中文摘要：

位于北羌塘地体北缘玉树隆宝地区三叠纪火山岩主要以英安岩为主。LA_ICP_MS锆石U_Pb定年结果显示这些火山岩的形成年龄约为230±2 Ma（MSWD=0.5）。岩石样品在成分上富硅和铝,并且相对于原始地幔富集大离子亲石元素（LILEs：Rb、Ba、Th和U等）和轻稀土元素,亏损高场强元素（HFSEs：Nb、Ta和Ti等）,其总体分布样式与典型弧火山岩的化学特征类似。样品均具有相对高的εNd（t）值（-0.91--0.53）、低的ISr值（0.707）以及正的εHf（t）值（＋3.81-＋7.61）,表明其源区应以新生地壳组分为主。与现已报道的其他三叠纪火山岩资料进行系统对比,发现中晚三叠世火山岩具有明显的分带性,分别集中出露在北羌塘地体的北缘和南缘。另外,与北缘火山岩相比,南缘火山岩在岩石组合上具有双峰式的特点,并且其中的长英质组分具有更低的εNd（t）值（-8.79--1.77）、相对高的ISr值（0.706-0.714）以及与南缘三叠纪S型花岗岩基本一致Hf同位素组成[εHf（t）=-15.3--10.1],反映了其源区应以古老陆壳物质为主。综合区域最新研究资料可以判断,北羌塘地体南缘中晚三叠世火山岩的形成应与南、北羌塘地体碰撞阶段的板片断离有关,而北缘中晚三叠世火山岩的形成则与甘孜-理塘古特提斯洋盆向南俯冲有关。

英文摘要：

Triassic Yushu volcanic rocks are mainly composed of dacites and distributed in the northern part of the North Qiangtang （NQ） terrane. Zircon LA-ICP-MS U-Pb ages of 230 ＋ 2 Ma （MSWD = 0.5） could be in- terpreted as the formation time of these volcanic rocks. Most samples from the Yushu volcanic rocks are characterized by high SiO2 and A1203, obvious enrichment of large ion lithophile elements （LILEs： Rb, Ba, Th and U） and strong depletion of high field strength elements （HFSEs, such as Nb, Ta and Ti） relative to the primitive mantle. They exhibit high εNd（ t ） （ - 0.91 - - 0.53）, low Isr （0. 707） and positive εHf（ t ） （ ＋ 3.81 ＋7.61）, suggesting that they probably originated from partial melting of a juvenile crustal component.Compared with the other reported Triassic volcanic rocks of the （NQ）, it could be found that most of the Middle to Late Triassic volcanic rocks （MLTV） are concentrated in the northern part or the southern part of the NQ. The Middle-Lower Triassic Yushu volcanic rocks from the south part of the NQ exhibit lower eNd（ t ） （ - 8.79 - 1.77）, higher Isr（0.706-- 0. 714） and negative εHf（ t ） （ - 15.3 -- - 10.1 ）, implying these rocks might be derived from partial melting of the old crustal materials. Combined with the other new available observations, the authors hold that the Middle-Lower Triassic Yushu volcanic rocks in the southern part of the NQ were genetically related to the slab break-off during the collision between South Qiangtang terrane and NQ, whereas the southward subduction of the Ganzi-Litang Paleo-Tethyan ocean resulted in the generation of the Middle-Lower Triassic Yushu volcanic rocks from the northern part of the NQ.