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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.
Dissertations / Theses on the topic "Magma emplacement"
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Roman, Alberto M. "Emplacement and Post-Emplacement Dynamics of Magma Reservoirs." Sorbonne Paris Cité, 2015. http://www.theses.fr/2015USPCC179.
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La composition évoluée de la croûte continentale suggère qu'une partie mafique a été perdue au cours du temps géologique. Cependant, certaines intrusions mafiques et ultramafiques, telles que le complexe du Bushveld, Afrique du Sud, et le Great Dyke, Zimbabwe, ont été conservés dans la croûte pendant des milliards d'années. La question est alors de savoir comment les cumulats mafiques sont perdus et, plus précisément, quelle est l'évolution à long terme d'un réservoir de magma y compris éventuellement les processus de post-emplacement et post-cristallisation. Ce travail vise à ce question avec l'approche suivante. Dans un premier temps, nous effectuons des expériences de laboratoire avec des fluides visqueux pour enquêter sur l'instabilité associée à une inversion de flottabilité et d'individuer des lois d'échelle simples régissant les différents régimes dynamiques. Nombreuses intrusions mafiques préservent structures d'écoulement prouvant qu'elles ont été affectées par des instabilités gravitationelles compatibles avec les régimes observés au laboratoire. Dans une deuxième partie, nous étudions les conditions physiques dans lesquelles les intrusions mafiques deviennent instables à l'aide des simulations numériques qui reproduisent les écoulements dans croûte terrestre. La conclusion la plus importante est que le paramètre principal contrôlant l'instabilité est la profondeur d'emplacement. Donc, le collapse gravitationnel des parties mafiques dans la croûte est un processus très commun dans les régions volcaniques. Ce mécanisme devrait faire la lumière sur les processus qui régissent la formation de la croûte terrestreThe evolved bulk composition of the continental crust suggests that a large mafic portion has been lost during the geological time. However, mafic and ultramafic bodies, such as the Bushveld complex, South Africa, and the Great Dyke Zimbabwe, have been preserved in the crust for billions of years. The implied question, then, is how mafic cumulates are lost and, more specifically, what is the long-term evolution of a magma reservoir, possibly including post-emplacement and post-crystallization processes. This work aims at this question with the following approach. First , we perform laboratory experiments with viscous fluids to investigate the instability associated to a buoyancy reversai and derive simple scaling laws governing the different dynamical regimes. Many mafic intrusions preserve flow structures, proving that they were affected by gravitational instabilities consistent with the regimes observed in the laboratory. In a second part, we investigate the physical conditions under which mafic intrusions become unstable using extensive numerical simulations which reproduce crustal flows. The mort important finding is that the main control on the instability is the emplacement depth. The results of this work thus suggests that many of the mafic intrusions we obsei:ve4today at the outcrop are the vestiges of much larger systems that became unstable. Consequently foundering and sinking of mafic cumulates through the crust may be a very common process in volcanic regions. This mechanism should shed light on the processes governing the formation and differentiation of the Barth crust
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Plankell, Eric Thomas. "Magma emplacement models for the Jurassic Ferrar Dolerite Province, Antarctica /." Connect to resource, 1997. http://hdl.handle.net/1811/28549.
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England, Richard W. "The ascent and emplacement of granitic magma : the Northern Arran granite." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6609/.
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This thesis is a study of the mechanisms by which granitic magmas rise through the crust to be empiaced at a level above their source, with particular reference to diapirisni. and how these mechanisms may be analysed by combined structural and petrological studies. The Northern Arran granite is used as an example of how this problem may be approached. The Northern Arran granite is a two component granite of Tertiary age intruded into structurally heterogeneous upper crustal rocks under regional tension. A synform concentric to the granite, synchronous with the development of a narrow thermal aureole, records the vertical ascent of a single body of magma with a hemispherical upper surface. Post ascent, radial expansion of this body, indicated by flattening strains parallel to its surface and superimposed on the concentric synform records a change in shape of the pluton. This was permitted by the reactivation of an existing fault which the pluton intersected during its ascent. Petrological studies of the outer coarse unit of the northern granite indicate that it is a single body of magma derived by differentiation of a crustally contaminated basaltic source. Theoretical modelling of the crystallisation of the coarse granite shows that textural and chemical variations, are consistent with solidification by sidewall crystallisation (liquid fractionation) but not fractional crystallisation. The inner (younger) fine granite is also a single body of magma derived from the same or a similar source as the coarse granite. The sharp undeformed contacts between the coarse and fine granites and the presence of internal sheets in the fine granite parallel to its contacts with the coarse granite are consistent with emplacement of the fine granite as a series of pulses which filled a propagating ring dyke fracture within the coarse granite. Theoretical modelling of the ascent of the coarse granite using the Hot Stokes equation indicates that bouyancy driven ascent aided by a reduction in wall rock viscosity controlled by the rate of heat loss of from the granite is a viable ascent mechanism. The patterns of strain in the aureole of the Northern Arran granite result from the ascent and emplacement of a single diapiric body. They provide examples of the types of structure which may be used to recognise and distinguish between diapiric ascent and radial expansion. This has important implications for the study of ballooning diapirs. The reactivation of an existing fault system during emplacement suggests that existing crustal structure can influence the final geometry of an intrusive body. It is shown that the complete evolution of the Northern Arran granite can be determined using a combination of structural and petrological data. Structural data provides constraints on the later stages of ascent and the emplacement of granitic plutons. Petrological data can be used to constrain the origin, early stages of ascent and the crystallisation of a magma body.
