ca sr and 87sr 86sr geochemistry of disseminated calcite in himalayan silicate rocks from nanga parbat influence on river water chemistry trace amounts of disseminated calcite were identified in gneiss schist and granite bedrock sampled from the raikhot watershed and other locations within the nanga parbat massif of northern pakistan the calcite grains occur interstitially within individual silicate minerals at grain boundaries and as fracture fillings that transect the mineralogic fabric of the rock disseminated calcite composes is 0 29 wt of silicate rocks sampled in the raikhot watershed and has ca sr mol nmol and 87sr 86sr ratios that range from 0 878 to 5 33 and from 0 794 039 to 0 930 619 respectively elsewhere in the nanga parbat region disseminated calcite composes 3 6 wt of the silicate rock samples and has ca sr mol nmol and 87sr 86sr ratios that range from 0 535 to 3 33 and from 0 715 757 to 0 771 244 respectively for all samples the 87sr 86sr ratios of disseminated calcite are similar to the 87sr 86sr ratios measured in the silicate host rock within the partially glaciated raikhot watershed the rapid weathering of disseminated calcite with high ca sr and 87sr 86sr ratios has a strong influence on the chemical composition of stream water and exceeds contributions from silicate mineral dissolution comparisons of disseminated calcite compositions with source water chemistry throughout the himalaya suggest that disseminated calcite may be a more important component of himalayan silicate rocks than previously recognized therefore calculations relating the sr isotope geochemistry of himalayan rivers to atmospheric co2 consumption should consider this widespread and compositionally variable carbonate end member

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

silicate weathering rates decoupled from the 87sr 86sr ratio of the dissolved load during himalayan erosion this study establishes that carbonate weathering dominates the supply of sr with elevated 87sr 86sr ratios in the bhote kosi sun kosi river system central nepal a major himalayan tributary to the ganges the dissolved load of the bhote kosi sun kosi displays a rapid increase in the 87sr 86sr ratio in its lower section downstream of the main central thrust a feature common to other himalayan tributaries of the ganges mass balance analysis of the contributing sources to the dissolved load identifies the weathering of palaeoproterozoic impure carbonates comprised largely of dolomite and mica from the lesser himalaya as the most significant lithological control upon elevated 87sr 86sr ratios in situ laser ablation analysis of the dolomite component yields 87sr 86sr ratios of 0 93 to 1 11 indistinguishable from bulk rock this confirms the presence of a highly soluble source of radiogenic strontium and suggests that diffusive exchange during a protracted metamorphic history has homogenised sr isotopes between silicate and carbonate phases within the assemblage weathering of the carbonate component of such rocks has yielded unusually high 87sr 86sr at significant sr fluxes in the dissolved load approximately 60 of the impact of the bhote kosi sun kosi on the marine 87sr 86sr ratio can be traced to weathering of this carbonate since similar lithologies outcrop within the catchments of most himalayan tributaries that feed the ganges and brahmaputra rivers the presence of such radiogenic carbonates undermines the inference that the impact of these rivers on sr isotopes in seawater is indicative of high silicate weathering rates that result from the uplift of tibet and the himalaya

strontium hydrothermal systems and steady state chemical weathering in active mountain belts abstract hydrothermal systems are a common feature of active collisional orogens these systems can have a profound effect on the sr fluxes and sr isotopic composition of riverine waters through the direct input of sr from hot springs and groundwaters and the chemical weathering of hydrothermal calcite in an effort to quantify the role of calcite weathering we present an analytical model that examines the relationship between rock uplift and steady state chemical weathering of granites and greywackes that contain trace amounts we compare model results with sr fluxes and isotopic composition of riverine waters from the southern alps of new zealand an area that is frequently used as an example of a steady state collisional orogen as our model predicts roughly 50 of sr flux is from the weathering of calcite in the areas of highest uplift along the west flank of the southern alps this proportion decreases substantially

authigenic potassium feldspar in cambrian carbonates evidence of alleghanian brine migration the shallow water limestones and dolostones of the conococheague limestone upper cambrian of western maryland contain large amounts of authigenic potassium feldspar the presence of halite daughter crystals in breached fluid inclusions low whole rock ratios of chlorine to bromine and thermochemical data suggest that the potassium feldspar formed at low temperature by the reaction of connate brines with intercalated siliciclastic debris analyses of argon age spectra indicate that the authigenic feldspar probably formed during late pennsylvanian to early permian time these results may indicate mobilization and migration of connate brines brought about by alleghanian folding the widespread occurrence of authigenic potassium feldspar in cambrian and ordovician carbonate rocks throughout the appalachians suggests that this may have occurred throughout the entire basin

variations in exhumation level and uplift rate along the obliqu slip alpine fault central southern alps new zealand we use geophysical and geological data from the southern alps to explore the relationship between plate motions and crustal structure on the geomorphology exhumation state and deformation style of rocks uplifted along amajor oblique slip fault a 50 km long segment of the southern alps has a higher uplift rate more relief deeper exhumation and a narrower width than surrounding regions there the delaminated east tilted crust of the pacific plate yields the youngest late cenozoic thermochronometric ages contours for fission track ar ar and k ar ages on several different minerals define an asymmetrically nested pattern of ages that increase away from the western side of the central southern alps eleven new 4 0 ar 3 9 ar samples of hornblende from the hanging wall of the alpine fault indicate that lower crustal rocks exhumed from 500 c in the late cenozoic are confined to a 20 km long culmination at the southern end of the central southern alps ages as low as 3 5 ma imply time integrated vertical exhumation rates as high as 6 9 mm yr this is the only part of this 5 8 ma range that may have achieved exhumational steady state remnant plugs of the original crustal hanging wall ramp are apparently preserved outside the central alps implying 70 km of fault convergence there 4 0 ar 3 9 ar age trends for hornblende near the alpine fault suggest that horizontal surfaces in the lower crust in the pacific plate have been overturned by reverse slip ductile shearing across a zone of distributed deformation that extends 2 km beyond the 1 km thick basal mylonite zone at the broadest orogen scale higher uplift rates throughout the central southern alps may be related to a rheologically controlled increase in the convergent velocity of points to the east of the alpine fault associated with a strengthening of the pacific crust at a more local scale maximum rates of uplift are inferred to occur near franz josef and fox glaciers because the alpine fault steepens at depth structural data suggests that its footwall ramp is curved and that the fault s dip steepens by 15 20 relative to its attitude farther to the south this 10 20 km long restraining bend may enhance local rates of rock uplift near franz josef and fox glaciers contemporary normal stress and shear resistance may also be increased on this part of the alpine fault helping to explain the central region s quiet historic seismicity and apparently strongly locked nature

chemical weathering in high sediment yielding watersheds new zealand 1 we have determined the chemical erosion yields for fifteen watersheds in new zealand ranging in size from 12 2 to 2928 km2 these rates coupled with previously measured physical erosion yields allow us to compare these two modes of landscape denudation the physical erosion yields are some of the highest measured in the world although in most instances the chemical erosion yields are only a small fraction of the total erosion yields the absolute values are very high our data strongly support the notion that chemical erosion rates are greatly influenced by the yield of physical erosion and that the rapid production of fresh surfaces as a result of high physical erosion rates and subsequent denudation is critical to the high chemical erosion yields observed

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

regional patterns of magnetite authigenesis in the appalachian basin implications for the mechanism of late paleozoic remagnetization we report paleomagnetic and rock magnetic data from sedimentary carbonates of the appalachian basin that have implications for the mechanism of widespread late paleozoic remagnetization in this rock type sampling was accomplished mostly along two across basin transects one in devonian carbonates of new york state and the other in ordovician and mississippian carbonates of tennessee and alabama paleomagnetic investigations of the new york devonian carbonates along a transect from albany to buffalo indicate that these rocks were completely remagnetized in alleghenian time rock magnetic studies show that magnetite concentration varies in a regular fashion along the transect with a local maximum near syracuse and decreasing gradually to the east and west this pattern shows a striking correlation with the degree of diagenetic alteration of clay minerals in a devonian bentonite horizon which took place during alleghenian time we conclude that most of the magnetite present in these carbonates is of authigenic origin and that clay mineral alteration and magnetite authigenesis were coeval late paleozoic events that were controlled by the same diagenetic factors thermoviscous remagnetization processes cannot be ruled out in this setting in light of the observed degree of thermal maturity however our results suggest that chemical factors played a critical role in remagnetization since they allow us to infer that magnetite authigenesis and remagnetization are about the same age we propose a geochemical model for magnetite authigenesis wherein the iron is derived from detrital smectites during diagenetic illitization which is triggered by the introduction of potassium rich brines results from the tennessee transect from nashville to chattanooga show a very different pattern paleomagnetic studies indicate that late paleozoic remagnetization has affected ordovician carbonates of the nashville dome paleozoic carbonates in the overthrust belt near chattanooga also carry the late paleozoic remagnetization however mississippian carbonates between the dome and the overthrust belt are very weakly magnetized and show no evidence for late paleozoic remagnetization samples show only a present field magnetization or at one locality in northwestern alabama a dual polarity magnetization of probable mississippian age rock magnetic studies indicate that higher concentrations of magnetite are present in the remagnetized rocks of the nashville dome and the overthrust belt than in the nonremagnetized mississippian carbonates we therefore conclude that magnetite authigenesis and remagnetization are related events in this setting and that the remagnetization must be due to chemical processes the presence of a remagnetization shadow in the younger rocks now exposed between the fold thrust belt and the flexural arch is attributed to westward flow of magnetite forming aqueous fluids through deep sub carboniferous aquifers during alleghenian time upward migration of the fluids through the mississippian carbonates may have been prevented by the devono mississippian chattanooga shale an impermeable stratum that is present throughout the region

fission track analysis of the late cenozoic vertical kinematics of continental pacific crust south island new zealand during the late cenozoic the pacific plate has been converging obliquely with the australia plate in south island new zealand a result of this convergence has been the growth of a major mountain range the southern alps at the leading edge of the pacific plate the results of fission track analysis of 140 samples from 13 transects across the alps reported here establish the late cenozoic vertical kinematics amount age and rate of rock uplift of the pacific crust underlying the alps the late cenozoic rock uplift of the pacific crust is asymmetrical with respect to the alpine fault being a maximum 19 km immediately east of the central part of the fault with lesser values at the eastern 3 km northern 10 km and southern 8 km extremities of the alps the age of the start of rock uplift varies spatially across the southern alps the earliest indications from fission track analysis being at 8 ma at the southern end of the alps decreasing to 5 ma at the northern end and 3 ma along the southeastern margin this age variation reflects the longer time over which the southern parts of the alps have been in collision the rate of propagation of rock uplift southeastward into the pacific plate has been 30 mm yr nearly 4 times the late cenozoic average rate of convergence normal to the plate boundary late cenozoic mean rock uplift rates range from a maximum of 2 8 mm yr at the alpine fault to a minimum of 1 0 mm yr in the east and have been sustained for periods of 3 8 m y accompanying denudation has exhumed amphibolite grade rocks immediately east of the alpine fault the rock uplift has been controlled by oblique slip displacement on the alpine fault a continental crustal section at least 19 km thick has been uplifted on the alpine fault comparison of the late cenozoic mean rock uplift rates with uplift rates derived from reset zircon data 2 10 mm yr near the alpine fault shows that uplift has accelerated over time but only significantly since 1 3 0 3 ma the amount of mesozoic uplift ranged from minimal amounts north of arthur s pass to 3 km near mount cook to 10 km in the south at lake wanaka

