CAJ | 학술논문

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.
본문대분포우장북남강당지구적주구유다착화납정착신생대화산암진행료암석학、동위소년대학화지구화학연구.량개지구화산암주요유조면현무암、감람조안암、안조암급조면암조성,구유종감성계렬화산암도고갑개감성화산암련속연화적특정.고석U-Pb정년표명량개지구화산암형성시대분별위34.64±0.55Ma화35.03±0.54Ma,령외재주구유다착안조암화조면암중발현료대량적포획고석.지구화학분석현시,암석ε_(Hf)(t)균위정치,단수SiO_2함량적증고,ε_(Hf)(t)유감소적추세.희토원소배분곡선상경중희토분류명현,무혹경미Eu부이상,우기시중희토출현분류,대다수양품(Sm/Yb)_N치개우6.30～8.25지간,표명원생암장기원우함유석류석적약우손형연류권지만,중산성암장소구유적유사애체극암적지구화학특정시원생만원암장경AFC작용형성적.시신세말기남강당지구적화산활동가능여향북부충적랍살지괴적암석권지만단리조성적연류권상용유관.
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 Zongouyouchacuo and Nadingcuo area were formed in 34.64 ± 0.55Ms and 35.03 ± 0.54Ma respectively, besides there are lots of captured zircons in Zougouyouchacuo latite and trachyte. All of the samples have positive ε_(Hf)(t) values, but ε_(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 ～ 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.