microbially induced cementation to control sand response to undrained shear current methods to improve the engineering properties of sands are diverse with respect to methodology treatment uniformity cost environmental impact site accessibility requirements etc all of these methods have benefits and drawbacks and there continues to be a need to explore new possibilities of soil improvement particularly as suitable land for development becomes more scarce this paper presents the results of a study in which natural microbial biological processes were used to engineer a cemented soil matrix within initially loose collapsible sand microbially induced calcite precipitation micp was achieved using the microorganism bacillus pasteurii an aerobic bacterium pervasive in natural soil deposits the microbes were introduced to the sand specimens in a liquid growth medium amended with urea and a dissolved calcium source subsequent cementation treatments were passed through the specimen to increase the cementation level of the sand particle matrix the results of both micp and

are there relict crustal fragments beneath the moho 1 the application of new data enhancement techniques on a lithoprobe seismic reflection profile in northwest canada has produced images of upper mantle structures that are overlain with angular discordance by the reflection moho and are underlain by a relict mesoproterozoic subduction zone the reflection moho is interpreted to postdate the underlying fabric and may thus have been superimposed on it by thermal and or structural processes reflections within the mantle that are subparallel to the east dipping subduction zone are interpreted as structural fabric that formed during and perhaps as a consequence of subduction interpretation of the lithology in the upper mantle layering is uncertain as peridotites eclogites mafic granulites and or pelitic restites can have velocities and densities appropriate for seismic mantle or a portion of it nevertheless if some layers beneath the moho were originally in the crust they may retain a structural memory

holocene trends in 18o in land snail shells from the negev desert and their implications for changes in rainfall source areas abstract the 18o value of the carbonate of land snail shells is related to the 18o content of precipitation which in turn relates to the source region and trajectory of the rain bearing air masses analyses of 18o of the shell carbonate of 76 radiocarbon dated holocene samples of the land snail trochoidea seetzeni from the northern negev desert in southern israel were carried out and the results were compared to modern snails from the same region early holocene 18o values are similar to modern but during the period centered around 6500 6000 yr b p a depletion of some 2 below modern is observed a change in the atmospheric circulation pattern for this period is thus indicated most likely an increase in the frequency of storm systems reaching the region from north eastern africa by 3500 yr b p 18o values had reached modern levels and indicate a stable pattern of atmospheric circulation since that time

stress strain behavior of sands cemented by microbially induced calcite precipitation abstractmicrobial induced calcite precipitation micp is a novel biomediated ground improvement method that can be used to increase the shear strength and stiffness of soil the evolution of the shear strength and stiffness of sand subjected to undrained and drained shearing is evaluated using triaxial tests micp treated sands with cementation levels ranging from young uncemented sand to a highly cemented sandstonelike condition are subjected to undrained shear a transition from strain hardening to strain softening behavior and a corresponding transition of global to localized failure as cementation is increased is observed moderately cemented specimens are subjected to various stress paths which result in a change to the shear strength and volumetric behavior shear wave velocity is used to nondestructively monitor the change in small strain stiffness during shearing which provides an indication of cementation degradation as a function of strain level because shear wave velocity is influenced by

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

correlating the end triassic mass extinction and flood basalt volcanism at the 100 ka level new high precision u pb geochronology from volcanic ashes shows that the triassic juras sic boundary and end triassic biological crisis from two independent marine stratigraphic sections correlate with the onset of terrestrial fl ood volcanism in the central atlantic mag matic province to 150 ka this narrows the correlation between volcanism and mass extinc tion by an order of magnitude for any such catastrophe in earth history we also show that a concomitant drop and rise in sea level and negative 13 c spike in the very latest triassic occurred locally in 290 ka such rapid sea level fl uctuations on a global scale require that global cooling and glaciation were closely associated with the end triassic extinction and potentially driven by central atlantic magmatic province volcanism

stable isotope anomalies in mediterranean pleistocene records oxygen and carbon isotope records of twelve mediterranean cores raised from west alboran sea to east off israel and of four atlantic cores raised from the western side of gibraltar and located respectively inside below and beyond the modern mediterranean outflow are compared to open ocean records of core 71 139c from the north atlantic and core v19 30 from the east pacific oxygen isotope stratigraphies can be established for deep mediterranean records and the major events of the last 150 ka are easily identifiable for instance the five substages of stage 5 or the 18 ka event stage 2 are identified but the 10 ka event younger dryas is only recorded by globigerina bulloides and benthic foraminifera suggesting that the cooling affected only winter sst 14c dates for the two terminations ia and ib of the last deglaciation which are recorded in sediment cores from areas with high sedimentation rates faro ridge alboran sea sicilian strait are in good agreement with the dates published for the same termination in atlantic cores an intermediate step however has been identified in some cores at 14 ka and divides termination ia into two phases oxygen isotope anomalies are recorded by the shallow water species globigerinoides ruber they correspond to 1 a higher amplitude glacial interglacial change in 18o values which exceeds that of the open ocean by 1 in the western basin and by 1 7 in the eastern basin 2 large isotopic depletions during the deposition of sapropel s1 s3 and s5 they are interpreted as the result of fresh water run off responsible for a strong dilution in the shallower layers of the east mediterranean waters the isotopic effect of this dilution averages 0 75 for sapropel s1 and 1 6 for sapropel s5 during the last glacial maximum the mediterranean still acted as a concentration basin and a gradient of 18o values similar to the modern one 0 75 existed from west to east in the deep waters apparently deep water temperatures were lower during the last glacial but the decrease did not exceed 4 c in the eastern basin major anomalies are also contained in the 13c records of g bulloides and benthic foraminifera the 13c records from surface intermediate and deep waters of the eastern basin and from intermediate and deep waters of the western basin are opposite to that of the open ocean during glacial time 13c values were higher in intermediate and deep waters of the whole mediterranean and also in surface water of the eastern basin at the same time the 13c gradient of surface to deep waters was low this gradient increased during the last deglaciation while 13c values of g bulloides and benthic foraminifera decreased this decrease interrupted at 10 ka may have been related to increased fresh water run off from the bordering contintents due to increased precipitation especially in the tropical belt the 13c depletion is clearly recorded in the levantine and deep water masses and can be traced westward in the mediterranean outflow oxygen and carbon isotope anomalies recorded simultaneously in the east mediterranean by the shallow water species globigerinoides ruber during sapropel deposition indicate that increased precipitation on the bordering continents and strong fresh water run off during the time of the last deglaciation may have caused a density stratification and deep stagnation in the eastern basin uncertainties arise from the fact that in the mixing model deglacial mediterranean waters are mixed with continental fresh waters the isotopic characteristics of which are not entirely understood although increased surface water production of biogenic material can not be excluded as a possible cause of 13c depletion it appears that the river discharge including the nile as well as black sea input are also plausible sources for the fresh water layering

tectonic erosion of the peruvian forearc lima basin by subduction and nazca ridge collision 1 subsidence of lima basin part of the peruvian forearc is controlled by tectonic erosion by the subducting nazca plate multichannel seismic reflection data coupled with age and paleowater depth constraints derived from ocean drilling program odp coring now allow the rates of erosion to be reconstructed through time in trenchward locations the forearc has experienced limited recent relative uplift 700 850 m likely due to preferential basal erosion under the center of lima basin long term subsidence driven by basal tectonic erosion dominates and is fastest closest to the trench since 47 ma eocene up to 148 km of the plate margin have been lost at an average rate of up to 3 1 km myr 1 appoximately 110 km of that total appears to be lost since 11 ma implying much faster average rates of trench retreat 10 km myr 1 since collision of the nazca ridge with the lima basin at 11 ma although there is no clear subsidence event at odp site 679 during the time at which nazca ridge was subducting beneath this part of the forearc 4 11 ma the more trenchward odp sites 682 and 688 show significant deepening after 11 ma indicating that subduction of the ridge accelerates tectonic erosion long term rates of crustal erosion in the region of lima basin are greater than estimates of regional arc magmatic productivity implying that such margins are net sinks of continental crust

strength stiffness and microstructure characteristics of biocemented calcareous sand calcareous sands are known as problematic soils in nature and challenge geotechnical engineers in many practical projects microbially induced calcite precipitation micp is an innovative soil imp

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

internal dynamics of a paleoaccretionary wedge insights from combined isotope tectonochronology and sandbox modelling of the south central chilean forearc forearc accretionary wedges are cyclic systems in which material is frontally and or basally accreted material cycling involves underthrusting subduction underplating exhumation erosion transfer to the trench and underthrusting again in this study we present a novel tectonochronologic approach to constrain long term exhumation rates of basally accreted wedge complexes based on isotopic dating of structural features on petrological data and sandbox analogue simulations congruence between the structural inventory in nature and structures generated in scaled sandbox experiments allows detailed insights into wedge dynamics for the present day surface material of the paleoaccretionary wedge of south central chile valdivia area 40 s published u pb ages of detrital zircon place a maximum age of 278 ma for subduction prograde metamorphism at transitional greenschist to blueschist facies conditions 420 c 8 9 kbar was immediately followed by progressive penetrative deformation associated with basal accretion dated at 250 245 ma using rb sr internal mineral isochrons the accretion process involved duplex tectonics and antiformal stacking with formation of near horizontal mylonitic shear zones at around 241 ma continuous basal accretion at depth gave rise to an extensional tectonic regime at higher structural levels both semi ductile small scale extensional shear zones and post kinematic vein mineralizations yield rb sr ages of 235 ma tension gashes representing the latest isotopically dateable stage of structural evolution were formed at 210 ma at conditions of 230 c at 1 5 3 kbar as constrained by fluid inclusion data zircon fission track data indicate final cooling to below 200 c at 186 24 ma the results suggest continuous basal accretion for at least 50 ma with long term average exhumation rates of 0 6 0 2 mm a most probably outbalanced by similar long term average erosion rates changing plate boundary conditions at about 210 200 ma terminated the accretion process as evident from a dramatic decrease of exhumation rates at that time since then the paleoaccretionary wedge remained stably in place despite its delicate geotectonic position within the andean active margin the tectonochronologic approach complements thermochronologic and geomorphologic methods of exhumation research as it provides direct constraints on mass flux rates even for high temperature increments of p t trajectories

late quaternary paleoclimate in the eastern mediterranean region from stable isotope analysis of speleothems at soreq cave israel abstract the eastern mediterranean continental paleoclimate during the past 25 000 years was determined by a high resolution petrographic stable isotopic and age study of speleothems from soreq cave israel 18o 13c trends indicate that all speleothems older than 7000 yr formed under conditions that differ from those of today the period from 25 000 to 17 000 yr b p was characterized by the highest 18o and 13c values which indicate deposition at temperatures of 12 16 c annual rainfall of 300 450 mm and vegetation typical of a mixed c3 c4type from 17 000 to 10 000 yr b p deglaciation in northern europe 18o values dropped progressively correlative with warming 2 3 c and a gradual increase in precipitation a simultaneous decrease in 13c gives a range expected for c3 type vegetation this period also shows significant 18o and 13c spikes which are correlatable with global events e g heinrich events and the younger dryas stade the speleothems that grew between 10 000 and 7000 yr b p have a unique petrography showing irregular thin laminae of various colors and much detritus they have the lowest 18o corresponding to 1000 mm rain coupled with the highest 13c caused by flooding events which stripped the soil cover from 7000 to 1000 yr b p conditions became closer to those of today this study demonstrates that global events which were recognized in northern europe and north africa are also evident in the eastern mediterranean and are reflected principally by large changes in the rainfall rate

