Data for: High-temperature chromium isotope fractionation and its implications: constraints from Kızıldağ ophiolite, SE Turkey

Chromium isotope data were obtained from olivine, orthopyroxene and chromite separates of the Kızıldağ ophiolite, SE Turkey, to investigate the effects of high temperature magma processes on Cr isotope fractionation. Harzburgite in the Kızıldağ ophiolite has the δ53Cr values of -0.14 to -0.12‰ in chromite, and -0.08 to -0.01‰ in bulk rocks. These Cr isotope fractionations could be driven by partial melting and metasomatism. The dunite and chromitite samples from the mantle-crust transition zone of the Kızıldağ ophiolite are cumulates, and their chromite and olivine have δ53Cr values of -0.29 to -0.06‰ and -0.11 to 0.41‰, respectively. The δ53Cr values of chromite are negatively correlated with the chemical indices of fractional crystallization (e.g., Fe# of chromite), suggesting that Cr isotopes were fractionated during fractional crystallization. In the chromitite, the degree of Cr isotope fractionation increases with fractional crystallization, with 0.23‰ Cr isotope fractionation occurring at mineral scale. During fractional crystallization, solid phases preferentially incorporate Cr, particularly heavy Cr isotopes, driving the depletion of Cr and enrichment of light Cr isotopes in the evolved melts. The δ53Cr values of olivine are higher than the coexisting chromite, which could be explained by the fact that the olivine grains were probably formed earlier than the chromite. The Cr isotopic features of chromite in the podiform chromitite (-0.22 to -0.04‰) from the mantle sequence are consistent with the modeling fractional crystallization trend, confirming the magmatic origin of the podiform chromitite. Therefore, a significant Cr isotope fractionation at chromite from the Kızıldağ ophiolite could be induced by the high-temperature fractional crystallization.本研究采集土耳其东南部基尔达格（Kızıldağ）蛇绿岩（ophiolite）的橄榄石（olivine）、斜方辉石（orthopyroxene）与铬铁矿（chromite）分离组分，获取其铬同位素数据（Chromium isotope data），旨在探究高温岩浆作用（high temperature magma processes）对铬同位素分馏（Cr isotope fractionation）的影响。基尔达格蛇绿岩中的方辉橄榄岩（Harzburgite），其铬铁矿的δ⁵³Cr值范围为-0.14‰至-0.12‰，全岩（bulk rocks）的δ⁵³Cr值范围为-0.08‰至-0.01‰。上述铬同位素分馏现象可由部分熔融（partial melting）与交代作用（metasomatism）驱动。采自基尔达格蛇绿岩壳幔过渡带（mantle-crust transition zone）的纯橄岩（dunite）与铬铁矿体（chromitite）样品均为堆晶岩（cumulates），其铬铁矿与橄榄石的δ⁵³Cr值分别为-0.29‰至-0.06‰与-0.11‰至0.41‰。铬铁矿的δ⁵³Cr值与分离结晶（fractional crystallization）的化学指标（如铬铁矿的Fe#）呈负相关关系，表明铬同位素在分离结晶过程中发生了分馏。在铬铁矿体中，铬同位素分馏程度随分离结晶作用增强而升高，在矿物尺度下可产生0.23‰的铬同位素分馏。在分离结晶过程中，固相优先富集铬，尤其是重铬同位素，进而导致演化熔体中铬发生亏损、轻铬同位素相对富集。橄榄石的δ⁵³Cr值高于共存的铬铁矿，这一现象可通过橄榄石晶粒形成时间早于铬铁矿这一机制得到解释。采自地幔序列（mantle sequence）的豆荚状铬铁矿体（podiform chromitite）中的铬铁矿，其δ⁵³Cr值范围为-0.22‰至-0.04‰，与分离结晶模拟趋势一致，证实了该豆荚状铬铁矿体的岩浆成因（magmatic origin）。综上，基尔达格蛇绿岩中铬铁矿的显著铬同位素分馏可由高温分离结晶作用诱发。