aligned buoyant highs across trench deformation clustered volcanoes and deep earthquakes are not aligned with plate tectonic theory abstract bathymetry shows the regional interaction of aseismic buoyant highs in northern pacific subduction zones seamounts ridges and fractures on the seaward side of the trench are associated with events that do not support the accepted plate tectonics paradigm including an altered slab dip angle benioff zone and the clustered volcanoes and earthquakes within the convergent margin most of the examples in this study show a reduction in the number of total earthquakes but an increase in the deeper earthquakes an abnormal amount of across trench deformation and a larger amount of volcanism on the active arc than if no bouyant highs existed in the subduction zone the connections between the seaward highs and the landward clustered highs are the transverse faults which widen by turbidite scour as they age forearc canyons are the modern day bathymetdc expression of these faults all of the parameters introduced disagree with the plate tectonic hypothesis making an alternate explanation for the genesis necessary that explanation falls into the realm of the surge tectonic hypothesis which can explain by fluid mechanics and eastward flow each of the introduced parameters

continental oceanic crustal transition off southwest africa more than 1 426 mi 2 300 km of 48 trace 12 fold seismic reflection profiles were used to examine the nature of the continent ocean boundary off southwest africa south of the orange river faulted blocks which we interpret as rifted continental crust can be traced seaward to the 3 km isobath the transition to oceanic basement occurs in a zone 19 to 25 mi 30 to 40 km wide beneath the continental rise although structural details are obscured by a thick seaward dipping wedge of pre aii pre late early cretaceous overburden oceanic crust at the presumed contact is not older than magnetic anomaly m9 126 to 121 m y b p north of the orange river a pronounced hinge in continental crust correlates with magnetic anomaly g of rabinowitz 1976 seaward of the hinge a complex fault block terrane is evident oceanic basement can not be traced with any certainty landward of anomaly m4 intracontinental stretching and associated volcanism appear to have been important in the early history of the cape basin rifting and local dike intrusion may explain the presence of some lineated magnetic anomalies previously attributed to sea floor spreading related extrusives form at least part of the pre aii wedge just seaward of the hinge zone our interpretation of the seismic data suggests that the initiation of normal spreading in the cape basin postdates by 4 to 9 m y the valanginian age derived from prevailing plate tectonic reconstructions of the south atlantic

high grade metamorphism and partial melting of basic and intermediate rocks rocks of basic and intermediate bulk composition occur in orogenic terranes from all geological time periods and are thought to represent significant petrological components of the middle and lower continental crust however the former lack of appropriate thermodynamic models for silicate melt amphibole and clinopyroxene that can be applied to such lithologies at high temperature has inhibited effective phase equilibrium modelling of their petrological evolution during amphibolite and granulite facies metamorphism in this work we present phase diagrams calculated in the na2o cao k2o feo mgo al2o3 sio2 h2o tio2 o2 nckfmashto compositional system for a range of natural basic and intermediate bulk compositions for conditions of 2 12 kbar and 600 1050 c using newly parameterized activity composition relationships detailed in a companion paper by green et al in this issue particular attention is given to mid ocean ridge basalt morb and diorite protolith bulk compositions calculated subsolidus mineral assemblages in all basic and intermediate rock types are modally dominated by hornblende and plagioclase with variable proportions of epidote clinopyroxene garnet biotite muscovite quartz titanite or ilmenite present at different pressures the h2o saturated wet solidus has a negative p t slope and occurs between 620 690 c at mid to lower crustal pressures of 5 10 kbar the lowest t melts generated close to the wet solidus are calculated to have granitic major element oxide compositions melting at higher temperature is attributed primarily to multivariate hydrate breakdown reactions involving biotite and or hornblende partial melt compositions calculated at 800 1050 c for morb show good correlation with analysed compositions of experimental glasses produced via hydrate breakdown melting of natural and synthetic basic protoliths with niggli norms indicating that they would crystallize to trondhjemite or tonalite diorite is shown to be significantly more fertile than morb and is calculated to produce high t melts 800 c of granodioritic composition subsolidus and suprasolidus mineral assemblages show no significant variation between different members of the basalt family although the p t conditions at which orthopyroxene stabilizes thus defining the prograde amphibolite granulite transition is strongly dependent on bulk rock oxidation state and water content the petrological effects of open and closed system processes on the mineral assemblages produced during prograde metamorphism and preserved during retrograde metamorphism are also examined via a case study analysis of a natural archean amphibolite from the lewisian complex northwest scotland

advances in fourier transform infrared spectroscopy of natural glasses from sample preparation to data analysis fourier transform infrared spectroscopy ftir is an analytical technique utilized to measure the concentrations of h and c species in volcanic glasses water and co2 are the most abundant volatile species in volcanic systems water is present in magmas in higher concentrations than co2 and is also more soluble at lower pressures and therefore it is the dominant volatile forming bubbles during volcanic eruptions dissolved water affects both phase equilibria and melt physical properties such as density and viscosity therefore water is important for understanding magmatic processes additionally quantitative measurements of different volatile species using ftir can be achieved at high spatial resolution recent developments in analytical equipment such as synchrotron light sources and the development of focal plane array fpa detectors allow higher resolution measurements and the acquisition of concentration maps these new capabilities are being used to characterize spatial gradients or lack thereof around bubbles and other textural features which in turn lead to new insights into the behavior of volcanic feeder systems here practical insights about sample preparation and analysis of the distribution and speciation of volatiles in volcanic glasses using ftir spectroscopy are discussed new advances in the field of ftir analysis produce reliable data at high spatial resolution that can be used to produce datasets on the distribution dissolution and diffusion of volatiles in volcanic materials

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

water in albitic glasses infrared spectroscopy has been calibrated to provide a precise and accurate method for determining the concentrations of molecular water and hydroxyl groups in hydrous albitic glasses at total water contents less than 4 wt most of the water is dissolved as hydroxyl groups at higher total water contents molecular water becomes the dominant species for total water contents above 4 wt the amount of water dissolved as hydroxyl groups is nearly constant at about 2 wt and additional water is incorporated as molecular water these trends in the concentrations of the h bearing species are similar to those observed in other silicate glasses using infrared and nmr spectroscopies the ratio of molecular water to hydroxyl groups at a given total water content is independent of the pressure and only weakly dependent on the temperature of equilibration molecular water and hydroxyl group concentrations in glasses provide constraints on the dissolution mechanisms of water in silicate liquids several mixing models involving homogeneous equilibria of the form h 2o o 2 2oh among melt species in albitic melts have been developed these models can account for the measured species concentrations if the effects of non ideal behavior or mixing of polymerized units are included or by allowing for several different anhydrous species we used two thermodynamic models of hydrous albitic melts to calculate phase equilibria the first assumes that henry s law holds for molecular water in albitic liquids i e that the activity of molecular water in the melt is proportional to its mole fraction as determined by infrared spectroscopy the second describes the speciation and thermodynamics of hydrous albitic melts using the formalism of a strictly regular solution these models can account reasonably well for the position of the vapor saturated solidus of high albite and the pressure and temperature dependence of the solubility of water in albitic melts to the extent that these models are successful our approach provides a direct link between measured species concentrations in hydrous albitic glasses and the macroscopic thermodynamic properties of the naalsi 3o 8 h 2o system

source of marine magnetic anomalies some results from dsdp leg 83 leg 83 of the deep sea drilling project represents the deepest penetration of undisturbed marine crust yet achieved providing samples from the lower part of the extrusive layer and the upper 300 m of the sheeted dike complex we present here measurements of the magnetic properties of rocks from leg 83 and address the question of their suitability as sources for marine magnetic anomalies we find that due to extensive hydrothermal alteration the extrusive part of the leg 83 section is insufficiently magnetized to be part of the magnetic source layer the sheeted dike complex on the other hand does have sufficient magnetization and contrary to recent models of marine magnetization based on ophiolite studies may be a contributor to magnetic anomalies the strong dependence of magnetic properties on the alteration history of the rocks however makes extension of these results to other regions problematical

melting experiments and thermodynamic analyses on silicate h2o systems up to 12 gpa abstract melting experiments on pyrope mg 3 al 2 si 3 o 12 h 2 o system were conducted in an ma8 type high pressure apparatus up to 12 gpa and approximately 2000 k pyrope melts congruently with its solidus temperature increasing from 1430 k at 4 2 gpa to 1510 k at 12 gpa these temperatures are lower than those of the anhydrous condition by 640 k and 930 k respectively a thermodynamic analysis was carried out on the hydrous melting of two major mantle silicates namely pyrope and forsterite mg 2 sio 4 on the basis of the ideal mixing model proposed by silver and stolper 1985 j geol 93 161 178 the experimental phase diagrams were reproduced successfully within experimental uncertainty by adjusting only three thermodynamic parameters the equilibrium constant for the chemical reaction between silicate and h 2 o in the melt the equilibrium constant for the dissolution of h 2 o gas into the melt at 0 5 gpa and the molar volume of h 2 o in the melt at atmospheric pressure furthermore the thermodynamic analysis suggests that pressure enhances the silicate h 2 o reaction in the melt

two interannual dominant modes of the south asian high in may and their linkage to the tropical sst anomalies the variations of the intensity and position of the south asian high sah in may are critical for the interannual change in the asian summer monsoon onset process the present work has defined two dominant modes of the sah in may via the principal component analysis of sah s strength zonal extension and ridgeline position indices during 1979 2015 the first mode sah intensity mode features a coherent enhancement of the sah strength and zonal extension while the second mode sah position mode exhibits a meridional swing of the sah ridgeline both diagnosis analysis and numerical experiments validate that the distinct evolution of enso in boreal spring determines its different influences on the two modes when an el nino decays quickly during march may its resultant warm anomalies of sea surface temperature sst in the tropical indian ocean can affect the sah intensity mode by modifying the tropical convection over the southwestern bay of bengal acting as a local sst forcing to the circulation however the sah position mode depends on the persistence of the enso event during boreal spring the remote el nino related sst forcing can enhance the large scale descent over the indo pacific ocean which suppresses the tropical convection to modify the mid upper level thermal structure over south asia inducing the interannual variation of the sah ridgeline in may

geochemistry and timing of the marginal basin and arc magmatism in the philippine sea available data enable the recognition of three periods of back arc crustal generation and three pulses of volcanic activity along the associated island arcs of the philippine sea the geochemistry of the basalts from the back arc basins of different ages indicates that in most cases they are identical to mid ocean ridge basalts and therefore should have similar sources and origins in contrast the island arc rock composition is variable in space and time reflecting the different source and more complex nature of corresponding magmatism geomagnetic studies and recent deep sea drilling project results suggest an alternate sequence of back arc and arc magmatic cycles both geochemical and geological observations provide important constraints on models of magmatism and extensions tectonics at convergent plate boundaries

