Intramontane late Carboniferous–Permian basins of western Europe developed during the latest orogenic stages of the Variscan Mountain Belt in eastern Pangaea, at equatorial palaeolatitudes. Their stratigraphic framework is mainly based on continental subdivisions (e.g. Stephanian and Autunian continental stages), which can be contentious owing to biostratigraphic biases, resulting in long-distance diachronous subdivisions. To provide precise inter-basinal and global correlations to the internationally recognized chronostratigraphic marine stages, this study reports new U–Pb geochronology from the Aumance and Decize–La Machine basins, located in the northern French Massif Central. Zircon grains extracted from three volcanic ash-fall layers give weighted mean 206 Pb/ 238 U ages of 299.11 ± 0.35, 298.73 ± 0.36 and 298.59 ± 0.35 Ma (2 σ total propagated uncertainty) by the chemical abrasion isotope dilution thermal ionization mass spectrometry method, coinciding with the Carboniferous–Permian transition (Gzhelian and Asselian stages). These ages imply that the northern Massif Central basins developed synchronously in relatively short periods of time (<10 myr), reflecting substantial sedimentation rates. Finally, the new chronology of infilling of these basins confirms that they were connected during the late Carboniferous and early Permian periods, improving the knowledge on the late orogenic Variscan geodynamic setting in this area. Supplementary material: Operating conditions and complete analytical results are available at https://doi.org/10.6084/m9.figshare.c.6805228

Our recent field investigations in western Pakistan have revealed that serpentinized peridotites here are crosscut by numerous intrusions of gabbro and tonalite. New zircon U–Pb dating of these plutons indicates Late Cretaceous–Early Eocene ages of their crystallization. They have arc-like geochemical signatures and constitute the middle crust of an island arc complex. Together with their extrusive counterparts they form the RasKoh island arc (RIA), defined for the first time in this study. The RIA and the Chagai continental arc to the north represent the manifestations of two separate subduction-zone systems within Neotethys, developed between India and Eurasia. We posit that this Neotethyan domain contained two oceanic plates. Subduction of the leading plate beneath Eurasia generated the Jurassic–Late Oligocene Chagai continental arc, and the northward subduction of the trailing plate resulted in the development of the Late Cretaceous–Oligocene, ensimatic RasKoh arc. Arrival of the Indian subcontinent at the latitude of the RasKoh arc in the earliest Miocene caused the emplacement of the RasKoh arc onto India via oblique arc–continent collision. The subsequent collision of this composite Indian plate with Eurasia resulted in extensive deformation of Late Cretaceous flysch deposits and the ophiolitic arc basement. Supplementary material: Rock compositions and analytical results are available at https://doi.org/10.6084/m9.figshare.c.6795686 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

The Sukhothai Terrane in northern Thailand comprises a continental basement and a Permo-Triassic magmatic arc related to the subduction of the main Paleo-Tethys Ocean. The Donchai Group represents the oldest sedimentary sequence of the Sukhothai Terrane and consists mainly of meta-sandstone, quartzo-feldspathic schist, phyllite and silty slate. This paper presents new detrital zircon U–Pb geochronology and Lu–Hf isotope data, and geochemical results for the sedimentary rocks of the Donchai Group to elucidate the depositional age, provenance and nature of the group. The youngest detrital zircon ages (433–403 Ma) suggest that the Donchai Group was accumulated between 433 Ma and 368 Ma, revealing Silurian–Devonian arc magmatic rocks on the western margin of the Sukhothai Terrane. Sediments of the Donchai Group were sourced from both the continental basement and a Silurian–Early Devonian magmatic arc, suggesting a depositional setting on the continental slope of a back-arc basin along the western flank of the Sukhothai Terrane. The Silurian–Devonian arc belt in SW China likely extend to the Chiang Rai region, to the west of the Sukhothai Terrane, northern Thailand, revealing the northward subduction of the Proto-Tethys Ocean along the western Simao and Sukhothai margin during the middle Paleozoic. The inferred arc and back-arc configuration of the Proto-Tethys in northern Thailand is comparable with that recently established in Yunnan, SW China. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6858373

