the lost inca plateau cause of flat subduction beneath peru abstract since flat subduction of the nazca plate beneath peru was first recognized in the 1970s and 1980s a satisfactory explanation has eluded researchers we present evidence that a lost oceanic plateau inca plateau has subducted beneath northern peru and propose that the combined buoyancy of inca plateau and nazca ridge in southern peru supports a 1500 km long segment of the downgoing slab and shuts off arc volcanism this conclusion is based on an analysis of the seismicity of the subducting nazca plate the structure and geochemistry of the marquesas plateau as well as tectonic reconstructions of the pacific farallon spreading center 34 to 43 ma these restore three sub parallel pacific oceanic plateaus the austral tuamotu and marquesas to two farallon plate counterparts the iquique and nazca ridges inca plateau is apparently the sixth and missing piece in an ensemble of v shaped hotspot tracks formed at on axis positions we argue the mirror image of the inca plateau the marquesas plateau is an ancient edifice overprinted by recent volcanism in disagreement with the widely accepted young

distinguishing between local versus regional extension as a control on orogenic gold mineralisation the new 2 4moz castle hill camp wa abstract the significance of regional extension for orogenic gold mineralisation in the archaean eastern goldfields of western australia is not well established and there is a lack of consensus on both the timing and nature of extensional deformation the 2 4 moz castle hill gold camp located in the coolgardie domain is spatially associated with a nw se trending granitic pluton the kintore tonalite this pluton intruded prior to the gold mineralisation and is coeval with emplacement of the lower succession of the kalgoorlie greenstone sequence the kintore tonalite is located at a major change in the geometry of the kunanalling shear zone where the strike of the shear zone changes from the regional nw se trend to n s this change in the geometry of the kunanalling shear zone is interpreted to highlight the presence of an early transfer fault intersecting the kunanalling shear zone or step over zone on the kunanalling shear zone that was active at the time of greenstone emplacement this early architecture created a crustal scale pathway that facilitated the sourcing and emplacement of the tonalitic magma and also later gold bearing fluids from lower crustal levels three main deformation events that reactivated this early architecture have been delineated d1 d3 d1 is associated with ne sw directed compression reactivating nw trending shear zones and lithological boundaries causing reverse shearing folding and development of a pervasive foliation d2 is synchronous with the main gold event which occurred during nw se directed far field compression causing sinistral shearing on nw trending structures the development of n s striking faults the formation of mineralised quartz veins associated and vertical axis rotation of the kintore tonalite during the d2 stage gold was deposited with tellurobismuthite assemblages over the castle hill region associated with synchronous extensional and contractional features at the southern and northern ends of the kintore tonalite respectively d2 extensional structures related to mineralisation are local features linked to development of sinistral movement on the n s striking faults d3 is associated with ne sw directed compression and the development of n to ne trending dextral faults dominated by brittle deformation the primary control on the regional location of the gold system is interpreted to be early pre existing crustal architecture marked by the major strike change that hosts the tonalite the geometry of structures developed within the step over zone exerts a second order control on the location of deposits within the castle hill camp and fluids were focussed into areas of enhanced permeability during deformation individual deposits in the camp are hosted in mineralised structures that locally exhibit extensional kinematics but developed in an overall compressional regime

the mesozoic marginal basin of central peru the west peruvian trough1 2 extends some 1 300 km from north of trujillo to about 150 km short of arequipa fig 1 it received upwards of 9 000 m of material during the mesozoic and within the cretaceous rocks there is a well defined west to east facies change whereby thick volcaniclastic turbidites and pillow lavas the eugeosyncline of cobbing3 thin eastward to be replaced by a mixed clastic shelf sequence the miogeosyncline we report here chemical analyses of the volcanic rocks and data on the association of cherts volcaniclastic turbidites dyke and sill complexes and large gabbro masses as well as geophysical evidence which suggests that the eugeosyncline is an extensional marginal basin similar to that seen in rocks of the same age in southern chile4 the coastal batholith is thought to have been emplaced within this marginal basin during the upper cretaceous5 and the evolution of this ensialic new crust therefore has important implications for the growth of the continental margin of south america as well as for batholith genesis

role of plate kinematics and plate slip vector partitioning in continental magmatic arcs evidence from the cordillera blanca peru new structural and geochronological data from the cordillera blanca batholith in the peruvian andes coupled with nazca south american plate slip vector data indicate that oblique convergence and associated strike slip partitioning strongly influenced continental magmatic arc evolution both the strain field and mode of magmatism plutonism vs volcanism in the late miocene peruvian andes were controlled by the degree to which the arc parallel component of the plate slip vector was partitioned into the arc strong strike slip partitioning at ca 8 ma produced arc parallel sinistral shear strike slip intercordilleran basins and east west oriented tension fractures that facilitated emplacement of the cordillera blanca batholith ca 8 2 0 2 ma periods during which the strike slip component was not partitioned into the arc ca 10 and ca 7 ma were associated with roughly arc normal contraction and ignimbrite volcanism the data thus support the contention that contraction within continental magmatic arcs favors volcanism whereas transcurrent shear favors plutonism the tie between oblique convergence and batholith emplacement in late miocene peruvian andes provides a modern analogue for batholiths emplaced as the result of transcurrent shear in ancient arcs

a study of zn and mo attenuation by waste rock mixing in neutral mine drainage using mixed material field barrels and humidity cells abstract we studied the attenuation of mo and zn in neutral ph drainage from waste rock at the antamina mine in peru we hypothesized that mo or zn contained in leachate produced in one waste rock type can be attenuated when the mo or zn containing leachate is allowed to contact a different waste rock type we tested the hypothesis using mixed material stacked field barrels and humidity cells connected in series where leachate from a mo or zn releasing waste rock type flows through a second waste rock material type results from both the humidity cells laboratory conditions and field barrels field conditions showed the same general attenuation patterns when drainage from mo releasing waste rock flowed through pb rich black marble waste rock mo was removed from solution molybdenum attenuation was not observed when the order of the waste rock materials was reversed such that drainage from pb rich waste rock flowed through mo releasing intrusive rock geochemical modeling mla and sem analyses supported the hypothesis that wulfenite precipitation was responsible for the observed attenuation of mo zinc is shown to be removed from leachate both by contact with mo releasing intrusive rock and by contact with calcite rich grey hornfels material results from geochemical modeling in phreeqc suggested that precipitation of zn carbonate or zn hydroxide minerals could not account for the degree of zn attenuation observed in this study scanning electron microscopy suggested that zn may have been incorporated into the crystal structure of phyllosilicate clay minerals

a comparative study of wollastonite skarn genesis in the central metasedimentary belt southeastern ontario canada abstract potentially economic wollastonite rich skarns are widespread in the central metasedimentary belt of southeastern ontario canada their genesis is evaluated through a comparative study of the platinova skarn ca 4 mt grading 35 wollastonite hosted by greenschist facies marble in the elzevir terrane the olden skarn ca 2 8 mt 35 in amphibolite facies marble of the sharbot lake terrane and the st lawrence skarn ca 9 mt 41 in granulite facies strata of the frontenac terrane the protolith for all of the wollastonite skarns was calcitic marble locally containing impurities but dolomitic marble may have been present at the st lawrence skarn each skarn is contiguous with an intrusive complex ranging from gabbro to granite in composition and displaying megascopic fabrics indicative of magma commingling and mixing the plutons are however of different ages and exhibit different geochemical characteristics in each skarn wollastonite is associated with varying proportions of diopside hedenbergite and grossular andradite skarn development is ascribed to the incursion of magmatogene silica rich co2 poor xco2 between 0 1 and 0 3 fluids rather than to regional metamorphism and pressures varying between 200 mpa at platinova and 350 mpa at olden at temperatures ca of 500 to 650 c the mountain grove pluton has an u pb zircon age of 1153 2 ma hornblende and biotite from the same sample gave 40ar 39ar plateau dates of 1058 14 and 1047 4 ma respectively and the olden skarn has been dated at 1074 5 ma 40ar 39ar phlogopite these 40ar 39ar dates are interpreted to record resetting by the contiguous 1070 ma mclean pluton u pb on titanite and 40ar 39ar on amphibole separates from the st lawrence skarn yield 1147 ca 8 and 1159 6 ma dates respectively similar to the u pb badelleyite age of the adjacent 1167 2 ma leo lake pluton the age similarities between the skarns and the adjacent plutonic rocks are permissive evidence for a genetic link evidence of magma mixing and commingling in all the plutons contiguous with the wollastonite skarns may indicate that the concentration and egress of magmatogene brines at pressures locally attending 400 mpa was facilitated by thermal and compositional perturbation in the parental magma chambers