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

an experimental study of bromine behaviour in water saturated silicic melts to assess the effect of the melt composition on bromine concentrations in magmas we have investigated bromide solubility for water saturated iron free silicic melts with variable na k al and si al molar ratios albite haplogranite rhyolite and pantellerite the experiments were performed in rapid quench cold seal autoclaves over a range of pressure 1 1 5 and 2 kbar and temperature 900 1000 and 1080 c with run durations from 5 to 7 days a series of natural volcanic glasses and melt inclusions hosted in magmatic minerals were analysed together with the synthetic glasses by pixe proton induced x ray emission the br concentrations range from 5360 to 7850 ppm for albite from 2800 to 3900 ppm for haplogranite from 4300 to 5900 ppm for rhyolite and from 9745 to 11 250 ppm for pantellerite br concentrations are negatively correlated with pressure in h2o saturated silicic melts and vary with na k al molar ratio with a minimum value at the ratio close to unity br behaves similarly to chlorine for all of these melt compositions the bromide solubility is similar in albitic and rhyolitic melts which implies that df m is nearly the same for both compositions and is applicable for natural rhyolites as suggested in our previous study bureau et al 2000 this means that the volcanic br contribution to the atmosphere may be significant in natural obsidian samples and mi hosted in quartz olivine and leucite the br concentration varies from 3 to 28 ppm with the highest concentrations in pantelleritic melts we attribute the low br concentrations of natural melts to a low initial abundance of this halogen in the earth mantle however because br behaves as an incompatible element before water exsolution our results imply that magmas could contain much more dissolved br before eruption and water degassing than the few ppm usually measured in volcanic rocks br behaviour during magma crystallisation is controlled by its partitioning into the h2o rich fluid phase when this occurs in addition its potential high solubility in silicate melts makes it a very sensitive chemical tracer of magma contamination by seawater and br rich material this infers that the investigation of br behaviour in subduction zone samples may help for a better understanding of volatiles cycling between the earth reservoirs

crustal movements and geodynamics in fennoscandia abstract morner n a 1981 crustal movements and geodynamics in fennoscandia in p vyskocil r green and h malzer editors recent crustal movements 1979 tectonophysics 71 241 251 the fennoscandian shield the classical area of glacial isostasy has been subjected to a complex sequence of motions throughout the late cenozoic still the geometry of the areas deformed has been roughly the same an asthenosphere of low viscosity 1020 1021 poises and a lithosphere of high flexural rigidity are established the present uplift represents an other mechanism than the rapid glacial isostatic readjustment of the low viscosity asthenosphere and seems to originate from mesospheric motions at around 1900 1910 there was a distinct geodynamic change which seems to be controlled by changes in the earth s rate of rotation the postglacial uplift of fennoscandia is found to be associated with intensive neotectonism faulting fracturing and seismicity

the east pacific rise near 21 n 13 n and 20 s inferences for along strike variability of axial processes of the mid ocean ridge abstract data obtained along various segments of the mid ocean ridge mor are used to construct an idealized model for crustal accretion the model seeks to predict the topographic volcanic tectonic and hydrothermal characteristics of any given spreading segment of the mor as a function of distance away from the bounding transform faults this model is based on a series of detailed mapping efforts carried out on segments of the mor having a broad range of spreading rates between 2 and 16 cm yr this paper includes the results of the french searise program carried out during the summer of 1980 aboard the n o jean charcot and two american cruises conducted in 1981 aboard the r v melville

tillamook volcanic series further evidence for tectonic rotation of the oregon coast range paleomagnetic directions from the eocene tillamook volcanic series of the oregon coast range point 46 o clockwise from the expected eocene field direction potassium argon dating of six dikes and flows from this formation yields a mean age of 44 3 0 6 m y these results establish that the oregon coastal block of simpson and cox 1977 extends north to the oregon washington border and that this block has rotated clockwise 46 o 13 o during the past 44 m y the block has undergone no detectable north south translation a two phase model is developed to explain the tectonic history and anomalous magnetic field directions of the pacific northwest region phase i of the rotation active between 50 and 42 m y b p results from fragmentation of the farallon plate with rotation of a fragment during its accretion to north america phase ii of the rotation active between 20 m y b p and the present occurs in association with extension in the basin and range province

age and structure of the southern rockall trough new evidence abstract the rockall trough separates the rockall plateau microcontinent from the shelf and slope west of the british isles the structure and age of the trough has been the source of considerable discussion although widely considered to be of oceanic origin postulated ages for the spreading range from permian to cretaceous new seismic profiles linked to the ipod sites in the bay of biscay and to oceanic anomalies of known age are used to present a new assessment of the age and structure of the southern rockall trough it is concluded that about 120 km of ocean crust is present in the trough and that spreading took place in the albian maastrichtian interval

a model for calculating the viscosity of natural iron bearing silicate melts over a wide range of temperatures pressures oxygen fugacites and compositions a new general model that takes into account the pressure and redox state effect is presented to calculate melt viscosities of natural fe bearing melts this new model is applicable to melts that span a wide range of temperatures from 733 to 1873 k pressures 0 001 15 kbar h2o content from 0 to 12 3 wt and compositions from ultramafic mafic to silicic melts the accuracy of the model is calculated to be 0 23 log units of viscosity which is within or close to experimental uncertainty the transport properties including glass transition temperature and melt fragility can also be calculated from this model a spreadsheet to calculate the viscosity is provided in an electronic supplement

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

volcanism and vertical tectonics in the pacific basin related to global cretaceous transgressions abstract the dominance of volcanic processes and the importance of vertical tectonics in the geological evolution of the pacific basin has been recognised since the time of charles darwin data gathered on several legs of the deep sea drilling project dsdp and numerous marine expeditions in the past decade have confirmed menard s postulate that the pacific basin was the scene of volcanism on an enormous scale in mesozoic time widespread mid plate volcanism between 110 and 70 m y b p characterised the area bounded by the line islands the mid pacific mountains and the nauru basin marshall islands heating of the pacific lithospheric plate during this period of volcanism resulted in regional uplift and the bathymetric evolution of the area diverged significantly from a normal parsons sclater subsidence curve the farallon plate now almost entirely subducted was also the scene of mid plate volcanism that produced such features as the nicoya plateau now found as an allochthonous ophiolitic terrain landward of the middle america trench large benthonic reef associated foraminifera comprising a pseudorbitoid fauna hitherto considered to be largely restricted to central america have now been additionally recorded from dsdp sites 165 315 and 316 in the line islands site 462 in the nauru basin and in new guinea the distribution of this fauna of campanian maastrichtian age is interpreted as indicating stepping stone connections aseismic ridges plateaus and seamounts between the caribbean farallon and pacific plates 70 80 m y b p similarities between the geology of the nauru basin and the caribbean ocean crust reinforce the interpretation of the latter as a former part of the farallon plate estimates of the sea level and continental freeboard change caused by the thermally induced uplift of the pacific and farallon plates as well as substantial areas in the atlantic and indian ocean basins indicate that such shallowing of the sea floor could have been the major factor in causing global cretaceous transgressions

tectonic rotation about the termination of a major strike slip fault marlborough fault system new zealand the marlborough fault system comprises a series of major right lateral strike slip faults that link the alpine fault to the hikurangi subduction zone in the pacific australia plate boundary zone in new zealand all of the major active faults of the marlborough fault system have continuous traces except for the clarence fault which terminates abruptly near the ward syncline paleomagnetic data from upper miocene and lower pliocene sedimentary rocks between the marlborough faults indicate a consistent post early pliocene regional clockwise rotation of about 20 an additional rotation of about 10 is evident at many localities near the termination of the clarence fault it is proposed that the additional rotation relative to the rest of the region is caused by a velocity gradient that likely exists between the active awatere fault and the termination of the clarence fault the existence of such a velocity gradient is consistent with inferences from geodetic strain data which suggest that one third of the displacement in the marlborough fault system occurs between the awatere and clarence faults the kinematics of rotation can be modelled by treating the area as a rigid block that pivots about the termination of the clarence fault the block rotation model satisfies field constraints on the styles of deformation observed at the boundaries of the block and is consistent with available paleomagnetic and geodetic data

using dissolved h2o in rhyolitic glasses to estimate palaeo ice thickness during a subglacial eruption at blahnukur torfajokull iceland the last decade has seen the refinement of a technique for reconstructing palaeo ice thicknesses based on using the retained h2o and co2 content in glassy eruptive deposits to infer quenching pressures and therefore ice thicknesses the method is here applied to blahnukur a subglacially erupted rhyolitic edifice in iceland a decrease in water content from 0 7 wt at the base to 0 3 wt at the top of the edifice suggests that the ice was 400 m thick at the time of the eruption as blahnukur rises 350 m above the surrounding terrain this implies that the eruption occurred entirely within ice which corroborates evidence obtained from earlier lithofacies studies this paper presents the largest data set 40 samples so far obtained for the retained volatile contents of deposits from a subglacial eruption an important consequence is that it enables subtle but significant variations in water content to become evident in particular there are anomalous samples which are either water rich up to 1 wt or water poor 0 2 wt with the former being interpreted as forming intrusively within hyaloclastite and the latter representing batches of magma that were volatile poor prior to eruption the large data set also provides further insights into the strengths and weaknesses of using volatiles to infer palaeo ice thicknesses and highlights many of the uncertainties involved by using examples from blahnukur the quantitative use of this technique is evaluated however the relative pressure conditions which have shed light on blahnukur s eruption mechanisms and syn eruptive glacier response show that despite uncertainties in absolute values the volatile approach can provide useful insight into the mechanisms of subglacial rhyolitic eruptions which have never been observed

