Melt-filled hybrid fractures in the oceanic mantle: Melt enhanced deformation during along-axis flow beneath a propagating spreading ridge axis

Mid-ocean ridges represent important locations for understanding the interactions between deformation and melt production, transport, and emplacement. Melt transport through the mantle beneath mid-ocean ridges is closely associated with deformation. Currently recognized transport and emplacement processes at ridges include: 1) dikes and sills filling stress-controlled fractures, 2) porous flow in a divergent flow field, 3) self-organizing porous dunite channels, and 4) shear zones. Our recent observations from the sub-oceanic mantle beneath a propagating ridge axis in the Oman ophiolite show that gabbronorite and olivine gabbro dikes fill hybrid fractures that show both shear and extensional components of strain. The magnitudes of shear strain recorded by the dikes are significant and comparable to the longitudinal extensions across the dikes. We suggest that the hybrid dikes form from the interactions between shear deformation and pressurized melt in regions of along-axis flow at mid-ocean ridges. The displacement across the dikes is kinematically compatible with high temperature flow recorded by plastic fabrics in host peridotites. Field observations and mechanical considerations indicate that the dikes record conditions of higher stress and lower temperature than those recorded by the plastic flow fabrics. The features of hybrid dikes suggest formation during progressive deformation as conditions changed from penetrative plastic flow to strain localization along melt-filled fractures. The combined dataset indicates that the dikes are formed during along-axis flow away from regions of diapiric upwelling at propagating ridge segments. Hybrid dikes provide a potentially powerful kinematic indicator and strain recorder and define a previously unrecognized mechanism of melt migration. Our calculations show that hybrid dikes require less melt pressure to form than purely tensile dikes and thus may provide a mechanism to tap melt reservoirs that are under-pressurized with respect to lithostatic pressure.     

Water and partial melting of Earth’s mantle

Water plays a crucial role in the melting of Earth’s mantle. Mantle magmatisms mostly occur at plate boundaries (including subduction zones and mid-ocean ridges) and in some intraplate regions with thermal anomaly. At oceanic subduction zones, water released by the subducted slab may induce melting of the overlying mantle wedge or even the slab itself, giving rise to arc magmatism, or may evolve into a supercritical fluid. The physicochemical conditions for the formation of slab melt and supercritical fluid are still under debate. At mid-ocean ridges and intraplate hot zones, water and CO₂ cause melting of the upwelling mantle to occur at greater depths and in greater extents. Low degree melting of the mantle may occur at boundaries between Earth’s internal spheres, including the lithosphere-asthenosphere boundary (LAB), the upper mantletransition zone boundary, and the transition zone-lower mantle boundary, usually attributed to contrasting water storage capacity across the boundary. The origin for the stimulating effect of water on melting lies in that water as an incompatible component has a strong tendency to be enriched in the melt (i.e., with a mineral-melt partition coefficient much smaller than unity), thereby lowering the Gibbs free energy of the melt. The partitioning of water between melt and mantle minerals such as olivine, pyroxenes and garnet has been investigated extensively, but the effects of hydration on the density and transport properties of silicate melts require further assessments by experimental and computational approaches.     

Material transportation and fluid-melt activity in the subduction channel: Numerical modeling

The subduction channel is defined as a planar to wedge-like area of variable size,internal structure and composition,which forms between the upper and lower plates during slab subduction into the mantle.The materials in the channel may experience complex pressure,temperature,stress and strain evolution,as well as strong fluid and melt activity.A certain amount of these materials may subduct to and later exhume from100 km depth,forming high to ultra-high pressure rocks on the surface as widely discovered in nature.Rock deformation in the channel is strongly assisted by metamorphic fluids activities,which change composition and mechanical properties of rocks and thus affect their subduction and exhumation histories.In this study,we investigate the detailed structure and dynamics of both oceanic and continental subduction channels,by conducting highresolution petrological-thermomechanical numerical simulations taking into account fluid and melt activities.The numerical results demonstrate that subduction channels are composed of a tectonic rock melange formed by crustal rocks detached from the subducting slab and the hydrated mantle rocks scratched from the overriding plate.These rocks may either extrude sub-vertically upward through the mantle wedge to the crust of the upper plate,or exhume along the subduction channel to the surface near the suture zone.Based on our numerical results,we first analyze similarities and differences between oceanic and continental subduction channels.We further compare numerical models with and without fluid and melt activity and demonstrate that this activity results in strong weakening and deformation of overriding lithosphere.Finally,we show that fast convergence of orogens subjected to fluid and melt activity leads to strong deformation of the overriding lithosphere and the topography builds up mainly on the overriding plate.In contrast,slow convergence of such orogens leads to very limited deformation of the overriding lithosphere and the mountain building mainly occurs on the subducting plate.     