geochemical and isotopic constraints on the diagenetic history of a massive stratal late cambrian royer dolomite lower arbuckle group slick hills sw oklahoma usa abstract the diagenetic history of the late cambrian massive royer dolomite from the lower arbuckle group slick hills sw oklahoma usa has been evaluated through comprehensive geochemical analyses the dolomite probably formed during early diagenesis from contemporaneous late cambrian seawater evidenced by similar 87 sr 86 sr ratios from 0 70891 to 0 70913 of most 70 dolomite samples to coeval late cambrian seawater from 0 7089 to 0 7092 very light 18o values 10 2 to 12 9 pdb however indicate that the dolomite was significantly modified during burial correlation of various geochemical parameters sr fe 18o and 87 sr 86 sr demonstrates that dolomite samples with increased modification are characterized by lower sr and higher fe concentrations lighter 18o values and less radiogenic 87 sr 86 sr ratios this correlation coupled with the light 18o values of the dolomite demonstrates that meteoric water recharged into overlying carbonates was responsible for burial modification of the dolomite geochemical comparison of the dolomite with associated limestone and quantitative modelling of 18o sr and 87 sr 86 sr variation during water rock interaction suggest that the dolomite underwent long lasting modification the timing of meteoric modification was coincident with the development of regional overlying unconformities corresponding to emergence of the carbonate platform similar diagenetic modification has probably been responsible for 18o depletion and trace element modification of ancient dolomites in many other areas although many of these dolomites have been interpreted to have formed either in mixing zone environments or in subsurface environments

chemical weathering of a marine terrace chronosequence santa cruz california i interpreting rates and controls based on soil concentration depth profiles abstract the spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal california are interpreted in terms of chemical weathering rates and processes in regoliths up to 15 m deep and 226 kyrs old quartz normalized mass transfer coefficients indicate non stoichiometric preferential release of sr ca na from plagioclase along with lesser amounts of k rb and ba derived from k feldspar smectite weathering results in the loss of mg and concurrent incorporation of al and fe into secondary kaolinite and fe oxides in shallow argillic horizons elemental losses from weathering of the santa cruz terraces fall within the range of those for other marine terraces along the pacific coast of north america residual amounts of plagioclase and k feldspar decrease with terrace depth and increasing age the gradient of the weathering profile bs is defined by the ratio of the weathering rate r to the velocity at which the profile penetrates into the protolith a spreadsheet calculator further refines profile geometries demonstrating that the non linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface to volume ratios and at high residual feldspar concentrations at greater depth by the approach to thermodynamic saturation these parameters are of secondary importance to the fluid flux qh which in thermodynamically saturated pore water controls the weathering velocity and mineral losses from the profiles long term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute cl balances qh 0 025 0 17 m yr 1 during saturation controlled and solute limited weathering the greater loss of plagioclase relative to k feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective reaction kinetics the steady state weathering rate under such conditions is defined as r q h m sol m total 1 s v b s the product of qh and the ratio of solubilized to solid state feldspar msat mtotal define the weathering velocity the weathering gradient bs reflects the kinetic rate of reaction where sv is the volumetric surface area of the residual feldspar both this rate expression and the spreadsheet calculations produce similar plagioclase weathering rates r 5 14 10 16 mol m 2 s 1 which agree with those reported for other environments of comparable climate and age weathering dependent concentration profiles are commonly described in literature the present paper provides methods by which these data can yield a more fundamental understanding of the weathering processes involved

evolution of carbon cycle over the past 100 million years it is generally accepted that progressive cooling of global climate since the late cretaceous results from decreasing partial pressure of atmospheric co2 pco2 however details on how and why the carbon cycle evolved and how it would affect pco2 have not been fully resolved while the long term decline of pco2 might be caused by the decrease of volcanic degassing through the negative feedback between pco2 and silicate weathering seafloor spreading the major control of co2 degassing seems to have remained relatively constant alternative explanation known as uplift driven climate change hypothesis proposes that tectonic uplift may have enhanced the sink of atmospheric co2 by silicate weathering and thus produced the decline of pco2 however increasing weathering sink of co2 could deplete atmosphere all of its co2 within several million years while holding volcanic outgassing constant in this work major fluxes of long term carbon cycle are calculated based on a reverse model constrained by marine c sr and os isotopic records and the spreading rate of sea floor weathering of island basalt and continental silicate rocks are separated in the new model the results indicate a long term decline of island basalt weathering in consistent with the global cooling trend over the past 100 million years dramatic changes of the co2 fluxes associated continental silicate weathering reverse weathering volcanic degassing and the growth of organic carbon reservoir have been observed disturbance of atmospheric co2 cycle by these fluxes seems to be maintained by the concomitant adjustments of island basalt weathering that were sensitive to the pco2 controlled environment factors such as temperature and runoff the negative feedbacks between pco2 and weathering of island basalt might have played a significant role in stabilizing the long term carbon cycle

sediment generation and delivery from large historic landslides in the southern alps new zealand abstract there is much variability of sediment yield in mountain river systems because it is influenced by both periodic e g snowmelt monsoonal circulation and episodic high intensity rainstorms earthquakes controls in the southern alps of new zealand landslides are dominant mechanisms of conveying large amounts of debris to river channels this paper attempts to quantify catastrophic modes of sediment delivery by presenting three recent examples of large landslides on the western slopes of the southern alps a combination of ground surveys dem based volume calculations and air photo interpretation attributes immediate postfailure sediment yields in excess of 70 000 t km 2 a 1 in the short term such landslide derived sediment pulses pose significant hazards to downstream settlements and infrastructure on alluvial fans where they cause massive aggradation increased flooding frequency and large scale channel avulsion in addition to intramontane valley floor obliteration or channel metamorphosis these geomorphic impacts may thus occur far beyond the initial locations of slope failure these catastrophic off site effects involve apparent net sediment delivery rates in the order of 10 5 10 6 m 3 a 1 the accurate quantification of the relative contribution of debris from the disturbing landslide to overall sediment flux is extremely difficult nonetheless are quantitative estimates of landslide derived sediment production and delivery important data to develop a more comprehensive understanding of the variability in alpine sediment flux such data are essential not only for use in hydraulic engineering or catchment management but also in gauging potential future impacts from rainstorm and earthquake induced landsliding in the southern alps

replacement of pyrite framboids by magnetite in limestone and implications for palaeomagnetism limestones are an important source of palaeomagnetic data with magnetite the dominant carrier of the magnetization because the magnetite is present in low concentrations however it has been directly observed only rarely and in trace amounts in acid treated separates such residues are composed primarily of spheres the ultimate origin of which has been enigmatic7 yet interpretation of the palaeomagnetic data depends on a knowledge of the origin of the magnetite which has been inferred to carry either a chemical or a viscous remanent magnetization here we present electron microscope data obtained from a sequence of samples of onondaga limestone from an east west traverse across northern new york which unambiguously show that magnetite spheres are derived by alteration and replacement of framboidal pyrite remagnetization is thus caused by chemical rather than viscous processes this chemical remanent magnetization is compatible with a fluid mediated event occurring on a regional scale induced by tectonic stress of alleghenian late palaeozoic age

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

determining mineral weathering rates based on solid and solute weathering gradients and velocities application to biotite weathering in saprolites abstract chemical weathering gradients are defined by the changes in the measured elemental concentrations in solids and pore waters with depth in soils and regoliths an increase in the mineral weathering rate increases the change in these concentrations with depth while increases in the weathering velocity decrease the change the solid state weathering velocity is the rate at which the weathering front propagates through the regolith and the solute weathering velocity is equivalent to the rate of pore water infiltration these relationships provide a unifying approach to calculating both solid and solute weathering rates from the respective ratios of the weathering velocities and gradients contemporary weathering rates based on solute residence times can be directly compared to long term past weathering based on changes in regolith composition both rates incorporate identical parameters describing mineral abundance stoichiometry and surface area weathering gradients were used to calculate biotite weathering rates in saprolitic regoliths in the piedmont of northern georgia usa and in luquillo mountains of puerto rico solid state weathering gradients for mg and k at panola produced reaction rates of 3 to 6 10 17 mol m 2 s 1 for biotite faster weathering rates of 1 8 to 3 6 10 16 mol m 2 s 1 are calculated based on mg and k pore water gradients in the rio icacos regolith the relative rates are in agreement with a warmer and wetter tropical climate in puerto rico both natural rates are three to six orders of magnitude slower than reported experimental rates of biotite weathering

calcium and magnesium isotope systematics in rivers draining the himalaya tibetan plateau region lithological or fractionation control abstract in rivers draining the himalaya tibetan plateau region the 26mg 24mg ratio has a range of 2 and the 44ca 42ca ratio has a range of 0 6 the average 26 mg values of tributaries from each of the main lithotectonic units tethyan sedimentary series tss high himalayan crystalline series hhcs and lesser himalayan series lhs are within 2 standard deviation analytical uncertainty 0 14 the consistency of average riverine 26 mg values is in contrast to the main rock types limestone dolostone and silicate which range in their average 26 mg values by more than 2 tributaries draining the dolostones of the lhs differ in their 44 42 ca values compared to tributaries from the tss and hhcs the chemistry of these river waters is strongly influenced by dolostone solute mg ca close to unity and both 26 mg 1 31 and 44 42 ca 0 64 values are within analytical uncertainty of the lhs dolostone these are the most elevated 44 42 ca values in rivers and rock reported so far demonstrating that both riverine and bedrock 44 42 ca values may show greater variability than previously thought although rivers draining tss limestone have the lowest 26 mg and 44 42 ca values at 1 41 and 0 42 respectively both are offset to higher values compared to bedrock tss limestone the average 26 mg value of rivers draining mainly silicate rock of the hhcs is 1 25 lower by 0 63 than the average silicate rock these differences are consistent with a fractionation of 26 mg values during silicate weathering given that the proportion of mg exported from the himalaya as solute mg is small the difference in 26mg 24mg ratios between silicate rock and solute mg reflects the 26mg 24mg isotopic fractionation factor silicate dissolved mg between silicate and dissolved mg during incongruent silicate weathering the value of silicate dissolved mg of 0 99937 implies that in the tss solute mg is primarily derived from silicate weathering whereas the source of ca is overwhelmingly derived from carbonate weathering the average 44 42 ca value in hhcs rivers is within uncertainty of silicate rock at 0 39 the widespread hot springs of the high himalaya have an average 26 mg value of 0 46 and an average 44 42 ca value of 0 5 distinct from riverine values for 26 mg but similar to riverine 44 42 ca values although rivers draining each major rock type have 44 42 ca and 26 mg values in part inherited from bedrock there is no correlation with proxies for carbonate or silicate lithology such as na ca ratios suggesting that ca and mg are in part recycled however in spite of the vast contrast in vegetation density between the arid tibetan plateau and the tropical lesser himalaya the isotopic fractionation factor for ca and mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of ca and mg in these catchments the discrepancy between solute and solid ca and mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of ca and mg bound as minerals in rock and released as cations in rivers the fractionation of ca and mg isotope ratios may prove useful for tracing mechanisms of chemical alteration ca isotope ratios of solute riverine ca show a greater variability than previously acknowledged the variability of ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global ca cycling if past variations in oceanic ca isotope ratios are to be of use in constraining the past carbon cycle