a possible explanation of gravity anomalies over mid ocean ridges gravity fields over the crests of slow spreading mid ocean ridges are characterized by small amplitude free air gravity anomaly lows 30 70 mgal with wavelengths of 40 60 km flanked by smaller gravity highs in general the amplitude and wavelength of these gravity lows decrease with increasing spreading rate until at fast spreading ridges 5 cm yr free air gravity highs 10 20 mgal are observed previous explanations of these anomalies which involve uncompensated ridges thermally expanded ridges and elastic plate compensation models are generally not consistent with the geological evidence regarding the nature of the crust and upper mantle beneath the ridge crest in particular the postulated presence of wide zones of partial melt in the uppermost mantle is inconsistent with petrologic data from mid ocean ridge basalts which indicates that primary melts are in equilibrium with and extracted from residual mantle at depths of 30 km or more in addition similar gravity lows observed over extinct spreading ridges suggest that the anomalies are not mainly due to any dynamic aspect of the accretion process taking place at active spreading centers geometrical models of mid ocean ridges derived from detailed structural and petrologic studies of the bay of islands ophiolite complex have been used to generate gravity anomalies over ridges with various spreading rates modeling results show that four main sources serve to define the amplitude and wavelength of the gravity anomaly the ridge topography the crustal level magma chamber the configuration of the isotherms near the ridge crest and a low density partially gabbroic cumulate root extending vertically into the mantle beneath the ridge systematic variations in the contributions from these sources with increasing spreading rate control the changes in character of the gravity anomaly from slow to fast spreading centers major contributions are found to come from the topography and from the lowdensity root which broadens with slower spreading rates resulting in both increasing amplitude and increasing wavelength with decreasing spreading rate at extinct spreading centers contributions from the magma chamber isotherms and topography gradually diminish with time once the ridge ceases to spread whereas the low density root remains a permanent part of the oceanic lithosphere and continues its contribution to the gravity field seismic evidence from slow spreading centers appears to support the existence of the lowdensity gabbroic root zone inferred from the study of the bay of islands ophiolite and the gravity analysis presented here

trace element partitioning at conditions far from equilibrium ba and cs distributions between alkali feldspar and undercooled hydrous granitic liquid at 200 mpa this study examines the effects of increasing supersaturation attained by single step liquidus undercooling t on the partitioning of barium and cesium between potassic alkali feldspar afs and hydrous granitic liquid at 200 mpa the investigation is motivated by trace element distribution patterns in granitic pegmatites which cannot be simulated by fractionation models using equilibrium partition coefficients and thus its purpose is to assess if how and why partition coefficients for compatible and incompatible trace elements may vary when crystal growth commences far from the crystal melt equilibrium boundary barium expands the liquidus stability field of potassic feldspar to higher temperatures such that liquidi for the ba rich 0 5 wt bao compositions used are 100 c higher than for ba absent analogues at low degrees of undercooling t 50 c values of dbaafs m 10 20 fall within the range of previous investigations as do values of dcsafs m 0 10 from experiments at all temperatures progressively greater undercooling is manifested in the run products by increasingly skeletal to cuneiform crystal morphologies increased compositional zonation of afs and the development of compositional boundary layers in glass whereas the partitioning behavior of cs incompatible is not measurably affected strong undercooling apparently causes the partitioning of ba highly compatible to deviate from equilibrium behavior feldspars produced by strong undercooling t 100 c are heterogeneous such that dbaafs m versus k k na varies linearly between the average value at 850 c and the equilibrium value appropriate to the temperature of growth hence high supersaturation accompanying undercooling produces feldspar compositions by isothermal growth which record a vestige of the liquid line of descent i e an ontogeny within zoned crystals which approximately tracks the feldspar liquidus from high temperature to the final low temperature of actual crystal growth such zoning patterns may mimic normal patterns produced by fractionation with decreasing temperature under near equilibrium near liquidus conditions increasing fluorine contents tend to exacerbate the effects of undercooling by inhibiting feldspar nucleation causing both k k na ratios and compatible trace element partitioning behavior in feldspar to deviate from equilibrium values this effect continues until nucleation lag is overcome whereupon a period of rapid growth from supersaturated liquid follows which is similar to that in f absent compositions electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1008 s00410 002 425 y

volcanic degassing of bromine and iodine experimental fluid melt partitioning data and applications to stratospheric chemistry abstract in order to understand the degassing behavior of heavy halogens in volcanic processes we experimentally studied the distribution of cl br and i between albite melt and hydrous fluids containing 0 01 2 wt of nacl nabr or nai respectively all experiments were carried out at 2 kbar and 900 c in rapid quench cold seal autoclaves with a run duration of 7 days the major element compositions and cl contents of the glassy run products were measured by electron microprobe bromine and iodine were measured by proton induced x ray emission fluid compositions were obtained by mass balance all halogens investigated were found to partition strongly into the fluid phase over the range of concentrations studied the halogen contents in the melt are proportional to the concentrations in the fluid the fluid melt partition coefficients df m are 8 1 0 2 for cl 17 5 0 6 for br and 104 7 for i the logarithm of df m is linearly correlated with the ionic radius of the halogenide ion on the basis of our experimental data we estimate the amount of bromine injected into the stratosphere by major volcanic explosions for the 1991 mount pinatubo eruption we obtain br yields of 11 25 kt as minimum estimates these numbers are comparable to the total annual influx of bromine into the stratosphere from all other natural and anthropogenic sources about 100 kt year since bromine is much more efficient in destroying stratospheric ozone than chlorine it could at least be partially responsible for the massive ozone depletion observed after the 1991 mount pinatubo eruption

two types of interannual variability of south china sea summer monsoon onset related to the sst anomalies before and after 1993 94 abstractan advance in the timing of the onset of the south china sea scs summer monsoon scssm during the period 1980 2014 can be detected after 1993 94 in the present study the interannual variability of the scssm onset is classified into two types for the periods before and after 1993 94 based on their different characteristics of vertical coupling between the upper and lower tropospheric circulation and the differences in their related sea surface temperature anomalies sstas on the interannual time scale type i scssm onset is characterized by anomalous low level circulation over the northern scs during 1980 93 whereas type ii scssm onset is associated with anomalies of upper level circulation in the tropics during 1994 2014 the upper tropospheric thermodynamic field and circulation structures over the scs are distinct between the two types of scssm onset and this investigation shows the importance of the role played by the spring sstas in the southern indian ocean sio and that of enso e

ion microprobe studies of water in silicate melts concentration dependent water diffusion in obsidian abstract the temperature dependence of water diffusivity in rhyolite melts over the range 650 950 c and pt h2o 700 bars is evaluated from water concentration distance profiles measured in glass with an ion microprobe diffusivities are exponentially dependent on concentration over this temperature range and vary from about 10 8 cm2 s at 650 c to about 10 7 cm2 s at 950 c at 2 wt water water solubility also varies with temperature at a rate of 0 14 wt per 100 c increase the avtivation energy ea appears to be constant at 19 1kal mole for 1 2 and 3 wt h2o comparison of these data with results for cation diffusion indicates that this value is a minimum ea for diffusion of any species in a rhyolite melt compensation plots of log10d0 the frequency factor versus ea indicate that hydrous rhyolite melts follow the same trend as anhydrous basalts d0 increases for h2o and ca2 1 as ea decreases this suggests that these molecules may diffuse by different mechanisms than do monovalent cations and that hydration of the melt affects diffusion of ca2 and h2o differently than it does monovalent cation diffusion the results imply that dramatic increases in cation diffusivities by hydration 1 may occur with additions of less than 1 wt h2o

asian summer monsoon onset barrier and its formation mechanism the onset process of asian summer monsoon asm is investigated based on diagnostic analysis of observations of precipitation and synoptic circulation results show that after the asm commences over the eastern bay of bengal bob around early may the onset can propagate eastwards towards the south china sea and western pacific but is blocked on its westward propagation along the eastern coast of india this blocking termed the monsoon onset barrier mob presents a gill type circulation response to the latent heating released by bob monsoon convection this convective condensation heating generates summertime wintertime vertical easterly westerly shear to its east west and facilitates air ascent descent the convection then propagates eastward but gets trapped on its westward path to the east of the central bob the surface air temperature sat cools faster than the underlying sea surface temperature sst due to monsoon onset thus more sensible heat flux supports the onset convection to propagate eastward to the west of the central bob however the land surface sensible heating over the indian peninsula is strengthened by the enhanced anticyclone circulation and air descent induced by the bob monsoon heating the strengthened upstream warm horizontal advection then produces a warm sat center over the mob region which together with the in situ cooled sst reduces the surface sensible heating and atmospheric available potential energy to prevent the occurrence of free convection therefore it is the change in both large scale circulation and air sea interaction due to bob summer monsoon onset that contributes to the mob formation

fluidization and melting of fault gouge during seismic slip identification in the nojima fault zone and implications for focal earthquake mechanisms 1 the record of physical processes that occur during seismic slip events is well preserved in fault rocks from the active nojima fault in japan the fault rocks formed at about 3 km depth and comprise thin alternating layers of very fine gouge and pseudotachylyte derived from granite each layer is thinner than a few millimeters and corresponds to one seismic slip event the very thin slip zone width suggests that some mechanisms of slip weakening operated and our studies of the fault rocks suggest that fluidization and melting of gouge were particularly important fluidized and nonfluidized gouges were distinguished using the detection probability of fragmented counterparts method it is known from granular material science that the phase transition from a grain friction regime to fluidization of granular materials can occur only by a very small decrease in volume fraction of solid grains once fluidization occurs the frictional resistance decreases abruptly to nearly zero even before thermal pressurization reaches its extreme state when fault gouge is melted frictional resistance is governed by the viscosity of melt which depends mainly on temperature chemical composition h2o concentration and the volume fraction of unmelted grains for each pseudotachylyte layer we estimated the temperature of melt using various temperature indices and measured volume fraction of unmelted grains we synthesized these data to reconstruct the change in viscosity during seismic slip events the melt viscosity is very high 107 9 pas during initial melting due to the combined effect of low temperature 750 800 c and large volume fraction of solid grains thus seismic slip is inevitably restrained instantaneously once this mechanical barrier is overcome the viscosity reduces continuously and dramatically as slip increases at 1000 c the viscosity reduces to 104pas and eventually to 10pas at 1280 c thus stress drops almost completely and rupturing tends to run away

