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Commingling between contemporaneous mafic and felsic magmas is now widely recognized in a broad range of intrusions and intrusive complexes. These interactions are important features for two main of reasons: (1) the rapidly chilled margins of mafic magma against silicic magma commonly preserve the compositions of mafic liquids, and (2) because the mafic magma solidifies rapidly, the resulting (final) configurations of mafic and felsic magmas can provide insights into physical processes and changing viscosity contrasts and rheologies of magmas and felsic crystal mush during crystallization of the mafic magma. Mingling of contrasted magmas was first recognized in the 1950s. Wider recognition of interactions between mafic and silicic liquids led to concepts of "net-veining" in the 1960s, "intramagmatic flows" (chilled basaltic layers separated by felsic cumulates) in the 1970s, and in the 1990s to "mafic-silicic layered intrusions" (MASLI), which could be as much as a few kilometers thick and more than 100 km2 in area. It was quickly appreciated that these MASLI preserved stratigraphic records of mafic replenishments into silicic magma chambers floored by felsic crystal mush. Volcanic studies had anticipated the occurrence of this last type of intrusion on the grounds that extensive ponding of basaltic magmas beneath silicic chambers was seen to be essential to keep large silicic systems like Yellowstone active for millions of years. This paper looks at the history of changing perceptions and interpretations of magma mingling and whether or not "sill complexes" are distinct from mafic-silicic layered intrusions. The stratigraphy of mafic-silicic layered intrusions records changing magmatic compositions, events, and processes in a temporal framework comparable to that provided by coeval volcanic rocks. As a result, careful study of MASLI has great potential for linking plutonic and volcanic processes and events. [ABSTRACT FROM AUTHOR]

This is important on several fronts: it suggests that arc magmas are reduced enough to saturate sulfide and, because the continental crust is also Cu-depleted, that sulfide-rich cumulates must have formed during continental differentiation. But Cin-Ty's reach goes far beyond mantle lithosphere. If there is a Renaissance "human" in geology, it is Cin-Ty Lee. [Extracted from the article]

Sulfides, although modally of low abundance in most igneous rocks, have strong influences on the geochemical behavior of many elements including Pb, Cu, Ni, and the PGEs. In a recent paper, we demonstrated a simple relationship between the sulfide-silicate partition coefficients DMsulf/sil of such elements and the FeO content of the coexisting silicate melt (Kiseeva and Wood 2013). logDMsulf/sil A-n/2 log [FeO] where n is the valency of element M, [FeO] is the concentration of FeO in the silicate in wt%, and A is a constant that depends on temperature and pressure. Elements that closely obey the simple model are Pb, In, Sb, Cd, Co, Zn, and Cr. We show here, however, that the fitted slope n depends not only on the valency of element M, but also on how M interacts with oxygen, the dissolution of which as FeO in the sulfide increases as the FeO content of the silicate melt increases. To take account of interactions of trace element M with FeO dissolved in the sulfide we introduce an additional parameter ... (Wagner 1962), which represents the difference between the lithophile and chalcophile properties of M and those of Fe. If ... is positive, then element M is more chalcophile than Fe and if negative more lithophile. We performed experiments to investigate partitioning of lithophile Nb, Ta, Ce, and Ti between sulfide and simplified basaltic melt and find that they all exhibit, as expected, concave upward behavior on a plot of logD vs. log[FeO]. New experiments on Cu at low FeO contents confirm that it is more chalcophile than Fe, yielding a concave-downward curve of logD vs. log[FeO]. The combined results mean that nominally lithophile elements may partition more strongly into sulfide than nominally chalcophile elements at either very low or very high FeO contents of the silicate melt. For example, as the FeO content of the silicate melt declines below about 1 wt%, the partition coefficient of Cu, DCusulf/sil declines to an unusually low value (DCusulf/sil ~80), whereas those for Nb (DNbsulf/sil ~600), and rare earths (REE's) increase strongly. Under these conditions, Nb is, therefore, substantially more "chalcophile" than Cu in that it partitions much more strongly into sulfide. The implications of these observations for the Earth are that under a wide range of conditions one would expect significant partitioning of REE, Nb, Ta, Ti, and other lithophile elements into sulfides. Wohlers and Wood (2015) have, for example, shown that the partitioning of U and the REE into sulfides at low FeO content of the silicate is sufficiently pronounced that addition of a reduced sulfur-rich body to the accreting Earth could generate observable fractionation of Nd from Sm and, together with S, transfer sufficient U to the core to provide a significant energy source for the geodynamo. [ABSTRACT FROM AUTHOR]

Lunar highlands are plagioclase-rich terrains produced by crystal floating in a Magma Ocean system. Lunar samples revealed the presence of anorthositic (plagioclase > 90%) samples from the Highlands, associated to more mafic rocks. Recently, remote sensing data permit mapping those terrains with high spatial and spectral resolution allowing detection of plagioclase and mafic crystal field (C.F.) absorptions. In this paper we have studied bidirectional spectral characteristics in the visible near-infrared (VNIR) of rocks from the Stillwater Complex, a cumulitic igneous stratified complex, with composition varying from mafic to sialic (e.g., pyroxenite, anorthosite). We investigated both slabs and powders of these rocks to give indication of the spectral variability of rock analogs of lunar crust, from a mineralogical point of view. Samples have been spectrally separated in four main groups considering the different C.F. absorption association, reflectance and spectral shape for both slab and powder spectra. More spectral details can be obtained from the analysis of powder spectra than from the slab spectra. The composition of rocks can be addressed by studying spectral parameters, such as the position and the intensity of the absorption (e.g., band center and band depth). The analysis of our plagioclasepyroxene- bearing samples indicates that mafic composition can be clearly obtained for samples characterized by one pyroxene phase, even for few amounts of pyroxene, from powder spectra. On the other hand, slab spectra show clear pyroxene absorptions only for rocks with mafic abundance at least >20%. The intensity of the mafic absorptions of these samples shows a linear trend with respect to the abundance of pyroxenes (orthopyroxene + clinopyroxene, for samples with ferrosilite amount less than ca. 25%). Considering all pyroxene-bearing samples, the band depth of slab spectra are linearly related to the volumetric distribution of ferrous iron in pyroxenes. [ABSTRACT FROM AUTHOR]

Magmatic gas exsolving during late-stage cooling of shallow magmas has been considered an important facilitator of low-pressure alteration and metal transport. However, the chemical properties of such gas, particularly its metal transport mechanisms and capacity, remain elusive. Trace elements in minerals produced by gas-mediated surface reaction or precipitation from gas capture details of gas composition and reaction pathways. However, interpretation of mineral trace element contents is dependent on understanding crystallographic controls on gas/mineral partitioning. This work investigates the structural accommodation of As, Mn, Ga, Ge, Fe, and Ti in vapor-deposited topaz of vesicular topaz rhyolite from the Thomas Range, Utah, through single-crystal synchrotron microbeam X-ray techniques on picogram quantities of those trace elements. X-ray absorption near edge structure (XANES) data indicates that these elements are incorporated into topaz as As5+, Fe3+, Mn3+, Ti4+, Ga3+, and Ge4+. Extended X-ray absorption fine structure (EXAFS) analysis for these trace elements, compared to EXAFS of structural Al and Si, reveals that As5+ and Ge4+ are incorporated directly into the tetrahedral site of the topaz structure, with the octahedral site accommodating Mn3+, Fe3+, Ga3+, and Ti4+. For As5+ and Fe3+, the structural impact of substitution extends to at least second neighbors (other elements were only resolvable to first neighbors). Further interpretation of the EXAFS results suggests that the substitution of Ti4+ results in increased distortion of the octahedral site, while the other trace elements induce more uniform expansion correlating in magnitude to their ionic radius. Comparison of quantified X-ray fluorescence (XRF) data for two topaz crystals from this rhyolite reveals variable trace element concentrations for As5+, Fe3+, Ga3+, and Ti4+, reflective of a source gas undersaturated in these trace elements changing in concentration over the period of topaz deposition. The identical Ge4+ content of the two topaz crystals suggests that Ge4+ in the gas was buffered by the growth of another Ge4+-bearing phase, such as quartz. The very low Mn3+ content in the topaz crystals does not reflect the abundance of Mn3+ in the gas (saturation of Mn is evidenced by coexisting bixbyite). Instead, it suggests a strong Jahn-Teller inhibitory effect to the substitution of Mn3+ for Al3+ in the distorted octahedral site of topaz. It is proposed that exsolution of an HF-enriched gas from cooling rhyolitic magma led to local scouring of Al, Si, and trace metals from the magma. Once topaz crystals nucleated, self-catalyzed reactions that recycle HF led to continued growth of topaz. [ABSTRACT FROM AUTHOR]

Fragmentation of crystals is an important mechanism, and a component of particle dynamics in igneous and metamorphic rocks that has received surprisingly little attention. Recent advances in textural analysis, extraction techniques, digital imaging, and computer-assisted measurements enable rapid accumulation of 3D data on particle shapes and size distributions. This paper reviews fragment size distributions (FSD) that result from fragmentation: lognormal, fractal, loggamma, and Weibull: discusses their genesis mechanisms: and presents relevant examples of fragmentation from experimental physics. Next, the paper considers FSDs of feldspars on digitized images of thin sections and on published images, and quartz extracted from vesicular pumice by acid from eight well-known large-volume eruptive units. The acid solution of pumice enables examination of volume abundance. 3D shapes, proportions of fragmented crystals, and measurements of their CSDs and FSDs. FSDs were also measured in samples of welded tuff and a granite disaggregated by electric pulse. Products of syneruptive shock wave fragmentation, and fragmentation by an electric pulse are found to be fractal with large breakage probabilities, branching ratios, and fractal dimensions of 2 to 3. In contrast, most quartz fragments in pumice obey a lognormal distribution and fragmentation is driven by a melt inclusion decrepitation mechanism, which results in low breakage probability and small number (2-3) of fragments per breakage cycle. These results are consistent with one atmosphere heating experiments of quartz phenocrysts that led to melt inclusion decrepitation and caused quartz to break up into several smaller pieces collectively having lognormal FSD. Measured melt inclusion size distributions suggest decrepitation of outermost melt inclusions, and low survival rate for large inclusions, and inclusions with large radius/crystal size ratio. The modeling of periodic fragmentation of crystals with melt inclusions due to overheating and/or decompression, which may occur many times during the lifetime of a long-lived magma body, may explain concave-down, lognormal CSDs abundant in igneous rocks. The genesis of lognormality can be explained by the fragmentation algorithm of Kolmogorov (1941). Other algorithms may generate lognormal-like loggamma distributions. Fragmentation serves as an important size limiting factor, a nucleation aid, and it facilitates isotopic and trace elemental exchange. [ABSTRACT FROM AUTHOR]

