Changes In Thermal Gradient Research Articles

Higher and bigger: How riparian bats react to climate change

The altitudinal distribution of animals and changes in their body size are effective indicators of climate change. Bats are sensitive to climate change due to their dependence on temperature during critical life stages. However, long-term studies documenting responses over extended periods are rare. We present a 24-year investigation of Myotis daubentonii, a riparian bat known for altitudinal sexual segregation, along a river course in Central Italy. While males occupy the entire river course, females are confined to downstream warmer areas supporting successful reproduction due to improved foraging site productivity. In 2000, females were absent above 900 m a.s.l in our study area. We hypothesise that a) this altitude threshold is now higher, due to thermal gradient changes along the river course; and b) thermoregulatory costs for reproductive females have declined, leading to increased energy investment in offspring and subsequent generational growth in bat body size. Confirming our hypotheses, females exhibited a 175-m upward shift in altitude limit. Furthermore, we found a concurrent increase in body size (but not condition). Temperatures increased in the 24 years, likely allowing females to extend their range to higher elevations and favouring an increase in newborn body mass. Riparian vegetation remained unchanged, excluding habitat quality changes as the cause for the observed responses. The rapid female elevation rise might imply future disruption of established social structures, altering intra- and intersexual competition for roosts and food. Given the global decline in insect populations, larger bats might face future difficulties in finding food to sustain their body size, increasing mortality. However, the full impact of such changes on bat fitness remains unexplored and warrants further investigation, including other bat populations. This knowledge is crucial for informing conservation in the face of ongoing climate change and preserving the ecosystem services bats deliver in riparian ecosystems.

Modulated Structure Formation in Dislocation Cells in 316L Stainless Steel Fabricated by Laser Powder Bed Fusion

Metal additive manufacturing enables producing complex geometric structures with high accuracy and breaks the design constraints of traditional manufacturing methods. Laser powder bed fusion, a typical additive manufacturing process, presents a challenge in experimentally understanding the nano-scaled microstructure-process relationship regarding the wide range of process parameters. In this study, we aim to reveal the novel nanoscale structural features by advanced scanning transmission electron microscopy to clarify the formation mechanisms in 316L stainless steel by laser powder bed fusion. Here we show that the slender columnar grains were confined to the centreline of the melt pool along the build direction, and the columnar cell structure at the side branching of the melt pool grew along orthogonal directions to follow drastic changes in thermal gradient across adjacent melt pools. Novel nano-scaled modulated structures have been observed in the dislocation cells parallel to the laser scan direction, which were mainly caused by the elastic strain involving the thermal gradient inside the melt pool and across adjacent melt pools as well as the effective strain field in the dislocation cell interiors. An in-depth understanding of microstructure developments is worthy of fabricating high-performance materials by controlling the additive manufacturing process.

Microstructural and mechanical analysis of double pass dissimilar welds of twinning induced plasticity steel to austenitic/duplex stainless steels

Double pass dissimilar welds between the twinning induced plasticity (TWIP) steel and austenitic stainless steel (ASS) AISI 304 L and duplex stainless steel (DSS) 2205 were studied theoretically and experimentally. A finite element (FE) thermal model linked to the liquid fraction calculation was used to estimate the optimal heat input level. The metallographic characterization of dissimilar weldments TWIP-SS 304 L and TWIP-DSS 2205 disclosed a priori the lack of hot cracking in the fusion zone (FZ) and liquation cracks in the heat-affected zone (HAZ). Later, the root bend test results corroborated a lack of fusion in the FZ-HAZ interface of the TWIP-DSS 2205 weld (TWIP steel side). The FE model predicted the heat accumulation in the SS 304 L and DSS 2205, which produced variation in the thermal gradient. The thermal gradient changes induced the ferritic-austenitic (FA) solidification mode in TWIP steel and SS 304 L and the massive austenite formation by epitaxial growth in the FZ-HAZ interface of the DSS 2205 side. Microhardness profiles corroborated the formation of homogenous FZs in both dissimilar welded joints. The microhardness increase/decrease was related to the solidification mode change in the FZ-HAZ interface. The mechanical strength and ductility of the TWIP-SS 304 L weld decreased 26% and 40%, respectively, compared to the reference autogenous similar weldment SS 304 L. The planar solidification growth detected in the FZ-HAZ interface was responsible for mechanical properties loss.

