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Silicate Liquid Immiscibility in Lunar Magmas, Evidenced by Melt Inclusions in Lunar Rocks
Abstract
Examination of multiphase melt inclusions in 91 sections of 26 lunar rocks revealed abundant evidence of late-stage immiscibility
in all crystalline rock sections and in soil fragments and most breccias. The two individual immiscible silicate melts (now
glasses) vary in composition, but are essentially potassic granite and pyroxenite. This immiscibility may be important in
the formation of the lunar highlands and tektites. Other inclusions yield the following temperatures at which the several
minerals first appear on cooling the original magma: ilmenite (?) liquidus, 1210°C; pyroxene, 1140°C; plagioclase, 1105°C;
solidus, 1075°C. The glasses also place some limitations on maximum and minimum cooling rates.
... By using analog elemental ratios (see below), the effect of post-entrapment crystallization would be circumvented. Post-entrapment crystallization might also be reversed using homogenization experiments (Roedder et al., 1970a(Roedder et al., , b, 1971Chen et al., 2015Chen et al., , 2022, although it is difficult to choose the right temperature, pressure, and duration for the perfect reversal of the post-entrapment crystallization effect (Pettke, 2006). Many crystalline MIs were studied without heating to homogenize them. ...
... v. Post-entrapment bubble growth (Roedder and Weiblen, 1970a;Wallace et al., 2015). Often a bubble can be found in an MI (e.g., Fig. 1c), which would have changed the concentrations of the volatile elements in the MI. ...
... The work on liquid immiscibility using lunar MIs (e.g., Roedder and Weiblen, 1970a, b, 1971, 1972a has also continued. Zeng et al. (2020) investigated the major and trace element composition of MIs hosted by the oldest zircon (4.382 ± 0.040 Ga) known, in lunar rock NWA10049. ...
Mineral-hosted melt inclusions provide a window into magmatic processes and pre-eruptive liquid compositions. Because melt inclusions are small (typically < 100 µm), the study of lunar melt inclusions is enabled by advancements of microbeam instrumental techniques. In the 1970s immediately following the Apollo and Luna missions, major and minor oxide concentrations of lunar melt inclusions were measured using electron microprobes. The data were used to understand magma evolution, and they revealed the immiscibility of two silicate liquids in the late stage of lunar magma evolution. More recently, the development of secondary ion mass spectrometry as well as laser ablation–inductively coupled plasma–mass spectrometry has enabled the measurement of key volatile elements and other trace elements in lunar melt inclusions, down to about the 0.1 ppm level. The applications of these instruments have ushered in a new wave of lunar melt inclusion studies. Recent advances have gone hand in hand with improved understanding of post-entrapment loss of volatiles. These studies have provided deep insights into pre-eruptive volatiles in lunar basalts, the abundance of volatiles in the lunar mantle, the isotopic ratios of some volatile elements, and the partition of trace elements between host olivine and melt inclusions. The recent studies of lunar melt inclusions have played a critical role in establishing a new paradigm of a fairly wet Moon with about 100 ppm H2O in the bulk silicate Moon (rather than a “bone-dry” Moon) and have been instrumental in developing an improved understanding of the origin and evolution of the Moon.
... The record of high temperature system dynamics preserved in fallout shares similarities with and thus can also assist in understanding other high temperature processes such as planetary formation in the early solar system (Day et al., 2017;Bonamici et al., 2017), meteorite impacts and tektite formation (Bunch et al., 2012;Glass et al., 1987), lightning strike fulgurite glass (Essene and Fisher, 1986;Pasek and Pasek, 2018), lunar glass (Roedder and Weiblen, 1970) and terrestrial magmatic systems (Kamenetsky et al., 2013;Veksler et al., 2007). In particular, cratering meteorite impact events mix impactor and target lithologies (Osinski et al., 2008;Grieve and Pesonen, 1996) resulting in complex melt evolution (Hamann et al., 2018;Osinski, 2003) which cools at similar rates as nuclear fireball systems (10s-100 s K/sec) (Cassata et al., 2014;Weisz et al., 2018;Ebert et al., 2017). ...
... Many distinct micron-scale (2-20 μm) iron-rich spheres lacking local gradations and consisting of two distinct L Fe and L Si phases with sharp phase boundaries are concentrated on or near (<50 μm) sample surfaces ( Fig. 2D-N). These distinct micro-scale spheres predominantly consist of the minority phase dispersed within the majority phase ( Fig. 2D-G), and resemble immiscible amoeboid inclusion textures (Roedder and Weiblen, 1970;Hamann et al., 2018). As such, we refer to distinct spherical micron-scale two-phase objects as amoeboids in this work to distinguish them from other emulsion and solidification micro-structures. ...
... systems (Essene and Fisher, 1986;Roedder and Weiblen, 1970;Roedder, 1978;Veksler et al., 2007). While some textural evidence of liquid immiscibility reported in this work resembles textures reported in trinitite glass formed in the first nuclear explosion (Bunch et al., 2012;Eby et al., 2015), ex situ amoeboids significantly deviate from previous immiscibility observations. ...
Above-ground nuclear explosions that interact with the surface of the earth entrain materials from the surrounding environment, influencing the resulting physical and chemical evolution of the fireball, which can affect the final chemical phase and mobility of hazardous radionuclides that are dispersed in the environment as fallout particles. The interaction of iron with a nuclear explosion is of specific interest due to the potential for iron to act as a redox buffer and because of the likelihood of significant masses of metals to be present in urban environments. We investigated fallout from a historic surface interacting nuclear explosion conducted on a steel tower and report the discovery of widespread and diverse iron-rich micro-structures preserved within the samples, including crystalline dendrites and micron-scale iron-rich spheres with liquid immiscibility textures. We assert these micro-structures reflect local redox conditions and cooling rates and can inform interpretation of high temperature events, enabling new insights into fireball condensation physics and chemistry when metals from the local environment (i.e. structural steel) are vaporized or entrained. These observations also significantly expand the availability of silicate immiscibility datasets applicable to rapidly quenched systems such as meteorite impact melt glass.
... Evidence of silicate liquid immiscibility in ferrobasalts is provided by co-existing Fe-and Si-rich melt inclusions (e.g. Fischer et al., 2016;Jakobsen et al., 2005;Jakobsen et al., 2011;Luais, 1987;Roedder and Weiblen, 1970c) and Fe-rich droplets dispersed in the Si-rich glassy mesostasis of rapidly cooled rocks (e.g. De, 1974;Philpotts, 1982;Philpotts and Doyle, 1980). ...
... Co-existing Fe-and Si-rich melt inclusions (e.g. Fischer et al., 2016;Jakobsen et al., 2005;Jakobsen et al., 2011;Luais, 1987;Roedder and Weiblen, 1970c) and Fe-rich droplets dispersed in Si-rich glassy mesostasis in rapidly cooled natural examples (e.g. De, 1974;Philpotts, 1982;Philpotts and Doyle, 1980), provide evidence of immiscibility in ferrobasaltic liquid. ...
... The unmixing of mafic magmas into immiscible pairs of Fe-rich and Si-rich conjugates was first identified in lunar samples (Roedder and Weiblen, 1970c) and subsequently in terrestrial volcanic and plutonic rocks (Charlier et al., 2013;De, 1974;Dixon and Rutherford, 1979;Jakobsen et al., 2005;Namur et al., 2012;Philpotts, 1979). Given the preferential partitioning of elements of economic interest into the Fe-rich conjugate (Veksler et al., 2006), a detailed understanding of the mechanisms by which significant differences in viscosity, density and wetting properties of the two liquids control the physical behaviour of the unmixed liquids in a crystal mush is essential to better understand the origin of ore deposits hosted in mafic bodies (Kolker, 1982;Nielsen et al., 2015;Ripley et al., 1998). ...
Evidence of silicate liquid immiscibility in ferrobasalts is provided by co-existing Fe- and Si-rich melt inclusions and Fe-rich droplets dispersed in the Si-rich glassy mesostasis of rapidly cooled rocks. Crucially, the different physical properties of these unmixed liquids mean that they may migrate and separate within a granular medium, forming chemically distinct accumulations. I combine experiments, geochemistry, image analysis and field observations to better quantify the physical behaviour of emulsions in ferrobasaltic magmas.
Quantification of the microstructural evolution of an emulsion in ferrobasaltic experiments shows that the Fe-rich liquid forms homogeneously nucleated droplets dispersed in an immiscible Si-rich liquid, together with droplets heterogeneously nucleated on plagioclase, magnetite, and pyroxene. Heterogeneous nucleation is likely promoted by localised compositional heterogeneities around growing crystals. The equilibrium wetting angle of Fe-rich droplets on both plagioclase and magnetite increases with decreasing temperature. Droplet coarsening occurs by diffusion-controlled growth (including Ostwald ripening), with an insignificant contribution from coalescence. The experimental observations are scaled to infer that in magma bodies < ~10 m in size, gravitationally-driven segregation of immiscible Fe-rich droplets is unlikely to be significant. The same concepts are investigated using natural samples with preserved immiscible textures found in tholeiitic basaltic glass from Hawaii (USA), the Snake River Plain (USA), and the Laki eruption (Iceland). High-resolution imaging, electron probe microanalysis, and atom probe tomography are combined to examine the role played by compositional boundary layers in promoting unmixing around growing crystals at melt-crystal interfaces. The effects of cooling rate on silicate liquid immiscibility microstructure are studied using basaltic dykes from Northeast England, coupled with simple 1D thermal models. The size of Fe-rich droplets within a continuous silicic phase is found to increase with decreasing cooling rate. At the even slower cooling rate of the Skaergaard Intrusion, field, whole rock and petrographic observations of late-stage immiscible segregations show that complete segregation of unmixed liquids on the metre scale is feasible; therefore, timescales of cooling are shown to be a key factor in immiscible liquid separation.
... By implication, late volatiles may be present locally, altering earlier dry assemblages. All this is consistent with our general knowledge about fractional crystallization of magmas on Earth (e.g., [23,24]) in which the last melts will increase in volatile and incompatible elements by orders of magnitude. This is also a fundamental aspect of thermodynamic modeling tools for the input conditions used when calculating mineral equilibria in such mineral assemblages (e.g., MELTS [25,26] and SPICES [27,28]). ...
... By implication, late volatiles may be present locally, altering earlier dry assemblages. All this is consistent with our general knowledge about fractional crystallization of magmas on Earth (e.g., [23,24]) in which the last melts will increase in volatile and incompatible elements by orders of magnitude. This is also a fundamental aspect of thermodynamic modeling tools for the input conditions used when calculating mineral equilibria in such mineral assemblages (e.g. ...
