Journal articles on the topic 'Magma emplacement'
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Dickson, F. W. "Chemical emplacement of magma." Journal of Geodynamics 30, no. 4 (November 2000): 475–87. http://dx.doi.org/10.1016/s0264-3707(00)00003-x.
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Paterson, Scott R., T. Kenneth Fowler, and Robert B. Miller. "Pluton emplacement in arcs: a crustal-scale exchange process." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 87, no. 1-2 (1996): 115–23. http://dx.doi.org/10.1017/s0263593300006532.
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ABSTRACT:Buddington (1959) pointed out that the construction of large crustal magma chambers involves complex internal processes as well as multiple country rock material transfer processes (MTPs), which reflect large horizontal, vertical and temporal gradients in physical conditions. Thus, we have attempted to determine the relative importance of different magmatic and country rock MTPs at various crustal depths, and whether country rock MTPs largely transport material vertically or horizontally, rather than seeking a single model of magma ascent and emplacement.Partially preserved roofs of nine plutons and in some cases roof–wall transitions with roof emplacement depths of 1·5–11 km were mapped. During emplacement, these roofs were not deformed in a ductile manner, detached or extended by faults, or significantly uplifted. Instead, sharp, irregular, discordant contacts are the rule with stoped blocks often preserved immediately below the roof, even at depths of 10 km. The upper portions of these magma chambers are varied, sometimes preserving the crests of more evolved magmas or local zones of volatile-rich phases and complex zones of dyking and magma mingling. Magmatic structures near roofs display a wide variety of patterns and generally formed after emplacement. Transitions from gently dipping roofs to steep walls are abrupt. At shallow crustal levels, steep wall contacts have sharp, discordant, stepped patterns with locally preserved stoped blocks indicating that the chamber grew sideways in part by stoping. Around deeper plutons, an abrupt transition (sometimes within hundreds of metres) occurs in the country rock from discordant, brittle roofs to moderately concordant, walls deformed in a ductile manner defining narrow structural aureoles. Brittle or ductile faults are not present at roof–wall joins.Near steep wall contacts at shallow to mid-crustal depths (5–15 km), vertical and horizontal deflections of pre-emplacement markers (e.g. bedding, faults, dykes), and ductile strains in narrow aureoles (0·1–0·3 body radii) give a complete range of bulk strain values that account for 0–100% of the needed space, but average around 30%, or less, particularly for larger batholiths. A lack of far-field deflection of these same markers rules out significant horizontal displacement outside the aureoles and requires that any near-field lateral shortening is accommodated by vertical flow. Lateral variations from ductile (inner aureole) to brittle (outer aureole) MTPs are typically observed. Compositional zoning is widespread within these magma bodies and is thought to represent separately evolved pulses that travelled up the same magma plumbing system. Magmatic foliations and lineations commonly cross-cut contacts between pulses and reflect the strain caused either by the late flow of melt or regional deformation.Country rocks near the few examined mid- to deep crustal walls (10–30 km) are extensively deformed, with both discordant and concordant contacts present; however, the distinction between regional and emplacement-related deformation is less clear than for shallower plutons. Internal sheeting is more common, although elliptical masses are present. Lateral compositional variations are as large as vertical variations at shallower depths and occur over shorter distances. Magmatic foliations and lineations often reflect regional deformation rather than emplacement processes.The lack of evidence for horizontal displacement outside the narrow, shallow to mid-crustal aureoles and the lack of lateral or upwards displacement of pluton roofs indicate that during emplacement most country rock is transported downwards in the region now occupied by the magma body and its aureole. The internal sheeting and zoning indicate that during the downwards flow of country rock, multiple pulses of magma travelled up the same magma system. If these relationships are widespread in arcs, magma emplacement is the driving mechanism for a huge crustal-scale exchange process.
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Clemens, J. D., P. A. Helps, and G. Stevens. "Chemical structure in granitic magmas – a signal from the source?" Earth and Environmental Science Transactions of the Royal Society of Edinburgh 100, no. 1-2 (March 2009): 159–72. http://dx.doi.org/10.1017/s1755691009016053.
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ABSTRACTThough typically exhibiting considerable scatter, geochemical variations in granitic plutons and silicic volcanic deposits are commonly modelled as products of differentiation of originally homogeneous magmas. However, many silicic igneous bodies, particularly those classified as S-types, are internally heterogeneous in their mineralogy, geochemistry and isotope ratios, on scales from hundreds of metres down to one metre or less. The preservation of these heterogeneities supports recent models for the construction of granitic magma bodies through incremental additions of numerous batches (pulses) of magma derived from contrasting sources. Such pulses result from the sequential nature of the melting reactions and the commonly layered structure of crustal magma sources. Internal differentiation of these batches occurs, but not generally on the scales of whole magma chambers. Rather than being created through differentiation or hybridisation processes, at or near emplacement levels, much of the variation within such bodies (e.g. trace-element or Mg# variation with SiO2 or isotope ratios) is a primary or near-source feature. At emplacement levels, the relatively high magma viscosities and slow diffusion rates of many chemical components in silicic melts probably inhibit processes that would lead to homogenisation. This permits at least partial preservation of the primary heterogeneities.
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Koukouvelas, I., G. Pe-Piper, and D. J. W. Piper. "Pluton emplacement by wall-rock thrusting, hanging-wall translation and extensional collapse: latest Devonian plutons of the Cobequid fault zone, Nova Scotia, Canada." Geological Magazine 133, no. 3 (May 1996): 285–98. http://dx.doi.org/10.1017/s001675680000902x.
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AbstractLatest Devonian A-type granite-gabbro plutons, in part ductilely deformed, are spatially associated with the strike-slip Cobequid fault zone. The youngest intrusions are close to the Cobequid fault zone, which was the main conduit for magma. Two phases of deformation accompanying magma emplacement are recognized. Early magmas intruded ductile rocks during left-lateral oblique thrust movements. A second stage of right-lateral oblique slip normal faulting accommodated uplift of the plutons when coarse granite was emplaced in the crestal regions. Cross-cutting late stage porphyries, granitic clasts in marginal basins cut by granitic dykes, and superposition of brittle on ductile structures all indicate rapid uplift of the plutons. The geometry of the Cobequid fault zone shows that pluton emplacement was not the result of extension in releasing bends during transcurrent shear. Rather, flower-structure high-angle faults acted as magma conduits and space was created by two processes: translation of wall rocks along thrust faults at depth, developing space away from the master fault zone and backward collapse of the uplifted magma chamber creating space towards the fault zone.
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Menand, Thierry, Michel de Saint-Blanquat, and Catherine Annen. "Emplacement of magma pulses and growth of magma bodies." Tectonophysics 500, no. 1-4 (March 2011): 1–2. http://dx.doi.org/10.1016/j.tecto.2010.05.014.
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Hutton, Donald H. W. "Granite emplacement mechanisms and tectonic controls: inferences from deformation studies." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 79, no. 2-3 (1988): 245–55. http://dx.doi.org/10.1017/s0263593300014255.
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ABSTRACTThis paper is a structural and tectonic approach to the emplacement and deformation of granitoids. The main methods available in structural geology are briefly reviewed and this emphasises that (a) a wealth of data, particularly strain and shear sense, which pertain to these problems, can be determined in and around plutons; (b) given the nature, unlike many other crustal rock types, of granites to crystallise from isotropic through weakly anisotropic crystal suspension fluids, that deformation which has occurred in these states may not be well preserved; and (c) it is entirely possible, using this methodology, to separate deformation resulting from externally originating tectonic stresses from that which is associated with internal magma-related stresses. It is also recommended that the genetically-based Cloosian classification of granite fabrics and structures into “primary” (magmatic flow/magmatic flow current) and “secondary”, be abandoned and that a more observationally-based approach which classifies granite deformation fabrics and structures according to their time of occurrence relative to the crystallisation state of the congealing magma, be adopted (i.e. pre-full crystallisation deformation and crystal plastic strain deformation).Examples of recent, structurally based, studies of emplacement mechanisms of plutons within tectonic settings are described and these show that, in general, space for magma can be created by the combination of tectonically-created cavities and internal magma-related buoyancy. This occurs in both transcurrent and extensional tectonic settings and there is no reason to doubt that it can happen in compressive-contractional regimes. It is concluded that transient and permanent space creation, such as may be exploited by available magmas, is a typical feature of the tectonically stressed and deforming lithosphere and this, in combination with the natural buoyancy and ascending tendency of magmas, can generate the varied emplacement mechanisms of granites.
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Hogan, John P., M. Charles Gilbert, and Jon D. Price. "Crystallisation of fine- and coarse-grained A-type granite sheets of the Southern Oklahoma Aulacogen, U.S.A." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no. 1-2 (2000): 139–50. http://dx.doi.org/10.1017/s0263593300007331.
