well hydraulics theory and data analysis of the constant head test in an unconfined aquifer with the skin effect 1 in a constant head test cht groundwater is withdrawn from a well that has a fixed drawdown accordingly the cht is particularly useful in aquifers of low transmissivity because the constant head well would not be dewatered owing to overpumping the problem of interest pertains to a cht in a homogeneous and anisotropic unconfined aquifer where water released by the water table decline is assumed to be instantaneous and the skin effect surrounding the constant head well is represented by a skin factor a two dimensional transient well hydraulics model is developed and its laplace domain solutions of aquifer drawdown and the constant head well discharge are determined it is found that the three distinct segments typically noted in the time drawdown history of a constant rate test crt are also characteristic of the temporal drawdown variation of the cht however the early time and late time asymptotes conform to the radial flow solution of a cht in confined aquifers as given by hantush 1964 under the late time radial flow conditions the asymptotic solution is in terms of an apparent storage coefficient equal to the sum of the storage coefficient and the specific yield and a specific mass balance relation exists among the constant head well discharge the discharge due to aquifer storage and the discharge resulted from the water table decline while aquifer drawdown and the constant head well discharge are under the influence of well skin their ratios are free from it a curve matching method using this ratio is developed to determine the horizontal and the vertical hydraulic conductivities the storage coefficient and the specific yield when the prescribed constant drawdown is not negligibly small in comparison to the initial saturated thickness aquifer drawdown in late times may be large and thus a drawdown correction is needed for data analysis it is found that the jacob correction for large drawdown of a crt can also be used for the late drawdown correction in a cht

generation of palaeoproterozoic tonalites and associated high k granites in southwestern tanzania by partial melting of underplated mafic crust in an intracontinental setting constraints from geochemical and isotopic data abstract the southwestern part of the 2 0 1 8 ga palaeoproterozoic usagaran belt in the njombe area of sw tanzania is intruded by two types of synchronous granitic rocks with different chemical and petrological characteristics the first type consists of hornblende rich tonalites that have major element compositions similar to those of archaean ttg but differ significantly in their trace element composition the tonalites are spatially and closely associated with felsic high k i type granites some of which are gneissic and or aplitic u pb zircon geochronology shows that the emplacement of tonalites at 1887 11 ma was largely contemporaneous with emplacement of high k granitic gneisses at 1877 15 ma and aplitic granites at 1857 19 ma the data also reveal the presence of archaean crust of 2648 25 ma in the zircon cores of some samples in the otherwise palaeoproterozoic terrane the tonalites are characterized by mgo contents of 1 60 4 11 wt at a sio2 range of 58 1 67 9 wt the mg of 34 55 lower sr contents 220 462 ppm and less fractionated ree patterns la ybcn 3 55 12 9 compared to archaean ttg sr 500 ppm la ybcn 20 these features coupled with the end 1887 ma values of 0 37 to 0 66 as well as the associated mafic enclaves are suggestive of derivation of the tonalites by low pressure below the garnet stability partial melting of a mantle derived mafic underplate that was subsequently contaminated with small amounts of pre existing igneous crustal rocks the evolved nature of the high k granites mgo 0 20 1 30 wt sio2 65 5 73 9 wt mg 25 42 end 3 20 to 4 75 coupled with old tdm ages which are 200 1000 ma older than their emplacement age requires a higher degree of assimilation of older crustal material by the magma derived from partial melting of the underplated mafic crust which was subsequently followed by crystal fractionation involving plagioclase pyroxene and amphibole the close spatial and temporal association of the tonalites mafic enclaves and the high k granites and gneisses in the njombe area provides the first direct evidence of the role of magmatic underplating for the regional thermal anomaly that caused widespread crustal anatexis leading to the generation of the 1 8 1 9 ga granitic rocks in njombe area and or associated felsic volcanism in the usagaran in ndembera and ubendian in ngualla belts of sw tanzania

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

origin of late archean granite geochemical evidence from the vermilion granitic complex of northern minnesota the 2 700 ma vermilion granitic complex of northern minnesota is a granite migmatite terrane composed of supracrustal metasedimentary rocks mafic rocks tonalitic and granodioritic plutonic rocks and granite the metasedimentary rocks are predominantly graywacke which has been regionally metamorphosed to garnet sillimanite muscovite bearing biotite schist and has locally undergone anatexis the mafic rocks form early phases within the complex and are of two types 1 basaltic amphibolite and 2 monzodiorite and essexite rich in large ion lithophile elements lile the members of the early plutonic suite form small bodies that intrude the metasedimentary rocks and mafic rocks producing an early migmatite the granite is of two distinct varieties 1 white garnet muscovite biotite leucogranite s type chappell and white 1974 and 2 grayish pink biotite magnetite lac la croix granite i type the leucogranite occurs in the early migmatite and in paragneissic portions of the complex whereas the lac la croix granite is a late stage intrusive phase that invades the early migmatite and metasediment producing a late migmatite and forms a batholith this study focuses specifically on the origin of granite in the vermilion granitic complex chemical mass balance calculations suggest that the s type two mica leucogranite had a metagraywacke source and that the i type lac la croix granite formed via partial fusion of calc alkaline tonalitic material which may have been similar to rocks of the early plutonic suite this model is satisfactory for petrogenesis of similar late archean post kinematic granites throughout the canadian shield

