《Table 1 SHRIMP U-Pb isotopic composition for zircons from the granitic gneiss in Cuoke village, Shi

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《The Discovery of the 2.35Ga Crystalline Basement in the Southwest of the Yangtze Block and its Geological Significance》

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Note:206 and Pb*indicate the common and radiogenic portions，respectively.Common Pb corrected using measured 204Pb.

The zircon grains are stubby or elongate in shape and show oscillatory zoning in CL images，though some grains have been blurred，it is still discernible，indicating that the zircons are magmatic in origin.The grains are dark in color and shows a distinctly of high U.Totally 18 spots were sampled from granitic gneiss.The value of U ranges from 963 ppm to 2942 ppm.The value of Th varies between 387 ppm and 2086 ppm.Th/U is among 0.29—0.89（Table 1）.2 spots were not located near the concordia，suggesting that they must have suffered Pb's loss，with the majority falling on the same concordia spots.16 pots are on Concordia，yielding a weighted mean207Pb/206Pb age of 2351.6±6.8 Ma（Fig.1），which indicates the forming age of zircons and granitic gneiss.