... Apatite is among the final mineral phases to crystallize within basaltic systems, commonly crystallizing within microdomains of residual, late-stage, interstitial melt pockets (mesostasis). These pockets display variable mineralogy, and commonly show evidence for having undergone silicate liquid immiscibility (SLI), (e.g., [6,23,29,30]). This process occurs during the late-stage differentiation of Fe-rich terrestrial and lunar basalts, commonly producing coeval Fe-rich and Si-rich liquid compositions (e.g., [23,24,31]). ...
We present reaction balancing and thermodynamic modeling based on microtextural observations and mineral chemistry, to constrain the history of phosphate crystallization within two lunar mare basalts, 10003 and 14053. Phosphates are typically found within intercumulus melt pockets (mesostasis), representing the final stages of basaltic crystallization. In addition to phosphates, these pockets typically consist of Fe-rich clinopyroxene, fayalite, plagioclase, ilmenite, SiO2, and a residual K-rich glass. Some pockets also display evidence for unmixing into two immiscible melts: A Si-K-rich and an Fe-rich liquid. In these cases, the crystallization sequence is not always clear. Despite petrologic complications associated with mesostasis pockets (e.g., unmixing), the phosphates (apatite and merrillite) within these areas have been recently used for constraining the water content in the lunar mantle. We compute mineral reaction balancing for mesostasis pockets from Apollo high-Ti basalt 10003 and high-Al basalt 14053 to suggest that their parental magmas have an H2O content of 25 ± 10 ppm, consistent with reported estimates based on directly measured H2O abundances from these samples. Our results permit to constrain in which immiscible liquid a phosphate of interest crystallizes, and allows us to estimate the extent to which volatiles may have partitioned into other phases such as K-rich glass or surrounding clinopyroxene and plagioclase using a non-destructive method.
... which immiscibility can occur are reduced into insignificance by the addition of small amounts of a third component (e.g., alkalis or alumina). It was not until the 1970s that the discovery of melt inclusions in lunar rocks containing two compositionally different glass phases (Roedder and Weiblen, 1970) and syenitic ocelli in lamprophyre dykes and sills in the Monteregian province, Québec (Philpotts, 1970) caused researchers to re-consider liquid immiscibility in igneous petrogenesis. Since then, large numbers of fieldbased and experimental studies have established that liquid immiscibility is an important mechanism for producing compositional diversity in igneous rocks (Philpotts, 1970;Roedder and Weiblen, 1970;Ferguson and Currie, 1971;Lapin, 1974;Rankin and Lebas, 1974;Philpotts, 1978;Roedder, 1978;Eby, 1979;Freestone and Hamilton, 1980;Treiman and Essene, 1985;Davidson and Kamenetsky, 2001;Veksler, 2004;Peretyazhko et al., 2007;Thomas and Davidson, 2008;Kamenetsky and Kamenetsky, 2010). ...
... It was not until the 1970s that the discovery of melt inclusions in lunar rocks containing two compositionally different glass phases (Roedder and Weiblen, 1970) and syenitic ocelli in lamprophyre dykes and sills in the Monteregian province, Québec (Philpotts, 1970) caused researchers to re-consider liquid immiscibility in igneous petrogenesis. Since then, large numbers of fieldbased and experimental studies have established that liquid immiscibility is an important mechanism for producing compositional diversity in igneous rocks (Philpotts, 1970;Roedder and Weiblen, 1970;Ferguson and Currie, 1971;Lapin, 1974;Rankin and Lebas, 1974;Philpotts, 1978;Roedder, 1978;Eby, 1979;Freestone and Hamilton, 1980;Treiman and Essene, 1985;Davidson and Kamenetsky, 2001;Veksler, 2004;Peretyazhko et al., 2007;Thomas and Davidson, 2008;Kamenetsky and Kamenetsky, 2010). Two main types of liquid immiscibility have been widely recognized, namely silicate-silicate immiscibility involving feldspathic and gabbroic alkaline magmas (Philpotts, 1970;Roedder and Weiblen, 1970;Philpotts, 1971;Roedder and Weiblen, 1978;Eby, 1979;Charlier et al., 2013;Kamenetsky et al., 2013) and silicate-carbonate immiscibility (Ferguson and Currie, 1971;Lapin, 1974;Rankin and Lebas, 1974;Freestone and Hamilton, 1980;Treiman and Essene, 1985;Panina and Motorina, 2008;Mitchell, 2009;Kamenetsky and Kamenetsky, 2010;Sharygin et al., 2012). ...
... Since then, large numbers of fieldbased and experimental studies have established that liquid immiscibility is an important mechanism for producing compositional diversity in igneous rocks (Philpotts, 1970;Roedder and Weiblen, 1970;Ferguson and Currie, 1971;Lapin, 1974;Rankin and Lebas, 1974;Philpotts, 1978;Roedder, 1978;Eby, 1979;Freestone and Hamilton, 1980;Treiman and Essene, 1985;Davidson and Kamenetsky, 2001;Veksler, 2004;Peretyazhko et al., 2007;Thomas and Davidson, 2008;Kamenetsky and Kamenetsky, 2010). Two main types of liquid immiscibility have been widely recognized, namely silicate-silicate immiscibility involving feldspathic and gabbroic alkaline magmas (Philpotts, 1970;Roedder and Weiblen, 1970;Philpotts, 1971;Roedder and Weiblen, 1978;Eby, 1979;Charlier et al., 2013;Kamenetsky et al., 2013) and silicate-carbonate immiscibility (Ferguson and Currie, 1971;Lapin, 1974;Rankin and Lebas, 1974;Freestone and Hamilton, 1980;Treiman and Essene, 1985;Panina and Motorina, 2008;Mitchell, 2009;Kamenetsky and Kamenetsky, 2010;Sharygin et al., 2012). In addition to these two main types of immiscibility, silicate magmas have also been shown to exsolve sulfide liquids (long accepted as a means of forming Cu-Ni-PGE ore deposits), phosphate liquids (Panina and Motorina, 2008), and chloride liquids (Webster, 2004;Panina and Motorina, 2008). ...
Pegmatites and adjacent subsolvus granites (two alkali feldspars) of the Mid-Proterozoic Strange Lake pluton (Québec-Labrador, Canada) host potentially economic concentrations of high field strength elements (HFSE), including the rare earth elements (REE), zirconium and niobium. Previous studies have proposed that these concentrations were the result of a combination of extreme fractionation of a peralkaline granitic magma and later hydrothermal remobilization. However, the recent discovery of melt inclusions which, after heating to 900 or 950 °C, quench to immiscible fluoride and silicate glasses, suggests an additional mechanism of HFSE concentration.
... Pioneering studies revealed the first unambiguous registers of immiscible silicate liquids in groundmass glasses of lunar and terrestrial basaltic rocks (De, 1974;Roedder, 1951Roedder, , 1979Roedder and Weiblen, 1970). Immiscibility resulting in the unmixing of Fe-rich and Si-rich paired silicate melts has been lately identified in tholeiitic and andesitic rocks from both volcanic and plutonic occurrences (e.g., Charlier et al., 2013;Jakobsen et al., 2005;Kamenetsky et al., 2013;Namur et al., 2012;Philpotts, 1982;Veksler and Charlier, 2015). ...
... In general, immiscibility is usually accepted as a late-stage differentiation mechanism of basalts, based on experiments conducted on average tholeiitic compositions (Na 2 O + K 2 O < 4 wt%, and 49 < SiO 2 < 51 wt%), herein considered as relatively "alkali-poor" (e.g., Charlier et al., 2011;Dixon and Rutherford, 1979;Roedder, 1951Roedder, , 1978. The average composition of the mesostasis containing unmixed glasses in natural occurrences, normally with SiO 2 contents >65 (wt%), also attests to highly evolved residual liquids (Philpotts, 1982;Roedder and Weiblen, 1970). For "alkali-rich" tholeiitic and transitional Ol-and Hy-normative bearing basalts (4 < Na 2 O + K 2 O wt% < 5, and 49 < SiO 2 wt% < 51), termed alkaline basalts by Philpotts (1982), immiscibility has been mostly ignored, despite experimental studies suggesting the enlargement of the immiscibility field by increasing the contents of alkalis, TiO 2 , and P 2 O 5 at lower iron contents (e.g., Charlier and Grove, 2012;Freestone, 1978). ...
The role of silicate liquid immiscibility in the magmatic evolution of basalts and accounting for the scarcity of intermediate compositions on Earth's surface (Daly Gap) remains a matter of debate. Here we report the first finding of natural, immiscible Fe- and Si-rich silicate melts entrapped as apatite-hosted silicate Melt Inclusions (MIs) in the sub-volcanic Limeira Intrusion, a basic-intermediate layered occurrence associated with the Paraná Magmatic Province (PMP), southeastern Brazil. At least three nested magma pulses constitute this igneous body, in which compositional and textural features of the youngest one indicate the effective redistribution of a Si-rich liquid to the top and the sinking of a paired Fe-Ti-P-rich one to the bottom. Compared to other well-known natural immiscible liquids through multivariate statistics (Principal Component Analysis), MIs and whole-rock compositions of the Limeira Intrusion strongly support the role of silicate liquid immiscibility in the evolution of this intrusion. The incomplete unmixing or the mixing between varying proportions of the immiscible liquids containing early-formed crystals within a mush is the best mechanism explaining the origin of intermediate compositions in this intrusion, possibly induced by multiple magma batches. Based on whole-rock compositions and thermodynamic models, when the liquid line of descent reaches relatively high amounts of alkalis (Na2O + K2O ≥ 5–6 wt%) and the SiO2 (55–57 wt%), residual liquids can unmix to give rise to a paired Fe-rich and Si-rich immiscible liquids if the temperature is kept at relatively high values during prolonged periods. To test this hypothesis, experimental studies were conducted on two natural basic and intermediate samples, representing the first basaltic pulse that initiated the intrusion and the third/last basaltic-andesitic batch, respectively. Experiments were conducted under atmospheric conditions and oxygen fugacities close to the Fayalite-Magnetite-Quartz (FMQ) buffer, and immiscible liquids were produced only in isothermal conditions (ca. 1010 °C) starting with the intermediate sample. Our findings suggest that silicate liquid immiscibility can be significant in making intermediate compositions in this recharging basaltic-fed system, owing to the incomplete/inefficient unmixing of paired immiscible liquids and heat maintenance in the magma reservoir. Additionally, our interpretations can be extended to the whole PMP and contribute to our understanding of the Daly Gap for the high-Ti, alkali-rich tholeiitic compositions, suggesting large-scale magmatic differentiation due to liquid immiscibility along the tholeiitic liquid line of descent.
