present day stress field changes along the baikal rift and tectonic implications intraplate extension in a frame of a global compressional stress field seems linked to local lithospheric perturbations lithospheric thinning or thickening able to modify the resulting state of stress zoback 1992 the baikal rift zone brz siberia is located north of the india asia collision zone and exhibits no direct communication with any oceanic domain it can thus be fully considered as an area of continental extension dominated by the global compressional intraplate stress field resulting from plate driving forces in order to address the problem of its dynamics and kinematics and their links with the india asia collision a comprehensive stress tensor analysis is presented based on 319 focal mechanisms of earthquakes located along the whole baikal rift the stress field is varying at different scales of observation when looking at central asia several thousands kilometers the maximum horizontal stress shmax directions remain rather constant with a fan shape geometry when the tectonic regime goes from compressional himalayas to extensional baikal when observing the baikal rift about 1000 km long clear variations of the stress regime are observed from an extensional regime in the central part of the rift to wrench ones in its northern and southern ends finally at the scale of 100 km systematic shmax reorientations occur close to major rift faults we thus infer that the interaction between collisional processes and inherited structures may have a strong influence on rift dynamics we then use computed stress tensors to predict slip vectors on major rift faults deformation patterns show two distinct parts of the rift the south baikal rift sbr is characterized by a constant trending around n100 e slip vector meanwhile the north baikal rift nbr exhibits a complex block rotation behavior involving at least three crustal blocks we propose to interpret these surficial structures and motions as the result of an interaction between the regional compression coming from the india asia collision and the geometry of the hardly deformable siberian platform this particular setting can explain most of the surficial deformation patterns which suggest a large scale cracking of the lithosphere in the baikal region other possible sources of stress could also be considered like deep mantellic upwelling or trench suction linked to the pacific subduction

a ductile thrust in the himalaya abstract although the nature and deformation pattern of basement rocks largely determine the structural behaviour of the continental crust in orogenic belts relatively little is known about the deformational processes at deep crustal levels this paper describes a large scale zone of intense ductile deformation from the himalayan region representing a major geotectonic element the main central thrust mct along which the homoclinal block of crystalline rocks of the greater himalaya is thrust over the younger sedimentary belt of the lesser himalaya it has been observed that a zone extending some 5 to 6 km on both sides of this moderately dipping thrust upto 45 n nne has undergone homogeneous ductile deformation strain measurements across this zone reveal a characteristic profile in which the mct coincides with the highest strains earlier pre mct folds and their interference patterns are absent around the thrust towards which there is a gradual increase in the intensity of deformation and grade of metamorphism in the framework of the himalaya the mct coincides with a line of hot springs and seismic activity the rocks around the mct appear to have undergone marked superimposition of homogeneous ductile strain in the light of our studies the mct has been regarded as a ductile thrust of deep intracrustal character involving a vertical displacement of about 18 km for the crystalline slab which today constitutes the greater himalaya a model of the mct is presented and its wider implications are discussed

quantitative finite strain and kinematic flow analyses along the zagros transpression zone iran abstract the ghouri area in southwest iran exposes a cross section through the zagros orogenic belt the area provides an opportunity to investigate quantitative finite strain rs kinematic vorticity number wk proportions of pure shear and simple shear components sense of shear indicators steeply plunging lineations and other moderate to steeply plunging stretching lineations in a transpressional zone based on a classical strain analysis of deformed microfossils with oblate strain ellipsoid shape the zagros orogenic belt is classified as a pure shear dominated zone of transpression but asymmetry of shear sense indicators suggests that a significant component of simple shear was involved along the deformation zone boundaries the long axes of the microfossils and stretched pebbles of a deformed conglomerate were used to indicate the stretching direction in this zone the stretching lineations have a steep to moderate plunge but a constant strain magnitude characteristics of dextral inclined transpressional kinematics in the zagros continental collision zone were quantified and indicate an estimated k value

permian sedimentary record of the turpan hami basin and adjacent regions northwest china constraints on postamalgamation tectonic evolution the permian marks an important yet poorly understood tectonic transition in the tian shan region of northwestern china between devonian carboniferous continental amalgamation and recurrent mesozoic cenozoic intracontinental orogenic reactivation the turpan hami basin accommodated up to 3000 m of sediment and is ideally positioned to provide constraints on this transition new stratigraphic data and mapping indicate that extension dominated early permian tectonics in the region whereas flexural foreland subsidence controlled late permian basin evolution lower permian strata in the northwestern turpan hami basin consist of coarse grained debris flow and alluvial fan deposits interbedded with mafic to intermediate volcanic sills and flows in contrast lower permian rocks in the north central and northeastern turpan hami basin unconformably overlie a late carboniferous volcanic arc sequence these lower permian strata include possible shallow marine carbonate rocks and thick volcanic and volcaniclastic rocks that are in turn overlain by littoral to profundal lacustrine facies above a regional lower permian upper permian unconformity regional sedimentation patterns record the development of a more integrated sedimentary basin the upper permian is entirely nonmarine and can be correlated east west along the depositional strike of the basin the lower upper permian consists of a broad belt of braided fluvial deposits shed northward these strata are overlain by fluctuating littoral and profundal lacustrine facies and associated fluvial facies the uppermost permian is characterized by shallow lake plain and fluvial environments the early permian association of diffuse volcanism and partitioning of subbasins by normal faulting is consistent with an early phase of lithospheric extension local relationships indicate west east extension in the turpan hami basin along faults oriented normal to late devonian carboniferous collisional sutures within the tian shan the cause of extension in the wake of carboniferous orogenesis remains enigmatic however the temporal and spatial relationships of the two strain regimes suggest that they are genetically related upper permian stratigraphy and unconformities and local late permian triassic contractional deformation record foreland basin development when the turpan hami region became a wedge top basin with respect to the north tian shan fold and thrust belt flexurally induced late permian subsidence is also manifested in the larger junggar basin to the north where 4000 m of strata are preserved in the foredeep region the turpan hami and junggar basins were depositionally connected for much of the late permian when a vast lacustrine system developed across northwestern china this lacustrine paleogeography was only occasionally interrupted possibly by structural damming during uplift of the orogenic wedge

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

stratigraphic architecture of extensional basins insights from a numerical model of sedimentation in evolving half grabens we present a numerical model for the tectonostratigraphic evolution of half grabens which duplicates many of the stratigraphic relationships observed in extensional terranes of the southwestern united states and elsewhere the model also generates insights and predictions on the impact of fault geometry rates of faulting and rates of erosion and sediment transport on landscape evolution stratal geometry and facies distributions three processes control basin development in the model faulting erosion deposition and isostasy assumptions are thin plate flexure normal fault hanging wall deformation by vertical simple shear linear dependence of sediment flux on slope and perfect sorting of sediment during deposition model limitations reflect oversimplification of the dynamics of sediment erosion and redistribution during periods of fault motion half grabens bounded by listric faults accumulate strongly asymmetric sedimentary units the degree of under or overfilling of the basin is controlled in the short term by basin geometry fault dip and in the longer term by extension rates sediment supply and out of plane sediment transport after fault motion ceases erosion and sedimentation redistribute the loads on the lithosphere resulting in progressively more symmetric sedimentary units which overlap the original basin boundaries model facies architecture is affected by changing subsidence patterns stratigraphic geometries and sediment flux under most conditions syntectonic gravels are trapped near the basin edge on the fault bounded side but prograde far out into the basin on the hinge opposite the fault side when fault movement ceases coarse grained sediment from the fault bounded side may initially be able to reach farther out into the basin but overall retrogression is observed on both sides of the basin as topography is eroded and as posttectonic sedimentation buries former sediment sources changing fault dips and lithospheric rigidity affect facies patterns whereas altering the ratio between rates of erosion and sediment transport affects landform development and depositional geometries

genesis and depositional model of subaqueous sediment gravity flow deposits in a lacustrine rift basin as exemplified by the eocene shahejie formation in the jiyang depression eastern china abstract subaqueous sediment gravity flow ssgf deposits have recently been recognized as a major reservoir plays in lacustrine basins research on their genesis and depositional models are crucial to understand gravity flow evolution and the distribution of their deposits this study analysed ssgf deposits in the third member of the shahejie formation in the jiyang depression eastern china based on 3 d seismic data well log data and core observations the types and origins of ssgf the distribution patterns and depositional models of ssgf deposits have been investigated the dominant types of ssgf include muddy debris flows sandy debris flows high density turbidity currents surge like low density turbidity currents and quasi steady low density turbidity currents which are mainly caused by river floods and sediment failures the overall distribution of ssgf deposits is controlled by the sediment supplies basin structure and sequence stratigraphic framework paleotopography flood energy triggering mechanism and the slope angle of the delta front are also important ssgf deposits associated with river floods can be further subdivided into elongated and fan shaped deposits elongated sandstones are composed predominantly of bedload dominated and suspension load dominated hyperpycnal flow deposits the fan shaped sandstones can be subdivided into an inner fan a middle fan and an outer fan inner fan deposits are dominated by gully filling debrites middle fan deposits are composed predominantly of channel fill deposits while outer fan deposits consist of thin bedded and laterally extensive lobe intervals ssgf deposits triggered by sediment failures can be further subdivided according to their proximity to slumping proximal intermediate and distal parts the proximal deposits are composed predominantly of slide and slump deposits the intermediate deposits are dominated by sandy debrite tongues while the distal deposits are composed predominantly of thin bedded surge like low density turbidites this study offers some insight into the types origin of gravity flow as well as the distribution of their deposits in a lacustrine rift basin

simple shear deformation and quartz crystallographic fabrics a possible natural example from the torridon area of nw scotland ln this paper the microstructures and crystallographic fabrics of a 30 cm wide deformed quartz vein from the torridon area of nw scotland are described the vein which lies along a joint separating two blocks of proterozoic gneiss was deformed by crystal plastic processes when the rigid joint blocks moved in opposite directions parallel to the vein margins mylonitic foliation within this quartzose ductile shear zone locally displays the classic orientation variation expected for heterogeneous simple shear deformation in thin section the vein is a mylonite composed of dynamically recrystallized elongate quartz grains aligned oblique to the mylonitic foliation fabrics within the central part of the vein have been examined by optical and x ray texture goniometry methods together with orientation distribution function odf analysis the a axis fabric consists of a dominant single point maximum orientated within the xz plane at 9 to the lineation x this point maximum occupies a pole position to the corresponding single girdle c axis fabric for individual positions on the c axis fabric skeleton the orientations of potential crystallographic slip systems slip plane and direction relative to shear zone co ordinates have been calculated by odf analysis the calculation of relative resolved shear stresses schmidfactors for the potential slip systems assuming a simple shear kinematic framework reveals an elegantly simple relationship between individual grain c axis orientation and correspond ing orientations of potential slip systems these results are readily interpreted in terms of bulk simple shear deformation

