TS7.10

The West Mediterranean Alpine belts of the Rif and its northern counterpart, the Betics, are famous for the subcontinental peridotites exposed in their Internal zones (Alboran Domain), the Beni Bousera (BB) and Ronda massifs, respectively. The Beni Bousera Marbles (BBMs) here described are known for long in the northern Rif, but remained overlooked so far. Since Kornprobst (1974), these marbles have been considered as simple intercalations within the kinzigites (migmatitic granulites) envelope of the BB peridotite. Based on the integration of field mapping, structural and petrology investigations and supported by SHRIMP U-Th-Pb geochronology, we present a new interpretation of these marbles and infer geodynamic implications at the local and regional scale. The field data show that the BBMs form minor, dismembered units within a ~30 to 300 m-thick mylonitic contact zone between the kinzigites and the overlying gneisses of the Filali Unit (Filali-Beni Bousera Shear Zone, FBBSZ). They display bedding structures marked by more or less siliceous marbles and some mica-rich or conglomeratic beds. The FBBSZ includes secondary ductile thrusts that determine kinzigite horses carried NW-ward over the marbles. Within the latter, NNE-trending folds are conspicuous. Brittle, northward-dipping normal faults crosscut the FBBSZ ductile structures. An unconformable contact, either of stratigraphic or tectonic origin, onto the kinzigites can be locally observed. The petrological investigation allows us to define pebbles and/or detrital grains, including K-feldspar, quartz, garnet, and zircon in these high-grade marbles. Peak mineral assemblage consists of forsterite, Mg-Al-spinel, phlogopite, and geikielite (MgTiO3) in dolomite marbles, phlogopite, scapolite, diopside, and titanite in calcite marbles. This characterizes a peak HT-LP metamorphism at ~700-750°C, 4-8 kbar. The BBMs compare with the Triassic carbonates deposited over the crustal units of the Alpujarrides-Sebtides. The detrital cores of the zircon grains from the BBMs yield two U-Th-Pb age clusters of ~270 Ma and ~340 Ma, distinct from the 290-300 Ma age of the zircon grains from the kinzigites (Rossetti et al., 2020), and supporting a Triassic age of the protoliths; the zircon rims yield ~21 Ma ages. The BBMs protoliths may have been deposited onto the kinzigites or carried later as extensional allochthons over a detachment in the frame of the incipient formation of the Alboran Domain continental margin, which is dated from the late Liassic-Dogger in the “Dorsale calcaire” detached units (Chalouan et al., 2008). Thus, the Beni Bousera mantle rocks would have been exhumed at shallow depth during the early rifting events responsible for the birth of the Maghrebian Tethys, i.e., as early as the Triassic-late Liassic.

Keywords: BBMs/ FFBSZ/ HT-LP metamorphism/ SHRIMP U-Th-Pb geochronology / hyperextended margin/ mantle rocks exhumation / Gibraltar Arc

References :

Please use this link for access to the cited references:  https://www.docdroid.net/hPSheTG/references-farah-et-al-2021-vegu-pdf 

How to cite: Farah, A., Michard, A., Saddiqi, O., Chalouan, A., Chopin, C., Montero, P., Corsini, M., and Bea, F.: Early exhumation of the Beni Bousera granulites and peridotites at the northern margin of the westernmost Tethys (Rif belt, Morocco); new constraints from overlying marbles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-581, https://doi.org/10.5194/egusphere-egu21-581, 2021.

Jurassic shallow-intrusive basic bodies within the Permian-Triassic Tethyan passive margin sedimentary sequences of the Lower Alpujarride units (Internal Betic Zone, Spain) locally show Alpine low-grade metamorphism in the greenschist and blueschist facies. A small sill-like mafic body near Redován town (Callosa Range) partially preserves igneous ophitic/subophitic texture and relics of augite, ferrohornblende-ferroedenite, kaersutite and K-feldspar (orthoclase). The metamorphic overprint corresponds to high-pressure and low-temperature mineral assemblages that comprise magnesioriebeckite, actinolite, albite, stilpnomelane, phengite and chlorite, with rutile, apatite and titanite as accessory minerals. Major and trace element geochemical data reveal igneous protoliths derived from magmas of alkaline basalt composition enriched in incompatible elements and E-MORB geochemical affinity. The intrusion emplacement occurred at shallow crustal levels in an extensional geodynamic setting (within-plate basalts) related to the breakoff of Pangea. Pressure-Temperature (P-T) conditions estimated by means of pseudosection calculations and the intersection of phengite (Si) and chlorite (Mg#) isopleths indicate a cold thermal gradient with calculated peak metamorphic conditions of ca. 8 kbar at 310 ºC. These conditions are consistent with metamorphism during burial down to ca. 24 km depth and a thermal gradient of ca. 13 ºC/km. Although the easternmost Lower Alpujarride units have been traditionally described as reaching only lower-greenschist to greenschist metamorphic peak conditions, the textures, mineral compositions and P-T conditions of the studied metagabbroic body reveal blueschist facies conditions that attest for a regional early stage (Eocene) of subduction of the lower Alpujarride units. This event predates the late Oligocene - early Miocene subduction-related metamorphism of the Intermediate and Upper Alpujarride units.

How to cite: Santamaría-Pérez, E., Blanco-Quintero, I. F., Martín-Algarra, A., Benavente, D., Cañaveras, J. C., González-Jiménez, J. M., and Garcia-Casco, A.: Blueschist facies conditions in Tethyan passive margin metabasaltic rocks of the easternmost Lower Alpujarride Units (Internal Betic Zone, Spain), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10913, https://doi.org/10.5194/egusphere-egu21-10913, 2021.

The Alps preserve abundant oceanic blueschists and eclogites that exemplify the selective preservation of fragments of relatively short-lived, small, slow-spreading North Atlantic-type ocean basins (here the ~400-700 km wide Alpine Tethys), whose subducting slabs reach down to the Mantle Transition Zone. Whereas none of the subducted fragments were returned during the first half of the subduction history, those exhumed afterwards experienced conditions typical of mature subduction zones worldwide. Sedimentary-dominated units were underplated intermittently, mostly at ~30-40 km depth, while mafic/ultramafic-dominated units subducted to ~80 km (In the W. Alps), whose protoliths had formed close to the continent, were offscraped from the slab only a few Ma before continental subduction. Spatiotemporal contrasts in burial and preservation of the fragments reveal how along-strike segmentation of the continental margin affects ocean subduction dynamics.

