origin of the copper cobalt deposits of the zambian copperbelt an epigenetic view from nchanga the zambian copperbelt is arguably the most significantly mineralized neoproterozoic basin on earth preserving a truly spectacular scale of mineralization in excess of 1 109 t of ore at 2 7 copper has been extracted to date and there are also major cobalt accumulations the origin of these deposits has been hotly debated for more than six decades yet the driving forces that generated this system are poorly understood in particular the relationships between tectonics paleo fluid circulation and ore deposition we present new field and isotopic data for the nchanga deposits in which the bulk of the mineralization is hosted by shale capped feldspathic arenites and arkoses that have undergone recrystallization and hydrothermal alteration within a host rock package controlled by low angle thrust faults by using in situ laser combustion we show for the first time that the range of 34s for copper cobalt ore sulfides 1 to 18 cannot have the same source as diagenetic pyrite 1 to 17 we suggest a new epigenetic model for the formation of these spectacular nchanga orebodies that involves the introduction of metal and sulfate bearing hydrothermal fluids into quartzofeldspathic units during basin inversion with sulfide derived from thermochemical reduction of the sulfate near the site of deposition

the sediment hosted stratiform copper ore system sediment hosted stratiform copper deposits comprise disseminated to veinlet cu and cu fe sulfides in siliciclastic or dolomitic sedimentary rocks sediment hosted stratiform copper deposits are extremely common though economically significant deposits are rare they account for approximately 23 percent of the world s cu production and known reserves in addition to being significant sources of co and ag three sedimentary basins the paleoproterozoic kodaro udokan in siberia the neoproterozoic katangan in central africa and the permian basin of central europe contain supergiant 24 million metric tons mt contained cu deposits sediment hosted stratiform copper deposits are the products of evolving basin scale fluid flow systems that include source s of metal and s source s of metal and s transporting fluids the transport paths of these fluids a thermal and or hydraulic pump to collect and drive the fluids and the chemical and physical processes which result in precipitation of the sulfides metal sources are undoubtedly red bed sedimentary rocks containing fe oxyhydroxides capable of weakly binding metals sulfur may be derived from marine or lacustrine evaporites reduced seawater or hydrogen sulfide bearing petroleum metals appear to have been transported at low to moderate temperatures in moderately to highly saline aqueous fluids with the temperature of the fluid largely dependent on the time of fluid migration in the basin s burial history these basinal fluids were focused to potential metal precipitation sites by thinning of the red bed sequence at basin margins by faults by differentially permeable sedimentary units by paleotopography within the basin or along the margins of salt diapirs fluid movement produced widespread basin scale alteration that has commonly been overlooked but can form an important exploration guide sulfide precipitation occurred due to reduction typically caused by reaction with carbonaceous rocks or petroleum the amount of sulfides present at any deposit may be either metals or sulfide limited or could have been controlled by the amount of available reductant e g petroleum while understanding of sediment hosted stratiform copper ore genesis at the deposit scale is relatively robust there are still significant questions in regards its position in terms of basin evolution a wide variety of basin architectures and processes can lead to the formation of sediment hosted stratiform copper deposits despite general agreement that sulfides postdate sedimentation the absolute age of mineralization in many deposits has been difficult to document and the available evidence suggests that deposits can form throughout a basin s evolution from early diagenesis of ore host sediments to basin inversion and metamorphism supergiant and giant deposits formed in basins which underwent prolonged periods of fluid flow and in which unique conditions allowed for the accumulation of large amounts of metal bearing fluid sufficient reduced s and large amounts of reductants

orographic clouds in terrain blocked flows an idealized modeling study abstract idealized numerical simulations of moist strongly stratified flow over topography are used to study the processes that control orographic clouds in terrain blocked flows as a joint function of the nondimensional flow parameter nh u the horizontal topographic aspect ratio and the rossby radius of deformation nh f the simulations show the competition between enhanced upstream condensation in the secondary vertically propagating gravity wave and the reduction of condensation owing to enhanced low level flow deflection as nh u increases above about 1 5 the tendency for flow to be deflected around the barrier reduces cloud formation in the primary gravity wave over the ridge while increasing expands low level clouds over a broader upstream area ice clouds may form aloft in the secondary vertically propagating gravity wave and extend upstream for several hundred kilometers in terrain blocked flows more than half of the condensate mass develops upstream of the barrier in the secondary gravi

gravity field structure and tectonics of the eastern ghats abstract the eastern ghats are a prominent topographic feature on the indian peninsula stretching from the southern tip of the peninsula to near bhubaneswar 20 n 86 e along the east coast the belt is characterised by occurrences of high grade metamorphic rocks such as pyroxene granulites sillimanite gneisses charnockites and gabbro anorthosite masses the gravity field over the eastern ghats is appreciably positive as compared to the surrounding low grade gneissic terrain analysis of the gravity field along the coastal and southern granulite terrain comprising the eastern ghats shows that a large number of gravity highs are associated with charnockites of basic and intermediate nature as well as gabbro anorthosite masses the lows appear to be associated with acid charnockites syenite masses or granitic intrusives the boundary between the eastern ghats terrain and the adjoining dharwar bastar cratons appears to be a faulted one the crust underneath the eastern ghats is inferred to be of a higher density than that of the dharwar bastar cratons to its west the gravity field over the eastern ghats is compared to that of similar terrains in other parts of the world it is inferred that the eastern ghats are characterised by a crust of higher than normal density

multiple step recrystallization within massive ancient dolomite units an example from the dinantian of belgium south of the caledonian brabant wales massif a more than 200 m thick tournaisian to lower visean replacive dolomite unit can be followed for several hundred kilometres from the boulonnais france to aachen germany field observations of features such as karst cavities occurring at the top of the lower visean dolomite which are filled by lower visean crinoidal limestone indicate that dolomitization and karstification took place during the early visean this early development of the dolomite is in agreement with the presence of stylolites cutting the dolomite fabric the minor element composition of the majority of the dolomites remains almost uniform throughout the entire studied area values for fe mn na and sr are normally in the range 700 4700 ppm 15 400 ppm 80 300 ppm and 50 200 ppm respectively the 13c values range 0 72 to 5 31 o mainly reflect the carbon isotopic composition of the precursor limestones the 18o values in contrast are highly variable ranging from 19 15 to 0 85 o this rather large range of 18o values is explained by multiple step re equilibration recrystallization during progressive burial and subsequent uplift of the dolomites these processes are also responsible for the high 87sr 86sr values of the dolomites which range from about 0 7088 to 0 7098 they are distinctly more radiogenic than lower visean marine carbonates 0 7076 0 7078 correlation however of 18o values or 87sr 86sr ratios with dolomite and or cathodoluminescenec cl textures has not been very successful this suggests that recrystallization may remain unrecognized if only petrographic techniques are used nevertheless certain cl textures can be related to specific interactions with the ambient recrystallizing fluids

proterozoic to mesozoic east gondwana the juxtaposition of india sri lanka and antarctica jurassic and cambro ordovician paleomagnetic pole positions deduced from rocks of sri lanka and antarctica generally conform when sri lanka is juxtaposed with the coast of lutzow holm bay east antarctica in a manner similar to a current gondwana reassembly the highland and southwest groups mostly proterozoic of sri lanka are correlated with the ongul and skallen groups of east antarctica on the basis of similar lithology structural characteristics structural trend tectonothermal history ranging from early proterozoic to mesozoic and the pressure temperature time path of the main metamorphism some neighboring lithotectonic units are also comparable between the two areas fracture lineament systems of sri lanka and antarctica formed after the latest silurian and during or before the jurassic conform in this reconstruction an improved fit of the 2000 m isobaths of india sri lanka antarctica and continuation of the latest archaean mobile belt from enderby land to peninsular india is obtained by fitting sri lanka into lutzow holm bay and enderby land into the embayment in the east coast of peninsular india this juxtaposition of peninsular india to east antarctica involves about 80 km northward movement and about 30 clock wise rotation of sri lanka relative to india the reassembly thus obtained accords well with data supporting the idea that east gondwana existed from the earliest proterozoic to middle mesozoic although some disruption collision events of limited scale are considered possible

