validating earth and ocean tide models using tidal gravity measurements summary o1 and m2 observations from well calibrated spring gravimeters and superconducting gravimeters from the global geodynamics project ggp are used to test models of the earth s body tide and 10 ocean tide models it is shown that some of the ocean tide models give anomalous results in various parts of the world for example the schwiderski ocean tide model gives discrepancies in several areas and the fes series of ocean tide models have problems in the western pacific china japan and australia the majority of the high quality tidal gravity measurements in europe are in close agreement with the dehant defraigne and wahr ddw elastic and inelastic body tide models the gravimetric factors for the ddw elastic and inelastic models only differ by 0 12 per cent and the present calibration accuracy does not allow us to distinguish between these models but does reduce the previous upper bound on inelastic gravimetric factors the european observations give a phase lag of a few hundredths of a degree for the o1 body gravity tide which is consistent with the mathews inelastic body tide model at some european and worldwide stations the gravimetric factors differ by up to 0 3 per cent from the ddw model and it is suggested that further checks on the gravimeter calibrations are required accurate determinations of instrumental phase lags are now easier to achieve and the imaginary out of phase component of tidal gravity can be used for accurate tests of this component of ocean tide models

middle jurassic rhyolite volcanism of eastern graham land antarctic peninsula age correlations and stratigraphic relationships silicic volcanism at c 168 ma has been identified previously on the antarctic peninsula and the mapple formation which includes those volcanic rocks has been defined and documented from one area of the east coast of graham land based on age and geochemical criteria correlations have been made to the extensive chon aike province of south america which has been demonstrated to be one of the largest silicic volcanic provinces in the world rhyolitic and intermediate composition volcanic successions from six separate localities on the east coast of the antarctic peninsula are described here and are confirmed as correlatives of the mapple formation based on newly acquired geochronology and field observations they are dominantly rhyolitic crystal tuffs and or ignimbrites with ages in the interval 162 168 ma overlapping with the age of the mapple formation 167 171 ma at the type locality andesitic agglomerates are also described which are included in the same event and demonstrate the occurrence of rare intermediate volcanism which is also seen in the chon aike province a new group the graham land volcanic group is defined here and criteria are established which allow the separation of some volcanic successions out of the previously defined antarctic peninsula volcanic group which takes no account of tectonic setting eruption age or geochemistry

on the antarctic peninsula batholith the plutonic rocks of the antarctic peninsula magmatic arc form one of the major batholiths of the circum pacific rim the antarctic peninsula batholith is a 1350 km long by 210 km wide structure which was emplaced over the period 240 to 10 ma with a cretaceous peak of activity that started at 142 ma and waned during the late cretaceous early jurassic and late jurassic early cretaceous gaps in intrusive activity probably correspond to episodes of arc compression in a northern zone of the antarctic peninsula the batholith intrudes palaeozoic mesozoic low grade meta sedimentary rocks and in a central zone it intrudes schists and ortho and paragneisses which have late proterozoic nd model ages and were deformed during triassic to early jurassic compression in a southern zone the oldest exposed rocks are permian sedimentary rocks and deformed jurassic volcanic and sedimentary rocks all these pre batholith rocks formed a belt of relatively immature crust along the gondwana margin with few exceptions jurassic plutons crop out only within the central zone many are peraluminous having s like mineralogies and relatively high 87sr 86sri they are considered to consist largely of partial melts of upper crust schists and gneisses and components of mafic magmas that caused the partial fusion by contrast early cretaceous plutons crop out along the length of the batholith few magma compositions appear to have been affected by upper crust the bulk being compositionally independent of the type of country rock they intrude they are dominated by metaluminous calcic si oversaturated 1 type granitoid rocks with relatively low 87sr 86sri intermediate silicic compositions 5 mgo we interpret these to represent partial melts of basic to intermediate igneous locally garnet bearing lower crust contemporaneous mafic magmas e g syn plutonic dykes form a more alkaline si saturated series having higher 143nd 144nd at the same87sr 86sr than the intermediate silicic series to which they are not petrogenetically related the change from limited partial fusion of upper crust in jurassic times to widespread partial fusion of lower crust in early cretaceous times is considered to be a result of an increasing volume of basaltic intrusion into the crust with time

early jurassic magmatism on the antarctic peninsula and potential correlation with the subcordilleran plutonic belt of patagonia early jurassic silicic volcanic rocks of the chon aike province v1 187 182 ma are recognized from many localities in the southern antarctic peninsula and ne patagonia and are essentially coeval with the extensive karoo 182 ma and ferrar 183 ma large igneous provinces of pre breakup gondwana until recently plutonic rocks of this age were considered either rare in or absent from the antarctic peninsula batholith which was thought to have been mainly constructed during the middle jurassic and the mid cretaceous new u pb zircon geochronology from the antarctic peninsula and recently published u pb ages from elsewhere in the peninsula and patagonia are used to demonstrate the more widespread nature of early jurassic plutonism eight samples are dated here from the central and southern antarctic peninsula they are all moderately to strongly foliated granitoids tonalite granite granodiorite and locally represent the crystalline basement they yield ages in the range 188 181 ma which overlap with published ages of 185 180 ma from granitoids from elsewhere on the antarctic peninsula and from the subcordilleran plutonic belt of patagonia 185 181 ma whereas early jurassic plutons of the subcordilleran plutonic belt of patagonia are directly related to subduction processes along the proto pacific margin of gondwana coeval volcanic rocks of the chon aike province are interpreted to be directly associated with extension and plume activity during the initial stages of gondwana breakup this indicates that subduction was continuing when chon aike province volcanism started the early jurassic plutonism on the antarctic peninsula is transitional between subduction related and breakup related magmatism supplementary material cathodoluminescence images of analysed zircon grains from sites on the antarctic peninsula are available at https doi org 10 6084 m9 figshare c 3521973

circum pacific mid cretaceous deformation and uplift a superplume related event evidence of short lived episodes of mid cretaceous deformation metamorphism uplift and hiatus in sedimentation is widespread in the lower cretaceous rocks that bordered the cretaceous pacific basin i present a model in which these coeval but widely spaced events are linked to increased ridge push force at subduction zones triggered by large scale upwelling of mantle associated with the mid cretaceous superplume this model can account for mid cretaceous terrane accretion and ophiolite obduction events and can explain brief compressional phases in predominantly extensional orogenies as recognized in alaska british columbia california western south america and west antarctica

large volume silicic volcanism along the proto pacific margin of gondwana lithological and stratigraphical investigations from the antarctic peninsula jurassic magmatism in western gondwana produced the most voluminous episode of continental volcanism in the phanerozoic era during the early to middle jurassic some 2 5 3 million km3 of dominantly basalt and to a lesser extent rhyolite were erupted onto a supercontinent in the early stages of break up the major silicic portion of the gondwana magmatic province is exposed in patagonian south america the volcanic rocks of patagonia have been collectively termed the chon aike province and constitute one of the world s most voluminous silicic provinces the volcanic rocks are predominantly pyroclastic dominated by ignimbrite units of rhyolite composition volcanic rocks crop out sporadically across much of the once contiguous antarctic peninsula and are considered to form an extension of the chon aike province a continuation of the province to include the antarctic peninsula would extend its strike length along the active pacific margin by c 2000 km volcanic rocks exposed along the east coast of the antarctic peninsula defined here as the mapple formation are also dominated by rhyolitic ignimbrite flows with individual units up to 80 m in thickness and a total thickness of c 1 km the ignimbrites vary in degree of welding from high grade rheomorphic ignimbrites with parataxitic textures to unwelded lithic rich ignimbrites rhyolite lava flows air fall horizons debris flow deposits and epiclastic deposits are volumetrically minor occurring as interbedded units within the ignimbrite succession the lithology and stratigraphy of the jurassic volcanic rocks of the mapple formation are presented and comparisons are made to the chon aike province a consistent stratigraphy of permo triassic metasedimentary rocks unconformably overlain by terrestrial mudstone siltstone sequences which are in turn conformably overlain by largely silicic subaerial volcanic rocks is present at several localities along the antarctic peninsula and at localities in the chon aike province precise zircon u pb middle jurassic ages exist for two volcanic formations from the antarctic peninsula and a middle lower jurassic age has been suggested for the underlying sedimentary formations based on fossil flora analysis the antarctic peninsula chronostratigraphy coupled with lithological similarities indicate a close relationship to those sequences of the chon aike province

