large scale three dimensional gravity analysis of the lithosphere below the transition zone from western europe to the east european platform abstract large scale three dimensional gravity modelling using data averaged on a 1 grid has been carried out for the transition area from western europe to the east european craton the model consists of two regional layers of variable thickness the sedimentary cover and the crystalline crust with lateral variation of average density removal of the calculated gravity effect of the crustal model from the observed gravity field reveals residual anomalies of mantle origin this is confirmed by the correlation between mantle gravity anomalies and upper mantle velocity heterogeneities imaged by seismotomographic studies the tornquist teisseyre zone ttz marked in general by a gradient zone of mantle gravity anomalies is considered as a deep density section traced in the upper mantle down to a depth of 200 km across this suture zone a dramatic change of the structure physical properties and composition of the lithosphere of the continent occurs the different characters of the mantle gravity anomalies over the two main parts of the ttz the danish scandinavian and polish segments are explained by the peculiarities of their evolution and the different character of the prevailing tectonic regimes during the proterozoic cenozoic

evaluation of paleomagnetism as a correlation criterion for mogollon datil ignimbrites southwestern new mexico paleomagnetic and rock magnetic data show that 36 24 ma ignimbrite outflow sheets in the mogollon datil volcanic field carry thermoremanent magnetizations trms that provide useful reliable correlation criteria over 90 of 404 ignimbrite sites exhibit well grouped 95 500 m intracaldera ignimbrite sequences agree in polarity with associated outflow sheets but show less consistent trm directions probably reflecting syncooling secular variation and discrepancies between eutaxitic foliations and the syncooling paleohorizontal mean virtual geomagnetic pole positions vgps of normal and reverse polarity ignimbrites are nearly antipodal 175 6 apart showing no evidence of long term differences in the zonal harmonics of the normal and reverse polarity states less antipodal mean vgps 161 2 apart from normal and reverse polarity lavas are interpreted as defects in the data set probably including incompletely removed normal polarity viscous overprints the mean paleomagnetic pole position for mogollon datil ignimbrites n 68 independent unit mean vgps is located at 78 8 n 166 6 e k 19 8 a95 4 0 18 2

gravity inversion of 2d bedrock topography for heterogeneous sedimentary basins based on line integral and maximum difference reduction methods based on the line integral li and maximum difference reduction mdr methods an automated iterative forward modelling scheme li mdr algorithm is developed for the inversion of 2d bedrock topography from a gravity anomaly profile for heterogeneous sedimentary basins the unknown basin topography can be smooth as for intracratonic basins or discontinuous as for rift and strike slip basins in case studies using synthetic data the new algorithm can invert the sedimentary basins bedrock depth within a mean accuracy better than 5 when the gravity anomaly data have an accuracy of better than 0 5 mgal the main characteristics of the inversion algorithm include 1 the density contrast of sedimentary basins can be constant or vary horizontally and or vertically in a very broad but ap rioriknown manner 2 three inputs are required the measured gravity anomaly accuracy level and the density contrast function 3 the simplification that each gravity station has only one bedrock depth leads to an approach to perform rapid inversions using the forward modelling calculated by li the inversion process stops when the residual anomalies the observed minus the calculated falls within an error envelope whose amplitude is the input accuracy level the inversion algorithm offers in many cases the possibility of performing an agile 2d gravity inversion on basins with heterogeneous sediments both smooth and discontinuous bedrock topography with steep spatial gradients can be well recovered limitations include 1 for each station position there is only one corresponding point vertically down at the basement and 2 the largest error in inverting bedrock topography occurs at the deepest points

3d gravity inversion of basement relief a depth dependent density approach we present a 3d gravity inversion technique based on the marquardt algorithm to analyze gravity anomalies attributable to basement interfaces above which the density contrast varies continuously with depth the salient feature of this inversion is that the initial depth of the basement is not a required input the proposed inversion simultaneously estimates the depth of the basement interface and the regional gravity background applicability and efficacy of the inversion is demonstrated with a synthetic model of a density interface we analyze the synthetic gravity anomalies 1 solely because of the structure 2 in the presence of a regional gravity background and 3 in the presence of both random noise and regional gravity background the inverted structure remains more or less the same regardless of whether the regional background is simulated with a second degree polynomial or a bilinear equation the depth of the structure and estimated regional background deviate only modestly from the assumed ones in the presence of random noise and regional background the analyses of two sets of real field data one over the chintalpudi subbasin india and another over the pannonian basin eastern austria yield geologically plausible models with the estimated depths that compare well with drilling data

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

paleomagnetic determination of emplacement temperatures of pyroclastic deposits an under utilized tool paleomagnetic data from lithic clasts collected from mt st helens usa volcan lascar chile volcan de colima mexico and vesuvius italy have been used to determine the emplacement temperature of pyroclastic deposits at these localities and to highlight the usefulness of the paleomagnetic method for determining emplacement temperatures at mt st helens the temperature of the deposits tdep at three sites from the june 12 1980 eruption was found to be 532 c 509 c and 510 570 c respectively one site emplaced on july 22 1980 was emplaced at 577 c these new paleomagnetic temperatures are in good agreement with previously published direct temperature measurements and paleomagnetic estimates lithic clasts from pyroclastic deposits from the 1993 eruption of lascar were fully remagnetized above the respective curie temperatures which yielded a minimum tdep of 397 c samples were also collected from deposits thought to be pyroclastics from the 1913 2004 and 2005 eruptions of colima at colima the sampled clasts were emplaced cold this is consistent with the sampled clasts being from lahar deposits which are common in the area and illustrates the usefulness of the paleomagnetic method for distinguishing different types of deposit tdep of the lower section of the lithic rich pyroclastic flow lrpf from the 472 a d deposits of vesuvius was 280 340 c this is in agreement with other recently published paleomagnetic measurements in contrast the upper section of the lrpf was emplaced at higher temperatures with tdep 520 c this temperature difference is inferred to be the result of different sources of lithic clasts between the upper and lower sections with the upper section containing a greater proportion of vent derived material that was initially hot our studies of four historical pyroclastic deposits demonstrates the usefulness of paleomagnetism for emplacement temperature estimation

structure and evolution of the northern barents kara sea continental margin from integrated analysis of potential fields bathymetry and sparse seismic data summary the northern barents kara sea continental margin is a poorly investigated area because of a permanent ice cover hampering seismic exploration the available geological and geophysical data show that the magma poor margin developed in response to early cenozoic breakup and subsequent opening of the arctic eurasia basin in this study a series of crustalscale geotransects illustrating the architecture of the continental margin are constructed using sparse seismic reflection profiles and a gravity inversion method incorporating a thermal model of rifting the continental side of the northern barents sea margin is underlain by palaeozoic early mesozoic deep sedimentary basins separated from the oceanic side by the marginal uplift a bathymetry analysis complements low resolution seismic data to predict the sedimentary depocenters beyond the shelf break these depocenters are associated with troughs perpendicular to the shelf edge the depocenter in front of the st anna trough may contain a sedimentary section more than 4 km thick the gravity correction for the effect of sedimentary cover was added to the inversion this correction used an exponential density depth function the inversion supports a narrow and steep continent ocean transition cot ca 100 km the conjugate lomonosov ridge margin is modelled using the same technique palaeoreconstructions were made to predict the break up setting the northern barents sea lomonosov ridge rift system can be described as an initially narrow symmetric rift a transitional zone of extreme thinning is assumed between the oldest spreading magnetic anomaly and the stretched continental crust the free air gravity anomaly in the western part ofthemargincanbepredicted bytheupwelling divergentflowmodel implying theexhumation of the lower crust and the continental upper mantle within the cot it is suggested that an episodeofshearorobliqueextensionbeforebreakupisrequiredtoexplaintheobservednarrow symmetric conjugate margins in the eurasia basin

