microstructures and c axis fabrics indicative of quartz dissolution in sheared quartzites and phyllonites abstract quartzites sheared in low metamorphic grade shear zones that extend along the contact with migmatitic gneissic complexes in the quadrilatere ferifero region southeastern brazil show quartz microstructures indicating deformation by dissolution dissolution occurred adjacent to the foliation planes preferentially in quartz porphyroclasts oriented with their 0001 planes parallel to the foliation dissolution worked as an efficient mechanism to remove porphyroclast edges smoothing foliations and enabling strain accommodation both dissolution and crystal plasticity were competitive crystallographically controlled processes operating in different domains of the evolving microstructure dissolution occurred along the foliation planes while isovolume crystal plasticity and accompanying recrystallization operated essentially in the quartzose domains between folia phyllonites formed in the most strained domains of the shear zones fine grained quartz grains in phyllonites show uncommon c axis fabrics c axis oriented at low angles to the stretching lineation which were interpreted to form either by direct reprecipitation or by residual concentration of grains unfavourably orientated to undergo dissolution domainal c axis fabrics reflect a deformation partitioning path with increasing participation of solution transfer strengthening c axis maxima at low angles with the stretching lineation at the expense of crystal plastic processes during progressive phyllonitization

uplift and a possible moho offset across the dead sea transform abstract the east africa rifts and the red sea spreading center are characterized by uplifted shoulders and sunken median valleys the dead sea transform on the northern extension of the arabian african plate boundary has a similar morphological character despite its well documented strike slip motion to understand the rift morphology and the crustal structure beneath the transform we compiled a 320 km long gravity and topography profile perpendicular to the dead sea transform the gravity field and the topography in the region surrounding the profile are generally parallel to the trend of the dead sea transform justifying the two dimensional approximation of the analysis the gravity profile was modeled using constraints from seismic refraction borehole and surface geology data the observed gravity anomaly can be explained by the juxtaposition of two different sedimentary and crustal sections which have been offset by a 105 km left lateral displacement across the transform boundary suggesting a step in the depth to moho the existence of a significant density anomaly under the median valley is not required by the model the current elevation of the transform shoulders appears not to be compensated locally assuming a state of local isostasy prior to the development of the transform the magnitude of the uplift in the vicinity of the profile is estimated at 700 900 m with a half width of 100 125 km this topography uplift can be fitted equally well by models which assume either dynamic support or regional compensation it is suggested that if the source of the uplift is thermal it is located within the upper mantle since there is no requirement for a shallow density anomaly under the rift itself or in the crust nearby

geology and structure of the continental margin off northern israel and the adjacent part of the levantine basin abstract the continental margin off northern israel and southern lebanon is characterized by a narrow coastal plain in places it is absent a narrow shelf a narrow slope which is incised by numerous submarine canyons and by a complex topography of the adjacent deep sea levantine platform detailed seismic reflection surveys have revealed the development of the area since the late miocene during the messinian when the level of the mediterranean sea dropped the present continental slope area was exposed eroded and covered by thinly scattered sediments in the deep basin evaporite bearing series accumulated reaching 1 km in thickness about 60 km offshore during the pliocene quaternary the area was covered by a fine clastic sequence up to 1 5 km thick that forms the present continental margin basinward gravitational slumping of these sediments over the messinian evaporites which acted as a lubricant resulted in a complex topography and many shore parallel rootless growth faults along the base of the continental slope and the adjacent deep sea young faults which are exposed in northern israel and extend seaward comprise the most important structural feature of the study area these faults were active during the pliocene and quaternary possibly also during the miocene the major nw trending young yagur carmel fault and e w trending rosh hanniqra fault extend to the base of the continental slope where they converge enclosing the complex western galilee graben the relief of the base of the pliocene quaternary sequence was affected by motions of these faults and of smaller faults inside the graben farther seaward a horst like block is developed along the extension of the carmel fault still farther basinward there is a group of diapiric ridges trending nw to e w they were formed by flowage of messinian evaporites in some cases these ridges seem to be aligned along underlying faults this group of diapirs is unique in the area the diapir ridges are interpreted as expressions of deeply rooted faults

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

determination of escarpment age using morphologic analysis an example from the galilee northern israel we used topographic and structural data and very limited age control to perform quantitative morphometric analyses and to determine relative ages of escarpments bounded by late cenozoic normal faults in the galilee israel the galilee is an extensional zone composed of a series of uplifted and tilted blocks forming large escarpments built mainly of carbonate rocks two parameters used to discriminate tectonic stages are the ratio between the height of the escarpment and the total stratigraphic displacement l and the degree of concavity of escarpment slopes relative to a reference slope the only dated reference slope is mount tur9an 300 m high and formed by the tur9an fault system which has a total stratigraphic displacement of 625 m a basalt flow that delimits the age of the tur9an escarpment is dated to 4 23 0 23 ma and displaced 300 m which is identical to the present day topographic expression of this escarpment the l value for this escarpment is 0 5 the tur9an fault system was active prior to 4 23 ma at slow uplift rates that enabled erosion to maintain the gentle slope over which the basalt flowed increased offset rates following the basalt extrusion led to the formation of the escarpment the preservation of the basalt at the top of the escarpment indicates that erosional lowering of the upper surface of the tur9an block has been minor since its formation the l values indicate two stages of uplift an early stage during which offset rates were probably low enough that they did not form topography and a later stage that formed topography which is preserved the timing of the change in displacement rates from a slow continuous stage to a fast topography forming stage was determined by comparing the shape of the dated slope of tur9an to that of other slopes we conclude the following 1 generally the topographic profiles of different parts of each individual escarpment have similar shapes indicating similar ages 2 escarpments having slopes that are more concave or convex than the reference tur9an escarpment are older or younger than 4 ma respectively and 3 the galilee escarpments did not form simultaneously a few escarpments were already major morphologic features by the early to middle pliocene whereas the rest formed during the late pliocene morphometric analysis is a useful method for studying the geologic history of a landscape controlled by normal fault uplift and characterized by the absence of sediment deposition and where carbonate dissolution is the main erosional process this and similar approaches can be used to discriminate tectonic stages and understand the relationship between tectonic activity and surface processes in other extensional regions

permian early mesozoic tectonism and continental margin formation in israel and its implications for the history of the eastern mediterranean summary the early mesozoic tectonic reorganization of the tethys region also affected the levant area here two processes were superimposed a the pattern of long wavelength vertical motions of the arabo nubian platform changed in the late permian when israel and nearby areas began to subside b rifting occurred in this subsiding area probably in several phases late anisian and ladinian carnian norian and liassic differential movements reached 2 3 km and magmatism occurred in the liassic and perhaps also in the triassic the tectonism was strongly felt up to 50 km landward of the present coast the crust was thinned and modified under the present continental margin and in the main rifts passive margin conditions were established in late liassic times over the previously faulted area later in the jurassic a carbonate shelf was constructed along this subsiding margin its basinward edge was 1 1 5 km high which shows that the adjacent se mediterranean was already a deep sea hence this basin and its passive margin are considered to have been shaped by the early mesozoic rifting which is recognized in israel the rifting process probably signifies oblique separation of the tauride block from the levant part of gondwana

