The Late Cretaceous Asteroussia event as recorded in the Cyclades: a potential key to Western Tethys tectonic evolution

2021 ◽  
Author(s):  
Sonia Yeung ◽  
Marnie Forster ◽  
Emmanuel Skourtsos ◽  
Gordon Lister
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Ore Deposits ◽  
Western Tethys ◽  
Pressure Medium ◽  
Flat Slab Subduction ◽  
Extreme Extension ◽  
Metamorphic Core ◽  
Tectonic Slice ◽  
Ar Geochronology

<div> <p>The Cretaceous arc system formed during closure of West Tethys closure has long been a research focus for crustal geometry and associated ore deposits. Understanding the Africa-Europe motion across time is the key to its resolution. Evidence as to the time that Tethys subduction initiated is preserved in subduction accreted tectonic slices such as in the Gondwanan basement terranes on Ios, Cyclades, Greece. <sup>40</sup>Ar/<sup>39</sup>Ar geochronology in its granitoid basement and the structurally overlying garnet-mica schist tectonic slice identified a Late Cretaceous high pressure, medium temperature (HP–MP) metamorphic event. The timing and metamorphic conditions are comparable with geochronology and metamorphic conditions reported from other Cycladic islands. We suggest the northward extension of the Asteroussia crystalline terrane on Crete should therefore include the Ios basement tectonic slices, thus revising the regional geometry of the terrane stack. The northern part of the Hellenic terrane stack is overlain by individual Cycladic Eclogite-Blueschist terrane slices (e.g., on Ios) and the southern part is underplated by the tectonic units of the external Hellenides (Crete). To make such an architecture possible, we propose a 250-300 km southward jump of the subduction megathrust when the Ios basement terranes were accreted to the European terrane stack. Such a significant leap of the subduction megathrust supports a tectonic mode switch in which crust above the subduction zone was first subjected to shortening followed by a stretching event.  Accretion of the Asteroussia slices to the terrane stack likely commenced at or about ~38 Ma. During accretion, the already stretched and exhumed terranes of the Cycladic Eclogite-Blueschist Unit begun to thrust over the newly accreted Ios basement. The subduction jump had likely been accomplished by ~35 Ma, with rollback recommencing after a period of flat slab subduction followed by slab break off in the new subduction zone. This would allow explanation of the extreme extension that exhumed the Ios basement terrane, with the Asteroussia slices defining the core of the Ios metamorphic core complex, followed by the onset of Oligo-Miocene extension and accompanying magmatism in the Cyclades.</p> </div>

scholarly journals Evidence for and significance of the Late Cretaceous Asteroussia event in the Gondwanan Ios basement terranes

Solid Earth ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 2255-2275
Author(s):  
Sonia Yeung ◽  
Marnie Forster ◽  
Emmanuel Skourtsos ◽  
Gordon Lister
Keyword(s):  
Late Cretaceous ◽  
Tectonic Evolution ◽  
Microstructural Analysis ◽  
Core Complex ◽  
Medium Temperature ◽  
Western Tethys ◽  
Pressure Medium ◽  
Extreme Extension ◽  
The Individual ◽  
Metamorphic Core

Abstract. The Late Cretaceous Asteroussia event as recorded in the Cyclades is a potential key to the tectonic evolution of Western Tethys. Microstructural analysis and 40Ar/39Ar geochronology on garnet–mica schists and the underlying granitoid basement terrane on the island of Ios demonstrates evidence of a Late Cretaceous high-pressure, medium-temperature (HP–MT) metamorphic event. This suggests that the Asteroussia crystalline nappe on Crete extended northward to include these Gondwanan tectonic slices. In this case, the northern part of the Asteroussia nappe (on Ios) is overlain by the terrane stack defined by the individual slices of the Cycladic Eclogite–Blueschist Unit, whereas in the south (in Crete) the Asteroussia slices are near the top of a nappe stack defined by the individual tectonic units of the external Hellenides. This geometry implies that accretion of the Ios basement terrane involved a significant leap of the subduction megathrust (250–300 km) southward. Accretion needs to have commenced at or about ∼38 Ma, when the already partially exhumed slices of the Cycladic Eclogite–Blueschist Unit began to thrust over the Ios basement. By ∼35–34 Ma, the subduction jump had been accomplished, and renewed rollback began the extreme extension that led to the exhumation of the Ios metamorphic core complex.

