摘要
中美洲火山弧是洋-陆俯冲带火山作用的典型代表,由科科斯板块向东俯冲到加勒比板块之下而形成。本次对尼加拉瓜境内中美洲火山弧康塞普西(Concepción)火山、马德拉斯(Maderas)火山和马萨亚(Masaya)火山采集的样品进行了岩石学和地球化学研究,分析熔岩内部的显微结构,统计熔岩内斜长石斑晶大小分布(CSD)特征,利用温压计估算岩浆房的温压条件,讨论三座火山岩浆演化过程及岩浆活动特征。结果显示三座火山岩样品显示典型的岛弧火山岩特征,岩浆来自受到科科斯板块流体交代的MORB型亏损地幔的部分熔融。康塞普西和马德拉斯火山岩全岩成分相似,范围很大,从玄武质演化到了粗安质,它们的稀土和微量元素标准化曲线相似。两火山熔岩的岩相学特征相近,在基性岩和中性岩中均含有自形的钙长石质斜长石。推测钙长石来自捕获的堆晶辉长岩,钙长石的混入导致统计的斜长石斑晶CSD曲线呈上凹形。计算它们的岩浆平衡温度和压力与岩浆SiO2含量呈负相关,岩浆平衡温度1039~1138℃,平衡压力1.8~9.7kbar,对应岩浆深度6.6~35.4km。马萨亚火山岩样品均为玄武岩,其全岩和斑晶内的FeO含量明显比康塞普西和马德拉斯火山中的FeO含量高,未见钙长石质斜长石,其轻稀土元素含量低,Nb和Ta强烈负异常,87Sr/86Sr比值略高与其他两座火山,岩浆部分熔融程度更高。
The Central American volcanic arc is a typical example of the volcanism of the subduction zone between the ocean and continent,formed by the eastward subduction of the Cocos plate under the Caribbean plate.Samples were collected from three volcanoes,Concepción,Maderas and Masaya,in the Central America volcanic arc in Nicaragua.Petrology,chemical composition,texture,crystal size distribution(CSD)of plagioclase,magma temperature and pressure of volcanic rocks were studied to investigate the magma evolution and magmatic activity before eruption.The results show that samples of volcanic rocks show the characteristics of typical island-arc volcanic rocks,and the source region is derived from the partial melting of the MORB-type depleted mantle,which is fluid metasomatism of the Cocos plate.The lavas from Concepción and Maderas have a similar and wide compositional range,and the magma evolved from basalt to trachyandesite.Their chondrite-normalized REE variation patterns and spider diagrams of primitive mantle-normalized trace element abundances have nearly same trends.They also have similar petrographic features,and there are euhedral anorthite crystals in basic and intermediate rocks,which are speculated to come from the captured cumulate gabbro.The mixing with anorthite crystals caused the plagioclase CSD curves concave-up.The calculated equilibrium temperatures and pressures are negatively correlated with the content of SiO2 in the magma,temperatures are 1039~1138℃,and pressures are 1.8~9.7kbar,corresponding to a depth of 6.6~35.4km.Samples from Masaya volcano are all basalt in composition.The FeO contents in bulk rocks and phenocrysts are all higher than those in the other two volcanoes.There are no anorthite crystals in Masaya lavas.The contents of light rare earth elements are lower,and Nb and Ta are strongly negative anomaly.The ratio of 87Sr/86Sr is slightly higher than those of the other two volcanoes.Thus,the degree of magma partial melting of Masaya volcano is higher.
作者
于红梅
白翔
魏海泉
许建东
陈正全
YU HongMei;BAI Xiang;WEI HaiQuan;XU JianDong;CHEN ZhengQuan(National Observation and Research Station of Jilin Changbaishan Volcano,Institute of Geology,China Earthquake Administration,Beijing 100029,China;Key Laboratory of Seismic and Volcanic Hazards,China Earthquake Administration,Beijing 100029,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2020年第7期2177-2196,共20页
Acta Petrologica Sinica
基金
中国地震局地质研究所基本科研业务专项(IGCEA1712、IGCEA1904)
国家自然科学基金项目(41272235)联合资助。
