three dimensional thermo mechanical modeling of the cenozoic uplift of the tianshan mountains driven tectonically by the pamir and tarim abstract we develop a three dimensional thermo mechanical model as an approximate representation of the lithosphere of the tianshan orogenic belt and adjacent geological units for simulating the uplift mechanism of the tianshan mountains in the cenozoic we apply a velocity boundary condition approximating the northward push of the pamir and tarim against the tianshan block to derive lithospheric deformation of the model in particular we investigate systematically the influence of gravity induced creep deformation on mountain uplift our modeling results indicate that 1 the modeled topographic pattern coincides well with the actual topography implying that the tectonic push of the pamir and tarim can cause significant uplift of the tianshan mountains 2 the lithosphere of the tianshan mountains is mechanically weaker than that of the platforms to the south and north of the tianshan orogenic belt and 3 the gravity induced creep deformation has a significant influence on the process and elevation of mountain uplift therefore when subjected to the tectonic compression resulting from the northward push of the pamir and tarim the relatively weak lithosphere of the tianshan mountains would deform easily and hence absorb more shortening resulting in lithospheric thickening and consequent mountain uplift

magnetic field modelling and interpretation of the himalayan tibetan plateau and adjoining north indian plains abstract a prominent magnetic low is seen over the himalayan tibetan plateau and the northern indian shield region in satellite anomaly data here we model the sources for the observed magnetic low in the region the induced magnetic field is modelled based on a crustal magnetisation model computed in a geographical information system with horizontal layers containing susceptibility derived from the geology and a tectonic map of the region and global seismic crustal thickness model the modelling results indicate that the upper crust of the himalayan tibetan plateau is magnetised while much of the middle crust and the lower crust appears non magnetic thermal modelling corroborates the predictions placing the curie isotherm in the southern tibetan plateau no deeper than 10 km the results suggest that the sources of the magnetic low observed in the region are likely to be a thin magnetised crust because of the elevated curie isotherm in this region the indian shield region is believed to extend up to the foothills of the himalayas in the north but most of the shield is obscured by a thick sediment cover of the gangetic plains to the north the magnetic field modelling suggests a weakly magnetic crust in the region indicating either the indian shield may not extend up to the base of the himalayas or the lower crust in the region has been modified

curie point depths in northeast china and their geothermal implications for the songliao basin abstract this work integrates processing and interpretation of the combined geomagnetic anomaly model of ngdc 720 v3 1 to better constrain thermal structures of the northeast china lithosphere which shows intensive extension and active volcanism during the mesozoic and cenozoic numerical tests demonstrate that magnetic anomalies calculated at 20 km altitude can be used for accurate curie depth estimation averaged curie depths using a 3d fractal exponent of 3 0 vary from 13 2 0 to 33 4 1 km with a mean of 22 2 4 km in northeast china with temperature dependent thermal conductivity models constrained by incorporated surface heat flow and curie depths in different geological blocks the thermal lithospheric thicknesses are estimated mostly between 45 and 90 km based on 1d steady state thermal conduction equation beneath the songliao basin the moho temperatures are abnormally high ranging from ca 700 to 1000 c and the mantle contributes about 65 of the total surface heat flow the shallow curie points and thermal lithosphere asthenosphere boundary together with high moho temperatures and mantle heat flow support abnormally high geotherms in the songliao basin originated from hot upper mantle upwelling triggered likely by lithospheric delamination

