Enriched mantle source for Paleoproterozoic high Mg and low Ti-P mafic dykes in central part of the North China craton: constraints from zircon Hf isotopic compositions

华北克拉通中部是古元古代岩墙群最为发育的地区。以镁铁质成分为主的岩墙群可以分为变质的和不变质的两类。不变质岩墙群是在1780～1760Ma之间大约20Ma时间内形成的,是华北克拉通古元古代最晚期铗铁质岩浆活动的产物。不变质岩墙又可以细分成高Mg-Ti低P、低Mg高Ti-P和高Mg低Ti-P等3组。本文报道了采自丰镇附近高Mg低Ti-P岩墙样品的锆石U-Pb年龄和Hf同位素组成分析结果。新获得的SHRIMP锆石U-Pb年龄为1769±4Ma,与其它不变质岩墙的锆石、斜锆石U-Pb年龄和~(40)At/~(39)Ar年龄的范围相同。高Mg低Ti-P岩墙的锆石ε_(Hf)(t)值的变化范围在-6.4...Paleoproterozoic mafic dyke swarms in central part of the North China craton can be divided into two types: metamorphosed and unmetamorphosed. The unmetamorphosed dykes formed in a short duration of similar to 20Ma from 1780 to 1760Ma and were produced by the latest Paleoproterozoic mafic mgmatism in the North China craton. They may be subdivided into following three groups: high Mg-Ti and low P, low Mg and high Ti-P, and high Mg and low Ti-P, and individual groups have different geochemical features. A new zircon U-Pb age obtained for the high Mg and low Ti-P mafic dykes to the northwest of Fengzhen city is 1769 +/- 4Ma, in good agreement with previous data such as Ar-40/Ar-39 and conventional and SHRIMP zircon and baddeleyite U-Pb ages for the unmetamorphosed dykes. The epsilon(Hf)(t) values of the dated zircons at 1770Ma vary from -6.4 to +0.4, with an average of -2.2, and are slightly higher than those of the granitic rocks formed at similar time, indicating that the magmas, with little crustal contamination during their ascent, emplacement and crystallization, were derived from an enriched source from the subcontinental lithospheric mantle induced by subducted sediments. In addition, the enriched mantle source for the high Mg and low Ti-P mafic dykes had the epsilon(Hf)( t) values of -5. 6 to -2.8 (average -4.4) and the initial Sr-87/Sr-86 ratios of 0.7040 to 0.7050 (average 0.7046), as shown by the data available from the literature.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000245763200008&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701SCI(E)中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)1702277-2842