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Early Paleogene alkaline magmatism in western Romania (Poiana Rusca): evidence for two different sources?
No full textPetrogenesis of convergent-margin calc-alkaline rocks and the significance of the low oxygen isotope ratios: the Rodna-Bargau Neogene subvolcanic area (Eastern Carpathians)
No full textNeogene calc-alkaline magmatites (from basaltic andesites to rhyolites including mafic cognate enclaves) of the Rodna-Bargau subvolcanic area (East Carpathian arc) are evaluated on the basis of new mineral compositional data, major and trace elements, as well as Sr and O isotope data. Two different series of rocks have been separated. The magmas of the medium-K series had a rapid ascent toward the surface, as proven by the presence of primary garner bearing rocks, or by the sporadic occurrence of mafic cognate enclaves. The 8180 values of amphiboles vary from 4.2 to 5.4 parts per thousand (SMOW). The delta(18)O value measured on garnet is 4.3 parts per thousand. The range of (87)Sr/(86)Sr ratios is from 0.70588 to 0.70887. The decrease of the delta(18)O values as (87)Sr/(86)Sr ratios and SiO(2) increase is interpreted as a progressive contamination of a mantle derived magma with a contaminant depleted in delta(18)O and enriched in (87)Sr/(86)Sr (i.e. hydrothermally altered lower crustal rocks). Within the high-K series the presence of intermediate magma chambers where assimilation-fractional crystallization processes took place is considered. The delta(18)O values measured on clinopyroxenes vary from 4.6 to 5.7 parts per thousand and on amphiboles from 3.8 to 6.7 parts per thousand. The range of (87)Sr/(86)Sr ratios is from 0.70605 to 0.70950. The covariation of the delta(18)O values and (87)Sr/(86)Sr ratios is scattered. The highest delta(18)O values correspond to the highest (87)Sr/(86)Sr ratios and are consistent with assimilation of the local upper-crustal rocks. The lower delta(18)O values and the observed oxygen isotope disequilibrium between coexisting pyroxenes and amphiboles are explained by interaction with heated meteoric water
Geochemistry and tectonic development of Cenozoic magmatism in the Carpathian–Pannonian region
Full text linkThis review considers the magmatic processes in the Carpathian–Pannonian Region (CPR) from Early Miocene to Recent times, as well as the contemporaneous magmatism at its southern boundary in the Dinaride and Balkans regions. This geodynamic system was controlled by the Cretaceous to Neogene subduction and collision of Africa with Eurasia, especially by Adria that generated the Alps to the north, the Dinaride–Hellenide belt to the east and caused extrusion, collision and inversion tectonics in the CPR. This long-lived subduction system supplied the mantle lithosphere with various subduction components. The CPR contains magmatic rocks of highly diverse compositions (calc-alkaline, K-alkalic, ultrapotassic and Na-alkalic), all generated in response to complex post-collisional tectonic processes. These processes formed extensional basins in response to an interplay of compression and extension within two microplates: ALCAPA and Tisza–Dacia. Competition between the different tectonic processes at both local and regional scales caused variations in the associated magmatism, mainly as a result of extension and differences in the rheological properties and composition of the lithosphere. Extension led to disintegration of the microplates that finally developed into two basin systems: the Pannonian and Transylvanian basins. The southern border of the CPR is edged by the Adria microplate via Sava and Vardar zones that acted as regional transcurrent tectonic areas during Miocene–Recent times.
