Early Paleozoic Cascadia-type active-margin evolution of the Dunhuang block (NW China): Geochemical and geochronological constraints

Abstract Origins of early Paleozoic metabasites (granulites and amphibolites) their host metasedimentary rocks in the Dunhuang block, NW China, are addressed by new geochronological geochemical data. The show back-arc basalt–like features, marked high Zr/Nb ratios Zr-Hf troughs, but they can be classified into two groups based on dissimilar protolith ages distinct Nd signatures. Most group I metabasaltic were emplaced before 455 Ma possess Ba/Nb (11.46–224), low (Nb/La)PM (0.10–0.71), negative whole-rock ?Nd(t) values (?12.7 to ?2.7), whereas II have around 445 Ma, (0.70–22.93), (0.78–1.51), less evolved isotopic features (?Nd[t]: ?2.0 +2.7). It is proposed that originated from an enriched lithospheric mantle, while derived depleted asthenospheric mantle. received detritus mainly neighboring Cambrian magmatic arc, compositionally similar active-margin sediments. Metamorphic zircon U-Pb ranging 462–422 investigated together with prominent magmatism further suggest high-grade metamorphism prevailing during Late Ordovician–early Silurian. Based these data, a Cascadia-type evolution involving Silurian suprasubduction stretching active continental margin, which culminated mantle upwelling. Recent paleogeographic reconstructions support assembly interior Proto–Tethys-Ran oceanic plates, including between 510 440 followed Panthalassan subduction beneath Tarim–North China assemblage at 440–430 Ma.