identification of wrench faults using subsurface structural data criteria and pitfalls 1 many structures imaged with reflection seismic can resemble a wrench fault system because of the great structural diversity of strike slip faults and the wide range of contractional and extensional features associated with these faults because of these resemblances numerous faults are misidentified as wrench faults by workers using subsurface structural data credible identification requires combinations of profile and map criteria 1 narrow long straight throughgoing solitary master fault or zone of deformation 2 steep to moderate dip of the master fault at depth 3 offset of the top of basement 4 changes in relative upthrown side separation sense and or fault dip direction at depth or along the strike of the master fault 5 narrow fault slices within the master fault zone that steepen and join at depth negative and positive flower structures 6 different separation sense and orientation of relative upthrown side at these fault slices and 7 coeval en echelon flanking structures the identification should be confirmed with other criteria that refute alternative interpretations the main pitfalls to a reliable identification are not considering alternative structural styles and the misinterpretation of features or patterns that superficially resemble wrench systems the profile geometries of basement involved reverse or normal faults particularly those with structural inversion can resemble the single strand of convergent or divergent wrench faults profile geometries of flower structures can be mimicked by narrow contractional horsts or narrow extensional grabens complexly faulted anticlines or synclines splay faults fault zones intruded by salt or shale and overprinted structures pitfalls in interpreting map relationships are possible when structural patterns combine several tectonic influences are controlled by rock anisotropy or include elements hat are not coeval and if the patterns characteristic of other styles are misinterpreted many erroneous identifications of wrench faults can be eliminated by demonstrating that the investigated fault or feature lacks a straight trace lateral length or throughgoing continuity

seismic evidence for conjugate slip and block rotation within the san andreas fault system southern california the pattern of seismicity in southern california indicates that much of the activity is presently occurring on secondary structures several of which are oriented nearly orthogonal to the strikes of the major through going faults slip along these secondary transverse features is predominantly left lateral and is consistent with the reactivation of conjugate faults by the current regional stress field near the intersection of the san jacinto and san andreas faults however these active left lateral faults appear to define a set of small crustal blocks which in conjunction with both normal and reverse faulting earthquakes suggests contemporary clockwise rotation as a result of regional right lateral shear other left lateral faults representing additional rotating block systems are identified in adjacent areas from geologic and seismologic data many of these structures predate the modern san andreas system and may control the pattern of strain accumulation in southern california geodetic and paleomagnetic evidence confirm that block rotation by strike slip faulting is nearly ubiquitous particularly in areas where shear is distributed and that it accommodates both short term elastic and long term nonelastic strain a rotating block model accounts for a number of structural styles characteristic of strike slip deformation in california including variable slip rates and alternating transtensional and transpressional features observed along strike of major wrench faults domains of evenly spaced antithetic faults that terminate against major fault boundaries continued development of bends in faults with large lateral displacements anomalous focal mechanisms and differential uplift in areas otherwise expected to experience extension and subsidence since block rotation requires a detachment surface at depth to permit rotational movement low angle structures like detachments of either local or regional extent may be involved in the contemporary strike slip deformation of southern california a block nature of the crust also implies that not only will strains be inhomogeneous and likely concentrated along edge bounding faults but that local stress orientations will largely be responding to local kinematic constraints of block rotation and fault interaction this behavior coupled with the presence of possible regional detachments accounts for some of the precursory changes observed at considerable distances prior to large earthquakes and the triggering of seismicity or slip on nearby faults or around adjacent block edges although fault displacements along secondary structures associated with block rotations remain small they may still influence the nucleation and the characteristic rupture length of large earthquakes a more complete description of what these structures are and how they interact may prove critical to any fundamental understanding of the earthquake process and any realistic assessment of the regional seismic hazard

hydrous albite magmas at lower crustal pressure new results on liquidus h2o content solubility and h2o activity in the system naalsi3o8 h2o nacl at 1 0 gpa the system albite h2o serves as an important model for the generation of granitic magmas yet relatively few experimental investigations have focused on phase relations at high pressure this study reports new experimental results at 1 0 gpa and 690 1050 c on the temperature and liquid composition at vapor saturated melting the h2o content of undersaturated silicate liquids in equilibrium with albite the solubility of albite in h2o nacl fluids immediately below the solidus and the activity of h2o in hydrous naalsi3o8 liquids along the liquidus albite melts and dissolves congruently at all temperatures and salinities in the nacl absent system the temperature of vapor saturated melting of low albite confirmed by x ray diffraction is 695 5 c and the liquid composition is 18 14 1 35 wt h2o the temperature dependence of the fluid undersaturated liquidus curve in the system naalsi3o8 h2o varies with h2o wt w text h 2 text o according to t 2 0331 times 10 3 w text h 2 text o 3 1 6497w text h 2 text o 2 58 963w text h 2 text o 1235 5 circ text c indicating positive curvature in temperature composition coordinates and a dry melting temperature of 1235 c at 690 c immediately below the solidus albite solubility decreases drastically with nacl content of the fluid phase from 8 8 0 6 wt in the nacl free fluid to 2 at nacl concentration of only 10 mol experiments determining the activity of h2o a text h 2 text o in liquids at vapor saturated melting exploited low cl solubility in liquids and low albite solubility in the presence of h2o nacl fluids the maximum cl content of quenched glasses only 0 95 wt and very low albite solubility together make possible h2o activity measurement in melts equilibrated with nacl h2o solutions when combined with activity data for h2o nacl fluids experimentally determined a text h 2 text o along the liquidus is described by t 469 16a h 2 o l frac 1 2 93 382a h 2 o l 1235 5 circ c at 1 gpa h2o activities in hydrous albitic melts in h2o nacl fluids agree with those in the presence of h2o co2 fluids provided appropriate fluid mixing data are used our results constrain an asymmetric regular solution model for the mixing of na1 8al1 8si3 8o and h2o yielding margules parameters of w ab 25 56 0 54 and w text h 2 text o 10 50 pm 0 74 text kj text mol the results imply critical mixing of liquid and vapor at 1100 c using existing speciation models our results imply that h2o dissolved in hydrous albitic liquids is almost entirely in the form of molecular h2o oh concentration is negligible at temperatures near vapor saturated melting the results provide a more complete experimental foundation for modeling the system naalsi3o8 h2o at high pressure

dsdp hole 504b the first reference section over 1 km through layer 2 of the oceanic crust hole 504b provides a reference section for correlation of in situ petrological and geophysical studies with regional crustal models based on dredged samples and remote surveys and at least for the medium spreading rate costa rica rift hole 504b confirms that the main features of the upper part of an idealized ophiolite sequence occurs in the oceanic crust

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

solubility of excess alumina in hydrous granitic melts in equilibrium with peraluminous minerals at 700 800 c and 200 mpa and applications of the aluminum saturation index we have studied the controls on the alumi num saturation index asi molec al2o3 cao na2o k2o and the concentration of normative corundum of granitic liquids saturated in alumina by equilibrating peraluminous minerals with initially meta luminous haplogranitic minimum composition liquids at 700 800 c and 200 mpa at and below h2o saturation the asi and normative corundum increase with increasing h2o concentration in the melt 0 04 to 0 10 moles excess al2o3 per mole of h2o temperature and with addition of the non haplogranitic components fe mg and b the asi parameter and concentration of normative corundum cannot be used to monitor aal2o3 between different mineral assemblages and melt because other components that affect the solubility of alumina including h2o fe mg and b do not appear in their formulations asi and normative corundum however provide petrogenetic information about magmas gener ated by partial melting of strongly peraluminous proto liths by virtue of their regular and predictable variation with melt composition e g h2o concentration and temperature for the application of these data to natural rocks it is necessary to choose as an analogue system the asi solubility or normative corundum solubility relations of the most chemically complex peraluminous mineral present in the rock comparison of asi values of anatectic leucosomes and allochthonous leucogranites with experimentally predicted values suggests low h2o concentrations in melt during crustal partial melting rapid melt segregation before equilibration with restitic peraluminous phases is also suggested in some cases

phenomena of pulsation tectonics related to the breakup of the eastern north american continental margin abstract new data from the recent ipod drilling of dsdp site 534 in the blake bahama basin give a definite age for the spreading center shift involved in the breakup of the north american atlantic margin a basal callovian age 155 m y is determined for the blake spur magnetic anomaly marking this spreadingcenter shift that signals the birth of the modern north atlantic ocean this is some 20 m y younger than previously thought an implication of this younger age for the blake spur event is that very high spreading rates are now required for the jurassic outer magnetic quiet zone along the north american margin this association of a relatively high spreading rate with a magnetic quiet zone is similar to that for the mid cretaceous and implies a link between the processes controlling plate spreading which are in the upper mantle and the processes controlling the magnetic field which are in the outer core a theory of pulsation tectonics involving the cyclic eruption of plumes of hot mantle material from the lowermost mantle could explain the correlation plumes carry heat away from the core mantle boundary and later reach the asthenosphere and lithosphere to induce faster spreading the pulse of fast spreading in the jurassic apparently followed the breakup of continents bordering the north atlantic ocean other pulses of fast spreading appear to correlate with major ocean openings on various parts of the globe implying that this might be a prevalent process rifting of passive margins may be controlled by the more fundamental global processes described by the theory of pulsation tectonics

granitic melt viscosity and dike formation melt viscosity is an important variable controlling the rates of granitic melt separation and transport from its source region viscosities of granitic melts are significantly affected by changes in temperature and volatile content addition of 2 wt h2o to anhydrous peraluminous and metaluminous granitic melts reduces viscosity by six orders of magnitude at 800 c which is equivalent to the effect of raising the temperature by 500 c addition of 10 wt more h2o only decreases melt viscosity by approximately 1 5 additional orders of magnitude at higher temperatures the effect of h2o addition on melt viscosity is less significant at lower temperatures more significant the effect of pressure on hydrous granitic melt viscosities at crustal conditions is insignificant in comparison between 0 5 and 1 5 gpa the viscosity at 1000 c increases by 0 4 log units or less this effect can be ignored in most petrological calculations using newly acquired viscosity data at low h2o contents the baker model for the calculation of metaluminous and peraluminous granitic melt viscosities has been updated and expanded the new model can predict hydrous 0 3 12 3 wt h2o granitic 69 77 wt sio2 melt viscosities between 577 and 1200 c at crustal pressures the new granitic melt viscosities have been used to investigate the possibility of granitic melt transport via diking diking can be an efficient mechanism of damp granitic melt transport through the crust for granitic melts containing a minimum of 2 wt h2o if the lower crust has been sufficiently heated modeling the thermal history of basaltic intrusions and surrounding lower crust demonstrates that a sheet like intrusion 5 km thick or a suite of intrusions with the same aggregate thickness that were rapidly emplaced can provide enough heat to allow granitic magmas to migrate through much of the crust in dikes the generation of granitic dikes associated with thinner intrusions appears unlikely

