Observed Heat Flow Research Articles

Thermal evolution of the Northern Cordillera Volcanic Province: implication for heat flow in remnant back-arc regions

ABSTRACT Active and remnant back-arc regions do not follow a typical conductive lithosphere cooling model, but instead have an apparent two-stage cooling, defined by a high heat flow back-arc region during subduction and a second post-subduction heating event that extends elevated heat flow for several 10s million years. Numerical one-stage cooling models have not reproduced observed heat flow anomalies in active subduction zones using physically realistic parameters and require a secondary post-subduction heating mechanism. Here, an extension driven-volcanism model is developed to examine extension driven heating and volcanism as a mechanism to produce a prolonged thermal anomaly within back-arc lithosphere. This model is tested using the recorded thermal evolution of the Northern Cordillera Volcanic Province (NCVP), a Neogene-Quaternary alkaline volcanic province located in the remnant back-arc region of the Pacific-North American subduction zone in British Columbia, Canada. A single steady-state lithosphere geotherm does not intersect all previously published temperature estimates, suggesting previous data record the thermal evolution of the NCVP. Calculated geotherms at equilibrium with the minimum and maximum MELTS temperatures predict an increase in reduced mantle heat flow (Qm ) from 43 to 72 mW/m2 and lithosphere thinning from a depth of 87 to 48 km. The newly developed extension-volcanism model reproduced the calculated pre- and post-volcanism thermal regimes for the NCVP and supports that extension within the remnant back-arc could produce the present heat flow anomaly and volcanism. The model most readily produces volcanism when Qm is ~45–65 mW/m2, a typical range for back-arcs. Back-arc regions are prime locations for limited volcanism because their warmer thermal regime minimizes tectonic stress requirements to produce volcanism. Additionally, two-stage cooling of back-arcs can be explained with a time-dependent extension-volcanism thermal feedback mechanism that is possible because of the subduction driven pre-heating of back-arc regions.

Adjoint inversion of the thermal structure of Southeastern Australia

SUMMARY The variation of temperature in the crust is difficult to quantify due to the sparsity of surface heat flow observations and lack of measurements on the thermal properties of rocks at depth. We examine the degree to which the thermal structure of the crust can be constrained from the Curie depth and surface heat flow data in Southeastern Australia. We cast the inverse problem of heat conduction within a Bayesian framework and derive its adjoint so that we can efficiently find the optimal model that best reproduces the data and prior information on the thermal properties of the crust. Efficiency gains obtained from the adjoint method facilitate a detailed exploration of thermal structure in SE Australia, where we predict high temperatures within Precambrian rocks of 650 °C due to relatively high rates of heat production (0.9–1.4 μW m−3). In contrast, temperatures within dominantly Phanerozoic crust reach only 520 °C at the Moho due to the low rates of heat production in Cambrian mafic volcanics. A combination of the Curie depth and heat flow data is required to constrain the uncertainty of lower crustal temperatures to ±73 °C. We also show that parts of the crust are unconstrained if either data set is omitted from the inversion.

Constraining the geotherm beneath the British Isles from Bayesian inversion of Curie depth: integrated modelling of magnetic, geothermal, and seismic data

