Catálogo de publicaciones - revistas
American Mineralogist
Resumen/Descripción – provisto por la editorial
No disponible.
Palabras clave – provistas por la editorial
No disponibles.
Disponibilidad
Institución detectada | Período | Navegá | Descargá | Solicitá |
---|---|---|---|---|
No detectada | desde feb. 1998 / hasta dic. 2023 | GeoScienceWorld |
Información
Tipo de recurso:
revistas
ISSN impreso
0003-004X
ISSN electrónico
1945-3027
País de edición
Estados Unidos
Fecha de publicación
1916-
Cobertura temática
Tabla de contenidos
doi: 10.2138/am-2022-8731
In-situ study of microstructures induced by the olivine to wadsleyite transformation at conditions of the 410 km depth discontinuity
Estelle Ledoux; Matthias Krug; Jeffrey Gay; Julien Chantel; Nadège Hilairet; Maxim Bykov; Elena Bykova; Georgios Aprilis; Volodymyr Svitlyk; Gaston Garbarino; Nicolas Guignot; Carmen Sanchez-Valle; Sergio Speziale; Sébastien Merkel
<jats:title>Abstract</jats:title> <jats:p>The olivine-wadsleyite transformation is believed to occur at depths of about 410 km in the Earth, producing a major seismic discontinuity in this region of the Earth’s mantle. The mechanism of this phase transition controls the microstructures of the newly nucleated wadsleyite, the major phase of the upper part of the mantle transition zone, and thus impacts seismic observations in the region. Here, we study the microstructures produced by the olivine-wadsleyite transformation using in situ laboratory experiments at pressures and temperatures relevant for the mantle transition zone. We transform pure olivine samples in laser-heated diamond-anvil cells at pressures ranging from 12.3 to 20.2 GPa and temperatures of 1400–1730 K. At different steps of the transformation we measure the orientation and size distribution of individual sample grains using multigrain crystallography at synchrotron radiation sources. We find that the olivine to wadsleyite transformation is incoherent at the conditions of the mantle transition zone, and is probably dominated by nucleation of wadsleyite at grain boundaries of the parent olivine. Thus, we expect that seismic anisotropy near 410 km would drop significantly due to the randomized lattice preferred orientation of newly nucleated wadsleyite induced by the incoherent transformation.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 2283-2293
doi: 10.2138/am-2022-8723
Effect of pre-existing crystals and melt homogeneity on the decompression-induced crystallization of hydrous rhyodacite magma
Kazuhisa Matsumoto; Satoshi Okumura; Akihiko Tomiya
<jats:title>Abstract</jats:title> <jats:p>Decompression-induced crystallization is an important process that controls the behavior of volcanic eruptions because it strongly affects magma rheology and degassing behavior in the shallow parts of volcanic conduits. Several decompression experiments have been performed to understand and model the crystallization processes; however, the effect of superheating (i.e., heating above the liquidus temperature for a definite period of time) before decompression has not been elucidated, despite the proposal of its importance in previous cooling experiments. As the superheating influences the number of pre-existing crystals and melt homogeneity, it is expected to control decompression-induced crystallization. In this study, we investigated the effects of pre-existing crystals and melt homogeneity on crystallization during the decompression of rhyodacitic magma at a temperature of 900 °C. The magma studied herein has a liquidus temperature of ~920 °C. Five starting materials were prepared via heating at different super-liquidus temperatures (940, 970, 1050, and 1300 °C) and a sub-liquidus temperature (900 °C) using an internally heated pressure vessel and a cold-seal pressure vessel, respectively. Decompression experiments using these starting materials were conducted from 130 to 30 MPa at decompression rates of 5, 20, and 100 MPa h–1. When the melt was completely homogenized (at 1050 and 1300 °C), no crystals were formed at 100 MPa h–1 and the small amounts of crystals heterogeneously formed along the capsule wall were found at 5 and 20 MPa h–1. At the same decompression rate, the number density of plagioclase formed during decompression increased as the superheating temperature decreased from 970 to 900 °C, despite