Original paper

Intergrowth of graphite within phlogopite from Finero ultramafic complex (Italian Western Alps): implications for mantle crystallization of primary-texture mica

Ferraris, Cristiano; Grobety, Bernard; Frü h-Green, Gretchen L.; Wessicken, Roland

Abstract

High Resolution Transmission and Analytical Electron Microscopy (HRTEM-AEM) of phlogopite crystals from the Finero lherzolite (Italian Western Alps) revealed nanometric intergrowths of graphite-like layers. The intergrowths consist of 4 to 6 graphite-like layers (c ≈ 3.3 Å) with the basal plane parallel to (001) of the phlogopite host. The phlogopite crystals contain between 0.024 and 0.048 wt % of carbon. The carbon isotope composition varies from δ13Cgraphite = −16.1 ‰ to -10.4 ‰ (VPDB). These values are compatible with carbon phases found in other mantle-derived ultramafic rocks. A Raman analysis confirms the presence of a graphite-like phase intergrown within phlogopite. Geochemical and microtextural data point to a primary origin of the phlogopite-graphite intergrowths and suggest simultaneous crystallization of both phases from a trapped partial melt.

Keywords

phlogopitegraphitehrtem-aemintergrowthfinero peridotite