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The Triassic volcanic rocks of Wrangellia erupted at an equatorial to tropical latitude that was within 3000 km of western North America. The mafic and ultramafic volcanic rocks are compositionally and isotopically similar to those of oceanic plateaux that were generated from a Pacific mantle plume-type source. The thermal conditions, estimated from the primitive rocks, indicate that it was a high temperature regime (TP > 1550 °C) consistent with elevated temperatures expected for a mantle plume. The only active hotspot currently located near the equator of the eastern Pacific Ocean that was active during the Mesozoic and produced ultramafic volcanic rocks is the Galápagos hotspot. The calculated mantle potential temperatures, trace elemental ratios, and Sr–Nd–Pb isotopes of the Wrangellia volcanic rocks are within the range of those from the Caribbean Plateau and Galápagos Islands, and collectively have similar internal variability as the Hawaii-Emperor island chain. The paleogeographic constraints, thermal estimates, and geochemistry suggests that it is possible that the Galápagos hotspot generated the volcanic rocks of Wrangellia and the Caribbean plateau or, more broadly, that the eastern Pacific (Panthalassa) Ocean was a unique region where anomalously high thermal conditions either periodically or continually existed from ~ 230 Ma to the present day.

The Guera Massif of South-Central Chad is composed of collisional and post-collisional intrusive rocks related to the Central African Orogenic Belt. Collisional granites were emplaced at 595–590 Ma...

The southern Saharan Metacraton is one of the least geologically constrained regions in the world as bedrock exposures are rare. To the west of Lake Fitri near the communities of Ngoura and Moyto in south-central Chad there are two granitic inliers that form a series of lenticular to ellipsoidal low laying hills. Very little is known about the Lake Fitri inliers and their regional correlation to larger massifs in Chad is undetermined. The granites yielded weighted-mean zircon 206Pb/238U ages of 554 ± 8 Ma and 546 ± 8 Ma indicating they were emplaced ~45 million years after the cessation of arc-related magmatism and the subsequent collision between the Congo-Sao Francisco Craton and the Saharan Metacraton. The rocks have distinct groupings of inherited zircons with ages of ~580 Ma and ~635 Ma suggesting they are at least in part derived by recycling of older crustal rocks. The biotite mineral chemistry, whole rock compositions and petrological modeling indicate the granites were derived by melting of crustal lithologies but the whole rock Nd isotopes (eNd(t) = +1.3–+2.9) are characteristic of a mantle source. The contrasting inheritance-rich nature of the granites with a juvenile Nd isotopic signature is likely due to mixing between magmas derived from juvenile (Neoproterozoic) arc-related crust and asthenospheric magmas. Asthenospheric upwelling was probably a response to post-orogenic lithospheric delamination related to fault movement along the Chad Lineament, a possible extension of the Tchollire-Banyo shear zone that extended to the interior of the Saharan Metacraton. The implications are that lithospheric delamination may not have occurred immediately after collision but rather propagated along a narrow belt that extended well into the central regions of the Saharan Metacraton.

Although Peninsular Malaysia abundant Permo-Triassic Malayan granitic plutons and volcanics (292–198 Ma) generate an enormous volume of detrital zircons that masks other detrital sources in fluvial sediments, there are suggestions that Peninsular Malaysia could recycle detrital zircons from Indochina (through Jurassic-Cretaceous strata) to other parts of Sundaland by paleoriver after the Indochina-Sundaland sediment link diminishes in the Cenozoic. As there is insufficient data to prove this, we compiled our new detrital zircon U-Pb isotopic data from modern river sands in Peninsular Malaysia with all available data to create a dataset that revealed five detrital zircon age pattern zones: (1) Northeast Coastal Zone (~73 Ma and ~223 Ma), (2) Mid-East Coastal Zone (~236 Ma and ~280 Ma), (3) Southeast Coastal Zone (~170 Ma, ~243 Ma, ~291 Ma, 400–416 Ma and 1545–1852 Ma), (4) Central Zone (~220 Ma) and (5) Mid-West Coastal Zone (~227 Ma and 1105–1173 Ma). All detrital age pattern zones show a clear detrital contribution from Malayan granitoids and volcanics. However, the Southeast Coastal Zone also shows significant contributions from Jurassic-Cretaceous strata in the northwest, e.g. Bertangga and Gerek sandstones, making them comparable with sources from Indochina and Lower Cretaceous strata in Singapore. We suggest a defunct drainage during Paleogene which transports the eroded sediments from the Jurassic-Cretaceous strata in the northwest to the sink in the southeast coast of Peninsular Malaysia recycled “Indochina signature” detrital zircons. If the sink connects with the Sundaland paleoriver system, it might contribute to the “Indochina signature” detrital provenance in West Borneo.

