GUO Feng , FAN Wei-ming, LI Chao-wen
Key Laboratory of Marginal Sea Geology , Guangzhou Institute of Geochemistry, Chinese Academy of Sciences , Wushan , Guangzhou 510640, China
Abstract: A comprehensive study ( including Ar-Ar, zircon U-Pb dating, mineralogy, major, trace element and Sr-Nd-Pb-Hf isotope analyses) on the Paleocene adakites from the Yanji area, NE China is presented in this paper. These adakites have high MgO, Cr and Ni, and extremely high Sr and low Y and H REE. They were considered as melts derived from a slab melt-metasomatized mantle wedge. During ascent they experienced mixing by crust ally derived intermediat e-felsic magma to interpret the reversely zoned clinopyroxene and amphibole. Our interpretation is quite different from the previous model-a result of slab melt-mantle interaction. This mixed magma further underwent crustal contamination and/or AFC processes to account for the systematic geochemical variations from the clinopyroxene to amphibole andesites, as well as the inherited zircon. Considering the regional tectonic evolution, the Yanji adakites were formed under a post-subduction extension, possibly related to the late Cretaceous ridge subduction and subsequent rollback of the Pacific Plate. This implies that such rocks could be formed in a variety of settings, where adakitic melt met as omatism occurs and the p-t conditions permit melting of the met asomat ized mantle. Generation of such rocks can be either contemporaneous with or after the young and hot ridge subduction.
Key words: Magma mixing; Adakite; Paleocene; Yanji area
*Corresponding Author, E-Mail:
guofengt@263.netBulletin of Mineralogy, Petrology and Geochemistry Vol. 30, No.1, 2011, page 1-10
