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1

Rifting and closure of two branches of the Tethys; from Neotethys to Alpine Tethys

Fodor Laszlo

Geotourism / Geoturystyka

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2023

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nr 1-2 (72-73)

19--20

EN

The western termination of the Neotethys is marked by a complex interaction of several small oceanic basins which were formed and closed progressively. The western end of the Neotethys was opened from Permian to Middle Triassic; spreading started from Anisian. The rifting was associated with acidic, sometimes basic magmatism; Permian intrusions are widespear in certain zones (Eastern Alps), and together with Middle Triassic volcanites, played a role in weakening of the extending continental lithosphere. The rifting process was interacting with evaporite tectonism in regions where Late Permian evaporites were formed potentially as a post-rift or intra-rift stage. Due to loading of the ovelying Early Triassic clastic-carbonate ramp sequence, and the still ongoing extensional deformation, and/ or gravitational sliding of shelf domains toward deepening extended continental margin, salt tectonics probably started in latest Early Triassic. The uprising salt walls strongly influenced shelf and eventually slope deposition; the minibasins between salt walls often hosted carbonate ramp or platform development while collapsing salt structures could turn to deep “intra-platform” basins. The salt tectonics controlled the continuing facies differentiation during the Late Triassic. The development of salt-cored normal faults are not characteristic for a typical post-rift passive margin, but due to their relation to underlying salt, facies differentiation was maintained. The earliest sign of rifting of the Alpine Tethys can be seen in the Late Triassic deep grabens (Southern Alps, southern Transdanubian Range). This is the reason that separation of salt-related deformation, and crustal extension is not evident in some zones. The closure of the Neotethys started with intra-oceanic subduction, probably with a double polarity, and the formation of a supra-subductional new oceanic lithosphere (the Vardar zone in some interpretations). The age of this process is somewhat controversial in different models. Isotopic ages of metamorphic sole of the Vardar ophiolites suggest 175–170 Ma while neutral to acidic differentiates in the eastern Vardar testify ongoing Late Jurassic oceanic magmatism (~155–155 Ma). A complex system of melange was formed under and in front of the emplacing upper plate Vardar ophiolite. While sub-ophiolitic melange with serpentinitic matrix formed below the overlying hot oceanic lithosphere, the sediment-hosted melange contains blocks from different zones of the passive margin and partly the overlying ophiolite. Stratigraphic ages indicate that this processes happend during the Middle and Late Jurassic. The obduction happened in latest Jurassic (Tithonian) indicated by reef limestone on top of ophiolites. This was followed by the imbrication of the underlying passive margine Adriatic continental lithospere during the entire Cretaceous and Cenozoic. Clastic foreland basins were formed within this lower plate supplied partly by the passive upper plate ophiolite. The Alpine Tethys went on intensive rifting which ended with break-up in late Middle or in the Late Jurassic on its southern Piemont-Ligurian branch. The onset of subduction is not exactly clear but could happen in the Late Cretaceous resulted in high-pressure metamorphism of the oceanic domains in the Eocene (Tauern window). The Transdanubian Range of Hungary was situated between the two oceanic domains during the whole Mesozoic. While this unit has not been buried and only deformed modestly, the sedimentary events reflect the complex evolution. Middle Triassic rifting resulted in disruption of Early Triassic mixed siliciclastic-carbonate ramp into platform and somewhat deeper grabens. Small-scale synsedimentary faults and neptunian dykes testify this phase. Away from the break-up zone, the area underwent important post-rift subsidence compensated by platform carbonate sedimentation through the Late Triassic. However, the trace of initial Late Triassic rifting is present in forms of synsedimentary faults in the western side, closer to the future Neotethys. Following the earliest Jurassic decline of platform biota, the ongoing Alpine rifting disintegrated the entire TR carbonate platform into shallower, sediment free ridges and somewhat deeper grabens. This rifting and subsidence resulted in deposition of pelagic red nodular limestone in the Aalenian-Bajocian. After cherty sedimentation in the Callovian–Oxfordian, very modest extension appeared in the latest Jurassic. Although this phase could be considered as the final extension of the Alpine Tethys rifting far to the west, it is more probable that in fact this is due to slight downbending of the TR below the distal ophiolite emplacement to the east. The Neotethyan influence prevaild in the eastern TR during the Early Cretaceous. A clastic foreland basin was supplied by ophiolite and supra-ophiolite detritus of the obducted Neotethyan Vardar unit. Structural cituation changed in the late Early Cretacoues, around 115 Ma (Albian). The entire TR underwent shortening. The unit, formerly the lower plate of the Neotethyan system, was emplaced, as the highest nappe, on to the other continental units of the Austroalpine system. Within the Eastern Alps, this was associated with intracontinental subduction initiated in zone of Permian magmatism having thermally weakened the lithosphere. The relationship of this subduction, and associated high to ultrahigh pressure metamorphism is not clear, but eventually could have connected to large-scale displacement of the Neotethyan subduction zone at its northernmost termination zone. The complete change of the TR, from lowermost position to upper plate, is the reflection of complex 3D geometry of overlapping oceanic domains and could happen in other Tethyan areas

