development of approaches for modelling coupled thermal hydraulic mechanical chemical processes in single granite fracture experiments the geological formation immediately surrounding a nuclear waste disposal facility has the potential to undergo a complex set of physical and chemical processes starting from construction and continuing many years after closure the decovalex project development of coupled models and their validation against experiments was established and maintained by a variety of waste management organizations regulators and research organizations to help improve capabilities in experimental interpretation numerical modelling and blind prediction of complex coupled systems in the present round of decovalex d 2015 one component of task c1 has considered the detailed experimental work of yasuhara et al appl geochem 26 2074 2088 2011 wherein three natural fractures in mizunami granite are subject to variable fluid flows mechanical confining pressure and different applied temperatures this paper presents a synthesis of the completed work of six separate research teams building on work considering a single synthetic fracture in novaculite a range of approaches are presented including full geochemical reactive transport modelling and 2d and 3d high resolution coupled thermo hydro mechanical chemical thmc models the work shows that reasonable fits can be obtained to the experimental data using a variety of approaches but considerable uncertainty remains as to the relative importance of competing process sets the work also illustrates that a good understanding of fracture topography interaction with the granite matrix a good understanding of the geochemistry and the associated multi scale thmc process behaviours is a necessary pre cursor to considering predictive models of such a system

evaluation of recent tectonomagmatic discrimination diagrams and their application to the origin of basic magmas in southern mexico and central america discrimination diagrams to decipher tectonic settings have been in use for nearly 40 years although old diagrams have been extensively used the recent ones based on discriminant functions of ratio variables with or without log transformation proposed during 2004 2010 for the discrimination of four tectonic settings of island arc continental rift ocean island and mid ocean ridge were newly evaluated to show their high success rates of 57 3 100 and 58 5 100 for major element and immobile element based diagrams respectively for the continental arc of the andes evaluated for its similarity to island arc these four sets of diagrams showed success rates of 62 1 83 8 these four sets of five diagrams per set were therefore used to infer tectonic setting of the mexican volcanic belt mvb los tuxtlas volcanic field ltvf and central american volcanic arc cava using this approach the mvb especially its western central and eastern parts and the ltvf of southern mexico show a dominantly continental rift setting and the cava shows an arc setting the west central part of the mvb is consistent with dual tectonics of arc and rift these results confirm the application of an unusual mantle upwelling rift model for the mexican on land volcanism whereas the conventional plate tectonic subduction model seems to be applicable for the cava from guatemala to north western costa rica

introduction to calderas special issue large pyroclastic eruptions and associated caldera collapse structures represent the most catastrophic geologic events that have occurred on the earth s surface in phanerozoic time other than large impacts of asteroids or meteorites calderas are large collapse depressions more or less circular in form the diameters of which are many times greater than the diameter of any included vents williams and mcbirney 1979 the largest known calderas associated with silicic pyroclastic eruptions that produce ash flow tuffs or ignimbrites are as much as 60 km in diameter related pyroclastic deposits have magmatic volumes exceeding 103 km3 in addition to potential problems of volcanic hazards calderas and associated volcanic activity are important controls on many of the earth s ore deposits and geothermal energy resources as well as providing key insights into the generation and evolution of large volume silicic magma bodies

hydraulic sealing due to pressure solution contact zone growth in siliciclastic rock fractures thermo hydro mechanical chemical simulations at the pore scale are conducted to study the hydraulic sealing of siliciclastic rock fractures as contact zones grow driven by pressure dissolution the evolving fluid saturated three dimensional pore space of the fracture results from the elastic contact between self affine randomly rough surfaces in response to the effective confining pressure a diffusion reaction equation controls pressure solution over contact zones as a function of their emergent geometry and stress variations results show that three coupled processes govern the evolution of the fracture s hydraulic properties 1 the dissolution driven convergence of the opposing fracture walls acts to compact the pore space 2 the growth of contact zones reduces the elastic compression of the pore space and 3 the growth of contact zones leads to flow channeling and the presence of stagnant zones in the flow field the dominant early time compaction mechanism is the elastic compression of the fracture void space but this eventually becomes overshadowed by the irreversible process of pressure dissolution growing contact zones isolate void space and cause an increasing disproportion between average and hydraulic aperture this results in the loss of hydraulic conductivity when the mean aperture is a third of its initial value and the contact ratio approaches the characteristic value of one half convergence rates depend on small wavelength roughness initially and on long wavelength roughness in the late time the assumption of a characteristic roughness length scale therefore leads to a characteristic time scale with an underestimation of dissolution rates before and an overestimation thereafter

the last glaciation in central magellan strait southernmost chile abstract glacial landforms and drift stratigraphy in central magellan strait southernmost chile document repeated fluctuations during the last glacial cycle of outlet lobes from an ice cap centered over the southern andes the lobes developed comparatively low gradient profiles because of low basal shear stresses over soft deformable beds and this made them sensitive to even small scale changes in the mass balance such low profiles and rapid calving in deep proglacial lakes during deglaciation may have made the magellan ice lobe particularly responsive to climatic fluctuations during the last glacial cycle and to advance and retreat over considerable distances study of the glacial landforms and drift stratigraphy has led to the identification of at least five glacier advances to limits at and south of the segunda angostura fragments of mollusc shells contained in basal till indicate marine incursions between some advances thus documenting extensive deglaciation a partial chronology based on amino acid studies and radiocarbon dating suggests that five of these advances occurred during the last glacial cycle the most extensive advances may have culminated during substages of marine isotope stage 5 substage 5b or 5d and or during stage 4 slightly less extensive advances occurred between ca 28 000 and 14 000 yr b p

temporal alteration of fracture permeability in granite under hydrothermal conditions and its interpretation by coupled chemo mechanical model abstract examining the evolution of fracture permeability under stressed and temperature elevated conditions a series of flow through experiments on a single rock fracture in granite has been conducted under confining pressures of 5 and 10 mpa under differential water pressures ranging from 0 04 to 0 5 mpa and at temperatures of 20 90 c for several hundred hours in each experiment measurements of fluid and dissolved mass fluxes and post experimental microscopy were conducted to constrain the progress of mineral dissolution and or precipitation and to examine its effect on transport properties generally the fracture aperture monotonically decreased with time at room temperature and reached a steady state in relatively short periods i e

geochemistry of evolved magmas and their relationship to subduction unrelated mafic volcanism at the volcanic front of the central mexican volcanic belt abstract this study reports new geochemical and radiogenic isotope data on hy normative pleistocene to recent 87 sr 86 sr 0 70370 0 70469 143 nd 144 nd 0 51278 0 51289 206 pb 204 pb 18 64 18 72 207 pb 204 pb 15 59 15 62 and 208 pb 204 pb 38 39 38 52 these isotopic ratios are generally similar to those for the associated mafic rocks although some differences do exist between them particularly for the 87 sr 86 sr ratios that are somewhat higher and 143 nd 144 nd that are slightly lower for the evolved rocks the available geochemical evidence does not support the generation of the scn evolved magmas by simple fractional crystallization fc or even by assimilation coupled with fractional crystallization afc of such mafic magmas nor by direct slab melting or indirect fluid transport to the mantle participation of the subducted cocos plate the viable mechanism seems to be that the most evolved andesitic and dacitic magmas in the scn were produced by partial melting of a heterogeneous mafic granulite source in the lower crust the magmas of intermediate compositions may reflect magma mixing processes between the most evolved andesitic and dacitic magmas generated in the lower crust and the mantle derived mafic magmas basalt and basaltic trachy andesite at the volcanic front of the central part of the mvb these results have direct bearing to other volcanic areas with complex tectonic setting

the sea level fingerprints of ice sheet collapse during interglacial periods abstract studies of sea level during previous interglacials provide insight into the stability of polar ice sheets in the face of global climate change commonly these studies correct ancient sea level highstands for the contaminating effect of isostatic adjustment associated with past ice age cycles and interpret the residuals as being equivalent to the peak eustatic sea level associated with excess melting relative to present day of ancient polar ice sheets however the collapse of polar ice sheets produces a distinct geometry or fingerprint of sea level change which must be accounted for to accurately infer peak eustatic sea level from site specific residual highstands to explore this issue we compute fingerprints associated with the collapse of the greenland ice sheet west antarctic ice sheet and marine sectors of the east antarctic ice sheet in order to isolate regions that would have been subject to greater than eustatic sea level change for all three cases these fingerprints are more robust than those associated with modern melting events when applied to infer eustatic sea level because 1 a significant collapse of polar ice sheets reduces the sensitivity of the computed fingerprints to uncertainties in the geometry of the melt regions and 2 the sea level signal associated with the collapse will dominate the signal from steric effects we evaluate these fingerprints at a suite of sites where sea level records from interglacial marine isotopes stages mis 5e and 11 have been obtained using these results we demonstrate that previously discrepant estimates of peak eustatic sea level during mis5e based on sea level markers in australia and the seychelles are brought into closer accord

geology and geochemistry of amealco caldera qro mexico amealco caldera located in the central part of the mexican volcanic belt mvb about 130 km nw of mexico city is characterized by a quasi circular 11 km diameter structure whose southern portion is partly truncated by a regional fault the caldera was formed 5 m y ago due to a voluminous eruption of 65 km3 eq magma volume of ignimbrites which covered an area of 1800 km2 this was followed by eruption of 2 km3 of andesitic and dacitic lava flows from the border of the caldera and emplacement of a total of 8 silicic rhyolitic domes 8 km3 inside the caldera finally postcaldera volcanism 4 km3 consisted of extrusion of andesitic and basaltic andesite lavas and scoriae we have analyzed 17 representative rock samples for their major and trace element contents by x ray fluorescence spectrometry and for rare earth elements by high performance liquid chromatography all samples were also analyzed for their sr and nd isotopic compositions which range as follows 87sr 86sr 0 70379 0 70451 143nd 144nd 0 51267 0 51278 the chemical and isotopic data are used to constrain the origin and evolution of magmas in the caldera no combination of altered morb and overlying sediments from the subducted slab cocos plate can produce the sr and nd isotopic compositions observed in rocks from amealco caldera further modelling reveals that the mantle derived primary magmas in amealco caldera may have assimilated up to 10 of a crustal component during their evolution from basaltic andesites to dacites but no further assimilation appears to have taken place during the evolution of the rhyolitic magmas the structure and genesis of the amealco caldera are comparable to some other calderas of the mvb

