新疆阿尔泰高级变质带中淡色花岗质脉体的特征及成因模拟  

Characteristics and petrogenetic simulation of leucogranitic veins in the Altay high-grade metamorphic zones, Xinjiang

作　　者：邱林[1] 魏春景[1] 娄玉行[1] 田伟[1] 

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871

出　　处：《岩石矿物学杂志》2007年第1期27-34,共8页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目(40525006;40372032)

摘　　要：在新疆阿尔泰地区的高级变质带中广泛发育着一系列规模不等的透镜状和条带状的浅色脉体，主要有含Al2SiO5的淡色花岗岩脉、白云母斜长花岗岩脉和白云母二长花岗岩脉。主量元素分析表明这3类脉体的A／CNK=1．1～2．14，属于S型花岗岩。从白云母二长花岗岩脉→白云母斜长花岗岩脉→含Al2SiO5的淡色花岗岩脉，SiO2的含量增高，Al2O3、Na2O、K2O的含量降低。在NKFMASH体系中的pT视剖面图上进行相平衡分析和熔体成分计算表明，含A12Si05的浅色花岗岩脉和白云母斜长花岗岩脉的熔体形成与蓝晶石型变质带的抬升降压过程有关，其熔融温度没有超过白云母脱水熔融反应，并且含Al2SiO5的淡色花岗岩脉不是由生成的熔体直接结晶形成的，而需要经历一定的碱性组分随流体迁移丢失；白云母二长花岗岩脉的熔体形成主要以增温为主，并与白云母脱水熔融反应有关。十字石的脱水熔融反应对熔体形成有明显贡献。A series of leucogranites occur in lentieular and banded forms in the Altay high-grade metamorphic zone, Xinjiang. According to their mineral assemblages, these leucogranites can be divided into three groups： Al2SiO5-bearing leucogranites, muscovite-plagioclase leucogranites and muscovite monzo-leucogranites. An analysis of major elements shows that these leucogranites belong to S-type with A/CNK being 1.1 -2.14. From the muscovite monzo-leucogranites through muscovite-plagioclase leucogranites to Al2SiO5-bearing leucogranites, SiO2 contents increase and Al2O3, Na2O and K2O contents decrease. The phase relations in pT pseudosection for the NKFMASH system and the calculation of melt composition at different pressures and temperatures show that the melts of Al2SiO5-bearing and muscovite-plagioclase leucogranites might have originated from an uplifting process of the kyanite-type metamorphic zone, with no relation to the muscovite dehydration-melting reaction. Moreover, the Al2SiO5-bearing leucogranites were probably not directly crystallized from the melt, but had to do with some losses of alkaline components through fluids. The muscovite monzo-leucogranites probably originated from a heating process through the muscovite dehydration-melting reaction. The modeling of phase relations also indicates that the staurolite dehydration-melting reaction must have played a very important role in the melt formation.

关 键 词：深熔作用 淡色脉体 变质相平衡 THERMOCALC 阿尔泰造山带 

分 类 号：P588.3[天文地球—岩石学] P588.121[天文地球—地质学]