strain gradients in zones of ductile thrusting insights from the external hellenides abstract new finite strain data from a thrust sense shear zone which extends for 600 km along strike in the high pressure belt of the external hellenides greece were used to describe the variation of ductile strain with structural distance d from the basal thrust sampling was carried out along four traverses across the central and southeastern parts of the zone the strain ratio in xz sections r xz of 120 samples was obtained using the theta curve the mean object ellipse and the mean radial length methods all methods give very consistent results based on these results four strain profiles were constructed depicting a non linear increase of r xz values with proximity to the basal thrust these profiles in combination with published strain data from the northwestern parts of the zone enabled us to obtain an empirical logarithmic function describing the relationship between r xz and d this function includes only one varying parameter which represents the strain gradient in linear r xz ln d space the value of strain gradient is directly correlated with the strain level in the thrust zone and provides information for strain localization at its base the proposed function may also be used for quantifying the strain profiles of ductile to semi ductile thrust zones in other orogenic belts such as the alps the appalachians and himalaya

the limitations of three dimensional kinematic vorticity analysis abstract the kinematic vorticity number wk can be calculated for three dimensional as well as two dimensional geologic deformations for steady state deformations wk can be correlated to and analyzed in terms of finite strains the analysis shows that assumptions commonly made for two dimensional deformations are not applicable to three dimensional deformations a single wk describes an infinite number of three dimensional deformations further even knowledge of flow apophyses orientation instantaneous stretching axes orientation and or wk are not sufficient to describe deformation three dimensional deformations also require knowledge of the deformation type or boundary conditions of deformation e g transpression hence in addition to being difficult to estimate the value of knowing wk for three dimensional deformations is greatly reduced compared with plane strain the most useful methods of determining wk from naturally deformed rocks are presented

fabric transitions in the saxony granulite terrain abstract quartz fabric transitions reported from the saxony granulite terrain and from the nearby ore mountains are interesting because of the changes in the pattern types and the variation in the opening angles of the fabric skeletons a short summary is presented of salient features in research documented in the east german literature between 1961 and 1978 the changes in fabric skeleton with decreasing metamorphic grade are proposed as mainly consequent to the deactivation of prism c glide systems as temperature decreases fabrics indicative of the appearance of the c burgers vector might be diagnostic for deformation in regimes of comparatively high temperatures or low strainrates or for deformation under conditions such that there is a relatively high kinetically effective hydroxyl content in the quartz structure

strain path partitioning within thrust sheets microstructural and petrofabric evidence from the moine thrust zone at loch eriboll northwest scotland abstract quartz c axis fabrics and microstructures have been investigated within a suite of quartzites collected from the loch eriboll area of the moine thrust zone and are used to interpret the detailed processes involved in fabric evolution the intensity of quartz c axis fabrics is directly proportional to the calculated strain magnitude a correlation is also established between the pattern of c axis fabrics and the calculated strain symmetry two kinematic domains are recognized within one of the studied thrust sheets which outcrops immediately beneath the moine thrust within the upper and central levels of the thrust sheet coaxial deformation is indicated by conjugate mutually interfering shear bands globular low strain detrital quartz grains whose c axes are aligned sub parallel to the principal finite shortening direction z and quartz c axis fabrics which are symmetric both in terms of skeletal outline and intensity distribution with respect to mylonitic foliation and lineation non coaxial deformation is indicated within the more intensely deformed and recrystallized quartzites located near the base of the thrust sheet by single sets of shear bands and c axis fabrics which are asymmetric with respect to foliation and lineation tectonic models offering possible explanations for the presence of kinematic strain path domains within thrust sheets are considered

microstructural evolution of the serido belt ne brazil the effect of two tectonic events on development of c axis preferred orientation in quartz the polyphase evolution of the serido belt ne brazil includes d crust formation at 2 3 2 1 ga d 2 thrust tectonics at 1 9 ga and crustal reworking by d 3 strike slip shear zones at 600 ma microstructural investigations within mylonites associated with d 2 and d 3 events were used to constrain the tectono thermal evolution of the belt d 2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions 600 650 degreesc through grain boundary migration subgrain rotation and operation of quartz q prism slip continued shearing and exhumation of the terrain forced the re equilibration of high t fabrics and the switching of slip systems from c prism to positive and negative a rhombs during d 3 enhancement of ductility by dissipation of heat that came from syn d 3 granites developed wide belts of amphibolite facies mylonites continued shearing uplift and cooling of the region induced d 3 shear zones to act in ductile brittle regimes marked by fracturing and development of thinner belts of greenschist facies mylonites during this event switching from a prism to a basal slip indicates a thermal path from 600 to 350 degreesc therefore microstructures and quartz c axis fabrics in polydeformed rocks from the serido belt preserve the record of two major events which includes contrasting deformation mechanisms and thermal paths c 2003 elsevier ltd all rights reserved

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

kinematic evolution of the ama drime detachment insights into orogen parallel extension and exhumation of the ama drime massif tibet nepal abstract the ama drime massif is a north south trending antiformal structure located on the southern margin of the tibetan plateau that is bound by the ama drime and nyonno ri detachments on the western and eastern sides respectively detailed kinematic and vorticity analyses were combined with deformation temperature estimates on rocks from the ama drime detachment to document spatial and temporal patterns of deformation deformation temperatures estimated from quartz and feldspar microstructures quartz c axis fabrics and two feldspar geothermometry of asymmetric strain induced myrmekite range between 400 and 650 c micro and macro kinematic indicators suggest west directed displacement dominated over this temperature range mean kinematic vorticity estimates record early pure shear dominated flow 49 66 pure shear overprinted by later simple shear 1 57 pure shear high strain 36 50 shortening and 57 99 down dip extension dominated flow during the later increments of ductile deformation exhumation of the massif was accommodated by at least 21 42 km of displacement on the ama drime detachment samples from the nyonno ri detachment were exhumed from similar depths we propose that exhumation on the nyonno ri detachment during initiation of orogen parallel extension 11 13 ma resulted in a west dipping structural weakness in the footwall that reactivated as the ama drime detachment

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

postorogenic origin of the stratiform cu mineralization at lufukwe lufilian foreland democratic republic of congo the central african copperbelt which stretches across the border between zambia and the democratic republic of congo is one of the largest sediment hosted stratiform cu co provinces in the world the triangular shaped lufilian foreland is located to the northeast of the copperbelt recently sediment hosted stratiform copper occurrences have been explored in the foreland including the kinkumbi prospect in the lufukwe anticline although the stratiform copper mineralization in the copperbelt is mainly concentrated in the roan group sedimentary rocks where it is commonly associated with cobalt the lufilian foreland copper mineralization occurs in sedimentary rock units of the nguba and kundelungu groups where it is mainly associated with silver this paper examines the metallogenesis of the stratiform copper mineralization at lufukwe the lufukwe anticline is situated in the eastern part of the lufilian foreland and is composed of neoproterozoic sedimentary rocks belonging to the katanga supergroup the kinkumbi prospect a sediment hosted stratiform copper silver occurrence is located in the northern part of the western flank of the anticline this part of the anticline is characterized by disseminated copper silver mineralization hosted in the lower 10 to 15 m of the monwezi sandstone nguba group a comparison between the location of high copper grades in surface samples and boreholes and the location of structural lineaments visible on aster images indicates that the mineralization is spatially related to northeast southwest to east northeast west southwest strike slip faults these faults are nearly perpendicular to the strike of the host rock and postdate both the lufilian folding and deposition of the entire katanga supergroup the monwezi sandstone was subjected to strong compaction and silica cementation authigenic quartz overgrowths followed by intense feldspar dissolution which resulted in a well developed secondary porosity represented by dissolution cavities copper sulfides are mainly concentrated in these cavities and partially replace the detrital grains the copper mineralization is both hypogene chalcopyrite bornite and chalcocite and supergene digenite covellite and minor native copper with malachite and chrysocolla as the main oxidation products point counting and grain size measurements demonstrate that the sandstone horizons with high copper content 1 25 cu are those with a detrital grain size larger than 175 m more than 35 percent altered feldspars and little or no fine grained matrix microthermometry of fluid inclusions indicates that the authigenic quartz overgrowths precipitated from a moderate temperature 80 130 c high salinity 18 8 23 4 wt cacl2 equiv h2o nacl cacl2 fluid the hypogene copper silver mineralization was deposited from a hot 120 180 c and low to moderate salinity 1 9 7 7 wt nacl equiv h2o nacl fluid with a general trend of increasing homogenization temperatures with increasing salinities the interpretation of the available structural stratigraphic petrographic and fluid inclusion microthermometric data constrain the timing of the mineralization to a time after the lufilian folding and deposition of the entire katanga supergroup the data presented support a postorogenic fluid mixing model in which the mineralization is related to the mixing of a copper rich mineralizing fluid with a temperature 180 c and salinity 7 7 wt percent nacl equiv likely migrating upward along northeast southwest to east northeast west southwest oriented strike slip faults with a colder low salinity reducing fluid in the monwezi sandstone the location and distance between the northeast southwest to east northeast west southwest faults strongly influenced the spatial distribution of the copper mineralization in the anticline and the variability in grain size and composition of the monwezi sandstone caused the preferential lateral migration of the mineralizing fluid through the lower 10 to 15 m copper precipitation was possibly induced by reduction by preexisting noncopper sulfides pyrite and arsenopyrite and hydrocarbons and by the drop in fluid temperature and salinity based on this research the areas with dominant northeast southwest to east northeast west southwest structural lineaments are considered favorable sites for further copper exploration in the lufilian foreland especially where these lineaments cut previously deformed katanga sediments coarse grained sandstones with no fine matrix that underwent intense feldspar dissolution are the most promising host rocks for the late disseminated stratiform copper mineralization in the lufilian foreland airborne gamma ray spectrometric surveys could be used as a powerful exploration tool for targeting ore related k depleted zones in these sandstones

sabkhas slumping and compaction at mufulira zambia algal structures such as stromatolites have long been recognized as closely associated with the cupriferous dolomitic shales of the katanga supergroup of zaire and zambia discovery of bioherms and biostromes in the predominantly arenaceous deposits of the mufulira copper mine indicates a similar origin with the more common copper deposits in dolomitic shale and their barren gaps due to bioherms renfro 1974 recognized the worldwide association of sabkhas algal mats and stratiform copper deposits his interpretation of sabkha environments in cyclic depositional sequences at mufulira is corroborated by detailed features in the mine recognition of abundant carbonized debris of algal mat from 0 5 m down to microscopic size in the marine sediments of mufulira indicates an accumulation of decomposing vegetable debris that is more than sufficient to promote anoxic conditions in the bottom waters of the lagoons with resulting precipitation of copper and iron sulfides contemporaneously with sedimentation compaction of algal material explains the 80 percent contraction of sun cracked mud flakes also compaction by roughly two thirds of the algal rich graywacke and the c orebody accounts for the rapid sagging of overlying sabkha and terrestrial sediments which was followed by a second marine invasion allowing deposition of the b orebody and central graywacke similar rapid compaction of the latter under its cover of sabkha and red bed sediment caused further sagging marine invasion and deposition of the a orebody and graywacke vertically above the c and b graywackes although renfro s hypothesis of mineralization by ascending groundwaters may account for some initial precipitation of sulfides beneath algal mats the bulk of the preserved mineralization at mufulira exhibits features more compatible with syngenetic deposition of sulfides associated with decaying transported algal material in marine lagoons