amino acid racemization geochronology of reworked quaternary mollusks on u s atlantic coast beaches implications for chronostratigraphy taphonomy and coastal sediment transport approximately 200 shells primarily mercenaria from 21 beach sites between new jersey and florida have been analyzed for the extent of racemization epimerization of their fossilized amino acids the greatest concentration of sites is in north carolina in regions least affected by human modification of natural beach sediment transport processes these results can be used to estimate the frequency of age mixing of pleistocene shell material in holocene depositional environments selected shells have also been dated by 14c conventional and or ams to provide direct calibration of the amino acid epimerization ratios shell taphonomic characteristics particularly color can be qualitatively related to apparent ages data for shell fragmentation combined with amino acid age estimates provide insights into probable transport distances of reworked shells shells with apparent pleistocene ages have epimerization values equivalent to those seen in onshore exposures of pleistocene coastal units amino acid epimerization measurements are a comparatively rapid and inexpensive chronologic tool for use in taphonomic and sediment shell transport studies paired amino acid 14c analyses on single shells provide insights into geochemical alteration of shells and permit modelling of the residence time of shells on beaches greater numbers of analyses at each site are needed before statistically valid estimates of age mixing can be obtained but the apparent distribution of pleistocene shells on atlantic coast beaches appears to be related to the distribution of pleistocene units in the shoreface and inner shelf and the thickness of holocene sedimentary cover in specific areas these observations provide useful criteria for the evaluation of possible age mixing of shells collected at outcrops of pleistocene units in the coastal plain

imaging surface contacts power law contact distributions and contact stresses in quartz calcite glass and acrylic plastic a procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials while the surfaces are subjected to static loads or undergoing frictional slip static loading experiments with quartz calcite soda lime glass and acrylic plastic at normal stresses to 30 mpa yield power law distributions of contact areas from the smallest contacts that can be resolved 3 5 m2 up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces in each material increasing normal stress results in a roughly linear increase of the real area of contact mechanisms of contact area increase are by growth of existing contacts coalescence of contacts and appearance of new contacts mean contacts stresses are consistent with the indentation strength of each material contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self similar the contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies the contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography

geochemical effects of decoupled fractional crystallization and crustal assimilation most models of crustal assimilation assume that the amount of assimilant added to the magma is proportional to each infinitesimally small amount of solid removed during crystallization afc in some magmatic systems however assimilation and crystallization are not strictly related and the mass assimilated is decoupled from and therefore varies independently of the mass crystallized fca the geochemical consequences of fca are examined and compared to those of afc the behavior of incompatible elements is identical during afc and fca and ratios of these elements do not allow discrimination between the two processes major oxide least squares mass balance models do not discriminate between afc and fca at f 0 7 f fraction of melt remaining however fca yields magmas richer in compatible elements and with higher sr isotopic ratios than afc at a given value of f repeated cycles of fca and afc combined with magma mixing fam may result in unusual geochemical trends such as the evolution of a calc alkaline basaltic parent to a tholeiitic daughter magma or the evolution of low and medium k calc alkaline basalts to high k andesites dacites trachyandesites or trachydacites lavas erupted by the volcano micro profitis ilias on santorini hellenic arc greece provide an example of magmas which evolved by combined fractionation assimilation by fca and mixing

roughness of fault surfaces over nine decades of length scales 1 we report on the topographic roughness measurements of five exhumed faults and thirteen surface earthquake ruptures over a large range of scales from 50 m to 50 km we used three scanner devices lidar laser profilometer white light interferometer spanning complementary scale ranges from 50 m to 10 m to measure the 3 d topography of the same objects i e five exhumed slip surfaces vuache sillingy bolu corona heights dixie valley magnola a consistent geometrical property i e self affinity emerges as the morphology of the slip surfaces shows at first order a linear behavior on a log log plot where axes are fault roughness and spatial length scale covering five decades of length scales the observed fault roughness is scale dependent with an anisotropic self affine behavior described by four parameters two power law exponents h constant among all the faults studied but slightly anisotropic h 0 58 0 07 in the slip direction and h 0 81 0 04 perpendicular to it and two pre factors showing variability over the faults studied for larger scales between 200 m and 50 km we have analyzed the 2 d roughness of the surface rupture of thirteen major continental earthquakes these ruptures show geometrical properties consistent with the slip perpendicular behavior of the smaller scale measurements our analysis suggests that the inherent non alignment between the exposed traces and the along or normal slip direction results in sampling the slip perpendicular geometry although a data gap exists between the scanned fault scarps and rupture traces the measurements are consistent within the error bars with a single geometrical description i e consistent dimensionality over nine decades of length scales

evolution of fracture normal stiffness due to pressure dissolution and precipitation abstract the normal stiffness of a fracture is a key parameter that controls for example rock mass deformability the change in hydraulic transmissivity due to stress changes and the speed and attenuation of seismic waves that travel across the fracture non linearity of normal stiffness as a function of stress is often attributed to plastic yield at discrete contacts similar surface altering mechanisms occur due to pressure solution and precipitation over larger timescales these processes partition the fracture surfaces into a flattened contact region and a rough free surface that bounds the void space under low loads contact occurs exclusively over the flattened part leading to rapid exponential stiffening at higher loads contact occurs over the rough surface fraction leading to the conventional linear increase of stiffness with stress it follows that a relationship exists between the history of in situ temperature and stress state of a rock fracture and its subsequent deformation behavior

geochemical evidence for a lithospheric source for magmas from los humeros caldera puebla mexico abstract this study reports new geochemical and sr nd pb radiogenic isotope data on hy normative quaternary basaltic to rhyolitic volcanic rocks as well as two samples of mesozoic to palaeozoic intrusive igneous rocks from los humeros caldera lhc located in the eastern part of the mexican volcanic belt mvb the isotopic ratios of mafic basaltic rocks range as follows 87 sr 86 sr 0 703350 0 703387 143 nd 144 nd 0 512867 0 512888 206 pb 204 pb 18 849 18 866 207 pb 204 pb 15 593 15 598 and 208 pb 204 pb 38 490 38 491 these values are similar to the rift related mafic rocks from the volcanic front of the central mvb for comparison the entire suite from basalt b to rhyolite r in the lhc shows the following ranges 87 sr 86 sr 0 703350 0 704678 143 nd 144 nd 0 512702 0 512888 206 pb 204 pb 18 710 18 866 207 pb 204 pb 15 593 15 631 and 208 pb 204 pb 38 444 38 594 the basaltic rocks from los humeros do not show the characteristic negative nb anomaly with respect to ba and ce as is typical of such magmas in volcanic arcs the available geochemical and isotopic evidence does not support the generation of the lhc mafic magmas by direct slab melting nor by indirect fluid transport to the mantle participation of the subducted cocos plate instead they could be generated in the upper mantle from a lithospheric source the evolved andesitic to rhyolitic magmas could have been originated from such mafic magmas through assimilation coupled with extensive fractional crystallisation two different compositions representing lower lc and upper crusts uc as well as a hypothetical crust ha were tested as plausible assimilants for the assimilation coupled with fractional crystallisation process

paricutin re examined a classic example of crustal assimilation in calc alkaline magma following its birth on the 20th of february 1943 the mexican volcano paricutin discharged a total of 1 38 km3 of basaltic andesite and andesite before the eruption came to an end in 1952 until 1947 when 75 of the volume had been erupted the lavas varied little in chemical or isotopic composition all were basaltic andesites with 55 to 56 sio2 18o of 6 9 to 7 0 and 87sr 86sr ratios close to 0 7038 subsequent lavas were hypersthene andesites with silica contents reaching 60 18o values up to 7 6 and 87sr 86sr of 0 7040 to 0 7043 the later lavas were enriched in ba rb li and k2o and depleted in mgo cu zn cr ni sr and co the isotopic and other chemical changes which appeared abruptly over a few months in 1947 are interpreted as the result of tapping a sharply zoned and density stratified magma chamber xenoliths of partially fused felsic basement rocks in the lavas have silica contents greater than 70 18o of 5 6 to 9 9 and 87sr 86sr between 0 7043 and 0 7101 in many respects they resemble samples of basement rocks collected from nearby outcrops three analysed samples of the latter have silica contents of 65 to 67 18o of 7 7 to 8 6 and 87sr 86sr between 0 7047 and 0 7056 these new data provide strong support for the original interpretations of wilcox 1954 who explained the chemical variations by a combination of fractional crystallization and concurrent assimilation of up to 20 weight continental crust except for a few trace elements particularly ba sr and zr the chemical and isotopic compositions of the xenoliths and basement rocks that crop out nearby match the type of contaminant required to explain the late stage lavas some of the discrepancies may be explained by postulating a contaminant that was older and richer in ba sr and zr than those represented by the analysed xenoliths others can be attributed to chemical changes accompanying disequilibrium partial melting contact metamorphism and meteoric hydrothermal alteration of the country rock many of the xenoliths show evidence of having been affected by such processes the lavas were erupted from a zoned magma chamber that had differentiated by liquid fractionation prior to the eruption the order of appearance of the lavas can be explained in terms of withdrawal of stratified liquids of differing densities and viscosities

geochemical and sr nd pb isotopic evidence for a combined assimilation and fractional crystallisation process for volcanic rocks from the huichapan caldera hidalgo mexico abstract this study reports new geochemical and sr nd pb isotopic data for miocene to quaternary basaltic to andesitic dacitic and rhyolitic volcanic rocks from the huichapan caldera located in the central part of the mexican volcanic belt mvb the initial sr and nd isotopic ratios except for one rhyolite range as follows 87sr 86sr 0 70357 0 70498 and 143nd 144nd 0 51265 0 51282 the sr nd pb isotopic ratios are generally similar to those for volcanic rocks from other areas of the central and eastern parts of the mvb the isotopic ratios of one older pre caldera rhyolite hp30 from the huichapan area particularly its high 87sr 86sr are significantly different from rhyolitic rocks from this and other areas of the mvb but are isotopically similar to some felsic rocks from the neighbouring geological province of sierra madre occidental smo implying an origin as a partial melt of the underlying crust the evolved andesitic to rhyolitic magmas could have originated from a basaltic magma through a combined assimilation and fractional crystallisation afc process different compositions representing lower crust lc and upper crust uc as well as a hypothetical crust similar to the source of high 87sr 86sr rhyolite hp30 were tested as plausible assimilants for the afc process the results show that the uc represented by granitic rocks from a nearby los humeros area or by cretaceous limestone l rocks outcropping in the northern part of the study area and the lc represented by granulitic xenoliths from a nearby san luis potosi slp area are not possible assimilants for huichapan magmas whereas a hypothetical crust ha similar in isotopic compositions to rhyolite hp30 could be considered a possible assimilant for the afc process chemical composition of assimilant ha although not well constrained at present was inferred under the assumption that hp30 type partial melts could be generated from its partial melting these data were then used to evaluate the proposed afc process to explain the evolution of the huichapan magmas

last interglacial isotope stage 5 glacial and sea level history of coastal chukotka peninsula and st lawrence island western beringia abstract study of glacial and marine sequences along the outer coast of chukotka peninsula bering strait is the basis for major revisions of the regional stratigraphy the val katlen suite at its type section at the mouth of the enmelen river records the youngest high sea stand of the last interglaciation on chukotka peninsula marine deposits and glacial diamicton stratigraphically below the type section record respectfully the peak of the last interglacial marine oxygen isotope substage 5e and rapid glacierization of the coastal mountains probably during substage 5d or 5b correlative deposits recording a similar sequence of intra stage 5 events but once thought to be of early and middle pleistocene age include the upper and lower pinakul suite at cape pinakul and marine deposits near the nunyamo river on the gulf of anadyr based upon amino acid analyses biostratigraphy and supporting geochronology these deposits enclose warmer than present faunas and floras comparible to last interglacial pelukian marine deposits found along the coast of alaska the last major advance of glacial ice from chukotka peninsula across anadyr strait and onto st lawrence island was likely initiated during the later part of stage 5 based on our reinterpretaion of the stratigraphy at cape pinakul near the nunyamo river and on northwestern st lawrence island chukotkan ice probably reached st lawrence island sometime during oxygen isotope stage 4 ice extend across chukotka during the lgm was very imited

