Origin of zoned tourmalines in graphite-rich metasedimentary rocks from Macedonia, northern Greece
Michailidis, Kleopas; Kassoli-Fournaraki, Anna; Dietrich, Richard V.
European Journal of Mineralogy Volume 8 Number 2 (1996), p. 393 - 404
published: Apr 26, 1996
manuscript accepted: Nov 28, 1995
manuscript received: Oct 19, 1994
ArtNo. ESP147050802019, Price: 29.00 €
Abstract Tourmalines are studied from graphite-rich metasedimentary rocks of the Polydentri-Kolchiko area in Macedonia (northern Greece). Associated minerals include quartz, muscovite, biotite, sericitized plagioclase, chlorite, titanite, calcite, graphite, rutile, limonitized pyrite, with minor apatite and ilmenite. Most of the tourmaline grains, which are of schorl-dravite composition, display a discontinuous and complex zoning of alternating Fe-rich and Mg-rich zones. Textural relations, chemistry and zoning patterns preclude a secondary growth of metamorphic tourmaline rims on detrital tourmaline fragments. Tourmaline chemistry confirms the metasedimentary origin of the host rocks. The studied tourmalines are considered as resulting from progressive metamorphism of boron-rich aluminous clay precursors. The discontinuous chemical zoning is interpreted as the result of a metamorphic fluid influx of different composition. The tourmalines are thought to have retained mostly their textural and chemical characteristics through subsequent deformational and retrogressive metamorphic events.