mid archaean evolution of the eastern indian craton geochemical and isotopic evidence from the bonai pluton abstract the archaean eastern indian craton consists of several granitoid batholiths intruding greenstone like sequences the bonai pluton one such body in the central sector of the craton consists of a dominant porphyritic and a subordinate equigranular variety ranging in composition from trondhjemite to granite xenoliths of massive trondhjemite migmatite and quartzite occur in both phases the granitoid xenoliths represent remnants of a sialic crust and are the oldest recognizable element in the bonai pluton these are high al 2 o 3 trondhjemites with a highly fractionated rare earth element ree pattern a pb pb isochron age of 3369 57 ma has been obtained from a few spatially related xenoliths the porphyritic and equigranular granitoids show similar petrographic characteristics and most of the samples show a calc alkaline trondhjemitic association a few granite samples however belong to a normal calc alkaline association the trondhjemitic samples are of the low al 2 o 3 type with fractionated light ree lree flat heavy ree hree and a marked negative eu anomaly granites of the calc alkaline association have an identical ree pattern pb isotopic data for all samples together yield a pb pb isochron age of 3163 126 ma the ree characteristics of the two trondhjemite suites can be generated by partial melting of a mafic source with variable residual phases at different depths on the other hand the normal calc alkaline granite may be generated by partial melting of trondhjemite similar in composition to that represented by the 3369 ma xenoliths isotopic ages and the chemical nature of the bonai pluton are similar to those identified in the adjacent singhbhum granite complex it is suggested that the entire eastern indian craton has a common mid archaean history the earliest sialic crust formed at 3400 ma and was followed by trondhjemitic addition at 3300 ma during this phase restricted reworking of the older sialic crust produced calc alkaline granites

downwearing rates of vertical limestone surfaces in the intertidal zone gulf of trieste italy abstract in 2007 we installed seven micro erosion meter stations on a vertical limestone slab located in the intertidal zone in the gulf of trieste italy in order to observe rock surface changes at elevations ranging between 0 75 m and 0 75 m m s l furlani et al 2010 in this paper we present the micro erosion metre mem data for most months between february 2008 and may 2013 and the traversing micro erosion metre tmem data collected twice a year since 2007 the mem and tmem data were consistent and indicated that the mean lowering rate ranged between 0 007 mm yr and 0 205 mm yr and 0 001 mm yr and 0 260 mm yr according to the elevation of the stations maximum downwearing rates were observed in the mid lower intertidal zone and decreased upward and downward the natural trend of erosion started in 2010 after 2 years of exposure when the slab formerly smoothed and not colonized by marine organisms started to be acclimated to the local environment after 2010 the erosion rate increased to a maximum of 0 31 mm yr this value can be more representative for long term studies and is similar to the downwearing rates locally collected on natural limestone surfaces this dataset represents the first collection of downwearing rates mainly measured using mems but also tmems on vertical limestone surfaces in an intertidal zone and provides interesting new information for addressing the debate on notch genesis and development the shape of a tidal notch has been found to be consistent with the distribution of erosion rates along the slab even if the present day notch was not surveyed in the gulf of trieste due to the local tectonic subsidence

holocene fire and vegetation changes in southeastern brazil as deduced from fossil charcoal and soil carbon isotopes abstract carbon isotopes of soil organic matter som and radiocarbon dating on charcoal from nine soil profiles collected under native forest vegetation in londrina state of parana anhembi botucatu and jaguariuna sao paulo and salitre minas gerais southeastern brazil were used to evaluate the vegetation changes and to establish the chronology 13 c and 14 c data in som and charcoal respectively indicate that c 4 plants were the dominant vegetation in londrina and jaguariuna during the late pleistocene until middle holocene probably associated with the presence of a drier climate in anhembi and botucatu c 3 plants dominate the landscape during the period a probable mixture of c 3 and c 4 plants occurred in salitre during the holocene this study is part of a main research program related to palaeoenvironmental reconstruction of vegetation and climate in distinct regions of brazil during the last 20 000 years

chemical evolution of granitic rocks in the east antarctic shield with particular reference to post orogenic granites granitic intrusives of the east antarctic shield range in age from early archaean 3930 ma to cambrian and show systematic variations in chemical and isotopic characteristics many archaean orthogneisses are of tonalitic to granodioritic composition and represent new continental crust derived from the mantle by a two stage process involving hydrous melting of mafic crustal rocks syn orogenic granitic rocks are generally of more potassic composition and were derived by intracrustal melting under lower ph2o conditions they are mostly of more typical i type derived from igneous source materials but there is an increasing proportion of s types derived by melting of sedimentary materials with time late and post orogenic intrusives are mostly granites s s with a type anorogenic affinities and were derived by melting of relatively anhydrous granulite facies lower crustal rocks they are characterised by marked enrichment of y zr nb la and ce relative to p ti and sr and commonly have high f femg znfe and gaal plagioclase apatite and ti minerals were probably residual phases during partial melting as well as being involved in fractional crystallisation whereas other minor phases such as zircon were apparently relatively soluble in the high temperature melts emplacement of a type granites at about 500 ma may have been associated with internal fracturing of gondwanaland before eventual break up

modeling the role of weathering in shore platform development a mathematical wave erosional model was modified to study the additional effect of weathering by wetting and drying and salt weathering on the development of shore platforms in macro to mesotidal environments model rates of downwearing by these processes at different tidal elevations were based on data obtained from a series of laboratory experiments on sandstones from eastern canada backwearing by mechanical wave erosion was calculated using basic wave equations there were several types of run which were designed to determine the effect of weathering and the production of fine grained sediment the periodic accumulation of debris on weathering in the upper intertidal zone and weathering in reducing rock resistance and facilitating wave quarrying the results implied that compared to mechanical wave erosion the direct effect of weathering and fine grained sediment production makes only a small contribution to the long term development of shore platforms the relationship between cliff foot debris occurrence and platform development and morphology was inconsistent because of the negative feedback relationship between erosion rates surface gradients and rates of wave attenuation the model suggested that weathering can play an important indirect role in assisting wave quarrying of joint blocks and other rock fragments

shore platform downwearing in eastern canada the mega tidal bay of fundy abstract laboratory and field work was conducted to determine rates of surface downwearing on shore platforms at two sites in the bay of fundy canada these data are needed to assess and model the effect of downwearing mechanisms on platform evolution sandstone and basalt samples 900 were exposed to semidiurnal tidal cycles over 3 years using de ionized water or artificial sea water they were immersed for 1 6 or 11 h over each 12 h tidal cycle representing the lowest high lht mid and highest low hlt tidal levels respectively a further 600 samples were immersed in de ionized water or artificial sea water for 90 min every 1 2 or 3 weeks representing increasingly higher elevations above the lht level or exposed for 90 min every 1 2 or 3 weeks representing increasingly lower elevations below the hlt level these experiments ran for 12 months in the field surface downwearing was measured at 108 transverse micro erosion meter tmem stations over 2 to 6 year periods in the laboratory mean downwearing rates between the lht and hlt levels were 0 61 1 80 mm yr 1 in sandstones and 0 01 0 18 mm yr 1 in basalts rates were highest at the lht level rates decreased with elevation above the lht level and were uniformly low below the hlt level salt weathering was dominant above the lht level salt weathering and wetting and drying were important in sandstones between the lht and hlt levels but salts inhibited rock breakdown in basalts in the field the mean downwearing rate was 1 254 mm yr 1 in sandstones which was similar to the experimental data and 0 722 mm yr 1 in basalts which was much higher than in the experiments with artificial sea water but similar to the experiments with de ionized water there was no relationship in the field between downwearing rate and rock hardness or tmem station elevation

submerged notches on the coast of skyros island greece as evidence for holocene subsidence article i nfo detailed mapping along the coasts of skyros island aegean sea provided new evidence concerning the rates and the modality of subsidence in the area the results are provided through the study of the shape and the dimensions of the two submerged notches detected around the carbonate coasts of the island itisapparentthattheislandhasbeensubmergednotonlyduetotheglobalsea levelriseduringthelasttwocen turies 1 8 0 3 mm year between 1950 and 2000 but also because of tectonic events testified by the type of the submerged notches some of these tectonic events seem to be of gradual and some of co seismic origin the transition of msl from the retreat point of the lower notch to the retreat point of the upper notch seems to have been produced by co seismic subsidence of about 55 cm at slightly less than 850 years bp