aminostratigraphic correlations and paleotemperature implications pliocene pleistocene high sea level deposits northwestern alaska abstract multiple periods of late pliocene and pleistocene high sea level are recorded by surficial deposits along the coastal plains of northwestern alaska analyses of the extent of amino acid epimerization in fossil molluscan shells from the nome coastal plain of the northern bering sea coast and from the alaskan arctic coastal plain of the chukchi and beaufort sea coasts allow recognition of at least five intervals of higher than present relative sea level three late pliocene transgressions are represented at nome by the complex and protracted beringian transgression and on the arctic coastal plain by the colvillian bigbendian and fishcreekian transgressions these were followed by a lengthy period of non marine deposition during the early pleistocene when sea level did not reach above its present position a middle pleistocene high sea level event is represented at nome by the anvilian transgression and on the arctic coastal plain by the wainwrightian transgression anvilian deposits at the type locality are considerably younger than previously thought perhaps as young as oxygen isotope stage 11 410 000 bp finally the last interglacial pelukian transgression is represented discontinuously along the shores of northwestern alaska amino acid epimerization data together with previous paleomagnetic measurements radiometric age determinations and paleontologic evidence provide geochronological constraints on the sequence of marine deposits they form the basis of regional correlations and offer a means of evaluating the post depositional thermal history of the high sea level deposits provisional correlations between marine units at nome and the artic coastal plain indicate that the temperature difference that separates the two sites today had existed by about 3 0 ma since that time the effective diagenetic temperature was lowered by about 3 4 c at both sites and the mean annual temperature was lowered considerably more this temperature decrease was largely accomplished by the close of the fishcreekian beringian iii transgression ca 2 5 2 1 ma since then intervals of warm temperature must have been extremely brief these data suggest that the steep latitudinal temperature gradient and the frigid temperatures that characterize the high latitudes of alaska today are ancient features of arctic climate

lead isotope studies of the guerrero composite terrane west central mexico implications for ore genesis new thermal ionization mass spectrometry and multi collector inductively coupled plasma mass spectrometry pb isotope analyses of three cenozoic ores from the la verde porphyry copper deposit located in the zihuatanejo huetamo subterrane of the guerrero composite terrane are presented and the metal sources are evaluated lead isotope ratios of 3 cenozoic ores from the el malacate and la esmeralda porphyry copper deposits located in the zihuatanejo huetamo subterrane and of 14 ores from the zimapan and la negra skarn deposits from the adjoining sierra madre terrane are also presented to look for systematic differences in the lead isotope trends and ore metal sources among the proposed exotic tectonostratigraphic terranes of southern mexico comparison among the isotopic signatures of ores from the sierra madre terrane and distinct subterranes of the guerrero terrane supports the idea that there is no direct correlation between the distinct suspect terranes of mexico and the isotopic signatures of the associated cenozoic ores rather these pb isotope patterns are interpreted to reflect increasing crustal contribution to mantle derived magmas as the arc advanced eastward onto a progressively thicker continental crust the lead isotope trend observed in cenozoic ores is not recognized in the ores from mesozoic volcanogenic massive sulfide and sedimentary exhalative deposits the mesozoic ores formed prior to the amalgamation of the guerrero composite terrane to the continental margin which took place during the late cretaceous in intraoceanic island arc and intracontinental marginal basin settings while the tertiary deposits formed after this event in a continental arc setting lead isotope ratios of the mesozoic and cenozoic ores appear to reflect these differences in tectonic setting of ore formation most pb isotope values of ores from the la verde deposit 206pb 204pb 18 674 18 719 are less radiogenic than those of the host igneous rocks but plot within the field defined by the huetamo sequence suggesting that these ores may also contain metals from the sedimentary rocks the pb isotope ratios of ore samples from the zimapan deposit 206pb 204pb 18 771 18 848 are substantially higher than the whole rock pb isotope compositions of the basement rocks the similarity of ore pb to igneous rock pb in the zimapan district 206pb 204pb 18 800 18 968 may indicate that the proximal source of ore metals in the hydrothermal system was the igneous activity

a model for intergranular pressure solution in open systems abstract intergranular pressure solution ips represents a well known mechanism of bulk deformation and pore volume change especially in sedimentary rocks which has been documented in the field and reproduced in laboratory experiments theoretical descriptions of the process in terms of simple pressure solution creep laws can explain features such as grain size dependence of creep rates but have typically remained restricted to closed system conditions with negligible long range transport in the fluid phase and somewhat biased toward grain boundary diffusion controlled creep the recasting of the classical weyl rutter model of ips considered in this paper emphasizes open system conditions and the competition between diffusion and dissolution reaction rate processes the thermodynamic force which drives ips is expressed in terms of an effective grain boundary normal traction and a solute supersaturation this suggests the occurrence of a transition from ips to grain boundary healing at a certain level of supersaturation of the pore fluid although the process of healing is not studied here the explicit appearance of the solute concentration in the driving force highlights the coupling of the ips deformation process to the long range transport of dissolved material and the need to model the diagenesis of compacting sedimentary sequences accordingly the conceptual grain boundary model used in this paper is that of a fluid invaded grain to grain contact zone which is visualized to remain in a roughened state during continued ips the use of simple linear phenomenological rate laws for dissolution and grain boundary diffusion allows the ranges of rate control by dissolution or diffusion to be succinctly characterized in terms of the ratio of corresponding time constants the associated compaction behaviour is explored quantitatively in this paper by presenting solutions for the uniaxial and isotropic compaction creep strain vs time for a simple cubic packing of spheres

composition and smnd isotopic data of the lower crust beneath san luis potosi central mexico evidence from a granulite facies xenolith suite quaternary volcanics from san luis potosi slp in central mexico sampled a xenolith suite comprising uppermantle nodules spinell lherzolites hornblende pyroxenites spinel pyroxenites and lower crustal xenoliths the latter consist of granulite facies mafic to intermediate metaigneous rocks and high grade metasediments precursors of the metaigneous suite range from gabbroic to tonalitic compositions whole rock ree patterns permit classification of metaigneous rocks into cumulates and fractionated melts mafic xenoliths consist of plagioclase clinopyroxene orthopyroxene garnet amphibole apatite rutile scapolite garnet has reacted extensively with clinopyroxene forming corona textures of secondary plagioclase orthopyroxene and amphibole intermediate xenoliths are garnet free and quartz bearing all samples display similar ca al zoning patterns documented in orthopyroxene clinopyroxene and plagioclase which are along with the presence of coronas around garnet interpreted as representing partial re equilibration stages from 940 60 c and 7 11 kbar down to lower temperatures and pressures there is no indication of a secondary heating event in these xenoliths sm nd isotopic compositions of the spinel lherzolites indicate a heterogeneous composition of the mantle segment beneath slp similar sr and nd isotopic signatures reveal that the hornblende pyroxenites are high pressure cumulates linked to the host basanites four mainly intermediate metaigneous granulites from a single vent which are free of secondary amphibole and two spinel pyroxenites regarded as the most primitive member of the metaigneous suite define a regression line in a sm nd isochron diagram yielding an age value of 1248 69 ma and an initial nd value of 2 3 metaigneous xenoliths containing secondary amphibole plot significantly above the regression line which is probably due to the introduction of externally derived nd during amphibole formation under retrograde p t conditions discussing the geological significance of the calculated age value there are some arguments for interpreting this age as representing the intrusion age of the magmatic precursors this gives evidence for formation of lower crust of basic to intermediate compositions during the mid proterozoic now situated beneath slp

fracturing and hydrothermal alteration in normal fault zones large normal fault zones are characterized by intense fracturing and hydrothermal alteration displacement is localized in a slip zone of cataclasite breccia and phyllonite surrounding corrugated and striated fault surfaces slip zone rock grades into fractured but less comminuted and hydrothermally altered rock in the transition zone which in turn grades abruptly into the wall rock fracturing and fluid flow is episodic because permeability generated during earthquakes is destroyed by hydrothermal processes during the time between earthquakes

aminostratigraphic relations and age of quaternary deposits northern espanola basin new mexico abstract amino acid ratios of gastropods provide a useful basis for correlation and approximate dating of middle to late quaternary fluvial deposits from the northern espanola basin new mexico sparsely fossiliferous slackwater deposits in the rio chama rio grande floodplain were buried episodically by piedmont alluvium during periods of climatic change as the axial river system cut down 120 m during the past 620 000 yr alloisoleucine isoleucine alle ile ratios in the total hydrolysate and free fraction of amino acids in succinea and vallonia are strongly correlated with elevation ratios in succinea range from 0 01 to 0 79 in the total hydrolysate and from 0 00 to 1 15 in the free fraction for deposits that range in age from modern to 620 000 yr old amino acid ratios are tightly clustered for deposits that contain the 620 000 yr old lava creek b tephra layer demonstrating their utility for correlation and providing a calibration point for a local dating curve two 14c ages from younger deposits and limiting ages for erosion surfaces that lie above gastropod bearing units tend to support the validity of much of the curve combining the dating curve with the geologic constraints suggests that aggradation events separated by episodes of net incision occurred at about 620 000 310 000 70 000 170 000 40 000 95 000 15 000 yr ago after 19 000 yr ago and during two minor periods between 80 000 and 25 000 yr ago

rapid racemization of aspartic acid in mollusc shells and potential for dating over recent centuries dating of deposits and materials less than 350 years old is hindered by the very poor time resolution of the radiocarbon method over this period1 2 fluctuations in atmospheric 14c levels result in the existence of several possible calendric ages for any given radiocarbon age for terrestrial samples in the marine record these fluctuations are dampened however only a small change in marine radiocarbon ages occurs over this period from ad 1700 to 1950 radiocarbon ages become only 100 yr younger2 consequently age resolution is poor furthermore there is an uncertainty in the amount of the correction for the reservoir effect the apparent radiocarbon age of modern marine carbon typically 400yr which reflects the average residence time of carbon in the oceans amino acid racemization epimerization analysis has been used primarily for dating samples older than the limit of radiocarbon dating 40 000 50 000 yr bp 3 4 here i show that aspartic acid asp in mollusc shells has racemized particularly rapidly over the past few centuries analyses done on land snails from deposits in the negev desert eolianites in madeira cave deposits in jamaica and from museum collections indicate racemization rates of 2 5 per century asp racemization thus provides a means of dating recent faunal assemblages of molluscs and other biogenic carbonates as well as recent terrestrial fluvial and marine sedimentary sequences that contain molluscs

