lithological control on the elevation of shore platforms in a microtidal setting the shore platforms on shag point southern new zealand are quasi horizontal surfaces and are developed between supratidal and low water spring levels a range of morphologies occur with more exposed platforms having a distinct low tide cliff in contrast to low tide surfaces where the seaward edge is buried beneath rubble and macro algal growth the platforms range in width from 20 to 80 m and are eroded into late cretaceous early tertiary fine marine sandstones and mudstones shore platforms have formed in two principal lithological units a homogeneous unit that is characterized by few discontinuities and a fractured unit with joints spaced about 0 5 m apart rock hardness is low in both units l type schmidt hammer rebound values of 31 4 and there is little systematic variation in values between the two units in which platforms have developed case hardened concretions within the sandstone are significantly harder than surrounding rock and cause local relief of metre scale as the spherical diagenetic features are eroded from the bedrock they do not however appear to affect broad scale platform geometry joints within the bedrock are a primary control on platform elevation platforms formed in jointed rock occur at the lower portion of the intertidal zone in contrast to platforms formed in unjointed bedrock in which horizontal surfaces occur at or above mean high water spring tide level rock structure therefore appears to be the primary determinant factor of platform geometry at shag point copyright 2006 john wiley sons ltd

micro seismic measurements of cliff motion under wave impact and implications for the development of near horizontal shore platforms abstract few high resolution measurements of process form interactions have been taken on rock coasts but recent studies in california have shown that portable seismometers enable useful proxy measurements of wave energy delivery to cliffs here we describe measurements over 20 days of high frequency ground motion of cliffs formed in sedimentary flysch rocks at okakari point north of auckland new zealand three sensors were located in a shore normal array inland from the cliff top and a fourth sensor was bolted to a ledge 2 m above the cliff toe the nearshore wave field in front of the cliff and shore platform was monitored using a shore normal array of 5 wave gauges the instrumentation provided measurements of wave energy delivery and consequent ground motion including the first observations of motion at the top and bottom of cliffs results showed that horizontal ground motion is dominant at the cliff top whereas vertical motion is dominant at the cliff toe power spectra show that several high frequency peaks occur in data from the cliff toe whereas a single broader peak frequency occurs at the cliff top resulting from signal modification as seismic waves pass through tens of metres of cliff rock a 100 m wide shore platform at the cliff toe fundamentally controls the patterns of observed energy delivery the shore platform is nearly horizontal elevated close to high water level and abruptly plunges into water 10 m deep at its seaward edge as expected the magnitude of ground motion at all sensors is greatest during larger waves measurements further show that ground motion both at the bottom and top of the cliff is strongest at low tide and weakest at high tide this observation is opposite to that noted at santa cruz where ground motion was greatest at high tide at okakari point the most significant high frequency ground motions occur at low tide when waves are forced to break sometimes violently against the seaward edge of the shore platform four distinctive frequency peaks between 1 and 50 hz increase in magnitude as tidal stage drops implying that wave breaking against the outside edge of the shore platform represents an important source of vibration a detailed understanding of the energy source e g short duration shock pressures and rock resonance is not provided by this study however quantifying the spatial and temporal patterns of energy delivery places strong emphasis on the important role of shore platform geometry in filtering wave energy delivery to the cliff during the 20 day experiment most wave energy was delivered to the outside edge of the shore platform not the cliff toe the geomorphic role of high frequency shaking from wave impacts remains to be clearly demonstrated but if wave impacts are capable of eroding rock then the data from this study imply that under present conditions the outside edge of the shore platform may be subject to higher erosion rates than the cliff toe it is possible that the shore platform is currently being destroyed rather than created but a longer programme of measurements is required to test this notion

debris bed friction of hard bedded glaciers 1 field measurements of debris bed friction on a smooth rock tablet at the bed of engabreen a hard bedded temperate glacier in northern norway indicated that basal ice containing 10 debris by volume exerted local shear traction of up to 500 kpa the corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0 05 and 0 08 a model of friction in which nonrotating spherical rock particles are held in frictional contact with the bed by bed normal ice flow can account for these measurements if the power law exponent for ice flowing past large clasts is 1 a small exponent n 2 is likely because stresses in ice are small and flow is transient numerical calculations of the bed normal drag force on a sphere in contact with a flat bed using n 1 show that this force can reach values several hundred times that on a sphere isolated from the bed thus drastically increasing frictional resistance various estimates of basal friction are obtained from this model for example the shear traction at the bed of a glacier sliding at 20 m a 1 with a geothermally induced melt rate of 0 006 m a 1 and an effective pressure of 300 kpa can exceed 100 kpa debris bed friction can therefore be a major component of sliding resistance contradicting the common assumption that debris bed friction is negligible

on the thermal structure of the southern tibetan crust summary we present a quantitative analysis of the heat flow measurements recently made in southern tibet by francheteau et al the data document a sharp heat flow anomaly of 54 12 mw m 2 the sediment ages now available and reported here show that thermal effects due to sedimentation are negligible three physical effects must be taken into account in the interpretation heat refraction across the complex structures of the tibetan crust erosion in transient thermal conditions and unsteady lateral heat transfer we show that the refraction of heat may be responsible for up to 30 per cent of heat flow variations we derive a new formula for the heat flow erosion correction and show that the correction which is usually applied can be a gross overestimate in thermally perturbed regions accounting for the possible magnitude of heat refraction across the geological features of southern tibet the amplitude of the anomaly could be as large as 70 mw m 2 the anomaly can only be due to a shallow and recent heat source we show that in such a case erosion effects are small less than 10 per cent whatever the erosion rate is and therefore do not affect the above values significantly using both the amplitude and the spatial characteristics of the anomaly we show that the source must be younger than 1 myr and shallower than 10 km this is in good agreement with the results of magnetotelluric soundings carried out in the same area the source could well be as young as 50 000 yr which would make it a likely origin for the widespread geothermal activity observed further north on the plateau these results are evidence that melting processes are active today in the tibetan crust near the yalu zangbo suture zone more than 45 myr after the india asia collision and more than 200 km away from the site of underthrusting of the indian lithosphere

origin of late archean granite geochemical evidence from the vermilion granitic complex of northern minnesota the 2 700 ma vermilion granitic complex of northern minnesota is a granite migmatite terrane composed of supracrustal metasedimentary rocks mafic rocks tonalitic and granodioritic plutonic rocks and granite the metasedimentary rocks are predominantly graywacke which has been regionally metamorphosed to garnet sillimanite muscovite bearing biotite schist and has locally undergone anatexis the mafic rocks form early phases within the complex and are of two types 1 basaltic amphibolite and 2 monzodiorite and essexite rich in large ion lithophile elements lile the members of the early plutonic suite form small bodies that intrude the metasedimentary rocks and mafic rocks producing an early migmatite the granite is of two distinct varieties 1 white garnet muscovite biotite leucogranite s type chappell and white 1974 and 2 grayish pink biotite magnetite lac la croix granite i type the leucogranite occurs in the early migmatite and in paragneissic portions of the complex whereas the lac la croix granite is a late stage intrusive phase that invades the early migmatite and metasediment producing a late migmatite and forms a batholith this study focuses specifically on the origin of granite in the vermilion granitic complex chemical mass balance calculations suggest that the s type two mica leucogranite had a metagraywacke source and that the i type lac la croix granite formed via partial fusion of calc alkaline tonalitic material which may have been similar to rocks of the early plutonic suite this model is satisfactory for petrogenesis of similar late archean post kinematic granites throughout the canadian shield

an exploratory numerical model of rocky shore profile evolution abstract rocky shores occur along much of the world s coastline and include a wide range of coastal morphologies such as intertidal shore platforms considerable research effort has been placed on trying to understand developmental processes on rocky shores but progress has been forestalled because these landscapes develop slowly and preserve little evidence of evolution through time this paper presents a new exploratory numerical model developed to study long term shore profile evolution on rock coasts the model purposely considers only a limited number of processes each represented in a highly abstracted way despite these simplifications the model exhibits a large range of emergent shore profile shapes this behavior is enabled both by broader spatial representation of the driving erosion forces and the flexibility provided by a grid discretization scheme initial model testing shows the development of varied rocky profile geometries ranging from steep plunging cliffs cliffs with narrow benches and cliffs with a variety of shore platform shapes most of the model geometries are similar to those observed in the field and model behavior is robust and internally consistent across a relatively large parameter space this paper provides a detailed description of the new model and its subsequent testing emphasis is placed on comparison of model results with published field observations in which morphometric relationships are described between shore platform gradient and tidal range and platform elevation and platform width the model adequately simulates these morphometric relationships while retaining its ability to simulate a wide range of profile shapes the simplicity of process representations and the limited number of processes implemented means that model outputs can be interpreted reasonably easily hence an opportunity is now provided following the testing described in this paper to use the model to systematically investigate the broader controlling conditions on rock shore profile development

partial melting of metagreywackes part ii compositions of minerals and melts a series of experiments on the fluid absent melting of a quartz rich aluminous metagreywacke has been carried out in this paper we report the chemical composition of the phases present in the experimental charges as determined by electron microprobe this analytical work includes biotite plagioclase orthopyroxene garnet cordierite hercynite staurolite gedrite oxide and glass over the range 100 1000 mpa 780 1025 c biotites are na and mg rich with ti contents increasing with temperature the compositions of plagioclase range from an17 to an35 with a significant orthoclase component and are always different from the starting minerals at high temperature plagioclase crystals correspond to ternary feldspars with or contents in the range 11 20 mol garnets are almandine pyrope grossular spessartine solid solutions with a regular and significant increase of the grossular content with pressure all glasses are silicic sio2 67 6 74 4 wt peraluminous and leucocratic feo mgo 0 9 2 9 wt with a bulk composition close to that of peraluminous leucogranites even for degrees of melting as high as 60 vol with increasing pressure sio2 contents decrease while k2o increases at any pressure the melt compositions are more potassic than the water saturated granitic minima the h2o contents estimated by mass balance are in the range 2 5 5 6 wt these values are higher than those predicted by thermodynamic models modal compositions were estimated by mass balance calculations and by image processing of the sem photographs the positions of the 20 to 70 isotects curves of equal proportion of melt have been located in the pressure temperature space between 100 mpa and 1000 mpa with increasing pressure the isotects shift toward lower temperature between 100 and 200 mpa then bend back toward higher temperature the melting interval increases with pressure the difference in temperature between the 20 and the 70 isotects is 40 c at 100 mpa and 150 c at 800 mpa the position of the isotects is interpreted in terms of both the solubility of water in the melt and the nature of the reactions involved in the melting process a comparison with other partial melting experiments suggests that pelites are the most fertile source rocks above 800 mpa the difference in fertility between pelites and greywackes decreases with decreasing pressure a review of the glass compositions obtained in experimental studies demonstrates that partial melting of fertile rock types in the crust greywackes pelites or orthogneisses produces only peraluminous leucogranites more mafic granitic compositions such as the various types of calk alkaline rocks or mafic s type rocks have never been obtained during partial melting experiments thus only peraluminous leucogranites may correspond to liquids directly formed by partial melting of metasediments other types of granites involve other components or processes such as restite unmixing from the source region and or interaction with mafic mantle derived materials

perpotassic granulites from southern bohemia garnetiferous perpotassic granulites associated with voluminous felsic calc alkaline garnet kyanite granulites in the blansk les massif are described as a new rock type a k2o content near 13 wt zr content ranging from 17 to 5877 ppm primary ca mg fe garnet pyrope up to 33 mol and the absence of primary plagioclase and quartz characterize the new type of granulite calcium is incorporated only in garnet and apatite owing to the content of garnet the bulk syenitic compositions are metaaluminous to peraluminous the perpotassic granulites are accompanied by subordinated melanocratic perpotassic granulite and alkali feldspar melanocratic granulite containing up to 20 vol quartz these rock types also contain highly variable amounts of zircon high pressure noneutectic partial melting of crustal rocks and crystallization under upper mantle conditions is suggested as the main process in generation of perpotassic granulites a polyphase ductile to brittle deformation and recrystallization in pyroxene granulite and later in amphibolite facies accompanied obduction of the granulite massif which carries numerous enclaves of pyrope peridotite euhedral equant zircon crystals up to 4 mm long enclosed in large garnet crystals and in the alkali feldspar matrix of perpotassic granulite represent a uniform high temperature population with a nearly concordant u pb system aftalion et al 1989 the hercynian age of this zircon indicates the role of the hercynian anatexis of crustal rocks under upper mantle conditions in generation of granulites in the moldanubian zone of the bohemian massif

