the coupled effects of mantle mixing and a water dependent viscosity on the surface ocean abstract water content plays a vital role in determining mantle rheology and thus mantle convection and plate tectonics most parameterised convection models predict that earth initially underwent a period of rapid degassing and heating followed by a slow and sustained period of regassing and cooling however these models assume water is instantaneously mixed and homogeneously distributed into the mantle this is a limitation because the mixing time for water entering and leaving the mantle is a function of the rayleigh number which varies dramatically with water content temperature and through time here we present an adapted parametrised model crowley et al 2011 to include the coupled effects of the time scale of mixing with a water dependent viscosity we consider two mixing types first where the mixing time is constant throughout the model and second where mixing time varies as a response to an evolving rayleigh number we find that facilitated by the effects of water content in the melt region at mid ocean ridges a constant mixing time can induce long periods of degassing the inclusion of a variable mixing time dependent on the rayleigh number acts to limit the period of degassing and also results in more water being stored in the mantle and less at the surface than in both the constant and instantaneous mixing cases mixing time cannot be more than 2 billion years as large mixing times trap water in the mantle leaving a dry surface even small changes in the surface ocean induced by mixing times on the order of 0 1 gyrs can cause changes in the global mean sea level on the order of 10 s of metres these changes in sea level could easily uncover topographic highs in the bathymetry potentially aiding sub aerial erosion a process thought to be important in early earth evolution even in this relatively simple model the inclusion of a mixing time between water entering and leaving the mantle creates a more dynamic water cycle

novae on venus geology classification and evolution 1 novae are radially fractured centers 100 300 km in diameter and 64 have been identified on venus dense radial fracturing and upraised topography are common and massive amounts of volcanism are seen in some novae are interpreted to be the result of updoming and fracturing of the surface due to interaction of mantle diapirs with the lithosphere and radial fracturing caused by dike emplacement we analyzed the topography and character of deformational and morphological structures of all 64 novae leading to a better understanding of their evolution and relation to diapir dynamics and their age we subdivided novae into four topographic classes 1 upraised 2 annular 3 flat and negative and 4 plateau like novae are located mostly in areas of regional rises and rift zones with a small number in the lowlands about one half the novae studied show association with rifts in some of these the rift troughs surround nova rises and form plateau like novae plateau like novae may predate postdate or form simultaneously with rifts our analysis generally confirms and updates previous models of novae evolution with the following geological factors being important 1 depth of the neutral buoyancy level of the rising mantle diapir 2 rheological characteristics of the overlying lithosphere 3 whether or not the visco plastic material above the diapir undergoes spreading and 4 the nature and influence of regional stress and rift structures these combined factors exert control on the direction of nova evolution and appear to determine the primary characteristics of nova such as topography tectonics and volcanism we found clear evidence for 1 the important role of dike swarm emplacement in the formation of radial patterns of novae and 2 the formation of concentric tectonic features during the relaxation stage of novae novae have multiple evolutionary stages and are long lived structures stratigraphic analysis of all 64 local areas showed a similarity in the sequence of regional geologic units we found that 40 3 of the novae population started to form before emplacement of regional plains with wrinkle ridges and that 11 3 completed their activity before this time 88 7 of the population of novae was active after regional plains formation in contrast to novae coronae activity was greatest before formation of regional plains which may be due to thickening of the lithosphere with time detailed structural analysis shows that novae evolution does not always lead to the formation of corona like features

efficient cooling of rocky planets by intrusive magmatism the earth is in a plate tectonics regime with high surface heat flow concentrated at constructive plate boundaries other terrestrial bodies that lack plate tectonics are thought to lose their internal heat by conduction through their lids and volcanism hotter planets io and venus show widespread volcanism whereas colder ones modern mars and mercury are less volcanically active however studies of terrestrial magmatic processes show that less than 20 of melt volcanically erupts with most melt intruding into the crust signatures of large magmatic intrusions are also found on other planets yet the influence of intrusive magmatism on planetary cooling remains unclear here we use numerical magmatic thermo mechanical models to simulate global mantle convection in a planetary interior in our simulations warm intrusive magmatism acts to thin the lithosphere leading to sustained recycling of overlying crustal material and cooling of the mantle in contrast volcanic eruptions lead to a thick lithosphere that insulates the upper mantle and prevents efficient cooling we find that heat loss due to intrusive magmatism can be particularly efficient compared to volcanic eruptions if the partitioning of heat producing radioactive elements into the melt phase is weak we conclude that the mode of magmatism experienced by rocky bodies determines the thermal and compositional evolution of their interior rocky planets dominated by intrusive magmatism can cool more efficiently than those dominated by extrusive volcanism according to numerical simulations of mantle convection

