Paleoproterozoic arc-continent collision in the North China Craton: Evidence from the Zanhuang Complex

Abstract

The Trans-North China Orogen (TNCO) marks the major (ca. 300km wide) Paleoproterozoic collisional suture between the Eastern and Western Blocks of the North China Craton (NCC), which also incorporates several microblocks or complexes. Here we investigate the Zanhuang Complex along the eastern margin of TNCO. We present petrological, geochemical, zircon U–Pb and Lu–Hf data on a suite of quartz-mica schist, metavolcanics and diorite from the Central Zanhuang Domain (CZD), as well as granitoids and amphibolite that constitute the basement rocks of the Western Zanhuang Domian (WZD) and Eastern Zanhuang Domain (EZD). Our study represents a cross section across two continental margins and covers the paleo-ocean tract in between. The metavolcanics show calc-alkaline to tholeiitic affinity, and negative correlations of (La/Sm)N vs. P/Nd, Ti/Ti∗, Ce/Ce∗, and positive with Nb/Nb∗. The granitoids fall within the VAG field. The IAB and MORB features of the volcanic suite are consistent with magma derivation in arc to back arc environment from an enrichment source. The magmatic suite also displays LREE enrichment, positive Rb, K, La, Pb, Nd anomalies and negative Ta, Nb, Ce, Ti anomalies. LA-CIPMS U–Pb geochronology of detrital zircon grains shows two age populations in the quartz-mica schist with 207Pb/206Pb mean ages of 2499±14Ma, and 2252±22–2216±39Ma, and the timing of deposition is estimated as ca. 2.3–2.2Ga. Zircons from the granodioritic gneiss yield 207Pb/206Pb mean age of 2508±14Ma, representing Neoarchean continental basement. The metavolcanics and two diorite samples yield ages of 2302±30Ma, 2089±63Ma marking the timing of an active arc. The metamorphic zircons from these rocks show an age of 1882±15Ma. The zircon Lu–Hf data yield both positive and negative εHf(t) values, suggesting depleted mantle source mixed with crustal components. Their crustal residence ages (TDMC) range from 3875 to 2224Ma and depleted model ages (TDM) range from 3415 to 2092Ma suggesting mixed juvenile and reworked crustal components and possible vestiges of Mesoarchean basement. We propose that the Zanhuang Complex is one of the Paleoproterozoic arcs within the TNCO which was accreted to the Neoarchean continent along the Eastern Block of the NCC during the suturing along the TNCO. The tectonics associated with crustal growth and recycling in the TNCO and the arc-continent collision broadly coincided with the building of the Columbia supercontinent.