Fluorine-rich granites and rhyolites occur throughout the southern Rocky Mountains, but the origin of F-enrichment has remained unclear. We test if F-enrichment could be inherited from ancient mafic lower crust by: (1) measuring amphibole compositions, including F and Cl contents, of lower crustal mafic granulite xenoliths from northern Colorado to determine if they are unusually enriched in halogens; (2) analyzing whole-rock elemental and Sr, Nd, and Pb isotopic compositions for upper crustal Cretaceous to Oligocene igneous rocks in Colorado to evaluate their sources; and (3) comparing batch melting models of mafic lower crustal source rocks to melt F and Cl abundances derived from biotite data from the F-rich silicic Never Summer batholith. This approach allows us to better determine if the mafic lower crust was pre-enriched in F, if it is concentrated enough to generate F-rich anatectic melts, and if geochemical data support an ancient lower crustal origin for the F-rich rocks in the southern Rocky Mountains. Electron microprobe analyses of amphibole in lower crustal mafic granulite xenoliths show they contain 0.56–1.38 wt% F and 0.45–0.73 wt% Cl. Titanium in calcium amphibole thermometry indicates that the amphiboles equilibrated at high to ultrahigh temperature conditions (805 to 940 °C), and semiquantitative amphibole thermobarometry indicates the amphiboles equilibrated at 0.5 to 1.0 GPa prior to entrainment in magmas during the Devonian. Mass balance calculations, based on these new measurements, indicate parts of the mafic lower crust in Colorado are at least 3.5 times more enriched in F than average mafic lower crust. Intrusions coeval with the Laramide Orogeny (75 to 38 Ma) pre-date F-rich magmatism in Colorado and have Sr and Nd isotopic compositions consistent with mafic lower crust ± mantle sources, but many of these intrusions contain elevated Sr/Y ratios (>40) that suggest amphibole was a stable phase during magma generation. The F-rich igneous rocks from the Never Summer igneous complex and Colorado Mineral Belt also have Sr and Nd isotopic compositions that overlap with the lower crustal mafic granulite xenoliths, but they have lower Sr/Y, higher Nb and Y abundances, and distinctly less radiogenic 206Pb/204Pbi compositions than preceding Laramide magmatism. Batch melt modeling indicates low-degree partial melts derived from rocks similar to the mafic lower crustal xenoliths we analyzed can yield silicic melts with >2000 ppm F, similar to estimated F melt concentrations for silicic melts that are interpreted to be parental to evolved leucogranites. We suggest that F-rich silicic melts in the southern Rocky Mountains were sourced from garnet-free mafic lower crust, and that fluid-absent breakdown of amphibole in ultrahigh temperature metamorphic rocks was a key process in their generation. Based on the composition of high-F amphibole measured from lower crustal xenoliths, the temperature of amphibole breakdown and melt generation for these F-enriched source rocks is likely >100 °C higher than similar lower crust with low or average F abundances. As such, these source rocks only melted during periods of unusually high heat flow into the lower crust, such as during an influx of mantle-derived magmas related to rifting or the post-Laramide ignimbrite flare-up in the region. These data have direct implications for the genesis of porphyry Mo mineralization, because they indicate that pre-enrichment of F in the deep crust could be a necessary condition for later anatexis and generation of F-rich magmas. [ABSTRACT FROM AUTHOR]

Part VI of the evolutionary system of mineralogy catalogs 262 kinds of minerals, formed by 18 different processes, that we suggest represent the earliest solid phases in Earth's crust. All of these minerals likely formed during the first tens of millions of years following the global-scale disruption of the Moon-forming impact prior to ~4.4 Ga, though no samples of terrestrial minerals older than ~4.37 Ga are known to have survived on Earth today. Our catalog of the earliest Hadean species includes 80 primary phases associated with ultramafic and mafic igneous rocks, as well as more than 80 minerals deposited from immiscible S-rich fluids and late-stage Si-rich residual melts. Earth's earliest crustal minerals also included more than 200 secondary phases of these primary minerals that were generated by thermal metamorphism, aqueous alteration, impacts, and other processes. In particular, secondary mineralization related to pervasive near-surface aqueous fluids may have included serpentinization of mafic and ultramafic rocks, hot springs and submarine volcanic vent mineralization, hydrothermal sulfide deposits, zeolite and associated mineral formation in basaltic cavities, marine authigenesis, and hydration of subaerial lithologies. Additional Hadean minerals may have formed by thermal metamorphism of lava xenoliths, sublimation at volcanic fumaroles, impact processes, and volcanic lightning. These minerals would have occurred along with more than 180 additional phases found in the variety of meteorites that continuously fell to Earth's surface during the early Hadean Eon. [ABSTRACT FROM AUTHOR]

Minerals of the amphibole group are found in igneous rocks on Earth and other rocky bodies. Since the O(3) site of amphibole can contain OH, O2-, F, and Cl, amphibole composition provides important information about water and halogen contents, oxidation state, and other features of its formation and alteration environments. However, the complexity of amphibole crystal chemistry means this information is difficult to extract. Furthermore, it has been regular practice in the era of the electron microprobe to neglect H and Fe3+ analyses for amphibole, critically reducing the amount of information available in amphibole analyses in the literature. We have assembled models and insights from previous work to create a methodology that allows the estimation of magmatic H2O and Cl contents from existing amphibole analyses. Since the methodology requires use of a cation norm, we begin with a deeper investigation of the consequences of different cation normalization schemes for amphibole analyses, and provide grounds for deciding which scheme best fits a given amphibole analysis. We then show how the existing model of Popp and coworkers can be reversed to estimate the OH and [O(3)]O2- contents of amphiboles in synthesis experiments. Using a synthetic data set collected from the literature (39 amphibole analyses), we calibrate a partitioning model for the OH/Cl competition on the O(3) site of igneous amphiboles KCl=(XCl/XOH)amphibole/([Cl]/[OH])melt where X signifies a mole fraction of an anion on the O(3) site; [Cl] and [OH] signify melt mole fractions of the anion in question on a one-oxygen (Stolper-Zhang) basis; K, Na, [A]⇔, Mg, and [6]Fe signify the amount of each component in the amphibole in atoms per amphibole formula unit, with [A] ⇔ denoting vacancies on the amphibole A site. We then combine the Popp et al. model with our new model to link the occupancy of the amphibole O(3) site and other crystal chemical parameters to the Cl and H2O content of melts crystallizing amphibole. The competition between OH and Cl for this site can be used to calculate the melt and amphibole OH/H2O contents, as well as the speciation of Fe in amphibole, provided that the Cl content of both the amphibole and its coexisting melt is known, without analyzing either phase for H or Fe3+/Fe2+. While the models in this paper should be recalibrated using future experimental data, this work shows that considerably more information about the volatile contents of magmas can be gleaned from amphibole than previously shown and provides additional information about the crystal chemistry of amphibole and how it affects Cl partitioning into minerals of this group. [ABSTRACT FROM AUTHOR]

Subvolcanic phonolite intrusions of the Kaiserstuhl Volcanic Complex (Germany) show variable degrees of alteration. Their secondary mineralogy has been characterized by petrographic textural observations, bulk-rock powder X-ray diffraction, thermogravimetry, differential thermal analysis, and electron probe microanalysis. The alteration assemblage is dominated by various zeolites that occur in fissures, vugs, and as replacement products of primary phases within the phonolite matrix. Phonolites in the eastern Kaiserstuhl were emplaced into a sedimentary sequence and are characterized by high zeolite contents (Endhalden: 48 wt%, Fohberg: 45 wt%) with the temporal sequence: ± thomsoniteCa ± mesolite -- gonnardite -- natrolite -- analcime. In the western Kaiserstuhl zeolite contents are lower (Kirchberg: 26 wt% or less) and the crystallization sequence is: ± thomsonite-Ca -- gonnardite -- natrolite -- chabazite-Ca. Pseudomorphic replacement textures and barite inclusions in secondary aggregates suggest that zeolites grew at the expense of a sulfate-bearing sodalite-group mineral, i.e., haüyne. Fresh grains of sodalite-haüyne are only found at Kirchberg, whereas the pervasive alteration at Fohberg and Endhalden transformed feldspathoid minerals completely to zeolites. [ABSTRACT FROM AUTHOR]

The chevkinite-group minerals (CGM) are dominantly monoclinic REE-Ti-Fe sorosilicates [(REE, Ca)4Fe[sup 2+](Fe[sup 2+],Fe[sup 3+],Ti)2Ti2 (Si2O7)2O8)], with REE2O3 contents up to ~50 wt%, but members with predominant Mg, Al, Mn, Cr, Sr, or Zr in one of the cation sites are also known. Twelve members have been approved by the Commission of New Minerals, Nomenclature and Classification International Mineralogical Association (CNMNC-IMA) but more will undoubtedly be identified. Minerals of the group are known from hundreds of terrestrial localities and have also been recorded in lunar and martian rocks. The main occurrences are in igneous rocks ranging from diamond in kimberlites through mafic and intermediate lithologies to metaluminous and peralkaline felsic rocks. They also occur in metamorphic rocks, including granulites, metacarbonates, and jadeitites, and in metasomatic rocks, such as skarns and fenites, and in rare-metal deposits. Chevkinite-group minerals may form over the pressure range 50 to <10 kbar, and over a wide temperature range. Their formation appears to be relatively insensitive to … and fO2. The stability of CGM vis-à-vis other REE-Ti-bearing accessories is poorly understood. They are often the major carriers of REE and actinides, and they have a high potential for fractionating the light lanthanides and Th from U. Very little systematic work has been done in determining CGM-melt partition coefficients, yet such data are critical in, inter alia, geochemical modeling. Similarly, CGM are amenable to geochronology due to their high Th abundances, commonly at the several percent level. In common with other REE-bearing accessories, CGM are prone to alteration by hydrothermal fluids. The nature and extent of the alteration are primarily determined by the composition of the fluids. Fluids poor in ligands tend to generate a Ti-enriched phase whose nature is unknown but is probably amorphous. With increasing F + CO2 levels, complex replacement assemblages are formed, usually in more than one step. Although observational evidence of the effects of alteration and element mobility is accumulating and chemical equations can be constructed to approximate the reactions, there is still no firm geochemical basis for understanding element redistribution during these processes. [ABSTRACT FROM AUTHOR]

