tectonic setting of synorogenic gold deposits of the pacific rim abstract more than 420 million oz of gold were concentrated in circum pacific synorogenic quartz lodes mainly during two periods of continental growth one along the gondwanan margin in the palaeozoic and the other in the northern pacific basin between 170 and 50 ma these ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary rock dominant terranes the auriferous veins contain only a few percent sulphide minerals have gold silver ratios typically greater than 1 1 show a distinct association with medium grade metamorphic rocks and may be associated with large scale fault zones ore fluids are consistently of low salinity and are co2 rich in the early and middle palaeozoic in the southern pacific basin a single immense turbidite sequence was added to the eastern margin of gondwanaland deformation of these rocks in southeastern australia was accompanied by deposition of at least 80 million oz of gold in the victorian sector of the lachlan fold belt mainly during the middle and late devonian lesser devonian gold accumulations characterized the more northerly parts of the gondwanan margin within the hodgkinson broken river and thomson fold belts additional lodes were emplaced in this flyschoid sequence in devonian or earlier palaeozoic times in what is now the buller terrane westland new zealand minor post devonian growth of gondwanaland included terrane collision and formation of gold bearing veins in the permian in australia s new england fold belt and in the jurassic early cretaceous in new zealand s otago schists collision and accretion of dozens of terranes for a 100 m y long period against the western margin of north america and eastern margin of eurasia led to widespread latest jurassic to eocene gold veining in the northern pacific basin in the former location late jurassic and early cretaceous veins and related placer deposits along the western margin of the sierra nevada batholith have yielded more than 100 million oz of gold additional significant ore forming events during the development of north america s cordilleran orogen included those in the klamath mountains region california in the late jurassic and early cretaceous the klondike district yukon by the early cretaceous the nome and fairbanks districts alaska and the bridge river district british columbia in the middle cretaceous and the juneau gold belt alaska in the eocene gold bearing veins deposited during the late jurassic and early cretaceous terrane collision that formed the present day russian far east have been the source for more than 130 million oz of placer gold the abundance of gold bearing quartz carbonate veins throughout the gondwanan north american and eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata the common temporal association between gold veining and magmatism around the pacific rim reflects these thermal episodes melting of the lower thickened crust during arc formation slab rollback and extensional tectonism and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initiation of the ore forming processes

transgressive dune formation along a cliffed coast at 75 ka in sardinia western mediterranean a record of sea level fall and increased windiness transgressive dunes develop frequently along strandplain coastlines however they may also form along rocky coasts dominated by cliffs and embayments two lithified transgressive dune systems developed along the cliffed alghero coast nw sardinia italy have been investigated one aeolian system forms a cliff front anchored aeolian dune accumulation the other is a valley head anchored sand ramp system optically stimulated luminescence ages indicate that both systems formed around 75 ka this period which corresponds to the beginning of mis 4 was characterized by a relatively low sea level stand 15 m below the present sea level and was preceded by a sea level highstand 1 m asl around 81 ka mis 5a our results show that this rapid sea level fall exposed an enormous amount of marine sand which was transported inland by strong northerly winds and deposited in front of cliffs or in valley heads therefore sediment supply and sea level fall seem to be critical factors controlling dune formation along rocky coasts which generate time transgressive aeolianites terra nova 00 000 000 2010

age of cu fe au mineralization and thermal evolution of the punta del cobre district chile the punta del cobre belt is located 15 km south of copiapo northern chile it comprises several cu fe au deposits in the punta del cobre and ladrillos districts east of the copiapo river and the ojancos nuevo district with the new candelaria mine and las pintadas district west of the river the mineralization in the punta del cobre belt is characterized by a simple hypogene mineral assemblage of chalcopyrite pyrite magnetite and hematite average ore grades are 1 1 to 2 cu 0 2 to 0 6 g t au and 2 to 8 g t ag massive magnetite occurs as veins and irregularly shaped bodies the ore is spatially associated with alkali metasomatism and in particular with potassic alteration the cu fe au deposits are hosted mainly in volcanic rocks of the punta del cobre formation pre upper valanginian that underlie neocomian limestones of the chanarcillo group this region experienced backarc basin formation in the neocomian uplift and granitoid intrusions in the middle cretaceous and eastward migration of the magmatic front of about 30 km between middle cretaceous and paleocene to determine the timing of ore deposition and to reconstruct parts of the thermal history of the punta del cobre district in the eastern part of the belt we have obtained 40ar 39ar incremental heating and rb sr analyses of mineral and whole rock samples an 40ar 39ar incremental heating experiment on hydrothermal biotite formed synchronous with the cu fe au mineralization yielded an inverse isochron age of 114 9 1 0 ma all errors reported at 2 consistent with a rb sr isochron of 116 8 2 7 ma calculated from 7 whole rock samples these data are interpreted to represent the age of potassic alteration that accompanies mineralization ore formation temperatures of 400 c to 500 c were previously estimated based on paragenetic relationships shearing at the candelaria deposit occurred after ore deposition and before the main stage of batholith emplacement published k ar ages for the middle cretaceous batholith near the punta del cobre belt range from 119 to 97 ma our data suggest that the mineralization is related to the earlier stages of batholith emplacement the biotite age spectrum indicates that the punta del cobre district was not affected by temperatures above 300 c 350 c the closure temperature for argon in biotite during the contact metamorphic overprint produced by later emplaced batholithic intrusions whole rock 40ar 39ar ages are considerably younger incremental heating experiments yielded an inverse isochron age of 90 7 1 2 ma and weighted mean plateau ages of 89 8 0 6 ma and 89 5 0 6 ma these samples are dominantly k feldspar for which we assume an argon closure temperature of 150 c thus they give the age of cooling below 150 c 200 c

geology of part of a long lived dynamic plate margin the coastal cordillera of north central chile latitude 30 51 31 s a complex composed of ultrabasic and basaltic lavas chert arkose and conglomerate was assembled in the coast of north central chile lat 30 30 31 s prior to 200 ma the character of and relationships between the rock formations exposed here are consistent with an autochthonous evolution of this part of chile in the last 200 ma three major episodes of deformation and metamorphism have been observed in this area the first episode f1 produced a compositional layering s1 and amphibolite facies metamorphism coeval with the intrusion of an extensive igneous complex between 220 and 200 ma a second episode of deformation f2 locally formed reverse faults and tight recumbent folds in s1 units in which f2 folds are well developed yield k ar and rb sr ages between 163 and 140 ma at between 140 and 126 ma upright open to tight folds f3 formed with sharp hinges and axial planes that strike north and dip steeply east structures of similar age style and orientation have been reported as far sou

the south pacific meridional mode as a thermally driven source of enso amplitude modulation and uncertainty abstractthis study seeks to identify thermally driven sources of enso amplitude and uncertainty as they are relatively unexplored compared to wind driven sources pacific meridional modes are argued to be wind triggers for enso events this study offers an alternative role for the south pacific meridional mode spmm in enso dynamics not as an enso trigger but as a coincident source of latent heat flux lhf forcing of enso ssta that if correctly incorrectly predicted could reduce increase enso prediction errors we utilize a coupled model simulation in which enso variability is perfectly periodic and each el nino experiences identical wind stress forcing differences in el nino amplitude are primarily thermally driven via the spmm when el nino occurs coincidentally with positive phase spmm the positive spmm lhf anomaly counteracts a fraction of the lhf damping of el nino allowing for a more intense el nino if the spmm phase is instead negative the spmm lhf amplifies the lhf damping of el nin

the south pacific meridional mode and its role in tropical pacific climate variability abstractthe pacific meridional mode a thermodynamically coupled mode of variability links extratropical pacific oceanic and atmospheric anomalies to the tropical pacific and may give rise to el n

the candelaria punta del cobre iron oxide cu au zn ag deposits chile several iron oxide rich cu au zn ag deposits define an approximately 5 km wide and at least 20 km long belt along the eastern margin of the coastal batholith near copiapo chile this belt includes the large candelaria mine and a group of middle and small sized mines in the punta del cobre district which is located about 3 km northeast of the candelaria deposit estimated geologic resources of the belt are on the order of 700 to 800 million metric tons mt at 1 0 percent cu the ore occurs in veins breccia and stringer bodies and in replacement bodies that are roughly concordant to bedding the orebodies are hosted mainly by volcanic and volcaniclastic rocks of the punta del cobre formation and in places also occur in volcaniclastic intercalations in the lower part of the overlying early cretaceous chanarcillo group most of the larger orebodies in the belt are located where northwest trending brittle faults intersect the contact between massive volcanic and volcaniclastic rocks these northwest faults and a major northeast trending ductile shear zone control portions of the ore of the candelaria deposit chalcopyrite is the only hypogene cu mineral the cu au ore is characterized by abundant magnetite and or hematite and by locally elevated concentrations of ag zn mo and light rare earth elements the ore is hosted mainly in zones with biotite potassium feldspar calcic amphibole epidote alteration at candelaria in the punta del cobre district ore in the deeper parts of the deposits is similarly associated whereas at shallow levels it occurs in zones of biotite potassium feldspar or albite chlorite calcite alteration mineralization at candelaria punta del cobre took place under relatively oxidized conditions manifested by the formation of specular hematite in parts of the district the pseudomorphic replacement of early specular hematite by magnetite during the main iron oxide formation marks a shift toward more reduced conditions or higher temperatures the bulk of the magnetite probably formed at temperatures of about 500 to 600 c the main sulfide stage followed with formation of pyrite and chalcopyrite at temperatures of 470 to 328 c subsequent martitization of the magnetite points to a temperature decrease cooling of the hydrothermal system is also indicated by the homogenization temperatures of 236 c of saline fluid inclusions in late stage calcite oxygen isotope combined with microthermometric data suggest that magmatic fluids or nonmagmatic fluids equilibrated with magmatic silicates were dominant during the main copper mineralization relatively light oxygen isotope signatures of fluids in equilibrium with late calcite suggest mixing with a nonmagmatic fluid e g basinal brines or meteoric waters during the late stages of hydrothermal activity sulfur isotope ratios of chalcopyrite pyrite pyrrhotite and sphalerite from the bronce candelaria las pintadas santos and socavon rampa deposits range from 34scdt values of 0 7 to 3 1 per mil this narrow range of sulfur isotope ratios near 0 per mil is consistent with sulfur of magmatic origin anhydrite from the candelaria mine paragenetically overlaps with chalcopyrite fluid inclusions in this anhydrite homogenize between 340 and 470 c and it has 34scdt values between 14 5 and 17 5 per mil a sulfate sulfide value of 13 4 per mil for a sample with coexisting anhydrite and chalcopyrite is consistent with sulfide sulfate fractionation at temperatures on the order of 400 c ore lead isotope signatures are homogeneous and similar to those of least altered volcanic host rocks and nearby intrusive rocks radiometric ages including new 40ar 39ar ages for hydrothermal alteration at candelaria point to a main cu au mineralization event at candelaria punta del cobre at around 115 ma the ages indicate that ore formation was broadly coeval with batholithic granitoid intrusions and with regional uplift they further imply that the cu au zn ag deposits formed at shallow crustal levels 3 km the stable isotope data the presence of previously reported hypersaline co2 rich fluid inclusions in the main cu ore stage and saline fluid inclusions in late stage calcite the oxidized character of the first ore fluid pulses and the mineralization age coeval with nearby intrusive activity are consistent with but not unequivocally evidence of magmatic fluid contribution into the hydrothermal system

