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

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• 作者：Shen Liu ; Caixia Feng ; Bor-ming Jahn ; Ruizhong Hu ; Shan Gao ; Guangying Feng ; Shaocong Lai ; Yuhong Yang ; Youqiang Qi ; Ian M. Coulson
• 关键词：Paleoproterozoic ; Mafic dykes ; Origin ; Extension ; Northern NCC
• 刊名：Precambrian Research
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：236
• 期：Complete
• 页码：182-192
• 全文大小：3700 K

文摘

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 ¡À 6 and 1621 ¡À 7 Ma 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 (2.5-2.9 wt % ), and as the calc-alkaline series according to their K₂O concentrations (0.05-0.72 wt % ). These dykes also contain low concentrations of the light rare earth elements [(La/Yb)_N = 1.5-2.4], with negligible Eu anomalies (¦ÄEu = 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 ?_Nd(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. 1.8-1.6 Ga, 1.3-1.2 Ga, and 0.8-0.7 Ga).