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Continental flood basalt (CFB) provinces are products of the largest known volumetric eruptions on Earth (~104 km3), with individual flow fields commonly covering well over 10 000 km2 with a mean lava thickness of over 5 m. Studies focusing on the emplacement style of such lava flows have relied extensively on morphological observations and comparisons with modern lava flows and experimental analogs. In the present study, we compare the textures of flood basalt lavas with those from different eruption settings all over the world using data collected from pre-existing literature to gain detailed insights into the style of eruption. Comparison of crystal size distribution data indicates that the eruption style of CFBs is similar to those of modern-day fissure eruptions (e.g. Iceland). This matches inferences based on observations of morphology. We also use a 1D thermal model to estimate the depth-dependent cooling rates within a single lava lobe and test the validity of assumptions built into the formulation of these models for large scale flood basalt lavas. The results reveal that, on average, flood basalt lavas need to conductively cool much faster than we would expect (up to order of ~102 times faster) to match the textural observations. The model is also frequently unable to replicate the observed depth-wise relative variations in length with depth for CFB lavas. Furthermore, the calculated cooling rates from crystal shapes also do not match those calculated from crystal lengths, indicating the assumptions in cooling flow models need to be modified for large CFB flow fields. Given the large areas of CFB flow fields and the relatively long eruption times inferred for the emplacement of individual flow fields, we hypothesize that inflation of lobes and formation of new lobes via breakouts combined with variable eruption rates are key processes that are missing when modeling the cooling of these flow fields. Accounting for these processes is essential to derive accurate cooling rates, which is important to better understand the environmental impact CFBs have at the time of emplacement. [ABSTRACT FROM AUTHOR]

Continental large igneous provinces are among the largest magmatic events on Earth, characteristically manifesting at the surface as stacks of monotonous flood basalt lavas that form through a dynamic pattern of eruptive pulses separated by hiatuses. Such dynamic patterns may be difficult to detect from the composition of the lavas. Instead, lava crystal cargoes can be used to study how the eruption cycles inherent to continental large igneous provinces are moderated by episodic recharge and evacuation at multiple crustal levels. Here, we present a stratigraphically well-constrained series of 56 flood basalt flows from the Eocene Initial Phase of magmatic activity in East Africa. These flows and their crystal cargo permit temporal insight into the development of one of the youngest and best-preserved continental large igneous provinces. The stratiform mafic lavas exposed in northern Kenya consist of alternating aphyric and plagioclase-phyric lava packages consistent with periods of eruption punctuated by volcanic hiatus, where magmas stall and crystallize plagioclase at medium to shallow crustal levels. Plagioclase compositions (n  = 541) exhibit little intra-crystal or intra-sample compositional diversity. Intra-crystal equilibrium calculations for Sr and Ti indicate internal chemical equilibrium, requiring storage at high temperatures over a prolonged time interval (10 000–100 000 years). Using a series of seven interlinked partial crystal fractionation models under equilibrium conditions, we replicate the observed stratigraphic patterns in plagioclase composition. We find that the balance between recharge, evacuation, and diffusive equilibration within a shallow magmatic system controls the composition of plagioclase in these flood basalts. We conclude that the shallow fractionation system modulates eruptive cycles and thus constitutes a critical component in studies of continental large igneous provinces. [ABSTRACT FROM AUTHOR]