geochemistry of the early proterozoic granitoids in the halls creek orogenic subprovince northern australia abstract the halls creek orogenic subprovince contains various types of early proterozoic granitoids three suites of tonalite have been recognized in the central part of the halls creek orogenic domain which is an eastern wing of the subprovince the oldest tonalite suite characteristically contains orthopyroxene and includes trondhjemite the youngest tonalite among the three is the sally downs tonalite and is a part of the mabel downs granitoid the tonalites and trondhjemite have low k2o and rb contents fractionated ree patterns with hree depletion these geochemical characteristics suggest each of the tonalite melts is likely to have been derived from the partial melting of mafic rocks leaving a residue consisting of garnet or amphibole it is inferred that subduction of an oceanic plate which had been present between the kimberley and north australian blocks was responsible for the generation of the tonalitic magma melting either subducted oceanic crust or lower mafic crust of an island arc the bow river granitoid suite occurs in the western part of the halls creek orogenic domain forming a large batholith granitoids of the suite are typically peraluminous and enriched in k2o and rb the sophie downs granitoid is an alkali feldspar granite and has a type characteristics the subduction and subsequent collision of the two blocks are considered to be responsible for the generation of those granitoids

observing coseismic gravity change from the japan tohoku oki 2011 earthquake with goce gravity gradiometry the japan tohoku oki earthquake 9 0 mw of 11 march 2011 has left signatures in the earth s gravity field that are detectable by data of the gravity field recovery and climate experiment grace mission because the european space agency s esa satellite gravity mission gravity field and steady state ocean circulation explorer goce launched in 2009 aims at high spatial resolution its measurements could complement the grace information on coseismic gravity changes although time variable gravity was not foreseen as goal of the goce mission we modeled the coseismic earthquake geoid signal and converted this signal to vertical gravity gradients at goce satellite altitude we combined the single gradient observations in a novel way reducing the noise level required to detect the coseismic gravity change subtracted a global gravity model and applied tailored outlier detection to the resulting gradient residuals furthermore the measured gradients were along track filtered using different gradient bandwidths where in the space domain gaussian smoothing has been applied one year periods before and after earthquake occurrence have been compared with the modeled gradients the comparison reveals that the earthquake signal is well above the accuracy of the vertical gravity gradients at orbital height moreover the obtained signal from goce shows a 1 3 times higher amplitude compared with the modeled signal besides the statistical significance of the obtained signal it has a high spatial correlation of 0 7 with the forward modeled signal we conclude therefore that the coseismic gravity change of the japan tohoku oki earthquake left a statistically significant signal in the goce measured gravity gradients

isotopic and geochemical evidence for crust mantle interaction during late archaean crustal growth abstract the charnockites and enderbites of the north marginal zone of the limpopo belt in southern zimbabwe represent a suite of dry magmas of tonalite trondhjemite granodiorite ttg affinity which crystallised directly in the lower crust they were emplaced between 2 6 and 2 7 ga and were derived from a source which showed remarkable lead isotope homogeneity unlike many other lower crustal rocks they have low k rb and low k u ratios and have not experienced depletion of their heat producing elements th u k and rb and thus represent an unusual suite of granulites in this study we have combined the constraints of trace element and isotope geochemistry to characterise the nature of the protolith to the nmz enderbites and charnockites we use a combination of high values calculated lead and strontium isotope initial ratios and old nd model ages to show that the enderbites and chamockites were derived from a protolith which was in part formed more than 500 ma before magma genesis we argue from the very high values that this protolith constituted two separate components an old high low sm nd crustal component and a younger low high sm nd mantle derived component both of which were homogenised by extensive mixing prior to 2 7 ga the presence of an older crustal component contrasts with other archaean ttg suites worldwide which show little evidence for a crustal prehistory the process of mantle crust interaction during late archaean crustal growth in southern zimbabwe invites comparison with modern convergent margins such as the andes

archean crustal evolution in china the taishan complex and evidence for juvenile crustal addition from long term depleted mantle abstract the main framework for crustal evolution of the late archean taishan complex in the shandong province of china is constructed using data from field investigation petrographic examination geochemical analysis and isotopic age determination the history of the complex began with emplacement of basic and tonalitic magmas about 2 7 2 75 ga ago which were metamorphosed designated as metamorphism i to amphibolites and grey gneisses shortly after their emplacement these rocks constitute a metamorphic basement termed the wangfushan gneisses the basement gneisses were later intruded by a plutonic association including 1 alkali and light rare earth element lree enriched dioritic rocks and their differentiates 2 6 ga ago 2 granites and trondhjemites collectively termed the hushan granites also 2 6 ga ago and 3 the aolaishan type granites sensu stricto 2 4 2 5 ga ago the plutonic association in conjunction with the older basement gneisses was later subjected to a second period of deformation and metamorphism metamorphism ii 2 ga ago as inferred from published k ar biotite dates the chronological order of all the above events has been determined by a multichronometric approach and the age results in ma with 2 uncertainties are summarized as follows the relatively low i sr initial 87 sr 86 sr ratio and high positive nd t values for the wangfushan gneisses and the diorite group provides strong evidence for continental growth by addition of juvenile material ultimately separated from long term depleted mantle sources by contrast the sr and nd isotopic data for the aolaishan type granites coherently suggest that they are likely to be derived by anatexis of the basement gneisses at shallow depths crustal evolution of the taishan complex offers an additional example supporting the concept of a continental accretion differentiation superevent that during such a worldwide tectonothermal episode particularly in the archean important differentiation of the upper mantle has contributed to the growth of the continental crust by addition of juvenile material

