Data to: Titanium isotopic compositions of bulk rocks and mineral separates from the Kos magmatic suite: Insights into fractional crystallization and magma mixing processes

We measured the Ti isotopic compositions of mineral separates and bulk rocks from the calc-alkaline Kos volcano-plutonic system, Aegean arc, Greece. Bulk rock Ti isotopic compositions (δ49Ti) increase with differentiation of the magmatic system, from δ49Ti of +0.042 ± 0.033‰ in basalt to +0.654 ± 0.034‰ in rhyolite. We document two different Ti isotope trends produced by (i) fractional crystallization, and (ii) mixing between a basaltic melt and an evolved (rhyolitic) magma. Trend (i) can be explained by a melt-cumulate Ti isotopic fraction factor α of 0.9998 (i.e., the bulk cumulate is on average 0.20‰ lighter than the melt). The mineral separates reveal variable δ49Ti values, with magnetite having the lightest 49Ti/47Ti isotopic composition, biotite being intermediate and neso- and tectosilicates (i.e., olivine, plagioclase and quartz) heaviest. Comparing the TiO2 concentrations of the low-Ti minerals olivine, plagioclase and quartz determined with LA-ICP-MS and isotope dilution shows that the δ49Ti values measured in these minerals reflect their isotopic compositions, and contamination by inclusions is minimal. The difference in δ49Ti between different minerals is smallest in a basalt (Δ49Tiolivine-magnetite = +0.426) and largest in two rhyolites (Δ49Tiquartz-magnetite = +1.083; both ± 0.046‰). Our data agree with theoretical predictions that Fe–Ti oxides have a light δ49Ti signature, and neso/tectosilicate minerals are heavy. Furthermore, the measured difference in δ49Ti between magnetite-olivine, magnetite-plagioclase and magnetite-quartz agree to first order with theoretically predicted inter-mineral Ti isotopic fractionation factors, thus suggesting that the measured inter-mineral Ti isotopic variations are equilibrium in nature.

Further information can be found in the open access publication, which should be cited when using the data:
Greber, N. D., Pettke, T., Vilela, N., Lanari, P., & Dauphas, N. (2021). Titanium isotopic compositions of bulk rocks and mineral separates from the Kos magmatic suite: Insights into fractional crystallization and magma mixing processes. Chemical Geology, 578, 120303.

我们针对希腊爱琴海弧钙碱性科斯火山-深成岩系统（calc-alkaline Kos volcano-plutonic system）的单矿物分选样与全岩样品开展了钛同位素组成(Ti isotopic compositions)测试。全岩钛同位素组成(δ⁴⁹Ti)随岩浆系统演化分异而升高，从玄武岩中的+0.042 ± 0.033‰升至流纹岩中的+0.654 ± 0.034‰。本研究识别出两种截然不同的钛同位素演化趋势：其一为分离结晶(fractional crystallization)作用趋势，其二为玄武质熔体与演化流纹质岩浆的混合作用趋势。趋势一可用熔体-堆晶钛同位素分馏系数α=0.9998解释，即整体堆晶的δ⁴⁹Ti平均较熔体低0.20‰。单矿物分选样的δ⁴⁹Ti值存在显著分异：磁铁矿(magnetite)的⁴⁹Ti/⁴⁷Ti同位素组成最轻，黑云母(biotite)居中，岛状硅酸盐与架状硅酸盐（neso- and tectosilicates，即橄榄石、斜长石和石英）的δ⁴⁹Ti值最重。通过激光剥蚀电感耦合等离子体质谱法(LA-ICP-MS)与同位素稀释法(isotope dilution)测定橄榄石、斜长石、石英等低钛矿物的二氧化钛(TiO₂)浓度后发现，上述矿物测得的δ⁴⁹Ti值可真实反映其本身的同位素组成，且包裹体污染的影响可忽略不计。不同矿物间的δ⁴⁹Ti差值在玄武岩中最小（橄榄石-磁铁矿Δ⁴⁹Ti=+0.426），在两件流纹岩样品中最大（石英-磁铁矿Δ⁴⁹Ti=+1.083；两者误差均为±0.046‰）。本研究数据与理论预测相符：铁-钛氧化物具有较轻的δ⁴⁹Ti同位素组成，而岛状/架状硅酸盐矿物的δ⁴⁹Ti值偏重。此外，测得的磁铁矿与橄榄石、斜长石、石英间的δ⁴⁹Ti差值，在一级近似上与理论预测的矿物间钛同位素分馏系数一致，这表明观测到的矿物间钛同位素差异本质上属于平衡分馏。

如需使用本数据集，请引用以下开源发表文献：
Greber, N. D., Pettke, T., Vilela, N., Lanari, P., & Dauphas, N. (2021). 科斯岩浆岩组合全岩与单矿物的钛同位素组成：分离结晶与岩浆混合过程的新认识. 化学地质学(Chemical Geology), 578, 120303.