the bonneville estates rockshelter rodent fauna and changes in late pleistocene middle holocene climates and biogeography in the northern bonneville basin usa abstract excavations at bonneville estates rockshelter nevada recovered rodent remains from stratified deposits spanning the past ca 12 500 14c yr bp 14 800 cal yr bp specimens from horizons dating to the late pleistocene and early holocene include species adapted to montane and moist and cool habitats including yellow bellied marmot marmota flaviventris and bushy tailed woodrat neotoma cinerea shortly after 9000 14c bp 10 200 cal yr bp these mammals became locally extinct or nearly so taxonomic diversity declined and the region became dominated by desert woodrats neotoma lepida and other species well adapted to xeric low elevation settings the timing and nature of changes in the bonneville estates rodent fauna are similar to records reported from nearby homestead and camels back caves and provide corroborative data on terminal pleistocene early holocene environments and mammalian responses to middle holocene desertification moreover the presence of northern pocket gopher thomomys talpoides at bonneville estates adds to a sparse regional record for that species and similar to homestead cave it appears that the ca 9500 14c yr bp 10 800 cal yr bp replacement of the northern pocket gopher by botta s pocket gopher in the great salt lake desert vicinity was also in response to climate change

experimental calibration of a new oxybarometer for silicic magmas based on vanadium partitioning between magnetite and silicate melt abstract partition coefficients of vanadium between magnetite and rhyolitic silicate melt d v mgt melt were experimentally determined as a function of oxygen fugacity 0 7 4 0 log units above the fayalite magnetite quartz buffer temperature 800 1000 c melt alumina saturation index asi 0 74 1 14 magnetite composition 0 2 14 wt tio 2 and pressure 1 5 kbar at h 2 o saturation experiments were performed by equilibrating small 20 m v free magnetite grains in v doped silicate melts 100 ppm v and then analyzing both phases by la icp ms attainment of equilibrium was demonstrated by several reversal experiments the results suggest that d v mgt melt depends strongly on f o 2 increasing by 1 5 1 7 log units from the mno mn 3 o 4 buffer to the ni nio buffer and to lesser but still considerable extents on melt alumina saturation index asi increasing by 0 3 0 7 log units over 0 4 asi units and temperature increasing by 0 3 0 7 log units over a 200 c interval at a fixed f o 2 buffer magnetite composition and melt water content seem to have negligible effects the data were fitted by the following linear regression equation log d v mgt melt 0 3726 10 000 t 2 0465 asi 0 4773 fmq 2 1214 in which temperature is given in k asi refers to molar al 2 o 3 cao na 2 o k 2 o and fmq refers to the deviation of f o 2 in log units from the fayalite magnetite quartz buffer this equation reproduces all of our data within 0 3 log units and 89 of them within 0 15 log units the main advantages of this new oxybarometer over classical magnetite ilmenite oxybarometry are 1 that it can be applied to rocks that do not contain ilmenite and 2 that it is easier to apply to slowly cooled rocks such as granites

the el teniente porphyry cu mo deposit from a hydrothermal rutile perspective mineralogical textural and chemical analyses epma and pixe of hydrothermal rutile in the el teniente porphyry cu mo deposit help to better constrain ore formation processes rutile formed from igneous ti rich phases sphene biotite ti magnetite and ilmenite by re equilibration and or breakdown under hydrothermal conditions at temperatures ranging between 400 c and 700 c most rutile nucleate and grow at the original textural position of its ti rich igneous parent mineral phase the distribution of mo content in rutile indicates that low temperature 400 550 c mo poor rutile 5 4 1 1 ppm is dominantly in the mo rich mafic wallrocks high grade ore while high temperature 550 700 c mo rich rutile 186 20 ppm is found in the mo poor felsic porphyries low grade ore rutile from late dacite ring dikes is a notable exception to this distribution pattern the sb content in rutile from the high temperature potassic core of the deposit to its low temperature propylitic fringe remains relatively constant 35 3 ppm temperature and mo content of the hydrothermal fluids in addition to mo ti ratio modal abundance and stability of ti rich parental phases are key factors constraining mo content and provenance in high temperature 550 c rutile the initial mo content of parent mineral phases is controlled by melt composition and oxygen fugacity as well as timing and efficiency of fluid melt separation enhanced reduction of so2 rich fluids and sulfide deposition in the fe rich mafic wallrocks influences the low temperature 550 c rutile chemistry the data are consistent with a model of fluid circulation of hot 550 c oxidized o2 nno 1 3 so2 rich and mo bearing fluids likely exsolved from deeper crystallizing parts of the porphyry system and fluxed through the upper dacite porphyries and related structures with metal deposition dominantly in the fe rich mafic wallrocks

seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

source parameters of earthquakes in eastern and western north america based on finite fault modeling the ground motion from large earthquakes is often predicted based on finite fault modeling in which the fault plane is discretized into small independently rupturing subfaults the radiation from all subfaults is summed at the observation point despite the success of the method in matching observed ground motion char acteristics the physical interpretation of the subfaults has remained largely unclear and a rationale for the choice of the subfault attributes has been lacking two key parameters the subfault size and the maximum slip velocity on the fault govern the amplitude of the source spectrum at intermediate and high frequencies respec tively we determined these key source parameters on an event by event basis for all well recorded moderate to large earthquakes in western north america wna by fitting simulated to observed response spectra we compare the values of these source parameters with those obtained previously for eastern north america ena and the michoacan mexico earthquakes a total of 26 modeled events we find that the characteristic subevent size increases linearly with moment mag nitude in an apparently deterministic manner the subevent size relationship obtained for wna is not statistically different from that obtained for ena in both regions the subevent size follows the trend of log dl 2 0 4 m 4 m 8 where dl is the subfault size in km this trend agrees well with independent studies by somerville et al 1999 and aki 1992 in which the characteristic size of the patches asperities or barriers on earthquake faults was determined these results indi cate that large earthquakes should be viewed as a sequence of smaller events that comprise the large rupture interestingly the characteristic size of these constituent small events appears to be directly related to the size of the overall rupture the slip velocities determined for all 26 earthquakes vary in a narrow range from about 0 25 to 0 60 m sec with a mean of 0 40 m sec and standard deviation of 0 09 m sec the slip velocities for the ena events are distributed randomly over this range while those for the wna region appear to exhibit a decreasing trend with increasing magnitude our results indicate that a generic region independent earthquake source model for engineering prediction of strong ground motions can be developed

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

the influence of oxygen fugacity on tungsten and molybdenum partitioning between silicate melts and ilmenite the partitioning of molybdenum and tungsten between ilmenite ilm and silicic melts has been determined at 800 degrees c 1 kbar of pressure and at two oxygen fugacities at the oxygen fugacity of the graphite methane water buffer d super ilm melt mo 0 42 and d super ilm melt w 0 39 near the nickel nickel oxide buffer d super ilm melt mo 0 22 and d super ilm melt w 0 5 the variations in the partition coefficients with f sub o 2 are significant at the 0 06 and 0 33 levels for molybdenum and tungsten respectively the observed variation with oxygen fugacity is tentatively extrapolated to more complex systems and implies that the oxygen fugacity which prevails during magmatic crystallization may play a role in determining the mo w ratio in porphyry skarn or other hydrothermal mineral deposits examination of the literature on molybdenum and tungsten bearing mineral deposits indicates that systems with high w mo ratios are rather reduced and exhibit high ch 4 co 2 ratios in fluid inclusions low fe super 3 fe super 2 ratios in iron bearing minerals and low oxygen fugacities in associated igneous rocks on the other hand deposits with high mo w ratios are associated with rather oxidized magmatic systems we suggest that f sub o 2 dependent sequestration of molybdenum and tungsten in ferromagnesian phases during plutonic consolidation exerts a control on the relative efficiencies of removal of these metals from magmas into ore forming fluids

s wave attenuation in the crust in northern greece abstract the attenuation of shear waves in the crust is estimated for frequencies between 1 5 and 12 0 hz by applying a single station method based on the rate of decay of the s wave to coda wave amplitude ratio with distance the data used come from local earthquakes that occurred in the thessaloniki area northern greece during the period 1983 through 1989 and were recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki the q s values obtained are 115 244 477 and 755 for 1 5 3 0 6 0 and 12 0 hz respectively these values are very close to the coda q values estimated for the same area using the s to s single scattering model for lapse times between 30 and 100 sec but they are higher than the coda q values for lapse times between 10 and 30 sec the estimated q s is found to be strongly frequency dependent proportional to f 0 91 which is very close to the frequency dependence of the coda q

