seismic imaging of subduction zone metamorphism combined analysis of high resolution seismic images of the alaska and cascadia subduction zones reveals where metamorphic fl uids are released both images show the subducted oceanic crust as a dipping low velocity layer with a clear termination depth however in alaska the crust is thicker 15 20 km compared to 8 km and terminates at greater depth 120 km com pared to 40 km than in cascadia based on metamorphic reaction estimates and geodynamic models we demonstrate that the termination depth corresponds to eclogitization of the crust triggered by dehydration of water bearing minerals and that the location of this reaction is dependent on the thermal structure of the subducted slab

holocene climate variability archived in the puruogangri ice cap on the central tibetan plateau two ice cores 118 4 and 214 7 m in length were collected in 2000 from the puruogangri ice cap in the center of the tibetan plateau tp in a joint us chinese collaborative project these cores yield paleoclimatic and environmental records extending through the middle holocene and complement previous ice core histories from the dunde and guliya ice caps in northeast and northwest tibet respectively and dasuopu glacier in the himalaya the high resolution puruogangri climate record since ad 1600 details regional temperature and moisture variability the post 1920 period is characterized by above average annual net balance contemporaneous with the greatest 18 o enrichment of the last 400 years consistent with the isotopically inferred warming observed in other tp ice core records on longer timescales the aerosol history reveals large and abrupt events one of which is dated 4 7 kyr bp and occurs close to the time of a drought that extended throughout the tropics and may have been associated with centuries long weakening of the asian indian african monsoon system the puruogangri climate history combined with the other tp ice core records has the potential to provide valuable information on variations in the strength of the monsoon across the tp during the holocene

geochronology of early to middle paleozoic tectonic development in the southwest newfoundland gander zone southwest newfoundland s gander zone was once considered part of the collided eastern margin of an early paleozoic iapetus ocean distinguished from the rest of the gander zone by the extensive exposure of a polydeformed amphibolite to greenschist facies sequence considered devonian in age overlying presumed precambrian basement it was later found that truly devonian strata were confined to the cape ray fault system the local northwestern boundary of the zone u pb zircon isotopic ages of 452 13 51 ma and 458 22 29 ma on metavolcanic rocks in the upper part of the sequence southeast of the fault system indicate that ordovician and possibly older rocks underlie the gander zone itself a temporal framework for the three main stages of regional deformation corresponding to pre metamorphic recumbent folding d 1 and transpression d 2 and d 3 is presented using u pb and 40 ar 39 ar dates of granitoid and metamorphic rocks d 1 is bracketed as late o

the provenance of granite boulders in conglomerates of the northern and central belts of the southern uplands of scotland rb sr whole rock isochrons from several suites of granite boulders which occur in ordovician and silurian conglomerates in the southern uplands of scotland yield ages of around 1200 ma 600 to 700 ma and 470 to 490 ma the plutonic and tectonic history recorded by these clasts corresponds more closely with that of nw newfoundland than with that of scotland the petrography of the clasts can also be matched with exposed granite plutons in newfoundland since the conglomerates were derived from the nw it is concluded that the southern uplands lay to the se of newfoundland a total of 1500 km strike slip displacement occurred between the caradoc and the early devonian consistent with oblique subduction of the iapetus ocean below the north american continental margin

collision along an irregular margin a regional plate tectonic interpretation of the canadian appalachians discussion stockmal et al recently presented a simple three dimensional plate tectonic model by which they attempted to explain the pre carboniferous evolution of the northern appalachians this model which in part follows the basic principles of the two stage collision model of colman sadd 1982 is mainiy based on the results of a marine seismic profile across northem newfoundland and on large scale geometrical considerations such models are useful because they provide geologists with a framework that can be tested against field data however in this case the existing geological data base in our opinion is incompatible with the model we will discuss the inconsistencies and present an altemative model the main thesis of the stockmal et al model is that the taconian and acadian orogenies are explained in terms of continuous southeastward subduction of iapetus oceanic lithosphere during the collision between the taconic magmatic arc and the irregular margin of north america the benioff zone clogged first in newfoundland and then in mainland canada the continuing convergence between the taconic arc and north america in newfoundland was then achieved by delamination of lithospheric mantle while b subduction continued between the taconic arc and north america in mainland canada evidence in support of this model includes the 300 400 km right hand offset of equivalent tectono stratigraphic zones between newfoundland and mainland canada and a difference in style and vergence of the acadian structures in newfoundland and new brunswick the idea of a diachronous collision is not a new one but the sense of diachronism remains unresolved see e g dallmey er 1977 clague et al 1981 lux 1986 considered the allochthonous ophiolites in the humber zone and argued in favour of a north to south diachronism his conclusion is consistent with the fact that the oldest fossil dated autochthonous flysch is younger in quebec than in newfoundland since there is no overstepping autochthonous cover in quebec stockmal et al argue that the timing of the final emplacement of the allochthons and the closure of iapetus is not well constrained there and they explain the acadian orogeny in mainiand canada as