the effect of holocene changes in relative sea level on the morphology of rocky coasts abstract a mathematical wave and weathering model was used to study the effect of holocene changes in relative sea level rsl on rock coast development model runs were made for fast and slow eroding coasts in macro and mesotidal environments using holocene rsl records from sweden northeastern usa southwestern britain central japan western africa and southern australia a further series of otherwise identical runs were made with constant sea level changes in rsl determined the amount of time that marine processes have operated within the modern intertidal zone and rates of wave attenuation and erosion continue to be influenced by subtidal morphology that developed in most areas when rsl was rising to its present level the model suggested that although tidal range is also important holocene rsl changes promoted subhorizontal platform development in australasia and over much of the southern hemisphere and sloping platforms over much of the northern hemisphere shore platforms may have been partly inherited from earlier periods in the holocene when rsl was similar to today s nevertheless most platforms continue to be eroded at all tidal levels where geological and wave conditions are less favourable erosion in the lower intertidal zone has essentially terminated in areas where rsl rose to its present position whereas erosion only occurs today in the lower intertidal zone in places where rsl rose to above its present level in the middle holocene

shore platform downwearing in eastern canada a 9 14 year micro erosion meter record abstract downwearing rates erosion in the vertical plane were measured with a micro erosion meter mem in eastern canada on an argillacious sub horizontal shore platform at mont louis in eastern quebec and on two sloping basaltic and sandstone platforms at respectively scots bay and burntcoat head in the bay of fundy nova scotia the original data covered a period from 2002 to 2009 this dataset was extended by measurements repeated at surviving mem stations in 2017 producing records ranging over 9 14 years depending on when each station was installed because of rapid surface downwearing many of the original mem stations were inoperable in 2017 especially at burntcoat head nevertheless data were obtained from 19 stations at burntcoat 35 of the 2009 original 25 at mont louis 83 of the original and 38 at scots bay 75 of the original for the stations at mont louis and scots bay that were still functioning in 2017 there were no significant differences in rates of downwearing over the shorter from station installation up to 2009 and extended periods from installation to 2017 mean rates of downwearing calculated from all the stations in each area declined through time however due to the loss of the more rapidly eroding stations a simple procedure which was proposed to compensate for this decrease produced mean downwearing rates that were broadly similar to those reported over the original measurement period there were significant relationships between downwearing rates and elevation r2 0 32 and downwearing rates and rock hardness r2 0 41 in the extended record at scots bay and a small but significant relationship between downwearing rates and rock hardness at mont louis r2 0 17 differences in downwearing rates across the platforms suggest that salt weathering and wetting and drying are dominant weathering mechanisms at scots bay and mont louis chemical weathering of the sandstone cementing agent and the premature removal of weathered grains by wave generated bottom currents may however be more important at burntcoat head

geochronological constraints on evolution of singhbhum mobile belt and associated basic volcanics of eastern indian shield abstract the singhbhum mobile belt smb of the eastern indian shield represents a roughly east west trending arcuate belt of folded supracrustals overlying the granite greenstone basement of the singhbhum orissa craton along its northern eastern and western margins and is bounded by the chotanagpur gneissic complex to further north the radiometric ages of the basement singhbhum and equivalent granites and the intrusive anorogenic mayurbhanj granite pluton constrain the time of evolution of this mobile belt between 3 12 and 3 09 ga hence the smb supracrustals also known as singhbhum group is late mesoarchaean in age and not proterozoic as thought earlier the evolution of the smb was followed by emplacement of some major basic igneous rocks within or adjacent to the supracrustals these include simlipal volcanics at 3 09 ga on the smb mayurbhanj gabbro along with mayurbhanj granite at 3 09 ga along the marginal part of the craton near the smb and the dalma volcanics on the smb along with the dhanjori volcanics adjacent to smb at 2 80 ga the 2 80 ga old basic volcanics is also associated with emplacement of some small granite plutons occurring along the marginal part of the craton one of them the tamperkola granite intrudes the smb the 3 09 ga onward igneous activities along the marginal part of singhbhum orissa craton took place essentially under anorogenic tectonic setting before being affected by a major metamorphism at 2 50 ga which is recorded on the dalma volcanics and on some small granite pluton occurs along the marginal part of the craton the jagannathpur and stratigraphically equivalent malangtoli volcanics occurring within the singhbhum orissa craton at the west were erupted at 2 25 ga the boundary between the smb supracrustals and the singhbhum orissa craton is demarked by a prominent shear zone known as the singhbhum shear zone which shows multiple reactivation the oldest being at 3 09 ga followed by subsequent reactivation during palaeo and mesoproterozoic periods at 2 2 1 8 1 6 1 5 1 4 and 1 0 ga respectively the singhbhum group and the adjacent chotanagpur gneissic complex appear to have evolved from a near shore syn rift and a distal post rift stable shelf sedimentary assemblages respectively which were deposited without any stratigraphic break in a marine basin existed in the present north of the singhbhum orissa craton both of these assemblages were deformed and metamorphosed together during proterozoic at 2 5 to 2 3 ga 1 6 ga and 1 0 ga

analysis of relationships between micro topography and short and long term erosion rates on shore platforms at kaikoura peninsula south island new zealand using long term data sets of erosion rates for the shore platform at kaikoura it is possible to assess the relationships between erosion rates over two and ten years erosion rates do not tend to vary significantly between the two measurement periods using linear regression analysis a difference in the nature of topographic change is identified between mudstone and limestone shore platforms the mudstone platforms show a consistent mode of topographic change parallel retreat or smoothing between the short and long terms limestone shore platforms show no consistent mode of topographic change it is suggested that the consistent behaviour of the mudstone platforms occurs because the mudstone surface is responding as a single unit at this scale of measurement erosion rates tend to increase with distance from the seaward edge of the platforms and this may reflect the increasing significance of wetting and drying cycles as well as the increasing mix of erosional processes as sub aerial processes increase in importance this changing mix of erosional processes may also explain the variations in gradient coefficients between short and long term erosion rates with distance from the seaward edge of the platforms

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

discovery of a neoproterozoic basin in the prydz belt in east antarctica and its implications for gondwana assembly and ultrahigh temperature metamorphism abstract detrital zircon u pb age data from ultrahigh temperature metasedimentary rocks 950 c and 10 12 kbar in the rauer group and a granulite grade metasedimentary rock 850 c and 7 8 kbar in the bolingen islands in prydz bay east antarctica indicate the existence of a neoproterozoic ediacaran cover sequence that was deposited on basement ranging in age between approximately 2800 ma and 940 ma the neoproterozoic succession has a maximum depositional age of approximately 600 ma with derivation from igneous and metamorphic sources of archaean palaeoproterozoic and neoproterozoic age the minimum depositional age is constrained to be approximately 575 ma based on existing th u pb monazite metamorphic ages from the uht metasedimentary rocks the identification of late neoproterozoic protoliths to the uht granulites in the rauer group demonstrate that ultrahigh temperature metamorphism in prydz bay must be ediacaran to cambrian in age the timing of basin development ca 600 575 ma is coincident with the amalgamation of eastern gondwana the palaeogeography of the prydz bay region during the amalgamation of gondwana is uncertain but in our proposed reconstruction we suggest that inherited zircons were derived from indo antarctic crust ocean closure is inferred to have occurred along a suture zone to the southeast of prydz bay and the prince charles mountains our palaeogeographic model invites further work on the possibility of a shared history between india and a large portion of east antarctica prior to the final amalgamation of eastern gondwana during the ediacaran cambrian

long term shore platform surface lowering rates revisiting gill and lang after 32 years abstract in 1978 e d gill and j g lang installed 53 micro erosion meter mem sites on shore platforms along the otway coast in south eastern australia surface lowering rates were originally determined from 2 yr of measurements 1979 and 1980 and showed that the mean annual rate of lowering from all sites was 0 37 mm yr 1 we re measured these mem sites 32 yr after the first set of readings were taken in february 1979 we relocated 49 of the original 53 bolt sites and were able to measure 45 of them from the sites we measured the mean annual rate of shore platform lowering was 0 31 mm yr 1 rates of surface lowering on shore platforms are commonly reported from studies of only two or three years and only one other record exceeds 30 yr kaikoura peninsula nz 1 09 mm yr 1 in that case fewer than half of the original bolt sites were functioning because erosion had removed bolts along the otway coast rates of erosion are much slower hence the greater number of still readable sites after 32 yr compared to other micro erosion meter studies the rates reported here are at the lower end of the range of values from around the world but nevertheless consistent with rates from the otway coast and others in similar lithology we found no statistical difference between erosion rates calculated over 2 yr 1979 to 1980 and 32 1979 to 2011 years supporting the view that shore platform lowering rates measured over 2 yr are representative of decadal scales

field techniques for measuring bedrock erosion and denudation bedrock erosion rates in natural landscapes are usually slow of the order of millimeters per year or less and sophisticated techniques have been developed to measure them different techniques have proved to be valuable depending on the spatial and temporal scale on which information is needed on the environment and on the scientific question that is asked here we give an overview of the various methods that have been developed we introduce their working principles and outline their advantages and disadvantages further we provide comprehensive references to relevant literature both on the methods and on scientific examples of their application 2016 the authors earth surface processes and landforms published by john wiley sons ltd

