Supra-subduction zone ophiolite generated by the initial subduction of an Early Paleozoic island arc system abutting the northern North China Craton: Evidence from meta-igneous rocks

Abstract

To constrain the evolution of an Early Paleozoic island arc belt abutting the North China Craton (NCC), this study presents new geochronological, geochemical, and Sr–Nd–Hf–O–Pb isotopic data for igneous rocks from the central part of Jilin Province within the southeastern part of the Central Asian Orogenic Belt. The igneous complex in this area hosts both mid-ocean ridge basalt (MORB)- and arc-type rocks that yield zircon 206Pb/238U ages of ca. 492 and 488–459 Ma, respectively. The MORB-type units in this area include metacumulate gabbros, metadiabases, and metabasalts that have normal MORB (N-MORB)-like compositions with (La/Yb)N values of 0.29–0.99, Th/Nb values of 0.07–0.52, whole rock εNd(t) values from +4.32 to +7.29, and initial 208Pb/204Pb values of 38.12–38.20. These compositions are indicative of derivation from the depleted asthenospheric mantle. The arc-type igneous rocks consist of amphibolite, epidiorite, and metagabbro with major- and trace-element and isotopic compositions that are similar to island arc tholeiite to calc-alkaline rocks, with (La/Yb)N values of 1.11–4.26, Th/Nb values of 0.11–2.25, zircon εHf(t) values from +6.03 to +15.30, zircon δ18O values from +4.32 to +5.1, whole-rock εNd(t) values from +2.09 to +7.25, and initial 208Pb/204Pb values of 38.09–38.11. These compositions are indicative of derivation from partial melting of the hydrous depleted mantle wedge material within an intra-oceanic arc setting. The MORB-type rocks formed within a forearc region of the SSZ ophiolite fragment, whereas the arc-type rocks record the evolution of this region from immature to mature island arc tectono-magmatic settings. Combining these new data with the results of previous research suggests that initial subduction of the Paleo-Asian oceanic plate abutting the northern NCC began during the latest Cambrian.