Indian plate paleogeography, subduction and horizontal underthrusting below Tibet: Paradoxes, controversies and opportunities

The India-Asia collision zone is the archetype to calibrate geological responses to continent-continent collision, but hosts a paradox: There is no orogen-wide geological record of oceanic subduction after initial collision around 60-55 Ma, yet thousands of kilometers of post-collisional subduction occurred before the arrival of unsubductable continental lithosphere that currently horizontally underlies Tibet. Kinematically restoring incipient horizontal underthrusting accurately predicts geologically estimated diachronous slab break-off, unlocking the Miocene of Himalaya-Tibet as a natural laboratory for unsubductable lithosphere convergence. Additionally, three endmember paleogeographic scenarios exist with different predictions for the nature of post-collisional subducted lithosphere but each is defended and challenged based on similar data types. This paper attempts at breaking through this impasse by identifying how the three paleogeographic scenarios each challenge paradigms in geodynamics, orogenesis, magmatism or paleogeographic reconstruction and identify opportunities for methodological advances in paleomagnetism, sediment provenance analysis, and seismology to conclusively constrain Greater Indian paleogeography

Основні напрямки маркетингу і менеджменту в архівній справі

Gondwana breakup since the Jurassic and the northward motion of India toward Eurasia were associated with formation of ocean basins and ophiolite obduction between and onto the Indian and Arabian margins. Here we reconcile marine geophysical data from preserved oceanic basins with the age and location of ophiolites in NW India and SE Arabia and seismic tomography of the mantle below the NW Indian Ocean. The North Somali and proto-Owen basins formed due to 160-133-Ma N-S extension between India and Somalia. Subsequent convergence destroyed part of this crust, simultaneous with the uplift of the Masirah ophiolites. Most of the preserved crust in the Owen Basin may have formed between 84 and 74-Ma, whereas the Mascarene and the Amirante basins accommodated motion between India and Madagascar/East Africa between 85 and circa 60-Ma and 75 and circa 66-Ma, respectively. Between circa 84 and 45-Ma, oblique Arabia-India convergence culminated in ophiolite obduction onto SE Arabia and NW India and formed the Carlsberg slab in the lower mantle below the NW Indian Ocean. The NNE-SSW oriented slab may explain the anomalous bathymetry in the NW Indian Ocean and may be considered a paleolongitudinal constraint for absolute plate motion. NW India-Asia collision occurred at circa 20-Ma deforming the Sulaiman ranges or at 30-Ma if the Hindu Kush slab north of the Afghan block reflects intra-Asian subduction. Our study highlights that the NW India ophiolites have no relationship with India-Asia motion or collision but result from relative India-Africa/Arabia motions instead. Key Points We present a new tectonic model for the evolution of NW Indian Ocean Subducted slab under the Carlsberg Ridge resulted from Arabia-India convergenc

Cretaceous slab break-off in the Pyrenees: Iberian plate kinematics in paleomagnetic and mantle reference frames

AbstractThe Pyrenees at the Iberia–Europe collision zone contain sediments showing Albian–Cenomanian high-temperature metamorphism, and coeval alkaline magmatic rocks. Stemming from different views on Jurassic–Cretaceous Iberian microplate kinematics, two schools of thought exist on the trigger of this thermal pulse: one invoking hyperextension of the Iberian and Eurasian margins, the other suggesting slab break-off. Competing scenarios for Mesozoic Iberian motion compatible with Pyrenean geology, comprise (1) transtensional eastward motion of Iberia versus Eurasia, or (2) strike-slip motion followed by orthogonal extension, both favoring hyperextension-related heating, and (3) scissor-style opening of the Bay of Biscay coupled with subduction in the Pyrenean realm, favoring the slab break-off hypothesis. We test these kinematic scenarios for Iberia against a newly compiled paleomagnetic dataset and conclude that the scissor-type scenario is the only one consistent with a well-defined ~35° counterclockwise rotation of Iberia during the Early Aptian. We proceed to show that when taking absolute plate motions into account, Aptian oceanic subduction in the Pyrenees followed by Late Aptian–Early Albian slab break-off should leave a slab remnant in the present-day mid-mantle below NW Africa. Mantle tomography shows the Reggane anomaly that matches the predicted position and dimension of such a slab remnant between 1900 and 1500km depth below southern Algeria. Mantle tomography is therefore consistent with the scissor-type opening of the Bay of Biscay coupled with subduction in the Pyrenean realm. Slab break-off may thus explain high-temperature metamorphism and alkaline magmatism during the Albian–Cenomanian in the Pyrenees, whereas hyperextension that exhumed Pyrenean mantle bodies occurred much earlier, in the Jurassic