a multi proxy palaeoecological and palaeoclimatic record within full glacial lacustrine deposits western tennessee usa the fulton section along the mississippi river in western tennessee usa is a 1 km continuous exposure 20 m vertically of quaternary fluvial and lacustrine deposits inset within eocene sediments and buried by thick loess fossiliferous slackwater lake sediments record maximum aggradation during the last two major glaciations with deposition between ca 190 140 ka and q1 24 18 14 c ka bp based on amino acid and radiocarbon chronology respectively during the onset of full glacial conditions ca 24 22 14 c ka bp a relatively permanent shallow lake environment is indicated by ostracodes aquatic molluscs and both pollen and macrofossils of aquatic plants by 21 8 14 c ka bp increasing emergent plants amphibious gastropods pomatiopsis and heavier d 18 o compositions suggest marsh like conditions in a periodically drying lake the surrounding uplands consisted of picea pinus woodlands mixed with cool temperate hardwoods e g quercus populus carya grasses and herbs more open conditions ensued ca 20 14 c ka bp with loess and slopewash gradually infilling the former lake by 18 14 c ka bp modern analogue analyses of ostracodes and palaeontological evidence imply a full glacial climate similar to today s mixed boreal zone in central minnesota usa about 98c cooler in mean annual temperature than present day western tennessee copyright 2009 john wiley sons ltd

shear enhanced nonlinear flow in rough walled rock fractures abstract nonlinear flow in 3d rough walled rock fractures is simulated by solving the navier stokes equations the emphasis is on the impact of shear caused aperture changes variable apertures and asperity contacts and flow conditions inertial term upon nonlinear flow behavior in order to compare shear effects two 3d fracture models with and without shear were established with identical initial rough walled surfaces topographies of a realistic rock sample five groups of simulations with different inflow boundary conditions of flowrates reynolds numbers re were conducted to demonstrate shear enhanced nonlinearity of flow fields and limitations of local cubic law lcl approach the flow results clearly show channeling flow along the preferential paths transverse flow around the contact spots and eddy flows behind contact spots with increasing re which cannot be observed in 2d models the effective transmissivity of the 3d fracture model was calculated from the modeling results of velocity and pressure fields the results showed that the effective transmissivity is a function of local apertures with important uncertainties even when re is small i e re 0 4 in this study thus the validity of the transmissivity evaluation using lcl approach for nonlinear flow in 3d rough walled rock fractures is questionable

rate laws for water assisted compaction and stress induced water rock interaction in sandstones mineral water interactions under conditions of nonhydrostatic stress play a role in subjects as diverse as ductile creep in fault zones phase relations in metamorphic rocks mass redistribution and replacement reactions during diagenesis and loss of porosity in deep sedimentary basins as a step toward understanding the fundamental geochemical processes involved using naturally rounded st peter sand we have investigated the kinetics of pore volume loss and quartz water reactions under nonhydrostatic hydrothermal conditions in flow through reactors rate laws for creep and mineral water reaction are derived from the time rate of change of pore volume sand water dissolution kinetics and flow rate independent steady state silica concentrations and reveal functional dependencies of rates on grain size volume strain temperature effective pressure confining minus pore pressure and specific surface areas together the mechanical and chemical rate laws form a self consistent model for coupled deformation and water rock interaction of porous sands under nonhydrostatic conditions microstructural evidence shows a progressive widening of nominally circular and nominally flat grain grain contacts with increasing strain or equivalently porosity loss and small quartz overgrowths occurring at grain contact peripheries the mechanical and chemical data suggest that the dominant creep mechanism is due to removal of mass from grain contacts termed pressure solution or solution transfer with a lesser component of time dependent crack growth and healing the magnitude of a stress dependent concentration increase is too large to be accounted for by elastic or dislocation strain energy induced supersaturations favoring instead the normal stress dependence of molar gibbs free energy associated with grain grain interfaces

volcanic stratigraphy of the los azufres geothermal area mexico abstract the los azufres volcanic center located 200 km northwest of mexico city is one of a number of pleistocene silicic volcanic centers with active geothermal systems that lie north of the axis of the mexican neovolcanic belt silicic volcanism began approximately 1 m y ago with eruption of the agua fria rhyodacite to high silica rhyolite lava domes and flows they are covered by rhyodacite and dacite lava domes and flows of the san andres volcano dated at 0 3 m y a north to northeast trending set of high angle normal faults is offset by a younger and more prominent east trending set that parallels the principal regional structural trend these faults cut all but the youngest volcanic rocks of the center the yerbabuena rhyodacites to high silica rhyolites these morphologically well preserved lava domes are approximately 0 15 m y old and are probably associated with air fall tuffs that blanket the western portion of the volcanic center two episodes of high heat flow suggested by studies of drill core samples and fluids from the los azufres geothermal field may correspond to two different episodes of magma injection to high levels the most recent one resulting in eruption of the yerbabuena lavas

isotopic and trace element constraints on the origin and evolution of alkaline and calc alkaline magmas in the northwestern mexican volcanic belt a wide variety of rock types has been produced by pliocene to recent volcanism in the northwestern portion of the mexican volcanic belt composite cones erupted rocks typical of calc alkaline volcanic belts associated with subduction monogenetic cinder cones surrounding the composite cones erupted mildly alkaline basalts and related rocks one larger center las navajas produced basalts trachytes and peralkaline rhyolites such alkaline rocks are typically associated with crustal extension related to rifting both subduction and rifting appear to be taking place in western mexico the most basic calc alkaline rocks although somewhat fractionated show depletion in high field strength elements hfse and enrichment in alkaline earth elements relative to other incompatible elements a characteristic typical of magmas in subduction related volcanic arcs the basic alkaline rocks show no depletion in hfse and show higher concentrations of incompatible elements than the basic calc alkaline rocks the calc alkaline rocks show a tight cluster of 87sr 86sr and 143nd 144nd ratios both of which correlate weakly with sio2 basic alkaline rocks have lower sr and higher nd isotopic ratios whereas the more differentiated alkaline rocks have isotopic ratios that overlap with and extend beyond the range of values found in calc alkaline rocks trace element data indicate that calc alkaline magmas could not have been derived by crystal fractionation from the alkaline magmas nor by assimilation of crustal materials by alkaline magmas the evolution of both calc alkaline and alkaline rocks requires a process of crystal fractionation accompanied by assimilation afc of crustal rocks to account for changes in isotopic ratios and trace element concentrations in the more differentiated members of each suite assuming a contaminant located in the lower or middle crust afc modeling shows that the amounts of assimilation required for alkaline magmas are somewhat higher than those for calc alkaline magmas calc alkaline and alkaline rocks appear to have resulted from melting of two distinct sources alkaline from an oib type source and calc alkaline from a mixed mantle and slab derived source

direct measurement of asperity contact growth in quartz at hydrothermal conditions earthquake recurrence requires interseismic fault restrengthening which results from solid state deformation in room temperature friction and indentation experiments in contrast exhumed fault zones show solution transport processes such as pressure solution and contact overgrowths influence fault zone properties in the absence of fluid flow overgrowths are driven by gradients in surface curvature where material is dissolved diffuses and precipitates at the contact without convergence normal to the contact to determine the rate of overgrowth for quartz we conducted single contact experiments in an externally heated pressure vessel convergence was continuously monitored using reflected light interferometry through a long working distance microscope contact normal force was constant with an initial effective normal stress of 1 7 mpa temperature was between 350 and 530 c and water pressure was constant at 150 mpa two control experiments were conducted one dry at 425 c and one bimaterial sapphire at 425 c and 150 mpa water pressure no contact growth or convergence was observed in the controls for wet single phase contacts growth was initially rapid and then decreased with time no convergence was observed fluid inclusions indicate that the contact is not uniformly wetted the contact is bounded by small regions of high aperture reflecting local free face dissolution as the source for the overgrowth the apparent activation energy is 125 kj mol extrapolation predicts rates of contact area increase orders of magnitude faster than in dry room temperature and hydrothermal friction experiments suggesting that natural strength recovery near the base of the seismogenic zone could be dominated by contact overgrowth

sea cave temperature measurements and amino acid geochronology of british late pleistocene sea stands calibrating amino acid ratios with uranium series dates requires an accurate knowledge of current mean annual temperatures cmats over the region studied to measure these test tube sized diffusion sensors were emplaced for 1 year in 1984 1985 and 1986 both outside and inside minchin hole sea cave in south wales and belle hougue sea cave in jersey both of which have yielded oxygen isotope substage 5e uranium series ages on speleothems our outside temperatures agreed with meteorological ones our inside temperatures were over 1 c lower to allow for this a mean of empirical linear and parabolic epimerisation calculations suggests that ratios from molluscs inside the caves should be multiplied by over 1 1 for comparison with outside ratios this raises bowen et al s pennard stage ratios from inside minchin and bacon hole up towards the unnamed stage ratios outside and suggests that the unnamed sites are also from oxygen isotope substage 5e as proposed by proctor and smart the same conclusion is reached more strongly by comparisons with the ratios and temperatures inside belle hougue to the south and at eemian assumed 5e sites in the netherlands germany and denmark to the east the pennard ratios from outside sites may provide further evidence for global sea stands close to the present level later in oxygen isotope stage 5

the instantaneous rate dependence in low temperature laboratory rock friction and rock deformation experiments 1 earthquake occurrence probabilities that account for stress transfer and time dependent failure depend on the product of the effective normal stress and a lab derived dimensionless coefficient a this coefficient describes the instantaneous dependence of fault strength on deformation rate and determines the duration of precursory slip although an instantaneous rate dependence is observed for fracture friction crack growth and low temperature plasticity in laboratory experiments the physical origin of this effect during earthquake faulting is obscure we examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by tullis and weeks 1987 we compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher temperature dislocation glide experiments the same normalization scheme is used to compare rate dependence in friction to rock fracture and to low temperature crack growth tests for particular weak phyllosilicate minerals the instantaneous friction rate dependence is consistent with dislocation glide in intact rock failure tests for each rock type considered the instantaneous rate dependence is the same size as for friction suggesting a common physical origin during subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible the instantaneous rate dependence measured during failure or creep tests at high stress has long been thought to be due to crack growth however direct comparison between crack growth and friction tests shows poor agreement the crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered

sr and nd isotopic evidence for petrogenesis of mid tertiary felsic volcanism in the mineral district of zacatecas zac sierra madre occidental mexico abstract twelve samples of mid tertiary felsic volcanic rocks from zacatecas and san luis potosi both belonging to the sierra madre occidental and one sample of lower tertiary porphyritic andesite from zacatecas are analyzed for 87 sr 86 sr k rb and sr eight selected samples are also analyzed for 143 nd 144 nd a linear regression of the present day 87 sr 86 sr and 87 rb 86 sr of the felsic volcanic rocks in zacatecas gives an approximate date of 30 8 ma the initial 87 sr 86 sr ratios are high and widely distributed from 0 705 to 0 712 or higher whereas the initial 143 nd 144 nd ratios are somewhat low and show a narrow range 0 5125 0 5127 the available isotopic and trace element data are best explained in terms of a binary mixing model in which the magmas derived from a slightly depleted mantle fractionate and mix with varying proportions of the overlying middle upper continental crust and undergo further shallow level fractional crystallization before eruption this model is also compatible with the trace element and sr isotopic data published from other areas of the sierra madre occidental for which a purely mantle origin has been proposed