large scale 3 d gravity analysis of the inhomogeneities in the european mediterranean upper mantle methods and the results of estimating the anomalies characterising the density inhomogeneities in the european mediterranean upper mantle are described these anomalies were obtained by subtracting the gravity effect of a crustal density model derived from seismic velocities from the observed gravity field averaging over an area of 1o 1o the 3 d density model of the study region comprises two regional layers of varying thickness with lateral variation of average density the sedimentary cover and the crystalline crust the average densities for model layers were evaluated by using a velocity density conversion function and taking into account sediment consolidation with depth clear correlation between residual gravity anomalies and both velocity heterogeneities and thermal regime data of the upper mantle has been revealed an agreement of positive anomalies over the alps the adriatic plate and the calabrian arc with high velocity domains in the upper mantle and reduced temperatures at the subcrustal layer are caused by lithospheric roots and thickened lithosphere below these structures gravity residual lows revealed over the western mediterranean basin and pannonian basin are in correspondence with both low velocities and high temperatures in the upper mantle these anomalies are the result of the presence of asthenosphere in shallow near moho depths below these basins

topography of the crust mantle boundary beneath the black sea basin abstract a map of moho depth for the black sea and its immediate surroundings has been inferred from 3 d gravity modelling and crustal structure has been clarified beneath the basin centre the thickness of the crystalline layer is similar to that of the oceanic crust in the western and eastern black sea basins the moho shallows to 19 and 22 km respectively below the tuapse trough northeastern margin adjacent to the caucasus orogen the base of the crust is at 28 km whereas in the sorokin trough it is as deep as 34 km the base of the crust lies at 29 and 33 km depths respectively below the southern and northern parts of the mid black sea ridge for the shatsky ridge between the tuapse trough and the eastern black sea basin the moho plunges from the northwest 33 km to the southeast 40 km the arkhangelsky ridge south of the eastern black sea basin is characterised by a moho depth of 32 km the crust beneath these ridges is of continental type

three dimensional magnetic imaging of the chicxulub crater although few magnetization measurements are available for the structural elements of the chicxulub impact crater the magnetization intensities of the melt sheet upper breccia unit and central uplift are 3 4 orders of magnitude greater than the 3 to 4 km thick carbonate and evaporite stratigraphy covering the yucatan block this allows three dimensional modeling of the crater s structure by inversion using a two layer model two layers are separately inverted by dividing the crater s magnetic field expression into 40 km wavelength components the upper layer average depth 2 km models the distribution of highly magnetized zones in the crater s melt sheet the lower layer average depth 5 km represents relief on the yucatan block s basement surface and effectively maps the crater s 50 km diameter central uplift and possibly the expression of the surrounding collapsed disruption cavity fill the shallower magnetized zones consist of two generally concentric distributions at radii of 20 and 45 km these highly magnetized zones are thought to result from hydrothermal systems localized at the edge of the central uplift and the collapsed disruption cavity having produced magnetic phases during alteration of the melt sheet

paleointensities of phonolitic obsidian influence of emplacement rotations and devitrification 1 a paleomagnetic study on phonolitic obsidian from six sites in tenerife spain is presented two sites are located at the 750 ka el pasajiron at the southern wall of las canadas caldera four sites correspond to the 115 17 bce montana blanca complex paleointensity determinations are performed with a modified thellier technique using checks for alteration and domain state additionally the anisotropy of the thermoremanence and the magnetic cooling rate dependency of each specimen are measured it was not possible to obtain good quality paleointensity data for el pasajiron thermal alteration was observed in most measurements systematic changes in rock magnetic properties and paleointensities within the profile of one site also suggest the presence of a chemical remanence crm which was probably acquired during devitrifiction of the upper part of the flow this crm cannot be seen in the arai plots themselves but only by comparison of data from different samples this underlines the importance of sampling only fresh glassy looking obsidians and not devitrified ones paleointensity determinations at montana blanca are of very good quality leading to an high success rate of 82 samples at one site show acquisition of trm during emplacement rotations however it could be shown that paleointensity data of rotated samples are reliable if the remanence carriers are in the single domain range an atrm anisotropy tensor of thermoremanent magnetization and cooling rate corrected paleointensity of 48 4 2 1 t and a vdm of 9 64 0 42 1022am2 were determined which are in very good agreement with other data from spain and morocco and to various geomagnetic field models

the permian to jurassic stratigraphy and structural evolution of the central cheshire basin new seismic reflection data reveal details of the permo triassic basin fill in the central cheshire basin the seismic stratigraphy indicates that the permian and triassic succession is far thicker than previously estimated seismic data and backstripping of the preserved permian to early jurassic sedimentary succession suggest that at least two phases of fault controlled subsidence occurred in early permian and early triassic times an intra triassic unconformity is seen on the seismic data near the top of the sherwood sandstone group this may equate with the hardegsen unconformity it is possible that this unconformity was generated by syn extensional regional uplift accompanying lithospheric thinning the gross morphology and location of the faults on the eastern margin of the cheshire basin are interpreted to be at least locally controlled by extensional re activation of a westwards dipping reverse fault possibly an extension of the pontesford linley lineament

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

automatic gravity optimization of 2 5d strike listric fault sources with analytically defined fault planes and depth dependent density an automatic gravity inversion technique in the space domain simultaneously estimates the parameters of strike limited listric fault sources and regional gravity background from a set of observed bouguer gravity anomalies the fault profile and regional effect are described by unknown polynomial functions of arbitrary but prescribed degree furthermore the density contrast within the fault structure is presumed to be known according to a prescribed parameterized nonlinear function of depth in geologic settings where the detached downthrown block consists of a series of sedimentary beds whose density increases with depth the inversion is automatic in that it initializes and determines polynomial coefficients for the fault boundary and regional gravity background from a set of observed bouguer gravity anomalies and improves them iteratively until the modeled gravity anomalies mimic the observed anomalies an analysis of a set of gravity anomalies attributable to a synthetic model of a listric fault structure in the presence of pseudorandom noise with and without regional background has disclosed that the algorithm yields reliable interpretations with modest error in model geometry even in the presence of pseudorandom noise in the presence of regional gravity background and pseudorandom noise the estimated parameters of the structure deviate marginally from the true ones the derived density depth model of the jharia coal basin in india a pull apart basin has been used to analyze the observed bouguer gravity anomalies of a boundary fault the interpretation has yielded information consistent with drilling results and geologic setting of the basin

three dimensional interpretation of gravity data from sedimentary basins using an exponential density depth function in mapping the topography of the basement of deep sedimentary basins by gravity modelling the accuracy can be improved by incorporating an exponential increase in density with depth for calculating the gravity effect of a three dimensional 3d structure with such an exponential density depth relation a frequency domain forward algorithm based on series expansion is presented the numerical evaluation of which can be performed efficiently by fast fourier transform the algorithm can be applied in a recursive procedure to give the inverse solution in terms of basement relief the inversion procedure is satisfactorily tested on a 2d synthetic example and a 3d field example of gravity data from the western margin of the pannonian basin in eastern austria where up to 2 2 km of tertiary sediments overlie an igneous or metamorphic basement the results are confirmed by basement intersections in several wells

stable inversion of gravity anomalies of sedimentary basins with nonsmooth basement reliefs and arbitrary density contrast variations we present a new stable method for interpreting the basement relief of a sedimentary basin which delineates sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of the density contrast the subsurface region containing the basin is discretized into a grid of juxtaposed elementary prisms whose density contrasts are the parameters to be estimated any vertical line must intersect the basement relief only once and the mass deficiency must be concentrated near the earth s surface subject to the observed gravity anomaly being fitted within the experimental errors in addition upper and lower bounds on the density contrast of each prism are introduced a priori one of the bounds being zero and the method assigns to each elementary prism a density contrast which is close to either bound the basement relief is therefore delineated by the contact between the prisms with null and nonnull estimated density contrasts the latter occupying the upper part

