dust a diagnostic of the hydrologic cycle during the last glacial maximum dust concentrations in ice of the last glacial maximum lgm are high in ice cores from greenland and antarctica the magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the lgm was about half of that at present this notion is consistent with a large decrease 5 c in ocean temperature during the lgm as recently deduced from measurements of strontium and calcium in corals

fluid absent melting of a layered crustal protolith implications for the generation of anatectic granites we report the result of h2o undersaturated melting experiments on charges consisting of a layer of powdered sillimanite bearing metapelite hq36 and a layer of powdered tonalitic gneiss agc150 experiments were conducted at 10 kbar at 900 925 and 950 c when run alone the pelite yielded 40 vol strongly peraluminous granitic melt at 900 c while the tonalite produced only 5 vol weakly peraluminous granitic melt at 950 c the pelite and the tonalite yielded 50 vol and 7 vol granitic melt respectively when run side by side the abundance of melt in the tonalite was 10 times higher at all temperatures than when it was run alone in the pelite the melt abundance increased by 25 vol when run alone biotite dehydration melting in the tonalite yielded orthopyroxene and garnet in addition to granitic melt when run side by side only garnet was produced in addition to granitic melt experiments of relatively short duration however also contained al rich orthopyroxene we suggest that the large increase in melt fraction in the tonalite is mainly a result of increased activity of al2o3 in the melt which lowers the temperature of the biotite dehydration melting reaction in the pelite the increase in the abundance of melt is caused by transport of plagioclase component in the melt from the tonalite layer to the pelite layer this has the effect of changing the bulk composition of this layer in the direction of minimum temperature granitic liquids our results show that rocks which are poor melt producers on their own can become very fertile if they occur in contact with rocks that contain components that destabilize the hydrous phase s and facilitate dehydration melting because of this effect the continental crust may have an even greater potential for granitoid melt production than previously thought our results also suggest that many anatectic granites most likely contain contributions from two or more different source rocks which will be reflected in their isotopic and geochemical compositions

protracted post collisional magmatism during plate subduction shutdown in early paleoproterozoic insights from post collisional granitoid suite in nw china abstract tectonic regimes display different styles worldwide during the early paleoproterozoic ranging from plate tectonic slowdown or shutdown to vigorous subduction related magmatism here we report a suite of early paleoproterozoic granitoids from the quanji massif in northwestern china that provides potential insights on the tectonic regime in this period the granitoids formed at 2 37 2 34 ga as evidenced by la icp ms zircon u pb ages these dioritic to granitic rocks with amphibole and biotite as the major mafic minerals display a wide range of sio2 55 8 66 2 wt low to moderate mgo 1 4 4 1 wt low to high k2o 1 6 5 9 wt and al2o3 16 3 21 5 wt with mg values in the range of 36 47 and relatively low cr 7 7 79 2 ppm and ni 2 3 19 3 ppm concentrations geochemically they correspond to high potassium calc alkaline i type granitoids with some showing dominantly adakitic but minor a type affinities both the i type and a type granitoids show moderately fractionated lree to hree and moderately to weakly negative eu anomalies however the adakitic granitoids display strongly fractionated ree patterns and weak negative to positive eu anomalies all the rock types from this suite show enrichment in liles and lrees and depletion in hfses ta nb the nd hf isotope data suggest that the granitoids were sourced from mesoarchean to neoarchean metamafic rocks in the lower crust the coeval nature of the complex genetic types of rocks in this suite suggest that their precursor magmas formed in an extensional tectonic regime similar to those previously reported for the 2 39 2 37 ga granitoids in central to eastern domains of the quanji massif our new results in conjunction with those from previous studies suggest protracted post collisional magmatism lasting for 50 myr along the periphery quanji massif following the cessation of plate subduction in the early paleoproterozoic

epidote in calcalkaline magmas an experimental study of stability phase relationships and the role of epidote in magmatic evolution experiments on tonalite and granodiorite were performed at conditions ranging from 2 1 to 18 kbar and 550 to 850 c to establish the magmatic stability field of epidote as a function of p t and f02 at water saturated conditions and f02 buffered by nno epidote has a wide magmatic stability field in tonalite at 13 kbar this field extends from the wet solidus at 630 to 790 0c the low pressure intersection of the magmatic epidote crystallization reaction and the h20 saturated tonalite solidus and hence the minimum pressure for magmatic epidote occurs at about 5 kbar the clapeyron slopes of epidote melting reactions are moderately positive in p t space at pressures below the intersection of the epidote melting and the gamet in reactions at 13 kbar 790 c at this intersection epidote reaches its maximal thermal stability 790 c in tonalite h20 in the presence of garnet that is above 14 kbar epidote melting reactions have steep negative clapeyron slopes in p t space at p t conditions near the low pressure intersection of the epidote melting reaction with the water saturated solidus experiments were also performed with f02 buffered by hm at these oxidizing conditions the magmatic stability field of epidote is enlarged down to a pressure of about 3 kbar in granodiorite the stability of epidote has been investigated at pressures from 7 5 to 18 kbar with respect to the tonalite the epidote out reaction is located almost at the same p t conditions at 10 kbar but the maximum thermal stability is about 50 c lower toward higher pressures although few experiments indicate that epidote stability does not increase dramatically with decreasing water activity at present state it is not possible to predict melting and crystallization behavior of epidote at waterundersaturated conditions modal abundances of epidote are low 05 vol in the presence of major 40 vol melt fractions thus epidote in calc alkaline magmatic rocks is not likely to affect major elements strongly by fractional crystallization

the δ15n of nitrate in the southern ocean consumption of nitrate in surface waters we report nitrogen isotope data for nitrate from transects of hydrocast and surface samples collected in the eastern indian and pacific sectors of the southern ocean focusing here on the data from the upper water column to study the effect of nitrate consumption by phytoplankton the 15n of nitrate increases by 1 2 from deep water into the antarctic summertime surface layer due to kinetic isotopic fractionation during nitrate uptake estimation of the nitrate uptake isotope effect from antarctic depth profiles yields values in the range of 5 6 in east indian sector and 4 5 in the east pacific sector surface transect data from the pacific sector also yield values of 4 5 the major uncertainty in the profile based estimation of the isotope effect involves the 15n of nitrate from the temperature minimum layer below the summertime antarctic surface layer which deviates significantly from the predictions of simple models of isotope fractionation for the subantarctic surface it is possible to distinguish between nitrate supplied laterally from the surface antarctic and nitrate supplied vertically from the subantarctic thermocline because of the distinctive relationships between the 15n and concentration of nitrate in these two potential sources our subantarctic samples collected during the summer and fall indicate that nitrate is supplied to the subantarctic surface largely by northward transport of antarctic surface water isotopic data from the pacific sector of the subantarctic suggest an isotope effect of 4 5 indistinguishable from the antarctic estimates in this sector

atlantic meridional overturning circulation during the last glacial maximum the circulation of the deep atlantic ocean during the height of the last ice age appears to have been quite different from today we review observations implying that atlantic meridional overturning circulation during the last glacial maximum was neither extremely sluggish nor an enhanced version of present day circulation the distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the atlantic only slightly greater than today however evidence from multiple water mass tracers supports a different distribution of deep water properties including density which is dynamically linked to circulation

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

unchanged nitrogen isotopic composition of organic matter in the south china sea during the last climatic cycle global implications the 15n of surface and down core sediments spanning the last 20 200 kyr from the entire south china sea scs ranges only from 3 0 to 6 5 with no correlation with discernible paleoclimatic oceanographic changes detailed profiles of the uppermost sediment column including fluff samples indicate a minor diagenetic overprint of 0 3 1 2 at the sediment water interface the absence of any correlation with reconstructed glacial interglacial changes in primary production terrigenous input and or sea level related basin configuration is attributed to a complete consumption of nitrate during primary production in this marginal basin during at least the last 140 000 years this in turn implies that the 15n of the nitrate used during primary production remained approximately constant during the last climatic cycle the proposed scenario infers an unchanged nitrogen isotopic composition of the western pacific subsurface nitrate between glacial and interglacial stages as well as during terminations and thus constrains proposed changes in the oceanic n inventory

complementary constraints from carbon 13c and nitrogen 15n isotopes on the glacial ocean s soft tissue biological pump a three dimensional process based model of the ocean s carbon and nitrogen cycles including 13c and 15n isotopes is used to explore effects of idealized changes in the soft tissue biological pump results are presented from one preindustrial control run pictrl and six simulations of the last glacial maximum lgm with increasing values of the spatially constant maximum phytoplankton growth rate max which accelerates biological nutrient utilization mimicking iron fertilization the default lgm simulation without increasing max and with a shallower and weaker atlantic meridional overturning circulation and increased sea ice cover leads to 280 pg more respired organic carbon corg storage in the deep ocean with respect to pictrl dissolved oxygen concentrations in the colder glacial thermocline increase which reduces water column denitrification and with delay nitrogen fixation thus increasing the ocean s fixed nitrogen inventory and decreasing 15nno3 almost everywhere this simulation already fits sediment reconstructions of carbon and nitrogen isotopes relatively well but it overestimates deep ocean 13cdic and underestimates 15nno3 at high latitudes increasing max enhances corg and lowers deep ocean 13cdic improving the agreement with sediment data in the model s antarctic and north pacific oceans modest increases in max result in higher 15nno3 due to enhanced local nutrient utilization improving the agreement with reconstructions there models with moderately increased max fit both isotope data best whereas large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well the best fitting models reproduce major features of the glacial 13cdic 15n and oxygen reconstructions while simulating increased corg by 510 670 pg compared with the preindustrial ocean these results are consistent with the idea that the soft tissue pump was more efficient during the lgm both circulation and biological nutrient utilization could contribute however these conclusions are preliminary given our idealized experiments which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes the analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes whereas carbon isotopes are sensitive to circulation changes and indicate well the three dimensional corg distribution nitrogen isotopes are more sensitive to biological nutrient utilization