experimentally determined mineral melt partition coefficients for sc y and ree for olivine orthopyroxene pigeonite magnetite and ilmenite our current lack of understanding of the partitioning behavior of sc y and the ree rare earth elements can be attributed directly to the lack of a sufficiently large or chemically diverse experimental data set to address this problem we conducted a series of experiments using several different natural composition lavas doped with the elements of interest as starting compositions microprobe analyses of orthopyroxene pigeonite olivine magnetite ilmenite and co existing glasses in the experimental charges were used to calculate expressions that describe ree partitioning as a function of a variety of system parameters using expressions that represent mineral melt reactions versus element ratio distribution coefficients it is possible to calculate terms that express low ca pyroxene melt partitioning behavior and are independent of both pyroxene and melt composition compositional variations suggest that sc substitution in olivine involves either a paired substitution with al or more commonly with vacancies the partitioning of sc is dependent both on melt composition and temperature our experimentally determined olivine melt ree ds partition coefficients are similar to but slightly higher than those reported by mckay 1986 and support their conclusions that olivines are strongly lree depleted y and ree mineral melt partition coefficients for magnetite range from 0 003 for la to 0 02 for lu ilmenite partition coefficients range from 0 007 for la to 0 029 for lu these experimental values are two orders of magnitude lower than many of the published values determined by phenocryst matrix separation techniques

deep geothermal wells in the los azufres mexico caldera volcanic basement stratigraphy based on major element analysis abstract the los azufres caldera michoacan mexico is located in the trans mexican volcanic belt mvb the pre caldera volcanic basement consists of a 3 km thick pile of andesitic flows intruded and or overlain by rhyolitic and dacitic domes and flows the geochemistry of the volcanic layers has been investigated in three deep wells a9 a25 and a48 down to 3 0 km such deep wells have given the opportunity to investigate the geochemical changes related to the hydrothermal metamorphism as well as the stratigraphy of the thick volcanic pile systematic analysis of major elements in cores and cuttings shows that the partial to total hydrothermal metamorphism of the series from the greenschist to the amphibolite facies produces significant geochemical changes on the whole rock geochemistry gains in co 2 h 2 o and depletions in alkalis are especially observed and may be related with the crystallization of carbonates and phyllosilicates however the depth concentration profiles have shown that most other elements such as al fe ca mg p and ti display moderate changes due to hydrothermal alteration in comparison with their initial variations of magmatic origin rythmic compositional changes are observed all along the volcanic pile with progressive changes in rock composition from basalts to dacites within four megasequences of a few hundred meters thickness elements rather immobile under hydrothermal conditions such as ti have been especially useful for the reconstruction of magmatic sequence stratigraphy variations of element concentrations seem mostly due to magmatic differentiation of parental basalts which produces compositions from basaltic andesites to dacites however the four magmatic suites distinguished display calc alkaline features coherent with other suites of the mvb volcanoes

emergent marine record and paleoclimate of the last interglaciation along the northwest alaskan coast the last interglacial high sea level stand the pelukian transgression of isotope substage 5e is recorded along the western and northern coasts of alaska by discontinuous but clearly traceable marine terraces and coastal landforms up to about 10 m altitude the stratigraphy indicates that sea level reached this altitude only once during the last interglacial cycle from the type area at nome to st lawrence island in the bering sea to the eastern limit of the beaufort sea pelukian deposits contain extralimital faunas indicating that coastal waters were warmer than present amino acid ratios in molluscs from these deposits decrease to the north toward barrow consistent with the modern regional temperature gradient fossil assemblages at nome and st lawrence island suggest that the winter sea ice limit was north of bering strait at least 800 km north of its present position and the bering sea was perennially ice free microfauna in pelukian sediments recovered from boreholes indicate that atlantic water may have been present on the shallow beaufort shelf suggesting that the arctic ocean was not stratified and the arctic sea ice cover was not perennial for some period in coastal regions of western alaska spruce woodlands extended westward beyond their modern range and in northern alaska on the arctic coastal plain spruce groves may have entered the upper colville river basin the flaxman member of the gubik formation on the alaskan arctic coastal plain was deposited during marine isotope substage 5a and records the breakup of an intra stage 5 ice sheet over northwestern keewatin

quaternary highstands in bear lake valley utah and idaho surficial deposits in bear lake valley utah and idaho demonstrate that bear lake and its surrounding wetlands expanded and contracted several times during the quaternary period deposits in 40 outcrops and the geomorphology of the valley were studied to reconstruct the water level history temporal control was provided by amino acid geochronology on 29 samples of aquatic mollusks calibrated by 14 c dating and tephrochronology samples of three molluscan genera were heated and analyzed to determine intergeneric differences in aspartic asp and glutamic glu acid racemization the covariance of asp and glu racemization in these genera was used to identify aberrant amino acid analyses the rate of glu racemization was calibrated by using a parabolic model that was used to estimate sample ages although the paucity of exposures uncertainty of the depositional setting and postdepositional uplift of deposits hamper an accurate reconstruction of water level in bear lake valley several conclusions can be drawn during the middle pleistocene lacustrine or wetland environments in northern bear lake valley may have extended up to 1830 masl meters above sea level 6000 ft twice between ca 1000 100 ka bear hollow phase during the late pleistocene the shoreline of bear lake transgressed at least three times 1 to 1817 masl 5960 ft at 47 39 cal calendar year corrected ka jensen spring phase 2 to 1814 masl 5950 ft at ca 16 15 cal ka raspberry square phase and 3 to 1814 masl at ca 9 cal ka willis ranch phase bear river currently bypasses bear lake but flowed into the lake during highstands and allowed the water level to rise to the valley threshold at nounan narrows water levels have lowered to 1806 masl 5923 ft since the middle pleistocene likely because of downcutting by bear river at nounan narrows because downcutting at nounan narrows controls the maximum attainable water level in bear lake valley effects of climate change on lake level are limited and bear lake may actually have been smaller than today when lake bonneville transgressed to its maximum shoreline during the last glacial maximum

stable isotope profiles of last interglacial pelukian transgression mollusks and paleoclimate implications in the bering strait region abstract the marine paleoclimate during the last interglaciation in the bering strait region is inferred from the stable oxygen and carbon isotope profiles of fossil bivalve mollusks specimens were collected from the marine highstand deposits of the pelukian transgression from the arctic alaskan coastal plain the nome coastal plain st lawrence island and the val katlen suite on the chukotka peninsula as a calibration modern mollusks were obtained from the major water masses in the bering chukchi seas system and from coastal environments near the fossil localities the 18 o composition of the modern mollusks accurately reflects the seawater 18 o differences among the water masses and the ambient temperature range at each site seasonal paleotemperature ranges are estimated from the 18 o profiles of the fossils by comparison with those of the modern specimens a simple model is developed to correct the paleotemperature ranges for the influence of differences in seawater 18 o between water masses and seasonal variations caused by freshwater discharge paleotemperatures calculated for the skull cliff site alaskan arctic coastal plain are close to but slightly cooler than those of modern specimens from peard bay and icy cape the isotopic composition of a pelukian specimen collected near wainwright shows the obvious influence of locally reduced salinities with a correction for lower seawater 18 o this profile yields a summer temperature of 13 c which is 3 c warmer than that from the modern icy cape specimen the isotope records of two specimens from the nome coastal plain suggest salinities that were 3 5 psu lower than the modern eastern bering shelf the paleotemperature range of 0 15 c is consistent with modern conditions in norton sound the character of the isotope profiles of the pelukian specimens from st lawrence island is very different than that of modern specimens near the island but matches the 18 o values of shells from deeper sites in anadyr water this suggests that the fossil mollusks were living in anadyr strait and were transported by a glacial advance from the chukotka peninsula the last interglacial specimens from the val katlen suite have isotope profiles with large seasonal 18 o ranges and the clear influence of a reduced salinity coastal water mass calculated paleotemperatures from the val katlen specimens range from 0 to 13 c differences in the 13 c of shell carbonate between sites appears to reflect the regional distribution of the 13 c of sedimentary organic matter som which is a mixture between terrestrial organic matter mean 13 c of 24 and marine phytoplankton 21 partitioning of 13 c between shallow and deep waters by phytoplankton productivity and remineralization may also affect the regional distribution differences in shell 13 c between taxa may relate to feeding mode and the type and isotopic composition of ingested particles the filter feeders mya and astarte typically have 13 c values 1 2 more positive than the deposit feeders macoma and serripes this effect is attributed to a 13 c difference between marine phytoplankton and som with a component of terrestrial organic carbon

magma genesis and chamber processes at los humeros caldera mexico nd and sr isotope data the mexican volcanic belt mvb a roughly east west structure consists of many late tertiary and quaternary cindercones domes calderas and stratovolcanoes1 2 los humeros caldera approximately 19 40 n latitude 97 25 w longitude lies on the northeastern part of the mvb where the belt overlaps with another major volcanic province the eastern cordillera3 fig 1 a compilation6 of the bulk chemical analyses of the two major volcanic provinces indicates that the mvb is characterized largely by calc alkaline series whereas rocks of the alkaline series dominate the eastern cordiliera ec pleistocene to recent basaltic to rhyolitic volcanism in los humeros caldera one of the best known examples of a well developed caldera in mexico7 9 presumably associated with the subduction of cocos plate along the middle america trench shows that the initial 87sr 86sr ratios range from 0 7039 to 0 7048 and the initial 143nd 144nd ratios from 0 5126 to 0 5129 we show here that these isotope ratios are negatively correlated and lie on the mantle array defined by morb and oceanic island rocks implying that los humeros magmas were generated in the upper mantle with very little if any contribution from the subducted oceanic crust sediments or continental crust

single fractures under normal stress the relation between fracture specific stiffness and fluid flow abstract fracture specific stiffness and fluid flow through a single fracture under normal stress are implicitly related through the geometry of the void space and contact area that comprise the fracture data from thirteen different rock samples each containing a single fracture show that relationships between fracture specific stiffness and fluid flow through a fracture fall into two general classes of behavior fractures either fall on a loosely defined universal curve relating fluid flow to fracture specific stiffness or else the flow is weakly dependent on fracture specific stiffness the second relationship shows that flow decreases slowly with increasing fracture specific stiffness the first relationship shows that flow decreases rapidly for increases in fracture specific stiffness to understand this behavior computer simulations on simulated single fractures were performed to calculate fluid flow fracture displacement and fracture specific stiffness as a function of normal stress simulated fractures with spatially correlated and uncorrelated aperture distributions were studied fractures with spatially uncorrelated aperture distributions tend to exhibit a weak dependence of fluid flow on fracture specific stiffness because these fractures tend to have multiple connected paths across the sample which can support flow with uniformly distributed contact area thus an increment in stress will increase the stiffness of the fracture without greatly reducing the amount of fluid flow on the other hand fractures with spatially correlated aperture distributions tend to belong to the universal relationship because correlated fractures tend to have only one or two dominant flow paths and the contact area is limited to a few regions resulting in a compliant fracture thus an increment in stress on a spatially correlated fracture will result in an increase in stiffness and rapid decrease in fluid flow these spatial correlations in fracture void geometry can be differentiated in the laboratory based on the observed fracture specific stiffness fluid flow relationship for a single fracture under normal loading

