10be signature of the cosmic ray event in the 10th century ce in both hemispheres as confirmed by quasi annual 10be data from the antarctic dome fuji ice core

ion microprobe analysis of oxygen isotopes in garnets of complex chemistry abstract accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias a component of which depends on the cation chemistry of the analyzed mineral in this study 26 garnet standards including 14 new standards that span the compositional range of pyrope almandine grossular spessartine and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets all analyses were normalized to a single master garnet standard uwg 2 before bias from cation composition was considered bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets bias is correlated with molar volume in garnets of all compositions in this study although this correlation is suitable as a correction scheme for bias a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed this method reproduces the bias of all but one standard to within a range of 0 4 an accuracy that is on the same order as the reproducibility 0 3 2 s d of the master garnet standard uwg 2 but that remains an independent source of error the new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic zoned skarn garnet from the adirondack mountains while previous analyses were at the mm scale the new data resolve a gradient of 18 o of 2 1 over 16 m if experimentally derived diffusion coefficients are correct these new results show that granulite facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 myr

fault reactivation control on normal fault growth an experimental study field studies frequently emphasize how fault reactivation is involved in the deformation of the upper crust however this phenomenon is generally neglected except in inversion models in analogue and numerical models performed to study fault network growth using sand silicon analogue models we show how pre existing discontinuities can control the geometry and evolution of a younger fault network the models show that the reactivation of pre existing discontinuities and their orientation control i the evolution of the main fault orientation distribution through time ii the geometry of relay fault zones iii the geometry of small scale faulting and iv the geometry and location of fault controlled basins and depocenters these results are in good agreement with natural fault networks observed in both the gulf of suez and lake tanganyika they demonstrate that heterogeneities such as pre existing faults should be included in models designed to understand the behavior and the tectonic evolution of sedimentary basins

evolution characteristics of transtensional faults and their impacts on hydrocarbon migration and accumulation a case study from the huimin depression bohai bay basin eastern china abstract the study of transtensional faults is significantly important for analysing migration and accumulation of hydrocarbons in petroliferous basins the purpose of this study is to present disparities in the temporal and spatial evolution of two boundary transtensional faults northern linshang fault and southern xiakou fault in the huimin depression by 2d structural restoration and quantitative calculations of fault activity this paper also reveals the controls of transtensional faults on the migration and accumulation of hydrocarbons by considering the stress normal to the fault plane p the shale gouge ratio sgr of the fault zone and models of migration pathways the results show that the transtensional systems within the huimin depression were generated from the reactivation of basement faults under an oblique extensional stress field the linshang fault linked two initially separated segments and then behaved as a single fault since the ek period whereas the xiakou fault retained significant three segment growth properties during the paleogene during the hydrocarbon charging period the weak activity and strong vertical sealing restricted the occurrence of vertical migration around the xiakou fault while the relatively strong movement and weak vertical sealing resulted in multilayer hydrocarbon accumulations around the linshang fault meanwhile the vertically closed fault with high sgr 0 6 acted as barriers and trapped hydrocarbons on the lateral migration pathways whereas the vertically closed fault with low sgr

differential compaction faults and their implications for fluid expulsion in the northern bozhong subbasin bohai bay basin china abstract a series of differential compaction faults was identified in the northern bozhong subbasin bohai bay basin china by using 3d seismic well log and lithology data the differential compaction faults display two obvious characteristics first they develop along a lithologic boundary which separates thick sandstone from underlying mudstones facies and thickness change such as an abrupt lithologic change between sandstone and mudstone a lateral thickness change of overlying sandstone are the basic controlling factors of these differential compaction faults second they have a definite strike direction according to the fault strike the differential compaction faults can be divided into three groups group a have an approximate orthogonal strike with the tectonic faults group b display a similar strike with the slope and group c show radial strikes on the circular basement uplift tectonic faults influence the planform patterns of differential compaction faults in their near vicinity and induce these faults displaying an approximate orthogonal intersection with the late period through going faults group a basin slope promote the formation of differential compaction faults by downslope gravity sliding and cause faults parallel to the strike of slope group b circular basement topography generates isotropic stress and leads the differential compaction faults above the basement dominated by radial strikes group c production and geochemistry data is an evidence of differential compaction faults developed in a late period when the strata reach a certain burial depth that the source rocks enter the oil generating window the presence of thermogenic fluid within shallow reservoirs represents as evidence of hydrocarbon drained and migrated through the differential compaction faults the differential compaction faults could serve as significant conduits for fluid expulsion and hydrocarbon accumulation in the bohai bay basin china

challenges in c 14 dating towards the limit of the method inferred from anchoring a floating tree ring radiocarbon chronology to ice core records around the laschamp geomagnetic field minimum the c 14 dating method is the cornerstone for inferring age estimates for natural archives covering the last 50 000 yrs however c 14 age calibration for the last ice age relies mostly on records that only indirectly reflect the atmospheric c 14 concentrations in consequence calendar age estimates are significantly more uncertain for the period of the last ice age compared to the past 14000 yrs where tree ring based calibration records exist here we connect a c 14 tree ring chronology from kauri trees in new zealand to ice core be 10 records via the common signal in the galactic cosmic ray flux around the period of the laschamp geomagnetic field minimum ca 41 000 yrs bp synchronous changes of modelled c 14 and c 14 inferred from u th dated speleothems support the ice core chronology independently and suggest that the published ice core time scale errors are rather conservative for this period our analysis puts c 14 age determinations directly into the context of ice core climate records and it shows that the c 14 records underlying the c 14 calibration curve overestimate the atmospheric c 14 concentration by more than 200 parts per thousand consequently c 14 age calibration presently yields too old calendar age estimates by about 1200 yrs for this period c 2014 elsevier b v all rights reserved less

channelized fluid flow and mass transfer along a rift related detachment fault eastern alps southeast switzerland remnants of a rift related low angle detachment system are spectacularly exposed in the continental err nappe and occur discontinuously in the underlying oceanic platta nappe in southeast switzerland rocks along the detachment fault exhibit systematic changes in mineralogy fabrics and structures that are related to deformation and hydration of granite to form cataclasite and subsequent gouge structural mineralogical and geochemical data indicate a continuous evolution of fluid flow and mass transfer along the detachment fault mass balance calculations together with stable isotope data suggest 1 an altered seawater source and local interaction with mantle rocks 2 limited fluid rock interaction and mass transfer during initial cataclasis at deeper crustal levels and temperatures of 150 to 200 c 3 increased fluid flux and mass transfer at slightly lower temperatures 100 150 c during gouge formation at shallower crustal levels and 4 strongly localized fluid rock interaction at low temperatures 65 80 c near the sea floor at a final stage of detachment faulting we propose a model in which seawater dominated fluids penetrated and locally interacted with mantle rocks before they were caught and channelized along large scale detachment faults flow direction is upward along the detachment from higher to lower temperatures suggesting that the driving force of fluid flow was thermal fluid convection associated with mantle exhumation our study suggests that this large scale detachment fault is a good analog for extensional structures along present day nonvolcanic rifted margins such structures along ocean continent transitions are important in controlling fluid pathways and mass transfer between mantle and continental crust

