement and discontinues salt layer formed different accommodation zones in the sub and supra salt layers model c in the sub salt layer the thrusts form imbricate structures on the basal decollement whereas the supra salt layer shows overlapping discontinuous faults and folds with kinds of salt tectonics and has greater structural variation than the sub salt layer

source of gold in neoarchean orogenic type deposits in the north atlantic craton greenland insights for a proto source of gold in sub seafloor hydrothermal arsenopyrite in the mesoarchean abstract given that gold au mostly remained in the incipient earth mantle until ca 3 9 3 8 ga a proto source of gold may have been present in the dominantly mafic crust precursor born through first stage melting of the early earth mantle in south westernmost greenland a fragment of the north atlantic craton is characterised by greenstone belts comprising mafic volcanic and magmatic rocks and harzburgite cumulates that were emplaced at ca 3 0 ga prograde amphibolite facies metamorphic assemblages and caused local dissolution of arsenopyrite during this retrograde tectono metamorphic stage in gold rich shear zones the re os geochronometer in arsenopyrite was reset to a neoarchean age while invisible gold was liberated and deposited as free gold with 2 66 ga pyrite re os isochron ages the initial os isotope ratios of neoarchean arsenopyrite 187os 188osi 0 13 0 02 and gold bearing pyrite 0 12 0 02 overlap with the estimated 187os 188os ratio of the mesoarchean mantle 0 11 0 01 and preclude contribution of radiogenic crustal os from evolved lithologies in the accretionary arc complex but instead favour a local contribution in os from basaltic rocks and serpentinised harzburgite protoliths by metamorphic fluids thus the ca 2 66 ga lode gold mineralisation identified in the north atlantic craton may illustrate a gold endowment in shear zones in earth s stabilizing continental crust at the time of the 2 75 2 55 ga global gold event through metamorphic upgrading of bulk gold which had originally been extracted from the mesoarchean mantle and concentrated in hydrothermal arsenopyrite deposits in oceanic crust beneath the overall reduced mesoarchean ocean

u pb geochronology of the opatica tonalite gneiss belt and its relationship to the abitibi greenstone belt superior province quebec u pb ages for zircon monazite and titanite from samples collected from two transects across the opatica tonalite gneiss belt in the superior province of quebec indicate that the belt contains rocks that are significantly older than those in the adjacent low grade northern abitibi belt tonalite and tonalite gneiss which make up most of the belt formed over an interval of 100 ma from pre 2800 to 2702 ma five samples have ages of ca 2807 13 2773 23 and 2702 3 ma zircon growth at 2718 2721 ma in the two oldest samples may record an early period of high grade metamorphism in the belt hornblende diorite monzodiorite and tonalite plutons were intruded at 2693 2696 ma particularly along the southern boundary with the abitibi belt these include the canet pluton at ma the lac ouescapis pluton at 2693 2 ma and the barlow pluton at 2696 3 ma pink granite plutons and dykes are the youngest intrusive rocks in the belt three samples have yielded zircon ages of 2690 2 and 2686 4 ma

the model of fracture development in the faulted folds the role of folding and faulting abstract tectonic fractures are otherwise known as joints or fissures the density of tectonic fractures is governed by the lithology layer thickness and structures the distribution and density of tectonic fractures in the kuqa depression in the northern tarim basin of northwest china are dominantly controlled by the regional faulted fold belt our purpose of this paper is to analyze how folding and faulting control the development of tectonic fractures based on outcrop and logs of drill data in the folded tight sandstone reservoirs in the kuqa depression the extensional area transition area and shortening area have been separated by two neutral lines which control the distribution and density of tectonic fractures in the buckle folds from the twelve sites of field measurements six logs of drill core data and analysis of the micro texture of tectonic fractures it can be deduced that the fracture development in the sub salt faulted fold belt is related to the neutral lines and related faults the high density tensile fractures in the vicinity of fold hinges are more developed than in the limbs of the fold folding is thus the first level of control over the general pattern of fracture distribution the fractures in the hanging wall of the thrust faults are more developed than those in the footwall further more the fractures in the hinge zone and steeply tilted limbs of folds close to thrust faults are more developed than the gently tilted limbs which are far from faulting this suggests that faulting is a secondary control over the development of local fractures within the faulted fold belt the development of fractures related to faulted folds in the kuqa depression can be also divided into three episodes pre folding syn folding and post folding which are identified by field observation