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

tectonic implication of the apatite fission track analysis of the mylonites from the terrane boundary shear zone of the eastern ghats mobile belt around lakhna orissa abstract apatite fission track analysis of the rocks within and adjoining the terrane boundary shear zone of the eastern ghats mobile belt india yield apparent ages ranging from 340246 to 268234 ma they are interpreted to be the result of slow ordovician to recent coolinglexhumation erosion rates are calculated at approximately 0 5 0 25 c my genetic algorithm modeling suggests the possibility of a minor heating event at approximately 120 ma this is the time when the region was passing over kerguelen hot spot as the indian plate separated from antarctica the rocks within and outside the shear zone do not show any difference in age suggesting that there has been no movement reactivation along the shear zone during this drifting based on this assumption the slightly higher rates of cooling following this event are attributed to continued slow denudation as well as thermal relaxation of the continent subsequent to hot spot influence

the internal geometry of nappes criteria for models of emplacement summary the geometric and stratigraphic properties of thrust sheets and fold nappes are controlled by the mechanisms by which they were initiated and emplaced thrust sheets that have developed by gravity gliding have their internal stratigraphies truncated by the basal thrusts which cut up section at the trailing edges in contrast thrust sheets that have developed by gravitational spreading have their internal stratigraphies truncated by the overlying thrust sheets and their basal thrusts cut up section at the leading edges fold nappes have complicated geometries and correlation of stratigraphy between successive nappes is difficult the basic geometric and stratigraphic properties of thrust sheets and fold nappes developed by different mechanisms may be used as criteria for testing the applicability of these mechanisms to particular areas of orogenic belts the valley and ridge province of the appalachians has geometric and stratigraphic properties consistent with thrust sheet development by gravitational spreading the western nappes of the central scandinavian caledonides are more complex but have properties suggesting development by buoyant upwelling of the orogen infrastructure there is however a lack of detailed cross sections of orogenic belts based on geophysical and or borehole data in addition to the geological data the interpretation of geological data in isolation is often too dependent on subjective information coloured by the mechanism preferred by the individual concerned

carbon and oxygen isotope halo in carbonates related to the mcarthur river hyc zn pb ag deposit north australia implications for sedimentation ore genesis and mineral exploration a study of carbon and oxygen isotope ratios in fine grained sedimentary dolomite in the barney creek formation of the mcarthur basin demonstrates the presence of an extensive isotope halo surrounding the giant stratiform hyc zn pb ag deposit dolomite within the halo shows an 18o enriched and 13c depleted isotope signature 18o 23 to 26 smow 13c 2 to 3 5 pdb relative to normal proterozoic sedimentary dolomite beyond the halo 18o 20 23 and 13c 0 to 2 the c o isotope halo within the dolomitic siltstones extends at least 15 km southwest of the hyc deposit and approximately coincides with a previously defined lithogeochemical halo of elevated fe mn zn pb and tl dolomitic siltstone lamellae within the stratiform zn pb ag ores at hyc exhibit an isotopic range similar to that of the halo dolomites suggesting that the ore and halo equilibrated with the same hydrothermal fluid modeling of isotopic exchange accompanying fluid rock interaction suggests that the halo dolomites equilibrated with low temperature fluids 50 120 c which were enriched in 18o 18o 5 5 but with an average crustal carbon isotope signature 13c 6 1 our preferred interpretation is that the oxygen and carbon isotope halo at hyc is related to the development of an extensive brine pool this pool was deepest in the vicinity of the hyc deposit adjacent to the emu fault and it became shallower to the southwest away from the fault using the carbon isotope fractionation equation between dolomite and hc batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document o 3 mbox end document it is possible to estimate the temperature variation at the base of the brine pool during the accumulation of the barney creek formation brine pool temperatures were highest in and adjacent to the hyc deposit 40 70 c and decreased to values of 17 to 30 c remote from the deposit these temperatures are similar to those recorded in the red sea brine pool associated with the atlantis ii metalliferous sediment deposit based on our work at hyc and lady loretta strata bound 18o enriched carbonate lithogeochemical halos may be a characteristic of the proterozoic stratiform zn pb ag deposits of northern australia these halos are more extensive than the narrow 18o depletion halos recorded in dolomites surrounding skarn mississippi valley type and irish style zn pb deposits this fundamental difference in the isotopic halo characteristics of these groups of zinc deposits is probably related to the low temperature synsedimentary brine pool origin of the north australian sedex deposits in contrast to the various replacement and open space fill origins of skarn mississippi valley type and irish style deposits

low froude number flow past three dimensional obstacles part ii upwind flow reversal zone abstract the present paper contains a continuation of our study of the flow of a density stratified fluid past three dimensional obstacles for froude number o 1 linear theory large froude number and potential flow type theory small froude number are both invalid in this range which is of particular relevance to natural atmospheric flows past large mesoscale mountains the present study was conceived to provide a systematic investigation of the basic aspects of this flow thus we have excluded the effects of friction rotation nonuniform ambient flow and the complexity of realistic terrain in part i of this study we focused on the pair of vertically oriented vortices forming on the lee side when the froude number decreases below 0 5 approximately and argued that their formation may be understood in terms of nonlinear aspects of inviscid gravity waves i e without invoking traditional arguments on the separation of the friction boundary layer herein we examine the zone of flow reversal on

genesis of copper lead mineralization in the regionally zoned agnigundala sulfide belt cuddapah basin andhra pradesh india shallow marine sandstone shale carbonate sedimentary rocks of the paleoproterozoic northern cuddapah basin host copper nallakonda deposit copper lead dhukonda deposit and lead mineralization bandalamottu deposit which together constitute the agnigundala sulfide belt the cu sulfide mineralization in sandstone is both stratabound and disseminated and pb sulfide mineralization occurs as stratabound fracture filling veins and or replacement veins within dolomite systematic mineralogical and sulfur carbon and oxygen isotope studies of the three deposits indicate a common ore fluid that deposited copper at nallakonda copper lead at dhukonda and lead at bandalamottu under progressive cooling during migration through sediments the ore fluid was of low temperature 200 c and oxidized thermochemical reduction of basinal water sulfate produced sulfide for ore deposition it is envisaged that basal red bed and evaporite bearing rift related continental to shallow marine sediments might have acted as the source for the metals rift related faults developed during sedimentation in the basin might have punctured the ore fluid pool in the lower sedimentary succession and also acted as conduits for their upward migration the ore bearing horizons have participated in deformations during basin inversion without any recognizable remobilization

formation of sedimentary rock hosted stratiform copper deposits through earth history sedimentary rock hosted stratiform copper deposits form by movement of oxidized copper bearing fluids across a reduction front that results in the precipitation of copper sulfides large scale production of such oxidized fluids as well as the formation of mobile hydrocarbons oil has probably been common since the formation of the first red beds in the paleoproterozoic and deposits of this type occur in rocks from the paleoproterozoic to the tertiary however supergiant deposits are currently recognized in only three basins the paleoproterozoic kodaro udokan basin of siberia the neoproterozoic katangan basin of south central africa and the permian zechstein basin of northern europe the paucity of data regarding the udokan deposit makes understanding this system difficult in terms of earth history events both the neoproterozoic and the permian were times of supercontinent breakup with major landmasses at low latitudes this global tectonic framework favored the formation of failed rifts that subsequently became significant intracratonic basins with basal synrift red bed sequences overlain by marine and or lacustrine sediments and in some basins located at low latitudes by thick evaporitic strata the intracratonic setting of these basins allowed the development of a hydrologically closed basinal architecture in which highly oxidized and saline moderate temperature basinal brines were produced that were capable of supplying reduction controlled sulfide precipitation over very long time periods tens to hundreds of millions of years the length of time available for the mineralizing process may be the key factor necessary to form supergiant deposits however examination of the absolute ages for the kupferschiefer zechstein basin and katangan deposits allows speculation that other factors may also have been important both the neoproterozoic and permian were times of major glacial events glaciation may also be conducive for the formation of supergiant sediment hosted stratiform copper deposits glacial periods correspond to magnesium and sulfate rich oceans that could have been responsible for additional sulfur in basinal brines developed during evaporite formation and would then be available during the long mineralization process

