Thermal evolution of Venus

The theory of three-dimensional and finite-amplitude convection in a viscous spherical shell with temperature and pressure dependent physical parameters is developed on the basis of a modified Boussinesq fluid assumption. The lateral dependences of the variables are resolved through their spherical harmonic representations, whereas their radial and time dependences are determined by numerical procedures. The theory is then applied to produce thermal evolution models for Venus. The emphasis is on illustrating the effects of certain physical parameters on the thermal evolution rather than proposing a specific thermal history for the planet. The main conclusions achieved in this paper are (1) a significant portion of the present temperature in the mantle and heat flux at the surface of Venus is probably owing to the decay of a high temperature established in the planet at the completion of its core formation, (2) the effective Rayleigh number of the mantle is so high that even the lower order modes of convection cool the planet sufficiently and maintain an almost adiabatic temperature gradient in the convecting region and high temperature gradients in the thermal boundary layers, (3) the convection is oscillatory with avalanche type properties which induces oscillatory features to the surface heat flux and the thickness of the crustal layer, and (4) a planetary model with a recycling crust cools much faster than those with a permanently buoyant crust.The models presented in this paper suggest that Venus has been highly convective during its history until ～ 0.5 Ga ago. The vigorous convection was bringing hot and fresh material from the deep interior to the surface and dragging down the crustal slags, floating on the surface, in to the mantle. The rate of cooling of the planet was so high that its core has solidified. In the last 0.5 Ga the vigour of convection diminished considerably and the crustal slags developed into a global and permanently buoyant crustal layer. The tectonic style on Venus has, consequently, changed from the recycling of crustal plates to hot spot volcanics. At the present time the planet is completely solid, except in the upper part of its mantle where partial melting may occur.     

金星非单调冷却热演化历史分析

金星表层年龄和构造活动特点表明其岩石层在最近的地质历史时期经历过广泛的更新.这种全球性的表层改造与其内部热演化历史进程密切相关.如果金星存在相变形成的上、下地幔,依据现今所了解的金星物理性质和参量化的热对流理论,并且考虑金星地幔相变边界层状态对对流的控制作用,我们计算了金星热演化历史.结果表明,金星的热演化历史是一种非单调的冷却过程,在这种非单调的热演化历史进程中,金星地幔会出现大体等周期的翻转.由于参数选取的不同,翻转时金星上、下地幔的温差随时间可能出现稳定变化、逐渐加强、逐渐减弱三种不同演化模式,目前尚不能确定实际金星热演化历史究竟是哪一种模式.金星地幔相变边界层的穿透对流可能是推动其表层岩石层全球性更新的关键,导致其表层火山活动和地表构造以大致500 Ma时间间隔更新和重造.     

南海西南海盆壳幔结构重力反演与热模拟分析

壳幔结构及扩张期后的岩浆活动是研究南海西南海盆形成演化的关键.本文针对NH973-1剖面开展壳幔密度结构重力反演,并依据重力反演的壳幔模型,定量模拟海底扩张期后的壳幔热结构与热演化过程.重力反演表明:西南海盆中央残余扩张脊之下存在一个较深的凹陷带,其下Moho面比两侧略深,呈现扩张期后的热沉降特点.热模拟发现:海盆扩张...     

Refroidissement d’un système de dykes et d’une chambre magmatique sous-jacente

In volcanic areas occurring in zones of extension, basaltic magma rises up to the surface, through fissures, to form dykes which in depth are connected with one or several magmatic chambers located in the crust or the upper mantle. Starting form this geological situation, we propose models of increasing complexity to study cooling by heat conduction of a system composed of parallel dykes and underlying magmatic chamber. This work has been carried out 1) by numerical methods which take into account the variation with temperature of the thermic parameters and 2) by using an analytical solution of the Fourier equation (an initial fictive temperature is then calculated). The thermic individuality of the dykes disappears quickly and the dyke system may be replaced by a single « intrusion » which cools slowly from a temperature = =2/β θ₀ much lower than θ₀ (θ₀=initial temperature; 1/β=injection density). The temperature gradient due to the dyke system has been estimated for different time intervals after the intrusion. For the calculation of the thermal effect of a magmatic chamber, we have taken into account its size, depth and age. Numerical application for appropriate geological cases have been carried out and allow one to estimate the respective effects of dykes and magma chamber.     