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

heterogeneous sub simple deformation in the gol e gohar shear zone zagros sw iran insights from microstructural and crystal fabric analyses petrofabrics and microstructural characteristics of the quartz rich mylonites were investigated in the nw se trending gol e gohar shear zone with length of ca 25 km within the zagros transpression zone sw iran the semi quantitative vorticity analysis using quartz c axis fabric rxz method and rigid porphyroclast geometry rigid grain net method reveals that mean kinematic vorticity number wm increases towards the baghat thrust fault displaying the occurrence of spatial and temporal variations of flow during progressive deformation the wm values show pure shear dominated flow progressively was changed to a simple shear dominated flow toward to the late stages of ductile deformation implying that the accelerating flow path was accompanied with progressive cooling and strain localization at the lower parts of the zone the measured vertical thinning dip parallel elongation suggests that thrust emplacement and metamorphic rock extrusion likely occurred by a combination of simple shear with a pure shear component of deformation i e general shear the estimated deformation temperatures based on the quartz c axis fabric patterns and their opening angles highlight greenschist to amphibolite facies conditions

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

textural and compositional variability across littoral segments of lake tanganyika the effect of asymmetric basin structure on sedimentation in large rift lakes lake tanganyika part of the east african rift system represents one of the most widely cited modern analogs for interpreting ancient rift lakes to date few published detailed sedimentologic studies of the modern sediments allow for comparisons to outcrop and well bore scale observations within ancient strata four recurrent structural margin types exist along the alternating half graben structure of the lake hinged margins axial margins accommodation zone margins and escarpment margins the hinged margin consists of a series of structurally controlled benches over which long continuous tracts of bioclastic lag deposits predominate clastic sands are limited to moderate size silty deltas and long narrow shoreface sands the axial margin is dominated by a wave dominated silt rich delta system accommodation zone margins consist of bioclastic lag deposits atop structural highs whereas carbonate and clastic mud accumulates farther offshore escarpment margins contain small fan delta deposits alternating along shore with talus deposits offshore carbonate and clastic mud is present away from active gravity flow deposition total organic carbon toc and pyrolysis data from fine grained samples subtly reflect the contrasts in margin types but these values are controlled more directly by water depth although facies are similar among all margin types their spatial distribution in particular the degree to which facies tracts trend parallel to shore best discriminates among the different margin types these data suggest that unique but predictable associations of reservoir seal and source facies exist along each of the different margin types

controls on the architecture of a triassic sandy fluvial system wolfville formation fundy basin nova scotia canada implications for the interpretation and correlation of ancient fluvial successions abstract architectural element analysis was developed to describe and reconstruct fluvial system stacking patterns and understand the controls on fluvial architecture the architecture of braided fluvial systems at the scale of channel belts is still poorly understood and upscaling from outcrop observations to basin scale architecture remains partly speculative nonetheless predictive sedimentary models are necessary to understand the connectivity of sand bodies from small scale outcrop to basin scale this contribution presents a dataset from the late triassic sandy braided fluvial system of the fundy basin nova scotia canada we describe facies associations architectural elements and stacking patterns at different scales and discuss the controls on fluvial architecture and upscaling issues the studied section shows at the base multilateral stacked channel bodies with little preservation of fine grained floodplain facies it changes upwards into multistory stacked channel bodies that form channel belt complexes intercalated with thicker floodplain deposits based on grain size evolution large scale sequences encompass several channel belt complexes controls on channel and channel belt migration or avulsion are considered to be related to autocyclic processes in contrast large scale vertical evolution and grain size variations record allocyclic signals in particular gradual grain size variations suggest a climatic control which influences the bedload transport capacity of the depositing fluvial system architectural evolution including an upward increase in the preservation of floodplain units is considered to be due to an increase in generation of accommodation space we question the existing definition of the order of large scale sixth to seventh order bounding surfaces recognized previously and highlight difficulties associated with reconstructing development of a regional fluvial system using these bounding surfaces

heterogeneous ductile deformation and quartz c axis fabric development within the hp lt sanandaj sirjan metamorphic belt iran abstract quartz c axis fabrics finite strain analysis and kinematic vorticity number w k were used to investigate the heterogeneous nature of ductile deformation along an extruding crustal shear zone along the hp lt sanandaj sirjan metamorphic belt and zagros thrust system in the zagros mountains of iran quartz c axis fabric transitions were studied in the well exposed quartz mylonites within this belt asymmetric quartz c axis fabrics confirm localized top to the southeast sense of shear quantitative data were used to establish differences in deformation history finite strain and deformation temperature during ductile deformation quantitative finite strain r xz 2 4 7 and mean kinematic vorticity number w k 0 76 0 14 analyses demonstrate that both the strain ratio and the simple shear component of deformation increase towards the basal thrust of the zagros thrust system i e from northeast to southwest on moving towards the basal thrust of the zagros thrust system the quartz c axis fabrics become progressively and gradually change from orthorhombic to monoclinic the sequential variation in quartz c axis fabrics is explained in terms of increasing finite strain and vorticity which is compatible with progressive increase of ductile shear strain and dynamic recrystallization during transpressional deformation

tectono stratigraphy of late archaean greenstone terranes in the southern eastern goldfields western australia abstract late archaean greenstone terranes in the southern part of the eastern goldfields are regionally extensive faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure the greenstones comprise volcano sedimentary successions that were all deposited at the same time c 2720 2675 ma on sialic crust hence the terranes are interpreted to represent contemporaneous probably adjacent basins these basins were affected by the same history of granite plutonism and regional deformation c 2675 2620 ma early subhorizontal deformation is poorly understood but includes at least locally significant thrust stacking d1 with a south to north movement direction this was followed by regional east west extension affecting all supracrustal successions above a province wide detachment now lying at depths between 4 and 7 km this detachment may have evolved from the greenstone basement contact but only after extensive reworking clastic basins developed along or above major extensional faults but no volcanism is associated with this extension subsequent east west d2 shortening resulted in regional scale thrusting folding and associated late stage transcurrent fault movements the d2 event is contemporaneous with a major thermal event represented by voluminous granite emplacement c 2660 ma and associated peak regional metamorphism in the greenstone succession predominantly monzo granite derived from older sialic crust was emplaced throughout the period of basin formation and deformation early synvolcanic granite c 2719 2710 ma is a minor component late synvolcanic granite c 2685 2675 ma is widespread and syn d2 granite c 2660 ma is abundant there are a few small late tectonic intrusions c 2640 ma to 2600 ma the lateral lithostratigraphic persistence of the contemporaneous basins the syn d2 low pressure regional metamorphism and the province wide monzo granite magmatism suggest that the greenstone basins possibly developed in a tectonic setting similar to that of failed rifts above aborted spreading centres the basins closed in response to far field compressional stresses

fabric transitions in quartz via viscoplastic self consistent modeling part i axial compression and simple shear under constant strain quartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures leading to the development of different types of crystallographic preferred orientation cpo patterns in this contribution we present the results of an extensive modeling of quartz fabric transitions via a viscoplastic self consistent vpsc approach for that we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems we have performed these simulations in axial compression and simple shear regimes under constant von mises equivalent strain of 100 1 73 assuming that the aggregates deformed exclusively by dislocation glide some of the predicted cpos patterns are similar to those observed in naturally and experimentally deformed quartz nevertheless some classical cpo patterns usually interpreted as result from dislocation glide e g y maxima due to prism slip are clearly not developed in the simulated conditions in addition we reported new potential preferred orientation patterns that might happen in high temperature conditions both in axial compression and simple shear we have demonstrated that cpos generated under axial compression are usually stronger that those predicted under simple shear due to the continuous rotation observed in the later simulations the fabric strength depends essentially on the dominant active slip system and normally the stronger cpos result from dominant basal slip in followed by rhomb and prism c slip whereas prism slip does not produce strong fabrics the opening angle of quartz 0001 fabric used as a proxy of temperature seems to be reliable for deformation temperatures of 400 c when the main slip systems have similar behaviors

heterogeneous deformation and quartz crystallographic fabric transitions natural examples from the moine thrust zone at the stack of glencoul northern assynt quartz crystallographic fabric transitions in well exposed mylonites immediately beneath the moine thrust at the stack of glencoul nw scotland have been investigated by optical microscopy x ray texture goniometry and orientation distribution function analysis a progressive change is observed from asymmetrical kinked single girdle c axis fabrics at 0 5 cm beneath the moine thrust through asymmetrical type i cross girdle fabrics to symmetrical type i cross girdle fabrics at 30 cm beneath the thrust this c axis fabric transition is accompanied by a transition from asymmetrical single a axis maximum fabrics 0 5 cm beneath the thrust through asymmetrical two maxima fabrics to essentially symmetrical two maxima a axis fabrics odf analysis of these s l and l s tectonites indicates that c axis positions on the leading edge of the fabric skeleton are related by a common a direction oriented within the xz plane at a moderate angle to the lineation x in contrast c axis positions on the peripheral trailing edge are related by a positive r rhomb pole oriented close to z a directions lying within this common rhomb plane progressively change through 180 in orientation traced around the c axis fabric skeleton such contrasting single crystal rhomb a preferred orientations on the leading and trailing edges of the fabric skeleton are interpreted as indicating localized grain scale plane strain and flattening deformation respectively they result in tectonites with essentially symmetrical c and a axis fabrics which display strongly asymmetrical positive r and negative z rhomb pole figures the observed transition in quartz c and a axis fabrics is interpreted as indicating an increasing importance of non coaxial plane strain deformation as the moine thrust is approached even immediately 1 cm beneath the thrust however flow has still significantly departed from bulk simple shear and involved an important heterogeneous component of contemporaneous flattening deformation

scientific drilling in the great rift valley the 2005 lake malawi scientific drilling project an overview of the past 145 000years of climate variability in southern hemisphere east africa abstract the recovery of detailed and continuous paleoclimate records from the interior of the african continent has long been of interest for understanding climate dynamics of the tropics and also for constraining the environmental backdrop to the evolution and spread of early homo sapiens in 2005 an international team of scientists collected a series of scientific drill cores from lake malawi the first long and continuous high fidelity records of tropical climate change from interior east africa the paleoclimate records which include lithostratigraphic geochemical geophysical and paleobiological observations documented in this special issue of palaeo3 indicate an interval of high amplitude climate variability between 145 000 and 60 000 years ago when several severe arid intervals reduced lake malawi s volume by more than 95 these intervals of pronounced tropical african aridity in the early late pleistocene around lake malawi were much more severe than the last glacial maximum lgm a well documented period of drought in equatorial and northern hemisphere tropical east africa after 70 000 years ago climate shifted to more humid conditions and lake levels rose during this latter interval however wind patterns shifted rapidly and perhaps synchronously with high latitude shifts and changes in thermohaline circulation this transition to wetter more stable conditions coincided with diminished orbital eccentricity and a reduction in precession dominated climatic extremes the observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical africa

kinematics of rock flow in a crustal scale shear zone implication for the orogenic evolution of the southwestern hellenides combined shear sense criteria finite strain data and vorticity analyses were used to study the deformation path in a curved crustal scale shear zone phyllite quartzite series of the southwestern hellenides the results are combined with data on the structural evolution of a cover nappe pindos thrust belt to provide new insights into the orogenic evolution of this region ductile deformation within the phyllite quartzite series was associated with a top to the west southwest shearing and was partitioned into two structural domains a root zone and a frontal domain the root zone is characterized by vertical coaxial stretching high strain and upward movement of the material while the frontal domain comprises simple shear deformation at the base and pure shear at the top this pattern suggests superposition of pure shear on simple shear deformation and implies tectonic extrusion of the material from the root zone the initiation of brittle deformation in the pindos thrust belt was associated with westward translation above the sub horizontal pindos thrust later as the mountain range elevated normal faulting at high altitudes and migration of thrusting to the west occurred while east directed folding and thrusting in the belt started to the east according to the proposed model crustal thickening was taking place throughout the oligocene and early miocene including the subduction of the apulian beneath the pelagonian microcontinent and the intracontinental subduction of the phyllite quartzite series during the lower miocene vertical buoyancy forces led to the successive steepening of the shear zone and the simultaneous duplexing of its basement facilitating tectonic extrusion of the material from its root zone finally an indentation process caused vertical expulsion of the orogenic wedge and gravity collapse in the brittle crust

