volume loss from antarctic ice shelves is accelerating the floating ice shelves surrounding the antarctic ice sheet restrain the grounded ice sheet flow thinning of an ice shelf reduces this effect leading to an increase in ice discharge to the ocean using 18 years of continuous satellite radar altimeter observations we have computed decadal scale changes in ice shelf thickness around the antarctic continent overall average ice shelf volume change accelerated from negligible loss at 25 64 cubic kilometers per year for 1994 2003 to rapid loss of 310 74 cubic kilometers per year for 2003 2012 west antarctic losses increased by 70 in the past decade and earlier volume gain by east antarctic ice shelves ceased in the amundsen and bellingshausen regions some ice shelves have lost up to 18 of their thickness in less than two decades

numerical model to determine the composition of h2o nacl cacl2 fluid inclusions based on microthermometric and microanalytical data natural fluids approximated by the h2o nacl cacl2 system are common in a wide range of geologic environments including sedimentary basins associated with hydrocarbon occurrences and mvt deposits submarine hydrothermal systems and other metamorphic magmatic and hydrothermal environments we present a comprehensive numerical model and microsoft excel based computer program to determine the compositions of fluid inclusions in the h2o nacl cacl2 system based on microthermometric and microanalytical data the model consists of six polynomial correlation equations that describe liquid salinity as a function of nacl cacl2 ratio and melting temperature on each of the ice hydrohalite halite antarcticite cacl2 4h2o and cacl2 2h2o vapor saturated liquidus surfaces the cotectic and peritectic boundaries are determined from the intersections of the liquidus surfaces the model is implicitly internally consistent and topologically correct the model expands upon the compositional range of applicability and the data types that can be used for compositional determination it reproduces experimental data for all compositions that lie within the h2o nacl cacl2 4h2o compositional triangle in the h2o nacl cacl2 system and yields accurate reproductions of the h2o nacl and h2o cacl2 binaries furthermore in comparison to previously published models the one presented here eliminates systematic errors wavy isotherms and cotectic and peritectic curves with local bumps

dolomitization of the latemar platform fluid flow and dolomite evolution abstract the anisian ladinian latemar platform northern italy presents a spectacularly exposed outcrop analogue for dolomitized carbonate reservoirs in relation to fracture controlled igneous intrusions although the latemar is one of the best studied carbonate platforms worldwide timing and evolution of dolomitization and the link to fractures and dikes have not been explored in detail previous dolomite observations are based on a stratigraphically limited portion of the platform this study extends observations to the complete exposed interval in which dolomite bodies occur including those within the less accessible valsorda valley numerous parallel mafic dikes crosscut the latemar platform and border several of its large dolomite bodies 50 m wide 100 m high within dikes and along dike carbonate contacts there are abundant dolomite veins that are geochemically related to surrounding dolomite bodies dolomitization is the result of limestone interaction with hydrothermal fluids delivered along these dikes at dike boundaries impermeable marble aureoles exist derived from contact metamorphism the marble aureoles have locally shielded surrounding limestone from dolomitizing fluid dolomite occurs only where the protective marble is missing or crosscut by fractures based on geometric relationships we conclude that dikes and their damage zones formed the pathways for the dolomitizing fluids and functioned as boundaries for dolomite bodies from field observations and petrography we established a detailed paragenesis dolomitization started shortly after dike emplacement there is an evolution in the fe content of matrix dolomite and dolomite veins from highly ferroan dolomite to non ferroan saddle dolomite alternating with episodes of silica cementation non ferroan calcite precipitation followed dolomitization possibly indicating concurrent depletion in mg this stage likely resulted in further limestone recrystallization rather than dolomitization stable and radiogenic isotopes suggest that the dolomitizing fluid comprised carnian seawater with elevated fe and mg from interaction with other lithologies possibly the nearby predazzo intrusion

subsidence of normal seafloor observations do indicate flattening 1 seafloor topography is a key observational constraint upon the evolution of the oceanic lithosphere specifically plots of oceanic depth z versus crustal age t for normal seafloor are well explained by depth age predictions of thermal contraction models such as the half space and cooling plate model old seafloor t 70 ma shallower than that predicted by half space cooling i e z t or flattening is a key but debated discriminator between the two models korenaga and korenaga 2008 in a recent paper find normal seafloor depths of all ages to be consistent with a z t model thus supporting a cooling half space model for all ages of seafloor upon reevaluation however the mean depths of their normal seafloor flatten at ages 70 ma e g by 723 2 0 5 m 1 standard error for t 110 ma this observed inconsistency with the z t model is statistically significant 99 9 and remains robust 94 even if the number of effective independent depth observations is argued to be low e g n 10 so if any statistically significant conclusion can be drawn from the observed depths of rare old normal seafloor it is that old seafloor flattens which is incompatible with the cooling half space model applying to all ages of seafloor but does not preclude a cooling plate style approximation to lithospheric evolution

the magnesium isotope δ26mg signature of dolomites abstract dolomite precipitation models and kinetics are debated and complicated due to the complex and temporally fluctuating fluid chemistry and different diagenetic environments using well established isotope systems 18 o 13 c 87 sr 86 sr fluid inclusions and elemental data as well as a detailed sedimentological and petrographic data set we established the precipitation environment and subsequent diagenetic pathways of a series of proterozoic to pleistocene syn depositional marine evaporative sabkha dolomites syn depositional non marine evaporative lacustrine and palustrine dolomites altered marine mixing zone dolomites and late diagenetic hydrothermal dolomites these data form the prerequisite for a systematic investigation of dolomite magnesium isotope ratios 26 mg dol dolomite 26 mg ratios documented here range from 2 49 to 0 45 26 mg mean 1 75 1 08 n 42 the isotopically most depleted end member is represented by earliest diagenetic marine evaporative sabkha dolomites 2 11 0 54 2 n 14 in comparing ancient compositions to modern ones some of the variation is probably due to alteration altered marine 1 41 0 64 2 n 4 and earliest diagenetic lacustrine and palustrine dolomites 1 25 0 86 2 n 14 are less negative than sabkha dolomites but not distinct in composition various hydrothermal dolomites are characterized by a comparatively wide range of 26 mg ratios with values of 1 44 1 33 2 n 10 by using fluid inclusion data and clumped isotope thermometry 47 to represent temperature of precipitation for hydrothermal dolomites there is no correlation between fluid temperature 100 to 180 c and dolomite mg isotope signature r 2 0 14 nor is there a correlation between 26 mg dol and 18 o dol magnesium isotope values of different dolomite types are affected by a complex array of different mg sources and sinks dissolution precipitation and non equilibrium fractionation processes and overprinted during diagenetic resetting further progress on the use of 26 mg dol as a proxy will require new theoretical and experimental data for 26 mg fluid dol that includes dehydration effects of the free mg aquo ion versus fluid temperature in ancient diagenetic systems complex variables must be considered these include fluid chemistry and physical properties mg sources and sinks temporal changes during precipitation and post precipitation processes including open and closed system geochemical exchange with ambient fluids all of these factors complicate the application of 26 mg dol as proxy for their depositional or diagenetic environments nevertheless the data shown here also indicate that 26 mg dol can in principle be interpreted within a detailed framework of understanding