Abstract. Curie depth offers a valuable constraint on the thermal structure of the lithosphere, based on its interpretation as the depth to 580 ∘C, but current methods underestimate the range of uncertainty. We formulate the estimation of Curie depth within a Bayesian framework to quantify its uncertainty across the British Isles. Uncertainty increases exponentially with Curie depth but this can be moderated by increasing the size of the spatial window taken from the magnetic anomaly. The choice of window size needed to resolve the magnetic thickness is often ambiguous but, based on our chosen spectral method, we determine that significant gains in precision can be obtained with window sizes 15–30 times larger than the deepest magnetic source. Our Curie depth map of the British Isles includes a combination of window sizes: smaller windows are used where the magnetic base is shallow to resolve small-scale features, and larger window sizes are used where the magnetic base is deep in order to improve precision. On average, the Curie depth increases from Laurentian crust (22.2±5.3 km) to Avalonian crust (31.2±9.2 km). The temperature distribution in the crust, and associated uncertainty, was simulated from the ensemble of Curie depth realizations assigned to a lower thermal boundary condition of a crustal model (sedimentary thickness, Moho depth, heat production, thermal conductivity), constructed from various geophysical and geochemical datasets. The uncertainty in the simulated heat flow field substantially increases from ±10 mW m−2 for shallow Curie depths at ∼15 km to ±80 mW m−2 for Curie depths >40 km. Surface heat flow observations are concordant with the simulated heat flow field except in regions that contain igneous bodies. Heat flow data within large batholiths in the British Isles exceed the simulated heat flow by ∼25 mW m−2 as a result of their high rates of heat production (4–6 µW m−3). Conversely, heat refraction around thermally resistive mafic volcanics and thick sedimentary layers induce a negative heat flow misfit of a similar magnitude. A northward thinning of the lithosphere is supported by shallower Curie depths on the northern side of the Iapetus Suture, which separates Laurentian and Avalonian terranes. Cenozoic volcanism in Northern Britain and Ireland has previously been attributed to a lateral branch of the proto-Icelandic mantle plume. Our results show that high surface heat flow (>90 mW m−2) and shallow Curie depth (∼15 km) occur within the same region, which supports the hypothesis that lithospheric thinning occurred due to the influence of a mantle plume. The fact that the uncertainty is only ±3–8 km in this region demonstrates that Curie depths are more reliable in hotter regions of the crust where the magnetic base is shallow.

Mapping Curie Depth Across Western Canada From a Wavelet Analysis of Magnetic Anomaly Data

AbstractIn western Canada, geophysical studies infer an abrupt change in crustal temperatures between the Canadian Cordillera and the adjacent North American craton, with important implications for the tectonics and geodynamics of the area. We use a wavelet analysis of magnetic anomaly data in western Canada to map the depth to the bottom of the magnetic source, or Curie depth. This depth corresponds to the point at which crustal rocks reach their Curie temperature, thus providing an estimate of geothermal gradient. Our model is defined by a fractal distribution of magnetization characterized by the parameter β, as well as the depths to the top (zt) and bottom (zb) of the magnetized layer. Synthetic tests reveal the increased accuracy of the estimated zb when values for zt and β are fixed prior to the inversion. We set zt to the thickness of sedimentary rocks overlying the magnetic bedrock and use various values of β to estimate zb. We determine β a posteriori by comparing Monte Carlo simulations of predicted heat flow values (assuming a Curie temperature of 580 °C) with observed heat flow in various regions. Our results suggest a β value of 2.5 for the Canadian Cordillera and Slave craton, and 2 for the remaining North American craton. The Curie depths resolve geological domains and important structural features, with estimates for zb averaging 15 ± 1 km in the Cordillera, 32 ± 3 km in the Slave craton, and 34 ± 3 km in the North American craton to the south.

Key parameters of the structure and evolution of the Okinawa Trough: Modelling results constrained by heat flow observations

Heat flow data (664 measurements) in the Okinawa Trough and adjacent areas are edited and analysed in this study. The distribution of heat flow in the study area is obviously correlated with tectonic zones. The heat flow is extremely high and variable in the back‐arc basin and extremely low in the trench. A 2D transient heat conduction‐advection model is used to test and determine the thermal structure and evolution of the Okinawa Trough under the heat flow distribution constraint. The results show that (a) high sedimentation rates can reduce heat flow by 30–35%; lower heat flow in the southern than in the central‐northern Okinawa Trough might be caused by the thick sediment covering due to the Taiwan orogenic uplift. (b) Heat flow can be enhanced dramatically by mantle upwelling, but magma intrusion accompanied by ascending fluid is necessary for the extremely high heat flow along the central Okinawa Trough axis. A magma intrusion age of 0.5 Ma, an intrusion depth of 1 km, and a fluid flow speed in the magma of 9 cm/year are the best fit parameters for the central Okinawa Trough. (c) Given the distribution of heat flow, we suggest that the evolutionary model differs between the central‐northern and the southern Okinawa Trough. The rifting in the central‐northern Okinawa Trough began at 10 Ma with a mean rate of 0.4 cm/a, while the rifting in the south Okinawa Trough started at 6 Ma with a higher rate of 0.6 cm/a. (d) A double magma chamber may exist underneath the axis of the Okinawa Trough at depths of 10 and 24–30 km beneath the seafloor. The temperatures and pressures at these depths support the existence of partial melting, which became the primary basis for maintaining the extremely high heat flow currently observed in the Okinawa Trough.