petroleum geology of kela 2 the most productive gas field in china abstract the kela 2 gas field located in the kuqa depression of tarim basin is the most productive gas field in china based on per unit surface acreage the gas trap is a subsurface anticline formed along an e w trending thrust belt in front of the southern tianshan mountains the gas pay zones are located in fine grained sandstones of a fan delta front facies in the lower cretaceous bashijiqik formation k l bs and eogene evaporitic rocks serve as regional cap rocks the gases were derived primarily from over mature jurassic coal measures peak gas generation and final shaping of the kela 2 structure occurred relatively late in the late himalayan orogeny 5 0 ma thrust faulting appears to have played a significant role in the hydrocarbon generation migration accumulation and preservation in this foreland basin detailed delineation of the kela 2 gas field indicates that high quality regional cap rocks are essential for the formation of the super rich abnormally pressured giant gas fields while buried anticlines under the overthrust zone are the favorable gas habitat late gas accumulation is considered to be decisive for the conservation of the giant gas fields

aerodynamic and geometric diameter of airborne particles discussion the paper by chen and fryrear 2001 addresses a much neglected topic in the general field of grain dynamic behavior but it is unfortunately marred by a number of omissions and inaccuracies first some minor errors have to be pointed out which may mislead some readers if not corrected 1 equation 1 should read r f 6 rv without the minus sign 2 equation 7 is valid only for reynolds numbers less than 1 not more than 1 as stated 3 in their table 1 the legend states that t m is the calculated mean settling velocity which should read the calculated mean settling time 4 the legend in fig 2 should read measured average settling times and not settling velocities 5 the values for v t and the geometric particle diameters given in table 1 do not correspond to the graph in fig 5 6 on page 366 it is mentioned that sieve intervals of 75 m were used for particles between 125 and 600 m and 10 m intervals between 125 and 10 m however in table 1 the intervals apparently vary from 105 m to 25 m for the first range and between 19 and 8 m for the second 7 it is implied on the same page that perfect spheres were selected by examining them under a microscope this cannot be done because all the grains would lie on their shortest axes they may therefore just as well

displacement distance methods in the analysis of fold thrust structures and linked fault systems a new method for analysing the internal strain in thrust sheets is described the displacement distance diagram can be used to quantify the relative shortening or relative stretch between the hangingwall and footwall beds of a thrust and is a useful way of analysing commonly occurring fold thrust structures the stretch is a function of the relative rates of thrust propagation and thrust slip the cumulative displacement distance diagram described here can be used to calculate the absolute shortening or extension when this is accommodated above a single decollement in a linked fault system this method offers a useful way of analysing duplex structures and large scale foreland thrust zones as well as extensional fault systems and can be used as an alternative to or in conjunction with balanced cross sections both methods can be used to quantify the variation in shortening above a single detachment zone this variation may be mechanically significant reflecting lithological control on thrust or normal fault growth

magma mobilization by downward propagating decompression of the eyjafjallajokull volcanic plumbing system 1 detailed observations of the 2010 eyjafjallajokull eruptions in iceland show seismic activity propagating vertically through the entire crust during a ten week period of volcanic unrest comprising multiple eruption episodes systematic changes in magma chemistry suggest a complex magmatic plumbing system tapping several accumulation zones at different depths containing magma of differing ages and compositions during the eruption a systematic downward propagation of seismicity through the crust and into the upper mantle to 30 km depth occurred in a series of steps each of which preceded an explosive surge in eruption rate here we show that the sequence of seismicity and eruptive activity may be explained by the downward propagation of a decompression wave that triggers magma release from progressively deeper sills in the crust comparing observations of the downward propagating seismicity with the decompression of a series of model elastic sills suggests that each sill was 1 10 km3 in size

slip vectors and fault mechanics in the makran accretionary wedge southwest pakistan the makran is a broadly east west trending arcuate accretionary wedge currently forming where the oceanic floor of the gulf of oman is being subducted north northeastward beneath the south asian margin two traverses across the makran coast ranges extending about 80 km inland from the coastline which lies about 100 km north of the wedge front show that the structure of this region is dominated by large back rotated south directed thrust faults and associated folds related structures include duplexes fault gouge containing reidel shears and melange along fault zones these structures are cut by later north directed backthrusts out of sequence south directed thrusts and apparently conjugate sets of nne trending sinistral and nw trending dextral strike slip faults slip vectors were determined from slickenlines fiber lineations gouge fabrics and riedel shears vectors from early thrusts and bedding parallel slip surfaces corrected for tectonic rotation form a broad south directed concentration lying between the normal to the regional strike varying from 160 to 180 and the present plate convergence vector 200 locally the concentration is bimodal this pattern may represent the interaction between plate forces and body forces in the accretionary wedge the late thrusts have widely variable slip vectors and stair step off the early thrusts they overlap in orientation and slip vector with gently dipping sinistral strike slip faults suggesting that they also stair step in plan off the latter the steep strike slip faults represent the final tectonic stage involving minor n s shortening and longitudinal extension these three stages probably occurred in sequence in any one area but migrated diachronously southward as the wedge grew