asymmetric late pleistocene glaciations in the north basin of the baikal rift russia new morphological sedimentological and radiocarbon data of quaternary deposits from the northern baikal rift document at least three extensive late pleistocene glaciations at 50 ka 40 35 ka and 26 13 ka respectively during these periods valley glaciers advanced from the high rift shoulders 2500 m down to the present day coast of lake baikal 456 m in places the glaciers advanced beyond the present day shoreline into the lake basin as indicated by large moraines exposed in steep cliffs along the lakeshore furthermore stratigraphic relations between lacustrine sequences and glacial deposits as well as 14 c ages of two palaeo shorelines 10 and 4 m above the present lake level show that the last and the penultimate glaciations were followed by relative lake highstands these land based observations document a significant influence of late pleistocene glaciations on the sedimentary development of this lacustrine rift basin the northern baikal rift is characterized by an asymmetric half graben geometry that controls river drainage and sedimentation this asymmetry greatly influenced the development and spatial distribution of pleistocene glaciers on both rift margins on the western flank tilted fault blocks parallel to the rift served as topographic barriers for valley glaciers advancing toward the lake basin only in two locations glaciers could reach the present day coast on the eastern rift flank in contrast structure and drainage conditions allowed the development of numerous consequent streams providing thoroughfares and space for recurrent valley glaciations thus the glaciers on the eastern flank could advance beyond the present day lakeshore into the lake basin in numerous locations these observations indicate that asymmetric rift structure in combination with the effects of global cooling were the important controls on the pleistocene glacial development of the baikal rift

role of the kazerun fault zone in the formation and deformation of the zagros fold thrust belt iran 1 the kazerun fault is a n s trending fault zone which obliquely truncates the nw se trending zagros fold thrust belt this active fault zone is an ancient structural lineament which has controlled the structure sedimentation and subsidence of the central part of the zagros since the early cambrian and has had an influence on the formation of the hydrocarbon system of the belt the kazerun fault limited the distribution of the cambrian hormuz salt the major decollement horizon that separates the precambrian basement from the thick sedimentary cover to the west its later reactivation with other n s trending fault zones e g the izeh fault zone during the cretaceous resulted in major sedimentary thickness and facies variations along the belt this study presents a new interpretation for the evolution of the kazerun fault zone based on field evidence and a review of various published and unpublished data it is argued that at the surface the fault zone is delineated by four north south trending segments and that marked differences occur in the distribution of deformation on either side of the fault segments in the late tertiary during this time these segments acted as transfer faults lateral ramps linking different segments of the zagros deformation fronts

late oligocene and miocene faulting and sedimentation and evolution of the southern rio grande rift new mexico usa abstract the distribution of nonmarine lithofacies paleocurrents and provenance data are used to define the evolution of late oligocene and miocene basins and complementary uplifts in the southern rio grande rift in the vicinity of hatch new mexico usa the late oligocene middle miocene hayner ranch formation which consists of a maximum of 1000 m of alluvial fan alluvial flat and lacustrine carbonate lithofacies was deposited in a narrow 12 km northwest trending northeast tilted half graben whose footwall was the caballo mountains block stratigraphic separation on the border faults of the caballo mountains block was approximately 1615 m an additional 854 m of stratigraphic separation along the caballo mountains border faults occurred during deposition of the middle late miocene rincon valley formation which is composed of up to 610 m of alluvial fan alluvial flat braided fluvial and gypsiferous playa lithofacies two new north trending fault blocks sierra de las uvas and dona ana mountains and complementary west northwest tilted half graben also developed during rincon valley time with approximately 549 m of stratigraphic separation along the border fault of the sierra de las uvas block in latest miocene and early pliocene time following deposition of the rincon valley formation movement continued along the border faults of the caballo mountains dona ana mountains and sierra de las uvas blocks and large parts of the hayner ranch and rincon valley basins were segmented into smaller fault blocks and basins by movement along new largely north trending faults analysis of the hayner ranch and rincon valley formations along with previous studies of the early oligocene bell top formation and late pliocene early pleistocene camp rice formation indicate that the traditional two stage model for development of the southern rio grande rift should be abandoned in favor of at least four episodes of block faulting beginning 35 ma ago with the exception of two northwest trending border faults of the caballo mountains block that may be reactivated along eocene compressional structures the majority of border faults and complementary basins throughout the history of the southern rio grande rift were north trending which challenges the conventional idea of a clockwise change in stress through time

late cretaceous and early miocene andean type plutonic activity in northern makran and central iran two calc alkaline plutonic complexes bazman and natanz intruded through the south eastern active and south western ancient continental margins of central iran have been dated by the rb sr whole rock isochron method at 74 2 and 24 4 5 ma respectively detailed trace element studies together with low 87 sr 86 sr initial ratios 87 sr 86 sr ratios and the gabbros at least were intruded some 10 ma earlier

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

deformation thermometry based on quartz c axis fabrics and recrystallization microstructures a review abstract for quartz rich tectonites two types of deformation thermometer are currently commonly employed 1 the quartz c axis fabric opening angle thermometer that provides an estimate of deformation temperatures when fabrics were locked in during dislocation creep and dynamic recrystallization 2 the quartz recrystallization thermometer that indicates a range of likely deformation temperatures based on observed microstructures and inferred mechanisms of dynamic recrystallization a critically important caveat in applying both thermometers is the assumption that deformation temperature is the primary controlling factor in recrystallization mechanisms and fabric development however fabric opening angles and recrystallization mechanisms are also sensitive to other variables such as strain rate and water weakening in this paper the development of these thermometers is reviewed and their potential sensitivities to competing factors such as temperature strain rate water weakening and in the case of opening angles 3d strain type are discussed examples of the application of these potential thermometers to naturally deformed quartz rich rocks are given and case studies of correlations between deformation temperatures estimated by these thermometers and temperatures of synkinematic metamorphism determined by petrology based thermobarometers are highlighted in the review attention is focused on problems associated with applying these thermometers to natural deformation and examples of such problems are discussed

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

rapid mineralogical and geochemical characterisation of the fisher east nickel sulphide prospects western australia using hyperspectral and pxrf data abstract the use of shortwave infrared swir and thermal infrared tir hyperspectral data in mineral exploration has been well documented in many mineralisation types but is limited in komatiite hosted nickel sulphide deposits this project combines hyperspectral portable x ray fluorescence pxrf and whole rock geochemical data to assess different analytical techniques in the exploration of these deposits we use the fisher east nickel sulphide prospects western australia for our case study the fisher east prospects lie in an area of the eastern goldfields that has historically been underexplored and understudied the rocks have undergone intense deformation with primary igneous textures being destroyed along with strong alteration to talc carbonate assemblages combining different analytical tools allowed for differentiation of a and b zones of original komatiite flows and the reconstruction of original volcanological facies in a setting where whole rock chemistry as well as igneous textures have been substantially modified by metamorphism by using different lithogeochemical techniques including pxrf this study shows the fisher east prospects are hosted within channelised komatiite flows and have similar characteristics to kambalda style deposits

anatomy of a lacustrine stratigraphic sequence within the fourth member of the eocene shahejie formation along the steep margin of the dongying depression eastern china a comprehensive study on rift stratigraphy requires a solid understanding of sequence architecture along the steep margins of rift basins this study analyzes an eocene lacustrine sequence along the steep margin of the dongying depression in eastern china through integrated core well log and three dimensional seismic analyses the lacustrine sequence is bounded by unconformities and their correlative conformities at the base and top and consists of three systems tracts namely an early expansion systems tract eest late expansion early contraction systems tract leecst and late contraction systems tract lcst which record a lake expansion contraction cycle these systems tracts differ in thickness and development of depositional systems the eest is the thickest and contains well developed marginal and basinal fan systems with an overall retrogradational stacking pattern the well developed fan systems are the most striking features within the sequence the leecst is the most widespread and contains dominantly profundal sublittoral deposits the lcst is the thinnest with poorly developed fan systems and is characterized by significant erosion by fluvial incision the variable thickness and development of depositional systems in the three systems tracts are the responses to the interplay of sediment supply and accommodation space accommodation space establishes the framework for sedimentary infill and sediment supply determines spatial distribution and temporal evolution of depositional systems within each systems tract this study provides a lake expansion contraction scheme to divide a lacustrine stratigraphic sequence into systems tracts and highlights the feasibility of applying this approach in studying sequence stratigraphy along the steep margin of a lacustrine rift basin the results also provide understandings for the development distribution and evolution of depositional systems and their controlling factors along the steep margin of other rift basins in the world

depositional and diagenetic controls on deeply buried eocene sublacustrine fan reservoirs in the dongying depression bohai bay basin china abstract this paper investigates the reservoir potential of deeply buried eocene sublacustrine fan sandstones in the bohai bay basin china by evaluating the link between depositional lithofacies that controlled primary sediment compositions and diagenetic processes that involved dissolution precipitation and transformation of minerals this petrographic mineralogical and geochemical study recognizes a complex diagenetic history which reflects both the depositional and burial history of the sandstones eogenetic alterations of the sandstones include 1 mechanical compaction and 2 partial to extensive non ferroan carbonate and gypsum cementation typical mesogenetic alterations include 1 dissolution of feldspar non ferroan carbonate cements gypsum and anhydrite 2 precipitation of quartz kaolinite and ferroan carbonate cements 3 transformation of smectite and kaolinite to illite and conversion of gypsum to anhydrite this study demonstrates that 1 depositional lithofacies critically influenced diagenesis which resulted in good reservoir quality of the better sorted middle fan but poor reservoir quality in the inner and outer fan lithofacies 2 formation of secondary porosity was spatially associated with other mineral reactions that caused precipitation of cements within sandstone reservoirs and did not greatly enhance reservoir quality and 3 oil emplacement during early mesodiagenesis temperatures 70 c protected reservoirs from cementation and compaction

depositional and tectonic framework of the rift basins of lake baikal from multichannel seismic data recent multichannel seismic reflection data from lake baikal located in a large active continental rift in central asia image three major stratigraphic units totaling 3 5 to 7 5 km thick in four subbasins a major change in rift deposition and faulting between the oldest and middle rift units probably corresponds to the change from slow to fast rifting in early pliocene time inferred from on land studies a minor modification of fault patterns characterizes the youngest unit a brief comparison of the basins of lake baikal with those of the east african rift system highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks

gravity flow deposits caused by different initiation processes in a deep lake system gravity flows may be triggered by different initiation processes in both marine and lacustrine basins recognizing the different initiation processes of gravity flow based on their deposits is vital to accurately establish gravity flow sandstone distribution which is important for defining paleogeography and for efficient oil and gas exploration gravity flow deposits in the dongying sag were analyzed using three dimensional seismic well log grain size and porosity and permeability data along with core descriptions eleven lithofacies nine bed types and six bed type associations were recognized in the gravity flow deposits in the dongying sag gravity flow deposits around well niu 110 were caused by delta fed sediment failure these deposits are characterized by medium to very fine grained sandstone abundant liquefaction and soft sediment deformation structures and thick laminae rich in plant debris they formed massive sandstones accompanied by normally graded sandstone and lenticular shaped sandbodies and are composed of chaotic deposits and tongue lobes the above features collectively are indicative of typical collapsed sediment transport to deep water by slumping and poorly cohesive debris flow to low density turbidity current gravity flow deposits around well shi 100 are interpreted to have been caused by flooding river fed hyperpycnal flows these deposits are characterized by gravel to very fine grained sand abundant erosional structures and climbing ripples and thin laminae rich in plant debris they formed massive sandstone with some space stratification accompanied by inverse then normal grading sandstone and elongate or fan shaped sandbodies and are composed of channel levee systems and lobes stratified hyperpycnal flow is prone to form a hydraulic jump at the slope break after the hydraulic jump coarse grained sediments were transported to the basin under the drag and shear of the upper part of the suspension flow gravity flow deposits caused by flooding river fed hyperpycnal flow are better reservoirs than those caused by delta fed sediment failure under the same conditions this study offers insight into the recognition criteria and flow processes of gravity flows caused by the different initiation processes in a lacustrine basin

late syn rift sequence architecture and sedimentary evolution of a continental rift basin a case study from fulongquan depression of the songliao basin northeast china abstract as an important stage in continental rift basin evolution late syn rift stage is characterized by the combination of broad crustal subsidence and episodic pulses of extension sequence architecture and sedimentary filling process during this period present a certain particularity due to distinctive tectonic subsidence and variable influencing factors this paper analyzes sequence stratigraphy and sedimentary facies development and their evolution in the fulongquan depression a continental rift basin of the songliao basin and discusses the determinants influencing the sequence architecture and depositional systems evolution during late syn rift stage a major transition in the depositional systems from predominantly lacustrine and correlated depositional systems to fluvial floodplain settings was recorded in the evolution of basin fill this gradual and slow peneplanation is the final response to the decrease of differential subsidence the spatial and temporal variability of sedimentary evolution are mainly associated with specific growth history of the major boundary faults sequence stratigraphic units recognized in the fulongquan depression are likely corresponded to different episodic pulses of extension respectively each sequence can be further divided into a lowstand systems tract lst transgressive systems tract tst and highstand systems tract hst maximum differential subsidence and water deepening mainly occur in the lst the expanded tst and hst of each sequence tend to be developed in a broader thermal subsidence regime the depositional systems transition and detrital provenance changes usually occur in the hst throughout the late syn rift stage in addition to major changes of provenance systems tectonic movement is likely to be the main factor in controlling the variations of sediment supply with the decrease of tectonic activity the impact of climate changes and lake level fluctuations on basin filling tends to be increased

geochemistry and origins of lacustrine ferromanganese nodules from the malawi rift central africa abstract ferromanganese nodules recovered from 100 130 m depth near likoma island eastern lake malawi have been analysed for some thirty four elements by dc arc optical emission spectrometry the concretions routinely hold in excess of 50 fe mn although actual fe mn ratios appear to vary inversely with nodule size subcrustal values are recorded for mg al si k ca and ti the abundance of these major elements is considered to primarily reflect the amount and mineralogy of detrital impurities within the nodule structures of the twenty six analysed trace elements zn co pb ba y la v zr ag be and nb are present at levels exceeding their average crustal abundances while subcrustal or subdetection limit values are recorded for sr ni cu cr sc rb ga li b mo cd bi sn ce and nd the high enrichment factor noted for ba 21 95 the limited enrichment of co 5 53 and zn 2 06 and depletion of ni 0 62 and cu 0 09 are characteristic of most lacustrine ferromanganese deposits and adequately distinguish the lake malawi nodules from their deep ocean counterparts while the ferromanganese deposits of the malawi rift are predominantly of diagenetic origin hydrothermal exhalations may significantly control the supply of elements such as fe v and be this implies a need to extend existing classification systems to include nodules formed through the simultaneous precipitation of metals from two or more sources the nodule sequences in the vicinity of likoma island are physically suited to economic exploitation but fail to meet prescribed chemical criteria for mn or ni co cu ores

lacustrine fan delta deposition alongside intrabasinal structural highs in rift basins an example from the early cretaceous jiuquan basin northwestern china development of fan deltas alongside intrabasinal structural highs has been overlooked compared to those forming on basin margins however these fan deltas may provide important clues regarding the tectonic and climatic controls on deposition during rift development this paper documents fan delta deposition alongside an intrabasinal structural high within the early cretaceous xiagou formation of the jiuquan basin china using subsurface geological and geophysical data deposits observed in drill core support fan delta deposition occurring almost exclusively through subaerial and subaqueous gravity flows subsurface mapping reveals a consistent decrease in the areal extent of fan deltas from lowstand to highstand system tracts suggesting that deposition alongside the structural high is sensitive to lake level changes the temporal and spatial distribution of the fan deltas display retrogradational stacking patterns where fan deltas exhibit a decreasing lateral extent up sequence until fan delta deposition terminated and was replaced by deposition of fine grained lacustrine deposits the retrogradational stacking patterns observed alongside the intrabasinal structural high are not observed in fan deltas along the basin margin in the lower parts of the xiagou formation subsidence profiles also show differential subsidence across the basin during the earliest stages of this formation likely resulting from border fault movements these data suggest that non uniform stacking patterns in the lower parts of the xiagou formation reflect basin scale tectonic movements as the dominant control on synrift deposition patterns however later stages of xiagou formation deposition were characterized by uniform subsidence across the basin and uniform retrogradational stacking patterns for fan deltas alongside the intrabasinal structural high and border fault these observations suggest that basin scale tectonic movements played a relatively limited role in controlling sediment deposition and imply a potential change to regional scale processes affecting fan delta deposition during later synrift stages climate change is favored here as the region scale control on the uniform retrogradational fan delta stacking patterns this assertion is supported by pollen assemblages isotope signatures and organic geochemical analyses which collectively suggest a change from a humid to semi arid environment during later synrift stages we suggest that variations in stacking patterns between different fan delta systems can provide insights into the basin and regional scale processes that control rift basin deposition

sequence stratigraphic architectures and sand body distribution in cenozoic rifted lacustrine basins east china cenozoic rifted lacustrine basins in east china display three main basin types 1 basins with steeply dipping boundary fault whose hanging walls tilt along pivot points 2 basins with listric boundary faults whose hanging walls bend along flexural bending points and 3 basins formed by earlier extensional rifting with later strike slip movement superimposed the sequence development is intimately linked to the tectonic movements in the area where second order sequences are regionally correlatable from basin to basin and relate to the large scale tectonic movements in the region third order sequences are related to local tectonic activity and are correlatable within basins between subbasins and sometimes between neighboring basins detailed sequence stratigraphic analysis and mapping of depositional systems demonstrate that sand body distribution patterns are related to sequence stratigraphic frameworks for the three kinds of basins the positions of pivot point zones flexural bend zones and strike slip faults plus the syndepositional faults all control the distribution of depositional systems systems tract and sand bodies these controlling factors can be attributed to different structural and stratigraphic features that change the accommodation structural elements include boundary faults syndepositional faults and abrupt changes in dip stratigraphic controls include preexisting surfaces with local channelization paleobathymetric lows and onlap onto clinoform slopes the lowstand sand bodies deposited at the downdip end of these controlling factors constitute the current and future exploration targets for conventional reservoirs

a double cycle lake basin formed in extensional to transtensional setting the paleogene nanpu sag bohai bay basin china abstract it has been known that both extensional and transtensional tectonics commonly trigger a one cycle evolution of lake sediments but lake cycle development co controlled by extensional and transtensional tectonics still need identification here we report a double cycle of lake sediments formed in extensional to transtensional phases in the paleogene nanpu sag of the bohai bay basin china the sag successively experienced five phases of lake type evolution characterized by 1 overfilled 2 balanced fill 3 overfilled 4 balanced fill and 5 overfilled extensional tectonics was responsible for the opening of the basin and the initial creation of accommodation 1st through 3rd phase next subsidence increased again through transtensional tectonics resulting in the creation of new accommodation 4th 5th phases investigations show this double cycle lake type evolution is also present in other lake basins with similar tectonic settings e g both extensional and transtensional tectonics a different exploration and exploitation strategy should be devoted to the double cycle evolution of lake basins controlled by extensional to transtensional tectonics in comparison to the single cycle evolution in extensional or transtensional lake basins

petrogenesis of a proterozoic nickel sulfide komatiite association the katiniq sill ungava quebec the katiniq nickel deposit is an example of an association of magmatic fe ni cu sulfides with komatiitic volcanism in the cape smith wakeham bay foldbelt in northern quebec the deposit is unusual because of its proterozoic age in contrast to the archcan ages of most other deposits of this type and is of interest in view of the relatively low degree of deformation and metamorphism to which it has been subjected nickel sulfide mineralization occurs within the katiniq sill an olivine rich subvolcanic intrusive lens up to 150 m thick the sill consists of a number of olivine rich intrusive units each characterized by a concentric zonation in olivine content from a maximum in the core to minimums at the margins this zonation is attributed to a mechanism whereby the sill behaved as an open channel forming part of a subvolcanic feeder system magma flowing through the channel carried a progressively higher proportion of intratelluric olivine phenocrysts with time while crystallization of earlier less olivine rich material occurred inward from the margins flowage eventually became choked off as the channel became clogged with olivine sulfide mineralization occurs dominantly at or close to the base of the sill and shows a marked correspondence with irregularities in the footwall topography typical intersections consist of massive ore at the base succeeded upward by net textured ore and disseminated sulfides these observations indicate a primary magmatic origin for the sulfides the average composition of the liquid portion of the magma olivine suspension intruded into the sill was that of a pyroxenitic komatiite having an mgo content of about 19 percent the chemical variations within the volcanic rocks overlying the sill are consistent with the derivation of these rocks from a liquid of this composition by low pressure fractionation of olivine the mean ni cu ratio of the katiniq sulfides is 4 3 close to that predicted for a sulfide liquid in equilibrium with a magma of the above composition massive sulfides may show significantly higher ni cu ratios than net textured and disseminated types a discrepancy which is attributed to hydrothermal remobilization of cu concentrations of precious metals particularly pt and pd are unusually high in the katiniq sulfides this may be partially due to higher concentrations of these elements in the parent silicate magma but is thought to be largely the consequence of equilibration of the sulfide liquid with very large volumes of silicate magma accumulation of immiscible sulfide liquid droplets in the sill probably occurred over a period of time when large volumes of silicate magma were flowing through the sill and subsequently on toward the surface