Fundamental Studies on Induction Heating and Stirring of Non-Metallic Molten Fluid

Induction heating of non-metallic molten fluid has been investigated, mainly performed on melt glass stirring. Because silicate glass has relatively high viscosity and low electric conductivity for induction stirring, their experiments require very high temperature above 1500°C, and are difficult for observation and measurements. In this report, observation and simulation of heat generation and flow in molten salt are presented. And flow states of molten vanadium oxide glass is observed, both of them have low melting points. It is intended to investigate them from both experimental and theoretical directions, as a fundamental research. It is demonstrated that molten NaCl-KCl possessed the low impedance value in frequency range of hundred kHz to 1MHz, preferable for giving rise to induction current generation. Circulating flow of the fluids from the container wall to the center was observed. Temperature measurement in the melt was also conducted at various positions with respect to the coil configuration. The flow velocity and temperature distribution were analyzed by numerical simulation, and compared with the measurements, taking account of the transparent nature of the molten salts. They are shown to explain the experimental results, mostly. Molten vanadium oxide glass having the similar physical properties exhibited the similar flow characteristics.

Refining the thermal structure of the European lithosphere by inversion of subsurface temperature data

Abstract We present an updated thermal model of the European lithosphere based on a new stochastic modeling work flow. We developed this work flow to estimate subsurface temperatures from site- to regional-scale, up to the depth of the lithosphere-asthenosphere boundary (LAB). Our model is composed of four layers, consisting of sediments, upper crust, lower crust and lithospheric mantle. We asigned thermal properties, including radiogenic heat production and temperature- and pressure-dependent bulk thermal conductivity on the base of broad-scale lithological variation within the European crust. We corrected thermal properties with a 1D steady-state temperature approximation, assuming only vertical heat flow. Using these corrected thermal properties, we calculated the 3D thermal field with a conjugate-gradient method, assuming fixed temperatures at the surface and at the base of the lithosphere. To obtain more robust results for our thermal model, we applied data assimilation, aiming at consistency between temperature and heat flow observations and tectonic model predictions. We used an Ensemble Smoother Multiple with Data Assimilation (ES-MDA) method to update prior estimates of thermal properties and the thermal field with temperature data. We calibrated our European thermal model with available regional thermal models due to the present lack of a unified dataset with public borehole temperature measurements. A large dichotomy is observed in the model along the Trans-European Suture Zone (TESZ). Northeast of the TESZ, geothermal gradients up to 10 km depth are mainly below 20 °C km−1. Southwest of the TESZ, gradients range from 20 °C km−1 near the Adriatic coast to more than 50 °C km−1 in volcanically and tectonically active regions. We show that the large scale thermal structure is locally and regionally perturbed by non-conductive heat transfer and affected by transient effects.

Heat flow in the Bushveld Complex, South Africa: implications for upper mantle structure