lithosphere structure of europe and northern atlantic from regional three dimensional gravity modelling summary large scale 3d gravity modelling using data averaged on a 1 grid has been performed for the whole european continent and part of the northern atlantic the model consists of two regional layers of variable thickness the sediments and the crystalline crust bounded by reliable seismic horizons the seismic basement and the moho surface inner heterogeneity of the model layers was taken into account in the form of lateral variation of average density depending on the type of geotectonic unit density parametrization of the layers was made using correlation functions between velocity and density for sediments sediment consolidation with depth was taken into account offshore a sea water layer was included in the model as a result of the modelling gravity effects of the whole model and its layers were calculated along with the gravity modelling an estimation of isostatic equilibrium state has been carried out for the whole model as well as for its separate units residual gravity anomalies obtained by subtracting the gravity effect of the crust from the observed field reach some hundred mgal 10 5 ms 2 in amplitude they are mainly caused by density heterogeneities in the upper mantle a mantle origin of the residual anomalies is substantiated by their correlation with the upper mantle heterogeneities revealed by both seismological and geothermal studies regarding the character of the mantle gravity anomalies type of isostatic compensation crustal structure age and supposed type of endogenic regime a classification of main geotectonic units of the continent was made as a result of the modelling a clear division of the continent into two large blocks precambrian east european platform eep and variscan western europe has been confirmed by their specific mantle gravity anomalies 0 50 10 5 ms 2 and 100 150 10 5 ms 2 correspondingly this division coincides with the tornquist teisseyre zone ttz marked by a gradient zone of mantle anomalies in the central part of the eep over the russian plate an extensive positive mantle anomaly probably indicating a core of ancient consolidation of the eep has been distinguished to the west and to the east of this anomaly positive mantle anomalies occur which coincide with a deep suture zone ttz and an orogenic belt the urals positive mantle anomalies of the alps the adriatic plate and the calabrian arc correlating well with both high velocity domains in the upper mantle and reduced temperatures at the subcrustal layer are caused by thickened lithosphere below these structures negative mantle anomalies revealed in the western mediterranean basin and in the pannonian basin are the result of thermal expansion of the asthenosphere shallowing to near moho depths below these basins

magnetic petrology of arc xenoliths from japan and aleutian islands xenoliths from japan and the aleutian islands were studied for the purpose of identifying source rocks with sufficient magnetization to account for positive subduction zone magsat anomalies two types of magnetic lithologies are identified 1 amphibolites and homblende gabbros containing up to 8 6 titanomagnetite mostly as large unoxidized multidomain crystals and 2 pyroxene gabbros and metagabbros with up to 20 3 titanomagnetite usually in association with primary ilmenite the first type is represented by xenoliths from ichinomegata japan and adak island in the aleutians the second restricted to iki island japan and kanaga island aleutians has abundant coarse grained titanomagnetite which in most samples has been oxidized producing secondary trellis type ilmenite lamellae a few iki island xenoliths show more advanced oxidation arc xenoliths show 3 orders of magnitude range in natural remanent magnetization and saturation remanence and about 2 orders of magnitude range in magnetic susceptibility nearly all iki island rocks and many from ichinomegata and the aleutians possess induced magnetization 2 a m 1 and greater with the expectation of additional magnetization due to viscous remanence at elevated temperature the tio 2 content of titanomagnetite together with the presence ot appreciable al 2 o3 and mgo ensure that most xenoliths have curie points between 400 and 550 c remanence acquisition curves exhibit a range reflecting varying degrees of magnetic hardening due to oxidation correspondingly each xenolith site groups distinctly on a plot of magnetic hysteresis ratios this paper indicates that lithologies with total magnetizations of many a m 1 exist in lower crust arc settings their volumetric distribution is uncertain based on the limited xenolith population reported herein

three dimensional gravity modelling of the european mediterranean lithosphere summary residual gravity anomalies characterizing the density heterogeneities in the upper mantle of the alpine belt of western europe are determined residual anomalies were calculated on a 1 x 1 grid by subtracting the gravity effect of the density model for the earth s crust from the observed gravity field our 3 d density model consists of two regional layers of varying thicknesses with a lateral variation in average density the sedimentary cover and the crystalline crust offshore the model is supplemented by a sea water layer this 3 d density model is based on a generalized velocity model represented by structure maps of the main seismic horizons the seismic basement and the moho boundary and a map of the average p wave velocity in the consolidated crust the density distribution within the model layers was obtained using the correlation functions between p wave velocity and density for sediments sediment consolidation with depth was taken into account the gravity effect of the model approximated by parallelepipeds 1 x 1 in planar size was calculated by a program designed for solving 3 d gravity problems the program takes into account the spherical configuration of the earth this method also permits the estimation of the isostatic state of the crust a mantle origin of residual gravity anomalies is confirmed by their close correlation with upper mantle velocity heterogeneities established by both seismic tomography and thermal regime data the residual gravity field is inverted into the distribution of anomalous density within the uppermost mantle layer between the moho and a bottom level at 200 km depth the most important anomalies are the high density domains caused by the thick lithosphere of the adriatic plate and by the lithosphere roots beneath the alps and the calabrian arc negative density anomalies over the pannonian basin and the western mediterranean basins reach 0 04 to 0 05 x lo3 kg m 3 due to thermal expansion of the asthenosphere

structural variation and the development of thick rhyolite lava a case study of the sanukayama rhyolite lava on kozushima island japan abstract geological studies of ancient rhyolite lavas are required for understanding flow dynamics because rhyolite lava eruption is an infrequent event the pleistocene sanukayama rhyolite lava is about 130 m thick and located on kozushima island japan vertical sections of the lava are well exposed in the sea cliff and in a dissected valley providing a good opportunity for the elucidation of the internal structural variations the vertical lithofacies variations are classified into three zones of pumiceous obsidian and crystalline from the top to the base respectively the exposed area is considered to correspond to the upper half of the lava in the boundaries between each zone the lithofacies are mingled rather than exhibiting gradual change this indicates that rheological contrasts are arisen within the lava due to differences of vesicularity and or crystallinity various heterogeneous structures are recognized throughout the lava such as obsidian and reddish layers in the pumiceous zone strongly deformed white colored bands and a clastic layer in the obsidian zone and dark colored bands in the crystalline zone we demonstrate on the basis of geological evidences and magnetic studies that these heterogeneous structures originated mostly from shear induced fracturing within the advancing lava this study indicates that brittle lava fracturing during ductile brittle transition likely governs the acceleration of rhyolite lava heterogeneity

a revision of the late cretaceous paleocene eutherian mammal cimolestes marsh 1889 cimolestes marsh is a north american eutherian mammal primarily known from latest cretaceous deposits in alberta wyoming saskatchewan and montana at present five species of cimolestes are considered valid all lancian in age they include one of the largest north american late cretaceous therian mammals as well as one of the smallest a size range far exceeding that within other genera of tribosphenic therians contemporary with cimolestes such as the leptictoid eutherian gypsonictops simpson or genera of alphadontid or pediomyid marsupials moreover the species of cimolestes display a disparity of dental morphology in addition to size well in excess of interspecific differences within these genera given these considerations cimolestes is clearly a grade taxon uniting species sharing an adaptively subzalambdodont dentition but showing divergent specializations within this pattern that are inconsistent with monophyly of its presently included species to correct these imbalances this paper limit

reconstruction of geologic bodies in depth associated with a sedimentary basin using gravity and magnetic data summary we present a comprehensive review of the most comm on gravity and magnetic interpretation methods to in depth retrieval of the geometry of two types of geologic bodies associated with a sedimentary basin 1 sedimentary basement relief and 2 salt bodies in reconstructing a basement topography we identify three groups of methods the automatic the spectral and the nonspectral methods the reconstruction of salt bodies geometries from gravity data usually uses the interactive forward modeling but recently gravity inversion methods have been developed to interpret this kind of geological environment

aceroryctes dulcis a new palaeoryctid mammalia eutheria from the early eocene of the wasatch formation of southwestern wyoming usa the palaeoryctidae are a group of small bodied likely insectivorous mammals known principally from the paleocene and early eocene from approximately 65 to 53 ma of north america here we report on a new palaeoryctid from the early eocene early wasatchian wa3 north american land mammal age main body of the wasatch formation washakie basin near bitter creek station in southwestern wyoming usa acerorcytes dulcis gen et sp nov is unique among palaeoryctids in having a double rooted p2 with a small anterior cusp p3 with pronounced para and metastylar cusps and a reduced but conspicuous metacone p4 with a weakly developed metacone and an anteroposteriorly compressed protocone and m1 2 with deep ectoflexus and a sharp metastylar blade a phylogenetic analysis based on 32 dental characters of the nine known north american palaeoryctid species including aceroryctes dulcis recovered eight equally parsimonious cladograms similar to prior studies the analysis suggests that the genus palaeoryctes