extension of gutenberg richter distribution to mw 1 3 no lower limit in sight 1 with twelve years of seismic data from tautona gold mine south africa we show that mining induced earthquakes follow the gutenberg richter relation with no scale break down to the completeness level of the catalog at moment magnitude mw 1 3 events recorded during relatively quiet hours in 2006 indicate that catalog detection limitations not earthquake source physics controlled the previously reported minimum magnitude in this mine within the natural earthquake laboratory in south african mines nelsam experiment s dense seismic array earthquakes that exhibit shear failure at magnitudes as small as mw 3 9 are observed but we find no evidence that mw 3 9 represents the minimum magnitude in contrast to previous work our results imply small nucleation zones and that earthquake processes in the mine can readily be scaled to those in either laboratory experiments or natural faults

fault zone structure at depth from differential dispersion of seismic guided waves evidence for a deep waveguide on the san andreas fault summary seismic guided wave dispersion can be used to image fault zone structure at seismogenic depth a two station differential group velocity technique previously used for surface waves was adapted to solve for local fault zone structure between two stations this method was extended to solve for fault zone structure between two earthquakes using differential group arrival times at a single station the method was tested with finite difference synthetic data for an inhomogeneous fault as well as with a pair of shallow earthquakes recorded in the san andreas fault observatory at depth safod borehole station results from a pair of deep earthquakes recorded in the safod borehole station indicate that the low velocity waveguide of the san andreas fault extends to 10 km depth the waveguide at 10 12 km depth is 120 190 m wide and the velocity contrast is 20 per cent similar to the values in the shallow subsurface multiple earthquakes and receivers could be used to map fault zone structure at seismogenic depth as a function of depth and strike

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

characterization of fault roughness at various scales implications of three dimensional high resolution topography measurements accurate description of the topography of active fault surfaces represents an important geophysical issue because this topography is strongly related to the stress distribution along fault planes and therefore to processes implicated in earthquake nucleation propagation and arrest to date due to technical limitations studies of natural fault roughness either performed using laboratory of field profilometers were obtained mainly from 1 d profiles with the recent development of light detection and ranging lidar apparatus it is now possible to measure accurately the 3 d topography of rough surfaces with a comparable resolution in all directions both at field and laboratory scales in the present study we have investigated the scaling properties including possible anisotropy properties of several outcrops of two natural fault surfaces vuache strike slip fault france and magnola normal fault italy in limestones at the field scale digital elevation models of the fault roughness were obtained over surfaces of 0 25 m2 to 600 m2 with a height resolution ranging from 0 5 mm to 20 mm at the laboratory scale the 3 d geometry was measured on two slip planes using a laser profilometer with a spatial resolution of 20 m and a height resolution less than 1 m

pleistocene raised marine deposits on wrangel island northeast siberia and implications for the presence of an east siberian ice sheet two previously undocumented pleistocene marine transgressions on wrangel island northeastern siberia question the presence of an east siberian or beringian ice sheet during the last glacial maximum lgm the tundrovayan transgression 459 000 780 000 yr b p is represented by raised marine deposits and landforms 15 41 m asl located up to 18 km inland the presence of high sea level 64 000 73 000 yr ago the krasny flagian transgression is preserved in deposits and landforms 4 7 m asl in the krasny flag valley these deposits and landforms were mapped dated and described using amino acid geochronology radiocarbon optically stimulated luminescence electron spin resonance oxygen isotopes micropaleontology paleomagnetism and grain sizes the marine deposits are eustatic and not isostatic in origin all marine deposits on wrangel island predate the lgm indicating that neither wrangel island nor the east siberian or chukchi seas experienced extensive glaciation over the last 64 000 yr

solute transport in a single fracture with time dependent aperture due to chemically medicated changes in addition to mechanical loading the transport properties of rock fractures are also affected by chemically mediated changes such as pressure solution stress corrosion and free face dissolution among others based on a time dependent model of fracture closure under constant normal stresses the transport behavior of contaminants in a slowly closing fracture is studied using a finite difference scheme the results show that the contaminant penetrating along the fracture plane gradually becomes slow or almost negligible during the process of fracture closure induced by chemical processes whereas the matrix diffusion of contaminants is active all the time this finding indicates that diffusion into the rock matrix perpendicular to the advective flow direction always plays an important role in determining the fate of contaminant in rock fractures the smaller the fluid flow due to fracture closure and the larger impact the matrix diffusion can further delay the solute transport

application of the gauss theorem to the study of silicic calderas the calderas of la primavera los azufres and los humeros mexico abstract we explored applications including limitations of gauss s theorem to the study of silicic calderas first it enables us to determine the mass deficiency from calderas mass deficiency itself has also other potential applications it enables to make qualitative comparisons between calderas we can use the mass deficiency to test in a quick way and as a preliminary step to a formal gravity inversion for the feasibility of caldera types of simple geometry i e piston subsidence and funnel models this application can be done in a straightforward way once the mass deficiency has been determined for this purpose the mass deficiency is converted to the volume of material missing at the caldera subsequently for example this volume and the respective caldera diameter enable us to estimate the height of the cylinder fitting the piston subsidence model if the obtained parameters are congruent with the known geology and geophysical information then the model may be considered further in the inversion of the gravity data for the detailed structure other simple models i e the funnel model can also be analyzed in this way in particular when working with a piston subsidence caldera type the gauss theorem enables us to estimate the caldera collapse very difficult to obtain based on geologic information alone these possible uses of gauss s theorem are illustrated with the calderas of la primavera los azufres and los humeros caldera mexico the obtained mass deficiency from these calderas follow the linear mass deficiency diameter trend observed for other calderas in particular because of their diameters and mass deficiencies la primavera and krakatau calderas can be considered equiparable this comparison is of the most importance considering that la primavera is located in the neighbourhood of a metropolis guadalajara city since geophysical studies have already established a piston subsidence model for these calderas we assessed gauss s theorem used to estimate their collapses the respective estimated subsidences for la primavera 600 m los humeros 500 m and los azufres calderas 800 and 1200 m respectively are supported by borehole data these relatively small subsidences in relation to many calderas in western us can be explained by the presence of cylindrical to sub spherical magma chambers of smaller size than those underlying the western us calderas of yellowstone valles and long valley for example in an epicontinental setting of young quaternary rocks against precambrian cratonic basement in western us a reassessment of all the available geological and geophysical information was also done in particular the caldera limits were checked and corrected when necessary based on available 2 d gravity modeling gravity gradients and the location of the volcanic vents regional tectonic lineaments might explain many of the particular details of their structures la primavera caldera might have formed through a piecemeal subsidence controlled by the pre caldera tectonics los humeros caldera is an example of a caldera that evolved by incremental growth as the vulsiniani calderas in italy the los azufres caldera comprises two contiguous calderas emplaced in a regional tectonic depression

geometry of the benioff zone and state of stress in the overriding plate in central mexico analysis of depths and focal mechanisms of 16 small earthquakes in central mexico along with previous data shows that a the subducted cocos plate becomes subhorizontal between 110 and 275 km from the trench reaching a depth of about 50 km and b the bottom part of the overriding continental plate is in tensional stress regime neotectonic structures in central mexico and stress orientations estimated from borehole elongations cinder cone alignments and fault slip analysis in the trans mexican volcanic belt which lies in the northeastern portion of the area under study also indicate the same stress regime absolute motion of the north american plate in the region has a component normal to the trench of 20 mm yr which if true would result in compressional stress in the upper plate if the trench position is fixed in an absolute frame of reference if we allow for seaward retreat of the trench then the tensional stress in the overriding plate and the observed geometry of the benioff zone can be explained this however implies that seaward retreat of a trench is possible even for a young 15 m y old subducting slab alternatively tectonic erosion of the leading edge of the continent which has been proposed to explain truncated igneous and metamorphic continental terrane could give rise to the tensional stress but would not explain the geometry of the benioff zone

mechanisms of compaction of quartz sand at diagenetic conditions the relative contribution of cracking grain rearrangement and pressure solution during experimental compaction of quartz sand at diagenetic conditions was determined through electron and optical microscopy and image analysis aggregates of st peter sand 255 60 m diameter grain size and porosity of approximately 34 were subjected to creep compaction at effective pressures of 15 34 5 70 and 105 mpa temperatures of 22 and 150 c nominally dry or water saturated pore fluid pressure of 12 5 mpa conditions and for times up to one year all aggregates displayed transient decelerating creep and volume strain rates as low as 2 10 10 s 1 were achieved the intensity of fracturing and degree of fragmentation increase with volume strain and have the same dependence on volume strain at all conditions tested indicating that impingement fracturing and grain rearrangement were the main mechanisms of compaction throughout the creep phase the increase in fracture density and decrease in acoustic emission rate at long times under wet conditions reflect an increase in the contribution of subcritical cracking no quantitative evidence of significant pressure solution was found even for long term creep at 150 c and water saturated conditions comparison of our findings to previous work suggests that pressure solution could become significant at temperatures or times somewhat greater than investigated here

calibration of water granite interaction with pressure solution in a flow through fracture under confining pressure fluid mineral interaction has an irreversible impact on the fracture permeability evolution in the life span of deep geological reservoirs to investigate the impact a preliminary study on water granite interaction in an undeformable fracture under confining pressure is conducted a 1 d flow and reactive transport model is therefore developed and validated against the experimental data in yasuhara et al appl geochem 26 12 2074 2088 2011 the model takes free face dissolution on pore walls as well as enhanced dissolution at asperity contacts into account together with a nested well equipped geochemical system the simulation is implemented by fem based simulator opengeosys with a plugin module of iphreeqc for speciation calculation after calibration the predictions of effluent element concentrations are in good agreement with the measurements the study indicates the high effluent concentrations arise from enhanced mineral dissolution at asperity contacts pressure solution at anorthite contacts may not take effect under experimental conditions because of the high level energy barrier to interpenetration and al bearing secondary minerals such as gibbsite may be formed in the current near equilibrium aqueous system the sensitivity analysis suggests that contact area ratio is a paramount parameter in determining the surface reactivity and reactive surface area at contacts

a synthesis of approaches for modelling coupled thermal hydraulic mechanical chemical processes in a single novaculite fracture experiment the geological formation immediately surrounding a nuclear waste disposal facility has the potential to undergo a complex set of physical and chemical processes starting from construction and conti