magma transport of heat on io a mechanism allowing a thick lithosphere models indicate that the high heat flow from io would result in a very thin approximately 5 km silicate lithosphere overlying a molten interior if all heat was transported through the lithosphere via conduction however the presence of mountains with relief in excess of 10 km would seem to demand a thick lithosphere at least locally a significant fraction of io s heat flow may be transported via advection through volcanoes advective heat transfer permits a thicker lithosphere than does pure conduction possibly reconciling io s high heat flow with the rugged topography

insights into corona formation through statistical analyses 1 statistical analysis of an expanded database of coronae on venus indicates that the populations of type 1 with fracture annuli and 2 without fracture annuli corona diameters are statistically indistinguishable and therefore we have no basis for assuming different formation mechanisms analysis of the topography and diameters of coronae shows that coronae that are depressions rimmed depressions and domes tend to be significantly smaller than those that are plateaus rimmed plateaus or domes with surrounding rims this is consistent with the model of smrekar and stofan 1997 and inconsistent with predictions of the spreading drop model of koch and manga 1996 the diameter range for domes the initial stage of corona formation provides a broad constraint on the buoyancy of corona forming plumes coronae are only slightly more likely to be topographically raised than depressions with type 1 coronae most frequently occurring as rimmed depressions and type 2 coronae most frequently occurring with flat interiors and raised rims most type 1 coronae are located along chasmata systems or fracture belts while type 2 coronae are found predominantly as isolated features in the plains coronae at hot spot rises tend to be significantly larger than coronae in other settings consistent with a hotter upper mantle at hot spot rises and their active state

mantle dynamics postglacial rebound and the radial viscosity profile abstract we infer the radial viscosity structure of the earth s mantle from observations of long wavelength geoid glacially induced sea level changes and changes in the earth s rotation and gravitational field we employ a combination of forward and formal inverse modeling of long term mantle circulation driven by large scale density differences deduced from seismic tomography based on the resulting unscaled mantle viscosity profiles we model the time dependent glacial isostatic adjustment of the earth related to past and present changes in the ice ocean mass imbalance and we deduce scaled mantle viscosity profiles which simultaneously fit the long wavelength geoid constraint and glacially induced changes of the earth s shape three mantle viscosity profiles are fitting the observational data equally well all profiles are characterized by a two order of magnitude variation of viscosity within the earth s mantle variations of viscosity in the upper mantle are less than one order of magnitude in the lower mantle the viscosity differs significantly with depth for all models average viscosities in the upper and lower mantle are around 2 5 1020 and 1 3 1022 pa s respectively

effects of continental insulation and the partitioning of heat producing elements on the earth s heat loss 1 continental lithosphere influences heat loss by acting as a local insulator to the convecting mantle and by sequestering heat producing radioactive elements from the mantle continental heat production can have a two part effect since it decreases the amount of internal heat driving convection which lowers mantle temperature while also increasing the local insulating effect of continental lithosphere which raises mantle temperature we explored these competing effects using simulations that incorporated enriched continents within a mixed internal and bottom heated convecting mantle increasing continental surface area was found to enhance global heat loss for a range of heat production distributions and rayleigh numbers the effect of enriched continents was evident as a double peak in the continental surface area values that maximize global heat loss that the presence of continental lithosphere could increase average mantle temperature despite the mantle being depleted suggests that continents can significantly influence mantle potential temperature