Shear localisation in upper mantle peridotites

Upper mantle peridotite bodies at the earth's surface contain relict structures and microstructures which provide direct information on the role and the mechanisms of shear localisation in the upper mantle. Deformation which occurred at high temperatures (T>950±50°C) is relatively homogeneous within domains ranging in scale from a few kilometres to a few tens of kilometres. Below 950±50°C strain is localised into centimetre to several hundred metre wide shear zones which commonly contain hydrated mylonitic peridotites. The microstructures developed in the peridotites suggest there is a correlation between the occurrence of shear localisation and the occurrence of strain softening and brittle deformation processes. The most important strain softening processes are inferred to be structural and reaction induced softening. Structural softening processes include dynamic recrystallisation and strain-induced transitions from dislocation creep to some form of grain-size-sensitive (GSS) creep. Reaction induced softening is related to the formation of fine grained polyphase reaction products which deform by GSS creep and the formation of weak sheet silicates such as phlogopite, chlorite, talc and antigorite. From experimental studies these softening processes and brittle deformation processes are inferred to occur mainly at temperatures less than about 910±160°C. This temperature range is inferred to be a significant rheological transition in the upper mantle. Below 910±160°C deformation during orogenesis may be accommodated by an anastomosing network of hydrated mylonitic shear zones with a distinct, perhaps weak, rheology. At higher temperatures strain is accommodated in much wider deformation zones.On the scale of the lithosphere the degree of localisation may be different to that determined at the scale of the periodotite massif. An anastomosing network of hundred metre wide mylonitic shear zones forming 0.05–0.3 by volume fraction of the mantle lithosphere atT<950°C could accommodate inhomogeneous or homogeneous bulk deformation depending on the spatial distribution and ordering of the mylonite zones. The higher temperature deformation at deeper levels in the mantle could be markedly inhomogeneous being concentrated in shear zones with widths in the range of 2–20 km, alternatively these zones may widen significantly during deformation, resulting in a decrease in the degree of localisation with increasing bulk strain.     

碳酸盐化橄榄岩的电性研究

为进一步探讨上地幔的高导层成因,了解碳酸盐在上地幔电性方面的作用并估算上地幔高导层的碳酸盐含量,本文对不同碳酸盐含量的橄榄岩及玄武岩样品在2~3 GPa、300~1300℃的条件下进行了电性实验研究.研究初步发现:碳酸盐熔体显著增强橄榄岩、玄武岩样品的导电能力;单纯用含硅酸盐熔体的橄榄岩或单纯用含水橄榄岩可能难以解释上地幔某些区域的异常高导现象;同样,单纯用碳酸盐化的橄榄岩可能也难以解释上地幔某些区域的高导现象;上地幔的高导区很可能是碳酸盐熔体、硅酸盐熔体及水的共存区域.     

Modelling the composition of melts formed during continental breakup of the Southeast Greenland margin

We have developed a generic dynamic model of extension of the lithosphere, which predicts major element composition and volume of melt generated from initial extension to steady state seafloor spreading. Stokes equations for non-Newtonian flow are solved and the mantle melts by decompression. Strengthening of the mantle due to dehydration as melting progresses is included. The composition is then empirically related to depletion. Using a crystallisation algorithm, the predicted primary melt composition was compared with mean North Atlantic mid-ocean ridge basalt (MORB). At steady state, using half spreading rates from 10 to 20 mm yr^− 1 and mantle potential temperatures of 1300 to 1325 °C we predict a major element composition that is within the variation in the mean of North Atlantic MORB.

This model is applied to the Southeast Greenland margin, which has extensive coverage of seismic and ODP core data. These data have been interpreted to indicate an initial pulse of magmatism on rifting that rapidly decayed to leave oceanic crustal thickness of 8 to 11 km. This pattern of melt production can be recreated by introducing an initial hot layer of asthenosphere beneath the continental lithosphere and by having a period of fast spreading during early opening. The hot layer was convected through the melt region giving a pulse of high magnesian and low silica melt during the early rifting process. The predicted major element composition of primary melts generated are in close agreement with primary melts from the Southeast Greenland margin. The observed variations in major element composition are reproduced without a mantle source composition anomaly.     