devonian extension in northwestern newfoundland 40ar 39ar and u pb data from the ming s bight area baie verte peninsula abstract the ming s bight group of northwestern newfoundland an outlier of humber zone continental margin rocks is entirely surrounded by ophiolitic rocks of the dunnage zone structures in the ming s bight group and adjacent units record three main phases of deformation the earliest structures relate to silurian sinistral transpression previously documented in the region two later phases of extensional deformation produced a series of dextral oblique normal shear zones and faults that now separate the ming s bight group in the footwall from ophiolitic and granitoid rocks in the hangingwall 40ar 39ar and u pb data constrain the times of oblique normal shear and cooling metagabbro in the point rousse ophiolite complex which lies in the hangingwall preserves disturbed ordovician hornblende 40ar 39ar ages whereas adjacent shear zones record devonian ages hornblendes in pacquet harbour group amphibolites within extensional shear zones mainly record 40ar 39ar ages of 390 380 ma synkinematic titanite

periodicity of climate conditions and solar variability derived from dendrochronological and other palaeoclimatic data in high latitudes abstract the periodicity of climatic processes in the barents sea region and along the arctic ocean coast during several hundred years has been studied by analyzing the tree ring chronologies for the regions close to the northern timberline in the barents sea region cyclicities of climatic processes with periods of around 90 30 35 22 23 18 and 11 12 years have been established by spectral analysis of the data for the kola peninsula wavelet analysis of annual series of conifer tree rings generalized for 10 regions along the northern timberline from the kola peninsula to chukotka for the period 1458 1975 has revealed the same periodicities for the vast areas of northern russia climatic cyclicity with a period of about 35 years is known as the bruckner cycle climatic cycles with periods of around 90 22 23 and 11 12 years correlate well with the corresponding solar activity cycles a possible solar forcing of periodic climatic processes and its nonlinear influence on the atmosphere ocean continental system are discussed

a 2 326 year tree ring record of climate variability on the northeastern qinghai tibetan plateau 1 high resolution climate proxy records covering the last two millennia on the qinghai tibetan plateau are scarce yet essential to evaluation of the patterns synchroneity and spatial extent of past climatic changes including those in the medieval warm period mwp and the little ice age lia here we present a 2326 year tree ring chronology of sabina przewalskii kom for dulan area of northeastern qinghai tibetan plateau we find that the annual growth rings mainly reflect variations in regional spring precipitation the greatest change in spring precipitation during the last two millennia seems to occur in the second half of the 4th century the north atlantic mwp was accompanied by notable wet springs in the study region during a d 929 1031 with the peak occurring around a d 974 three intervals of dry springs occurred in the period of lia our tree ring data will facilitate intercontinental comparisons of large scale synoptic climate variability for the last two millennia

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

tree ring based precipitation reconstruction in the south slope of the middle qilian mountains northeastern tibetan plateau over the last millennium 1 a tree ring sabina przewalskii kom based millennial precipitation reconstruction on the south slope of the middle qilian mountains in the northeastern margin of tibetan plateau china was completed which explains 48 5 of the variance in the instrumental precipitation from 1958 to 2004 the long term precipitation variation patterns were confirmed on the basis of the duration magnitude and intensify of the multidecadal dry wet events there are several stronger multidecadal dry periods 1092 1172 1441 1517 and 1564 1730 whereas there is only one outstanding severe wet event of 1352 1440 the variations of the precipitation reconstruction are accordant with the glacier accumulation and dust contents of dunde ice core and also with the variations of the precipitation runoff palmer drought severity index and tree ring width series in the northeastern tibetan plateau the spatial extent of the great drought in the latter half of the 15th century also concentrated on the northeastern tibetan plateau the moisture variations in the northeastern tibetan plateau are synchronous over a large spatial and temporal range in multidecadal scale for the last millennium especially during dry periods wavelet analyses and comparisons with the minimal solar activity show that the precipitation variations for the last millennium may have some association with the solar activity on multidecadal to centennial scales