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

anorogenic felsic magmatism rift sedimentation and giant proterozoic pb zn deposits the giant lead deposits that developed after 1 8 ga in australia north america and africa are absent in the earlier geologic record these proterozoic lead zinc deposits were all preceded by major outbreaks of anorogenic felsic magmatism that brought significant amounts of lead rich material 30 ppm to the surface of proterozoic cratons erosion of these volcanics apparently transferred major quantities of the lead to rift basins where giant lead deposits were generated all known giant proterozoic sediment hosted lead zinc deposits more than 50 mt of lead metal are explained by a model that is supported by sm nd data relevant to mantle separation ages of volcanics and the metasedimentary source rocks for the lead ores

deformation history of the nw salient of the eastern ghats mobile belt india abstract the eastern ghats mobile belt of india displays fold thrust belt structure with a prominent salient on its nw margin the salient consists of lathore nappe and turekela klippe that have overthrust the craton to nw the rocks of the nappes have undergone granulite facies metamorphism and multiple phases of folding corresponding to the eastern ghats orogeny prior to thrusting as a result the granulites along the thrust are retrograded to amphibolites and the axial traces of the folds have been truncated against the thrust plane the basal decollement of the fold thrust belt is represented by the terrane boundary shear zone that defines the tectonic margin between the craton and the mobile belt it occurs as a ductile thrust affecting the cratonic basement as well as the mobile belt suggesting that the basement did not behave as a rigid body during thrusting thus the study area is comparable with the caledonide fold thrust belt further two large lateral ramps namely khariar and paikamal lateral ramps have been developed on the decollement at the lithological contact between tonalite trondhjemite gneisses granite gneisses and the latetectonic potassic granites of the craton fault bend folds associate with these ramps too it is suggested that the salient structure of the fold thrust belt is the combined result of 1 lateral ramps on the decollement and 2 differential displacement along the sole thrust due to lateral variation in detachment strength

a reassessment of the archean mesoproterozoic tectonic development of the southeastern chhattisgarh basin central india through detailed aeromagnetic analysis abstract we constrained the geological framework over polydeformed paleoproterozoic sonakhan greenstone belt and addressed the tectonic evolution of singhora basin in the fringes of bastar craton central india by utilizing aeromagnetic data interpretation 2 5d forward modelling and 3d magnetic susceptibility inversions the sonakhan greenstone belt exposes volcano sedimentary sequences of the sonakhan group within nnw sse to nw se trending linear belts surrounded by granite gneisses which are unconformably overlain by sedimentary rocks of chhattisgarh basin the orientations of aeromagnetic anomalies are coincident with geological trends and appear to correlate with lithology and geologic structure regional magnetic anomalies and lineaments reveal both nnw sse and ne sw trends prominent e w trending linear high amplitude magnetic anomalies are interpreted as the trans chhattisgarh aeromagnetic lineament tcal nw se trending aeromagnetic signatures related to sonakhan greenstone belt extends below the singhora sedimentary rocks and forms the basement in the west the analysis suggests that tcal is a block fault with northern block down thrown and affected the basement rocks comprising the sonakhan greenstone belt and samblapur granitoids the episode of faulting represented by the tcal is pre singhora sedimentation and played a vital role in basin evolution the basement configuration image generated by estimates of depth to magnetic basement suggests a complex pattern of nne ssw to ne sw trending depressions separated by a linear n s trending basement ridge it is inferred from the 3d magnetic susceptibility inversion that the thickness of sediments is more towards the eastern basin margin and the n s ridge is a manifestation of post sedimentary faulting results of 2 5d modelling of a wnw ese profile across the singhora basin combined with results from 3d inversion suggest suggests the basin subsidence was controlled by ne sw trending regional faults in an active system the basin geometry evolved by e w block faulting overprinted by ne sw trending pre to syn depositional normal faults generating ne sw depression which are affected by n s trend post sedimentary faulting though the present work relates the basin evolution with the initiation of rift basin it warrants further work to establish the deformation within the basin pertaining to the proximal thrust and uplift along the craton fringe

simulations of moist nearly neutral flow over a ridge although a fairly common atmospheric condition in orographic rain scenarios there is relatively little known about moist neutral flows over a ridge from theory and modeling presented in this paper are numerical simulations of the orographic flow modification occurring for a two dimensional moist nearly neutral flow over a ridge in the regime where the coriolis force can be neglected if an initially saturated moist neutral flow were to remain everywhere saturated as it flows over an obstacle then the expected solution would be the linear solution because the condition for linearity hill height less than the ambient wind velocity static stability is always met however for higher mountains the solutions indicate the development of areas of unsaturated air with correspondingly larger values of local static stability this internal switching from small to large values of static stability is an inherent nonlinearity which has far reaching consequences for understanding the orographic flow modification in this regime the sensitivity of the solution to the mountain height and to the initial cloud water content is analyzed here the authors find that the solutions fall into three basic categories if the mountain height is small enough a saturated flow can be maintained everywhere given sufficient initial cloud water for tall mountains the atmosphere upwind of the mountain is maintained in a saturated state and transitions to an unsaturated downslope flow on the lee side which has characteristics associated with downslope windstorms for mountains of intermediate height the solutions show the existence of an upwind propagating disturbance that has the effect of desaturating the atmosphere above the mountain

the rayner complex of east antarctica complex isotopic systematics within a proterozoic mobile belt new isotopic rb sr u pb zircon and sm nd and petrological data are presented for part of an extensive proterozoic mobile belt locally known as the rayner complex in east antarctica much of the belt is the product of mid proterozoic 1800 2000 ma juvenile crustal formation melting of this crust at about 1500 ma ago produced the felsic magmas from which the dominant orthogneisses of this terrain were subsequently derived deformation and transitional granulite amphibolite facies conditions which peaked at 750 50 c and 7 8 kbar 0 7 0 8 gpa produced open to tight folding about e w axes and syn tectonic granitoids about 960 ma ago subsequent felsic magmatism occurred at about 770 ma and not as has been widely advocated at 500 550 ma which appears to have been a time of widespread upper greenschist facies 400 500 c metamorphism localized shearing and faulting sm nd model ages of 1 65 2 18 ga disprove a previously favoured hypothesis that the rayner complex mostly represents reworked archaean rocks from the neighbouring craton napier complex models that involve rehydration of the napier complex are no longer required since the rayner complex was its own source of water two episodes of proterozoic crustal growth are identified the later of which occurred between about 1200 ma and 1000 ma and was relatively minor sedimentation took place only shortly before late proterozoic orogenesis the multiphase history of the rayner complex has resulted in complex isotopic behaviour three temporally discrete episodes of pb loss from zircon have been identified the earliest two of which are responses to the c 960 ma and 540 ma tectonothermal events fluid leaching was operative during the later event for there is a good correlation between degree of isotopic discordance and secondary mineral growth pb loss during the high grade event was probably governed by the same process or by lattice annealing some zircon suites also document recent pb loss most lower concordia intercepts have no direct geological meaning and are explicable as mixed ages produced by incomplete pb loss during two or more secondary events whereas all zircon separates from the orthogneisses produce u pb isotopic alignments zircons from the only analysed paragneiss produce scattered data in part reflecting a range of provenance the 960 ma event was also associated with the growth of a characteristically low u zircon 300 g g in rocks of inferred high zr content there is ubiquitous evidence for the resetting of rb sr total rock isochrons even samples separated by up to 10 km fail to produce igneous crystallization ages minor mineralogical changes produced by the 540 ma upper greenschist facies metamorphism were sufficient to almost completely reset some rb sr isochrons and to produce open system conditions on outcrop scale at least in one location

sensitivities of orographic precipitation to terrain geometry and upstream conditions in idealized simulations abstractthis study examines how variations in relatively simple terrain geometries influence orographic precipitation and its spatial patterns of sensitivity to small changes in upstream conditions an idealized three dimensional model is used to simulate a moist flow impinging upon three alpine scale terrain shapes a straight ridge a concave ridge and a convex ridge a variety of simulations are conducted to investigate the sensitivity of precipitation patterns to ridge length and upstream thermodynamic and wind conditions for an impinging flow with a nondimensional mountain height of approximately unity it is found that for the straight and convex ridges the flow response is mostly linear for the conditions examined here and passes over the obstacles with little lateral deflection the concave ridge however exhibits strengthened flow deceleration wave breaking in the lee and flow confluence between the ridge arms the concave ridge also generates substantially more precipitation than the other

