aeolian desertification in china s northeastern tibetan plateau understanding the present through the past abstract under a background of a significantly warming climate current aeolian desertification in china s northeastern tibetan plateau netp has been widely studied but disagreements related to its causes continue to persist in order to understand the present through the past this study determined the various phases of aeolian desertification in the netp based on the statistical analysis of 40 optically stimulated luminescence osl aeolian sand dates from 23 aeolian sections because the redistribution of aeolian sand by wind processes can reduce the number of older sand dates this research only affects exactly the past millennium following this we analyzed the relationships between aeolian desertification phases in conjunction with reconstructed climatic data results revealed three distinct aeolian desertification phases that approximately correspond to 1480 ce 1680 ce and 1800 ce respectively by comparing these dates to well established paleoclimate records we determined that these three aeolian desertification phases all occurred under a cold and dry climate background accordingly aeolian desertification in the netp today under its current warm and wet climate background can therefore be attributable to irrational human activities rather than rising temperatures accordingly we can infer that under the current warmer and wetter climate background aeolian desertification in the netp today can be reversed as long as human activities remain moderate even without the implementation of artificial revegetation initiatives

evaluating large eddy simulations using volume imaging lidar data the authors apply data analysis techniques that demonstrate the power of using volume imaging lidar observations to evaluate several aspects of large eddy simulations less they present observations and simulations of an intense and spatially evolving convective boundary layer on 13 january 1998 during the lakeinduced convection experiment lake ice to enable comparison of observed and simulated eddy structure aerosol scattering was estimated from les output of relative humidity a passive tracer and liquid water spatial and temporal correlation functions of aerosol structure from horizontal planes reveal the mean and turbulent convective structure the correlation functions of the observed and simulated aerosol backscatter are presented as a function of altitude and offshore distance best fit ellipses to the closed contours encircling the origin of the correlation functions are used to obtain the mean ellipticity and orientation of the structures the authors demonstrate that these two parameters are not sensitive to minor changes in the functional relationship between humidity and optical scattering the lidar derived mean wind field is used as a reference for evaluating the les mean flow the ellipses from lidar data indicate that structures near the surface tend to be aligned with the mean wind direction while in the entrainment zone they are aligned perpendicular to the mean wind direction in the middle of the mixed layer convective plumes tended to be circular and therefore had no preferred orientation at small lags at longer lags however the correlation functions from the middle of the mixed layer show that the observed convective plumes were organized into linear bands oriented perpendicular to the mean wind direction the perpendicular bands suggest the important role of gravity waves in organizing convective structures the study shows that the model generates reasonable coherent structures open cells where the les technique is expected to perform poorly near the surface and fails to capture the wind perpendicular organization of closed cells in the middle of the mixed layer where the les technique is expected to be robust the authors attribute this failure to the boundary conditions that limited the growth of waves above the mixed layer

the mesoproterozoic copperwood sedimentary rock hosted stratiform copper deposit upper peninsula michigan copperwood is located in gogebic county upper peninsula michigan within the porcupine mountains copper district it was discovered in 1956 and in 2008 orvana minerals corp began exploration and development work with production projected in the near future stratiform copper mineralization is hosted by gray to black shales and siltstones of the basal nonesuch formation copper mineralization is overlain by laminated gray siltstones of the nonesuch formation and is underlain by red bed sandstones conglomerates and minor siltstones of the copper harbor formation these rocks are part of a thick section of clastic sedimentary rocks that comprise the upper fill of the mesoproterozoic 1 1 1 0 ga midcontinent rift the copper deposit is a tabular body that averages 2 5 m thick lacks significant basal undulations and dips 8 to 12 northward on the southwest limb of the western syncline an open fold with a shallow plunge to the northwest chalcocite is the only cu bearing mineral in the orebody and occurs as concentrations along stratigraphic laminations and as disseminated grains within the orebody there is no mineral or metal zoning cu ag and s are strongly enriched zn is very slightly enriched and pb and co lack enrichment gangue minerals in the orebody are quartz clinochore muscovite illite plagioclase k feldspar calcite and hematite which are consistent with temperatures of less than 130 c only one significant fault a shallow nw dipping reverse fault with displacement of up to 7 m has disturbed the section the mineralized zone at copperwood is stratigraphically equivalent to that at the white pine mine but copperwood lacks the structural complexity and the hydrothermal overprint manifested by the native cu mineralization at white pine reported canadian national instrument 43 101 compliant measured indicated and inferred resources are 33 million metric tonnes mt of 1 60 cu and 4 1 ppm ag for total contained cu of about 1 165 billion lb and 4 32 moz of ag the characteristics of copperwood are consistent with those of reduced facies or kupferschiefer type sedimentary rock hosted stratiform copper deposits the proposed genetic model is chalcocite replacement of pyrite in unlithified sediments during diagenesis as a result of emanating upward focused compaction driven cu bearing saline basinal waters with cu leached from the underlying red bed paleoquifer the simplicity of the mineralizing event and the undeformed nature of the deposit distinguish copperwood from most other examples of reduced facies or kupferschiefer type sedimentary rock hosted stratiform copper deposits throughout the world

volume imaging lidar observations of the convective structure surrounding the flight path of a flux measuring aircraft the university of wisconsin volume imaging lidar has been used to portray images of the three dimensional structure of clear air convective plumes in the atmosphere surrounding the flight path of the instrumented twin otter aircraft operated by the national aeronautical establishment nae of canada lidar images provide a context for interpretation of the aircraft measurements the position of data points within a convective element can be determined and the temporal development of the plume can be observed to time the observation with respect to the life cycle of the plume plots of the vertical flux of water vapor q w superimposed on lidar images clearly demonstrate the well known sampling difficulties encountered when attempting to measure fluxes near the top of the convective layer when loran was used to determine average aircraft velocity flight leg averaged horizontal winds measured by the aircraft and area averaged winds measured by lidar agree to within 0 2 m s 1 in speed and 1 in direction

