Geochemistry and Geochronology of the Jinghong Ophiolites: Implications for the Tectonic Evolution of the Eastern Paleo‐Tethys

Abstract

AbstractThe Jinghong mafic–ultramafic complex, exposed in the eastern margin of the Lancangjiang tectonic belt, is related to the subduction of the Paleo‐Tethys Ocean. Its petrogenesis plays a key role in constraining the tectonic evolution of the eastern Paleo‐Tethys Ocean in southwestern China. In this study, we present petrological, geochemical and geochronological results of the Jinghong complex rocks, in order to decipher their origin and tectonic significance. The Jinghong mafic–ultramafic complex was composed of peridotite, gabbro, basalt and minor plagiogranite. Whole‐rock geochemical data of the mafic rocks indicate that they have both MORB and IAB affinities and plot in the back‐arc basin basalt (BABB) field in the FeO∗/MgO vs. TiO2 diagram. Combined with their trace element characteristics, it can be concluded that the Jinghong mafic–ultramafic complex represents an ophiolite suite that was formed in a back‐arc ocean basin. Precise LA‐ICP‐MS zircon U‐Pb dating yielded weighted mean 206Pb/238U ages of 298.4 ± 1.7 Ma, 294.3 ± 1.6 Ma, and 292.8 ± 2.0 Ma for gabbroic rocks from this complex, which indicates that the Jinghong ophiolites were formed during the early Permian (298–293 Ma). We propose that during subduction of the main Paleo‐Tethys Ocean, a back‐arc ocean basin was formed at the east of the Lancangjiang tectonic belt.