deglacial climatic oscillations in the gulf of california a high resolution accelerator radiocarbon dated climate record of the interval 8 000 18 000 years b p from deep sea drilling project site 480 guaymas basin gulf of california shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation nonlaminated sediments are associated with cooler climatic conditions during the late glacial up to 13 000 years b p and from 10 300 to 10 800 years b p equivalent to the younger dryas event of the north atlantic region we propose that the changes from laminated varved to nonlaminated sediments resulted from increased oxygen content in pacific intermediate waters during the glacial and the younger dryas episodes and that the forcing for the latter event was global in scope prominent events of low 18o are recorded in benthic foraminifera from 8 000 to 10 000 and at 12 000 years b p evidence for an earlier event between 13 500 and 15 000 years b p is weaker maximum 18o is found to have occurred 10 500 13 500 and 15 000 years ago and beyond oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of pacific waters of intermediate depth during deglaciation or environmental changes within the gulf of california region several lines of evidence suggest that during deglaciation the climate of the american southwest was marked by increased precipitation that could have lowered salinity in the gulf of california recent modelling studies show that cooling of the gulf of mexico due to glacial meltwater injection which is believed to have occurred at least twice during deglaciation would have resulted in increased precipitation with respect to evaporation in the american southwest during summertime the timing of deglacial events in the gulf of mexico and the gulf of california supports such an atmospheric teleconnection

evidence of early cretaceous transpression in the sulu orogenic belt eastern china abstract recent studies have documented marine turbidites with syn sedimentary deformation features in the central sulu orogenic belt of eastern china these units preserve essential information on the late mesozoic evolution of the sulu orogenic belt referred to as the baxiandun formation the turbidites exhibit similar lithologic characteristics to nearby units such as the lingshandao formation that have been well studied even though precise geochronologic constraints are lacking for a more precise correlation this study reports detrital zircon u pb age data that correlate the baxiandun formation turbidites of the central sulu orogenic belt to the early cretaceous lingshandao formation we also report al in hornblende emplacement depth estimates for granitic intrusions of the sulu orogenic belt s laoshan mountain a sharp contact between the laoshan granites and the marine baxiandun formation indicates that the baxiandun basin rapidly subsided to the emplacement depth of the laoshan plutons lateral correlation among the marine turbidites the lingshandao and baxiandun formations combined with information established by previous studies indicates initiation of transpressional tectonics at 122 121 ma transpression ceased with the emplacement of the laoshan granites whose a1 type composition indicates a return to extensional tectonics at ca 111 ma

teleseismic time functions for large shallow subduction zone earthquakes broadband vertical p wave records are analyzed from 63 of the largest shallow subduction zone earthquakes which have occurred in the circum pacific in the last 45 yr most of the records studied come from a common instrument the pasadena california benioff 1 90 seismometer propagation and instrument effects are deconvolved from the p wave records using a damped least squares inversion to obtain the teleseismic source time function the inversion has the additional constraint that the time function be positive everywhere the period band over which the time functions are considered reliable is from 2 5 to 50 sec fourier displacement amplitude spectra computed for each of the 1 90 p wave trains indicate spectral slopes measured between 2 and 50 sec of 1 0 to 2 25 with an average value of 1 5 these values assume an average attenuation of t 1 0 the seismic moments derived from the p wave time functions compare well with other published values for earthquakes having moments smaller than 2 5 10 28 dyne cm m w 8 2 because the 1 90 seismometer has little response at very long periods this technique underestimates the moments of the very largest events the time functions are characterized using five parameters 1 spectral slope between 2 and 50 sec 2 roughness of the time function 3 multiplicity of sources 4 pulse widths of individual sources and 5 overall signal duration the 63 earthquakes studied come from 15 subduction zones with a wide range in the ages of subducted lithosphere convergence rates and maximum size of earthquakes comparing the time function parameters with age rate and m w of the subduction zone does not yield obvious global trends however most of the subduction zones do behave characteristically and can be grouped accordingly

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

differentiation conditions of a basaltic magma from santorini and its bearing on the production of andesite in arc settings santorini volcano in the aegean region greece is characterized by andesitic to silicic dominated explosive activity and caldera forming eruptions sourced from magmatic reservoirs located at various structural levels beneath the volcano there is a good understanding of the silica rich magmatism of the island whereas the andesite dominated volcanism and the petrogenesis of the parental mafic magmas are still poorly understood to fill this gap we have performed crystallization experiments on a representative basalt from santorini with the aim of determining the conditions of differentiation pressure temperature volatile fugacities and the parental magma relationship with the andesitic eruptive rocks experiments were carried out between 975 and 1040 c in the pressure range 100 400 mpa fo2 from qfm to nno 3 5 where qfm is quartz fayalite magnetite and nno is nickel nickel oxide with h2omelt contents varying from saturation to nominally dry conditions the results show that basalt phenocrysts within the basalt crystallized at around 1040 c in a magma storage reservoir located at a depth equivalent to 200 400 mpa pressure with 3 5 wt dissolved h2o and fo2 around qfm comparison with the xenocryst and phenocryst assemblages of the upper scoria 1 andesite shows that andesitic liquids are produced by fractionation of a similar basalt at 1000 c and 400 mpa following 60 80 wt crystallization of an ol cpx plag ti mag opx 6 pig ilm assemblage with melt water contents around 4 6 wt at santorini the andesitic low viscosity and water rich residual liquids produced at these depths segregate from the parent basaltic mush and feed the shallow magma reservoirs eventually erupting upon mixing with resident magma changes in prevailing oxygen fugacity may control the tholeiitic calc alkaline character of santorini magmas explaining the compositional and mineralogical differences observed between the recent thyra and old eruptive products from akrotiri

pressure temperature and time indicators in mafic schist their application to reconstructing the polymetamorphic history of vermont mineral chemistry and overgrowth relationships in mafic schist from vermont are shown to be sensitive indicators of pressure temperature and relative time and to be good chronicles of the paleozoic history of this polymetamorphic terrane within the common assemblage amphibole chlorite epidote plagioclase quartz ti phase carbonate k mica fe 3 oxide electron microprobe analyses show that increasing metamorphic grade as defined by intercalated pelitic schist is recorded by an increase in the edenite glaucophane and tschermakite contents of amphibole in the anorthite content of plagioclase and in the substitution of al vi f 2 ti al iv for fe 2 mg mn si in biotite chlorite and muscovite with increasing pressure the glaucophane component of amphibole increases for medium pressure metamorphism the albite oligoclase gap is in the garnet zone where amphibole has between 1 2 and 1 8 formula proportion al iv and al vi fe 3 ti cr this gap is below the garnet isograd in low pressure mafic schist where al iv and al vi fe 3 ti cr in the amphibole are both less than 0 6 mineral growth periods observed are characterized by metamorphic grade and facies series and are assigned to two ordovician taconic and two devonian acadian events silurian devonian mafic schist in northeastern vermont records two periods of low pressure devonian metamorphism these events are expressed by medium pressure and low pressure metamorphism in the cambrian and ordovician rocks to the west and south in the pre silurian rocks high pressure and medium pressure metamorphism is assigned to the ordovician the observed high pressure metamorphism is confined to a 110 by 40 km area along the green mountain anticlinorium axis in north central vermont

glacial interglacial modulation of the marine nitrogen cycle by high latitude o2 supply to the global thermocline 1 an analysis of sedimentary nitrogen isotope records compiled from widely distributed marine environments emphasizes the global synchrony of denitrification changes and provides evidence for a strong temporal coupling of these variations to changes in nitrogen fixation as previously inferred we explain the global coherence of these records by a simple physical control on the flux of dissolved oxygen to suboxic zones and the coupling to fixation via the supply of phosphorus to diazotrophs in suitable environments according to our hypothesis lower glacial stage sea surface temperature increased oxygen solubility while stronger winds in high latitude regions enhanced the rate of thermocline ventilation the resultant colder rapidly flushed thermocline lessened the spatial extent of denitrification and consequently n fixation during warm periods sluggish circulation of warmer less oxygen rich thermocline waters caused expansion of denitrification zones and a concomitant increase in n fixation local fluctuations in export productivity would have modulated this global signal

nitrogen isotope dynamics of the cariaco basin venezuela 1 we report 15n 14n measurements of water column nitrate and ammonium sinking particles and sediments from the cariaco basin an anoxic marine basin off the coast of venezuela water column denitrification occurring in the basin has only a very small isotopic imprint on nitrate in the basin because nitrate consumption is nearly complete in the actively denitrifying water near the oxic anoxic interface 275 m being free of a large denitrification signal the 15n of shallow thermocline nitrate is 3 5 significantly lower than the mean deep ocean nitrate 15n of 5 this may be due to the nitrification of newly fixed n whether it occurs within the basin or in open atlantic waters that flow into the cariaco over the sill the 15n 14n of the sinking flux in the deepest trap 1250 m is similar to that of thermocline nitrate as expected given the complete consumption of nitrate in the surface layer moreover the 15n 14n of the seafloor sediment is similar to that of the sinking flux as is common in environments of high export production low o2 and good organic matter preservation thus the modern cariaco basin records the 15n 14n of the thermocline nitrate which in turn may record the input of newly fixed n to the upper ocean be it local or more regional in origin

