内蒙卓资-凉城地区古元古代变质过铝/强过铝花岗岩的形成温度:区域高温/超高温变质作用证据

内蒙古卓资-凉城地区孔兹岩系出露大量古元古代过铝/强过铝花岗岩。野外地质和岩石地球化学特征均显示它们存在两种类型。一类来自孔兹岩部分熔融,与孔兹岩呈渐变过渡关系并以含有粗大的石榴石、石英和堇青石斑晶为特征,出露广泛(A类);另一类花岗岩为花岗侵入岩体,矿物粒度相对细小,无矿物斑晶,其起源尚待进一步查证(B类)。电子探针(EPMA)分析石英单颗粒Ti含量并运用钛温度计进行计算,结果显示两类花岗岩石英Ti温度存在较明显差异:A类中石英钛温度多集中在680℃～800℃和>800℃间,而B类花岗岩多集中在650℃～750℃间,前者较后者普遍存在高的Ti温度值;两类花岗岩的锆饱和温度也存在差异,两者分别集中在820℃～890℃和700℃～780℃间。结果表明,来自孔兹岩部分熔融的A类花岗质岩石形成温度应高于900℃,B类花岗岩侵入体的石英和锆饱和温度均反映出正常花岗质侵入体结晶温度范围。由于A类花岗岩广泛分布在卓资-凉城地区,因此我们认为本区发生的超高温变质作用属于区域高温/超高温变质作用的结果。

FORMING TEMPERATURES OF PALEOPROTEROZOIC METAMORPHIC PERALUMINOUS-STRONG PERALUMINOUS GRANITES IN ZHUOZI-LIANGCHENG, INNER MONGOLIA: EVIDENCE FOR REGIONAL HIGH-ULTRA-HIGH TEMPERATURE METAMORPHISM

Paleoproterozoic peraluminous-strong peraluminous granites occurred in Zhuozi-Liangcheng area of Inner Mongolia can be classified into two types(type A and type B) in terms of their field occurrence and petrochemistry.Type A granitoid is apparently generated by partial melting of khondalites characterized by small amount of volume and gradual change of boundaries with its country rock.The mineral grains of type A granitoid are coarse with garnets,quartz and cordierites as phenocrysts.Type B granitoid is intrusive body with fine grain minerals,and no mineral phenocrysts,with its origin still unclear.In order to acquire their forming temperatures,the Titanium content of the single quartz is analyzed by means of EPMA,and the corresponding Ti temperature is calculated.It is indicated that some grains of quartz in the type A granitoid are formed at the temperature of over 800 ℃ and mainly in the range of 680 ℃~800 ℃,whereas,their zircon saturation temperatures(Tzr) vary from 820 ℃ to 890 ℃.The quartz grains from type B granitoid record their forming temperatures ranging from 650 ℃ to 750 ℃ with their zircon saturation temperatures concentrated in the range of 700 ℃~780 ℃.It is considered that the type A granites are resulted from partial melting of khondalites under high to ultra-high temperatures of over 900 ℃,and most of quartz form during cooling or re-equilibriam processes during granulite metamorphism.Type B granites reflect normal crystallized granitic intrusions.The fact that type A granitoids are widespread in the Zhuozi-Liangcheng area indicates that ultra-high temperature metamorphism plays a role in the regional high-ultra-high temperature metamorphism.