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

spatial and temporal antarctic ice sheet mass trends glacio isostatic adjustment and surface processes from a joint inversion of satellite altimeter gravity and gps data we present spatiotemporal mass balance trends for the antarctic ice sheet from a statistical inversion of satellite altimetry gravimetry and elastic corrected gps data for the period 2003 2013 our method simultaneously determines annual trends in ice dynamics surface mass balance anomalies and a time invariant solution for glacio isostatic adjustment while remaining largely independent of forward models we establish that over the period 2003 2013 antarctica has been losing mass at a rate of 84 22 gt yr 1 with a sustained negative mean trend of dynamic imbalance of 111 13 gt yr 1 west antarctica is the largest contributor with 112 10 gt yr 1 mainly triggered by high thinning rates of glaciers draining into the amundsen sea embayment the antarctic peninsula has experienced a dramatic increase in mass loss in the last decade with a mean rate of 28 7 gt yr 1 and significantly higher values for the most recent years following the destabilization of the southern antarctic peninsula around 2010 the total mass loss is partly compensated by a significant mass gain of 56 18 gt yr 1 in east antarctica due to a positive trend of surface mass balance anomalies

a stable isotope study of microbial dolomite formation in the coorong region south australia abstract the coorong region of south australia is a classic location for the study of modern dolomite formation a number of ephemeral lakes here contain dolomite whilst other lakes in close proximity contain aragonite with minor magnesite our previous field and experimental work has revealed that sulphate reducing bacteria play a key role in overcoming kinetic inhibitors to dolomite formation in this area we here use a combination of oxygen carbon and sulphur isotopes to help to further constrain the processes leading to dolomite precipitation in modern hypersaline environments we report isotopic data from four dolomite and three aragonite containing lakes 34 s data for dissolved lake and porewater sulphates reveal 34 s enrichment of residual sulphate in all seven lakes consistent with bulk closed system microbial fractionation by sulphate reducing bacteria calculations using temperature dependent oxygen isotope fractionation factors between dolomite and the solution from which it precipitated are consistent with a strong microbial component to carbonate precipitation in these lakes a comparison of 18 o data from dolomite and aragonite sediment and from their associated lakewaters indicates seasonal mineral precipitation occurs late in the evaporative cycle of the lakes within a yoghurt like saturated mud horizon coincident with the zone of sulphate reduction surprisingly 13 c data from the carbonates do not show the characteristic wide range of values often associated with organogenic carbonates but instead show that these bacterially mediated precipitates incorporate carbon primarily from the inorganic lakewater reservoir partially diluted by an organic component a coorong type microbial model of dolomite formation may be particularly applicable to for example precambrian sedimentary dolomites where benthic microbial communities which are today restricted to extreme environments dominated the shallow marine ecosystem prior to the emergence of metazoa

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

impact of diagenesis and low grade metamorphosis on isotope δ26mg δ13c δ18o and 87sr 86sr and elemental ca mg mn fe and sr signatures of triassic sabkha dolomites abstract dolomite is a common rock forming mineral in the geological record but its value as archive of ancient seawater 26 mg signatures and their variations in time is at present underexplored unknown factors include the sensitivity of 26 mg ratio to processes in the diagenetic and low grade metamorphic domain this paper documents and discusses the first detailed 26 mg data set from early diagenetic and burial dolomites samples come from the upper triassic hauptdolomit dolomia principale the dolomites italy and include coeval dolomicrites that underwent differential burial diagenesis and low grade metamorphosis in a temperature range between about 100 and more than 350 c magnesium isotope data are complemented by dolomite 13 c 18 o and 87 sr 86 sr isotope ratios as well as ca mg mn fe and sr elemental abundances and data on the dolomite crystal structure as indicated by dolomicrite 87 sr 86 sr ratios and petrographic evidence sabkha calcian d1 dolomites precipitated from evaporated seawater and stabilized at an early marine pore water diagenetic stage to d2 dolomites analysed here with increasing burial temperature dolomite 26 mg ratio scatter in the data set decreases with increasing mg ca ratio and degree of order specifically 26 mg ratio variability is reduced from 0 36 2 at burial temperatures beneath 100 c to about 0 14 2 at temperatures in excess of 350 c respectively with mean 26 mg values ranging constantly near 1 9 this suggests that at least for the rock buffered system investigated here dolomicrite 26 mg proxy data are conservative and preserve near pristine values even at elevated burial temperatures at present the main element of uncertainty is the mg isotope fractionation factor between evaporated seawater and dolomite a possible solution to this problem includes the compilation of data from modern sabkha environments including pore water and calcian dolomite 26 mg isotope signatures

interplay of variable thermal conductivity and expansivity on the thermal structure of oceanic lithosphere we have extended our previous analysis of the effects of constant vs variable i e pressure and temperature dependent thermal conductivity k and constant thermal expansivity on the thermal structure of the oceanic lithosphere we apply our analysis to the actual data set including information on the geoid slope the heat flow and ocean floor depth data constrain the thermal expansivity 3 10 5 1 c including geoid slope data may loosely constrain both the thermal expansivity and the thermal conductivity the probable value of thermal conductivity is 3 w m c for the constant k case and 4 w m c at ambient conditions for the variable k case these a and k are generally consistent with laboratory data of appropriate lithospheric materials our analysis supports the plate model with thin lithosphere and high bottom temperature such as gdh1 95 km 1450 c variable k case requires slightly thinner and higher temperature lithosphere 85 km and 1500 c and gives a slightly better fit to the geoid slope data