dating the cooloola coastal dunes of south eastern queensland australia abstract the cooloola sand dunes are part of a series of aeolian parabolic dunes that stretch along the east coast of australia they form a chronosequence showing increasing weathering soil formation and water erosion across six geomorphically recognized soil landscapes these landscapes were recognized from air photographs and further refined on the basis of some 150 auger holes across the dunes data about the structure and floristics of the vegetation were collected at the same time there is a significant body of literature about the cooloola dunes but there are two areas that have not been satisfactorily considered first the previous dating which gave inconsistent results has been superseded by single grain osl dates and second cooloola has not been considered in a regional context here we report the results of single grain optically stimulated luminescence osl analyses for 31 samples for 21 sites across the geomorphic landscapes the sites were selected near the apex of each dune as this represents the last depositional date and the least disturbed by sand movement we recognized 10 units across the dunes on the basis of the dates available the dune ages ranged from recent to 725 ka the largest dunes at some 320 m high were dated at around 140 ka and these dunes carry the maximum vegetation biomass of this dunefield beyond this vegetation maximum the dunes had lost their parabolic shape due to prolonged weathering and erosion and the vegetation is greatly reduced in height and biomass the depth to the soil b horizon gradually deepens with age to form giant podzols in the older dunes the depth to the b horizon was remarkably consistent within the geomorphic landscapes across the length and breadth of the dunes these studies place the cooloola dunes in a unique position as the chronosequence is intact the possible processes that lead to the formation of the dunes and the regional implications are discussed secondly it shows the buildup and decline of the dune ecosystems and acts as a model for all ecosystems forest succession models which place less emphasis on soil development miss this important process

holocene coastal dune formation in southern australia a case study abstract the 14 500 km long southern australian coast is exposed to high energy wave and wind regimes which have mobilized shelf derived sediments to produce extensive holocene shoreface deposits the 8000 km of sandy coast are backed by over 2000 km 2 of holocene dunes of varying degrees of stability in places dune deposition above present sea level accompanied the post glacial marine transgression commencing as early as 10 ka b p and has continued episodically to the present day the dunes are widespread in extent but vary in type size and evolution the oldest and often most extensive primary dune fields accompanied the post glacial marine transgression they occurred and in some places continue to form in areas of high wave and wind energy and abundant sand supply many of these systems exhausted their sediment supply by mid holocene and remain as stranded clifftop dunes where sand ramps were eroded or as eroding barriers secondary phases of dune activity occurred on moderate to high energy coasts following an initial period of post stillstand barrier progradation diminished sediment supply resulted in shoreline erosion and secondary dune formation the location size and evolution both of dunes types is largely controlled by the breaker wave regime which in turn influences the rate and volume of sediment supply beach morphodynamics and resulting aerodynamic boundary conditions and foredune erosion a study of dune formation along the 3700 km long south australian coast provides a basis for an overview of dune formation throughout southern australia

lead isotope provinces of the central andes inferred from ores and crustal rocks the central andean cordillera of peru bolivia northwestern argentina and northern chile may be divided into three fundamental geologic provinces based on the age and dominant geology of the exposed rocks we define these provinces as follows province i the coastal volcanic arc comprising the jurassic early tertiary coastal batholith complex and related volcanic rocks of the western cordillera and coastal belt based on differences in the isotopic composition of ore lead province i is further subdivided into subprovince ia comprising the coastal volcanic belt of northern and central chile subprovince ib in central peru north of 13 degrees s and subprovince ic in southern peru and northernmost chile between 19 degrees s and 13 degrees s province ii the jurassic and cretaceous miogeosynclinal sedimentary belt that dominates the geology of the high andes of peru province iii the eastern cordillera of southeastern peru central bolivia and northwestern argentina made up mainly of early paleozoic clastic sediments we have also divided this into two subprovinces due to different ore lead isotope characteristics subprovince iiia in bolivia and northern argentina and subprovince iiib in southeastern peru these provinces are bordered by noncordilleran units of the brazil and guyana shields the arequipa massif and the metamorphic terranes of southern chile and central western argentina we present 45 new analyses of ore minerals from 31 mining districts and two of host rocks from province iii and summarize our results together with other data available in the literature isotopic compositions of ore lead from the above provinces conform to neighboring but distinct fields on pb isotope covariation diagrams lead from province i ores has 206 pb 204 pb 18 21 to 18 82 207 pb 204 pb 15 55 to 15 69 and 208 pb 204 pb 38 11 to 38 95 lead from province ii ores is less variable with consistently higher 206 pb 204 pb and 208 pb 204 pb than the province i ores and slightly higher average 207 pb 204 pb we consider the province i and ii ore leads to reflect different degrees of mixing between magmatic upper mantle derived lead and crustal sources most assimilation of crustal lead is probably magmatic and results from incorporation of lead from subducted sediments at the magma source and or from the crust during ascent of the parent magma from the upper mantle province iii ore leads are much more variable than those of provinces i and ii having 206 pb 204 pb 17 97 to 25 18 207 pb 204 pb 15 51 to 16 00 and 208 pb 204 pb 37 71 to 40 07 they have consistently higher 207 pb 204 pb and 208 pb 204 pb for given values of 206 pb 204 pb than ore leads from the other provinces province iii leads indicate more radiogenic heterogenous source regions and suggest that fusion of continental crust has played an important role in the genesis of magmas and associated ore deposits this is substantiated by the metaluminous to strongly peraluminous character of much of the magmatism in province iii detailed comparisons of lead isotope data available in the literature for andean volcanic rocks with compositions of ores are problematic because analyses are rarely reported from related ores and igneous bodies where such data exist ore pb isotope compositions correlate closely with those in the associated intrusions

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

environmental controls morphodynamic processes and ecogeomorphic interactions of barchan to parabolic dune transformations the transformation of barchans into parabolic dunes has been observed in various dune systems around the world precise details of how environmental controls influence the dune transformation and stabilisation mechanism however remain poorly understood a horns anchoring mechanism and a nebkhas initiation mechanism have previously been proposed and selected environmental controls on the transformation have been explored by some modelling efforts but the morphodynamic processes and eco geomorphic interactions involved are unclear and comparison between different dune systems is challenging this study extends a cellular automaton model informed by empirical data from fieldwork and remote sensing to fully explore how vegetation characteristics boundary conditions and wind regime influence the transformation process and the resulting dune morphologies a dynamic growth function is introduced for clump like perennials to differentiate between growing and non growing seasons and to simulate the development of young plants into mature plants over multiple years modelling results show that environmental parameters interact with each other in a complex manner to impact the transformation process the study finds a fundamental power law relation between a non dimensional parameter group so called the dune stabilising index s and the normalised migration distance of the transforming dune which can be used to reconstruct paleo environmental conditions and monitor the impacts of changes in climate or land use on a dune system four basic eco geomorphic interaction zones are identified which bear different functionality in the barchan to parabolic dune transformation the roles of different environmental controls in changing the eco geomorphic interaction zones transforming processes and resulting dune morphologies are also clarified

parabolic dune development modes according to shape at the southern fringes of the hobq desert inner mongolia china since the 1970s parabolic dunes at the southern fringe of the hobq desert inner mongolia china have exhibited many different shapes v shaped u shaped and palmate each with a unique mode of development in the study area parabolic dunes are mainly distributed in regions a b and c with an intermittent river running from the south to the north we used high resolution remote sensing images from 1970 to 2014 and rtk gps measurements to study the development modes of different dune shapes the modes are characterized by the relationship between the intermittent river and dunes formation of the incipient dune patterns the predominant source supply of dunes and the primary formation of different shapes v shaped u shaped and palmate most parabolic dunes in region a are v shaped and closer to the bank of the river the original barchans in this region exhibit disconnected arms behavior with the sand blown out of the riverbed through gullies the nebkhas on the disconnected arms acquire the external sand source through the fertile island effect thereby developing into triangular sand patches and further developing into v shaped parabolic dunes most parabolic dunes in regions b and c are palmate the residual dunes cut by the re channelization of river from transverse dune fields on the west bank are the main sand source of region b the parabolic dunes in region c are the original barchans having then been transformed the stoss slopes of v shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape the dune crest of v shaped parabolic dune is the deposition area which forms the arc shaped sand ridge their two arms are non parallel the lateral airflow of the arms jointly transport sand to the middle part of dunes resulting in a narrower triangle that gradually becomes v shaped palmate parabolic dunes have a steeper stoss slope and height the dune crest of the palmate parabolic dune is the erosion area which forms a long and narrow trough between nebkhas by the funnelling effect this process forces sand towards lee slopes which transform from concave original barchans into convex ultimately resulting in the formation of palmate parabolic dunes

formation of parabolic dunes from barchan and transverse dunes along israel s mediterranean coast the mediterranean coastal dunes of israel underwent a land use change during the second half of the 20th century due to intense agricultural and pastoral activity the coastal dunes were stripped of natural vegetation until the end of the first half of the 20th century the barchan and transverse dunes were shaped by strong southwesterly winter winds a decrease in human activity during the second half of the 20th century brought about a renewal of natural vegetation on the dune crest the only area with neither erosion nor deposition the establishment of vegetation on the crest changes the dynamics of these barchan and transverse dunes so that not all of the sand eroded from the windward side is carried to the lee slip face some is trapped by plants consequently there is a change in the shape of the windward slope from convex to concave and the dune gradually becomes parabolic in this study we trace the morphodynamics of the dunes by analysing 12 sets of aerial photographs which were taken from 1944 to 1995 the average rate of advance of 15 dunes has decreased from 3 4 m a 1 to 1 9 m a 1 while the vegetation cover has increased from 4 3 to 17 per cent during this period copyright 2002 john wiley sons ltd