calculation of area averaged vertical profiles of the horizontal wind velocity from volume imaging lidar data area averaged horizontal wind measurements are derived from the motion of spatial inhomogeneities in aerosol backscattering observed with a volume imaging lidar spatial averaging provides high precision reducing sample variations of wind measurements well below the level of turbulent fluctuations even under conditions of very light mean winds and strong convection or under the difficult conditions represented by roll convection wind velocities are measured using the two dimensional spatial cross correlation computed between successive horizontal plane maps of aerosol backscattering assembled from three dimensional lidar scans prior to calculation of the correlation function three crucial steps are performed 1 the scans are corrected for image distortion by the wind during a finite scan time 2 a temporal high pass median filtering is applied to eliminate structures that do not move with the wind and 3 a histogram equalization is employed to reduce biases to the brightest features

the 1100ma sturgeon falls paleosol revisited implications for mesoproterozoic weathering environments and atmospheric co2 levels abstract during the active rifting stage of the 1100 ma midcontinental rift in north america alluvial sediments were deposited intermittently between basalt flows on the north and south shores of present day lake superior at times of depositional quiescence paleosols developed in both areas on the alluvial sediments and on the antecedent basalt new results from the sturgeon falls paleosol in michigan characterizing the weathering processes at the time of its formation indicate moderate maturity high degrees of hydrolysis and leaching and a low degree of salinization geochemical provenance indices indicate a homogeneous source for the paleosols and in contrast to earlier work there is little evidence for k metasomatism as a result atmospheric co 2 levels of 4 6 pre industrial atmospheric levels were calculated using a mass balance model this result is consistent with previous calculations from nearly contemporaneous paleosols from the other side of the keweenawan rift and from the 100 ma younger sheigra paleosol in scotland the calculated co 2 values are also consistent with the calculated weathering environment proxies that indicate weak to moderate weathering at this time frame and suggest that the higher greenhouse gas loads indicated by paleoproterozoic paleosols had dissipated by the mid late mesoproterozoic

high altitude aeolian research on the tibetan plateau aeolian processes and their role in desertification have been studied extensively at low elevations but have been rarely studied at high elevations in areas such as the tibetan plateau where aeolian processes were active in the geologic past and remain active today in this review we summarize research that improves our understanding of aeolian processes on the tibetan plateau including the distribution characteristics and provenance of aeolian sediments the history of aeolian activity aeolian geomorphology and wind driven land degradation contemporary aeolian processes primarily occur in dry basins in wide river valleys on lakeshores on mountain slopes and on gravel pavements sediment characteristics suggest a local origin and provide interesting contrasts with those of china s loess plateau the history of aeolian activity and its paleoclimatic implications reconstructed based on aeolian archives is short mostly since the late glacial and shows wide regional differences aeolian geomorphology is simple and suggests short formation time wind driven land degradation is less severe than previously thought driven by different factors in different areas and exhibited complex interactions with freeze thaw processes aeolian research has been conducted within the general framework of aeolian science but addresses issues specific to the tibetan plateau that arise due to the low air temperature low air density and the presence of a cryosphere we propose six priorities for future research aeolian physics the effect of freeze thaw cycles comparisons with other areas regional differences effects of wind driven land degradation and integrated observation and monitoring

environmental conditions in the donggi cona lake catchment ne tibetan plateau based on factor analysis of geochemical data abstract we present a methodological approach for the characterization of spatial variations of environmental and transport conditions based on geochemical data we analyzed the geochemical characteristics of terrestrial sediments on an alluvial fan and adjacent areas in the eastern part of the donggi cona catchment the geochemical characteristics of the sediment samples were measured using x ray fluorescence spectroscopy a factor model based on nine elements sr rb zn fe mn v ti ca and k gave the best results using factor analysis our results show that factor analysis of geochemical data can explain spatial variations in the catchment even within a relatively small area with more or less constant climatological conditions the four most important factors of our model explain 68 4 of the total variance within the dataset the four factors represent a carbonate weathering and two redox condition signals respectively the spatial distribution of factor loadings points to regions with specific environmental conditions these regions show a certain carbonate input or production factor 1 specific weathering rates factor 2 or specific redox conditions factors 3 and 4 the factor loadings of the first and second factor are used to reclassify the data into four groups being dune loess lake and fluvial gravel sediments this reclassification confirms or improves the prior field classification in 70 of all cases for 23 of the samples the model gave a different interpretation the factor loadings in these cases represent the origin of the material rather than its present sediment type thereby giving valuable information about sediment provenance since the third and fourth factor seem more dependent on location they do not differentiate between different sediment types multivariate statistics of the geochemistry of terrestrial sediments i allows the subdivision of samples into different sediment types ii indicates dominant regions for weathering carbonate production and manganese washout and iii gives suggestions about the provenance of the sediments this is the first detailed study of geochemical parameters on the tibetan plateau not focusing on lake cores resulting in a spatial characterization of the local geochemistry this gives insight in the sediment transport connections between the catchment and the lake illustrating the value of terrestrial sediments as additional indicator of environmental variations