scholarly journals Evidence for the Late Cretaceous Asteroussia event in the Gondwanan Ios basement terranes

2020 ◽  
Author(s):  
Sonia Yeung ◽  
Marnie Forster ◽  
Emmanuel Skourtsos ◽  
Gordon Lister
Keyword(s):  
High Pressure ◽  
Late Cretaceous ◽  
Metamorphic Core Complex ◽  
Metamorphic Event ◽  
Core Complex ◽  
Medium Temperature ◽  
Pressure Medium ◽  
Extreme Extension ◽  
The Individual ◽  
Metamorphic Core

Abstract. 40Ar/39Ar geochronology on garnet-mica schists and the underlying Gondwanan granitoid basement terrane on Ios demonstrates evidence of a Late Cretaceous high pressure, medium temperature (HP–MP) metamorphic event. This suggests that the Asteroussia crystalline nappe on Crete may extend northward and include Ios, in the Cyclades. If this is correct, the northern part of the Asteroussia nappe (on Ios) is overlain by the terrane stack defined by the individual slices of the Cycladic Eclogite-Blueschist Unit, whereas in the south (in Crete) the Asteroussia nappe is at the top of a nappe stack defined by the individual tectonic units of the external Hellenides. This geometry implies that the accretion of the Ios basement terrane involved a significant leap (250–300 km) southwards of the surface outcrop of the subduction megathrust. This accretion would have commenced at or about ~38 Ma, when the already exhumed terranes of the Cycladic Eclogite-Blueschist Unit had begun to thrust over the Ios basement. By ~35 Ma, we suggest the subduction jump had been accomplished, and renewed rollback began the extreme extension that led to the exhumation of the Ios metamorphic core complex.

Orogenic listening posts along the margins of western Tethys reveal a major tectonic event involving extreme extension at the start of the Eocene–Miocene transition

2021 ◽  
Author(s):  
Marnie Forster ◽  
Gordon Lister
Keyword(s):  
High Vacuum ◽  
Ultra High Vacuum ◽  
Metamorphic Core Complex ◽  
Core Complex ◽  
Nw Himalaya ◽  
Time Curve ◽  
Tectonic Event ◽  
Western Tethys ◽  
Extreme Extension ◽  
Metamorphic Core

<p>Orogenic listening posts have been established along the northern margins of western Tethys: i) in the west and central Alps; ii) in the Cyclades, Aegean Sea, Greece; and iii) along a traverse in the NW Himalaya. We report on modelling and simulation of data from the conjoint inversion of argon geochronology and ultra-high-vacuum (UHV) diffusion experiments, on rocks from these locations. In the Alps, samples come from either side of the Lepontine dome, a metamorphic core complex that resulted from orogen-parallel extension, with a major pulse of stretching coinciding with the onset of the Eocene–Oligocene transition. In the Cyclades, the samples come from Ios, a metamorphic core complex that began its existence at about the same time, related to extreme extension caused by southward rollback of the Hellenic slab, after an immediately preceding accretion event that incorporated Gondwanan slices into the terrane-stack. In the NW Himalaya, samples come from yet another Tethyan metamorphic core complex, the giant schist and gneiss dome that includes the Tso Morari, in Ladakh, India.<span> </span></p><p>Inversion of data from these locations reveals unprecedented detail in the inferred temperature-time curve, allowing recognition that a rapid cooling event took place in the lower plate of the detachment system at each of these locations, almost at the same time. We discuss the tectonic implications of a synchronised tectonic mode switch at the start of the Eocene–Oligocene transition. In each location there was a preceding period of compressional orogenesis, involving accretion of multiple tectonic slices to the terrane stack after an accretion event, followed by a period during which extreme extension of the continental lithosphere appears to have taken place. This supports our 2001 hypothesis that tectonic mode switches during collisional orogenesis are globally synchronized, in consequence of torque balance being continuously maintained in the planetary assemblages of moving lithospheric plates. Accretion events perturb that torque balance, with tectonic mode switches the result of mechanical adjustment caused by the creation of new subduction systems, with the initiation of rollback offering a potential explanation for the rapid exhumation of core complexes in the over-riding lithosphere.</p>