tectonic implications of palaeoproterozoic post collisional high k felsic igneous rocks from the kimberley region of northwestern australia abstract palaeoproterozoic high k i type granites high level porphyry intrusions and felsic volcanic rocks of the whitewater volcanics dominate the hooper and lamboo complexes in the kimberley region of northwestern australia the granites porphyries and volcanic rocks are gradational into each other in the field and they have the same mineralogy similar major and trace element abundances and indistinguishable shrimp u pb zircon ages of 1865 1850 ma there is evidence of widespread mingling between the granites and coeval gabbros magma mixing may be important in the formation of some of the mafic granites but most of the rocks probably formed from felsic parent magmas that underwent variable degrees of fractional crystallization the felsic igneous rocks may have formed by partial melting of intermediate to felsic calc alkaline rocks along the southern and eastern margins of the kimberley craton following accretion of various earlier palaeoproterozoic terranes to the craton therefore models for palaeoproterozoic high k granites in northern australia that invoke intracratonic rifting of a stable archaean craton may need to be revised

late mesozoic post collisional intermediate to silicic magmatism in the badjal area far east of russia abstract the late cretaceous badjal intrusive suite at the far east of russia includes a spectrum of rocks having emplaced successively in four phases from i diorite and quartz diorite to ii granodiorite iii granite and iv high silica granite various facies being distinguished within the phases the generation of these rocks took place after the collision of a number of island arcs and a terrane now locally preserved in sikhote alin region with the asian continent that had happened in the end of early to the beginning of late cretaceous the massifs intrude in early mesozoic sedimentary and volcanic sedimentary rocks topping the basement and in comagmatic volcanic rocks chemically the granitoid rocks have high k calc alkaline character and form continuous and regular trends of most of major oxides and trace elements with the sio2 contents ranging from 55 to 77 wt that favors the concept of crystal fractionation major oxides and ree have a break at 70 wt sio2 pointing to a change of precipitating mineral assemblage such change is also documented by the negative eu anomaly we believe that the fractionation of mafic minerals had to take place at the first stage of fractionation whereas plagioclase and possibly biotite began precipitating later as supposed by abrupt decrease of ba this hypothesis is in accordance with the mass balance calculations diorite magma compositionally similar to the first intrusive phase rocks should be taken for parental for the entire badjal suite small volume of these oldest rocks makes us suggest that the parental magma was a mixture of silicic liquid and restite mineral phases that would result from the partial melting of a heterogeneous metapelite basaltic or metapelite amphibolitic protolith almost total absence of basalt and gabbro of close age in the area makes a suggestion of crustal silicic contamination of a mantle produced basic magma unlikely after the melting the differentiation of the derived magmatic mixture during ascent and the separation of mineral phases acquired from the protolith restite phases and of newly formed ones are believed to produce the entire range of rocks of the badjal intrusive suite provided the progressive succession of emplacement from less to more silicic species

a tale of two plutons petrographic and mineralogic constraints on the petrogenesis of the red lake and eagle peak plutons central sierra nevada california the red lake and eagle peak plutons are similar in age k ar 87 89 m y and range in composition from granodiorite to granite the red lake pluton is equigranular has a locally greisened marginal zone and shows only minor mineralogical and chemical zoning whereas the eagle peak pluton is mineralogically compositionally and texturally zoned with an equigranular margin and a porphyritic core modal and normative trends within each pluton are consistent with separation of plagioclase and mafic minerals leading to a residual liquid enriched in quartz and alkali feldspar the formation of the prominent alkali feldspar megacrysts in the eagle peak core was promoted by plagioclase separation h 2 o undersaturation and a slower cooling rate relative to the red lake magma early loss of volatiles and a resulting increase in magma melt crystals viscosity inhibited crystal segregation within the red lake pluton and prevented the development of zoning late stage aplites associated with both plutons f

geochronological constraints on tectonic models for australian palaeoproterozoic high k granites high k granites extensively intruded all the palaeoproterozoic terrains of northern australia and have been interpreted as the culmination of widespread intracratonic orogeny one of these terrains the lamboo complex developed between the kimberley and north australian cratons the complex is divided into three terranes referred to as the western central and eastern zones and was intruded by a variety of i type granites and gabbros high k granites of the 1865 1850 ma paperbark supersuite are restricted to the western zone tonalite sheets of the dougalls suite and unassigned leucogranite sheets intruded the central zone at c 1850 ma the 1835 1805 ma sally downs supersuite is composed of tonalite and high k granite that mainly intruded the central zone however high k granites of the sally downs supersuite intruded all three zones from c 1820 ma onwards and mark the amalgamation of the terranes the youngest granites in the complex are high k granites of the 1805 1790 ma san sou suite which intrude the eastern and central zones the temporal and spatial distribution of the granites is not easily reconciled with previous intracratonic models but is consistent with tectonic processes similar to those operating at present

magma reservoir conditions beneath tsurumi volcano sw japan evidence from amphibole thermobarometry and seismicity abstract calcic amphibole phenocrysts in the tsurumidake summit ts lava which was produced during the most recent eruption at tsurumi volcano sw japan at around 7 5 10 5 ka have been analyzed to determine the pre eruptive conditions such as temperature t pressure p oxygen fugacity fo2 sio2 content sio2melt and feo mgo ratio feo mgomelt of coexisting silicate melts in the magma reservoir beneath the volcano although most of the amphibole phenocrysts have been completely decomposed to a fine grained opaque symplectite 6 of the grains remain intact the degree of amphibole breakdown dab defined as the ratio of the area of symplectite to the area of symplectite plus relict amphibole in each phenocryst varies from 20 to 100 compositional zoning was not observed in the amphibole grains however two distinct groups of amphibole phenocrysts have been identified based on their chemical compositions group i amphiboles which are relatively si poor and 6 al rich and have a relatively high mg 100mg mg fe2 and group ii amphiboles which are si rich and 6 al poor and have a relatively low mg empirical equations for geothermobarometry oxygen barometry and chemometry that exclusively rely on the amphibole composition were applied to estimate the t p fo2 sio2melt feo mgomelt conditions of the silicate melts with which the amphibole crystals equilibrated the results show that group i and group ii amphiboles equilibrated with andesitic melts group i melts and dacitic rhyolitic melts group ii melts respectively the t p fo2 conditions of group i melts were estimated as 374 483 mpa 13 9 17 9 km depth 950 c and nno 1 3 respectively and those of group ii melts were 93 242 mpa 3 4 9 0 km depth 824 913 c and nno 0 6 1 7 respectively the estimated t p fo2 sio2melt feo mgomelt conditions were almost constant for group i melts whereas the t nno and feo mgomelt values of group ii melts decreased with increasing sio2melt the dab decreased as the temperature increased low dab grains are absent in group ii amphiboles our results suggest that 1 a deeper reservoir at a depth of 16 km stored an andesitic melt coexisting with group i amphiboles at 950 c 2 a chemically zoned reservoir at shallower depth 6 4 km was filled with dacitic rhyolitic melts that coexisted with group ii amphiboles at 824 913 c 3 the ts lava was the product of magma mixing of at least three components including the andesitic melt derived from the deeper reservoir the dacitic and rhyolitic melts from the shallower reservoir and a mafic magma derived from the lower crust and or upper mantle and 4 the ts lava eruption occurred within a month or less of the magma mixing

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

expansion of pelagic denitrification during early pleistocene cooling bioavailable nitrogen is removed from the oceans in oxygen deficient benthic and pelagic environments by denitrification future warming is predicted to reduce ocean oxygenation and to cause hypoxic regions to expand potentially accelerating denitrification a compilation of high resolution sedimentary nitrogen isotope delta n 15 records from the eastern tropical pacific north pacific and the arabian sea and a global multi site survey are presented as evidence for weak pelagic denitrification at the end of the pliocene warm period mean delta n 15 values increased in the major oxygen minimum zones omzs between 2 1 and 1 5 ma pelagic denitrification strengthened during a period of long term global cooling despite solubility driven increases in initial oxygen contents of antarctic intermediate and subantarctic mode waters ventilating the omzs this trend is opposite to the predicted mean trend for a cooling ocean as well as to the observed glacial interglacial variation several alternatives to explain the shift are proposed including a rise in net respiration a progressive increase in the ventilation age of the deep ocean associated with million year scale secular cooling and a shoaling of the remotely ventilated thermocline to shallow depths corresponding to the zone of peak subsurface respiration given no evidence for a net increase in production we assert that large scale climate driven changes in ocean circulation regulate long timescale variations in the extent of pelagic denitrification additional data and modeling are required to fully explain the observations c 2013 elsevier b v all rights reserved

contrast of metamorphic and structural histories across the work channel lineament coast plutonic complex british columbia a prominent topographic lineament along the western margin of the coast plutonic complex of southeast alaska and adjacent parts of british columbia separates terranes of contrasting metamorphic histories where it enters british columbia near prince rupert as the work channel lineament the western terrane preserves a regional medium high pressure metamorphic facies series increasing from chlorite grade in the west to kyanite muscovite migmatite near the lineament the metamorphic structural and age relations of the western terrane are consistent with a model of crustal thickening accompanied by westward transport of higher over lower grade metamorphic units during the jurassic this terrane was uplifted and cooled by cretaceous time 85 ma east of work channel lineament high temperature relatively low pressure assemblages are overprinted onto high pressure assemblages the low pressure metamorphic assemblages developed in the eocene during rapid uplift 2 mm yr of rocks which initially may have been metamorphosed at the same time and along the same pt gradient as those of the western terrane structures along the work channel lineament suggest vertical motion during uplift of the eastern terrane and after metamorphism of the western terrane because the metamorphic discontinuity across the lineament is 3 5 kbar at about 700 the lineament in the prince rupert area marks a major crustal break