combined effect of carbonate and biotite dissolution in landslides biases silicate weathering proxies abstract long term estimates of the dissolution of silicate rock are generally derived from a range of isotopic proxies such as the radiogenic strontium isotope ratio 87 sr 86 sr which are preserved in sediment archives for these systems to fairly represent silicate weathering the changes in isotopic ratios in terrestrial surface waters should correspond to changes in the overall silicate dissolution this assumes that the silicate mineral phases that act as sources of a given isotope dissolve at a rate that is proportional to the overall silicate weathering bedrock landsliding exhumes large quantities of fresh rock for weathering in transient storage and rapid weathering in these deposits is controlled primarily by dissolution of the most reactive phases in this study we test the hypothesis that preferential weathering of these labile minerals can decouple the dissolution of strontium sources from the actual silicate weathering rates in the rapidly eroding western southern alps wsa of new zealand we find that rapid dissolution of relatively radiogenic calcite and biotite in landslides leads to high local fluxes in strontium with isotopic ratios that offer no clear discrimination between sources these higher fluxes of radiogenic strontium are in contrast to silicate weathering rates in landslides that are not systematically elevated on a mountain belt scale radiogenic strontium fluxes are not coupled to volumes of recent landslides in large 100 km 2 catchments but silicate weathering fluxes are such decoupling is likely due first to the broad variability in the strontium content of carbonate minerals and second to the combination of radiogenic strontium released from both biotite and carbonate in recent landslides this study supports previous work suggesting the limited utility of strontium isotopes as a system to study silicate weathering in the wsa crucially however in settings where bedrock landsliding is a dominant erosive process there is potential for both random and systematic bias in isotope proxies if the most reactive phases exposed for dissolution by landslides disproportionately contribute to the proxy of choice this clearly suggests that the isotopic composition of marine sr is a proxy for periods of rapid mountain uplift and erosion rather than for the associated enhanced silicate weathering

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

diagenetic sources of stable remanence in remagnetized paleozoic cratonic carbonates a rock magnetic study hysteresis measurements lowrie fuller tests cisowski tests and low temperature demagnetization experiments on samples of the knox dolomite trenton limestone and onondaga limestone indicate that the remanence in these remagnetized carbonate units resides principally in single domain magnetite in contrast to previous interpretations volumetrically however a significant fraction of the magnetite is coarser grained as previous scanning electron microscopic work on magnetic extracts has shown these conclusions are based mainly on the characteristic wasp waisted shape of the hysteresis loops and on the anomalously high ratios of remanent coercivity to bulk coercivity both of which clearly indicate a bimodal distribution of coercivities grain sizes the magnetization is controlled mainly by cubic magnetocrystalline anisotropy consistent with the spheroidal particles commonly observed in extracts hysteresis trends show that especially the finest particles lack shape anisotropy in view of these conclusions the two components of natural remanence in these rocks are interpreted as 1 a late paleozoic kiaman chemical remanence carried by single domain diagenetic magnetite and 2 a cenozoic thermoviscous overprint residing principally in coarser pseudosingle domain and multidomain magnetite also of late paleozoic diagenetic origin

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

strontium isotope composition of runoff from a glaciated carbonate terrain abstract the relationship between subglacial chemical weathering processes and the sr isotope composition of runoff from robertson glacier alberta canada is investigated this glacier rests on predominantly carbonate bedrock of upper devonian age but silicate minerals are also present the provenance of solute in meltwaters is found to vary systematically with solute concentration and by inference subglacial water residence time in dilute waters the principal process of solute acquisition is calcite dissolution fueled by protons derived from the dissolution of co 2 and subsequent dissociation of carbonic acid at higher solute concentrations dolomite dissolution coupled to sulfide oxidation is more important sr concentration is found to increase with total solute concentration in two separate meltwater streams draining from the glacier but 87 sr 86 sr only increases in the eastern melt stream carbonate and k feldspar sources are shown to dominate the sr content of the western stream irrespective of concentration they also dominate the sr content of the eastern stream at low and intermediate concentrations but at higher concentrations muscovite with high 87 sr 86 sr is also an important sr source this reflects the outcrop of muscovite bearing lithologies in the catchment of the eastern stream and an increase in the rate of weathering of k silicates relative to that of carbonates as more concentrated solutions approach saturation with respect to carbonates nonstoichiometric release of 87 sr 86 sr and preferential release of sr over k from freshly ground k silicate surfaces may also occur this may help to explain the radiogenic nature of runoff from distributed subglacial drainage systems which are characterized by long water rock contact times and water flow through environments in which crushing and grinding of bedrock are active processes although the exchangeable sr in tills has higher 87 sr 86 sr than local carbonate bedrock only the more concentrated meltwaters from the eastern stream display similarly high values the most dilute waters which probably transport the bulk of the dissolved sr flux from the glacier have 87 sr 86 sr characteristic of local carbonate bedrock thus the results suggest that although enhanced weathering of silicate minerals containing radiogenic sr such as muscovite does occur in glaciated carbonate terrains it is unlikely to contribute to any enhanced flux of radiogenic sr from glaciated continental surfaces to the oceans

magnetic studies of the pendleside limestone evidence for remagnetization and late diagenetic dolomitization during a post asbian normal event the pendleside formation a sequence of bioclastic wackestones and grainstones has been extensively dolomitized and silicified especially towards the top and near the axis of the clitheroe anticline undolomitized limestones are characterized by the presence of magnetite and primary style magnetic fabrics and an exclusively reversed nrm with mean direction of dec 204 inc 21 the magnetization is considered to be a depositional postdepositional remanent magnetization acquired before any significant alteration of the limestones dolomitized and silicified limestones are characterized by hematite some silicified limestones show the intermediate state of co existing hematite and magnetite these rocks have non primary style magnetic fabrics and a complex nrm with normal components the best estimate of this component is dec 22 inc 20 almost antiparallel to the primary remanence the magnetization is considered to be a chemical remanent magnetization crm generated during the dolomitization of the pendleside formation the origin of the dolomitization may be associated with mudrock dewatering as the sequence was buried the normal crm indicates that the remagnetization spanned a post asbian normal event possibly in the westphalian coincident with the maximum burial of the pendleside formation

remagnetization by basinal fluids testing the hypothesis in the viola limestone southern oklahoma migration of orogenic or basinal fluids is a recently invoked mechanism to explain the widespread presence of late paleozoic secondary magnetizations in the rocks of north america paleomagnetic and geochemical results from the ordovician viola limestone in southern oklahoma are evaluated to assess the role of basinal fluids in leading to secondary magnetizations in the unit the viola limestone contains what we interpret to be a pervasive pennsylvanian synfolding magnetization residing in magnetite and a localized permian magnetization which resides in hematite and occurs in alteration zones around mineralized veins both secondary magnetizations are interpreted as chemical remanent magnetizations crm based on low burial temperatures and the presence of authigenic magnetic phases the relative proportion of the permian crm in hematite gradually decreases whereas the magnetite crm increases with distance from the veins fluid inclusion and sr isotope studies indicate that the vein mineralization calcite with mississippi valley type oxides and sulfides precipitated from basinal fluids which were warm saline and radiogenic the radiogenic 87sr 86sr values of the limestones in the alteration zones and the fact that there is more significant alteration closer to the veins suggests that the basinal fluids were also responsible for alteration in the limestones the coincidence of the geochemical and remagnetization trends suggests that the permian crm dates the migration of basinal fluids through the veins geochemical results from the viola limestone containing the pervasive crm indicate that it is relatively unaltered with no evidence for basinal fluids the lack of evidence for basinal fluids suggests that other mechanisms for the origin of the pervasive crm need to be tested the results of this study indicate that flow of basinal fluids was focused in veins and only locally altered the host limestone

evolution of cenozoic seawater lithium isotopes coupling of global denudation regime and shifting seawater sinks abstract the li isotopic record of seawater shows a dramatic increase of 9 over the past 60 million years here we use a model to explore what may have caused this change we focus particularly on considering how changes in the reverse weathering sinks that remove li from seawater can contribute to explain the observed increase our interpretation is based on dividing the oceanic sink which preferentially removes light li into two components i removal into marine authigenic clays in sediments at low temperatures with associated high fractionation factors and ii removal into altered oceanic basalt at higher temperatures and resulting lower fractionation factors we suggest that increases in the flux of degraded continental material delivered to the oceans over the past 60 ma could have increased removal of li into sedimentary authigenic clays versus altered basalt because altered basalt is associated with a smaller isotopic fractionation an increasing portion of the lower temperature authigenic clay associated sink could contribute to the rise of the seawater li isotope value this effect would moderate the extent to which the isotopic value of continental inputs must have changed in order to explain the seawater record over the cenozoic nonetheless unless the magnitude of fractionation during removal differs significantly from current understanding substantial change in the li 7 of inputs from continental weathering must have occurred our modeling suggests that dissolved riverine fluxes in the early eocene were characterized by li 7 of 0 to 13 with best estimates of 6 6 12 6 these values imply increases over the past 60 myrs of between 10 and 24 and we view a 13 increase as a likely scenario these changes would have been accompanied by increases in both the dissolved li flux from continental weathering and the removal flux from seawater into marine authigenic clays increases in li 7 of continental input are consistent with a change in the global denudation regime as a result of increasing continental erosion rate through the cenozoic changes in denudation may have meant increasing climate sensitivity of weathering over time but do not require globally supply limited and thus entirely climate insensitive weathering in the early cenozoic

geochemical constraints on the origin of secondary magnetizations in the cambro ordovician royer dolomite arbuckle mountains southern oklahoma abstract geochemical and paleomagnetic results from cambro ordovician royer dolomite in the arbuckle mountains southern oklahoma suggest a connection between dolomite type and magnetizations one dolomite type which is most common in the vicinity of the arbuckle anticline has a dull luminescence low 18 o values coeval to slightly lower 87 sr 86 sr ratios and contains an easterly cambro ordovician magnetization in magnetite to the southeast closer to the ouachita mountain front most of the royer dolomite contains a southeasterly and shallow magnetization in magnetite that is interpreted to be late paleozoic in age in contrast to the other dolomites these dolomites contain abundant authigenic k feldspar and pyrite radiogenic 87 sr 86 sr ratios and have a bright red luminescence all of which are consistent with alteration by basinal fluids at one site a stromatolitic bioherm dolomites similar to those at the arbuckle anticline are surrounded by the altered dolomites the distribution of specimen directions at this site is streaked between a cambro ordovician and late paleozoic direction the results of this study suggest a connection either direct by causing precipitation or indirect by increasing permeabilities for another fluid between a radiogenic fluid and a chemical magnetization in magnetite the relatively unaltered dolomites at the stromatolitic bioherm site escaped the almost pervasive alteration and remagnetization caused by the basinal fluids close to the ouachita mountains a potential source for the fluids