phase transformations in subducted oceanic crust and buoyancy relationships at depths of 600 800 km in the mantle abstract phase transformations in a representative oceanic crust composition morb have been studied at pressures up to 28 gpa at 1200 c and 1500 c using a multi anvil apparatus the assemblage of majorite casio 3 rich perovskite stishovite which is displayed by the morb composition at pressures above 20 gpa was found to transform further into an assemblage containing a new aluminous phase at pressures above 25 gpa this al phase has a complex composition and is also relatively sodium rich its x ray diffraction pattern is similar to that observed for mgal 2 o 4 calcium ferrite type and is tentatively indexed on the basis of an orthorhombic cell yielding a zero pressure density of 3 87 2 g cm 3 majorite garnet was found to remain as the most abundant phase at the highest pressure studied 28 gpa and does not appear likely to transform to perovskite until pressures exceed 29 30 gpa these results imply that the basaltic crust component of subducted oceanic lithosphere would be 0 1 0 2 g cm 3 less dense than surrounding mantle pyrolite between the depths of 660 800 km thereby confirming an earlier hypothesis of anderson moreover the underlying layer of harzburgite would be 0 05 g cm 3 less dense than pyrolite throughout most of this depth interval these buoyancy relationships contribute to a barrier which impedes and may sometimes prevent the entry of slabs into the lower mantle

quaternary glaciations recorded by glacial and fluvial landforms in the shaluli mountains southeastern tibetan plateau abstract the shaluli mountains a tectonically controlled mountain range between the jinsha and yalong river rifts are located in southeastern tibetan plateau in the central shaluli mountains an ice cap of 3600 km 2 once developed on the haizi shan abundant glacial landforms are present on the haizi shan and in the surrounding river valleys together with the outwash terraces in the yazheku river the northeastern part of the haizi shan provides an ideal site to examine the quaternary glacial history of the region sedimentological and morphostratigraphical analysis field mapping and dating by electron spin resonance esr define at least seven major glacier advances in the haizi shan area six major glacier advances likely occurred during marine oxygen isotope stage mis 16 mis 14 12 mis 6 mis 3 early mis 2 and the global last glacial maximum these can be defined on the basis of esr dating and stratigraphical analysis of the glacial landforms in front of the kuzhaori glacial trough on the southern slope of the haizi shan the outwash terraces in the yazheku river also record four major glacier advances which occurred during mis 16 mis 12 mis 6 and mis 2 in addition the moraines preserved on the southwestern part of the haizi shan suggest that a glacial advance likely occurring during the lateglacial the extent of glaciation on the haizi shan decreased with time

minimum heat flow from the core and thermal evolution of the earth abstract the role of heat flow coming from the core is often overlooked or underestimated in simple models of earth s thermal evolution throughout most of earth s history the mantle must have been extracting from the core at least the amount of heat that is required to operate the geodynamo in view of recent laboratory measurements and theoretical calculations indicating a higher thermal conductivity of iron than previously thought the above constraint has important implications for the thermal history of the earth s mantle in this work we construct a paramaterized mantle convection model that treats both the top and the core mantle boundary heat fluxes according to the boundary layer theory or alternatively employs the model of labrosse 2015 to compute the thermal evolution of the earth s core we show that the core is likely to provide all the missing heat that is necessary in order to avoid the so called thermal catastrophe of the mantle moreover by analyzing the mutual feedback between the core and the mantle we provide the necessary ingredients for obtaining thermal histories that are consistent with the petrological record and have reasonable initial conditions these include a sufficiently high viscosity contrast between the lower and upper mantle whose exact value is sensitive to the activation energy that governs the temperature dependence of the viscosity

some mineral physics constraints on the rheology and geothermal structure of earth s lower mantle we explore the implications of recent mineral physics measurements of diffusion coefficients and melting temperatures of lower mantle materials on the rheological and geothermal structure of earth s lower mantle we show that mgsio3 perovskite is significantly stronger than mgo periclase and therefore the rheology of the lower mantle depends strongly on the geometry of a weaker phase periclase we calculate viscosities of the lower mantle for two cases 1 where periclase occurs as isolated grains and 2 where periclase occurs as continuous films using mineral physics data and models of two phase rheology we find that the effective viscosity for the former is about 10 1000 times higher than the latter we therefore suggest that the rheology of the lower mantle is structure and hence strain dependent leading to weakening at large strains due to the formation of continuous films of periclase overall depth variation of viscosity depends not only on the pressure dependence of creep but also on the geothermal gradient both mgsio3 perovskite and periclase have relatively small activation energies e g r t m with g 10 14 where r is the gas constant and t m is melting temperature and therefore the depth variation of viscosity is rather small even for a nearly adiabatic temperature gradient however the geothermal gradients consistent with the geodynamical inference of nearly depth independent viscosity are sensitive to the pressure dependence of viscosity which is only poorly understood a superadiabatic gradient of up to 0 6 k km is also consistent with mineral physics and geodynamical observations

