A possible mechanism for the thermal asymmetry of the Ligurian basin

ABSTRACT We propose a thermo-mechanical model and a new interpretation of heat flux data for the Ligurian basin that may be a key to understanding the evolution of the NW Mediterranean. The model incorporates the removal of a portion of mantle lithosphere to explain the heat-flux and subsidence anomaly of the eastern (Corsican) margin of the basin. This process is envisaged as a result of eastward asthenosphere flow induced by the Apennines subduction system. After a heating phase, time-dependent conductive cooling and re-thickening of the lithosphere result in re-equilibrium of the thermal gradient to its initial value. Such a rifting mode can account for the asymmetric heat-flux and subsidence pattern observed across the basin and the present-day lithospheric thickness.     

Criteria for recognition of localization and timing of multiple events of hydrothermal alteration in sandstones illustrated by petrographic,fluid inclusion,and isotopic analysis of the Tera Group,Northern Spain

Stratigraphic relations, detailed petrography, microthermometry of fluid inclusions, and fine-scale isotopic analysis of diagenetic phases indicate a complex thermal history in Tithonian fluvial sandstones and lacustrine limestones of the Tera Group (North Spain). Two different thermal events have been recognized and characterized, which are likely associated with hydrothermal events that affected the Cameros Basin during the mid-Cretaceous and the Eocene. Multiple stages of quartz cementation were identified using scanning electron microscope cathodoluminescence on sandstones and fracture fills. Primary fluid inclusions reveal homogenization temperatures (Th) from 195 to 350°C in the quartz cements of extensional fracture fillings. The high variability of Th data in each particular fluid inclusion assemblage is related to natural reequilibration of the fluid inclusions, probably due to Cretaceous hydrothermal metamorphism. Some secondary fluid inclusion assemblages show very consistent data (Th = 281–305°C) and are considered not to have reequilibrated. They are likely related to an Eocene hydrothermal event or to a retrograde stage of the Cretaceous hydrothermalism. This approach shows how multiple thermal events can be discriminated. A very steep thermal gradient of 97–214°C/km can be deduced from δ¹⁸O values of ferroan calcites (δ¹⁸O −14.2/−11.8‰ V-PDB) that postdate quartz cements in fracture fillings. Furthermore, illite crystallinity data (anchizone–epizone boundary) are out of equilibrium with high fluid inclusion Th. These observations are consistent with heat-flux related to short-lived events of hydrothermal alteration focused by permeability contrasts, rather than to regional heat-flux associated with dynamo-thermal metamorphism. These results illustrate how thermal data from fracture systems can yield thermal histories markedly different from host-rock values, a finding indicative of hydrothermal fluid flow.     

近30年上海地区暴雨的气候变化特征

利用上海地区11个气象站1979-2008年5～9月降水资料分析了近30年上海地区暴雨的年、月际及暴雨成因的变化特征.结果表明:1995年以来,上海地区暴雨逐渐向强、局部、特短时间方向变化.7、8月暴雨较多,以短时局部性暴雨为主;6、9月暴雨次之,6月长和特长暴雨要多于短和特短暴雨,9月反之;5月暴雨最少.从形成上海地区暴雨天气系统的分析表明,静止锋暴雨最多,稳定时能形成持续时间长的强暴雨,不稳定时形成短的弱暴雨;其次是暖区暴雨,它是上海地区形成夏季短时局部性强暴雨的主要天气型;另外,台风、台风切变、台风倒槽、低压、冷锋、暖锋和东风扰动形成的暴雨也占有一定的比例.1995年以来,暖区暴雨整体增加,而静止锋暴雨进入21世纪逐渐减少,这可能主要归因于气候变暖和城市热岛效应.     

基于同步挤压改进短时傅立叶变换的分频蚂蚁追踪在断裂识别中的应用

在地球物理领域,时频分析方法在资料处理过程中占据着愈发重要的位置;运用分频属性检测断层、裂缝等应用广泛;因此,寻求更高精度的时频分析方法一直是地震信号处理领域所追求的目标。改进短时傅立叶变换方法由于窗函数的限制导致时频分析结果准确度不理想,为了更大限度地提升时频分辨率,对改进短时傅立叶变换后的时频谱进行挤压,发展了同步挤压改进短时傅立叶变换;根据合成信号结果可知,同步挤压改进短时傅立叶变换其时频汇聚程度更加明显,在刻画信号的时频特征上更有优势。理论表明,地震数据高频成分可以对微小的次生裂缝进行精确的雕刻,而蚂蚁追踪技术是检测裂缝、断层信息的有效手段。因此,本文基于高分辨的时频分析方法,并结合蚂蚁追踪技术对三维数据体进行裂缝预测,结果表明:该方法可以更好地勾勒出微小裂缝以及伴生褶皱,识别精度与传统蚂蚁追踪算法相比有了明显的提高,同时也证实了该方法在实际应用中可行且有效。     

