volcanic plutonic parity and the differentiation of the continental crust the continental crust is central to the biological and geological history of earth however crustal heterogeneity has prevented a thorough geochemical comparison of its primary igneous building blocks volcanic and plutonic rocks and the processes by which they differentiate to felsic compositions our analysis of a comprehensive global data set of volcanic and plutonic whole rock geochemistry shows that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but are divergent in continental rifts offsets in major and trace element differentiation patterns in rift settings suggest higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas relative to dry rift volcanics in both tectonic settings our results indicate that fractional crystallization rather than crustal melting is predominantly responsible for the production of intermediate and felsic magmas emphasizing the role of mafic cumulates as a residue of crustal differentiation a global geochemical data set of volcanic and plutonic rocks indicates that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but are divergent in continental rifts brenhin keller and co authors present a global geochemical dataset of the two fundamental building blocks of the continental crust volcanic externally erupted and plutonic internally solidified rocks their results indicate that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but divergent in continental rifts offsets in major and trace element differentiation patterns in rift settings suggest higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas relative to dry rift volcanics this work indicates that in both tectonic settings fractional crystallization rather than crustal melting is predominantly responsible for the production of intermediate and felsic magmas

earth s early o2 cycle suppressed by primitive continents a decrease in mafic continental crust coincides with the rise of o2 in the earth s surface environments about 3 billion years ago according to an analysis of sediment chemistry reduced rates of serpentinization of mafic material which produces chemicals that react with o2 could explain the link

emergence of modern continental crust about 3 billion years ago the continental crust provides a record of earth s evolution analysis of the geochemical signature of continental crust formed since the hadean points to the initiation of plate tectonics about 3 billion years ago

fine scale structure of the mid mantle characterised by global stacks of pp precursors abstract subduction zones are likely a major source of compositional heterogeneities in the mantle which may preserve a record of the subduction history and mantle convection processes the fine scale structure associated with mantle heterogeneities can be studied using the scattered seismic wavefield that arrives as coda to or as energy preceding many body wave arrivals in this study we analyse precursors to pp by creating stacks recorded at globally distributed stations we create stacks aligned on the pp arrival in 5 distance bins with range 70 120 from 600 earthquakes recorded at 193 stations stacking a total of 7320 seismic records as the energy trailing the direct p arrival the p coda interferes with the pp precursors we suppress the p coda by subtracting a best fitting exponential curve to this energy the resultant stacks show that pp precursors related to scattering from heterogeneities in the mantle are present for all distances lateral variations are explored by producing two regional stacks across the atlantic and pacific hemispheres but we find only negligible differences in the precursory signature between these two regions the similarity of these two regions suggests that well mixed subducted material can survive at upper and mid mantle depth to describe the scattered wavefield in the mantle we compare the global stacks to synthetic seismograms generated using a monte carlo phonon scattering technique we propose a best fitting layered heterogeneity model brt2017 characterised by a three layer mantle with a background heterogeneity strength 0 8 and a depth interval of increased heterogeneity strength 1 between 1000 km and 1800 km the scalelength of heterogeneity is found to be 8 km throughout the mantle since mantle heterogeneity of 8 km scale may be linked to subducted oceanic crust the detection of increased heterogeneity at mid mantle depths could be associated with stalled slabs due to increases in viscosity supporting recent observations of mantle viscosity increases due to the iron spin transition at depths of 1000 km

influence of provenance and transport process on the geochemistry and radiogenic hf nd and sr isotopic composition of pleistocene glacial sediments minnesota usa abstract we develop a broad geochemical dataset from 50 samples of pleistocene glacial till matrix including three lacustrine samples representing four sediment provenances collected from across minnesota usa such a dataset is useful both in the context of regional studies of glaciation and in efforts to understand how provenance and glacial processes impact the geochemistry of sediment archives the principal sediment sources of the four provenances include materials from the archean proterozoic canadian shield the proterozoic midcontinent rift paleozoic carbonates and cenozoic and mesozoic clastic sediments we measured major element geochemistry in all till samples in both

archean upper crust transition from mafic to felsic marks the onset of plate tectonics the archean eon witnessed the production of early continental crust the emergence of life and fundamental changes to the atmosphere the nature of the first continental crust which was the interface between the surface and deep earth has been obscured by the weathering erosion and tectonism that followed its formation we used ni co and cr zn ratios in archean terrigenous sedimentary rocks and archean igneous metaigneous rocks to track the bulk mgo composition of the archean upper continental crust this crust evolved from a highly mafic bulk composition before 3 0 billion years ago to a felsic bulk composition by 2 5 billion years ago this compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks suggesting the onset of global plate tectonics at 3 0 billion years ago