Evolution of double diffusion convection in a felsic magma chamber

The onset of double diffusion convection (DDC) is modeled in a two-dimensional case in respect to magma chambers. The viscosity model for the melt takes into account the effects of temperature and concentration of the dissolved component (H₂O). The upper boundary of the convecting magma chamber is assumed to be anhydrous and at constant temperature, whereas the lower boundary is treated as being hydrous permeable with a temperature greater than that within the upper boundary. The case of positive compositional and thermal buoyancy of melt is studied assuming a H₂O diffusion coefficient small in comparison with thermal diffusivity. The DDC has been modeled using a system of equations solved by the finite difference method on a square grid. The convective pattern evolution has been studied for fixed boundary conditions as well as for cooling and degassing. Due to the higher viscosity in the upper zone, the upper boundary layer is thicker than the lower one. The variation of water concentration in this zone of the convective cell can be significant. In nature, the high gradient of water concentration can be responsible for the observed variations of water content in minerals crystallized from a granite melt (e.g., biotite). Because of a high Lewis number (= 100), temperature variations in the magma chamber decay much faster than the water concentration. In this case the intensive convection can continue at a constant temperature due to the non-zero water content in the chamber. In principle, the effect can be applied to the formation of magmatic bodies. If the cooling and degassing system reaches a uniform temperature distribution prior to the crystallization temperature, water content throughout the body may still remain variable.     

Phenocryst crystallization during ascent of alkali basalt magma at Rishiri Volcano, northern Japan

Phenocrysts in volcanic rocks are commonly used to deduce crystallization processes in magma chambers. A fundamental assumption is that the phenocrysts crystallized in the magma chambers at isobaric and nearly equilibrium conditions, on the basis of their large sizes. However, this assumption is not always true as demonstrated here for a porphyritic alkali basalt (Kutsugata lava) from Rishiri Volcano, northern Japan. All phenocryst phases in the Kutsugata lava, plagioclase, olivine, and augite, have macroscopically homogeneous distribution of textures showing features characteristic of rapid growth throughout the crystals. Rarely, a core region with distinct composition is present in all phenocryst phases. Phenocrysts, excluding this core, are occasionally in direct contact with each other, forming crystal aggregates. The equilibrium liquidus temperature of plagioclase, the dominant phase (35 vol%) in the Kutsugata lava, can never exceed the estimated magmatic temperature, unless the liquidus temperature increases significantly due to vesiculation of the magma during ascent. This suggests that most phenocrysts in the Kutsugata lava were formed by decompression of the magma during ascent in a conduit, rather than by cooling during residence in a magma reservoir. In the magma chamber before eruption, probably located at depth of more than 7 km, only cores of the phenocrysts were present and the magma was nearly aphyric (<5 vol% crystals), though the observed rock is highly porphyritic with up to 40 vol% crystals. The Kutsugata magma is inferred to have been rich in dissolved H₂O (>4 wt.%) in the magma chamber, and liquidus temperatures of phenocryst phases were significantly suppressed. Large undercooling caused by decompression and degassing of the magma was the driving force for significant crystallization during ascent because of the increase in liquidus temperature due to vapor exsolution. Low ascent rate of the Kutsugata magma, which is suggested by pahoehoe lava morphology and no association of pyroclastics, gave sufficient time for crystallization. Furthermore, the large degree of superheating of plagioclase in the magma chamber caused plagioclase crystallization with low population density and large crystal size, which characterizes the porphyritic nature of the Kutsugata lava. Alkali basalt is likely to satisfy these conditions and similar phenomena are suggested to occur in other volcanic systems.     