the higher number densities of pre-existing crystals before decompression in the samples with lower superheating. Such finding indicates that nucleation occurs easily when the number density is initially high. This result is inconsistent with the idea that nucleation occurs when supersaturation is sufficient to overcome the energy barrier for nucleation, and the growth of pre-existing crystals decreases supersaturation. In contrast, the results of our experiments can be explained by considering that higher superheating results in a more homogeneous melt structure with few pre-crystal clusters, which are growth sites, and ultimately the suppression of nucleation. Based on these results, we conclude that pre-existing crystals and melt homogeneity strongly affect the crystal texture formed by decompression. For application to natural systems, the high number density of microlites found in natural samples may be due to heterogeneous nucleation caused by the presence of pre-crystal clusters and other mechanisms. Furthermore, the superheating of magma in a reservoir caused by the injection of high-temperature mafic magma may influence the crystal texture during magma ascent and, hence, control the explosivity of the eruption.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 2294-2307
doi: 10.2138/am-2022-8715
Origin of clinopyroxene-ilmenite symplectites in mafic granulites from eastern parts of the Chotanagpur granite gneissic complex, East Indian shield
Somdipta Chatterjee; Shreya Karmakar; Subham Mukherjee; Sanjoy Sanyal; Pulak Sengupta
<jats:title>Abstract</jats:title> <jats:p>In this manuscript, we report a rare occurrence of rod-like intergrowths of clinopyroxene-ilmenite that variably replace titanite in a suite of high-pressure mafic granulites from the Chotanagpur Granite Gneissic Complex, Eastern Indian Shield. Garnet proximal to the clinopyroxene-ilmenite intergrowth is invariably replaced with symplectic clinopyroxene-plagioclase or a rind of plagioclase. Textural modeling of the reaction textures and mineral compositions suggests that the garnet-titanite became unstable and the ilmenite-clinopyroxene preferentially develop after titanite. The presence and texture of halogen rich apatites within the ilmenite-clinopyroxene symplectite are consistent with a fluid mediated process. Thermodynamic modeling in the NCFMAST (+H2O) system, demonstrates that the clinopyroxene-ilmenite symplectite was formed along a steeply decompressive retrograde P-T path (from ~13 to ~7 kbar, at ~800 °C), in the presence of partial melts. The study demonstrates that relative to Fe, Mg, and Ca, Ti was less mobile and that the mobility of Ti was restricted within the confines of titanite being replaced by the clinopyroxene-ilmenite symplectite. This study implies that besides the ligand activity, the fluid/rock ratio exerts a strong control on the length scale of Ti transport in natural rocks.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 2308-2322
doi: 10.2138/am-2022-8432
Crystal structure of calcium-ferrite type NaAlSiO4 up to 45 GPa
Fei Qin; Ye Wu; Shengchao Xue; Dongzhou Zhang; Xiang Wu; Steven D. Jacobsen
<jats:title>Abstract</jats:title> <jats:p>Alkali-rich aluminous high-pressure phases including calcium-ferrite (CF) type NaAlSiO4 are thought to constitute ~20% by volume of subducted mid-ocean ridge basalt (MORB) under lower mantle conditions. As a potentially significant host for incompatible elements in the deep mantle, knowledge of the crystal structure and physical properties of CF-type phases is therefore important to understanding the crystal chemistry of alkali storage and recycling in the Earth’s mantle. We determined the evolution of the crystal structure of pure CF-NaAlSiO4 and Fe-bearing CF-NaAlSiO4 at pressures up to ~45 GPa using synchrotron-based, single-crystal X-ray diffraction. Using the high-pressure lattice parameters, we also determined a third-order Birch-Murnaghan equation of state, with V0 = 241.6(1) Å3, KT0 = 220(4) GPa, and KT0′ = 2.6(3) for Fe-free CF, and V0 = 244.2(2) Å3, KT0 = 211(6) GPa, and KT0′ = 2.6(3) for Fe-bearing CF. The addition of Fe into CF-NaAlSiO4 resulted in a 10 ± 5% decrease in the stiffest direction of linear compressibility along the c-axis, leading to stronger elastic anisotropy compared with the Fe-free CF phase. The NaO8 