petrology and geochemistry of siliciclastic rocks of mixed feldspathic and ophiolitic provenance in the northern apennines italy provenance in clastic sedimentary rocks in the northern apennines is determined by integrated petrographic and geochemical criteria thus mafic poor arkoses in the gottero formation senonian paleocene deposited prior to the alpine orogeny were derived from granitic provenance in the sardinian corsican massif in the gottero formation chemical criteria distinguish between very low input of detrital mafic material and co c and ni added entirely by adsorption on clay minerals post alpine orogeny feldspathic sandstones in the macigno formation mid oligocene lower miocene and cervarola formation lower miocene reflect a more diverse provenance of granitic metamorphic ophiolitic and sedimentary rocks in the apennines and alps the macigno and cervarola rocks are distinguished by serpentine gabbro and diabase fragments and higher chlorite contents than in the gottero rocks chemically the macigno and cervarola rocks contain distinctive signatures expressed in higher mgo co cr and ni contents of the mafic ultramafic detritus a wider range and more scattered cr and ni variation and higher niggli ti for a given niggli al alk content the mgo co cr and ni abundances indicate up to 10 ultramafic ophiolitic detritus in the macigno and cervarola sandstones and up to 17 ophiolitic detritus in associated shales estimated by comparison of mixtures of feldspathic sands with ligurian peridotites up to 10 basaltic ophiolitic detritus in these sediments is suggested by cao and fe2o3 total abundances petrographic data indicate that a major part of the detritus in the macigno and cervarola formations is from alpine granitic basement of calc alkaline granite to tonalite plutons and gneisses but apart from higher ba in macigno and cervarola sandstones than in the gottero sandstones this is difficult to identify chemically the trace elements cr ni ba rb ce la y co cu ga pb and zn generally have positive correlations with niggli al alk a chemical surrogate measure of sheet mineral clays micas and chlorites content whereas sr which is associated with carbonate and feldspar shows negative correlation with al alk an olistostrome unit contains the most weathered detritus but otherwise shows similar chemical variation to the other formations methods to 1 identify separately mafic and ultramafic inputs 2 recognize in shales co cr and ni derived from ophiolitic sources and non ophiolitic sources 3 estimate the minimum mafic ultramafic proportion in a sediment may have general application elsewhere in sedimentary and metasedimentary rocks

extensive crustal extraction in earth s early history inferred from molybdenum isotopes estimates of the volume of the earliest crust based on zircon ages and radiogenic isotopes remain equivocal stable isotope systems such as molybdenum have the potential to provide further constraints but remain underused due to the lack of complementarity between mantle and crustal reservoirs here we present molybdenum isotope data for archaean komatiites and phanerozoic komatiites and picrites and demonstrate that their mantle sources all possess subchondritic signatures complementary to the superchondritic continental crust these results confirm that the present day degree of mantle depletion was achieved by 3 5 billion years ago and that earth has been in a steady state with respect to molybdenum recycling mass balance modelling shows that this early mantle depletion requires the extraction of a far greater volume of mafic dominated protocrust than previously thought more than twice the volume of the continental crust today implying rapid crustal growth and destruction in the first billion years of earth s history

rates of generation and destruction of the continental crust implications for continental growth less than 25 of the volume of the juvenile continental crust preserved today is older than 3 ga there are no known rocks older than approximately 4 ga and yet a number of recent models of continental growth suggest that at least 60 80 of the present volume of the continental crust had been generated by 3 ga such models require that large volumes of pre 3 ga crust were destroyed and replaced by younger crust since the late archaean to address this issue we evaluate the influence on the rock record of changing the rates of generation and destruction of the continental crust at different times in earth9s history we adopted a box model approach in a numerical model constrained by the estimated volumes of continental crust at 3 ga and the present day and by the distribution of crust formation ages in the present day crust the data generated by the model suggest that new continental crust was generated continuously but with a marked decrease in the net growth rate at approximately 3 ga resulting in a temporary reduction in the volume of continental crust at that time destruction rates increased dramatically around 3 billion years ago which may be linked to the widespread development of subduction zones the volume of continental crust may have exceeded its present value by the mid late proterozoic in this model about 2 6 2 3 times of the present volume of continental crust has been generated since earth9s formation and approximately 1 6 1 3 times of this volume has been destroyed and recycled back into the mantle this article is part of a discussion meeting issue earth dynamics and the development of plate tectonics9