The Mannar Basin is a rift basin formed during the breakup of Gondwana, comprising sedimentary deposits from multiple cycles. Exploration for hydrocarbons has uncovered igneous sequences distributed throughout the basin's sedimentary sequences. These sequences exhibit geochemical characteristics, typical for flood basalts formed during a series of eruptions from 60 to 62 Ma. Previous studies have focused on the petroleum system, tectonostratigraphy, lithostratigraphy, and the paleo-environmental setting, therefore, little was known about the petrogenesis of this flood basalt sequence. This study investigates the petrogenesis of the flood basalt sequence, focusing on crystallization temperature, source magma characteristics, and the nature of magma fractional crystallization. Additionally, it examines the mineralogical characteristics, including clay minerals, of the interstratified sedimentary layers to interpret their origins—an area that has not been previously studied in depth. Petrographic thin sections were prepared from unwashed drill cuttings taken from a depth of 4000–4200 m in the Barracuda petroleum exploration well. A detailed petrographic study was conducted on these samples to investigate the petrogenesis. Additionally, electron probe microanalysis (EPMA) was performed to determine the mineral chemistry of the basalt and interstratified sedimentary rock samples. The basalts are primarily composed of plagioclase (An62-82) and clinopyroxene (mostly augite), with minor occurrences of orthopyroxene (En54-67) and ulvöspinel. Only the lower-most basalt layers (4200–4210 m) contain olivine (Fo56-71). High-Al orthopyroxenes were observed in the shallower sequence. Mineral zoning and mineral chemical variations record fractional crystallization of the mafic magma. Together, these minerals reflect a complex magmatic evolution, where, initially, high-temperature conditions prevailed, followed by differentiation and fractional crystallization; a transition from primitive to more evolved conditions. Geothermometric calculations indicate crystallization temperatures of the basalt varying from 1330 to 1340 °C, typically associated with mantle-derived magmas and representing high-temperature magmatic processes.The interlayered sedimentary rocks within the basalt sequence are dark-coloured and consist of weathered feldspar and clinopyroxenes, with minor quartz and calcite. Powder x-ray diffraction (XRD) analyses reveal the presence of clay minerals such as smectite, antigorite, attapulgite, and chlorite in these sedimentary rocks. While unpublished reports suggest that the interlayered rocks are sandstones and shales (based on gamma-ray log data), these analyses indicate that they are volcaniclastic sediments resulting from the weathering of individual layers of the flood basalt sequence after their eruption.

The Miocene Columbia River Basalt Group (CRBG) of the Pacific Northwest of the United States is the world's youngest and smallest large igneous province. Its earliest formations are the Imnaha, Steens, and now the Picture Gorge Basalt (PGB), and they were sourced from three different dike swarms exposed from SE Washington to Nevada to northcentral Oregon. PGB is often viewed to be distinct from the other formations, as its magmas are sourced from a shallow, relatively depleted, and later subduction-induced metasomatized mantle, along with its young stratigraphic position. It has long been known that the lowermost American Bar flows (AB1&2) of the Imnaha Basalt are chemically similar to those of the PGB, yet the Imnaha Basalt is generally thought to carry the strongest plume source component. These opposing aspects motivated us to revisit the compositional relationships between AB1&2 and PGB. Our findings suggest that tapping a shallow, variably depleted, and metasomatized mantle reservoir to produce earliest CRBG lavas occurred across the province, now pinpointed to ~17 Ma. Moreover, compositional provinciality exists indicating regional differences in degree of depletion and subduction overprint that is preserved by regionally distributed lavas, which in turn implies relatively local lava emplacement at this stage. [ABSTRACT FROM AUTHOR]

The Late Aptian Rajmahal Traps originated through Kerguelen-Plume-related volcanism at the eastern margin of the Indian Shield. Clinopyroxene and whole-rock thermobarometry reveals that the Rajmahal magmas crystallized at P-T conditions of ≤~5 kbar/~1100–1200 °C. These pressures correspond to upper crustal depths (≤~19 km). Modeling shows that the Rajmahal primary magmas were last in equilibrium with mantle at P-T conditions of ~9 kbar/~1280 °C. The corresponding depths (~33 km) are consistent with gravity data that indicate a high-density layer at lower crustal depths below an upwarped Moho. Thus, the high-density layer probably represents anomalous mantle. It is likely that the mantle-derived magmas accumulated below the upwarped Moho and were subsequently transported via trans-crustal faults/fractures to the upper crust where they evolved by fractional crystallization in small staging chambers before eruption. In the lower part of the Rajmahal plumbing system, buoyant melts from the Kerguelen Plume may have moved laterally and upward along the base of the lithosphere to accumulate and erode the eastern Indian lithospheric root. The Rajmahal plumbing system was probably shaped by tectonic forces related to the breakup of Gondwana. [ABSTRACT FROM AUTHOR]

