Petrogenesis of mafic to intermediate rocks within the crustal sequence of the Luqu ophiolite in the Yarlung-Tsangpo suture Zone, southern Tibet and implications for the Neo-Tethys evolution

Ophiolites provide insights into the lithosphere of vanished oceans and serve as key archives for reconstructing their evolutionary histories. In southern Tibet, ophiolites exposed within the Yarlung-Tsangpo Suture Zone are interpreted as remnants of the Cretaceous Neo-Tethyan lithosphere. However, origin and source characteristics of these lithospheric remnants remain controversial. This study presents new geochemical data from crustal rocks (dolerites, basalts, and leugogabbros) within the Luqu section of the Xigaze ophiolites. The northern Luqu section preserves intact crustal sequence dominated by doleritic dykes, sill complexes, and massive to pillowed lavas. Notably, minor leucogabbro intrusions within the dolerites were identified. Geochemical analyses reveal that the dolerites and basalts exhibit flat to moderately depleted LREE patterns, consistent with derivation from a depleted mantle source. The leucogabbros yield crystallization ages (132 – 125 Ma) overlapping with those of the mafic dolerites (∼125 Ma) and other YTSZ crustal sequences (134 – 120 Ma). Mineralogically, they contain high-Mg# clinopyroxene, high-An plagioclase, and amphibole, suggesting hydrous parental melts. The leucogabbro display distinct isotopic compositions — unradiogenic Sr-Hf coupled with enriched Nd. Petrological and geochemical evidence indicates these leucogabbros originated via partial melting of lower crustal gabbros, with contributions from enriched components within their sources. Gabbro solidus was likely lowered by infiltration of seawater-derived hydrothermal fluids, a process facilitated by detachment faults in ultraslow-spreading settings. These faults enable seawater penetration, enhancing fluid-rock interaction and melt hybridization. Our findings suggest that mafic rocks and leucogabbros in the Xigaze ophiolites were sourced from distinct mantle domains within an ultraslow-spreading ridge.