u pb geochronological constraints on the triassic jurassic ayu complex southern mexico derivation from the western margin of pangea a abstract we present la icp ms laser ablation inductively coupled plasma mass spectrometry u pb detrital and igneous zircon data of poly deformed metamorphic and igneous rocks of the ayu area southern mexico these rocks were previously inferred to be part of the late paleozoic acatlan complex but new age data indicate that they formed in the mesozoic and should be placed in the newly designated ayu complex the ayu complex comprises polydeformed metasedimentary rocks chazumba lithodeme of a turbidite like protolith that are intercalated with boudinaged ortho amphibolites with transitional arc to morb tholeiitic geochemistry in the south the metasedimentary sequence is affected by a ca 171 ma partial melting which formed the magdalena migmatite migmatization was accompanied by 171 168 ma intrusions of granodioritic dioritic and granitic dikes and sheets as well as pegmatite bodies which are characterized by inherited zircon populations of ca 260 290 320 360 420 480 880 990 and 1080 1250 ma that are also found in the chazumba lithodeme u pb detrital zircon dating of seven metasedimentary samples from the migmatized and unmigmatized chazumba lithodeme yielded youngest detrital zircons and clusters of 192 198 214 250 266 and 291 ma and are interpreted to reflect the late triassic middle jurassic deposition of turbiditic rocks the transitional arc tholeiitic geochemistry of the chazumba amphibolites is consistent with turbidite sedimentation in a back arc environment along a rifted passive margin close to a contemporaneous magmatic arc inferred flattening of the subduction zone led to subduction erosion during the early middle jurassic and underthrusting of the chazumba lithodeme to depths equivalent to amphibolite facies metamorphism steepening of the subducting slab and diachronous rifting within the gulf of mexico contributed to extensional tectonics recorded on the mexican mainland and facilitated the tectonic exhumation of the chazumba lithodeme by normal faulting along the reactivated providencia shear zone during the middle late jurassic more generally the documentation of arc back arc assemblages in the ayu complex requires deposition adjacent to a subducting ocean and thus supports a pangea a reconstruction that was synchronous with the breakup of pangea

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

cretaceous early paleocene drainage shift of amazonian rivers driven by equatorial atlantic ocean opening and andean uplift as deduced from the provenance of northern peruvian sedimentary rocks huallaga basin abstract the northern part of south america has undergone several major changes in its tectonic setting since the triassic evolving from rifting to the development of a retroarc foreland basin on its andean margin leading to margin extension and continental uplift following the breakup between africa and south america so far it is unclear when and how these geodynamic events affected the paleo amazonian drainage in this study we investigate the provenance of triassic eocene sedimentary rocks deposited in the northern peruvian amazonian basin based on their sr nd isotopic compositions and u pb zircon dating the triassic jurassic samples have end 0 values ranging from 7 9 to 10 0 and main u pb zircon peaks at 0 9 1 3 ga 31 33 and 0 5 0 7 ga 21 28 that suggest a mixed clastic supply from the western and eastern cordillera or craton within a rift to post rift setting samples from the albian maastrichtian interval yield much lower end 0 values 16 8 to 18 6 and a dominance of zircon grains derived from terranes in the easternmost brazilian shield ventuari tapajos 2 0 1 82 ga rio negro jurena 1 82 1 54 ga and rondonia san ignacio 1 54 1 3 ga thus indicating a cratonic source for these sedimentary rocks finally the early paleocene eocene sedimentary rocks record the first arrival of andean detritus in the amazonian retroarc foreland with end 0 values ranging between 5 6 to 12 0 and up to 16 of the zircon grains yielding ages younger than 120 ma together with recently published studies these provenance data document the existence of a long lived aptian maastrichtian continent wide cratonic drainage in the northern part of south america this cratonic drainage developed in response to the late cretaceous uplift of the northeastern part of the south america craton likely driven by geodynamic processes related to post rift opening of the atlantic equatorial ocean the formation of a late maastrichtian early paleocene mountain chain in the peruvian andes associated with the onset of provenance from the andean orogenic belt led to a shift of the amazon drainage pattern hence the earliest andean amazonian rivers are no younger than late maastrichtian early paleocene

the mejillonia suspect terrane northern chile late triassic fast burial and metamorphism of sediments in a magmatic arc environment extending into the early jurassic the mejillonia terrane named after the mejillones peninsula northern chile has been traditionally considered an early paleozoic block of metamorphic and igneous rocks displaced along the northern andean margin in the mesozoic however u pb shrimp zircon dating of metasedimentary and igneous rocks shows that the sedimentary protoliths were triassic and that metamorphism and magmatism took place in the late triassic norian field evidence combined with zircon dating detrital and metamorphic further suggests that the sedimentary protoliths were buried deformed foliated and folded and metamorphosed very rapidly probably within few million years at ca 210 ma the metasedimentary wedge was then uplifted and intruded by a late arc related tonalite body morro mejillones at 208 2 ma only a short time after the peak of metamorphism the mejillones metamorphic and igneous basement represents an accretionary wedge or marginal basin that underwent contractional deformation and metamorphism at the end of a late permian to late triassic anorogenic episode that is well known in chile and argentina renewal of subduction along the pre andean continental margin in the late triassic and the development of new subduction related magmatism are probably represented by the early jurassic bolfin punta tetas magmatic arc in the southern part of the peninsula for which an age of 184 1 ma was determined we suggest retaining the classification of mejillonia as a tectonostratigraphic terrane albeit in this new context

the cristal zn prospect amazonas region northern peru part ii an example of supergene enrichments in tropical areas abstract the cristal zn prospect is located in the northernmost part of a wide mining district corresponding to the charlotte bongara zinc project which covers an area of approximately 110 km2 in the amazonas region in northern peru the mineralized area consists of many zn occurrences that contain mixed sulfide and nonsulfide mineralizations the nonsulfide ores are interpreted to be the product of weathering of primary mvt sulfide bodies the zn concentrations of the cristal prospect are hosted by platform carbonates of the condorsinga formation early jurassic which belongs to the pucara group the prospect extends over an area of approximately 2 1 km with nearly continuous zones of zn enrichment that has been detected in soil and rock samples the nonsulfide mineralization consists mainly of semi amorphous orange to brown zinc oxides that include hemimorphite smithsonite and fe hydr oxides the most important mineralized areas are the esperanza and yolanda occurrences which were also most intensively explored in both occurrences the supergene zn carbonates and silicates infill solution cavities or replace the carbonate host rocks and or the primary sulfides forming smithsonite and hemimorphite rich mineralizations the analyzed drill core samples have on average 20 wt zn and maximum ge concentrations of 200 ppm the bongara area experienced a prolonged phase of weathering from miocene to recent under tropical climatic conditions in these conditions the weathering processes affected many pre existing sulfide deposits e g cristal florida canyon mina grande where supergene profiles were developed under locally different settings that are defined primarily on the basis of mineralogical and geochemical data contrary to the mina grande deposit at cristal the development of a karst network was minor due to limited uplift and supergene alteration did not completely obliterate the roots of the original sulfide orebody the mineralogy and geochemistry of bongara nonsulfides is dependent on two main factors at the local scale 1 uplift rates and 2 host rock composition the latter may have favored the development of more e g mina grande or less e g cristal alkaline supergene environments uplift was controlled by the activity of local faults which allowed the exposure of sulfide protores at variable elevations in different periods of time and hydrological settings such different settings resulted in the precipitation of isotopically different supergene carbonates e g smithsonites and calcites at mina grande and cristal

high temperature 350 c thermal histories of the long lived 500 ma active margin of ecuador and colombia apatite titanite and rutile u pb thermochronology abstract quantitative reconstruction of thermal histories can be a powerful tool to study numerous natural processes such as tectonic plate interaction cratonic stability and extra terrestrial phenomena such as asteroid ejection a majority of thermochronological studies have focused on temperatures lower than 300 c few previous studies have demonstrated that u pb data from apatite and other accessory phases can be used to recover thermal history information at t 350 c we present u pb data from apatite to constrain the thermal histories of triassic peralluminous anatectites from the northern andes between the temperatures of 350 550 c the accuracy of the thermal history models is assessed by comparisons with previous geological models and comparisons with pre existing and newly acquired u pb titanite and rutile 40ar 39ar muscovite and low temperature thermochronological data this study also examines the feasibility of using a large regionally dispersed apatite u pb data set to obtain continuous thermal history paths along a long lived 500 ma active margin a second aim of this study is to further test the hypothesis that the dominant mechanism for pb displacement through apatite is volume diffusion as opposed to aqueous fluid interaction the thermal history models derived from the triassic anatectites exposed in the andes of colombia and ecuador are entirely consistent with lower temperature thermochronological constraints and previously established geochronological and geochemical constraints they reveal and quantify trench parallel changes in the amount of jurassic early cretaceous extension significantly bolstering and adding to previous tectonic interpretations confirmation of the utility of u pb thermochronology provides geologists with a powerful tool for investigating the high temperature thermal evolution of accessory minerals

biogeochemical processes and geotechnical applications progress opportunities and challenges consideration of soil as a living ecosystem offers the potential for innovative and sustainable solutions to geotechnical problems this is a new paradigm for many in geotechnical engineering realising the potential of this paradigm requires a multidisciplinary approach that embraces biology and geochemistry to develop techniques for beneficial ground modification this paper assesses the progress opportunities and challenges in this emerging field biomediated geochemical processes which consist of a geochemical reaction regulated by subsurface microbiology currently being explored include mineral precipitation gas generation biofilm formation and biopolymer generation for each of these processes subsurface microbial processes are employed to create an environment conducive to the desired geochemical reactions among the minerals organic matter pore fluids and gases that constitute soil geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance sequestration of carbon soil erosion control groundwater flow control and remediation of soil and groundwater impacted by metals and radionuclides challenges in biomediated ground modification include upscaling processes from the laboratory to the field in situ monitoring of reactions reaction products and properties developing integrated biogeochemical and geotechnical models management of treatment by products establishing the durability and longevity reversibility of the process and education of engineers and researchers