the effect of fluid and deformation on zoning and inclusion patterns in poly metamorphic garnets within the bergen arcs of w norway caledonian eclogite facies assemblages t 650 c p 15 kbar have formed from grenvillian granulites t 800 900 c p 10 kbar along shear zones and fluid pathways garnets in the granulites grti pyr56 40 alm45 25gro19 14 are unzoned or display a weak ca 1 wt feo over 1000 m zoning the eclogite facies rocks contain garnets inherited from their granulite facies protoliths these relict garnets have certain areas with compositions identical to the garnets in their nearby granulite but can be crosscut by bands of a more almrich composition grtii pyr31 41alm40 47gro17 21 formed during the eclogite facies event these bands orientated preferentially parallel or perpendicular to the eclogite foliation may contain mineral filled veins or trails of eclogite facies minerals omphacite amphibole white mica kyanite quartz and dolomite steep compositional gradients up to 9 wt feo over 40 m separate the two generations of garnets indicating limited volume diffusion the bands are interpreted as fluid rich channels where element mobility must have been infinitely greater than it was for the temperature controlled volume diffusion at mineral interfaces in the granulites the re equilibration of granulite facies garnets during the eclogite facies event must therefore be a function of fracture density deformation and fluid availability the results cast doubts on modern petrological and geochronological methods that assume pure temperature controlled chemical re equilibration of garnets

timing and climate forcing of volcanic eruptions for the past 2 500 years volcanic eruptions contribute to climate variability but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual to decadal temperature variability in the northern hemisphere during the past 2 500 years our results are based on new records of atmospheric aerosol loading developed from high resolution multi parameter measurements from an array of greenland and antarctic ice cores as well as distinctive age markers to constrain chronologies overall cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth century pandemics famines and socioeconomic disruptions in eurasia and mesoamerica while allowing multi millennium quantification of climate response to volcanic forcing

rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth we present laser ablation microprobe inductively coupled mass spectrometry analyses of y yb er dy and gd in garnet crystals from high grade metamorphic and migmatitic rocks from the sierras pampeanas of argentina these rocks contain large garnet porphyroblasts 4 mm that are compositionally zoned rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores a notable feature of this zonation is the inversion of yb er and yb dy ratios from 1 in the cores to 1 in the rims we show quantitatively that the spatial distribution of these trace elements in garnet can be most simply and effectively explained as arising from rayleigh fractionation during garnet growth we also analyzed a small garnet crystal 2 mm representative of a garnet population that is associated with migmatitic leucosomes this crystal displays uniformly low concentrations of all trace elements that are virtually identical in both absolute and relative magnitudes to those in the rims of the larger garnet porphyroblasts the small crystals and perhaps part of the porphyroblast rims are likely to be peritectic products of incongruent melting reactions we argue that melts formed from garnet bearing sources may generally be unable to equilibrate with metamorphic garnet cores and may thus be more strongly depleted in heavy rare earth elements and y than modeling based on bulk source rock abundances of these elements would indicate

an experimental study of secondary oil migration experiments using long glass columns packed with glass beads or sand have been done to investigate secondary oil migration under hydrostatic conditions different combinations of bead sizes oil densities oil water interfacial tensions and column orientations have been tested in some experiments the oil was replaced by air the observations included the oil migration pathway the minimum oil column height needed for migration and the rate of advance of the migration front migration was found to take place along restricted pathways and an imbibition front often formed at the bottom of the oil zone the minimum oil zone height needed for migration can be predicted accurately if the values of the drainage and imbibition capillary pressures are known for the saturations at which the oil just becomes disconnected in most experiments the migration front advanced at a constant rate which depended on the fluid properties bead size initial oil height and pore structure migration rate is dependent on buoyant and capillary forces but the dependence on capillary forces becomes weaker as the oil length increases column orientation also has been found to affect migration efficiency

large variations in holocene solar activity constraints from 10be in the greenland ice core project ice core 1 cosmogenic radionuclides extracted from ice cores hold a unique potential for reconstructing past solar activity changes beyond the direct instrumental period taking the geomagnetic modulation into account the solar activity in terms of the heliospheric modulation function can quantitatively be reconstructed in high resolution throughout the holocene for this period our results reveal changes in heliospheric modulation of galactic cosmic rays significantly larger than the variations reconstructed on the basis of neutron monitor measurements of galactic cosmic rays for the last 50 years moreover the 10be data from the greenland ice core project ice core as well as 14c support a high current solar activity however although the reconstruction of solar activity on long timescales is difficult our result suggests that the modern activity state of the sun is not that exceptional regarding the entire holocene this extended solar activity record provides the basis for further detailed investigations on solar and cosmic ray physics as well as on solar forcing of the earth s climate whose importance is suggested by increasing paleoclimatic evidences

on the common solar signal in different cosmogenic isotope data sets 1 in this article we aim to determine frequency ranges and intervals of time in which the solar signal dominates in different cosmogenic isotope data from a 14c based reconstruction of cosmic ray intensity over the last millennia we computed expected 10be variations in two antarctic sites dom fuji and south pole and two greenland sites dye 3 and gisp 2 and compared them with the actually measured 10be abundance at the sites by applying different methods of analysis such as bivariate correlation conventional fft coherence and wavelet coherence we found the following 1 the modeled series on the basis of 14c data are in good agreement with the measured 10be data sets on different timescales and at different locations confirming the existence of a common solar signal in both isotope data 2 the 10be data are driven by the solar signal on timescales from about 100 years up to 1000 years or even to multimillennial scales at the longer scales paleomagnetism plays an increasingly important role 3 the local climate dominates the 10be data mostly on short 100 years timescales but the solar signal becomes important even at short scales during periods of grand minima of solar activity 4 there is an indication of a possible systematic uncertainty in the early holocene likely due to a not perfectly stable thermohaline circulation which requires additional studies we have shown that both 14c and 10be based records are consistent with each other over a wide range of timescales and time intervals they form a robust basis for quantitative reconstructions of solar activity variations in the past

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

cosmic ray event in 994 c e recorded in radiocarbon from danish oak we present measurements of radiocarbon in annual tree rings from the time period 980 1006 ce hereby covering the cosmic ray event in 994 ce the new radiocarbon record from danish oak is based on both earlywood and latewood fractions of the tree rings which makes it possible to study seasonal variations in 14c production the measurements show a rapid increase of c 10 0 from 993 to 994 ce in latewood followed by a modest decline and relatively high values over the ensuing 10 years this rapid increase occurs from 994 to 995 ce in earlywood suggesting that the cosmic ray event most likely occurred the the period between april june 994 ce our new record from danish oak shows strong agreement with existing 14c records from japan thus supporting the hypothesis that the 994 ce cosmic ray event was uniform throughout the northern hemisphere and therefore can be used as an astro chronological tie point to anchor floating chronologies of ancient history