temperature and strain rate dependent microfabric evolution in monomineralic mylonite evidence from in situ deformation of norcamphor norcamphor c7h10o was subjected to plane strain simple shear in a see through deformation rig at four different strain rate and temperature conditions two transient stages in the microfabric evolution to steady state are distinguished the grain scale mechanisms associated with the microstructural and textural evolution vary with the applied temperature strain rate and strain in high temperature low strain rate experiments computer integrated polarization microscopy reveals that the texture evolution is closely related to the crystallographic rotation paths and rotation rates of individual grains high c axis rotation rates at low to intermediate shear strains are related to the development of a symmetrical c axis cross girdle by the end of the first transient stage 1 5 to 2 during the second transient stage 1 5 to 6 the cross girdle yields to an oblique c axis single girdle as c axis rotation rates decrease and the relative activity of grain boundary migration recrystallization increases steady state 8 is characterized by a stable end orientation of the sample texture and the cyclic growth rotation and consumption of individual grains within the aggregate

deformation temperatures and flow vorticities near the base of the greater himalayan series sutlej valley and shimla klippe nw india abstract we report new deformation temperature and flow vorticity data from the base of the greater himalayan series ghs exposed in the sutlej valley and shimla klippe of nw india we focus on three groups of transects across the hanging wall of the main central thrust mct in order of relative foreland hinterland positions they are the shimla klippe western and eastern sutlej transects deformation temperatures indicated by quartz c axis fabric opening angles increase both from foreland to hinterland at a given structural distance above the mct and up structural section from the mct within individual transects deformation temperatures in the immediate hanging wall to the mct are estimated at 510 535 535 550 and 610 c on the shimla western sutlej and eastern sutlej transects respectively the steepest inferred field gradients in deformation temperatures are recorded adjacent to the mct and progressively decrease up structural section following a power law relationship comparison with temperature estimates based on multi mineral phase equilibria data suggests that penetrative shearing occurred at close to peak metamorphic conditions vorticity analyses indicate that shearing along the base of the ghs occurred under sub simple shear conditions wm values of 0 9 1 0 with a minor component of pure shear

geochronology of the mkushi gneiss complex central zambia abstract rb sr and k ar ages are reported from the mkushi gneiss complex and its intrusives in central zambia of the rb sr whole rock data of the mkushi gneisses three suites 22 samples only one suite six samples defines an isochron of 1777 89 ma with initial 87sr 86sr of 0 713 0 0006 errors 95 confidence level 87rb 1 42 10 11 a 1 the other samples scatter below this isochron but above a 1480 ma line four hornblendes from amphibolitic dykes yield k ar ages between 864 and 804 ma whole rocks of the red facies of the intrusive mtuga granite nine samples define an isochron of 607 39 ma with initial 87sr 86sr of 0 730 0 005 the white facies of the mtuga granite four samples and probably also the copper bearing aplitic veins seven samples are of the same age but with even higher initial 87sr 86sr ratios seven biotites from the mkushi gneisses yield rb sr and k ar ages between 469 ma and 444 ma these data are interpreted to signal 1 about 1780 ma ago emplacement of the granitoid precursors of the mkushi gneisses derived from older continental material 2 between about 1480 ma and 860 ma ago formation of the mkushi gneisses and the amphibolites probably during the irumide orogeny about 1350 ma ago 3 between about 860 ma and 800 ma ago closure of the hornblendes to k ar 490 550 c after resetting probably in relation to the c 860 ma old tectono thermal event widespread in eastern and eastern central africa 4 about 600 ma ago intrusion of the mtuga granite and the copper bearing splites post tectonic pan african possibly derived from the mkushi gneisses and 5 about 460 450 ma ago closure of the biotites to rb sr and k ar approximately 400 c reflecting the final regional cooling termination of the pan african events some regional implications are discussed

the geotectonic environment of zambian copper cobalt mineralization suggestions that the ore shale of the lower roan group is part of a series of sedimentary fades produced by the north easterly transgression of the sea over dominantly arenaceous strata of littoral deltaic lacustrine and continental origin have been viewed with scepticism by the author the lack of proven transition facies from silty carbonaceous argillites of the type found close to the south western limits of the ore shale in the zambian copperbelt to dolomites found further to the sw has tended to accentuate this feeling the intensity of exploration drilling in these areas must imply that whatever the cause the cut out of the ore shale is rapid at the same time a 9normal9 lower roan succession of the chambishi type suddenly becomes attenuated and dolomites and dolomitic chloritic schists are found immediately overlying argillaceous gritty sandstones conglomerates and arkosic quartzites characteristic of footwall formations locally this contact may be reddened porous and brecciated amphibolite bodies of the type normally found at a much higher stratigraphic level in the upper roan group are present a short distance above this contact it is thus proposed that this feature represents a hiatus in the succession and that all rocks from the ore shale to the top of the lower roan and possibly into the base of the upper roan are missing due to non deposition and or erosion this interruption of the succession coincides with the western cut out of the ore shale from the konkola dome in the nw down to the western end of the roan basin in the s in view of various authors9 contention that the zambian copperbelt is the site of an ancient aulacogen the above observations take on an important genetic significance the present paper thus reviews the location of copper cobalt mineralization in relation to sedimentary facies changes and cut outs structural features and amphibolitic bodies and proposes a geotectonic model for the copperbelt which it is hoped provides a more satisfactory and comprehensive explanation for the facts this model also provides a source for the metals which were converted to sulphides by diagenetic processes it is believed that the complex mineral chemistry of the ore shale associated ores and in particular the presence of localized concentrations of mo co ag as bi and te bearing phases is best explained by high level seepage of magmatically enriched hydrothermal solutions along precambrian rift systems and associated fractures these metals were either dispersed by wave and current action in the sedimentary environment or were concentrated by porosity and physico chemical and bacteriogenic controls in the diagenetic environment

calcite textures examples from nappes with strain path partitioning abstract strain path partitioning partitioning of deformation into components of pure and simple shear in two alpine nappes is qualitatively indicated by a variation in orientation of foliation microkinematic criteria quartz textures and a comparison with strain path partitioning in theoretical nappe models the degree of non coaxial deformation relative to the total deformation is quantified by using the asymmetry of textures in calcite tectonites the texture interpretation is based on both polycrystal plasticity models and experimental data calcite tectonites in the graz paleozoic thrust sheet austria and the morcles nappe switzerland were deformed in a strain path with both pure and simple shear components texture asymmetry supports the strain path derived from geological observations as an exception a high strain ultramylonite deformed nearly exclusively in pure shear it is suggested that this represents a softening instability since deformation in pure shear is energetically more favorable than in simple shear the incompatibilities caused by heterogeneous pure shear are accommodated by detachments and heterogeneous simple shear adjacent to the pure shear zone

strain and fabric analyses based on porphyroclast interaction abstract two dimensional computer models of the interaction of elliptical clasts in a variety of kinematic conditions are used to study how clast imbrication and shape fabric development relate to strain and strain history the models provide templates for a known clast density and clast ellipticity that correlate clast imbrication angle of collision and clast shape fabric to strain and kinematics of deformed rocks modeling also shows that the mode of clast interaction plays a significant role in the accumulation of imbricated clasts and the development of shape fabric upon collision between clasts the trains formed can remain fixed or rotate if they rotate imbricated clasts can become independent when they are no longer forced together by the flow based upon the mode of clast and train rotation using the march rotation of passive lines and the jeffery rotation of rigid particles as end members three models are defined in an attempt to simulate the conditions of clast interaction under varying conditions the march fixed train march rotating train and jeffery rotating train models simulate solid state intermediate and magmatic conditions respectively modeling shows that the two march models produce similar results but the jeffery model of train rotation always produces a lower proportion of imbricated clasts and a much weaker shape fabric application of the modeling to the study of a syntectonic granite in the sierra nevada suggests that deformation was dominated by simple shear some k feldspar imbrication and fabric development took place initially in the magmatic stage and culminated in the solid state to produce a large proportion of imbricated k feldspar porphyroclasts which define a strong shape fabric this type of analysis provides a rationale to determine syn vs post emplacement deformation in the granite

strain and vorticity analysis using small scale faults and associated drag folds abstract small scale faults with associated drag folds in brittle ductile rocks can retain detailed information on the kinematics and amount of deformation the host rock experienced measured fault orientation drag angle and the ratio of the thickness of deflected layers at the fault l and further away t can be compared with and l t values that are calculated with a simple analytical model using graphs or a numerical best fit routine one can then determine the kinematic vorticity number and initial fault orientation that best fits the data the proposed method was successfully tested on both analogue experiments and numerical simulations with basil using this method a kinematic vorticity number of one dextral simple shear and a minimum finite strain of 2 5 3 8 was obtained for a population of antithetic faults with associated drag folds in a case study area at mas rabassers de dalt on cap de creus in the variscan of the easternmost pyrenees spain

metal sources for the nkana and konkola stratiform cu co deposits zambian copperbelt insights from sr and nd isotope ratios abstract the central african copperbelt lies within the lufilian orogenic belt in the border region between the democratic republic of congo drc and zambia a sr and nd isotope study was performed on gangue carbonates associated with multiphase mineralisation at the zambian konkola and nkana deposits comparison with isotopic signatures of basement rocks provides new insights into the likely metal source s for the cu co mineralisation at least three mineralisation phases can be identified with respect to the lufilian orogeny gangue carbonates of the first pre to syn kinematic mineralisation phase in both deposits have sr and nd isotopic compositions that correspond to felsic rocks of the domes region a tectonic zone in the zambian part of the lufilian belt where basement rocks crop out however the isotopic signatures from both deposits differ this can be attributed to local variation in isotopic composition of the basement below the deposits radiogenic isotope ratios suggest that subsequent syn kinematic mineralisation at both sites occurred due to the remobilisation of precursor ore petrographic evidence indicates that the third late kinematic mineralisation phase at nkana resulted from a renewed input of metals with a mafic affinity e g co ni however sr and nd isotope ratios resemble those of the earlier mineralisation phases and do not reflect a change in source composition nonetheless comparison with the isotopic signatures of the co poor konkola deposit and co rich stratiform deposits in the drc might indicate a mafic component in the nkana metal source calculated mixed isotopic compositions support such a mafic component

variations in the kinematics of deformation along the zagros inclined transpression zone iran implications for defining a curved inclined transpression zone abstract the combination of inclined collision and plate boundary shape can control the nature of deformation and the sense of shear along a transpression zone the present study investigated the effects of a boundary zone with curvilinear shape along a transpression zone on the kinematics of deformation the kinematics of the zagros transpression zone varies with the orientation of the zone boundary detailed structural and microstructural studies showed sinistral sense of shear on the southeastern part of the zagros inclined transpression zone fars arc but dextral sense of shear on the northwestern part of the zone it is inferred that the both senses of shear were developed coevally under a bulk general shear regional scale deformation along a curved inclined transpression miming the shape of the fras arc of the zagros and the reentrant of the bandar abbas syntaxis the zagros transpression zone formed by inclined continental collision between the afro arabian continent and iranian microcontinent

