IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P4

Date/Time: July 24 Poster

Magma-mixing and -mingling as key magmatic processes controlling the development of
the volcanic events in the Gutâi Neogene Volcanic Zone, Eastern Carpathians, Romania
Marinel Kovacs1 , Alexandrina Fülöp2 , Zoltan Pécskay3 , Maria Jurje4
1Tech.Univ.Cluj-Napoca, North Univ.Center Baia Mare, Baia Mare, Romania, 2 DeBeers Canada Inc.,
Toronto, Ontario, Canada, 3 Institute of Nuclear Research of the Hungarian Academy of Sciences,Debrecen, Hungary, 4 Mineralogy Museum of Baia Mare, Baia Mare, Romania
E-mail: marinelkovacs@yahoo.com

The Gutâi Volcanic Zone (GVZ) belongs to the Neogene-Quaternary volcanic chain of the Carpathians developedon the north-western part of the Romanian territory. A calc-alkaline intermediate volcanism represented by a seriesof rocks ranging from basalts to rhyolites (andesites are the prevalent ones) took place during Miocene (13.4-7.0
Ma). The mineralogical, textural and geochemical features of many of the igneous rocks from GVZ suggest thatmagma-mixing and -mingling processes were involved during their genesis (e.g. the large-sized embayed sanidine
crystals coexisting with high Mg# (85-90) chromian-diopside and high amount of gabbroic-type MME in the same
biotite dacite and the large-sized sieve-textured or strong reverse zoned plagioclases together with large-sized
embayed quartz crystals in the same andesite rock). Most of the rock types are dacites and subordinately
andesites mainly related to extrusive domes (13.2-8.0 Ma). In some cases, two different but co-genetic rocktypes appear spatially and temporally associated as a result of magma-mixing and -mingling (e.g. biotite dacite
and biotite andesite). Sometimes, one of the rocks is a hybrid rock such as a MME-hosting dacite and the otherone is compositionally close to the potential basic end-member such as a basaltic andesite with 51.5-54.3 SiO2 .
Some of the magma-mixing and -mingling products show compositions matching with the acidic end-members(e.g. the biotite dacites/rhyolites with glassy, perlitic groundmass texture). The mineralogical and geochemicalsimilarities between the MME of the dacite rocks and some of the basaltic rocks from GVZ suggest the involvementof such basaltic magmas as basic end-members. These features enable the reconstruction of the magmatic
processes developed in the crustal magma chambers or in the volcanic conduit, processes which controlled theemplacement of these rocks. Many volcanic events controlled by repeated magma-mixing and -mingling processes
took place during the volcanic activity of GVZ and conducted to the emplacement of important volcanic structures bytriggering the eruption events timewise in different locations of the area. The different PT parameters of the mineralphases contained in the hybrid rocks, suggest different conditions of evolution of the magma-mixing and -mingling
processes involving different magmatic sources. The small-volume acidic MME-hosting volcanic rocks (e.g. theDănesti dacite/rhyolite -11.6 Ma, Valea Morii dacite -10.1 Ma and Laleaua Albă dacite -8.0 Ma) resulted frommagma-mixing and -mingling processes developed in small-sized, shallow level evolved/silicic reservoirs. Opposite
to these, some hybrid rocks which represent one of the dominant volcanic phases in GVZ (e.g. the large-spreadquartz andesite complexes – 11.3-10.5 Ma) resulted from magma-mixing and -mingling processes developed inlarge-sized differentiated magma chambers with near-continuous replenishment by new basaltic magmas.

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