nd and sr isotopic variations in acidic rocks from japan significance of upper mantle heterogeneity initial nd and sr isotopic ratios have been measured for cretaceous acidic and related intermediate rocks 24 volcanic and two plutonic rocks from the inner zone of southwest japan izswj to investigate the genesis of acidic magmas the initial nd and sr isotopic ratios for these rocks show three interesting features 1 end values for acidic rocks 2 to 9 are negatively correlated with esr values 10 to 90 together with those for intermediate rocks end 3 to 8 esr 0 to 65 2 the end values for silica rich rocks 60 sio2 correlate with the longitude of the sample locality decreasing from west to east in a stepwise fashion four areas characterized by uniform end values are discriminated 3 low silica rocks 60 sio2 in a certain area have distinctly different end values from those of the high silica rocks in the same area

ascent of a granitoid diapir in a temperature varying medium a relationship for the ascent velocity of a granitoid diapir is derived and used in conjunction with a crustal heat flow model which incorporates a depth dependent temperature to predict emplacement histories ascent rate is strongly dependent on the width of a deformation layer of variable viscosity that is formed by the transfer of heat to the country rock and on the buoyancy force which propels the diapir through it ascent velocity is described by the expression u 2 gd3z 0r where is the density contrast between diapir and country rock g is gravitational acceleration d is the deformation zone width z is a parameter which describes the increase in viscosity across the zone 0 is the country rock viscosity at the contact and r is the diapir radius the width of the deformation zone as dictated by the temperature distribution and rheological function is the point at which the viscosity increases by a factor f from the contact value although ascent rates vary with choice of this parameter ascent distances are not strongly dependent on f results of simulations which incorporate a spectrum of input parameters reveal that ascent distance is strongly dependent on both the rheology and ambient temperature of the encompassing rock but only weakly dependent on the initial diapir temperature ascent velocity varies with the diapir size with larger bodies moving more slowly and ascending for longer periods relative to smaller plutons as a result of the proportionately larger amount of thermal energy available for ascent larger bodies will rise greater distances than smaller diapirs however the additional ascent appears nominal relative to the contrast in available energy modeling diapirs using a no slip boundary condition decreases ascent velocity by a factor of about 3 relative to results incorporating a stress free boundary condition the time scale of granitoid diapirism over crustal distances cannot be less than 104 years due to the rate limiting effect of thermal conduction above the body and not greater than 105 years reflecting solidification times of kilometer sized plutons a consequence of ascent by a deformation zone mechanism is the generation following emplacement of a mechanically weakened crust which extends from beneath the diapir to near the source perhaps explaining the relatively common occurrence of synmagmatic to postmagmatic mafic dikes within granites believed to be derived from interaction of basalt with the lower crust

anatexis of ultrahigh pressure eclogite during exhumation in the north qaidam ultrahigh pressure terrane constraints from petrology zircon u pb dating and geochemistry plagioclase rich leucosomes and k feldspar rich veins are widely distributed within retrogressed eclogite in the xitieshan area of the north qaidam ultrahigh pressure metamorphic terrane western china in this contribution a combined study of petrology zircon internal structure zircon u pb age zircon trace element composition whole rock geochemistry and sr nd isotopes in plagioclase rich leucosomes and k feldspar rich veins provides insight into the nature and timing of partial melting in these rocks petrological evidence for partial melting is provided by elongated highly cuspate feldspars quartz along grain boundaries e g muscovite garnet and clinopyroxene and felsic veinlets composed of quartz and feldspar along the boundaries of garnet clinopyroxene and clinopyroxene plagioclase symplectite in the metabasite whole rock geochemistry suggests that the plagioclase rich leucosomes have lower contents of both rare earth elements rees and high field strength elements hfses but higher large ion lithophile elements liles e g rb ba k sr and pb than the metabasite hosts the plagioclase rich leucosomes may be divided into two subgroups according to their distinct ree patterns 1 higher total ree content with or without weak negative eu anomalies and 2 lower total ree content with conspicuous positive eu anomalies the eu rich group also shows higher sr content than those in the eu poor group however the k feldspar rich veins show higher ree hfse and lile concentrations than the plagioclase rich leucosomes and metabasites the inherited cores of k feldspar rich veins are of typical magmatic origin oscillatory zoning with high th u ratios enriched heavy h rees and negative eu anomalies yielding 206 pb 238 u ages ranging from 904 8 ma to 915 28 ma the zircon cores of plagioclase rich leucosomes and mantles of k feldspar rich veins exhibit no zoning or weak zoning with flat hree patterns and no negative eu anomalies and they contain mineral inclusions of garnet and clinopyroxene implying that these zircon domains were formed during an episode of eclogite facies metamorphism with 206 pb 238 u ages ranging from 444 10 ma to 452 9 ma internal textures and mineral inclusions quartz plagioclase and k feldspar and trace element systematics steep hree patterns with negative eu anomalies and low th u ratios of the zircon rims from plagioclase rich leucosomes and k feldspar rich veins are similar to anatectic zircon these anatectic zircon domains yielded 206 pb 238 u ages ranging from 430 10 ma to 440 12 ma and 406 12 ma to 430 13 ma respectively an integrated study of petrology geochronology and geochemistry demonstrated that the metabasites of the north qaidam ultrahigh pressure terrane likely experienced initial partial melting with plagioclase rich leucosome formation under eclogite facies conditions and partial melt crystallization during the granulite facies stage triggered by dehydration melting involving zoisite and rare muscovite the k feldspar rich veins within the metabasites may be the result of injected melts that were derived from partial melting of nearby gneisses

magma flow paths and strain patterns in magma chambers growing by floor subsidence a model based on magnetic fabric study of shallow level plutons in the stiavnica volcano plutonic complex western carpathians the miocene stiavnica volcano plutonic complex western carpathians exposes two nearly coeval intra caldera plutons their roof basement of a stratovolcano and associated volcanic rocks the complex thus provides insights into mechanisms of magma chamber growth beneath large volcanoes as inferred from the anisotropy of magnetic susceptibility ams these plutons were emplaced through significantly different processes the diorite as a discordant stock with steep fabric and the granodiorite as a tabular bell jar pluton in detail we interpret that the latter was assembled in two stages first an upper layer intruded as a thin sill along a major subhorizontal basement cover detachment the subhorizontal magnetic fabric and strongly oblate ams ellipsoid in this layer record intrusive strain where the magma flow paths were subparallel to the pluton roof second in the lower layer of the pluton magnetic foliations dip moderately to the nw and wnw to vertical and are associated with down dip to subhorizontal lineations and prolate to weakly oblate shapes of the ams ellipsoids such a fabric pattern is compatible with piecemeal floor subsidence where magma flowed along multiple subsiding fault bounded blocks based on this case example we develop a conceptual model for magma flow paths and strain patterns for four main modes of floor subsidence 1 piston cauldron subsidence is characterized by convergent flow and radial principal stretching above the magma chamber floor 2 the piecemeal floor subsidence leads to steep to inclined magma flow paths in conduits along fault bounded blocks 3 asymmetric trapdoor subsidence produces first divergent flow paths near the conduit sides changing into convergent paths in the narrower space near the kinematic hinge and 4 symmetric cantilever funnel subsidence will lead to divergent flow from a central feeder and thus circumferential principal stretching of the magma if the growing pluton develops a two layer structure all the flow paths and associated strains are affected by the flat lying pluton roof and will convert into horizontal flattening as the roof is approached

phase equilibria of a fluorine rich leucogranite from the st austell pluton cornwall highly evolved leucogranitic rocks in the st austell pluton cornwall of hercynian age contain accessory muscovite topaz and fluorite the authors have studied the h sub 2 o saturated melting behavior of one representative sample its solidus and liquidus pass through the points 663 and 725 sup 0 c respectively at 1 kbar 640 and 665 sup 0 c at 2 kbar 610 and 717 sup 0 c at 4 kbar and 608 and 700 sup 0 c at 8 kbar plagioclase is on the liquidus at low pressure and topaz is on the liquidus at 4 kbar the fluorite is consumed in the formation of the first formed liquid calcium can partition into an evolved granitic melt if complexed by fluorine the fluorite appears to be largely primary in fresh fluorite granite at st austell and not to reflect the albitization of oligoclase in the surrounding biotite granite such fluorine rich leucogranites can be expected to be of subsolvus character

calculated temperatures in overthrust terrains and possible combinations of heat sources responsible for the tertiary granites in the greater himalaya there are three obvious sources of heat that affect the temperature in a region of thrust faulting heat supplied from below the lower thrust plate radiogenic heating within the crusts of both the upper and especially the lower plates and frictional heating along the fault we assume that heat is conducted primarily in the vertical direction and that solutions to the one dimensional time dependent heat conduction equation can be used to describe the temperature field in overthrust zones the effects of these three sources of heating can be isolated from one another treated separately and then combined in ratios proportional to various assumed rates of heating provided by each we then use calculations for a range of possible combinations of heat sources that may have caused two media granites of late tertiary age in the greater himalaya because of the uncertainties in the age of the granites in the depth at which they formed in the amounts of heat flux supplied to the base of the lithosphere and of radiogenic heat production in the crust inb the value of the coefficient of thermal conductivity and in other parameters a broad range of possible combinations of parameters is possible temperature can reach themore solidus for granite melts with various plausible combinations of parameters both that include no shear heating and that require frictional stresses of 100 s of mpa on the main central thrust for instance if the initial steady state geotherm in the crust now comprising the himalaya were that of a typical shield then frictional heating with a stress in excess of 100 mpa 1 kbar would be necessary to raise the temperature of material near a thrust fault at 20 or 30 km depth to 650 sup 0 c less

petrology and geochemistry of lavas from antuco volcano a basaltic volcano of the southern andes 37 25 s sierra velluda plio pleistocene cerro condor pleistocene and antuco holocene volcanoes form a volcanic group located in the southern andes at latitude 37 25 s lavas from these volcanoes become less silicic with decreasing age antuco volcano consists of two units pre and post caldera collapse antuco i and antuco ii and a parasitic cone antuco lavas are basalts and those from antuco i and ii are relatively uniform in mineral and chemical composition common phenocrysts are plagioclase an65 an81 18 33 vol olivine fo 78 3 18 vol and clinopyroxene 0 5 3 vol the same phenocrysts occur in the parasitic cone lavas but plagioclase is much more abundant key compositional features of antuco lavas are 52 sio2 17 al2o3 3 3 4 2 na2o 1 2 tio2 0 9 k2o and mg mg fe ratios 0 60 these major element features characterize many circumpacific basalts in island arc and continental margin environments the antuco i and ii lavas have light ree abundances equal to 26 33 chondrites and heavy ree abundances equal to 8 9 chondrites some samples have positive 10 eu anomalies but no negative eu anomalies occur in these lavas trace element abundances in the antuco lavas are similar to those in theoretical liquids derived by 5 10 partial melting of garnet free peridotite followed by 10 fractionation of a clinopyroxene 40 and olivine 60 cumulate thus a plausible model is that the lavas were derived from the mantle by partial melting followed by mafic mineral fractionation