Sedimentary geology of the Middle Carboniferous of the Donbas region (Dniepr-Donets basin, Ukraine)

Peer reviewedPublisher PD

MORGen: an Algorithm to Compute Spreading Centre and Transform Geometries from Simple Initial Plate Boundaries and Euler Rotations

The age structure of the global ocean floor is a key feature in paleogeographic reconstructions, which in turn forms the quantitative basis for Earth System Science. However, much of the ocean floor in paleogeographic reconstructions has been lost to subduction. The age structure of such lost ocean floor is constructed from the reconstructions of adjacent continents, using the relative rotations, around Euler poles to predict the geometry of spreading centres and transform faults. Building such mid-ocean ridge features in paleogeographic reconstructions is laborious, as it requires redrawing of ridge-transform systems upon every Euler pole shift in the model. In this paper, we present the Mid-Ocean Ridge Generator (MORGen) algorithm, based on pyGPlates. MORGen reduces the laborious task by automating the drawing of mid-ocean ridge geometries from geometrically simple plate boundary input assuming ridge-perpendicular spreading and adjusts ridge geometries in a simplest-scenario fashion by gradually adjusting ridge orientation and transform fault length upon Euler pole shifts, inspired by observations from the modern sea floor. The code takes as input curved line features, representing approximate divergent plate boundaries, and a set of Euler poles. These are then converted into spreading centre-transform geometries. Upon Euler pole shifts, the geometries are adjusted to fit the set of small circles and great circles dictated by the new Euler pole. For studies of paleo-environment and paleo-oceanography MORGen can be used in combination with other algorithms for full reconstructions of ocean floors, including their age, bathymetry, and roughness. For in-situ preserved ocean floor, the paleo-age distribution can be reconstructed directly in high resolution from geophysical and geological data from the modern ocean floor and MORGen would not normally be the option of choice. In cases where models contain ocean floor that has now been subducted, MORGen straightforwardly facilitates mid-ocean ridge geometry reconstruction. To illustrate how well the MORGen algorithm reproduces real ocean floor age structure, we show a synthetic ridge evolution for the South Atlantic and Southern Oceans and compare this to geophysically constrained ocean floor geometry. In addition, we show examples of use cases where direct (re)construction of mid ocean ridges is not possible: now-subducted ocean basins in the Mediterranean region and an ocean in a future supercontinent scenario

Інтертекстуальність та гіпертекстуальні трансформації в турецьких народних оповідях

In this paper, some of the Turkish minstrel tales are analyzed in the frame of Gérard Genette’s ‘palimpsests’ approach. In the transtextuality category; the minstrel tales demonstrate both intertextual relations and hypertextual transformations. In terms of intertextuality, the tales present self-conscious intertextual relations by referring to other texts. The paper focuses on that in terms of hypertextuality, the mistrel tales transform the other texts by the process of reduction, extension, amplification and so on. Because of this process, the structure, the plot and the meaning of the previous text is transformed. As a result, the Turkish minstrel tales, as oral literary texts, can actively have role in intertextual relations as hypertexts.Türk halk hikâyelerine Fransız anlatıbilimci Gérard Genette’in “palempsest” imgesi ile yaklaşıldığında, halk hikâyelerinin ötemetinsellik sınıflandırmasında “metinlerarasılık” ve “ana metinsellik” ilişkilerini yansıttıkları görülmektedir. Halk hikâyeleri, göndermeler yoluyla bir başka metni somut olarak içinde barındırarak metinlerarasılık ilişkisi kurmaktadır. Bunun yanında, diğer sözlü ve yazılı metinleri biçimsel ve izleksel ya da anlamsal olarak dönüştürerek anlatısını yeniden kompoze etmek noktasında ana metinsellik ilişkisini kurmaktadır. Bu çalışmada Türk halk hikâyelerinin ana metinsellik dönüşümleri biçimsel ve anlamsal dönüşümler yoluyla incelenecektir. Türk halk hikâyeleri odağında yapılan çalışmalarda, genellikle kaynak ve etki alanı arayışları ile karşılaştırmalı eleştiri yaklaşımından yararlanılmıştır. Türk halk hikâyelerine metinlerarasılık ile yaklaşmak, anlatıların anlamsal ve yapısal olarak nasıl katmanlaştığını görmek ve anlatıyı metin olarak çözümlemek açısından somut veriler sağlayan bir yöntemdir

Palinspastic Reconstruction Versus Cross-Section Balancing: How Complete Is the Central Taurides Fold-Thrust Belt (Turkey)?

