冀东黄柏峪—羊崖山地区太古宙岩浆作用和变质作用——SHRIMP锆石U-Pb定年

报道了冀东黄柏峪—羊崖山地区太古宙变质辉长岩、黑云斜长片麻岩、片麻状二长花岗岩、片麻状富钾花岗岩等不同类型变质岩浆岩(8个样品)的SHRIMP锆石U-Pb定年结果。首次发现3.1Ga二长花岗岩,黑云斜长片麻岩形成时代约为3.0Ga。变质辉长岩的侵入时代很可能为新太古代晚期,存在少量3.2~3.6Ga捕获锆石。几乎所有岩石样品都记录了约2.5Ga的变质锆石年龄。结合前人资料认为,(1)冀东地区新太古代晚期构造热事件十分发育,被认为与地幔软流圈上涌导致的岩浆板底垫托有关;(2)冀东地区中太古代以前的陆壳物质广泛分布,黄柏峪—羊崖山地区很可能存在一古老陆核。

Archean magmatism and metamorphism in the Huangbaiyu-Yangyashan area, eastern Hebei Province: Evidence from SHRIMP zircon U-Pb dating

This paper reports SHRIMP zircon U-Pb ages of eight samples for different types of Archean meta-magmatic rocks in the Huangbaiyu-Yangyashan area, eastern Hebei Province, which include meta-gabbro, biotite plagioclase gneiss, gneissic monzogranite and gneissic K-rich granite. 3.1Ga monzogranite (sample J1111) was identified for the first time in the area. Biotite plagioclase gneiss (sample J1116) also probably formed at ~3.0Ga. In meta-gabbros (samples J1109 and J1110), which are considered to form at the end of the Neoarchean although no ~2.5Ga magmatic zircon age has been determined, there are a few trapped zircons of 3.2~3.6Ga. Almost all samples record ~2.5Ga metamorphic zircon ages. Combined with early studies, the authors have arrived at following conclusions: (1) Tectono-thermal events of the Late Neoarchean were well developed, ~2.5Ga metamorphism, mantle magmatism and crust-derived granite formation were all caused by magma underplating resulting from upwelling of asthenosphere;(2)>2.8Ga continental materials widely occur in eastern Hebei Province, and there might exist an ancient continental nucleus in the Huangbaiyu-Yangyashan area.