geochemical modeling of bacterially induced mineralization of schwertmannite and jarosite in sulfuric acid spring water mineralogy and geochemistry of a sulfuric acid spring water with a ph of 3 37 to 2 89 were investigated to verify the formation processes of iron minerals and the effects of bacteria on their formation to estimate the solubility of schwertmannite experimental dissolution in 10 0 mm h2so4 was conducted and this solubility data was used for geochemical modeling experimental incubation of the spring water containing bacteria was also performed and compared with a simulated abiotic system to evaluate the role of bacteria in the mineral formation the spring water seeps through cracks of hydrothermally altered andesitic rocks containing pyrite and precipitates schwertmannite and jarosite schwertmannite appears as a film like thin layer floating on the water surface and composed of aggregates of spherical particles with diameters of 1 to 5 m jarosite is produced as a precipitate on submerged rock surfaces the precipitate contains well crystallized jarosite spheres 5 to 10 m in diameter some ellipsoidal to rod shaped bacteria covered or decorated by poorly ordered iron minerals are also present in close association with the schwertmannite spheres results of the experimental incubation demonstrate that the oxidation rates of fe2 are 5 3 103 to 7 2 103 times greater than those of the simulated abiotic system suggesting that the formation of the iron minerals is promoted by bacterial oxidation of fe2 the dissolution experiment indicates that the solubility product of the schwertmannite having an average chemical composition of fe8o8 oh 5 9 so4 1 05 is approximately log k s 7 06 0 09 using this data geochemical modeling reveals that the spring water is supersaturated with respect to schwertmannite and also goethite and jarosite but undersaturated with respect to ferrihydrite additionally it is confirmed that the bulk solution chemistry deviates slightly into the stability field of goethite rather than jarosite this suggests that the aquatic environments in contact with the rock surfaces may be more acidic and or enriched in so2 4 relative to the bulk solution which may eventually lead to the formation of jarosite instead of goethite

relic magma chamber structures preserved within the mesozoic north atlantic crust the north atlantic transect seismic reflection data collected southwest of bermuda have been reinterpreted following post stack migration and reveal two major intracrustal reflections the shallower of these two events located 1 s below the igneous basement is a subhorizontal undulating surface that in some places is continuous for as much as 10 km on the basis of its position within the section and its laterally discontinuous nature we believe that this upper crustal reflection corresponds to the intermittently sharp contact between the sheeted dikes and the underlying isotropic gabbro a second set of lower crustal reflections dipping 20 40 eastward is also prominent on the migrated profile and terminates downdip against the subhorizontal reflection moho several lines of evidence argue against these features being either artifacts or out of the plane events instead their presence may be ascribed either to crustal penetrating fault zones or to mafic ultramafic cumulate layers frozen into the oceanic crust at the time of formation at the paleo spreading center because of the laminated character of these events and their typical occurrence within 1 0 to 1 5 s of the reflection moho we prefer a compositional versus a structural interpretation for their origin the gradual thinning in the crust approaching the fracture zones is shown to be more complex than was originally inferred although the interpretation that the crust gradually thins toward fracture zones may still apply in a few localities significant departures are recognized elsewhere similarly the improved image on the migrated profile documents an increase in complexity across the localized region directly surrounding the blake spur fracture zone an interpretation advocating crustal thickening in this narrow zone is proposed as an alternative to the crustal thinning model of mutter and others

microearthquakes beneath median valley of mid atlantic ridge near 23 n tomography and tectonics data from a microearthquake experiment in the median valley of the mid atlantic ridge near 23 n in 1982 are used to measure earthquake source parameters to determine the laterally heterogeneous seismic velocity structure across the inner floor and to develop a kinematic tectonic model for this portion of the median valley fifty three microearthquakes occurred over a 10 day period beneath the median valley inner floor and eastern rift mountains twenty of 23 well located inner floor epicenters define a line of activity about 17 km long having a strike of n25 e and located near an along axis depression some 300 400 m deeper than surrounding regions earthquakes with well resolved hypocenters generally have focal depths of 4 8 km beneath the seafloor of both the inner floor and the rift mountains the hypocentral locations are robust with respect to plausible lateral variations in seismic velocity structure composite fault plane solutions for inner floor events indicate normal faulting on planes dipping at angles near 45 normal faulting mechanisms although poorly constrained are also indicated for the rift mountain microearthquakes seismic moments approximate fault dimensions and average stress drops for the largest events recorded are 1019 1020 dyn cm 200 400 m and 1 70 bars respectively a twodimensional tomographic inversion of p wave travel time residuals from microearthquakes and local shots indicates a well resolved lateral heterogeneity in crustal velocity structure across the median valley inner floor p wave velocities at 1 5 km depth within a zone less than 10 km wide beneath the central inner floor are lower by several percent than in surrounding regions the most likely explanation for the low velocities is that the region is the site of the most recent local magmatic injection and remains pervasively fractured as a result of rapid hydrothermal quenching of the newly emplaced crustal column by this view the seismic velocity structure at the ridge axis evolves probably by the sealing of cracks and pores within the first few hundred thousand years of crustal accretion consideration of the detailed sea beam bathymetry in this region of the inner floor the characteristics of large earthquakes that the region has experienced during the past 25 years and the results of the microearthquake and tomography analysis suggests that this section of the median valley has been undergoing continued horizontal extension and block faulting without significant crustal injection of magma for at least the past 104 years

along axis variability in crustal accretion at the mid atlantic ridge results from the ocean study the ocean experiment is an integrated geophysical study of a region of the cape verde abyssal plain that formed at 140 ma deep seismic reflection and ocean bottom hydrophone obh refraction data were acquired along lines parallel and perpendicular to the paleoridge axis trend identified from a detailed magnetic anomaly survey the igneous basement is overlain by about 1 3 km of sediment which enables improved imaging of intracrustal structure beyond that possible near the mid atlantic ridge axis we describe the results of a 150 km long profile oriented parallel to magnetic anomalies m15 and m16 along which deep seismic reflection data collected by the british institutions reflection profiling syndicate are complemented by refraction data constrained by four obhs the line spans an entire spreading segment between two fracture zones the northern of which has an offset of 40 km and the other central has an offset of only 10 km away from the fracture zones the mean igneous crustal thickness is 7 2 km near both fracture zones thinning of up to 4 km is observed giving a mean igneous crustal thickness over the whole segment of approximately 6 5 km differences are seen between the two fracture zones in their seismic velocity structure in the associated basement topography and in the presence of a strong reflection extending into the mantle beneath the northern fracture zone the boundary between oceanic layers 2 and 3 correlates with variably coherent normal incidence reflections and a change in the character of the reflectivity a number of planar reflections up to 10 km in length are present within the middle and lower crust dipping outward from beneath low amplitude basement highs at 15 these appear to be present only within layer 3 the moho has several expressions in the reflection data including isolated reflection events a local increase in reflected amplitudes and a downward decrease in coherent reflections at the center of the segment there is a zone at the base of the crust within which both high and low velocity materials are present this zone shows an enhanced level of discontinuous normal incidence reflectivity and may represent an initial fractionation event as melt was emplaced at the spreading ridge