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

possible solar origin of the 1 470 year glacial climate cycle demonstrated in a coupled model dansgaard oeschger events are rapid climate fluctuations that occurred during and at the end of the last ice age with remarkable regularity there were 23 such events between 110 000 and 23 000 years bp with a periodicity of 1 470 years identify the source of this cycle and it should be possible to say what triggered these events the sun had been excluded as a possible cause because of the lack of a 1 470 year spectral contribution in records of solar variability despite this braun et al present a new hypothesis that convincingly explains the 1 470 year period as the net result of two well known solar cycles the devries and gleissberg cycles with periods of 210 years and 87 years many palaeoclimate records from the north atlantic region show a pattern of rapid climate oscillations the so called dansgaard oeschger events with a quasi periodicity of 1 470 years for the late glacial period1 2 3 4 5 6 various hypotheses have been suggested to explain these rapid temperature shifts including internal oscillations in the climate system and external forcing possibly from the sun7 but whereas pronounced solar cycles of 87 and 210 years are well known8 9 10 11 12 a 1 470 year solar cycle has not been detected8 here we show that an intermediate complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the dansgaard oeschger events with a spacing of 1 470 years when forced by periodic freshwater input into the north atlantic ocean in cycles of 87 and 210 years we attribute the robust 1 470 year response time to the superposition of the two shorter cycles together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation for holocene conditions similar events do not occur we conclude that the glacial 1 470 year climate cycles could have been triggered by solar forcing despite the absence of a 1 470 year solar cycle

seismic tomography and earthquake locations in the nicaraguan and costa rican upper mantle the central american subduction zone exhibits large variations in geochemistry downgoing plate roughness and dip and volcano locations over a short distance along the arc results from joint inversions for vp vp vs and hypocenters from the tomography under costa rica and nicaragua tucan experiment give insight into its geometry and structure in both costa rica and nicaragua the intermediate depth seismic zone is a single layer no more than 10 to 20 km thick tomographic images show that throughout nicaragua and costa rica the slowest mantle p wave velocities appear below and behind the volcanic front indicating likely zones of highest temperature extending 80 to 120 km depth a sheet of high vp vs thought to be caused by melt is imaged directly beneath the nicaraguan volcanoes whereas a weaker broader anomaly is imaged beneath the costa rican volcanoes potentially indicating a greater extent of melting beneath nicaragua within the downgoing plate anomalously low velocities occur at least 20 30 km below wadati benioff zone seismicity to depths of 140 km beneath nicaragua and to 60 km depth beneath costa rica they indicate 10 20 serpentinized upper mantle of the downgoing plate beneath nicaragua similar to that inferred from refraction seaward of the trench but continuing to subarc depths this unusually hydrated lithosphere may introduce more water into the nicaraguan mantle initiating increased amount of melting and fluid flux to the arc

sharp thermal transition in the forearc mantle wedge as a consequence of nonlinear mantle wedge flow 1 in the forearc mantle wedge the thermal field depends strongly on slab driven mantle wedge flow the flow is in turn affected by the thermal field via the temperature dependence of mantle rheology using thermal modeling we show that the nonlinear feedback between the thermal and flow fields always leads to complete stagnation of the mantle wedge over a shallow weakened part of the slab mantle interface and an abrupt onset of mantle flow further down dip the abrupt increase in flow velocity leads to a sharp thermal transition from a cold stagnant to a hot flowing part of the wedge this sharp thermal transition is inherent to all subduction zones explaining a commonly observed sharp arc ward increase in seismic attenuation

a displaced and metamorphosed peralkaline granite related to the late proterozoic labrador and gardar suites the doolough granite of county mayo northwest ireland the chemically and lithologically distinct doolough granite from the annagh division in northwest county mayo ireland includes part of the northwesternmost exposures of precambrian basement in europe the doolough granite is similar to precambrian granitic intrusions found in labrador and southwest greenland although its age of emplacement at u pb in zircon is slightly younger than the canadian intrusions a reconstruction of the pre iapetus disposition of the eastern laurentian margin suggests that the doolough granite was probably emplaced at a location sufficiently close to both southwest greenland and labrador for it to have formed part of the same magmatic province during a period of restricted crustal extension that preceded the grenville event