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

beryllium 10 in the greenland ice core project ice core at summit greenland concentrations of the cosmogenic isotope 10be have been measured in more than 1350 samples from the greenland ice core project grip ice core drilled at summit greenland although a dust associated component of 10be retained by 0 45 m filters in some of the samples complicates the interpretations the results confirm that the first order origin of 10be concentration variations is changes in precipitation rate associated with different climate regimes this effect is seen not only between glacial and interglacial periods but also during the shorter dansgaard oeschger interstadials by contrast the 10be data do not support the interpretation of rapidly varying accumulation i e climate during the last interglacial they can however be used to help place limits on the origin of the ice in these events after taking into account variable snow accumulation effects variations in the 10be flux are observed probably caused by solar and geomagnetic modulation but possibly also by primary cosmic ray variations the most dramatic is a 10be peak 40 000 years ago similar to that found in the vostok ice core thus permitting a very precise correlation between climate records from arctic and antarctic ice cores the 36cl 10be ratio considering either total or only ice associated 10be shows significant variability over the whole core depth thus confirming the difficulty in using this parameter for dating ice cores

effects of fluid rock interaction on 40ar 39ar geochronology in high pressure rocks sesia lanzo zone western alps abstract in situ uv laser spot 40ar 39ar analyses of distinct phengite types in eclogite facies rocks from the sesia lanzo zone western alps italy were combined with sims boron isotope analyses as well as boron b and lithium li concentration data to link geochronological information with constraints on fluid rock interaction in weakly deformed samples apparent 40ar 39ar ages of phengite cores span a range of 20 ma but inverse isochrons define two distinct main high pressure hp phengite core crystallization periods of 88 82 and 77 74 ma respectively the younger cores have on average lower b contents 36 g g than the older ones 43 48 g g suggesting that loss of b and resetting of the ar isotopic system were related phengite cores have variable 11b values 18 to 10 indicating the lack of km scale b homogenization during hp crystallization overprinted phengite rims in the weakly deformed samples generally yield younger apparent 40ar 39ar ages than the respective cores they also show variable effects of heterogeneous excess 40ar incorporation and ar loss one acceptable inverse isochron age of 77 1 1 1 ma for rims surrounding older cores 82 6 0 6 ma overlaps with the second period of core crystallization compared to the phengite cores all rims have lower b and li abundances but similar 11b values 15 to 9 reflecting internal redistribution of b and li and internal fluid buffering of the b isotopic composition during rim growth the combined observation of younger 40ar 39ar ages and boron loss yielding comparable values of both parameters only in cores and rims of different samples is best explained by a selective metasomatic overprint in low permeability samples this overprint caused recrystallization of phengite rims whereas higher permeability in other samples led to complete recrystallization of phengite grains strongly deformed samples from a several km long blueschist facies shear zone contain mylonitic phengite that forms a tightly clustered group of relatively young apparent 40ar 39ar ages 64 7 68 8 ma yielding an inverse isochron age of 65 0 3 0 ma almost complete b and li removal in mylonitic phengite is due to leaching into a fluid the b isotopic composition is significantly heavier than in phengites from the weakly deformed samples indicating an external control by a high 11b fluid 11b 7 4 we interpret this result as reflecting phengite recrystallization related to deformation and associated fluid flow in the shear zone this event also caused partial resetting of the ar isotope system and further b loss in more permeable rocks of the adjacent unit we conclude that geochemical evidence for pervasive or limited fluid flow is crucial for the interpretation of 40ar 39ar data in partially metasomatized rocks

application of k feldspar jadeite quartz barometry to eclogite facies metagranites and metapelites in the sesia lanzo zone western alps italy the eclogite facies assemblage k feldspar jadeite quartz in metagranites and metapelites from the sesia lanzo zone western alps italy records the equilibration pressure by dilution of the reaction jadeite quartz albite the metapelites show partial transformation from a pre alpine assemblage of garnet alm 63 prp 26 grs 10 k feldspar plagioclase biotite sillimanite to the eo alpine high pressure assemblage garnet alm 50 prp 14 grs 35 jadeite jd 80 97 di 0 4 hd 0 8 acm 0 7 zoisite phengite plagioclase is replaced by jadeite zoisite kyanite k feldspar quartz and biotite is replaced by garnet phengite or omphacite kyanite phengite equilibrium was attained only in local domains in the metapelites and therefore the k feldspar jadeite quartz kjq barometer was applied only to the plagioclase pseudo morphs and k feldspar domains the albite content of k feldspar ranges from 4 to 11 mol in less equilibrated assemblages from val savenca and from 4 to 7 mol in the partially equilibrated samples from monte mucrone and the equilibrated samples from montestrutto and tavagnasco thermodynamic calculations on the stability of the assemblage k feldspar jadeite quartz using available mixing data for k feldspar and pyroxene indicate pressures of 15 21 kbar 1 6 1 9 kbar at 550 50 c this barometer yields direct pressure estimates in high pressure rocks where pressures are seldom otherwise fixed although it is sensitive to analytical precision and the choice of thermodynamic mixing model for k feldspar moreover the kjq barometer is independent of the ratio p h 2 o p t the inferred limiting a h 2 o for the assemblage jadeite kyanite in the metapelites from val savenca is low and varies from 0 2 to 0 6

brittle shear tectonics in a narrow continental rift asymmetric nonvolcanic barmer basin rajasthan india abstractour field studies emphasizing brittle shear p and y planes along the margins of the barmer basin rajasthan india support its two phase nw se followed by ne sw extension during early cretaceous and late cretaceous paleocene periods we also document nearly ne trending megascale transfer zones along the northern margin of the barmer basin preexisting brittle planes in the malani basement rocks guided the relay structures here structures at the western basin shoulder margin indicate ne sw extension and the crosscut relation connotes the relative timing of the two extension phases the crosscutting conjugate fault sets are non andersonian the nw trending faults produced by the second phase extension and the inherited nnw trending brittle features are dominantly dip slip prior fractures of the malani rocks at 45 to the ne sw principal extension direction extended the barmer basin obliquely during the late cretaceous paleocene period the asymmetric nature of the rift too connotes its ob

secondary migration of oil experiments supporting efficient movement of separate buoyant oil phase along limited conduits geologic note experimental data suggest that the secondary migration of oil in porous permeable sediments probably occurs in most circumstances along restricted pathways or conduits these conduits are formed after the oil has reached a high enough saturation in the reservoir rock for the buoyancy of the oil to overcome the capillary pressure in the pore throats the oil probably moves vertically until it reaches the top of the reservoir interval the oil then moves updip along the top of the reservoir interval via a narrow restricted pathway until it reaches the trap and begins to accumulate depending on the area of the original oil saturation at the bottom of the reservoir unit and the structural geometry multiple conduits may form along which the oil may flow because these conduits are limited in diameter the amount of oil lost during secondary migration could be limited to the irreducible oil saturation left behind in the conduit provided no small scale traps exist along the path to the main trap rates of oil movement are very rapid in a geologic context suggesting that the timing of primary migration is a good indicator of the timing of secondary migration