2

Timing of rifting and drifting in the central part of Atlantic Ocean

Ledvenyiova L

Geologia Sudetica

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2014

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Vol. 42

53--53

3

Jurassic syn-rift and Cretaceous syn-orogenic, coarse-grained deposits related to opening and closure of the Vahic (South Penninic) Ocean in the Western Carpathians – an overview

Plasienka D.

Geological Quarterly

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2012

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Vol. 56, No. 4

601--628

EN

Although no undoubted oceanic crustal rock complexes of Penninic affinity participate in the present surface structure of the Western Carpathians, indirect lines of evidence suggest prolongation of the South Penninic-Vahic oceanic tract into the ancient Carpathians. The sedimentary record of both the syn-rift and syn-orogenic clastic deposits reveal their origin between the outer Tatric (Austroalpine) and the inner Oravic (Middle Penninic) margins. The rifting regime is exemplified by the normal fault-related scarp breccias of the Jurassic Borinka Unit in the Male Karpaty Mts., which are characterized by local, gradually denuded source areas. Two other regions provide examples of a contractional regime, both related to shortening and closure of the Vahic oceanic domain. The Belice Unit in the Povazsky Inovec Mts. includes Upper Jurassic-Lower Cretaceous eupelagic, mostly siliceous deposits and a thickening-upwards Senonian sequence of turbiditic sandstones, conglomerates and chaotic breccias. It is inferred that this succession represents the sedimentary cover of oceanic crust approaching a trench, its incorporation in the accretionary complex and finally underthrusting below the outer Tatric margin. In the Oravic units of the Pieniny Klippen Belt, deep-marine conglomerate/breccia bodies with olistoliths indicate collision-related thrust stacking that started from the Maastrichtian (Gregorianka Breccia of the Sub-Pieniny Unit) and terminated with the Lower Eocene Milpos Breccia in the Saris Unit. In addition, a tentative recycling scheme of “exotic” clastic material from mid-Cretaceous conglomerates of the Klape Unit to various Klippen Belt units is outlined. This material is considered to be unrelated to the Vahic oceanic realm and its closure, and likely represents erosional products of more distant orogenic zones.

4

Sinemurian to lowermost Toarcian ammonites of the Brescian Prealps (Southern Alps, Italy): preliminary biostratigraphical framework and correlations

Meister Ch., Schirolli P., Dommergues J-L.

Volumina Jurassica

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2009

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Vol. 7, no. 1

9-18

EN

A set of 28 ammonite biohorizons or faunal assemblages is proposed for the Sinemurian, the Pliensbachian and the lowermost Toarcian of the Brescian Prealps, in part based on the published data of the authors of this contribution and partly on new results, derived both from recent field investigations and from the study of the historical collection of Lower Jurassic ammonites preserved in the Museum of Natural Sciences of Brescia (Northern Italy). The biohorizons are present in the Liassic carbonate succession of the Brescian Prealps, cropping out between the eastern surroundings of Brescia (Botticino), to the east, and Lake Iseo, to the west. Since the Hettangian this region was subjected to Jurassic rifting. The area of study was located on the eastern border of the wide Lombardian Basin, a part of the southern continental passive margin of Tethys. An articulated fault-system, trending from Brescia to the North, separated the western subsiding area of the Val Trompia-Sebino Basin from the eastern Botticino structural high. After the drowning of the Rhetian-Hettangian Corna Platform, the very thick synrift succession of the Medolo Group accumulated in the Val Trompia-Sebino Basin, whereas the coeval reduced sequence of the Rezzato Encrinite and the overlying Botticino Corso Rosso covered the Botticino High, subsequent to the Early Sinemurian. The ammonite biohorizons and assemblages recognised are quite well integrated and correlable with either the NW European standard zonation or the different zonations proposed for the Tethyan Realm.