multicomponent magnetizations from the mississippian mauch chunk formation of the central appalachians and their tectonic implications previous paleomagnetic study of mississippian red beds of the mauch chunk formation from the central appalachians reported shallow inclination directions a positive fold test was obtained after thermal demagnetization typically to only 550 c the near equatorial position for north america indicated by these results has been used to support the idea of a circa 15 latitudinal tectonic offset of the acadia displaced terrain in the northern appalachians the present study of 153 samples from 29 sites occupied in the mauch chunk formation of eastern and southern pennsylvania reveals multicomponent magnetizations a characteristic component declination d 161 0 inclination i 27 8 alpha95 a95 7 9 with unblocking temperatures usually concentrated above 650 c and with dual polarity 10 sites normal 13 sites reversed is isolated in 23 sites and passes a fold test at the 99 confidence level it is interpreted as an early acquired hematitic detrital or chemical magnetization of pre alleghanian orogeny and pre kiaman reverse polarity interval age a southern hemisphere paleolatitude of 15 for the sampling area is indicated another component has generally lower unblocking temperatures which however can extend up to 650 c or more and therefore is also likely to be carried by hematite this secondary magnetization d 170 6 i 5 3 a95 5 0 isolated in 25 sites is of uniform reverse polarity and application of fold tests suggests that it is of synfolding origin a near equatorial paleolatitude 3 n at the time of acquisition is obtained consistent with permo carboniferous kiaman directions from north america incomplete removal of the secondary component can explain the previous results from the mauch chunk comparison of the present paleomagnetic results with those from similar age rocks in the canadian maritimes does not support a latitudinal offset of acadia with respect to interior north america in the early carboniferous in fact according to these and other paleomagnetic data thought to be representative of this age the atlantic bordering continents already were near to a pangea configuration the alleghanian and particularly the hercynian orogenies therefore may not be associated with the closure of a large latitudinal ocean later in the carboniferous and permian alleghanian deformation however may have resulted in the partial bending of the pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

influence of rice cultivation on the abundance and fractionation of fe mn zn cu and al in acid sulfate paddy soils in the pearl river delta abstract many of the areas dominated by acid sulfate as soils in southern china have been reclaimed for rice cultivation and represent an important source of agricultural production and food security for the local population in this study we examined the abundance and partitioning of fe mn zn cu and al in both rice paddy fields and uncultivated fields by using a six step sequential extraction procedure rice cultivation significantly reduced acidity levels at soil depths of 0 100 cm but acidity at depths of 100 140 cm increased significantly a substantial loss of mn in the oxide and acidified soil layer 0 100 cm compared to the underlying parent material was observed but there were few changes in the concentrations of fe and zn throughout the soil profile however both cu and al were substantially enriched in the superficial soil 0 40 cm compared to the underlying subsoil 40 140 cm in general leaching of fe mn and al was higher in the paddy fields because of intensified irrigation and flood conditions whereas accumulation of cu mainly in the form of acid soluble and crystalline iron oxide cu was higher in the paddy fields than in the uncultivated fields the most marked declines in metal concentrations occurred in the labile and acid soluble fractions as a result of rice cultivation which increased leaching of the readily mobilized labile and acid soluble fractions of heavy metals in these soils

granitic plutonism as an indicator of microplates in the palaeozoic of central and eastern maine abstract oxygen and strontium isotope ratios have been used to characterize source regions for granitic magmas for a transect across the northern appalachian orogen in central and eastern maine the northwestern plutons katahdin and seboeis have 18 o values of 10 3 13 3 and initial 87 sr 86 sr ratios of 0 7083 and 0 7066 respectively the central plutons bottle lake and center pond have lower 18 o values 8 2 9 9 and initial 87 sr 86 sr ratios 0 7043 0 7055 the southeastern plutons lucerne and deblois have 18 o values 9 0 11 0 but initial 87 sr 86 sr ratios 0 7077 and 0 7041 respectively which are intermediate between the northwestern and central plutons source models derived from these results and other petrological and geochemical data reflect the juxtaposition of discrete source regions by transcurrent faulting which may be related to oblique plate motions this model illustrates the importance of microplate accretion in the palaeozoic history of the northern appalachian orogen

paleomagnetic study of devonian rocks from ste cecile st sebastien region quebec appalachians three devonian rock units were collected for paleomagnetic study from the ste cecile st sebastien region located in the gaspe connecticut valley synclinorium of quebec appalachians 15 sites 48 samples from the metasediments subgreenschist facies siltstones sandstones of the compton formation early middle to late early devonian age based on fossil plants which were tightly folded during middle devonian acadian orogeny 14 sites 61 samples from the ste cecile st sebastien granitic body 362 m y k ar age which intruded the metasediments 14 sites 62 samples from the hornfels created subsequent to the emplacement of the intrusive detailed thermal cleaning of the metasediments yielded a mean remanence direction characterized by linear vector trajectories after tilt correction at d 209 i 20 k 30 95 7 2 with unblocking temperature spectrum 300 550 c carried probably by magnetite the predeformational origin of this remanence is tested at 99 confidence level as well as antipodal normal and reverse polarity directions the corresponding paleomagnetic pole ms falls at 28 n 77 e dp dm 6 11 in agreement with the recently reported poles which are mostly early devonian in age and derived from the southeastern margin of the presumed proto atlantic ocean af demagnetization of granites resulted in a univectorial mean remanence at 1 d 332 i 39 k 31 for n 5 sites in fine grained granite fg unit 2 d 313 i 25 k 19 for n 9 sites in medium grained granite mg unit and 3 d 319 i 30 k 17 for all the total n 14 granite g sites af demagnetization of hornfels revealed a post intrusive mean remanence direction hf at d 346 i 22 k 8 for n 14 sites the individual site mean remanence directions with coercivity spectra 10 60 mt from both granites and hornfels suffer from a large declination spread of about 60 but the confidence ovals for the fg and hf remanences overlap this indicates that the fg and hf remanences are indistinguishable from each other and therefore are proximal in time and probably originated during middle to late devonian period interpretation of this kind is speculative in the absence of a convincing evidence for a two fg younger than mg or three phase intrusive history of the pluton since the pole positions of g 18 n 150 e mg 18 n 158 e fg 18 n 137 e and hf 32 n 125 e spread over 40 in longitude these data cannot confirm or negate the possibility of a mid paleozoic transcurrent motion proposed for northern appalachians we regard only the pole ms with probable late early or early middle devonian age as reliable for the apparent polar path construction

kinematic history of the narragansett basin massachusetts and rhode island constraints on late paleozoic plate reconstructions the formation of the narragansett basin of rhode island and massachusetts and the polyphase deformation geometry of the pennsylvanian age basin sediments can be explained by collision and strike slip interactions between an avalonian microcontinent the european north american plate and the african plate during the late paleozoic sinistral movement between an avalonian microcontinent and the european north american plate resulted in formation of pull apart basins subsequently africa moved toward north america along an east west trending dextral megashear zone and collided with the eastern margin of southern north america the narragansett basin is located on the avalonian microcontinent near the suture with the north american continent and in the transition zone between the megashear and the collision tectonic regimes the basin shape stratigraphy and sedimentary relationships can be explained by the coalescence of two composite grabens which formed at different times the thicker northern graben is only affected by one deformation whereas the southern graben shows evidence of four distinct phases of postrifting deformation the first two coaxial folding deformations of the basin sediments are attributed to the closure of the basin complex during collision of africa and north america the third and fourth deformations are interpreted as sinistral r riedal and dextral shears respectively associated with the east west trending megashear system a prograde barrovian metamorphic front started in the western portion of the southern graben slightly after the first deformation and migrated northward and eastward where it is synchronous with the second deformation