Structural evolution and sediment depositional system along the transform margin- Palar–Pennar basin, Indian east coast

Continental transform margins are characterized by sub-vertical strike-slip faults and rapid change in thermal gradient across the margin from continental to oceanic crust. The continental crust terminates abruptly along such sheared margins. Tectonic evolution associated with sedimentation in continental slope of the Palar–Pennar transform margin is inadequately understood due to limited seismic data and/or poor imaging with few well controls. Exploratory drilling attempts for hydrocarbon presence have resulted in some promising outcomes in the Palar–Pennar basin.The Palar–Pennar graben in onland is bound by steep normal rift faults, which reactivated by strike-slip movement during late syn-rift time as Antarctica separated along the NNW to ∼ N-trending Coromandal transform margin in the offshore part. The pre-existing Precambrian shear zones and lineaments in the basement have played a governing role in the basin development. The onland drainage pattern is structurally controlled as observed from its rectangular drainage pattern, tectonic index and sinuosity index. In offshore area of the basin, seismic interpretation identifies distinct pull-apart rift basin along the Coromandal transform margin with syn-rift deposits in the lower continental slope portion. Strike-slip movement uplifted the fault blocks in the southern part of the pull-apart basin. This has also reactivated some of the rift faults in the syn-rift section. Such reactivation results in early post-rift seal breach. This tectonic event has implication in the depositional sequences, which has been portrayed by seismic stratigraphic analysis and construction of chronostratigraphic section across the transform margin in this work. Thickening of post-rift deposition towards E -SE, major hiatus, large scale mass transport complexes and erosional events have been identified from such analysis. On this basis, seven distinct tectonic sequences, M1 to M5 in Mesozoic and T1 and T2 in Tertiary, have been identified. The chronostratigraphic section can help in deciphering the relative sea level changes based on the nature of stratal terminations, extent of erosion and non-deposition. This study emphasizes the tectonic-controlled drainage system and geometry as well as sedimentation pattern in onland and offshore deepwater area of Palar – Pennar basin alongside the Coromondal transform margin.

Genesis of natural hydrogen: New insights from thermodynamic simulations

The present work revises hypotheses to explain the molecular hydrogen genesis in Earth's crust based on iron cycle under water and sulfur environment. Indeed, known reactions are usually associated to minerals reacting with water under oxidizing conditions, such as the serpentinization. From geological observations, other gases have been identified in mid-oceanic ridges, in ophiolitic sites and in Proterozoic continental rocks (more than 550 million years) such as CH4, N2 and He in various proportions. We use thermodynamic simulations to predict the direction of a range of possible metamorphic reactions regarding Gibbs free energies as a function of depth in Earth's crust, temperatures up to 1500 °C, pressure up to 10 kbar and including the relative partial pressures of the gases expressed by the reaction quotient Qr. While the oxidation of ferrous into ferric iron forming molecular hydrogen has been already extensively studied through the serpentinization and siderite decomposition, the role of pyritization has been significantly underestimated. We show that iron-based oxide precursors under hydrogen sulfide lead to H2 formation and pyrite FeS2 down to the middle level of the crust (down to 12 km in the crust-using the thermal gradient of 30 °C, at ΔG = ΔG0, Qr = 1). As the crust can be considered as a semi-open system (with H2 leaking), its genesis is likely to appear also at deeper levels. The slow cooling of continental rocks through time in cratonic area is also compatible with the enhancement of pyritization reactions. The serpentinization is favored at lower temperatures. Those complementary processes can co-exist in black and white smokers and are key indices for hydrogen prospection as they involve redox reactions, impacting pH, with magnetic changes (through magnetite formation), thermal gradient changes and pyrite formation. The ‘olivinization’ of serpentinites (without hydrogen involved in the reaction), i.e. the inversion of serpentinization in order to close the iron cycle in the mantle, is evaluated to occur from 10 to 12 km using a normal thermal gradient. We find then that the iron cycle can be completed as the ferrous ion can be regenerated from the ferric iron via different mechanisms. It implies that natural hydrogen appears as a renewable raw matter on Earth, with clear interest in terms of industrial valorization.

