Late Paleozoic subduction–accretion along the southern margin of the North Qinling terrane, central China: Evidence from zircon U-Pb dating and geochemistry of the Wuguan Complex

Abstract

The Qinling Orogen separating the North China plate from the Yangtze plate is a key area for understanding the timing and process of aggregation between the two plates. Two competing and highly contrasting tectonic models currently exist to explain the timing and nature of collision; one advocates a Devonian continental collision while the other favors a Triassic collision. The Wuguan Complex, between the early Paleozoic North Qinling and the Mesozoic South Qinling terranes, can provide important constraints on the late Paleozoic evolutionary processes of the Qinling Orogen. Metamorphosed sedimentary rock of the Wuguan Complex have a detrital zircon age spectrum with two major peaks at 453Ma and 800Ma, several minor age populations of 350–430Ma and 1000–2868Ma, and a youngest weighted mean age of 358±3Ma, indicating a mixed source from the North Qinling terrane. The recrystallized zircons yield a weighted mean age of 333±2Ma, representing the metamorphic age. Geochemical analyses imply that the sedimentary rocks were originally deposited in an active continental margin dominated by an acidic-arc source with a subordinate mafic-ultramafic source. The youngest population of detrital zircons (358Ma) suggests that the Wuguan Complex developed as forearc basin along the southern accreted margin of the North Qinling terrane during the early Carboniferous, whereas the ca. 520–460Ma mafic rocks with E-MORB, N-MORB, OIB or island arc basalt signatures probably derived from the Danfeng Group. In combination with regional data, we suggest that the depositional age of the Wuguan Complex is ca. 389–330Ma, but it was subsequently incorporated into tectonic mélange by the northward subduction of the Paleo-Qinling Ocean. A long-lived southward-facing subduction-accretionary system in front of the North Qinling terrane probably lasted until at least the early Carboniferous.