华南诸广山花岗岩体中段锶氧铅硫同位素研究

STUDY ON STRONTIUM, OXYGEN,LEAD AND SULPHUR ISOTOPES OF GRANITIC BODY IN ZHUGUANGSHAN, SOUTH CHINA

诸广山中段花岗岩体的Rb-Sr同位素等时线年龄为215.23Ma,属印支期。锶同位素初始比值为0.7229,Rb/Sr比值为1.09～15.6,初始^(206)Pb/^(204)Pb(18.216～19.042)和^(207)Pb/^(204)Pb(15.605～15.801)较高。全岩δ^(18)O为10.6‰～12.4‰,δ^(18)O-^(87)Sr/^(86)Sr相关趋势呈水平方向展布。硫同位素绝大部分在零值左右摆动,从早到晚变化范围逐渐变小。这些表明岩体是源于上地壳的改造型花岗岩,并经过了岩浆阶段,且在早期岩浆岩基础上又经过了多次重熔演化。

The Rb-Sr isochronous age of granitic body in middle zone of Zhuguangshan is 215.23Ma. It belongs to Indo-China orogeny. The initial ^(87)Sr/^(88)Sr ratios of granitic body locate above increase line of continental crust. The Rb/Sr ratios are large and they change from 1.09 to 15.6. So it is clear that the rock-forming materials of granitic body come from continental crust. The whole rock oxygen isotope values of granitic body range from 10.6‰ to 12.4‰. On the diagram of δ^(18)O-^(87)Sr/^(88)Sr the correlation trend of granitic body extends in a horizontal direction. This makes it clear that the granitic body belongs to transformation type granite. The initial ^(208)Pb/^(204)Pb and ^(207)Pb/^(204)Pb ratios are rather large. They have the character of derivation from the upper crust. On the diagram of plumbotectonie model the initial ^(206)Pb/^(204)Pb and ^(207)Pb/^(204)Pb values locate between the evolution lines for orogenic belt and the upper crust indicating that the rock-forming materials of granitic body come from the upper crust. The calculated model age by lead isotopes neither fits the model of singular stage evolution nor fits the two stages evolution model. When the granitic body formed it was not contaminated by mantle materials. The sulphur isotopes of granitic body are near zero in most cases, and from early to late stages their variation range decreases. This implies that the granitic body passed the magma stage during which the sulphur isotopes had reached certain uniformity. The evolution and multifold remelting of granitic bodies are developed on the basis of the early igneous bodies,