geology geochemistry and pb pb zircon geochronology of the paleoproterozoic magmatism of vila riozinho tapajos gold province amazonian craton brazil abstract pb pb zircon geochronologic data define two different periods of intense igneous activity in the vila riozinho region tapajos gold province tgp south central amazonian craton at 2 00 1 97 ga the vila riozinho volcanic sequence 2000 4 ma 1998 3 ma and the older sao jorge granite 1981 2 ma 1983 8 ma were formed at 1 89 1 87 ga the younger sao jorge 1891 3 ma jardim do ouro 1880 3 ma and maloquinha 1880 9 ma granites and the moraes almeida volcanic sequence 1890 6 ma 1881 4 ma 1875 4 ma were emplaced similar age intervals are registered throughout the tgp that is thus a little younger than the paleoproterozoic terranes of the maroni itacaiunas province in the guiana shield geochemical and geochronologic data demonstrate that the sao jorge pluton is composed of two different granitoids the older and younger sao jorge granites these as well as the jardim do ouro granite are i type and magnetite series the sao jorge granites are high k calc alkaline and show significant geochemical variation the jardim do ouro granite is more iron rich and less oxidized the vila riozinho formation is calc alkaline to shoshonitic and geochemically similar to the sao jorge granites the maloquinha granite and the moraes almeida formation differ from the other studied rocks in petrographic and geochemical characteristics have aluminous a type affinities and were probably derived by low temperature crustal melting the volcanic sequences of the studied area formerly included into the iriri group of the uatuma supergroup are divided into the vila riozinho and moraes almeida sequences the presence of these two sequences in the same tectonic domain demonstrates the heterogeneity of the uatuma supergroup the tgp registers accretionary processes related to the formation of the atlantica supercontinent at 2 00 ga this was followed at 1 88 ga by an intracontinental taphrogenic event that lasted throughout the mesoproterozoic the tectonic setting of the tgp was thus transitional between a subduction related magmatic arc and a stable continental block undergoing extension

distributed fault slip model for the 2011 tohoku oki earthquake from gnss and grace goce satellite gravimetry the gravity recovery and climate experiment grace mission launched 2002 and the gravity field and steady state ocean circulation explorer goce mission march 2009 to november 2013 collected spaceborne gravity data for the preseismic and postseismic periods of the 2011 tohoku oki earthquake in addition the dense japan geonet global navigation satellite systems gnss network measured with approximately 1050 stations the coseismic and postseismic surface displacements we use a novel combination of gnss grace and goce observations for a distributed fault slip model addressing the issues with gravimetric and geometric change over consistent time windows our model integrates the coseismic and postseismic effects as we include goce observations averaged over a 2 year interval but their inclusion reveals the gravity change with unprecedented spatial accuracy the gravity gradient grid evaluated at goce orbit height of 265 km has an estimated formal error of 0 20 me which provides sensitivity to the mainly coseismic and integrated postseismic induced gravity gradient signal of 1 03 me we show that an increased resolution of the gravity change provides valuable information with goce gravity gradient observations sensitive to a more focused slip distribution in contrast to the filtered grace equivalent the 2 year averaging window of the observations makes it important to incorporate estimates of the variance covariance of unmodeled processes in the inversion the gnss and grace goce combined model shows a slip pattern with 20 m peak slip at the trench the total gravity change 200 gal and the spatial mapping accuracy would have been considerably lower by omitting the goce derived fine scale gravity field information

contrasting high and intermediate pressures of metamorphism in the archaean sargur schists of southern india the archaean karnataka craton of southern india contains eastern and western crustal blocks separated by a major thurst in which sargur schists occur as lenses within tonalitic peninsular gneisses the schist complex comprises pelites quartzitic psammites carbonates and calc silicates iron formations and basic rocks and thus provides many mineral assemblages ideal for the calculation of pt conditions with their gneisses the sargur rocks are unconformably overlain by the dharwar greenstone belts and are generally thought to be older than 3 000 my

tectonic implications of palaeoproterozoic post collisional high k felsic igneous rocks from the kimberley region of northwestern australia abstract palaeoproterozoic high k i type granites high level porphyry intrusions and felsic volcanic rocks of the whitewater volcanics dominate the hooper and lamboo complexes in the kimberley region of northwestern australia the granites porphyries and volcanic rocks are gradational into each other in the field and they have the same mineralogy similar major and trace element abundances and indistinguishable shrimp u pb zircon ages of 1865 1850 ma there is evidence of widespread mingling between the granites and coeval gabbros magma mixing may be important in the formation of some of the mafic granites but most of the rocks probably formed from felsic parent magmas that underwent variable degrees of fractional crystallization the felsic igneous rocks may have formed by partial melting of intermediate to felsic calc alkaline rocks along the southern and eastern margins of the kimberley craton following accretion of various earlier palaeoproterozoic terranes to the craton therefore models for palaeoproterozoic high k granites in northern australia that invoke intracratonic rifting of a stable archaean craton may need to be revised

sources of continental magmatism adjacent to the late archean kolar suture zone south india distinct isotopic and elemental signatures of two late archean magmatic series conspicuous nd sr and pb isotopic differences exist between the archean gneiss terranes adjoining the suture at the kolar schist belt south india these gneisses which are the deformed equivalents of plutonic and volcanic rocks have known or inferred igneous ages of 2630 to 2530 ma initial isotopic ratios of nd sr and pb suggest that metaplutonic gneisses west of the kolar schist belt were emplaced into and variably contaminated by an evolved continental crust that formed prior to 3200 ma felsic metaigneous gneisses that occur as slivers on the western margin of the schist belt have an isotopic character similar to that of the metaplutonic rocks on the same side of the kolar schist belt on the east side of the kolar schist belt the isotopic evidence suggests that the 2530 ma granitic gneisses were not derived from or contaminated by an older continental crust their source probably evolved with a nd isotopic composition similar to that of typical archean mantle but became light rare earth element enriched after 2900 to 2700 ma the inferred tectonic setting for the west side of the kolar schist belt is an andean continental magmatic arc for the east side of the kolar schist belt a possible phanerozoic analog is an evolved island arc such as japan