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A-type felsic magmatism associated with the Cambrian Southern Oklahoma Aulacogen began with eruption of voluminous rhyolite to form a thick volcanic carapace on top of an eroded layered mafic complex. This angular unconformity became a crustal magma trap and was the locus for emplacement of later subvolcanic plutons. Rising felsic magma batches ponding along this crustal magma trap crystallised first as fine-grained granite sheets and then subsequently as coarser-grained granite sheets. Aplite dykes, pegmatite dykes and porphyries are common within the younger coarser-grained granite sheets but rare to absent within the older fine-grained granite sheets. The older fine-grained granite sheets typically contain abundant granophyre.The differences between fine-grained and coarse-grained granite sheets can largely be attributed to a progressive increase in the depth of the crustal magma trap as the aulacogen evolved. At low pressures (<200MPa) a small increase in the depth of emplacement results in a dramatic increase in the solubility of H2O in felsic magmas. This is a direct consequence of the shape of the H2O-saturated granite solidus. The effect of this slight increase in total pressure on the crystallisation of felsic magmas is to delay vapour saturation, increase the H2O content of the residual melt fractions and further depress the solidus temperature. Higher melt H2O contents, and an extended temperature range over which crystallisation can proceed, both favour crystallisation of coarser-grained granites. In addition, the potential for the development of late, H2O-rich, melt fractions is significantly enhanced. Upon reaching vapour saturation, these late melt fractions are likely to form porphyries, aplite dykes and pegmatite dykes.For the Southern Oklahoma Aulacogen, the progressive increase in the depth of the crustal magma trap at the base of the volcanic pile appears to reflect thickening of the volcanic pile during rifting, but may also reflect emplacement of earlier granite sheets. Thus, the change in textural characteristics of granite sheets of the Wichita Granite Group may hold considerable promise as an avenue for further investigation in interpreting the history of this rifting event.
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Wilson, Penelope I. R., Ken J. W. McCaffrey, and Robert E. Holdsworth. "Magma-driven accommodation structures formed during sill emplacement at shallow crustal depths: The Maiden Creek sill, Henry Mountains, Utah." Geosphere 15, no. 4 (June 24, 2019): 1368–92. http://dx.doi.org/10.1130/ges02067.1.
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Abstract In areas of exceptional exposure, upper-crustal intrusions and their immediate wall rocks commonly preserve direct evidence of the emplacement, magma flow pathways, and strains associated with the intrusion process. Such excellent exposure is displayed by the Paleogene Maiden Creek intrusion—a small satellite body related to the Mount Hillers intrusive complex, Henry Mountains, Utah. An intermediate plagioclase-hornblende porphyritic magma was intruded into the Entrada Sandstone Formation at an estimated depth of ∼3 km. The southern part of the intrusion is overlain by the newly identified Maiden Creek shear zone (MCSZ): a subhorizontal, top-to-the-WNW detachment formed at the contact with the overlying sandstone country rocks. From observations of both syn-emplacement deformation and the exposed intrusion geometries, it is proposed that the southern Maiden Creek intrusion comprises westerly derived, inclined sill sheets. Host-rock sandstones were sandwiched (∼E–W constriction) between these intrusive bodies beneath the MCSZ. It is proposed that the MCSZ is a syn-emplacement magma-driven accommodation structure, with a shear sense antithetic to the magma flow direction, which played a critical role in accommodating the westerly derived sill intrusion. Our results show that inelastic syn-emplacement deformation structures, such as the MCSZ, are very important in the accommodation of magma in the subsurface. Such small structures are unlikely to be imaged by seismic-reflection surveys, highlighting the importance of detailed field studies in our understanding of intrusion geometry and emplacement mechanisms.
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Thorpe, R. S., and R. Macdonald. "Geochemical evidence for the emplacement of the Whin Sill complex of northern England." Geological Magazine 122, no. 4 (July 1985): 389–96. http://dx.doi.org/10.1017/s0016756800031836.
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AbstractThe Whin Sill comprises a major quartz tholeiite sill of late Carboniferous age underlying an area of c. 5000 km2 and with a volume of c. 200 km3, associated with contemporaneous dykes emplaced within Carboniferous sedimentary rocks in northeast England. New trace element analyses of chilled margins, sill interiors and dykes indicate that the Whin Sill complex magmas show significant chemical variations in terms of the relatively stable trace elements Th, Ce, Y, Zr, Nb and Ni. These data indicate that the complex was fed by a large number of compositionally distinct magma pulses, and that certain of the dykes may have formed feeder channels for the sill. The chemical characteristics of the sill and dyke samples are consistent with derivation by extensive polybaric fractional crystallization of olivine tholeiite magma derived by partial melting of compositionally heterogeneous mantle peridotite and/or crustal contamination of mantle-derived magmas.
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LATYPOV, RAIS, and SOFYA CHISTYAKOVA. "Phase equilibria testing of a multiple pulse mechanism for origin of mafic–ultramafic intrusions: a case example of the Shiant Isles Main Sill, NW Scotland." Geological Magazine 146, no. 6 (May 27, 2009): 851–75. http://dx.doi.org/10.1017/s0016756809006499.
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AbstractIn this paper we examine the role of multiple emplacement of sills into partly solidified rocks (an intrusive mechanism ‘liquid into solid’) as a possible explanation for some textural and compositional ‘anomalies’ of single-cyclic mafic intrusions. As a case study we used the Shiant Isles Main Sill that is widely regarded as a classical example of a multiple, picrite–picrodolerite–crinanite alkaline sill. This sill is currently interpreted as having been formed by several olivine phenocryst-rich pulses of magma, which were successively emplaced into their almost solidified predecessors. Such an intrusive mechanism is a random process in which many parameters vary independently and unpredictably. Among them are: the number, relative volume and bulk composition of magma pulses, and their place, sequence and timing of emplacement, as well as modal abundance, phase composition and distribution of intratelluric phenocrysts in magmas upon emplacement. In terms of these variables, one can envisage countless different profiles through alkaline sills produced from only three randomly intruded magma pulses of picritic, picrodoleritic and crinanitic composition. Such multiple sills can readily be distinguished from simple ones formed from a single pulse of magma by anomalous compositional profiles with several prominent breaks in crystallization and compositional sequences. The compositional profile of the Shiant Isles Main Sill is remarkably similar to an M-shaped profile expected from fractional crystallization of a single pulse of olivine-saturated magma along a crystallization path Ol+Sp+L (picrite), Ol+Pl±Sp+L (picrodolerite = troctolite), Ol+Pl+Cpx+L (crinanite). The probability of the accidental formation of such a compositional profile by multiple intrusion ‘liquid into solid’ is exceedingly small, even for the single case of the Shiant Isles Main Sill. The probability approaches zero when considering that exactly the same sequence of intrusive events must have been repeated in about 20 neighbouring alkaline sills with similar compositional profiles. This can only be achieved by some universally operating differentiation process. The best candidate for this is the classical fractional crystallization of magma constrained by liquidus phase equilibria. This suggests that the Shiant Isles Main Sill can be best interpreted and modelled as a simple sill that crystallized from one large pulse of magma, with possible involvement of minor refilling events. Further progress in our knowledge of intrachamber magma fractionation processes will probably enable us to interpret many ‘anomalous’ textural and compositional features of mafic–ultramafic intrusions in the frame of a single magma pulse model.
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Vigneresse, Jean Louis. "Granitic batholiths: from pervasive and continuous melting in the lower crust to discontinuous and spaced plutonism in the upper crust." Transactions of the Royal Society of Edinburgh: Earth Sciences 97, no. 4 (December 2006): 311–24. http://dx.doi.org/10.1017/s0263593300001474.
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ABSTRACTThe generation of granitic magmas begins with melting in the lower crust, under active participation of the underlying mantle. Thermally driven, melting is a pervasive and continuous process that develops over a wide region. In contrast, the building of a granitic pluton is highly discontinuous in time and space. Several inputs of magma, sometimes with a different chemical compositions, are focused toward a region where they accumulate, forming a large pluton, often separated by some 50 km from an adjacent one. The switch from a continuous to a discontinuous process represents a fundamental point of magma generation. It gives place to the modified model m(M-SAE), in which the mantle (m) and Melting (M) are separated from the Segregation (S), Ascent (A) and Emplacement (E) modes. Discontinuities result from non-linear processes that develop during segregation and ascent of the magma. They rely on the non-linear rheology of partially molten rocks. Thresholds control the change from a solid-like to liquid-like behaviour of the magma. In between, the rheology exhibits sudden jumps between states. Because two phases continuously coexist (matrix and melt), strain is highly partitioned between them. This may induce highly discontinuous melt segregation, which needs both pure and simple shear to develop. Melt focusing is controlled by the viscosity contrast between the two phases. It gives rise to different compaction lengths depending on the region, a partially melting source or a nearly brittle crust, where it develops. Because ascent and emplacement are discontinuous in time, this allows the crust to relax, avoiding the room problem for a pluton intruding the upper crust. Intermediate magma chambers could develop with different temperature and magma composition. They could be the place of enhanced magma mixing. Finally, the stress conditions, which differ for each tectonic setting, influence the shape of the granitic body.