... The occurrence of slicate melts splitting into Si-rich felsic and Fe-rich mafic conjugate liquids (i.e., SLI mechanism) is generally observed in the late-stage mesostasis pockets and melt inclusions within both terrestrial and lunar basalts (e.g., Roedder and Weiblen, 1970;Hess et al., 1975;Longhi, 1998;Potts et al., 2016;He et al., 2022) and at least has been recorded in a lunar intrusive rock, merrillite-QMD 14161,7373 (Jolliff et al., 1999). In recent years, large-scale SLI mechanism has been proposed to explain the formation of Apollo granitic rocks (e.g., Taylor et al., 1980;Jolliff, 1998;Jolliff et al., 1999), but whether it plays a role in the petrogenesis of young lunar silicic rocks needs to be evaluated. ...
... Three main processes have been proposed to produce highly evolved compositions: highly differentiation of mafic magma through fractional crystallization (e.g., Ryder, 1976;Neal and Taylor, 1989b;Jolliff et al., 2011;Filiberto et al., 2014), magma differentiation with SLI (e.g., Roedder and Weiblen, 1970;Hess, 1989;Jolliff, 1991), and low-degree partial melting of crustal rocks (e.g., Bergantz, 1989;Lawrence et al., 2005;Hagerty et al., 2006;Day et al., 2012;Gullikson et al., 2016;Srinivasan et al., 2018). The two types of highly evolved lithic clasts reported in this study, Type A and Type B, might have distinct origins according to their different textures and mineral compositions. ...
Highly evolved lithology distributes across the Moon sparsely but serves as a critical record of the extensive differentiation processes of lunar magmas. In contrast to the Apollo-returned highly evolved rocks that essentially formed before the end of the Nectarian period, silicic lithologies detected by remote sensing within the nearside Procellarum KREEP Terrane (PKT) have cratering model age as young as ∼2.5 Ga (Chevrel et al., 2009). The formation mechanism of the young silicic magmatism remains enigmatic. Here we present a detailed study of lithic clasts with highly evolved compositions from the northwestern PKT returned by Chang’E-5 mission. Two different types of highly evolved lithic clasts were recognized: (a) Type A clasts predominately consist of granophyric intergrowths of K-feldspar and quartz. They are highly depleted in incompatible elements (except for K, Rb, Cs, and Ba) and have a V-shaped REE pattern, which can be explained by silicate liquid immiscibility (SLI) following the fractionation of merrillite from a KREEP-like melt. The microtextural features of quartz in Type A clasts indicate that they could have crystallized through relatively slow cooling at temperature below 870 ℃, supporting a shallow intrusive origin. The silicic intrusion exposed in the interior, rim, and ejecta of Aristarchus crater has a cratering model age of ∼2.5-3.7 Ga, which could be the source for Type A clasts; (b) Type B clast has little MgO, high incompatible element concentrations, and an REE pattern inclined to the right. Thermodynamic calculations indicate that Type B clast likely formed through SLI of the ∼25% residual melt of Em3 basalts in the Chang’E-5 landing region. This is consistent with the crystallization age of 2.57 ± 0.26 Ga for the zirconolite in Type B clast. The highly evolved samples from Chang’E-5 regolith provide new evidence that SLI may have played an important role in the young highly evolved intrusive bodies’ formation on the Moon. Furthermore, our thermodynamic modeling results show that compared to KREEP basalt, partial melting of quartz monzodiorite/monzogabbro at ∼930-1000 ℃ can produce melts with composition close to lunar granites and felsites. Thus, if a series of silicic volcanisms distributed mostly within the PKT was generated through this mechanism, quartz monzodiorite/monzogabbro may also widely distribute within the lunar nearside upper crust.
... The globules of Krich glass are both fine-grained and coarse-grained and irregular in morphology. All these textures are consistent with the low Mg# mesostasis pockets described by Roedder and Weiblen (1970, 1971 and Pernet-Fisher et al. (2014), implying the late-stage residual liquids are relatively low-Mg#. ...
... From a petrological perspective, large numbers of highly evolved fragments present in CE-5 material suggests that they may be important evidence for significant basaltic magma evolution, all the way to Fe and Si late-stage silicate liquid immiscibility (SLI). Typical mare basalts undergo silicate liquid immiscibility (SLI) at ≥85% crystallization (Roedder and Weiblen, 1970;Rutherford et al., 1974;Pernet-Fisher et al., 2014). However, the petrologic experiments suggest that the Apollo sample 12,032,366-18 (Th-rich) start SLI at ~80% crystallization and began at 1030 • C and 1002 • C (Stadermann et al., 2022). ...
Lunar mare basalts provide a probe to study the magmatic and thermal evolution of the Moon. The Chang'e-5 (CE-5) mission returned samples from a young and hitherto unsampled mare terrain, providing fresh opportunities to understand lunar volcanic history. A detailed petrologic survey was conducted in this study on basalt fragments and glasses from the returned CE-5 soil samples. Relatively large-sized (100–400 μm) basaltic fragments were hand-picked and examined for texture, mineral assemblage and mineral chemistries. Basaltic fragments exhibit dominantly subophitic textures and are phenocryst-free, with low to intermediate-Ti (2.1–5.5 wt%) and low Mg# (Mg/(Mg + Fe) × 100, 19–47, with an average whole-rock Mg# of 33) consistent with olivine-melt equilibrium calculation (Mg# = 34). A range of highly evolved basaltic materials have been identified, in which abundant fayalitic olivine, symplectitic intergrowths, and Si + K-rich mesostasis co-exist were found resulting from late-stage silicate liquid immiscibility. Basaltic glass compositions largely overlap with basaltic fragment compositions suggesting they are locally derived. The CE-5 basalts have a relatively limited range of eruption temperatures of 1150–1230 °C. Based on their petrographic and geochemical characteristics, some CE-5 mare basalts are highly evolved and some of the resultant basaltic melt products underwent high crystallization. Thermodynamic modeling using MELTS suggests highly evolved basaltic magma was produced by a low-pressure and simple fractional crystallization under reduced conditions. This may have occurred at the surface in the inflated Em4/P58 flow with a thickness of ~50 m. The low degree of partial melting mantle source of the parental melts is the late-stage lunar magma ocean cumulates in a similar manner to some evolved low-Ti mare basalt meteorites, although the source of CE-5 basalts may have been slightly more Ti-rich.
... Описываемая в многочисленных экспериментальных работах [17,19,28,29,30] область стабильной высокотемпературной ликвации не может оказывать значительного влияния на природные силикатные расплавы, в связи с тем, что область несмесимости исчезнет еще до начала основных кристаллизационных процессов. Максимальный эффект на эволюцию природного расплава должна оказывать метастабильная ликвационная дифференциация, происходящая в силикатных расплавах одновременно с кристаллизационной дифференциацией. ...
... Так, в системе лейцит-фаялит-SiO 2 поле низкотемпературной метастабильной ликвации (при низких давлениях) находится в области составов, обогащенных щелочами и глиноземом, и отделено от поля высокотемпературной лик-вации, локализованной по краевому сечению "фаялит-SiO 2 " фазовой диаграммы. На основе фазовой системы лейцит-фаялит-SiO 2 построена адаптированная для природных систем "псевдотройная" диаграмма в координатах SiO 2 -(Na 2 O + Ka 2 O + Al 2 O 3 )-(CaO + MgO + FeO + TiO 2 ) [30], которая позволяет, оперируя содержаниями петрогенных окислов, воспользоваться системой состояния. ...
New data from the high-precision �LA-ICP-MS geochemical study of silicate immiscibility products in picro-picrobasaltic
melts of Palaeoproterozoic (Suisarian) age from the Yalguba Ridge, Central Karelia, are reported. The results of the geochemical study of mineral parageneses and the composition of liquation phases are presented. The composition of pre-liquation melt was found to be consistent with that of picrobasalt geochemically similar to matrix of type I; liquation fractionation in picritic melt was initiated by contamination of crustal material. Liquation in the system was a multi-stage process which proceeded at all melt outflow stages.
... Melt inclusions are highly suitable for addressing this question. They provided the first sound documentation of liquid immiscibility in volcanic rocks (Roedder & Weiblen, 1970, 1971) and perhaps are even more useful in plutonic rocks because they provide insights into melt compositions in a situation where melts are fully crystallized and not preserved (HanghÖj et al., 1995;Veksler et al., 1998a;Spandler et al., 2000;Jakobsen et al., 2005Jakobsen et al., , 2010Li et al., 2005). ...
... Nevertheless, liquid immiscibility has been demonstrated in a number of melt inclusion studies (e.g. Roedder & Weiblen, 1970, 1971Krasov & Clocciatti, 1979;Philpotts, 1981b;Ryabov, 1989;Kamenetsky, 2006). All these cases are very far into the immiscibility field and are more strongly supersaturated than the Skaergaard plagioclase-hosted melt inclusions, which are on the edge of the field (Fig. 10). ...
The presence of Fe- and Si-rich liquids found as melt inclusions in apatite and olivine in the Upper Zone of the Skaergaard intrusion, East Greenland, demonstrates the occurrence of liquid immiscibility in the late-stage evolution of tholeiitic magmas in a plutonic setting. However, it remains unclear at which stage of crystallization unmixing began. To constrain the onset and the petrological importance of liquid immiscibility in the Skaergaard and tholeiitic magmas in general, we have studied crystallized melt inclusions entrapped in early primocryst plagioclase. Such melt inclusions become abundant from the top of the Lower Zone and upwards in the Layered Series, in primocryst plagioclase of composition An(54-26). The daughter phase assemblage is the same in all the inclusions, although the modal proportions of the daughter phases are highly variable: plagioclase (42-59%), clinopyroxene (28-41%), ilmenite (4-9%), magnetite (3-10%), apatite (1-9%) and accessory phases (<1%). Accordingly, the bulk compositions of reheated and homogenized melt inclusions show large variations in SiO(2) (40-54 wt%), FeO(t) (7-23 wt%), P(2)O(5) (0-1.9 wt%) and K(2)O (0-2.8 wt%), and have variable CaO/Al(2)O(3) ratios. These variations are best explained by trapping of varying proportions of immiscible iron- and silica-rich melts and demonstrate that liquid immiscibility started in the upper part of the Lower Zone. We conclude that a significant part of the Skaergaard intrusion crystallized from an emulsion of Fe- and Si-rich immiscible melts. The heterogeneous trapping of a mixture of Fe- and Si-rich immiscible liquids in primocryst plagioclase indicates that the dispersed droplets in the Lower and Middle Zones were smaller than the size of the inclusion (<500 mu m). In the Upper Zone, most of the inclusions in apatite are composed of the conjugate end-member liquids, indicating a larger size for the dispersed droplets. Metre-sized pods and layers of melanogranophyre in the upper part of the intrusion are believed to represent pooled bodies of the immiscible Si-rich liquid. Differentiation of an emulsified magma must be considered in petrogenetic models for the Skaergaard intrusion.