late collisional granites in the variscan erzgebirge germany the late collisional erzgebirge granites 325 318 ma were introduction emplaced at shallow crustal levels in the variscan metamorphic the erzgebirge is a ne sw trending antiformal structure basement shortly after large scale extension caused by orogenic exposing variscan crystalline basement rocks at the northcollapse these granites comprise mildly peraluminous transitional ern margin of the bohemian massif the region is famous i s types and strongly peraluminous s type rocks which can be among economic geologists for its extensive and highly subdivided into three major groups low f biotite granites low f variable metallic ore deposits which have been mined two mica granites and high f high p2o5 li mica granites the since the middle ages e g stemprok seltmann 1994 highest degree of differentiation is reached in the li mica granites tischendorf forster 1994 and for the classic studies which exhibit strongly elevated concentrations of p f li rb cs in the fields of economic geology mining and metallurgy ta sn w and u but very low ti mg co ni sr ba y zr chemistry and mineralogy e g werner 1791 breithaupt hf th and rare earth elements crystal melt fractionation is the 1849 agricola 1974 dominant process controlling the bulk composition of all groups of as in many of the other variscan provinces in central granites however metasomatic processes involving late stage residual europe granitic rocks make up a large proportion of the melts and high t orthomagmatic fluids became increasingly more exposed rocks in the erzgebirge and a great variety of important in highly evolved units and have modified the abundances compositional and textural types occur fig 1 knowof mobile elements p f li rb cs ba sr in the li mica ledge of the processes involved in the generation and granites particularly isotopic and geochemical characteristics suggest evolution of these silicic magmas is essential for underthat the three granite groups cannot be derived from a common standing heat and mass transport during the variscan precursor magma their discrete compositions are source related orogeny and also for the formation of metallic ore and are attributed to melting of quartzo feldspathic and pelitic deposits several lines of evidence indicate that early crustal lithologies in different proportions granites are common in high temperature sn w deposits are associated with the the central european variscides but the erzgebirge is unusual for emplacement of highly evolved volatile rich granitic the predominance of evolved li mica granites associated with melts tischendorf 1986 forster tischendorf 1992 economically important sn w and u deposits the abundance of stemprok 1993 the role of the granites in formation of li mica granites is attributed to a combination of favourable factors later permian u pb zn and younger ore mineralization 1 low degrees of anatectic melting of crustal protoliths 2 wide f ba is controversial but good evidence exists that the distribution of fertile lithologies rich in large ion lithophile elements vein type u deposits owe their uranium to leaching from and ore elements 3 extended magmatic differentiation by crystal the uraninite rich granites e g tischendorf forster melt fractionation and subsequent autometasomatism 1994

a middle holocene vegetation record from the mojave desert of north america and its paleoclimatic significance abstract packrat middens from the mccullough range in the southeastern mojave desert of nevada record vegetation conditions during the periods 6800 to 5060 yr b p and 1250 yr b p to present their age and location are ideal to test for middle holocene aridity the period between 6800 and 5060 yr b p does appear to have been more arid than during the late holocene period of record this agrees with other evidence for middle holocene aridity from the southwest arguments for strengthened middle holocene monsoons in the region are based chiefly on packrat midden samples older than 7500 yr b p or on samples that are younger than 5500 yr b p simulations of 6000 yr b p climate that fail to show strong subtropical flow into the southwest are therefore supported by evidence for enhanced aridity in that region

magmatic evolution and related w mo mineralization in the larong deposit eastern tibet evidence from zircon u pb ages geochemistry and sr nd hf isotopes abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 is the first discovered giant w mo deposit in the leiwuqi zogang metallogenic belt sanjiang region multi stage granitoids including the dacite porphyry dp granodiorite porphyry gp biotite granite porphyry bgp monzogranite porphyry mp biotite granite bg and granite aplite ga have been identified in the larong deposit however the magmatic evolution and related w mo mineralization in this deposit are still poorly understood la icp ms zircon u pb dating of the dp gp bgp mp bg and ga yield weighted mean 206pb 238u ages of 214 0 0 7 ma 213 8 1 3 ma 104 4 0 9 ma 93 9 1 3 ma 91 7 0 5 ma and 36 2 0 6 ma respectively the late triassic dp and gp should be classified as peraluminous a cnk values of 0 95 1 57 s type granitoids they are characterized by pronounced negative end t values 10 01 to 13 92 and ehf t values 8 5 to 16 6 with old tdm2 nd and tdm2 hf ages 1 81 2 12 ga and 1 79 2 30 ga respectively indicating that the dp and gp were mainly derived from partial melting of ancient crustal materials after break off of the paleo tethyan oceanic slab the late cretaceous bgp mp and bg and late eocene ga have low a cnk ratios 0 92 1 06 but high sio2 70 57 77 34 and differentiation index di 87 55 98 06 similar to the characteristics of highly fractionated i type granite detailed elemental e g depletion in nb ta ti sr ba eu and p and isotopic data 87sr 86sr i 0 71192 0 72932 end t 11 81 to 9 11 ehf t 10 4 to 1 4 demonstrate that they were the result of magma mixing between ancient crust derived melts and mantle derived melts the bgp was produced during the final stage of bangong nujiang tethyan ocean bnto subduction the mp and bg were formed under a post collisional tectonic setting related to slab break off of the bnto and the ga was likely associated with delamination of the thickened eclogitic lower crust together with lithospheric mantle the w mo mineralization in the larong deposit is genetically associated with the mp with four favorable factors that can account for the formation of this deposit 1 high w background 2 multi stage magmatism 3 highly evolved relatively oxidized and f rich magmatic system and 4 sufficient calcium obtained by intense fluid rock interaction

el nino controls holocene rabbit and hare populations in baja california abstract the el nino southern oscillation enso is a major source of climatic variation worldwide with significant impacts on modern human and animal populations however few detailed records exist on the long term effects of enso on prehistoric vertebrate populations here we examine how lagomorph rabbit and hare deposition rate population age structure and taxonomic composition from abrigo de los escorpiones a well dated trans holocene vertebrate fauna from northern baja california mexico vary as a function of the frequency of wet el nino events and eastern pacific sea surface temperatures ssts derived from eastern pacific geological records faunal indices vary significantly in response to el nino based precipitation and sst with substantial moisture driven variability in the middle and late holocene the late holocene moisture pulse is coincident with previously documented changes in the population dynamics of other vertebrates including humans as the frequency and intensity of enso is anticipated to vary in the future these results have important implications for change in future vertebrate populations

re os geochronology and systematics in molybdenite from the endako porphyry molybdenum deposit british columbia canada precise re os molybdenite ages for the endako porphyry molybdenum deposit and the nithi mountain occurrence british columbia canada yield new information on the timing of molybdenite deposition three episodes of mineralization are indicated 1 154 ma 2 148 to 146 ma and 3 145 ma re os dates agree well with new u pb and 40 ar 39 ar data from granitoids of the nithi phase 155 2 1 5 ma the endako phase 148 4 1 5 ma and a preore dike 147 4 0 6 ma and the casey phase 145 1 0 2 ma plus hydrothermal biotite 144 5 0 75 ma villeneuve et al 2001 the excellent correlation between the re os dates from molybdenite and the ages of granitoids from the area indicates a direct genetic relationship between these plutons and molybdenite mineralization these re os data also provide further insight into the systematics and robustness of re os in molybdenite the endako molybdenum deposit is the product of two episodes of mineralization both associated with moderate salinity 5 15 wt nacl equiv and high temperature 440 c fluids a third low temperature 190 300 c hydrothermal event is associated with eocene faulting selby et al 2000 the clear distinction between two of the re os molybdenite dates in the deposit and the close agreement of these dates to the ages of granitoid intrusions suggest that the re os system in molybdenite is not reset by high temperature 440 c moderate salinity hydrothermal fluids in contrast magmatic biotite in a 147 ma preore dike has a 40 ar 39 ar age of 145 ma identical to the age of the hydrothermal biotite indicating that 440 c fluids reset the ar ar system in biotite hence we interpret that the re os isotope system in molybdenite is resistant to resetting by high temperature fluids 440 c in contrast to the 40 ar 39 ar system in biotite the re os system in molybdenite is also unaffected by postore hydrothermal fluids these data show that molybdenite can provide critical information in understanding sulfide mineral deposition in ore systems which is not recorded by other isotopic systems in alteration minerals

