Attenuation in Southeastern Carpathians area: Result of upper mantle inhomogeneity

Popa, Mihaela; Rădulian, Mircea; Grecu, Bogdan; Popescu, Emilia; Plăcintă, Anica Otilia

doi:10.1016/j.tecto.2004.12.037

Cited by 32 publications

(25 citation statements)

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“…The complexity of the geophysical properties of the structure above the Vrancea seismogenic zone and towards the inner side of the Carpathians arc has been pointed out by a variety of studies related to anisotropy and attenuation of seismic waves (e.g., IVAN et al 2008;IVAN 2011;MARTIN et al 2005;POPA et al, 2005;RUSSO et al, 2005) or magnetotellurics (STȂ NICȂ et al, 2000). Although a low-velocity zone associated with asthenospheric upraise has been pointed out by such investigations, there was no detailed image that could connect it to the geological features and evolution.…”

Section: Resultsmentioning

confidence: 99%

“…The most relevant of these is the attenuation of the seismic waves coming from the Vrancea intermediate-depth earthquake foci showing an abrupt increase (low Q values) for paths directed toward the southern edge of the Harghita Mountains region (LAZARESCU, Personal communication, 1985;POPA et al, 2005;RUSSO et al, 2005). South Harghita, and Ciomadul in particular, is also the site of the most intense thermal anomaly in all Romania (800°C at 20 km depth) and over the entire inner side of the Carpathians (DEMETRESCU AND ANDREESCU, 1994).…”

Section: Introductionmentioning

confidence: 99%

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New Seismic and Tomography Data in the Southern Part of the Harghita Mountains (Romania, Southeastern Carpathians): Connection with Recent Volcanic Activity

Popa

Rădulian

Szakács

et al. 2011

Pure Appl. Geophys.

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The southern part of the southeastern Carpathians represents the site of the most recent volcanic eruptions of the entire Carpathian-Pannonian region. The products of these eruptions range from 42 to 10 Ka radiocarbon ages in the South Harghita Mountains (high K calc-alkaline rocks with adakite-like features), and at 1.2-0.6 Ma K-Ar ages in the Perşani Mountains (alkali basalts). They were emplaced in a post-collisional regime. Ciomadul volcano is located at the southernmost part of the NW-SE oriented Cȃlimani-Gurghiu-Harghita range crossing the inner part of the southeastern Carpathians and in the rough proximity of the Vrancea seismic zone (at ca. 60 km toward NW). Its magma generation is attributed to geodynamic events closely related to the seismogenic area. A number of particular geophysical and geochemical features located in the study region, including (1) the abrupt attenuation of the seismic waves originating from the Vrancea intermediate-depth foci, (2) the most intense heat-flow anomaly in Romania, (3) the most prominent 3 He/ 4 He anomaly measured in natural ''postvolcanic'' gas emanations, are all in favor of the hypothesis of a still existing hot local magma chamber. Data acquired during recent seismic monitoring of the Vrancea zone and its neighborhoods suggest an enhancement of the local seismicity beneath the southern edge of the South Harghita Mts., both at crustal and subcrustal levels. At the same time, recent tomography images obtained using local earthquake data correlate well with the presence of a vertically extended low-velocity zone coming from the upper mantle to the assumed magmatic chambers located in the crust. The present data, supporting the presence of an active crustal magma chamber beneath Ciomadul, allow us to consider that future volcanic activity at this volcano cannot be discarded.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

New Seismic and Tomography Data in the Southern Part of the Harghita Mountains (Romania, Southeastern Carpathians): Connection with Recent Volcanic Activity

Popa

Rădulian

Szakács

et al. 2011

Pure Appl. Geophys.

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“…Secondly, gravitational sinking of the slab beneath the Vrancea region induces convection in the asthenospheric mantle with downwelling adjacent to the sinking slab and upwelling beneath the eastern part of the Transylvanian Basin (Ismail-Zadeh et al, 2005). The upwelling part is demonstrated by seismic attenuation beneath the internal part of the Carpathian bend zone (Russo et al, 2005;Popa et al, 2005;Ivan 2008), by the low velocity anomaly observed in seismic tomography beneath the Transylvanian Basin (Martin et al, 2006), and by high 3He/4He values of post126 volcanic gas emanations (Vaselli et al, 2000). The neighboring high velocity anomaly coincides with a series of frequent and strong intermediate mantle-level earthquakes clustered in a narrow zone which extends almost vertically from around 70 to 170km in depth, known as the Vrancea mantle seismic zone ( Fig.…”