sinking of the dharwar basin south india implications for archaean tectonics abstract archaean tectonic regimes can be constrained by structural analysis of greenstone belts and adjacent granite gneiss masses the late archaean bababudan greenstone belt dharwar craton south india contains a low grade volcanosedimentary basin sequence the dharwar supergroup which unconformably overlies a previously eroded basement made up mainly of granite and gneiss fabric trajectories kinematic indicators and superimposed deformation patterns show that greenstones have undergone a radial converging downward flow with respect to underlying basement rocks as well as strike slip shearing this is attributed to the progressive sagduction gravity sinking of the greenstone belt into its basement along a decollement horizon and to late transcurrent shearing we propose a deformation model for the bababudan belt that may explain common features of many greenstone belts such as decollements and superimposed upright fold patterns which are attributed to the progressive sinking of the supracrustals into their basement the results of our study and other field investigations in the crust of the dharwar craton as well as structural evidence from other cratons zimbabwe and pilbara raise the possibility that a unique continental tectonic regime existed during the archaean controlled by the emplacement of dense volcanic traps mantle underplating and thermal blanketing of the continental crust this tectonic regime differs from that observed within the modern lithosphere as it is characterized by the pervasive development of gravity i e rayleigh taylor instabilities between the volcanic traps and the rest of the continental crust it allowed heat and material transfer through the crust and has to be seen as an efficient recycling mechanism for the young continental crust during periods of mantle underplating the diapiric phenomenon is independent of the boundary forces acting at the limits of the protocontinents and is associated in time and space with large scale accretion events of the continental crust perhaps in hot spot environments

age and geochemistry of coeval felsic volcanism and plutonism in the palaeoproterozoic ndembera group of southwestern tanzania constraints from shrimp u pb zircon and sm nd data abstract the ndembera metavolcanic rocks represent a continuum of compositions ranging from intermediate to more siliceous calc alkaline trachyandesites dacites trachytes rhyolites which have been intruded by largely metaluminous calc alkaline i type granites in the palaeoproterozoic usagaran belt of southwestern tanzania shrimp u pb zircon age data show that the ndembera metavolcanic rocks were extruded at 1871 30 ma an event that was largely coeval with the emplacement of cross cutting microcline biotite rich granites at 1896 29 ma despite some compositional differences both the granites and metavolcanic rocks share similar geochemical features including very coherent ree patterns characterized by enrichment of the lree relative to the hree la ybcn 13 6 32 8 average 23 9 for metavolcanic rocks and la ybcn 10 8 38 2 average 21 8 for granites negative eu anomalies eu eu 0 45 1 01 average 0 83 for volcanic rocks and eu eu 0 48 0 70 average 0 60 for granites negative ta ti and nb anomalies nb lapm 0 14 0 29 average 0 20 for volcanic rocks and nb lapm 0 01 0 37 average 0 16 for granites the metavolcanic rocks have nd 1871 ma values of 0 03 to 4 89 and tdm ages of 2243 2714 which are broadly similar to those of the granites nd 1896 ma values of 3 56 to 4 59 and tdm ages of 2469 2646 ma the geochemical similarities between the ndembera volcanic rocks and granites coupled with their similar emplacement age suggest that the two rock suites were derived by the same processes in the same tectonic setting from an isotopically similar source these geochemical features coupled with the paucity of mafic rocks suggest the derivation of the pluto volcanic suite by crustal anatexis of basic meta igneous rocks mixed with a minor metasedimentary component in an intra continental setting the more siliceous compositions in the suite may have formed by subsequent fractionation involving hornblende plagioclase biotite titanite and apatite as indicated by the negative correlation between sio2 and mgo fe2o3 al2o3 cao tio2 and p2o5 low sr contents and negative eu and ti anomalies the 1 87 ga coeval felsic volcanic and granitic magmatic event documented in the ndembera group is also a feature of the nearby ubendian belt to the west pointing to a palaeoproterozoic regional thermal event that occurred in southwestern and western tanzania

progressive metamorphism of mafic rocks from greenschist to granulite facies in the dharwar craton of south india in the archean dharwar craton of southern india n s trending belts of metabasic rocks are exposed which underwent regional metamorphism at about 2 5 ga ago the progressive changes in the assemblages and mineral chemistry of metabasites was studied in a n s traverse covering the chitradurga and nagaman gala belts the sargur area and the nilgiri hills towards the south with increasing metamorphic grade greenschists chl act ab ep pm carb qtz give way to amphibolites hbl plag pm qtz gar cumm and mafic granulites pyx plag gar pm hbl qtz the amphibole composition changes from actinolite in the greenschist zone to tschermakitic hornblende in the amphibolite zone and pargasitic hastingsitic hornblende in the granulite zone the ti content of the amphiboles systematically increases in this direction the plagioclase composition changes from albite in the greenschist zone to oligoclase andesine in the amphibolite zone and andesine labradorite in the granulite zone almandin

