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The mutual intersection of three plate boundaries, so-called triple junctions, has long been recognized as crucial boundaries for unraveling the spatiotemporal motion of tectonic plates. Yet, the dynamic and tectonic processes ruling their migration remain enigmatic. At the Rodrigues triple junction, the Southwest Indian Ridge lengthens northeastward in response to the unsteady linearity of the Southeast Indian Ridge–Central Indian Ridge dueling ridge system. This mechanism is episodically compensated by the southeastward propagation of the Central Indian Ridge and alternating stages of recession and progression of the Southeast Indian Ridge. This has led to an apparent length constancy of the first Southeast Indian Ridge segment over the past ca. 8 Ma. These multiple ridge propagation episodes, from northwest, southwest, and southeast, result in a net northeastward migration of the Rodrigues triple junction. Here, we suggest that its migration since ca. 8 Ma is a consequence of short-term readjustments of its plate boundaries induced by transitory motion changes of the Capricorn plate, driven by episodic push forces exerted from ephemeral captures of the Amsterdam–St. Paul plume tail by the Southeast Indian Ridge at the southeastern part of the Capricorn plate (77.3°E–78.6°E). [ABSTRACT FROM AUTHOR]

The driving processes responsible for producing the Central Atlantic Magmatic Province, the Large Igneous Province associated with end‐Triassic rifting of Pangea, remain largely debated. Because their compositions encompass most of the Central Atlantic basalt spectrum, tholeiites from southern Eastern North America are considered pivotal for identifying magma origins. New 176Hf/177Hf measurements for 201 Ma Eastern North American tholeiites dominantly record a local petrogenetic history. Their εHf ratios, corrected to an emplacement age of 201 Ma (−7.85 to +5.86), form a positive but shallowly sloped array slightly deviating from the terrestrial array on a εHf versus εNd diagram. Comparison of 176Hf/177Hf to other isotope ratios and trace elements helps to rule out several petrogenetic scenarios, particularly mixing of melts from global depleted or enriched mantle components. In contrast, partial melting of subduction‐metasomatized mantle can explain the parental magma composition for southern Eastern North America. Such metasomatism likely occurred during Paleozoic subduction around Pangea and may have been dominated by sediment‐derived fluid reactions. The observed 176Hf/177Hf versus 143Nd/144Nd array may reflect subsequent assimilation of lower continental crust, perhaps together with limited direct melting of recycled continental crust in the asthenosphere. The proposed recycling scenario does not specifically support or preclude a mantle plume origin for the Central Atlantic Magmatic Province but instead points toward the presence of a distinct local mantle source and crustal assimilation processes during magma transport. Detailed understanding of these local effects is needed in order to more accurately understand the origins of Large Igneous Provinces. Key Points: End‐Triassic tholeiites from Eastern North America were likely products of melting Paleozoic age, subduction‐metasomatized mantleDirect melting of recycled crustal rocks may also have occurred but cannot fully explain the tholeiite isotopic compositions observedSouthern Eastern North American tholeiites likely also experienced assimilation of lower continental crust, possibly intermediate granulite [ABSTRACT FROM AUTHOR]