prograde metamorphism decompressional partial melting and subsequent melt fractional crystallization in the weihai migmatitic gneisses sulu uhp terrane eastern china abstract in order to decipher fluid melt activity during subduction and subsequent exhumation of felsic continental crust we carried out a combined study of zircon internal structure zircon u pb age zircon trace element composition and whole rock geochemistry on migmatitic gneisses from the weihai region in the sulu ultra high pressure uhp metamorphic terrane eastern china the weihai migmatitic gneisses are composed of intercalated compositional layers of melanosome and plagioclase pl rich leucosome and k feldspar kfs rich pegmatite veins whole rock geochemistry suggests that mgo fe2o3t cao tio2 p2o5 rare earth elements ree and large ion lithophile elements hfse are nearly completely retained in the melanosome whereas significant amounts of lile e g rb ba k sr pb and u are partitioned into the pl rich leucosome and the kfs rich pegmatite veins the kfs rich pegmatite vein has much higher k2o u pb and rb but lower cao and na2o contents than those of the pl rich leucosome layer protolith magmatic zircon domains with an upper intercept age of about 780 ma are common in the cores of zircon grains from the melanosome and the pl rich leucosome layers indicating that the protolith of the migmatitic gneiss is mid neoproterozoic magmatic rock metamorphic zircons with concordant ages ranging from 243 to 256 ma occur as overgrowth mantles on the protolith magmatic zircon cores they are characterized by remarkably flat heavy rare earth element hree patterns without obviously negative eu anomalies and have low y and th contents low th u and high hf y ratios indicating a prograde metamorphism in the hp eclogite facies during subduction recrystallized rims of zircons 228 2 ma in the pl rich leucosome layer are similar to magmatic zircons in terms of their hree enriched patterns with negative eu anomalies high y and low th contents and low hf y and th u ratios this indicates that the gneiss has experienced decompressional partial melting and the pl rich leucosome layers were formed by fractional crystallization of the primary melt during the early stage hot exhumation zircon grains 219 2 ma in the kfs rich veins are characterized by aqueous fluid melt related signatures with strongly hree enriched patterns high u pb and low th contents and low th u and high lu hf ratios indicating that the pegmatite vein was formed by crystallization of residual aqueous melt after the crystallization of pl rich leucosome layers during later stage cooling during exhumation our results suggest that the migmatitic gneiss successively recorded information concerning the protolith prograde hp metamorphism during subduction fractional crystallization of primary melt and crystallization of the residual melt during exhumation

tectonic and climatic controls of alluvial fan size and source catchment relief the geometries of alluvial fans and their upland catchments subject to known rates of basin subsidence v and upland precipitation p respectively are compared with predictions from a quantitative analysis of an idealized landscape we find that the dimensionless ratio v p explains systematic trends in relative fan size and source catchment relief previously reported from environmentally wide ranging regions worldwide and contributes to the interpretation of recently reported observations of fan like phenomena on mars

multistage anatexis during tectonic evolution from oceanic subduction to continental collision a review of the north qaidam uhp belt nw china abstract the north qaidam ultra high pressure uhp metamorphic belt in the northern tibetan plateau is considered as a typical alpine type uhp metamorphic belt due to the early paleozoic subduction of the qaidam block beneath the qilian block the well preserved paleozoic metatexite migmatite diatexite migmatite felsic sheet dyke and anatectic granite in the north qaidam uhp metamorphic belt provide us with an excellent opportunity to study the generation transport and final fate of crustal melt and geodynamic processes associated with orogenesis based on structural relationships petrology geochronology whole rock geochemistry and sr nd isotope data the early paleozoic anatexis during oceanic subduction to continental collision in the north qaidam uhp metamorphic belt can be further divided into three stages of development 470 ma 446 428 ma and 432 420 ma the first stage granitic leucosomes are rich in k poor in na with low sr y and enrichment of large ion lithophile elements liles which were probably derived from partial melting of ancient felsic gneiss in continental arc circumstances during oceanic subduction the second stage na rich leucosomes and tonalite plutons are characterized by high na sr sr y and la yb and low heavy rare earth elements hrees with positive end t values of 0 1 4 3 and zircon ehf t values of 8 3 10 2 similar to typical tonalite trondhjemite granodiorites ttgs these ttg like magmas were produced through partial melting of newly emplaced gabbroic rocks with arc affinity under high pressure hp granulite facies conditions in a thickened lower crust during continental collision the volumetrically significant migrated plutons evolved from ttg like melt will become segments of continental crust and contribute to crustal growth with partial residual products of hp granulite and or garnet pyroxenite to the mantle by delamination the third stage of anatexis was preserved in both migmatitic uhp gneiss and eclogite in the xitieshan and luliangshan terranes the kfs rich felsic leucosomes inside uhp gneisses in the third stage are characterized by high alkali contents and low mafic component with feot mgo tio2 2 0 2 high la yb and sr y and low y and hrees 3 high al2o3 and low mg values and 4 enriched in liles e g rb ba k sr pb and poor in high field strength elements hfses partial melting of uhp eclogite and felsic gneiss during the initial retrogression stage with pl rich and kfs rich leucosome formation was triggered by dehydration melting involving predominant zoisite and muscovite the anatectic melts from partial melting of deeply subducted uhp gneiss have accumulated and migrated outside the deeply subducted crustal slice in the form of syn collisional plutons the melt evolution from the leucosomes produced at the early exhumation stage to syn collisional granitoids produced at the late exhumation might contribute greatly to the exhumation of the north qaidam uhp metamorphic belt from mantle depths to the lower crustal levels

evaluating major controls on basinal stratigraphy pine valley nevada implications for syntectonic deposition the interpretation of prograded gravel as an indicator of tectonic uplift that is syntectonic deposition is not necessarily correct increases in sediment supply induced by tectonic uplifting did not control the progradation of gravel in the pine valley basin an actively subsiding half graben in northeastern nevada rather the distribution of lithofacies in the pine valley basin is primarily controlled by the uneven distribution of subsidence within the basin differences in subsidence along the axis of the basin indicate a strong inverse relationship between the long term subsidence rate since late miocene time and the distance of gravel transport out into the basin differential progradation of alluvial gravel into the basin from various drainages along the footwall is not related to uplift or lithology of the source area size of the catchment area or climate in addition the relatively fixed location of the topographic low within the basin through time as indicated by the distribution of lacustrine deposits and the position of the modern axial drainage suggests that a balance between basin subsidence and sediment supply to the basin has been generally maintained through time thus if subsidence rates are a measure of tectonic activity gravel progradation may record times of reduced not increased tectonism

the system tonalite peridotite h 2 o at 30 kbar with applications to hybridization in subduction zone magmatism we present data on the phase relationships of mixtures between natural tonalite and peridotite compositions with excess h2o at 30 kbar and on the composition of the piercing point where the peridotite tonalite mixing line intersects the l ga opx reaction boundary these data in conjunction with earlier analogous data along peridotite granite and basalt granite mixing lines permit construction of a pseudoternary liquidus projection that is relevant to interaction of peridotite with slab derived magmas knowledge of the liquidus phase and temperature for a range of compositions within this projection enables us to map primary crystallization fields for quartz garnet orthopyroxene clinopyroxene and olivine and to estimate the distribution of isotherms across the projection using this projection we explore the consequences of peridotite assimilation by mafic to intermediate basalt to dacite hydrous slab derived melts progressive assimilation under isothermal conditions results in garnet precipitation as the melt composition traverses the garnet liquidus surface and then garnet orthopyroxene crystallization once the melt reaches the l ga opx field boundary the melt is constrained to remain on this field boundary and further assimilation of peridotite simply results in continued precipitation of garnet orthopyroxene until the melt is consumed the product is a hybrid solid assemblage consisting of ga opx it is noteworthy that this process drives the melt composition in a direction nearly perpendicular to the mixing line between peridotite and the initial melt if assimilation occurs with increasing temperature as might occur if a slab derived magma rises into the hotter mantle wedge intermediate magmas e g andesites will again precipitate garnet until they reach the l ga opx reaction boundary at which point ga re dissolves and orthopyroxene precipitates as the melt composition moves up temperature along this boundary the product of this process is a hybrid solid assemblage with garnet subordinate to orthopyroxene for more mafic initial compositions e g basalts originally plotting in the cpx field it appears possible to avoid field boundaries involving garnet and shift in composition more directly toward peridotite if assimilation is accompanied by a sharp increase in temperature considering published ree evidence arguing against garnet playing a significant role in the genesis of many subduction related magmas in light of our results it appears unlikely that peridotite assimilation by intermediate magmas under conditions of constant or increasing temperature is an important process in subduction zones however if assimilation is accompanied by an increase in temperature our data do permit the derivation of high mg basalts from less refractory precursors e g high al basalts by peridotite assimilation

a new model for the dynamic evolution of chinese lithosphere continental roots plume tectonics abstract chinese continental lithosphere comprises three tectonic domains 1 eastern china a region characterized by rifting extensional basins and voluminous basaltic volcanism 2 central china a plexus of cratonic terrains with low heat flow 40 50 mw m2 including the tarim erdos and yangtze blocks welded by pre cenozoic orogenic belts and 3 western china a region comprising the qinghai tibet himalaya orogen the relatively thin crust 35 km and lithosphere 70 km of eastern china is believed to reflect mantle upwelling while near normal crust 45 km and thickened lithosphere 200 km in central china suggest a mantle lithosphere root resembling those inferred for the kaapvaal and siberian cratons thickened crust 70 km and lithosphere 150 km in western china reflect the advanced development of an orogen root the lower density and relative buoyancy of central cratonic mantle roots appear to have contributed to the long term tectonic stability of the central chinese lithospheric blocks in contrast gravitational instability produced by thickening of the denser western chinese lithosphere and the resulting subsidence and eventual delamination of orogenic roots are believed to have led to postorogenic extensional collapse although the geological relationships suggest compressional forces caused both mountain building and orogen root development extensional stress resulting from gravitational collapse is believed to have induced lithospheric and crustal thinning with concomitant reduction of topography the term continental roots plume tectonics has been adopted to describe the configuration and dynamic condition of subcontinental lithosphere and upper mantle beneath china accordingly it is proposed that supracrustal tectonic forms represent the surface expressions of and responses to deep continental roots plume tectonics while the prevailing view is that the western orogenic belt is not genetically related to eastern continental rifting such a relationship is inherent to the continental roots plume tectonics model it is further proposed that the formation of orogenic lithosphere roots triggered eastward extrusion of the asthenosphere along the 400 km depth mantle interface and in response to subduction at the eastern margin produces plume like upwelling beneath eastern china we suggest that processes involved in continental roots plume tectonics are directly responsible for the formation and evolution of the eurasian supercontinent

the subtidal morphology of microtidal shore platforms and its implication for wave dynamics on rocky coasts abstract the subtidal portions of shore platforms are important geomorphic features as they can modify deep water wave energy before it impacts the intertidal platform edge in this study an integrated marine and terrestrial aerial lidar dataset is used to analyse the morphology of the subtidal portion of shore platforms semi horizontal intertidal platforms on an 85 km along stretch of microtidal open ocean rocky coast in victoria australia are investigated and described quantitatively three distinct types of subtidal morphology occur i a steep cliff with a mean slope of 8 18 ii a gently sloping ramp with a mean slope of

evidence for low temperature ultrapotassic siliceous fluids in subduction zone environments from experiments in the system k2omgoal2o3sio2h2o kmash experiments in the system k2o mgo al2o3 sio2 h2o kmash were undertaken with the piston cylinder apparatus to study the reactions 1 1 phengite quartz k mg rich siliceous fluid feldspar phologopite h2o 2 2 phengite talc k mg rich siliceous fluid phlogopite quartz coesite h2o at temperatures between 400 and 700 c the ultrapotassic fluid appearing at pressures above 15 kbar on the low temperature sides of the corresponding reaction curves which show positive dp dt slopes is probably supercritical the p t positions of the reactions are compatible with kmash mineral reactions studied previously and with melting investigations in the kmash system undertaken at temperatures higher than 700 c it is possible that natural rocks chiefly k rich metasediments subducted as minor portions of the oceanic crust could give rise to low temperature ultrapotassic fluids mainly at temperatures between 300 to 600 c and pressures between 15 and 30 kbar the ascending k rich fluids would penetrate the overlying mantle to metasomatize it after termination of the subduction process heating of this mantle material previously cooled by the subducted lithosphere could lead to the formation of high temperature k rich magmas

micro erosion meter measurements of rock wear on the otway coast of southeast australia abstract the use of the micro erosion meter mem has been refined by providing 1 a base plate on which to check the relationship of legs and probe and 2 a micrometer level to check the relationships of the three studs countersunk in the rock at each site along 50 km of the otway coast lines of mem stations were installed across shore platforms normal to the shore and surveyed to mean low water readings were made bimonthly from 1978 to 1980 average site downwear ranged from 0 02 to 1 8 mm yr 1 according to rock type and the amount of exposure to the almost continuous swell waves the results of this study combined with other information available are used to discuss the origin and evolution of otway coastal morphologies