polyhedra volume is 2.6 times larger and about 60% more compressible than the octahedral (Al,Si)O6 sites, with K0NaO8 = 127 GPa and K0(Al,Si)O6 ~304 GPa. Raman spectra of the pure CF-type NaAlSiO4 sample shows that the pressure coefficient of the mean vibrational mode, 1.60(7) cm–1/GPa, is slightly higher than 1.36(6) cm−1/GPa obtained for the Fe-bearing CF-NaAlSiO4 sample. The ability of CF-type phases to contain incompatible elements such as Na beyond the stability field of jadeite requires larger and less-compressible NaO8 polyhedra. Detailed high-pressure crystallographic information for the CF phases provides knowledge on how large alkali metals are hosted in alumina framework structures with stability well into the lowermost mantle.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 2331-2337
doi: 10.2138/am-2022-8588
Revision of the CaMgSi2O6-CO2P-T phase diagram at 3–6 GPa
Anton Shatskiy; Yulia G. Vinogradova; Anton V. Arefiev; Konstantin D. Litasov
<jats:title>Abstract</jats:title> <jats:p>We reexamined the phase relationships in the system diopside-CO2 in the range of 3–6 GPa and 850–1500 °C in multi-anvil experiments, including reversal ones lasting up to 169 h. The reaction CaMgSi2O6 (clinopyroxene) + 2CO2 (fluid) = 2SiO2 (quartz/coesite) + CaMg(CO3)2 (dolomite) passes through 3 GPa/950 °C with a slope of 6 MPa/°C and terminates at an invariant point near 4.5 GPa/1200 °C, where carbonate liquid coexists with clinopyroxene, coesite, dolomite, and CO2 fluid. The newly determined boundary has the equation P(GPa) = 0.006 × T(°C) – 2.7. As temperature increases to 1250 °C at 4.5 GPa, liquid, dolomite, and coesite disappear, and clinopyroxene coexists with CO2 fluid. As pressure increases to 6 GPa, the solidus temperature increases to 1300 °C revealing a slope of 15 MPa/°C. At 4.5 and 6 GPa, solidus melts contain about 1 wt% SiO2. As temperature increases to 1400 and 1500 °C at 6 GPa, the silica contents in the carbonate melt increase to 6 and 13 wt%, respectively. Our data, combined with that of Luth (2006), indicate that above 4.5 GPa the liquidus reaction involving clinopyroxene and CO2 sweeps down through 350 °C via a pressure maximum near 5.3 GPa to meet the invariant point at 4.5 GPa. The shape of the diopside-CO2 solidus resembles that of lherzolite-CO2 (Wyllie and Huang 1975a) but shifted by 2 GPa to higher pressure. Thus, the deep depression along the solidi in the system CaO-MgO-SiO2-CO2 is a fundamental feature of both ultramafic and mafic assemblages at depths of 70–150 km.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 2338-2347
doi: 10.2138/am-2022-8851
Crystal growth according to the law of proportionate effect
D.D. Eberl
<jats:title>Abstract</jats:title> <jats:p>This paper summarizes an approach to crystal growth that was published in parts in various articles over the course of 25 years by the present author and his colleagues. Evidence for this approach, which is confirmed in detail by data in the cited publications and in the figures and equations in the supplementary material that accompanies this paper (see the Online Materials1), comes mainly from the shapes of crystal size distributions (CSDs). Such distributions reveal the growth histories of natural minerals and synthetic compounds, histories that can be used to make geological interpretations and to guide industrial syntheses.</jats:p> <jats:p>CSDs have three fundamental shapes: log-normal, asymptotic, and Ostwald. These shapes result from different degrees of supersaturation near the time of nucleation. The first two distribution shapes form according to the Law of Proportionate Effect (LPE) at moderate supersaturation, and the latter rare distribution forms by Ostwald ripening at large supersaturation. Initially, the first two distributions have mean diameters of up to tens of nanometers and grow by surface-limited growth kinetics. The slow step in this reaction is the incorporation of nanoparticles (bits of crystal or adparticles) onto the crystal surface. As the crystals become larger, their demand for nutrients, as calculated by the LPE, increases exponentially. Then the slow step in the reaction changes to the rate of transfer of nutrients to the crystal (supply- or transport-limited growth). Crystal diameters often grow the most during this latter stage, and the initial CSD shapes that originally formed during surface-limited growth are retained and scaled up proportionately.