Geoid and topography of Venus in various thermal convection models

Important though indirect information about the internal structure of Venus is provided by its topography and geoid. In the last decades this information has been used to constrain the Venus mantle viscosity structure and its dynamic regime. Recently, the geodynamic inversion of the Venus?? geoid and topography resulted in a group of best fitting viscosity profiles. We use these viscosity models here as an input to our mantle convection code. We carry out simulations of the Venus?? mantle evolution in a 3D spherical shell with depth dependent viscosity and check whether the character of the dynamic topography and the geoid represented by their power spectra fits the observed quantities. We compare the results with several other models obtained for different viscosity stratifications (constant, constant with highly viscous lithosphere, linear increase of viscosity). Further, we estimate the effect of other factors such as internal heating and varying Rayleigh number. We use a 2D spherical axisymmetric convection code to study the effect of lateral viscosity variations. In these 2D models we monitor the topography and the geoid developing above the axisymmetric plume and compare them with the observed elevations of Venus?? geoid and topography in several Regia. Though none of the models fits observed data perfectly, we can generally conclude, that the best fit between the observed and predicted quantities is reached for viscosity profiles with 200 km thick lithosphere followed by a gradual increase of viscosity with depth and with the upper mantle viscosity of 2 × 10 ²¹ Pa s. For all viscosity profiles the predicted geoid and topography spectra match the observed ones only up to the degree 40, thus indicating other than dynamic origin of these quantities for higher degrees.     

A nonstationary model of the thermal regime of axial zones of mid-ocean ridges: Formation of crustal and mantle magma chambers

A nonstationary model of spreading with periodic intrusions of a molten material into an axial zone of a mid-ocean ridge (MOR) is applied to numerical analysis of the thermal state in MOR axial zones and the formation of crustal and mantle magma chambers in them. The model satisfactorily explains the positions, dimensions, and shapes of magma chambers, as well as variations in these parameters depending on the spreading rate, temperature, and composition of crustal and mantle rocks. The release and absorption of the latent heat of rock melting, hydrothermal heating of the crust, and variations in the solidus and liquidus temperatures of crustal and mantle rocks as a function of their composition are factors controlling the shape and position of crustal magma chambers.     

Steady-state operation of Stromboli volcano,Italy: constraints on the feeding system

Stromboli volcano has been in continuous eruption for several thousand years without major changes in the geometry and feeding system. The thermal structure of its upper part is therefore expected to be close to steady state. In order to mantaim explosive activity, magma must release both gas and heat. It is shown that the thermal and gas budgets of the volcano lead to consistent conclusions. The thermal budget of the volcano is studied by means of a finite-element numerical model under the assumption of conduction heat transfer. It is found that the heat loss through the walls of an eruption conduit is weakly sensitive to the dimensions of underlying magma reservoirs and depends mostly on the radius and length of the conduit. In steady state, this heat loss must be balanced by the cooling of magma which flows through the system. For the magma flux of about 1 kg s^-1 corresponding to normal Strombolian activity, this requires that the conduits are a few meters wide and not deeper than a few hundred meters. This implies the existence of a magma chamber at shallow depth within the volcanic edifice. This conclusion is shown to be consistent with considerations on the thermal effects of degassing. In a Strombolian explosion, the mass ratio of gas to lava is very large, commonly exceeding two, which implies that the thermal evolution of the erupting mixture is dominated by that of the gas phase. The large energy loss due to decompression of the gas phase leads to decreased eruption temperatures. The fact that lava is molten upon eruption implies that the mixture does not rise from more than about 200 m depth. To sustain the magmatic and volcanic activity of Stromboli, a mass flux of magma of a few hundred kilograms per second must be supplied to the upper parts of the edifice. This represents either the rate of magma production from the mantle source feeding the volcano or the rate of magma overturn in the interior of a large chamber.     