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Liss, Dirk. "Emplacement processes and magma flow geometries of the Whin Sill complex." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403441.
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The emplacement processes of the Whin Sill complex and its associated dykes have been studied using a combined approach of detailed field and magnetic investigations. Regional palaeodirectionai results show two different but consistent palaeomagnetic signatures and allow the sill complex to be subdivided into three geographically separate intrusions: the 'Holy Island Sill', the 'Alnwick Sill' and the ' Hadrian's Wall-Pennine Sill', The Little Whin Sill has been identified previously as a fourth, separate sill on petrological evidence. On the basis of the palaeodirectional results it is also possible to relate the exposed contemporaneous dykes to the individual intrusions. The magma flow geometries within the individual Whin Sill intrusions were detennined by AMS analyses, and both traditional and newly identified magma flow indicators. For the Holy Island Sill the results suggest that the magma flow was homogeneously southwards directed and that the Holy Island Dyke acted as the feeder to this intrusion. In the Alnwick Sill the magma flow was homogeneously westwards directed and it is proposeU that an offshore, en echelon segment of the High Green Dyke fed the Alnwick Sill. The magma flow geometry for the Hadrian's Wall-Pennine Sill is complex. The results suggest that this intrusion was fed by the Hett Dyke and that the magma flow within the sill was generally north and north westwards directed. It is proposed that the intrusion was emplaced during a phase of late Variscan, E-W compression and that pre-existing faults at a high angle to this compression direction acted as a magma flow barrier along which the magma became deflected. The geometry of the sills is approximately that of a quarter- to half-saucer-shape, with the dykes being situated at the saucer truncation. From the feeder dykes magma was injected into the individual sill bodies and the magma flow was generally up dip or parallel to the strike of the host rock bedding, thus out of the basin centres and into levels of lower lithospheric pressure. It is proposed that a compressional stress field and locally overpressured horizons had a significant impact on the initiation and emplacement of the Whin Sill complex.
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McGowan, Ellen. "Magma emplacement and deformation in rhyolitic dykes : insight into magmatic outgassing." Thesis, Lancaster University, 2016. http://eprints.lancs.ac.uk/81586/.
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Exposed rhyolitic dykes at eroded volcanoes arguably provide in situ records of conduit processes during rhyolitic eruptions, thus bridging the gap between surface and sub-surface processes. This study involved micro- to macro-scale analysis of the textures and water content within shallow (emplacement depths <500 m) rhyolitic dykes at two Icelandic central volcanoes. It is demonstrated that dyke propagation commenced with the intrusion of gascharged currents that were laden with particles, and that the distribution of intruded particles and degree of magmatic overpressure required for dyke propagation were governed by the country rock permeability and strength, with pre-existing fractures playing a pivotal governing role. During this stage of dyke evolution significant amounts of exsolved gas may have escaped. Furthermore, during later magma emplacement within the dyke interiors, particles that were intruded and deposited during the initial phase were sometimes preserved at the dyke margins, forming dykemarginal external tuffisite veins, which would have been capable of facilitating persistent outgassing during dyke growth. It is further demonstrated that following initial dyke-opening, geochemically homogenous dykes grew via the incremental emplacement of magma, with fluctuations in the shallow-dyke permeability occurring via bubble collapse, and this is deemed to have been critical in dictating pressure within the deeper magma source region and fragmentation. Of further significance, it is also shown that shear deformation was localised during magma emplacement, with localised vesiculation occurring along emplacement boundary layers via viscous heating, which temporarily promoted magma ascent, but with later bubble collapse culminating in brittle failure of bubble-free magma, after shear zone migration. However, in some instances high strain rates during viscous bubble deformation resulted in ductile-brittle transitions, with resultant slip triggering micro-tensile failure of bubbly magma, as the slipped magmatic plug experienced decompression. This tensile failure probably occurred distal to shear zones, where bubbles where relatively isolated. Interlinking of the micro-cracks formed extensive internal tuffisite vein networks, which acted as efficient outgassing pathways, given their access to significant quantities of preexsolved volatiles. The models presented in this thesis are relevant to the conduit processes that take place during rhyolitic eruptions; insight is provided into how rhyolitic magma ascends through the shallow (<500 m deep) crust and also into how the magma deforms during its ascent and into the processes that govern magmatic outgassing.
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Emblin, S. R. "The Reinfjord ultramafic complex, Seiland province : emplacement history and magma chamber model." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355634.
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Risby, Olle. "Crystallization and Emplacement of the Monte Amarelo Dikes: Magma Storage Assessment on Fogo, Cape Verde Islands." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-316988.