</jats:p> <jats:p>Proportionate growth during the supply-limited stage can be simulated approximately by multiplying the diameter of each crystal in a distribution by a constant. Crystals can also grow by a constant rate law in which a constant length is added to each crystal diameter in the distribution. This rare process causes the original CSD to narrow so that its initial shape is not preserved. The growth law that prevails, either proportionate or constant, is determined by the manner in which nutrients are supplied to the crystal. Supply is by advective flow during proportionate growth, with the nutrient solution moving with respect to the crystals. Constant growth relies on the random diffusion of nutrients through a quiescent solution. Proportionate growth is by far the most common growth law, and therefore, nutrient supply by diffusion alone during crystal growth is uncommon.</jats:p> <jats:p>Distributions formed by Oswald ripening and those formed by other rare processes are also discussed. During Ostwald ripening, nucleation caused by mixing reactants at large supersaturation forms crystals that are extremely fine and numerous. The larger crystals grow at the expense of the finer, less stable crystals, thereby forming, on completion, the universal steady-state CSD shape predicted by the Lifshitz-Slyozov-Wagner (LSW) theory. This unique CSD shape, as well as other rare shapes, then are scaled up to larger sizes by supply limited proportionate growth.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 2-7
doi: 10.2138/am-2022-8824
Melt-mediated re-equilibration of zircon produced during meltdown of the Chernobyl reactor
Denis Fougerouse; Thorsten Geisler; Steven M. Reddy; Matvei Aleshin; Laure Martin; Luc S. Doucet; Zakaria Quadir; David Saxey; William Rickard
<jats:title>Abstract</jats:title> <jats:p>The mineral zircon is used widely to constrain the age of rocks and the processes that formed them. Although zircon is robust to a range of physical and chemical processes, it may show evidence for rapid re-equilibration that is generally considered to reflect interaction with hydrous fluids. Here, we show that zircon grains that crystallized from melt produced during the catastrophic meltdown of the Chernobyl nuclear reactor exhibit re-equilibration textures that occurred in an environment without free water. The process of re-equilibration involved a melt-mediated interface-coupled dissolution-reprecipitation that took place over a few days to produce textures that are commonly observed in igneous and anatectic systems. Thus, the composition of zircon can be modified even in the absence of hydrous fluids in a short time frame. Through this process, zircon crystals may track the timing of the last silicate melt they interacted with.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 8-14
doi: 10.2138/am-2022-8790
Subsolidus breakdown of armalcolite: Constraints on thermal effects during shock lithification of lunar regolith
Tian-Ran Trina Du; Ai-Cheng Zhang; Jia-Ni Chen; Yuan-Yun Wen
<jats:title>Abstract</jats:title> <jats:p>Shock lithification of regolith breccias is a ubiquitous process on the surfaces of airless planetary bodies and may induce thermal effects, including melting on regolith breccia minerals. However, potential thermal effects on lithic and mineral clasts in regolith breccias have seldom been quantitatively constrained. Here, we report two types of micro-textures of armalcolite [(Mg,Fe2+)Ti2O5] in an Mg-suite lithic clast from lunar regolith breccia meteorite Northwest Africa 8182. One type of armalcolite contains oriented fine-grained ilmenite grains; the other occurs as an aggregate of ilmenite, rutile, spinel, and loveringite. We propose that the two types of micro-textures formed through subsolidus breakdown of armalcolite by different processes. The formation of ilmenite inclusions in armalcolite is related to slow cooling after the solidification of its source rock, whereas the ilmenite-rutile-spinel-loveringite aggregates probably formed during the shock lithification event of NWA 8182. The results indicate that the temperature at the margin of lithic clasts could be raised up to at least 600 °C during strong shock lithification of lunar regolith and has profound thermal effects on the mineralogical and isotopic behaviors of lithic and mineral fragments in lunar regolith breccias.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 24-34