a 600 year annual 10be record from the ngrip ice core greenland understanding the link between the sun and climate is vital in the current incidence of global climate change and 10be in natural archives constitutes an excellent tracer for this purpose as cosmic rays enter the atmosphere cosmogenic isotopes like 10be and 14c are formed variations in solar activity modulate the amount of incoming cosmic rays and thereby cosmogenic isotope production atmospherically produced 10be enters natural archives such as sediments and glaciers by wet and dry deposition within about a year of production 10be from natural archives therefore provides information on past solar activity and because these archives also contain climate information solar activity and climate can be linked one remaining question is to what degree 10be in natural archives reflects production and to what extent the local and regional environment overprints the production signal to explore this 10be was measured at annual resolution over the last 600 years in a greenland ice core measurement potentials for these samples benefited from the development of a new laboratory method of co precipitating 10be with niobium to diversify geographic location and archive media type a pioneer study of measuring 10be with annual resolution in varved lake sediments from finland was conducted with samples from the entire 20th century pathways of 10be into lake sediments are more complex than into glacial ice inferring that contemporary atmospheric conditions may not be recorded here it is shown for the first time that tracing the 11 year solar cycle through lake sediment 10be variations is possible results also show that on an annual basis 10be deposition in ice and sediment archives is affected by local environmental conditions on a slightly longer timescale however diverse 10be records exhibit similar trends and a negative correlation with solar activity cyclic variability of 10be deposition persisted throughout past grand solar minima when little or no sunspot activity was recorded 10be levels indicate that although solar activity has been high during the 20th century levels are not unprecedented in the investigated 600 years aerosol 10be 7be values indicate possible influence of stratosphere troposphere exchange on isotope abundance and the production signal

origins of yttrium and rare earth element distributions in metamorphic garnet highly variable distributions of yttrium and rare earth elements y rees are documented in pelitic garnet from the picuris mountains new mexico and from passo del sole switzerland and in mafic garnet from the franciscan complex california the wide variety of these y ree zoning patterns and those described previously in other occurrences imply diverse origins linked to differing degrees of mobility of these elements through the intergranular medium during garnet growth in the picuris mountains large early nucleating crystals have radial profiles of y ree dominated by central peaks and annular maxima in patterns that vary systematically with atomic number superimposed on these features are narrow spikes in hrees and mrees located progressively rimward with decreasing atomic number in contrast profiles in small late nucleating crystals contain only broad central maxima for all y rees in garnet from passo del sole y ree zoning varies radically from sample to sample in some rocks crystals of all sizes display only central peaks for all y rees in others profiles exhibit irregular fluctuations in y ree contents that match up with small scale patchy zoning in y and ca x ray maps in the franciscan complex y ree in garnet cores fluctuate unsystematically but mantles and rims display concentric oscillatory zoning for both major elements and y rees our interpretation of the complexity of y ree distributions in metamorphic garnet centres on the concept that these distributions vary primarily in response to the length scales over which these elements can equilibrate during garnet growth very short length scales of equilibration due to low intergranular mobility produce overprint zoning characterized by small scale irregularities higher but still restricted mobility yields diffusion controlled uptake characterized by patterns of central peaks and annular maxima that vary with atomic number and are strongly influenced by t t paths during garnet growth still greater mobility permits progressively greater potentially rock wide equilibration with major and accessory phase assemblages leading to mineralogical controls an unchanging mineral assemblage during garnet growth produces bell shaped profiles resembling those produced by rayleigh fractionation whereas changes in major and or accessory phase assemblages produce profiles with distinct annuli and sharp discontinuities in concentration the very high mobility associated with influxes of y ree bearing fluids can cause these element distributions to be dominated by factors external to the rock yielding profiles characterized by abrupt shifts or oscillations that are not correlated to changes in mineral assemblages

tertiary age and paleostructural inferences of the eclogitic imprint in the austroalpine outliers and zermatt saas ophiolite western alps the austroalpine sesia lanzo inlier and upper austroalpine dent blanche mt mary and pillonet outliers occur on top of the western alpine orogenic wedge and as a whole override the structurally composite ophiolitic piemonte zone instead the mt emilius glacier rafray etirol levaz and other lower austroalpine eclogitic outliers are inserted within the piemonte zone between its upper combin and lower zermatt saas tectonic elements or within the latter rb sr dating on phengitic micas show that the eclogitic imprint in the lower austroalpine outliers conventionally regarded as late cretaceous by comparison with the sesia lanzo inlier is of eocene age 49 40 ma like the underlying zermatt saas ophiolite 45 42 ma between the aosta valley and gran paradiso massif 40ar 39ar plateau ages on the same mica concentrates of the ophiolitic zermatt saas nappe 46 43 ma are consistent with rb sr dating whereas that on the austroalpine glacier rafray klippe 92 ma is influenced by argon excess the lower austroalpine outliers underwent the subduction metamorphism concurrently with the zermatt saas nappe 20 25 ma later than the eclogitic sesia lanzo inlier and blueschist pillonet klippe the temporal gap and present intra ophiolitic position mean that the lower austroalpine outliers were probably derived from an intraoceanic extensional allochthon mt emilius domain stranded inside the piemonte ligurian ocean far from the dent blanche sesia domain and adriatic margin

oblique extensional tectonics in the malawi rift africa the malawi rift is the southern segment of the western branch of the east african rift system there has been little agreement as to whether this rift is opening perpendicularly or obliquely to its north south axis and little agreement on a mechanism for the formation of the asymmetric basins that make up the rift our analysis combines landsat image interpretation and field measurement of the latest slip direction on faults to produce a kinematic model of rift evolution the fault slip data are consistently compatible with a late cenozoic northwest southeast directed divergence between the nubian and somalian blocks plates across the rift the northwest striking livingstone fault at the northern limit of the malawi rift and the northwest striking zambezi fault zone to the south serve as dextral intracontinental transform zones between left stepping segments of the western branch of the east african rift system within the rift second order northwest striking transfer faults separate adjacent asymmetric basins the transform and transfer faults form a pattern that is similar to overlapping right stepping strike slip faults with a releasing geometry fault surfaces with two sets of striations indicate a progression from predominantly strike slip toward oblique normal faulting we hypothesize that during initial rift formation most northwest striking faults were dextral and that fault interaction between these structures resulted in curved stress trajectories and a pull apart component arcuate north to northeast striking border faults and subsiding basins then formed between these northwest striking faults in response to the right stepping dextral shear the maximum distance over which fault interaction is significant may control basin dimensions as opening of the rift proceeds slip partitioning and gravity failure result in increasing normal slip perpendicular to major escarpments and decreasing strike slip parallel to them

structural interpretation of hydrocarbon traps sealed by basement normal block faults at stable flank of foredeep basins and at rift basins closures sealed by basement normal block faults are most commonly formed by a grid of faults with multiple orientations and by a favorable dip of the reservoir strata hydrocarbons are trapped updip by structural upturns along the edge of the downdropped blocks or at the upthrown or downthrown edge of blocks where block tilt is away from the sealing faults closure parallel with reservoir strike is provided by 1 updip junction of primary oblique or oblique and longitudinal block bounding faults 2 internal secondary faults that trend transverse or oblique to the block boundaries 3 positive bend of reservoir strata 4 plunge of block edge folds and or 5 stratigraphic terminations of the reservoir fault seal upward along the faults is most likely where a thick section of impervious strata above the reservoir is in contact with itself across the fault or where the fault does not extend upward into shallower permeable zones seal across the fault surface is most certain where impermeable rocks are laterally juxtaposed against the reservoir impervious material within the fault zone such as shaly smear gouge cataclastic gouge mineral deposits and asphalt or tar impregnations can be effective barriers where reservoir facies are juxtaposed across the fault the traps can form a major hydrocarbon play on the stable shelves of foredeep or foreland basins as demonstrated by the san joaquin valley and eastern venezuela basins the traps provide secondary prospects in rift basins uch as the viking graben and vienna basin