Whole Field Measurements to Understand the Role of Varying Depths of Nucleation Site on Vapor Bubble Dynamics and Heat Transfer Rates

Abstract This work studies the possible effects of varying depths of cavity on bubbling features and the associated heat transfer rates in nucleate pool boiling regime. A single vapor bubble has been generated on a substrate with a cylindrical cavity at its center that acts as the nucleation site. Experiments have been conducted for three cavity depths (250, 500, and 1000 μm), while keeping its throat diameter constant at 200 μm. With the bulk fluid maintained under saturated conditions, for each cavity depth, surface superheat level has been varied in the range of ΔTsuperheat = 8, 10 and 12 °C. A gradient-based visualization technique, coupled with a high speed camera, has been employed to simultaneously map the changes in thermal gradients during the formation of the vapor bubble as well as bubble dynamic parameters. The image sequence obtained has been qualitatively and quantitatively analyzed to elucidate the dependence of bubbling features and various heat transfer processes on cavity depth. With an increase in the depth of cavity, the net effect of reduction in the available thermal energy due to the increased convection effects and significant depletion of superheated layer are identified as the dominant heat transfer processes that influence the bubbling features. Furthermore, based on the statistics of bubble departure characteristics, the cavity with higher depth (1000 μm) showed a much stable bubble formation with minimal variation in the bubble departure frequency as compared to the bubbling features from a cavity with smaller depth (250 μm). Evaporative heat transfer process has been identified as the primary cause for increased inconsistency of bubbling features at high superheat conditions for experiments performed for low cavity depths.

Ferro-advection aided evaporation kinetics of ferrofluid droplets in magnetic field ambience

The present article discusses the physics and mechanics of evaporation of pendant, aqueous ferrofluid droplets, and modulation of the same by an external magnetic field. We show experimentally and by mathematical analysis that the presence of a horizontal magnetic field augments the evaporation rates of pendant ferrofluid droplets. First, we tackle the question of improved evaporation of the colloidal droplets compared to water and propose physical mechanisms to explain the same. Experiments show that the changes in evaporation rates aided by the magnetic field cannot be explained on the basis of changes in surface tension or based on classical diffusion driven evaporation models. Probing via particle image velocimetry shows that the internal advection kinetics of such droplets plays a direct role toward the augmented evaporation rates by modulating the associated Stefan flow. Infrared thermography reveals changes in thermal gradients within the droplet and evaluating the dynamic surface tension reveals the presence of solutal gradients within the droplet, both brought about by the external field. Based on the premise, a scaling analysis of the internal magneto-thermal and magneto-solutal ferroadvection behavior is presented. The model incorporates the role of the governing Hartmann number, the magneto-thermal Prandtl number, and the magneto-solutal Schmidt number. The analysis and stability maps reveal that the magneto-solutal ferroadvection is the more dominant mechanism, and the model is able to predict the internal advection velocities with accuracy. Furthermore, another scaling model to predict the modified Stefan flow is proposed and is found to accurately predict the improved evaporation rates.

The role of side-branching in microstructure development in laser powder-bed fusion

In-depth understanding of microstructure development is required to fabricate high quality products by additive manufacturing (for example, 3D printing). Here we report the governing role of side-branching in the microstructure development of alloys by laser powder bed fusion. We show that perturbations on the sides of cells (or dendrites) facilitate crystals to change growth direction by side-branching along orthogonal directions in response to changes in local heat flux. While the continuous epitaxial growth is responsible for slender columnar grains confined to the centreline of melt pools, side-branching frequently happening on the sides of melt pools enables crystals to follow drastic changes in thermal gradient across adjacent melt pools, resulting in substantial broadening of grains. The variation of scan pattern can interrupt the vertical columnar microstructure, but promotes both in-layer and out-of-layer side-branching, in particular resulting in the helical growth of microstructure in a chessboard strategy with 67° rotation between layers.

A quantitative temperature reconstruction of the ‘Little Ice Age’ in southern China

We present a branched glycerol dialkyl glycerol tetraethers (brGDGTs)–based mean annual temperature reconstruction covering the last millennium from a subtropical lake in Guangxi Province, southern China (23°N). We demonstrate that the pattern and absolute values of mean annual temperatures reconstructed using the eastern African lake brGDGTs calibration based on the methylation of 5-methyl branched tetraethers index provided the most reliable and accurate temperature estimates from the site. The results resemble regional and Northern Hemisphere changes over this period. The pattern shows a general cool period between ca. AD 1450 and 1950, including cooling minima centred at ca. AD 1600, 1750 and 1900, coeval with the ‘Little Ice Age’ temperature fluctuations in the Northern Hemisphere, followed by a warming trend from the mid-20th century to the present. The results suggest that both solar forcing and high-latitude Northern Hemisphere climate fluctuations play a role in influencing the terrestrial temperatures in southern China, possibly on different timescales. In addition, our results support the hypothesis that changes of the East Asian summer monsoon are primarily driven by the land–sea thermal gradient change between terrestrial southern China and the Indo-Pacific Warm Pool regions during the last millennium, owing to external radiative and/or volcanic forcings.