How to cite: Agard, P. and Handy, M.: Ocean subduction dynamics in the Alps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5235, https://doi.org/10.5194/egusphere-egu21-5235, 2021.

The Alps as part of the Alpine mountain belts are one of the classical examples of orogenesis where the Mesozoic-Cenozoic tectonic evolution is well known, but not of the basement because poor age data. New data from the  pre–Alpine basement of the Austroalpine megaunit indicate that this basement is composed of a series of continental rocks, island arcs, ophiolites and subduction mélanges，accretionary wedges, and seamounts with different metamorphic, but often amphibolite facies grade. This study presents new results of LA–ICP–MS U–Pb and MC–ICP–MS Lu–Hf dating of zircons from three key areas of Austroalpine basement units: i) the Wechsel–Waldbach–Sieggraben, (ii) the Saualpe–Koralpe –Pohorje, and (iii) the Schladming Mts. areas. As a result, the Wechsel unit is a continental magmatic arc during 500-560 Ma, and 2.1 to 2.2 Ga-and 2.5 to 2.8 Ga age show the close relationship to northern Gondwana, with depleted mantle model ages as old as 3.5 Ga. Even the Wechsel Phyllite Unit overlying the Wechselgneiss, but they have partly different sources, include juvenile crust formed at ca. 530 Ma. The Waldbach Complex is constantly added new crustal material during 490-470Ma, and considerably more positive εHf(t) values from 700 to 500 Ma interpreted being part of a magmatic arc during closure of the Prototethys and got metamorphosed during Variscan orogenic events. We consider that Schladming to Wechsel Complexes represent a Cambrian-Ordovician volcanic-magmatic arc system followed proto-Tethys subduction, and the ophiolitic Speik complex represent a back-arc basin. Many granites were formed during Permian (Grobgneiss and various granites in Pohorje Mts.) likely in an extensional environment, remelting a crust with mainly Middle Proterozoic model Hf isotopic model ages. The Plankogel Complex represents accreted oceanic, ocean island and continental-derived materials, it should belong to the accretion complex formed during Permotriassic closure of Paleotethys. We argue that the various basement complexes of the Austroalpine are different sources of ages of different tectonic evolutionary histories and likely represent, different locations before drifting. Consequently, the Austroalpine meagunit represents a composite pre-Alpine mega-unit likely assembled not earlier as Permian or Triassic times.

How to cite: Chang, R., Neubauer, F., Genser, J., Liu, Y., Yuan, S., Huang, Q., Guan, Q., and Yu, S.: Hf isotopic constraints for Austroalpine basement evolution of Eastern Alps: review and new data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10909, https://doi.org/10.5194/egusphere-egu21-10909, 2021.

Timing of the opening of the West Paleo-Tethys Ocean in Eastern Alps remains controversial. The debate over the timing has revolved mainly around three possible periods, namely Silurian, Early Devonian and Middle–Late Devonian. To constrain this event, we present new zircon U-Pb ages, Hf isotopic compositions, and whole-rock major- and trace-element data for the meta-mafic rocks in the southern Saualpe crystalline basement, Eastern Alps. Zircon U-Pb dating results from three samples yielded crystallization ages of 418 ± 6 Ma, 417 ± 3 Ma and 415 ± 3 Ma, indicating that they formed during the Early Devonian. Geochemically, these meta-mafic rocks have relatively low SiO₂ and MgO contents and high TiO₂ contents. They are enriched in light rare earth elements (LREE), particularly in Nb and Ta, and show relatively flat heavy rare-earth elements (HREE) patterns, indicating that they have affinities with the alkaline oceanic island basalts (OIB). The geochemical characteristics, together with the positive ε_Hf(t) values of 0.7–11.1, imply that the OIB-like meta-mafic rocks originated from partial melting of a lherzolite source including spinel and garnet. And the primary magma showed complex sources involving the asthenospheric, lithospheric mantle and subducted slab components and subsequently modified by crustal contamination, revealing that the magma formed in a slab window environment associated with mid-ocean ridge subduction. The contemporaneous OIB-like alkaline amphibolites were also found in the central Austroalpine basement and Northwestern Turkey. We suggest that the Late Silurian–Early Devonian OIB-like magmatism is related to a back-arc extension setting in the northern margin of Gondwana leading to the detachment of the European Hunic terranes and hence placing an age on the opening of the West Paleo-Tethys Ocean.

How to cite: Liu, Y., Guan, Q., Neubauer, F., Genser, J., Yuan, S., Chang, R., and Huang, Q.: Opening of the West Paleo-Tethys Ocean: New insights from Early Devonian meta-mafic rocks in the southern Saualpe crystalline basement, Eastern Alps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8301, https://doi.org/10.5194/egusphere-egu21-8301, 2021.

In the geodynamic context of the slow Africa-Europe plates convergence, the Central-Western Mediterranean region has been involved in a complex subduction process, which in the last 30 Myr was characterized by the rapid retreat of the Ionian slab, the opening of back-arc extensional basins (i.e., Liguro-Provençal, Algerian, Alboran, and Tyrrhenian basins) and episodes of slab lateral tearing, segmentation and break-off.  A proper modelling of 3-D mantle flow evolution beneath the Mediterranean could provide important clarifications about the complex mantle dynamics of this region and help us understanding the interaction between surface tectono-magmatic processes and mantle convection patterns. 

The mantle flow and its relations with plate horizontal and vertical motions can be determined by measuring seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals. Seismic anisotropy is widespread in the Mediterranean and it shows an intricate pattern that likely has some relations with the recent (20-30 Myr) behavior of subducting slabs. The extrapolation of the mantle flow from seismic anisotropy is neither simple nor always warranted, especially at subduction zones where complex and non-steady-state 3D flow patterns may establish.  A promising approach, which helps reducing the number of plausible models that can explain a given anisotropy dataset, is to compare seismic measurements with predictions of numerical and experimental flow models (Long et al.,2007). Recently, Faccenda and Capitanio (2013) and Faccenda (2014) have extended this methodology to account for the non-steady state evolution typical of many subduction zones, yielding mantle fabrics that are physically consistent with the deformation history.