episodic fluid expulsion from geopressured sediments numerical simulation of fluid explusion from geopressured sediments using a one dimensional finite difference model shows that large volumes of fluid can be transported through a fractured seal during short lived 100 year expulsion events in this model abnormal fluid pressures are maintained by an impermeable seal when the fluid pressure exceeds 85 of the lithostatic pressure a vertical fracture opens in the seal providing a permeable pathway from the geopressured sediments into the overlying section fluid pressure in the seal decreases as fluid flows through the fracture closing the fracture as sediments in the seal compact once the fracture closes the seal remains impermeable until fluid flowing from deeper in the section increases fluid pressure to the fracture criteria a process that takes 10 000 500 000 years fractures emplaced in relatively incompressible seals such as compacted and or cemented sediments remain open for 20 50 years fluid fluxes through the seal integrated over the life of these events are 1 5 107 kg m2 and temperatures in the overlying sediments are increased by 5 20 c these temperature anomalies decay to less than half their original value in 300 years suggesting that the thermal anomalies observed in wells that are attributed to fluid expulsion formed in response to a very recent or currently active event

patterns of displacement along large normal faults implications for basin evolution and fault propagation based on examples from east africa seismic reflection data across six boundary faults from east africa have revealed information about the way boundary faults develop with respect to the synkinematic basin fill previous models of basin fill assume that lateral fault propagation and deposition occur simultaneously which gives rise to along axis onlap of the basin fill onto the prerift basement propagating basin model seismic reflection data from boundary faults in east africa show only rare evidence for along axis broadening of the basins instead the basin margins appear to be fixed from a very early stage in the basin history nonpropagating basin model depocenters shift not by gradual lateral propagation but by abrupt changes in location such observations indicate that boundary fault propagation to near maximum length occurs rapidly during the very early stages of rifting probably by linkage of numerous small faults displacement then builds following the b value earthquake model along the fault during basin development out of phase with the main propagation phase mature fault systems may have experienced several phases of jumps in fault length or the location of fault activity major boundary faults exhibit three basic patterns of evolution these patterns of evolution can have many variants and include 1 simple displacement where maximum displacement is approximately at the center of the fault and decreases gradually toward the fault tips 2 variable along strike displacement that incorporates linkage of in line or en echelon relatively large displacement faults of similar age leaving transverse anticlines and synclines and 3 asymmetric propagation where one tip of a fault remains more or less fixed while the other tip propagates a relatively long distance asymmetric propagation can occur smoothly and gradually or alternatively there can be a jump in the location of the fault and a new fault of different age can form along strike from the older fault eventually the new fault propagates and links with the older fault segment reactivating the older fault to some extent addition ally long lived faults may be composites of fault types 1 3

cosmic ray event of a d 774 775 shown in quasi annual 10be data from the antarctic dome fuji ice core 14c content in tree rings and 10be concentration records in polar ice core provide information about past cosmic ray intensities the a d 774 775 cosmic ray event has been identified by 14c measurement in several tree rings from all over the world although the quasi decadal 10be dome fuji data in the antarctic ice core also shows a sharp peak around a d 775 annual 10be variations in the dome fuji core or in other cores have not been revealed we have measured quasi annual 10be concentrations from approximately a d 763 794 in the dome fuji ice core and detected a clear increase 80 above the baseline in 10be concentration around a d 775 however an accurate height of this increase is not straightforwardly estimated due to the background variation in 10be concentration the 10be increase can be due to the same cosmic ray event as shown in the 14c content in a d 774 775

preservation of permian allanite within an alpine eclogite facies shear zone at mt mucrone italy mechanical and chemical behavior of allanite during mylonitization this study addresses the mechanical and chemical behavior of allanite during shear zone formation under high pressure metamorphism understanding physico chemical processes related to the retention or resetting of pb isotopes in allanite during geological processes is essential for robust petrochronology dating of allanite in meta granodiorite showing variable amounts of strain from an undeformed protolith to mylonite at monte mucrone sesia zone nw italy gave surprising results based on structural and petrographic observations the shear zones at mt mucrone are alpine yet allanite located within an eclogite facies mylonite yielded permian ages 208pb 232th average age 287 7 ma these mm sized allanite grains are rimmed by an aggregate of coarse grained garnet phengite thought to derive from former epidote these aggregates were immersed in a weak matrix that experienced granular flow and they were thus chemically and mechanically shielded during alpine mylonitization in undeformed samples 8a and 8b two populations of epidote group minerals were found allanite forms either coronas around permian monazite or individual grains with patchy zoning both types yield permian ages 208pb 232th age 291 5 ma on the other hand grains of ree rich clinozoisite of cretaceous age are found in undeformed rocks these grains appear as small fragments with embayed surface outlines and minute satellites or rims around permian allanite these re crystallized grains are sr rich and show mosaic zoning these results indicate that allanite crystals retained their chemical and isotopic characteristics and thus their permian age as a result of strong strain partitioning between the epidote group porphyroclasts and the eclogite facies matrix in hp mylonites the observed partial mobilization of pb isotopes which lead to the cretaceous aged rims or grains in undeformed samples was facilitated by re crystallization of allanite and not by mere pb diffusion alone under the hp conditions

tectonic implications of lawsonite formation in the sesia zone western alps lawsonite of early alpine age formed in different tectonic sub units of the sesia zone western italian alps in the southern part of the eclogitic micaschists subunit em lawsonite grew with quartz jadeite during the early alpine retrograde path which just post dates the eclogite thermal peak the early retrograde path of the southern em occurred at decreasing temperature and at p t conditions comparable to those of the metamorphic peak in some blueschist facies thrust sheets which separate the em from the southern alps such a post eclogitic cooling path may have been induced by conductive cooling linked to migration of the underthrust surfaces and to stacking with colder nappes like the other sesia subunits or the piemonte metaophiolites stacking and thermal interaction between the different units probably occurred at depth during the early stages of exhumation which followed subduction underthrusting of early mid cretaceous age during the paleogene continental collision between the european and african plates determined further underthrusts of more westerly units these units underwent a high pressure very low temperature recrystallization meso alpine event characterized by the growth of lawsonite at the peak metamorphic conditions consequently propagation of the underthrust surfaces may represent an effective mechanism to prevent the rise of the isotherms and to favor post peak cooling paths in some units of the western alps this effect is more obvious in the structurally upper units which were first brought to deep crustal levels in the early alpine imbricated subduction zone

