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Abstract: Tertiary I- and S-type plutonism is widespread in the Aegean region and frequently associated with extensional tectonic structures. This investigation presents the first evidence of protracted magmatism on the island of Serifos in the western Cyclades and at least two discrete generations of plutonism and coeval dyke generations can be distinguished: (1) An older granitoid with S-type characteristics intruded the Attic–Cycladic crystalline rocks. The granitoid and its host rocks were mylonitized by an earlier phase of deformation at temperature conditions >~450 °C and WSW directed shear. This crustal-scale ductile shear zone has been reactivated during the initial stage of a metamorphic core complex formation recording top-SSW sense of shear. Rb–Sr muscovite data from the orthogneiss yield cooling, respectively deformation ages of 15–11.3 Ma. (2) An I-type hornblende–biotite–granodiorite pluton with dacitic to andesitic dyke generations intruded syn- to post-kinematically during ongoing extensional deformation at shallow crustal levels. Single grain zircon TIMS U–Pb ages of the main granodiorite body and its associated dykes are 11.6–9.5 Ma. Cooling ages of these samples scatter between 8.5 and 7.7 Ma (Rb–Sr on biotite). [Copyright &y& Elsevier]

The geology of Kea Island shows further evidence for low-angle normal fault (LANF) formation in the Western Cyclades. Structural investigations have demonstrated the existence of a hitherto unrecognised ductile-brittle shear zone with strikingly consistent top-to-SSW extensional kinematics together with a WNW-ESE oriented shortening component. The tectonostratigraphy comprises a >380 m thick, shallowly-dipping schist-calcite marble unit, overlain by ca. 150 m thick fault rocks consisting of cohesive cataclasites, ultramylonitic calcite marbles, brecciated dolostones and protomylonitic calcite marbles. The presence of blueschist-facies lenses and 40Ar/39Ar geochronology point to a significant role of LANFs in exhumation processes and greenschist-facies overprint during Miocene crustal evolution. [ABSTRACT FROM AUTHOR]

On the island of Serifos SSW-directed low-angle faults accommodated crustal thinning during Miocene extension. Cross-cutting relationships suggest that the low-angle faults interacted with WNW-ESE striking conjugate high-angle normal faults in both the hanging and the footwall. Although high- and low-angle faults were likely synkinematic, the deformation mechanism differs significantly in both systems. The low-angle faults are characterized by several meters of low-grade, ultrafine grained marble mylonites below several decimetres of ultracataclasites. The high-angle faults represent mainly brittle deformation resulting in slickensides, cataclasites and pseudotachylites. The Ar/Ar mica geochronology yields uniform ages across the low-angle faults suggesting a nearly horizontal detachment at temperatures coincident with the brittle-ductile transition zone. [ABSTRACT FROM AUTHOR]

The Khlong Marui Fault, lying to the NNE of Phuket, has a strong geomorphic signal, with marked fault-strike parallel topographic ridges. The fault is ca. 150 km long with a 210-030° trend. The lithologies within the strike-slip zone mainly consist of vertical layers of mylonitic metapelites, migmatitic gneiss, mylonitic granite, pegmatites and cataclasites. The foliation and stretching lineations in ductile rocks indicate a dextral strike-slip displacement at mid- to upper-crustal levels. Pegmatites cross-cut the mylonitic foliation but are in turn sheared at their margins, indicating synkinematic emplacement. Although clear age-constraints are still lacking, the dextral strike-slip kinematics of the Khlong Marui fault is likely to be related to the escape tectonics arising from the India-Asia collision. [ABSTRACT FROM AUTHOR]

Spectacular folded, but virtually unconsolidated sediments in a sand pit in the Vienna basin have been used as one of the key arguments of an E-W shortening event during the Late Miocene in the eastern Alps and western Carpathians. The outcrop has been re-excavated recently and several new observations like the occurrence of refold structures, the fold shapes and the large amount of localized shortening bring into question the established tectonic interpretation. Alternatively, we propose that gravitational forces caused the folding in the frontal part of a slump along the eastern slope of the Vienna basin. [ABSTRACT FROM AUTHOR]

Abstract: Giant groove casts have been found in the upper Proterozoic to Lower Cambrian Phe Formation (Haimanta Group), a siliciclastic sandstone/shale succession in the Tethyan Zone of the Higher Himalaya tectonic unit. The grooves are among the largest linear erosion structures related to submarine mass-movements observed in the geologic record. They are up to 4 m wide, about 0.2 m deep and can be traced for more than 35 m without changing their character. The grooves are straight, subparallel to cross-cutting striations with shallow semi-circular cross-sections and well-defined superimposed minor ridges and grooves. Groove casts exist on the soles of several sandstone beds within a 73 m thick logged section, commonly associated with flute casts. Their characteristics were compared with several other types of ancient and modern submarine linear erosion structures. A sand-rich, non-channelized basin floor depositional environment is inferred from the lithofacies, the combination of sedimentary structures, the lack of coarse-grained pebbly facies, the lateral continuity of beds, and the lack of channel structures. The grooves probably formed by laminar debris flows/concentrated density flows dragging blocks of already lithified sediment across the basin floor. When the bedding is structurally rotated back to horizontal, the groove casts show consistent North–South oriented palaeocurrent trends, with South-directed palaeocurrent directions indicated by flute casts. These palaeocurrent orientations contrast with previous palaeogeographic reconstructions of this area, which propose sediment delivery from the South. We therefore suggest a new “double provenance” model for the spatial relationship of late Proterozoic to Early Cambrian strata of the Himalaya, in which Lesser and Tethyan Himalayan age-equivalent sediment was deposited in a connected basin, where the former received detritus from the South, and the latter from a hitherto unknown source in the North. One possible candidate for this northern source is the South China Block and an associated Neoproterozoic volcanic arc. [Copyright &y& Elsevier]

Recent field investigations have revealed a high-strain zone in the south of Kythnos (Greece). Massive layers of ultrafine-grained Mn-rich calcitic mylonitic marbles and several generations of cataclasites hint at a high-strain event in the crust and are associated with a low-angle shear zone. We investigate fold-fault-relationships and deformation events preceding and post-dating normal faulting and compare the tectono-metamorphic history with adjacent islands in the Western Cyclades. [ABSTRACT FROM AUTHOR]