Terrestrial and extraterrestrial rocks exhibit significant mass-dependent Ti isotopic variations, with basalts being isotopically lighter than evolved lithologies. The observed trend from light to heavy Ti isotopic compositions from more primitive to more differentiated rocks agrees with theoretical predictions that light Ti isotopes are sequestered in FeTi oxides. However, there are lingering questions about the exact extent of this fractionation and whether it is influenced by the nature of oxides and silicate melt. To improve on this matter, 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 progressive fractionation 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 Ti 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 the isotopic compositions of the minerals, and contamination by inclusions is minimal. The difference in δ⁴⁹Ti between different minerals is smallest in a basalt (Δ⁴⁹Ti_{olivine-magnetite} = +0.426 ± 0.046‰) and largest in two rhyolites (Δ⁴⁹Ti_{quartz-magnetite} = +1.083 ± 0.046‰). Our data agree with theoretical predictions that FeTi 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.

陆地和地外岩石表现出显着的质量相关的Ti同位素变化，玄武岩的同位素比演化的岩性轻。观察到的趋势是从较轻的Ti同位素到较重的Ti同位素，从较原始的岩石到分化程度更高的岩石，与理论上的预测相吻合，即轻Ti同位素被螯合在Fe Ti氧化物中。但是，对于这种分馏的确切程度以及它是否受氧化物和硅酸盐熔体的性质影响，还有很多疑问。为了对此问题进行改进，我们测量了希腊爱琴海钙碱性柯斯火山-火山岩系统中矿物分离物和大块岩石的Ti同位素组成。散装岩石的Ti同位素组成（δ ⁴⁹Ti）的增加与岩浆系统的渐进分馏，从δ ⁴⁹的0.042±0.033的Ti‰玄武岩在流纹岩0.654±0.034‰。我们记录了两种不同的钛同位素趋势，这些趋势是由（i）分步结晶和（ii）玄武质熔体与演化的（流纹岩）岩浆之间产生的。趋势（i）可以通过熔体累积的Ti同位素分数因子α为0.9998来解释（即，总的熔体平均比熔体轻0.20‰）。矿物中隔离揭示变量δ ⁴⁹的Ti值，与具有最轻的Ti同位素组成磁铁矿，黑云母在中间并且neso-和网状硅酸盐（即，橄榄石，斜长石和石英）最重。在TiO比较₂的低钛矿物的浓度橄榄石，长石和石英与LA-ICP-MS和同位素稀释显示判断为δ ⁴⁹的Ti值在这些矿物测量反映了矿物的同位素组成，和由夹杂物污染是最小的。在δ之差⁴⁹不同的矿物之间的Ti是最小的玄武岩（Δ ⁴⁹的Ti_{橄榄石磁铁矿} = 0.426±0.046‰），并在两个流纹岩最大（Δ ⁴⁹的Ti_{石英磁铁矿} = 1.083±0.046‰）。我们的数据与理论预测一致认为，铁钛氧化物具有光δ ⁴⁹钛标志物和中/硅硅酸盐矿物很重。此外，在δ所测量的差⁴⁹钛磁铁矿橄榄石，磁铁矿的斜长石和磁铁矿的石英之间同意与理论预测矿物间的Ti同位素分馏因子一阶，从而表明所测量的矿物间的Ti的同位素变体处于平衡状态自然。