Specifics of the Neoarchean Plume–Lithospheric Processes in the Kola–Norwegian Province of the Fennoscandian Shield: II. Petrology and Geodynamic Nature of Komatiite–Tholeiite Association

Resumo

Numerical modeling of the generation and evolution of parental melts of the komatiite–tholeiite association of the Uraguba structure was carried out using previously obtained geochemical and isotope data. It was established that komatiite, komatiite and tholeiite basalts depleted in LREE and having ε_Nd(Т = 2.79) = +2.9…+3.2 were generated by equilibrium partial melting (F > 15%) of a depleted source (garnet-bearing Ol_0.63 + Opx_0.22 + Cpx_0.06 + Grt_0.09 mantle peridotite) at 4–8 GPa, while the genesis of primary melts of LREE-enriched komatiites (La_N/Sm_N ~ 1.2–1.6) with ε_Nd(Т = 2.79) = +2.5…+2.2 was related to the equilibrium partial melting (F > 20%) of an “enriched mantle peridotite” (EM–Ol_0.60 + Opx_0.20 + Cpx_0.08 + Grt_0.12) at pressure of 2.5–4 GPa. Coexistence in space and time of two types of melting products of mantle peridotites formed at different depths is explained by melting of different parts of adiabatically ascending mantle plume.