广西合浦烟墩岭火山岩的K-Ar年代学和地球化学初步研究  

Preliminary study on K-Ar chronology, petrology and geochemistry of Yandunling volcanic rocks, Hepu county, Guangxi

作　　者：李霓[1] 樊祺诚[1] 王团华[1] 孙谦[1] 隋建立[2] 

机构地区：[1]中国地震局地质研究所,北京100029 [2]中国科学院地质与地球物理研究所,北京100029

出　　处：《岩石学报》2007年第6期1423-1430,共8页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40572044);中科院广州地球化学所同位素年代学和地球化学重点实验室合作基金项目(GIGIso-06-01);南京大学内生金属矿床成矿机制研究国家重点实验室(12-06-05)以及南京大学"研究生访学项目"联合资助.

摘　　要：广西合浦县烟墩岭火山是一座第四纪小型中心式喷发的火山,是我国华南火山在第四纪喷发活动的代表之一。烟墩岭火山岩岩性为粗面玄武岩,Mg~#值(59～69)中等偏高,而钛和碱质成分相对较高。烟墩岭火山岩及周边的烟头岭样品的稀土含量较为稳定,配分型式极其相似,几乎一样,REE 丰度模式呈稍陡的向 HREE 倾斜的轻稀土富集型。它们的微量元素原始地幔配分型式也很相似,暗示有共同的岩浆源区。烟墩岭火山岩的 Ba/Nb 比值变化范围远小于琼北和涠洲岛玄武岩,而 La/Nb 比值三者相近,都是低而稳定,与洋岛玄武岩数值接近,不相容元素 Nb/U-Th 图解也说明烟墩岭火山岩来自于类似于洋岛玄武岩的地幔源区。岩石学和地球化学化学证据都表明,烟墩岭地区火山岩虽不是原生地幔玄武岩浆的喷出物,但只经过低程度演化,未受到强烈的结晶分异的影响,也未受到地壳的混染。其^(87)Sr/^(86)Sr 和^(143)Nd/^(144)Nd 数据变化范围很小,具有低Sr 同位素比值和高 Nd 同位素比值的特点。本文采用火山岩 K-Ar 法测定了烟墩岭火山活动的时代,结合火山岩地质特征和前人资料,火山活动时代确定为第四纪早更新世,与北部湾涠洲岛早期火山活动及琼北早更新世多文岭期火山活动时代大致相当。Yandunling volcano, which is located in Hepu county, the Guangxi Zhuang Autonomous Region, is a small volcano with central eruption style in the Quaternary Period. Its eruption represents the volcanic activity in south China in Quaternary. The products of Yandunling volcano are trachybasalt. Mg# values （59 - 69） are from middle to high, and titanium and alkali are comparatively high. The chondrite-normalized abundances of REE diagrams of Yandunling and its neighbour Yantouling volcanic rocks are quite similar and the curves are almost overlapped. The curves show a little steep tilt to HREE, which belongs to LREE-enriched type. The primitive- mantle normalized trace element abundance curves are also similar, indicating they have the same magma source. The variations of Ba/ Nb ratios of Yandunling volcanic rocks are smaller than those from north Hainan and Weizhou Islands, but La/Nb ratios are low and stable which are similar to those from OIB. The plot of incompatible elements of Nb/U and Th also shows that the rocks come from a magma source similar to OIB. The evidences from petrology and geochemistry suggest that the volcanic rocks in Yandunling are little evolved magma rather than primitive basalt from mantle source and they weren＇t affected by crystal differentiation, were they contaminated by crustal materials. These rocks have similar ST Sr/S6 Sr and ^143 Nd/^144 Nd ratios. The volcanic activities could be dated back to early Pleistocene according to K-Ar dating combined with geological characteristics of volcanic rocks and previous works, which correspond to early volcanic activities of Weizhou Island in Beibu Bay and Duowenling period of volcanic activities in north Hainan Island.

关 键 词：烟墩岭火山 岩石学与地球化学 涠洲岛 琼北 

分 类 号：P588.145[天文地球—岩石学] P597.3[天文地球—地质学]