using lidar data to map gullies and headwater streams under forest canopy south carolina usa abstract the southeastern piedmont of the usa was severely gullied during the early 20th century a thick canopy established by reforestation in many areas now inhibits the identification or mapping of gullies by aerial photography or other conventional remote sensing methods an airborne laser scanning als or lidar mapping mission flown for the u s forest service in april 2004 acquired bare earth topographic data this paper tests the ability of the als topographic data to identify headwater channels and gullies for two branching gully systems in forested areas and to extract gully morphologic information comparisons are made with field traverses using differential gps and reference cross sections measured by leveling surveys at the gully network scale lidar data provide accurate maps the best available with robust detection of small gullies except where they are narrow or parallel and closely spaced errors in mapping channel location and network topological connectivity under forest canopy increase with attempts to identify smaller features such as large rills the ability of lidar data to map gullies and channels in a forested landscape should improve channel network maps and topological models at the gully reach scale attempts to use lidar data to extract gully cross section morphologic information under forest canopy were less successful due to systematic underestimation of gully depths and overestimation of gully top widths limited morphologic accuracy of the data set at this scale may be due to low bare earth point densities shadowing of gully bottoms and filtering of topographic discontinuities during post processing the als data used in this study are not suitable for detailed morphometric analysis or subtle change detection to monitor gullies or develop sediment budgets data collection may be improved by orienting flights over gullies and with increased point densities through improved scanner technology or better filtering and software capabilities to differentiate between vegetation and ground surfaces

assessment of erosion and deposition in steep mountain basins by differencing sequential digital terrain models abstract digital elevation models dems built from repeated topographic surveys permit producing dem of difference dod that enables assessment of elevation variations and estimation of volumetric changes through time in the framework of sediment transport studies dem differencing enables quantitative and spatially distributed representation of erosion and deposition within the analyzed time window at both the channel reach and the catchment scale in this study two high resolution digital terrain models dtms derived from airborne lidar data 2 m resolution acquired in 2005 and 2011 were used to characterize the topographic variations caused by sediment erosion transport and deposition in two adjacent mountain basins gadria and strimm vinschgau venosta valley eastern alps italy these catchments were chosen for their contrasting morphology and because they feature different types and intensity of sediment transfer processes a method based on fuzzy logic which takes into account spatially variable dtms uncertainty was used to derive the dod of the study area volumes of erosion and deposition calculated from the dod were then compared with post event field surveys to test the consistency of two independent estimates results show an overall agreement between the estimates with differences due to the intrinsic approximations of the two approaches the consistency of dod with post event estimates encourages the integration of these two methods whose combined application may permit to overcome the intrinsic limitations of the two estimations the comparison between 2005 and 2011 dtms allowed to investigate the relationships between topographic changes and geomorphometric parameters expressing the role of topography on sediment erosion and deposition i e slope and contributing area and describing the morphology influenced by debris flows and fluvial processes i e curvature erosion and deposition relations in the slope area space display substantial differences between the gadria and the strimm basins while in the former erosion and deposition clusters are reasonably well discriminated in the latter characterized by a complex stepped structure we observe substantial overlapping erosion mostly occurred in areas that show persistency of concavity or transformation from convex and flat to concave surfaces whereas deposition prevailingly took place on convex morphologies less expected correspondences between curvature and topographic changes can be explained by the variable sediment transport processes which are often characterized by alternation of erosion and deposition between different events and even during the same event

geomorphometric assessment of spatial sediment connectivity in small alpine catchments abstract complex and rugged topography induces large variations in erosion and sediment delivery in the headwaters of alpine catchments an effective connection of hillslopes with the channel network results in highly efficient sediment transfer processes such as debris flows in contrast morphological conditions producing decoupling of hillslopes from channels e g glacial cirques may exclude large areas of the catchment from sediment delivery to its lower parts moreover an efficient connection between hillslopes and channel network does not always ensure an effective downstream transfer of sediment low slope channel reaches e g in hanging valleys cause sediment deposition which often results in changes of the sediment transport processes typically from debris flow to streamflow with low bedload and suspended load rates the availability of high resolution digital terrain models such as those derived from aerial lidar improves our capability to quantify the topographic controls on sediment connectivity a geomorphometric index based on the approach by borselli et al 2008 was developed and applied to assess spatial sediment connectivity in two small catchments of the italian alps featuring contrasting morphological characteristics the results of the geomorphometric analysis were checked against field evidences showing good performance and thus potential usefulness of the index

the agulhas plateau structure and evolution of a large igneous province summary large igneous provinces lip are of great interest due to their role in crustal generation magmatic processes and environmental impact the agulhas plateau in the southwest indian ocean off south africa has played a controversial role in this discussion due to unclear evidence for its continental or oceanic crustal affinity with new geophysical data from seismic refraction and reflection profiling we are able to present improved evidence for its crustal structure and composition the velocity depth model reveals a mean crustal thickness of 20 km with a maximum of 24 km where three major units can be identified in the crust in our seismic reflection records evidence for volcanic flows on the agulhas plateau can be observed the middle crust is thickened by magmatic intrusions the up to 10 km thick lower crustal body is characterized by high seismic velocities of 7 0 7 6 km s 1 the velocity depth distribution suggests that the plateau consists of overthickened oceanic crust similar to other oceanic lips such as the ontong java plateau or the northern kerguelen plateau the total volume of the agulhas plateau was estimated to be 4 10 6 km 3 of which about 10 per cent consists of extruded igneous material we use this information to obtain a first estimate on carbon dioxide and sulphur dioxide emission caused by degassing from this material the agulhas plateau was formed as part of a larger lip consisting of the agulhas plateau itself northeast georgia rise and maud rise the formation time of this lip can be estimated between 100 and 94 5 ma