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Ferré, Eric C., Olivier Galland, Domenico Montanari, and Thomas J. Kalakay. "Granite magma migration and emplacement along thrusts." International Journal of Earth Sciences 101, no. 7 (January 17, 2012): 1673–88. http://dx.doi.org/10.1007/s00531-012-0747-6.
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Schmiedel, Tobias, Steffi Burchardt, Tobias Mattsson, Frank Guldstrand, Olivier Galland, Joaquín Palma, and Henrik Skogby. "Emplacement and Segment Geometry of Large, High-Viscosity Magmatic Sheets." Minerals 11, no. 10 (October 11, 2021): 1113. http://dx.doi.org/10.3390/min11101113.
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Understanding magma transport in sheet intrusions is crucial to interpreting volcanic unrest. Studies of dyke emplacement and geometry focus predominantly on low-viscosity, mafic dykes. Here, we present an in-depth study of two high-viscosity dykes (106 Pa·s) in the Chachahuén volcano, Argentina, the Great Dyke and the Sosa Dyke. To quantify dyke geometries, magma flow indicators, and magma viscosity, we combine photogrammetry, microstructural analysis, igneous petrology, Fourier-Transform-Infrared-Spectroscopy, and Anisotropy of Magnetic Susceptibility (AMS). Our results show that the dykes consist of 3 to 8 mappable segments up to 2 km long. Segments often end in a bifurcation, and segment tips are predominantly oval, but elliptical tips occur in the outermost segments of the Great Dyke. Furthermore, variations in host rocks have no observable impact on dyke geometry. AMS fabrics and other flow indicators in the Sosa Dyke show lateral magma flow in contrast to the vertical flow suggested by the segment geometries. A comparison with segment geometries of low-viscosity dykes shows that our high-viscosity dykes follow the same geometrical trend. In fact, the data compilation supports that dyke segment and tip geometries reflect different stages in dyke emplacement, questioning the current usage for final sheet geometries as proxies for emplacement mechanism.
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Corriveau, Louise, and David Morin. "Modelling 3D architecture of western Grenville from surface geology, xenoliths, styles of magma emplacement, and Lithoprobe reflectors." Canadian Journal of Earth Sciences 37, no. 2-3 (April 2, 2000): 235–51. http://dx.doi.org/10.1139/e99-121.
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Information derived from regional geology, styles of magma emplacement, xenoliths, and western Grenville Lithoprobe reflectors is integrated to model the architecture of the Central Metasedimentary Belt in Quebec. The belt comprises a thin-skinned western marble domain that projects structurally to the east above a quartzite domain; both domains are underlain by a series of gneiss domes. In contrast, the seismic reflectors dip systematically to the east. They stem from exposed high-strain zones and tectonic boundaries hosting concordant, 1.7-1.16 Ga, postmetamorphic sheetlike plutons. Though discontinuous, the reflectors reach highly reflective crust segments near the Moho. The reflections are interpreted as series of plutons positioning crustal-scale structures rooted in underplated, felsic, and mafic magmas reservoirs. These structures served as magma conduits and ponding sites. The nonreflective segments of the inferred structures are interpreted as through-going pathways for magmas in gneissose crust. Based on the thousands of felsic to ultramafic xenoliths brought up by a 1.07 Ga minette dyke, the nature of the intermediate and lower crust is interpreted as interleaving of nonexposed quartzite-bearing supracrustal assemblages with mylonites, gneisses, and a series of mafic to ultramafic intrusive bodies, many of them inferred to be underplated material. In western Quebec, crustal growth along the pre-Grenvillian Laurentian margin involved pre-1.2 Ga stacking of allochthons including nonexposed metasedimentary and intrusive components during an early stage of Grenvillian collision. Subsequent, 1.7-1.6 Ga magma emplacement along high-strain zones shaped much of the seismic reflectivity of the belt.
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Kargi, Hulusi, and Calvin G. Barnes. "A Grenville-age layered intrusion in the subsurface of west Texas: petrology, petrography, and possible tectonic setting." Canadian Journal of Earth Sciences 32, no. 12 (December 1, 1995): 2159–66. http://dx.doi.org/10.1139/e95-168.
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The Nellie intrusion is a thick (more than 4420 m) mafic to ultramafic layered intrusion with a radiometric age of ~1163 Ma. Rock types change abruptly with stratigraphic height and include norite, pyroxenite, gabbronorite, hornblende gabbro, gabbro, anorthosite, harzburgite, and lherzolite. Norite is most abundant, but gabbro and hornblende gabbro are locally abundant. Rare olivine-rich layers are also present. The general order of crystallization was olivine, orthopyroxene, plagioclase + clinopyroxene, and hornblende. Mg#'s, expressed as 100 Mg/(Mg + Fe), range from 76.3 to 85.8 for olivine, 56.7 to 84.9 for orthopyroxene, 62.5 to 90.3 for clinopyroxene, and 52.4 to 82.8 for amphibole. Mg#'s vary with height and display abrupt reversals, which indicate open-system addition of new mafic magma. Eleven cyclic units were identified on the basis of evidence for injection of basaltic magma; these can be grouped into three megacyclic units. The abundance of orthopyroxene, and mineral compositional evidence for Fe enrichment within cyclic units, indicates that parental magmas were subalkaline and tholeiitic. Plagioclase in equilibrium with olivine ranges from An65 to An46, which precludes an arc-related magma source. Although the intrusion is approximately coeval with Keweenawan magmatism and with emplacement of diabasic dikes in western North America, it is dissimilar in detail to both suites of rocks. Nevertheless, its composition and geophysical setting are consistent with emplacement in an extensional tectonic environment.
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Annen, Catherine, Jonathan D. Blundy, and R. Stephen J. Sparks. "The sources of granitic melt in Deep Hot Zones." Transactions of the Royal Society of Edinburgh: Earth Sciences 97, no. 4 (2008): 297–309. http://dx.doi.org/10.1017/s0263593300001462.
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AbstractA Deep Hot Zone develops when numerous mafic sills are repeatedly injected at Moho depth or are scattered in the lower crust. The melt generation is numerically modelled for mafic sill emplacement geometries by overaccretion, underaccretion or random emplacement, and for intrusion rates of 2, 5 and 10mm/yr. After an incubation period, melts are generated by incomplete crystallisation of the mafic magma and by partial melting of the crust. The first melts generated are residual from the mafic magmas that have low solidi due to concentration of H20 in the residual liquids. Once the solidus of the crust is reached, the ratio of crustal partial melt to residual melt increases to a maximum. If wet mafic magma, typical of arc environments, is injected in an amphibolitic crust, the residual melt is dominant over the partial melt, which implies that the generation of I-type granites is dominated by the crystallisation of mafic magma originated from the mantle and not by the partial melting of earlier underplated material. High ratios of crustal partial melt over residual melt are reached when sills are scattered in a metasedimentary crust, allowing the generation of S-type granites. The partial melting of a refractory granulitic crust intruded by dry, high-T mafic magma is limited and subordinate to the production of larger amount of residual melt in the mafic sills. Thus the generation of A-type granites by partial melting of a refractory crust would require a mechanism of selective extraction of the A-type melt.
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ROBINS, BRIAN. "The mode of emplacement of the Honningsvåg Intrusive Suite, Magerøya, northern Norway." Geological Magazine 135, no. 2 (March 1998): 231–44. http://dx.doi.org/10.1017/s0016756898008395.
