magnetotelluric multiscale 3 d inversion reveals crustal and upper mantle structure beneath the hangai and gobi altai region in mongolia

magnetotelluric imaging of upper crustal convection plumes beneath the taupo volcanic zone new zealand 1 broadband mt magnetotelluric data were recorded that form an array of measurements at the south eastern margin of the tvz taupo volcanic zone in the central north island of new zealand these array data are used to investigate mechanisms by which the tvz s extraordinarily high heat flux is transported to the surface taken together with seismological data these mt data show compelling evidence that support a model of hydrothermal convection within the brittle upper 6 7 km part of the crust both 2 d and 3 d inversion models of these mt data show vertical low resistivity zones that connect surface geothermal fields to an inferred magmatic heat source that lies below the brittle ductile transition

a new methodology to estimate magnetotelluric mt tensor relationships estimation of local transfer functions by combining interstation transfer functions elicit summary anewmethodologytoestimatemagnetotelluric mt tensorrelationships calledestimationof local transfer functions by combining interstation transfer functions elicit is proposed wherebythemttensorrelationshipsofthelocalsitearederivedusingonlyinterstationtransfer functions the mt impedance tensor and the geomagnetic transfer function at the local site are characterised by combining interstation tensor relationships between electric and magnetic fields at the local site with the horizontal magnetic fields acquired at a neighbouring site the main property of the proposed method is that the employed interstation transfer functions are independently constrained without the need to acquire the electric and the magnetic fields at the local site simultaneously to recover the local mt tensor relationships due to this property the elicit method offers new possibilities for mt data acquisition and processing providing significant improvements when the magnetic time series at the local site are affected by local noise or are truncated error analysis shows that even when magnetic fields are truncated the quality of the results obtained following the elicit method are similar to those we would obtainifthemagneticfieldshadnotbeentruncated anotherimportantpropertyisthatdifferent neighbouring sites can be used to recover the tensor relationships at the local site averaging of results obtained using different neighbouring sites can be performed to improve the statistics for our example data when the elicit method is used to improve the statistics errors of the estimates for periods between 1000 and 20000 s periodicities are clearly reduced all interstation transfer functions are calculated doing remote reference and the bootstrap method is used to compute the errors when necessary long period magnetotelluric data acquired in the pyrenees and in the atlas mountains in morocco and magnetic data provided by

active tectonics of an apparently aseismic region distributed active strike slip faulting in the hangay mountains of central mongolia summary we identify and describe a series of east west left lateral strike slip faults named the songinomargats the hag nuur the uliastay and the south hangay fault systems in the hangay mountains of central mongolia an area that has little in the way of recorded seismicity and which is often considered as a rigid block within the india eurasia collision zone the strikeslip faults of central mongolia constitute a previously unrecognized hazard in this part of mongolia each of the strike slip faults show indications of late quaternary activity in the form of aligned sequences of sag ponds and pressure ridges developed in alluvial deposits total bed rock displacements of 3 km are measured on both the songino margats and south hangay fault systems bed rock displacements of 11 km are observed across the hag nuur fault cumulative offset across the uliastay fault systems are unknown but are unlikely to be large we have no quantitative constraint on the age of faulting in the hangay the 20 km of cumulative slip on the hangay faults might at least in part be inherited from earlier tectonic movements our observations show that despite the almost complete absence of instrumentally recorded seismicity in the hangay this part of mongolia is cut through by numerous distributed strike slip faults that accommodate regional left lateral shear between siberia and china central mongolia is thus an important component of the india eurasia collision that would be overlooked in models of the active tectonics based on the distribution of seismicity we suggest that active faults such as those identified in the hangay of mongolia might exist in other apparently aseismic regions within continental collision zones

