冀北赤城二堡子片麻状角闪二长岩的锆石SIMS U-Pb年龄及其地质意义  

ZIRCON SIMS U-Pb DATING OF ERBUZI AMPHIBOLE MONZONITE IN CHICHENG COUNTY,NORTH HEBEI AREA AND ITS GEOLOGICAL IMPLICATION

作　　者：商光锐 倪志耀[1] 刘瑶[1] 张虹 王阳阳 Shang Guangrui;Ni Zhiyao;Liu Yao;Zhang Hong;Wang Yangyang(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]成都理工大学地球科学学院

出　　处：《矿物岩石》2019年第3期32-41,共10页Mineralogy and Petrology

基　　金：国家自然科学基金（41272087,41072050,40472041)

摘　　要：运用岩相学研究理论和元素地球化学研究理论,针对冀北赤城二堡子片麻状角闪二长岩,进行岩相学(4件样品)和地球化学分析(4件样品),结果表明:角闪二长岩的矿物成分为斜长石(30%~35%)、碱性长石(25%~30%)、角闪石(15%~20%)、石英(10%~15%)和黑云母(5%~10%)等。岩石中w(SiO2)介于60.16%~62.16%之间,w(K2O+Na2O)为8.56%~8.82%,稀土总量较高(ΣREE为246.30×10-6~317.76×10-6),(La/Yb)N值为28.18~42.79,具有轻稀土富集、重稀土亏损的分配模式,Eu异常(Eu/Eu*值为0.90~1.03)及Ce异常(Ce/Ce*值为0.91~0.98)均不明显,富集大离子亲石元素(如Ba,Rb,Sr和Th等)及轻稀土元素(如La,Ce和Nd等),亏损高场强元素(如Nb,Ta,Zr和Hf等)。角闪二长岩的锆石SIMS U-Pb年龄为243.1Ma±1.8 Ma,锆石的Th/U比值为0.709~1.258,表明其形成于三叠纪,应该是中生代印支期岩浆作用的产物,这是赤城地区确定的第二个印支期中酸性侵入岩体,其形成可能与赤城-崇礼断裂带在印支期重新活动有关。赤城印支期角闪二长岩体的确定表明赤城、崇礼地区存在印支期(~239Ma^243Ma)岩浆-变质-构造热事件,这对于冀北大地构造演化特征的确定具有重要的指示意义。4samples of gneissic amphibole monzonite from Erbuzi of Chicheng County in northern Hebei Province are studied by means of geochemistry and petrography.Perological study reveals that the gneissic amphibole monzonite consists of plagioclase(30%~35%),alkali feldspar (25%~30%)and minor amphibole (15%~20%),quartz(10%~15%)and biotite (5%~ 10%).The analyzed amphibole monzonite samples display intermediate composition with w(SiO2) ranging from 60.16%to 62.16% and w(K2O+Na2O)from 8.56%to 8.82%.REE pattern is characterized by LREE-enrichment with chondrite-normalized(La/Yb)Nof 28.18~42.79and total REEs of 246.30×10^-6~317.76×10^-6,showing no obvious Eu and Ce anomaly and with the Eu/Eu*values of 0.90~1.03,and with Ce/Ce*values of 0.91~0.98.The primitive mantlenormalized trace element pattern shows enrichment in LILES,such as Ba,Rb,Sr and Th,and in LREE,such as La,Ce and Nd,deplete in HFSES,such as Nb,Ta,Zr and Hf.Zircon SIMS isotopic dating for one amphibole monzonite sample yields a weighted mean age of 243.1 Ma±1.8 Ma with the Th/U value of 0.709~1.258,which is interpreted as the magmatic crystallization age of the amphibole monzonite and considered as the Triassic magmatic thermal event related to activity of Chicheng-Chongli fault during the Mesozoic.It is the second Indosinian intermediate-acid pluton which has been confirmed within Chicheng County in addition to the Bingshanliang granitic pluton with the ages of 228Ma^231Ma.The confirmation of Indosinian amphibole monzonite provides reliable evidence for constraining the Indosinian(~239Ma^243Ma)magmatic-metamorphic- thermal event in the Chicheng and Chongli Counties,and for the understanding of tectonic evolution of north Hebei area.

关 键 词：岩石学 地球化学 锆石SIMS U-PB定年 角闪二长岩 冀北赤城 

分 类 号：P597.3[天文地球—地球化学] P588.122[天文地球—地质学]