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part i geologic relations and formation of the vein system the sigma deposit consists of an archean gold bearing vein system in metavolcanic rocks intruded by an irregular body of porphyritic diorite both affected by regional deformation and in turn cut by younger undeformed feldspar porphyry dikes the veins cut all rock types and are composed chiefly of quartz and tourmaline with minor amounts of carbonates pyrite chlorite scheelite and free gold they were emplaced during or after a greenschist facies metamorphism postdating the intrusion of feldspar porphyry dikes the veins were not significantly affected by any subsequent metamorphism or tectonism two principal types of veins occur in the mine subvertical veins and subhorizontal veins they are contemporaneous and cogenetic subvertical veins occur within steeply dipping east west trending ductile shear zones along which reverse subvertical displacements have taken place the veins occupy openings created by overriding of undulations and irregularities of foliation and slip planes during progressive shearing movements within the shears subhorizontal veins occupy extensional fractures which developed between ductile shear zones preferentially in the more competent host rocks these veins were formed by one or several episodes of open space filling geologic relations indicate that the mineralized veins were emplaced progressively in a dynamic tectonic environment during and shortly after the formation of ductile shear zones a structural analysis has shown that the ductile shear zones and the two vein types can be related to a single strain ellipsoid of the following orientation the z axis trending north south and horizontal the y axis plunging 10 degrees west and the x axis plunging 80 degrees east the deformation responsible for the generation of ductile shear zones and emplacement of the veins is ascribed to a late north south trending compression postdating regional deformation

near equatorial ctd observations at 85 w in october 1982 ctd data collected about the equator along 85 w between october 8 and 12 1982 are used to investigate stratification changes in the upper 1 km associated with the 1982 83 el nino with respect to the thermal field observed in november 1981 virtually the entire section exhibited downward displacements in the upper kilometer of the water column observed displacements at the depth of the mean thermocline were large 150 m and relatively symmetric about the equator displacements around 1 km depth were near zero this stratification change appears to have been produced by a zonal convergence of mass at temperatures above 15 c with divergence below least square modal decompositions of the vertical displaced profiles revealed significant contributions from modes 1 and 2 with meridional structure consistent with kelvin waves the observations thus support current theories that relate el nino onset in the eastern pacific to anomalous wind forcing in the west

stress field fluctuations along the dead sea rift since the middle miocene the dead sea transform dst is the suture between the african and the arabian plates both of which subduct northward under the eurasian plate the collision of these plates with eurasia and their relative motion are the source for their internal deformation especially in the vicinity of the dead sea transform geological observations indicate that two distinct paleostrain regimes operated adjacent to the dead sea rift and in the sinai israel subplate 1 wnw shortening less than 10 and nne extension beginning in the turonian is associated with the development of the syrian arc fold belt and attributed to the syrian arc stress field sas and 2 middle miocene to recent nnw shortening and ene extension associated with the 105 km sinistral displacement along the dead sea transform and the opening of the red sea is attributed to the dead sea stress field dss it was originally suggested that the sas terminated during the middle miocene with initiation of the dss however trend and age analysis of many structures shows that formation of sas compatible structures continued after the middle miocene up to the recent in some middle miocene and younger rocks structures such as faults dikes volcanic lineaments and tectonic stylolites compatible with both stress fields were reported in a few locations structures compatible with both stress fields crosscut each other it is suggested that the movements which resulted in the development of the syrian arc and other sas compatible structures are continuing to the recent and that dss movements are superimposed upon them the overlapping of sas and dss structures adjacent to the dst results from spatial and temporal fluctuations in the overall stress state we propose that such variations could be caused by the superposition of large earthquake stress drops associated with movements along the dst on a steady background plate scale stress regime associated with the sas thus dss compatible structures should form in preseismic activity periods when dst related elastic strain is high on the other hand the sas compatible structures should form during interseismic activity times subsequent to large local stress release along the dst

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

the structure of the dead sea basin abstract the dead sea basin is located along the left lateral transform boundary between the arabian and sinai plates its structure and history are known from surface geology drilling seismic reflection and other geophysical data the basin comprises a large pull apart almost 150 km long and mostly 8 10 km wide which is flanked by a few kilometres wide zones of normal faulting the basin formed at about 15 ma or earlier close to the beginning of the transform motion and it reached about half its present length before the end of the miocene a strong negative gravity anomaly records a thick sediment basin fill 5 km under half its length reaching a maximum of 10 km the fill includes a few km of salt ca 6 4 ma which forms several diapirs at any one time large parts of the basin subsided simultaneously but the site of fastest subsidence seems to have shifted northward sedimentation rates reached at least hundreds of metres per million years or more in the miocene and 1 km myr in later periods the basin structure is dominated by longitudinal faults intrabasinal faults which delimit the pull apart and which are the extensions of the major strike slip faults north and south of the basin and normal faults which extend along the basin margins the latter faults express a small component of extension across the basin whereas the pull apart resulted from the much larger lateral motion along the basin in addition transverse faults divide the pull apart into several segments with somewhat different histories the pull apart grew by becoming longer parallel to the transform motion at shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed the crust under the basin was stretched and thinned during basin lengthening which caused its subsidence basin formation was accompanied by uplifting of its flanks by 1 km sparse igneous activity occurred along the basin and its flanks its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform

tectonic processes in offshore northern israel and the evolution of the carmel structure abstract the carmel structure in northern israel is an elevated tilted block that extends from the land into the continental shelf and divides the levant continental margin into two distinct provinces its axis trends at a high angle to the levant margin and deflects mesozoic and cenozoic sedimentary and basement rocks the carmel structure is probably older than the levant margin itself and has been through several phases of activity most of the multichannel seismic profiles in the offshore of northern israel were reprocessed through time migration and then interpreted the resultant maps combined with gravimetric magnetic and bathymetric maps show a complex tectonic picture of the carmel structure and its vicinity four evolutionary stages can be recognized in this area a early mesozoic rifting along the present levant margin we speculate that the carmel was at that time a triple junction a thick mesozoic volcanic and carbonatic section of more than 6500 m indicates rapid subsidence probably accompanied by normal faulting b folding along the nne axis this is probably part of the syrian arc compressional system which was active from the late cretaceous until the eocene normal faults of the previous stage were probably reactivated becoming reverse faults c left lateral strike slips faulting this formed a north west fault system which resulted in a clockwise rotation of segments of the fold axis and was active from the late miocene to early pliocene d a tensional tectonic regime prevails since the pliocene and is probably still active at present the well pronounced kishon graben which extends from land to the continental shelf was formed during this period the first two stages are of regional extent whereas the latter stages are the reslt of local modification of the regional stress fields