Abstract Geothermal measurements in South Africa since 1939 have resulted in a good coverage of heat flow observations. The Archaean Kaapvaal Craton, in the central part of South Africa, is the best-studied tectonic domain, with nearly 150 heat flow measurements. The greatest density of heat flow sites is in the Witwatersrand Basin goldfields, where geothermal data are essential for determining refrigeration requirements of deep (up to 4 km) gold mines; the average heat flow is 51 ± 6mWm-2. The Bushveld Complex north of the Witwatersrand Basin is an extensive 2.06 Ga ultramafic-felsic intrusive complex that hosts the world’s largest reserves of platinum. The deepest platinum mines reach ~2 km and the need for thermal information for mine refrigeration engineering has led to the generation of a substantial geothermal database. Nearly 1000 thermal conductivity measurements have been made on rocks constituting the Bushveld Complex, and borehole temperature measurements have been made throughout the Complex. The temperature at maximum rock-breaking depth (~2.5 km) is 70°C, approximately 30°C higher than the temperature at equivalent depth in the Witwatersrand Basin; the thermal gradient in the Bushveld Complex is approximately double that in the Witwatersrand Basin. The main reason for this is the low thermal conductivity of rocks overlying platinum mines. The Bushveld data also resulted in 31 new estimates for the heat flux through the Earth’s crust. The overall average value for the Bushveld, 47 ± 7 mW m-2, is the same, to within statistical error, as the Witwatersrand Basin average. The heat flow for platinum mining areas (45 mW m-2) and the heat flux into the floor of the Witwatersrand Basin (43 mW m-2) are typical of Archaean cratons world-wide. The temperature structure of the Kaapvaal lithosphere calculated from the Witwatersrand geothermal data is essentially the same as that derived from thermobarometric studies of Cretaceous kimberlite xenoliths. Both lines of evidence lead to an estimated heat flux of ~17 mW m-2 for the mantle below the Kaapvaal Craton. The estimated thermal thickness of the Kaapvaal lithosphere (235 km) is similar to that defined on the basis of seismic tomography and magnetotelluric studies. The lithosphere below the Bushveld Complex is not significantly hotter than that below the Witwatersrand Basin. This favours a chemical origin rather than a thermal origin for the upper mantle anomaly below the Bushveld Complex that has been identified by seismic tomography studies and magnetotelluric soundings.

Analysis of a conductive heat flow profile in the Ecuador Fracture Zone

We report 18 new conductive heat flow measurements collected from a sediment pond located in the inactive part of the Ecuador Fracture Zone in the Panama Basin. The data were collected along an east–west transect coincident with a multi-channel seismic reflection profile that extends from ODP Hole 504B to west of the sediment pond. Conductive models indicate that heat flow should decrease from ≈400 mW m−2 on the 1.5 Ma western plate to ≈200 mW m−2 on the 6 Ma eastern plate; however the observed heat flow increases nearly linearly toward the east from approximately 140 mW m−2 to 190 mW m−2. The mean value of 160 mW m−2 represents an average heat flow deficit of ≈50%, which we attribute to lateral advective heat transfer between exposed outcrops on the western and eastern margins of the sediment pond. We apply the well-mixed aquifer model to explain this eastwardly flow, and estimate a volumetric flow rate per unit length in the north–south direction of ≈400±250 m2yr−1 through the basement aquifer. Using a Darcy flow model with the mean flow rate, we estimate permeabilities of ∼10−11 and 10−12 m2 for aquifer thicknesses of 100 and 1000 m, respectively. The estimated permeabilities are similar to other estimates in young oceanic upper crust and suggest that vigorous convection within the basement significantly modifies the thermal regime of fracture zones. Additional heat flow data are needed to determine the prevalence and importance of advective heat transfer in fracture zones on a global scale.

Thermal state of the Explorer segment of the Cascadia subduction zone: Implications for seismic and tsunami hazards

AbstractThe Explorer segment of northernmost Cascadia is an end‐member “warm” subduction zone with very young incoming plate and slow‐convergence rate. Understanding the megathrust earthquake potential of this type of subduction zone is of both geodynamic and societal importance. Available geodetic observations indicate that the subduction megathrust of the Explorer segment is currently locked to some degree, but the downdip extent of the fault area that is potentially seismogenic is not known. Here we construct finite‐element models to estimate the thermally allowed megathrust seismogenic zone, using available knowledge of regional plate kinematics, structural data, and heat flow observations as constraints. Despite ambiguities in plate interface geometry constrained by hypocenter locations of low‐frequency earthquakes beneath Vancouver Island, the thermal models suggest a potential rupture zone of ∼60 km downdip width located fully offshore. Using dislocation modeling, we further illustrate that a rupture zone of this size, even with a conservative assumption of ∼100 km strike length, can cause significant tsunami‐genic deformation. Future seismic and tsunami hazard assessment in northern Cascadia must take the Explorer segment into account.