In this study, we apply a similar modelling approach to the complex Central-Western Mediterranean convergent margin. We use the wealth of observations from the Mediterranean region available in the literature to design and calibrate 3D thermo-mechanical subduction modelling. We test different initial configurations defined at 30 Ma according to the paleogeographic and tectonic reconstructions derived from (Lucente and Speranza, 2001; Carminati et al., 2012; van Hinsbergen et al., 2014) in order to optimize the fit between predicted and observed slabs position and obtain a final model configuration resembling the present-day surface and deeper structures.

In particular, here we want to evaluate the influence on rollback rates, trench shape and the occurrence and timing of slab tears (Mason et al., 2010) of structural heterogeneities within the Adria plate as proposed by (Lucente and Speranza, 2001). In all models, subduction migrates south-eastward driven by the subducting oceanic lithosphere, and slab lateral tearing or break-off occurs when a continental margin enters the trench. More importantly, we show that the presence of a stiffer continental promontory in central Adria together with a thinned continental margin in the Umbria-Marche region plays a fundamental role on (i) the development of a slab window below the Central Apennines, (ii) the retreat of the Northern Apenninic trench till the Adriatic Sea, and (iii) the retreat of the Ionian slab till the present-day position.

How to cite: Lo Bue, R., Faccenda, M., and Yang, J.: Role of the Adria plate structural heterogeneities on the dynamics of the Central-Western Mediterranean region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9978, https://doi.org/10.5194/egusphere-egu21-9978, 2021.

Here we present the first 4D tectonic reconstruction that models the Vrancea slablet and incorporates the floated slab as a constraint on the magnitude of slab rollback during collapse of the Palaeo-Pannonian Basin. Seismic tomographic images provide insight into the geometry and tectonic history of subducted slabs. High velocity anomalies can be interpreted as ‘cold’ lithosphere penetrating ‘warmer’ lower velocity asthenosphere, and 3D models created using the SKUA-GOCAD modelling software. Combined with information from the 3D distribution of earthquake hypocentres, we thereby obtain a simple approximation to slab geometry beneath the Vrancea region. The resultant DXF was imported into the Pplates tectonic reconstruction software, and floated back to the Earth’s surface. The method utilised assumes no significant deformation (stretching, buckling, folding, shortening) during or after subduction, so that the obtained geometry estimates the pre-subduction configuration. The resultant floated slab is then incorporated as a constraint on 2D + time tectonic reconstructions. We apply a double-saloon-door rollback model, which involves propagation of a slab tear along the mid-Hungarian lineament. Each saloon-door rolls back independently of the other and this leads to two epochs of extension. AlPaCa is ‘pulled’ eastwards and rotated counter-clockwise as the western saloon-door rolls back. The Tisza-Dacia unit is then ‘pulled’ eastward, and rotated, but in a clockwise sense as the eastern saloon-door rolls back. Once the subduction hinge reached the East European Platform, the slab was left hanging. Gravitational forces then drove slab-boudinage and detachment in a similar fashion as occurs today beneath the Hindu Kush. This model explains the large opposing-sense vertical-axis rotations that occurred during convergence of the AlPaCa and Tisza-Dacia terranes. The zipper fault model rotates the microplates without requiring large-scale thrusting. Interpretation of the Mid-Hungarian lineament as a zipper-fault system is also consistent with the geodynamic effects expected because of tearing in a subducting plate leading to a double-saloon-door rollback. The vertical extent of the slab is roughly 300 km, which only fills half of the basin, consistent with the double-saloon-door roll-back model interpretation.

How to cite: Muston, J., Spakman, W., and Lister, G.: Floating the Vrancea slab and tectonic reconstruction of the collapse of the PalaeoPannonian Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13235, https://doi.org/10.5194/egusphere-egu21-13235, 2021.

We report updated results of our ongoing research on constraining geodynamic conditions associated with the final closure of the Vardar branch of the Tethys Ocean by means of application of numerical simulations (previous interim results reported in EGU2020-5919).

The aim of our numerical study is to test the hypothesis that a single eastward subduction in the Jurassic is a valid explanation for the occurrence of three major, presently observed geological entities that are left behind after the closure of the Vardar Tethys. These include: ophiolite-like igneous rocks of the Sava-Vardar zone and presumably subduction related Timok Magmatic Complex, both Late Cretaceous in age as well as Jurassic ophiolites obducted onto the Adriatic margin. In our simulations we initiate an intraoceanic subduction in the Early/Middle Jurassic, which eventually transitions into an oceanic closure and subsequent continental collision processes.

In the scope of our study numerical simulations are performed by solving a set of partial differential equations: the continuity equation, the Navier-Stokes equations and the temperature equation. To this end we used I2VIS thermo-mechanical code which utilizes marker in cell approach with finite difference discretization of equations on a staggered grid [Gerya et al., 2000; Gerya&Yuen, 2003].

The 2D model consists of two continental plates separated by two oceanic slabs connected at a mid-oceanic ridge. Intraoceanic subduction is initiated along the ridge by assigning a weak zone beneath the ridge. Time-dependent boundary conditions for velocity are imposed on the simulation in order to model a transient spreading period. The change of sign in plate velocities is found to be useful for both obtaining obduction / ophiolite emplacement [Duretz et al., 2016] and causing back-arc extension. Changes in velocities are linear in time. Simulations follow a three-phase evolution of velocity boundary conditions consisting of two convergent phases separated by a single divergent phase where spreading regime is dominant. Effect of duration and magnitude of the second phase on model evolution is also explored.

Our so far obtained simulations were able to reproduce the westward obduction and certain extension processes along the active (European) margin, which match the existing geological relationships. However, the simulations involve an unreasonably short geodynamic event (cca 15-20 My) and we are working on solving this problem with new simulations. 

How to cite: Stanković, N., Cvetkov, V., and Cvetković, V.: Numerical simulation of the Late Jurassic closure of the Vardar Tethys, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9893, https://doi.org/10.5194/egusphere-egu21-9893, 2021.