subsidence in late paleozoic basins in the northern appalachians during the interval between continental collision in the devonian and continental breakup in the triassic the northern appalachians became the site of a wide plate boundary zone of dominantly right lateral strike slip as is typical of intracontinental transforms tectonism was both diachronous and rapidly variable along strike through regimes of pure strike slip transpressional deformation and rapid subsidence of extensional basins up to 9 km of mainly nonmarine clastic sediments accumulated in these local depocenters which subsided episodically in two stages 1 an initial phase of stretching and thinning of the lithosphere when subsidence was rapid fault controlled and often accompanied by volcanism and 2 a subsequent phase of gradual thermal subsidence during which the depositional basins expanded to bury the earlier border faults and progressively younger sedimentary units onlapped basement the largest depocenter the magdalen basin opened as a pull apart between strike slip faults in newfoundland and new brunswick from late devonian to early carboniferous subsequent thermal subsidence affected a large area during medial and late carboniferous a phenomenon that is well recorded to the north and west where no later tectonism occurred in areas to the south and east of the basin strike slip on other faults continued into the time of thermal subsidence introducing complications such as localized transpressional deformation and rapid subsidence in smaller pull aparts

calculating the balance between atmospheric co2 drawdown and organic carbon oxidation in subglacial hydrochemical systems in order to constrain co2 fluxes from biogeochemical processes in subglacial environments we model the evolution of ph and alkalinity over a range of subglacial weathering conditions we show that subglacial waters reach or exceed atmospheric pco2 levels when atmospheric gases are able to partially access the subglacial environment subsequently closed system oxidation of sulfides is capable of producing pco2 levels well in excess of atmosphere levels without any input from the decay of organic matter we compared this model to published ph and alkalinity measurements from 21 glaciers and ice sheets most subglacial waters are near atmospheric pco2 values the assumption of an initial period of open system weathering requires substantial organic carbon oxidation in only 4 of the 21 analyzed ice bodies if the subglacial environment is assumed to be closed from any input of atmospheric gas large organic carbon inputs are required in nearly all cases these closed system assumptions imply that order of 10 g m 2 y 1 of organic carbon are removed from a typical subglacial environment a rate too high to represent soil carbon built up over previous interglacial periods and far in excess of fluxes of surface deposited organic carbon partial open system input of atmospheric gases is therefore likely in most subglacial environments the decay of organic carbon is still important to subglacial inorganic chemistry where substantial reserves of ancient organic carbon are found in bedrock in glaciers and ice sheets on silicate bedrock substantial long term drawdown of atmospheric co2 occurs

long term denudation of ocean crust in the central north atlantic ocean near bottom sidescan bathymetric and visual observations of fault scarps in 4 24 ma sea floor show that basaltic ocean crust undergoes extensive denudation that creates wide complex scarp zones most denudation is caused by mass wasting probably accompanied by abrasion by disaggregated debris in 11 24 ma crust trellis drainage patterns are formed by deep cross scarp canyons and intersecting scarp parallel gullies that appear to follow weak zones of fracturing and intracrustal weathering until stabilized e g by sediment burial fault scarps will continue to degrade with time yielding increasingly distorted representations of apparent fault geometry in remotely sensed morphological data

self consistent rolling hinge model for the evolution of large offset low angle normal faults the nature of the physical processes responsible for the formation of continental and oceanic metamorphic core complexes is widely debated the controversy focuses primarily on whether the low angle normal faults observed in these environments formed and slipped at low angles or were rotated from an original high angle orientation after large offsets we describe a self consistent numerical model for the extension of a brittle layer that can spontaneously produce normal fault structures in our formulation a fault or faults form because strength is locally reduced with increasing strain if the reduction in fault strength is 10 of the total strength of the layer then faults lock after an offset smaller than the layer thickness and new faults form larger strength reduction leads to single faults that continue to slip no matter how large the fault offset if the strength reduction occurs by the loss of cohesion then we see the unlimited offset faults for layers 11 22 km thick for reasonable values of cohesion the key result of this study is that structures very similar to those observed in both oceanic and continental core complexes are produced by rotation of the inactive part of the model fault after very large offset

characteristics and evolution of the segmentation of the mid atlantic ridge between 20 n and 24 n during the last 10 million years abstract high resolution bathymetry and geophysical data collected along the slow spreading axis and flanks of the mid atlantic ridge between 20 n and 24 n reveal the characteristics and history of different wavelengths of segmentation during the last 10 m y the bathymetric data exhibit a morphotectonic pattern dominated by ridge normal and oblique bathymetric lows that partition the ridge flanks into rhomb shaped areas of relatively high elevation at least four different types of oblique bathymetric lows have been identified which represent the off axis traces of axial discontinuities and suggest a complex and ongoing evolution of ridge axis segmentation one group of oblique structures is represented by two deep ridge normal depressions with typical fracture zone characteristics that are connected to the present active transform by oblique depressions near the ridge axis these oblique traces correspond to the southward shift of axial discontinuities associated with the propagation of the ridge axis while maintaining a constant offset of the latter two other types of oblique structures correspond to elongate bathymetric lows and oblique alignments of ridge parallel bathymetric lows symmetric about the ridge axis both types of oblique structures frequently change their orientation from normal to subparallel to the ridge axis and appear to merge and diverge off axis these oblique depressions are characterized by positive filtered mantle bouguer anomalies high magnetizations complex magnetic anomaly patterns and possible exposure of mantle lithologies the ridge segments defined by these oblique depressions lengthen or shorten along the ridge axis with propagation rates varying from 0 to 25 km m y 1 the last and smallest discontinuities observed in this area correspond to small ridge axis offsets and off axis traces identified by alignments of the terminations of abutting abyssal hills the ridge flank morphotectonic patterns produced by the evolution of these elementary segments of accretion may represent temporally variable upwelling volumes of melt the centres of the rhomb shaped areas correspond to maximum crust production and thin lithosphere and the discontinuities correspond to a thick lithosphere with very thin crust and possible outcrops of peridotites we propose a model which accounts for the punctuated injection of magma and the evolution of elementary segments of accretion over periods of several million years

biogeochemistry of glacial landscape systems abstractglaciers affect biogeochemistry of landscapes through their sediments glacial erosion rates are high and the sediments produced are distinctively fine grained hence glaciers can be thought of as producers of mineral surface area although this mineral surface area is highly reactive temperature limits chemical weathering fluxes from glaciers and their surroundings more significant effects may be associated with silt deposited in loess and on continental margins thick deposits in both settings contribute to carbon cycling through both silicate weathering and organic carbon burial the impact of glaciers on biogeochemical cycles will be long lasting as the legacy of glacial erosion processes continues as long as sediment yields are elevated

tectonics of the acadian orogeny in new england and adjacent canada paleogeographic analysis of post taconian rocks in new england and adjacent parts of canada has revealed the existence of two volcanic arcs which shut off at the time of the acadian orogeny one was built on arc basement previously accreted to north america during the taconic orogeny the other on precambrian continental basement of avalonia in the intervening merrimack fredericton trough metamorphosed and poly deformed turbidites and black shales record deep water conditions in silurian following mckerrow and ziegler 1971 this tract is interpreted as the site of an ocean which closed in siluro devonian by simultaneous subduction beneath both continental margins in the molucca sea in indonesia a comparable arc arc collision is in an early stage of development moore et al 1982 suggested that an accretionary prism built against one arc is overthrusting its counterpart which developed on the other side of the ocean an identical geometry with an avalonian accretionary prism overriding the conve

