Geochemistry and Texture of Clinopyroxene Phenocrysts from Paleoproterozoic Picrobasalts, Karelian Craton, Fennoscandian Shield: Records of Magma Mixing Processes

Abstract

This paper presents an integrated major and trace element data and crystal size distribution analysis for zoned clinopyroxene phenocrysts hosted in variolitic and massive picrobasalts of the Suisaari Formation, Karelian Craton, Eastern Fennoscandian Shield. Clinopyroxenes in variolitic and massive lavas occur as unzoned, reverse, and normally zoned crystal. Oscillatory-zoned clinopyroxenes are only observed in variolitic lavas. The obtained data were examined in order to evaluate the contribution of magmatic processes such as magma mixing, contamination and fractional crystallization to the formation of various zoning patterns of clinopyroxene phenocrysts. Clinopyroxene phenocrysts in both variolitic and massive lavas originate from similar primary melts from a single magmatic source. The obtained data on composition and texture of clinopyroxene phenocrysts together with the crystal size distribution (CSD) analysis suggest that crystallization of the massive lavas mainly involves fractionation in a closed magmatic system, whereas the crystallization of the variolitic lavas is determined by processes in an open magmatic system. The results provide novel information on the evolution of Paleoproterozoic magmatic systems in the Karelian Craton.

Compositional Evolution of the Variscan Intra-Orogenic Extensional Magmatism in the Valencia del Ventoso Plutonic Complex, Ossa-Morena Zone (SW Iberia): A View from Amphibole Compositional Relationships

“…However, the composition of phenocrysts (crystallized directly from the magma), xenocrysts (extraneous to the whole magma plumbing system), and antecrysts (recycled in their own active magma plumbing system by various events) can provide valuable constraints on the nature of the components involved in hybrid magmas (e.g., [2][3][4][5][6][7][8][9]). Amphibole is very useful for this purpose because it can record the compositional changes in host magma from early to late crystallization stages.…”

Black Agates from Paleoproterozoic Pillow Lavas (Onega Basin, Karelian Craton, NW Russia): Mineralogy and Proposed Origin

“…The composition of pillow lavas ranges from basaltic andesite in ZF to picrobasalts in SF. Variolitic structure in the pillows was recognised in the lower part of the SF and is absent in ZF [32][33][34]. The inter-pillow matrix is represented by lava breccia, tuff, tuffites, or sandstones, sometimes with an admixture of CM.…”

Geochemical Insights from Clinopyroxene Phenocrysts into the Magma Evolution of an Alkaline Magmatic System from the Sanshui Basin, South China

“…The textural characteristics and compositional zoning of clinopyroxene record magmatic crystallization history and constrain magma storage conditions, which provides an opportunity to investigate the processes during magma ascent [2,9,10]. Clinopyroxene has been studied worldwide for a long period of time [2,7,[11][12][13][14][15][16][17][18][19][20]. Granular scale studies of clinopyroxene with different textures and compositions can be used to distinguish open-and closed-magma systems and provide the evidence necessary to unravel the evolution of magma systems and establish magma plumbing systems [1,2,11].…”