the october 1980 earthquake sequence near the new hebrides four large earthquakes occurred in 1980 in a seismic gap near the loyalty islands in the new hebrides at 3 25 ut on october 24 an event with m s 6 7 initiated the sequence three events m s 6 7 7 2 and 6 5 followed on the next day we investigated this sequence by using the seismicity first motion and waveform data and long period surface waves the first motion data constrain one of each pair of nodal planes with this constraint inversion of rayleigh and love wave spectra at 256 seconds determines the other nodal plane the mechanisms of all four events are almost pure thrust on a plane dipping about 20 degrees east and striking parallel to the local strike of the new hebrides trench the first day aftershocks indicate an initial rupture zone of about 2 000 km which is consistent with the estimated seismic moment of 3 10 27 dyne cm during the next two days the aftershock activity expanded to an area of 10 000 to 20 000 km in the directions both along and perpendicular to the trench within 5 hours after the third and largest event the initial rupture zone had become mostly quiescent modeling of waveforms suggests a body wave moment of between 0 5 and 1 0 10 27 dyne cm and a source process time of 11 seconds this pattern suggests that the initial rupture zone represents a zone of increased strength i e an asperity and the stress change due to failure of this asperity subsequently migrated outward during the two year period before the main event seismicity in the initial rupture zone was very low except near the point where the first mainshock initiated a very tight clustering of activity occurred there this pattern indicates gradual stress concentration near the asperity which finally failed during the mainshock sequence

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

an inhomogeneous fault model for gaps asperities barriers and seismicity migration we develop a model for a fault in which various areas of the fault plane have different stress slip constitutive laws the model is conceptually simple involving nonlinear algebraic equations which can easily be solved by a graphical method of successive iterations application is made to the problem of explaining seismicity patterns associated with great earthquakes the model quantitatively explains phenomena associated with seismic gaps asperities and barriers

melting of the patagonian ice sheet and deglacial perturbations of the nitrogen cycle in the eastern south pacific local 230 th normalized biogenic vertical fluxes from the chilean continental margin they document in detail the sharp transition from relatively low wcd rates during the last glacial maximum lgm to high ones during the deglaciation and holocene but give no evidence that the glacial interglacial difference of wcd could have been caused by changes in local primary productivity furthermore we found no evidence that changes in ventilation due to samw formation could explain the nitrogen isotope record we present evidence for an alternative mechanism related to the melting of the patagonian ice sheet pis which is consistent with recent published proxy data and the regional physical oceanography

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

a multidisciplinary study of the emplacement mechanism of the qingyang jiuhua massif in southeast china and its tectonic bearings part ii amphibole geobarometry and gravity modeling abstract the late mesozoic geology of the lower yangtze area is characterized by extensional sedimentary basins numerous granitic plutons and several world class ore deposits regionaly the coeval tectonic and geodynamic framework remains inadequately investigated in order to provide a more comprehensive understanding of the regional tectonic context we performed a multidisciplinary study of the emplacement mechanism of the qingyang jiuhua massif it consists of the granodioritic qingyang and the monzogranitic jiuhua plutons u pb dated at 142 1 0 ma and 131 2 6 ma respectively biotite and amphibole cooling ages are 5 8 myr younger results deduced from field structural observation petrographic and magnetic fabrics paleomagnetism show that this massif was probably vertically emplaced by permissive intrusion coeval with weak regional extension however detailed information on the characteristics of this tectonic event and its emplacement depth was not documented therefore we carried out an investigation of amphibole geobarometry and gravity modeling in order to address the emplacement mode of the plutons within their regional tectonic framework amphibole data show that the qingyang jiuhua massif was emplaced in the upper crust at a depth between 5 and 12 km gravity modeling indicates that the massif is laccolithic it is characterized by several ne sw striking linear thickening zones that we interpret as the feeder roots of the massif these results led us to conclude that 1 the qingyang jiuhua massif was fed by vertical ne sw striking tension gashes 2 consequently the late early cretaceous tectonics in the study area was characterized by nw se extension

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

time space relationships among structural and metamorphic aureoles related to granite emplacement a case study from the serre massif southern italy tectonic and thermal perturbations related to emplacement of granodiorite in the upper continental crust have been investigated in the late hercynian basement exposed in southern calabria italy here the structural aureole is marked by the presence of a major rim fold adjacent to the intrusive contact for a length of at least 20 km geometrical analysis of the structural aureole and related foliations lineations and crenulations reveals that the perturbed zone is at least 3000 m wide and characterized by an open synform trending nearly parallel to the intrusive contact this pattern is compatible with a laccolith like mode of magma emplacement related to the accretion of the pluton that shouldered weak phyllitic and slaty wall rocks the metamorphic aureole about 1800 m wide is characterized by biotite cordierite and andalusite that appear sequentially in spotted schists and hornfelses approaching the intrusive contact the peak assemblage equilibrated between 535 and 590 c at pressures between 175 and 200 mpa confirmed by al in hornblende barometry on granodiorite microstructural analysis allowed the inference of a time lag between the thermal and tectonic perturbations with the aid of thermal modelling it was possible to quantify the time required to reach the peak temperature at a distance from the intrusive contact where cordierite spots and andalusite porphyroblasts clearly overprint crenulations this estimate represents the time limit to accomplish deformation in the inner portion of the aureole and thus indicates a minimum strain rate of 4 10 14 s 1 within the country rocks during granodiorite intrusion

glacial to interglacial changes in surface nitrate utilization in the indian sector of the southern ocean as recorded by sediment δ15n we present a new approach for paleoceanographic reconstruction of surface nutrient utilization in the southern ocean it has been observed in the contemporary ocean that due to preferential uptake of 14no3 during photosynthesis the 15n of planktonic organic matter increases with increasing nitrate depletion in surface waters our results demonstrate that the 15n signal produced in surface waters is reflected in the underlying surface sediments core top 15n is inversely correlated with surface nitrate concentration along a transect across the subtropical convergence and the polar front in the southeast indian ocean these results are consistent with a four box model showing that the nitrogen isotopic composition of sinking organic matter depends on percent nitrate utilization in the euphotic zone by comparing the 15n of surface sediments with that measured in the glacial sections of several cores we infer changes in the intensity and latitudinal distribution of nitrate uptake in this region during the last glacial maximum these preliminary results argue against increased biological uptake of nutrients in southern polar waters as a major mechanism for glacial lowering of atmospheric co2 they also suggest that subantarctic waters in the se indian sector became more nutrient depleted as they migrated northward increased nitrate depletion might have also occurred slightly south of the glacial polar front we use a six box model to explore the possible impact of this observation on atmospheric co2

coupled nitrification denitrification in sediment of the eastern bering sea shelf leads to 15n enrichment of fixed n in shelf waters 1 we studied the nitrogen biogeochemistry of the ice covered eastern bering sea shelf using the isotope ratios 15n 14n and 18o 16o of no3 and other n species the 15n 14n of late winter no3 on the shelf decreases inshore and is inversely correlated with bottom water nh4 consistent with an input of low 15n 14n no3 from partial nitrification of nh4 remineralized from the sediments an inshore 15n 14n increase in total dissolved n tdn suggests that 1 the sediment derived nh4 is elevated in 15n due to the same partial nitrification that yields the low 15n 14n no3 and 2 15n deplete no3 from partial nitrification within the sediments is denitrified to n2 the proportion of newly nitrified no3 on the shelf evidenced by an inshore decrease in no3 18o 16o is correlated with the n deficit further implicating nitrification coupled to denitrification however a simple n isotope budget indicates a comparable rate of denitrification supported by diffusion of no3 into the sediments the isotopic impact of benthic n loss is further demonstrated by a correlation between the 15n 14n of shelf surface sediment and the n deficit of the overlying water column both of which increase inshore and northward as well as by arctic no3 isotope data indicating that the fixed n transported through bering strait has a 15n 14n higher than is found in the open bering sea the significant net isotope effect of benthic n loss on the bering shelf 6 8 is at odds with previous assumptions regarding the global ocean s n isotope budget

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

age and tectonic setting of the camaguey volcanic intrusive arc cuba late cretaceous extension and uplift in the western greater antilles abstract ar ar ages determined on rocks and minerals from the camaguey area in central cuba provide age constraints on events that accompanied the northward migration of cuba into the caribbean region and its subsequent collision with the bahamas bank whole rock samples from the camujiro and piragua formations part of the camaguey volcanic sequence yielded ar ar ages of 74 72 ma distinctly younger than the 100 80 ma ages indicated by fossils in interlayered sedimentary rocks syenite and granodiorite in the camaguey batholith which cut these volcanic rocks yield generally similar ar ar ages of 75 72 ma for hornblende biotite and feldspar these ages are interpreted to reflect relatively rapid uplift and cooling of most of the volcanic intrusive arc additional constraints on the timing of this uplift are provided by ar ar ages of 71 75 ma for rhyolite rhyodacite domes of the la sierra formation and 52 ma for andesitic basalt of la mulata formation which appear to have been emplaced onto erosion s

