大陆下地壳流动:渠流还是层流?

大量的地质、地球物理、地球化学、实验和模拟资料证明大陆岩石圈存在壳内流层,目前创建了渠流和层流两种假说来解释大陆下地壳的流动规律和流动机理。渠流模式是指厚地壳、高地势的造山带或高原中、下地壳低粘度物质在地貌负荷的侧向压力梯度或剥蚀作用驱动下从山根向外侧向扩张。笔者在研究青藏高原的基础上于1992年提出的层流模式是指在大陆边缘俯冲板片脱水熔融和大陆内部地幔柱(枝)底辟上隆的热动力及其相关的重力驱动下的盆山地壳物质循环系统,盆地热软化下地壳物质在重力作用下顺层流向相邻的山根,盆地地壳减薄,造山带地壳加厚,加厚的下地壳部分熔融物质带动深层变质岩向上运动,热-重力派生的垂直主应力形成热隆伸展的变质核杂岩和低角度拆离断层,隆升的山体在重力势能作用下侧向扩张,盆山边界形成逆冲推覆和滑覆构造,同时遭受强烈的剥蚀作用,造山带源粗碎屑沉积物快速堆积在盆缘受下地壳拖曳的壳内有限俯冲坳陷带内。渠流构造和层流构造在大陆板内变形、中下地壳韧性挤出、造山带的挤压和伸展同步转换、中深变质岩的韧性变形及剥露过程、部分熔融及岩浆活动等方面存在相似之处,但是,在发育背景、产出部位、流层边界、流层规模、流动型式、流动体制、流动方向、流动物质、流动效应、流动时间、驱动力等方面存在本质的差异。渠流构造基本上可作为层流构造时空结构中的一个组成部分,层流的驱动力是热能和重力,而不是地表剥蚀作用和山体负荷作用。从全球角度来看,层流只是地球多级物质循环流动系统的一个组成部分。     

关于现代海底热液活动系统模式的思考

现代海底热液活动往往与岩浆作用相伴生.传统的热液系统循环模式认为:海水沿裂隙（通道）下渗,被加热并与围岩发生水岩反应,萃取岩石中的金属元素,形成热液流体并上涌喷出海底,沉积生成多金属硫化物矿体.这一模式合理地解释了构成现代海底热液系统的3个基本要素:流体、通道和热源,与我们现今条件下所观察到的许多事实相吻合.然而,基岩渗透率、热液流体性质、热液生态系统和热液产物上的差异表明现代海底热液活动系统可能存在另一种注入式循环模式,即热液流体来自深部岩浆房流体和挥发性组分的直接注入.据此提出现代海底热液活动系统可能存在两种模式:一种是浅层循环模式,即传统的热液循环模式;另一种是岩浆后期热液注入模式（简称"注入模式"）.在岩浆作用强烈和构造裂隙发育的环境中,两种模式可能同时存在,形成双扩散对流循环模式.双扩散对流循环模式可以很好地解释现代海底热液活动研究中近期所发现的多种现象和事实.对弧后盆地而言,在研究其岩浆作用与热液活动时,还要考虑板块俯冲的构造背景和俯冲组分及陆壳组分加入等因素,同时构建了适用于弧后盆地海底热液活动系统的理论模型.      

俯冲带部分熔融

俯冲带是地幔对流环的下沉翼,是地球内部的重要物理与化学系统。俯冲带具有比周围地幔更低的温度,因此,一般认为俯冲板片并不会发生部分熔融,而是脱水导致上覆地幔楔发生部分熔融。但是,也有研究认为,在水化的洋壳俯冲过程中可以发生部分熔融。特别是在下列情况下,俯冲洋壳的部分熔融是俯冲带岩浆作用的重要方式。年轻的大洋岩石圈发生低角度缓慢俯冲时,洋壳物质可以发生饱和水或脱水熔融,基性岩部分熔融形成埃达克岩。太古代的俯冲带很可能具有与年轻大洋岩石圈俯冲带类似的热结构,俯冲的洋壳板片部分熔融可以形成英云闪长岩-奥长花岗岩-花岗闪长岩。平俯冲大洋高原中的基性岩可以发生部分熔融产生埃达克岩。扩张洋中脊俯冲可以导致板片窗边缘的洋壳部分熔融形成埃达克岩。与俯冲洋壳相比,俯冲的大陆地壳具有很低的水含量,较难发生部分熔融,但在超高压变质陆壳岩石的折返过程中可以经历广泛的脱水熔融。超高压变质岩在地幔深部熔融形成的熔体与地幔相互作用是碰撞造山带富钾岩浆岩的可能成因机制。碰撞造山带的加厚下地壳可经历长期的高温与高压变质和脱水熔融,形成S型花岗岩和埃达克质岩石。     