lead sources in mesozoic and cenozoic andean ore deposits north central chile 30 34 s mesozoic and cenozoic ore deposits in the chilean andes between la serena 30 s and santiago 34 s include polymetallic vein low and high sulfidation epithermal vein skarn porphyry copper molybdenum and porphyry copper gold these deposits are associated with volcanic and plutonic complexes emplaced in eastward migrating longitudinal arcs which formed during subduction along the continental margin of south america since the middle jurassic stratabound but epigenetic volcanic rock and sedimentary rock hosted manto deposits contain additional copper resources lead isotopic compositions in ore minerals from 29 deposits vary with age and geographic location and hence with basement and host rocks lead in most ore deposits is derived from temporally related igneous rocks except for the manto deposits whose lead is derived from host volcanic and sedimentary rock sequences lead in the ore deposits is dominated by two crustal sources low 207pb 204pb characterizes one source whereas high 207pb 204pb characterizes the second source lead isotopic compositions of jurassic and miocene ore minerals 206pb 204pb 18 50 207pb 204pb 15 61 lie along the average crustal growth curve by contrast most cretaceous deposits have ore minerals with lower 206pb 204pb 18 39 and 207pb 204pb 15 58 than jurassic ore minerals the shift in lead isotopic composition to lower lead isotopic values precludes derivation of lead from a source of similar composition to those in the jurassic or tertiary deposits for cretaceous deposits polymetallic and low sulfidation epithermal veins and a skarn have lower 206pb 204pb than a porphyry copper gold system and peripheral gold veins at andacollo 18 43 18 50 late cretaceous veins from the bellavista deposit have the lowest 206pb 204pb 18 33 of all deposits ore minerals in miocene and pliocene porphyry copper molybdenum deposits have higher 206pb 204pb 18 58 18 67 than cretaceous deposits consistent with their age being younger the miocene and pliocene ore minerals also have higher 207pb 204pb 15 58 15 66 than cretaceous ore minerals thereby requiring an additional input from the high 207pb 204pb source into the younger deposits miocene auriferous deposits in the north have similar 206pb 204pb values as the miocene and pliocene porphyry copper molybdenum deposits in the south but they are distinguished by higher and variable 207pb 204pb 15 61 15 66 and 208pb 204pb 38 54 39 01 which are arrayed along steep mixing trends these ore minerals have the largest input of high 207pb 204pb material in the deposits studied by contrast lead in the epigenetic manto deposits appears to be derived from the host volcanic or sedimentary rock dominated sequences and locally exhibits large scale isotopic heterogeneity within a deposit overall the lead isotopic compositions of ore minerals mimic the values and variations established in age equivalent rock sequences the low 207pb 204pb material in the deposits is derived from cretaceous igneous rocks or their sources as they evolved with time low 207pb 204pb characterizes these rocks by contrast high 207pb 204pb material is likely derived from carboniferous to triassic igneous rocks or their sources as this lead isotopic characteristic dominates these rocks

the victoria mode in the north pacific linking extratropical sea level pressure variations to enso the victoria mode vm represents the second dominant mode empirical orthogonal function eof2 of north pacific variability independent of the pacific decadal oscillation and is defined as the eof2 of sst anomalies in the north pacific poleward of 20 n the present study indicates that the vm is closely linked to the development of el nino southern oscillation enso the vm may effectively act as an ocean bridge or conduit through which the extratropical atmospheric variability in the north pacific influences enso the vm can trigger the onset of enso via the following two dominant processes 1 surface air sea coupling associated with the vm in the subtropical tropical pacific and 2 evolution of subsurface ocean temperature anomalies along the equator associated with the vm these two processes may force sufficient surface warming to occur in the central eastern equatorial pacific from spring to summer which in turn initiates an enso event the vm influence on enso relies on a basin scale air sea interaction dynamic as opposed to more local scale dynamics typically associated with the seasonal footprinting mechanism or pacific meridional mode the majority of vm events are followed by enso events these enso events triggered by vm include el nino modoki em as well as conventional el nino there is no evidence that the vm tends to be more conducive to the initialization of em than conventional el nino

characterizing earthquake recurrence parameters for offshore faults in the low strain compressional kapiti manawatu fault system new zealand 1 seafloor fault scarps and near surface deformation of late quaternary seismic reflectors occur along the eastern margin of the wanganui basin 200 km behind the active hikurangi subduction front southern north island new zealand the offshore scarps are associated with the low strain compressional kapiti manawatu fault system kmfs which comprises high angle 60 reactivated reverse and normal faults oriented ne sw highly oblique to the coast seafloor scarps range from 10 m high and moderate to long fault seafloor rupture lengths and those in central parts of the fault system are characterized by low scarps 10 000 a suggest that the seismic hazard of the kapiti manawatu region is relatively low incorporation of these new geological data however is likely to increase slightly the expected seismic hazard in southern north island the method of determining the earthquake recurrence parameters of offshore faults has potentially wider applications elsewhere

extensional tectonics cretaceous andes northern chile 27 s in the andes of northern chile the sierra fraga puquios region 27 s exposes a complete record of superposed deformation that affected this part of the orogen during the mesozoic and cenozoic a major extensional event which probably occurred between the aptian and cenomanian generated a suite of structures remarkably similar to those observed in the extensional terranes of western north america four allochthons involving paleozoic and mesozoic strata are bounded by low angle normal faults that place younger rocks over older omitting as much as several kilometers of stratigraphic section in one area an extensional chaos is composed of domino and boudined blocks of neocomian limestone floating in a matrix of cataclastically deformed volcanics domino orientation boudin asymmetry sheath folds and mesoscopic sense of shear indicators identify two senses of movement on the detachments the first and less important was top to the northwest and the second major event was top to the northeast the parautochthonous upper paleozoic basement core of the extensional terrane differs from the metamorphic core complexes in that it is not highly metamorphosed or ductilely deformed we attribute this difference to the lack of a prior crustal thickening event in the andes and to the position of the sierra fraga puquios at the margin of the central chile aborted marginal basin the extensional events occurred during a global episode of rapid spreading which was accompanied along the andean margin by a substantial increase in magmatism

the south pacific meridional mode a mechanism for enso like variability in this study the authors investigate the connection between the south pacific atmospheric variability and the tropical pacific climate in models of different degrees of coupling between the atmosphere and ocean a robust mode of variability defined as the south pacific meridional mode spmm is identified in a multimodel ensemble of climate model experiments where the atmosphere is only thermodynamically coupled to a slab ocean mixed layer the physical interpretation of the spmm is nearly identical to the north pacific meridionalmode npmm withtheoff equatorialsoutheasttradewindvariabilityalteringthelatentheatflux and sea surface temperature sst and initiating a wind evaporation sst feedback that propagates signals into the tropics the authors also show that a positive cloud feedback plays a role in the development of this mode butthiseffectismodeldependent whilephysicallyanalogoustothenpmm thespmmhasastronger expression in the equatorial pacific and directly perturbs the zonal gradients of sst and sea level pressure slp on the equator thus leading to enso like variability despite the lack of ocean atmosphere dynamical coupling further analysis suggests that the spmm is also active in fully coupled climate models and observations this study highlights the important role of the southern hemisphere in tropical climate variability and suggests that including observations from the data poor south pacific could improve the enso predictability

implications of pb isotope signatures of rocks and iron oxide cu au ores in the candelaria punta del cobre district chile lead isotope ratios of ores of the candelaria punta del cobre iron oxide cu au deposits and associated early cretaceous volcanic and batholithic rocks have been determined for the igneous rocks a whole rock acid attack technique based on the separate analyses of a leachate and the residual fraction of a sample was used the lead isotope systematics of leachate residue pairs are significantly different for unaltered and altered igneous rocks of the candelaria punta del cobre district residues of unaltered igneous rocks likely represent the common lead in contrast residues of all the altered igneous rocks except two samples have higher pb isotope ratios than those of unaltered magmatic rocks and cannot represent common lead we suggest that this is a result of the hydrothermal alteration suffered by these rocks and that the common lead composition of the altered igneous volcanic and plutonic rocks must have been similar to that of the unaltered batholith rocks the conclusion that the altered volcanic rocks originally had a similar common lead isotope composition as the batholith is consistent with geological and geochemical arguments e g setting regional geologic evolution ages and relative distribution of volcanic and intrusive rocks magmatic affinities which indicate that these rocks were derived from similar early cretaceous parent magmas the modification of the leachate residue pair lead isotope systematics of most altered igneous rocks is consistent with a selective removal of lead and uranium from these rocks by an oxidized hydrothermal fluid the result of the hydrothermal leaching has been to alter magmatic rocks in a way that 1 their leachable fraction is presently a mix of common lead similar to that of the ore event and of radiogenic lead evolved from a source with a consistently high th u and that 2 their residual fraction has less common lead than unaltered rocks the outcrop area with altered volcanic rocks displaying anomalously high lead isotope ratios extends over 25 km along the eastern margin of the batholith since lead of the ores in the candelaria punta del cobre district has the same isotopic composition as the common lead of unaltered magmatic rocks of the area the lead isotope data are consistent with a derivation of the ore lead and by inference of other metals like cu both directly from a magmatic fluid exsolved during crystallization of the batholith and or from hydrothermal leaching of the volcanic rocks originally having similar isotopic compositions as the batholith

interannual and decadal temperature variability in the southwest pacific ocean between 1955 and 1988 abstract the spatial and temporal variability of the southwest pacific ocean is examined with the aim of describing the physical processes operating on interannual and decadal timescales the study takes advantage of a new temperature atlas of the upper 450 m of the southwest pacific ocean obtained from 40 000 bathythermograph profiles between 1955 and 1988 rotated principal components analysis was used to filter the important spatial and temporal scales of temperature variability in the data three different analyses are presented they include two intraocean analyses and a joint analysis of subsurface ocean temperature sea level pressure and surface winds the dominant el nino mode describes the large vertical excursions of the thermocline in the western tropical pacific in response to atmospheric forcing at a 3 6 month lag more importantly most of the retained modes outside of the equatorial region have time variations that correlate with el nino one ocean mode with a spatial pattern represen

geologic and metallogenic significance of the isotopic composition of lead in galenas of the chilean andes eighty galena samples from different mineral deposits within the chilean andes from the mesozoic and cenozoic eras were analyzed for lead isotopes the results show a restricted dispersion between 18 65 to 18 28 15 68 to 15 56 and 38 72 to 38 11 on 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios respectively galenas from deposits hosted by pre jurassic to jurassic rocks are relatively enriched in radiogenic pb reflecting the involvement of old crustal pb galenas from lower cretaceous hosted deposits are less radiogenic and may reflect a mantlelike component those from tertiary rocks are isotopically more variable reflecting the influence of a more evolved crust there is no obvious correlation between the isotopic composition of the galena leads and the age of the hydrothermal event that gave rise to the particular mineral deposit when such ages can be determined from independent geologic evidence it is concluded that the galena leads were derived from a mixture of different lead reservoirs as defined in zartman and doe 1981 the correlation of isotopic composition with age of host rocks suggests either that the concentration of lead to form galena was more or less contemporaneous with the formation of the host rock or that the galena lead was essentially derived from the country rocks and inherited their original isotopic signature other workers have reported an overall similarity between the isotopic composition of galena leads and whole rock leads from the chilean andes however the isotopic compositions of galena leads from the argentinian andes show different characteristics from those of the chilean andes but the data are insufficient to allow firm conclusions

barchan parabolic dune pattern transition from vegetation stability threshold 1 many dune fields exhibit a downwind transition from forward pointing barchan dunes to stabilized backward pointing parabolic dunes accompanied by an increase in vegetation a recent model predicts this pattern transition occurs when dune surface erosion deposition rates decrease below a threshold of half the vegetation growth rate we provide a direct test using a unique data set of repeat topographic surveys across white sands dune field and find strong quantitative support for the model threshold we also show the threshold hypothesis applied to a barchan dune results naturally in its curvature inversion as the point of threshold crossing progresses from the horns to the crest this simple general threshold framework can be an extremely useful tool for predicting the response of dune landscapes to changes in wind speed sediment supply or vegetation growth rate near the threshold a small environmental change could result in a drastic change in dune pattern and activity

