乔彦波　张瀚夫　田艳丽　斯琴毕力格

摘要：玻镁安山岩因其独特的成因特征及地球化学特征对研究区域构造环境具有重要意义。内蒙古克什克腾旗二零四一带的大石寨组中发育少量玻镁安山岩。通过对玻镁安山岩及安山岩、英安岩、辉长岩的地球化学分析及对比，确定该二叠纪玻山安岩具有岩浆分异演化程度低，岩浆具有岛弧地球化学性质，物质来源具幔源岩浆的特征，岩浆形成与消减作用有关，形成于俯冲消减环境中等特点；并推断华北北缘在二叠纪期间仍处于古亚洲洋的俯冲构造环境中，古亚洲洋向华北北缘之下的俯冲尚未结束，华北北缘的俯冲作用应该持续至二叠纪末——三叠纪初，此时华北北缘尚未进入克拉通演化阶段。

关键词：玻镁安山岩；二叠纪；华北北缘；构造环境

The Geochemical Characteristics of Boninite from 204 Region of Keshiketeng qi，Inner Mongolia

Abstract：Based the special cause and the major element chemistry，the research of Boninite may be help us to find out the tectonic setting where it was found. Boninite was found in 204 region of Keshiketeng qi，Inner Mongolia. By geochemical analysis and confrontation with andesite，dacite，gabbro，determined that Boninite have many characteristics such as the low magmatic differentiation，the feature of arc geochemistry，the characteristics of mantle-derived magma，the relevance with subduction，the special diving setting etc. By researching the geochemical characteristics of Boninite，the tectonic setting was surmised that northern margin of The North China plate was in a Paleo-Asian Oceans subduction setting in Permian，when the subduction wasnt finished from Paleo-Asian Ocean plate to northern margin of The North China plate. The subduction of northern margin of The North China plate maybe continued until the end of the Permian – the start Triassic，when northern margin of The North China plate hasnt enter the Craton stage.

Key words： Boninite，Permian，Northern margin of The North China plate，Tectonic setting

1. 引言

玻镁安山岩（Boninite）是一种富含玻璃质、几乎没有斜长石斑晶，但含橄榄石、古铜辉石和普通辉石斑晶的橄榄石古铜辉石安山岩，其主要化学成分以富硅（SiO2=52%～66%），富镁（MgO=9%～25%），贫钛、磷及高场强元素为特征（谭劲等，1991； Piercey et al.2001）。玻镁安山岩最早是在日本的无人岛（Bonin island）上发现的，因此把它命名为Boninite。该种岩石在西太平洋和其他若干地区均有发现，它们通常与岛弧拉斑玄武岩和钙碱性火山岩伴生，但其地球化学特征往往明显不同于上述岩石，为此进一步把它们和类似的岩石统称为玻镁安山岩系列，由此与其他火山岩类相区别。玻安岩系火山岩主要出现在岛弧或弧后盆地演化的初期阶段（Cameron et al.1979；……