... 40-43 ,), discovered in the interstitial melts in lunar basalts (e.g. [44][45][46] ,), or mesostasis of tholeiites (e.g. 31,47 ,). ...
The origin of magnetite-(apatite) iron deposits (MtAp) is one of the most contentious issues in ore geology with competing models that range from hydrothermal to magmatic processes. Here we report melt inclusions trapped in plagioclase phenocrysts in andesite hosting the MtAp mineralization at El Laco, Chile. The results of our study reveal that individual melt inclusions preserve evidence of complex processes involved in melt immiscibility, including separation of Si- and Fe-rich melts, the latter hosting Cu sulfide-rich, phosphate-rich, and residual C-O-HFSE-rich melts, with their melting temperature at 1145 °C. This association is consistent with the assemblages observed in the ore, and provides a link between silicate and Fe-P-rich melts that subsequently produced the magnetite-rich magmas that extruded on the flanks of the volcano. These results strongly suggest that the El Laco mineralization was derived from crystallization of Fe-P-rich melts, thus providing insight into the formation of similar deposits elsewhere.
... In 1951, Roedder published his experimental study which shows that liquid immiscibility occurs at low temperature (1,100 °C) in the system K 2 O-FeO-Al 2 O 3 -SiO 2 (Pernet-Fisher et al., 2014). Then petrographic evidence of silicate liquid immiscibility was found in many lunar rocks and terrestrial basalts (Roedder and Weiblen, 1970;De, 1974;Phillpotts, 1979Phillpotts, , 1982 and this has been found to likely be an indisputable fact. In basaltic magma system, magma splitting into Si-rich and Ferich melts only occurs at the later stage of magma evolution just above 1,000 °C (Philpotts, 2008;Charlier and Grove, 2012). ...
The Panzhihua mafic intrusion, which hosts a world‐class Fe‐Ti‐V ore deposit, is in the western Emeishan large igneous province, SW China. The formation age (∼260 Ma), Sr, and Nd isotopes indicate that the Panzhihua intrusion is part of the Emeishan large igneous province and has little crustal contamination. However, the ore genesis of the Panzhihua Fe‐Ti‐V ore deposit has been extensively debated. Two different models have been provided to explain the formation of the Panzhihua oxide deposit, namely silicate immiscibility and normal fractional crystallization. Silicate immiscibility occurrings around 1,000 °C at the late stage of basaltic magma evolution argues against the silicate immiscibility model. Apatite‐hosted melt inclusion research indicates that silicate immiscibility occurred at the late stage of Panzhihua magma evolution. However, this may have little potential to form large ore deposits like Panzhihua. However, the continuous compositional variations of the Panzhihua intrusion and the calculations by thermodynamic modelling software support the Panzhihua deposit being formed by normal fractional crystallization. The reciprocal trace element patterns of the Panzhihua intrusion and the nearby felsic rocks also coincide with the fractional crystallization model. Normal fractional crystallization of high‐Ti basaltic magma played a key role in the formation of the Panzhihua Fe‐Ti‐V ore deposit.
... 1.2.1). Contrary to that, the Raman spectra of the sodium and potassium tetrasilicate glasses do not present such signals, but two new peaks centred at 518 and 595 cm -chambers, and, once retrieved at the surface, they provide fundamental information about geological processes on Earth [e.g., [161][162][163] or the Moon [164,165]. On a fundamental note, if we assume the presence of a magmatic ocean at the surface of the Earth after its formation 4.567 Ga ago [see 166 and references cited therein], it then must be said that the properties of the alumino-silicate melt composing the magma ocean drove the segregation of Earth iron core and the formation of Earth mantle and crust. ...
... Scores of basaltic intrusions are known around the world with commercially viable mineralization resulting from dense immiscible liquids at their bases (Lightfoot and Hawkesworth, 1997;, and references therein), so, logically there is nothing surprising in expecting such mineralization near the bases of basaltic lava flows. 4. The operation of liquid immiscibility processes in lunar basalts is well known (e.g., Roedder and Weiblen, 1970), and the new model proposed here implies that pipe vesicles should be as common in lunar as in terrestrial pāhoehoe lavas. ...
... T he unmixing of mafic magmas into immiscible pairs of Feand Si-rich conjugates was first identified in lunar samples 1 and subsequently in terrestrial volcanic and plutonic rocks [2][3][4][5][6][7] . Given the preferential partitioning of elements of economic interest into the Fe-rich conjugate 8 , a detailed understanding of the mechanisms by which significant differences in viscosity, density and wetting properties control the physical behaviour of the unmixed liquids in a crystal mush is essential, to better understand the origin of ore deposits hosted in mafic bodies [9][10][11] . ...
The separation of immiscible liquids has significant implications for magma evolution and the formation of magmatic ore deposits. We combine high-resolution imaging and electron probe microanalysis with the first use of atom probe tomography on tholeiitic basaltic glass from Hawaii, the Snake River Plain, and Iceland, to investigate the onset of unmixing of basaltic liquids into Fe-rich and Si-rich conjugates. We examine the relationships between unmixing and crystal growth, and the evolution of a nanoemulsion in a crystal mush. We identify the previously unrecognised role played by compositional boundary layers in promoting unmixing around growing crystals at melt-crystal interfaces. Our findings have important implications for the formation of immiscible liquid in a crystal mush, the interpretations of compositional zoning in crystals, and the role of liquid immiscibility in controlling magma physical properties.
... Co-existing Fe-and Si-rich melt inclusions (e.g., Fischer et al. 2016;Jakobsen et al. 2005Jakobsen et al. , 2011Luais 1987;Roedder and Weiblen 1970) and Fe-rich droplets dispersed in Si-rich glassy mesostasis in rapidly cooled natural examples (e.g., De 1974;Philpotts 1982;Philpotts and Doyle 1980) provide evidence of immiscibility in ferrobasaltic liquid. The physical behaviour of these immiscible liquids in a crystal mush may play an important role in the evolution of mafic intrusions, particularly if there is relative movement of the two liquids (e.g., Holness et al. 2011;VanTongeren and Mathez 2012;Zhou et al. 2013). ...
An experimental study of the microstructural evolution of an immiscible basaltic emulsion shows that the Fe-rich liquid forms homogeneously nucleated droplets dispersed in a continuous Si-rich liquid, together with droplets heterogeneously nucleated on plagioclase, magnetite, and pyroxene. Heterogeneous nucleation is likely promoted by localised compositional heterogeneities around growing crystals. The wetting angle of Fe-rich droplets on both plagioclase and magnetite increases with decreasing temperature. Droplet coarsening occurs by a combination of diffusion-controlled growth and Ostwald ripening, with an insignificant contribution from coalescence. Characteristic microstructures resulting from the interaction of immiscible Fe-rich liquid with crystal grains during crystal growth can potentially be used as an indicator of liquid unmixing in fully crystallised natural samples. In magma bodies < ~ 10 m in size, gravitationally driven segregation of immiscible Fe-rich droplets is unlikely to be significant.
... Based on trace element and Fe-O isotope compositions of magnetite, Knipping et al. (2015a) proposed a model for IOA formation by flotation of magmatic magnetite suspensions to explain the variation in chemical composition of magnetite. Identification of igneous/magmatic magnetite in the Sossego IOCG deposit and El Romeral IOA deposit indicates that some IOCG deposits may have experienced a process similar to that of IOA deposits, where original Fe was derived from magmatic process, i.e., through either magnetite flotation processes (Knipping et al., 2015a, b) or crystallization from Fe-rich melt (25-32 wt % FeO; 38-42 wt % SiO2) separated from Si-rich melt (60-70 wt % SiO2) by liquid immiscibility (Roedder and Weiblen, 1970;De, 1974;Dixon and Rutherford, 1979;Philpotts, 1982;Jakobsen et al., 2005;Hou et al., 2018). There are other examples that support a magmatic source for ore-forming fluids in IOCG and Kiruna-type IOA deposits from the Missouri IOA (USA), Kiruna IOA (Sweden), and Olympic Dam IOCG (Australia) districts . ...
Textural and compositional data of magnetite from Igarapé Bahia, Alemao, Sossego, Salobo, and Candelaria iron oxide copper-gold (IOCG) and El Romeral Kiruna-type iron oxide-apatite (IOA) deposits show that some magnetite grains display oscillatory zoning or have been reequilibrated by oxy-exsolution, coupled dissolution and reprecipitation (CDR) reactions, and/or recrystallization. Textures formed via CDR are most widespread in the studied samples. The original oscillatory zoning was likely derived from the crystal growth during fluctuating fluid compositions rather than from variation in temperature and oxygen fugacity. The oxy-exsolution of ilmenite in magnetite is attributed to increasing oxygen fugacity and decreasing temperature with alteration and mineralization, resulting in product magnetite with lower Ti and higher V contents. Recrystallization of some magnetite grains is commonly due to high-temperature annealing that retained primary compositions. Two different types of CDR processes are defined according to textures and chemical compositions of different generations of magnetite. The first generation of magnetite (Mag-1) is an inclusion-rich and trace element-rich core, which was replaced by an inclusion-poor and trace element-poor rim (Mag-2). The third generation of magnetite (Mag-3), inclusion poor but trace element rich, occurs as veins replacing Mag-2 along fractures or grain margins. Type 1 CDR process transforming Mag-1 to Mag-2 is more extensive and is similar to processes reported in skarn deposits, whereas type 2 CDR process is local, transforming Mag-2 to Mag-3. During type 1 CDR process, minor and trace elements Si, K, Ca, Mg, Al, and Mn in magnetite are excluded, and Fe contents increase to various extents, in contrast to type 2 CDR process, which is characterized by increased contents of Si, K, Ca, Mg, Al, and Mn. Type 1 CDR process is possibly induced by the changing fluid composition and/or decreasing temperature during progressive alteration and ore formation, whereas type 2 CDR process can be interpreted as post-ore replacement due to a new pulse of magmatic-hydrothermal fluids. The identification of magnetite core (Mag-1) with igneous origin and rim (Mag-2) with magmatic-hydrother-mal origin in the Sossego IOCG and El Romeral IOA deposits supports a fluid changing from magmatic to mag-matic-hydrothermal during IOCG and IOA formation and indicates a genetic link between these two deposit types. The large data set here further demonstrates that magnetite is susceptible to textural and compositional reequilibration during high-temperature magmatic and magmatic-hydrothermal processes. The reequilibrated magnetite, particularly after CDR processes, has geochemical patterns that may be different from its precursor , complicating the application of discrimination plots for genetic and provenance interpretation. Therefore, in situ chemical analysis of magnetite combined with textural characterization is necessary to understand the origin of magnetite in IOCG and IOA deposits.