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

a new estimate of the conditions for transition from basal a to prism c slip in naturally deformed quartz abstract quartz c axis fabrics of naturally deformed quartz in metacherts from the ryoke metamorphic belt in the yanai district southwestern japan suggest that the prism c prism a and basal a slip systems were activated during the plastic deformation under high temperature metamorphic conditions with increasing temperature quartz c axis fabric patterns change from girdle type through x maximum with a faint crossed girdle to x maximum the dominant orientation of subgrain boundaries in the quartz also changes from prism to basal with increasing temperature closely correlated with the change in quartz c axis fabric the fabric transition is also accompanied by an abrupt increase of recrystallized quartz grain size moreover observations with transmission electron microscopy tem clearly identify the dominant activation of c slip through the presence of basal subgrain boundaries and free dislocations with the 0001 burgers vector in the quartz from the metachert samples exhibiting x maximum c axis fabric based on these observations it is concluded that the mechanism switch from basal a to prism c slip systems occurred with increasing temperature in the metacherts the transition temperature is petrologically estimated to be ca 550 600 c at the natural strain rate

transient groundwater lake interactions in a continental rift sea of galilee israel the sea of galilee located in the northern part of the dead sea rift is currently an intermediate fresh water lake it is postulated that during a short highstand phase of former lake lisan in the late pleistocene saline water percolated into the subsurface since its recession from the kinarot basin and the instantaneous formation of the fresh water lake the sea of galilee the previously intruded brine has been flushed backward toward the lake numerical simulations solving the coupled equations of fluid flow and of solute and heat transport are applied to examine the feasibility of this hypothesis a sensitivity analysis shows that the major parameters controlling basin hydrodynamics are lake water salinity aquifer permeability and aquifer anisotropy results show that a highstand period of 3000 yr in lake lisan was sufficient for saline water to percolate deep into the subsurface because of different aquifer permeabilities on both sides of the rift brine percolated into aquifers on the western margin whereas percolation was negligible on the eastern side in the simulation after the occupation of the basin by the sea of galilee the invading saline water was leached backward by a topographydriven flow it is suggested that the percolating brine on the western side reacted with limestone at depth to form epigenetic dolomite at elevated temperatures therefore groundwater discharging along the western shores of the sea of galilee has a higher calcium to magnesium ratio than groundwater on the eastern side

geodynamics of the eastern yilgarn craton abstract over the last decade there have been significant advances in our understanding of the stratigraphy magmatism deformation metamorphism and timing of mineralisation in the eastern yilgarn craton eyc of western australia the integration of these disciplines has enabled a holistic review of the tectonic history of the eyc which favours a paraautochthonous tectonic model a significant advance has been the recognition of a 2810 ma rifting event off the eastern margin of the youanmi terrane which set up the north northwest trending architecture of the eyc rifting was followed by a 100 myr long phase of tectonic activity initiated by the establishment of a convergent margin at 2715 ma characterised by a west dipping subduction zone to the east of the eyc subduction was associated with the deposition of 2715 2670 ma volcanic stratigraphy and the emplacement of voluminous tonalite trondhjemite granodiorite magmatism which resulted in magmatic thickening of the crust volcanism was terminated by a 5 myr pulse of east northeast contraction followed by mid orogenic extension possibly linked to lithospheric and lower crustal delamination the lack of ultra high pressure metamorphism and the presence of high geothermal gradients preclude this contractional event from recording continent continent collision mid orogenic extension at 2665 ma resulted in the introduction of metasomatised mantle melts mafic granites and syenites deposition of siliciclastic basins which record metamorphic anticlockwise ptt paths and the start of significant economic gold mineralisation in the eyc high stretching factors and or delamination associated with this extension event resulted in significant heat input into the base of the crust which eventually led to the emplacement of low ca crustal melt granites and cratonisation of the eyc major gold mineralisation postdates mid orogenic extension and was associated with renewed compression transpression 2650 ma and the development of steep predominantly north northwest striking sinistral and later north to north northeast striking dextral strike slip faults during low ca granite emplacement

quaternary depositional systems in northern lake baikal siberia abstract new high resolution seismic reflection data from northern lake baikal and detailed land based morphological and sedimentological data reveal a variety of coarse grained deposits in the northern baikal rift each depositional facies is assigned to a specific structural domain alluvial fans onshore and small fan deltas offshore dominate the western border fault flank glacial deposits onshore and large glacio lacustrine fans offshore characterize the eastern flexural margin in the north the axial rift termination comprises a large fluvial delta this distinct pattern of depositional environments reflects the pronounced asymmetry of the rift and emphasizes the role of rift structure in controlling drainage and the location and type of rift basin fill climate however exerts a profound influence on the generation and availability of coarse grained material this is best documented along the eastern rift margin where pleistocene valley glaciers advanced at 50 40 35 and 26 13 ka from th

late quaternary sequence stratigraphy of lake malawi nyasa africa high resolution seismic data multichannel seismic data and sediment cores were used to examine the songwe sequence the uppermost of four depositional sequences identifiable on multichannel seismic data from lake malawi nyasa the sequence has a maximum thickness of about 115 m in two areas of the lake but is typically less than 70 m thick over most of the basin the sequence is distributed along the entire length of the 560 km long lake and is concentrated in three main depocentres 14c age dates from sediment piston cores are extrapolated to provide an age estimate of about 78 000 yr bp for the oldest sediments within the songwe sequence in the north and central bathymetric basins of the lake high resolution seismic data indicate a dynamic depositional environment dominated by turbidity and mass flow deposits seismic data from the southern basin show acoustically transparent sediments with relatively low amplitude internal reflections indicative of pelagic and hemipelagic sedimentation in many areas the songwe sequence is underlain by a pronounced angular unconformity suggestive of a significant prolonged low lake stage prior to deposition of the sequence seismic reflectors within the songwe sequence can be correlated to younger low lake stages identified from sediment core data major late quaternary low lake level stages in lake malawi interpreted from features identified in the seismic data and sediment core analyses are tentatively interpreted at 6000 to 10 000 yr bp 28 000 to 40 000 yr bp and prior to 78 000 yr bp budget calculations indicate mean sediment concentrations from catchment runoff during the period of deposition of the songwe sequence to be about 190 mg 1 1 comparable to estimates of modern rainy season discharges from the major river systems erosion rates within the drainage basin are estimated to be higher than the african average by a factor of three or more probably due to the high relief within the lake malawi catchment

stratigraphic and structural evolution of the tertiary cosmelli basin and its relationship to the chile triple junction at the taitao peninsula in southern chile 46 5 s an active mid ocean ridge is being subducted under the south american continent continental crust south of the current triple junction has experienced subduction of three ridge segments since the mid miocene a series of mid late tertiary sedimentary basins lies inboard of the triple junction the cosmelli basin lies in the region which has experienced the earlier ridge subduction events within the cosmelli basin fill abrupt facies dislocations give clear evidence of marked base level changes four sequence boundaries are delineated with an upward increase in degree of facies dislocation which is believed to reflect increasing magnitudes of base level fall the lower part of the basin fill is folded and then thrust eastward as a series of imbricate slices while the overlying greater thickness of fluvial sediments is only gently tilted westwards this geometry indicates that the early basin fill was deforming due to contractional tectonics while the later basin fill was being deposited these processes controlled accommodation space and thus stratigraphic architecture during much of the basin life this complex basin history plus the presence of basaltic sheet intrusions may reflect the underlying slab history as successive ridge segments were subducted

hydrogeology sequence stratigraphy and diagenesis in the paleoproterozoic western thelon basin influences on unconformity related uranium mineralization abstract the paleoproterozoic statherian thelon formation consists of unmetamorphosed sandstone and conglomerate that was deposited in the thelon basin a continental basin in northern canada this study presents the first detailed sedimentological and sequence stratigraphic analysis of the expansive and under studied western thelon basin and its relation to uranium mineralizing processes in the vicinity of the boomerang lake unconformity related u prospect four lithofacies comprise the thelon formation in the western thelon basin consisting of breccia conglomerate sandstone and minor mudstone these are grouped into four facies associations that represent deposition in alluvial fans and braided fluvial streams three stratigraphic sequences were identified based on the recognition of widespread surfaces that mark significant periods of subaerial exposure or changes in depositional environment these unconformity bounded sequences are composite in nature and can be subdivided into six high frequency sequences hfs low accommodation and high accommodation systems tracts are delineated instead of the traditional systems tracts that are linked to changes in relative sea level as no marine deposits are recognized in the thelon formation two significant strataform paleohydrogeological units were distinguished in the thelon formation based on the relative timing of key diagenetic events such as compaction grain dissolution and cementation diagenetic aquicludes became isolated from basinal fluid flow due to stylolite catalyzed early diagenetic quartz cementation and occlusion of secondary intergranular macroporosity by kaolinite and muscovite and minor dickite during later peak diagenesis diagenetic aquifers conducted u bearing basinal fluids throughout diagenesis and are marked by an abundance of peak diagenetic dickite sequence stratigraphic correlation indicates that diagenetic aquicludes which were not effective at conducting u bearing basinal fluids overlie the unconformity at the boomerang lake prospect and extend along the entire strike length of a related exploration trend in contrast thick diagenetic aquifers lie approximately 10 km to the north of the boomerang lake prospect along a different exploration trend the western and eastern portions of the thelon basin experienced depositional environments and diagenetic conditions distinct from one another suggesting that they were separate sub basins the western thelon basin contains fewer of the well cemented facies that compartmentalized basinal fluid flow than the eastern thelon basin and contains a kaolin dominated diagenetic mineral assemblage rather than a muscovite dominated assemblage that is common in the eastern thelon basin in these regards the western thelon basin evolved more similarly to the eastern portion of the athabasca basin where thick regional kaolin rich diagenetic aquifers were fluid conduits for the movement of the u rich fluids that formed high grade unconformity related u deposits

quantitative kinematic flow analysis from the main central thrust zone nw himalaya india implications for a decelerating strain path and the extrusion of orogenic wedges quantitative kinematic indicators from the main central thrust zone mctz in the nw himalaya have been used to characterize the type of flow during deformation different generations of tension gashes have been rotated by variable angles with respect to the mylonitic foliation forming associated fringe folds these record the late stage brittle ductile flow and reveal that a strong pure shear component of deformation occurred throughout the mctz to characterize earlier deformation increments fabrics from highly deformed quartz ribbons were analyzed well developed shape and lattice preferred orientation patterns show a systematic change of the glide systems and suggest inverted palaeotemperatures within the mctz investigations of the c axes patterns reveal a strong asymmetry at the top of the mctz whereas the samples from the base of the mctz show almost perfectly symmetrical type i crossed girdles deformation within the mctz probably started close to simple shear flow at higher temperatures which progressively became a more general shear during cooling and ended in a pure shear dominated flow during the final stages of brittle ductile deformation i e a decelerating strain path using the higher himalaya crystalline as an example a kinematic model for the extrusion of crustal wedges above major thrust zones is suggested

development of coarse grained facies in lacustrine rift basins examples from east africa detailed studies of high resolution and multifold seismic reflection data from the two largest east african rift lakes malawi and tanganyika reveal a complex suite of coarse grained depositional facies these facies occur within specific regions of the controlling half grabens that compose the rift lakes sand prone environments include subaqueous channels and small drowned fluvial complexes channel systems range from large erosional canyons to deep water turbidite channel levee systems lowstand and highstand deltas of axial and shoaling side rivers are volumetrically important coarse grained facies fan deltas develop along the base of major border faults during lake lowstands subaqueous talus fan deposits occur along the base of the border faults during lake highstands lowstand deltas are the best preserved progradational facies in these rift lakes in addition to simple tectonic control drastic tectonically or climatically induced lake level change significantly regulates the production of coarse grained lacustrine synrift deposits

