An Erratum to this paper has been published: https://doi.org/10.1134/S0016702923210024

A quantitative local analytical method with the application of inductively coupled plasma mass spectrometry with laser ablation (LA-ICP-MS) was tested at Vernadsky Institute for the determination of contents of trace elements (Cu, Zn, Co, Ni, Mn, Cr, Sc, V, Ca, Ti, Al, Y, and REE) in olivine. Olivine phenocrysts from volcanic rocks of various geological settings have been studied: island-arc basalts, mid-ocean ridge (MOR) basalts, and high-alkaline continental volcanic rocks. The contents of some elements (Ni, Co, Mn, Cr, Sc, and Zn) systematically vary during the evolution of the composition of olivine, and the concentration fields of these elements in olivine from different settings overlap one another. At the same time, the contents of some other elements (Ca, Al, Ti, V, and Cu) fundamentally differ in olivine from different geological settings. Copper content in olivine from oceanic tholeiites and highly alkaline continental volcanics is 1–3 ppm, which is systematically lower than copper content in olivine from island-arc basalts (3–9 ppm). The concentrations of vanadium in olivine in MOR basalts are higher than in island-arc and alkaline continental ones, which may be due to relatively more reduced crystallization conditions as more favorable for the incorporation of V3+ into the olivine structure. Variations in the distribution coefficients of trace elements between olivine and silicate melt ( D_element^Ol/ . -0em M ) were determined for volcanic rocks from Kamchatka, the Bouvet Triple Junction, and Gaussberg volcano. It has been demonstrated that the unusually high values D_Ni^Ol/ . -0em M of D_Ni^Ol/ . -0em M = 50–150 previously identified for the lamproites of Gaussberg volcano indicate a mismatch between the composition of the quenched glass and the composition of the equilibrium melt for olivine phenocrysts. When using the bulk compositions of Gaussberg rocks, values of D_Ni^Ol/ . -0em M = 11–21 were obtained, which correspond to experimental estimates for high-potassium rocks. The redox crystallization conditions of the studied rocks were estimated using several oxybarometers based on the distribution of vanadium between coexisting olivine and melt. These values were: ΔQFM= +0.6 to +1.5 for oceanic tholeiites of the Bouvet Triple Junction area, South Atlantic, and ΔQFM = +1.5 to +2.4 for Mutnovsky volcano, Kamchatka. Estimates of the redox crystallization conditions of the highly alkaline rocks of Gaussberg volcano significantly vary depending on which model is chosen: ΔQFM= +0.2 to +4.8, which may be due to the strong effect of K2O content in the melt involved in one of the models. The newly acquired analytical data confirmed the possibility of using contents of trace elements in olivine to characterize igneous systems from different geological settings and highlighted the need for additional experimental studies on the distribution of these elements between olivine and melt, especially in highly alkaline systems.

The paper presents the very first data on concentrations of major and trace elements; Sr, Nd, and Pb isotopic ratios of rocks; and the composition of olivine phenocrysts of 38-Ma basalts recovered by Hole 513a (DSDP Leg 71) in the South Atlantic. The bulk-rock samples and the chilled glasses are mildly magnesian (7–8 wt % MgO) and bear elevated FeO and low Na2O concentrations, as is typical of MORB of the TOR-1 type. Olivine phenocrysts (Fo84.5–88) in these rocks contain concentrations of trace elements (Ni, Mn, Cr, and Zn) that are typical of classic MORB, which are produced by partial melting of mantle peridotite. The rocks are strongly depleted in incompatible elements [(La/Sm)n ~ 0.6] but have elevated Ba/Nb, K/Nb, and Pb/Ce ratios and Cu, Ag, and Au concentrations that are 1.5–4 times higher than in typical depleted MORB (N-MORB) and in most rift basalts in the South Atlantic. Isotope compositions of the basalts (average ratios 206Pb/204Pb ~ 18.0; 207Pb/204Pb ~ 15.6, 208Pb/204Pb ~ 38.0, 143Nd/144Nd ~ 0.5130, and 87Sr/86Sr ~ 0.7040) are close to those in modern tholeiites from the southern MAR segment (SMAR) north of the Agulhas Fracture Zone. The data indicate that the magmas were derived from a strongly depleted mantle source that contained a minor (~3%) admixture of an enriched component, which is discernible in the magmas of the Discovery hotspot. The composition of the source, which is more depleted than DM, and the high degrees of melting of this source explain why the basalts from DSDP Hole 513a are enriched in chalcophile elements. It is believed that spreading magmatism at 45°–48° S in SMAR as far back as 40 Ma was already affected by the Discovery hotspot. This hotspot might be related to the Tristan plume system, and its origin and long-lasting influence on spreading magmatism in the South Atlantic are regarded as evidence of the extensive effect of the Tristan plume.