Section: Tectonic Constraintsmentioning

confidence: 99%

Tectonic significance of changes in post-subduction Pliocene–Quaternary magmatism in the south east part of the Carpathian–Pannonian Region

et al. 2011

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The south-eastern part of the Carpathian-Pannonian region records the cessation of convergence between the European platform/ Moesia and the Tisza-Dacia microplate. 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, K24 alkalic, mafic Na-alkaline and ultrapotassic) in the Pliocene-Quaternary, 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 geodynamics 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-collision Călimani-Gurghiu-Harghita volcanic chain in front of the European convergent plate margin. At ca. 3 Ma magma compositions changed in South Harghita 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 varieties, signifying changes in the source and melting mechanism. We attribute the progressive change 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) inversion tectonics (Na and K alkalic magmas). Contemporaneous post-collision 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 rifting and inversion tectonics. 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. Key words: Post-collisional slab mechanics, calc-alkaline, adakite-like, Na-alkalic, K-alkalic and ultrapotassic magmas. IntroductionPost-collision magmatism at convergent plate boundaries is very complex and is usually characterized by the presence of adakite-like and/or alkaline magmas, e.g. in the Mediterranean (Duggen et al., 2005), Tibet (Turner et al., 1996;Mo et al., 2006) and Baja California (Negrete-Aranda and Cañon-Tapia, 2008). The existence of such magmas may be associated with the post-collisional evolution of inherited slabs. A typical Africa-European collision zone includes a subduction stage characterized by roll-back associated with extensional back-arc volcanism in highly arcuate orogenic settings (Faccenna et al., 2004;Harangi et al., 2006). The SE Carpathians is a region where the post-collisional stage of a highly arcuate orogen is associated with unusual volcanism, where the final stage of roll-back of the slab can be seen in the high-velocity intermediate-depth mantle anomaly detected by seismic tomography studies (e.g., Martin et al., 2006), associated with the Vrancea seismic zone (e.g., Oncescu and Bonjer, 1997). After the collision at 11...

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“…The earthquake hypocenters are concentrated in an area with 20 × 50 km lateral and 110 km vertical extent in the 70-180-km-depth range beneath the Vrancea zone (Oncescu and Bonjer, 1997;Sperner et al, 2001). In addition, subcrustal seismic attenuation has been also detected northwest and partly below the Vrancea zone, which can indicate the presence of shallow, hot asthenosphere, possibly with partially melted zones (Hauser et al, 2001;Popa et al, 2005;Russo et al, 2005). It seems to be clear that there is a geodynamic relationship between these processes (volcanic and seismic activity); however, interpretations of the magma genesis and the origin of the vertical slab are fairly controversial.…”

Section: Calc-alkaline Volcanism In the Eastern Part Of The Carpathiamentioning

confidence: 99%

Genesis of the Neogene to Quaternary volcanism in the Carpathian-Pannonian region: Role of subduction, extension, and mantle plume

Harangi

Lenkey

2007

Cenozoic Volcanism in the Mediterranean Area

124

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Neogene to Quaternary volcanism of the Carpathian-Pannonian region is part of the extensive volcanic activity in the Mediterranean and surrounding regions. Using the spatial and temporal distribution of the magmatic rocks, their major-and traceelement features, and Sr-Nd-Pb isotope characteristics, we suggest that lithospheric extension in the Pannonian Basin had a major role in the generation of the magmas. Dehydration of subducting slab should have resulted in thorough metasomatism in the mantle wedge during Cretaceous to early Miocene that would have lowered the melting temperature, therefore playing an indirect role in the generation of magmas later on. Mixing between mantle-derived magmas and lower-crustal melts was an important process at the fi rst stage of the silicic and calc-alkaline magmatism in the Northern Pannonian Basin. However, the crustal component gradually decreased with time, which is consistent with magmatic activity in a continuously thinning continental plate. Calc-alkaline volcanism along the Eastern Carpathians was mostly postcollisional and could have been related to slab break-off processes. However, the fairly young (<1.5 Ma) potassic magmatism at the southeasternmost segment of the Carpathian volcanic arc could be explained by lithospheric delamination under the Vrancea zone. Alkaline basaltic volcanism began at the end of rifting of the Pannonian Basin (11 Ma) and continued until recently. We suggest that a mantle plume beneath the Pannonian Basin is highly unlikely and the mafi c magmas were formed by small degree partial melting in a heterogeneous asthenospheric mantle, which has been close to the solidus temperature due to the lithospheric extension in the Miocene. Magmatism appears to have been in a waning phase for the last 2 m.y., but recent volcanic eruptions (<200 k.y.) indicate that future volcanic activity cannot be unambiguously ruled out.

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Attenuation in Southeastern Carpathians area: Result of upper mantle inhomogeneity

Cited by 32 publications

References 23 publications

New Seismic and Tomography Data in the Southern Part of the Harghita Mountains (Romania, Southeastern Carpathians): Connection with Recent Volcanic Activity

New Seismic and Tomography Data in the Southern Part of the Harghita Mountains (Romania, Southeastern Carpathians): Connection with Recent Volcanic Activity

Tectonic significance of changes in post-subduction Pliocene–Quaternary magmatism in the south east part of the Carpathian–Pannonian Region

Genesis of the Neogene to Quaternary volcanism in the Carpathian-Pannonian region: Role of subduction, extension, and mantle plume

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