An analysis of MONTBLEX data on heat and momentum flux at Jodhpur

Parameterization of sensible heat and momentum fluxes as inferred from an analysis of tower observations archived during MONTBLEX-90 at Jodhpur is proposed, both in terms of standard exchange coefficientsC _H andC _D respectively and also according to free convection scaling. Both coefficients increase rapidly at low winds (the latter more strongly) and with increasing instability. All the sensible heat flux data at Jodhpur (wind speed at 10 m Ū₁₀ < 8 ms⁻¹) also obey free convection scaling, with the flux proportional to the ‘4/3’ power of an appropriate temperature difference such as that between 1 and 30 m. Furthermore, for Ū₁₀ < 4 ms⁻¹ the momentum flux displays a linear dependence on wind speed.     

Response of saturated porous media to cyclic thermal loading

The response of a semi‐infinite saturated porous medium subjected to a harmonic thermal loading on its free face is studied herein. The pressure diffusion equation that governs the fluctuation of the interstitial pressure is established. It allows us to obtain prevalent parameters, i.e. the thermal and fluid mass diffusivities and the coefficient of relative bulk variation. Closed‐form solutions of the maximum fluid pressure P_max and its location x_cr are derived. It is shown that the location x_cr of P_max is localized and depends on the diffusivity ratio and the frequency of the thermal loading while the magnitude of P_max depends on the diffusivity ratio and the thermal amplitude. Master curves for x_cr and P_max versus diffusivity ratio are built. It follows that three regimes can be distinguished: namely, thin spalling, thick spalling or in‐depth cracking and no cracking. Copyright © 2003 John Wiley & Sons, Ltd.     

Ultrahigh‐temperature osumilite gneisses in southern Madagascar record combined heat advection and high rates of radiogenic heat production in a long‐lived high‐T orogen

We report the discovery of osumilite in ultrahigh‐temperature (UHT) metapelites of the Anosyen domain, southern Madagascar. The gneisses equilibrated at ~930°C/0.6 GPa. Monazite and zircon U–Pb dates record 80 Ma of metamorphism. Monazite compositional trends reflect the transition from prograde to retrograde metamorphism at 550 Ma. Eu anomalies in monazite reflect changes in fO₂ relative to quartz–fayalite–magnetite related to the growth and breakdown of spinel. The ratio Gd/Yb in monazite records the growth and breakdown of garnet. High rates of radiogenic heat production were the primary control on metamorphic grade at the regional scale. The short duration of prograde metamorphism in the osumilite gneisses (<29 ± 8 Ma) suggests that a thin mantle lithosphere (<80 km) or advective heating may have also been important in the formation of this high‐T, low‐P terrane.     

塔里木盆地顺南地区中-下奥陶统正演沉积数值模拟

利用正演沉积数值模拟,恢复了塔里木盆地顺南地区中-下奥陶统沉积演化过程。综合分析基础地质条件,以Dionisos软件为平台,建立了塔里木顺南地区中-下奥陶统正演沉积数值模拟的初始模型。通过调整构造沉降、海平面变化、沉积物产率、波浪强度和方向等参数及模型校验,以正演方法再现了该地区三维沉积演化过程,并分析了沉积旋回演化、关键界面特征和内部沉积格局。早中奥陶世,塔里木盆地顺南地区发育四个沉积旋回,四次相对海平面下降形成了中-下奥陶统蓬莱坝组下段、蓬莱坝组上段、鹰山组下段、鹰山组上段等顶面多个局部或区域短期暴露面,形成了非断裂控制的短期暴露岩溶。     

Wastage of the Klutlan ice-cored moraines,Yukon Territory,Canada

A series of ice-cored Neoglacial moraines at the terminus of the Klutlan Glacier covers an area of 90 km². Studies were made to determine empirically how long ice persisted in the Klutlan moraines and to develop models that can accurately predict wastage rates under current climatic conditions. A meltout curve based on climatological data reflects the sum of three melting processes: surficial melting, melting by lake water, and melting by geothermal heat. About 950 yr are required to melt 180 m of ice with a debris concentration of 1%, or about 1200 yr for a 1.5% debris load. Another meltout curve, based on seismic data, suggests total meltout in about 875 yr. When all geologic factors are considered, the empirical meltout curve is remarkably similar to that derived by considering the major heat-flux parameters. Meltout rates can be predicted if (1) the fundamental climatic parameters can be ascertained, and (2) the sediment concentration in the ice is known.     

