冀东地区始太古代早期—冥古宙锆石发现

内容提要:最古老大陆地壳的形成、组成和演化是阐释地球壳幔物质分异、构造演化的逻辑起点.由于长期地质作用改造,地球上保存的古老陆壳物质十分稀少,寻找和研究都极具挑战性.在冀东卢龙喇叭山地区,早期研究发现含有大量3.4～3.8 Ga碎屑锆石的铬云母石英岩,岩石特征和碎屑锆石年龄分布与迁安黄柏峪地区的铬云母石英岩十分类似.本...

Discovery of early Eoarchean Hadean zircons in eastern Hebei, North China Craton

The formation,composition and evolution of the oldest continental crust is the logical starting point for discussing the differentiation and development of the crust-mantle system of the Earth.However,the rarity of preserved ancient continental crust due to its long-term reworking make this research extremely challenging.Fuchsite quartzite with abundant 3.4~3.8 Ga detrital zircons have been discovered in early study in the Labashan area,Lulong,which is very similar in rock feature and detrital zircon age distribution to that in the Huangbaiyu area,Qian’an.This study carried out SHRIMP U-Pb dating on zircons from meta-sedimentary rocks associated with fuchsite quartzite in the Labashan area.Ninety-four analyses on zircons from biotite plagioclase gneiss(J2006)reveal that detrital zircons commonly show strong lead loss with data being mainly distributed along two discordant lines with upper intercept ages of 3.8 Ga and 3.45 Ga.An age of 3.08 Ga was obtained for metamorphic zircons.In feldspar quartzite(J2009)for which 68 analyses have been finished,six detrital zircons of 3.92~4.0 Ga have been identified together with abundant 3.4~3.8 Ga detrital zircons.The discovery of early Eoarchean to Hadean detrital zircons assuredly indicates that the North China Craton has a long-term history of formation and evolution up to 4.0 Ga.The 3.1~3.4 Ga Caozhuang-Labashan rock series defined in this study is mainly composed of meta-sedimentary rocks and meta-mafic to ultramafic rocks,suggesting an environment of plume-continental crust interaction.In terms of the shape features of detrital zircons and the different age distribution of abundant ancient detrital zircons from different samples,it is speculated that the source region from which the detrital materials were derived is at short range and in a large scale,and contains multiple granitic magmatism at the periods of 3.92~4.0 Ga,3.8 Ga,3.6~3.7 Ga and 3.4~3.45 Ga,respectively.