摘要
滇西的临沧岩体(LG)与平和街岩体(PMG),是中国西南和东南亚巨型同碰撞岩基带最北段的两个岩体,出露面积共约11000km^2,具壳源(S型)花岗岩许多共性:①过铝质,ANKC接近于1.10(PMG为1.082;LG为1.106);②富钾质,Na/K比小于1.0(PMG为0.88;LG为0.95);③低的Sm/Nd比(PMG为0.17;LG为0.20);④高的Rb/Sr比(PMG为1.35;LG为1.56);⑤高的Sn丰度(PMG为13.7ppm;ILG14.6ppm);⑥高的锶初始比(PMG为0.7205;LG为0.7240);⑦负的ε~tNd值(LG为-12.6)等。根据二无锶混合模型,定量摸拟了这两个岩体的源区物质相当于70％～80％上部地壳与30％～20％下部地壳物质的混合物。根据Rb、Sr等微量元素在部分熔融中的行为计算,这一源区物质30％～35％熔融便形成平和街和临沧岩体的初始岩浆。
In the territory of SW China and SE Asia, there is a NS trending syn-collision type granite belt. At the northern end of this granite belt beginswith the Linchang granite body (LG) and the Pinhejie massive granite body(PMG)of west Yunnan. These two granite bodies of the exposed area of 11000km^2 have several features of crust-derived origin. They are:(1)Peralumious,with ANKC values about 1.10(1.082 for PMG; 1.106 for LG); (2) Rich in potashrelative to sodium, with Na/K ratios less than 1.00 (0.88 for PMG; 0.95 forLG); (3) Lower Sm/Nd ratio (0.17 for PMG; 0.20 for LG); (4) HigherRb/Sr ratio (1.35 for PMG; 1.56 for LG); (5) Enrichment in Sn (13.7ppmfor PMG; 14.6 for LG); (6) Larger initial Sr ratio (0.7205 for PMG;0.7240 for LG); (7) Negative ε_(Nd)~t value (-12.6 for LG) etc..The source materials for these two granite bodies are a mixtures of aboutthe 70%～80% upper continental crust plus the 30%～20% lower continentalcrust materials by modeling of mixing for two different Sr components.Themagmas for LG and PMG were generated from 30%～35% partial melting ofthis source materials based on the calculation for partial melting equationof Rb and Sr.
关键词
花岗岩
成岩模式
印支期
海西期
granite
Hercynian
Indosinian
petrogenetic model
Yunnan