The Catalão II and Catalão I carbonatite complexes are Cretaceous intrusions in the northwestern part of the Alto Paranaíba Igneous Province, central Brazil, and contain various trioctahedral micas. Drill-hole sampling and mineralogical and geochemical data suggest the existence of different types of cumulate rocks as carbonatites (calcio- and ferrocarbonatites in Catalão II; magnesiocarbonatites in Catalão I), magnetitites, apatitites, and phlogopitites. In Catalão II complex the presence of ultramafic lamprophyres (phlogopite-picrites) and fenites (syenites and clinopyroxenites) are identified. Phlogopite, Fe3+-rich phlogopite, and tetraferriphlogopite are ubiquitous, with marked and variable pleochroism. In the Catalão II, micas from magnetitites, apatitites, and calciocarbonatites are close in composition to the tetraferriphlogopite end-member. The Mg/(Mg+[VI]Fetot) average value is 0.959 for micas from magnetitites, 0.878 for micas from apatitites, and 0.875 for micas from calciocarbonatites, suggesting an enrichment of octahedral iron in crystals from calciocarbonatites. The trioctahedral micas from the fenites are intermediate in composition between phlogopite and tetraferriphlogopite, with 0.227 ≤ [IV]Fe ≤ 0.291 apfu. Micas of phlogopitites, ferrocarbonatites, and phlogopite-picrites show a significant variation in [IV]Fe, [IV]Al, [VI]Mg, and [VI]Fe contents, suggesting the existence of different mica populations. In the Catalão I magnetitites micas show a quite constant Mg content but marked differences in [IV]Fe3+ and [IV]Al content, so there are [IV]Fe3+-bearing phlogopite and tetraferriphlogopite. The micas from Catalão I apatitites have variable [IV]Fe3+, [IV]Al, and Mg contents and are mainly tetraferriphlogopite with a minor phlogopite population. Trioctahedral micas from Catalão I magnesiocarbonatites contain crystals close to tetraferriphlogopite with [IV]Fe3+ and a limited variation in Mg content. In these complexes, heterovalent octahedral substitutions are mainly related to Ti4+ and, only in a few samples, to Fe3+. The primary mechanism regulating Ti uptake into the mica structure is the Ti-oxy [[VI]Ti4+[VI](Mg,Fe)2–+1(OH)––2O22–] substitution. Crystal structural analysis shows that all mica crystals are 1M polytypes with the expected space group C2/m. The nearly equal size and mean electron count between M1 and M2 octahedral sites suggest a disorder of octahedral cations between these two sites. The low Al and the high Fe3+ content in the tetrahedral site of these micas, as well as the high (OH)– content, reflects the general enrichment in FeO and H2O and the peralkaline nature of magma from which Catalão I and Catalão II micas crystallized. Micas strongly enriched in Fe3+ and poor in Ti and Al, are used, for the first time, as indicators of crystallization temperature using published geothermometers. Temperatures range between ~800 and 558 °C for the Catalão II cumulate rocks, in high oxygen fugacity conditions, mainly over the HM condition. In contrast, the variability in temperature (703–631 and 1050–952 °C) for Catalão II phlogopite-picrites is consistent with mica crystallization in an HM-NiNiO environment. The calculated temperatures for Catalão I cumulate rocks (742–542 °C for magnesiocarbonatites, 923–540 °C for magnetitites, and 679–550 °C for apatitites) are quite similar with those of Catalão II rocks, but they generally show higher oxygen fugacity conditions (over HM condition). [ABSTRACT FROM AUTHOR]

Capo Marargiu Volcanic District (CMVD) is an Oligo-Miocene calc-alkaline complex located in northwestern Sardinia (Italy) and characterized by the widespread occurrence of basaltic to andesitic domes. One of these domes hosts abundant crystal-rich enclaves with millimeter-to-centimeter sized clinopyroxenes showing intriguing textural features as a result of complex magma dynamics. To better understand the mechanisms governing the early evolution of the CMVD magmatic system, such clinopyroxene phenocrysts have been investigated in terms of their major, trace element, and isotopic compositions. Three distinct clinopyroxene populations have been identified, i.e., Type 1, Type 2, and Type 3. Type 1 appears as the sub-rounded cores of diopsidic clinopyroxenes with overgrowth textures corresponding to Type 2 and Type 3. These latter populations may also occur as single isolated crystals. Type 2 diopsidic pyroxene exhibits oscillatory zoning and spongy cellular textures with Type 3 overgrowths, whereas Type 3 are polycrystalline augitic glomerocrysts with occasional Type 2 overgrowths. The crystal overgrowths are striking evidence of magma recharge dynamics. Type 1 (CpxMg#83–92), Type 2 (CpxMg#75–82), and Type 3 (CpxMg#72–79) are, respectively, in equilibrium with Sardinian mantle-derived high-Mg basalts (HMB with meltMg#56–73), least differentiated basaltic andesites (BA with meltMg#45–56) and evolved basaltic andesites (EBA with meltMg#41–50). Type 1 and Type 2 are diopsidic phenocrysts that have evolved along a similar geochemical path (i.e., linear increase of Al, Ti, La, and Hf contents, as well as negligible Eu-anomaly) controlled by olivine + clinopyroxene + amphibole fractionation. This differentiation path is related to phenocryst crystallization from hydrous HMB and BA magmas stalling at moderate crustal pressures. The occurrence of globular sulfides within Type 1 suggests saturation of the HMB magma with a sulfide liquid under relatively low redox conditions. Moreover, Type 1 clinopyroxenes show variable 87Sr/86Sr ratios ascribable either to assimilation of crustal material by HMB magma or a mantle source variably contaminated by crustal components. In contrast, Type 3 augitic phenocrysts recorded the effect of plagioclase and titanomagnetite fractionation (i.e., low Al and Ti contents associated with high La and Hf concentrations, as well as important Eu-anomaly) from more degassed EBA magmas ponding at shallow depths. Rare titanite associated to Type 3 and titanomagnetite crystals point to high oxidizing conditions for EBA magmas. The 87Sr/86Sr ratios of both Type 2 and Type 3 are almost constant, suggesting a limited interaction of BA and EBA magmas with the country rock. The overall textural and compositional features of Type 1, Type 2, and Type 3 clinopyroxene phenocrysts lead to the conclusion that CMVD was characterized by a polybaric plumbing system where geochemically distinct magmas crystallized and mixed under variable environmental conditions. [ABSTRACT FROM AUTHOR]

Efforts to map the vertical distribution of mafic and ultramafic igneous rocks in the Earth's crust and uppermost mantle have long been hampered by the lack of precise geobarometers for the appropriate mineral assemblages. The average P (avP) method (Powell and Holland 1994) is a multiple-reaction approach that uses a least-squares minimization to average the pressures derived from individual mineral equilibria, taking into account both their uncertainties and correlations. We applied average P to a carefully selected database of published phase-equilibrium experiments in dry to H2O-saturated, andesitic to basaltic and peridotitic systems at P = 0.6-9.3 kbar, T = 940-1240 °C, with log fO2 from NNO-2.6 to NNO+3.6 log units (where NNO is nickel-nickel oxide buffer). We made minor modifications to the thermodynamic models of clinopyroxene, spinel, and olivine to improve the accuracy and precision of the results given by the avP method. Tests on the experimental database, using the modified thermodynamic models and spinel + clinopyroxene + olivine + plagioclase equilibria, showed that average P can reproduce the experimental P, within the calculated 1s uncertainties (0.9-2.6 kbar; 1.6 kbar on average), for 67% of the database. No systematic deviations of the calculated pressure (P) with temperature (T) or mineral compositions are observed. Given the large compositional range of the experimental database, these results suggest that the method can be applied to any gabbroic, pyroxenitic, or peridotitic rocks that contain the appropriate phase assemblage clinopyroxene + olivine + plagioclase ± spinel. For assemblages equilibrated at P < 5 kbar, the calculated P shows a slight dependence on T, which therefore needs to be well constrained to keep the overall P uncertainties as low as possible. T can be estimated using either available independently calibrated geothermometers or a simple calculation routine suggested in this work. Application of average P to gabbroic xenoliths from Dominica, Lesser Antilles, and to gabbroic and peridotitic xenoliths from Wikieup, Arizona, demonstrates the ability of the method to produce precise P estimates for natural assemblages equilibrated at both mid- and lower crustal conditions, respectively. Depending on the errors on mineral composition, appropriateness of the T estimate, and attainment of equilibrium of the assemblage, P uncertainty for natural rocks is ≤1.0 kbar. Such a level of precision can help to discriminate between rival petrogenetic processes in subduction zone, intra-plate, and mid-oceanic ridge settings. [ABSTRACT FROM AUTHOR]

Many plutons preserve evidence of magma mixing between hydrous mafic magmas and resident felsic crystal-rich mushes. To investigate water transfer processes in such systems following thermal equilibration, we conducted 24 h experiments to establish the petrological evolution of a waterundersaturated (4 wt% H[sub 2]O in the interstitial melt) quartz-bearing dacite crystal mush (0.5-0.8 in crystal fraction) intruded by a water-saturated (≥6 wt% H[sub 2]O), initially crystal-free, andesite magma at 950 °C and 4 kbar (12 km depth). Our results show isothermal undercooling resulting from a change in liquidus temperatures of the interacting magmas due to their changing water content. Specifically, mafic samples dramatically crystallize during water escape into the felsic end-members and consequent increase in liquidus temperature. Conversely, the addition of water to the felsic mush reduces the liquidus temperature, leading to an increase in melt fraction. The experiments provide insights into how volatiles contribute to crystal mush rejuvenation (i.e., increase of melt fraction). However, H[sub 2]O diffusion alone is not sufficient to promote melt extraction from short- and long-lived mushes in the Earth's crust. [ABSTRACT FROM AUTHOR]