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

petrology of matthew and hunter volcanoes south new hebrides island arc southwest pacific abstract matthew and hunter the two southernmost active volcanoes of the new hebrides island arc southwest pacific differ markedly from the other mainly tholeiitic quaternary volcanoes of this arc geodynamically related to the new hebrides subduction zone they also lie close to the southern limb of the active expanding ridge of the north fiji basin both volcanoes are made up of acid medium k calcalkaline orogenic andesites containing a variety of inclusions pyroxene and gabbroic cumulates as well as doleritic cognate inclusions this paper presents the first systematic petrographic and chemical study of these volcanics and their inclusions trace element geochemistry and rare earth element modelling suggest that the two volcanoes developed from successive batches of similar parental magmas originating from limited partial fusion of garnet peridotite in the mantle wedge various degrees of fractional crystallization of these batches led to the formation of three volcanic suites hunter little fractionated west matthew moderately fractionated and east matthew highly fractionated moreover on matthew island no correlation exists between the degree of fractionation and the eruptive chronology the youngest edifice west matthew being less evolved than the older one east matthew

the stability of amphibole in andesite and basalt at high pressures reinvestigation of earlier work on mt hood andesite and kilauea olivine tholeiite under n no conditions and with silver capsules the revised curve for the appearance of garnet is significantly lower in pressure no orthopyroxene appeared in the run products in contrast to the results of the earlier work the high temperature segment of the amphibole out curve for the tholeiite is at least as high as 1040 degrees c at 13 kbar and 1050 degrees c at 16 kbar and the high pressure part of this curve is at about 27 kbars about 6 kbar higher than in the earlier work amphibole is the sole silicate phase on the vapor saturated liquidus in the andesite at pressures below the garnet in curve 15 5 kbar revised phase relationships are consistent with the derivation of andesite by amphibole liquid equilibria in basaltic magma and reveal stability to depths of nearly 100 km the great depths to which amphiboles are stable make it probable that they are a source of h 2 o for martial melting in deeply subducted oceanic crust modified journal abstract

mantle derivation of archean amphibole bearing granitoid and associated mafic rocks evidence from the southern superior province canada amphibole bearing late archean 2 73 2 68 ga granitoids of the southern superior province are examined to constrain processes of crustal development the investigated plutons which range from tonalite and diorite to monzodiorite monzonite and syenite share textural mineralogical and geochemical attributes suggesting a common origin as juvenile magmas despite variation in modal mineralogy the plutons are geochemically characterized by normative quartz high al2o3 15 wt na rich fractionation trends mol na2o k2o 2 low to moderate rb generally 150 ppm are comagmatic with the evolved granitoids and indicate that the suites are mantle derived isotopic studies of archean monzodioritic rocks have shown lree enrichment and initial 143nd 144nd ratios indicating derivation from mantle sources enriched in large ion lithophile elements lile shortly before melting mineral assemblages record lower ph2o with increased alkali contents of the suites this evidence in conjunction with experimental studies suggests that increased alkali contents may reflect decreased ph2o during mantle melting these features indicate that 2 73 ga tonalitic rocks are derived from more hydrous mantle sources than 2 68 ga syenitic rocks and that the spectrum of late archean juvenile granitoid rocks is broader than previously recognized comparison with phanerozoic and recent plutonic suites suggests that these archean suites are subduction related

glacial interglacial variations in production and nitrogen fixation in the cariaco basin during the last 580 kyr the effect of sea level change on nutrient supply to the anoxic cariaco demonstrates the fundamental importance of nitrogen n2 fixation and phosphate to oceanic production as n2 fixation produces biomass of low 15n and has been reported to be an important component of the nitrogen cycle in the modern cariaco basin we propose that it contributes to the light interglacial 15n 2 3 values observed in the ocean drilling program odp site 1002 sediment record during the glacials the sediments are bioturbated oxic conditions with low total organic carbon toc contents and sedimentary 15n values of 5 suggesting that nitrogen n2 fixation contributed little to the n nutrition of cariaco surface waters the most plausible explanation for the inferred glacial interglacial changes in n2 fixation in the cariaco is that they have occurred in response to variations in the n p ratio of the nutrient supply driven by changes in denitrification

a bimodal hybrid model for time dependent probabilistic seismic hazard analysis the evaluation of evidence provided by geological studies and historical catalogs indicates that in some seismic regions and faults multiple large earthquakes occur in cluster then the occurrences of large earthquakes confront with quiescence and only the small to moderate earthquakes take place clustering of large earthquakes is the most distinguishable departure from the assumption of constant hazard of random occurrence of earthquakes in conventional seismic hazard analysis in the present study a time dependent recurrence model is proposed to consider a series of large earthquakes that occurs in clusters the model is flexible enough to better reflect the quasi periodic behavior of large earthquakes with long term clustering which can be used in time dependent probabilistic seismic hazard analysis with engineering purposes in this model the time dependent hazard results are estimated by a hazard function which comprises three parts a decreasing hazard of last large earthquake cluster and an increasing hazard of the next large earthquake cluster along with a constant hazard of random occurrence of small to moderate earthquakes in the final part of the paper the time dependent seismic hazard of the new madrid seismic zone at different time intervals has been calculated for illustrative purpose

petrological constraints on crystallization conditions of mesoarchean sanukitoid rocks southeastern amazonian craton brazil we report petrological and geochemical data for the 2 87 ga rio maria sanukitoid granodiorite and associated rocks from mesoarchean granite greenstone terranes of the eastern amazonian craton brazil the dominant rocks have granodiorite to subordinate monzogranitic compositions with minor proportions of intermediate quartz diorites or quartz monzodiorites in addition to mafic endmembers occurring as layered rocks or as enclaves the mineral assemblage is dominated by amphibole plagioclase biotite and epidote minerals all of inferred magmatic origin pyroxenes being notably absent textural and compositional criteria indicate that amphibole is a principal mineral on the liquidus of all the rio maria rocks crystallization conditions have been derived from a comparison between natural phase assemblages proportions and compositions and experimental studies carried out on similar magma compositions the comparison shows that the parental magmas were water rich with more than 7 wt dissolved h2o with crystallization temperatures in the range 950 680 c the mg mg fe ratios of both amphibole and biotite indicate fo2 conditions in the range nno 0 5 to nno 2 5 where nno is nickel nickel oxide buffer therefore pointing to both water rich and oxidizing conditions for sanukitoid magmas amphibole compositions indicate emplacement at around 200 mpa and record a high pressure stage of magma crystallization around 600 900 mpa sanukitoid magmas share two of the principal characteristics of modern arc magmas elevated redox state and volatile contents which suggest that they may have formed in a geodynamic environment broadly similar to present day subduction zones

deglacial nitrogen isotope changes in the gulf of mexico evidence from bulk sedimentary and foraminifera bound nitrogen in orca basin sediments 1 constraining variations in marine n2 fixation over glacial interglacial timescales is crucial for determining the role of the marine nitrogen cycle in modifying ocean productivity and climate yet paleo records from n2 fixation regions are sparse here we present new nitrogen isotope 15n records of bulk sediment and foraminifera test bound fb nitrogen extending back to the last ice age from the oligotrophic gulf of mexico gom previous studies indicate a substantial terrestrial input during the last ice age and early deglacial for which we attempt to correct the bulk sediment 15n using its observed relationship with the c n ratio both corrected bulk and fb 15n reveal a substantial glacial to holocene decrease of 15n toward holocene values of around 2 5 similar to observations from the caribbean this 15n change is most likely due to a glacial to holocene increase in regional n2 fixation a deglacial peak in the fb 15n of thermocline dwelling foraminifera orbulina universa probably reflects a whole ocean increase in the 15n of nitrate during deglaciation the 15n of the surface dwelling foraminifera globigerinoides ruber and the corrected bulk 15n show little sign of this deglacial peak both decreasing from last glacial values much earlier than does the 15n of o universa this may indicate that g ruber and bulk n reflect the euphotic zone signal of an early local increase in n2 fixation our results add to the evidence that during the last ice age the larger iron input from dust did not lead to enhanced n2 fixation in this region rather the glacial to holocene decrease in 15n is best explained by a response of n2 fixation within the atlantic to the deglacial increase in global ocean denitrification

isotopic constraints on glacial interglacial changes in the oceanic nitrogen budget early deglacial maximum in nitrate 15 n 14 n in suboxic zones and no significant glacialto late holocene change in global ocean nitrate 15 n 14 n consistent with the work of brandes and devol 2002 we find that the steady state 15 n 14 n of oceanic nitrate is controlled primarily by the fraction of total denitrification that occurs in the water column therefore a deglacial peak in the ratio of water column to sediment denitrification caused by either a strong feedback between water column denitrification and the n reservoir or by an increase in sediment denitrification due to sea level rise can explain the observed deglacial 15 n 14 n maximum in sediments underlying water column denitrification zones the total denitrification rate and the mean ocean nitrate concentration are also important determinants of steady state nitrate 15 n 14 n for this reason modeling a realistic deglacial 15 n 14 n maximum further requires that the combined negative feedbacks from n2 fixation and denitrification are relatively strong and n losses are relatively small our results suggest that the glacial oceanic n inventory was at most 30 greater than today s and probably less than 10 greater index terms 4267 oceanography general paleoceanography 4805 oceanography biological and chemical biogeochemical cycles 1615 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes keywords feedback nitrogen isotopes paleoceanography

