摘要
新疆阿尔泰可可托海 3号伟晶岩脉 ,由一陡倾斜的巨大岩钟和缓倾斜的板状体联合组成 ,总体形态似一实心草帽。其空间分带十分明显 ,自外向内可依次划分出如下九个共生 -结构带 :Ⅰ文象、变文象伟晶岩带 ;Ⅱ糖粒状钠长石带 ;Ⅲ块状微斜长石带 ;Ⅳ白云母 -石英带 ;Ⅴ叶钠长石 -锂辉石带 ;Ⅵ石英 -锂辉石 (-叶钠长石 )带 ;Ⅶ白云母 -薄片状钠长石带 ;Ⅷ锂云母 -薄片状钠长石带 ;Ⅸ石英和微斜长石核。根据伟晶岩各共生 -结构带的时空关系、矿物的多世代性和矿物中的包裹体等特征 ,从岩浆 -热液演化的角度 ,探讨了伟晶岩的成因问题 ,认为 :Ⅰ、Ⅲ带和部分Ⅱ、Ⅳ带主要是富水但水不饱和的伟晶岩浆直接结晶的产物 ;Ⅴ、Ⅵ、Ⅶ带是在晶体相、熔体相和流体相三相并存的条件下 ,即岩浆—热液过渡阶段结晶形成的 ;Ⅸ带是在热液早阶段从高温富硅酸盐溶质的超临界流体中结晶出来的 ;Ⅷ带和部分Ⅱ、Ⅳ带则是热液交代的产物。但交代流体不是从深部外来 ,而是从伟晶岩浆体系本身在分异演化过程中发生液相分离的结果。
The Koktokay No 3 Li Be Ta Nb Cs bearing pegmatite dyke of the Upper Paleozoic age is located in the Altai Caledonian Hercynian fold belt, Xinjiang Autonomous Region, China It consists of two major parts: a gently dipping “plate”, and a steeply dipping cupola protruding from the plate upwards The overall shape of the dyke looks like a solid hat The Koktokay pegmatite cupola is emplaced in the amphibolitized gabbro and characterized by a well developed internal zonal structure From the border wall inwards the following 9 mineralogical-textural zones can be subdivided: Ⅰ Graphic and pseudo graphic pegmatite zone; Ⅱ Saccharoidal albite zone; Ⅲ Blocky alkali feldspar zone; Ⅳ Muscovite-quartz zone; Ⅴ Cleavelandite-spodumene zone; Ⅵ Quartz-spodumene (-cleavelandite) zone; Ⅶ Thin sliced albite-muscovite zone; Ⅷ Lepidolite-thin sliced albite (-pollucite) zone; Ⅸ Blocky quartz and microcline core Studies on the melt inclusions, fluid-melt inclusions and fluid inclusions in the minerals of pegmatite provide important clues in judging the magmatic-hydrothermal evolution history for the pegmatite formation The quartz, microcline, garnet and beryl from zones Ⅰ and Ⅲ contain melt inclusions which are homogenized at the temperature range of 610℃～900℃ The spodumene, beryl and quartz from zones Ⅳ-Ⅶ contain fluid-melt inclusions and fluid inclusions The crystal phases in the fluid-melt inclusions comprise albite, quartz, spodumene, beryl and pollucite etc The coexisting fluid inclusions in these minerals are of H 2O-CO 2-NaCl character, with Th of 310℃～420℃ The salinities are high (with NaCl and/or KCl crystal) or moderate (10%～18%) The quartz from core zone contains only fluid inclusions, with Th of 300℃～320℃ and salinities of 5%～12% All above mentioned temperature measurements are not pressure corrected The formation pressures are estimated as 3 2～1 5kb Based on the zonal distribution and textural relationship of mineral assemblages, multiple generations of rock forming and rare metal minerals, as well as the features of inclusions and their thermometric data etc, it is interpreted that the zones Ⅰ, Ⅲ and partly Ⅱ、Ⅳ were crystallized from the volatile undersaturated silicate melt; zones Ⅴ, Ⅵ and Ⅶ were crystallized from the volatile oversaturated rare metal rich residual silicate melt at the magmatic-hydrothermal transition stage where the residual melt phase, silicate crystal phase and exsolved fluid phase coexist The blocky quartz and microcline of zone Ⅸ might be directly crystallized from the high temperature supercritical hydrothermal solution enriched in silicate solute The zone Ⅷ and partly zones Ⅱ and Ⅳ might be considered as metasomatic units However, the metasomatizing hydrothermal solutions were derived from the pegmatitic residual magma system itself during its crystallization and evolution, but not from the outside environment [KH2D][WT5HZ]
出处
《高校地质学报》
CAS
CSCD
2000年第1期40-52,共13页
Geological Journal of China Universities
基金
国家自然科学基金!(编号 495 73185
498730 17)
中国有色金属工业总公司基金资助
关键词
伟晶岩
空间分带
岩浆-热液演化
岩石成因
Altai
pegmatite
internal zonal structure
multiple generations of minerals
fluid inclusions
magmatic-hydrothermal evolution
