ocean dynamical processes associated with the tropical pacific cold tongue mode the cold tongue mode ctm is the second eof mode of sea surface temperature anomaly ssta variability over the tropical pacific and represents the out of phase relationship in ssta variability between the pacific cold tongue region and elsewhere in the tropical pacific a positive ctm is characterized by cold ssta in the pacific cold tongue region and warm ssta in the rest of the tropical pacific with conditions reversed for a negative ctm the ctm is a coupled air sea mode and its long term variability is most probably induced by ocean dynamical processes in response to global warming zhang et al 2010 this study focuses on the specific ocean dynamical processes associated with the ctm and its possible relationship with global warming a heat budget diagnosis of ocean temperature in the eastern equatorial pacific shows that the net heat flux plays a damping role and the four ocean advection terms 2u0 t x 2 v t0 y 2 w t0 z and 2w0 t z contribute to the temperature change associated with the ctm among them the vertical advection of the anomalous temperature by the mean upwelling 2 w t0 z makes a dominant contribution to the long term change in the ctm the long term change of the term 2 w t0 z is controlled mainly by the decreasing vertical gradient of the ocean temperature anomaly t0 z the other three advection terms make a minor contribution to the long term change in the ctm

nao implicated as a predictor of northern hemisphere mean temperature multidecadal variability 1 the twentieth century northern hemisphere mean surface temperature nht is characterized by a multidecadal warming cooling warming pattern followed by a flat trend since about 2000 recent warming hiatus here we demonstrate that the north atlantic oscillation nao is implicated as a useful predictor of nht multidecadal variability observational analysis shows that the nao leads both the detrended nht and oceanic atlantic multidecadal oscillation amo by 15 20 years theoretical analysis illuminates that the nao precedes nht multidecadal variability through its delayed effect on the amo due to the large thermal inertia associated with slow oceanic processes an nao based linear model is therefore established to predict the nht which gives an excellent hindcast for nht in 1971 2011 with the recent flat trend well predicted nht in 2012 2027 is predicted to fall slightly over the next decades due to the recent nao decadal weakening that temporarily offsets the anthropogenically induced warming

impacts of two types of la nina on the nao during boreal winter the present work identifies two types of la nina based on the spatial distribution of sea surface temperature sst anomaly in contrast to the eastern pacific ep la nina event a new type of la nina central pacific or cp la nina is featured by the sst cooling center over the cp these two types of la nina exhibit a fundamental difference in sst anomaly evolution the ep la nina shows a westward propagation feature while the cp la nina exhibits a standing feature over the cp the two types of la nina can give rise to a significantly different teleconnection around the globe as a response to the ep la nina the north atlantic na western european we region experiences the atmospheric anomaly resembling a negative north atlantic oscillation nao pattern accompanied by a weakening atlantic jet it leads to a cooler and drier than normal winter over western europe however the cp la nina has a roughly opposing impact on the na we climate a positive nao like climate anomaly is observed with a strengthening atlantic jet and there appears a warmer and wetter than normal winter over western europe modeling experiments indicate that the above contrasting atmospheric anomalies are mainly attributed to the different sst cooling patterns for the two types of la nina mixing up their signals would lead to difficulty in seasonal prediction of regional climate since the la nina related sst anomaly is clearly observed during the developing autumn the associated winter climate anomalies over western europe could be predicted a season in advance

fission track analysis of basement apatites at the western margin of the gulf of suez rift egypt evidence for synchroneity of uplift and subsidence fifty six apatite fission track ages and 52 horizontal confined track length measurements are reported from precambrian crystalline rocks along the western margin of the gulf of suez egypt ages fall in the range of ca 11 385 m y and older ages often occur within very close geographic proximity to younger ones indicating non uniform uplift the wide range in ages is accompanied by a systematic variation in the distribution of horizontal confined fission track lengths on the basis of apatite fission track ages and their length distributions data fall into three distinct groups group i ages ranging from 43 to 385 m y length distributions are all positively skewed and with decreasing age become progressively broader with shorter mean track length group ii ages ranging from 23 to 31 m y length distributions are negatively skewed with either a distinct tail or a small peak of short tracks group iii ages ranging from 11 to 20 5 m y length distributions are al unimodal narrow negatively skewed and have the longest mean lengths among samples studied apatite ages from groups i and ii are interpreted as mixed ages as a result of cooling during uplift from different levels within the apatite partial track annealing zone ages from group iii are interpreted as cooling ages due to uplift from the apatite total track annealing zone with minor partial annealing correcting the ages of the two oldest samples in this group for track length reduction yields ages of21 2 2and23 1 5m y it is proposed that the onset of rift flank uplift in the gulf of suez northern red sea area occurred between 21 and 23 m y ago fission track analysis in combination with subsidence data from the gulf of suez basin indicate that commencement of basement uplift postdate the start of rifting and is interpreted as evidence for passive rifting at the gulf of suez furthermore this uplift is contemporaneous with and is directly related to the process of extension and subsidence at the gulf of suez

spatial and temporal features of enso meridional scales 1 the spatial and temporal features of the el nino southern oscillation enso meridional scales are investigated using the hadley center global sea ice and sea surface temperature hadisst data for the period of 1950 2007 the results show that the meridional scales of the enso warm and cold events are asymmetric and exhibit interdecadal changes the meridional extent of the sea surface temperature anomalies ssta during la nina years is wider than that during el nino years this is because strengthened trades and thus strengthened upwelling and meridional currents during la nina events more effectively spread ssta away from the equator with the walker circulation weakening in recent decades which tends to reduce upwelling and meridional currents over the central and eastern equatorial pacific the meridional scales of both el nino and la nina events also decrease citation zhang w j li and f f jin 2009 spatial and temporal features of enso meridional scales geophys res lett 36 l15605

experimental vnir reflectance spectroscopy of gypsum dehydration investigating the gypsum to bassanite transition the spectral behavior of gypsum dehydration in the visible to near infrared 350 2500 nm wavelength range was investigated by partially dehydrating the four main habits of gypsum alabaster satin spar selenite and massive to form bassanite powdered samples of gypsum dehydrated at 100 115 c and hand samples dehydrated at 115 130 c coinciding with a peak in mass water loss in the samples as gypsum dehydrates its characteristic h2o absorption bands at 1443 and 1945 nm shift to shorter wavelengths band depths and widths of absorptions at 1200 1400 1600 1750 1945 2100 2200 and 2400 nm all decrease with increasing temperature the samples also underwent visible changes upon dehydration both at the macroscopic and microscopic level becoming very friable with an increase in fine grains no consistent relationship was observed between dehydration temperature and grain size or habit the samples were monitored for up to 20 months after dehydration during which time none rehydrated to form gypsum while the transition from gypsum to bassanite is very abrupt bassanite does not readily rehydrate to form gypsum again in ambient conditions and therefore may not be as unstable as previously thought by terrestrial occurrences of bassanite being predominantly restricted to hyperarid climates

thermal elastic stresses and the criticality of the continental crust 1 heating or cooling can lead to high stresses in rocks due to the different thermal elastic properties of minerals in the upper 4 km of the crust such internal stresses might cause fracturing yet it is unclear if thermal elasticity contributes significantly to critical stresses and failure deeper in earth s continental crust where ductile creep causes stress relaxation we combined a heating experiment conducted in a synchrotron microtomograph advanced photon source usa with numerical simulations to calculate the grain scale stress field in granite generated by slow burial we find that deviatoric stresses 100 mpa can be stored during burial with relaxation times from 100 s to 1000 s ka even in the ductile crust hence grain scale thermal elastic stresses may serve as nuclei for instabilities thus rendering the continental crust close to criticality