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The volcanic island of Fogo belongs to the Cape Verde archipelago, a two-tiered chain of islands situated 500 km west of the African coast. Fogo is regarded as one of the most active volcanoes in the world with 10 eruptions during the last 250 years. The former shield volcano Monte Amarelo reached 3500 m.a.s.l. before it collapsed into the Atlantic Ocean. The massive landslide event occurred between 124 and 86 ka, forming the Bordeira cliffs and the high plateau Cha das Caldeiras on Fogo. We have collected rock samples from the Bordeira dikes, which intruded into the Bordeira wall prior to collapse. The purpose of the project is to produce a magmatic storage model for Fogo using mineral chemistry and thermobarometric methods. Additionally, I aim to determine the processes prevailing in the magmatic system, the link between the volcanic and plutonic system. Previous studies on the magma storage beneath Fogo have focused on the volcanics, which show crystallization pressures between 0.45 to 0.68 GPa using clinopyroxene-melt thermobarometry on rims. The Bordeira dikes are basanitic to nephelinitic in composition. The mineral assemblage of the 20 dike samples consist of phenocrystic clinopyroxene ± olivine ± plagioclase ± xenocrystic amphibole. Accessory minerals are titanomagnetite, apatite, nepheline, plagioclase and alkali feldspar in a microcrystalline groundmass. Clinopyroxene displays a large compositional variation, ranging from Mg#38 to Mg#85, with a mean of Mg#71±10 2s.d. (n=614). Xenocrystic amphibole varies from Mg#37 to Mg#72, with a mean of Mg#62±15 2s.d. (n=78). Interstitial feldspar forms two groups, one of An#24 to An#79, with a mean of An#66±19 2s.d., (n=125) and a second with Or#19 to 100 with a mean of Or#69±42 2s.d.(n=71). Bulk geochemistry of the 20 samples range from 1.82 to 11.5 MgO wt%. Our clinopyroxene-melt thermobarometry show crystallization pressures ranging from 0.02 to 0.85 GPa, with a mean of 0.47±0.29 2s.d. (n=502) (Putirka et al. 2003). Structural data from the intrusive dikes in the Bordeira contain three preferred orientations, N-S, NW-SE and E-W (n=371). The main process occurring in the magmatic system is fractional crystallization, however there is some evidence for phenocryst accumulation and magma recharge. Our magma storage model show that clinopyroxene crystallization initiates in the lithospheric mantle, between 15 to 28 km depth. Significant clinopyroxene rim and microcryst crystallization occur above Moho, between 9 to 12 km, implying that magma storage levels do exist in the oceanic crust. The intrusive and extrusive rocks present on Fogo show common storage levels, suggesting that they are formed in the same system but the difference being their residence time in the crustal level storage. Our structural data and 3D model suggest that the Monte Amarelo rift zone was composed of three components, being oriented NW-SE, N-NE and E-W. The flank collapse was caused by dike intrusions of N-S orientation which enabled a E-W extension of the shield volcano.Vulkanön Fogo är en del av ögruppen Kap Verde i Atlanten. Ögruppen bildar en två delad arkipelag positionerad 500 km väster om det afrikanska fastlandet. Ön, tillika vulkanen Fogo har på senare tid varit en av de mest aktiva vulkanerna i världen med 10 utbrott under de senaste 250 åren. Ön byggdes upp av sköldvulkanen Monte Amarelo nådde 3500 m ö h innan delar av den kollapsade ned i Atlanten. Det massiva skredet som skedde mellan 86 och 124 tusen år sedan skapade högplatån Cha das Caldeiras samt den omringande klippsektionen Bordeira. Vi har samlat stenprover från de plutoniska bergarter som har trängt in sig i klippsektionen Bordeira. Målet med vår studie är att skapa en modell för hur magma lagringen fungerar under Fogo. Vi ämnar kartlägga magmalagringsdjupet med hjälp av kemiska variation i mineral som kan användas för att kartlägga kristalliseringstryck och temperatur som i t.ex. klinopyroxen. Vi är samtidigt intresserade av att veta vilka processer som sker i det magmatiska systemet och sambandet mellan vulkanska bergarter t.ex. lava och plutoniska bergarter. Tidigare studier av Fogos magmalagring har använt vulkaniska bergarter, som kristalliserar sig mellan 0.45 till 0.68 GPa när man undersökt kemin på kristallkanter av klinopyroxen. 20 prover har analyserats från Bordeiraklipporna och de innehåller låga kiselhalter, mellan 37 till 47% samt höga mängder alkaliska oxider så som kalium och natrium. Provernas mineralinnehåll består främst av större kristaller av silikatmineralen klinopyroxen ± olivin± fältspat ± främmande amfibolkristaller. De större kristallerna är omringande av en mikrokristallin grundmassa bestående av järn-titanoxider, apatit och fältspatoider. Klinopyroxen har en relativt stor kemisk variation, med Mg#37 till Mg#85, med ett medelvärde på Mg#71. Vi har även två olika sorter av fältspat, en grupp med ett kalciumrik rikt innehåll klassificeras som anortit, och en annan med ett kaliumrikt innehåll, som ortoklas. Vår analys av klinopyroxen-smälta har gett oss kristalliseringstryck som sträcker sig mellan 0.02 till 0.85 GPa med ett medelvärde på 0.47 GPa. Detta innebär att den dominerande processen i magmalagringssystemet är fraktionerad kristallisering då vi kan se ett linjärt avtagande för många ämnen när de jämförs mot magnesiumhalten. Vår magmalagringsmodell för vulkanen Fogo visar att klinopyroxenkrystallisering påbörjas i den litosfäriska manteln, mellan 15 och 28 km djup. Kristallisering av kanter på klinopyroxenkristaller samt mindre kristaller i grundmassan sker ytligare och visar på att det finns en eller flera magmalagringsnivåer i den oceaniska jordskorpan, mellan 9 till 12 km djup. Vulkaniska och plutoniska bergarter vittnar om ett delat magmasystem, vilket indikerar att skillnaden mellan de två bergarterna främst är tiden de befinner sig på respektive lagringsnivå. Vår strukturgeologiska data samt 3D modell visar att den intrusiva aktiviteten var primärt orienterad NV-SO, N-NO och O-Vriktning. Monte Amarelo-vulkanens skred och kollaps orsakades av intruderande gångar med en generell N-S orientering vilket ledde till ett skred på östsidan.
