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首页> 外文期刊>Contributions to Mineralogy and Petrology >Experimental calibration of vanadium partitioning and stable isotope fractionation between hydrous granitic melt and magnetite at 800 degrees C and 0.5 GPa
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Experimental calibration of vanadium partitioning and stable isotope fractionation between hydrous granitic melt and magnetite at 800 degrees C and 0.5 GPa

机译：800℃和0.5GPa的含水花岗岩熔体和磁铁矿之间钒分区和稳定同位素分馏的实验校准

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Vanadium has multiple oxidation states in silicate melts and minerals, a property that also promotes fractionation of its isotopes. As a result, vanadium isotopes vary during magmatic differentiation, and can be powerful indicators of redox processes at high temperatures if their partitioning behaviour can be determined. To quantify the partitioning and isotope fractionation factor of V between magnetite and melt, piston cylinder experiments were performed in which magnetite and a hydrous, haplogranitic melt were equilibrated at 800 degrees C and 0.5 GPa over a range of oxygen fugacities (fO(2)), bracketing those of terrestrial magmas. Magnetite is isotopically light with respect to the coexisting melt, a tendency ascribed to the VI-fold V3+ and V4+ in magnetite, and a mixture of IV- and VI-fold V5+ and V4+ in the melt. The magnitude of the fractionation factor systematically increases with increasing logfO(2) relative to the Fayalite-Magnetite-Quartz buffer (FMQ), from Delta V-51(mag-gl) = -0.63 +/- 0.09 parts per thousand at FMQ - 1 to - 0.92 +/- 0.11 parts per thousand (SD) at approximate to FMQ + 5, reflecting constant V3+/V4+ in magnetite but increasing V5+/V4+ in the melt with increasing log fO(2). These first mineral-melt measurements of V isotope fractionation factors underline the importance of both oxidation state and co-ordination environment in controlling isotopic fractionation. The fractionation factors determined experimentally are in excellent agreement with those needed to explain natural isotope variations in magmatic suites. Furthermore, these experiments provide a useful framework in which to interpret vanadium isotope variations in natural rocks and magnetites, and may be used as a potential fingerprint the redox state of the magma from which they crystallise.
机译：钒在硅酸盐和矿物质中具有多种氧化态，其特征也促进其同位素的分馏。结果，如果可以确定它们的分区行为，钒同位素在岩型分化期间变化在岩化过程中，并且可以是在高温下的氧化还原过程的强大指标。为了量化磁铁矿和熔体之间V的v分配和同位素分馏因子，进行活塞缸实验，其中磁铁矿和含水的储料料熔体在一系列氧气度假率（FO（2））上以800℃和0.5GPa平衡（FO（2）） ，包围陆地岩浆。磁铁矿相对于共存熔体具有同位性的光，易于熔融物中的VI折叠V3 +和V4 +的趋势，以及熔体中的IV-和VI折叠V5 +和V4 +的混合物。分馏因子的幅度随着达到氟矾 - 磁铁矿 - 石英缓冲液（FMQ）的增加，来自Delta V-51（Mag-G1）= -0.63 +/- 0.09‰，在FMQ下在近似为FMQ + 5时，1至-0.92 +/- 0.11份（SD），反映磁铁矿中的恒定V3 + / V4 +，但随着LOG FO（2）的增加，熔体中的V5 + / V4 +增加。这些v同位素分级因子的首次矿物熔体测量强调氧化态和协调环境控制同位素分馏的重要性。确定的分馏因子与解释岩浆套房中的自然同位素变化所需的分馏因素非常一致。此外，这些实验提供了一种有用的框架，其中用于解释天然岩石和磁纤维中的钒同位素变化，并且可以用作岩浆的磁铁的氧化还原状态的潜在指纹。

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