Constraints on the tectonic setting of the upper Triassic to lower Jurassic in the Sverdrup Basin can be elucidated from detrital-zircon U-Pb ages. During the Triassic, there was a dual provenance system into sedimentary basins along the western and northern margins of Laurentia. One of the sediment sources was from an extra-basinal igneous source of Permian-Triassic zircon while the other source was recycled sediment eroded from older sedimentary basins. The Heiberg Formation/Group was deposited during a period of significant siliciclastic sedimentation into the basin from the upper Triassic to the lower Jurassic and comprises three members: Romulus, Fosheim and Remus. Previous work has interpreted that the Carboniferous-Permian-Triassic detrital zircon had stopped reaching the northern part of the Sverdrup Basin by deposition of the upper Heiberg Formation (lower Jurassic). New detrital-zircon age analyses from samples along the northern part of the basin spanning different horizons in the Heiberg Formation show that the typical extra-basinal signature, with abundant Carboniferous-Permian-Triassic ages, was no longer recorded during the initial deposition of the Fosheim Member during the latest Triassic. Previously published basin analysis from the Sverdrup Basin interprets syn-Jurassic extensional faults and so we relate the provenance change to the onset of extension. It is interpreted that the Sverdrup Basin transitioned from a basin that received sediment from a northern extra-basinal igneous source during deposition of the Romulus Member to an extensional basin by the deposition of the Fosheim Member in the latest Triassic, as the northern sediment source was interrupted by intervening extensional basins of the proto-Amerasia Basin.

Geodynamic models implying subduction of continental crust either consider this process happening during collision, when the continental margin of the lower plate attempts subduction, or in pre-collisional stages, when tectonic erosion of the upper plate or subduction of continental extensional allochthons drag continental crust in the subduction channel. In the Zagros orogen (W Iran), high-pressure rocks are known only from the Sanandaj-Sirjan Zone, NE of the Main Zagros Thrust. Here, eclogites of the North Shahrekord Metamorphic Complex suggest subduction of continental crust slices derived from the upper plate (Central Iran) during the onset of the Neo-Tethys subduction along the southern margin of Iran. Eclogites record a clockwise pressure-temperature-time path, with pre-eclogitic epidote-amphibolites-facies phase assemblages preserved in garnet cores, a high-pressure stage, and a subsequent retrogression at amphibolite-facies conditions. By means of forward thermodynamic modelling and 40Ar/39Ar geochronology, the peak metamorphism has been constrained at 1.9-2.1 GPa and 550-600 °C, in the 191-194 Ma time span. The following retrogression during exhumation lasted at least until 144 Ma. Our data suggest that the onset of the Neo-Tethys subduction traces back prior to 190 Ma, involving together with the Neo-Tethys oceanic lithosphere also slices of the upper plate continental crust scraped off by means of tectonic erosion processes.

The issue of oversimplified Norian conodont taxonomy has set back the development of Norian conodont biostratigraphy of the western Tethys Realm for decades. The majority of stratigraphic studies used the name Epigondolella multidentata, a North American endemic, to gather specimens indicative of strata from the lower part of the middle Norian substage. Detailed conodont biostratigraphic investigations were carried out on the Norian hemipelagic cherty dolostones of the Mátyás Hill section in the Buda Hills (Hungary) in order to resolve the ‘multidentata problem’. The age of the section ranges from the upper part of the lower Norian substage (Lacian-3) to the lower part of the middle Norian substage (Alaunian-1). The new species Ancyrogondolella manueli n. sp. is introduced, and A. transformis is documented for the first time in the Tethys. The studied conodont fauna significantly improves the correlation potential between the western Tethys and the eastern Pacific.