evidence for a two phase palmer land event from crosscutting structural relationships and emplacement timing of the lassiter coast intrusive suite antarctic peninsula implications for mid cretaceous southern ocean plate configuration 1 new analysis of the relationships between geological structural data and radiometric ages for the lassiter coast intrusive suite indicate that the collisional mid cretaceous palmer land event orogeny in the antarctic peninsula has had two kinematic phases forming an intersection orocline one of which can be related to cretaceous southern ocean plate motions both are compressional phases along the eastern palmer land shear zone phase 1 occurred at 107 ma with a principal paleostrain axis of 341 and is best expressed in southern palmer land although evident elsewhere on the antarctic peninsula phase 2 occurred at 103 ma with a principal paleostrain axis of 259 5 but is confined to between 68 s and 74 s a peak in lassiter coast intrusive suite magma emplacement rate was coeval with phase 1 whereas phase 2 may have coincided with a lull during phase 1 the allochthonous central and western domain terranes may have been transported to the gondwana margin represented by the para autochthonous eastern domain on board the phoenix plate or on board the south american plate the variable provenance indicators from the central and western terranes can be cited to support either or a combination of these scenarios the convergence direction evident from phase 2 structures cannot easily be reproduced in regional plate kinematic models this and the localized evidence for superposition of phase 2 structures on phase 1 structures suggests that phase 2 is unlikely to have occurred solely in response to changes in the kinematics of the large plates considered

autochthonous v accreted terrane development of continental margins a revised in situ tectonic history of the antarctic peninsula the allochthonous terrane accretion model previously proposed for the geological development of the antarctic peninsula continental margin arc is reviewed in light of recent data and the geology is reinterpreted as having evolved as an in situ continental arc this is based upon the following factors 1 the presence of early palaeozoic basement and stratigraphic correlation of sequences between the autochthonous and previously proposed allochthonous terranes 2 isotopic evidence for similar deep crustal structure across the different terranes 3 ocean island basalt magmas and deep marine sedimentary rocks formed during continental margin extension within the previously proposed accretionary wedge sequence i e not formed against an active oceanic arc 4 the distribution of magnetic susceptibility measurements and aeromagnetic data locating the palaeo subduction zone along the west of the peninsula 5 a lack of clear palaeomagnetic distinction between the terranes the following alternative tectonic history is proposed 1 amalgamation and persistence of gondwana 2 subsequent silicic large igneous province magmatism and extension 3 development and history of andean subduction until its cessation in the cenozoic a number of features in the antarctic peninsula correlate with those of other circum pacific margins supporting a global evaluation of allochthonous v autochthonous margin development to aid our understanding of crustal growth mechanisms

geochronology of the central tanzania craton and its southern and eastern orogenic margins geological mapping and zircon u pb hf isotope data from 35 samples from the central tanzania craton and surrounding orogenic belts to the south and east allow a revised model of precambrian crustal evolution of this part of east africa the geochronology of two studied segments of the craton shows them to be essentially the same suggesting that they form a contiguous crustal section dominated by granitoid plutons the oldest orthogneisses are dated at ca 2820 ma dodoma suite and the youngest alkaline syenite plutons at ca 2610 ma singida suite plutonism was interrupted by a period of deposition of volcano sedimentary rocks metamorphosed to greenschist facies directly dated by a pyroclastic metavolcanic rock which gave an age of ca 2725 ma this is supported by detrital zircons from psammitic metasedimentary rocks which indicate a maximum depositional age of ca 2740 ma with additional detrital sources 2820 and 2940 ma thus 200 ma of episodic magmatism in this part of the tanzania craton was punctuated by a period of uplift exhumation erosion and clastic sedimentation volcanism followed by burial and renewed granitic to syenitic magmatism in eastern tanzania handeni block in the heart of the east african orogen all the dated orthogneisses and charnockites apart from those of the overthrust neoproterozoic granulite nappes have neoarchaean protolith ages within a narrow range between 2710 and 2630 ma identical to but more restricted than the ages of the singida suite they show evidence of ediacaran pan african isotopic disturbance but this is poorly defined in contrast granulite samples from the wami complex nappe were dated at ca 605 and ca 675 ma coeval with previous dates of the eastern granulites of eastern tanzania and granulite nappes of adjacent ne mozambique to the south of the tanzania craton samples of orthogneiss from the northern part of the lupa area were dated at ca 2730 ma and clearly belong to the tanzania craton however granitoid samples from the southern part of the lupa block have palaeoproterozoic ubendian intrusive ages of ca 1920 ma outcrops further south at the northern tip of lake malawi mark the se continuation of the ubendian belt albeit with slightly younger ages of igneous rocks ca 1870 1900 ma which provide a link with the ponte messuli complex along strike to the se in northern mozambique in sw tanzania rocks from the mgazini area gave ubendian protolith ages of ca 1980 1800 ma but these rocks underwent late mesoproterozoic high grade metamorphism between 1015 and 1040 ma one granitoid gave a crystallisation age of ca 1080 ma correlating with known mesoproterozoic crust to the east in se tanzania and ne mozambique however while the crust in the mgazini area was clearly one of original ubendian age reworked and intruded by granitoids at ca 1 ga the crust of se tanzania is a mixed mesoproterozoic terrane and a continuation from ne mozambique hence the mgazini area lies at the edge of the ubendian belt which was re worked during the mesoproterozoic orogen south irumide belt providing a further constraint on the distribution of ca 1 ga crust in se africa hf data from near concordant analyses of detrital zircons from a sample from the tanzania craton lie along a pb loss trajectory lu hf 0 extending back to 3 9 ga this probably represents the initial depleted mantle extraction event of the cratonic core furthermore the hf data from all igneous samples regardless of age from the entire study area including the neoproterozoic granulite nappes show a shallow evolution trend lu hf 0 028 extending back to the same mantle extraction age this implies the entire tanzanian crust sampled in this study represents over 3 5 billion years of crustal reworking from a single crustal reservoir and that the innermost core of the tanzanian craton that was subsequently reworked was composed of a very depleted mafic source with a very high lu hf ratio our study helps to define the architecture of the tanzanian craton and its evolution from a single age source in the early eoarchaean

new seismic data support cenozoic rifting in george vi sound antarctic peninsula summary new multifold seismic reflection and wide angle reflection refraction data across george vi sound antarctic peninsula show the presence of graben and horst structures indicating an extensional origin the data suggest that rocks of an accretionary complex and fore arc basin underlie the sound and are in faulted contact along its eastern boundary with volcanic and plutonic rocks of the associated mesozoic arc of western palmer land a cover of possible syn and postglacial cenozoic deposits drapes the structures the combination of new seismic synthetic aperture radar and previously acquired data suggests subduction related rifting in the sound was segmented with opening in the south predominately by normal extension whilst in the north dextral transtension predominated

