Discovery of Archaean Felsic Rocks with Anomalous REE Compositions in the Anshan Area and Its Significance
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    Abstract:

    Anshan, one of the most important areas in the North China craton, underwent a l ong geological process in the Archaean from 3.8 Ga to 2.5 Ga. Recently we have found a lot of felsic rocks with anomalous REE compositions, including different kinds of granitic rocks (veins) and meta sedimentary rocks, in the area. They gener ally occur in small scales and are formed in different stages of the Archaean. Their REE patterns can be subdivided into 5 types: (1) LREE enrichment, with a positive Eu anomaly; (2) LREE enrichment, without obvious Eu anomaly; (3) LREE enrichment, with a negative Eu anomaly; (4) LREE depletion, with anegative Eu anomaly; (5) MREE enrichment, with a strong negative Eu anomaly. All of the rocks are characterized by a high content of SiO2 and low contents of ΣFeO, MgO, CaO, TiO2 and ΣREE. Some of them give meaningless tDM ages of the Nd isotope. The discovery of the rocks with REE patterns of types Ⅳ and Ⅴ is of especially important significance. Granitic rocks with the same REE patterns, mostly being young granites,have been found in the South China platform and other areas of the world and show genetic relationships with W, Sn, Nb and Ta mineral deposits. They are considered to be highly evolved rocks formed by strong fractional crystallization and hydrothermal interactions. Their existence in Anshan indicates that at least in the late Archaean, the area was in geological and physicalchemical conditions similar to those under which theyoung granites were formed. It is consistent with the view that the Anshan area underwent a long geological evolution history in the Archaean. It is also interesting to note that there is a clear linear relationship between the Eu anomaly and the Ba anomaly in rocks with anomalous REE patterns, a fact that has been identified in many felsic materials elsewhere

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WAN Yusheng, SONG Biao, LIU Dunyi.2002. Discovery of Archaean Felsic Rocks with Anomalous REE Compositions in the Anshan Area and Its Significance[J]. Geological Review,48(SUPP):45-52.

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