Multi‐Stage Mafic Magmatism in the Indus–Tsangpo Suture Zone, Southwestern Tibet and Implications for Evolution of the Neo‐Tethys Ocean Before the Cretaceous

ABSTRACT

Discontinuous ophiolites along the Indus–Tsangpo Suture Zone (ITSZ) currently represent remnants of ancient oceanic lithosphere in southern Tibet, providing an excellent window into the evolution of the Neo‐Tethys Ocean. In this contribution, combined with field observations and geochemical analyses, two types of gabbro blocks were recognized in the tectonic mélange of the western ITSZ, southwestern Tibet. Zircon grains from these gabbros yield crystallization ages of 310.4 ± 0.95 Ma with ε _Hf ( t ) = +4.2 to +8.4 and 169.3 ± 0.45 Ma with ε _Hf ( t ) = +5.6 to +12.8, providing petrological and geochronological evidence for multi‐stage mafic magmatism in the Neo‐Tethys Ocean. These gabbros show LREE enrichment, with elevated Th, U, Nb, and Ta, but depletion in Rb and Pb. The initial ( ⁸⁷ Sr/ ⁸⁶ Sr) _i ratios are 0.70464–0.70594 and 0.70447–0.70493, with corresponding ε _Nd ( t ) values of +12.30 to +13.73 and +3.33 to +6.13. These isotopic and geochemical features reflect OIB‐like affinities, indicating the enriched, homogeneous mantle source under an oceanic intraplate setting. Together with previous reports, our results indicate that multi‐stage intra‐oceanic magmatism occurred within the Neo‐Tethys Ocean from the late Palaeozoic to the Mesozoic.