andean flat slab subduction through time the analysis of magmatic distribution basin formation tectonic evolution and structural styles of different segments of the andes shows that most of the andes have experienced a stage of flat subduction evidence is presented here for a wide range of regions throughout the andes including the three present flat slab segments pampean peruvian bucaramanga three incipient flat slab segments carnegie guanacos tehuantepec three older and no longer active cenozoic flat slab segments altiplano puna payenia and an inferred palaeozoic flatslab segment early permian san rafael based on the present characteristics of the pampean flat slab combined with the peruvian and bucaramanga segments a pattern of geological processes can be attributed to slab shallowing and steepening this pattern permits recognition of other older cenozoic subhorizontal subduction zones throughout the andes based on crustal thickness two different settings of slab steepening are proposed slab steepening under thick crust leads to delamination basaltic underplating lower crustal melting extension and widespread rhyolitic volcanism as seen in the caldera formation and huge ignimbritic fields of the altiplano and puna segments on the other hand when steepening affects thin crust extension and extensive within plate basaltic flows reach the surface forming large volcanic provinces such as payenia in the southern andes this last case has very limited crustal melt along the axial part of the andean roots which shows incipient delamination based on these cases a palaeozoic flat slab is proposed with its subsequent steepening and widespread rhyolitic volcanism the geological evolution of the andes indicates that shallowing and steepening of the subduction zone are thus frequent processes which can be recognized throughout the entire system

zircon and titanite recording 1 5 million years of magma accretion crystallization and initial cooling in a composite pluton southern adamello batholith northern italy abstract the southern part of the adamello batholith the so called re di castello unit is an example of a composite pluton ranging from gabbro to granodiorite in composition u pb dating of single zircon crystals from four tonalitic to granodioritic lithologies reveals that zircon crystallization is protracted in all studied lithologies showing apparent durations of growth between 90 and 700 ka the youngest zircons crystallized near the solidus and yield identical or slightly older ages than titanite the formation of these autocrystic zircons is considered to approximate the age of emplacement of the melt and its final crystallization in contrast to antecrystic zircons present in the same sample which had formed earlier in the magmatic column or were derived from re mobilized earlier magma the autocryst derived emplacement ages range from 42 43 0 09 ma to 40 90 0 05 ma recording 1 5 ma of intrusion and crystallization history we anticipate that extended periods of zircon crystallization may be common in silicic rocks whereas the zircons from residual melts from initially undersaturated mafic liquids should yield far more precise emplacement ages within our present analytical uncertainties of 0 1 0 2 in 206 pb 238 u age decreasing th u ratios of dated zircons within one melt batch document the depletion of the residual melt portion in th due to the contemporaneous crystallization of titanite preliminary hf isotopic compositions of the dated zircon grains suggest that the early stage melts of the southern re di castello unit represent hybrid melts with an important crustal component e hf between 2 8 and 3 0 subsequently emplaced melts are more juvenile at e hf values at 6 4 to 8 9 and may thus reflect the addition of large volumes of mafic melt to the magmatic system

permo triassic anatexis continental rifting and the disassembly of western pangaea crustal anatectites are frequently observed along ocean continent active margins although their origins are disputed with interpretations varying between rift related and collisional we report geochemical isotopic and geochronological data that define an 1500 km long belt of s type meta granites along the andes of colombia and ecuador which formed during 275 223 ma these are accompanied by amphibolitized tholeiitic basaltic dykes that yield concordant zircon u pb dates ranging between 240 and 223 ma a model is presented which places these rocks within a compressive permian arc setting that existed during the amalgamation of westernmost pangaea anatexis and mafic intrusion during 240 223 ma are interpreted to have occurred during continental rifting which culminated in the formation of oceanic crust and initiated the break up of western pangaea compression during 275 240 ma generated small volumes of crustal melting rifting during 240 225 ma was characterized by basaltic underplating the intrusion of tholeiitic basalts and a peak in crustal melting tholeiitic intrusions during 225 216 ma isotopically resemble depleted mantle and yield no evidence for contamination by continental crust and we assign this period to the onset of continental drift dissected ophiolitic sequences in northern colombia yield zircon u pb dates of 216 ma the permo triassic margin of ecuador and colombia exhibits close temporal faunal and geochemical similarities with various crustal blocks that form the basement to parts of mexico and thus these may represent the relict conjugate margin to nw gondwana the magmatic record of the early disassembly of pangaea spans 20 ma 240 216 ma and the duration of rifting and rift drift transition is similar to that documented in cretaceous tertiary rift settings such as the west iberia newfoundland conjugate margins and the taupo lau havre system where rifting and continental disassembly also occurred over periods lasting 20 ma

annual trace element variations in a holocene speleothem high resolution secondary ionization mass spectrometry sims analysis along the growth axis of a holocene speleothem from northern scotland reveals high frequency oscillations and longer term trends in mg ca sr ca and ba ca at the scale of the high frequency oscillations mg ca and sr ca display a well defined anticorrelation while sr ca and ba ca are positively correlated imaging of elemental ratios in two dimensions reveals that the high frequency signal is well preserved and laterally continuous across the sample tims 230th ages and annual ultraviolet luminescence banding provide chronological control and demonstrate that the high frequency cyclicity is annual trace element variations in speleothem calcite are a reflection of hydrochemical processes in the unsaturated zone overlying the cave supply effects and partitioning at the water calcite interface mg partitioning between water and calcite is temperature dependent calculations suggest that the annual mg ca oscillations may be caused by seasonal temperature changes however the longer timescale variations in mg ca are too great to be explained by this mechanism seasonal variations in water residence time in the unsaturated zone which reflect effective precipitation provide a more probable explanation for the observed annual oscillations and also explain the inverse relationship between mg ca and sr ca this record suggests that trace elements in speleothems have the potential to provide the high resolution insights into interannual palaeoclimatic variability required for assessment of general circulation models

late paleozoic to triassic evolution of the gondwana margin evidence from chilean frontal cordilleran batholiths 28 s to 31 s upper paleozoic to triassic chilean granitoids in the andean frontal cordillera between 28 s and 31 s record crustal and mantle conditions at the gondwana margin during the final assembly and initial breakup of the pangea supercontinent this period overlaps the end of paleozoic terrane accretion and precedes andean subduction integration of new trace element and isotopic data with other information on the granitoids and the regional geology leads to a tectonic model that has implications for other parts of the gondwana margin in the model the carboniferous to early permian is a period of oblique convergence associated elqui complex granitoids are diverse those in the guanta and montosa units are predominantly related to subduction processes whereas those in the cochiguas and el volcan units are dominated by melting of the subduction complex and older crust progressive oblique collision of the last pre pangea terrane equis along the margin resulted in crustal thickening associated with shortening deformation of foreland basinal sedimentary rocks and uplift of the elqui complex subsequent gravitational collapse of the inactive slab and lithospheric delamination resulted in the production of large amounts of basalt which intruded and melted the crust producing the post collisional ingaguas complex the los carricitos granitoids formed in thickened crust whereas the chollay el colorado and el leon units formed in thinner crust the ingaguas complex is part of the choiyoi granite rhyolite province whose formation similar to that of other gondwana silicic provinces was probably accentuated by anomalously hot upper mantle associated with the pangea supercontinent

spatial coincidence and similar geochemistry of late triassic and eocene oligocene magmatism in the andes of northern chile evidence from the mmh porphyry type cu mo deposit chuquicamata district the mmh porphyry type copper molybdenum deposit in northern chile is the newest mine in the chuquicamata district one of largest copper concentrations on earth mineralized eocene oligocene porphyry intrusions are hosted by essentially barren triassic granodiorites despite a century of exploitation geologists still have problems in the mine distinguishing the triassic granodiorite from the most important ore carrying eocene porphyries in the district to resolve the problem internally consistent high quality geochemical analyses of the triassic and tertiary intrusives were carried out explaining the confusion they show that the rock units in question are nearly identical in composition and thus respond equally to hydrothermal alteration in detail the only difference in terms of chemical composition is that the main eocene oligocene porphyries carry relatively less fe and ni unexpectedly the mineralized eocene oligocene porphyries have consistently less u and th than other tertiary intrusions in the district a characteristic that may be valuable in exploration the supergiant copper molybdenum deposits in the central andes were formed within a narrow interval between 45 and 31 ma close to 7 of the 200 my duration of andean magmatism which resulted from subduction of oceanic lithosphere under south america since the jurassic although recent work has shown that subduction was active on the margin since paleozoic times pre andean pre jurassic gondwanan magmatism is often described as being very different having involved crustal melting and the generation of massive peraluminous rhyolites and granites this study shows that the indistinguishable late triassic and eocene oligocene intrusions occupy the same narrow ns geographic belt in northern chile if it is accepted that magma character may determine the potential to generate economic cu mo deposits then late triassic volcano plutonic centres in the same location in the south american margin could have contained valuable ore deposits although their preservation will depend on the level attained by pre mid jurassic erosion both late triassic and eocene oligocene magmatic events occurred during the waning stages of vigorous volcano plutonic cycles and both preceded apparent gaps in igneous activity rhaetian and post oligocene abrupt lateral shifts of the volcanic front and radical changes in the character of the magmas generated both late triassic and eocene oligocene intrusions were emplaced along the same narrow strip of crust it is probable that they both exploited the same deep crustal structures the eocene oligocene magmatic front was controlled by an orogen parallel shear system caused by oblique subduction it is possible that late triassic magmatism along the same belt had a similar setting the identified rhaetian gap in subduction and magmatism may have widespread implications

spatial and temporal evolution of liassic to paleocene arc activity in southern peru unraveled by zircon u pb and hf in situ data on plutonic rocks cordilleran type batholiths are built by prolonged arc activity along active continental margins and provide detailed magmatic records of the subduction system evolution they complement the stratigraphic record from the associated forearcs and backarcs we performed in situ u pb geochronology and hf isotope measurements on zircon grains from a large set of plutonic rocks from the coastal batholith in southern peru this batholith emplaced into the precambrian basement and the mesozoic sedimentary cover we identify two major periods of voluminous arc activity during the jurassic 200 175 ma and the late cretaceous paleocene 90 60 ma jurassic arc magmatism mainly resulted in the emplacement of a dominantly mafic suite with ehf values ranging from 9 5 to 0 1 published ages south of the arequipa area suggest that the arc migrated southwestward out of the study area during the middle jurassic after a magmatic gap of 85 ma arc activity abruptly resumed 90 ma ago in arequipa intrusive bodies emplaced into both basement and older jurassic intrusions and strata this activity culminated between 70 and 60 ma with the emplacement of very large volumes of dominantly quartz dioritic magmas this last episode may be considered as a flare up event characterized by intense magmatic transfers into the crust and rapid relief creation the late cretaceous paleocene initial ehf are shifted toward positive values up to 3 3 and 2 6 compared to the jurassic ones indicating either a larger input of juvenile magmas a lesser interaction with the ancient crust or an increase of re melting of young mantle derived mafic lower crust these magmatic fluxes with juvenile component are coeval with the onset of the crustal thickening at 90 ma and represent a significant contribution to the formation of the continental crust in this area

