Petrogenesis of rodingite in the Ngamring massif, Xigaze ophiolite (Southern Tibet): Implications for the evolution of the Neo-Tethys Ocean

Rodingites, although volumetrically minor, are integral to the Yarlung Zangbo ophiolites in southern Tibet. However, their tectonic setting, protolith, petrogenesis, and fluid sources remain incompletely understood. This study focuses on rodingites from the Ngamring massif of the Xigaze ophiolite, central Yarlung Zangbo Suture Zone (YZSZ), integrating petrology, mineral and whole-rock geochemistry, and phase equilibrium modeling. The rodingites are structurally heterogeneous and classified into type IA and IB, both featuring metasomatic assemblages of prehnite, chlorite, garnet, and salitic clinopyroxene. Phase equilibrium modeling constrains their formation to low pressure–temperature conditions (<4 kbar and 200–290 °C), while relict magmatic clinopyroxenes with high Mg# values [73–87; Mg# = MgO/(MgO + FeO), with all measured iron considered as FeO] suggest a gabbroic protolith crystallized at ∼ 6.0–7.4 kbar. Both rodingites types display rare earth and multi-element patterns similar to normal mid-ocean ridge basalt (MORB), comparable to other MORB-like rodingites within the Xigaze ophiolite. The host peridotites show trace-element features characteristic of abyssal peridotites, representing residues after ∼ 7–14 % spinel-facies melting of a depleted MORB mantle-like source. The rodingites have variable ⁸⁷Sr/⁸⁶Sr ratios (0.7036–0.7054) and MORB-like ɛNd(t) values (7.3–8.6), suggesting interactions between MOR-derived gabbroic protoliths and serpentinizing fluids derived from the peridotite. Given the presence of metamorphic soles with MORB-type protoliths and both MORB-like and supra-subduction zone magmatic rocks in the YZSZ, it is suggested that the ophiolites likely originated in a MOR environment before evolving into a supra-subduction zone setting as the Neo-Tethys ridge transitioned into an infant subduction system.