冀北甲山正长岩的矿物学、地球化学及Sr-Nd同位素特征  

Mineralogy,Geochemical and Sr and Nd Isotopic Characteristics of the Jiashan Syenite in Northern Hebei

作　　者：杨富全[1] 吴海[2] 刘晓文[2] 夏浩东[2] 马伯永[3] 邓会娟[2] 左文喆[4] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]国土资源部实物地质资料中心,河北燕郊065201 [3]中国地质科学院地质研究所,北京100037 [4]中国地质大学水资源与环境学院,北京100083

出　　处：《现代地质》2005年第4期522-530,共9页Geoscience

基　　金：国家自然科学重点基金项目(40132020);国土资源部国土资源大调查项目(DKD2001008)

摘　　要：甲山岩体形成于早白垩世晚期,可划分为3个单元。电子探针分析结果表明,碱性长石主要为Na-正长石和歪长石,少量为正长石;角闪石主要为钙角闪石中的铁浅闪石,少数为铁角闪石和铁阳起石;单斜辉石属钙铁辉石和普通辉石。化学成分上,该岩体富S i、全碱、全Fe、REE、Th、Ga、Nb、Zr、H f,贫Mg、Ba、Sr、Ti,Cr、Co、N i、V等过渡元素亏损,富轻稀土,中等铕负异常,具有A型花岗岩的特点。甲山正长岩的N(87Sr)/N(86Sr)初始比值ISr=0.701 41~0.707 41,εNd(t)值为-2.27^-5.58,表明岩浆为富集的大陆岩石圈地幔部分熔融形成。岩石圈的拆沉和减薄作用是引发岩石圈地幔部分熔融的原因之一,岩石圈地幔的富集作用可能发生在中元古代晚期。The Jianshan pluton was emplaced in the late Early Cretaceous, which can be divided into three rock units. The analytical results of electron-microprobe show that the alkali feldspars are mainly Na-orthoclase and anorthoclase, with minor orthoclase, the amphiboles of the Jiashan pluton are ferro-edenite with minor ferrohornblende and ferro-actinolite, and the clinopyroxene includes hedenbergite and augite. Geochemically the Jiashan syenite is rich in Si, alkalis, Fe, REE, Th, Ga, Nb, Zr and Hf, poor in Mg, Ba, Sr and Ti, and depleted in transition elements such as Cr, Co, Ni, and V, and is enriched in light REE with a moderate Eu negative anomaly, which show that the Jiashan syenite belong to an A-type granite. The STSr/S6Sr initial ratios of the rock ranging from 0. 701 41 to 0. 707 41 and the end（t） values of -2. 27 to -5. 58 indicate that the magma was derived from partial melting of an enriched subcontinental lithospheric mantle. Delamination or lithospheric thinning probably caused the partial melting of the enriched subcontinental lithospheric mantle. Nd depleted mantle model age implys that mantle enrichment beneath Yanshan area may occur in the late Mesoproterozoic.

关 键 词：正长岩 锶-钕同位素组成 地球化学 岩石成因 甲山 冀北 

分 类 号：P588.1[天文地球—岩石学] P584[天文地球—地质学]