Detrital Zircon Geochronology And Its Implications:the Carboniferous Bauxite Deposits In The North China Craton

The North China Craton (NCC) is bounded by two Paleozoic arc terranes, i.e., Bainaimiao arc terrane in the south of Central Asian Orogenic Belt (S-CAOB) to the north and the North Qinling arc terrane in the North Qinling orogenic belt (NQO) to the south. In Paleozoic, the NCC experienced an exposure of-150 Ma from Middle Ordovician to Late Carboniferous, and formed bauxite in the lower member of the Carboniferous Benxi Formation, which unconformably overlaid the Ordovician Majiagou Formation. In this paper, the U-Pb ages, Hf isotopes and trace elements of the detrital zircons exacted from the typical bauxite ores are tested to discuss the provenance of the ores, and discuss the Paleozoic evolution of surrounding orogens and its constraint on the intraplate paleotopography.CL images and trace elemental compositions of the zircons indicate that the most zircons in the bauxite are magmatic zircons. The zircons from the samples are obviously clustered around two peaks,-450 Ma and ?320 Ma. The sHf(t) isotopes of the zircons with ages of ?450 Ma are consistent with the ?Nd(t) of the NQO and different from the ?Nd(t) and ?Hf(t) in igneous rocks in the S-CAOB. Therefore, the zircons with ages around ?450 Ma are inferred to come from the NQO, supporting a Devonian accretion of the North Qinling arc terrane to the NCC, an uplift of the Erlangping back-arc basin, and a north-tilting paleography in most part of the NCC. On the other hand, it denotes the north margin of the NCC is a passive margin before Late Carboniferous, and Bainaimiao arc terrane is not an in situ one and it accreted to the NCC until the Late Carboniferous. The ?320 Ma peak, which is obvious in the bauxite samples in the central NCC yet feeble in the south samples, is consistent with the magmatism and rapid uplift of the north margin of the NCC (N-NCC) caused by the southwards subduction of the ancient Asian ocean. This uplift induced a south-tilting in the central to north NCC. Some young zircons with ages around 310 Ma, approximating to hanging wall of the bauxite, are with volcanic origin, suggesting the volcano events have a capacious influence in the NCC. The detrital zircons analysis reflects the evolution of surrounding orogens influenced intraplate paleotopography of the NCC.