crustal reworking and hydration insights from element zoning and oxygen isotopes of garnet in high pressure rocks sesia zone western alps subduction zones represent one of the most critical settings for fluid recycling as a consequence of dehydration of the subducting lithosphere a better understanding of fluid flows within and out of the subducting slab is fundamental to unravel the role of fluids during burial in this study major and trace element geochemistry combined with oxygen isotopes were used to investigate metasediments and eclogites from the sesia zone in order to reconstruct the effect of internal and external fluid pulses in a subducted continental margin garnet shows a variety of textures requiring dissolution precipitation processes in presence of fluids in polycyclic metasediments garnet preserves a partly resorbed core related to pre alpine high temperature low pressure metamorphism and one or multiple rim generations associated with alpine subduction metamorphism in eclogites garnet chemical zoning indicates monocyclic growth with no shift in oxygen isotopes from core to rim in metasediments pre alpine garnet relics show 18o values up to 5 3 higher than the alpine rims while no significant variation is observed among different alpine garnet generations within each sample this suggests that an extensive re equilibration with an externally derived fluid of distinct lower 18o occurred before or in correspondence to the first alpine garnet growth while subsequent influxes of fluid had 18o close to equilibrium the observed shift in garnet 18o is attributed to a possible combination of 1 interaction with sea water derived fluids during pre alpine crustal extension and 2 fluids from dehydration reactions occurring during subduction of previously hydrated rocks such as the serpentinised lithospheric mantle or hydrated portions of the basement

factors controlling reservoir properties and hydrocarbon accumulation of lacustrine deep water turbidites in the huimin depression bohai bay basin east china abstract lacustrine deep water turbidite plays are a novel area for exploration in the huimin depression bohai bay basin turbidites in the shang 847 block a typical turbidite play in the huimin depression provide an opportunity to study the factors controlling the reservoir properties and hydrocarbon accumulation in lacustrine turbidite sandstones the reservoir quality of turbidite sandstones very fine grained moderately to well sorted mainly lithic arkose in this study area are mainly controlled by the distribution patterns of carbonate cements and pseudomatrix significant inverse relationships exist between the volume of carbonate cement and both porosity and permeability of the turbidite sandstones carbonate cement is located preferentially near the margins of the sandstone bodies sandstones with distance from the sandstone mudstone contact surface less than 0 7 m or with thickness less than 1 2 m are commonly tightly cemented carbonate cement 15 with low porosity and permeability lower than 10 and 0 1 md respectively the source of carbonate cement was most likely external probably derived from the surrounding mudstone most pore filling carbonate cements occurred during late diagenesis at burial depths greater than 2200 m the petrophysical properties of turbidites have a positive relationship with the content of kaolinite and chlorite but have a negative relationship with the content of illite 2 d and 3 d reconstructions of non oil bearing and oil bearing layers indicate that dissolution of carbonate cement feldspars and unstable rock fragments was more developed in oil bearing layers than in non oil bearing layers and hance oil bearing layers have higher porosity and larger pore sizes petrophysical property appears to have a significant effect on the hydrocarbon accumulation in the turbidite sandstones sandstones with porosities lower than 9 and or permeabilities lower than 0 78 md are not prone to contain oil

10be in the akademii nauk ice core first results for ce 1590 1950 and implications for future chronology validation temporal variations of the radionuclide 10be are broadly synchronous across the globe and thus provide a powerful tool to synchronize ice core chronologies from different locations we compared the 10be record of the akademii nauk an ice core russian arctic for the time period ce 1590 1950 to the 10be records of two well dated greenland ice cores dye3 and ngrip a high correlation r 0 59 was found between the an and dye3 records whereas the correlation with ngrip was distinctly lower r 0 45 sources of deviations may include local fluctuations in the deposition of 10be due to changes in the precipitation patterns and artefacts due to the core sampling strategy in general the existing age model was validated confirming the an ice core to be a unique and welldated source of palaeoclimate parameters for the russian arctic we further used numerical simulations to test the influence of the core sampling strategy on the results and derived an optimized sampling strategy for the deeper parts of the ice core

volcanic and solar activity and atmospheric circulation influences on cosmogenic 10be fallout at vostok and concordia antarctica over the last 60years abstract the cosmogenic nuclide beryllium 10 10be recovered from ice cores is often used to study solar activity on long timescales however the 10be signal is also influenced by factors other than the sun to identify and quantify various contributions to the 10be signal two antarctic snow records from the vostok and concordia sites spanning the last 60 years were studied at a sub annual resolution three factors that contribute to the 10be signal were identified first a significant period of approximately 11 yr that can be associated with the modulation of 10be production by solar activity was detected in both records the solar imprint constitutes 20 35 of the variance within the total signal the 11 yr 10be snow component was attenuated by a factor of 0 5 and was delayed by 1 4 yr compared to the 10be production expected within the polar atmosphere the result could be interpreted as the composite response of a stratospheric 10be reservoir with an 11 yr modulation that was attenuated and delayed with respect to 10be polar production and to a tropospheric 10be reservoir with an 11 yr modulation that was not attenuated or delayed then peaks in 10be concentrations that were 66 and 35 higher than the average concentration were observed during the stratospheric volcanic eruptions of agung in 1963 and pinatubo in 1991 respectively in light of these new results published 10be ice core records could be reinterpreted because spikes in 10be concentration appear at the time of several stratospheric events the data indicate that stratospheric volcanic eruptions can impact 10be transport and deposition as a result of the roles played by the sedimentation of sulfate aerosols and the formation and rapid settling of polar stratospheric clouds psc also an interannual variability of 4 yr was determined in both 10be records corresponding to 26 of the variance within the signal at vostok as with species of marine origin sodium this 4 yr variability is interpreted as a tropospheric modulation the 4 yr variability could be associated with atmospheric circulation associated with the coupled southern ocean ocean atmosphere system the results presented here from sites within the high antarctic plateau open new possibilities for ice core dating over the last few centuries and for the reconstruction of past solar activity in relation to climate

excursions in the 14c record at a d 774 775 in tree rings from russia and america the calibration of radiocarbon dates by means of a master calibration curve has been invaluable to earth environmental and archeological sciences but the fundamental reason for calibration is that atmospheric radiocarbon content varies because of changes in upper atmosphere production and global carbon cycling improved instrumentation has contributed to high resolution interannual radiocarbon activity measurements which have revealed sudden and anomalous activity shifts previously not observed at the common resolution of 5 10 years of most of the calibration scale one such spike has been recently reported from tree rings from japan and then again in europe at a d 774 775 for which we report here our efforts to both replicate its existence and determine its spatial extent using tree rings from larch at high latitude northern siberia and bristlecone pine from lower latitude the white mountains of california our results confirm an abrupt 15 14c activity increase from a d 774 to 776 the size and now the hemispheric extent of which suggest that an extraterrestrial influence on radiocarbon production is most likely responsible

solar modulation of cosmogenic nuclide production over the last millennium comparison between 14c and 10be records for about the last 30 years it has been recognized that the high frequency component of the tree rings 14c 12c record is dominated by the modulation of the cosmic ray flux by the solar wind in particular it has been demonstrated that the three most recent periods of low sunspot occurrence were characterized by high values of atmospheric 14c 12c during the last millennium other periods of high 14c 12c values were observed but their solar origin is still debatable in the present work we compare these fluctuations with an independent record of cosmogenic 10be measured in ice from the south pole to check the solar origin of the observed 14c 12c variations in order to compare quantitatively the results obtained on 10be and 14c it is necessary to take into account the different behaviour of these two cosmogenic isotopes and especially the damping effect of the carbon cycle in the case of 14c as an input to a 12 box numerical model we used the relative fluctuations of the 10be concentrations record measured in south pole ice and converted it into a synthetic 14c record we took into account the fact that 10be modulation is enhanced in polar regions due to the orientation of the geomagnetic field as expected the fluctuations of the modelled 14c record are much smaller a factor of 20 than those observed for the raw 10be record in addition the variations are smoother and shifted in time by a few decades the 10be based 14c variations closely resemble the 14c measurements obtained on tree rings r 0 81 in particular it is easy to identify periods of maximal 14c 12c which correspond to solar activity minima centred at about 1060 1320 wolf 1500 sporer 1690 maunder and 1820 dalton yr a d cross correlation calculations suggest that there is no significant lag between the 10be based 14c and the tree ring 14c records our study strongly suggests the dominance of the solar modulation on the cosmonuclide production variations during the last millennium

