International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Magmatic fluid segregation and overprinting hydrothermal processes in gabbro pegmatites of the Neotethyan ophiolitic Szarvaskő Complex (Bükk Mountains, NE Hungary)

Pages: 433 - 446

Authors: ATTILA PENTEK, FERENC MOLNAR, DAVID H. WATKINSON

Abstract: Pegmatites of the Szarvaskő Ophiolite Complex, Bükk Mts, NE Hungary were classified according to their shape (pockets, dykes) and texture (zoned, homogeneous), representing different stages of fluid enrichment during crystallization of the host gabbro. Local assimilation of adjacent sedimentary rocks increased the volatile-, and incompatible-element content of the melt. Most pegmatites crystallized from a locally segregated hydrous silicate melt, but some were intruded later. Pegmatites have mineral contents similar to their host gabbro, but are enriched in amphibole, biotite, Fe-Ti-oxides, quartz, and apatite. During formation of the pegmatites a fluid phase separated and caused deuteric alteration under magmatic-submagmatic conditions. Post-magmatic sea-floor hydrothermal activity is recognized by intense alteration and formation of a greenschist facies mineral assemblage at temperatures of 250–400 °C. Fluid inclusion studies revealed two aqueous fluid types related to this polyphase hydrothermal process. Alpine regional metamorphism caused intense deformation of the rocks, accompanied by veining of a low-grade metamorphic mineral assemblage. Primary fluid inclusions in vein-filling minerals and chlorite thermometry were used to obtain proposed conditions of 270–285 °C and 150–200 MPa for this process.

Keywords: Hungary, Bukk Mts, Alpine metamorphism, sea-floor hydrothermal alteration, deuteric alteration, magmatic fluid, gabbro pegmatite

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Volume 57 no. 6 / December 2006

Volume 57 no. 6