stochastic finite fault modeling of ground motions from the 1994 northridge california earthquake i validation on rock sites the stochastic method of simulating ground motions from finite faults is validated against strong motion data from the m 6 7 1994 northridge california earthquake the finite fault plane is subdivided into elements each element is as signed a stochastic o92 spectrum and the delayed contributions from all subfaults are summed in the time domain simulated horizontal acceleration time histories and fourier spectra at 28 rock sites are compared with observations we first perform simulations using the slip distribution on the causative fault derived from strong motion teleseismic gps and leveling data wald et al 1996 we then test the performance of the method using quasi random distributions of slip and alternative hypocenter locations this is important because the rupture initiation point and slip distribution are in general not known for future earthquakes the model bias is calculated as the ratio of the simulated to the observed spectrum in the frequency band of 0 1 to 12 5 hz averaged over a suite of rock sites the mean bias is within the 95 confidence limits of unity showing that the model provides an accurate prediction of the spectral content of ground motions on average the maximum excursion of the model bias from the unity value when averaged over all 28 rock stations is a factor of approximately 1 6 at most frequencies it is below a factor of 1 4 interestingly the spectral bias and the standard deviation of the stochastic simu lations do not depend on whether the fault slip distribution and hypocenter location are based on data or are randomly generated this suggests that these parameters do not affect the accuracy of predicting the average characteristics of ground motion or they may have their predominant effect in the frequency range below about 0 1 hz below the range of this study the implication is that deterministic slip models are not necessary to produce reasonably accurate simulations of the spectral content of strong ground motions this is fortunate because such models are not available for forecasting motions from future earthquakes however the directivity effects controlled by the hypocenter location are important in determining peak ground ac celeration at individual sites although the method is unbiased when averaged over all rock sites the simulations at individual sites can have significant errors generally a factor of 2 to 3 which are also frequency dependent factors such as local geology site topography or basin propagation effects can profoundly affect the recordings at individual stations to generate more accurate site specific predictions empirical responses at each site could be established

geology mineralization and fluid inclusion characteristics of the koitash redox intermediate w mo skarn and w au stockwork deposit western uzbekistan tien shan the koitash w mo skarn deposit in the tien shan gold belt contained resources of 60 kt wo3 in altered skarn averaging 0 56 wo3 and 0 029 mo and an additional 42 kt wo3 in separate zones of phyllic alteration averaging 0 30 wo3 0 97 g t au 0 67 cu and 0 02 bi it is related to an early permian multiphase granodiorite granite leucogranite pluton that is composed of medium to high k transitional metaluminous to peraluminous weakly oxidized weakly reduced ilmenite titanite series granitoids the pluton was emplaced in a tectonic domain with inferred ancient continental crust the latter coupled with possible ascent of hot asthenospheric material has likely defined a distinct w mo au metallogenic assemblage forming in a post collisional environment the deposit includes redox intermediate prograde and retrograde pyroxene garnet skarns partially overprinted by propylitic and phyllic alteration assemblages comprising scheelite molybdenite cu bi ag te sulfides and sulfosalts as well as native bi and au compositional similarities between w mo deposits containing au w cu bi mineralization in late alteration assemblages and coeval intrusion related au dominant with minor w bi etc deposits in the region support their possible genetic links fluid inclusion data indicate the involvement of carbonic free moderately saline 10 5 15 0 to 8 0 11 7 wt nacl eq high pressure 2000 to 1500 bars hot 550 600 c aqueous fluid which was sourced from crystallizing magma and formed prograde calcic skarn this fluid was followed by moderately saline ca rich 14 16 wt nacl 19 21 wt cacl2 lower pressure 800 bars fluids toward the retrograde skarn stage with the deposition of scheelite in association with pyrrhotite and molybdenite locally with minor fluorite propylitic quartz amphibole chlorite oligoclase calcite with scheelite pyrrhotite locally molybdenite assemblages formed from boiling high methane aqueous carbonic fluids at temperatures of 370 400 c and pressures of 950 1000 bars phyllic quartz sericite fe carbonate locally with albite fluorite chlorite scheelite molybdenite and other sulfides also bi and au minerals alteration assemblages initially formed from homogeneous and then from boiling aqueous carbonic low salinity fluids at temperatures of 365 370 to 300 315 c and pressures of 2000 bars 34s increases from retrograde skarn 34s 2 0 to 2 3 through propylitic 34s 3 0 to 3 4 to phyllic alteration 34s 4 2 to 4 7 stages

late wisconsin early holocene vegetation in the bonneville basin abstract woodrat middens from the northern bonneville basin allow a reconstruction of vegetation changes from 14 000 to 9000 yr ago cold montane steppe dominated by sagebrush covered much of the western bonneville basin prior to 13 000 yr ago from 13 000 10 800 yr ago the region was vegetated by limber pine woodlands in lower montane settings and a mosaic of limber pine and sagebrush steppe along basin flour margins these low elevation limber pine woodlands began to retreat upslope after about 11 000 yr ago due to increasingly drier climatic conditions and were replaced by relatively more xeric desert scrub dominated by sagebrush and shadscale the growth of limber pine at low elevations suggests that summer temperatures were as much as 6 c lower than at present this evidence is in apparent conflict with the currently accepted post provo lake bonneville chronology especially the magnitude of the postulated near dessication of lake bonneville from ca 13 000 12 200 yr ago

holocene bison in the great basin western usa bison bison bison were widespread in the eastern and northern parts of the great basin the area of internal drainage in the arid western usa during the late holocene particularly after 1600 14

molybdenite re os dating of biotite dehydration melting in the rogaland high temperature granulites s norway abstract the ability of the re os system in molybdenite to record and preserve the age of granulite facies metamorphism in polymetamorphic belts is tested using the orsdalen w mo district rogaland s norway a low pressure high temperature granulite facies domain displaying osumilite and pigeonite isograds is exposed around the 931 2 ma rogaland anorthosite complex available u pb monazite and zircon data show that a 0 93 ga contact metamorphism overprints a 1 03 0 97 ga regional sveconorwegian metamorphism in the gneiss basement molybdenite and scheelite in the orsdalen district occur in orthopyroxene bearing leucocratic veins parallel to the regional foliation the veins are interpreted as migmatic leucosomes formed by fluid absent incongruent melting of the biotite rich host rock above ca 800 c producing a granulite facies orthopyroxene garnet residual assemblage molybdenite is interpreted as a product of the melting reaction crystallized from trace amounts of mo released from biotite in the host rock during partial melting four re os analyses of molybdenite from three samples representing two mines yield an isochron age of 973 4 ma the isochroneity of the data indicates that the precipitation of molybdenite and the partial melting event are recorded on the district scale the re os system in molybdenite was not affected by subsequent 0 93 ga contact metamorphism corresponding to formation of garnet quartz coronitic textures around molybdenite and other minerals in the deposits the results indicate that granulite facies conditions prevailed at 973 4 ma near the end of a protracted event of regional metamorphism 1 03 0 97 ga biotite dehydration melting recorded in orsdalen took place at a pressure of ca 5 5 kbar orthopyroxene garnet plagioclase quartz thermobarometry possibly in association with regional decompression the study shows that granulite facies metamorphism 0 97 ga took place before intrusion of massif type anorthosites in rogaland 0 93 ga the study suggests that the high temperature osumilite bearing assemblage may be related to the 0 97 ga event and that massif type anorthosites may not be a cause for the high temperature thermal anomaly in the crust but a late expression of it

paleobiogeographic changes at the pleistocene holocene boundary near pintwater cave southern nevada abstract in 1996 approximately 70 000 mammal and lizard bones were recovered from pintwater cave in the northern mojave desert of southern nevada these bones date between 32 000 and 7350 14c yr b p between 32 000 and 10 100 14c yr b p the local fauna consisted of a mix of xeric and cool mesic adapted species ochotona princeps and thomomys talpoides then occupied the region although these animals were extirpated by the onset of the middle holocene sauromalus obesus and dipodomys deserti probably migrated to the region during the latest pleistocene dipsosaurus dorsalis entered the pintwater cave record after 8000 14c yr b p consistent with climatic interpretations for the northern great basin these data suggest a cool and moist latest pleistocene climate for the northern mojave desert in contrast to the northern great basin however this region experienced predictable summer precipitation coupled with increasingly warmer winters by 10 100 14c yr b p in both regions the warm middle holocene began ca 8300 14c yr b p however whereas the northern great basin probably experienced warm and dry conditions at that time the northern mojave desert remained warm with relatively predictable summer precipitation the modern northern mojave desert biota probably was not established until after 8300 14c yr b p

mineralogy and geochemistry of archaean greenstone belt hosted mn formations and deposits of the dharwar craton redox potential of proto oceans

subevent structure of large earthquakes a ground motion perspective our ability to predict ground motions from future earthquakes hinges on the accurate modeling of the radiation from the earthquake source a successful approach to modeling earthquake radiation has been to represent faults as a series of discrete independently rupturing subfaults although their physical interpretation has remained largely unclear our simulation of ground motions from twenty six well recorded moderate to large earthquakes substantiates the hypothesis that large ruptures are made up of a sequence of smaller subevents the size of a subevent follows a simple linear relationship with the size of the earthquake fault in an apparently deterministic manner the strength of the high frequency radiation is controlled by the maximum slip velocity which varies stochastically over a small range both the characteristic subevent size and the slip velocity appear to be region independent indicating a remarkable uniformity in earthquake source properties this observation helps to reduce the uncertainty in ground motion prediction by constraining its essential and previously ambiguous parameters

