Thermodynamic modeling of post-entrapment crystallization in igneous phases (original) (raw)
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Journal of Petrology, 2011
Melt inclusions (MI) represent the best source of information concerning the pre-eruptive volatile contents of magmas. If the trapped melt is enriched in volatile species, following trapping the MI may generate a vapor bubble containing volatiles that have exsolved from the melt. Thermodynamic modeling of vapor-saturated albitic composition (NaAlSi 3 O 8 ) MI shows that the CO 2 content of the melt phase in the MI is sensitive to small amounts of post-entrapment crystallization (PEC), whereas the H 2 O content of the melt is less sensitive to PEC. During PEC, CO 2 is transferred from the melt to the vapor phase and the vapor bubble may contain a significant amount, if not most, of the CO 2 in the MI.The contrasting behaviors of H 2 O and CO 2 during PEC lead to H 2 O^CO 2 trends that are similar to those predicted for open-system degassing during magma ascent and decompression. Thus, similar H 2 O^CO 2 trends may be produced if (1) vapor-saturated MI are trapped at various depths along a magmatic ascent path, or (2) MI having the same volatile content are all trapped at the same depth, but undergo different amounts of PEC following trapping. It is not possible to distinguish between these two contrasting interpretations based on MI volatile data alone. However, by examining the volatile trends within the context of other geochemical monitors of crystallization or magma evolution progress, it may be possible to determine whether the volatile trends were generated along a degassing path or if they reflect various amounts of PEC in an originally homogeneous melt inclusion assemblage. The volatile trends resulting from PEC of MI described in this study are directly applicable to silica-rich (granitic) MI trapped in non-ferromagnesian host phases, and are only qualitatively applicable to more mafic melt compositions and/or host phases owing to modifications resulting from Fe exchange with the host and to post-entrapment re-equilibration processes.
New software models thermodynamics of magmatic systems
Eos, Transactions American Geophysical Union, 1994
New Software Models Thennodynamics of Magmatic Systems PAGES 571,575,576 A new software package, MELTS, is now available for modeling crystal-liquid equili bria in magmatic systems. MELTS is based on experimentally calibrated models for the ther modynamics of solution of magmatic liquids and solids . The package com putes equilibrium phase assemblages-the compositions and proportions of coexisting liquids and solids-by direct minimization of the thermodynamic potential of the system [Ghiorso and . MELTS has a menu driven, interactive, graphical user inter face and may be used to model a range of igneous processes including equilibrium or fractional crystallization of specified bulk compositions, crystallization paths under specified T-fo2, total enthalpy, total entropy, or total volume constraints, and assimilation or magma mixing in evolving magmatic systems.
Journal of Petrology, 2002
changes that cannot be reversed. Short residence times also imply A technique is described for determining the cooling history of olivine that large unzoned cores of high-Fo phenocrysts cannot reflect diffusive phenocrysts. The technique is based on the analysis of the diffusive re-equilibration of originally zoned phenocrysts. The unzoned cores re-equilibration of melt inclusions trapped by olivine phenocrysts are a result of fast efficient accumulation of olivines from the during crystallization. The mechanism of re-equilibration involves crystallizing magma, i.e. olivines are separated from the magma diffusion of Fe from and Mg into the initial volume of the inclusion. faster than melt changes its composition. Thus, the main source of The technique applies to a single crystal, and thus the cooling high-Fo crystals in the erupted magmas is the cumulate layers of history of different phenocrysts in a single erupted magma can be the magmatic system. In other words, olivine-phyric rocks represent established. We show that melt inclusions in high-Fo olivine mixtures of an evolved transporting magma (which forms the phenocrysts from mantle-derived magmas are typically partially regroundmass of the rock) with crystals that were formed during equilibrated with their hosts at temperatures below trapping. Our crystallization of more primitive melt(s). Unlike high-Fo olivine analysis demonstrates that at a reasonable combination of factors phenocrysts, the evolved magma may reside in the magmatic system such as (1) cooling interval before eruption (<350°C), (2) eruption for a long time. This reconciles long magma residence times estimated temperatures (>1000°C), and (3) inclusion size (<70 m in from the compositions of rocks with short residence times of highradius), partial re-equilibration of up to 85% occurs within Fo olivine phenocrysts. 3-5 months, corresponding to cooling rates faster than 1-2°/day. Short residence times of high-Fo phenocrysts suggest that if eruption does not happen within a few months after a primitive magma begins cooling and crystallization, olivines that crystallize from it KEY WORDS: melt inclusions; olivine; picrites; residence time; diffusion are unlikely to be erupted as phenocrysts. This can be explained by efficient separation of olivine crystals from the melt, and their rapid incorporation into the cumulate layer of the chamber. These results * Corresponding
Applications of Melt Inclusions to Problems in Igneous Petrogenesis
Understanding the different igneous processes that magmas undergo is important for a variety of reasons including potential hazards associated with volcanoes in populated regions, magmatic hydrothermal ore deposition, and tectonic processes. One method of obtaining geochemical data that can help constrain petrogenetic processes is through the study of melt and fluid inclusions. The research presented here examines melt inclusions through experimental, analytical and field studies to better understand igneous petrogenesis.