Three-dimensional Mapping of Magma Source and Transport Regions from Seismic Data: The Mantle Wedge beneath Northeastern Japan

—We investigate the distribution of partial melt in island arc using the seismic velocity structure of the mantle wedge beneath northeastern Japan. The comparison of the seismic tomography with laboratory velocity data on a partially-molten mantle rock yields estimates of melting zones in three dimensions. We employ experimental data on the degree of partial melt in hydrous peridotite to give constraints on the melt fraction and temperature. Melting and magma-rich zones derived from the velocity structure coincide with observed low Q zones. The results of the three-dimensional mapping indicate that the source of magma in island arc is diapir-like melting patches localized within the low velocity zones of the mantle wedge. Extensive volcanic activity along the volcanic front is due to the presence of vast magma-rich zones just beneath the Moho. Those melting zones in the uppermost mantle may, in turn, cause melting of lower crustal materials and produce felsic magma. Melt appears to stay at and beneath the Moho, where crystallization fractionation may proceed. Melt exists at greater depths in the back-arc region, which may correlate with across-arc variations of chemical compositions of the volcanic rocks observed in northeastern Japan. We suggest that magma migration in the ductile lower crust may cause low-frequency microearthquakes, and magma penetration into the brittle upper crust may produce mid-crustal S-wave reflectors.     

Terrestrial heat and volcanism

Summary Although active volcanic territories are not characterised by extreme high heat flow, yet terrestrial heat is one of the main, if not hte first cause of volcanic activities. About 94 per cent of the known active volcanoes are in connection with orogenic zones including ocean ridges, which mean that processes responsible for the evolution of the continents cause the overwhelming majority of volcanism.There stages of the evolution of the continental crust can be distinguished: 1.) Growth of the continental cores by differentiation, 2.) Existence of peripheral growing zones around the first core, 3.) Intergrowth of the existing continents.Volcanism, as well as seismicity are manifestations of the evolution of the crust which is caused by the development of heat sources in the mantle. The heat partly melt the upper mantle and induce slow plastic flow in connection of differentiation. The space, left empty by continental uplift is filled by the slow plastic inflow of mantle from the ocean. This slow redistribution of mantle and curstal rocks disturbs the stress field, the rocks fail along the strained zones and zones of fractures appear sometimes with volcanic activity.     

地幔热导率的选取对动力学数值模拟的影响——以岩石圈张裂过程为例

目前存在有多种地幔热导率模型,不同模型在数值和随温压变化的特征上有明显的差异.为探究不同热导率模型对动力学数值模拟结果的影响,本文对不同模型下的岩石圈张裂过程进行模拟研究,探讨地幔热导率对岩石圈热传输、变形和熔融过程的影响及其作用机理.结果显示,不同热导率模型下,岩石圈的变形和熔融特征表现出明显差异.高热导率模型下,岩石圈破裂较晚,形成陆缘较为宽阔,地壳熔融强烈而地幔熔融较弱;低热导率模型下,岩石圈破裂较早,形成陆缘较为狭窄,地幔熔融强烈而地壳熔融较弱.这种差异源于不同地幔热导率下岩石圈和地幔热状态的变化及相应力学性质的改变.高热导率下,热传导的增温效应显著,岩石圈呈现较热的状态,其强度整体较低,壳幔耦合减弱;而低热导率下,热对流的增温效应显著,岩石圈呈较冷的状态,其强度整体较高,壳幔耦合增强.基于模拟结果,本文认为地幔热导率的选取对动力学模拟的结果有着较为显著的影响,相对于随温压的变化,热导率数值的差异对动力学数值模拟的结果影响更大,尤其是对于地幔熔融过程的影响.     