causes and processes of sandy desertification in guinan county qinghai tibet plateau by means of field investigations interpretation of remote sensing images analysis of a digital elevation model and grain size tests we analyzed the causes and processes responsible for sandy desertification in guinan county on the qinghai tibet plateau the desertified land is mainly distributed on the mugetan region and covered 566 km2 about 96 1 of which distributed on the sandy hills we found that reactivation of the underlying fossil dunes supplied the sand that contributed to modern sandy desertification the surface turf which supports a dense growth of grass and its matted roots covers the underlying cohesive silty sands in the sandy hills and both layers protect the dunes against erosion mechanical destruction of the protective shell leads to exposure of fossil dune sands the exposed loose fossil sands are then carried away by the wind creating scarps followed by lateral recession at the bottom of the scarp leading to its collapse the process then repeats with the expansion of recession caused by wind erosion abundant sands are supplied and aeolian activity intensifies repetition of this process expands the blowouts leading to merger of the blowouts and the evolution of mobile dunes similar processes occur at the top of cliffs above the yellow river and mangla river

the midcontinent rift in the lake superior region with emphasis on its geodynamic evolution abstract the midcontinent rift is a middle proterozoic continental rift which records about 15 m y of extension subsidence and voluminous volcanism in the period 1109 1094 ma in the central part of north america during that time the crust was nearly totally separated and as much as 25 km of subaerial basalts accumulated in a deep central depression following extension and volcanism a longer period of subsidence resulted in development of a post rift sedimentary basin in which as much a 8 km of fluvial and lacustrine clastic rocks were deposited partial inversion of the central depression occurred about 30 50 m y after extension to produce the current configuration of a central horst composed mostly of thick volcanic accumulations between shallower flanking basins

geochemistry and geochronology of native copper mineralization related to the emeishan flood basalts yunnan province china abstract native copper mineralization in northeastern yunnan is related to the emeishan flood basalts which have high cu background concentrations the deposits are located in the ludian maoling and yiche synclines between the flood basalts and the overlying xuanwei formation evidence from ree and hsfe concentrations oxygen isotope compositions bitumen reflectance and mineral paragenesis indicates that the high grade copper orebodies were deposited from moderate to low temperature hydrothermal solutions 420 to 100 c in a reducing environment 40 ar 39 ar spectra for the laumontites that coexist with native copper in the high grade ores yield consistent plateau and isochron ages 226 to 228 ma these are interpreted to represent the age of the first stage of hydrothermal mineralization which took place at temperatures of 200 to350 c concordant with that of zn pb ag ge mineralization also occurring in the area the heulandites yield a stable 40 ar 39 ar plateau age of 134 0 1 7 ma consistent with isochron ages indicated by u th pb isotopic systematics indicating a second stage of native copper mineralization at lower temperatures 100 to 200 c that took place during the early cretaceous

genesis of native copper lodes in the keweenaw district northern michigan a hybrid evolved meteoric and metamophogenic model the keweenaw peninsula of northern michigan is well known for early diagenetic sulfide dominant sediment hosted stratiform copper mineralization hosted mainly by basal siltstone shale units of the nonesuch formation in the white pine district and later native copper lodes hosted mainly by flow top breccias and amygdaloidal portions of flood basalts and interbedded conglomerates of the stratigraphically lower portage lake volcanics the native copper mineralization is generally attributed to downdip burial metamorphism of the host strata an alternative model is proposed here involving a complementary influx of evolved meteoric water elevated in salinity and progressively equilibrating with its aquifers similar to the fluid which formed the white pine mineralization this model has several advantages over the metamorphogenic model alone it would provide the salinity by dissolution of evaporites and moderately oxidizing conditions as a result of hematitization i e reddening of coarse continental rift sediments necessary for copper transport and the evolved meteoric water would have been an important cupriferous brine owing to the leaching of trace amounts of copper from the voluminous aquifers further reduction of the evolved fluid would also explain the updip deposition of native copper in association with dehematitized pumpellyite and chlorite dominant i e reduced hydrothermal mineral assemblages at the same time this influx of meteoric water from highlands adjacent to the keweenaw rift basin would have provided a mechanism to move the deep seated hot dense ore brine upward along the aquifers of the portage lake volcanics on its ascent from deep portions of the rift basin the gravity driven evolved meteoric brine would have mixed with the fluid generated by burial metamorphism to form a hybrid evolved meteoric metamorphogenic oreforming hydrothermal brine

post rift deformation of the midcontinent rift under grenville tectonism abstract using a thin viscous sheet model we investigate the hypothesis that compressive stresses resulting from the grenville orogeny caused uplift along the midcontinent rift the objective of this study is to investigate factors involved in shaping the post rift structure of the midcontinent rift including the size and location of the colliding terranes and the convergence angle between the colliding terranes and the north american craton we find a linear relationship between the size of the terrane and the deformation within the midcontinent rift the calculations predict comparable deformation along both the eastern and western arms of the midcontinent rift our results demonstrate that the geologically indicated ne sw deformation can be produced without a multistage compression event because of the nonlinear interaction of far field compressive stress and the mechanically weak rift therefore it is not possible to determine which compression direction is representative of the compression associated with the grenvillian orogenic event based on the post rift pattern of deformation

characterisation of transport processes and sedimentary deposits by statistical end member mixing analysis of terrestrial sediments in the donggi cona lake catchment ne tibetan plateau abstract unmixing of grain size distributions with multivariate statistical analysis gives indications of the main sediment transport processes and related environmental conditions in an area we performed end member mixing analysis emma of sedimentological data from 912 terrestrial sediment samples collected in the donggi cona catchment north eastern tibetan plateau up to the present this is the largest sedimentological dataset on the tibetan plateau emma resulted in the characterisation of three end members that explain 88 of the variance within the dataset the end members all represent aeolian deposits the first end member em 1 represents very fine dune sediments that were deflated from a former lake system em 2 represents medium sand deposits that were blown out from playa and alluvial fan sediments em 3 represents fine loess like sediments mainly found at higher elevations different transformations adding of a fourth end member and adding of up to 200 loess samples do not change the composition of the end members demonstrating the robustness of the model emma allows the synchronous interpretation of very large datasets resulting in a general characterisation of sediment transport in a particular area performing emma on the dataset demonstrates the importance of aeolian transport in this part of the world