rock magnetic properties of trm carrying baked and molten rocks straddling burnt coal seams the subsurface spontaneous combustion of coal seams in xinjiang nw china during pleistocene to recent times produced large areas of thermally altered sedimentary rocks with large magnetic moments the natural remanent magnetization nrm and thermoremanent magnetization trm intensities and low field susceptibilities of such combustion metamorphic rocks range from 0 1 to 10 a m and 100 10 4 to 1000 10 4 si respectively which is two to three orders of magnitude higher than values typical of their sedimentary protoliths the dominant magnetic carriers in the burnt rocks appear to include relatively pure forms of magnetite maghemite and hematite as well as more complex spinel phases these magnetic phases mainly occur as fine pseudo single domain psd particles conspicuous is the presence of pure metallic iron fe in some samples this highly magnetic phase is inferred to appear as more or less elongated super paramagnetic and single domain sd inclusions in host silicate phases which prevent them from oxidizing the sd fe particles can carry a highly stable remanence having remanent coercivities ranging 70 140 mt the arm and irm stability of all burnt rock samples to alternating fields is shown to be relatively high median destructive fields b 1 2 a and b 1 2 i respectively range of 25 46 and 20 30 mt for dominant spinel bearing samples 34 36 and 47 53 mt for maghemite hematite bearing samples and 48 89 and 64 84 mt for metallic iron bearing samples consequently burnt rocks are high quality geomagnetic field recorders their very nature makes them useful for paleointensity determinations although age determination is a limiting factor furthermore remanence intensities and susceptibilities of these magnetically enhanced rocks are sufficient to produce observable magnetic anomalies this property illustrates the potential to delineate the areal extent and depth of extinct coal fires with magnetic exploration such information is necessary to refine estimates of hazardous co 2 emission and furthers our understanding of natural coal fires 2001 elsevier science b v all rights reserved

the origin and evolution of breakouts in a cooling limited rhyolite lava flow understanding lava flow processes is important for interpreting existing lavas and for hazard assessments although substantial progress has been made for basaltic lavas our understanding of silicic lava flows has seen limited recent advance in particular the formation of lava flow breakouts which represent a characteristic process in cooling limited basaltic lavas but has not been described in established models of rhyolite emplacement using data from the 2011 2012 rhyolite eruption of puyehue cordon caulle chile we develop the first conceptual framework to classify breakout types in silicic lavas and to describe the processes involved in their progressive growth inflation and morphological change by integrating multiscale satellite field and textural data from cordon caulle we interpret breakout formation to be driven by a combination of pressure increase from local vesiculation in the lava flow core as well as from continued supply via extended thermally preferential pathways and a weakening of the surface crust through lateral spreading and fracturing small breakouts potentially resulting more from local vesiculation than from continued magma supply show a domed morphology developing into petaloid as inflation increasingly fractures the surface crust continued growth and fracturing results in a rubbly morphology with the most inflated breakouts developing into a cleft split morphology reminiscent of tumulus inflation structures seen in basalts these distinct morphological classes result from the evolving relative contributions of continued breakout advance and inflation the extended nature of some breakouts highlights the role of lava supply under a stationary crust a process ubiquitous in inflating basalt lava flows that reflects the presence of thermally preferential pathways textural analyses of the cordon caulle breakouts also emphasize the importance of late stage volatile exsolution and vesiculation within the lava flow although breakouts occur across the compositional spectrum of lava flows the greater magma viscosity is likely to make late stage vesiculation much more important for breakout development in silicic lavas than in basalts such late stage vesiculation has direct implications for hazards previously recognized from silicic lava flows enhancing the likelihood of flow front collapse and explosive decompression of the lava core

prediction of sediment thickness in the norwegian greenland sea from gravity inversion 1 we explore the feasibility of inverting freely available altimetry derived gravity grids for sediment thickness on oceanic crust a four layer earth model is adopted assuming that the gravity signal from the base of the sedimentary layer can be fully isolated from the observed free air gravity the following additional data are required 1 shipboard bathymetry for reliable bouguer correction 2 oceanic crustal ages to correct for gravity anomalies related to the thermal history of lithospheric breakup and seafloor spreading and 3 some wide angle seismic observations of sediment thickness a fixed relationship between the base of the sedimentary layer and the moho is also required because of limited gravity resolution at large depths the final inversion setup searches for three control parameter values density of uppermost sediments density of oceanic crystalline crust and thermal diffusivity of mantle rock that minimize misfit between the earth model and observations applied to the norwegian greenland sea the inversion successfully predicts locations of 20 25 km wide depocenters and crystalline crustal highs yet 1 km thickness errors are common even in well constrained areas the largest errors are associated with underplated crust active mid ocean ridges and the continent ocean boundary indicating locally incorrect assumptions of mantle thermal structure and crystalline crustal thickness the thicknesses of 4 km thick submarine fans are underpredicted probably because of too low sedimentary densities in the earth model if these limitations are acceptable or do not apply because of simple crustal structure gravity inversion may be used for mapping regional sedimentary patterns e g in the arctic ocean

combining geophysical data sets to study the dynamics of shallow evaporites in urban environments application to hamburg germany summary shallowly situated evaporites in built up areas are of relevance for urban and cultural development and hydrological regulation the hazard of sinkholes subrosion depressions and gypsum karst is often difficult to evaluate and may quickly change with anthropogenic influence the geophysical exploration of evaporites in metropolitan areas is often not feasible with active industrial techniques we collect and combine different passive geophysical data as microgravity ambient vibrations deformation and hydrological information to study the roof morphology of shallow evaporites beneath hamburg northern germany the application of a novel gravity inversion technique leads to a 3 d depth model of the salt diapir under study we compare the gravity based depth model to pseudo depths from h v measurements and depth estimates from small scale seismological array data while the general range and trend of the diapir roof is consistent a few anomalous regions are identified where h v pseudo depths indicate shallower structures not observed in gravity or array data these are interpreted by shallow residual caprock floaters and zones of increased porosity the shallow salt structure clearly correlates with a relative subsidence in the order of 2 mm yr 1 the combined interpretation of roof morphology yearly subsidence rates chemical analyses of groundwater and of hydraulic head in aquifers indicates that the salt diapir beneath hamburg is subject to significant ongoing dissolution that may possibly affect subrosion depressions sinkhole distribution and land usage the combined analysis of passive geophysical data may be exemplary for the study of shallow evaporites beneath other urban areas

crustal architecture and moho topography beneath the eastern indian and bangladesh margins new insights on rift evolution and the continent ocean boundary the thick sedimentary cover 18 km along the eastern continental margin of india ecmi and over the bay of bengal has hindered understanding of the mechanisms of rifting that operated on the eastern indian and bangladesh margins analysis of multichannel seismic reflection data together with 3d gravity inversion and 2d gravity forward modelling illuminates basement configuration crustal thickness and moho topography thereby revealing the modes of rift evolution and the location of the continent ocean boundary cob along these margins the basement particularly in the shelf and slope regions of eastern peninsular india is traversed by nearly coast perpendicular graben and their seaward continuity is delineated up to 125 km from the coastline three different types of continental margin are present along the ecmi 1 sheared rift on the southern segment of the ecmi up to 14 n latitude offshore the southern granulite terrain 2 hyper extended rift in the central segment between 14 n and 17 n offshore the dharwar craton and 3 hypo extended rift on the northern segment between 17 n and 20 n offshore the eastern ghats mobile belt the graben terminations crustal thickness and moho topography of both the ecmi and offshore bengal basin clearly suggest that the cob runs nearly parallel to the coastline of peninsular india but takes an orthogonal turn offshore in the bengal basin and connects the palaeo continental shelf and the rajmahal sylhet line onshore in the bengal basin crustal thickness 8 10 km and depth to the moho discontinuity 28 km beneath the bangladesh margin are unusual because the crustal thickness increased through interaction of the kerguelen plume with the existing oceanic lithosphere the moho deepened largely due to the load of the bengal fan sediments the absence of rifted crustal blocks on the bangladesh margin and the continuity of the cob into the onshore bengal basin together imply that the present bangladesh region was under marine conditions at least until the beginning of bengal fan sedimentation i e no less than 23 ma