goce gravity gradients versus global gravity field models summary the goce mission a part of esa s living planet programme aims at improved gravity field modelling at high spatial resolution on board goce a gradiometer in combination with a scientific on board gps receiver measures the earth s gravity field with unprecedented accuracy these measurements have been used to compute goce gravity field solutions and combined goce grace solutions the main difference between the solutions is how they incorporate the required a priori information which consists either of existing gravity field models or kaula s rule for the signal variances of the gravity field we assessed four series of models by comparing the gravity gradients they predict with the measured goce gradients the analysis of the gravity gradients fits may reveal differences between the different solutions that can be attributed to the solution strategy assuming that the measurement errors are homogeneous we compared the goce gradients with existing state of the art global gravity field models and conclude that the gradient errors are indeed globally homogeneous with the exception of the cross track gradient especially south of australia furthermore we find that the use of existing global gravity field models as a priori information should be avoided because this may increase the gradient residuals in spatial and spectral domain finally we may conclude that the goce and grace data are compatible and complementary

rotation of goce gravity gradients to local frames summary esa s goce mission aims at improved global and regional gravity field information with high spatial resolution by measuring gravity gradients a local analysis of the goce gravity gradient tensor may benefit from a rotation from the gradiometer reference frame to local reference frames such as the local north oriented reference frame as the goce gravity gradients include accurate and less accurate measured gradients the point wise tensor rotation of the goce only measurements may suffer from the projection of the errors of the less accurate gravity gradients onto the accurate gravity gradients in addition the goce gravity gradients have high accuracy in the measurement bandwidth but low accuracy below and tensor rotation may cause leakage of the large error below the measurement bandwidth to the measurement bandwidth degradation of the rotated gravity gradients is circumvented by replacing the less accurate tensor components as well as the signal below the measurement bandwidth of the accurate gravity gradients with model signal the combination of goce and model gravity gradients is performed by determining the effective measurement bandwidth emb that is the bandwidth in which the integrated signal to noise ratio of the goce gravity gradients is maximized we find that the determination of the emb is relatively independent of the reference gravity field model that is used the lower bound of the emb is well below the pre mission specifications for the four accurate gravity gradients in addition we assess how much goce contributes to the gravity gradient signal in local frames and how much the model for the radial gravity gradient the relative goce contribution is 98 per cent on average whereas this is 65 97 per cent for the other gravity gradients these numbers strongly depend on the local frame under consideration and on the geographical position

pillow lava basalts with back arc morb affinity from the usagaran belt tanzania relics of orosirian ophiolites the paleoproterozoic usagaran orogenic belt in east africa is an exemplary site of preserved relics of paleoproterozoic volcanic arc magmas and subducted and displaced oceanic crust this paper describes the geochemical characteristics of displaced pillow basalts from the usagaran belt konse group our data indicate that the konse pillow basalts have tholeiitic composition and are overprinted by greenschist facies metamorphic conditions but their primary geochemical signatures are preserved by ree and fluid immobile elements the la sm n ratios 0 62 1 09 and ree patterns point to normal mid ocean ridge basalt n morb and transitional morb t morb mantle source the analysis of high valency elements and trace element patterns points to a mixed signature of morb tholeiites and island arc tholeiites with elevation of ba th u eu and sr this composition is similar to that of phanerozoic back arc suprasubduction zone ophiolites therefore usagaran belt pillow basalts are an analogue of the tethyan type suprasubduction zone ophiolite evolution and emplacement in the precambrian the emplacement of the konse pillow basalts is older than the neighbouring 1920 1870 ma volcanic arc magmas and is probably coeval with the formation of the 2000 ma yalumba eclogites with morb affinity thus the konse pillow basalts might have been displaced from their suprasubduction zone tectonic setting of igneous construction within the yalumba ocean basin around 2000 ma thematic collection this article is part of the tethyan ophiolites and tethyan seaways collection available at https www lyellcollection org cc tethyan ophiolites and tethyan seaways

late archaean granites a typology based on the dharwar craton india abstract extensive field work in the eastern dharwar craton associated with petrographic and geochemical major and trace elements investigations allows four main types of late archaean granitoids to be distinguished 1 na rich granitoids of trondhjemitic tonalitic and granodioritic composition ttg that are characterised by strongly fractionated ree patterns and low hree contents and generally interpreted as slab melts generated by partial melting of metamorphosed hydrated basalt most likely in a subduction environment 2 sanukitoids which are k and mg rich monzonites and granodiorites with ttg like ree patterns associated with marked lile enrichment and considered to result from the reaction of slab melts generated in a subduction environment with and assimilation of mantle wedge peridotite 3 uncommon high hfse mg and k granites with strongly ree and lile enrichment that probably formed by partial melting of an enriched mantle source unlike in the genesis of sanukitoids in this case the slab melt is considered to be wholly consumed by reaction with mantle minerals resulting in mantle enrichment subsequent melting of this enriched mantle probably in a post subduction setting gives rise to high hfse mg and k magmas as demonstrated for the closepet granite dharwar craton the hot mantle derived magma can induce melting of continental crust and then mix with the anatectic products 4 k rich mg poor anatectic biotite granites with ree patterns that are less fractionated and show negative eu anomalies these granites result from the remelting of old basement or recently accreted plutons both with ttg compositions such anatexis can occur either in a subduction or in a post subduction environment this typology based on the well exposed dharwar craton can be extended to late archaean granitoids from all over the world about such 500 analysis were compiled and a number of discriminant diagrams based on both major and trace elements are proposed the most likely tectonic setting for the observed rock types is an accretionary orogen with accretion of continental blocks above a subduction system followed by thermal reworking of the newly accreted continental material however it has been found that archaean subduction related granitoids are significantly different from their modern counterparts implying progressive changes in the modes of magma generation at convergent margins from the archaean to the present