Lithospheric scale 3D thermal model of the Alpine–Pannonian transition zone

In this paper we present the results of 3D conductive thermal modeling of the Alpine–Pannonian transition zone. The study area comprises the Vienna, Danube, Styrian and Mura–Zala basins, surrounded by the Eastern Alps, the Western Carpathians and Transdanubian Range. The model consists of three layers: Tertiary sediments, the underlying crust and lithospheric mantle. The crust and mantle were homogenous with constant thermal properties. Heat production in the sediments and crust was 1 μW/m3. The thermal conductivity of sediments varied horizontally and vertically and based on laboratory measurements. We tested two scenarios: a steady-state and a time-dependent case. The conductive heat transport equation was solved by finite element method using Comsol Multiphysics. The results of the steady-state model fit to the observation in the northern part of the study area, but this model predicts lower heat flow density and temperatures than observed in the southern part of the study area including the Styrian basin. The area underwent lithospheric stretching during the Early-Middle Miocene time, therefore the temperature field in the lithosphere is not steady-state. We calculated the initial temperature distribution in the lithosphere at the end of rifting using non-homogeneous stretching factors, and we modeled the present day thermal field. The results of the time-dependent model fit to the observed heat flow density and temperatures, except in those areas where intensive groundwater flow occurs in the carbonatic basement of the Transdanubian Range and Northern Calcareous Alps, and the metamorphic basement high between the Mura trough and Styrian basin. We conclude that time-dependent model is able to predict the temperature field in the upper 6–8 km of the crust, and is a valuable tool in EGS exploration.

海溝近傍の熱流量異常

Recent heat flow surveys in the Japan Trench and Nankai Trough areas delineate prominent heat flow anomalies correlated with the structure of the subducting oceanic crust. On the seaward side of the Japan Trench, anomalously high heat flow values are pervasively observed within 150 km of the trench axis. The broad high heat flow zone can be attributed to trenchward thickening of a permeable layer (aquifer) in the oceanic crust associated with fracturing due to plate bending. Fluid circulation in the thickening aquifer efficiently pumps heat up from the underlying unfractured part. Overlapping the broad anomaly, local variations at a scale of a few kilometers are detected, indicating heterogeneous development of fractures. On the floor of the Nankai Trough off the Kii Peninsula, observed heat flow varies from extremely high and variable values on the western side to normal values for the seafloor age on the eastern side. The transition occurs at around 136°E, which may correspond to the structural boundary in the Shikoku Basin between the seafloor formed by spreading in the NE–SW direction and that formed by spreading in the E–W direction. The high heat flow west of the boundary is considered to result from heat transport along the plate interface by fluid circulation in an aquifer in the subducted oceanic crust. The heat flow transition around 136°E may reflect a change in permeability structure across the boundary between the two spreading directions. The two types of hydrothermal heat transport, fluid circulation in the subducted aquifer in the case of the Nankai Trough and circulation in the thickening aquifer in the case of the Japan Trench, have distinctive features. The subducted-aquifer type is effective for heat transport in a young subducting plate with a highly permeable aquifer, while the thickening-aquifer type can transport heat even in an old plate. The subducted-aquifer type has a more significant influence on the temperature structure of the plate boundary. Some heat flow anomalies observed in other trenches may also be caused by either of these types of hydrothermal heat transport.

