摘要
扬子地台西缘钾质煌麻岩的矿物组合中缺少钾碱镁门石、柱红石等富钾贫铝矿物，其辉石和白榴石富Ａｌ２Ｏ３，金云母贫ＴｉＯ２，透长石的Ｎａ２Ｏ含量高。全岩Ａｌ２Ｏ３高，Ｋ２Ｏ／Ａｌ２Ｏ３（＜０．７）低，（Ｇｄ／Ｙｂ）Ｎ低。岩体中含有二辉橄榄岩包体、镁铝榴石捕虏体晶。这些特点表明其岩浆源区的亏损程度低。此外，钾质煌斑岩明显亏损Ｎｂ、Ｔｉ，可能是与其源区经受过板块边缘活动影响有关。
There are a lot of potasslc lamprophyres along the western border of Yangzi Platform. On the latest information, they form the biggest potassic lamprophyre province in China. According to a classifical table proposaled by Lu(1991 ), the potassic lamprophyres in the researching area could be named Ol-Cpx-minette, Lc-Ol-Cpx-minette, Cpx-minette and LcCpx-minette.Compared with the lamproites,the cores of the phlogopite phenocrysts from the potassic lamprophyres are poor in TiO2(<2% ). Diopside in matrix and sanidine are relatively rich in Al2O3 and Na2O. The ratio of K/AI in leucite is quite low. No potassic richterite and peridrite have been found. As to bulk composition. potassic lamprophyres are rich in Al2O3 (9% on average), CaO (10%±) and with low ratio of K2O/Al2O3 (<0. 7). Low (Gd/Yb)Nvalue and Gt-Sp-lherzolote inclosions in some potassic lamprophyre pipes prove that the source region is less depletive than the one forming lamproites. Therefore, the differences btween two kinds of rocks are obvious. The potassic lamprophyres from the researchingg area are not lamproites.The trace element spider diagrams show Nb and Ti negative anomaly in potassic lamprophyres. The values of Sr isotope (0. 706 ~ 0. 704) of the magma imply that there are no strong crust contamination during the magma asent. Then,it is considered that source region of the magma usedd to be affected by the subduction of ocean plate. The subduction may occur before the formation of the magma.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1994年第3期248-260,共13页
Acta Petrologica Sinica
基金
国家教委博士导师基金
关键词
钾质煌斑岩
岩石学
煌斑岩
Lamproite
Potassic lamprophyres
Petrology