geochemistry of fine grained clastic sediments in the archean abitibi greenstone belt canada implications for provenance and tectonic setting abstract archean sandstone and shale samples from turbiditic tf and alluvial facies af in the southern volcanic zone of the abitibi greenstone belt canada have been analyzed for major and trace elements the sandstones from tf are mainly greywackes whereas those from af are lithic arenite sio 2 ranges from 51 to 68 geochemically the clastic sediments cluster into mafic element mep and low mafic element lmep populations the mep sediments which include turbiditic facies sediment samples from the larder lake group in the kirkland lake area are characterized by elevated abundances of mgo 5 ni 200 ppm cr 400 ppm sc 22 ppm and feo 7 5 abundances lower contents of incompatible elements such as th u ta hf zr and total rees n ratios are 4 5 with eu eu 1 the lmep sediments which include samples from the beatty dome and three nations lake formations in timmins the kewagama group noranda area and timiskaming group in the kirkland lake area however show reverse abundance distributions the geochemical gaps shown by the major and trace elements define two populations of sediments suggesting contrasting provenances for them the mep sediments require a dominantly mafic and ultramafic 90 source with 10 felsic contribution whereas the lmep sediments require a mixture of felsic 75 and mafic 25 rocks this compositional distribution of the sediments is closely related to their tectonic environments the mep was formed in basins proximal to or within an active oceanic rift consequently having ultramafic and mafic rocks as the major source for the lmep calc alkaline volcanic sequences formed in an island arc like setting were the major source these two contrasting volcanic plutonic terranes were tectonically juxtaposed during late archean collisional tectonics

secular changes in tonalite trondhjemite granodiorite composition as markers of the progressive cooling of earth archean tonalite trondhjemite granodiorite associations ttg are classically thought to generate through partial melting of hydrous metabasalts however the chemical composition of the least differentiated ttg parental magmas evolved from 4 0 to 2 5 ga during this interval the mg as well as the ni and cr contents increased which is interpreted as reflecting increased interactions between felsic melts generated by metabasalt melting and mantle peridotite similarly cao na2o and sr also increased over time thus reflecting an increase in the abundance of plagioclase in the melt residue the presence or absence of residual plagioclase is interpreted in terms of melting depth the demonstrated interaction between ttg parental magmas and the mantle rules out their genesis by fusion of previously underplated metabasalt and favors the melting of subducted slab material at 4 0 ga earth s geothermal gradient was sufficiently high to allow slab melting at shallow depths where plagioclase was stable consequently due to the small thickness of the overlying mantle wedge felsic magmas interacted little with the mantle at 2 5 ga however owing to lower geothermal gradients the melting depth was greater and plagioclase became no longer stable in the thick mantle wedge overlying the subducted slab as a result felsic magmas reacted strongly with the mantle peridotite the changes of ttg composition during archean time can be thus interpreted as reflecting the progressive cooling of earth

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

deep deformation pattern from electrical anisotropy in an arched orogen betic cordillera western mediterranean long period magnetotelluric data acquired in the iberian massif and the betic cordillera arched orogen provide the first evidence of electrical anisotropy in the upper mantle of the mediterranean region strike analysis at different periods reveals preferred structure orientation related to olivine elongation in the mantle and points to a heterogeneous anisotropy pattern at deep levels periods 104 s all the sites show a common north south geoelectrical strike n170 e which may represent a low intensity deformation possibly related to frozen prealpine plate tectonics for periods between 10 and 103 s a north south constant strike n180 e at the betic cordillera sites contrasts with the east west strike n85 e in the iberian massif an increase in the magnitude of the induction arrows from the iberian massif to the inner part of the betic cordillera probably reflects higher deformation toward the axis of the eurasian african plate boundary the integration of electrical anisotropy data with seismic anisotropy allows us to discuss mantle deformation patterns produced by delamination and subduction suggesting that the latter mechanism may be more suitable for the alpine evolution of the western gibraltar arc