deformation and pore pressure in dehydrating gypsum under transiently drained conditions abstract the development of pore fluid pressure in dehydrating rocks is a competition between the reaction which produces water and the change in permeability caused by the reduction in solid volume our study explores the development of pore fluid pressure and the mechanical behavior of dehydrating rocks under conditions where the relative drainage is transient i e drainage evolves as the reaction progresses the dehydration system studied was gypsum to bassanite plus water hydrostatic pressure and axial compression experiments were performed at 23 to 150 c confining pressures p c of 0 1 to 200 mpa pore pressures p p of 10 to 100 mpa and strain rates of 7 10 7 to 6 10 5 1 s the volume of water expelled from the sample during dehydration the differential stress the reaction ratio and the porosity distribution were determined as a function of time the expulsion of water with time is divided into three stages broadly defined as i the formation of a connected pore network ii the maximum water expulsion rate and iii the completion of the reaction at high effective pressures p e p c p p gypsum deforms by plastic flow and cataclasis at temperatures below that necessary for dehydration above the dehydration temperature samples show weakening and embrittlement indicative of low effective pressures when deformed in stage i in stages ii and iii the sample strength increases gradually with time eventually exceeding the pre dehydration strength of gypsum these results suggest that high pore pressures low effective pressures are only transient and occur in stage i the exceptional strengthening in stages ii and iii occurs because the new phase bassanite is stronger than gypsum the evolution of pore pressure with time in a transiently drained dehydrating system has been modeled by incorporating fluid release and porosity change rates into a hydraulic diffusion equation the numerical simulations show that initially pore pressure increases following an undrained path and a pore pressure in excess of hydrostatic is possible later the increase in porosity and permeability makes drainage more efficient and the pore pressure decreases rapidly the magnitude and duration of the excess pore pressure are sensitively dependent on the dehydration kinetics and the hydro mechanical properties the pore pressure peak predicted from the numerical simulations correlates with the experimental results that weakening and embrittlement occur only in stage i our results suggest that even under natural conditions where rocks have a finite drainage high excess pore pressures may occur

dehydration induced damage and deformation in gypsum and implications for subduction zone processes 1 experimental heating tests were performed on volterra gypsum to study the micromechanical consequences of the dehydration reaction the experimental conditions were drained at 5 mpa fluid pressure and confining pressures ranging from 15 to 55 mpa one test was performed with a constantly applied differential stress of 30 mpa the reaction is marked by 1 a porosity increase and homogeneous compaction 2 a swarm of acoustic emissions 3 a large decrease in p and s wave velocities and 4 a decrease in vp vs ratio wave velocity data are interpreted in terms of crack density and pore aspect ratio which modeling pores as spheroids is estimated at around 0 05 crack like spheroid complementary tests performed in an environmental scanning electron microscope indicate that cracks first form inside the gypsum grains and are oriented preferentially along the crystal structure of gypsum most of the visible porosity appears at later stages when grains shrink and grain boundaries open extrapolation of our data to serpentinites in subduction zones suggest that the signature of dehydrating rocks in seismic tomography could be a low apparent poisson s ratio although this interpretation may be masked by anisotropy development due to preexisting crystal preferred orientation and or deformation induced cracking the large compaction and the absence of strain localization in the deformation test suggests that dehydrating rocks maybe seen as soft inclusions and could thus induce ruptures in the surrounding nonreacting rocks

recharge oscillator mechanisms in two types of enso the el ni oscillation enso tends to behave arguably as two different types or flavors in recent decades one is the canonical cold tongue type enso with major sea surface temperature anomalies ssta positionedoverthe easternpacific theotheris awarm pool typeensowith sstacenteredin the central pacific near the edge of the warm pool in this study the basic features and main feedback processes of these two types of enso are examined it is shown that the interannual variability of upper ocean heat content exhibits recharge discharge processes throughout the life cycles of both the cold tongue ct and warm pool wp enso types through a heat budget analysis with focus on the interannual frequency band the authors further demonstrate that the thermocline feedback plays a dominant role in contributing to the growth and phase transitions of both enso types whereas the zonal advective feedback contributes mainly to their phase transitions the westward shift of the ssta center of the wp enso and the presence of significant surface easterly wind anomalies over the far eastern equatorial pacific during its mature warm phase are the two main factors that lead to a reduced positive feedback for the eastern pacific ssta nevertheless both the wp and ct enso can be understood to a large extent by the recharge oscillator mechanism

the role of mean state on changes in el nino s flavor recently many studies have argued for the existence of two types of el nino phenomena based on different spatial distributions the conventional el nino or eastern pacific ep el nino and the central pacific cp el nino here we investigate the decadal modulation of cp el nino occurrences using a long term coupled general circulation model simulation focusing in particular on the role of climate state in the regime change between more and fewer cp el nino events the higher occurrence regime of the cp el nino coincides with the lower occurrence regime of ep el nino and vice versa the climate states associated with these two opposite regimes resemble the leading principal component analysis pca modes of tropical pacific decadal variability indicating that decadal change in climate state may lead to regime change in terms of two different types of el nino in particular the higher occurrence regime of cp el nino is associated with a strong zonal gradient of mean surface temperature in the equatorial pacific along with a strong equatorial trade wind over the area east of the dateline in addition the oceanic variables the mixed layer depth and the thermocline depth show values indicating increased depth over the western to central pacific the aforementioned climate states obviously intensify zonal advective feedback which promotes increased generation of the cp el nino frequent cp el nino occurrences are not fully described by oceanic subsurface dynamics and dynamical or thermodynamical processes in the ocean mixed layer and air sea interaction are important contributors to the generation of the cp el nino furthermore the atmospheric response with respect to the ssta tends to move toward the west which leads to a weak air sea coupling over the eastern pacific these features could be regarded as evidence that the climate state can provide a selection mechanism of the el nino type

a new paradigm for the predominance of standing central pacific warming after the late 1990s canonical el nino has a warming center in the eastern pacific ep but in recent decades el nino warming center tends to occur more frequently in the central pacific cp the definitions and names of this new type of el nino however have been notoriously diverse which makes it difficult to understand why the warming center shifts here we show that the new type of el nino events is characterized by 1 the maximum warming standing and persisting in the cp and 2 the warming extending to the ep only briefly during its peak phase for this reason we refer to it as standing cp warming cpw global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of cpw however we find that since the late 1990s the standing cpw becomes a dominant mode in the pacific meanwhile the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased contrary to the global warming induced weakening trades and flattening thermocline we propose that the recent predominance of standing cpw arises from a dramatic decadal change characterized by a grand la nina like background pattern and strong divergence in the cp atmospheric boundary layer after the late 1990s the anomalous mean cp wind divergence tends to weaken the anomalous convection and shift it westward from the underlying sst warming due to the suppressed low level convergence feedback this leads to a westward shift of anomalous westerly response and thus a zonally in phase sst tendency preventing eastward propagation of the sst anomaly we anticipate more cpw events will occur in the coming decade provided the grand la nina like background state persists

fault zone architecture and deformation processes within evaporitic rocks in the upper crust 1 recently in the northern apennines geophysical data have identified the triassic evaporites te anhydrites and dolomites as the source region of the major extensional earthquakes of the area m 6 in order to characterize fault zone architecture and deformation processes within the te we have studied exhumed evaporite bearing normal faults within the upper crust the structure of large displacement 100 m normal faults is given by 1 a zoned fault core with a wider portion of fault parallel foliated ca sulphates ductile deformation overprinted by an inner fault core ifc of localized brittle deformation and 2 wide dolostones to absent ca sulphates damage zones of fault fracture patterns fault rock assemblage within the ifc is characterized by fault breccia gouge and cataclasites of different grain size most of the deformation within the ifc is localized along thin and fault parallel principal slip surfaces pss made of dolomite rich fine grained cataclasite sem analyses show an evolution from ca to st to gypsum rich mineralization due to episodic fluid flow events channeled along the fault zones during different stages of fault exhumation the development of the observed fault geometry can be explained by a mechanical fault evolution model where initial faulting occurs along broad and ductile shear zones within the anhydrites and causes fracturing within the dolostones progressive deformation within the fault core leads to the development of fault parallel dolomite rich cataclastic layers their reactivation coupled with transient fluid overpressures can produce embrittlement and localization of brittle deformation within the ifc