structural and lithological characteristics of the bayankhongor ophiolite zone central mongolia the mechanism of continental growth of central asia is currently debated between models invoking continuous subduction accretion or punctuated accretion due to closure of multiple ocean basins ophiolites in central asia may represent offscraped fragments in an accretionary complex or true collisional sutures the bayankhongor ophiolite a nw se striking sublinear belt 300 km long and 20 km wide is the largest ophiolite in mongolia and possibly central asia we present results of the first detailed structural and lithological study of the ophiolite the study area is divided into four zones baidrag complex burd gol bayankhongor and dzag zones the archaean baidrag complex comprises tonalitic granulites and metasediments the burd gol zone is a metamorphosed sedimentary and igneous melange the bayankhongor zone contains the dismembered ophiolite forming a serpentinite melange the dzag zone consists of asymmetrically folded chlorite mica schists resembling meta turbidites the structure is dominated by steeply dipping ne directed thrusts and ne vergent folds we suggest the bayankhongor ophiolite marks the closure of an ocean separating two microcontinents the baidrag complex with the burd gol accretionary complex to the south and a northern continent that forms the basement for the hangai region subduction was towards the sw with ne directed ophiolite obduction onto a passive margin represented by the dzag zone

structure of the tongariro volcanic system insights from magnetotelluric imaging abstract the dynamics of magma reservoirs the main repositories for eruptible magma play a fundamental role in the style and behaviour of volcanic systems a key first step in understanding these systems is to identify their location and size accurately we present results from a broadband magnetotelluric study of the tongariro volcanic system and discuss how the results fit within current petrological models the tongariro volcanic system is a composite andesitic cone complex located at the southern end of the taupo volcanic zone in the central north island of new zealand we use data from 136 broadband magnetotelluric soundings within a 25 35 km area covering the volcanic system to construct a 3d image of the magmatic system of the tongariro volcanic complex including mount ngauruhoe the structure of the tongariro magmatic system has been determined from 3d forward and inverse modelling of the magnetotelluric data and allowed for an estimation of the melt fraction present within the system 3d inverse modelling of the magnetotelluric data shows a well developed shallow low resistivity zone outlining the geothermal system a zone of even lower resistivity representing a shallow crustal magma accumulation zone located at a depth of 4 12 km offset to the east of the tongariro vent system and a zone with a slightly higher resistivity connecting these two components of the magmatic system providing the path for magmatic fluids from the deeper source region to reach the surface during eruptive events

asthenospheric imprints on the lithosphere in central mongolia and southern siberia from a joint inversion of gravity and seismology mobal experiment summary we present a joint inversion of gravity and teleseismic data to enlighten the lithospheric structures of the baikal mongolia region an area characterized by high topographic contrasts sporadic cenozoic volcanism extension and large transcurrent faulting in the vicinity of the baikal rift central asia the study uses a 1000 km long seismic transect that cross cuts the main tectonic structures from north to south namely the siberian platform tunka basin hangay dome and gobi altai belt the siberian platform depicts a high velocity lithosphere down to about 150 km we evidence strong velocity contrasts within the crust below the hangay dome and the tunka depression interpreted as a thickened crust a low velocity density region is located at various depths below the hangay dome thanks to the dense spatial coverage of gravity data we are able to define the 3 d geometry of this particular low velocity density anomaly the hangay dome anomalous body extends from 60 to 225 km depth at his largest point and slightly thins to no more than 40 km at its easternmost end a deep low velocity zone below 150 km with only a weak negative density contrast is observed on the eastern part of the transect we propose that the late cenozoic uplift of the whole mongolian plateau and associated rifting magmatism high heat flow and lithospheric thinning are not externally driven by the india asia collision but results from the interaction of two mantle plumes with the overlying lithosphere conversely recent faulting may be the major expression of the india asia collision in this region as well as n s striking rift basins that connect and interact with major strike slip faults such as the bolnai fault the comparison between time residuals of this experiment and the baikal rift seismic data shows an undeniable disproportion for the hangay anomaly the hangay time residuals are far more positive than through the baikal arguing for an asthenospheric signature that is not seen beneath the baikal rift furthermore the southern edge of the thick siberian cratonic lithosphere may favour the rise of a sublithospheric mantle flow at the contact with the baikal mongolia lithosphere