a burial diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly marked negative 13c excursions in ediacaran age carbonate sediments have been identified in several sections globally but are not recognized in all sections of similar age the presence of 13ccarb values as low as 12 has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today the 13ccarb anomalies are strongly correlated with 18ocarb values but are not represented in 13corg records while no primary depositional processes have been identified that can produce the correlated 18o 13c arrays simulations show that fluid rock interaction with high pco2 fluids is capable of producing such arrays at geologically reasonable pco2 and water rock ratios variations in the mg ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs calcite and anhydrite in the resulting mineral assemblage incorporation of an initially aragonitic mineralogy demonstrates that high sr low mn sr and modest alteration of 87sr 86sr in ancient carbonates are all compatible with a burial diagenesis mechanism for generation of the 13c anomalies and do not necessarily imply preservation of primary values the profound ediacaran negative 13c anomalies can be adequately explained by well understood diagenetic processes conflated with the difficulty of correlating precambrian sections independently of chemostratigraphy they are not a record of primary seawater variations and need not have independent stratigraphic significance

further evidence for a jurassic mineralizing event in central europe k ar dating of hydrothermal alteration and fluid inclusion systematics in wall rocks of the kafersteige fluorite vein deposit in the northern black forest germany the hydrothermal fluorite vein deposit of kafersteige ranks among the biggest in central europe it is located along the suture zone that separates the moldanubian and saxothuringian units in the northern black forest and is hosted in bunter sandstone and underlying granitic basement k ar ages of authigenic illite from the wall rocks give a jurassic formation age of around 145 ma for the deposit age data scatter down to 80 ma in illite from the clay gouge and indicate a younger cretaceous tertiary hydrothermal overprint the pyrophyllite component in authigenic illite from wall rocks and the re equilibration of illite suggest a formation temperature around 200 c secondary fluid inclusions in quartz from the wall rocks define a syn mineralization fluid episode involving ca mg k na cl rich brines about 27 wt nacleq with a t h of about 125 c and a post mineralization na cl rich fluid overprint with a t h of about 100 c both generations of fluid inclusions relate to the final event of each cycle while authigenic illite composition and re equilibration of illite in the clay gouge may document initial temperatures of formation the upper jurassic fluid system can be traced all over western europe it is probably an expression of continent wide rifting and concomitant regional fluid circulation in connection with major tectonic disturbances magmatism and abnormal heat flow during the opening of the north atlantic ocean the younger barren fluid overprint could be related to the onset of the alpine orogeny

subsidence of normal oceanic lithosphere apparent thermal expansivity and seafloor flattening abstract seafloor topography has been a key observational constraint on the thermal evolution of oceanic lithosphere which is the top boundary layer of convection in earth s mantle at least for the first 70 myr the age progression of seafloor depth is known to follow the prediction of half space cooling and the subsidence rate is commonly believed to be 350 m ma 1 2 here we show that based on a new statistical analysis of global bathymetry the average subsidence rate of normal oceanic lithosphere is likely to be 320 m ma 1 2 i e 10 lower than the conventional value we define the normal seafloor as regions uncorrelated with anomalous crust such as hotspots and oceanic plateaus but the lower subsidence rate appears to be a stable estimate not depending on how exactly we define the normal seafloor this low subsidence rate can still be explained by half space cooling with realistic mantle properties if the effective thermal expansivity of a viscoelastic mantle is taken into account in light of a revised model of half space cooling the normal seafloor unperturbed by the emplacement of anomalous crust exists for all ages and the so called seafloor flattening seems to be mostly caused by hotspots and oceanic plateaus

late neogene recent uplift of the cabo de gata volcanic province almeria se spain abstract cabo de gata is a miocene volcanic province in the betic cordillera in southeastern spain the distribution of coastal deposits in the successive marine sedimentary units overlying the last volcanic episode about 7 5 ma old has been used to reconstruct the post volcanic palaeogeographic evolution of the region during the late neogene the current elevation of well dated shoreline marker rocks has been used to estimate uplift amount and rates since the late tortonian a n45 e aligned the strike of the carboneras fault system topographic relief was emergent in the cabo de gata region the extension and height of this island increased throughout the late neogene smaller independent islands were emergent and finally became connected to the main island during the messinian the carboneras and agua amarga pliocene sub basins were the last two marine basins prior to the final emergence of the region since the last volcanic eruption ca 7 5 ma maximum uplift of sedimentary rocks in cabo de gata has taken place on the western margin of the n45 e aligned palaeorelief the altitude of the shoreline marker rocks in the successive sedimentary units decreases eastwards to the present day coast and northwards of the rambla del plomo uplift rates since deposition remain nearly constant for the successive messinian rocks and decrease slightly for the lower pliocene outcrops most of the uplift took place before the pliocene while the main island enlarged uplift amounts and rates since deposition of the upper neogene sedimentary units in the cabo de gata area are similar to the ones estimated for laterally equivalent units in the eastern betic basins approximately 50 m ma despite its volcanic nature and the occurrence of the carboneras fault system the cabo de gata probably became elevated as a consequence of regional uplift in connection with the rest of the betic cordillera

control of seafloor aging on the migration of the izu bonin mariana trench article i nfo recent global kinematic studies reveal that most of the trenches roll back but a significant number of them advance toward the upper plate those advancing trenches are mostly located in the western pacific and correspond to the subduction of very old mesozoic oceanic lithosphere while retreating trenches are commonly explained by the slab pull action of the descending lithosphere the origin of advancing trenches is still debated since this relationship is dependent upon the adopted reference frame we select region where geological studies show the variability of trench migration style with time the izu bonin mariana ibm region represents a key example the detailed reconstruction of the trench migration of the ibm subducting system reveals that after a long episode of asymmetric rollback the ibm trench recently started advancing we propose that this change from retreating to advancing trench mode results from the subduction of progressively older and stiffer lithospheric material we test this hypothesis by means of two dimensional 2 d numerical models reproducing the effects of the lithospheric aging during subduction the result of our numerical tests shows that the entrance of old and stiff lithosphere forces the trench to advance because the increasing stiffness of the slab prevents the slab to unbend once it has subducted we adapt this physical result to the ibm evolution showing that the switch from trench retreat to trench advance can reconcile the shape of ibm slab as previously suggested finally we discuss the possibility that the subduction of the cretaceous lithosphere might have triggered the change of the motion of the pacific plate around 5 ma