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MICHAIL, Maria. "Emplacement of the Middle Triassic Monzoni Intrusive Complex (Dolomites, Italy): Insights from Analogue Models and Field Observations." Doctoral thesis, Università degli studi di Ferrara, 2018. http://hdl.handle.net/11392/2488199.
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The Dolomites form the central-eastern portion of the Southern Alps, in Northern Italy. The stratigraphic framework of the Dolomitic area includes mainly Permian to Cretaceous terrains, while it is largely dominated by the magnificent Triassic carbonate platforms and basinal systems. The area of the Dolomites recorded several tectonic and magmatic events, from Permian up to Cretaceous. During the Middle Triassic transtensional tectonics, associated with differential subsidence and uplifting, the south-western part of the Dolomites has witnessed a massive and short-lived Ladinian (Middle Triassic) tectono-magmatic event, forming a series of significant magmatic features. The Monzoni, Predazzo and Cima Pape Intrusive Complexes are situated in the southwestern Dolomites and represent the main intrusive expressions of the Ladinian magmatism. This PhD project offers new insights regarding the emplacement mechanisms of the Monzoni Intrusive Complex, by combining fieldwork data and analogue models on magma emplacement.
The Monzoni pluton is located parallel to San Pellegrino Valley and appears elongated, with an NE-SW orientation, covering an area of approximately 4.0 km2. The main characteristics of Monzoni pluton, that is the elongated shape and the shoshonitic orogenic affinity, suggest a potential correlation and emplacement control by the Triassic developing and/or reactivated inherited strike-slip structure. The generation, ascent and emplacement of Monzoni pluton and its relation to strike-slip faulting, is still a matter of debate. The lack of direct field observations attributed to the volcano-tectonic activity, keeps the mechanisms of magma–strike-slip fault interactions poorly understood.
Updated geological maps, based on field campaign data, bring new insights regarding intrusion, fault-controlled boundaries and deformational pattern of the pluton and host-rock formations. In addition, investigations on anisotropy of magnetic susceptibility (AMS) on Monzoni pluton, reveal zonation within the pluton and indicate the presence of magmatic feeder in the north-eastern part of the intrusion. Finally, the 3D modelling of the Monzoni Intrusive Complex, projecting all geological data, constrains the pluton’s volume to 4.35km3 and offers a simplified profile-view projection of the pluton/host-rock system.
The Monzoni Intrusive Complex, due to its excellent three-dimensional exposure, is particularly suited for the study of volcano-tectonic systems allowing the application and comparison to analogue models. During this project we conducted sandbox-type analogue modelling experiments on magma emplacement along crustal scale strike-slip fault zones. We investigate two tectonic regimes, strike–slip and transtension, and three temporal relationships between magmatism and tectonics; pre-tectonic, syn-tectonic and post-tectonic intrusion. Experimental results show that there is a strong interaction between tectonic structures, evolving or inherited, and magmatism and that the geometrical characteristics of the experimental plutons represent a good indicator for the classification of plutons, defining the timing and tectonic setting of emplacement. The combination of all applied methodologies suggests magmatic emplacement in transtensional tectonic regime with two possible kinematic scenarios; a left lateral strike –slip direction along the N70° fault set or a right-lateral strike slip direction, along the N30° faults.Le Dolomiti formano la parte centro-orientale delle Alpi meridionali, nel Nord Italia. L’organizzazione stratigrafica dell'area dolomitica comprende principalmente terreni dal Permiano al Cretaceo, mentre è in gran parte dominata dalle magnifiche piattaforme carbonatiche triassiche e dai relativi bacini. L'area delle Dolomiti ha registrato numerosi eventi tettonici e magmatici, dal Permiano fino al Cretaceo. Durante la tettonica transtensionale del Triassico medio, associata a subsidenza differenziale, la parte sud-occidentale delle Dolomiti è stata soggetta a un evento tettonico-magmatico Ladinico (Medio Triassico) di breve durata, sviluppando una serie di rilevanti strutture magmatiche. I complessi intrusivi di Monzoni, Predazzo e Cima Pape sono situati nelle Dolomiti sud-occidentali e rappresentano le principali espressioni intrusive del magmatismo Ladinico. Questo progetto di dottorato offre nuove conoscenze sui meccanismi di messa in posto del Complesso Intrusivo dei Monzoni, combinando dati sul campo e modelli analogici su postazioni di magma. Il plutone dei Monzoni, che si trova parallelo alla Valle di San Pellegrino, appare allungato, con orientamento NE-SO, coprendo un'area di circa 4,0 km2. Le principali caratteristiche del plutone dei Monzoni, la forma allungata e l'affinità shoshonitica orogenica, suggeriscono una potenziale correlazione e controllo della messa in posto da parte di strutture trascorrenti ereditate o medio-triassiche. La generazione, l'ascesa e la messa in posto del plutone dei Monzoni e il suo rapporto con le strutture trascorrenti, sono ancora oggetto di dibattito. La mancanza di osservazioni dirette sul campo attribuite all'attività vulcano-tettonica, rende difficile la comprensione dei meccanismi di interazione tra faglie e magmatismo. Le mappe geologiche aggiornate basate sui nuovi dati di terreno, forniscono nuove informazioni sui limiti di intrusione controllati da faglie e sul modello deformativo delle formazioni