赣杭构造带相山火山侵入杂岩的岩浆演化特征--来自斜长石和黑云母的化学成分研究

Magmatic evolution characteristics of Xiangshan volcanic-intrusive complex from the Gan-Hang Belt:Studies on the mineral chemistry of plagioclase and biotite

黑云母、斜长石等矿物可作为寄主岩石的岩浆演化的指示剂。本文借助电子探针微区分析技术,通过对赣杭构造带中相山盆地火山侵入杂岩中这些矿物的化学组成进行定量分析发现:碎斑熔岩、花岗斑岩及石英二长斑岩的斜长石环带不明显,并且主要是中长石;石英二长斑岩中黑云母矿物成分为镁质黑云母和铁质黑云母,化学成分更为接近研究区镁铁质微粒包体中黑云母的成分,而碎斑熔岩及花岗斑岩中黑云母的镁含量较低。结合黑云母、斜长石矿物的化学特征及前人的工作研究,相山碎斑熔岩和花岗斑岩的物质来源主要是壳源,没有明显地幔物质的加入,而石英二长斑岩有一定量的地幔物质的加入,并且这个地幔物质的加入发生在石英二长斑岩的黑云母开始结晶之前。

Biotite and plagioclase can be the indicator of magma evolution. We analyze the chemical compositions of these minerals which crystallized from the Xiangshan volcanic-intrusive complex in the Gan-Hang Belt,SE China,through EPMA method. The study shows that the plagioclase from the porphyroclastic rhyolitic lava,granitic porphyry and quartz monzonite porphyry is andesine without zoning structure. The magnesio-biotite and ferri-biotite which are found in quartz monzonite porphyry are similar to that in the mafic microgranular enclaves（ MMEs） in the classification diagram for biotite. But the biotite from porphyroclastic rhyolitic lava and granitic porphyry has lower Mg content than the biotite from quartz monzonite porphyry. Combined the characteristics of biotite and plagioclase with former research data,it shows that the porphyroclastic rhyolitic lava and granitic porphyry were derived from crustal material,without significant addition of mantle-derived magma. The higher Mg contents of biotite from quartz monzonite porphyry indicate an involvement of mantle-derived magma,and the crust-mantle mixing occurred before the crystallization of biotite.