The Effect of Different Li(Ni1-x-yMnxCoy)O2 Positive Electrode Materials and Coatings on Parasitic Heat Flow as Measured by Isothermal Microcalorimetry, Ultra-High Precision Coulometry and Long Term Cycling

Isothermal microcalorimetry is used to investigate the effect of different Li(Ni1-x-yMnxCoy)O2 materials (NMC442, NMC532, NMC622) and coatings (Al2O3 and a proprietary high voltage coating) on parasitic reactions that occur in Li-ion pouch type cells. NMC/graphite pouch cells were prepared with a typical organic carbonate-based electrolyte containing a well-known additive blend and were tested up to 4.4 V at 40°C. A new method of extracting the parasitic heat flow during both charge and discharge is introduced. Differences between charge and discharge parasitic heat flow yielded more insight into the behavior of high voltage parasitic reactions. Ultra-high precision coulometry, long-term charge discharge cycling, in-situ gas measurements, and electrochemical impedance spectroscopy were also used to compare the observed heat flow to well-known performance metrics. All coated cell types performed significantly better than uncoated NMC442/graphite cells. It was found that the magnitude of the parasitic heat flows did not correlate as expected to the precision coulometry results nor to the long term cycling results. In particular, cells with Al2O3-coated NMC622 had the highest parasitic heat flow among the cells with coated electrodes but competed for best performance in the cycling tests. The possible reasons for this unexpected result are explored.

Thermal modeling and heat flow density interpretation of the onshore Northwest Java Basin, Indonesia

Studies pertaining to heat flow density distribution in Indonesian tertiary sedimentary basins have been conducted intermittently throughout more than two decades. Even so, all of these studies have always concentrated on the basic compilations of thermal gradient, thermal conductivity, and terrestrial heat flow datasets or the study of basin thermal history rather than on the investigations into their present thermal regime. In addition, syntheses on the possible causes to the observed heat flow density distribution in these basins have been largely determined only on the basis of its correlation with geological and geophysical evidences. One basin experiencing this particular problem is the onshore Northwest Java Basin, where knowledge of the present-day subsurface temperature structure is virtually absent and interpretation of heat flow distribution has been mainly qualitative. For these reasons, in this study we have attempted to quantitatively characterize the present subsurface temperature distribution and surface heat flow density of the onshore Northwest Java Basin using a simple numerical thermal modeling approach, based on the most recent heat flow datasets. Taking into account a conductive heat transfer process, the modeling exercise is aimed at deriving a 3-D subsurface temperature distribution. The temperature distribution is translated into the predicted surface heat flow distribution. The modeled temperature field reveals its dependence on the geometrical aspects of the basin’s basement. Comparison between the computed and the observed heat flow densities, taking into account the uncertainties of both, suggests that advective heat transport by groundwater flow may be present, in addition to conduction. The modeling results are thus capable of demonstrating the importance of a quantitative approach in studying the present thermal state of a sedimentary basin.

Crustal control of dissipative ocean tides in Enceladus and other icy moons

Could tidal dissipation within Enceladus’ subsurface ocean account for the observed heat flow? Earthlike models of dynamical tides give no definitive answer because they neglect the influence of the crust. I propose here the first model of dissipative tides in a subsurface ocean, by combining the Laplace Tidal Equations with the membrane approach. For the first time, it is possible to compute tidal dissipation rates within the crust, ocean, and mantle in one go. I show that oceanic dissipation is strongly reduced by the crustal constraint, and thus contributes little to Enceladus’ present heat budget. Tidal resonances could have played a role in a forming or freezing ocean less than 100 m deep. The model is general: it applies to all icy satellites with a thin crust and a shallow ocean. Scaling rules relate the resonances and dissipation rate of a subsurface ocean to the ones of a surface ocean. If the ocean has low viscosity, the westward obliquity tide does not move the crust. Therefore, crustal dissipation due to dynamical obliquity tides can differ from the static prediction by up to a factor of two.

