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The Saxon granulites, the type granulite locality, were deeply buried, extremely heated and then rapidly exhumed during the Variscan Orogeny; thus their evolution differs from many granulites elsewhere. The peak-metamorphic assemblages of layered felsic-mafic granulites from a 500 m deep borehole consist of garnet, kyanite, rutile, ternary feldspar and quartz in felsic granulite, and garnet, omphacite, titanite, ternary feldspar and quartz in mafic granulite. A minimum temperature of 1000-1020degreesC, calculated from reintegrated hypersolvus feldspar in felsic and mafic granulites, is consistent with the highest temperature estimates from garnet-clinopyroxene equilibria. Various equilibria in felsic and mafic granulites record a peak pressure of about 23 kbar. Diffusion zoning and local homogenisation of minerals reflect near-isothermal decompression that preceded cooling and partial hydration at medium- to low-pressure. U-Pb dating of titanite yields an age of peak metamorphism at 340.7+/-0.8 Ma (2sigma). However, chemical inheritance from precursor rutile and post-peak Pb loss are also evident, suggesting a protolith age of 499+/-2 Ma (2sigma) and partial resetting down to an age of 333+/-2 Ma (2sigma). Rb-Sr mica ages of 333.2+/-3.3 Ma (2sigma) are interpreted as dating cooling through about 620degreesC. Hence the Saxon granulites were exhumed to the upper crust during the short period of 6-11 Ma, which corresponds to average exhumation and cooling rates of 10 mm/year and 50degreesC/Ma, respectively. Such rapid exhumation is inconsistent with recent numerical models that assume foreland- directed transport of the Saxon granulites in the lower crust followed by extensional unroofing. Instead, high-pressure rocks of the Saxon Granulite Massif and the nearby Erzgebirge experienced a buoyant rise to the middle crust and subsequent juxtaposition with structurally higher units along a series of medium- to low-pressure detachment faults
Different tectonic episodes from Late Triassic to recent times in the eastern Binalud Mountains have resulted from convergence and transpression between the Turan and Central Iran plates. Heterogeneous deformation and variable portions of pure and simple shear, demonstrated by finite strain and vorticity analysis in the Mashhad metamorphic rocks, indicate strain partitioning during the first tectonic episode. Modern strain partitioning is characterized by reverse and strike-slip faulting along the Neyshabur fault system and Shandiz fault zone in the southern and northern flanks of the eastern Binalud, respectively. Time-transgressive regional deformation migrated from the hinterland of the belt into the foreland basin, from northeast to the southwest of the mountains. Different generations of deformation resulted in obliteration of the subduction-related accretionary wedge, and growth of an orogenic wedge resulted from collision between the Central Iran and Turan plates.
The International Union of Geological Sciences (JUGS) is evaluating whether there are additional geoscientific activities that would be beneficial in helping mitigate the impacts of tsunami. Public concerns about poor decisions and inaction, and advances in computing power and data mining call for new scientific approaches. Three fundamental requirements for mitigating impacts of natural hazards are defined. These are: (1) improvement of process-oriented understanding, (2) adequate monitoring and optimal use of data, and (3) generation of advice based on scientific, technical and socio-economic expertise. International leadership/coordination is also important.
To increase the capacity to predict and mitigate the impacts of tsunami and other natural hazards a broad consensus is needed. The main needs include the integration of systematic geological inputs - identifying and studying paleo-tsunami deposits for all subduction zones; optimising coverage and coordination of geodetic and seismic monitoring networks; underpinning decision making at national and international scales by developing appropriate mechanisms for gathering, managing and communicating authoritative scientific and technical advice information; international leadership for coordination and authoritative statements of best approaches. All these suggestions are reflected in the Sendai Agreement, the collective views of the experts at the International Workshop on Natural Hazards, presented later in this volume.
Albian-Turonian subduction-accretionary complexes are exposed widely in the Central Pontides. A major portion of the accretionary complexes is made up of a metaflysch sequence consisting of slate/phyllite and metasandstone intercalation with blocks of marble, Na-amphibole bearing metabasite, and serpentinite. The metaflysch sequence represents distal parts of a large Lower Cretaceous submarine turbidite fan deposited on the Laurasian active continental margin that was subsequently accreted and metamorphosed during the Albian. Raman spectra of carbonaceous material of the metapelitic rocks revealed that the metaflysch consists of metamorphic packets with distinct peak metamorphic temperatures. The majority of the metapelites are low-temperature (ca. 330 degrees C) slates characterized by lack of differentiation of the graphite (G) and D2 defect bands. They possibly represent offscraped distal turbidites along the toe of the Albian accretionary wedge. Other phyllites are characterized by a slightly pronounced G band with a D2 defect band occurring on its shoulder. Peak metamorphic temperatures of these phyllites are constrained to 370-385 degrees C. The phyllites are associated with a strip of incipient blueschist facies metabasites and are found as a sliver within the offscraped distal turbidites. We interpret the phyllites as underplated continental sediments together with oceanic crustal basalt along the basal decollement. Tectonic emplacement of the underplated rocks into the offscraped distal turbidites was possibly achieved by out-of-sequence thrusting causing tectonic thickening and uplift of the wedge.
The tectono-metamorphic signature of detachments in high-pressure mountain belts, Tethyan examples
(1998)
The sidi Mohamed peridotites (Edough Massif, NE Algeria) - evidence for an upper mantle origin
(2013)
The Hercynian Edough massif is the easternmost crystalline massif of the Algerian coast. It consists of two tectonically superposed units composed of micaschists, gneisses, and peridotite. This study concentrates on the small and isolated Sidi Mohamed peridotite outcrop area (0.03 km(2)). The Sidi Mohamed peridotite is composed mainly of harzburgites (Mg-rich olivine and orthopyroxene as major minerals). The Ni (2051-2920 ppm), Cr (2368-5514 ppm) and MgO (similar to 28-35 wt.%) whole-rock composition and the relative depletion in Nb make these harzburgites comparable to depleted peridotites related to a subduction zone. We suggest that the Sidi Mohamed ultramafic body was derived directly from the upper mantle and tectonically incorporated into the gneiss units of the Edough metamorphic core complex in a subduction environment.
The Sabzevar ophiolites mark the Neotethys suture in east-north-central Iran. The Sabzevar metamorphic rocks, as part of the Cretaceous Sabzevar ophiolitic complex, consist of blueschist, amphibolite and greenschist. The Sabzevar blueschists contain sodic amphibole, epidote, phengite, calcite +/- A omphacite +/- A quartz. The epidote amphibolite is composed of sodic-calcic amphibole, epidote, albite, phengite, quartz +/- A omphacite, ilmenite and titanite. The greenschist contains chlorite, plagioclase and pyrite, as main minerals. Thermobarometry of a blueschist yields a pressure of 13-15.5 kbar at temperatures of 420-500 A degrees C. Peak metamorphic temperature/depth ratios were low (similar to 12 A degrees C/km), consistent with metamorphism in a subduction zone. The presence of epidote in the blueschist shows that the rocks were metamorphosed entirely within the epidote stability field. Amphibole schist samples experienced pressures of 5-7 kbar and temperatures between 450 and 550 A degrees C. The presence of chlorite, actinolite, biotite and titanite indicate greenschist facies metamorphism. Chlorite, albite and biotite replacing garnet or glaucophane suggests temperatures of > 300 A degrees C for greenschist facies. The formation of high-pressure metamorphic rocks is related to north-east-dipping subduction of the Neotethys oceanic crust and subsequent closure during lower Eocene between the Central Iranian Micro-continent and Eurasia (North Iran).