model assessment of decadal variability and trends in the tropical pacific ocean abstract in this report global coupled ocean atmosphere models are used to explore possible mechanisms for observed decadal variability and trends in pacific ocean ssts over the past century the leading mode of internally generated decadal 7 yr variability in the model resembles the observed decadal variability in terms of pattern and amplitude in the model the pattern and time evolution of tropical winds and oceanic heat content are similar for the decadal and enso timescales suggesting that the decadal variability has a similar delayed oscillator mechanism to that on the enso timescale the westward phase propagation of the heat content anomalies however is slower and centered slightly farther from the equator 12 vs 9 n for the decadal variability cool sst anomalies in the midlatitude north pacific during the warm tropical phase of the decadal variability are induced in the model largely by oceanic advection anomalies an index of observed sst over a broad triangular region of the tropi

characterization of the co2 fluid adsorption in coal as a function of pressure using neutron scattering techniques sans and usans abstract small angle neutron scattering techniques have been applied to investigate the phase behavior of co2 injected into coal and possible changes in the coal pore structure that may result from this injection three coals were selected for this study the seelyville coal from the illinois basin ro 0 53 baralaba coal from the bowen basin ro 0 67 and bulli 4 coal from the sydney basin ro 1 42 the coals were selected from different depths to represent the range of the underground co2 conditions from subcritical to supercritical which may be realized in the deep subsurface environment the experiments were conducted in a high pressure cell and co2 was injected under a range of pressure conditions including those corresponding to in situ hydrostatic subsurface conditions for each coal our experiments indicate that the porous matrix of all coals remains essentially unchanged after exposure to co2 at pressures up to 200 bar 1 bar 105 pa each coal responds differently to the co2 exposure and this response appears to be different in pores of various sizes within the same coal for the seelyville coal at reservoir conditions 16 c 50 bar co2 condenses from a gas into liquid which leads to increased average fluid density in the pores pore with sizes r 1 105 r 1 104 a pore 0 489 g cm3 as well as in small pores with size between 30 and 300 a pore 0 671 g cm3 these values are by a factor of three to four higher than the density of bulk co2 co2 under similar thermodynamic conditions co2 0 15 g cm3 at the same time in the intermediate size pores with r 1000 a the average fluid density is similar to the density of bulk fluid which indicates that adsorption does not occur in these pores at in situ conditions for the baralaba coal 35 oc 100 bar the average fluid density of co2 in all pores is lower than that of the bulk fluid pore co2 0 6 neutron scattering from the bulli 4 coal did not show any significant variation with pressure a phenomenon which we assign to the extremely small amount of porosity of this coal in the pore size range between 35 and 100 000 a

mechanism of subsidence of ancient cratonic rift basins cratonic basins commonly occur over ancient rift zones these inactive rift basins are recognizable by a positive linear bouguer gravity anomaly that may correspond to the axial gravity high found in modern rift valleys many of these basins undergo discrete periods of increased subsidence rates or reactivations long after the mass excess responsible for the linear gravity high was emplaced furthermore the reactivation of many cratonic basins occurs simultaneously with large scale compressional tectonics it is suggested that the driving force for subsidence is the isostatically uncompensated ancient mass excess the subsidence of these basins is modelled by a lithospheric flexure model with a nonlinear maxwell viscoelastic rheology solutions to this model indicate that basins may experience a low subsidence rate throughout geologic time the subsidence of a basin will stop only when isostatic compensation of the mass excess is achieved since ancient rift mass excesses may be uncompensated over long geologic time intervals the early thermal and structural evolution of rifts may not significantly influence later basin subsidence the models suggest that basins may be reactivated by any mechanism which lowers the effective viscosity of the lithospheric material allowing the uncompensated basin to settle toward an isostatic compensation depth faster than normal since viscosity is a strong function of temperature reactivation by a world wide increase in heat flow is suggested as a possible mechanism for the synchroneity of basin subsidence throughout a continent an increase of 15 in the geothermal gradient for example from 16 5 18 9 k km will cause about a 5 increase in subsidence this increase in heat flow however seems unlikely of producing by itself the magnitude of basin subsidence during a reactivation phase that is observed in the geologic record where up to 100 increase in subsidence might occur since the rheology of the lithosphere is nonlinear effective viscosity is also a strong nonlinear function of stress the presence of a regional compressive stress during periods of tectonism of 1 1 108 pa about 2 8 of the buckling strength of the lithosphere produces a short period of reactivated subsidence 105 yr during the reactivated subsidence the newly imposed regional stress relaxes sufficiently in the lower lithosphere to restore the effective viscosity to values similar to that before reactivation this suggests that reactivated subsidence caused by regional compression can be maintained as long as the stress level remains high in the lower lithosphere this may be accomplished by an intermittent application of the regional stress over time

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

modeling metamorphic fluid flow with reaction compaction permeability feedbacks existing models of metasomatic flow do not allow for the effect that reaction has on the flow patterns instead it is assumed that the volatiles produced are negligible in volume compared to those infiltrated and that reaction does not modify permeability this is clearly unlikely to be true for infiltration driven decarbonation reactions the rates of porosity creation by reaction and porosity loss by creep have been calculated for a representative volume of calcite quartz wollastonite marble and it is found that even for a weak calcite matrix the rate of porosity generation by reaction is likely to outstrip the collapse of porosity as long as the system is out of equilibrium we have applied a self consistent 1d finite difference model to the reaction of calcite quartz to wollastonite in a 10m thick marble in response to influx of h2o rich fluid with fixed boundary conditions the model allows us to evaluate the effect of reaction on the porosity structure and fluid pressure variation across the layer from which local darcy fluxes can be evaluated the progress of reaction that we model is constrained by hydrological considerations with the requisite parameters recalculated as reaction progresses assuming creep compaction of rock under the stress difference between lithostatic and fluid pressures we fnd that the volume of fluid realised by decarbonation driven by influx of h20 is sufficient to create a back flow so that further advancement of the reaction front is only possible as a result of diffusion of water against the darcy flux the effect of creep driven by differences between fluid pressure and lithostatic pressure is to reduce the permeability of the layer and especially reduce the secondary porosity developed in the zone at and behind the advancing reaction front we predict that in a 3d situation the porous zone of reacted marble becomes a conduit for layer parallel flow and the secondary porosity is infilled by calc silicate minerals due to silica metasomatism