a spectral assessment review of current satellite only and combined earth gravity models 1 the realization over the last decade of dedicated gravity field satellite missions enabled the production of a series of new satellite only and combined models for the earth s gravity field using different sensors measurement techniques and algorithmic procedures the final product in each case is a set of spherical harmonic coefficients representing the series expansion of the gravitational potential up to a certain maximum degree depending on the mission characteristics and the range of the available data the present review performs a detailed quantified analysis of a representative selection of currently available champ challenging minisatellite payload grace gravity recovery and climate experiment goce gravity field and steady state ocean circulation explorer and combined earth gravity models in this comparative analysis we also include the so called topographic isostatic gravity models that represent the contribution of global digital elevation maps for the topography and ocean bathymetry applying a range of available spatial and spectral accuracy and assessment measures such as correlation per degree and order smoothing per degree and order signal to noise ratio gain degree variances and error degree variances one gains a quantified peek inside the quality of these models spanning over their whole spectrum the applied error and assessment measures are defined both in an absolute and relative manner with respect to other similar models or some reference earth gravity models furthermore the nature of the performed analysis degree wise order wise and cumulative permits the identification of distinct spectral bandwidths in these models enables the quantification of some standard features of the observed field such as its long wavelength short wavelength or very high frequency part and specifies the attenuation of the gravity signal with increasing altitude from the earth s surface an examination of the assessment quantities reveals certain bandwidths of these models with characteristic statistical features a band limited synthesis of these bandwidths in the space domain quantifies the corresponding contributions in terms of selected gravity field functionals including second order derivatives at goce altitude

geochemical and nd isotopic systematics of granites from the arunta inlier central australia implications for proterozoic crustal evolution geochemical and sm nd isotopic results are reported for granites from the proterozoic arunta inlier of central australia these combined with new geochronological data for the granites zhao and bennett 1995 allow important constraints to be placed on proterozoic tectonic and crustal evolution in central australia granites from the arunta inlier can be divided into three major geochemical groups a calcalkaline trondhjemitic group cat a high heat production group hhp and a volumetrically significant main group the cat group which occurs only in the southern margin of the inlier is characterised by high na2o nak sr krb and sry and relatively low k2o rb rbsr th u ree nb and y analogous to calc alkaline suites occurring in modern convergent plate margins the hhp group which occurs mainly in the interior of the arunta inlier and is spatially associated with the main group is characterised by high k rb th u rbsr and rbzr and relatively low sr ba nak krb barb mgo cr and ni the main group which occurs throughout the arunta inlier is geochemically intermediate between the cat and hhp groups it is geochemically analogous to the 1880 1850 ma old barramundi igneous association recognised in other proterozoic terrains of central australia and can be further subdivided into four age subgroups 1820 1780 1750 1650 and 1615 1600 ma respectively all three groups show similar negative nb anomalies on the trace element normalized diagrams despite the geochemical diversity of the arunta granites no correlations between the nd isotopic and geochemical signatures are observed the ranges of initial nd values and nd depleted mantle model ages tnddm for the three groups of granites overlap with each other overall there are two groups of tnddm ages the most common ranging from 2 33 to 1 96 ga and the other from 1 83 to 1 72 ga although initial nd values of the granites show large variations there is a general trend for the nd values to increase i e become less negative with decreasing crystallization ages the large geochemical and isotopic variations of the arunta granites reflect considerable heterogeneity in the sources of the granites and do not support a uniform 2 3 2 1 ga old barramundi type underplate source for the origin of the granites the combined geochemical and nd isotopic data suggest the sources of the granites contain at least two main components an palaeoproterozoic mantle derived component and an older crustal component the older crustal component was incorporated into the source region of the granites either through magma assimilation of crustal materials at lower crustal levels or more probably via sediment subduction and mantle wedge metasomatism the increasing nd values with decreasing crystallization ages may be a result of progressively increasing proportions of newly accreted island arc materials being incorporated in the subducted sediments alternatively a juvenile mantle derived component may have been added to the source region of the younger granites it is apparent that the nd isotopic signatures in the granites has resulted from complex processes and neither simple mixing nor simple two stage protolith models can as yet satisfactorily explain the observations the petrogenesis of the three geochemical groups of granites can be interpreted in a plate tectonics scenario it is considered that the cat group was formed by fractionation of arc type magmas and or partial melting of arc related intrusions or underplates in a subduction related continental margin setting whilst the formation of the main group may involve partial melting of fractionated and or modified arc related underplates but not necessarily in a subduction environment the younger hhp group was probably generated by remelting of the coexisting main group during subsequent tectonothermal events

hydraulics of a drainage well fully penetrating a leaky aquifer through a multisection screen abstractthe authors develop a transient semianalytical solution for evaluating the hydraulic head distribution in a leaky aquifer under constant surface ponding conditions while draining through a fully penetrating multisection screen of an injection well the authors use integral transform techniques such as laplace and finite fourier cosine for solving the said problem analytically the solution in the laplace domain is inverted to the time domain numerically the authors test the performance of the derived semianalytical solution by comparing its results with field data subsequently they use the solution to evaluate the hydraulic head distribution within the flow medium for a drainage event analyses show that the hydraulic head distribution within the radius of partial screening influence rps in the aquifer is controlled by both the radial distance from the well and the monitoring depth but only by the radial distance beyond rps further the rps does not depend on the screen sections lengths and