流体输运,化学反应与交代作用

在成矿及变质作用过程中， 体运移促使热量发生传输及周围岩石发生化学反应和交代作用。流体输过一化学反应耦合动力学方程能定量评价热液系统组分浓度、温度和流量函数的人演化，对于区域变质和交代韧性断裂带等变质系统，还可通过流体运称方向和时间积分流体能量来定量描述流体输运一化学反应耦合客观变持地体中水力破裂的形成与流体运移和失挥发分反应耦合过程有关。     

Cretaceous crustal thinning in North Africa: Implications for magmatic and thermal events in the Eastern Tunisian margin and the Pelagic Sea

The integrated use of geological, geophysical, and geochemical data from Eastern Tunisia onshore and offshore samples indicate a crustal thinning induced from the Tethyan rifting. This is responsible for the subsequent evolution of the North African passive margin during the Late Cretaceous, and the creation of the fold–thrust belt and associated foreland deformations. This thinned crust was an area of mantle upwelling that favoured the increase of isotherms, the uprise of basalt magma, and the circulation of hydrothermal fluids. The Cretaceous magmatism generated a major hydrothermal event characterised by the circulation of hot fluids along faults and a relatively high heat flow in the basin. Temperature elevation and hydrothermal conditions led to alteration of basalts and generated a new mineral equilibrium around the enclosing sedimentary deposits.     

Cretaceous crustal thinning in North Africa: Implications for magmatic and thermal events in the Eastern Tunisian margin and the Pelagic Sea

The integrated use of geological, geophysical, and geochemical data from Eastern Tunisia onshore and offshore samples indicate a crustal thinning induced from the Tethyan rifting. This is responsible for the subsequent evolution of the North African passive margin during the Late Cretaceous, and the creation of the fold–thrust belt and associated foreland deformations. This thinned crust was an area of mantle upwelling that favoured the increase of isotherms, the uprise of basalt magma, and the circulation of hydrothermal fluids. The Cretaceous magmatism generated a major hydrothermal event characterised by the circulation of hot fluids along faults and a relatively high heat flow in the basin. Temperature elevation and hydrothermal conditions led to alteration of basalts and generated a new mineral equilibrium around the enclosing sedimentary deposits.     

Topography of the Variscan orogen in Europe: failed–not collapsed

The Variscan orogenic collage consists of three subduction-collision systems (Rheno-Hercynian, Saxo-Thuringian and Massif Central-Moldanubian). Devonian to early Carboniferous marine strata are widespread not only in the individual foreland fold and thrust belts, but also in post-tectonic basins within these foreland belts and on the Cadomian crust of peri-Gondwanan microcontinental fragments, which represent the upper plates of the subduction/collision zones. These marine basins preclude high elevations in the respective areas and also in their neighbourhood. Widespread late Carboniferous intra-montane basins with their coal-bearing sequences are likewise incompatible with high and dry plateaus. While narrow belts with high elevations remain possible along active margins within the orogen, comparison of the Variscides with the Himalaya/Tibetan plateau is unfounded. Plausible reasons for the scarcity of high Variscan relief include subduction of oceanic and even continental crust, subduction erosion, orogen-parallel extension and—most important—lithospheric thinning accompanied by high heat flow and magmatism. In many areas, timing and areal array of magmatism and HT metamorphism are not compatible with a model of tectonic thickening and subsequent gravitational collapse. It is suggested, instead, that lithospheric thinning and heating are due to mantle activities caused by the Tethys rift. The lower and middle crust were thermally softened and rendered unfit for stacking and isostatic uplift: in terms of topography, the Variscides represent a failed orogen. The HT regime also explains the abundance of granitoids and HT/LP metamorphic rocks typical of the Variscides. Melting in the HT regime extracted mafic components from Variscan and Cadomian crust as well as from Cadomian metasomatized lithospheric mantle, thus mimicking subduction-related magmatism. The onset of the HT regime at c. 340 Ma may also have triggered the final ascent of HP/UHP felsic metamorphic rocks.     