Electrochemical Calorimetry of Li1.2Ni0.15Mn0.55Co0.1O2

Introduction Li-rich oxides, Li(Li x Me1-x )O2 (Me = Co, Ni, Mn), are promising positive electrode active materials for lithium-ion cells because of their ability to deliver capacities over 250 mAhg-1.[1, 2] However, the mechanisms responsible for their unique voltage profiles, such as the activation voltage plateau in the 1st delithiation cycle and voltage hysteresis during cycling, are not fully understood. Electrochemical calorimetry is a powerful tool to observe reversible / irreversible reactions during charge and discharge of the electrode. In addition, the observed reversible heat flow can be described in terms of the change in configurational entropy of lithium ions (DS) in the structure, the heat of polarization, and side reactions. DS is also obtained using the temperature dependence of the open circuit voltage (dE/dT). Here, we compare the heat flow during charge and discharge, open circuit voltage (OCV), and dE/dT to evaluate reversible and irreversible reaction factors of the Li-rich oxides. Experimental All data reported here are obtained on the cathode material denoted as Li(Li0.2Ni0.15Mn0.55Co0.1)O2= (0.5Li2MnO3 - 0.5LiNi0.375Co0.25Mn0.375O2). Coin-type half cells containing c.a. 10 mg cathode material with counter lithium metal were prepared, and the heat flow during charge and discharge was observed using an isothermal microcalorimeter. We also measured OCV and dE/dT at every 2.5 % state of charge (SOC), and correlated the values to the obtained heat flow. In the case of OCV assumption, the relaxation time of OCV (t) was also determined. Results and Discussion As is well known, the lithium-rich oxide material shows the wide voltage plateau only during the 1st cycle.[3] We observed a large gap between the 1st cycle charge voltage and OCV (Figure 1(a)) and also large exothermic heat in the corresponding region (capacity > 100 mAhg-1) as shown in Figure 1(b). dE/dT values are negative (which means endothermic reaction during charge as shown in Figure 1(b); £). The estimated total heat flow (red dots), taking into consideration the heat of polarization from OCV (Figure 1(b); œ) is obviously lower than the observed heat flow (blue line). This observation suggests large irreversible exothermic heat flow for oxide capacities >100 mAhg-1. In addition, the relaxation time constant (Figure 1(c); °) also drastically increases in the corresponding region, which suggests that the irreversible reactions are slower than the reversible reactions. The heat flow during the 2nd charge cycle is distinctly different from that of the 1st cycle. However, the gap between observed heat flow (blue line in Figure 1 (e)) and the estimated one from dE/dT and heat of polarization (Figure 1 (e); œ) remained, which indicates the persistence of irreversible reactions. These irreversible heat flows may be associated with the energy required to induce structural changes within the oxide particles. In our presentation we will discuss the origins of the oxide voltage hysteresis using the heat flow, dE/dT, OCV, and the OCV relaxation times (t) obtained from the charge and discharge cycles. Figure 1

Smectite, illite, and early diagenesis in South Pacific Gyre subseafloor sediment

Subseafloor sediment and basalt rock samples at seven sites in the South Pacific Gyre (SPG) were recovered by Integrated Ocean Drilling Program Expedition 329 (2010.10.8–2010.12.13). Microscopic and spectroscopic measurements on the structural Fe-redox states and the elemental composition of smectite, and polytypes of illite in the sediment at two sites (U1365 and U1369) were performed to understand the origin/formation mechanism of clay minerals in the oligotrophic open ocean. The dominant phases of clay minerals found in the present study were smectite and illite polytypes. Suggestive of non-uniform early diagenetic processes in the expansive SPG seafloor, higher ordering of illite polytypes (1M, 2M1, and 3T) were identified at site U1369 while disordered 1Md illite were found at U1365. Smectites of hydrothermal origin (Al-rich beidellite, and saponite) were observed at U1369. Fe-rich montmorillonite minerals that are likely associated with the terrigenous input, were dominant at U1365. Nontronite (Fe-rich smectite) was detected at both sites. Red-brown to yellow-brown semiopaque oxide minerals (RSO) were widely distributed with Fe-rich smectite near the basaltic crust at U1365. Lower observed heat flow at U1365 relative to U1369 provides a possible explanation for the observed variability in clay mineral speciation between these two sites. The presence of K-nontronite at the basalt/sediment interface at both sites indicates an oxidative basalt alteration; however variations in the oxidation states of structural Fe in nontronite measured by EELS indicate that reductive environment persists locally at the basalt/sediment interface.