Pressure is one of the key variables that controls magmatic phase equilibria. However, estimating magma storage pressures from erupted products can be challenging. Various barometers have been developed over the past two decades that exploit the pressure-sensitive incorporation of jadeite (Jd) into clinopyroxene. These Jd-in-clinopyroxene barometers have been applied to rift zone magmas from Iceland, where published estimates of magma storage depths span the full thickness of the crust, and extend into the mantle. However, tests performed on commonly used clinopyroxene-liquid barometers with data from experiments on H[sub 2]O-poor tholeiites in the 1 atm to 10 kbar range reveal substantial pressure-dependent inaccuracies, with some models overestimating pressures of experimental products equilibrated at 1 atm by up to 3 kbar. The pressures of closed-capsule experiments in the 1-5 kbar range are also overestimated, and such errors cannot be attributed to Na loss, as is the case in open furnace experiments. The following barometer was calibrated from experimental data in the 1 atm to 20 kbar range to improve the accuracy of Jd-in-clinopyroxene barometry at pressures relevant to magma storage in the crust: Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. This new barometer accurately reproduces its calibration data with a standard error of estimate (SEE) of ±1.4 kbar, and is suitable for use on hydrous and anhydrous samples that are ultramafic to intermediate in composition, but should be used with caution below 1100 °C and at oxygen fugacities greater than one log unit above the QFM buffer. Tests performed using with data from experiments on H[sub 2]O-poor tholeiites reveal that 1 atm runs were overestimated by less than the model precision (1.2 kbar); the new calibration is significantly more accurate than previous formulations. Many current estimates of magma storage pressures may therefore need to be reassessed. To this end, the new barometer was applied to numerous published clinopyroxene analyses from Icelandic rift zone tholeiites that were filtered to ex- clude compositions affected by poor analytical precision or collected from disequilibrium sector zones. Pressures and temperatures were then calculated using the new barometer in concert with Equation 33 from Putirka (2008). Putative equilibrium liquids were selected from a large database of Icelandic glass and whole-rock compositions using an iterative scheme because most clinopyroxene analyses were too primitive to be in equilibrium with their host glasses. High-Mg# clinopyroxenes from the highly primitive Borgarhraun eruption in north Iceland record a mean storage pressure in the lower crust (5.7 kbar). All other eruptions considered record mean pressures in the mid-crust, with primitive clinopyroxene populations recording slightly higher pressures (3.1-3.6 kbar) than evolved populations (2.6-2.8 kbar). Thus, while some magma processing takes place in the shallow crust immediately beneath Iceland's central volca- noes, magma evolution under the island's neovolcanic rift zones is dominated by mid-crustal processes. [ABSTRACT FROM AUTHOR]

The Half Dome Granodiorite, Yosemite National Park, California, is recognized in the field by euhedral, fresh-looking, black hornblende phenocrysts up to 2 cm in length. This variety of granodiorite typifies intermediate-age hornblende-phyric units of Cretaceous nested plutonic suites in the Sierra Nevada batholith. Although only inclusions of feldspar are evident in hand samples, the phenocrysts are riddled with up to 50% inclusions of every major mineral found in the host granodiorite plus metamorphic minerals formed during cooling. Amphibole compositions within single phenocrysts vary from actinolite with less than 1 wt% Al2O3 to magnesiohornblende with over 8 wt%. Elemental zoning within the amphibole is highly irregular on the micrometer scale, showing patches and polygonal zones with dramatically different compositions separated by sharp to gradual transitions. The chemical compositions of entire phenocrysts are equivalent to hornblende plus a small proportion of biotite, suggesting that the non-biotite inclusions are the result of metamorphism of the phenocrysts. Backscattered electron imaging shows evidence of brecciation that may have been the result of volume changes as hornblende was converted to actinolite. Pressure calculations using the Al-in-hornblende barometer show unreasonably wide variations on the micrometer scale that cannot have been produced by temperature or pressure variations during crystallization. These hornblende phenocrysts would thus be unsuitable for geobarometry, and caution must be used to avoid similarly zoned phenocrysts in the application of the Al-in-hornblende geobarometer. [ABSTRACT FROM AUTHOR]

Cordierite commonly contains H2O and CO2 in the channels formed by its ring structure. In many studies cordierite has been shown to have volatile contents and carbon isotope ratios consistent with high-temperature equilibrium, suggesting preservation of protolith carbon isotope ratios and motivating this survey of carbon isotopes in cordierite CO2. Cordierite CO2 from pelitic country rocks in the Etive aureole have δ13C values of -20.70 ± 1.27‰ (n = 10) that are unaffected by a ca. 150 °C thermal gradient and fluid-saturated and undersaturated regimes. These δ13C values are consistent with expected carbon isotope ratios of organic carbon in protolith sediments. Similar lithologies from the Cooma and Huntly aureoles show more variable behavior in a more limited data set, with some rocks preserving organic carbon δ13C values and others that may have been affected by externally derived fluids. In cordierite-gedrite gneisses, carbon isotopes of cordierite (Crd) are distinct from those of cordierite in pelites; when excluding one outlier new data plus those from the literature average δ13C(Crd) = -12.51 ± 2.45‰ (n = 17). These isotope ratios are higher than those of cordierite in typical metasedimentary protoliths and are similar to published carbon isotope ratios of trace carbonate in altered submarine volcanic rocks, which are likely analogs for protoliths of many cordierite-gedrite rocks. Igneous cordierite from granitic plutons have δ13C = -23.61 ± 2.08‰ (n = 13), which is interpreted as reflecting a magmatic carbon budget dominated by organic carbon from sedimentary source rocks. In contrast, small pegmatites reported in the literature have δ13C(Crd) = -10.20 ± 3.06‰ (n = 6), which may indicate derivation from orthogneiss source materials. These new data show that carbon isotopes in cordierite can be used to help understand the protolith of even carbon-poor metamorphic rocks, and can also shed light on carbon in the sources of magmatic rocks. This latter approach has the potential for helping constrain the source rocks of peraluminous granitoids, which is controversial. Determining the extent to which organic carbon δ13C is preserved in granitoids is important for understanding the deep carbon cycle, and could serve as an important constraint in the search for low-δ13C graphite inclusions in Hadean detrital zircons, which have been reported as a potential biosignature for the early Earth. [ABSTRACT FROM AUTHOR]

Erupted absarokitic-shoshonitic volcanics in subduction zones make up a relatively small proportion of the total erupted volcanic material. However, they are a critical component for quantifying subduction metasomatism and mantle source heterogeneity. This study examines the geochemistry of anomalous olivine within a forearc absarokite lava and associated tephra, a compositional end-member of the Cascadia subduction zone magmatism, to infer mantle heterogeneity and magma petrogenesis. Ni concentrations from the young (42 ka) Quartzville absarokitic basalt lava flow and tephra in the Cascade forearc are up to ~6400 ppm Ni with correspondingly low Ca, averaging ~850 ppm Ca in Fo91 olivine cores. Decreasing Ni and Ca toward olivine rims cannot be accounted for by simple fractional crystallization and instead necessitates magma mixing ± diffusive re-equilibration between the high-Ni, low-Ca olivine cores and low-Ni, high-Ca rims. δ18O of olivine phenocrysts (5.64‰) are elevated compared to other Cascade compositional components and outside of the range typically associated with peridotitic olivine or olivine crystallizing from peridotite-derived basaltic magmas. Trace element contents of whole rock, melt inclusions, and scoria glass have high Sr, high Dy/Yb, and low Y, characteristic of adakitic slab melts; however, major element compositions are of an alkali-rich basalt. In addition, similar trace element compositions between all analyzed glasses indicate a related petrogenesis between all components. We propose that a slab partial melt has reacted with depleted harzburgite in the mantle wedge, underlying the older Western Cascades (~40-10 Ma). Reaction of the siliceous slab-derived melt with depleted harzburgite could produce a metasomatized, zoned pyroxenite-harzburgite mantle source. High-Ni, low-Ca olivine crystallizes from melts of the subarc mantle reaction-pyroxenite. Later melting of the metasomatized harzburgite produces the absarokitic bulk composition, with olivine compositions recording diffusive re-equilibration following incorporation of pyroxenite-derived olivine in a peridotitic magma. Importantly, then, the observed olivine chemistry reflects mineralogical variations in the subarc mantle while melt trace element variations record melts/fluids derived from the subducting plate. High-Fo olivine rims (up to ~Fo94) appear to be the result of late-stage oxidation in the lava flow resulting from SO2 degassing and are unrelated to the otherwise complex magma petrogenesis. [ABSTRACT FROM AUTHOR]

The mixing of magmas of distinct temperature, bulk composition, mineralogy, and physical properties plays a central role in explaining the diversity of magma types on Earth and in explaining the growth of continental and oceanic crust. Magma mixing is also of practical importance. For example, the mixing of distinct magmas has been cited as an important process in creation of economically important horizons in layered intrusions as well as a triggering mechanism for initiation of volcanic eruptions. The motivation for better quantifying the dynamics and thermodynamics of magma mixing and its attendant plutonic and volcanic products is clear. The degree of magma mixing, which spans a continuum from mingling to complete hybridization, depends upon initial and boundary conditions, magma properties, driving forces, and time available for mixing. Magma mingling produces a heterogeneous mixture of discrete clumps of the end-member magmas, whereas complete hybridization involves the thermodynamic equilibration of two distinct magmas to form a third. Qualitatively, mixing occurs via reduction in the size of compositional heterogeneities (i.e., clumps) through stretching and folding by viscous flow, followed by homogenization, once shear has reduced the size of compositional anomalies to diffusive length scales. Quantification of this process relies on two statistical measures: the linear scale of segregation (Λ) defined as the spatial integral of the compositional correlation function related to the size-distribution of the segregated clumps within the mixture, and the intensity of segregation (I) a measure that quantifies how much the composition at each location differs from the average. The mixing dynamics of a layered system are analyzed in terms of the parameters governing mixing (Rayleigh, Lewis, and buoyancy numbers and viscosity ratio) to estimate how the timescale for magma hybridization, tH, compares to solidification, recharge, diffusive, and assimilation timescales. This analysis illustrates that hybridization times can be shorter than or comparable to thermal, solidification, and replenishment timescales; thus, formation of hybridized or nearly hybridized magmas is one anticipated outcome of mixing. The machinery of thermodynamics can be used to compute the hybrid magma state. An exploratory model for the thermochemistry of hybridization is developed based on binary eutectic phase relations and thermodynamics. Eight thermodynamic parameters define the phase diagram and associated energetics, and six parameters (initial temperatures, compositions, mass ratio of mixing magmas, and an enthalpy parameter) are necessary and sufficient to determine the state of hybrid magma uniquely. While relevant combinations of 14 thermodynamic and mixing parameters might suggest that the number of mixing outcomes (i.e., products) is too high to systematize, Monte Carlo simulations using the exploratory model document how millions of arbitrary initial states evolve into five possible final (mixed) states. Such an analysis implies that a magma mixing taxonomy that defines possible mixed product states can be developed and tied to petrologic indicators of mixing. Additional insights gained from this exploratory model that are supported by independent results from a multicomponent, multiphase thermodynamic model of magma mixing (Magma Chamber Simulator) include: (1) the proclivity of invariant point hybrid states, which may explain some instances of compositionally monotonous melts associated with mixed magma eruptions; (2) a surprising thermal effect such that the temperature of hybridized magma can be significantly less than the initial temperature of either of the mixing magmas. This type of magma mixing may result in crystal resorption, thus invalidating an assumption that resorption textures in crystals are typically the result of a magma heating event; (3) illustration of the differing effects of stoped block temperature and composition on hybrid magma temperature and phase state; and (4) illustration of a cessation of crystallization effect that may pertain to the MORB pyroxene "paradox." Differences between adiabatic or R-hybridization and diabatic or RFC-hybridization are also explored. The model can be used to elucidate the thermodynamic principles underlying magma mixing in the hybridization limit. These principles are of general applicability and carry over to more compositionally complicated systems. [ABSTRACT FROM AUTHOR]