a review of intermediate sulfidation epithermal deposits and subclassification abstract intermediate sulfidation is veins is one of the subtypes of epithermal deposits formed in subduction related arc settings or post collisional orogenic belts the economic and scientific significance of is deposits has been highlighting importance in ag au pb zn exploration and study of porphyry epithermal systems this epithermal clan of deposits typically have a close relationship with andesitic dacitic volcanic subvolcanic rocks and formed at a depth of 0 3 to as much as 1 km is deposits are typically related to oxidized calcic to calc alkaline magmatism fluid homogenization temperatures and salinities range between 150 and 350 c and 0 and 23 wt nacl equivalent respectively the o and h isotope compositions are consistent with a mixture of magmatic and meteoric water with an increase in meteoric diluent as the hydrothermal system wanes most of the is deposits in the world particularly those in circum pacific metallogenic belts formed during cenozoic time several mesozoic and paleozoic is deposits in the central asian orogenic belt imply great exploration potential for pre cenozoic is deposits in this area the presence of mn carbonate such as rhodochrosite and manganocalcite locally mn silicate e g rhodonite helvite typically in mid to late hydrothermal stages is a common diagnostic feature to discern is from low sulfidation ls deposits in addition the occurrence of intermediate sulfidation state sulfides such as pyrite chalcopyrite sphalerite galena and tetrahedrite tennantite associations are another indicator of the is type light colored fe poor sphalerite is typical of is deposits consistent with relatively oxidized fluids elevated fluid salinity is another characteristic with maximum salinity values of base metal rich is veins usually 5 wt nacl equiv the reported is deposits worldwide show that they develop in compressional volcanic arcs as well as in some extensional settings in this review is deposits are subdivided into nc neutral compressional type is with a low ag au ratio 60 formed in extensional settings such as extensional intra arc post collisional orogenic belts and back arc settings another notable feature of e type is deposits is their large ag endowment compared to nc type is nc type is au ag deposits can be associated with porphyry cu au and or high sulfidation hs au cu deposits and their economic metals are mainly gold and or silver by contrast some e type is deposits can occur on the flanks of porphyry molybdenum deposits e type is veins can also occur together with ls precious metal veins in back arcs or extensional continental margins the most representative examples occurring in mexico the occurrence of the two subtypes of is are largely controlled by the parent magma with parent magma of nc type is primarily derived from depleted mantle or juvenile crust while parent magma of e type is mainly from ancient continental crust the occurrence of is deposits is presumably controlled by tectono magmatic settings and fluid evolution paths neutral to compressive stress regime relatively great depth to an exsolving magma 4 km and low exsolution rate of magmatic fluids plus the presence of syn ore dikes in conjunction with the development of interconnected fracture networks above the porphyry stock could be conducive for the occurrence of is and also hs au veins upon porphyry copper deposits pcds confirmation of sub types and variations of is veins can aid in exploration for spatially and genetic related mineralization types such as porphyry and hs deposits

monitoring sediment source areas in a debris flow catchment using terrestrial laser scanning abstract geomorphic changes caused by three debris flow events in a small mountain catchment moscardo torrent eastern italian alps were investigated by means of multitemporal terrestrial laser scanning tls surveys over three areas exposed to debris flow dynamics for these areas dem of differences dods with a 0 2 m spatial resolution allowed the assessment of elevation uncertainty as spatially variable by applying the fuzzy inference system fis proposed by wheaton et al 2010 along with two commonly used parameters affecting digital elevation model dem accuracy such as terrain slope and point density we developed and employed in the fis a new index named vegetation noise that takes into account the disturbance caused by the vegetation cover on the dem accuracy the results of volumetric budgets of the surveyed sediment source areas derived from the dod analysis were compared with debris flow volumes estimated from flow stage measurements at the instrumented channel reach on the one hand the discrepancies arising from this comparison underline the limitations of tls surveys over morphologically complex areas such as debris flow catchments on the other hand the tls unveils the geomorphic changes at the scale of the single event because a terrestrial survey is usually easier to carry out than an aerial one the analysis of dem quality and uncertainty indexes correlation may help to refine methods for spatializing elevation errors and improving the reliability of the models

application of geomorphons for analysing changes in the morphology of a proglacial valley case study the scott river sw svalbard abstract the progressive degradation of the cryosphere of high arctic areas causes an increase in the dynamics of geomorphic processes that shape the valleys of rapidly retreating glaciers those especially sensitive to global environmental changes are the small land ending valley glaciers that are in the phase of strong retreat under these conditions the river valley s floors that are drained by proglacial waters are constantly undergoing intensive changes for the analysis of these changes two methods were used simultaneously as a synthesis to allow for quantitative and qualitative evaluation the first one is the increasingly more common dod method dem of difference which allows quantifying volumetric changes as a result of topographic differentiation the second one which was applied for the first time on a small valley spatial scale is the geomorphons method that makes it possible to assess the stability of landforms and to determine the directions of their new development to judge the applicability advantages and disadvantages of both methods for analysis of geomorphic changes in rapidly changing proglacial environments the study was carried out over a 3 3 km distance of the non glaciated section of the scott river valley course nw wedel jarlsberg land sw svalbard this area 1 3 km2 is currently shaped by a braided gravel bed river more accurately the study focused on the section spanning from the glacier terminus which is the source of the scott river to its outlet at the rechersche fjord bellsundfiorden the foundation for the development of comparative elevation models was a collection of terrestrial laser scanning tls surveys that were taken with a leica scanstation c10 scanner during the 2010 and 2013 snowmelt seasons on the basis of these surveys and with the use of tin interpolation high resolution 0 2 m digital terrain models dtms were generated the dtm models that had been prepared in this manner were used for the analysis of surface changes by employing geomorphic change detection gcd software and by simultaneously generating geomorphons maps for four selected test areas that covered characteristic fragments of the valley bottom 1 on the close forefield of the scott glacier terminus 2 in the immediate vicinity of the narrow valley outlet at the foot of the marginal moraine ridge 3 in the enlargement of the central section of the non glaciated valley floor 4 within the alluvial fan outlet to the fjord a comparison of the obtained results dod and geomorphons maps zonal statistics as well as a compilation of both the quantitative assessment of the scale of changes and the qualitative assessment of the transformation s direction allowed for reconstructing the range and rate of three year long changes in morphology at the analysed sections of the valley floor it was found that the pattern and rate of changes were closely related to the location of the test areas in the scott river s catchment system significant differences in the dynamics of processes shaping the valley landforms along the longitudinal valley course were found

evidence for magmatic hydrothermal fluids and ore forming processes in epithermal and porphyry deposits of the baguio district philippines the baguio district contains a diverse array of epithermal porphyry and skarn deposits together with a large broadly strata bound advanced argillic lithocap magmatism mineralization and alteration occurred in response to subduction of the south china sea plate and the scarborough ridge beneath northern luzon over the past 3 m y rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry cu au deposits most of the epithermal au ag deposits of the baguio district including antamok and acupan the two largest au deposits are intermediate sulfidation state quartz carbonate adularia illite base metal sulfide veins that contain electrum and minor au ag tellurides in contrast high sulfidation mineralization at kelly includes enargite tennantite electrum and precious metal tellurides and is associated with advanced argillic alteration although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type the epithermal mineralizing fluids were dilute generally 600 c hypersaline brines 30 to 70 wt nacl equiv and low density vapor sulfur isotope compositions of sulfides in the porphyry skarn and intermediate sulfidation epithermal veins of the southern and central baguio district are mostly between 1 and 6 per mil consistent with a predominance of h2s in the mineralizing fluids i e reducing conditions in contrast sulfides from the high sulfidation porphyry and intermediate sulfidation deposits located adjacent to the baguio lithocap mostly have negative sulfur isotope values 6 9 to 0 8 consistent with oxidizing so42 predominant mineralizing fluids intermediate sulfidation epithermal veins at acupan have crosscut a well mineralized porphyry cu au stock work at ampucao the two deposits cannot be distinguished on the basis of radiometric age determinations ampucao 0 51 0 26 ma acupan 0 65 0 07 ma and are interpreted to be cogenetic with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction measured 34ssulfide 1 1 to 6 6 34ssulfate 10 4 to 31 8 values and initial strontium ratios of anhydrite 0 70378 0 70385 are consistent with identical and predominantly magmatic sources of these components for the ampucao porphyry and acupan epithermal veins helium isotopes provide further evidence of mantle derived components in the epithermal veins r ra values of 6 0 and 6 7 oxygen deuterium and carbon isotopes provide evidence for predominantly magmatic water at ampucao and for hybrid magmatic meteoric waters at acupan that precipitated precious metals due to boiling the proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at acupan the common observation of cross cutting relationships between porphyry and epithermal veins observed throughout the baguio district imply that the evolution of porphyry style to intermediate sulfidation style mineralization was a common phenomenon in this region and contributed significantly to its rich metal endowment