short term rock surface expansion and contraction in the intertidal zone transverse micro erosion meter tmem stations were installed in rock slabs from shore platforms in eastern canada the slabs were put into artificial sea water for 1 6 or 11 hours representing high mid and low tidal areas respectively the tmems were used to record changes in surface elevation as the rocks dried during the remainder of the 12 h of a semi diurnal tidal cycle a similar technique was used on the same rock types at intertidal tmem stations in the field as the rocks dried during low tide argillite and basalt surface contraction was from 0 to 0 04 mm there was little surface expansion sandstones contracted by up to 0 03 mm in the field but there was almost no contraction in the laboratory argillite and basalt contraction tended to be greatest in the upper intertidal zone and to increase with rates of longer term surface downwearing but there was little relationship with rock hardness or air temperature and humidity changes in elevation at the same points at tmem stations in the laboratory and field were quite consistent from one tidal cycle to the next but there were considerable variations within single tidal cycles between different points within each station the data suggest that contraction within the elevational zone that is normally submerged twice a day by the tides is by alternate wetting and drying short term changes in elevation are generally low compared with annual rates of downwearing owing to erosion but they may generate stresses that contribute to rock breakdown copyright 2007 john wiley sons ltd

207pb 206pb zircon ages and the evolution of the singhbhum craton eastern india an ion microprobe study1this paper is dedicated to prof a k saha one of the senior co authors who passed away after submission of the paper 1 abstract we used an ion microprobe to measure 207 pb 206 pb ages of single zircons from four key lithologies from the singhbhum craton of eastern india detrital zircons from the oldest recognized sedimentary sequence of the craton the older metamorphic group yielded 3 5 3 6 ga ages indicating that crustal formation had already been initiated by 3 6 ga in this region this data also established an older limit of 3 5 ga for the age of sediment deposition the first appearance of extensive continental crust in the singhbhum region marked by the emplacement of the older metamorphic tonalite gneisses is dated at 3 44 ga our data from both of these units reveal that a 3 2 ga event induced overgrowths within each of these pre existing zircon populations we determine an age of 3328 7 ma for the singhbhum granite phase ii the most widespread of this granite s three phases the emplacement of the two phases of the mayurbhanj granite marking the youngest major episode of acid plutonism in this craton took place in rapid succession at 3 1 ga marking the broad scale stabilization of this terrain

in situ u pb geochronology and hf isotope analyses of the rayner complex east antarctica in situ zircon u pb and hf isotopic analysis via laser ablation microprobe inductively coupled plasma mass spectrometer lam icpms of samples from kemp and macrobertson lands east antarctica suggests that the kemp land terrane evolved separately from the rest of the rayner complex prior to the ca 940 ma rayner structural episode several archaean metamorphic events in rocks from western kemp land can be correlated with events previously reported for the adjacent napier complex recently reported ca 1 600 ma isotopic disturbance in rocks from the oygarden group may be correlated with a charnockitic intrusion in the stillwell hills before ca 1 550 ma despite being separated by some 200 km t hf dm ages indicate felsic orthogneiss from rippon point the oygarden group havstein island and the stillwell hills share a ca 3 660 3 560 ma source that is indistinguishable from that previously reported for parts of the napier complex more recent additions to this crust include proterozoic charnockite in the stillwell hills and the vicinity of mawson station these plutons have distinct 176hf 177hf ratios and formed via the melting of crust generated at ca 2 150 2 550 ma and ca 1 790 1 870 ma respectively

ultrahigh temperature granulite metamorphism 1050 c 12 kbar and decompression in garnet mg70 orthopyroxene sillimanite gneisses from the rauer group east antarctica highly magnesian and aluminous migmatitic gneisses from mather peninsula in the rauer group eastern antarctica preserve ultrahigh temperature uht metamorphic assemblages that include orthopyroxene sillimanite quartz garnet sillimanite quartz and garnet orthopyroxene sillimanite garnet that ranges up to xmg of 71 5 coexists with aluminous orthopyroxene that shows zoning from cores with 7 5 8 5 wt al2o3 to rims with up to 10 6 wt al2o3 adjacent to garnet peak p t conditions of 1050 c and 12 kbar are retrieved from fe mg al thermobarometry involving garnet and orthopyroxene in very good agreement with independent constraints from petrogenetic grids in feo mgo al2o3 sio2 and related chemical systems sapphirine orthopyroxene and cordierite form extensive symplectites and coronas on the early phases the specific reaction textures and assemblages involving these secondary phases correlate with initial garnet xmg with apparent higher pressure reaction products occurring on the more magnesian garnet and are interpreted to result from an initial phase of ultrahigh temperature near isothermal decompression uht itd from 12 to 8 kbar at temperatures in excess of 950 c later textures that involved biotite formation and then partial breakdown along with garnet relics to symplectites of orthopyroxene cordierite or cordierite spinel may reflect hydration through back reaction with crystallizing melts on cooling below 900 850 c followed by itd from 7 to 8 kbar to c 5 kbar at temperatures of 750 850 c the tectonic significance of this p t history is ambiguous as the rauer group records the effects of archean tectonothermal events as well as high grade events at 1000 and 530 ma late stage biotite formation and subsequent itd can be correlated with the p t history preserved in the proterozoic components of the rauer group and hence with either 1000 or 530 ma collisional orogenesis however whether the preceding uht itd history reflects a temporally unrelated event e g archean or is simply an early stage of either the late proterozoic or pan african tectonism as recently deduced for similar uht rocks from other areas of the east antarctica remains uncertain

ice cover landscape setting and geological framework of lake vostok east antarctica abstract lake vostok located beneath more than 4 km of ice in the middle of east antarctica is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment melting and freezing at the base of the ice sheet which slowly flows across the lake controls the flux of water biota and sediment particles through the lake the influx of thermal energy however is limited to contributions from below thus the geological origin of lake vostok is a critical boundary condition for the subglacial ecosystem we present the first comprehensive maps of ice surface ice thickness and subglacial topography around lake vostok the ice flow across the lake and the landscape setting are closely linked to the geological origin of lake vostok our data show that lake vostok is located along a major geological boundary magnetic and gravity data are distinct east and west of the lake as is the roughness of the subglacial topography the physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake s circulation lake vostok is a tectonically controlled subglacial lake the tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small but significant amounts of thermal energy into the lake

new constraints on metamorphism in the rauer group prydz bay east antarctica granulite facies metapelites of the mather and filla paragneisses within the rauer group east antarctica possess markedly different compositions the metamorphic evolution of the two metapelite types has been interpreted as temporally distinct with the rauer group preserving at least two distinct granulite facies tectonothermal episodes calculated p t pseudosections and orthopyroxene al content indicate the revised maximum preserved p t conditions within the mather paragneiss to lie in the vicinity of 950 975 c and 10 10 6 kbar less extreme than previous estimates the range of possible p t paths for the mather paragneiss consistent with mineral textural relationships and pseudosections contoured for mineral proportion are significantly shallower dp dt than previous estimates a near isothermal decompression p t path and extreme peak metamorphic conditions are not necessary to explain the development of preserved mineral reaction textures the filla paragneiss contains pelitic assemblages less amenable to rigorous quantitative analysis nevertheless possibilities for the shared or otherwise metamorphic evolution of the mather and filla paragneisses may be postulated on the basis of calculated pseudosections in the context of existing geochronology for the rauer group and preserved microstructures a shared evolution most likely during pan african granulite facies metamorphism is plausible and consistent with mineral assemblage development geochronology and microstructures a revised interpretation of the rauer group s preserved metamorphic evolution may warrant the revision of existing tectonic models applicable also to the remainder of prydz bay more generally the employed approach may incite a revision of peak p t and p t paths in other granulite facies terranes

the micro erosion meter use and limitations detection of anomalies in measurements of low rates of limestone surface lowering with a traversing micro erosion meter mem led to temperature controlled laboratory and field investigations of some sources of error in the method regressions for the correction of temperature change in the instrument and in the stud rock interface were obtained probe erosion tests permitted a correction to be devised and also provided information whereby a measure of operational irregularity was adopted corrections and error terms were applied to field measurements from two southern new south wales karsts and a collection of australian limestone slabs exposed at one site examination of these results and of published mem rates from other parts of the world validated the mem method marine platforms are lowered at such gross rates that these error sources may be neglected there however limestone lowering in terrestrial environments cannot be assumed to proceed at rates which permit this and recommendations are made about procedures to ensure that investigations are prosecuted within the limitations of the method

