Time-space evolution and volcanological features of the Late Miocene-Quaternary Calimani-Gurghiu-Harghita Volcanic Range, East Carpathians, Romania. A Review.

The Carpathian-Pannonian Region (CPR) hosts one of the major Cainozoic volcanic provinces of Europe extending in space over 6 eastern European countries.The lithospheric evolution of this large area governed by large-scale asthenospheric processes is recorded by products of volcanic activity occurred during a time interval of more than 21 million years. According to their surface occurrence areas, ages and composition the Neogene volcanics of CPR were systematized in three main groups: 1) mostly explosive products of felsic magmas generated at the beginning of volcanism in the whole CPR and in their particular occurrence areas (21-12 Ma) developed in the actual intra-Carpathian Pannonian Basin, 2) mostly intermediate calc-alkaline rocks emplaced in both the intra-Carpathian areas and along the arcuate Carpathian fold-and-thrust belt, and 3) Na- and K- alkaline and ultra-alkaline products clustered in a number of monogenetic volcanic fields across the whole intra-Carpathian realm developed in the final stages of volcanic activity of the CPR as a whole and of their particular occurrence areas. The ca. 160 km long Călimani-Gurghiu-Harghita volcanic range (CGH) developed as part of the intermediate calc-alkaline volcanism closely related in space with the fold-and-thrust belt of the Carpathians, representing the south-eastern segment of the CPR. Although its map view and general petrochemical and volcanological characteristics are quite similar with those of other segments of the orogene belt- tied calc-alkaline volcanic segments, at a closer look CGH displays a number of unique features. The time-space evolution of CGH is particular not only in that it is the youngest (10.5 to < 0.05 Ma) dominantly calc-alkaline segment in CPR but also it shows a transient character. Unlike other segments along which volcanism occurred simultaneously forming true subduction-related 400 to 800 km long volcanic fronts which were stable in time for millions of year, in CGH volcanic activity migrated continuously along the range from NW to SE. So, during any given 1 Ma time interval active volcanism was restricted to very limited areas and to just a few active volcanic centers. The along-range shift of volcanic foci was concurrent with progressively lower volumes of magma erupted and decreasing magma output rates. As a result, gradually lower-volume and less complex volcanic edifices were built up. Moreover, at the range-ending and youngest South Harghita sub-segment, magma compositions gradually changed from normal calc-alkaline to high-K calc-alkaline and shoshonitic, and adakitic features emerged at the end of volcanic activity, after a time gap of 0.5 Ma. This marks a major geodynamic event in the development of the East Carpathians themselves. During the transient volcanism of CGH, edifices of varying volume and complexity were built up forming a row of tightly- packed adjoining stratovolcanoes/composite volcanoes whose peripheral volcaniclastic aprons complexly juxtaposed, overlapped and merged with each other. The largest ones (Călimani caldera, and Fâncel-Lăpuşna) developed until caldera stage. Some of them (Rusca-Tihu in the Călimani Mts., Vârghiş in the North Harghita Mts.) became unstable during their growth and collapsed, generating widespread large-volume debris avalanche deposits. Edifice instability was solved by volcano-basement interaction processes, such as volcano spreading, at some large-volume volcanoes (in particular those in the Gurghiu Mts.). Volcano typology changed at the smaller-volume constructs toward the southeastern terminus of the range in the South Harghita Mts. from typical large stratovolcanoes to smaller composite volcanoes, dome clusters and isolated domes and simpler internal structures. As a whole, CGH displays an extremely particular evolutionary pattern strongly suggesting a transient character and decreasing to extinguishing volcanic activity along its length from NW to SE

Noble gas and carbon isotope systematics at the seemingly inactive Ciomadul volcano (Eastern‐Central Europe, Romania): evidence for volcanic degassing

Ciomadul is the youngest volcano in the Carpathian-Pannonian Region, Eastern-Central Europe, which last erupted 30 ka. This volcano is considered to be inactive, however, combined evidence from petrologic and magnetotelluric data, as well as seismic tomography studies suggest the existence of a subvolcanic crystal mush with variable melt content. The volcanic area is characterized by high CO2 gas output rate, with a minimum of 8.7 × 103 t yr-1. We investigated 31 gas emissions at Ciomadul to constrain the origin of the volatiles. The δ13C-CO2 and 3He/4He compositions suggest the outgassing of a significant component of mantle-derived fluids. The He isotope signature in the outgassing fluids (up to 3.10 Ra) is lower than the values in the peridotite xenoliths of the nearby alkaline basalt volcanic field (R/Ra 5.95Ra±0.01) which are representative of a continental lithospheric mantle and significantly lower than MORB values. Considering the chemical characteristics of the Ciomadul dacite, including trace element and Sr- Nd and O isotope compositions, an upper crustal contamination is less probable, whereas the primary magmas could have been derived from an enriched mantle source. The low He isotopic ratios could indicate a strongly metasomatized mantle lithosphere. This could be due to infiltration of subduction-related fluids and postmetasomatic ingrowth of radiogenic He. The metasomatic fluids are inferred to have contained subducted carbonate material resulting in a heavier carbon isotope composition (13C is in the range of -1.4 to -4.6 ‰) and an increase of CO2/3He ratio. Our study shows the magmatic contribution to the emitted gases

Neogene calc-alkaline intrusive magmatism of post-collisional origin along the Outer Carpathians: a comparative study of the Pieniny Mountains and adjacent areas

A petrographical and geochemical analysis was carried out on intrusive rocks from the Pieniny and Moravian areas, with special attention to boron content and K-Ar radiometric ages. The intrusions form medium- to high-potassium calc-alkaline andesitic suites, which are compositionally slightly different from each other and from the other calc-alkaline sequences in the Carpathian-Pannonian Region. No significant geochemical differences were observed within the different phase intrusions in the Pieniny areas. However, there is a slight difference in major and trace element composition between the Moravian and Pieniny intrusions. The andesitic rocks in the Pieniny and Moravian area are enriched in large ion lithophile elements and light rare earth elements and depleted in high field strength elements, indicating a metasomatized mantle source of the parent magmas. The low boron concentration of the andesitic rocks in the Pieniny area is in the range measured in back-arc, intraplate basalts of the Bakony-Balaton Highland volcanic field, whereas the higher boron content of the Moravian rocks overlaps with that of the Western Carpathian andesites. This may indicates the heterogeneity of the mantle lithosphere below the areas, or indicates different magma evolution histories. On the basis of the systematic geochronological study, the intrusive rocks along the Outer Carpathians can be divided on three groups, which overlap with each other temporally. The oldest magmatism occurred from 14.8 Ma to 11.0 Ma in the Uhersky Brod area, Moravia, which was followed by the emplacement of andesitic dikes and sills in the Pieniny Mts., south Poland (13.5–10.8 Ma). In the Pieniny area, two intrusive phases were distinguished. Partly overlapping with this area, but generally younger than this magmatism, the emplacement of the youngest intrusions is referable to the Poiana Botizei-Ţibleş-Toroiaga-Rodna-Bârgâu intrusive area, Romania, where magmatic activity started at ~11.8 Ma and terminated at 8.0 Ma