paleomagnetism and paleosecular variations from the plio pleistocene golan heights volcanic plateau israel author s behar nicole shaar ron tauxe lisa asefaw hanna ebert yael heimann ariel koppers anthony ap ron hagai

magnetic lineations in marginal basins of the western pacific this paper separates the small oceanic basins around the western perimeter of the pacific ocean into marginal basins that have formed through back arc extension and those that apparently have not and reviews our knowledge of magnetic lineation patterns observed in possible and probable back arc basins magnetic lineations in these basins resemble lineations commonly associated with the world s mid oceanic spreading systems indicating that similar processes of crustal accretion occur in both tectonic environments in some back arc basins of the southwestern pacific magnetic lineation and other evidence suggest that back arc basins can evolve through the interaction and growth of multi plate systems because of the small time and space characteristics of back arc basins compared with the world s major oceanic spreading systems tectonic conditions favourable for the generation of back arc basins are either relaxed rapidly or easily interrupted models proposed to account for back arc basin development include a local models where back arc extension is mechanically driven by the downgoing slab and b global plate kinematics models where conditions favourable for back arc extension are governed by the motion of the overriding plate relative to the trench axis

geochemistry of the rhyolitic magmas from the streltsovka caldera transbaikalia russia a melt inclusion study the streltsovka caldera located in transbaikalia near the chinese mongolian border represents the largest uranium field associated with volcanics in the world all the rocks volcanics and underlying granites are deeply altered by hydrothermal fluids and their original major and trace element chemistry was strongly modified particularly their primary mobile element concentrations such as fluorine alkalis uranium to determine the primary geochemical characteristics of the magma associated with this giant ore field a study of melt inclusions has been undertaken on the rhyolites many of the melt inclusions are well preserved in quartz phenocrysts from strongly altered rhyolites of the caldera si al fe na k ca f cl mn ti p s and mg were analyzed by electron microprobe u by fission tracks and h u th la ce pr nd sm eu gd dy er yb lu sc ti v sr y nb ba hf by ion microprobe the presence in melt inclusions of daughter minerals such as fluorite f rich mica and ree fluocarbonate and the composition of the silicate melt after homogenization indicate that the streltsovka rhyolites correspond to highly fractionated mildly peralkaline melts 1 04 na k al 1 10 whereas whole rock analyses indicate a peraluminous composition the streltsovka rhyolitic melts are rich in f from 1 4 to 2 7 wt and in u 14 to 23 ppm they are relatively dry with a water content inferior to 2 4 h2o the low cl contents 0 2 cl in melt inclusions of the present study may be related to the mildly peralkaline character of the streltsovka melts nk al 1 04 to 1 10 these melts are rich in ree and present moderate lree fractionation low hree fractionation and a strongly negative eu anomaly the similar ree contents of tulukuevskoe melt inclusions and whole rock indicate that there was no significant fractionation after trapping of the magma on the other hand the glasses from krasny kamen and streltsovskoe rhyolites are richer in hree than the whole rock this agrees with an ree saturation of the magma at the trapping time that is confirmed by the crystallization of parisite as a daughter mineral in melt inclusions melt temperatures obtained from homogenization of the inclusions are relatively high for such magma 1015 30 c and may be overestimated because of a possible volatile loss since the rhyolite formation the lower th 1000 20 c obtained in tulukuevskoe inclusions agrees with their higher f content 2 2 to 3 2 the higher homogenization temperature of krasny kamen inclusions also agrees with the lower f content 0 6 to 0 8

major marine cycles in the mesozoic the cycles postulated by fischer 1979 are considered in the light of the mesozoic stratigraphical and palaeontological record it is suggested that the most important events were i the late permian regression ii the late mid triassic transgression iii the late late transgression iv the late early jurassic transgression v the late mid jurassic transgression vi the end jurassicre gression vii the late early cretaceous transgression viii the end cretaceous regression these are related to episodicity in ocean floor spreading climatic changes and major happenings in the history of the shallow marine benthos

continental crust beneath the agulhas plateau southwest indian ocean the agulhas plateau lies 500 km off the cape of good hope in the southwestern indian ocean acoustic basement beneath the northern one third of this large aseismic structural high has rugged morphology but basement in the south is anomalously smooth excepting a 30 to 90 km wide zone with irregular relief that trends south southwest through the center of the plateau seismic refraction profiles across the southern plateau indicate that the zone of irregular acoustic basement overlies thickened oceanic crust and that continental crust locally thinned and intruded by basalts underlies several regions of smooth acoustic basement recovery of quartzo feldspathic gneisses in dredge hauls confirms the presence of continental crust the smoothness of acoustic basement probably results from erosion perhaps initially subaerial of topographic highs with redeposition and cementation of debris in ponds to form high velocity beds basalt flows and sills also may contribute locally to form smooth basement the rugged basement of the northern plateau appears to be of oceanic origin a plate reconstruction to the time of initial opening of the south atlantic places the continental part of the southern plateau adjacent to the southern edge of the falkland plateau and both abut the western mozambique ridge both the agulhas and falkland plateaus were displaced westward during initial rifting in the early cretaceous formation of an rrr triple junction at the northern edge of the agulhas continental fragment during middle cretaceous time may explain the origin of the rugged thickened oceanic crust beneath the northern plateau as well as the apparent extension of the continental crust and intrusion of basaltic magmas beneath the southern plateau

quantitative models linking igneous amphibole composition with magma cl and oh content minerals of the amphibole group are found in igneous rocks on earth and other rocky bodies since the o 3 site of amphibole can contain oh o 2 f and cl amphibole composition provides important information about water and halogen contents oxidation state and other features of its formation and alteration environments however the complexity of amphibole crystal chemistry means this information is difficult to extract furthermore it has been regular practice in the era of the electron microprobe to neglect h and fe 3 analyses for amphibole critically reducing the amount of information available in amphibole analyses in the literature we have assembled models and insights from previous work to create a methodology that allows the estimation of magmatic h 2 o and cl contents from existing amphibole analyses since the methodology requires use of a cation norm we begin with a deeper investigation of the consequences of different cation normalization schemes for amphibole analyses and provide grounds for deciding which scheme best fits a given amphibole analysis we then show how the existing model of popp and coworkers can be reversed to estimate the oh and o 3 o 2 contents of amphiboles in synthesis experiments using a synthetic data set collected from the literature 39 amphibole analyses we calibrate a partitioning model for the oh cl competition on the o 3 site of igneous amphiboles k cl x cl x oh amphibole cl oh melt ln k cl 6 59 k na a 0 679 mg 0 487 f 6 e where x signifies a mole fraction of an anion on the o 3 site cl and oh signify melt mole fractions of the anion in question on a one oxygen stolper zhang basis k na a mg and 6 fe signify the amount of each component in the amphibole in atoms per amphibole formula unit with a denoting vacancies on the amphibole a site we then combine the popp et al model with our new model to link the occupancy of the amphibole o 3 site and other crystal chemical parameters to the cl and h 2 o content of melts crystallizing amphibole the competition between oh and cl for this site can be used to calculate the melt and amphibole oh h 2 o contents as well as the speciation of fe in amphibole provided that the cl content of both the amphibole and its coexisting melt is known without analyzing either phase for h or fe 3 fe 2 while the models in this paper should be recalibrated using future experimental data this work shows that considerably more information about the volatile contents of magmas can be gleaned from amphibole than previously shown and provides additional information about the crystal chemistry of amphibole and how it affects cl partitioning into minerals of this group

a possible precursor of the south china sea summer monsoon onset effect of the south asian high in climatology the south china sea scs summer monsoon scssm generally onsets in pentad 28 16 20 may the eastward extension of the south asian high into the scs in pentad 27 is a possible precursor to the scssm onset in the upper troposphere the south asian high sah warms the air by inducing the positive potential vorticity advection which strengthens precipitation over the southern scs when local convection becomes strong enough to decrease the vertical temperature gradient in pentads 28 29 the upper level warming center overlies the subcloud warm region over the scs to satisfy the requirement of the angular momentum conservation a cross equatorial flow then forms together with strong vertical easterly wind shear and deep monsoon convection over the scs marking the full establishment of the scssm the abrupt change in the sah in may could therefore be an early indicator of the onset of the scssm

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

h 2 o solubility in basalt at upper mantle conditions this study presents a new experimental approach for determining h2o solubility in basaltic melt at upper mantle conditions traditional solubility experiments are limited to pressures of 600 mpa or less because it is difficult to reliably quench silicate melts containing greater than 10 wt dissolved h2o to overcome this limitation our approach relies on the use of secondary ion mass spectrometry to measure the concentration of h dissolved in olivine and on using the measured h in olivine as a proxy for the concentration of h2o in the co existing basaltic melt the solubility of h2o in the melt is determined by performing a series of experiments at a single pressure and temperature with increasing amounts of liquid h2o added to each charge the point at which the concentration of h in the olivine first becomes independent of the amount of initial h2o content of the charge added adsorbed h2o indicates its solubility in the melt experiments were conducted by packing basalt powder into a capsule fabricated from san carlos olivine which was then pressure sealed inside a ni outer capsule our experimental results indicate that at 1000 mpa and 1200 c the solubility of h2o in basaltic melt is 20 6 0 9 wt 2 standard deviation this concentration is considerably higher than predicted by most solubility models but defines a linear relationship between h2o fugacity and the square of molar h2o solubility when combined with solubility data from lower pressure experiments further our solubility determination agrees with melting point depression determined experimentally by grove et al 2006 for the h2o saturated peridotite solidus at 1000 mpa melting point depression calculations were used to estimate h2o solubility in basalt along the experimentally determined h2o saturated peridotite solidus the results suggest that a linear relationship between h2o fugacity and the square of molar solubility exists up to 1300 mpa where there is an inflection point and solubility begins to increase less strongly with increasing h2o fugacity

tectonic analysis of the dead sea rift region since the late cretaceous based on mesostructures we have measured the orientations of small faults slickensides tectonic stylolites vein with secondary mineralization small folds and dikes in israel and sinai these structures are indicators of paleo stress or strain and provide the pattern of tectonic deformation data were collected at 130 stations most with tens of separate measurements most stations showed consistent deformation stations were located on exposures ranging from precambrian crystalline rocks to pleistocene sediments we have defined two tectonic stress fields each relatively uniform in both time and space one stress field with dominating maximum horizontal compression trending w to wnw in the late cretaceous to eocene rocks in the folds and plateaus west of the dead sea rift the second field with dominating horizontal extension trending e to ene in all rocks inside the rift and proximal thereto the first stress field is called the syrian arc stress and the second is called the dead sea stress a change in style of tectonic deformation which corresponds to the two stress fields is manifested also in the major structures in israel the late cretaceous to neogene deformation is characterized by long wavelength folds and monoclines whereas the neogene to recent deformation is characterized by normal and strike slip faults and volcanic activity

