Geochronology and Hf-Fe isotopic geochemistry of the Phanerozoic mafic-ultramafic intrusions in the Damiao area, Northern North China craton: implications for lithospheric destruction

Timing and source of several Fe-mineralized mafic-ultramafic intrusions in the Damiao area are investigated here by coupling new geochronological and Hf-Fe isotopic data with previous results. Although regarded as a Late Paleoproterozoic assemblage previously, two ∼140 Ma intrusions are recognized by zircon U-Pb dating, indicating emplacement of these intrusions from Middle Devonian to Early Cretaceous times. Both Hf and Fe isotopic features lead to the conclusion that distinct mantle components contributed to their magma generation. As the first magmatic phase, the 395 Ma intrusions were mainly derived from the slightly-enriched SCLM that was prevalent during the Paleozoic. However, asthenospheric material was strongly involved in the formation of the ∼ 215 Ma Gaositai intrusion. Therefore, the initiation of lithospheric destruction in the northern NCC is inferred to have occurred in Late Triassic time, triggered by post-orogenic extension following the ∼ 250 Ma collision between the Siberian Craton and the NCC. The ∼140 Ma intrusions originated from a significantly-enriched mantle component probably resided in the predominant slightly-enriched SCLM. This mantle source would have melted in the Late Mesozoic, when the thin lithosphere enabled enhanced heat transfer from the asthenosphere. In summary, these distinct mantle sources of mafic-ultramafic magmatism provide a record of mantle heterogeneity and the gradual upward migration of the lithosphere-asthenosphere boundary during lithospheric destruction. (author)