simulating the thermochemical magmatic and tectonic evolution of venus s mantle and lithosphere two dimensional models 1 numerical convection models of the thermochemical evolution of venus are compared to present day topography and geoid and recent resurfacing history the models include melting magmatism decaying heat producing elements core cooling realistic temperature dependent viscosity and either stagnant lid or episodic lithospheric overturn in stagnant lid convection the dominant mode of heat loss is magmatic heat pipe which requires massive magmatism and produces very thick crust inconsistent with observations partitioning of heat producing elements into the crust helps but does not help enough episodic lid overturn interspersed by periods of quiescence effectively loses venus s heat while giving lower rates of volcanism and a thinner crust calculations predict 5 8 overturn events over venus s history each lasting 150 myr initiating in one place and then spreading globally during quiescent periods convection keeps the lithosphere thin magmatism keeps the mantle temperature constant over venus s history crustal recycling occurs by entrainment in stagnant lid convection and by lid overturn in episodic mode venus like amplitudes of topography and geoid can be produced in either stagnant or episodic modes with a viscosity profile that is earth like but shifted to higher values the basalt density inversion below the olivine perovskite transition causes compositional stratification around 730 km breakdown of this layering increases episodicity but far less than episodic lid overturn the classical stagnant lid mode with interior temperature rheological temperature scale lower than tcmb is not reached because mantle temperature is controlled by magmatism while the core cools slowly from a superheated start core heat flow decreases with time possibly shutting off the dynamo particularly in episodic cases

the viscosity of earth s lower mantle inferred from sinking speed of subducted lithosphere abstract the viscosity of the mantle is indispensable for predicting earth s mechanical behavior at scales ranging from deep mantle material flow to local stress accumulation in earthquakes zones but mantle viscosity is not well determined for the lower mantle particularly only few constraints result from elaborate high pressure experiments karato 2008 and a variety of viscosity depth profiles result from joint inversion of the geoid and postglacial rebound data forte and mitrovica 1996 kaufmann and lambeck 2000 mitrovica and forte 2004 here we use inferred lower mantle sinking speed of lithosphere subduction remnants as a unique internal constraint on modeling the viscosity profile this entails a series of elaborate dynamic subduction calculations spanning a range of viscosity profiles from which we select profiles that predict the inferred sinking speed of 12 3 mm yr van der meer et al 2010 our modeling shows that sinking speed is very sensitive to lower mantle viscosity good predictions of sinking speed are obtained for nearly constant lower mantle viscosity of about 3 4 1022 pa s viscosity profiles incorporating a viscosity maximum in the deep lower mantle as proposed in numerous studies only lead to a good prediction in combination with a weak postperovskite layer at the bottom of the lower mantle and only for a depth average viscosity of 5 1022 pa s

