MORB ‐Type Rocks From the Proto‐Tethyan N antinghe Ophiolite, Southwestern Y unnan: Implication for the

ABSTRACT

The evolution of the Early Palaeozoic Proto‐Tethys Ocean is closely linked to the breakup of the Rodinia supercontinent. However, whether its mantle domain exhibited DUPAL isotopic anomalies similar to those of the modern Indian Ocean remains unclear. In this study, we systematically investigate meta‐basalts from the relatively well‐preserved Nantinghe ophiolitic mélange within the Changning‐Menglian suture zone in southwestern Yunnan, using zircon U–Pb dating, whole‐rock geochemistry, and Sr‐Nd‐Hf isotopes, to constrain the nature of the Proto‐Tethyan mantle domain. The results show that the meta‐basalts yield a weighted mean zircon U–Pb age of 466.0 ± 3.5 Ma, indicating formation during the Early Palaeozoic. They exhibit MORB‐like rare earth element and trace element patterns, consistent with partial melting of depleted spinel lherzolite. The samples display consistently depleted Nd‐Hf isotopic compositions, with ε _Nd (t) values ranging from +5.6 to +7.2 and ε _Hf (t) values from +11.1 to +14.6. The calculated ΔεHf _(P/I)i and ΔεNd _(P/I)i values fall entirely within the field of Indian Ocean‐type MORB, demonstrating that the mantle source preserves the DUPAL isotopic anomaly. These findings indicate that the Proto‐Tethyan mantle domain belonged to the Indian Ocean‐type and extend the known record of the DUPAL anomaly back to at least ca. 466 Ma.