a chronostratigraphic framework for the upper stormberg group implications for the triassic jurassic boundary in southern africa abstract the upper stormberg group elliot and clarens formations of the main karoo basin is well known for its fossil vertebrate fauna comprising early branching members of lineages including mammals dinosaurs and turtles despite 150 years of scientific study the upper stormberg group lacks radioisotopic age constraints and remains coarsely dated via imprecise faunal correlations here we synthesise previous litho and magnetostratigraphic studies and present a comprehensive biostratigraphic review of the upper stormberg fauna we also present the results of the first geochronological assessment of the unit across the basin using u pb dates derived from detrital zircons obtained from tuffaceous sandstones and siltstones the youngest of which are considered maximum depositional ages our results confirm that the elliot formation contains the triassic jurassic boundary making it one of the few fossiliferous continental units that records the effects of the end triassic mass extinction event our work suggests a mid norian rhaetian age for the lower elliot formation and a hettangian sinemurian age for the upper elliot formation although the precise stratigraphic position of the triassic jurassic rhaetian hettangian boundary remains somewhat uncertain a mainly pliensbachian age is obtained for the clarens formation the new dates allow direct comparison with better calibrated triassic jurassic faunas of the western hemisphere e g chinle and los colorados formations we show that sauropodomorph but not ornithischian or theropod dinosaurs were well established in the main karoo basin 220 million years ago and that typical norian faunas e g aetosaurs phytosaurs are either rare or absent in the lower elliot formation which is paucispecific compared to the upper elliot while this is unlikely the result of geographic sampling biases it could be due to historical sampling intensity differences

heterogeneous melt and hypersaline liquid inclusions in shallow porphyry type mineralization as markers of the magmatic hydrothermal transition cerro de pasco district peru recently identified occurrences of porphyry style mineralization evidence the link of the world s second largest known epithermal base metal cerro de pasco deposit peru to a porphyry system emplaced at depth they consist of i quartz monzonite dykes and ii the south western part of the large diatreme dome complex adjacent to the main ore bodies of cerro de pasco and iii stockwork of banded quartz magnetite chalcopyrite pyrite porphyry type veinlets crosscutting trachyte porphyritic intrusion cropping out at surface in the central part of the diatreme dome complex the latter porphyry type mineralization observed at the same erosion level as the main epithermal base metal carbonate replacement ore bodies is the subject of this work geological constraints indicate a shallow emplacement level depth 1 km p 270 bar implying rather unusual low pressure and high temperature environment for the formation of porphyry style mineralization the banded porphyry type veinlets record a multiphase history of formation with two successive high temperature n600 c stages followed by a lower temperature b350 c stage more than 90 of the quartz in veinlets precipitates during the first two high temperature stages stage 1 is characterized by the entrapment in hydrothermal quartz of inclusions containing variable proportions of both silicate melt and metal rich hypersaline n90 wt nacl eq liquid hereafter referred to as heterogeneous silicate melt inclusions hsmis the latter are rarely described in porphyry type mineralization we suggest that during stage 1 the inclusions result from heterogeneous entrapment of an evolved hydrous rhyolitic melt mixed with a hypersaline fluid phase at low pressure 270 bar and high temperature n600 c the stage 2 is marked by the entrapment of metaland sulfur rich hypersaline liquid inclusions with salinity around 70 wt nacl eq originated from the adiabatic ascent of magmatic hypersaline fluids transferred fromdeeper parts of the system the lower temperature stage 3 is characterized by an important temperature drop from n600 c to b350 c as revealed bymicrothermometry of aqueous two phase liquid vapor l v inclusions quartz textures revealed by sem cl imaging allowascribing the sulfide precipitation to the low temperaturemineralization stage 3 in situ sims 18o 16o isotope analyses of quartz across the veinlets are indicative of a magmatic signature of the fluids during the first two stages while quartz from stage 3 has oxygen isotopic compositions suggestive of minor contribution of meteoric waters to a predominantly magmatic aqueous fluid 10 vol of meteoric input which probably triggered cu fe sulfide precipitation in the stockwork high metal and sulfur contents of hsmis and hypersaline liquid inclusions determined by la icp ms are interpreted to represent the fluid composition prior to the main sulfide precipitation event the similar pb zn ratio of the bulk ore extracted from the epithermal ore bodies at cerro de pasco and the hsmis and hypersaline liquid inclusions suggest a common source of the fluids associated with the different mineralization styles at cerro de pasco

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

distinguishing between in situ and accretionary growth of continents along active margins abstract active continental margins represent both sites of crustal loss by tectonic erosion and gain by juvenile magmatism and oceanic arc plateau accretion estimating the gain component depends on distinguishing between growth of margins by either accretion of oceanic crust or juvenile magmatic addition during extension distinguishing between these allochthonous and autochthonous models is frequently ambiguous due to difficulties in interpreting the tectonic origin of mafic rocks we present a detailed geochronological and isotopic study constraining the evolution of the continental margin of northwest south america during 190 113 ma semi continuous slab rollback resulted in crustal thinning juvenile magmatism and ultimately the removal of continental slivers negating previous hypotheses that the margin evolved by the accretion of an island arc however basic crustal growth estimates along with comparisons between rocks exposed in northern peru and the northern andes imply that uneven losses of continental crust occurred along northwest south america for mesozoic exposures and that the accretion of the caribbean large igneous province clip onto nw south america probably played a crucial role in maintaining and preserving mesozoic continental crust north of the huancabamba deflection

the applicability of microbially induced calcite precipitation micp for internal erosion control in gravel sand mixtures seepage induced internal erosion in earth filled embankment dams has been attracting the attention of civil engineering researchers and practitioners for decades microbially induced carbonate prec

germanium enrichment in supergene settings evidence from the cristal nonsulfide zn prospect bongara district northern peru supergene nonsulfide ores form from the weathering of sulfide mineralization given the geochemical affinity of ge to si4 and fe3 weathering of ge bearing sulfides could potentially lead to ge enrichments in silicate and fe oxy hydroxide minerals although bulk rock ge concentrations in supergene nonsulfide deposits are rarely reported here we present the results of an investigation into ge concentrations and deportment in the cristal supergene zn nonsulfide prospect bongara northern peru which formed from the weathering of a preexisting mississippi valley type mvt sulfide deposit material examined in this study originates from drillcore recovered from oxidized zn rich bodies 15 20 m thick containing 5 45 wt zn and ge concentrations 100 ppm microanalysis and laser ablation icp ms show that precursor sphalerite is rich in both fe mean fe 8 19 wt and ge mean ge 142 ppm using the mineral geothermometer ggimfis geothermometer for ga ge in mn and fe in sphalerite proposed by frenzel et al ore geol rev 76 52 78 2016 sphalerite trace element data from the cristal prospect suggest a possible formation temperature tggimfis of 225 50 c anomalously high for a mvt deposit germanium concentrations measured in both goethite mean values 100 to 229 ppm max 511 ppm and hemimorphite mean values 39 to 137 ppm max 258 ppm are similar to concentrations measured in hypogene sphalerite additionally the ge concentrations recorded in bulk rock analyses of sphalerite bearing and oxidized samples are also similar a persistent warm humid climate is interpreted for the region resulting in the development of an oxidation zone favoring the formation of abundant zn hydrosilicates and fe hydroxides both able to incorporate ge in their crystal structure in this scenario ge has been prevented from dispersion during the weathering of the ge bearing sulfide bodies and remains in the resultant nonsulfide ore

tectono sequence stratigraphy and u pb zircon ages of the rincon blanco depocenter northern cuyo rift argentina abstract extensional processes that followed the gondwanan orogeny rise to the development of a series of rift basins along the continental margin over older accreted eopaleozoic terranes stratigraphic structural paleontological and isotopic studies are presented in this work in order to constrain the ages of the sedimentary infilling and to analyze the tectosedimentary evolution of one of the cuyo basin depocenters known as rincon blanco this asymmetrical half graben was filled by continental sediments under a strong tectonic control the infilling was strongly controlled by tectonics which in term produced distinctive features along the whole sedimentary sequence using a combination of lithological and structural data the infilling was subdivided into packages of genetically linked units bounded by regional extended surfaces several tuffs and acid volcanic rocks have been collected across the whole section of the rincon blanco sub basin for shrimp and la mc icpms u pb zircon dating the ages obtained range from 246 4 1 1 ma to 230 3 1 5 ma which is the time elapsed for the deposition of three tectono sequence units separated by regional unconformities and mainly constrained to the middle triassic they are interpreted as a result of a reactivation of the extensional system that has evolved along strike as segments of faults that linked together and or as laterally propagating faults regional correlation with coeval rift basins permits to establish north south propagation in the extensional regime along the western margin of sw gondwana this trending started in the lowermost triassic and extended until the latest triassic two of them were precisely correlated with cerro puntudo and cacheuta half graben systems the new data indicate that the three sequences were mostly deposited during the middle triassic 246 to 230 ma with no evidence of sedimentation during norian and rhaetian which is in conflict with some previous biostratigraphic studies

slow rates of subduction erosion and coastal underplating along the andean margin of chile and peru marine seismic and drilling data from the andean margin of peru and northern chile show trench retreat and tectonic erosion since at least 20 ma however the onshore coastal zone has undergone modest regional uplift since ca 2 ma this argues against subduction erosion of the margin by steady state retreat such as recognized in tonga or south sandwich instead we identify a new style of slow tectonic erosion uplifted forearc sediments indicate underplating of subducted material beneath the base of the coastal forearc synchronous with tectonic erosion under the trenchward part of the forearc these observations require slow rates of forearc crust subduction in the region during this time period averaging no more than 13 km3 m y km since 20 ma as the forearc wedge taper increased isostatic volume estimates suggest that as much as 85 of subducted material was underplated under the forearc since 330 ka and does not contribute to crustal growth under the andes the switch in tectonic style parallels that in the southern andes but cannot be triggered by increased sediment flux to the trench as proposed for that area

mesozoic arc magmatism along the southern peruvian margin during gondwana breakup and dispersal abstract a high resolution u pb zircon geochronological study of plutonic units along the south peruvian margin between 17 and 18 s allows the integration of the geochemical geodynamic and tectonic evolution of this part of the andean margin this study focuses on the composite jurassic early cretaceous ilo batholith that was emplaced along the southern peruvian coast during two episodes of intrusive magmatism a first period between 173 and 152 ma with a peak in magmatic activity between roughly 168 and 162 ma and a second period between 110 and 106 ma emplacement of the jurassic part of the composite ilo batholith shortly post dated the accumulation of the volcanosedimentary succession it intruded chocolate formation which allows to estimate a subsidence rate for this unit of 3 5 km ma the emplacement of the main peak of jurassic plutonism of the ilo batholith was also closely coeval with widespread and repeated slumping during deposition of the cachios formation in the back arc region suggesting a common causal link between these phenomena which is discussed in the context of an observed 100 km trenchward arc migration at 175 ma and the relation with extensional tectonics that prevailed along the central andean margin during pangaea break up