neoarchean disaggregation and reassembly of the superior craton the southern and western superior craton of canada swsc is widely considered to be a tectonic collage accreted from north to south by multiple coeval subduction zones we propose an alternative non plate tectonic scenario where swsc continental fragments are not exotic but derived by partial disaggregation of a heterogeneous older superior i craton in response to a mantle overturn event that started at ca 2780 ma during overturn radial mantle outflow stretched and disaggregated the lithosphere to create the concentric neoarchean fabric of the superior craton the southern part of which swsc broke up into ribbon continents separated by oceanic tracts neoarchean calc alkaline magmas record interaction between plume related magma and older crust a change in the mantle flow field at ca 2720 ma caused southward drift of the northern superior cratonic block as a result of mantle traction on its lithospheric keel and swsc terranes accreted to its leading edge

a sub salt structural model of the kelasu structure in the kuqa foreland basin northwest china abstract the kuqa foreland basin adjacent to the south tianshan mountains is a major hydrocarbon accumulation basin in western china the kelasu structural belt is the focus for hydrocarbon exploration in the basin due to the presence of ramp related anticline traps and a thick salt seal the model of the kelasu sub salt structure is still contentious because of the structural complexity and poor seismic imaging below the salt layer the area depth strain ads method is applied to the southern part of the kelasu fault a regional fault that cuts basement rocks the ads results are consistent with the seismic data which indicate that both thin skinned thrusting and basement involved deformation occur within the kelasu structure with the kelasu fault acting as the boundary between the two regions of contrasting deformation the ads results also suggest that the depth of the lower detachment of the thin skinned thrust belt is 9 5 10 km which may correspond to the base of the triassic the kelasu structure has undergone approximately 8 15 10 76 km of horizontal shortening in the east and 16 34 km in the west of the structure

strains developed in the hangingwalls of thrusts due to their slip propagation rate a dislocation model discussion abstract modern seismic data indicate that the sole fault of the turner valley thrust sheet does not lose displacement in an up dip direction and that it does not crop out but rather flattens into the triangle zone on the eastern edge of the rocky mountain foothills belt well constrained balanced cross sections drawn through this part of the belt do not incorporate significant folding related to the propagation of thrust faults

duplexes as slip transfer zones application to the himalayan fold thrust belt abstract duplex fault zones and imbricate fans originally termed schuppen schuppenstruktur or imbricate structure were first described in the late 1800s from the alps nw highlands scotland and montana rockies lewis thrust sheet as originally defined duplexes contained shingled imbricate slices bounded above and below by through going thrusts these duplex fault zones commonly occur along the base of major regional thrust sheets or within the body of such sheets accommodating regional bed parallel shortening and transferring slip from a lower stratigraphic horizon to a higher one thereby providing a mechanical advantage to the emplacement of large thrust sheets however faulting is not the only means of layer parallel shortening lps and displacement transfer within duplexes lps cleavage and detachment folds are also common and can play the same role as imbricate faults based on some selected examples we recognize three types of duplexes 1 fault duplex 2 cleavage duplex and 3 fold duplex the style of duplex that forms is likely a function of mechanical stratigraphy and deformation conditions the relationships among the three basic duplex styles can be plotted on a ternary diagram each duplex type constituting an apex given the complexities of most sedimentary sequences hybrid duplexes with a mix of fault fold and cleavage shortening can also form hybrid duplexes plot along the side of the triangle as fault fold fold cleavage and fault cleavage duplexes while those combining all three mechanisms plot in the middle if the partitioning of shortening by the different mechanisms can be quantified the ternary diagram provides a means of representing the contributions of the three mechanisms in shortening and slip transfer along much of the himalayan fold thrust belt a significant portion of the lesser himalayan shortening is taken up by the lesser himalayan duplex a first order fault duplex with subsidiary cleavage and fold development the geometry of and shortening within the duplex varies significantly along the length of the himalaya