cm5 a pre swarm comprehensive geomagnetic field model derived from over 12 yr of champ orsted sac c and observatory data a comprehensive magnetic field model named cm5 has been derived from champ rsted and sac c satellite and observatory hourly means data from 2000 august to 2013 january using the swarm level 2 comprehensive inversion ci algorithm swarm is a recently launched constellation of three satellites to map the earth s magnetic field the ci technique includes several interesting features such as the bias mitigation scheme known as selective infinite variance weighting sivw a new treatment for attitude error in satellite vector measurements and the inclusion of 3 d conductivity for ionospheric induction sivw has allowed for a much improved lithospheric field recovery over cm4 by exploiting champ along track difference data yielding resolution levels up to spherical harmonic degree 107 and has allowed for the successful extraction of the oceanic m2 tidal magnetic field from quiet nightside data the 3 d induction now captures anomalous solar quiet features in coastal observatory daily records cm5 provides a satisfactory continuous description of the major magnetic fields in the near earth region over this time span and its lithospheric ionospheric and oceanic m2 tidal constituents may be used as validation tools for future swarm level 2 products coming from the ci algorithm and other dedicated product algorithms

first scalar magnetic anomaly map from champ satellite data indicates weak lithospheric field 1 satellite magnetic anomaly maps derived by different techniques from magsat pogo data vary by more than a factor of 2 in the deduced strength of the lithospheric magnetic field here we present a first anomaly map from new champ scalar magnetic field data after subtracting a recent orsted main and external field model we remove remaining unmodeled large scale external contributions from 120 track segments by subtracting a best fitting uniform field in order to preserve n s trending features the data are not filtered along track direct integration of the spherically gridded data yields the final degree 14 65 spherical harmonic expansion of the total intensity anomaly at the mean satellite altitude of 438 km apart from enhanced long wavelength features and a smoother general appearance our initial map is strikingly similar to one of the lower strength magsat pogo maps

thermal history of an early paleozoic epithermal deposit constraints from 40ar 39ar and u th he thermochronology at zhengguang eastern central asian orogenic belt abstract the zhengguang epithermal au zn deposit located in heilongjiang province ne china is an early paleozoic intermediate sulfidation epithermal deposit which is adjacent to the duobaoshan and tongshan porphyry cu deposits in the duobaoshan magmatic arc eastern central asian orogenic belt caob our new 40ar 39ar dating presents plateau ages of 276 9 1 2 ma mswd 1 5 for adularia and 265 7 1 2 ma mswd 3 5 for illite these ages are clearly younger than the mineralization age of zhengguang 480 ma and therefore represent a post ore event which reset the adularia and illite argon systems the resetting event could be related to post collision of xing an block and songliao xilinhot block the weighted mean of zircon u th he ages zhe and apatite u th he ages ahe from the same dacite porphyry with illite dating sample are 192 10 ma mswd 2 2 and 98 8 5 3 ma mswd 2 1 respectively the zhe age 190 ma indicates a tectonothermal resetting event possibly related to the development of tongshan fault whereas the ahe age 100 ma likely reflects 3 km deep burial at zhengguang the intra sample variations of u th he ages for zircon grains are mainly due to radiation damage while those for apatite are unknown we argue that the post ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the paleo pacific plate could facilitate burial and preservation of the epithermal and by inference porphyry deposits in ne china considering the complex collisional and amalgamation history in this area we believe that there is exploration potential for ancient porphyry and epithermal deposits within the eastern section of the caob

resolution of direction of oceanic magnetic lineations by the sixth generation lithospheric magnetic field model from champ satellite magnetic measurements the champ satellite continues to provide highly accurate magnetic field measurements from decreasing orbital altitudes 350 km at solar minimum conditions using the latest 4 years 2004 2007 of readings from the champ fluxgate magnetometer including an improved scalar data product we have estimated the lithospheric magnetic field to spherical harmonic degree 120 corresponding to 333 km wavelength resolution the data were found to be sensitive to crustal field variations up to degree 150 down to 266 km wavelength but a clean separation of the lithospheric signal from ionospheric and magnetospheric noise sources was achieved only to degree 120 this new mf6 model is the first satellite based magnetic model to resolve the direction of oceanic magnetic lineations revealing the age structure of oceanic crust

hydrothermal breccias and veins at the kelian gold mine kalimantan indonesia genesis of a large epithermal gold deposit mineralized hydrothermal breccias and veins formed during and after the waning stages of maar diatreme related volcanic activity at kelian kalimantan indonesia subsurface phreatic explosions occurred around the margins of the diatreme breccia complex focusing high temperature fluid flow and generating several large mineralized hydrothermal breccia bodies tectonic phreatomagmatic and hydraulic processes also contributed to hydrothermal brecciation explosive phreatic brecciation was followed by in situ hydraulic brecciation and then by minor veining as the system returned to steady state geothermal conditions brecciation and mineralization mostly occurred 400 to 700 m below the paleowater table the kelian deposit contained more than 240 t au prior to mining precious metals occur with sulfide minerals as disseminations in sheeted and conjugate veins and as breccia cement there is a progression from pyrite dominated stage 1 to base metal sulfide dominated stages 2 and 3 to sulfosalt dominated hydrothermal breccias and veins stage 4 in terms of gangue minerals the system evolved from illite quartz to adularia and or quartz and or illite dominated and then carbonate dominated boiling produced abundant bladed carbonate during stages 3 and 4 overall carbonate and base metal sulfide minerals are abundant whereas quartz is comparatively minor free gold is most abundant in stages 3 and 4 but also occurs in stages 1 and 2 native gold occurs principally as inclusions in pyrite sphalerite galena arsenopyrite quartz bladed carbonate and sulfosalts hydrothermal alteration assemblages are zoned about contacts faults breccias and veins and consist of secondary quartz illite pyrite chlorite and various carbonate minerals kelian preserves evidence of a magmatic component to the mineralizing fluids fluid inclusion analyses revealed the presence of saline fluid inclusions in particular from stage 3 isothermal mixing of low salinity 0 to 2 wt nacl equiv with moderate salinity fluids 10 to 25 wt nacl equiv rather than boiling resulted in the range of salinity and homogenization temperatures of fluid inclusions in sphalerite carbonate and quartz deposited during stage 3 salinities of 4 to 6 wt percent nacl equiv for inclusions in adularia and quartz from stages 2 and 4 and in rhodochrosite and proustite pyrargyrite from stage 4 may also reflect a component of mixing of low salinity water with a moderately saline fluid sulfur isotope values from kelian sulfides 34s 1 4 to 5 5 per mil are consistent with a magmatic sulfur source both boiling and fluid mixing contributed to high grade au mineralization at kelian rapid formation hundreds of years or less is inferred for the individual hydrothermal breccia bodies 2008 society of economic geologists inc