Major, trace element and isotopic data of post-Early Miocene magmatic rocks from the CPR suggest that subduction components were preserved in the lithospheric mantle after the Cretaceous–Miocene subduction and were reactivated especially by extensional tectonic processes that allowed uprise of the asthenosphere. Changes in the composition of the mantle through time support geodynamic scenarios of post-collision and extension processes linked to the evolution of the main blocks and their boundary relations. Weak lithospheric blocks (i.e. ALCAPA and western Tisza) generated the Pannonian basin and the adjacent Styrian, Transdanubian and Zărand basins which show high rates of vertical movement accompanied by a range of magmatic compositions. Strong lithospheric blocks (i.e. Dacia) were only marginally deformed, where strike–slip faulting was associated with magmatism and extension. At the boundary of Adria and Tisza–Dacia strike–slip tectonics and core complex extension were associated with small volume Miocene magmatism in narrow extensional sedimentary basins or granitoids in core-complex detachment systems along older suture zones (Sava and Vardar) accommodating the extension in the Pannonian basin and afterward Pliocene–Quaternary inversion. Magmas of various compositions appear to have acted as lubricants in a range of tectonic processes
Petrological characterization of the upper Miocene Rodna-Bârgău sub-volcanic district (Eastern Carpathians, Romania)
No full textDuring Neogene, the Eastern Carpathians were the locus of abundant igneous activity with subduction-related
geochemical characteristics. Among the various districts, the Rodna-Bârgău sub-volcanic complex represents a
potentially key-area due to its peculiar position at the junction point between ALCAPA, Tisza-Dacia and East European
plates, the exclusively sub-volcanic nature of its products, compared with the mainly effusive nature of the products
from the other districts and the occurrence of a wide range of chemical compositions coupled with xenoliths of various
nature, testifying complex low-pressure evolution. Despite this, little attention has been so far devoted to the study of
the products of the area, which still remain poorly characterized. The present work is thus aimed to a full petrological
investigation of the products of the Rodna-Bârgău district, which will possibly shed some new light on the magmagenetic
and geodynamic evolution of the entire Carpathian arc.
The preliminary analyses on representative samples allowed the recognition of numerous petrographic types,
ranging from basalt/microgabbro to mainly andesite/microdiorite up to dacite/granodiorite and rhyolite/microgranite.
Rock compositions show a well defined calcalkaline serial affinity in which, however, a clear distinction between a
low-K and a high-K magmatic suites can be observed. Rocks of the first series are amphibole-bearing
andesites/microdiorites, dacites and rhyolites/microdiorites with SiO2 = 58.0-74.6, MgO = 3.36-0.09 and K2O = 1.49-
2.93 wt.%, whereas rocks of the high-K suite are microgabbros, amphibole-bearing basaltic andesites/andesites and
dacites with SiO2 = 53.4-64.1, MgO = 10.2-2.18 and K2O = 1.29-3.23 wt.%. Intermediate-evolved terms of the two
series are remarkably different also on petrographic grounds, given that 1) low-K rocks (K2O = 1.71-3.23 wt.%) display
a yellow-pale green tschermakite to Mg-hornblende amphibole (Si = 6.01-6.94, K = 0.03-0.09 a.p.f.u.), whereas high-K
ones (K2O = 1.16-1.46 wt.%) feature a green hastingsite-pargasite (Si = 5.82-6.36, K = 0.16-0.34 a.p.f.u.); 2) low-K
andesites display rare Na-rich alkali feldspar (Or ~49) in the groundmass, whereas high-K equivalents have higher
abundances of a K-richer variety (Or ~70); 3) accessory biotite (Mg# = 0.57-0.61) is present only in high-K andesites
and dacites. Incompatible element abundances suggest subduction-modified magma sources and again indicate a clear
distinction between the two rock series, with rocks of the high-K suite displaying a stronger enrichment in LILE (e.g.,
Rb = 34-57 and 56-118 ppm, Ba = 359-631 and 578-819 ppm, in least evolved and intermediate-evolved terms,
respectively) and LREE (e.g., LaN = 22.7-31.6 and 30.6-44.4, NdN = 12.1-14.9 and 13.0-20.0) with respect to those of
the low-K one (Rb = 27-46 and 38-107 ppm, Ba = 158-288 and 253-619 ppm, LaN = 15.3-22.4 and 17.0-42.6, NdN =
8.1-11.2 and 9.7-13.4, respectively for intermediate and evolved rocks)
Petrological features of mantle xenoliths from Eastern Transylvanian Basin: a very fertile mantle or re-fertilisation processes?