the estuarine chemistry of rare earth elements comparison of the amazon fly sepik and the gulf of papua systems abstract a comparison of the amazon fly gulf of papua and sepik river systems has shown that there are two distinct processes operating on dissolved rare earth elements ree in estuaries large scale salt induced coagulation in the low salinity region and small to extensive release in the mid to high salinity region fractionation of the ree occurs during both removal and release the order of removal follows lree mree hree and the order of release follows hree mree lree where l m and h refer to light middle and heavy ree respectively hence estuarine reactions can modify the relative abundance of dissolved ree reaching the oceans operating in tandem the removal and release lead to the preferential removal of the lree and the preferential release of hree during estuarine mixing this combination in turn results in an effective river water flux river flux after modifications by estuarine chemistry which is evolved toward the ree composition of seawater which has a heavy ree enriched composition when normalized against the ree composition of rivers or the earth s continental crust the increase of dissolved ree in the mid to high salinity waters of the amazon and fly estuaries suggests a sediment and or suspended sediment source the lack of ree increases in the sepik river estuary strengthens this explanation as the mixing zone of this estuary is located over a deep shelf where there is little physical contact between bottom sediment and estuarine waters in marked contrast the amazon and fly estuaries are dominated by the active resuspension and deposition of bottom sediments the resupply of ree accompanied by fractionation may result from ree carbonate complexation during the reaction of seawater with suspended particles and or bottom sediment estuarine and shelf sediments may be important sources of dissolved nd to the oceans thereby helping to maintain the inter ocean differences in the nd isotopic composition of seawater by reducing the residence time of nd in the oceans

the migration history of the nazca ridge along the peruvian active margin a re evaluation abstract the collision zone of the 200 km wide and 1 5 km high nazca ridge and the peruvian segment of the convergent south american margin between 14 s and 17 s is characterized by deformation of the upper plate and several hundred meters of uplift of the forearc this is evident by a narrowing of the shelf a westward shift of the coastline and the presence of marine terraces as the nazca ridge is oblique with respect to both trench and convergence direction of the nazca plate it migrates southward along the active plate boundary for reconstructing the migration history of the nazca ridge this study uses updated plate motion data resulting from a revision of the geomagnetic time scale the new model suggests that the ridge crest moved laterally parallel to the margin at a decreasing velocity of 75 mm a before 10 8 ma 61 mm a 10 8 4 9 ma and 43 mm a 4 9 ma to present intra plate deformation associated with mountain building in the peruvian andes since the miocene reduces the relative convergence rate between nazca plate and peruvian forearc taking an intra plate deformation at a rate of 10 mm a estimated from space geodetic and geological data into account does not significantly reduce these lateral migration velocities constraining the length of the original nazca ridge by its conjugate feature on the pacific plate yields a length of 900 km for the subducted portion of the ridge using this constraint ridge subduction began 11 2 ma ago at 11 s therefore the nazca ridge did not affect the northern sites of ocean drilling program odp leg 112 located at 9 s this is supported by benthic foraminiferal assemblages in odp leg 112 cores indicating more than 1000 m of subsidence since at least middle miocene time and by continuous shale deposition on the shelf from 18 to 7 ma recorded in the ballena industrial well at 11 5 s the model predicts the passage of the ridge crest 9 5 ma ago this agrees with the sedimentary facies and benthic foraminiferal stratigraphy of odp leg 112 cores which argue for deposition on the shelf in the middle and late miocene with subsequent subsidence of a minimum of several hundred meters onshore at 12 s the sedimentary record shows at least 500 m uplift prior to the end of the miocene also in agreement with the model

rare earth elements ree and yttrium in stream waters stream sediments and fe mn oxyhydroxides fractionation speciation and controls over ree y patterns in the surface environment we have collected 500 stream waters and associated bed load sediments over an 400 km 2 region of eastern canada and analyzed these samples for fe mn and the rare earth elements ree y in addition to analyzing the stream sediments by total digestion multi acid dissolution with metaborate fusion we also leached the sediments with 0 25 m hydroxylamine hydrochloride in 0 05 m hcl to determine the ree y associated with amorphous fe and mn oxyhydroxide phases we are thus able to partition the ree into dissolved 0 45 lm labile hydroxylamine and detrital sediment fractions to investigate ree fractionation and in particular with respect to the development of ce and eu anomalies in oxygenated surface environments surface waters are typically lree depleted la sm nasc ranges from 0 16 to 5 84 average 0 604 n 410 where the ree are normalized to the north america shale composite have strongly negative ce anomalies ce ce nasc ranges from 0 02 to 1 25 average 0 277 n 354 and commonly have positive eu anomalies eu eu nasc ranges from 0 295 to 1 77 average 0 764 n 84 in contrast the total sediment have flatter ree y patterns relative to nasc la sm nasc ranges from 0 352 to 1 12 average 0 778 n 451 and are slightly middle ree enriched gd yb nasc ranges from 0 55 to 3 75 average 1 42 most total sediments have negative ce and eu anomalies ce ce nasc ranges from 0 097 to 2 12 average 0 799 and eu eu nasc ranges from 0 39 to 1 43 average 0 802 the partial extraction sediments are commonly less lree depleted than the total sediments la sm nasc ranges from 0 24 to 3 31 average 0 901 n 4537 more mree enriched gd yb nasc ranges from 0 765 to 6 28 average 1 97 and ce and eu anomalies negative and positive are more pronounced the partial extraction recovered on average 20 of the fe in the total sediment 80 of the mn and 21 29 of the rees ce 19 and y 32 comparison between rees in water partial extraction and total sediment analyses indicates that rees y in the stream sediments have two primary sources the host lithologies i e mechanical dispersion and hydromorphically transported the labile fraction furthermore eu appears to be more mobile than the other ree whereas ce is preferentially removed from solution and accumulates in the stream sediments in a less labile form than the other rees y despite poor statistical correlations between the rees y and mn in either the total sediment or partial extractions based on apparent distribution coefficients and the ph of the stream waters we suggest that either sediment organic matter and or possibly d mno2 feooh are likely the predominant sinks for ce and to a lesser extent the other ree in the stream sediments

thermotectonic history of the maranon fold thrust belt peru insights into mineralisation in an evolving orogen fold thrust belts along convergent margins around the world host major ore deposits the origin of such ore deposits is commonly episodic and so are the temporal and spatial variations in deformation styles in these fold thrust belts here we focus on the maranon fold thrust belt mftb of the peruvian andes and demonstrate a link between the spatio temporal distribution of ore deposits and thick skinned tectonics we present low temperature thermochronology results from the mftb that document the uplift exhumation history and timing of thick skinned tectonics and vergence reversal our results suggest that the thermal history of the mftb involved two discrete intervals of opposed vergence large scale crustal deformation since the late cretaceous an early interval at 80 20 ma was associated with folding and east vergent thin skinned tectonics and was followed by west vergent thick skinned deformation at 20 0 ma furthermore our findings suggest that thick skinned contraction was coincident with increased focusing of mineralising fluids and ore deposition in the mftb during the early miocene and in the mid miocene both mineralisation and deformation were enhanced by subduction of the nazca ridge underneath the south american plate

