胶东群部分熔化实验及其对花岗岩成因的指示  

Partial melting experiments of Jiaodong Group and their implication for the origin of the granites

作　　者：曲晓明[1] 王鹤年[1] 饶冰[1] 

机构地区：[1]南京大学地球科学系,江苏南京210093

出　　处：《地球化学》2000年第2期153-161,共9页Geochimica

基　　金：国家教委博士点基金;南京大学内生金属矿床成矿机制研究国家重点实验室开放基金

摘　　要：以胶东群组合样及胶东群的主要岩性单元黑云变粒岩和黑云斜长片麻岩为初始物，在 １５０ ＭＰａ、水过饱和 条件下研究了胶东群地层在不同温度下（７４０ ℃，７７０℃，８１０℃，８５０℃）的熔融行为及熔体成分的演变。结果表明， 不同初始物的初熔温度、熔融程度及熔体产率差别很大，明显受源岩成分（ＳｉＯ_２－Ｋ_２Ｏ－Ｎａ_２Ｏ的相对比例）控制。黑云斜 长片麻岩由于ＳｉＯ_２：Ｋ_２Ｏ：Ｎａ_２０的比例（７３．０６：３．９２：２．５８）与花岗岩体系“最低点熔体”的比例（７９．２４：４．５７： ４．２５）接近，因而初熔温度低（在７４０～７５０℃之间），熔融程度高（８５０℃时为７５％左右）。黑云变粒岩（６３．３９：１．９９： ５． １１）则由于 ＳｉＯ_２和 Ｋ_２Ｏ质量分数明显降低，偏离“最低点熔体”较远，初熔温度升高（接近 ７７０ ℃），熔融程度大大降 低（８５０ ℃时为３０％左右）。对贫钾的源岩来讲，黑云母通过熔融分解向周围基质提供钾质，对源岩熔融具有明显的 促进作用。分熔熔体都含少量的刚玉标准分子（０．１０％～１．８４％），属弱过铝质。在Ｑ－Ａｂ－Ｏｒ图上，胶东群在８１０℃条件下熔融产生的熔体与尚庄斑状花岗岩成分一致，熔融程度约为３０％；?Using composite sample of Jiaodong Group strata as well as the biotite granulitite and biotite plagiogneiss both of which are the main components of Jiaodong Group as initial materials, melting behavior and melt composition variation of Jiaodong Group strata was experimentally studied at different temperatures (74℃, 770 ℃, 810 ℃, 850 ℃ ) under 150 MPa and water-saturated condition. The results show that initially melting temperature, melting degree and melt productivity of various initial materials are very different from each other and are strictly controlled by compositions of source rocks. Due to its composition (SiO_2: K_2O: Na_2O = 73. 06: 3. 92: 2. 58) being close to that (79. 24: 4. 57: 4. 25) of 'minimum melt' in granite system, biotite plagiogneiss has a low initially melting temperature (from 740 ℃ to 750℃ ) and a high melting degree (about 75% at 850 ℃ ). In contrast, biotite granulitite has a high initially melting temperature (near 770 ℃ ) and a sharply decreased melting degree (- 30% at 850 ℃ ) due to its composition (SiO_2 K_2O: Na_2O = 63. 39: 1. 99: 5. 11 ) far deviated from 'minimum melt'. Biotite show notable promoting function for melting of source rocks through releasing K to surrounding matrix during its melting decomposition. The partial melts generally contain a small amount of normative corundum (0. 10% - 1. 84% ) and appear weakly peraluminous. In Q-Ab-Or diagram, the melt produced in 810 ℃ melting of Jiaodong Group is consistant with Shangzhuang porphyritic granite and has a melting degree of about 30%. Meanwhile, melting of Jiaodong Group at 850 ℃ gives melt being very close to Linglong gneissic granite and having a melting degree of about 40%.

关 键 词：胶东群 熔化实验 花岗岩 岩石成因论 

分 类 号：P588.121[天文地球—岩石学] P599[天文地球—地质学]