advancements in satellite gravity gradient data for crustal studies in recent years global gravity models both based only on satellite data and from combination with terrestrial data are increasingly available and particularly useful to construct regional models before more local interpretations on the exploration scale are carried out often it is challenging to distinguish clearly between near surface and regional or even subcrustal signals in the gravity field applying simple techniques like wavelength filtering might lead to an incorrect estimate of the regional and residual field which may significantly alter estimates of the thickness of sedimentary basins or the size of mineral deposits an alternative is to use satellite gravity gradients to establish the regional components before studying local geology sampietro 2011 presented a global mohorovicic discontinuity moho depth map which sparked a discussion about the validity of such results especially the question remains about whether crustal thickness estimates based on gravity field and steady state ocean circulation explorer goce satellite data have a higher accuracy than models based on global gravity models or terrestrial data for example the density contrast between crust and mantle remains a main factor of uncertainty here we join this discussion by describing how satellite gravity gradients can be used in addition to terrestrial data sets or global models like egm2008 and how the combined use of data sets at multiple levels above the earth s surface can help confine the uncertainty in both regional and local modeling studies

palaeoproterozoic volcanism and granitic magmatism in the ngualla area of the ubendian belt sw tanzania constraints from shrimp u pb zircon ages and sm nd isotope systematics abstract secondary ion microprobe u pb zircon data and sm nd isotopic compositions are presented for the volcanic and associated granitic rocks in the northern part of the lupa terrane in the ngualla area of the ubendian belt southwestern tanzania the u pb data reveals two distinct episodes of volcanism in the area a 1943 ma volcanism involving the eruption of basaltic andesites and a 1871 ma event during which porphyritic dacites and minor rhyolites erupted the data further shows that the last episode of volcanism was coeval with the emplacement of potassic granites at 1878 ma an older age of 2682 ma was obtained from zircons inherited from the pre existing archaean crust in a potassic granite the basaltic andesites exhibit nd 1943 ma values of 3 33 to 6 24 and t dm ages of 2521 2883 ma whereas the porphyry dacites show nd 1871 values of 5 72 to 5 94 and t dm ages are 2546 2573 ma these t dm ages are 600 700 ma older than the emplacement ages of both the basaltic andesites and porphyry dacites the potassic granites exhibit the most negative nd 1878 values of all the rocks 6 00 to 11 2 in the area and their t dm ages are 2568 3283 ma which are 700 1400 ma older than their emplacement age the nd t values for both the ngualla volcanic and granitic rocks are much lower than the corresponding mantle value of 6 13 at 1871 ma the emplacement of 1 87 ga coeval felsic plutonic and volcanic rocks in the ngualla area of the ubendian belt is also a feature of the nearby usagaran belt and this corroborates previous evidence that plutonism and volcanism in both the usagaran and ubendian belts took place at the same time the presence of 1 87 ga granites in both the usagaran and the ubendian belt implies that granitic magmatism of this age was a regional thermal event that covered a significant portion of the proterozoic terranes of southeastern and southwestern tanzania inherited archaean zircon crystals coupled with negative nd and nd model ages 600 1400 ma older than their respective emplacement ages all suggest palaeoproterozoic crust is derived in part by re worked archaean crust at the southwest corner of the tanzanian craton

combined satellite gravity field model goco01s derived from goce and grace 1 the satellite only gravity field model goco01s is a combination solution based on 61 days of goce gravity gradient data and 7 years of grace gps and k band range rate data resolved up to degree order 224 of a harmonic series expansion the combination was performed consistently by addition of full normal equations and stochastic modeling of goce and grace observations the model has been validated against external global gravity models and regional gps leveling observations while low to medium degrees are mainly determined by grace significant contributions by the new measurement type of goce gradients can already be observed at degree 100 beyond degree 150 goce becomes the dominant contributor correspondingly with goco01s a global gravity field model with high performance for the complete spectral range up to degree order 224 is now available this new gravity model will be beneficial for many applications in geophysics oceanography and geodesy

nd and sr isotopic mapping of the archaean proterozoic boundary in southeastern tanzania using granites as probes for crustal growth abstract granitoids of two different generations occur across the archaean proterozoic boundary in southeastern tanzania the first generation which is confined to the archaean tanzania craton yields rb sr whole rock isochron ages of 2600 ma and low mantle like initial 87sr 86sr ratios 0 702 0 704 these coupled with positive or near zero e nd values 0 2 to 2 0 suggest that these granitoids represent juvenile mantle material which was added to the continental crust at about 2600 ma the second generation of granitoids intrudes the palaeoproterozoic usagaran belt and is characterised by rb sr whole rock isochron ages of about 1900 ma these granitoids show sm nd crustal formation ages which are 200 to 600 ma older than their emplacement ages and negative e nd values 2 2 to 6 2 mixing calculations suggest that the proterozoic granitoids may have formed by partial melting of 2000 ma usagaran mantle derived material which had incorporated between 15 and 45 of an archaean component from the adjacent tanzania craton

