秦岭东江口和柞水花岗岩的矿物成分特征及其形成的温压条件

Mineral composition and temperature-pressure conditions of Dongjiangkou and Zhashui granites in the Qinling Mountains

对南秦岭东江日和柞水岩体的似斑状花岗岩类进行了偏光显微镜观察和电子探针（EPMA）、扫描电镜（SEM）矿物分析，在此基础上对岩体形成的温压条件进行了讨论。结果表明，这两种岩石的主要造岩矿物为石英、斜长石（更～奥长石）、钾长石、镁角闪石和镁质黑云母，副矿物为锆石、榍石、磁铁矿和磷灰石等。岩浆成分的变化可能是矿物环带结构和环斑结构形成的原因之一。东江口和柞水花岗岩类锆石结晶时岩浆温度为759～784℃，平均771℃；稀土元素在岩浆中饱和时岩浆的温度为741～800℃，平均773℃；斜长石结晶时岩浆温度624～641℃，平均632℃；角闪石结晶时岩浆温度610～668℃，平均632℃。岩体侵位深度约5．8km，压力约1．77×100Pa，具有壳幔混源的特点。

Dongjiangkou and Zhashui granites are located in southern Shangdan fault of the south Qinling Mountains. Samples were collected from porphyroid granites. The systematic mineralogical characteristics of Dongjiangkou and Zhashui rocks and the rocks-forming p-T estimates were investigated by means of petrological observation, electron microprobe analysis and scanned electron microscope （SEM）. The results demonstrate that porphyroid granodiorite and porphyroid granite are composed of quartz, plagioclase （oligoclase）, K-feldspar, magnesiohornblende and magnesian biotite, whereas the accessory minerals include zircons, sphene, magnetite and apatitc. It can be inferred that the variations of magma composition account for the zoned structure and ra- pakivi texture in minerals. Zircon in Dongjiang and Zhashui granitoids crystallized when the magma temperature varied in the range of 759-784℃ （771℃ on average）. The rare earth elements were saturated in magma when its temperature reached 741--800℃ （773℃ on average）. Plagioclase crystallization when the magma tempera- ture varied from 624℃ to 641℃ （632℃ on average）, whereas hornblende crystallized when the magma temperature was in the range of 610- 668℃ （63YC on average）. The probable emplacement depth of the rocks was -5.8 kin, with the corresponding pressure being about 1.77 × 10^8 Pa.