U-Pb ages and Hf isotope data from detrital zircons in the Neoproterozoic sandstones of northern Jiangsu and southern Liaoning Provinces, China: Implications for the Late Precambrian evolution of the southeastern North China Craton

摘要

The tectonic evolution of the North China Craton (NCC) from the Late Mesoproterozoic to the Neoproterozoic has been unclear. This paper reports the results of LA-ICP-MS U-Pb dating and in situ Hf isotope analysis of detrital zircons from Neoproterozoic strata in the northern Jiangsu and southern Liaoning provinces of southeastern NCC, and we go onto discuss how these results help constrain the Late Precambrian evolution of the NCC. Most analyzed zircon grains exhibit oscillatory growth zoning, and they have relatively high Th/U ratios (>0.4) and positive Ce anomalies as well as negative Eu anomalies, all of which suggests a magmatic origin. The detrital zircons from the Xinxing and Jinshanzhai formations in northern Jiangsu Province give weighted mean ages of 1753, 1635, 1486, and 1121Ma, and 2515, 2305, 1856, 925, and 825Ma, respectively, and the detrital zircons from the Diaoyutai and Xingmincun formations in southern Liaoning Province give ages of 1745, 1619, 1484, 1175, and 1077Ma, and 1798, 1623, 1150, 1020, and 934Ma, respectively. These results, together with previously published ages, indicate that (1) the Neoproterozoic strata in the northern Jiangsu and southern Liaoning provinces were deposited during a period from the Late Mesoproterozoic to Neoproterozoic, and (2) the sediments in the Neoproterozoic strata were sourced mainly from igneous rocks of Late Paleoproterozoic, Mesoproterozoic, and Early Neoproterozoic age, as well as from the ancient Precambrian basement of the NCC. The concordia plots for 291 detrital zircon grains give three prominent age groups of 1.86-2.5, 1.5-1.8, and 0.9-1.2Ga. The detrital zircon ages of 1.86-2.5Ga in the Neoproterozoic strata tie in with most of the Precambrian tectonic-magmatic-thermal events that occurred in the NCC. Zircon ages of 1.6-1.8Ga can be linked to rift magmatism of Late Paleoproterozoic age in the NCC. The detrital zircon ages of 0.9-1.2Ga can be related to Grenville-aged magmatism in the southeastern NCC. The zircons show negative e{open}_(Hf) (t) values (-8.8 to -0.1), suggesting that the source rocks were dominated by reworked ancient Precambrian crust. The positive e{open}_(Hf) (t) values (+0.3 to +10.8) and Hf model ages indicate that growth of continental crustal occurred at ~2.7Ga, ~1.9Ga, and ~1.5Ga in the southeastern NCC.