赤城伙房村和崇礼上新营变质岩的地球化学特征、年龄及其区域地壳形成时间

Geochemistry and Ages of Archean Metamorphic Rocks in Northwestern Hebei Province, China, and Formation Time of the Paleocrust in the Region

冀西北麻粒岩是我国北方麻粒岩带的重要组成部分，其年龄对探讨我国地壳早期演化历史具有重要价值。本文报道了采自赤城伙房村和崇礼上新营变质岩样品的地球化学特征和Ｓｍ－Ｎｄ同位素年龄。赤城伙房村变质岩年龄为２５１３±５５（２σ）Ｍａ，ＩＮｄ＝０．５０９４４±５（２σ），εＮｄ（ｔ）＝＋１．２±０．５；崇礼上新营变质岩年龄为２６６７±９０（２σ）Ｍａ，ＩＮｄ＝０．５０９３０±８（２σ），εＮｄ（ｔ）＝＋２．４±０．７。冀西北变质岩可能存在两个系列，其原岩分别形成于２９００～２８００Ｍａ和２７００～２６００Ｍａ。

This paper deals with the geochemical characters and Sm Nd ages of metamorphic rocks in Huofangcun of Chicheng County and Shangxinying of Chongli County in northwestern Hebei Province, China, and discusses the original ages of the supracrustal rocks and the formation time of the regional continental crust. The samples from the metamorphic rocks in Huofangcun of Chicheng County give a Sm Nd isochron age of 2513±55(2σ) Ma with I Nd =0.50944±5(2σ), corresponding to ε Nd ( t )=+1.2±0.5. Their model age t DM is 2891±134(σ)Ma. The Sm Nd isotopic data of the metamorphic rocks in Shangxinying of Chongli County present an isochron age of 2667 ±90(2σ)Ma, with I Nd =0.50930±8(2σ), ε Nd ( t )=+2.4±0.7, the model age t DM =2838±41(σ)Ma. The Nd isotopic data of the metamorphic rocks in the region show that the protoliths of the metamorphic rocks in northwestern Hebei Province were two systems: the one has the original age of 2700￣2600Ma, the other 2900￣2800Ma. In this region, the paleocrusts might be composed of the basic metamorphic rocks, which were formed early in about 2932±84(σ)Ma ago.