Precambrian crust within southern Chad and eastern Cameroon preserves rocks that were remobilized and emplaced during and after the Neoproterozoic (∼650 Ma to ∼610 Ma) collision between the Congo, Sao Francisco, West African cratons and the Saharan Metacraton. The Guera Massif of south-central Chad and granites located near Lake Fitri are inferred to be of Neoproterozoic age but there are no radio-isotopic dates available to confirm their association with the Pan-African Orogeny (Central African Fold Belt). New zircon U/Pb geochronology of granitic rocks from the Guera Massif, Lake Fitri region and the Doba Basin of the southern Chad yielded weighted-mean 206Pb/238U ages from 595 ± 8 Ma to 545 ± 6 Ma. The oldest inherited zircons indicate that the Guera Massif is either built upon Meso- to Paleoproterozoic (1000 Ma–1900 Ma) continental crust or that pre-Neoproterozoic rocks were the source of the silicic Ediacaran rocks. The identification of ∼590 Ma volcanic-arc granites within the Guera Massif suggest that subduction continued in the eastern regions of Chad after collision had occurred (≥610 Ma) in the west (Cameroon). The younger granites (≤570 Ma) are post-collisional in nature and are closely linked to deformation cycles recorded in eastern Cameroon after the main continental collision episode between the Congo Craton and the Saharan Metacraton. The post-collisional granites located in the Lake Fitri region likely represent a westward extension of the Guera Massif as there are temporal and compositional similarities between the granitic rocks. The age and composition of the diorite from the Doba Basin of southern Chad is similar to post-collisional granites from the Central African Fold Belt of Cameroon and implies that the southern boundary of the Saharan Metacraton may be north of the Doba Basin.

The South China Sea (SCS) is one of the classical example of a non-volcanic passive margin situated within three tectonic plates of the Eurasian, Indo-Australian and Philippine Sea plate. The development of SCS resulted from interaction of various types of plate boundaries, and complex tectonic assemblage of micro blocks and accretionary prisms. Numerous models were proposed for the formation of SCS, yet none can fully satisfy different aspects of tectonic forces. Temporal and geographical reconstruction of Cretaceous and Cenozoic magmatism with the isochrones of major basins was conducted. Our reconstruction indicated the SE margin of Asia had gone through two crustal thinning events. The sites for rifting development are controlled by localized thermal weakening of magmatism. NW–SE extension setting during Late Cretaceous revealed by magmatism distribution and sedimentary basins allow us to allocate the retreated subduction of Pacific plate to the cause of first crustal thinning event. A magmatic gap between 75 and 65 Ma prior to the initiation of first basin rifting suggested a significant modification of geodynamic setting occurred. The Tainan basin, Pearl River Mouth basin, and Liyue basins started to develop since 65 Ma where the youngest Late Cretaceous magmatism concentrated. Sporadic bimodal volcanism between 65 and 40 Ma indicates further continental extension prior to the opening of SCS. The E–W extension of Malay basin and West Natuna began since late Eocene followed by N–S rifting of SCS as Neotethys subducted. The SCS ridge developed between Pearl River Mouth basin and Liyue basin where 40 Ma volcanic activities concentrated. The interaction of two continental stretching events by Pacific followed by Neotethys subduction with localized magmatic thermal weakening is the cause for the non-volcanic nature of SCS.

Taiping Island, also known as Itu Aba, is the largest natural terrestrial landmass in the South China Sea and is centrally located. Using bathymetry and marine multi-channel seismic data, we explored the seismic stratigraphic features of the offshore and isolated carbonate platform north of Taiping Island. The western flank of the carbonate platform is characterized by an intercalation between high-amplitude and low-amplitude reflections, showing the landward and seaward migration of the platform foreslope deposits. In addition, there are two offshore carbonate build-ups that are underlain by normal faults. Six sequence boundaries and five depositional sequences caused by eustatic sea level cycles are identified and correlated with the eustatic sea level change chart. Although the evolution of the seismic sequences is partly controlled by local tectonics, the overall stacking pattern of the sedimentary strata in our study area reveals five third-order cycles and one second-order cycle, which is in accordance with the eustatic sea level chart. Additionally, the formations of the Western Taiping Seamount Group and the Zhenghe-Daoming Trough are preliminarily analyzed based on seismic data.

