The Aegean region is a concentrate of the main geodynamic processes that shaped the Mediterranean region: oceanic and continental subduction, mountain building, high-pressure and low-temperature metamorphism, backarc extension, post-orogenic collapse, metamorphic core complexes, gneiss domes are the ingredients of a complex evolution that started at the end of the Cretaceous with the closure of the Tethyan ocean along the Vardar suture zone. Using available plate kinematic, geophysical, petrological and structural data, we present a synthetic tectonic map of the whole region encompassing the Balkans, Western Turkey, the Aegean Sea, the Hellenic Arc, the Mediterranean Ridge and continental Greece and we build a lithospheric-scale N-S cross-section from Crete to the Rhodope massif. We then describe the tectonic evolution of this cross-section with a series of reconstructions from ~70 Ma to the Present. We follow on the hypothesis that a single subduction has been active throughout most of the Mesozoic and the entire Cenozoic, and we show that the geological record is compatible with this hypothesis. The reconstructions show that continental subduction (Apulian and Pelagonian continental blocks) did not induce slab break-off in this case. Using this evolution, we discuss the mechanisms leading to the exhumation of metamorphic rocks and the subsequent formation of extensional metamorphic domes in the backarc region during slab retreat. The tectonic histories of the two regions showing large-scale extension, the Rhodope and the Cyclades are then compared. The respective contributions to slab retreat, post-orogenic extension and lower crust partial melting of changes in kinematic boundary conditions and in nature of subducting material, from continental to oceanic, are discussed.

/pdf/cenozoic-geodynamic-evolution-of-the-aegean-2w6i0upj7j.pdf

Cenozoic geodynamic evolution of the Aegean

A multidisciplinary study including field geology, microstructure analysis, 40Ar/39Ar dating, and fluid inclusion microthermometry and Raman spectrometry has been carried out on the Muteh gold deposit located in a greenschist to amphibolite facies metamorphic rock complex of the Sanandaj-Sirjan tectonic zone, Zagros orogen, Iran. The Muteh gold deposit has been previously interpreted as genetically related to Precambrian granitic intrusions, as an exhalative hot-spring deposit related to Paleozoic rhyolitic-acidic tuffs, and to local metamorphic processes. Host rocks of the gold deposit are predominantly schist and gneiss, and subsidiary amphibolite and quartzite, and are intruded by leucogranites. In the vicinity of the gold deposit, the metamorphic and granitic rocks display a subhorizontal mylonitic foliation, containing a northeast-oriented stretching lineation. Field investigations in one of the producing open pits show that the gold orebodies are controlled by northwest-oriented normal faults and joints, dipping to the northeast and the southwest, and crosscutting the ductile fabric of the host rocks. Both the ductile fabric of the host rocks and the gold ore-controlling brittle structures are interpreted to have formed within a single, continuous extensional event, which started with ductile deformation and gradually changed into brittle deformation. Hydrothermal alteration associated with ore formation consists of quartz, muscovite, pyrite, dolomite-ankerite, and albite, which crosscuts the ductile fabric and overprints the metamorphic minerals of the host rocks. Pyrite is the dominant opaque mineral and is the major phase associated with gold. Chalcopyrite, marcasite, bismuth, galena, sphalerite, and pyrrhotite are subsidiary to rare phases. 40Ar/39Ar incremental-heating and in situ laser-ablation age data reveal a coherent sequence of cooling and hydrothermal events in the metamorphic complex hosting the Muteh gold deposit. Muscovite samples from the alteration zone and from one quartz vein from the orebodies yield 40Ar/39Ar ages between 55.7 and 38.5 Ma and show that gold mineralization is the youngest among the different dated events. This Eocene age is consistent with the young structural setting of the gold orebodies revealing an emplacement along northwestoriented normal faults, which can be correlated with Tertiary extensional tectonic events reported by previous field investigations. The data also indicate that gold ore formation is coeval with magmatism in the adjacent Tertiary Urumieh-Dokhtar magmatic belt and with intrusive activity within the Sanandaj-Sirjan zone, with a 40Ar/39Ar age of 54 Ma near Muteh according to our study. The remaining 40Ar/39Ar data reveal a Cretaceous to early Tertiary metamorphic, magmatic, and deformation history of the complex hosting the Muteh gold deposit. The fluid inclusion study showed that distinct fluids were present during the regional geologic evolution predating ore formation and later Eocene gold ore formation. Early regional fluids consist of an H2O-CO2-NaCl fluid with subsidiary N2 and CH4 that underwent local unmixing. The salinities of the liquid-rich inclusions resulting from unmixing range between 2.2 and 17.5 wt percent NaCl equiv, and those of the CO2-rich, vaporrich inclusions range between 2.8 and 7.2 wt percent NaCl equiv. The high salinity of the regional liquid-rich fluids is attributed to metamorphism of evaporite-bearing sedimentary rocks, magmatic intrusions, retrograde hydration reactions, metamorphism of impure marbles, and migmatization. The fluid inclusions spatially associated with the gold veins postdating regional metamorphism and ductile deformation of the host rocks contain a low-salinity aqueous fluid with a dilute, low-density CO2 component, and maximum salinities between 2.6 and 5.8 wt percent NaCl equiv. Gold deposition at Muteh occurred during or after late stages of Eocene brittle extension as a result of exhumation of the host metamorphic complex, possibly during magmatic activity in the Sanandaj-Sirjam zone. It is most likely linked to the introduction of a distinct low-salinity, low CO2 content aqueous fluid during crustal extension. These fluids are younger than, and therefore unrelated to, the highly saline and CO2-rich, regional metamorphic-magmatic fluids. Our results refute previous models advocating Precambrian to Paleozoic ages of the Muteh gold deposit.