morphological and structural relations in the galilee extensional domain northern israel the lower galilee and the yizre el valley northern israel are an extensional domain that has been developing since the miocene prior and contemporaneously to the development of the dead sea fault dsf it is a fan shaped region bounded in the east by the n s trending main trace of the dsf in the north by the bet kerem fault system and in the south by the nw se trending carmel fault the study area is characterized by high relief topography that follows fault bounded blocks and flexures at a wavelength of tens of km a synthesis of the morphologic structural relations across the entire galilee region suggests the following characteristics 1 blocks within the lower galilee tilt toward both the southern and northern boundaries forming two asymmetrical half graben structures opposite facing and oblique to one another 2 the lower galilee s neighboring blocks which are the upper galilee in the north and the carmel block in the southwest are topographically and structurally uplifted and tilted away from the lower galilee 3 the southern half graben along the carmel fault is topographically and structurally lower than the northern one combining structural and geological data with topographic analysis enables us to distinguish several stages of structural and morphological development in the region using a semi quantitative evolutionary model we explain the morpho structural evolution of the region our results indicate that the galilee developed as a set of two isostatically supported opposite facing half grabens under varying stress fields the southern one had started developing as early as the early miocene prior to the formation of the dsf the northern and younger one has been developing since the middle pliocene as part of the extension process in the galilee elevation differences between the two half grabens and their bounding blocks are explained by differences in isostatic subsidence due to sedimentary loading and uplift of the northern half graben due to differential influences of the regional folding d 2003 elsevier b v all rights reserved

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

intraplate deformation by block rotation and mesostructures along the dead sea transform northern israel combined analysis of mega and meso structures yield the strain inferred stress and tectonic history of the margin of the sinai sub plate in northern israel along the dead sea transform three major stress regimes were developed and have affected the region since the middle miocene one is regional and controlled the left lateral shear along the dead sea transform this one has been active since post early miocene is characterized by 1 trending c 345 and deformed the plate margin by horizontal shear and contemporaneous block rotation this style of deformation is similar to simple shear the second one was local and may be subdivided into distinct stress and strain domains it was characterized by 1 trending e w and 3 trending n s which produced a conjugate set of strike slip faults the region underwent n s elongation by horizontal shear and block rotation similar to the pure shear mechanism this stress regime was active in late miocene to early pliocene time the third and youngest stress regime is extentional with 1 vertical and 3 oriented n s this one has been active since post middle pliocene time producing e w normal faults and minor n s elongation the second and third stress regimes show local distribution and developed as a consequence of the bent geometry of the transform vis a vis the plate slip vector finite element and photoelastic models predict the development of local stress fields and elongation of the plate margin parallel and subparallel to the transform plate boundary the strain of the plate margin in northern israel and southern lebanon indicate remarkable elongation parallel to the dead sea transform by a factor of 1 5 2 1 since the miocene this process of intraplate deformation and the consequent strain is unique to the parts of the plate margin which are adjacent to the bent segment of the transform

second and first baroclinic kelvin modes in the equatorial pacific at intraseasonal timescales 1 topex poseidon sea level and time series from the tao tropical atmosphere ocean array of moorings over 1992 1999 are used to investigate the spatiotemporal characteristics of equatorial kelvin waves in the pacific at period shorter than 180 days spectral analyses show high oceanic energy in two separate bands of period around 70 days and 120 days signals are coherent in both bands all along the equator ocean general circulation model ogcm simulations forced by different wind stress fields are also analyzed and exhibit the same features observed and modeled sea level dynamic height and 20 c isotherm depth band pass filtered around 70 days show an eastward propagation at phase speed of 2 4 2 9 m s 1 typical of the first baroclinic kelvin mode the meridional and vertical structures of the equatorial waves at the onset of the 1997 el nino are also those expected for a first kelvin mode at 120 day period phase speeds meridional and vertical structures are closer to those expected for a second baroclinic mode both modes are nevertheless present in the two frequency bands a simple kelvin wave model shows that the wind at 120 day period seems to force the kelvin waves at the same period however the predominance of second baroclinic mode at 120 day period cannot be explained solely by the characteristics of the wind ogcm simulations rather suggest the importance of internal oceanic processes such as vertical redistribution of energy from first to second baroclinic mode as the waves propagate eastward model outputs over 1984 1999 indicate that these equatorial kelvin waves at 70 and 120 day period may have an effect on el nino since they seem to be stronger at its onset

a single late orogenic permian episode of gold mineralization in the hodgkinson province north queensland australia quartz hosted gold deposits in the hodgkinson province north queensland are widely distributed with the most heavily endowed areas comprising three separate spatially distant goldfields the west normanby goldfield the palmer river goldfield and the hodgkinson goldfield relationships among quartz vein and shear hosted deposits in each of the three goldfields indicate that the introduction of gold bearing quartz displays consistent structural timing relative to a regionally recognized deformation history gold was emplaced during the waning stages of d4 the main contractional phase of the permian triassic hunter bowen orogeny mineralization and structures have been structurally timed relative to isotopically dated plutons of the spatially associated syn d4 whypalla supersuite indicating emplacement of the mineralization in the early permian or later emplacement of gold bearing quartz veins in the fossiliferous permian normanby formation in the north of the province supports this contention the permian age is younger than the originally published carboniferous 300 ma age for gold mineralization in the hodgkinson province fluid generation and gold transport were related to regional scale devolatilization during province wide metamorphism the final distribution of fluids and contained gold was controlled by faults produced during the hunter bowen orogeny and by major late devonian shear zones that were reactivated during this orogeny heat from synchronously emplaced d4 granites focused enhanced fluid flow into spatially associated dilatant structures in these faults

seismicity of the eastern mediterranean region perspective from the sinai subplate we conducted a comprehensive study of the seismicity of the eastern mediterranean and examined its relation to the regional plate tectonics based on various published catalogs we have constructed a new list of ml 4 earthquakes which were recorded during the years 1900 1991 and represents most of the seismic moment released in the area over this period b values are 1 02 1 0 and 1 07 for the whole sinai subplate the dead sea transform and the cypriot arc respectively seismic efficiency of the dead sea transform is very low about 7 stressing the role of aseismic deformation in that plate border most of the major and moderate events ml 5 occur in belts associated with the geologically documented borders of the sinai subplate the cypriot convergent arc in the north the dead sea transform in the east and the rift of suez in the southwest the latter like the gulf of eilat aqaba was considered aseismic during the first half of the century the northwestern border however could not be delineated low level activity appears within the subplate especially north of latitude 32 n reflecting the breakdown of this part of sinai as it approaches the cypriot convergence zone though most of the seismic moments tend to concentrate along the subplate borders some moderate activity spreads out in wide belts which reflect the complexity of deformation accompanying motion along the subplate borders

