Intra-continental basalt data mining: The diversity of their constituents and the performance in basalt discrimination diagrams

It is generally considered that continental flood basalts (CFB), rift basalts (CRB), within-plate basalt (WPB) are produced in the plate tectonic setting which is related to the mantle plume activities from the enriched lower mantle, similar to OIB in terms of geochemistry characteristics. In this paper, a GEOROC database of the global CFB, CRB and WPB is used to find that these three categories almost fall in all various basalt tectonic environment areas, some even primarily falls in MORB or IAB, but not in WPB area. This result suggests that the original discriminant function of the basalt discrimination diagrams is still questionable, especially, there exist some problems in most of the discrimination diagrams of continental basalt. All these tremendous changes of CFB, CRB and WPB geochemistry compositions suggest that the source may be strongly heterogeneous: some of CFB, CRB and WPB come from enriched mantle plume with classic characteristics of OIB, some of them derive from MORB source related with the slab-recycled effect, and others from depleted mantle source beneath the island arc lithosphere, characterized by obvious Nb-Ta depletion, similar to island arc basalts. In many places, continental basalts can be divided into two types: low titanium and high titanium. Low-Ti basalts are depleted or strongly depleted, and high-Ti basalts are usually enriched. The study of this paper shows that enriched-type basalts may come from enriched lower mantle, but strongly-depleted-type or depleted-type basalts may derive from the astheospheric mantle characterized by MORB or TAB. The study further points out that the nature of the source may be the main controlling factor of the qualities of continental basalts. Meanwhile, there are many other important factors leading to the diversity of continental basalts, such as the degree of partial melting, melting depth, fractional crystallization, crustal contamination and AFC process.