a seismologically consistent expression for the total area and volume of earthquake triggered landsliding we present a new seismologically consistent expression for the total area and volume of populations of earthquake triggered landslides this model builds on a set of scaling relationships between key parameters such as landslide spatial density seismic ground acceleration fault length earthquake source depth and seismic moment to assess the model we have assembled and normalized a catalog of landslide inventories for 40 shallow continental earthquakes low landscape steepness causes systematic overprediction of the total area and volume of landslides when this effect is accounted for the model predicts the total landslide volume of 63 of 40 cases to within a factor 2 of the volume estimated from observations r2 0 76 the prediction of total landslide area is also sensitive to the landscape steepness but less so than the total volume and it appears to be sensitive to controls on the landslide size frequency distribution and possibly the shaking duration some outliers are likely associated with exceptionally strong rock mass in the epicentral area while others may be related to seismic source complexities ignored by the model however the close match between prediction and estimate for about two thirds of cases in our database suggests that rock mass strength is similar in many cases and that our simple seismic model is often adequate despite the variety of lithologies and tectonic settings covered this makes our expression suitable for integration into landscape evolution models and application to the anticipation or rapid assessment of secondary hazards associated with earthquakes

miocene 87sr 86sr ratios of ostracods in the northern qaidam basin ne tibetan plateau and links with regional provenance weathering and eolian input abstract late cenozoic changes in chemical weathering and the dust cycle in response to the regional aridification and global cooling in the tectonically active northern tibetan plateau is an intriguing issue although it remains poorly understood the change in the 87sr 86sr ratio of basin water is linked to variations in the overall input of various sr sources with different 87sr 86sr ratios and analyses of such changes can be a useful tool for revealing changes in regional lithology weathering regimes and the dust cycle linked to tectonics and climate in this study we collected fossil shells of ostracods and gastropods from the miocene dahonggou section to reconstruct the paleolake water 87sr 86sr ratio from 14 8 ma to 11 1 ma in the northern qaidam basin on the northeastern tibetan plateau the reconstructed paleolake water 87sr 86sr ratios based on fossil shells and bulk carbonates from sediments display a coincident and stable 87sr 86sr ratio of approximately 0 7115 which did not show any detectable change in response to the enhanced aridification since 13 ma as inferred by the ostracod assemblage and its stable carbon and oxygen isotopes the results indicate that the sr influx regime from various sources did not change significantly during the aridification processes 13 ma which may have been caused by a less detectable change in proportion of silicate versus carbonate weathering and or an overwhelming sr source e g extrabasinal eolian dust that occurred from 14 8 ma to 11 1 ma further the 87sr 86sr ratios of modern lake water and river sand carbonates in the study region are significantly higher approximately 0 001 than those of the miocene lake water this observation can be explained by two possible mechanisms that need to be tested in the future 1 given a miocene sr input regime that is similar to today a large contribution from some extrabasinal sr source e g eolian dust with a much lower 87sr 86sr ratio is expected to have prevailed from 14 8 ma to 11 1 ma but is absent in the modern setting or 2 given a miocene sr input regime that could yield an overall lower lake water 87sr 86sr ratio of approximately 0 7115 a significant increase in the 87sr 86sr ratio of catchment scale sr source may have occurred after 11 ma in response to the uplift of the qilian mountains which would have enhanced hydrothermal activity metamorphism glaciation and landslide processes thereby resulting in more radiogenic sr source our study suggests that reconstructions of river lake water 87sr 86sr ratios can place powerful constraints on the complex interactions among tectonics climate and landscape evolution in the northeastern tibetan plateau based on a new perspective

chemical and strontium oxygen and carbon isotopic compositions of carbonates from the lesser himalaya implications to the strontium isotope composition of the source waters of the ganga ghaghara and the indus rivers samples of precambrian carbonate mostly dolomite outcrops collected across the lesser himalaya have been analysed for their mineralogy chemical composition and isotope ratios of sr o and c to assess the extent of their preservation and their role in contributing to the high radiogenic strontium isotope composition of the source waters of the ganga ghaghara and the indus their sr concentrations range from 20 to 363 ppm 18opdb 1 4 to 12 8 and mn 11 2036 ppm the petrography of the samples their low sr concentrations and wide range of 18o values are suggestive of their postdepositional alteration the 87sr 86sr of the bulk samples and their carbonate fractions are similar to one another with values ranging from 0 7064 to 0 8935 and are generally more radiogenic than that of contemporaneous seawater comparison of the 87sr 86sr and sr ca ratios among the carbonates and silicates from the lesser himalaya and the source waters of the ganga ghaghara and the indus shows that the values for the source waters overlap with those of the silicates but are much higher than those in carbonates an upper limit of carbonate sr in the various source waters is calculated to be between 6 and 43 assuming that all the ca in the rivers is of carbonate origin the results show that on the average weathering of the precambrian carbonates is unlikely to be a major contributor to the highly radiogenic strontium isotope composition of these source waters however they can be a dominant supplier of radiogenic sr to some rivers on a regional scale the silicate sr component in some of the source waters of the ganga bhagirathi bhilangna alaknanda and ganga ghaghara kali and sarju and the indus sutlej was calculated from the ca na sr na ratios and strontium isotope compositions of these rivers and the silicate endmember these calculations suggest that 33 89 of sr in the bhagirathi bhilangna alaknanda ganga and sarju rivers is of silicate origin whereas in the kali and the sutlej it is much lower only 8 the remaining sr to all these waters has to be supplied from other sources such as weathering of carbonates and evaporites this study underscores the importance of weathering of silicates carbonates and evaporites in contributing to the sr mass balance and 87sr 86sr of the source waters of the ganga ghaghara and the indus the present day silicate and carbonate sr contributions to the sr budget of the rivers vary considerably but among the major source waters of the ganga silicate sr exerts a more dominant control on their sr abundance and 87sr 86sr

isotopic ratios and release rates of strontium measured from weathering feldspars based upon dissolution of feldspars under controlled laboratory conditions we conclude that sr release at ph 3 is neither consistently stoichiometric nor constant for the feldspars measured bytownite microcline and albite all initially release sr at rates which are 5 bytownite to 160 microcline times faster than steady state release rates the sr si ratios in the early effluents are significantly elevated compared to the bulk mineral values the 87sr 86sr measured in effluent early in dissolution is higher than the bulk mineral 87sr 86sr for bytownite but lower than bulk mineral ratios for microcline and albite 87sr 86sr ratios for the feldspar powders also changed markedly during dissolution of the three phases in part nonstoichiometric release of sr can be explained by the presence of secondary phases exsolution lamellae or minute quantities of accessory phases or by surface leaching although we infer that these feldspars eventually release sr with isotopic composition roughly equal to that of the bulk mineral at steady state the feldspars dissolve at extremely different rates bytownite releases sr at a steady state rate 102 to 103 times faster than albite and microcline at ph 3 therefore a mixture of these feldspars or of other minerals exhibiting vast differences in dissolution rate will release 87sr 86sr ratios distinctly different from the bulk whole rock in addition initial sr release rates of the minerals bytownite microcline albite differ from steady state release rates bytownite albite microcline complicating analysis of weathering solutions log rate constants for bytownite albite and microcline decrease from 13 5 to 16 4 to 17 2 mol sr cm 2 s 1 interpretation of catchment scale riverine 87sr 86sr ratios on the basis of whole rock sr isotopes is therefore problematic at best and would require normalization of bulk isotopic ratios by relative rates of dissolution of sr contributing phases we also argue that abraded feldspar particles formed naturally for example during glaciation will show this initial transient nonstoichiometric release however once the transient release is completed perhaps 102 to 103 yr after abrasion as long as the solution chemistry remains relatively constant stoichiometric release of cations from feldspars including sr is expected the most likely way therefore to increase riverine fluxes of major cations or radiogenic 87sr 86sr is to create highly flushed and therefore far from equilibrium water rock systems such as glacial sediments and soils with reactive minerals e g carbonate plagioclase or biotite containing significant radiogenic strontium

strontium isotopes and rubidium in the ganga brahmaputra river system weathering in the himalaya fluxes to the bay of bengal and contributions to the evolution of oceanic87sr 86sr the concentrations of rb and sr and87sr 86sr isotopic ratios have been measured in the dissolved load of the ganga brahmaputra g b river system the ganga was sampled extensively from its source at gangotri in the higher himalaya to patna on the alluvial plains the brahmaputra was sampled in its stretch in assam in india the average sr concentration in the ganga at patna is 1 2 mol l and that in the brahmaputra at goalpara is 0 73 mol l the mean87sr 86sr ratios are 0 7239 and 0 7192 respectively the87sr 86sr in the ganga source waters the alaknanda the bhagirathi and their tributaries range between 0 7300 and 0 7986 considerably higher than the global average runoff value of 0 7119 the high87sr 86sr in the ganga source waters result from the intense weathering of precambrian granites and gneisses enriched in radiogenic sr the sr isotope systematics of the ganga waters is dominated by silicate weathering whereas carbonate weathering plays a significant role in their major ion chemistry the g b system transports about 910 million moles of dissolved sr annually to the bay of bengal with an average87sr 86sr of 0 7213 the sr transported by the g b system is about 2 7 of the global dissolved sr flux to the oceans via rivers model calculations reveal that the g b system has contributed significantly to the sr isotope evolution of seawater during the past 20 ma the flux of rb through the g b system is 24 million moles per year this is about 5 of the global river supply of rb to the oceans nearly twice the contribution of water via the g b system to the oceans our study suggests that the marine geochemistries of sr and rb and possibly u may have been influenced considerably by the himalayan orogeny

