科研之友
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摘要
We investigated the meta-gabbronorites in Liangcheng and used detailed petrography, geochemistry, zircon geochronological and in-situ Hf isotopic studies to clarify their formation and metamorphic ages, petrogenesis, tectonic setting and provide constraints on the tectonic evolution of Khondalite Belt (KB). The zircon U-Pb dating results show that the meta-gabbronorites crystallized at similar to 1.94 Ga and were metamorphosed at similar to 1.91-1.89 Ga. They can be subdivided into the low-Mg and high-Mg groups. The low-Mg meta-gabbronorites contain relatively lower MgO and higher SiO2 contents than high-Mg meta-gabbronorites. They are enriched in light rare earth elements and large ion lithophile elements, depleted in high field strength elements, and exhibit positive (high-Mg meta-gabbronorites) and negative (low-Mg meta-gabbronorites) Sr and Eu anomalies. The zircon in-situ epsilon(Hf)(t) of meta-gabbronorites is 0.07-4.12, with Hf model ages (T-DM) of 2169-2400 Ma. The meta-gabbronorites in Liangcheng originated from the asthenospheric mantle and experienced fractional crystallization of olivine, orthopyroxene, clinopyroxene, and plagioclase. They were contaminated by the crustal rocks (mainly khondalite series) during ascent, especially for low-Mg gabbronorites. The ridge subduction is the most plausible tectonic setting for meta-gabbronorites, indicating the eastern segment of KB was in a ridge subduction setting at similar to 1.94 Ga following an orogenic thickening event during a prolonged orogenic process.
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