Eocene Gold Ore Formation at Muteh, Sanandaj-Sirjan Tectonic Zone, Western Iran: A Result of Late-Stage Extension and Exhumation of Metamorphic Basement Rocks within the Zagros Orogen

The objective of this article is to use the geology and tectonics of a critical part of the Tethyan orogen, represented by Greece and Albania, to shed light on the tectonic development of Tethys on a regional to global scale. A review of existing Tethyan reconstructions reveals little consensus concerning key aspects, such as the timing and direction of subduction, arc magmatism, ophiolite genesis, and continental collision. The regional to local-scale geology of individual regions, therefore, has to be considered in detail to test existing models and to develop a viable tectonic reconstruction. For Carboniferous time, much evidence suggests that the Korabi–Pelagonian crustal unit as exposed in Albania and Greece formed above a northward-dipping subduction zone along the Eurasian continental margin, with Palaeotethys to the south. However, there is also evidence of southward subduction beneath Gondwana, especially from southern Greece and central-southern Turkey. Palaeotethys is inferred to have closed in...

Late Palaeozoic–Cenozoic tectonic development of Greece and Albania in the context of alternative reconstructions of Tethys in the Eastern Mediterranean region

pdf/kinematic-reconstructions-and-magmatic-evolution-537ume11fm.pdf

Kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern Mediterranean region since the late Cretaceous

. The island of Seram, which lies in the northern part of the 180°-curved Banda Arc, has previously been interpreted as a fold-and-thrust belt formed during arc-continent collision, which incorporates ophiolites intruded by granites thought to have been produced by anatexis within a metamorphic sole. However, new geological mapping and a re-examination of the field relations cause us to question this model. We instead propose that there is evidence for recent and rapid N–S extension that has caused the high-temperature exhumation of lherzolites beneath low-angle lithospheric detachment faults that induced high-temperature metamorphism and melting in overlying crustal rocks. These "Kobipoto Complex" migmatites include highly residual Al–Mg-rich garnet + cordierite + sillimanite + spinel + corundum granulites (exposed in the Kobipoto Mountains) which contain coexisting spinel + quartz, indicating that peak metamorphic temperatures likely approached 900 °C. Associated with these residual granulites are voluminous Mio-Pliocene granitic diatexites, or "cordierite granites", which crop out on Ambon, western Seram, and in the Kobipoto Mountains and incorporate abundant schlieren of spinel- and sillimanite-bearing residuum. Quaternary "ambonites" (cordierite + garnet dacites) emplaced on Ambon were also evidently sourced from the Kobipoto Complex migmatites as demonstrated by granulite-inherited xenoliths. Exhumation of the hot peridotites and granulite-facies Kobipoto Complex migmatites to shallower structural levels caused greenschist- to lower-amphibolite facies metapelites and amphibolites of the Tehoru Formation to be overprinted by sillimanite-grade metamorphism, migmatisation, and limited localised anatexis to form the Taunusa Complex. The extreme extension required to have driven Kobipoto Complex exhumation evidently occurred throughout Seram and along much of the northern Banda Arc. The lherzolites must have been juxtaposed against the crust at typical lithospheric mantle temperatures in order to account for such high-temperature metamorphism and therefore could not have been part of a cooled ophiolite. In central Seram, lenses of peridotites are incorporated with a major left-lateral strike-slip shear zone (the "Kawa Shear Zone"), demonstrating that strike-slip motions likely initiated shortly after the mantle had been partly exhumed by detachment faulting and that the main strike-slip faults may themselves be reactivated and steepened low-angle detachments. The geodynamic driver for mantle exhumation along the detachment faults and strike-slip faulting in central Seram is very likely the same; we interpret the extreme extension to be the result of eastward slab rollback into the Banda Embayment as outlined by the latest plate reconstructions for Banda Arc evolution.