testing the preservation potential of early diagenetic dolomites as geochemical archives early marine diagenetic dolomite is a rather thermodynamically stable carbonate phase and has potential to act as an archive of marine porewater properties however the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity here the archive potential of early marine dolomites exposed to extreme post depositional processes is tested using various types of analyses including petrography fluid inclusion data stable 13c and 18o isotopes 87sr 86sr ratios and u pb age dating of various dolomite phases in this example a triassic carbonate platform was dissected and overprinted diagenetic temperatures of 50 to 430 c in a strike slip zone in southern spain eight episodes of dolomitization a dolostone cataclasite and late stage meteoric vadose cementation were recognized the following processes were found to be diagenetically relevant i protolith deposition and fabric preservation and marine dolomitization of precursor aragonite and calcite during the middle late triassic ii intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a proto atlantic opening stress regime t ca 250 c during the early middle jurassic iii dolomite cement precipitation during early alpine tectonism rapid burial to ca 15 km and high grade anchizone overprint during alpine tectonic evolution in the early eocene to early miocene iv brecciation of dolostones to cataclasite during the onset of the carboneras fault zone activity during the middle miocene and v late stage regression and subsequent meteoric overprint data shown here document that under favourable conditions early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 108 or more years evidence for this preservation includes preserved late triassic seawater 13cdic values and primary fluid inclusion data data also indicate that oversimplified statements based on bulk data from other petrographically complex dolomite archives must be considered with caution

anisotropic horizontal thermal contraction of young oceanic lithosphere inferred from stress release due to oceanic intraplate earthquakes how freely the oceanic lithosphere contracts horizontally due to thermal contraction is important information because it reflects the boundary condition of the oceanic lithosphere which includes information regarding the magnitude of driving resisting forces of plate tectonics we investigated the horizontal thermal contraction of young oceanic lithosphere using an analysis of the intraplate stress release due to oceanic intraplate earthquakes oceqs and numerical simulations the stress release due to oceqs in young oceanic lithosphere 5 15 ma shows significant differences between the spreading directional component and the ridge parallel component the extensional stress release of the ridge parallel component is six times as large as that of the spreading directional component while the compressional stress release of the ridge parallel component is one seventh that of the spreading directional component we conducted a numerical simulation of the thermal stress evolution of the oceanic lithosphere to investigate how the difference in the horizontal contraction rates between the spreading direction and the ridge parallel direction can explain the observed anisotropic stress release the result indicates that young oceanic lithosphere 5 15 ma barely contracts in the ridge parallel direction only 0 30 of the spreading directional contraction rate while it contracts freely in the spreading direction due to the weakness of the oceanic ridge strength and the low viscosity asthenosphere from the results we constrained the magnitude of the basal traction working on the bottom of the oceanic lithosphere to be smaller than 0 44 mpa

quaternary tectonic activity of the carboneras fault in the la serrata range se iberia geomorphological and chronological constraints the eastern betic shear zone ebsz in southern iberia is known to accommodate part of the 4 5 mm yr convergence between africa and iberia but its seismic hazard is not sufficiently understood for an accurate risk assessment one of the main structures of the ebsz the left lateral 150 km long carboneras fault displays no clear instrumental and historical activity despite being morphologically expressive detailed geomorphological mapping geochronological analysis and structural observation on the la serrata segment of the carboneras fault were designed to investigate its recent evolution quaternary sediments and geomorphic features were targeted and 42 new numerical ages were obtained based on 66 samples thermoluminescence u series 14c 10be the chronological framework of la serrata was constructed by combining these numerical ages with a conceptual model previously developed in the region which assumes that alluvial fan aggradation was produced during cold and dry periods glacials and stadials whereas stability and phases of calcrete formation were favored during warm and wetter periods interglacials and interstadials the spatial distribution of dated alluvial fans suggests an early phase of uplift that probably occurred between 1 ma and 56 6 ka in the northeastern portion of the study area whereas in the southwest sector the main uplift phase occurred later than 110 3 ka a decline in fault activity would have taken place after 30 8 ka vertically offset dated units indicate minimum dip slip rates of 0 05 mm yr and 0 18 mm yr averaged for the last 1 ma and the last 110 3 ka respectively deflected channels and associated dated units yield a minimum left lateral strike slip rate of 1 31 mm yr averaged for the last 110 3 ka the most recent fault movement of the fault could be younger than ad 637 our results suggest therefore that the carboneras fault is among the fastest in iberia and should be considered in future hazard analyses

river piracy and drainage basin reorganization led by climate driven glacier retreat river piracy the diversion of the headwaters of one stream into another one can dramatically change the routing of water and sediment with a profound effect on landscape evolution stream piracy has been investigated in glacial environments but so far it has mainly been studied over quaternary or longer timescales here we document how retreat of kaskawulsh glacier one of canada s largest glaciers abruptly and radically altered the regional drainage pattern in spring 2016 we use a combination of hydrological measurements and drone generated digital elevation models to show that in late may 2016 meltwater from the glacier was re routed from discharge in a northward direction into the bering sea to southward into the pacific ocean based on satellite image analysis and a signal to noise ratio as a metric of glacier retreat we conclude that this instance of river piracy was due to post industrial climate change rapid regional drainage reorganizations of this type can have profound downstream impacts on ecosystems sediment and carbon budgets and downstream communities that rely on a stable and sustained discharge we suggest that the planforms of slims and kaskawulsh rivers will adjust in response to altered flows and the future kaskawulsh watershed will extend into the now abandoned headwaters of slims river and eventually capture the kluane lake drainage river piracy the diversion of one stream s headwaters into another has occurred on long timescales an analysis of streamflow and digital elevation models documents river re routing in response to glacier retreat in yukon canada in may 2016