significance of transport parallel strain variations in part of the raft river shear zone raft river mountains utah usa this paper examines part of the raft river shear zone rrsz in northwestern utah that exhibits an extreme transport parallel increase in strain intensity coupled with a transition from flattening to constrictional strain detailed geologic mapping and finite strain quartz c axis fabric and kinematic vorticity analyses demonstrate local necking of the shear zone associated with an increase in transport parallel elongation accommodated by a stretching fault at the base of the shear zone the domain of intense deformation and necking of the shear zone is localized where the basal stretching fault cuts rheologically weak rocks this domain is characterized by strain in the constrictional field caused by transport perpendicular flow into the area of high transport parallel elongation where rocks cut by the stretching fault are rheologically strong the rrsz locally records flattening strain and lower strain intensities limiting the amount of stretching needed at the base of the shear zone in any one direction and or recording transport perpendicular flow into adjacent highly extended domains the rheology of rocks cut by the stretching fault directly controlled the amount and style of zone normal shortening and transport parallel elongation and these observations provide an example of deformation partitioning in a crustal scale structure driven by local rheological transitions

rheological control on the initial geometry of the raft river detachment fault and shear zone western united states the strain exhumation history and field orientation of a well exposed shear zone and detachment fault in the raft river mountains of northwestern utah a cordilleran metamorphic core complex have been studied to determine the kinematics of ductile shearing and initial orientations of the shear zone and detachment fault mapping and strain and kinematic analysis indicate that the top to the east raft river shear zone initially developed parallel to an unconformity separating archean rocks from overlying proterozoic quartzite and schist for at least 24 km in the shear direction experimental rock deformation data from lithologies similar to the archean and proterozoic rocks suggest the unconformity represented a significant rheological boundary at the deformation temperatures the base of the shear zone was localized along the boundary between relatively weak quartzite above and stronger monzogranite below an extensive thermochronological database is used to reconstruct the position of the basement unconformity in temperature lateral distance coordinates the initial average dip of the shear zone and basement unconformity is estimated between 7 and 30 assuming subhorizontal isotherms and geothermal gradients of 20 40 c km the east dip of the unconformity at the onset of miocene extension is interpreted to have resulted from late eocene unroofing and flexure beneath a top to the wnw extensional shear zone in the western raft river grouse creek and albion mountains the observations from the raft river shear zone suggest that the orientation of some midcrustal shear zones may not reflect the predicted orientation for ductile faults according to ductile failure criteria but rather the orientation of rheological boundaries along which deformation is localized furthermore detachment faults that are superimposed on mylonite during progressive displacement and footwall unroofing may use an inherited mechanical anisotropy from the mylonite and their orientations may not reflect the predicted orientation of shear fractures in isotropic rock the common parallelism between detachment faults and mylonitic foliation may indicate a mechanical and kinematic preference for localization of throughgoing brittle faults parallel to preexisting mylonitic foliation because of this preference studies restricted to detachment faults which lack footwall mylonite or restricted to structural levels between the breakaway and mylonitic front have more bearing on the question of the initial dip of normal sense shear fractures faults within the seismogenic crust

geometry of eclogite facies structural features implications for production and exhumation of ultrahigh pressure and high pressure rocks western gneiss region norway 1 well preserved eclogite facies structural features in metamorphosed gabbro and diorite gneiss in baltica crust formed at a minimum depth of 60 70 km during the scandian orogeny allow direct inferences to be made regarding the geometry of folds kinematics and original structural orientations related to production and exhumation of high pressure rocks folds associated with eclogite facies fabrics are isoclinal to tubular with axes parallel to the trend of a stretching lineation strain estimates and l s or l s fabrics indicate that these structures were formed in a constrictional strain field locally they are well preserved in eclogite facies mylonite zones at least 40 m thick that cut proterozoic gabbro and adjacent gneiss where steeply dipping they show a north side up shear sense across a younger northeast trending shallowly plunging amphibolite facies anticlinorium formed in a constrictional noncoaxial strain field where original structural facing direction can be inferred small circle rotation of the eclogite facies lineation about the anticline axis indicates that the relative motion vector of baltica with respect to overlying imbricated crust and laurentia was oriented 320 in a present day reference frame this result is identical to the orientation of the relative motion vector estimated from paleomagnetic plate reconstructions and consistent with late silurian to early devonian oblique sinistral convergence between baltica and laurentia results of this study indicate that coherent baltica crust at 60 70 km depth experienced subvertical and horizontal shortening while extending toward the foreland during tops southeast thrusting parallel to plate motion high pressure rocks were progressively imbricated and stacked along eclogite facies mylonite zones with the deforming zone separating coherent baltica crust from imbricated basement above the constrictional strains under eclogite facies conditions are interpreted to have resulted from stretching associated with sinking of the cool dense mantle lithosphere

reconnaissance lead isotope characteristics of the blackbird deposit implications for the age and origin of cobalt copper mineralization in the idaho cobalt belt united states strata bound cobalt copper deposits occur in the metasedimentary rocks of the apple creek formation mesoproterozoic in a linear belt called the idaho cobalt belt near salmon idaho we report the first set of lead isotope measurements on silicate rocks and sulfide ores and new sulfur isotope data on sulfide ores the pb isotope compositions of cobalt copper co cu ores 206pb 204pb 30 8 40 4 207pb 204pb 16 8 17 6 208pb 204pb 49 7 63 9 are very radiogenic much more radiogenic than any known sedimentary exhalative sedex deposits the data plot well beyond the crustal growth model curves a feature shared by the mississippi valley type mvt deposits which is characteristic of an upper crustal source it is unlikely that the ore lead could have come from any mafic igneous source of mantle origin proterozoic moyie sill and its equivalent or the tertiary challis volcanic group the cretaceous felsic igneous rocks of the region the idaho batholith and related rocks also have much lower pb isotope ratios than the co cu ores the pb isotope ratios of proterozoic crystalline rocks partially overlap pb isotope ratios of the apple creek formation but would have been much less radiogenic than the ores at an assumed mineralization age of about 1400 ma only the host apple creek formation is known to have appropriate pb isotope compositions 206pb 204pb 26 8 86 7 207pb 204pb 16 3 21 1 208pb 204pb 47 9 64 8 to be the source of co cu ores leaching of metals from the host sedimentary sequence by hydrothermal fluids and subsequent deposition of ores at chemically and structurally favorable sites could have resulted in the formation of co cu deposits in the idaho cobalt belt

kinematic vorticity and strain rate patterns associated with ductile extrusion in the chelmos shear zone external hellenides greece abstract kinematic vorticity strain rate finite strain and structural data have been used to describe the heterogeneous nature of ductile deformation in an extruding crustal scale shear zone the chelmos shear zone csz of the external hellenides the csz has a curved shape which is marked by a frontal flat and a steep zone the spatial variation in the kinematic vorticity number is strongly correlated with the geometry and the structural depth of the shear zone the pure shear component of deformation decreases from back to front and from top to bottom the ductile thinning normal to the shear zone s boundaries is higher in the steep zone and decreases westwards quartz grain size and strain rate in the csz is distributed into two approximately homogeneous domains the higher strain rate is recorded in the steep zone and the base of the frontal flat zone with lower rates in the upper parts of the frontal flat zone based on mesoscopic structural data and the spatial distribution of the shear strain rate the existence of a west dipping back flow zone in the boarder zone between these two domains is inferred the overall pattern of deformation in the csz implies that tectonic extrusion from the steep zone occurred at the final stages of ductile deformation and was associated with the formation of the backflow zone in the front of the shear zone ductile deformation of rocks probably started close to simple shear on a planar low angle shear zone progressively became penetrative and more general shear occurred as the csz steepened up this progressive increase in pure shearing may have occurred in a heterogeneous manner and was higher close to both the eastern margin of the steep zone and the top of the frontal flat zone solid state extrusion in the csz was also associated with a heterogeneous and progressive increase in strain rate

geology of the enterprise hydrothermal nickel deposit north western province zambia the enterprise nickel deposit 40 mt of 1 07 ni is located on the eastern edge of the kabompo dome in the north western province of zambia the deposit area contains basement schists overlain by neoproterozoic metasedimentary rocks nickel sulfides are hosted within a sequence of quartz carbonate and carbon rich metasedimentary rocks that interfinger with and overlie siliciclastic metasedimentary rocks the host rocks contain significant kyanite talc and magnesian chlorite silicification and magnesian metasomatism occurred prior to or concurrent with a regional metamorphic event 590 500 ma mineralization resulted in the precipitation of nickel and iron nickel sulfides in veins and as semimassive replacements of the host rocks nickel sulfides precipitated in two main stages a millerite vaesite pyrite assemblage that formed disseminations and semimassive replacements in vuggy textured rocks and a later millerite bravoite molybdenite assemblage in quartz kyanite veins and local semimassive replacements the deposit contains minor copper and trace amounts of cobalt and platinum group elements pges a discrete zone of copper sulfides underlies a portion of the nickel sulfide zone re os geochronology on molybdenite yields a 540 6 1 8 ma age for mineralization at enterprise the approximate age of metamorphism sulfur isotope results indicate that the sulfur at enterprise was derived largely from neoproterozoic marine sulfate by thermochemical sulfate reduction significant volumes of mafic igneous rocks are not present in the immediate area of the enterprise deposit no evidence of prealteration concentrations of nickel exists within the sedimentary rock sequence at the deposit the alteration and mineralization style of the enterprise deposit is similar to the much less metamorphosed nickel bearing shinkolobwe uranium deposit in the democratic republic of congo drc though the enterprise deposit does not contain significant uranium the sediment hosted nickel rich deposits of central african copperbelt exemplified by enterprise appear to represent a new style of hydrothermal nickel mineralization