intrusion related high temperature gold quartz veining in the cosmopolitan howley metasedimentary rock hosted gold deposit northern territory australia in the proterozoic cosmopolitan howley gold deposit northern australia quartz vein hosted gold mineralization occurs predominantly within 50 m of the noncarbonaceous footwall of carbonaceous slates although abundant veins farther away from or within carbonaceous slate are barren except for hydrofracture stock works in the hinge zone the gold bearing quartz veins qv1 are bedding concordant and occur in hornfels and slate in the steeply dipping fold limbs of the howley anticline the qv1 veins formed near the peak of contact metamorphism 550 degrees 620 degrees c and 240 200 mpa following the intrusion of the cullen granite batholith the vein alteration assemblage is k feldspar biotite andalusite or cordierite and mineralization was accompanied by large scale potassium metasomatism whereas sodium and calcium were leached from the country rocks the qv1 veins were overprinted first by superposed folding and then by reverse faulting later transpressional strike slip faulting was accompanied by extensive retrograde alteration the precipitation of sulfide lenses delta 34 s arsenopyrite 0 3 to 4 8 quartz veins qv2 with subeconomic gold enrichments and barren pegmatitic veins qv3 the involvement of a magmatic fluid in ore genesis at the cosmo howley deposit is indicated by 1 high fluorine contents in biotite from the alteration selvages of the gold quartz veins qv1 f 5 573 6 616 ppm 49 000 ppm at mt shoobridge 7 km west 2 mutual crosscutting relations of gold quartz veins with aplite dikes 3 the location of the deposit above i type granite at a vertical distance of less than 2 km most likely or 1 km and 4 the high salinity of the mineralizing fluid as estimated from the cl content of biotite in the alteration halos of the veins a magmatic derivation of the sulfur in the auriferous sulfides is consistent with isotopic data 0 3 to 7 2 5a4s calculated oxygen isotope compositions of the fluids which precipitated the successive generations of quartz veins qvi delta 18 o sub h 2 o 13 6 qv3 delta 18 o sub h 2 o 11 8 indicate that the isotopically heavy country rock chert nodules delta 18 o or 18 5 was infiltrated by an isotopically light

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

digital topography and bathymetry of the area of the dead sea depression abstract the dead sea depression occupies the central part of that segment of the syrian african rift extending from the mountains of southern lebanon to the arava valley north of the gulf of aqaba on the red sea the lowest continental feature in the world it encloses the dead sea whose surface now lies at about 409 m this shrunken sea consists of a shallow southern basin occupied by evaporation pans and a northern basin 50 km in length by 13 17 km in width with a flat floor some 731 m below msl the depression is asymmetric with the mountains to the east being up to 500 m higher the closed depression has two outlets one at 60 5 m altitude into the mediterranean via the jezreel valley near afula and a second into the red sea at about 200 m altitude in the arava valley a digital terrain model dtm based upon the local 1 50 000 scale topographic maps and modern bathymetric surveys gives elevations to decimeter resolution on a grid with 25 m spacing when visualized as shaded relief or in coloured hypsometric format the dtm graphically shows the overall morphology and its many features these include the local tectonics from the major boundary faults to the associated subsidiary faults and lineaments and their possible relationships with the incised canyons offshore also clearly visible are the volcanic cones on the golan heights the coast paralleling kurkar ridges and the halokinetic disruptions to the deep offshore topography the dtm was used to compute a hypsometric curve for the closed depression from 731 m to 60 m the maximum area and volume of a lake extending to the afula spillway would be 5985 km 2 and 1602 km 3 respectively inflection points were observed at 715 m where the dead sea s flat bottom meets its steep flanks at 385 m where the northern basin meets the flat floor of the southern basin and surrounding plain at 228 with the step up to the basin of the sea of galilee and at mediterranean sea level

structural analysis and vein episode of the penjom gold deposit malaysia implications for gold mineralisation and tectonic history in the central belt of malaysia abstract gold mineralisation at the penjom gold deposit in the central belt of peninsular malaysia is dominantly hosted in structurally controlled quartz carbonate veins that display a variable degree of overprinting events under a ductile brittle regime mineralised veins are categorised into two main episodes fold and thrust related veins mainly comprised of bedding and penjom thrust parallel shear veins and associated extension veins developed during a d2 event in addition ne to nne trending splays and penjom thrust parallel reverse dextral and locally nnw to ns reverse sinistral faults overprint earlier vein events forming a new episode of extensional veins during d3 event mostly at the fault contacts of intrusives either as shallow dipping or vertical sheeted stockwork or brecciated veins at least two episodes of faulting d4 d5 are evident which postdates the main episodes of veining and mineralisation this is indicated by a series of late episodes ns trending sinistral and oblique to normal faults which transect and displace the penjom thrust and the folded footwall sequence at low angles and responsible for intensive vein deformation along the penjom thrust and displacement of ore body structural interpretations of mineralised veins suggest that the veins were formed under a compressional to transpressional regime with later post vein displacement in a transtensional to extensional regime vein formation in response to deformation observed at penjom reflects regional structural deformation within the central belt of peninsular malaysia and specifically along the bentong raub suture zone

the vertical structure of the zonal pressure gradient in the eastern equatorial pacific ctd data from the epocs and norpax experiments were used to construct a mean zonal pressure gradient profile between 110 w and 150 w for the 1979 to 1981 pre el nino time period the mean zonal pressure gradient referenced to 100 dbar had a value of 4 5 10 7 m s 2 at the surface and decreased to within two standard errors of zero at 200 dbar below this depth the mean was not significantly different from zero deviations from this mean were not related to fluctuations of the zonally averaged zonal wind stress between 150 w and 110 w rather the largest deviations in the boreal springs of 1979 and 1980 appeared to be associated first with vertical mode kelvin wave pulses propagating eastward along the equator the 1979 81 mean profile was also used as a reference to examine variations in zonal pressure gradient during the 1982 83 enso event the sea surface was more sharply sloped upward from the east to west in april and september 1982 before arid near the beginning of the event the surface slope was below normal in april and october 1983 vertical profiles of the zonal pressure gradient deviations showed large high vertical mode contributions during the vent than in the prevent samples