gps measurements of crustal deformation in the baikal mongolia area 1994 2002 implications for current kinematics of asia 1 we present new geodetic results of crustal velocities over a large part of northern asia based on gps measurements in the baikal rift zone and mongolia spanning the 1994 2002 period we combine our results with the gps velocity field for china of wang et al 2001 and derive a consistent velocity field for most of asia we find contrasted kinematic and strain regimes in mongolia with northward velocities and n s shortening in westernmost mongolia but eastward to southeastward motion and left lateral shear for central and eastern mongolia this eastward to southeastward motion of central and eastern mongolia is accommodated by left lateral slip on the e w trending tunka bolnay and gobi altay faults 2 1 2 mm yr 1 2 6 1 0 mm yr 1 and 1 2 mm yr 1 respectively and by about 4 mm yr 1 of extension across the baikal rift zone consequently 15 of the india eurasia convergence is accommodated north of the tien shan by n s shortening combined with dextral shear in the mongolian altay and by eastward displacements along major left lateral strike slip faults in central and eastern mongolia we find a counterclockwise rotation of north and south china as a quasi rigid block around a pole north of the stanovoy belt which rules out the existence of an amurian plate as previously defined and implies 2 mm yr 1 of left lateral slip on the qinling shan fault zone

teleseismic traveltimes topography and the lithospheric structure across central mongolia 1 teleseismic travel times recorded along a 1000 km long n s transect across central mongolia are used together with topography and gravity data to constrain the deep lithospheric structure of this region time residuals appear positively correlated with the topography suggesting that p wave velocity changes correspond to density variations which in turn cause an isostatic uplift of the topography using a simple local isostasy model and a monte carlo inversion for the crust and asthenosphere velocities and density velocity conversion factors we determine best fitting moho and lithosphere asthenosphere boundary lab geometries which satisfyingly reproduce the observed topography and gravity data the model is validated using previously published 1d s wave velocity models obtained from receiver function analyses our results indicate that most of the long wavelength topography is supported by the asthenosphere buoyancy the hangai dome in the southern half of the transect appears mainly supported by a rather shallow 60 70 km asthenospheric uplift whereas the siberian platform at the extreme north of the profile is underlain by a very thick 200 km lithosphere misfits to the observed bouguer gravity anomaly occur near major faults probably because of lithospheric flexure

on the possibility of the telluric method some results on faulted structures the telluric method of geophysical investigation is re evaluated and several improvements are suggested besides the traditional jacobian several new parameters that bear information on the structure under investigation are proposed as sounding tools these parameters are calculated for several two dimensional models and plotted as pseudo sections the model results calculated over a wide frequency band 10 4 10 2 hz suggest that these new parameters can give very detailed information about the subsurface structures by way of example we present experimental results obtained along two profiles across familiar structures the interpretation of the results leads to two dimensional models of the subsurface that are in good agreement with known geophysical and geological features of these two sections

mantle structure and rifting processes in the baikal mongolia region geophysical data and evidence from xenoliths in volcanic rocks abstract the origin of the baikal rift zone brz has been debated between the advocates of passive and active rifting since the 1970s a re assessment of the relevant geological and geophysical data from russian and international literature questions the concept of broad asthenospheric upwelling beneath the rift zone that has been the cornerstone of many active rifting models results of a large number of early and recent studies favour the role of far field forces in the opening and development of the brz this study emphasises the data obtained through studies of peridotite and pyroxenite xenoliths brought to the surface by alkali basaltic magmas in southern siberia and central mongolia these xenoliths are direct samples of the upper mantle in the vicinity of the brz of particular importance are suites of garnet bearing xenoliths that have been used to construct p t composition lithospheric cross sections in the region for the depth range of 35 80 km xenolith studies have shown fundamental differences in the composition and thermal regime between the lithospheric mantle beneath the ancient siberian platform sampled by kimberlites and beneath younger mobile belts south of the platform the uppermost mantle in southern siberia and central mongolia is much hotter at similar levels than the mantle in the siberian craton and also has significantly higher contents of basaltic major elements ca al na and iron higher fe si and fe mg the combination of the moderately high geothermal gradient and the fertile compositions in the off cratonic mantle appears to be a determining factor controlling differences in sub moho seismic velocities relative to the siberian craton chemical and isotopic compositions of the off cratonic xenoliths indicate small scale and regional mantle heterogeneities attributed to various partial melting and enrichment events consistent with long term evolution in the lithospheric mantle age estimates of mantle events based on os sr nd isotopic data can be correlated with major regional stages of crustal formation and may indicate long term crust mantle coupling the ratios of 143 144nd in many lree depleted xenoliths are higher than those in morb or oib source regions and are not consistent with a recent origin from asthenospheric mantle mantle xenoliths nearest to the rift basins 30 50 km south of southern lake baikal show no unequivocal evidence for strong heating unusual stress and deformation solid state flow magmatic activity or partial melting that could be indicative of an asthenospheric intrusion right below the moho comparisons between xenoliths from older and younger volcanic rocks east of lake baikal together with observations on phase transformations and mineral zoning in individual xenoliths have indicated recent heating in portions of the lithospheric mantle that may be related to localised magmatic activity or small scale ascent of deep mantle material overall the petrographic p t chemical and isotopic constraints from mantle xenoliths appear to be consistent with recent geophysical studies which found no evidence for a large scale asthenospheric upwarp beneath the rift and lend support to passive rifting mechanism for the brz

