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SHRIMP U-Pb zircon age of tuff from the Kunyang Group in central Yunnan： Evidence for Grenvillian orogeny in South China
Ist Teil von
Chinese science bulletin, 2007-06, Vol.52 (11), p.1517-1525
Ort / Verlag
State Key Laboratory of Geological Processes and Mineral Resources & Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education, School of Earth Sciences and Mineral Resources, China University of Geosciences, Beijing 100083, China%Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
Erscheinungsjahr
2007
Link zum Volltext
Beschreibungen/Notizen
Whether or not Grenvillian orogeny occurred in South China still remains highly controversial because high-quality, discriminating data are lacking, and therefore, the key to resolve this matter is to find datable volcanic and/or sedimentary rocks related to Grenvillian orogeny. Such rocks are apparently present in the Fuliangpeng Member from the lower-middle part of Kunyang Group in central Yunnan; here the unit is more than 100 m thick and consists of andesitic ignimbrite, tuffite, terrigeous clastic rocks and carbonates. These volcanic rocks, developed south of the Sibao fold-thrust belts, represent the earliest calc-alkaline volcanic activity in late Precambrian time from central Yunnan and are coeval with both a change in sedimentary facies from detritus to carbonates and the beginning of seismite development elsewhere. Two samples for SHRIMP analysis were collected from this volcanic unit. Sample G3-29-2, from the bottom of Fuliangpeng Member, is an ignimbrite, and about 100 zircon crystals recovered from it have euhedral shapes and display relatively simple sector zonation under csthodoluminescent （CL） imaging, suggesting a magmatogenic origin. Twenty-five of the zircons were analyzed and a weighed-mean U-Pb age of 1032±9 Ma was obtained. Sample G3-29-3 from uppermost part of Fuliangpeng Member is a tuffite, and many rounded, evidently detrital zircons were recovered. Nine of these zircons were analyzed, and the oldest single-grain U-Pb zircon age is 1938±2.6 Ma, implying that Paleoproterozoic basement developed in Cathaysia. The dating result, combined with the geotectonic research on the Fuliangpeng Member, leads us to conclude that late Mesoproterozoic orogenic volcanic activity occurred in the western part of South China, and that the related collision of Yangtze and Cathaysian cratons was an integral part of the assembly of Rodinia.