下扬子地区中生代火山岩的微量元素及其大地构造意义

本文对下扬子地区五个火山盆地（庐枞、宁芜、溧水、溧阳和天目山）中生代火山岩的微量元素进行了系统的研究。该区火山岩的 ＲＥＥ含量较高，配分曲线以 ＬＲＥＥ相对富集，并且具Ｅｕ负异常为特征。在１７种元素的标准化曲线图上，具Ｒｂ、Ｋ的峰和 Ｔａ、Ｔｉ的谷，表明了火山岩中大离子半径元素的相对富集和高场强元素的贫化。这些特点相似于岛弧及活动大陆边缘的火山岩。在 Ｈｆ／３－Ｔｈ－Ｔａ和 Ｔｈ／Ｙｂ－Ｔａ／Ｙｂ判别图解上，本区火山岩的成分点都落在破坏性板块边缘及岛弧的区域内。这些分析结果有力地证实了下扬子地区的火山活动是中生代时期库拉－太平洋板块俯冲作用的产物。

Trace Elements and Their Tectonic Implication of Mesozoic Volcanic Rocks in Lower Reach of Yangze River

The trace elements of Mesozonic volcanic rocks from five volconic basins (Luzhong, Ningwu, Lishui, Liyang and Tianmushan) in the lower reach of the Yangze River have been investigated. REE in most rocks show the LREE-enriched patterns with negative Eu anomaly. In the chondrite-normalized multiple-element diagrams(spidergram) the peaks at K and Rb and the troughs at Ta and Ti have been observed, which indicate relative enrichment of K-group elements and depletion of some HFS elements in the volcanic rocks. These patterns are quite similar to that of rocks from island arcs and active continental mar- gins, rather than from continental rifts. All the volcanic rocks plot in the field of the destruc- tive plate margin and island-are setting in the Hf/ 3-Th-Ta and Th/Yb-Ta/Yb diagrams. These evidences strongly support the conclusion that the volcanic activities in the lower reach of Yangze River, castern China, are closely related to the subduction of the Kula-Pacific plate during Mesozoic Era.