Controlled boiling on Enceladus. 1. Model of the vapor-driven jets

Plumes of water vapor and ice particles have been observed from the so-called tiger stripes at the south polar terrain (SPT) of Saturn’s satellite, Enceladus. The observed high salinity (∼0.5–2%) of the ice particles in the plumes may indicate that the plumes originate from a subsurface liquid ocean. Additionally, the SPT is the source of strong infrared radiation (∼4.2 GW), which is especially intense near (within tens of meters) the tiger stripes. This could indicate that the radiation is associated with plume activity, but the connection remains unclear. Here we investigate the constraints that plume observations place on the widths of the cracks, the depth to the liquid-vapor interface, and the mechanisms controlling plume variability. We solve the fluid dynamics of the flow in the crack and the interaction between the flow and ice walls assuming that the flows of water vapor and ice particles originate from a few kilometers deep liquid ocean. For a crack with a uniform width, we find that our model could explain the observed vapor mass flow rate of the plumes when the crack width is 0.05–0.075 m. A wider crack is not favorable because it would produce a higher vapor mass flow rate than the observed value, but it may be allowed if there are some flows that do not reach the surface of Enceladus either due to condensation on the icy walls or the tortuosity of the crack. The observed heat flow can be explained if the total crack length is approximately 1.7 × 500 km. A tapering crack (a crack which is ∼1 m wide at the bottom of the flow and sharply becomes 0.05–0.075 m at shallower depths) can also explain the observed vapor mass flow rate and heat flow. Widths of 1 m or more are necessary to avoid freezing at the liquid-vapor interface, as shown in our paired paper (Ingersoll and Nakajima [2016] Icarus). The observed intense heat flow along the tiger stripes can be explained by the latent heat release due to vapor condensation onto the ice walls near the surface. The resulting buildup of ice causes the vents to seal themselves on time scales less than a year. We also find that the ice to vapor ratio of the plumes is sensitive to the ice mass fraction at the bottom of the flow (liquid–vapor interface). We find that the total mass flow rate of the plumes becomes larger when the crack width is larger, which is consistent with the observation that the flow rate increases near the orbital apocenter, where the crack is expected to be widest.

Fractal density and singularity analysis of heat flow over ocean ridges.

Peak heat flow occurs at mid-ocean ridges and decreases with the age of the oceanic lithosphere. Several plate models, including the Parsons and Sclater (PSM) model, Global Depth and Heat (GDH1) model and Constant Heat flow Applied on the Bottom Lithospheric Isotherm (CHABLIS) model, have been used to predict heat flow in the ocean lithosphere. The discrepancy between the predicted and measured heat flow in the younger lithosphere (i.e. younger than 55 Myr) influenced by local hydrothermal circulation has been used to estimate hydrothermal heat flux and investigate hydrothermal processes. We can modify the cooling models by substituting the ordinary mass density of lithosphere by fractal density with singularity. This new model provides a modified solution to fit the observed heat flow data used in other models in the literature throughout the age range. This model significantly improves the results for prediction of heat flow that were obtained using the PSM, GDH1 and CHABLIS models. Furthermore, the heat flow model does not exhibit special characteristics around any particular age of lithosphere. This raises a fundamental question about the existence of a “sealing” age and accordingly the hydrothermal flux estimation based on the cooling models.

Heat flow structure in the Paleozoides of the Central Asian Fold Belt

Heat generation produced by radioactive decay of long-lived isotopes in the Earth’s crust (radiogenic heat flow) within the Paleozoic provinces of the Central Asian Fold Belt is considered. Heat flow from the mantle is calculated as the difference between the observed heat flow and the radiogenic flow. The major cause of this heat flow is the transition of potential energy of gravity differentiation into heat; in this respect, mantle heat flow is called gravigenic. Calculation shows that the fractions of radiogenic and gravigenic heat flows in the Paleozoides studied are nearly equal.