linking the southern west junggar terrane to the yili block insights from the oldest accretionary complexes in west junggar nw china abstract west junggar is known to tectonically correlate with east kazakhstan however the tectonic link of the southern west junggar terrane to adjacent regions still remains uncertain here we examined the oldest accretionary complexes thus constraining its tectonic evolution and link during the early middle paleozoic they have contrasting lithologic geochemical and geochronological features and thus provenances and tectonic settings the laba unit was derived from the late ordovician early devonian continental arc system peaking at 450 420 ma with precambrian substrate which formed as early as the early devonian and metamorphosed during the permian however the kekeshayi unit was accumulated in an intra oceanic arc setting and includes the pre late silurian and late silurian subunits with or without precambrian sources integrated with the regional data the southern west junggar terrane revealed a tectonic link to the northern yili block during the late silurian to early devonian as suggested by the comparable precambrian zircon age spectra between the southern west junggar terrane and the micro continents in the southern kazakhstan orocline the proximal accumulation of the laba unit in the continental arc atop the yili block and the sudden appearance of precambrian zircons in the kekeshayi unit during the late silurian this link rejects the proposals of the southern west junggar terrane as an extension of the northern kazakhstan orocline and the middle paleozoic amalgamation of west junggar a new linking model is thus proposed in which the southern west junggar terrane first evolved individually and then collided with the yili block to constitute the kazakhstan continent during the late silurian the independent and contrasting intra oceanic and continental arcs also support the paleozoic archipelago type evolution of the central asian orogenic belt

crustal magnetic anomaly in the ordos region and its tectonic implications abstract in this paper the ngdc 720 v3 model is utilized to investigate the distribution of crustal magnetic anomaly and curie surface in the ordos block and its surrounding areas the curie surface is compared with the regional heat flow bouguer anomalies moho and seismicity the interior block has strong wide distributed magnetic anomalies well corresponding to the basement lithofacies the surrounding areas have weak anomalies of various strikes and intensities the magnetic anomaly confirms the geological finding that the yabulai and bayanhot basins are small blocks detached from the northern ordos block the magnetic anomalies at the satellite altitude reveal that deep materials flow northward from the northeast margin of tibet plateau to the qilian fold belt the depth of curie surface ranges from 24 to 42 km and the ordos block is dominated by curie surface depth over 32 km and average heat flow value of 44 mw m2 the distribution of bouguer anomalies is consistent with that of magnetic anomalies the well correlation between the curie surface and the seismicity is also explained

wavelet analysis for the regional residual and local separation of potential field anomalies a method based on the discrete wavelet transform was applied to the regional residual separation of potential fields and to the filtering of local anomalies a specific space scale wavelet analysis called multiresolution analysis allowed decomposition of the signal with respect to a vast range of scales different analysing wavelets were applied to anomalies in both synthetic and real cases but the more appropriate basis needed to be chosen by requiring the maximum compactness for the multiresolution analysis moreover since such analysis was found not to be shift invariant the same criterion was applied to choosing the best signal shift application of the technique to both synthetic and real cases produced an optimal space scale representation of the fields and a consistent regional residual separation furthermore the space localization allowed a variety of filtered signals to be obtained each one with a specific scale and local area content fourier and wavelet analyses were both applied to the filtering out of the intense etna anomaly from the aeromagnetic field of sicily the wavelet method was more powerful suppressing only the etna volcano anomaly and leaving the rest of the map practically unchanged

geophysical interpretation of the magnetic anomalies of china derived from magsat data the ambiguities about geophysical implications based on the correlation of scalar magnetic anomalies and geological features were investigated a method was developed to convert scalar magnetic anomalies into a map of the lateral variations of magnetic susceptibility of the lithosphere this map is directly correlated with the causative sources the method is based on spherical harmonic analysis of lateral variations seen on the scalar magnetic anomaly map and those of the lithospheric magnetic susceptibility the harmonic coefficients are related through the fundamental causality relationship governing a magnetized body and its associated scalar magnetic anomaly the main features of the resulting magnetic susceptibility anomalies are outlined

features and effects of basement faults on deposition in the tarim basin the tarim basin as the largest inland oil producing basin in china is a large scale composite basin which formed from a palaeozoic craton basin that was overprinted by a mesozoic cenozoic foreland basin based on comprehensive analyses of gravitational data aeromagnetic data and seismic data from the basin 38 basement faults can be identified demonstrating that the tarim basin has undergone several tectonic cycles according to their distributional locations in the basin basement faults can be divided into marginal and internal basin basement faults moreover on the basis of the distribution characteristics in the plane and controlling effects on the basin the basement faults can be divided into 20 primary basement faults and 18 secondary basement faults combined with the interpretations of seismic profiles we can determine the relationship between the basement faults and sedimentary cover faults considering the section balance of seismic profiles we find that some basement faults are syn depositional with continuous long term activity during the basin s evolution and control the deposition in the basin by counting fault growth indexes of the main sections it is obvious that different parts of the same fault have different growth indexes but show similar activity within the same geological period the faults stress states remain consistent with their geological history although the growth indexes of different faults are inconsistent

