广西花山复式花岗岩体成因的锶、钕和氧同位素研究

Sr, Nd AND O ISOTOPE STUDIES ON THE GENESIS OF THE HUASHAN GRANITE COMPLEX

对广西花山复式花岗岩体进行了锶,钕和氧同位素的系统研究。结合地质学、岩石学和地球化学资料,认为花山复式岩体3个阶段的花岗岩类不是同一个母岩浆分异演化的产物,而是由不同时代,不同成因和不同物质来源组成的杂岩体:其中第一阶段为印支期壳-幔混合源同熔型或Ⅰ型,第二阶段为燕山早期壳-幔混合源同熔型或Ⅰ型,第三阶段为燕山晚期地壳来源改造型或S型。

The Huashan granite body of the Guangxi Autonomous Region is a magmatic compiex consisting of three stages of granitic rocks. For a long time it has been considered as the product of differentiation, evolution and multi-staged emplacement of consanguineous magma. This paper systematically studies the Sr, Nd and O isotopic geochemical characteristics of the complex. The Rb-Sr isochron ages, initial Sr isotope ratios (I. R.), St, Nd and O isotope compositions of these three stages of granitoids are given below: stage one, stocks of the Niumiao quartz-monzodiorite and the Tong'an quartz-monzonite, 210.5Ma, I. R. = 0.70597,∈_(Sr) = 3 — 28, ∈_(Nd) = (—2.3) — (—2.4), δ^(18)O = 8.4 — 8.6‰; stage two, Huashan mainbody batholith of biotite^- and hornblende-biotite-granite, 164.7 Ma, I. R. = 0.70703,∈_(Sr) = 32 — 38, ∈_(Nd) = (—2.5) — (—3.2),δ^(18)O = 8.7 — 10.9‰; stage three, stocks, apophyses and dykes of fine-grained granites, 129 — 121 Ma, I. R. = 0.71663 — 0.73033, ∈_(Sr) = 152 — 210, ∈_(Nd) = (—4.4) — (—5.0), δ^(18)O = 10.2 — 11.4‰.In combination with the geological, petrological and geochemcal data, it is believed that the Huashan magmatic complex consists of granitoids of different ages, different geneses, and different source ma(?)erials The granitoids of stage one are of the Indosinian (Triassic) syntectic type or ;Ⅰ-type, derived from a mixed mantle-crustal source and possibly formed by a differentiated mantle magma assimilated and contaminated with crustal materials; those of stage two are of the early Yanshanian (Jurassic) syntectic type or Ⅰ type, also derived from a mixed mantle-crustal source, and possibly formed by partial melting of predominantly sedimentary parental rocks.