Estimating Influence of Crystallizing Latent Heat on Cooling-Crystallizing Process of a Granitic Melt and Its Geological Implications

Based on the theory of thermal conductivity, in this paper we derived a formula to estimate the prolongation period （AtL） of cooling-crystallization process of a granitic melt caused by latent heat of crystallization as follows：△tL=QL×△tcol/（TM-TC）×CP where TM is initial temperature of the granite melt, Tc crystallization temperature of the granite melt, Cp specific heat, △tcol cooling period of a granite melt from its initial temperature （TM） to its crystallization temperature （Tc）, QL latent heat of the granite melt.
The cooling period of the melt for the Fanshan granodiorite from its initial temperature （900℃） to crystallization temperature （600℃） could be estimated -210,000 years if latent heat was not considered. Calculation for the Fanshan melt using the above formula yields a AtL value of -190,000 years, which implies that the actual cooling period within the temperature range of 900°-600℃ should be 400,000 years. This demonstrates that the latent heat produced from crystallization of the granitic melt is a key factor influencing the cooling-crystallization process of a granitic melt, prolongating the period of crystallization and resulting in the large emplacement-crystallization time difference （ECTD） in granite batholith.     

A multi‐level parallelized substructuring‐frontal solution for coupled thermo/hydro/mechanical problems in unsaturated soil

This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd.     

Quantitative Expression of Heat Flow versus Tectonic Deformation in the China Continent： The Effects of Plastic-Flow Network and Stable Block

1 Introduction It has been understood in the study of terrestrial heat flow that the distribution of heat flow in the interior of continent is influenced by a large number of factors, involving heat sources (e.g. mantle heat flow, heat production of radioactive elements in the crust, magmatic activity, and heat production of tectonic deformation), heat transfercondition (e.g. thermal conductivity and thickness of media), groundwater circulation, etc. On the background of these factors it is pa…     

Recent developments and the future of low‐T calorimetric investigations in the Earth sciences: Consequences for thermodynamic calculations and databases

Low‐T calorimetry is an experimental science that measures the thermodynamic function heat capacity, C_p(T), from which the standard third‐law entropy (298.15 K), S°, is calculated. The recent technological development of relaxation calorimetry allows both new experimental strategies and types of C_p investigations to be made, which were previously not possible. The C_p measurements are fast and automated and can be made on mg‐sized mineralogical samples between 2 and 400 K. These advantages, when careful measurement procedures are used, permit better determinations of C_p(T) behaviour. The C_p of synthetic single‐crystal MgO was measured between 5 and 302 K, and S° calculated using relaxation calorimetry to further investigate the method's precision and accuracy. A number of synthetic and natural end‐member or nearly end‐member compositions of silicate garnet were investigated in the past via adiabatic calorimetry, an old and established technique, and more recently and extensively with the relaxation method. First C_p(T) and S° results, using relaxation calorimetry, have been obtained on spessartine (Mn₃Al₂Si₃O₁₂) and knorringite (Mg₃Cr₂Si₃O₁₂). Furthermore, reinvestigations on pyrope (Mg₃Al₂Si₃O₁₂), almandine (Fe₃Al₂Si₃O₁₂), grossular (Ca₃Al₂Si₃O₁₂) and andradite (Ca₃Al₂Si₃O₁₂), often on multiple samples, have resolved uncertainties and certain problems with published thermodynamic data. S° can be affected by various low‐T physical phenomena, such as cooperative magnetic phase transitions or Schottky anomalies at temperatures of <15 K, which were not described fully in some older adiabatic calorimetric studies. New C_p results show that small differences in the thermodynamic behaviour between some natural and synthetic silicates may exist as demonstrated by extensive work on grossular. Important and “new” research questions on the thermodynamic behaviour of minerals are coming to light and are being investigated. The C_p behaviour and S° values for six silicate garnet end‐members are analysed and the latter are compared to the “best fit or optimized” S° values given in various internally consistent thermodynamic databases. Conclusions are drawn on what types and directions of calorimetric study are required in order to obtain better thermodynamic property determinations of minerals, as well as achieving a better understanding of the underlying microscopic physical behaviour that determines the macroscopic C_p and S° functions.     

