LA-ICP-MS zircon U-Pb ages for pisolitic welded tuff from the bottom of the Neoproterozoic Suxiong Formation in western Sichuan and their geological significance

With the aid of LA-ICP-MS,the zircon U-Th-Pb age dating for the pisolitic welded tuff sample from the bottom of the Neoproterozoic Suxiong Formation in western Sichuan was carried out for the first time,and two groups of highly concentrated age data were obtained as follows:805.9±4.4 Ma (N=11,MSWD=0.58)and 849.4±6.2 Ma (N=6,MSWD=0.34). The younger one,i. e. 805.9±4.4 Ma,represents the age of the deposition of tuff. This age agrees well with the previously reported SHRIMP zircon U-Pb age 803±12 Ma for the rhyolites from the Suxiong Formation,and represents the initial age for the volcanic activity at the bottom of the Suxiong Formation. The study of the tectonic-magmatic thermal events shows that the age 805.9±4.4 Ma represents the ca. 800 Ma volcanic event on the Yangtze landmass in South China while the age 849.4±6.2 Ma may well correspond to the syn-rifting magmatic activity during the initial rifting of the supercontinent Rodinia at ca. 850 Ma.