Впервые изучены содержания главных и рассеянных элементов, изотопные отношения Sr, Nd, Pb в породах и состав вкрапленников оливина в базальтах с возрастом 38 млн лет, вскрытых скважиной 513а (71-й рейс DSDP) в западной части Южной Атлантики. Валовые составы пород и закалочные стекла имеют умеренно магнезиальный состав (MgO=7–8 мас.%), повышенные содержания FeO и низкие Na 2 O, характерные для БСОХ типа ТОР-1. Породы содержат вкрапленники оливина с составом Fo84.5-88 с содержаниями примесных элементов (Ni, Mn, Cr, Zn), характерными для типичных БСОХ – продуктов частичного плавления мантийного перидотита. В отношении несовместимых элементов породы имеют сильно деплетированный состав (La/Sm n ~0.6), но в то же время характеризуются повышенными отношениями Ba/Nb, K/Nb, Pb/Ce и в 1.5–4 раза повышенными содержаниями Cu, Ag и Au по сравнению с типичными деплетированными БСОХ (N-MORB) и большинством рифтогенных базальтов Южной Атлантики. Отношения радиогенных изотопов в изученных базальтах (в среднем 206 Pb/ 204 Pb ~18.0; 207 Pb/ 204 Pb ~15.6, 208 Pb/ 204 Pb ~38.0, 143 Nd/ 144 Nd ~0.5130 и 87 Sr/ 86 Sr ~0.7040) близки к составам современных толеитов из сегмента южной части САХ (ЮСАХ), севернее разломной зоны Агульяс. Полученные данные указывают на образование магм из сильно деплетированного перидотитового источника с небольшой примесью (около 3%) обогащенного компонента, проявленного в магмах горячей точки Дискавери. Более деплетированным, чем DM, составом источника и высокими степенями его плавления также объясняется обогащенность базальтов скв. 513а халькофильными элементами. Предполагается, что в процессе раскрытия Южной Атлантики на спрединговый магматизм ЮСАХ в районе 45–48° ю.ш. уже около 40 млн лет оказывала влияние горячая точка Дискавери. Эта горячая точка может быть дочерней для плюмовой системы Тристан, а ее возникновение и длительное влияние на спрединговый магматизм Южной Атлантики рассматривается как свидетельство обширного распространения влияния плюма Тристан.

The strong dependence of vanadium partitioning between olivine and silicate melt (D-V(Ol-M)) on redox conditions (f(O2)) can be used as sensitive oxybarometer in magmatic systems. Here we extend the experimental database on D-V(Ol-M), obtained so far at high temperatures (mainly above 1250 degrees C), to lower temperatures that are typical for island-arc basalts. Crystallization experiments were performed using a composition from Mutnovsky volcano (Kamchatka), and the investigated temperature, pressure, and oxygen fugacity ranges were 1025-1150 degrees C, 0.1 and 0.3 GPa, and Delta QFM of -0.5 to +3.2, respectively. The water content in melts ranged from 0.6 to similar to 6.5 wt% H2O. The data demonstrate a strong negative correlation between D-V(Ol-M) and oxygen fugacity, similar to the behavior observed previously at higher temperatures and in MgO-rich compositions. The correlation between D-V(Ol-M) and Delta QFM in the range from -0.5 to +3.2 is described for melts with MgO < 12 wt% and Na2O < 4 wt% at temperatures <= 1250 degrees C by the empirical equation: Delta QFM = -3.07(-0.29)(+0.26) logD(V)(Ol-M) - 3.34(-0.49)(+0.40) with the standard error (SE) as a function of logD(V)(Ol-M): 2SE(Delta QFM) = -0.275logD(V)(Ol-M) + 0.4. We suggest that this equation can be used as an oxybarometer, which is particularly well applicable to the hydrous island-arc magmas at relatively low temperature. Application of the equation to the composition of melt inclusions and their host olivine phenocrysts from basalts of Mutnovsky volcano, containing vanadium concentrations in the range of 250-370 and 4-6 ppm, respectively, reveals an oxygen fugacity in the range Delta QFM + 1.9 to + 2.3. The estimates are in a good agreement with olivine-spinel oxybarometry for Mutnovsky basalts and may be typical for moderately evolved island-arc magmas.

Ag and Cu are strongly chalcophile elements, and their behavior in magmatic systems is highly dependent on the presence of solid or liquid sulfide phase in magmas and their sources...

A promising method for the quantification of the redox conditions (oxygen fugacity, fO2) in basaltic systems, which might be applied to quenched melt inclusions in olivine, exploits the partitioning of vanadium between olivine and coexisting silicate melt (DV Ol‐M). Strong correlation of DV Ol‐M with fO2 was investigated in a number of experimental works on dry mafic and ultramafic melts in a wide range of fO2 conditions at pressures of 1 atm and 0.5–2 GPa, temperature range of 1150–1530°C (e.g., CanilF MallmannO 2013). Only a few melt compositions equilibrated with olivine at T≤1250°C were studied so far. Although it was shown that melt composition, pressure and temperature have small effect on DV Ol‐M, more data are required to extend the calibration of the V oxybarometry to hydrous low‐temperature basalts representing island arc magmas.

