Ordovician-Devonian multiple-phase subduction-accretion with crust-mantle interactions in the Proto-Tethys: Implications for plate driving mechanism

Abstract

The tectonic evolution of the Proto-Tethys records the dispersal of the Gondwana and the formation of the Asian continent, based on which the driving force of plate tectonics was majorly attributed to slab pull. However, no consensus has been achieved on the driving force and some fundamental aspects of its geodynamic processes have been controversial. This study presents detailed petrological, geochronological, and geochemical analyses of northern West Kunlun Orogen (WKO) adakites to constrain subduction processes and the magma sources, advancing tectonic reconstruction of the Proto-Tethys. Two samples (OMS-60 and OMS-62) were collected from an ophiolitic mélange within the Omixia complex, where they occur in association with mafic rocks. Another sample (OMS-64) was obtained from a granitoid body located on the northern margin of this ophiolitic mélange. These samples yield zircon U-Pb ages of 399 ± 5 Ma, 434.0 ± 2 Ma, and 462 ± 3 Ma, displaying typical adakitic signatures (high Sr/Y = 49.6–193, LREE enrichment, HREE depletion) and variable isotopic compositions (εNd(t) = −8.42 to −0.78; εHf(t) = −3.97 to −0.51). These features indicate magma generation through partial melting of Proto-Tethys oceanic crust and overlying sediments, coupled with mantle interaction during ascent. Combined with regional data, two adakite groups are identified: (1) northern 462–443 Ma suites formed during northward subduction, and (2) younger 434–399 Ma suites within of the Omixia complex linked to southward subduction. The sequential subduction regimes, potentially driven by ridge subduction or slab tearing, promoted oceanic crust melting and high-SiO₂ magma emplacement in forearc accretionary prisms. These findings, corroborated by regional evidence, challenge slab-pull dominance and instead support a hybrid geodynamic mechanism involving back-arc rifting and multi-force interactions. This work resolves Proto-Tethys subduction polarity shifts and provides new constraints on arc-related crust-mantle processes during Ordovician-Devonian orogenesis.