Dichotomous high-Ti and low-Ti magmas are ubiquitous in large igneous provinces (LIPs). These magmas often form economically critical Fe–Ti oxide ores in layered intrusions via mechanisms that remain debated. To constrain the evolution of high-Ti and low-Ti basalts during fractionation, we performed stepwise equilibrium crystallization experiments at atmospheric pressure. We specifically aimed to quantify the influences of starting composition and oxygen fugacity (fO2) on phase stability, phase compositions, and the onset of silicate liquid immiscibility during cooling. Both types of magma crystallize similar phase assemblages at QFM (quartz–fayalite–magnetite thermodynamic equilibrium) and QFM + 2: olivine, clinopyroxene, plagioclase, Fe–Ti oxides, and whitlockite. Tridymite crystallizes late in experiments at QFM + 2. The starting composition exerts a strong influence on phase and melt compositions. High CaO and Al2O3 contents in the melt favor the early crystallization of plagioclase and enhance FeO enrichment before Fe–Ti oxide saturation. fO2 affects the composition and stability of Fe–Ti oxides, and high fO2 conditions may promote melt differentiation into the calc-alkaline field. Silicate liquid immiscibility occurs in both compositional trajectories, producing Fe-rich melt globules in equilibrium with Si-rich melts. Strong iron enrichment is not necessary for immiscibility to develop; unmixing also occurs in Fe depleted compositions. We propose a new parameterization to map the binodal surface in temperature-composition space that successfully fits the two-liquid field in experiments and natural immiscible compositions. Our results indicate that Fe–Ti oxide ores in layered intrusions associated with LIPs form by the segregation of Fe-rich melts and/or the accumulation of early crystallized Fe–Ti oxides during fractionation. [ABSTRACT FROM AUTHOR]

High‐temperature melting in mantle plumes produces voluminous eruptions that are often temporally coincident with mass extinctions. Paleocene Baffin Island lavas—products of early Iceland mantle plume activity—are exceptionally well characterized geochemically but have poorly constrained stratigraphy, geochronology, and eruptive tempos. To provide better geologic context, we measured seven stratigraphic sections of the volcanic deposits and collected paleomagnetic data from 38 sites in the lavas and underlying Cretaceous sediments (Quqaluit Fm.). The average paleomagnetic pole from this study does not overlap with the expected pole for a stable North American locality at 60 Ma, yet the data have sufficient dispersion to average out secular variation. After ruling out other possibilities, we find that the picrites were probably erupted during a polarity transition, over less than 5 kyr. If so, the average eruption interval was ∼67 years per flow for the thickest sequence of exposed lavas. We also calculate that the flood basalts had a minimum total volume of ∼176 km3 (excluding submerged lavas in Baffin Bay). This implies a minimum eruption rate of ∼0.035 km3 yr−1, which is similar to rates found in West Greenland lavas but less than rates found in larger flood basalts. Despite this, the Baffin and West Greenland lavas temporally correlate with the "End C27n event" (a period of ∼2°C global warming) and may be its underlying cause. Plain Language Summary: Lavas erupted about 60 million years ago on Baffin Island, Canada, are well studied by geochemists because they are thought to derive from the Iceland mantle plume. However, the age and eruptive frequencies of the flows are not well known. We report geologic observations from seven packages of lava flows and present paleomagnetic data from 38 sites. We calculate that at least 0.035 km3 of lava was being produced every year during the volcanic episode. Based on the paleomagnetic data, all the flows erupted in less than five thousand years with an average of 67 years between eruptions. This is consistent with results from similar lavas in West Greenland, which likely erupted at the same time. For unknown reasons, the Baffin Island and West Greenland eruptions did not cause a mass extinction but may have caused a global warming event. Key Points: New stratigraphic and paleomagnetic data are presented from flood basalts on Baffin Island, CanadaThe exposed lavas erupted in less than 5,000 years, with an average eruption interval of 67 yearsMinimum long‐term eruption rates were less than rates found in larger flood basalt provinces [ABSTRACT FROM AUTHOR]