a reactive transport model for examining tectonic and climatic controls on chemical weathering and atmospheric co2 consumption in granitic regolith we developed a 1d reactive transport model for examining how tectonic and climatic parameters namely uplift rate water seepage velocity and temperature control chemical weathering and atmospheric co2 consumption rates during regolith development the model consists of mass conservation equations describing how mineral and solute concentrations change temporally and spatially vertically during weathering of granite containing 30 plagioclase an20 and up to 3 accessory calcite the equations are coupled by volumetric weathering rates which depend on mineral abundances intrinsic dissolution rate constants and surface areas as well as the departure of pore water from thermodynamic equilibrium we numerically solve a non steady state non dimensional version of the model by eliminating the need to prescribe regolith thickness non dimensionalization introduces two key scaling parameters that drive variations in the model results the rock residence time r the time for rock to travel upward through the model domain and the water residence time w the time for water to travel downward through the model domain we use the model to examine fundamental properties of chemical weathering especially reaction front propagation with the primary aim of characterizing weathering regimes and identifying factors that maximize the dissolution of plagioclase because only silicate weathering regulates atmospheric co2 levels over geological timescales weathering regimes are commonly classified as transport or supply limited versus weathering or kinetically limited but as outgrowths of geomorphology these terms primarily refer to the role of r in regulating regolith thickness our findings suggest that the paradigm should be expanded to include kinetic controls determined by w both regimes can experience far from and near equilibrium mineral dissolution however transport limited regimes generally have lower w r ratios compared to kinetically limited regimes under transport limitation thick to thin reaction fronts propagate downward indefinitely yielding extensive mineral depletion deeply weathered regolith and high ratios of silicate to carbonate weathering under kinetic limitation thin to non existent reaction fronts evolve to steady state yielding minimal mineral depletion no regolith development and low ratios of silicate to carbonate weathering kinetically limited regimes typifying tectonically active mountain ranges have low long term atmospheric co2 consumption rates transport limited regimes typifying tectonically stable cratons also have low long term atmospheric co2 consumption rates but because much of the earth s surface is transport limited we infer that such environments have the greatest impact on the global atmospheric co2 consumption flux the model output leads us to hypothesize that the maximum contribution should occur for extensive regions of silicate bedrock consolidated in warm wet climates because the combination of tectonic stability high temperatures and rapid seepage velocities accelerates reaction front propagation facilitates calcite depletion and sustains deep regolith development over long timescales our findings point to the importance of internal climate feedbacks for stabilizing long term atmospheric co2 levels

the role of climate driven chemical weathering on soil production climate plays an important role in controlling rates of weathering and weathered regolith production regolith production functions however seldom take climate parameters into account based on a climate dependent weathered regolith production model at low denudation rates relative regolith thicknesses are less sensitive to changes in precipitation rates while at high denudation rates small changes in climatic parameters can result in complete stripping of hillslopes this pattern is compounded by the long residence times and system response times associated with low denudation rates and vice versa as others have shown the transition between regolith mantled and bedrock slopes is dependent on the ratio of denudation to production here we further suggest that this is itself a function of precipitation rate and temperature we suggest that climatic parameters can be easily incorporated into existing soil production models and that such additions improve the predictive power of soil production models

neogene himalayan weathering history and river87sr86sr impact on the marine sr record abstract clastic sediments in the bengal fan contain a neogene history of erosion and weathering of the himalaya we present data on clay mineralogy major element stable and radiogenic isotope abundances from lower miocene pleistocene sediments from odp leg 116 nd and sr isotope data show that the himalayan provenance for the eroded material has varied little since 17 ma however from 7 to 1 ma smectite replaces illite as the dominant clay while sediment accumulation decreased implying an interval of high chemical weathering intensity but lower physical erosion rates in the ganges brahmaputra gb basin o and h isotopes in clays are correlated with mineralogy and chemistry and indicate that weathering took place in the paleo gangetic flood plain the87sr86sr ratios of pedogenic clays vermiculite smectite record the isotopic composition of sr in the weathering environment and can be used as a proxy for87sr86sr in the paleo gb basin the sr data from pedogenic clays shows that river87sr86sr values were near 0 72 prior to 7 ma rose rapidly to 0 74 in the pliocene and returned to 0 72 in the middle pleistocene these are the first direct constraints available on the temporal variability of87sr86sr in a major river system the high87sr86sr values resulted from intensified chemical weathering of radiogenic silicates and a shift in the carbonate silicate weathering ratio modeling of the seawater sr isotopic budget shows that the high river87sr86sr values require a ca 50 decrease in the sr flux from the gb system in the pliocene the relationship between weathering intensity 87sr86sr and sr flux is similar to that observed in modern rivers and implies that fluxes of other elements such as ca na and si were also reduced increased weathering intensity but reduced sr flux appears to require a late miocene pliocene decrease in himalayan erosion rates followed by a return to physically dominated and rapid erosion in the pleistocene in contrast to the view that increasing seawater87sr86sr results from increased erosion mio pliocene to mid pleistocene changes in the seawater sr budget were the result of reduced erosion rates and sr fluxes from the himalaya

paleomagnetism of the cambrian royer dolomite and pennsylvanian collings ranch conglomerate southern oklahoma an early paleozoic magnetization and nonpervasive remagnetization by weathering the cambrian royer dolomite in the arbuckle mountains oklahoma contains an early paleozoic magnetization and a nonpervasive late paleozoic remagnetization caused by meteoric fluids the royer was uplifted and underwent karst conditions and eroded clasts were deposited in the collings ranch conglomerate during the pennsylvanian an early paleozoic depositional or chemical remanent magnetization dec 109 inc 10 tilt corrected residing in magnetite is found in gray brown ferroan dolomite a pennsylvanian permian chemical remanent magnetization crm residing in hematite dec 147 inc 4 in situ is associated with dedolomitized rocks in an alteration zone around and below the karst features clasts of the royer in the pennsylvanian collings ranch conglomerate correlated with the parent rock by petrographic isotopic and rock magnetic methods also contain two magnetizations the clast centers contain a predepositionai magnetization whereas the clast margins contain a postdepositional crm dec 152 inc 4 in situ conglomerate tests using these magnetization components constrain the timing of remanence acquisition in the royer dolomite field relations and the results of oxygen and carbon stable isotope analyses indicate that the dedolomitization events were caused by near surface meteoric fluids that altered the royer around the margin of the karst dissolution caves and the outer rims of royer dolomite clasts remagnetization was not pervasive and an early paleozoic magnetization is preserved in the dolomite below the zone affected by weathering

siderite formation in anoxic deep sea sediments a synergetic bacteria controlled process with improtant implications in paleomagnetism recent work on magnetic properties of limestones has demonstrated that the mineral siderite can be very important in paleomagnetism for two reasons first oxidation of siderite produces secondary daughter magnetic minerals magnetite maghemite and hematite either before during or after sampling these daughter products can completely change the magnetic properties of limestone samples and if unrecognized may be one of the primary reasons why many paleomagnetic studies of limestones especially paleozoic limestones are unsuccessful second siderite in weakly magnetized rocks may indicate the potential for successful paleomagnetic results because the presence of siderite indicates that the primary magnetic carriers are still intact appropriate demagnetization methods should yield successful results we conclude that microenvironmental conditions in anoxic marine sediments may permit the formation of siderite from iron ii produced during bacterial dissimilatory iron reduction

chemical denudation and silicate weathering in himalayan glacier basins batura glacier pakistan original article can be found at http www sciencedirect com science journal 00221694 copyright elsevier b v doi 10 1016 s0022 1694 02 00036 7 full text of this article is not available in the uhra

fluvial geochemistry of the eastern slope of the northeastern andes and its foredeep in the drainage of the orinoco in colombia and venezuela abstract the fluvial geochemistry of the tributaries of the orinoco draining the eastern branch of the northern andes in colombia and venezuela is determined by lithology and ranges from rivers dominated by aluminosilicate weathering mainly of shales and mafic rocks to those bearing the signatures of dissolution of marine limestones and evaporites and of continental playa deposits these left bank tributaries of the orinoco provide the overwhelming proportion of the suspended and dissolved loads transported by the main stem although feeding only half the discharge however due to the extreme severity of weathering on the guayana shield the right bank tributaries supply about half the silica and 40 of the k carried by the orinoco there is a similar partitioning between the andes and the lowlands in the amazon drainage in contrast the mackenzie which drains the northern extremity of the continental arc of the western americas is completely dominated by the weathering of limestones and evaporites and transports very little silica this again appears to be a reflection of lithology since the yukon in similar latitudes and terrain has silica concentrations comparable to the tropical systems in addition a conservative deconvolution of the data gives estimates of the net consumption of atmospheric co 2 by aluminosilicate weathering that follows the same pattern thus the available evidence from the western americas indicates that exposure and lithology rather than the climatic variables temperature and runoff dominate the weathering yields in active orogenic belts these observations contradict the conventional view of weathering processes and their controls and are at complete variance with the assumptions parameterised in most models of the geochemical cycle

episodic potassic diagenesis of ordovician tuffs in the mississippi valley area cambrian ordovician strata of the mississippi valley have been extensively modified by potassic diagenesis ordovician vitric tuffs are altered to k feldspar and illite rich mixed layer illite smectite i s both of which have been dated by k ar rb sr dates for k feldspar support its reliability as a k ar clock despite a dislocation density of 10 sup 9 10 sup 10 cm sup 2 age data document three paleozoic episodes of potassic diagenesis which have mean ages of 396 ma early devonian for k feldspar of the upper mississippi valley umv 362 ma late devonian for i s of the umv and 265 ma permian for i s of missouri devonian dates from the umv correspond to times of wide spread epeirogeny in the us midcontinent and diagenetic episodes are attributed to regional flow of basinal brines caused by ground water recharge on uplifted arches potassium for k feldspar may have come from the michigan basin and k for illite may have come from the east central iowa basin k feldspar and i s of the umv are in oxygen isotopic disequilibrium indicating that the k feldspar crystallized from fluid that was either warmer or had lower delta sup 18 o values than that of the i s permian illitization apparently records northward movement of warm saline fluid as a result of the ouachitamore orogeny less

controls on the 87sr 86sr ratio of carbonates in the garhwal himalaya headwaters of the ganges abstract the episodic variation of the seawater 87sr 86sr ratio has been attributed to either variations in the sr flux or the sr isotopic composition of the riverine dissolved load derived from weathering of the continental crust the discovery that himalayan rivers are characterized by high concentrations of dissolved sr concentrations with high 87sr 86sr ratios has raised the possibility that collisional orogens play a critical role in moderating the variations in seawater 87sr 86sr ratios here we describe himalayan carbonates and calc silicates from garhwal the headwaters of the ganges with extreme 87sr 86sr ratios 1 0 elevated sr isotope ratios result from exchange with rb rich silicate material during both himalayan and pre himalayan metamorphic episodes and the carbonates contribute a significant fraction to the ganges 87sr flux particularly elevated 87sr 86sr ratios are found in calc silicates from the deoban formation of the lesser himalaya a detailed traverse of shales and calc silicat

transport mechanisms by fluid flow in metamorphic rocks oxygen and strontium decoupling in the trois seigneurs massif a consequence of kinetic dispersion

synfolding magnetization in the jurassic preuss sandstone wyoming idaho utah thrust belt the jurassic preuss sandstone exposed in five thrust plates of the wyoming idaho utah thrust belt carries directions of remanent magnetization that group most tightly after only partial unfolding field petrographic and rock magnetic evidence indicates that the carrier of this magnetization is detrital low ti titanomagnetite the detrital titanomagnetite was remagnetized at low temperatures 75 150 c probably completely during folding anisotropy of magnetic susceptibility and petrographic observations indicate that the detrital titanomagnetite has been affected by tectonic strain we suggest that low temperature remagnetization of the detrital titanomagnetite was either a viscous partial thermoremanent magnetization the acquisition of which was enhanced by stress or a piezoremanent magnetization that involved stress induced movement of domain walls during intracrystalline strain or was a combination of the two mechanisms stress may promote remagnetization at temperatures much lower than predicted by current theoretical models other mechanisms such as acquisition of chemical remanent magnetization during folding deflection of a prefolding magnetization by internal strain or combination of components of magnetization with different direction cannot account for the geometry of magnetization in the preuss the locus of acquisition of synfolding magnetization in the preuss migrated in conjunction with deformation in the thrust belt a model is presented in which synfolding magnetization was acquired during cooling and folding as strata moved up thrust ramps a lack of reverse polarity directions remains a puzzling feature of the remanence the remanent direction is tentatively interpreted to reflect the predominant polarity state during its acquisition over an extended rather than a discrete time period during folding in late cretaceous and early tertiary periods of predominantly normal polarity