characterisation and tracing of permian magmatism in the south western segment of the gondwanan margin u pb age lu hf and o isotopic compositions of detrital zircons from metasedimentary complexes of northern antarctic peninsula and western patagonia abstract metasedimentary rocks in the antarctic peninsula and south western patagonia record detrital zircon evidence for significant permian magmatic events along the palaeo pacific margin of south west gondwana however it is unclear where and how this magmatism formed due to the lack of outcropping permian igneous sources at similar latitudes combined u pb o and lu hf isotope analyses of detrital zircon grains in permo triassic metasedimentary rocks indicate that the permian magmatism resulted from the interaction of crust and mantle derived sources in an active continental margin permian detrital zircons from the trinity peninsula group in the antarctic peninsula range from crustal signatures in the northern part 18 o of 8 initial e hf of 6 to mantle like values in the south 18 o of 5 initial e hf of 3 zircons from the northern domain have isotopic features similar to those from the patagonian duque de york complex they also share a secondary ordovician component of ca 470 ma the middle jurassic cape wallace beds in low island record a ca 250 ma igneous source with stronger crustal signatures 18 o and initial e hf values of 7 5 to 10 8 and 3 2 to 14 2 respectively in contrast zircons from the upper jurassic miers bluff formation on livingston island and cretaceous sediments on james ross island have similar permian u pb ages o and hf trends to their trinity peninsula group counterparts suggesting reworking after the late jurassic our results provide evidence for a permian subduction related magmatic arc partly located in patagonia and extending to west antarctica the southerly decrease in 18 o coupled with increasing initial e hf indicate fewer sedimentary components in the magma source and is consistent with a glaciated cold and dry climate these conditions are comparable with west antarctica climate settings located close to the south pole during the carboniferous and permian

non tidal ocean loading correction for the argentinean german geodetic observatory using an empirical model of storm surge for the rio de la plata the argentinean german geodetic observatory is located 13 km from the rio de la plata in an area that is frequently affected by storm surges that can vary the level of the river over 3 m water level information from seven tide gauge stations located in the rio de la plata are used to calculate every hour an empirical model of water heights tidal non tidal component and an empirical model of storm surge non tidal component for the period 01 2016 12 2016 using the spotl software the gravimetric response of the models and the tidal response are calculated obtaining that for the observatory location the range of the tidal component 3 6 nm s2 is only 12 of the range of the non tidal component 29 4 nm s2 the gravimetric response of the storm surge model is subtracted from the superconducting gravimeter observations after applying the traditional corrections and a reduction of 7 of the rms is obtained the wavelet transform is applied to the same series before and after the nontidal correction and a clear decrease in the spectral energy in the periods between 2 and 12 days is identify between the series using the same software east north and up displacements are calculated and a range of 3 2 and 11 mm is obtained respectively the residuals obtained after applying the non tidal correction allow to clearly identify the influence of rain events in the superconducting gravimeter observations indicating the need of the analysis of this and others hydrological and geophysical effects

the wiley glacier complex antarctic peninsula pluton growth by pulsing of granitoid magmas early cretaceous gabbro quartz diorite granodiorite and tonalite granodiorite plutons of the wiley glacier complex in the antarctic peninsula magmatic arc were emplaced in a zone of syn magmatic extensional shearing the oldest component pluton is the creswick gap quartz diorite granodiorite pluton and this is cut by slightly younger hornblende gabbro of the moore point pluton these plutons form the wall rock to the burns bluff tonalite granodiorite pluton the youngest component of the complex the burns bluff pluton comprises tonalite granodiorite sheets which at the plutons margins are interleaved with screens of mylonite wall rock the moore point hornblende gabbro has nd141 of ca 4 and sr141 of ca 1 it is predominantly mantle in origin although its parent magma assimilated some continental crust during emplacement the creswick gap pluton has nd141 between ca 4 quartz diorite and ca 1 granodiorite and sr141 from ca 1 quartz diorite to ca 22 granodiorite this pluton contains both mantle and crustal components we suggest that the quartz diorite facies fractionated from a similar parent magma to that of the moore point gabbro whilst the granodiorite fractionated from a gabbro quartz diorite magma during continued crustal assimilation geochemical variations within the creswick gap pluton cannot be generated by afc models some of the granodiorite samples have chemical characteristics which typify partial melts of amphibole garnet bearing crust we conclude that the pluton comprises fractionates of basaltic magma and crustal partial melt the burns bluff tonalite granodiorite sheets have nd141 between ca 4 and ca 2 and sr141 from ca 5 to ca 31 their isotopic and chemical compositions suggest that some are fractionates of basalt gabbro magma others are predominantly partial melts of amphibole garnet bearing crust and some are mixtures of these two magma types the chemical and isotopic compositions of the burns bluff plutons constituent tonalite sheets and its dyke like internal structure suggest that it grew incrementally via the addition of melt batches from a variety of crustal and mantle sources the growth of this pluton via dyking may reflect magma pulsing associated with transtensional movement along the creswick gap shear zone moreover the burns bluff pluton may be a frozen conduit system for structurally higher plutons in the antarctic peninsula batholith

the age and stratigraphy of fore arc magmatism on alexander island antarctica fore arc magmatic sequences associated with high mg number andesite lavas unconformably overlie lemay group accretionary complex in alexander island high resolution 40ar 39ar u pb zircon fission track and k ar ages demonstrate that subduction related fore arc magmatism migrated northwards along the length of alexander island between c 80 ma and c 46 ma the magmatic rocks represent a third of the western margin of the antarctic peninsula magmatic arc and are critical to the understanding of the final phase of subduction along the southern antarctic peninsula margin the onset of late cretaceous magmatism is recorded by poorly exposed volcanic rocks on monteverdi peninsula 79 7 2 5 ma in central and northern alexander island the magmatic rocks can be distinguished by the proportion range and types of lithofacies present and by the periods of magmatism represented the volcanic rocks of the colbert mountains range in age from c 69 62 ma and are dominated by large volume dacitic and rhyolitic crystal rich ignimbrites interpreted as caldera fill deposits elgar uplands sequences range in age from c 55 50 ma and contain approximately equal proportions of pyroclastic deposits and less evolved basaltic andesite and andesite lavas including high mg number andesite lavas near the base of three sequences the volcanic rocks of finlandia foothills probably represent the youngest calc alkaline units on alexander island 48 2 ma the sequence is lithologically similar to the elgar uplands and also contains high mg number andesite lavas but it is dominated by polymict conglomerates with minor lavas which were deposited in a graben associated with regional extension plutonic rocks exposed in the rouen mountains adjacent to the elgar uplands yielded a u pb age of 56 3 ma which is in discordance with a previously published rb sr age 46 3 ma probably due to hydrothermal perturbation of the rb sr system northwards migration of magmatism was caused by the progressive collision and subduction of three ridge segments prior to the previously reported ridge crest trench collisions that occurred c 20 30 ma later and following which subduction ceased