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The Honningsvåg Intrusive Suite consists of several layered mafic/ultramafic intrusions and a transgressive body of igneous breccia that appears to represent a magma conduit. It is emplaced into a Silurian, flysch-type sedimentary sequence that is thermally metamorphosed to spotted slate, cordierite–andalusite or pyroxene hornfels and agmatitic migmatite. Folds and flattened reduction spots in the hornfelses suggest that emplacement took place after Caledonian deformation and development of a slaty cleavage. Tectonic rotation subsequent to emplacement has led to exposure of the Honningsvåg Intrusive Suite in a natural cross-section corresponding to ∼10 km of crustal depth. Basaltic magma was initially emplaced as a several-kilometre-tall pipe that crystallized to form Intrusion 1. A second magma chamber was initiated alongside this pipe and subsequently expanded laterally into a sill-like magma body as batches of olivine-saturated basalt were added. A later magma chamber, represented by Intrusion 4, developed largely within the cumulates forming the upper part of Intrusion 2 and appears to have been accompanied by opening of a broad inclined feeder into which blocks and slabs of older cumulates collapsed. The resulting igneous breccias of Intrusion 3 are chaotic and largely clast-dominated in the lower part of the conduit, but enclosed slabs are matrix supported and orientated parallel to an originally subhorizontal banding in the feldspathic peridotite matrix in the upper part. The core of the breccia body has a troctolite matrix and contains blocks of older breccia, suggesting re-opening of the conduit, either during the crystallization of Intrusion 4 or possibly during the development of chambers represented by the younger layered intrusions. The cumulates in Intrusion 4 subsided sufficiently to invert marginal parts of the Layered Series before a further magma chamber was initiated in its roof rocks. The last major magma chamber opened alongside Intrusion 5 and extended upwards as a pipe or broad dyke to the highest structural levels exposed. Cross-cutting relationships show that the Honningsvåg magma chambers were not active simultaneously but were emplaced sequentially, generally at successively higher structural levels. Olivine tholeiite magma initially pooled in a crustal zone where it had neutral buoyancy. Subsequent chambers are suggested to have been initiated by emplacement of magma along the density discontinuities that existed above and around crystallized intrusions and their associated hornfelses. Chambers evolved by fractional crystallization, assimilation of country rocks and periodic replenishment. The abandonment of magma chambers may have resulted from the expulsion of low-density residual melts.
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Westrich, H. R., H. W. Stockman, and J. C. Eichelberger. "Degassing of rhyolitic magma during ascent and emplacement." Journal of Geophysical Research 93, B6 (1988): 6503. http://dx.doi.org/10.1029/jb093ib06p06503.
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Corti, Giacomo, Marco Bonini, Fabrizio Innocenti, Piero Manetti, and Genene Mulugeta. "Centrifuge models simulating magma emplacement during oblique rifting." Journal of Geodynamics 31, no. 5 (July 2001): 557–76. http://dx.doi.org/10.1016/s0264-3707(01)00032-1.
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Yoshinobu, Aaron S., and Gary H. Girty. "Measuring host rock volume changes during magma emplacement." Journal of Structural Geology 21, no. 1 (January 1999): 111–16. http://dx.doi.org/10.1016/s0191-8141(98)00100-x.
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Bevins, R. E., G. J. Lees, and R. A. Roacht. "Petrogenesis of Ordovician igneous rocks in the southern part of the Welsh Basin." Geological Magazine 129, no. 5 (September 1992): 615–24. http://dx.doi.org/10.1017/s0016756800021786.
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AbstractDuring early Ordovician times volcanic and high-level intrusive activity occurred at numerous centres across North Pembrokeshire. Previous work suggested a geochemical transition in this activity from calcalkaline through to tholeiitic with time. However, new data indicate more extensive calc-alkaline magmatism and that both magma types were coeval. The origin of the calcalkaline magmas remains equivocal, but the tholeiitic magmas appear to have been derived from a source similar to N-type MORB, variably modified by supra-subduction zone fluids, combined with some fractionation during ascent. These data are consistent with emplacement in a supra-subduction zone marginal basin.
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MacDonald, R., B. Bagiński, B. G. J. Upton, H. Pinkerton, D. A. MacInnes, and J. C. MacGillivray. "The Mull Palaeogene dyke swarm: insights into the evolution of the Mull igneous centre and dyke-emplacement mechanisms." Mineralogical Magazine 74, no. 4 (August 2010): 601–22. http://dx.doi.org/10.1180/minmag.2010.074.4.601.
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AbstractGeochemical data are presented for five large Palaeogene dykes, members of the Mull swarm in southern Scotland and northern England (the Moneyacres, Hawick-Acklington, Barrmill, Muirkirk- Hartfell and Dalraith-Linburn dykes). The rock types range from basalt through andesite to dacite, although the range in individual intrusions is more restricted. The dykes are divisible into two groups; those where the compositional variation was generated by fractional crystallization of basaltic magmas, and those where it resulted from variable degrees of mixing of basaltic and silicic magmas. Several dykes are composite; the marginal facies can be more or less evolved than the central facies. The dyke magmas are thought to have originated from stratified magma chambers beneath the Mull centre and models are presented to show how the different components were derived from the chambers. Some dykes appear to have been terminated at or near the Southern Upland Fault, perhaps as a result of the chilling of early magma pulses by water in the fault. The Palaeogene dyke swarm is considerably more complex than previously recognized and has a significant input to models of the evolution of the Mull magmatic system.
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Schöpa, Anne, Catherine Annen, John H. Dilles, R. Stephen J. Sparks, and Jon D. Blundy. "Magma Emplacement Rates and Porphyry Copper Deposits: Thermal Modeling of the Yerington Batholith, Nevada." Economic Geology 112, no. 7 (November 1, 2017): 1653–72. http://dx.doi.org/10.5382/econgeo.2017.4525.
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Abstract Many porphyry copper deposits are associated with granitoid plutons. Porphyry copper deposit genesis is commonly attributed to degassing of pluton-forming intermediate to silicic magma chambers during slow cooling and crystallization. We use numerical simulations of thermal evolution during pluton growth to investigate the links between pluton construction, magma accumulation and solidification, volatile release, and porphyry copper deposit formation. The Jurassic Yerington batholith, Nevada, serves as a case study because of its exceptional exposure, revealing the geometry of three main intrusions. The last intrusion, the Luhr Hill granite, is associated with economic porphyry copper deposits localized over cupolas where dikes and fluid flow were focused. Our simulations for the conceptual model linking porphyry copper deposits with the presence of large, highly molten magma chambers show that the Luhr Hill granite must have been emplaced at a vertical thickening rate of several cm/yr or more. This magma emplacement rate is much higher than the time-averaged formation rates of other batholiths reported in the literature. Such low rates, although common, do not lead to magma accumulation and might be one of the reasons why many granitoid plutons are barren. Based on our results, we formulate the new testable hypothesis of a link between porphyry copper deposit formation and the emplacement time scale of the associated magma intrusion.
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Allen, Charlotte M. "A nested diapir model for the reversely zoned Turtle Pluton, southeastern California." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 179–90. http://dx.doi.org/10.1017/s0263593300007872.
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ABSTRACTMost zoned plutons described in the geological literature have mafic rims and felsic cores and are referred to as “normally zoned”, whereas relatively few “reversely zoned” intrusions (felsic rims and mafic cores) have been described. That unusual zonation pattern has been variously attributed to in situ processes or to the reordering of an underlying, vertically stratified, magma chamber either by intrusion through an orifice or by emplacement of composite diapirs. The Turtle Pluton is an early Cretaceous, reversely zoned, intrusion that is divided into four facies: a Rim Sequence that is graditionally zoned from bt + ilm + muse monzogranite to hb + bt + mt + sph granodiorite; a Core Facies of more homogeneous hb + bt + mt + sph granodiorite to quartz monzodiorite; between these two facies, a structural discontinuity termed the Schlieren Zone; and an Eastern Facies of monzogranite to granodiorite. Field relationships, distribution of strain, and geochemical and isotopic studies (including a range of initial87Sr/86Sr from 0·7085–0·7065) suggest that the reverse zonation of the Turtle Pluton is the result of sequential emplacement of two diapirs each derived from the same underlying, vertically stratified, magma chamber, and that the Rim Sequence zonation is chiefly the result of mixing of intermediate and felsic magmas from distinct sources accompanied by minor fractional crystallisation.
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Zhou, Bing, Zhixue Zhang, Zeming Shi, Hao Song, and Linsong Yu. "Geochemistry, Geochronology, and Prospecting Potential of the Dahongliutan Pluton, Western Kunlun Orogen." Applied Sciences 12, no. 22 (November 15, 2022): 11591. http://dx.doi.org/10.3390/app122211591.
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Triassic granitoids are abundant on the northwestern margin of the Tibetan Plateau. The Dahongliutan pluton, located in the eastern Western Kunlun orogen, formed in the Late Triassic.Previous field studies have identified potential mixing of crustal and mantle magmas. In this study, we used zircon U–Pb ages and major and trace elemental analyses to investigate the tectonic evolution of the pluton, and to determine whether any exchange of mantle-derived material occurred between the pluton and the source area. We found that the pluton has relatively high SiO2 contents, and the aluminum saturation index is consistent with peraluminous high-K calc-alkaline granite. The pluton is enriched in light rare earth elements; both light and heavy rare earth elements are highly fractionated. The magma that formed the pluton was predominantly derived from the crust; however, a small amount of upper mantle material was involved in the early stages of magma formation. The pluton underwent composite emplacement as a result of tectonic extension and magmatic emplacement, which may have occurred in the late Triassic post-collisional orogenic stage. Late Triassic magmatism provided heat and ore-forming material for Pb–Zn, Cu, Fe, and rare metal mineralization, which is of considerable importance for geological prospecting.