中国东南部P波速度结构与构造分析

利用中国东南部地震台站的波形数据,通过远震P波层析成像方法反演了福建及台湾地区的上地幔P波速度结构,据此分析了华夏块体的构造属性并探讨了中国东南部上地幔的深部动力学机制.结果表明,研究区上地幔速度结构存在明显的横向非均匀性,它们与区域构造的深部动力学成因密切相关.宏观上,NE向展布的低速异常与东南沿海地区中新生代火成岩的条带状分布保持了较好的一致性,推测其上地幔可能存在幔源物质上涌;以政和—大埔断裂带为界,东、西华夏块体的速度结构存在差异,结合前人的研究结果分析,东、西华夏块体岩石圈减薄和中新生代岩浆活动的驱动机制有所不同,西华夏块体为"板块俯冲+岩浆底侵(岩石圈拆沉)"的动力学模式,东华夏块体是"玄武质岩浆迁移+岩浆底侵"的动力学模式.     

Failed magmatic eruptions: late-stage cessation of magma ascent

When a volcano becomes restless, a primary question is whether the unrest will lead to an eruption. Here we recognize four possible outcomes of a magmatic intrusion: “deep intrusion”, “shallow intrusion”, “sluggish/viscous magmatic eruption”, and “rapid, often explosive magmatic eruption”. We define “failed eruptions” as instances in which magma reaches but does not pass the “shallow intrusion” stage, i.e., when magma gets close to, but does not reach, the surface. Competing factors act to promote or hinder the eventual eruption of a magma intrusion. Fresh intrusion from depth, high magma gas content, rapid ascent rates that leave little time for enroute degassing, opening of pathways, and sudden decompression near the surface all act to promote eruption, whereas decreased magma supply from depth, slow ascent, significant enroute degassing and associated increases in viscosity, and impingement on structural barriers all act to hinder eruption. All of these factors interact in complex ways with variable results, but often cause magma to stall at some depth before reaching the surface. Although certain precursory phenomena, such as rapidly escalating seismic swarms or rates of degassing or deformation, are good indicators that an eruption is likely, such phenomena have also been observed in association with intrusions that have ultimately failed to erupt. A perpetual difficulty with quantifying the probability of eruption is a lack of data, particularly on instances of failed eruptions. This difficulty is being addressed in part through the WOVOdat database. Papers in this volume will be an additional resource for scientists grappling with the issue of whether or not an episode of unrest will lead to a magmatic eruption.     

Thermal evolution of the Earth: Secular changes and fluctuations of plate characteristics

The average secular cooling rate of the Earth can be deduced from compositional variations of mantle melts through time and from rheological conditions at the onset of sub-solidus convection at the end of the initial magma ocean phase. The constraint that this places on the characteristics of mantle convection in the past are investigated using the global heat balance equation and a simple parameterization for the heat loss of the Earth. All heat loss parameterization schemes depend on a closure equation for the maximum age of oceanic plates. We use a scheme that accounts for the present-day distribution of heat flux at Earth's surface and that does not depend on any assumption about the dynamics of convection with rigid plates, which remain poorly understood. We show that heat supply to the base of continents and transient continental thermal regimes cannot be ignored. We find that the maximum sea floor age has not changed by large amounts over the last 3 Ga. Calculations lead to a maximum temperature at an age of about 3 Ga and cannot be extrapolated further back in time. By construction, these calculations are based on the present-day tectonic regime characterized by the subduction of large oceanic plates and hence indicate that this regime did not prevail until an age of about 3 Ga. According to this interpretation, the onset of rapid continental growth occurred when the current plate regime became stable.     