petrochemistry and tectonic significance of carboniferous volcanic rocks in new brunswick carboniferous volcanic rocks from the new brunswick platform in the maritimes basin are divided into three age groups late tournaisian to early visean volcanic rocks are tholeiitic basalts and andesites that in southern new brunswick are inter bedded with abundant calc alkalic rhyolite late visean to namurian volcanic rocks consist of an interbedded sequence of alkalic basalts and trachyandesites late westphalian volcanic rocks change in composition up section from trachyte to peralkalic rhyolite all three age groups display petrochemical features indicative of an intraplate tectonic setting the volcanic geochemistry is consistent with the development of the maritimes basin either as a failed rift formed along the margin of a late paleozoic ocean or as a rhomb graben formed within a transcurrent zone the former model is preferred the change in basaltic composition from tholeiitic to alkalic apparently coincided with a decrease in rate of extension between the tournaisian and namurian local peral

internal structure of a spreading segment of mesozoic oceanic crust we define the crustal architecture and internal structure of a 70 km long segment of mesozoic oceanic crust combined reflection and wide angle refraction profiles show the relations between reflectivity and seismic velocity within the crust the crust thins by 4 km from the segment center to the bounding fracture zones a 2 km thick lens at the base of the crust in the segment center exhibits enhanced reflectivity in the otherwise mainly opaque lower crust which coincides with abnormally high seismic velocities of 7 5 km s we attribute these characteristics to the presence of a melt injection region the reflection profiles in the 4 km spaced grid show that there are two distinct approximately orthogonal sets of dipping reflectors within the crust ridge normal reflectors dip at typically 25 in both directions the majority dip west toward the spreading center and their common association with basement steps suggests that they represent normal faults they terminate above or near the base of the crust ridge parallel reflectors are shallower dipping averaging 15 and planar many are restricted to the middle crust and we speculate that they represent magmatic rather than tectonic features a prominent dipping reflector beneath a fracture zone cuts at 20 into the upper mantle similar reflectors are found elsewhere beneath fracture zones in the north atlantic and may be caused by thermal stresses generated as the lithosphere cooled and moved away from the spreading axis

influence of glacial sediments on the chemical quality of surface water in the ulta valley cordillera blanca peru the rio santa ancash peru and its tributaries are an essential source of drinking and irrigation water its discharge relies on glacial meltwater which is diminishing due to the rapid decrease in glacial extent as a secondary effect water quality can be compromised e g ph 3 and high concentrations of so42 and trace metals although this has previously been attributed to pyrite rich chicama bedrock exposed by glacial retreat little is known about the occurrence of chicama fragments in quaternary glacial sediments and its influence on water quality this research aims at elucidating this effect by relating observed changes in water quality in streams to presence and chemical composition of morainic ridges in the quebrada ulta in the rio santa basin changes in water quality before and after contact with a morainic ridge were assessed using carbonate alkalinity titration ion analysis and elemental analysis moreover relative contributions of glacial meltwater and precipitation were assessed qualitatively using stable water isotope analysis we used a novel method to explain the provenance of contaminated glacial sediments using a reconstruction of their source area the mineralogical composition of a morainic ridge was strongly related to the geology of the source area indicating that mineralogical composition of tills may be predicted using this technique effects of glacial sediments in morainic ridges on water quality were minimal but depended on their mineralogical composition morainic ridges with a high content of chicama shales tended to increase solute loads of mg and so42 additionally isotope signatures suggest that during the dry season moraines may act as reservoirs for precipitation derived shallow groundwater clear trends in water quality were observed along the whole flow path of the rio buin which could potentially be explained by increased groundwater contribution downstream and shifts in dominant weathering mechanisms future research should focus on disentangling these various drivers of water quality in glacial catchments

paleomagnetism of lower carboniferous tournaisian to namurian volcanic rocks of new brunswick canada and its tectonic implications as part of a major study of the northern appalachians the paleomagnetism of well dated lower carboniferous volcanic flows is described the tectonostratigraphic zones of new brunswick and the distribution of paleomagnetic sampling sites are shown in figure 1 detailed alternating field and thermal experiments performed on the new brunswick volcanic rocks indicate that they are characterized by two different mean directions of magnetization in the 20 50 mt coercivity and 400 600 c temperature spectra ese d 160 i 15 k 9 n 11 sites and w d 264 i 34 k 9 n 3 sites for the formation in situ and ese d 158 i 16 k 8 5 and w d 267 i 38 k 10 after tilt correction after exclusion of site c 7 an altered acidic tuf the predominent cleaned ese component is d 159 i 12 k 9 the anti parallel direction is d 166 i ll k 25 and the corresponding palepole position 37 n 131 e it is not significantly different from early carboniferous poles from the stable north american craton

brittle faulting in the canadian appalachians and the interpretation of reflection seismic data abstract brittle faults in the canadian appalachians mostly late devonian or younger in age are divided into two groups on the basis of their movement vectors a strike slip group and a dip slip group the two groups are subdivided on the basis of orientation and sense of movement they are interpreted in terms of palaeozoic transpression and mesozoic extension during atlantic opening the palaeozoic faults comprise strike slip and reverse faults which were active in devono carboniferous times mesozoic strike slip faults are interpreted as transfer faults and they are coupled with normal faults many of which developed by reactivation of earlier reverse faults or steeply dipping surfaces including bedding and earlier foliations together these mesozoic faults comprise an adequate mechanism for crustal extension perpendicular to the orogen evidence for listric normal faults is rare in the older rocks of the orogen and it is suggested that this is due to the adequacy of the deformation mechanisms afforded by the pre existing planes of weakness the data presented demonstrate clearly that geological structures are commonly repeated at all scales from outcrop to regional following this principle prominent shallowly dipping reflectors imaged in the lithoprobe east seismic profiles are interpreted as large scale representatives of the palaeozoic reverse faults seen in outcrop that were reactivated as normal faults during atlantic opening it is suggested that reverse faulting is to be expected as a deformation mechanism in general in the late stages of a collisional orogen we draw attention to the importance of the mesozoic faults in modifying the attitude of earlier surfaces such a bedding foliations and faults

surface water quality in a sulfide mineral rich arid zone in north central chile learning from a complex past addressing an uncertain future this study presents an analysis of up to 30 years of hydrological variables and selected water quality parameters ph so4 fe cu as in the upper area of the elqui river basin in north central chile a correlation analysis determined statistically significant positive relationship for so4 cu fe as and fe cu in terms of historical behaviour no statistically significant trends were detected for precipitation or temperature in contrast for flow there is an overall decreasing pattern for the entire area of study although only in one case this trend was statistically significant along with the fore mentioned analysis a characterization of the flow water quality relationships is considered for the time period analyzed although erratic behaviours were confirmed a negative i e inverse flow concentration relationship was identified for so4 a positive i e direct relationship for fe and undefined relationships for as and cu were obtained from these analyses and based on previous studies on projections regarding climate change for the andean region and in particular for the upper elqui zone an estimation of the possible effects of the change in water regimes on water quality in the area of study is developed it is likely that a decrease in surface flow as a consequence of climate change could translate into improvements in water quality in terms of fe and eventually as and cu but into an impairment in the case of so4 in any case this is a complex situation that demands special attention in the face of industrial activities that could be developed in tributaries like the claro river which currently play an important role in depurating or diluting contaminants in the waters of the elqui river finally it should be noted that this study addresses an issue that goes beyond the local interest and could be used as a reference to compare other transitional environments containing sulphide ores or areas of hydrothermal alterations which are considered to be highly vulnerable to climate change and variability this article is protected by copyright all rights reserved

monazite chemical weathering rare earth element behavior and paleoglaciohydrology since the last glacial maximum for the loch vale watershed colorado usa rare earth element ree release from weathering of accessory monazite ree po4 since the last glacial maximum at 18 1 ka was investigated in sediment recovered from an outlet lake within the glaciated loch vale watershed colorado usa labile rees in the sediments reveal monazite weathering increased during the younger dryas chronozone ydc 13 2 to 11 1 ka when alpine glaciers advanced as climate cooled and bedrock comminution increased monazite dissolution peaked at approximately the pleistocene holocene transition 10 5 ka during the holocene ree concentrations decline reflecting a reduction in monazite weathering the ree cerium ce may occur as trivalent or tetravalent cations and the ce anomaly ce n ce n in sediment permits interpretations of paleoredox conditions the ce n ce n decreases from 18 1 ka to the pleistocene holocene boundary initially oxidizing conditions within the watershed increased because of enlargement of the proglacial area as the ice retreated at the onset of the ydc oxidation further escalated in response to enhanced chemical weathering associated with glacial advance a more stable holocene climate and landscape resulted in relatively small changes in ce n ce n values slightly decreasing ce n ce n values over the last several hundred years are consistent with present day stream water values and may reflect the onset of present day hydrobiogeochemical conditions

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

segmentation and crustal structure of the western mid atlantic ridge flank 25 25 27 10 n and 0 29 m y we conducted a detailed geological geophysical survey of the west flank of the mid atlantic ridge between 25 25 n and 27 10 n and from the ridge axis out to 29 ma crust acquiring hydrosweep multibeam bathymetry hawaii mr1 sidescan sonar imagery gravity magnetics and single channel seismic reflection profiles the survey covered all or part of nine spreading segments bounded by mostly nontransform right stepping discontinuities which are subparallel to flow lines but which migrated independently of one another some discontinuities alternated between small right and left stepping offsets or exhibited zero offset for up to 3 4 m y despite these changes the spreading segments have been long lived and extend 20 m y or more across isochrons a large shift 9 in relative plate motion about 24 22 ma caused significant changes in segmentation pattern the nature of this plate boundary response together with the persistence of segments through periods of zero offset at their bounding discontinuities suggest that the position and longevity of segments are controlled primarily by the subaxial position of buoyant mantle diapirs or focused zones of rising melt within segments there are distinct differences in seafloor depth morphology residual mantle bouguer gravity anomaly and apparent crustal thickness between inside corner and outside corner crust this demands fundamentally asymmetric crustal accretion and extension across the ridge axis which we attribute to low angle detachment faulting near segment ends cyclic variations in residual gravity over the crossisochron run of segments also suggest crustal thickness changes of at least 1 2 km every 2 3 m y these are interpreted to be caused by episodes of magmatic versus relatively amagmatic extension controlled by retention and quasiperiodic release of melt from the upwelling mantle detachment faulting appears to be especially effective in exhuming lower crust to upper mantle at inside corners during relatively amagmatic episodes creating crustal domes analogous to turtleback metamorphic core complexes that are formed by low angle detachment faulting in subaerial extensional environments

minor and trace elements as indicators of solute provenance and flow routing in a subglacial hydrological system mitchell a c brown g h fuge r 2006 minor and trace elements as indicators of solute provenance and flow routing in a subglacial hydrological system hydrological processes 20 4 877 897 sponsorship university of wales aberystwyth studentship am university of wales aberystwyth research grants 56 95 and 36 96 ghb and rf and nerc grant no gr3 11216

sorption of trace metals to an aluminum precipitate in a stream receiving acid rock drainage snake river summit county colorado the quality of water in streams that are contaminated by acid drainage from mines and from the weathering of mineralized rocks improves as the water flows downstream the purpose of this study was to investigate the geochemical processes that occur in one such stream and to determine the fate of the trace metals that are removed from the water the stream chosen for this purpose was the snake river summit county colorado which is affected by natural acid rock drainage ard containing so4 al fe and various trace elements such as zn cu pb ni and others most of the fe in the snake river is removed from solution by the oxidation of fe2 to fe3 and the subsequent precipitation of fe oxyhydroxides that form a massive ferricrete deposit near the springs that feed the river further downstream the snake river ph 3 0 mixes with water from deer creek ph 7 0 thereby increasing its ph to 6 3 and causing so4 rich precipitates of al oxyhydroxide to form the precipitates and associated organic c complexes sorb trace metals from the water and thus have high concentrations of certain elements including zn 540 11 400 ppm cu 34 221 ppm pb 90 340 ppm and ni 11 197 ppm the concentrations of these elements in the precipitates that coat the streambed rise steeply in the zone of mixing and then decline downstream the trace element concentrations of the water in the mixing zone at the confluence with deer creek decrease by 75 or more and are up to 3 orders of magnitude lower than those of the precipitates sorption curves for zn cu pb ni and so4 were derived by stepwise neutralization of a sample of snake river water collected above the confluence with deer creek and indicate that the trace metals are sorbed preferentially with increasing ph in the general order pb cu zn and ni sulfate is removed between ph 4 and 5 to form an al hydroxysulfate and or by sorption to microcrystalline gibbsite the sorption data determined from the neutralization experiment were used to account for the downstream decrease of trace metal concentrations in the precipitates the results of this study demonstrate that the partitioning of trace metals in the snake river is not only a function of ph but also depends on the progressive removal of trace metals as the water of the snake river flows through its confluence with deer creek the chemical composition of the water also determines what compounds precipitate with increasing ph

tropical glacier meltwater contribution to stream discharge a case study in the cordillera blanca peru original abstract discharge measurements climate observations and hydrochemical samples gathered monthly 1998 99 in the yanamarey and uruashraju glacier fed catchments of the cordillera blanca peru permit an analysis of the glacier meltwater contribution to stream flow these glacier catchments feed the rio santa which discharges into the pacific ocean based on a water balance computation glacier melt contributes an estimated 35 of the average discharge from the catchments for comparison a volumetric end member mixing model of oxygen isotopes shows glacier melt contributes 30 45 to the total annual discharge based on stream geochemistry discharge from the yanamarey glacier catchment provides 30 of the annual volume discharged from the querococha watershed which is 10 glacierized by analogy the larger rio santa watershed also 10 glacierized receives at least 12 of its annual discharge from melting glacier ice tributary watersheds to the rio santa with larger fractions of glacier cover have less variable runoff and enhanced discharge demonstrating that the glaciers effectively buffer stream discharge seasonally with continued glacier melting stream flow will likely become more variable and there will be less dry season runoff

seismic structure of 15 ma oceanic crust formed at an ultrafast spreading east pacific rise evidence for kilometer scale fracturing from dipping reflectors 1 a grid of seismic reflection data from 15 ma cocos plate offers an unprecedented view of the structure of mature oceanic crust formed at an ultrafast spreading 200 mm yr full rate east pacific rise epr the data contain an unexpected quantity of bright reflectors throughout the crust generally 5 km in length significant reflection dip angles 10 30 are seen only on the isochron profiles and several reflectors have a confirmed isochron dip orientation certain upper crustal reflectors ucrs appear to form a single network with isochron dip the most prominent example apparent reflection coefficient 0 2 projects toward a 70 m disruption in the igneous seafloor and waveform analysis demonstrates that the reflector is likely the product of a low velocity zone on the order of tens of meters thick our observations suggest that the isochron dipping ucrs represent small slip kilometer scale faults fractures and none are primarily related to the seismic 2 3 boundary or to the sheeted dike gabbro transition lower crustal reflectors lcrs have no preferred orientation or regular pattern on the 30 km scale of this survey certain lcrs may be similar to the ucrs in origin while others may originate from near axis ductile flow lithologic banding off axis magmatism or some combination thereof overall reflectors in this area are abundant and complex consistent with previous off axis studies but at odds with observations of young crust 5 ma near the epr this dichotomy may be resolved by a delay in reflector formation through some combination of postaccretionary tectonics magmatism and hydrothermal alteration