geology and genesis of the early paleozoic zhengguang intermediate sulfidation epithermal au zn deposit northeast china abstract zhengguang is a partly eroded about 500 m being eroded structurally controlled intermediate sulfidation is epithermal gold zinc deposit characterized by wide distribution of base metal sulfides fe poor sphalerite and mn calcite hosted by the late cambrian early ordovician basaltic andesitic volcanic and volcano sedimentary rocks in northeast china the deposit is located 4 and 8 km from the early ordovician tongshan including several is veins about 500 m away in the east called east tongshan and duobaoshan porphyry copper deposits respectively a 484 8 8 7 ma mswd 198 of re os isochron age on pyrite indicates that it is the most ancient intermediate sulfidation deposit that has been dated four stages of veins have been discerned at zhengguang early magnetite chalcopyrite epidote chlorite and k feldspar pyrite chalcopyrite veins stage i were associated with restricted k feldspar epidote locally with chlorite alteration and propylitic epidote chlorite calcite assemblages two primary epithermal gold stages developed at zhengguang pyrite quartz fe poor sphalerite chalcopyrite galena electrum petzite hessite tetrahedrite tennantite adularia veins stage ii and mn calcite quartz pyrite fe poor sphalerite chalcopyrite galena hessite native gold stage iii plus a late barren stage characterized by little sulfides calcite chlorite hematite quartz stage iv gold occurs chiefly as micro inclusions of electrum and petzite in pyrite and sphalerite of stages ii and iii stable isotope analyses and fluid inclusion results indicate a magmatic hydrothermal component in the ore fluids fluid inclusion data from stage i yielded the highest salinity 6 9 wt nacl and homogenization temperature average 264 c calculated oxygen isotope composition of fluid 18owater up to 4 9 equilibrated with quartz indicates a magmatic hydrothermal source during stage i a progressive addition of meteoric water component is suggested from stage i to iv of zhengguang based on the average 18owater values equilibrated with quartz and homogenization temperatures stage i 18owater 3 3 th 264 c stage ii 18owater 1 4 th 182 c stage iii 18owater 3 4 th 154 c stage iv 18owater 6 3 th 121 c our new pyrite re os dating result shows that zhengguang formed at the same time with tongshan and duobaoshan within errors comparable sulfur isotopic compositions of pyrite from zhengguang and tongshan analogous low fe content in sphalerite and similar mineral assemblage and alteration pattern between zhengguang and east tongshan is veins collectively indicate a genetic connection between zhengguang and tongshan which may derive from fluids exsolved from the same magma chamber high temperature assemblages e g k feldspr pyrite chalcopyrite at zhengguang indicate that there is potential for the discovery of porphyry copper gold mineralization below the current level of diamond drilling the confirmation of the zhengguang as an early paleozoic epithermal deposit implies a good preservation and exploration potential of ancient epithermal deposits in eastern central asian orogenic belt

genesis of the zhengguang gold deposit in the duobaoshan ore field heilongjiang province ne china constraints from geology geochronology and s pb isotopic compositions abstract the zhengguang gold deposit in the duobaoshan ore field hosted in volcanic rocks of the middle ordovician duobaoshan formation is one of the largest gold deposits in the northeastern great xing an range of the central asian orogenic belt caob the deposit comprises the no i ii and iii ore zones with a total resource exceeding 35 tonnes of au 100 000 tonnes of zn and 100 tonnes of ag a genetic relationship between gold mineralization and concealed tonalite porphyry is inferred based on the characteristics of cryptoexplosive breccia and hydrothermal alteration indicative of porphyry type and epithermal mineralization zircon la icpms u pb dating reveals that the tonalite porphyry was emplaced at 462 1 1 8 ma middle ordovician the 34 s v cdt values of sulfide minerals range from 3 0 to 1 7 with an average of 2 33 indicating that sulfur was mainly derived from a magmatic source the pb isotopic compositions 206 pb 204 pb ranging from 17 572 to 17 629 207 pb 204 pb from 15 424 to 15 486 and 208 pb 204 pb from 37 206 to 37 418 suggest a major mantle component for pb and by inference for other ore metals therefore we suggest that the ore forming elements in the zhengguang gold deposit may be related to the mantle sourced tonalite porphyry on the basis of the geological characteristics and geochemical signatures documented in this study we conclude that the zhengguang gold deposit was formed in a porphyry to epithermal transitional environment associated with the concealed tonalite porphyry as part of the duobaoshan porphyry epithermal ore system that is related to the subduction of the paleo asian ocean during the ordovician

mercury s internal magnetic field constraints on large and small scale fields of crustal origin abstract messenger and mariner 10 observations of mercury s magnetic field suggest that small scale crustal magnetic fields if they exist are at the limit of resolution large scale crustal magnetic fields have also been suggested to exist at mercury originating from a relic of an internal dipole whose symmetry has been broken by latitudinal and longitudinal variations in surface temperature if this large scale magnetization is confined to a layer averaging 50 km in thickness it must be magnetized with an intensity of at least 2 9 a m fits to models constrained by such large scale insolation variations do not reveal the predicted signal and the absence of small scale features attributable to remanence further weakens the case for large scale magnetization our tests are hindered by the limited coverage to date and difficulty in isolating the internal magnetic field we conclude that the case for large and small scale remanence on mercury is weak but further measurements by messenger can decide the issue unequivocally across the terrestrial planets and the moon magnetization contrast and iron abundance in the crust show a positive correlation this correlation suggests that crustal iron content plays a determining role in the strength of crustal magnetization

high resolution topography for understanding earth surface processes opportunities and challenges abstract in the last decade a range of new remote sensing techniques has led to a dramatic increase in terrain information providing new opportunities for a better understanding of earth surface processes based on geomorphic signatures technologies such as airborne and terrestrial lidar light detection and ranging to obtain high resolution topography have opened avenues for the analysis of landslides hillslope and channellization processes river morphology active tectonics volcanic landforms and anthropogenic signatures on topography this review provides an overview of the recent flourishing literature on high resolution topographic analyses underlining their opportunities and critical issues such as their limitations the goal is to provide answers to questions such as what kind of processes can be analyzed through high resolution topographic data and how to do it the review focuses on two different environments natural and engineered landscapes in both contexts high resolution topography offers opportunities to better understand geomorphic processes from topographic signatures particular attention is given to engineered landscapes in which the direct anthropic alteration of processes is significant the last part of the review discusses future challenges

