Provenance of sedimentary rocks of Nanhua System in the northern Guangxi Province: Evidence from detrital zircon U-Pb ages

The southwestern Jiangnan Orogenic is one of the regions in the Yangtze craton where the Neoproterozoic strata well developed. The Nanhua System in the northern Guangxi Province is composed of the Chang' an, Fulu, Datangpo and Lijiapo formations in the ascending sequence. The strata thickness range from tens of meters to several kilometers and there is a general tendency toward decreasing thickness from west to east. In this paper, detrital zircons U-Pb ages from 5 samples of the Chang' an, Fulu and Lijiapo formations were analyzed by LA-ICP-MS method. The detrital zircon U-Pb ages of the Chang' an Formation display a age peak between 724Ma and 972Ma and the weighted average age of the youngest zircons is 746 +/- 5Ma (n = 19), indicating that the Chang' an Formation of. the Nanhua System may be deposited between 746Ma and 780Ma; For the Fulu Formation, detrital zircon U-Pb ages have three peaks with the main peak at 705 similar to 936Ma and two sub-peaks at 1823 similar to 2163Ma and 2241 similar to 2673Ma; detrital zircons from the lower Lijiapo Formation (Sample 121109-4) have a major peak at 1966 similar to 2118Ma and two sub-peaks at 724 similar to 921Ma and 2221 similar to 2688Ma. Sample 121109-4 of the middle Lijiapo Formation is featured by the major age peak of 1813 similar to 2192Ma and two sub-peaks of 748 similar to 944Ma and 2296 similar to 2726Ma; For the upper Lijiapo Formation, Sample 121109-5 is characterized by the major age peak of 1984 similar to 2193Ma and two sub-peaks of 653 similar to 1007Ma and 2215 similar to 2675Ma. Detrital zircon age ranges of the 5 samples from the Chang' an, Fulu and Lijiapo formations of the Nanhuan System in the northern Guangxi Province are similar, but the main peaks and the sub-peaks are significantly different, reflecting their different provenance and different depositional environments. Detrital zircon age distribution between 653Ma and 1007Ma indicate strong magmatic activities in the southeastern margin of the Yangtze craton and the northern Guangxi Province located in the southwestern Jiangnan orogenic belt, which may be related to amalgamation and breakup of the Rodinia supercontinent, and the 1792 similar to 2261Ma magmatic activities are correlated with amalgamation and breakup of the supercontinent Columbia. The 2298 similar to 2500Ma detrital zircons are indicative of the Paleoproterozoic basement in the southern margin of the Yangtze craton and a small amount of zircons older than 2500Ma imply the Archean basement in the southern margin of the Yangtze craton there. Absence of 1100 similar to 1300Ma Greenville orogenic period records of the 5 samples indicating that the Jiangnan orogenic belt was not located in the center of the Rodinia supercontinent. In short, the southern margin of the Yangtze craton and the southwestern Jiangnan orogenic experienced at least three strong tectono-thermal events, which are well recorded in the Nanhua strata at the northern Guangxi Province.