The response of tropical precipitation to Earth's precession: the role of energy fluxes and vertical stability

Abstract. The changes in Earth's precession have an impact on the tropical precipitation. This has been attributed to the changes in seasonal solar radiation at the top of the atmosphere. The primary mechanism that has been proposed is the change in thermal gradient between the two hemispheres. This may be adequate to understand the zonal mean changes, but cannot explain the variations between land and oceans. We have used a simple model of the intertropical convergence zone (ITCZ) to unravel how precipitation changes with precession. Our model attributes the changes in precipitation to the changes in energy fluxes and vertical stability. We include the horizontal advection terms in this model, which were neglected in the earlier studies. The final response of the land and oceans is a result of complex feedbacks triggered by the initial changes in the insolation. We find that the changes in precipitation over the land are mainly driven by changes in insolation, but over the oceans, precipitation changes on account of changes in surface fluxes and vertical stability. Hence insolation can be a trigger for changes in precipitation on orbital timescales, but surface energy and vertical stability play an important role too. The African monsoon intensifies during a precession minimum (higher summer insolation). This intensification is mainly due to the changes in vertical stability. The precipitation over the Bay of Bengal decreases for minimum precession. This is on account of a remote response to the enhanced convective heating to the west of the Bay of Bengal. This weakens the surface winds and thus leads to a decrease in the surface latent heat fluxes and hence the precipitation.

On Consonance between a Mathematical Method for the CET Prediction and Constrained / Unconstrained Solidification

Abstract Some properties of the functions yielding from the temperature field have been employed as a tool to determine the structural zones’ localization in a large static steel ingot. Thus, a numerical simulation was performed to generate the temperature field converged subsequently into the thermal gradient field. As a result, the selection of a zone, in which a columnar into equiaxed structure transformation (CET) is expected, is possible. It is shown that the CET - zone is formed when the thermal gradient becomes temporarily constant. Moreover, the CET localization can be easily controlled / shifted by the mold thickness selection. Both temperature and thermal gradient fields were also calculated to predict mathematically the creation of some structural zones in the continuously solidifying brass ingot. The columnar structure resulting from the constrained growth seems dominant in these ingots. However, when the s/l interface rate and velocity of the liquidus isotherm movement are subjected to a separation then the birth of the equiaxed structure is to be expected. In the industrial practice, the following structural zones are evinced in a continuously cast brass ingot: chilled columnar grains-, (CC), fine columnar grains-, (FC), columnar grains-, (C), equiaxed grains zone, (E), and eventually the single crystal, (SC), situated axially. The current innovative method for the mathematical predictions of the CET appearance in the static ingot turns out also useful in the reproduction of the all mentioned structural zones’ localization. In particular, a study of the behavior of the velocity of the liquidus isotherm movement and thermal gradient changes versus solidification time delivers a precise information about these structural zones’ situation.

Process-Defect-Structure-Property Correlations During Laser Powder Bed Fusion of Alloy 718: Role of In Situ and Ex Situ Characterizations

Components made by laser powder bed fusion (L-PBF) additive processes require extensive trial and error optimization to minimize defects and arrive at targeted microstructure and properties. In this work, in situ infrared thermography and ex situ surface roughness measurements were explored as methodologies to ensure Inconel® 718-part quality. For a given laser energy of 200 Watts, prismatic samples were produced with different exposure times (80 to 110 µs) and point spacings (80 to 110 µm). The infrared intensities from laser–material interaction zones were measured spatially and temporally. The conditions leading to higher IR intensity and lowest surface roughness values correlated well with less porosity and coarse solidification grain structure. The transition from highly columnar to misoriented growth is attributed to changes in thermal gradients and liquid–solid interface velocities. Hardness measurements and electron microscopy of the as-processed and post-processed heat-treated samples show complex transitions in microstructural states including the heavily dislocated FCC matrix, reduction of dislocation density, and copious precipitation, respectively. These results show that the geometry-process-structure-property correlations are dynamic, and they cascade depending on the transitions of phase states from powder to liquid to solid, as well as phase decompositions and deformations within the solid FCC phase. Validity of using analytical weld process models to describe the above phenomena is also highlighted.

