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High-quality Sr isotope data are critically dependent on the quality of reference materials that are used for instrumental calibration and data monitoring during LA-MC-ICP-MS analysis. A suite of natural plagioclase samples (BDL-1, BDL-2 and BDL-3) from the Badaling intrusive complex, Beijing were investigated here to test their suitability as a plagioclase Sr isotope reference material. Major and trace element analyses by EPMA and LA-ICP-MS showed that plagioclase crystals separated from two troctolites (BDL-1 and BDL-3) and one gabbro (BDL-2) were all characterized by extremely low Rb/Sr ratios (0.00012–0.00047), and low heavy rare earth elements (HREEs) and high Sr contents (2377–2836 μg g−1). A total of 200 LA-MC-ICP-MS analyses for plagioclases BDL-1, BDL-2 and BDL-3 showed consistent and homogeneous Sr isotopic compositions with an average 87Sr/86Sr ratio of 0.70535 ± 0.00007 (2SD), which was in good agreement with solution-based data determined by TIMS or SN-MC-ICP-MS (0.70533 ± 0.00004; 2SD, n = 12), thus suggesting that BDL plagioclase can be used as a potential reference material for microbeam Sr isotopic analysis. Compared to the other available plagioclase Sr isotopic reference materials, the large quantities, long-term availability, high Sr content and extremely low isobaric interference (Rb, Er and Yb) of BDL plagioclase make it especially suitable for instrumental calibration and to adjust for inter-laboratory bias of the measured 87Sr/86Sr ratios. [ABSTRACT FROM AUTHOR]

We present new whole rock major and trace element and, Sr–Nd–Hf isotope data for Mesozoic basalts and andesites from the Siziwangqi area, northwestern China, in order to constrain their petrogenesis and regional tectonic implications. The basalts belong to the shoshonitic series and can be subdivided into olivine (Ol-) and plagioclase (Pl-)basalts. The Ol-basalts have moderate MgO contents (5.1–5.5 wt%) and Mg# values (48.7–50.3), and trace element patterns similar to typical ocean island basalts with positive Nb–Ta and negative Pb anomalies. We interpret the Ol-basalts as mantle-derived rocks. The Pl-basalts and andesites are more differentiated than the Ol-basalts, and have low MgO contents (3.9–4.5 and 0.55–3.4 wt%, respectively) and Mg# values (40.3–43.3 and 26.9–47.4; respectively). Trace element (e.g., low Nb/U and Ce/Pb ratios) and Sr–Nd–Hf isotope data for the Pl-basalts and andesites indicate an origin by fractionation and mixing between the mantle-derived magma parental to the Ol-basalts and a crust-derived silicic magma. Crustal melting was induced by the underplating of the mafic parental magmas of the Ol-basalts. Geochemical features of the Ol-basalts, including high SiO 2 , Nb, Ta, Na 2 O/K 2 O, and Fe/Mn and low Rb/Sr and Dy/Yb, are best explained by the vein-plus-wall rock melting of a metasomatized mantle source consisting of amphibole–clinopyroxene-rich veins and surrounding peridotites. The Ol-basalts have enriched Sr–Nd isotopic compositions ((87Sr/86Sr) i = 0.70585–0.70597; ε Nd (t) = −2.8 to −2.6) and decoupled Hf–Nd isotopes with positive ∆ε Hf (t) (+4.5 to +5.0) that are consistent with recent enrichment of the lithosphere by subduction components from the Paleo-Asian oceanic slab. We propose that the Siziwangqi magmatism was related to intra-continental extension of the North China Craton. • New whole rock geochemical data for the Siziwangqi volcanic rocks, western NCC. • Geochemical variations of the rocks caused by magma mixing and fractionation. • A vein-plus-wall rock melting model for the genesis of olivine-basalts. • The Siziwangqi magmatism related to intra-continental extension in the NCC. [ABSTRACT FROM AUTHOR]