utilizing the onset of time lapse changes a robust basis for reservoir monitoring and characterization time lapse monitoring is useful for imaging changes in geophysical attributes due to fluid flow in trying to use time lapse data for reservoir characterization difficulties often arise when relating changes in geophysical observations to changes in fluid saturation and pressure as an alternative approach for reservoir monitoring and characterization we introduce the idea of an onset time the time at which a measured quantity such as a seismic traveltime or a reflection amplitude begins to deviate from its background value we illustrate the idea and demonstrate its utility through the consideration of traveltimes recorded by the continuous active source seismic monitoring system at the frio pilot site near houston texas the system which transmits an elastic wave every 15 min is used to monitor the movement of carbon dioxide injected into a permeable sand formation from these data we can estimate the onset of changes in seismic traveltimes to six receivers in an adjacent borehole numerical simulation and synthetic tests indicate that the onset times are not very sensitive to the method used to compute the effective fluid bulk modulus and correspondingly the seismic compressional velocity rather the onset times are strongly influenced by saturation changes within the formation specifically by the break through time of the injected fluid phase by means of an iterative inversion algorithm we use the onset times to estimate permeability variations between the boreholes at the frio pilot site the authors 2014 published by oxford university press on behalf of the royal astronomical society

heterogeneous aquifer characterization from ground penetrating radar tomography and borehole hydrogeophysical data using nonlinear bayesian simulations it is known that the heterogeneity of hydraulic conductivity drives the groundwater flow and the transport of contaminants however in conventional characterization methods the lack of densely sampled hydrological data does not permit us to describe the aquifer heterogeneity at an appropriate scale in this study we integrate ground penetrating radar gpr tomographic data with hydraulic conductivity logs to estimate the hydraulic conductivity of a heterogeneous unconsolidated aquifer at a decimetric scale between two boreholes the integration of these different data sets is achieved using a nonlinear bayesian simulation algorithm the prior hydraulic conductivity distribution is estimated under gaussian hypothesis by simple kriging of the hydraulic well data the likelihood of hydraulic conductivity given the relative permittivity and the electrical conductivity functions is obtained from a kernel probability density function estimator that describes the in situ relationship between the electric and the hydraulic properties measured along boreholes the proposed method is tested on a synthetic heterogeneous model of permeability to validate the methodology we show that permeability realizations obtained from the proposed algorithm present a higher correlation with the synthetic model than other classical simulation methods the method is then applied on data acquired over an unconsolidated aquifer located in saint lambert de lauzon quebec canada the data set consists of measurements from i gpr crosshole acquisition ii cone penetration testing with pressure measurement combined with soil moisture resistivity and iii a borehole electromagnetic flowmeter by using the presented bayesian approach we generated multiple hydraulic conductivity realizations that are in good agreement with the hydrogeological model of the area

robust geophysical integration through structure coupled joint inversion and multispectral fusion of seismic reflection magnetotelluric magnetic and gravity images example from santos basin offshore brazil abstractwe have applied a crossgradient joint inversion and geospectral visualization method to marine seismic reflection magnetotelluric gravity and magnetic data sets acquired along a 162 km profile across a segment of santos basin oil province in the continental margin of southeast brazil the main exploration targets are the top of the fractured precambrian crystalline basement and any concealed basement grabens the overlying presalt and salt carbonate deposits and the postsalt cover deposits the results of joint inversion clearly mapped the various units and are a significant improvement over previous models derived from separate 2d seismic reflection processing and 2d magnetotelluric imaging additionally multispectral fusion of these models resulted in a single image that permits highly constrained geologic interpretations enabling a better understanding of basin architecture we suggest that joint inversion and image fusion is the way forward for effective geophysical integration

time lapse joint inversion of crosswell dc resistivity and seismic data a numerical investigation abstracttime lapse joint inversion of geophysical data is required to image the evolution of oil reservoirs during production and enhanced oil recovery co2 sequestration geothermal fields during production and to monitor the evolution of contaminant plumes joint inversion schemes reduce space related artifacts in filtering out noise that is spatially uncorrelated and time lapse inversion algorithms reduce time related artifacts in filtering out noise that is uncorrelated over time there are several approaches that are possible to perform the joint inverse problem in this work we investigate the structural crossgradient scg joint inversion approach and the crosspetrophysical cp approach which are appropriate for time lapse problems in the first case the inversion scheme looks for models with structural similarities in the second case we use a direct relationship between the geophysical parameters time lapse inversion is performed with an actively time constrained atc approach in this a