the influence of rapid millennial scale climate change on nitrogen isotope dynamics of the cariaco basin during marine isotope stage 3 understanding changes to the marine nitrogen cycle on millennial and shorter time scales can help determine the influence of rapid climate change on the fixed n pool and its sources and sinks rapid changes in denitrification have been observed in the eastern tropical north pacific etnp and arabian sea however millennial scale 15n records in regions influenced by n2 fixation are sparse we present a sedimentary 15n record from the cariaco basin during marine isotope stage mis 3 35 55 ka the 15n record displays a pattern of millennial scale variability that tracks the greenland ice core dansgaard oeschger cycles with higher values observed during interstadial periods lower values during stadial periods and abrupt transitions in between conditions during interstadials are similar to those at present in the cariaco basin with the sedimentary 15n signal reflecting a combination of local processes and an imported regional signal if interpreted to reflect regional processes the interstadial 15n values average 5 1 support the argument that n2 fixation did not increase in the tropical north atlantic during the last glacial the lower 15n values during stadials when lower sea level resulted in increased physical isolation of the basin can be explained primarily by local processes in spite of the importance of local processes striking similarity is observed between the cariaco record and millennial scale 15n records from the etnp and arabian sea the apparent synchronicity of changes observed in all three regions suggests an atmospheric teleconnection between the three sites and high latitude climate forcing during mis 3

elevated foraminifera bound nitrogen isotopic composition during the last ice age in the south china sea and its global and regional implications 1 we report a new foraminifera bound d 15 n fb d 15 n record from the south china sea scs extending back to 42 ka this record shows a 1 2 glacial to interglacial d 15 n decrease with a deglacial d 15 n maximum similar to that observed in many bulk sedimentary d 15 n records and in a caribbean fb d 15 n record the glacial to interglacial d 15 n decrease is smaller than in the caribbean record indicating that at least half of the caribbean d 15 n decrease into the holocene was regional not global supporting the interpretation of a holocene increase in atlantic nitrogen fixation at the same time the glacial to interglacial d 15 n decrease observed in the scs may also be explained as a regional signal of increasing nitrogen fixation into the holocene other aspects of the scs record suggest an effect of physical circulation on fb d 15 n fb d 15 n starts to increase toward its deglacial maximum before the last ice age ends and it continues to decrease through the later holocene in contrast to the more pure glacial deglacial interglacial steps in the caribbean record these changes have parallels in other pacific d 15 n records precessionally driven east asian monsoon records and the slow holocene warming of scs surface waters in addition the scs record exhibits two one point high d 15 n spikes in multiple foraminiferal species that coincide with apparent hydrographic events thinning or weakening of the thermocline in the late glacial and early holocene as well as during the noted events may have yielded a higher d 15 n for thermocline nitrate and thus a higher fb d 15 n

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time

worldwide doublets of large shallow earthquakes abstract we investigated all the pairs of mw 7 5 shallow earthquakes in the harvard catalog that occurred at a centroid distance of less than 100 km we showed that most of these pairs have similar focal mechanisms because these earthquakes generally should have focal regions in excess of 100 km diameter their rupture zones apparently intersect for all these pairs the time interval is significantly less than the time span needed for plate motion to accumulate the strain released by the first event these observations conflict strongly with quasi periodic recurrence models on which the seismic gap hypothesis is based power law recurrence fits these earthquake ob servations much better introduction many models used to forecast long term seismic hazard are based on the quasi periodic or seismic cycle hypothesis of large earthquake occurrence this hypothesis assumes that the probability of a large earthquake is low after signifi cant release of seismic energy and that danger increases only when tectonic plate motion accumulates strain sufficient for a new strong event several models have been formulated to apply this idea to long term earthquake prediction mccann

phosphorus accumulation in marine sediments and the oceanic phosphorus cycle ideas about key factors in the oceanic mass balance of dissolved reactive phosphate have changed substantially i present an integrated overview of these here with an emphasis on evaluating the burial sinks for p and defining areas needing further research the major source of reactive p to the ocean is river input reactive p is delivered to the oceanic sediment water interface primarily in particulate organic matter p scavenged by hydrothermal iron rich oxyhydroxide particles with uptake in proportion to deep water phosphate concentrations represents a substantially smaller flux to the sediment water interface diagenetic transformations are important influences on the form of reactive p burial in marine sediments p burial occurs with organic carbon burial and as p associated with iron rich oxyhydroxide particles and coatings formation of authigenic p rich phases presumably apatite at the expense of organic p and oxide associated p is significant in open ocean marine sediments the authigenic p sink may represent a substantially larger portion of the sedimentary burial than indicated by previous estimates focused on p burial in organic rich continental margin sediments

40ar 39ar age pattern associated with differential uplift along the eastern highlands shear zone cape breton island canadian appalachians abstract the eastern highlands shear zone in cape breton island is a crustal scale thrust it is characterized by an amphibolite facies deformation zone 5 km wide formed deep in the crust that is overprinted by a greenschist facies mylonite zone 1 km wide that formed at a more shallow level hornblende 40ar 39ar plateau ages on the hanging wall decrease towards the centre of the shear zone in the older zone over 7 8 km from the centre the ages are between 565 and 545 ma in the younger zone within 4 5 km of the centre they are between 425 and 415 ma and in the transitional zone in between they decrease abruptly from 545 to 425 ma pressures of crystallization of plutons in the hanging wall based on the al in hornblende barometer and corresponding to depth of emplacement increase towards the centre of the shear zone and indicate a differential uplift of up to 28 km associated with movement along the shear zone the age pattern is interpreted to have resulted from the differential uplift the pressure data show that rocks exposed in the younger zone were buried deep in the crust and did not cool through the hornblende ar blocking temperature 500 c until differential uplift occurred the 40ar 39ar ages in the zone 425 415 ma thus date shear zone movement or the last stage of it in contrast rocks in the older zone were more shallowly buried before differential uplift and cooled through the blocking temperature soon after the emplacement of 565 555 ma plutons in the area long before shear zone movement the transitional zone corresponds to the ar partial retention zone before differential uplift the 40ar 39ar age pattern thus reflects a neoproterozoic to silurian cooling profile that was exposed as a result of differential uplift related to movement along the shear zone a similar k ar age pattern has been reported for the alpine fault in new zealand it is suggested that such isotopic age patterns can be used to help constrain the ages kinematics displacements and depth of penetration of shear zones

aftershock area expansion and mechanical heterogeneity of fault zone within subduction zones we investigate global variations in the pattern of aftershock area expansion associated with large subduction zone earthquakes the expansion of aftershock areas with time is relatively small in the subduction zones of alaska the aleutians mexico and parts of the kuriles and south america these subduction zones are interpreted to be characterized by moderate to strong interplate coupling in contrast the extent of aftershock expansion is greater for events within the subduction zones of northeast japan and western and south pacific where interplate coupling is inferred to be weak these results are interpreted in terms of an asperity model where a fault zone is represented by a distribution of strong spots asperities and weaker zones the immediate aftershock area is assumed to extend over an area occupied by asperities and the subsequent expansion to occur into the surrounding weaker zones if large asperities abut each other on a fault plane interplate coupling is strong and little expansion of aftershock area occurs smaller and more sparsely distributed asperities cause weak interplate coupling and significant expansion of aftershock area small and densely distributed asperities result in moderate interplate coupling and little aftershock expansion

spatial distribution and mechanisms of earthquakes in the southern new hebrides arc from a temporary land and ocean bottom seismic network and from worldwide observations in 1977 a wide aperture seismic network of land and ocean bottom stations obs was operated for 6 weeks in the southern new hebrides island arc data on the spatial distribution and mechanisms of small events recorded by this local network were integrated with worldwide observations of moderate to large size new hebrides earthquakes of the past 17 years to study the structure and deformational processes in the new hebrides subduction zone surprisingly small differences less than about 10 km were found between the locations of shallow and intermediate depth earthquakes as located by the temporary local network and by the international seismological centre using worldwide stations analysis of the p wave travel time data from the obs station closest to the trench shows limited evidence for a high velocity zone about 5 higher than the surrounding mantle associated with the descending plate the thrust zone between the descending and upper plates is defined mainly by the spatial distribution and focal mechanisms of moderate to large size events and their aftershocks but it is not very well defined by the spatial distribution of small size events located in this study shallow seismic activity located beneath the trench and beneath the interplate thrust zone indicates a lower limit of about 40 km for the thickness of the seismically active part of the descending plate beneath the thrust zone focal mechanisms of moderate to large size earthquakes located within the upper plate and geological observations on the islands suggest that the upper plate in the region of erromango and tanna is divided into a series of blocks that are differentially uplifted along mainly nw se striking faults during the obs experiment several shallow events were well located beneath the coriolis trough a riftlike feature located to the east of the volcanic arc well determined depths of these events are between 11 and 22 km the well located intermediate depth events define a 20 km thick benioff zone that has a dip of about 70 the spatial distribution of events within the descending slab is very strongly clustered in a persistent pattern that is seen in both the short term sample of small events determined by the local network and the long term sample of locations based on worldwide data several focal mechanisms of moderate to large size intermediate depth events show components of lateral extension along the strike of the arc and some show components of lateral compression both of which could be interpreted as the result of a lateral bending of the descending plate in the part of the southern new hebrides arc where the trench begins to curve around to the east