trace element partitioning between ilmenite armalcolite and anhydrous silicate melt implications for the formation of lunar high ti mare basalts abstract we performed a series of experiments at high pressures and temperatures to determine the partitioning of a wide range of trace elements between ilmenite ilm armalcolite arm and anhydrous lunar silicate melt to constrain geochemical models of the formation of titanium rich melts in the moon experiments were performed in graphite lined platinum capsules at pressures and temperatures ranging from 1 1 to 2 3 gpa and 1300 1400 c using a synthetic ti enriched apollo black glass composition in the cao feo mgo al2o3 tio2 sio2 system ilmenite melt and armalcolite melt partition coefficients d show highly incompatible values for the rare earth elements ree with the light ree more incompatible compared to the heavy ree d la ilm melt 0 0020 0 0010 to d lu ilm melt 0 069 0 010 for ilmenite d la arm melt 0 0048 0 0023 to d lu arm melt 0 041 0 008 for armalcolite d values for the high field strength elements vary from highly incompatible for th u and to a lesser extent w for ilmenite d th ilm melt 0 0013 0 0008 d u ilm melt 0 0035 0 0015 and d w ilm melt 0 039 0 005 and for armalcolite d th arm melt 0 008 0 003 d u arm melt 0 0048 0 0022 and d w arm melt 0 062 0 03 to mildly incompatible for nb ta zr and hf e g d hf ilm melt 0 28 0 05 and d hf arm melt 0 76 0 07 both minerals fractionate the high field strength elements with dta dnb and dhf dzr between 1 3 and 1 6 for ilmenite and 1 3 and 1 4 for armalcolite armalcolite is slightly more efficient at fractionating hf from w during lunar magma ocean crystallisation with dhf dw 12 13 compared to 6 7 7 5 for ilmenite the transition metals vary from mildly incompatible to compatible with the highest compatibilities for cr in ilmenite d 7 5 and v in armalcolite d 8 1 d values show no clear variation with pressure in the small range covered crystal lattice strain modelling of d values for di tri and tetravalent trace elements shows that in ilmenite divalent elements prefer to substitute for fe while armalcolite data suggest ree replacing mg tetravalent cations appear to preferentially substitute for ti in both minerals with the exception of th and u that likely substitute for the larger fe or mg cations crystal lattice strain modelling is also used to identify and correct for very small 0 3 wt melt contamination of trace element concentration determinations in crystals our results are used to model the lu hf ti concentrations of lunar high ti mare basalts the combination of their subchondritic lu hf ratios and high tio2 contents requires preferential dissolution of ilmenite or armalcolite from late stage lunar magma ocean cumulates into low ti partial melts of deeper pyroxene rich cumulates

stochastic strong ground motion simulation of the 7 september 1999 athens greece earthquake the stochastic method for finite faults is applied to simulate strong ground motion from the 7 september 1999 moment magnitude m 5 9 athens earthquake the method includes descritization of the fault plane into a certain number of subfaults each of which is assigned an 2 spectrum a slip distribution model derived from previous studies of this earthquake is used to specifically account for the source effect contributions from all subfaults are then empirically attenuated to the observation sites where they are summed to produce the synthetic acceleration time history the method is first calibrated against its ability of reproducing the recordings at 19 strong motion stations at epicentral distances ranging from 16 to 61 km the calibrated model is then applied to calculate synthetics at a large number of grid points covering the area around the fault plane simulated peak values are subsequently used to produce synthetic peak ground acceleration and spectral acceleration maps at hard rock both peak ground acceleration and spectral acceleration maps imply energy directivity toward the east where most of the damage was concentrated the directivity effect is most prominent at large periods 2 sec and in the period range 0 2 to 0 3 sec independent geotechnical studies showed considerable site effect at periods 0 5 sec within the meizoseismal area this result coupled with the results of the present study imply that the damage distribution pattern of the 1999 athens earthquake can be explained by the destructive combination of two factors the source directivity and the site effect

the late quaternary biogeographic histories of some great basin mammals western usa the great basin of arid western north america provides one of the most detailed late pleistocene and holocene mammal records available for any part of the world though the record is by far strongest for small mammals of the 35 genera of now extinct north american pleistocene mammals 19 are known to have occurred in the great basin a list that is likely to be complete or nearly so of these 19 seven can be shown to have survived beyond 12 000 radiocarbon years ago a proportion similar to that for north america as a whole horses camels mammoth and helmeted musk oxen appear to have been the most abundant of these genera pygmy rabbits brachylagus idahoensis yellow bellied marmots marmota flaviventris and bushy tailed woodrats neotoma cinerea declined in abundance at the end of the pleistocene at about the same time as populations south of their current arid western distributional boundary were extirpated subsequent declines occurred during the hot dry middle holocene pygmy rabbits also declined as modern pinyon juniper woodlands developed across the great basin the snake range of eastern nevada has seen the late pleistocene or holocene extinction of both northern pocket gophers thomomys talpoides and pikas ochotona princeps coupled with the rarity of yellow bellied marmots here these histories make the snake range a biogeographic oddity these and other great basin mammal histories provide significant insights into the possible responses of great basin small mammals to global warming

magnitude assessment for the historical earthquake based on strong motion simulation and liquefaction analysis case of the 1894 atalanti earthquake greece abstract the historical earthquake of the 1894 in atalanti greece produced widespread liquefaction effects on the broader coastal area although this earthquake has been extensively studied in the past its magnitude still remains controversial in the present study we propose an indirect method for assessing its magnitude by simulating the ground motion and liquefaction effects caused by a scenario earthquake with the characteristics of the 1894 event at several sites located at the coastal zone of atalanti bay for this purpose we utilize information about the near surface soil conditions obtained by geophysical tools data of recent seismic events and results of stochastic simulation of strong ground motion for the scenario earthquake of the 1894 event we confirm the high liquefaction potential of the investigated sites and establish that the low limit of magnitude m w for the 1894 earthquake is equal to 7 0 electronic supplement results of liquefaction analysis

attenuation of coda waves in northern greece the single scattering model has been applied for the estimation of codaq values for local earthquakes that occurred in northern greece during the period 1983 1989 and recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki codaq estimations were made for four frequency bands centered at 1 5 hz 3 0 hz 6 0 hz and 12 0 hz and for the lapse time windows 10 20 sec 15 30 sec 20 45 sec 30 60 sec and 50 100 sec the codaq values obtained show a clear frequency dependence of the formq c q 0 f n whileq 0 andn depend on the lapse time window q 0 was found equal to 33 andn equal to 1 01 for the time window of 10 to 20 sec while for the other windowsq 0 increased from 60 to 129 withn being stable close to 0 75 this lapse time dependence is interpreted as due to a depth dependent attenuation the high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity in agreement with studies in other seismic regions

immiscible phases of magmatic fluid and their relation to be and mo mineralization at the yermakovka f be deposit transbaikalia russia abstract melt and fluid inclusions in minerals from the peralkaline granite intrusion and associated mineralized country rocks from the yermakovka f be deposit were studied to characterize the behaviour of trace elements and exsolved fluids in the transition from magmatic to hydrothermal processes ore mineralization was mostly due to volatile release from a deep seated pluton for which crystallization history and fluid exsolution can be tracked by three batches of magma gr1 gr3 intruded at the level of the ore deposition to form the yermakovka stock each batch of the sequential granite group is found to intrude at decreasing temperature from 840 to 730 c and progressively increasing extent of crystallization of magma in the parental pluton this resulted in the enrichment of the ascending melts in h2o 3 9 to 6 1 wt f 2 6 to 4 1 wt and some incompatible elements zr nb th rb pb although the earliest evidence for the exsolution of homogeneous fluoride sulphate brine correlates with the final stage of the gr2 ascent the most intensive volatile s release from the emplaced magmas is shown to occur during their in situ crystallization which was associated with the separation of exsolved fluid into immiscible phases brine and low salinity solution compositions of these fluid phases are determined using atomic emission spectroscopy of the appropriate fluid inclusions opened by a laser microprobe and empa and sem eds analyses of daughter crystals the brine phase is enriched in mo mn be up to 17 8 and 0 3 g kg respectively and contains perceptible abundances of ce la pb zn whereas the low salinity phase is enriched only in be up to 0 6 g kg the selective mobilization of the metals from the melt into fluids is considered to result from the oxidized state of the melt and fluids peralkalinity of the melt during crystallization and high f content of the melt the immiscible fluid phases are shown to migrate together through the solidifying stock giving rise to the albitized granite that is enriched in molybdenite but devoid of be minerals in the country rocks solutions similar to the brine and low salinity phases of the magmatic fluid made up separate fluid flows which produced be and mo mineralization and were issued predominantly from the parental pluton both types of mineralization are nearly monometallic which suggests that of the metals jointly transported by the brine only mo and in part ce and la precipitated separately at the level where the low salinity solutions deposited be ores