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

mineral specific chemical weathering rates over millennial timescales measurements at rio icacos puerto rico abstract mineral weathering plays a prominent role in many biogeochemical and geomorphological processes it supplies nutrients to soils and streams accelerates physical erosion by weakening bedrock and producing easily erodible soil and modulates earth s long term climate by drawing down atmospheric carbon dioxide we calculate mineral specific chemical weathering rates at two field sites in the rio icacos catchment puerto rico by combining new mineral abundance measurements from quantitative powder x ray diffraction xrd with existing measurements of i soil production rates from cosmogenic nuclides ii chemical alteration of the regolith from x ray fluorescence xrf and iii dust deposition rates the central purpose of this paper is to show that combining measurements of cosmogenic nuclides with xrf based geochemistry and xrd based mineralogy can in favorable cases provide weathering rates of abundant soluble mineral phases in actively eroding terrain to an accuracy of better than 20 of the mean even in places with high dust deposition rates mineral weathering at our two field sites is dominated by plagioclase at rates of 3274 575 mol ha 1 yr 1 and 3077 541 mol ha 1 yr 1 followed by hornblende at 187 71 mol ha 1 yr 1 and 308 93 mol ha 1 yr 1 within the uncertainty of our data all weathering of these primary minerals occurs below the saprolite soil interface our measurements imply that kaolinite production in saprolite is roughly 1 3 times faster than kaolinite weathering in the soil our results are the first to show that field measurements of cosmogenic nuclides xrf xrd and dust fluxes can be combined within the geochemical mass balance method to quantify long term mineral weathering rates even in locations with high dust deposition rates this implies that the mass balance method can be a valuable tool for quantifying the effects of climate vegetation tectonics and other factors on weathering rates of individual mineral phases

a silicate weathering mechanism linking increases in marine 87sr 86sr with global glaciation the 87sr 86sr ratio of sea water is generally regarded as a proxy for the rate of chemical weathering of the continents interpretation of the 87sr 86sr record in marine limestones requires an understanding of how changes in this quantity are linked to climate and tectonic events a connection between the strontium isotope record and the extent of global glaciation has been proposed1 8 but without a well established mechanism glaciation may influence marine 87sr 86sr by changing global riverine sr fluxes that is rock weathering rates and or 87sr 86sr ratios that is relative mineral weathering rates here we investigate how the 87sr 86sr release from silicate weathering is affected by glaciation using the sr isotope systematics of granitoid soils on alpine glacial moraines in the wind river range wyoming we observe a negative correlation between the 87sr 86sr ratio of exchangeable sr in soils and the soil age indicating that the 87sr 86sr ratio of sr released in the early stages of weathering is significantly higher than in later stages we estimate that this mechanism can increase global riverine 87sr 86sr by an average of 0 0002 during periods of glacial interglacial cycling when superimposed on long term trends controlled by tectonic processes2 7 9 10 this shift can account for the correlation between the rate of change of marine 87sr 86sr and the intensity of glaciation over at least the past 10 myr

minimal climatic control on erosion rates in the sierra nevada california climate is widely thought to regulate erosion rates but the relationships among precipitation temperature and erosion rate have remained speculative because long term erosion rates have been difficult to measure we used cosmogenic nuclides to measure long term erosion rates at climatically diverse sites in the sierra nevada california spanning 20 180 cm yr in annual precipitation and 4 15 8c in mean annual temperature average erosion rates vary by only 2 5 fold across these sites and are not correlated with climate indicating that climate only weakly regulates nonglacial erosion rates in mountainous granitic terrain

late quaternary slip rates and slip partitioning on the alpine fault new zealand abstract published geological data on late quaternary offsets on the alpine fault new zealand have been assembled into a common format and analysed with respect to uncertainties uncertainties arise mainly from measurement of offset features relating apparent offsets to actual fault slip and dating the offset features despite the considerable uncertainties the data form a coherent set consistent with a relatively constant rate of strike slip of 27 5 mm year between milford sound and hokitika this rate represents 70 75 of the fault parallel interplate motion north of the confluence with the hope fault the rate drops substantially dip slip rates on the other hand show considerable variation along strike rising to a maximum of more than 10 mm year in the central section and decreasing to zero at the southern end partitioning of c 25 of the interplate slip on to structures east of the alpine fault occurs in the central section consistent with predictions from critical wedge models the partitioning of all the fault normal component of displacement on to other structures in the south may be related in part to a doubling in width of the deforming wedge to the east most probably however the fault normal displacement is mainly accommodated by underthrusting of the australian plate offshore due to a change in the nature of the crust from continental to oceanic

climatic and tectonic controls on chemical weathering in the new zealand southern alps abstract climatic and tectonic controls on the relative abundance of solutes in streams draining the new zealand southern alps were investigated by analyzing the elemental and sr isotope geochemistry of stream waters bedload sediment and hydrothermal calcite veins the average relative molar abundance of major cations and si in all stream waters follows the order ca2 50 si 22 na 17 mg2 6 k 5 for major anions the relative molar abundance is hco3 89 so42 7 cl 4 weathering reactions involving plagioclase and volumetrically small amounts of hydrothermal calcite define the ionic chemistry of stream waters but nearly all streams have a carbonate dominated ca2 and hco3 mass balance stream water ca sr and 87sr 86sr ratios vary from 0 173 to 0 439 mol nmol and from 0 7078 to 0 7114 respectively consistent with the ionic budget these ratios lie solely within the range of values measured for bedload carbonate ca sr 0 178 to 0 886 mol nmol 87sr 86sr 0 7081 to 0 7118 and hydrothermal calcite veins ca sr 0 491 to 3 33 mol nmol 87sr 86sr 0 7076 to 0 7097 streams draining regions in the southern alps with high rates of physical erosion induced by rapid tectonic uplift and an extremely wet climate contain 10 more ca2 and 30 more sr2 from carbonate weathering compared to streams draining regions in drier more stable landscapes similarly streams draining glaciated watersheds contain 25 more sr2 from carbonate weathering compared to streams draining non glaciated watersheds the highest abundance of carbonate derived solutes in the most physically active regions of the southern alps is attributed to the tectonic exhumation and mechanical denudation of metamorphic bedrock which contains trace amounts of calcite estimated to weather 350 times faster than plagioclase in this environment in contrast regions in the southern alps experiencing lower rates of uplift and erosion have a greater abundance of silicate versus carbonate derived cations these findings highlight a strong coupling between physical controls on landscape development and sources of solutes to stream waters using the southern alps as a model for assessing the role of active tectonics in geochemical cycles this study suggests that rapid mountain uplift results in an enhanced influence of carbonate weathering on the dissolved ion composition delivered to seawater

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

sediment flux from a mountain belt derived by landslide mapping in humid uplands landsliding is the dominant mass wasting process in the western southern alps of new zealand landslides are scale invariant and have a power law magnitude frequency distribution independent studies from other regions suggest that this is a general property of landsliding this observation is of critical importance to the evaluation of the impact of events of different length scales over different time intervals on landscape evolution it is particularly useful when estimating regional geomorphic rates because it constrains the frequency and overall significance of extreme events which cannot otherwise be evaluated by integrating the complete response of the system we estimate the regional denudation rate due to landsliding to be 9 4 mm yr 1 sediment discharge from the western southern alps is dominated by landslide derived material

chemical weathering response to tectonic forcing a soils perspective from the san gabriel mountains california abstract what controls the chemical weathering of soils in tectonically active landscapes recent field and modeling studies suggest that tectonic forcing and associated increases in erosion rates may either promote or hinder soil chemical weathering these competing trajectories are dependent on two primary controls the availability of fresh minerals and their residence time on the landsurface here we explore rates and extents of soil weathering in the san gabriel mountains of california where previous work has measured clear tectonic fingerprints on rates of long term exhumation hillslope erosion and landscape morphology we quantify chemical weathering across this landscape by elemental analysis of soils saprolites and bedrock on six sites that bracket the low gradient hillslopes of the relict upland plateau and the high gradient hillslopes at the margins of the tectonically driven incising landscape average chemical depletion fractions which measure weathering losses from soil relative to unweathered parent material decrease with increasing elevation and decreasing temperature reflecting a combination of climate influence and potential dust inputs from the mojave desert weathering fluxes from non dust affected sites with similar elevations climates and lithology correlate with both erosion rates and hillslope gradient on low gradient hillslopes 25 weathering intensities and rates both decrease as erosion rates increase and soils thin at the highest denudation rates 300 t km 2 y 1 saprolite production is outpaced and soils are produced directly from fractured rock these patterns are consistent with those predicted by a previously published model for denudation weathering relationships based on mineral weathering kinetics variable weathering extents in soils indicate that weathering in the sgm is largely kinetically limited this study is the first to quantify decreases in both rates and extents of soil chemical weathering with increasing erosion rates and suggests tectonic uplift in rapidly eroding and incising landscapes may not stimulate increased silicate weathering

