Rock-forming mechanism of Fenghuangshan rockbody in Tongling area
来源期刊：中南大学学报(英文版)2003年第3期
论文作者：邵拥军 彭省临 吴淦国 刘亮明 赖健清 张达
文章页码：216 - 221
Key words：complex rockbody; upper mantle; orogenic belt; island arc; alkalic basalt; assimilation and fractional crytalization mechanism
Abstract: Based on the detailed geological investigation and record of galleries and drill holes, a new idea has been advanced that granodiorite is earlier than quartz monzodiorite porphyry. Both of them are products of two different magmatic intrusive activities. The analysis results of trace elements show that the Sr content is beyond any other crustal rock and the Th content is beyond that of Ta. The whole-rock analysis indicates that rockbody is rich in CaO and poor in K2O.In the composition of Pb is tope of rockbody, the ratio of 207 Pb to 204Pb is less than 15. 60. All these show that the magma mainly comes from the upper mantle. Ti, Zr, Cr, Nb trace elements and the relation between the Gardini index(r) and the Rittmann index(a) indicate that the rockbodies are formed in the orogenic belt and island arc tectonic setting. The summation(FREE) and the characteristic value ( m(La)/m(Yb)) of the rare earth elements show that the original rock is alkalic basalt. The analysis of the characteristic values of REE and the quantitative modeling calculation indicate that the rock-forming process is dominated by mixed crystallization. According to the analysis on the rock-forming order, magmatic source, tectonic setting and rock-forming process, combiped with the achievements of regional rock-controlling structures and division of sublayer of crust, it is believed that Fenghuangshan rock body derives from the deep-seated alkalic basalt magma. The rock-forming process has updertaken sialic and calcareous assimilation and contamination of two different degrees. The rock-forming model belongs to the typical assimilation and fractional cryatalization mechanism.
