Can we identify source lithology of basalt?

Area of Science:

• Geochemistry
• Petrology
• Earth Science

Background:

• Understanding basaltic magma source rocks is crucial for deciphering Earth's composition and evolution.
• Identifying the precise lithology of basaltic source rocks remains a significant challenge in geochemistry and petrology.

Purpose of the Study:

• To introduce a novel parameter, the FC3MS value, for distinguishing between peridotite and pyroxenite sources of basaltic magmas.
• To re-evaluate the source lithology of continental oceanic island basalt-like volcanic rocks (C-OIBs) in eastern China and Mongolia.

Main Methods:

• Utilized multi-decadal melting experiments on various peridotite and pyroxenite compositions.
• Developed and applied the FC3MS value (FeO/CaO-3*MgO/SiO2, in wt%) as a diagnostic tool.
• Analyzed phase diagrams to determine equilibrium conditions for C-OIBs.

Main Results:

• The FC3MS value effectively identifies most pyroxenite-derived basalts.
• C-OIBs from eastern China and Mongolia exhibit FC3MS values inconsistent with a peridotite source.
• Phase equilibria indicate garnet pyroxenite as the dominant source for the majority of studied C-OIBs.

Conclusions:

• Garnet pyroxenite is identified as a primary source lithology for many C-OIBs.
• Many evolved low-magnesian C-OIBs are likely primary melts from pyroxenites, not evolved peridotite melts.
• Previous interpretations of basaltic origins based solely on peridotite models require re-evaluation.