crustal thickness and lithospheric thermal state beneath the junggar basin and adjacent mountain ranges northwest china abstract in this paper data of gravimetry aeromagnetic survey and surface heat flow are utilized in a combined manner to investigate the crustal thickness curie surface and lithospheric thermal state beneath the junggar basin and adjacent mountain ranges the moho depth curie depth and thermal lithospheric thickness are found to be 38 52 km 32 50 km and 120 260 km respectively the moho and curie surface present a rough inverse correspondence between each other in the tianshan and altai mountain ranges moho interface is deep but curie surface is shallow in the junggar basin turpan basin and yili basin the situation is in reverse the uppermost mantle in the central depression and eastern uplift of the junggar basin the turpan basin the yili basin as well as the north west area off fuhai is investigated to have been magnetized the aeromagnetic anomalies and the curie surface in the junggar basin surprisingly reveal that the northward subduction of the north tarim block slab under the junggar basin accompanied by the uplift of the tianshan mountain range also in response to the northward movement the rigid central depression of the junggar basin extruded from its east and west sides the westward extrusion is manifested by the west uplift of the western junggar mountain range

the downward continuation of magsat crustal anomaly field over southeast asia a general method for the local downward continuation at ground level of geopotentials measured by low orbiting satellites at different altitudes is proposed such a continuation is the inverse solution of the external dirichlet problem the stability of the solution with respect to the altitude and the distribution of data points is discussed principal component analysis is shown to perform well and leads to a stable solution the method proposed has the advantage of being directly applicable to measured data points which are not evenly spaced and at different altitude as an illustration it is applied to magsat data over southeast asia two independent maps of the vertical component of the anomaly field at a constant altitude near ground level are derived for dawn descending orbits and dusk ascending orbits data separately the two maps reveal similar anomalies and confirm the correlation of the magsat derived anomaly field with the mosaic structure of the continental crust in southeast asia stable continental blocks are associated with positive anomalies and intervening collision belts correspond to well defined negative anomalies a very prominent low is observed above the himalaya and extends over the tibet plateau confirming an anomalous crustal and thermal structure of the plateau

distribution of the crustal magnetic anomaly and geological structure in xinjiang china based on the high order crustal magnetic field model ngdc 720 v3 we investigate the distribution of crustal magnetic anomaly the decay characteristics of the anomaly and the relationship between the magnetic anomaly and geological structure in xinjiang china topography of the magnetic layer basement is studied through curie isothermal surface using the power spectrum method it is found that south tarim basin junggar basin and turpan hami basin have strong positive magnetic anomaly whereas west kunlun mountain altun mountain tianshan mountain and altai mountain have weak or negative anomaly the magnetic anomaly well reflects the regional tectonic structure i e three alternating mountains intervened by two basins the magnetic anomaly on the ground surface in tarim basin is well corresponding to the mafic dykes the decay of the magnetic anomaly with altitude indicates that xinjiang is a large massif composed of several magnetic blocks with different sizes in different directions the curie surface presents a feature of being shallow under mountains whereas being deep under basins roughly having an anti mirror correspondence with the moho depth

accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield kroner a windley b f badarch g tomurtogoo o hegner e jahn b m gruschka s khain e v demoux a and wingate m t d 2007 accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield in hatcher r d jr carlson m p mcbride j h and martinez catalan j r eds 4 d framework of continental crust geological society of america memoir 200 p 181 209 doi 10 1130 2007 1200 11 for permission to copy contact editing geosociety org 2007 the geological society of america all rights reserved kroner kroener mail uni mainz de windley brian windley btinternet com tomurtogoo igmr magicnet mn hegner hegner lmu de jahn jahn earth sinica edu tw khain khain ginras ru demoux demoux uni mainz de wingate mwingate tsrc uwa edu au

why no anomaly is visible over most of the continent ocean boundary in the global crustal magnetic field abstract it is generally believed that an anomaly should be expected over the continent ocean c o boundary in the global magnetic anomaly maps however such maps prepared at satellite altitude do not show an anomaly over most of the c o boundary we address this issue by a forward modelling technique we use a geographic information system gis technique to integrate information of the various geological units of continents and oceans the seismic crustal structure and standard susceptibility values of the rock types and compute a global vertically integrated susceptibility vis model in addition a remanent magnetisation model is used for the oceanic crust combining the induced and remanent magnetisation models the crustal field anomaly is predicted at a satellite altitude of 400 km for spherical harmonic degrees 16 80 the results show that an anomaly is indeed not predicted over the c o boundaries where the oceanic crust is flanked by continental regions phanerozoic in age we demonstrate that largely a c o anomaly over these regions is not even expected in the global magnetic anomaly map for degrees 1 80 confirming that it is not a long wavelength feature masked by the core field an anomaly however is predicted over some parts of the c o boundary where the flanking geological provinces over the continents are precambrian in age we argue that the vis values for the continents and oceans are largely comparable and therefore no anomaly is expected over most of the c o boundary

curie isotherm map of indian subcontinent from satellite and aeromagnetic data abstract estimating depth to the bottom of the magnetic crust synonymously called the curie isotherm on a regional scale from long wavelength magnetic anomalies requires that large areas of survey data be used for the calculations there is still no consensus on the minimum survey area required to arrive at a reliable estimate of the curie isotherm depth from the available aeromagnetic data over india depth to the curie isotherm is estimated using spectral techniques we found that the significant spectral maxima required to calculate the depth to the curie isotherm existed only for 4 4 blocks in southern peninsular india up to 18 n latitude and for 5 5 blocks for the rest of the region in central india as aeromagnetic data coverage over india is incomplete we also calculate the magnetic crustal thickness from the lithospheric model of the champ satellite data for the whole country using an iterative forward modeling approach the calculated curie isotherm is shallow in the mobile belts and deeper in the cratons in both the derivations as the curie isotherms calculated from the two data sets collected at very different altitudes using totally different techniques match reasonably well it lends credence to the methodology adopted the derived curie isotherm depth map is in accordance with the basic structural trend of the major tectonic units within the indian subcontinent a comparison is made of the calculated curie isotherm depth with moho depths along available dss profiles over india and it is found that the curie depth is generally shallower than the moho depth implying that it possibly represents a thermal boundary rather than a compositional change further we find that high magnitude earthquakes are associated with high gradients in curie depth

problems in applying preservation facies and sequence models to sinian neoproterozoic glacial sequences in australia and asia abstract the sinian 800 530 ma is an extraordinary period of earth history characterized by the transition from simple to complex multicellular organisms and by extreme variations in climate eustasy and possibly tectonics understanding sinian stratigraphy may help interpret the co evolution of life and environment during the period though sinian successions are poorly dated and difficult to correlate preservation facies and sequence models based on mesozoic recent successions may be used to interpret them preservation models based on basin subsidence permit estimates of how thick and complete successions can be in different tectonic settings and how long it took for them to be deposited facies models for rift craton shelf slope and basin environments help in identification of these different tectonic settings sequence models facilitate interpretation of the interplay of tectonic subsidence eustasy rates of sedimentation and climate such models applied to the sinian successions of australia and asia indicate the following great shallowing upwards megacycles occur in sinian successions and each ends with regional glaciations deep rift basins formed around 850 800 ma preserve the oldest megacycles but these basins soon were filled with rapidly deposited glaciogenic sediments relatively complete sequences are found only in deep basins subject to repeated rifting cratons and shallow shelves preserve only the youngest megacycles older deposits have been removed by younger glacial advances deep shelves and slopes preserve one to three megacycles depending on the timing of the start of passive margin subsidence megasequences can be correlated based on limited radiometric dating and inferred regional distribution of unique rock types but these sequences are not developed to the same extent in all blocks problems in correlating the four great megacycles recognized elsewhere with those of asia will persist until the requisite facies analysis and u pb dating of interbedded volcanics are done

