Abstract:

Based on the major element analyses of Qipanyan gabbro of the Mentougou area, Beijing and TAS classification diagram proposed by Middlemost, 4 samples can be classified into peridotgabbro and foid gabbro. And the 4 samples are characterized by high Fe(total FeO*>14%）and low silica contents (SiO₂<45%), thus belonging to ferrogabbro. This is the first report of ferrogabbros in the Yanshan orogenic belt. The petrogenesis of Qipanyan ferrogabbro will need to be studied detailedly though the SiO₂-FeO*/MgO diagram of Qipanyan ferrogabbro shows the Fenner trend, because there are different opinions about the petrogenesis of ferrogabbro. The study of ferrogabbro and its petrogenesis will play an important role in studying tectonic setting and dynamic background, deep process of the Beijing area during Yanshanian Movement.

Key words: Qipanyan pluton, ferrogabbro, high-Fe and low Si, Yanshan orogenic belt