大兴安岭北部诺敏河地幔金云母及钾质地幔熔体研究  

Phlogopites and potassic melts in mantle xenoliths from Nuomin volcanic field,northern Great Xing’an Range

作　　者：隋建立[1] 李霓[1] 樊祺诚[1] 徐义刚[2] 

机构地区：[1]中国地震局地质研究所活动构造与火山实验室,北京100029 [2]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广州510640

出　　处：《岩石学报》2014年第12期3587-3594,共8页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40972048);同位素地球化学国家重点实验室开放基金联合资助

摘　　要：在大兴安岭北部诺敏河第四纪钾质火山岩携带的地幔捕虏体中,发现少量金云母矿物和富钾地幔熔体。金云母颗粒大小1~5mm,呈网脉状充填在橄榄石和辉石、石榴子石等地幔矿物间隙。电子探针研究表明地幔橄榄石、单斜辉石、斜方辉石和石榴石等矿物几乎不含钾质成分(K2O<0.01%),而金云母矿物成分具有高钾(K2O^10%)、高钛(Ti O25.41%~7.74%)的特点,暗示区域地幔钾的富集与金云母矿物有密切关系。地幔金云母的成因往往与富钾地幔流体/熔体的交代作用有关,在地幔捕虏体矿物反应边的硅酸盐熔体(囊体)中,发现富硅、富钾的熔体,K2O 4%~8%。结合前人地幔熔体研究,认为区域地幔经历了多期、不同成分地幔熔体的富集作用,其中富钾熔体对地幔钾质成分的富集起到重要作用。诺敏钾质火山正是富钾地幔部分熔融的产物,钾质熔体成分的来源可能与俯冲再循环的壳源物质有关。Phlogopites and potassic melts have been found in mantle xenoliths from Nuomin volcanic field, northern Great Xing＇ an Range; here we report the electronic microprobe （EMP） studies. The phlogopites are small, varying in 1 -5mm, and filled in small grains and veinlets among the mantle minerals. EMP analysis indicates that the olivine, orthopyroxene, clinopyroxene and garnet have very low potassium compositions （ K20 〈0. 01% ）, while the phlogopites have very high potassium （ K20 - 10% ） and high titanium （ TiO2 5.41% - 7.74% ）. This fact indicates that the mantle enrichment of potassium in Nuomin is closely concerned with phlogopite, which is one of the typical products of mantle metasomatism. Although the chemical compositions of silicate melts show a wild rang, there are some high-silicon and high-potassium melts （K20 4% - 8% ）. Then we can tell a story of mantle enrichment of potassium as that melts with different Si and K compositions enriched the mantle source, and high-K melts caused enrichment of potassium. The potassic magma in Nuomin is originated from partial melting of K-rich mantle, and this enrichment of potassium in Nuomin may be associated with recycled crustal materials.

关 键 词：诺敏河火山 地幔捕虏体 高钛金云母 钾质地幔熔体 钾质火山成因 大兴安岭北部 

分 类 号：P575.1[天文地球—矿物学] P588.14[天文地球—地质学]