Effect of the Heat Input on the Heat Affected Zone in the Austenitic Stainless Steel Welding by the GTAW Process-An Experimental and Computational Analysis

ABSTRACTArc welding processes such Gas Tungsten (GTAW), Gas Metal (GMAW) and Submerged Arc (SAW) are typically used in order to produce a weld joint in stainless steels (SS). However, welding thermal cycle generates a sensitization by formation of chromium carbides. In addition, the heat affected zone (HAZ) is also susceptible to sensitization and fracture of the weldment. Weld bead geometric parameters such depth penetration, fusion zone (FZ) width and size of HAZ are mainly determined by welding operation parameters. This research work studies the influence of welding current, welding speed and arc gap on the width and grain size in the HAZ produced by a single pass of autogenous GTAW process applied to a plate butt-welded joint of AISI 304 SS. The welded specimens were prepared for analysis by light optical (LOM) and scanning electron (SEM) microscopies to identify the interfaces between FZ-HAZ and base material as well as the grain growth in the HAZ. Adams equation for 2-D heat distribution was used to estimate theoretically the width of the HAZ. Furthermore, computational simulation which solved a convective-diffusion problem of the volumetric heat applied during the weld pool formation allowed to correlate the thermal gradient and the molten material flow of the FZ with the welding depth penetration, and width and grain size in the HAZ. The results demonstrated that the high heat input generates an important grain growth in the HAZ caused by low heat diffusion in the adjacent material to the fusion line. Welding speed was the main factor in the thermal gradient changes. Simulation results indicate that outward recirculating flow in the molten metal produced by surface tension forces is responsible for the shallow penetration of the autogenous GTAW process. Theoretical and computational estimations of the HAZ are in good agreement with the experimental results.

Geothermal Gradients and Heat Flow Variations in Parts of the Eastern Niger Delta, Nigeria

Abstract: Geothermal gradients and present day heat flow values were evaluated for about seventy one wells in parts of the eastern Niger delta, using reservoir and corrected bottom – hole temperatures data and other data collected from the wells. The results showed that the geothermal gradients in the shallow/continental sections in the Niger delta vary between 10 - 18° C/km onshore, increasing to about 24° C/km seawards, southwards and eastwards. In the deeper (marine/paralic) section, geothermal gradients vary between 18 - 45° C/km. Heat flow values computed using Petromod 1–D modeling software and calibrated against corrected BHT and reservoir temperatures suggests that heat flow variations in this part of the Niger delta range from 29 – 55 mW/m2 (0.69 – 1.31 HFU) with an average value of 42.5 mW/m2 (1.00 HFU). Heat flow variations in the eastern Niger delta correspond closely to variations in geothermal gradients. Geothermal gradients increase eastwards, northwards and seawards from the coastal swamp. Vertically, thermal gradients in the Niger delta show a continuous and non-linear relationship with depth, increasing with diminishing sand percentages. As sand percentages decrease eastwards and seawards, thermal gradient increases. Lower heat flow values (< 40 mW/m2) occur in the western and north central parts of the study area. Higher heat flow values (40 - 55 mW/m2) occur in the eastern and northwestern parts of the study area. A significant regional trend of eastward increase in heat flow is observed in the area. Other regional heat flow trends includes; an eastwards and westwards increase in heat flow from the central parts of the central swamp and an increase in heat flow from the western parts of the coastal swamp to the shallow offshore. Vertical and lateral variations in thermal gradients and heat flow values in parts of the eastern Niger delta are influenced by certain mechanisms and geological factors which include lithological variations, variations in basement heat flow, temporal changes in thermal gradients and heat flow, related to thicker sedmentary sequence, prior to erosion and evidenced by unconformities, fluid redistribution by migration of fluids and different scales of fluid migration in the sub-surface and overpressures.