... They are slightly vesiculated (<1%) and dominated by compositionally zoned and skeletal pyroxene, plagioclase, and ilmenite (Klein 1972). For both samples, fractionation of the basaltic magma due to crystallization at low f O2 produced Fe-rich, late-stage liquids, which then separated into two immiscible liquids upon further crystallization-one very Si-rich, Fe-poor melt that occurs as quenched glass containing 78 wt% SiO 2 , 0.5 wt% FeO*, 3.2 wt% K 2 O, 4.48 wt% CaO, and <0.03 wt% MgO (vs. the bulk lava with ~47 wt% SiO 2 , 20.39 wt% FeO*, 0.11 wt% K 2 O, 11.6 wt% CaO, and ~8.6 wt% MgO; Boyce et al. 2014), and another lower silica, Fe-rich melt (SiO 2 ~47.8 wt%, FeO* ~ 20 wt%, K 2 O ~0.3 wt%, CaO ~11.2 wt%, MgO ~ 2.3 wt%; Roedder and Weiblen 1970;Pernet-Fisher et al. 2014). Apatite can be in contact with either glass in both samples (Pernet-Fisher et al. 2014), and recent experimental data indicate that the composition of apatites among conjugate liquids are indistinguishable with respect to major and minor elements in systems that undergo silicate-liquid immiscibility (McCubbin and Ustunisik 2018). ...
Lunar apatites contain hundreds to thousands of parts per million of sulfur. This is puzzling because lunar basalts are thought to form in low oxygen fugacity (f_(O_2)) conditions where sulfur can only exist in its reduced form (S^(2–)), a substitution not previously observed in natural apatite. We present measurements of the oxidation state of S in lunar apatites and associated mesostasis glass that show that lunar apatites and glass contain dominantly S^(2–), whereas natural apatites from Earth are only known to contain S^(6+). It is likely that many terrestrial and martian igneous rocks contain apatites with mixed sulfur oxidation states. The S^(6+)/S^(2–) ratios of such apatites could be used to quantify the f_(O_2) values at which they crystallized, given information on the portioning of S^(6+) and S^(2–) between apatite and melt and on the S^(6+)/S^(2–) ratios of melts as functions of f_(O_2) and melt composition. Such a well-calibrated oxybarometer based on this the oxidation state of S in apatite would have wide application.
... Role of liquid immiscibility has immense importance in petro genesis of basaltic magmas. Roedder, Weiblen [1,2] postulated that high silica and high iron glasses of the lunar basaltic rocks have widespread petro genetic significance. In lunar basalts, generally, the globules of dark brown glass appear to have composition equivalent to Pyroxene + Iron ore. ...
... Silicate-sili-cate liquid immiscibility produces a silicate-iron liquid phase rich in phosphorus. Relics of this phase were found in terrestrial and extraterrestrial mafic and intermediate rocks (Röedder and Weiblen, 1970;Philpotts, 1982;Veksler et al., 2007;Jakobsen et al., 2011;and others). A silicate-iron liquid phase can also occur in fluorine-enriched trachyrhyolitic magma . ...
An Early Cretaceous (120 ± 5 Ma) trachyrhyolite lava sheet in the Nyalga basin, Central Mongolia, includes a domain (~0.5 km2) of unusual fluorite-enriched rocks with
annomalously high concentrations of CaO (1.2–25.7 wt %) and F (0.6–15 wt %). The textures and structures of the rocks suggest that they were produced by two immiscible melts: fluoride–calcium (F–Ca) and trachyrhyolitic. Data on mineral-hosted inclusions and SEM EDS studies of the matrixes of the rocks indicate that a F–Ca melt occurred in the trachyrhyolitic magmas during its various evolutionary episodes, starting from the growth of minerals in a magmatic chamber and ending with eruptions on the surface. Elevated fluorine concentrations (up to 1.5–2 wt %) in local domains of the trachyrhyolitic melt may have resulted in the onset of its liquid immiscibility and the exsolution of a F–Ca liquid phase. This was associated with the redistribution of trace elements: REE, Y, Sr, and P were preferably concentrated in the F–Ca melt, while Zr, Hf, Ta, and Nb were mostly redistributed into the immiscible silicate liquid. The F–Ca melt contained oxygen and aqueous fluid and remained mobile until vitrification of the trachyrhyolitic magma. The oxygen-enriched F–Ca phase was transformed into fluorite at 570–780°С and a high oxygen fugacity Δlog fO2 (0.9–1.7) relative to the NNO buffer. Ferrian ilmenite, monazite-group As-bearing minerals, and cerianite crystallized under oxidizing conditions, and the titanomagnetite was replaced by hematite. The Ca- and F-enriched rocks were affected by low-density (0.05–0.1 g/cm3) aqueous fluid, which was released from the crystallizing trachyrhyolitic melt, and this led to the partial removal of REE from the F–Ca phase. The chondrite-normalized REE and Y patterns of the fluidmodified rocks show positive Y anomalies and W-shaped minima from Gd to Ho. A composition of the F–Ca phase close to the original one is conserved in mineral-hosted inclusions and in relict isolations in the
rocks matriх. It is so far unclear why fluorite did not crystallize from the F–Ca melt contained in the trachyrhyolitic magma. Conceivably, this was favored by high-temperature oxidizing conditions under which the melt accommodated oxygen and aqueous fluid. The possible origin of mobile oxygen-bearing fluorite–calcic melt at subsolidus temperature should be taken into account when magmatic rocks and ores are studied. Fluorite and accompanying ore mineralization might have been formed in certain instances not by hydrothermal–metasomatic processes but during the fluid–magmatic stage as a result of the transformation of F–Ca melt enriched in REE, Y, and other trace elements.
... The experimental study of Roedder (1951) on the system Fayalite -Leucite -SiO 2 led to the discovery of a large field of liquid immiscibility in the center of this ternary system. The first lunar samples from the Apollo 11 landing site were iron-and titanium -rich basalts, and these contained the abundant immiscible melt blebs in the mesostasis (Roedder and Weiblen, 1970). The immiscible melts consisted of coexisting silica-rich, iron-poor and silica-poor, iron-rich pairs and their discovery established the viability of liquid immiscibility in natural systems. ...
Here we present a perspective on the evolution of thought on the origin of compositional diversity in igneous rocks, starting with the pioneer Norman Levi Bowen. In pursing this question of diversity, which was first clearly identified by Daly (1914), Bowen established the utility of experimentally determined phase equilibria as an aid to understanding geologic processes. His work ultimately led him to attribute igneous rock diversity to a singular path of fractional crystallization. We summarize the evolution of understanding acquired by petrologists during and after Bowen's time. Experimentalists beyond Bowen were crucial in furthering the understanding of the origin of the diversity of igneous rocks by discovering that more than one fractional crystallization path can occur in nature: at a minimum, differentiation can either be dry (tholeiitic) or hydrous (calc-alkaline). We also reassess the five alternative igneous processes that may give rise to compositional diversity that Bowen considered, but found to be wanting. These are magma mixing, liquid immiscibility, Soret diffusion, compositional gradients in liquids, and contamination of magma by foreign material (assimilation). These processes play important roles in igneous petrogenesis, that is, roles larger than Bowen envisioned, yet fractional crystallization remains fundamentally important.
... Continued fractionation also leaded to strong enrichment of Fe, Ti and P. Thus, apatite and ilmenite saturated at late stage and formed apatite gabbro and Fe-Ti-P oxide ores in the UZb (Fig. 14c). The preferential trapping of melt droplets by different host minerals were discussed by Roedder and Weiblen (1970). They showed that the abundance and morphology of melt droplets as inclusions strongly depend on the wetting properties and the compositional difference between the liquids and the host minerals. ...
The Emeishan large igneous province (ELIP) in SW China is characterized by voluminous high-Ti and low-Ti basalts and spatially associated Fe-Ti oxide-bearing mafic-ultramafic and syenitic/granitic intrusions. The Baima layered mafic intrusion in the central part of the ELIP is surrounded by syenitic and granitic rocks and contains a Lower Zone of interlayered Fe-Ti oxide ores, troctolites and clinopyroxenites and an Upper Zone of isotropic olivine gabbros and gabbros (UZa) and apatite gabbros and Fe-Ti-P oxide ores (UZb). Polycrystalline mineral inclusions, for the first time, were observed in primocryst plagioclase from the basal part of the UZa through to the top of the UZb and consist mostly of clinopyroxene, plagioclase, magnetite, ilmenite and apatite with minor orthopyroxene, sulfide and hornblende. These minerals are commonly anhedral and form irregular shapes. Daughter plagioclase usually crystallizes on the walls of host primocryst plagioclase and has An contents typically 3-6 An% lower than the host plagioclase. Daughter clinopyroxene has similar Mg# but lower TiO2 and Al2O3 contents than primocryst clinopyroxene. These polycrystalline mineral inclusions are considered to crystallize from melts contemporaneous with host plagioclase. The compositional differences between daughter and primocryst minerals can be attributed to equilibrium crystallization in a closed system of the trapped melt inclusions in contrast to fractional crystallization and possible magma replenishment in an open system typical for primo-cumulates of large layered intrusions. Heated and homogenized melt inclusions have variable SiO2 (33 to 52 wt.%), CaO (7 to 20 wt.%), TiO2 (0.1 to 12 wt.%), FeOt (5 to 20 wt.%), P2O5 (0.2 to 10 wt.%) and K2O (0 to 2.2 wt.%). The large ranges of melt compositions are interpreted to result from heterogeneous trapping of different proportions of immiscible Si-rich and Fe-Ti-rich silicate liquids, together with entrapment of various microphenocrysts. The separation of micrometer-scale Si-rich melts at least started from the lower part of the Upper Zone. We thus infer that the Baima high-Ti basaltic magmas evolved into the field of immiscible Fe-rich and Si-rich melts. Prolonged fractional crystallization of olivine, plagioclase and clinopyroxene from the Fe-rich melts formed gabbro and olivine gabbro in the UZa, before the melts became saturated in Fe-Ti oxides and apatite and formed apatite-rich Fe-Ti oxide ores in the UZb. Immiscible Si-rich melts migrated upwards and coalesced to form fayalite syenite around the Baima intrusion. Silicate liquid immiscibility may have played an important role in the petrogenesis of Fe-Ti oxide-rich layered mafic intrusions and syenitic rocks in the ELIP and elsewhere. This mechanism may be common and may explain the traditionally thought bi-modal assemblages of large igneous provinces in intra-continental extensional settings.
