安康双龙桥碱性辉长杂岩中磷灰石和榍石的矿物成分研究

X射线衍射分析和化学成分研究表明,磷灰石为氟磷灰石,榍石成分中存在着的主要类质同象替代是(Fe~(3+)、Al)+(F,OH)~-=Ti~(4+)+O~(2-)。磷灰石和榍石是碱性辉长岩的REE、Ba、Zr等微量元素的主要载体;它们是在较高氧逸度的条件下结晶的。磷灰石的Sr同位素特征说明形成双龙桥碱性辉长杂岩的物质来源于上地幔。

A STUDY OF MINERAL COMPOSITIONS OF APATITE AND SPHENE IN SHUANGLONGQIAO ALKALI GABBRO COMPLEX IN ANKANG

The apatite and sphene are important accessory minerals in Shuanglongqiao alkali gabbro complex in Ankang. The mincralogical study indicates that apatite is fluorapatite and the main substitution of chemical composition of sphene is (Al+Fe~(3+))+(F,OH)~- = Ti~(4+)+O~(2-).The apatite and sphene contain high REE, Zr, Ba, Th, Ta, etc. Their REE abundances are about 3500ppm for apatite and 5000ppm for sphene. The (La/Yb)cn ratios are 37 and 20 respectively. All the characteristics show that the apatite and sphene arc the main carriers of REE in alkali gabbro complex especially the latter. The fo_2 in formation of apatite and sphene that primary magma of alkali gabbro complex is derived form the upper mantle.