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 ...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.展开更多
The principle, analytical procedures and applications of Rb-Sr dating for minerals and rocks are described. Sr was separated by ion exchange resin 71-616 (1) (made in China) and inorganic ion-exchanger ZrP (prepared i...The principle, analytical procedures and applications of Rb-Sr dating for minerals and rocks are described. Sr was separated by ion exchange resin 71-616 (1) (made in China) and inorganic ion-exchanger ZrP (prepared in our laboratory). All Sr determinations were made by isotope dilution and mass spectrometry. The concentration of Rb was analysed by flame spcetrophotometry. Rb-Sr ages of three micas (one from pegmatite from Inner Mongolia, and the other two are from granites from Kiangsi province) are in agreement with the K-Ar.rages and geological observations, indicating that the retention of radiogenic Sr^87 in micas is excellent. But systematic defferenee between K-Ar and Rb-Sr mica ages has been found in the other granite from Kiangsi province, suggesting possible eontaminations of radiogenic Sr^87 from magraas of different resources. Based on the isochrons formed by six total rocks and one feldspar, two metamorphie episodes of Jolmo Lungma series, Tibet, China (659±20, 17±6 m.y.) have been established. A similar conclusion has been reached by the U-Pb two stage model(modified eoncordia) ages, K-Ar dating as well as field investigations. It is believed that if sufficient geological data and suitable specimens are avilable, Rb-Sr isochron method may be a powerful toot to bring out multi-metamorphism in a given geological system.展开更多
文摘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.
文摘The principle, analytical procedures and applications of Rb-Sr dating for minerals and rocks are described. Sr was separated by ion exchange resin 71-616 (1) (made in China) and inorganic ion-exchanger ZrP (prepared in our laboratory). All Sr determinations were made by isotope dilution and mass spectrometry. The concentration of Rb was analysed by flame spcetrophotometry. Rb-Sr ages of three micas (one from pegmatite from Inner Mongolia, and the other two are from granites from Kiangsi province) are in agreement with the K-Ar.rages and geological observations, indicating that the retention of radiogenic Sr^87 in micas is excellent. But systematic defferenee between K-Ar and Rb-Sr mica ages has been found in the other granite from Kiangsi province, suggesting possible eontaminations of radiogenic Sr^87 from magraas of different resources. Based on the isochrons formed by six total rocks and one feldspar, two metamorphie episodes of Jolmo Lungma series, Tibet, China (659±20, 17±6 m.y.) have been established. A similar conclusion has been reached by the U-Pb two stage model(modified eoncordia) ages, K-Ar dating as well as field investigations. It is believed that if sufficient geological data and suitable specimens are avilable, Rb-Sr isochron method may be a powerful toot to bring out multi-metamorphism in a given geological system.