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

ridge segmentation and the magnetic structure of the southwest indian ridge at 50 30 e 55 30 e and 66 20 e implications for magmatic processes at ultraslow spreading centers 1 the aim of this paper is to investigate the relationships between the segmentation and the magnetic structure of the ultraslow spreading southwest indian ridge contrary to faster spreading ridges magnetization usually decreases from high values along the neovolcanic axis to low values in the nontransform discontinuities there is a direct correlation between the deepening of the axial valley and the decrease of the magnetization from the neovolcanic axis toward the deepest parts of the axial discontinuities we suggest that less frequent eruptions as the distance from the segment center and the length of these discontinuities increase result in thinner extrusive lavas and thus control the along axis magnetization variations by thinning the magnetic source layer a unique segment centered at 50 28 e shows a marked low magnetization anomaly at its center similarly to the segments of the slow spreading mid atlantic ridge we suggest that in this segment both the mantle temperature and the magmatic activity are high enough for the lavas not to be highly fractionated a higher rate of melt production to the west of gallieni transform fault may have created some form of reservoir where mixing of melts occurs and where crystalline fractionation is low producing low magnetization lavas to the east magma chambers may be smaller with cooler mantle temperatures resulting in restricted mixing and significant fractionation which may lead to relatively high intensity magnetization lavas finally we propose that serpentinization of peridotites has no significant contribution to the variation of the magnetization along the axial valley off axis in thin crust areas upper mantle rocks may become progressively more altered as distance from the axis increases the strong faulting and alteration of a thin basaltic cap and underlying upper mantle rocks can produce the disappearance of the magnetic reversal pattern and the increase of the magnetization which is observed along the traces of the largest amagmatic discontinuities by contrast in thicker crust areas the upper mantle rocks are shielded from the alteration and the serpentinization process may be delayed resulting as on the mid atlantic ridge in slightly more positive magnetization values along the traces of axial discontinuities regardless of polarity

biogeochemistry of nautiloids and paleoenvironmental aspects of buckhorn seawater pennsylvanian southern oklahoma abstract sediments in the buckhorn quarry and adjacent outcrops southern oklahoma are shallow water carbonates which are intercalated with coals and minor conglomerates they belong to the boggy formation of the deese group and are desmoinesian pennsylvanian in age strontium concentrations of shell septa and cameral deposits of pennsylvanian cephalopods are variable and fall either in the low range with 0 17 0 22 or the high range with 0 39 0 60 sr ca atomic ratios these values suggest that extrapallial and or cameral fluids responsible for the formation of all three cephalopod macrostructures were in chemical disequilibrium with ambient seawater thus the biological discrimination for sr was well establihed by pennsylvanian time for nautiloids the mg concentrations appear to be controlled at the species genus levels in contrast the na mn and fe contents of nautiloids are influenced and controlled by the physicochemical conditions of the surrounding seawater information obtained from brachiopod and from the least altered cephalopod samples suggest that buckhorn seawater was physiochemically similar to that of modern ocean water and the postulated temperature and salinity values represent the most reasonable intepretations considering paleontological sedimentological and biogeochemical data salinity of the buckhorn sea which was within 5 s of the pennsylvanian equator ranged from 29 to 34 ppt with a mean of 32 ppt this near normal salinity was complemented by an average water temperature of 36 c 34 38 c for the shallower and of 21 c 14 30 c for the deeper parts of the buckhorn sea of southern oklahoma overall water temperatures fluctuated between 14 and 38 c

evaluation of the application of rare earth elements to paleoceanography anomalous departures of rare earth elements ree from similarity of chemical behaviour are most evident in a comparison of ce with its neighbors under reducing conditions ce3 acts like other ree but oxidized ce4 is adsorbed on mn fe oxyhydroxides or organic particulates and consequently the remaining solution will tend to exhibit a negative ce anomaly in addition more subtle fractionations may emphasize the light or the heavy or the middle ree a pattern of ree may be recorded by immediate diagenesis on a suitable chemical substrate such as apatite fish debris conodonts carbonate or chert this record was originally thought to reflect the paleoredox conditions of primary deposition however any such primary record may be overprinted by late diagenetic alteration early analyses of ree in conodonts from a wide range of sediments suggested a prevalence of reducing conditions no ce anomaly in pre carboniferous oceans and more common oxidation negative ce anomaly in the late paleozoic however recent research by other investigators indicates that variations in cean are more diverse in origin and in particular many are distorted to an unknown extent by late diagenesis in any case it is now clear that geological age does not show a consistent relationship to the level of the ce anomaly the ce anomaly apparently does not play any regular role in the isotopic events that accompany prominent mass extinctions further research is required to understand and thus make useful the controls on the ce anomaly

geochemistry and s pb isotope of the yangla copper deposit western yunnan china implication for ore genesis abstract the yangla copper deposit situated in the middle section of jinshajiang tectonic belt between zhongza zhongdian block and changdu simao block is a representative and giant copper deposit that has been discovered in jinshajiang lancangjiang nujiang region in recent years there are coupled relationships between yangla granodiorite and copper mineralization in the yangla copper deposit five molybdenite samples yielded a well constrained 187 re 187 os isochron age of 233 3 3 ma the metallogenesis is therefore slightly younger than the crystallization age of the granodiorite s pb isotopic compositions of the yangla copper deposit indicate that the ore forming materials were derived from the mixture of upper crust and mantle also with the magmatic contributions in the late early permian the jinshajiang oceanic plate was subducted to the west resulting in the formation of a series of gently dipping thrust faults in the jinshajiang tectonic belt meanwhile accompanied magmatic activities in the early late triassic which was a time of transition from collision related compression to extension in the jinshajiang tectonic belt the thrust faults were tensional it would have been a favorable environment for forming ore fluids the ascending magma provided a channel for the ore forming fluid from the mantle wedge after the magma arrived at the base of the early stage yangla granodiorite the platy granodiorite at the base of the body would have shielded the late stage magma from the fluid the magma would have cooled slowly and some of the ore forming fluid in the magma would have entered the gently dipping thrust faults near the yangla granodiorite resulting in mineralization

structural control of low sulfidation epithermal gold mineralization in the rosario bunawan district east mindanao ridge philippines the rosario bunawan district is situated about 200 km north of davao city the capital of the mindanao island southern philippines gold is produced from the co o mine containing about 2 034 000 t of ore at 10 9 g t au and in numerous small scale operations by local miners epithermal gold mineralization in the rosario bunawan district and the co o mine is confined to narrow 0 2 4 m low sulfidation quartz chalcedony calcite veins in volcanic and volcaniclastic wall rocks three major vein orientations are distinguished 1 the nnw sse trending set with a sinistral strike slip sense of deformation philippine fault trend 2 the ene wsw trending dextral strike slip set palawan trend and associated veins in the riedel geometry and 3 the wnw ese trending conjugate set co o trend three structural stages are defined 1 extensional shear or shear veins formed in the co o the philippine fault and palawan trends during regional nw se compression and near vertical vein opening d1 2 reactivation of veins in the philippine fault veins associated with the palawan and to a lesser extent the co o trends during e w compression and near horizontal n s oriented vein opening d2 new d2 extensional shear or shear veins formed in the philippine fault and structures associated with the palawan and associated riedel trends 3 the d3 stage block faulting subsequently displaced all of the auriferous veins the auriferous rosario bunawan district is situated between two splays of the philippine fault which acted as a lateral ramp system during the oblique convergence of the philippine sea plate and the eurasian plate the oblique convergence resulted in a change from a compressional d1 to a transpressional d2 regime which was a prerequisite for the two stage vein opening and hydrothermal mineralization leading to an economic gold enrichment d1 compressional tectonics may have caused an elevated geothermal gradient in shallow crustal levels forming the heat source for the fluid plumbing system which is at variance to typical epithermal deposits formed in extensional zones d2 thrusting of a limestone nappe together with syn tectonic diorite intrusions may have further increased the geothermal gradient maintaining the fluid plumbing system the limestone nappe may at the same time have represented an aquitard forcing the hydrothermal fluids into the volcanic and volcaniclastic wall rocks which is regarded as critical for the two stage gold mineralization in the rosario bunawan district