造山过程中的流体—岩石相互作用和质量传输的评述

在汇聚板块边缘,滑脱面的滑动和沉积岩系的逆冲堆叠,导致孔隙水被压实排出,流体润滑了脱面,从而引起增生楔的生长。流体对流体制是地壳深熔的先驱事件。碱性花岗岩在次固相下有丰富的岩浆水的出溶,并且促进了碱性长石的微组构重组织。上部地壳浅表流体的循环主要受岩浆侵位驱动。韧性剪切带Ｔｉ、Ｆｅ、Ｍｇ残留富集,Ｓｉ、Ｃａ、Ｓｒ带出,流体不混溶和相分离是Ａｕ沉淀的重要机制。断层带尤其深部断层带具有高的流体／岩石比     

3D numerical modelling of fluid flow in the Val-d’Or orogenic gold district: major crustal shear zones drain fluids from overpressured vein fields

Fluid flow patterns have been determined using oxygen isotope isopleths in the Val-d’Or orogenic gold district. 3D numerical modelling of fluid flow and oxygen isotope exchange in the vein field shows that the fluid flow patterns can be reproduced if the lower boundary of the model is permeable, which represents middle or lower crustal rocks that are infiltrated by a metamorphic fluid generated at deeper levels. This boundary condition implies that the major crustal faults so conspicuous in vein fields do not act as the only major channel for upward fluid flow. The upper model boundary is impermeable except along the trace of major crustal faults where fluids are allowed to drain out of the vein field. This upper impermeable boundary condition represents a low-permeability layer in the crust that separates the overpressured fluid from the overlying hydrostatic fluid pressure regime. We propose that the role of major crustal faults in overpressured vein fields, independent of tectonic setting, is to drain hydrothermal fluids out of the vein field along a breach across an impermeable layer higher in the crust and above the vein field. This breach is crucial to allow flow out of the vein field and accumulation of metals in the fractures, and this breach has major implications for exploration for mineral resources. We propose that tectonic events that cause episodic metamorphic dehydration create a short-lived pulse of metamorphic fluid to rise along zones of transient permeability. This results in a fluid wave that propagates upward carrying metals to the mineralized area. Earthquakes along crustal shear zones cause dilation near jogs that draw fluids and deposit metals in an interconnected network of subsidiary shear zones. Fluid flow is arrested by an impermeable barrier separating the hydrostatic and lithostatic fluid pressure regimes. Fluids flow through the evolving and interconnected network of shear zones and by advection through the rock matrix. Episodic breaches in the impermeable barrier along the crustal shear zones allow fluid flow out of the vein field.     

变质核杂岩与岩浆作用成因关系综述

对岩浆与伸展作用的关系、伸展作用中岩浆的成因和需加强的工作进行了讨论,并重点论述了变质核杂岩形成机制与侵入作用的关系。在造山带重力势能差和深部作用等各种因素导致的拉伸应力场作用下,岩石圈地幔和地壳通过减压或深部热活动发生部分熔融而形成岩浆,岩浆的上涌强化了地壳伸展,对地壳的弱化作用触发伸展构造的发生。岩浆作用是变质核杂岩形成的主导因素之一,其主要包括对地壳的加热、弱化导致拆离断层的形成及由其浮力和密度产生不均一隆升而形成穹隆。     

Copper‐gold mineralisation in New Guinea: Numerical modelling of collision,fluid flow and intrusion‐related hydrothermal systems

Two‐ and three‐dimensional numerical modelling techniques, constrained by key geodynamic data, provide insights into the controls on development of porphyry‐related Cu–Au mineralisation in the Tertiary collision zone of New Guinea. Modelling shows that the creation of local dilation to facilitate magma emplacement can be caused by reactivation of arc‐normal transfer faults, where they cut the weakened fold belt. Additionally, dilation occurs where fluid overpressuring is caused by collision‐related, south‐directed fluid flow being localised into the more permeable units of the Mesozoic passive‐margin sedimentary succession. Rapid uplift and erosion, which may be a mechanism for magmatic fluid release in these systems, is shown to be greatest in the west of West Papua, where the stronger Australian crust acts as a buttress. Within the Papuan Fold Belt, uplift is greatest near the margins, where the weaker fold belt abuts the stronger crust and/or major faults have been reactivated. Increased orographically induced precipitation and erosion exposes the lower parts of the stratigraphy within or on the margins of these uplifted zones. On a smaller scale, 2–D coupled fluid‐flow ‐ thermal‐chemical modelling uses a scenario of fluid mixing to calculate metal precipitation distribution and magnitude around an individual intrusive complex. Modelling highlights the interdependence of the spatial permeability structure, the regional temperature gradient, and the geometry of the convection cells and how this impacts on the distribution of metal precipitation.     

