Zircon U–Pb and Lu–Hf isotopic and whole-rock geochemical constraints on the Lanhe and Heichashan Groups: Implications for the Paleoproterozoic tectonic basin evolution of the Lüliang Complex

Abstract

The Lüliang Complex is located at the western margin of the middle segment of the Trans-North China Orogen, along which the Western and Eastern Blocks collided to form the North China Craton. The complex mainly consists of metamorphosed granitic plutons and supracrustal rocks, of which the latter are subdivided into the Jiehekou, Lüliang, Yejishan, Lanhe and Heichashan Groups. The Lanhe Group is composed of meta-conglomerates, quartzites, and phyllites with minor meta-basalts, whereas the Heichashan Group consists of molasse-like meta-conglomerates and coarse-grained quartzites. Geochemistry of the Yejishan meta-sedimentary rocks indicates weak source weathering and dominantly chemical immature features, whereas the Lanhe and Heichashan samples display opposite features. U–Pb ages of detrital zircons from the Lanhe Groups yield four age peaks at ~2180Ma, ~2370Ma, ~2520Ma and ~2700Ma. The former three peaks coincide with ages of the Chijianling–Guandishan TTG gneisses (2199–2151Ma) and meta-volcanic rocks from the Lüliang and Yejishan Groups (2213–2156Ma), age of the Gaijiazhuang porphyritic gneisses (2375–2364Ma) and age of the Yunzhongshan TTG gneisses (2499Ma) respectively, whereas detrital zircons forming the oldest age peak were most likely derived from the early Neoarchean crust of the Eastern Block. For the Heichashan Group, the dominant 2.2–2.0Ga detrital zircons were probably recycled from the underlying Jiehekou Group and the minority is directly derived from the early Paleoproterozoic granitoids in the Lüliang Complex. The youngest detrital zircon age peaks of ~2.17Ga and ~1.82Ga place maximum depositional ages on the Lanhe and Heichashan Groups respectively, whereas the local 1.81–1.79Ga massive granites place constraint on their minimum depositional ages. Taking into account the lithostratigraphic features, provenance and formation ages, we suggest that the Lanhe Group formed in a shrinked remnant back-arc basin and the Heichashan Group was deposited in a foreland basin. Conversion of the tectonic basin from the middle Paleoproterozoic back-arc basin to the late Paleoproterozoic foreland basin is well consistent with the model that the single collision to form the basement of the North China Craton happened at ~1.85Ga.