crustal structure in the carpatho pannonian region insights from three dimensional gravity modelling and their geodynamic significance a three dimensional gravity modelling of the carpatho pannonian region was carried out to get a better image of the moho boundary and the most prominent intra crustal density heterogeneities at first only the major density boundaries were considered the bottom of the tertiary basin fill the moho discontinuity and the lithosphere to asthenosphere boundary density contrasts were represented by relative densities the improved density model shows a transitional unit of high density at the base of the crust along the teisseyre tornquist zone in the western carpathians an extensive relatively low density unit was inferred in mid crustal levels the border zone between the southern carpathians and the transylvanian basin is characterized by a sharp step like contact of the two crustal units the moho configuration reveals important information on the tectonic evolution of the region zones of continental collision are represented by thick moho roots eastern alps eastern carpathians transpressional orogenic segments however are different in the western carpathians the moho is a flat surface in the dinarides a medium moho root is observed the southern carpathians are characterized by a thick crustal root the differences are explained with the presence or absence of subductible oceanic crust along the carpathians during the extrusion of pannonian blocks

three dimensional gravity inversion model of the deep crustal structure of the central drake passage shackleton fracture zone and west scotia ridge antarctica 1 gravity and bathymetric data collected by the spanish r v hesperides over the shackleton fracture zone sfz and the west scotia ridge wsr were used to invert for the three dimensional 3 d structure of the deep crust data from the global gravity grid and global seafloor topography ggsft were also employed to enlarge the cruise area the merged data were analyzed to determine 3 d deep structure by numerical inversion water layer contribution to the gravity anomaly was eliminated taking into account the bathymetry spectral analysis of the reduced data yielded mean crust mantle interface cmi depths of 10 5 1 2 km inversion of the regional anomaly gave a 3 d detailed geometry of the cmi which generally agrees with the 2 d models established along profiles where gravity data and multichannel seismic lines are available the wsr shows an asymmetrical structure with a reverse fault located southeastward to the central valley this fault was developed probably as a consequence of the nw se compressive deformations which occurred following the spreading the 3 d view shows that the sw end of the spreading axis was affected more intensely by the compression the sfz represents an active sinistral transpressive fault zone of the scotia antarctica plate boundary and shows crustal thickening related to bathymetric highs the crustal thinning detected at the intersection with the inactive wsr suggests a complex interaction between these two structures

fault textures in volcanic conduits evidence for seismic trigger mechanisms during silicic eruptions it is proposed that fault textures in two dissected rhyolitic conduits in iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows detailed field and petrographic analysis of such textures may shed light on the origin of long period and hybrid volcanic earthquakes at active volcanoes there is evidence at each conduit investigated for multiple seismogenic cycles each of which involved four distinct evolutionary phases in phase 1 shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow forming the angular fracture networks that initiated faulting cycles transient pressure gradients were generated as the fractures opened which led to fluidisation and clastic deposition of fine grained particles that were derived from the fracture walls by abrasion fracture networks then progressively coalesced and rotated during subsequent slip phase 2 developing into cataclasite zones with evidence for multiple localised slip events fluidisation and grain size reduction phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction controlled stick slip behaviour increasing cohesion of cataclasites then led to aseismic distributed ductile deformation phase 3 and generated deformed cataclasite zones which are enriched in metallic oxide microlites and resemble glassy pseudotachylite continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite rich flow bands in obsidian phase 4 overall the mixed brittle ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle ductile transition with the rheological response mediated by strain rate variations and frictional heating fault processes in highly viscous magma are compared with those elsewhere in the crust and this comparison is used to appraise existing models of volcano seismic activity based on the textures observed it is suggested that patterns of long period and hybrid earthquakes at silicic lava domes reflect friction controlled stick slip movement and eventual healing of fault zones in magma which are an accelerated and smaller scale analogue of tectonic faults

deformation of rhyolite lava crust associated with intermittent inner flow of lava palaeomagnetic evidence a palaeomagnetic study has been conducted to examine the deformation of thick crusts of rhyolite lava while its inner portions continue to flow the sanukayama rhyolite lava which erupted in the pleistocene in kozushima island japan was chosen as the investigation site because of its well exposed vertical lithofacies variations classified into three distinct zones pumiceous obsidian and crystalline the targets of this study are the pumiceous and obsidian zones which constitute the crust of the lava thermal demagnetization reveals three remanent magnetization components from the pumiceous and obsidian samples but only a single magnetization component from the inner crystalline rhyolite samples alternating field demagnetization is ineffective in isolating the magnetization components in the pumiceous and obsidian samples the multiple components of remanent magnetization of the crust are interpreted to have been acquired during cooling as thermoremanent magnetizations we suspect intermittent lava transport of the inner portions the primary mode of rhyolite lava advancement to be responsible for the presence of multiple components in pumice and obsidian of the lava crust when the inner portions of the lava retain mobility to flow out of the crust the solidified crust of the lava surface below the magnetite curie temperature remains susceptible to deformation analysis of palaeomagnetic directions from the crust allows the deformation of the crust to be described in terms of rotation although the mode of rhyolite lava advancement is not well understood because of its infrequent occurrence our observations offer an important insight on how the mobile part of the lava is associated with the deformation of the crust during continued lava advance

gravity effect of sediment compaction examples from the north sea and the rhine graben abstract a fourier domain expression for calculating the gravity effect of a continuously varying density structure is used to investigate the way in which sediment compaction modifies the shape of the gravity anomaly across a sedimentary basin in general sediment density increases with depth in a basin as the overburden thickness increases the effect of the increase in sediment density is to reduce the gravity contribution from the density contrasts in the deeper parts of the basin relative to near surface contributions for a theoretical uncompensated basin the gravity effect of the sediments is calculated for a density depth variation described by 1 a simple exponential increase in sediment density with depth and 2 an exponential modified to include a local density inversion representative of sediment overpressuring it is shown that for both cases the calculated gravity does not necessarily reflect the morphology of the sediment basement interface the gravity effect is most sensitive to the distribution of the youngest stratigraphic units within the basin results of modeling observed gravity anomalies across the viking and rhine graben show that the small peak to trough amplitude of the gravity anomalies across these basins can be attributed to the increase in sediment density with depth rather than the compensation of the basin for the rhine graben it is further shown that the wavelength of the gravity anomaly is strongly controlled by the flexural strength of the lithosphere together these results suggest that while the amplitude of gravity anomalies across extensional basins may be primarily reflecting compaction of the sediment infill the anomaly wavelength is more sensitive to the compensation mechanism

determination of crustal interface topography from potential fields we present a method for determination of the topography of an interface separating two uniformly but differently magnetized media the technique is developed within the framework of discrete linear inverse theory and exploits the quasi linearity of the problem to derive a simple efficient algorithm suitable for use on large gridded data sets variation of auxiliary parameters allows a suite of acceptable models to be produced rapidly these parameters can be appraised in light of available geologic and geophysical evidence because very large matrices are involved when large amounts of data are interpreted approximate resolution measures requiring no matrix inversion provide useful information concerning averages of the constructed topography

3d gravity inversion of the cheshire basin1 three dimensional inverse gravity modelling is used to determine the structure of the carboniferous sediments underlying the jurassic and permo triassic formations in the cheshire basin the gravity effect of the jurassic and permo triassic rocks was first removed from the observations and the resulting residual gravity field was then inverted to map variations in depth of the carboniferous formations the inversion technique is performed in the frequency domain enabling rapid computation of solutions for large gridded data sets evaluation of results shows that there is good agreement between calculated and observed values with interpreted depths to the base of the carboniferous in excess of 6 km gravity inversion results also delineate areas of faulting on the south western and eastern edges of the basin

imaging of the moho depth in madagascar through the inversion of gravity data geodynamic implications several e w profiles of bouguer anomalies across the precambrian basement were inverted by applying a linearized inversion procedure in the spectral domain and using a simplified two layer model with a crust upper mantle interface of constant density contrast from these inverted profiles a contour map of moho topography has been constructed which covers the area of exposed precambrian basement in the eastern and central parts of the island such imaging of the moho depth in particular exhibits a n20 e trending zone of substantially thinned crust along the axis of the island this parallels the east coast margin which resulted from the northward motion of india relative to madagascar in the upper cretaceous from combined analysis of geological tectonic and metamorphic observations this prominent crustal feature in the precambrian basement of madagascar is interpreted as the relic of continental lithospheric extension and thinning possibly related to panafrican collapse tectonics on the eastern edge of the mozambique belt this extensional feature would have been reactivated only in part during the rifting and dislocation stages of the madagascar and india continental blocks as evidenced by an axis of cretaceous volcanism emphasized by the ankaratra and itasy massifs final separation nevertheless occurred further east at the site of the east coast margin