... The existence of silicate liquid immiscibility in natural lavas of ferrobasaltic-ferrodacitic composition has long been recognized (e.g., Roedder 1992 andPhilpotts 1982), and in recent years traces of immiscibility and liquid-liquid fractionation have been found in plutonic rocks in several mafic layered intrusions worldwide, such as immiscible silica-and Fe-rich melt inclusions in apatite and late-stage reactive microstructures (Jakobsen et al. 2005(Jakobsen et al. , 2011Holness et al. 2011;Namur et al. 2012;Veksler and Charlier 2015). Stable coexistence of Fe-rich and silica-rich immiscible liquids in equilibrium with typical gabbroic mineral assemblages has been reproduced in numerous experiments (Charlier and Grove 2012;Dixon and Rutherford 1979;Longhi 1990;Philpotts and Doyle 1983) but, with only few exceptions (e.g., Roedder and Weiblen 1970;Krasov and Clocchiatti 1979), unmixing of ferrobasaltic melts has been documented only at temperatures close to the liquidus of melts that have low liquidus temperatures, usually below 1020-1040 °C. The existence of high-temperature, super-liquidus silicate liquid immiscibility at temperatures up to 1200 °C has been proposed for some multicomponent ferrobasaltic-ferroandesitic compositions on the basis of centrifuge experiments (Veksler et al. 2006(Veksler et al. , 2007, but the evidence and interpretation of experimental results were challenged by Philpotts (2008) who argued that the products of centrifuge experiments were metastable phases formed during quenching. ...
Here we report the results of an experimental study aimed at testing the existence of stable, super-liquidus immiscibility
between silica- and Fe-rich multicomponent melts at temperatures above 1100 °C. Four pairs of the potentially immiscible compositions
were tested in a 1-atm gas-mixing furnace (Ar/H2-CO2 gas mixture) at 1150 and 1200 °C and at the oxygen fugacity corresponding to that of the QFM buffer. Pre-synthesized pairs
of the silica-rich and Fe-rich starting compositions were loaded in Pt wire loops, fused separately at 1300 °C, then brought
in contact and kept at constant experimental temperature for more than 24 h. Three pairs of compositions out of four used
in this study did not mix. Some temperature-dependent chemical re-equilibration was observed in the Fe-rich liquid phase but,
in the cases of immiscibility, the two liquids remained compositionally distinct and showed sharp compositional gradients
at contacts. One pair of liquids crystallized some tridymite, whereas the other compositions were clearly above the liquidus.
Overall, the results of the experiments are in good agreement with the earlier centrifuge study and confirm the existence
of stable, super-liquidus immiscibility in some Fe-rich basaltic-andesitic compositions at temperatures up to 1200 °C.
... Entrapment of minerals and melts, on the other hand, can provide robust information about the early stage of magma evolution (e.g. Roedder & Weiblen, 1970;Schiano et al., 1997;Jakobsen et al., 2005;Pang et al., 2008a). In the Permian Emeishan large igneous province (ELIP), the Panzhihua, Hongge and Baima mafic^ultramafic intrusions in the Panxi (Panzhihua^Xichang) region host significant FeT i^(V) oxide ores in their lower or middle parts. ...
Multiphase solid inclusions within cumulus silicates, particularly olivine, in Fe–Ti oxide ores from the Lower Zone of the Baima intrusion, Emeishan large igneous province, SW China, have been identified for the first time using 2-D scanning electron microscope and 3-D high-resolution X-ray computed tomography. These inclusions are spherical to subspherical and range from 100 to 300 µm in diameter. They are composed dominantly of titanomagnetite and ilmenite with minor apatite, hornblende, phlogopite and pyrrhotite. The titanomagnetite in the inclusions has a low Cr content (
... The tendency of the globules to coat grains of Plagioclase preferentially to olivine suggests further that the interfacial tension between globule and Plagioclase was lower than that between globule and olivine at the time of quenching. Experimental evidence supporting the theory of liquid immiscibility in silicate magmas has been presented by Ferguson and Currie (1972), Roedder and Weiblen (1970), and Philpotts and Hodgson (1968). The immiscible liquids produced by Ferguson and Currie closely approach the compositions of the globules analyzed in this study. ...
Basalts cored on DSDP Leg 16 fall into two groups. Those from the west flank of the East Pacific Rise (DSDP 159-163) are geochemically homogeneous tholeiites. In contrast, the Panama Basin samples (DSDP 155-158) range from alkali basalts to tho-leiites and may have formed over a mantle "hot spot" rather than at a mid-ocean ridge. Based on core relationships, all the Leg 16 basalts are extrusive. DSDP 163 penetrated 18 meters of basalt made up of seven cooling units with chilled glassy margins. Even in this Campanian (Cretaceous) sequence, severe alteration affects only the upper-most few centimeters. Sideromelane appears particularly resistant to low-temperature alteration. Microprobe analyses of spheroidal "globules" (probably spherulites) at the inner margins of sidero-melane masses show bimodal chemical compositions: reddish spherulites are enriched in Na2θ, A1 2 O 3 and SiC>2, whereas opaque ones are enriched in MgO and FeO relative to glass. The bulk composition of the "globular" zone is the same as that of the bulk rock, pointing to partitioning in situ.
... The role of SLI is an important, yet commonly unappreciated, magmatic feature of ferro-basalts on Earth, typically developing after significant crystal fractionation (>90%) and Fe-enrichment (e.g., Philpotts, 1982). In basaltic rocks, SLI is generally observed on small-scales (50-300 lm), within melt inclusions and late-stage residual melt pockets in both terrestrial and lunar basalts (e.g., Roedder and Weiblen, 1970;Taylor et al., 1971;Rutherford et al., 1974;Hess et al., 1975;Philpotts, 1979;Longhi, 1998;Shearer et al., 2006;Veksler et al., 2007;Taylor, 2011). These residual liquids have been overlooked in previous petrologic descriptions of lunar rocks, due to their small size and difficulty of mineral identification with transmitted-light optical microscopy (e.g., Fig. 2). ...
The discovery of water within the lunar mantle has broad implications for the formation of the Earth-Moon system, differentiation of the Moon, and the magmatic evolution of lunar basalts, as well as the highland rocks. Recently, there has been considerable interest in using combined water abundances and H-isotope systematics of lunar apatites from mare basalts to quantify the origin and extent of water within the Moon’s mantle. However, the petrologic and geochemical conditions that govern apatite crystallization are not well-constrained, especially for high-FeO basaltic melts that crystallize at fO2 values below the iron-wüstite buffer. Apatites are typically located within the late-stage interstitial regions. In this contribution, we present detailed textural descriptions of late-stage inter-cumulus, residual-liquid pockets (i.e., mesostasis pockets), in order to understand the petrogenesis of lunar apatite. Results from five mare basalts demonstrate that the majority of the residual liquids in mesostasis regions have undergone silicate-liquid immiscibility (SLI) splitting into Si-K-rich (felsic) and Fe-rich (Fe-basaltic) conjugate liquids. We demonstrate the complexity of these residual liquids by documenting a wide range of water contents for apatites in several mesostasis pockets within a single mare basalt, a complexity common to many basalts. These data illustrate that individual apatite-hosting mesostasis pockets behave as independent sub-systems, even within a single rock. Furthermore, we present water concentrations for another phosphate phase, merrillite, indicating additional uncertainties during considerations of water partitioning into apatite.
... The stage for this rise was set between 1940 and 1980, when Russian geologists described observations on igneous rocks, including some pegmatites, which indicated extensive immiscibility in silicate systems (Zakharchenko 1968;Clocchiatti 1975;Sobolev & Kostyuk 1975). Elsewhere, Roedder & Coombs (1967) described complex inclusions containing silicate glass, saline fluid, and gas that were thought to represent 'simultaneous coexistence of immiscible silicate and saline fluid phases in the granitic melt', and Roedder & Weiblen (1970, 1971 showed the importance of immiscibility in lunar samples. ...
The long-standing controversy about the origin of magnetite-(apatite) mineral deposits pertains to how they form. The Pleistocene El Laco deposit in northern Chile is a critical location because the host andesite contains immiscible melt inclusions trapped in plagioclase and clinopyroxene phenocrysts that reveal the involvement of immiscible melts in the evolution of the El Laco Volcanic System hosting the magnetite-(apatite) mineralization. We present results from the first-ever whole-rock and in situ Pb isotope investigation at El Laco, which provides a better understanding of the relationships between immiscible melts preserved in the melt inclusions, the magnetite ore, and the host andesite, and helps identify sources of the ore metals by analyzing potential sources of crustal lead. Our study reveals that the phenocrysts and the melt inclusions contain homogenous Pb isotope compositions that overlap with the host andesite, which confirms that they are coeval and cogenetic. The magnetite ore, however, has significantly more primitive 206Pb/204Pb ratios, which points to Pb isotopic disequilibrium between the magnetite ore and host andesite. Model ages of 367−167 Ma for the magnetite ore suggest that the Pb was inherited from a U−Th-depleted reservoir that could be represented by sedimentary rocks found in the basement of the Andean Cordillera under El Laco, for example, the Palaeozoic P-rich ironstones sequence. These results are consistent with the major role of crustal contamination in the formation of magnetite-(apatite) mineralization elsewhere and suggest that the magnetite ore crystallized from immiscible Fe-rich melts contaminated by the underlying sedimentary sequences.