proto andean evolution of the eastern cordillera of peru abstract the eastern cordillera of peru represents one of the longest 1200 km paleozoic metamorphic and magmatic belts exposed along the western andean margin of south america in this study we examine the tectonothermal evolution of a key segment of the metasedimentary basement of the eastern cordillera of peru the huaytapallana complex and demonstrate that it has experienced a hitherto undocumented high grade orogenic event at 260 ma latest middle permian based on u pb and th pb monazite age data from paragneisses and u pb dating of zircon rims from leucosomes these ages are interpreted as recording crystallization and are consistent with 255 ma rutile growth in lower grade units u pb apatite data c 260 230 ma in all units are consistent with slow cooling from this 260 ma metamorphic peak u pb zircon geochronology of pre tectonic plutons yield ages ranging from c 302 ma to c 260 ma these geochronological data are augmented by new u pb apatite age data from other segments along the eastern cordillera of peru a regional synthesis of existing geochronological constraints from the eastern cordillera of peru demonstrates that the margin has experienced a polycyclic orogenic history deformation and magmatism occurred at c 480 ma and c 435 ma during the famatinian orogenic cycle was followed by a late silurian to early carboniferous c 420 350 ma magmatic and metamorphic gap and terminated with gondwanide magmatism and metamorphism at c 315 ma and c 260 ma these famatinian and gondwanide orogenic phases can be correlated into the proto andean margin of argentina and chile and are thus of regional extent the evolution of the proto andean margin is thus best explained by changes in tectonic plate reorganization in a long lived paleozoic accretionary orogen which was undergoing phases of advance and retreat resulting in magmatic pulses and orogenic phases which can be correlated along the length of the plate boundary

cyclic dilution of magmatic metal rich hypersaline fluids by magmatic low salinity fluid a major process generating the giant epithermal polymetallic deposit of cerro de pasco peru the giant mid miocene cerro de pasco cordilleran polymetallic zn pb ag cu bi deposit in central peru formed during three successive mineralization stages resulting in low to high sulfidation mineral associations emplaced at a paleodepth from 500 to 1 500 m 1 pyrrhotite pipes grading outward to sphalerite and galena replacement bodies stage a 2 deep quartz pyrite veins stage b1 and a funnel shaped massive replacement body of pyrite quartz stage b2 with quartz sericite kaolinite alteration and 3 well zoned zn pb bi ag cu carbonate replacement orebodies stage c1 and e w trending cu ag au zn pb enargite pyrite veins stage c2 stages c1 and c2 are accompanied by advanced argillic alteration field evidence indicates that the epithermal polymetallic mineralization has formed in the shallow part of a porphyry system a detailed microthermometric and laser ablation inductively coupled plasma mass spectrometry la icpms study of fluid inclusions hosted in gangue and using near infrared microscopy opaque ore minerals from the different mineralization stages as well as available bulk and in situ secondary ion mass spectrometry sims stable isotopic data allow reconstruction of the evolution and tracing of the source s of the mineralizing fluids fluid inclusions are two phase l v homogenize to liquid at moderate temperatures 220 280 c in stages a b1 b2 and c2 and down to 150 c in stage c1 and show a wide salinity range 1 2 19 wt nacl equiv with no evidence of phase separation fluids during mineralization stages a b1 b2 and c1 are the result of mixing between a moderate salinity metal rich magmatic fluid and a low salinity fluid at the shallow site of deposition the moderate salinity metal rich magmatic fluid cannot be interpreted as an evolved intermediate density fluid or its boiling product due to its salinity up to 19 wt nacl equiv its high base metal concentration 1 wt mn fe zn and pb and its high li b as and sb contents up to several thousands of ppm the obtained results suggest that the moderate salinity metal rich magmatic fluid results from mixing at depth between metal rich hypersaline fluids and low salinity magmatic fluids exsolved late in the lifetime of the magmatic hydrothermal system the moderate salinity metal rich magmatic fluid resulting from this deep mixing rose to the epithermal environment where it in turn mixed with low salinity fluids that were stored below the paleowater table and had similar temperatures to the moderate salinity fluid in contrast enargite pyrite veins of stage c2 were formed by the ascent of co2 bearing contracted vapor like fluids that subsequently mixed with cold meteoric water no interaction with the moderate salinity metal rich magmatic fluids has been registered in stage c2 the similarity between fluid compositions and evolution during stages a b1 b2 and c1 contrasts with their significantly different mineral assemblages that are rather controlled by changing fo2 ph fs2 and temperature trace element la icp ms analyses of sphalerite pyrite and enargite also reveal important compositional differences the trace elements in the measured minerals reside to a significant extent in micro to nanoscale solid sulfide and or sulfosalt inclusions a direct correlation between fluid composition recorded in the studied fluid inclusion assemblages and the measured trace element composition of sphalerite pyrite and enargite has not been found in most cases the cyclic rise of metal rich moderately saline fluids that issued from dilution of hypersaline fluids stored at depth by low salinity magmatic fluids is a major process in the formation of stages a b1 b2 and c1 of the giant epithermal polymetallic deposit of cerro de pasco such a mechanism may also explain moderate salinity fluids 20 wt nacl equiv recorded in other magmatic related polymetallic epithermal deposits worldwide

experimental optimization of microbial induced carbonate precipitation for soil improvement abstractimplementation of laboratory tested biomediated soil improvement techniques in the field depends on upscaling the primary processes and controlling their rates microbial induced carbonate precipitation micp holds the potential for increasing the shear stiffness and reducing the hydraulic conductivity by harnessing a natural microbiological process that precipitates calcium carbonate the study presented herein focuses on controlling micp treatment of one dimensional flow half meter scale column experiments treatment was optimized by varying procedural parameters in five pairs of experiments including flow rates flow direction and formulations of biological and chemical amendments monitoring of column experiments included spatial and temporal measurements of the physical chemical and biological properties essential to the performance of micp including shear wave velocity permeability calcium carbonate content aqueous calcium aqueous ammonium aqueous urea and bacterial density rela

continuous early last glacial palaeoenvironmental record from a tasmanian speleothem based on stable isotope and minor element variations a columnar stalagmite from a limestone cave in the florentine valley tasmania has been dated by three 230th 234u age determinations continuous profiles of 170 18o and 13c values as well as magnesium and strontium concentrations are presented 18o values indicate temperatures lower than today with a gradual temperature decline in the basal part of the profile punctuated by two short cooling events and culminating in a double temperature minimum between 70 and 60 ka the profile shows marked similarities with the gisp ice core record from greenland which shows two short intense stadials centred on 74 and 70 ka preceding the last glacial temperature minimum they have been correlated with heinrich events in north atlantic marine cores which in turn have been attributed to periodic massive discharges of icebergs into the north atlantic the tasmanian speleothem record suggests that these events may also have affected climates in the southern hemisphere the 13c variations also appear to indicate periodic environmental change minor element variations were found to be significantly correlated with isotopic changes strontium concentrations show a bimodal distribution indicating control by a switching mechanism tentatively attributed to variations in calcitic dust supply to the ground surface above the site

geochronological constraints on post extinction recovery of the ammonoids and carbon cycle perturbations during the early jurassic abstract this paper presents the first quantitative study of the early jurassic recovery of ammonoids after the end triassic mass extinction based on detailed u pb id tims isotope dilution thermal ionization mass spectrometry geochronology from ash bed zircons placed within a clear phylogenetical and biochronological framework at the subzonal and species level this study was triggered by the discovery of a rich peruvian succession of ammonites deposited concomitantly with an unusually large number of ash beds two major phases of rediversification are observed during the psiloceras spelae and angulaticeras zones that correspond to positive peaks in the 13corg curve providing a possible link between biodiversity and the global carbon cycle in the case of the post extinction recovery the development of the earliest hettangian ammonites occurs within the genus psiloceras which begins with the occurrence of p spelae and then explodes into worldwide development of smooth psiloceratids of the psiloceras planorbis group s l this rapid biodiversification likely occurred less than 100 ka after the end triassic crisis the genus psiloceras occupied all the possible ecological niches worldwide from the pacific deep waters to the nw european shallow deposits and also in some rare tethyan occurrences like at germig in tibet this global dispersion allowed the differentiation of the group in several major phyla the schlotheimiidae discamphiceratinae arietitidae and lytocerataceae which were the roots of all other jurassic and cretaceous ammonites

late permian middle jurassic lithospheric thinning in peru and bolivia and its bearing on andean age tectonics abstract integrated studies and revisions of sedimentary basins and associated magmatism in peru and bolivia 8 22 s show that this part of western gondwana underwent rifting during the late permian middle jurassic interval rifting started in central peru in the late permian and propagated southwards into bolivia until the liassic dogger along an axis that coincides with the present eastern cordillera southwest of this region lithospheric thinning developed in the early jurassic and culminated in the middle jurassic producing considerable subsidence in the arequipa basin of southern peru this 110 ma long interval of lithospheric thinning ended 160 ma with the onset of malm earliest cretaceous partial rift inversion in the eastern cordillera area the lithospheric heterogeneities inherited from these processes are likely to have largely influenced the distribution and features of younger compressional and or transpressional deformations in particular the altiplano plateau corresponds to a paleotectonic domain of normal lithospheric thickness that was bounded by two elongated areas underlain by thinned lithosphere the high eastern cordillera of peru and bolivia results from late oligocene neogene intense inversion of the easternmost thinned area

tectonics and sedimentation in southern south america during triassic abstract triassic continental sedimentation in southern south america is related to the gondwanides orogenesis directly there were two distinct phases of sedimentation 1 the wide alluvial basins during early triassic and 2 the restricted extensional basins during middle and late triassic the main early triassic deposits are the sanga do cabral supersequence southernmost brazil and uruguay and the talampaya and tarjados sequences western argentina these deposits represent poorly channelized braided rivers with source areas in the gondwanides units under compressional tectonic setting the main middle and late triassic strata are rifts in the back arc setting such as the ischigualasto and cuyo basins western argentina and in the intracontinental setting santa maria supersequence southernmost brazil these basins are mainly composed of alluvial lacustrine and deltaic deposits with a great pyroclastic contribution in the case of the basins of argentina two rift sequences were identified in the western argentina basins composed of syn rift alluvial deposition followed by lake transgression the sag phase is marked by the progradation of deltaic and high sinuosity rivers the southernmost brazil deposits were divided into three rift sequences composed of low sinuosity rivers followed by lake transgression the progradation of deltaic and fluvial systems marks the sag phase the accommodation space generation within the back arc rifts was high if compared to the intracontinental coeval basin due to higher base level and higher tectonic subsidence rates the development of deep organic matter rich lakes suggests a more humid palaeoclimate in the back arc region than in the intracontinental setting where playa lakes dominated the back arc rifts are related to sinistral transtensional stresses in the western branch of gondwanides region the intracontinental rifts the southernmost brazil deposits and coeval rift basins of southern africa were generated by transtensional stresses within a dextral shear zone the shear is related to stress transmission from the southern branch of the gonwanides where oblique compression occurred