organic matter and copper mineralization at white pine michigan u s a mauk j l and hieshima g b 1992 organic matter and copper mineralization at white pine michigan u s a in p a meyers l m pratt and b nagy guest editors geochemistry of metalliferous black shales chem geol 99 189211 indigenous and exogenous organic matter in sediments of the north american midcontinent rift were involved in precipitation of cu bearing minerals during main and second stage mineralization events at white pine michigan samples of the proterozoic nonesuch formation from the white pine mine and adjacent areas were investigated petrographically and geochemically in order to determine the influence of organic matter on the precipitation of cu and to determine whether mineralization influenced thermal maturity of organic matter during main stage mineralization introduction of cupriferous fluids into the lower nonesuch fro formed cu bearing sulfides by replacement of pyrite sulfur may have been added to the system via abiogenic sulfate reduction with organic matter providing a direct source of reducing potential in basal ore horizons where all sulfide had been incorporated into chalcocite during main stage mineralization native cu also precipitated locally with organic matter presumably acting as a direct reductant later compressional faulting at white pine provided conduits for additional cupriferous fluids these fluids deposited second stage cu mineralization inclusions of liquid petroleum and solid pyrobitumen in veins filling fractures associated with compressional faults record migration of petroleum into the white pine district from the deeper hotter axis of the rift penecontemporaneous with second stage fluids some of this petroleum may have acted as a reductant during precipitation of native cu in basal ore horizons biomarker compositions of bitumens and isotopic compositions of individual n alkanes from petroleums and bitumens suggest that these materials were all derived from organic matter deposited during sedimentation of the nonesuch fro biomarker data demonstrate that bitumens from the white pine area have significantly higher levels of thermal maturity than bitumens from unmineralized strata outside the mine area therefore cu mineralization at white pine coincides with a thermal anomaly seep petroleums from the northeast and southwest domains of the mine contain different n alkane distributions we propose that this difference reflects elevated thermal maturity of seep petroleums spatially associated with second stage mineralization in the southwestern domain of the mine

paleomagnetism of the native copper mineralization keweenaw peninsula michigan the age and genesis of michigan s world class native copper deposits are poorly constrained the copper is hosted by basaltic flow tops and conglomeratic interbeds of the 1095 2 ma keweenawan por

formation of sedimentary rock hosted stratiform copper deposits through earth history sedimentary rock hosted stratiform copper deposits form by movement of oxidized copper bearing fluids across a reduction front that results in the precipitation of copper sulfides large scale production of such oxidized fluids as well as the formation of mobile hydrocarbons oil has probably been common since the formation of the first red beds in the paleoproterozoic and deposits of this type occur in rocks from the paleoproterozoic to the tertiary however supergiant deposits are currently recognized in only three basins the paleoproterozoic kodaro udokan basin of siberia the neoproterozoic katangan basin of south central africa and the permian zechstein basin of northern europe the paucity of data regarding the udokan deposit makes understanding this system difficult in terms of earth history events both the neoproterozoic and the permian were times of supercontinent breakup with major landmasses at low latitudes this global tectonic framework favored the formation of failed rifts that subsequently became significant intracratonic basins with basal synrift red bed sequences overlain by marine and or lacustrine sediments and in some basins located at low latitudes by thick evaporitic strata the intracratonic setting of these basins allowed the development of a hydrologically closed basinal architecture in which highly oxidized and saline moderate temperature basinal brines were produced that were capable of supplying reduction controlled sulfide precipitation over very long time periods tens to hundreds of millions of years the length of time available for the mineralizing process may be the key factor necessary to form supergiant deposits however examination of the absolute ages for the kupferschiefer zechstein basin and katangan deposits allows speculation that other factors may also have been important both the neoproterozoic and permian were times of major glacial events glaciation may also be conducive for the formation of supergiant sediment hosted stratiform copper deposits glacial periods correspond to magnesium and sulfate rich oceans that could have been responsible for additional sulfur in basinal brines developed during evaporite formation and would then be available during the long mineralization process

geological controls of copper gold and silver in the serra geral group realeza region parana brazil abstract the serra geral group has high cu concentrations in southern brazil including the realeza parana region where au and ag also occur the basalts 46 7 50 8 wt sio 2 have breccias at the top of 10 out of 31 studied flows in the realeza section and at the top of 5 out of 7 analyzed flows in the capanema section sand injectites occur at the top of basalts in 18 out of 23 flows from the realeza section the average content of cu in three samples of mineralized breccias is 3788 ppm one sample from a silicified sandstone sill intruded at the top of a basalt flow has up to 0 66 ppm au k 2 o was not leached during basalt alteration the hydrothermal breccias particularly when sand is present show enrichment in u which leads to higher values of scintillometry rate of emission of k u and th in the basalts breccias and sandstones pd 17 5 8 4 ppb is higher than pt 12 5 5 ppb suggesting a hydrothermal remobilization of the metals the serra geral group is thus shown to have high potential for precious and base metal deposits

district scale concentration of native copper lodes from a tectonically induced thermal plume of ore fluids on the keweenaw peninsula northern michigan economic native copper lodes in the lake superior district are confined to a 45 km long portion of the portage lake volcanics on the keweenaw peninsula despite similar host rocks extending for more than 1 000 km around lake superior the focus of ascending ore forming brine into a narrow segment of portage lake strata may be attributed to upward thrusting on the keweenaw fault during closure of the midcontinent rift forming anomalously hot steeply dipping aquifers on the keweenaw promontory and to the development of a single dominant thermal plume within the incipiently buoyant brine at the scale of the mine district on that promontory