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

short wavelength infrared swir spectral analysis of hydrothermal alteration zones associated with base metal sulfide deposits at rosebery and western tharsis tasmania and highway reward queensland spectral analysis of rock samples by short wavelength infrared swir analysis using the portable infrared mineral analyzer pima spectrometer is a relatively new field method with applications in mineral exploration the technique allows rapid field based identification of hydrothermal alteration minerals and delineation of alteration zones variations in mineral composition crystallinity and relative abundance may also be determined phyllosilicates including white mica and chlorite are particularly amenable to short wavelength infrared analysis these are prominent alteration minerals in the felsic volcanic rocks in the mount read volcanics tasmania and the mount windsor subprovince north queensland they have regional distributions as diagenetic and metamorphic products and exist locally in alteration zones associated with volcanic hosted sulfide deposits a geochemical and spectral investigation of white micas in the least altered rocks in the mount read volcanics has shown considerable background compositional variations the white micas range from phengite to moderately sodic muscovite and swir spectral measurements provide reliable estimates of their compositions chlorites also have a broad compositional range in these rocks however swir spectral analysis has proven to be unreliable in determining chlorite composition in samples where chlorite exists in low proportions relative to white mica or in mixed assemblages with epidote white micas in footwall alteration zones of the rosebery stratiform zn pb deposit tasmania are variably phengitic similar to those in regional background volcanics a unit of relatively unaltered volcaniclastic sandstone in the rosebery hanging wall sequence contains anomalous sodic muscovite in proximity to ore lenses white micas associated with the disseminated to massive pyritic cu au deposits at western tharsis tasmania and highway reward north queensland range in composition from phengite to slightly sodic muscovite in these symmetrically zoned alteration systems white micas grade in composition from phengite in peripheral zones to slightly sodic muscovite in proximal zones near ore in all three cases the white mica compositional variation is a vector to ore that is effectively measured by swir spectrometry with particular application in prospect scale exploration chlorite compositions at rosebery are not strictly spatially related to ore but tend to be most magnesian in zones of high chlorite abundance in the outer alteration zone at western tharsis there is a faint proximal trend to iron rich chlorites however it does not represent a well defined vector to ore in either case attempts at quantitative estimation of the relative abundance of white mica and chlorite in mixed samples by spectral analysis have produced results that are imprecise in comparison to geochemically derived estimates the data scatter relates to the low proportions of chlorite in the majority of the samples analyzed resulting in weak chlorite absorptions better results may be obtainable in specific alteration or lithostratigraphic domains by use of customized spectral unmixing software this investigation has shown that pima based swir spectrometry is a potent field method of mapping compositional variations in white micas that represent empirical vectors to at least some types of volcanic hosted sulfide deposits it has also highlighted its effectiveness in field identification of megascopically difficult or indeterminate alteration minerals such as pyrophyllite zunyite and topaz which may have genetic implications and exploration significance

inclined transpression in the neka valley eastern alborz iran three major nappes in the neka valley in the eastern alborz mountains of iran allow the cimmerian to present convergence following the oblique collision between iran and the southern margin of eurasia this work reports the identification of an inclined transpression zone recognized by field investigations and strain analyses of the geometries of formations and detailed mesoscopic structural analyses of multiple faults folds and a cleavage the main structures encountered include refolded recumbent asymmetric fold nappes highly curved fold hinges in a transpression zone that dips 37 to the nw between boundaries thrusts striking from n050 to n060 the angle the angle between the zone boundary and direction of horizontal far field shortening is about 80 the north west and south east boundaries of this zone coincide with the haji abad thrust and the shah kuh thrust respectively fold axes generally trend ne sw and step to both right and left as a result of strike slip components of fault displacements strain analyses using fry s method on macroscopic ooids and fusulina deformed into oblate ellipsoids indicate that the natural strain varies between 2 1 and 3 14 the estimated angle between the maximum instantaneous strain axis isamax and the transpression zone boundary is between 6 and 20 the estimated oblique convergence angle therefore ranges between 31 and 43 the average kinematic vorticity number wk is 0 6 in a zone of sinistral pure shear dominated inclined triclinic transpression these results support the applicability of kinematic models of triclinic transpression to natural brittle ductile shear zones

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

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

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

komatiitic sills and multigenerational peperite at dundonald beach abitibi greenstone belt ontario volcanic architecture and nickel sulfide distribution the density and the tectonic stresses in the deep crust and the physical properties of komatiitic magmas determine the level to which they will rise but once in the near surface environment the density and rheology of the near surface rocks consolidated and dense lava flows and sedimentary rocks versus unconsolidated sedimentary or volcaniclastic deposits govern whether they will be emplaced as lava flows invasive flows or sills where near surface strata are competent i e flow dominated or consolidated sedimentary and or volcaniclastic successions komatiitic magma erupts as flows that form extensive lava shields e g kambalda however where near surface strata are not competent i e unconsolidated volcaniclastic and or sediment dominated successions komatiitic magmas typically are emplaced as high level sills that increase the bulk density of the volcano sedimentary pile and eventually allow the eruption of lava and the construction of complex sub volcanic volcanic lava shields e g dundonald and shaw dome abitibi belt raglan cape smith belt pechenga kola peninsula thompson ni belt manitoba the latter environment is illustrated in the volcano sedimentary succession in dundonald township which is only weakly metamorphosed and deformed and superbly exposed in glacially polished outcrops the volcano sedimentary succession in this area comprises from base to top 1 the mcintosh formation composed of a succession of pillowed and massive intermediate volcanic flows 2 the dundonald formation composed of a lower section of komatiite sills argillites and felsic volcaniclastic deposits and an upper section of komatiite flows komatiitic sills and pillowed intermediate volcanic flows and 3 the frederick house lake formation composed of massive and pillowed mafic flows the distribution and thickness of argillites and felsic volcaniclastic rocks define a synvolcanic graben in which the dundonald south and alexo ni cu pge deposits occur within the center and the margin respectively sills and peperites in the lower komatiitic succession at dundonald beach exhibit a multigenerational emplacement history recording progressive lithification and increases in the bulk density and rheological strength of the unconsolidated argillites which ultimately permitted the eruption of lavas at alexo importantly the nature of the near surface rocks also influences the localization of ni cu pge deposits in lava shields e g kambalda the initial eruptions are typically most voluminous and if erupted at sufficient flow rates form channelized flows conducive to thermomechanical erosion of sulfur rich footwall rocks in sub volcanic volcanic lava shields however channelized units may occur within the subvolcanic plumbing system and or within overlying lavas where only sills are channelized e g thompson mineralization will occur only within the subvolcanic environment where only the flows are channelized e g damba silwane zimbabwe mineralization will occur only within the volcanic environment where both sills and lava flows are channelized e g dundonald shaw dome raglan the distribution of the mineralization is more diverse and may occur as subsea or sea floor ni cu pge deposits

archean komatiite volcanism controlled by the evolution of early continents the generation and evolution of earth s continental crust has played a fundamental role in the development of the planet its formation modified the composition of the mantle contributed to the establishment of the atmosphere and led to the creation of ecological niches important for early life here we show that in the archean the formation and stabilization of continents also controlled the location geochemistry and volcanology of the hottest preserved lavas on earth komatiites these magmas typically represent 50 30 partial melting of the mantle and subsequently record important information on the thermal and chemical evolution of the archean proterozoic earth as a result it is vital to constrain and understand the processes that govern their localization and emplacement here we combined lu hf isotopes and u pb geochronology to map the four dimensional evolution of the yilgarn craton western australia and reveal the progressive development of an archean microcontinent our results show that in the early earth relatively small crustal blocks analogous to modern microplates progressively amalgamated to form larger continental masses and eventually the first cratons this cratonization process drove the hottest and most voluminous komatiite eruptions to the edge of established continental blocks the dynamic evolution of the early continents thus directly influenced the addition of deep mantle material to the archean crust oceans and atmosphere while also providing a fundamental control on the distribution of major magmatic ore deposits

early pleistocene lake formation and hominin origins in the turkana omo rift abstract prior research has correlated the formation of plio pleistocene lakes in east africa to global regional climate changes and interpreted the lacustrine basins as significant settings of hominin evolution paleo lake lorenyang from the turkana omo rift is important to these issues as its marginal deposits contain some of if not the earliest currently known specimens of acheulian stone tools and african homo erectus magnetostratigraphic and sedimentological evidence indicates that the oldest preserved paleo lake lorenyang deposits are dated at 2 148 2 128 ma and derive from the nw turkana basin predating those from the omo basin by 100 kyr and the ne turkana basin by 190 kyr apparently the lake expanded asynchronously in the rift potentially due to a volcano tectonic influence on the location of drainage networks depositional slopes or topographic elevation differences within and between the basins at the time of flooding the onset of the lake temporally coincides with the eruption of basalt lava flows dated to 2 2 2 0 ma that blocked the southeast outlet of the turkana basin this provides a plausible mechanism for hydrologic closure and lacustrine basin formation through volcano tectonic impounding it also points to a non climatic cause for the initial formation of paleo lake lorenyang at 2 14 ma first appearances for african h erectus 1 87 ma and acheulian tools 1 76 ma in the turkana omo rift postdate the lake s initial formation by about 270 kyr and 380 kyr respectively such timing differences contrast with studies that correlate all three to the 400 kyr eccentricity maximum at 1 8 ma although the turkana omo rift is just one example it does provide alternative insights to views that link climate hominin evolution and lake formation in east africa

biases in three dimensional vorticity analysis using porphyroclast system limits and application to natural examples a description of the systematic errors associated with the measurement of the vorticity number from poryhroclasts in natural systems is presented and discussed we show that strong biases and systematic errors could derive both from some erroneous physical i e no slip across clast matrix boundary homogeneity within the matrix as well as geometrical assumptions i e the radius ratio and angular measurements carried out in two dimensions on outcrop surfaces and thin section by comparing natural datasets of porphyroclast shape preferred orientation spo with different theoretical curves plots we suggest that at least one of the jeffery physical assumptions can be tested when applying vorticity techniques the comparison of different possible sources of systematic errors indicates that for medium to low vorticity numbers wm 0 8 vorticity data are strongly biased and that a minimum systematic error of 0 2 should be taken into account finally we use data from natural shear zones from the southern variscan belt in sardinia to test and discuss the starting assumptions of the jeffery model one of the main challenges of modern structural geology is to try to obtain information about the rheology and kinematics of flow occurring in the deepest crust and upper mantle several microstructure fabrics e g fabric asymmetry associated with mylonites represent potentially important sources of information to obtain kinematic data as well as for estimation of deformation parameters see passchier trouw 2005 for a review in particular porphyroclast systems have been shown to be a sensitive indicator of flow parameters and can be used to constrain the relative ratio of combined pure and simple shear i e the vorticity of the flow several theoretical and practical studies indicate that syn kinematic recrystallization of mantles sor d shaped tails around porphyroclasts and shape preferred orientation spo of porphyroclasts may store information on the amount of shear strain with the aim of developing a vorticity gauge theoretical and experimental models for study of the rotation and behaviour of elliptical porphyroclasts in a fluid have been proposed and developed the first attempt began with the pioneering works of jeffery 1922 and eshelby 1957 that found solutions for rigid objects immersed in a viscous and linear elastics fluid respectively bretherton 1962 ghosh ramberg 1976 and bilby kolbuszewski 1977 further adapted the basic jeffery analytical solution to material science and structural geology subsequent investigations used the previous theoretical calculation to develop efficient strain and vorticity gauge techniques capable of quantifying the flow parameters within shear zones passchier 1987 wallis 1992 simpson de paor 1993 holcombe little 2001 three main analytical techniques passchier 1987 wallis 1995 holcombe little 2001 are commonly employed to characterize flow within shear zones using rigid porphyroclats jessup et al 2007 all these techniques use the measurement of the axial ratio of porphyroclast r the shape factor fig 1 and the angle of long axis porphyroclast with respect to foliation or stretching direction h fig 1 and the distribution of the cross plotted curves to define the mean vorticity number wm these curves define a threshold number rc below which the porphyroclasts continuously rotate and above which they record stable sink position however as many authors passchier 1987 marques coelho 2001 have already noted the jeffery model assumes 1 rigid particles immersed in a non confined viscous flow 2 a perfect coupling on matrix particle interface and 3 no interference between particles during deformation use of the jeffery model implies that these physical assumptions are met and or need to be at least preliminarily tested although techniques to estimate the vorticity of flow have become routinely used on sheared rocks in a variety of tectonic settings e g klepeis et al 1999 xypolias doutsos 2000 xypolias koukouvelas 2001 bailey eyster 2003 law et al 2004 carosi et al 2006 2007 iacopini et al 2008 sarkarinejad et al 2008 2010 frassi et al 2009 larson godin 2009 relatively few detailed analysis of error sources have been proposed and a critical discussion from prior d j rutter e h tatham d j eds deformation mechanisms rheology and tectonics microstructures mechanics and anisotropy geological society london special publications 360 301 318 doi 10 1144 sp360 17 the geological society of london 2011 publishing disclaimer www geolsoc org uk pub ethics at university of aberdeen on november 19 2012 http sp lyellcollection org downloaded from