crustal density structure in the spanish central system derived from gravity data analysis central spain abstract shallow and deep sources generate a gravity low in the central iberian peninsula long wavelength shallow sources are two continental sedimentary basins the duero and the tajo basins separated by a narrow mountainous chain called the spanish central system to investigate the crustal density structure a multitaper spectral analysis of gravity data was applied to minimise biases due to misleading shallow and deep anomaly sources of similar wavelength first an estimation of gravity anomaly due to cenozoic sedimentary infill was made power spectral analysis indicates two crustal discontinuities at mean depths of 31 1 3 6 and 11 6 0 2 km respectively comparisons with seismic data reveal that the shallow density discontinuity is related to the upper crust lower limit and the deeper source corresponds to the moho discontinuity a 3d depth model for the moho was obtained by inverse modelling of regional gravity anomalies in the fourier domain the moho depth varies between a mean depth of 31 km and 34 km maximum depth is located in a nw se trough gravity modelling points to lateral density variations in the upper crust the central system structure is described as a crustal block uplifted by ne sw reverse faults the formation of the system involves displacement along an intracrustal detachment in the middle crust this detachment would split into several high angle reverse faults verging both nw and se the direction of transport is northwards the detachment probably being rooted at the moho

total variation regularization for depth to basement estimate part 1 mathematical details and applications we have developed an inversion approach that estimates the basement relief of a fault bounded sedimentary basin the sedimentary pack is approximated by a grid of 3d or 2d vertical prisms juxtaposed in the horizontal directions of a right handed coordinate system the prisms thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data to obtain depth to basement estimates we introduce the total variation tv regularization as a stabilizing function this approach lets us estimate a nonsmooth basement relief because it does not penalize sharp features of the solution we have deduced a compact matrix form of the gradient vector and the hessian matrix of the approximation to the tv function that allows a regularized gauss newton minimization approach because the hessian matrix of the approximation to the tv function is ill conditioned we have modified this hessian matrix to improve its condition and to accelerate the convergence of the gauss newton algorithm tests conducted with synthetic data show that the inversion method can delineate discontinuous basements presenting large slips or sequences of small slip step faults tests on field data from the almada basin brazil and from the san jacinto graben california u s a confirm the potential of the method in detecting and locating in depth normal faults in the basement relief of a sedimentary basin

an algorithm to calculate the gravity anomaly of sedimentary basins with exponential density depth relationships we derive wavenumber domain expressions to calculate the gravity anomaly of a body with irregular bounding surfaces and an exponential density depth relationship we apply the method to sedimentary basins which commonly have this type of geometry and density distribution the mathematical formulation also allows the exponential density depth relationship to be measured from an arbitrary irregular surface rather than the top surface using this arrangement the gravity anomaly of exhumed sedimentary basins can be predicted if the amount of eroded section can be estimated the corresponding inverse algorithms are also derived examples of the use of the forward algorithms from the galicia interior basin and the central irish sea basin are used to illustrate these methods

three dimensional analysis of gravity anomalies of sedimentary basins by polygonal prismatic model with a quadratic density function the decrease of density contrast in sedimentary strata may be approximated by a quadratic function a sedimentary basin may be considered as a number of horizontal polygonal prisms of finite thickness placed one over the other equations for the gravity anomaly of ann sided polygon prism have been derived using a quadratic density function a method has been developed for inversion of the gravity anomalies using a polygonal prismatic model an analytical method has been employed for evaluating the necessary derivatives as the computing time by this method is much slower than by a numerical method approximate equations have been derived for rapid calculation of the anomalies and derivatives efficient computer programs have been developed for calculation of the anomalies and derivatives by an appropriate use of the exact and approximate equations the depths to the polygon prisms constituting the basin are iteratively adjusted by minimizing the sum of the squares of the differences between the observed and calculated anomalies these methods have been applied to analyze the bouguer anomaly map of the los angeles basin california

3d and 2 d modelling of gravity anomalies with variable density contrast1 the decrease of density contrast in sedimentary basins may be approximated by a quadratic function a sedimentary basin may be viewed as a number of prisms placed in juxtaposition equations in closed form for the gravity anomalies of 3d and 2 d prismatic models are derived approximate equations for these models are also derived for rapid calculations efficient methods are developed for anomaly calculation by an appropriate use of the exact and approximate equations and hence for 3d and 2 d modelling the depths to the basement are adjusted iteratively by comparing the calculated anomalies with the observed anomalies these methods are applied for analysis of the residual anomaly map of the los angeles basin california

internal textures of rhyolite flows as revealed by research drilling recent drilling of 550 and 140 000 yr old rhyolite lava flows in the inyo dome chain california and valles caldera new mexico and field inspection of 8 ma flows in western arizona reveal a more detailed vertical zonation of lava textures in glassy rhyolite flows than has previously been recognized the upper vitrophyre of a flow can usually be subdivided into a surficial finely vesicular pumice underlain by obsidian coarsely vesicular pumice and a second obsidian layer beneath these layers is the crystalline center of the flow which in turn is underlain by a basal obsidian layer lower vitrophyre differences in lava vesicularity and crystallinity between zones in a flow result from primary effervescence devitrification lava rheology and migration of water vapor

magnetic petrology of the 1991 1995 dacite lava of unzen volcano japan degree of oxidation and implications for the growth of lava domes abstract to understand the oxidation state and process of oxidation of lava domes we carried out magnetic petrological analyses of lava samples obtained from domes and block and ash flow deposits associated with the 1991 1995 eruption of unzen volcano japan as a result we recognize three different types of magnetic petrology each related to deuteric high temperature oxidation during initial cooling type a oxides are characterized by homogenous titanomagnetite and titanohematite indicating a low oxidation state and high titanomagnetite concentrations type b oxides are weakly exsolved and contain titanohematite laths and rutile lenses indicating a higher oxidation state type c oxides which represent the highest oxidation state are completely exsolved and composed of ti poor titanomagnetite titanohematite rutile and pseudobrookite indicating high hematite concentrations some grains in types a and b show indications of reduction which was related to interaction with volcanic gases subsequent to high temperature oxidation in terms of geological occurrence the oxidation processes probably differed for endogenous and exogenous domes endogenous dome lavas are oxidized concentrically and are classified into the three types according to their location within the dome samples from the surface are strongly oxidized and classified as type c while the inner part is unoxidized and classified as type a exogenous dome lavas are unoxidized and assigned to type a some samples show signs of reduction which may have occurred around fumaroles we propose that location within the dome and the process of dome growth are the factors that control oxidation

marquardt optimization of gravity anomalies of anticlinal and synclinal structures with prescribed depth dependent density an inversion technique using the marquardt optimization is developed to interpret the gravity anomalies due to anticlinal and synclinal structures with density contrast varying continuously with depth the algorithm simultaneously estimates the parameters of the respective models in addition to the regional gravity background that is invariably associated with the residual gravity anomaly forward modelling is realized through analytically derived gravity expressions for the respective models in the space domain the efficacy of the inversion is demonstrated with the gravity anomaly due to a theoretical model in each case with and without the regional background in addition the applicability is illustrated using the gravity anomalies of the pays de bray anticline situated north west of paris france the interpreted depth of the pays de bray anticline using the present inversion compares well with the drilling depth