sedimentary record of late neoproterozoic rifting in the nw tarim basin china abstract upper neoproterozoic sediments which have been exhumed in the nw tarim basin china comprise a 600 900 m thick non marine to marine synrift succession that reveals an early phase of extension this study presents new data from two measured and interpreted stratigraphic sections near aksu and wushi the synrift succession unconformably overlies high grade metamorphic basement and consists of the non marine sugaitebulake fm and the marine qegebulake fm the sugaitebulake fm is characterised by a basal alluvial fan conglomerate that passes upwards into fluvial and lacustrine facies sandstones and siltstones the stratigraphic position of the basal unconformity and the thickness of the basal conglomerate is locally variable which reflects the formation of small isolated depocentres during the onset of extension in addition to a pre existing topography the sugaitebulake fm also contains a series of concordant extrusive basalts which record episodic volcanism and together with the fluvial and lacustrine facies indicate the development of the rift system and the growth interaction and linkage of extensional faults the conformable qegebulake fm is characterised by foreshore to intertidal facies dolomites that contain abundant stromatolites representing a basin wide marine transgression and the rift climax stage this synrift sequence is shown to correlate with a similar succession in nw australia and corresponds to at least partial separation of the tarim block from east gondwana during the latest neoproterozoic to early palaeozoic

permian bimodal dyke of tarim basin nw china geochemical characteristics and tectonic implications abstract this study reports for the first time the occurrence of bimodal dyke in the shuigongtuan area of bachu county tarim basin nw china here quartz syenite porphyry and diabase dykes occur in direct contact showing bimodal feature the quartz syenitic porphyry is metaluminous enriched in k2o na2o 10 11 wt and total rare earth elements ree with low mg mg fe ratios high lree hree and negative eu anomalies the chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with a type granites the diabase dyke shows 45 52 wt sio2 and mg mg fe ratio in the range of with high total ree high lree hree ratios and lack of eu anomalies broadly corresponding to tholeiitic composition based on low y nb as low as 0 4 and less than 1 2 enrichment in lile and hfse and uniform nb enrichment patterns in spider diagram for the quartz syenitic porphyry together with the geochemical patterns of the diabases this biomodal association is interpreted to be derived from a mantle source and formed under typical within plate environment the quartz syenitic porphyry and diabase have daly gap of 46 wt 67 wt in sio2 which is explained through formation under bimodal rifting the quartz syenitic dyke probably formed during early permian 277 ma and has geochemical affinity with the xiaohaizi syenitic body we propose that magmas sourced from the mantle intruded into middle upper crust and were emplaced as dykes which indicate large scale extension during the permian in tarim basin the bimodal dyke has genetic affinity with the huge volume of permian basalts and igneous rocks 248 292 ma that occur in the tarim basin the magmatism manifests the culmination of the major thermal event in the tarim basin

magnetic anomaly map of the world merging satellite airborne marine and ground based magnetic data sets abstract we report here a simple but practical method to combine systematically the magnetic surveys of disparate specifications from marine ground aeromagnetic and satellite platforms that aims to be helpful in the framework of the world digital magnetic anomaly map project because the satellite coverage and data quality is more uniform than near surface surveys it is adopted as the base map for wavelengths larger than 400 km and up to spherical harmonic degree inclusive of 16 2500 km after checking that satellite models and large aeromagnetic wavelengths are not consistent we filter out wavelengths longer than 400 km in aeromagnetic compilations existing regional grids and when available individual surveys are merged to give a more uniform spatial variation of the magnetic anomalies the effects of merging the grids are examined by plotting profiles and difference maps of the overlapping regions a preliminary global map is obtained after combining the magnetic anomaly map with the downward continued champ satellite derived magnetic anomaly map forthcoming availability of new datasets as well as improvements in the procedure will help to produce increasingly reliable maps