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

deformation of antigorite serpentinite at high temperature and pressure abstract deformation experiments were conducted in a griggs type apparatus to constrain the rheology of antigorite serpentinite at high temperatures and pressures samples deformed at temperatures of 400 625 c and pressures of 0 85 1 5 gpa experienced semi brittle deformation resulting in localization on faults at 5 to 25 strain samples deformed at 300 c exhibited transitional behavior the stresses measured for our samples are in good agreement with recent experiments conducted in the deformation dia apparatus however our results indicate that steady state ductile flow is not achieved in contrast with interpretations based on the deformation dia experiments extrapolation of our data to geologic conditions suggests that serpentinites may be weak enough during localized frictional sliding to account for slab wedge decoupling inferred from geologic observations experiments conducted above the thermal stability of antigorite at 700 c and 1 5 gpa show evidence for distributed deformation this observation does not support the hypothesis that intermediate depth earthquakes result directly from dehydration embrittlement in addition samples exhibit velocity strengthening from 300 to 700 c a frictional behavior that inhibits earthquake nucleation

a 2000 year temperature reconstruction in the animaqin mountains of the tibet plateau china a 2665 year ring width chronology was developed based on qilian juniper from the upper treeline of the animaqin mountains on the eastern tibetan plateau correlation analysis results showed that the chronology was significantly negatively correlated with april june maximum temperature at nearby meteorological stations indicating that maximum temperature is the factor that limits tree growth in this area accordingly we reconstructed the average april june maximum temperature variations since 261 bc our regression model explained 37 9 of the total variance for the whole calibration period of 1960 2012 our reconstruction revealed that the maximum temperature started to increase from approximately 1750 without a rapid warming trend and the warmest period was from ad 890 to 947 as opposed to the recent period whereas the period from ad 351 483 was the coldest significant periods in the wavelet power spectrum were approximately 2 8 years 20 30 years 30 60 years and 60 130 years as well as some long term periods more than 200 years comparisons with other temperature series from neighboring regions and the northern hemisphere as a whole support the validity of our reconstruction and suggest that it provides a representation of the temperature change for the animaqin area although asymmetric variation patterns in minimum and maximum temperatures were found

depth of the decoupling plate interface and thermal structure under arcs subduction proceeds as thrust movements at the boundary between the subducting plate and the rigid overlying plate at depth below this mechanically decoupling plate interface the subducting plate couples with the overlying mantle and flow is induced in the mantle wedge this induced flow is the main factor that controls thermal structure under arcs depth of this decoupling to coupling transition at the plate interface is estimated from observed surface heat flow in the northeastern japan arc using a two dimensional numerical simulation of thermal structure the estimated depth is about 70 km the termination depth of thrust earthquakes agrees well with the depth of the coupling transition which indicates that these earthquakes occur at the decoupling plate interface the mechanism of this decoupling plate interface is discussed in this paper it is believed that water associated with the subducting oceanic crust reduces the frictional stress at the plate interface and thrust movement thus becomes possible petrological studies show that dehydration reaction in the subducting oceanic crust terminate at about 2 0 gpa and have little temperature dependence termination depths of thrust earthquakes estimated from seismic studies are nearly the same 60 80 km for various arcs this indicates that depth of the decoupling to coupling transition is controlled by the termination depth of dehydration reaction in the subducting oceanic crust across arc heat flow profiles observed in various subduction zones show similar features heat flow is very low in the forearc region and increases steeply at the volcanic front considering that the depth of the slab is about 100 km at the volcanic front for various arcs this heat flow feature is closely related to the depth of the slab thus it is concluded that thermal structure under arcs is mainly controlled by the depth of the pressure dependent dehydration reactions in the subducting oceanic crust