holocene millennial scale summer temperature variability inferred from sediment parameters in a non glacial mountain lake danntjorn jotunheimen central southern norway holocene changes in summer temperature in the jotunheimen area have been inferred from variations in several sediment parameters from a composite combined from two overlapping sediment cores lake core record mean time resolution of 15 years from lake danntjorn a small mountain lake located close to the modern pine tree limit in jotunheimen central southern norway loss on ignition analysis at contiguous 0 5 cm intervals throughout the cores revealed that the variations in residue after ignition of the sediments at 5501c in the upper 260 cm 8500 calendar years were not associated with variations in magnetic susceptibility in the basal deglacial and early holocene sequence of the lake sediments however the two sediment parameters fluctuated mainly in phase in addition the biogenic silica bsi concentration is relatively high thus in the early part of the holocene the variations in the residue were probably primarily driven by input of minerogenic detrital material inwash and or windblown and biological productivity including bsi from diatoms in the lake itself and in the lake surroundings from approximately 8500 calendar years bp variations in the residue probably primarily reflect variations in low minerogenic low magnetic susceptibility with little variations and diatom bsi productivity as demonstrated with analysis of bsi concentration between 260 and 233 cm 8500 7760 calendar years bp the highest residue values probably mainly reflecting high diatom productivity occurred at 7800 7200 7000 6700 6200 5400 5050 4300 2500 1800 1550 900 700 and o100 calendar years bp the most significant o8000 calendar years bp residue minima mainly low diatom productivity were recorded at 7100 6800 6600 6000 5700 5000 4400 4200 3800 3600 3200 3000 2750 2300 1900 1700 1070 740 600 380 and 80 calendar years bp bp ad 2000 the lake record from jotunheimen is discussed in the context of holocene terrestrial and marine records from the north atlantic region and possible natural climate forcing factors r 2004 elsevier ltd all rights reserved

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

the pressure weakening effect in super earths consequences of a decrease in lower mantle viscosity on surface dynamics 1 the quest to identify habitable planets has raised interest in the surface dynamics of terrestrial bodies in this context super earths a new class of exoplanets have become of special interest in the past decade scalings to super earth sizes when compared to the earth suggest changes to convective stresses and mantle temperatures which can cause either an increase in surface mobility or in plate resistance mantle viscosity which depends on temperature stress and pressure plays a critical role in both cases new mineralogical assumptions suggest that the viscosity in super earths acts differently than in the earth and what had been assumed for super earths in planets larger than the earth pressure will become so high that pressure weakening and a decrease of viscosity in the lowermost mantle results we present a numerical convection study featuring this viscosity decrease and find that this leads to a reduction in surface mobility

preliminary analysis of an expanded corona database for venus we have conducted an extensive survey of the magellan data to reassess the population of coronae we identify a new type of coronae here referred to as type 2 coronae having the same basic morphology as previously identified coronae type 1 but lacking a significant 50 annulus of closely spaced fractures 106 type 2 coronae are included in the new database giving a total of 515 coronae on venus the characteristics of the expanded population of type i coronae are similar to those of the previously described population but the type 2 coronae are smaller tend to have relatively flat interiors surrounded by a topographic rim and are more likely to be found isolated from other features our observations in particular the morphology and setting of the type 2 coronae may provide supporting evidence for the existence of a depleted mantle layer under the venusian plains

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

magma ascent by porous flow porous flow of buoyant liquid through partially molten rock is regarded as the initial transport process leading to magma segregation in the mantle recent work has identified the importance of matrix deformation and compaction in this process we present finite difference calculations based on a generalized form of darcy s law that includes matrix deformation in two dimensional cartesian and cylindrical coordinates we emphasize the existence of solitary wave solutions called magmons these waves are regions of locally high porosity that ascend through regions of low uniform porosity they differ from diapirs where the liquid and matrix ascend together the one dimensional waves that were previously reported are found to be unstable in two dimensions breaking down to form two dimensional waves of circular cross section both the development of the instability and the form of the two dimensional waves are supported by theoretical analysis numerical experiments in which two dimensional waves collide show that the extent to which they are conserved after collision depends on the lateral offset of the waves the conservation can be very good in other cases larger waves appear to grow at the expense of smaller waves although the quantification of the relevant permeability and rheological parameters remains uncertain geophysically plausible estimates suggest wavelengths of kilometers and velocities of centimeters per year in our preliminary assessment of the relevance of these results to igneous processes we find that magmons are unlikely to be important in regions of broad upwelling such as beneath spreading centers here the transport of liquid adjusts to match the supply by melting and compaction processes are not important if liquid is supplied from below to a stable partially molten region of the asthenosphere it is expected to ascend in magmons this may occur beneath oceanic volcanic centers or in subcontinental mantle it is possible that magma ascent in magmons leads to spatial and temporal episodicity of volcanic activity if higher level processes do not obscure this influence the waveform of a magmon ascends faster than the liquid within the magmon so new liquid is taken in from above while original liquid is lost from below consequently magmons can mobilize small degrees of partial melt and deliver it rapidly to the surface

