Abstract:

LA-ICP-MS zircon U-Pb age and geochemical data are presented for the Mesoproterozoic diabase from Tonghua region, Jilin Province, with the aim of constraining the Mesoproterozoic tectonic setting in the northeastern part of the North China block and its relationship with the break-up of the Columbia supercontinent. The analyzed zircons from the diabase show euhedral crystals in shape, and yield high Th/U ratios (0.21-1.45). Their REE patterns are characterized by depletion in light rare earth elements (LREEs) and enrichment in heavy rare earth elements (HREEs), as well as positive Ce anomalies and negative Eu anomalies, indicating a magma origin. Zircon U-Pb dating results exhibit that seven analyzed points constitute a discordant line, with the upper intercept age of (1 244±28) Ma, which represent the forming age of the diabase, i.e. Mesoproterozoic. Geochemically, the samples from the diabase have SiO₂=49.3%-49.5%, Mg^#=42.2-42.6, and TFe₂O₃=13.6%-14.1%, and belong to tholeiitic series. Their trace elements are characterized by enrichment in LREEs and large ion lithophile elements (LILEs), and depletion in HREEs, and weakly depletion in Nb and Ta and enrichment in Ti, as well as no obvious Eu anomalies. Ba/Nb and La/Nb ratios of them are 15.8-17.3 and 1.15-1.20 respectively. Based on the above-metioned evidences, the Mesoproterozoic diabase is derived from the partial melting of lithospheric mantle with the involvement of the melts from the asthenosphere mantle. Combined with the available research on the Precambrian geological events on the northern margin of the North China block, it is suggested that the Mesoproterozoic diabase formed in a strongly extensional setting, as a result of the break-up of Columbia supercontinent.

Key words: Tonghua region, Mesoproterozoic, diabase, zircon U-Pb dating, geochemistry, Columbia supercontinent