In many fold-thrust belts, cross section-derived shortening estimates are significantly lower than predicted based on plate convergence. This has led to controversial hypotheses that shortening may be largely underestimated due to wholesale underthrusting (convergence without shortening) below far-traveled continent or ocean-derived nappes. The Late Cretaceous-Eocene Taurides fold-thrust belt (southern Turkey) may contain a highly incomplete shortening record of convergence likely caused by wholesale underthrusting. To estimate this underthrusting, we calculate convergence across the belt using a map-view palinspastic reconstruction that takes into account major rotations of tectonic units during their accretion. We use paleomagnetic and fault kinematic analysis, timing of accretion, and Africa-Eurasia convergence to constrain our reconstruction. Our paleomagnetic results confirm an ~40 degrees clockwise vertical axis rotation of the Geyikda nappe that forms the core of the belt, which we interpret is accommodated by a lateral gradient in underthrusting on faults structurally above and below the Geyikda nappe. We reconstruct ~400-450km of convergence across the Taurides during their accretion. We compare this predicted convergence to shortening calculated from balanced cross sections, in which we reconstruct a minimum of 154-km shortening: 57km within far-traveled nappes, 70-km thrusting of far-traveled nappes over the Geyikda nappe, and 27-km shortening within the Geyikda nappe. Shortening in the Taurides created a significant nappe stack, but the majority of convergence was accommodated by wholesale underthrusting with barely a trace at the surface, including ~160km of convergence by rotation of the belt, and 90-130km related to missing Africa-Eurasia convergence

Reply to Ali & Aitchison's comment on 'Restoration of Cenozoic deformation in Asia, and the size of Greater India'

International audienceNo abstrac

Subduction and Slab Detachment Under Moving Trenches During Ongoing India-Asia Convergence

The dynamics of slab detachment and associated geological fingerprints have been inferred from various numerical and analog models. These invariably use a setup with slab-pull-driven convergence in which a slab detaches below a mantle-stationary trench after the arrest of plate convergence due to arrival of continental lithosphere. In contrast, geological reconstructions show that post-detachment plate convergence is common and that trenches and sutures are rarely mantle-stationary during detachment. Here, we identify the more realistic kinematic context of slab detachment using the example of the India-Asia convergent system. We first show that only the India and Himalayas slabs (from India's northern margin) and the Carlsberg slab (from the western margin) unequivocally detached from Indian lithosphere. Several other slabs below the Indian Ocean do not require a Neotethyan origin and may be of Mesotethys and Paleotethys origin. Additionally, the still-connected slabs are being dragged together with the Indian plate forward (Hindu Kush) or sideways (Burma, Chaman) through the mantle. We show that Indian slab detachment occurred at moving trenches during ongoing plate convergence, providing more realistic geodynamic conditions for use in future numerical and analog experiments. We identify that the actively detaching Hindu Kush slab is a type-example of this setting, whilst a 25–13 Ma phase of shallow detachment of the Himalayas slab, here reconstructed from plate kinematics and tomography, agrees well with independent, published geological estimates from the Himalayas orogen of slab detachment. The Sulaiman Ranges of Pakistan may hold the geological signatures of detachment of the laterally dragged Carlsberg slab

Orogenic architecture of the Mediterranean region and kinematic reconstruction of its tectonic evolution since the Triassic

The basins and orogens of the Mediterranean region ultimately result from the opening of oceans during the early break-up of Pangea since the Triassic, and their subsequent destruction by subduction accommodating convergence between the African and Eurasian Plates since the Jurassic. The region has been the cradle for the development of geodynamic concepts that link crustal evolution to continental break-up, oceanic and continental subduction, and mantle dynamics in general. The development of such concepts requires a first-order understanding of the kinematic evolution of the region for which a multitude of reconstructions have previously been proposed. In this paper, we use advances made in kinematic restoration software in the last decade with a systematic reconstruction protocol for developing a more quantitative restoration of the Mediterranean region for the last 240 million years. This restoration is constructed for the first time with the GPlates plate reconstruction software and uses a systematic reconstruction protocol that limits input data to marine magnetic anomaly reconstructions of ocean basins, structural geological constraints quantifying timing, direction, and magnitude of tectonic motion, and tests and iterations against paleomagnetic data. This approach leads to a reconstruction that is reproducible, and updatable with future constraints. We first review constraints on the opening history of the Atlantic (and Red Sea) oceans and the Bay of Biscay. We then provide a comprehensive overview of the architecture of the Mediterranean orogens, from the Pyrenees and Betic-Rif orogen in the west to the Caucasus in the east and identify structural geological constraints on tectonic motions. We subsequently analyze a newly constructed database of some 2300 published paleomagnetic sites from the Mediterranean region and test the reconstruction against these constraints. We provide the reconstruction in the form of 12 maps being snapshots from 240 to 0 Ma, outline the main features in each time-slice, and identify differences from previous reconstructions, which are discussed in the final section