the malaguide alpujarride boundary a major extensional contact in the internal zone of the eastern betic cordillera se spain abstract the internal zone of the betic cordillera in southern spain was formed by thrusting and horizontal ductile shortening in the late cretaceous palaeogene but was subjected to a major phase of vertical thinning during the neogene the contact between the malaguide the structurally highest thrust complex and the underlying alpujarride complex is an example of several major tectonic contacts across which the stratigraphy has been repeated by thrusting but the metamorphic grade increases abruptly downwards detailed work in the eastern betic cordillera documents the relationships across this contact in the sierra espuna petrographic and illite crystallinity studies show that the highest imbricate thrusts of malaguide rocks have only been diagenetically altered whereas the deeper parts of the thrust stack exhibit anchizone facies metamorphism in the northern sierra de las estancias apatite fission track studies confirm that there too malaguide rocks have never been above 200 c in both areas the underlying alpujarride rocks exhibit epizone or greenschist facies metamorphism and a major fault zone with both brittle and ductile structures separates the two complexes the observed rapid increase in metamorphic grade over very small structural thicknesses suggests that part of the original metamorphic zonation has been excised across the contact thus in its present form we interpret the malaguide alpujarride boundary as an extensional contact the extensional motion took place in early middle miocene times as constrained by fission track cooling ages the fault zone at the contact is sub horizontal in the sierra espuna but in the sierra de las estancias it is mainly sub vertical kinematic data from a 5 20 m thick calcmylonite layer within the fault zone in the sierra de las estancias corrected for later tilting indicates that the extensional movement was originally directed with the top to the east northeast the interpretation of the malaguide alpujarride boundary as an extensional contact is similar to recent interpretations of the nevado filabride alpujarride contact at deeper structural levels in the central and eastern betics the identification of another major extension fault system confirms that miocene extension was widespread at all structural levels during the early middle miocene the sierra espuna and the northern margin of the sierra de las estancias lay on the boundary between the region undergoing horizontal extension in the internal zones and the alboran sea to the south and the region undergoing horizontal shortening in the external zones to the north as a result the detailed history of the alpujarride malaguide contact is complicated extensional structures cross cut structures related to earlier alpine shortening and were then affected by further shortening as convergence with the external zones continued

component specific petrographic and geochemical characterization of fine grained carbonates along carboniferous and jurassic platform to basin transects abstract fine grained carbonates are present throughout much of the geological record and are widely used as geochemical archives even though their origin and diagenetic pathways remain poorly understood here petrographical and geochemical properties of granulometrically separated component spectra of marine mudstones sampled along two proximal to distal transects carboniferous of spain and jurassic of morocco are documented these settings represent end members in terms of platform geometry steep flanked versus gentle ramp and the aragonite versus calcite sea mode the data from spain reveal a bimodal organization of microcrystalline carbonate isotope values from platform top and slope and toe of slope settings the data from morocco lack a clear spatial and bathymetrical pattern the significance of the complex site specific biological and physico chemical parameters is emphasized mudstones have been separated in granulometric fractions of 8 5 5 3 and

origin characteristics and distribution of fault related and fracture related dolomitization insights from mississippian carbonates isle of man abstract the southwest davis zinc field sdzf is among the westernmost mvt districts associated with the allegheny ouachita orogeny in the midcontinent u s it consists of a series of small zinc sulfide deposits and associated dolomitization covering an area of 16 km2 6 mi2 adjacent to the arbuckle anticline in southern oklahoma mineralization occurs within the royer dolomite upper cambrian and the butterly dolomite lower ordovician of the arbuckle group and is associated with faults and breccia bodies that parallel the trend of the anticline mining activity in the sdzf was restricted to the early part of the 20th century ore mineralization consists chiefly of sphalerite and subordinate smithsonite with minor galena chalcopyrite and pyrite as well as supergene alterations of these minerals homogenization temperatures th of fluid inclusions in gangue dolomite cement range from 88 to 101 c and have salinities of 6 5 to 20 9 wt nacl equivalent rarer fluid inclusions in sphalerite have an average th value of 105 c and average salinity of 19 2 wt nacl equivalent gangue dolomite cements have 18o values of 6 9 to 9 1 vpdb and 13c values of 0 2 to 1 1 vpdb the 87sr 86sr ratios for these dolomites range from 0 7088 to 0 7105 mineralization likely occurred from a flow system in which basement influenced brines entered the host formations through faults and circulated through the brecciated zones as the ore hydrothermal system waned the relative importance of local brines within the carbonate section increased and resulted in precipitation of late dolomite cements

on the extent of mantle hydration caused by plate bending when bent at subduction zones oceanic plates are damaged by normal faulting and this bending related faulting is widely believed to cause deep mantle hydration down to 20 30 km deep the buoyancy of water or equivalently confining pressure however makes it difficult to bring water down even if faulting is deep extension associated with plate bending generates negative dynamic pressure but the magnitude of such dynamic pressure is shown to be insufficient to overcome confining pressure seismic velocity anomalies that have been used to infer the extent of mantle hydration are reviewed and it is suggested that small crack like porosities which can be produced by thermal cracking and further enhanced by bending related faulting is sufficient to explain such velocity anomalies the presence of such porosities however does not necessarily lead to the substantial hydration of oceanic plates because of confining pressure whereas the depth extent of bending generated porosities is uncertain the theory of thermal cracking can be used to place a lower bound on the amount of water contained in the slab mantle 0 03 0 07 wt h2o and this lower bound is suggested to be more than sufficient to explain the lower plane earthquakes of the double seismic zone by dehydration embrittlement

temperatures and oxygen isotopic composition of phanerozoic oceans abstract the temperature of ancient oceans is an important constraint for understanding the climate history of our planet the classical oxygen isotope paleothermometry on fossil shells while very proficient when applied to the younger cenozoic portion of the geologic record is believed to yield only unreliable results for the phanerozoic deep time either because the empirically well documented secular trend to more negative 18 o values with increasing age was generated by post depositional recrystallization processes or if primary implies ecologically unpalatable hot early oceans here we present a compilation of 18 o measurements for 58 532 low mg calcite marine shells that cover almost the entire phanerozoic eon argue that the secular decline of about 6 is primary propose that it reflects the changing oxygen isotopic composition of sea water and define a new baseline trend for 18 o of paleo sea water the latter providing a new template for calculation of ambient habitat temperatures of fossil specimens the resulting pattern for fossil taxa foraminifera brachiopods belemnites and bivalves mimics their modern counterparts in temperature ranges and modes this conceptual framework enables application of actualistic concepts to ambient habitat temperatures of fossils and provides us with a long overdue tool for interpretation of deep time geologic history