measuring erosion with the micro erosion meter contributions to understanding landform evolution abstract we review the contribution made to understanding landform evolution through the use of the micro erosion meter mem and the variant the traversing micro erosion meter tmem the mem has allowed the direct measurement of bedrock erosion in terrestrial and coastal settings as well as of building stone as recorded in mem measurements world wide the average rate of surface lowering on shore platforms is 1 486 mm a 1 and on terrestrial rock surfaces measured lowering rates are on average 0 903 mm a 1 reported means obscure significant variation in rates from a range of environmental settings and lithologies the mem has in a number of examples allowed the identification of the contribution of individual processes in polygenetic settings particularly in shore platform studies the dynamic nature of rock weathering has been highlighted where the tmem has revealed rock surfaces swelling and contracting at time scales ranging from hours to years the mem will continue to provide useful data on erosion rates and processes but the most fruitful investigations will be those that combine the t mem with other techniques that transcend time and space scale issues in erosion and process measurement

modelling the effect of waves weathering and beach development on shore platform development a mathematical model was used to study shore platform development mechanical wave erosion was dependent on such variables as tidal range wave height and period breaker height and depth breaker type surf zone width and bottom roughness submarine gradient rock resistance and the elevational frequency of wave action within the intertidal zone also included were the effects of sand and pebble accumulation cliff height and debris mobility and downwearing associated with tidal wetting and drying the occurrence location and thickness of beaches often depended on initially quite minor variations in platform morphology but owing to their abrasive or protective effect on underlying rock surfaces they were able to produce marked differences in platform morphology generalizations are difficult but the model suggests that platform gradient increases with tidal range platform width also increases with tidal range with slow downwearing but it decreases with fast downwearing platform gradient decreases and width increases with wave energy and decreasing rock resistance and platform roughness with low tidal range platform gradient is generally lower and platform width greater with beaches of fine sand than with gravel but the relationship is more variable with a high tidal range platform width increases and platform gradient decreases with the rate of downwearing on bare surfaces particularly in low tidal range environments but the pattern is less clear on beach covered platforms platforms with large amounts of beach sediment tend to be narrower and steeper than bare platform surfaces platform gradient increases and platform width decreases with increasing cliff height and with decreasing cliff debris mobility copyright 2005 john wiley sons ltd

comparison between coastal and inland karst limestone lowering rates in the northeastern adriatic region italy and croatia a comparison among lowering rates collected in the limestones of the northeastern adriatic region italy and croatia gives a picture of the erosion patterns in the inland and coastal classical karst and istrian karst erosion rates were measured using either a micro erosion meter or a traversing micro erosion meter beginning from a large dataset spread over a maximum of 26 years significant differences in limestone lowering rates have been recognized in the surveyed area the mean lowering rate for the inland classical karst area is 0 018 mm yr whereas in the inland istrian karst it is 0 009 mm yr in the coastal sectors the mean erosion rate varies between 0 14 mm yr in the gulf of trieste and 0 04 mm yr in the sites located along the istrian shoreline these differences are probably due to the climatic setting of the classical karst area mediterranean continental to sub alpine climate and istrian peninsula mediterranean climate moreover along the coasts of the gulf of trieste there are many submarine springs which are absent along the istrian coast it is hypothesized that these underwater springs stress the effect of rainfall along the coast which is both direct rain on the measurement site and mainly indirect freshwater outflow from submarine springs higher lowering rates were surveyed during autumn rainfall therefore also freshwater outflow from submarine springs is particularly high at the end of the summer and in autumn

short term microscale topographic changes of coastal bedrock on shore platforms we report a series of short term diurnal rock surface monitoring studies on inter and supra tidal shore platforms using a traversing micro erosion meter at two sites kaikoura peninsula new zealand and apollo bay victoria australia statistically signi cant day to day changes were measured surface rise and lowering occurred at rates above instrument error with a maximum range of 3 378 mm between 1 697 mm lowering and 1 681 mm rise individual measurements showed rises greater than 2 mm these daily variations reveal that surface lowering and rise occur at a much shorter time scale than previously reported from other studies the patterns observed suggest wetting and drying is the most likely process causing surface changes at these temporal scales we argue that traversing micro erosion meter studies operating at a short term time scale of day to day provide meaningful results that open new opportunities for studying rock weathering and erosion in a coastal environment copyright 2004 john wiley sons ltd

the multidecadal spatial pattern of erosion on sandstone shore platforms in south eastern australia abstract knowledge of the spatial pattern of erosion on shore platforms is needed to better understand their evolution the long term spatial and temporal variation of downwearing remains difficult to interpret from erosion data commonly collected over 1 3 years of monitoring we report erosion data recorded with a micro erosion meter mem over 40 years 1979 2019 on sandstone shore platforms in a micro tidal environment along the otway coast victoria australia this well preserved monitoring network 43 out of 44 original mem sites allowed a detailed investigation over a multidecadal timescale not previously considered over 40 years the mean erosion rate was 0 25 mm yr this value was statistically similar to erosion rates calculated over 2 year 0 32 mm yr and 32 year 0 26 mm yr periods in the vertical plane two significant but opposite relationships between elevation and erosion rates were displayed in the central intertidal zone there was also a peak in the erosion rate near mean higher high water level this spatial pattern was strongly associated with wetting and drying controlled by tides and waves at elevations lower than mean higher low water downwearing rates were one or two orders of magnitude lower than the average rate of the entire platform the low erosion rates may be caused by the longer wetting condition of surfaces at lower elevation fast erosion rates were recorded in the upper intertidal zone where the bedrock was only inundated by spring high tides or storm waves salt weathering may be the primary mechanism but the effect of thermal weathering cannot be neglected at higher elevation based on the experience from the near complete mem network in the study area suggestions were provided to extend the longevity of monitoring network for future long term erosion records on shore platforms

geochemistry and geochronology of high grade rocks from the grove mountains east antarctica evidence for an early neoproterozoic basement metamorphosed during a single late neoproterozoic cambrian tectonic cycle abstract the grove mountains of east antarctica are an inland continuation of the prydz belt the high grade metamorphic complex in this area is composed of felsic orthogneisses and mafic granulites with minor paragneisses and calc silicate rocks u pb zircon analyses using shrimp and la icp ms techniques reveal that the protoliths of mafic granulites and felsic orthogneisses were emplaced during a short time interval of ca 920 910 ma mafic granulites can be divided into low and high ti groups they have initial nd values nd t ranging from 0 8 to 1 9 tio 2 is positively correlated with feo t mgo and la nb ratios whereas it shows a negative correlation with nd t values indicating that the petrogenesis of their protoliths involved partial melting of a weakly enriched subcontinental lithospheric mantle and fractional crystallization of the magma accompanied by minor crustal contamination felsic orthogneisses have an affinity of a 2 type granites characterized by enrichment in ree y zr th and ga and high ga al and y nb ratios most of them have nd t values of 0 7 to 3 5 and nd depleted mantle model ages t dm of 1 76 1 65 ga and a few have low nd t values of 10 4 to 10 6 and old t dm of 2 46 2 27 ga reflecting a heterogeneity in their source region their protoliths were probably produced by high temperature partial melting of tonalitic granodioritic rocks triggered by the underplating of mantle derived mafic magma during post orogenic extension u pb analyses also reveal a metamorphic age of ca 2050 ma from detrital zircons in a paragneiss suggesting that the sedimentary materials of the paragneiss may have come from an as yet undiscovered early paleoproterozoic orogen of unknown provenance voluminous mafic felsic intrusives and a small amount of sedimentary rocks constitute an early neoproterozoic basement of the grove mountains subsequently this basement experienced only a single late neoproterozoic cambrian metamorphic cycle at ca 550 535 ma the available data indicate that the prydz belt is a collage of multiple basement terranes and each of them has a distinct tectonic evolution this supports the suggestion that the prydz belt may represent a late neoproterozoic cambrian collisional orogen that resulted in the final phase of the gondwana assembly

shore platform abrasion in a para periglacial environment galicia northwestern spain abstract the schmidt rock test hammer was used to study the effect of abrasion on shore platforms in galicia northwestern spain on platforms where tidally induced weathering salt wetting and drying etc is dominant rock strength is significantly lower than in areas where abrasion is or has been active in the recent past this suggests that abrasion removes weathered surface material exposing the stronger less weathered rock below abrasion downwearing measured with a transverse micro erosion meter ranged between 0 13 and 1 8 mm yr 1 over the last year most active abrasion occurs in the upper part of the intertidal zone but weathering is slowly destroying formerly abraded surfaces at lower elevations these abandoned surfaces were abraded by materials supplied by erosion of fluvio nival and periglacial slope deposits that covered or partially covered parts of the galician coast during the middle and late weichselian during the holocene rising sea level and erosion of the slope deposits caused the abrasion zone to gradually migrate up to its present position near the high tidal level the spatial and temporal role of abrasion on this coast is therefore closely associated with the exhumation and inheritance of ancient platform surfaces from beneath weichselian deposits