crustal growth in south eastern australia evidence from lower crustal eclogitic and granulitic xenoliths mafic and ultramafic xenoliths in a basaltic cone at the anakies in south eastern australia are geochemically equivalent to continental basaltic magmas and cumulates the xenolith microstructures range from recognizably meta igneous for intrusive rocks to granoblastic for garnet pyroxenites contact relationships between different rock types within some xenoliths suggest a complex petrogenesis of multiple intrusive metamorphic and metasomatic events at the crust mantle boundary during the evolution of south eastern australia unaltered spinel lher zolite typical of the uppermost eastern australian mantle is interleaved with or veined by the metamorphosed intrusive rocks of basaltic composition geothermobarometry calculations by a variety of methods show a concordance of equilibration temperatures ranging from 880 c to 980 c and pressures of 12 to 18 kbar 1200 1800 mpa these physical conditions span the gabbro to granulite to eclogite transition boundaries the water vapour pressure during equilibration is estimated to be about 0 5 of the load pressure using amphibole breakdown data large fluid inclusions of pure co2 are abundant in the mineral phases in the xenoliths and it is suggested that flux of co2 from the mantle has been an important heat source and fluid medium during metamorphism of the mafic and ultramafic protoliths at the lower crust upper mantle boundary the calculated pressures and temperatures suggest that the south eastern australian crust has sustained a high geothermal gradient in addition the nature of the mineral assemblages and the contact relationships of granulitic rock with spinel lherzolite characteristic of mantle material suggest that the moho is not a discrete feature in this region but is represented by a transition zone approximately 20 km thick these inferences are in agreement with geophysical data including seismic heat flow and electrical resistivity data determined for south eastern australia underplating at the crust mantle boundary by continental basaltic magmas may be an important alternative or additional mechanism to the conventional andesite model for crustal accretion

the dynamics of the marine nitrogen cycle across the last deglaciation 1 we use a geochemical box model to investigate the changes in marine n fixation and denitrification required to match the observed sedimentary 15n changes between 30 kyr b p and the late holocene this is achieved by optimizing a set of seven parameters that describe the strengths of three ocean internal n feedbacks and the response of the oceanic n cycle to four external forcings scenarios that best match the 15n constraints indicate a strong transient decrease in n fixation in the early deglacial in response to the decrease in iron input by dust around 15 kyr b p n fixation rebounds primarily in response to an abrupt increase in water column denitrification caused by an expansion of anoxia benthic denitrification is not well constrained by our model but tends to increase in sync with water column denitrification as a result of the transient imbalance between n fixation and denitrification we infer a glacial to interglacial decrease in the marine n inventory of between 15 and 50 the model diagnoses this reduction in order to simultaneously fit the data from all ocean basins requiring it to reduce the degree by which water column denitrification in the oxygen minimum zones is influencing the 15n of nitrate of the whole ocean dilution effect our optimal solution suggests a glacial n cycle that operated at nearly the same rates as that in pre industrial times but sensitivity cases with substantially lower rates fit the data only marginally worse an important caveat of our study is the assumption of an unchanging ocean circulation an initial sensitivity experiment shows that this affects primarily the magnitude of the change in the n inventory while the diagnosed deglacial dynamics with global marine n fixation taking a dip before the onset of denitrification remains a robust result

large climate driven changes of oceanic oxygen concentrations during the last deglaciation during the last glacial termination the solubility of gases in the ocean decreased as ocean temperatures rose however marine sediments have not unanimously recorded ocean deoxygenation throughout this time some records show increasing oxygenation since the last glacial maximum particularly in the deep sea while many document abrupt oxygenation changes often associated with apparent changes in the formation rate of north atlantic deep water here we present a global compilation of marine sediment proxy records that reveals remarkable coherency between regional oxygenation changes throughout deglaciation the upper ocean generally became less oxygenated but this general trend included pauses and even reversals reflecting changes in nutrient supply respiration rates and ventilation the most pronounced deoxygenation episode in the upper ocean occurred midway through the deglaciation associated with a reinvigoration of north atlantic deep water formation at this time the upper indo pacific ocean was less oxygenated than today meanwhile the bulk of the deep ocean became more oxygenated over the deglaciation reflecting a transfer of respired carbon to the atmosphere the observed divergence from a simple solubility control emphasizes the degree to which oxygen consumption patterns can be altered by changes in ocean circulation and marine ecosystems

comment on blundy and holland s 1990 calcic amphibole equilibria and a new amphibole plagioclase geothermometer

the 1968 tokachi oki and the 1969 kurile islands earthquakes variability in the rupture process the may 16 1968 tokachi oki mw 8 2 and the august 11 1969 kurile islands mw 8 2 shallow thrust earthquakes occurred along the japan kurile arc about 500 km apart and possess similar static fault parameters their dynamic source processes were investigated using the observable directivity in the source time functions deconvolved from long period p waves the rupture processes of both earthquakes can be understood in terms of a combination of the end member asperity and barrier models of earthquake rupture the 1969 kurile islands earthquake ruptured in the sense of the asperity model one region of the fault plane radiated most of the seismic moment i e the asperity and is surrounded by the rupture zones of large precursor events the rupture process of the 1968 tokachi oki earthquake contains elements of both end member rupture models a dominant asperity is bounded to the south by a region of the fault plane ruptured by a large precursor event and is bounded to the north by a geometric barrier where the plate margin changes direction this geometric feature is responsible for the abrupt termination of the rupture front it appears that the tectonic setting plays a vital role in determining the rupture mode earthquakes that occur along linear trenches where no geometric or topographic complications exist seem to rupture in the sense of the asperity model whereas earthquakes that occur in the vicinity of such complications are more likely to possess rupture processes intermediate between the two end member models

deglacial weakening of the oceanic soft tissue pump global constraints from sedimentary nitrogen isotopes and oxygenation proxies abstract among the many potential explanations for the 80 ppm rise of atmospheric co2 concentrations at the end of the last ice age most involve a weakening of the oceanic soft tissue pump here we use global data compilations of sedimentary nitrogen isotopes and benthic oxygenation proxies to provide a synoptic global perspective on the deglacial soft tissue pump weakening the net change between the last glacial maximum and holocene shows a removal of respired carbon everywhere that proxy data is available with the exception of the upper 1 5 km of the north pacific while excess nitrate accumulated in polar oceans these observations could be explained by intensifying iron limitation a shoaling of organic matter remineralization and or a change in ocean circulation but are inconsistent with a change in the magnitude or position of the southern mid latitude westerlies the net soft tissue pump weakening was front loaded in the early deglaciation 17 5 14 ka when atmospheric 13c and 14c were changing rapidly and appears to have contributed little net change thereafter superimposed on the overall deglacial trend were pronounced transient changes that coincided with variability in the atlantic meridional overturning circulation amoc and bipolar seesaw the seesaw variability is most clearly expressed as anti phased oxygenation changes between the upper 1 5 km of the north pacific and the deep north atlantic consistent with an atlantic pacific ventilation seesaw but it dominated transient variability in records throughout the world although the soft tissue pump seesaw made little contribution to the contrast between the glacial and interglacial states it could have contributed to deglacial variability in atmospheric co2 and might have catalyzed the deglaciation

isotopic fractionation of oxygen and nitrogen in coastal marine sediments abstract the bulk and isotopic exchanges of o2 n2 no3 and nh4 between sediments and the overlying water benthic flux were measured at three shallow locations in puget sound using a benthic tripod oxygen consumption by the sediments averaged 4 4 mmol m 2 d 1 while n2 gas fluxes averaged 1 1 mmol m 2 d 1 the nitrogen gas flux out of the sediments was always greater than the corresponding no3 flux into the sediments indicating a large nitrification contribution to the n2 flux isotopic changes in overlying water 18o of o2 were small with an average apparent sediment respiration fractionation factor e of 3 this fractionation factor is much smaller than that measured in either the open ocean or in the laboratory the low degree of fractionation is hypothesized to occur because of the interaction of diffusive layers around reactive microsites within these sediments there was no apparent isotopic fractionation of downward diffusing no3 e 0 while the ammonium that diffused out of the sediments averaged 4 5 o heavier than both source organic matter within the sediments and overlying water no3 the large discrepancy in isotopic composition between the source organic material and nh4 can be attributed to significant isotopic fractionation of ammonium during nitrification in the oxic zone finally the 15n of n2 did not change significantly over the course of the incubations in agreement with the nitrogen isotopic budget for these sediments

mass balance and mass transfer in migmatites from the colorado front range metasomatic exchanges between the infiltrating fluids and wall rocks most likely initiated the formation of nine leucosomes in two large samples of the precambrian biotite quartz feldspar migmatites from the east central colorado front range the leucosomes 2 to 20 mm thick and enclosed in mafic salvages 1 to 10 mm thick are granitic to tonalitic in composition mass balance calculations suggest that each leucosome formed by local introduction of mass the net gains and losses calculated assuming that all such gains and losses were contained within the leucosome show that in general neither the gains nor the losses fit the composition of any silicate melt it is more likely that the components were transported in a fluid recalculated on constant al basis the most significant relative mass transfers were gain of k and losses of na and mg by the rocks the metasomatic reactions calculated are those for replacement of plagioclase by microcline and breakdown of biotite the reactions must have been the cause of incipient migmatization a mafic selvage formed from the paleosome by the loss of material whose composition is tonalitic to granodioritic varying systematically with the paleosome composition