comment on effective thermal expansivity of maxwellian oceanic lithosphere by jun korenaga earth planet sci lett 257 343 349 2007 abstract korenaga korenaga j effective thermal expansivity of maxwellian ocean lithosphere earth planet sci lett 257 2007 343 349 apparently unaware of pollack pollack h n on the use of the volumetric thermal expansion coefficient in models of ocean floor topography tectonophysics 64 1980 t45 47 has confirmed pollack s essential result the apparent volumetric thermal expansivity of oceanic lithosphere is less than the intrinsic value indicated by mineral physics data and less than the value suggested by models in which oceanic lithosphere is treated as a fully relaxed fluid

thermal evolution of the oceanic lithosphere an alternative view abstract the most common model used for representing the evolution with age of the oceanic lithosphere is the plate model where the temperature is set at a fixed depth called the base of the plate this base of the plate has no physical meaning but this model provides a mathematical substitute for a system where small scale convection occurs through instabilities growing at the base of the cooling lithosphere and becomes effective only below old ocean another possible view is that convection provides heat at the base of the lithosphere whatever the age of the overlying plate this last process can be modeled by a constant heat flow applied on the bottom lithospheric isotherm chablis model a good fit to the observables bathymetry and geoid as function of age and old age heat flow can be obtained both for plate and chablis models in spite of an experimentally determined thermal expansion coefficient much larger than assumed in previous plate models these models have important consequences for several geodynamic processes the plate at an age of 100 ma is only 80 km thick for both models melting above a hot spot can then occur in the garnet spinel transition field without much plate thinning in the plate model the subsidence is stopped at an age of about 80 ma while according to the chablis model several hundred meters of subsidence are expected after 100 ma thus the two models predict quite a different long term pattern of subsidence in the sedimentary basins finally in the chablis model the global cooling of the mantle coming from cold material eroded by secondary convection at the base of the plates is considerably larger than in plate models it amounts to 40 the remaining 60 being due to the subduction process

the magnesium isotope budget of the modern ocean constraints from riverine magnesium isotope ratios we have measured the magnesium mg isotope ratios in 45 rivers including 16 of the largest rivers in the world covering a range of geologic tectonic and climatic drainage basin environments the range in riverine 26mg is 2 5 half the variation in terrestrial rock although the mg isotopic composition of the source rock is important for small rivers at a global scale lithology is of limited significance for mg isotope ratios in rivers part of the variability at a global scale may be attributed to fractionation in the weathering environment the rivers analysed constitute 30 of the global mg riverine flux to the oceans and a flux weighted mg isotope composition of global runoff has been estimated at 1 09 even taking into account uncertainty this is distinct from seawater at 0 82 this difference arises either from the fractionation of mg isotope ratios in the ocean and or a mg budget which is not at steady state the difference is consistent with fractionation by carbonate precipitation in the simplest steady state scenario where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output mg isotope ratios imply a minimum dolomite mg flux of 9 of the total output mg flux the implications of the distinct isotopic composition of the riverine flux from modern seawater is that the mg isotope ratio of seawater has probably varied outside of current analytical uncertainty mg isotope ratios may therefore provide a valuable new tracer in palaeo oceanography

variation of the subsidence parameters effective thermal conductivity and mantle dynamics abstract the subsidence of young seafloor is generally considered to be a passive phenomenon related to the conductive cooling of the lithosphere after its creation at mid oceanic ridges recent alternative theories suggest that the mantle dynamics plays an important role in the structure and depth of the oceanic lithosphere however the link between mantle dynamics and seafloor subsidence has still to be quantitatively assessed here we provide a statistical study of the subsidence parameters subsidence rate and ridge depth for all the oceans these parameters are retrieved through two independent methods the positive outliers method a classical method used in signal processing and through the mifil method from the subsidence rate we compute the effective thermal conductivity k eff which ranges between 1 and 7 w m 1 k 1 we also model the mantle flow pattern from the s40rts tomography model the density anomalies derived from s40rts are used to compute the instantaneous flow in a global 3d spherical geometry we show that departures from the k eff 3 w m 1 k 1 standard value are systematically related to mantle processes and not to lithospheric structure regions characterized by k eff 3 w m 1 k 1 are associated with mantle uplifts mantle plumes or other local anomalies regions characterized by k eff 3 w m 1 k 1 are related to large scale mantle downwellings such as the australia antarctic discordance aad or the return flow from the south pacific superswell to the east pacific rise this demonstrates that mantle dynamics plays a major role in the shaping of the oceanic seafloor in particular the parameters generally considered to quantify the lithosphere structure such as the thermal conductivity are not only representative of this structure but also incorporate signals from the mantle convection occurring beneath the lithosphere the dynamic topography computed from the s40rts tomography model reproduces the subsidence pattern observed in the bathymetry overall we find a good correlation between the subsidence parameters derived from the bathymetry and the dynamic topography this demonstrates that these parameters are strongly dependent on mantle dynamics

neoproterozoic aragonite dolomite seas widespread marine dolomite precipitation in cryogenian reef complexes the extraordinary abundance of dolomite in the proterozoic challenges our understanding of precambrian marine environments here we show that synsedimentary marine dolomite precipitation was pervasive within cryogenian reef complexes from the adelaide fold belt south australia although these reefs are composed of dolomite textural evidence indicates an originally aragonitic mineralogy for depositional components in common with many other neoproterozoic carbonates allochthonous slope debris from the reefs invariably contains both limestone and dolomite clasts indicating synsedimentary dolomitization in the reefs we describe several new forms of fibrous marine dolomite cement from the reefs that have a length slow optical character these fascicular slow radial slow and rhombic dolomite cements have finely preserved cathodoluminescent growth zones and optical characteristics that indicate they originally precipitated as dolomite rather than replacing calcite or aragonite cements abundant early marine dolomite precipitation implies a radically different seawater chemistry for the cryogenian perhaps these aragonite dolomite seas are associated with extreme neoproterozoic glacial events and or ocean anoxia