How to cite: Yeung, S., Forster, M., Skourtsos, E., and Lister, G.: The Late Cretaceous Asteroussia event as recorded in the Cyclades: a potential key to Western Tethys tectonic evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3890, https://doi.org/10.5194/egusphere-egu21-3890, 2021.

The birth and death of oceanic areas have often proved to involve contemporaneous destruction of previously created and evolved oceanic domains and the initiation of new ones in back-arc areas. As a result, several and often competing geodynamic processes, have been taking place at the same time, thus creating a complex tectonostratigraphy.

The Attic-Cycladic Crystalline Complex (ACCC), in the Aegean Sea (Greece), the outcome of the formation and destruction of Paleotethyan and Tethyan oceanic domains, is one such case. Four major units have been identified in the ACCC. These are from top to bottom, the complex Upper Cycladic Nappe, the Cycladic Blueschist Unit, the pre-alpine Cycladic Basement, and the Basal Unit. The present-day configuration has resulted from an Eocene stage of subduction and metamorphism under blueschist to eclogite facies and an Oligocene-Miocene exhumation and metamorphic core complex formation, through a combination of contractional and extensional mechanisms. Original relations between these four units have been obscured from the Cenozoic tectonometamorphic processes and several conflicting views have been expressed in the literature, regarding the nature of the Cycladic Blueschist domain, the relation between the Cycladic Blueschist Unit and the Cycladic Basement.

In this paper, we make a reconstruction of the domain, from which the Cycladic Blueschist Unit originated, based on a synthesis of structural, tectonostratigraphic, geochemical, and geochronological data. Through this reconstruction, we attempt to reconcile existing controversies and differences of views in the literature and to highlight the major structures that controlled the main features and geological evolution of this remarkable area.

How to cite: Soukis, K. and Stockli, D.: A reconstruction of the Cycladic Blueschist Domain (Cyclades, Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15918, https://doi.org/10.5194/egusphere-egu21-15918, 2021.

Across the Tethyan realm, subduction zones are characterized by phases of forearc and backarc extension, and subsequent collisions are protracted and polygenetic, often resulting in significant discrepancies among proxies of collision age. The closure of the northern branch of the Neotethys Ocean along the İzmir-Ankara-Erzincan suture in Anatolia has been variously estimated from the Late Cretaceous to Eocene. It remains unclear whether this age range results from a protracted, multi-phase collision or disparities between proxies and geographic location. Near-continuous Jurassic through Eocene deposition in the forearc-to-foreland Central Sakarya Basin system in western Anatolia makes it an ideal location to integrate pre-collisional extension and multi-stage collision into a holistic reconstruction of subduction through collision. The Central Sakarya Basin system is located north of the Izmir-Ankara-Erzincan suture, where the Gondwanan-derived Anatolide and Tauride terranes to the south collided with the Laurasian-derived Pontide terrane in the north. By integrating new sandstone petrography and detrital zircon U-Pb and Hf isotopes with other geologic proxies, we demonstrate four phases of evolution of subduction and collision. (1) Magmatism began on the Pontides at 110 Ma, potentially the signal of subduction (re-)initiation, and is coincident with extension in the forearc. (2) Forearc obduction began around 94 Ma with initial subduction of lower plate continental lithosphere. Extension migrated to the backarc and opened the Black Sea. (3) The onset of intercontinental collision at 76 Ma is marked by gradual arc shutdown, basement exhumation, and uplift of the suture zone. (4) This first contractional phase is followed by thick-skinned deformation and basin partitioning starting around 54 Ma, coeval with regional syn-collisional magmatism. The 20-Myr protracted collision in western Anatolia could be explained by three non-exclusive mechanisms that produced a change in plate coupling: relict basin closure, progressive underthrusting of thicker lithosphere, and slab breakoff.

How to cite: Mueller, M., Licht, A., Campbell, C., Ocakoğlu, F., Akşit, G., Métais, G., Coster, P., Beard, K. C., and Taylor, M.: Closing the Neotethys Ocean in western Anatolia: Insights from forearc and foreland sedimentary basin records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13757, https://doi.org/10.5194/egusphere-egu21-13757, 2021.

Upper Cretaceous arc-related volcanic and volcanoclastic units overlying the Paleozoic sedimentary rocks of the Istanbul Zone are a key unit related to the opening of the Black Sea as a back-arc basin. They formed as a result of north dipping subduction of the Neo-Tethys Ocean beneath Laurasia. We studied the Upper Cretaceous volcanic units north of Istanbul along several stratigraphic sections, and present new geochemical data from the volcanic rocks in order to understand Cretaceous geodynamic evolution of the İstanbul Zone.

The Upper Cretaceous  volcanic units north of Istanbul are divided into two formations. At the base there is a fore-arc turbidite succession,the İshaklı Formation, which is made up of volcaniclastic sandstone, shale, marl, tuff, debris flow horizons and epiclastic rocks of Turonian age. The İshaklı Formation is conformably overlain by the volcanoclastics,  tuffs, andesite and basalt lavas and agglomerates- the Riva Formation, which represents the arc/ intra-arc series.

Geochemically, basalts and basaltic andesites of the Riva Formation are low K calc-alkaline to medium-high K calc-alkaline and with magnesium numbers ranging from 32.6% to 51.5% Primitive mantle normalized spider diagram of trace elements show  enrichment in LILE elements (K, Rb, Sr, Cs, Ba, Th and U) and depletion in HFS elements ( Nb,Ta and Ti) . The high ratio of LILE/ HFS and negative Nb-Ta anomalies indicate that the volcanism evolved in subduction setting. Chondirite-normalized REE pattern display slight negative Eu anomalies and the La/Yb ratios of the samples range between 2,76 and 4,89. Our new geochemical, stratigraphical and the regional geological data suggest that north of Istanbul there was a transition from fore-arc deposition to arc volcanism during the Late Cretaceous opening of the Western Black Sea.  Considering the whole Pontide – Sredna-Gora Upper Cretaceous magmatic arc, it can be stated that calc-alkaline volcanism developed in relation to northward subduction of the Neo-Tethys oceanic lithosphere during the Turonian, and may have passed into high-K calc alkaline and shoshonitic magmatism as a result of the progressive extentional tectonism during the Campanian.