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

drivers of reduced enso variability in mid holocene in a coupled model the drivers of el nino southern oscillation enso intensity change during the mid holocene mh are investigated through employing a coupled model that exhibits excellent performance in simulating the present day enso behaviors the model shows a 28 decrease in enso intensity in the mh simulation compared to the pre industrial pi simulation showing an agreement with the ranges indicated by the paleo proxies based on quantitative analyses we reveal that the changes in the oceanic dynamic processes including the thermocline zonal advection and ekman feedback terms in the order from being most to least important were the major drivers of the reduced enso intensity in the mh further diagnosis analyses show that the weakening in all three oceanic dynamic terms could be traced back to the weakened thermocline response to zonal wind stress anomaly in the mh compared to that in the pi such weakened thermocline response was due to the relatively flattened meridional structure of enso related interannual anomaly field e g zonal wind stress anomaly field in the mh which arose from the strengthening of the mean meridional overturning circulation namely the mean pacific subtropical cell stc the process oriented analyses throughout this study suggest a critical linkage between enso intensity change and mean stc change in the mh through documenting how the mean stc change altered the oceanic dynamic processes and thus drove the enso intensity change

creep cavitation bands control porosity and fluid flow in lower crustal shear zones shear zones channelize fluid flow in earth s crust however little is known about deep crustal fluid migration and how fluids are channelized and distributed in a deforming lower crustal shear zone this study investigates the deformation mechanisms fluid rock interaction and development of porosity in a monzonite ultramylonite from lofoten northern norway the rock was deformed and transformed into an ultramylonite under lower crustal conditions temperature 700 730 c pressure 0 65 0 8 gpa the ultramylonite consists of feldspathic layers and domains of amphibole quartz calcite which result from hydration reactions of magmatic clinopyroxene the average grain size in both domains is 25 mm microstructural observations and electron backscatter diffraction analysis are consistent with diffusion creep as the dominant deformation mechanism in both domains festoons of isolated quartz grains define c type bands in feldspathic layers these quartz grains do not show a crystallographic preferred orientation the alignment of quartz grains is parallel to the preferred elongation of pores in the ultramylonites as evidenced from synchrotron x ray microtomography such c type bands are interpreted as creep cavitation bands resulting from diffusion creep deformation associated with grain boundary sliding mass balance calculation indicates a 2 volume increase during the protolith ultramylonite transformation which is consistentmore with synkinematic formation of creep cavities producing dilatancy thus this study presents evidence that creep cavitation bands may control deep crustal porosity and fluid flow nucleation of new phases in creep cavitation bands inhibits grain growth and enhances the activity of grain size sensitive creep thereby stabilizing strain localization in the polymineralic ultramylonites less

evolution of microstructure and elastic wave velocities in dehydrated gypsum samples 1 we report on changes in p and s wave velocities and rock microstructure induced by devolatilization reactions using gypsum as a reference analog material cylindrical samples of natural alabaster were dehydrated in air at ambient pressure and temperatures between 378 and 423 k dehydration did not proceed homogeneously but via a reaction front moving sample inwards separating an outer highly porous rim from the remaining gypsum which above approximately 393 5 k concurrently decomposed into hemihydrate overall porosity was observed to continuously increase with reaction progress from approximately 2 for fully hydrated samples to 30 for completely dehydrated ones concurrently p and s wave velocities linearly decreased with porosity from 5 2 and 2 7 km s to 1 0 and 0 7 km s respectively it is concluded that a linearized empirical raymer type model extended by a critical porosity term and based on the respective time dependent mineral and pore volumes reasonably replicates the p and s wave data in relation to reaction progress and porosity

electron backscatter diffraction ebsd analysis of bassanite transformation textures and crystal structure produced from experimentally deformed and dehydrated gypsum dehydration reactions have important effects on fluid flow porepressure and brittle failure in the earth the rates and mechanismsof reaction are relevant to understanding those effects the micro structures ofa set ofsamples containing bassanite and gypsum fromdehydration experiments on volterra gypsum have been analysed byconventional transmitted light microscopy and electron backscatterdiffraction ebsd these techniques have been used to character ize the varying crystal morphology and to measure the crystallo graphic preferred orientation cpo of the samples in somesamples bassanite grains show two distinct morphologies large 0 5 2 mm euhedral crystals and small 550mm acicular crys tals these represent the two different bassanite crystal habits bassanite was indexed using ebsd for thefirsttime and problemsrelated tosignificant mis indexing resulting from the pseudotrigonalsymmetry of bassanite are resolved the original starting materialhas a strong local and measurable cpo a strong cpo inpost experiment bassanite is found to mimic the original gypsumc axis orientation bassanite grain size is related to the degree ofreaction overstep spatial heterogeneity in bassanite distributionmay indicate the development of fluid pathways within the samples

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

the initiation and developing mechanisms of central pacific el ninos abstractthe initiation and developing mechanisms of four major central pacific cp el nino events in 1994 2002 2004 and 2009 were investigated by analyzing oceanic and atmospheric reanalysis data a mixed layer heat budget analysis was conducted and the result shows that the initiation mechanism of the 1994 cp el nino is very different from other cp el ninos in 2000s while the developing mechanisms are similar among these events the initial sea surface temperature sst warming of the 1994 el nino was caused by enhanced solar radiation which was related to atmospheric meridional overturning circulation in association with positive sst anomaly forcing in the subtropical pacific the subtropical sst anomalies also induced anticyclonic surface wind stress curl anomalies which caused the formation of subsurface warmer waters in the off equatorial regions the off equatorial subsurface warmer waters were transported farther equatorward by the mean subsurface ocean currents leading to the subsurface wa

anomalous tropical ocean circulation associated with la nina modoki 1 el nino modoki is a variant of el nino characterized by warming around the dateline flanked by anomalous cooling in the east and west however the opposite phase la nina modoki has received little attention because the prominent cooling of sea surface temperature sst during major la nina events is observed in the central pacific and thus it is difficult to define the two different types of cold events from the sst anomaly pattern here we demonstrate that cold events in 2000 and 2008 can be clearly distinguished from traditional la nina events using surface currents derived from satellite observations during 2000 and 2008 anomalous zonal currents in the equatorial pacific demonstrate divergence with westward currents west of the dateline and eastward currents east of it these currents are opposite to the circulation pattern during the 2004 el nino modoki event an empirical orthogonal function eof analysis of surface currents for the period 1993 2009 shows a circulation anomaly pattern similar to that in 2000 2004 and 2008 in the second eof the first eof is consistent with traditional el nino la nina events and does not exhibit a current reversal along the equator our results also indicate that strong cyclonic anticyclonic circulation anomalies occur in the tropical western pacific around 5 n 15 n during the 2004 2000 and 2008 el nino la nina modoki events and during the strong traditional el nino la nina events of 1997 1998 these circulation anomalies are related to an sst gradient in the western and central pacific

thermo poro mechanics of chemically active creeping faults 3 the role of serpentinite in episodic tremor and slip sequences and transition to chaos during the last decade knowledge over episodic tremor and slip ets events has increased dramatically owing to the widespread installation of gps and seismic networks the most puzzling observations are i the periodic nature of slow seismic events ii their localization at intermediate depths estimated 15 40 km and iii the origin of the nonvolcanic fluids that are responsible for the tremor activity we reconcile these observations using a first principles approach relying on physics continuum mechanics and chemistry of serpentinite in the megathrust interface the approach reproduces the gps sequences of 17 years of recording in cascadia north america as well as over 10 years in the hikurangi trench of new zealand we show that strongly endothermic reactions such as serpentinite dehydration are required for ets events we report that in this tectonic setting it is its chemical reaction kinetics not the low friction that marks serpentinite as a key mineral for stable self sustained oscillations we find that the subduction zone instabilities are driven from the ductile realm rather than the brittle cover even when earthquakes in the cover perturb the oscillator it relaxes to its fundamental mode such a transition from stable oscillations to chaos is witnessed in the ets signal of nz following the m6 8 2007 seismic event which triggered a secondary mode of oscillations lasting for a few years we consequently suggest that the rich dynamics of ductile modes of failure may be used to decipher the chaotic time sequences underpinning seismic events

