摘要
大别造山带北缘晚中生代富钾火山岩分布在磨子潭 -晓天断裂以北的上叠式火山盆地中 ,主要为一套以钾玄岩 -粗安岩 -安粗岩 -粗面岩为主体的中偏碱性岩石组合 ,晚期出现少量碱性火山岩。化学成分上具有富碱、富钾、贫钛、氧化系数较高等特点。岩石的 Rb、Ba、Th、Pb等大离子亲石元素含量高 ,富轻稀土 ,L a/ Nb、Ba/ Nb及 L REE/ HREE比值高 ,并具有显著的Nb、Ti负异常和 Pb正异常 ,而铕异常则不明显。富钾火山岩的 ISr值较高 (=0 .70 872～ 0 .70 895 ) ,εNd(t)值显著偏低(= - 14 .6 2～ - 18.5 1)。根据对岩石产出动力地质背景及地球化学特征的综合分析 ,结合同位素组成的混合模拟 ,表明本区富钾火山岩最可能起源于受俯冲陆壳析出流体交代作用所形成的富集地幔 (EM )
The late Mesozoic potash-rich volcanic rocks in the northern margin of Dabie orogenic belt are distributed in superimposed-type volcanic basing north of the Mozitan-Xiaotian fault. These rocks mainly belong to a set of intermediate to alkaline rock association composed predominantly of shoshonite, trachyandesite, latite and trachyte. In the late volcanic eruption stage, minor alkaline volcanic rocks occurred there. Chemically they are characterized by enrichment in alkaline, potassium, poor in titanium, and have higher Fe2O3/(Fe2O3+FeO) ratios. These rocks also have high LILE (such as Rb, Ba, Th, Pb, etc.) and LREE concentrations, high La/Nb, Ba/Nb and LREE/HREE ratios, and display clearly negative anomalies of Nb, Ti and positive anomalies of Pb, but do not show obviously Eu anomalies. The I-Sr values of these potash-rich volcanic rocks are relatively high (= 0.70872 - 0.70895) and epsilon(Nd)(t) values of them are obviously low (= -14.62 similar to 18.51). Based on a comprehensive analysis of the geological setting and geochemical characteristics, and in combination with isotopic mixing modeling, it is concluded that these potash-rich volcanic rocks were most likely originated from the partial melting of enriched mantle (EM I), which was presumably a result of metasomatism by fluids from dehydration of the subducted continental crust materials.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2002年第3期319-330,共12页
Acta Petrologica Sinica
基金
国家自然科学基金资助项目 ( 4 9872 0 2 8)成果之一
国土资源部壳幔体系组成
物质交换及动力学开放实验室研究基金资助