How to cite: Ay, C., Sunal, G., and Okay, A. I.: Stratigraphy, geochemistry, and petrology of the Upper Cretaceous volcanic arc sequence north of Istanbul, Pontides, NW Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6240, https://doi.org/10.5194/egusphere-egu21-6240, 2021.

The Upper Cretaceous volcanic and volcaniclastic rocks crop out along the Black Sea coastline in Turkey. They are part of a magmatic arc that formed as a result of northward subduction of the Tethys ocean beneath the southern margin of Laurasia. The lower part of the Upper Cretaceous volcanism in the Kefken region, 100 km northeast of Istanbul, is represented by basaltic andesites, andesites, agglomerates and tuffs, which have yielded Late Cretaceous (Campanian, ca. 83 Ma) U-Pb zircon ages. The volcanic and volcanoclastic rocks are stratigraphically overlain by shallow to deep marine limestones, which range in age from Late Campanian to Early Eocene.  Geochemically, basaltic andesites and andesites display negative anomalies in Nb, Ta and Ti, enrichment in large ion lithophile elements (LILE) relative to high field strength elements (HFSE). Light rare earth elements (LREE) show slightly enrichment relative to heavy rare earth elements (La_cn/Yb_cn =2.51-3.63) and there are slight negative Eu anomalies (Eu/Eu* = 0.71-0.95) in basaltic andesite and andesite samples. The geochemical data indicate that Campanian volcanic rocks were derived from the partial melting of the mantle wedge induced by hydrous fluids released by dehydration of the subducted oceanic slab.

There is also a horizon of volcanic rocks, about 230 m thick, within the Late Campanian-Early Eocene limestone sequence.  This volcanic horizon, which consists of pillow basalts, porphyritic basalts,  andesites and dacites, is of Maastrichtian age based on paleontological data from the intra-pillow sediments and U-Pb zircon ages from the andesites and dacites (72-68 Ma).  The Maastrichtian andesites and dacites are geochemically distinct from the Campanian volcanic rocks. They show distinct adakite-like geochemical signatures with high ratios of Sr/Y (>85.5), high La_cn/Yb_cn (16.4-23.7) ratios, low content of Y (7.4-8.6 ppm) and low content of heavy rare-earth elements (HREE). The adakitic rocks most probably formed as a result of partial melting of the subducting oceanic slab under garnet and amphibole stable conditions.

The Upper Cretaceous arc sequence in the Kefken region shows a change from typical subduction-related magmas to adakitic ones, accompanied by decrease in the volcanism.

How to cite: Duzman, T., Sağlam, E., and Okay, A. I.: Petrogenesis of the Upper Cretaceous volcanism in the Kefken region, Western Pontides, NW Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5108, https://doi.org/10.5194/egusphere-egu21-5108, 2021.

Continental deformation can be described in two end-member approaches: block (or microplate) and continuum models. The first considers a strong lithosphere with deformation localized in fault zones. For the latter, however, the lithosphere is weak and deforms as a thin viscous sheet. The Anatolia – Aegean domain represents both continuum and plate-like deformation. Furthermore, recent modeling studies suggest a dynamic support mechanism of the Anatolian plateaus, with dynamic topography estimates ranging from 1 to 3 km for various crustal models and geodynamic scenarios, although the gravity and crustal thickness data support predominant Airy isostasy. The solution to both intricacies relies on the thermal structure of the crust and the lithosphere. Available thermal considerations stem from either the uppermost mantle velocity structure or thermal modeling with assumptions on radiogenic heat production and boundary conditions. Yet, homogeneous and independent constraints on the lithospheric structure are scarce. We aim to contribute to this knowledge gap by providing Curie Point Depths (CPDs), which corresponds to the depth at which rock-forming minerals lose their magnetization at the Curie temperature, ~580 ^oC.

Resolution of deep magnetic sources requires spectral methods with large windows, which reduce the CPD resolution. Moving & overlapping smaller windows have been used in order to increase the resolution, but these introduce spectral leakage and bias. In previous studies, subjective wavenumber ranges of the magnetic anomaly spectra were used, often combined with wrong scaling factors between map units and the equations. This resulted in generally erroneous CPD estimates. Furthermore, CPD uncertainties have often been unquantified for the study area. We use a wavelet transform method, which overcomes the artifacts due to segmentation of magnetic signal to finite windows, results in higher spatial resolution as well as enabling uncertainty estimation. We used as large an area as possible for constraining the edge effects away from the study area. The resultant CPD map spatially correlates well with low Pn velocity areas, locations of volcanoes, and thermal springs.

How to cite: Ozbakir, A. D. and Karabulut, H.: New thermal constraints for the Anatolian lithosphere from Curie depth point and Pn tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9926, https://doi.org/10.5194/egusphere-egu21-9926, 2021.

Young back-arc rift basins, because of the not yet dissipated extensional thermal signature, can be easily inverted following changes in the geodynamic regime and/or far-field stress transmission. Structural inversion of such basins mainly develops through reactivation of normal faults, particularly if the latter are favourably oriented with respect to the direction of stress transfer. The Adjara-Trialeti fold-and-thrust belt of SW Georgia is an example of this mechanism, resulting from the structural inversion of a continental back-arc rift basin developed on the upper plate of the northern Neotethys slab in Paleogene times, behind the Pontides-Lesser Caucasus magmatic arc. New low-temperature thermochronological data [apatite fission-track (AFT) and (U-Th)/He (AHe) analyses] were obtained from a number of samples, collected across the Adjara-Trialeti belt from the former sedimentary fill of the basin and from syn-rift plutons. AFT central ages range between 46 and 15 Ma, while AHe ages cluster mainly between 10 and 3 Ma. Thermal modelling, integrating AFT and AHe data with independent geological constraints (e.g. depositional/intrusion age, other geochronological data, thermal maturity indicators and stratigraphic relationships), clearly indicates that the Adjara-Trialeti back-arc basin was inverted starting from the late Middle Miocene, at 14-10 Ma. This result is corroborated by many independent geological evidences, found for example in the adjacent Rioni, Kartli and Kura foreland basins and in the eastern Black Sea offshore, which all suggest a Middle-Late Miocene phase of deformation linked with the Adjara-Trialeti FTB building. Adjara-Trialeti structural inversion can be associated with the widespread Middle-to-Late Miocene phase of shortening and exhumation that is recognised from the eastern Pontides to the Lesser Caucasus, the Talysh and the Alborz ranges. This tectonic phase can in turn be interpreted as a far-field effect of the Arabia-Eurasia collision, developed along the Bitlis suture hundreds of kilometres to the south.

