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Seismic hazard assessment for the Caucasus test area (2006)

Balassanian, S. ; Ashirov, T. ; Chelidze, T. ; [et al.]

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Publication Date: 2021-04-07

Description: The GSHAP CAUCAS test area was established under the INTAS Ct.94-1644 (Test Area for sismic Hazard Assessment in the Caucasus) and NATO ARW Ct.95-1521 (Historical and Prehistorical Earthquakes in the Caucasus), with the initial support of IASPEI, UNESCO and ILP. The high tectonic interest and seismicity rate of the whole area, the availability of abundant multi-disciplinary data and the long established tradition in hazard assessment provide a unique opportunity to test different methodologies in a common test area and attempt to establish some consensus in the scientific community. Starting from the same input data (historical and instrumental seismic catalogue, lineament and homogeneous seismic source models) six independent approaches to seismic hazard assessment have been used, ranging from pure historical deterministic to seismotectonic probabilistic and areal assessment methodologies. The results are here compared.

Description: JCR Journal

Description: open

Keywords: Seismic hazard assessment ; Caucasus ; historical earthquake ; UN/IDNDR ; active faults ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk

Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)

Type: article

Format: 3841063 bytes

Format: application/pdf

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Earthquake Hazard and Risk (1996)

Schenk, V., Ed.

Kluwer Academic Publishers

In: Dordrecht, Kluwer Academic Publishers, vol. 20, no. Publ. No. 12, pp. 23-40, (ISBN 1-4020-3326-5, VIII + 343 pp.)

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Publication Date: 1996

Keywords: Seismicity ; Earthquake hazard ; Earthquake risk ; Strong motions ; Aftershocks ; Stress ; EUROPROBE (Geol. and Geophys. in eastern Europe) ; Magnitude

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BIBLIOGRAPHY SEISMOLOGY

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From Closure of the Mozambique Ocean to Gondwana Breakup: New Evidence from Geochronological Data of the Vohibory Terrane, Southwest Madagascar (2008)

Emmel, B. ; Jöns, N. ; Kröner, A. ; [et al.]

University of Chicago Press

In: The Journal of Geology. 2008; 116(1): 21-38. Published 2008 Jan 01. doi: 10.1086/524121.

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Publication Date: 2008-01-01

Print ISSN: 0022-1376

Electronic ISSN: 1537-5269

Topics: Geosciences

Published by University of Chicago Press

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Neoarchean UHT Metamorphism and Paleoproterozoic UHT Reworking at Uweinat in the East Sahara Ghost Craton, SW Egypt: Evidence from Petrology and Texturally Controlled in situ Monazite Dating (2015)

Karmakar, S., Schenk, V.

Oxford University Press

In: Journal of Petrology

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Publication Date: 2015-11-01

Description: The Uweinat–Kamil basement complex, in the central part of the East Sahara Ghost Craton (ESGC) in NE Africa, is the only inlier in the craton that contains rocks with Archean formation ages, and is hence a key to understanding the ancient crustal evolution of the otherwise enigmatic and poorly known ESGC. The craton is thought to have been decratonized during the Neoproterozoic after thickening as a result of Pan-African collisional events along its margins. Textural and compositional relationships preserved in the metapelitic granulites from the Uweinat–Kamil inlier suggest a two-stage metamorphic evolution of the rocks. Stage I saw the growth of sapphirine + quartz + garnet 1 at ~10 kbar and ~1050°C, from an initial assemblage containing kyanite, sillimanite ± biotite, which are now preserved only as inclusions in porphyroblastic garnet 1. This stage was followed by near-isobaric cooling stabilizing the assemblage garnet 1 + sillimanite 1 ± orthopyroxene 1 ± sapphirine coexisting with melt. Stage II saw the breakdown of this assemblage forming a variety of symplectite assemblages (orthopyroxene 2 + cordierite or orthopyroxene 2 + cordierite + sapphirine ± sillimanite 2 or cordierite + spinel) through near-isothermal decompression from ~9 kbar to ~6 kbar at ultrahigh temperatures of 900–1000°C. This was followed by near-isobaric cooling of the rocks to temperatures of 700°C at ~5·5–6 kbar, as evidenced by the growth of garnet 2 and the formation of late-stage biotite, owing to back-reaction of melt with residual garnet 1 and symplectite minerals. The second stage of the evolution is also observed in the associated metabasic granulites. Complete to partial replacement of garnet 1 porphyroblasts and clinopyroxene by orthopyroxene + plagioclase + hornblende ± spinel symplectites represents a stage of near-isothermal decompression, whereas the growth of garnet 2 around the symplectitic minerals represents a stage of isobaric cooling. Texturally controlled in situ Th–U–total Pb monazite dating of the metapelitic granulites reveals the polymetamorphic nature of the rocks. Stage I occurred at ~2·6 Ga, as indicated by monazite inclusions within garnet 1 porphyroblasts (coexisting with sapphirine + quartz), and represents a previously unknown Neoarchean ultrahigh-temperature metamorphism. Stage II occurred 700 Myr later at ~1·9 Ga, as indicated by monazite grains in the symplectites and matrix, and represents a previously uncharacterized Paleoproterozoic ultrahigh-temperature isothermal decompression event. No evidence of any metamorphism during the Neoproterozoic has been found. In this context, it is possible that the proposed decratonization occurred during a Paleoproterozoic decompression event instead of in the Neoproterozoic. The Paleoproterozoic evolution of the Uweinat–Kamil inlier is very similar to that described from other Paleoproterozoic orogenies across the world, which are considered to have resulted from collisions during the formation of the supercontinent Columbia. Future attempts at Columbia reconstructions should take into account the Paleoproterozoic evolution of the Uweinat–Kamil inlier in NE Africa.

Print ISSN: 0022-3530

Electronic ISSN: 1460-2415

Topics: Geosciences

Published by Oxford University Press

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Late Neoproterozoic P-T evolution of HP-UHT Granulites from the Palni Hills (South India): New Constraints from Phase Diagram Modelling, LA-ICP-MS Zircon Dating and in-situ EMP Monazite Dating (2011)

Brandt, S., Schenk, V., Raith, M. M., Appel, P., Gerdes, A., Srikantappa, C.

Oxford University Press

In: Journal of Petrology

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Publication Date: 2011-08-21

Description: Late Neoproterozoic ( c. 555 Ma) high-pressure–ultrahigh-temperature (HP–UHT) metamorphism has been documented for MgAl-rich migmatitic granulites from the Palni Hills in the Southern Granulite Terrane (South India). Conspicuous reaction textures indicate a clockwise P–T evolution, which is constrained through P–T pseudosection modelling and thermobarometry. The transformation of sillimanite to kyanite, which coexisted with orthopyroxene and/or garnet, records an early stage of loading. During subsequent heating to UHT conditions at deep-crustal levels ( c. 1000°C, 13·0 kbar) kyanite was transformed to sillimanite, and distinct peak-temperature assemblages (orthopyroxene + sillimanite + mesoperthite + rutile ± garnet ± quartz ± sapphirine, garnet + biotite + sillimanite + spinel + corundum + rutile + plagioclase and garnet + orthopyroxene + rutile + plagioclase ± quartz) formed in specific bulk compositions through biotite-dehydration-melting reactions. A sequence of corona and sapphirine-bearing symplectite textures records subsequent isothermal decompression of the order of c. 6 kbar at persistent extreme temperatures (1010–920°C). UHT decompression is consistent with the uniformly high Al contents of porphyroblastic, coronitic and symplectitic orthopyroxene (up to 10·4 wt % Al 2 O 3 ). Regrowth of garnet and biotite documents post-decompressional cooling to subsolidus conditions of 〈800°C at mid-crustal levels ( c. 6 kbar). HP–UHT metamorphism and the clockwise P –T path of the Palni Hills granulites is attributed to a single late Neoproterozoic tectono-metamorphic event, which has been consistently dated at c. 555 Ma through laser ablation inductively coupled plasma mass spectrometry U–Pb analyses of zircon and in situ electron microprobe U–Th–total Pb analyses of monazite. The MgAl-rich granulites occur as enclaves in enderbitic orthogneiss. The intrusion of the orthogneiss in the late Archean (2534 ± 28 Ma) marks the beginning of voluminous granitoid emplacement in the Southern Granulite Terrane between 2530 and 2440 Ma, which presumably caused a first high-grade metamorphic event in the early Paleoproterozoic (2469 ± 13 Ma), recorded by zircon cores in the MgAl-rich granulites. The clockwise P–T–t evolution indicates that HP–UHT metamorphism in the central part of the Southern Granulite Terrane is related to collisional tectonics during the final assembly of Gondwana in the late Neoproterozoic. Extreme heating is ascribed to upwelling of the asthenosphere during delamination of the thickened lithospheric mantle. Fast uplift of the rocks followed by mid-crustal isobaric cooling reflects extension of the hot overthickened crust and its subsequent cooling to a normal geotherm.