Earth's inventory of principle volatiles C, H, N, and S is a legacy of its early stages of accretion and differentiation. Elemental ratios (C/H, C/N, C/S) are powerful tools for understanding early processing of Earth's volatiles, as they monitor relative fractionations through important processes even when absolute concentrations are less well defined. The C/H ratio of the bulk silicate Earth (BSE), defined from surface reservoirs and minimally degassed oceanic basalts is 1.3 ± 0.3, which is 5-15 times lower than the C/H ratio of carbonaceous and enstatite chondrites and 2-5 times lower than ordinary chondrites. The BSE C/N ratio is superchondritic (40 ± 8; Bergin et al. 2015) while the C/S ratio (0.49 ± 0.14) is nearly chondritic. Successful models of volatile acquisition and processing must account for the effects of accretion, core formation, and atmospheric loss on all three of these ratios. Simple models of equilibration between a magma ocean, the overlying atmosphere, and alloy destined for the core are used to explore the influence of core formation and atmospheric loss on major volatile concentrations and ratios. Among major volatile elements, C is most siderophile, and consequently core formation leaves behind a non-metallic Earth with low C/H, C/N, and C/S ratios compared to originally accreted materials and compared to the BSE. Compared to the predicted effect of early differentiation, the relatively high C/X ratios of the BSE argue in part that significant volatile replenishment occurred after core formation ceased, possibly in the form of a late veneer. However, a late veneer with chondritic composition is insufficient to explain the pattern of major volatile enrichments and depletions because BSE C/H and C/N ratios are non-chondritic. The C/H ratio is best explained if an appreciable fraction of H in the BSE predates delivery in the late veneer. Although atmospheric blow-off is an attractive explanation for the high C/N ratio, available data for C and N solubility and metal/silicate partitioning suggest that atmospheric blow-off cannot counter core formation to produce subchondritic C/N. Thus, unless virtually all core-forming metal segregated prior to volatile accretion (or relative C and N solubilities are appreciably different from those assumed here), the BSE C/N ratio suggests that accreting materials had elevated ratios compared to carbonaceous chondrites. One possibility is that a fraction of Earth's volatiles accreted from differentiated C-rich planetesimals similar to the ureilite parent body. Reconciling C/H, C/N, and C/S ratios of the BSE simultaneously presents a major challenge that almost certainly involves a combination of parent body processing, core formation, catastrophic atmospheric loss, and partial replenishment by a late veneer. The chondritic C/S ratio of the BSE and relatively low S content of the BSE constrains the BSE C concentration, but a potential complicating factor in interpreting the BSE C/S ratio is the possible effect of segregation of an S-rich matte to the core during the later parts of core-mantle differentiation. [ABSTRACT FROM AUTHOR]

Here we report on the coexistence between Na-rich ringwoodite and bridgmanite in the system MgSiO3-Na2CO3-Al2O3 at 24 GPa and 1700 °C. In our experiments ringwoodite incorporates up to 4.4 wt% Na2O, with Na entering the octahedral site together with Si, according to the mechanism: Mg2+ → ⅔Na+ + ⅓Si4+. The volume of the unit cell increases along with the Na content. A similar behavior is observed for the unit-cell volume of Na-bearing bridgmanite, although the mechanism of Na incorporation into this structure remains unknown because of the lack of sufficient crystallographic data. Na2O is compatible in ringwoodite relative to bridgmanite with a partition coefficient (D) of 5 (+5/-4), but is incompatible in ringwoodite relative to carbonate-rich melt/fluid, with the D value ranging between 0.5 and 0.1. Al is highly enriched in bridgmanite relative to the other coexisting phases. Carbonatitic melt metasomatism in the deep transition zone may lead to local Na-enrichment, and ringwoodite may be an important host for Na in the deep transition zone. Subsequent convection or subduction of metasomatized mantle may lead to enrichment of alkaline elements in the upper and lower mantle. [ABSTRACT FROM AUTHOR]

Despite claims to the contrary, the compositions of magnetite and ilmenite in the Bishop Tuff correctly record the changing conditions of T and fO2 in the magma reservoir. In relatively reduced (ΔNNO < 1) siliceous magmas (e.g., Bishop Tuff, Taupo units), Ti behaves compatibly (DTi ≈ 2-3.5), leading to a decrease in TiO2 activity in the melt with cooling and fractionation. In contrast, FeTioxides are poorer in TiO2 in more oxidized magmas (ΔNNO > 1, e.g., Fish Canyon Tuff, Pinatubo), and the d(aTiO2)/dT slope can be negative. Biotite, FeTi-oxides, liquid, and possibly plagioclase largely maintained equilibrium in the Bishop Tuff magma (unlike the pyroxenes, and cores of quartz, sanidine, and zircon) prior to and during a mixing event triggered by a deeper recharge, which, based on elemental diffusion profiles in minerals, took place at least several decades before eruption. Equilibrating phases and pumice compositions show evolving chemical variations that correlate well with mutually consistent temperatures based on the FeTi-oxides, sanidine-plagioclase, and Δ18O quartz-magnetite pairs. Early Bishop Tuff (EBT) temperatures are lower (700 to ∼780 °C) than temperatures (780 to >820 °C) registered in Late Bishop Tuff (LBT), the latter defined here not strictly stratigraphically, but by the presence of orthopyroxene and reverse-zoned rims on quartz and sanidine. The claimed similarity in compositions, Zr-saturation temperatures and thermodynamically calculated temperatures (730-740 °C) between EBT and less evolved LBT reflect the use of glass inclusions in quartz cores in LBT that were inherited from the low-temperature rhyolitic part of the reservoir characteristic of the EBT. LBT temperatures as high as 820 °C, the preservation of orthopyroxene, and the presence of reverse-zoned minerals (quartz, sanidine, zircons) are consistent with magma recharge at the base of the zoned reservoir, heating the cooler rhyolitic melt, partly remelting cumulate mush, and introducing enough CO2 (0.4-1.4 wt%, mostly contained in the exsolved fluid phase) to significantly lower H2O-activity in the system. [ABSTRACT FROM AUTHOR]

The active Lassen hydrothermal system includes a central vapor-dominated zone or zones beneath the Lassen highlands underlain by ∼240 °C high-chloride waters that discharge at lower elevations. It is the best-exposed and largest hydrothermal system in the Cascade Range, discharging 41 ± 10 kg/s of steam (∼115 MW) and 23 ± 2 kg/s of high-chloride waters (∼27 MW). The Lassen system accounts for a full 1/3 of the total high-temperature hydrothermal heat discharge in the U.S. Cascades (140/400 MW). Hydrothermal heat discharge of ∼140 MW can be supported by crystallization and cooling of silicic magma at a rate of ∼2400 km3/Ma, and the ongoing rates of heat and magmatic CO2 discharge are broadly consistent with a petrologic model for basalt-driven magmatic evolution. The clustering of observed seismicity at ∼4-5 km depth may define zones of thermal cracking where the hydrothermal system mines heat from near-plastic rock. If so, the combined areal extent of the primary heat-transfer zones is ∼5 km², the average conductive heat flux over that area is >25 W/m², and the conductive-boundary length <50 m. Observational records of hydrothermal discharge are likely too short to document long-term transients, whether they are intrinsic to the system or owe to various geologic events such as the eruption of Lassen Peak at 27 ka, deglaciation beginning ∼18 ka, the eruptions of Chaos Crags at 1.1 ka, or the minor 1914-1917 eruption at the summit of Lassen Peak. However, there is a rich record of intermittent hydrothermal measurement over the past several decades and more-frequent measurement 2009-present. These data reveal sensitivity to climate and weather conditions, seasonal variability that owes to interaction with the shallow hydrologic system, and a transient 1.5- to twofold increase in high-chloride discharge in response to an earthquake swarm in mid-November 2014. [ABSTRACT FROM AUTHOR]

Petrologic investigations of martian rocks have been accomplished by mineralogical, geochemical, and textural analyses from Mars rovers (with geologic context provided by orbiters), and by laboratory analyses of martian meteorites. Igneous rocks are primarily lavas and volcaniclastic rocks of basaltic composition, and ultramafic cumulates; alkaline rocks are common in ancient terranes and tholeiitic rocks occur in younger terranes, suggesting global magmatic evolution. Relatively uncommon feldspathic rocks represent the ultimate fractionation products, and granitic rocks are unknown. Sedimentary rocks are of both clastic (mudstone, sandstone, conglomerate, all containing significant igneous detritus) and chemical (evaporitic sulfate and less common carbonate) origin. High-silica sediments formed by hydrothermal activity. Sediments on Mars formed from different protoliths and were weathered under different environmental conditions from terrestrial sediments. Metamorphic rocks have only been inferred from orbital remote-sensing measurements. Metabasalt and serpentinite have mineral assemblages consistent with those predicted from low-pressure phase equilibria and likely formed in geothermal systems. Shock effects are common in martian meteorites, and impact breccias are probably widespread in the planet's crustal rocks. The martian rock cycle during early periods was similar in many respects to that of Earth. However, without plate tectonics Mars did not experience the thermal metamorphism and flux melting associated with subduction, nor deposition in subsided basins and rapid erosion resulting from tectonic uplift. The rock cycle during more recent time has been truncated by desiccation of the planet's surface and a lower geothermal gradient in its interior. The petrology of Mars is intriguingly different from Earth, but the tried-and-true methods of petrography and geochemistry are clearly translatable to another world. [ABSTRACT FROM AUTHOR]