How to cite: Gusmeo, T., Cavazza, W., Alania, V., Enukidze, O., Zattin, M., and Corrado, S.: Miocene structural inversion of the Adjara-Trialeti back-arc basin as a far-field effect of the Arabia-Eurasia collision, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-179, https://doi.org/10.5194/egusphere-egu21-179, 2021.

The Iranian plateau is a natural laboratory for studying the early stage of continental collision and plateau development. The collisional front and northern plateau are the major areas accommodating the Arabia-Eurasia convergence. GPS observations suggest that the blocks of central Iran with minor shortening may be relatively rigid. However, recent seismic imaging results suggest that the lithosphere in this region might not be rigid for it is thin and not seismically fast. Widespread mantle-derived magmatism since Middle Miocene also lends support to a relatively hot and weak lithosphere. It may raise a question of why these blocks could behave rigidly when transmitting stresses to the north.

Deformation patterns of the lithosphere and asthenosphere in the northeastern and eastern Iranian plateau, which can be constrained by seismic anisotropy, may help to understand the nature of the lithosphere within the continental interior and its responses to the Arabia-Eurasia collision. We studied the seismic anisotropy of the region via teleseismic shear-wave splitting analysis on dense array data and compared the new results with multidisciplinary observations, particularly the surface strain rates and the structure of the lithosphere-asthenosphere system. In northeastern Iran around the Paleo-Tehtys suture, the dominant fast polarization direction (FPD) is NW-SE, subparallel to the strikes of thrust faults and orogenic belts. This combined with the relatively higher strain rates and thicker crust and lithosphere suggests that northeastern Iran with pre-existing weakness may have experienced considerable lithospheric shortening. The Lut block, which is a major block of eastern Iran bounded by large-scale strike-slip faults and previously assumed rigid, shows a complex anisotropic structure. In its northern part where the strain rates are low, the average NE-SW FPD has no obvious link to active faults but is roughly parallel to the collision-induced asthenospheric flow. The area to the south around the Dasht-e-Bayaz fault shows high strain rates and a complex structure of Moho. The generally NW-SE FPDs are subparallel to the direction of the surface right-lateral shear, possibly reflecting a fault-controlled lithospheric deformation pattern. Further south is the central Lut area with moderate strain rates. It is characterized by a two-layer structure of anisotropy, with the FPDs in the upper and lower layers being similar to those of the area around the Dasht-e-Bayaz fault and the northern Lut block, respectively. This feature indicates that the anisotropy and deformation of the central Lut area could be affected by both large-scale strike-slip faults and collision-induced mantle flow.

Collectively, our observations suggest that both the collisional processes at the plate boundary and the nature and structural heterogeneities of the continental lithosphere may control the intracontinental deformation of the Iranian plateau. The observed minor deformation of the Lut block and also other blocks within this young plateau does not necessarily mean that these blocks are rigid, but is probably because of significant deformation preferentially taking place at not only the collision front but also mechanically weak zones in the hinterland, which may have accommodated most of the Arabia-Eurasia convergence.

How to cite: Gao, Y., Chen, L., Talebian, M., Wu, Z., Wang, X., Lan, H., Ai, Y., Jiang, M., Khatib, M. M., Xiao, W., and Zhu, R.: Spatial variation in seismic anisotropy beneath the eastern and northeastern Iranian plateau and its geodynamic implications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8590, https://doi.org/10.5194/egusphere-egu21-8590, 2021.

A Cretaceous paleo-accretionary wedge (the Ashin Complex) now exposed along the Zagros suture zone in southern Iran exhibits mafic and metapelitic lithologies. Field, geochemical and petrological observations point to a high-temperature event that gave rise to the formation of peritectic (trondhjemitic) melts associated with restitic garnet-bearing amphibolites in the structurally highest sliver of the Ashin Complex. SHRIMP U-Pb zircon dating of grains crystallized in trondhjemitic leucosomes yields a ²⁰⁶Pb/²³⁸U weighted mean age of 104 ±1 Ma, interpreted as the peak temperature event, which occurred in the amphibolite facies (c. 640-650°C at 1.1-1.3 GPa), based on thermodynamic modeling. Rutile crystals from several leucosomes yield Zr-in-rutile temperatures between 580-640°C and LA-ICP-MS U/Pb ages of 87-94 Ma. This rutile generation may be related to the observed static formation of Na-clinopyroxene and Si-rich phengite rims, as well as the growth of lawsonite in late fractures. The latter paragenetic sequence has been previously interpreted as reflecting a long-term isobaric cooling that occurred at least until the end of the Cretaceous (ages in Angiboust et al., 2016).

While the latter observations point to a long-term cooling of the Zagros subduction thermal gradient down to 7°C/km during late Cretaceous times, this first report of an earlier melting event in the Zagros paleo-accretionary wedge indicates an abnormally high thermal gradient of 17-20°C/km. GPLATES paleogeographic reconstructions of the Tethyan realm evolution during Cretaceous times reveal the presence of a spreading ridge jump followed by the subduction of the formerly active ridge-segment between 105-115 Ma, which possibly left an imprint marked by the unusually hot gradient seen in Ashin amphibolites. The model further predicts the subduction of progressively aging oceanic lithosphere, possibly explaining the observed cooling of the subduction thermal regime.

How to cite: Holtmann, R., Muñoz-Montecinos, J., Angiboust, S., Cambeses, A., Bonnet, G., Glodny, J., Gharamohammadi, Z., Kananian, A., and Agard, P.: The Zagros Suture Amphibolites Record the Cretaceous Thermal Evolution of the Closing Tethyan Realm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3259, https://doi.org/10.5194/egusphere-egu21-3259, 2021.