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

an exhumation model of the south peloponnesus greece an exhumation model comprising forward and backward thrusting and late orogenic collapse is proposed in order to explain the kinematics of the tectonic windows in the south peloponnesus the model is based on mapping mesoscopic structural data and strain analysis syn compressional thickening took place throughout the oligocene and early miocene which includes the subduction of the pindos ocean at the western margin of the pelagonian microcontinent and the intracontinental subduction of the phyllite quartzite and the plattenkalk series the latter subduction was associated with blueschist metamorphism westward directed ductile thrusting and folding the exhumation history of the deeper parts of the orogen began at the oligocene miocene boundary with the progressive entrance of the low density crust and the plattenkalk carbonates in the subduction zone increased buoyancy caused a the initiation of the phyllite quartzite series extrusion b vertical coaxial stretching and c the evolution of two pop up structures i e the parnon and taygetos anticlines this syn compressional exhumation was taking place in the lower miocene with decreasing rates from 7 to 1 5 mm year the change in the local stress field from compression to extension began in the middle miocene with the formation of hinterland dipping normal faults the exhumation denudation rate caused by the footwall uplift along these faults does not exceed 0 2 mm year

investigation on mineralogy geochemistry and fluid inclusions of the goushti hydrothermal magnetite deposit fars province sw iran a comparison with iocgs abstract the goushti iron deposit from dehbid area located in the sanandaj sirjan metamorphic belt ssb sw iran is hosted by the early mesozoic silicified dolomite mineralized zones are lithostructurally controlled and oriented nw se parallel to the zagros orogenic belt zob magnetite the major ore mineral occurs as open space fillings and is accompanied by the secondary mineral phases hematite goethite and martite gangue minerals mainly include quartz dolomite and k feldspar are associated with minor hydrosilicates calc silicates such as wollastonite and diopside minerals typical of skarns are virtually absent from the ore zones fe2o3 content in the mineralized zones varies in the range of 38 75 wt the concentrations of au cu p ti cr and v as well as co ni cr v lree hree eu sm and la lu values and eu ce anomalies of the studied ores indicate that the goushti deposit is a hydrothermal magnetite type the subvolcanic rhyolite and basalt in this area are regarded as the source of iron and heat in the mineralizing system the fluid inclusion data showed that magnetite deposited from the ore bearing fluid with salinities 1 7 wt nacl equivalent at temperatures of 130 200 c a decrease in temperature and pressure supplemented by fluid mixing is the major controlling factor in iron oxide precipitation the field relationships and mineralogical geochemical characteristics of iron ores indicate that the goushti hydrothermal deposit could not be classified as a member of the iocg iron oxide copper gold deposits

sedimentology and mechanism of a lacustrine syn rift fan delta system a case study of the paleogene gaobei slope belt bohai bay basin china abstract fan delta systems have long been studied as a kind of good hydrocarbon reservoirs although many models have been raised according to their local conditions there still exists some controversies regarding the formations of the ones developed in continental syn rift settings taking paleogene es32 3 of gaobei slope belt as an example this paper conducted a comprehensive geological study and a forward depositional modeling the results show that the sediment within the study area came mainly from the northeastern baigezhuang uplift and the northwestern xinanzhuang uplift over a short distance the sedimentary system is characterized by subaerial debris flow subaerial braided channels subaqueous distributary channels front sand bars and front sand sheets furthermore the study area is a balance filled basin that experienced a 3rd order normal regression followed by a transgression during the development of the study interval the results also show that a stable subsidence rate with small magnitude climate changes would be a plausible explain for the entire sequence of the fan delta system in the study area the tectonic subsidence was indeed the dominant driving force to a continental syn rift fan delta system although the climate sediment supply or lake level might bring some lower order e g 4th and 5th order superimpositions this paper proposed a likely model for fan deltas developed in continental syn rift settings which is expected to gain some insights into the forming mechanism and provide some supports for the reservoir characterization of similar and correlative sedimentary systems

lake baikal record of continental climate response to orbital insolation during the past 5 million years the sedimentary record of biogenic silica from lake baikal in south central siberia suggests that this region of central asia was impacted by two major cooling episodes at 2 8 to 2 6 and 1 8 to 1 6 million years ago the spectral evolution of this continental interior site parallels the evolutionary frequency spectra for various marine oxygen isotope records in the baikal record the 41 000 year obliquity cycle is particularly strong from 1 8 to 0 8 million years ago variance in the 100 000 year eccentricity band increases during the past 0 8 million years the expected precession frequency of 23 000 years is highest during the past 400 000 years the modulation of the predicted 23 000 and 41 000 year insolation forcing by the 100 000 and 400 000 year eccentricity bands indicates that the transfer of variance from the precession and obliquity frequencies to the eccentricity part of the spectrum occurred in the eurasian continental interior as well as in tropical and high latitude ocean sites

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab everest massif tibet this paper presents quantitative data on strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab the data were collected from the tibetan side of the everest massif where two low angle normal faults bound the upper surface of the greater himalayan slab the earlier and structurally lower lhotse detachment and the later and structurally higher qomolangma detachment greenschist to sillimanite grade quartz rich metasedimentary rocks exposed in the rongbuk to north col region of the everest massif are characterized by cross girdle quartz c axis fabrics indicating approximate plane strain conditions fabric opening angles progressively increase with depth beneath the overlying lhotse detachment and indicate progressively rising deformation temperatures of 525 625 50 c at depths of 300 600 m beneath the detachment deformation temperatures of c 450 c are indicated by fabric opening angles in epidote amphibolite facies mylonites located closer to the overlying detachment a top down to the north normal shear sense is indicated by the asymmetry of microstructures and c axis fabrics but the degree of asymmetry is low at distances greater than 400 m beneath the detachment and sillimanite grains are drawn into adjacent conjugate shear bands but still appear pristine indicating that deformation occurred at close to peak metamorphic temperatures these quenched fabrics and microstructures indicate rapid exhumation in agreement with previous isotopic dating studies mean kinematic vorticity numbers w m were independently calculated by three analytical methods calculated w m values range between 0 67 and 0 98 and indicate that although a simple shear component is generally dominant particularly in greenschist facies mylonites located between the lhotse and overlying qomolangma detachments there is also a major component of pure shear in samples located at 400 600 m beneath the lhotse detachment pure and simple shear make equal contributions at w k 0 71 our integrated strain and vorticity data indicate a shortening of 10 30 perpendicular to the upper surface of the greater himalayan slab and confirm that the upper surface of the slab is a stretching fault with estimated down dip stretches of 10 40 assuming plane strain deformation measured parallel to the flow plane transport direction

response of unconfined turbidity current to normal fault topography turbidity currents descending the slopes of deep water extensional basins or passive continental margins commonly encounter normal fault escarpments but such large magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory this study uses advanced computational fluid dynamics numerical simulations to monitor the response of large natural scale unconfined turbidity currents 100 m thick and 2000 m wide at the inlet gate to normal fault topography with a maximum relief of nearly 300 m for comparative purposes the turbidity current is first released on a non faulted pristine slope of 1 5 simulation model 1 the expanding and waxing flow bypasses the slope without recognizable deposition within the vertical resolution limit of 2 m similar flow is then released towards the tip model 2 and towards the centre model 3 of a normal fault escarpment in both of these latter models the sand carried by flow tends to be entrapped in four distinct depozones an upslope near gate zone of flow abrupt expansion and self regulation a flow transverse zone at the fault footwall edge a flow transverse zone at the immediate hangingwall and a similar transverse zone near the crest of the hangingwall counter slope where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow the near bottom reverse flow appears to be generated on a counter slope of 1 1 increased to 2 by deposition the kelvin helmholtz interface instability plays an important role by causing three dimensional fluctuations in the flow velocity magnitude and sediment concentration the thick deposits of large single surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows the study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope fan conceptual models when it comes to the spatial prediction of main sand depozones this article is protected by copyright all rights reserved

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

unusual transition in quartzite dislocation creep regimes and crystal slip systems in the aureole of the eureka valley joshua flat beer creek pluton california a case for anhydrous conditions created by decarbonation reactions abstract microstructures and quartz c axis fabrics were analyzed in five quartzite samples collected across the eastern aureole of the eureka valley joshua flat beer creek composite pluton temperatures of deformation are estimated to be 740 50 c based on a modified c axis opening angle thermometer of kruhl j metamorph geol 16 1998 142 in quartzite layers located closest 140 m to the pluton wall rock contact flattened detrital grains are plastically deformed and partially recrystallized the dominant recrystallization process is subgrain rotation dislocation creep regime 2 of hirth and tullis j struct geol 14 1992 145 although grain boundary migration dislocation creep regime 3 is also evident complete recrystallization occurs in quartzite layers located at a distance of 240 m from the contact and coincides with recrystallization taking place dominantly through grain boundary migration regime 3 within the quartzites strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains the c axis fabrics indicate that a slip operated within the quartzites closest to the pluton wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism c slip the spatial inversion in microstructures and slip systems apparent high temperature deformation and recrystallization further from the pluton contact and apparent low temperature deformation and recrystallization closer to the pluton contact coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units marble and calc silicate assemblages dominate close to the pluton wall rock contact whereas mixed quartzite and pelite assemblages are dominant further from the contact we suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton decarbonation reactions in marble layers interbedded with the inner aureole quartzites and calc silicate assemblages in the inner aureole quartzites may have produced high x co 2 water absent fluids during deformation the presence of high x co 2 fluid is inferred from the prograde assemblage of quartz calcite and not wollastonite diopside k feldspar in the inner aureole quartzites we suggest that it was these dry conditions that suppressed prism c slip and regime 3 recrystallization in the inner aureole and resulted in a slip and regime 2 recrystallization which would normally be associated with lower deformation temperatures in contrast the prograde assemblage in the pelite dominated outer part of the aureole is biotite k feldspar these wet pelitic assemblages indicate fluids dominated by water in the outer part of the aureole and promoted prism c slip and regime 3 recrystallization because other variables could also have caused the spatial inversion of c axis fabrics and recrystallization mechanisms we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz our conclusions are based on a small number of samples and therefore the unusual development of crystal fabrics and microstructures in the aureole to the ejb pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks

rift related sedimentary evolution and its response to tectonics and climate changes a case study of the guaizihu sag yingen ejinaqi basin china abstract distinguished from most existing rift basin evolutionary models the succession of deep water deposits in the guaizihu sag were mainly developed during rift initiation instead of the greatest tectonic subsidence phase this paper focuses on the detailed analysis of rift related sequence stratigraphy and sedimentary evolution in this continental rift sag and discusses tectonic and climatic controls on filling patterns the deposits of the guaizihu sag can be ascribed to four major depositional systems alluvial fan and fan delta braided delta sublacustrine fan and shallow to deep lacustrine deposits they are in part contemporaneous and some succeeding each other forming five sequence units and corresponding substages of basin evolution i rift initiation ii early rift climax iii middle rift climax iv late rift climax and v late syn rift substages with the onset of fault movement and hot humid climate conditions the first substage is characterized by a number of poorly linked depocenters which consist of alluvial fan fan delta and deep lacustrine deposits with organic rich mudstones the second substage is associated with an enhanced activity of border faults and block rotation this unit is dominated by lacustrine deposits but fan or braided delta and sublacustrine fans also can be observed the third substage is marked by the maximum subsidence rate and shallow lakes fringed by fan and braided deltas the arid environment is likely to be the main factor controlling the lithofacies and filling characteristics of this unit during the fourth substage two early sub sags gradually converged to form a uniform one the relative tectonic quiescence and climate fluctuations sub humid to sub arid favored carbonate deposition the late syn rift unit which is dominated by fine grained deposits is a consequence of degradation of source area mostly tectonic this study shows that the effects of tectonics and climate on lacustrine sedimentation are intimately interwoven tectonism determines the sag structure stratigraphic architecture and spatial distribution pattern of depositional systems climatic conditions superimposed on tectonics tends to be the major control on sediment supply lithofacies types and sedimentary features

low potassium hydrothermal alteration in low sulfidation epithermal systems as detected by irs and xrd an example from the co o mine eastern mindanao philippines abstract detailed hydrothermal alteration investigations including petrography infrared reflectance spectroscopy irs and xrd of the low sulfidation epithermal co o mine located in eastern mindanao philippines revealed that both distal and intermediate hydrothermal alteration zones contain dominantly illite and chlorite whereas the proximal alteration zone comprises mainly illite chalcopyrite and pyrite the gold bearing veins and the proximal hydrothermal alteration zone display a distinct absence of k rich hydrothermal alteration minerals such as k feldspar adularia gold mineralization in the co o mine is controlled by an extensive quartz breccia vein system which is characterized by three distinct stages of vein incl breccias formation gold is mainly observed in stages 2 and 3 veins stage 1 veins appear as fragments in stage 2 veins and display boiling textures such as quartz pseudomophs after bladed calcite these veins further display colloform to crustiform banding and contain pyrite chalcopyrite and minor gold located in the colloform bands and between bladed quartz pseudomorphs stage 2 veins comprise mostly banded to massive quartz and contains sulfides parallel to bands or disseminated these veins are fine grained with mosaic jigsaw quartz and contain calcite blebs and or fragments of stage 1 veins gold is in textural equilibrium with chalcopyrite sphalerite and locally pyrite stage 3 veins consist of quartz and carbonate locally mn rich and display irregular banded and comb textures in auriferous veins of this stage gold is in textural equilibrium with chalcopyrite and pyrite with local abundance of sphalerite other sulfide minerals observed with gold in stages 2 and 3 are galena acanthite and locally jalpaite the xrd and irs provide inconsistent results regarding the abundance of k rich clays e g illite associated with auriferous veins illite with possibly interlayered swelling clays such as al smectite was identified in auriferous vein stages 2 and 3 using irs but could not be confirmed by xrd comparative analysis of the results of these techniques with respect to the ordering of micaceous minerals suggest less ordered white mica proximal to the veins vein textures such as banded quartz the absence of k feldspar and the abundance of illite interlayered al smectite suggest relatively low temperatures of formation of the hydrothermal alteration system and point to a potential boiling horizon located deeper or marginal to the currently exploited levels of the co o mine the absence of k feldspar may also be related to relatively low temperatures of the hydrothermal fluid the medium potassium rich magma series of the host rocks and or a relatively low oxidation state of the hydrothermal fluid

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

sedimentology and sequence stratigraphy of a transfer zone coarse grained delta miocene suez rift egypt this study focuses on miocene sedimentation and stratigraphic evolution in a major transfer zone at the northern tip of the thal fault segment gulf of suez the succession generally shoals upwards from offshore mudstone containing pro delta turbidites into conglomeratic delta foresets and topsets with sandstone dominated shoreface facies coexisting laterally despite this upward shoaling key stratal surfaces marking abrupt changes in relative sea level allow the succession to be divided into four stratal units the stacking pattern of the stratal units suggests an initial relative sea level rise that generated a major marine flooding surface a relative sea level fall followed resulting in widespread exposure and incision during the ensuing relative sea level rise a lowstand coarse grained delta and coeval shoreface succession prograded several kilometres basinward the stratigraphic development of the transfer zone delta is in marked contrast to that of aggradationally stacked deltas that occur near the centre of the baba sidri fault segment further south at the transfer zone low rates of subsidence and accommodation development coupled with a high sediment supply derived from a large fault tip drainage catchment have produced a strongly progradational delta subject to marked changes in relative sea level in the fault centre location however higher rates of accommodation development coupled with lower rates of sediment supply from footwall catchments have produced aggradationally stacked deltas the results from this study have implications for sequence stratigraphic models and hydrocarbon exploration within extensional basins

shortwave infrared spectral analysis of hydrothermal alteration associated with the pebble porphyry copper gold molybdenum deposit iliamna alaska the pebble cu au mo porphyry deposit is located approximately 320 km southwest of anchorage alaska shortwave infrared swir spectroscopy on drill core from the deposit has been used to document the distribution of alteration assemblages characterized by subtle variations in phyllosilicate minerals that cannot be confidently distinguished by visual criteria alone at pebble these phyllosilicate alteration types have different histories of metal introduction and or redistribution delineation of the distribution of these assemblages is critical to the geologic and genetic interpretations of the deposit spectral absorption features between 1 300 and 2 500 nm in particular small shifts in the position of the absorption wavelength related to aloh bonds around 2 200 nm allows distinction among illite sericite kaolinite and pyrophyllite bearing alteration assemblages electron microprobe and x ray diffraction analyses were used to validate the chemical composition and crystallinity of the phyllosilicate minerals identified using spectral data the results confirm the use of swir spectroscopy to confidently identify and spatially delineate phyllosilicate alteration assemblages at pebble these alteration types include potassic illite kaolinite quartz illite pyrite sericite pyrophyllite quartz sericite pyrite and sodic potassic assemblages the highest gold and copper concentrations within the deposit are in the eastern pluton and are coincident with low aloh values associated with pyrophyllite and sericite alteration an additional zone of low aloh values not associated with high metal grades occurs in the northeast along the margins of the deposit coincident with quartz sericite pyrite alteration the approach described here has significantly improved three dimensional alteration mapping and shows that short wave infrared spectroscopy may successfully distinguish variations in phyllosiclicate species this has implications for exploration because clay speciation is genetically related to the distribution of metals in the pebble deposit the recognition and utilization of these relationships has produced a robust three dimensional alteration model which can be applied to optimizing mine planning comminution and mineral process design

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

the association between ni cu pge sulfide and ni co lateritic ores and volcanic facies within the komatiites of the 2 7 ga east yilgarn craton large igneous province western australia abstract a critical factor in the generation of komatiite hosted ni cu pge sulfide deposits the addition of external sulfur via assimilation of s bearing substrate beneath channelised lava flows is a function of the komatiite flow field architecture this architecture is also critical in the development of magnesium rich bedrock lithologies that are prerequisites for the formation of komatiite hosted ni co laterite deposits to better understand the controls on the spatial distribution of both these deposit types a gis referenced map of komatiite flow regimes within the komatiitic component of the c 2 7 ga east yilgarn large igneous province and from parts of adjacent older greenstone belts in the yilgarn craton has been constructed using data from the field and the literature the regimes essentially divide komatiite sequences into those composed of thin 0 5 100 m laterally restricted 50 m 3 km cooling units and those composed dominantly of thick 100 m 1 km and laterally extensive 3 100 km cooling units the regimes are subdivided into six facies and five sub facies based on both stratigraphic and lateral variations in lithologies the facies define regional scale variations reflecting markedly different spatial and temporal crystallisation conditions within komatiite flow fields there is a marked spatial association between known magmatic nickel sulfides and particular komatiite facies facies favourable for hosting magmatic sulfides are those that contain early formed very magnesian cumulate sequences requiring high effusion rates of very hot turbulently flowing lava to form and thus have the potential to be contaminated by s bearing substrate rocks sulfide mineralised komatiites make up about 9 of the area of the current outcrop of the 2705 ma komatiite lip facies that have a low potential for nickel sulfide mineralisation are sheet like bodies in which basal rocks were emplaced under relatively quiescent conditions and where hot turbulently flowing lava and crystallisation of olivine rich cumulates developed only after the build up of a pile of high porosity olivine cumulates allowing no interaction with the substrate nickel cobalt laterite deposits are associated with thick originally laterally extensive high magnesian sequences some such sequences are also favourable for magmatic sulfide mineralisation but others occur in sheet like sequences

tectonic controls on rift basin morphology evolution of the northern malawi nyasa rift radiometric k ar and ar 40 ar 39 age determinations of volcanic and volcaniclastic rocks combined with structural gravity and seismic reflection data are used to constrain the age of sedimentary strata contained within the seismically and volcanically active northern malawi nyasa rift and to characterize changes in basin and flank morphologies with time faulting and volcanism within the tukuyu karonga basin began at approximately 8 6 ma when sediments were deposited in abroad initially asymmetric lake basin bounded on its northeastern side by a border fault system with minor topographic relief extensions primarily by a slip along the border fault and subsequent regional isostatic compensation led to the development of a 5 km deep basin bounded by broad uplifted flanks along the low relief basin margin opposite border fault younger stratigraphic sequences commonly onlap older wedge shaped sequences although their internal geometry is often progradational intrabasinal faulting flankuplift and basaltic and felsic volcanism from centers at the northern end of the basin became more important at about 2 5 ma when cross rift transfer faults developed to link the tukuyu karonga basin to the rukwa basin local uplift and volcanic construction at the northern end of the basin led to a southeastward shift in the basin s depocenter sequence boundaries are commonly erosional along this low relief hanging wall margin and conformable in the deep lake basin the geometry of stratigraphic sequences and the distribution of the erosion indicate that horizontal and vertical crustal movements both across and along the length of the rift basin led to changes in levels of the lake irrespective of paleoclimatic fluctuations