source depth determination using multi modal rayleigh spectral ratios and linear discriminant analysis a study of the reservoir induced seismic sequence at lake kariba africa september 1963 to august 1974 abstract the source depths of 12 reservoir induced seismic events at lake kariba were determined using the short to long period spectral ratios of multi modal rayleigh data recorded at two african stations source depths of less than 10 km were confirmed through the analysis of short period pp p time differentials two separate source to receiver crustal path models were employed in the analysis an african shield model with low velocity surficial layers and a low shear velocity zone between 7 and 18 km was utilized to reproduce the observed multi modal rayleigh waves acquired from the kariba to nairobi path the model is consistent with published evidence that the east african rift system extends south to lake kariba a conventional south african shield model was utilized for the kariba to pretoria path synthetic multi modal rayleigh waveforms were computed for a range of source depths for the two crustal models the spectral ratios obtained from these waveforms provided the synthetic data base to which the observed rayleigh wave spectral ratios were compared using linear discriminant analysis due to the limitations in the available data the source depths could not be determined at a statistical level of confidence however the demonstration of the feasibility of the procedure should stimulate its application to many other problems associated with source parameter inversion

the association of mafic ultramafic intrusions and a type magmatism in the tian shan and altay orogens nw china implications for geodynamic evolution and potential for the discovery of new ore deposits abstract the nw china region is characterised by tectonic and lithostratigraphic domains such as the tian shan and altay orogens the tarim junggar and turpan basins the tian shan and altay orogens are part of the central asian orogenic belt the nw china region was affected by a series of thermal events that occurred between the silurian and the triassic which resulted in the emplacement of numerous granitic plutons and mafic ultramafic intrusions a number of these granitic plutons are of a type affiliation which on the basis of the positive end values are likely to have been derived from mantle sources in addition at least two large igneous provinces lips can be recognised in nw china namely the 345 325 ma tian shan lip and the ca 270 280 ma tarim lip age and field data suggest a spatial and temporal relationship between the mafic ultramafic intrusions and a type granites within the lips in this paper we discuss mafic ultramafic intrusions that host magmatic ni cu sulphide deposits kalatongke in the altay huangshan and poyi poshi in the eastern tian shan these intrusions are typically zoned characterised by an envelope of early gabbroic rocks that enclose later ultramafic units these zoned mafic ultramafic intrusions have some features that are comparable with alaskan type complexes taking into consideration the spatial temporal relationship of the mafic mafic ultramafic rocks and a type granites we suggest that these magmatic events occurred during an extensional regime possibly related to a mantle superplume event that affected much of central asia during the permian of which the siberian traps and the emeishan continental flood basalts of sw china are part if the a type felsic magmatism took place during a superplume event we also suggest that these rocks may be conducive to host iron oxide copper gold iocg style mineralisation we conclude with a model that attempts to explain the relationship between the zoned mafic ultramafic intrusions and mantle plume activity in nw china during the permian

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

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

late neoproterozoic paleomagnetic results from the sugetbrak formation of the aksu area tarim basin nw china and their implications to paleogeographic reconstructions and the snowball earth hypothesis abstract in order to better constrain the neoproterozoic paleogeographic reconstruction of continents and to improve the understanding of the snowball earth hypothesis paleomagnetic investigations were carried out in the aksu area of the northwestern tarim basin forty eight sites of samples were collected from the sugetbrak and chigebrak formations twenty four sites of sandstone and volcanic rock from the sugetbrak formation revealed stable characteristic remanent components chrm isolated between 500 and 680 c the computed magnetic directions from these components are consistent and significantly distinguished from those of younger ages both normal and reverse polarities have been observed and a positive fold test is revealed after bedding corrections at 95 confidence level anisotropy of magnetic susceptibility measurements shows primary sedimentary fabrics with weak anisotropy degrees a paleomagnetic pole is calculated at 19 1 n 149 7 e k 11 2 a95 9 3 with n 24 yielding a paleolatitude of 27 n for the sampling area the chemo stratigraphic correlation of this section with reference ones reveals an average age of 595 ma a new paleogeographic reconstruction has been attempted showing general low paleolatitude positions for the australia south china and tarim blocks at about 600 ma this observation provides new evidences for the snowball earth hypothesis