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

transpressional deformations within the sanandaj sirjan metamorphic belt zagros mountains iran abstract polyphase deformation structures of the sanandaj sirjan metamorphic belt in the neyriz area zagros mountains iran are consistent with dextral transpressional deformation which is related to the oblique collision between the african arabian continent and the iranian microcontinent the collision started in the late cretaceous and is continuing to the present day quantitative kinematic analyses quartz textures suggest localized shear zones deformed with a significant pure shear component spatial orientation of lineation and semi quantitative kinematic indicators indicate shear zone parallel stretching and shear zone perpendicular shortening the occurrence of a horizontal stretching component parallel to the deformation zone boundary allows a kinematic model of combined transpression and lateral extrusion for this part of the zagros orogeny

stratiform copper deposits hosted by low energy sediments iii aspects of metal transport the approximate compositions of closed basin saline waters that existed in probable source rocks of stratiform copper deposits hosted by low energy sediments were derived by the simulated evaporation of dilute inflow waters from basalt and granite provenances the saline water derived from dilute inflow water in the basalt provenance had a ph of 7 6 and was saturated with talc dolomite and gypsum the saline water derived from dilute inflow water in the granite provenance had a ph of 7 7 and was saturated with quartz calcite talc and gypsum both waters were 3 molal in chloride and were also saturated with hematite fluorite and fluorapatite the waters probably represent likely end members in the compositional spectrum of metal transporting waters which existed in the source rocks of the stratiform copper deposits copper and cobalt exhibit solubility maxima of 1 500 ppm or greater and 150 ppm respectively at oxygen fugacities in the range 10 super 35 to 10 super 55 bars lead solubility is similar in the two waters and is a maximum of 20 ppm at oxygen fugacities greater than 10 super 60 bars zinc solubility is a maximum of 80 ppm in the basalt derived saline water and 20 ppm in the granite derived saline water silver solubility is a maximum of 200 ppm at oxygen fugacities above 10 super 35 bars barium and iron solubilities are less than 5 ppm abundances of copper silver and in some instances cobalt in all common source rocks result in concentrations of these metals in the saline waters less than their saturation limits concentrations of barium iron lead manganese and zinc in the saline waters are limited by water composition rather than by abundance in source rocks the high copper cobalt lead and zinc solubilities are consistent with the hypothesis haynes 1986a that most sulfides in stratiform copper deposits hosted by low energy clastic sediments are deposited within 50 cm of the sediment water interface during bacterial sulfate reduction porosity and permeability constraints imposed by uncompacted analogs of ore hosting sediments show that the copper contents of the metal transporting waters must be greater than 100 ppm for formation of ore which grades 1 percent or more copper the modeling demonstrates that the proposed waters are potentially effective metal transporters capable of forming stratiform copper ore when the prevailing oxygen fugacity is within the range 10 super 35 to 10 super 55 bars the saline waters are capable of transporting at least 100 ppm copper and therefore are likely to produce copper ore under the porosity and permeability constraints imposed by the hypothesis

origin of the nchanga copper cobalt deposits of the zambian copperbelt the zambian copperbelt forms the southeastern part of the 900 km long neoproterozoic lufilian arc and contains one of the world s largest accumulations of sediment hosted stratiform copper mineralization the nchanga deposit is one of the most significant ore systems in the zambian copperbelt and contains two major economic concentrations of copper and cobalt hosted within the lower roan group of the katangan supergroup a lower orebody copper only and upper orebody copper and cobalt occur towards the top of arkosic units and within the base of overlying shales the sulfide mineralogy includes pyrite bornite chalcopyrite and chalcocite although in the lower orebody sulfide phases are partially or completely replaced by malachite and copper oxides carrollite is the major cobalt bearing phase and is restricted to fault propagation fold zones within a feldspathic arenite hydrothermal alteration minerals include dolomite phlogophite sericite rutile quartz tourmaline and chlorite quartz veins from the mine sequence show halite saturated fluid inclusions ranging from 31 to 38 wt equivalent nacl with homogenisation temperatures thtot ranging between 140 and 180 c diagenetic pyrites in the lower orebody show distinct relatively low 34s ranging from 1 to 17 whereas arenite and shale hosted copper and cobalt sulfides reveal distinctly different 34s from 1 to 12 for the lower orebody and 5 to 18 for the upper orebody there is also a clear distinction between the 34s mean of 12 1 3 3 n 65 for the upper orebody compared with 5 2 3 6 n 23 for the lower orebody the 13c of dolomites from units above the upper orebody give 13c values of 1 4 to 2 5 consistent with marine carbon however dolomite from the shear zones and the alteration assemblages within the upper orebody show more negative 13c values 2 9 to 4 0 and 5 6 to 8 3 respectively similarly shear zone and upper orebody dolomites give a 18o of 11 7 to 16 9 compared to lower roan dolomites which show 18o of 22 4 to 23 0 two distinct structural regimes are recognized in the nchanga area a weakly deformed zone consisting of basement and overlying footwall siliciclastics and a moderate to tightly folded zone of meta sediments of the katangan succession the fold geometry of the lower roan package is controlled by internal thrust fault propagation folds which detach at the top of the lowermost arkose or within the base of the overlying stratigraphy and show vergence towards the ne faulting and folding are considered to be synchronous as folding predominantly occurred at the tips of propagating thrust faults with local thrust breakthrough the data from nchanga suggests a strong link between ore formation and the development of structures during basin inversion as part of the lufilian orogeny sulfides tend to be concentrated within arenites or coarser grained layers within shale units suggesting that host rock porosity and possibly permeability played a role in ore formation however sulfides are also commonly orientated along but not deformed by a tectonic fabric or hosted within small fractures that suggest a significant role for deformation in the development of the mineralization the ore mineralogy hydrothermal alteration and stable isotope data lend support to models consistent with the thermochemical reduction of a sulfate and metal enriched hydrothermal fluid at the site of mineralization there is no evidence at nchanga for a contribution of bacteriogenic sulfide produced during sedimentation or early diagenesis to the ores

kinematic interpretation of shearband boudins new parameters and ratios useful in ht simple shear zones partial funding to jp was provided by the centro de investigacao geolugica ordenamento e valorizacao de recursos that is supported by the pluriannual program of the fundacao para a cilncia e a tecnologia funded by the european union feder program and the national budget of the portuguese republic very insightful and helpful reviews were done by c fernandez university of huelva and two reviewers for which we are grateful we want to acknowledge to t valente university of minho for her suggestions that helped to simplify the manuscript structure and to a mccaig university of leeds for his final comments and english revision that significantly improved this manuscript

ductile shear as a cause of inverted metamorphism example from the nepal himalaya a discussion hubbard 1996 postulated the cause of well known development of kyanite as well as other index minerals representing dominant metamorphism was metamorphic inversion in a section of the eastern nepal himalaya due to the intense ductile shearing either preor synchronous with but outlasted the deformation because of paucity of growth of metawithin the main central thrust mct zone and the overlying tibetan slab on the basis of geologimorphic minerals across the main tectonic fabric hubbard 1996 p 496 cal and textural data cf hubbard 1989 the main thesis of her recent paper revolves around the fact the metamorphic belts of the nw himalaya and the eastern nepal are characterized by i ductile that the distribution of inverted metamorphic isograds is confined to intensely sheared 5 km thick shear zones of high strain revealing s c fabric and other shear structures having a top to south southzone of the mct which either post dated or outlasted predominant metamorphic assemblages p west vergence not only in the basal parts but also in the tibetan slab at higher structural levels 495 conceptually right way up metamorphic iso ii growth of metamorphic minerals is dominantly preto synchronous but occasionally outlasting grads in the young orogenic belts like the himalaya can be very efficiently inverted due to intense the main deformation iii lack of large scale overturned or recumbent folds in many sections except shearing in a broad ductile shear zone we wish to point out that the model proposed by hubbard zanskar searle et al 1992 and the beas valley himachal pradesh frank et al 1977 and iv pres 1996 for the eastern nepal is the same in principle as ours for the northwestern himalayas pubence of inverted metamorphism in the lower and middle sequences and a normal sequence in the lished in geology in 1993 earlier hubbard 1989 fixed the upper boundary upper parts near the tethyan sedimentary cover numerous structures having predominantly topof the 3 5 km thick mct zone from this area arbitrarily as she has documented that the upper and to southwest sense of ductile shearing have been frequently documented across many tectonic units lower boundaries of the mct zone are not distinct so for the sake of discussions the author defines of the lesser himalaya hhc and tethyan sedimentary zone brunel 1986 treloar and rex 1990 boundaries that include the majority of high strain zone p 20 ductile shear zones were also obpatel et al 1993 and can therefore be correlated with the intense ductile shearing irrespective of the served by her in the overlying tibetan slab where gneisses of the tibetan slab are foliated though presence of the discrete thrusts or wide thrust zones jain and anand 1988 foliation is somewhat less penetrative than probable coeval mylonitic fabric within the mct zone the ductile shear model postulated by hubbard 1996 bears strong structural similarities to the p 21 indicating synchrony of two dominant planar structures in this region within the mct zone one given earlier by jain and manickavasagam 1993 as it is evident from the simplified version she recorded that the apparent metamorphic grade across the mct zone gradually increases toof our model where effects of post metamorphic thrusting folding and other zones of high strain wards structurally higher levels p 20 where fibrolite and sillimanite are developed along the folihave not been considered figure 1 keeping in mind the regional geological and tectonic variaation as well as in the tibetan slab hubbard 1989 thus an apparent structural and metamorphic grations that may be expected over the distance of about 1000 km from the nw himalaya it is likely dation persists near the upper contact of the mct zone with the tibetan slab within the mct zone that the growth of metamorphic minerals may be diachronous within the higher himalayan shear zone one of the very basic fact of the nw hima1 manuscript received february 1 1997

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

kinematic vorticity and tectonic significance of superposed mylonites in a major lower crustal shear zone northern fiordland new zealand abstract new structural metamorphic finite strain and kinematic vorticity data from a 4 km wide subvertical shear zone in fiordland new zealand reveal a history of deformation reflecting different tectonic regimes an analysis of ductile fabrics within the shear zone and its wall rocks shows two distinctive stages of amphibolite facies mylonitic deformation dasz2 and dasz3 that are superimposed on older paleozoic or early mesozoic structures variations in strain intensity and well defined shear zone boundaries have allowed us to examine the progressive development of lasz2 sasz2 and lasz3 sasz3 fabrics and compare the types kinematics and conditions of deformation that produced them mineral assemblages defining lasz2 sasz2 provided calculated peak conditions of 11 9 1 1 kbar and 581 34 c indicative of lower crustal depths mineral assemblages defining lasz3 sasz3 provided calculated peak conditions of 8 7 1 2 kbar and 587 42 c finite strain and kinematic vorticity studies show that dasz2 involved ductile normal faulting and crustal thinning leading to decompression and exhumation of lower crustal rocks at some time during the cretaceous rifting of ancestral new zealand from gondwana dasz3 represents an episode of mid crustal dextral transpression that may have resulted from latest mesozoic or cenozoic oblique convergence reactivation of the subvertical sasz3 foliation by cataclastic shear zones and brittle faults dasz4 was accompanied by limited recrystallization at greenschist facies conditions dasz4 shear zones record upper crustal dextral strike slip faulting that resembles late tertiary deformation patterns associated with the australian pacific transform plate boundary