fluid evolution in a volcanic hosted epithermal carbonate base metal gold vein system alto de la blenda farallon negro argentina alto de la blenda is a 6 6 ma intermediate sulphidation epithermal vein system in the farallon negro volcanic complex which also hosts the 7 1 ma porphyry cu au deposit of bajo de la alumbrera the epithermal vein system is characterised by a large extent and continuity 2 km 400 m open to depth 6 m maximum width and an average gold grade of 8 g t the vein is best developed within an intrusion of a fine grained equigranular monzonite interpreted as the central conduit of a stratovolcano whose extrusive activity ended prior to porphyry cu au emplacement at bajo de la alumbrera which is in turn cut by minor epithermal veins the alto de la blenda vein consists predominantly of variably mn rich carbonates and quartz with a few percent of pyrite sphalerite galena and other sulphide and sulphosalt minerals four phases of vein opening hydrothermal mineralisation and repeated brecciation can be correlated between different vein segments stages 2 and 3 contain the greatest fraction of sulphide and gold they are separated by the emplacement of a polymictic breccia containing clasts of quartz feldspar porphyry as well as basement rocks fluid inclusions in quartz related to stages 2 to 4 are liquid rich with 2 4 wt nacl eq they homogenise between 160 and 300 c with very consistent values within each assemblage vapour inclusions are practically absent in the epithermal vein quartz fragments in the polymictic breccia contain inclusions of intermediate to vapour like density and similar low salinity 3 wt nacl eq besides rare brine inclusions containing halite laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of epithermal inclusions indicate high concentrations of k fe as sb cs and pb that significantly vary within and through subsequent vein stages careful consideration of detection limits for individual inclusions shows high gold concentrations of 0 5 to 3 ppm dissolved in the ore fluid which contains variably high sulphur concentrations in excess over fe and other chalcophile metals compositional variations are interpreted to reflect cooling and contraction of lower density magmatic fluids at depth like those preserved in porphyry clasts that were mechanically transported up by the polymictic breccia ore mineral precipitation from the magmatic fluid occurred by further cooling and possibly minor mixing with surface derived water leading to sulphide saturation de sulphidation of the magmatic fluid and consequent gold precipitation the absence of flash boiling and or reduction by carbonaceous host rocks has led to relatively modest but constant gold grades in the carbonate base metal gold veins of alto de la blenda

earth s lithospheric magnetic field determined to spherical harmonic degree 90 from champ satellite measurements summary the champ magnetic field mission is providing highly reliable measurements from which the global lithospheric magnetic field can be determined in unprecedented resolution and accuracy using almost 5 yr of data we derive our fourth generation lithospheric field model termed mf4 which is expanded to spherical harmonic degree and order 90 after subtracting from the full magnetic field observations predicted fields from an internal field model up to degree 15 an external field model up to degree two and the predicted magnetic field signatures for the eight dominant ocean tidal constituents we fit and remove remaining external fields and polar electrojet signatures in a track by track scheme from a subset of least disturbed tracks we estimate the mf4 model by least squares damping ill determined coefficients by regularization the resulting mf4 model provides a good representation of the lithospheric field down to an altitude of about 50 km at lower latitudes with reduced accuracy in the polar regions crustal features come out significantly sharper than in previous models in particular bands of magnetic anomalies along subduction zones become visible by satellite for the first time

magnetic field gradients from the st 5 constellation improving magnetic and thermal models of the lithosphere received 20 august 2007 revised 17 october 2007 accepted 6 november 2007 published 25 december 2007 1 we report the development of a new technique magnetic gradiometry for satellite based remote sensing of the lithosphere the measurements reported here represent the first systematic measurements of lithospheric magnetic field gradients and were collected from a spinning spacecraft the three satellite st 5 mission collected vector magnetic field observations at 300 800 km altitudes over mid and high northern latitudes in 2006 away from the auroral oval and over the continents the gradients of the low altitude 400 km total anomaly field are dominated by lithospheric magnetic fields using a seismic starting model and magnetic field observations from st 5 and other recent satellite missions we demonstrate how these techniques can be used to improve our knowledge of the processes involved in the thickened crust of the colorado plateau and the sierra madre occidental citation purucker m t sabaka g le j a slavin r j strangeway and c busby 2007 magnetic field gradients from the st 5 constellation improving magnetic and thermal models of the lithosphere geophys res lett 34 l24306 doi 10 1029 2007gl031739

intermediate sulfidation type base metal mineralization at aliabad khanchy tarom hashtjin metallogenic belt nw iran abstract the aliabad khanchy epithermal base metal deposit is located in the tarom hashtjin metallogenic belt thmb of northwest iran the mineralization occurs as cu bearing brecciated quartz veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation ore formation can be divided into five stages with most ore minerals such as pyrite and chalcopyrite being formed in the early stages the main wall rock alteration is silicification and chlorite argillic and propylitic alteration microthermometric measurements of fluid inclusion assemblages show that the ore forming fluids have eutectic temperatures between 30 and 52 c trapping temperatures of 150 290 c and salinities of 6 6 12 4 wt nacl equiv these data demonstrate that the ore forming fluids were medium to high temperature medium to low salinity and low density h2o nacl cacl2 fluids calculated 18o values indicate that ore forming hydrothermal fluids had 18owater ranging from 3 6 to 0 8 confirming that the ore fluid system evolved from dominantly magmatic to dominantly meteoric the calculated 34sh2s values range from 8 1 to 5 0 consistent with derivation of the sulfur from either magma or possibly from local volcanic wall rock combined the fluid inclusion and stable isotope data indicate that the aliabad khanchy deposit formed from magmatic hydrothermal fluids after rising to a depth of between 790 and 500 m the fluid boiled and subsequent hydraulic fracturing may have led to inflow and or mixing of early magmatic fluids with circulating groundwater causing deposition of base metals due to dilution and or cooling the aliabad khanchy deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the mineralization at aliabad khanchy and other epithermal deposits of the thmb formed by hydrothermal activity related to shallow late eocene magmatism the altered eocene volcanic and volcaniclastic rocks especially at the intersection of subvolcanic stocks with faults were the most favorable sites for epithermal ore bodies in the thmb

the geomagnetic power spectrum summary combining champ satellite magnetic measurements with aeromagnetic and marine magnetic data the global geomagnetic field has now been modelled to spherical harmonic degree 720 an important tool in field modelling is the geomagnetic power spectrum it allows the comparison of field models estimated from different data sets and can be used to identify noise levels and systematic errors a correctly defined geomagnetic power spectrum is flat white for an uncorrelated field such as the earth s crustal magnetic field at long wavelengths it can be inferred from global spherical harmonic models as well as from regional grids marine and aeromagnetic grids usually represent the anomaly of the total intensity of the magnetic field appropriate corrections have to be applied in estimating the geomagnetic power spectrum from such data the comparison of global and regional spectra using a consistently defined azimuthally averaged geomagnetic power spectrum facilitates quality control in field modelling and should provide new insights in magnetic anomaly interpretation

