Mineralogical, geochemical characteristics, and genesis of Shangdong meta-basalt in Southern Jiangxi

Objectives The recently discovered meta−basalt in Shangdong, southern Jiangxi Province, is situated at the southern margin of the Cathaysia Caledonian fold belt. Investigating its petrogenesis and tectonic setting of formation is crucial for elucidating the tectonic nature of the South China Caledonian fold belt.

Methods This study focuses on the Shangdong meta−basalt, employing a comprehensive approach combining mineralogical observations and detailed geochemical analyses to constrain its geological history.

Results Mineralogical examination reveals that the Shangdong meta−basalt is primarily composed of hornblende, plagioclase, pyroxene, and biotite. Geochemical data indicate that it belongs to the sub−alkaline tholeiite series, characterized by moderate Mg^# values (40.44~45.16), a distinct Na−rich/K−poor signature (K₂O/Na₂O=0.07~0.16), moderate enrichment of light rare earth elements, negligible Eu anomalies (Eu=1.03~1.11), and notable depletion in Sr, Nb, and Ta despite relative Nb enrichment. Mineral−specific analyses further demonstrate that pyroxene is a Mg−Ca−rich augite with a crystallization temperature of 1184 °C; biotite is ferrobiotite, crystallizing at 660 °C and exhibiting high Al and Fe contents with low Mg and K; hornblende is a Ca−rich, Ti−poor, Fe−Al−enriched common hornblende within the calcic amphibole group, crystallizing at 594°C; and plagioclase is a Ti−poor, Na−Al−rich andesine−oligoclase.

Conclusions Collectively, these findings suggest that the Shangdong meta−basalt formed under high−temperature and high oxygen fugacity conditions, originating from a magma generated by crust−mantle mixing. Its geochemical and mineralogical features are indicative of an island arc tectonic setting, strongly implying that the South China region experienced a subduction−related tectonic regime during the Early Paleozoic Caledonian orogeny.