西藏南部某些中酸性岩体的铷-锶同位素研究

Rb-Sr ISOTOPIC STUDIES OF SOME INTERMEDIATE-ACIDIC PLUTONS IN SOUTHERN XIZANG

Widespread in Southern Xizang are intermediate-acidic rocks characterized by their regular distribution in space and time. In order to explore their formation ages and genesis, we have determined the Rb-Sr whole rock isochron ages on granodiorite from the Quxu pluton in Kangdese belt (18m.y., Sr^87/Sr^88 initial ratio = 0.7036), gneissose two-mica granite from the Kangmar pluton in Lhagoi Kangri belt (484.55 ± 6.34 m.y.,Sr^87/Sr^86 initial ratio = 0.7186 ± 0.0018) ; and tourmaline-muscovite granite from the Gabug pluton in Himalaya belt (42.95 ± 2.6 m.y., Sr^87/Sr^84 initial ratio=0.7478±0.00097). From the initial Sr^87/Sr^86 ratios it is shown that the granodiorites are most likely to be derived from the upper mantle; the gneissose two-mica granites may contain significant amounts of sialic material during emplacement; and the tourmalinemusco vite granites are typically of crustal origin.

Widespread in Southern Xizang are intermediate-acidic rocks characterized by their regular distribution in space and time. In order to explore their formation ages and genesis, we have determined the Rb-Sr whole rock isochron ages on granodiorite from the Quxu pluton in Kangdese belt (18 m.y., Sr87/Sr86 initial ratio = 0.7036), gneissose two-mica granite from the Kangmar pluton in Lhagoi Kangri belt (484.55 ± 6.34 m.y., Sr87/Sr86 initial ratio = 0.7186 ± 0.0018); and tourmaline-muscovite granite from the Gabug pluton in Himalaya belt (42.95 ± 2.6 m.y., Sr87/Sr86 initial ratio = 0.7478 ± 0.00097).From the initial Sr87/Sr86 ratios it is shown that the granodiorites are most likely to be derived from the upper mantle; the gneissose two-mica granites may contain sig-nificant amounts of sialic material during emplacement; and the tourmalinemusco-vite granites are typically of crustal origin.