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

geochronology of the baie verte peninsula newfoundland implications for the tectonic evolution of the humber and dunnage zones of the appalachian orogen u pb analyses of zircon from the burlington granodiorite suggest intrusion at c 460 465 ma hornblende and biotite from central portions of the pluton record markedly younger sup 40 ar sup 39 ar plateau dates 410 420 ma which are interpreted to date contact metamorphic effects associated with the widespread emplacement of silurian devonian igneous suites northern portions of the burlington granodiorite are polydeformed and regionally metamorphosed hornblende and biotite from this terrane yield sup 40 ar sup 39 ar plateau ages of 345 350 ma u pb analyses of zircon from the dunamagon granite indicate emplacement at c 440 460 ma thereby providing an upper limit for tectonic juxtapositioning of the humber and dunnage zones along the baie verte line similar ages are also recorded by hornblende and biotite throughout northerly portions of the mings bight humber zone and pacquet harbour dunnage zone groups these results indicate that the tectonic evolution of the baie verte line as polygenetic and involved 1 regionally significant tectonothermal activity prior to the middle ordovician and 2 middle to late paleozoic tectonothermal activity centered along easterly segments of the baie verte line the regional metamorphism associated with this orogenic activity altered primary u pb and rb sr isotopic systems within various igneous suites exposed in northeastern portions ofmore the burlington peninsula which may explain some inconsistent geochronological results previously obtained 54 references 6 figures 5 tables less

seismic attenuation and mantle wedge temperatures in the alaska subduction zone 1 anelastic loss of seismic wave energy or seismic attenuation 1 q provides a proxy for temperature under certain conditions the q structure of the upper mantle beneath central alaska is imaged here at high resolution an active subduction zone where arc volcanism is absent to investigate mantle thermal structure the recent broadband experiment across the alaska range beaar provides the first dense broadband seismic coverage of this region the spectra of p and sh waves for regional earthquakes are inverted for path averaged attenuation operators between 0 5 and 20 hz along with earthquake source parameters these measurements fit waveforms significantly better when the frequency dependence of q is taken into account and in the mantle frequency dependence lies close to laboratory values inverting these measurements for spatial variations in q reveals a highly attenuating wedge with q 500 assuming frequency dependence comparison with p results shows that attenuation in bulk modulus is negligible within the low q wedge as expected for thermally activated attenuation mechanisms bulk attenuation is significant in the overlying crust and subducting plate indicating that q must be controlled by other processes the shallowest part of the wedge shows little attenuation as expected for a cold viscous nose that is not involved in wedge corner flow overall the spatial pattern of q beneath alaska is qualitatively similar to other subduction zones although the highest wedge attenuation is about a factor of 2 lower the q values imply that temperatures exceed 1200 c in the wedge on the basis of recent laboratory based calibrations for dry peridotite these temperatures are 100 150 c colder than we infer beneath japan or the andes possibly explaining the absence of arc volcanism in central alaska

geochronology of the baie verte peninsula newfoundland implications for the tectonic evolution of the humber and dunnage zones of the appalachian orogen a discussion

centennial scale process activity in a complex landslide body in the qilian mountains northeast tibetan plateau china abstract mass movements in china typically encompass landslides rockfalls and debris flows and these processes affect almost 70 of all mountain areas of china an improved understanding of geomorphic process dynamics and their drivers and process histories are important prerequisites for a proper assessment and a sustainable management of mountain hazards tree rings have on varied occasions proven to be a reliable tool for the acquisition of data on past mountain hazards here we present the first reconstruction of past landslide activity on a slope in the qilian mountains northeast tibetan plateau china to this end a total of 543 qilian juniper sabina przewalskii kom samples were selected from 239 trees growing on or next to a complex landslide body with the aim to reconstruct past landslide histories at the site the dataset of disturbed trees was complemented with 174 increment cores from 84 reference qilian juniper trees growing on three adjacent yet undisturbed sites based on the dating of the samples and the interpretation of growth disturbances gd in the tree ring series of affected trees we provide the first reconstruction of past landslides as retrieved from a dendrogeomorphic record covering more than a millennium 956 2011 ce results show that the first detectable gd occurred as early as in 1042 ce followed by seven major landslide reccurrences in 1703 1816 1848 1863 1913 1970 and 1982 comparison between our landslide record and a dendroclimatic precipitation reconstruction points to the crucial role of major longer term wet precipitation anomalies on landslide occurrence

