甘肃夏河地区印支期埃达克岩的厘定及其意义

对出露于甘肃夏河地区，隶属西秦岭的印支晚期复式岩体的地质地球化学研究表明。其岩石具有与典型埃达克岩相似的特征：SiO2多数（72％～58％），高Al2O3（16．7％～14．6％），Sr多数大于（400×10^-6），低Y（16×10^-6～7×10^-6）和Yb（1．7×10^-6～0．56×10^-6），明显亏损Nb和Ta，稀土元素分异强烈，富集LREE，低HREE，并有较弱的Eu负异常（δEu为0．9～0．4）在（La／Yb）N-Yb和Sr／Y-Y图解上样品主要落入埃达克质岩区域。该套埃达克质岩的厘定，对研究秦岭造山带晚古生代古特提斯洋的构造演化、地球动力学特征具有重要意义。

GEOCHEMICAL CHARACTERISTICS AND GEOLOGICAL SIGNIFICANCE OF ADAKITIC GRANITOIDS IN XIAHE COUNTY OF GANSU PROVINCE

The late Indosinian granitoids in Xiahe area of Gansu Province belong to west Qinling orogenic belt. A study of their petrochemical and geochemical characteristics shows that they have the typical characteristics of ＂adakite＂. These rocks have the following characteristics： Most of SiO2 （70%-58%）, high Al2O3（16.7%-14.6%） and Sr （most of them〉400×10^-6）, and low in Sr/Y（16×10^-6～7×10^-6） and Y ratio （1.7×10^-6～0.56×10^-6）; There exist very prominent negative Nb and Ta anomaly in the trace element spidergram. REE distribution pat- terns show strong REE segregation and belong to the type of enriched LREE, but depletion in HREE, and weak negative Eu （δEu=0.9～0.4） auanomaly can be observed; and most samples fall into the extent of adakite on （La/ Yb）N-YbN and Sr/Y-Y diagrams. Therefore, the discovery of the adakitic rocks have great significance for the study on Late Paleozoic tectonic evolution of Qinling orogenic belt.