Helium isotopes are used as a tracer for primitive reservoirs that have persisted in the Earth's mantle. Basalts erupted at several intraplate oceanic islands, including Hawaii, Iceland, Galapagos, and Samoa, have hosted the highest 3He/4He ratios (>30 Ra, where Ra is atmospheric 3He/4He ratio) globally that are far in excess of the 3He/4He typical of the upper mantle sampled at mid-ocean ridges (8 Ra). These lavas have been suggested to be melts of a primitive, or possibly slightly depleted, mantle reservoir, i.e., either fertile or a depleted peridotite. Here we report evidence for geochemical enrichment in the high-3He/4He mantle sampled by lavas with the highest 3He/4He from Hawaii, Samoa, and possibly Galapagos. The titanium concentrations in high-3He/4He lavas from Samoa are too high to be explained by melts of a mantle peridotite, even at infinitesimally small degrees of melting, and the elevated Ti corresponds to elevated Pb-isotopic ratios. The highest 3He/4He lavas from Loihi, Hawaii, also have Ti concentrations that are too high to be melts of primitive mantle peridotite at the degrees of melt extraction proposed for this ocean island. Thus, Ti-rich material must have been added to the high-3He/4He mantle reservoir, and this material is likely to be recycled mafic crust similar to MORBlike eclogite, which is consistent with the elevated Pb-isotopic ratios. We show that fractionation corrected, major element compositions of high-3He/4He alkalic lavas can be satisfactorily modeled by melting and melt-rock interaction scenario in a fertile peridotite-MORB-eclogite hybrid system. Primitive peridotitic and recycled eclogitic reservoirs are suggested to be intimately associated in the deepest mantle and high-3He/4He lavas from several localities may sample a mantle source that hosts a component of recycled oceanic crust. [ABSTRACT FROM AUTHOR]

The solubility of H2O- and CO2-bearing fluids in trachytic and trachybasaltic melts from erupted magmas of the Campi Flegrei Volcanic District has been investigated experimentally at 1100 and 1200 °C, respectively, and at 100, 200, 300, 400, and 500 MPa. The solubility of H2O in the investigated melts varies between 3.48 ± 0.07 wt% at 100 MPa to 10.76 ± 0.12 wt% at 500 MPa in trachytic melts and from 3.49 ± 0.07 wt% at 100 MPa to 9.10 ± 0.11 wt% at 500 MPa in trachybasaltic melts. The content of dissolved CO2 in melts coexisting with the most CO2-rich fluid phase increases from 281 ± 24 ppm at 100 MPa to 2710 ± 99 ppm at 500 MPa in trachyte, and from 727 ± 102 ppm at 100 MPa to 3565 ± 111 ppm at 500 MPa in trachybasalt. Natural samples from the Campanian Ignimbrite eruption (trachyte) and from the Solchiaro eruption (trachybasalt) were collected around the city of Naples and on Procida Island. Deuterium/hydrogen (D/H) ratios were analyzed in natural pumices pre-heated at different temperatures to remove water adsorbed and/or imprinted by glass alteration processes. It has been determined that heating of the glass to 350 °C efficiently removes most of secondary water and the remaining concentrations represent primary magmatic water preserved in the erupted material. Hydrogen isotope composition (with δD values ranging between -70‰ and -110‰) and its correlation with bulk water content in selected pumice samples of the Campanian Ignimbrite eruption are consistent with isotopic fractionation between magmatic fluid and melt during degassing of erupting magma. Hence, the H2O and CO2 contents in natural glasses from pumice samples are considered as minimum estimates on volatile concentrations in the melt just prior to the eruption or at the fragmentation event. The water contents in natural glasses vary from 0.83 ± 0.07 to 3.74 ± 0.06 wt% for trachytes from the Campanian Ignimbrite eruption and from 1.96 ± 0.06 to 3.47 ± 0.07 wt% for trachybasalts from the Solchiaro eruption. The CO2 contents vary from 78 ± 120 ppm CO2 to 1743 ± 274 ppm for trachytes from the Campanian Ignimbrite eruption and from 240 ± 293 to 1213 ± 250 ppm for trachybasalts from the Solchiaro eruption. A combination of natural and experimental data provides minimum pressure estimates for the storage and ascent conditions of magmas. The Campanian Ignimbrite magma could have been stored or ponded during its rising path at two different levels: a deeper one corresponding to depth of about 8 to 15 km and a shallower one at about 1 to 8 km. Trachybasalts from Solchiaro erupted from the deepest level of about 11 km with a storage or ponding level at around 2 to 8 km depth. Although an uncertainty of at least a kilometer has to be considered in estimating storage or ponding depths, these estimates point to significantly deeper magmatic sources for both eruptions as those considered previously. [ABSTRACT FROM AUTHOR]

Capsule pre-saturation has been traditionally employed to circumvent Fe loss from the charge to the container in petrological experiments. However, the method is time-consuming and fraught with theoretical and practical difficulties. An alternative method, based on the use of starting materials pre-enriched in Fe, is presented. Test experiments on two natural basalts, both non Fe-enriched and Fe-enriched with the addition of Fe oxides, have been carried out at 1 atm and 50 MPa (H2O-saturated), 1200 and 1250 °C, between NNO and NNO-1 and in Pt and Au80Pd20 capsules. Glasses and capsules were analyzed by electron microprobe. Fe-concentrations in the capsule near the glass interface strongly depend on the capsule material, being 5-10 times less for Au80Pd20 than for Pt. For non Fe-enriched compositions, Fe loss reaches -15% (Au80Pd20) and -60% (Pt). Increasing the level of Fe-enrichment reduces Fe loss, the amount of Fe alloyed with the capsule being compensated by the amount of Fe added to the starting composition. FeOt concentrations in high-pressure glasses bracket the nominal FeOt of the two starting basalts, demonstrating that Fe alloying has been successfully counteracted. Combination of AuPd containers with Fe pre-enriched starting materials offers excellent perspectives to solve the Fe loss issue in high-pressure experiments on basaltic compositions. [ABSTRACT FROM AUTHOR]

An unusual rare earth element (REE) mineralization occurs at a locality known as the 'Rusty Gold' within the anorogenic 1.4 Ga Longs Peak-St. Vrain monzo- to syenogranite Silver Plume-type intrusion near Jamestown, Colorado (U.S.A.). Irregular-shaped centimeter- to decimeter-sized mineralized pods and veins consist of zoned mineral assemblages dominated by fluorbritholite-(Ce) in a gray-colored core up to 10 cm thick, with monazite-(Ce), fluorite, and minor quartz, uraninite, and sulfides. The core zone is surrounded by a black, typically millimeter-thick allanite-(Ce) rim, with minor monazite-(Ce) in the inner part of that rim. Bastnäsite-(Ce), törnebohmite-(Ce), and cerite-(Ce) appear in a thin intermediate zone between core and rim, often just a few hundreds of micrometers wide. Electron microprobe analyses show that the overall REE content increases from rim to core with a disproportionate increase of heavy REE (∑HREE increases 10-fold from 0.2 to 2.1%) compared to light REE (∑LREE increases twofold from 21.3 to 44.3%). The fluorbritholite-(Ce) contains minor U, Th, Fe, Mn, and Sr (total 0.10 apfu), with Al, Mg, Na, K, Ti, Pb, S, and Cl below instrument detection limits. Cerite-(Ce) is a minor constituent of the thin zone between the inner rim and the core. The cerite-(Ce) is Fe-rich with low Ca, and minor Al, Mg, and Mn, whereas törnebohmite-(Ce) is Al-rich and Ca-poor. Monazite-(Ce) and uraninite U-Th-Pb microprobe ages yield 1.420(25) and 1.442(8) Ga, respectively, confirming a co-genetic relationship with the host ca. 1.42(3) Ga Longs Peak-St. Vrain granite. We suggest the origin of the REE mineralization is a F-rich and lanthanide-rich, either late-magmatic hydrothermal fluid or residual melt, derived from the granite. This late-stage liquid, when becoming progressively enriched in REE as it crystallized, could explain the observed concentric mineralogical and geochemical zoning. [ABSTRACT FROM AUTHOR]

Baddeleyite is a frequently found accessory mineral in silica undersaturated lavas. Because it is typically enriched in uranium, while having low initial lead, baddeleyite has long been a prime target for U-Pb geochronology of mafic rocks. The difficulties in retrieving small baddeleyite grains from volcanic samples and the lack of a detailed understanding of baddeleyite occurrence, however, have limited baddeleyite chronology largely to coarse-grained mafic intrusive rocks. Here, the development of U-Th in situ baddeleyite analysis using secondary ionization mass spectrometry (SIMS) is presented together with an assessment of baddeleyite occurrence in Quaternary silica-undersaturated lavas from Campi Flegrei (Naples, Italy). Samples studied comprise the pre- and post Campanian Ignimbrite (ca. 40 ka) lava domes of Cuma and Punta Marmolite, and Astroni and Accademia, respectively. The in situ sample preparation required initial identification of baddeleyite crystals from sawed and polished rock billets using scanning electron microscope (SEM) backscatter imaging and energy-dispersive X-ray analysis. U-Th baddeleyite isochron ages for intra-caldera Astroni and Accademia lava domes are 5.01+2.61-2.55 ka (MSWD = 2.0; n = 17) and 4.36+1.13-1.12 ka (MSWD = 2.9; n = 24), respectively. The ages for Punta Marmolite (62.4+3.9-3.8 ka; MSWD = 1.2; n = 11) and Cuma (45.9+3.6-3.5 ka; MSWD = 2.2; n = 11) predate the Campanian Ignimbrite. Rapid baddeleyite crystallization at the time of emplacement is supported by petrologic observations that >50% of the baddeleyite crystals documented in this study occur either in vesicles or in vesicle-rich regions of the host lavas whose textures developed over timescales of a few years to a few decades based on microlite crystal size distribution (CSD) analysis. Radiometric U-Th baddeleyite ages are mostly in agreement with previously determined K-Ar eruption ages, except for the Punta Marmolite lava dome whose U-Th baddeleyite age predates the K-Ar age by ca. 15 ka. Baddeleyite thus records eruptive emplacement with little evidence for significant pre-eruptive crystal residence, and has potential as an eruption chronometer for Quaternary silica-undersaturated volcanic rocks. [ABSTRACT FROM AUTHOR]