the evolution and significance of microfracturing within feldspars in low grade granitic mylonites a case study from the eastern ghats mobile belt india abstract patterns of microfracturing are investigated in plagioclase and k feldspar porphyroclasts formed within granitic mylonites along the boundary of the eastern ghats mobile belt india the mineral assemblage comprising quartz feldspar biotite and hornblende suggests lower greenschist facies conditions during mylonitisation with the contrasting ductile behaviour of quartz and brittle fracturing of feldspars restricting the temperature range during deformation to 300 350 c microfracturing of feldspars takes place by concentration of pure shear within the feldspar rich layers this may reflect strain partitioning into dominantly pure and simple shear due to the competency contrasts between the two major constituent minerals quartz and feldspar the microfractures occur in conjugates here designated t 1 and t 2 with t 1 inclined in the same direction as the s fabric and showing an antithetic sense to the nw verging shear while t 2 is inclined in an opposite sense to the s fabric and displays synthetic shear the direction of maximum compression occurs at high angles to the c fabric and the t 1 and t 2 fractures are the result of pure shear localized into brittle layers within the mylonite with progressive shear the fractures along with their host feldspar grains are rotated theoretical graphs are plotted between bulk shear and the angle of initiation of t 1 and t 2 with respect to c planes for fractures hosted in a circular or elliptical objects the kinematics of these fractures are also analyzed with regard to variations in shear strain and sense of shear along them the sense of shear may vary or remain stable within fractures depending on their initial angle of inclination with respect to the c fabric as t 1 is inclined at low angles to the xy plane and in the same direction as the s fabric it undergoes maximum shear strain compared to t 2 and may even exceed the bulk shear this facilitates breakdown of feldspar porphyroclasts during progressive deformation the t 1 set maintains an antithetic sense of shear even at low angles with the c fabric while t 2 displays a synthetic sense in spite of being at high angles to c the t 1 and t 2 fractures therefore differ significantly from the classic riedel p and y shears where low angle fractures display synthetic shear and high angle ones r show antithetic displacement with respect to the bulk shear sense

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

discussion of saha et al 2012 precambrian research tectono magmatic evolution of the mesoproterozoic singhora basin central india evidence for compressional tectonics from structural data ams study and geochemistry of basic rocks abstract the discussion of saha et al precambrian research 2012 doi 101016 j precamres 2012 03 004 2012 tectono magmatic evolution of the mesoproterozoic singhora basin central india evidence for compressional tectonics from structural data ams study and geochemistry of basic rocks in precambrian research is placed within the broader context of what is known and what is unknown about the shallow crustal deformation structures and the interplay of deformation in the basement and cover rocks

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

strain partitioning along the mahanadi shear zone implications for paleo tectonics of the eastern ghats province india abstract during indo antarctic collision at c 1 0 ga eastern ghats province egp granulites amalgamated with the archean indian craton the northern boundary of the egp was subsequently reworked undergoing dextral strike slip shearing at 0 5 ga this study documents a phase of dextral shearing within the egp along wnw ese trending shear planes in c 0 5 ga mylonites of the mahanadi shear zone regional structural trends in the egp show a swing from ne sw to the south of the shear zone to wnw ese to its north the mylonitic shear zone foliation has a sub horizontal lineation associated with a prominent dextral shear sense in near horizontal sections electron back scatter diffraction ebsd studies on quartz confirm that mylonitisation was associated with dextral strike slip movement in the greenschist facies north of the mahanadi shear zone strain was partitioned into narrow dextral strike slip shear zones along which the older granulite fabrics were transposed parallel to later wnw ese trending shear planes at lower grades of metamorphism this regional scale shearing at 500 ma possibly resulted in a significant dextral shift of the northern egp with respect to the south the shear zone was reactivated in the permian time during deposition of gondwana sediments in the mahanadi basin

deformation pattern in the kurnool and nallarnalai groups in the northeastern part palnad area of the cuddapah basin south india and its implication on rodinia gondwana tectonics abstract the proterozoic basins of india adjoining the eastern ghats granulite belt eggb in eastern and southern india contain both mesproterozoic and neoproterozoic successions the intracratonic set up and contractional deformation fo the neoproterozoc successions in the paland sub basin in the northeastern part of cuddapah basin and similar crustal shortening in contemporaneous successions lying west of the eggb and nellore schist belt nsb are considered in relation to the proposed geodynamic evolution of the the rodinia and gondwana supercontinents tectonic shortening in the palnad sub basin northeast cuddapah partitioned into top to westnorthwest thrust shear flexural folds and cleavage development under overall e w contraction suggests foreland style continental shortening within an intracratonic set up a thrust sheet containing the nallamalai rocks and overlying the kurnool rocks in the northeastern part of palnad sub basin exhibits early tight to isoclinal folds and slaty phylllitic cleavage which can be correlated with early mesoproterozoic deformation structures in the nothern nallamalai fold belt nfb nne ssw trending folds and cleavage affect the kurnool group and overprint earlier structures in the thrust sheet thrusting of the nallamalai rocks and the later structures may have been related to convergence of the eastern ghats terrane and the east dharwar bastar craton during early neoproterozoic greenvillian and or later rejuvenation related to pan african amalgamation of east and west gondwana

strains and folds within thrust sheets an analysis of the heilam sheet northwest scotland abstract the changes of shape and orientation of fossil worm burrows have been used to carry out a detailed strain analysis of the heilam thrust sheet in the moine thrust zone northwest scotland the strains have been factorised into components of layer parallel shear 1 layer normal shear 2 and layer parallel shortening or elongation variations in the 1 shear are largely lithologically controlled some strain is due to flexural processes as the thrusts and overlying beds change dip over thrust ramps or are tightened by later deformation while there may also be a component of drag which increases towards the overlying thrust this predating the shear due to flexure a contoured map of the values suggests that major folds within the thrust sheet developed as a result of stick or drag on the floor thrust prior to ramp climb this led to differential movement in the transport direction causing layer parallel shortening accompanied or followed by buckling of the layers a map showing layer normal shear strains 2 suggests that the heilam sheet forms a major surge zone the central part having moved further wnw than the northern and southern parts this has led to components of lateral shear along parts of the sheet especially in the north producing curvature of the imbricate faults

detrital mineral age radiogenic isotopic stratigraphy and tectonic significance of the cuddapah basin india abstract the cuddapah basin is one of a series of proterozoic basins that overlie the cratons of india that due to limited geochronological and provenance constraints have remained subject to speculation as to their time of deposition sediment source locations and tectonic geodynamic significance here we present 21 new stratigraphically constrained u pb detrital zircon samples from all the main depositional units within the cuddapah basin these data are supported by hf isotopic data from 12 of these samples that also encompass the stratigraphic range and detrital muscovite 40ar 39ar data from a sample of the srisailam formation taken together the data demonstrate that the papaghni and lower chitravati groups were sourced from the dharwar craton in what is interpreted to be a rift basin that evolved into a passive margin the nallamalai group is here constrained to be deposited between 1659 22 ma and 1590 ma it was sourced from the coeval krishna orogen to the east and was deposited in its foreland basin nallamalai group detrital zircon u pb and hf isotope values directly overlap with similar data from the ongole domain metasedimentary rocks depositional age constraints on the srisailam formation are permissive with it being coeval with the nallamalai group and it was possibly deposited within the same basin the kurnool group saw a return to dharwar craton derived provenance and is constrained to being neoproterozoic it may represent deposition in a long wavelength basin forelandward of the tonian eastern ghats orogeny detrital zircons from the gandikota formation which is traditionally considered a part of the chitravati group constrain it to being deposited after 1181 29 ma more than 700 ma after the lower chitravati group it is possible that the gandikota formation is correlative with the kurnool group the new data suggest that the nallamalai group correlates temporally and tectonically with the somanpalli group of the pranhita godavari valley basin which is tightly constrained to being deposited at 1620 ma these syn orogenic foreland basin deposits firmly link the se india proterozoic basins to their orogenic hinterland with their discovery filling a missing link in the tectonic development of the region

large lateral ramps in the eocene valkyr shear zone extensional ductile faulting controlled by plutonism in southern british columbia abstract a 2 5 km high s facing lateral ramp links northern and southern segments of the ductile eocene valkyr extensional shear zone which defines the upper and outer boundary of the valhalla core complex in southern british columbia canada the evolution of the valkyr shear zone and of the lateral ramp is strongly influenced by the setting and geometry of middle jurassic tonalitic plutons and of paleocene eocene leucogranite aplite and pegmatite middle jurassic plutons were emplaced in the region of the valhalla complex as a series of interconnected flatbottomed laccoliths with the basal surfaces of adjacent bodies at the same structural level however on a large scale the southern portion of the laccolithic complex is structurally 2 5 km lower than the northern portion the lower surface of the laccolithic complex formed the upper limit of injection of gently dipping paleocene eocene leucogranite sheets as a consequence the upper margin of leucogranite is 2 5 km structurally lower in the south than in the north during the eocene extensional shear zones propagated along the interface between the upper plate stiffened by the cool strong middle jurassic tonalite and the lower plate made weak and ductile by voluminous hot paleoceneeocene leucogranite sheets the northern and southern segments of the valkyr shear zone propagated at two different structural levels and a lateral ramp formed in the intervening zone the ramp was localized at a rheological change across a s dipping boundary between hot ductile paleocene eocene leucogranite and an adjacent strong middle jurassic pluton maximum displacement of 15 20 km occurs in the central portion of the northern segment of the valkyr shear zone the southern segment has only 1 3 km of displacement this has left the pre eocene geological relationships of the southern valhalla complex and its surrounding rocks nearly intact and it can be demonstrated that the valkyr shear zone formed with a gentle original dip

