山西省早白垩纪碳酸岩元素同位素和锆石U-Pb定年研究(英文)

Geochemical,Sr-Nd isotope,and zircon U-Pb geochronological constraints on the origin of Early Cretaceous carbonatite dykes,northern Shanxi Province,China

碳酸岩广泛出露在华北克拉通的山西省。此文中,针对研究区的碳酸岩墙,我们给出新的地球化学、Sr-Nd同位素和锆石U-Pb年龄。LA-ICP-MS锆石定年结果显示,该岩墙的侵位年龄为132.9Ma,全岩K-Ar年龄为131.3~132.6 Ma。碳酸岩墙具有非常一致的主量元素组成,富集轻稀土元素和大离子亲石元素(Ba、U、Pb、Sr),以及亏损K和高场强元素(Ta、P和Ti)。另外,该岩墙具有相对一致的(87Sr/86Sr)i(0.7079~0.7083)和负的εNd(t)(-16.7^-15.2)。以上地球化学特征表明,该岩墙为大陆地壳和此大陆岩石圈地幔混合时期,受明显地壳混染的下岩石圈地幔的部分熔融作用。

Carbonatite dyke swarms are widespread across the North China Craton（ NCC） in Shanxi Province. Here,we present new geochemical,Sr-Nd isotope,and U-Pb zircon age data for representative samples of the dykes. Laser ablation-inductively coupled plasma-mass spectrometry（ LA-ICP-MS） U-Pb analyses yielded a Cretaceous age of 132. 9 ± 0. 6Ma for zircons extracted from one dyke. Whole rock K-Ar ages for three samples range from 131. 3Ma to 132. 6Ma. The carbonatites have highly uniform major element compositions and are enriched in light rare earth elements and large ion lithophile elements（ LILEs; e. g.,Ba,U,Pb,and Sr）,and depleted in K and high field strength elements（ HFSEs; e. g.,Ta,P,and Ti）. The carbonatite dykes have relatively uniform（87Sr / 86Sr） i values that range from 0. 7079 to 0. 7083,and negative values of ε Nd（ t）（-16. 7 to-15. 2）. These data suggest that the dyke magmas were derived from the partial melting of an enriched region of the lower lithospheric mantle,with evident crustal contamination. The carbonatite dykes within the northern NCC formed during the mixing of the continental crust with sub-continental lithospheric mantle.