comment on paleozoic reactivation structures in the appalachian ouachita marathon foreland far field deformation across pangea by j craddock d malone r porter j compton j luczaj a konstantinou j day and s johnston earth science reviews 169 2017 1 34

holocene aeolian activity in the headwater region of the yellow river northeast tibet plateau china a first approach by using osl dating abstract the headwater region of the yellow river hryr is the catchment upstream of duoshi gorge covering an area of 29 588 km2 the hryr is located in the northeastern tibet plateau with an altitude higher than 4000 m above sea level and is especially sensitive to climate change since the late 19th century the mean annual temperature in tibet plateau has increased sharply as a result of increasing air temperature a significant number of environmental problems have occurred during the past decades including aeolian desertification in recent decades aeolian desertification has become a severe environmental problem in the tibet plateau due to permafrost degradation because permafrost plays an important role in maintaining the grassland vegetation with the increase in ground temperature the aeolian activity in the hryr is likely to become more serious however the history of aeolian activity in the hryr remains unknown due to a lack of chronological studies in this study 15 optical stimulated luminescence osl ages from three typical sections were used to reveal the history of aeolian activities in the hryr during the holocene all of the osl ages were late holocene and the oldest age is 2 13 0 16 ka bp the relative young osl ages and deep aeolian sediment indicated very high sedimentation rates in the late holocene especially after around 1 ka bp the intensive aeolian activity and low toc content indicate a drier climate in the late holocene the well sorted sediments and similar grain size distributions of the three sections imply their similar wind regimes based on the evolution history of the yellow river s headward erosion it is inferred that little aeolian activity occurred in this region during the early and mid holocene

atmospheric boundary layer studies in fife challenges and advances in a brief review and introduction of 13 other articles concerning the atmospheric boundary layer abl attention is focused on challenges and advances in experimental design and analysis represented by those studies which are part of the first international satellite land surface climatology project islscp field experiment fife the articles not only address problems posed by the experimental site itself size inhomogeneity of terrain and vegetation but also examine relationships between the abl and remote sensing measurements they also scrutinize various abl data for internal consistency for example in budget studies and for comparisons with other abl results and with data from surface measurements finally new and existing analysis techniques are presented and evaluated for example for abl self preservation extraction of wind velocities from lidar reflectivity data estimation of surface heat flux from doppler lidar data two dimensional maps of abl and surface variables sensitivity of aircraft data to surface variations and contribution of individual abl structures to flight level fluxes besides adding to our understanding of abl processes the studies point out several problems that need to be addressed by the measurement and modeling communities

age of native copper mineralization keweenaw peninsula michigan amygdaloidal flood basalts and conglomerates are the host for substantial deposits of native copper within the portage lake volcanics in the keweenaw peninsula of michigan a wide variety of gangue minerals are associated with the regional hydrothermal alteration mineralization event application of the rb sr method to amygdule filling microcline calcite epidote and chlorite suggests an age of mineralization between 1 060 and 1 047 m y or asymp 20 m y these results are supported by a fission track age on epidote of 1 044 or 169 m y the age of native copper mineralization determined in this study is consistent with geologic evidence which suggests that mineralization postdated the deposition of most or all of the overlying freda sandstone variable initial 87 sr 86 sr ratios between the low rb sr phases suggest mixing of isotopically distinct sources of sr during the generation and equilibration of the hydrothermal solutions

pedogenesis permafrost substrate and topography plot and landscape scale interrelations of weathering processes on the central eastern tibetan plateau article i nfo weathering indices wi and pedogenic oxidesratios por were used to describe patterns of weathering inten sities and pedogenesis along climatic gradients mainly affected by varying influences of the asian and indian monsoon these climate settings induce particular soil moisture sm conditions in turn closely related to per mafrost state substrate and topography nine sites including a total of 30 soil profiles were examined along an eastern and a western transect across the central eastern qinghai tibet plateau additionally differences between four soil groups were analysed according to our knowledge the presented study is the first attempt of a comprehensive application of different wi and por to substrates of currently permafrost affected soils it providesanevaluation ofvarious tools intermsof chemicallydescribinganddifferentiating the relatedprocesses todistinctenvironmentalsettingsinlow weatheringregions wefoundthatweatheringtrendsalongtheclimat ic gradients could be clearly outlined by wi whereas por rather account for small scale variations describing significant differences of pedogenesis between continuous and discontinuous permafrost conditions pyrophos phate soluble iron fep proved to be useful for differentiating permafrost and ground water influenced soils showing a strong correlation to total organic carbon r 0 89 the chemical index of alteration cia is the

titaniferous accessory minerals in very low grade metamorphic rocks keweenaw peninsula michigan usa abstract titanite tio 2 and pseudorutile are associated with primary igneous fe oxide grains in basalt and rhyolite clasts from the keweenaw peninsula michigan usa which were metamorphosed to the prehnite pumpellyite facies pseudorutile occurs with titanite tio 2 in broad lamellae within titaniferous magnetites it also occurs as intergrowths with titanite and fe oxide in embayments within primary oxide grains and in composite fe oxide titanite grains that appear to represent nearly complete replacement of original ti bearing fe oxides thin 111 lamellae in titaniferous magnetite grains contain titanite titanite tio 2 and titanite tio 2 fe oxide tio 2 also occurs by itself in networks of closely spaced small elongated lenses in fe ti oxides concentrations of caalsio 4 f caalsio 4 oh in titanite range from 0 to 30 the large variation in titanite compositions suggests that equilibrium was not achieved except on a very local scale a conclusion also supported by local variations in the assemblages of ti bearing secondary minerals textures and mineral assemblages indicate that ulvospinel lamellae were altered to titanite and or tio 2 polymorphs while ilmenite was altered to pseudorutile and titanite tio 2 the relative proportions of tio 2 and titanite appear to reflect local variations in the composition of the metamorphic fluid phase that may be linked to the degree of interaction with a hydrothermal fluid titanite rich regions may indicate a greater degree of fluid flushing than tio 2 rich regions textures and mineral assemblages cannot distinguish between models in which pseudorutile and a tio 2 polymorph formed during weathering or diagenesis followed by conversion of tio 2 to titanite during metamorphism and models in which pseudorutile formed together with titanite and tio 2 during metamorphism in either case pseudorutile was able to persist through prehnite pumpellyite metamorphism suggesting that it can be a significant ti rich accessory mineral in very low grade metamorphic rocks