Volcanic history, geologic analysis and map of the Prometheus Patera region on Io

Data from Jupiter's moon Io returned by the Galileo spacecraft have been used to create a geologic map of Prometheus Patera, its associated flow field, and nearby features. We have identified the location of the vent that fed the Prometheus flow field during the Galileo epoch in the north-eastern portion of the main Prometheus flow field. This vent is the probable source of a small sulphur-rich plume. Previous studies suggested that the vent may be atop a tectonic fault but we find that the vent is offset from the putative fault. It is plausible that, in the past, magma exploited the fault to reach the surface at Prometheus Patera, but subsequent magma cooling in the conduit could have caused an obstruction preventing further eruptions from providing significant contributions to the Prometheus flow field. We also speculate on how a new Prometheus plumbing system may be fed by mafic magmas after melt stalls in magma reservoirs during its ascent through the lithosphere from the mantle.     

华南陆缘高热流区的壳幔温度结构与动力学背景

华南陆缘是我国重要的矿产、地热资源区.晚中生代以来,在太平洋板块西向俯冲,地幔热对流活动共同作用下,该区出现多期岩浆-热事件和大规模爆发式成矿作用.在前人研究基础上,本文利用地表热流观测资料、地震剪切波资料、重力位球谐系数,计算了壳-幔温度结构,分析了动力学背景.计算结果表明：华南陆缘东南沿海地带,地壳10 km以浅温度达200℃以上,居里点温度475℃,莫霍面平均温度550℃.地壳浅层较热,花岗岩中放射性元素衰变放热是地壳浅层地下水热活动的重要热源,但地壳总体温度不高,为"冷壳热幔"型热结构.地幔中,90 km深度,温度950~1250℃;120 km深度,温度1050~1400℃;150 km深度,温度1200~1450℃;220 km深度,温度1500~1700℃."热"岩石圈底界深度在110~150 km之间,西深东浅.岩石圈内,地幔应力场为挤压-伸展相间格局;岩石圈之下,地幔应力场为一个以南昌为中心、长轴NE-SW向的椭圆.分析认为,晚中生代以来,太平洋板块的西向俯冲,导致华南陆缘在区域性SE向地幔对流背景上叠加局域性不稳定热扰动,在175~85Ma期间,上地幔物质向上流动,形成不同的岩浆活动高峰期.同时,岩石圈地幔受俯冲洋壳流体的影响,含水量高,黏度小,在地幔流切向应力场作用下,岩石圈底界由西向东"波浪"状减薄.现今岩石圈之下仍具备地幔小尺度热对流温度条件,但除地表浅层外,地壳整体温度不高,岩石圈构造稳定.     

Magma dynamics, crystallization, and chemical differentiation of the 1959 Kilauea Iki lava lake, Hawaii, revisited

Using constraints from an extensive database of geological and geochemical observations along with results from fluid mechanical studies of convection in magma chambers, we identify the main physical processes at work during the solidification of the 1959 Kilauea Iki lava lakes. In turn, we investigate their quantitative influence on the crystallization and chemical differentiation of the magma, and on the development of the internal structure of the lava lake. In contrast to previous studies, vigorous stirring in the magma, driven predominately by the descent of dense crystal-laden thermal plumes from the roof solidification front and the ascent of buoyant compositional plumes due to the in situ growth of olivine crystals at the floor, is predicted to have been an inevitable consequence of very strong cooling at the roof and floor. The flow is expected to have caused extensive but imperfect mixing over most of the cooling history of the magma, producing minor compositional stratification at the roof and thermal stratification at the floor. The efficient stirring of the large roof cooling is expected to have resulted in significant internal nucleation of olivine crystals, which ultimately settled to the floor. Additional forcing due to either crystal sedimentation or the ascent of gas bubbles is not expected to have increased significantly the amount of mixing. In addition to convection in the magma, circulation driven by the convection of buoyant interstitial melt in highly permeable crystal-melt mushes forming the roof and the floor of the lava lake is envisaged to have produced a net upward flow of evolved magma from the floor during solidification. In the floor zone, mush convection may have caused the formation of axisymmetric chimneys through which evolved magma drained from deep within the floor into the overlying magma and potentially the roof. We hypothesize that the highly evolved, pipe-like ‘vertical olivine-rich bodies’ (VORBs) [Bull. Volcanol. 43 (1980) 675] observed in the floor zone, of the lake are fossil chimneys. In the roof zone, buoyant residual liquid both produced at the roof solidification front and gained from the floor as a result of incomplete convective mixing is envisaged to have percolated or ‘leaked‘ into the overlying highly-permeable cumulate, displacing less buoyant interstitial melt downward. The results from Rayleigh fractionation-type models formulated using boundary conditions based on a quantitative understanding of the convection in the magma indicate that most of the incompatible element variation over the height of the lake can be explained as a consequence of a combination of crystal settling and the extensive but imperfect convective mixing of buoyant residual liquid released from the floor solidification front. The remaining chemical variation is understood in terms of the additional influences of mush convection in the roof and floor on the vertical distribution of incompatible elements. Although cooling was concentrated at the roof of the lake, the floor zone is found to be thicker than the roof zone, implying that it grew more quickly. The large growth rate of the floor is explained as a consequence of a combination of the substantial sedimentation of olivine crystals and more rapid in situ crystallization due to both a higher liquidus temperature and enhanced cooling resulting from imperfect thermal and chemical mixing.     