upper equatorial pacific ocean current and salinity variability during the 1996 1998 el nino la nina cycle the recent el nino la nina cycle exhibited striking patterns of current and salinity variability in the upper equatorial pacific ocean this evolution is described from mid 1996 through 1998 using a remarkable data set of 35 meridional conductivity temperature depth ctd acoustic doppler current profiler adcp sections along with buoy data the sections nominally from 8 s to 8 n between 165 e and 95 w were occupied over the course of 27 months a wide range of current variability was sampled with currents that appeared or disappeared some time during the cycle including an equatorially trapped eastward surface current the equatorial undercurrent the northern branch of the south equatorial current and the north equatorial countercurrent basin wide interannual changes in upper ocean and pycnocline zonal transports were as large as 64 32 106 m3 s 1 changes in the salinity structure included a deep and fresh mixed layer in the central equatorial pacific that built up during the el nino and was then disrupted by upwelled salty water with the onset of la nina a very fresh mixed layer observed in the eastern equatorial pacific late in the el nino and a reduction in the strength of the meridional equatorial salinity gradient within the pycnocline to one third of the usual value during the el nino finally the zonal transports above the thermocline from 5 s to 5 n were well correlated with the rate of change of warm water volume west of the individual ctd adcp sections

syn orogenic extensional and contractional deformation related to granite emplacement in the northern tasman orogenic zone australia abstract the hodgkinson province of the northern tasman orogenic zone comprises uniform low grade metasediments of mid palaeozoic age that host numerous permian granite intrusions three widely developed sequential deformations d2 d4 are recognized on the basis of penetrative fabrics and folds which show clear regionally consistent overprinting relationships d3 and d4 were contemporary with phases of granite emplacement as shown by relationships of s3 and s4 microstructures to porphyroblasts which grew in thermal aureoles adjacent to intrusive contacts granitic dyke relationships with s3 and the deflection of s3 and s4 foliation trajectories around plutons support this view granites of d3 and d4 affiliation have a close spatial relationship and strong geochemical similarities suggesting that they were closely associated in time isotopic dating of granites of d4 association show that this deformational phase represents the hunter bowen orogeny which has been recognized as the terminal permian triassic episode of tectonism for the eastern sector of the tasman orogenic zone d3 fabrics are best developed in zones of enhanced metamorphic grade and are typically subhorizontal or of gentle inclination and associated with recumbent folds when not affected by subsequent deformation d3 is attributed to a phase of tectonism linked to the hunter bowen orogeny but preceding the main episode of compression uplift above tracts of rising magma combined with the thermal weakening of crustal material and the reduction of compressive stress due to plate convergence sponsored widespread ductile extension at a high crustal level the zone of failure was a discontinuous carapace above the magmatic front d4 is attributed to the main episode of the hunter bowen orogenic compression and involved crustal shortening with the imposition of upright structures and the widespread emplacement of granite s3 foliation surfaces have been reoriented in the vicinity of d4 granite bodies which behaved as rigid bodies during d4 compression the preparation of crustal pathways by d3 granite was utilized by granites of the d4 generation with the hodgkinson province displaying an intimate interplay of magmatism stress regime and structural evolution over a time period of perhaps 15 20 ma

quaternary stratigraphy and paleogeography of the galilee coastal plain israel the quaternary deposits in the galilee coastal plain comprise alternating calcareous sandstone red loam dark clay and uncemented sand the calcareous sandstone in the lower part of the sequence represents a pliocene to early pleistocene marine transgression and is covered unconformably by the late quaternary sequence the base of this sequence has an estimated age of 500 000 yr it is covered unconformably by marine calcareous sandstone in the west which represents the global high sea level stand of isotope stage 7 1 and is known as one of the tyrrhenian events in the mediterranean area the overlying members represent the low sea level stand of stage 6 the first a red paleosol indicating a relatively wet phase and the second an eolianite unit representing a drier phase the eolianite forms longitudinal subparallel ridges that formed contemporaneously the overlying marine sandstone which contains one of the diagnostic fossils of the tyrrhenian events the gastropodstrombus buboniuslmk accumulated during the global high stand of stage 5 5 the last glacial period left no sedimentary record the holocene is represented by a marine clay unit that is covered by sand the present study establishes a complete and detailed chronostratigraphic sequence for an eastern mediterranean beach which contains the gastropods buboniuslmk s buboniuson the galilee coast is attributed to stage 5 5 and therefore establishes an east west mediterranean correlation which can be used for linking mediterranean events to paleo sea levels and global climate changes

grain boundary microstructures in micaceous quartzite significance for fluid movement and deformation processes in low metamorphic grade shear zones observation by scanning electron microscopy of a sericitic quartzite from a low grade 1 cm wide shear band developed from an originally pure quartzite revealed a nonconnected intergranular porosity the isolated pores occur principally on quartz quartz grain boundaries pores surrounding isolated mica flakes show very irregular geometries reflecting a highly unstable disequilibrium crystal fluid interface but regular frequently crystallographic pore shapes predominate in other grain boundaries statistical analysis reveals that the pores are principally concentrated on grain boundaries oriented perpendicular to the two foliations developed within the shear band i e grain boundaries at 45 and 90 to the shear band boundaries indicating that the fluid phase occupied extensional sites relative to both the overall and local scale of one microlithon strain ellipsoids there is a strong spatial relationship between interfacial porosity and the presence of mica with the most porous grains occurrin

utilization of pre existing competent and barren quartz veins as hosts to later orogenic gold ores at huangjindong gold deposit jiangnan orogen southern china most if not all orogenic gold deposits form during the late stages of deformation in some cases there is barren pre mineralization hydrothermal alteration which may be part of a single progressive hydrothermal event or a temporally distinct event relative to deposition of gold at the huangjindong orogenic gold deposit in the jiangnan orogen of southern china there are two phases of vein generation the earlier of which is largely barren structural analysis petrography mineralogy and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms gold mapping of different generations of gold bearing sulfides reveal the relationship between different phases of hydrothermal alteration and quartz veins pre existing barren and brittle quartz veins which are controlled by tight folds and thrust faults provide favorable competent hosts for later overprinting by gold bearing ore bearing fluids that infiltrated during ongoing reverse sinistral fault movement these overpressured fluids caused hydrofracturing to complete brecciation of segments of the earlier quartz veins and associated pre existing breccias with deposition of auriferous quartz sulfide veins and breccia cements or matrices within them although fluid inclusion data are non definitive fluid pressure fluctuations are interpreted to have resulted in phase separation within the ore fluid which was primarily responsible for destabilization of gold complexes and deposition of native gold with other invisible gold bearing ore related sulfides formed by sulfidation reactions in hydrofractures and breccia matrices thus competent barren quartz veins in fold thrust belts may locally host superimposed gold mineralization and provide favorable targets for gold resources