boiling and dilution in the shallow portion of the waiotapu geothermal system new zealand abstract the waiotapu geothermal system is the largest in terms of surface extent and heat flow 17 km2 and 600 mw respectively of the 20 major geothermal systems in the taupo volcanic zone new zealand two extinct dacite cones and a rhyolite dome rise about 500 m above the waiotapu valley the majority of thermal features occurs in the valley over a relief of only 100 m and lies within coincident apparent resistivity and 30 m depth thermal anomalies thermal features comprise near neutral ph chloride springs often boiling acid sulfate springs and mud pools and mixed waters the latter including both bicarbonate chloride and acid sulfate chloride springs the majority of the sulfate discharges to the surface in the northern higher altitude area while most chloride that reaches the surface does so in the southern portion of the system comparison of measured and calculated surface chloride flux the latter from measured heat flow and reservoir chloride concentrations indicates that at least half of the deep chloride does not discharge at the surface but flows laterally to the south at shallow depths mixing with groundwater the composition of well discharges indicates a shallow 400 m reservoir of chloride fluid about 1350 mg cl kg at 230 c is diluted by a co2 rich steam heated water nil chloride at about 160 c the latter located on the margins of the system this same dilution trend is apparent from the compositional variation and k na and k mg geothermometry of hot spring waters however there is chemical and stable isotope evidence from hot springs that cold groundwater also acts as a diluent at shallow levels and very near the surface steam heated acid sulfate waters mix with the upflow boiling of the deep chloride fluids prior to dilution results in the stabilization of k feldspar in contrast dilution at shallower depths by the steam heated waters both co2 rich and acid sulfate leads to the water compositions initially shifting to k mica and interstratified clay stability and to kaolinite stability with further dilution and temperature decrease the composition and distribution of these fluids are consistent with alteration mineralogy and zonation observed in drill core although boiling occurs at deeper levels and up to the surface in the upflow zone at waiotapu mixing is also common and is the dominant process on the margin and in the near surface portion of the system boiling of deep chloride fluid is very common in the upper 1 2 km of the upflow zone of most geothermal systems though it may be quenched by mixing with marginal waters either cold groundwater in high relief terrane or steam heated waters in areas of lower relief co2 rich steam heated waters are common on the margins of systems and will generally underlie the near surface acid sulfate steam heated waters interaction with co2 rich waters will form k mica and interstratified clays while acid sulfate waters cause kaolinite and even alunite to form the former assemblage is commonly associated with typical low sulfidation epithermal gold mineralization as wallrock alteration where gold bearing veins comprise adularia and illite in contrast kaolinite is rare and alunite absent from a direct spatial and genetic association with gold mineralization in this environment this implies that mixing of the deep neutral ph chloride fluid with surficial acid sulfate waters does not commonly lead to ore grade gold deposition mixing with and cooling by co2 rich steam heated waters leads to clay stability accounting for the large halos of clay alteration and low grade metal anomalies which often surround veins of high gold grade in contrast mixing with surficial acid sulfate waters is unlikely to cause precious metal mineralization because the chloride fluids have already lost the majority of their gold through deeper boiling and dilution

diagenetic and metallogenic ages of duobaoshan porphyry cu mo deposit in heilongjiang province the duobaoshan porphyry cu mo deposit is an important cu deposit in northeast china systematic isotope dating was conducted to determine the metallogenic age of the deposit la icp ms zircon u pb dating indicates that the parent granite porphyry rocks and the host rocks intruded at 474 8 4 7 ma and 478 1 4 1 ma respectively the biotite granodiorite outside the parent granite porphyry was formed at 483 9 4 5 ma meanwhile seven re os isotopic analyses of molybdenite yield a weighted average model age of 475 1 5 1 ma these data show that the ore forming process and the intrusion of the host rocks were completed in the early ordovician according to the ages of mineralization and intrusion of host rocks the sedimentary setting of the duobaoshan formation and the geochemical characteristics of rocks hosting the deposit the authors hold that the porphyry cu mo deposit was formed in an island arc regime related to plate subduction in the early ordovician and that the prospecting direction for such a type of porphyry copper deposits should be in the magma island arc belt distributed in duobaoshan yi ershi area

an early permian epithermal gold system in the tulasu basin in north xinjiang nw china constraints from in situ oxygen sulfur isotopes and geochronology abstract the axi and jingxi yelmand gold deposits being the largest gold deposits in the chinese north tianshan nw china are located ca l0 km apart in the tulasu basin and are hosted by the late devonian early carboniferous dahalajunshan formation in situ la icp ms titanium analyses on quartz from the axi and jingxi yelmand deposits are broadly identical accordingly the calculated ore forming temperatures by ti in quartz thermometer give average temperatures of 279 c and 294 c respectively results of in situ sims analyses of oxygen and sulfur isotopes on quartz and pyrite from these two deposits are similar temperature corrected fluids of the axi deposit have 18 o values of 2 6 8 1 and 34 s values of 0 8 2 4 whereas the fluids of the jingxi yelmand deposit have 18 o of 6 4 8 9 and 34 s of 0 4 to 4 0 the oxygen and sulfur isotopes from the two deposits indicate a magmatic origin la icp ms zircon u pb ages of aqialehe formation sandstone provided a lower limit for the mineralization timing of the axi deposit 288 ma in situ sims u pb analyses on entrapped zircon 297 ma and newly recognized 284 5 ma columnar rhyolite implies that the jingxi yelmand deposit formed in the early permian based on the magmatic affinity of the ore fluids similar age and ore formation temperatures we propose that the axi and jingxi yelmand deposits comprise an epithermal gold system which was driven by the same permian magma in the tulasu basin the ore geological features together with our new results indicate that the axi and jingxi yelmand deposits are intermediate and high sulfidation type epithermal deposits respectively

geomorphic effectiveness of check dams in a debris flow catchment using multi temporal topographic surveys abstract torrent control works such as grade control dams and sediment retention dams are structural measures for controlling debris flows and debris floods in spite of the widespread presence of such hydraulic structures in steep mountain streams worldwide there are still few studies monitoring the effects of check dams on sediment dynamics the use of repeated topographic surveys allows us to characterize debris flow activity at multiple temporal and spatial scales and its interaction with torrent control works structure from motion sfm technique paired with multi view stereo mvs algorithms represents a low cost opportunity to conduct such multi temporal surveys this enables us to better study the effects of individual debris flows track geomorphic changes and evaluate the effectiveness of torrent control works e g check dams the effect of check dams on sediment dynamics is investigated by means of multi temporal topographic surveys before and after debris flow events in the moscardo torrent eastern italian alps where two check dams have recently been built multi temporal sfm based on images taken from the ground in combination with imagery taken by an unmanned aerial vehicle uav is used to obtain dems and to study topographic changes through the comparison of repeat dems dem of difference i e dod the results show that the new check dams considerably modified sediment dynamics in the studied channel but their performance cannot be considered satisfactory the sediment flowed around the upstream check dam on the right wing while deep erosion observed downstream of the check dam threatened to undermine the foundation s stability moreover debris flow lobes deposited upstream of the check dams could act as sources of sediment further increasing downstream debris flow volume the analysis proposed in this work could help improve design strategies and permitting the identification of a proper site for check dam building