scholarly journals Tectonic denudation of a Late Cretaceous–Tertiary collisional belt: regionally symmetric cooling patterns and their relation to extensional faults in the Anatolide belt of western Turkey

2003 ◽  
Vol 140 (4) ◽  
pp. 421-441 ◽  
Author(s):  
UWE RING ◽  
CHRISTOPHER JOHNSON ◽  
RALF HETZEL ◽  
KLAUS GESSNER
Keyword(s):  
Late Cretaceous ◽  
Metamorphic Core Complex ◽  
Early Miocene ◽  
Second Phase ◽  
Late Oligocene ◽  
Core Complex ◽  
Cooling History ◽  
Western Turkey ◽  
Structural Levels ◽  
Metamorphic Core

Thermochronological data reveal that the Late Cretaceous–Tertiary nappe pile of the Anatolide belt of western Turkey displays a two-stage cooling history. Three crustal segments differing in structure and cooling history have been identified. The Central Menderes metamorphic core complex represents an ‘inner’ axial segment of the Anatolide belt and exposes the lowest structural levels of the nappe pile, whereas the two ‘outer’ submassifs, the Gördes submassif to the north and the Çine submassif to the south, represent higher levels of the nappe pile. A regionally significant phase of cooling in the Late Oligocene and Early Miocene affected the outer two submassifs and the upper structural levels of the Central Menderes metamorphic core complex. In the northern part of the Gördes submassif, cooling was related to top-to-the-NNE movement on the Simav detachment, as the apatite fission-track ages show a northward-younging trend in the direction of movement on this detachment. In the Çine submassif, relatively rapid cooling in Late Oligocene and Early Miocene times may have been related to top-to-the-S extensional reactivation of the basal thrust of the overlying Lycian nappes. The second phase of cooling in the Anatolide belt is related to Pliocene to Recent extension resulting in the formation of the Central Menderes metamorphic core complex in the inner part of the Anatolide belt. Core-complex development caused the formation of supra-detachment graben, which document the ongoing separation of the Central Menderes metamorphic core complex from the outer submassifs.

Geodynamic evolution of Upper Cretaceous Zagros ophiolites: formation of oceanic lithosphere above a nascent subduction zone

2011 ◽  
Vol 148 (5-6) ◽  
pp. 762-801 ◽  
Author(s):  
HADI SHAFAII MOGHADAM ◽  
ROBERT J. STERN
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Oceanic Lithosphere ◽  
Radiometric Dating ◽  
Northern Margin ◽  
Suprasubduction Zone ◽  
Margin Distribution ◽  
Ophiolitic Belt ◽  
Felsic Rocks