lithospheric structure of an archean craton and adjacent mobile belt revealed from 2 d and 3 d inversion of magnetotelluric data example from southern congo craton in northern namibia 1 archean cratons and the stitching proterozoic orogenic belts on their flanks form an integral part of the southern africa tectonic landscape of these virtually nothing is known of the position and thickness of the southern boundary of the composite congo craton and the neoproterozoic pan african orogenic belt due to thick sedimentary cover we present the first lithospheric scale geophysical study of that cryptic boundary and define its geometry at depth our results are derived from two dimensional 2 d and three dimensional 3 d inversion of magnetotelluric data acquired along four semiparallel profiles crossing the kalahari craton across the damara ghanzi chobe belts dgc and extending into the congo craton two dimensional and three dimensional electrical resistivity models show significant lateral variation in the crust and upper mantle across strike from the younger dgc orogen to the older adjacent cratons we find damara belt lithosphere to be more conductive and significantly thinner than that of the adjacent congo craton the congo craton is characterized by very thick to depths of 250 km and resistive i e cold lithosphere resistive upper crustal features are interpreted as caused by igneous intrusions emplaced during pan african magmatism graphite bearing calcite marbles and sulfides are widespread in the damara belt and account for the high crustal conductivity in the central zone the resistivity models provide new constraints on the southern extent of the greater congo craton and suggest that the current boundary drawn on geological maps needs revision and that the craton should be extended further south

a new methodology for the acquisition and processing of audio magnetotelluric amt data in the amt dead band distant lightning activity the natural energy source for the audio magnetotelluric amt method has a signal minimum between 1 and 5 khz the so called amt dead band the energy in this band exhibits both diurnal and annual variation magnetic field amplitudes during the daytime are often well below the noise levels of existing sensors coil magnetometers thus reducing the effectiveness of the method for quantitative high resolution studies of near surface targets to overcome this deficiency we propose a hybrid acquisition and processing methodology based on combining the telluric telluric t t and telluric magnetotelluric t mt methods in this frequency range our method records the telluric channels at several sites and at base and remote reference stations during the day and records the full magnetotelluric mt components at the base and remote stations only during the night applying a tensor multiplicative relationship between these responses we obtain the t mt amt transfer functions for the sites these transfer functions can represent a reasonable approximation of the real amt impedance tensors to test the approach a t mt experiment was carried out in sudbury northern ontario during summer 2000 we compare the processed daytime data using the conventional mt approach to those obtained from our t mt approach the results demonstrate that our method can determine high quality estimates in the dead band although the estimates can be severely affected by noise