substratum transverse faults in kuqa foreland basin northwest china and their significance in petroleum geology abstract the importance of transverse faults in basin evolution and petroleum geology has been often emphasized however the transverse faults in the kuqa foreland basin the most important gas producing area in china have rarely been studied interpreted seismic sections and earthquake focal mechanism solutions as well as other geological and geophysical data allow us to identify a few widely spaced approximately ns trending transverse strike slip faults separating major structural units and to clarify the geometry and kinematics of these transverse faults hidden below thrust faults in the kuqa foreland basin two major structural domains can be distinguished transverse faults in the northern kuqa foreland basin are mainly nne trending sinistral indicating clockwise rotation of fault bounded blocks in contrast the predominant nw trending dextral faults in the southern kuqa foreland basin imply counterclockwise rotation of fault bounded blocks we propose a tectonic model in which crustal blocks are bounded by strike slip faults in a zone of simple shear rotation about vertical axis the strike slip faulting and thrust faulting in the kuqa foreland basin suggest that some of the convergence between south tianshan and tarim blocks may have been accommodated not only by obvious crustal shortening and thickening along thrust faults but also by rotation and possible lateral movement of the crust along transverse faults controlled by the remote collision of indian block with eurasian block since the miocene these reactivated substratum faults which may inherit from paleozoic deformation control various elements relevant to gas accumulation in the kuqa foreland basin which should expect to be paid more attention in the future these elements include maturity of tertiary and jurassic source rocks a difference in the regional cap of kumugelimu salt beds from east to west reservoir bed properties gas migration channels and traps formation in addition the strike slip faulting of the transverse faults may affect deformation of the sedimentary cover including making the western qiulitag structural belt to form an arcuated structure curved to the ssw

depositional gaps in abitibi greenstone belt stratigraphy a key to exploration for syngenetic mineralization models of greenstone belt development are crucial for exploration allochthonous models predict belts to be a collage of unrelated fragments whereas autochthonous models allow for prediction of syngenetic mineral deposits within specific stratigraphic intervals superior province greenstone belts consist of mainly volcanic units unconformably overlain by largely sedimentary timiskaming style assemblages and field and geochronological data indicate that the abitibi greenstone belt developed autochthonously we describe major revisions to stratigraphy of the abitibi greenstone belt and the implications of an autochthonous development of the volcanic stratigraphy for exploration for syngenetic mineralization the abitibi greenstone belt is subdivided into seven discrete volcanic stratigraphic episodes on the basis of groupings of numerous u pb zircon ages of pre 2750 2750 to 2735 2734 to 2724 2723 to 2720 2719 to 2711 2710 to 2704 and 2704 to 2695 ma we present revised lithotectonic and or stratigraphic nomenclature using these time intervals including 1 isotopic inheritance in younger episodes which indicates that the older episodes 2750 2735 and 2734 2724 ma had greater extent than is presently seen 2 dikes feeding younger volcanic episodes 2706 ma cutting older volcanic units 2734 2724 ma and 3 2710 to 2704 ma mafic to ultramafic sills intruding the 2719 to 2711 ma episode changes to the nomenclature include the identification of pre 2750 ma volcanic episode supracrustal fragments in the northern and southern abitibi greenstone belt and subdivision of the 2719 to 2711 ma 2710 to 2704 ma and 2704 to 2695 ma episodes into lower and upper parts we present the results of this lithostratigraphic subdivision as the first geochronologically constrained stratigraphic and or lithotectonic map of the abitibi greenstone belt many of the volcanic episodes are intercalated with and capped by a relatively thin sedimentary interface zone dominated by chemical sedimentary rocks stratigraphic and geochronological analysis of these zones indicates discontinuous deposition with localized gaps of 2 to 27 m y between volcanic episodes the zones consist of up to 200 m of iron formation chert breccia heterolithic debris flows of volcanic provenance sandstone and or argillite and conglomerate modeling of the time required for deposition of the volcanic units based on rates of magma production in modern arc and plume environments is on the order of 103 to 104 years whereas the time interval between basalt rhyolite cycles is 106 years the sedimentary interface zones are therefore interpreted as condensed sections zones with very low rates of sedimentation in a basinal setting or zones with negligible rates of sedimentation marked by silicification of existing rock types the sedimentary interface zones are therefore considered submarine correlative conformities disconformities or unconformities separating the equivalent of group level stratigraphic and lithotectonic units the unconformity bounded stratigraphic model provides a new regional to deposit scale interpretive model for use in exploration for syngenetic mineralization