the effect of climate warming and permafrost thaw on desertification in the qinghai tibetan plateau abstract four sets of remote sensing images from 1987 1994 2000 and 2006 50 years of meteorological and soil moisture data corresponding to different desertified lands were combined with populations and livestock data to analyze the process and cause of desertification in a portion of the qinghai tibetan plateau qtp it showed that surface soil temperature in the region has increased at an average rate of 0 6 c per decade between 1980 and 2005 the thawing days on the surface have increased by 60 days from 1983 to 2001 and the depth of the seasonal thawing layer has increased by 54 cm 102 cm and 77 cm in april may and june respectively from 1983 to 2003 as a result the upper soil layer has become drier due to the thickening active layer and soil water infiltration these changes in turn have inhibited the growth of alpine meadow vegetation that has shallow root systems it is concluded that climate warming and permafrost thawing have caused desertification in grazing regions of the qinghai tibetan plateau qtp

geomorphological and palaeoclimate dynamics recorded by the formation of aeolian archives on the tibetan plateau abstract aeolian sediments are an important archive for palaeoclimate reconstructions on the tibetan plateau the accumulation of aeolian sediments and the formation of palaeosols are used as a proxy for dry and wet phases respectively during the last decade the number of osl optically stimulated luminescence ages of aeolian sediments has been rapidly increasing this study summarises the results from more than 300 individual osl ages despite the widespread occurrence of aeolian sediments on the tibetan plateau nearly all osl samples are located on the northeastern and the southern part in most regions the strongest accumulation occurred during the late glacial and in the early holocene this coincides with the strengthening of the asian summer monsoon on the tibetan plateau and wetter climate conditions after the relatively dry glacial times the development of a sufficient vegetation cover acting as a sediment trap seems to be an important requirement for the preservation of aeolian archives short dry periods like the younger dryas led to a more enhanced aeolian accumulation without destruction of previously formed archives in some regions the formation of palaeosols occurred mainly during the wet early and mid holocene but the number of ages is relatively small in contrast a second phase of aeolian accumulation during the late holocene was related to the weakening of the asian summer monsoon and drier climate conditions this indicates that the reaction of aeolian accumulation on the tibetan plateau depends on the previous climate state a comparison between the osl ages from aeolian sands and loess deposits yields a different timing of deposition of these two sediment types while the sand deposits in different basins resemble wet and dry phases loess deposits show no common signal between the analysed areas this indicates an influence of local factors such as varying source areas and erosive processes on the slopes in general the aeolian archives in the high mountain environment are governed by numerous factors besides the climatic influence

structure of the atmosphere in an urban planetary boundary layer from lidar and radiosonde observations the planetary boundary layer pbl over mexico city was probed with a scanning backscatter lidar to characterize and evaluate the multidimensional structure of the atmosphere comparisons were made between radiosonde and lidar derived pbl heights which showed the two techniques to be in close agreement the spatial properties of the free atmosphere pbl interface were found to be approximately the same size as the entrainment zone thickness below the interface the lidar observed spatially resolved structures such as thermal plumes convective eddies low level jets and entrainment into the pbl these structures were spatially correlated with the local diabatic condition and wind stress one highly unstable atmosphere contains a lidar visualized convective structure rising to a height of 0 45 the inversion base which was predicted from earlier turbulence models other features such as low level jets were found to be associated with neutral atmospheres in the mixing layer the analysis indicates that the transport of pollutants is not a continuous and gradient driven process but low frequency and spatially discontinuous the high spatial and temporal resolution afforded by the scanning lidar depicts surface atmosphere interactions which are neither spatially homogeneous nor horizontally uniform

crustal scale thrusting and origin of the montreal river monocline a 35 km thick cross section of the midcontinent rift in northern michigan and wisconsin a structurally simple 35 km thick north facing stratigraphic succession of late archean to middle proterozoic rocks is exposed near the montreal river which forms the border between northern wisconsin and michigan this structure the montreal river monocline is composed of steeply dipping to vertical sedimentary rocks and flood basalts of the keweenawan supergroup middle proterozoic along the south limb of the midcontinent rift and disconformably underlying sedimentary rocks of the marquette range supergroup early proterozoic these rocks lie on an archean granite greenstone complex about 10 km of which is included in the monocline this remarkable thickness of rocks appears to be essentially structurally intact and lacks evidence of tectonic thickening or repetition tilting to form the monocline resulted from southward thrusting on listric faults of crustal dimension the faults responsible for the monocline are newly recognized components of a well known regional fault system that partly closed and inverted the midcontinent rift system resetting of biotite ages on the upper plate of the faults indicates that faulting and uplift occurred at about 1060 20 ma and followed very shortly after extension that formed the midcontinent rift system