https://openresearch-repository.anu.edu.au/bitstream/1885/153380/2/01_Pownall_Extreme_extension_across_Seram_2013.pdf

Extreme extension across Seram and Ambon, eastern Indonesia: evidence for Banda slab rollback

Crustal extension in the overriding plate at the Aegean subduction zone, related to the rollback of the subducting African slab in the Miocene, resulted in a detachment fault separating high-pressure/low-temperature (HP-LT) metamorphic lower from non-metamorphic upper tectonic units on Crete. In western Crete, detachment faulting at deeper crustal levels was accompanied by structural disintegration of the hangingwall leading to the formation of half-graben-type sedimentary basins filled by alluvial fan and fan-delta deposits. The coarse-grained clastic sediments in these half-grabens are exclusively derived from the non-metamorphic units atop the detachment fault. Being in direct tectonic contact with HP-LT metamorphic rocks of the lower tectonic units today, the basins must have formed in the period between c. 20 and 15 Ma, prior to the exposure of the HP-LT metamorphic rocks at the surface, and juxtaposed with the latter during ongoing deformation.

Tectono‐sedimentary evolution of lower to middle Miocene half‐graben basins related to an extensional detachment fault (western Crete, Greece)

Small iron deposits at Kakopetros and Ravdoucha in western Crete are hosted
by an extensional detachment zone at the roof of the high-pressure–low-temperature
metamorphic core complex known as the Phyllite-Quartzite unit. The iron oxides
occur in a brecciated layer of phyllite, quartzite, and marble up to tens of
meters thick. They fill fractures and vugs in the breccia and partly impregnate
the marble. The iron oxides, which were formerly mined in open pits, are
predominantly composed of goethite and subordinate oxyhydroxides of the
manganomelane group. The field relationships and microstructures indicate that
precipitation of the iron-oxide minerals was related to fluid flow focussed
along the detachment fault. δ 18 O values of goethite
indicate crystallization at low temperatures (31°–40°C) and at a shallow
depth of about 1 km. Microscopic investigations show that the deposition of iron
oxides was syntectonic and occurred during deformation in the uppermost crust.
Similar iron oxides are reported from low-angle brittle detachment horizons in
the Cordilleran metamorphic core complexes of North America and suggest that
small iron- and manganese-oxide deposits of this type may be a characteristic
feature of detachment zones.

The kakopetros and ravdoucha iron-oxide deposits, western crete, greece: fluid transport and mineralization within a detachment zone