microthermometry of enargite hosted fluid inclusions from the lepanto philippines high sulfidation cuau deposit abstract the spatial relation between porphyry and high sulfidation epithermal deposits is particularly well revealed in the mankayan mineral district of northern luzon philippines where the lepanto high sulfidation cu au deposit lies over and adjacent to the far southeast fse porphyry cu au deposit consequently a study was undertaken to characterize the fluids responsible for epithermal mineralization in this environment the ore stage at lepanto consists of enargite luzonite cu 3 ass 4 pyrite tennantite tetrahedrite and chalcopyrite infrared petrography of the enargite reveals variable transparency with growth banding and twinning visible in euhedral specimens two phase liquid vapor fluid inclusions occur as primary and secondary types ranging from t h of fluid inclusions in enargite were measured from within the lateral 3 0 km and vertical 0 5 km extent of the enargite mineralization these values show a cooling trend toward the northwest away from the area over the porphyry deposit with average t h ranging from 285 c proximal to 166 c distal ice melting temperatures t m were measured using a cycling technique as ice was usually not visible in frozen inclusions apparent salinities range from 4 5 to 0 2 eq wt nacl with samples from the margins of the deposit showing a general decrease in apparent salinity with lower t h secondary fluid inclusions in quartz phenocrysts tend to have a higher average t h and lower apparent salinities compared to enargite hosted inclusion fluids from the same locations several samples of pyrite are also transparent to ir radiation and show internal features such as growth banding and in one instance a two phase liquid vapor fluid inclusion this inclusion yielded a salinity of 1 2 eq wt nacl there is a large discrepancy in t h and apparent salinities between the enargite mineralization and the subjacent porphyry deposit despite contemporaneous formation suggesting that the hot 500 c hypersaline magmatic brines associated with porphyry mineralization did not directly ascend to the elevation of the enargite deposit however absorbtion of magmatic vapors into overlying meteoric water may have created the mineralizing fluid of the lepanto deposit as this liquid moved to the northwest along the lepanto fault it was cooled and diluted by mixing with groundwater resulting in enargite deposition

collision belt between the khanka block and the north china block in the yanbian region northeast china the pre jurassic geotectonics in northeast china and its adjacent regions are characterized by collision of microcontinental blocks the yanbian region lies between the north china block ncb and the khanka block kb along the dashanzui antu kaishantun collision belt the yanbian pre jurassic fold belt can be divided into two parts one part represents the western margin of the kb which consists of late proterozoic metamorphic basement and a permian active continental margin the other one is located at the eastern margin of the ncb and is composed of proterozoic passive margin deposits where the seluohe and qinglongcun groups are developed and rocks of the permian passive margin collision of these two parts took place along the dashanzui antu kaishantun collision zone during the late permian to early triassic as evidenced by the emplacement of syncollision granites and a type granites in northeast china and adjacent regions a series of microcontinental blocks collided with one other from the end of early paleozoic to the early triassic the collision event that took place in the yanbian region may represent the latest collision event in the paleo asian oceanic domain c 2003 elsevier ltd all rights reserved

from experimental plots to experimental landscapes topography erosion and deposition in sub humid badlands from structure from motion photogrammetry in the last decade advances in surveying technology have opened up the possibility of representing topography and monitoring surface changes over experimental plots 10 m2 in high resolution 103 points m 1 yet the representativeness of these small plots is limited with structure from motion sfm and multi view stereo mvs techniques now becoming part of the geomorphologist s toolkit there is potential to expand further the scale at which we characterise topography and monitor geomorphic change morphometrically moving beyond previous plot scale work using terrestrial laser scanning tls surveys this paper validates robustly a number of sfm mvs surveys against total station and extensive tls data at three nested scales plots 30 m2 within a small catchment 4710 m2 within an eroding marl badland landscape 1 km2 sfm surveys from a number of platforms are evaluated based on i topography ii sub grid roughness and iii change detection capabilities at an annual scale oblique ground based images can provide a high quality surface equivalent to tls at the plot scale but become unreliable over larger areas of complex terrain degradation of surface quality with range is observed clearly for sfm models derived from aerial imagery recently modelled doming effects from the use of vertical imagery are proven empirically as a piloted gyrocopter survey at 50m altitude with convergent off nadir imagery provided higher quality data than an unmanned aerial vehicle uav flying at the same height and collecting vertical imagery for soil erosion monitoring sfm can provide data comparable with tls only from small survey ranges 5 m and is best limited to survey ranges 10 20 m synthesis of these results with existing validation studies shows a clear degradation of root mean squared error rmse with survey range with a median ratio between rmse and survey range of 1 639 and highlights the effect of the validation method e g point cloud or raster based on the estimated quality

computing spatially distributed sediment delivery ratios inferring functional sediment connectivity from repeat high resolution digital elevation models high resolution digital elevation models dems from repeat lidar or sfm surveys have become an important tool in process geomorphology the spatial pattern of negative and positive changes of surface elevation on raster dems of difference dod can be interpreted in terms of geomorphic processes and has been used for morphological budgeting we show how the application of flow routing algorithms and flow accumulation opens new opportunities for the analysis of dod by accumulating the values of the dod along downslope flowpaths delineated on a dem these algorithms lend themselves to computing the net balance i e sediment yield sy for the contributing area of each cell doing the same for the negative subset of the dod yields a minimum estimate of erosion e within the contributing area the division of sy by e yields a maximum estimate of the sediment delivery ratio sdr that is the proportion of material eroded within the contributing area of each cell that has been exported from that area the resulting sdr is a spatially distributed measure of functional sediment connectivity in this letter we develop the computationally simple approach by means of an example dod from a lateral moraine section in the upper kaunertal valley austrian central alps we also discuss advantages assumptions and limitations and outline potential applications to connectivity research using field laboratory and model based dod

gold behavior in intermediate sulfidation epithermal systems a case study from the zhengguang gold deposit heilongjiang province ne china abstract the zhengguang gold deposit a typical intermediate sulfidation epithermal deposit is located in the southeastern part of the duobaoshan orefield west of the hegenshan heihe suture zone in the eastern part of the central asian orogenic belt the deposit comprises five ore zones with total au reserves exceeding 35 tonnes with potential additional resources at depth all vein type orebodies are hosted by paleozoic volcanic rocks and comprise multiple vein sets 1 100 cm in thickness although gold generally occurs in native form or as electrum in epithermal deposits like zhengguang both pyrite and sphalerite are known to accommodate modest concentrations of invisible gold this study employs a combination of petrography and sulfide chemistry to determine the role of invisible gold in the zhengguang ores and the mechanisms of gold incorporation into epithermal sulfides three sulfide stages are identified an early quartz pyrite py1a py1b chalcopyrite ccp1 stage a subsequent quartz sphalerite sph2a sph2b pyrite py2a py2b py2c py2d chalcopyrite ccp2a ccp2b galena calcite stage and a late stage containing deformed quartz pyrite py3a py3b sphalerite petrography and sulfide chemistry allow three groups of pyrite au poor au rich and a distinct sb rich group to be distinguished alongside three groups of chalcopyrite bi rich intermediate bi and bi poor and two groups of sphalerite au poor au rich a potential porphyry system is indicated beneath the epithermal system by the appearance of au poor pyrite and bi poor chalcopyrite after precipitation of early au poor sulfides inflow of relatively low temperature epithermal fluids led to alteration and replacement of early porphyry related sulfides and to precipitation of au rich pyrite bi rich and intermediate bi chalcopyrite and sphalerite gold rich pyrite contains up to 140 ppm au interpreted as both as lattice scale substitution au1 and as included particles of native gold au0 epithermal chalcopyrite is an important silver carrier but although au is measurable it is a not a good carrier for gold a strong positive correlation between au and cu in pyrite from the first two stages indicate that gold and other metals were likely sourced from magma derived hydrothermal fluids the deposit was formed in the early paleozoic but some gold ores appear deformed and partially destroyed by a later metamorphic event during which a distinct sb rich pyrite crystallized this study should catalyze exploration in the orefield as it provides further support for an as yet undiscovered porphyry system close to the zhengguang deposit