episodic metamorphic reactions during orogenesis the control of deformation partitioning on reaction sites and reaction duration textural unconformities or truncations are common in porphyroblasts with complex inclusion trails they reflect cycles of successive foliations that develop against competent porphyroblasts during orogenesis and are preserved by successive growth increments their truncational character results from shear and dissolution along a particular foliation generating a differentiated crenulation cleavage the increment of porphyroblast growth that follows a textural unconformity may or may not mark a significant compositional change depending on the amount of movement of the rock through p t space between cleavage forming events although historically interpreted to result from a significant metamorphic hiatus most textural unconformities indicate that the reactions involved in the formation of these minerals are episodic during continuous prograde metamorphism starting and stopping as a function of the stage of crenulation of the matrix foliation and the pattern of deformation partitioning such episodic reaction behaviour can only occur for multivariant reactions or successive but different univariant reactions the reason why garnet is the most common porphyroblast to exhibit evidence for episodic reactions is probably the fact that it grows by multivariant reactions over a much wider p t range than most other common porphyroblast phases porphyroblast growth is micrometasomatic it is episodic because a significant reduction of strain occurs within domains of progressive shortening each time continuous progressive shearing domains form on their margins this stops microfracture development across the progressive shortening domains thereby preventing rapid access and interaction of fluid ions and complexes with porphyroblast boundaries shifting patterns of deformation partitioning and resulting small scale juxtaposition of different compositional layers spreads the duration and location of multivariant reactions and causes differential timing of porphyroblast growth along a particular stratigraphic horizon it may also locally preserve metastable metamorphic assemblages in regionally metamorphosing deforming pelites near simultaneous cessation of porphyroblast growth on all rims once continuous differentiated progressive shearing domains have formed nearby precludes fluid recirculation as a significant process for removal of material during cleavage development alternatively diffusion of simple molecules and dissociated ions along actively shearing and micro gaped phyllosilicates with recomplexing in fluid filled microfractures readily explains the control of deformation partitioning on reaction site and reaction duration

pyrite textures and compositions from the zhuangzi au deposit southeastern north china craton implication for ore forming processes the zhuangzi au deposit in the world class jiaodong gold province hosts visible natural gold and pyrite as the main ore mineral making it an excellent subject for deciphering the complex hydrothermal processes and mechanisms of gold precipitation three types of zoned pyrite crystals were distinguished based on textural and geochemical results from epma sims sulfur isotopic analyses and nanosims mapping py0 has irregular shapes and abundant silicate inclusions and was contemporaneous with the earliest pyrite sericite quartz alteration it has low concentrations of as 0 0 3 wt au and cu py1 precipitated with stage i mineralization shows oscillatory zoning with the bright bands having high as 0 4 3 9 wt au and cu contents whereas the dark bands have low contents of as 0 0 4 wt au and cu the oscillatory zoning represents pressure fluctuations and repeated local fluid phase separation around the pyrite crystal the concentration of invisible gold in py1 is directly proportional to the arsenic concentration py1 is partially replaced by py2 which occurs with arsenopyrite chalcopyrite and native gold in stage ii the replacement was likely the result of pseudomorphic dissolution reprecipitation triggered by a new pulse of au rich hydrothermal fluids the 34s values for the three types of pyrite are broadly similar ranging from 7 1 to 8 8 suggesting a common sulfur source fluid inclusion microthermometry suggests that extensive phase separation was responsible for the gold deposition during stage ii mineralization uranium pb dating of monazite constrains the age of mineralization to ca 119 ma coincident with a short compressional event around 120 ma linked to an abrupt change in the drift direction of the subducting pacific plate

tectonic analysis of the dead sea rift region since the late cretaceous based on mesostructures we have measured the orientations of small faults slickensides tectonic stylolites vein with secondary mineralization small folds and dikes in israel and sinai these structures are indicators of paleo stress or strain and provide the pattern of tectonic deformation data were collected at 130 stations most with tens of separate measurements most stations showed consistent deformation stations were located on exposures ranging from precambrian crystalline rocks to pleistocene sediments we have defined two tectonic stress fields each relatively uniform in both time and space one stress field with dominating maximum horizontal compression trending w to wnw in the late cretaceous to eocene rocks in the folds and plateaus west of the dead sea rift the second field with dominating horizontal extension trending e to ene in all rocks inside the rift and proximal thereto the first stress field is called the syrian arc stress and the second is called the dead sea stress a change in style of tectonic deformation which corresponds to the two stress fields is manifested also in the major structures in israel the late cretaceous to neogene deformation is characterized by long wavelength folds and monoclines whereas the neogene to recent deformation is characterized by normal and strike slip faults and volcanic activity

crusader castle torn apart by earthquake at dawn 20 may 1202 the crusader castle of vadum jacob an outpost overlooking the jordan river was deformed during a destructive earthquake triggered by motion along the dead sea transform the m 7 earthquake occurred at dawn 20 may 1202 and offset the castle walls by 1 6 m this exceptional precision in dating and estimating displacement was achieved by combining accounts from primary historical sources by excavating the dead sea transform where it bisects the castle and by dating faulted archaeological strata the earthquakes of october 1759 and or january 1837 may account for the remaining 0 5 m out of a total 2 1 m of offset our study exploits the potential embodied in interdisciplinary historical archaeological geological research and illustrates how detailed histories of seismogenic faults can be reconstructed

crustal structure of northern israel abstract in the course of a seismic refraction wide angle reflection experiment in the eastern mediterranean an east west reversed refraction profile was recorded onshore northern israel the purpose of the line was to obtain reliable velocity and structural information about the crust in this area in addition a multi coverage reflection profile was shot over part of the refraction profile the results indicate that the crust in northern israel is a high velocity continental crust considerably thinner than the crust to the south the reflection profile indicates an unusually reflective upper crust and a transparent lower crust similar to those recorded at a number of compressional belts the overall results confirm the presence of a crust which is markedly different from that encountered to the south the provenance of which is probably very different

displacement history of a limestone normal fault scarp northern israel from cosmogenic 36cl the abundance of cosmogenic 36 cl measured in 41 limestone samples from a 9 m high bedrock fault scarp allows us to construct the 14 kyr fault displacement history of the nahef east normal fault northern israel 300 m above sea level n33 latitude the nahef east fault is one of a series of fault scarps located along the 700 m high zurim escarpment a major geomorphic feature samples at the top of the scarp have the highest nuclide concentrations 79 x 10 4 atoms g rock 1 samples at the base have the lowest 11 x 10 4 atoms g rock 1 using chemical data from the samples nahef east fault scarp geometry and surface and subsurface production rates for the 36 cl producing reactions we have constructed a numerical model that calculates 36 cl accumulation on a scarp through time given a series of unique displacement scenarios the resulting model 36 cl concentrations are compared to those measured in the scarp samples faulting histories that result in a good match between measured and modeled 36 cl abundances show three distinct periods of fault activity during the past 14 kyr with over 6 vertical meters of motion occurring during a 3 kyr time period in the middle holocene smaller amounts of displacement occurred before and after the period of most rapid motion the episodic behavior of the nahef east fault indicates that the average displacement rate of this fault system has varied through time

