Diagnosing open-system magmatic processes using the Magma Chamber Simulator (MCS): part II\u2014trace elements and isotopes

Major and trace element data on basanitic to phonolitic lavas of different ages and from different parts of Tenerife (Canary Islands), and their mafic silicates have been used to obtain more detailed information about processes taking place in crustal magma chambers associated with ocean island magmatism in Tenerife. Clinopyroxene phenocrysts in basanitic to phonolitic lavas consist of diopside–salite (referred to as Al-salite) with alternating normal and reverse zoning, and commonly contain a rounded or corroded core of homogeneous Na-rich diopside–salite (referred to as Na-salite). In general Al-salite contains lower amounts of rare earth elements (REE) and Y, and more Mg, Al, Ti, Cr, Sc and Ni than Na-salite. Variations in trace element concentrations and ratios are only weakly related to variations in mg-number. Petrographic and compositional relations among the lavas and mafic silicates are interpreted as the results of fractional crystallization in periodically refilled magma chambers (FCM processes). The FCM processes took place at temperatures of 1040–1260°C and pressures of about 0.2–0.5 GPa; that is, partly within the old oceanic crust and partly within the overlying sequence of Canary Islands lavas. FCM processes may lead to significant fractionation between incompatible trace elements whose ratios in mafic magmas are used to characterize their mantle source(s). Melts subjected to FCM processes will, furthermore, produce significantly larger masses of cumulates than melts of similar mg-number that have only been subjected to simple fractional crystallization.

Significant petrogenetic processes governing the geochemical evolution of magma bodies include magma Recharge (including formation of ‘quenched inclusions’ or enclaves), heating and concomitant partial melting of country rock with possible ‘contamination’ of the evolving magma body (Assimilation), and formation and separation of cumulates by F ractional Crystallization (RAFC). Although the importance of modeling such open-system magma chambers subject to energy conservation has been demonstrated, the effects of concurrent removal of magma by eruption and/or variable assimilation (involving imperfect extraction of anatectic melt from wall rock) have not been considered. In this study, we extend the EC-RAFC model to include the effects of Eruption and variable amounts of assimilation, Ax. This model, called EC-E 0RAcFC, tracks the compositions (trace elements and isotopes), temperatures, and masses of magma body liquid (melt), eruptive magma, cumulates and enclaves within a composite magmatic system undergoing simultaneous eruption, recharge, assimilation and fractional crystallization. The model is formulated as a set of 4 þ t þ i þ s coupled nonlinear differential equations, where the number of trace elements, radiogenic and stable isotope ratios modeled are t, i and s, respectively. Solution of the ECE 0RAcFC equations provides values for the average temperature of wall rock (Ta), mass of melt within the magma body (Mm), masses of cumulates (Mct), enclaves (Men) and wall rock (M o a) and the masses of anatectic melt generated (M a ) and assimilated (cM a ). In addition, t trace element concentrations and i þ s isotopic ratios in melt and eruptive magma (Cm, em, dm), cumulates (Cct, em, dm), enclaves (Cen, er , d o r ) and anatectic melt (Ca, ea, d o a) as a function of magma temperature (Tm) are also computed. Input parameters include the (user-defined) equilibration temperature (Teq), a factor describing the efficiency of addition of anatectic melt (c) from country rock to host magma, the initial temperature and composition of pristine host melt (Tom, C o m, em, d o m), recharge melt (T o r , C o r , er , dor ) and wall rock (T o a, C o a, ea, d o a), distribution coefficients (Dm, Dr, Da) and their temperature dependences (DHm, DHr, DHa), latent heats of transition (melting or crystallization) for wall rock (Dha), pristine magma (Dhm) and recharge magma (Dhr) as well as the isobaric specific heat capacity of assimilant (Cp,a), pristine (Cp,m) and recharge (Cp,r) melts. The magma recharge mass and eruptive magma mass functions,Mr(Tm) andMe(Tm), respectively, are specified a priori. Mr(Tm) and Me(Tm) are modeled as either continuous or episodic (step-like) processes. Melt productivity functions, which prescribe the relationship between melt mass fraction and temperature, are defined for end-member bulk compositions characterizing the local geologic site. EC-E 0RAcFC has potential for addressing fundamental questions in igneous petrology such as: What are intrusive to extrusive ratios (I/E) for particular magmatic systems, and how does this factor relate to rates of crustal growth? How does I/E vary temporally at single, long-lived magmatic centers? What system characteristics are most profoundly influenced by eruption? What is the quantitative relationship between recharge and assimilation? In cases where the extraction efficiency can be shown to be less than unity, what geologic criteria are important and