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Mattsson, Tobias, Steffi Burchardt, Karen Mair, and Joachim Place. "Host-rock deformation during the emplacement of the Mourne Mountains granite pluton: Insights from the regional fracture pattern." Geosphere 16, no. 1 (December 16, 2019): 182–209. http://dx.doi.org/10.1130/ges02148.1.
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Abstract The Mourne Mountains magmatic center in Northern Ireland consists of five successively intruded granites emplaced in the upper crust. The Mourne granite pluton has classically been viewed as a type locality of a magma body emplaced by cauldron subsidence. Cauldron subsidence makes space for magma through the emplacement of ring dikes and floor subsidence. However, the Mourne granites were more recently re-interpreted as laccoliths and bysmaliths. Laccolith intrusions form by inflation and dome their host rock. Here we perform a detailed study of the deformation in the host rock to the Mourne granite pluton in order to test its emplacement mechanism. We use the host-rock fracture pattern as a passive marker and microstructures in the contact-metamorphic aureole to constrain large-scale magma emplacement-related deformation. The dip and azimuth of the fractures are very consistent on the roof of the intrusion and can be separated into four steeply inclined sets dominantly striking SE, S, NE, and E, which rules out pluton-wide doming. In contrast, fracture orientations in the northeastern wall to the granites suggest shear parallel to the contact. Additionally, contact-metamorphic segregations along the northeastern contact are brecciated. Based on the host-rock fracture pattern, the contact aureole deformation, and the north-eastward–inclined granite-granite contacts, we propose that mechanisms involving either asymmetric “trap-door” floor subsidence or laccolith and bysmalith intrusion along an inclined or curved floor accommodated the emplacement of the granites and led to deflection of the northeastern wall of the intrusion.
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BRUNN, J. H., I. ARGYRIADIS, and J. BRAUD. "Magmatic emplacement of northwestern Geece ophiolites." Bulletin of the Geological Society of Greece 34, no. 6 (January 1, 2002): 2127. http://dx.doi.org/10.12681/bgsg.16856.
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New field observations reinforce the interpretation that was admitted from 1956 to 1970 according to which the ophiolites of Northwestern Greece were generated and emplaced as a massive submarine flow of mantelle magma which had risen through the opening of an orogenic rift. As it opened, the still narrow rift left out submarin tuffs and lavas (pillows) which have been found in different places under the basal peridotites of ophiolitic suits.
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Köpping, Jonas, Craig Magee, Alexander R. Cruden, Christopher A. L. Jackson, and James R. Norcliffe. "The building blocks of igneous sheet intrusions: Insights from 3-D seismic reflection data." Geosphere 18, no. 1 (January 6, 2022): 156–82. http://dx.doi.org/10.1130/ges02390.1.
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Abstract The propagating margins of igneous sills (and other sheet intrusions) may divide into laterally and/or vertically separated sections, which later inflate and coalesce. These components elongate parallel to and thus record the magma flow direction, and they can form either due to fracture segmentation (i.e., “segments”) or brittle and/or non-brittle deformation of the host rock (i.e., “magma fingers”). Seismic reflection data can image entire sills or sill-complexes in 3-D, and their resolution is often sufficient to allow us to identify these distinct elongate components and thereby map magma flow patterns over entire intrusion networks. However, seismic resolution is limited, so we typically cannot discern the centimeter- to meter-scale host rock deformation structures that would allow the origin of these components to be interpreted. Here, we introduce a new term that defines the components (i.e., “elements”) of sheet-like igneous intrusions without linking their description to emplacement mechanisms. Using 3-D seismic reflection data from offshore NW Australia, we quantify the 3-D geometry of these elements and their connectors within two sills and discuss how their shape may relate to emplacement processes. Based on seismic attribute analyses and our measurements of their 3-D geometry, we conclude that the mapped elements likely formed through non-elastic-brittle and/or non-brittle deformation ahead of the advancing sill tip, which implies they are magma fingers. We show that thickness varies across sills, and across distinct elements, which we infer to represent flow localization and subsequent thickening of restricted areas. The quantification of element geometries is useful for comparisons between different subsurface and field-based data sets that span a range of host rock types and tectonic settings. This, in turn, facilitates the testing of magma emplacement mechanisms and predictions from numerical and physical analogue experiments.
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Barbey, P., H. Nachit, and J. Pons. "Magma–host interactions during differentiation and emplacement of a shallow-level, zoned granitic pluton (Tarçouate pluton, Morocco): implications for magma emplacement." Lithos 58, no. 3-4 (September 2001): 125–43. http://dx.doi.org/10.1016/s0024-4937(01)00053-6.
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SANT’OVAIA, H., P. NOGUEIRA, J. CARRILHO LOPES, C. GOMES, M. A. RIBEIRO, H. C. B. MARTINS, A. DÓRIA, et al. "Building up of a nested granite intrusion: magnetic fabric, gravity modelling and fluid inclusion planes studies in Santa Eulália Plutonic Complex (Ossa Morena Zone, Portugal)." Geological Magazine 152, no. 4 (November 14, 2014): 648–67. http://dx.doi.org/10.1017/s0016756814000569.
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AbstractThe Santa Eulália Plutonic Complex (SEPC), located in the Ossa Morena Zone (south Portugal), is composed of a medium- to coarse-grained pink granite (G0-type) and a central grey medium-grained biotite granite (G1-type). Available Rb–Sr data indicates an age of 290 Ma. An emplacement model for the SEPC is proposed, taking into account magnetic fabric, 2D gravity modelling and fluid inclusion planes studies. The G0 and G1 types demonstrate different magnetic behaviour: G0 is considered a magnetite-type granite and G1 is an ilmenite-type granite. The formation of G0 required oxidized conditions related to the interaction of mafic rocks with a felsic magma. The 2D gravity modelling and subvertical magnetic lineations show that the feeder zone of the SEPC is located in the eastern part of the pluton, confirming the role of the Assumar and Messejana Variscan faults in the process of ascent and emplacement. The magma emplacement was controlled by ENE–WSW planar anisotropies related to the final brittle stages of the Variscan Orogeny. The emplacement of the two granites was almost synchronous as shown by their gradational contacts in the field. The magnetic fabric however suggests emplacement of the G0-type first, closely followed by emplacement of the G1-type, pushing the G0 laterally which becomes more anisotropic towards the margin. The G1-type became flattened, acquiring a dome-like structure. The SEPC is a nested pluton with G0-type granite assuming a tabular flat shape and G1-type forming a rooted dome-like structure. After emplacement, SEPC recorded increments of the late Variscan stress field documented by fluid inclusion planes in quartz.
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Woolley, Alan R., and R. Garth Platt. "The mineralogy of nepheline syenite complexes from the northern part of the Chilwa Province, Malawi." Mineralogical Magazine 50, no. 358 (December 1986): 597–610. http://dx.doi.org/10.1180/minmag.1986.050.358.05.
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AbstractThe mineralogy, including the accessory phases låvenite, rosenbuschite, and catapleiite, and consequent petrogenetic implications have been investigated for a group of four overlapping nepheline syenite complexes (Chikala, Chaone, Mongolowe, and Chinduzi) and for spatially associated silica-saturated and over-saturated perthosites, from the northern part of the Chilwa Alkaline Province, Malawi.The complexes are thought to have formed by injection into high-level chambers of magma pulses genetically related to a common source magma at depth. Evidence for the source magma is preserved in salitic cores observed in the pyroxenes and a trend to more hedenbergite-rich compositions is believed to have formed by evolution of this magma. Subsequent trends of acmite enrichment followed magma injection into the higher-level chambers; the actual pyroxene trend associated with each individual complex is a function of the evolution attained by the source magma, oxidation potential, and perhaps even alkali activity. On the basis of such a two-stage model, the pyroxene data suggest emplacement of the Chaone and Mongolowe magmas somewhat earlier than that of Chikala, with the Chinduzi magma migrating even later.Amphiboles and biotites are believed to have formed after high-level injection of the magmas. Their compositions broadly reflect the nature of the crystallizing pyroxenes in that magnesian hastingsitic hornblendes and more Mg-rich biotites are associated with more Mg-rich sodic pyroxenes, whereas katophorites and annite-rich micas are generally associated with sodic pyroxenes somewhat richer in hedenbergite. Sub-solidus crystallization in some of the complexes is represented by aegirine and magnesio-arfvedsonite. Nepheline compositions indicate broadly similar crystallization temperatures within the complexes, namely 950 to 750°C. Oxygen fugacities for these magmas obtained from biotite/annite compositions vary from 10−19 to 10−14 bars for this temperature range. Mineralogical data, particularly from pyroxenes and amphiboles, strongly suggest that the perthosites, spatially associated with the nepheline syenite complexes, are genetically unrelated.