strontium and oxygen isotopic variations in mesozoic and tertiary plutons of central idaho regional variations in initial 87sr 86sr ratios r i of mesozoic plutons in central idaho locate the edge of precambrian continental crust at the boundary between the late paleozoic mesozoic accreted terranes and precambrian sialic crust in western idaho the r i values increase abruptly but continuously from less than 0 704 in the accreted terranes to greater than 0 708 across a narrow 5 to 15 km zone characterized by elongate lens shaped highly deformed plutons and schistose metasedimentary and metavolcanic units the chemical and petrologic character of the plutons changes concomitantly from ocean arc type diorite tonalite trondhjemite units to a weakly peraluminous calcic to calcalkalic tonalite granodiorite granite suite the idaho batholith plutons in both suites yield late cretaceous ages but permian through early cretaceous bodies are confined to the accreted terranes and early tertiary intrusions are restricted to areas underlain by precambrian crust the two major terranes were juxtaposed between 75 and 130 m y ago probably between 80 and 95 m y oxygen and strontium isotopic ratios and rb and sr concentrations of the plutonic rocks document a significant upper crustal contribution to the magmas that intrude precambrian crust magmas intruding the arc terranes were derived from the upper mantle subducted oceanic lithosphere and may have been modified by anatexis of earlier island arc volcanic and sedimentary units plutons near the edge of precambrian sialic crust represent simple mixtures of the precambrian wall rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r i of 0 7035 rb sr varies linearly with r i producing pseudoisochrons with apparent ages close to the age of the wall rocks measured 18o values of the wall rocks are less than those required for the assimilated end member by sr o covariation in the plutons however indicating that wall rock 18o was reduced significantly by exchange with circulating fluids metasedimentary rocks of the belt supergroup are similarly affected near the batholith documenting a systematic depletion in 18o as much as 50 km from the margin of the batholith plutons of the bitterroot lobe of the idaho batholith are remote from the accreted terranes and represent mixtures of precambrian wall rocks with melts dominated by continental lower crust r i 0 708 rather than mantle pseudoisochrons resulting from these data are actually mixing lines that yield apparent ages less than the true age of the wall rocks and meaningless ri assimilation fractional crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region

on the shape of paleomagnetic data sets a quick and easy method to analyze the shape of paleomagnetic data sets is described and illustrated the elongation e of a set of directions of virtual geomagnetic poles vgp is defined as e k2 k3 where k2 and k3 are the second and third eigenvalues of the bingham distribution it is shown that e 3 or so indicates that the distribution is significantly elongate although the size of the sample and the paleolatitude both affect this conclusion because the azimuth of k2 gives the direction of elongation it can be used to help determine why a particular distribution is elongate it is shown that for most units from the craton both directions and vgp are nearly circular except for units magnetized at very low latitudes in general poles are more circular than directions some units formed in plate margin locations also are circular but many are highly elongate many units from the western cordillera of north america have highly elongate distributions that are compatible with origin within a shear zone others are obviously underformed internally units formed during extension are less commonly elongate but some show the probably effects of normal faulting it is hoped that shape analysis will be part of any complete paleomagnetic study in the future

high frequency non tidal ocean loading effects on surface gravity measurements summary we model atmospheric and non tidal oceanic loading effects on surface gravity variations using global surface pressure field provided by the european centre for medium range weather forecasts ecmwf and sea surface height from the toulouse hydrodynamic unstructured grid ocean model hugo m barotropic ocean model we show the improvement in terms of reduction of variance of 15 different superconducting gravimeters of the worldwide global geodynamics project ggp network compared to the classical inverted barometer assumption we also study two storm surges over the western european shelf in 2000 and 2003 we compare the hugo m sea surface height variations to various tide gauges measurements as well as the induced loading effects to the computations of fratepietro et al using the proudman storm surge model for the membach belgium station the agreement between modelled ocean loading and gravity observations is largely improved when using a global atmospheric loading correction compared to the classical local approach the remaining discrepancies are mainly due to hydrological loading contributions

origins of large volume rhyolitic volcanism in the antarctic peninsula and patagonia by crustal melting voluminous rhyolitic volcanism along the palaeo pacific margin of gondwana was marked by three principal episodes of magmatism the first of these v1 is essentially coincident with the main episode of karoo ferrar magmatism at 184 ma a younger v2 episode occurred at 168 ma and a third episode v3 occurred in the interval 157 153 ma we evaluate the origin of v1 and v2 rhyolites from the antarctic peninsula using major and trace element and isotopic sr nd o data an isotopically uniform 87sr 86sri 0 707 endi 3 andesite dacite magma was generated as a result of anatexis of grenvillian age hydrous mafic lower crust linked to earlier arc related underplating the lower crustal partial melts would have mixed with fractionated components of the mafic underplate followed by subsequent storage and homogenization early jurassic v1 rocks of the southern antarctic peninsula are interpreted as melts of upper crustal paragneiss which have mixed with the isotopically uniform magma in upper crustal magma chambers the v2 rhyolites are the result of assimilation fractional crystallization of the isotopically uniform magma this occurred in upper crustal magma chambers involving assimilants with similar isotopic composition to that of the magma a continental margin setting was crucial in developing hydrous readily fusible lower crust lower crustal anatexis was in response to mafic underplating associated with the discovery shona bouvet group of plumes thought to be responsible for the karoo magmatic province the progression old to young of volcanism from ne to sw in patagonia and south to north in the antarctic peninsula is consistent with migration away from the mantle plumes towards the proto pacific margin of gondwana during rifting and break up

the auriga nunataks shear zone mesozoic transfer faulting and arc deformation in northwest palmer land antarctica the auriga nunataks shear zone places new tectonic and temporal constraints on the mesozoic evolution of west antarctica the shear zone is a long lived arc orthogonal ductile transfer fault that preserves a history of regional mesozoic compressional basement deformation and extensional arc pluton emplacement in the antarctic peninsula magmatic arc it forms an east west trending positive flower structure 2 4 km wide exposed along 5 km of strike marble graphite bearing pyroxene granulite granodiorite diorite amphibolite and gabbro are deformed to mylonite and marble hosted tectonic breccia the mesozoic history of the shear zone is interpreted as follows emplacement of granodiorite diorite at circa 206 ma during early jurassic dextral transtension and metamorphism that peaked at circa 188 ma d1 brecciation of marble and mylonitization of gneiss by late jurassic to early cretaceous sinistral shear during the peninsula wide palmer land orogeny d2 early cretaceous dextral transtension with emplacement of gabbro and garnet leucogranite between 140 and 135 ma d3 and mid cretaceous ocean vergent thrusting and sinistral transpression between 125 ma and 80 ma with a peak at circa 110 ma that folded mylonitized and brecciated preexisting plutonic and metamorphic rocks d4 this is responsible for the current geometry of the shear zone the auriga nunataks shear zone transferred motion between arc parallel compressional and extensional structural elements and by hosting plutons appears to have acted like a leaky transform fault during episodes of regional extension

crustal displacements due to continental water loading the effects of long wavelength 100 km seasonal variability in continental water storage on vertical crustal motions are assessed the modeled vertical displace ments arm have root mean square rms values for 1994 1998 as large as 8 mm with ranges up to 30 mm and are predominantly annual in character regional strains are on the order of 20 nanostrain for tilt and 5 nanostrain for hori zontal deformation we compare arm with observed global positioning system gps heights aro which include ad justments to remove estimated effects of atmospheric pres sure and annual tidal and non tidal ocean loading for 147 globally distributed sites when the aro time series are ad justed by arm their variances are reduced on average by an amount equal to the variance of the arm of the aro time series exhibiting a strong annual signal more than half