Print ISSN: 0022-3530

Electronic ISSN: 1460-2415

Topics: Geosciences

Published by Oxford University Press

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Vesuvianite in high-pressure-metamorphosed oceanic lithosphere (Raspas Complex, Ecuador) and its role for transport of water and trace elements in subduction zones (2013)

Halama, R., Savov, I. P., Garbe-Schonberg, D., Schenk, V., Toulkeridis, T.

Schweizerbart

In: European Journal of Mineralogy

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Publication Date: 2013-05-30

Description: Metamorphosed, vesuvianite-bearing dykes occur in serpentinised peridotites of the Raspas Complex (Ecuador), which represents a piece of oceanic lithosphere that has experienced high-pressure, subduction-related metamorphism. The serpentinite mantle protoliths are geochemically indistinguishable from modern oceanic lithosphere entering subduction zones. Positive Eu anomalies (Eu/Eu* = 1.3–7.2) and relative LREE enrichments (La N /Sm N = 1.2–5.5) point to hydrothermal alteration of the peridotite precursor rocks at or near the seafloor. Major mineral phases in the metamorphosed dykes include chlorite, diopside, amphibole and vesuvianite. In each dyke, only two of these phases – either amphibole + vesuvianite, diopside + chlorite, or amphibole + chlorite dominate the modal mineralogy with 〉~90 vol.%, suggesting metasomatic replacement at elevated P-T conditions during subduction, controlled by an external fluid. This fluid caused the decrease in coexisting mineral phases and overprinting of initial Sr isotope ratios (0.7025–0.7031). Preserved geochemical signatures from the dyke protoliths, including positive Eu anomalies (Eu/Eu* = 1.2–2.0) and Na enrichment due to spilitisation, reveal that the dykes originated as oceanic olivine gabbros and troctolites. Vesuvianite in the Raspas Complex formed by hydration and silica removal from gabbroic mineral assemblages during subduction. It has a wide stability in P-T space for hydrated and silica deficient bulk compositions so that it potentially represents a significant repository for the cycling of elements during subduction. In addition to Ca, Mg and Al, incorporation of significant amounts of Ti, Fe and Na (up to 2.4, 1.7 and 1.6 atoms per formula unit, respectively) in vesuvianite bears evidence for the potential of vesuvianite as petrogenetic indicator, although lack of relevant thermodynamic and experimental data precludes the extraction of quantitative information. For cold subduction zones in particular, vesuvianite appears to be able to carry significant amounts of water to mantle depths. Preferential incorporation of HREE (up to 2.2 ppm Yb), Sr (up to ~ 300 ppm) and Pb (up to 4.5 ppm) in vesuvianite underlines its potentially important role for the storage, transport and release of these key elements in radiogenic isotope geochemistry during subduction zone cycling.

Print ISSN: 0935-1221

Electronic ISSN: 1617-4011

Topics: Geosciences

Published by Schweizerbart

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