extensional extrusion insights into south eastward expansion of tibetan plateau from magnetotelluric array data abstract despite extensive effort over many decades to understand the tectonic evolution of the tibetan plateau the geodynamic processes creating the iconic south eastward expansion of the plateau at the eastern himalayan syntaxis ehs are still unclear and are hotly debated two popular but not necessarily exclusive geodynamic models namely crustal flow at mid to lower crustal depths and coherent deformation between the crust and lithospheric mantle are commonly invoked to explain the expansion mechanism however neither of these is able to reconcile all of the abundant geological and geophysical data here we present a three dimensional 3d geo electrical model derived from new sinoprobe magnetotelluric mt array data that reveals the geo electrical and by inference rheological structure of southeast tibet instead of nw se conductive channels proposed in prior two dimensional 2d mt studies distinct nne ssw directed quasi linear conductive anomalies are identified in the mid to lower crust which are separated by a large scale electrically resistive structure that extends from the crust to the upper mantle this argues against the prior proposed model of south eastward conductive anomalies and hence against the southeast lower crust flow of material to interpret our observations and resultant model a new mechanism of extensional extrusion is proposed to address the lithospheric deformation of the south eastward expansion of tibetan plateau

plateau uplift in western canada caused by lithospheric delamination along a craton edge mantle convection helps create continental plateaux seismic imaging of the mantle beneath the canadian cordillera an ancient plateau suggests the plateau formed when upwelling mantle caused a block of lithosphere to detach

reinterpretation of the active faulting in central mongolia we present remote sensing and fi eld observations of an 350 km long east west left lateral strike slip fault the south hangay fault in the hangay mountains of central mongolia an area previously believed to be deforming solely by slip on scattered and randomly oriented normal faults the known dip slip faults are shown to be short segments introduced at bends in the much longer strike slip fault our observations show that the active faulting in the hangay mountains is consistent with the regional strain fi eld of mongolia and does not require as suggested in other studies that the faults result from stresses introduced by the locally elevated topography our observations help to defi ne the active tectonics of this important part of the india eurasia collision the south hangay strike slip fault is a potential source of large magnitude earthquakes and constitutes a previously unrecognized hazard in this part of mongolia

mongolian plateau evidence for a late cenozoic mantle plume under central asia the 2500 x 700 km mongolian plateau average elevation 2000 m is situated between the altai orogen and the siberian craton and occupies much of mongolia and transbaikalia in russia the plateau is characterized by 1 basin and range topography and two major domes hentai 600 x 300 km and hangai 800 x 550 km where altitudes reach 3905 m 2 lithosphere that is thinner than adjacent areas minimum 50 km 3 elevated heat flow up to 120 mw m2 4 dominantly alkaline basaltic volcanism in the form of cones lava fields and volcanic plateaus mostly of miocene quaternary age and 5 rifts including baikal main evolution in the pliocene quaternary tunka oligocene early miocene and hobsogol pliocene quaternary existing models explain these features in terms of diapiric upwelling of a mantle asthenolith below the main rifts and or as a long distance effect of the india asia collision we propose that the late cenozoic uplift of the whole mongolian plateau and associated rifting magmatism high heat flow and lithospherec thinning are not externally driven by the india asia collision but are the expression of the interaction of a mantle plume with overlying lithosphere some rifts link and interact with major strike slip faults such as the bolnai such faults may be the major expression of the india asia collision in this region

melt distribution beneath a young continental rift the taupo volcanic zone new zealand 1 taupo volcanic zone tvz is a zone of intense volcanism and rifting associated with the subduction of the pacific plate beneath the continental crust of new zealand s north island an image of the conductivity structure beneath the central part of the tvz has been constructed using 2 d inverse modeling of magnetotelluric data a rapid increase in conductivity at a depth of 10 km beneath the tvz 3 km beneath the base of the seismogenic zone but well above the base of the quartzo feldspathic crust 16 km is interpreted to mark the presence of an interconnected melt fraction 4 within the lower crust beneath the quartzo feldspathic crust the model shows a zone of increased conductivity on the eastern side of the tvz consistent with an increased concentration of melt at deeper levels the pacific plate is resistive compared with the overlying mantle

