Search

We have performed experiments at 1.5 GPa and 1400 °C on 25 different bulk compositions to determine the effects of major element compositions on the Cl contents of silicate melts at known fugacities of Cl2 and O2. The experimental method involved mixing a "sliding" Cl buffer, a mixture of AgCl, AgI, and Ag with the silicate bulk composition and performing the experiment in a graphite capsule together with a source of CO2 (AgCO3). The graphite capsules were sealed inside welded Pt tubes to maintain a CO2-CO atmosphere with oxygen fugacity fixed at the C-CO-CO2 (CCO) buffer. During the experiment, the Cl buffer segregates leaving a Cl-bearing melt, which quenches to a glass. We used the results to define chloride capacity CCl for each melt at the pressure and temperature of the experiment: C C l = C l (w t f C l 2 × f O 2 4 Chloride capacity was found to correlate positively with optical basicity and NBO/T and negatively with ionic porosity and the Larsen index. We combined our new data with the results of Thomas and Wood (2021) to derive an equation describing the composition, pressure and temperature dependence of the chloride capacity: log C C l = 1.601 + 4470 X C a − 3430 X S i + 2592 X F e − 4092 X K − 894 P / T. In this equation, XCa, XSi, and so on refer to the oxide mole fractions on a single-cation basis, P is in GPa and T in K. The equation reproduces 58 data points with an r2 of 0.96 and a standard error of 0.089. The addition of literature data on hydrous experiments indicates that the effects of <4.3 wt% H2O are small enough to be ignored. We also performed experiments aimed at determining the conditions of NaCl saturation in melts. When combined with literature data we obtained: log C l − = log a N a C l + 0.06 − 2431 X C a + 3430 X S i − 2592 X F e + 3484 X N a + 4092 X K − 2417 / T where (Cl–) is the Cl content of the melt in wt% aNaCl is the activity of NaCl (liquid) and the other symbols are the same as before. The results indicate that basalt dissolves ~8 times more Cl than rhyolite at a given NaCl activity i.e., Cl is ~8 times more soluble in basalt than in rhyolite. [ABSTRACT FROM AUTHOR]

In Figure 6, we compare Mg#s (where Mg# = Mg/[Fe SP 2+ sp +Mg], atomic) of bulk olivine-phyric shergottites to the most Mg-rich olivine phenocrysts. Keywords: Olivine-phyric shergottites; Fe2+-Mg partitioning; olivine; basalt; Mars EN Olivine-phyric shergottites Fe2+-Mg partitioning olivine basalt Mars 1442 1452 11 07/05/22 20220701 NES 220701 Introduction The partitioning of elements between solid and liquid phases is an important tool for understanding and modeling igneous processes. Measuring Fe SP 3+ sp /Fe SP 2+ sp in silicate liquids is difficult; as a result, Fe SP 3+ sp /Fe SP 2+ sp of a melt it is often assumed to be negligible (e.g., [27]) or calculated using prior experimental calibrations (e.g., [79]; [52]). To ensure olivine saturation at the liquidus, we added ~17% synthetic olivine (enough to ensure olivine saturation but still dominated by liquid to facilitate rapid equilibration) with an Mg# of 77 (the estimated Mg# of olivine in the primitive martian mantle; [27]). [Extracted from the article]

Magmas erupted at convergent margins consist of components from both mantle wedge and subducted slab. In an effort to quantify the relative contributions of these sources, we have determined 19 trace element partition coefficients (D values) for orthopyroxene and clinopyroxene, in equilibrium with spinel and hydrous high-MgO melt under conditions appropriate to melting in the mantle wedge, i.e., 1.3 GPa, 1245 [degrees]C, and [f.sub.O2] of NNO + 1. All trace elements are more incompatible in clinopyroxene during hydrous melting than during anhydrous melting of fertile and depleted peridotite. Orthopyroxene D values are relatively insensitive to pressure, temperature, and phase composition. The new D values are used to calculate the trace-element composition of the mantle wedge, which produced primitive South Sandwich Islands and St. Vincent (Lesser Antilles) arc basalts. Both sources correspond to previously depleted mantle that has been enriched in LILEs and LREEs by slab-derived fluids. In the case of the South Sandwich Islands, the calculated source is in very close agreement with dredged fore-arc lherzolites. Our partitioning data confirm that hydrous melting of wedge peridotite itself cannot produce the characteristic enrichments of LILEs over REEs and HFSEs. Our estimates of the slab component in South Sandwich Islands and St. Vincent are consistent with estimates from other arcs, derived by alternative methods.

