青藏高原北部新生代走构油茶错、纳丁错火山岩年代学、地球化学特征及其构造意义  

Chronology,geochemistry and tectonic significances of the Cenozoic Zougouyouchacuo and Nadingcuo volcanic rocks in northern Tibetan Plateau.

作　　者：刘建峰[1] 迟效国[1] 赵秀羽[1] 赵芝[1] 董春艳[2] 黎广荣[3] 赵院东[4] 

机构地区：[1]吉林大学地球科学学院,长春130061 [2]中国地质科学院地质研究所,北京100037 [3]南京大学地球科学系,南京210093 [4]中国地质调查局沈阳地质矿产研究所,沈阳110032

出　　处：《岩石学报》2009年第12期3259-3274,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40572034)资助成果

摘　　要：本文对分布于藏北南羌塘地区的走构油茶错和纳丁错新生代火山岩进行了岩石学、同位素年代学和地球化学研究。两个地区火山岩主要由粗面玄武岩、橄榄粗安岩、安粗岩及粗面岩组成,具有从碱性系列火山岩到高钾钙碱性火山岩连续演化的特征。锆石U-Pb定年表明两个地区火山岩形成时代分别为34.64±0.55Ma和35.03±0.54Ma,另外在走构油茶错安粗岩和粗面岩中发现了大量的捕获锆石。地球化学分析显示,岩石ε_(Hf)(t)均为正值,但随SiO_2含量的增高,ε_(Hf)(t)有减小的趋势。稀土元素配分曲线上轻重稀土分馏明显,无或轻微Eu负异常,尤其是重稀土出现分馏,大多数样品(Sm/Yb)_N值介于6.30～8.25之间,表明原生岩浆起源于含有石榴石的弱亏损型软流圈地幔,中酸性岩浆所具有的类似埃达克岩的地球化学特征是原生幔源岩浆经AFC作用形成的。始新世末期南羌塘地区的火山活动可能与向北俯冲的拉萨地块的岩石圈地幔断离造成的软流圈上涌有关。This paper reported petrology, geochronology and geochemistry of the Cenozoic volcanics from Zougouyouchacuo and Nadingcuo in South Qiangtang area, northern Tibetan Plateau. The volcanic rock in the study area is mainly composed of trachybasalt, mugearite, latite and trachyte. The volcanics show evolutionary trend from alkaline series to high-K calk-alkaline series. Zircon U-Pb dating indicates the volcanic rocks in Zougouyouchacuo and Nadingcuo area were formed in 34. 64 +/- 0. 55Ma and 35. 03 +/- 0. 54Ma respectively, besides there are lots of captured zircons in Zougouyouchacuo latite and trachyte. All of the samples have positive epsilon(Hf)( t) values, but epsilon(Hf)(t) decreases with the increase of SiO(2). The fractionation between LREE and HREE is obvious, without or having minor negative Eu anomalies. The fractionation between HREE is also notable, with (Sm/Yb)(N) = 6.30 similar to 8.25, which indicates the primary magma originated from weakly depleted garnet-bearing asthenosphere. Through analysis the adakitic geochemical characteristics of the intermediate-acid magma in the area is formed by AFC (assimilation and fractional crystallization) of primary mantle-originated magma. The Late Eocene volcanism in South Qiangtang area may have relation to the upwelling of asthenosphere caused by breaking-off of northward subducted Lhasa lithosphere mantle.

关 键 词：青藏高原北部 新生代火山岩 油茶 高钾钙碱性火山岩 同位素年代学 地球化学特征 构造意义 Tibetan Plateau northern geochemical characteristics fractional crystallization area Cenozoic VOLCANICS 稀土元素配分曲线 羌塘地区 volcanic rocks 轻重稀土分馏 岩石圈地幔 软流圈上涌 地球化学分析 

分 类 号：P58[天文地球—岩石学]