No full text
The seismic attenuation signature of collisional orogens and sedimentary basins within the Carpathian Orogen
No full textSedimentary basins in collisional settings result from interactions within and between lithospheric plates and sublithospheric mantle. Imaging their structure brings fundamental constraints to both the extraction of hy-drocarbon or geothermal resources and seismic hazard analyses, especially in seismogenic areas affected by fluid percolation. Seismic attenuation is highly sensitive to stress, fluid saturation, and fluid-rock interaction and can often constrain small changes in the Earth's matrix better than seismic velocity. Here, we separate different attenuation mechanisms (scattering and absorption) at multiple frequencies and map them in space to constrain the properties of the Carpathian Orogen and the surrounding basins. The separation is achieved by determining S-wave peak delay times and late-time coda quality factors based on first-order Tikhonov inversion and analytical sensitivity kernels. We analysed 366 small-to-moderate crustal local earthquakes (0.7 < ML < 5.8) recorded by permanent and temporary stations operated by the Romanian Seismic Network between 2008 and 2021. Scattering and absorption appear to be frequency-dependent and highly heterogeneous throughout the region. High scattering and absorption characterise the Vrancea Seismic Zone, located in the Eastern Carpathian bend region, at all frequencies, likely due to high-stress rate and fluid inclusions. The seismically-active bend of the collisional orogen also shows high absorption and high scattering, particularly at low frequencies (similar to 3 Hz). Low scattering and high absorption features are observed across the Danubian section of the South Carpathians, marking the contact with the Pannonian Basin, which sits on top of a thin and highly-extended lithosphere. A transition from high to low-scattering regimes with increasing frequencies could mark small-scale heterogeneous structures in the Transylvanian Basin, an elevated sedimentary unit surrounded by high topography, comprising Cretaceous Neogene sediments deposited on top of oceanic ophiolites
Tectonic significance of changes in post-subduction Pliocene-Quaternary magmatism in the south east part of the Carpathian-Pannonian Region
Full text linkThe south-eastern part of the Carpathian–Pannonian region records the cessation of convergence between the European platform/Moesia and the Tisza–Dacia microplate. Plio-Quaternary magmatic activity in this area, in close proximity to the ‘Vrancea zone’, shows a shift from normal calc-alkaline to much more diverse compositions (adakite-like calc-alkaline, K-alkalic, mafic Na-alkalic and ultrapotassic), suggesting a significant change in geodynamic processes at approximately 3 Ma. We review the tectonic setting, timing, petrology and geochemistry of the post-collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration. The calc-alkaline volcanism (5.3–3.9 Ma) marks the end of normal subduction-related magmatism along the post-collisional Călimani–Gurghiu–Harghita volcanic chain in front of the European convergent plate margin. At ca. 3 Ma in South Harghita magma compositions changed to adakite-like calc-alkaline and continued until recent times (< 0.03 Ma) interrupted at 1.6–1.2 Ma by generation of Na and K-alkalic magmas, signifying changes in the source and melting mechanism. We attribute the changes in magma composition in front of the Moesian platform to two main geodynamic events: (1) slab-pull and steepening with opening of a tear window (adakite-like calc-alkaline magmas) and (2) renewed contraction associated with deep mantle processes such as slab steepening during post-collisional times (Na and K-alkalic magmas). Contemporaneous post-collisional volcanism at the eastern edge of the Pannonian Basin at 2.6–1.3 Ma was dominated by Na-alkalic and ultrapotassic magmas, suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the Adriatic indentation. Similar timing, magma chamber processes and volume for K-alkalic (shoshonitic) magmas in the South Apuseni Mountains (1.6 Ma) and South Harghita area at a distance of ca. 200 km imply a regional connection with the inversion tectonics
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