To constrain the crystallization of alkaline and volatile-rich lavas present in intraplate settings, we studied the petrological features and the geochemical composition of major, trace, and volatile elements of mineral and bulk-rock of two sodalite-bearing phonolites: (1) haüyne-plagioclase-bearing Si-K-rich phonolite from Laacher See (Germany) and (2) nosean-nepheline-bearing Si-poor phonolite from Saghro (Morocco). In haüyne-bearing phonolites (55-59 wt% SiO2, K > Na, Na+K/Al = 0.96-1.08), we found that the low silica and low sodium activity promoted the early crystallization of S-rich haüyne (13.7-13.9 wt% SO3, 0.4 wt% Cl) + S-rich apatite (0.7-0.9 wt% SO3), titanite, and rare pyrrhotite followed by clinopyroxene-plagioclase-sanidine at relatively low pressure and temperature (P = 250 MPa and T = 850 °C) and oxidized condition (ΔNNO-NNO+1, where NNO is nickel-nickel oxide buffer). The crystallization of haüyne occurred at fluid-undersaturated conditions from a silicate melt with 6 wt% H2O, 0.17-0.23 wt% Cl, 0.11-0.4 wt% S, and 0.07-0.14 wt% F. Nosean-bearing phonolites from Saghro are silica-poor and peralkaline (52-54 wt% SiO2, Na > K, Na+K/Al = 1.2) and crystallized at higher P and T (300 MPa and 950 °C) and more reduced conditions (NNO) compared to haüyne-bearing phonolites. The incongruent reaction to form nosean requires high silica and Na2O activity. The mineral assemblage and composition suggest early crystallization of nepheline followed by nosean (7.8-8.8 wt% SO3; 1-1.1 wt% Cl). The sequence of crystallization is: clinopyroxene + nepheline + S-poor apatite (<0.04 wt% SO3) + pyrrhotite followed by nosean and titanite. Noseanbearing magmas are fluid-undersaturated with relatively low volatile content (4 wt% H2O, <0.25 wt% Cl, <0.056 wt% S, 0.08-0.1 wt% F), although Cl may have exsolved during ascent and formed a fluid phase (NaCl-bearing). Both haüyne- and nosean-bearing phonolites are last equilibrated at relatively low pressure and high temperature. Haüyne and nosean crystallized at oxidized and volatile-rich pre-eruptive conditions. They record the volatile concentrations at depth and may be used as oxybarometer. The incongruent reactions involved to form haüyne and nosean suggest that phonolitic magmas became more oxidized during crystallization. The initial volatile concentrations in basanite/nephelinite magmas, from partial melting of volatile-bearing K2O-rich mantle rock, should have been one important factor influencing the crystallization of haüyne-bearing Si-K-rich phonolite and nosean-bearing Si-poor phonolite in intracontinental setting. [ABSTRACT FROM AUTHOR]

Phosphoran olivine (1-7 wt% P2O5) is a metastable phase known from fewer than a dozen meteoritic or terrestrial occurrences. We have thoroughly examined phosphoran olivine in the Springwater pallasite to characterize its distribution, textural relationships, and geochemistry. Phosphoran olivine is abundant in Springwater as randomly distributed millimeter-scale partial overgrowths on the P-free olivine crystals. Geochemical analyses support the substitution mechanism of P into the tetrahedral Si site with octahedral site vacancies for charge balance; observed trace element variations, on the other hand, are not related to P substitution. Element mapping reveals fine-scale oscillatory P zoning in unusual serrate patterns, indicating rapid crystal nucleation from a melt as proposed by Boesenberg and Hewins (2010) and a subsequently variable rate of crystallization. The timing of phosphoran olivine formation in Springwater is constrained to after the period of macroscopic olivine rounding but before the cooling of the metal matrix; because the phosphoran overgrowths overprint specific host grain boundary modifications, we suggest that the episode of extremely rapid cooling necessary to crystallize and preserve this rare phase may have been triggered by an additional impact to the parent body. [ABSTRACT FROM AUTHOR]

Most models of early lunar evolution predict that the anorthositic highlands crust is the result of plagioclase flotation on a magma ocean. However, the lunar highlands crust typically contains 4 wt% FeO and so is more mafic than the strict definition of the anorthosites thought to comprise it. We used new Clementine-based mineral maps of the Moon as inputs to a series of mixing models that calculate the abundance and distribution of major highland rock types and shed light on three possible sources of excess mafic material in the lunar highlands: mafic (15 vol% mafic minerals) anorthosites, postmagma ocean igneous activity, and mafic basin ejecta. Mixing models that feature pure anorthosites like the purest anorthosite (PAN) described by Ohtake et al. (2009) and Pieters et al. (2009) are most compatible with the data. They allow us to place an upper limit of 10-20 vol% mantle material that could be mixed with the primary highlands crust. The upper limit on mantle material indicated by the mixing models is significantly lower than the 30-40 vol% mantle material expected from simple geometric calculations of the major lunar basins' excavation cavities based on an excavation cavity depth/diameter ratio of 1/10; this discrepancy allows us to conclude that the excavation cavities of the three largest lunar basins may have been significantly shallower than those of the smaller basins. Our results are consistent with excavation cavity depth/diameter ratios for these largest basins in the range of 0.035 to 0.06, which agrees with previous gravity measurements by Wieczorek and Phillips (1999). [ABSTRACT FROM AUTHOR]

The Phepane Dome is a circular outcrop of metasedimentary rock within the Eastern Lobe of the Bushveld Complex hypothesized to have formed as a diapir, when underlying wallrock rose into the overlying magma body. Interactions between the metasedimentary rock of the Phepane Dome and the magma of the Bushveld Complex were investigated through measurements of oxygen and lithium isotopic compositions, determination of mineral modes and major-element mineral compositions, cathodoluminescence imaging, and dihedral angle analysis. Evidence from cathodoluminescence imaging and dihedral angle analysis suggest that heat transfer during diapirism caused partial melting and complete recrystallization of the Phepane Dome metasedimentary rock. Oxygen isotope analysis of samples from traverses spanning the contact between metasedimentary and igneous rocks demonstrates that relatively minimal exchange of oxygen (over distance ~4 m) occurred across the contact between the Phepane Dome and the surrounding Bushveld magma. The lithium concentrations and isotopic compositions of metasedimentary rock are significantly different from the associated igneous rocks. Lithium isotope analysis of samples from traverses across the contact demonstrates exchange of Li over somewhat greater distances (~60 m) than oxygen, consistent with evidence that suggests a higher diffusivity of Li than most major elements. Models of oxygen diffusion through intergranular melt and aqueous fluid are used to place maximum constraints on the duration of diffusive exchange across the contact, resulting in estimates ranging from 5 kyr to 5 Myr. These values are consistent with previous estimates of the duration of crystallization of the Bushveld Complex and Phepane diapir development. [ABSTRACT FROM AUTHOR]

The direct crystallization of dolomite from an aqueous solution at temperatures between 60-220 °C was followed in situ through time-resolved synchrotron-based energy-dispersive X-ray diffraction combined with offline high-resolution imaging, X-ray diffraction, and infrared spectroscopy. Crystalline CaMg(CO3)2 phases form through a three-stage process. In the first stage, a nanoparticulate magnesium-deficient, amorphous calcium carbonate (Mg-ACC) with a nominal formula of Ca0.606Mg0.394CO3·1.37H2O forms. After a temperature-dependent induction time, during stage 2 the Mg-ACC partially dehydrates and orders prior to its rapid (<5 min) crystallization to non-stoichiometric proto-dolomite. This occurs via the dissolution of Mg-ACC, followed by the secondary nucleation of proto-dolomite from solution. The proto-dolomite crystallization proceeds via spherulitic growth that follows a growth front nucleation mechanism with a de-nuovo and continuous formation of nanocrystalline proto-dolomite subunits that form spherical aggregates. In stage three of the reaction, the proto-dolomite transforms to highly crystalline and stoichiometric dolomite on a much longer timescale (hours to days), via an Ostwald-ripening mechanism. Such a three-stage crystallization can explain microbially induced proto-dolomites observed in modern hypersaline settings and may also be the route by which the Cryogenian cap dolomite deposits of the Neoproterozoic formed. [ABSTRACT FROM AUTHOR]

Anorthositic rocks dominate the Moon's upper crust. As remnants of the lunar magma ocean (LMO), small variations in the mineralogy of these rocks may hold key information about the homogeneity of LMO composition and solidification processes. Orbital near-infrared (NIR) sensors are sensitive to mineralogy, but technologic advances have only recently enabled detection of the plagioclase component in crustal rocks based on an absorption band centered near 1250 nm. Anorthosites occupy a unique mineralogic range that is well suited for NIR studies: the highly transparent component, plagioclase, is present in high abundances while the spectrally dominant mafic or oxide minerals are present in only minor abundance. As a result, spectra of anorthosites are more likely than many other rock types to contain visually discernable signatures from more than one mineral component, facilitating their identification and characterization in NIR data. In support of new NIR measurements for the Moon, we present laboratory spectral analyses of well-controlled plagioclase-dominated mineral mixtures. We focus on the spectral effects of varying mafic and oxide composition and abundance in mixtures with a common plagioclase end-member. The results demonstrate that plagioclase can be a significant contributor to reflectance spectra when strongly absorbing minerals are present in low abundance. We show that the contribution of plagioclase is more pronounced in mixtures with pyroxenes and certain spinels, but more easily masked in mixtures containing small amounts of olivine. Differences in minor mineral composition are clearly expressed in bulk spectra. Modeling of mixtures using a Hapke nonlinear approach accurately estimates mineral abundances in laboratory spectra to within 5 vol% for mixtures with ⩾90 vol% plagioclase. Together, these results imply that not only should orbital NIR data sets be able to discern the presence of plagioclase in anorthositic crustal exposures, but also that detailed information about anorthosite mineral assemblages can be reliably accessed in reflectance spectra. [ABSTRACT FROM AUTHOR]