The timings of the onset of oceanic spreading, subduction and collision are crucial in plate tectonic reconstructions, but not always straightforward to resolve. The evolution of the Paleo-Tethys Ocean dominated the Paleozoic-Early Mesozoic tectonics of West Asia, but the timeline of events is still poorly-constrained. In this study we present detrital zircon ages from NE Iran, in order to determine the timing of tectonic events in the region, and the wider implications for regional tectonics, paleogeography and climate change. Paleozoic clastic rocks record two major age peaks at ~800 Ma and ~600 Ma. The consistency in age patterns shows a dominant provenance from the Neoproterozoic basement of northern Gondwana. We interpret deposition on a long-lasting passive continental margin after the initial spreading of the Paleo-Tethys Ocean. Initial collision between the South Turan (Eurasia) and Central Iran (Gondwana) blocks caused coarse clastic deposition, the protolith of the Mashhad Phyllite, in a peripheral foreland basin on the Paleozoic passive margin. The Mashhad Phyllite yields major zircon age clusters at 450-250 Ma and 1900-1800 Ma, with a clear provenance from the active, Eurasian, margin. The Paleozoic ages reveal a long-lived subduction zone under the South Turan Block began in the latest Ordovician. Analysis of the age spectra allows us to constrain the timing of initial collision as no later than 228 Ma, which is also a constraint on the maximum depositional age of the Mashhad Phyllite. Based on our new results and previous data, we discuss the interaction between the Rheic and Paleo-Tethys oceans, and explain how a new subduction zone may have initiated after continental collision. The timing of collision is similar to the Carnian Pluvial Event (CPE). Paleo-Tethys collision has previously been suggested as the trigger for this climatic change, and our study provides timing evidence that reinforces Paleo-Tethys closure as a causal mechanism for the CPE.

How to cite: Chu, Y., Wan, B., Allen, M. B., Chen, L., Lin, W., and Talebian, M.: Tectonic evolution of Paleo-Tethys in NE Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3557, https://doi.org/10.5194/egusphere-egu21-3557, 2021.

The Eastern Iranian Orocline provides us several opportunities to study magmatism in relation to tectonic events. The buckling of this orocline is accompanied by an extreme extension in its Khorasan outer arc during which a calc-alkaline dike swarm, generally andesite to dacite, intruded in a radial pattern into the Paleocene-Eocene volcano-sedimentary units, belonging to the platform of the Lut block. The azimuth of these dikes shows a declination of 30 degrees, from N300^o to N330^o. The U²³⁵/Pb²⁰⁷ age of ~41±74 Ma from zircon crystals taken from the dikes represents a considerable buckling with an extension occurred during the middle-upper Eocene. In fact, this time refers to the buckling in the boundary of the inner- and outer-arc of the orocline. This could be a noticeable document of syn-orocline magmatism in the Tethyan realm in the east of the Iranian plateau. The dikes and their host rocks are also sampled for AMS analysis and paleomagnetic measurements to test the amount of the oroclinal buckling in the Qayen area.

How to cite: Rojhani, E., Bagheri, S., Hinsbergen, D., Azizi, H., Ghaemi, F., Lom, N., and Qayyum, A.: Age of the Eastern Iranian oroclinal Buckling inferred from a U235/Pb207 dating on radial dikes in the Qayen Area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14258, https://doi.org/10.5194/egusphere-egu21-14258, 2021.

The geology of the Oman Mountains was shaped by the SW-directed obduction of allochthonous deep-sea rocks (Hawasina), trench-facies rocks (Haybi) and oceanic lithosphere (Semail Ophiolite) onto Arabian autochthonous shelf carbonates during the Late Cretaceous. Locally, the resulting obduction orogen was overprinted by significant post-obductional extension. NNE-directed extension occurred during at least two episodes which took place from the latest Cretaceous to early Eocene and late Eocene to Oligocene/Miocene, respectively. Moreover, the Oman Mountains, between the eastern Batinah Coastal Plain and the Sur area (Qalhat Fault) display numerous ~N/S-oriented folds and reverse faults. These structures overprinted mid-Eocene to at least Oligocene/Miocene formations (i.e., the Seeb to Barzaman formations).

Detailed structural/field work and satellite image analyses provide ample evidence that these ~N/S-compressional features are cogenetic with ~WNW to NW-striking sinistral faults. All these post-mid-Eocene structures are part of one major left-lateral WNW- to NW-striking shear zone from the Batinah Coastal Plain in the NW to the Batain area in the SE. Sinistral shearing is localized along the southwestern margin of the Saih Hatat Dome, crosses the Fanja area and continues to the northern part of the Jabal Akhdar Dome (Jabal Nakhl Subdome). The straight southwestern margin of the Saih Hatat Dome may correlate with a Permo-Triassic major extensional fault, active during the Pangea rifting. Shearing also affected rocks northeast of this zone, i.e., within the Salma Plateau and the Rusayl Embayment. Thus, shearing affected an area of 250 km by 40 km in width. We term this shear zone hereafter the “Hajar Shear Zone” (HSZ). The amount of sinistral shearing is unknown due to the absence of markers and wide strain distribution, but is likely to be at the order of a few tens of kilometers.

The cause for the WNW-directed sinistral shearing is the overall E/W-directed shortening between the Arabian and Indian plates. During shortening, a pre-existing WNW-striking basement fault zone was reactivated, creating the HSZ. A G-Plates reconstruction between the two plates reveals an ~8° counter-clockwise rotation of India (with respect to fixed Arabia) between 32.5 and 20 Ma, resulting in ~150 km E/W-shortening between both plates at the easternmost tip of Arabia. The area northeast of the HSZ underwent most E-W-shortening. The 150 km interplate E/W-shortening is the maximum value for sinistral shearing along the HSZ and other faults. Some of the shortening may have been absorbed offshore Oman across the Owen Basin and/or along the continental/oceanic transitions of both plates.

How to cite: Mattern, F., Bolhar, R., Scharf, A., Scharf, K., Mattern, P., and Callegari, I.: Novelly discovered post-mid-Eocene sinistral slip in the eastern Oman Mountains: widely distributed shear with wrench-fault assemblage related to Arabia-India convergence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8321, https://doi.org/10.5194/egusphere-egu21-8321, 2021.