冀东长城式金矿成矿中一些问题的初步探讨

长城式金矿主要受长城系岩石层间角砾岩破碎带,褐铁矿化和有机质（碳）含量控制,与岩石层位和性质无关。成矿热液可能是在伸展构造体系的控制下,超糜棱岩化变质作用衍生的变货流体或溶熔岩浆作用衍生的岩浆热液流体,在构造动力驱动下上升至盖层破碎带与天水混合的产物。它们在白云岩破碎带中渗流形成碳质含矿热液;在碎屑岩破碎带中渗流形成硅质含矿热液。     

Middle Archean ocean ridge hydrothermal metamorphism and alteration recorded in the Cleaverville area, Pilbara Craton, Western Australia

A hydrothermally metamorphosed greenstone complex, capped by bedded cherts and banded iron formations (BIFs), is exposed in the Cleaverville area, Pilbara Craton, Western Australia. It has been interpreted as an accretionary complex characterized by both a duplex structure and an oceanic plate stratigraphy, and is shown to represent a 3.2 Ga upper oceanic crust. Three metamorphic zones are identified in the basaltic greenstones. The metamorphic grade increases from sub-greenschist facies (zones A and B) to greenschist facies (zone C) under low-pressure conditions. The boundaries between three mineral zones are subparallel to the bedding plane of overlying chert/BIF, and metamorphic temperature increases stratigraphically downward. The zones correspond to the thermal structure of ocean-floor metamorphism, at a mid-ocean ridge.
The uppermost greenstone in the study area is more pervasively altered and carbonatized than the modern upper oceanic crust. This indicates the enrichment of CO₂ in the metamorphic fluid by which widespread formation of carbonate occurred, compared with a narrow stability region of Ca-Al silicates. It is, therefore, suggested that the Archean hydrothermal alteration played a more important role in fixation of CO₂ than present-day ocean-ridge hydrothermal alteration, as an interaction between sea water and oceanic crust.     

Convergence in a thermally softened thick crust: Variscan intracontinental tectonics in Iberian plate rocks

The subduction phase in the development of the Variscan Orogen in SW Europe was followed by an extended period of ‘intracontinental’ tectonics. The progressive temperature rise in the hinterland during plate convergence was accompanied by widespread partial melting in the lower crust and the nucleation of kilometric buckle folds and crustal‐scale shear zones in the stronger upper crust. Thermal mechanical weakening in the core of the orogen was contemporaneous with shortening and thickening in the foreland fold‐and‐thrust belt. We evaluate lithospheric strength profiles in the hinterland and foreland based on the metamorphic and structural record for three tectonic stages. We find that lower crustal strength varied in space as well as in time during orogenesis. Strength contrasts between the foreland and the hot hinterland during convergence may have led to the additional indentation of the foreland into the hinterland of the Ibero‐Armorican Arc.     

Magmatism at continental passive margins inferred from Ambient‐Noise Phase‐velocity in the Gulf of Aden

Non‐volcanic continental passive margins have traditionally been considered to be tectonically and magmatically inactive once continental breakup has occurred and seafloor spreading has commenced. We use ambient‐noise tomography to constrain Rayleigh‐wave phase‐velocity maps beneath the eastern Gulf of Aden (eastern Yemen and southern Oman). In the crust, we image low velocities beneath the Jiza‐Qamar (Yemen) and Ashawq‐Salalah (Oman) basins, likely caused by the presence of partial melt associated with magmatic plumbing systems beneath the rifted margin. Our results provide strong evidence that magma intrusion persists after breakup, modifying the composition and thermal structure of the continental margin. The coincidence between zones of crustal intrusion and steep gradients in lithospheric thinning, as well as with transform faults, suggests that magmatism post‐breakup may be driven by small‐scale convection and enhanced by edge‐driven flow at the juxtaposition of lithosphere of varying thickness and thermal age.     

Tectonically driven fluid flow and gold mineralisation in active collisional orogenic belts: comparison between New Zealand and western Himalaya

Hydrothermal activity and mesothermal-styled gold mineralisation occurs near the main topographic divide of most active or young collisional mountain belts. The Southern Alps of New Zealand is used in this study as a model for the mineralising processes. The collisional tectonics results in a two-sided wedge-shaped orogen into which rock is transported horizontally. Upper crustal rocks pass through the orogen and leave the orogen by erosion, whereas lower crustal rocks are deformed into the mountain roots. High relief drives meteoric water flow to near the brittle–ductile transition. Lower to upper greenschist facies metamorphic reactions, driven by deformation at the crustal decollement and in the root, release water-rich fluids that rise through the orogen. Intimate chemical interaction between fluid and rock results in dissolution and later precipitation of gold, arsenic and sulphur. Fluid flow and mineralisation in the topographic divide region is facilitated by a network of steeply dipping faults and associated rock damage zones where oblique strike-slip faults intersect the thrust faults that strike subparallel to the main mountain range.The Nanga Parbat massif of the western Himalaya is an example of an active collisional zone which hosts hydrothermal activity but no gold mineralisation. The lack of gold mineralisation is due to the following factors: CO₂-dominated rising metamorphic fluid in dehydrated amphibolite-granulite facies metamorphic rocks does not dissolve gold and arsenic; hot (up to 400 °C) meteoric water confined to fractures in the gneiss limits dissolution of gold and arsenic; low density of hot water/dry steam, and low reduced sulphur content of fluid, restrict solubility of gold and arsenic; absence of fracture networks in the core of the massif and the small volumes of circulating fluid limit metal concentration; and lack of reactive rock compositions limits chemically mediated metal deposition.     