Cobalt is in high demand because of the key role that cobalt-lithium-ion batteries are playing in addressing the issue of global warming, particularly in facilitating the transition from the internal combustion engine to electrically driven vehicles. Here, we review the properties of cobalt and the history of its discovery, briefly describe its mineralogy, and explore the processes that concentrate it to potentially exploitable levels. Economic cobalt deposits owe their origin to the compatible nature of Co2+, its concentration in the mantle in olivine, and its release, after high degrees of partial melting, to komatiitic and (to a lesser extent) basaltic magmas. Primary magmatic deposits, in which Co is subordinate to Ni, develop through the separation of immiscible sulfide liquids from mafic and ultramafic magmas and the very strong partitioning of these metals into the sulfide liquid. We evaluate the factors that concentrate cobalt to economic levels by these processes. Cobalt is also concentrated by aqueous fluids, either at ambient temperature in laterites developed over ultramafic rocks or hydrothermally in sediment-hosted copper deposits and in cobalt-rich vein deposits, where it crystallizes mainly as sulfide and arsenic-bearing minerals, respectively. Using the available thermodynamic data for aqueous Co species, we evaluate cobalt speciation as a function of temperature and show that, whereas it is transported at ambient temperature in most environments as the simple ion (Co2+), it is most mobile in hydrothermal systems as chloride species. Based on thermodynamic data compiled from a variety of sources, we evaluate stability relationships among some of the principal cobalt sulfide and oxide minerals as a function of temperature, pH, fO2, and αH2S and, in conjunction with the aqueous speciation data, determine their solubility. This information is used, in turn, to predict the physicochemical conditions most favorable for cobalt transport and ore formation by hydrothermal fluids. As thermodynamic data are not available for the cobalt arsenide and sulfarsenide minerals that form the vein-type ore deposits, we use chemographic analysis to qualitatively evaluate their stability relationships and predict the physicochemical controls of ore formation. The data and interpretations of processes presented in this paper provide the theoretical basis for a companion paper in this issue in which we develop plausible models for the genesis of the principal cobalt deposit types.
Sample 12032,366‐18 is a 41.2 mg basaltic rock fragment collected during the Apollo 12 mission to the Moon. It is enriched in incompatible trace elements (e.g., 7 ppm Th), but does not have a bulk composition that would be considered a KREEP (enriched in potassium, rare earth elements, and phosphorous) basalt. The sample is of particular interest because it may be representative of some of the mare basalts within Oceanus Procellarum that are inferred to be Th‐rich, based on remote sensing data. The major mineral assemblage of 12032,366‐18 is pyroxene, plagioclase, olivine, and ilmenite, and the bulk composition has 4.2 wt% TiO2, 11.7 wt% Al2O3, and 0.25 wt% K2O. The sample contains regions of late‐stage crystallized minerals and glass (collectively termed mesostasis), including K‐feldspar, apatite, rare earth (RE) merrillite, ilmenite, troilite, silica, and relatively sodic plagioclase adjacent to ferroan pyroxene. The mesostasis also occurs in several areas that are highly enriched in silica and intergrown with K‐feldspar and very fine‐grained, high‐mean‐atomic‐number phases. We explore the petrology of this sample, including the origin of the Si‐K‐rich mesostasis to assess whether the mesostasis had formed by silicate liquid immiscibility (SLI). We used experiments to determine if the bulk composition of 12032,366‐18 is representative of a bulk liquid composition, how the residual liquid evolves, and to investigate the partitioning of elements between phases as the melt evolves. Experiments support that the mesostasis formed by SLI after crystallization of minerals closely matches the major‐mineral assemblage of 12032,366‐18. Experiments bracket the onset of SLI and merrillite saturation between 1024 and 1002 °C. Some high field strength elements, such as Zr and P, partition preferentially into the Fe‐rich liquid. From the experiments, we infer that the bulk composition of 12032,366‐18 represents the magma from which it crystallized. Based on the Th‐rich and KREEP‐bearing chemistry of this sample, along with experimental evidence showing that the sample is representative of a bulk liquid composition and not a cumulate, we conclude that basalt fragment 12032,366‐18 was delivered to the Apollo 12 landing site as ejecta from a distant impact and could represent an Oceanus Procellarum basalt. Missions to Oceanus Procellarum, such as Chang’E 5, have the potential to confirm whether some of those basalts are indeed enriched in Th and other incompatible trace elements as indicated by remote sensing.
One atmosphere experimental studies have been conducted on two amygdule‐free representative samples from Khandwa, Madhya Pradesh, Central India, belonging to Eastern Deccan Volcanic province in order to understand mineral petrogenesis, crystallization history of the parent magma and role of liquid immiscibility. One atm experiments were carried out on these two samples at specified temperatures on designated time in order to understand crystallization history. The run products were identified both by optical means and electron microprobe analysis. The identified run products include pyroxenes, feldspar, opaques phase (oxide and sulphide), silica phases, and glass (both brown and colourless variety). The run product pyroxenes belong to quadrilateral pyroxene, and species‐wise correspond to augite, clinoenstatite, and pigeonite. Feldspars in majority are found to be anorthoclase (which are interpreted to have been formed during sudden crystallization in contact with water at shallow depth during experiments) and less commonly calcic plagioclase (in the range of labradorite to anorthite). Opaque phases have both oxide and sulphide, namely hematite, magnetite, martite, and pyrite, respectively. The zoned nature between the oxide and sulphide phases is suggestive of oscillation of oxygen fugacity during crystallization. The run product silica phase corresponds to tridymite. The silica‐rich glass (colourless) is overwhelmingly dominant, whereas silica‐poor glass (brown glass) is a manifestation of liquid immiscibility. The silica‐rich glasses give rise to direct crystallization of tridymite, whereas silica‐poor glasses act as the main driving liquid (or parent liquid) to further the crystallization towards lower temperature. The crystallization behaviour of the parent magma, and liquid immiscibility can be well documented with reference to forsterite‐silica phase diagram; in this phase diagram, the parent liquid corresponds to normative Qtz: 2.542, Fo: 0.098, and En: 0.34. The ambient parent liquid plots very close to Ab apex with reference to the Di‐Ab‐An phase diagram. The clear and distinct zonation pattern present in the opaque phases signifies that crystallization straddles between both oxidizing and reducing condition yielding crystallization of both oxide and sulphide phases. Our study indicates a unique role of liquid immiscibility of the parent magma supplemented by oscillation of oxidizing and reducing conditions giving rise to ensemble of variety of glass compositions, silicate, and opaque phases.
The Northwest Africa (NWA) 773 clan of lunar meteorite stones are coarse‐grained breccias that provide an opportunity to examine a lunar igneous system that includes inferred intrusive and extrusive lithologies, possibly related through a common liquid line of descent from a single source region. Such extensive sampling of a single very low‐Ti (VLT) magmatic system on the Moon is unprecedented among the lunar samples. This study focuses on the olivine gabbro (OG), anorthositic gabbro (AG), and ferroan gabbro (FG) lithologies variably contained in NWA 773, NWA 2727, NWA 3160, NWA 3170, NWA 7007, and NWA 10656. Mineral compositions in the three gabbros indicate the crystallization sequence OG → AG → FG. Petrologic modeling of these three lithologies, and an olivine phyric basalt that also occurs in the NWA 773 clan, however, suggests that the relationship among the lithologies is more complex. The OG and basalt can be modeled as originating from a VLT KREEP‐bearing parental melt similar to the Apollo 14 Green Glass b1 composition through mainly equilibrium crystallization. The AG and FG, however, do not fit this simple model and require either a more complex crystallization sequence involving fractional crystallization, magma chamber recharge, or perhaps heterogeneity in the source region.
Cambridge Core - Mineralogy, Petrology and Volcanology - A Practical Guide to Rock Microstructure - by Ron H. Vernon
В покрове раннемеловых трахириолитов (120 ± 5 млн. лет) Нилгинской депрессии (Центральная Монголия) обнаружен участок площадью около 0.5 км2, сложенный необычными обогащенными флюоритом породами с аномально высокими концентрациями CaO (1.2–25.7 мас. %) и F (0.6–15 мас. %). Структурно-текстурные особенности пород указывают на их образование при участии двух несмесимых
расплавов – фторидно-кальциевого (F-Ca) и трахириолитового. Данные по включениям в минералах и СЭМ ЭДС изучения матрикса пород свидетельствуют о существовании F-Ca жидкой фазы (расплава) в трахириолитовой магме на разных стадиях ее эволюции – от роста вкрапленников минералов в магматической камере до излияния на земную поверхность. Предполагается, что повышение концентрации фтора в локальных областях трахириолитового расплава до 1.5–2 мас. % привело к его ликвации и образованию F-Ca жидкой фазы. При этом произошло перераспределе- ние элементов-примесей: РЗЭ, Y, Sr и P концентрировались во F-Ca, а Zr, Hf, Ta и Nb – в силикатных несмесимых расплавах. Фторидно-кальциевый расплав содержал кислород, водный флюид и находился в подвижном (текучем) состоянии до стеклования трахириолитовой магмы. Процессы преобразования обогащенной кислородом F-Ca
фазы во флюорит происходили в интервале температур 570–780°С при высокой летучести кислорода ΔlgfO2 (0.9–1.7) по отношению к буферу NNO. В
окислительных условиях кристаллизовались ферро-ильменит, As-содержащие минералы группы монацита, церианит, по титаномагнетиту развивался гематит. Воздействие на обогащенные Ca и F породы низкоплотного (0.05–0.1 г/см3) водного флюида, выделяющегося в процессе дегазации и кристаллизации
трахириолитового расплава, привело к частичному удалению РЗЭ из F-Ca фазы. В нормированных к хондриту спектрах РЗЭ и Y пород, измененных при взаимодействии с флюидом, появилась положительная аномалия Y и прогиб W-типа от Gd до Ho. Близкий к первичному состав F-Ca фазы (продукта закаливания
F-Ca расплава) сохранился во включениях минералов и в реликтовых обособлениях среди матрикса пород. Остаются неясными причины существования F-Ca расплава без кристаллизации флюорита в трахириолитовой магме. Этому могли способствовать высокотемпературные окислительные условия, при которых в такой расплав входи- ли кислород и водный флюид. Образование
подвижного кислородсодержащего F-Ca расплава до субсолидусных температур необходимо учитывать при изучении магматических пород и руд. Воз- можно, флюорит и сопутствующая ему рудная минерализации в некоторых случаях формировались не гидротермальным или метасоматическим путем, а на
флюидно-магматической стадии в результате преобразования F-Ca расплава, обогащенного РЗЭ, Y и другими элементами-примесями.
Recent developments, however, suggest that hypotheses using processes of unmixing in the liquid phase may be viable. The discovery of two silicate glasses in lunar rocks showing immiscible textures has been verified by experiment3^5. The compositions of these glasses are essentially that of a potassic granite and a pyroxenite.