The study was undertaken to determine the effects of various substances (manure, clay, charcoal, zeolite, and calcium oxide) applied to a cobalt-contaminated soil (0, 20, 40, 80, 160 and 320 mg kg−1 of soil) on the content of certain trace elements in spring barley (main crop) and white mustard (after-crop). The effect of cobalt on the contents of the trace elements was ambiguous and was either antagonistic or synergistic in nature, depending on the organ and plant species. Generally, the substances applied to soil reduced the content of most trace elements in above-ground parts of both plants and in the roots of white mustard, in contrast to the roots of spring barley. Of all the substances, calcium oxide had the strongest and generally reducing effect on the content of trace elements in the tested organs of the plants; however, its effect was the weakest in the roots of white mustard. Statement of Novelty It is difficult to find in the literature the results of studies into the effect of mineral and other amendments used in our research (manure, clay, charcoal, zeolite, and calcium oxide) on trace elements content in plants if they are used with a view to weakening the effect of cobalt on plants. We think that it is the novelty in the results of environmental sciences. The literature refer to the application of organic matter, bentonite, zeolite and calcium oxide to neutralize other heavy metals. The research was carried out in the two plants system used for phytoremediation with main crop (spring barley—Hordeum vulgare L.) and after-crop (white mustard—Synapis alba L.). The trace elements were analyzed in test plants. The results of the research allowed to select the most effective substance to support the phytoremediation of soil contaminated with cobalt.

The petrographic, mineralogical and geochemical features of the serpentinites recovered at the top of three seamounts located in the Izu-Bonin-Mariana forearc (South Chamorro, Site 1200, ODP Leg 195; Conical, Site 779A, Leg 125; Torishima, Site 784A, Leg 125) evidence a complex, multistage, evolution of the pristine mantle sequences, involving partial melting, reactive porous flow melt migration, subsolidus metamorphic re-equilibration under decreasing T and open system conditions, and, finally, lowgrade hydrothermal alteration processes. In spite of pervasive serpentinisation, there are areas in which the mantle mineral assemblages are preserved and provide information about the high-T petrologic evolution. The analysed peridotites varied from spinel harzburgite to orthopyroxene-bearing spinel dunite in early modal composition with clinopyroxene modal content mostly in the range of 0 to 2% by volume. Petrologic and geochemical modelling indicates that peridotites experienced up to 25% partial melting. Successively, they were percolated by ascending melts of variable composition. The melt-peridotite interaction is revealed by the following petrochemical features: 1) exsolved and deformed orthopyroxene porphyroclasts are partially replaced by secondary fine-grained assemblage consisting of Ol ± Opx ± Cpx: moreover, secondary clinopyroxene ubiquitously grows in correspondence of fractures across the orthopyroxene porphyroclasts; 2) interstitial clinopyroxene is concentrated locally in clusters or pseudo-veins; 3) the bulk rock major element variation does not match the trends expected for refractory residua after basalt removal; 4) the chemical compositions of the minerals is not correlated with the variation of the modal and chemical composition of bulk rock. Valuable information about the geochemical affinity of the migration melts are furnished by the trace element composition of clinopyroxenes (Cpx). The composition of the Cpx from the Torishima peridotites records the migration of extremely depleted melts with relatively enriched LREE and Sr content. As a whole the trace element fractionation of the putative liquids is consistent with that of boninitic melts. A different story is recorded by the Cpx from the South Chamorro and Conical peridotites. In particular, the geochemical composition of the Cpx from the South Chamorro samples is strongly heterogeneous. Thus, for sake of clarity, three different compositional groups can be recognised: Type1, 2 and 3. Type 1 Cpx are in equilibrium with a calculated liquid characterised by REE composition closely approaching that expected for melt increments produced by 15% fractional melting of spinel-facies depleted mantle. By contrast, Type 3 has Cpx characterised by an exceptional depletion in incompatible trace elements. C1-normalised REE patterns have the maximum at LuN (0.73-1.25). The low REE concentration is accompanied by very low Ti, Zr, Hf, Y, V and Sc concentration (e.g. Ti about 30 ppm). Type 2 Cpx has trace element contents in between those of Type 1 and 3. The REE patterns are characterised by a fractionation in the MREE-HREE region steeper than that expected for liquid produced by fractional melting of spinel facies assemblages (SmN/HoN=0.08-0.14; HoN/YbN = 0.21- 0.46) at the given HREE level (YbN = 2.1-2.7). A stronger MREE-HREE fractionation characterise the REE patterns of the Cpx from the Conical peridotites (SmN/HoN=0.05-0.08; HoN/YbN a 0.55), which show again the YbN in the range of 2.3-2.5. Similar REE fractionations have been documented in Cpx from abyssal peridotites (e.g Johnson, 1998; Hellebrand et al., 2002;), ophiolitic harzburgites (e.g. Kelemen et al., 1995; Dijkstra et al., 2003; Barth et al., 2003)and interstitial Cpx from “replacive” harzurgite-dunite bodies (e.g. Suhr et al., 1998, Suhr, 1999; Zanetti et al., 2005). Geochemical modelling indicates that this compositional character of the percolating melts can be explained by the following three petrologic processes: 1) polybaric evolution of their mantle source, involving an early phase under garnet- facies conditions followed by a second stage under spinel-facies ones; 2) transient composition acquired during the migration of extremely-depleted liquids (e.g. those calculated in equilibrium with Type 3 Cpx through a mantle column with a chemical composition approaching that of residual peridotite after 15% fractional melting. The meltperidotite interaction was mainly controlled by chromatographic- type chemical exchange; 3) transient composition acquired during the migration of less depleted liquids (e.g., those in equilibrium with Type 1 Cpx), through an extremely depleted mantle column. The melt-peridotite interaction involved a significant assimilation of the peridotite orthopyroxene. The model (3) is preferred, because it documents the overall petrochemical features shown by the South Chamorro and Conical peridotites. In conclusion, the strongly refractory characters acquired during the early partial melting episodes affection mantle peridotites from Izu-Bonin-Mariana supra-subduction zone has successively been overprinted by the migration of extremely depleted melts. The boninitic affinity recognised for the melts migrating through the mantle section in the Torishima Seamount area suggests that they were related to island- arc magmatism established in a MOR lithosphere. By contrast, the occurrence of depleted to extremely melts in the South Chamorro and Conical seamounts peridotites is more conceivable with the extinction of the magmatism in a MOR lithosphere.