The Early Palæogene Silhouette/North Island volcano-plutonic complex was emplaced during the rifting of the Seychelles microcontinent from western India. The complex is thought to have been emplaced during magnetochron C28n. However, the magnetic polarities of the rocks are almost entirely reversed and inconsistent with a normal polarity. In this study we present new in situ zircon U/Pb geochronology of the different intrusive facies of the Silhouette/North Island complex in order to address the timing of emplacement and the apparent magnetic polarity dichotomy. The rocks from Silhouette yielded weighted mean 206Pb/238U ages from 62.4 ± 0.9 Ma to 63.1 ± 0.9 Ma whereas the rocks from North Island yielded slightly younger mean ages between 60.6 ± 0.7 Ma to 61.0 ± 0.8 Ma. The secular latitudinal variation from Silhouette to North Island is consistent with the anticlockwise rotation of the Seychelles microcontinent and the measured polarities. The rocks from Silhouette were emplaced across a polarity cycle (C26r-C27n-C27r) and the rocks from North Island were emplaced entirely within a magnetic reversal (C26r). Moreover, the rocks from North Island and those from the conjugate margin of India are contemporaneous and together mark the culmination of rift-related magmatism.

The late Permian Doba (257 ± 1 Ma) gabbro was discovered at the base of an exploration well through the Cretaceous Doba Basin of Southern Chad. The gabbro is at least 250 m thick, has cumulus mineral textures and consists of plagioclase, clinopyroxene, orthopyroxene, Fe–Ti oxide, apatite and quartz. The composition of the silicate minerals (i.e. plagioclase, pyroxenes) from the lowest part of the intrusion tend to be more primitive (i.e. An59, Wo40-44En33-47Fs12-25) than the upper part (i.e. An41, Wo39-43En30-44Fs14-29) suggesting the magmatic system differentiated internally by crystal fractionation and crystal redistribution. Based on the chemistry of the pyroxenes, the parental magma was compositionally similar to a Ti-rich, within-plate continental tholeiite that had a bulk Mg# of ∼44. The relative oxidation state of the magma was initially moderately reducing (i.e. ΔFMQ-0.3) and then became more reducing after a period of fractionation (i.e. ΔFMQ-1.2). The estimated initial magma temperature was at least 1100 °C. The within-plate composition suggests there was rifting-related magmatism near the boundary of the Saharan Metacraton that could be related to edge-driven mantle convection.

The Guera Massif of South-Central Chad is one of the least studied regions of the Saharan Metacraton. The oldest known rocks were emplaced during the Ediacaran and have geochemical characteristics of collision-related granites. The granites can be subdivided into two series on the basis of their compositions: 1) ferroan and alkalic to alkali calcic, and 2) magnesian and alkali calcic to calc-alkalic. The ferroan rocks (589 ± 6 Ma, 589 ± 6 Ma, 593 ± 7 Ma, 590 ± 8 Ma) tend to be younger than the magnesian rocks (595 ± 8 Ma) indicating there was a secular compositional change. The chemical variability within each series can be explained by fractional crystallization, but the ferroan series requires lower water content (~1 wt%) and relatively reducing conditions (ΔFMQ −1) compared to the magnesian series (H2O = ~2 wt%; ΔFMQ + 0.7). The older magnesian series is isotopically chondritic to moderately enriched (ISr = 0.7037 to 0.7073; eNd(t) = −3.2 to + 0.2) and was likely derived from a subduction-modified mantle source at an ‘Andean-type’ margin. In contrast, the ferroan series is isotopically enriched (ISr = 0.7048 to 0.7176; eNd(t) = −9.4 to −14.1) and has a significant amount of inherited Mesoproterozoic zircons (206Pb/238U = 1039 ± 24 Ma), indicating that it was likely derived by partial melting of an older crustal source. The changing nature of the granites likely records the transition from an active margin to a collisional zone between the Congo- Sao Francisco Craton and the Saharan Metacraton.

