Carboniferous appinitic intrusions from the northern North China craton: geochemistry, petrogenesis and tectonic implications
Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating and geochemical study document Carboniferous (c. 320–317 Ma) appinitic intrusions from the northern North China craton. The rock suite mainly consists of hornblende diorites and monzodiorites, with an SiO2 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 87Sr/86Sri ratios of 0.7058–0.7093, unradiogenic ϵNd(t) of −9.3 to −13.9 and zircon ϵHf(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.