Titanium stable isotopic compositions of chondrites and ancient to modern terrestrial mantle-derived lavas

We report ultra-high precision 49Ti/47Ti ratios for chondrites, ancient terrestrial mantle-derived lavas ranging from 3.8 to 2.0 Ga and modern oceanic island basalts (OIBs). Our new Ti bulk silicate Earth (BSE) estimate based on chondrites is 0.052±0.006‰ heavier than the modern upper mantle sampled by normal-type mid-ocean ridge basalts (N-MORBs). The 49Ti/47Ti ratio of Earth’s upper mantle was chondritic before 3.5 Ga and evolved to a N-MORB-like composition between ~3.5-2.7 Ga. Modern OIBs record variable 49Ti/47Ti ratios ranging from chondritic to N-MORBs compositions.

本研究报道了球粒陨石、年龄介于3.8至2.0 Ga的古老地球地幔源熔岩，以及现代洋岛玄武岩（Oceanic Island Basalts, OIBs）的超高精度49Ti/47Ti同位素比值。
本研究基于球粒陨石得到的全新整体硅酸盐地球（Bulk Silicate Earth, BSE）钛同位素比值估算值，较正常型洋中脊玄武岩（Normal-type Mid-Ocean Ridge Basalts, N-MORBs）采样获得的现代上地幔值高出0.052±0.006‰。
地球上地幔的49Ti/47Ti比值在3.5 Ga前与球粒陨石一致，并在约3.5~2.7 Ga期间演化至接近正常型洋中脊玄武岩的同位素组成。
现代洋岛玄武岩（OIBs）的49Ti/47Ti比值存在显著变化，范围覆盖从球粒陨石型至正常型洋中脊玄武岩型的组成。