earthquake geology of the bulnay fault mongolia the bulnay earthquake of 23 july 1905 mw 8 3 8 5 in north central mongolia is one of the world s largest recorded intracontinental earthquakes and one of four great earthquakes that occurred in the region during the twentieth century the 375 km long surface rupture of the left lateral strike slip n095 e trending bulnay fault associated with this earthquake is remarkable for its pronounced expression across the landscape and for the size of features produced by previous earthquakes our field observations suggest that in many areas the width and geometry of the rupture zone is the result of repeated earthquakes however in those areas where it is possible to determine that the geomorphic features are the result of the 1905 surface rupture alone the size of the features produced by this single earthquake are singular in comparison to most other historical strike slip surface ruptures worldwide along the 80 km stretch between 97 18 e and 98 33 e the fault zone is characterized by several meters width and the mean left lateral 1905 offset is 8 9 0 6 m with two measured cumulative offsets that are twice the 1905 slip these observations suggest that the displacement produced during the penultimate event was similar to the 1905 slip morphotectonic analyses carried out at three sites along the eastern part of the bulnay fault allow us to estimate a mean horizontal slip rate of 3 1 1 7 mm yr over the late pleistocene holocene period in parallel paleoseismological investigations show evidence for two earthquakes prior to the 1905 event with recurrence intervals of 2700 4000 yrs

three dimensional electrical resistivity of the north central usa from earthscope long period magnetotelluric data abstract we present initial results from three dimensional inversion of long period earthscope magnetotelluric mt transportable array data from 232 sites covering the north central us the study area covers the 1 1 ga mid continent rift mcr system which cuts across a series of archean and paleoproterozoic lithospheric blocks the western arm of the mcr is clearly evident in shallow depth sections with a narrow resistive core flanked by elongate conductive basins other prominent upper crustal features mapped include the moderately conductive michigan and illinois basins and extremely high conductivities in foreland basin rocks at the southern margin of the superior craton the most prominent conductive anomalies in an otherwise relatively resistive mid lower crust are two elongate east west oriented structures which are closely aligned with previously inferred continental sutures the first underlies the southern margin of the superior craton just north of the niagara fault nf and can be associated with the 1 85 ga penokean orogeny a second further south beneath iowa and western wisconsin lies just south of the spirit lake tectonic zone sltz and can be identified with yavapai accretion at 1 75 ga both of these conductive sutures are cleanly cut by the mcr which is otherwise not clearly evident in the deeper parts of the resistivity model the break in the anomalies is narrow comparable to the surface expression of the mcr indicating that rifting impacts on the entire crustal section were highly localized both suture related anomalies are imaged as extending into and perhaps through the lithosphere as dipping diffuse zones of reduced mantle resistivity sense of dip of these structures southward for the nf anomaly northward for sltz agrees with previously inferred models for subduction and accretion suggesting that a conductive phase most likely carbon has been thrust deep into the lower crust and uppermost mantle providing a marker of the three dimensional boundary between lithospheric blocks resistivities drop below 100 m below 200 km depth in rough agreement with the seismically determined lithosphere asthenosphere boundary lab there are modest lateral variations in this deep low resistivity layer but the reliability and significance of these are not yet clear

mantle driven uplift of hangai dome new seismic constraints from adjoint tomography the origin of hangai dome an unusual large scale high elevation low relief landform in central mongolia remains enigmatic partly due to lack of constraints on its underlying seismic structure using adjoint tomography a full waveform tomographic technique and a large seismic waveform data set in east asia we discover beneath the dome a deep low shear wave speed low v conduit indicating a slightly warmer 54 k to 127 k upwelling from the transition zone this upwelling is spatially linked to a broader uppermost mantle low v region underlying the dome further observations of high compressional to shear wave speed ratios and positive radial anisotropy in the low v region suggest partial melting and horizontal melt transport we propose that the mantle upwelling induced decompression melting in the uppermost mantle and that excess heat associated with melt transport modified the lithosphere that isostatically compensates the surface uplift at upper mantle depths 80 km