Oxygen isotope geochemistry of the Omeo Metamorphic Complex,Victoria: Implications for metamorphic fluid flow,mineralisation and anatexis

Metamorphosed turbidites from the Omeo Metamorphic Complex show only minor changes in δ¹⁸O values with increasing metamorphic grade from 13.4 ± 1.7% in the chlorite and biotite zones to 12.3 ± 1.0% in the sillimanite + K‐feldspar zone. Rocks within 5 km of the S‐type granite at Hume Dam have δ¹⁸O values of 6.8–8.1% that probably reflect interaction with heated meteoric‐igneous fluids. Interaction with igneous fluids has also occurred close to other I‐ and S‐type granites in this region. However, pervasive metamorphic fluid‐rock interaction in this terrain did not occur, which limits the region's potential for hydrothermal mineralisation. Anatexis at high grades was probably via dehydration‐melting reactions that consumed muscovite and biotite, which is consistent with there being little fluid present during metamorphism. Small (kilometre scale or less) S‐type granites in the sillimanite + K‐feldspar zone have δ¹⁸O values similar to those of the surrounding metasediments and probably formed by melting of those rocks. By contrast, larger (tens of kilometres scale) Ca‐rich, peraluminous, S‐type granites have lower δ¹⁸O values than the surrounding metasediments, and may represent melts of underlying middle to lower crust.     

Crustal thickening and lateral flow during compression of hot lithospheres,with particular reference to Precambrian times

Many ancient deformation belts, especially of Archean and Palaeoproterozoic age, show large areas marked by primary flat‐lying fabrics associated with rather monotonous metamorphic conditions of HTLP type and affected by steep transpressive zones involving vertical stretch. These features do not support strain localization along large‐scale thrusts and (or) extensional detachments, as common in modern orogens. Instead, they are consistent with hot and weak lithospheres where gravity‐driven horizontal flow may compete with distributed thickening from early stages of collisional processes. Relevant deformation features are reviewed and highlighted by lithosphere‐scale analogue models involving low‐viscosity lower crust and sub‐Moho mantle. Both nature and models argue that compression of such lithospheres may induce combined distributed thickening and lateral channel flow of the ductile crust accommodated by transpressive zones.     

Gliding and overthrust nappe tectonics in the Barberton Greenstone Belt

Regional recumbent folds, inverted stratigraphy, nappes and olistostromes are described from the southern part of the 3.3–3.5 Ga Barberton Greenstone Belt. Overthrusting of thin rigid silicified slabs with minimum dimensions of 25 km² and up to 500 m in thickness, occurred over minimum distances of 86 km. More ductile and coherent units were overfolded up to at least 2 km during their emplacement. The glide planes on which these nappes travelled were zones of high fluid pressures related to hydrothermal fluid circulation patterns, driven by heat sources from igneous intrusions. The upwelling areas of the geothermal convection cells were sites of mud-pools and hydrothermal vents which may mark the trailing edges (pull aparts) of the overthrust units. Progressive silica and carbonate precipitation due to decreasing temperatures, within the zones of fluid migration distant from the areas of high heat flow, probably acted as built-in braking systems below the travelling slabs. Active sedimentation and metasomatism during this tectonism indicates a protracted history for the evolution of the greenstone belt. The recognition of nappe and overthrust tectonics in the Barberton Belt, processes which may have been commonplace in Archaean terrains, necessitates a re-evaluation of the stratigraphy of this belt.     

成矿热液分类兼论岩浆热液的成矿效率

根据流体中H2O、CO2、NaCl三组分的相对含量,结合H2O-NaCl体系临界压力和石盐融化曲线温度,可以将地壳中的成矿流体分为5类：大气降水、海水、盆地卤水、变质流体和岩浆流体。这种基于地壳环境中普遍存在的三元系结合流体临界性和石盐融化温度的分类,对于理解地壳中沿地温地压梯度流动流体的多样性和流体混合与不混溶具有重...