incassanti e del plutone. Inoltre, indagini su anisotropia di suscettività magnetica (AMS) sull’intrusione dei Monzoni, rivelano la zonazione all'interno del plutone e indicano la presenza di un condotto di alimentazione principale nella parte nord-orientale dell'intrusione. Infine, la modellazione geologica 3D del complesso intrusivo dei Monzoni, coerente con i dati geologici, limita il volume del plutone a 4.35 km3 e offre una visione - semplificata dei rapporti tra plutone e rocce incassanti. Il Complesso Intrusive di Monzoni, grazie alla sua eccellente esposizione tridimensionale, è particolarmente adatto allo studio di sistemi vulcano-tettonici, permettendo anche l'applicazione e il confronto con modelli analogici. Durante questo progetto, sono stati condotti esperimenti di modellazione analogica di tipo sandbox, su lungo zone di taglio trascorrenti a scala crostale. Sono stati distinti due regimi tettonici, trascorrenza pura e transtensione, e tre relazioni temporali tra magmatismo e tettonica; intrusione pre-tettonica, sin-tettonica e post-tettonica. I risultati sperimentali mostrano che esiste una forte interazione tra le strutture tettoniche, in evoluzione o ereditate, ed il magmatismo e che le caratteristiche geometriche dei plutoni sperimentali rappresentano un buon indicatore per la classificazione dei plutoni, definendo i tempi e l'ambiente tettonico della messa in posto. La combinazione di tutte le metodologie applicate, suggerisce la messa in posto del plutone durante un regime tettonico transtensionale con due possibili scenari cinematici; una transtensione sinistra - direzione N70° o una transtensione destra lungo faglie N30°.
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Wiegand, Miriam [Verfasser], and R. [Akademischer Betreuer] Greiling. "Magmatism and rifting at the South Atlantic margin: Magma transport and emplacement mechanisms of mafic dykes from magnetic studies / Miriam Wiegand ; Betreuer: R. Greiling." Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/113116900X/34.
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Blacic, Tanya Marie. "Magma supply and storage in volcanic systems : shallow crustal emplacement processes and causes of the large axial high along the western Galápagos Spreading Center, and relation of earthquakes to tectonic and magmatic features near Lassen Peak, northern California /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
Full textBook chapters on the topic "Magma emplacement"
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Vauchez, Alain, Sergio Pacheco Neves, and Andréa Tommasi. "Transcurrent Shear Zones and Magma Emplacement in Neoproterozoic Belts of Brazil." In Petrology and Structural Geology, 275–93. Dordrecht: Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-017-1717-5_17.
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Wilson, J. Richard, Julian F. Menuge, Svend Pedersen, and Ole Engell-Sørensen. "The Southern Part of the Fongen-Hyllingen Layered Mafic Complex, Norway: Emplacement and Crystallization of Compositionally Stratified Magma." In Origins of Igneous Layering, 145–84. Dordrecht: Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-017-2509-5_5.
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Nutman, A. P., and A. A. Garde. "Fluid Control on Emplacement of Sialic Magmas During Archaean Crustal Accretion." In Fluid Movements — Element Transport and the Composition of the Deep Crust, 235–43. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-0991-5_21.
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Ferré, Eric, Gérard Gleizes, M. Toufik Djouadi, Jean Luc Bouchez, and Francis X. O. Ugodulunwa. "Drainage and Emplacement of Magmas along an Inclined Transcurrent Shear Zone: Petrophysical Evidence from a Granite-Charnockite Pluton (Rahama, Nigeria)." In Petrology and Structural Geology, 253–73. Dordrecht: Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-017-1717-5_16.
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Bouchez, Jean-Luc, and Adolphe Nicolas. "Magmatic fabrics, structures and microstructures." In Principles of Rock Deformation and Tectonics, 137–63. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780192843876.003.0007.
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A magma is a two-phase material made of crystals immersed in a silicate melt, which displays a high viscosity contrast between the liquid and the solid fractions. A specific rheological behaviour is therefore expected from such a material, particularly as a function of the volume ratio between phases. Emplacement of magma to shallower levels of earth’s crust results in crystallization. As a consequence, crystal percentage increases and volume ratio between phases changes. Different structures at both the mesoscopic (field) and microscopic scales develop, which are characteristic of a particular crystal fraction. These aspects, and how shape preferred orientations (shape fabrics) develop in magmas, are discussed in this chapter. Rheological aspects of magma systems are presented, illustrated by significant microstructural features observed in granites. Our focus will then concern the construction mode of magmatic fabrics. Examples will demonstrate that, with the help of microstructures and sometimes of near-field gravity data distribution, emplacement modes of plutons are rather simple to analyse. Finally, mafic rocks will be considered at the end of chapter through case studies concerning, principally, the Skaergaard complex and gabbros from the oceanic crust.
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Ripley, E., and C. Moore. "Multiple episodes of thin-layer magma emplacement in the Duluth Complex." In Water-Rock Interaction. Taylor & Francis, 2007. http://dx.doi.org/10.1201/noe0415451369.ch19.