oxygen isotope heterogeneities and diffusion profile in composite metamorphic magmatic garnets from the pyrenees unusually large 1 8 o heterogeneities 4 within single crystals are reported in garnets from dioritic migmatites in the pyrenees these heterogeneities together with contrasting ca and p zoning allow the identification of different growth zones garnet cores with high 1 8 o values 12 14 are relatively poor in ca 7 9 mol grs and rich in p 400 900 ppm p 2 o 5 in contrast garnet rims with lower 1 8 o values 7 12 o are richer in ca 12 14 grs and poorer in p 100 200 ppm these growth zones can be ascribed to a metamorphic event followed by crustal partial melting and contamination by magmas from the mantle high 1 8 o intra crystalline contrasts result from mineral growth in an open magmatic system involving the interaction of partial melts with distinct 1 8 o signatures at the garnet core rim interface compositional profiles in major divalent cations are consistent with the relaxation of an initial sharp step in ca fe and mg by ca fe mg interdiffusion at the same interface an o isotope profile is documented the analogy of ca and o isotope profiles suggests that the 1 8 o distribution may also result from a diffusion process in this particular case temperature garnet composition oxygen fugacity o diffusion appears to be of the same order of magnitude as ca fe mg interdiffusion considering a duration of 10 ma for the plutono metamorphic event in the pyrenees ca and o diffusivities in the range 10 2 2 m 2 s at 850 c are retrieved from the measured profiles like ca o diffusion in garnet at magmatic temperatures 850 900 c is both slow enough to preserve large 1 8 o heterogeneities and fast enough to generate relaxation profiles

emplacement at granulite facies conditions of the sesia lanzo metagabbros an early record of permian rifting the evolution of the pre alpine corio and monastero metagabbros points to strong chemical and mineralogical similarities with that of other permian gabbro bodies of the alps which are concentrated in the southalpine and austroalpine domains the structural and metamorphic pre alpine evolution of these gabbros records a re equilibration following the emplacement in the deep crust p 0 6 0 9 gpa and t 850 70 c exhumation through amphibolite facies conditions p 0 5 0 35 gpa and t 570 670 c followed by a greenschist facies imprint 0 25 p 0 35 gpa and t 550 c this retrograde p t evolution suggests that the exhumation occurred in a high thermal gradient regime such as that induced by upwelling of an asthenospheric plume during continental rifting this would be consistent with the crustal thinning known to have occurred in both the southalpine and austroalpine domains during permian times the gabbros and their country acid granulites are spatially associated with the serpentinised subcontinental mantle of the lanzo massif this lithologic association and the metamorphic evolution is similar to that of the fedoz gabbro austroalpine domain of the central alps and completely different from that observed in passive margins where no remnants of the lower crust occur and the upper granitic crust directly overlies the serpentinized lherzolites the location of permian gabbro bodies in the austroalpine and southalpine domains and their absence in the helvetic domain is evidence for asymmetric rifting

precollisional multistage exhumation of subducted continental crust the sesia zone western alps 1 the sesia zone within the tertiary arc of the western alps is a relic of the subducted part of the adriatic continental margin along the se border of the tethyan ocean the sesia zone comprises three basement nappes which individuated during late cretaceous 65 80 ma subduction to different depths at high pressure hp blueschist eclogite facies conditions peak pressures of 1 0 1 2 1 0 1 5 and 1 5 2 0 gpa the thrusts bounding these nappes developed where the crust was previously thinned during jurassic rifting crustal scale shear zones partly overprinted these early thrusts and exhumed coherent slices of crust containing hp rocks initial exhumation of the internal part of the accreted margin involved thrusting d1 and transpressional shearing d2 along a subvertical e w trending mylonitic shear zone under retrograde blueschist to greenschist facies conditions this exhumation was nearly isothermal to a depth of about 25 km where the basement nappes were juxtaposed subsequent exhumation of these nappes to a common depth of about 15 20 km occurred in the footwall of a greenschist facies top se extensional shear zone d3 preserved in some of the highest mountain peaks of the sesia zone new rb sr mineral ages constrain d2 to have occurred at about 60 65 ma and d3 at about 45 55 ma thus top se extensional exhumation was broadly coeval with eocene se directed subduction of the liguro piemont oceanic lithosphere beneath the adriatic margin slow cooling and erosional denudation of the sesia zone from 45 to 30 ma occurred in the hanging wall of the gressoney extensional shear zone d4 which itself contributed to the exhumation of eocene hp and ultra hp oceanic rocks in its footwall by 30 ma hp rocks of the sesia zone were intruded by shallow granitic plutons which were eroded and redeposited within volcanoclastic sediments oligo miocene insubric backfolding and thrusting d5 only exhumed northeastern parts of the sesia zone where hp metamorphism is absent or was overprinted by tertiary temperature dominated metamorphism most exhumation of continental hp rocks in the sesia zone therefore preceded tertiary alpine collision and coincided with late cretaceous to early tertiary subduction of the adriatic and tethyan lithosphere the transition from d2 to d3 in the sesia zone is interpreted to mark a change from high stress oblique se directed subduction and accretion of the distal adriatic continental margin to nw retreating low stress subduction of the liguro piemont oceanic lithosphere

petrological constraints on the eclogite and blueschistfacies metamorphism and p t t paths in the western alps phase relationships in the model mafic system and geothermobarometry allow discrimination of four main groups of high p rocks in the nappes of the western alps very high p eclogite facies including kyanite eclogites and coesite pyrope assemblages eclogite facies paragonite zoisite eclogites high t blueschist facies glaucophane garnet lawsonite assemblages and low t blueschist facies glaucophane lawsonite pumpellyite assemblages the blueschist facies eclogite facies transition is promoted chiefly by increasing t low bulk xmg and relatively low h2o the variety of assemblages and the heterogeneous approach to equilibrium observed in the alpine rocks are not only constrained by the intersection of the reaction surfaces in p t x space but also by the effect and timing of the processes which control kinetics i e pervasive deformation and fluid infiltration the faster rate of dehydration reactions relative to hydration reactions along with the fact that different bulk compositions crossed the reaction curves at different temperatures and times all may have induced h2o gradients and contributed to the heterogeneous distribution of deformation through a process of reaction enhanced ductility also mass transfer may have been an effective process in determining the type of high p assemblage in particular rock volumes as regards the p t t paths only the post climax histories are recorded well in the alpine nappes post eclogitic exhumation paths at decreasing temperatures characterize structurally higher nappes which were first subducted during the early alpine cretaceous event in contrast more or less isothermal decompression paths characterize structurally deeper nappes formed by westward propagation of the underthrust surfaces during the early alpine event and the subsequent meso alpine palaeogene collision between the european and african plates in the western alps prevalent eclogite facies conditions were attained during the metamorphic climax of the early alpine subduction while blueschist facies recrystallization characterizes the early alpine exhumation of the eclogitized units and the subsequent intracontinental underthrusts linked to the meso alpine continental collision