three dimensional structure of the laguna salada basin and its thermal regime a comprehensive reinterpretation of the available gravity magnetic geothermal geological and borehole information has been made of the laguna salada basin to establish a 3d model of the basement and sedimentary infill according to statistical spectral analysis the residual gravity anomaly is due to sources with a mean regional depth of 2 8 km the topography of the basement was obtained from a three dimensional inversion carried out in the wavenumber domain using an iterative scheme the maximum density contrast of 300 kg m 3 estimated from previous studies and the mean depth of 2 5 km finally constrained this inversion the resulting model indicated that the sedimentary infill is up to 4 2 km thick at its deepest point according to the gravity derived basement topography the basin presents an asymmetry i e it is of the half graben type it is deeper to the east where it is delimited from the sierra cucapah by a step fault by contrast the limit with the sierra de juarez is a gently sloping fault i e a listric fault the basement is not even but it comprises a series of structural highs and lows n s to nw se and e w to ne sw faults delimit these structural units the magnetic modelling was constrained by i the gravity derived basement topography ii a curie isotherm assumed to be between 7 km and 10 km iii assuming induced magnetization only iv the available geological and borehole information the magnetic anomalies were interpreted successfully using the gravity derived basement sedimentary interface as the top of the magnetic bodies i e the magnetic modelling supports the gravity basement topography an elongated n s to nw se trending highly magnetized body running from south to north along the basin is observed to the west of the basin this magnetic anomaly has no gravity signature such a feature can be interpreted as an intrusive body emplaced along a fault running through the laguna salada basin treatment of the gravity and magnetic information and of their horizontal gradients with satellite image processing techniques highlighted lineaments on the basement gravity topography correlating with mapped faults based on all this information we derived detailed geological models along four selected profiles to simulate numerically the heat and fluid flow in the basin we used a finite difference scheme to solve the coupled darcy and fourier differential equations according to our results we have fluid flow in the sedimentary layers and a redistribution of heat flow from the basin axis toward its rims sierra de juarez and sierra cucapah our model temperatures agree within an error of 4 with the observed temperature profiles measured at boreholes our heat flow determinations agree within an error of 15 with extrapolated observations the numerical and chemical analyses support the hypothesis of fluid circulation between the clay lutite layer and the fractured granitic basement thermal modelling shows low heat flow values along the laguna salada basin deep fluid circulation patterns were observed that redistribute such flow at depth two patterns were distinguished one displays the heat flow increasing from the basin axis towards its borders temperature increase of 20 c the second pattern shows an increasing heat flow from south to north of the basin such behaviour is confirmed by the temperature measurements in the thermometric boreholes

lithotype discrimination within a gridded model by inverting gravity data summary in this paper we present a method which allows delineation of geologic structures in a bi modal lithotype setting we propose to use gravity data in combination with a priori information about the density contrast between the two lithotypes the iterative method uses an objective function with five tunable parameters which need to be set using an efficient parameter search suitable ranges of these are investigated to determine their optimal values respectively which in turn ensures good inversion results the approach produces structural images of the subsurface without the need of an a priori density model the depth to the top of the inhomogeneity is also retrieved besides synthetic simulations the methodology has also been applied to a small gravity data set acquired by the industry over a basinal structure a consistent bi modal image of the bedrock depression is obtained from the data which in this case was the goal other potential areas of application include delineation of salt structures and ore deposits

geological setting of vertebrate microfossil localities across the cretaceous paleogene boundary in southwestern saskatchewan canada the frenchman and ravenscrag formations of southwestern saskatchewan canada record an apparently continuous sequence of nonmarine clastic sediments across the cretaceous paleogene k pg boundary extensive exposures of these fossil rich sediments occur in the frenchman river valley near the towns of ravenscrag eastend and shaunavon and have been a focus of study since the 1970s despite this long history of investigation a comprehensive account of the geographic and stratigraphic positions of many of the significant fossil localities has yet to be published given this state of affairs the goals of this paper are to i document the geographic locations stratigraphic positions and lithologies of 11 key vertebrate microfossil localities including several new localities that have been recently discovered and ii provide an update on the status of these fossil localities the majority of which have not been sampled in the last 20 years four fossil localities are known from the lower paleocene

examining rhyolite lava flow dynamics through photo based 3d reconstructions of the 2011 2012 lava flowfield at cordon caulle chile during the 2011 2012 eruption at cordon caulle chile an extensive rhyolitic flowfield was created in excess of 0 5 km3 in volume affording a unique opportunity to characterise rhyolitic lava advance in 2012 and 2013 we acquired approximately 2500 digital photographs of active flowfronts on the north and east of the flowfield these images were processed into three dimensional point clouds using structure from motion and multi view stereo sfm mvs freeware from which digital elevation models were derived sequential elevation models separated by intervals of three hours six days and one year were used to reconstruct spatial distributions of lava velocity and depth and estimate rheological parameters three dimensional reconstructions of flowfronts indicate that lateral extension of the rubbly a like flowfield was accompanied by vertical inflation which differed both spatially and temporally as a function of the underlying topography and localised supply of lava beneath the cooled upper carapace compressive processes also drove the formation of extensive surface ridges across the flowfield continued evolution of the flowfield resulted in the development of a compound flowfield morphology fed by iterative emplacement of breakout lobes the thermal evolution of flow units was modelled using a one dimensional finite difference method which indicated prolonged residence of magma above its glass transition across the flowfield we compare the estimated apparent viscosity 1 21 4 03 1010 pa s of a breakout lobe based on its advance rate over a known slope with plausible lava viscosities from published non arrhenian temperature viscosity models and accounting for crystallinity 50 vol there is an excellent correspondence between viscosity estimates when the lava temperature is taken to be magmatic despite the breakout being located 3 km from the vent and advancing approximately nine months after vent effusion ceased this indicates the remarkably effective insulation of the lava flow interior providing scope for significant evolution of rhyolitic flow fields long after effusive activity has ceased

3 d density model for the lithosphere of europe construction method and preliminary results summary a map of the observed gravity field of europe has been constructed by averaging anomalies on a 1 x 1 grid in a combined reduction of bouguer anomalies on land and free air anomalies offshore on the basis of the observed gravity field and recent seismic data on crustal structure a 3 d density model for the lithosphere of europe has been calculated the model is represented by two complementary parts each obtained by its own specific method for the south of eastern europe the 3 d density model of the earth s crust comprising the sedimentary cover and three layers within the crystalline crust upper intermediate and lower crust was obtained by the following procedure 1 the velocity model was transformed into a density distribution using the velocity density relation 2 the gravity field of this density distribution was calculated by solving the 3 d direct gravity problem 3 the residual gravity field was obtained by subtracting the total gravity effect of the model and the regional component from the oberved gravity field 4 the isostatic equilibrium of the model was evaluated 5 in accordance with the residual anomalies and isostasy estimates some changes mainly in density distribution within the sedimentary cover were entered into the initial density model and the final version of the density model was obtained for the consolidated crust as well as for areas with density inhomogeneities within the upper mantle the correlation between moho traveltimes and crustal gravity influence obtained from the results of 3 d modelling for the south of eastern europe supplemented by 2 d modelling data available over western europe makes it possible to estimate without solving the direct gravity problem the crustal gravity field for the whole european continent residual anomalies due to subcrustal density inhomogeneities have been interpreted in the light of seismic tomography and heat flow distribution for both parts of the model geological and geodynamical interpretations of the results have been made in particular differences in the deep structure of the two major geoblocks of the continent the west and east european platforms have been confirmed regions of relatively light upper mantle have been outlined beneath the east and north west of the east european platform while a heavier upper mantle has been distinguished below the alps the caucasus and the calabrian arc as well as under the south caspian depression

using thermal remanent magnetisation trm to distinguish block and ash flow and debris flow deposits and to estimate their emplacement temperature 1991 1995 lava dome eruption at mt unzen volcano japan abstract the 1991 1995 mt unzen eruption kyushu japan produced 13 lava domes approximately 9400 block and ash pyroclastic flows baf resulting from lava dome collapse events and syn and post dome collapse debris flow df events in the field it can be very difficult to distinguish from field facies characteristics which deposits are primary hot baf cold baf or rock avalanche or secondary df deposits in this study we use a combination of field observations and thermal remanent magnetisation trm analysis of juvenile lava dome derived clasts from seven deposits of the 1991 1995 mt unzen eruption in order to distinguish between primary baf deposits and secondary df deposits and to determine their emplacement temperature four major trm patterns were identified 1 type i clasts with a single magnetic component oriented parallel to the earth s magnetic field at time and site of emplacement this indicates that these deposits were deposited at very high temperature between the curie temperature of magnetite 540 c and the glass transition temperature of the lava dome 745 c these clasts are found in high temperature baf deposits 2 type ii clasts with two magnetic components of magnetisation the lower temperature magnetic components are parallel to the earth s magnetic field at time of the unzen eruption temperature estimations for these deposits can range from 80 to 540 c we found this paleomagnetic behaviour in moderate temperature baf or warm df deposits 3 type iii clasts with three magnetic components with a lower temperature component oriented parallel to the earth s magnetic field at unzen the individual clast temperatures estimated for this kind of deposit are usually less than 300 c we interpret this paleomagnetic behaviour as the effect of different thermal events during their emplacement history there are several interpretations for this paleomagnetic behaviour including remobilisation of moderate temperature baf warm df or syn eruptive granular flows 4 type iv clasts with single or two magnetic components that are randomly oriented suggesting an emplacement at ambient temperature these clasts are found in df and syn eruptive rock avalanche deposits containing high proportion of well rounded clasts and non carbonised vegetation we demonstrate that trm analysis associated with field observations can be a viable method for determining the emplacement temperature of hot baf and cold df deposits characterised by similar componentry and sedimentological facies this has implications for hazard assessment of older dormant volcanic systems to reconstruct the eruptive history