regional metamorphic dehydration and seismic hazard we use a one dimensional model of coupled heat transport fluid transport porosity feedback and metamorphism to investigate how dehydration reactions proceeding during burial of hydrous rocks in the footwall of thrusts or the hanging wall of normal faults may influence the temporal evolution of pore fluid pressure pf based on a new interpretation of existing kinetic data for the dehydration of model serpentinite we advance the hypothesis that pf buildup to tensile failure may be possible within decades of the onset of dehydration in low permeability metamorphic rocks of the middle crust this model contrasts with both 1 typical earthquake nucleation models which involve preexisting fluids that play a passive role responding to tectonic stresses rather than generating them and 2 conventional treatments of pf generation based on equilibrium thermodynamics and constant rates of dehydration which require 10 106 years to produce significant pf increases our results suggest that repeated cycles dehydration induced seismicity are plausible in low permeability areas of the mid crust and can be sustained throughout an orogenic episode if fresh hydrous minerals descend into the metamorphic zone along the downgoing face of a thrust or normal fault system

dehydration kinetics of talc and 10 a phase consequences for subduction zone seismicity abstract the process of dehydration embrittlement is usually proposed as an explanation for the presence of intermediate depth earthquakes in subduction zones it assumes that the release of water by hydrous mineral breakdown is fast enough to provoke brittle failure we performed high pressure high temperature dehydration experiments of talc and 10 a phase coupled with in situ measurement of reaction kinetics using synchrotron x ray diffraction newly developed x ray transparent pressure sealed titanium capsule ensured a closed thermochemical environment from isothermal kinetics data fitted to the avrami s equation and from the texture of reaction products we conclude that dehydration rates of these minerals are limited by diffusion predicted minimum rates of fluid release range from 10 4 to 9 10 6 m 3 fluid m 3 rock s 1 and are fast enough to provoke hydraulic rupture since maxwell relaxation rate of rocks relevant of subduction zones are slower than the rate of fluid release these rates are comparable between talc 10 a phase and antigorite also perrillat j p daniel i koga k t reynard b cardon h crichton w a 2005 kinetics of antigorite dehydration a real time x ray diffraction study earth planet sci lett 236 899 913 consequently we suggest that the dehydration of hydrous minerals may eventually be fast enough to trigger the intermediate depth earthquakes and that the deepest among intermediate depth earthquakes may actually locate the limits for dehydration of hydrous minerals in the downgoing lithosphere

small angle neutron scattering signature of oil generation in artificially and naturally matured hydrocarbon source rocks abstract we have demonstrated for the first time the application of a small angle neutron scattering sans technique for the precise determination of the onset of hydrocarbon transport primary migration in shaly source rocks we used a sequence of rocks pyrolysed in the laboratory under nitrogen at temperatures in the range 310 370 c these rocks contained several percent of dispersed marine type ii organic matter geochemical analysis indicated a peak of the hydrocarbon generation in the middle of the temperature range at 340 c we observed a sharp decrease of sans intensity in a narrow maturity range within the geochemically determined region of the onset of hydrocarbon generation this decrease was a direct consequence of the sans contrast variation caused by the invasion of the pore space by bitumen during the primary migration of hydrocarbons a similar phenomenon was observed for a natural maturity sequence of source rocks originating from the same location

the significance of grain scale stresses in the kinetics of metamorphism during metamorphism phases grow and dissolve dominantly along grain boundaries bulk diffusion models for the development of metamorphic textures often assume that diffusion is homogeneous in regions of each phase rather than being localised along phase boundaries under isotropic stress chemical potentials of components involved in reactions are likely to be buffered along grain boundaries between phases thus inhibiting diffusion and growth motive forces must exist which overcome this and it is proposed here that local heterogeneous stresses will be important a mathematical theory for stress controlled growth is derived this theory predicts that the growth rates of two phases along their mutual interface will be linked in a quantifiable way it forms a basis for considering the important effects of stresses induced by local volumetric changes during metamorphism and it provides a link between these effects and those related to pressure solution in deforming rocks

water and geodynamics hydrogen is the most abundant element fig 1 in the galaxy and our solar system lodders 2003 therefore it is not astonishing that hydrogen is a key player in the geodynamic evolution of planets its fate in the early earth after condensation of the solar nebula the accretion of our planet and hydrogen reprocessing through early asteroidal and cometary bombardment dauphas et al 2000 and segregation of a proto earth into iron core and silicate mantle is described elsewhere in this volume marty and yokochi 2006 figure 1 abundance of elements in the solar system in numbers of atoms per 106 atoms of silicon lodders 2003 this chapter concerns itself with the geodynamics of the modern earth where nowadays hydrogen occupies only a very small mass fraction less than 0 1 wt although its abundance is thus drastically diminished it is still believed to have a profound influence on the geodynamics of the present planet the reason why hydrogen can have a profound influence on geodynamics even when it is diluted to ppm levels relies on its fundamental influence on both rock mechanics kohlstedt 2006 and the melting relationships kohn 2006 however both the micromechanical mechanism and the large scale implications are not yet fully understood in this review geodynamic processes which may be triggered by a rock mechanical hydrogen threshold value are reviewed in addition to resulting styles of planetary convection controlled by melt and rock mechanics this review will conclude with a more speculative discussion of the possible implications for planetary evolution from an early earth to the present day and highlight areas of future work following current practice in the literature the term water will be used interchangeably for hydrogen recent breakthroughs in computational geodynamics are throwing a new light on the possible evolution of planetary tectonics simulations

on the bias in simulated enso ssta meridional widths of cmip3 models the fidelity of coupled climate models simulating el nino southern oscillation enso patterns has been widely examined nevertheless a systematical narrow bias in the simulated meridional width of the sea surface temperature anomaly ssta of enso has been largely overlooked utilizing the preindustrial control simu lations of 11 coupled climate models from phase 3 of the coupled model intercomparison project cmip3 it was shown that the simulated width of the enso ssta is only about two thirds of what is observed through a heatbudgetanalysisbased onsimulationsandocean reanalysisdatasets itisdemonstrated thatthesstaoutside of the equatorial strip is predominantly controlled by the anomalous meridional advection by climatological currents and heat flux damping the authors thus propose a simple damped advective conceptual model to describe enso width the simple model indicates that this width is primarily determined by three factors meridionalcurrent ensoperiod andthermaldampingrate whenthemeridionalcurrentisweak itspreadsthe equatorial ssta away from the equator less effectively and the enso width thus tends to be narrow a short enso period allows less time to transport the equatorial ssta toward the off equatorial region and strong damping prevents expansion of the ssta away from the equator both of which lead to the meridional width becoming narrow the narrow bias of the simulated enso width is mainly due to a systematical bias in weak trade winds that lead to weak ocean meridional currents and partly due to a bias toward short enso periods

very little water is necessary to make a dry solid silicate system wet the standard rim forming mineral reaction olivine quartz orthopyroxene ol qtz opx has been experimentally performed at very dry conditions i e only 20 wt ppm of water present in the sample container as a fluid and most water was hydrogen dissolved within the solid crystals reaction rates and resulting fabrics at ol qtz interfaces mimic reaction features previously known from water rich conditions tens of thousands ppm our experiment indicates that very small amounts of water tens of ppm of the entire sample are highly effective in facilitating mineral reactions where water acts as a catalyst and creates porosity that might start to migrate from the initial centers of self propagating mineral reaction if rock deformation allows the threshold between dry and wet in granulite and eclogite facies rocks is crossed once the nominally anhydrous minerals are saturated with hydrogen

causes of the el nino and la nina amplitude asymmetry in the equatorial eastern pacific abstract the amplitude asymmetry between el nino and la nina is investigated by diagnosing the mixed layer heat budget during the enso developing phase by using the three ocean assimilation products simple ocean data assimilation soda 2 0 2 soda 1 4 2 and the global ocean data assimilation system godas it is found that the nonlinear zonal and meridional ocean temperature advections are essential to cause the asymmetry in the far eastern pacific whereas the vertical nonlinear advection has the opposite effect the zonal current anomaly is dominated by the geostrophic current in association with the thermocline depth variation the meridional current anomaly is primarily attributed to the ekman current driven by wind stress forcing the resulting induced anomalous horizontal currents lead to warm nonlinear advection during both el nino and la nina episodes and thus strengthen weaken the el nino la nina amplitude the convergence divergence of the anomalous geostrophic mixed layer currents dur