Multianvil experiments were conducted at 1400 to 1600 [degrees] C on olivine and peridotite starting compositions to determine the partitioning of Ti, Al, Cr, Ni, Ca, and Na between coexisting olivine and wadsleyite. All of these elements occur as minor amounts in mantle olivine. Our experiments indicate that all, except Ca, partition preferentially into wadsleyite relative to olivine. The order of preference for wadsleyite is Ni[less than]Na[less than]Cr[less than]Ti[less than]Al, with [Mathematical Expression Omitted] of about 2 for Ni, 3 for Na, and between 5 and 8 for Cr, Ti, and Al. We observe a strong negative correlation between the Si and Cr (+Al) contents of wadsleyite, indicating a coupled substitution of 2[Cr.sup.3+] for [Mg.sup.2+] + [Si.sup.4+]. Modeling the influence of the trace elements on the olivine-wadsleyite transformation in the mantle indicates broadening effects on the order of 1-3 km, much smaller than that predicted to arise from mantle concentrations of [H.sub.2]O. Therefore, effects of these trace elements on the properties of the 410 km seismic discontinuity are considered negligible. The maximum solubility of Ti[O.sub.2] in wadsleyite (about 0.6%) is consistent with the suggestion that olivines containing about 1 vol% FeTi[O.sub.3] could be inverted wadsleyite.

Researchers created molecular dynamics (MD) simulations of CO2-H2O mixtures at XCO2 of 0.25, 0.5 and 0.75, using the TIP4P and MSM3 intermolecular potentials. Excess volumes quickly fall with pressure at 400 and 1200 degrees centigrade, but simulations predict that major excess volumes of around 0.5cm to the third power/mol continue at pressures of more than 20 kbar. Simulations predict only a negligible fall in excess volumes as the temperature rises from 400 to 1200 degrees centigrade.

We performed experiments at 3.0 GPa and 1530-1565 [degrees] C to investigate the effects of crystal composition on trace element partitioning between garnet and anhydrous silicate melt. Bulk compositions along the pyrope (Py: [Mg.sub.3][Al.sub.2][Si.sub.3][O.sub.12])-grossular (Gr: [Ca.sub.3][Al.sub.2][Si.sub.3][O.sub.12])join, doped with a suite of trace elements (Li, B, K, Sc, Ti, Sr, Y, Zr, Nb, Cd, In, REE, Hf, Ta, Th, and U) produced homogeneous garnets, ranging in composition from [Py.sub.84][Gr.sub.16] to [Py.sub.9][Gr.sub.91], in equilibrium with melt. Trace element partition coefficients (D-values), measured by SIMS, depend greatly on the Mg/(Mg + Ca) of garnet. For example, from [Py.sub.84] to [Py.sub.9], [D.sub.La] increases from 0.004 to 0.2, whereas [D.sub.U] increases from 0.029 to 0.42. These variations can be explained by the lattice strain model of Blundy and Wood (1994), which describes trace element partitioning of an element i in terms of the ionic radius of i ([r.sub.i]), the size of the lattice site on which i partitions ([r.sub.0]), the Young's modulus of the site (E), and the (theoretical) partition coefficient Do for an ion of radius [r.sub.0]. For trivalent cations substituting in the garnet X-site (Y, REE, Sc, and In), apparent values of [r.sub.0] fitted to our data vary systematically from 0.935 [+ or -] 0.004 [Angstrom] ([Py.sub.84]) to 0.99 [+ or -] 0.01 [Angstrom] ([Py.sub.9]), a trend consistent with variations in the size of the X-site. Values of [D.sub.0] show an increase from [Py.sub.9] ([D.sub.0] = 2.8 [+ or -]0.1) to [Py.sub.84] (4.8 [+ or -] 0.1) and Young's modulus E varies from 257 [+ or -] 20 GPa for [Py.sub.60] to 590 [+ or -]40 GPa for [Py.sub.84]. These results allow a quantitative assessment of the influence of crystal chemistry on garnet-melt D-values, thereby forming the basis for a predictive model similar to that recently developed for clinopyroxene-melt partitioning by Wood and Blundy (1997). Our new data emphasize the importance of taking into account crystal composition when modeling trace element behavior in natural systems.