Vice Professor ZHANG Xiaohui and his team present new laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb age, whole-rock geochemistry and Sr–Nd isotopes, and in situ zircon Hf isotopic compositions for the Carboniferous mafic to intermediate intrusive rocks from southern Inner Mongolia along the northern North China craton.

They try to document the geochemical characteristics of these rocks; to trace their magma sources and constrain their petrogenesis; and to probe the tectonic environment in which they evolved.

The rock suite mainly consists of hornblende diorites and monzodiorites, with 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.

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.

Zhang et al. Carboniferous appinitic intrusions from the northern North China craton: geochemistry, petrogenesis and tectonic implications. Journal of the Geological Society (London). 2012, 169: 337-351 (Download Here)