Understanding the tectonic evolution of the Proto-Tethys Ocean is important for exploring the initial assembly of the Gondwana supercontinent. The closure of the Proto-Tethys Ocean represents the end of convergence along the northern edge of Eastern Gondwana. However, the timing and processes of the closing of the ocean have different interpretations. This work focuses on the early Paleozoic granitic rocks in the Baoshan Block (BSB), SW China, to constrain the tectonic evolution of the Proto-Tethys Ocean. Zircons from the Pinghe and Zhen'an granitic plutons yield concordant U–Pb ages from 489.8 Ma to 467.7 Ma. The bulk-rock geochemical features suggest that these samples are high-K, calc-alkaline, S-type granites enriched in LREEs and depleted in HREEs. With obvious negative Eu-anomalies and high K 2 O/Na 2 O ratios (1.01–2.57), they are enriched in LILEs and depleted in HFSEs. Thus, these rocks were derived from partial crustal melting associated with subduction of the converging plate. Previous studies on the Changning–Menglian suture zone suggested that the Early Paleozoic magmatic activity in the BSB was related to the westward subduction of the Proto-Tethys Ocean, combining the Early Paleozoic subduction-related magmatic activity to the east, it is suggested that the Changning–Menglian Ocean experienced bidirectional subduction.

We present new geophysical observations of the Mull Dyke Swarm in the Southern North Sea. Two- and three-dimensional seismic reflection and aeromagnetic data were used to map the dykes. The three main dyke groups recognized onshore (Cleveland, Blyth and Hawick–Acklington) are found to extend to varying distances into the North Sea, crossing a number of major crustal-scale fault zones and domain boundaries, with almost no reorientation. The Blyth Dyke Group extends furthest, for a distance of 672 km from the source on Mull. The seismic data show extensive development of pit chain craters above the upper tips of these dykes, which can be approximately dated to the late Paleocene from the ages of crater fills. Volumetric estimates are made of the intrusive volumes associated with each group, ranging from 90 to 202 km 3 . These three main axes of intrusion probably formed in different intrusive events within a c. 1 myr period, from 59 to 58 Ma, during magnetic chron C26R.

Understanding the northern extension of Greater India is vital for modelling the India–Asia collision process and the formation of the Tibetan Plateau. We present new palaeomagnetic data from the mid-Cretaceous ( c. 106 Ma) Gyabula Formation red beds in the Tethyan Himalaya. Well-defined high laboratory unblocking temperature component magnetizations were isolated from 19 sites and pass the fold tests, indicating that they are pre-folding magnetizations. The tilt-corrected site-mean direction is D s  = 222.9°, I s  = +39.4° with α 95  = 4.2°. The site-mean inclination increases from 39.4° to 45.8° after anisotropy-based inclination shallowing correction. The declination and inclination differ considerably from those of neighbouring sections. This directional discrepancy of the red beds may be attributed to the fact that the sampled section (sites ZB1–11, 40–52) is overturned and to local vertical-axis rotation. The combination of our new and previously published palaeomagnetic data shows that the Tethyan Himalaya was located at 27.5° ± 2.4°S for the sampled area. Our new results, together with the reliable Cretaceous palaeomagnetic data obtained from the Tethyan Himalaya as well as coeval palaeolatitudes expected from the Indian craton, support a smaller Greater India and that the Tethyan Himalaya did not rift from the Indian craton during the mid-Cretaceous. Supplementary material: Detrital zircon U–Pb ages data, hysteresis parameters data, palaeomagnetic datasets for the Gyabula Formation, anisotropy of isothermal remanent magnetization data, available latest Jurassic–Early Cretaceous palaeomagnetic results from the Tethyan Himalaya and supplementary figures are available at https://doi.org/10.6084/m9.figshare.c.6795683 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

The collage of the Indochina Block to the Eurasian continent during the Mesozoic resulted in major changes in source-to-sink systems of East Asia, whilst the sedimentation in the Khorat-Simao Basin of the Indochina Block transited from marine to continental environments. Previous studies conducted the existence of transcontinental river systems in the East Asia mainland during the Cretaceous to early Cenozoic with few studies on pre-Cretaceous drainage systems. To determine the impact on the evolution of paleo-drainage systems triggered by tectonic movement of the Indochina Block, we performed paleomagnetic and U-Pb geochronologic analyses on the Late Triassic to Early Cretaceous sedimentary rocks in the Simao Basin. Paleomagnetic data indicate stable Jurassic tectonic environments between the Indochina and Songpan Ganzi-South China blocks, following their Late Triassic collision. Based on detrital zircon U-Pb dating, the Late Triassic age spectra consist of mainly Phanerozoic components, while the Jurassic to Cretaceous age spectra displayed more Precambrian age peaks. The contribution of potential provenance to the Simao Basin changed during the Early Cretaceous, suggesting several sedimentary provenance transitions. Also, we believe that large continental-scale drainage systems sourced from the Songpan-Ganzi Block flowing through North Qiangtang, Sichuan, Simao, and Khorat basins since after the Late Jurassic. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.6862918