hydrothermal native copper in ocean island alkali basalt from the mineoka belt boso peninsula central japan native copper grains are found in aphyric amygdaloidal basalt of early miocene age ca 20 ma in the southern mineoka belt of boso peninsula central japan the native copper was precipitated in the amygdules or veins along with calcite and analcime the temperature of precipitation and salinity of the fluids related to the native copper are approximately 133 to 183 c and 0 9 to 3 9 wt as estimated by fluid inclusions trapped in the calcite containing grains of the native copper the native copper is interpreted as related to low temperature reducing alkaline hydrothermal fluids a sulfur poor environment is inferred by the lack of sulfur bearing minerals the host rock of the mineoka native copper is alkali basalt of oceanic island affinity native copper is well known to occur in mid ocean ridge island arc oceanic island tholeiitic basalts and continental tholeiitic basalt but this is the first detailed description of an occurrence in ocean island alkali basalt

accuracy analysis of wind profiles calculated from volume imaging lidar data this paper presents a study of the vertical profiles of horizontal mean winds calculated from data obtained with the university of wisconsin volume imaging lidar vil during the 1989 first international satellite land surface climatology project islscp field experiment program wind profiles are determined from cross correlation functions between subsequent constant altitude plan position indicator planes calculated from volume scans of the convective boundary layer an objective technique to identify unreliable measurements is developed an error analysis based on determining the errors due to random noise in the data is performed the vil wind profiles are compared with radiosonde aircraft based and ground based measurements on the basis of internal consistency tests we estimate that in the convective boundary layer the hourly averaged vil wind estimates which have passed the reliability analysis have root mean square errors of 0 03 0 1 ms 1 in speed and 0 4 2 0 in direction

calculation of divergence and vertical motion from volume imaging lidar data boundary layer divergences are calculated from a sequence of images of the inhomogeneities in aerosol backscattering observed with volume imaging lidar two dimensional spatial cross correlations are calculated between successive horizontal plane images 10 km 5 km which are interpolated from the lidar returns the image at the first time represents the actual aerosol pattern an assumed divergence is included in the interpolation of the second image the divergence is determined by calculating correlations for a matrix of assumed divergences and selecting that value which optimizes the correlation the results from this process are consistent with predictions for divergence over the spatial scale measured and the apparent resolution of the results agrees with the image resolution a higher pulse rate volume imaging lidar system would allow for increased image resolution and increased image area both of which should improve the resolution in the divergence measurements

assessment of aeolian desertification trends from 1975 s to 2005 s in the watershed of the longyangxia reservoir in the upper reaches of china s yellow river abstract global climate change will affect the ecology and environment of the qinghai tibet plateau thus increasing attention is being paid to the aeolian desertification that is occurring in the watershed that supplies the longyangxia reservoir in the upper reaches of china s yellow river we must assess the aeolian desertification trends before developing a plan to restore the region s degraded eco environment in this study land suffered from aeolian desertification was classified into four levels slight moderate severe and extremely severe using a series of indices interpretation of landsat mss and tm data from 1975 s 1989 s and 2005 s was used to establish databases of aeolian desertified land at these three times we then derived the aeolian desertification trends during the study period by overlaying the consecutive databases and we analyzed the driving factors responsible for the observed aeolian desertification the results show a total of 1 721 478 02 ha of aeolian desertified land in 2005 s accounting for 13 of the region s total area from 1975 s to 1989 s the area of aeolian desertified land increased by 229 307 26 ha which represents a 15 increase compared to the 1975 s area and from 1989 s to 2005 s the area of aeolian desertified land decreased by 19 079 87 ha which represents a 1 decrease compared to the 1989 s area the main driving factors responsible for this increased aeolian desertification were climate factors high wind velocity and an increase in annual temperature combined with low precipitation and high evaporation as well as unsustainable human activities and inappropriate policy measures a series of key national projects initiated to combat degradation of the study area s eco environment led to a decrease of aeolian desertified land through obvious restoration of vegetation

dry periods on the ne tibetan plateau during the late quaternary abstract environmental conditions on the tibetan plateau are changing rapidly this study reconstructs late quaternary environmental changes on the northeastern tibetan plateau based on sand deposits the study area is located close to the present maximum extent of the east asian summer monsoon and is likely to register shifts in monsoon extent furthermore different sediment deposits are available that allow reconstruction of sediment pathways between the different archives sediment deposition in the catchment is dominated by deposition of sand sandy deposits in the form of dune fields and sand sheets are widespread on the northeastern tibetan plateau and are an important archive for paleoclimatic reconstruction this study shows that sand deposits on the northeastern tibetan plateau are local phenomena that still bear the sedimentological and geochemical fingerprint of their source materials reconstruction of transport processes in the local sediment cascade shows that local sand deposits are the main source of tibetan mountain loess six long sections were sampled and analysed for their geochemical and sedimentological characteristics showing that both sand and loess deposits have a local source a special focus was placed on the manganese concentration and the related environmental implications in several sections an increase in mn concentration from 318 44 to 878 294 ppm was found independent of concentrations in fe and organic compounds since the increase in mn is caused by solid mn3 and mn4 alone it is interpreted as increased dust input the synchronicity with climatic variations on the northeastern tibetan plateau confirms the climatic interpretation of the variations in mn sand and dust transport both took place around 11 ka followed by a period of fixation or even erosion of sediments although increased sand transport in the catchment already started around 3 ka the increased dust input did not take place before 0 7 ka therefore the mn concentrations are interpreted as an indication of increased dust transport during the very late holocene related to colder and drier circumstances during that time the use of manganese as a proxy for dust is a valuable addition to the toolbox of paleoclimate reconstruction since it is a direct proxy of dust in deposits however further validation and testing should be performed before general acceptation of mn as a paleoclimate proxy in terrestrial sediments