Status of trace element emission in a coal combustion process: a review

The composition of continental subduction-zone fluids varies dramatically from dilute aqueous solutions at subsolidus conditions to hydrous silicate melts at supersolidus conditions, with variable concentrations of fluid-mobile incompatible trace elements. At ultrahigh-pressure (UHP) metamorphic conditions, supercritical fluids may occur with variable compositions. The water component of these fluids primarily derives from structural hydroxyl and molecular water in hydrous and nominally anhydrous minerals at UHP conditions. While the breakdown of hydrous minerals is the predominant water source for fluid activity in the subduction factory, water released from nominally anhydrous minerals provides an additional water source. These different sources of water may accumulate to induce partial melting of UHP metamorphic rocks on and above their wet solidii. Silica is the dominant solute in the deep fluids, followed by aluminum and alkalis. Trace element abundances are low in metamorphic fluids at subsolidus conditions, but become significantly elevated in anatectic melts at supersolidus conditions. The compositions of dissolved and residual minerals are a function of pressure-temperature and whole-rock composition, which exert a strong control on the trace element signature of liberated fluids. The trace element patterns of migmatic leucosomes in UHP rocks and multiphase solid inclusions in UHP minerals exhibit strong enrichment of large ion lithophile elements (LILE) and moderate enrichment of light rare earth elements (LREE) but depletion of high field strength elements (HFSE) and heavy rare earth elements (HREE), demonstrating their crystallization from anatectic melts of crustal protoliths. Interaction of the anatectic melts with the mantle wedge peridotite leads to modal metasomatism with the generation of new mineral phases as well as cryptic metasomatism that is only manifested by the enrichment of fluid-mobile incompatible trace elements in orogenic peridotites. Partial melting of the metasomatic mantle domains gives rise to a variety of mafic igneous rocks in collisional orogens and their adjacent active continental margins. The study of such metasomatic processes and products is of great importance to understanding of the mass transfer at the slab-mantle interface in subduction channels. Therefore, the property and behavior of subduction-zone fluids are a key for understanding of the crust-mantle interaction at convergent plate margins.