saddle dolomite as a by product of chemical compaction and thermochemical sulfate reduction petrographic stable and radiogenic isotope trace element and fluid inclusion data from the devonian nisku reef trend in the subsurface of alberta canada suggest that saddle dolomite was a by product of chemical compaction and thermochemical sulfate reduction in subsiding dolomitized rocks furthermore thermochemical sulfate reduction may be representative of other processes that increase the amount of saddle dolomite via an increase in carbonate alkalinity the data also confirm that saddle dolomite is most likely to form at elevated temperatures from hypersaline brines

hangingwall strain a function of duplex shape and footwall topography abstract the concept of piggy back thrust tectonics implies that foreland is progressively accreted onto a developing thrust sheet during duplex formation lateral shape changes in duplexes in the hangingwall of a thrust and corrugations in the footwall will fold higher thrust sheets to give culminations and depressions balancing of parts of high level thrust sheets with lower sheets and foreland requires a sequence of extensional and compressional strains orientated normal to the thrust transport direction culmination walls will be sites of strike parallel extension subsequent adjacent culminations will compress early culmination walls which will result in a sequence of irrotational strains examples of this geometry are given from the moine thrust zone of northwest scotland the model allows a re examination of strains and hangingwall evolution in some thrust sheets in the helvetic and external zones of the alps

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

petrogenesis of the kunavaram alkaline complex and the tectonothermal evolution of the neighboring eastern ghats belt granulites se india abstract geochemical and geochronological study of the kunavaram alkaline rocks near the craton eastern ghats belt egb contact in se india indicates that alkaline magma was emplaced at 1384 ma along a ne sw mesoproterozoic rift at the cratonic margin this paleo rift can be delineated by the several mesoproterozoic alkaline intrusives at the cratonic margin e g khariar kunavaram jojuru elchuru and others the geochemical variations in the kunavaram alkaline suite can be explained by an assimilation fractional crystallization afc process dominated by the fractionation of clinopyroxene amphibole apatite titanite zircon and allanite and the simultaneous assimilation of bulk upper crustal material from the craton the alkaline complex and other craton margin rocks and the marginal granulites of the egb were overprinted by an amphibolite facies tectonothermal event during the neoproterozoic paleozoic 611 484 ma when pan african tectonism thrust the egb granulites westward over the cratonic foreland along a number of northwest vergent shear zones the pan african thrust stacking has the cratonic boundary and the alkaline rocks in the footwall and the egb granulites in the hanging wall the continuous nature of the pan african shear fabric across the craton egb contact near kunavaram implies that the two crustal segments shared a common boundary during the neoproterozoic paleozoic prior to the pan african event the evolutionary history of the egb is characterized by the presence of an early neoproterozoic 1017 1087 ma granulite facies tectonometamorphic overprint during the grenvillian orogeny evidence for which is lacking in the alkaline and other craton margin rocks the craton egb contact thus represents a rifted mesoproterozoic margin deformed during pan african collisional tectonics

investigation of orographic precipitation over an isolated three dimensional complex topography with a dense gauge network radar observations and upslope model abstractthis study uses a dense rain gauge network radar observations and an upslope model to document the detailed aspects of precipitation over da tun mountain dt of northern taiwan under pre

origin and evolution of granulites in normal and thickened crusts rocks buried in the upper part of a doubly thickened crust during orogeny can show prograde reactions with transitional features from lower grade rocks up to granulite facies they can be exposed at the earth9s surface within this one erogenic cycle for example the granulites exposed in british columbia have concordant u pb zircon ages of 65 85 ma in contrast rocks buried in the lower part of a thickened crust will crystallize granulites that typically show only retrograde relations with younger lower grade rocks at the cessation of orogeny such rocks will undergo near isobaric cooling from the peak metamorphism and can have very long residence times at the base of a crust of normal thickness these granulites require a second orogeny to uplift and expose them at the surface as an example the archean granulites of enderby land antarctica were metamorphosed at 3070 ma at 1000 c at 8 10 kbar pressure they then followed at least a 400 c isobaric cooling path they also had a prolonged residence time of 2000 m y near the base of the crust before uplift no doubt a continuum exists between these extremes but it is proposed that many intermediate and high pressure granulites form in the lower parts of thickened crust and therefore require a two stage cycle of tectonism to be uplifted and exposed at the earth9s surface although most granulites probably form in thickened crust at active plate margins underplating of normal 30 40 km thickness crust by mantle melts during extension can also produce granulites these granulites would also undergo isobaric cooling and require a later orogeny to expose them an example is the paleozoic lachlan fold belt of eastern australia which has undergone only minor uplift since the major ultrametamorphism at about 400 ma however isotopic petrologic and geochemical differences are to be expected between these extremes of granulite formation

on the dynamics of hawaiian cloud bands comparison of model results with observations and island climatology abstract this paper presents a detailed comparison study of three dimensional model results with an aircraft wind field mapping for the island of hawaii model runs were initialized using an aircraft sounding from 1 august 1985 and detailed predictions from the model are compared with observations from that day the strength and location of the upwind convergence zone were well simulated as well as the strong deflection and deceleration of the flow around the island and the geometry and location of the upstream cloud bands the good agreement between the model results and observations supports the results of our previous study in which we show that the flow pattern and associated cloud processes around the island of hawaii can be understood by considering the flow of a stably stratified fluid around a large three dimensional obstacle model runs with different wind directions showed that increasing northerly tradewind flow resulted in the band clouds moving closer to the shore line and the large scale

pogallo line south alps northern italy an intermediate crystal level low angle normal fault the pogallo line is a major crustal shear zone in the crystalline south alps of northern italy which separates middle amphibolite granulite facies rocks of the ivrea zone from lower middle amphibolite facies rocks of the strona ceneri zone u pb rb sr and k ar whole rock and mineral ages for samples from this region indicate that the two zones pursued different time temperature paths after caledonian peak metamorphism cooling curves for the two terrains finally converge in the late triassic early jurassic a time of large scale crustal extension in the south alps that anticipated the opening of the western tethys we suggest that the pogallo line may represent a low angle normal fault that developed at intermediate crustal levels during this period of extension and attained its present subvertical orientation during alpine deformation

age and p t evolution of the neoproterozoic turkel anorthosite complex eastern ghats province india abstract massif type anorthosite complexes constitute a distinct component of the proterozoic eastern ghats province in india they intruded the poly deformed and poly metamorphic granulite facies terrane near its western and northern tectonic contacts with the archaean bastar and singhbhum cratons respectively following their emplacement the complexes were variously affected by high grade metamorphism and deformation the turkel anorthosite complex comprises an anorthosite leuconorite diapir encircled by voluminous crust derived quartz monzonite intrusions hosted within an expansive batholithic complex of megacrystic k feldspar granite and remnants of an older gneissic unit this contribution evaluates the pressure temperature history of the anorthosite complex based on textural relations paragenetic characteristics and mineral chemistry and provides for the first time constraints on the timing of emplacement and subsequent metamorphism of the rocks through in situ u pb dating of zircon from several members of the suite emplacement of the turkel anorthosite complex occurred after the fabric defining late mesoproterozoic deformation d 1 d 3 and high grade metamorphism of the country rocks and was shortly preceded by the surrounding expansive intrusion of the megacrystic k feldspar granite the leuconorite anorthosite suite crystallized at 980 8 ma while the other components including the monzonite quartz monzonite and ferrodiorite were emplaced later between 956 6 and 945 5 ma the post intrusion evolution of the complex is characterized by partial re equilibration of the igneous parageneses and textures during an initial episode of cooling and decompression from the magmatic crystallization stage 1100 950 c 12 7 kbar towards the ambient thermobaric regime and following prolonged slow cooling by an episode of renewed compressional deformation late d 3 ca 750 c 6 5 7 0 kbar that caused the thorough high grade recrystallization of the rocks and produced the monophase planar fabric of the complex u pb spot ages from metamorphic domains of zircon grains constrain the age of this metamorphism to 901 879 ma the complex was moderately affected by the late neoproterozoic to early palaeozoic pan african tectonothermal event which led to internal tectonic segmentation and westward thrusting of the khariar and rampur domains of the northern eastern ghats province onto the bastar craton