Thermal distortion of disc-shaped ductile iron castings in vertically parted moulds

A disc-shaped casting with an inner boss and an outer rim, separated by a thin walled section, was examined. This measurable deformation varied with the feeding modulus. The influence of alloy composition, particularly Si content, was examined with a pearlitic ductile iron (EN-GJS-500-7) and a fully ferritic ductile iron (EN-GJS-450-10).The experiment showed that both the alloy composition and choice of feeder influenced the degree of deformation measured in the finished casting. It was found that the deformation of the pearlitic alloy was influenced controllably by changing the feeder modulus, whereas the deformation of the fully ferritic alloy was less affected by a change in thermal gradient. Both alloys underwent comparable deformations with respect to size, shape, and location.

Impact of abrupt deglacial climate change on tropical Atlantic subsurface temperatures

Both instrumental data analyses and coupled ocean-atmosphere models indicate that Atlantic meridional overturning circulation (AMOC) variability is tightly linked to abrupt tropical North Atlantic (TNA) climate change through both atmospheric and oceanic processes. Although a slowdown of AMOC results in an atmospheric-induced surface cooling in the entire TNA, the subsurface experiences an even larger warming because of rapid reorganizations of ocean circulation patterns at intermediate water depths. Here, we reconstruct high-resolution temperature records using oxygen isotope values and Mg/Ca ratios in both surface- and subthermocline-dwelling planktonic foraminifera from a sediment core located in the TNA over the last 22 ky. Our results show significant changes in the vertical thermal gradient of the upper water column, with the warmest subsurface temperatures of the last deglacial transition corresponding to the onset of the Younger Dryas. Furthermore, we present new analyses of a climate model simulation forced with freshwater discharge into the North Atlantic under Last Glacial Maximum forcings and boundary conditions that reveal a maximum subsurface warming in the vicinity of the core site and a vertical thermal gradient change at the onset of AMOC weakening, consistent with the reconstructed record. Together, our proxy reconstructions and modeling results provide convincing evidence for a subsurface oceanic teleconnection linking high-latitude North Atlantic climate to the tropical Atlantic during periods of reduced AMOC across the last deglacial transition.

Use of40Ar/39Ar K‐feldspar thermochronology in basin thermal history reconstruction: an example from the Big Lake Suite granites, Warburton Basin, South Australia

ABSTRACTThe potential use of40Ar/39Ar thermochronologic data from K‐feldspars in reconstructing basin thermal history has been evaluated using the example of the Warburton/Cooper/Eromanga Basin, Australia's largest onshore oil‐ and gas‐producing basin. Results from40Ar/39Ar step‐heating experiments reveal details of the evolution of the basin system, including the following: (1) the operation of high geothermal gradient regimes during the earliest basin evolution, suggesting that basin formation was active rather than passive; (2) slow cooling from a Permo‐Triassic temperature peak of at least 250–300°C; (3) a rise in thermal gradients to contemporary bottom hole temperatures in the last 5–10 Myr; and (4) spatially variable recrystallization events between 100 and 50 Ma and at around 20 Ma. Initial microstructural observations serve as a useful predictor of the quality and nature of the obtainable age information. Data from ‘pristine’ K‐feldspars may constrain the peak temperature conditions experienced in the basin, the basin's early thermal history and also any recent changes in thermal gradient. Contrasting data from texturally modified K‐feldspars may constrain times of thermal transients and/or fluid flow, with the preferred interpretation that K‐feldspars recrystallize in response to such events. The Warburton/Cooper/Eromanga Basin example suggests that the40Ar/39Ar technique may serve as a useful adjunct to apatite and zircon fission track analysis and conventional organic maturation indices in basin thermal history analysis.

Effects of hydrogeological and climate change on the subsurface thermal regime in the Sendai Plain

We estimated the effects of hydrogeological and surface temperature warming on subsurface thermal regime from the temperature–depth profiles and hydrological data of groundwater quality both in the quaternary and tertiary systems in the Sendai Plain as a preliminary step toward reconstruction of climate changes. Annual mean air temperature in the plain has increased about 1.5 °C in the last 70 years and this surface warming resulted in low or negative thermal gradient. However, anomaly of thermal gradient was recognized in not all temperature–depth profiles. Groundwater chemical compositions and stable isotope data (δD and δ 18O) show that the groundwater flow system has marked difference between those of tertiary and quaternary systems. Calculated results of three dimensional groundwater flow and heat transport model ensure the above hypothesis and shows that thermal gradient changes at close to basement of the quaternary system. The differences in groundwater flow systems are expressed as subsurface thermal gradient anomalies in the temperature–depth profiles in the Sendai Plain. Furthermore, one-dimensional numerical analyze including the effect of surface warming indicates that calculated profile has departure from steady state line at depths in 60–80 m agree well with observed one.