latent thermal effects from porcupine volcanics calderas underlying the white pine presque isle stratiform copper mineralization northern michigan economic stratiform copper mineralization in the fine grained carbonaceous basal nonesuch formation of the 50 km wide white pine presque isle mining district northern michigan has long been explained by the essentially vertical infiltration of cupriferous brine across the full width of basal nonesuch strata from the underlying copper harbor conglomerate aquifer followed by copper precipitation mainly by reactions with in situ iron sulfide based on that model why do lesser amounts of total copper measured in vertical sections occur in coarser grained presumably more permeable basal nonesuch strata situated laterally to the east and west of the mining district the answer may lie in increased infiltration rates for copper harbor hosted ore forming brine warmed locally by latent volcanic heat from a resurgent caldera or calderas located within the large porcupine volcanics dome underlying the mine district not only would caldera heat have warmed the brine and lowered its density but more importantly it would have produced a remarkable decrease in the brine viscosity an increase in temperature from 15 to 100 c could have increased the brine infiltration rate by more than four times in very early diagenetic time when the sediments were poorly compacted and highly porous because progressive compaction would have opposed the temperature effect a very early diagenetic timing is suggested for main stage copper mineralization over the porcupine volcanics caldera textural evidence has also long supported an early mineralization event at the rift basin scale the exceptionally rapid upward flux of warmed brine into fine grained nonesuch over the caldera would have required equivalent volumes of replacement brine which would in turn have required a lateral convergence of brine within the footwall copper harbor conglomerate aquifer toward the white pine presque isle district this lateral focus of brine toward the warm caldera area would have created a more efficient basin scale ore forming system than that resulting from a linear hydrogeologic flow most concepts described here deserve further evaluation through quantitative hydrogeologic modeling thermal effects on ore brine viscosities and densities developed here for the sediment hosted stratiform copper mineralization of the white pine presque isle district could be considered in genetic models for other deposits and deposit types the effects are especially strong for solutions warmed from low temperatures e g 20 c or lower to 100 c and could also be important to ore fluid flow for ores involving much higher hydrothermal temperatures if solutions with initially low temperatures played a role in their genesis

evidence for grenville age seismicity and thick skinned deformation in northern wisconsin u s a abstract one of the great continental rifts in all of earth s history the ca 1 1 ga midcontinent rift of the lake superior region was closed and inverted less than 100 m yr after its initiation when rift bounding normal faults were reactivated as reverse faults this was a major crustal event involving thick skinned deformation but its tectonic importance has not been fully appreciated owing in part to the lack of good outcrop along the traces of the rift closing faults a rare exposure of one of these faults occurs near the falls of the marengo river in southeastern bayfield county wisconsin the atkins lake marenisco fault is a crustal scale structure that juxtaposes archean granitic gneisses with paleoproterozoic and neoproterozoic metasedimentary and metavolcanic rocks pseudotachylytes cataclasites and microbreccias in the fault zone record large documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont

magnetization age from paleomagnetism of the copper harbor red beds northern michigan usa and its keweenawan geologic consequences the copper harbor formation on lake superior s keweenaw peninsula records the transition from volcanic to sedimentary infilling of north america s 1 1 ga keweenawan rift radiometric dating shows t

paleomagnetism and the age of copper mineralization in the portage lake volcanics upper peninsula michigan the close association of hematite with native copper in the flow tops of the portage lake volcanics invites the opportunity to establish the relative age of copper mineralization for this purpose

metallogeny of the midcontinent rift system of north america abstract the 1 1 ga midcontinent rift system of north america is one of the world s major continental rifts and hosts a variety of mineral deposits the rocks and mineral deposits of this 2000 km long rift are exposed only in the lake superior region in the lake superior region the rift cuts across precambrian basement terranes ranging in age from 1850 ma to more than 3500 ma where exposed the rift consists of widespread tholeiitic basalt flows with local interlayered rhyolite and clastic sedimentary rocks beneath the center of lake superior the volcanic and sedimentary rocks are more than 30 km deep as shown by recent seismic reflection profiles this region hosts two major classes of mineral deposits magmatic and hydrothermal all important mineral production in this region has come from hydrothermal deposits rift related hydrothermal deposits include four main types 1 native copper deposits in basalts and interflow sediments 2 sediment hosted copper sulfide and native copper 3 copper sulfide veins and lodes hosted by rift related volcanic and sedimentary rocks and 4 polymetallic five element veins in the surrounding archean country rocks the scarcity of sulfur within the rift rocks resulted in the formation of very large deposits of native metals where hydrothermal sulfides occur i e shale hosted copper sulfides the source of sulfur was local sedimentary rocks magmatic deposits have locally supported exploration and minor production but most are subeconomic presently these deposits occur in intrusions exposed near the margins of the rift and include cu ni pge and ti fe v in the duluth complex u ree nb in small carbonatites and breccia pipes resulting from local hydrothermal activity around small felsic intrusions mineralization associated with some magmatic bodies resulted from the concentration of incompatible elements during fractional crystallization most of the sulfide deposits in intrusions however contain sulfur derived from country rocks the interaction between magma and country rocks was important in generation of the magmatic cu ni sulfide deposits a mantle plume origin has been proposed for the formation of the midcontinent rift more than 1 million km3 of mafic magma was erupted in the rift and a comparable volume of mafic intrusions are inferred beneath the rift providing a ready and structurally confined supply of mafic source rocks that were available for leaching of metals by basinal brines these brines were heated by a steep geothermal gradient that resulted from the melting and underplating of magma derived from the plume hydrothermal deposits were emplaced for at least 30 40 m y after rift magmatism and extension ceased this time lag may reflect either the time required to heat deeply buried rocks and fluids within the rift or may be due to the timing of post rift compression that may have provided the driving mechanism for expulsion of hydrothermal fluids from deep portions of the rift