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

remanence in authigenic magnetite testing the hydrocarbon magnetite hypothesis paleomagnetic rock magnetic petrographic and geochemical studies of hydrocarbon saturated speleothems in southern oklahoma indicate there is a relation between hydrocarbons and a chemical magnetization that resides in magnetite the speleothems which are composed of light and dark calcite bands occur in caves of karst origin in the ordovician kindblade formation vertebrate fossils interbedded with the deposits indicate they are permian in age the dark bands contain primary hydrocarbon filled fluid inclusions the dark calcites possess over an order of magnitude stronger natural remanent magnetization than the lighter bands which do not yield stable decay during demagnetization alternating field af and thermal demagnetization of specimens of the dark bands reveal a permian direction of magnetization declination 160 inclination 3 k 17 95 5 n 56 the results of rock magnetic experiments and the fact that most maximum unblocking temperatures are below 580 c suggest that the dominant component resides in magnetite in some specimens stable decay to 640 c suggests the presence of a weak component residing in hematite the presence of authigenic magnetite spheres in magnetic extracts of the dark calcites supports a chemical origin for the magnetization shallow burial depths probably eliminate the possibility of a thermoviscous magnetization the occurrence of primary hydrocarbon inclusions suggests that hydrocarbons seeped into the caves during precipitation of the speleothems and were trapped in the calcite crystals the relationship between intensity of magnetization and hydrocarbon abundance leads us to propose that chemical conditions created by the hydrocarbons caused precipitation of authigenic magnetite and acquisition of the associated chemical remanence

thickness of the chemical weathering zone and implications for erosional and climatic drivers of weathering and for carbon cycle feedbacks quantitative understanding of variability in weathering fluxes on the modern earth is limited because little is known about where the most important weathering reactions take place this is partly because the locus of weathering is difficult to measure empirically inverse analysis of a parametric model presented here provides first order constraints on variability in the thickness of the zone of active weathering results suggest that the effective thickness of the weathering zone varies relatively little across several orders of magnitude of denudation rate at low to moderate denudation rates reactions in soils may dominate weathering fluxes at the catchment scale but the contribution from soil weathering decreases at higher denudation rates consequently increased erosion leads to higher weathering fluxes sustained by progressively greater contributions from weathering in bedrock the effect of climate temperature and runoff on weathering fluxes is apparently weaker at low denudation rates than at high denudation rates such that erosion and potentially associated bedrock weathering may be important for maintaining climate stabilizing feedbacks in earth s carbon cycle

using a reactive transport model to elucidate differences between laboratory and field dissolution rates in regolith the reactive transport model flotran was used to forward model weathering profiles developed on granitic outwash alluvium over 40 3000 ka from the merced california usa chronosequence as well as deep granitic regolith developed over 800 ka near davis run virginia usa baseline model predictions that used laboratory rate constants km measured fluid flow velocities v and bet volumetric surface areas for the parent material a o m were not consistent with measured profiles of plagioclase potassium feldspar and quartz reaction fronts predicted by the baseline model are deeper and thinner than the observed consistent with faster rates of reaction in the model reaction front depth in the model depended mostly upon saturated versus unsaturated hydrologic flow conditions rate constants controlling precipitation of secondary minerals and the average fluid flow velocity va unsaturated hydrologic flow conditions relatively open with respect to co2 g resulted in the prediction of deeper reaction fronts and significant differences in the separation between plagioclase and potassium feldspar reaction fronts compared to saturated hydrologic flow relatively closed with respect to co2 g under saturated or unsaturated flow conditions the rate constant that controls precipitation rates of secondary minerals must be reduced relative to laboratory rate constants to match observed reaction front depths and measured pore water chemistry additionally to match the observed reaction front depths va was set lower than the measured value v for three of the four profiles the reaction front gradients in mineralogy and pore fluid chemistry could only be modeled accurately by adjusting values of the product kma o m by assuming km values were constrained by laboratory data field observations were modeled successfully with tst like rate equations by dividing measured values of a o m by factors from 50 to 1700 alternately with sigmoidal or alinhibition rate models this adjustment factor ranges from 5 to 170 best fit models of the wetter hydrologically saturated davis run profile required a smaller adjustment to a o m than the drier hydrologically unsaturated merced profiles we attributed the need for large adjustments in va and a o m necessary for the merced models to more complex hydrologic flow that decreased the reactive surface area in contact with bulk flow water e g dead end pore spaces containing fluids that are near or at chemical equilibrium thus rate models from the laboratory can successfully predict weathering over millions of years but work is needed to understand how to incorporate changes in what controls the relationship between reactive surface area and hydrologic flow

relationship between mechanical erosion and atmospheric co2 consumption in the new zealand southern alps to examine the influence of mountain uplift on the long term carbon cycle we used geochemical hydrologic and suspended load data for 12 streams draining the new zealand southern alps to quantify rates of erosion weathering and atmospheric co 2 consumption rapid uplift in the western southern alps elevates mechanical erosion rates by a factor of 13 relative to those on the tectonically stable eastern side 125 10 8 vs 9 4 10 8 g km 2 yr respectively similarly the average chemical weathering rate is 5 times higher on the western compared to eastern side of the mountain range 9 8 10 7 vs 2 0 10 7 g km 2 yr respectively however because the proportion of stream water ca 2 and mg 2 from carbonate weathering increases as the rate of mechanical erosion increases the long term atmospheric co 2 consumption rate on the western side is 2 times higher than that on the eastern side 14 10 4 vs 6 9 10 4 mol km 2 yr respectively and only 1 5 times higher than the global mean value 9 10 4 mol km 2 yr data for major world rivers including himalayan rivers provide a consistent interpretation regarding the relationship between mechanical erosion intensity and the ratio of silicate to carbonate weathering thus we conclude that mountain building increases atmospheric co 2 consumption rates by only a factor of 2 which is much lower than previous estimates

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

ca sr and sr isotope systematics of a himalayan glacial chronosequence carbonate versus silicate weathering rates as a function of landscape surface age we explored changes in the relative importance of carbonate vs silicate weathering as a function of landscape surface age by examining the ca sr and sr isotope systematics of a glacial soil chronosequence located in the raikhot watershed within the himalaya of northern pakistan bedrock in the raikhot watershed primarily consists of silicate rock ca sr 0 20 mol nmol 87 sr 86 sr 0 77 to 1 2 with minor amounts of disseminated calcite ca sr 0 98 to 5 3 mol nmol 87 sr 86 sr 0 79 to 0 93 and metasedimentary carbonate ca sr 1 0 to 2 8 mol nmol 87 sr 86 sr 0 72 to 0 82 analysis of the exchangeable carbonate and silicate fractions of seven soil profiles ranging in age from 0 5 to 55 kyr revealed that carbonate dissolution provides more than 90 of the weathering derived ca and sr for at least 55 kyr after the exposure of rock surfaces even though carbonate represents only 1 0 wt of fresh glacial till the accumulation of carbonate bearing dust deposited on the surfaces of older landforms partly sustains the longevity of the carbonate weathering flux as the average landscape surface age in the raikhot watershed increases the ca sr and 87 sr 86 sr ratios released by carbonate weathering decrease from 3 6 to 0 20 mol nmol and 0 84 to 0 72 respectively the transition from high to low ca sr ratios during weathering appears to reflect the greater solubility of high ca sr ratio carbonate relative to low ca sr ratio carbonate these findings suggest that carbonate weathering controls the dissolved flux of sr emanating from stable himalayan landforms comprising mixed silicate and carbonate rock for tens of thousands of years after the mechanical exposure of rock surfaces to the weathering environment copyright 2002 elsevier science ltd

competition between erosion and reaction kinetics in controlling silicate weathering rates article i nfo weathering rates of minerals may be limited by the reaction kinetics of the constitutive minerals or the supply of fresh minerals delivered to the near surface by denudation we use a model of denudation and reaction kinetics to analyze the relative importance of each in moderating silicate weathering fluxes in different erosional environments for different commonly occurring silicate minerals we find that minerals that reside in the near surface weathering zone for far longer than the reaction takes to complete as is the case with slow denudation produce weathering fluxes that respond most strongly to changes in denudation rate conversely when transit through the weathering zone is rapid relative to a given mineral s weathering timescale the weathering responds most vigorously to changes in the reaction kinetics based on field and laboratory measured values of silicate weathering kinetic constants observed weathering zone thicknesses in relation to denudation rates and denudation rates inferred from topography it appears that fresh mineral supply may play a sub equal or dominant role in moderating silicate weathering fluxes for four mineral phases considered if correct this suggests that the concentration of atmospheric co2 which is regulated by silicate weathering over geologic timescales may depend on those factors that control long term erosion rates across earth s surface

gold mineralization as a consequence of continental collision an example from the southern alps new zealand abstract formation of gold quartz veins within the alpine schist near the alpine fault was synchronous with uplift the temperature of vein formation was greater than 320 c at a depth of 4 5 km vein precipitation was due to dilution and cooling of metamorphic metal bearing fluids by cooler less saline meteoric fluids numerical modeling of the topographic and thermal processes associated with continental collision has identified the time and space scales necessary for the generation of the geochemical conditions which resulted in vein genesis a predictable topographic pattern of 1500 m high ridges normal to the plate boundary leading to the main divide is established within the first 500 ka of uplift producing the head driven flow patterns of meteoric circulation the high thermal inertia of a rapidly uplifted region provides the thermal driving force leading to buoyancy driven convection of metamorphic fluids when the geothermal gradient is in excess of 50 c km using boundary conditions derived from the southern alps elevation of temperatures to 300 c at 5 km occurs after 1 8 ma of uplift at which time gold formation may occur if the intersection of head and buoyancy driven fluids lies within greenschist facies rocks further uplift causes erosion of the greenschist facies rocks together with the gold deposits adjacent to the fault and migration of the loci of mineralization further into the uplifting block the results of the examination of the southern alps gold regions are extended to other phanerozoic and archean deposits which are spatially related to major fault zones the characteristic topographic and thermal behavior of major collisional zones provides the driving forces necessary for gold mineralization to occur in the absence of any igneous heat source

chemical weathering in active mountain belts controlled by stochastic bedrock landsliding in active mountain belts erosion is driven by bedrock landsliding river water chemistry in new zealand s southern alps suggests that stochastic mass wasting processes also enhance chemical weathering in such environments a link between chemical weathering and physical erosion exists at the catchment scale over a wide range of erosion rates1 2 however in mountain environments where erosion rates are highest weathering may be kinetically limited3 4 5 and therefore decoupled from erosion in active mountain belts erosion is driven by bedrock landsliding6 at rates that depend strongly on the occurrence of extreme rainfall or seismicity7 although landslides affect only a small proportion of the landscape bedrock landsliding can promote the collection and slow percolation of surface runoff in highly fragmented rock debris and create favourable conditions for weathering here we show from analysis of surface water chemistry in the southern alps of new zealand that weathering in bedrock landslides controls the variability in solute load of these mountain rivers we find that systematic patterns in surface water chemistry are strongly associated with landslide occurrence at scales from a single hillslope to an entire mountain belt and that landslides boost weathering rates and river solute loads over decades we conclude that landslides couple erosion and weathering in fast eroding uplands and thus mountain weathering is a stochastic process that is sensitive to climatic and tectonic controls on mass wasting processes

stable isotopic evidence for mixing between metamorphic fluids and surface derived waters during recent uplift of the southern alps new zealand recent studies have shown that the southern alps of new zealand have active hydrothermal systems driven by tectonic uplift these studies have concentrated on the rapidly exhumed rocks immediately adjacent to the alpine fault we present new stable isotopic evidence that shows that fluid flow and fluid mixing processes thought to be restricted to rocks near the alpine fault also occurred in the low uplift rate region of the southern alps orogen during the kaikouran orogeny 10 ma to present low 18ocalcite values of post metamorphic veins in the eastern southern alps indicate that meteoric waters have penetrated to hot midcrustal levels 350 300 c 5 km depth and mixed with metamorphic fluids in areas far removed from the alpine fault in addition the isotopic values of calcites precipitated in active faults in the mackenzie basin define a trend of increasing 18o decreasing 13c and decreasing temperature and form an isotopic mixing line between fault and vein calcites crosscutting metamorphic rocks and authigenic calcites precipitated in mackenzie basin sediments the isotope data indicate a second phase of mixing between a modified metamorphic fluid and a surficial diagenetic fluid at shallow depths we suggest that mixed metamorphic meteoric hydrothermal systems have developed in the east side of the southern alps during uplift and that active faults have played a critical role in transporting metamorphic fluids outward from the mountain front and into the adjacent intermontane basins