biotite porphyroblast nucleation and growth control by microfracture of pre existing foliations in schists in the robertson river metamorphics australia a macroscopic fold formed during the fourth deformation d 4 in the robertson river metamorphics north queensland australia growth of biotite garnet staurolite and andalusite porphyroblasts also occurred synchronous with d 4 only biotite porphyroblasts have formed preferred alignments across the fold and they define two dominant orientations the more common is parallel to d 4 fold axes which is also parallel to d 1 d 2 and d 4 intersection lineations the other varies up to 90 from this within the d 4 axial plane mineral elongation lineations do not reflect the extension direction of the deformation in which they formed d 4 but are a function of pre existing anisotropics in the rock parallel to intersection lin eations porphyroblast growth is inferred to be a result of microfracturing along favourably oriented linear anisotropics formed by multiple intersection of foliations as well as parting of the the s 1 and s 2 foliations

mechanism of emplacement of the cannibal creek granite with special reference to timing and deformation history of the aureole abstract the ovoid cannibal creek granite consists of a minor phase emplaced during the regional d 3 deformation and a major phase emplaced during the regional d 4 deformation it possesses an intense contact parallel foliation on its margin and in the adjacent porphyroblastic schist that formed through partitioning of the shearing component of deformation against the crystallized pluton margin during synchronous e w d 4 shortening during this process a pre existing shallow s 3 foliation was updomed around the pluton and re used reactivated by d 4 shear with associated dissolution of quartz resulting in the formation of an ovoid closed foliation around the pluton thus the granite is located within a domal shaped approximately n s trending pluton scale f 3 4 antiform that formed synchronous with emplacement three successive stages of porphyroblast growth record the history of processes operating during progressive emplacement and the structures that developed space problems were solved through upward movement of the rocks above the granite due to movement on the s 4 cleavage as well as on pre existing subvertical bedding and cleavages and by reactivation of steep d 2 faults

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

regional slaty cleavage formation and fold axis rotation by re use and reactivation of pre existing foliations the fiery creek slate belt north queensland abstract a deformation history comprised of six separate deformation events of differing intensity has affected the rocks of the south palmer river region of the the hodgkinson province north queensland within this region a zone of pervasive slaty cleavage herein termed the fiery creek slate belt has developed as a result of the superposition of fabrics formed during several of these events the most important processes in the formation of this composite cleavage were the re use and reactivation of the favourably oriented steep n s trending s2 foliation by the intense fourth deformation event d4 this produced micro meso and macroscopic folds in an originally shallow s3 foliation produced during the intervening d3 deformation with an axial planar s2 s4 foliation the d4 stretching lineation l44 plunges subvertically to steeply north and indicates that shear during d4 was oriented steeply north south in the fiery creek slate belt d2 fold axes are interpreted to have formed in much shallower orientations than their present moderately n s plunging to subvertical orientations we consider this to be a result of d4 shear which caused variable degrees of rotation of d2 fold axes toward the d4 stretching lineation due to subparallelism of the bulk shortening directions of the d2 and d4 events near total destruction of the pre d4 foliations during slaty cleavage formation has produced a misleading impression of a simple deformation history there is no relationship between metamorphic grade and intensity of slaty cleavage development

rock matrix structures in a zone influenced by a stylolite abstract a stylolitic structure is one of the visible manifestations of the pressure solution process in a rock the stylolitic process zone as defined in previous studies on both sides of a stylolite is studied by sem the chosen samples concern tectonic stylolites within a high porosity limestone 16 without tension gashes this zone corresponds to a local increase of porosity and comprises a large number of stylolitic joints showing a decreasing size from the macroscopic structure to simple contact between two grains two hypotheses are presented for the stylolite formation 1 the macroscopic stylolite is the result of the coalescence of earlier minor pressure solution structures 2 small stylolites nucleate gradually from a major stylolite joint the mass transfer can be realized either by diffusion between particles or by seepage through previously undescribed process zone fractures the mass deposition can be localized in the porous volume and the microcracks without requiring any additional tectonic openings including tension gashes the rock deformation is therefore limited to shortening parallel to 1 without normal extension

the influence of deformation partitioning on dissolution and solution transfer in low grade tectonic melange dissolution of quartz and the recryst allization and re equilibration of phyllosilicates produce the dark anastomosing seams that dominate microstructures of tectonic melange which occur in a low grade imbricated and multiply deformed mid palaeozoic intracra tonic fiysch sequence in northeastern australia seams are composed of very closely spaced or coalesced cleavage lamellae which are very thin layers of extremely fine grained phyllosilicates cleavage seams enclose lenses of silt stone or greywacke which formerly occurred in continuous sedimentary layers indicating extremely heterogeneous and disruptive deformation microphacoids enclosed by cleavage seams have subtle shape asymmetries analogous to those of porphyroclasts phyllosilicate preferred orientations within microphacoids commonly lie at a low angle to enclosing seams and asymmetric relationships occur within seams the shape and fabric asymmetries appear to be constant and are regarded as analgous to s and c planes the number and extent of seams the amount of dissolution they indicate and the efficiency of deformation partitioning imply some enhancement of chemical activity and substantial silica loss from the system this in turn suggests the passage of large amount of silica undersaturated fluid and melanges may be zones of high fluid flow however the microstructures and the disruptive nature of the fabrics may also reflect the influence of high bulk shear strains and suggest some relationship between the shearing component of deformation and the development of cleavages and foliations

the deep structure of the carmel fault zone northern israel from gravity field analysis the carmel yizre el jordan fault system is a major structural feature in the geology of israel there is a great difference in topographical features structural style seismic activity crustal structure and other geological characteristics to the north and south of this fault system we examine the gravity field of the region around the fault system by combining the techniques of upward continuation and horizontal gradient analysis the results suggest the existence of a system of deep seated n s trending faults that are probably related to the continental breakup of the region in the triassic jurassic the present complex deformation of the area is the result of interaction between the older faults system and the younger stresses resulting from the formation of the dead sea rift

