Geochemistry of mafic extrusive lavas in the Bayankhongor Ophiolite, Mongolia
DOI:
https://doi.org/10.5564/mgs.v30i61.4029Keywords:
Pillow lava, EMORB, OIBAbstract
This study presents new geochemical data on pillow lavas from the Bayankhongor Ophiolite in western Mongolia, revealing compositions that range from sub-alkaline to alkaline basalts. While most of these basalts are tholeiitic, some show transitional geochemical variations. Except for one sample resembling normal mid-ocean ridge basalt, all others are enriched in light rare earth elements and closely resemble enriched mid-ocean ridge basalt and ocean island basalt. The presence of high-field strength elements such as Th, Ta, Nb, Zr, Hf, and Ti indicates a mantle-derived origin. Tectonic discrimination diagrams demonstrate a transition between enriched mid-ocean ridge basalt and within-plate basalt, characteristic of mid-ocean ridges. The samples are categorized into three groups based on the LREE variation: low- normal mid-ocean ridge basalt, high- enriched mid-ocean ridge basalt, and ocean island basalt, suggesting advanced partial melting of the mantle and a mixing of mid-ocean ridge basalt with ocean island basalt. The Bayankhongor Ophiolite is widely recognized as a subduction-unrelated ophiolite and represents one of the largest Neoproterozoic oceanic rift basins in the Central Asian Orogenic Belt. Consequently, subduction-unrelated tectonic models are often favored for the Bayankhongor Ophiolite, which somewhat aligns with our findings. However, recent studies highlight the importance of subduction-related models and timing. Our model aims to integrate both aspects.
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