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Philpotts, Anthony R. "A model for emplacement of magma in the Mesozoic Hartford basin." In Geological Society of America Special Papers, 137–48. Geological Society of America, 1992. http://dx.doi.org/10.1130/spe268-p137.
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Cruden, A. R., and R. F. Weinberg. "Mechanisms of Magma Transport and Storage in the Lower and Middle Crust—Magma Segregation, Ascent and Emplacement." In Volcanic and Igneous Plumbing Systems, 13–53. Elsevier, 2018. http://dx.doi.org/10.1016/b978-0-12-809749-6.00002-9.
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Frost, Carol D., and B. Ronald Frost. "Petrologic constraints on the origin of Proterozoic ferroan granites of the Laurentian margin." In Laurentia: Turning Points in the Evolution of a Continent. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.1220(10).
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ABSTRACT Ferroan granite is a characteristic rock type of the Laurentian margin. It is commonly associated with anorthosite and related rocks. Ferroan granites are strongly enriched in iron, are alkalic to alkali-calcic, and are generally metaluminous. These geochemical characteristics reflect their tholeiitic parental magma source and relatively reducing and anhydrous conditions of crystallization. Their compositions distinguish them from arc magmas, which are magnesian and calcic to calc-alkalic. Ferroan granite magmas are hot, which promotes partial melting of their crustal wall rocks. Assimilation of these silica-rich and peraluminous melts drives the resulting magmas to higher silica and aluminum saturation values. Where Proterozoic ferroan granites intrude Archean crust, their mantle component is readily identified isotopically, but this is more difficult where they intrude relatively juvenile crust. Ferroan granite forms in tectonic environments that allow partial melts of tholeiitic mantle to pond and differentiate at or near the base of the crust. Phanerozoic examples occur in plume settings, such as the Snake River Plain and Yellowstone, or under certain conditions involving slab rollback, such as those that formed the Cenozoic topaz rhyolites of the western United States or ferroan rhyolites of the Sierra Madre Occidental. It is possible that the long-lived supercontinent Nuna-Rodinia, of which Laurentia was a part, formed an insulating lid that raised underlying mantle temperatures and created a unique environment that enabled emplacement of large volumes of mafic melt at the base of the crust. Ascent of felsic differentiates accompanied by variable crustal assimilation may have created large volumes of Proterozoic ferroan granite and related rocks.
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Horsman, Eric, Sven Morgan, Michel de Saint-Blanquat, Guillaume Habert, Andrew Nugent, Robert A. Hunter, and Basil Tikoff. "Emplacement and assembly of shallow intrusions from multiple magma pulses, Henry Mountains, Utah." In Sixth Hutton Symposium on The Origin of Granites and Related Rocks: Proceedings of a Symposium held in Stellenbosch, South Africa, 2- 6 July 2007. Geological Society of America, 2010. http://dx.doi.org/10.1130/2010.2472(08).
Full textConference papers on the topic "Magma emplacement"
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van Wijk, Jolante, Shuoyu Yao, and Gary Axen. "A Model for Socorro Magma Body Emplacement." In 2017 New Mexico Geological Society Annual Spring Meeting. Socorro, NM: New Mexico Geological Society, 2017. http://dx.doi.org/10.56577/sm-2017.549.
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Mattsson, Tobias, Steffi Burchardt, Bjarne S. G. Almqvist, Olivier Galland, Erika Ronchin, and Octavio J. Palma. "MAGMA DEFORMATION DURING LACCOLITH EMPLACEMENT: EXAMPLES FROM ICELAND AND ARGENTINA." In GSA Annual Meeting in Indianapolis, Indiana, USA - 2018. Geological Society of America, 2018. http://dx.doi.org/10.1130/abs/2018am-323736.
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Okhai, Disha, Michael Eddy, Joel DesOrmeau, and Ayla Pamukcu. "MAGMA EMPLACEMENT AND DIFFERENTIATION IN THE OLIGOCENE IXL PLUTON, NEVADA." In GSA Connects 2022 meeting in Denver, Colorado. Geological Society of America, 2022. http://dx.doi.org/10.1130/abs/2022am-378854.
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Eddy, Michael, and Robert B. Miller. "MAGMA EMPLACEMENT PROCESSES IN THE RAPIDLY CONSTRUCTED GOLDEN HORN BATHOLITH, WASHINGTON." In Cordilleran Section-117th Annual Meeting-2021. Geological Society of America, 2021. http://dx.doi.org/10.1130/abs/2021cd-363152.
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Shields, Sarah, Vladislav Rapprich, Jennifer Lindline, and Michael Petronis. "COMPLEX ALKALINE MAGMA EVOLUTION AND EMPLACEMENT HISTORY OF THE MIOCENE MONOGENETIC ZEBIN VOLCANO (CZECH REPUBLIC)." In GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-284579.
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Borel, Megan, and James J. Vogl. "FROM BRITTLE TO DUCTILE: THE RELATIONSHIP BETWEEN FOOTWALL FAULTS, MAGMA EMPLACEMENT AND ITS ASSOCIATED HEAT." In GSA 2020 Connects Online. Geological Society of America, 2020. http://dx.doi.org/10.1130/abs/2020am-359924.
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McMurtry, Gary, Luis Dasilveira, Tobias Fischer, David Bekaert, and Peter Barry. "Helium isotopes constrain magma sources and emplacement beneath Kīlauea caldera during the 2018 and 2020 eruptions." In Goldschmidt2022. France: European Association of Geochemistry, 2022. http://dx.doi.org/10.46427/gold2022.9847.