mesozoic tectonics in the eastern block of the north china craton implications for subduction of the pacific plate beneath the eurasian plate engebretson d c cox a and gordon r g 1985 relative motions between oceanic and continental plates in the pacific basin geol soc am spec paper pp 1 59 faure m lin w breton n l 2001 where is the north china south china block boundary in eastern china geology 29 2 119 122 faure m sun y shu l s monie p and charvet j 1996 extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china tectonophysics 263 77 106 gao s zhang b r jin z m kern h 1999 delamination of the lower crust of the qinling dabie orogenic belt science in china 29 6 532 541 in chinese gilder s a and courtillot v 1997 timing of the north south china collision from new middle to late mesozoic paleomagnetic data from the north china block journal of geophysics research 102 17713 17727 hacker b r ratschbacher l webb l mcwilliams m o ireland t calvert a dong s w wenk h r 2000 exhumation of ultrahigh pressure continental crust in east central china late triassic early jurassic tectonic unroofing journal of geophysical research 105 b6 13339 13364 halim n kravchinsky v gilderm s cognem j p alexyutinm m sorokinm a courtillotm v chenm y a 1998 palaeomagnetic study from the mongol okhotsk region rotated early cretaceous volcanics and remagnetized mesozoic sediments earth and planetary science letters 159 3 4 133 145 hong z m 1989 research progresses and implication of upper precambrian in the liaonan area liaoning geology 1 87 94 in chinese with eaglisn abstract ichikawa k mizutani s hara i et al 1990 pre cretaceous terrances of japan publication of igcp 224 pre jurassic evolution of eastern asia osaka pp 1 413 kim j h 1996 mesozoic tectonics in korea journal of southeast asian earth sciences 13 3 5 251 265 kusky t m li j h 2003 paleoproterozoic tectonic evolution of the north china craton journal of asian earth sciences 22 383 397 kusky t m bradley d c donley d t rowley d and haeussler p 2003 controls on intrusion of near trench magmas of the sanak baranof belt alaska during paleogene ridge subduction and consequences for forearc evolution in sisson v b roeske s and pavlis t l eds geology of a transpressional orogen developed during a ridge trench interaction along the north pacific margin geological society of america special paper 371 pp 269 292 li s z han z z liu y j yang z s 2001a constrains of geology and geochemistry on palaeoproterozoic pre orogenic deep processes in the jiao liao massif scientia geological sinica 36 189 195 in chinese with english abstract li s z han z z liu y j yang z s ma r 2001b continental dynamics and regional metamorphism in the liaohe group geological review 47 9 18 in chinese with english abstract li s z liu y j yang z s ma r 1998 relations between deformation and metamorphic recystallization in metaperlite of liaohe group acta petrologica sinica 14 3 352 366 in chinese with eaglisn abstract li s z yang z s 1997b types and genesis of palaeoproterozoic granites in the jiao liao massif northwest geology 43 6 21 27 in chinese with english abstract li s z yang z s liu y j liu j l 1997a emplacement model of palaeoproterozoic early granite in the jiao liao ji area and its relation to layered gravitational sliding structure acta petrologica sinica 13 189 202 in chinese with english abstract

persistent link between solar activity and greenland climate during the last glacial maximum changes in solar activity have previously been proposed to cause decadal to millennial scale fluctuations in both the modern and holocene climates1 direct observational records of solar activity such as sunspot numbers exist for only the past few hundred years so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as 10be and 14c from ice cores and tree rings2 3 here we present a high resolution 10be record from the ice core collected from central greenland by the greenland ice core project grip the record spans from 22 500 to 10 000 years ago and is based on new and compiled data4 5 6 using 14c records7 8 to control for climate related influences on 10be deposition we reconstruct centennial changes in solar activity we find that during the last glacial maximum solar minima correlate with more negative 18o values of ice and are accompanied by increased snow accumulation and sea salt input over central greenland we suggest that solar minima could have induced changes in the stratosphere that favour the development of high pressure blocking systems located to the south of greenland as has been found in observations and model simulations for recent climate9 10 we conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and last glacial maximum climate conditions

four dimensional analysis of the sembo relay system offshore angola implications for fault growth in salt detached settings subsurface mapping of several relay ramps from a raft related fault array in the lower congo basin offshore angola reveals a full spectrum of fault linkage styles a comprehensive three dimensional geometric and kinematic appraisal of a more complex relay system within the fault array the sembo relay system srs highlights differences with current structural models of relay ramp genesis evolution and breaching the srs is a rearward upper ramp breached relay system with a maximum fault overlap and spacing of 9500 and 3600 m 31 000 and 11 800 ft respectively this system is characterized by a structural geometry that becomes increasingly complex with depth as the relay system is gradually assimilated into the structural architecture of a separate and structurally deeper fault system a detailed kinematic appraisal of the srs indicates that the throw patterns on the frontal and rearward segments are intrinsically different throw backstripping reveals different initiation ages for the rearward and frontal segments of about 5 5 and 2 5 ma respectively mutual overlap is estimated to first occur about 2 5 ma at the 5 0 ma structural level with fault linkage and ramp breaching occurring subsequently the srs therefore represents a complex amalgamation of faults that have each developed independently at different times the genesis and evolution of the srs have been governed through time by both salt withdrawal and associated fault detachment histories in conjunction with increased congo fan progradation and sedimentation rates and phases of tectonic tilting of the underlying salt detachment surface

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

information on past solar activity and geomagnetism from 10 be in the camp century ice core a nearly continuous record of the concentration of 10be from ice core data is compared with the tree ring derived record for 14c over the same period and it is found that short term trends in these data sets provide a record of solar activity no definitive relationship between the long term trends and the geomagnetic dipole moment is found

how do the properties of a pre existing normal fault population influence fault development during a subsequent phase of extension abstract we use scaled experimental analog models to investigate how the properties of a population of pre existing normal faults influence fault development during a subsequent phase of extension in the models a homogeneous layer of wet clay undergoes two phases of extension whose extension directions differ by 45 to vary the properties of the first phase fault population we vary the magnitude of the first phase extension as the magnitude of the first phase extension increases the number average and maximum length and average and maximum displacement of the first phase normal faults increase for a poorly developed first phase fault population new normal faults which strike perpendicular to the second phase extension direction form during the second phase for a well developed first phase fault population many first phase normal faults are reactivated as oblique slip faults during the second phase new normal faults also form these second phase normal faults are shorter and have displacement maxima adjacent to the reactivated first phase faults they are less likely to cut the pre existing first phase faults than second phase normal faults that form in models with a less developed first phase fault population in all models pre existing faults serve as nucleation sites for new faults in models with a well developed first phase fault population the pre existing faults also act as obstacles to the propagation of the second phase normal faults fault geometries in the models vary considerably parallel zig zag or intersecting fault geometries develop depending on whether the first phase fault population is poorly moderately or well developed respectively