Naslov
Ca-amphiboles in the gabbroic rock blocks from the ophiolite mélange of the Medvednica Mts. (Croatia)

Autori
Slovenec, Damir ; Lugović, Boško

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
22nd IAS Meeting of Sedimentology, Abstracts Book / Vlahović, Igor - Zagreb : Institut za geološka istraživanja, Zagreb, 2003, 200-200

Skup
22nd IAS Meeting of Sedimentology

Mjesto i datum
Opatija, Hrvatska, 17.09.2003. - 19.09.2003

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
Medvednica Mts.; ophiolite mélange; gabbroic blocks; Ca-amphiboles

Sažetak
Ophiolite mélange, or in the other words subduction-accretion prism rock assemblage, is a chaotic sedimentary complex in term of dimension, lithology, age and tectonic setting of archived blocks. Detailed and systematic investigation of sedimentary and magmatic members of an ophiolite-bearing mélange may help to reconstruct integral geodynamic evolution of an oceanic branch or realm. Here we present the brief report of initial investigations on mega-blocks of mafic intrusives from the ophiolite mélange of the Medvednica Mts. Medvednica Mt. is located at southwesternmost part of Zagorje-Mid-Transdanubian Zone and represent locus where the northwesternmost ophiolitic rocks assigned to the Sava segment of the Vardar Ophiolite Zone crop out. The blocks of these rocks, thought to represent a fragmented oceanic crust, are found bound by pelitic to siltous matrix along with the blocks of various sedimentary rocks, including radiolarites. This unit is interpreted as tectonic ophiolite mélange (Pamić & Tomljenović, 1998). The exact age and tectonic setting of the ophiolite(s) formation including mélange is still disputable. Mafic intrusives with cumulus and isotropic textures and gabbro-pegmatites are found subordinately amongst ophiolitic blocks dominated by extrusives. These rocks are altered to metagabbros whereby albitization is the most severe alteration. Both gabbroic textural varieties contain three successive generations of Ca-amphiboles: texturally equilibrated igneous Ti-tschermakite, magnesiohornblende as late stage crystallization product and as reaction product after clinopyroxene, and late stage actinolite alterations after all ferromagnesian minerals. The gabbroic rocks (following the order of crystallization) are assembled of: chromian spinel, olivine, clinopyroxene - augite (Wo44-45En42-44Fs13-14), plagioclase, tschermakite (Al2O3 > 7 wt.% AlVI/AlIV = 0.009-0.062 ; TiO2 &#8805 ; ; 1.7 wt.%) and magnesiohornblende. Chemical mapping of Ti-tschermakite showed compositional zoning patterns typical of fractional crystallization and cooling with Ti, Al and Na continuously decrease and Si and Mg increase towards the grain periphery. The maximum P-T conditions of the last equilibration of tschermakite in gabbroic rocks are estimated up to 850°C at up to 0.55 GPa. The occurrence of igneous amphiboles of tschermakitic composition in the early stage of the crystallization decipher the formation of the Medvednica Mt. ophiolitic deep crustal sequence in a tectonic setting best represented by supra-subduction zone. The conclusion corroborates with low-Ti bulk composition of the host rocks. However, the abundant occurrence of high-Ti extrusive blocks admixed in the mélange strongly suggests a complex geodynamic evolution of a Tethyan ocean segment where ophiolitic rocks of Medvednica Mt. formed.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA