apatite as a monitor of late stage magmatic processes at volcan irazu costa rica apatite phenocrysts from the 1963 and 1723 eruptions of irazu volcano costa rica record a volatile evolution history that confirms previous melt inclusion studies and provides additional information concerning the relative and absolute timing of subvolcanic magmatic events measurements of h cl and f by secondary ion mass spectrometry reveal multiple populations of apatite in both 1723 and 1963 magmas assuming nominal apatite melt partition coefficients allows us to compare the pattern of melt inclusions and apatites in ternary space demonstrating the fidelity of the record preserved in apatite and revealing a complex history of magma mixing with at least two components the preservation of heterogeneous populations of apatite and of internally heterogeneous crystals requires short timescales days to years for these magmatic processes to occur

downward water flow through sloping layers in the vadose zone time dependence and effect of slope length abstract we develop a 2 d numerical model to simulate both steady state and transient downward water flow through sloping layers in the vadose zone with a deep water table the horizontal flow component obtained with the 2 d numerical model varies with position along the slope but was nearly the same as the 1 d analytical solution once beyond a few meters from blocked vertical boundaries at the upper or lower end of the slope under time variable precipitation both the time delay and the peak magnitude of the response deep within the profile are not simply proportional or in one to one correspondence to the strength of each rainfall event but rather depend on the initial moisture status in the profile as well as the previous rainfall events an interesting phenomenon for the transient case is that the horizontal flow component reversed direction to upslope during the time of heavy rain this is due to the flow pattern near the upper surface boundary a sloping wetting front and is a consequence of the sloping geometry previous studies warrick et al 1996 have shown that multidimensional steady state water flow through a sloping interface can essentially be solved by a one dimensional analytical solution for an infinite long slope the simulations suggest that a 1 d numerical analysis should also be valid for 2 d transient flow cases if the slope is of sufficient length and the point of evaluation is sufficiently far from the beginning or end of the slope

u pb geochronology of zircon and polygenetic titanite from the glastonbury complex connecticut usa an integrated sem empa tims and shrimp study abstract u pb ages for zircon and titanite from a granodioritic gneiss in the glastonbury complex connecticut have been determined using both isotope dilution thermal ionization mass spectrometry tims and the sensitive high resolution ion microprobe shrimp zircons occur in three morphologic populations 1 equant to stubby multifaceted colorless 2 prismatic dark brown with numerous cracks and 3 elongate prismatic light tan to colorless cathodoluminescence cl imaging of the three populations shows simple concentric oscillatory zoning the zircon tims age weighted average of 207pb 206pb ages from group 3 grains 450 5 1 6 ma mswd 1 11 and shrimp age composite of 206pb 238 u age data from all three groups 448 2 2 7 ma mswd 1 3 are interpreted to suggest a relatively simple crystallization history titanite from the granodioritic gneiss occurs as both brown and colorless varieties scanning electron microscope backscatter bse images of brown grains show multiple cross cutting oscillatory zones of variable brightness and dark overgrowths colorless grains are unzoned or contain subtle wispy or very faint oscillatory zoning electron microprobe analysis empa clearly distinguishes the two populations brown grains contain relatively high concentrations of fe2o3 ce2o3 up to 1 5 wt nb2o5 and zr cerium concentration is positively correlated with total ree y concentration which together can exceed 3 5 wt oscillatory zoning in brown titanite is correlated with variations in ree concentrations in contrast colorless titanite both as discrete grains and overgrowths on brown titanite contains lower concentrations of y ree fe2o3 and zr but somewhat higher al2o3 and nb2o5 uranium concentrations and th u discriminate between brown grains typically 200 400 ppm u all analyses but one have th u between about 0 8 and 2 and colorless grains 10 60 ppm u th u of 0 0 17 in contrast to the zircon u pb age results shrimp u pb data from titanite indicate multiple growth episodes in brown grains oscillatory zoned cores formed at 443 6 ma whereas white in bse cross cutting zones are 425 9 ma colorless grains and overgrowths on brown grains yield an age of 265 8 ma using the total pb method or 265 5 ma using the weighted average of the 206pb 238u ages however empa chemical data identify zoning that suggests that this colorless titanite may preserve three growth events oscillatory zoned portions of brown titanite grains are igneous in origin white cross cutting zones probably formed during a previously unrecognized event that caused partial dissolution of earlier titanite and reprecipitation of a slightly younger generation of brown titanite colorless titanite replaced and grew over the magmatic titanite during the permian alleghanian orogeny these isotopic data indicate that titanite like zircon can contain multiple age components coupling shrimp microanalysis with empa and sem results on dated zones as presented in this study is an efficient and effective technique to extract additional chronologic data to reveal the complexities of igneous crystallization and metamorphic growth

size and shape characteristics of drumlins derived from a large sample and associated scaling laws abstract ice sheets flowing across a sedimentary bed usually produce a landscape of blister like landforms streamlined in the direction of the ice flow and with each bump of the order of 102 to 103 m in length and 101 m in relief such landforms known as drumlins have mystified investigators for over a hundred years a satisfactory explanation for their formation and thus an appreciation of their glaciological significance has remained elusive a recent advance has been in numerical modelling of the land forming process in anticipation of future modelling endeavours this paper is motivated by the requirement for robust data on drumlin size and shape for model testing from a systematic programme of drumlin mapping from digital elevation models and satellite images of britain and ireland we used a geographic information system to compile a range of statistics on length l width w and elongation ratio e where e l w for a large sample mean l is found to be 629 m n 58 983 mean w is 209 m and mean e is 2 9 n 37 043 most drumlins are between 250 and 1000 metres in length between 120 and 300 metres in width and between 1 7 and 4 1 times as long as they are wide analysis of such data and plots of drumlin width against length reveals some new insights all frequency distributions are unimodal from which we infer that the geomorphological label of drumlin is fair in that this is a true single population of landforms rather than an amalgam of different landform types drumlin size shows a clear minimum bound of around 100 m horizontal maybe drumlins are generated at many scales and this is the minimum or this value may be an indication of the fundamental scale of bump generation proto drumlins prior to them growing and elongating a relationship between drumlin width and length is found with r2 0 48 and that is approximately w 7 l 1 2 when measured in metres a surprising and sharply defined line bounds the data cloud plotted in e w l space and records a scale dependent maximum elongation limit approximated by emax l1 3 when l measured in metres for a given length for some reason as yet unknown drumlins do not exceed the elongation ratio defined by this scaling law we also report and compare our statistics to an amalgamated sample 25 907 drumlins of measures derived from around 50 published investigations any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling

transient hydraulic tomography in a fractured dolostone laboratory rock block experiments 1 the accurate characterization of fractured geologic medium imaging of fracture patterns and their connectivity have been a challenge for decades recently hydraulic tomography has been proposed as a new method for imaging the hydraulic conductivity k and specific storage ss distributions of fractured geologic media while encouraging results have been obtained in the field the method has not been rigorously assessed in a controlled laboratory setting in this study we assess the performance of transient hydraulic tomography tht in a fractured dolomitic rock block the block is characterized through flow through tests and multiple pumping tests the pumping test data were then analyzed with the tht code of zhu and yeh 2005 to image the fracture patterns and their connectivity through the delineation of k and ss distributions or tomograms results show that the tht analysis of pumping tests yields high k and low ss zones that capture the fracture pattern and their connectivity quite well and those patterns become more vivid as additional pumping test data are added to the inverse model the performance of the estimated k and ss tomograms are then assessed by 1 comparing the tomograms obtained from synthetic to real data 2 comparing the tomograms from two different pumping configurations 3 comparing the estimated geometric mean of the hydraulic conductivity kg from the k tomogram to the effective hydraulic conductivity keff estimated from the flow through tests and 4 predicting five independent pumping tests not used in the construction of the k and ss tomograms the performance assessment of the k and ss tomograms reveals that tht is able to image high k and low ss zones that correspond to fracture locations in the fractured rock block and that the tomograms can be used to predict drawdowns from pumping tests not used in the construction of the tomograms with reasonable fidelity

downward water flow through sloping layers in the vadose zone analytical solutions for diversions abstract steady downward water flow through a vadose zone of sloping strata of different materials is studied the resulting streamlines are mostly vertical but are deflected at the strata interfaces depending on the related unsaturated hydraulic conductivity functions and the flow rate updip or downdip deflection can occur for either fine over coarse or coarse over fine material this phenomenon is of particular interest as related to flow regimes and the diversion capacity around buried wastes and in the engineering design of capillary barriers assuming that the pressure head distribution is only a function of the normal distance from the sloping interface which allows a one dimensional analysis we calculated pressure profiles streamlines and deflection distances the calculations confirm that a considerable downdip deflection can occur for low flow rates and a finer textured soil overlying a coarser material updip deflections are most likely to be significant for high flow velocities which occur for artificial recharge or humid climates

apatite in granitoids related to polymetallic mineral deposits in southeastern hunan province shi hang zone china implications for petrogenesis and metallogenesis abstract the area of southeastern hunan province china located within the southwestern part of the shi hang metallogenic zone is characterized by abundant cu pb zn w and sn polymetallic ore deposits that are closely associated with coeval late mesozoic granodiorite porphyries and biotite granites respectively here we present new major and trace element concentrations and 87 sr 86 sr ratios of apatites from six ore bearing granitic rocks as determined by electron microprobe laser ablation inductively coupled plasma mass spectrometry and thermal ionization mass spectrometer which allow us to determine the main controls on the formation of these different types of mineralization and to explore how these controls are reflected in variations in apatite chemical and isotopic compositions the apatite data indicate that granodiorite porphyry intrusions related to cu pb zn mineralization are oxidized and formed as a result of slab dehydration melting of the mantle wedge overlying a subducted slab and the partial melting of crustal material the release of abundant cl and h 2 o rich fluids from the slab triggered mantle melting and the extraction of metals that were precipitated within the deposits in comparison granites related to w and sn deposits are moderately oxidized to reduced and were generated by the partial melting of crustal material with only limited input from mantle derived magmas granites associated with the w and sn mineralization formed in an intra arc rifting related tectonic environment the fact that these numerous polymetallic ore deposits formed in the same area during two successive periods of mineralization the first from 180 to 160 ma and the second from 160 to 140 ma indicates that the tectonic environment of southeastern hunan province evolved from a continental arc associated with the subduction of the paleo pacific plate and the formation of cu pb zn deposits to a later intra arc rifting environment associated with the formation of w and sn deposits as a consequence of slab roll back and mantle upwelling during the late jurassic this study reveals that apatite compositions can be used as a proxy to reflect the differences between granitoids and their associated mineralization and identify regional metallogeny and tectonic evolution

reconstructing the last irish ice sheet 2 a geomorphologically driven model of ice sheet growth retreat and dynamics the ice sheet that once covered ireland has a long history of investigation much prior work focussed on localised evidence based reconstructions and ice marginal dynamics and chronologies with le

glacier stress patterns and sediment transfer associated with the formation of superimposed flutes abstract glacial flutes superimposed on megaflutes in the foreland of austre okstindbreen north norway provide information suitable for the identification of the areas of erosion and deposition during the formation of the superimposed flutes and the calculation of the volumes of sediment involved in this process detailed analysis of the geometry particle size and clast fabric of the sediments involved in these landforms indicate that material was transferred to an incremental zone from an adjacent erosional trough along with additional material derived directly from the glacier sediment transfer is restricted to an upper till with a thickness of about 0 40 m but deformation imposed during the formation of the superimposed flutes can be traced to a depth of around 0 75 m in a lower sheared silty sand stress patterns revealed by clast fabric analysis in the superimposed flutes and adjacent parts of the megaflute indicate compressive flow at the proximal end of the bedform in the lee of an apparently obstructing boulder convergent extending flow in the central part of the bedform with a characteristic herringbone pattern and divergent extending flow at the terminal zone of the feature the convergent divergent pattern is considered to be a response to ice flow cells caused by high pressure over the troughs between the flutes and low pressure over the flute crestline these ice flow cells are considered to be initiated by factors such as upstanding boulders and bedrock knobs clusters of boulders within the diamicton and lateral and longitudinal oscillations developed in response to identifiable perturbations first order estimates of the rates of sediment transfer involved in the formation of the superimposed flutes vary between 0 0077 m3 m 2 a 1 and 0 38 m3 m 2 a 1 these figures have been applied in an exploratory fashion to megaflutes and drumlins from elsewhere in order to estimate the time required for glacier bedforms to develop and test the reliability of the figures derived the most meaningful results suggest that glacier bedforms are created within a period of between 4 and 400 years irrespective of their size this suggests that glacier bedforms develop rapidly and are maintained in a condition of steady state that reflects the balance between glacier energy and resisting bed material

apatite chemical composition determined by electron microprobe and laser ablation inductively coupled plasma mass spectrometry as a probe into granite petrogenesis abstract major minor and trace element abundances in apatites from various i and s type igneous and sedimentary granites of the lachlan fold belt have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometer the results show that apatite can accommodate many minor and trace elements whose concentrations and ratios are relatively sensitive to factors controlling many of the fundamental differences between i and s type granites apatites from s type granites generally have higher f but lower cl contents than those from i type granites which is ascribed mainly to the loss of cl during the weathering processes forming the source rocks of s type granites although fractional crystallisation can cause significant enrichment in f as well high mn and fe contents in apatites from s type granites and high s and as abundances in apatites from mafic i type granites result from different oxygen fugacities and degrees of al saturation or aluminosity between metaluminous mafic i type magmas and peraluminous s type and felsic i type magmas there are systematic and distinctive differences in absolute rare earth element ree abundances ree distribution patterns and element ratios e g la y sm nd etc between apatites from different types of granite the strong eu depletion that characterises apatites from s and felsic i type granites is interpreted here to be a result of the uniqueness of crystal chemistry of apatite and high eu2 eu3 ratios in s type and felsic i type magmas which are more reduced and peraluminous than mafic i type magmas strong ree la to eu and th enrichment in apatites from mafic i type granites and marked nd depletion in apatites from most s type and felsic i type granites are caused by the precipitation and fractionation of monazite in the parental magmas of the latter rocks substitution mechanisms are responsible for high na in apatites from s type and felsic i type granites and for high si in apatites from mafic i type granites and may also have important effects on ree partitioning between apatite and melt thus apatite chemistry can be used as an excellent indicator of granite petrogenesis the results have important implications for identifying different types of granite and are potentially significant for determining the provenance of sedimentary rocks

reconstructing ice flow fields from streamlined subglacial bedforms a kriging approach the orientation of several landforms e g drumlins flutes crag and tails and mega scale glacial lineations records the direction of the overlying ice flow that created them populations of such features are used routinely to infer former ice flow patterns which serve as the building blocks of reconstructions of palaeo ice sheet evolution currently the conceptualisation of flow patterns from these flow direction records is done manually and qualitatively so the extractable glaciological information is limited we describe a kriging method with matlab code implementation that calculates continuous fields of ice flow direction convergence and curvature from the flow direction records and which yields quantitative results with uncertainty estimates we test the method by application to the subglacial bedforms of the tweed valley basin uk the results quantify the convergent flow pattern of the tweed palaeo ice stream in detail and pinpoint its former lateral shear margins and where ice flowed around basal bumps ice flow parameters retrieved by this method can enrich ice sheet reconstructions and investigations of subglacial till processes and bedform genesis

investigations of the stillwater complex part v apatites as indicators of evolving fluid composition variations in the f cl and oh contents of apatite are not constrained by crystal chemical factors in contrast to micas and amphiboles and thus changes in the abundance of these components provide an indicator of halogen fugacity variations and insights into the degassing history of igneous rocks microprobe analysis of intercumulus apatites from the stillwater complex reveal that cl rich apatites typically containing 6 0 wt cl occur throughout the lower 1 3 of the complex excluding the basal series a change from cl rich to more f rich apatite occurs within olivine bearing zone i ob i of the banded series the host zone of the platiniferous j m reef although apatite compositions are somewhat variable above the j m reef more f rich apatites predominante and typically contain 1 2 wt f and 3 0 wt cl the most f rich apatites occur in the uppermost exposed cumulates pristine apatites from coeval sills and dikes from below the complex and from the basal series are similarly f rich in all apatites the cl and f contents are lower in rocks affected by later metamorphic fluids rare earth element ree concentrations in chlorapatites show a marked peak in the olivine rich rocks of the j m reef and contain up to 2 wt ce2o3 la2o3 the trend of first increasing then decreasing cl f ratios with stratigraphic height is modeled by a vapor driven zone refining process occurring within the cumulate pile causing cl enrichment in the interstitial melt accompanied by degassing at the top of the magma chamber causing overall loss of cl from the magma as crystallization proceeded the abrupt change from cl rich to more f rich apatites within ob i is interpreted as the result of a breakdown of the cl rich zone refining front and mixing with cl poor supernatant melt any high temperature fluids that exsolved and circulated through the lower 1 3 of the complex must have been enriched in cl and could have transported ree and trace metals

the diversion capacity of capillary barriers an arrangement of unsaturated fine grained soil overlying unsaturated coarse grained soil along a sloping contact can under appropriate circumstances divert infiltrating water away from the coarser material such an arrangement is called a capillary barrier the water diverted by a capillary barrier flows downdip above the contact the volume of water moving laterally increases in the downdip direction as additional infiltration is diverted by the barrier sufficiently far downdip the laterally moving water wets the contact to the point that an amount of water equal to the infiltration flows downward through the coarse soil the lateral flow at such a point represents the diversion capacity of the capillary barrier because this flow will not increase farther downdip if the width measured in the direction of dip of the system is large enough that total infiltration exceeds the diversion capacity the downdip portion of the barrier will not be effective the diversion capacity can be calculated exactly in the quasi linear approximation where the relationship between relative permeability krel and pressure potential takes the form krel e this calculation shows that an upper bound on the width of capillary barriers is ks tan o q where ks is the saturated hydraulic conductivity of the fine soil o is the dip angle of the contact and q is the infiltration rate

palaeoglaciology of the last irish ice sheet reconstructed from striae evidence abstract a database comprising some 5200 individual striation measurements on bedrock surfaces across the island of ireland was used to produce maps of flowsets corresponding to individual ice flow events during the last late devensian glacial cycle these flowsets were identified on the basis of regional scale correspondence between striae orientations which when linked together spatially are able to identify consistent ice flow vectors four main chronological stages are identified on the basis of this evidence i incursion of scottish ice into ireland ii glacial maximum conditions iii ice retreat and dissolution and iv development of localised ice domes striae based reconstructions of the glaciology of the last irish ice sheet are qualitatively different from those based on bedform mainly drumlin and ribbed moraine evidence significant differences are apparent in upland areas which have fewer preserved bedforms and a higher concentration of striae combining bedform and striae datasets will enable a better understanding of the temporal evolution of the ice sheet it is likely that both datasets record a snapshot of ice flow direction and subglacial conditions and environments immediately prior to preservation of this directional evidence

dynamic cycles ice streams and their impact on the extent chronology and deglaciation of the british irish ice sheet we present results from a suite of forward transient numerical modelling experiments of the british and irish ice sheet biis consisting of scottish welsh and irish accumulation centres spanning the last glacial period from 38 to 10 ka bp the 3d thermomechanical model employed uses higher order physics to solve longitudinal membrane stresses and to reproduce grounding line dynamics surface mass balance is derived using a distributed degree day calculation based on a reference climatology from mean 1961 1990 precipitation and temperature patterns the model is perturbed from this reference state by a scaled ngrip oxygen isotope curve and the specmap sea level reconstruction isostatic response to ice loading is computed using an elastic lithosphere relaxed asthenosphere scheme a suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities to yield a subset of experiments that showed close correspondence to offshore and onshore ice directional indicators broad biis chronology and the relative sea level record three of these simulations are described in further detail and indicate that the separate ice centres of the modelled biis complex are dynamically interdependent during the build up to maximum conditions but remain largely independent throughout much of the simulation the modelled biis is extremely dynamic drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time scale a series of binge purge advance retreat cycles are identified which correspond to alternating periods of relatively cold based ice associated with a high aspect ratio and net growth and wet based ice with a lower aspect ratio characterised by streaming the timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling but are modulated and phase lagged to the oscillations within the ngrip record of climate forcing phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate resulting in major iceberg melt discharge events into the north sea and atlantic ocean the broad chronology of the modelled biis indicates a maximum extent at 20 ka with fast flowing ice across its western and northern sectors that extended to the continental shelf edge fast flowing streams also dominate the irish sea and north sea basin sectors and impinge onto sw england and east anglia from 19 ka bp deglaciation is achieved in less than 2000 years discharging the freshwater equivalent of 2 m global sea level rise a much reduced ice sheet centred on scotland undergoes subsequent retrenchment and a series of advance retreat cycles into the north sea basin from 17 ka onwards culminating in a sustained younger dryas event from 13 to 11 5 ka bp modelled ice cover is persistent across the western and central highlands until the last remnant glaciers disappear around 10 5 ka bp

temporal damping effect of the yucca mountain fractured unsaturated rock on transient infiltration pulses performance assessment of the yucca mountain unsaturated zone uz as the site for an underground repository of high level radioactive waste relies on the crucial assumption that water percolation processes in the unsaturated zone can be approximated as a steady state condition justification of such an assumption is based on temporal damping effects of several geological units within the unsaturated tuff formation in particular the nonwelded tuff of the painbrush group ptn unit at yucca mountain because of its highly porous physical properties has been conceptualized to have a significant capacity for temporally damping transient percolation fluxes the objective of this study is to investigate these damping effects using a three dimensional 3 d mountain scale model as well as several one dimensional 1 d models the 3 d model incorporates a wide variety of the updated field data for the highly heterogeneous unsaturated formation at yucca mountain the model is first run to steady state and calibrated using field measured data and then transient pulse infiltrations are applied to the model top boundary subsequent changes in percolation fluxes at the bottom of and within the ptn unit are examined under episodic infiltration boundary conditions the 1 d model is used to examine the long term response of the flow system to higher infiltration pulses while the damping effect is also investigated through modeling tracer transport in the uz under episodic infiltration condition simulation results show the existence of damping effects within the ptn unit and also indicate that the assumption of steady state flow conditions below the ptn unit is reasonable however the study also finds that some fast flow paths along faults exist causing vertical flux quick responses at the ptn bottom to the episodic infiltration at the top boundary

geology and origin of the post collisional narigongma porphyry cu mo deposit southern qinghai tibet narigongma is a poorly studied mo rich similar to 0 06 wt post collisional porphyry cu deposit located in southern qinghai province tibet 400 km northwest of the yulong porphyry cu mo au belt the narigongma deposit has a similar age 43 40 ma to porphyry deposits in the yulong belt but different ore assemblages the narigongma deposit is associated with eocene granodiorite and granite intrusions that were emplaced into a permian volcanic sedimentary rock sequence an similar to 43 3 ma biotite granite stock p1 porphyry is the earliest eocene intrusion and this was itself intruded by a number of smaller similar to 43 6 ma fine grained granite porphyry stocks p2 porphyry and several post ore quartz diorite porphyry dikes similar to 41 7 ma the main cu mo mineralization at narigongma is associated with the p1 porphyry hydrothermal alteration surrounding the deposits is generally characterized by concentric zones that range from an inner potassic zone outward to phyllic and argillic alteration zones and an outer propylitic zone hypogene mineralization at narigongrna was characterized by early stage precipitation of molybdenite during potassic alteration and late stage deposition of chalcopyrite during phyllic alteration deposition of both the mo and cu mineralization stages was caused by decreasing temperature a high degree of crystallization of the p1 porphyry occurred prior to fluid saturation that produced mo enrichment in the residual melt due to the incompatible behavior of mo however compatible cu was sequestered by the crystallizing phases and resulted in the generation of a high mo cu magmatic hydrothermal fluid and the final mo cu mineralization assemblage zircon epsilon hf t values of 4 1 to 7 9 are indicative of magma derivation from a depleted source these isotopic data coupled with other geochemical characteristics of the narigongma porphyry such as high sio2 and k2o contents low mgo contents and compatible element abundances and highly fractionated rare earth element patterns indicate a mixing model for the origin of the porphyry bodies generation of the post collisional ore forming porphyries occurred in two stages 1 partial melting of metasomatized phlogopite bearing lithospheric mantle that generated potassic to ultra potassic mafic melts and 2 underplating of such melts beneath thickened juvenile lower crust which triggered partial melting of the lower crust to produce the ore forming high k adakitic magma c 2013 international association for gondwana research published by elsevier b v all rights reserved

geology geochemistry geochronology and economic potential of neogene volcanic rocks in the laguna pedernal and salar de aguas calientes segments of the archibarca lineament northwest argentina abstract this study presents new geochemical geochronological isotopic and mineralogical data combined with new geological mapping for a 2400 km 2 area of neogene volcanic rocks in northwestern argentina near the border with chile between 25 10 s and 25 45 s the area covers the zone of intersection between the main axis of the cordillera occidental and a set of nw se trending structures that form part of the transverse archibarca lineament this lineament has localized major ore deposits in chile e g the late eocene la escondida porphyry cu deposit and large volcanic centers such as the active llullaillaco and lastarria volcanoes on the border between chile and argentina and the neogene archibarca antofalla and cerro galan volcanoes in argentina neogene volcanic rocks in the laguna pedernal and salar de aguas calientes areas are mostly high k calc alkaline in composition and range from basaltic andesites through andesites and dacites to rhyolites magmatic temperatures and oxidation states estimated from mineral compositions range from 1000 c and fmq 1 0 1 5 in andesites to 850 c and fmq 1 5 2 0 in dacites and rhyolites the oldest rocks consist of early middle miocene andesite dacite plagioclase pyroxene phyric lava flows and ignimbrites with 40 ar 39 ar ages ranging from 17 14 0 10 ma to 11 76 0 27 ma their major and trace element compositions are typical of the andean central volcanic zone and show strong crustal contamination trends for highly incompatible elements such as cs rb th and u these rocks are geochemically grouped as sub suite 1 this widespread intermediate composition volcanism was followed in the middle late miocene by a period of more focused rhyodacitic flow dome complex formation these felsic rocks are characterized by less extreme enrichments in highly incompatible elements and increasing depletion of heavy rare earth elements these rocks are geochemically grouped as sub suite 2 the youngest rocks in this sub suite show the highest la yb ratios and are characterized by abundant hornblende phenocrysts not commonly seen in other rocks from the area in the pliocene pleistocene there was a return to more typical andesite dacite volcanism with geochemical characteristics similar to the early middle miocene lavas and are also grouped in sub suite 1 finally extensional tectonics in the quaternary led to localized outpouring of mafic basaltic andesitic to andesitic monogenetic lava flows and cones one particularly large flow the vega aguas calientes lava flow covers approximately 90 km 2 and samples form two groupings with affinities similar to the least evolved samples from sub suites 1 and 2 sub groups ba1 and ba2 respectively nd and sr isotopic compositions indicate moderate to strong crustal contamination especially in more felsic rocks and extend from 87 sr 86 sr 0 706 and end 2 4 values typical of central volcanic zone rocks to more evolved compositions 0 709 and 6 8 respectively typical of large volume ignimbrites of the altiplano puna volcanic complex and cerro galan the latter compositions are thought to be derived by extensive interaction between mantle derived arc magmas and paleozoic granitoid rocks that form much of the crustal column in this region the distinctive mineralogy and geochemistry of the sub suite 2 middle late miocene rhyodacitic flow dome complexes indicate that these magmas had higher water content than both the earlier and later sub suite 1 andesites dacites they were erupted during a period of tectonic quiescence following the quechua orogenic phase and geophysical evidence suggests that they were proximally derived from a large upper crustal magma chamber which partially collapsed to form a trap door caldera strong fumarolic alteration associated with the youngest of these felsic volcanoes cerro abra grande suggests the potential for the existence of epithermal type mineralization within the volcanic edifice or porphyry type mineralization at depth

subglacial bedform geomorphology of the irish ice sheet reveals major configuration changes during growth and decay the belated realisation that ribbed rogen moraines form such an integral part of irish geomorphology and the piecemeal approach to previous drumlin mapping is probably responsible for the highly contrasting views of palaeoflow patterns of the irish ice sheet using a high resolution 25 m digital elevation model we present morphological maps of a large part 100 100 km of the so called drumlin belt of north central ireland the landforms comprise mostly ribbed moraine much larger than found elsewhere up to 16 km in length which in places are superimposed on each other contrary to most prior assessments we find the bedform record to contain numerous and overlapping episodes of bed formation ribbed moraine drumlins and crag and tails that provide a palimpsest record of changing flow geometries these demonstrate an ice sheet with a centre of mass and flow geometry that changed during growth and decay using distinctive flow patterns and relative age relationships between them we reconstruct ice sheet evolution into four phases during a single glacial cycle in phase 1 early in the glacial cycle scottish and local ice coalesced to form a northeast centred irish ice sheet as it grew its centre of mass migrated southwards culminating in a major n s divide positioned down the east of ireland phase 2 ca last glacial maximum during retreat the centre of mass migrated at least 120 km northwards and became established in northwest ireland and at this point a dramatic bedforming event produced one of the world s largest and most contiguous ribbed moraine fields phase 3 final deglaciation is thought to be by fragmentation into many topographically controlled minor ice caps phase 4 rather than any dramatic or unexpected behaviour the reconstructed phases indicate a relatively predictable pattern of ice sheet growth and decay with changes in centres of mass and does not require major readvances or ice stream events copyright 2001 john wiley sons ltd

the role of early sulfide saturation in the formation of the yulong porphyry cu mo deposit evidence from mineralogy of sulfide melt inclusions and platinum group element geochemistry abstract sulfide melt inclusions enclosed in silicate minerals have been observed in many oxidized cu bearing porphyries the origin of such sulfide melt inclusions could bear critical information of metal enrichment or depletion during magma evolution of porphyry systems the giant yulong porphyry cu mo deposit in eastern tibetan plateau consists of a series of felsic intrusions among which the mineralized yulong intrusion emplaced at a late stage of the magmatic activity this study reports detailed texture and composition of sulfide melt inclusions from barren and mineralized intrusions as well as platinum group elements of these intrusions to evaluate potential role of early sulfide saturation in the porphyry mineralization system these sulfide melt inclusions occurring as globules or droplets are preserved in zircon amphibole and quartz grains most of them are composed of a major phase of pyrrhotite and minor pyrite chalcopyrite and pentlandite smooth boundaries between these phases suggest the origin of fractionation from sulfide melt upon cooling small amounts of cu and ni are heterogeneously distributed in the pyrrhotite the sulfide melt inclusions could be observed in both the pre and syn mineralization intrusions at yulong indicating that sulfide saturation had commonly occurred during magma evolution magnetite mineral inclusions could be observed in zircon and amphibole grains as well the mineral assemblage of magnetite pyrrhotite pyrite of the mineral inclusions constrains the yulong magmatic system to redox conditions near the magnetite pyrite pyrrhotite buffer and above the fayalite magnetite quartz buffer fmq high eu eu values 0 56 0 78 of the hosting zircons and high calculated nno values 0 5 of the hosting amphibole indicate highly oxidized nature of the parental magma both pre and syn mineralization intrusions have low pge contents pt 0 04 to 0 17 ppb pd 0 19 0 60 ppb with compositions plotting in the au poor porphyry cu fields in discriminating diagrams early sulfide saturation may have been reached and small amounts of sulfides have been segregated from magma most pges and au but little cu have been removed from the evolved magma because the partition coefficient of cu between sulfide and silicate melt is about two orders of magnitude lower than pge or au as a consequence the evolved magma would have high cu but very low pge and au resulting in the au poor porphyry cu mineralization at yulong

rapid transition to long lived deep crustal magmatic maturation and the formation of giant porphyry related mineralization yanacocha peru abstract the yanacocha magmatic field northern peru hosts the largest high sulfidation gold deposit on earth mineralization is associated with porphyritic intrusions distributed along a ne trending magmatic structural corridor eight of these intrusions investigated in this study range in age from 12 4 to 8 4 ma and show systematic chemical and isotopic changes through time they are interpreted to derive from hydrous mafic magmas evolving through amphibole clinopyroxene garnet fractionation and lower crust melting leaving a garnet residue at deeper levels which led to variably strong adakite like signatures and through plagioclase amphibole fractionation at shallower levels both accompanied by crustal assimilation and recharge recharge assimilation fractional crystallization rafc processes systematic geochemical and isotopic changes with intrusion ages coupled with plagioclase zoning and amphibole geobarometry suggest that the evolution of the magmatic system occurred through interaction of mantle derived melts with an increasing length of the crustal column and propagation from deep towards shallower crustal levels through time this was probably the result of a steadily increasing compression that has progressively slowed down magma ascent forcing magmas to evolve at a series of intermediate level chambers between the lower and upper crust increased compression might have been related to the onset of subduction of the buoyant inca oceanic plateau estimated to occur at 12 ma i e the same time of the onset of the rapid transition from normal to adakite like signatures the giant yanacocha ore system developed in coincidence with the 3 6 4 0 ma long intrusion of the adakite like magmas 12 4 12 0 8 4 ma formed by the above processes into a small upper crustal volume and peaked during the last 2 4 ma 10 8 8 4 ma of magmatic activity after a 1 4 ma long 12 4 11 0 ma maturation of magmas at deep crustal levels further investigation is needed to understand whether the association of adakite like magmas with ore which is typical of other giant porphyry systems is the result of the build up of incompatible volatiles and metals in oxidized magmas that evolve under high pressure conditions of recycling of lower crustal sulfide rich cumulates and or of a long lived focused transfer of magmas from deep to shallow crustal levels

relative oxidation states of magmas inferred from ce iv ce iii in zircon application to porphyry copper deposits of northern chile major and trace element compositions of zircons and whole rocks from 14 barren and seven ore bearing calc alkaline intrusions from the chuquicamata el abra porphyry copper belt of northern chile have been measured in situ by excimer laser ablation ela icp ms these data permit the ce iv ce iii ratio within zircon to be calculated using a lattice strain model for mineral melt partitioning of ce iv and ce iii zircon ce iv ce iii and eun eun ratios and by inference magmatic oxidation states generally increase from older mafic to younger felsic units within this sequence porphyry copper mineralization is directly associated only with intrusions with zircon ce iv ce iii 300 and eun eun 0 4 such trends can be understood in terms of interdependent relations between oxygen fugacity sulfur speciation and solubility and chalcophile element partitioning in silicate magmas because zircon occurs in most calc alkaline intrusions and is resistant to subsolidus alteration zircon ce iv ce iii ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic hydrothermal cu au mineralization the approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks

helium and argon isotope geochemistry of alkaline intrusion associated gold and copper deposits along the red river jinshajiang fault belt sw china abstract the red river jinshajiang strike slip fault zone on the eastern margin of the tibetan plateau was originally produced by the india eurasia collision 60 70 myr ago numerous post collisional mantle derived alkaline igneous rocks with ages of 40 30 ma have been intruded along this fault zone in recent years several copper and gold deposits associated with the alkaline intrusions of this region were discovered such as the yao an and beiya gold deposits and the yulong and machangqing copper deposits studied in this paper the mineralised intrusions are felsic with sio 2 ranging from 61 4 to 67 7 wt k 2 o na 2 o from 8 1 to 11 5 wt and k 2 o na 2 o 1 the deposits are located at both the exo and endo contact zones of the intrusions the mineral deposits are of hydrothermal origin with the ore forming temperatures mainly in the range 150 450 c this paper presents he and ar isotope analyses of these four deposits the concentrations of 4 he trapped in fluid inclusions of pyrites from the ores are 0 7 54 1 10 6 cm 3 stp g 1 and those of 40 ar are 0 6 7 3 10 6 cm 3 stp g 1 3 he 4 he ratios are 0 3 2 5 ra ra represents the 3 he 4 he ratio of air 1 39 10 6 40 ar 36 ar ratios are 316 1736 and 3 he 36 ar ratios are 0 2 11 2 10 3 generally the 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios for the gold deposits are higher than those for the copper deposits we suggest that the ore forming fluids of both gold and copper deposits were differentiated from the mantle derived alkaline magmas but were diluted by modified air saturated water masw that experienced intensive interaction with crustal rocks however the magmatic fluids responsible for the gold deposits were less extensively diluted by masw resulting in higher 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios than the copper deposits

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

sulfur partition coefficient between apatite and rhyolite the role of bulk s content experimental studies have been performed to constrain sulfur behavior during apatite crystallization and to determine sulfur partition coefficient between apatite and melt kd s apatite melt at oxidizing conditions crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk sulfur contents 0 15 to 2 wt s at 900 and 1 000 c 200 mpa and log f rm o 2 nno 3 6 the sulfur content in the glass increases with increasing amount of added s anhydrite crystallizes for s added 0 75 wt 0 10 and 0 13 wt so3 in glass at 900 and 1 000 c respectively the amount of anhydrite increases and the amount of apatite decreases with increasing amount of added sulfur the sulfur exchange reaction in apatite is influenced by the bulk composition of the melt e g p content however changing melt composition has only little effect on kd s apatite melt for the investigated rhyolitic composition the kd s apatite melt does not depend directly on temperature decreases from 14 2 to 2 7 with increasing s content in glass from so3 0 03 to 0 19 wt respectively and can be predicted from the following equation ln kd 0 0025 s in melt in ppm 2 9178 the combination of experimental data obtained for rhyolitic and andesitic melts reveals that the sulfur partition coefficient tends toward a value of 2 for high sulfur content in the glass 0 2 wt so3 using s in apatite as proxy for determining s content in melt is promising but additional experimental data are needed to clarify the individual effects of t f rm s 2 and p and ca content in the melt on s partitioning

geochemistry in situ sr nd hf o isotopes and mineralogical constraints on origin and magmatic hydrothermal evolution of the yulong porphyry cu mo deposit eastern tibet abstract the giant yulong porphyry cu mo deposit was formed in postsubduction setting in eastern tibet origin of the ore related yulong intrusion remains a matter of debate this study presents new whole rock major and trace element geochemistry in situ apatite sr nd and zircon hf o isotopes and mineralogical chemistry of the yulong intrusion least altered samples from the yulong intrusion have high sio2 66 3 69 5 wt and al2o3 14 9 15 5 wt contents high la yb 36 4 68 0 and sr y 46 0 76 3 ratios and low mgo 0 63 1 24 wt and cr nd isotopes show limited variations 87sr 86sr i 0 7060 0 7068 end t 4 8 0 2 which plot between paleo tethys ocean related arc magmas and the ancient crust in eastern tibet zircon grains from this study and published studies have mostly positive yet variable ehf t values 20 6 to 12 2 and young hf model ages that overlap those of the paleo tethys ocean related arc magmas the above sr nd hf isotopes together with the elevated zircon 18o values 6 4 to 9 3 and arc like trace element patterns collectively suggest that the yulong intrusion may have originated from partial melting of juvenile lower arc crust related to the subduction of the paleo tethys ocean with incorporation of a small amount of ancient crustal materials two generations of amphibole were recognized at yulong their compositions are used to calculate crystallization depths magmatic oxidation states and water contents the caculated results show that the early stage euhedral high al 5 87 8 51 wt amphibole phenocrysts may have crystallized in the underlying magma chamber 7 1 12 5 km in depth whereas the late stage xenomorphic low al 3 47 4 87 wt amphibole grains may have crystallized in the porphyritic stock 4 0 5 6 km magmatic water contents decrease from early 3 5 4 6 wt to late stage 2 8 3 5 wt amphibole which is interpreted to indicate fluid exsolution from the magma chamber during emplacement of the yulong intrusion caculated oxidation states increase from early nno 0 6 1 5 to late stage nno 1 9 2 3 amphibole plagioclase phenocrysts show periodic or reverse core to rim zonation of an contents range up to 25 mol which are coupled by feo contents probably suggesting magma recharge events collectively we propose that the magma chamber beneath yulong was recharged by a less evolved magma and was saturated in fluids to produce intensive alteration and mineralization the relatively high oxidation states allow the metals to be enriched in the evolving magma and to be deposited in the hydrothermal alteration stage

stochastic simulations of steady state unsaturated flow in a three layer heterogeneous dual continuum model of fractured rock abstract unsaturated flow through fractured rocks is a concern in the siting and performance of waste disposal facilities such as the proposed geological repository at yucca mountain nevada we simulated a small two dimensional cross section of welded volcanic tuff representative of yucca mountain stratigraphy using spatially correlated randomly heterogeneous fracture permeability fields and homogeneous matrix permeability continua representing various degrees of welding ten realizations each of fracture permeability fields for four different variances 2 0 5 1 0 1 5 and 2 0 were generated by the direct fourier transform method robin m j l gutjahr a l sudicky e a wilson j l 1993 cross correlated random field generation with the direct fourier transform method water resour res 29 7 2385 2398 independently for the welded tiva canyon tuff tcw the non welded paintbrush tuff ptn and the welded topopah spring tuff tsw the latter being the proposed primary repository horizon numerical simulations were run for steady state flow at three different uniform water flux boundary conditions boundary conditions along the sides were impermeable and the base was open to gas and liquid flow numerical simulations were performed using the dual continuum two phase flow simulator metra which represents matrix and fractures as dual overlapping continua where liquid flux between continua can be restricted by a uniform factor fracture matrix interaction was modeled as being less restricted in the ptn as compared to the tcw tsw heterogeneous fracture permeability fields generated strong preferential flow in the tcw tsw fracture continuum and significant preferential flow in the uniformly permeable ptn matrix continuum flow focusing led to a local increase in saturation which in turn increased relative permeability to water along the preferential pathways causing water to flow faster the development of the preferential pathways reduced the wetted surface area for fracture matrix interaction leaving a large volume of the rock isolated from the preferential flow pathways statistical analysis of water flux values in the three units showed that the magnitude of the ensemble variance indicating preferential flow pathways increased with both the variance of fracture permeability and the water flux boundary condition reaching a plateau in the tcw tsw fracture continuum units after flowing approximately 10 correlation scales of the vertical fracture permeability ensemble covariance of water flux normal to the layering revealed long range correlations in all units which is longer than the correlation length of the fracture permeability fields this suggests that the water flux boundary condition influences preferential flow in unsaturated dual continua media these results suggest that careful analysis of information on fracture permeability variability obtained from pneumatic and hydraulic tests is an important component in understanding deep percolation processes