microstructural trace element and geochronological characterization of tio 2 polymorphs and implications for mineral exploration abstract the geochemistry of rutile tio2 has recently found its use in mineral exploration with some studies reporting anomalous concentrations of fe w v sn and sb in rutile associated with mineralized ore systems however the use of rutile as a prospecting tool is likely to be complicated by the systematic changes in trace element composition with tio2 polymorph type anatase brookite and rutile here we present tio2 trace element and u pb geochronological data from the mineralized and barren portions of the palaeoproterozoic moorarie supersuite and capricorn orogen western australia with a focus on the minnie creek molybdenum prospect in the northern part of the gascoyne province the barren samples contain all three tio2 polymorphs anatase brookite and rutile textures suggest anatase and brookite may have formed during low t metamorphism either through replacement of previous rutile grains or titaniferous minerals rutile grains from barren samples yield variable u pb ages ca 3 0 2 2 ga as well as variable textures and chemical compositions suggesting detrital origins thus most likely representing metasedimentary units intruded by the moorarie supersuite rutile grains from the minnie creek prospect yield palaeoproterozoic ca 1 77 1 75 ga u pb cooling ages and nb ta concentrations of up to 17 wt that along with inclusions of manganocolumbite oscillatory and patchy zonation of nb and fe suggest a magmatic origin the commonly used pathfinder elements for gold and base metal mineralisation fe cr v w sn and sb are shown to be systematically lower in anatase and brookite thus yielding false negatives if polymorph type is not identified during reconnaissance studies for this reason a ternary diagram was constructed based on the systematic changes in chemistry of tio2 polymorphs to provide a relatively fast and easy chemical discrimination of polymorphs in large volumes of reconnaissance data furthermore it is shown that high al concentrations are characteristic of brookite and to a lesser degree anatase but not rutile in addition sn nb ta and w concentrations in rutile may be more sensitive to igneous processes and may be used to track processes occurring in strongly fractionated granitic magmas such as pegmatites and associated deposits

the partitioning of trace elements between ilmenite ulvospinel armalcolite and silicate melts with implications for the early differentiation of the moon mineral melt trace element partition coefficients for a large number of trace elements zr hf ta nb v co cu zn sr ree sb sn mo cr w u th were determined experimentally for ilmenite fetio3 ulvospinel fe2tio4 minerals of the armalcolite solid solution fe mg ti2o5 the measured partition coefficients indicate that the high field strength elements zr hf nb and ta and some transition metals v cr co sn are moderately compatible in iron titanium oxides whereas other elements ree y sr u th mo sb and w are strongly incompatible the partition coefficients for u are always significantly higher than the th partition coefficients which makes fe ti oxides efficient in fractionating u from th our data also indicate that ilmenite and other iron titanium oxides are able to fractionate w from hf the latter of which is much more compatible this makes the iron titanium oxides very effective agents to influence hf w isotopic ratios during the evolution of the moon in addition we also present some trace element partition coefficients for iron and titanium bearing orthopyroxene

petrogenetic evolution of felsic volcanic sequences associated with phanerozoic volcanic hosted massive sulphide systems the role of extensional geodynamics abstract felsic volcanic hosted massive sulphide deposits form in many different geotectonic environments usually associated with episodes of extension however empirical geochemical links between felsic volcanism geotectonic environment and extensional geodynamics have not been adequately documented so as to distill the fundamental relationships between these features and formation of volcanic hosted massive sulphide vhms mineralization which is important considering most vhms deposits are hosted in felsic volcanic bearing sequences using felsic geochemical data from six different vhms mineralized phanerozoic geotectonic settings it seems that the felsic geochemical data are consistent with the overall geotectonic interpretations for these areas which in turn helps in stratigraphic and geotectonic interpretations for detailed vhms exploration in extensional geodynamic settings bimodal volcanism is common compared to the continuum of compositions observed under compressional to neutral high stress regimes in calc alkaline arc building environments the empirical geochemical metallogenic vhms relationships evident in the archean felsic volcanic rocks in particular the low zr y n yb n 2 o conditions in different source areas and geotectonic environments they seem to be the predominant controls on the compositional evolution of felsic magmas in extensional settings because of the limited degree of assimilation and fractional crystallization afc affecting their compositions with rapid intrusion into the uppermost crust to positions were they achieve neutral buoyancy in the volcanic to subvolcanic environment within plate felsic or a type anorogenic type and anomalous ocean ridge or type felsic magmas that have tholeiitic affinities relatively low alkali elements are common within parts of the volcanic sequences hosting massive sulphide deposits reflecting in part a relationship to extension the high contents of high field strength elements zr ga lree hree y nb etc and other lines of evidence indicate they are relatively high temperature relatively reduced magmas probably derived from previously dehydrated granulitic or melted oceanic simatic or continental sialic crust low p granulites or amphibolites but also in some cases possibly mantle rocks such that they are significantly water undersaturated during melting i e a h 2 o 1 reduced viscosities typical of high temperature melts enable rapid intrusion to higher levels diking vs diapirism higher rates of heat advection from mantle mafic magmas into the thickened oceanic and or continental crust during lithospheric extension are needed to facilitate melting of these rock to form a type and or or type partial melts tholeiitic felsic this usually results in bimodal magmatism as magma mixing is not favored in extensional settings especially at high magma production intrusion and extrusion rates i e high heat flow this would inhibit ferromagnesian phase in particular hornblende and magnetite fractionation especially at low f o 2 in the felsic magmas that would deplete the melt in y hree as well as ore related elements particularly zn which is 2 to 3 times higher in a type and or type rocks compared to other magma types therefore the empirical felsic igneous geochemical metallogenic relationships observed by others low zr y n yb n

site amplification assessment in the east corinth gulf using 3d finite difference modeling and local geophysical data elastic 3d wave field simulations were performed in the seismically active region of eastern gulf of corinth in the area of loutraki city a new methodology was tested with the aim of performing multiple simulations for a large variety of realistic sources located around the study area by employing 3d finite difference modeling using matrix operations for the calculation of the spatial velocity and stress derivatives the new methodology was proven to be quite efficient in simulating the near surface 3d site effect of the study area by greatly minimizing the simulation time thus allowing the use of 3d finite difference modeling for a large number of simulations the complex geological features of the study area were obtained by performing multiple passive masw surveys within the busy urban area of loutraki by processing the acquired geophysical data a highly inhomogeneous near surface velocity structure in the study area was obtained and was implemented in the 3d wave field simulations the near surface amplification that is caused by the 3d subsurface structure was proven to be highly significant for the area of loutraki with high spectral amplification compared to the amplification that is caused by an equivalent 1d model in the area the dominant frequencies of the spectral amplification for the 3d model were also confirmed by processing hvsr measurements that were also taken in the area finally we also investigated how the propagation direction affects the near surface amplification

magmatic sulfides and au cu ratios in porphyry deposits an experimental study of copper and gold partitioning at 850 c 100 mpa in a haplogranitic melt pyrrhotite intermediate solid solution gold metal assemblage at gas saturation abstract the behavior of copper and gold in the phase assemblage pyrrhotite po intermediate solid solution iss haplogranitic melt gold metal capsule at 850 c 100 mpa and gas saturation ah2o 0 9 has been investigated the results are presented as nernst partition coefficients the partition coefficient dcupo melt 2 6 0 3 103 1 was determined for po and melt in equilibrium with an iss of composition cu 19 1 fe 30 1 s 51 1 2 for gold the partition coefficients are dauiss melt 5 7 2 2 103 1 between iss and melt and daupo melt 140 40 1 between po and melt these imply dauiss po 42 9 1 between iss and po the oxygen fugacity for the experiments log f o 2 13 2 0 3 1 was determined by using the hydrogen sensor technique the sulfur fugacity log f s 2 1 0 0 7 1 was calculated from the composition of po in our experiments melts at iss saturation have cu fe by weight of ca 1 100 the results indicate that crystallization of iss may deplete a melt in gold and crystallization of po may deplete a melt in copper however a melt saturated with iss at a given bulk composition temperature pressure oxygen and sulfur fugacity and feo concentration will have a fixed concentration of cu preventing strong depletion of the melt in cu until iss is fractionated from the melt or changes in environmental conditions destabilize iss a thermodynamic model for the partitioning of cu and au between po and melt in terms of oxygen and sulfur fugacity indicates that dcupo melt and daupo melt may increase greatly with increasing sulfur fugacity and decreasing oxygen fugacity within the po stability field the model also suggests that destabilization of both iss and po relative to magnetite due to changes in oxygen and sulfur fugacities can result in the release of cu and au from the sulfides to the melt