surface swelling of coastal bedrock on inter tidal shore platforms kaikoura peninsula south island new zealand this paper reports the occurrence of swelling of coastal bedrock measured with a traversing micro erosion meter tmem on inter tidal mudstone and limestone shore platforms while numerous micro erosion meter mem studies have been made only a small number have reported surface swelling during this study 24 055 measurements were made with a tmem of those 4047 indicated swelling or 17 of the total number of measurements vertical swelling of up to 8 9 mm was measured and values of 3 and 4 mm were common swelling displayed a complex pattern with minor swelling being superimposed on longer period episodes duration of swelling events in excess of 697 days were recorded while other events were commonly in the order of 3 to 4 months there is a distinct seasonal variation with greater and more frequent swelling occurring during summer months compared with winter explanation for swelling includes the growth of salt crystals in rock lattices and expansion from wetting and drying warm summer temperatures provide the best conditions for both processes swelling appears to be an important precursor to erosion of material from shore platform surfaces the conclusion drawn is that subaerial weathering makes an important contribution to the lowering of the shore platforms on the kaikoura peninsula

decadal scale micro erosion rates on shore platforms abstract knowledge of the long term rates of erosion of shore platforms are needed to assist modeling platform development understand rates and modes of development and decipher issues of inheritance from former sea level few studies report rates from more than 2 years of monitoring we report decadal scale erosion rates using both a micro erosion meter and a traversing micro erosion meter with measurements from 30 years and 10 years respectively gross mean surface lowering rates measured over 10 years with a traversing micro erosion meter were 0 901 s e 0 116 mm yr compared with 1 130 s e 0 217 mm yr over two years over thirty years 1973 2003 12 micro erosion meter sites provide a mean surface lowering rate of 1 09 s e 0 126 mm yr compared to 1 43 s e 0 128 mm yr calculated over twenty years 1973 1993 from 15 bolt sites and 1 53 s d 1 45 mm yr from 31 bolt sites rates calculated over longer time periods are reduced compared to short term rates as a result of faster eroding bolt sites being removed from the data set comparison of means between short and long time periods for existing bolts show no significant difference that is short term measurements over two years are representative of decadal scale erosion rates in fact decadal scale rates may under represent rates of platform development because of the loss of faster eroding bolt sites the loss of such bolts means that obtaining long term erosion rates is problematic future modeling of shore platform development can use mem rates with more certainty but we recommend using higher rates from shorter term studies unless longer records are complete

forty three years of micro erosion meter monitoring of erosion rates on shore platforms at kaikōura peninsula south island new zealand abstract using micro erosion meters mem and traversing micro erosion meters tmem surface lowering rates of shore platforms on kaik ura peninsula south island new zealand have been measured over a total of 43 years this record is the longest monitored network of this type since 1973 erosion rates have been calculated over two two year periods 1973 1975 n 31 and 1993 1996 n 55 and at decadal scales 1973 1993 n 15 1973 2004 n 12 1993 2004 n 46 1993 2008 n 34 1993 2016 n 18 1973 2016 n 6 after 43 years surface lowering rates remain similar to previously published rates at an average of 0 525 to 1 181 mm a 1 statistical analysis shows that erosion rates over all measurement periods are derived from the same population thus short term rates derived from two years of monitoring remain indicative of decadal rates of erosion variations between measurement periods are best explained by the loss of the more rapidly eroding bolt sites these losses point to the difficulty of maintaining monitoring over longer time scales a means of statistical manipulation previously published allows for these losses to be accounted for in determining long term rates of platform lowering in november 2016 a mw 7 8 earthquake raised the kaik ura peninsula approximately 0 8 1 m elevating much of the shore platforms above the tide range this earthquake has reset the mem record ending this long running erosion monitoring site of shore platform surface lowering however the mem network is now being used to monitor post earthquake response of the uplift shore platforms and new marine terraces

linking growth episodes of zircon and metamorphic textures to zircon chemistry an example from the ultrahigh temperature granulites of rogaland sw norway in situ u th pb analyses by ion microprobe on zircon in intact textural relationships are combined with backscatter and cathodoluminescence imaging and trace element analyses to provide evidence for growth episodes of zircon this approach helps a to unravel the polymetamorphic history of aluminous migmatitic and granitoid gneisses of the regional contact aureole around the rogaland anorthosite norite intrusive complex and b to constrain the age of m 2 ultrahigh temperature uht metamorphism and the subsequent retrograde m 3 event all samples yield magmatic inherited zircon of c 1035 ma some an additional group at c 1050 ma this suggests that loss of pb by volume diffusion in non metamict zircon is not an important factor even under extreme crustal conditions furthermore the identical inheritance patterns in aluminous garnet cordierite osumilite bearing migmatites and orthogneisses indicate a metasomatic igneous instead of a sedimentary protolith for the migmatite results for the m 1 metamorphic event at c 1000 ma bp are consistent in all samples including those from outside the orthopyroxene in isograd the latter do not show evidence for zircon growth during the m 2 metamorphic episode zircon intergrown with or included within m 2 metamorphic minerals magnetite spinel orthopyroxene give an age of 927 7 ma 2 n 20 the youngest observed results are found in zircon outside m 2 minerals some overgrown by m 3 mineral assemblages late garnet coronas garnet quartz and orthopyroxene garnet symplectites and yield a slightly younger pooled age of 908 9 ma 2 n 6 these textures are relative time markers for the crystallization of zircon overgrowths during discrete stages of the uht event these youngest age groups are consistent with the emplacement age of the rogaland intrusive complex and the last magmatic activity tellnes dyke intrusion respectively this is direct and conclusive evidence for uht metamorphism in the regional aureole being caused by the intrusions and corrects earlier notions that the events are not linked trace element behaviour of zircon tb u and y content has been tracked through time in the samples and shows variations both within and between samples this heterogeneous behaviour at all scales appears to be common in metamorphic rocks and precludes the use of rules of thumb in the interpretation of zircon chemistry but chemical tracers are useful for recognition of zircon growth or recrystallization during metamorphism

mesoarchaean crustal history of the eastern indian craton smnd and upb isotopic evidence abstract a variety of xenoliths representing high al trondhjemites and supracrustal lithologies occur within mesoarchaean granitoid rocks of the eastern indian craton a trondhjemitic xenolith from the bonai pluton yields a u pb age of 3380 6 4 ma for magmatic zircon and a minimum age of 3448 ma for xenocrystic zircon grains this sample also shows an nd value of 4 2 and t dm of 3 9 ga whereas four other xenoliths yield nd values ranging from 0 3 to 1 8 and t dm of 3 54 to 3 37 which are consistent with published data from the region and suggest a derivation from protoliths with relatively short lived crustal residence times

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

the morphodynamics of shore platforms in a micro tidal setting interactions between waves and morphology abstract the interactions between waves and morphology on shore platforms were investigated at four platforms located at kaikoura peninsula new zealand and the otway coast victoria australia waves were measured over six tidal peaks of a spring tidal sequence at each site during a six month period february 2007 july 2007 this paper reports the results of an investigation into the research question how are waves modified by platform morphology in a micro tidal setting through the investigation of wave interactions on shore platforms it was found that complex hydrodynamic patterns formed on the shore platforms studied through direct measurement of waves on the platforms it was found that wave attenuation was not dependent on platform width but rather influenced by platform gradient and depth of water on the platform spectral analysis was used to assess how wave energy was transformed across the platforms at three of the four platforms investigated energy gradients formed across the platform with wave energy recorded within the infragravity range

the evolution of a layered metaigneous complex in the rauer group east antarctica evidence for a distinct archaean terrane abstract the rauer group in prydz bay east antarctica contains both archaean and proterozoic crustal components archaean geological relationships have been defined from the scherbinina layered complex slc a polydeformed and metamorphosed fe tholeiite intrusive cut by several generations of deformed metabasite dykes the slc and three of these dyke generations are intruded by tonalitic and trondhjemitic sheets representative of archaean felsic orthogneisses present outside the complex u pb shrimp dating of zircons precisely defines the magmatic age of the slc as 2844 6 ma a tonalite sheet that cuts the slc preserves a complex zircon isotopic array dominated by inherited grains derived from source rocks up to 3470 30 ma old but from field evidence was emplaced at ca 2800 2550 ma the presence of 3470 ma source rocks is unique in the east antarctic shield and this feature as well as the prominence of 2840 2800 ma orthogneisses establishes the rauer group as a distinct archaean terrane the archaean of the rauer group is not comparable with the nearby vestfold hills where ca 2520 2480 ma orthogneisses form the dominant rock units it is likely that the vestfold hills and rauer group terranes were amalgamated at either 1000 or 500 ma rather than at the end of the archaean a mid proterozoic tectonothermal event documented in the rauer group from syn metamorphic 1030 1000 ma intrusives kinny p d black l p and sheraton j w 1993 zircon ages and the distribution of archaean and proterozoic rocks in the rauer islands antarctic sci 5 193 206 has not been detected in the zircon u pb data obtained on the archaean gneisses examined here instead the slc and intrusive tonalite show resetting of zircon u pb systematics at ca 520 ma this resetting reflects pb loss within irregular compositional zones and healed cracks in older zircon and is attributed to the effects of fluid infiltration under greenschist to amphibolite facies conditions these effects correlate in time with ca 530 510 ma higher grade deformation and metamorphism evident in proterozoic paragneisses exposed in areas to the south west of the rauer group and may record amalgamation of the rauer group with these areas during the east gondwanian pan african orogeny

