Paleoproterozoic ophiolitic mélanges and orogenesis in the northern Yangtze Craton: Evidence for the operation of modern-style plate tectonics

Abstract

Ophiolitic mélange that forms along convergent plate margins plays an important role in reconstructing the tectonic evolution of ancient orogenic belts and associated geodynamic settings. However, ophiolitic mélanges have rarely been documented in the Archean and Paleoproterozoic geological records, which led to the controversy surrounding the onset or not of plate tectonics at that time. Here we present an integrated study of petrography, geochemistry, zircon U-Pb-Lu-Hf isotope, and metamorphic P–T estimations on the newly-recognized 2.12–2.03 Ga ophiolitic mélange that contains amphibolite and serpentinite blocks in the North Kongling Complex (NKC), northern Yangtze Craton to better constrain the tectonic evolution of the northern Yangtze Craton and prevailing geodynamic backgrounds. The amphibolites and serpentinites in the mélange exhibit slightly-enriched light rare earth elements (LREEs), large-ion lithophile elements (LILEs, e.g., Rb, Ba) and negative high field strength elements (HFSEs, e.g., Nb, Ta, Zr, Hf, and Ti) anomalies, suggesting their derivation from a subarc mantle wedge metasomatized by slab-derived fluids/melts. The mafic–ultramafic components likely represent the dismembered fragments of a ca. 2.12 Ga suprasubduction zone (SSZ) arc/forearc complex. The garnet amphibolite underwent intermediate T/P metamorphism at ca. 2.03 Ga, with a clockwise P–T path. The estimated (near) peak P–T conditions of ∼10.1–10.6 kbar/660–670 °C correspond to thermobaric ratios of ∼625–635 °C/GPa, consistent with subduction-collision-related geothermal gradients. Collectively, the mélange recorded an intra-oceanic subduction-accretion event at ca. 2.12 Ga and subsequent collision at ca. 2.03 Ga. In combination with regional geological data, the accretionary-to-collisional orogenic events in the NKC of the northern Yangtze Craton could be a response to global-scale convergence and assembly of the Paleoproterozoic supercontinent Nuna/Columbia. The Paleoproterozoic (2.12–2.03 Ga) ophiolitic mélanges and orogenesis in the northern Yangtze Craton thus support the operation of the modern-style plate tectonic regime at that time.