uplift of central mongolia recorded in vesicular basalts abstractepeirogenic histories of highland areas have confounded earth scientists for decades as there are few sedimentary records of paleoelevation in eroding highlands for example mechanisms that have led to the high elevations of the hangay mountains in central mongolia are not clear nor is it well understood how the epeirogenic history of central mongolia is connected to that of a broader region of high elevation that extends hundreds of kilometers to the north east and west however preserved basaltic lava flows record paleoelevation in the size distributions of vesicles at the tops and bottoms of flow units as an initial step toward better understanding the tectonics of this part of asia we collected and analyzed samples from several basaltic lava flows from throughout the hangay mountains to use as a paleoaltimeter on the basis of lava flow vesicularity samples were dated and scanned with x ray tomography to provide quantitative information regarding their internal vesicle size distributio

electrical conductivity structure of north west fennoscandia from three dimensional inversion of magnetotelluric data abstract new magnetotelluric mt data in north west fennoscandia were acquired within the framework of the project magnetotellurics in the scandes masca the project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable precambrian cratonic interior to passive continental margin beneath the caledonian orogen and the scandinavian mountains in western fennoscandia an array of 59 simultaneous long period and 220 broad band mt sites were occupied in the summers of 2011 to 2013 the 3 d inversion of the masca data was obtained using the modem 3 d code the full impedance and tipper data were used for the inversion the rocks of archaean and proterozoic basement towards east and the caledonian nappes towards west are modelled as resistive structures in the central and southern parts the whole crust is resistive and reflects the trans scandinavian igneous belt granitoids the middle to lower crust of the svecofennian province is conductive an uppermost crustal conductor is revealed in the skelleftea ore district the south end of the kittila greenstone belt is seen in the models as a strong upper to middle crustal conductor in the caledonides the highly conductive alum shales are observed along the caledonian thrust front a map of the crustal conductance for the north west fennoscandian shield is presented

cenozoic normal faulting and regional doming in the southern hangay region central mongolia implications for the origin of the baikal rift province abstract the hangay dome in central mongolia is a mountainous region covering more than 200 000 km2 with numerous flat topped peaks over 3000 m that preserve a late cretaceous paleogene erosion surface doming began in the middle oligocene producing more than 2000 m of regional topographic uplift the range represents an important kinematic link between the baikal rift province to the north and altai transpressional ranges to the south and west structural field investigations of major faults visible on satellite imagery indicate that the southern hangay dome region is dominated by late cenozoic normal faults that bound small half graben most faults are ne striking and faults at the highest elevations are the most recently active most graben appear to be isolated systems that constitute small sediment sinks perched on the flanks and crests of the dome the first order feature is the dome itself and most sediment eroded off of the dome is deposited in the mongolian valley of lakes or is carried northwards by the selenga river and its extensive tributaries the basement of the dome is a precambrian craton although the shape and dimensions of the craton are poorly constrained to the north and east late cenozoic uplift of the southern dome region appears to be confined to the area underlain by cratonic basement whereas the altai region to the south and west is underlain by mechanically weaker palaeozoic arc and accretionary belts with respect to the regional northeast directed shmax the hangay craton appears to have acted as a rigid passive indentor focusing late cenozoic transpressional deformation around its west and southern margins models invoking a late cenozoic plume as the driving force for doming and widespread alkaline volcanism on the dome are not strongly supported by geochemical and isotopic data on neogene recent volcanics and the spatial correlation between areas that are domed and older cratonic crust appears too coincidental to be ignored convective removal of an overthickened lithospheric root leading to adiabatically decompressed asthenosphere could explain regional doming and volcanism however major crustal thickening last occurred in the permian in the southern hangay region and the time lag between thickening and postulated root removal and plateau uplift 200 myr appears too long an alternative model is explored based on speculated lithospheric mantle flow patterns driven by india s continued northeastward indentation it is suggested that lithospheric mantle flow diversion around the overthickened hangay craton crustal keel could cause lithospheric thinning beneath the craton and passive asthenospheric upwarp leading to regional topographic uplift and decompression melting alkali volcanism in general the angular relationship between precambrian craton boundaries and the prevailing northeasterly shmax appears to control the kinematics of late cenozoic deformation throughout the hangay altai sayan and baikal regions