5

The mid-Frasnian subsidence pulse in the Lublin Basin (SE Poland) : sedimentary record, conodont biostratigraphy and regional significance

Narkiewicz K., Narkiewicz M.

Acta Geologica Polonica

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2008

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Vol. 58, no. 3

287-301

EN

Most of the thickness of Frasnian sediments in the central segment of the Lublin Basin, i.e. up to 300 metres, is represented by a single transgressive-regressive Cycle VIa, developed in the carbonate-sulphate platform facies. The age of the transgressive part falls into the interval between the upper part of theUpper hassi Zone and the jamieae Zone, whereas the upper boundary runs between the upper part of the Lower rhenana Zone and the lower part of the Upper rhenana Zone. Basin architecture and conodont biostratigraphic data confirm the tectonic nature of the cycle, which represents a short-termincrease in Frasnian subsidence and depositional rates. Based on the conodont data, it is plausible that the onset of the tectonic subsidence in the Lublin Basin and the incipient Pripyat Graben rifting correspond closely in age. They can thus be attributed to the common tectonic mechanism of regional extension in the south-west part of the East European Platform. The lack of any Late Devonian magmatic activity in the Lublin Basin and the synchronous development of this basin with the Pripyat Graben favour the idea that intraplate stresses were the primary factors controlling subsidence in both depocentres during the mid Frasnian to Famennian. The hypothetical mantle plume could have merely amplified the effects of crustal extension in the Pripyat Graben, thus facilitating a typical rift development.

6

The Kashafrud Basin (NE Iran): a key for understanding the Jurassic geodynamic evolution of the Iran Plate

Wilmsen M., Fürsich F., Taheri J., Brunet M.-F., Seyed-Emami K., Majidifard M.

Volumina Jurassica

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2006

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Vol. 4, no. 1

69-69

EN

The boundary between the Koppeh Dagh and the Binalud Mountains in northeastern Iran corresponds to the suture of the Palaeotethys, an ocean which, in the area of present-day Iran, had been completely subducted below the Turan Plate as part of Eurasia in the north towards the end of the Triassic (Early Cimmerian orogeny). At this boundary between the Turan Plate and the Iran Plate, the latter a part of the so-called Cimmerian Microcontinent Collage, a strongly subsiding, NW-SE-trending basin formed during the Late Bajocian-Bathonian, which became infilled with a thick (>2000 m) pile of fluvial to deep-marine siliciclastic sediments, combined in the so-called Kashafrud Formation. This Kashafrud Basin is a key for understanding the geodynamic history of the Iran Plate during the Middle-Late Jurassic. The Kashafrud Formation overlies, often with angular unconformity and a thick basal conglomerate, Triassic and older rocks. In the area of the southwestern basin margin (Binalud Mountains), coarse-grained fluvial sediments grade into marine sediments (fan deltas, deltas, storm-influenced shelf). Short transport distances and steep relief are indicated by high compositional and textural immaturity. In the northeastern part of the outcrop belt, towards the Koppeh Dagh Mountains, the Kashafrud Formation is marine throughout and rapidly grades into deep-marine, dark shales with turbidite intercalations, indicating a slope to basin plain environment. By the Early Callovian, siliciclastic sedimentation was gradually replaced by carbonates and the Kashfrud Basin was infilled with carbonate platform and slope sediments of the Chaman Bid and Mozduran formations (Callovian - Upper Jurassic). Estimates of subsidence rates indicate very high values of 700 m/my and more during the Late Bajocian-Bathonian, indicative of young continental rift zones, and the Kashafrud Basin is thus interpreted as a rift basin. Integrated facies and stratigraphic analyses indicate that the bulk of the sediments entered the basin from the SW, derived from erosion of the uplifted rift shoulders in the Binalud Mountains. Deeper marine, basinal areas extended to the NE, probably far below the Cretaceous cover of the Koppeh Dagh. A coeval subsidence pulse of similar magnitude, related to the Mid-Cimmerian tectonic movements, also occurred in northern Iran (deep marine marls of the Dalichai Formation in the Alborz Mountains). From a geodynamic viewpoint, the Kashafrud Basin is the southeastern extension of the rapidly subsiding South Caspian Basin (SCB) which, in northern Iran, started to develop already in the Toarcian-Aalenian. In the Bajocian-Bathonian, this basin was enlarged towards the E-SE (opening of the Kashafrud Basin), leading to a renewed separation of the Iran and Turan plates after the Early Cimmerian collision. The reactivation of a former ocean suture for the development of a strongly subsiding basin is rather exceptional (the SCB possibly also reached the spreading stage) and the reasons for its opening are still poorly understood.

