Geochemical, Sr–Nd isotopic, and zircon U–Pb geochronological constraints on the petrogenesis of Late Paleoproterozoic mafic dykes within the northern North China Craton, Shanxi Province, China

• Published in: Precambrian research 2013-10, Vol.236, p.182-192
• Main Authors: Liu, Shen, Feng, Caixia, Jahn, Bor-ming, Hu, Ruizhong, Gao, Shan, Feng, Guangying, Lai, Shaocong, Yang, Yuhong, Qi, Youqiang, Coulson, Ian M.
• Format: Article
• Language: English
• Subjects: Extension; Mafic dykes; Northern NCC; Origin; Paleoproterozoic
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2013.07.007

•Late Paleoproterozoic mafic dykes in the North China Craton were dated at ∼1620Ma.•The dykes were derived from depleted mantle source.•The origin of the dykes is related to the foundered lower crustal. The ages and source of Precambrian mafic dolerite dykes of the North China Craton (NCC) were determined using geochronological, geochemical, and whole-rock Sr–Nd isotopic data. Laser ablation–inductively coupled plasma-mass spectrometry (LA–ICP-MS) U–Pb analysis of zircons yielded consistent ages of 1621±6 and 1621±7Ma for two mafic dykes (SYG01 and SYG02) within the NCC. The dykes are classified as the sub-alkaline series according to their K2O+Na2O concentrations (2.5–2.9wt%), and as the calc-alkaline series according to their K2O concentrations (0.05–0.72wt%). These dykes also contain low concentrations of the light rare earth elements [(La/Yb)N=1.5–2.4], with negligible Eu anomalies (δEu=0.9–1.1), positive Ba, Pb, and K anomalies, and depletions in Th, U, and high field strength elements (P and Ti). In addition, the dykes contain relatively low amounts of radiogenic Sr[(87Sr/86Sr)i=0.7025–0.7035] and have high ɛNd(t) values (5.6–5.8). These data suggest that the dykes were derived from a depleted mantle source that was hybridized during interaction with foundered lower crustal material. The parental mafic magmas underwent the fractionation of olivine, pyroxene, hornblende, and Fe–Ti oxides (e.g. rutile, ilmenite, titanite) during ascent, with negligible evidence for crustal contamination prior to emplacement at a high crustal level. The NCC extension was related to foundering of lower crust, and there were three episodes of lithosphere extension during Proterozoic time (i.e. 1.8–1.6Ga, 1.3–1.2Ga, and 0.8–0.7Ga).