Theoretical Calculation Model of Heat Transfer for Deep-derived Supercritical Fluids with a Case Study

Based on a set of equations established by Duan et al. (1992, 1996) for a geofluid system H2O-CO2-CH4(-N2), a formula is obtained to calculate the heat changes. Combining the geological T-P conditions (geothermal gradients and lithostatic and hydrostatic pressures), the enthalpy of some typical geofluids is figured out. Then the principles of heat transfer of deep-derived supercritical fluids are discussed. The result shows that deep-derived geofluids can bring a large amount of thermal heat and release most heat to the shallow surroundings as they move up, because the molar enthalpies vary very greatly from the deep to shallow, increasing with the increases of T and P. Generally, more than tens of kilojoules heat per molar can be released. Furthermore, the molar enthalpy is affected by the compositions of the geofluids, and the molar enthalpy of CO2, CH4, or N2 is greater than that of H2O, being twice, more than twice, and about 140% of H2O, respectively. Finally, a case study is conducted by investigat     

Meso‐Cenozoic thermal structure of the lithosphere in the Bohai Bay Basin,eastern North China Craton

Thermal structure of the lithosphere studies the partition of crustal and mantle heat flow of the continental area and is of significant importance to understand various energy‐related geodynamic processes. The study addresses the spatial distribution of the Meso‐Cenozoic mantle heat flow and Moho temperatures in the region of the Bohai Bay Basin based on the thermal history of the sedimentary basin, radioactive heat production rate and thickness of crustal layering. The results show that the ratio of the mantle and surface heat flow (q_m/q_s) experienced two peaks in the late period of the Early Cretaceous (q_m/q_s ~ 68%) and the Middle to Late Palaeogene (q_m/q_s ~ 75%), respectively. Based on the q_m/q_s ratio, the lithosphere of the Bohai Bay Basin transformed its thermal structure during the Meso‐Cenozoic, from the ‘cold mantle but hot crust’ stage in the Triassic–Jurassic to the ‘hot mantle but cold crust’ stage in the Cretaceous and Cenozoic. The Moho temperatures (T_m) during the Meso‐Cenozoic were also calculated by using the equation of one‐dimensional heat conduction, and the result shows that there exist three T_m peaks occurring in the late period of the Early Cretaceous (930–1080 °C), the Middle‐Late Palaeogene (820–890 °C) and the Early Neogene (770–810 °C). The q_m/q_s ratio began to exceed 50%, and the Moho temperature started to go over 700 °C from the Cretaceous to the present day, which revealed that the activity of the upper mantle in the eastern North China Craton (NCC) increased significantly accompanied by the strong crustal movement in the Cretaceous. The thermal structure revealed the Cretaceous to be a revolutionary period during the evolution of the Bohai Bay Basin, and this paper may provide some thermal evidence for the studies of the geodynamic evolution during the destruction of the NCC. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimation of surface heat flux and inversion height with a Doppler acoustic sounder

In this paper, acoustic sounder (sodar) derived vertical velocity variance (σ _w ² ) and inversion height (Z _i) are used to compute the surface heat flux during the convective activity in the morning hours. The surface heat flux computed by these methods is found to be of the same order of magnitude as that obtained from tower measurements. Inversion heights derived from sodar reflectivity profiles averaged for an hour are compared with those obtained from the σ _w ² /Z profile. Variation of σ _w ² in the mixed layer is discussed. The data were collected during the Monsoon Trough Boundary Layer Experiment 1990 at Kharagpur. The analysis is made for four days which represent the pre-monsoon, onset, active and relatively weak phases of the summer monsoon 1990. The interaction of the ABL with the monsoon activity is studied in terms of the variation of inversion height, vertical velocity variance and surface heat flux as monsoon progresses from June to August.     

Experimental and numerical investigations of the behaviour of a heat exchanger pile

The geothermal use of concrete geostructures (piles, walls and slabs) is an environmentally friendly way of cooling and heating buildings. With such geothermal structures, it is possible to transfer energy from the ground to fluid‐filled pipes cast in concrete and then to building environments. To improve the knowledge in the field of geothermal structures, the behaviour of a pile subjected to thermo‐mechanical loads is studied in situ. The aim is to study the increased loads on pile due to thermal effects. The maximum thermal increment applied to the pile is on the order of 21°C and the mechanical load reached 1300 kN. Coupled multi‐physical finite element modelling is carried out to simulate the observed experimental results. It is shown that the numerical model is able to reproduce the most significant thermo‐mechanical effects. Copyright © 2006 John Wiley & Sons, Ltd.     