stochastic simulation of strong motion records from the 26 september 1997 mw 6 umbria marche central italy earthquake we simulated the strong motion time histories recorded during the main shock m w 6 0 of the umbria marche seismic sequence central italy of september october 1997 ground motion waveforms were computed using the stochastic modeling technique proposed by beresnev and atkinson 1997 1998 for finite faults in this approach the high frequency amplitudes are simulated as a summation of stochastic point sources we used the finsim code beresnev and atkinson 1998 which incorporates regional attenuation and frequency dependent site amplification factors we divided the fault plane into 60 elements whose length and width are 1 2 km and 1 5 km respectively the resulting subfault corner frequency and rise time are 0 91 hz and 0 5 sec we found that the site amplification functions play an important role in the simulation process improving the fit to the observed time histories and spectra the strong motion waveforms recorded at the nocera noc station located at the northern end of the causative fault show an important directivity effect thus to fit the observed ground motions we used an inhomogeneous slip distribution weighting the slip on the fault heavier toward the north we tested two models one that simulates a fault rupture with two main slip patches and a second model that ruptures northward with a less heterogeneous slip distribution where slip is mostly concentrated near the rupture nucleation at the southern edge of the fault plane the simulated low frequency amplitudes at noc however require an additional frequency dependent directivity correction e g bernard et al 1996 in conclusion we found that stochastic finite fault simulations calculated using adequate site amplification functions and crustal attenuation reproduce reasonably well the ground motions from the m w 6 0 umbria marche earthquake

the 26 january 2001 m 7 6 bhuj india earthquake observed and predicted ground motions although local and regional instrumental recordings of the devastating 26 january 2001 bhuj earthquake are sparse the distribution of macroseismic effects can provide important constraints on the mainshock ground motions we compiled available news accounts describing damage and other effects and interpreted them to obtain modified mercalli intensities mmis at 200 locations throughout the indian subcontinent these values are then used to map the intensity distribution throughout the subcontinent using a simple mathematical interpolation method although preliminary the maps reveal several interesting features within the kachchh region the most heavily damaged villages are concentrated toward the western edge of the inferred fault consistent with western directivity significant sediment induced amplification is also suggested at a number of locations around the gulf of kachchh to the south of the epicenter away from the kachchh region intensities were clearly amplified significantly in areas that are along rivers within deltas or on coastal alluvium such as mudflats and salt pans in addition we use fault rupture parameters inferred from teleseismic data to predict shaking intensity at distances of 0 1000 km we then convert the predicted hard rock ground motion parameters to mmi by using a relationship derived from internet based intensity surveys that assigns mmi based on the average effects in a region the predicted mmis are typically lower by 1 3 units than those estimated from news accounts although they do predict near field ground motions of approximately 80 g and potentially damaging ground motions on hard rock sites to distances of approximately 300 km for the most part this discrepancy is consistent with the expected effect of sediment response but it could also reflect other factors such as unusually high building vulnerability in the bhuj region and a tendency for media accounts to focus on the most dramatic damage rather than the average effects the discrepancy may also be partly attributable to the inadequacy of the empirical relationship between mmi and peak ground acceleration pga when applied to india the mmi pga relationship was developed using data from california earthquakes which might have a systematically different stress drop and therefore a different frequency content than intraplate events when a relationship between response spectra and mmi is used we obtain larger predicted mmi values in better agreement with the observations

u pb and re os isotopic systematics and zircon ce4 ce3 ratios in the shiyaogou mo deposit in eastern qinling central china insights into the oxidation state of granitoids and mo au mineralization article i nfo the newly discovered shiyaogou molybdenum deposit is located in the eastern qinling metallogenic belt in central china the deposit contains at least 152 000 t of mo metal and bears typical porphyry type features in terms of its concentric alteration zonation quartz vein hosted mo mineralization veining sequence and the spatial association with concealed granite porphyries re os isotope analyses of molybdenite from the de posit yield an ore forming age of 132 3 2 8 ma la icp ms u pb zircon dating of ore related porphyries yields crystallization ages from 135 ma to 132 ma indicating a temporal link between granitic magmatism and mo mineralization a population of captured magmatic zircons indicates another pulse of magmatism at 143 ma a barren granite intrusion near the deposit gives a zircon u pb age of 148 1 1 1 ma these magmatic activities were concurrent with the emplacement of the nearby heyu granitic batholith a largely ore barren intrusive complex formed from 148 ma to 127 ma zircon ce 4 ce 3 ratios of ore related por phyries are obviously higher than those of contemporaneous barren granitoids implying an affinity between mo mineralization and highly oxidized magmas moreover zircons from these granitoids overall have de creasing ce 4 ce 3 ratios from 148 ma to 132 ma reflecting decreasing oxygen fugacities during magma evolution available geological radiometric and stable isotopic evidence suggests that the decrease of magma oxygen fugacity was probably associated with an increase of mantle contribution to granitic magmatism and metallogenesis which probably gave rise to successive mineralization of mo and au in the eastern qinling the intense magmatic metallogenic events in the eastern qinling during late jurassic to early cretaceous times are interpreted as a response to the large scale lithosphere thinning and subsequent asthenosphere upwelling beneath the eastern part of the north china craton

small mammal data on early and middle holocene climates and biotic communities in the bonneville basin usa abstract archaeological investigations in camels back cave western utah recovered a series of small mammal bone assemblages from stratified deposits dating between ca 12 000 and 500 14c yr b p the cave s early holocene fauna includes a number of species adapted to montane or mesic habitats containing grasses and or sagebrush e g lepus townsendii marmota flaviventris reithrodontomys megalotis and brachylagus idahoensis which suggest that the region was relatively cool and moist until after 8800 14c yr b p between ca 8600 and 8100 14c yr b p these mammals became locally extinct taxonomic diversity declined and there was an increase in species well adapted to xeric low elevation habitats including ground squirrels lepus californicus and neotoma lepida the early small mammal record from camels back cave is similar to the 11 300 6000 14c yr b p mammalian sequence from homestead cave northwestern utah and provides corroborative data on bonneville basin paleoenvironments and mammalian responses to middle holocene desertification

a gis model for predicting wetland habitat in the great basin at the pleistocene holocene transition and implications for paleoindian archaeology the great basin s earliest inhabitants relied heavily on wetland systems that underwent a great decline culminating in the early holocene in this paper we derive expectations for regional paleoindian archaeology by modeling the distribution and disappearance of lake margin wetland habitats basin geomorphology and hydrology are used to predict change through time in the occurrence of these habitats fifty two pluvial lakes are drained from their pleistocene highstands by computer simulation using gis and the changing extent of associated wetlands is quantified we find that as these lakes declined to shallow depths many experienced corresponding increases in wetland habitat prior to complete desiccation thus while the total area of wetland habitat in the region could have maintained some stability through this process the number of available basin wetlands would have dropped relatively rapidly as smaller basins completely dried up the model therefore implies that those lakes that disappeared earliest should hold the archaeological signatures most restricted to early paleoindian times assemblages associated with these lakes should also reflect higher forager mobility corresponding with the greater number of basin wetlands available we find preliminary support for the model in several archaeological cases but emphasize the need for further basin specific research to clarify the nature and timing of wetland habitat loss and the extent to which this was a constraint for paleoindian populations

the tule springs local fauna rancholabrean vertebrates from the las vegas formation nevada abstract a middle to late pleistocene sedimentary sequence in the upper las vegas wash north of las vegas nevada has yielded the largest open site rancholabrean vertebrate fossil assemblage in the southern great basin and mojave deserts recent paleontologic field studies have led to the discovery of hundreds of fossil localities and specimens greatly extending the geographic and temporal footprint of original investigations in the early 1960s the significance of the deposits and their entombed fossils led to the preservation of 22 650 acres of the upper las vegas wash as tule springs fossil beds national monument these discoveries also warrant designation of the assemblage as a local fauna named for the site of the original paleontologic studies at tule springs the large mammal component of the tule springs local fauna is dominated by remains of mammuthus columbi as well as camelops hesternus along with less common remains of equus including e scotti and bison large carnivorans including canis dirus smilodon fatalis and panthera atrox are also recorded micromammals amphibians lizards snakes birds invertebrates plant macrofossils and pollen also occur in the deposits and provide important and complementary paleoenvironmental information the fauna occurs within the las vegas formation an extensive and stratigraphically complex sequence of groundwater discharge deposits that represent a mosaic of desert wetland environments radiometric and luminescence dating indicates the sequence spans the last 570 ka and records hydrologic changes in a dynamic and temporally congruent response to northern hemispheric abrupt climatic oscillations the vertebrate fauna occurs in multiple stratigraphic horizons in this sequence with ages of the fossils spanning from 100 to 12 5 ka