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Kent, R. W., N. C. Ghose, P. R. Paul, M. J. Hassan, and A. D. Saunders. "Coal—magma interaction: an integrated model for the emplacement of cylindrical intrusions." Geological Magazine 129, no. 6 (November 1992): 753–62. http://dx.doi.org/10.1017/s0016756800008475.
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AbstractOlivine-bearing lamproite magmas intruded into Permian coal seams in northeast India occur as root-like cylinder stockworks, extending for up to several kilometres up-dip along the bedding planes of their sedimentary host. Clusters of eight or more conduits are typical, linked by thin tubular cross-branches. Cylindrical geometry may arise by injection of hot, low-viscosity fluid through a slot, with the development of multiple tube-like instabilities at the interface between the moving fluid and a higher-viscosity host. This behaviour appears more complex than the models of Chouke, van Meurs & van der Pod, and Saffman & Taylor, which predict the development of a single dominant tube in porous or layered flow. Cylinder emplacement may be an essentially passive process, in which the sediment column is reduced by expulsion of heated pore fluids at the head of the moving intrusion, creating a space into which the melt can propagate. Generation of a superheated vapour envelope by non-nucleated film boiling of these fluids around the hot lamproite magma (the Leidenfrost effect) allows melt flow to be maintained in a lengthening tube thermally insulated from the surrounding coal, in a manner analogous to submarine lava tubes. Cooling of the magma through the Nukiyama temperature (the temperature at which maximum evaporation of the heated fluid occurs) may give rise to violent surface boiling and the formation of large vapour bubbles at the magma–coal interface. Implosion of these bubbles could then result in the formation of shock breccias, comparable to hyaloclastites produced by bubble or surface film collapse in the vicinity of pillow lava tubes. The operation of such a process around lamproite magma is suggested by the presence of complex breccias composed of highly fragmented coal, sandstone, and lamproite, at the termini of certain cylinders.Surface and subsurface exposures of the cylinders reveal the presence of a carbonate–chlorite–clay halo surrounding each intrusion, resulting from the alteration of mafic mineral phases by fugitive volatiles released from the protective vapour jacket. The coal seams proximal to intrusion clusters are relatively undeformed, with no evidence of assimilation by the invading melts. The coals have experienced extensive carbonization, probably as a result of slow conductive heating from the cooling lamproite bodies, or fluids derived therefrom. Field observations indicate that these thermal effects are not merely confined to the coal–melt interface, but occur for some considerable distance away from the intrusions, producing large areas of naturally coked coal.
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Vigneresse, Jean Louis. "A new paradigm for granite generation." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 95, no. 1-2 (March 2004): 11–22. http://dx.doi.org/10.1017/s0263593300000882.
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ABSTRACTIdeas about granite generation have evolved considerably during the past two decades. The present paper lists the ideas which were accepted and later modified concerning the processes acting during the four stages of granite generation: melting, melt segregation and ascent, and emplacement. The active role of the mantle constitutes a fifth stage.Fluid-assisted melting, deduced from metamorphic observations, was used to explain granite and granulite formation. Water seepage into meta-sedimentary rocks can produce granitic melt by decreasing melting temperature. CO2 released by the mantle helps to transform rocks into granulites. However, dehydration melting is now considered to be the origin of most granitic melts, as confirmed by experimental melting. Hydrous minerals are involved, beginning with muscovites, followed by biotite at higher temperatures. At even deeper conditions, hornblende dehydration melting leads to calc-alkaline magmas.Melt segregation was first attributed to compaction and gravity forces caused by the density contrast between melt and its matrix. This was found insufficient for magma segregation in the continental crust because magmas were transposed from mantle conditions (decompression melting) to crustal conditions (dehydration melting). Rheology of two-phase materials requires that melt segregation is discontinuous in time, occurring in successive bursts. Analogue and numerical models confirm the discontinuous melt segregation. Compaction and shear localisation interact non-linearly, so that melt segregates into tiny conduits. Melt segregation occurs at a low degree of melting.Global diapiric ascent and fractional crystallisation in large convective batholiths have also been shown to be inadequate and at least partly erroneous. Diapiric ascent cannot overcome the crustal brittle-ductile transition. Fracture-induced ascent influences the neutral buoyancy level at which ascent should stop but does not. Non-random orientation of magma feeders within the ambient stress field indicates that deformation controls magma ascent.Detailed gravity and structural analyses indicate that granite plutons are built from several magma injections, each of small size and with evolving chemical composition. Detailed mapping of the contact between successive magma batches documents either continuous feeding, leading to normal petrographic zoning, or over periods separated in time, commonly leading to reverse zoning. The local deformation field controls magma emplacement and influences the shape of plutons.A typical source for granite magmas involves three components from the mantle, lower and intermediate crusts. The role of the mantle in driving and controlling essential crustal processes appears necessary in providing stress and heat, as well as specific episodes of time for granite generation. These mechanisms constitute a new paradigm for granite generation.
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Coulson, Ian M., James K. Russell, and Gregory M. Dipple. "Origins of the Zippa Mountain pluton: a Late Triassic, arc-derived, ultrapotassic magma from the Canadian Cordillera." Canadian Journal of Earth Sciences 36, no. 9 (September 1, 1999): 1415–34. http://dx.doi.org/10.1139/e99-045.
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The Zippa Mountain intrusion is of Late Triassic age and is situated in the Iskut River area of northwest British Columbia. The pluton is elliptical in shape and 3.5 by 5 km in diameter. The pluton intrudes Palaeozoic and Triassic rocks within Stikinia and is compositionally zoned from clinopyroxenite at the pluton margins to a core of syenite. The Zippa Mountain pluton comprises aegirine-augite, potassium feldspar, and minor biotite, hornblende, nepheline, vishnevite, titanian andradite, titanite, and apatite. Based on new field, petrographic, and chemical data this intrusion is shown to be silica-undersaturated, strongly alkaline, and ultrapotassic. We interpret the pluton as a single pulse of magma, which entered a shallow-level crustal magma chamber. The potassic nature is a characteristic of the parental magma, but is enhanced by fractional crystallization and crystal sorting processes. The parental magma has affinities with arc-type magmas related to subduction (shoshonitic magma series), as is evidenced by high LILE/LREE ratio, and select depletion of HFSE. Upon emplacement, crystallization of clinopyroxene and then K-feldspar, and efficient physical sorting within the magma chamber, resulted in sidewall, marginal pyroxenite and roof-zone syenites, respectively. Continued fractionation in the core of the intrusion increased volatile contents and led to the crystallization of feldspathoids. Potentially, a mass of residual melt, and crystals of K-feldspar and feldspathoid, was buoyant relative to the surrounding pyroxenite, which allowed it it to rise and partly intrude the syenites.
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Sigmundsson, Freysteinn, Michelle Parks, Andrew Hooper, Halldór Geirsson, Kristín S. Vogfjörd, Vincent Drouin, Benedikt G. Ófeigsson, et al. "Deformation and seismicity decline before the 2021 Fagradalsfjall eruption." Nature 609, no. 7927 (September 14, 2022): 523–28. http://dx.doi.org/10.1038/s41586-022-05083-4.
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AbstractIncreased rates of deformation and seismicity are well-established precursors to volcanic eruptions, and their interpretation forms the basis for eruption warnings worldwide. Rates of ground displacement and the number of earthquakes escalate before many eruptions1–3, as magma forces its way towards the surface. However, the pre-eruptive patterns of deformation and seismicity vary widely. Here we show how an eruption beginning on 19 March 2021 at Fagradalsfjall, Iceland, was preceded by a period of tectonic stress release ending with a decline in deformation and seismicity over several days preceding the eruption onset. High rates of deformation and seismicity occurred from 24 February to mid-March in relation to gradual emplacement of an approximately 9-km-long magma-filled dyke, between the surface and 8 km depth (volume approximately 34 × 106 m3), as well as the triggering of strike-slip earthquakes up to magnitude MW 5.64. As stored tectonic stress was systematically released, there was less lateral migration of magma and a reduction in both the deformation rates and seismicity. Weaker crust near the surface may also have contributed to reduced seismicity, as the depth of active magma emplacement progressively shallowed. This demonstrates that the interaction between volcanoes and tectonic stress as well as crustal layering need to be fully considered when forecasting eruptions.
