We report the results of experiments designed to separate the effects of temperature and pressure from liquid composition on the partitioning of Ni between olivine and liquid, $$D_{\text{Ni}}^{\text{ol/liq}}$$DNiol/liq. Experiments were performed from 1300 to 1600 °C and 1 atm to 3.0 GPa, using mid-ocean ridge basalt (MORB) glass surrounded by powdered olivine in graphite–Pt double capsules at high pressure and powdered MORB in crucibles fabricated from single crystals of San Carlos olivine at one atmosphere. In these experiments, pressure and temperature were varied in such a way that we produced a series of liquids, each with an approximately constant composition (~12, ~15, and ~21 wt% MgO). Previously, we used a similar approach to show that $$D_{\text{Ni}}^{\text{ol/liq}}$$DNiol/liq for a liquid with ~18 wt% MgO is a strong function of temperature. Combining the new data presented here with our previous results allows us to separate the effects of temperature from composition. We fit our data based on a Ni–Mg exchange reaction, which yields $$\ln \left( {D_{\text{Ni}}^{\text{molar}} } \right) = \frac{{ -\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } }}{RT} + \frac{{\Delta _{r(1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } }}{R} - \ln \left( {\frac{{X_{\text{MgO}}^{\text{liq}} }}{{X_{{{\text{MgSi}}_{ 0. 5} {\text{O}}_{ 2} }}^{\text{ol}} }}} \right).$$lnDNimolar=-Δr(1)HTref,Pref∘RT+Δr(1)STref,Pref∘R-lnXMgOliqXMgSi0.5O2ol. Each subset of constant composition experiments displays roughly the same temperature dependence of $$D_{\text{Ni}}^{\text{ol/liq}}$$DNiol/liq (i.e.,$$-\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$-Δr(1)HTref,Pref∘/R) as previously reported for liquids with ~18 wt% MgO. Fitting new data presented here (15 experiments) in conjunction with our 13 previously published experiments (those with ~18 wt% MgO in the silicate liquid) to the above expression gives $$-\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$-Δr(1)HTref,Pref∘/R = 3641 ± 396 (K) and $$\Delta _{r(1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$Δr(1)STref,Pref∘/R = − 1.597 ± 0.229. Adding data from the literature yields $$-\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$-Δr(1)HTref,Pref∘/R = 4505 ± 196 (K) and $$\Delta _{r(1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$Δr(1)STref,Pref∘/R = − 2.075 ± 0.120, a set of coefficients that leads to a predictive equation for $$D_{\text{Ni}}^{\text{ol/liq}}$$DNiol/liq applicable to a wide range of melt compositions. We use the results of our work to model the melting of peridotite beneath lithosphere of varying thickness and show that: (1) a positive correlation between NiO in magnesian olivine phenocrysts and lithospheric thickness is expected given a temperature-dependent $$D_{\text{Ni}}^{\text{ol/liq}} ,$$DNiol/liq, and (2) the magnitude of the slope for natural samples is consistent with our experimentally determined temperature dependence. Alternative processes to generate the positive correlation between NiO in magnesian olivines and lithospheric thickness, such as the melting of olivine-free pyroxenite, are possible, but they are not required to explain the observed correlation of NiO concentration in initially crystallizing olivine with lithospheric thickness.

中文翻译：

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液体成分对橄榄石和硅酸盐熔体中镍分配的影响

我们报告了旨在将温度和压力与液体组成对 Ni 在橄榄石和液体之间分配的影响分开的实验结果，$$D_{\text{Ni}}^{\text{ol/liq}}$$ DNiol/液体。实验在 1300 至 1600 °C 和 1 atm 至 3.0 GPa 的条件下进行，使用大洋中脊玄武岩 (MORB) 玻璃，在高压下被石墨-Pt 双胶囊中的橄榄石粉末包围，在由 San 单晶制成的坩埚中使用粉末 MORB卡洛斯橄榄石在一个大气压下。在这些实验中，压力和温度的变化使得我们产生了一系列液体，每种液体的成分大致恒定（~12、~15 和~21 wt% MgO）。之前，我们使用类似的方法来证明 $$D_{\text{Ni}}^{\text{ol/liq}}$$DNiol/liq 对于具有~18 wt% MgO 的液体是温度的强函数。将此处提供的新数据与我们之前的结果相结合，我们可以将温度的影响与成分分开。我们基于 Ni-Mg 交换反应拟合我们的数据，得到 $$\ln \left( {D_{\text{Ni}}^{\text{molar}} } \right) = \frac{{ -\ Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } }}{RT} + \frac{{\Delta _{r (1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } }}{R} - \ln \left( {\frac{{X_{\文本{MgO}}^{\text{liq}} }}{{X_{{{\text{MgSi}}_{ 0. 5} {\text{O}}_{ 2} }}^{\text {ol}} }}} \right).$$lnDNimolar=-Δr(1)HTref,Pref∘RT+Δr(1)STref,Pref∘R-lnXMgOliqXMgSi0.5O2ol。恒定组成实验的每个子集显示出与 $$D_{\text{Ni}}^{\text{ol/liq}}$$DNiol/liq 大致相同的温度依赖性（即，$$-\Delta _{r( 1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$-Δr(1)HTref,Pref∘/R) 如前所述含约 18 wt% MgO 的液体。将此处提供的新数据（15 个实验）与我们之前发表的 13 个实验（在硅酸盐液体中含有约 18 wt% MgO 的实验）拟合到上述表达式给出 $$-\Delta _{r(1)} H_{{ T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$-Δr(1)HTref,Pref∘/R = 3641 ± 396 (K) 和 $$\ Delta _{r(1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$Δr(1)STref,Pref∘/R = − 1.597 ± 0.229。从文献中添加数据产生 $$-\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$- Δr(1)HTref, Pref∘/R = 4505 ± 196 (K) 和 $$\Delta _{r(1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R$$Δr(1)STref,Pref∘/R = − 2.075 ± 0.120，一组系数导致 $$D_{\text{Ni}}^{\text{ol/liq} 的预测方程}$$DNiol/liq 适用于广泛的熔体成分。我们使用我们的工作结果来模拟不同厚度岩石圈下橄榄岩的熔化，并表明：（1）在与温度相关的 $$D_{\text {Ni}}^{\text{ol/liq}} ，$$DNiol/liq 和（2）自然样品的斜率大小与我们实验确定的温度依赖性一致。产生镁橄榄石中 NiO 与岩石圈厚度正相关的替代方法，