generation of earth s early continents from a relatively cool archean mantle this research has been supported by dfg grant spp 1833 building a habitable earth and magma consolidator grant erc project 71143

plate tectonics on the early earth limitations imposed by strength and buoyancy of subducted lithosphere the tectonic style and viability of modern plate tectonics in the early earth is still debated field observations and theoretical arguments both in favor and against the uniformitarian view of plate tectonics back until the archean continue to accumulate here we present the first numerical modeling results that address for a hotter earth the viability of subduction one of the main requirements for plate tectonics a hotter mantle has mainly two effects 1 viscosity is lower and 2 more melt is produced which in a plate tectonic setting will lead to a thicker oceanic crust and harzburgite layer although compositional buoyancy resulting from these thick crust and harzburgite might be a serious limitation for subduction initiation our modeling results show that eclogitization significantly relaxes this limitation for a developed ongoing subduction process furthermore the lower viscosity leads to more frequent slab breakoff and sometimes to crustal separation from the mantle lithosphere unlike earlier propositions not compositional buoyancy considerations but this lithospheric weakness could be the principle limitation to the viability of plate tectonics in a hotter earth these results suggest a new explanation for the absence of ultrahigh pressure metamorphism uhpm and blueschists in most of the precambrian early slabs were not too buoyant but too weak to provide a mechanism for uhpm and exhumation

continental crust formation on early earth controlled by intrusive magmatism the global geodynamic regime of early earth which operated before the onset of plate tectonics remains contentious as geological and geochemical data suggest hotter archean mantle temperature and more intense juvenile magmatism than in the present day earth two crust mantle interaction modes differing in melt eruption efficiency have been proposed the io like heat pipe tectonics regime dominated by volcanism and the plutonic squishy lid tectonics regime governed by intrusive magmatism which is thought to apply to the dynamics of venus both tectonics regimes are capable of producing primordial tonalite trondhjemite granodiorite ttg continental crust but lithospheric geotherms and crust production rates as well as proportions of various ttg compositions differ greatly which implies that the heat pipe and plutonic squishy lid hypotheses can be tested using natural data here we investigate the creation of primordial ttg like continental crust using self consistent numerical models of global thermochemical convection associated with magmatic processes we show that the volcanism dominated heat pipe tectonics model results in cold crustal geotherms and is not able to produce earth like primordial continental crust in contrast the plutonic squishy lid tectonics regime dominated by intrusive magmatism results in hotter crustal geotherms and is capable of reproducing the observed proportions of various ttg rocks using a systematic parameter study we show that the typical modern eruption efficiency of less than 40 per cent leads to the production of the expected amounts of the three main primordial crustal compositions previously reported from field data low medium and high pressure ttg our study thus suggests that the pre plate tectonics archean earth operated globally in the plutonic squishy lid regime rather than in an io like heat pipe regime

insulation and depletion due to thickened crust effects on melt production on mars and earth 1 the growth of thickened crustal units both depletes the mantle of heat producing elements and thermally insulates it these effects either cool or heat the mantle respectively and play an important role in subsequent crustal formation we employ mantle convection models including thickened crustal units of variable heat production to show that for increasing crustal extent mantle temperatures and melt production can either increase of decrease depending on the degree of enrichment of the crust with respect to the mantle the total heat production and the rayleigh number the formation of the continents on earth efficiently cooled the upper mantle resulting in lower subsequent rates of melt production and continental formation in contrast the growth of the martian highlands would have raised the temperatures of the martian mantle increasing rates of melt production and leading to runaway crustal growth this would have continued as long as the lithosphere of mars was mobile