variation of micro topographic and geotechnical limits on weathering progress on the constructional triassic sandstone aachen city germany case study rock s surface micro topography and geotechnical properties limits are expected to be altered on weathering progress to a new form s and limits respectively the quantification of weathering damage for a given rock is of value e g to compute weathering rate weathering intensity and rock s durability to weathering processes and to take a decision regarding restoration urgency the current study aims to examine the variation constancy of micro topography and geotechnical properties limits of the triassic sandstone constituting well aged wall at aachen city on weathering progress over short duration 12 years of investigation from 2007 to 2019 the equotip hardness tester and micro erosion meter are tools used for micro topographic and rock s surface hardness investigations on one hand and the mercury intrusion porosimetry has been used for measuring rock s pore size distribution and salt susceptibility on the other hand these tools are accurate numerical comprehensive easily applicable and preferable particularly for ancient buildings and archaeological sites where sampling is not recommended or prohibited the wall side under consideration has been selected as its constructional blocks present a wide spectrum of weathering forms as well as rock s surface micro topography over 12 years of investigation through increasing the weathering forms dimensions and or creation of new weathering forms the net result of the current study indicated a noticeable variation in stone s micro topography on weathering progress the rock s stone surface hardness highly controls rock s weathering susceptibility and no clear relation can be noted between stone s surface roughness and its susceptibility the pore size distribution is the most controlling parameter for rock s weathering susceptibility

rates of erosion of till in the nearshore zone measurements of vertical erosion of till in water depths ranging from 1 1 m to 5 m have been obtained using a modified micro erosion meter measurements in this environment are hindered by poor underwater visibility and losses due to high erosion rates and ice action there is considerable spatial and temporal variability in the erosion rates measured but average values show a general increase from 11 mm y 1 in 6 m of water to about 35 mm y 1 in 2 3 m of water and even higher rates closer to shore the measured values in shallow water are in good agreement with long term rates extrapolated from shoreline recession it is suggested that erosion occurs through abrasion and fluid stressing and that these mechanisms are aided by softening of the upper surface of the till possibly through cyclic fatigue failure

rock coasts with particular emphasis on shore platforms rock coasts are one of the most common elements of the world s littoral zone and they are often important sources of sediment for estuaries and beaches economic development growing populations and the potential effects of rising sea level provide a practical need to understand the dynamics of these coasts although there have been significant advances in our understanding of rocky coastal systems further progress has been hindered by a lack of researchers and by the often imperceptible changes that generally occur within human time scales this paper reviews rock coast processes and landforms in a variety of morphogenic environments one of our most fundamental challenges is to determine the degree to which rock coasts are contemporary rather than inherited features from the quaternary when changes in sea level and climate were responsible for marked variations in the nature intensity and elevational distribution of the marine and subaerial processes that sculpture rock coasts

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

age of younger tonalitic magmatism and granulitic metamorphism in the south indian transition zone krishnagiri area comparison with older peninsular gneisses from the gorur hassan area abstract a major episode of continental crust formation associated with granulite facies metamorphism occurred at 2 55 2 51 ga and was related to accretional processes of juvenile crust dating of tonalitic trondhjemitic granitic gneisses and charnockites from the krishnagiri area of south india indicates that magmatic protoliths are 2550 2530 5 ma as shown by both u pb and 207pb 206pb single zircon methods monazite ages indicate high temperatures of cooling corresponding to conditions close to granulite facies metamorphism at 2510 10 ma these data provide precise time constraints and sr nd isotopes confirm the existence of late tonalitic granodioritic juvenile gneisses at 2550 ma pb single zircon ages from the older peninsular gneisses gorur hassan area are in agreement with some previous sr ages and range between 3200 20 and 3328 10 ma these gneisses were derived from a 3 3 3 5 ga mantle source as indicated from nd isotopes they did not participate significantly in the genesis of the 2 55 ga juvenile magmas all these data together with previous work suggest that the 2 51 ga granulite facies metamorphism occurred near the contact of the ancient peninsular gneisses and the 2 55 2 52 ga juvenile tonalitic trondhjemitic terranes during synaccretional processes subduction mantle plume rb sr biotite ages between 2060 and 2340 ma indicate late cooling probably related to the dextral major east west shearing which displaced the 2 5 ga juvenile terranes toward the west

petrography chemistry and isotopic ages of peninsular gneiss dharwar acid volcanic rocks and the chitradurga granite with special reference to the late archean evolution of the karnataka craton southern india abstract new petrographic major and trace element and isotopic age data are presented for four suites of rocks from the low to medium grade part of the south indian archaean craton in central karnataka two suites are from the peninsular gneiss basement to the late archaean dharwar supergroup the third is a suite of dharwar potassic rhyolites and the fourth is from the chitradurga granite which has intrusive contacts with the dharwar supergroup the chikmagalur granite granodiorite which with its host gneisses forms part of the basement peninsular gneiss to the dharwar supergroup in the bababudan basin yields rb sr and pb pb whole rock isochron dates of 3080 110 ma and 3175 45 ma respectively an initial 87 sr 86 sr ratio of 0 7013 0 0009 and a 1 value 238 u 204 pb of 7 98 host tonalitic gneisses to the chikmagalur granite give an rb sr whole rock isochron date of 3060 160 ma with an initial 87 sr 86 sr ratio of 0 7015 0 0004 and a pb pb whole rock isochron date of 3190 100 ma with a model 1 value of 8 00 a suite of granites and granodioritic tonalitic gneisses chitradurga granitic rocks and gneisses forming part of the peninsular gneiss basement to the dharwar supergroup west of the chitradurga belt yields rb sr and pb pb whole rock isochron dates of 2970 100 ma and 3028 28 ma respectively with an initial 87 sr 86 sr ratio of 0 7035 0 0013 and a model 1 value of 7 62 the suite of dharwar acid volcanic rocks from north of honnali defines a poorly fitted 207 pb 206 pb linear array mswd 15 8 which gives an apparent age of 2565 28 ma and a model 1 value of 7 46 the poor fit of this isochron shows that a closed system was not maintained a conclusion supported by high k abundances which are attributed to a syn or post magmatic ion exchange process the chitradurga granite which intrudes the older rocks of the dharwar supergroup in the chitradurga belt yields a well fitted pb pb whole rock isochron date of 2605 18 ma with a model 1 value of 7 68 the u pb relations in these suites from karnataka are in marked contrast with the commonly severe u depletion and consequently unradiogenic pb isotopic compositions observed in deeply eroded high grade archaean gneiss terranes such as those bordering the north atlantic this contrast indicates that the cratonic rocks in central karnataka represent a relatively high level in the original archaean continental crust

downwearing rates on shore platforms of different calcareous lithotypes article i nfo vertical lowering downwearing of shore platform surfaces is a very important mechanism in their morphological evolution albeit much remains incompletely understood the efficacy of mechanical and chemical weathering acting on a given substrate together with erosional processes influences downwearing rates in order to determine the relationship between lithotypes and downwearing rates data collected from a transverse micro erosion meter were obtained for shore platforms of three different calcareous lithotypes biocalcarenite calcarenite and carbonated siltstone along the central algarve coast southern portugal downwearing rates ranged between 0 096 mm year 1 and 1 676 mm year

shore platform erosion and evolution implications for cosmogenic nuclide analysis abstract determining rates and modes of shore platform development and the age of associated elements are among the greatest challenges facing rock coast researchers today these coasts generally lack dateable deposits but cosmogenic nuclide analysis cna can be applied directly to bare rock surfaces to estimate erosion rates or the time that a surface has been exposed over millennial timescales therefore this technique has the potential to revolutionize current theories on rock coast evolution and modes of development because environmental and geomorphological factors affect rates of nuclide accumulation and retention however the results of cna analysis are dependent on the validity of the theoretical models that have to be employed according to the particular application among the important assumptions that may be made are those concerned with shading tidal immersion beach sediment covers and other factors that influence rates of nuclide accumulation and with possible spatial and temporal patterns in shore platform erosion primarily by wave generated backwearing and weathering induced downwearing that reduce nuclide concentrations our lack of understanding of the factors that control these variables and in particular shore platform erosion which is the subject of this review has important implications for modelling rock coast evolution assessing the possible contribution of inheritance and dating especially by cna the occurrence of important formative events