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

simulation of el nino southern oscillation like variability in a global aogcm and its response to co2 increase abstract a 75 year integration of a coupled atmosphere ocean model is examined for tropical interannual variability the atmospheric model has interactive cloud and a seasonal cycle the fluxes of heat and salinity into the ocean component of the model are flux corrected the model has tropical variability that is qualitatively similar to that of the observed el nino southern oscillation enso the maximum amplitude of the model nino3 signal is approximately half that observed and the modeled enso timescale is greater than that observed in the first 50 years of the integration the model has eight warm events each event is one of two types one characterized by a standing sst anomaly in the central and eastern pacific and the other by a westward propagating sea surface temperature anomaly the majority of the model warm events are of the first type the first type of event is triggered by the eastward propagation of kelvin waves across the pacific and the second by westward propagation of warm temperat

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

intermediate depth earthquake faulting by dehydration embrittlement with negative volume change earthquakes are observed to occur in subduction zones to depths of approximately 680 km even though unassisted brittle failure is inhibited at depths greater than about 50 km owing to the high pressures and temperatures it is thought that such earthquakes particularly those at intermediate depths of 50 300 km may instead be triggered by embrittlement accompanying dehydration of hydrous minerals principally serpentine a problem with failure by serpentine dehydration is that the volume change accompanying dehydration becomes negative at pressures of 2 4 gpa 60 120 km depth above which brittle fracture mechanics predicts that the instability should be quenched here we show that dehydration of antigorite serpentinite under stress results in faults delineated by ultrafine grained solid reaction products formed during dehydration this phenomenon was observed under all conditions tested pressures of 1 6 gpa temperatures of 650 820 degrees c independent of the sign of the volume change of reaction although this result contradicts expectations from fracture mechanics it can be explained by separation of fluid from solid residue before and during faulting a hypothesis supported by our observations these observations confirm that dehydration embrittlement is a viable mechanism for nucleating earthquakes independent of depth as long as there are hydrous minerals breaking down under a differential stress

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

transient porosity resulting from fluid mineral interaction and its consequences the term porosity is very widely used in geosciences and normally refers to the spaces between the mineral grains or organic material in a rock measured as a fraction of the total volume these spaces may be filled with gas or fluids and so the most common context for a discussion of porosity is in hydrogeology and petroleum geology of sedimentary rocks while porosity is a measure of the ability of a rock to include a fluid phase permeability is a measure of the ability for fluids to flow through the rock and so depends on the extent to which the pore spaces are interconnected the distribution of pores and pore neck size as well as on the pressure driving the flow this chapter will be primarily concerned with how reactive fluids can move through tight rocks which have a very low intrinsic permeability and how secondary porosity is generated by fluid mineral reactions a few words about the meaning of the title will help to explain the scope of the chapter 1 fluid mineral interaction when a mineral is out of equilibrium with a fluid it will tend to dissolve until the fluid is saturated with respect to the solid mineral we will consider fluids to be aqueous solutions although many of the principles described here also apply to melts the generation of porosity by simply dissolving some minerals in a rock is one obvious way to enhance fluid flow dissolution of carbonates by low ph solutions to produce vugs and even caves would be one example however when considering the role of fluid mineral reaction during metamorphism the fluid provides mechanisms that enable re equilibration of the rock i e by replacing one assemblage of minerals by a more stable assemblage this not only involves the dissolution of the parent mineral phases but the

apatite fission track results from ireland and the porcupine basin and their significance for the evolution of the north atlantic abstract apatite fission track analysis was applied to samples from the irish mainland and exploration boreholes 13 3 1 26 26 1 and 26 28 1 in the northern porcupine and donegal basins to study the regional thermal and tectonic history of the irish continental margin samples from the irish mainland have apatite ages ranging from 301 25 to 56 5 ma with mean track lengths in the range 13 89 0 25 to 11 19 0 22 m and indicate higher temperatures during the middle jurassic about 160 180 ma and during the late cretaceous to early tertiary about 50 80 ma these two periods of increased palaeotemperatures correlate with major reorganizations in plate movements and suggest that uplift and erosion after the maximum palaeotemperatures was achieved as a consequence of a variation in the regional pattern of crustal stress the results from borehole 26 28 1 indicate that within the resolution of the data all samples are presently at their maximum post depositional burial temperatures to produce the mean track length results in the range 11 24 0 49 to 11 81 0 20 m from borehole 26 26 1 it is necessary to invoke post palaeocene geothermal gradients in excess of 50 c km increased relative to the present day gradient 28 c km similar increased geothermal gradients are recognized during the early tertiary in adjacent sedimentary basins and may be explained as a result of heat advection by gravity driven fluid flow established in response to tectonic uplift of the basin margins

influence of el nino modoki on spring rainfall over south china 1 using observed data sets from 1979 to 2006 the relationship between el nino modoki and spring rainfall over south china sc is investigated of particular interest is the difference in the influence on spring rainfall of typical el nino events and the recently recognized el nino modoki events which are characterized by distinct warm sea surface temperature anomalies ssta in the central pacific and weaker cold anomalies in the western and eastern parts of the basin associated with the ssta anomalous ascent occurs over the central pacific and downward flow is observed over the eastern and western pacific the anomalous flow is associated with anomalous convergence in the upper troposphere over the western pacific sc is influenced by an anomalous anticyclonic circulation with prevailing northeasterly anomalies the convective activity in sc becomes weaker resulting in reduced rainfall however the situation is different in the case of el nino in terms of the influence on rainfall over sc while el nino modoki events are accompanied by a significant reduction in rainfall over sc there is enhanced rainfall associated with el nino events moreover there exists a strong asymmetry in the relationship between sc spring rainfall typical el nino southern oscillation enso and enso modoki events it appears that these relationships are only statistically significant for positive events the asymmetric influence of positive and negative in two enso phenomena may explain the difference in their respective relationships with spring rainfall over sc

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

dehydration induced porosity waves and episodic tremor and slip episodic tremor and slip ets along the subduction interface takes place where there is abundant evidence for elevated near lithostatic pore pressures at sufficiently great depths 30 45 km that chemical dehydration reactions must act as their dominant source we simulate fluid and heat flow while tracking the location of a vertically oriented one dimensional column of material as it subducts through the slow slip and tremor zone the material in the column is transformed through a pressure dependent and temperature dependent dehydration reaction that we describe with a generalized nonlinear kinetic rate law column deformation is largely dominated by viscous creep with a closure rate that depends linearly on porosity this behavior causes the dehydration reaction to generate traveling porosity waves that transport increased fluid pressures within the slow slip region to explore the possibility that the observed periodicity of slow slip and tremor in subduction zones can be explained by the migration of such porosity waves we derive a dispersion relation that accurately describes our numerical results we also obtain an expression for how the thickness of the dehydrating layer is expected to vary as a function of the parameters in the reaction rate law although the amplitudes of pore pressure perturbations rival those that are produced by known external forcings e g tides or passing surface waves our analysis suggests that given reasonable estimates of rock viscosity permeabilities in the range 6 5 10 15 to 5 10 10 m2 are required for porosity wave trains to form at periods comparable to those of slow slip and tremor