Magmatic structures in the Krkonoše–Jizera Plutonic Complex,Bohemian Massif: evidence for localized multiphase flow and small-scale thermal–mechanical instabilities in a granitic magma chamber

The present paper examines magmatic structures in the Jizera and Liberec granites of the Krkonoše–Jizera Plutonic Complex, Bohemian Massif. The magmatic structures are here interpreted to preserve direct field evidence for highly localized magma flow and other processes in crystal-rich mushes, and to capture the evolution of physical processes in an ancient granitic magma chamber. We propose that after chamber-wide mixing and hybridization, as suggested by recent petrological studies, laminar magma flow became highly localized to weaker channel-like domains within the higher-strength crystal framework. Mafic schlieren formed at flow rims, and their formation presumably involved gravitational settling and velocity gradient flow sorting coupled with interstitial melt escape. Local thermal or compositional convection may have resulted in the formation of vertical schlieren tubes and ladder dikes whereas subhorizontal tubes or channels formed during flow driven by lateral gradients in magma pressure. After the cessation or deceleration of channel flow, gravity-driven processes (settling of crystals and enclaves, gravitational differentiation, development of downward dripping instabilities), accompanied by compaction, filter pressing and melt segregation, dominated in the crystal mush within the flow channels. Subsequently, magmatic folds developed in schlieren layers and the magma chamber recorded complex, late magmatic strains at high magma crystallinities. Late-stage magma pulsing into localized submagmatic cracks represents the latest events of magmatic history of the chamber prior to its final crystallization. We emphasize that the most favorable environments for the formation and preservation of magmatic structures, such as those hosted in the Jizera and Liberec granites, are slowly cooling crystal-rich mushes. Therefore, where preserved in plutons, these structures may lend strong support for a “mush model” of magmatic systems.     

The history and dynamics of a welded pyroclastic dam and its failure

Igneous intrusions in coal seams are found in 80 % of coal mines in the Huaibei coalfield, China, and coal and gas outburst accidents have occurred 11 times under a 120-m-thick sill in the Haizi mining field. The magma’s heat had a significant controlling effect on coal seam gas occurrence. Based on theoretical analysis, experimental tests and site validation, we analyzed the temperature distribution following magma intrusion into coal measure strata and the variations in multiple physical parameters and adsorption/desorption characteristics between the underlying coal seams beneath the sill in the Haizi mining field and coal seams uninfluenced by magma intrusion in the adjacent Linhuan mining field. The research results show that the main factors controlling the temperature distribution of the magma and surrounding rocks in the cooling process include the cooling time and the thickness and initial temperature of the magmatic rock. As the distance from sill increases, the critical effective temperature and the duration of sustained high temperatures decrease. The sill in the Haizi mining field significantly promoted coal seam secondary hydrocarbon generation in the thermally affected area, which generated approximately 340 m³/t of hydrocarbon. In the magma-affected area, the metamorphic grade, micropore volume, amount of gas adsorption, initial speed of gas desorption, and amount of desorption all increase. Fluid entrapment by sills usually causes the gas pressure and gas content of the underlying coal seams to increase. As a result, the outburst risks from coal seams increases as well.     