effects of chemical fractionation of heat producing elements on mantle evolution inferred from a numerical model of coupled magmatism mantle convection system abstract a numerical model of a coupled magmatism mantle convection system has been developed to study how a strong chemical fractionation of heat producing elements as a result of mantle magmatism influences the evolution of the uppermost mantle mantle convection is modeled by a convection of a binary eutectic material a b 1 with a newtonian rheology in a two dimensional rectangular box a stands for olivine and b stands for a mixture of pyroxene and garnet the viscosity depends strongly on temperature and the density increases with decreasing and temperature the material contains decaying heat producing elements mantle magmatism is modeled by an extraction of melt generated at depth by a pressure release partial melting and a deposit of the extracted melt in a thin crustal layer at the top of the box the melt extraction and deposit give rise to heterogeneity in the distribution of heat producing elements as well as in distribution a dense low magmatic product is more enriched in heat producing elements than is a less dense high residual material the positive thermal buoyancy that a low material gains owing to its enrichment with heat producing elements causes a catastrophic change in the chemical structure of the uppermost mantle with time when the viscosity in the top thermal boundary layer lithosphere is sufficiently high a chemically stratified structure with a high residual material in the upper part and a low material in the lower part of the box develops at the beginning when active magmatism occurs owing to strong internal heating as the heat producing elements decay and the magmatism becomes weaker a steep gradient or a discontinuity in distribution develops between the high part and the low part of the box and the convection occurs temporarily as a layered convection the chemically layered structure is however catastrophically destroyed and the box suddenly becomes more chemically homogeneous at a subsequent time when the positive thermal buoyancy of the low material at depth becomes stronger than the chemically induced negative buoyancy of the low material the catastrophic change in chemical structure induces a drop in temperature at depth and a sudden enhancement of mantle magmatism when the viscosity in the lithosphere is sufficiently low in contrast the chemically layered structure is stable and the catastrophic change from a chemically layered structure to a more chemically homogeneous structure does not occur a catastrophic destruction of a chemically layered structure in the upper mantle as a result of strong fractionation of heat producing elements may have occurred in the early earth

plume induced crustal convection 3d thermomechanical model and implications for the origin of novae and coronae on venus novae and coronae are large volcanotectonic features on venus with a contentious and possibly non unique origin and enigmatic relationship their formation is most commonly explained by flexure and fracturing of the strong rigid venus lithosphere atop mantle upwelling and or downwelling here we present new 3d high resolution thermomechanical model of mantle plume diapir impingement into warm and thin lithosphere with venus like surface temperature numerical results suggests that nova like and corona like structures can result from magma assisted convection of weak ductile crust induced by decompression melting of the hot rising mantle plume during the initial stage nova forms by stellate fracturing of a topographic rise forming atop the growing crustal convection cell few million years later nova can convert to coronae by inward dipping concentric fracturing of the nova rise margins and subsequent outward thrusting of partially molten crustal rocks over the surface an outer annulus of concentric normal faults forms in the outer rise region of the downbending brittle upper crust whereas an inner annulus of concentric thrust faults forms in front of the outward thrusting crustal wedge a trench like depression forms between these two annuli resembling retreating subduction the rudimentary concentric upper crustal slab warms up rapidly and recycles into the convection cell the convection cell remains active for up to 15 million years fueled by heat and magma from the plume predicted surface topography and fracturing patterns agree with some small to moderate size novae and coronae on venus

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

the primitive nature of large low shear wave velocity provinces abstract the lowermost 2400 km earth s mantle mapped by seismic tomography is strongly heterogeneous the most striking feature being two large regions where shear wave velocity drops by a few percent compared to averaged mantle additional seismic observations indicate that these structures cannot result from purely thermal effects compositional anomalies are required to fully explain seismic observations but their exact nature is still debated here we show that low shear wave velocity provinces unlikely consist of recycled oceanic crust morb we calculated seismic sensitivity to high pressure morb and found that in the lowermost mantle shear wave velocity increases with increasing fraction of morb therefore unless they are heated up to unrealistic temperatures high pressure morb would induce high shear wave velocity in contradiction with the observations instead material enriched in iron by 3 0 and in mg fe perovskite by 20 compared to regular mantle provides a good explanation for the low shear wave velocity provinces and for the high bulk sound velocities observed in the same areas in addition several geochemical and geodynamical arguments support a primitive origin for this material low shear wave velocity provinces may thus consist of reservoirs of primitive material that have differentiated early in the earth s history

