ZIRCON U-PB AGES FOR THE EARLY CAMBRIAN TIME-SCALE

被引:1150
作者
COMPSTON, W
WILLIAMS, IS
KIRSCHVINK, JL
ZICHAO, Z
GUOGAN, MA
机构
[1] CALTECH,DIV GEOL & PLANETARY SCI,PASADENA,CA 91125
[2] YICHANG INST GEOL & MINERAL RESOURCES,YICHANG 443003,PEOPLES R CHINA
关键词
D O I
10.1144/gsjgs.149.2.0171
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
Single zircons from two Early Cambrian volcanic horizons have been analysed using the SHRIMP ion microprobe. Full details of the analytical procedures and data reduction are given. Zircons from tuff within the Lie de Vin Formation, near Tiout, Morocco, show little spread in U-Pb age and have a mean value of 521 +/- 7 Ma (2-sigma). Those from a bentonite within unit 5 of the Meishucun section near Kunming, southern China, show relatively dispersed U-Pb ages, revealing the presence of both detrital or xenocrystic grains as well as areas within grains that have lost radiogenic Pb. The main population has as mean age of 525 +/- 7 Ma, but a mean Pb-207/Pb-206 age of 539 +/- 34 Ma which is a maximum estimate for the bentonite age. These results conflict with previous Rb-Sr whole rock ages of c. 580 Ma for overlying Cambrian shales at Meishucun, and c. 570 Ma for Atdabanian shales from the E. Yangtse Gorges area.
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页码:171 / 184
页数:14
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