pb isotopes of the hualgayoc area northern peru implications for metal provenance and genesis of a cordilleran polymetallic mining district the hualgayoc district of northern peru is typical of several pb zn ag cu deposits in the peruvian cordillera in which veins are closely associated with stratiform manto orebodies steeply dipping veins containing mainly galena sphalerite pyrite chalcopyrite tetrahedrite and rhodochrosite are hosted by miocene andesitic plutons and by the gently folded and faulted cretaceous miogeosynclinal sediments they intrude the sediments also host concordant pyrite rich orebodies that are crosscut by the veins a comprehensive survey of the isotopic composition of lead in crustal rocks of the hualgayoc region demonstrates that the tertiary plutons which partly host the veins contain less radiogenic lead than either the cretaceous sedimentary rocks that host the ores or the regional metamorphic basement rocks believed to underlie the hualgayoc district sedimentary and metamorphic rocks from the hualgayoc region contain no component of the highly nonradiogenic lead found in ancient high grade rocks like those of the southern peru coast or inferred to exist in eastern colombia and also differ from basement rocks of the guyana shield in venezuela lead in vein and manto galenas from hualgayoc is isotopically indistinguishable and coincides with the composition of the tertiary plutons the vein and the manto ores thus probably formed from the same solutions ion microprobe traverses across the growth zones of large euhedral vein galena crystals reveal little isotopic variability of pb during their growth these data indicate that the ore forming solutions had essentially a single source of lead that this source was the tertiary plutons in the district and that local mixing of lead from several sources was not important although the plutons may have assimilated some lead from crustal rocks at depth these inputs were homogenized by the time of ore formation the manto ores are interpreted to be metasomatic bodies formed during the same event that produced the veins rather than syngenetic massive sulfide ores overprinted by a later episode of vein mineralization as proposed by other workers this interpretation is supported by the lead isotope evidence by the overlap of paragenetic sequences in the vein and manto ores and the orderly progression of fluid inclusion homogenization temperatures and salinities from the manto to the vein minerals by the absence of local igneous activity during the interval of sedimentation and by the abundance of replacement textures in the manto ore sufides the absence in the ores of lead leached from supracrustal rocks indicates 1 that processes within the magma determined the supply of metals to the ore forming system 2 that supracrustal host rocks enriched in ore metals are not necessary for the formation of this type of deposit and 3 that meteorically derived waters though probably comprising part of the ore solutions did not scavenge important amounts of crustal lead

age and paleotectonic setting of volcanogenic massive sulfide deposits in the guerrero terrane of central mexico constraints from u pb age and pb isotope studies the guerrero terrane of central and western mexico comprises volcanic and sedimentary strata of mainly mesozoic age with geochemical signatures indicating formation in juvenile back arc to slightly more evolved arc environments at least 60 volcanogenic massive sulfide vms deposits have been discovered thus far within the guerrero terrane they comprise two main belts the coastal belt mainly comprising deposits in the zihuataneo subterrane including the cuale bramador district and the central belt which includes deposits in the teloloapan subterrane campo morado tlanilpa azulaquez tizapa rey de plata etc the guanajuato subterrane el gordo las gavalinas and the zacatecas subterrane san nicolas and el salvador deposits the age of host rocks for the vms mineralization in the various subterranes was poorly constrained prior to this study eleven new u pb zircon ages for volcanic host rocks from the campo morado tlanilpa azulaquez leon guanajuato and san nicolas el salvador vms districts together with recently determined u pb ages from the cuale area demonstrate that vms deposits in the guerrero terrane range from latest middle jurassic to early early cretaceous callovian to valanginian in age the oldest ages were obtained from the cuale district total age range of 157 4 4 1 ma for three units and the youngest are from the tlanilpa azulaquez district total age range of 139 7 2 5 ma for two samples volcanogenic massive sulfide deposits in the central belt resemble those of the bimodal siliciclastic deposit type whereas those in the coastal belt are more similar to the bimodal felsic type published geochemical and radiogenic isotope data from the various subterranes suggest that vms deposits in the coastal belt and most of those in the central belt are hosted within juvenile to slightly evolved arc settings the san nicolas and el salvador deposits of the zacatecas subterrane are the only deposits that unequivocally formed in a back arc setting our new u pb dating results together with existing stratigraphic geochemical and radiogenic isotope data from throughout the guerrero terrane are consistent with the guerrero terrane having developed as a west facing continental margin arc that was built on mainly oceanic crust and overlying early mesozoic siliciclastic fans shed from the east along the western margin of nuclear mexico slab rollback in the middle jurassic led to the development of a rocas verdes type continental back arc inboard of the arc which is now preserved as the arperos basin in the central and southern guerrero terrane and the host rocks for the san nicolas and el salvador deposits farther to the north in southeastern zacatecas state we have determined pb isotope compositions of sulfides from vms deposits and several other styles of mineralization from throughout the guerrero terrane a compilation of these and previously published data shows that isotopic compositions from the various vms deposits fall in a relatively confined field that overlaps the average upper crustal growth curve this suggests that metals were mainly sourced from continentally derived sedimentary strata that are interlayered with or immediately underlie the host volcanic section and or from the host volcanic rocks themselves or subvolcanic intrusive equivalents that had assimilated significant quantities of upper crustal material either at the point of origin or during subsequent ascent and eruption lead isotope compositions from the francisco i madera deposit in zacatecas state indicate that most of the sulfides in this deposit are epigenetic rather than syngenetic in origin and are likely tertiary in age

jurassic u pb and re os ages for the newly discovered xietongmen cu au porphyry district tibet prc implications for metallogenic epochs in the southern gangdese belt the gangdese belt in southern tibet includes the cretaceous to early eocene gangdese continental magmatic arc a newly recognized middle jurassic magmatic arc and post gangdese arc magmatism of miocene age that is well known for its association with important copper molybdenum deposits although the tectonic history of the gangdese continental arc is relatively well constrained the tectonomagmatic setting of the jurassic and miocene magmatic events was poorly constrained previously geochronological analysis of samples from the xietongmen copper gold porphyry district has identified a previously unknown metallogenic event related to middle jurassic arc magmatism the occurrence of several metallogenic epochs within the southern gangdese belt highlights the importance of systematic metallogenic studies of this belt

late archean granitoid hosted lode gold deposits yilgarn craton western australia deposit characteristics crustal architecture and implications for ore genesis granitoid hosted lode gold deposits constitute a sub group of late archean lode gold deposits in the yilgarn craton of western australia they share a number of common characteristics including 1 a strong structural control on a variety of scales 2 in most instances the presence of mineralisation in adjacent supracrustal sequence 3 wallrock alteration and vein assemblages consistent with the addition of sio2 k2o co2 s na2o but dependent on the p t conditions of the host environment and ore fluid 4 a metal association comprising au ag as bi te w mo and low concentrations of cu pb and zn and 5 deposition from a low moderate salinity near neutral h2o co2 ch4 fluid over a temperature and pressure range from 250 to 600 c and 1 to 4 kbar which corresponds to a range of crustal environments from lower greenschist to upper amphibolite facies these characteristics suggest that the granitoid hosted lode gold deposits represent a coherent genetic group that is equivalent to the more abundant greenstone hosted lode gold deposits of the craton in combination lode gold deposits irrespective of their host rocks and host terrane formed over a range of crustal levels and developed late in the tectonic sequence of the craton granitoids which host lode gold mineralisation are older than the inferred age of mineralisation by at least 10 million years and in combination with thermodynamic and isotope studies indicate that the host granitoids are not the dominant source of the ore fluid however the host granitoids do provide a structural and to a lesser extent chemical trap for gold bearing fluids in combination trace element and isotope studies of greenstone and granitoid hosted deposits suggest that the ore fluid originated from a deep mid to lower crustal source and at least interacted with granitic rocks at some stage the ore fluid composition is quite constant over the range of crustal levels from deep to shallow implying that the extent of modification by interaction with fluid conduit rocks is variable but not substantial

linking the pacific meridional mode to enso coupled model analysis abstract the occurrence of a boreal spring phenomenon referred to as the pacific meridional model mm is shown to be intimately linked to the development of el nino southern oscillation enso in a long simulation of a coupled model the mm characterized by an anomalous north south sst gradient and anomalous surface circulation in the northeasterly trade regime with maximum variance in boreal spring is shown to be inherent to thermodynamic ocean atmosphere coupling in the intertropical convergence zone itcz latitude and the mm existence is independent of enso the thermodynamic coupling enhances the persistence of the anomalous winds in the deep tropics forcing energetic equatorially trapped oceanic waves to occur in the central western pacific which in turn initiate an enso event the majority of enso events in both nature and the coupled model are preceded by mm events

development and age structure of holocene coastal sand dunes at horn head near dunfanaghy co donegal ireland two areas of holocene coastal sand dunes on the western side of the horn head peninsula extend from low ground immediately inland of their respective source beaches onto flanking higher ground 100 m od stratigraphic investigations supported by 14c dating of buried organic rich horizons and shells demonstrate several phases of sand accumulation in the pollaguill croaghadara system in contrast to the larger tramore anloge hill system where the available evidence points to relatively recent dune emplacement a broadly synchronous phase of dune development occurred during the thirteenth to fourteenth centuries ad and is viewed as part of a regional northwestern europe dune building episode resulting from climatic deterio ration earlier phases pre 3300 2800 14c years bp of aeolian sand deposition at pollaguill croaghadara have no apparent equivalents at tramore anloge hill and repeated fluvial incision and sand reworking during the last 2000 14c years is also evident at the former site dated organi

geometry and kinematics of large arcuate structures formed by impingement of rigid granitoids into greenstone belts during progressive shortening regional scale arcuate structures in the central part of the archean yilgarn craton western australia were generated by impingement of competent granitoid blocks into less competent greenstone belts during progressive east west shortening sinistral shear zones developed along northwest trending margins of the granitoid blocks whereas dextral shear zones developed along northeast trending margins in apex regions these northeast and northwest trending shear zones are linked by north trending contractional zones along which shortening was accommodated by the formation of folds and reverse faults in the greenstone belts and a coaxial flattening fabric in granitoid rocks lateral escape of the greenstone belts is indicated by the progressive rotation of early macroscopic folds into parallelism with the strike slip shear zones during granitoid impingement this recently recognized deformation style may have important tectonic implications for other archean granite greenstone terranes and where rock heterogeneity and competency differences are significant