rates and patterns of bedrock denudation by coastal salt spray weathering a seven year record rapid surface lowering of bedrock is taking place in the supratidal zone by salt spray weathering a seven year run of data demonstrates a mean rate of lowering of 0 625 mm a 1 considerable variation exists in annual point lowering values within measurement sites although between site variation is not significant aggregate year to year variations in surface lowering are not significant spatial variation in individual point values may be compensated by temporal variation over an 11 year period there is a marked summer maximum in surface lowering rate and this is strongly correlated with monthly air temperature spatially and temporally episodic swelling of the rock surface is demonstrated this does not correlate statistically with any available climatic variable and is deemed to be a real and largely stochastic phenomenon it is interpreted as rock bursting at the granular scale due to haloclasty the processes most likely to be responsible for the observed rapid denudation are crystallization and thermal expansion of halite both of which are enhanced by high summer temperatures

an integrated microtextural and chemical approach to zircon geochronology refining the archaean history of the napier complex east antarctica integrated textural and chemical characterisation of zircon is used to refine the u pb geochronology of the archaean ultra high temperature napier complex east antarctica scanning electron microscope characterisation of zircon and the rare earth element compositions of zircon garnet and orthopyroxene are integrated to place zircon growth in an assemblage context thereby providing tighter constraints on the timing of magmatic and metamorphic events data indicate that magmatism occurred in the central and northern napier complex at ca 2 990 ma a regional relatively low pressure metamorphic event occurred at ca 2 850 2 840 ma mineral ree data from garnet bearing orthogneiss indicate that ca 2 490 2 485 ma u pb zircon ages provide an absolute minimum age for the ultrahigh temperature uht foliation preserved in this rock internal zircon zoning relationships and estimated zircon garnet dree values from paragneiss suggest that an absolute minimum age of ultra high temperature metamorphism is ca 2 510 ma but that it is more likely to be older than ca 2 545 ma we suggest that the high proportion of published zircon u pb data with ages between ca 2 490 2 450 ma reflects late post peak zircon growth and does not date the timing of peak uht metamorphism

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

the influence of seasonal and local weather conditions on rock surface changes on the shore platform at kaikoura peninsula south island new zealand abstract a traversing micro erosion meter tmem was used to measure micro scale surface changes in a 45 cm2 area of an intertidal mudstone shore platform on kaikoura peninsula new zealand with hourly readings taken over 5 days for two seasons within 4 h either side of low tide for all monitoring events the relative height of a total of 120 co ordinates were obtained resulting in 4200 and 4800 measurements for the summer and winter seasons respectively within seasons samples were grouped according to the presence of rain or no rain significant changes were found in the micro topography with variations in temperature and among rain and no rain sample groups for both seasons in the absence of rain there were positive linear relationships between rock surface temperatures and rock surface elevations and regression analysis explained 42 3 and 46 5 of this variation for the summer y 0 098 0 004x p value 0 007 and winter y 0 007 0 012x p value

the relative influence of lithology and weathering in shaping shore platforms along the coastline of the gulf of la spezia nw italy as revealed by rock strength abstract along the rock coasts of the gulf of la spezia which are characterised by a mediterranean microtidal environment a limited number of small rock platforms are scattered constrained in elevation within 5 m above present day sea level this work deals with a number of these rock platforms formed in different rock types one in limestone and two in dolomite that show differences in their morphology this paper aims to provide a quantitative examination of why there are morphological differences between platforms in this region to achieve this purpose factors controlling platform morphology and the processes acting on them are investigated through a comparative analysis of rock strength rebound values obtained testing rock surfaces with the schmidt hammer were compared between different platforms and between different sectors of the same platform each platform was subdivided into two parts based on visual difference in rock surface colour characterised by differences in occurrence of weathering microforms and bioerosive agents rebound values in the lower part of the platforms proved to be lower than in the upper part providing quantitative assessment of the occurrence of weathering acting to different extents in the upper and lower part of the shore platforms weathering degraded rock strength in the lower part by about 15 it was demonstrated that on the upper part of platforms displaying moderate evidence of physical and biological weathering lithology significantly influences the rock strength on the portion of platforms closer to sea level instead differential exposure histories of the same rock type in the same environmental setting can yield statistically significant variations in rock strength values thus it is clear that in the lower part of the investigated platforms the degree of weathering has strong bearing on rock strength and that variations in rock strength are not solely due to lithology according to the results of this work experimental values of rock strength of platforms in the study area depend both on the rock type and on physical weathering due to frequently repeated wetting and drying and bioerosion lithology is then an important factor controlling platform shape and weathering is an important process operating on them

four zircon ages from one rock the history of a 3930 ma old granulite from mount sones enderby land antarctica ion microprobe u th pb analyses of zircons from a granulite grade orthogneiss from mount sones enderby land antarctica record the ages of four principal events in the history of the gneiss three of which already have been recognized through previous isotopic dating of other samples the structure of the zircons indicates at least four different stages of growth the several zircon ages were obtained by grouping the analyses according to the stage they represented in the observed stratigraphic succession of growth and thereby defining separate u pb discordance patterns for each stage the stratigraphically oldest zircon rare discrete cores is indistinguishable in age from the most common euhedrally zoned zircon both crystallized when the tonalitic precursor of the orthogneiss was emplaced into the crust 3927 10 ma ago making the orthogneiss currently the oldest known terrestrial rock the outer parts of most grains and some whole grains recrystallized at 2948 31 17 ma during or immediately after possibly 100 ma of high granulite grade metamorphism the recrystallized zircon was isotopically disturbed by tectonism associated with reactivation of the southern margin of the napier complex at 1000 ma in the intervening time at 2479 23 ma the cores and zoned zircon suffered a major isotopic disturbance involving movement of radiogenic pb which left most of the crystals with radiogenic pb deficiencies but produced local radiogenic pb excesses in others a new generation of zircon characterized by very high th u and low u grew at that time that event deformation and possibly a minor rise in temperature produced widespread perturbations of other isotopic systems throughout the napier complex

modelling the quaternary evolution of shore platforms and erosional continental shelves a mathematical model was used to investigate the effect of glacially induced fluctuations in sea level on the evolution of wave cut shore platforms and erosional continental shelves during the quaternary the model used two deep water wave sets which were used to calculate breaker height and depth and the force of the waves at the waterline according to the width and bottom roughness of the surf zone and the gradient of the submarine slope the model also incorporated an erosional threshold related to the strength of the rocks the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot most runs were made using a sea level model that consisted of 26 glacial cycles from 2 million to 0 9 million years ago and nine of approximately twice the amplitude and wavelength in the last 0 9 million years the model emphasized the dynamic association between the contemporary intertidal platform and the continental shelf both surfaces trend towards a state of static equilibrium under oscillating sea level conditions when attenuated waves are unable to continue eroding the rock if there has not been enough time to reduce the gradient of the shallower portions of the continental shelf however intertidal shore platforms can be in a temporary though possibly long lasting state of dynamic equilibrium the model suggests that most platforms are at least in part inherited from one or in many cases more interglacial stages when sea level was similar to today s copyright 2001 john wiley sons ltd

reactions and textures in wollastonite scapolite granulites and their significance for pressure temperature fluid histories of high grade terranes reaction textures in wollastonite scapolite calc silicates provide important evidence for pressure temperature fluid histories in granulites pressure temperature t aco2 and p aco2 diagrams calculated for appropriate mineral compositions using the internally consistent dataset of holland and powell 1990 are presented and used to provide a framework for interpretation of the reaction textures garnet rims replacing wollastonite and scapolite in calc silicate gneisses is a common texture in many granulite terranes this texture can plausibly be developed in post peak p t histories dominated by cooling e g near isobaric cooling and does not generally imply the infiltration of hydrous fluids examples from the arunta complex australia and the northern prince charles mountains antarctica are consistent with cooling without fluid influx at 7 8 kbar and aco2 of 0 3 0 5 contrasting textures involving the replacement of garnet by wollastonite scapolite or wollastonite plagioclase symplectites and the growth of wollastonite plagioclase rims or coronas on scapolite quartz boundaries can be interpreted as essentially closed system features and modelled through modal analysis of reaction products in the case of the rauer group antarctica near isothermal decompression from ca 8 to 6 kbar at 850 800 c and aco2 in the range 0 35 0 45 is indicated by these textures based on calculated p t aco2 grids in the cao al2o3 sio2 co2 casv and more complex systems calculated reactions producing wollastonite scapolite from garnet bearing assemblages do not involve decarbonation but may consume co2 with increasing temperature in the absence of calcite hence these calc silicates may act as co2 sinks on the prograde segments of clockwise p t paths conversely scapolite wollastonite granulites will act as sources of post peak co2 rich fluids liberated upon cooling and potentially trapped elsewhere as post peak carbonic fluid inclusions