new perspectives on beringian quaternary paleogeography stratigraphy and glacial history abstract aspects of the paleogeography stratigraphy and glacial history of beringia have been greatly revised over the past 15 20 yr access to north east russia in particular has provided the opportunity to evaluate the beringia landscape as a contiguous subcontinent during the quaternary for the first time new research has made clearer the connection between tectonic forces and the submergence of the bering strait during the middle pliocene revisions in the regional stratigraphy of glacial and interglacial deposits in northwest alaska and northeast russia provide a new foundation for assessing the causes for differences in glacial ice extent through time the consensus of all field workers verifies that glacial ice throughout most of beringia was of very limited extent during the last glacial maximum the onset of regional glaciation during the waning stages of the last interglaciation is clearly out of phase with glaciation at lower latitudes despite the lack of much glacial activity during the early holocene alaska contains a rich record of late holocene glacial response to neoglacial cooling changes in the holocene environment of beringia likely had a profound affect on early inhabitants the curiosity driven vision and spirit of both david hopkins and the late troy pewe have had a profound influence on arctic paleoenvironmental research

fault controlled geothermal fluids of the northern trans mexican volcanic belt a geochemical and isotopic study of the los geysers field valley of queretaro mexico abstract this study focuses on the geochemical and isotopic composition of natural spring waters and gases discharging at los geysers thermal area northern trans mexican volcanic belt tmvb and its relations to the regional tectonic framework water is of na hco3 type and samples were collected at temperatures ranging from 48 c to 98 c and ph from 6 8 to 9 3 stable isotope compositions 10 0 to 8 0 for 18o and 75 6 to 69 7 for d deviate from the global and local meteoric lines suggesting fractionation by steam loss the 87sr 86sr values of the thermal waters range from 0 70664 to 0 70698 indicating that most of the strontium comes from the dissolution of carbonate belonging to the late berriasian to early valanginian in the guanajuato conglomerate group and a minor component of less radiogenic sr from paleogene neogene volcano sedimentary and volcanic rocks solute geothermometers reveal a reservoir temperature around 164 c a mixture between air and hydrothermal co2 composes the bubbling gases helium isotopes data r ra 0 96 1 71 and 4he 20ne ratios 0 53 9 41 reveal that helium is dominated by a radiogenic component with a considerable mantle he contribution up to 20 8 since there is no active volcanism at the northern tmvb mantle he is best explained by transport of volatiles along active faults reaching the crust mantle boundary the conceptual hydrogeochemical model involves a thermal aquifer at 1000 m depth which is recharged by regional meteoric water flow a high thermal gradient 153 c km and fast fluid upflow to the surface along discontinuities related to regional horst and graben tectonics

generation of high silica rhyolite a nd sr and o isotopic study of sierra la primavera mexican neovolcanic belt high silica rhyolites of the sierra la primavera a late pleistocene center near guadalajara are extremely sr poor 0 3 1 3 ppm yet with one exception values of 87sr 86sri are relatively low at 0 7041 0 7048 values of 143nd 144nd for all the rhyolites are within errors identical to a basalt at 0 5129 these surprisingly primitive values along with feldspar 18o of 6 6 are consistent with an origin by fractional crystallization of mantle derived basalt however absence of the large volume of associated intermediate rocks that would be expected if the 40 km3 of erupted rhyolite were produced mainly by fractional crystallization suggests alternative processes involving partial melting of mesozoic or tertiary mafic intrusive rocks or lower crustal metamorphic equivalents the latter interpretation is preferred especially in light of comparative data for other north american cenozoic high silica rhyolites isotopic compositions correlate with basement age but generally lie between values for associated basalts and the underlying crust nearly all can be interpreted as containing both a young mantle derived component and a crustal component probably derived by partial melting at intermediate to deep levels of the crust no matter what the proportions of mantle and crust derived material in parental magmas the extremely low concentrations of sr and ba in the high silica rhyolites require extensive fractional crystallization of feldspar rich assemblages after parental liquids attain rhyolitic compositions

age of pre late wisconsin glacial estuarine sedimentation bristol bay alaska pleistocene glacial estuarine sediment deposited in an intertidal environment of northeastern bristol bay southwestern alaska was dated using a variety of approaches including infrared stimulated and thermoluminescence irsl and tl techniques analysis of modern and14c dated holocene tide flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation thereby lending confidence to ages obtained from similar pleistocene deposits by luminescence techniques irsl seems to be especially well suited for dating with resolution on time scales of 10 000 yr the ages of tide flat mud of the nushagak formation derived from the ahklun mountains to the northwest of bristol bay and of halfmoon bay drift derived from the alaska peninsula to the southeast suggest contemporaneous glacial estuarine deposition related to independent glacial source areas about 75 000 80 000 yr ago this age is consistent with other geochronological data that indicate a pre late wisconsin and post substage 5e age including nonfinite14c ages a lack of interglacial indicators and old crow tephra 140 000 yr atop the drift normal paleomagnetic inclinations and amino acid isoleucine epimerization ratios aile ile aile ile ratios inportlandia arctica 0 052 0 003 from a marine lag horizon at south naknek beach which separates halfmoon bay drift above from older glacial estuarine drift below are only slightly higher than inmya truncata 0 041 0 007 from last interglacial pelukian deposits at nome as laboratory heating experiments show that the two genera epimerize at similar rates these data imply correlation of the marine lag at south naknek beach with pelukian deposits hence glaciers on the alaska peninsula experienced major pre late wisconsin advances both before and after the last interglaciation shells reworked into halfmoon bay drift yield aile ile ratios of 0 028 0 005 forportlandiaat second point and 0 027 0 001 forhiatella arcticaat etolin point together with assumptions about the postdepositional temperature history these ratios indicate that the shells are at least 55 000 yr and probably closer to 90 000 yr although the uncertainty in this age estimate is broad the amino acid and luminescence data converge on an age between about 75 000 and 90 000 yr late during oxygen isotope stage 5 for a major ice advance far beyond late wisconsin limits

strontium isotopic composition of pliocene and pleistocene molluscs from emerged marine deposits north american arctic high precision strontium sr isotopic measurements were obtained for 53 pliocene and pleistocene molluscan shells from emerged marine deposits around the coasts of arctic north america to test whether such data can be used for chronostratigraphic purposes 87sr 86sr ratios from sr isotopic measurements on many marine fossils from arctic ocean borderland sites are broadly consistent with their expected values based on independent age control and on a comparison with the sr isotopic evolution of seawater recorded in deep sea cores all 87sr 86sr ratios measured for shells from middle and late pleistocene deposits are consistent with expected values but only 9 of 22 ratios in shells from older deposits are consistent with independent age estimates aberrant 87sr 86sr ratios are consistently higher than expected at nome alaska and baffin island canada all 87sr 86sr ratios are higher than expected because these shells were formed along the pacific ocean and atlantic ocean margins respectively their h

partition coefficients for rare earth elements in mafic minerals of high silica rhyolites the importance of accessory mineral inclusions abstract ree concentrations of mafic mineral separates from high silica rhyolites measured by inaa are high and variable compared to electron microprobe analyses of the minerals themselves the mafic phases commonly contain inclusions or have adhering grains of accessory rare earth element ree rich minerals optical and electron microscopic observation revealed discrete grains of chevkinite rare earth titano silicate included within clinopyroxenes from the sierra la primavera mexico rhyolite and monazite grains adhering to ortho and clinopyroxenes from the bishop tuff california during hand picking of mineral separates inclusions are only partly removed as a result the magnitude and variability of true mineral melt partition coefficients for light ree have been overestimated the true ree partition coefficients of la primavera and bishop tuff pyroxenes obtained by microprobe are only slightly higher than they are in lower silica rhyolites and are not as variable as previously thought the partitioning slope is positive as in less silicic systems the relative partitioning behavior of ree in high silica rhyolites is dominated by crystal chemical controls and not by liquid structural effects when a partition coefficient is used for crystallization calculations adhering phases and inclusions should be retained or the minor phases must be accounted for separately alternatively a bulk distribution coefficient can be calculated using whole rock and glass compositions and the glass mode

pre late wisconsin glacial history coastal ahklun mountains southwestern alaska new amino acid thermoluminescence and 40ar 39ar results abstract new stratigraphic and geochronologic data from the togiak bay area of southwestern alaska indicate that glaciers advanced from the southern ahklun mountains at least three and as many as six times prior to the late wisconsin the oldest glaciations are represented by glacial marine sediment in coastal exposures on hagemeister island the extent of amino acid isoleucine epimerization in fossil molluscs indicates that at least one and possibly four older middle pleistocene glacial intervals are represented with age estimates spanning 500 280 ka and averaging 400 100 ka the youngest glacial marine drift on hagemeister island may correlate with the eruption of the togiak tuya a new 40 ar 39 ar age on basalt that overlies pillow lava indicates that the volcano erupted through glacial ice at least 300 m thick 263 22 ka the youngest drift in the region overlies the old crow tephra 140 10 ka and a 70 10 ka basaltic lava flow dated by thermoluminescence analysis of underlying baked sediment the drift delimits flat piedmont lobes that spread out onto the continental shelf and terminated 100 km from their source areas during the early wisconsin sensu lato the glacial geologic evidence suggests that major expansions of glaciers were out of phase with global ice volume

aminostratigraphy of pliocene pleistocene high sea level deposits nome coastal plain and adjacent nearshore area alaska amino acid epimerization ratios aile ile measured in 295 fossil molluscan shells of 3 genera provide a basis to evaluate the number and relative timing of high sea level events represented by deposits blanketing the nome coastal plain and adjacent nearshore area northwestern alaska frequency distribution analysis along with a new approach that relies on the ranked data distribution was used to identify clusters aminozones in the aile ile data each of which presumably represents a discrete period of marine inundation of the study area six periods of high relative sea level were distinguished some are recognized only by redeposited shells rather than in situ bio or lithostratigraphic units the oldest period is represented by shells recovered from the deepest sections of two offshore boreholes aile ile ratios in these shells 1 0 are much higher than in any found onshore and probably date to the late miocene early pliocene the oldest aminozone lies below nonfossiliferous sediments which in turn are overlain by glacigenic and marine deposits containing largely fragmented shells with aile ile ratios ranging from 0 35 to 0 65 this range coincides with aile ile ratios from various onshore deposits previously ascribed to the middle pliocene 3 m y beringian transgression ratios in this range can be subdivided into three evenly spaced aminozones each of which may represent multiple short duration 10 4 yr high sea stands separated by a longer period 10 5 yr sea level oscillation on the basis of a new empirical model of parabolic epimerization kinetics and an assumed age of 3 2 m y for the oldest beringian aminozone the approximate age of the initial submergence of bering strait the estimated length of time represented by the three beringian aminozones is between 0 5 and 1 7 m y the youngest beringian highstand was followed in the late pliocene or early pleistocene by a lengthy period of nonmarine deposition during which local valley glaciers advanced onto the coastal plain at least once relative sea level apparently did not again surpass that of today until the middle pleistocene anvilian transgression the oldest higher than present stand of the pleistocene yet considerably younger than previously thought glaciers overran the nome coastal plain at least once following the anvilian transgression incorporating abundant shells into their drift the drift is notched by a shoreline formed during the pelukian transgression of the last interglaciation although well represented onshore no pelukian deposits have been found offshore