calcium isotope record of phanerozoic oceans implications for chemical evolution of seawater and its causative mechanisms a total of 280 brachiopods of ordovician to cretaceous age complemented by published data from belemnites and planktonic foraminifera are used to reconstruct the evolution of calcium isotope composition of seawater 44 40casw over the phanerozoic the compiled 44 40casw record shows a general increase from 1 3 nist srm 915a at the beginning of the ordovician to 2 at present superimposed on this trend is a major long term positive excursion from the early carboniferous to early permian as well as several short term mostly negative oscillations a numerical model of the global cycles of calcium carbon magnesium and strontium was used to estimate whether the recorded 44 40casw variations can be explained by varying magnitudes of input and output fluxes of calcium to the oceans the model uses the record of marine 87sr 86sr ratios as proxy for seafloor spreading rates a record of oceanic mg ca ratios to estimate rates of dolomite formation and reconstructed atmospheric co2 discharge and erosion rates to estimate continental weathering fluxes the model results indicate that varying magnitudes of the calcium input and output fluxes cannot explain the observed 44 40casw trends suggesting that the isotope signatures of these fluxes must also have changed as a possible mechanism we suggest variable isotope fractionation in the sedimentary output flux controlled by the dominant mineralogy in marine carbonate deposits i e the oscillating calcite aragonite seas the ultimate control of the calcium isotope budget of the phanerozoic oceans appears to have been tectonic processes specifically variable rates of oceanic crust production that modulated the hydrothermal calcium flux and the oceanic mg ca ratio which in turn controlled the dominant mineralogy of marine carbonates hence the 44 40casw as to the causes of the short term oscillations recorded in the secular 44 40casw trend we tentatively propose that these are related to variable rates of dolomite formation and or to changing chemical composition of the riverine flux in particular and ratios induced by variable proportions of silicate vs carbonate weathering rates on the continents

effective thermal expansivity of maxwellian oceanic lithosphere abstract the thermal expansivity of oceanic lithosphere is a key mineral physics parameter that controls the rate of seafloor subsidence because of strongly temperature dependent mantle rheology effective expansivity for lithosphere as a whole could be substantially lower than indicated by mineral physics data viscoelastic modeling indicates that this reduction in expansivity could be as high as 15 30 for a plausible range of mantle viscosity though brittle relaxation by thermal cracking is likely to alleviate this reduction tension cracking results in fractured lithosphere with finite crack porosity thereby prohibiting the recovery of fully equilibrated density even with complete brittle relaxation effective thermal expansivity could still be lower by up to 20

marine ice sheet collapse potentially under way for the thwaites glacier basin west antarctica resting atop a deep marine basin the west antarctic ice sheet has long been considered prone to instability using a numerical model we investigated the sensitivity of thwaites glacier to ocean melt and whether its unstable retreat is already under way our model reproduces observed losses when forced with ocean melt comparable to estimates simulated losses are moderate 1 mm per year of sea level rise collapse in the different simulations within the range of 200 to 900 years

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

continental weathering following a cryogenian glaciation evidence from calcium and magnesium isotopes a marked ocean acidification event and elevated atmospheric carbon dioxide concentrations following the extreme environmental conditions of the younger cryogenian glaciation have been inferred from boron isotope measurements calcium and magnesium isotope analyses offer additional insights into the processes occurring during this time data from neoproterozoic sections in namibia indicate that following the end of glaciation the continental weathering flux transitioned from being of mixed carbonate and silicate character to a silicate dominated one combined with the effects of primary dolomite formation in the cap dolostones this caused the ocean to depart from a state of acidification and return to higher ph after climatic amelioration differences in the magnitude of stratigraphic isotopic changes across the continental margin of the southern congo craton shelf point to local influences modifying and amplifying the global signal which need to be considered in order to avoid overestimation of the worldwide chemical weathering flux

precambrian dolomites petrographic and isotopic evidence that they differ from phanerozoic dolomites dolomites are more common in precambrian than in phanerozoic rocks and from a petrographic isotopic study of the middle to upper proterozoic beck spring dolomite of eastern california it is suggested that precambrian dolomites are different from those of the phanerozoic petrographically all fabric details of precambrian dolomites studied are preserved just as if they were limestones and isotopically they show the same trend as limestones increasingly negative i8 o and to a lesser extent increasingly light i8 c from depositional components through early fibrous dolomite cements to later dolomite spar cements the data suggest that in precambrian time dolomite was the principal carbonate mineral precipitated from seawater and during diagenesis and this implies that precambrian seawater was different from that of the phanerozoic

dolomite formation within microbial mats in the coastal sabkha of abu dhabi united arab emirates microbial mediation is the only demonstrated mechanism to precipitate dolomite under earth surface conditions a link between microbial activity and dolomite formation in the sabkha of abu dhabi has until now not been evaluated even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences such an evaluation is the purpose of this study which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of abu dhabi along a transect from the intertidal to the supratidal zone this investigation revealed a close association between microbial mats and dolomite suggesting that microbes are involved in the mineralization process observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats in current models microbial dolomite precipitation is linked to an active microbial activity that sustains high ph and alkalinity and decreased sulphate concentrations in pore waters such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone by contrast these models cannot be applied to the supratidal zone where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity as no abiotic mechanism is known to form dolomite at earth surface conditions two different hypotheses can reconcile this result in a first scenario all of the dolomite present in the supratidal zone formed in the past when the mats were active at the surface in a second scenario dolomite formation continues within the buried and inactive mats in order to explain dolomite formation in the absence of active microbial metabolisms a revised microbial model is proposed in which the mineral template properties of exopolymeric substances play a crucial role