variations in water content in opal a and opal ct from geyser discharge aprons abstract opal a sio2 nh2o and its diagenetic derivative opal ct are found in environments that range from the deep ocean floor to terrestrial spring geyser systems although the loss of water may be a critical factor in the transition from opal a to opal ct analytical difficulties in determining the distributions and quantities of molecular water h2omol and silanols h2osioh has hindered a full understanding of the processes involved with this diagenetic transition electron microprobe emp and micro fourier transform infrared ftir analyses of opal a and opal ct collected from geyser discharge aprons on iceland and the north island of new zealand produce compatible and reliable derivations of the total weight water in opal a and opal ct provided that they contain 1 wt of other elements such as al emp analyses produce excellent results where microscale variations in total water content are required but it cannot determine if that water is formed of molecular water h2omol or silanols h2osioh in contrast ftir analyses yield total water molecular water and silanol contents of the opal microscale variations however are commonly masked because the scale of ftir analysis is coarser than that for emp analyses analyses of sinters from iceland and new zealand show that the opal a contains 2 1 12 1 average 7 3 wt total water whereas the opal ct contains 1 0 8 9 average 5 5 wt total water based on ftir analyses the opal a contains 1 2 9 8 average 6 8 wt molecular water and 0 4 2 4 average 1 0 wt silanols compared to opal ct which contains 3 8 8 2 average 6 7 wt molecular water and 0 1 0 7 average 0 2 wt silanols the dual usage of emp and ftir analyses provide important information on the distribution of different types of water in opal a and opal ct irrespective of the environments where they formed

neogene strike slip faulting in sakhalin and the japan sea opening we describe structural data from a 2000 km n s dextral strike slip zone extending from northern sakhalin to the southeast corner of the japan sea satellite images field data and focal mechanisms of earthquakes in sakhalin are included in the interpretation since miocene time the deformation in sakhalin has been taken up by n s dextral strike slip faults with a reverse component and associated en echelon folds narrow en echelon neogene basins were formed along strike sup faults and were later folded in a second stage of deformation we propose a model of basin formation along extension al faults delimitating dominos between two major strike slip faults and subsequent counterclockwise rotation of the dominos in a dextral transpressional regime basins becoming progressively oblique to the direction of maximum horizontal compression and undergoing shortening the association of both dextral and compressional focal mechanisms of earthquakes indicates that the same transpressional regime still prevails today in sakhalin we present fault set measurements undertaken in noto peninsula and yatsuo basin at the southern end of the sakhalin east japan sea strike slip zone early and middle miocene formations recorded the same transtensional regime as observed along the west coast of ne honshu during the early and middle miocene the strike slip regime was transpressional to the north in sakhalin and hokkaido and transtensional to the south along the west coast of ne honshu as far as noto peninsula and yatsuo basin dextral motion accommodated the opening of the japan sea as a pull apart basin with the tsushima fault to the west the opening of the japan sea ceased at the end of the middle miocene when transtension started to change to e w compression in the japan arc subduction of the japan sea lithosphere under the japan arc started 1 8 ma ago the evolution of the stress regime from transtensional to compressional in the southern part of the strike slip zone is related to the inception of the subduction of the young philippine sea plate lithosphere under the japan arc during the late miocene subduction related extension is a necessary condition for the opening of the japan sea two possible mechanisms can account for dextral shear in this area 1 counterclockwise rotation of crustal blocks due to the collision of india with asia 2 extrusion of the okhotsk sea block squeezed between the north america and eurasia plates

sea floor lava fields on the east pacific rise a seabeam and seamarc i survey of a seamount group located several kilometres west of the axis of the east pacific rise epr at lat 9 53 n defines the existence of a large submarine lava field at the base of one of the volcanoes mib the field must be relatively young with respect to the surrounding terrain because lavas lap up against the base of mib seamount obscuring older erosional terrain and extend out over the faulted sedimented terrain of the flank of the epr volcanic cones within the lava field are aligned with the strike of fault scarps that are buried by the lavas mib seamount is characterized by a large well developed caldera and we suggest that the lava field was created during a recent volcanic episode when magmas migrated laterally away from the seamount9s reservoir along preexisting faults parallel to the ridge axis the withdrawal of magmas from the mib reservoir into the flanking parasitic eruptive plumbing system created the lava field and deflated the seamount summit this event contributed to the development of the mib caldera draining of shallow level magma chambers under seamounts by pressure controlled basal flank eruptions that form lava fields is an important mechanism for the development of seamount morphology

search for a seasonal trend in earthquake occurrence in the hellenic arc abstract a search for a seasonal trend for earthquakes in the hellenic arc area was carried out considering main instrumental and shallow m 5 2 as well as intermediate depth m 6 0 events the seasonal trend was found to be statistically significant at the 95 level for m 6 0 intermediate depth events whereas no such trend was found for shallow events

thermal infrared spectral character of hawaiian basaltic glasses multispectral thermal infrared remote sensing of hawaiian basalts younger than a few hundred years old can be used to discriminate basalt lava flows that are difficult to map with visible and near infrared images laboratory thermal infrared reflectance spectra of the exposed surfaces of mauna loa and kilauea basalts show systematic changes with age fresh glass collected from active lava flows shows a broad reflectance feature between 8 and 12 m indicative of a strong degree of disorder after a few weeks of exposure to the environment the spectra of the top surfaces of samples begin to exhibit spectral features suggestive of ordering into silicate chainlike and sheetlike units with progressive aging features of apparent sheetlike structures become the preferred mode as soon as 3 years after emplacement a silica rich coating can begin to develop on the surfaces adding another spectral feature to the laboratory reflectance measurements the thermal infrared multispectral scanner tims with six channels between 8 and 12 m has been used to take advantage of these spectral differences in basalts to map flows in hawaii remote sensing instruments with increased spectral resolution in the thermal infrared would aid in further discrimination of basalts with more subtle differences in age quenching and weathering histories

h2o in rhyolitic glasses and melts measurement speciation solubility and diffusion dissolved h2o in silicate melts and glasses plays a crucial role in volcanic eruptions on terrestrial planets and affects glass properties and magma evolution in this paper major progress on several aspects of the h2o melt or glass system is reviewed consistency among a variety of data is investigated discrepancies are evaluated and confusion is clarified on the infrared measurement of total h2o and species concentrations calibration for a variety of glasses has been carried out at room temperature the measurements for h2o in rhyolitic glasses have undergone the most scrutiny resulting in the realization that absorptivities for the near infrared bands depend on total h2o content although the variation of the absorptivities does not seem to significantly affect the determination of total h2o it does affect the determination of molecular h2o and oh species concentrations calibration of the infrared technique for h2o in rhyolitic glasses still needs much improvement especially at high total h2o furthermore it is now almost certain that the molar absorptivities also depend on the measurement temperature in in situ studies hence it will be necessary to carry out calibrations in situ at high temperatures on h2o speciation results from two experimental approaches the quench technique and the in situ technique are very different leading to controversy in our understanding of true speciation a solution is presented to reconcile this controversy it is almost certain that the quench technique does not suffer from a quench problem but interpretation of in situ results suffered from ignoring the dependence of the molar absorptivities on measurement temperature accurate calibration at high temperatures is necessary for the quantitative application of the in situ technique to h2o speciation in silicate melts and glasses on h2o solubility in silicate melts recent experimental work has significantly expanded the t p range of solubility measurements and recent solubility models fill a gap for predicting solubility for a wide range of melt compositions i present a solubility model for rhyolitic and quasi rhyolitic melts over a wide range of t and p 500 1350 c 0 8 kbar by incorporating the role of speciation the solubility model is able to recover the experimental solubility data and has extrapolative value although the partial molar volume of h2o derived from the solubility model differs from that derived from density measurements on h2o diffusion recent studies on h2o diffusion in a quasi rhyolitic melt at 800 1200 c 0 5 5 kbar and up to 7 total h2o not only provide important new diffusion data but are also challenging earlier understanding of h2o diffusion based on data in rhyolitic glasses at 400 550 c 1 bar and 0 2 1 8 total h2o a comparison between the earlier model and recent data is made the recent high temperature diffusivities at total h2o 2 can be predicted by the earlier model however at higher total h2o the earlier model fails new work is under way to understand the diffusion mechanisms at high h2o contents

evidence for small scale mantle convection from seasat altimeter data evidence for the early development of convective instability in the thermal boundary layer associated with cooling plates has been found from gravity anomalies and residual sea surface heights derived from seasat altimeter data subtle lineated patterns trending in the direction of plate motion in the hot spot reference frame are observed over the younger portions of the fast moving pacific and indo australian plates in particular for the east central pacific ocean the seasat derived data sets reveal lineations with 1 wavelengths in the range 150 500 km perhaps increasing with plate age and 2 peak to trough amplitudes of 5 20 mgal for gravity anomalies the lineated pattern over the pacific plate which first becomes discernable over seafloor 5 to 10 m y old west of the east pacific rise is clearly oblique to the trends of the prominent pacific farallon fracture zones onset of convective instability at such early ages can be understood if young oceanic lithosphere is underlain by a layer having a viscosity of about 1018 pa s 1019 p which is about 3 orders of magnitude less than mantle viscosity inferred from postglacial rebound studies recent numerical studies of convection in fluids with a temperature and pressuredependent viscosity support an early onset time for convective instability and low viscosity zones in the upper mantle beneath young lithosphere such low viscosity zones may correspond to similarly located regions of low shear wave velocities resolved through studies of surface waves

different types of cold vortex circulations over northeast china and their weather impacts abstracta deep and cold vortex circulation often occurs over northeast china known as the northeast china cold vortex nccv the phenomenon is most active from may to mid june and can lead to extremely cold local temperatures this study used rotated principle component analysis to categorize nccv events into four types which were characterized by ridges or blocks over the following regions lake baikal bkl the yenisei river valley yns the ural mountains ur and the yakutsk okhotsk region yo on the intraseasonal time scale it was found that bkl and yns type nccvs formed when the wave train height anomalies originating from the north atlantic and europe propagated to east asia in contrast yo and ur type nccvs formed in conjunction with the development of a meridional dipole pattern over northeast asia the existence of a blocking type circulation over the yakutsk okhotsk region favored maintenance of the nccv circulation for the long lived more than 5 days nccv events of the four type