ocean dynamics and tropical pacific climate change in ocean reanalyses and coupled climate models the role of ocean dynamics in tropical pacific climate change is studied using an ensemble run of simple ocean data assimilation sparse input version 1 sodasi 1 and the coupled model intercomparison project phase 5 cmip5 historical runs an eight member ensemble of ocean reanalyses sodasi 1 from 1871 to 2008 is produced by using forcing from eight ensemble members of an atmospheric reanalysis the long term trends of tropical pacific surface temperature wind stress subsurface temperature and strength of the subtropical cells stcs are analyzed the ensemble reanalysis shows that there is a slight cooling trend of surface and subsurface temperature in the central tropical pacific due to enhanced tropical pacific circulation the stcs which consist of equatorial upwelling ekman transport extratropical subduction and pycnocline transport from the subtropical to the tropical region strengthen from 1900 to 2008 when the stcs are accelerated equatorial upwelling increases bringing cold water from the subsurface that cools the surface an increasing trend in convergence transport is mainly from the southern hemisphere in contrast with the reanalysis most of the cmip5 models have warming trends at the surface and the transport of the stcs has a decreasing trend the cmip5 models also underestimate tropical pacific ocean circulation relative to the reanalysis that is mostly due to differences in wind forcing

neutron scattering study of vitrinite insights into sub micrometer inclusions in north american carboniferous coals of bituminous rank abstract results of sans and usans measurements performed on a series of six vitrinite samples having vitrinite reflectance ro values ranging from 0 55 high volatile bituminous rank to 1 28 medium volatile bituminous rank were analyzed experimental data were acquired for two sample forms platelets cut parallel to the bedding and pellets made up of randomly oriented nearly monodisperse particles numerical analysis indicates the presence of sub micron sized inclusions embedded in the organic matrix for the lowest rank vitrinites the dominating inclusions are monodisperse are 7 12 nm in diameter and have concentrations of the order of 1017 cm 3 their shape is anisotropic with the surface to volume ratio about three times larger than for a solid sphere the higher rank vitrinites contain much larger monodisperse inclusions having diameters of 50 nm concentrations of 1014 cm 3 large surface to volume ratios and fuzzy interfaces with the organic matrix inclusions of a similar size and concentration are also present in the lowest rank sample but are much less frequent than the small inclusions we provisionally interpret those objects as inclusions of mineral matter most likely associated with original plant material the internal specific surface area ssa calculated for the small mineral matter inclusions is 100 m2 cm3 and for the large inclusions 2 m2 cm3

tracking metamorphic dehydration reactions in real time with transmission small and wide angle synchrotron x ray scattering the case of gypsum dehydration we present a review of a unique non destructive method for the real time monitoring of phase transformations and nano pore evolution in dehydrating rocks transmission small and wide angle synchrotron x ray scattering saxs waxs it is shown how saxs waxs can be applied to investigating rock samples dehydrated in a purpose built loading cell that allows the coeval application of high temperature axial confinement and fluid pressure or flow to the specimen because synchrotron sources deliver extremely bright monochromatic x rays across a wide energy spectrum they enable the in situ examination of confined rock samples with thicknesses of 1 mm at a time resolution of order seconds hence fast kinetics with reaction completion times of about hundreds of seconds can be tracked with beam sizes of order tens to hundreds of micrometres it is possible to monitor multiple interrogation points in a sample with a lateral extent of a few centimetres thus resolving potential lateral spatial effects during dehydration and enlarging sample statistics significantly therefore the saxs waxs method offers the opportunity to acquire data on a striking range of length scales for rock samples with thicknesses of 10 3 m and widths of 10 2 m a lateral interrogation point spacing of 10 5 m can be achieved within each irradiated interrogation point volume information concerning pores with sizes between 10 9 and 10 7 m and the crystal lattice on the scale of 10 10 m is acquired in real time this article presents a summary of the physical principles underpinning transmission x ray scattering with the aim of providing a guide for the design and interpretation of time resolved saxs waxs experiments it is elucidated 1 when and how saxs data can be used to analyse total porosity internal surface area and pore size distributions in rocks on length scales from 1 to 300 nm 2 how waxs can be employed to track lattice transformations in situ and 3 which limitations and complicating factors should be considered during experimental design data analysis and interpretation to illustrate the key capabilities of the saxs waxs method we present a series of dehydration experiments on a well studied natural gypsum rock volterra alabaster our results demonstrate that saxs waxs is excellently suited for the in situ tracking of dehydration kinetics and the associated evolution of nano pores the phase transformation from gypsum to bassanite is correlated directly with nano void growth on length scales between 1 and 11 nm for the first time a comparison of the saxs waxs kinetic results with literature data emphasises the need for future dehydration experiments on rock specimens because of the impact of rock fabric and the generally heterogeneous and transient nature of dehydration reactions in nature it is anticipated that the saxs waxs method combined with in situ loading cells will constitute an invaluable tool in the ongoing quest for understanding dehydration and other mineral replacement reactions in rocks quantitatively

coupled dissolution and precipitation at mineral fluid interfaces reactions occurring at mineral fluid interfaces are important in all geochemical processes and essential for the cycling of elements within the earth understanding the mechanism of the transformation of one solid phase to another and the role of fluids is fundamental to many natural and industrial processes problems such as the interaction of minerals with co2 saturated water the durability of nuclear waste materials the remediation of polluted water and mineral reactions that can destroy our stone based cultural heritage are related by the common feature that a mineral assemblage in contact with a fluid may be replaced by a more stable assemblage

anomalous winter climate conditions in the pacific rim during recent el nino modoki and el nino events present work compares impacts of el nino modoki and el nino on anomalous climate in the pacific rim during boreal winters of 1979 2005 el nino modoki el nino is associated with tripole dipole patterns in anomalies of sea surface temperature precipitation and upper level divergent wind in the tropical pacific which are related to multiple boomerangs of ocean atmosphere conditions in the pacific zonal and meridional extents of those boomerangs reflect their independent influences which are seen from lower latitudes in the west to higher latitudes in the east in the central pacific more moisture is transported from the tropics to higher latitudes during el nino modoki owing to displacement of the wet boomerang arms more poleward toward east discontinuities at outer boomerang arms manifest intense interactions between tropical and subtropical extratropical systems the pacific north american pattern and related climate anomalies in north america found in earlier studies are modified in very different ways by the two phenomena the seesaw with the dry north and the wet south in the western usa is more likely to occur during el nino modoki while much of the western usa is wet during el nino the moisture to the southwestern usa is transported from the northward shifted itcz during el nino modoki while it is carried by the storms traveling along the southerly shifted polar front jet during el nino the east asian winter monsoon related anticyclone is over the south china sea during el nino modoki as compared to its position over the philippine sea during el nino causing opposite precipitation anomalies in the southern east asia between the two phenomena

simulations of two types of el nino events by an optimal forcing vector approach in this paper an optimal forcing vector ofv approach is proposed the ofv offsets tendency errors and optimizes the agreement of the model simulation with observation we apply the ofv approach to the well known zebiak cane model and simulate several observed eastern pacific ep el nino and central pacific cp el nino events during 1980 2004 it is found that the zebiak cane model with a proper initial condition often reproduces the ep el nino events however the zebiak cane model fails to reproduce the cp el nino events the model may be much more influenced by model errors when simulating the cp el nino events as expected when we use the ofv to correct the zebiak cane model the model reproduces the three cp el nino events well furthermore the simulations of the corresponding winds and thermocline depths are also acceptable in particular the thermocline depth simulations for the three cp el nino events lead us to believe that the discharge process of the equatorial heat content associated with the cp el nino is not efficient and emphasizes the role of the zonal advection in the development of the cp el nino events the ofvs associated with the three cp el nino events often exhibit a sea surface temperature anomaly ssta tendency with positive anomalies in the equatorial eastern pacific therefore the sst tendency errors occurring in the equatorial eastern pacific may dominate the uncertainties of the zebiak cane model while simulating cp el nino events a further investigation demonstrates that one of the model errors offset by the ofvs is of a pattern similar to the sst cold tongue cooling mode which may then provide one of the climatological conditions for the frequent occurrence of cp el nino events the ofv may therefore be a useful tool for correcting forecast models and then for helping improve the forecast skill of the models