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Valley, Peter M., and Gregory Walsh. "MAGMA MINGLING AND CONTACT METAMORPHISM DURING ANORTHOSITE-MANGERITE-CHARNOCKITE-GRANITE SUITE EMPLACEMENT; EASTERN ADIRONDACK MOUNTAINS, NEW YORK." In Northeastern Section-56th Annual Meeting-2021. Geological Society of America, 2021. http://dx.doi.org/10.1130/abs/2021ne-361907.
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Horsman, Eric, Laura de Sousa, Ryan Currier, and Scott Giorgis. "DETAILED LACCOLITH EMPLACEMENT HISTORY DEMONSTRATES MECHANICAL INTERPLAY BETWEEN HYPABYSSAL MAGMA AND HOST ROCK: MOUNT ELLEN, HENRY MOUNTAINS, UTAH." In GSA Annual Meeting in Phoenix, Arizona, USA - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019am-334231.
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Shields, Sarah, Jennifer Lindline, Vladislav Rapprich, and Michael Petronis. "NEW GEOCHEMICAL AND PETROGRAPHIC DATA REGARDING MAGMA EVOLUTION AND EMPLACEMENT PROCESSES OF THE OLIGOCENE ZAKUPY DIATREME (CZECH REPUBLIC)." In GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-284960.
Full textReports on the topic "Magma emplacement"
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Neyedley, K., J. J. Hanley, Z. Zajacz, and M. Fayek. Accessory mineral thermobarometry, trace element chemistry, and stable O isotope systematics, Mooshla Intrusive Complex (MIC), Doyon-Bousquet-LaRonde mining camp, Abitibi greenstone belt, Québec. Natural Resources Canada/CMSS/Information Management, 2021. http://dx.doi.org/10.4095/328986.
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The Mooshla Intrusive Complex (MIC) is an Archean polyphase magmatic body located in the Doyon-Bousquet-LaRonde (DBL) mining camp of the Abitibi greenstone belt, Québec, that is spatially associated with numerous gold (Au)-rich VMS, epizonal 'intrusion-related' Au-Cu vein systems, and shear zone-hosted (orogenic?) Au deposits. To elucidate the P-T conditions of crystallization, and oxidation state of the MIC magmas, accessory minerals (zircon, rutile, titanite) have been characterized using a variety of analytical techniques (e.g., trace element thermobarometry). The resulting trace element and oxythermobarometric database for accessory minerals in the MIC represents the first examination of such parameters in an Archean magmatic complex in a world-class mineralized district. Mineral thermobarometry yields P-T constraints on accessory mineral crystallization consistent with the expected conditions of tonalite-trondhjemite-granite (TTG) magma genesis, well above peak metamorphic conditions in the DBL camp. Together with textural observations, and mineral trace element data, the P-T estimates reassert that the studied minerals are of magmatic origin and not a product of metamorphism. Oxygen fugacity constraints indicate that while the magmas are relatively oxidizing (as indicated by the presence of magmatic epidote, titanite, and anhydrite), zircon trace element systematics indicate that the magmas were not as oxidized as arc magmas in younger (post-Archean) porphyry environments. The data presented provides first constraints on the depth and other conditions of melt generation and crystallization of the MIC. The P-T estimates and qualitative fO2 constraints have significant implications for the overall model for formation (crystallization, emplacement) of the MIC and potentially related mineral deposits.
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Brenan, J. M., K. Woods, J. E. Mungall, and R. Weston. Origin of chromitites in the Esker Intrusive Complex, Ring of Fire Intrusive Suite, as revealed by chromite trace element chemistry and simple crystallization models. Natural Resources Canada/CMSS/Information Management, 2021. http://dx.doi.org/10.4095/328981.
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To better constrain the origin of the chromitites associated with the Esker Intrusive Complex (EIC) of the Ring of Fire Intrusive Suite (RoFIS), a total of 50 chromite-bearing samples from the Black Thor, Big Daddy, Blackbird, and Black Label chromite deposits have been analysed for major and trace elements. The samples represent three textural groups, as defined by the relative abundance of cumulate silicate phases and chromite. To provide deposit-specific partition coefficients for modeling, we also report on the results of laboratory experiments to measure olivine- and chromite-melt partitioning of V and Ga, which are two elements readily detectable in the chromites analysed. Comparison of the Cr/Cr+Al and Fe/Fe+Mg of the EIC chromites and compositions from previous experimental studies indicates overlap in Cr/Cr+Al between the natural samples and experiments done at &gt;1400oC, but significant offset of the natural samples to higher Fe/Fe+Mg. This is interpreted to be the result of subsolidus Fe-Mg exchange between chromite and the silicate matrix. However, little change in Cr/Cr+Al from magmatic values, owing to the lack of an exchangeable reservoir for these elements. A comparison of the composition of the EIC chromites and a subset of samples from other tectonic settings reveals a strong similarity to chromites from the similarly-aged Munro Township komatiites. Partition coefficients for V and Ga are consistent with past results in that both elements are compatible in chromite (DV = 2-4; DGa ~ 3), and incompatible in olivine (DV = 0.01-0.14; DGa ~ 0.02), with values for V increasing with decreasing fO2. Simple fractional crystallization models that use these partition coefficients are developed that monitor the change in element behaviour based on the relative proportions of olivine to chromite in the crystallizing assemblage; from 'normal' cotectic proportions involving predominantly olivine, to chromite-only crystallization. Comparison of models to the natural chromite V-Ga array suggests that the overall positive correlation between these two elements is consistent with chromite formed from a Munro Township-like komatiitic magma crystallizing olivine and chromite in 'normal' cotectic proportions, with no evidence of the strong depletion in these elements expected for chromite-only crystallization. The V-Ga array can be explained if the initial magma responsible for chromite formation is slightly reduced with respect to the FMQ oxygen buffer (~FMQ- 0.5), and has assimilated up to ~20% of wall-rock banded iron formation or granodiorite. Despite the evidence for contamination, results indicate that the EIC chromitites crystallized from 'normal' cotectic proportions of olivine to chromite, and therefore no specific causative link is made between contamination and chromitite formation. Instead, the development of near- monomineralic chromite layers likely involves the preferential removal of olivine relative to chromite by physical segregation during magma flow. As suggested for some other chromitite-forming systems, the specific fluid dynamic regime during magma emplacement may therefore be responsible for crystal sorting and chromite accumulation.