study of the atmospheric pressure loading signal in very long baseline interferometry observations 1 redistribution of air masses due to atmospheric circulation causes loading deformation of the earth s crust which can be as large as 20 mm for the vertical component and 3 mm for horizontal components rigorous computation of site displacements caused by pressure loading requires knowledge of the surface pressure field over the entire earth surface a procedure for computing three dimensional displacements of geodetic sites of interest using a 6 hourly pressure field from the national centers for environmental prediction numerical weather models and the ponte and ray 2002 model of atmospheric tides is presented we investigated possible error sources and found that the errors of our pressure loading time series are below the 15 level we validated our model by estimating the admittance factors of the pressure loading time series using a data set of 3 5 million very long baseline interferometry observations from 1980 to 2002 the admittance factors averaged over all sites are 0 95 0 02 for the vertical displacement and 1 00 0 07 for the horizontal displacements for the first time horizontal displacements caused by atmospheric pressure loading have been detected the closeness of these admittance factors to unity allows us to conclude that on average our model quantitatively agrees with the observations within the error budget of the model at the same time we found that the model is not accurate for several stations that are near a coast or in mountain regions we conclude that our model is suitable for routine data reduction of space geodesy observations

the role of material anisotropy in the neotectonic extension of the western idaho shear zone mccall idaho basin and range normal faulting in west central idaho reactivates preexisting cretaceous structures resulting in a series of normal fault bound basins the most intense extensional deformation is concentrated in the late cretaceous western idaho shear zone resulting in the development of the long valley basin the area affected by the western idaho shear zone displays two orientations of steep faults one set of normal faults strikes north south and is parallel to fabrics within the western idaho shear zone the other set strikes east west and accommodates components of both normal and strike slip movement areas within the idaho batholith that do not have strong cretaceous fabrics i e outside of the western idaho shear zone are characterized by a strong preferred north northeast orientation of faults from this preferred orientation we infer that the maximum infinitesimal stretch is oriented at 110 290 in this part of the idaho batholith gravity inversion indicates that the north end of long valley is an asymmetric basin about one kilometer deep with the largest basin bounding normal fault on the west side of the long valley paleomagnetic analysis of the columbia river basalts indicates that the north south elongate fault blocks within the western idaho shear zone have not rotated one block located just to the west of the western idaho shear zone may have rotated counterclockwise the lack of rotation of north south oriented fault blocks in combination with the fault orientations of the idaho batholith indicate that the regional neotectonic deformation within and east of the western idaho shear zone is characterized by dextral transtension with a divergence vector oriented 130 310 the extensional reactivation of the western idaho shear zone demonstrates the effect of material anisotropy at local and regional scales on a local scale the mylonitic foliation of the western idaho shear zone is reactivated as normal faults even though the regional flow field is oblique to the foliation on a regional scale the possible counterclockwise fault block rotation recorded west of the western idaho shear zone is inconsistent with dextral transtension suggesting that extensional deformation has reactivated the western edge of the arc craton boundary as a kinematic domain boundary we conclude that the preservation of initial features in vertical shear zones and or plate boundaries is unlikely due the tendency for well developed subvertical fabrics to reactivate particularly in extension

cretaceous arc volcanism of palmer land antarctic peninsula zircon u pb geochronology geochemistry distribution and field relationships abstract the cretaceous marks an episode of enhanced magmatism sedimentation and tectonic processes along the entire proto pacific convergent margin of west gondwana cretaceous magmatism across the antarctic peninsula is dominated by the intrusive lassiter coast intrusive suite which developed as episodic flare up events during the mid cretaceous at a time of increased convergence volcanic rocks of this age are poorly defined as a consequence of limited field observations and an absence of accurate geochronology recent field mapping combined with unpublished field observations has identified a region 10 000 km2 of dominantly subaerial rhyolitic pyroclastic and epiclastic successions from northern palmer land of the antarctic peninsula volcanic successions up to 1500 m in thickness consist of dominantly silicic ignimbrites lavas heterolithic breccias and lahar deposits fed by caldera forming eruptions the volcanic rocks of this region were widely considered to be early cretaceous in age based on field relationships and early geochronology new u pb zircon ages identify three distinct volcanic episodes during the late cretaceous early cenozoic at 108 ma 93 ma and 64 ma lu hf data indicate significant proportions of ancient crust in the petrogenesis of the volcanic rocks and the slightly negative ehf values are consistent with a mid position 120 km within the magmatic arc relative to more juvenile compositions close to the trench

use of anisotropy to determine the origin of characteristic remanence in the siwalik red beds of northern pakistan it is often difficult or impossible to determine the origin of the characteristic remanent magnetization of red beds from the bulk remanence alone however anisotropy of remanence or susceptibility is strongly controlled by the statistical alignment of hematite grains this in turn may reflect the development of the magnetic fabric of the sediment over time so the shape of the anisotropy ellipsoid may provide clues to the origin of remanence in this work we make a study of the anisotropy of magnetic susceptibility ams in siwalik red beds of miocene age from northern pakistan comparison of the results with detailed petrographic studies and other information suggests that advanced soil development leads to the destruction of primary fabrics and often with it a coherent magnetization furthermore it should be possible to use ams fabric information to quantify the degree of pedogenesis in these miocene soils we attempted to determine the anisotropy of isothermal remanence air but found ams to be the technique of choice because of apparent changes in coercivity during air experiments we interpret the air data as resulting from metastable domains in hematite grains which change domain state during the air experiment

mountain building strike parallel motion and mantle anisotropy abstract geophysical and geological evidence indicates that tectonic movements parallel to the strike of orogenic belts and suture zones are the most important mode of displacement during continental collision and oblique subduction several hundred to a few thousand kilometers of displacement may have occurred this way resulting in a pervasive ductile deformation of the lithosphere consequently both crustal and mantle fabrics may reflect these movements and their study using both geological and geophysical methods could supply important clues to lithosphere behavior during mountain building on the basis of kinematic analysis of ductilely deformed crustal rocks in zones of movement a variety of tectonic models have been proposed which differ in 1 1 the timing of strike parallel motions early before or during continental accretion or late after accretion was completed 2 2 the geometric pattern of strike parallel displacement zones low angle or high angle and 3 3 the location of orogen parallel movement zones in outboard terranes on the subducting plate along the suture zone or within the continental hangingwall large scale displacements parallel to mountain belts also suggest that they occurred along lithospheric faults rooted in the upper mantle although few studies have been carried out from this view point thermal structural and petrological data support the conclusion that lithospheric faults involving the upper mantle may be discriminated from crustal faults rooted in some crustal decoupling zone where available data on mantle flow beneath orogenic belts are in agreement with mountain parallel displacements inferred from crustal studies this has an important bearing on the seismic anisotropy pattern which can be predicted in the lithospheric mantle below mountain belts the fast velocity direction which is parallel to the flow direction should therefore be recorded parallel to the strike of the belt