water flow in unsaturated soil in layered slopes abstract the water flow in unsaturated soil in layered slopes sandwiching coarse materials was measured using inclined soil containers placed under a rain simulator the refraction law of water flow in saturated soils was extended to the flow in unsaturated soils the extended refraction law of water flow in saturated and unsaturated soils was applied to the flow at the interface between the masa sandy loam and either the plant or gravel layer using a jump condition and particular assumptions of hydraulic conductivity of materials the data obtained on infiltration steady percolation and drainage in the soil containers could be well explained by the proposed new concept of saturated and unsaturated refraction flow so far as we know the work reported here is the first specifically designed to elucidate the effects of abrupt change of hydraulic conductivity on the flow of water in unsaturated soil slopes

glacial geomorphological mapping a review of approaches and frameworks for best practice geomorphological mapping is a well established method for examining earth surface processes and landscape evolution in a range of environmental contexts in glacial research it provides crucial data for a wide range of process oriented studies and palaeoglaciological reconstructions in the latter case providing an essential geomorphological framework for establishing glacial chronologies in recent decades there have been significant developments in remote sensing and geographical information systems gis with a plethora of high quality remotely sensed datasets now often freely available most recently the emergence of unmanned aerial vehicle uav technology has allowed sub decimetre scale aerial images and digital elevation models dems to be obtained traditional field mapping methods still have an important role in glacial geomorphology particularly in cirque glacier valley glacier and icefield ice cap outlet settings field mapping is also used in ice sheet settings but often takes the form of necessarily highly selective ground truthing of remote mapping given the increasing abundance of datasets and methods available for mapping effective approaches are necessary to enable assimilation of data and ensure robustness this paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available with a focus on their applicability in particular glacial settings we distinguish two overarching work streams that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes i mapping of ice sheet geomorphological imprints using a combined remote sensing approach with some field checking where feasible and ii mapping of alpine and plateau style ice mass cirque glacier valley glacier icefield and ice cap geomorphological imprints using remote sensing and considerable field mapping key challenges to accurate and robust geomorphological mapping are highlighted often necessitating compromises and pragmatic solutions the importance of combining multiple datasets and or mapping approaches is emphasised akin to multi proxy approaches used in many earth science disciplines based on our review we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment comparison and integration of geomorphological data these will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions finally we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and or sedimentological evidence and that such data should ideally be collected as part of a holistic assessment of the overall glacier system

the influence of amphibole fractionation on the evolution of calc alkaline andesite and dacite tephra from the central aleutians alaska petrologic studies of tephra from kanaga adak and great sitkin islands indicate that amphibole fractionation and magma mixing are important processes controlling the composition of calc alkaline andesite and dacite magmas in the central aleutians amphibole is ubiquitous in tephra from kanaga and adak islands whereas it is present only in a basaltic andesite pumice from great sitkin dacitic tephra from great sitkin do not contain amphibole hornblende dacite tephra contain hb plag ox opx cpx phenocrysts with simple zoning patterns suggesting that the dacites evolved in isolated magma chambers andesitic tephra from adak contain two pyroxene and hornbelende populations and reversely zoned plagioclase indicating a more complex history involving mixing and fractional crystallization mass balance calculations suggest that the andesitic tephra may represent the complements of amphibole bearing cumulate xenoliths both formed during the evolution of high al basalts the presence of amphibole in andesitic and dacitic tephra implies that aleutian cale alkaline magmas evolve in the mid to lower crust under hydrous 4 wt h2o and oxidizing ni nio conditions amphibole bearing andesites and pyroxene bearing dacites from great sitkin indicates fractionation at several levels within the arc crust despite its absence in many calc alkaline andesite and dacite lavas open system behavior involving amphibole fractionation can explain the trace element characteristies of lavas found on adak island neither open nor closed system fractionation involving a pyroxene bearing assemblage is capable of explaining the trace element concentrations or ratios found in the adak suite we envision a scenario where amphibole was initially a liquidus phase in many calc alkaline magmas but was later replaced by pyroxenes as the magmas rose to shallow levels within the crust the mineral assemblage in these evolved lavas reflects shallow level equilibration of the magma whereas the trace element chemistry provides evidence for a earlier amphibole bearing mineral assemblage

the evolution of aqueous vapor from silicate melts effect on oxygen fugacity abstract the simplest possible aqueous vapor evolved from an iron bearing magma under normal conditions is an h 2 o h 2 mixture hydrogen is produced by the oxidation of fe ii to fe iii by water in the magma yielding an increase in f o 2 equations are derived which model this mass transfer process the resulting differential equation expresses the change in magmatic f o 2 as a function of a change in n 1 h 2 o the vapor evolution progress variable the calculations demonstrate that in this simple scheme very iron poor magmas h 2 o feo are required to produce significant increases in magmatic f o 2 the incremental increase in o 2 during vapor evolution becomes progressively smaller as o 2 increases with this process becoming highly inefficient as the hematite stability field is approached other more complete processes involving meteoric water assimilation of altered rocks and subsolidus processes may produce the observed increase in f o 2 inferred to have occurred in systems of normal iron contents in low iron systems such as the high silica rhyolitic magmas associated with climax type porphyry molybdenum systems high oxygen fugacities may be obtained by this mechanism

the alkaline porphyry associated yao an gold deposit yunnan china rare earth element and stable isotope evidence for magmatic hydrothermal ore formation the yao an vein type gold deposit is located in the ailaoshan jinshajiang alkaline intrusive belt yunnan province china and is associated both in time and space with 33 5 1 0 ma old alkaline intrusions the gold mineralization is associated with potassic wall rock alteration the ree distribution patterns of secondary k feldspar are generally similar to those of the igneous perthite but with about seven times higher total ree abundances the alteration is ascribed to a high ree magmatic fluid derived from the yao an alkaline intrusive suite the hydrothermal yao an gold deposit formed during two gold bearing stages i e a sulfide pyrite stage and a sulfide oxide stage pyrite specularite the ree abundance of early stage i pyrite is relatively high with strong enrichment in lree la yb n of 40 290 generally positive eu anomalies eu eu 0 86 1 55 and ree patterns very similar to those of secondary feldspar in contrast the later stage ii pyrite has much lower ree concentrations and lower la yb n of 5 5 11 8 eu eu of 0 49 0 76 and flat chondrite normalized spidergram patterns the stage i pyrite has 34s in the range of 2 2 to 3 2 and overlaps with regionally distributed pyrite in least altered syenite porphyry in contrast stage ii pyrite has much higher 34s values between 7 8 and 16 5 carbon isotope data for four samples from stage ii revealed 13c pdb values between 6 and 8 these stable isotope and ree data suggest that magmatic fluids of the alkaline intrusions caused both potassic alteration and stage i sulfide mineralization the system evolved from stage i to stage ii mineralization by influx of meteoric fluids with relatively heavier sulfur although calcite carbon isotope data suggest that the co2 remained dominantly of magmatic origin

hf isotopic characteristics of yulong copper molybdenum porphyry deposit in tibet and their geological significance the yulong ore deposit is a superlarge porphyry copper molybdenum deposit in the sanjiang region zircon in situ analysis gives 176hf 177hf ratios ranging from 0 282 681 to 0 282 884 and the average ehf t of 1 60 4 86 yulong rock 176hf 177hf ratios ranging from 0 282 812 of 0 282 884 and the average ehf t values of 2 39 4 92 ganlongla rock 176hf 177hf ratios ranging from 0 282 449 to 0 282 894 and the average ehf t values of 0 81 10 51 najiazha y3 rock these data indicate that the source rook or source region of the yulong porphyry copper molybdenum belt might have been the depleted upper mantle combined with geophysical data the authors hold that along with the asthenosphere upwelling the yulong porphyry rocks might have been derived from the partial melting of the thickened crust resulting from the underplating

using the continuum approach to model unsaturated flow in fractured rock the appropriateness of using the continuum approach for simulations of unsaturated flow through fractured rock is examined in a numerical study of water seepage into an underground opening a continuum model is calibrated against data generated with a high resolution model that created discrete flow and seepage behavior probabilistic predictions of injection data and seepage rates are then compared to the values from the discrete model the study shows that reasonable results can be obtained with a calibrated continuum model even for fractured systems in which the underlying flow processes are discrete calibration is a crucial step in this approach because it yields effective model related and process specific parameters the impact of discretization on the estimated parameters is discussed prediction uncertainty is evaluated by means of monte carlo simulations including both the impact of parameter uncertainties and the effect of local heterogeneity in this paper the advantages and limitations of the continuum approach are discussed from a practical perspective which includes a critical examination of project objectives data needs robustness of assumptions and prediction uncertainty