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Harris, L. B., P. Adiban, and E. Gloaguen. The role of enigmatic deep crustal and upper mantle structures on Au and magmatic Ni-Cu-PGE-Cr mineralization in the Superior Province. Natural Resources Canada/CMSS/Information Management, 2021. http://dx.doi.org/10.4095/328984.
Full textAbstract:
Aeromagnetic and ground gravity data for the Canadian Superior Province, filtered to extract long wavelength components and converted to pseudo-gravity, highlight deep, N-S trending regional-scale, rectilinear faults and margins to discrete, competent mafic or felsic granulite blocks (i.e. at high angles to most regional mapped structures and sub-province boundaries) with little to no surface expression that are spatially associated with lode ('orogenic') Au and Ni-Cu-PGE-Cr occurrences. Statistical and machine learning analysis of the Red Lake-Stormy Lake region in the W Superior Province confirms visual inspection for a greater correlation between Au deposits and these deep N-S structures than with mapped surface to upper crustal, generally E-W trending, faults and shear zones. Porphyry Au, Ni, Mo and U-Th showings are also located above these deep transverse faults. Several well defined concentric circular to elliptical structures identified in the Oxford Stull and Island Lake domains along the S boundary of the N Superior proto-craton, intersected by N- to NNW striking extensional fractures and/or faults that transect the W Superior Province, again with little to no direct surface or upper crustal expression, are spatially associated with magmatic Ni-Cu-PGE-Cr and related mineralization and Au occurrences. The McFaulds Lake greenstone belt, aka. 'Ring of Fire', constitutes only a small, crescent-shaped belt within one of these concentric features above which 2736-2733 Ma mafic-ultramafic intrusions bodies were intruded. The Big Trout Lake igneous complex that hosts Cr-Pt-Pd-Rh mineralization west of the Ring of Fire lies within a smaller concentrically ringed feature at depth and, near the Ontario-Manitoba border, the Lingman Lake Au deposit, numerous Au occurrences and minor Ni showings, are similarly located on concentric structures. Preliminary magnetotelluric (MT) interpretations suggest that these concentric structures appear to also have an expression in the subcontinental lithospheric mantle (SCLM) and that lithospheric mantle resistivity features trend N-S as well as E-W. With diameters between ca. 90 km to 185 km, elliptical structures are similar in size and internal geometry to coronae on Venus which geomorphological, radar, and gravity interpretations suggest formed above mantle upwellings. Emplacement of mafic-ultramafic bodies hosting Ni-Cr-PGE mineralization along these ringlike structures at their intersection with coeval deep transverse, ca. N-S faults (viz. phi structures), along with their location along the margin to the N Superior proto-craton, are consistent with secondary mantle upwellings portrayed in numerical models of a mantle plume beneath a craton with a deep lithospheric keel within a regional N-S compressional regime. Early, regional ca. N-S faults in the W Superior were reactivated as dilatational antithetic (secondary Riedel/R') sinistral shears during dextral transpression and as extensional fractures and/or normal faults during N-S shortening. The Kapuskasing structural zone or uplift likely represents Proterozoic reactivation of a similar deep transverse structure. Preservation of discrete faults in the deep crust beneath zones of distributed Neoarchean dextral transcurrent to transpressional shear zones in the present-day upper crust suggests a 'millefeuille' lithospheric strength profile, with competent SCLM, mid- to deep, and upper crustal layers. Mechanically strong deep crustal felsic and mafic granulite layers are attributed to dehydration and melt extraction. Intra-crustal decoupling along a ductile décollement in the W Superior led to the preservation of early-formed deep structures that acted as conduits for magma transport into the overlying crust and focussed hydrothermal fluid flow during regional deformation. Increase in the thickness of semi-brittle layers in the lower crust during regional metamorphism would result in an increase in fracturing and faulting in the lower crust, facilitating hydrothermal and carbonic fluid flow in pathways linking SCLM to the upper crust, a factor explaining the late timing for most orogenic Au. Results provide an important new dataset for regional prospectively mapping, especially with machine learning, and exploration targeting for Au and Ni-Cr-Cu-PGE mineralization. Results also furnish evidence for parautochthonous development of the S Superior Province during plume-related rifting and cannot be explained by conventional subduction and arc-accretion models.