7

Late Jurassic-Miocene evolution of the Outer Carpathian fold-and-thrust belt and its foredeep basin (Western Carpathians, Poland)

Oszczypko N.

Geological Quarterly

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2006

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Vol. 50, No. 1

169-194

EN

The Outer Carpathian Basin domain developed in its initial stage as a Jurassic-Early Cretaceous rifted passive margin that faced the eastern parts of the oceanic Alpine Tethys. Following closure of this oceanic basin during the Late Cretaceous and collision of the Inner Western Carpathian orogenic wedge with the Outer Carpathian passive margin at the Cretaceous-Paleocene transition, the Outer Carpathian Basin domain was transformed into a foreland basin that was progressively scooped out by nappes and thrust sheets. In the pre- and syn-orogenic evolution of the Outer Carpathian basins the following prominent periods can be distinguished: (1)Middle Jurassic- Early Cretaceous syn-rift opening of basins followed by Early Cretaceous post-rift thermal subsidence, (2) latest Cretaceous- Paleocene syn-collisional inversion, (3) Late Paleocene toMiddle Eocene flexural subsidence and (4) Late Eocene-EarlyMiocene synorogenic closure of the basins. In the Outer Carpathian domain driving forces of tectonic subsidence were syn-rift and thermal post-rift processes, as well as tectonic loads related to the emplacement of nappes and slab-pull. Similar to other orogenic belts, folding of the Outer Carpathians commenced in their internal parts and progressed in time towards the continental foreland. This process was initiated at the end of the Paleocene at the Pieniny Klippen Belt/Magura Basin boundary and was completed during early Burdigalian in the northern part of the Krosno Flysch Basin. During Early and Middle Miocene times the Polish Carpathian Foredeep developed as a peripheral foreland basin in front of the advancing Carpathian orogenic wedge. Subsidence of this basin was controlled both by tectonic and sedimentary loads. The Miocene convergence of the Carpathian wedge with the foreland resulted in outward migration of the foredeep depocenters and onlap of successively younger deposits onto the foreland.

8

Development of Trans-European Suture Zone in Poland: from Ediacaran rifting to Early Palaeozoic accretion

Nawrocki J., Poprawa P.

Geological Quarterly

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2006

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Vol. 50, No. 1

59-76

EN

This contribution summarizes selected results of the “Palaeozoic Accretion of Poland” Project. Emphasis is placed on geochronological, geochemical and palaeomagnetic constraints on the Late Neoproterozoic to Early Palaeozoic development of the Trans-European Suture Zone (TESZ). During the Late Neoproterozoic break-up of Rodinia, a major rift developed in the area of the future TESZ along which Baltica was separated from peri-Gondwana and Laurentia, resulting in opening of the Tornquist Ocean and development of the southwestern Baltica passive margin. This was paralleled by the development of the Cadomian orogenic system along the margin of Gondwana and the eastern and southern margins of Baltica. Some tectonic units involved in the TESZ, such as the Brunovistulian Terrane and the Małopolska Massif characterized by Cadomian basement, were derived fromthe internal and external parts of the Cadomian Orogen, presumably somewhere at the SE or SW corners of Baltica. Determination of areas where these terrains were originally located depends strongly on the Ediacaran plate model that is adopted for Baltica. The Małopolska Massif was reaccreted to Baltica, presumably due to latest Ediacaran strike-slip tectonics, during the late Middle to Late Cambrian, causing at that time an interruption of its passive margin subsidence pattern and minor erosion. During Late Ordovician to Silurian times, the Caledonian collision of Gondwana-derived East Avalonia Terrane with Baltica gave rise to the development of a foredeep basin along the southwestern margin of Baltica. The proximal part of this foredeep corresponds to the Pomeranian region to the Koszalin-Chojnice Zone, and its distal parts to the Baltic Basin, both of which developed on Baltica basement. During Ordovician and Silurian times clastics were shed into the Koszalin-Chojnice Zone and the Baltic Basin from the evolving Caledonian orogenic wedge, consisting of a subduction-related volcanic arc, obducted ophiolites and accretionary prism, as well as crustal units that were detached from basement of Baltica and Avalonia. The Brunovistulian Terrane was accreted to theMałopolskaMassif at the turn from the Silurian to the Devonian. Proximal terranes, such as the Pomerania and Łysogóry units remained after Late Neoproterozoic rifting in a position close to the relatively mobile SW margins of Baltica.