The Saharan Metacraton is largely covered by the Sahel and Sahara with only sparse bedrock exposure making it one of the most poorly studied cratons in the World. Consequently, detrital zircon geochronology is invaluable to discern the lithotectonic development of the Saharan Metacraton in the absence of outcrop. Detrital zircons from the northern Chari River, the largest river system of North-Central Africa, have ages between ~700 Ma and ~500 Ma with a small Cambrian to Ordovician (486 ± 11 Ma and 422 ± 11) population, a few Devonian to Middle Jurassic zircons (394 ± 9 Ma–159 ± 4) and a single Mesoproterozoic (959 ± 19 Ma) zircon. The absence of ancient detrital zircons suggests that the crust in the vicinity of Lake Chad is primarily juvenile. A significant (~17%) proportion of zircons yielded ages of ~580 Ma that are broadly coeval with nappe and wrench faulting, and granulite exhumation in the Central African and Trans-Saharan orogenic belts. Moreover, we identified a gabbro from the Guera Massif of south-central Chad that yielded an in situ zircon weighted-mean 238U/206Pb age of 580 ± 6 Ma. The age of the gabbro is similar to the Kekem gabbro-norite complex (576 ± 4 Ma) in west Cameroon, inherited zircons from silicic rocks near Lake Fitri and Lake Chad, and the detrital zircons from the Chari River. Our results unequivocally demonstrate that there was magmatism at ~580 Ma and that it was contemporaneous with deformation along the Tchollire-Banyo and Central Cameroon shear zones indicating there was a major regional tectonomagmatic episode at that time. We suggest the mafic magmatism was related to post-orogenic mantle upwelling that may have been responsible for or contributed to lithospheric delamination of the southern Saharan Metacraton.

The Linzizong volcanic successions that crop out in the Lhasa terrane, southern Tibet have been conventionally regarded as the products of northward subduction of the Neotethyan oceanic slab beneath South Asia. This study reports geochemical data of 100+ volcanic rocks from the Lhasa terrane to better constrain the temporal–spatial distribution and petrogenesis of the Linzizong volcanism. The Linzizong volcanic successions consist dominantly of calc-alkaline rocks that erupted from ca. 69 to 43 Ma and show typical arc-lava geochemical features marked with LILE enrichment and HFSE depletion in the spidergram. Their Sr and Nd isotope ratios [ e Nd ( T ) = +3.3 to −2.4; I Sr = 0.7048–0.7072] are generally similar to those of the associated Gangdese I-type granitoids. The Linzizong volcanism is characterized by a flare-up period (ca. 50 Ma) that shows significant geochemical variations, manifested by the coexistence of five types of volcanic rocks: (1) the main suite of calc-alkaline rocks [SiO 2 = 45–80 wt.%; La = 12–45 ppm; e Nd ( T ) = +3.8 to −4.9; I Sr = 0.7037–0.7105] that could be interpreted by partial melting of the mantle wedge followed by assimilation and fractional crystallization (AFC) processes with >10% crustal contamination and/or magma mixing; (2) the low-K, low-REE suite (SiO 2 = 48–61 wt.%; K 2 O = 0.5–1.1 wt.%; La = 7–10 ppm) that has the highest Nd isotope ratios [ e Nd ( T ) = +5.9 to 3.5], suggesting a juvenile mantle origin possibly related to decompression melting of the asthenosphere; (3) the shoshonitic suite [SiO 2 = 53–71 wt.%; K 2 O = 3.8–6.7 wt.%; e Nd ( T ) = −2.8 to −6.1] from small-degree melting of the metasomatized lithospheric mantle; (4) the high-REE suite [SiO 2 = 61–75 wt.%; La = 36–87 ppm; e Nd ( T ) = −2.6 to −3.2] originating from remelting of a newly underplated basaltic lower crust; and (5) the evolved suite of rhyolitic flows and ignimbrites (SiO 2 > 65 wt.%) that have the lowest e Nd ( T ) values of −14 to −18, representing remelting products of the basement or continental crust of the Lhasa terrane. Such geochemical heterogeneities are attributed to breakoff of the subducted Neotethyan slab under southern Tibet that occurred in the early stage of the India–Asia collision.

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