AbstractThe Zagros fold-and-thrust belt of SW Iran is a young continental convergence zone, extending NW–SE from eastern Turkey through northern Iraq and the length of Iran to the Strait of Hormuz and into northern Oman. This belt reflects the shortening and off-scraping of thick sediments from the northern margin of the Arabian platform, essentially behaving as the accretionary prism for the Iranian convergent margin. Distribution of Upper Cretaceous ophiolites in the Zagros orogenic belt defines the northern limit of the evolving suture between Arabia and Eurasia and comprises two parallel belts: (1) Outer Zagros Ophiolitic Belt (OB) and (2) Inner Zagros Ophiolitic Belt (IB). These belts contain complete (if disrupted) ophiolites with well-preserved mantle and crustal sequences. Mantle sequences include tectonized harzburgite and rare ultramafic–mafic cumulates as well as isotropic gabbro lenses and isolated dykes within the harzburgite. Crustal sequences include rare gabbros (mostly in IB ophiolites), sheeted dyke complexes, pillowed lavas and felsic rocks. All Zagros ophiolites are overlain by Upper Cretaceous pelagic limestone. Limited radiometric dating indicates that the OB and IB formed at the same time during Late Cretaceous time. IB and OB components show strong suprasubduction zone affinities, from mantle harzburgite to lavas. This is shown by low whole-rock Al2O3and CaO contents and spinel and orthopyroxene compositions of mantle peridotites as well as by the abundance of felsic rocks and the trace element characteristics of the lavas. Similarly ages, suprasubduction zone affinities and fore-arc setting suggest that the IB and OB once defined a single tract of fore-arc lithosphere that was disrupted by exhumation of subducted Sanandaj–Sirjan Zone metamorphic rocks. Our data for the OB and IB along with better-studied ophiolites in Cyprus, Turkey and Oman compel the conclusion that a broad and continuous tract of fore-arc lithosphere was created during Late Cretaceous time as the magmatic expression of a newly formed subduction zone developed along the SW margin of Eurasia.

Pre-Priabonian Palaeogene formations in southwestern Bulgaria and northern Greece: stratigraphy and tectonic implications

1998 ◽  
Vol 135 (1) ◽  
pp. 101-119 ◽  
Author(s):  
IVAN S. ZAGORCHEV
Keyword(s):  
Late Cretaceous ◽  
Middle Eocene ◽  
Regional Metamorphism ◽  
Late Eocene ◽  
Thin Layers ◽  
The South ◽  
Northern Greece ◽  
The North ◽  
Early Oligocene ◽  
Metamorphic Core

The Paril Formation (South Pirin and Slavyanka Mountains, southwestern Bulgaria) and the Prodromos Formation (Orvilos and Menikion Mountains, northern Greece) consist of breccia and olistostrome built up predominantly of marble fragments from the Precambrian Dobrostan Marble Formation (Bulgaria) and its equivalent Bos-Dag Marble Formation (Greece). The breccia and olistostrome are interbedded with thin layers of calcarenites (with occasional marble pebbles), siltstones, sandstones and limestones. The Paril and Prodromos formations unconformably cover the Precambrian marbles, and are themselves covered unconformably by Miocene and Pliocene sediments (Nevrokop Formation). The rocks of the Paril Formation are intruded by the Palaeogene (Late Eocene–Early Oligocene) Teshovo granitoid pluton, and are deformed and preserved in the two limbs of a Palaeogene anticline cored by the Teshovo pluton (Teshovo anticline). The Palaeocene–Middle Eocene age of the formations is based on these contact relations, and on occasional finds of Tertiary pollen, as well as on correlations with similar formations of the Laki (Kroumovgrad) Group throughout the Rhodope region.The presence of Palaeogene sediments within the pre-Palaeogene Pirin–Pangaion structural zone invalidates the concept of a ‘Rhodope metamorphic core complex’ that supposedly has undergone Palaeogene amphibolite-facies regional metamorphism, and afterwards has been exhumed by rapid crustal extension in Late Oligocene–Miocene times along a regional detachment surface. Other Palaeogene formations of pre-Priabonian (Middle Eocene and/or Bartonian) or earliest Priabonian age occur at the base of the Palaeogene sections in the Mesta graben complex (Dobrinishka Formation) and the Padesh basin (Souhostrel and Komatinitsa formations). The deposition of coarse continental sediments grading into marine formations (Laki or Kroumovgrad Group) in the Rhodope region at the beginning of the Palaeogene Period marks the first intense fragmentation of the mid- to late Cretaceous orogen, in particular, of the thickened body of the Morava-Rhodope structural zone situated to the south of the Srednogorie zone. The Srednogorie zone itself was folded and uplifted in Late Cretaceous time, thus dividing Palaeocene–Middle Eocene flysch of the Louda Kamchiya trough to the north, from the newly formed East Rhodope–West Thrace depression to the south.

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