classifying el nino modoki i and ii by different impacts on rainfall in southern china and typhoon tracks based on their opposite influences on rainfall in southern china during boreal fall this paper classifies el nino modoki into two groups el nino modoki i and ii which show different origins and patterns of sst anomalies the warm sst anomalies originate in the equatorial central pacific and subtropical northeastern pacific for el nino modoki i and ii respectively thus el nino modoki i shows a symmetric sst anomaly distribution about the equator with the maximum warming in the equatorial central pacific whereas el nino modokiii displays an asymmetric distribution with the warmsstanomaliesextending fromthe northeastern pacifictotheequatorialcentralpacific additionally thewarmsstanomaliesintheequatorialcentralpacific extend farther westward for el nino modoki ii than for el nino modoki i similar to the canonical el nino el nino modoki i is associated with an anomalous anticyclone in the philippine sea that induces south westerly wind anomalies along the south coast of china and carries the moisture for increasing rainfall in southern china for el nino modoki ii an anomalous cyclone resides east of the philippines associated with northerly wind anomalies and a decrease in rainfall in southern china the canonical el nino and el nino modoki i are associated with a westward extension of the western north pacific subtropical high wnpsh whereas el nino modoki ii shifts the wnpsh eastward differing from canonical el nino and el nino modoki i el nino modoki ii corresponds to northwesterly anomalies of the typhoon steeringflow which are unfavorable for typhoons to make landfall in china

reaction fronts permeability and fluid pressure development during dehydration reactions abstract fluids released by prograde metamorphism are often invoked to explain a range of crustal processes from earthquake triggering to metasomatism these fluids can be either trapped and overpressured or released and channelized depending on the interplay between permeability reaction rate and compaction experimental data are presented measuring permeability porosity and microstructural evolution throughout the dehydration of gypsum to form bassanite reaction fronts regions over which the reaction largely occurs are used as a framework to explain the results experiments were conducted under hydrostatic conditions at a constant temperature of 115 c at two effective pressures of 60 mpa and 110 mpa and three pore fluid pressures of 20 40 and 60 mpa at high effective pressure creep of the gypsum solid framework results in low porosity and permeability producing high pore fluid pressure build up that slows the reaction rate a clearly defined narrow reaction front migrates along the sample and the average permeability remains low until the front sweeps across the entire sample conversely at low effective pressure the reaction front is wide producing a permeable drained network average permeability is enhanced significantly after only a small fraction of the reaction has completed by the interconnection of open pores this study shows that the width of reaction fronts and hence the permeability development is strongly controlled by compaction the reaction front velocity is broadly dependent on permeability and the reaction driving force a simple quantitative model for these relationships is developed

a possible mechanism for epeirogenic uplift continental geology is dominated by vertical movements some of these are the result of crustal shortening and extension associated with large horizontal displacements involving processes which are now understood at least in outline however both uplift and subsidence can occur without associated shortening or extension of the continental crust most investigations of such epeirogenic movements have been concerned with subsidence partly because of the economic importance of the resulting sedimentary basins and partly because of the existence of a simple model for the process1 which can account for the development of several basins in some detail2 4 however uplift has been relatively neglected and cannot be produced by the same mechanism the purpose of this paper is to examine whether epeirogenic uplift can result from the intrusion of large thicknesses of basic magma into the lower part of continental crust this suggestion was considered as a possible mechanism for the regional uplift of the colorado plateau by gilbert5 more than 100 years ago and also by holmes6 though both rejected the idea however a recent discussion of no less than 14 different mechanisms for generating uplift7 did not include this process even though it seems able to produce the observed vertical motions and also to account for some of the features of the evolution of sedimentary basins that cannot be explained by the uniform stretching model3 8 9 although the suggestion is not new the argument used here to support it is and depends on an understanding of the relationship between ocean island volcanoes and mantle circulation

3d modelling of the effect of thermal elastic stress on grain boundary opening in quartz grain aggregates abstract during the exhumation of rocks and the associated temperature and pressure decrease the anisotropic thermoelastic properties of minerals lead to internal stresses on the grain scale which in turn cause fracturing and opening of grain and phase boundaries to gain deeper insight into the onset of grain boundary cracking and the subsequent evolution of grain boundary fracture networks after crack initiation 3d grain scale numerical modelling has been performed in detail the fracturing and opening of quartz grain boundaries during exhumation of quartzite with millimeter scale grains and randomly oriented crystallographic axes accompanied by cooling from 300 to 25 c and decompression from 300 to 22 mpa have been modelled with contact mechanics and the finite element method model grains have an anisotropic linear elastic rheology and an anisotropic thermal expansion tensor grain boundaries are modelled as contact surfaces with a non linear strain softening rheology in tension and a mohr coulomb rheology in shear grain boundary fractures nucleate at grain vertices and triple lines in agreement with observations in nature and experiment comparison with grain boundary opening data from natural quartzite indicates that the tensile yield strength y of quartz grain boundaries has an upper bound of 75 mpa with best fit results for y 25 mpa moreover the best fit model implies that quartz grain boundary opening initiates after a temperature and pressure decrease of around 80 c and 80 mpa

a deep seismic reflection transect across the irish caledonides new reflection profiles recorded to 18s c 60km along a 600 km north south transect west of ireland wire lines provide a cross section of the irish caledonides from lewisian basement in the north to the variscan fold and thrust belt in the south and constrain the offshore extrapolations of major caledonide structures we interpret the profiles as showing the great glen fault and associated ne trending strike slip faults as near vertical structures which cut the whole crust and the uppermost mantle beneath the surface trace of the fair head clew bay line we image a north dipping zone which soles into horizontal layers just above the reflection moho the north dipping zone separates south dipping reflections above and to the north from north dipping reflections below and to the south from the fair head clew bay line as far south as the iapetus suture the lower crust contains north dipping packages of reflectors possibly related to acadian accretionary underplating the iapetus suture zone can be identified as a zone more than 50 km wide dipping north at 30 from 5 km depth offshore dingle peninsula to sole into the moho at c 30 km depth west of the shannon estuary in the upper crust the shallow part of the iapetus suture zone appears to be transported to the north by late caledonian retrocharriage or by variscan thrusting the iapetus suture does not penetrate through the present day reflection moho but there are scattered reflectors in the mantle not continuous with crustal reflectors perhaps relics of a subducted slab we recognize lower crustal reflectivity and the reflection moho along almost all the wire profiles regionally the travel time to the reflection moho varies from 9 s c 28 km offshore donegal northwest of ireland to 12 s c 35 km offshore kerry and cork southwest of ireland apparent moho offsets rapid lateral changes in the travel time to the reflection moho north of donegal and north of mayo are probably due to the great glen fault and associated faults the lower crustal reflectivity varies considerably in thickness and prevalent dip direction along the wire profiles in donegal bay this reflectivity is observed at depths less than 5 km c 1 5s whereas west of kerry prominent reflectivity is only observed beneath 6s c 17 km though the age of crustal reflectors cannot in general be determined beneath central ireland from donegal to dingle the lower crustal reflectors mimic in dip direction the structural vergence of the exposed dalradian and early palaeozoic rocks so that the lower crustal reflectivity patterns and probably much of the crust must be caledonian in age

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event