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

作　　者：M.Bogina V.Zlobin S.Svetov E.Sharkov A.Chistyakov 

机构地区：[1]Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences [2]Geological Institute, Russian Academy of Sciences [3]Institute of Geology, Karelian Scientific Center, Russian Academy of Sciences

出　　处：《Geoscience Frontiers》2018年第1期207-221,共15页地学前缘（英文版）

基　　金：supported by the Russian Foundation for Basic Research (Project Nos.16-05-00708 and 15-05-01214)

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_(εNd)(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 _(εNd)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_(εNd)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_(εNd)with Cr and Mg#,negative correlation with Th,and slight decrease of_(εNd)in the more evolved varieties.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 _(εNd)(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 _(εNd) 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 _(εNd) 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 _(εNd) with Cr and Mg#, negative correlation with Th, and slight decrease of _(εNd) in the more evolved varieties.

关 键 词：EARLY PALAEOPROTEROZOIC Siliceous high-magnesian SERIES (SHMS) rocks Sanukitoids MANTLE plume Depleted MANTLE Crustal contamination 

分 类 号：P[天文地球]