the ahar varzeghan earthquake doublet mw 6 4 and 6 2 of 11 august 2012 regional seismic moment tensors and a seismotectonic interpretation abstract on 11 august 2012 an earthquake doublet m w 6 4 and 6 2 occurred near the city of ahar northwest iran both events were only 6 km and 11 minutes apart producing a surface rupture of about 12 km in length historical and modern seismicity has so far been sparse in this area spatially the region represents a transitional zone between different tectonic domains including compression in iran westward extrusion of the anatolian plate and thrusting beneath the caucasus in this study we inverted the surface waveforms of the two mainshocks and 11 aftershocks m w 4 3 to obtain regional seismic moment tensors the earthquakes analyzed can be grouped into pure strike slip including the first mainshock and oblique reverse mechanisms including the second mainshock the sequence provides information about faulting mechanisms at the spatial scale of the entire rock volume affected by the earthquake doublet including coinciding deformation on minor faults sub parallel to the main fault and riedel shears it occurred on a so far unknown fault structure which we call the ahar fault alongside the seismological data we used geological maps satellite images and digital elevation data to analyze the geomorphology of the region our analysis suggests that the adjacent north tabriz fault which accomodates up to 7 mm yr of right lateral strike slip faulting does not compensate the entire lateral shear strain and that part of it is compensated farther north combined our results suggest a temporally and spatially complex style of deformation reverse and strike slip overprinting older reverse deformation

phosphorus imbalance in the global ocean the phosphorus budget of the pre human modern ocean is constrained applying the most recent estimates of the natural riverine eolian and ice rafted input fluxes the phosphorus burial in marine sediments and the hydrothermal removal of dissolved phosphate from the deep ocean this review of current flux estimates indicates that the phosphorus budget of the ocean is unbalanced since the accumulation of phosphorus in marine sediments and altered oceanic crust exceeds the continental input of particulate and dissolved phosphorus the phosphorus mass balance is further tested considering the dissolved phosphate distribution in the deep water column the marine export production of particulate organic matter rain rates of phosphorus to the seafloor benthic dissolved phosphate fluxes and the organic carbon to phosphorus ratios in marine particles these independent data confirm that the phosphate and phosphorus budgets were not at steadystate in the pre human global ocean the ocean is losing dissolved phosphate at a rate of 11 6 x 1010 mol yr 1 corresponding to a decline in the phosphate inventory of 4 5 kyr 1 benthic data show that phosphate is preferentially retained in pelagic deep sea sediments where extended oxygen exposure times favor the degradation of particulate organic matter and the up take of phosphate in manganese and iron oxides and hydroxides enhanced c p regeneration ratios observed in the deep water column 400 m water depth probably reflect the preferential burial of phosphorus in pelagic sediments excess phosphate is released from continental margin sediments deposited in low oxygen environments the dissolved oxygen threshold value for the enhanced release of dissolved phosphate is 20 m benthic phosphate fluxes increase drastically when oxygen concentrations fall below this value

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

exhumation and tilting of the western metamorphic belt of the coast orogen in southern southeastern alaska the uplift history of the western metamorphic belt in southern southeastern alaska can be traced using emplacement depths and cooling ages of mid cretaceous plutons which intruded the metamorphic belt during the period 101 ma to 89 ma during the period 101 ma to 94 ma the rocks of the metamorphic belt now at the surface were buried to a depth of approximately 30 km pressure data indicate that by 89 ma the western portion of the metamorphic belt was at a shallower crustal level 23 km within the study area while the eastern side remained at a depth of approximately 30 km cooling curves constructed from minerals in mid cretaceous plutonic rocks indicate that the western side of the metamorphic belt cooled earlier than the eastern side an observation consistent with the inferred uplift history southwestward transport of metamorphic belt rocks within the hanging walls of thrust and high angle faults may have provided one mechanism for uplift during mid to late cretaceous time the eastern portion of the western metamorphic belt cooled rapidly at 55 ma probably in response to a period of rapid uplift the coast shear zone an early tertiary high angle fault with west side up displacement bounds the east side of the metamorphic belt we suggest tertiary uplift occurred by tilting of the metamorphic belt due to movement along this fault

thermal history of the giant qulong cu mo deposit gangdese metallogenic belt tibet constraints on magmatic hydrothermal evolution and exhumation abstract a complete thermal history for the qulong porphyry cu mo deposit tibet is presented zircon u pb geochronology indicates that the mineralization at qulong resulted from brecciation veining events associated with the emplacement of a series of intermediate felsic intrusions combined with previously published ages our results reveal a whole intrusive history of the qulong composite pluton causative porphyries were emplaced at 16 0 ma as revealed by 40ar 39ar dating of hydrothermal biotite 15 7 0 2 ma and sericite 15 7 0 2 ma zircon and apatite u th he zhe and ahe dating of qulong revealed that both followed similar monotonic thermal trajectories from 900 c u pb ages 17 5 15 9 ma to 200 c zhe 15 7 14 0 ma and that the causative porphyries experienced faster cooling at a maximum rate of greater than 200 c myr the qulong deposit was exhumed between 13 6 ma and 12 4 ma ahe at an estimated rate of 0 16 0 24 mm y which is consistent with previous estimates for other gangdese miocene porphyry deposits our ahe thermochronology results suggest that neither the gangdese thrust system nor the yadong gulu graben affected or accelerated exhumation at the qulong deposit

the acceleration of oceanic denitrification during deglacial warming the marine nitrogen cycle was altered during the transition from glacial to interglacial conditions an analysis of 15n records throughout the world s oceans suggests that rates of denitrification in the water column accelerated during the last deglaciation

a global marine fixed nitrogen isotopic budget implications for holocene nitrogen cycling 1 a nitrogen stable isotopic model was constructed in order to constrain the holocene marine fixed nitrogen budget the primary sources and sinks considered were riverine and atmospheric sources nitrogen fixation sedimentary and water column denitrification and sediment burial the source budget was found to be insensitive to changes in nitrogen fixation rates and thus could not be used to constrain this term however the isotopic value of fixed nitrogen losses was very sensitive to the amount of sedimentary denitrification if the isotopic value of marine fixed nitrogen has not changed during the holocene as supported by sedimentary records then in order to balance the isotopic value of sinks and sources approximately 280 tg n yr 1 of sedimentary denitrification is required if such a high rate of denitrification has been sustained throughout the holocene it implies that present day estimates of marine nitrogen fixation are grossly underestimated it also implies that the marine nitrogen budget has a residence time of less than 2000 years

large earthquake doublets and fault plane heterogeneity in the northern solomon islands subduction zone in the solomon islands and new britain subduction zones the largest earthquakes commonly occur as pairs with small separation in time space and magnitude this doublet behavior has been attributed to a pattern of fault plane heterogeneity consisting of closely spaced asperities such that the failure of one asperity triggers slip in adjacent asperities we analyzed body waves of the january 31 1974 m w 7 3 february 1 1974 m w 7 4 july 20 1975 14 37 m w 7 6 and july 20 1975 19 45 m w 7 3 doublet events using an iterative multiple station inversion technique to determine the spatio temporal distribution of seismic moment release associated with these events although the 1974 doublet has smaller body wave moments than the 1975 events their source histories are more complicated lasting over 40 seconds and consisting of several subevents located near the epicentral regions the second 1975 event is well modeled by a simple point source initiating at a depth of 15 km and rupturing an approximate 20 km region about the epicenter the source history of the first 1975 event reveals a westerly propagating rupture extending about 50 km from its hypocenter at a depth of 25 km the asperities of the 1975 events are of comparable size and do not overlap one another consistent with the asperity triggering hypothesis the relatively large source areas and small seismic moments of the 1974 doublet events indicate failure of weaker portions of the fault plane in their epicentral regions variations in the roughness of the bathymetry of the subducting plate accompanying subduction of the woodlark rise may be responsible for changes in the mechanical properties of the plate interface

global survey of aftershock area expansion patterns we developed an objective method to define the aftershock areas of large earthquakes as a function of time after the main shock the definition is based upon the amount of energy released by aftershocks the spatial distribution of the energy release is first determined and is contoured the 1 day aftershock area is defined by a contour line corresponding to the energy release level of 10 15 6 ergs 100 km 2 day the 10 day 100 day and 1 y aftershock areas are similarly defined by contour lines corresponding to 10 14 8 10 14 0 and 10 13 5 ergs 100 km 2 day respectively we also define the expansion ratios at time t by the ratio of the aftershock area at t to that at 1 day using this method we study the aftershock area expansion patterns of 44 large m s 7 5 and five moderate shallow earthquakes which occurred from 1963 to 1980 each aftershock sequence is examined at four different times i e 1 day 10 days 100 days and 1 y after the main event we define the aftershock area expansion ratios and e by s 100 s 1 and l 100 l 1 respectively here s t and l t are the area and the length of the aftershock area respectively at time t our study suggests that a distinct regional variation of aftershock area expansion patterns is present it is strongly correlated with the tectonic environment in general the subduction zones of the mariana type have large expansion ratios and those of the chilean type have small expansion ratios some earthquakes that occurred in the areas of complex bathymetry such as aseismic ridges tend to have large expansion ratios these results can be explained in terms of an asperity model of fault zones in which a fault plane is represented by a distribution of strong spots called the asperities and weak zones surrounding the asperities the rupture immediately after the main shock mostly involves asperities after the main rupture is completed the stress change caused by the main shock gradually propagates outward into the surrounding weak zones this stress propagation manifests itself as expansion of aftershock activity in this simple picture if the fault zone is represented by relatively large asperities separated by small weak zones chilean type then little expansion of aftershock activity would be expected on the other hand if relatively small asperities are sparsely distributed mariana type significant expansion occurs the actual distribution of asperities is likely to be more complex than the two cases described above however we would expect that the expansion ratio is in general proportional to the spatial ratio of the total asperity area to the fault area