constraints on the viscosity of the continental crust and mantle from gps measurements and postseismic deformation models in western mongolia 1 we use gps measurements and models of postseismic deformation caused by seven m6 8 to 8 4 earthquakes that occurred in the past 100 years in mongolia to assess the viscosity of the lower crust and upper mantle we find an upper mantle viscosity between 1 1018 and 4 1018 pa s the presence of such a weak mantle is consistent with results from independent seismological and petrological studies that show an abnormally hot upper mantle beneath mongolia the viscosity of the lower crust is less well constrained but a weak lower crust 3 1016 to 2 1017 pa s is preferred by the data using our best fit upper mantle and lower crust viscosities we find that the postseismic effects of viscoelastic relaxation on present day horizontal gps velocities are small 2 mm yr 1 but still persist 100 years after the 1905 m8 4 bolnay earthquake this study shows that the gps velocity field in the baikal mongolia area can be modeled as the sum of 1 a rigid translation and rotation of the whole network 2 a 3 5 mm yr 1 simple shear velocity gradient between the siberian platform to the north and northern china to the south and 3 the contribution of postseismic deformation mostly caused by the 1905 bolnay tsetserleg sequence and by the smaller but more recent 1957 bogd earthquake

alaska north slope regional gas hydrate production modeling forecasts abstract a series of gas hydrate development scenarios were created to assess the range of outcomes predicted for the possible development of the eileen gas hydrate accumulation north slope alaska production forecasts for the reference case were built using the 2002 mallik production tests mechanistic simulation and geologic studies conducted by the us geological survey three additional scenarios were considered a downside scenario which fails to identify viable production an upside scenario describes results that are better than expected to capture the full range of possible outcomes and balance the downside case an extreme upside scenario assumes each well is exceptionally productive starting with a representative type well simulation forecasts field development timing is applied and the sum of individual well forecasts creating the field wide production forecast this technique is commonly used to schedule large scale resource plays where drilling schedules are complex and production forecasts must account for many changing parameters the complementary forecasts of rig count capital investment and cash flow can be used in a pre appraisal assessment of potential commercial viability since no significant gas sales are currently possible on the north slope of alaska typical parameters were used to create downside reference and upside case forecasts that predict from 0 to 71 bm3 2 5 tcf of gas may be produced in 20 years and nearly 283 bm3 10 tcf ultimate recovery after 100 years outlining a range of possible outcomes enables decision makers to visualize the pace and milestones that will be required to evaluate gas hydrate resource development in the eileen accumulation critical values of peak production rate time to meaningful production volumes and investments required to rule out a downside case are provided upside cases identify potential if both depressurization and thermal stimulation yield positive results an extreme upside case captures the full potential of unconstrained development with widely spaced wells the results of this study indicate that recoverable gas hydrate resources may exist in the eileen accumulation and that it represents a good opportunity for continued research

lithospheric reworking at the proterozoic phanerozoic transition of australia imaged using auslamp magnetotelluric data abstract seventy four stations from the long period australia wide auslamp australian lithospheric architecture magnetotelluric project dataset were used to image the electrical resistivity beneath the neoproterozoic ikara flinders ranges and adjacent palaeo mesoproterozoic curnamona province results from 3d inversions using modem software show a relatively resistive ikara flinders ranges with two parallel arcuate conductors at 20 to 80 km depth in the nackara arc there is a good correlation of diamondiferous kimberlites occurring over conductors which we interpret as evidence for these conductors to be residing on large lithospheric structures that have been conduits for partial melt and volatile movement in the jurassic the curnamona province is remarkably conductive for a region that is thought to have a cratonic core with delamerian reworking only at its edges the conductor covers most of the province at depths of 10 40 km and its presence at lower crustal depths suggests that conductive sediments can not entirely explain it fluids associated with subduction may have pervasively modified the crust in the past resulting in an enrichment of carbon enhancing the conductivity additionally we conclude that the notion of a single continuous arcuate flinders conductivity anomaly is unlikely and that the anomalous response observed is instead a result of the combined response of three separate anomalies the curnamona province conductor and the two nackara arc conductors