oblique slip tectonics in an active volcanic chain a case study from the southern andes abstract oblique slip tectonics in the intra arc region of the southern andes accommodates heterogeneous deformation derived from plate convergence during the pliocene and quaternary long term mechanical interaction between andean transverse faults i e nw striking sinistral faults and margin parallel faults i e nne striking faults results in linked transtensional fault damage zones that facilitate structural conditions for the migration and emplacement of geofluids in the upper crust we investigated the architecture of pre eruptive units and the nature of faulting at the tatara san pedro pellado volcanic complex in the southern andes here oblique slip faulting crosscuts miocene folded strata and granitoids our main results suggest that quaternary volcanism and an associated geothermal systems developed on top of an ene oriented structural anisotropy defined by hundreds of faults and dikes interacting in a ca 9 km long and 4 km wide rock volume named the tatara damage zone deformation in this domain is characterized by ene to wnw striking transtensional oblique slip faults flanked by 1 the seismically active ns striking dextral melado fault to the west 2 discrete ns to ene striking dextral splay faults to the east and 3 the sinistral nw striking los condores fault to the north east which is reported for the first time in this work the latter fault represents an excellent example of a long lived andean transverse fault furthermore we suggest that the los condores fault accommodates a margin oblique slip component of bulk transpressional deformation we demonstrate that pliocene quaternary intra arc oblique faulting developed after pre late miocene compressional tectonics and that this oblique faulting constrains the geometry of permeable pathways for the flow emplacement and eruption of quaternary geofluids furthermore we evaluated the stress field for a discrete volcanic complex and provided key elements to better understand the role of andean transverse faults in the spatial organization of quaternary arc volcanism and geothermal systems in the southern andes

development of shore platforms on kaikoura peninsula south island new zealand ii the role of subaerial weathering the role of subaerial weathering in the development of shore platforms on kaikoura peninsula is investigated evidence for weathering came from a number of distinctive surface morphologies on platforms salt crystal growth water layer weathering and slaking schmidt hammer test data showed that weathering had occurred and that rock strength was reduced through weathering by as much as 50 weathering processes on shore platforms rely on repeated wetting and drying and for this reason the number of wetting and drying cycles was estimated it was found that the number of wetting and drying cycles depend not only on the pattern of tidal water levels but also on algae growth and desiccation the number of cycles ranged from 104 to 379 per year at elevations low in the tide range fewer cycles occurred the greatest number occurring between the peaks of spring and neap tides and where rainfall adds to the number the zone of most cycles was estimated to occur between 0 6 and 0 9 m above mean sea level on the more landward margins of platforms it is at these elevations that the highest rates of erosion occur based on these results it is argued that the development of shore platforms at kaikoura results from subaerial weathering caused by repeated wetting and drying this is contrary to the view that shore platforms result from marine erosion

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

from grain size to tectonics 1 regional grain size trends in fluvial successions can reveal important information regarding the dynamics of sediment routing systems self similar solutions for down system grain size fining have recently been proposed to explore how key variables such as the spatial distribution of deposition sediment discharge and sediment supply characteristics control spatial distribution of grain size in fluvial successions over time scales of 104 106 years we explore the sensitivity of these solutions to changes in key variables and assess their applicability to ancient fluvial successions several sensitivity analyses are presented to investigate the relative control of the key model variables on the spatial pattern of down system grain size fining in fluvial successions sensitivity analyses demonstrate that 1 an increase in the initial value of sediment discharge to a basin causes a decrease in the rate of grain size fining in fluvial successions an effect that becomes nonlinear for large values of initial sediment discharge 2 a short wavelength high amplitude subsidence regime generates a greater rate of down system grain size fining and a long wavelength lower amplitude subsidence regime generates a lesser rate of down system grain size fining in fluvial successions and 3 an increase in the spread of grain sizes in the sediment supply generates a greater rate of down system grain size fining we apply this modeling technique to grain size data sets collected from two time surfaces within conglomerates of the upper eocene montsor fan succession of the pobla basin spanish pyrenees these data sets exhibit approximately self similar grain size distributions further the observed increase in down system grain size fining associated with smaller depositional system lengths provides support for the application of self similar solutions to fluvial successions by applying these solutions to carefully collected grain size data from fluvial successions we are able to relate explicitly the initial grain size supplied to the system the spatial distribution of subsidence and the sediment discharge into the basin to the rate of grain size fining in fluvial successions this method thus offers a powerful means of elucidating sediment routing system dynamics over time

mesozoic to quaternary continental margin dynamics in south central chile 36 42 s the apatite and zircon fission track perspective zircon and apatite fission track data provide constraints on the exhumation history fault activity and thermal evolution of the south central chilean active continental margin 36 s 42 s which we use to assess the tectonic and geomorphic response of the margin to the andean subduction regime several domains with different exhumation histories are identified the coastal cordillera is characterized by uniform and coherent exhumation between late triassic 200 ma and late miocene times with surprisingly slow average rates of 0 03 0 04 mm a thermal anomalies related to late cretaceous and early miocene magmatism have regionally modified fission track age patterns the upper cretaceous thermal overprint is of previously unrecognized significance and extent in the coastal cordillera south of 39 s with the exception of a local but distinct pliocene to recent exhumation period in the high relief cordillera nahuelbuta segment between 37 s and 38 s cenozoic overall exhumation in the coastal cordillera was very slow the sedimentary record shows that uplift and subsidence here was episodic with low amplitudes and durations this rules out large scale long term cenozoic accretion trench parallel tilting and tectonic erosion processes in the forearc the main andean cordillera shows markedly greater long term exhumation rates than the coastal cordillera and at 39 s a steep exhumation gradient to the south long term average pliocene to recent exhumation rates of 1 to 2 mm a in the liquine area 39 45 s are almost an order of magnitude more rapid than average paleogene to recent exhumation near lonquimay 38 30 s and farther north while no imprint of the intra arc liquine ofqui fault zone on the exhumation pattern is evident long term exhumation rates decrease from the crest of the andes toward the western foothills exhumation gradients correlate with climatic gradients suggesting a causal link to the variable intensity of late miocene to pleistocene glacial erosion

hot little crucibles are pressured to reveal and calibrate igneous processes the fires of hutton s 1726 1797 plutonists could not be quenched by the oceans of werner s 1750 1817 neptunists hall 1761 1832 was convinced that hutton s theory could be proved by experiments but he deferred to the fears of his older colleague that failed experiments might discredit the theory which needed no further proof and completed the experiments only after hutton s death hutton censured those who judge of the great operations of the mineral kingdom from having kindled a fire and looked into the bottom of a little crucible hall believed that the imitation of the natural process is an object which may be pursued with rational expectation of success following many discussions between hutton and hall three topics were pursued in hall s experiments 1790 the magmatic origin of granites younger than schists 1798 whinstones dolerites are as magmatic as known lavas 1805 powdered calcite is transformed to marble and melted by the effects of compression and water in modifying the action of heat the latter involved the first high pressure high temperature apparatus and earned hall the title father of experimental petrology subsequent development of these topics is outlined with reference to debates about primary basalts granitization and carbonatites

heat focussing granite genesis and inverted metamorphic gradients in continental collision zones abstract the thermal conductivity of sedimentary rocks is usually much lower than that of crystalline rocks gneisses and granites continental collision zones are characterized by large scale thrusts which superpose crystalline basement and sedimentary layers this leads to heat refraction effects of significant magnitude sedimentary layers act as a barrier to the transport of heat we show that the peculiar geometry of a gently sloping sedimentary layer thrust into more conductive rocks is very efficient in diverting the vertical flux of heat temperatures can vary by more than 50 along the horizontal and reach a marked maximum at the top of crystalline layers these results are in general agreement with the main features of orogenic belts as exemplified by the himalayas they explain why the young leucogranites of the main central thrust mct are confined to a narrow belt at the top of the basement slab they also account for the inverted metamorphic gradient observed there in a crustal accretionary wedge folding and thrusting modify the structure of the upper crust by thickening the sedimentary cover and by introducing sedimentary rocks at depth this leads to high temperatures at shallow depths in specific places les zones de collision continentale se caracterisent par de grands chevauchementsafaible pendage qui empilent les unes sur les autres des couches de socle cristallin et des couches sedimentaires cette structure particuliere engendre d importants effets de refraction thermique en effet leur conductibilitethermiqueetant normalement bien plus faible que celle des roches cristallines les formations sedimentaires font office de barrieres pour le transfert thermique le flux de chaleur se trouve fortement devie dans un plan horizontal la temperature peut varier de plus de 50 les maximaetant situesal interface superieur des dalles cristallines en ces endroits precis les isothermes profonds remontent tres significativement ces resultats rendent bien compte de plusieurs faits essentiels observes dans l himalaya zoneographie inverse du metamorphisme localisation des leucogranites le long d une bandeetroite situee au sommet de la dalle du tibet

influence of lithologic erodibility on alluvial fan area western white mountains california and nevada differences in lithologic erodibility and sediment storage within a drainage basin affect the relationship between alluvial fan area and drainage basin area along the western white mountains large fans are produced by basins underlain by resistant rocks which have steep and narrow trunk stream canyons with little sediment in storage small fans are produced by basins composed of erodible lithologic units which have wider valley floors lower valley side slopes and considerably more sediment stored along trunk stream canyons than is the case in basins underlain by resistant rocks

carbon isotope record and palaeoenvironmental changes during the early toarcian oceanic anoxic event in shallow marine carbonates of the adriatic carbonate platform in croatia geochemical 13 c 18 o and mn compositions of lower jurassic shallow water carbonates cropping out in croatia were analyzed to elucidate the impact of the early toarcian oceanic anoxic event t oae on the adriatic carbonate platform adcp the bulk rock carbon isotope records through the studied sections velebit a velebit b and gornje jelenje are characterized by two significant excursions i an initial positive trend interrupted by a pronounced negative shift c 2 5 that is followed by ii an increasing trend of positive values up to 4 5 a comparison with 13 c trends obtained from well calibrated sections from other localities in europe shows that the overall character of the early toarcian negative excursion is clearly reproduced in the curves derived from croatian shallow water deposits which helps to date the sequences and reinforces the global character of the carbon cycle perturbation lower jurassic sedimentary successions in the studied area show a gradual deepening trend corresponding to deposition of the toarcian spotted limestones assuming that the distinctive negative excursion in the carbon isotope curves is synchronous across the adcp the contact between the spotted limestones and the underlying beds rich in lithiotid bivalves appears to be diachronous within the study area the mn record through the croatian velebit a section and in particular the rise in concentration up to 100 ppm coinciding with the beginning of the 13 c carb positive shift reflects a change in the redox conditions in seawater that allowed diagenetic incorporation of reduced manganese into the calcite structure of the carbonate sediment during the onset of the t oae

late pleistocene holocene development of the tista megafan west bengal india 10 be cosmogenic and irsl age constraints abstract the himalayan proximal foreland is characterized by quaternary megafans of which the formational mechanisms remain debated the tista megafan spreads over more than 16 000 km2 from the mountain front where it is strongly incised to the confluence of the tista river with the jamuna brahmaputra river and stores sediments produced in the sikkim himalaya we propose a scenario for the late pleistocene holocene development of the tista megafan based on new 10be cosmogenic and infra red stimulated luminescence irsl age constraints and discuss the main potential controls on its evolution we suggest that two distal lobes developed successively downstream from a common proximal lobe deposition in the proximal lobe took place since at least 135 ka and incision began at 3 7 0 7 1 0 ka the western distal lobe of the megafan was deposited early in the history of the megafan when the sikkim himalaya catchment was drained by a tributary of the ganga river and was abandoned in the early holocene 10 11 ka the eastern recent

a possible uhp eclogite in the leaota mts south carpathians and its history from high pressure melting to retrograde inclusion in a subduction melange abstract an unusual eclogite pod containing impure jadeite to omphacite pyroxene with anti phase domain apd visible under the optical microscope is hosted in a medium grade matrix in the leaota massif textural relationships support the hypothesis of garnet formation by peritectic reactions involving high jadeite clinopyroxene while inclusions entrapped in garnet mainly a wide range of amphibole compositions seemingly crystallised from a fluid phase in disequilibrium with the garnet host thermobarometric estimates indicate uhp ht peak conditions 2 8 3 2 gpa 780 840 c inconsistent with those of the associated rocks followed by a complicated exhumation path the p t array of the retrograde path suggests syn subduction exhumation and tectonic inclusion in a melange with a matrix derived from the accretionary wedge partial melting of the subducting slab which induces tectonic weakening may be an effective mechanism in detaching and enclosing small eclogite pods in metamorphic terrains

partial assimilative recycling of the mafic plutonic roots of arc volcanoes an example from the chilean andes at long lived arc volcanic centers open system interactions between new magma and the plutonic roots of the arc will increase with time relative to interactions with older crust assimilative recycling of mafic plutonic arc roots will have different isotopic consequences than incorporation of aged continental crust in the tatara san pedro complex 30 comagmatic basaltic lavas are characterized by xenocrysts and microxenoliths of olivine augite and plagioclase derived from solidified cumulates wide but poorly correlated ranges of incompatible and compatible major and trace elements and limited isotopic variability this mineralogical chemical signature reflects assimilation wherein grain boundary melting and disaggregation of xenoliths led to blending of incompatible element enriched melts derived mainly from hornblende phlogopite and plagioclase in combination with variable retention of xenocrysts hence variable but high compatible element concentrations

a late miocene pliocene origin for the central himalayan inverted metamorphism abstract perhaps the best known occurrence of an inverted metamorphic sequence is that found immediately beneath the himalayan main central thrust mct generally thought to have been active during the early miocene however in situ 208 pb 232 th dating of monazite inclusions in garnet indicates that peak metamorphic recrystallization of the mct footwall occurred in this portion of the central himalaya at only ca 6 ma the apparent inverted metamorphism appears to have resulted from activation of a broad shear zone beneath the mct which tectonically telescoped the young metamorphic sequence this explanation may resolve some outstanding problems in himalayan tectonics such why the mct and not the more recently initiated thrusts marks the break in slope of the present day mountain range it also renders unnecessary the need for exceptional physical conditions e g high shear stress to explain the generation of the himalayan leucogranites

phase relationships of i type granite with h2o to 35 kilobars the dinkey lakes biotite granite from the sierra nevada batholith the dinkey lakes biotite granite from the sierra nevada batholith was reacted with varying percentages of h 2o in sealed platinum capsules in a piston cylinder apparatus between 10 and 35 kbar the results were combined with the results from previously published experiments to provide comprehensive phase relationships for an i type granite a p t diagram with excess h 2o isobaric t x h 2o diagrams at 25 30 and 35 kbar showing h 2o undersaturated relations the h 2o undersaturated liquidus surface mapped with contours for constant h 2o contents and fields for near liquidus minerals and the solubility of h 2o in granite liquids to 35 kbar results and their implications show 1 the solidus temperature decreases from 680 c at 2 kbar to 620 c at 10 kbar then increases to 700 c at 35 kbar because of changes from less dense to more dense subsolidus mineral assemblages 2 the melting interval with excess h 2o which is only 35 c at 2 kbar increases to 105 c at 10 kbar and 150 c at 35 kbar because the liquidus minimum in the complex rock system departs from granite composition with increasing pressure 3 the solubility of h 2o in granite liquid is 27 2 5 weight percent at 35 kbar and 850 c indicating that a miscibility gap persists between h 2o saturated silicate magmas and aqueous vapor phase at least to pressures corresponding to 120 km depth in the mantle dissolution of alkali feldspar 20 of rock in the subsolidus aqueous vapor phase indicates that deep seated aqueous fluids are concentrated solutions 4 quartz and coesite are the liquidus minerals at mantle pressures for all h 2o contents indicating that granites and rhyolites cannot be primary magmas from mantle peridotite or subducted oceanic gabbroic crust 5 the liquidus surface at crustal pressures with plagioclase and quartz as primary minerals indicates that primary liquids of granite composition with moderate h 2o contents can be generated in the crust at reasonable temperatures these liquids could rise to near surface levels without vesiculation granite liquid together with residual crustal minerals could constitute plutonic magmas of intermediate composition

timing and nature of the partial melting processes during the exhumation of the garnet bearing biotite gneiss in the southern altyn tagh hp uhp belt western china abstract partial melting of the garnet grt bearing biotite gneiss from the jianggalesayi area in the southern altyn tagh high pressure hp ultra high pressure uhp metamorphic belt has been identified and reported here felsic veins were distributed along the foliation plane and deformed together with the grt bearing biotite gneiss which dominated the main outcrop and preserved diagnostic features of anataxis highly cuspate and irregular quartz qz melt and plagioclase pl melt surrounded or stretched into biotite and or quartz grains with obvious eroded boundaries further provided the microstructural evidences for partial melting of the gneiss cl images showed that zircons from the grt bearing biotite gneiss were characterized by multizone structures of core rim i rim ii rim iii the different zircon zones from the gneiss had integrated recordings of the protolith ages 836 1613 ma the peak metamorphic age of 503 5 ma the retrograded age of 456 4 ma and the anatectic age of 418 3 ma zircons from felsic veins also exhibited core rim structures on cl images the felsic veins yielded similar protolith ages 1099 1072 ma and anatectic age 417 2 ma as the host gneiss the zircons from the host gneiss and felsic veins had plotted identical crustal evolution curves in the ehf t vs u pb age diagram with identical tdm ages the u pb ages and lu hf isotope both suggested that the felsic veins were internally derived by the partial melting of the host gneiss moreover the high content of al2o3 and rb in felsic veins indicated that the decomposition of biotite accounted for the partial melting of the gneiss the temperatures calculated by ti in zircon thermometer for the anatectic zircons from the felsic veins 582 694 c were identical to the conditions of the amphibolite facies stage of the grt bearing biotite gneiss t 619 646 c which indicated that the crystallization of the melt had taken place during the amphibolite facies stage of the exhumation the anatectic ages 418 3 ma and 417 2 ma of the gneiss and felsic veins were determined to be within the range of the fourth episode of the early paleozoic magmatism 420 385 ma which had formed in a post collisional extensional setting therefore the combination of the magmatic heat events and stress release may have played an important role in the partial melting of the gneiss

flexural isostatic response of the alps to increased quaternary erosion recorded by foreland basin remnants se france we test the hypothesis that flexural isostatic compensation of the mass removed by enhanced quaternary erosion is responsible for uplift of the western european alps and their forelands we use two well preserved and well dated 1 8 ma abandonment surfaces of foreland basin remnants in se france the chambaran and valensole plateaux as passive benchmarks for tilting of the foreland estimating their initial slope from morphometric scaling relationships we determine bulk post depositional tilting of 0 5 0 8 for these surfaces the calculated isostatic response of the alpine lithosphere to erosional unloading using the method recently proposed by champagnac et al geology 35 2007 195 198 yields a predicted tilting of 0 3 0 4 in the considered areas explaining approximately half of the determined post depositional tilting such long term deformation being insensitive to cyclic loading unloading because of glaciations we suspect the other half to be related to as yet undetermined long wavelength and long lived tectonic process es

petrology and geochemistry of shoshonitic plutons from the western kunlun orogenic belt xinjiang northwestern china implications for granitoid geneses abstract a series of granitoids from proterozoic to cenozoic age occurred in the western kunlun orogenic belt xinjiang northwestern china several intrusions such as the west datong middle caledonian age north kuda late caledonian age and kuzigan karibasheng zankan himalayan age plutons have shoshonitic affinity their rock assemblages include quartz monzodiorite quartz monzonite quartz syenite middle caledonian or monzonitic granite granite late caledonian or biotite monzonitic granite diopside granite diopside syenite himalayan generally biotite is iron phlogopite with some eastonite and high mg mg fe t and fe 3 fe 2 ratio amphibole is mainly edenitic hornblende and magnesian hastingsitic hornblende with some edenite and higher mg mg fe t and fe 3 fe 2 ratio the rocks show sio 2 contents of 52 77 71 85 and high k 2 o na 2 o mostly 8 average 9 14 k 2 o na 2 o mostly 1 average 1 50 and fe 2 o 3 feo 0 85 1 51 average 1 01 and low tio 2 contents 0 15 1 12 average 0 57 al 2 o 3 contents 13 01 19 20 are high but variable the granitoids are prominently enriched in lile lree and volatiles such as f however the studied shoshonitic granitoids among the three intrusive periods also show differences in isotopic compositions and trace element concentrations suggesting their different geneses the origin of the west datong pluton is probably related to the involvement of subducted oceanic crust sediments into the mantle source the north kuda and himalayan plutons could have been generated by partial melting of subducted oceanic crust sediments or metasediments of thickened continental lower crust in the process of late orogenic slab break off or lithospheric thinning

water saturated and undersaturated melting of metaluminous and peraluminous crustal compositions at 10 kb evidence for the origin of silicic magmas in the taupo volcanic zone new zealand and other occurrences

discussion of de lange w p and moon v g 2005 estimating long term cliff recession rates from shore platform widths engineering geology 80 292 301

subduction of continental crust and terrigenous and pelagic sediments an experimental study abstract an important role for the recycling of terrigenous sediments in the mantle was proposed by armstrong 1 2 aspects of this hypothesis have been tested via an experimental study of phase equilibria in a composition similar to that of average upper continental crust over the pressure interval 6 24 gpa this composition is sufficiently close to those of the principal argillaceous and siliceous classes of pelagic sediments to use the results to interpret the behaviour of these latter sediments in addition to terrigenous sediments during subduction the subsolidus phase relationships displayed by lithologies derived from these materials are complex with major roles being played by k hollandite garnet na clinopyroxene and stishovite continentally derived lithologies achieve densities similar to or greater than surrounding mantle at depths greater than 200 km the geodynamical implications of these buoyancy relationships are discussed a reconnaissance study has also been made to assess the melting and element partitioning behaviours in the subducted continental crust lithologies during partial melting at relatively low pressures 5 10 gpa orthoclase wadeite and k hollandite are eliminated near the solidus whereas the stability field of na clinopyroxene extends to temperatures well above the solidus liquids formed by small to moderate degrees of partial melting of subducted continentally derived lithologies in this pressure interval have high k na ratios and high sio2 contents at higher pressures 16 24 gpa the stability fields of k hollandite and stishovite extend towards the liquidus whereas sodium bearing phases are eliminated much closer to the solidus resultant partial melts consequently possess relatively low k na ratios and sio2 contents lead possesses a high crystal liquid partition coefficient in k hollandite whereas uranium is excluded the broad stability field of k hollandite during partial melting of these lithologies at pressures above 15 gpa therefore has the capacity to cause fractionation of lead from uranium the petrological and geochemical implications of these results are discussed in the context of the partial melting of terrigenous materials during subduction and the interactions of the partial melts with the surrounding mantle

age and duration of the matuyama brunhes geomagnetic polarity reversal from 40ar39ar incremental heating analyses of lavas abstract constraints on the timing of geomagnetic polarity reversals have come mainly from k ar or more recently 40 ar 39 ar age determinations of lavas or their k rich phenocrysts that erupted prior or subsequent to particular geomagnetic events we have obtained 40 ar 39 ar isochron ages using incremental heating techniques on groundmass separates phenocryst poor whole rock samples or plagioclase from eight basaltic to andesitic lavas that erupted during the matuyama brunhes m b polarity transition at four geographically dispersed sites these eight lavas range from 784 6 7 1 ka to 770 8 5 2 ka 1 errors the weighted mean 778 7 1 9 ka gives a high precision age that is remarkably consistent with revised astronomical age estimates for the m b polarity transition 6 12 13 despite uncertainties in absolute calibration of 40 ar 39 ar ages relative to mineral standards used as neutron fluence monitors our age determinations are consistent with five other 40 ar 39 ar studies focused on the m b transition these results confirm that the earlier k ar based geomagnetic polarity time scale underestimated the age of the m b reversal by about 6 none of the eight isochron ages are distinguishable from one another at the 95 confidence level however we are tantalizingly close to testing for the duration of this reversal one lava at the base of a sequence of transitionally magnetized flows in chile and the uppermost lava in a similar sequence on maui are only just indistinguishable in age at the 95 confidence level and preserve different magnetic orientations we suggest that the 12 kyr difference in age represents an upper limit for the duration of the reversal and is similar to the period of low magnetic field intensity associated with records of the m b reversal from deep sea sediment cores together with the short duration 2 kyr of the directional reversal observed in several different marine sediment sections our data suggest that reversal of the field s direction could have occurred at slightly different times depending on the position of the recording site

rates and patterns of erosion on inter tidal shore platforms kaikoura peninsula south island new zealand this paper presents measured rates of erosion on shore platforms at kaikoura peninsula south island new zealand surface lowering rates were measured with a micro erosion meter and traversing micro erosion meter the mean lowering rate for all shore platforms was 1 130 mm a 1 differences in lowering rates were found between different platform types and lithologies the rate of surface lowering on type a sloping mudstone platforms was 1 983 mm a 1 and 0 733 mm a 1 on type b mudstone platforms subhorizontal on limestone platforms the lowering rate was 0 875 mm a 1 a previously reported cross shore pattern of surface lowering rates from kaikoura was not found rates were generally higher on the landward margins and decreased in a seaward direction season is shown statistically to influence erosion rates with higher rates during summer than winter the interpretation given to this is that the erosive process is subaerial weathering in the form of wetting and drying and salt weathering this is contrary to views of shore platform development that have favoured marine processes over subaerial weathering copyright 1998 john wiley sons ltd

petrology geochemistry zircon u pb dating and lu hf isotope of granitic leucosomes within felsic gneiss from the north qaidam uhp terrane constraints on the timing and nature of partial melting abstract granitic leucosomes are widely distributed within felsic gneiss in the north qaidam ultrahigh pressure uhp metamorphic terrane in western china which is crucial to understanding the relationships between partial melting metamorphic evolution and orogenic processes we have applied petrology whole rock geochemistry and sr nd isotope zircon u pb geochronology trace element composition and lu hf isotope of these granitic leucosomes to determine the nature and timing of partial melting of these rocks anatexis of the felsic gneiss is evidenced by 1 highly cuspate elongated feldspar grains along quartz quartz and quartz feldspar boundaries 2 cuspate wedge shaped pockets of k feldspar quartz plagioclase muscovite along the boundaries of quartz and or plagioclase and 3 felsic veinlets of k feldspar quartz plagioclase muscovite along grain boundaries major elements feo t mno mgo and tio 2 as well as lrees hrees and hfses are mainly retained in the melanosomes whereas the large ion lithophile elements liles e g rb ba k sr pb are preferentially partitioned into the granitic leucosomes three discrete u pb ages are recorded in the zoned zircons from the melanosomes and granitic leucosomes the inherited magmatic pre metamorphic zircon cores from melanosomes and granitic leucosomes contain quartz feldspar inclusions and record a neoproterozoic protolith age of approximately 950 ma the unzoned zircon mantles in the melanosomes and granitic leucosomes show characteristics similar to metamorphic zircons in terms of such as remarkably flat heavy rare earth element hree patterns an absence of obviously negative eu anomalies and low th u ratios these zircon mantles record an eclogite facies metamorphic age of 444 449 ma the last discrete age at 433 435 ma is preserved in anatectic zircon rims which display pronounced oscillatory zoning and contain felsic mineral inclusions of k feldspar plagioclase quartz the anatectic zircons have negative eu anomalies and pronounced positive ce anomalies and their low th u ratios and lu hf isotope features that are indistinguishable from those of the metamorphic domains the similarity in lu hf signatures indicates a closed system whereby no hf was added either from the outside via fluids or surprisingly from the pre metamorphic cores during partial melting muscovite relicts coexist with cuspate feldspars in the granitic leucosomes suggesting that the anatectic melts originate from dehydration melting due to breakdown of the muscovite in the felsic gneiss in conclusion an integrated study of the petrology geochronology and geochemistry demonstrates that partial melting of felsic gneiss in the nqd uhp terrane could mainly occurred during the initial retrogression stage and anatectic melt crystallized probably under granulite facies conditions

phase relations of tourmaline leucogranites and the significance of tourmaline in silicic magmas by means of melting and recrystallization tourmaline seeded experiments phase relations of two natural tourmaline bearing fe rich members of the schorl dravite series leucogranites have been determined between 1 and 3 kbar under h2o saturation with fo2 close to ni nio the presence of tourmaline slightly lowers the solidus temperatures of both samples from 5 to 20 c compared to the corresponding tourmaline free solidus quartz k feldspar and plagioclase phase relations are not significantly dependent on the presence of tourmaline tourmaline is the last major phase to disappear for both samples and a demonstrated liquidus phase exists for one in the recrystallization experiments the compositions of the tourmalines growing from the melt change from more mg rich at high temperatures to more fe rich at lower temperatures the tourmalines are always richer in mg than the melt is but fe and mg are not especially partitioned between crystallizing tourmaline and melt melt compositions do not depart

development of shore platforms on kaikoura peninsula south island new zealand abstract the role of waves in shore platform development has been investigated on kaikoura peninsula by direct measurement of waves in deep water and on platforms at high tide this showed that the deepwater wave environment off the kaikoura peninsula is very energetic but the amount of energy delivered to platforms is very low in deep water wave power ranged from 5900 to 106 700 n m s 1 per m of crest when calculated from mean significant wave height and when calculated from maximum wave height it ranged from 31 400 to 5 370 000 n m s 1 per m of crest a comparison of deep water wave energy flux with wave energy flux at the high tide cliff of platforms showed that there was a reduction by as much as five orders of magnitude during storm conditions an analysis of the role of breaking waves revealed that these are ineffective as an erosional agent because the depth of water offshore causes breaking before waves arrive on platform surfaces depth of water controlling wave breaking causes larger storm waves to break further from shore preventing direct attack at the cliff base shear stresses and dynamic forces under waves were calculated from waves measured on shore platforms this showed that these forces never exceeded the compressive strength of the platform rocks at kaikoura it is concluded that wave forces are not directly capable of causing erosion on shore platforms at kaikoura

tertiary tectonic history of the southern andes the subvolcanic sequence to the tatara san pedro volcanic complex lat 36 s the tatara san pedro volcanic complex a quaternary to holocene composite volcano in central chile is underlain by late miocene 6 ma plutons and tertiary metavolcanic rocks the plutons were intruded into greenschist facies metavolcanic rocks at a depth of about 4 5 km together these rocks reveal important information about the development of continental arcs in some cases apparent eruptive ages of metavolcanic rocks are younger than ages of intruding plutons indicating that there was 1 pervasive reheating of metavolcanic rocks or 2 that metavolcanic rocks were locally derived and intruded by their own magma chambers plutons we have estimated uplift or denudation rates of nearly 1 mm yr since late miocene time normal faulting currently dominates the brittle behavior of the upper crust therefore uplift is probably related to magmatic addition to the crust rather than to compression and shortening although plutonic and metavolcanic rocks display expected arc geochemical affinities the isotopic similarity of metavolcanic and plutonic rocks to quaternary volcanic rocks is strong this makes it difficult to use subvolcanic rocks as upper crustal contaminants to evaluate the igneous evolution of the quaternary deposits most plutonic metavolcanic and quaternary volcanic rocks exhibit the isotopic characteristics of juvenile crust some samples however exhibit sparse but unmistakable evidence 87 sr 86 sr and 40 ar 39 ar isotopic data for the presence of older probably precambrian through triassic radiogenic crust beneath the volcano crustal structure in this arc can be described by a three layer model in which a central section of precambrian through triassic rock is underplated by juvenile material is intruded by juvenile material or has juvenile material transported through it to be emplaced at or near the surface continued erosion of juvenile material at the surface may be balanced to some degree by continued volcanism and epizonal plutonism

distribution of coastal cliffs in kerala india their mechanisms of failure and related human engineering response the 560 km long kerala coast is characterised by long barriers with narrow beaches and steep cliffs distribution of cliffs from nine sections measuring a cumulative length of 63 5 km is evaluated in arcgis software using topomaps and field survey data the cliff sections in the southern coast comprise both permeable and impermeable rocks whereas those along northern coast are comprised of either precambrian crystalline and or tertiary formations notches caves and even small arches are developed in cannanore dharmadam and kadalundi cliffs where only primary laterites are exposed to wave attack stacks composed of laterite and precambrian crystallines found in nearshore of cliffed coast indicate recession of shoreline mass wasting mudslide and mudflow type of cliff failures are common in permeable to semi permeable rocks whereas rotational sliding rockfall and toppling failure are found in hard rock cliffs retreat of cliff sections are induced by natural or anthropogenic activities or both rate of recession vary from a few centimetres to one metre year depending upon the nature of lithology structures and recession agents acting upon the cliffs various methods of cliff protection for e g hard structures revetments groins seawalls breakwater and jetties and soft measures artificial reefs marsh creation floating breakwaters beach nourishment beach scraping and vegetation planting are suggested

where is the seaward edge a review and definition of shore platform morphology abstract shore platforms are erosional coastal landforms that have attracted scientific attention since the mid 19th century the defining element of a platform is width that is used in many calculations such as determining a platform s evolutionary state or inferring how wave energy is distributed along the shore although a critical variable there are no uniform criteria for defining the seaward edge quantification of platform width has been driven by site specific variables with the seaward edge defined on the basis of tides morphology biology processes and sediment coverage the lack of a uniform definition has meant that comparative studies are difficult and results are possibly spurious as widths derived from very different criteria can vary by an order of magnitude just on the basis of which criteria is used to determine its edge in this review a combination of morphologic and process elements is used to define the seaward edge of a shore platform the development of strict criteria is especially needed in an environment of rising sea levels if measurements of landscape change are to be made in addition the advent of seamless datasets that cross the land sea boundary means that the delineation of platform morphology is no longer limited by physical access this review concludes that the seaward edge of a shore platform will occur at or landward of wave base and should be defined as the point where active erosion of the bedrock ceases characterised by erosional features such as notches and block plucking scars or the deposition of sediment of such a thickness that the underlying bedrock is not exposed during storm events

beginning of melting and composition of first melts in the system qz ab or h 2 o co 2 solidus temperatures have been determined for minimum melt compositions in the system qz sio2 ab naalsi3o8 or kalsi3o8 at p fluid 2 5 and 10 kbar and at various water activities the dry solidus was investigated in a dry argon environment water activities ah2o between 0 0 and 1 0 were obtained by using h2o co2 mixtures the or ab or ratio of first melts increases considerably with decreasing water activity at 10 kbar it is 0 28 in the water saturated system and 0 56 at water activity 0 1 the qz content does not change with changing water activities the ab content of minimum melts formed at high pressures and low ah2o may remain almost constant in ascending magmas that are cooling and crystallizing qz content increases at the expense of the or component solidus temperatures decrease considerably when ah2o increases slightly from zero at 10 kbar the temperature difference between dry melting and the solidus for ah2o 0 1 is 120 c the influence of pure co2 on the solidus is very limited in the investigated p t range the solidus is approximatively 760 c at ah2o 0 5 between 2 and 10 kbar and approximatively 830 c at ah2o 0 3 this means that melting of quartz feldspar assemblages may induce dehydration reactions at p t conditions of the granulite facies

fractionated melting of metapelite and further crystal melt equilibria the example of the blanca unit migmatite complex north of estepona southern spain abstract the blanca unit is a tectonic element of the western betic zone betic cordilleras of southern spain whose rock sequence essentially built of metamorphic derivatives from pelites semipelites and carbonatic rocks is characterized by the prevalence of high to very high grade metamorphic assemblages this paper presents a first attempt at interpreting some of these rocks in terms of melting and its implications regarding both origin of metamorphism and geological evolution of the region the investigated migmatite complex consists essentially of two contrasting types of granitoid mobilizates type i mobilizates bear indications of a comparatively higher mobility have a wide range of compositions granitic to tonalitic and lack of cogenetic enclaves type ii mobilizates have a limited compositional range mainly granitic and contain abundant restitic material particularly in the form of small aluminous cordierite garnet sillimanite enclaves field and compositional relationships suggest that type i mobilizates represent early fractionated water saturated melts derived from rock systems initially having the highest ab an ratios type ii mobilizates may represent a residual fraction that underwent further melting at higher temperatures but under water undersaturated conditions phase relations among solidus minerals in type ii mobilizates and their contained aluminous enclaves indicate that melting may have started at pressures higher than 5 kb but also that this event was followed by nearly adiabatic decompression before final cooling and crystallization as a consequence of this decrease of total pressure extensive reaction between suspended crystals and melt took place accompanied by further melting due to an increase in water activity towards saturation these processes are analyzed for consequences regarding the diversity and generation of granitic rocks through crustal anatexis several possible modes of origin of metamorphism in the blanca unit are reviewed and it is concluded that it was most probably caused by heat transfer from the sierra bermeja peridotite intrusion during initial hot emplacement of the latter into the crust furthermore a comparison of the estimated p t evolution of the blanca unit rocks and that of adjacent metamorphic series is possible which suggests that the late decompression of the complex was related to the occurrence of syn metamorphic crustal thinning around the intruded ultramafic body

revisiting the deformed high shoreline of lake bonneville abstract since g k gilbert s foundational work in the eastern great basin during the late 1800s the late pleistocene lake bonneville 30 10 ka has been recognized as a natural laboratory for various quaternary studies including lithospheric deformation due to surface loading and climate forced water balance changes such studies rely on knowledge of the elevations of lake bonneville s paleoshoreline features and depositional landforms which record a complex history of lake level variations induced by deglacial climate change in this paper we present 1 a new compilation of 178 elevation measurements of shoreline features marking lake bonneville s greatest areal extent measured using high precision differential gps dgps and 2 a reconstructed outline of the highest shoreline based on dgps measurements submeter resolution aerial imagery topographic digital elevation models dems and field observations we also 3 devise a simplified classification scheme and method for standardizing shoreline elevation measurement for different shoreline morphologies that includes constraints on the position of the still water level swl relative to each feature type the deformation pattern described by these shoreline features can help resolve the relative effects of local hydro isostasy due to the lake load and regional solid earth deflection due to the laurentide ice sheet with potential implications for earth rheology glacial isostatic adjustment and eustatic sea level change

subaerial weathering versus wave processes in shore platform development reappraising the old hat island evidence one of the longest standing debates in rocky coast geomorphology is whether subaerial weathering or wave processes dominate shore platform evolution the origins of this debate date to the mid nineteenth century when the first descriptions of old hat islands were provided from northern new zealand old hat islands are surrounded by a broad near horizontal shore platform their formation was inferred to relate to subaerial weathering of bedrock to a level of permanent saturation with wave processes acting only to remove the weathered debris to date no detailed topographic surveys have been conducted on the old hat islands in new zealand that initiated this debate in this study we provide the first quantitative data on the original field sites topographical surveying and schmidt hammer hardness testing were conducted on 25 profiles of varying wave exposure in contrast to the classic descriptions platform elevation varies from just above mean high water spring mhws at the most exposed sites to mean high water neap mhwn at the most protected sites or mean sea level msl where beaches occur on the platform surface there is no significant difference between the hardness of the cliffs and the platforms fronting them and no clear relationship between wave exposure and platform width rather than being exclusively dominated by subaerial process the formation of microtidal sheltered old hat island platforms is considered to be a function of i the rate of weathering ii exposure to wave energy iii nearshore water depth and iv rock resistance shore platform elevation in the study area is thought to be a function of the level at which waves erode cliff rock and the action of weathering which lowers platform surfaces the width of platforms is strongly influenced by the ability of waves to dissect the platform edge along vertical joint lines copyright 2010 john wiley sons ltd

shore platform development around lord howe island southwest pacific this paper describes the morphology of near horizontal basalt and calcarenite shore platforms around lord howe island as well as the lithological and process environment in which they occur the morphology of platforms around the island is highly varied for instance they occur at a wide range of elevations between low tide level and several metres above the highest tides and their width ranges between just a few metres to over 100 m however common to most platforms is that they have near horizontal surfaces that terminate abruptly in a steep scarp at their seaward edge correlations indicate that the variability in platform elevation and width is attributable to variability in key parameters of erosion such as rock resistance and shoreline water depth whereas wider platforms occur in rocks of lesser resistance platform elevation is shown to increase both as rock resistance and the depth of water at the shoreline increases wave exposure has a significant control on platform width in some instances but an over arching relationship was not detected most platforms around the island appear to have developed over the holocene and a conceptual model is proposed to account for the varied morphology of platforms that have developed over this period resistant plunging cliffs occur along about 18 of the rocky coastline of lord howe island and represent the starting point for the model where cliffs have yielded to wave erosion platforms have been initiated at an elevation controlled predominantly by rock resistance and shoreline water depth at lord howe island narrow platforms up to about 20 m wide in exposed locations generally occur about 4 to 6 m above high tide level and have apparently been subject to very infrequent erosion shore platforms about 20 to 40 m wide have generally formed in less resistant rocks are somewhat lower at about 2 to 3 m above high tide level and have been subject to more frequent erosion over the holocene most basalt platforms around the island fall within these first two categories but there are some instances of platforms about 50 m wide these platforms have formed in rocks of comparatively low resistance and are relatively low in elevation occurring close to the level of high tide an interesting feature of some of these wide platforms is that unlike the morphology of narrower platforms raised ramparts sometimes occur on their outer edge

controls on modern fan morphology in calabria southern italy abstract alluvial fans are widespread throughout calabria but only a minority display evidence of current activity in order to understand if and to what extent fan types and their morphology are dependent on the physical environment including characteristics and processes of the depositional site and drainage basin we performed a series of discriminant analyses these analyses used as classification factors the presence or absence of fill in the feeder channel conditions of confinement by host terrain the dominant depositional process debris flow or sheetflood and morphometric attributes of fans and drainage basins as the discriminant function variables in general fan slope area and width length ratio and for basins melton s ruggedness number and source ratio were the most useful variables for classification best results were obtained by discriminating the types of fan deposits and the presence versus absence of fill in the feeder channel if the feeder source is singular fan morphology is controlled by constructional processes and is tightly linked to basin morphology on the other hand fan and basin morphology are also strongly dependent on the rock mechanical characteristics with hard rocks imparting to the basin a high ruggedness and to fans a high gradient larger fans however are those where sheetflooding predominates results of discriminant analysis based on fan and basin variables are much more significant than those based on fan variables only this means that the differences between characteristics of fan and basin systems are better defined than those between characteristics of fans only

investigating the use of alluvial fan volume to represent fan size in morphometric studies studies of the morphometric properties of alluvial fans have predominantly used a two dimensional planimetric area to represent fan size even though fans are three dimensional sediment deposits but the validity of this substitution has been questioned volumes of fans in nonsubsiding settings were estimated with the objective of investigating the relationship between fan volume and fan area a simple geometric approach was developed so that volumes of noncoalescent fans could be estimated with measurements from topographic maps data were collected from two study areas with humid temperate climates the bow valley in alberta canada and the absaroka range in wyoming usa because these landscapes were glaciated the fans are of paraglacial origin and are not related to contemporaneous tectonic subsidence using functional relation analysis results indicate that the proportional power law relationship between fan volume and fan area is not significantly different from 1 1 in both study areas morphometric relationships between fans and drainage basins are also examined with fan volume and cumulative sediment yield employed as variables

eruptive stratigraphy of the tatara san pedro complex 36 s southern volcanic zone chilean andes reconstruction method and implications for magma evolution at long lived arc volcanic centers

sea cliff retreat and shore platform widening steady state equilibrium we challenge the notion of steady state equilibrium in the context of progressive cliff retreat on micro tidal coasts ocean waves break at or close to the abrupt seaward edge of near horizontal shore platforms and then rapidly lose height due to turbulence and friction conceptual models assume that wave height decays exponentially with distance from the platform edge and that the platform edge does not erode under stable sea level these assumptions combine to a steady state view of holocene cliff retreat we argue that this model is not generally applicable recent data show that 1 exponential decay in wave height is not the most appropriate conceptual model of wave decay 2 by solely considering wave energy at gravity wave frequencies the steady state model neglects a possible formative role for infragravity waves here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances and longer timescales than imaginable under the established conceptual model copyright 2013 john wiley sons ltd

lacustrine shore platforms at lake waikaremoana north island new zealand this paper examines the morphology and processes governing the development of shore platforms at lake waikaremoana north island new zealand shore platforms at lake waikaremoana are recent features and were formed when a new sequence of shoreline development was initiated due to lowering of the lake by 5 m in 1946 for hydroelectric power development three predominant platform morphologies were identified around the lake these include gently sloping platforms c 1 5 to 3 9 ramp platforms c 6 8 to 9 2 and concave ramp platforms c 7 9 to 12 platform widths ranged from 11 to 31 m with the gently sloping platforms characterized by the widest morphologies erosion rates were estimated using perched sandstone boulders and were found to range from 3 4 to 12 5 mm a 1 with a mean erosion rate of 5 9 mm a 1 higher rates of erosion were identified at lower platform elevations due to a greater frequency of wetting and drying cycles coincident with storm waves while lower erosion rates were identified at higher elevations field evidence suggests that shore platforms at lake waikaremoana were likely initiated and continue to develop as a result of subaerial wetting and drying cycles waves coincident with fluctuating lake levels play an important role by removing the weathered material from the platforms and appear to control the width of the platforms a conceptual model of platform development is presented and analogies are drawn between this model and the formation of shore platforms in oceanic environments copyright 2002 john wiley sons ltd

dating of subduction and differential exhumation of uhp rocks from the central dabie complex e china constraints from microfabrics rb sr and u pb isotope systems abstract the correlation of deformation fabrics and metamorphic reactions with geochronologic data of uhp metamorphic rocks demonstrate that the multistage subduction and exhumation history of the central dabie complex requires rapid subduction and rapid initial exhumation moreover these data show that volume diffusion is not the major resetting mechanism of radiogenic isotope systems thus our age data do not simply reflect a thermal cooling history in the investigated section the maximum age for uhp is given by the 244 3 ma 2 u pb age of a pre uhp titanite phenocryst that survived uhp metamorphism and subsequent tectonometamorphic events a minimum age for uhp is set by the 238 1 ma 2 238 u 206 pb mineral isochron age of titanite and cogenetic epidote these minerals formed from local partial melts during ascent and their age suggests fast exhumation and emplacement in the middle crust in the period of ca 238 218 ma the uhp terrain records ht metamorphism local partial melting and extensive pervasive strain below the eclogite jd grt stability field exhumation was polyphase with a first phase of fast exhumation succeeded by episodes of ht metamorphism and concomitant deformation at deep mid crustal level between 238 and 218 ma slow exhumation related to the final emplacement of tectonic units along greenschist facies shear zones did not cease before ca 209 204 ma the resetting and homogenization of radiogenic isotope systems were aided by dissolution precipitation creep which was the dominant deformation mechanism in quartz feldspar rocks in combination with fluid influx

phase relationships of s type granite with h2o to 35 kbar muscovite granite from harney peak south dakota muscovite granite 13 8 muscovite 4 8 normative corundum was reacted with varying percentages of h 2o in cold seal vessels at 2 kbar and in piston cylinder apparatus between 10 and 35 kbar the diagrams illustrating melting crystallization relationships are p t sections with both excess h 2o and with no h 2o added 0 66 h 2o in rock t x h 2o sections at 15 kbar and 25 kbar showing h 2o undersaturated conditions the h 2o undersaturated surface for the crystallization of quartz coesite small amounts of aluminosilicate minerals persist to higher temperatures glass compositions measured by electron microprobe from samples with 5 h 2o at 15 kbar confirm that liquids are syenitic through at least 100 c above the solidus as predicted from the effect of pressure on the residua system results are explained successfully by phase relationships involving muscovite quartz and orthoclase in k 2o al 2o 3 sio 2 h 2o with reactions depicted in a p total p e h 2o t model with special reference to the divariant surfaces in the region p e h 2o p total with reduced p e h 2o or a h 2o produced either by small amounts of h 2o and h 2o undersaturation or by co 2 h 2o mixtures subsolidus dehydration reaction temperatures decrease vapor present solidus temperatures increase and muscovite stability in presence of liquid increases in general muscovite biotite and amphibole can be precipitated from magmas containing only a few tenths per cent h 2o although the h 2o undersaturated liquids coexisting with crystals may contain 3 or more dissolved h 2o this particular granite cannot be a primary magma from mantle or subducted oceanic crust it is a possible product of partial fusion of pelitic rocks between about 20 km and 40 km depth given sufficient h2o and xenocrystal muscovite or sillimanite from the source rocks the phase relationships are consistent with the idea of s type granites but not sufficient to prove the origin of this rock additional tests require phase relationships of other associated granitic rocks and details of geochemistry geophysics and field relationships

comprehensive characterization of elevated coastal platforms in the north iberian margin a new template to quantify uplift rates and tectonic patterns abstract the cantabrian margin at the northern iberian peninsula shows elevated coastal platforms extending from west to east for 200 km these erosional surfaces are several kilometers wide and are bounded inland by a paleoshoreline and towards the sea by the retreating current cliff the origin and evolution of these geomorphologic markers remains controversial one of the main challenges arising from the difficulties in correlating the patchy distribution of the platforms and their variable heights along the margin due to lithological differences local tectonism and varying degrees of preservation with the aim of understanding recent coastal evolution a systematic quantitative gis analysis of lidar elevation models 5 m resolution was carried out along 4 000 km2 of the cantabrian coast between 4 15 w and 7 30 w longitude the coastline runs parallel to the cantabrian mountains which are supported by an orogenic root present only beneath the eastern half of the coastline under study the integration on the gis template of the crust mantle boundary as a controlling factor of landscape development has helped in the understanding of the recent evolution of the coastal platforms and in the interpretation of previously unexplained features of their distribution the two main outcomes of this multiscale approach are 1 the correlation of most of the fragmented rasas as part of an original unique coastal platform along the cantabrian margin and 2 the differentiation of two sectors separated by a highly tectonized area associated to the ventaniella fault the western sector has one main continuous surface showing a 0 08 tilt towards the west sometimes interrupted by local and recent minor faults with net slips of meters to tens of meters the eastern sector has several steps of erosional surfaces spread out at various heights without tilt the ventaniella fault separating both sectors produces an apparent vertical offset of 50 m in the main erosional surface our study shows that this fault also separates two distinct evolutions in the elevation of the coastal platform 1 the western coast which has risen continuously probably in response to a lateral gradient in crustal thickness and 2 the eastern coast where uplift is discontinuous over time since several of these surfaces formed below the main paleoshoreline the cantabrian coast captures the influence that crustal structure has on the expression and evolution of geomorphologic markers at the surface and vice versa landform features at the surface can be very sensitive to differential crustal thickness while responding to the same external and climatic forces in the context of the western european framework our work provides a regional template within which future absolute geochronological dating can be based to improve our knowledge of the recent evolution of the atlantic margins

high temperature metamorphism in a major strike slip shear zone the ailao shan red river people s republic of china abstract petrographic and thermobarometric analysis provides constraints on thept path of the mylonitic gneisses of the left lateral ailao shan red river shear zone which has accommodated the lateral extrusion of indochina during the tertiary two different paragenesis p1 and p2 are coeval with this deformation and correspond respectively to the amphibolite and greenschist facies microprobe analysis reveals that p1 garnets bear a chemical zonation from core to rim this zonation indicates a temperature increase during garnet growth conditions of formation of garnet rims p1b which are estimated using biotite garnet and plagioclase garnet thermobarometers are close to the granitic solidus 710 70 c and4 5 1 5 kbar p2 conditions are estimated to be approximately 500 c and

on the role of discontinuities in mediating shore platform erosion in this paper we quantitatively demonstrate that dominant erosion processes on different shore platforms can be explained in part by geological properties we selected sites with a considerable history of rock coast geomorphology study to evaluate whether geological data can improve our understanding of spatial variations in erosion between sites schmidt hammer tests and discontinuity data were collected on blue lias limestone shore platforms in wales uk and sandstone platforms in victoria australia significant differences in joint spacing persistence of discontinuities and block size were found between the australian and welsh study sites these data were related to evidence of meso scale erosion to examine how geological contingency influences the nature and scale of erosion processes and thresholds this study quantitatively demonstrates that discontinuities play a fundamental role in altering rock resistance the findings of this research have important implications for the design of rock coast erosion studies concerned with measuring rates of change and determining the relative contributions of different processes to platform development

the elevation of shore platforms a laboratory approach to the unsolved problem a wave flume experiment was conducted to investigate the influence of wave height and rock strength upon the elevation of shore platforms having a marked scarp at the seaward margin breaking waves were allowed to act on a steep model cliff to produce a platform results indicated that platform elevation increases with increasing rock strength if other factors are constant it was suggested that a considerable difference in platform elevation in the field can arise depending on wave height and rock strength the water depth in front of platforms proved to be important for the study of platform elevation

alluvial fan slope as a function of sediment transport efficiency abstract the nature of slope acquisition by alluvial fans was studied by comparing the slope evolution of 37 tributary fans to the san juan river in an arid region of western argentina each of these fans is characterized by truncation of the distal end as a result of incision by the san juan river the alluvial fan slope prior to incision and the slope of the active channel for each fan was measured river accumulation terraces indicate that fan incision was probably synchronous along the valley incised channels in each fan evolved over the same interval but they show different degrees of advance of erosion values of old fan slope fit well with known power laws relating them to drainage area r 0 865 slopes of incised channels also fit with power laws but with a lower regression coefficient r 0 741 the regression lines in each case have almost the same slope 0 218 sd 0 02 and 0 215 sd 0 03 respectively which suggests that although the incised channel slope is not an equilibrium feature both the original and the secondary fans follow the same law of variation an explanation for this phenomenon is that the transport efficiency of the fans may be related to the size of the basin if mean runoff and peak floods are roughly regulated by drainage area fan slopes of larger drainage basins will evolve faster than those of smaller basins apparently as a group of fans approach an equilibrated state their slopes become distributed along successive parallel regression lines progressively displaced upward in the diagram as long as climatic conditions remain constant to see the effects of water availability on fan slope we also compared slopes and drainage basin areas of fans located in settings with different specific runoff which is approximately a function of annual rainfall the regression lines for each set of alluvial fans are roughly parallel the smaller intercept value for humid fans indicates that for a given drainage area fans in arid settings are steeper than those in more humid settings fans dominated by mud flows and dilute flash floods were plotted together but no major differences were observed in this general behavior this suggests that the steepness of a fan is not primarily related to compositional factors or to the sediment transport process but to transport efficiency episodic flood fans of argentina show slopes comparable to the mudflow fans of death valley because water supply and therefore transport efficiency are similar drainage basin area combined with mean annual rainfall may largely determine transport efficiency by controlling mean runoff across the fan as a result transport efficiency may define not only alluvial fan slope but also the rate at which the alluvial fan slope reestablishes equilibrium after some external change

lahar hazard assessment using titan2d for an alluvial fan with rapidly changing geomorphology whangaehu river mt ruapehu abstract rapid changes in small areas at the apex of alluvial fans may have devastating consequences by directing downstream flood or lahar impacts into catchments of widely varying population or infrastructure vulnerability during a series of lahars in 1995 at mt ruapehu new zealand aggradation of the whangaehu fan apex draining the eastern edifice caused the onset of avulsion of flows northward into the highly vulnerable tongariro catchment an earth training dike or bund was constructed to protect this catchment by retaining flows on the southern side and the normal lahar outlet path to the south surveys in 2001 late 2005 and following a major lahar in march 2007 now show net degradation of a channel in the whangaehu fan apex bordered by the bund this indicates a net increase in the channel capacity at this site and shows that the bund remains at its effective design capacity past hydrological modelling used for the bund design provided a large range of discharge estimates but lacked precise constraints on the size and nature of lahars from eruption and lake breakout events new modelling has been carried out using titan2d to examine the impacts of a 6 106 m3 volume granular flow down this catchment this simulates either an eruption or a lake breakout induced lahar with a historically typical volumetric bulking factor of 4 these simulations predict minimum discharges between 1800 and 2100 m3 s at the bund site by comparison the largest 1995 flow at this site was estimated at around 1200 m3 s further any single modelled flow from the normal outlet channel of crater lake could not be induced to overtop the bund because discharge appears to be limited by the narrow upper reaches of the whangaehu gorge theoretical discharge levels required to overtop the bund are estimated to be 6800 m3 s assuming no aggradation of the channel by the decelerating flow maximum potential discharge at the bund site is additionally modified by potential bifurcation of lahars above a certain size threshold at a point 2 5 km upstream of the bund a major side channel the chute effectively diverts part of the flows away to the southern side of the whangaehu fan this potential for splitting of the flow appears to have increased since 1995 from aggradation of lahar deposits and reworked sediment in the area immediately upstream of the divide despite remaining at design capacity for lahar events in the whangaehu erosion of new channels following the 2007 lahar renders the bund vulnerable to undercutting

pleistocene slip rates on the bocono fault along the north andean block plate boundary venezuela the bocono fault is a strike slip fault lying between the north andean block and the south american plate which has triggered at least five mw 7 historical earthquakes in venezuela the north andean block is moving toward nne with respect to a stable south american plate this relative displacement at 12 mm yr 1 in venezuela within the maracaibo block was measured by geodesy but until now the distribution and rates of quaternary deformation have remained partially unclear we used two alluvial fans offset by the bocono fault yaracuy valley to quantify slip rates by combining 10be cosmogenic dating with measurements of tectonic displacements on high resolution satellite images pleiades based upon a fan dated at 79 ka and offset by 1350 1580 m and a second fan dated at 120 273 ka and offset by 1236 1500 m we obtained two pleistocene rates of 5 0 11 2 and 20 0 mm yr 1 consistent with the regional geodesy this indicates that the bocono fault in the yaracuy valley accommodates 40 to 100 of the deformation between the south american plate and the maracaibo block as no aseismic deformation was shown by insar analysis we can assume that the fault is locked since the 1812 event this implies that there is a slip deficit in the yaracuy valley since the last earthquake ranging from 1 to 4 m corresponding to a mw 7 7 6 earthquake this magnitude is comparable to the 1812 earthquake and to other historical events along the bocono fault

differential features of alluvial fans controlled by tectonic or eustatic accommodation space examples from the betic cordillera spain abstract the creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area along basin margin faults or to a rise in base level depending amongst others on the relative importance of these two factors the margins of terrestrial sedimentary basins where alluvial fans develop produce aggradational progradational or retrogradational stratigraphic architecture we studied a total of 43 quaternary alluvial fans in the granada and bajo segura basins betic cordillera spain the analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns which is the result of differences in eustasy and tectonics the qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related in each case to the main mechanism operative in the creation of accommodation space these patterns are described as follows 1 alluvial aggradation is the main result of high tectonic subsidence with the development of quite open but small fans with a constant steep slope lacking incised channels and headward eroding gullies 2 in contrast when the principal mechanism in creating accommodation space is low tectonic subsidence progradation occurs and the fans are narrower and larger moreover the slopes of such fans are less steep in relation to the drainage area than in the above case being constant or even concave in longitudinal profile they also have short deep incised channels culminating downfan in a depositional lobe in inactive zones long deep headward eroding gullies develop 3 areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin although with a pronounced mountain embayment which gives them a characteristic mushroom shape in plan view in the latter case retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas usually showing a segmented longitudinal profile with a low gradient the feeder channels do not surpass stream order 3 and various extremely long and shallow incised channels can appear 4 contrary to the case of fans developing under a regime of subsidence when the accommodation is due to base level rise the fan slopes bear no relation to the extent of the catchment basins in such a case the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet flows over the alluvial surface

cooling history of the puttetti alkali syenite pluton southern india abstract the puttetti alkali syenite pluton in southern india belongs to the suite of felsic magmatic intrusives emplaced during the late neoprotrozoic cambrian time during the final phase of amalgamation of the gondwana supercontinent in this study we evaluate the cooling history of this pluton based on various isotopic systems we present whole rock pb pb data on the syenite which yields an isochron age of 508 25ma three phlogopite separates from the syenite pluton give k ar ages of 454 0 9 0 448 5 8 9 and 445 6 8 8 ma indicating cooling age at temperatures of 415 c u pb analyses of zircons from this syenite yielded an age of 572 2 ma in a previous study with u pb closure temperatures 800 o c this age probably indicates the timing of emplacement of the puttetti pluton collectively we estimate from the isotopic age data and respective closure temperatures that the syenite body cooled at about 3 2 o c ma from about 800 o c to about 415 o c the markedly low cooling rate of the syenite pluton absence of chilled margin effects and common occurrence of pyroxene feldspar phlogopite and zircons megacrysts in the rock indicate that the host granulites were at high temperatures during the emplacement of the syenite magma the cooling history of puttetti syenite estimated in this study is closely comparable with the 3 4 o c ma cooling rate estimated for a granite pluton in a previous study from madagascar our study suggests protracted cooling rates for the late pan african intrusives emplaced within the gondwana crust with a long residence history in a hot crust bore they were exhumed to shallower levels

late quaternary tectonics of the vallo di diano basin southern apennines italy italian ministry of university and research project firb research and development of new technologies for protection and defence of territory from natural risks w p c3 crustal imaging in italy