the structure of cretaceous oceanic crust of the nw pacific constraints on processes at fast spreading centers a 725 km long transect along a flow line in the nw pacific provides new images of the internal structure of cretaceous oceanic crust formed at fast spreading rates reflections from the moho transition zone document changes in crustal travel time along the profile variations with a wavelength of 100 150 km may representing fluctuations in the magma supply with a 2 3 m y periodicity to the south the crust may be several kilometers thicker than normal in places possibly resulting from increased magma supply due to the distal effects of the shatsky hotspot at about the depth expected for the boundary between seismic layers 2 and 3 sub horizontal reflections are imaged over much of the profile the clearest are positive polarity and of an amplitude consistent with a reflection coefficient of 0 1 implying a sharp velocity and density discontinuity northward ridgeward dipping reflections in the lower crust are imaged over much of the profile particularly toward the north away from the region possibly affected by the hotspot these reflections stop at the moho reflection but die out perhaps 1 s beneath top basement they probably represent lithological layering as predicted by models of ductile flow accompanying passive upwelling during plate separation although they could represent secondary shears generated by basal drag during active mantle upwelling beneath the spreading center the discrete character and in places regular spacing every 8 km of these features hint at a cyclicity in the layering and thus at some episodicity in magmatic processes over a timescale of 0 1 0 2 m y

elevated stream trace and minor element concentrations in the foreland of receding tropical glaciers globally the ongoing retreat of mountain glaciers will ultimately diminish fresh water supplies this has already begun in watersheds with greatly reduced glacial coverage still unknown are the affects of glacial retreat on downstream water quality including the threats to human and ecosystem health in the cordillera blanca retreating glaciers have exposed sulfide rich rock outcrops negatively affecting the quality of the glacial meltwater this study has evaluated glacial melt stream hydrogeochemistry in the sulfide bearing rio quilcay watershed 927 0 s 7722 0 w during the 2008 dry season surface water samples were collected from the upper 12 km of the watershed during the 2008 dry season dissolved 0 4 lm and unfiltered acidified ph 2 al co cu fe ni mn pb zn and dissolved major ions and organic c doc concentrations were quantified and ph and temperature were measured in the field twenty of 22 stream samples had ph values below 4 generating significantly p 0 01 a 0 05 greater cation denudation normalized to discharge than other worldwide glacier fed streams additionally dissolved trace and minor element concentrations were comparable to acid mine drainage non conservative dissolved element behaviors resulted from adsorption desorption reactions in tributary mixing zones at low ph values hydrous fe oxides acted as the dominant sorption surfaces the poor water quality observed in cordillera blanca headwaters coupled with the likely exposure of additional sulfide rich outcrops from ongoing glacial retreat may pose water quality challenges

comparative geochronology in the reversely zoned plutons of the bottle lake complex maine u pb on zircons and rb sr on whole rocks the bottle lake complex is a composite granitic batholith emplaced into cambrian to lower devonian metasedimentary rocks both plutons whitney cove and passadumkeag river are very coarse grained hornblende and biotite bearing granites showing petrographic and geochemical reverse zonation two linear whole rock rb sr isochrons on xenolith free whitney cove and passadumkeag river samples indicate ages of 379 5 m y and 381 4 m y respectively in close agreement with published k ar ages for biotite from whitney cove of 377 m y and 379 m y and for hornblende 40ar 39ar determinations from passadumkeag river which indicate an age of 378 4 m y the initial sr isotopic ratio for whitney cove is 0 70553 and for passadumkeag river is 0 70414 a whole rock isochron on a suite of xenoliths from the passadumkeag river granite indicates a whole rock rb sr age of 496 14 m y with an initial sr isotopic ratio of 0 70262 two types of zircon exhibiting wide petrographic diversity are evident in variable proportions throughout the batholith one of these types is preferentially found in a mafic xenolith and it is widely dispersed in the host granites forming discrete grains and probably as inclusions in the other type of zircon u pb analyses of zircons give concordia intercept ages of 399 8 m y for whitney cove 388 6 m y for passadumkeag river 415 m y for a mafic xenolith in passadumkeag river and 396 32 for combined whitney cove and passadumkeag river granite the zircons show a spread of up to 20 m y in the 207pb 206pb ages omitting the finest zircon fraction in the passadumkeag river results in a concordia intercept age of 381 3 m y in better agreement with the whole rock rb sr and mineral k ar ages for the whitney cove pluton exclusion of the finest fraction does not bring the zircon age into agreement with the rb sr data age estimates by the whole rock rb sr mineral k ar and ar ar methods suggest that the crystallization age of the plutons is about 380 m y slightly younger than the u pb zircon intercept ages a possible reason for this discrepancy is that the zircons contain inherited lead thus zircon u pb ages might represent a mixture of newly developed zircon and older inherited zircon whereas the rb sr whole rock age 380 m y reflects the time of crystallization and the argon ages result from rapid cooling after emplacement

trace element and major ion concentrations and dynamics in glacier snow and melt eliot glacier oregon cascades we present concentrations of environmentally available unfiltered acidified 2 v v hno3 as cu cd pb v sr and major ions including ca2 cl and so42 in a july 2005 and a march 2006 shallow snow profile from the lower eliot glacier mount hood oregon and its proglacial stream eliot creek low enrichment factors ef with respect to crustal averages suggests that in fresh march 2006 snow environmentally available elements are derived primarily from lithogenic sources soluble salts occurred in lower and less variable concentrations in july 2005 snow than march 2006 conversely environmentally available trace elements occurred in greater and more variable concentrations in july 2005 than march 2006 snow unlike major solutes particulate associated trace elements are not readily eluted during the melt season additionally elevated surface concentrations suggest that they are likely added throughout the year via dry deposition in a 1 h stream sampling ratios of dissolved 0 45 m v cl sr cl and cu cl are enriched in the eliot stream with respect to their environmentally available trace element to cl ratios in eliot glacier snow suggesting chemical weathering additions in the stream waters dissolved pb cl is depleted in the eliot stream with respect to the ratio of environmentally available pb to cl in snow corresponding to greater adsorption onto particles at greater ph values copyright 2009 john wiley sons ltd

