河北小觉地区阜平岩群斜长角闪岩及深熔产物的稀土和Nd同位素地球化学研究

工作中重点对河北平山小觉地区阜平岩群两类角闪质岩石深熔作用的地球化学进行了研究。一类为厚层状斜长角闪岩，相邻新生浅色体常量元素组成上向TTG花岗质岩石方向转化，稀土和高场强元素含量明显降低，轻重稀土分离程度增高，tDM减小，εNd(t0)增大。另一类为与黑云变粒岩－片麻岩互层的条带状、石香肠状斜长角闪岩，相邻新生浅色体与之存在不同的地球化学关系：（1）稀土总量相对增高，轻重稀土分离程度有所降低；（2）稀土总量和轻重稀土分离程度都有明显增高。后者Nd同位素组成与斜长角闪岩也存在很大区别。这些现象可用熔融母岩、形成条件等差异得到合理的解释。

Study on Geochemistry of Hornblendic Rocks and Their Anatectic Derivatives of the Fuping Group in the Xiaojue Area, Hebei Province

The Neoarchaean high amphibolite facies Fuping Group consists mainly of meta arkosic leuco leptite, semipelitic biotite leptite gneiss, hornblendic rocks, marbles and calcsilicate rocks, which have been partly subjected to differential anatexis. In the Xiaohuilonggou section, northwest of the Xiaojue town , the hornblendic rocks occur in a relatively high proportion and can be divided into two types. One is thick bedded amphibolite, consisting of plagioclase, hornblende, and locally small amounts of quartz, garnet and biotite, with some accessory minerals such as zircon and apatite. In which, there are some felsic patches of various shapes and scales as the products of the initial stage of anatexis. The anarectic derivatives are low in REE and HFS element contents and somewhat high in LREE/HREE ratio compared with their parent rock. The main reason is that in the anatectic process the accessory minerals , especially zircon, behaved as restitic crystals. The other is bedded or boudinage like amphibolite interbedded with biotite leptite gneiss. It is composed mainly of plagioclase and hornblende, without or only with very little accessory minerals. So being different from what mentioned above, the newly formed felsic derivatives are higher in REE contents and lower in LREE/HREE ratio than the amphibolite. In the both cases, the felsic derivatives are obviously lower in LREE/HREE ratio than the typical Archaean TTG rocks because of that the anatexis of the Fuping Group happened under middle low pressure conditions. It is also observed that the thick bedded amphibolite and its anatectic product are quite different in Nd isotopic compositions, showing the preservation of isotopic disequilibrium. Some felsic materials nearby the bedded amphibolite, being very high in LREE/HREE ratio and quite different in Nd isotopic composition from the amphibolite, are considered to be formed by the anatexis of the biotite leptite gneiss.