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

cordilleria a newly defined canadian microcontinent palaeomagnetic data and geological field evidence indicate that most of the western canadian cordillera lay 1 500 km south of its present position in the early cretaceous we suggest that this region comprised a microcontinent termed cordilleria which moved on the kula plate and collided with the craton 100 myr ago to form first the mackenzie mountains and then the rockies

the evolution of craters and calderas on young seamounts insights from sea marc i and sea beam sonar surveys of a small seamount group near the axis of the east pacific rise at 10 n a northwest trending group of seamounts located just west of the east pacific rise epr axis has been mapped using high resolution sea marc i side scan sonar and sea beam multibeam bathymetry these seamounts have 9 13 km basal diameters and the shapes of the volcanos change from conical domes near the epr axis to truncated cones and larger elliptical truncated cones farther away from the rise axis the detailed resolution of constructional volcanic features on these seamounts and the progressive development of summit depressions craters to large complex calderas and summit plateaus suggest to us a succession of evolutionary stages through which seamounts grow our evolutionary scheme for constructing these volcanos calls for the development of satellite extrusive centers around the base of a growing seamount which serve to drain off magmas and precipitate summit collapse the creation of a summit depression on a seamount will structurally constrain the style of eruptive volcanism to be principally along ring fractures which localize vents around the margin of a crater or caldera the concentration and channelization of volcanic eruptions around the top of the volcano lead to a progradation of the summit area and the establishment of a summit plateau the steep sides of a seamount reflect growth of the summit area out over the upper flanks of the volcano caused by continued eruption of lavas around the margin of the caldera the steep constructional slopes are sites for vigorous mass wasting that shapes and modifies flank terrain as a seamount evolves the crestal topography is the product of many volcanic cycles characterized by filling and subsequent draining of the caldera and expansion of caldera area through progressive collapse and migration of primary magmatic conduits the final phase of volcanism may be a calderafilling episode that builds a rough conical mount over the summit plateau

evidence for extensive basalt flows on the sea floor spatially limited strong acoustic reflectors interbedded with turbidite sediments appear in abundance in the region flanking the dellwood knolls northeast pacific where turbidite sediments nearly cover a newly formed spreading center near the continental margin off central british columbia in the median valley similar reflective layers are seen within the sediments as well as on the sediment surface and the conclusion has been made that all of the strong reflections are from extensive basalt flows which have had their source at the dellwood knolls and have been subsequently buried by rapid sedimentation the smooth gently sloping turbidite sediment surface appears to provide an ideal base over which flows can travel easily some of the flows are seen as far as 60 km from their source evidence for the existence of extensive flows is also found on the juan de fuca ridge where at one location the regional topographic relief of the axial valley floor along a 30 km section of the ridge axis is only 30 m such extreme low relief must be due in part to extensive basalt flows a simple model for the cooling of an underwater flow yields the general dependence of the flow extent on such parameters as the flow thickness and initial temperature as an example a flow 1 m thick can probably travel several kilometres if erupted at 1 250 c even the most extensive flows observed need be only about 3 m thick if erupted at this temperature

extremely early summer monsoon onset in the south china sea in 2019 following an el nino event abstractthe el nino southern oscillation enso is regarded as one of the most important factors for onset of the south china sea summer monsoon scssm previous studies generally indicated that a

partial melting of metabasic rocks and the generation of tonalitic trondhjemitic granodioritic ttg crust in the archaean constraints from phase equilibrium modelling abstract rocks of tonalitic trondhjemitic granodioritic ttg composition preserved in archaean terranes represent fragments of the earth s earliest formed continental crust and are thought to have formed via partial melting of hydrated metabasalt the geodynamic environments in which such high grade metamorphism and anatexis may have occurred in the early earth is strongly debated constraining the pressure p and temperature t conditions at which melts of appropriate composition can be derived from protoliths containing plausible mineral assemblages is central to addressing this question phase equilibrium modelling has been undertaken for an enriched archaean tholeiite bulk composition a suggested protolith for early earth ttg magmas using newly parameterised thermodynamic models that were specifically developed to evaluate the anatectic behaviour of metabasalt assuming minimal h 2 o saturation at the wet solidus the potential fertility of the studied metabasalt is greatest if the solidus is crossed at a pressure of 11 kbar where the solidus temperature reaches a minimum of 610 c major element compositions and proportions of calculated partial melts show the best correlation with those of natural archaean ttgs when in the p t range 800 950 c and 10 18 kbar which we suggest are optimal conditions for their petrogenesis normative geochemistry suggests that these melts would crystallise to broadly trondhjemitic or tonalitic lithologies calculated modal proportions of garnet plagioclase amphibole and rutile in the residuum which control diagnostic trace element signatures in the melt also show the best agreement with natural and experimental data at these conditions importantly although partial melts calculated outside of this p t range still produce ttg like major element compositions and normative mineralogies they would poorly match the diagnostic trace element signatures of natural archaean examples owing to the absences of key minerals in the residuum this optimal p t range of 800 950 c and 10 18 kbar defined herein is most likely to characterise metamorphism of hydrated basalt at the base of a 40 km thick archaean oceanic plateau overthickened crust or else tectonic underplating via shallow subduction which we therefore suggest are the most likely tectonic settings for the formation of the first voluminous continental crust on the early earth

seasonal variation abrupt transition and intraseasonal variability associated with the asian summer monsoon in the gla gcm abstract in this paper a description of the global and regional features of the asian summer monsoon in the goddard laboratory atmospheres gla general circulation model gcm is presented based on a 10 yr 1979 1988 integration of the model under the atmospheric model intercomparison project it is found that the earliest signal of onset of the asian monsoon is represented by the emergence of convection over the indo china land bridge in early may followed by the sudden jump of the equatorial itcz intertropical convergence zone to 10 n over the south china sea and indian ocean in mid may this sudden jump is linked to an abrupt northward shift of the ascending branch of the local hadley circulation possibly stemming from symmetric instability of the basic flow in may in agreement with observations the model shows a pronounced intraseasonal oscillation along the equator and enhanced synoptic scale activities identified as easterly waves in the tropical and subtropical western pacific these int

extremely late onset of the 2018 south china sea summer monsoon following a la nina event effects of triple sst anomaly mode in the north atlantic and a weaker mongolian cyclone

electrical conductivity of dry and hydrous naalsi 3 o 8 glasses and liquids at high pressures we report the first study of electrical conductivities of silicate melts at very high pressures up to 10 gpa and temperatures up to 2 173 k impedance spectroscopy was applied to dry and hydrous albite naalsi3o8 glasses and liquids with 0 02 5 7 wt h2o at 473 1 773 k and 0 9 1 8 gpa in a piston cylinder apparatus using a coaxial cylindrical setup measurements were also taken at 473 2 173 k and 6 10 gpa in two multianvil presses using simple plate geometry the electrical conductivity of albite melts is found to increase with temperature and water content but to decrease with pressure however at 6 gpa conductivity increases rapidly with temperature above 1 773 k so that at temperatures beyond 2 200 k conductivity may actually increase with pressure moreover the effect of water in enhancing conductivity appears to be more pronounced at 6 gpa than at 1 8 gpa these observations suggest that smaller fractions of partial melt than previously assumed may be sufficient to explain anomalously high conductivities such as in the asthenosphere for dry melt at 1 8 gpa the activation energy at t 1 073 k is higher than that at t 1 073 k and the inflection point coincides with the rheological glass transition upon heating at 6 10 gpa dry albite glass often shows a conductivity depression starting from 1 173 k due to crystallization followed by rapid conductivity enhancement when temperature approaches the albite liquidus for hydrous melts at 0 9 1 8 gpa the activation energies for conductivity at 1 373 k are lower than those at 973 k with a complex transition pattern in between electrical conductivity and previously reported na diffusivity in albite melt are consistent with the nernst einstein relation suggesting the dominance of na transport for electrical conduction in albite melts

tectonic controls of phanerozoic sedimentary rock cycling the cyclic nature of the phanerozoic sedimentary rock distribution carbon sulphur coupling and material transfer among sedimentary reservoirs appears to be controlled by tectonic factors the distribution of preserved sedimentary mass in terms of rock mass remaining u geologic age shows a minimum c 300 350 ma ago which separates two subcycles of erosion and deposition of sedimentary rocks the older subcycle was interrupted because of the major continental collisions of the devonian and late carboniferous these collisions resulted in a reduction of outcrop areas of rocks of the older cycle relative to their masses leading to a decline in the probability of destruction and an increase in half life of these older sediments a strong correlation exists between the long term cyclicity in the phanerozoic global sea level curve and the distribution of carbon and sulphur among their major exogenic reservoirs this correlation is related to two principal tectonic modes of the phanerozoic oscillatory and submergent it is postulated that the submergent mode of active plate convergence obduction and subduction of sediments large ridge volume and high sea level gave rise to low erosion and sedimentation rates less restricted environments of carbonate deposition and relatively high atmospheric co 2 levels high temperatures resulting from an increased rate of production of co 2 from diagenetic and metamorphic reactions at subduction zones as sea level rose carbon was transferred from the sedimentary reservoir of reduced organic carbon to that of oxidized inorganic carbon in limestones whereas sulphur moved from the oxidized sulphate reservoir to the reduced sulphide reservoir as sea level fell reservoir transfers were opposite to those above culminating in the oscillatory mode of generally elevated continental interiors these reservoir transfers are consistent with secular changes observed in the distribution of 13 c and 34 s in sedimentary materials during the phanerozoic petrographic examination of phanerozoic oolite formations shows that ooids with preserved calcitic relict textures are characteristic of pre carboniferous carbonate rocks whereas ooids with relict textures indicative of initial aragonite mineralogy are dominant in rocks of younger age these changes in ooid mineralogy may be interpreted as reflecting changes in co 2 levels of the ocean atmosphere system consistent with the above tectonic considerations atmospheric co 2 levels were higher prior to carboniferous time favouring formation of calcitic ooids and skeletal parts after the carboniferous co 2 levels fell and aragonite and mg calcites of greater than 8 mol mg increased in abundance as precipitates

