Trace Element Contents of Mantle-Derived Magmas Through Time

Abstract A large compilation of quality-curated major and trace element data has been assembled to investigate how patterns mafic ultramafic magmas have varied with time through particular settings from the Archean Phanerozoic, primary objective being recognise at what times variation emerge, similar these are baseline sets representing tectonic in modern Earth. The most informative combinations involve Nb, Th REE, where REE represented by ‘lambda’ parameters describing slope shape patterns. Combinations ratios Th, La lambda values early Proterozoic basalts komatiites reveal a distinctive pattern that is common well-sampled terranes, defining roughly linear trend multi-dimensional space compositions intermediate between n-MORB primitive mantle one end, towards approximating middle-to-upper continental crust other. We ascribe this ‘Variable Th/Nb’ instances varying degrees crustal contamination oceanic plateau basalts. Komatiites had slightly more depleted sources than basalts, consistent hypothesis derivation plume tails heads, respectively. significant difference Precambrian Phanerozoic plume-derived OIB-like enriched source component appears be largely missing geologic record, although isolated examples characteristics evident datasets even oldest preserved greenstones. intra-cratonic LIPs, such as 260 Ma Emeishan LIP China, fundamentally different geochemical Paleoproterozoic assemblages; we identified type ‘modern’ signal Midcontinent Rift 1100 Ma. tail having changed dominantly Earth Earth, while head hardly all. Trace considered diagnostic subduction locally present but rare terranes become prevalent Proterozoic, conclusion tempered degree overlap compositional arc flood This reflects difficulty distinguishing effects supra-subduction metasomatizm flux melting those contamination. Additional factors must also borne mind, particularly partitioning systematics may all environments hotter planet, large-scale asthenospheric overturns might predominant over modern-style plumes Some basaltic suites notably western parts both Yilgarn Pilbara cratons Western Australia Superior Craton, restricted, predominant, akin arcs, suggesting some process was belts. Ferropicrite typical OIBs LIPs (notably Emeishan) implying were beginning fertilised enriched, probably subducted, components far back Mesoarchean. see no evidence for discontinuous secular changes mantle-derived magmatism could ascribed reorganisation events. Archean–Proterozoic transition entirely gradational standpoint. Archean-style Phanerozoic-style took place somewhere 1900 (age Circum-Superior komatiitic basalt suites) (the age LIP).