Iron-titanium oxides such as ilmenite (FeTiO₃), titanite (CaTiSiO₅) and perovskite (CaTiO₃) are the common Ti-rich mineral phases crystallised during magmatic and metamorphic processes on Earth. Depending on magma types or conditions of phase equilibria, formation of these Ti-rich minerals can result in Ti isotopic fractionation in the range of -1.52‰ to +2.90‰ on δ⁴⁹Ti_OL-Ti (i.e., the per mil difference of ⁴⁹Ti/⁴⁷Ti ratio relative to the OL-Ti reference material), making the Ti isotope ratios of these minerals potential tracers for conditions of magmatism and metamorphism. Due to their resistance to aqueous alteration, these Ti-rich accessory minerals are also commonly present as pristine, detrital phases in sedimentary rocks, which offer an opportunity to study the evolution of magmatism and metamorphism throughout the Earth's geological history. Here we have developed a novel technique for in situ Ti isotopic measurement in ilmenite, titanite and perovskite using femtosecond laser ablation multi-collector inductively coupled plasma-mass spectrometry (fs-LA-MC-ICP-MS) under wet plasma conditions. Samples were ablated with different laser spot sizes (15–50 μm) and different laser energy densities (0.6–4.2 J cm^-2) to obtain adequate Ti signal intensity at a fixed laser repetition rate of 2 Hz. When ⁴⁹Ti signal intensity of samples ranged from 0.3 to 3.7 V, no significant signal-dependent Ti isotopic fractionation was observed under wet plasma conditions. Repeated measurements on twelve Ti-rich minerals using different analytical protocols provided comparable δ⁴⁹Ti_OL-Ti values within uncertainties, confirming the accuracy of the proposed fs-LA-MC-ICP-MS method. With one exception (i.e., RUS1), all analysed minerals are homogeneous in their Ti isotopic compositions between individual chips with an intermediate precision of ±0.13‰ to ±0.17‰ (2s) on δ⁴⁹Ti_OL-Ti. Collectively, these minerals record a significant δ⁴⁹Ti_OL-Ti variation ranging from -0.46‰ to +2.12‰. These warrant the suitability of these materials as Ti isotopic reference materials for in situ Ti isotopic measurement.

中文翻译：

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用于 LA-MC-ICP-MS 原位钛同位素测量的天然富钛矿物（钛铁矿、钛矿和钙钛矿）参考材料

钛铁矿（FeTiO ₃）、钛矿（CaTiSiO ₅）和钙钛矿（CaTiO ₃）等铁钛氧化物是地球上岩浆和变质过程中结晶的常见富钛矿物相。根据岩浆类型或相平衡条件，这些富钛矿物的形成可导致 δ ⁴⁹ Ti _OL-Ti上的 Ti 同位素分馏范围为 -1.52 ‰ 至 +2.90 ‰ （即，每密耳差异为⁴⁹ Ti/ ⁴⁷ Ti 比率（相对于 OL-Ti 参考材料），使得这些矿物的 Ti 同位素比率成为岩浆作用和变质作用条件的潜在示踪剂。由于它们对水蚀变的抵抗力，这些富含钛的副矿物通常也以原始碎屑相的形式存在于沉积岩中，这为研究整个地球地质历史中岩浆作用和变质作用的演化提供了机会。在这里，我们开发了一种在湿等离子体条件下使用飞秒激光烧蚀多接收器电感耦合等离子体质谱（fs-LA-MC-ICP-MS）原位测量钛铁矿、钛矿和钙钛矿中钛同位素的新技术。使用不同的激光光斑尺寸（15-50 μm）和不同的激光能量密度（0.6-4.2 J cm ^-2 ）烧蚀样品，以在 2 Hz 的固定激光重复率下获得足够的 Ti 信号强度。当样品的⁴⁹ Ti 信号强度范围为 0.3 至 3.7 V 时，在湿等离子体条件下未观察到明显的信号依赖性 Ti 同位素分馏。使用不同的分析方案对 12 种富钛矿物进行重复测量，在不确定性范围内提供了可比的 δ ⁴⁹ Ti _OL-Ti值，证实了所提出的 fs-LA-MC-ICP-MS 方法的准确性。除一个例外（即 RUS1）外，所有分析的矿物在各个碎片之间的 Ti 同位素组成都是均匀的，在 δ ⁴⁹ Ti _OL-Ti上的中间精度为 ±0.13 ‰ 至 ±0.17 ‰ (2 s )。总的来说，这些矿物记录了显着的 δ ⁴⁹ Ti _OL-Ti变化，范围为 -0.46 ‰ 至 +2.12 ‰。这些保证了这些材料作为原位钛同位素测量的钛同位素参考材料的适用性。