Petrogenesis of siliceous high-Mg series: Evidence from Early Paleoproterozoic mafic volcanic rocks of the Vodlozero Domain, Fennoscandian Shield

摘要

Compositional peculiarities of the siliceous high-Mg series (SHMS) rocks formed at the Archean–Paleoproterozoic boundary as a function of plume activity are discussed using example of Early Paleoproterozoic mafic volcanic rocks of the Vodlozero Domain, Fennoscandian Shield. These rocks are characterized by wide variations in Mg# (33–67) and Cr contents (25–1123?ppm), LREE enrichment, and weakly negative ε Nd (from –0.7 to –2.9). The high Gd/Yb ratio in the primitive high-Mg rocks of the Vodlozero Domain suggests their generation from a garnet-bearing source. At the same time, their negative ε Nd in combination with LREE enrichment points to the crustal contamination. A new model was proposed to explain the remarkable global-scale similarity of SHMS. Such rocks can be generated by the contamination of a high-degree (30%) partial melt derived from a depleted mantle. The lower crustal sanukitoid-type rocks can be considered as a universal crustal contaminant. Modeling showed that such mixing can provide the observed narrow ε Nd variations in Early Paleoproterozoic volcanics. The Neoarchean sanukitoid suites, which are widespread on all cratons, presumably composed the lower crust at the beginning of the Paleoproterozoic. Therefore, this mechanism can be considered universal for the genesis of the SHMS rocks. The high- to low-Cr rock series can be produced by the fractionation of the mafic melt coupled with an insignificant crustal assimilation of felsic end members of the sanukitoid suite of the Vodlozero Domain en route to the surface, as suggested by the positive correlation of ε Nd with Cr and Mg#, negative correlation with Th, and slight decrease of ε Nd in the more evolved varieties. Graphical abstract Display Omitted Highlights ? ～2.45?Ga mafic volcanics of the SHMS series of the Vodlozero block are studied. ? Their derivation via mixing of depleted mantle and adakitic lower crust is proposed. ? The entire rock series is modeled by AFC with Ol, Cpx, and Pl as liquidus phases.