fifth generation lithospheric magnetic field model from champ satellite measurements 1 six years of low orbit champ satellite magnetic measurements have provided an exceptionally high quality data resource for lithospheric magnetic field modeling and interpretation here we describe the fifth generation satellite only magnetic field model mf5 the model extends to spherical harmonic degree 100 as a result of careful data selection extensive corrections filtering and line leveling the model has low noise levels even if evaluated at the earth s surface the model is particularly suited for inferring large scale structure and composition of the lithosphere it is also meant to serve as the long wavelength part of continental and global scale marine and aeromagnetic anomaly maps

satellite observations of magnetic fields due to ocean tidal flow the ocean is an electrically conducting fluid that generates secondary magnetic fields as it flows through earth s main magnetic field extracting ocean flow signals from remote observations has become possible with the current generation of satellites measuring earth s magnetic field here we consider the magnetic fields generated by the ocean lunar semidiurnal m2 tide and demonstrate that magnetic fields of oceanic origin can be clearly identified in satellite observations

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

a global lithospheric magnetic field model with reduced noise level in the polar regions 1 due to persistent ionospheric current systems at high latitudes satellite magnetic measurements have high noise levels in the polar regions consequently small scale lithospheric features are much more difficult to resolve there than at lower latitudes using linear combinations of spherical harmonics sh we define localized functions which are band limited to a given maximum degree thus a model s sh resolution can be varied over the globe we produce a lithospheric field model from champ satellite data which resolves features to sh degree 90 at low latitudes but only to sh degree 60 in the polar regions the new model can be downward continued from satellite altitude to the earth s surface without generating spurious high latitude anomalies citation lesur v and s maus 2006 a global lithospheric magnetic field model with reduced noise level in the polar regions geophys res lett 33 l13304

extending comprehensive models of the earth s magnetic field with orsted and champ data summary a new model of the quiet time near earth magnetic field has been derived using a comprehensive approach which includes not only pogo and magsat satellite data but also data from the orsted and champ satellites the resulting model shows great improvement over its predecessors in terms of completeness of sources time span and noise reduction in parameters with its well separated fields and extended time domain of 1960 to mid 2002 the model is able to detect the known sequence of geomagnetic jerks within this frame and gives evidence for an event of interest around 1997 because all sources are coestimated in a comprehensive approach intriguing north south features typically filtered out with other methods are being discovered in the lithospheric representation of the model such as the s atlantic spreading ridge and andean subduction zone lineations in addition this lithospheric field exhibits significantly less noise than previous models as a result of improved data selection the f region currents through which the satellites pass are now treated as lying within meridional planes as opposed to being purely radial results are consistent with those found previously for magsat but an analysis at orsted altitude shows exciting evidence that the meridional currents associated with the equatorial electrojet likely close beneath the satellite besides the model a new analysis technique has been developed to infer the portion of a model parameter state resolved by a particular data subset this has proven very useful in diagnosing the cause of peculiar artefacts in the magsat vector data which seem to suggest the presence of a small misalignment bias in the vector magnetometer

third generation of the potsdam magnetic model of the earth pomme the potsdam magnetic model of the earth pomme is a geomagnetic field model providing an estimate of the earth s core crustal magnetospheric and induced magnetic fields the internal field is represented to spherical harmonic sh degree 90 while the secular variation and acceleration are given to sh degree 16 static and time varying magnetospheric fields are parameterized in geocentric solar magnetospheric gsm and solar magnetic sm coordinates and include disturbance storm time dst index and interplanetary magnetic field imf by dependent contributions the model was estimated from five years of champ satellite magnetic data all measurements were corrected for ocean tidal induction and night side ionospheric f region currents the model is validated using an independent model from a combined data set of orsted and sac c satellite measurements for the core field to sh degree 13 the root mean square rms vector difference between the two models at the center of the model period is smaller than 4 nt at the earth s surface the rms uncertainty increases to about 100 nt for the predicted field in 2010 as inferred from the difference between the two models

national geophysical data center candidate for the world digital magnetic anomaly map marine and airborne magnetic anomaly data have been collected for more than half a century providing global coverage of the earth furthermore the german champ satellite is providing increasingly accurate information on large scale magnetic anomalies the world digital magnetic anomaly map project is an international effort to integrate all available near surface and satellite magnetic anomaly data into a global map database teams of researchers were invited to produce candidate maps using a common pool of data sets here we present the national geophysical data center ngdc candidate to produce a homogeneous map the near surface data were first line leveled and then merged by least squares collocation long wavelengths were found to agree surprisingly well with independent satellite information this validates our final processing step of merging the short wavelength part of the near surface data with long wavelength satellite magnetic anomalies

timing of magmatic activity and mineralization and evidence of a long lived hydrothermal system in the fresnillo silver district mexico constraints from 40ar 39ar geochronology the ore deposits of fresnillo have produced silver for more than 450 years and contain resources of approximately 1 goz mineralization in fresnillo occurs in epithermal veins hosted by a middle jurassic to late cretaceous volcanosedimentary sequence guerrero terrane late paleocene conglomerates and eocene to oligocene tuffs and flows of trachyte rhyolite and rhyodacite lie unconformably on top of the guerrero terrane steam heated acid sulfate alteration containing alunite veins occurs in eocene tuffs above some of the mineralized veins oligocene rhyolitic domes and a quartz monzonite stock also occur in the area whereas sporadic miocene basaltic flows and dikes are the youngest igneous rocks in the district spatial association of tertiary volcanic rocks intrusions acid sulfate alteration and epithermal veins makes the district ideal for evaluating the temporal relations between magmatism and hydrothermal activity using precise 40ar 39ar geochronology sanidine single crystal laser fusion analyses reveal discrete volcanic eruptions at 44 73 0 04 40 92 0 04 40 83 0 04 31 55 0 03 and 31 04 0 05 ma dating of orthoclase from the fortuna quartz monzonite was problematic due to excess argon contamination but a preferred age of 32 65 0 05 ma is suggested two adularia samples from the jarillas vein give statistically identical ages of 29 75 0 12 and 29 68 0 10 ma adularia from valdecanas vein shows a climbing age spectrum related to hydrothermal alteration however a terminal step with an age of 29 74 0 07 ma suggests that the two veins may be coeval alunite recorded two distinct ages at 30 56 0 04 and 31 03 0 05 ma alunite and adularia ages suggest that acid sulfate alteration and mineralization occurred separately well after emplacement of the dated phase of the fortuna stock and consequently it cannot be the source of heat for the hydrothermal system that formed those finally the 3 m y difference in age between epithermal mineralization and the fortuna stock is indicative of a long lived but episodic hydrothermal system which could have been driven by multiple pulses of small and shallow intrusions