lead isotope signatures of the igneous rocks and porphyry copper deposits from the kerman cenozoic magmatic arc se iran and their magmatic metallogenetic implications abstract copper deposits in the kerman cenozoic magmatic arc kcma of iran are genetically related to miocene porphyries the porphyries and their associated cu deposits were intruded and emplaced into eocene volcanic sedimentary successions lead isotope compositions of the eocene volcanic rocks exhibit homogeneous non radiogenic values 206 pb 204 pb 18 40 to 18 49 207 pb 204 pb 15 41 to 15 48 and 208 pb 204 pb 38 15 to 38 36 in contrast the miocene ore hosting porphyries and associated sulfide minerals also show a relatively radiogenic and homogenous pb isotopic values with orogen character 206 pb 204 pb 18 52 to18 60 207 pb 204 pb 15 58 to 15 64 and 208 pb 204 pb 38 57 to 38 80 the shift in the pb isotopic composition of igneous rocks with time towards higher pb isotopic values precludes derivation of the ore hosting porphyries from a reservoir of similar composition to those in the eocene volcanic rocks the non radiogenic pb isotope signature of the eocene volcanic rocks indicates an origin from subduction related mantle derived magmas whereas the higher pb isotopic values of the miocene ore hosting porphyries suggest an increasing involvement of crustal materials with lower u pb ratios than the upper crust in the source region of these rocks combining the pb isotope data with petrogenetic considerations suggests derivation of the middle miocene ore hosting porphyries from a mixed reservoir with slightly radiogenic pb values such as a hybridized lower continental crustal source this source probably formed because of the involvement of cretaceous oligocene subduction related mantle derived mafic magmas at the base of arc crust the contribution of the miocene collision related mantle derived mafic magma in melting of the hybridized lower continental crust caused generation of the middle miocene porphyries hosting large copper deposits with the least 206 pb 204 pb ratios among other porphyries the higher 206 pb 204 pb ratios of the late miocene pliocene porphyries hosting small copper deposits as well as barren porphyries may reflect a decreasing involvement of collision related mantle derived mafic magma in the source of the late miocene pliocene porphyries the overall similarity in pb isotope values between sulfide minerals and ore hosting porphyries suggests a magmatic source for most of the pb and possibly other metals the more radiogenic isotopic ratios of some late sulfide minerals suggest an insignificant metal contribution from an external source such as local country rocks during hydrothermal circulation

mineralogical and isotopic zonation in the sur sur tourmaline breccia rio blanco los bronces cu mo deposit chile implications for ore genesis the sur sur tourmaline breccia is located in the southeast part of the rio blanco los bronces porphyry copper molybdenum deposit central chile the breccia hosts approximately one quarter of the total resource of 57 mt of fine copper at rio blanco the breccia is hosted within and contains altered clasts of granodiorite from the 12 to 8 ma san francisco batholith which intruded a sequence of miocene volcanic and volcaniclastic rocks a series of weakly mineralized to barren felsic porphyries cut the breccia and indicate a minimum age of approximately 6 ma for mineralization at sur sur the sur sur breccia dike is at least 3 km long 0 2 km wide and has a vertical extent of at least 1 km the breccia has been cemented by early biotite and anhydrite at depth and by tourmaline and specularite at higher altitudes these early formed cements have been overgrown and in some cases replaced by chalcopyrite magnetite pyrite and quartz mineralogical zonation in the breccia includes a transition from biotite cement and related biotite alteration upward to tourmaline cement and quartz sericite tourmaline alteration at approximately 3 000 m elevation iron oxide minerals are also zoned with a transition upward from a magnetite dominated zone below 3 330 m to a specularite dominated zone above 3 600 m pyrite is the dominant sulfide at altitudes above 4 000 m secondary liquid rich vapor rich and hypersaline fluid inclusions are preserved in quartz and tourmaline cement measured homogenization temperatures are mostly between 300 degrees and 450 degrees c and salinities range from 0 to 69 wt percent nacl equiv sulfur isotope compositions of sulfide cement range from 4 1 to 2 7 per mil the lowest delta 34s sulfide values are in samples from between 3 700 and 4 000 m elevation where they correspond to the highest copper grades in the tourmaline breccia this high grade zone also contains abundant specularite locally replaced by magnetite modeling of sulfate sulfide equilibrium indicate that approximately 150 degrees c of cooling over a vertical interval of 100 m would be required to account for the zonation of sulfide isotope compositions at sur sur making conductive cooling an unlikely ore forming mechanism measured 206pb 204pb values of lead in anhydrite cement in the sur sur tourmaline breccia and the rio blanco magmatic breccia range from 17 558 to 18 479 207pb 204pb values range from 15 534 to 15 623 and 208pb 204pb values range from 37 341 to 38 412 the lead in anhydrite is considerably less radiogenic than that indicated by values obtained previously for lead in sulfide ores and igneous host rocks at rio blanco los bronces the source of lead in anhydrite must have been from rocks external to the main magmatichydrothermal system probably the precordilleran basement a magmatic hydrothermal explosion from a deep seated crystallizing intrusion triggered breccia formation at sur sur hydrostatic pressures catastrophically exceeded lithostatic load plus the tensile strength of the confining granodiorite leading to widespread brecciation and subsequent invasion by large volumes of magmatic gas and hypersaline brine the low density gas phase carrying h2o so2 hcl and b2o3 separated physically from the dense copper bearing brine and flushed through the breccia column first where it condensed into ground waters of uncertain derivation anhydrite specularite and tourmaline were deposited from this lowsalinity acidic oxidized hybrid solution subsequent upwelling of magmatic hydrothermal brine resulted in sulfide deposition high grade copper deposition is interpreted to have occurred in response to mixing of the oxidized acidic water with the copper bearing magmatic hydrothermal brine

major phases of coastal erosion ca 6700 6000 and ca 3000 2000 bp between cervantes and dongara western australia abstract relict foredune plains developed along parts of the coast between cervantes and cliff head during holocene time evidence for major episodes of marine erosion was provided by the presence of extensive erosional scarps or discontinuities within or at the inner margin of many of the plains such features often truncate older coastal landforms such as parabolic dunes shells within foreshore deposits immediately seaward of the erosional cuts were dated to obtain an approximate age for the end of erosional episodes at two locations dating suggests that erosion occurred ca 6700 6000 bp dates from four other sites suggest that a major erosional episode occurred between ca 2000 and 3000 bp there was no evidence for the occurrence of major episodes of marine erosion at other times since the attainment of modern holocene sea level the first erosional episode is likely to have been associated with the final stages of the postglacial marine transgression the second which was also associated with the initiation of transgressive dunes was probably caused by an increase in the occurrence and or intensity of either tropical cyclones or winter cyclonic storms however the occurrence at that time of a minor marine transgression cannot be discounted

impact of the south and north pacific meridional modes on the el nino southern oscillation observational analysis and comparison abstractan interannual variability mode in the southeast pacific with a physical interpretation similar to that of the pacific meridional mode pmm in the north pacific was recently identified both modes have been shown to influence the subsequent development of el nino southern oscillation enso events this study investigates the relationship between enso and the two pmms using observational and reanalysis data the results show that the south pacific meridional mode spmm mainly favors the development of sea surface temperature anomalies sstas in the eastern equatorial pacific whereas the north pacific meridional mode npmm mainly favors the development of sstas in the central equatorial pacific both of the meridional modes are considered to be analogous in terms of their physical interpretation and can be important predictors of enso when considering different flavors of enso neither the npmm nor the spmm can be precluded as accurate indicators when forecasting particular flavors of enso

the pacific meridional mode as a trigger for enso in a high resolution coupled model 1 this study investigates el nino precursors in a high resolution version of ccsm3 5 first using an empirical orthogonal function analysis of all non enso tropical pacific variability we find that the pacific meridional mode pmm acts as an enso trigger 7 9 months prior to large el nino events in the model which is consistent with previous model and observational studies however because not every pmm event triggers an enso event we also find that pmm appears to be an effective trigger when the western to central pacific is preconditioned i e anomalously high sea surface heights or heat content second this study looks at the contribution of western pacific variability namely westerly wind bursts wwbs as well as all other non enso variability in the tropical pacific we find that the relative importance of low frequency climate variability associated with pmm dominates over other non enso variability between 15 n and 15 s including high frequency atmospheric variability and wwbs in acting as a precursor to el nino events

separate lead isotope analyses of leachate and residue rock fractions implications for metal source tracing in ore deposit studies separate lead isotope analyses of leachate and residue fractions are applied to a broad spectrum of rocks commonly investigated in metallogenic studies resulting data highlight a systematic behavior of leachate and residue fractions with respect to lead isotope compositions which essentially depends on the mineralogical composition of the rock granitoid and high grade metamorphic rocks have residue compositions virtually identical to common lead in contrast low grade metasedimentary rocks may have residue compositions swamped by radiogenic lead of leach resistant zircons mafic magmatic rocks have residues that are often more radiogenic than leachates depending on the ratio of leach refractory zircons to common lead in the residual fraction of these rocks separate leachate and residue analyses of source rocks provide two lead isotope end members whose mixture may represent lead with the appropriate ore fluid composition our leaching experiments indicate that hot acid solutions and by inference hydrothermal fluids preferentially leach radiogenic lead from medium to high grade metamorphic and granitoid rocks whereas they preferentially leach common lead from low grade metasedimentary and mafic magmatic rocks the method presented in this study provides a reliable alternative to other methods i e age correction of bulk rock compositions for the determination of the common lead signature of felsic to intermediate magmatic rocks this may be preferable to age corrected bulk rock analyses where ages to apply for corrections of bulk rock data are not known or where moderately to highly altered rocks must be used case studies of orogenic gold and mvt districts of peru pataz and san vicente respectively show that separate leachate and residue lead isotope analyses carried out systematically on whole rocks allow a more thorough evaluation of metal source reservoirs than does the standard method of age corrected or uncorrected bulk rock analyses

dune phases as time transgressive phenomena manawatu new zealand abstract new zealand s most extensive holocene dunefield is situated in the manawatu and adjoining regions evidence collected from the area including 25 radiocarbon dates suggests that the dunefield developed in phases with the first probably initiated at the coast earlier than 6000 years ago the first phase may have ceased near the coastline around 4500 years ago but dunes continued to migrate until they reached 16 km inland ca 1600 years ago about 3500 years ago dunes again began migrating inland from the coast with some still active 400 years ago the time transgressive nature of transgressive dune deposits and the possible causes of the dune phases are discussed