Knowing the original size of Greater India is a fundamental parameter to quantify the amount of continental lithosphere that was subducted to help form the Tibetan Plateau and to constrain the tectonic evolution of the India-Asia collision. Here, we report Early Cretaceous paleomagnetic data from the central and eastern Tethyan Himalaya that yield paleolatitudes consistent with previous Early Cretaceous paleogeographic reconstructions. These data suggest Greater India extended at least 2,675 ± 720 and 1,950 ± 970 km farther north from the present northern margin of India at 83.6°E and 92.4°E, respectively. The paleomagnetic data from Upper Cretaceous rocks of the western Tethyan Himalaya that are consistent with a model that Greater India extended ~2700 km farther north from its present northern margin at the longitude of 79.6°E before collision with Asia. Our result further suggests that the Indian plate, together with Greater India, acted as a single entity since at least the Early Cretaceous. An area of lithosphere ≥4.7 × 10⁶ km² was consumed through subduction, thereby placing a strict limit on the minimum amount of Indian lithosphere consumed since the breakup of Gondwanaland. The pre-collision geometry of Greater India’s leading margin helped shape the India-Asia plate boundary. The proposed configuration produced right lateral shear east of the indenter, thereby accounting for the clockwise vertical axis block rotations observed there.

How to cite: Meng, J., Gilder, S., Li, Y., and Wang, C.: Expanse of greater india in the cretaceous, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-636, https://doi.org/10.5194/egusphere-egu21-636, 2021.

Recent paleomagnetic data from early Late Cretaceous and late Eocene rocks from Myanmar (1,2) demonstrate that the Burma Terrane (BT) underwent an important northward translation alongside India in the Cenozoic. We present new paleomagnetic results from Paleocene to Eocene sediments that confirm the slightly southern to equatorial paleolatitudes during the Paleocene to mid Eocene. However, these paleomagnetic results imply a new paleogeography not compatible with the typical view of the geology of Myanmar as an andean-type margin above an active subduction of the Tethys/India oceanic crust below Sundaland.  Most previous models proposed an active subduction below Myanmar during the Paleogene but a slab anchored in the mantle would impede the large northward motion of the BT implied by our paleomagnetic data. We thus review the geology of the BT in light of the new latitudinal constraints provided by the paleomagnetic data. The BT contains >10km thick Cenozoic basins (Central Myanmar Basins (CMBs)) recording the Cenozoic geological evolution of the BT. The CMBs were previously interpreted with sediment sources located within the Myanmar magmatic arc and to the east in Sibumasu. The numerous studies on detrital zircons from the Late Cretaceous - Paleogene sediments  of  the CMBs highlight a clear correlation in the distribution of the ages of the pre-Cretaceous zircons (~40% of the zircons in the sediments) with the one from the Triassic turbidites (Pane Chaung Formation) of the Indo-Burman Ranges and the Triassic sediments from the Tethyan Himalaya (Langjiexue Fm.). Thus, the source of sediments is unlikely to be in Sibumasu but proposed to be in an actively eroding north-western extension of the Indo-Burman ranges (Greater Burma block, (2)) possibly linked to the Tethyan Himalaya and consistent with a BT position within the India plate during the Cenozoic. In any case, we find little evidence for a nearby active magmatic arc in the detrital zircon record supporting the hypothesis of an active subduction below the BT. Thus this review of the geology of the BT supports a rapid northward moving BT alongside India during the Cenozoic. We will discuss the implication of this new paleogeography on the India-Asia collision models.

(1) Westerweel et al. « Burma Terrane Part of the Trans-Tethyan Arc during Collision with India According to Palaeomagnetic Data ». Nature Geoscience 12, no 10 (octobre 2019): 863‑68. https://doi.org/10.1038/s41561-019-0443-2.

(2) Westerweel et al. « Burma Terrane Collision and Northward Indentation in the Eastern Himalayas Recorded in the Eocene‐Miocene Chindwin Basin (Myanmar) ». Tectonics 39, no 10 (octobre 2020). https://doi.org/10.1029/2020TC006413.

How to cite: Westerweel, J., Roperch, P., Dupont-Nivet, G., Licht, A., Cogne, N., and Poblete, F.: Northward motion of the Burma Terrane alongside India during the Cenozoic., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15621, https://doi.org/10.5194/egusphere-egu21-15621, 2021.

Deciphering the exhumation mechanism of high-pressure, low-temperature (HP-LT) metamorphic rocks can provide important insights into the tectonic evolution of oceanic subduction zones at active continental margins. Here we present a multidisciplinary study examining the exhumation tectonics of the Permo–Triassic eclogite-bearing Lanling HP-LT terrane within the Central Qiangtang metamorphic belt (CQMB). Field relations and microscopic observations show that the HP-LT rocks are separated from the Permian ophiolite mélange of the hanging wall by low-angle detachments and exhibit five stages of deformation. The pervasive top-to-the-SW and -S shearing structures imply that the Lanling HP-LT terrane was exhumed as a transtensional metamorphic core complex (mcc). The results of the petrological and mineralogical analysis and pseudosection modeling of eclogites indicate that the eclogites and blueschists are characterized by synexhumation mineral growth pulses with decompressional P-T trajectories. A compilation of previous geochronological data and our ⁴⁰Ar/³⁹Ar dating results of shearing structures in HP-LT rocks indicate a continuous exhumation at ca. 244–210 Ma. Moreover, the CQMB experienced lithospheric transtension, as shown by the Middle–Late Triassic geological events, which include mantle upwelling at ca. 237–230 Ma and abyssal basin development in the Anisian–middle Norian. These observations indicate that the CQMB is likely a autochthonous accretionary wedge resulting from northward subduction of the Paleo-Tethys Ocean beneath the North Qiangtang Block (NQB). Moreover, the transtension of the CQMB occurred in the late stage of the oceanic subduction, which was probably triggered by oceanic slab rollback.

How to cite: Liang, X., Wang, G., Cao, W., Forster, M., and Lister, G.: Lithospheric Extension of the Accretionary Wedge: An Example From the Lanling High-Pressure Metamorphic Terrane in Central Qiangtang, Tibet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2055, https://doi.org/10.5194/egusphere-egu21-2055, 2021.