Age and origin of a Palaeozoic nepheline syenite from northern Shanxi Province, China: U-Pb zircon age and whole-rock geochemical and Sr-Nd isotopic constraints

摘要

Geochronological, geochemical, and whole-rock Sr-Nd isotopic analyses were performed on a suite of Palaeozoic nepheline syenites from Zijinshan to characterize their ages and petrogenesis. Laser ablation inductively coupled plasma-mass spectrometry U-Pb zircon analyses yield consistent ages of 525.7 ± 2.8 million years for a sample (HYK01). These intrusive rocks belong to the foid syenite magma series in terms of K₂O + Na₂O contents (14.3-15.2 wt.%) and to the shoshonitic series based on their high K₂O contents (5.42-5.61 wt.%). The nepheline syenites are further characterized by high light rare earth element contents [(La/Yb) _N  = 29.1-36.1]; show modest negative Eu anomalies (δEu = 0.5-0.6) and positive anomalies in Rb, Th, U, Pb, Zr, and Hf; are depleted in Ba and high field strength elements (P and Ti). In addition, all the nepheline syenites in this study display relatively low radiogenic Sr (87Sr/86Sr) _i (0.7042-0.7043) and positive ϵ_Nd (t) (0.7-0.8). These results suggest that the nepheline syenites were derived from depleted continental crust. The parent magmas likely experienced fractional crystallization of plagioclase, Ti-bearing oxides (e.g. rutile, ilmenite, and titanite), apatite, and zircon during ascent, with negligible crustal contamination before final emplacement at a high crustal level.View full textDownload full textKeywordsnepheline syenites, petrogenesis, Palaeozoic, Shanxi Province, North China CratonRelated var addthis_config = { ui_cobrand: "Taylor & Francis Online", services_compact: "citeulike,netvibes,twitter,technorati,delicious,linkedin,facebook,stumbleupon,digg,google,more", pubid: "ra-4dff56cd6bb1830b" }; Add to shortlist Link Permalink http://dx.doi.org/10.1080/00206814.2011.638436