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Extension-related Miocene calc-alkaline magmatism in the Apuseni Mountains, Romania: origin of magmas.

Domenii publicaţii > Ştiinţele pământului şi planetare + Tipuri publicaţii > Articol în revistã ştiinţificã

Autori: Roşu, E., Seghedi, I., Downes, H., Alderton, D.H.M., Szakács, A., Pécskay, Z., Panaiotu, C., Panaiotu , C.E., Nedelcu, L.

Editorial: Albrecht von Quadt ed., Schweizerische Mineralogische und Petrographische Mitteilungen, 84/1-2, Special issue, p.117-146, 2004.


The Miocene magmatism of the Apuseni Mountains in the Carpatho-Pannonian area hosts some of Europe’s largest porphyry epithermal Cu-Au ore systems associated with shallow subvolcanic intrusions. Detailed field observations combined with K-Ar ages, geochemical analyses, Sr-Nd isotopes and paleomagnetic data constrain a model for the geotectonic evolution and processes of melt generation that may account for the exceptional mineralizing potential of the magmatic activity in this region. The magmatic activity developed mainly between 14.7 and 7.4 Ma and after a gap ceased at around 1.6 Ma. Geotectonic conditions do not support contemporaneous subduction processes, but were represented by transtensional and rotational tectonics, which generated horst and graben structures and favoured
the generation and ascent of magmas. The “subduction signature” of the magmas emphasizes the significant involvement of fluids (mantle lithosphere and/or lower crust) inherited during previous geodynamic events. The mechanism of magmagenesis is considered to be related to decompressional melting (various degrees of) of a heterogeneous source situated at the crust-lithosphere mantle boundary. Mixing with asthenospheric melts generated during
the extension-related attenuation of the lithosphere may also be implied. The evolution from normal to adakitic-like calc-alkaline and alkaline magmas generally is time-dependent as a consequence of variable fluid-present melting.
Fractional crystallization-assimilation processes in shallow magma chambers are suggested for early magmatism
but were almost absent from later magmatism, which related to an increasingly extensional regime. The youngest alkalic (shoshonitic) magmatism (1.6 Ma) is asthenosphere-derived, but in a different extensional event, being almost coeval with the OIB-like alkali-basaltic magmatism (2.5 Ma) occurring along the South Transylvanian fault. The fluid-present melting of the source seems to be the critical factor for the presence of the copper-gold-bearing mineralizing fluids.

Cuvinte cheie: Romania, Apuseni Mountains, Miocene, calc-alkaline, alkaline, adakite-like, extension