3d gravity analysis in the spatial domain model simulation by multiple polygonal cross sections coupled with exponential density contrast an automatic 3d modeling technique is developed in the spatial domain to analyze the gravity anomalies produced by a concealed density interface with mass density contrast differing exponentially with depth the sedimentary column above the interface is described with a stack of multiple vertical polygonal sections of unit thickness each for such a case the depth ordinates of the vertices of the cross sections become the unknown parameters to be estimated from gravity data forward solution of the model space is realized in the spatial domain by a technique that combines both analytic and numeric approaches initial depths to the interface are calculated based on the bouguer slab approximation and subsequently improved iteratively based on the ratio of the product of the observed gravity anomaly and existing depth parameter to the corresponding model gravity response the iterative process continues until one of the predefined termination criteria is accomplished unlike the existing methods the advantage of the proposed method is that the observed gravity anomalies need not necessarily be sampled available at regular spatial grid intervals the applicability of the proposed model is exemplified with a set of noisy gravity anomalies attributable to a synthetic structure before being applied to a real world gravity data in the case of the synthetic example the method has yielded a structure that was compatible with the assumed structure even in the presence of random noise application of the proposed method to the gravity data set from the los angeles basin california using a prescribed exponential density function has yielded a model that concurs reasonably well with the published models

an integrated geophysical approach for imaging subbasalt sedimentary basins case study of jam river basin india an integrated geophysical strategy comprising deep electrical resistivity and gravity data was devised to image subbasalt sedimentary basins a 3d gravity inversion was used to determine the basement structure of the permian sediments underlying the cretaceous formation of the jam river basin in india the thickness of the cretaceous formation above the permian sediments estimated from modeling 60 deep electric sounding data points agrees well with drilling information the gravity effect of mass deficit between the cretaceous and permian formations was found using 3d forward modeling and subsequently removed from the bouguer gravity anomaly along with the regional gravity field the modified residual gravity field was then subjected to3d inversion to map the variations in depth of the basement beneath the permian sediments inversion of gravity data resulted in two basement ridges running almost east to west dividing the basin into three independent depressions it was found that the katol and kondhali

strike slip tectonics and quaternary basin formation along the vienna basin fault system inferred from bouguer gravity derivatives 1 the vienna basin at the transition between the alpine and carpathian belt hosts a number of large pleistocene sub basins forming along an active continental scale strike slip fault vienna basin strike slip fault we utilize first order derivatives from industrial bouguer gravity data to unravel the impacts of pleistocene kinematics on the vienna basin and to compensate for the lack of near surface fault data anomalies have been evaluated by independent geophysical and geological data and were integrated to build up a tectonic model factors influencing the wavelength and the amplitude of anomalies were additionally investigated by 2 d models to better interpret field data subsidence and related accumulation of quaternary sediments in the vienna basin produce significant gravity signals related to the activity of the strike slip fault the constrained fault patterns and structures highlight tight and elongated transtensional pull apart basins with typically associated features like separated depocenters and riedel fractured sidewalls in an en echelon alignment further pleistocene basins are highlighted as tectonic grabens developing along branches of the master fault the vienna basin is additionally affected by minor deformation represented by both subsidence along major miocene sidewalls and nw se faulting resulting in distinct topographic features which manifests kinematics on a regional scale the clear density contrasts between miocene marine and quaternary terrestrial sediments as well as the exceptional database provide a unique framework to demonstrate advantages of incorporating gravity derivatives for near surface fault analysis

modelling of sedimentary basins from gravity anomalies with variable density contrast summary the decrease of density contrast with depth in sedimentary basins could be approximated by a quadratic function the sedimentary basin is viewed as a number of outcropping vertical prisms put in juxtaposition at each observation point equations are derived for the gravity anomaly of a vertical prism for a quadratic density function the initial model is obtained by calculating the thicknesses of the prisms at each station by an infinite slab formula the differences between the observed anomalies and the anomalies of the initial model at each station are used to modify the initial model a computer program is developed for initial estimates and refinement of the model the method is applied to interpret the gravity anomaly of san jacinto graben california where sediments filling the graben have a density contrast that can be approximated to a quadratic function finally the convergence of the method is discussed

lithosphere structure of european sedimentary basins from regional three dimensional gravity modelling abstract a three dimensional 3d density model approximated by two regional layers the sedimentary cover and the crystalline crust offshore a sea water layer was added has been constructed in 1 averaging for the whole european continent the crustal model is based on simplified velocity model represented by structure maps for main seismic horizons the seismic basement and the moho boundary laterally varying average density is assumed inside the model layers residual gravity anomalies obtained by subtraction of the crustal gravity effect from the observed field characterize the density heterogeneities in the upper mantle mantle anomalies are shown to correlate with the upper mantle velocity inhomogeneities revealed from seismic tomography data and geothermal data considering the type of mantle anomaly specific features of the evolution and type of isostatic compensation the sedimentary basins in europe may be related into some groups deep sedimentary basins located in the east european platform and its northern and eastern margins peri caspian dnieper donets barents sea basins fore ural trough with no significant mantle anomalies basins located on the activated thin crust of variscan western europe and mediterranean area with negative mantle anomalies of 150 to 200 10 5 ms 2 amplitude and the basins associated with suture zones at the western and southern margins of the east european platform polish trough south caspian basin characterized by positive mantle anomalies of 50 150 10 5 ms 2 magnitude an analysis of the main features of the lithosphere structure of the basins in europe and type of the compensation has been carried out

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

3 d gravity analysis of the dniepr donets basin and donbas foldbelt ukraine abstract the dniepr donets basin ddb is a linear nw se trending late palaeozoic and younger sedimentary basin on the east european platform separating the ukrainian shield from the voronezh massif its northwestern dniepr segment has the characteristics of a typical rift basin to the southeast through a transition zone of approximately 200 km length the ddb is progressively uplifted and compressionally deformed into the correlatable donbas foldbelt df along the axis of the dniepr segment a series of gravity highs has been previously explained by high density crystalline crust beneath the axis of the basin caused by intrusion of mafic and ultramafic rocks in this paper the results of a 3 d gravity analysis using a gravity backstripping technique is described that investigates the crustal and upper mantle structure in the region of the ddb df transition zone and df a residual gravity field i obtained by subtracting the gravity influence of the sedimentary succession of the ddb from the observed field reveals a distinct positive anomaly along the axis of the rift basin increasing in amplitude to the southeast in concert with increasing sedimentary thickness a residual gravity field ii derived by removing the gravity effects of a modelled homogeneous crystalline crust from residual field i reaches 200 and 100 mgal amplitude in the df for two respective moho models based on different interpretations of the published crust and upper mantle seismic velocity models the first of these model a assumes crustal thickening beneath the transition zone and df to a moho depth up to 50 km whereas the second model b assumes a moho shallowing to depths in the range 35 37 km along the whole basin axis for each residual anomaly ii the best fitting 3 d distribution of average density in the crystalline crust has been computed both models indicate the existence of a high density body in the crystalline crust along the ddb axis increasing in density from the dniepr segment to the df with higher average crustal density required in the case of moho model a 3 17 103 kg m 3 versus 3 06 103 kg m 3 for model b the preferred interpretation of the density models is one in which the denser crystalline crust underlying the ddb df transition zone and df is explained by intrusion of mafic and ultramafic rocks during late palaeozoic rifting processes invocation of processes related to the uplift and inversion in the df are not required to explain the observed gravity field although reworking of the crust during permian and younger tectonism in the df cannot be ruled out

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined