Magma-mixing and -mingling as key magmatic processes controlling the development of the volcanic events in the Gutâi Neogene Volcanic Zone, Eastern Carpathians, Romania. Kovacs1, M., Fülöp2, A., Pécskay3, Z., Jurje4 M. 1. Technical University of Cluj-Napoca, Baia Mare North Univ. Center, Baia Mare, Romania;
[email protected]. 2. De Beers Canada 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.
General data Location of the CarpathianPannonian Region (CPR)
A calc-alkaline intermediate volcanism took place in the GVZ, northern part of the Romanian territory during Miocene (Sarmatian-Pannonian/13.4-7.0 Ma, Pécskay et al.,2006). A series of rocks ranging from basalts to rhyolites (medium-K andesites are the prevalent ones) emplaced and overlapped the previous felsic volcanic rocks (Badenian ignimbrites).
Gutâi Volcanic Zone (GVZ) in the CPR GVZ
The mineralogical, textural and geochemical features of many of the igneous rocks from GVZ suggest that magma-mixing and -mingling processes were involved during their genesis. The majority of these rock-types consist of dacites (and subordinately andesites) mainly related to extrusive domes of different ages (13.2-8.0 Ma) and with different location in the volcanic area:
1. Şatra dacite extrusive dome (13.2 Ma); 2. Dăneşti-Piatra Roşie rhyolite-dacite interconnected domes (11.6 Ma); 3. Quartz andesite lava flows and domes (11.3-10.5 Ma); 4. Valea Morii dacite extrusive dome (10.3 Ma); 5. Pleşca Mare composite (dacite-andesite) extrusive dome (9.3 Ma); 6. Gutin andesite extrusive dome (9.0 Ma); 7. Laleaua Albă composite complex (dacite-andesite of 8.58.0 Ma).
The Gutâi Volcanic Zone (GVZ) belongs to the Neogene-Quaternary volcanic chain of the Carpathians built up during the Miocene subduction of the European Plate beneath the two microplates Alcapa and Tisza-Dacia in the Carpathian-Pannonian Region (CPR).
Constraints of the magma-mixing and -mingling processes Laleaua Albă composite complex (8.5-8.0 Ma) [7] Extrusive dome comprised of sanidine dacites core (hosting abundant mafic microgranular enclaves/MME) enveloped by aphyric andesites.
A
A
Quartz andesite lava flows and domes (11.3-10.5 Ma) [3]
Large-sized embayed sanidine crystals co-existing with high Mg# (85-90) chromiandiopside. Dacite The mineralogical and geochemical similarities between the MME of the dacite rocks and some of the basaltic rocks from GVZ suggest the involvement of basaltic magmas as basic end-members.
Disequilibrium textures and high chemistry variation of the phenocrysts: Large-sized embayed quartz crystals
Strong oscillatory zoned plagioclase
Extreme compositions in the same crystal (An26-85)
3 mm
D
Clinopyroxenes
MME
High Al CA basalt (8.1-7.0 Ma)
Andesite
Microscopic scale contact as mingling between dacitic (D) and andesitic/hybrid (A) material
High Mg# (73-85) zoned clinopyroxene, similar with the basaltic rocks
D A
MME 0.7 mm
3 mm
Dăneşti-Piatra Roşie rhyolite-dacite interconnected domes (11.6 Ma) [2]
0.2 mm
1 mm
Gutin andesite extrusive dome (9.0 Ma) [6]
High Mg# augite as crystal clusters in the rhyolite
The small-volume acidic MME-hosting volcanic rocks (e.g. the Dănesti rhyolite/dacite [2], Valea Morii dacite [4] and Laleaua Albă dacite [7]) resulted from the magma-mixing and -mingling processes developed in small-sized, shallow level evolved (silicic) Conclusions reservoirs.
1mm 1mm
MME from rhyolite
Mingling between the silicic endmember and the dacitic hybrid rock
Some of the magma-mixing and -mingling products show Volcanic events controlled by compositions matching with the acidic end-members (e.g. the repeated magma-mixing and mingling processes biotite rhyolites/dacites with glassy, perlitic groundmass texture)
Quartz crystals with pyroxene coronas
1mm 0.5mm
1mm
Opposite to these, the hybrid rocks which are among the dominant volcanic phases in GVZ (e.g. the large-spread quartz andesite complexes [3]) resulted from the magma-mixing and mingling processes developed in large-sized differentiated magma chambers with near-continuous replenishment by new basaltic magmas. P-T parameters suggest that the mafic parental magma was stored and crystallized at 16-20 km (Al in hornblende and amph-plg barometers)
Conclusions A series of volcanic events recorded during the evolution of the volcanism in GVZ were triggered by repeated magma-mixing and -mingling processes developed from time to time in different locations. The Neogene volcanism from the Gutâi Volcanic Zone had a complex evolution. The mineralogical, chemical and textural features of the volcanic rocks suggest complex opensystem processes, dominantly magma-mixing and -mingling between the basaltic and the silicic magmas.
Selected references Browne et al. (2006): Generation of porphiritic and equigranular mafic enclaves during magma recharge events at Unzen volcano, Japan. Journal of Petrology, 47(2):301-328 Hiragana et al. (2009): Petrogenesis of mafic and associated silicic end-member magmas for calc-alkaline mixed rocks in the Shirataka volcano, NE Japan. Contrib Mineral Petrol, 157:709-734 Kovacs, M.& Fülöp, A. (2003): Neogene volcanism in Gutâi Mts. (Eastern Carpathians). A review. Studia Universitatis Babeş - Bolyai, GEOLOGIA, XLVIII, 1: 3-16. Kovacs, M. & Fülöp, A. (2010): Laleaua Alba quarry: a Neogene composite igneous body., Acta Mineralogica-Petrographica, 19: 32-35. Pécskay et al. (2006): Geochronology of Neogene magmatism in the Carpathian arc and intra-Carpathian area: a review. Geologica Carpathica, 57, 6: 511-530.