Most fluid inclusion trapped from a homogeneous fluid but some may trapped from a heterogeneous fluids (immiscibility process). In the nature, there are a lot of immiscible processes and systems, including immiscibility between basic magma and felsic magma, magma and hydrothermal fluids; magma and CO(2) fluid; saline fluids and CO(2) fluid etc. The fluid inclusions trapped from homogeneous and heterogeneous processes are with different characteristics and in somewhat is not easy to be distinguished. The immiscibility process is an important process of mineralization. Especially in the gold deposition, pegmatite formation and porphyry Cu-Mo system.
The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville B core hole, drilled into the 35.5-Ma-old Chesapeake Bay impact crater, Virginia, has recovered postimpact sediments, crater-fill breccias, megablocks of the crystalline basement, and suevites with fresh glass shards. Bulk rock analyses of 2 glass shards, 21 crystalline target rocks, and microchemical analyses of 7 glass shards and 3 bediasites (tektites of the North American strewn field) were performed in order to contribute to the understanding of formation processes and to better constrain the precursor materials of these glasses as well as of the bediasites. Statistical treatment (hierarchical cluster analyses) yielded an assignment of the data for the crystalline basement samples into four groups; two of those (various schists, meta-graywackes, and gneisses) display characteristics similar to the impact glasses in the suevites and the bediasites. However, the suevitic glasses show a broad range in composition at the micrometer scale. These data show the frequent presence of schlieren, and in particular, enhanced TiO2 contents that require admixture of an "amphibolitic component" to the melt. Evidence for such a process is provided by the occurrence of relict, in-part thermally corroded grains of rutile and ilmenite, and by formation of Ti-rich tiny mineral aggregates in the glass. The three studied bediasites show only minor inter- and intrasample heterogeneity, and their chemical composition agrees well with previously published data. The new data for the bediasites are compatible with heating of the "tektite melt" to extreme temperatures, followed by quenching.
The Datongxi pluton outcropping in western part of the West Kunlun orogen, consisted of high-K calc-alkaline quartz diorite, quartz monzonite and granite. The quartz diorites contain abundant mafic mierogranular enclaves ( MMEs)of different shapes. The quartz diorites span a SiO2 range of 56. 5% ∼65.3% and Mg# range of 0.45 ∼ 0.46. characterized by moderate LREE/HREE fractionation, strong LILE enrichment and depleted Nb-Ta and weakly Eu depletion. Relatively to the quartz diorites, the quartz monzonites and granites have high content of SiO2( 65. 0% ∼ 73. 3% ) and low Mg# (0. 36 ∼ 0.44), stronger Nb-Ta, Ti and Eu depletion. The calculated P-T conditions are 638 ∼ 768 °C and 1.7 ∼ 4. 3kbar for the quartz diorites and 752 ∼771°C for the quartz monzonites and granites, respectively. Zircon U-Pb dating results give an emplacement age of 470 ± 1. 2Ma for the quartz monzonites, slightly younger than the emplacement ages of 478 ∼ 473Ma for the quartz diorites. The younger quartz monzonite-granite suite cannot be formed through differentiation of the older quartz diorite, indicating that both of them were derived from different melting sources. The quartz diorites and MMEs were formed through melting of the metasomatized mantle wedge in a subduction setting, while the younger quartz monzonite-granites were derived from metasedimentarv protoliths in response to post-eollisional extension and thermal supply from the underplating of the upwelling mantle-derived magmas. The origin of the Datongxi felsie intrusive complex may record the tectonic evolution of western Kunlun orogenie belt from the oceanic slab subduction to the post-collisional extension during Early Ordovician time.
Most fluid inclusion trapped from a homogeneous fluid but some may trapped from a heterogeneous fluids (immiscibility process). In the nature, there are a lot of immiscible processes and systems, including immiscibility between basic magma and felsic magma, magma and hydrothermal fluids; magma and CO2 fluid; saline fluids and CO2 fluid etc. The fluid inclusions trapped from homogeneous and heterogeneous processes are with different characteristics and in somewhat is not easy to be distinguished. The immiscibility process is an important process of mineralization. Especially in the gold deposition, pegmatite formation and porphyry Cu-Mo system.
В статье приводятся результаты изучения продуктов силикатной несмесимости в вулканитах палеопротерозойского возраста Центральной Карелии на примере андезибазальтов Кумсинской структуры (сумий, 2.4 млрд лет) и пикробазальтов Ялгубского кряжа (суйсарский комплекс, 2.1–1.9 млрд лет). В работе детально описана морфология ликвационных образований, показаны результаты геохимического изучения ликвационных фаз. Впервые проведено прецизионное геохимическое изучение матрикса вариолитовых лав, позволившее установить его гетерогенность, отражающую влияние процессов коровой контаминацией на первичный базальтовый расплав. Контаминация стала инициальным процессом, вызвавшим ликвационное фракционирование системы, при этом процесс ликвации силикатного расплава был многоступенчатым и проходил на всех стадиях излияния.
В работе приведены комплексные результаты литогеохимического, петрологического изучения
породных ансамблей, развитых в пределах верхнеархейского Ведлозерско-Сегозерского
зеленокаменного пояса, расположенного в юго-восточной части Фенноскандинавского щита.
Геодинамические реконструкции позволяют автору выделить в геологической истории
формирования пояса магматические системы, приуроченные к древней (3,05–2,95 млрд. лет)
островодужной системе, задуговому бассейну (3.05–2.95 млрд. лет) и молодой (2.90–2.85 млрд. лет)
вулканической дуге, что укладывается в схему формирования зеленокаменного пояса в рамках
модели развития конвергентной межмикроплитной зоны «протоокеан – протоконтинент».
Qitianling granite is a complex massif with multi-stage intrusions during the Early Yanshanian Period. Petrochemical data show that it belongs to alkali-rich and highly evolved A-type granite formed in tension setting within a plate. The centimetre- and metre-sized pegmatoid cystidium and miarolitic quartz widely occurred in the second stage medium-fine grain biotite granite, implying that it is resulted from differentiation of the oversaturated-volatile magma. In addition, the coexist of melt-fluid inclusions and fluid inclusions in quartz indicated that the pegmatoid cystidium and miarolitic quartz were produced in the transition stage from granite magmatic melt to hydrothermal solution. The data of micro-thermometry showed that the trapped temperatures of melt-fluid inclusions are over 530°C, the homogenization temperatures of fluid inclusions are between 172°C and 454°C, indicating the temperature of fluids in hydrothermal stage, and the homogenization temperatures of fluid inclusions in sphalerite are between 285°C and 417°C, indicating the temperature and salinity of ore-forming fluid. Their evolution process from middle-fine grain biotite granite to pegmatoid cystidium to miarolitic quartz implied that magmatic and hydrothermal system underwent an evolution process: from volatile-rich fluid to melt and high salinity fluid to high salinity fluid to low salinity fluid and finally formed magmatic hydrothermal fluid in the CaCl2-NaCl-H2O-CO2 system. Based on the data of petrography and Raman spectrum of fluid inclusions, the existence of feldspar, calcite, rutile and metallic oxides in the fluid and crystal-rich melt-fluid inclusions implies that the captured fluids have a competent ore-forming potentiality.
Although laboratory experiments in the past have not encouraged hopes of
finding terrestrial rocks showing textures resulting from liquid
immiscibility, this article describes work suggesting such an origin for
features in some alkaline rocks.
In connection with the discovery of lunar rock textures indicating
late-stage formation of a K2O-rich silicate liquid, serious
consideration is being given to the possible importance of silicate
liquid immiscibility. The results of a reinvestigation of the
K2O-FeO-Al2O3-SiO2 system are discussed, taking into account electron
scanning microscopy studies combined with electron microprobe analyses.
The investigation makes it possible to delineate the extent of the
two-liquid field and to determine the compositions of the two coexisting
liquids. An evaluation of the results of the investigation confirms the
validity of the suggestion that the granophyres found in close
association with ferro-gabbroic rocks may be produced by a process of
liquid immiscibility.
On July 24, 1969, the first extraterrestrial samples, with the exception
of meteorites, were returned to earth by Apollo 11. Since then these
samples and the samples returned by Apollo 12 have been subjected to
scientific investigations by hundreds of scientists from many countries.
Drawing on advances from the last 25 years of study of meteorites and
terrestrial rocks the variety and sophistication of the techniques used
on these samples is truly impressive. It can truthfully be said that 10
years ago we could not have made the measurements, and that, even if we
had had the data, we could not have interpreted it. The electron
microprobe, the scanning electron microscope, and the mass spectrometer,
as well as other instruments and techniques, have joined the microscope
as routine tools with which to attack a petrologic problem.
Quartz and alkali feldspar from vuggy granitic blocks contain up to 10 10 fluid inclusions per cubic centimeter, of three main compositional types, I-III; the inclusions are presumably the result of the trapping of three discrete, individually homogeneous fluids, plus fewer inclusions of other compositions, including several mixed types. The original fluid trapped in inclusions of type I was a silicate-rich magma; at room temperature it consists of silicate glass, with a small, very low-pressure gas bubble and sometimes a crystal of fluorite(?). The original material trapped in type II was a dense saline fluid with 50-70 weight per cent NaCl; at room temperature it consists of saturated water solution, a large halite crystal (usually with other crystalline phases), and a large gas bubble containing some CO 2. The original material trapped in type III was a dense aqueous-rich fluid or steam; at room temperature it consists of a dilute water solution and a very large, high-pressure CO 2 gas bubble.Type III apparently represents vapor coexisting with type II fluids (i.e. boiling); it occurs both as independent primary inclusions and in intimate association with type II in planes of secondary inclusions.It is believed that type II represents immiscible globules of dense saline fluid, suspended in silicate magma, and trapped, possibly because of preferential surface wetting during crystal growth. If both types I and II are primary, their random interdistribution implies immiscibility. Regardless of primary or secondary origin, the examples of mixed type I-II inclusions, containing (at room temperature) a saturated water solution, a large halite crystal, a gas bubble, and a variable amount of silicate glass, seem to require simultaneous coexistence of silicate and saline fluids as a heterogeneous mixture, i.e. immiscibility.Similar inclusions are found in blocks quenched from both above and below the alkali feldspar solvus. Despite the complex geological history of the samples, such inclusions throw light on the chemical nature of the residual fluids produced during crystallization of these granites, and may permit environmental P-T estimates. They should be looked for in other granites.
On the evidence which has been presented for liquid silicate immiscibility in the laboratory and in the rocks of Agate Point
- J W Greig