SilMush: A procedure for modeling of the geochemical evolution of silicic magmas and granitic rocks

Petrology and geochemistry of volcanic rocks from the island of Panarea: implications for mantle evolution beneath the Aeolian island arc (southern Tyrrhenian sea)

We present the first quantitative model of heat, mass and both major and trace element transport in a mush undergoing compaction that accounts for component transport and chemical reaction during melt migration and which is applicable to crustal systems. The model describes the phase behavior of binary systems (both eutectic and solid solution), with melt and solid compositions determined from phase diagrams using the local temperature and bulk composition. Trace element concentration is also determined. The results demonstrate that component transport and chemical reaction generate compositional variation in both major and trace elements that is not captured by existing geochemical models. In particular, we find that, even for the simplest case of a homogenous, insulated column that is instantaneously melted then allowed to compact, component transport and reaction leads to spatial variations in major element composition that, in this case, produces melt that is more enriched in incompatible elements than predicted by batch melting. In deep crustal hot zones (DCHZ), created by the repeated intrusion of hot, mantle-derived magmas, buoyant melt migrating upwards accumulates in high porosity layers, but has a composition corresponding to only a small fraction of batch melting, because it has locally equilibrated with mush at low temperature; moreover, melt migration and chemical reaction in a layered protolith may lead to the rapid formation of high porosity melt layers at the interface between different rock compositions. In both of these cases, the melt in the high porosity layer(s) is less enriched in incompatible trace elements than predicted if it is assumed that melt with the same major element composition was produced by batch melting. This distinctive decoupling of major and trace element fractionation may be characteristic of magmas that originate in DCHZ. Application of the model to a number of crustal systems, including the Ivrea-Verbano zone, the Rum layered intrusion, and the Holyoke flood basalt, suggests that compositional heterogeneity can be explained by buoyancy-driven melt migration and component transport through a reactive crystalline mush.

The effect of temperature on the equilibrium distribution of trace elements between clinopyroxene, orthopyroxene, olivine and spinel in upper mantle peridotite

The Critical Zone is an important source of trace elements to headwater streams during the snowmelt runoff period, yet the mechanisms of trace element release are poorly characterized. To evaluate changes in water chemistry in response to snowmelt, we measured trace element and major ion concentrations at three sites in the upper Provo River in northern Utah, USA, over a five–year period spanning years with below– and above–average discharge. We also sampled snowpack, ephemeral streams, and soil water to investigate trace element sources. The river drains siliciclastic bedrock above the upper site, carbonate rocks between the upper and middle sites, and volcanic rocks between the middle and lower sites, with minimal anthropogenic impacts in the watershed. Concentrations of specific trace metals (Be, Al, Cu, and Pb) and rare earth elements (represented by La and Y) increased during snowmelt runoff each year at all three sites, with decreasing concentrations from upstream to downstream. In contrast, major ion concentrations, including Ca2+ and SO42-, were similar year–round at the upper site and were diluted during snowmelt at the lower sites, with increasing concentrations from upstream to downstream. The snowmelt runoff period (April–June) accounted for >84% of the annual trace element loading, with most trace element inputs occurring above the upper sampling site. Concentration–discharge (C–Q) relationships revealed variations in solute behavior from upstream to downstream. For example, at the upstream site the trace elements had a slight positive slope in log C–log Q space, while Ca2+ and SO42- had zero slope. At the downstream sites, the trace elements had a strong positive slope and Ca2+ and SO42- had a negative slope. Trace element concentrations were relatively low in snowpack but elevated in ephemeral streams and soil water, suggesting that flushing of shallow soils by snowmelt causes increased trace element concentrations with positive C–Q relationships in the upper part of the river. Trace element loads propagate downstream where concentrations are diluted by groundwater inputs from carbonate bedrock. Our results demonstrate that soil water flushing in the Critical Zone at the headwaters of mountain streams is an important control on downstream water chemistry.