polymetallic mineralization at the browns deposit rum jungle mineral field northern territory australia the rum jungle mineral field northern territory australia forms part of the paleoproterozoic pine creek orogen the geology of the area comprises two archean granitic basement domes overlain by a paleoproterozoic sequence of metasedimentary and subordinate metavolcanic rocks the rocks have been deformed and metamorphosed to greenschist facies during the 1880 ma barramundi orogeny but the original stratigraphic succession has been preserved the browns deposit browns and its extension browns east hosted within black carbonaceous pelites of the paleoproterozoic whites formation is the largest base metal deposit found to date in the pine creek orogen present resource estimates are 39 million metric tons mt at 0 44 percent cu 3 61 percent pb 0 11 percent co and 0 09 percent ni browns and 31 mt at 1 29 percent cu 1 28 percent pb 0 13 percent co and 0 13 percent ni browns east major sulfide minerals in the ore zone are galena sphalerite chalcopyrite pyrite and the main carrier of ni and co siegenite ni co 3 s 4 digenite group minerals and bornite ca bearing plumbogummite pbal 3 po 4 2 oh 5 h 2 o arsenopyrite and gersdorffite are present in minor quantities ore minerals occur as fine grained wisps parallel to the main bedding parallel foliation and as coarse grained mono and polyminerallic aggregates that crosscut the foliation total noncarbonate carbon contents of unaltered rocks range from 1 07 to 7 51 wt percent total sulfur contents range from 2 13 to 6 14 wt percent petrographic studies and raman spectroscopy identify three varieties of carbonaceous matter primary syngenetic premetamorphic epigenetic grain coating and postmetamorphic epigenetic uraniferous migrated altered rocks are rarely encountered values of 34 s for sulfides range from 5 to 15 per mil and are interpreted to reflect a combination of inorganic thermochemical reduction of seawater and bacterial activity no specific sulfur isotope patterns for individual minerals can be established indicating nonequilibrium conditions homogeneous lead isotope signatures of galena 206 pb 204 pb 16 20 16 22 207 pb 206 pb 15 48 15 51 208 pb 207 pb 35 86 35 92 suggest that all pb was derived from a single crustal source and paragenetically late crosscutting galena appears to have been remobilized from bedding parallel galena despite the occurrence of uranium in similar rocks nearby uranium is quantitatively insignificant in the browns deposit and is not genetically related to base metal mineralization instead it is linked to brittle deformation in the waning stages of orogenesis the browns deposit differs from other well known sediment hosted stratiform ore deposits both the zambian copperbelt and the polish kupferschiefer deposits are copper dominant and hosted in sedimentary sequences with significant psammitic components the pb zn ag deposits of the proterozoic australian zinc province also have significant carbonate in their host rocks e g carbonaceous dolomitic and siltstone at mcarthur river and lack economically interesting cu co and ni the nearby woodcutters pb zn ag deposit in rocks of similar age also differs in structural setting veins dominant metals and pb isotopes from the browns deposit

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

the geology of the nifty copper deposit throssell group western australia implications for ore genesis the nifty syndeformational sediment replacement cu deposit is located approximately 450 km southeast of port hedland western australia in subgreenschist grade rocks of the neoproterozoic paterson orogen the resource of 99 million metric tons mt 1 7 percent cu is hosted in a syncline within carbonaceous and dolomitic shales of the upper broadhurst formation the cu mineralization occurred during neoproterozoic dy2 deformation and formed at the center of a zoned hydrothermal alteration system interbedded dolomitic and carbonaceous shale of the upper and lower units of the nifty member was altered s in two stages early siliceous s alteration with minor chlorite pyrite hematite sericite and stilpnomelane which was replaced by syntectonic black quartz in the core of the deposit on the fringes of the alteration framboidal pyrite in the carbonaceous shale was replaced by quartz chalcopyrite euhedral pyrite sphalerite and galena inward is a sequence of interlayered hydrothermal quartzdolomite and unaltered shale beds the hydrothermal quartz dolomite first appears as spots and 2 to 4 mm thick veins with light gray diffuse margins in areas of intense spotty alteration dolomitic alteration forms bedding parallel zones farther inward and proximal to the highest ore grade is silicified dolomitic shale which grades into fine grained quartz and chalcopyrite with minor fluorapatite and carbonaceous material synmineralization fluid inclusions are small 10 microns liquid vapor inclusions with homogenization temperatures between 200 degrees to 370 degrees c median 270 degrees c and salinity of 8 to 27 wt percent nacl equiv median 15 wt nacl equiv sulfur isotope data from framboidal pyrite range between delta 34 scdt of 27 and 16 per mil chalcopyrite delta 34 scdt ranges between 6 and 6 per mil and delta 34 scdt for euhedral synmineralization pyrite ranges between 12 to 12 per mil carbon and oxygen isotope results from synmineralization vein stage carbonates and dolomitic alteration overlap with delta 13 cvpdb values from 2 to 10 per mil and delta 18o vsmow values from 14 to 21 per mil it is likely that decarbonation of host rock caused the large shift in delta 13 cvpdb values the formation of the nifty cu deposit is linked to deformation tectonic loading associated with the miles orogeny driving fluids from deep in the yeneena basin hydrothermal fluids were focused along dy2 thrust faults during tightening of the nifty syncline thrust faulting penetrated carbonaceous and dolomitic shales allowing hydrothermal fluids to react with the nifty member early fluid pulses were weakly oxidized and contained low concentrations of base metals these fluids altered the host rock and precipitated green quartz the fluid evolved to a hotter more saline reduced and moderately acidic fluid with significant cu concentration these fluids reacted with the dolomite dominated nifty member forming the dolomitic alteration and siliceous replacement of carbonaceous shale and dolomitic mudstone chalcopyrite precipitation was controlled mainly by changes in ph accompanied by a slight decrease in temperature the mineralization and alteration styles at nifty are similar to the copper orebodies at mount isa

a 3 d kinematic model of fabric development in polycrystalline aggregates comparisons with experimental and natural examples abstract a 3 d generalization of the approach previously developed by etchecopar for the simulation of fabrics in polycrystalline aggregates is presented the model is based on a geometric minimization of gaps overlaps and boundary displacements between deformed neighbouring cells each cell may deform using a small number

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

mineralization controls and source of metals in the lufilian fold belt shaba zaire zambia and angola the pan african lufilian fold belt hosts extensive and rich polymetallic mineralization dominated by cu co and zn pb sulfides u oxides and noble metals stratiform vein and skarn deposits are present in the late proterozoic rocks of the katangan supergroup mineralization is regionally widespread the sedimentary basin evolution included three phases the first two characterized by rift fault controlled rapid subsidence followed by slower thermal subsidence were associated with bimodal magmatism and probably related to two thermal events the third phase reflects the onset of tectonic deformation and uplift in the southern part of the basin the stratiform mineralization emplaced before the folding of the basin is concentrated in lithologically varied permeable rocks of the roan group that underlie the impermeable rocks of the lower kundelungu group the stratiform mineralization was emplaced by convective circulation of basinal brines forced by a thermal gradient created by a wedge shaped lithosome of lower kundelungu pelitic rocks with low thermal conductivity hypabyssal igneous intrusions and volcanic and volcaniclastic rocks were the source of metals the metals were introduced to the aquifer horizons saturated with basinal brines by hydrothermal circulation associated with the hypabyssal intrusions and by compactional dewatering of a 5 000 m thick body of pelitic rocks rich in volcaniclastic material vein mineralization located on major late faults resulted from regional metamorphism driven dewatering of the folded basin the skarn metasomatic mineralization is associated with small post katangan acid intrusions and blocks of thermally rejuvenated basement details of the distribution of mineralization are stratigraphically and structurally controlled

the diagenetic origin of stratiform copper mineralization coates lake redstone copper belt n w t canada extensive stratiform copper mineralization occurs in three upper proterozoic embayments along a 250 km long arcuate belt in the mackenzie mountains supergroup northwest territories canada mineralization is found in transgressive strata between the continental red beds of the redstone river formation and shallow restricted marine carbonates of the overlying coppercap formation a mafic volcanic succession lying stratigraphically beneath the red beds possibly provided copper bearing detritus to the red beds the coates lake deposit the object of this study contains cupriferous sulfides principally chalcocite bornite and chalcopyrite hosted by microbial laminated limestones and dolostones these carbonates are intercalated with red siltstones to form as many as seven red bed carbonate couplets within the 110 m thick transition zone regional and local studies indicate that the host sediments were deposited in a peritidal setting associated with a sabkha environment paragenetic studies reveal a consistent order of precipitation for gangue and ore forming minerals these minerals can be related to the diagenetic evolution of the host sediments their presence at the coates lake deposit may be divided chronologically into four syngenetic to early diagenetic stages syndiagenesis precipitation of gypsum anhydrite after gypsum dolomitization diagenesis 1 deposition of calcite with partial replacement of anhydrite preore pyrite authigenic silica with partial replacement of anhydrite and calcite and authigenic feldspar diagenesis 2 precipitation of copper bearing sulfides in the presence of reduced sulfur sulfate reducing bacteria and organic matter and partial replacement of preore pyrite anhydrite calcite and quartz and diagenesis 3 neomorphism of calcite mineralization identified with the second stage of diagenesis would have preceded the marked reduction in permeability associated with the formation of neomorphic calcite

kinematic analysis of rock flow and deformation temperature of the sirjan thrust sheet zagros orogen iran microstructural finite strain and vorticity analyses of quartz rich mylonites were used in order to investigate kinematics of rock flow and deformation temperature in the sirjan thrust sheet exposed in a structural window within the sanandaj sirjan high pressure low temperature hp lt metamorphic belt that forms part of the hinterland of the zagros orogenic belt of iran a dominant top to the sw sense of shear in the study area is indicated by several shear sense indicators such as asymmetric boudins rotated porphyroclasts mica fish and s c fabrics quantitative analyses reveal approximately plane strain deformation conditions with r xz values ranging from 2 5 to 4 3 and increasing towards the sirjan thrust opening angles of quartz c axis fabrics and recrystallization regimes suggest deformation temperatures vary from 430 to 625 50 c in the hanging wall rocks oblique grain shape and quartz c axis fabrics were used to estimate the degree of non coaxiality during deformation the obtained vorticity profile indicates a down section increase in kinematic vorticity number w m from 0 6 to 0 89 this range of vorticity numbers confirms contributions of both simple 41 68 and pure shear 32 59 deformation components the structural characteristics of the study area ultimately were controlled by oblique motion of the afro arabian plate relative to the iranian plate

quartz shape fabric variations and c axis fabrics in a ribbon mylonite arguments for an oscillating foliation abstract this paper describes quartz ribbons parallel to foliation containing elongate recrystallized quartz grains aligned oblique to the foliation within a mylonite of the southern tasman belt southeastern australia the shape fabric of quartz grains varies in obliquity with respect to the foliation and intensity grain aspect ratio from one ribbon to another whereas the c axis fabric pattern is stable with respect to the mylonitic foliation and lineation it is argued that the grain shape fabric is an oscillating foliation due to competition between deformation and syntectonic recrystallization

stratigraphic and compositional complexities of the late quaternary lethe tephra in south central alaska abstract recently discovered lethe tephra has been proposed as a latest pleistocene marker bed in bristol bay lowland ne to the cook inlet region alaska on the basis of correlations involving a single lethe average glass composition type deposits in the valley of ten thousand smokes however are chemically heterogeneous individual lapilli as well as aggregate ash deposits have glass compositions that range from the average mode to much higher sio2 and k2o moreover a lake sediment core from the cook inlet region contains one ash deposit similar to lethe average and other closely underlying deposits that resemble a mixture of the average mode and high si high k mode of proximal deposits synthesis of previously published radiocarbon ages indicates a major eruption mainly of lethe average mode about 13 000 14c yr bp as many as six deposits in the cook inlet region five chiefly lethe average mode range from about 13 000 to 15 16 000 14c yr bp and an early holocene deposit in the bristol bay lowland extends the minimum age range of lethe tephra throughout this region to 8000 14c yr bp because of the appearance of lethe average composition in multiple deposits spanning thousands of years we urge caution when using a lethe like composition as a basis for inferring a latest pleistocene age of a tephra deposit in south central alaska linear variation plots suggest that magma mixing caused the lethe heterogeneity multiple magmas were involved as well in other large pyroclastic eruptions such as katmai alaska and rotorua new zealand lethe is an example of a heterogeneous tephra that may be better compared with other tephras by use of plots of individual analytical points rather than by calculating similarity coefficients based on edited data