During the existence of Proto-Tethys Ocean (550–430 Ma), microcontinents in northern East Gondwana merged with the northern margin of India-Australia, completing the assembly of Gondwana. Ongoing controversy surrounds the disappearance of the Proto-Tethys Ocean, the dynamic mechanisms of suturing and the palaeogeographic relationships among microcontinents in northern East Gondwana, contributing to the uncertainty about the tectonic evolution of the region. This paper concerns the lower Silurian Zusailing Formation in the Hainan Island and focuses on the affinity between Hainan Island and various microcontinents in northern East Gondwana during the early Silurian. We use detrital zircon geochronology to reconstruct the closure process of the Proto-Tethys Ocean and show that the detrital zircon U–Pb age groups of the lower Silurian Zusailing Formation are 2800–2200, 2100–1350, 1250–950, 600–480 and 480–430 Ma, with a significant age peak of ca. 449 Ma. Furthermore, the analysis of detrital zircon geochemistry and europium anomalies shows that the Hainan Island crust continued to thicken during 600–434 Ma. Comparing the age spectrum of early Palaeozoic detrital zircons from Hainan Island and various microcontinents in northern East Gondwana, as well as the affinity among them during the Silurian, we conclude that the closure of the eastern Proto-Tethys Ocean evolved from unidirectional subduction (600–480 Ma) to bidirectional subduction (480–430 Ma).

Contrary to the southern Appalachians, where Alleghanian magmatism is widespread and well documented, the expressions of magmatism in the Canadian Appalachians are limited. In this study, a suite of leucocratic dykes from the Cape Spencer area in southern New Brunswick, Canada, were investigated to determine the nature, timing and source of these magmas using zircon and monazite U-Pb geochronology, whole-rock geochemistry and Nd-Hf isotopes. An LA-ICP-MS U-Pb monazite Alleghanian age of 273.7 ± 1.3 Ma obtained for these dykes constitutes a new example of magmatism in the northern segment of the orogen, where significant strike-slip movement and reheating have been the primary markers of the Alleghanian Orogeny. These metaluminous leucocratic dykes are enriched in light rare elements, U and Th; depleted in high-field strength elements (HFSE; Nb, P, Ti); and have slight negative Europium anomalies [(Eu/Eu*)N = 0.72–0.95]. All the dykes samples have negative εNd(t) values (−9.76 to −5.7), negative εHf(t) values (−1.8 to −1.0) and Mesoproterozoic Nd depleted-model ages (TDM = 1371–1618 Ma). The geochemical and isotopic characteristics suggest that the dykes were formed by the partial melting of lower crust that assimilated Meguma metasedimentary rocks and/or Avalonian sedimentary rocks, following terminal subduction of the Rheic Ocean and thermal re-equilibration during the Alleghanian orogeny. The effects of the closure of the Rheic Ocean in the oblique collision between composite Laurentia and Gondwana were, to a certain extent, accommodated along the Minas Fault Zone, where magmatism and regional fluid flow were concentrated.

Both radiating dykes and proximal cone sheets converge onto a positive aeromagnetic anomaly of an inferred carbonatitic centre, hidden beneath a retreating edge of the Frederikshåbs Isblink glacier. This convergence, together with sub-parallel incompatible element patterns by all intrusions, suggests a cogenetic relationship that warrants investigation into potential diversification processes. More primitive high- and low-Mg damtjernites, which for three dykes conform to more porphyritic dyke cores and aphyric margins, respectively, can be explained by high-Mg trends being controlled by the fractionation/accumulation of mainly augite and olivine (or other mafic phases), while discordant low-Mg trends require additional decoupled magnetite fractionation. It is proposed that each dyke intrusion tapped the differentiated top of a central magma chamber, occasionally followed by an unconsolidated mafic cumulate mush, excluding denser magnetites, with in situ flow segregation playing a subordinate additional role. Beyond the most differentiated damtjernite, more evolved phonolitic nephelinites to carbonaceous alnöites split into bulk rock geochemical T-trends that can only relate to late-stage segregations into magmas with varying proportions of interstitial igneous (not secondary) analcime and carbonate – collectively increasing in volume with differentiation. While the analcime component also appears to segregate more readily into veins and ocelli than carbonatite, it is speculated if such low viscosity, density and liquidus rest melts, inside igneous centres, more efficiently aggregated into voluminous, buoyant analcime caps above slightly denser carbonatites. Similar converging plumbing systems and diversification processes are proposed for other complexes, where kimberlitic parents were simply extracted from deeper mantle sources.