geochemistry and u pb hf zircon data for plutonic rocks of the troia massif borborema province ne brazil evidence for reworking of archean and juvenile paleoproterozoic crust during rhyacian accretionary and collisional tectonics abstract rhyacian c 2 30 2 05 ga subduction accretion and collisional processes are thought to represent an important event of crustal growth and reworking often reported in the so called tranzamazonian eburnean granite greenstone terranes of n ne brazil and west african craton in this work we present whole rock geochemistry and u pb hf zircon ages for rhyacian plutonic rocks that intrude paleoproterozoic granite greenstone terranes and archean basement rocks of the troia massif borborema province ne brazil u pb shrimp zircon age of 2185 4 ma was obtained for a metatonalite sample mirador metatonalites the metatonalites show geochemical affinity similar to those of adakites like rocks with all classic slab derived adakitic signature e g high sr y la yb and low hree but more akin to those evolved from partial melting of the metasomatized mantle wedge followed by fractional crystallization zircon hf crustal model ages of the metatonalite sample range between 2800 and 2660 ma evidencing that archean crustal components contributed to its magma genesis probably via subduction of continental derived sediments to the mantle wedge for potassic plutons of the troia massif bananeira suite we obtained u pb shrimp zircon age of 2079 4 ma for a deformed quartz monzonite with geochemical affinities similar to those derived from low pressure partial melting of a k rich mafic protolith for less deformed equigranular granites we obtained a u pb la icpms zircon age of 2068 5 ma they are high k calc alkaline and slightly peraluminous granites that probably derived from low pressure partial melting of tonalitic crustal sources metatonalites and or metagraywackes zircon hf crustal model ages of a granite sample range from 2713 to 2535 ma evidencing archean crustal contribution to magma genesis however two analyzed c 2307 ma inherited zircon grains show ehf t values of c 4 87 indicating that crustal reworking of less radiogenic paleoproterozoic sources also participated in its genesis regional correlations of our results with the paleoproterozoic record of the troia massif borborema province and surrounding cratonic domains suggest that the studied plutons are related to the c 2 2 2 0 ga transamazonian eburnean orogenic cycle the c 2185 ma metatonalites are associated to pre collisional setting while the c 2079 2068 ma quartz monzonites and granites evolved during collisional setting

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

geochemistry and zircon geochronology of the i type high k calc alkaline and s type granitoid rocks from southeastern roraima brazil orosirian collisional magmatism evidence 1 97 1 96 ga in central portion of guyana shield abstract the understanding of the geological evolution of the uatuma anaua domain in southeastern roraima central region of guyana shield is of major significance in the study of the amazonian craton this region lies between some major paleoproterozoic geological geochronological provinces tapajos parima or ventuari tapajos dominant maroni itacaiunas or transamazon northwest and central amazonian or central amazon southeast and east geological mapping of the northern area of uatuma anaua domain integrated with whole rock geochemistry data and previous and new pb evaporation and u pb zircon geochronology point out for a plutonic collisional magmatic event 1975 1968 ma represented by i type high k calc alkaline martins pereira and s type serra dourada granitoid rocks this magmatism was probably generated from crustal sources by partial melting during amalgamation of the ttg like anaua magmatic arc 2028 ma with transamazonian 2 2 2 0 ga and central amazonian older than 2 3 ga terranes local cumulatic leucogranites fills planar structures of the martins pereira granites these leucogranites show younger ages 1909 ma and several inherited zircons 2354 2134 1997 and 1959 ma suggesting origin from crustal sources

a flowing partially penetrating well in a finite thickness aquifer a mixed type initial boundary value problem abstract an analytical approach using integral transform techniques is developed to deal with a well hydraulics model involving a mixed boundary of a flowing partially penetrating well where constant drawdown is stipulated along the well screen and no flux condition along the remaining unscreened part the aquifer is confined of finite thickness first the mixed boundary is changed into a homogeneous neumann boundary by discretizing the well screen into a finite number of segments each of which at constant drawdown is subject to unknown a priori well bore flux then the laplace and the finite fourier transforms are used to solve this modified model finally the prescribed constant drawdown condition is reinstated to uniquely determine the well bore flux function and to restore the relation between the solution and the original model the transient and the steady state solutions for infinite aquifer thickness can be derived from the semi analytical solution complementing the currently available dual integral solution if the distance from the edge of the well screen to the bottom top of the aquifer is 100 times greater than the well screen length aquifer thickness can be assumed infinite for times of practical significance and groundwater flow can reach a steady state condition where the well will continuously supply water under a constant discharge however if aquifer thickness is smaller the well discharge decreases with time the partial penetration effect is most pronounced in the vicinity of the flowing well decreases with increasing horizontal distance and vanishes at distances larger than 1 2 times the aquifer thickness divided by the square root of aquifer anisotropy the horizontal hydraulic conductivity and the specific storage coefficient can be determined from vertically averaged drawdown as measured by fully penetrating observation wells the vertical hydraulic conductivity can be determined from the well discharge under two particular partial penetration conditions

drainage of ponded land through irrigation well in a leaky aquifer unsteady flow through an irrigation well installed in an inundated leaky aquifer underlying a semi pervious soil layer has been analysed solutions for unsteady piezometric head distribution and rate of recharge into the aquifer under constant and variable surface ponding conditions have been developed for two cases namely flow from gravity well and constant rate injection well using approximate method of laplace inversion technique schapery r a 1961 approximate methods of transform inversion for viscoelastic stress analysis proc iv us national congress of applied mechanics pp 1075 1085 the developed solutions for constant surface ponding condition have been verified with the field data at tabageria village of shaldahari watershed near indian institute of technology kharagpur west bengal india the daily runoff depth drainage depth and proceeding ponding depth have been analysed using solutions for variable surface ponding for tabageria village in the monsoon year 1978 the total volume and duration of water drained into aquifer through irrigation cum drainage well from a given command area of the watershed were computed the analysis indicates that the gravity cum injection well is the best feasible solution for reclaiming surface impounding before sowing of winter season crop