The effect of the anhydrous composition on the solubilities of H2O and CO2 in mafic melts varying from MORB to nephelinite was investigated experimentally between 50 and 500MPa at 1200 to 1250°C. In all compositions, CO2 is only present as carbonate species in the quenched glasses. The concentrations of dissolved H2O and CO2 have been analyzed by KFT (Karl–Fischer titration) and FTIR (Fourier-transform infrared spectroscopy). The Mid-Infrared (MIR) absorption coefficients for the H2O band at 3500cm−1 are identical within error for all investigated melt compositions and equal to 59.2±4L/(mol∗cm). The absorption coefficients for the carbonate bands vary in the range 306±32 to 360±24L/(mol∗cm) for the 1430cm−1 band and in the range 349±25 to 394±27L/(mol∗cm) for the 1520cm−1 band. However, a simple correlation with the melt composition could not be determined.Water solubility in mafic to intermediate melts increases slightly with the total alkali content and the effect of composition is more pronounced at higher pressures. At 500MPa, the solubility of H2O in melts coexisting with nearly pure H2O fluids varies from 8.8 to 9.5wt.% H2O. A strong effect of melt composition on the solubility of CO2 is observed at all investigated pressures. For instance, at 500MPa, mafic melts coexisting with nearly pure CO2 fluids can dissolve from around 0.32 to more than 1.30wt.% CO2 as melt composition changes from tholeiite to nephelinite. The compositional effect on the solubility of CO2 in melts coexisting with pure CO2 fluid is best described by non-linear (exponential) correlations with compositional parameters such as the parameter Π proposed by Dixon (1997; American Mineralogist, 82: 368–378) or structural parameters (e.g., nonbridging oxygen per tetrahedrally coordinated cation). The obtained relationships are used to propose empirically derived equations of the form ln(CO2)=1.150·lnP+6.71·Π*−1.345, where CO2 is the solubility of CO2 in silicate melts in wt.% (at 1200 to 1250°C), P is pressure in MPa and Π* is a compositional parameter (Π*=Ca2++0.8K++0.7Na++0.4Mg2++0.4Fe2+)/(Si4++Al3+) with cations expressed as cation fractions in melt.

The solubility of H2O- and CO2-bearing fluids in tholeiitic basalts has been investigated experimentally at temperature of 1250 °C and pressures of 50, 100, 200, 300, 400 and 500 MPa. The concentrations of dissolved H2O and CO2 have been determined using FTIR spectroscopy with an accurate calibration of the absorption coefficients for hydrogen- and carbon-bearing species using synthesized standards of the same tholeiitic composition. The absorption coefficients are 0.65 ± 0.08 and 0.69 ± 0.08 L/(mol cm) for molecular H2O and OH groups by Near-Infrared (NIR), respectively, and 68 ± 10 L/(mol cm) for bulk H2O by Mid-Infrared (MIR). The carbonate groups determined by MIR have an absorption coefficient of 317 ± 23 L/(mol cm) for the band at 1430 cm−1.The solubility of H2O in the melt in equilibrium with pure H2O fluid increases from about 2.3 ± 0.12 wt.% at 50 MPa to about 8.8 ± 0.16 wt.% at 500 MPa, whereas the concentration of CO2 increases from about 175 ± 15 to 3318 ± 276 ppm in the melts which were equilibrated with the most CO2-rich fluids (with mole fraction of CO2 in the fluid, XflCO2, from 0.70 to 0.95). In melts coexisting with H2O- and CO2-bearing fluids, the concentrations of dissolved H2O and CO2 in basaltic melt show a non-linear dependence on both total pressure and mole fraction of volatiles in the equilibrium fluid, which is in agreement with previous studies. A comparison of new experimental data with existing numerical solubility models for mixed H2O–CO2 fluids shows that the models do not adequately predict the solubility of volatiles in basaltic liquids at pressures above 200 MPa, in particular for CO2, implying that the models need to be recalibrated. The experimental dataset presented in this study enables a quantitative interpretation of volatile concentrations in glass inclusions to evaluate the magma storage conditions and degassing paths of natural island arc basaltic systems. The experimental database covers the entire range of volatile compositions reported in the literature for natural melt inclusions in olivine from low- to mid-K basalts indicating that most melt inclusions were trapped or equilibrated at intermediate to shallow levels in magmatic systems (< 12–15 km).

In this paper we address allivalites, coarse-and giant-textured olivine-anorthite rocks occurring as separate blocks in the eruption products of many volcanoes from the frontal part of the Kuril-Kamchatka arc. New data are reported on the petrography, mineralogy, and composition of melt inclusions in minerals from ten allivalite samples from Ksudach, Il’inskii, Zavaritskii, Kudryavyi, and Golovnin volcanoes. The crystallization temperatures of allivalite minerals were estimated as 970–1080°C at a melt water content of 3.0–3.5 wt % and oxygen fugacity NNO = 1–2. A genetic link was established between the compositions of melt inclusions and interstitial glasses in allivalites and volcano rocks. The cumulate nature of allivalites was demonstrated. Using mass balance calculations, the degree of fractionation of primary melts during the formation of cumulate layers was estimated for various volcanoes as 22–46%.