melting induced crustal production helps plate tectonics on earth like planets abstract within our solar system earth is the only planet to be in a mobile lid regime it is generally accepted that the other terrestrial planets are currently in a stagnant lid regime with the possible exception of venus that may be in an episodic lid regime in this study we use numerical simulations to address the question of whether melting induced crustal production changes the critical yield stress needed to obtain mobile lid behaviour plate tectonics our results show that melting induced crustal production strongly influences plate tectonics on earth like planets by strongly enhancing the mobility of the lid replacing a stagnant lid with an episodic lid or greatly extending the time in which a smoothly evolving mobile lid is present in a planet finally we show that our results are consistent with analytically predicted critical yield stress obtained with boundary layer theory whether melting induced crustal production is considered or not

superlakes megafloods and abrupt climate change about 8200 years ago the climate of much of the northern hemisphere cooled abruptly for a period of about 200 years in their perspective clarke et al examine the most likely culprit for this cooling an outburst of fresh water from a vast ice dammed glacial lake in north america the superlake had formed when the kilometers thick ice sheet covering much of north america disintegrated when the ice dam became unstable fresh water flooded from the lake into the north atlantic it remains unclear how this fresh water affected ocean circulation or whether the outburst occurred in more than one stage but the timing points strongly to the outburst flood as the trigger of the 8200 year climate event

plate tectonics on super earths equally or more likely than on earth abstract the discovery of extra solar super earths has prompted interest in their possible mantle dynamics and evolution and in whether their lithospheres are most likely to be undergoing active plate tectonics like on earth or be stagnant lids like on mars and venus the origin of plate tectonics is poorly understood for earth likely involving a complex interplay of rheological compositional melting and thermal effects which makes it challenging to make reliable predictions for other planets nevertheless as a starting point it is common to parameterize the complex processes involved as a simple yield stress that is either constant or has a byerlee s law dependence on pressure because the simplifying assumptions made in developing analytical scalings may not be valid over all parameter ranges numerical simulations are needed one numerical study on super earths finds that plate tectonics is less likely on a larger planet o neill and lenardic 2007 in apparent contradiction of an analytical scaling study valencia et al 2007 to try and understand this we here present new calculations of yielding induced plate tectonics as a function of planet size focusing on the idealized end members of internal heating or basal heating as well as different strength profiles and compared to analytical scalings in the present study we model super earths as simple scaled up versions of earth i e assuming constant physical properties keeping the ratio of core mantle radii constant and applying the same temperature difference between top bottom boundaries and the same internal heating rate effects that originate outside of the planet such as tidal forces meteor impacts and intense surface heating from a nearby star are not considered we find that for internally heated convection plate tectonics is equally likely for terrestrial planets of any size whereas for basally heated convection plate tectonics becomes more likely with increasing planet size this is indicated both by analytical scalings and the presented numerical results which agree with each other when scalings are adjusted to account for increasing mean density with increasing planet size plate tectonics becomes more likely with increasing planet size for all scenarios the influence of the pressure variation of viscosity thermal expansivity and conductivity may however act in the opposite sense and needs to be determined in future studies at least in the simplest case factors other than planet size such as the presence of surface water are likely most important for determining the presence or absence of plate tectonics

a positive feedback between magmatism and mantle upwelling in terrestrial planets implications for the moon a series of two dimensional numerical models of magmatism and mantle convection in small planetary bodies are presented to discuss how the small size of the moon exerts control over its mantle evolution mantle convection is modeled by a solid state convection of internally heated materials with temperature dependent viscosity magmatism is modeled as upward permeable flow of basaltic magma generated by decompression melting of upwelling mantle materials migration of the generated magma causes compaction expansion of the coexisting matrix the volume change of matrix and the buoyancy of magma induced by magmatism enhance the upwelling flow and hence the magmatism itself when the rayleigh number exceeds a threshold that is around the critical rayleigh number for the onset of thermal convection this positive feedback makes magmatism vigorous and episodic and causes efficient cooling and stirring of the mantle in large planets like venus and the earth in small planetary bodies where the rayleigh number is lower than the threshold however magmatism occurs more continuously with a characteristic time of several hundred million years cooling and convective stirring of the mantle caused by magmatism are less important and a compositionally stratified structure develops in the mantle these features of magmatism and mantle structure fit in with the observations on the moon the positive feedback is a key to understanding why the evolution of the lunar mantle is so different from that of lager planets like the earth and venus