stratiform copper deposits hosted by low energy sediments ii nature of source rocks and composition of metal transporting water several factors suggest that hematite bearing sediments composed principally of alluvial fan sediments were the source of metal transporting water and of metals in stratiform copper deposits hosted by low energy sediments first such sediments are associated with all examples of larger stratiform copper deposits hosted by low energy sediments second a zonal sequence corresponding to an approximate sulfide solubility product increase is developed laterally into the basin from sandy sediments in contact with the hematite bearing sediments and upward from the contact of the ore hosting sediments with the hematite bearing sediments third the zonal sequence is developed basinward from pinchouts and wedge downs of the hematite bearing sediments and copper mineralization is absent from host horizons where hematite bearing sediments are not developed fourth authigenic mineral assemblages with the exception of hematite sulfides and organic carbon are similar in both the host sediments and in the hematite bearing sediments the authigenic and evaporite mineral assemblages and the nature of associated sediments indicate that most occurrences of the hematite bearing sediments were probably deposited in closed continental basins published sedimentological and paleogeographic analyses show that the rotliegende associated with the kupferschiefer hosted deposits was deposited in a closed continental basin no consistent composition of the hematite bearing sediments is evident although basalt flows or basalt derived clastic components occur in the alluvial fan sediments associated with three of the larger stratiform copper deposits authigenic and evaporite minerals and compositions of modern continental closed basin waters show that the waters originally within the closed basins were na cl so 4 types with variable mg ca and so 4 contents in equilibrium with hematite and with a ph constrained either by carbonate minerals atmospheric carbon dioxide or by quartz microcline muscovite chloride concentrations were likely to have been about six times seawater waters with higher mg and lower ca contents were likely to be associated with alluvial fan sediments containing basalt or dolomite derived clastic components water rock ratios in the alluvial fan sediments were probably 33 percent or less if the 50 cm hypothesis i e that chalcocite in stratiform copper deposits hosted by low energy sediments was precipitated as a result of bacterial sulfate reduction within 50 cm of the surface of the host sediment is true then metal transporting waters were being released from the hematite bearing sediments very early in their burial history if so the metal transporting water was the original closed basin water with a temperature of less than 50 degrees c

conditions of contact metamorphism papoose flat pluton eastern california usa implications for cooling and strain histories petrological study of highly strained carbonate and pelitic rocks within the contact aureole surrounding the western part of the papoose flat pluton yields thermal profiles plots of metamorphic temperature versus distance across the aureole that show temperature gradients which are relatively flat and narrow 100m the gradients occur close to the contact and indicate a slight decrease in temperature from 500 550 c at the pluton wall rock contact to 450 500 c at the outer margin of the aureole one thermal profile across low strain metasedimentary rocks located in the southern part of the aureole shows that thermal effects from emplacement extend no further than 600 m from the contact coexistence of andalusite and cordierite in pelitic rocks of the aureole constrain pressures to 4 kbar thermal modelling using an analytical solution of the conductive heat flow equation for a rectangular shaped pluton reproduces the observed thermal maxima and profile shape conductive rather than convective cooling also is supported by isotopic and field evidence for limited fluid flow along the strongly deformed margin of the pluton simple thermal models coupled with observed high temperature deformation features and a measured 90 attenuation of stratigraphic units in the plastically deformed western part of the pluton s aureole indicate that strain rates may have been of the order of 10 12s 1 evidence for episodic heating such as two distinct generations of andalusite growth in pelites from the aureole alternatively may indicate a longer heating event and therefore slower strain rates thermal models also indicate that parts of the pluton still may have been above the solidus during deformation of the pluton margin and aureole

pb isotope constraints on the age of sulfide ore deposition and u pb age of late uraninite veining at the musoshi stratiform copper deposit central africa copper belt zaire the musoshi copper deposit is a typical ore shale type deposit located centrally in the zaire zambian copper belt cu fe sulfides are disseminated in a 20 m thick laminated black siltstone unit the ore shale which occurs above a thick approximately 1 km sequence of oxidized arkosic sediments of the roan group at the base of the katangan sedimentary basin uraninite occurs in veins which cut the ore shale and extend from major hydrothermal alteration zones in the footwall rutile accompanying this veining was dated by richards et al 1988 at 514 or 2 m y 2sigma in the present study nine analyses of five uraninite samples give a u pb age of 514 or 3 m y 2sigma in exact agreement with the rutile age information concerning the age and source of the copper mineralization at musoshi has been sought by study of pb isotopes in the cu fe sulfides and other minerals leach residue analyses of most ore samples show poor correlations on 207 pb 204 pb vs 206 pb 204 pb diagrams and scatter in a band these samples typically display mature recrystallized textures and may contain thin concordant sulfide veinlets with coarse secondary biotite quartz and carbonate however analyses of three samples from near the center of the ore shale which show less evidence for recrystallization and contain no veinlets form a wellcorrelated line mswd 2 54 15 analyses corresponding to a two stage model age of 645 or 15 m y 2sigma data from the other samples scatter below this line on the pb pb diagram and toward the secondary isochron obtained from the hydrothermal rutiles similar phenomena are observed on a 208 pb 204 pb vs 206 pb 204 pb diagram where addition of u to the disturbed samples is clearly demonstrated we conclude that the samples record disturbance of pb isotopes in a simple two stage system by the late uranium depositing hydrothermal event at 514 m y the significance of the 645 m y fractionation event is not clear however at least two interpretations may be given that the event reflects primary cu fe sulfide ore deposition or that pb isotopes were homogenized at this time in a preexisting orebody by some process which also introduced u and th into the deposit we are not able at present to distinguish between these two alternatives but whichever is correct it is clear that copper ore deposition occurred at or before 645 m y and is thus unrelated to the later 514 m y hydrothermal event a high integrated u pb source ratio mu 10 2 obtained from the 645 m y sulfide isochron suggests an evolved crustal source for pb in the orebody and rules out a significant contribution from mafic igneous rocks if cu and pb are assumed to share a common source these results do not support derivation of the metals from mantle derived materials at musoshi this u pb ratio contrasts strongly with a value of mu 9 7 calculated from the rutile analyses for the late hydrothermal overprint and further confirms that this later event was not involved in the formation of the copper deposit other than in coarsening and locally concentrating the ore the high temperature 397 degrees or 5 degrees c fluids associated with this event were probably derived from deep levels in the crust and appear to have been expelled during a late pulse of activity at the close of the lufilian orogeny

kinematics and vorticity of flow associated with post collisional oblique transpression in the variscan inner zone of northern sardinia italy abstract quartz c axis fabrics vorticity of flow and deformation temperatures were analyzed in samples collected in the central sector of the variscan inner zone in sardinia italy in order to constrain the kinematics of exhumation of medium and high grade metamorphic rocks during d2 post collisional deformation we investigated two shear belts with opposing shear senses these shear belts are developed parallel to the trend of the inner zone which marks the boundary between two metamorphic complexes our data suggest that the sinistral shear belt initiated during the early stage of d2 deformation in a simple shear dominated regime whereas the dextral shear belt initiated later in a pure shear dominated regime we document a general non coaxial flow regime with contemporaneous pure and simple shear components geometrical relationships reveal the operation of oblique extrusion during a compressive regime where the coaxial component acted sub horizontal and orthogonal to the trend of the axial zone changes in the kinematics vorticity of flow and strain geometry that occurred during d2 deformation may be related to post collisional orogen parallel displacement caught up in the variscan orogeny

cobalt in the zambian copperbelt abstract a review of available information concerning the regional distribution of cobalt in the zambian copperbelt is presented which emphasises the limitation of this metal to a narrow possibly tectonically controlled zone on the southwestern flanks of the kafue anticline the stratigraphic location of cobalt bearing mineralisation is also examined though the majority of the known deposits are within the ore shale horizon cobalt has been found from the basement lower roan unconformity to the top of the lower roan and in one case high in upper roan dolomites the behaviour of cobalt relative to copper can best be summarised by considering arenite hosted deposits separately from those in the ore shale it is shown that though the latter appear to contain cobalt within the confines of the copper orebody a marked vertical antipathetic relationship exists the arenite hosted deposits on the other hand tend to display a marked lateral differentiation of the metals in that the cobalt has apparently migrated or been precipitated at or beyond the fringes of the copper orebody compositional variations within the cobalt bearing phases are described which are attributed to corresponding variations in host rock lithology primary porosity the availability of sedimentary or diagenetic sulphate and in particular to the activity of reduced sulphur a genetic model is thus presented which envisages influx of hot hydrothermal solutions into sediments during early diagenesis cooling of these solutions by mixing with connate waters together with the differing solubilities of the various metals results in the precipitation of the metals in a zonal fashion variable bacterial and possibly inorganic reduction of interstitial sulphate and consumption of the reduced sulphur controls not only the quantity but also the composition of the sulphides precipitated in the past the original source of the metals now contained in the orebodies has been dismissed as somewhat irrelevant but generally they were seen as having been derived from erosion of the basement granites or contained mineralisation a case is made that such a source is not compatible with the presence of high cobalt concentrations and that derivation from a differentiated basic magma is a more satisfactory explanation of the facts crustal rifting is the required mechanism for high level penetration of metal enriched hydrothermal fluids

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

kinematics and vorticity in kangmar dome southern tibet testing midcrustal channel flow models for the himalaya 1 kinematic kinematic vorticity wm and deformation temperature analyses were completed to test the hypothesis that midcrustal rocks exposed in the core of the kangmar gneiss dome southern tibet record ductile deformation patterns of a frozen segment of a southward flowing midcrustal channel microscopic and mesoscopic kinematic indicators exhibit a downward transition from a subequal mix of top north and top south shear in garnet zone rocks to dominantly top north shear in staurolite kyanite zone and deeper rocks kinematic vorticity values indicate an increase in pure shear component with depth from 48 pure shear in chloritoid zone rocks through 62 in garnet zone to staurolite kyanite zone rocks to 68 pure shear in an orthogneiss the deepest exposed rocks deformation temperatures inferred from grain scale microstructures and quartz lattice preferred orientations increase from 300 c 400 c in chloritoid zone rocks to 600 c in the deepest exposed rocks these temperatures are equivalent to temperatures derived from garnet biotite thermobarometry indicating that wm was recorded during peak metamorphism this ductile deformation zone was cut by the brittle southern tibetan detachment system stds that juxtaposed metasedimentary rocks upon the orthogneiss on the basis of these relations midcrustal rocks in the core of kangmar dome record 1 general shear vertical thinning and n s horizontal extension with a component of top north shear during peak metamorphism within a ductile shear zone corresponding to the northern and deeper portion of the stds 2 an increase in pure shear with structural depth a consequence of an increase in lithostatic load and 3 displacement of the high temperature shear zone by the brittle stds our data are compatible with the deformation patterns predicted for the top part of a southward flowing midcrustal channel

