Zircon U-Pb ages and Hf-O isotope compositions of the Zhaheba ophiolite in the northern margin of the Junggar terrane and their tectonic implications

The Zhaheba ophiolite, located in the northern margin of Junggar terrane, is part of the Zhaheba-Aerman ophiolitic melange belt. Through U-Pb zircon age and Hf-O composition analysis for two samples from the ophiolitic melange belt, this study obtained a crystallization age of 485±4Ma for cumulate gabbros and an eruptive age of 401±2.5Ma for tuffs. The gabbros are characterized by extreme depletion of Hf isotopic composition with ε_Hf(t)of 13～20 and δ¹⁸O peak value of +5.37‰, indicating a mantle-sourced feature. Hf isotope depletion degree of zircons from the tuffs is lower than that from cumulate gabbros, with ε_Hf(t)of 1.4～9.2. All this features suggest that the Zhaheba ophiolite is of typical characteristic of the SSZ type ophiolite, which results from subduction accretion to the front of intra-oceanic arc.