The Cimmerian evolution of the Nakhlak–Anarak area, Central Iran, and its bearing for the reconstruction of the history of the Eurasian margin

Abstract

New structural, sedimentological, petrological and palaeomagnetic data collected in the region of Nakhlak-Anarak provide important constraints on the Cimmerian evolution of Central Iran. The Olenekian-Upper Ladinian succession of Nakhlak was deposited in a forearc setting, and records the exhumation and erosion of an orogenic wedge, possibly located in the present-day Anarak region. The Triassic succession was deformed after Ladinian times and shows south-vergent folds and thrusts unconformably covered by Upper Cretaceous limestones following the Late Jurassic Neo-Cimmerian deformation. Palaeomagnetic data obtained in the Olenekian succession suggest a palaeoposition of the region close to Eurasia at a latitude around 208N. In addition, the palaeopoles do not support large anticlockwise rotations around vertical axes for central Iran with respect to Eurasia since the Middle Triassic, as previously suggested.The Anarak Metamorphic Complex (AMC) includes blueschist-facies metabasites associated with discontinuous slivers of serpentinized ultramafic rocks and Carboniferous greenschistfacies 'Variscan' metamorphic rocks, including widespread metacarbonates. The AMC was formed, at least partially, in the Triassic. Its erosion is recorded by the Middle Triassic Bāqoroq Formation at Nakhlak, which consists of conglomerates and sandstones rich in metamorphic detritus. The AMC was repeatedly deformed during post-Triassic times, giving origin to a complex structural setting characterized by strong tectonic fragmentation of previously formed tectonic units.Based on these data, we suggest that the Nakhlak-Anarak units represent an arc-trench system developed during the Eo-Cimmerian orogenic cycle. Different tectonic scenarios that can account for the evolution of the region and for the occurrence of this orogenic wedge in its present position within Central Iran are critically discussed, as well as its relationships with a presumed 'Variscan' metamorphic event.

The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny

“…According to recent paleogeographic reconstructions proposed by Angiolini et al (2007) and by Muttoni et al (2009aMuttoni et al ( , 2009b, the Iranian plate was rifted apart from Gondwana and began its northward drift during the end of the Lower Permian, colliding with southern Eurasia in the Late Triassic giving rise to the Cimmerian orogenic event (Sengör, 1979(Sengör, , 1984Zanchi et al, 2009aZanchi et al, , 2009b. On the base of our data and previous considerations, we suggest that the Fariman and the Darreh Anjir complexes of NE-Iran were part of the southern Eurasia (Turan plate) active margin, developed in the upper plate of the north to northeast directed Palaeotethys subduction zone.…”

“…In N Iran, the position of the Palaeotethys suture zone between the Eurasian margin and the Iran block, has been inferred based on the occurrence of thin strips of serpentinites and mafic-ultramafic complexes (Shanderman complex, Gorgan area) interpreted as remnants of the Palaeotethys ocean floor (Davies et al, 1972;Stocklin, 1974;Sengör, 1990;Alavi, 1996). Recent investigations Zanchi et al, 2009aZanchi et al, , 2009b have demonstrated the occurrence of an important orogenic event although the occurrence of remnants of the Palaeotethys ocean in the Alborz chain is controversial.…”

Nakhlak carbonate-hosted Pb(Ag) deposit, Isfahan province, Iran: a geological, mineralogical, geochemical, fluid inclusion, and sulfur isotope study

“…The Alam consists of finegrained volcanic arenite, nodular limestone, and marl with turbidites at the base and intercalations of fluvial conglomerate that become more numerous upward (Zanchi et al, 2009;Balini et al, 2009). The…”

The Sanandaj–Sirjan Zone in the Neo-Tethyan suture, western Iran: Zircon U–Pb evidence of late Palaeozoic rifting of northern Gondwana and mid-Jurassic orogenesis

“…2); well south of the main strand of the suture in the Alborz and Kopet Dagh mountains (Bagheri and Stampfli, 2008). Carboniferous accretion (Variscan) at the northern margin of Palaeo-Tethys, prior to the collision within the Yazd Block, has been determined from radiometric ages on metamorphic rocks (Bagheri and Stampfli, 2008;Zanchi et al, 2009Zanchi et al, , 2015. Palaeomagnetic data show that the various blocks of Central Iran have undergone considerable counter-clockwise rotations in the Late Jurassic and Neogene so that their present-day configuration differed considerably to that in the Palaeozoic and early Mesozoic (Mattei et al, 2012(Mattei et al, , 2015.…”

“…Data from Central Iran, including radiometric ages and mapping of a Variscan suture in the Anarak-Jandaq block, indicate that this block may have been connected with the Palaeo-Tethyan suture in northeast Iran (Bagheri and Stampfli, 2008;Zanchi et al, 2009Zanchi et al, , 2015. Palaeomagnetic data from Central Iran indicate substantial counter-clockwise rotations of the Lut, Tabas and Yazd blocks in the Late Jurassic and Neogene (Mattei et al, 2012(Mattei et al, , 2015, and thus requires substantial changes to the Jurassic and older palaeogeography (Fig.…”