fluid inclusion characteristics and u pb rutile age of late hydrothermal alteration and veining at the musoshi stratiform copper deposit central african copper belt zaire hydrothermal veining at the musoshi stratiform copper deposit in zaire has caused extensive alteration in the arkosic footwall sediments and in the mineralized ore shale argillaceous siltstone horizon pervasive growth of secondary rutile biotite and muscovite in the wall rocks accompanied this activity whereas hematite biotite calcite k feldspar barite and accessory rutile occur with quartz in footwall veins in contrast veins cutting the ore shale carry cu fe sulfides uraninite and molybdenite with quartz calcite biotite k feldspar and minor rutile linear zones of particularly intense alteration and veining probably represent structurally controlled fluid conduits fluid inclusions in vein quartz from such zones identify an apparently halite saturated liquid at 397 degrees or 5 degrees c with approximately 39 wt percent nacl 15 wt percent kcl and minor amounts of co 2 and other components rutile is found pervasively both as a wall rock alteration phase and as large euhedra up to 3 cm in the quartz veins the hydrothermal growth of this normally very insoluble mineral is explained by the high temperature and salinity of the aqueous phase the widespread occurrence of rutile in the deposit makes it suitable for determining the age of hydrothermal alteration six samples of rutile picked from footwall and ore shale veining and alteration give a u pb concordia upper intercept of 514 or 2 m y 2 sigma this value is confirmed on a 207 pb 204 pb vs 206 pb 204 pb plot four of these samples contained common pb concentrations in excess of blank which yields a slope age of 513 or 5 m y 2 sigma a seventh sample from an unusual footwall hematite vein gave a slightly younger 207 pb 206 pb age 496 or 1 m y the 514 or 2 m y alteration event is considerably younger than the minimum age of the host sediments 602 or 20 m y and probably also postdates ore deposition believed to be older than 600 m y no unambiguous evidence was seen at musoshi to support a relationship between hydrothermal alteration and stratiform cu mineralization although sulfide textures were modified at this time as shown by intergrowths with rutile dated here at 514 m y the hydrothermal activity is concluded therefore to be a late overprint unrelated to cu ore deposition but perhaps related to compressional deformation and metamorphism associated with the lufilian orogeny

a sensitive vorticity gauge using rotated porphyroblasts and its application to rocks adjacent to the alpine fault new zealand variable aspect ratio porphyroblasts deformed in non coaxial flow and internally containing rotated relicts of an external foliation can be used to characterise plane strain flow regimes the distribution obtained by plotting the orientation of the long axis of such grains classified by aspect ratio against the orientation of the internal foliation is potentially a sensitive gauge of both the bulk shear strain as previously suggested and kinematic vorticity number we illustrate the method using rotated biotite porphyroblasts in the alpine schist a sequence of mid crustal rocks that have been ramped to the surface along the alpine fault a major transpressional plate boundary results indicate that at distances greater than or equal to similar to1 km from the fault the rocks have undergone a combination of irrotational fattening and dextral oblique normal sense shear with a bulk shear strain of similar to0 6 and kinematic vorticity number of similar to0 2 the vorticity analysis is compatible with estimates of strongly oblate bulk strain of similar to 75 maximum shortening dextral reverse transpressional flow characterises higher strain s tectonite mylonite within similar to1 km of the alpine fault these relationships provide insight into the kinematics of flow and distribution of strain in the hangingwall of the alpine fault and place constraints on numerical mechanical models for the exhumation of these mid crustal rocks c 2001 elsevier science ltd all rights reserved

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

diagenetic processes and the mineralization in the triassic of central england continental red beds are the host rocks of a characteristic style of mineralization which suggests a genetic link between red bed formation and ore formation samples of unmineralized and mineralized triassic sediments from central england have been studied sedimentologically petrographically and geochemically with the aim of clarifying this link which may provide valuable guides for exploration on the basis of sedimentological and petrographic observations it is suggested that these red beds were formed as a result of diagenetic alteration whereby detrital silicates and oxides are progressively dissolved and the iron released is deposited as hematite a model for mineralization is proposed involving the release of trace metals from detrital minerals during diagenesis their retention in saline interstitial solutions migration to suitable sites of precipitation and deposition by reaction with trapped hydrocarbons or reduced sulphur

alternative sources of metals for stratiform copper deposits abstract the controversy between sedimentary and epigenetic emplacement of copper in stratiform copper deposits appears to be subsiding in favour of an essentially synsedimentary enrichment of sulphur e g disseminated pyrite and or sulphates which undergo biogenic reduction to sulphide followed by an early diagenetic addition of copper to the host sediment the source of the copper has yet to be conclusively identified since the copper is deposited upon migrating into reducing zones e g sulphide rich organic bearing black shales and sulphate bearing microbial laminated carbonates the closest source of copper could be the commonly adjacent red beds where oxidising conditions would favour solution of copper in the presence of interstitial brines the thickness of these red bed sections is typically measured in 100 s to 1000 s of metres and they commonly contain abundant immature detrital grains including mafic minerals which could provide sufficient trace element copper to form major ore deposits copper in red beds may also include metal initially absorbed on amorphous iron oxides and released during diagenetic reddening of these oxides to form haematite on the other hand the ubiquitous red beds might be discounted as a principal source of copper and could be considered for the most part to have behaved as permeable beds through which cupriferous solutions from other sources migrated toward the grey beds for example mafic volcanics are found in important quantities in stratigraphic sequences hosting several stratiform copper deposits and could contribute large volumes of metalliferous solutions during metamorphic dehydration alternatively these same volcanic rocks may suggest volcanic associated pene exhalative activity with hydrothermal fluids emptying into subsurface red bed aquifers rather than onto surface sediments as commonly proposed for exhalative models although fluids of 250 c are generally considered necessary to transport copper in significant quantities in sulphide bearing exhalations lower temperatures are sufficient for chloride complexing in the absence of sulphide the large volumes of red beds could also have a major cooling effect on initially hot solutions the pene exhalative model may be closely related to fault bounded hot spring models of the type envisaged for so called shale hosted submarine exhalative base metal deposits

structural signatures and 40ar 39ar geochronology of the indosinian xuefengshan tectonic belt south china block abstract to advance our understanding of the kinematics of the xuefengshan tectonic belt xfstb and the mesozoic tectonics of the south china block scb this paper presents new data and interpretations from our structural studies and thermochronological dating the xfstb is characterized by greenschist facies metamorphism and development of s and s l tectonic fabrics an asymmetric positive flower structural pattern is composed of nw wnw and se ese dipping cleavages faults and shear zones kinematic indicators indicate a dominant top to wnw thrusting with a sinistral strike slip component on the ese dipping shear zones and top to ese back thrusting on the wnw dipping shear zones the quartz c axis orientations of mylonitic rocks exhibit monoclinic point maximum asymmetry indicative of a sinistral shear sense under the a basal gliding condition the timing of the major deformation event has been constrained to the middle triassic to early jurassic 244 195 ma on the basis of 40ar 39ar geochronology and other geological observations the structural characteristics of the xfstb are probably related to an indosinian oblique convergent zone in combination with tectonic wedging and associated back thrusting all above a low angle se dipping basal detachment oblique northwestward and upward movement along the basal detachment was partitioned into the nw wnw directed thrusting se ese directed back thrusting and subsidiary strike slip movement along the ne and nne trending faults and shear zones the xfstb may represent part of a huge structural fan between the yangtze and cathaysian blocks and can be interpreted as a product of the indosinian intracontinental collision involving a weak zone

sulfide bearing veinlets throughout the stratiform mineralization of the central african copperbelt temporal and genetic implications the central african copperbelt of zambia and democratic republic of congo along with its broad time equivalents in botswana and namibia the kalahari copperbelt is the world s largest sediment hosted stratiform copper province the economically dominant stratiform copper cobalt or silver mineralization accepted by many as at least partly early diagenetic in origin is ubiquitously accompanied by sulfide bearing quartz carbonate veins and veinlets traditionally this veining is considered to be the product of either metamorphic lateral secretion or discrete late diagenetic to synorogenic mineralization events this view is challenged because identical sulfide assemblages and textures characterize both the disseminated and accompanying veinlet mineralization throughout the zoned sulfide assemblages that constitute many of the stratiform orebodies a situation that is taken to imply contemporaneity of the two styles consequently during the mineralization the siltstone sandstone or dolomite host rocks must have been sufficiently competent to undergo widespread brittle fracturing implying that the disseminated mineralization cannot have been introduced by passive fluid infiltration during early diagenesis this conclusion is further supported by the local occurrence of minor disseminated and veinlet mineralization hosted by mafic sills and dikes both the disseminated and veinlet mineralization styles lack ductile deformation features in many congolese deposits but are variably metamorphosed and deformed in some deposits in zambia botswana and namibia in conjunction these observations suggest that the stratiform copper orebodies were the results of massive saline fluid expulsion by hydraulic fracturing after the mafic magmatism 765 715 ma most probably spanning peak damara lufilian metamorphism and ductile deformation 530 ma and continuing in places until at least 500 ma thus basin inversion contractional tectonism and associated uplift and exhumation and not the earlier extension and rifting seem more likely to have been the ultimate drivers for the fluid mobilization and expulsion

accommodation of arabia eurasia convergence in the zagros makran transfer zone se iran a transition between collision and subduction through a young deforming system 1 at iranian longitude the arabian plate is moving northward relative to eurasia 20 mm yr 1 according to gps to the east this relative motion is accommodated by northward subduction under the e w makran emerged accretionary prism to the west it is accommodated partly by the zagros fold and thrust belt and partly by the alborz kopet dagh deforming zones further north this work investigates the nnw striking transition zone that connects zagros and makran the minab zendan fault system satellite images and structural and geomorphic field observations show a distributed deformation pattern covering a wide domain five north to nw trending major faults were identified they exhibit evidence for late quaternary reverse right lateral slip and correspond to two distinct fault systems the western one transferring the zagros deformation to the makran prism and the eastern one northward transferring the deformation to the alborz kopet dagh tectonic study and fault slip vector analyses indicate that two distinct tectonic regimes have occurred successively since the miocene within a consistent regional ne trending compression 1 an upper miocene to pliocene tectonic regime characterized by partitioned deformation between reverse faulting and en echelon folding 2 a ne trending 1 axis transpressional regime homogeneously affecting the region since upper pliocene the change is contemporaneous with major tectonic reorganization regionally recorded therefore this study provides evidence for active deformation that is not localized but distributed across a wide zone it accommodates the convergence and transfers it from collision to subduction by transpressional tectonics without any partitioning process in the present day period

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

ductile shear as a cause of inverted metamorphism example from the nepal himalaya in many mountain belts metamorphic sequences occur in an inverted arrangement such that rocks of higher metamorphic grade overlie rocks of lower metamorphic grade in some locations such as the main central thrust mct zone of the himalaya the metamorphic inversion is coincident with the zone of ductile thrust deformation although many explanations have been suggested for the metamorphic inversion of the himalaya none are consistent with all of the observed features a new model based on observations from the eastern nepal himalaya consists of inversion of the metamorphic sequence due to ductile shearing of a pre existing zone of right way up metamorphism this simple structural explanation creates an inverted metamorphic sequence consistent with observations of 1 a zone of distributed deformation 2 metamorphic textures overprinted by deformation and 3 metamorphic isograds sub parallel to shear fabric these observations are not all well accounted for by previously proposed models in this st

