High water content in primitive continental flood basalts

As the main constituent of large igneous provinces, the generation of continental flood basalts (CFB) that are characterized by huge eruption volume (>10(5) km(3)) within short time span (<1–3 Ma) is in principle caused by an abnormally high temperature, extended decompression, a certain amount of mafic source rocks (e.g., pyroxenite), or an elevated H(2)O content in the mantle source. These four factors are not mutually exclusive. There are growing evidences for high temperature, decompression and mafic source rocks, albeit with hot debate. However, there is currently no convincing evidence of high water content in the source of CFB. We retrieved the initial H(2)O content of the primitive CFB in the early Permian Tarim large igneous province (NW China), using the H(2)O content of ten early-formed clinopyroxene (cpx) crystals that recorded the composition of the primitive Tarim basaltic melts and the partition coefficient of H(2)O between cpx and basaltic melt. The arc-like H(2)O content (4.82 ± 1.00 wt.%) provides the first clear evidence that H(2)O plays an important role in the generation of CFB.