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 Sr-87/Sr-86(i) ratios of 0.7058-0.7093, unradiogenic epsilon(Nd)(t) of -9.3 to -13.9 and zircon epsilon(Hf)(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.