9

Geodynamic evolution of the Tatra Mts. and the Pieniny Klippen Belt (Western Carpathians) : problems and comments

Jurewicz E.

Acta Geologica Polonica

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2005

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Vol. 55, no. 3

295-338

EN

The geodynamic evolution of the Pieniny Klippen Belt (PKB) and the Tatra Mts. assumes that: The Oravic-Vahic Basin developed due to Jurassic rifting processes with thinned continental crust. The oblique rift without rift-related volcanism had probably a WSW-ENE course. Late Cretaceous thrust-folding of the Choč, Križna and High-Tatric nappes took place underwater and at considerable overburden pressure (ok. ~6-7 km). The geometry of the structures was strongly disturbed by pressure solution processes leading to considerable mass loss. Nappe-folding in the PKB was connected with the slow and flat subduction of thinned continental crust of the Vahicum-Oravicum under the northern margin of the Central Carpathians Block.In the Tatra Mts. and the PKB, the nappe thrust-folding was influenced by a strike-slip shear zone between the edge of the Central Carpathians and the PKB and caused e.g. the counter-clockwise rotation of the Tatra block and relative changing directions of thrusting. The consequence of Miocene oblique subduction and subsequent collision of the North-European continental crust with the Central Carpathian Block was the activation of NNW-SSE deep fault zones. With one of these - the Dunajec Fault - were connected en echelon shears trading on the andesite dykes swarm. Miocene collision caused the disintegration of the Central Carpathian Block into individual massifs and their rotational uplift. The value of rotation around the horizontal axis for the Tatra Massif is estimated at ~40°.

10

The structural position and tectonosedimentary evolution of the Polish Outer Carpathians

Oszczypko N.

Przegląd Geologiczny

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2004

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Vol. 52, nr 8/2

780-791

EN

The sedimentary basins of the Outer Carpathians are regarded as the remnant oceanic basins that were transformed into the foreland basin. These basins developed between the colliding European continent and the intra-oceanic arcs. In the pre-orogenic and syn-orogenic evolution of the Carpathian basins the following prominent periods can be established: Middle Jurassic — Early Cretaceous opening of basins and post-rift subsidence, Late Cretaceous—Palaeocene inversion, Palaeocene toMiddle Eocene subsidence, Late Eocene–Early Miocene synorogenic closing of the basins. In the Outer Carpathian sedimentary area the important driving forces of the tectonic subsidence were syn- and post-rift thermal processes as well as the emplacement of the nappe loads related to the subduction processes. Similar to the other orogenic belts, the Outer Carpathians were progressively folded towards the continental margin. This process was initiated at the end of the Palaeocene at the Pieniny Klippen Belt Magura Basin boundary and completed during Early Burdigalian in the northern part of the Krosno flysch basin.

11

Genesis and evolution of Sudetic late Hercynian volcanic rocks inferred from trace element modelling

Dziedzic K.

Geologia Sudetica

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1998

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Vol. 31, nr 1

79-91

EN

The late Hercynian volcanic complexes in the Sudetes originated due to decompressional melting of the subcontinental lithospheric source region. The volcanic activity started with the calc-alkaline andesite magma in an Early Permian, followed by the picritic relicts and the andesitic assemblage rocks both of tholeiitic affinity. The tholeiitic andesites originated by AFC processes involving mantle-and lower crust-derived material. The differentiation of the andesitic parental magma within high-level magma chamber(s) by AFC processes involving upper crust components yielded the acid volcanic varieties in the area. The geodynamic processes and geological relations correspond with those of continental rift zones.