alteration of plagioclase to nepheline in the khariar alkaline complex se india constraints on metasomatic replacement reaction mechanisms abstract at the khariar alkaline complex in southeastern india some tholeiitic amphibolites inter layered with syenite and nepheline syenite show microtextural evidence of fenitization typical metasomatic textures include the replacement of plagioclase by vein nepheline and albitic plagioclase or by symplectitic nepheline albite na al rich clinopyroxene whole rock mass balance calculations indicate that the fenitized variants gained alkalis na k some large ion lithophile elements sr rb and ba and high field strength elements like zr and hf during the metasomatic exchange the plagioclase replacement textures can be explained by a fluid mediated coupled dissolution reprecipitation process whereby the infiltration of alkali bearing fluid along grain boundaries and deformation induced intragranular fractures led to the dissolution of the host plagioclase along an inward moving reaction interface na ions were introduced and ca 2 ions removed by the fluid phase the al and si released from the breakdown of the anorthite component of the plagioclase combined with na from the fluid to precipitate nepheline albitic plagioclase or na al rich clinopyroxene reaction enhanced cracking during metasomatism due to local volume changes in the alteration zone produced a hierarchical system of fractures mass balance calculations using the volume proportion of phases in the plagioclase replacement zones show that sio 2 and al 2 o 3 were broadly conserved during the replacement there was significant loss of cao ca 73 and huge gains of na 2 o and k 2 o these results indicate that alkali and alkaline elements na k and ca were exchanged freely between the fluid phase and the reaction zone whereas si and al released during plagioclase dissolution were consumed in the replacement zone itself to form nepheline and albite rich plagioclase or na al rich clinopyroxene the trace element and sr nd isotope signature of the rocks indicate that the fenitizing fluids were derived from the nepheline syenites

multi stage deformation in the nallamalai fold belt cuddapah basin south india implications for mesoproterozoic tectonism along southeastern margin of india abstract the common occurrence of small scale refolded folds deformed lineations and overprinting of foliation in the northern nallamalai fold belt nfb within the intracratonic cuddapah basin south india suggest three phases of deformation d 1 d 2 and d 3 during the late paleoproterozoic to neoproterozoic d 1 structures are represented by tight to isoclinal folds a slaty cleavage and local development of mylonites d 2 structures include ne trending tight to open folds f 2 with variable plunge indicating control of large domal structures and a steep crenulation cleavage developed in phyllites and other schistose rocks the above structures are overprinted by e w trending d 3 folds and cleavage which affect mesoproterozoic rocks of the srisailam formation uppermost nallamalai group in the e w trending vami konda range and metasediments of the palnad area thought to be equivalent of the neoproterozoic kurnool group taking into account the ages of intrusive vellaturu granite 1575 ma which is post d 2 deformation in the nfb and the chelima lamproite 1400 ma which intrudes the folded nallamalai rocks we suggest that the earlier episodes of multiple deformation in the nfb represent either late paleoproterozoic or early mesoproterozoic nw se compression in this part of the east gondwana the e w fold thrust structures affecting the srisailam quartzite and adjacent metasediments in the palnad area represent late mesoproterozoic and or neoproterozoic event the granite gneisses and schists of the nellore schist belt bordering the nfb are affected by both early and later events and thrust over rocks of the nallamalai group we propose that early deformation in the nfb lying southwest of the eastern ghats and roughly parallel to the present southeastern coast of india was unrelated to and occurred prior to the main deformation in the eastern ghats which is generally correlated with the 1000 ma old grenville event alternatively in view of the complex protracted evolution of the eastern ghats and published geochronological data supporting pre grenvillian tectonism particularly in the western charnockite zone of the eastern ghats d 1 and d 2 deformation in the nfb may be linked to this older 1600 1400 ma tectonic disturbance in the eastern ghats

mechanisms of intense alpine rainfall abstract numerical studies by the authors and others of the 1994 piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall to uncover the precise mechanism of orographic rainfall occurring in full physics mm5 simulations of the 1994 piedmont flood the authors carried out simulations with the same real data initial and boundary conditions but with the real orography replaced by an idealized one with excellent agreement between real and idealized orography on the rainfall rate versus time in the piedmont area analysis of the idealized orography simulation provides a clear picture of the model s mechanism of orographically induced rainfall as noted in previous studies of the 1994 piedmont case a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains while an unsaturated airstream is stable and tries to flow around toward the left in the northern hemisphere in the 1994 piedmont case t

tectono sedimentary setting of the paleoproterozoic zawar pb zn deposits rajasthan india abstract the paleoproterozoic aravalli basin of rajasthan india hosts a number of pb zn sulphide deposits various ore genetic models for these deposits are available in the literature but none of them are backed by comprehensive basin models reconstructed on the basis of sedimentological analysis in the present work an attempt has been made to propose an actualistic basin model for the aravalli basin which was conducive to pb zn sulphide mineralization the zawar mineralized belt is one of the producing pb zn sulphide belts in the aravalli basin the aravalli sedimentary succession which is developed on the basement rocks in the zawar area is more than 2500 m thick the whole basin fill succession an unconformity bounded single mega sequence has been classified into four facies assemblages the sedimentary facies attributes and their architecture in each facies assemblage advocate in favour of an ensialic rift basin which experienced repeated down sagging and exhumation each foundering event of the rift basin was related to movements along some basin marginal and or intrabasinal faults which are manifestation of crustal stretching such faults were directly responsible for sediment dispersal in the basin in this overall tectono sedimentary frame the ore bearing sediments were deposited as a slope base fan deposit in deep marine environment the granitic basement derived sediments that underlie the mineralized horizons are conceived as a source for metals pb b isotopic signatures in galena and tourmaline and the intrabasinal faults that were active during sedimentation might have acted as conduits for upward transmission of the ore brine

pressure temperature time paths and a tectonic model for the evolution of granulites petrologic studies and application of well calibrated mineralogic thermometers and barometers reveal several important features common to many granulite terrains 1 peak metamorphic pressure and temperature conditions cluster around values of 7 5 pm 1 kbar and 800 pm 50 c implying average geothermal gradients of 30 35 c km 2 in comparison with upper amphibolite facies rocks especially in paired amphibolite granulite terrains it is evident that granulites are distinguished from amphibolites by the former s higher metamorphic temperatures but not higher pressure 3 initial cooling of granulite terrains from peak conditions is nearly isobaric for garnet closure temperatures of 600 pm 50 c the dp dt retrograde paths inferred from compositionally zoned garnet rims are 2 8 b c in most granulites 4 primary coarse sillimanite is found in most granulites and retrograde kyanite is known in a few these data suggest that granulites form as a result of anomalous thermal gradients

deformation pattern of the nw terrane boundary of the eastern ghats mobile belt india a tectonic model and correlation with antarctica abstract thrusts interspersed with lateral ramp and wrench structures mark the join between proterozoic eastern ghats mobile belt and archaean cratons of the eastern india the join referred to as terrane boundary shear zone exhibits an arcuate geometry at the nw margin of the eastern ghats where the mobile belt shows the presence of northwesterly verging nappes based on this the area has been described to represent the salient part of a fold thrust belt juxtaposition of the granulites over the low grade craton is largely attributed to thrusting along the terrane boundary shear zone as the folds are disoriented and the granulites are retrograded along the thrusts the terrane boundary shear zone is interpreted to be a retrograde shear zone the shear zone hosts a number of synkinematic alkali intrusive rocks that constrain the age of thrusting to 1 4 ga in the correlative framework of gondwanaland the terrane boundary shear zone is very likely to be contiguous with the rayner napier boundary of antarctica