2d joint inversion of geophysical data using petrophysical clustering and facies deformation geologic expertise and petrophysical relationships can be brought together to provide prior information while inverting multiple geophysical data sets the merging of such information can result in more realistic solution in the distribution of the model parameters we have evaluated the geophysical inverse problem in terms of gaussian random fields with mean functions controlled by petrophysical relationships and covariance functions controlled by a prior geologic cross section including the definition of spatial boundaries for the geologic facies the petrophysical relationship problem is formulated as a regression problem upon each facies the inversion of the geophysical data is performed in a bayesian framework we have developed the usefulness of this strategy using a first synthetic case for which we have performed a joint inversion of gravity and galvanometric resistivity data with the stations located at the ground surface the joint inversion was used to recover the density and resistivity distributions of the subsurface in a second step we considered the possibility that the facies boundaries were deformable and their shapes were inverted as well we used the level set approach to perform such deformation preserving a priori topological properties of the facies throughout the inversion with the help of a priori facies petrophysical relationships and the topological characteristics of each facies we made a posteriori inference about multiple geophysical tomograms based on their corresponding geophysical data misfits we have applied this method to a second synthetic case showing that we can recover the heterogeneities inside the facies the mean values for the petrophysical properties and to some extent the facies boundaries using the 2d joint inversion of gravity and galvanometric resistivity data

controls on chemical weathering on a mountainous volcanic tropical island guadeloupe french west indies abstract guadeloupe island is a natural laboratory ideally suited to the study of biogeochemical processes in tropical and mountainous volcanic environments the island s east west rainfall gradient 1200 8000 mm yr is superimposed on a north south age gradient 2 7 ma to present providing a unique opportunity to investigate the influence of rainfall and rock age on the chemical weathering of volcanic terrains taking advantage of this configuration we present the first temporal survey 2007 2013 of the geochemical composition of the dissolved load of rain and river waters in guadeloupe our data demonstrate that the chemical composition of river water is influenced by rainfall abundance hydrothermal alteration from active or fossilized volcanic systems and interactions between water and minerals during chemical weathering processes the contribution of rain to the overall chemical balance is especially significant in the older northern part of the island where the ferralitic soils are base cation depleted between 15 and 65 of the ca or mg riverine budgets comes from atmospheric deposits highlighting the major role of rainfall in the geochemical budgets of small tropical and mountainous watersheds the river water dataset indicates that different chemical weathering processes dominate the budget depending on the age of the local bedrock in the younger southern part of the island a pool of easily weatherable andesitic minerals from the bedrock dominates the contribution from this pool decreases significantly to 5 15 wt of the bulk soil towards the older terrains in the north the northern rivers are characterized by low ca mg ratios 0 5 1 0 intermediate between those of fresh rocks 1 7 3 3 and soil 0 1 weathering in the northern part of the island is therefore dominated by the dissolution of depleted secondary minerals into soils the ca mg ratio of the river water increases from north to south eventually reaching values similar to those of the bedrocks arguing for congruent dissolution of the youngest volcanic rocks the magnesium isotopic composition of river water 26mg reflects inputs from both rain and weathering processes in southern and central rivers the mg isotopic value of waters after correction for rain inputs 26mgwea is systematically depleted in heavy isotopes mean value of 0 34 relative to that of the bedrock 0 24 to 0 15 in the north the 26mgwea of the river water 0 09 is heavier than that of the andesitic bedrock possibly reflecting the dissolution of 26mg rich secondary minerals ferralitic soil measured around 0 13 the robustness of 26mg and ca mg as proxies of the degree of soil weathering should be investigated further via more detailed sampling campaigns in the future by combining high frequency monitoring of river discharge with measurements of concentration discharge relationships for a wide range of chemical elements we estimate the mean annual chemical weathering fluxes for three rivers that belong to the obsera critical zone observatory fluxes vary from 51 7 to 91 8 t km2 yr north to south along the bedrock age gradient and are among the highest recorded in volcanic tropical regions flash floods can explain 21 31 of the annual chemical weathering fluxes the results highlight the importance of monitoring rivers over periods of several years in order to obtain accurate estimates of chemical exports in tropical and mountainous environments

archaean crustal growth through successive partial melting events in an oceanic plateau like setting in the tanzania craton the detrital zircon population in quartzitic conglomerates from the northern tanzania craton yield ages between 2640 ma and 2790 ma which includes most of the igneous history from this part of the craton the igneous evolution is characterised by mafic volcanism with an oceanic plateau like geochemical signature at 2800 ma followed by diorite and tonalite trondhjemite granodiorite dominated magmatism between 2790 and 2700 ma which transitioned into more evolved high k magmatism between 2700 and 2620 ma the ehf values of the detrital zircons range from 2 4 to 1 4 and change with time from radiogenic hf pre 2700 ma 98 positive ehf to unradiogenic hf post 2700 ma 41 positive ehf the petrological progression from mafic to felsic crust is reflected in the detrital age distribution and ehf isotopes and is consistent with juvenile mafic crust slowly maturing into more evolved felsic crust through a series of successive partial melting events in an oceanic plateau like environment