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

interseismic deformation and earthquake hazard along the southernmost longitudinal valley fault eastern taiwan about half of the 8 cm yr of oblique convergence across the active convergent plate boundaries of taiwan occurs in eastern taiwan across the longitudinal valley significant shortening and left lateral slip occurs across the longitudinal valley fault there both as shallow fault creep and as seismogenic fault slip the southernmost longitudinal valley fault comprises an eastern peinan strand and a western luyeh strand we derive an interseismic block model for these two strands using data from a small aperture global positioning system gps campaign and leveling the model provides estimates of fault slip rates and quantifies slip partitioning between the two strands a 45 mm yr dip slip rate on the northern peinan strand diminishes southward whereas the left lateral component increases in contrast nearly pure dip slip motion of about 20 mm yr on the southern luyeh strand diminishes northward to about 8 mm yr and picks up a component of left lateral motion of about 15 mm yr before it dies out altogether at its northern terminus the luyeh and the northern peinan strands record near surface creep but the southern peinan strand appears locked the potential earthquake magnitude for the two strands may be as high as m w 6 5 we anticipate seismic rupture mainly on the locked portion of the peinan strand

ocean loading deformations caused by storm surges on the northwest european shelf 1 a model of the non tidal ocean loading deformations caused by storm surges on the northwest european shelf has been developed using the output from a 12 km grid storm surge model the spatial distributions of displacements and gravity variations caused by a typical storm surge event are computed in order to show the magnitudes of the effects that can be expected in space geodetic or gravity measurements a storm surge of just over 2 m in the southern north sea produces vertical displacements of 20 to 30 mm and increases of gravity of 6 to 8 gal in the coastal areas of denmark germany the netherlands and the east coast of england it is shown that the loading deformations due to surges affect a wide area of northwest europe and that high resolution non tidal loading models are required for correcting geodetic measurements made in areas near shallow continental shelves

basement chronology of the antarctic peninsula recurrent magmatism and anatexis in the palaeozoic gondwana margin abstract a revised pre jurassic chronology is presented for the antarctic peninsula on the basis of new u pb zircon dating using both conventional 11 samples and shrimp microprobe data 10 samples the age range for plutonism and high grade metamorphism is from 435 8 ma silurian to c 206 ma approximately the triassic jurassic boundary with peaks of activity in devonian carboniferous permian and mid triassic times although some are represented by rocks with limited outcrops the new data confirm the importance of mid and latest triassic magmatic events previously identified using rb sr geochronology the adie inlet gneiss previously thought to be neoproterozoic is recognized as a permian migmatite derived from paragneiss with a provenance dominated by cambrian granitoids granite gneiss from nw palmer land previously dated as cambrian is shown to be triassic detrital zircons in metasedimentary rocks and inherited zircons in granitoids are dominated by mesoproterozoic to cambrian components with sparse palaeoproterozoic to archaean grains suggesting sources within gondwana at times these sources were nearby as shown by an archaean cobble sized granite clast from a permo triassic conglomerate another clast in the same conglomerate previously thought to be devonian in age has an ordovician crystallization age

detecting storm surge loading deformations around the southern north sea using subdaily gps summary a large storm surge event occurred on 2007 november 2009 in the southern north sea where strong winds caused the sea level to rise drastically by up to 3 m within several hours based on the proudman oceanographic laboratory storm surge model the predicted loading displacements at coastal stations can reach a few centimetres in the vertical and several millimetres in the horizontal directions in this study we used two hourly global positioning system gps positions at 26 stations around the southern north sea to identify the loading displacements caused by this storm surge event we find that the mean rms of the differences between the estimated and predicted displacements are 4 9 1 3 and 1 4 mm which are insignificant compared to the one sigma gps positioning errors of 5 1 2 0 and 2 4 mm for the up east and north components respectively more interestingly in both vertical and horizontal directions the estimated displacements successfully tracked the temporal evolution ofthestormsurgeloadingeffects inaddition withinthewholeof2007november weusedthe predicted displacements to correct the two hourly gps positions and consequently reduced the rms of the estimated displacements on average from 9 3 3 0 and 2 9 mm to 7 8 2 8 and 2 8 mm for up east and north components respectively therefore subdaily loading effects due to storm surges should be paid attention to in the gps positioning that contributes to crustal motion studies around shallow seas such as the north sea the baltic sea and the gulf of mexico

indication of the uplift of the ardenne in long term gravity variations in membach belgium summary we report on the results of 7 yr of collocated gravity observations made with an fg5 absolute ag gravimeter and a gwr c series superconducting gravimeter sg located at the membach geophysical station in eastern belgium the sg gravity residuals track changes in gravity periodically observed by the ag at the microgal level further in the sg residual signal we distinguish a quasi seasonal term that can be mostly explained by variations in local water storage effects in the ag time series we observe a small trend in the gravity of 0 6 0 1 gal yr 1 perhaps indicating that the membach station is being displaced upwards by about 3 0 mm yr 1 an uplift of the region is confirmed by global positioning system gps measurements performed 3 km away we are able to explain the features in the gravity time series in terms of water storage variability post glacial rebound and tectonic activity

87 sr 86 sr and 18 o 16 o isotopic systematics and geochemistry of granitoid plutons across a steeply dipping boundary between contrasting lithospheric blocks in western idaho a spatially abrupt geochemical boundary is preserved within four plutonic complexes along the western margin of the cretaceous idaho batholith near mccall idaho these intrusives ranging in composition from tonalite to granite were emplaced across a regional boundary between accreted oceanic arc terranes and the continental margin and their isotopic major element and trace element geochemistry provide detailed information about this change in crustal characteristics at depth indicating that the boundary is nearly vertical and extends deep into the lithosphere the hazard creek complex emplaced west of the transition in wall rock lithology has initial 87sr 86sr ri less than 0 7045 and 18o greater than 7 5 indicating little or no continental crust in its source region however elevated 18o requires some incorporation of rocks formed or altered at the earth s surface a large shift in ri and 18o is observed across the 5 8 km wide little goose creek complex which was emplaced across the wall rock boundary this is interpreted as mixing between 1 a basaltic or andesitic magma with low k2o and high na2o al2o3 and sr similar to that forming the hazard creek complex and 2 materials similar to precambrian sedimentary sedimentary rocks with low sr high 18o 15 and high ri 0 83 at 100 ma the payette river complex emplaced east of the wall rock boundary exhibits at least one additional component with low 18o 6 moderate ri 0 708 and mafic composition this component is inferred to be old basaltic material in the lower crust or upper mantle similar to that inferred to be a minor part of the peninsular ranges batholith in se california silver et al 1979 hill et al 1986 the easternmost complex in the idaho transect is made up of granites that may contain a component of granitic cratonal basement the entire west to east geochemical transition from oceanic arc magmas to cratonal magmas takes place over a lateral distance of less than 20 km although the zone of transitional protolith dominated by metasedimentary rocks is unusually narrow and may have been in part tectonically removed the striking geochemical similarities between this traverse and several other transects across much broader areas of nevada and california suggest that the craton itself was not rifted apart but that juxtaposition of the accreted oceanic arc terranes occurred along the preexisting craton margin the data confirm that the isotopic geochemistry of granitoid plutons can be used as a probe of deep lithospheric character and that major lateral variations in the lithosphere on the order of one to two kilometers in width can be recognized in favorable circumstances

oblique plate motion and continental tectonics three dimensional deformation is necessarily associated with oblique plate convergence and commonly results in partitioning of deformation between contractional and transcurrent components along plate margins kinematic models of strike slip partitioning for transpression and transtension allow the exact relation among three critical parameters plate motion instantaneous strain axes and degree of strike slip partitioning to be calculated application to two end member tectonic environments characterized by a low south island new zealand and high central california degree of strike slip partitioning demonstrates a remarkable consistency among the three parameters suggesting that strike slip partitioned transpression is a valid model for deformation in these regions the extreme degree of strike slip partitioning in wrench dominated systems such as central california is tentatively associated with a fundamental misorientation of finite and instantaneous strain axes