Instrumental neutron activation analysis (INAA) was used to investigate REEs in carbonatite from Kpong southeastern, Ghana. Total rare earth element (TREEs) obtain were in the range of 540 mg/kg to 705 mg/kg. The total number of rare earth elements (REEs) determined by INAA in the carbonatite rocks from Kpong were 11, namely; La, Ce, Nd, Sm, Eu, Tb, Dy, Ho, Tm, Yb, Lu. The INAA results from the carbonatite show a high enrichment of light rare earth elements (LREEs) deposits, marking the Kpong carbonatite as a potential REE source. [ABSTRACT FROM AUTHOR]

We present a calibration for attenuated total reflectance (ATR) micro-FTIR for analysis of H2O in hydrous glass. A Ge ATR accessory was used to measure evanescent wave absorption by H2O within hydrous rhyolite and other standards. Absorbance at 3450 cm-1 (representing total H2O or H2Ot) and 1630 cm-1 (molecular H2O or H2Om) showed high correlation with measured H2O in the glasses as determined by transmission FTIR spectroscopy and manometry. For rhyolite, wt%H2O = 245(±9)⋅A3450 - 0.22(±0.03) and wt%H2Om = 235(+ll) ⋅A1630 - 0.20(±0.03) where A3450 and A1630 represent the ATR absorption at the relevant infrared wavelengths. The calibration permits determination of volatiles in singly polished glass samples with spot size down to ~5 µm (for H2O-rich samples) and detection limits of ~0.1 wt% H2O. Basaltic, basaltic andesite and dacitic glasses of known H2O concentrations fall along a density-adjusted calibration, indicating that ATR is relatively insensitive to glass composition, at least for calc-alkaline glasses. The following equation allows quantification of H2O in silicate glasses that range in composition from basalt to rhyolite: wt% H2O = (ω⋅A3450/ρ) + b where ω = 550 ±21, b = -0.19 ± 0.03, ρ = density, in g/cm³, and A3450 is the ATR absorbance at 3450 cm-1. The ATR micro-FTIR technique is less sensitive than transmission FTIR, but requires only a singly polished sample for quantitative results, thus minimizing time for sample preparation. Compared with specular reflectance, it is more sensitive and better suited for imaging of H2O variations in heterogeneous samples such as melt inclusions. One drawback is that the technique can damage fragile samples and we therefore recommend mounting of unknowns in epoxy prior to polishing. Our calibration should hold for any Ge ATR crystals with the same incident angle (31°). Use of a different crystal type or geometry would require measurement of several H2O-bearing standards to provide a crystal-specific calibration. [ABSTRACT FROM AUTHOR]

The Dabie-Sulu Triassic collisional orogen in eastern Asia was created by northward subduction of the Yangtze continental-crust capped plate beneath the Sino-Korean craton. Eclogites, garnet peridotites, and surrounding country rock gneisses and marbles were all subjected to in situ UHP metamorphism, as indicated by the presence of rare but widespread coesite inclusions in eclogitic minerals and in zircon crystals in the country rocks, as well as by virtually identical metamorphic ages of various UHP rock types. Metamorphic P-T estimates, combined with investigations of mineral exsolution textures and high-P polymorphs, indicate that recovered depths of continental subduction may have exceeded 200 km. Parageneses of mineral inclusions in zoned zircon domains combined with U-Pb ages delineate a well-constrained P-T-time path, suggesting exhumation rates of 5-10 km/Myr. A similar P-T-time trajectory has been established for the microdiamond-bearing Kokchetav Massif. Thus far, however, diamond inclusions have not been confirmed from coesite-bearing zircon domains of Dabie-Sulu UHP rocks despite numerous detailed studies. Oxygen isotopes of minerals from many outcrop samples and the Chinese Continental Scientific Drilling (CCSD) project main hole cores indicate that δ18O depletion took place in a volume of Proterozoic protoliths exceeding 100 000 km³ along the northern edge of the Yangtze craton. Evidently, passive-margin sediments and bimodal igneous rocks that had formed during rifting and breakup of the supercontinent Rodinia were subjected to extensive meteoric water-rock interactions attending terminal Neoproterozoic Snowball Earth conditions. Such hydrothermal alteration volatilized and depleted C from the relatively oxidized protoliths, accounting for the rare occurrences of graphite and apparent lack of microdiamond in Dabie-Sulu UHP rocks. [ABSTRACT FROM AUTHOR]

Petrologic, chemical, and polytype data are presented for dioctahedral potassic micas from K-feldspar-bearing metamorphic and igneous rocks of acidic composition unaffected by high-pressure (HP) conditions. The paper aims to demonstrate that: (1) under non-HP conditions, in both metamorphic and igneous plutonic environments, a given bulk-rock compositional constraint imposes a more or less marked phengitic composition to dioctahedral potassic mica; and (2) this muscovite crystallizes as 2M1, notwithstanding its phengitic composition. The samples (157 in number) are from widespread provenances. We conclude that the growth of 3T polytype of muscovite is not a function of mica composition. This is consistent with the recent crystallographic knowledge on polytypism, cation ordering, elastic properties, and structural deformational mechanisms of muscovite, which address the stabilization of 3T with pressure. [ABSTRACT FROM AUTHOR]

The recently developed titanium-in-quartz (TitaniQ) geothermobarometer of Wark and Watson (2006) and Thomas et al. (2010) has the potential to be applied to a wide range of igneous and metamorphic rocks. For Ti concentrations > ~10 ppm, the concentrations can be measured using an electron microprobe, but lower concentrations are below detection limits and require techniques such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS). SIMS is ideal for this purpose as it maximizes lateral and depth resolution. We used SIMS to analyze synthetic quartz crystals characterized for Ti concentration by electron probe (18-813 ppm Ti) and compare this calibration to the commonly available NIST 61X glasses using both high mass resolution (HMR) and conventional energy filtering (CEF) techniques. We used a primary beam of 16O- ions and detected positive secondary ions. During HMR sessions, the mass spectrometer was operated at a mass resolving power (M/ΔM) of ~2000 to separate molecular ions from elemental Ti peaks. For CEF analyses, the instrument detected secondary ions sputtered from the sample with excess kinetic energies of 75 ± 20 eV. Titanian quartz measurements reveal general homogeneity and a linear increase in Ti+/Si+ ion ratios with increasing Ti concentrations. Background signals represent 0-1 ppm. The slopes of the calibration curves for the titanian quartz crystals are ~70% of the curves constructed using NIST glasses, indicating a much higher ion yield for Ti from the glasses compared to the simple oxide of silicon. We demonstrate, however, that a simple correction factor allows NIST glasses to be used to quantitatively determine the Ti concentrations of quartz (with 3.8% error using HMR, and 8.2% error using CEF) until homogenous, well-characterized samples of SiO2 become generally available. [ABSTRACT FROM AUTHOR]

Electrical resistivity of synthetic nanocrystalline (30-40 nm crystallite size) and a crystalline natural sample of geikielite MgTiO3 has been measured at simultaneous high pressure and high temperature up to 6 GPa and 800 K, respectively. The temperature dependence of the electrical resistivity of both the synthetic and natural sample obeys the Arrehenius behavior in the temperature range between 3 and 800 K and pressure range up to 6.0 GPa. The activation volume of the electrical conduction for coarse crystalline natural sample of geikielite is almost twice that of the synthetic nanocrystalline geikielite indicating the increase of activation volume with the crystallite size. The activation energy for the electronic conduction decreases from 0.39 eV at room pressure to 0.25 eV at 6.0 GPa for natural geikielite, and 0.68 to 0.225 eV in the same pressure range for synthetic geikielite. The pressure dependence of the activation energy of geikielite sample is found to obey the following expressions Δ (eV) = 0.39 - 0.026(1 )P + 0.0036 P² for natural sample, and Δ (eV) = 0.68 - 0.080 (2) P + 0.0007 P² for synthetic sample, where P is pressure in GPa. We observe a crossover from extended state type conduction to hopping conduction at 4.0 GPa and 350 K for nano-crystalline geikielite. However, there is no such change of conduction mechanism observed for the natural geikielite at high pressures and high temperatures. The present study reveals the phase stability of nano-crystalline geikielite and natural geikielite up to mantle pressure and temperature conditions, viz. 6 GPa and 800 K, and no phase transition or decomposition is observed in the sample. [ABSTRACT FROM AUTHOR]

In this paper, we report analysis of various basaltic lunar samples including 14053 and 14072, KREEP basalt 15386, thirty basalt clasts from Apollo 14 breccia 14321, as well as impact-generated samples (matrix from breccia 14168, olivine vitrophyres 14321,1180 and 14321,1539, and impact melt 14310) using a combination of solution and laser ablation inductively coupled plasma mass spectrometry (ICP-MS). The basalt clast samples were previously analyzed by instrumental neutron activation. On plots of incompatible trace elements (ITEs) vs. compatible trace elements, the Apollo 14 high-Al basalts form three approximately subparallel trends that, on the basis of current data, are also separated by age. Plots of ITE ratios (i.e., Nb/Ce vs. Zr/Y) can be used to indicate source composition, and also divide the basalts into three groups: Group A (∼4.3 Ga); Group B (∼4.1 Ga); and Group C (∼3.9 Ga). New data for 14072 suggest the sample does not Þ t with any of the three groups defined here, and may indicate the presence of a fourth group of high-Al basalts in the proximity of the Apollo 14 site. The Apollo 14 high-Al basalts are compositionally distinct from known Apollo 14 impact melts and impact-generated lithologies. The three groups cannot be related by varying degrees of partial melting of a single, KREEP-contaminated source and, therefore, require three separate source regions. The new data indicate that Group A basalts evolved through closed-system crystal fractionation. However, the new data from basalts forming Groups B and C require open-system evolution that involves combined assimilation and fractional crystallization (AFC). Unlike previous AFC modeling of the Apollo 14 high-Al basalts, an assimilant composed of KREEP is not sufficient to generate the compositional ranges of each basalt group. The modeling of both groups requires a mixture of KREEP and granite as the assimilant, which supports the notion of a genetic relationship between these two lunar components. [ABSTRACT FROM AUTHOR]

In-situ U-Th dating is among the most challenging analytical techniques, requiring extreme sensitivity to quantify the low-abundance 230Th. Consequently, not all mineral phases are suitable for this technique. In this issue, Wu et al. have demonstrated that baddeleyite in basic rocks can provide meaningful U-Th ages when analyzed using secondary ionization mass spectrometry. [ABSTRACT FROM AUTHOR]