The Tian Shan is one of the world's largest intracontinental orogens and provides an excellent example for deciphering the intracontinental responses to the tectonics of plate boundaries. Despite its significance, the timing and driving mechanism of the Cenozoic mountain building of the Tian Shan in the context of the India-Eurasia collision remain controversial. In this study, Cenozoic stratigraphy of the Tiereke section along the western Kuqa Depression of the northern Tarim Basin on the south foreland of Eastern Tian Shan (east of 80°E) has been investigated. The results indicated that the Cenozoic deposition of the Tiereke region sequentially experienced a transgression from the Kumugeliemu Group to the Suweiyi Formation and a regression from the Suweiyi to the Kuqa Formations. Based on the contact relationships and conglomerate textures, three stages of high-energy alluvial deposition have been identified in the lower Kumugeliemu Group, upper Jidike, and Kangcun-Kuqa Formations, respectively. These sedimentary events were interpreted to represent phases of Eastern Tian Shan mountain building at ca. 54 Ma, ca. 27 Ma and since ca. 9.7 Ma according to previous magnetostratigraphic results, which were possibly related to the initial India-Eurasia collision, the collision between the India and Tarim lithospheric mantles, and the basinward propagation of deformation, respectively. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Increasing mineralogical and textural evidence from podiform chromitites in ophiolites show their ultra–high pressure origin (>150 km), challenging the conventional models for their formation under low pressure conditions (< 60 km) in the upper mantle. However, this challenge remains controversial due to the lack of in-situ mineralogical evidence. Here, we report new data and observations from the Skenderbeu massif in Mirdita ophiolite, Albania. Transmission electron microscopy (TEM) analysis reveal for the first time that these chromitites (Cr#= 41.8-43.2) have numerous exsolution lamellae of diopsidic clinopyroxene and orthoenstatite. TEM analysis also show that these lamellae have a crystallographic topotaxy relationship with the host chromite, i.e., (020) Cpx ∥︀ (22(—)0) Chr , (2(—)00) Cpx ∥︀ (111) Chr , and (010) Opx ∥︀ (22(—)0) Chr , (200) Opx ∥︀ (22(—)0) Chr , indicating an exsolution origin. The abundant presence of pyroxene exsolution lamellae in center of the host chromites implies the incorporation of Si 4+ and Ca 2+ cations in the precursor chromite, a CaFe 2 O 4 -structured high-pressure polymorph, which was stable >12.5 GPa (i.e., 380 km deep). These in-situ, nano-scale observations, and geological occurrence, together with previously discovered ophiolitic diamonds in the Mirdita ophiolite, suggest a much deeper origin for ophiolitic chromitites than conventional interpretations, and provide a valuable opportunity to understand the composition of the deep mantle. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

The fault locations and orientation of the Zabargad Transform Fault Zone, also called the Zabargad Fracture Zone (ZFZ), have previously only been delineated by satellite-based geophysical data, causing intense debate over the last few decades. Newly recognized geomorphological features identified in bathymetric and LiDAR data from the NE Red Sea margin present the first ground evidence for the northern extent of the ZFZ. The features are aligned over 84 km, starting from the Mabahiss Deep, near the spreading axis, and continuing to the shallow Saudi Arabian shelf along the northern termination of the Al Wajh carbonate platform. Analysis of the seafloor morphology reveals three geomorphic terrains: (1) a deeply incised canyon feeding into the Mabahiss Deep, which is characterized by dozens of amphitheatre-shaped scarps; (2) a 22 km wide head-scarp that follows the edge of the Al Wajh platform; and (3) multiple fault scars and graben-like structures on the shallow shelf. We interpret these morphological features as deformation indicators associated with the deformation processes in the ZFZ and postulate that they represent the northern end of the ZFZ. In addition, the fault zone delineates the NW margin of the Al Wajh carbonate platform and most likely continues to shape it. This paper gives new insights into the interaction between fracture zones and continental margins and their role in the morphogenesis of the seafloor.