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

ore genesis and hydrothermal evolution of the donggebi porphyry mo deposit xinjiang northwest china evidence from isotopes c h o s pb fluid inclusions and molybdenite re os dating

textures paragenesis and wall rock alteration of lode gold deposits in the charters towers district north queensland implications for the conditions of ore formation ore deposits of the charters towers goldfield ctgf are mainly hosted by fault fill veins extensional 8 of all veins and stockwork like 3 veins are less common and of little economic significance crosscutting relationships and published structural and geochronological data indicate a late silurian to early devonian timing of gold mineralization coincident with regional shortening d4 and i type magmatism paragenetic relationships which are uniform in veins everywhere within the ctgf suggest that vein formation commenced with the deposition of large volumes of buck quartz stage i followed by buck and comb quartz and significant pyrite and arsenopyrite precipitation stage ii gold was introduced during stage iii after earlier sphalerite and coincident with galena and chalcopyrite narrow discontinuous calcite veins of stage iv mark the waning of gold related hydrothermal activity or a later unrelated episode ore zones within the veins are everywhere composed of comb and or gray quartz calcite and or ankerite and bands or clusters of fractured pyrite that are spatially associated with galena sphalerite or chalcopyrite low grade or barren vein sections on the other hand are mainly composed of milky buck quartz with little evidence for modification overprinting or interaction with later fluids gold related hydrothermal wall rock alteration is symmetrically zoned displaying proximal sericite ankerite and distal epidote chlorite hematite assemblages that may be taken to imply wall rock interaction with near neutral fluids ph 5 6 isocon plots assuming immobile al p ti y and zr consistently indicate as k pb s and zn enrichment and na si and sr depletion in altered wall rock specimens relative to the least altered rocks alteration assemblages quartz textures fault rocks and published fluid inclusion and stable isotope data imply that the veins were formed under conditions of episodic fluid overpressuring 0 9 3 8 kbar at a depth of 7 km and a temperature of 310 c the published fluid inclusion data also imply that gold precipitation may have been brought about by fluid mixing however physi and chemisorption of gold complexes onto sulfide surfaces may have been important depositional processes and controls on gold enrichment at the millimeter to centimeter scale given that most gold particles are attached to the surfaces of pyrite crystals of stage ii or to etch pits and fracture surfaces within the earlier pyrite

constraints on the development of orogenic style gold mineralisation at mineral de talca coastal range central chile evidence from a combined structural mineralogical s and pb isotope and geochronological study mineral de talca is a rare occurrence of mesozoic gold bearing quartz vein mineralisation situated within the coastal range of northern chile quartz veins controlled by nnw sse trending faults are hosted by devonian carboniferous metasediments of greenschist facies and younger undeformed granitoid and gabbro intrusions the principal structural control in the area is the easterly dipping nnw sse trending el teniente fault which most likely developed as an extensional normal fault in the triassic but was later reactivated as a strike slip fault during subsequent compression a dilational zone in the el teniente fault appears to have focussed fluid flow and an array of nw se trending veins is present as splays off the el teniente fault mineralised quartz veins typically up to a metre thick occur in three main orientations 1 parallel to and within nnw sse trending e dipping faults throughout the area 2 along nw se trending ne dipping structures which may also host andesite dykes and 3 rarer e w trending subvertical veins all mineralised quartz veins show evidence of multiple fluid events with anastomosing and crosscutting veins and veinlets some of which contain up to 3 5 vol base metal sulphides mineralogically au is present in three textural occurrences identified by 3d ct scanning 1 with arsenopyrite and pyrite in altered wall rock and along the margins of some of the veins 2 with cu pb zn sulphides within quartz veins and 3 as nuggets and clusters of native au within quartz fluid inclusion work indicates the presence of co2 ch4 bearing fluids with homogenisation temperatures of 350 c and aqueous fluids with low moderate salinities 0 4 15 5 wt nacl eq with homogenisation temperatures in the range of 161 321 c the presence of au with arsenopyrite and pyrite in structurally controlled quartz veins and in greenschist facies rocks with evidence of co2 bearing fluids is consistent with an orogenic style classification for the mineralisation however the significant amounts of base metals and the moderate salinity of some of the fluids and the proximity to felsic granitoid intrusions have raised the possibility of an intrusion related origin for the mineralisation vein sulphides display s isotope signatures 34s 2 1 to 4 3 that are intermediate between the host rock metasediments 34s 5 3 to 7 5 and the local granitoids 34s 1 3 to 1 4 indicating a distinct crustal source of some of the s in the veins and possibly a mixed magmatic crustal s source the local granite and granodiorite give u pb zircon ages of 219 6 1 and 221 3 2 8 ma respectively lead isotopic compositions of galena in the veins are consistent suggesting derivation from a homogeneous source differences however between the isotopic signatures of the veins and igneous feldspars from nearby intrusions imply that these bodies were not the source of the metals though an igneous source from depth cannot be discounted the triassic age of the granitoids is consistent with emplacement during regional crustal extension with the el teniente fault formed as an easterly dipping normal fault the change to a compressional regime in the mid jurassic caused reactivation of the el teniente fault as a strike slip fault and provided a structural setting suitable for orogenic style mineralisation the intrusions may however have provided a structural competency contrast that focused the mineralising fluids in a dilational jog along the el teniente fault to form wnw trending veins as such the mineralisation is classified as orogenic style and the identification of the key mineralogical isotopic and structural features has implications for exploration and the development of similar deposits along the coastal range

late quaternary geomorphology of the manawatu coastal plain north island new zealand this review examines the geomorphological evolution of the manawatu coastal plain from the last glacial maximum through the holocene post glacial marine transgression c 7500 cal yr bp until the present providing a context within which to examine the extent to which the holocene evolution of the lower manawatu valley follows tripartite evolutionary models of incised valley infill during the last glaciation the manawatu river incised a broad deep valley while tributaries within the catchment dissected relict marine terraces this occurred concurrently with the formation of a parabolic dune field at koputaroa with sediment sourced from the bars of the manawatu river during the post glacial marine transgression rising sea levels inundated the incised valley at the culmination of the holocene marine transgression the himatangi anticline and poroutawhao high restricted oceanic influences in the proto manawatu estuary which was partially infilled with estuarine sediment estuarine deposition was quickly succeeded by fluvial deposition and floodplain due to high volumes of fluvial sediment introduced by the manawatu river a lack of characteristic bay head delta development may be explained by rapid infill and consequent sediment bypass

equatorial signatures of the pacific meridional modes dependence on mean climate state extratropical atmospheric variability can impact tropical climate in the pacific sector via the pacific meridional modes pmms the south pmm spmm has a larger equatorial signature than the north pmm npmm for the same amount of extratropical variability here we explain this interhemispheric asymmetry using an atmospheric general circulation model coupled to a slab ocean model by imposing an anomalous interhemispheric heating gradient we strengthen the northeasterly trades and weaken the southeasterly trades shifting the intertropical convergence zone south of the equator as a result the spmm no longer influences the equatorial region while the npmm shows strengthened linkages to the central western equatorial pacific by demonstrating that background winds determine the propagation of the wind evaporation sea surface temperature feedback fundamental for the pmms we conclude that the interhemispheric asymmetry between the pmms is largely attributed to the asymmetric mean trades in the pacific the results have implications for both paleoclimate studies and model development

age of mineralization of the candelaria fe oxide cu au deposit and the origin of the chilean iron belt based on re os isotopes re os isotopes are used to determine the age of iron oxide cu au mineralization at candelaria chile and to explore possible genetic links with the batholithic intrusions in the area re os ages calculated from molybdenite are 114 2 0 6 ma and 115 2 0 6 ma and they are interpreted to represent the age of mineralization these ages are consistent with previously reported ages for biotite alteration that range from 114 to 116 ma an isochron calculated by re os ratios from hydrothermal magnetite and sulfides constrains an initial 187 os 188 os ratio of 0 36 0 10 the initial 187 os 188 os ratio for sulfide from bronce mine a small satellite of the candelaria orebody is 0 33 0 01 these values are broadly similar to the calculated initial 187 os 188 os ratio for magmatic magnetite in nearby batholithic rocks that range from 0 20 to 0 41 the relatively radiogenic initial 187 os 188 os ratio represents a mixture of mantle and crustal components in the ores and batholitic rocks the similarity in initial 187 os 188 os ratio of the ore and magmatic oxides suggest that the granitic plutons could be the source of metals in the candelaria district these data are consistent with the existence of a significant magmatic fluid component in the hydrothermal system as suggested by previously published work in order to establish a regional perspective we analyzed ore minerals from other chilean deposits of the iron oxide cu u au rare earth elements ree class magnetite from the manto verde iron oxide cu au deposit has os and re concentrations of 11 to 17 parts per trillion ppt and 4 to 6 parts per billion ppb respectively the initial 187 os 188 os ratio is approximately 0 20 and is similar to that of ore minerals from candelaria and of the early cretaceous batholithic intrusions these data indicate a similar metal source for the mineralization at manto verde and candelaria magnetite from three magnetite apatite deposits of the chilean iron belt have re concentrations between 0 8 and 3 ppb and os concentrations between 11 and 76 ppt calculated initial 187 os 188 os ratios of these magnetites range from 1 2 to 8 4 and are distinctly different from those of the iron oxide cu au deposits the cause of the comparatively high radiogenic signatures in the magnetite apatite ores is probably related to fluid interactions with i e leaching the surrounding sedimentary rocks during their genesis in contrast to the iron oxide cu au systems the os in magnetite apatite ores could be derived from sedimentary rocks this evidence suggests that predominantly basin derived nonmagmatic brines formed these magnetite apatite deposits

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

history of crustal growth and recycling at the pacific convergent margin of south america at latitudes 29 36 s revealed by a u pb and lu hf isotope study of detrital zircon from late paleozoic accretionary systems detrital zircon provides a powerful archive of continental growth and recycling processes we have tested this by a combined laser ablation icp ms u pb and lu hf analysis of homogeneous growth domains in detrital zircon from late paleozoic coastal accretionary systems in central chile and the collisional guarguaraz complex in w argentina because detritus from a large part of w gondwana is present here the data delineate the crustal evolution of southern south america at its paleopacific margin consistent with known data in the source regions zircon in the guarguaraz complex mainly displays an u pb age cluster at 0 93 1 46 ga similar to zircon in sediments of the adjacent allochthonous cuyania terrane by contrast zircon from the coastal accretionary systems shows a mixed provenance age clusters at 363 722 ma are typical for zircon grown during the braziliano pampean famatinian and post famatinian orogenic episodes east of cuyania an age spectrum at 1 00 1 39 ga is interpreted as a mixture of zircon from cuyania and several sources further east minor age clusters between 1 46 and 3 20 ga suggest recycling of material from cratons within w gondwana the youngest age cluster 294 346 ma in the coastal accretionary prisms reflects a so far unknown local magmatic event also represented by rhyolite and leucogranite pebbles it sets time marks for the accretion history maximum depositional ages of most accreted metasediments are middle to upper carboniferous a change of the accretion mode occurred before 308 ma when also a concomitant retrowedge basin formed initial hf isotope compositions reveal at least three juvenile crust forming periods in southern south america characterised by three major periods of juvenile magma production at 2 7 3 4 ga 1 9 2 3 ga and 0 8 1 5 ga the 176hf 177hf of mesoproterozoic zircon from the coastal accretionary systems is consistent with extensive crustal recycling and addition of some juvenile mantle derived magma while that of zircon from the guarguaraz complex has a largely juvenile crustal signature zircon with pampean famatinian and braziliano ages 660 ma originated from recycled crust of variable age which is however mainly mesoproterozoic by contrast the carboniferous magmatic event shows less variable and more radiogenic 176hf 177hf pointing to a mean early neoproterozoic crustal residence this zircon is unlikely to have crystallized from melts of metasediments of the accretionary systems but probably derived from a more juvenile crust in their backstop system