Simple 2-D models for melt extraction at mid-ocean ridges and island arcs

A general set of 2-D equations for the conservation of mass and momentum of a two-phase system of melt in a deformable matrix is used to derive analytic solutions for the corner flow of a constant porosity melt-saturated porous medium. This solution is used to model the melt extraction processes at mid-ocean ridges and island arcs. The models indicate that flow of melt is controlled by pressure gradients induced by the Laplacian of the matrix velocity field and by the dimensionless percolation velocity which measures the relative contributions of buoyancy-driven flow to advection by the matrix. The models can account for many features of ridge and arc volcanism. Matrix corner flow at ridges causes melt to be drawn to the ridge axis enabling the extraction of small melt fractions from a wide melting zone while showing a narrow zone of volcanism at the surface. At subduction zones melts do not percolate vertically but are drawn to the junction of the upper plate and subducting slab by corner flow in the mantle wedge. For subduction zones, if the dimensionless percolation velocity is below a critical value, slab-derived fluids will be carried down by the matrix and cannot interact with the mantle wedge. The geochemistry of island arcs will be controlled by the geometry of melt streamlines. This model is consistent with geophysical and geochemical data from the Aleutian arc.     

Peridotite composition from the North Atlantic: regional and tectonic variations and implications for partial melting

Mineral chemical parameters and modal abundances for mantle-derived abyssal peridotite tectonites from 14 locations in the North Atlantic (0–79°N) vary over considerable ranges and are correlated together. The data indicate that there are differences in the bulk chemistry of the peridotites which correspond to the amount of basaltic melt that has been extracted from them. These differences appear to be regional in extent. Peridotites from 34° to 45°N are the most refractory. The more intense depletion could have resulted from greater extents of partial melting, possibly caused by the presence of the Azores hotspot in this region; or it could be a pre-existing depletion, due to an earlier melting event. Basalt chemical data does not rule out either possibility, but supports greater extents of partial melting occurring in this region.The regional variations in mantle peridotite composition correlate with long-wavelength variations of crustal elevation and gravity along the northern Mid-Atlantic Ridge. These correlations support the existence of regional variations of upper mantle thermal structure and composition.Peridotites collected from fracture zones are compared with those collected away from fracture zones in the same region. Based on basalt studies, there may well be a decrease in the amount of melting as certain fracture zones are approached. The peridotite data suggest that this may be true for some fracture zones but not others. In general, peridotites collected from fracture zones are representative of the suboceanic mantle.     

Anisotropy and Flow in Pacific Subduction Zone Back-arcs

—We have obtained constraints on the strength and orientation of anisotropy in the mantle beneath the Tonga, southern Kuril, Japan, and Izu-Bonin subduction zones using shear-wave splitting in S phases from local earthquakes and in teleseismic core phases such as SKS. The observed splitting in all four subduction zones is consistent with a model in which the lower transition zone (520–660 km) and lower mantle are isotropic, and in which significant anisotropy occurs in the back-arc upper mantle. The upper transition zone (410–520 km) beneath the southern Kurils appears to contain weak anisotropy. The observed fast directions indicate that the geometry of back-arc strain in the upper mantle varies systematically across the western Pacific rim. Beneath Izu-Bonin and Tonga, fast directions are aligned with the azimuth of subducting Pacific plate motion and are parallel or sub-parallel to overriding plate extension. However, fast directions beneath the Japan Sea, western Honshu, and Sakhalin Island are highly oblique to subducting plate motion and parallel to present or past overriding plate shearing. Models of back-arc mantle flow that are driven by viscous coupling to local plate motions can reproduce the splitting observed in Tonga and Izu-Bonin, but further three-dimensional flow modeling is required to ascertain whether viscous plate coupling can explain the splitting observed in the southern Kurils and Japan. The fast directions in the southern Kurils and Japan may require strain in the back-arc mantle that is driven by regional or global patterns of mantle flow.     