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Bussell, M. Andrew. "Structure and petrogenesis of a mixed-magma ring dyke in the Peruvian Coastal Batholith: eruptions from a zoned magma chamber." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 79, no. 2-3 (1988): 87–104. http://dx.doi.org/10.1017/s0263593300014140.
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ABSTRACTRing complex granites of the Peruvian Batholith are tabular bodies with flat roofs emplaced by cauldron subsidence. Marginal precursory ring dykes extend upwards above roof level and a typical intrusion is “H”-shaped in cross-section. Advance of magma by repeated subsidence would give a ladder-shaped profile for such intrusions above the brittle-ductile transition. Close relationships exist between intrusion geometry, emplacement process and petrogenetic evolution. Initially a granodioritic magma chamber lay beneath the present erosion level, trapping a rising mass of dioritic magma. Expansion of granodioritic liquid resulted in the injection of microgranite and tuffisite cone sheets accompanied by roof uplift within a ring fault. Next, during subsidence within the ring fault, liquids from deeper levels in the underlying chamber rose by stoping along the outer margin of the fault to form a ring dyke. Prior to intrusion, this liquid was vertically zoned from rhyodacite downwards to diorite and these liquids became partially mixed during emplacement. Finally, granodioritic magma rose to the present level by subsidence of a roof slab bounded by the ring fault. The precursory ring structures preserve evidence of significant but transient events in the underlying chamber. Liquid differentiation may be significant in the evolution of many large plutons.
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Owens, W. H. "Measuring host rock volume changes during magma emplacement: Discussion." Journal of Structural Geology 22, no. 4 (April 2000): 519–20. http://dx.doi.org/10.1016/s0191-8141(99)00166-2.
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Yoshinobu, Aaron S., and Gary H. Girty. "Measuring host rock volume changes during magma emplacement: Reply." Journal of Structural Geology 22, no. 4 (April 2000): 521–22. http://dx.doi.org/10.1016/s0191-8141(99)00170-4.
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Vukmanovic, Z., M. L. Fiorentini, S. M. Reddy, and B. Godel. "Microstructural constraints on magma emplacement and sulfide transport mechanisms." Lithosphere 11, no. 1 (December 12, 2018): 73–90. http://dx.doi.org/10.1130/l743.1.
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Svensen, Henrik, Fernando Corfu, Stéphane Polteau, Øyvind Hammer, and Sverre Planke. "Rapid magma emplacement in the Karoo Large Igneous Province." Earth and Planetary Science Letters 325-326 (April 2012): 1–9. http://dx.doi.org/10.1016/j.epsl.2012.01.015.
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Wang, X., W. L. Griffin, S. Y. O’Reilly, X. M. Zhou, X. S. Xu, S. E. Jackson, and N. J. Pearson. "Morphology and geochemistry of zircons from late Mesozoic igneous complexes in coastal SE China: implications for petrogenesis." Mineralogical Magazine 66, no. 2 (April 2002): 235–51. http://dx.doi.org/10.1180/0026461026620025.
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AbstractThe Pingtan and Tonglu igneous complexes in SE China are typical of the calc-alkaline series developed at active continental margins. These two complexes are dominated by felsic rocks, temporally and spatially associated with minor mafic rocks. Morphological and trace-element studies of zircon populations in rocks from each of these complexes show that the zircon populations may be divided into 3–4 distinct growth stages, characterized by different distributions of morphological indices (Ipr, Ipy and Iel), and different contents of the substituting elements (Hf, U, Th, Y and P). The four growth stages recognized in the zircons are believed to have formed successively in the magma chamber, during the emplacement, and in the early and later stages of magma consolidation, respectively. All four stages are recognized in the plutonic Pingtan complex, whereas the stages 3 and 4 are less developed in the volcanic/subvolcanic Tonglu complex. Based on the chemistry and morphology of the different zircon populations of the Pingtan and Tonglu complexes, it is suggested that basaltic magmas underplating at the boundary between crust and mantle caused partial melting of the mid–lower crust and produced granitoid magmas. Subsequently, mixing between magmas was important.
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Barbey, Pierre, Arnaud Villaros, Christian Marignac, and Jean-Marc Montel. "Multiphase melting, magma emplacement and P-T-time path in late-collisional context: the Velay example (Massif Central, France)." Bulletin de la Société Géologique de France 186, no. 2-3 (2015): 93–116. http://dx.doi.org/10.2113/gssgfbull.186.2-3.93.
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AbstractThe West European Variscan chain is a remarkable illustration of how partial melting marks out the geodynamic evolution of mountain belt through time. Here, we focus on the Late Carboniferous melting events reported in the southeastern French Massif Central (Velay dome), with emphasis on the modes of partial melting, relationships between partial melting and magma emplacement, transition between the melting episodes and related P-T-t path. Following nappe stacking events under medium pressure/temperature conditions (M1 and M2 events), three melting events are identified in the southern envelope of the Velay dome. A first melting episode (M3 event) occurred within the biotite stability field at 325–315 Ma (T ≈ 720°C and P = 0.5–0.6 GPa). It led to the complete disappearance of muscovite and to the formation of migmatites consisting of biotite ± sillimanite melanosome and of granitic/tonalitic leucosomes depending on protolith composition. It is interpreted as the result of internal heating mainly linked to decay of heat producing elements accumulated in a thickened crust. It resulted in the formation of a partially molten middle crust with decoupling between the lower and upper crust, late-collisional extension and crustal thinning.The second episode of melting (M4 event) occurred at ca. 304 Ma (T 800°C and P 0.4 GPa), synchronously with emplacement of the Velay granites and growth of the dome. It led to the breakdown of biotite and growth of cordierite (locally garnet or tourmaline), with formation of diatexites and heterogeneous granites. This high-T event synchronous with crustal extension is considered to result from intrusion of hot mantle-derived and lower crustal magmas triggering catastrophic melting in the middle crust. This event ends with local retrograde hydrous melting within the stability field of biotite close to the solidus in response to local input of water during temperature drop in the late stage of emplacement of the Velay dome.The last evidence of melting in this area (M5 event) corresponds to emplacement of late granites generated under conditions estimated at ≈850°C and 0.4–0.6 GPa. They may have been generated from melting of specific lithologies triggered by injection of mafic magmas. These granites emplaced in a partly cooled crust (medium-grade conditions). The emplacement age of these granites is not well constrained (305–295 Ma) though they clearly post-date the Velay granites.The melting episodes in the Velay area and generation of granites appear to correspond to the conjunction between (i) the effects of collision-related crust thickening and (ii) those related to slab break off and asthenospheric mantle decompression melting. The driving process is mainly the internal radiogenic heat in a first stage, relayed by the propagation of a thermal anomaly initially located in the lower crust (M3 event), but which subsequently rose to the middle and upper crustal levels through magma transfer (M4 event). Overall, the Velay example is a remarkable illustration of the progressive dehydration and sterilisation of a thickened crustal segment. It documents how large amounts of granitic magmas can be produced at shallow crustal levels in relation to the injection of mantle-derived magmas.
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Berzina, A. N., A. P. Berzina, and V. O. Gimon. "The Aksug Porphyry Cu–Mo Ore-Magmatic System (Northeastern Tuva): Sources and Formation of Ore-Bearing Magma." Russian Geology and Geophysics 62, no. 4 (April 1, 2021): 445–59. http://dx.doi.org/10.2113/rgg20194115.
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Abstract ––Two stages are recognized in the evolution of the Aksug ore-magmatic system (OMS): (1) formation of the Aksug granitoid pluton and (2) emplacement of small ore-bearing intrusions. Intrusive bodies of the two stages are composed of rocks of the same type and bear copper mineralization: poor dispersed and large-scale veinlet-disseminated, respectively. The pluton and small intrusions are formed by gabbroid and granitoid rocks, with similar petrogeochemical characteristics of igneous rocks of the same type. The plutonic gabbroic association includes gabbro, gabbrodiorites, and pyroxene–amphibole diorites/quartz diorites. The small subvolcanic gabbroic intrusions are gabbrodiorite and diorite porphyrites. The trace element patterns of the gabbroids are similar to those of igneous rocks in subduction zones. The gabbroids are characterized by isotope parameters εNd(500) = +6.1 to +7.2 and (87Sr/86Sr)500 = 0.7022–0.7030 and model age TNd(DM) = 0.85–0.74 Ga. As follows from the geochemical parameters, the depleted mantle metasomatized by subduction fluids was the source of basaltic magma. The plutonic granitoid association includes tonalites, plagiogranites, and amphibole diorites/quartz diorites; the small subvolcanic granitoid intrusions are tonalite porphyry and quartz diorite porphyrites. The trace element patterns and Nd and Sr isotope compositions of the granitoids are much similar to those of the gabbroids. According to the geochemical parameters, tonalitic and plagiogranitic magmas formed through the melting of juvenile mafic crust, and dioritic magma resulted from the mixing of basaltic and tonalitic/plagiogranitic magmas. In the course of the OMS formation, metals and volatiles were introduced by basaltic and granitoid magmas from the metasomatized mantle and juvenile mafic crust. The compression setting during the pluton formation hampered the separation of ore-bearing fluids, which led to poor dispersed mineralization. The extension setting during the emplacement of small intrusions favored the intense separation of ore-bearing fluids. The interaction of magma and fluids of the small intrusions with rocks of the pluton was accompanied by the removal of metals from the latter and their involvement in the ore-forming process. This increased the ore potential of the magmatic system and favored the formation of rich mineralization at the final stage of its evolution.
