Igneous activity in central-southern Italy: Is the subduction paradigm still valid?

ABSTRACT The Pliocene–Quaternary igneous record of the Tyrrhenian Sea area features a surprisingly large range of compositions from subalkaline to ultra-alkaline and from ultrabasic to acid. These rocks, emplaced within the basin and along its margins, are characterized by strongly SiO2-undersaturated and CaO-rich to strongly SiO2-oversaturated and peraluminous compositions, with sodic to ultrapotassic alkaline and tholeiitic to calc-alkaline and high-K calc-alkaline affinities. We focused on the different models proposed to explain the famous Roman Comagmatic Region, part of the Quaternary volcanism that spreads along the eastern side of the Tyrrhenian area, in the stretched part of the Apennines thrust-and-fold belt. We reviewed data and hypotheses proposed in the literature that infer active to fossil subduction up to models that exclude subduction entirely. Many field geology observations sustain the interpretation that the evolution of the Tyrrhenian-Apennine system was related to subduction of the western margin of Adria continental lithosphere after minor recycling of oceanic lithosphere. However, the lateral extent of the subducting slab in the last millions of years, when magmatism flared up, remains debatable. The igneous activity that developed in the last millions of years along the Tyrrhenian margin is here explained as originating from a subduction-modified mantle, regardless of whether the large-scale subduction system is still active.

Evolution of mafic lavas in Central Anatolia: Mantle source domains

We present new Sr-Nd-Pb-Hf isotopic data on mafic lavas from the Sivas, Develidağ, Erciyes, and Erkilet volcanic complexes in central Turkey and Tendürek in eastern Turkey to evaluate the mantle sources for volcanism in the context of the geodynamic evolution of the Anatolian microplate. Early Miocene through Quaternary volcanism in Western Anatolia and latest Miocene through Quaternary activity in Central Anatolia were dominated by contributions from two distinct source regions: heterogeneous metasomatized or subduction-modified lithosphere, and roughly homogeneous sublithospheric ambient upper mantle; we model the source contributions through mixing between three end members. The sublithospheric mantle source plots close to the Northern Hemisphere reference line (NHRL) with radiogenic 206Pb/204Pb of ~19.15, while the other contributions plot substantially above the NHRL in Pb isotope space. The lithospheric source is heterogeneous, resulting from variable pollution by subduction-related processes likely including direct incorporation of sediment and/or mélange; its range in radiogenic isotopes is defined by regional oceanic sediment and ultrapotassic melts of the subcontinental lithospheric mantle. The geochemical impact of this contribution is disproportionately large, given that subduction-modified lithosphere and/or ocean sediment dominates the Pb isotope signatures of mafic Anatolian lavas. Subduction of the Aegean or Tethyan seafloor, associated with marked crustal shortening, took place throughout the region until ca. 16–17 Ma, after which time broad delamination of the thickened lower crust and/or the Tethyan slab beneath Central Anatolia allowed for sediment and/or mélange and slab-derived fluids to be released into the overlying evolving modified mantle. Aggregation of melts derived from both mantle and lithospheric domains was made possible by upwelling of warm asthenospheric material moving around and through the complexly torn younger Aegean-Cyprean slab that dips steeply to the north beneath southern Anatolia.

Focal Mechanisms of West Bohemia, Central Europe, Earthquakes—End of May 2014: Evidence of Volume Changes

West Bohemia is a region with a lot of mineral springs and gas outflows, which seems to be related to the remains of Quaternary volcanism in Central Europe. Earthquake swarms in shallow depths (less than 15 km) are very frequent there. We focused on the strongest earthquake over the past 30 yr (31 May, 2014 Mw∼3.8) and on two smaller ones (Mw∼2.9 and 2.5) from the same day. Seismograms from local and regional seismic stations were used to calculate the full and deviatoric moment tensors using low-frequency full-waveform inversion. The studied events have similar source mechanisms. The aforementioned earthquake sequence was selected to observe the isotropic part (negative value = implosion) of full moment tensors. It could relate to the motion and phase transition of fluids, especially water, and CO2. The main goal of this study is to contribute to clarification of the nature of earthquake swarms in the western edge of the Bohemian Massif. Negative value of the isotropic part of full moment tensor could be related to the closing of cracks and fissures during a rupture process.

Constraints on the pre-eruption thermal and fO2 conditions in the magma reservoir of Ciomadul (SE Carpathians, Romania) based on Fe-Ti oxide geochemistry