new capillary number definition for displacement of residual nonwetting phase in natural fractures we propose a new capillary number for flow in fractures starting with a force balance on a trapped ganglion in a fracture the new definition is validated with laboratory experiments using five distinctive model fractures capillary desaturation curves were generated experimentally using water air forced imbibition the residual saturation capillary number relationship obtained from different fractures which vary in aperture and roughness can be represented approximately by a single curve in terms of the new definition of the capillary number they do not fit a single trend using the conventional definition of the capillary number

amino acid chronology of the lower pleistocene deposits of venta micena orce granada andalusia spain abstract this paper deals with a model adjustment for the estimation of age by means of amino acid racemization analysis two model families were obtained on the basis of the different genera of molluscs analysed and were applied to a palaeontological site located in the cullar baza basin venta micena orce granada the analytical results obtained from the study of fossil gastropods have provided a very coherent average dating of 983 58 ky this coinciding to a large extent with the most widespread palaeontological geological and stratigraphical datings for the site there is however no agreement with certain recent theories that situate venta micena chronologically at the pliocene pleistocene boundary ca 1 6 my or before the validity of the dating fit was tested on the basis of another classical palaeontological site cullar baza where a coherent dating of 441 27 ky was obtained

do major oxide tectonic discrimination diagrams work evaluating new log ratio and discriminant analysis based diagrams with indian ocean mafic volcanics and asian ophiolites many geochemical diagrams exist that classify old volcanic terranes of ambiguous provenance into various modern plate tectonic settings with variable success recently proposed diagrams based on log ratios and linear discriminant analysis with large datasets of major oxides were tested here with data for ocean island arc and mid ocean ridge lavas from the indian ocean success rates are 45 100 with misclassifications potentially caused by alteration although alteration demonstrably need not cause misclassification the diagrams were further applied to some asian ophiolites representing tethyan and indian ocean crusts to see if the diagrams confirm their tectonic setting inferred from trace and isotopic data lower success rates 30 60 but 75 100 for specific suites are not surprising in view of the ubiquitous and complex alteration in ophiolites log ratio transformation and linear discriminant analysis appear to be powerful methods when discrimination diagrams are based on major oxide data alone

compaction creep of quartz sand at 400 600 c experimental evidence for dissolution controlled pressure solution intergranular pressure solution ips is an important compaction and deformation mechanism in quartzose rocks but the kinetics and rate controlling process remain unclear the aim of the present study is to test microphysical models for compaction creep by ips against isostatic hot pressing experiments performed on quartz sand under conditions expected to favor pressure solution confining pressure 300 mpa pore water pressure 150 250 mpa temperature 400 600 c microstructural observations revealed widespread intergranular indentation features and confirmed that intergranular pressure solution was indeed the dominant deformation mechanism under the chosen conditions for porosities down to 15 the mechanical data agree satisfactorily with a microphysical model incorporating a previously determined kinetic law for dissolution of loose granular quartz suggesting that the rate limiting mechanism of ips was dissolution the model also predicts ips rates within one order of magnitude of those measured in previous experiments at 150 350 c and thus seem robust enough to model sandstone compaction in nature such applications may not be straightforward however as the present evidence for dissolution control implies that the compositional variability of natural pore fluids may strongly influence ips rates in sandstones

enhanced age resolution of the marine quaternary record in the arctic using aspartic acid racemization dating of bivalve shells abstract aspartic acid asp racemization occurs at a significantly higher rate than isoleucine epimerization and consequently provides better temporal resolution of arctic marine deposits from alaska spitsbergen and baffin island heating experiments at 100 c on the bivalvesmyaandhiatellashow the asp racemization rate decreases with increasing d l values as is typical for biogenic carbonates based on these experimental racemization rates and rates determined from racemization of samples radiocarbon dated to ca 10 000 12 000 yr b p activation energies formyaandhiatellaare estimated to be 30 6 and 30 0 kcal mol respectively for asp racemization and 29 0 and 29 5 for isoleucine epimerization analysis of a time series of plio pleistocenehiatellafrom the north coast of alaska shows that last interglacial mollusks can be readily distinguished from modern samples by asp but not by isoleucine d l asp values indicate a younger age for the fishcreekian transgression than does isoleucine epimerization for spitsbergen d l asp shows a slight age difference ca 12 000 yr between two units of the episode b interstadial and suggests that the age of these units may be closer to 65 000 than to 80 000 yr b p two possible ages suggested by other evidence the age of the loks land interstadial on baffin island is likely to be greater than that indicated by radiocarbon ages within deposits from each region d l asp values are less variable among individual shells than isoleucine epimerization values this may indicate better reliability of asp for geochronology

adakitic like magmatism in western ossa morena zone portugal geochemical and isotopic constraints of the pavia pluton abstract granitic rocks are a major component of the earth s continental crust and occur in a wide variety of tectonic settings their chemical and isotopic characterization is crucial to the recognition of the potential sources and mechanisms involved in their generation in this study we present the first whole rock chemical and isotopic sr nd o data for the pavia pluton 328 317 ma located near the western border of the ossa morena zone evora massif portugal major and trace element geochemistry suggests that the different granitic phases composing this intrusive body enclaves granites s l and crosscutting dikes represent independent magma pulses and the majority is similar to ttgs and adakites the little sr nd o isotopic variation with 87 sr 86 sr 328 0 70428 0 70560 end 328 ranging between 3 4 and 0 4 and 18 o varying from 5 6 to 8 4 implies an isotopically similar protolith for all phases the most viable mechanism for the generation of the pavia pluton adakitic like magmatism is assimilation fractional crystallization of a mantle derived magma this mechanism was also invoked to explain the genesis of other plutons within the evora massif but they have a distinct chemistry typical arc calc alkaline rocks the chemical differences between them and the pavia pluton granitic rocks are interpreted as the result of lower degrees of crustal assimilation and higher degrees of contamination of mantle derived magmas by the sinking slab after subduction blocking and subsequent slab break off

amino acid composition as a taxonomic tool for molluscan fossils an example from pliocene pleistocene arctic marine deposits abstract amino acid compositions of more than 550 individuals of three common subarctic arctic molluscan genera hiatella mya and astarte were measured to determine the feasibility of using such data to classify unidentifiable shell fragments belonging to one of these genera to account for diagenetically induced variation in amino acid composition of the fossils equations were developed to reconstruct the original composition of each shell based on its extent of amino acid epimerization the classification procedure involved calculating the multivariate similarity coefficient of similarity cs between the adjusted amino acid composition of an unknown shell and that of a set of references css were calculated for an additional 141 identifiable shells of the three common genera to evaluate the performance of the classification method the procedure correctly classified 93 of the shells in addition css were calculated for 162 identifiable shells of five other common subarctic arctic genera portlandia spisula macoma cardita and arctica to test the ability of the method to discriminate shells belonging to genera not included in the reference set and are therefore necessarily misclassified overall css for correctly classified shells x 0 891 are higher than for misclassified shells x 0 809 and the ratio of correctly to incorrectly classified individuals increases with increasing cs based on these empirical tests only those classifications supported by css greater than 0 88 were considered reliable and of these approximately 6 may be misclassified the classification procedure was applied to sixty four unidentifiable molluscan shell fragments recovered from boreholes drilled onshore of nome alaska of which twenty six were classified as hiatella mya or astarte with a cs greater than 0 88

evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions an experimental study we performed flow through laboratory experiments on five cylindrically cored samples of ultramafic rocks in which we generated a well mated through going tensile fracture to investigate evolution of fracture permeability during serpentinization the samples were tested in a triaxial loading machine at a confining pressure of 50 mpa pore pressure of 20 mpa and temperature of 260 c simulating a depth of 2 km under hydrostatic conditions a pore pressure difference of up to 2 mpa was imposed across the ends of the sample fracture permeability decreased by 1 2 orders of magnitude during the 200 330 h experiments electron microprobe and sem data indicated the formation of needle shaped crystals of serpentine composition along the walls of the fracture and chemical analyses of sampled pore fluids were consistent with dissolution of ferro magnesian minerals by comparing the difference between fracture permeability and matrix permeability measured on intact samples of the same rock types we concluded that the contribution of the low matrix permeability to flow is negligible and essentially all of the flow is focused in the tensile fracture the experimental results suggest that the fracture network in long lived hydrothermal circulation systems can be sealed rapidly as a result of mineral precipitation and generation of new permeability resulting from a combination of tectonic and crystallization induced stresses is required to maintain fluid circulation

pervasive pressure solution transfer in a quartz sand the kinetics of deformation of a quartz aggregate by pervasive pressure solution can be under certain conditions of temperature and grain size strongly dependent upon the diffusivity of silica into the grain to grain contacts an analysis of the factors affecting this key parameter and less well constrained in the analysis of the problem of rock deformation by pressure solution is presented this analysis is based on recent advances on studying silica surfaces and particularly on the existence of a silica gel layer on the silica surfaces undergoing dissolution by reinvestigating the electroviscous effect occurring at the grain to grain contact the present analysis shows that the diffusivity of silica at the grain to grain contacts is likely to be relatively similar to that in the bulk pore water maybe 1 order of magnitude smaller but not more this contradicts the previous work by rutter 1976 which has been the key reference used in many subsequent papers to justify an extremely low value for the diffusivity of silica at the grain to grain contacts 5 orders of magnitude smaller than the diffusivity of silica in free water this finding has dramatic implications concerning the deformation rate of quartz sands and sandstones by pressure solution in sedimentary basins with regard to 1 the limiting step affecting the kinetics of the process diffusion of the solute or dissolution precipitation chemistry and 2 the existence of a thermodynamic equilibrium state when deformation by pressure solution occurs over geological timescales a poroviscoplastic model is used to describe deformation associated with pervasive pressure solution transfer in quartz sands this model is shown to be consistent with the current state of knowledge of the surface chemistry of silica in addition the comparison between this model and both laboratory and field data is rather good

a rheologic model for wet crust applied to strike slip faults the strength and stability of crustal faults are not adequately addressed by the widely used two mechanism rheologic models of the crust based on byerlee s law and power law creep the models neglect the fluid assisted mechanisms of deformation that are important to strength of the crust and do not describe the variation in rate dependence of friction that governs the stability of fault slip several distinct mechanisms of frictional slip are defined on the basis of variations in frictional behavior and microfabric of simulated fault gouge in laboratory experiments state variable constitutive relations are used in a multiple mechanism formulation to describe the rate and temperature dependence of three friction mechanisms in wet quartz gouge at elevated temperatures this multimechanism description of friction is substituted for byerlee s law in the two mechanism models to generate a multimechanism rheologic model for the crust the multimechanism model is used to predict the rate and temperature dependence of crustal strength and the slip rate and depth temperature conditions over which each mechanism dominates application of the model to strike slip faults in the crust illustrates that the thickness of the actively shearing zone within faults is a critical parameter governing fault strength and stability the model predicts that frictional strength at midcrustal depths is significantly reduced relative to byerlee s law only for thick fault zones the reduction in strength is due to the operation of a strain rate sensitive friction mechanism involving combined cataclasis and solution transfer the rheologic model predicts that only very thin faults display the rate dependent characteristics necessary for initiation of seismic slip to any significant depth in the crust