On the heat and mass transfer from an ascending magma

The maximum heat transfer possible from a sphere of magma ascending through a viscous lithosphere is estimated using a Nusselt number formulation. An upper bound is found for the Nusselt number by using the characteristics of a potential flow which, it is argued, is similar in the limit to a non-isothermal Stokes-flow in which the fluid (wall rock) viscosity is sensitive to temperature. A set of cooling curves are calculated for a magma ascending at a constant velocity beneath an island arc. If the magma is to arrive at the surface without solidifying its ascent velocity must be greater than about 5.8 × 10^?3 cm s^?1, for a magma radius of 1 km, and greater than about 2.7 × 10^?5 cm s^?1, for a magma radius of 6 km. If the magma begins its ascent crystal free it will generally become superheated over most of its ascent. Using essentially the same formulation as for heat transfer the mass transfer to or from a spherical body of magma ascending at these velocities is given approximately by ΔC ? ΔW/10, where ΔC is the change in weight percent of a component in the magma during ascent and ΔW is the compositional contrast of that component between the magma and its wall rock.     

Thermal structure about southwest sub-basin of South China Sea

There are some factors, such as the topographic relief, sedimentary thickness and thermal conductivity, magmatic activity and thermal cooling, influencing the seafloor heat flow and the evolution of lithosphere structure in southwest sub-basin (SWSB), South China Sea. On the base of the geological structure characteristic of SWSB this paper will discuss some other factors including thermal anomaly area, dike produced by magma intrusion and lithosphere relief, by modeling and calculating. Calculating results indicate partial areas where temperature is higher than vicinity in the lithosphere, which we call thermal anomaly here containing thermal anomaly area and dike in this paper, could decrease heat flow below, increase above, and gradually increase to two sides; heat flow in upwelling parts of lithosphere is usually higher than sinking parts, and in the middle is of a gradual transition.     

A mathematical model for 2D heat transfer dynamics in fluid systems with localized sink of magmatic fluid into local fractured zones above the top of crystallizing intrusions

A model describing two-dimensional (2D) dynamics of heat transfer in the fluid systems with a localized sink of a magmatic fluid into local fractured zones above the roof of crystallizing crustal intrusions is suggested. Numerical modeling of the migration of the phase boundaries in 2D intrusive chambers under retrograde boiling of magma with relatively high initial water content in the melt shows that, depending on the character of heat dissipation from a magmatic fluid into the host rock, two types of fluid magmatic systems can arise. (1) At high heat losses, the zoning of fluidogenic ore formation is determined by the changes in temperature of the rocks within the contact aureole of the intrusive bodies. These temperature variations are controlled by the migration of the phase boundaries in the cooling melt towards the center of the magmatic bodies from their contacts. (2) In the case of a localized sink of the magmatic fluid in different parts of the top of the intrusive chambers, a specific characteristic scenario of cooling of the magmatic bodies is probably implemented. In 2D systems with a heat transfer coefficient ?? _k < 5 × 10⁴ W/m² K, an area with quasi-stationary phase boundaries develops close to the region of fluid drainage through the fractured zone in the intrusion. Therefore, as the phase boundaries contract to the sink zone of a fluid, specific thermal tubes arise, whose characteristics depend on the width of the fluid-conductive zone and the heat losses into the side rocks. (3) The time required for the intrusion to solidify varies depending on the particular position of the fluid conductor above the top of the magmatic body.