numerical simulation of the evolution and propagation of aeolian dune fields toward a desert oasis zone abstract in this study the evolution and propagation of aeolian dune fields toward a desert oasis transitional zone are numerically investigated through considering the spatial variation of wind speed and the influence of vegetation on sand erosion and transportation etc the propagation speed at the edge of desertified land and the influence of a straw checkerboard are quantitatively analyzed results show that evolution time wind speed and sand diameter have obvious impacts on the propagation of desert and desertified land a formula describing the propagation speed of desertified land with respect to wind speed and vegetation coverage is given in addition when considering the effects of straw checkerboards the propagation speed of the downwind desertified land is found to be related to the length of and distance from the checkerboard area

influence of system controls on the late quaternary geomorphic evolution of a rapidly infilled incised valley system the lower manawatu valley north island new zealand abstract the manawatu incised valley estuary was rapidly infilled between 12 000 4700 cal yr bp a combination of empirical measurements of sedimentation rates a reconstruction of relative sea level rsl change and digital elevation models of key surfaces within the holocene sedimentary fill of the valley were integrated to produce a numerical model to investigate the influence of the system controls of sea level change sediment flux and accommodation space on the rapid infilling history of the palaeo estuary the numerical model indicates that sediment flux into the palaeo estuary was greatest during the holocene marine transgression between 12 000 8000 years bp the average rate of sediment deposition in the estuary during this period was 1 0 m m 3 yr 1 this rapid rate of sedimentation was controlled by the rate of accommodation space creation as regulated by the rate of sea level rise and the antecedent configuration of the valley by the time sea levels stabilised c 7500 cal yr bp the palaeo estuary had been substantively infilled limited accommodation space resulted in rapid infilling of the central basin though sediment flux into the estuary between 7100 and 4500 cal yr bp was at a lower rate of 234 000 m 3 yr 1 the limited accommodation space also influenced hydrodynamic conditions in the estuarine central basin driving export of fine grained sediment from the estuary once the accommodation space of the estuarine basin was infilled sediment bypassed the system with a consequent reduction in the sedimentation rate in the valley more accurate partitioning of the sources of sediment driving the infilling is necessary to quantify sediment bypassing post depositional lowering of rsl index points from the valley is driven by neotectonics and sediment compaction

metal sources in mineral deposits and crustal rocks of ecuador 1 n 4 s a lead isotope synthesis ecuador consists of terranes having both continental chaucha tahuin loja terranes and oceanic macuchi alao salado terranes affinity which were accreted to the amazon craton from late jurassic to eocene four main magmatic arcs were formed by the subduction of the farallon nazca plate since the juras sic a jurassic continental arc on the western margin of the amazon craton a jurassic island arc alao terrane an early tertiary island arc macuchi terrane and a middle late tertiary continental arc encompassing the ter ranes of macuchi chaucha tahuin loja and alao after complete assembly of the ecuadorian crust mineral deposits formed during these magmatic arc activities include porphyry cu and gold skarn deposits in associa tion with the jurassic continental arc polymetallic volcanic hosted massive sulfide deposits vhms in associ ation with the jurassic island arc of alao au cu zn vhms deposits in association with the early tertiary is land arc of macuchi and porphyry cu and precious metal epithermal deposits in association with the middle late tertiary continental arc magmatism on the newly assembled crust of ecuador macuchi chaucha tahuin loja and alao terranes in this study we have compiled 148 new and 125 previously published lead isotope analyses on paleozoic to miocene metamorphic intrusive volcanic and volcanosedimentary rocks as well as on jurassic to miocene magmatic related ore deposits of ecuador lead isotope compositions of the magmatic rocks of the four main arc events derive from mixing of various sources including mantle variably enriched by pelagic sediments and or by a high 238u 204pb component and heterogeneous continental crust rocks lead isotope compositions of the ecuadorian ore deposits display a broad range of values 206pb 204pb 18 3 19 3 207pb 204pb 15 54 15 74 208pb 204pb 38 2 39 2 which is as large as the range previously re ported for all magmatic related ore deposits of the central andean provinces i and ii combined ore deposits formed before complete assembly of the ecuadorian crust through complete accretion of the several terranes i e pre eocene have lead isotope compositions overlapping those of the associated magmatic rocks sug gesting a largely magmatic origin for their lead in contrast post assembly ore deposits i e post eocene have lead isotope compositions that only partly overlap those of the coeval magmatic rocks of the continental arc in fact several ore deposits have lead isotope compositions shifted toward those of the basement rocks that host them suggesting that lead derives from a mixture of magmatic lead and basement rock lead leached by hy drothermal fluids most ecuadorian ores have high 207pb 204pb values 15 55 suggesting a dominant continental crust or pelagic sediment origin of the lead however we caution against concluding that chalcophile metals for ex ample cu and au also have a continental crust origin ore deposits of the different terranes of ecuador irrespective of their age plot in distinct isotopic fields which are internally homogeneous this suggests that lithologic factors had an important control on the lead isotope compositions ultimately lead isotope compositions of the ore deposits of ecuador mirror the isotopic compositions of the rocks of the host terranes and are consistent with the multiterrane nature of the ecuado rian crust

geomorphic response to late holocene climate variation and anthropogenic pressure northeastern prince edward island canada abstract geomorphic response provides an index to climate change and variability differing time scales of both weather climate events and landform response complicate interpretation anthropogenic modification particularly in coastal and aeolian dune environments represents a further geomorphic influence northeastern prince edward island pei canada is a marine dominated environment subjected to rising sea level throughout the late holocene the combination of rising sea levels increased anthropogenic utilization of the coast for residential and tourism purposes and limited offshore winter ice conditions have resulted in accelerated erosion and degradation of the dunes and coastline the aeolian succession indicates that temporal and spatial transitions from isolated shield dunes to parabolic dunes to linked coastal transverse dune complexes are characteristic of the coastal dune fields sand supply is the most significant control on dune morphology development and extent superimposed dome dunes and shield dunes are prevalent in areas of anthropogenic disturbance dune migration along the coastal zone has varied considerably with rates locally in excess of 10 m a over short times winters marked by relatively limited sea ice and scarce snow cover resulting from more temperate winter conditions allow increased erosion by strong storms deflation of dune crests and development of blowouts is notably accentuated along human trails the climate variations recorded in atlantic canada over the past decade fall within the range of those recorded previously within the twentieth century and thus do not indicate conclusive evidence of a pronounced trend of climate change in this region however analysis of northeastern pei demonstrates that dune coastlines can evolve rapidly in response to short term and intermediate term climate variation particularly when coupled with anthropogenic pressure similar geomorphic effects in combination with climate variation and storm activity should be anticipated along other dune coastlines that have been subjected to intense anthropogenic utilization during earlier periods of the quaternary

origin of paleozoic granitoids in the yuhai cu mo deposit eastern tianshan nw china and implications for regional metallogeny abstract the yuhai porphyry cu mo deposit is located at the eastern section of the dananhu tousuquan arc in eastern tianshan nw china cu mo mineralization generally occurs as disseminations and veins in potassic and phyllic alteration zones and is predominantly hosted in the yuhai quartz diorite granodiorite and minor syenogranite intrusions new la icp ms zircon u pb dating indicates that the acidic syenogranite was emplaced at 318 320 ma younger than the intermediate rocks i e quartz diorite and granodiorite with silurian ages the acidic to intermediate intrusions exhibit geochemical affinities with normal arc rocks e g high y and yb contents and low sr y ratios in contrast with the subducted slab derived adakites hosting large porphyry cu deposits e g tuwu yandong in the middle section of the dananhu tousuquan arc the yuhai acidic syenogranite rocks have high sio2 74 90 wt and k2o 3 48 wt relatively low mg and compatible element contents e g cr 0 65 3 37 ppm ni 0 63 1 02 ppm and strong depletions in hfse e g nb ta and ti these geochemical features coupled with isotopic data such as low initial 87sr 86sr 0 7033 positive end t 4 0 to 5 9 and ehf t 11 values young hf model ages and variable 206pb 204pb ratios 18 549 to 19 465 reported in this study suggest that their parental magmas originated from the partial melting of a juvenile lower crust and mixed with some old crustal components beneath the dananhu tousuquan arc in contrast the yuhai intermediate intrusions exhibit relatively low sio2 and k2o contents high mg values 40 56 and a wide range of ehf t values suggesting a source of sub continental lithospheric mantle metasomatized by slab derived fluids and melts zircon trace element and plagioclase compositions of the yuhai granitoids further imply that the silurian intermediate intrusion related magma was moderately oxidized mostly eun eun 0 6 and water rich 9 wt favorable for the copper mineralization whereas the carboniferous syenogranite related magma was weakly oxidized mostly eun eun 0 3 0 6 but also hydrous 6 wt combined with the regional tectono magmatic activities and metallogenic processes we suggest that the yuhai cu mo deposit and associated granitoids were formed in an arc setting and that the magma nature and its source components are the key factors constraining the distribution scale and style of the porphyry copper mineralization in eastern tianshan

facies architecture morphostratigraphy and sedimentary evolution of a rapidly infilled holocene incised valley estuary the lower manawatu valley north island new zealand water well logs and vibracores recovered from the lower manawatu valley record the facies architecture morphostratigraphy and sedimentary evolution of this drowned river incised valley estuary over the past c 30 000 years the manawatu incised valley estuary was rapidly infilled during the holocene and as a result preserves a complete record of holocene estuary evolution the base of the holocene fill is marked by fluvial gravels deposited by the manawatu river during the lowstand of the last glacial maximum the gravels are overlain by back stepping transgressive fluvial silts and clays the transgressive fluvial unit is present only in the lower reaches of the valley due to accelerated sea level rise during the latter stages of the marine transgression large volumes of transgressive marine sediment were delivered to the mouth of the valley by rising sea levels during the early holocene forming a large subaqueous tidal delta this delta accreted and subsequently evolved to form a subaerial barrier in the mid holocene as sea levels stabilised during the sea level highstand the central basin of the estuary was rapidly infilled by marine and fluvial sediment and consequently lacks the mud facies characteristic of less rapidly evolved estuaries the transition from the sandy central basin estuarine environment to the overlying floodplain environment was extremely rapid in some locations in the valley the transitional fluvial bay head delta is missing completely while in most locations it is present only as a very thin deposit indicative of this rapid environmental transition infilling of the estuarine central basin was extremely rapid taking only 2000 2700 years the unique features of the manawatu estuary s evolutionary history are interpreted to primarily reflect the rapid infilling of the palaeo estuary driven by the high rates of sediment supplied to the valley from both marine and fluvial sources