rare earth elements in solnhofen biogenic apatite geochemical clues to the palaeoenvironment rare earth element ree concentrations in biogenic apatite samples coprolite bone and soft tissue were used to investigate the environment of deposition of the celebrated solnhofen fossil lagerstatten the measured ree patterns are similar between different localities lithologies flinz faule and levels in the upper solnhofen plattenkalk suggestive of a stable ree supply during deposition the behaviour of cerium in the solnhofen samples implies that bottom water conditions were not anoxic and variations in the cerium anomaly can be explained by differences in burial rate these results provide further geochemical support for current depositional models barthel k w 1978 solnhofen ein blick in die erdgeschichte ott verlag thun barthel k w swinburne n h m conway morris s 1990 solnhofen a study in mesozoic palaeontology cambridge univ press cambridge that propose that extra basinal processes are responsible for the interbedded nature of the solnhofen deposits rather than intra basinal processes such as water turnover events

rare earth element evolution of phanerozoic seawater recorded in biogenic apatites rare earth element ree contents of marine biogenic apatites have been shown to record seawater compositions a data base of available and newly acquired rare earth element ree contents of marine biogenic apatites has been created to assess the past seawater ree compositions to ensure that this data base contains only the pristine ree signals altered samples characterized by very low la sm n ratios where n stands for ree ratios normalized to the nasc composition gromet et al 1984 geochim cosmochim acta 48 1984 2469 acquired during apatite recrystallization are not included in the database these data reveal a change in the tethyan seawater composition between 110 and 80 ma after the end of the cretaceous the ree chemistry of seawater remains constant until present day this seawater composition change is likely due to concurrent changes in ree scavenging processes a strong correlation between decreasing sm yb n ratios and increasing ce anomalies for samples deposited during the 80 110 ma period is observed as ce anomalies are attributed to ocean water redox conditions changes in ree scavenging could reflect an evolution from stratified and poorly oxygenated waters towards well mixed and oxygenated waters this could have resulted from changing current patterns stemming from the contemporaneous opening of the atlantic ocean a major change in middle and late cretaceous oceanic circulation linked to plate tectonics would have favored the colonization of pelagic environments

sedimentary evolution of an active margin during middle and upper cretaceous times the north peruvian margin from late aptian up to senonian the sedimentary evolution of the north peruvian margin during upper cretaceous can be summarized as follows

episodic sedimentation on an early silurian storm dominated carbonate ramp becscie and merrimack formations anticosti island canada the 150 160 m thick lowermost silurian rhuddanian becscie and merrimack formations of anticosti island canada represent continuous deposition on a shallow open marine carbonate ramp several rock types are identified a laminated and homogenous mudstone b laminated and homogenous packstone c argillaceous mudstone and packstone d calcareous shale e laminated calcisiltite f medium to fine grained grainstone and g bio intraclastic rudstone these rock types are arranged into five distinct lithofacies lf1 calcareous mudstone shale lf2 laminated homogenous mudstone lf3 calcareous grainstone shale lf4 laminated mudstone grainstone and lf5 laminated calcisiltite grainstone the sequence reflects deposition on a low energy muddy carbonate to argillaceous ramp subject to short lived episodic high energy storms these events produced fining upwards storm units 5 80 cm thick or tempestites consisting of a sharp scoured base overlain by intra bioclastic rudstone grading upwards into medium grained grainstone finely laminated calcisiltite and mudstone or shale these are interbedded with low energy fairweather mudstones and calcareous shales deposition progressed from a carbonate mud dominated ramp in the becscie formation to an argillaceous mud dominated ramp in the merrimack formation lateral tempestite proximality trends and lithofacies distribution indicate that the anticosti basin deepened to the south east into the iapetus ocean and shallowed towards a sw ne orientated shoreline to the north west vertical tempestite proximality trends and lithofacies changes identify third order eustatic sea level changes after an initial deepening at the base of the formation a shallowing deepening event dominated the sequence several higher order fluctuations defined by lithofacies and tempestite proximality trends are superimposed on these changes the fluctuations identified with the aid of tempestite proximality trends are of an order of magnitude higher than those identified by either lithofacies or palaeontological methods

carbon isotope composition in modern brachiopod calcite a case of equilibrium with seawater abstract we examined a large number of modern shallow water articulated brachiopods representing the orders terebratulida rhynchonellida thecideida and one inarticulated brachiopod of the order craniida from polar to tropical regions for their carbon isotope compositions based on our detailed investigation we recommend avoiding fast growth areas such as the youngest shell increments in addition the primary layer and transition zone calcites of brachiopods must be avoided because they are in carbon and oxygen isotope disequilibrium with ambient seawater after adjusting isotope compositions for the mg effect we observed no significant difference p 0 05 in 13 c values between dorsal and ventral valves of our articulated brachiopods using the calcite bicarbonate enrichment factor e in conjunction with 13 c values of dissolved inorganic carbon of habitat seawater we conclude that modern shallow water articulated and some inarticulated brachiopods incorporate oxygen brand et al 2013 and carbon isotopes into shell calcite of secondary and or tertiary layers in apparent equilibrium with ambient seawater within the general concept of equilibrium incorporation with seawater shell 13 c values are an excellent recorder of local global seawater environments and water mass circulation thus application of the mg effect permits brachiopods to be an extremely powerful archive and 13 c values more precise proxy and tracer of past changes in marine productivity evolution of seawater carbon chemistry and variation in the global carbon cycle

mixed layer modeling in the east pacific warm pool during 2002 two vertical mixing models the modified dynamic instability model of price et al pwp and k profile parameterizaton kpp are used to analyze intraseasonal sea surface temperature sst variability in the northeast tropical pacific near the costa rica dome during boreal summer of 2002 anomalies in surface latent heat flux and shortwave radiation are the root cause of the three intraseasonal sst oscillations of order 1 c amplitude that occur during this time although surface stress variations have a significant impact on the third event a slab ocean model that uses observed monthly varying mixed layer depths and accounts for penetrating shortwave radiation appears to well simulate the first two sst oscillations but not the third the third oscillation is associated with small mixed layer depths 5 m forced by and acting with weak surface stresses and a stabilizing heat flux that cause a transient spike in sst of 2 c intraseasonal variations in freshwater flux due to precipitation and diurnal flux variability do not significantly impact these intraseasonal oscillations these results suggest that a slab ocean coupled to an atmospheric general circulation model as used in previous studies of east pacific intraseasonal variability may not be entirely adequate to realistically simulate sst variations further while most of the results from the pwp and kpp models are similar some important differences that emerge are discussed

the importance of early crustal architecture for subsequent basin forming magmatic and fluid flow events the granites tanami orogen example abstract the paleoproterozoic granites tanami orogen gto consists of tightly folded predominantly greenschist facies rocks the orogen a component of the north australian craton includes a ca 1864 ma succession of turbiditic and pelagic sedimentary rocks interbedded with volcanic rocks and abundant dolerite sills in a back arc basin setting which is intruded by collision related ca 1800 ma granitic rocks integrated 4d interpretation of deep seismic profiles gravity and magnetic field observations associated with available surface geology and igneous isotope geochemistry suggest that the gto forms an imbricated crust developed on a partially inverted s dipping rifted archean basement the rifting took place in the paleoproterozoic around 1864 ma and was followed by e w orientated compressional deformation ca 1850 ma with the development of northerly trending isoclinal folds and associated faults orthogonal collisional tectonics followed at ca 1800 ma which is associated with s verging kilometre scale folds faults and orogenic lode gold deposits in the region recognition of the preserved early rift architecture in the gto has major implications for the subsequent evolution of the orogen the early architecture has influenced all subsequent deposition deformation magmatic and fluid events including spatial control of the ca 1864 ma rock succession to the location of intrusive bodies and fluid transfer during formation of ca 1800 ma orogenic gold mineralization