geodynamic evolution of the northern and central andes during early to middle mesozoic times a tethyan model the early to middle mesozoic sedimentary and magmatic history of the northern and central andes i e the nne trending colombian ecuadorian segment and the nw trending peruvian segment exhibits a spatially contrasted evolution involving several successive tectonic and geodynamic settings the late triassic to late liassic period began with a widespread marine transgression from the latest triassic the colombian marine shelf was progressively destroyed by southward propagating extensional tectonic activity but marine sedimentation continued in peru during this time no significant magmatic activity is recorded except in the emerging colombian area this period is interpreted as the result of rifting of a tethyan oceanic arm which separated the colombian and palaeo mexican margins from latest liassic an important calc alkaline magmatic arc developed along the emergent colombian segment further south the north peruvian shelf probably emerged but marine sedimentation continued in southern peru during middle and early late jurassic times the colombian segment was characterized by important magmatic activity and by coarse clastic continental sedimentation along the peruvian segment a turbiditic trough emergent areas and continental basins were created and the scarcity of calc alkaline magmatism suggests that only very local subduction took place this period is regarded as one of the southeastward subduction beneath the colombian segment and of tethyan oceanic crust originating in the newly formed colombian oceanic arm this pattern would have induced a chiefly left lateral transform motion along the peruvian segment by kimmeridgian tithonian times the palaeogeographic framework had drastically changed along the colombian segment magmatic activity ceased and continental accretions occurred along dextral strike slip sutures in peru tectonic activity was recorded by the creation of a new turbiditic trough and by the resumption of detrital sedimentation in the coastal area arc related volcanism indicated that subduction took place beneath this segment this geodynamic change is interpreted as the result of a sharp decrease in the spreading activity of the tethyan ridges and replacement by pacific spreading centres inducing a roughly northeastward convergence direction

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

enhancing the axial compression response of pervious concrete ground improvement piles using biogrouting abstractthis paper presents an innovative grouted ground improvement pile alternative biogrouted pervious concrete pile biogrouting is a potential ground improvement technique that utilizes soil bacteria to induce calcium carbonate caco3 precipitation to cement soil particles the most commonly investigated biogrouting method is microbial induced carbonate precipitation micp previous large scale applications of micp have encountered practical difficulties including bioclogging which results in a limited zone of cemented soil around injection points and heterogeneous distribution of caco3 the research presented in this paper focuses on evaluating the feasibility of micp biogrouting of a limited soil zone surrounding permeable piles to improve their responses when subjected to axial compression loading to investigate this two instrumented pervious concrete piles with diameters of 76 mm and lengths of 1 07 m with and without micp biogrouting were subjected to compression loading at the soil struc

sulfide replacement processes revealed by textural and la icp ms trace element analyses example from the early mineralization stages at cerro de pasco peru the large cerro de pasco cordilleran base metal deposit in central peru is the result of three successive mineralizing stages comprising both low and high sulfidation mineral associations a several pyrrhotite pipes grading outward to sphalerite and galena replacement bodies b a massive funnel shaped pyrite quartz replacement orebody and c e w trending cu ag au zn pb enargite pyrite veins and well zoned zn pb bi ag cu carbonate replacement orebodies this superposition of hydrothermal events leads to complex replacement textures and crosscutting relationships a detailed study of the textures and mineral composition of the up to 15 m wide replacement front existing between the pyrrhotite pipes and the pyrite quartz body allows for clarification of the relative chronology of the hydrothermal events the results show that in contrast to previous interpretations the emplacement of the pyrrhotite pipes and their zn pb mineralized rims precedes that of the pyrite quartz body the replacement textures affecting pyrrhotite and arsenopyrite and the nature of the newly formed minerals have been used as a qualitative way to track the evolution of fs2 fo2 and ph of the mineralizing fluids two steps of pyrrhotite replacement have been recorded the first one takes place under moderate acidity and relatively reduced to moderately oxidized conditions and is marked by replacement of pyrrhotite by euhedral nonporous pyrite the second step occurs under more acidic and oxidized conditions and is characterized by replacement of pyrrhotite by porous marcasite and replacement of arsenopyrite by pyrite subsequently marcasite is partly replaced by fine grained euhedral nonporous pyrite la icp ms trace element analyses of the replaced pyrrhotite and arsenopyrite and of the newly formed marcasite and pyrite support dissolution reprecipitation as the main mechanism for replacement positive correlations between some of the elements e g pb sb pb ag are indicative of the possible presence of nanoscale solid inclusions as main carriers for those elements however coupled substitutions and incorporation of some of the elements at a ppm level into the pyrite and marcasite structures cannot be excluded the obtained as sb pb and bi values in pyrite are systematically higher than published data of pyrite in epithermal and porphyry systems nature and trace element content of the newly formed minerals yield information on the physicochemical conditions during their precipitation the initial trace element content of replaced minerals and the subsequently dissolved neighboring phases the results show that the metal concentration of the fluid is locally influenced by the composition of the dissolved minerals this study leads to a simpler interpretation of the fluid evolution than previously proposed with a progressive increase of fs2 fo2 and ph as a result of decreasing wall rock buffering during the three successive mineralizing stages at cerro de pasco

magmatic rifting of pangaea linked to onset of south american plate motion abstract the causes of the transition from amagmatic to magmatic rifting during continental break up are not always clear and have been often linked to the break through of a plume however stress fields recorded in the crust may offer new insights into the relationship between changes in the stress field and the onset of magmatism in this paper stress fields recorded in the crust of north america are used to test possible causes of the break up of pangaea and the transition from amagmatic to magmatic rifting finite element models reveal that the most likely scenario for the break up involves the initial northwest motion of north america at 230 ma followed by a south southeast motion of south america at 200 ma with the initiation of magmatism and finally a weakened area between north and south america sometime soon after 200 ma which resulted in north america being dominated by northwest motion once again it was also determined that plate boundary structure and orientation play a large part in the recorded stress fields and must be taken into consideration when modeling continental break ups and rifting

deciphering the late cretaceous cenozoic structural evolution of the north peruvian forearc system the link between plate tectonics and the evolution of active margins is still an ongoing task to challenge since the acceptance of plate tectonic paradigm this paper aims at deciphering the structural architecture and uplift history of the north peruvian forearc system to better understand the evolution and the mechanics that govern the late cretaceous cenozoic building of this active margin in this study we report surface structural geology data interpretation of seismic reflection profiles apatite fission track data and the construction of two offshore onshore crustal scale balanced cross sections the structure of the north peruvian forearc system is dominated by an accretionary style with northwestward propagation of thrust related structural highs involving continental oceanic basement rocks and off scrapped sediments the thrust systems bound thick thrust top forearc depocenters mainly deformed by crustal normal to strike slip faults and thin skinned gravitational instabilities the sequential restoration of the margin calibrated with apatite fission track data suggests a correlation between uplift shortening and plate convergence velocity during late cretaceous and miocene pliocene quaternary shortening and uplift of the coastal zone is rather related to the subduction of asperities during convergence rate decrease the development of crustal normal to strike slip faulting and subsidence zones might be the consequence of slab flexure local basal erosion along subduction fault and or oblique subduction associated with sediment loading control we conclude that the evolution of the north peruvian forearc system was controlled by subduction dynamics strong sediment accumulation and recent ridge subduction and it recorded the orogenic loading evolution of the andes over the cenozoic

influence of confinement and cementation level on the behavior of microbial induced calcite precipitated sands under monotonic drained loading abstractmicrobial induced calcite precipitation micp is a novel ground improvement method to increase strength and stiffness of sand using natural biogeochemical processes cementation level and confining pressure are two important factors that control the behavior of micp sand the monotonic mechanical response of micp cemented sand is systematically investigated using four cementation levels untreated lightly treated moderately treated and heavily treated and three levels of effective confining pressure 100 200 and 400 kpa the results indicate that the stiffness peak shear strength and dilation increases with an increase in calcite content at a given effective confining pressure and the dilation is suppressed with an increase in effective confining pressure this behavior is consistent with soil like behavior therefore all the micp soils presented herein are evaluated using critical state soil mechanics and not an analogous fracture mechanics framework the experimental results also indi

paleolimnology evolution in rift basins the ischigualasto villa union basin central western argentina during the triassic abstract extensional basins offer a high preservation potential for sedimentary and fossil records nonmarine rift basins contain diverse environments including fluvial and lacustrine lake deposits have long been recognized as significant archives of the paleoenvironmental record the ischigualasto villa union basin represents the only nearly continuous continental triassic record with up to 6000 m of alluvial fluvial and lacustrine deposits the deep lacustrine interval is known as the los rastros formation and consists of several lacustrine deltaic cycles a detailed facies analysis allowed the characterization of five facies associations and two types of cycles 1 a shoreline dominated progradational type i cycle containing facies association a offshore lacustrine deposits and facies association b marginal palustrine deposits along the shoreline of the lake or facies association c lacustrine siliciclastic coastal deposits and 2 a delta dominated progradational type ii cycle characterized by facies association a offshore lacustrine and prodelta deposits facies association d delta front deposits and facies association e delta plain deposits the sedimentary evolution of the chanares los rastros sequence is defined within this extensional setting as one depositional sequence with three system tracts lowstand transgressive and highstand system tract biotic abiotic and sedimentologic data allowed the interpretation of the limnologic dynamics of the los rastros paleolake as a deep freshwater lake within a half graben exhibiting meromixis and showing a change from moderate eutrophic conditions with low oxygen content to relatively oxygenated oligotrophic conditions the successive fluctuations recorded in lake level are considered in the sequence stratigraphic framework of bohacs et al to reflect the relative balance of sediment and water input versus accommodation in an overfilled lacustrine basin

high resolution temporal record of holocene ground water chemistry tracing links between climate and hydrology strontium isotope analysis of precisely dated calcite growth layers in holocene speleothems from barbados west indies reveals high resolution temporal variations in ground water composition and may provide a new approach to documenting the links between climate variability andfluctuations in the hydrologic cycle such as recharge rates andflow paths the speleothems grew in a cave that developed in a fresh water aquifer in upliftedpleistocenereeflimestones threeperiodsofground watersrisotopeevolutionare observed 87 sr 86 srvaluesdecreasedfrom6to4ka increasedfrom4to1ka anddecreased again after 1 ka the sr isotope oscillations appear to record periodic variations in the relative sr fluxes to ground water from exchangeable soil sites vs carbonate mineral reactions asreflectedin 87 sr 86 srvaluesofmodernbarbadosgroundwaters ahydrologic model that explains changes in ground waterflow routes in karst aquifers as a function of amountofrainfallrechargecanaccountforthespeleothemsrisotoperecord independent holoceneclimaterecordsthatindicateamajorperiodofaridityataround1 3 1 1kainthe american tropics correspond with periodic variations in rainfall on barbados that are predicted by this hydrologic model