sedimentology and structure of the trench slope to forearc basin transition in the mesozoic of alexander island antarctica the mesozoic forearc of alexander island antarctica is one of the few places in the world where the original stratigraphic relationship between a forearc basin and an accretionary complex is exposed newlydiscovered sedimentary rocks exposed at the western edge of the forearc basin fill the kimmeridgian albian fossil bluff group record the events associated with the basin formation these strata are assigned to the newly defined selene nunatak formation bathonian and atoll nunataks formation bathonian tithonian within the fossil bluff group the selene nunatak formation contains variable thicknesses of conglomeratesand sandstones predominantly derived from the lemay group accretionary complex upon which it is unconformable the formation marks emergence and subsequent erosion of the inner forearc area it is conformably overlain by the1 km thick atoll nunataks formation characterized by thinly bedded mudstones and silty mudstones representing a marine transgression followed by trench slope deposition the atoll nunataks formation marks a phase of subsidence possibly in response to tectonic events in the accretionary prism that are known to have occurred at about the same time the atoll nunataks formation is conformably overlain by the himalia ridge formation a thick sequence of basin wide arc derived conglomerates this transition from fine to coarse grained deposition suggests that a well developed depositional trough and hence trench slope break had formed by that time the atoll nunataks formation therefore spans the formation of the forearc basin and marks the transition from trench slope to forearc basin deposition

the source of granitic gneisses and migmatites in the antarctic peninsula a combined u pb shrimp and laser ablation hf isotope study of complex zircons zircons gneisses and migmatites collected from the antarctic peninsula have different core rim hafnium isotope ratio relationships depending on whether evidence for zircon dissolution is present or absent two samples contain inherited zircon that is partially dissolved in these samples the 176hf 177hf rations of the inherited zircon and new magmatic zircon rims are on average indistinguishable and consistent with in situ melting in such cases the hafnium isotopic composition of the melt was probably strongly influenced by the dissolved zircon component at the source variation in 176hf 177hf within the magmatic zircon rims from grain to grain suggests that hf isotopes were only partially homogenized during melt migration alternatively zircon growth may have taken place within small volumes of partial melt other samples do not preserve textural evidence for zircon dissolution during melt generation in these samples the 176hf 177hf values of the inherited zircon and new magmatic zircon rims are different the zircon rims apparently suggest a source of less evolved hafnium than that contained within the inherited zircon whether this relates to a separate juvenile source or alternatively is derived from minerals other than zircon at the source cannot be resolved inherited zircon irrespective of age has been strongly influenced by the reworking of a juvenile late mesoproterozoic source suggesting that such crust underlies the antarctic peninsula our results therefore suggest that hf isotope analyses provide great potential for future studies investigating the source and processes involved in the generation of crustal melts

the eastern palmer land shear zone a new terrane accretion model for the mesozoic development of the antarctic peninsula a major ductile fault zone the eastern palmer land shear zone has been identified east of the spine of the southern antarctic peninsula this shear zone separates newly identified geological domains and indicates that during late jurassic terrane accretion and collision two and possibly three separate terranes collided resulting in the palmer land orogeny the orogeny is best developed in eastern palmer land and eastern ellsworth land there shallow marine sedimentary rocks of the latady formation and a metamorphic and igneous basement complex of possible lower palaeozoic to pre early jurassic age are thrust and folded this forms an arcuate east directed foreland fold and thrust belt up to 100 km wide and 750 km long parallel to the axis of the antarctic peninsula the newly identified antarctic peninsula domains include 1 a parautochthonous eastern domain that represents part of the margin of the gondwana continent comparable to the western province of new zealand the ross province superterrane of marie byrd land the eastern series of south central chile the pampa de agnia and tepuel rocks of north patagonia and the cordillera darwin rocks of tierra del fuego 2 a suspect central domain that represents an allochthonous microcontinental magmatic arc terrane comparable to the median tectonic zone of new zealand the amundsen province superterrane of marie byrd land and coastal cordillera of north chile and 3 a suspect western domain with strong similarities to the eastern province of new zealand western series of south central chile and chonos metamorphic complex of north patagonia that represents either a subduction accretion complex to the central domain or another separate crustal fragment although an allochthonous terrane hypothesis for the antarctic peninsula remains to be fully tested this has much in common with models for the new zealand and south american parts of the pacific margin of gondwana the identification of a potential allochthonous terrane continent collision zone allows us to define the edge of the gondwana continent in the antarctic peninsula sector of the supercontinent margin which has implications for mesozoic reconstructions of gondwana

capturing transient mass changes for the 2011 tohoku tsunami on a spring gravity meter the 11 march m w 9 0 tohoku earthquake 5 46 utc produced severe damage in northern honshu japan and generated a tsunami which devastated japan s northeast coast and impacted most of the pacific basin distal tsunami waves approaching 0 5 m peak to peak were recorded at tauranga new zealand beginning 19 00 utc a contemporaneous 6 gal peak to peak oscillation was observed on a continuously recording spring gravity meter located at white island volcano about 90 km northeast of tauranga we modeled the gravity oscillation by application of a tsunami wave field simulation which incorporates theoretical tohoku earthquake source rupture time history and local white island bathymetry the simulation yielded discrete wave heights that were converted to a theoretical gravity response and that agreed with the observed gravity oscillation the successful capture of tsunami waves by a spring gravity meter may have implications for improving tsunami modeling from distal tsunami waves

quaternary reactivation of the kern canyon fault system southern sierra nevada california the kern canyon fault the longest fault in the southern sierra nevada is an active structure and has been reactivated at discrete times over the past 100 m y in response to changing lithospheric stresses after initiation as a cretaceous transpressional structure the kern canyon fault transitioned into a dextral strike slip shear zone that remained active as it was exhumed into the brittle regime during regional late cretaceous uplift of the sierra nevada batholith the kern canyon fault was reactivated during miocene regional extension as part of a transfer zone between two differentially extending domains in the southern sierra nevada subsequent normal displacement along the fault began in pliocene time new evidence for fault activity which continued into late quaternary time includes its current geomorphic expression as a series of meters high west side up scarps that crop out discontinuously along the fault s 130 km length relocated focal mechanisms of modern earthquakes confirm ongoing normal faulting and geodetic measure ments suggest that the sierra nevada is uplifting relative to the adjacent valleys this evidence for recent activity overturns a long held view that the kern canyon fault has been in active for more than 3 5 m y its reactivation indicates that deformation repeatedly localized along a pre existing crustal weakness a cretaceous shear zone we propose that a system of inter related normal faults including the kern canyon fault is responding to mantle lithosphere removal beneath the southern sierra nevada region the location of the active kern canyon fault within the sierra nevada great valley microplate indicates that deformation is occurring within the microplate

a new stratigraphy for the latady basin antarctic peninsula part 2 latady group and basin evolution recent detailed mapping section logging and an improved understanding of the geological evolution of the antarctic peninsula provide a robust framework for an improved lithostratigraphic subdivision of the latady basin eastern ellsworth land within the latady basin we recognize two main groups ellsworth land volcanic group and latady group the focus of this paper is the latady group which is formally subdivided into five formations anderson formation witte formation hauberg mountains formation cape zumberge formation and nordsim formation middle jurassic shallow marine deposits of the anderson formation are overlain by quiet anoxic deposits assigned to the witte formation the start of the late jurassic is marked by the deposition of higher energy deposits of the hauberg mountains formation subdivided into three members long ridge mount hirman and novocin members that reflect varying lithological and environmental characteristics thermal subsidence during the latest jurassic led to deposition of the basinal cape zumberge formation while uplift of an active continental arc along the antarctic peninsula led to deposition of the terrestrial nordsim formation in the latest jurassic to earliest cretaceous the evolution of the latady basin reflects early extension during gondwana break up from the early jurassic to earliest cretaceous and is consistent with a shift in the underlying forces driving extension in the weddell sea area from intracontinental rifting related to a mantle plume to active margin forces in response to subduction

