Ocean Plate Stratigraphy of a long-lived Precambrian subduction-accretion system: The Wutai Complex, North China Craton

Abstract

Ocean Plate Stratigraphy (OPS) is the travelogue of the oceanic lithosphere from its birth at the Mid Ocean Ridge to its demise at the subduction zone in convergent plate margins. Here we present an OPS succession preserved onland in the Wutai Complex of the North China Craton (NCC), representing a prolonged subduction-accretion-collision system and continental growth during the Neoarchean-Paleoproterozoic. The OPS succession in Wutai includes metabasalts and banded iron formation representing the pelagic sequences together with intercalated metacarbonates. Phyllite, greenschist, and mica schist represent the hemipelagic sequence. Quartzite and conglomerate correspond to the turbidite sequence, with a progressive southward accretion towards a magmatic arc in the north. We present results from petrological, geochemical, zircon U-Pb, REE, and Lu-Hf studies from representative rocks in the OPS sequence of the Wutai Complex. The trace elements including the rare-earth element (REE) data of the metabasalt show transitional features between normal mid-ocean ridge basalt (N-MORB) and enriched mid-ocean ridge basalt (E-MORB). The REY (lanthanide elements and Y) data of the banded iron formation (BIF), greenschists, and phyllite suggest the interaction of high-temperature hydrothermal fluids and seawater. Magmatic zircon grains from the quartzite show 206Pb/207Pb upper intercept age of 2443 ± 21 Ma, whereas zircon grains in the phyllite show upper intercept age of 2494 ± 32 Ma, with minor xenocrysts with older ages of 2726 ± 46 Ma and 2672 ± 48 Ma. Zircon grains in the metaconglomerate show upper intercept age of 2569 ± 32 Ma. Those from the siliceous and intercalated bands in the BIF yield upper intercept ages of 2583 ± 34 Ma and 2524 ± 49 Ma. The zircon Lu-Hf data on zircon grains from the BIF, phyllite, quartzite, and metaconglomerate all show positive εHf(t) values (+1.3 to +7.4) in the range of depleted mantle to new crust, suggesting Neoarchean intra oceanic arc subduction. Combined with the zircon U-Pb and Hf isotopic data previously reported from the Wutai Complex, we infer the following four tectonic evolution stages: ca. 2800 Ma subduction initiation, ca. 2750–2300 Ma arc-accretionary complex, ca. 2300–2100 Ma back-arc rifting, and ca.1900–1750 Ma arc-continent collision. The metavolcanics and part of the metasedimentary rock assemblages in the Wutai Complex represent a deformed and dismembered OPS sequence generated through northward subduction and closure of the Wutai Ocean.