paired metamorphism in the neoarchean a record of accretionary to collisional orogenesis in the north china craton abstract paired metamorphism is the hallmark of asymmetric subduction at phanerozoic convergent plate margins yet spatially and temporally linked paired metamorphic belts have rarely been documented in the archean rock record here we investigate the neoarchean dengfeng complex a typical granite greenstone belt in the southern part of the north china craton ncc using petrography geochronology and phase equilibrium constraints on rocks from different lithostructural units we suggest the ca 2 54 2 50 ga dengfeng complex represents a remnant of a spatially and temporally linked neoarchean paired metamorphic belt in the western part of the complex a garnet amphibolite from a dominantly metabasic unit mbu records near peak p t conditions of 6 3 10 kbar and 675 750 c corresponding to a high thermobaric ratio t p of 720 1200 c gpa tonalite trondhjemite granodiorite ttg gneisses preserve evidence for partial melting also consistent with relatively high t p 875 1400 c gpa in the eastern part of the dengfeng complex two garnet amphibolites and three garnet quartz mica schists from a dominantly metasedimentary unit msu record peak p t conditions of 9 8 kbar and 525 655 c corresponding to intermediate thermobaric ratios of 425 600 c gpa zircon and titanite u pb dating coupled with existing ages of post kinematic intrusions constrain the metamorphic age to ca 2 52 2 50 ga the metamorphic p t data indicate that the msu was buried to 30 km then exhumed to the near surface by the early paleoproterozoic our metamorphic results when combined with recent structural and geochemical data suggest the dengfeng complex records neoarchean paired metamorphism in which the higher thermal gradients reflect the arc forearc region and the lower thermal gradients correspond to the accretionary complex our data indicate that the southern ncc experienced accretionary to collisional orogenesis with intra oceanic subduction forearc accretion ca 2 54 2 50 ga and subsequent arc continent collision ca 2 50 2 47 ga the recognition of paired metamorphism in the ncc is consistent with widespread subduction and the operation of a plate tectonic regime in the late archean

lithological structural and geochemical characteristics of the mesoarchean târtoq greenstone belt southern west greenland and the chugach prince william accretionary complex southern alaska evidence for uniformitarian plate tectonic processes the mesoarchean t rtoq greenstone belt southern west greenland consists of tectonically imbricated slices of metamorphosed basalt gabbro peridotite and sedimentary rocks and is intruded by fel

a change in the geodynamics of continental growth 3 billion years ago models for the growth of continental crust rely on knowing the balance between the generation of new crust and the reworking of old crust throughout earth s history the oxygen isotopic composition of zircons for which uranium lead and hafnium isotopic data provide age constraints is a key archive of crustal reworking we identified systematic variations in hafnium and oxygen isotopes in zircons of different ages that reveal the relative proportions of reworked crust and of new crust through time growth of continental crust appears to have been a continuous process albeit at variable rates a marked decrease in the rate of crustal growth at 3 billion years ago may be linked to the onset of subduction driven plate tectonics

joint inversion of geophysical and hydrological data for improved subsurface characterization understanding fluid distribution and movement in the subsurface is critical for a variety of subsurface applications such as remediation of environmental contaminants sequestration of nuclear waste and co2 intrusion of saline water into fresh water aquifers and the production of oil and gas it is well recognized that characterizing the properties that control fluids in the subsurface with the accuracy and spatial coverage needed to parameterize flow and transport models is challenging using conventional borehole data alone integration of conventional borehole data with more spatially extensive geophysical data obtained from the surface between boreholes and from surface to boreholes shows promise for providing quantitative information about subsurface properties and processes typically estimation of subsurface properties involves a two step procedure in which geophysical data are first inverted and then integrated with direct measurements and petrophysical relationship information to estimate hydrological parameters however errors inherent to geophysical data acquisition and inversion approaches and errors associated with petrophysical relationships can decrease the value of geophysical data in the estimation procedure in this paper we illustrate using two examples how joint inversion approaches or simultaneous inversion of geophysical and hydrological data offer great potential for overcoming some of these limitations