palaeozoic to early jurassic history of the northwestern corner of gondwana and implications for the evolution of the iapetus rheic and pacific oceans abstract the palaeozoic to mesozoic igneous and metamorphic basement rocks exposed in the merida andes of venezuela and the santander massif of colombia are generally considered to define allochthonous terranes that accreted to the margin of gondwana during the ordovician and the carboniferous however terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains a general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the merida andes and the santander massif we present new zircon u pb icp ms data from 52 igneous and metamorphic rocks which we combine with whole rock geochemical and pb isotopic data to constrain the tectonic history of the precambrian to mesozoic basement of the merida andes and the santander massif these data show that the basement rocks of these massifs are autochthonous to gondwana and share a similar tectono magmatic history with the gondwanan margin of peru chile and argentina which evolved during the subduction of oceanic lithosphere of the iapetus ocean the oldest palaeozoic arc magmatism is recorded at 500 ma and was followed shortly by barrovian metamorphism peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at 477 ma and the intrusion of synkinematic granitoids until 472 ma subsequent retrogression resulted from localised back arc or intra arc extension at 453 ma when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement continental arc magmatism dwindled after 430 ma and terminated at 415 ma coevally with most of the western margin of gondwana after pangaea amalgamation in the late carboniferous to early permian a magmatic arc developed on its western margin at 294 ma as a result of subduction of oceanic crust of the palaeo pacific ocean intermittent arc magmatism recorded between 294 and 225 ma was followed by the onset of the andean subduction cycle at 213 ma in an extensional regime extension was accompanied by slab roll back which led to the migration of the arc axis into the central cordillera of colombia in the early jurassic

the geological history of northwestern south america from pangaea to the early collision of the caribbean large igneous province 290 75ma abstract northwestern south america preserves a record of the assembly of western pangaea its disassembly and initiation of the far western tethys wilson cycle subsequent pacific margin magmatism and ocean plateau continent interaction since the late cretaceous numerous models have been presented for various time slices although they are based on either spatially restricted datasets or dates that are inaccurate estimates of the time of crystallisation here we review a very large quantity of geochronological geochemical thermochronological sedimentological and palaeomagnetic data that collectively provide tight constraints for geological models these data have been collected over a trench pacific parallel distance of 1500 km colombia and ecuador and reveal important temporal trends in rifting and subduction the temporal framework for our model constraints are obtained from robust concordant zircon u pb ages of magmatic rocks during 290 75 ma the late cretaceous thermal history of the margin

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

mineralized breccia clasts a window into hidden porphyry type mineralization underlying the epithermal polymetallic deposit of cerro de pasco peru cerro de pasco peru is known for its large epithermal polymetallic zn pb ag cu bi mineralization emplaced at shallow level a few hundred meters below the paleo surface at the border of a large diatreme dome complex porphyry style veins crosscutting hornfels and magmatic rock clasts are found in the diatreme breccia and in quartz monzonite porphyry dikes such mineralized veins in clasts allow investigation of high temperature porphyry style mineralization developed in the deep portions of magmatic hydrothermal systems quartz in porphyry style veins contains silicate melt inclusions as well as fluid and solid mineral inclusions two types of high temperature 600 c quartz molybdenite chalcopyrite pyrite veins are found in the clasts early thin 1 2 mm and sinuous ht1 veins are crosscut by slightly thicker up to 2 cm and more regular ht2 veins the ht1 vein quartz hosts co2 and sulfur rich high density vapor inclusions two subtypes of the ht1 veins have been defined based on the nature of mineral inclusions hosted in quartz i ht1bt veins with inclusions of k feldspar biotite rutile and minor titanite and ii ht1px veins with inclusions of actinolite augite titanite apatite and minor rutile using an emplacement depth of the veins of between 2 and 3 km 500 to 800 bar derived from the diatreme breccia architecture and the supposed erosion preceding the diatreme formation multiple mineral thermobarometers are applied the data indicate that ht1 veins were formed at temperatures 700 c ht2 veins host assemblages of polyphase brine inclusions generally coexisting with low density vapor rich inclusions trapped at temperatures around 600 c rhyolitic silicate melt inclusions found in both ht1 and ht2 veins represent melt droplets transported by the ascending hydrothermal fluids la icp ms analyses reveal a chemical evolution coherent with the crystallization of an evolved rhyolitic melt quartz from both ht1 and ht2 veins also contains secondary low temperature 300 c brine and aqueous fluid inclusions that record the cooling of the system both vein types are locally crosscut and or reopened by a pre diatreme polymetallic event consisting of pyrite sphalerite with chalcopyrite disease galena chalcopyrite tetrahedrite tennantite and minor quartz la icp ms analyses of mineral and high temperature fluid inclusions hosted in ht1 and ht2 veins and in situ secondary ion mass spectrometry oxygen isotope analyses of vein quartz indicate a magmatic signature for the mineralizing fluids with no major meteoric water input and allow reconstruction of the source and chemical evolution of fluids that formed these porphyry style veins as snapshots of the early and deep mineralizations at cerro de pasco this detailed study of the porphyry type mineralization hosted in clasts offers a unique opportunity to reconstruct the late magmatic and early hydrothermal evolutions of porphyry mineralization underlying the world class cerro de pasco epithermal polymetallic zn pb ag cu bi deposit

evidence for an early holocene climatic optimum in the antarctic deep ice core record in the interpretation of the antarctic deep ice core data little attention has been given to the holocene part of the records as far as translation of the stable isotope content in terms of temperature is concerned this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no 14c dating has yet been available for this type of sequence in this article we focus on the dome c and vostok cores and on a new 850 m long ice core drilled out at komsomolskaia by the soviet antarctic expeditions these three sites are located in east antarctica on the antarctic plateau in a region essentially undisturbed by ice flow conditions so that their detailed intercomparison may allow us to identify the climatically significant isotopic signal our results compare well with the proximal records of southern hemisphere high latitudes and support the existence of a warmer climatic optimum between 10 and 6 ka y bp maximum temperatures are reached just at the end of the last deglaciation which confirms previous observations at high latitudes in contrast with later dates for the atlantic and hypsithermal optima in europe and north america

late paleozoic to jurassic silicic magmatism at the gondwana margin analogy to the middle proterozoic in north america a vast region of upper paleozoic to middle jurassic 300 150 ma silicic magmatic rocks that erupted inboard of the gondwana margin is a possible phanerozoic analogue to the extensive middle proterozoic 1500 1350 ma silicic magmatic province that underlies much of the southern mid continent of north america like the north american rocks the gondwana silicic magmas appear to be melts of crust that formed about 200 300 m y earlier in the north american case this older crust formed and was accreted to the continent during a major period of crustal formation 1700 1900 ma whereas in the gondwana case the crust that melted consisted mainly of magmatic are terranes accreted to the continental margin during the paleozoic in both cases basic to intermediate magmatic rocks are extremely rare and magmatism is less abundant in regions that contain older and previously melted crust the similarities between the north american and gondwana silicic rocks suggest that both suites formed in extensional settings where basaltic magmas ponded at the base of the preheated crust caused extensive crustal melting that inhibited upward passage of the basalts in both cases silicic volcanism occurred after major assembly of a supercontinent by subduction and accretion processes and before breakup of the supercontinent by analogy with the polar wander curves for gondwana the granite rhyolite provinces may have formed during a period of very slow motion of the supercontinents relative to the poles

mass spectrometric dating of flowstones from stump cross caverns and lancaster hole yorkshire palaeoclimate implications a terrestrial flowstone sequence 97 cm thick from stump cross caverns yorkshire has been dated by both mass spectrometric and alpha spectrometric 238u 234u 230th dating and is demonstrated to have been deposited predominantly during interstadial periods over the last 170 ka with no growth in periods of glaciation or within the oxygen isotope stage 5 interglacial growth also occurs within oxygen isotope stages 4 and 6 the former possibly correlating with interstadials recognised in high resolution ice and ocean core records comparison with the timing of growth of a mass spectrometrically dated lancaster hole flowstone also from the same region demonstrates only limited agreement these differences are due to two factors limiting deposition at stump cross flooding of the cave passage in warm periods and the development of continuous permafrost or glacier cover in periods of severe climatic deterioration deposition at lancaster hole was controlled by limitations in ground water supply rather than flooding of the cave passage the results presented here demonstrate that in addition to regional palaeoclimate factors local site conditions may limit speleothem growth we conclude that in future palaeoclimate studies the growth record from several coeval speleothem samples must be considered before a regional palaeoclimate interpretation can be made

multiple rejuvenation episodes of a silicic magma reservoir at the origin of the large diatreme dome complex and porphyry type mineralization events at cerro de pasco peru abstract the cerro de pasco district in central peru hosts one of the world largest porphyry related epithermal polymetallic deposits the district is centered onto a large diatreme dome complex crosscut by numerous dacite to rhyodacite bodies showing domal structures and quartz monzonite dykes three temporally distinct high temperature porphyry type mineralization events have been recognized pm1 pm2 and pm3 dating of the latter by molybdenite re os and by zircon u pb la icp ms and ca id tims geochronology complements the already available dataset of zircon u pb ages of the subvolcanic and volcanic rocks mostly dacitic in composition occurring in the district and shows the existence of successive short lived episodes 50 at pressures between 0 9 and 3 4 kbar and at temperatures between 680 c and 725 c at such conditions magma is beyond the point of rheological lock up and is not eruptible the emplacement of the mostly dacitic subvolcanic and volcanic rocks has required a series of rejuvenation events of the upper crustal high crystallinity silicic magma reservoir field relationships and geochronology indicate that emplacement of the subvolcanic and volcanic rocks is preceded each time by high temperature 600 c quartz pyrite magnetite chalcopyrite and quartz molybdenite veining forming the three recognized porphyry type mineralization events hydrothermal quartz of these veins host silicate melt inclusions a rare feature in hydrothermal veins their composition determined by la icp ms analysis indicates that the mineralizing fluids potentially sourced from intermediate magma recharges have circulated in a magma reservoir in which the residual interstitial melt was more evolved than the melt trapped as inclusions in the magmatic quartz the combined geochemical and geochronological data obtained show that several episodes of rejuvenation of a highly crystallized upper crustal silicic magma reservoir probably triggered by intermediate magma recharges and by circulation of co2 and s rich fluids exsolved from them are at the origin of the large diatreme dome complex and porphyry type mineralization events at cerro de pasco

characterisation of triassic rifting in peru and implications for the early disassembly of western pangaea abstract triassic igneous and sedimentary rocks exposed within the basement of the andes were deposited in a series of rifts and may record the early disassembly of western pangaea these rocks are sporadically exposed along almost the entire length of western south america although reliable geochronological and isotopic data are sparse we combine new geochronological zircon u pb isotopic hf nd and geochemical data with stratigraphic observations to constrain the age and tectonic setting of the mitu rift of southern peru the peruvian mitu rift is compared with other triassic rifts in colombia and ecuador palanda rift 240 225 ma bolivia mitu rift triassic bolivia chile and argentina e g cuyo basin 246 230 ma and conclusions are reached regarding the relationship between triassic extension along the western margin of pangaea and the eventual formation of the proto caribbean and central atlantic oceans the mitu rift peru was active during 245 240 to 220 ma and was synchronous with rifting along the pacific margin of colombia and ecuador along the chilean margin and western argentina and probably rifting within bolivia rifting north of the huancabamba deflection was accompanied by subduction and led to seafloor spreading whereas rifting along the peruvian and chilean margins mainly occurred in the absence of subduction and terminated prior to the formation of extensive transitional crust extension within peru and chile probably occurred via a combination of transtension steepening and detachment of an arrested slab we propose that plate tectonic forces initiated the early break up of pangaea by attenuating its margins and enhancing mantle upwelling prolonged extension may have propagated along pre existing weak zones that extended into the continental interior captured melts derived from the upwelled mantle forming a lip e g central atlantic magmatic province became hot and weak and eventually lead to the formation of a juvenile ocean e g central atlantic

