攀西地区钾质煌斑岩岩石地球化学及源区构造环境分析

分布于攀西及邻近地区的煌斑岩主要为云辉正煌岩-黑云正煌岩、白榴橄榄云辉岩、透辉云煌岩,常量元素特征表明岩石属于碱性系列、钾质钙碱性煌斑岩;过渡元素分配模式为幔源岩石的"W"型、不相容元素分配模式为大离子亲石元素和高场强元素富集的"驼峰"型、稀土元素分配模式为"右倾"的轻稀土富集型,表明该区煌斑岩为交代富集地幔部分熔融的产物.Ta-Nb-Ti负异常分配模式说明源区煌斑岩具有的交代富集地幔可能和板块俯冲有关.源区大地构造环境为活动大陆边缘的陆缘岛弧或陆缘火山弧区.

STUDY ON PETRO-GEOCHEMICAL CHARACTERISTICS OF THE POTASSIC LAMPORPHYRES AND THE TECTONIC SETTING OF MAGMATIC SOURCE REGION IN PANXI AREA

There are a lot of potassiic lamporphyres disperseing over Panxi and its neighboring area. They are mainily minettes and named further Lc-Ol-Cpx-minette, La-Cpx-minette and Bio-Cpx-mintette. Major elements show that lamporphyres are alklic series and potassic cala-alkaline lamporpyres. Chondrite-normalized transition element pattern of lamporpyres is "W" type which suggest the rocks are mantle-derived. The lamporphyres are riched in large iron lithophile elements, high field strength elements and rare earth element. All the characteristics as noted above suggest that the source of the lamporphyres is imcompatible element-enriched metasomatic mantle. The tectonic setting of magmatic source region is active continental margin. (Ta-)Nb-Ti negative anormaly in potassic lamporphyres indicate source region of magma used to be affected by the subduction of ocean plate. The subduction may occur before the formation of the magma.