Abstract The Northern Carnarvon Basin (NCB) located on Australia's North West Shelf hosts an extensive (∼40 000 km 2) intrusive igneous complex related to Mesozoic rifting and break-up. Using an extensive suite of modern 3D seismic reflection surveys, we have mapped this intrusive system across the NCB. We identify three predominant intrusion morphologies: stacked sheets of large interconnected sill intrusions (up to ∼170 km long) and smaller (8–30 km long) isolated, strata concordant intrusions, which often interact with normal faults emplaced into deltaic sedimentary rocks, and variably sized (10–40 km long) saucer-shaped intrusions emplaced into marine shales, spread across seven zones (geographically constrained groups of intrusions of a specific morphology). We consider the zones’ margin-parallel orientation, suggesting control by subcrustal extensional processes during rifting, and the variation in intrusion morphology between these zones, suggesting a dominant control by host rock mechanical properties. We integrate previous work with our observations, constraining emplacement to between the Kimmeridgian and Valanginian, coinciding with key phases of margin evolution. Finally, we assess the impact of this intrusive complex on local petroleum systems. There is likely little to no adverse impact on source rock maturation or reservoir contamination by CO 2 , but there is a spatial dissociation between the location of groups of intrusions and the gas fields, particularly in the Exmouth Plateau. This suggests that migrating hydrocarbons may be blocked, baffled and/or redirected by emplaced igneous rocks.

Abstract Measurements of surface deformation provide valuable insight into sub-volcanic processes operating before, during and after eruptions. Here, we investigate the drivers behind the 2020–21 effusive–explosive episode at La Soufrière volcano in St Vincent using Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data between 2018 and 2021, and geodetic modelling. We observe inflation up to six months before the start to the effusive phase, which continued as the dome extruded. Once the eruption transitioned to the explosive phase, the volcano rapidly deflated, the bulk happening within the first three days of explosions. Our analytical modelling distinguishes three pressure source depth ranges contributing to this eruptive episode: 16–20, c. 6 and <1 km. Deformation data are therefore in line with a vertically extensive magmatic system being tapped pre- and syn-eruption with interaction between deep and shallow reservoirs by ascending magma batches. The combined use of GPS and InSAR proved to be instrumental for constraining the deformation field active during this eruptive episode. The direction of future geodetic monitoring at La Soufrière should therefore utilize both techniques with a view towards maximizing coverage while making up for shortfalls in station upkeep and variations in satellite overpass regularity.

Abstract The 2020–21 eruption of La Soufrière, St Vincent began with extrusion of a viscous lava dome, which was destroyed upon transition to a major explosive phase. Here we present petrological data to reconstruct the processes leading up to these events. Bulk-rock SiO 2 contents range from 52.8 to 55.4 wt%, classifying the lava and the subsequent scoria as basaltic andesite, the latter being slightly more mafic. Macrocrystal chemistry and modes (plag–cpx–opx–tmt–ol) and crystallinity (45–50 vol%) are largely identical for both phases of the eruption. Pyroxenes are homogenous and precipitated mostly from andesitic melts. Conversely, plagioclase shows strong normal zonation resulting from magma ascent and stalling at multiple crustal levels. Clinopyroxene thermobarometry reveals that crystallization predominantly took place between 8 and 13 km depth at temperatures of 997 − 35 + 18 ∘ C . A lack of evidence for mafic recharge and changes in volatile content and the omnipresence of xenoliths, suggests pre-eruptive destabilization of an andesitic–dacitic melt pocket that disrupted and entrained antecedent mush. Olivine diffusion profiles show that this interaction preceded the onset of eruption. Low dissolved sulfur contents (≤270 ppm S) place constraints on the total SO 2 gas release. Melt–mush disruption appears to be a dominant driver of eruptions at La Soufrière. Supplementary material: Supplementary figures and tables, as well as electronic data tables, are available at https://doi.org/10.6084/m9.figshare.c.6484877

Abstract The Early to Late Cretaceous Mundwara alkaline complex (comprising the Musala, Mer and Toa plugs) displays a broad spectrum of alkaline rocks closely associated in space and time with the Deccan large igneous province in NW India. Petrology and Nd–Sr isotopic data on the two youngest and altogether compositionally different lamprophyre dykes of the Mundwara alkaline complex are presented in this paper to understand their petrogenesis and also to constrain the magmatic processes responsible for generation of the rock spectrum in the complex (pyroxenite, picrite ankaramite, carbonatite, shonkinite, olivine gabbro, feldspathoidal and foid-free syenite). The two lamprophyre dykes occurring in the Mer and the Musala hills are referred to as basaltic camptonite I and camptonite II, respectively. The basaltic camptonite I is highly porphyritic and contains olivine, clinopyroxene and magnetite macrocrysts embedded within the groundmass of microphenocyrsts composed of clinopyroxene, phlogopite, magnetite and feldspar. Camptonite II, however, with a more or less similar texture, contains amphibole, biotite, magnetite and clinopyroxene within the microphenocrystic groundmass of amphibole, biotite, apatite and feldspar. Pyroxenes are chemically zoned and display corrosion of the cores, revealing that they are antecrysts developed during the early stages of magma evolution and later on inherited by more evolved magmas. The mineral chemistry and trace element composition of the lamprophyres reveal that fractional crystallization was a dominant process. Early segregation of olivine + Cr-rich clinopyroxene + Cr-spinel from a primary hydrous alkali basalt within a magmatic plumbing system is inferred, which led to the generation of basaltic camptonitic magma (M1) forming the Mer hill lamprophyre. Subsequently, progressive fractionation of pyroxene and Fe–Ti oxides from the basaltic camptonitic (M1) magma generated camptonitic (M2) magma forming the Musala hill lamprophyre. Both lamprophyre dykes on the Sr–Nd isotopic array reflect plume-type asthenospheric derivation, which largely corresponds to the Réunion plume and other alkaline rocks of the Deccan large igneous province. Our study brings out a complex sequence of processes such as crystal fractionation, accumulation and corrosion in the magmatic plumbing system involved in the generation of the Mundwara alkaline complex.

Abstract Volcanic eruptions, despite causing large-scale disasters, also provide important natural resources and are an effective way to understand the Earth's internal structure and its evolution. Herein, a comprehensive review is presented on recent progress in geophysical imaging of the structure and origin of intraplate volcanoes in Mainland China. We primarily focus on the Changbaishan, Wudalianchi, Tengchong, Hainan and Ashikule volcanoes as they are currently active and hence pose potential hazards during future eruptions, particularly the Changbaishan volcano. The Changbaishan and Wudalianchi volcanoes are widely believed to be caused by the dehydration of the stagnant Pacific slab in the mantle transition zone along with wet upwelling in the big mantle wedge. There are a number of different views regarding the formation mechanism of the Tengchong volcano. Some studies suggest that a big mantle wedge structure is also present under eastern Tibet, and the Tengchong volcano has a deep origin, similar to volcanism in NE China. Others suggest that the Tengchong volcano is caused by a local and shallow process. Most tomographic studies suggest that the Hainan volcano is a hotspot, and its track has been located in SE China by combining seismological, geochemical and numerical modelling data. A gap exists between the subducted Indian Plate and the Tarim lithosphere beneath the Ashikule volcano, which provides a channel for asthenospheric upwelling to give rise to intraplate volcanism in the Ashikule basin. The interactions of lithospheres may produce shear heating of the subcontinental lithospheric mantle, which can generate localized melting. This process has been proposed as an explanation for the intraplate volcanism in Ashikule.