structure of the high grade opatica belt and adjacent low grade abitibi subprovince canada an archaean mountain front plutonic gneisses in the archaean opatica belt in canada record crustal scale wsw vergent i e longitudinal high temperature d1 ductile shearing similar structures occur in adjacent greenstone belts but only in narrow amphibolite facies zones near the base metavolcanics in the greenschist facies portions do not record penetrative d1 structures the greenstone belts are interpreted as allochthonous on the gneisses they form the uppermost d1 thrust sheets sse vergent i e approximately transverse d2 thrusting imbricated the opatica belt and formed a large antiform either a culmination or an antiformal stack in the southern opatica the imbricated opatica belt wedged under the northern part of the abitibi subprovince and created a tight syncline with nnw vergent d2 thrusts interpreted as backthrusts on its northern limb the opatica belt abitibi subprovince contact therefore resembles some phanerozic mountain fronts further southwards propagating imbrication of the crust beneath the abitibi subprovince created a s vergent foreland fold and thrust belt in the overlying greenstones high grade opatica gneisses and adjacent low grade abitibi greenstones contain complementary structural patterns and may therefore represent the internal and foreland parts of an archaean mountain belt similar in many respects to phanerozoic examples

comparison of eruptive and intrusive samples from unzen volcano japan effects of contrasting pressure temperature time paths abstract core samples from the conduit of unzen volcano obtained only 9 years after cessation of the 1991 1995 eruption exhibit important differences in physical characteristics and mineralogy and subtle differences in bulk chemistry from erupted samples these differences in the conduit samples reflect emplacement under a confining pressure where about half of the original magmatic water was retained in the melt phase maintenance at hypersolidus temperature for some unknown but significant time span and subsequent subsolidus hydrothermal alteration in contrast magma that extruded as lava underwent decompression to 1 atm with nearly complete loss of magmatic water and cooling at a sufficiently rapid rate to produce glass the resulting hypabyssal texture of the conduit samples while clearly distinct from eruptive rocks is also distinct from plutonic suites given the already low temperature of the conduit less than 200 c nakada s uto k yoshimoto m eichelberger j c shimizu h 2005 scientific results of conduit drilling in the unzen scientific drilling project usdp sci drill 1 18 22 when it was sampled by drilling this texture must have developed within a decade and perhaps within a much shorter time after emplacement the fact that all trace element concentrations of the conduit and the last emplaced lava of the spine 1300 m above it are identical to within analytical uncertainty provides strong evidence that both were produced during the same eruption sequence changes in conduit magma that occurred between emplacement and cooling to the solidus were collapse of vesicles from less than or equal to the equilibrium value of about 50 vol to about 0 1 vol continued resorption of quartz and reaction of biotite phenocrysts due to heating of magma prior to ascent by intruding mafic magma breakdown of hornblende and micro crystallization of rhyolitic melt to feldspar and quartz subsolidus changes were deposition of calcite and pyrite growth of sericite in anorthite rich zones of plagioclase and development of montmorillonite as an alteration product significant changes in bulk composition were depletion of mg fe and na and enrichment in c and s these changes were due mainly to the breakdown of hornblende and plagioclase and addition of carbonate and pyrite respectively the identical concentrations of rees in the conduit and surface lava are consistent with low water to rock ratios during alteration this suggests to us that despite convective hydrothermal removal of heat from the conduit chemical open system effects were limited to early loss of magmatic water and later addition of magmatic co2 and so2 and or h2s streaming up the conduit from deeper levels

the distribution of deformation in parallel fault related folds with migrating axial surfaces comparison between fault propagation and fault bend folding abstract in fault related folds that form by axial surface migration rocks undergo deformation as they pass through axial surfaces the distribution and intensity of deformation in these structures has been impacted by the history of axial surface migration upon fold initiation unique dip panels develop each with a characteristic deformation intensity depending on their history during fold growth rocks that pass through axial surfaces are transported between dip panels and accumulate additional deformation by tracking the pattern of axial surface migration in model folds we predict the distribution of relative deformation intensity in simple step parallel fault bend and fault propagation anticlines in both cases the deformation is partitioned into unique domains we call deformation panels for a given rheology of the folded multilayer deformation intensity will be homogeneously distributed in each deformation panel fold limbs are always deformed the flat crests of fault propagation anticlines are always undeformed two asymmetric deformation panels develop in fault propagation folds above ramp angles exceeding 29 for lower ramp angles an additional more intensely deformed panel develops at the transition between the crest and the forelimb deformation in the flat crests of fault bend anticlines occurs when fault displacement exceeds the length of the footwall ramp but is never found immediately hinterland of the crest to forelimb transition in environments dominated by brittle deformation our models may serve as a first order approximation of the distribution of fractures in fault related folds