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

diurnal dynamics of minor and trace elements in stream water draining dongkemadi glacier on the tibetan plateau and its environmental implications abstract global warming has resulted in rapid glacier retreat on the tibetan plateau tp and the impacts of glacier melting on downstream ecosystems remain largely unknown minor and trace elements in stream water draining dongkemadi glacier dg were examined during the ablation season of 2013 dominant ions and elements are hco 3 ca 2 fe and sr water chemistry is controlled by the weathering of calcite oxidation of pyrite and dissolution of evaporites correlations suggests the hydrological e g meltwater generation and routing water residence time and physicochemical e g sorption precipitation oversaturation controls on species concentrations the distribution of metals is featured by the mixture of soluble metal and non metal ligand complexes and free monovalent and divalent ions downstream increased concentrations and or fluxes of some metals and metalloid e g cr cu and as suggest potential environmental impacts discharge normalized cation denudation rate 372 meq m 3 in the dg basin is larger than those from alpine and polar glaciers suggesting a stronger weathering of carbonate with greater abundance on the tp in comparison to other mountain and polar glacial catchments the maximum fe concentration exceeds the usepa guideline and al zn and pb are close to or of the same order of magnitude as liminal values this implies that the tp may face a challenge of ecosystem health and environmental issue in a warming climate

centroid depths of mid ocean ridge earthquakes dependence on spreading rate from inversions of teleseismic p and sh waveforms we have determined the source parameters of 50 large earthquakes that occurred during 1962 1983 on slowly spreading mid ocean ridges all events are characterized by predominantly normal faulting on planes that dip at approximately 45 and strike parallel to the local trend of the ridge axis centroid depths range from 1 to 6 km beneath the seafloor the p waves from these earthquakes show strong water column reverberations suggesting that fault rupture extended to the seafloor under the assumption that the centroid depth marks the mean depth of fault slip earthquake faulting extended to a depth of 2 10 km for these earthquakes the water depths inferred from the predominant periods of the water column reverberations constrain the epicenters of these earthquakes to lie within the relatively deep inner floor of the median valley the maximum centroid depths of ridge crest earthquakes decrease with increasing spreading rate and the maximum seismic moment may also decrease with increasing spreading rate these results indicate a general decrease with spreading rate in maximum thickness of the mechanically strong layer beneath the ridge axis region the concentration of large earthquakes within the deepest parts of the median valley and the depth extent of seismic faulting support lithospheric necking models for the origin of the median valley

sulfide oxidation and distribution of metals near abandoned copper mines in coastal environments prince william sound alaska usa abstract the oxidation of sulfide rich rocks mostly leftover debris from cu mining in the early 20th century is contributing to metal contamination of local coastal environments in prince william sound alaska analyses of sulfide water sediment precipitate and biological samples from the beatson ellamar and threeman mine sites show that acidic surface waters generated from sulfide weathering are pathways for redistribution of environmentally important elements into and beyond the intertidal zone at each site volcanogenic massive sulfide deposits composed of pyrrhotite and or pyrite chalcopyrite sphalerite with subordinate galena arsenopyrite and cobaltite represent potent sources of cu zn pb as co cd and hg the resistance to oxidation among the major sulfides increases in the order pyrrhotite sphalerite chalcopyrite pyrite thus pyrrhotite rich rocks are typically more oxidized than those dominated by pyrite the pervasive alteration of pyrrhotite begins with rim replacement by marcasite followed by replacement of the core by sulfur fe sulfate and fe al sulfate the oxi dation of chalcopyrite and pyrite involves an encroachment by colloform fe oxyhydroxides at grain margins and along crosscutting cracks that gradually consumes the entire grain the complete oxidation of sulfide rich samples results in a porous aggregate of goethite lepidocrocite and amorphous fe oxyhydroxide enclosing hydrothermal and sedimentary silicates an inverse correlation between ph and metal concentrations is evident in water data from all three sites among all waters sampled pore waters from ellamar beach gravels have the lowest ph 3 and highest concentrations of base metals to 25 000 g l which result from oxidation of abundant sulfide rich debris in the sediment high levels of dissolved hg to 4100 ng l in the pore waters probably result from oxidation of sphalerite rich rocks the low ph and high concentrations of dissolved fe al and so4 are conducive to precipitation of interstitial jarosite in the intertidal gravels although pore waters from the intertidal zone at the threeman mine site have circumneutral ph values small amounts of dissolved fe2 in the pore waters are oxidized during mixing with seawater resulting in precipitation of fe oxyhydroxide flocs along the beach seawater interface at the beatson site surface waters funneled through the underground mine workings and discharged across the waste dumps have near neutral ph 6 7 7 3 and a relatively small base metal load however these streams probably play a role in the physical transport of metalliferous particulates into intertidal and offshore areas during storm events somewhat more acidic fluids to ph 5 3 occur in stagnant seeps and small streams emerging from the beatson waste dumps amorphous fe precipitates in stagnant waters at beatson have high cu 5 2 wt and zn 2 3 wt concentrations that probably reflect adsorption onto the extremely high surface area of colloidal particles conversely crystalline precipitates composed of ferrihydrite and schwertmannite that formed in the active flow of small streams have lower metal contents which are attributed to their smaller surface area and therefore fewer reactive sorption sites seeps containing precipitates with high metal contents may contribute contaminants to the marine environment during storm induced periods of high runoff preliminary chemical data for mussels mytilus edulis collected from beatson ellamar and threeman indicate that bioaccumulation of base metals is occurring in the marine environment at all three sites

geometry of extensional faults developed at slow spreading centres from pre stack depth migration of seismic reflection data in the central atlantic canary basin we present depth images from portions of profiles that are close to flow lines of cretaceous oceanic crust in the eastern central atlantic compared with post stack time migrations the images illustrate the improvement resulting from the application of pre stack depth migration the images document the scale and geometry of normal faulting in oceanic crust formed over 25 myr at a half spreading rate of less than 10 mm yr 1 and the variation in extensional style with position within the spreading segment away from major fault zones fzs most faults are subplanar dip more than 35 are associated with moderate basement relief 0 2 1 km relief and may penetrate to deep crustal levels these faults could be related to the lifting of the lithosphere out of the median valley to the flanking mountains also observed away from fzs are gently dipping to subhorizontal reflections in the upper crust which resemble detachment faults in contrast the inside corner crust is more rugged with basement highs rising up to 2 km above the intervening basins this larger scale topography is associated with a different style of faulting the depth images reveal gently dipping 35 faults that are rooted in the deep crust and that project to the ridgeward flank of the dome shaped large basement highs 1 2 km vertical relief the faults seem to continue as the ridge facing flank of these highs and some may extend over the crest of the high to breakaways beyond in this case the domal highs that form the exhumed footwall to the faults can be described as oceanic core complexes these controlling faults are up to 20 km long and have a heave of 10 km sufficient to have accommodated up to 50 per cent extension and to have exhumed deep crustal and perhaps even mantle rocks we suggest that similar faults can explain the structure and lithologies found at megamullion structures oceanic core complexes at inside corners near the present day spreading ridge

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

evolution of a transcurrent fault system in shallow crustal metasedimentary rocks the norumbega fault zone eastern maine abstract differential exhumation in maine exposes nearly half of the crustal profile of the norumbega fault zone nfz a major transcurrent fault zone of the northern appalachians a large exposure of turbidites in eastern maine records a multi stage deformation history that provides insight into the epizonal evolution of the nfz early deformation stage 1 involved episodic bed parallel faulting with fluids playing a progressively smaller role strain was broadly distributed at the exposure but was localized by lithic anisotropy in pelitic layers little stage 1 deformation occurred in the dominant wacke beds by diffusive mass transfer most took place in subordinate pelitic horizons by combined diffusive mass transfer and crystal plastic mechanisms later stage 2 activity was almost entirely brittle producing isolated ne trending faults and two deformation zones filled with cataclasite the latter comprise complexly anastomosing fault strands with multiple slickenline generations indicating episodic faulting regional scale nfz structures and history mirror those at outcrop scale late brittle faulting was superimposed on a broad region that had experienced largely ductile shearing and the regional scale brittle deformation was concentrated in three deformation zones characterized by anastomosing fault strands it is the stage 2 features that are mapped elsewhere in the northern appalachians as the norumbega fault zone