Chemical Geology, 2002
Melt inclusions in phenocrysts are a potentially powerful tool in petrological research that can provide the only direct information available on the physical parameters (P, T and melt composition) of crystallisation at various stages in the evolution of magmatic systems. However, melt inclusions also differ in principle from other parts of the magmatic system in that their composition, after trapping, may be controlled by the composition of the host phenocryst and therefore the direct application of our understanding of macro-scale magmatic processes to the interpretation of melt inclusion data can lead to erroneous conclusions. Our results indicate that the compositions of melt inclusions in early formed phenocrysts (olivine, pyroxene, plagioclase and spinel), often of most interest in petrological studies, can be affected by processes such as volatile dissociation, oxidation and/or partial re-equilibration with their host, both during natural cooling and homogenisation experiments. In particular, melt inclusions in all minerals are prone to hydrogen diffusion into or out of the inclusions after trapping and prior to eruption, and during homogenisation experiments. If not taken into account, this can significantly affect the crystallisation temperatures derived from the homogenisation experiments. Melt inclusions in highmagnesian olivine phenocrysts commonly have lower Fe contents compared to the initially trapped composition due to reequilibration with the host at lower temperatures. This often leads to the appearance of sulphide globules and in some cases high-magnesian clinopyroxene daughter crystals, and may cause an increase in the oxidation state of the inclusions. Homogenised melt inclusions in plagioclase phenocrysts in MORB usually have lower Ti and Fe, and higher Si contents compared to the melt composition at the moment of trapping. However, homogenisation experiments can provide reliable estimates of trapping temperature and the MgO, Al 2 O 3 , CaO, Na 2 O, and K 2 O contents of the host magma at the moment of trapping. Some of these processes can be identified by observing the behaviour of melt inclusions during homogenisation experiments using low-inertia visually controlled heating stages, and their effects can be minimised by using appropriate experimental conditions as determined by kinetic experiments, ideally completed for each phenocryst type in every sample. We also discuss general aspects of melt inclusion studies aimed at recovering H 2 O content of primary mantle-derived magmas and demonstrate that, in cases of low-pressure crystallisation, it is important to identify the
The International Workshop on Petrological Analysis of Pre-eruptive Magma (PAPEMP) abstracts
BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
近年急速に進みつつある．こうして得られた最新の知見の共有と，関連研究者間の相互交流等を目的とし，国際 ワークショップ "International Workshop on Petrological Analysis of Pre-eruptive Magma Processes (PAPEMP)" ［噴火準 備過程の岩石学的解析に関する国際ワークショップ］ を，活断層・火山研究部門主催で行った．ワークショップ は，所内 34 名・所外 42 名・合計 76 名を集め，活発な議論が行われた．以下では，国内外から招聘した 5 名の 招待基調講演 (30 分) ，および総合討論の要旨を報告する．それ以外のショートトーク (5 分) ・ポスター発表に ついては，タイトルと著者名のみを挙げる．なお，発表は全て英語で行われたが，利便性を考え，各発表の英文 タイトルに和訳を付けるとともに，国内招待講演者の要旨の一部は日本語で掲載する． Keywords: magma process, magma system, time scale, pre-eruptive magma condition, magma decompression 講演要旨 -Abstract ＊ 平成 28 年 11 月 9 日 産業技術総合研究所つくばセンター中央 第一事業所 ネットワーク会議室において開催
Fluid Inclusion and Petrological Studies Elucidate Reconstruction of Magma Conduits
Eos, Transactions American Geophysical Union, 2004
In the summer of 1982, the Phlegraean Fields, a nested resurgent caldera located in the densely populated Naples area of Italy, started to give signals of unrest.However,after about 30 months of soil uplift (up to 5 mm per day) and intense shallow-depth, swarm-type seismicity (up to 100 shocks/hr), these phenomena diminished and alert warning for an imminent volcanic eruption ceased.A similar scenario went on at Vulcano, Italy, where an increase in the amount of fumarolic output and in gas temperatures (more than 700°) began in the winter of 1992. Also in this case,no eruption occurred,and gas temperatures and emission rates slowly returned to their normal values.
Introduction to Minerals, Inclusions and Volcanic Processes
Reviews in Mineralogy and Geochemistry, 2008
Minerals are intrinsically resistant to the processes that homogenize silicate liquids-their compositions thus yield an archive of volcanic and magmatic processes that are invisible at the whole rock scale. Minerals and their inclusions record diverse magma compositions, the depths and temperatures of magma storage, the nature of open system processes, and the rates at which magmas ascend. The potential for understanding volcanic systems through minerals and their inclusions has long been recognized (Sorby 1858). Sorby's (1863) study of James Hall's reversal experiments helped resolve the "basalt controversy" in favor of a volcanic origin, while zirkel's (1863) discovery of quartz within a volcanic rock helped tip the balance in favor of a magmatic origin for granite (Young 2003). Studies of phenocrysts have also long illustrated the importance of wall rock assimilation and magma mixing (e.g., Fenner 1926; Finch and Anderson 1930; Larson et al. 1938), and the potential for geothermometry (Barth 1934). Darwin's (1844) mineralogical field-studies in the Galapagos archipelago, followed by King's (1878) studies at Hawaii, also inaugurated the establishment of fractional crystallization as an important evolutionary process (Becker 1897; Bowen 1915). Recent advances in micro-analytical techniques open a new realm of detail, building upon a long history of mineralogical research; this volume summarizes some of this progress. Our summary focuses on volcanologic and magmatic processes, but the methods reviewed here extend well beyond terrestrial applications. Samples from the Stardust return mission, for example, show that olivine, plagioclase and pyroxene pervade the solar system (Brownlee et al. 2006)-while the topics covered here surely apply to all terrestrial-like planetary bodies, relevance may extend to a cosmic scale. Our more modest hope is that this volume will aid the study of disparate fields of terrestrial igneous systems, and perhaps provide a catalyst for new collaborations and integrated studies. OVerVIeW OF the VOLuMe Our review begins by tracing the origins of mineral grains, and methods to estimate pressures (P) and temperatures (T) of crystallization. Key to such attempts is an understanding of textures, and in her review, Hammer (2008) shows how "dynamic" experiments (conducted with varying P or T), yield important insights into crystal growth. Early dynamic experiments (e.g., Lofgren et al. 1974; Walker et al. 1978) have shown that porphyritic textures can result from a single episode of cooling. More recent experiments demonstrate that crystals can form during ascent due to loss of volatiles (Hammer and Rutherford 2002). Hammer (2008) describes these and other advances, and additional challenges that require new experimental The next four chapters document insights obtained from isotopic studies and diffusion profiles. Ramos and Tepley (2008) review developments of micro-analytical isotope measurements, which now have the potential to elucidate even the most cryptic of open system behaviors. 87 Sr/ 87 Sr ratios, for example, can be matched to dissolution surfaces to identify magma recharge events (Tepley et al. 2000). And 87 Sr/ 86 Sr-contrasts within and between phenocrysts allow differentiation between the roles of wall rock assimilation and enriched mantle sources to explain elevated 87 Sr/ 86 Sr (Ramos and Reid 2005). In the next chapter, Cooper and Reid
Dynamic crystallization in magmas
Mineral reaction kinetics: Microstructures, textures, chemical and isotopic signatures, 2017
Undercooling and crystallization kinetics are recognized increasingly as important processes controlling the final textures and compositions of minerals as well as the physicochemical state of magmas during ascent and emplacement. Within a single volcanic unit, phenocrysts, microphenocrysts and microlites can span a wide range of compositions, develop complex zoning patterns, and show intricate textures testifying to crystallization far from equilibrium. These petrographic complexities are not associated necessarily with magma chamber processes such as mixing or mingling of distinctly different bulk compositions but, rather, may be caused by variable degrees of initial magma-undercooling and the evolution of undercooling through time. Heat-dissipation and decompression are the most effective driving forces of cooling and volatile loss that, in turn, exert a primary control on the solidification path of magma. Understanding these kinetic aspects over the temporal and spatial scales at which volcanic processes occur is therefore essential to interpret correctly the time-varying environmental conditions recorded in igneous minerals. This contribution aims to summarize and integrate experimental studies pertaining to the crystallization of magmas along kinetic or time-dependent pathways, where solidification is driven by changes in temperature, pressure and volatile concentration. Fundamental concepts examined in the last decades include the effect of undercooling on crystal nucleation and growth as well as on the transition between interface-and diffusion-controlled crystal growth and mass transfer occurring after crystals stop growing. We summarize recent static and dynamic decompression and cooling experiments that explore the role of undercooling in syn-eruptive crystallization occurring as magmas ascend in volcanic conduits and are emplaced at the surface. The ultimate aim of such studies is to decode the textural and compositional information within crystalline phases to place quantitative constraints on the crustal transport, ascent and emplacement histories of erupted and intrusive magmas. Magma crystallization under dynamic conditions will be assessed also through a comparative description of the disequilibrium features in minerals found in experimental and natural materials. A variety of departures from polyhedral growth, including morphologies indicating crystal surface instability, dendritic structures, sector zoning and growth twins are linked to the rate at which crystals grow. These have implications for the entrapment of melt inclusions and plausibility for interpreting the growth chronology of individual crystals. A simple ''tree-ring'' model, in which the oldest part of the crystal lies at the centre and the youngest at the rim, is not an appropriate description when growth is non-concentric. Further, deviation from chemical