The Central Atlantic Magmatic Province (CAMP) is a large igneous province (LIP) composed of basic dykes, sills, layered intrusions and lava flows emplaced before Pangea break-up and currently distributed on the four continents surrounding the Atlantic Ocean. One of the oldest, best preserved and most complete sub-provinces of the CAMP is located in Morocco. Geochemical, geochronologic, petrographic and magnetostratigraphic data obtained in previous studies allowed identification of four strato-chemical magmatic units, i.e. the Lower, Intermediate, Upper and Recurrent units. For this study, we completed a detailed sampling of the CAMP in Morocco, from the Anti Atlas in the south to the Meseta in the north. We provide a complete mineralogical, petrologic (major and trace elements on whole-rocks and minerals), geochronologic (40Ar/39Ar and U–Pb ages) and geochemical set of data (including Sr–Nd–Pb–Os isotope systematics) for basaltic and basaltic–andesitic lava flow piles and for their presumed feeder dykes and sills. Combined with field observations, these data suggest a very rapid (<0·3 Ma) emplacement of over 95% of the preserved magmatic rocks. In particular, new and previously published data for the Lower to Upper unit samples yielded indistinguishable 40Ar/39Ar (mean age = 201·2 ± 0·8 Ma) and U–Pb ages (201·57 ± 0·04 Ma), suggesting emplacement coincident with the main phase of the end-Triassic biotic turnover (c.201·5 to 201·3 Ma). Eruptions are suggested to have been pulsed with rates in excess of 10 km3/year during five main volcanic pulses, each pulse possibly lasting only a few centuries. Such high eruption rates reinforce the likelihood that CAMP magmatism triggered the end-Triassic climate change and mass extinction. Only the Recurrent unit may have been younger but by no more than 1 Ma. Whole-rock and mineral geochemistry constrain the petrogenesis of the CAMP basalts. The Moroccan magmas evolved in mid-crustal reservoirs (7–20 km deep) where most of the differentiation occurred. However, a previous stage of crystallization probably occurred at even greater depths. The four units cannot be linked by closed-system fractional crystallization processes, but require distinct parental magmas and/or distinct crustal assimilation processes. EC-AFC modeling shows that limited crustal assimilation (maximum c.5–8% assimilation of e.g. Eburnean or Pan-African granites) could explain some, but not all the observed geochemical variations. Intermediate unit magmas are apparently the most contaminated and may have been derived from parental magmas similar to the Upper basalts (as attested by indistinguishable trace element contents in the augites analysed for these units). Chemical differences between Central High Atlas and Middle Atlas samples in the Intermediate unit could be explained by distinct crustal contaminants (lower crustal rocks or Pan-African granites for the former and Eburnean granites for the latter). The CAMP units in Morocco are likely derived from 5–10% melting of enriched peridotite sources. The differences observed in REE ratios for the four units are attributed to variations in both source mineralogy and melting degree. In particular, the Lower basalts require a garnet peridotite source, while the Upper basalts were probably formed from a shallower melting region straddling the garnet–spinel transition. Recurrent basalts instead are relatively shallow-level melts generated mainly from spinel peridotites. Sr–Nd–Pb–Os isotopic ratios in the CAMP units from Morocco are similar to those of other CAMP sub-provinces and suggest a significant enrichment of the mantle-source regions by subducted crustal components. The enriched signature is attributed to involvement of about 5–10% recycled crustal materials introduced into an ambient depleted or PREMA-type mantle, while involvement of mantle-plume components like those sampled by present-day Central Atlantic Ocean Island Basalts (OIB, e.g. Cape Verde and Canary Islands) is not supported by the observed compositions. Only Recurrent basalts may possibly reflect a Central Atlantic plume-like signature similar to the Common or FOZO components. [ABSTRACT FROM AUTHOR]

Lying atop the relatively motionless Antarctic plate (velocity ~6.46mm a-1), the Crozet archipelago, midway between Madagascar and Antarctica, is a region of unusually shallow (1543-1756 m) and thickened oceanic crust (10-16.5 km), high geoid height, and deep low-velocity zone, which may represent the surface expression of a mantle plume. Here, new major and trace element data are presented for Quaternary alkali basalts of the subaerial eruptive stage of East Island, the most easterly and oldest island (~9 Ma) of the Crozet archipelago. Crystallization at uppermost mantle depths and phenocryst accumulation have strongly affected the parental magma compositions. Trace element patterns show a large negative K anomaly relative to Ta-La, moderate depletions in Rb and Ba with respect to Th-U, and heavy rare earth element depletions relative to light rare earth elements. These characteristics allow limits to be placed upon the composition and mineralogy of the mantle source of the magmas. The average trace element pattern of the East Island basalts can be matched by ~1.7% melting of a garnet-phlogopite-bearing peridotite source. The stability field of phlogopite restricts melting depths to lithospheric levels. The modelled source composition requires a multistage evolution in which the mantle has been depleted by melt extraction before being metasomatized by alkali-rich plume-derived melts. The depleted mantle component is inferred to be sourced from residual mantle plume remnants that stagnated at the melting locus owing to a weak lateral flow velocity inside the melting region, whose accumulation progressively forms a depleted lithospheric root above the plume core. Low-degree, alkali-rich melts are probably derived from the plume source. Such a mantle source evolution may be general to both terrestrial and extraterrestrial environments in which the lateral component velocity of the mantle flow field is extremely slow. [ABSTRACT FROM AUTHOR]

