Isotope geochronology of Dapingzhang spilite-keratophyre formation in Yunnan Province and its geological significance

On the basis of the geological field investigations and isotope geochronolo gical studies the Sm-Nd isochron age (513 Ma+/-40 Ma), Rb-Sr isochron age ( 511 Ma+/-8 Ma) and K-Ar age (312-317 Ma) of the Dapingzhang spilite-keratop hyre formation in Yunnan Province are presented. From these geochronologica l data it is evidenced that this suite of volcanic rocks was formed in the Cambrian and the parent magma was derived from a depleted mantle, which was influenced by crustal contamination and/or seawater hydrothermal alteratio n. During the Late Carboniferous the volcanic rocks experienced relatively strong geological reworking. This study provides geochronological evidence for the occurrence of Cambrian volcanic rocks in the Sanjiang (three-river) area.