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

tidal wetting and drying on shore platforms an experimental assessment abstract rocks were subjected to wetting and drying cycles with de ionized water under real time conditions using tidal simulators one third of the samples experienced 11 h of exposure and 1 h of inundation over a 12 h tidal cycle representing high tidal conditions one third experienced 6 h of exposure and 6 h of inundation representing mid tidal conditions and one third experienced 1 h of exposure and 11 h of inundation representing low tidal conditions we obtained 324 cores from igneous metamorphic and sedimentary rocks from ontario which were exposed to more than 930 wetting and drying cycles over 16 months we obtained 675 cores and cubes from basalts sandstones and argillites from shore platforms in eastern canada which were exposed to about 700 cycles over 12 months many of the cores and cubes experienced very little to no breakdown particularly those from the igneous and metamorphic rocks of ontario sandstones from a sloping platform in the macrotidal bay of fundy and argillites from a horizontal mesotidal platform in gaspe quebec were the most susceptible rock types with equivalent surface downwearing rates ranging from 0 to 4 mm year 1 the results suggest that downwearing rates decrease with elevation within the intertidal zone probably because rocks require much longer to desorb than to absorb water the experiments demonstrated that wetting and drying can be an important process on shore platforms in some types of rock helping to lower the height and reduce the gradient of sloping macrotidal platforms and to reduce the height of horizontal micro and mesotidal platforms

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

transverse micro erosion meter measurements determining minimum sample size two transverse micro erosion meter tmem stations were installed in each of four rock slabs a slate shale basalt phyllite schist and sandstone one station was sprayed each day with fresh water and the other with a synthetic sea water solution salt water to record changes in surface elevation usually downwearing but with some swelling 100 measurements the pilot survey the maximum for the tmem used in this study were made at each station in february 2010 and then at two monthly intervals until february 2011 the data were normalized using box cox transformations and analyzed to determine the minimum number of measurements needed to obtain station means that fall within a range of confidence limits of the population means and the means of the pilot survey the effect on the confidence limits of reducing an already small number of measurements say 15 or less is much greater than that of reducing a much larger number of measurements say more than 50 by the same amount there was a tendency for the number of measurements for the same confidence limits to increase with the rate of downwearing although it was also dependent on whether the surface was treated with fresh or salt water about 10 measurements often provided fairly reasonable estimates of rates of surface change but with fairly high percentage confidence intervals in slowly eroding rocks however many more measurements were generally needed to derive means within 10 of the population means the results were tabulated and graphed to provide an indication of the approximate number of measurements required for given confidence limits and the confidence limits that might be attained for a given number of measurements

can shore platforms be produced solely by weathering processes field measurements and laboratory experiments provided data on surface downwearing rates on horizontal mesotidal and sloping macrotidal shore platforms in eastern canada the experimental data were used in a simple mathematical model to determine whether weathering acting alone can produce shore platforms the model failed to produce realistic platform profiles it did not account for the relationship in the field between platform gradient and tidal range and downwearing rates were much too low to produce wide platforms in the few thousand years that the sea has been at its present level although weathering undoubtedly plays an important role in the development of shore platforms it cannot by itself account for characteristic differences in platform morphology in different morphogenic environments it seems more likely that platform morphology is the result of mechanical wave erosion controlled by the tidally controlled expenditure of wave energy and some related or independent mechanism that controls weathering efficacy at different tidal elevations according to the tidal range

measuring erosion rates using the micro erosion meter 20 years of data from shore platforms kaikoura peninsula south island new zealand abstract fifteen micro erosion meter sites giving 42 individual readings of erosion were remeasured twenty years after installation on mudstone and limestone shore platforms on the kaikoura peninsula south island new zealand the mean annual surface lowering rate was calculated to be 1 43 mm yr longer term data were compared to shorter term data collected over a two year period between 1973 and 1975 to test the validity of extrapolating average erosion rates from shorter term data it was found that the average lowering rate for the shorter term data were in statistically acceptable agreement with those for the longer term data extrapolation of short term micro erosion meter data is therefore acceptable in this particular environment in previous work it has been suggested that measurements from as few as thirty individual micro erosion meter positions are required to calculate a mean annual lowering rate on shore platforms measurements from 30 mem positions provided an statistically acceptable mean annual lowering rate for shore platforms on the kaikoura peninsula

patterns of surface downwearing on shore platforms in eastern canada downwearing rates were measured on shore platforms at about 200 transverse micro erosion meter tmem stations over periods ranging from 2 to 6 years there were seven study areas in eastern canada the platforms were surveyed and a schmidt rock test hammer was used to measure rock hardness more than 1200 rock samples from three of the study areas were also subjected each day over a 3 year period to two tidal cycles of immersion and exposure which simulated the central intertidal zone a further 840 samples were subjected to longer periods of exposure and immersion over a 1 year period which represented different elevations within the upper and lower intertidal zone respectively these experiments suggested that tidally generated weathering and debris removal is an effective erosional mechanism particularly at the elevation of the lowest high tides in the field mean rates of downwearing for each study area ranged from 0 24 mm yr 1 to more than 1 5 mm yr 1 rates tended to increase with elevation in the field with maxima in the upper intertidal zone this trend in the field cannot be attributed entirely to the tidally induced weathering processes that were simulated in the laboratory and must reflect in part the effect of waves frost ice and other mechanisms it is concluded that there are no strong spatial downwearing patterns on shore platforms and that downwearing rates in the intertidal zone are the result of a number of erosional mechanisms with different elevation efficacy characteristics furthermore even if only one or two mechanisms were dominant in an area any resulting relationship between downwearing rates and elevation would be obscured or eliminated by the effect of variations in the chemical and physical characteristics of the rocks copyright 2010 john wiley sons ltd

crustal evolution of the east antarctic mobile belt in prydz bay continental collision at 500 ma the east antarctic mobile belt as exposed in prydz bay presents an excellent example of a poly metamorphic terrain where complicated high grade structures can be grouped on the basis of lineation direction sense of shear and metamorphic grade in this way local intricacies resulting from truncating and interfering foliations and folds can be simplified by ordering structures with respect to their kinematic connotation the resulting deformation scheme is simple and facilitates regional correlations and simultaneously places metamorphic textures in a kinematic structural background the mobile belt in prydz bay is exposed along 200 km of coastline and consists of granulite facies gneiss in which low to mid crustal compressional d1 2 structures and mid to upper crustal extensional d3 6 structures and relateddecompression cooling textures are best explained in an exhumation model involving extensional collapse of upper crust in an overall compressional tectonic setting this implies that compression and extension structures are genetically related however d3 6 structures in the larsemann hills appear to have formed between 550 and 500 ma whilst d2 structures in the rauer group have been dated at 1100 1000 ma reinterpretation of the latter dates is possible implying that most high grade deformation in prydz bay is early palaeozoic

two hourly surface change on supra tidal rock marengo victoria australia a traversing micro erosion meter was used to measure rock surface micro topography over 40 cm2 on a supra tidal cliff face from early morning to late evening in late spring from 06 00 hours to 22 00 hours the relative heights of 188 coordinates were obtained using the meter at 2 hour intervals resulting in a data set of 1607 readings monitoring shows that rock surfaces are dynamic entities with significant rise and fall relative to the first measurement at shorter timescales than previously reported the maximum positive rise between readings was 0 261 mm and lowering was 0 126 mm the pattern of change did not relate as expected to environmental variables such as temperature or insolation rather the surface showed greater surface change in the early morning and late afternoon it is hypothesized that this pattern relates to the expansion and contraction of lichen thalli as moisture is absorbed during higher humidity in the morning and late afternoon the implications of these results for weathering studies are considered copyright 2006 john wiley sons ltd

a decompressional p t path reinbolt hills east antarctica granulites exposed in the reinbolt hills east antarctica are part of the extensive late proterozoic granulite complex of east antarctica which includes the rauer group to the east and the northern prince charles mountains to the west the deformation history includes three pervasive deformation phases no chemical or mineralogical distinction between these phases has been detected and this is interpreted to be the result of complete re equilibration at the end of the third deformation phase two late deformation phases post date the metamorphism and record a medium temperature cooling path a short segment of the p t path of these rocks was inferred from mineral reactions that occurred during these late deformation phases the path passes from 800 c 7 kbar to 690 c 5 kbar indicating strong decompression which is typical of a thrust dominated crustal thickening followed by rapid erosion or extensional collapse