The origin of ocean island basalt end-member compositions: trace element and isotopic constraints

Iceland post-glacial magmatism (<13ka) is primarily restricted to three neovolcanic on-axis rift zones, which are dominated by the production of large volumes of tholeiitic lavas. Unlike the rift zones, off-axis flank zones produce small volumes (<2% post-glacial magmatism) of transitional to alkaline lavas. Flank zone basalts are generally more enriched in incompatible trace elements and have higher La/Yb and Dy/Yb, indicating a smaller degree of melting and greater average depth of melting. The Snaefellsnes Peninsula is one of three flank zones. Snaefellsnes’s distance from the rift zones (40-170 km) and the suggested center of the plume (220-330 km) make it well suited to characterize the enriched component of Iceland. We present new radiogenic (Pb-Sr-Hf) and stable (δ18O) isotope data on a comprehensive suite of post-glacial basalts from Snaefellsnes’s three volcanic systems (Ljósufjöll, Lysuskard, and Snaefellsjökull), integrated with major and trace elemental data, to characterize the enriched component beneath Snaefellsnes. Broad east to west trends have previously been defined across the peninsula: increasing alkalinity, increasing trace element enrichment, decreasing silica content, and decreasing 3He/4He. New data from this study highlights important differences in the trace element composition between lavas from the Snaefellsjökull-Lysuskard and Ljósufjöll systems. Compared with Ljósufjöll lavas, lavas from the Snaefellsnes have higher Ba/Th (131–315 vs. 75–138), Nb/U (56–86 vs. 40–61), a positive Eu anomaly (Eu/Eu* = 1.0–1.2 vs. 0.9–1.1), and lower δ18O (+4.4–5.5‰ vs. +4.9–5.7‰). The chemical characteristics of Snaefellsjökull-Lysuskard lavas, which resemble those of plagioclase-rich gabbros, have been considered the result of crustal interaction with gabbroic cumulates or incorporation of ancient recycled gabbro in the mantle source. Good correlations exist between decreasing δ18O with decreasing 206Pb/204Pb, increasing Ba/Th, Nb/U, and Eu/Eu* suggesting the compositional characteristic of Snaefellsjökull-Lysuskard lavas are feature of the source. Differences between Snaefellsjökull-Lysuskard and Ljósufjöll systems emphasize regional-scale heterogeneity in the enriched component beneath Snaefellsnes.

The high frequency of historical eruptions at Kīlauea Volcano presents an exceptional opportunity to address fundamental questions related to the transport, storage, and interaction of magmas within rift zones. The Nāpau Crater area on Kīlauea’s East Rift Zone (ERZ) experienced nine fissure eruptions within 50 years (1961–2011). Most of the magma intruded during these frequent eruptions remained stored within the rift zone, creating a potential magma mixing depot within the ERZ. The superbly monitored and sampled 2011 eruption (Puʻu ʻŌʻō episode 59) presents an extraordinary opportunity to evaluate magma mixing processes within the ERZ. Whole-rock, glass, and olivine compositions were determined, not only for lava from the 2011 eruption, but also for a new suite of Nāpau Crater area samples from the 1963, 1965, 1968, 1983, and 1997 eruptions, as well as the previously undocumented 1922 eruption. Whole-rock XRF data revealed two geochemically distinct magma batches for episode 59: one less evolved (∼6·6 wt % MgO, 0·46 wt % K2O) than the other (∼6·2 wt % MgO, 0·58 wt % K2O). Episode 59 lava is remarkably aphyric (∼0·1 vol. % phenocrysts), making use of mineralogy to identify parent magma affinities problematic. Linear compositional trends of whole-rock major and trace elements, and reversely zoned olivine crystals indicate episode 59 lavas underwent magma mixing. Least squares regression calculations and plots of major and trace element data, were used to evaluate whether the episode 59 samples are products of mixing summit-derived magma with residual magma from previous Nāpau Crater area eruptions. The regression results and trace element ratios are inconsistent with previously proposed mixing scenarios, but they do support mixing between summit-derived magma and residual magma from the 1983 and 1997 Nāpau Crater area eruptions. These magmas were stored in physically and chemically distinct pods at depths of 1·6–3·0 km prior to mixing with new magma intruded from the summit to produce the episode 59 lava. One pod contained a fractionated equivalent of 1983 lava, and the other a hybrid of compositions similar to 1983 and 1997 lavas. The petrology of episode 59 lava demonstrates that magmas from two previous eruptions (1983 and 1997) were available to mix with magma intruded from the summit region. This study clarifies the pre-eruptive history of the mixed episode 59 lava, and elucidates the evolution of the volcano's magmatic system in a region of frequent eruptions.

Diagenetic history of sedimentary carbonates: Constraints from combined cathodoluminescence and trace element analyses by micro-PIXE