the s reflector west of galicia spain evidence from prestack depth migration for detachment faulting during continental breakup the mechanism of continental extension and breakup and the role of detachment faults in these processes are currently the subject of intense debate one possible detachment fault is the s reflector imaged as an undulating in time locally discontinuous reflection on existing seismic profiles west of iberia here we present new images in depth of the four margin normal profiles across the west galicia rifted margin where the s reflector was originally defined and is best imaged it is shown that faults bounding wedge shaped units of late synrift sediments which hence were active during rifting immediately prior to breakup appear to detach at shallow levels onto the s reflector s itself appears as a continuous locally domal feature and does not generally appear offset the waveform of s is compatible with a reflection from a single interface such as a sharp tectonic boundary the depth sections show that s was active at 1 3 km below the seafloor during final rifting s is interpreted as a brittle detachment fault which controlled the final breakup of the continent west of galicia furthermore the data provide constraints on the sense of shear of s analogy with detachment terranes the present synrift and structural dips of s and the identification of a breakaway to s imply that s accommodated top to the west shear toward the east of the profiles s becomes more complex possibly because of different phases of detachment faulting and the development of both incisement and excisement structures from the geometry of wedge shaped sedimentary units deposited during faulting above s it also appears that s was active at an angle of 20 or less and hence may be considered a genuine low angle normal fault

decadal changes in glacier parameters in the cordillera blanca peru derived from remote sensing we present spatial patterns of glacier fluctuations from the cordillera blanca peru glacier area terminus elevations median elevations and hypsography at decadal timescales derived from 1970 aerial photography 2003 spot5 satellite data geographic information systems gis and statistical analyses we derived new glacier outlines from the 2003 spot images and ingested them in the global land and ice measurements from space glims glacier database we examined changes in glacier area on the eastern and western side of the cordillera in relation to topographic and climate variables temperature and precipitation results include 1 an estimated glacierized area of 569 6 21 km 2 in 2003 2 an overall loss in glacierized area of 22 4 from 1970 to 2003 3 an average rise in glacier terminus elevations by 113 m and an average rise in the median elevation of glaciers by 66 m showing a shift of ice to higher elevations especially on the eastern side of the cordillera and 4 an increase in the number of glaciers which indicates disintegration of ice bodies annual air temperature showed a significant upward trend in the last 30 years with larger temperature increases at lower elevations there was a slight but not significant decrease in precipitation our results are consistent with glacier retreat and warming trends noted in the last three decades in the tropics

evidence for asymmetric accretion and low angle planar faults in slow spreading oceanic crust new seismic reflection data in the eastern atlantic have enabled two large scale dipping reflectors imaged within mesozoic ocean crust to be mapped in three dimensions and placed in their sea floor spreading context one of the reflectors dips to the west and extends from a step in the igneous basement to the moho the other reflector dips to the east and extends between 4 and 10 km below basement both reflectors are oriented approximately parallel to isochrons lie just north of a 5 km offset third order discontinuity are planar in cross section and dip at 30 we interpret both these reflectors as lithospheric scale faults formed within the median valley at the axis we suggest that the lower part of the eastward dipping fault was captured from the north american plate possibly by rapid propagation of an active volcanic rift across the discontinuity

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

source mechanisms of earthquakes near mid ocean ridges from body waveform inversion implications for the early evolution of oceanic lithosphere to investigate the early tectonic evolution of oceanic lithosphere we present a synthesis of the characteristics of near ridge earthquakes i e earthquakes which occur off the axis of major mid ocean spreading centers but in lithosphere less than 35 m y old near ridge seismicity for the past two decades has been rather evenly distributed along the major ridge systems with the exception of the central indian ocean and the eastern part of the cocos plate which have experienced a high rate of earthquake activity during that time for 32 near ridge earthquakes we determined the double couple orientation seismic moment centroid depth and source time function using a formal inversion technique based on matching synthetic and observed p and sh waveforms all types of faulting styles are observed seismogenic deformation in young oceanic lithosphere is concentrated in the first 15 m y and occurs almost entirely in the uppermost mantle from just below the moho to depths at which the temperature estimated from standard thermal models exceeds 800 c thrust faulting is not observed at depths greater than 10 km below the seafloor the deepest near ridge earthquakes are generally characterized by normal faulting focal mechanisms with the t axis oblique or perpendicular to the local spreading direction most of these earthquakes occur in the central indian ocean the transition from mechanisms characteristic of ridge axes to those characteristic of the near ridge environment occurs within the first few million years for lithosphere less than 35 m y old horizontal compressive stress associated with the cooling and subsidence of the lithosphere ridge push does not appear to be the dominant source of stress released in earthquakes this result may be used to place a lower bound of several hundred bars on the typical stress difference in young oceanic lithosphere this bound together with the observed depth of faulting implies that the strain rate associated with seismic deformation is locally at least 10 15 s 1 we propose that thermoelastic stresses associated with plate cooling play an important role in near ridge earthquakes this source of stress can account for the mechanisms and depths of many near ridge earthquakes and for the concentration of activity in very young lithosphere the comparative aseismicity of the oceanic crust may reflect the concentration of thermoelastic stress below the moho due to different material properties for the crust and upper mantle or the early release of thermoelastic stresses through hydrothermal circulation and cracking throughout the crust at or near the ridge axis the higher level of near ridge seismicity in the indian ocean may be the result of modification or enhancement of the more typical near ridge stress state by such local processes as the continental collision between india and asia or active secondary convection beneath the young lithosphere of the indian plate

glacier meltwater hydrochemistry abstract glacierised areas present an ideal environment in which to study water rock interaction since chemical weathering rates are high and anthropogenic impacts are often minimal detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles most notably the role of meltwaters in co2 sequestration during episodes of deglaciation has attracted considerable attention since this may impact on climate at glacial interglacial timescales however there is still considerable uncertainty surrounding estimates of co2 drawdown by meltwaters which remains to be resolved water flow through glaciers exerts an important control on ice mass dynamics and influences the quantity and quality of water delivered to environments downstream of glacierised basins thus the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding but also to allow effective water resource utilisation in glacierised headwater catchments bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment here significant advances have been made in understanding the controls on chemical weathering reactions based on the identification of key dissolved indicator species this has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations as a result this area of glaciology has received considerable attention in recent years utilising an increasing range of dissolved ions and integrating field and laboratory studies however uncertainty still surrounds certain areas of meltwater quality science including the role of microorganisms in a system which to date has largely been viewed as abiotic a better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment and to facilitate the exploitation of water quality variations for both scientific and applied objectives in this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed and problems and future directions identified this will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications

tectonic significance of the carboniferous big pond basin cape breton island nova scotia detailed mapping in southeastern cape breton island has revealed a strike slip origin for the small carboniferous outlier at big pond topographically low carboniferous sedimentary rocks occur between splays of a previously unrecognized northeast trending set of high angle faults the big pond fault system the section is dominated by fanglomerates which coarsen toward the faulted basin margins and which were deposited and or reworked by currents flowing toward the basin s center and along its axis we interpret the fanglomerates as syntectonic interbedded limestones of visean age windsor b subzone provide age control for the upper part of the 300 m section and by inference for at least some of the fault motion dextral motion on the big pond fault system is indicated by 1 slickenside stepping directions on minor faults which juxtapose basement against basement and which parallel the main northeast striking fault 2 northeast striking mesoscale faults within the basin which produce dextral