global tectonics since the breakup of pangea 180 million years ago evolution maps and lithospheric budget abstract pangea the earth s youngest single supercontinent broke up 180 million years ago tectonic plates were subsequently formed by dispersal of the continental fragments and accretion of new oceanic lithosphere the configurations of all the major lithospheric plates at 0 20 65 95 140 180 ma bp are reconstructed on six globes of the earth each with a radius of 10 cm it appears that plate boundaries maintain a remarkably close fit on model globes of constant radii if the reconstructions include the recovery of subducted spreading patterns this is illustrated with maps in equatorial orthographic oblique orthographic and transverse hammer aitoff projections the snug fit of the tectonic plates at every tested time since the breakup of pangea 180 ma bp is consistent with the theory of plate tectonics on a non expanding earth and contradicts rapidly expanding earth models the areas of oceanic lithosphere produced and consumed during the past 180 ma bp are estimated from surface measurements of the globes reconstructed on the basis of particular assumptions these measurements suggest a consistent increase in the production rate of oceanic lithosphere during the past 140 ma it was decided to revise the assumptions and see if alternative reconstructions of the ancient spreading patterns on the floors of the tethys and eo pacific oceans could avoid implying an increase of lithospheric production rates with time this appeared to be possible the revised maps suggest that ophiolites older than 180 ma bp may have been obducted in cenozoic collision zones of the himalayas andes rockies and the western part of the banda arc timor new guinea estimates of the ocean floor production and consumption budget appear to be quite similar for both map series and only the possible ranges are summarized here time averaged for the past 180 ma world wide production and consumption of oceanic lithosphere appears to have varied between 2 6 and 3 5 km2 a 1 at most the mean of world wide spreading velocities ranges between 2 4 and 3 5 cm a 1 and world wide means of subduction velocities lie between 4 2 and 6 3 cm a 1 more accurate estimates are possible on the basis of particular assumptions and have been specified for the various time intervals distinguished i e the neogene 0 20 ma bp palaeogene 20 65 ma bp upper cretaceous 65 95 ma bp lower cretaceous 95 140 ma bp and middle and upper jurassic 140 180 ma bp

overlapping spreading centres new accretion geometry on the east pacific rise in a detailed seabeam investigation of the east pacific rise epr from 8 n to 18 n a new kind of volcano tectonic geometry associated with fast spreading centres has been discovered figs 1 2 at several locations along the rise axis the neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast to a classic ridge transform ridge plate boundary however the offset ridge terminations overlap each other by a distance approximately equal to or greater than the offset they curve sharply towards each other and often merge into one another along strike separating the overlapping spreading centres oscs is a closed contour depression up to several hundred metres deep which is sub parallel to the trend of the oscs the region between the oscs is a complex zone of both shear and rotational deformation with no obvious transform parallel structures based on wax model studies of spreading centres we suggest here that transform faults fail to develop at fast spreading centres where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate spreading centre transform fault pattern the osc geometry is unstable and evolves rapidly one of the two oscs prevails while the other is abandoned a significant area of sea floor created at fast spreading rates may bear the imprint of this newly observed process

evidence of displaced terranes from permian to jurassic faunas around the pacific margins for the permian to jurassic time interval tethyan marine invertebrate faunas which are generally accepted as having lived at low latitude can be distinguished from less diverse higher latitude faunas displacement of these low latitude faunas to positions of high latitude around the pacific margins therefore provides key evidence for the movement of so called suspect or displaced terranes the fullest story so far has been worked out for the western margin of n america as far north as southern alaska but there is also convincing evidence for the substantial northward movement of continental segments along the ne asian margin as regards the southern hemisphere the torlesse terrane of new zealand appears to have moved a considerable distance southwards but there is no fauna1 evidence of comparable far travelled suspect terranes along the andean margin of south america not only tethyan and boreal but e and w pacific elements are detectable in the faunas and the distribution of these argues for a panthalassia studded with islands of various sizes fringing the adjacent continents rather than for the disintegration of a single continent pacifica

marine triassic faunas of north america their significance for assessing plate and terrane movements the distribution of marine triassic invertebrate faunas in north america is reviewed to recognize forms that may have paleolatitudinal significance

geoid pangea and convection abstract we show that the present geoid has a simple low order configuration with an axis of symmetry in the equatorial plane we show further that it is a tennis ball pattern with an equatorial high belt and a polar low one which is clearly controlled by the rotation of the earth finally we show that the outline of pangea between at least 200 ma and 125 ma ago lay along a great circle passing through the paleo poles of rotation thus it also had an axis of symmetry in the equatorial plane this hemispheric super continent configuration ended in middle cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading hotspot outbreaks and high sea level stands we interpret this evidence in terms of separate steady state lower mantle convection responsible for the present geoid weakly coupled to the upper mantle one this weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal the complete cycle from one supercontinent to the next might be of the order of 400 ma

magnetic properties of marine limestones numerous paleomagnetic investigations have been carried out on limestones but their rock magnetic properties have often been neglected in this review geological and rock magnetic factors which determine whether marine limestones are suitable for paleomagnetic study are summarized and laboratory techniques for the identification of the magnetic mineralogy are evaluated the conditions under which pelagic limestones form are especially favorable for the acquisition of a stable primary natural remanence nrm probably by a postdepositional alignment process the effectiveness and timing of acquisition of this remanence are influenced by the thoroughness of bioturbation other remanence components can be acquired during diagenesis in the soft sediment right after deposition or much later even in the indurated limestone the magnetic mineralogy of a limestone is difficult to describe optically because of the small grain size and low concentration magnetic techniques are more convenient direct analysis of extracted magnetic minerals is handicapped by the difficulty of obtaining a representative extract a particularly useful technique involves combined observations of isothermal remanent magnetization irm acquisition in strong fields up to at least 4 t and the subsequent destruction of this irm during stepwise or continuous thermal demagnetization the magnetic minerals most commonly identified by these techniques are magnetite goethite hematite and maghemite these magnetic minerals occur in different combinations in the marine limestones of central europe and the mediterranean realm pyrite is common in certain limestones where it can be the precursor of an unwelcome late goethite pyrrhotite may be responsible for unstable magnetization in the swiss helvetic limestones but otherwise is rare thermal demagnetization of some limestones causes changes of susceptibility and coercivity at quite low temperatures 300 400 c due to the breakdown of a metastable mineral such as maghemite goethite or pyrrhotite at high temperatures above 500 c pronounced changes of magnetic mineralogy occur in all limestones because of the growth of new magnetite this necessitates great care in interpretation of thermal demagnetization of high blocking temperature components and often results in observational difficulties due to viscous remanent vrm behavior of the newly formed magnetite vrm is a widespread component of nrm in many limestones but it can usually be removed effectively by standard magnetic cleaning techniques the susceptibility serves as a simple control of mineralogical change during heating and can serve as an indicator of lithologic variation of magnetic mineral concentration and type in magnetostratigraphic profiles the susceptibility is anisotropic and shows a classical depositional pattern of the distribution of principal axes however the probable postdepositional mechanism of nrm acquisition especially in bioturbated sediments implies that the anisotropy pattern results from postdepositional compaction of the sediment

textures water content and degassing of silicic andesites from recent plinian and dome forming eruptions at mount pelee volcano martinique lesser antilles arc previous petrological and phase equilibrium experimental studies on recent silicic andesites from mount pelee volcano have evidenced comparable pre eruptive conditions for plinian and dome forming pelean herein eruptions implying that differences in eruptive style must be primarily controlled by differences in degassing behaviour of the mount pelee magmas during eruption to further investigate the degassing conditions of plinian and pelean magmas of mount pelee we study here the most recent mount pelee s products p1 at 650 years b p 1902 and 1929 eruptions which cover a range of plinian and pelean lithologies for bulk rock vesicularities glass water contents glass inclusions in phenocrysts and matrix glasses and microtextures water contents of glass inclusions are scattered in the plinian pumices but on average compare with the experimentally deduced pre eruptive melt water content i e 5 3 6 3 wt whereas they are much lower in the dominant pelean lithologies crystalline poorly vesicular lithics and dome samples this indicates that the glass inclusions of the pelean products have undergone strong leakage and do not represent pre eruptive water contents the water content of the pyroclast matrix glasses are thought to closely represent the residual water content in the melt at the time of fragmentation determination of the water contents of both the pre eruptive melt and matrix glasses allows the estimation of the amount of water exsolved upon syn eruptive degassing we find the amount of water exsolved during the eruptive process to be higher in the pelean products than in the plinian ones typically 90 100 and 65 70 of the initial water content respectively the vesicularities calculated from the amount of exsolved water compare with the measured vesicularities for the plinian pumices consistent with a closed system near equilibrium degassing up to fragmentation by contrast the low residual water contents low groundmass vesicularities and extensive groundmass crystallization of the pelean products are direct evidence of open system degassing microtextural features including silica bearing and silica free voids in the pelean lithologies may represent a two stage vesiculation

vertical axis rotation of the upper portions of the north east rift of tenerife island inferred from paleomagnetic data abstract paleomagnetic sampling sites were established in 82 dykes along an 8 km long section of the north east rift zone nerz of tenerife canary islands spain of the 70 interpretable sites 16 are of normal polarity and 54 of reversed polarity four normal polarity sites and fifteen reverse polarity sites were excluded from the grand mean calculation for statistical reasons after inverting the reverse polarity sites through the origin the in situ grand mean yields a declination d 023 8 an inclination i 42 3 95 3 2 39 0 n 51 that is discordant to the expected late miocene to pleistocene field direction d 357 6 i 38 8 95 4 7 this discordance can be explained as either a 26 clockwise vertical axis rotation or a 28 wnw side down tilt about an average 009 horizontal tilt axis the sampled section is composed of numerous semi vertical dykes cutting mainly lava flow units that are sub horizontal and cross cut by steeply dipping faults 70 90 field evidence is therefore more compatible with a vertical axis rotation rather than a horizontal axis tilt of the drilled units we argue that this clockwise vertical axis rotation is likely related to strike slip movements that occurred along the edges of the collapse scars and accommodate the emplacement and growth of the underlying intrusive core and associated dykes six new 40ar 39ar age determinations constrain the main interval of dyke emplacement within the nerz between 0 99 ma and 0 56 ma the intrusive activity in the sampled section of the rift appears to have been almost continuous with several intrusion pulses that are probably related to flank destabilisation event s during the mid pleistocene our study thus demonstrates a long lived multi faceted history that shaped the nerz