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

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 e 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.