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

plate reconstructions aseismic ridges and low angle subduction beneath the andes low angle subduction segments beneath peru and chile are believed to represent interaction of the subduction zone with the aseismic nazca and juan fernandez ridges on the basis of symmetric sea floor spreading models and plate hotspot reconstructions predicted continuations of the relatively buoyant ridges correspond well with the limits of the low angle subduction segments further the history of interaction of the aseismic ridges with the subduction zone as predicted by plate reconstructions is not inconsistent with available information on volcanic episodes of the andes if the contemporary correlation of volcanic gaps and low angle subduction is also applicable to the rest of the late cenozoic the occurrence of deep seismicity beneath the eastern flanks of the andes is also believed to reflect the effects of low angle subduction the deep seismic segments are adjacent to segments which are presently or were recently experiencing low angle subduction thus the deep seismicity is interpreted as representative of remnants of normal oceanic lithosphere subducted before interaction of aseismic ridges with the subduction zone other geologic phenomena are associated with low angle subduction beneath south america including landward shift in loci of tectonism surficial subsidence and laramide style deformation the aseismic ridge buoyancy hypothesis appears to be a valuable predictive tool for the interpretation of such geologic effects

rare earth elements of shallow water articulated brachiopods a bathymetric sensor abstract variations in environmental physicochemical parameters result in corresponding changes in seawater rare earth element ree distributions for an archive to be utilized in paleoceanographic and paleoenvironmental reconstructions it should record these variations therefore an archive s proxy potentiality should be assessed analogous to modern oceanic settings articulated brachiopods of several shallow water localities the mean ree sn pattern of shallow water brachiopods is significantly different from that of their deep water counterparts with lower enrichments in lrees and mrees and depletion in hrees depth exercises a major control on the lree and mree fractionation with a milder one on hree fractionation the ce ce anomaly is not affected by either of these parameters in shallow water settings but in deep settings the depth effect dominates due to the importance of depth on ree fractionation in the shells from shallow settings their lree sn to hree sn ratios l h were divided into six discrete intervals for the bathymetric sensor the bathymetric sensor was applied to some fossils and whole rock in order to estimate their paleodepths the evaluation was successful in placing the permian gyanyima the pennsylvanian naco boggy and the silurian chicotte becscie and jupiter formations in shallow depths

acquisition of the neodymium isotopic composition of the north atlantic deep water the north atlantic deep water nadw neodymium isotopic composition nd ic is increasingly used in oceanography and paleoceanography to trace large scale circulation and weathering processes notably to investigate past variations of the global thermohaline circulation although the present day nadw nd ic is well characterized at nd 13 5 the acquisition of this isotopic signature in other words the causes of this value has so far been very sparsely documented such an understanding is however fundamental to the interpretation of paleo records nd ic and rare earth element concentrations were measured at 9 stations within the north atlantic subpolar gyre signature cruise summer 1999 the comparison of this data set with our understanding of water mass circulation provides a description of how the three layers constituting the nadw the labrador sea water lsw nd 13 9 0 4 north east atlantic deep water neadw nd 13 2 0 4 and north west atlantic bottom water nwabw nd 14 5 0 4 acquire their nd ic through distinct water mass mixings and lithogenic inputs these different mechanisms acting upon water masses from very diverse sources seem to bring the nd ic of the three nadw layers to values close together and similar to that of the nadw it is suggested that sediment seawater interactions significantly lower the neadw and nwabw nd ic along the south east greenland margin since these interactions do not significantly modify the nd content of these water masses sediment remobilizations leading to the nd ic variations are probably associated with nd removal fluxes from the water mass toward the sediment a process called boundary exchange on the other hand lsw seems to acquire its nd ic from the subpolar mode waters from which it is formed by deep convection and no other mechanism needs to be invoked its unradiogenic signature could ultimately be linked to fresh water runoff from the canadian shield these conclusions should allow more precise interpretations of paleoceanographic nd ic records taking into account the distinct histories of the three nadw layers including distinct water mass mixings and distinct lithogenic inputs

the effect of diagenesis and fluid migration on rare earth element distribution in pore fluids of the northern cascadia accretionary margin analytical challenges in obtaining high quality measurements of rare earth elements rees from small pore fluid volumes have limited the application of rees as deep fluid geochemical tracers using a recently developed analytical technique we analyzed rees from pore fluids collected from sites u1325 and u1329 drilled on the northern cascadia margin during the integrated ocean drilling program iodp expedition 311 to investigate the ree behavior during diagenesis and their utility as tracers of deep fluid migration these sites were selected because they represent contrasting settings on an accretionary margin a ponded basin at the toe of the margin and the landward tofino basin near the shelf s edge ree concentrations of pore fluid in the methanogenic zone at sites u1325 and u1329 correlate positively with concentrations of dissolved organic carbon doc and alkalinity fractionations across the ree series are driven by preferential complexation of the heavy rees simultaneous enrichment of diagenetic indicators doc and alkalinity and of rees in particular the heavy elements ho to lu suggests that the heavy rees are released during particulate organic carbon poc degradation and are subsequently chelated by doc ree concentrations are greater at site u1325 a site where shorter residence times of poc in sulfate bearing redox zones may enhance ree burial efficiency within sulfidic and methanogenic sediment zones where ree release ensues cross plots of la concentrations versus cl li and sr delineate a distinct field for the deep fluids z 75 mbsf at site u1329 and indicate the presence of a fluid not observed at the other sites drilled on the cascadia margin changes in ree patterns the presence of a positive eu anomaly and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous crescent terrane located east of the drilled transect

mineralogy fluid inclusions and c h o s pb isotopes of the palaeocene longgen pb zn deposit in the western nyainqentanglha belt tibet abstract the medium sized longgen pb zn deposit deposit proven pb zn resources of 0 13 mt 3 21 pb and 2 43 zn is located in the western nyainqentanglha belt in southern tibet the orebodies occurring as stratiform lenticular and vein types are hosted in the skarn or marble along the contacts between the limestones and the granite porphyries alteration zonations are observed from granite porphyry to limestone the proximal garnet is reddish brown and becomes more pale brown and green with distance the values of grossular gradually increase while the andradite end members gradually decrease with distance and 92 5 99 5 gro 0 5 7 5 pra 0 0 0 1 to and 9 0 36 5 gro 63 4 90 9 pra 0 1 0 5 similarly the values of diopside di9 2 30 4hd65 9 89 9 jo0 6 3 7 to di65 2 77 6hd21 33 2jo1 3 1 7 gradually increased close to the limestone retrograde metasomatic minerals overprint the prograde skarn and are dominantly composed of epidote actinolite ilvaite and chlorite the ore minerals consist mainly of galena and sphalerite followed by magnetite pyrite pyrrhotite chalcopyrite molybdenite and bornite at least five stages have been recognized and from stage i to stage v the 18ofluids values are 7 7 to 8 3 6 0 to 4 4 8 8 to 6 4 8 7 to 3 3 and 13 2 respectively the d values from stages i to v are 141 1 to 129 4 136 5 to 124 2 129 5 to 106 4 126 6 to 101 4 and 106 8 respectively the d and 18ofluids indicate that the ore forming fluids gradually evolved from magmatic to meteoric in origin the main types of fluid inclusions for the longgen deposit are liquid rich inclusions laser raman analysis indicates that the fluid inclusions within the studied minerals are dominated by h2o although some contain co2 gas given the fluid inclusion data the ore forming fluids of stages i and ii were most likely high temperature 460 480 and 340 360 c and low moderate salinity 7 9 15 0 and 2 4 12 6 wt nacl eq fluids which were formed in a magmatic hydrothermal system in stage i and as a mixture of magmatic and meteoric waters in stage ii in the subsequent stages iii and iv the fluids changed to moderate temperature 230 270 and 160 200 c and low moderate salinity 0 2 14 8 and 0 9 10 6 wt nacl eq mixed fluids of magmatic and meteoric waters in the last stage v the fluids changed to low temperature 130 160 c and low salinity 0 2 5 6 wt nacl eq meteoric water the 13c values in calcite lie within a narrow range of 6 1 to 4 4 similar to that for the magmatic source which indicates that the carbon was sourced from the granite porphyry sulfur 34s 0 4 5 estimated 34sfluids 2 77 and lead isotopic compositions of sulfides 206pb 204pb 18 549 18 776 207pb 204pb 15 685 15 839 and 208pb 204pb 38 94 39 592 similar to the whole rock values for the granite porphyry indicate that the ore forming materials were derived mainly from the granite porphyry which originated from the nyainqentanglha group consequently taking the data together suggests that the longgen pb zn deposit is a typical skarn deposit related to palaeocene magmatic hydrothermal systems and that fluid cooling caused by fluid mixing is the most crucial mechanism for pb zn deposition