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

global surface temperatures over the past two millennia 1 we present reconstructions of northern and southern hemisphere mean surface temperature over the past two millennia based on high resolution proxy temperature data which retain millennial scale variability these reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the northern hemisphere conclusions for the southern hemisphere and global mean temperature are limited by the sparseness of available proxy data in the southern hemisphere at present

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

geochemical and geological evidence bearing on the origin of the bay of islands and coastal complex ophiolites of western newfoundland abstract suggestions that ophiolitic rocks of the bay of islands complex boic and coastal complex cc of southwestern newfoundland were formed at a seafloor spreading center are supported by 1 1 whole rock trace and major element data from diabases and basalts 2 2 spinel mineral chemistry from ultramafic rocks 3 3 the internal geology of the ophiolite terranes and 4 4 regional geologic and tectonic constraints in the western newfoundland appalachians diabase and basalt samples from the boic and the northern cc massifs are tholeiitic and geochemically indistinguishable from present day mid ocean ridge basalts morbs many diabases from the lewis hills massif the southernmost part of the cc are also identical to morbs but there is also an unusual suite of diabases from the lewis hills that is unlike any other suite yet reported from a variety of tectonic settings including island arcs ocean islands or spreading centers this suite is interpreted to have been produced by unusual magma generation processes in the deep structural levels of an oceanic ridge ridge transform fault approximately 90 of spinels from ultramafic rocks in the boic and cc have cr cr al ratios that are less that 0 60 comparable to those values reported from ultramafic rocks of the present day ocean basins these geochemical constraints in combination with previously described geological relationships within the ophiolite terranes and regional tectonic relationships in the western newfoundland appalachians suggest that the boic and cc ophiolites formed within a main ocean basin i e the early paleozoic iapetus ocean along a seafloor spreading center and ridge ridge transform fault respectively there is little evidence to suggest formation in either an island arc or back arc basin tectonic setting as such the boic and cc ophiolites are probably well suited for detailed petrologic structural and geophysical studies to determine the processes involved in the generation and evolution of contemporary oceanic crust and upper mantle

hydrometeorological reconstructions for northeastern mongolia derived from tree rings 1651 1995 reconstructions of annual prior august current july precipitation and streamflow 345 yr in length 1651 1995 are presented for northeastern mongolia based on tree ring width data these precipitation and streamflow reconstructions account for 54 and 48 of the respective variance in instrumental data over the past 50 years variations in instrumental precipitation and streamflow are within the range of those reconstructed over the length of tree ring records however there appear to be more frequent extended wet periods during the twentieth century multitaper spectral analysis revealed statistically significant peaks at 10 8 and 12 8 yr for the precipitation reconstruction and at 12 8 and 20 3 23 8 yr for the streamflow reconstruction similarly singular spectrum analysis identified spectral modes of variation at 12 and 21 yr for both series these spectra resemble those found for tree ring based precipitation reconstructions in central china as well as the western united states and may reflect solar influences on the climate of mongolia

complex patterns of fluid and melt transport in the central andean subduction zone revealed by attenuation tomography abstract we present a high resolution 3 d model of p wave attenuation q p 1 for the central andean subduction zone data from 1500 mostly intermediate depth 60 250 km earthquakes recorded at three temporary seismic networks covering the forearc arc and backarc around 23 s were used for tomographic inversion the forearc is characterised by uniformly high q p values indicating low temperature rocks in accordance with low surface heat flow values prominent low q p anomalies are found beneath the magmatic arc and the backarc in the crust and mantle continuous regions of low q p connect earthquake clusters at 100 km and 200 km depth with zones of active volcanism in the arc and backarc fluids fluxed from the subducted oceanic lithosphere into the overlying mantle wedge where they induce melting explain our observations we propose that low q p regions indicate source and ascent pathways of metamorphic fluids and partial melts ascent of fluids and melts as imaged by seismic q p are not vertical as is often implicitely assumed instead sources of fluids are located at different depth levels and ascent paths are complex and exhibit significant variation within the study area the largest quaternary backarc volcano cerro tuzgle is fed by mantle melts which are imaged as a plume of low q p material that reaches to the strong earthquake cluster at 200 km depth