中文摘要：

在阿尔金走滑断裂与祁连山北缘逆冲断裂带交汇的酒西盆地出露年龄约为85Ma的富锆安山岩脉，切割年龄大约为105Ma的基性熔岩（粗面玄武岩和玄武安粗岩）。这条安山岩脉具有十分特殊的地球化学特征，具体表现为（1）强烈过碱性，Na2O＋K2O达11．8％，A／CNK比值为0．5540；（2）强烈富集高场强元素（HFSE），如Zr（1421μg／g），Hf（26．4μg／g），Y（48．2μg／g），Nb（104．0μg／g），Ta（8．5μg／g）等；（3）明显的Ce正异常；（4）近平直的MKEE和HREE稀土配分模式；（5）与基性熔岩相似的初始Sr但明显较低的Nd同位素比值（大于2εNd单位）。这些差异性不仅反映了它们各自源区地球化学特征的差异性，而且反映了部分熔融和岩浆后期演化过程中主要矿物和副矿物溶解或结晶行为的差异性。分析表明，钙长石的结晶分离作用和部分熔融过程中锆石溶解程度的升高是导致该岩脉异常地球化学特征的主控因素。该岩脉所揭示的地球化学过程有助于解译青藏高原内部中生代以来的相似中酸性碱性火山岩的成因。

英文摘要：

The Hongliuxia volcanic field is located at the junction of the Altyn Tagh strike-slip fault and the northern Qilian Shah frontal trust fault. In this area, an andesitic dike, -85 Ma old, cuts through -105 Ma shoshonitic and basaltic lavas. Major and trace element studies and Sr and Nd isotopic analyses of this suite of rocks show that this younger dike has anomalous geochemistry, as compared to nearby basalts. This dike has the following salient features： （1） peralkaline with Na2O＋K2O=11.8% and A/CNK=0.5540; （2） highly enriched in HFSE （e.g. Zr=1421 μg/g, Hf=26.4 μg/g, Y=48.2μg/g, Nb=104.0μg/g and Ta=8.5μg/g）;（3） a pronounced positive Ce anomaly （Ce/Ce^＊=1.128）;（4） nearly flat chondrite-normalized MREE and HREE distribution patterns;and （5） similar initial Sr but notably low Nd （by 〉2 εNd units） isotope ratios, as compared to those in the Hongliuxia shoshointic basalts. These differences reflect not only the difference in geochemistry of their respective source regions but also the difference in behaviors of dissolution or crystallization of dominant minerals and accessory minerals during partial melting and magmatic evolution.fractional crystallization of anorthite and enhanced dissolution of zircons in its source regions are the main controlling factors responsible for the anomalous geochemistry of this dike. The geochemical processes recorded by this dike may help the interpretation of similar intermediate-acid alkaline volcanic rocks since the Mesozoic on the Qinghai-Tibet Plateau.