deciphering kinetic metabolic and environmental controls on stable isotope fractionations between seawater and the shell of terebratalia transversa brachiopoda this study presents carbon and oxygen stable isotope data obtained from high resolution sampling 500 m of the brachiopod terebratalia transversa from the san juan islands washington state usa the aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite based on an sem study of the shell a three dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects the primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as 7 for 13c and 6 for 18o relative to expected equilibrium values the significant positive correlations between 18o and 13c values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects the ontogenetic 13c and 18o variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years the extent of apparent o 18 disequilibrium observed in this study is about as large as any yet measured in any organism which makes this brachiopod an interesting and important case the carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer where they reach values of 0 0 8 and 0 8 to 0 2 respectively corresponding calculated temperatures are between 12 and 13 8 c and fall in the range of seawater temperatures recorded off the san juan islands 7 13 c these results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animal s life finally approximating isotopic equilibrium this study illustrates that the stable isotopic composition of the modern brachiopod t transversa is predominantly influenced by kinetic fractionation and to a minor degree by metabolic effects except for the innermost part of the shell the measured isotope ratios do not reflect environmental conditions during shell precipitation it remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects these results point out the need for re examination of paleozoic oceanographic conditions

u pb systematics and alteration trends of pennsylvanian aged aragonite and calcite abstract carbonate allochems from the mid pennsylvanian buckhorn fauna of the boggy formation oklahoma usa consist of primary aragonite preserved in nautiloids and of secondary low mg calcite present in crinoids and corals unaltered nautiloids contain 11 38 ppb u and 23 422 ppb pb and have low 238 u 204 pb values from 4 1 14 8 they give a 238u 206pb isochron age of 311 48 ma 2 which is in agreement with the assigned stratigraphic age mid desmoinsian 305 ma of the boggy formation sediments their initial lead isotope ratios are 206 pb 204 pb 19 11 0 08 207 pb 204 pb 15 70 0 04 and 208 pb 204 pb 38 7 and reflect an upper crustal source for pb in mid pennsylvanian seawater these values are similar to those of coals of this age the contents of both u and pb in the buckhorn nautiloids are significantly higher than those found in the modern nautilus nautilus pompilius these enrichments are attributed to bitumen which was added to the carbonates during diagenesis the diagenetic transformation of aragonite to low mg calcite in the buckhorn nautiloids was apparently associated with a net loss of pb thereby increasing their values the secondary carbonates of crinoids contain 265 352 ppb u 136 262 ppb pb and their values range from 68 111 consequently their present day uranogenic lead isotopic ratios are higher than those of the buckhorn nautiloids the u pb data for some diagenetic low mg components indicate an age of 280 ma suggesting an early timing for the post depositional alteration process the apparent initial lead isotope ratios of crinoids are variable and some are significantly higher than the coexisting aragonite 206 pb 204 pb 20 50 207 pb 204 pb 15 73 this very radiogenic signature is similar to those of mississippi valley type ore deposits and both types may share a similar genesis

neotethys seawater chemistry and temperature at the dawn of the end permian mass extinction abstract the end of the permian was a time of great death and massive upheaval in the biosphere atmosphere and hydrosphere over the last decades many causes have been suggested to be responsible for that catastrophe such as global warming anoxia and acidification the gyanyima limestone block was an open ocean seamount in the southern neotethys at subtropical latitude and it affords us insight into open ocean oceanographic changes during the end of the permian after careful screening using multiple tests we reconstructed carbonate seawater curves from the geochemical data stored in pristine brachiopod shell archives from the shallow water limestone of the changhsingian gyanyima formation of tibet the reconstructed strontium isotope curve and data for the late changhsingian are relatively invariant about 0 707013 but in the upper part of the succession the values become more radiogenic climaxing at about 0 707244 the 87 sr 86 sr curve and trend are similar to those observed for the upper permian succession in northern italy but dissimilar less radiogenic to whole rock results from austria iran china and spitsbergen the ce ce anomaly results ranging from 0 310 to 0 577 for the brachiopods and from 0 237 to 0 655 for the coeval whole rock before the event and of 0 276 for whole rock during the extinction event suggest normal redox conditions these ce values are typical of normal open ocean oxic water quality conditions observed in modern and other ancient counterparts the biota and ce information clearly discounts global anoxia as a primary cause for the end permian biotic crisis carbon isotopes from brachiopod shells and whole rock are relatively invariant for most of the latest permian interval which is in stark contrast to the distinct negative carbon isotope excursion observed near and about the event estimates of seawater temperature at shallow depth fluctuated from 22 2 to 29 0 c up to unit 8 2 and then gradually rise from 29 7 c in unit 8 13 to values exceeding 35 c at a stratigraphic level about 120 ky before the permian triassic boundary and just before the onset of the extinction interval this dramatic increase in seawater temperature has been observed in global successions from tropical to mid latitude and from restricted to open ocean localities e g northern italy iran the brachiopod archive and its geochemical proxies from tibet support the paradigm that global warming must have been an important factor of the biotic crisis for the terrestrial and marine faunas and floras of the late paleozoic world

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

physiographic and tectonic settings of high sulfidation epithermal gold silver deposits of the andes and their controls on mineralizing processes abstract gold and silver ores in the vast majority of andean high sulfidation epithermal au ag deposits occur at high present day elevations and typically 200 500 m below low relief landforms situated at 3500 to 5200 m a s l most deposits are middle miocene and younger and include el indio tambo pascua lama veladero el indio belt chile argentina cerro de pasco central peru pierina lagunas norte yanacocha northern peru quimsacocha ecuador and the california vetas mining district santander colombia jointly accounting for 130 moz au resources slightly older examples are only preserved in the atacama desert and include the middle eocene el guanaco and el hueso and the late oligocene early miocene la coipa deposits the absence of paleocene and older high sulfidation epithermal deposits can be explained by limited preservation potential imposed by transpressional tectonics within overall contractile episodes and surface uplift these conditions prevailed predominantly in segments of shallow angle subduction of the nazca or caribbean plate below the south american continent a tectonic setting also common for porphyry style cu au mo deposits stratovolcanoes are uncommon ore hosts and volcanic rocks coincident with mineralization are in most cases volumetrically restricted or absent recording the terminal stages of local arc magmatism however dacitic domes are important at e g yanacocha and la coipa at lagunas norte a small stratovolcano largely pre dating but temporally overlapping with mineralization occurs immediately east of the deposit and volcanic sector collapse may have occurred during hydrothermal activity mineralization is typically located near the backscarp of pediments or the heads of valleys incising now high elevation low relief surfaces in the california vetas mining district and el indio belt hydrothermal alunite ages become generally younger upstream along the incising valleys indicating that hydrothermal activity and by inference ore deposition were facilitated by erosion the lowering of the water table and reduction of hydrostatic and lithostatic pressure at these sites of high local relief are believed to have enhanced both boiling and mixing of magmatic with meteoric fluids ultimately enhancing ore deposition the host rock composition permeability and location of the water table control the distribution of alteration zones and ore intermediate volcanic rocks are the most common ore hosts but they typically pre date mineralization by several ma however high sulfidation epithermal mineralization can be hosted in any conceivable rock type including high grade metamorphic rocks california vetas mining district significantly older plutonic rocks pascua lama or quartzites lagunas norte large vuggy quartz alteration zones and commonly oxidized low grade large tonnage mineralization are best developed in relatively permeable volcaniclastic rocks or hydrothermal breccia bodies whereas coherent volcanic plutonic or metamorphic rocks may host fault and breccia controlled ores the near surface steam heated zone can attain a thickness of several hundred meters in dry climates e g veladero pascua lama tambo but is typically poorly developed and less than 20 m thick in humid climatic zones the physiographic and tectonic settings of high sulfidation epithermal deposits are distinct from low sulfidation epithermal districts such as those of patagonia el penon chile or fruta del norte ecuador the latter range to significantly older ages jurassic to early eocene occur at mainly lower elevations and were emplaced in extensional settings a temporal coincidence between uplift erosion and mineralizing processes as well as a spatial and temporal association with porphyry style mineralization is not evident for these low sulfidation districts