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

the purana basins of southern cratonic province of india a case for mesoproterozoic fossil rifts abstract since its cratonization in the palaeoproterozoic southern peninsular india witnessed the development of a number of large intracratonic sedimentary basins traditionally referred to as purana basins spanning in age from late palaeoproterozoic through neoproterozoic the localization of these intracratonic basins namely pranhita godavari pg chattisgarh and cuddapah basins is apparently controlled by pre existing sutures and or weak zones the pg basin and the cuddapah basin host unconformity bound thick sediment dominated successions attesting to several cycles of fluvial shallow marine to shelf slope basin sedimentation deposition was punctuated by block uplifts resulting in local hiatuses and or volcanic upheavals leading to intercalation of thin but persistent basaltic flows and acid tuffs and ignimbrites basin margin deep faults apparently played a role in the facies distribution in these basins based on these features we propose that these basins initiated as continental rifts which however never opened up into a full fledged ocean basin but links with open seaway are evident from frequent occurrence of deposits representing tidal and storm influence particularly in upper part of the chattisgarh succession spatial distribution of facies and sediment thickness in the cuddapah and pg basins suggest that an open seaway existed to the east of the south indian cratonic province during the mesoproterozoic while similar criteria point to the existence of an open seaway north of the chattisgarh basin development history including nature of inversion suggest that the southern cratonic province of india existed as a single large continental mass since the mesoproterozoic in spite of episodes of supercontinent build up and fragmentation involving india and east gondwana during the proterozoic

two brine model of the genesis of strata bound zechstein deposits kupferschiefer type poland these kupferschiefer deposits were probably formed as a result of a mixing of two brines the upper cold brine ucb is an unmineralized brine rich in na ca cl and so4 with a ph 7 and originating from evaporites overlying the metal bearing zechstein rocks the lower hot brine lhb rich in mg k cl so4 and co3 with a ph 7 formed in sediments in the central part of the zechstein basin at a depth of 7 000 m this brine was subjected to heating and upward convection toward the fore sudetic monocline along the bottom of the z1 carbonates during its migration it caused albitization serpentinization and leaching of the primary metal deposits in rocks underlying the zechstein becoming enriched in heavy metals the mineralization process being a result of the mixing of the two brines ucb and lhb and catalytic oxidation of the organic matter of the black shale were initiated at shallow depths in the area of the fore sudetic monocline the boundary of the two brines generally overlapped the strike of the black shale

collision tectonics in the late precambrian eastern ghats mobile belt mesoscopic to satellite scale structural observations regional mapping of a section across the eastern ghats mobile belt egmb north of the godavari graben in eastern peninsular india by using landsat thematic mapper data enables recognition of a number of shear zones lineaments and structural domes and basins a conspicuous megashear occurs at the western boundary of the granulite facies rocks of the egmb adjacent to the archean granite greenstone craton the confinement of a suite of alkaline igneous rocks to this shear zone is a notable feature the strike extensions of this shear belt extend through to the elchuru alkaline complex prakasam district andhra pradesh and the syenite plutons of koraput district orissa the contrasting lithologies metamorphism and structural history on either side of the shear zone suggests that it might be a precambrian suture zone the mesoscopic structural features in the egmb include prominent foliation with moderate to steep dips folds faults shears s c fabrics pinch and swell structures and other linear fabric elements these observations favour the consideration of drastic crustal shortening and thickening and a complex deformational sequence the major rock units in this part of egmb comprise garnetiferous sillimanite gneisses quartzites and calc granulites forming the khondalitic suite of rocks and a wide variety of charnockitic rocks the contact of the two rock units is generally sheared and often migmatised the structural fabric suggests two major tectonic events an essentially horizontal tectonic regime resulting in thrust systems and associated structures subsequently followed by strike slip tectonics characterized by high shear strains features such as westward verging thrusts large scale recumbent folds major shear zones structural domes and basins indications of tectonic crustal shortening extensive calc alkali magmatism and widespread migmatization in the region are attributed to collisional processes during proterozoic times the spatial disposition of the egmb and its linkage with the distribution of similar rock units during the late precambrian time in a global tectonic scenario are discussed

stratigraphic and structural development of the precambrian cuddapah basin s e india abstract the present work recognizes a subdivision of the cuddapah basin into 3 separate main units of deposition some of the earlier correlations proved to be untenable for practical reasons king s widely used stratigraphy is retained where possible in a revised form we recognise the cuddapah group 2000 1490 1450 ma nallamalai group 1490 1450 1090 870 ma and the kurnool group 1090 870 500 ma on the basis of surface geology mapping and photo interpretation we discern 5 tectonic zones the boundaries of these zones coincide with deep crustal faults encountered in a deep seismic sounding survey three phases of tectonic activity are 1 1 crustal movements resulting in broad folds affecting the cuddaph rocks exposed in the western area followed by 2 2 folding of the nallamalai rocks east of the rudravaram line and 3 3 later folding and metamorphism in the eastern tectonic zones structural sections allow an interpretation of an eastward continuation of the cuddapah basin rocks into the highly metamorphosed series underlying the eastern ghats complex a colour geological map and sections are included

alteration of early formed dolomite during shallow to deep burial mississippian mission canyon formation central to southwestern montana dolomite in the mississippian mission canyon formation osagean to middle meramecian of central and southwestern montana precipitated during multiple episodes of dolomitization and or recrystallization the earliest generation of dolomite most likely precipitated from evaporated sea water in near surface diagenetic environments when the mission canyon platform intermittently aggraded to sea level this dolomite has relatively positive delta sup 18 o values minus 1 5 to 7 5 and typically is nonstoichiometric and trace element enriched a second generation of dolomite has very negative delta sup 18 o values minus 11 2 to minus 1 5 and always is stoichiometric and trace element depleted dolomite with delta sup 18 o values minus 6 8 is in the upper 100 180 m of the mission canyon formation beneath a regional post mission canyon unconformity and karst surface that extends across the entire study area dolomite depleted in sup 18 o may have 1 precipitated initially in a regional mixing zone during post mission canyon subaerial exposure and karstification 2 precipitated at elevated temperatures during later diagenesis or 3 recrystallized from an earlier generation of dolomite during later shallow to deep burial diagenesis very negative delta sup 18 o values and low trace element contents for the second generation of dolomite suggest that diagenetic solutions were dominated by meteoric water whereas delta sup 13 c values indicate that diageneticmore fluids were buffered by osagean carbonate rocks 54 refs 10 figs less

carbon and oxygen isotopic covariations in hydrothermal calcites isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes 1 mixing between two different fluids which leads to the precipitation of calcite 2 mixing between fluid and rock a calcite precipitation due to fluid rock interaction b secondary alteration of primary calcite by interaction with a subsequent fluid the models are derived from mass balance equations a distinction among the three mixing processes can be made on a 13c vs 18o diagram which places important constraints on the genesis of hydrothermal mineralization the variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock temperature and dissolved carbon species owing to significant temperature dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid the mixing processes may be distinguished by telltale patterns of isotopic data in 13c vs 18o space in particular caution must be exercised in postulating the fluid mixing as the cause for mineral deposition this is demonstrated for hydrothermal pb zn deposits in the western harz mountains germany a positive correlation between 13c and 18o values is observed for calcites from the bad grund deposit in the upper harz two sample profiles through calcite veins show similar correlations with the lowest values at the center of the veins and the highest values at the vein margins because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike it is assumed that a fluid rock interaction is responsible for the observed correlation and thus for the precipitation of calcite a deep seated fluid is inferred with a 13c value of 7 and a 18o value of 10 as well as h2co3 as the dominant dissolved carbon species precipitation temperatures of the calcites are estimated to be about 280 170 c quite different isotopic distributions are observed for calcites from the st andreasberg deposit in the middle harz an alteration model is suggested based mainly on the isotopic distribution through a calcite vein in addition to a primary fluid which has the same isotopic composition as that in the bad grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides an evolved hco 3 dominant subsurface fluid with 13c about 20 15 and 18o 0 is deduced to alter the primary calcite at low temperatures of 70 40 c