tracing the evolution and distribution of f and cl in plutonic systems from volatile bearing minerals a case study from the liujiawa pluton dabie orogen china fluorine and chlorine play an important role in magmatic differentiation hydrothermal alteration and related mineralization processes but tracing their evolution in magmatic and especially plutonic systems is not an easy task the f and cl in melts can be estimated from f and cl concentrations in minerals provided that partitioning between minerals and melts are constrained based on available partitioning models between mineral melt mineral fluid and melt fluid a set of equations has been derived to determine f and cl concentrations in melts from the compositions of amphibole biotite and apatite the new calculation procedure has been applied to a plutonic system the liujiawa pluton eastern dabie orogen china cl and f concentrations in amphiboles biotites and apatites from different rock types gabbronorite two pyroxene diorite clinopyroxene diorite and hornblende gabbro have been determined by electron microprobe most amphiboles show a negative correlation between log cl oh and mg number and a positive correlation between log f oh and a site occupation biotites from the gabbronorite and two pyroxene diorite show a slight positive correlation between log cl oh and mg which is however not the case for the clinopyroxene diorite apatites from all the samples are rich in f and show negative correlations between cl and f concentrations in our case study we demonstrate that the cl concentration in melt remains approximately constant at 1 000 2 000 ppm over the major crystallization interval but decreases strongly at near solidus temperatures as a result of fluid exsolution the f concentration in melt remains nearly constant at ca 2 000 3 000 ppm at high temperatures as well as near solidus conditions indicating that it is not largely affected by fluid exsolution because of its strongly preferred incorporation into melt interestingly the evolution of cl and f concentrations in melt with magmatic differentiation is similar to that determined in volcanic systems suggesting that the evolution of cl and f in melts during crystallization and late magmatic stages at depth plutonic systems is similar to that observed in volcanic systems during decompression and degassing

sulfur abundance and its speciation in oxidized alkaline melts abstract the sulfur concentrations and the relative proportions of s2 and s6 were measured by electron microprobe in a series of melt inclusions trapped in phenocrysts from different subduction related and within plate volcanoes the melt inclusions correspond to potassic and shoshonitic primary melts to tholeiitic and hawaiitic primitive melts in the tholeiitic and the transitional basaltic melt inclusions sulfur is mainly present as s2 s 6 s total 0 03 to 0 08 and varies from 0 13 to 0 18 wt the occurrence of immiscible sulfides attests to their saturation in shoshonitic and potassic primary melts sulfur s 0 12 to 0 32 wt is dissolved as both s2 and s6 s 6 s total 0 3 to 0 7 their oxygen fugacity estimated from the s 6 s total ratios ranges from ninio to ninio 1 log unit hawaiitic melts may also dissolve up to 0 3 wt sulfur possibly because of their oxidation state close to ninio as illustrated by samples from mt etna italy variations of sulfur at constant s 6 s total ratio and temperature in both the potassic and shoshonitic primary melts indicate that these melts are undersaturated with respect to a s rich condensed phase in agreement with their relatively high oxidation state it strongly suggests that sulfur behavior in relatively oxidized primary alkaline melts is controlled by the mantle source melting conditions

clustre semi automated lineament clustering for palaeo glacial reconstruction datasets containing large numbers 10 000 of glacial lineaments are increasingly being mapped from remotely sensed data in order to develop a palaeo glacial reconstruction or inversion the palimpsest landscape presents a complex record of past ice flow and deconstructing this information into a logical history is an involved task one stage in this process requires the identification of sets of genetically linked lineaments that can form the basis of a reconstruction this paper presents a semi automated algorithm clustre for lineament clustering that uses a locally adaptive region growing methodology after outlining the algorithm it is tested on synthetic datasets that simulate parallel and orthogonal cross cutting lineaments encompassing 1 500 separate classifications results show robust classification in most scenarios although parallel overlap of lineaments can cause false positive classification unless there are differences in lineament length case studies for dubawnt lake and victoria island canada are presented and compared to existing datasets for dubawnt lake 9 out of 14 classifications directly match incorporating 89 of lineaments for victoria island 57 out of 58 classifications directly match incorporating 95 of lineaments differences are related to small numbers of unclassified lineaments and parallel cross cutting lineaments that are of a similar length clustre enables the automated repeatable assignment of lineaments to flow sets using defined user criteria this is important as qualitative visual interpretation may introduce bias potentially weakening the testability of palaeo glacial reconstructions in addition once classified summary statistics of lineament clusters can be calculated and subsequently used during the reconstruction process

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

mesozoic multiphase magmatism at the xinan cu mo ore deposit zijinshan orefield geodynamic setting and metallogenic implications abstract the xinan cu mo deposit newly discovered in the zijinshan au cu mo orefield the largest porphyry epithermal system in se china is featured by the presence of abundant multi phase granitoids which reflects the complex mesozoic tectono magmatic evolution in the region new and published la icp ms zircon u pb age data reveal that the mesozoic zijinshan magmatism occurred in two major phases 1 middle to late jurassic ca 169 150 ma forming the zijinshan complex granite and the xinan monzogranite 2 late early cretaceous to earliest late cretaceous ca 112 98 ma forming the shimaoshan volcanic rocks sifang granodiorite and the xinan fine grained granodiorite porphyry porphyritic granodiorite and late aplite dykes additionally a possible earliest cretaceous magmatism ca 141 ma may have occurred based on inherited zircon evidence major and trace element geochemistry indicates that all the zijinshan igneous rocks show subduction related geochemical affinities zircon ce 4 ce 3 values of the late early cretaceous to earliest late cretaceous granitoids ce 4 ce 3 190 1706 are distinctly higher than the middle to late jurassic ones ce 4 ce 3 27 457 suggesting that the former were derived from more oxidized parental magma the middle to late jurassic zijinshan complex granite and monzogranite have e hf t values of 8 02 to 10 00 with the two stage hf model ages t dm2 of 1 72 to 1 84 ga similar to the paleoproterozoic metamorphosed cathaysia block basement suggesting that they were derived from partial melting of the basement the late early cretaceous to earliest late cretaceous sifang granodiorite and xinan fine grained granodiorite porphyry porphyritic granodiorite and aplite dykes contain higher and wider range of e hf t values 0 66 to 6 05 with t dm2 of 1 12 to 1 56 ga indicating that they were also partial melting product of the cathaysia basement but with more mantle and or juvenile mafic lower crustal input we propose that the zijinshan orefield was in a compressive pacific subduction related tectonic setting during the middle to late jurassic the regional tectonic regime may have changed to extensional in the late early cretaceous to earliest late cretaceous during which the pacific plate subduction direction change and the accompanying subduction roll back and slab window opening occurred the tectonic regime transition high oxygen fugacity and mantle mafic lower crustal materials involvement in the late early cretaceous to earliest late cretaceous may have generated the zijinshan porphyry related au cu mo mineralization

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

a highly mobile laurentide ice sheet revealed by satellite images of glacial lineations satellite images of the north american continent reveal previously unrecognized patterns of crossing drift lineations reflecting unexpected shifts of centres of mass of the laurentide ice sheet throughout the last glacial cycle such shifts must must have been associated with major global atmospheric circulation changes

major changes in ice stream dynamics during deglaciation of the north western margin of the laurentide ice sheet abstract victoria island lies at the north western limit of the former north american laurentide ice sheet in the canadian arctic archipelago and displays numerous cross cutting glacial lineations previous work suggests that several ice streams operated in this region during the last wisconsinan glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the arctic ocean this paper produces the first detailed synthesis of their behaviour from the last glacial maximum through to deglaciation 21 9 5 cal ka bp based on new mapping and a previously published radiocarbon constrained ice sheet margin chronology over 70 discrete ice flow events flow sets are fitted to the ice margin configuration to allow identification of several ice streams ranging in size from large and long lived thousands of years to much smaller and short lived hundreds of years the reconstruction depicts major ice streams in m clure strait and amundsen gulf which underwent relatively rapid retreat from the continental shelf edge at some time between 15 2 and 14 1 cal ka bp a period which encompasses climatic warming and rapid sea level rise meltwater pulse 1a following this overall retreat was slower and the ice streams exhibited asynchronous behaviour the amundsen gulf ice stream continued to operate during ice margin retreat whereas the m clure strait ice stream ceased operating and was replaced by an ice divide within 1000 years this ice divide was subsequently obliterated by another short lived phase of ice streaming in m clintock channel 13 cal ka bp the timing of this large ice discharge event coincides with the onset of the younger dryas subsequently a minor ice divide developed once again in m clintock channel before final deglaciation of the island shortly after 9 5 cal ka bp it is concluded that large ice streams at the nw margin of the laurentide ice sheet equivalent in size to the hudson strait ice stream underwent major changes during deglaciation resulting in punctuated delivery of icebergs into the arctic ocean published radiocarbon dates constrain this punctuated delivery as far as is possible within the limits imposed by their precision and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores

sulfur evolution of oxidized arc magmas as recorded in apatite from a porphyry copper batholith uniformly sulfur rich cores abruptly zoned to sulfur poor rims 1 to 0 2 wt so3 in apatite from the yerington batholith nevada indicate that early magma that is crystal poor oxidizing and sulfate rich evolved to sulfate poor magma via crystallization of anhydrite a mineral observed in magmas from pinatubo and el chichon we predict that the characteristic zonation to sulfur poor rims of apatite in the yerington batholith is common in other oxidized hydrous calc alkaline magmas and can be used to track cryptic anhydrite saturation as well as to monitor sulfur evolution sulfate rich arc magmas such as yerington magmas may crystallize to produce hydrothermal fluids rich in chlorine copper and sulfur and porphyry copper ores

high water contents of magmas and extensive fluid exsolution during the formation of the yulong porphyry cu mo deposit eastern tibet abstract the yulong porphyry cu mo ore district in eastern tibet features a series of eocene felsic porphyry intrusions only one of which is intensively mineralized in this study zircon u pb ages and major and trace element compositions of whole rock samples and in situ accessory minerals zircon apatite and titanite from these various intrusions were analyzed to determine the factors controlling cu mineralization new zircon u pb dating together with published zircon u pb ages suggest that these porphyry intrusions were emplaced over a relatively short period of time 43 9 0 6 ma to 40 9 0 3 ma with the mineralized yulong intrusion emplaced at a late stage of the magmatic activity 41 1 0 3 ma to 40 9 0 3 ma these intrusions have indistinguishable whole rock major and trace element compositions but the mineralized yulong intrusion has higher apatite and titanite la yb ratios average apatite la yb 115 1 28 5 n 52 average titanite la yb 22 4 4 9 n 38 than the earlier subeconomic intrusions average apatite la yb 50 4 12 3 n 72 average titanite la yb 12 4 3 5 n 58 suggesting more fractionation of amphibole from the magmas that sourced it additionally a negative relationship between la yb and cen cen ratios in apatite and titanite are interpreted to reflect increasing oxidation states through magma evolution indistinguishable zircon eun eun values and apatite core so3 contents from the mineralized zircon eun eun 0 69 0 06 n 25 apatite so3 0 65 0 24 wt n 21 and subeconomic intrusions zircon eun eun 0 62 0 05 n 64 apatite so3 0 61 0 27 wt n 15 suggest that the entire magmatic suite was relatively oxidized hydrous and sulfur rich and was therefore fertile for ore formation however apatite crystals from the mineralized yulong intrusion have significantly lower cl contents 0 08 0 03 wt n 72 and higher f cl ratios 47 80 21 97 n 72 than those from the subeconomic intrusions cl 0 29 0 29 wt f cl 12 87 5 16 n 78 these data may reflect more extensive fluid exsolution from the parental magma chamber at the time of emplacement of the mineralizing yulong magmas sudden and voluminous release of volatiles coeval with emplacement of the yulong intrusion was triggered by an as yet unidentified process but possibly including magmatic recharge

formation of mega scale glacial lineations on the dubawnt lake ice stream bed 1 size shape and spacing from a large remote sensing dataset abstract mega scale glacial lineations msgls are the largest flow parallel bedforms produced by ice sheets and are formed beneath rapidly flowing ice streams knowledge of their characteristics and genesis is likely to result in an improved understanding of the rate at which ice and sediment are discharged by ice sheets but there is little consensus as to how they are formed and there are few quantitative datasets of their characteristics with which to formulate or test hypotheses this paper presents the results of a remote sensing survey of 46 000 bedforms on the dubawnt lake palaeo ice stream bed focussing on a central transect of 17 038 that includes highly elongate bedforms previously described as msgls within this transect lineations exceed 10 km in length max 20 km and 23 have elongation ratios 10 1 max 149 1 highly elongate features are interspersed with much shorter drumlin like features but longer bedforms are typically narrower suggesting that their length develops more quickly than or at the expense of their width bedforms are broadly symmetrical in plan form and have a preferred lateral spacing of 50 250 m which implies a regular rather than random pattern of corrugations comparison with drumlins reveals that the more attenuated msgls simply extend the tail of the distribution of data rather than plotting as a separate population taken together this supports the idea of a subglacial bedform continuum primarily controlled by ice velocity but existing hypotheses of msgl formation are either not supported or are insufficiently developed to explain our observations rather we conclude that under conditions of rapid ice flow msgls attain their great length relatively quickly decades through a probable combination of subglacial deformation which attenuates ridges and erosional processes that removes material from between them

magmatic process recorded in plagioclase at the baogutu reduced porphyry cu deposit western junggar nw china abstract despite the fact that porphyry cu deposits contain large amounts of cu in one or more small stocks few studies have discussed evidence for significant magma recharge in porphyry cu deposits a systematic elemental and sr isotopic study of plagioclase crystals from mineralized diorite and granodiorite porphyry constrains the processes of crystallization and magma recharge at the baogutu reduced porphyry copper deposit western junggar nw china large compositional changes in an 12 24 mol are observed along with strong positive correlations between an and feo significant resorption textures are also preserved in plagioclase crystals as well as repeated oscillatory zoning in an and feo and complex sr isotope variations three types of crystals with different core to rim sr isotope variations are recognized type i crystals have core to rim increases in 87sr 86sr i that could be explained by diffusion for example sr isotope variations recorded in bck2 1 2 crystal could be generated by diffusion with simulated maximum crystal residence times of 100 500 years with the proximate value of 300 years type ii crystals with different variation trends in 87sr 86sr i on opposite sides of the core could be produced either by multi stage crystallization or by analytical uncertainty whereas type iii crystals with complex core to rim variations in 87sr 86sr i may record repeated magma recharge events all these results suggest repeated recharging of the magma chamber by hotter more mafic and less radiogenic sr isotope melts therefore more mafic melt injection recorded in plagioclase profiles may provide significant metal contributions to the magma chamber which ultimately results in cu mineralization at the baogutu reduced porphyry copper deposit

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

modeling capillary barriers in unsaturated fractured rock 1 this work presents a series of numerical modeling studies that investigate the hydrogeologic conditions required to form capillary barriers and the effect that capillary barriers have on fluid flow and tracer transport processes in the unsaturated fractured rock of yucca mountain nevada a potential site for storing high level radioactive waste the modeling approach is based on a dual continuum formulation of coupled multiphase fluid and tracer transport through fractured porous rock the numerical modeling results showed that effective capillary barriers can develop where both matrix and fracture capillary gradients tend to move water upward under the current hydrogeologic conceptualization of yucca mountain strong capillary barrier effects exist for diverting a significant amount of moisture flow through the relatively shallow paintbrush nonwelded unit with major faults observed at the site serving as major downward pathways for laterally diverted percolation fluxes in addition we used observed field liquid saturation and goechemical isotopic data to check model results and found consistent agreement

in situ la mc icp ms trace element and nd isotopic compositions and genesis of polygenetic titanite from the baogutu reduced porphyry cu deposit western junggar nw china abstract titanite sphene catisio 5 is sensitive to changes in temperature oxygen and water fugacity and fluid composition in order to understand formation processes and the nature of hydrothermal fluids various types of titanite from cu ores at the baogutu reduced porphyry cu deposit were chosen for detailed study magmatic titanite is associated with biotite plagioclase and k feldspar whereas hydrothermal titanite occurs with k feldspar chlorite actinolite and calcite the formation of hydrothermal titanite was related to hydration of igneous minerals under high f h 2 o whereas the widespread replacement of ilmenite by titanite without magnetite indicates a relatively low oxygen fugacity magmatic titanite has low al high fe y sn zr nb and ree contents relative to hydrothermal titanite on the basis of the zr in titanite and al in chlorite geothermometers formation temperatures for magmatic and hydrothermal titanite are estimated to be 687 739 c and 250 670 c respectively the gradual decrease in ree y and sn contents from magmatic to late hydrothermal titanite was probably caused by precipitation of ree bearing minerals magmatic and hydrothermal titanites have similar chondrite normalized ree patterns with negative eu anomalies and relatively flat hree randomly selected titanites have nd isotopic compositions similar to the host rocks thus both magmatic and hydrothermal titanite are believed to have been predominantly derived from a mantle source