the incorporation of rare earth elements in modern coral we report measurements of rare earth elements rees which show that these trace elements are being incorporated in modern coral in proportion to their seawater concentrations four bermuda north rock coral species diploria strigosa diploria labyrinthiformis montastrea annularis and porites astreoides and two tarawa atoll samples of the species hydnophora microconos were analyzed by ti idms following cleaning techniques to isolate the lattice bound rees based on the replicate analyses of the same piece of diploria strigosa excellent reproducibility was achieved the ree ca ratios 0 1 3 nmol mol of the bermuda and tarawa corals are similar to those of cd ca the trace metal with the lowest seawater concentration used in coral studies with the exception of ce the distribution coefficients e g dnd nd coral nd seawater ca seawater ca coral between bermuda coral lattice and sargasso seawater have fairly flat patterns across the ree series the values of d range from 1 to 3 like those reported for other trace elements in corals this suggests but does not prove that rees are incorporated in the aragonite lattice of these corals the shale normalized ree patterns of the tarawa corals also have seawater like distributions however no local seawater data are available to calculate values of d two bermuda species d labyrinthiformis and p astreoides have values of d for ce that are high with respect to the d values of la and nd implying that there is preferential uptake of ce into the lattice this may be related to the fact that ce is the only ree with an active redox chemistry in seawater there is considerable interest in using the chemical and isotopic composition of coral as indicators of climatic variations the combination of ree ca ratios and neodymium isotopic composition of coral has the potential to help understand important natural processes a primary application could be directed toward a tracer for river water discharge in tropical regions and by inference a proxy for rainfall climate variation and weathering history this application would exploit the fractionated composition of rees in river water as a terrigenous signature in coastal corals

variation of the distribution coefficients of rare earth elements in modern coral lattices species and site dependencies abstract rare earth element ree concentrations in the carbonate lattice of four species of coral have been analyzed and compared with the dissolved ree in ambient seawaters the corals were from two areas of different salinity marine 34 34 5 and bay 33 34 the measurement of ree in coral was carried out with inductively coupled plasma mass spectrometry icp ms after meticulous washing of coral samples digestion with acetic acid and preconcentration of ree the concentrations of ree in the two ambient seawaters were quite different being ten times higher in the bay area and enriched in light ree however the average distribution coefficients d s were almost identical in the two areas substantial distribution coefficient differences were observed among the four coral species and the magnitude of inter species variation in d was also species dependent theoretical calculations imply that ph variation could cause variations in d large enough to account for the small differences between the two areas

the andean orogenic period and its major structures in central and northern peru the andean orogenic period began in the albian and consisted of at least 6 discrete compressional phases which are albian to late miocene in age deformation migrated progressively toward the amazonian foredeep the major andean structures in central and northern peru are related to the eocene incaic early miocene quechua 1 and late miocene quechua 3 phases the maranon thrust and fold belt mtfb which bounds the western cordillera to the ne rose in the eocene it was reactivated partly by the quechua 1 phase which also folded the altiplano farther e and possibly part of the eastern cordillera the sub andean thrust and fold belt stfb is related to the quechua 3 phase in both mtfb and stfb the imbricate thrusts merge at depth in large decollement faults gravity sliding does not play a dominant role for these faults have to be rooted westward in the pre andean basement the corresponding crustal shortening played a significant part in the creation of the sialic root of the andes

petrogenetic and metallogenetic relationships in the eastern cordillera occidental of central peru abstract ore deposits spatially and temporally related to high k calc alkaline intrusions or domes are widespread in the central peruvian cordillera occidental geochronology and petrochemistry of intrusive rocks associated with mineralization reveal that most ore deposits 1 were emplaced in the late middle to early late miocene and 2 are related to calc alkaline igneous rocks of granodioritic composition with documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm sm mathrm yb 3 end document documentclass aas

neodymium isotopic composition and rare earth element concentrations in the deep and intermediate nordic seas constraints on the iceland scotland overflow water signature neodymium isotopic composition and rare earth element concentrations were measured in seawater samples from eleven stations in the nordic seas these data allow us to study how the iceland scotland overflow water isow acquires its neodymium signature in the modern ocean the waters overflowing the faroe shetland channel are characterized by nd 8 2 0 6 in good agreement with the only other data point published 19 years ago in the greenland and iceland seas the water masses leading to the formation of the isow display lower neodymium isotopic composition with nd around 11 and 9 respectively since no water masses in the nordic seas are characterized by nd 8 the radiogenic signature of the isow likely reflects inputs from the highly radiogenic norwegian basin basaltic margins jan mayen iceland faroe with nd 7 in addition to the neodymium isotopic composition the rare earth element patterns suggest that these inputs occur via the remobilization which includes resuspension and dissolution of sediments deposited on the margins whereas the neodymium isotopic composition behaves conservatively in the oceans in the absence of lithogenic inputs and can be used as a water mass tracer these results emphasize the role of interactions between sediments deposited on margins and seawater in the acquisition of the neodymium isotopic composition of water masses these results should allow a better use of this parameter to trace the present and the past circulation in the north atlantic

decelerating nazca south america and nazca pacific plate motions space geodetic estimates of the rate of nazca south america convergence and nazca pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average nuvel 1a model the implied rates of deceleration are consistent with longer term trends extending back to at least 20 ma about the time of initiation of andes growth and may reflect consequences of ongoing subduction and construction of the andes e g increased friction and viscous drag on the subducted slab as the leading edge of south america thickens

rare earth elements and neodymium isotopes in ferromanganese oxide coatings of cenozoic foraminifera from the atlantic ocean abstract an evaluation has been made of the method of establishing the ree contents and patterns and nd isotopic compositions of sea water over cenozoic time from their record in the femn oxide coatings of foraminiferal calcite using 0 60 ma samples from the rio grande rise dsdp site 357 it has been established that the ree contents of the coatings are generally similar to those of recent samples however in the cenozoic samples the surface coatings have been diagenetically modified under suboxic conditions resulting in a distinctly different ree pattern although the original 143 nd 144 nd ratios appear to have been preserved the nd isotopic curve for cenozoic sea water in the s atlantic shows clear temporal trends although these are not so extreme as to show 143 nd 144 nd ratios outside the range observed in modem sea water with the principal exception of the oldest samples there is an approximate inverse relationship between the nd and sr isotopic compositions of the foraminifera it is suggested that the changes reflect both global changes in the relative proportions of nd and sr derived from continental input and from the weathering of volcanic debris together with short term and local variations to which the sr curve is insensitive reflecting the different response times of the two elements to changes in oceanic input functions the nd isotope curve appears to be a potentially useful tracer of ocean palaeochemistry

the role of early formed structures on the development of the world class st ives goldfield yilgarn wa a revised structural interpretation for the victory to kambalda area of the world class st ives goldfield in the archean yilgarn craton has mapped out the distribution of wnw trending faults within this area of the field these previously cryptic wnw trending structures had been identified in gravity data and also by isopach thickness variations the wnw trending faults acted as transfers syn gold mineralization although only discrete segments of these faults were active during the main stage of gold mineralization where mineralized the faults transferred strain from a complex combination of block on block movement associated with thrusting and strike slip movement on nw and n trending faults along some segments n trending mineralized faults terminate against the wnw trending faults many of the wnw trending faults correlate with major strike changes on regional and camp scale faults and they are domain boundaries for the critical n trending fault segments that host high grade gold within contractional jogs the wnw trending faults also show evidence for an older deformation history prior to main stage gold which may extend back to early basin development associated with ultramafic and mafic volcanism they are inferred to have been a series of early wnw trending normal faults and breached relay ramps associated with oblique rifting along an older nnw trending basement boundary