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

the himalayan main central thrust pile and its quartz rich tectonites in central nepal as a consequence of the india asia collision a deeply rooted crustal slice has been moved southwards over the northern boundary of the indian plate at the present level of observation the main central thrust pile a rock pile of several kilometers thickness is affected by shear deformation which imprinted a flat foliation and a constant n s trending lineation these tectonites were deformed under a wide range of metamorphic conditions grading from lower greenschists up to the sillimanite field the m c t shear zone is studied from the view point of the quartz rich rocks over 100 samples helped to define a microstructural zonation roughly parallel to the thermal one 35 samples particularly rich in quartz have been used for the preferred orientation study of their c axes and a few of them for their a axes strong lattice orientations when undisturbed by mainly secondary recrystallization attest to large plastic strains in quartz the c axes are mostly distributed along unequally populated crossed girdles which may evolve into an inclined single girdle the a axes concentrate perpendicular to the more populated girdle concerning quartz the following is suggested 1 1 the deformation has a dominant shear component responsible for the dominant stretching lineation it could be simple shear in case of inclined single girdles 2 2 one set of a axes line up parallel to the shear direction slip on various planes in the a direction may be an important deformation mechanism 3 3 asymmetry in the lattice preferred orientations could be used to predict the sense of shear for the himalayan thrusting in more than 80 of cases

red bed and basement sourced fluids recorded in hydrothermal mn fe as veins sailauf germany a la icpms fluid inclusion study the hydrothermal mn fe as vein mineralization at sailauf germany hosts a complex sequence of oxide and carbonate minerals that record a protracted fluid history the mineralization is related to a major unconformity that separates permian zechstein sedimentary rocks from underlying variscan crystalline basement the hydrothermal veins contain two principal mineralization stages which are mn oxides associated with calcite and hematite associated with mn calcite the fluid evolution of the hydrothermal system has been reconstructed from fluid inclusion petrography microthermometry and la icpms microanalysis coupled with stable isotope geochemistry of carbonate and oxide minerals the fluid inclusions are high salinity sodic calcic brines and the bulk fluid properties show no major differences between the mn oxide and the hematite stage la icpms analysis of major and trace elements demonstrates that the mineralization formed from chemically distinct fluid pulses characterized by variations in their k li b pb and zn concentrations the fluid that precipitated the mn oxide stage has anomalous pb zn and li b ratios which closely resemble fluids found in fracture fillings in red beds of the permian rotliegend basin by contrast the fluids associated with the hematite stage have pb zn and li b ratios typical of crustal fluids that were derived from interaction with crystalline basement both fluids possess characteristic element ratios including cl br but variable absolute concentrations of most metals this suggests that both fluids were modified by mixing with a common metal depleted brine that had a similar cl br ratio most likely a formation water from the overlying zechstein sedimentary rocks the sailauf mineralization provides insight into the protracted post variscan fluid evolution at the basement cover interface the compositionally anomalous fluid that precipitated the mn oxides is comparable to brines derived from interaction with red beds and likely represents the ore fluid of kupferschiefer type sediment hosted cu deposits conversely the fluid that deposited the hematite mineralization resembles fluids that typically form basement and sediment hosted pb zn deposits

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

deformation path partitioning within the transpressional white mountain shear zone california and nevada most numerical simulations of transpression zones predict a change in finite stretching direction from subhorizontal to subvertical for simple shear dominated zones we provide a detailed description of a dextral transpression zone the white mountain shear zone wmsz with a range of lineation orientations and compare these natural data to numerical models the wmsz is characterized by steeply dipping foliations with dominant shallowly plunging lineations and coeval subordinate domains of steeply plunging lineations within shallowly lineated domains foliation geometry shear sense indicators and quartz c axis fabrics indicate a large component of simple shear while microstructural and quartz c axis fabric data from steeply lineated domains indicate a large component of pure shear geometric relationships between foliations and lineations and quartz c axis fabrics demonstrate that lineation orientation has remained constant during much of the deformation history comparison of numerical models with the data collected from wmsz shows that the shear zone geometry and the observed strain path partitioning do not match any of these models we propose a conceptual kinematic model for the wmsz involving stable segregated coeval kinematic domains of simple shear dominated fabrics and pure shear dominated fabrics that accommodate the transcurrent and contractional components of deformation respectively

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

slip partitioning and inclined dextral transpression along the zagros thrust system iran abstract flexural duplex structures and shear zones are well developed in the heneshk area in southwestern iran the zagros thrust system in this area consists of eight sheets of nw striking ne dipping dextral strike slip duplexes that are linked with imbricate fans and oblique slip thrusts the zagros thrust system is a portion of the internal zone of the zagros orogenic belt this internal zone is characterized by penetrative plastic deformation and metamorphism based on the kinematic vorticity number w k 0 73 0 02 calculated from quartz porphyroclasts of the goshti shear zones along the zagros thrust system the estimated angle between the maximum instantaneous strain axis isa and the transpressional zone boundary is 33 the estimated angle of the plate convergence or the flow apophysis of the displacement field is 25 the presence of dominantly dextral shear sense indicators in the area is consistent with dextral inclined transpressional convergence the mean estimated finite deformation w m value indicates relative contributions of 47 pure shear and 53 simple shear for the deformation which involved both strike slip and oblique slip displacements in this inclined transpression about 40 strike slip partitioning was required to accommodate the finite strain and re orientation of instantaneous strain

grain boundary migration microstructures in a naturally deformed quartzite abstract in this study several grain scale microstructures are presented that are thought to demonstrate the migration direction of once mobile grain boundaries in a naturally deformed quartzite an analysis is presented of the sense of migration of the boundaries and the characteristics of the patterns of relative grain growth and shrinkage grain boundary migration seems to be correlated with the relative crystallographic orientations of neighbouring grains for the quartz quartz grain boundaries and the pattern of preferred grain growth is roughly symmetrical about the mica foliation plane

genesis of the ores of the zambian copperbelt abstract the theories for the origin of the ores of the copperbelt of zambia and zaire are reviewed following an account of the historical development of ideas from epigenetic through syngenetic to syngenetic diagenetic and ultimately to neohydrothermalist theories models for the genesis of these deposits are critically assessed in the light of the data currently available this examination is conducted with particular regard to the questions of the sources of copper and cobalt the timing of mineralizing events and the physicochemical conditions of metal sulphide precipitation although accepting that the origin of these ores remains controversial it is concluded that the most likely sources of both copper and cobalt are the rocks of the basement complex that metals were probably transported both in surface and ground waters and that the main mineralizing event took place during early diagenesis with sulphide precipitation occurring via bacterial reduction of seawater sulphate the precipitation of sulphides probably occurred at temperatures around 20 60 c and at near neutral ph with minor fluctuations in eh and variations in the solubilities of the metals involved causing mineral zonation the burial and compaction of these sediments probably resulted in the expulsion of metal rich fluids and formation of sulphides in the immediate footwall and hanging wall of the main ore horizon with continued burial resulting in the formation of sulphide bearing pods and veins of lateral secretion origin tectonic deformation and metamorphism in the lufilian orogeny although resulting in a set of cross cutting high temperature mineralized veins appears not to have resulted in significant remobilization of the sulphides

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

structures and microstructures related to steady state mantle flow in the neyriz ophiolite iran abstract structural analysis in the well exposed and well preserved neyriz ophiolite suggests that it is a relatively undisturbed piece of oceanic lithosphere detailed structural mapping of high t deformation mantle flow revealed the presence of three elliptical shaped diapirs trending nw se these diapirs are characterized by vertical mantle foliations associated with vertical plunging stretching lineations which progressively incline toward parallelism with the gently ne dipping moho the nw se direction of asthenospheric upwelling of diapirs is parallel with the orientations of the vertical sheeted dike complex this suggests that the neyriz ophiolite was created by two nw se palaeo ridge axes these palaeo ridges are classified as fast spreading ridges these ridges are segmented by a dextral palaeo transform fracture zone this is consistent with fast spreading ridges comparison between the neyriz and oman ophiolites reveals that they show similar characteristics most of the oman palaeo ridge systems are oriented nw se and nnw se they also display similar sheeted dike complex orientations and crustal thickness variations these two ophiolites originally were part of the neo tethyan oceanic lithosphere and afterwards were separated by the oman line during continental collision of the iranian micro continent and afro arabian continent

fabric development during shear deformation in the main central thrust zone nw himalaya india abstract quartz microfabrics and associated microstructures have been studied on a crustal shear zone the main central thrust mct of the himalaya sampling has been done along six traverses across the mct zone in the kumaun and garhwal sectors of the indian himalaya the mct is a moderately north dipping shear zone formed as a result of the southward emplacement of a part of the deeply rooted crust that now constitutes the central crystalline zone of the higher himalaya over the less metamorphosed sedimentary belt of the lesser himalaya on the basis of quartz c and a axis fabric patterns supported by the relevant microstructures within the mct zone two major kinematic domains have been distinguished a noncoaxial deformation domain is indicated by the intensely deformed rocks in the vicinity of the mct plane this domain includes ductilely deformed and fine grained mylonitic rocks which contain a strong stretching lineation and are composed of low grade mineral assemblages muscovite chlorite and quartz these rocks are characterized by highly asymmetric structures microstructures and quartz c and a axis fabrics that indicate a top to the south sense that is compatible with south directed thrusting for the mct zone an apparently coaxial deformation domain on the other hand is indicated by the rocks occurring in a rather narrow belt fringing and structurally above the noncoaxial deformation domain the rocks are highly feldspathic and coarse grained gneisses and do not possess any common lineation trend and the effects of simple shear deformation are weak the quartz c axis fabrics are symmetrical with respect to foliation and lineation moreover these rocks contain conjugate and mutually interfering shear bands feldspar quartz porphyroclasts with long axes parallel to the macrosopic foliation and the related structures microstructures suggesting deformation under an approximate coaxial strain path on moving towards the mct the quartz c and a axis fabrics become progressively stronger the c axis fabric gradually changes from random to orthorhombic and then to monoclinic in addition the coaxial strain path gradually changes to the noncoaxial strain path all this progressive evolution of quartz fabrics suggests more activation of the basal rhomb and a slip systems at all structural levels across the mct

diagenetic origin of the stratiform cu co deposit at kamoto in the central african copperbelt sediment hosted stratiform ore deposits that underwent metamorphism and orogenesis are interpreted either to have a multiphase origin that might in part predate these events or to be exclusively related to fluid migration during the orogeny this controversy concerns the formation of many world class sediment hosted ore deposits such as in the central african copperbelt here we present re os dating results for disseminated and stratiform cu co sulfide pseudomorphs after anhydrite in nodules and layers from the copperbelt results demonstrate that at least some of the ores formed at around 800 ma during rifting and basin development and thus predate the pan african lufilian orogeny younger re os ages i e between 682 28 and 230 36 ma may be due to the replacement of the early cu co sulfides by younger sulfide phases alternatively these younger ages may result from the disturbance or resetting of the re os system during recrystallization metamorphism or the transition of chalcocite from its high to its low temperature polymorph