Thermal conductivity contrast due to gas saturated pore space -- application in basin simulation: ABSTRACT

Calibration of thermal histories in basin modeling usually relies on matching temperature and vitrinite reflectance distribution in wells. The four main temperature, maximum depth of burial (or eroded overburden), and thermal conductivity of the individual layers of rocks. The last parameter can be used to match the fine structure of the vertical temperature distribution, thermal gradient changes and heat anomalies. While most commercial simulation packages use thermal conductivity values calculated with water as the pore fluid, we have experimented with using decreased conductivity resulting from high gas saturation in the pore space of specific formations in our modeling. One such case study is the Alberta Deep Basin in western Canada, where a large part of the lower Cretaceous section is thought to be gas saturated, underneath a water-saturated seal. Another case study comes from northwestern Siberia, where the largest gas accumulations on earth have been discovered. Results show that the thermal effect of gas in pores, as opposed to water, are significant and cannot be neglected in basin modeling. Such gas saturations can explain frequently observed sudden increases in vitrinite reflectance gradients or so called [open quote]kinky[close quote] reflection profiles. The gas effect can also be used to model heatmore » anomalies in past geologic periods where hypothetical increased heatflow evens cannot be justified.« less

Paragenesis of sodic pyroxene-bearing quartz schists: implications for the P-T history of the Sanbagawa belt

Sodic pyroxene (jadeite content X jd=0.1–0.3) occurs locally as small inclusions within, albite porphyroblasts and in the matrix of hematite-bearing quartz schists in the Sanbagawa (Sambagawa) metamorphic belt, central Shikoku, Japan. The sodic, pyroxene-bearing samples are characteristically free from chlorite and their typical mineral assemblage is sodic pyroxene+subcalcic (or sodic) amphibole+phengitic mica+albite+quartz+hematite+titanite±epidote. Spessartine-rich garnet occurs in Mn-rich samples. Sodic pyroxene in epidote-bearing samples tends to be poorer in acmite content (average X Acm=0.26–0.50) than that in the epidote-free samples (X Acm=0.45–0.47). X Jd shows no systematic relationship to metamorphic grade, and is different among the three sampling regions [Saruta-gawa, Asemi-gawa and Bessi (Besshi)]. The average X Jd of the Saruta-gawa samples (0.21–0.29) is higher than that of the Asemi-gawa (0.13–0.17) and Bessi (0.14–0.23). The P-T conditions of the Asemi-gawa and Bessi regions are estimated at 5.5–6.5 kbar, >360°C in the chlorite zone, 7–8.5 kbar, 440±15°C in the garnet zone and 8–9.5 kbar, 520±25°C in the albite-biotite zone. Metamorphic pressure of the Saruta-gawa region is systematically 1–1.5 kbar higher than that of the Asemi-gawa and Bessi regions, and materials of the Saruta-gawa region have been subducted to a level 3–5 km deeper than materials that underwent metamorphism at equivalent temperatures and are now exposed in the Asemi-gawa and Bessi regions. Pressure slightly increases toward the north (structurally high levels) through the Sanbagawa belt of central shikoku. Two types of zonal structure were observed in relatively coarse-grained sodic pyroxenes in the matrix. One type is characterized by increasing X Jd from core to rim, the other type by decreasing X Jd from core to rim. Both types of zoned pyroxenes show an increase in X Fe 2+[=Fe2+/(Fe2++Mg)] from core to rim. The first type of zoning was observed in a sample from the chlorite zone of lowest grade, whereas the latter occurs in the garnet and albite-biotite zones of higher grade. The contrast in zonal structure implies that dP/dT during prograde metamorphism decreased with increasing metamorphic grade and may have been negative in some samples from the higher-grade zones. The estimated dP/dT of the prograde stage of the chlorite zone is 3.2 kbar/100°C, and that of the garnet and albite-biotite zones is -1.8 to 0.9 kbar/100°C. The variation of dP/dT at shallow and deep levels of a subduction system probably reflects the difference of heating duration and/or change in thermal gradient of the subduction zone by continuous cooling of the surrounding mantle.