rare earth elements in saanich inlet british columbia a seasonally anoxic basin rare earth element and manganese distributions have been investigated in saanich inlet british columbia a seasonally anoxic basin redox cycling of ce and mn takes place across an oxic suboxic boundary approximately 20 m shallower than the o2h2s interface the remaining strictly trivalent ree undergo scavenging above this oxic suboxic boundary and regeneration from dissolving host phases below it these processes result in pronounced removal of ce from solution above the oxic suboxic boundary due to oxidative precipitation along with preferential uptake of the lighter trivalent ree during scavenging below the oxic suboxic boundary regeneration of particulate ree into solution leads to a less pronounced ce depletion and a less pronounced hree enrichment in the anoxic bottom waters dissolved ree concentrations in the sediment pore waters exhibit an approximately ten fold increase across the seawater sediment interface but then decrease with increasing depth indicating removal from solution during later diagenesis calculated diffusive fluxes of the ree and mn from the sediments into the overlying anoxic water column are insufficient to account for the accumulated trace metal enrichments observed in the water column we propose an annual redox cycle for saanich inlet in which flushing causes extensive oxidative precipitation and scavenging of trace elements from the water column each autumn the same material is rapidly regenerated from the underlying near surface sediments when the basin next turns anoxic

the empire cu zn mine idaho exploration implications of unusual skarn features related to high fluorine activity the empire cu zn skarn deposit is unusual because of the proximal position of zn mineralization abundance of endoskarn and the extremely vermicular texture of quartz phenocrysts in the related intrusive rocks cu zn skarn occurs at the contact between upper mississippian white knob limestone and the granite porphyry phase of the mackay stock which consists from early to late of quartz monzodiorite granophyre granite porphyry porphyritic granite and many dikes the late phases have high f and also extremely vermicular quartz phenocrysts endoskarn is more abundant than exoskarn the earliest alteration of the intrusive rocks consists of disseminated diopsidic pyroxene di64hd36 to di88hd12 actinolite and titanite this assemblage was cut by early scapolite me18 to me35 mostly me18 26 and or green pyroxene di14hd80 to di20hd77 veinlets with or without wollastonite halos these early veins were then cut by main stage endoskarn veins that typically have a garnet minor pyroxene inner zone a wollastonite and or pyroxene ca rich plagioclase an56 to an89 envelope and a halo containing disseminated fine grained alteration minerals of the same assemblage as the envelope some veins contain only the envelope assemblage and are interpreted to represent the alteration front the inner zone locally contains vesuvianite where many veins intersect endoskarn is massive pyroxene is zoned around fluid conduits the distal pyroxene is fe rich hedenbergitic whereas the proximal pyroxene is fe poor diopsidic the garnet changes in the opposite way being fe poor al rich grossularitic in locations distal to the fluid conduits and fe rich andraditic in proximal locations in contrast in the exoskarn all pyroxene is diopsidic and garnet is andraditic weak retrograde alteration composed of quartz calcite chlorite with minor fluorite talc and epidote overprinted both endoskarn and exoskarn magnetite precipitated after garnet pyroxene in both endoskarn and exoskarn sphalerite precipitated together with chalcopyrite in proximal locations and is associated with retrograde alteration other ore minerals include minor molybdenite bornite pyrite galena arsenopyrite native au as well as supergene minerals such as chrysocolla malachite azurite native cu and limonite fluid xenoliths from pyroxene in early endoskarn veinlets homogenize at 600 c massive endoskarn and exoskarn replacing limestone inclusions in granite porphyry formed at 500 to 700 c whereas the highest temperature inclusions 700 c occur in narrow garnet minor pyroxene veins fluid inclusions in exoskarn replacing wall rock have homogenization temperatures of 500 to 650 c retrograde alteration and cu zn mineralization occurred at 250 to 300 c fluid inclusions in prograde minerals contain daughter minerals whereas fluid inclusions in retrograde minerals do not indicating a decrease in salinity with time late stage fluids have low eutectic temperatures indicating the possible presence of kcl nacl fecl2 cacl2 mgcl2 k2co3 and or na2co3 formation of the unusually abundant endoskarn the proximal position of zn mineralization and the extremely vermicular texture of quartz phenocrysts are all believed to have been promoted by the high f content of the magmatic fluid these features may serve as exploration indicators of associated high f mineralization such as buried porphyry mo deposits

dissolved rare earth elements tracing lithogenic inputs over the kerguelen plateau southern ocean abstract dissolved rare earth elements rees were measured in the water masses upstream from and over the kerguelen plateau indian sector of the southern ocean upstream from the plateau the ree profiles were consistent with published data from the southern and indian oceans over the plateau a one box model yields a lithogenic nd flux from the dissolution of lithogenic material of 89 20 t nd y 1 and a corresponding dissolved iron input larger than 100 000 t fe y 1 however despite evidence of this significant lithogenic input dissolved fe is strongly depleted in the upper layers contrasting with the enriched ree concentrations this contrast stresses the different behaviours of ree and iron in the surface waters and the fact that strong fertilization does not imply dissolved fe replete waters

shell structure patterns and trends of oxygen and carbon stable isotopes in modern brachiopod shells this study investigates 13c and 18o variations in the shells of modern brachiopods representing all extant groups of calcite precipitating brachiopods collected live from 8 locations sem examinations determined the ultrastructural characteristics of each species prior to isotope analyses 13c and 18o analyses of shell carbonate were carried out with samples representing disparate morphological features and ultrastructural shell layers of both ventral and dorsal valves generally 18o values from the fibrous secondary or prismatic tertiary shell layers of the articulated terebratulida and rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures 18o values were relatively unaffected by shell specialisation the only exception was antarctic species liothyrella uva which did not have a complete tertiary shell layer typical of this genus and had 18o values of the innermost layer strongly correlated with 13c and mostly not in oxygen isotopic equilibrium with ambient seawater with the exception of the rhynchonellid notosaria nigricans the outer primary layer material was depleted in 13c and 18o and highly variable inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature therefore only fossil secondary layer material should be used the anomalous articulated thecideidine brachiopod thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium 18o values from the laminar secondary layer material of the inarticulated craniida are highly variable therefore these species are not recommended for use as palaeoenvironmental proxies this study suggests caution when employing fossil brachiopod shells with similar ultrastructures to modern craniid and thecideidine brachiopods the carbon isotope composition is highly variable in all of the brachiopods studied analysis of samples from specialised regions of the secondary shell layer show a pattern of depletion in 13c relative to non specialised secondary material the carbon isotope variability is independent of 18o and is repeated in most of the articulated species regardless of geographical location this is possibly a vital effect produced by metabolic prioritisation

stable isotope composition and rare earth element content of vertebrate remains from the late cretaceous of northern spain lano did the environmental record survive abstract oxygen and carbon isotope measurements have been performed on phosphatic remains from faunal associations dinosaurs crocodiles turtles and fish of the late cretaceous continental and marine sediments from northern spain basque country the environmental meaning of the oxygen isotope record in fossil reptiles is discussed on the basis of known paleoecology modern fauna analogs and apatite chemistry rare earth elements ree co32 and po43 contents fossil remains in sandstones and argillites from two localities urria and cuezva have low down to 16 and scattered 18o po4 co3 and 13c values with ree patterns characterized by strong middle ree enrichments these geochemical compositions of the biogenic apatites have most likely been acquired during a multi stage late diagenesis involving complete recrystallization of the apatite in the presence of aqueous fluids ree contents of fossils preserved in the clayey sands from the site of lano suggest that samples have only been affected by early diagenesis despite the diversity of analyzed taxa and the close association of marine sharks and rays and freshwater species crocodiles and turtles evolving in a littoral environment the narrow range of phosphate 18o values is interpreted as reflecting the temperature and isotopic composition of groundwaters that prevailed in the burial environment the potential information relative to the physiology and thermal regime of the vertebrates has been erased during the process of early diagenesis if all oxygen in the phosphate has exchanged with groundwaters the oxygen isotope composition of vertebrate remains suggests that a warm climate t 20 25 c prevailed in northern spain during the late cretaceous

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

age and regional tectonic and metallogenetic implications of igneous activity and mineralization in the andahuaylas yauri belt of southern peru