modeling finite fault radiation from the ωn spectrum the high frequency seismic field near the epicenter of a large earth quake is modeled by subdividing the fault plane into subelements and summing their contributions at the observation point each element is treated as a point source with an o92 spectral shape where co is the angular frequency ground motion contributions from the subsources are calculated using a stochastic model attenuation is based on simple geometric spreading in a whole space coupled with regional anelastic atten uation q operator the form of the co n spectrum with natural n follows from point shear dislocation theory with an appropriately chosen slip time function the seismic moment and comer frequency are the two parameters defining the point source spectrum and must be linked to the subfanlt size to make the method complete two coefficients aa and k provide this link assigning a moment to a subfault of specified size introduces the stress parameter ao the relationship between comer frequency dislocation growth rate and fault size is established through the coefficient k which is inherently nonunique these two parameters control the number of subsources and the ampli tudes of high frequency radiation respectively derivation of the model from shear dislocation theory reveals the unavoidable uncertainty in assigning ogn spectrum to faults with finite size this uncertainty can only be reduced through empirical vali dation the method is verified by simulating data recorded on rock sites near epicenters of the m8 0 1985 michoacan mexico the m8 0 1985 valparaiso chile and the m5 8 1988 saguenay qurbec earthquakes each of these events is among the largest for which strong motion records are available in their respective tectonic environ ments the simulations for the first two earthquakes are compared to the more de tailed modeling of somerville et al 1991 which employs an empirical source function and represents the effects of crustal structure using the theoretical impulse response both methods predict the observations accurately on average the precision of the methods is also approximately equal the predicted acceleration amplitudes in our model are generally within 15 of observations an unexpected result of this study is that a single value of a parameter k provides a good fit to the data at high frequencies for all three earthquakes despite their different tectonic environments this suggests a simplicity in the modeling of source processes that was unanticipated

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

the late pleistocene of death valley a climatic reconstruction based on macrofossil data abstract wood rat neotoma macrofossil deposits from death valley california northern mohave dessert dating from the wisconsinan glacial epoch provide a basis for reconstruction of the glacial age climate at low elevations of the area elevational depression of the woodland zone 1200 1500 m relative to today presence of a woodland semidesert ecotone at approximately 450 m and species composition of the low elevation semidesert which included a yucca species yucca whipplei chaparral yucca now locally extinct point toward a pleistocene climate which was less arid and more equable than today precipitation is estimated to have been three to four times the present values and summers 8 14 c cooler the increase in precipitation is inferred to be part of a generally wetter regional in the northern mohave desert and the central great basin during the last glacial presence of warm desert species at 10 200 yr b p indicates that climatic conditions similar to those of the present were established at the lower elevations by this time

geochronological isotopic and mineral geochemical constraints on the genesis of the diyanqinamu mo deposit inner mongolia china abstract the diyanqinamu mo deposit located in central inner mongolia in china is a newly discovered mo deposit due to the lack of detailed deposit scale studies the metallogenesis of the deposit has been a matter of debate in this study petrography zircon u pb geochronology sr nd and pb isotopes and apatite mineral geochemistry have been used to constrain the genesis of the diyanqinamu mo deposit petrographic evidence indicates that the granites in the diyanqinamu deposit have experienced fluid exsolution as demonstrated by the corroded quartz in the porphyritic granites skeletal quartz in the aplitic granites and the unidirectional solidification texture ust in the apex of the aplitic granites sr and nd isotopic data of the purple fluorite from the fluorite molybdenite veins showing the 87sr 86sr i 0 7046 0 7052 avg 0 7048 and end t values 2 4 3 8 avg 3 3 are similar to those of the porphyritic and aplitic granites this similarity implies that the mo ore forming fluids may have been derived from the granitic magmas the hypothesis is further supported by the fluorine content 3 79 5 48 wt avg 4 53 wt in apatite from the porphyritic granites and the widely distributed fluorite in the hydrothermal alteration mineral assemblages which indicate that the porphyritic granites contain high f content and the hydrothermal fluids are also f rich petrographic observation also shows that magnetite occurs commonly in the hydrothermal mineral assemblages indicating that the hydrothermal fluids are characterized by high oxygen fugacity fo2 it is important to note that the intruding granites are essentially barren and the mo is mainly hosted in the andesite and volcaniclastic rocks in comparison pb isotopic compositions of molybdenite are similar to those of both the andesite and k feldspar from the porphyritic granites which suggests that both the intruding granites and ore hosting andesite have contributed to the ore forming materials this hypothesis is further supported by the abnormally high mo for the andesite our new evidence suggests that the diyanqinamu mo deposit may have formed in a post collisional extensional environment ore forming materials may have been derived mainly from the granites and minimally from the host rocks the ore fluids are characterized by high fo2 and being f rich and the trigger for the mo mineralization has been attributed to the reduction of fo2 and or temperature for the ore fluids

geochronological and petrogeochemical constraints on the skarn deposits in tongshanling ore district southern hunan province implications for jurassic cu and w metallogenic events in south china abstract southern hunan province south china is located in the central part of the qin hang metallogenic belt and is characterized by abundant cu pb zn and w sn polymetallic ore deposits the cu pb zn deposits are associated with jurassic granodiorite porphyries whereas the w sn deposits occur within jurassic granite porphyries here we present geochronologic and geochemical data for the tongshanling cu mo pb zn deposit and the weijia w deposit in the district of tongshanling southern hunan zircon u pb dating and molybdenite re os geochronology indicate that the emplacement of the tongshanling granodiorite porphyry and the associated cu mineralization occurred at 162 160 ma slightly earlier than the formation of the xianglinpu granite porphyry and associated w mineralization at 159 158 ma the tongshanling granodiorite is high k calc alkaline weakly peraluminous and weakly fractionated with zircon e hf t values of 15 1 to 5 6 in contrast the xianglinpu granite is alkaline peraluminous and highly fractionated with e hf t values of 9 5 to 0 9 our data indicate that the tongshanling granodiorite is relatively oxidized and was formed by the partial melting of paleoproterozoic crustal material with inputs of mafic magma which was derived from a subduction modified lithospheric mantle in contrast the xianglinpu granite porphyry is relatively reduced and was formed by direct interaction between the crust and asthenospheric mantle the difference in magma generation and tectonics is considered to have resulted in the different types of mineralization associated with these two intrusive bodies

graphite mo w s 2 intergrowth as a palaeoenvironmental proxy in metasedimentary rocks abstract molybdenum enrichment in pristine organic c rich sedimentary rocks forms the basis for inferring the presence of dissolved oxygen in seawater organic matter removes dissolved hexavalent mo from seawater where anoxic and euxinic conditions are attained however it is unknown whether this mo based proxy is retained under metamorphic conditions where organic c is no longer preserved here we describe aggregates of graphite and molybdenite mos2 containing up to 21 mass per cent of w as tungstenite ws2 in solid solution these aggregates are disseminated in a sulfide rich mn silicate carbonate rock queluzite metamorphosed under amphibolite facies conditions within the archaean barbacena greenstone belt in minas gerais brazil our finding indicates that i w is like mo a palaeoenvironmental proxy ii the w proxy is sensitive to high fs2 fo2 environments iii both mo and w proxies survive amphibolite facies overprint as mo w s2 intergrown with graphite archaean greenstones are potential candidates for storing palaeoenvironmental information as mo w s2 graphite intergrowths

stable isotope and petrologic evidence for the origin of regional marble hosted magnetite deposits and the zinc deposits at franklin and sterling hill new jersey highlands united states mesoproterozoic marble in the new jersey highlands hosts small magnetite deposits that occur in discrete groups along linear trends and are concentrated mainly in the western part of the region magnetite also forms a layer structurally beneath the zn fe mn orebody at the franklin mine marble host rocks are interlayered at fe and zn fe mn deposits with bimodal metavolcanic rocks amphibolite and rhyolitic gneiss that were deposited synchronously in a back arc basin developed on the eastern margin of laurentia between 1 3 and 1 25 ga magnetite in the deposits ranges from massive to disseminated and is characterized by low ti variable mn and locally high s concentrations of as v sb and zn are enriched in magnetite compared to marble host rocks and associated metavolcanic rocks carbon and oxygen isotope ratios of the marbles are consistent with water rock interaction between the marble protolith and a mixture of igneous fluids and seawater regional geology petrology and isotope data indicate that fe was introduced into the carbonate protolith as low temperature fe oxides and hydroxides via hydrothermal fluids discharged along basinal fracture zones on the sea floor related marble hosted zn fe mn deposits at franklin and sterling hill contain the assemblage willemite zincite franklinite stable isotope compositions of the zn deposits are consistent with alteration of host rocks by water rich fluids preserving protolith carbon isotope ratios stable isotope modeling suggests that zn silicate oxides or hydroxides represent an appropriate protolith for the high grade zn ores alteration of metavolcanic rocks at the fe deposits combined with the isotope data and other petrologic and geochemical evidence document the presence of an extensive hydrothermal system of grenville age centered in the western highlands metals precipitating from this hydrothermal system were responsible for fe in the marble hosted magnetite deposits and zn in the deposits at franklin and sterling hill from the same or a related hydrothermal system underplating of the back arc by mafic magma provided the heat to melt the lower crust and drive the hydrothermal system resulting in carbonate hosted fe and zn ore deposits and associated bimodal volcanism

