浙西北中生代火山岩的微量元素地球化学特征与岩石成因探讨

A PRELIMINARY STUDY ON THE GEOCHEMICAL BEHAVI-ORS OF TRACE ELEMENTS AND THE ORIGIN OF MESOZOIC VOLCANIC ROCKS IN NORTH- WESTERN ZHEJIANG PROVINCE

本文论述浙西北中生代火山岩中微量元素的地球化学特征,探讨火山岩的成因。研究结果表明:在该区不同的火山盆地和火山洼地中,酸性和中酸性火山岩主要富亲石微量元素,而贫亲铁元素;稀土元素分布模式相似,均呈向右倾的“V”型曲线,具铕负异常;火山岩的初始。^(87)Sr/^(86)Sr值变化范围为0.7079～0.7139。这表明所研究的火山岩为陆壳成因,是由硅铝层物质重熔所形成的岩浆进行分异、演化和火山喷发而成的。成岩温度为1020～1200℃。

This paper deals with the composition and distribution of trace elements in the Mesozoic volcanic rocks, so as to shed light on the origin of Mesozoic volcanic rocks in northwestern Zhejiang Province.The REE distribution patterns in the acid and intermediate-acid Mesozoic volcanic rocks in various volcanic basins and depressions display great similarities, though their absolute REE contents are different. All these rock types are characterized by rightward declined V-shaped curves with negative Eu anomalies. Significant differences in REE parameters (6Eu, La/Yb, REE and ∑Ce/∑Y) are evident. The initial 87Sr/86Sr ratios for the volcanic rocks range from 0.7079 to 0.7139, showing their crustal origin. A mechanism of comagmatic remelting of the sialic crust with differentiation, evolution, intrusion and volcanic extrusion is suggested. Rock-forming temperatures range from 1020 to 1200℃.