direct observations of evolving subglacial drainage beneath the greenland ice sheet simultaneous observations of moulins and boreholes in western greenland show that water delivery to the base of the ice sheet via moulins affects short term ice velocity fluctuations but not late season ice velocity decelerations increased meltwater delivery to the base of the greenland ice sheet will increase the ice sheet velocity accelerating its inevitable rush towards the ocean and subsequent sea level rise or will it debate on this topic is at the forefront of cryospheric research but has been hampered by the lack of simultaneous observations of hydraulic head in moulins vertical shafts that deliver water to the base of the ice sheet and boreholes which monitor basal water pressure lauren andrews and colleagues now provide these observations from a small region in western greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short term fluctuations in ice velocity late season decelerations in ice velocity however seem to be controlled by changes in unchannelized flow rather than any shifts in the moulin system seasonal acceleration of the greenland ice sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed1 2 via crevasses and moulins vertical conduits connecting supraglacial water to the bed of the ice sheet as the melt season progresses the subglacial hydrologic system drains supraglacial meltwater more efficiently1 2 3 4 decreasing basal water pressure4 and moderating the ice velocity response to surface melting1 2 however limited direct observations of subglacial water pressure4 5 6 7 mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby 0 3 2 kilometres away boreholes indicating that moulins connect to an efficient channelized component of the subglacial hydrologic system which exerts the primary control on diurnal and multi day changes in ice velocity our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the paakitsoq region of western greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin connected channels to convey supraglacial melt instead these observations suggest that decreasing late season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt season dynamics affect ice velocity beyond the conclusion of the melt season8 9 10

the record and stratigraphie implications of organic walled microfossils from the ediacaran terminal proterozoic of south australia two assemblages of organic walled microfossils have been recognized in drillcore samples from the late proterozoic rodda beds in the eastern officer basin south australia the fossils include tube like remains and large simple and sculptured acritarchs lithostratigraphic studies and seismic information in conjunction with previous albeit limited acritarch finds allow local correlation of the rodda beds with ediacaran or terminal proterozoic sequences in the northern adelaide fold belt site of the nominated ediacaran stratotype the new palynofloras are comparable with acritarch assemblages in the amadeus basin of central australia and suggest tentative correlations with sequences in china and the u s s r the presence of isotopically heavy marine carbonate in the lower fossiliferous horizons of the rodda beds pcpdb 3 to 6 0 is consistent with isotopic data from the equivalent interval in china in contrast the upper fossiliferous strata occur higher in the rodda beds where carbonate is significantly lighter 13 cpdb 1 to 3 o

saying goodbye to glaciers global glacier volume is shrinking this loss of earth s land ice is of international concern rising seas to which melting ice is a key contributor are expected to displace millions of people within the lifetime of many of today s children but the problems of glacier loss do not stop at sea level rise glaciers are also crucial water sources integral parts of earth s air and water circulation systems nutrient and shelter suppliers for flora and fauna and unique landscapes for contemplation or exploration

zebra and boxwork fabrics in hydrothermal dolomites of northern canada indicators for dilational fracturing dissolution or in situ replacement zebra and boxwork fabrics in manetoe and presqu ile hydrothermal dolomites provide critical data for discrimination between hypotheses for their origin in a unique occurrence sets of weakly imbricated decimetre sized curvilinear lenticles of white dolospar are developed within sub metre sized tongues of greyish white dolomitized crinoidal packstone and grainstone this nascent zebra fabric has developed along wavy to nodular intra bed sedimentary partings primary bedding can be traced through dolomitized masses containing these fabrics into the surrounding undolomitized limestone all zebra and boxwork fabrics are confined within single beds consistent with an early burial time of origin no change in bed thickness occurs across zebra or boxwork fabrics within beds this indicates a dissolutional rather than a dilational origin for the creation of pore space partly cemented with white dolospar the dolomitized groundmass displays an abruptly gradational or sharp transition to centripetal saddle dolomite cement which partially to nearly completely occludes vugs circulation of geothermally heated hypersaline devonian elk point basinal sea water brines led to dissolution and replacive dolomitization of limestone adjacent to vugs and near contemporaneous precipitation of white dolospar within dissolutional vugs consistent with geochemical simulations the presence of downward extending galleries of white dolospar cemented solution collapse breccia provides further support for an interpretation of regional thermally driven convection of hydrothermal evaporative sea water brines across a broad area of northern canada the absence of gases under pressure in vacuoles within fluid inclusions from manetoe and presqu ile dolospars is also more consistent with a dissolutional and contemporaneous dolomitization origin for these fabrics rather than an origin involving dilational fracturing for space creation and dolospar precipitation the ubiquitous presence of zebra and boxwork fabrics in hydrothermal dolomite reservoirs indicates that they are not confined fault zones and instead occur wherever precursor limestones had relatively greater porosity and permeability prior to dolomitization

thermal cracking and the deep hydration of oceanic lithosphere a key to the generation of plate tectonics 1 the development of transient thermal stress in suboceanic mantle is investigated on the basis of two dimensional thermoviscoelastic models incorporating composite rheology appropriate for dry oceanic lithosphere thermal stress is shown to be sufficiently high to deeply fracture the coldest part of lithosphere e g to the depth of at least 30 km and possibly down to 50 km in 100 ma old lithosphere the release of thermal stress by tension cracking is limited to the vicinity of cracks and the cascade crack system is suggested to be required given the finite fracture strength of mantle materials possible physical and chemical consequences of deep thermal cracking are also discussed the rheological evolution of oceanic lithosphere is likely to be affected by thermal cracking and subsequent serpentinization which introduces the localized zones of weakness in the otherwise stiffest part of lithosphere this localized weakening may help to explain why plate tectonic convection not stagnant lid convection operates in earth s mantle

the geometry and evolution of a transpressional strike slip system the carboneras fault se spain the carboneras fault system is a 40 km long 1 km wide neogene ne sw trending left lateral transpressional strike slip fault system which is part of the trans alboran shear zone in se spain the carboneras fault system is an anastomosing array of sub vertical individual fault planes or fault zones which surround pods or lenses of less intensely strained rocks displacements along the individual fault planes exhibit reverse components of slips and form positive flower structures faults have either sharp boundaries or wider bands of gouge typically a few metres thick and are hundreds of metres in length second order fault splays are well developed and usually exhibit p shear rather than riedel shear orientations these are interpreted to be related to the transpressional displacement and may also characterize other oblique convergent zones elsewhere the second order faults are interpreted to have formed as shear strain increased along the first order fault and was transferred laterally to branch segments this process produced pods or shear lenses bounded by the fault segments the length to width aspect ratios of the shear lenses were found to be scale independent across five orders of magnitude with the most common values between 3 l and 6 l a model is proposed for the development of the fault zone by incremental finite displacements along the segmented fault surfaces this model is based on field evidence that displacement switched with time from one fault strand to another