内蒙卓资山地区深熔作用形成的石榴混合花岗岩

The Formation of the Garnet-bearing Migmatitic Granite in Zhuozishan Area, Inner Mongolia,China

内蒙古卓资山地区太古宙高级变质区中分布着一系列规模不等的混合花岗岩体 ,其产出严格受孔兹岩系层位控制。岩体中含有大量矽线石榴片麻岩残留体 ,二者界线模糊 ,具渐变过渡的特征。花岗岩中富含石榴石 ,具斑杂状构造 ,浅色组分 (熔体 )含量偏高 ,暗色组分 (难熔组分 )显著减少 ,但在残留体中 ,暗色组分有富集现象。岩石化学成分富铝Al2 O3含量 10 .6 1%～ 17.10 % ,A NKC =1.2 9～ 1.81;离子半径小、熔融活化度低的微量元素Cr、Ni、Cu、Co、V、Zr含量极低 ,而一些熔融活化度高、大离子半径的微量元素Sr、Ba含量明显偏高。HREE含量偏低 ,δEu具正异常 ;87Sr 86 Sr=0 .72 0 4 2～ 0 .72 933。形成混合花岗岩的温度为 735～ 785℃ ,压力范围可能为8.6～ 9.7Kb(1b =10 5Pa)。这一类独特的“石榴混合花岗岩” ,不是因熔融体占绝对优势的典型岩浆侵入结晶而成 ,而是孔兹岩系变质岩层就地深熔作用的产物。

There is a series of garnet bearing migmatitic granites in the Archean high grade metamorphic rock in Zhuozishan Area,Inner Mongolia. And they distrabute in khodalite strata, in which a lot of sillimanite garnet gneiss relicts can be found. The bound between the gneiss and the migmatitic granite is indistinct. The migmatitic granite mottled texture is rich in garnet, and leucosome is concentrated in the granite, melanosome in the relict. Al 2O 3(10.61%～17.10%) is high, A /NKC=1.29～1.18. Microelements Cr, Ni, Cu, Co, V. Zr are very low. But some elements with high activity and big ionic radius, such as Sr and Ba, appear higher. HREE is low too, with positive anomal Eu value. 87 Sr / 86 Sr=0.720 42～0.729 33. The temperature of the magmatitic granite formation is about 735～785℃. The pressure is 8.6～9.7 kb(1b=10 5 Pa). All above mentioned suggests the formation of the rock is not from magma intruding but in sita ana migmatization of khodalite series. the process may take place during the granlitic metamorphizm of Jining group in Mid Archean.