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首页> 外文期刊>Lithos: An International Journal of Mineralogy, Petrology, and Geochemistry >Neoarchean (2.7-2.8 Ga) accretion beneath the North China Craton: U-Pb age, trace elements and Hf isotopes of zircons in diamondiferous kimberlites
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Neoarchean (2.7-2.8 Ga) accretion beneath the North China Craton: U-Pb age, trace elements and Hf isotopes of zircons in diamondiferous kimberlites

机译：华北克拉通下的新古宙（2.7-2.8 Ga）增生：含钻石的金伯利岩中锆石的U-Pb年龄，微量元素和Hf同位素

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摘要

Zircon xenocrysts from the Early Paleozoic Mengyin and Fuxian diamondiferous kimberlites, on opposite sides of the translithospheric Tanlu fault in the North China Craton, have been used to probe the deep crust Based on detailed studies of external forms and internal structures, the zircons can be roughly divided into magmatic and metamorphic zircons. There are no consistent differences in U, Th or Th/U between the two zircon populations. The trace-element affinities of the igneous zircons vary widely from mafic, through intermediate, to felsic rocks with minor populations similar to zircons from carbonatite and syenite. In situ isotopic analysis for U-Pb and Lu-Hf reveals that all zircons both from Mengyin and Fuxian kimberlites, regardless of their chemical affinities, have similar formation ages (2.5-2.7 Ga) and depleted mantle model ages (T_(DM). 2.7-2.8 Ga). These ages are also similar within error to those of zircons in mafic granulite xenoliths from the Fuxian kimberlites, implying that the lower crust was similar (Neoarchean cratonic basement) beneath the Mengyin and Fuxian areas, but the latter experienced stronger thermal modification in Proterozoic time. The magmatic zircons may be derived from late differentiates of underplated mafic magmas with some contamination by crustal components, and the metamorphic populations developed during heating events linked to the ongoing underplating. The addition of juvenile material (up to +9.5 ε_(Hf)) at this time (2.7-2.8 Ga) corresponds to a known major episode of global crustal formation.
机译：来自华北克拉通跨岩圈Tan庐断裂的早古生代蒙阴锆石和福县菱形金伯利岩的锆石异晶被用来探测深层地壳。根据对外部形态和内部结构的详细研究，锆石可以粗略地分为岩浆锆石和变质锆石。两个锆石种群之间的U，Th或Th / U没有一致的差异。火成锆石的痕量元素亲和力变化很大，从镁铁质到中间，再到长英质岩石，其少数群体与碳酸盐岩和正长岩中的锆石相似。对U-Pb和Lu-Hf进行的原位同位素分析表明，无论孟金和福县金伯利岩的所有锆石，无论其化学亲和力如何，都具有相似的形成年龄（2.5-2.7 Ga）和耗尽的地幔模型年龄（T_（DM）。 2.7-2.8 Ga）。这些年龄在误差上也与福建金伯利岩中镁铁质粒状异种岩中的锆石相似，这暗示着孟金和福县地区的下地壳相似（新古纪克拉通基底），但后者在元古代时期经历了更强的热变质。岩浆性锆石可能来自底板镁铁质岩浆的晚期分化，并受到地壳成分的一定污染，并且在加热事件期间发育的变质种群与正在进行的底板作用有关。此时（2.7-2.8 Ga）添加的幼物质（高达+9.5ε_（Hf））对应于全球地壳形成的已知主要事件。

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