The transport of water in subduction zones

The transport of water from subducting crust into the mantle is mainly dictated by the stability of hydrous minerals in subduction zones. The thermal structure of subduction zones is a key to dehydration of the subducting crust at different depths. Oceanic subduction zones show a large variation in the geotherm, but seismicity and arc volcanism are only prominent in cold subduction zones where geothermal gradients are low. In contrast, continental subduction zones have low geothermal gradients, resulting in metamorphism in cold subduction zones and the absence of arc volcanism during subduction. In very cold subduction zone where the geothermal gradient is very low(?5?C/km), lawsonite may carry water into great depths of ?300 km. In the hot subduction zone where the geothermal gradient is high(25?C/km), the subducting crust dehydrates significantly at shallow depths and may partially melt at depths of 80 km to form felsic melts, into which water is highly dissolved. In this case, only a minor amount of water can be transported into great depths. A number of intermediate modes are present between these two end-member dehydration modes, making subduction-zone dehydration various. Low-T/low-P hydrous minerals are not stable in warm subduction zones with increasing subduction depths and thus break down at forearc depths of ?60–80 km to release large amounts of water. In contrast, the low-T/low-P hydrous minerals are replaced by low-T/high-P hydrous minerals in cold subduction zones with increasing subduction depths, allowing the water to be transported to subarc depths of 80–160 km. In either case, dehydration reactions not only trigger seismicity in the subducting crust but also cause hydration of the mantle wedge. Nevertheless, there are still minor amounts of water to be transported by ultrahigh-pressure hydrous minerals and nominally anhydrous minerals into the deeper mantle. The mantle wedge overlying the subducting slab does not partially melt upon water influx for volcanic arc magmatism, but it is hydrated at first with the lowest temperature at the slab-mantle interface, several hundreds of degree lower than the wet solidus of hydrated peridotites. The hydrated peridotites may undergo partial melting upon heating at a later time. Therefore, the water flux from the subducting crust into the overlying mantle wedge does not trigger the volcanic arc magmatism immediately.     

Fluid/melt in continental deep subduction zones: Compositions and related geochemical fractionations

Plate subduction is the most magnificent process in the Earth. Subduction zones are important sites for proceeding matter- and energy- transports between the Earth's surface and the interior, continental crust growth, and crust-mantle interactions. Besides, a number of geological processes in subduction zones are closely related to human beings' daily life, such as volcanic eruptions and earthquakes, formation of mineral deposits. Subduction process thus has long been the centric topic of Earth sciences. The finding in 1980 s that continental crust could be subducted to mantle depths is a revolutionary progress in plate tectonic theory. Compared to oceanic crust, continental crust is colder, drier, lighter, and much more geochemically/isotopically heterogeneous. Hence, continental subduction process would affect the structure, compositions and evolutions of the overlying mantle wedge even more. During continental subduction and subsequent exhumation, fluids and melts can be generated in the(de)hydration process and partial melting process, respectively. These melts/fluids play important roles in crust-mantle interactions, elemental migrations, isotopic fractionations, and mantle metasomatism. By summarizing recent research works on subduction zones in this paper, we present a review on the types, physicochemical conditions and compositions of fluids/melts, as well as the migration behaviors of fluid-related characteristic elements(Nb-Ta-V) and the fractionation behaviors of non-traditional stable isotopes(Li-Mg) in subduction zones. The aim of this paper is to provide the readers an update comprehensive overview of the melt/fluid activities in subduction zones and of Li-Mg isotope systematics in subduction-related rocks and minerals.     

Source depletion and extent of melting in the Tongan sub-arc mantle

The fluid immobile High Field Strength Elements (HFSE) Nb and Ta can be used to distinguish between the effects of variable extents of melting and prior source depletion of the Tongan sub-arc mantle. Melting of spinel lherzolite beneath the Lau Basin back-arc spreading centres has the ability to fractionate Nb from Ta due to the greater compatibility of the latter in clinopyroxene. The identified spatial variation in plate velocities and separation of melt extraction zones, combined with extremely depleted lavas make Tonga an ideal setting in which to test models for arc melt generation and the role of back-arc magmatism.We present new data acquired by laser ablation-ICPMS of fused sample glasses produced without the use of a melt fluxing agent. The results show an arc trend towards strongly sub-chondritic Nb/Ta (< 17) with values as low as 7.2. Melting models show that large degree melts of depleted MORB mantle fail to reproduce the observed Nb/Ta. Alternatively, incorporation of residual back-arc mantle that has undergone less than 1% melting into the sub-arc melting regime reproduces arc values. However, the extent of partial melting required to produce the composition of the Lau Basin back-arc basalts averages 7%. This apparent discrepancy can be explained if only the lowermost 4 km of the residua from the mantle melt column beneath the back-arc is added to the source of arc magmas. We have identified that the degree of arc/back-arc coupling displayed in the rock record provides an index of the depth of hydrous melting beneath the arc. In this case, this would imply a depth of ~ 75 km for generation of arc magmas, indicating that hydrous melting in the mantle wedge is triggered by the breakdown of hydrous phases in the subducting slab.     