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

further sensitivities of orographic precipitation to terrain geometry in idealized simulations abstractthis study examines how variations to the nondimensional mountain height and the horizontal aspect ratio of a straight ridge and a concave ridge influence orographic precipitation an idealized three dimensional model is used to simulate a moist flow impinging upon these two ridges with 0 66 2 0 and 1 0 8 0 the concave ridge generates substantially more precipitation than the straight ridge via an established precipitation enhancing funneling mechanism near the ridge vertex when the flow is unblocked based on previous work it was hypothesized that when the approaching flow becomes blocked the strength of the precipitation enhancement by the concave ridge relative to the straight ridge becomes negligible this study reveals that if is sufficiently large to induce flow reversal on the windward slope then a secondary circulation develops that is strengthened by the concave ridge with a subsequent enhancement of precipitation it is also shown that the competing effects of the ridg

structural trends in the cuddapah basin from deep seismic soundings dss and their tectonic implications abstract structural trends in the upper proterozoic cuddapah basin at the basement level and at the moho level have been discussed based on deep seismic sounding dss studies results of dss studies along the alampur koniki profile profile 2 of fig 1 crossing the northern part of the cuddapah basin have been discussed in detail these results combined with the results of the kavali paranpalle section of the kavali udipi dss profile profile 1 of fig 1 kaila et al 1979 crossing the basin on its southern flank along with geological data and earthquake epicentral locations are used to explain the structural trends of the area it has been shown that the cuddapah basin was first created in its western part by downfaulting of the crustal block between faults 7 and 14 towards the west and fault 6 in the east fig 1 subsequently the eastern part was downfaulted against fault 6 before the commencement of upper cuddapah sedimentation further downfaulting towards the north along fault 5 created the srisailam block minor scale downfaulting between faults 7 and 13 in the west and fault 6 in the east and fault 8 in the north gave rise to the kurnool sub basin at a later stage similar downfaulting east of fault 9 and north of fault 5 gave rise to the palnad sub basin both these sub basins received kurnool sediments after the close of kurnool sedimentation the blocks between faults 4 and 6 along profile ii and between 11 and 6 along profile i were uplifted at the basement level thus giving rise to the nallamalai hills and iswarakuppam dome fig 1 the low angle thrust fault 3 on the eastern margin of the cuddapah basin might be a post cuddapah phenomenon the low angle thrust fault 2 probably occurred in the post dharwar period faults 1 17 and 10 near the east coast of india seem to be comparatively younger probably of mesozoic time along which the coastal block is downfaulted giving rise to the sedimentary basins

the dharwar craton and the assembly of peninsular india peninsular india can be separated into five discrete crustal areas the bhandara singhbhum and aravalli bundelkhand cratons the eastern ghats and a block in southern india containing the dharwar craton and adjoining granulite terrain these areas are separated by four major joins eastern ghats front godavari rift mahanadi rift sukinda thrust and narmada son lineament and associated thrusts all joins except the godavari rift are former orogenic belts where thrusts juxtapose rocks of different metamorphic grade these thrusts and the absence of clear correlation of suites among different cratons suggest that the indian shield formed by accretion of separate continental fragments epicontinental late archean early pro terozoic sediments throughout india however may indicate that the joins are intracontinental formed within a coherent block the term dravidian shield is used for the southernmost of the five crustal blocks including all of india south of the deccan basalts and godavari rift

the origin of retrograde shear zones in the napier complex implications for the tectonic evolution of enderby land antarctica abstract retrograde shear zones rszs in granulites at fyfe hills in the napier complex east antarctica formed during a late proterozoic or early palaeozoic reactivation event these rszs preserve a structural and metamorphic record of excavation from depth equivalents of 6 8 kbar 20 26 km to depth equivalents of 3 5 kbar 10 17 km excavation was essentially isothermal suggesting that the rszs formed in an allochthonous terrain during crustal thickening by low angle thrusting rehydration of the rszs was accompanied in part by large ion lithophile element enrichment and reduction in k rb features which are attributed to 1 the retrograde fluid having originated in continental crust that had not previously undergone granulite facies metamorphism and 2 the fluid having been introduced into the rszs by the intrusion of granitic dykes and pegmatites the saturation of these rsz pegmatites in components characteristically depleted in deep crustal and mantle sources such as boron and beryllium supports a low grade source for the retrograde fluid furthermore a rehydration mechanism involving intrusion of pegmatites suggests that the fyfe hills granulites are underlain by a significantly lower grade hydrous terrain

unraveling sedimentary provenance and tectonothermal history of high temperature metapelites using zircon and monazite chemistry a case study from the eastern ghats belt india abstract the geochemical behavior of detrital zircon and monazite during granulite facies anatexis in metapelites from the eastern ghats belt egb india is explored using u pb geochronology hf isotopes and trace elements in a metapelite from the ongole domain detrital zircon reequilibrated by coupled dissolution reprecipitation and diffusion reaction during ultrahigh temperature metamorphism at 1 63 ga the event completely reset the u pb systems but hf isotopes and trace elements were only partially reequilibrated overgrowths on the altered cores date migmatization at 1 61 ga monazite yields metamorphic ages similar to those of zircon in metapelites from the eastern ghats province egp detrital zircon grains give 2 44 1 40 ga ages and metamorphic ones 1 2 0 5 ga ages metamorphic components include detrital grains reequilibrated by coupled dissolution reprecipitation in the presence of anatectic melt and newly crystallized overgrowths and grains in reequilibrated domains the u pb system wa

alkaline magmatism along the southeastern margin of the indian shield implications for regional geodynamics and constraints on craton eastern ghats belt suturing abstract deformed alkaline complexes at the contact between the eastern ghats belt egb and the archaean cratons in southeastern india mark the location of a collisional suture superimposing an earlier mesoproterozoic 1 5 1 3 ga rift this article offers a plausible geodynamic model explaining the alkaline magmatism and its relationship to regional crustal evolution the mesoproterozoic rift can be correlated to the breakup of the supercontinent columbia and may have opened an ocean between eastern india and east antarctica where the sedimentary sequences of the eastern ghats province egp were deposited between 1 4 and 1 2 ga inversion of the rift basin during the late mesoproterozoic 1 0 ga led to the collision of eastern india with east antarctica during rodinia assembly the collision formed the grenvillian egp rayner complex orogen where the egp sediments and the rocks of the rayner complex were deformed metamorphosed and migmatized at granulite facies condition the mesoproterozoic rifting and grenvillian basin closure may thus represent a wilson cycle related to the breakup of columbia and the assembly of rodinia the craton egb suture was subsequently modified significantly during pan african tectonism 0 5 0 6 ga when the egb granulites were thrust westward over the cratonic foreland along a number of amphibolite facies shear zones at the contact the shearing deformed and metamorphosed the cratonic margin and the alkaline complexes it hosts the thrust stacking in many places has the craton boundary and the alkaline rocks in the footwall and the egb granulites in the hanging wall the continuity of the pan african shear fabric across the craton granulite contact and the lack of grenvillian ages from the alkaline and other craton margin rocks in such regions give the apparent impression that the two crustal segments amalgamated during pan african tectonism and not during the earlier grenvillian collision geodynamic constraints however indicate that this was unlikely and the inconsistency arises because the present crustal geometry exposes only the eroded pan african thrust contact between the craton and the egb and not the original grenvillian suture which may be lying unexposed under the granulite thrust sheets

fold thrust belt structure of the proterozoic eastern ghats mobile belt a proposed correlation between india and antarctica in gondwana abstract the proterozoic eastern ghats mobile belt along the east coast of india shares a thrusted lower contact with the surrounding cratons the thrust known as the terrane boundary shear zone is associated with two large lateral ramps resulting in a curved outline on the northwestern corner of the mobile belt the eastern ghats mobile belt is divided into two lithotectonic units the lathore group and the turekela group based on their lithological assemblages and deformational history on the basis of published data from a deep seismic sounding dss profile of the eastern ghats crust the terrane boundary shear zone is considered to be listric in nature and acts as the sole thrust between craton and mobile belt the lathore and turekela groups are nappes with this structural configuration the nw part is described as a fold thrust belt however the thrusting postdates folding and granulite metamorphism that occurred in the eastern ghats as in the caledonide type of fold thrust belt of nw scotland the terrane boundary shear zone is interpreted to be contiguous with the rayner napier boundary of the enderby land in a gondwana assembly

precipitation over concave terrain abstract many topographic barriers are comprised of a series of concave or convex ridges that modulate the intensity and distribution of precipitation over mountainous areas in this model based idealized study stratiform precipitation associated with stratified moist airflow past idealized concave ridges is investigated with a focus on windward blocking flow confluence and the associated precipitation enhancement it is found that flow confluence and precipitation enhancement by a concave ridge are controlled by the nondimensional ridge height m m nmhm u where nm is the moist buoyancy frequency hm is the maximum ridge height and u is the wind speed based on which three dynamical regimes can be defined in the linear regime m 0 4 a flow confluence zone is present over the upwind slope of the ridge vertex where precipitation is significantly enhanced the precipitation enhancement is due to the additional updraft driven by the horizontal flow convergence with a considerable contribution fr