source of copper in the giant shimensi w cu mo polymetallic deposit south china constraints from chalcopyrite geochemistry and oxygen fugacity of ore related granites abstract porphyry type copper mineralization is generally considered to be related to ore forming fluid exsolution from oxidized magnetite bearing intermediate to felsic magmas however copper deposits associated with ilmenite bearing per aluminous evolved granites also exist and their origin remains obscure the shimensi w cu mo polymetallic deposit located in the northern segment of the jiangnan orogen south china composed mainly of the neoproterozoic shuangqiaoshan group meta sediments volcanic rocks and biotite granite is one of the largest tungsten deposits in the world the w cu mo polymetallic orebodies occur at the contact zone between the mesozoic ilmenite bearing fluorite bearing f rich highly fractionated granite and the neoproterozoic granite the reason for the accompanying cu mineralization within ilmenite bearing granites is unclear in this paper we present a detailed study of chalcopyrite geochemistry including s pb isotopes trace elements and nd isotopes and oxygen fugacity fo2 of ore related granites in the shimensi deposit to constrain the origin of copper sulfur isotope values of the sulfides give a narrow 34s interval of 3 3 to 0 5 mean 1 5 n 32 suggesting the ore forming fluid is of magmatic origin the similarity of pb isotopes of the majority of sulfides and k feldspars from mesozoic granites indicates their genetic relationship however chalcopyrite samples show a wider range of pb isotopic compositions than that of k feldspars suggesting an extra source for the ore forming fluids chalcopyrite from the ore deposit show features of lree enriched patterns variable eu negative anomalies eu eu 0 26 0 75 and la sm n values 0 77 5 93 while the two figures for the mesozoic f rich evolved granites are eu eu 0 18 0 45 and la sm n 2 42 4 09 this along with and the larger range of end values 12 4 to 2 7 of the chalcopyrites than for the mesozoic granites and neoproterozoic granite therein 8 6 to 6 2 suggest that the ore forming fluids cannot be attributed to the mesozoic granites alone the local cu enriched neoproterozoic shuangqiaoshan group rocks should have contributed to the mineralization the low bulk rocks fe3 fe2 ratios 0 02 1 00 average 0 22 fe2 enriched biotite compositions fe2 fe3 5 64 143 average 22 combined with the low ce4 ce3 ratios 3 509 average 142 negative eu anomalies eu eu 0 05 0 56 average 0 25 and low fo2 fmq 3 4 1 9 fmq 1 5 1 7 for the mesozoic magmatic zircons suggest that the granites in the shimensi deposit are relatively reduced the low oxygen fugacity below nno of granites is favorable for significant tungsten mineralization accompanying by minor cu mineralization

geology mineralization stable isotope and fluid inclusion characteristics of the vostok 2 reduced w cu skarn and au w bi as stockwork deposit sikhote alin russia abstract the large 180 kt wo 3 and at least 10 15 t au vostok 2 deposit is situated in a metallogenic belt of w sn w au and au w deposits formed in late to post collisional tectonic environment after cessation of active subduction the deposit is related to an ilmenite series high k calc alkaline plutonic suite that by its petrologic signatures is transitional between those at w dominant and au dominant reduced intrusion related deposits consistently besides large w cu skarns of the reduced type the deposit incorporates quartz stockworks with significant au w bi mineralization also formed in a reduced environment the hydrothermal stages include prograde and retrograde essentially pyroxene skarns hydrosilicate amphibole chlorite quartz alteration and phyllic quartz sericite albite apatite and carbonate alteration assemblages these assemblages contain abundant scheelite associated with pyrrhotite chalcopyrite and at the phyllic stage also with bi minerals as bi sb te pb zn sulfides and sulfosalts as well as au mineralization the fluid evolution included hot high pressure 420 460 c 1 1 1 2 kbar low salinity 5 4 6 0 wt nacl equiv aqueous fluids at the retrograde skarn stage followed by lower temperature cyclic releases of high carbonic low salinity to non carbonic moderate salinity aqueous fluids at the hydrosilicate stage a high carbonic ch 4 dominated hot 350 380 c low salinity fluid was followed by cooler 300 350 c non carbonic moderate salinity 5 7 14 9 wt nacl equiv fluid at the phyllic stage a high carbonic co 2 dominated moderately hot 330 355 c 0 9 kbar low salinity fluid was followed by cooler 230 265 c non carbonic moderate salinity 6 6 12 0 wt nacl equiv fluid a homogenized magmatic source of water 18 o h2o 8 3 to 8 7 and a sedimentary source of sulfur 34 s 6 9 to 6 2 and carbon 13 c fluid 20 1 to 14 9 at the hydrosilicate stage are suggested a magmatic source of water 18 o 8 6 to 9 2 and a sedimentary source of sulfur 34 s 9 3 to 4 1 but a magmatic mantle to crustal derived source of carbon 13 c fluid 6 9 to 5 2 are envisaged for fluids that formed the early mineral assemblage of the phyllic stage then the role of sedimentary carbon again increased toward the intermediate 13 c fluid 16 4 to 14 5 and late 13 c fluid 16 3 to 14 7 phyllic mineral assemblages the magmatic differentiation was responsible for the fluid enrichment in w whereas au and bi could also have been sourced from mafic magma the decreasing temperatures together with elevated ca content in non boiling fluids promoted scheelite deposition at the early hydrothermal stages the most intense scheelite deposition at the phyllic stage was caused by co 2 removal due to boiling of co 2 rich fluids further cooling of non boiling fluids favoured joint deposition of scheelite bi and au

terminal pleistocene change in mammal communities in southeastern washington state usa abstract small mammal communities in western north america experienced declines in taxonomic richness across the late pleistocene to holocene transition pht a recent natural global warming event one community also experienced a decline in evenness and others replaced one species with a congener variability in response of small mammal communities to pht warming is apparent at the presently arid and xeric marmes site in the columbia basin of southeastern washington state megafauna were absent by about 13 000 cal yr bp evenness of small mammals declined about 11 700 cal yr bp and again about 11 400 cal yr bp whereas richness declined about 11 400 cal bp regional faunal turnover was however minimal among small bodied taxa local mammal communities are depauperate as a result of megafaunal extinctions and subsequent decreases in small mammal richness and evenness the latter chronologically corresponds with a decrease in primary productivity driven by increasing warmth and aridity more faunas must be studied in order to fully document the range of variability in the responses of mammalian communities to pht warming documentation of patterns in those responses will facilitate understanding and enhance predictive accuracy with respect to responses of mammalian communities to modern global warming

black mats spring fed streams and late glacial age recharge in the southern great basin black mats are prominent features of the late pleistocene and holocene stratigraphic record in the southern great basin faunal geochemical and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge ranging from wet meadows to shallow ponds small land snails such asgastrocopta tappanianaandvertigo berryiare the most common mollusk taxa present semiaquatic and aquatic taxa are less abundant and include catinellids fossaria parva gyraulus parvus and others living today in and around perennial seeps and ponds the ostracodescypridopsis okeechobiandscottia tumida typical of seeps and low discharge springs today as well as other taxa typical of springs and wetlands are common in the black mats several new species that lived in the saturated subsurface also are present but lacustrine ostracodes are absent the 13c values of organic matter in the black mats range from 12 to 26 reflecting contributions of tissue from both c3 sedges most shrubs and trees and c4 saltbush saltgrass plants carbon 14 dates on the humate fraction of 55 black mats fall between 11 800 to 6300 and 230014c yr b p to modern the total absence of mats in our sample between 6300 and 230014c yr b p likely reflects increased aridity associated with the mid holocene altithermal the oldest black mats date to 11 800 11 60014c yr b p and the peak in the14c black mat distribution falls at 10 00014c yr b p as the formation of black mats is spring related their abundance reflects refilling of valley aquifers starting no later than 11 800 and peaking after 11 00014c yr b p reactivation of spring fed channels shortly before 11 20014c yr b p is also apparent in the stratigraphic records from the las vegas and pahrump valleys this age distribution suggests that black mats and related spring fed channels in part may have formed in response to younger dryas yd age recharge in the region however the inception of black mat formation precedes that of the yd by at least 40014c yr and hydrological change is gradual not rapid