鞍山-本溪地区鞍山群含BIF表壳岩形成时代新证据:锆石SHRIMP U-Pb定年

鞍本是华北克拉通最为重要的BIF铁矿集中区之一，BIF赋存于鞍山群表壳岩中.通过对广泛分布的鞍山群表壳岩的12个样品进行锆石SHRIMP U-Pb定年，大都获得2.50~2.55 Ga岩浆锆石年龄，一些岩石中存在2.7~3.5 Ga碎屑锆石或外来锆石.一些东北部（东部）岩石记录了新太古代晚期-古元古代早期变质锆石年龄.结合前人研究成果，可得出如下结论:（1）鞍本地区广泛分布的鞍山群含BIF表壳岩形成时代为新太古代晚期；（2）鞍山群表壳岩形成于陆壳基底之上.该研究进一步支持了已有认识:鞍本为东部古陆块西缘新太古代晚期巨型BIF成矿带的重要组成部分，稳定的构造环境有利于大规模BIF形成. 

Formation Age of BIF-Bearing Anshan Group Supracrustal Rocks in Anshan-Benxi Area: New Evidence from SHRIMP U-Pb Zircon Dating

Anshan-Benxi is one of the most important BIF concentration areas in the North China Craton, the BIF occurred in the Anshan Group supracrustal rocks. Using SHRIMP U-Pb zircon dating technique, 12 supracrustal samples of the Anshan Group were analyzed. Most samples present 2.50-2.55 Ga zircon ages and 2.7-3.5 Ga detrital or xenocrystal zircons are observed in some samples. Combined with previous studies, main conclusions can be drawn as follows. (1) The widespread BIF-bearing Anshan Group supracrustal rocks in the Anshan-Benxi area were deposited during the Late Neoarchean. (2) The Anshan Group supracrustal rocks were formed over a continental basement. This study confirms that Anshan-Benxi is an important conponent of the huge Late Neoarchean BIF belt along the western margin of the eastern ancient terrane, and stable tectonic environment seems to be a key factor for the formation of huge-scale BIF ore deposit.