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

the eastern mediterranean paleoclimate as a reflection of regional events soreq cave israel the climate of the eastern mediterranean region of the last 60 ky was determined by a high resolution study of the oxygen and carbon isotopic composition 1500 measurement pairs of speleothems from the soreq cave israel with chronology provided by 53 precise 230 th 234 u tims ages the high precision of the speleothem tims ages permits us to determine the timing of regional climatic events in the eastern mediterranean region and to see if they correlate with global events during the period from 60 to 17 ky the 18 o and 13 c values were generally 2 2 5 higher than during the period from 17 ky to present this is consistent with the climatic transition from glacial to interglacial within the 60 to 17 ky period the soreq cave stable isotope profile includes four cold peaks at 46 35 25 and 19 ky and 2 warm peaks at 54 and 36 ky in addition the period 17 ky has two more cold peaks at 16 5 and from 13 2 to 11 4 ky the ages of four of the six cold peaks correlate well with the ages of three heinrich events h1 h2 h5 and with the age of the younger dryas however the other two heinrich events are not reflected in the soreq cave record several other isotope peaks which appear during the last 7 ky are contemporaneous with regional climatic events in the middle east and north africa in addition to the drop in 18 o and 13 c observed between the last glacial and the holocene sharp simultaneous drops in 234 u 238 u 0 ratios sr concentrations and in 87 sr 86 sr are also observed suggesting that the latter are climate related these variations are interpreted in terms of major changes in the temperature the mean annual rainfall and its isotopic composition the isotopic composition of the mediterranean vapor source the soil moisture conditions and in the mixing proportions of sources with different 87 sr 86 sr ratios sea spray dust particles and dolomitic host rock

lithospheric evolution of the pre and early andean convergent margin chile abstract the proto andean and early andean evolution of the southwestern gondwana margin comprises three stages that differ in their magmatic evolution and deformational style the gondwana cycle 330 280 ma the pre andean stage 280 210 ma and the early andean cycle 210 100 ma these stages have been traditionally interpreted as the upper crustal response to changes in the tectonic setting which include cordilleran style continental arc gondwana cycle orogenic collapse and possibly slab break off that led to continental rifting and extensive crustal melting pre andean stage and subsequent subduction re initiation in oceanic arc style context early andean cycle the petrological and geochemical characteristics of carboniferous to jurassic igneous rocks from this region however do not support the described model elemental and sr nd pb isotopic data of 86 samples along with a compilation of 1230 samples from the literature suggest that subduction was the most likely process by which the magmatic record was generated sub alkaline affinities lile enrichment over hfse nb ta troughs porphyritic textures and hornblende and biotite bearing lithologies are present in all studied units whereas isotopes suggest that magma sources are a mixture of depleted mantle and variable contribution from the continental crust even though the aforementioned features are common to all igneous rocks some changes point to a decline in the contribution of crustal lithospheric sources to the magmatism with time thus sio2 lan ybn and 87sr 86srinitial exhibit a systematic decrease from 285 to 150 ma whereas the endinitial parameter increases in the same period these changes were accompanied by the shift from dominant compressional carboniferous early permian to transtentional middle permian jurassic stresses in the upper crust suggesting that the margin went from advancing to retreating due to pangea reorganization and break up following a potential flat slab event slab roll back may have induced extension in the upper crust and lithospheric loss as a consequence of delamination or thermal erosion

sea land correlation of pollen records in the eastern mediterranean for the glacial interglacial transition biostratigraphy versus radiometric time scale abstract pollen diagrams based on marine cores from the eastern mediterranean and arabian seas and land cores from greece turkey the levant and western iran during the last deglaciation reveal a similar succession of conspicuous pollen abundance maxima an early phase with chenopodiaceae signaling the highest aridity a late phase with pistacia and gramineae in the mediterranean domain and tropical humid taxa in the arabian sea domain indicating conditions of mildest winter and wettest summer between these two phases the record for deciduous oak in the mediterranean and near east shows a continuous increase that points to rising moisture the chronology of this succession and its exact relationship with the marine isotopic record of global climate are established using marine cores the marine records dated by the ams 14 c method show that the chenopodiaceae phase correlates with the younger dryas chronozone globally dated 11 000 to 10 000 bp during which the climate reversed to quasi glacial conditions at least in the northern hemisphere they also show that the pistacia phase during which the mediterranean climate reached its seasonal optimum occurred from 9000 to 6000 14 c years bp boreal and early atlantic chronozones defined in nw europe in the first half of the holocene the oak pollen abundance increases rapidly from 10 000 to 9000 bp preboreal chronozone thus in terms of climate the younger dryas chronozone is regionally expressed by wide spread desert conditions as a cold and arid period during the pistacia phase the climate was most favourable both for plants that require frost free winters such as the mediterranean pistacia and those that need spring summer moisture such as gramineae at low annual moisture level seasonally 300 mm and deciduous oak at higher levels 600 mm all year without summer drought during the brief intermediary phase the climate changed drastically through an increase of winter temperature and of spring summer moisture the chronologies of the land cores however based on few 14 c dates show significant discrepancies with the marine based time frame these discrepancies imply a lack of coherence in the climate history of this mediterranean irano turanian region we propose using the chronology derived from the marine records for the entire region the local 14 c dates generally appear too old perhaps because of geological contamination of the material by older carbon

quantifying level of microbial induced cementation for cyclically loaded sand abstractmicrobial induced calcite precipitation micp is a novel soil improvement technique that improves the behavior of sands subjected to dynamic loading the level of cementation of micp treat

mechanical behavior of sands treated by microbially induced carbonate precipitation abstractthe mechanical behavior of sands treated using microbially induced carbonate precipitation micp has been investigated at the macroscale and the microscale triaxial and confined compression tests with embedded shear and compression wave s wave and p wave sensors were conducted on two micp treated sands ottawa 50 70 and 20 30 silica sands triaxial compression tests were conducted at three different confining pressures 25 50 and 100 kpa tests were also performed at calcium chloride cacl2 concentrations of 0 1 and 0 3 m resulting in specimens with average calcium carbonate caco3 content ranging from 1 5 to 2 5 for the 50 70 sand and from 1 to 1 6 for the 20 30 sand in contrast to previous research the results of triaxial tests presented in this paper show an increase of the soil strength even at 1 calcium carbonate content after the tests samples taken from the specimens were utilized to measure the caco3 content and to perform analysis using scanning electron microscopy sem

mesozoic rifting evolution of sw gondwana a poly phased subduction related extensional history responsible for basin formation along the argentinean atlantic margin abstract the opening of the south atlantic in the early cretaceous was the final stage of the complex rifting history of sw gondwana in this contribution we reassess the chronology of mesozoic basin formation in southern south america and africa and integrate it in the long term breakup history of sw gondwana triassic rifting is characterized by intracontinental rifting in africa karoo i phase and retro arc extension on the sw margin of gondwana in the early jurassic the impingement of the karoo plume triggered rifting in eastern africa producing the karoo ii basins and the colorado and salado basins on the argentinean shelf east africa rifting ultimately lead the breakup of eastern from western gondwana in the middle jurassic in patagonia the austral malvinas and other related basins formed in association with the synextensional emplacement of the chon aike magmatic province in the patagonian retro arc in the late jurassic the rocas verdes back arc basin opened in southern patagonia while oblique rifting in the core of the late paleozoic gondwanides orogen produced the outeniqua and rawson valdes basins the south atlantic rift initiated in the early cretaceous associated with present day e w extension rifting occurred diachronically from south to north initiating in the previously thinned rawson valdes outeniqua segment a precursor oblique rift system and a larger degree of extension in this segment could explain the lack of seaward dipping reflectors sdr south of the colorado cape fracture zones rifting and sdr emplacement occurred progressively to the north along different rift segments producing strongly asymmetric conjugate margins

u th isotope systematics from the soreq cave israel and climatic correlations precise 230 th 234 u ages were obtained on thirty one growth laminae in speleothem samples which are self consistent with the detailed layer stratigraphy samples with low 232 th 238 u ratios give ages with analytical uncertainties of 40 years at 2 ky and 1000 years at 90 ky some growth zones with high but variable 232 th 238 u were dated by intermal isochrons this permits the determination of the initial 230 th 232 th assuming equilibrium of 232 th and 238 u series in the source of the high 232 th component this shows initial 230 th 232 th in activity units of from 1 3 to 2 9 the calculated atomic ratios of 232 th 238 u for the high 232 th component range from 1 08 to 2 4 which is well below the average crustal value speleothem materials with high 232 th 238 u are found to exhibit clear correlations of 232 th with si al and fe while 238 u correlates with sr and ba analyses of soreq cave drip waters show that the particulates in the waters have high 232 th concentrations and a 232 th 238 u ratio much lower than that found in the high 232 th component in speleothems but with 230 th 232 th 1 0 to 2 4 we infer that the trapped high th component in speleothems is from particulate matter in water with a large concentration of adsorbed u and not simply from detrital material the speleothems have only small234u excess the initial 234 u 238 u 0 show a range of 1 02 to 1 14 that was found to correlate with age over the past 25 ky the youngest samples have values in the same range as the modern drip waters there appears to be a correlation of 234 u 238 u 0 with the 18 o values there is a drop of 18 o in the time interval 20 to 15 ky which then remains relatively constant to recent times as the high 18 o values have been related to rainfall and associated climatic conditions we suggest that the 234 u 238 u in the speleothem reflects the effects of rainfall and soil weathering conditions on drip water composition and may provide a proxy for climate change