doi: 10.2138/am-2022-8594
Melting and melt segregation processes controlling granitic melt composition
Yang Yu; Xiao-Long Huang; Roberto F. Weinberg; Min Sun; Peng-Li He; Le Zhang
<jats:title>Abstract</jats:title> <jats:p>Several important processes in the petrogenesis of granite are still debated due to a poor understanding of complex interactions between minerals during the melting and melt segregation processes. To promote an improved understanding of the mineral-melt relationships, we present a systematic petrographic and geochemical analysis for melanosome and leucosome samples from the Triassic Jindong migmatite, South China. Petrographic observations and zircon U-Pb geochronology indicate that the Jindong migmatite was formed through water-fluxed melting of the Early Paleozoic gneissic granite (437 ± 2 Ma) during the Triassic (238 ± 1 Ma), with the production of melt dominated by the breakdown of K-feldspar, plagioclase, and quartz. The Jindong leucosomes may be divided into lenticular and net-structured types. Muscovite, plagioclase, and K-feldspar in the net-structured leucosome show higher Rb and much lower Ba and Sr contents than those in the lenticular leucosome. This may be attributed to the elevation of Rb and decreasing Ba and Sr abundances in melts during the segregation process due to early fractional crystallization of K-feldspar and plagioclase. These leucosomes show negative correlation between εNd(t) and P2O5, reflecting increasing dissolution of low-εNd(t) apatite during the melting process. The continuous dissolution of apatite caused saturation of monazite and xenotime in melt, resulting in the growth of monazite and xenotime around apatite in the melanosome. This process led to a sharp decrease of Th, Y, and REE with increasing P2O5 in the leucosome samples. This complex interplay of accessory mineral reactions in the source impacts REE geochemistry and Nd isotope ratios of granites. As the granites worldwide exhibit similar compositional and isotopic patterns to the Jindong leucosomes, we suggest that both the melting and melt segregation processes strongly control the granitic melt compositions.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 35-50
doi: 10.2138/am-2022-8610
Magmatic degassing controlled the metal budget of the Axi epithermal gold deposit, China
Nuo Li; Bo Zhang; Thomas Ulrich; A.E. Williams-Jones; Yanjing Chen
<jats:title>Abstract</jats:title> <jats:p>From integrated textural and compositional studies of auriferous and barren pyrite/marcasite in the epithermal Axi gold deposit, China, we have identified a relationship between multiple gold mineralizing events, mafic magma recharge, and fluid-rock reactions. Three generations of pyrite (Py1–3) and four generations of marcasite (Mar1–4) record episodic gold mineralizing events, followed by silver-copper-lead-zinc-cadmium enrichment. The gold mineralizing events are recorded by high concentrations of subnanometer-sized gold in Py1, Py3, and Mar3 (max. = 147, 129, and 34 ppm, med. = 39, 34, and 12 ppm). Based on previous Re-Os age determinations of pyrite and U-Pb zircon ages of the andesitic wallrock, these gold events slightly postdate pulsed mafic magma recharge and represent the incursion of Au-As-S-rich magmatic volatiles into circulating meteoric water. Silver-Cu-Pb-Zn-Cd enrichment in Py2, Mar2, and Mar4 are consistent with quiescent degassing and gradual Ag-Cu-Pb-Zn-Cd enrichment in an evolved felsic magma. Barren Mar1 records the dominance of meteoric water and a limited magmatic fluid contribution. High-Co-Ni-V-Cr-Ti contents in porous cores of Py1 and Mar2 are attributed to wall rock alteration and dissolution-reprecipitation. The results provide convincing evidence that the metal budget (especially for Au, Ag, Cu, Pb, Zn, Sb) of the hydrothermal fluids and sulfides in epithermal systems are controlled by the influx of magmatic fluids and associated magma, whereas the enrichment of certain fluid-immobile elements, such as Co, Ni, V, Cr, and Ti, is caused in part by fluid-rock interaction.</jats:p>
Palabras clave: Geochemistry and Petrology; Geophysics.
Pp. 51-60