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

on discrimination between carbonate and silicate inputs to himalayan rivers we review new and published analyses of river waters bedloads and their constituent minerals from the dhauli ganga and alaknanda headwaters of the ganges in garhwal and the marsyandi in nepal and their tributaries these data are used to discriminate between the inputs of major cations and sr from silicate and carbonate sources methods of estimating the proportion of the carbonate and silicate inputs to river waters using mixing arrays in sr ca mg na k 87sr 86sr space are shown to suffer from systematic correlations between the magnitude of the precipitation of secondary calcite and the fraction of the silicate component this results in factor of two overestimates of the fractions of silicate derived ca mg and sr to correct for this the magnitude of secondary calcite precipitated and relative fractions of silicate and carbonate derived cations are instead calculated by modeling the displacement of water compositions from the compositions of the carbonate and silicate components of the bedload in subsets of sr ca mg na k 87sr 86sr space the compositions of the carbonate and silicate end members in the bedload are determined by sequential leaching the results of this modeling are compared with modeling of the modal mineral inputs to waters where mineral compositions are derived from electron microprobe analyses of the minerals in the bedload in the upper marsyandi catchment which drains low grade tethyan sedimentary series formations a set of mainstem samples collected over a two year period define tight correlations in sr ca mg na k 87sr 86sr space modeling of the magnitude of secondary carbonate precipitation and fractions of silicate derived ca mg and sr in sr ca mg 87sr 86sr space gives self consistent results that are compatible with both the calculations of mineral modes and published mg isotopic compositions if the ratio of chlorite to biotite weathering is high or if there is another silicate source of mg these calculations imply that between 12 and 31 percent of the sr and 44 and 72 percent of the mg is derived from silicate minerals where the range reflects the seasonal change in the ratio of silicate derived to carbonate derived cations modeling in sr ca na and or k space is inconsistent with the sr isotopic and mg isotopic constraints and we conclude that in this catchment dissolution of na and k are incongruent relative to sr ca mg potassium is preferentially retained in micas whereas the controls on na are unclear modeling of the catchments underlain by high himalayan crystalline and lesser himalayan series in garhwal is complicated by the presence of dolomite as well as calcite in the carbonate and the results imply that dolomite dissolves faster in the acetic acid leaches than in nature up to 60 percent of the sr in the catchment on high himalayan crystalline series and 20 to 30 percent of sr in the catchments on lesser himalayan series are estimated to be derived from silicates however it should be noted that the element budgets are not all self consistent and the use of bedrock element ratios to model the sources of chemical inputs to river waters remains subject to uncertainties

hydrothermal alteration in anthracite from eastern pennsylvania implications for mechanisms of anthracite formation orthogonal joint sets cleat in anthracite rank coal beds from eastern pennsylvania contain two mineralogically and chemically different authigenic clay mineral assemblages in localities from all four anthracite fields the systematic cleat contains significant quantities 20 to 95 wt of authigenic rectorite sudoite or tosudite which are clay minerals primarily associated with hydrothermal veins and ore deposits the strike of systematic cleat in this region roughly parallels the inferred direction of lateral compressive stress during the alleghany orogeny the opposing nonsystematic cleat contains mostly authigenic nh 4 illite a clay that also occurs in the coal matrix all of these authigenic clay minerals formed during anthracitization t 200 c by replacement of kaolinite and quartz both of which formed during an earlier stage of coalification and are present in the joints and matrix of nearly all coal samples these distinct mineralogical structural relations are observed throughout the anthracite region and suggest that 1 mineralogical variations in the coal joints are related primarily to permeability variations that were controlled by the orientation of alleghanian stress fields 2 hydrothermal fluids passed through the systematic cleat during anthracitization and 3 hydrothermal alteration influenced diagenesis in this region hydrothermal alteration may be related to basin wide fluid migrations that were driven by alleghanian age uplift basinal fluid flow concentrated along permeable joints and detachment zones could have efficiently transported heat from depth and thereby increased the rate of coalification and decreased the postulated minimum depths at which anthracitization occurred perhaps 5km vs 6 10 km

metamorphism and uplift of alpine schist in the franz josef fox glacier area of the southern alps new zealand geothermometry and geobarometry of 10 garnet oligoclase zone schists in the franz josef fox glacier area southern alps new zealand give temperatures ranging from 415 to 625 c and pressures from 5 2 to 9 2 kbar indicating a t p array of about 50 c kbar and inferred peak temperature conditions over a c 15 km thick section at depths between c 20 and 34 km the present day distribution of the schist samples implies that only about one third of the original crustal section is now exposed the garnet oligoclase zone schists represent the deeper part of a metamorphosed and deformed accretionary complex that was associated with late palaeozoic early mesozoic subduction along the gondwana continental margin partial uplift c 0 2 m ma and erosion of the complex during jurassic cretaceous times rangitata uplift was synchronous with d2 deformation and recrystallization as recorded by the p t array cenozoic kaikoura uplift and exhumation of the schist since c 30 ma to form the southern alps was associated with oblique slip movement on the alpine fault the present day position and steep eastward dip of isograds and d2 structures suggest considerable clockwise rotation during uplift associated with ductile attenuation and tectonic thinning by over two thirds of the original schist sequence largely due to simple shear along schistosity planes as the schist generally shows only incipient greenschist facies retrograde recrystallization an apparently complete although contracted prograde mineral sequence has been preserved by rapid uplift 5 km ma of hot rock and the effects of limited shear heating near the alpine fault

how rivers react to large earthquakes evidence from central taiwan earthquakes and bedrock river incision are fundamental processes in the evolution of tectonically active landscapes yet little work has focused on understanding how a bedrock river responds to a single large earthquake data from the 1999 m w 7 6 chi chi earthquake in central taiwan show dramatic differences in river response that depend on the proximity to the rupture zone near the fault scarp vertical ground deformation intensifi es river incision on a time scale of years to decades while distal to the fault landslides induced by the earthquake mantle bedrock on the river bed with sediment impeding incision for decades to centuries as the material is evacuated this surprising spatial and temporal variability in bedrock incision caused by earthquakes has implications for the paleoseismic interpretation of bedrock terraces and for the evolution of tectonically active landscapes

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

transformation textures in post perovskite understanding mantle flow in the d layer of the earth 1 deformation and texture formation in mg fe sio3 post perovskite ppv is a potential explanation for the strong seismic anisotropy that is found in the d layer of the earth however different experimental approaches have resulted in different lattice preferred orientations lpo in deformed ppv that have led to ambiguity in the interpretation of deformation in the lowermost mantle here we show that deformation of the analogue substance cairo3 during a phase transformation from perovskite to ppv leads to a transformation texture that differs from the cairo3 ppv deformation texture but resembles the results from ppv deformation experiments in diamond anvil cells assuming material spreading parallel to the core mantle boundary our results predict a widespread shear wave splitting with fast horizontal s waves which is compatible with seismic studies downwelling material that undergoes a phase transformation may develop a transformation texture that would locally result in vertically polarized fast s waves

the dissolution kinetics of major sedimentary carbonate minerals abstract among the most important set of chemical reactions occurring under near earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals these minerals comprise about 20 of phanerozoic sedimentary rocks calcite and to a significantly lesser extent dolomite are the major carbonate minerals in sedimentary rocks in modern sediments aragonite and high magnesian calcites dominate in shallow water environments however calcite is by far the most abundant carbonate mineral in deep sea sediments an understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel co 2 on climate diagenesis of sediments and sedimentary rocks it also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs and the preservation of buildings and monuments constructed from limestone and marble in this paper we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions we will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments such complex topics are clearly worthy of review papers on their own merits calcite has been by far the most studied mineral over a wide range of conditions and solution compositions in recent years there has been a substantial shift in emphasis from measuring changes in solution composition to determine batch reaction rates to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy afm however there remain major challenges in integrating these two very different approaches a general theory of surface dissolution mechanisms currently lacking although see lasaga and luttge science 291 2001 2400 is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components studies of aragonite high magnesian calcites magnesite and dolomite dissolution kinetics are much more limited in number and scope than those for calcite and provide at best a rather rudimentary understanding of how these minerals are likely to behave in natural systems although the influences of a limited number of reaction inhibitors have been studied probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of foreign ions and organic matter on the near equilibrium dissolution kinetics of carbonate minerals

early cenozoic glaciation antarctic weathering and seawater 87sr 86sr is there a link abstract stable and radiogenic isotopic and sedimentological data from sub antarctic deep sea sediment cores reveal a temporal link between changes in seawater 87 sr 86 sr ratios and major episodes of late eocene early oligocene climate change the 87 sr 86 sr records show two major inflections one at 38 39 ma near the middle late eocene boundary followed by another at 33 4 ma similarly the oxygen isotope ice rafted debris and clay assemblage records indicate two important climatic events the appearance of alpine glaciers and or small ice sheets on antarctica in the late eocene at 38 39 ma followed by a rapid transition to larger and more permanent temperate ice sheets in the early oligocene at 33 4 ma moreover during the early oligocene 30 33 ma three to four inferred peaks in glacial activity appear to coincide with subtle steps in the 87 sr 86 sr record the coupled variations in climate and seawater sr isotope ratios during the eocene oligocene imply a strong causal link between the two either changes in climate directly influenced patterns of continental weathering and hence seawater chemistry and or a tectonic event e g uplift as reflected in weathering and seawater chemistry triggered relatively abrupt changes in global climate

millennial lag times in the himalayan sediment routing system abstract any understanding of sediment routing from mountain belts to their forelands and offshore sinks remains incomplete without estimates of intermediate storage that decisively buffers sediment yields from erosion rates attenuates water and sediment fluxes and protects underlying bedrock from incision we quantify for the first time the sediment stored in 38 000 mainly postglacial himalayan valley fills based on an empirical volume area scaling of valley fill outlines automatically extracted from digital topographic data the estimated total volume of 690 242 452 km 3 is mostly contained in few large valley fills 1 km 3 while catastrophic mass wasting adds another 177 31 km 3 sediment storage volumes are highly disparate along the strike of the orogen much of the himalaya s stock of sediment is sequestered in glacially scoured valleys that provide accommodation space for 44 of the total volume upstream of the rapidly exhuming and incising syntaxes conversely the step like long wave topography of the central himalayas limits glacier extent and thus any significant glacier derived storage of sediment away from tectonic basins we show that exclusive removal of himalayan valley fills could nourish contemporary sediment flux from the indus and brahmaputra basins for 1 kyr though individual fills may attain residence times of 100 kyr these millennial lag times in the himalayan sediment routing system may sufficiently buffer signals of short term seismic as well as climatic disturbances thus complicating simple correlation and interpretation of sedimentary archives from the himalayan orogen its foreland and its submarine fan systems