Average compositions of igneous melts from main geodynamic settings according to the investigation of melt inclusions in minerals and quenched glasses of rocks |
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Authors: | V B Naumov V I Kovalenko V A Dorofeeva A V Girnis V V Yarmolyuk |
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Institution: | 1.Vernadsky Institute of Geochemistry and Analytical Chemistry,Russian Academy of Sciences,Moscow,Russia;2.Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM),Russian Academy of Sciences,Moscow,Russia |
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Abstract: | We compiled a database containing more than 480000 determinations for 73 elements in melt inclusions in minerals and quenched
glasses of volcanic rocks. These data were used to estimate the mean contents of major, volatile, and trace elements in igneous
melts from main geodynamic settings. The following settings were distinguished: (I) oceanic spreading zones (mid-ocean ridges);
(II) zones of mantle plume activity on oceanic plates (oceanic islands and plateaus); (III) and (IV) settings related to subduction
processes, including (III) zones of island-arc magmatism generated on the oceanic crust and (IV) magmatic zones of active
continental margins involving the continental crust into magma generation processes; (V) intracontinental rifts and continental
hot spots; and (VI) back-arc spreading centers. The histogram of SiO2 contents in the natural igneous melts of all geodynamic settings exhibits a bimodal distribution with two maxima at SiO2 contents of 50–52 wt % and 72–74 wt %. The range 62–64 wt % SiO2 comprises the minimum number of determinations. Primitive mantle-normalized spidergrams were constructed for average contents
of elements in the igneous melts of basic, intermediate, and acidic compositions from settings I–V. The diagrams reflect the
characteristic features of melt compositions for each geodynamic setting. On the basis of the analysis of data on the composition
of melt inclusions and glasses of rocks, average ratios of incompatible trace and volatile components (H2O/Ce, K2O/Cl, Nb/U, Ba/Rb, Ce/Pb, etc.) were estimated for the igneous melts of all of the settings. Variations of these ratios were
determined, and it was shown that, in most cases, the ratios of incompatible elements are significantly different between
settings. The difference is especially pronounced for the ratios of elements with different degrees of incompatibility (e.g.,
Nb/Yb) and for some ratios with volatile components (e.g., K2O/H2O). |
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