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Benn, Keith, Francis Odonne, Sharon K. Y. Lee, and Ken Darcovich. "Analogue scale models of pluton emplacement during transpression in brittle and ductile crust." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no. 1-2 (2000): 111–21. http://dx.doi.org/10.1017/s0084255900006021.
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Analogue experiments were used to investigate pluton emplacement during transpression in a layered crust. Models consisted of (1) a silicone gum-PbO suspension as analogue magma, (2) a silicone gum-Pb suspension as a basal ductile layer, and (3) an overlying sand pack representing brittle crust. The models were transpressed at 3 mm/hr causing the extrusion of the analogue magma from a progressively closing slot, and its emplacement into the ductile layer. The thicknesses of the layers were critical in controlling the shapes of intrusions and the structures that developed in the brittle overburden. Thicker sand packs led to flattened, symmetrical laccolith-shaped intrusions and the nucleation of one oblique thrust in the sand pack above the extremity of the intrusion. Thinner sand packs led to thicker, asymmetrical laccolith-like intrusions with uplift of the overburden on an oblique thrust, and the formation of a shallow graben in the extrados of a bending fold. Reducing the thickness of the basal ductile layer resulted in a larger number of shear zones in the sand pack, and structural geometries approaching those produced in experiments involving only a brittle analogue crust and no ductile layer. Shear zones in the sand pack were localised by intrusions, and also played a key role in displacing analogue brittle crust to make space for intrusions. The results suggest that tectonic forces may play an important role in displacing blocks of crust during pluton emplacement in transpressional belts. They also suggest that pluton shapes, and the geometries and kinematics of emplacement-related shear zones and faults, may depend on the depth of emplacement. In nature, depending on the structural level exposed in the map plane, faults and shear zones that helped make space for emplacement may not appear to be spatially associated with the pluton.
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Gagnevin, D., J. S. Daly, and G. Poli. "Insights into granite petrogenesis from quantitative assessment of the field distribution of enclaves, xenoliths and K-feldspar megacrysts in the Monte Capanne pluton, Italy." Mineralogical Magazine 72, no. 4 (August 2008): 925–40. http://dx.doi.org/10.1180/minmag.2008.072.4.925.
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AbstractA detailed field study to determine quantitatively the distribution of K-feldspar megacrysts, mafic microgranular enclaves (MME) and metasedimentary xenoliths has been carried out in the Monte Capanne pluton (Elba, Italy) with a view to evaluating the utility of this approach to petrogenetic investigations. Mafic microgranular enclaves are inferred to result from interactions between mafic and felsic magmas, while xenoliths attest to crustal assimilation occurring in the Monte Capanne magma chamber. In particular, we emphasize, based on our field data, that both processes are intimately linked, such that xenolith dissolution during assimilation was triggered by replenishment with hot mafic magma. It is suggested that the previously defined ‘San Piero’ and ‘San Francesco’ facies do not differ substantially, and are thus amalgamated and renamed as the ‘Pomonte’ facies. Results also indicate that the abundance of K-feldspar megacrysts is positively correlated with the volumetric abundance of MME in the Sant’ Andrea facies, which we link to a recharging, mingling and textural coarsening event that occurred at a rather late stage of magma-chamber evolution prior to emplacement. This study demonstrates how petrogenetic processes can be deciphered by detailed field quantitative analyses of granite-forming components, thus complementing geochemical investigations.
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Gansecki, Cheryl, R. Lopaka Lee, Thomas Shea, Steven P. Lundblad, Ken Hon, and Carolyn Parcheta. "The tangled tale of Kīlauea’s 2018 eruption as told by geochemical monitoring." Science 366, no. 6470 (December 5, 2019): eaaz0147. http://dx.doi.org/10.1126/science.aaz0147.
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Changes in magma chemistry that affect eruptive behavior occur during many volcanic eruptions, but typical analytical techniques are too slow to contribute to hazard monitoring. We used rapid energy-dispersive x-ray fluorescence analysis to measure diagnostic elements in lava samples within a few hours of collection during the 2018 Kīlauea eruption. The geochemical data provided important information for field crews and civil authorities in advance of changing hazards during the eruption. The appearance of hotter magma was recognized several days before the onset of voluminous eruptions of fast-moving flows that destroyed hundreds of homes. We identified, in near real-time, interactions between older, colder, stored magma—including the unexpected eruption of andesite—and hotter magma delivered during dike emplacement.
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Jahn, Bor-ming, Fuyuan Wu, and Bin Chen. "Granitoids of the Central Asian Orogenic Belt and continental growth in the Phanerozoic." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no. 1-2 (2000): 181–93. http://dx.doi.org/10.1017/s0263593300007367.
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The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calcalkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion.Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive εNd(T) values and young Sm—Nd model ages (TDM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their ‘juvenile’ character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative εNd(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes.The evolution of the CAOB is probably related to accretion of young arc complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.
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Barbarin, Bernard, and Jean Didier. "Genesis and evolution of mafic microgranular enclaves through various types of interaction between coexisting felsic and mafic magmas." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 145–53. http://dx.doi.org/10.1017/s0263593300007835.
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ABSTRACTThermal, mechanical and chemical exchange occurs between felsic and mafic magmas in dynamic magma systems. The occurrence and efficiency of such exchanges are constrained mainly by the intensive parameters, the compositions, and the mass fractions of the coexisting magmas. As these interacting parameters do not change simultaneously during the evolution of the granite systems, the exchanges appear sequentially, and affect magmatic systems at different structural levels, i.e. in magma chambers at depth, in the conduits, or after emplacement. Hybridisation processes are especially effective in the plutonic environment because contrasting magmas can interact over a long time-span before cooling. The different exchanges are complementary and tend to reduce the contrasts between the coexisting magmas. They can be extensive or limited in space and time; they are either combined into mixing processes which produce homogeneous rocks, or only into mingling processes which produce rocks with heterogeneities of various size-scales. Mafic microgranular enclaves represent the most common heterogeneities present in the granite plutons. The composite enclaves and the many types of mafic microgranular enclaves commonly associated in a single pluton, or in polygenic enclave swarms, are produced by the sequential occurrence of various exchanges between coexisting magmas with constantly changing intensive parameters and mass fractions. The complex succession and repetition of exchanges, and the resulting partial chemical and complete isotopic equilibration, mask the original identities of the initial components.
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Breheny, C., K. R. Moore, A. Costanzo, and M. Feely. "Reconstruction of an Ordovician seafloor volcanohydrothermal system: a case study from the Copper Coast, southeastern Ireland using field, geochemical and fluid inclusion data." Mineralogical Magazine 80, no. 1 (February 2016): 157–74. http://dx.doi.org/10.1180/minmag.2015.079.7.09.
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AbstractVolcanic rocks in south County Waterford include flow-top hyaloclastite, pillow lavas and peperite, which are formed typically by sub-aqueous eruption or intrusion into unconsolidated sediment. Element mobility in wet sediment during emplacement of volcanic intrusions was reconstructed on a variety of spatial scales using bulk-rock and mineral analysis. Magma-sediment and magma-water interactions enhanced hydrothermal alteration. The chemistry of chlorite was a function of mixing between an Fe-rich magmatic fluid and a Mg-rich meteoric fluid. Chlorite geothermometry yields temperatures of formation between 230 and 388°C compatible with other metamorphic indicators. Fluid inclusion microthermometric data from genetically-related mineralized quartz veins reveal a hydrothermal vein mineralization event that occurred at lower temperatures during the end stage of volcanic activity. A convection driven mixing trend reflects the trapping of co-existing brine with entrained seawater concomitant with, the late stages of emplacement of the Bunmahon Volcano intrusions.
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Petford, N., A. R. Cruden, K. J. W. McCaffrey, and J. L. Vigneresse. "Granite magma formation, transport and emplacement in the Earth's crust." Nature 408, no. 6813 (December 2000): 669–73. http://dx.doi.org/10.1038/35047000.
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