The geometry and timing of orogenic extension: an example from the Western Italian Alps

Contacts between rocks recording large differences in metamorphic grade are indicative of major tectonic displacements. Low-P upon high-P contacts are commonly interpreted as extensional (i.e. material points on either side of the contact moved apart relative to the palaeo-horizontal), but dating of deformation and metamorphism is essential in testing such models. In the Western Alps, the Piemonte Ophiolite consists of eclogites (T ≈550–600 °C and P≈18–20 kbar) structurally beneath greenschist facies rocks (T ≈400 °C and P≈9 kbar). Mapping shows that the latter form a kilometre-wide shear zone (the Gressoney Shear Zone, GSZ) dominated by top-SE movement related to crustal extension. Rb–Sr data from micas within different GSZ fabrics, which dynamically recrystallized below their blocking temperature, are interpreted as deformation ages. Ages from different samples within the same fabric are reproducible and are consistent with the relative chronology derived from mapping. They show that the GSZ had an extensional deformation history over a period of c. 9 Myr between c. 45–36 Ma. This overlaps in time with the eclogite facies metamorphism. The GSZ operated over the entire period during which the footwall evolved from eclogite to greenschist facies and was therefore responsible for eclogite exhumation. The discrete contact zone between eclogite and greenschist facies rocks is the last active part of the GSZ and truncates greenschist facies folds in the footwall. These final movements were therefore not a major component of eclogite exhumation. Pressure estimates associated with old and young fabrics within the GSZ are comparable, indicating that during extensional deformation there was no significant unroofing of the hangingwall. Since there are no known extensional structures younger than 36 Ma at higher levels in this part of the Alps, exhumation since the final juxtaposition of the two units (at 36 Ma) seems to have been dominated by erosion. Key words: deformation age, eclogite, exhumation, Rb–Sr dating, tectonic.     

Modeling geothermal regime in the Qinghai-Tibet Plateau: an examination of the upper-boundary condition

This study describes to which degree the numerical prediction of ground temperatures in the Qinghai-Tibet Plateau is influenced by the upper-boundary adoptions. A temperature-controlled upper boundary and a heat-flux upper boundary (HFUB) are, respectively, applied to model the ground temperatures at a typical section on the plateau. Predicted temperatures are compared to the field-observed temperature profile at this test section, in order to distinguish the predicted deviations. Comparison of these deviations confirms that a HFUB model promises better prediction accuracy, especially in the modeling ground-temperature zero-curtain effect. Adoption of a HFUB, however, requires examining whether the specified initial ground temperature is in its thermal equilibrium state. Special emphasis is paid on how to use a HFUB to simulate the temperature under a pavement in the plateau and on the pro and con regarding the uses of different upper-boundary models.     

THEORETICAL ANALYSIS OF AN IMPERVIOUS,HEATED-CYLINDER ‘GROUNDWATER VELOCIMETER’

An isothermally heated, impervious cylinder, which is placed normal to the path of flowing groundwater, is theoretically evaluated for its potential to serve as a kind of ‘groundwater velocimeter’. The essential task is to determine whether the variation in heat output along the cylinder perimeter is sufficiently large to permit measurement for typical groundwater velocities. Using finite elements, the governing equations of advective thermal transport in saturated porous media are solved to obtain the variation in heat output along the circumference of the heated cylinder. An annular region of different hydraulic conductivity is assumed to separate the cylinder from the surrounding formation. The creation of such a region during placement of a cylinder is inevitable. A parametric study led to the following conclusions: (1) A smaller cylinder radius is preferable since the time to achieve a particular degree of asymmetry in heat output is then greatly reduced. (2) An annular region of lower hydraulic conductivity, relative to formation, reduces output asymmetry by no more than 25%, but if hydraulic conductivity is increased, output asymmetry can increase several times. (3) For annular regions having a higher hydraulic conductivity than the surrounding formation, annular thickness is not important. (4) The least groundwater speed which may be accurately measured by such a device will depend heavily upon instrumentation but is tentatively placed at about 5⋅0×10⁻⁵ cm/s. Theoretical results are approximately confirmed by preliminary experiments with a prototype device which has been constructed so as to directly measure the expected variation in thermal output. Partial construction details are provided.