| 垭口片麻岩的主要岩石化学特征 |
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| 引用本文： | 吴根耀.垭口片麻岩的主要岩石化学特征[J].岩石学报,1990,6(1):82-91. |
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| 作者姓名： | 吴根耀 |
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| 作者单位： | 中国科学院地质研究所 北京 |
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| 摘 要： | 出露于川西滇中地区的垭口片麻岩及相应岩石是一套英云闪长质-奥长花岗质(为主)-花岗闪长质片麻岩(灰色片麻岩即TTG岩套)和花岗质片麻岩组合,后者可能是前者活化时遭受钾长石化的结果。其常量元素、过渡金属元素和稀土元素特征与早前寒武纪低铝型灰色片麻岩一致,是本区晚太古代结晶基底(花岗地体)。
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| 关 键 词： | 灰色片麻岩 低铝型 花岗质片麻岩 晚太古代基底 川西滇中地区 |
MAIN PETROCHEMISTRY FEATURES OF YAKOU GNEISS |
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| Wu Genyao.MAIN PETROCHEMISTRY FEATURES OF YAKOU GNEISS[J].Acta Petrologica Sinica,1990,6(1):82-91. |
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| Authors: | Wu Genyao |
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| Abstract: | Yakou gneiss distributed in the border region of Sichuan and Yunnan Province is the oldest basement rock of the area. Its relevants stretch northwards to Xichang and Mianning, West Sichuan and southwards to Yuanmou, Mouding and Xinping, Mid Yunnan. Perhaps it might extend down to North. Vietnam (Songchay Gneiss). The isotopic dating demonstrates that they might form during Late Archaean.
The gneiss is composed of trondhjemitic-tonalitic-granodioritic gneiss (gray gneiss) and granitic gneiss. The latter might result from reformation (potassium feldsparization) of the gray gneiss. The linear relations can be found between silica and other oxides of the gneisses. The decreasing Na_2O K_2O with increasing MgO can be observed in both cases. The relationships between Ca and K/Na ratio show a tonalite-trondhjemite trend in the gray gneiss, and a more typical calc-alkaline one in the granitic gneiss, respectively. The mineral controlling the change of Al_2O_3, Na_2O,. K_2O and CaO contents in gneiss is feldspar. The chemical composition and mineral assemblage of the gray gneiss reveal that they are compatible with gabbro-trondhjemite trend of Archaean TTG suite.
The gray gneiss belongs to the low-Al_2O_3 type. Compared with high-Al_2O_3 type, the contents of Al_2O_3, MgO, CaO, P_2O_5, Co and Sr are lower, while Zr, La, Ba, Rb and Th higher. Its REE distribution is characterized by slight Eu negative anomaly, different from the Eu positive anomaly in high-Al_2O_3 type gneiss. In addition, an increasing Y with increasing SiO_2 of the gneiss confirms the gray gneiss low-Al_2O_3 type. The REE pattern of the granitic gneiss, whose Al_2O_3 is as low as the tronhjemitic one, shows a clear Eu negative anomaly. |
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| Keywords: | Gray gneiss Low-Al_2O_3 type Granitic gneiss Early Precambrian basement West Sichuan and Mid Yunnan |
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