Regional axial depths, mantle Bouguer anomaly values, geochemical proxies for the extent of partial melting and tomographic models along the Southwest Indian Ridge (SWIR) all concur in indicating the presence of thicker crust and hotter mantle between the Indomed and Gallieni transform faults (TFs; 46°E and 52°20′E) relative to the neighbouring ridge sections. Accreted seafloor between these TFs over the past ∼10 Myr is also locally much shallower (>1000 m) and corresponds to thicker crust (>1.7 km) than previously accreted seafloor along the same ridge region. Two large outward facing topographic gradients mark the outer edges of two anomalously shallow off-axis domains on the African and Antarctic plates. Their vertical relief (>2000 m locally) and their geometry, parallel to the present-day axis along a >210-km-long ridge section, suggest an extremely sudden and large event dated between ∼8 (magnetic anomaly C4n) and ∼11 Ma (magnetic anomaly C5n). Asymmetric spreading and small ridge jumps occur at the onset of the formation of the anomalously shallow off-axis domains, leading to a re-organization of the ridge segmentation. We interpret these anomalously shallow off-axis domains as the relicts of a volcanic plateau due to a sudden increase of the magma supply. This event of enhanced magmatism started in the central part of the ridge section and then propagated along axis to the east and probably also to the west. However, it did not cross the Gallieni and Indomed TFs suggesting that large offsets can curtail or even block along-axis melt flow. We propose that this melting anomaly may be ascribed to a regionally higher mantle temperature provided by mantle outpouring from the Crozet hotspot towards the SWIR. [ABSTRACT FROM AUTHOR]

• Sills from Hank, Hodh and Kaarta basins are coeval to the peak activity of the CAMP. • CAMP basalts sourced from a crust-enriched asthenospheric mantle. • Melting of the mantle was favoured under a relatively thin lithosphere. • CAMP basalts are preferentially located at the edges of deep cratonic keels. • Cratonic keels exerted a control on the production and emplacement of CAMP magmas. Large Igneous Provinces (LIPs) are exceptionally voluminous magmatic events frequently related to continental break-up, global climate changes and mass extinctions. One interesting aspect of many LIPs is their spatial proximity to cratons, begging the question of a potential control of thick lithosphere on their emplacement. In this study, we investigate the relationship between the emplacement of the Central Atlantic Magmatic Province (CAMP) and the thick lithospheric mantle of the Precambrian cratons that formed the central portion of Pangea and are currently located on the continents surrounding the Central Atlantic Ocean. CAMP outcrops are frequently located over the margins of the thick cratonic keels, as imaged by recent tomographic studies, suggesting a role of lithosphere architecture in controlling magma genesis and emplacement. Here we focus on CAMP dykes and sills from the Hank, Hodh, and Kaarta basins in North-Western Africa (NW-Africa, Mali and Mauritania) emplaced at the edge of the Reguibat and Leo-Man Shields. The investigated intrusive rocks show compositions similar to most CAMP magmas, in particular those of the Tiourjdal geochemical group, limited to NW-Africa, and of the Prevalent group, occurring all over the CAMP. Geochemical modelling of CAMP basalts requires a Depleted MORB Mantle (DMM) source enriched by recycled continental crust (1-4%) and melting beneath a lithosphere of ca. 80 km in thickness. On the contrary, melting under a significantly thicker lithosphere (>110 km) does not produce magmas with compositions similar to those of CAMP basalts. This suggests that CAMP magmatism was likely favoured by decompression-induced partial melting of the upwelling asthenospheric mantle along the steep lithospheric boundaries of stable cratons. The architecture of the pre-existing lithosphere (i.e., the presence of stable thick cratonic keels juxtaposed to relatively thinner lithosphere) appears to have been a critical factor for localizing mantle upwelling and partial melting during extensive magmatic events such as in the CAMP. [ABSTRACT FROM AUTHOR]