<p>Ciomadul is the southernmost eruptive centre of the post-collisional Călimani-Gurghiu-Harghita andesitic-dacitic volcanic chain (SE Carpathians, Romania) and represents the latest manifestation of the Neogene to Quaternary volcanism in the Carpathian-Pannonian Region. Ciomadul consists of older, peripheral shoshonitic to dacitic lava domes formed episodically between 1 Ma and 300 ka and a voluminous, central volcanic complex developed within the last 200 ka. Although several lines of evidence (based on petrology, geophysics and gas monitoring) suggest a long-lived magmatic plumbing system holding a potentially active magma storage (“PAMS” volcano) beneath Ciomadul, the pre-eruptive conditions of the upper crustal magma reservoir (including temperature, oxygen fugacity and TiO<sub>2</sub> activity) are not completely explored so far. In this study 23 rock samples, representing the whole volcanic activity of Ciomadul in time, were involved. Fe-Ti oxide (magnetite-ilmenite) grains were selected from magnetic heavy minerals, but only a few of the samples contained both magnetite and ilmenite crystals. Equilibrium between Ti-magnetite and ilmenite was tested by their chemical composition (Mg/Mn ratios).</p><p>Various geothermobarometer calibrations, including Andersen and Lindsley (1985, 1988) as well as Ghiorso and Evans (2008), were applied to calculate temperature and oxygen fugacity from Fe-Ti oxide compositions. Our results show that, in case of dacitic pyroclastic rocks, temperature values gained by the method of Ghiorso and Evans are significantly lower (640–780 °C) than those obtained by the geothermometers of Andersen and Lindsley (1985, 1988), showing 750–830 and 710–790°C temperatures, respectively. On the other hand, andesitic lava dome rocks of Dealul Mare show higher, 800–900 °C temperature according to all of these methods. The obtained temperature was compared with amphibole-plagioclase thermometry results and this shows a better agreement with the values yielded by the Andersen and Lindsley (1985) Fe-Ti oxide thermometry, particularly for the pumice samples.</p><p>In case of oxygen fugacity, the Ghiorso and Evans (2008) and Andersen and Lindsley (1985) methods showed fairly similar values (fO<sub>2</sub>=0.9–1.8) whereas the Andersen and Lindsley (1988) calculations gave higher oxygen fugacity (fO<sub>2</sub>=1.1–2.5). Nevertheless, these results, irrespective the applied calculation methods, suggest relatively oxidized conditions (ΔNNO>1) what is comparable with many other andesitic to dacitic volcanic systems (e.g. Mount St. Helens, Mount Unzen, Santorini). Values of TiO<sub>2</sub> activity was calculated and obtained a range between 0.76 and 0.98 what is consistent with the common presence of titanite.</p><p> </p><p>This study was financed by NKFIH K135179 project.</p><p> </p><p>Andersen, D.J. & Lindsley, D.H. (1985). EOS Transactions of the American Geophysical Union, 66, 416.</p><p>Andersen, D.J. & Lindsley, D.H. (1988). Amer Miner 73:714–726.</p><p>Ghiorso, M.S. & Evans, B.W. (2008). Amer J Sci 308:957–1039.</p>

Dense GPS derived deformation and rotation of intraplate blocks in Central Europe - comparison to seismicity and volcanism

<p>Intraplate deformation is often small but can nowdays be resolved from high precision GNSS velocity fields derived from decade-long time series and high precision network or point wise  solutions if uncertainties are smaller than ~0.2 mm/a.</p><p>If local effects are discarded, dense velocity fields may resolve regional patterns of intraplate deformation and motion, which are related to the bending of lithospheric plates, to mantle upwelling, the diffuse or zoned deformation along structural weaknesses or faults, and the rotation of rigid blocks within a plate. </p><p>We derive for the first time, dense high precision network solutions at 323 GNSS stations in Germany and adjacent areas and resolve regions experiencing uplift with velocities of up to ~2 mm/a, rotational relative motions with angular velocities of ~0.7±0.3 mas/a, and horizontal shear along an extended,  NS trending zone with strain rates in the range of 10-8 1/a. </p><p>We integrate European dense velocity solutions into our dataset to discuss the geodynamic context to European microplate motions, the Alpine collision, the structure of the European mantle, Quaternary volcanism and historical seismicity. </p><p>Unexpectedly, the zones of high horizontal strain rates only partly correlate to seismicity. Such a non-correlation between ongoing horizontal strain and seismicity has been recognized before. We discuss possible reasons for the absence of intraplate seismicity in regions experiencing recent strain, including the stress shadow effects if the strain buildup is reducing shear stresses from plate tectonics. The combination of GNSS derived dense velocity fields with time dependent seismicity models may change our current understanding of intraplate seismicity and impact the assessment of intraplate seismic hazard in future. </p>

Investigation of some volcanic glasses of georgian deposits

The paper presents research materials on some hydrogen-containing volcanic glasses of Transcaucasia of acidic composition, concentrated in areas of late Tertiary-Quaternary volcanism, in particular, the central part of the Akhalkalaki plateau, within the Akhaltsikhe valley (Georgia). Studies of natural materials of perlite, obsidian and pechstein were carried out by geological, physico-chemical: petrography, chemical analysis, X-ray diffractometry, and IR spectroscopic methods. The work shows the genesis, structural features and prospects of using these minerals. It has been found that the chemical composition of the minerals studied is characterized by a different content of aluminum oxide Al2O3. It is shown that silicon oxide SiO2, which is a part of volcanic glasses, occurs in an amorphous state. Perlites of the studied deposits differ from each other both visually and in composition. The perlites of the Toloshi deposit are dark gray in color and the Paravani deposits are white. In the perlite spectra of the Tolosh deposit, the vibrational frequencies of both the intratetrahedral and in the intertetrahedral space of Si-O-Si (Al) indicate that silicon is replaced by aluminum to a lesser extent than in the perlite of the Paravan deposit. The prospects of using expanded volcanic glasses are also shown.

An Overview of the Mafic and Felsic Monogenetic Neogene to Quaternary Volcanism in the Central Andes, northern Chile (18-28°Lat.S)

Monogenetic volcanism produces small eruptive volumes with short eruption history, different chemical compositions, and relatively simple conduit. The Central Volcanic Zone of the Andes is internationally known as a natural laboratory to study volcanism, where mafic and felsic products are present. In this contribution, the spectrum of architectures, range of eruptive styles, lithological features, and different magmatic processes of the mafic and felsic monogenetic Neogene to Quaternary volcanoes from the Central Volcanic Zone of the Andes in northern Chile (18°S-28°S) are described. The major volcanic activity occurred during the Pleistocene, where the most abundant activity corresponds to effusive and Strombolian eruptions. This volcanism is characterized by external (e.g., magma reservoirs or groundwater availability) and internal (e.g., magma ascent rate or interaction en-route to the surface) conditions, which determine the changes in eruptive style, lithofacies, and magmatic processes involved in the formation of monogenetic volcanoes.