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

the chon aike province of patagonia and related rocks in west antarctica a silicic large igneous province the field occurrence age classification and geochemistry of the mesozoic volcanic rocks of patagonia and west antarctica are reviewed using published and new information dominated by rhyolitic ignimbrites which form a bimodal association with minor mafic and intermediate lavas these constitute one of the largest silicic igneous provinces known equivalent in size to many mafic lips diachronism is recognized between the early middle jurassic volcanism of eastern patagonia marifil and chon aike formations and the middle jurassic earliest cretaceous volcanism of the andean cordillera el quemado ibanez and tobifera formations this is accompanied by a change in geochemical characteristics from relatively high zr and nb types in the east to subalkaline arc related rocks in the west although the predominance of rhyolites remains a constant factor all of the associated mafic rocks are well fractionated compared to direct mantle derivatives petrogenetic models favour partial melting of immature lower crust as a result of the intrusion of basaltic magmas possibly with some hybridisation of the liquids and subsequent fractionation by crystal settling or solidification and remelting the formation of large amounts of intracrustal silicic melt acted as a density barrier against the further rise of mafic magmas which are thus rare in the province

chrono and lithostratigraphy of a mesozoic tertiary fore to intra arc basin adelaide island antarctic peninsula the mesozoic fore arc of the antarctic peninsula is exposed along its west coast on adelaide island a 2 3 km succession of turbiditic coarse sandstones and volcanic rocks is exposed four u pb zircon ages are presented here that in combination with a new stratigraphy have permitted a robust chrono and lithostratigraphy to be constructed which in turn has allowed tentative correlations to be made with the fossil bluff group of alexander island where the type fore arc sequences are described the lithostratigraphy of adelaide island includes the definition of five volcanic sedimentary formations the oldest formation is the buchia buttress formation 149 5 1 6 ma and is correlated with the himalia ridge formation of alexander island the sandstone conglomerate dominated succession of the milestone bluff formation 113 9 1 2 ma is tentatively correlated with the pluto glacier formation of alexander island three dominantly volcanic formations are recognized on adelaide island akin to the volcanic rocks of the alexander island volcanic group the mount liotard formation is formed of 2 km of basaltic andesite lavas whilst the bond nunatak formation is also dominated by basaltic andesite lavas but interbedded with volcaniclastic rocks the reptile ridge formation has been dated at 67 6 0 7 ma and is characterized by hydrothermally altered rhyolitic crystal lithic tuffs tentative correlations between adelaide island and alexander island preclude the two areas forming part of distinct terranes as has been suggested previously and a proximal source for volcaniclastic sediments also indicates an exotic terrane origin is unlikely

emplacement and deformation history of the western margin of the idaho batholith near mccall idaho influence of a major terrane boundary cretaceous plutons of the western margin of the idaho batholith were emplaced along and to the west of the major terrane boundary separating middle proterozoic and paleozoic continental rocks from mostly mesozoic accreted oceanic arc terranes of the blue mountain province this boundary is marked by a change in the lithology of pendants and inclusions within the batholith plutons form two newly named complexes of igneous and metamorphosed igneous rocks the hazard creek complex emplaced west of the boundary between the oceanic arc and the continental margin consists primarily of a series of variably deformed and metamorphosed quartz diorite to trondhjemite plutons the little goose creek complex which intruded the boundary between the oceanic arc and the continental margin is primarily porphyritic granodiorite to granite orthogneiss a preliminary u pb age of 111 ma for this porphyritic orthogneiss is a minimum age for the formation of the oceanic arc continent boundary the plutonic rocks were deformed both during and after emplacement in response to east west compressive stresses cretaceous deformation was localized along the boundary between the accreted terranes and the continental margin and is interpreted to have occurred after the formation of this boundary the major deformation of the hazard creek complex occurred during its emplacement the dominant fabric in the little goose creek complex is due to subsolidus ductile deformation the localization of two deformation events along the pre existing boundary between the accreted terranes and the continental margin suggests that a terrane boundary may form a long lasting crustal flaw

predictions of crustal deformation and of geoid and sea level variability caused by oceanic and atmospheric loading summary in this paper we consider several small effects related to oceanic loading of the earth and atmospheric loading of the oceans non tidal ocean loading induces changes in oceanic bottom pressure which in turn deform the geoid and the nearby crust changes in bottom pressure are derived from estimates of sea surface height variability and density changes output from an oceanic general circulation model sea surface heights measured by the topex poseidon altimeter are also used to infer changes in bottom pressure we estimate that non tidal ocean loading can typically cause 5 mm of peak to peak 2 mm root mean square rms vertical motion at sites near the shore with displacements of up to 10 mm possible amplitudes of horizontal displacements are about one third those of vertical ones deformation associated gravity changes are usually of the order of 2 3 pgal however peak to peak changes of 5 pgal are also predicted loading induced geoid perturbations in mid ocean regions are typically 5 10 mm peak to peak 3 mm rms and can extend over a region of 20 in the case of atmospheric loading of the oceans we estimate the difference between the inverted barometer correction usually used to describe the ocean s response to atmospheric pressure and the complete equilibrium response there are two sources of this difference one is that the inverted barometer correction does not conserve oceanic mass we use national meteorological center nmc global pressure data to estimate the time dependent average change in pressure over the oceans a time series of the net pressure over the oceans contains an annual signal with a peak to peak amplitude of 1 2 mbar superimposed on a linear trend of 0 09 mbar yr the secular signal is caused by a redistribution of atmospheric mass from over continental land masses to the oceans we conclude that this effect introduces additional variability into the ocean s response to pressure at annual secular and multi year timescales with a total peak to peak amplitude of a few tens of millimetres the second difference between the inverted barometer response and the complete equilibrium response is due to gravitational forcing by the atmosphere and by the displaced mass in the solid earth and oceans caused by the atmospheric loading this effect is largest within about 1000 km of the coast and at high latitudes we use nmc pressure data to estimate the effect and find that it causes differences from the inverted barometer solution in those regions of up to 10 30mm peak to peak with values as large as 50 60 mm possible at certain locations the time dependence of this effect is negatively correlated with the inverted barometer response the effect causes an apparent reduction of the inverted barometer response by a few per cent within a few hundred kilometres of the coast with reductions of more than 6 7 per cent at a few places

u pb studies of zircon cores and overgrowths and monazite implications for age and petrogenesis of the northeastern idaho batholith u pb isotopic studies of zircons many containing xenocrystic cores with euhedral overgrowths and monazite from igneous rocks and metasedimentary inclusions of the northeastern idaho batholith yield linear arrays on concordia diagrams we interpret these as mixing lines between an old component cores and a young component overgrowths and zircons without cores the lower intercept of such arrays with concordia may yield the minimum age of the rocks if the overgrowths and zircons without cores are discordant or the crystallization age if they are concordant monazites yield apparently concordant ages either equal or less than the lower intercept zircon ages the samples studied yield lower intercept ages ranging from 73 5 pm 6 m y foliated quartz diorite to 46 5 pm 1 m y feldspar megacryst granite ages obtained are consistent with crosscutting relations observed in the field upper intercepts yield ages of 1700 to 2349 m y these are interpreted to indicate the mean age of xenocrystic zir