seismic activity along fault branches of the dead sea jordan transform system the carmel tirtza fault system abstract about 550 earthquakes 1 0 m l 5 3 along the carmel tirtza fault a branching fault of the jordandashdead sea transform system recorded by the israel seismograph network isn between 1984 and 1994 were analyzed the seismicity pattern reveals significant activity often confined to known surface traces of active faults or within local grabens earthquake clusters are also observed the seismicity pattern within the mediterranean seems more diffuse possibly due to observational inaccuracies and insufficient knowledge of how the carmel tirtza fault system extends towards the northwest the seismicity along the carmel tirtza fault system since the beginning of this century is characterized by a b value of about 0 9 for 15 events with 3 1 m l 5 3 we found seismic moment estimates m 0 of 0 7 10 14 m 0 10 17 nm and brune stress drop estimates between 0 9 and 16 4 mpa these characteristics are comparable to those for events occurring on the main dead sea jordan transform fault ten individual earthquake focal mechanisms and three joint focal mechanisms for earthquake clusters have been obtained towards the northeastern part of the carmel tirtza fault system a left lateral motion seems to dominate while the seismicity pattern and the focal mechanism solutions near the branching of the carmel tirtza fault and the dead sea jordan rift suggest the present day existence of a complicated tectonic regime stress inversion assuming one stress tensor for the whole region indicates nne ssw extension and wnw ese compression

observations of horizontal velocities and vertical displacements in the equatorial pacific ocean associated with the early stages of the 1982 83 el nino abstract pacific near equatorial absolute velocity data and ctd o2 observations collected from the r v conrad in the northern fall of 1982 are presented quite by chance the cruise took place during the early stages of the 1982 83 el nino the data obtained are generally consistent with the fundamental ideas about el nino onset in that abnormal eastward flow near the surface and large thermocline depressions were observed these changes are quantified by comparing with previously collected data and are discussed in terms of simple equatorially trapped wave dynamics the results indicate that first and second mode disturbances probably kelvin waves were prominent in the equatorial pacific in the fall of 1982

crack seal fibre growth mechanisms and their significance in the development of oriented layer silicate microstructures abstract an analysis of crack seal fibre growth mechanisms has shown two important implications of the crack seal process for the interpretation of microstructures in low grade metamorphic rocks 1 1 the ability of fibre growth to track the incremental separation history of crack walls depends on details of the nucleation and growth mechanisms 2 2 fibrous crystals may develop cristallographic preferred orientations in certain crack seal situations the microstructures of layer silicates and associated phases developed in several examples of syntectonic intragranular microfracture sites and veins indicates that layer silicate 001 and grain shape preferred orientation can develop during crack seal deformation by oriented growth mechanisms during successive crack seal increments preferred orientation may develop in response to an interaction between anisotropic growth kinetics and the displacement history resulting in preferential rejoining by syntaxial overgrowth of pulled apart grains having fast growth directions parallel to the incremental displacement direction across a microcrack preferred orientation may also be developed and enhanced in crack seal growth sites by overgrowth of previously oriented layer silicates in the microcrack walls in this case the crystallographic preferred orientation need not be simply related to the displacement history during crack seal fibre growth since crack seal processes may operate on all scales down to the minimum size of a microfracture in a deforming rock such mechanisms of layer silicate preferred orientation development are expected to be very significant in developing and enhancing foliation during deformation involving microfracture and solution transfer processes

relationships between gold concentration and structure in quartz veins from the hodgkinson province northeastern australia the hodgkinson province is a tract of multiply deformed silurian devonian rocks in north queensland australia gold bearing quartz veins from the west normanby goldfield in the northern hodgkinson province were emplaced during the permian d4 event broadly coeval with regional granite emplacement taylors fault a major structure that formed during d2 hosts the veins which infill dilatational jogs opened during sinistral normal reactivation of the fault in d4 veins contain graphitic laminations that formed when fault planes segmented wallrocks adjacent to the veins producing tabular clasts that were tectonically sliced into the reefs laminations are the result of progressive shear strain associated with continued movement on the faults which caused strain enhanced dissolution of silicate minerals and residual graphite enrichment in the clasts this process produced graphite coated shear planes that delimit zones of grain size reduction in the veins laminations commonly contain stylolites which nucleated on pronounced sinuosities of the shear planes due to progressive shortening during d4 gold particles have preferentially nucleated in zones of relatively coarser grained quartz adjacent to the shear planes where shortening strain caused microfracturing and allowed fluid access gold may have been introduced with the quartz but was redistributed within the reefs and localized along the laminations by the effects of synchronous progressive deformation regionally gold deposits show close spatial relationships with granite plutons of the permian whypalla supersuite relationships in the west normanby gold field support a regional model of reef emplacement and gold mineralization during the permian d4 event

the geometry and evolution of a transpressional strike slip system the carboneras fault se spain the carboneras fault system is a 40 km long 1 km wide neogene ne sw trending left lateral transpressional strike slip fault system which is part of the trans alboran shear zone in se spain the carboneras fault system is an anastomosing array of sub vertical individual fault planes or fault zones which surround pods or lenses of less intensely strained rocks displacements along the individual fault planes exhibit reverse components of slips and form positive flower structures faults have either sharp boundaries or wider bands of gouge typically a few metres thick and are hundreds of metres in length second order fault splays are well developed and usually exhibit p shear rather than riedel shear orientations these are interpreted to be related to the transpressional displacement and may also characterize other oblique convergent zones elsewhere the second order faults are interpreted to have formed as shear strain increased along the first order fault and was transferred laterally to branch segments this process produced pods or shear lenses bounded by the fault segments the length to width aspect ratios of the shear lenses were found to be scale independent across five orders of magnitude with the most common values between 3 l and 6 l a model is proposed for the development of the fault zone by incremental finite displacements along the segmented fault surfaces this model is based on field evidence that displacement switched with time from one fault strand to another

lack of porphyroblast rotation in the otago schists new zealand implications for crenulation cleavage development folding and deformation partitioning porphyroblasts of garnet and plagioclase in the otago schists have not rotated relative to geographic coordinates during non coaxial deformation that post dates their growth inclusion trails in most of the porphyroblasts are oriented near vertical and near horizontal and the strike of near vertical inclusion trails is consistent over 3000 km2 microstructural relationships indicate that the porphyroblasts grew in zones of progressive shortening strain and that the sense of shear affecting the geometry of porphyroblast inclusion trails on the long limbs of folds is the same as the bulk sense of displacement of fold closures this is contrary to the sense of shear inferred when porphyroblasts are interpreted as having rotated during folding several crenulation cleavage fold models have previously been developed to accommodate the apparent sense of rotation of porphyroblasts that grew during folding in the light of accumulating evidence that porphyroblasts do not generally rotate the applicability of these models to deformed rocks is questionable whether or not porphyroblasts rotate depends on how deformation is partitioned lack of rotation requires that progressive shearing strain rotational deformation be partitioned around rigid heterogeneities such as porphyroblasts which occupy zones of progressive shortening or no strain non rotational deformation therefore processes operating at the porphyroblast matrix boundary are important considerations five qualitative models are presented that accommodate stress and strain energy at the boundary without rotating the porphyroblast a a thin layer of fluid at the porphyroblast boundary 2 grain boundary sliding 3 a locked porphyroblast matrix boundary 4 dissolution at the porphyroblast matrix boundary and 5 an ellipsoidal porphyroblast shadow unit