西大别高压-超高压片麻岩中电气石化学特征

报道了大别山西段高压、超高压片麻岩中电气石矿物化学特征.所研究含电气石片麻岩为深色、呈夹层或透镜体状分布于广泛的浅色片麻岩中,主要由石榴石、黑云母、斜长石、石英、角闪石和钛铁矿组成,少量矿物有多硅白云母、金红石、绿泥石、绿帘石和磷灰石,电气石零星分布.电子探针分析结果表明,电气石化学成分贫铝、贫钙、富镁,为镁电气石；晶体具有弱成分环带,从核部到边缘呈钙增加、钠减少的趋势.根据电气石成分与成岩环境图解,电气石形成于变泥质岩和变砂质岩环境,与片麻岩产出地质环境相一致.根据电气石化学成分确定其变质温度和变质压力,目前仍然需要积累更多资料进行论证.

Chemistry of the tourmaline in the HPUHP gneisses from the western Dabie Mountain central China

It is reported that the mineralogic chemistry of the tourmalines in the high-pressure (HP) and ultrahigh-presure (UHP) gneisses from the western Dabie Mountain. The tourmaline-bearing gneisses are dark-colored and occur as interlayer or lentoid mass in the extensive light-colored gneisses. They are mainly composed of garnet, biotite, plagioclase, quartz, amphibole and ilmenite, and in the minor of phengite, rutile, chlorite, epidote and apatite, while the tourmaline crystals are scattered. By the electron microprobe analysis, the tourmalines are poorer in aluminum and calcium, richer in magnesium, and belong to dravite; their crystals show weak compositional zonation with calcium increase and sodium decrease from core to rim. In the diagram of tourmaline composition and their genetic environments, the tourmalines are formed in the metapelites and metapsammites, which are consistent with the geologic setting of the gneisses. As for determination of the temperature and pressure in metamorphic rocks by the tourmaline composition, more information and discussion are still necessary at present.