In their comment, van Hinsbergen et al. (2008) question the validity of the tectono-sedimentary model proposed by Seidel et al. (2007) for the Topolia type breccia deposits in western Crete. Apart from various sedimentological aspects that could probably be sorted out in the field, they argue that the proposed time brackets of c. 20–15 Ma for the formation of the Topolia breccia do not reflect the onset of extensional deformation in the overriding plate of the Hellenic subduction zone after collision. Instead, they propose that the onset of extensional deformation is reflected by the formation of a late Miocene (c. 12–11 Ma) sedimentary basin unconformably overlying the Topolia type breccia deposits. Notwithstanding the fact that the age of the breccia is otherwise not well constrained apart from being deposited prior to the exposure of the highpressure metamorphic units in western Crete, we do not concur with this view. Whatever van Hinsbergen et al. (2008) mean with terms syn-orogenic and post-orogenic in the present context, they claim that the onset of crustal scale, post-orogenic N–S extension is dated by the oldest Cretan supradetachment basin. They also state that this basin formed well after the deposition of the oldest Neogene sedimentary unit in western Crete – the Topolia breccia . First, it should be noted that Crete represents a narrow horst structure developed in the forearc of the active Hellenic subduction zone since the Pliocene. When dealing with crustal scale processes, the highly incomplete Neogene sedimentary record on the island is just one limited source of information. Moreover, the buoyant escape model proposed by Thomson et al. (1998, 1999) should not be misunderstood to invoke extrusion from a subduction channel , as quoted by van Hinsbergen et al. (2008), which may rather be a potential cause of the marked uplift of Crete since the Pliocene (Meier et al., 2007). In the buoyant escape model, the partly subducted microcontinent is proposed to return towards the Earth surface by filling the space created by continuous roll back as a more or less coherent slice, becoming exhumed beneath an extensional detachment fault (e.g. Fassoulas et al., 1994; Kilias et al., 1994; Jolivet et al., 1996). This process probably causes extensional deformation in the hangingwall to the detachment, which is represented by the unmetamorphic upper units on Crete; extensional deformation continues because of roll back into the present. Any record of normal faulting in the upper plate to the extensional detachment does not allow an unequivocal distinction to be made between the buoyant escape stage (Thomson et al., 1999) and a subsequent stage of more coaxial crustal extension (Thomson et al., 1999; Rahl et al., 2005), stages possibly referred to as syn-orogenic and post-orogenic by van Hinsbergen et al. (2008). The structural record of the high-pressure metamorphic Phyllite–Quartzite Unit shows an episode of intense extensional deformation in the brittle field (e.g. Seidel et al., 2005), which took place between c. 20 and 15 Ma, according to fission track thermochronometry (Thomson et al., 1998, 1999) and at a depth of less than about 10 km (Kuster and Stockhert, 1997). This extensional deformation therefore happened after the major part of rapid exhumation from more than 30 km depth, when the high-pressure metamorphic Phyllite–Quartzite Unit already resided in the upper crust. We suspect that this marked extensional deformation of the Phyllite–Quartzite Unit should have had dramatic effects also in the higher levels of the upper crust and consequently at the surface. We therefore envisage that the formation of fault scarps, which are required to produce the fault-bound proximal breccia deposits with a minimum thickness of several hundred meters, preserved in western Crete, could be contemporaneous with the buoyant escape stage as well as with this later stage of extensional deformation. The breccia deposits, as all other units of the upper plate to the extensional detachment, were juxtaposed with the high-pressure metamorphic Phyllite–Quartzite Unit along normal faults during ongoing extension. In our simple structural model (Seidel et al., 2007), we propose that the normal fault presently bounding the Topolia breccia towards the south could have evolved by progressive deformation (or by repeated reactivation) from the fault along which the breccia was deposited on the hangingwall block, the rocks of the Phyllite– Quartzite unit forming the footwall block being juxtaposed with the breccia at a late stage of deformation. The proposed half-graben geometry corresponds to that observed in other extensional tectonic settings (e.g. Davis and Coney, 1979; Wernicke, 1981; Davis et al., 1986) with a more complete structural record and is motivated by the clast size and roundness trends observed in the Topolia area. We feel that the interpretation in terms of a major half-graben bounding fault with progressive exhumation of the footwall block is consistent with Correspondence: Dr Markus Seidel, Am Lindbruch 29, D-41470 Neuss, Germany. E-mail: markus.seidel@gmx.net

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Reply to comment on 'Tectono-sedimentary evolution of lower to middle Miocene half-graben basins related to an extensional detachment fault (western Crete, Greece)'

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Tectono‐sedimentary evolution of lower to middle Miocene half‐graben basins related to an extensional detachment fault (western Crete, Greece)

The kakopetros and ravdoucha iron-oxide deposits, western crete, greece: fluid transport and mineralization within a detachment zone

Reply to comment on 'Tectono-sedimentary evolution of lower to middle Miocene half-graben basins related to an extensional detachment fault (western Crete, Greece)'