pacific meridional mode and el nino southern oscillation 1 we present intriguing evidence that the majority of el nino events over the past four decades are preceded by a distinctive sea surface warming and southwesterly wind anomaly in the vicinity of the intertropical convergence zone itcz during the boreal spring this phenomenon known as the meridional mode mm is shown to be intrinsic to the thermodynamic coupling between the atmosphere and ocean the mm effectively acts as a conduit through which the extratropical atmosphere influences enso modeling results further suggest that the mm plays a vital role in the seasonal phase locking behavior of enso the findings provide a new perspective for understanding the important role of thermodynamic ocean atmosphere feedback in enso and may have profound implications for enso prediction particularly the unresolved issue of the spring predictability barrier citation chang p l zhang r saravanan d j vimont j c h chiang l ji h seidel and m k tippett 2007 pacific meridional mode and el nino southern oscillation geophys res lett 34 l16608 doi 10 1029 2007gl030302

petrogenetic and metallogenetic responses to miocene slab flattening new constraints from the el indio pascua au ag cu belt chile argentina the eocene miocene volcanic and hypabyssal rocks of the el indio pascua au ag cu belt in the southern central andean flat slab region are medium high k calc alkaline arc suites ranging in composition from andesite to rhyolite a significant transition in magmatic trace element chemistry coinciding with a pronounced reduction in magma output occurred in the late middle miocene as documented by 40ar 39ar geochronology the upper eocene lower middle miocene rocks exhibit low sr y ratios 50 minor heavy ree fractionation with sm yb ratios not exceeding 3 5 and in some cases minor negative eu anomalies in contrast the largely dacitic rocks erupted after ca 13 ma are depleted in y 10 ppm have generally high but variable sr y ratios 30 200 exhibit moderate middle and heavy ree fractionation sm yb 3 7 5 9 and lack negative eu anomalies the latter features are characteristic of adakitic suites i e slab melts but the regional temporal and spatial distribution of arc magmatism precludes a major magma source in the downgoing slab this evolution is interpreted as reflecting a progressive increase in pressure and the availability of water in the lower crustal site of magma generation establishing both garnet and hornblende as major stable phases in the residuum the pressure in the lower crust increased in response to episodic crustal thickening related to the shallowing of the slab a process recorded by the incision of three regional pediplains over the period 17 6 ma elimination of the subarc asthenospheric mantle and much of the lithospheric mantle by ca 10 ma permitted direct incursion of slab derived highly oxidised metal and volatile rich supercritical fluids into the lower crust stimulating melting of mafic garnet amphibolitic and eclogitic assemblages

lead and oxygen isotope evidence for the origin of the monte rosa gold lode deposits western alps italy a comparison with archean lode deposits in the monte rosa area of the northwestern italian alps swarms of epigenetic quartz sulfide gold bearing veins occur within a terrane affected by tertiary regional metamorphism of greenschist to amphibolite grade they are preferentially associated with the felsic rocks of the upper penninic nappes field evidence and available geochronologic data imply emplacement ages postdating the metamorphic peak 38 or 2 m y the spatial distribution of the veins is related to late metamorphic large scale tectonic disturbances which displace truncate or fold the isograds lead isotope analyses of galenas and other sulfides were compared with those of feldspars clinozoisites and whole rocks from various unaltered host rocks the data suggest derivation of the ore lead from caledonian metapelites with a possible contribution from hercynian granitoids but they rule out significant contributions from the neighboring ophiolitic greenstones and associated stratiform massive sulfide deposits the separation of the ore leads into two distinct data fields is probably the result of ore deposition from at least two hydrothermal systems which were separated in space and possibly also in time the hypothesis of two distinct mineralization ages is also supported by geochronologic data oxygen isotope data indicate that the ore fluids had isotopic compositions consistent with a metamorphic origin with the notable exception of the val toppa mine where lighter possibly surface derived water was involved oxygen isotope fractionations between mineral pairs in metasediments and granites indicate metamorphic peak temperatures of 530 degrees to 605 degrees c in agreement with those inferred from petrologic evidence these temperatures and preliminary fluid inclusion data were used to predict oxygen isotope compositions of gangue quartz the comparison of predicted with measured delta 18 o values shows consistency with the assumption that the fluids were generated by metamorphic devolatilization within the metapelites and granitoids in agreement with the lead isotope data the results suggest that the gold bearing fluids and the lead were supplied by rocks derived from the continental crust in opposition to the data from many greenstone hosted archean gold lode deposits which indicate a mantle source this implies that metamorphic hosted quartz gold lodes do not necessarily derive metals and fluids from source beds within a greenstone sequence therefore the assumption that the archean gold was derived from greenstones should be checked by isotope tracing studies the common lead method appears to be particularly promising in distinguishing greenstone metamorphic from granitic sources in precambrian terranes in view of the contrasting u pb ratios usually stated in these lithologies

extremely negative and inhomogeneous sulfur isotope signatures in cretaceous chilean manto type cu ag deposits coastal range of central chile abstract chilean manto type cmt cu ag hydrothermal deposits share a characteristic association of volcano sedimentary jurassic to lower cretaceous host rocks style of mineralization ore and associated mineralogy and geochemistry with ore grades typically 1 cu that make this family of deposits significant and interesting both academically and economically although often stratabound geological evidence supports an epigenetic origin for these deposits we present a detailed stable isotope study of la serena and melipilla naltahua lower cretaceous deposits central chile which reveals extremely negative 34 s values to 50 which are among the lowest values found in any ore deposit in addition the range of 34 s values from sulfides in the two areas is very wide 38 3 to 6 9 in la serena and 50 4 to 0 6 in melipilla naltahua these new data significantly extended the reported range of 34 s data for cmt deposits co existing sulfates range from 7 9 to 14 3 and are exclusive to la serena deposit the wide sulfide isotopic range occurs at deposit and hand specimen scale and suggests a polygenic sulfur source for these deposits where bacteriogenic sulfide dominates while sulfur isotope data for the bulk of jurassic cmt deposits northern chile suggests a predominant magmatic source in their origin mean 2 7 1 9 1 contributions of a magmatic component is only likely to be involved at melipilla naltahua deposit the 13 c values obtained for calcites associated with the mineralization range from 20 1 to 0 2 also suggesting polygenic carbon sources with the likely strong involvement of degradation of organic matter and leaching of limestone two different genetic models with involvement of hydrocarbon are proposed for both areas for melipilla naltahua a two step model can be developed as follows 1 framboidal pyrite growth with very low 34 s formed by bacterial sulfate reduction in an open system and with diagenetic degradation of oil related brines leaving pyrobitumen 2 cu bearing stage replacing of framboidal pyrite inheriting depleted sulfur as low as 50 4 together with sulfides directly precipitated from a hydrothermal fluid with 34 s close to 0 for la serena a single step model fits best without framboidal pyrite generation cu bearing sulfides were precipitated mainly in veins where cu plus base metal bearing hydrothermal fluids mixed with h 2 s generated by bacterial sulfate reduction in the host rocks isotopic evidence clearly illustrates that bacterial activity perhaps enhanced by hydrothermal activity was fed by hydrocarbon brines and sulfate remobilized from continental evaporites it is possible that variable ecological conditions led to different extents of isotopic fractionation adding to the typical sulfur isotopic heterogeneity of such bacterial systems for both areas the cu bearing stage occurred during the peak to waning stages of the very low grade metamorphism that affected the lower cretaceous sequence

dune phases in the otaki te horo area new zealand a geomorphic history optical dating sedimentological analysis and soil profile development have been used to develop a chronology for and an understanding of the geomorphic evolution of the holocene coastal plain between otaki and te horo north island of new zealand the coastal plain has prograded 0 48 m a 1 since sea levels reached their post glacial maximum 6500 years ago dune development on the plain which is dependent on the supply of sediment suitable for dune building has been episodic three periods of dune activity have been identified the foxton motuiti and waitarere phases the last two of which are believed to have resulted from anthropogenic activities the dunes north of the otaki river and south of mangaone stream are typical of a coastal dune system that extends from patea in the north to paekakariki in the south however this system is disrupted by the otaki river and the gravels it delivers to the coastal zone immediately south of the river mouth the dunes are significantly smaller coarser and contain significantly more magnetic material the character of the landforms is the result of the reworking of the last glacial deposits ongoing coastal progradation variation in the input of sediment suitable for dune formation the change in beach character because of gravel input and the position of the otaki river mouth copyright 2006 john wiley sons ltd

multiple sources for the coastal batholith of central chile 31 34 s geochemical and sr nd isotopic evidence and tectonic implications abstract the coastal batholith of central chile between 31 and 34 s represents a locus of long lived c 200 ma plutonic activity it is composed of four plutonic complexes santo domingo limari papudo quintero and illapel these complexes which occur as north trending discontinuous belts that decrease in age eastward were emplaced during four major episodes of arc magmatism the santo domingo complex carboniferous comprises hornblende biotite bearing tonalites and granodiorites with abundant mafic enclaves and enclave free granites the association of enclave bearing granitoids and enclave free granites resulted from different degrees of mixing of crustal and mantle derived magmas the limari complex lower jurassic is a bimodal association of crustal leucogranites and mantle derived gabbros the lithology of the papudo quintero complex middle jurassic varies from hornblende pyroxene diorite to biotite granite the main rock types namely tonalites and granodiorites commonly contain mafic enclaves the granitoids and the enclaves have remarkably similar ree patterns and are similar in sr nd isotope composition which suggest that they represent a cogenetic suite of mantle origin the illapel complex cretaceous consists of hornblende bearing tonalites trondhjemites and granodiorites that resemble the rocks of ttg suites the end values and initial 87 sr 86 sr ratios sri for the mafic rocks of the carboniferous complex end 2 0 and 3 5 sri c 0 7057 differ markedly from those of the mesozoic mafic rocks end 1 9 to 5 4 sri 0 7033 to 0 7039 the cretaceous rocks being the most depleted with regard to sr nd a change from carboniferous lithosphere dominated sources to mesozoic asthenosphere dominated sources of the magmas that started in the early jurassic is recognized slab components can be recognized in the source of the cretaceous rocks the crustal source of the lower jurassic leucogranites was more isotopically depleted and refractory than that of the carboniferous granites on the other hand no crustal participation in the origin of the middle jurassic and cretaceous felsic granitoids is recognized they are differentiated from mantle derived magmas progressive removal of old lithospheric mantle during the mesozoic due to a process of lithospheric delamination would explain the profound change in the subcrustal source as well as the melting and modification towards a more refractory nature of the continental crust

measurements and numerical simulations of the degree of activity and vegetation cover on parabolic dunes in north eastern brazil in this work we present measurements of vegetation cover over parabolic dunes with different degrees of activation along the north eastern brazilian coast we extend the local values of the vegetation cover density to the whole dune by correlating measurements with the relative brightness index c of high resolution quickbird panchromatic satellite images of the dune field we then introduce the vegetation data into a continuous model for vegetated dunes coupling sand erosion and vegetation growth and perform simulations of the evolution of the morphology and vegetation cover of parabolic dunes finally from the comparison of both the measurements and the simulation results we show that the model is able to predict the dune shape and the vegetation distribution of real parabolic dunes as result of the evolution of a blow out