Melt flow control on lithological and geochemical heterogeneity of the oceanic upper mantle

The Earth's upper mantle is heterogeneous in lithology and geochemistry, as demonstrated by variations in both abyssal peridotites and fossil oceanic mantle peridotites. The scarcity of spatial relationships between these peridotites, however, hinders further interpretation of the origin of mantle diversity as well as corresponding geodynamic processes. Here, we report the petrographic and chemical data of peridotites from the first fresh drill core (∼1300 m) across a Tibetan ophiolitic mantle sequence. This mantle column shows a primarily heterogeneous lithological structure consisting of repetitive 'layered' lherzolite, harzburgite, and dunite. Lherzolite and harzburgite have experienced 10%-15% and 15%-25% melt depletion, respectively. Such depletion cannot be generated by conventional partial melting models alone, but also requires melt-peridotite interaction in the asthenospheric mantle. Our work provides a high-resolution snapshot of the lithological structure and chemistry of the uppermost oceanic mantle and offers a melt flow model within the asthenosphere to explain the lithological variability of mantle rocks found in both mid-ocean ridges and supra-subduction zones.