Velocity structure of the crust and upper mantle in Xingtai earthquake region and its adjacent area

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Late Cenozoic fields of the tectonic stresses in Western and Central Mongolia

The paper addresses the Late Cenozoic fault tectonics and the stress state of the Earth’s crust within the Mongolian microplate, embracing Central and Western Mongolia. We analyze the results of reconstructing the stress fields and the tectonic deformations in the zones of active faulting, located at the uplands and in the intermountain trenches, which bound the microplate (Mongolian Altai; Gobi Altai; Dolinoozersk trough; Khan-Taishir-Nuruu, Khan-Houkhei, and Bolnai uplands) and the Khangai dome. Deformations related with the northeastern general-scale collisional compression are concentrated along the periphery of the Mongolian microplate, and the maximum compression is focused on its western and southern boundaries, thus forming the right- and the left-lateral transpressive structures of the Mongolian and Gobi Altai. The deformations associated with the shortening of the Earth’s crust involve not only the mountain ridges framing the block, but also the intermountain troughs that separate the Gobi and Mongolian Altai from the Khangai dome, and the southern portion of the Khangai Uplift. The diversity in the deformations within the central Khengai region ensues from the coupling of tension caused by the dynamical impact of the mantle anomaly, which is located east of 100°E, with a regional NE compression. Owing to the relatively rigid Khangai block, the deformations are transferred to the northern bound of this structure, namely the seismically active North Khangai fault. The role of compression increases to the west of the zone, where it conjugates with the transpressive structures of the Mongolian Altai. The tension becomes more important in the western part of this zone where the releasing bends are formed. A region characterized by extra tension is localized also to the east of 100° E. In terms of the gradient in the lithosphere thickness and the structure types of the upper crust, the submeridional line running along 100°E is interpreted as the key interblock boundary.     

Large strain deformation studies using polycrystalline magnesium as a rock analogue. Part I: grain size paleopiezometry in mylonite zones

The results of large strain deformation studies of polycrystalline magnesium are reported. Shear zones develop at temperatures below 0.65 Tm for strain rates between 10^?4?10^?5 s^?1. The zones are characterised by small recrystallised grains and are analogues of mylonite zones in crustal and mantle rocks. Their development is marked by a stress drop but the recrystallised grains in the zones do not re-equilibrate and remain equilibrated to the peak stress. However, the recrystallised grains in the areas bordering the shear zones undergo a strain dependent coarsening and their sizes re-equilibrate to the relaxed stresses at natural strains of 1. The geological implications of these results are discussed.     

Characteristics of mantle degassing and deep-seated geological structures in different typical fault zones of China

Large-scale fault zones play an important role in controlling and adjusting all kinds of geological proc-esses,such as deposition,magmatism,metamorphism,metallogenesis,tectonic stress field,tectonic deforma-tion,even the movement of geological massifs,earth-quakes,and they also are the key to solving geological problems concerned,especially regional and even global structures.Due to their special geological tec-tonic significance,they are one of the main research fields of tectonic geology and …     

地幔柱与岩石圈相互作用过程中熔融问题的数值模拟

地幔柱是最可能形成大火成岩省的原因之一,同时地幔柱与岩石圈的相互作用也极大的影响着岩石圈的构造演化.本文主要集中研究地幔柱与岩石圈相互作用过程中熔融相关的问题.利用开源程序Ellipsis3D,基于质量守恒方程、动量守恒方程、能量守恒方程和岩石流变本构关系,以及不同的熔融损耗关系,通过有限元数值方法模拟得到地幔柱与岩石圈相互作用过程中熔融程度的动态变化.数值模拟结果显示,地幔柱与岩石圈相互作用的熔融相关过程分为三个阶段：地幔柱的初融阶段,地幔柱自身熔融占主导,减压熔融为主因;地幔柱与岩石圈的纵向作用阶段,岩石圈地幔开始熔融,地幔柱以减压熔融为主,岩石圈地幔以升温熔融为主;地幔柱的横向展平阶段,随着地幔柱的扩展岩石圈地幔熔融范围增加,以升温熔融为主,地幔柱自身熔融程度减小.最后基于数值模拟结果及现场资料对峨嵋山大火成岩省地幔柱的发展演化以及峨眉山大火成岩省的形成进行了讨论.