Carboniferous appinitic intrusions from the northern North China craton: geochemistry, petrogenesis and tectonic implications

<p>Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating and geochemical study document Carboniferous (<em>c</em>. 320–317 Ma) appinitic intrusions from the northern North China craton. The rock suite mainly consists of hornblende diorites and monzodiorites, with an SiO<sub>2</sub> range from 46.8 to 55.4%. These rocks exhibit high alkali contents, strong enrichment in large ion lithophile elements and light rare earth elements, and depletion in high field strength elements, with radiogenic <sup>87</sup>Sr/<sup>86</sup>Sr<sub>i</sub> ratios of 0.7058–0.7093, unradiogenic ϵ<sub>Nd</sub>(t) of −9.3 to −13.9 and zircon ϵ<sub>Hf</sub>(t) from −8.5 to −18.4. These geochemical features suggest that their generation may involve a distinctive two-stage process: (1) a precursory metasomatism stage of mantle peridotites by melts from subduction-related sediments; (2) a delayed partial melting stage probably initiated by post-subduction transcurrent movements along pre-existing lithospheric shear zones. These mafic to intermediate intrusions, plus other coeval mafic– ultramafic complexes and high Ba–Sr granites from neighbouring regions, not only witness a heterogeneously enriched subcontinental lithospheric mantle along the northern North China craton, but also attest to a reworking-dominated metacratonic process within a post-subduction transtensional regime. </p>