中文摘要：

北羌塘枕头崖地区新生代火山岩主要岩石类型为安山岩和英安岩类。其中，安山岩在一定程度上显示了埃达克质火山岩的特征，如高Sr（〉1000×10^-6）、St／Y〉50以及低Yb（〈2×10^-6），表明其应源于榴辉岩相的青藏高原加厚陆壳中下部（〉45km深度）。而英安岩类富集LILE．如Rb、Ba、Th、U和K等，亏损HFSE，如Ti、Nb、Ta和Sr等，尤其是Sr显著亏损，表明其应源于斜长石稳定的麻粒岩相源区。该区新生代安山岩和英安岩中麻粒岩捕虏体可分为两种类型，即二辉石麻粒岩和单斜辉石麻粒岩。二辉石麻粒岩平衡温度为783～818℃，单斜辉石麻粒岩形成压力在0．845～0．858GPa之间，来源深度约为27．9～28．3km，表明它们是来自青藏高原加厚陆壳中部的岩石样品，代表了本区英安岩类火山岩的源区物质组成。

英文摘要：

Cenozoic volcanic units in Zhentouya area of north Qiangtang are mainly andesite and dacite lavas. The andesite, to some extent, shows an adakitic compositional characteristics, such as high Sr （〉 1 000× 10^-6）, Sr/Y ratios 〉50 and low Yb contents （〈2×10^-6）. Evidently plagioclase broke down in the andesitic magma source region under the p-T conditions of partial melting. Compared with the dacite series, it seems that partial melting of the lower part of the thickened eclogite-facies Tibetan crust was responsible for the generation of the andesitic magma. The dacite is characterized by enriched LILE such as Rb, Ba, Th, U and K, and depleted HFSE such as Ti, Nb, Ta and St. It is noteworthy that the dacite exhibits a relatively low Sr （Sr〈 660×10^-6）, and this may imply that the plagioclase was still stable in the dacitic magma source region at the pressure and temperature of partial melting. Two-pyroxene granulite and clinopyroxene granulite xendoths were discovered in the andesite and dacite volcanic rocks outcropped in north Qiangtang of central Tibetan Plateau. Based on electron microprobe analyses, the authors have concluded that the xenoliths provide constraints for the equilibrium temperatures of the two-pyroxene granulite, i.e., about 783 to 818℃as determined by two-pyroxene thermometry, and that the formation pressure of the clinopyroxene granulite should be about 0. 845 to 0. 858 GPa, equal to 27.9-28.3 km in depth. It is indicated that these granulite xenoliths represent the samples derived from the middle part of the thickened Tibetan crust. This discovery is of great importance to the further investigation of the components and thermal regime of the deep crust of Tibetan Plateau. Geochemistry of dacite and characteristics of granulite xenolith suggest that partial melting of the middle part of thickened Tibetan crust might have produced the primary dacite magma series.