[Display omitted] • We report the first reliable age data for Karoo rift magmatism in Mozambique. • Our U/Pb ages prove Karoo rift magmatism started during ca. 185 – 190 Ma. • Eruption of 182–178 Ma rift magmas released abundant volatiles into atmosphere. New U-Pb ages for zircons constrain the duration of silicic magmatism and timing of coeval mafic magmatism across the main rift zone of the Karoo large igneous province in Mozambique. Our 190 ± 2 Ma, 188.4 ± 0.9 Ma, 181.7 ± 1.0 Ma, 180 ± 3 Ma, 178 ± 2 Ma and 172 ± 2 Ma ages support periodicity of Karoo magmatism previously inferred from 40Ar/39Ar age data. The ∼ 190–188 Ma ages confirm early onset of magmatism and the ∼ 182–178 Ma ages correlate the bimodal volcanic successions of the Lower Zambezi and the Movene Formation with widespread silicic magmatism across the rift zone. The ∼ 172 Ma age corresponds to waning magmatic activity. The age range and Hf isotopic compositions of zircons indicate up to ∼9 Ma lifespan for the Jurassic silicic magma chambers and suggest that the ∼2700–400 Ma xenocrysts represent crustal sources of the host rocks. The available chronological data indicate that the ∼183 Ma main phase magmatism was largely confined within the main Karoo and Kalahari basins and that the preceding and subsequent phases were mainly associated with the Karoo rift zone. Judging from geochemical literature, different kinds of magmas were erupted during the successive magmatic phases. We calculate from published geochemical data that the mafic main phase magmas were relatively poor in CO 2 and SO 2 and the lava stacking patterns point to low eruption rates, which suggests that degassing of sedimentary wall-rocks of intrusions probably triggered the coeval Pliensbachian-Toarcian extinction. In contrast, the mafic late phase magmas were rich in CO 2 and SO 2 and at least some of the lavas indicate high eruption rates. We propose that efficient degassing from widespread mafic magmatism and explosive eruption of over 30,000 km3 of silicic magmas in the Karoo rift zone linked the ∼182–178 Ma late phase magmatism with contemporaneous global biosphere crises. [ABSTRACT FROM AUTHOR]

Abstract High‐temperature melting in mantle plumes produces voluminous eruptions that are often temporally coincident with mass extinctions. Paleocene Baffin Island lavas—products of early Iceland mantle plume activity—are exceptionally well characterized geochemically but have poorly constrained stratigraphy, geochronology, and eruptive tempos. To provide better geologic context, we measured seven stratigraphic sections of the volcanic deposits and collected paleomagnetic data from 38 sites in the lavas and underlying Cretaceous sediments (Quqaluit Fm.). The average paleomagnetic pole from this study does not overlap with the expected pole for a stable North American locality at 60 Ma, yet the data have sufficient dispersion to average out secular variation. After ruling out other possibilities, we find that the picrites were probably erupted during a polarity transition, over less than 5 kyr. If so, the average eruption interval was ∼67 years per flow for the thickest sequence of exposed lavas. We also calculate that the flood basalts had a minimum total volume of ∼176 km3 (excluding submerged lavas in Baffin Bay). This implies a minimum eruption rate of ∼0.035 km3 yr−1, which is similar to rates found in West Greenland lavas but less than rates found in larger flood basalts. Despite this, the Baffin and West Greenland lavas temporally correlate with the “End C27n event” (a period of ∼2°C global warming) and may be its underlying cause.

Volcanic flood basalt eruptions have been linked to or are contemporaneous with major climate disruptions, ocean anoxic events, and mass extinctions throughout at least the last 400 M years of Earth's history. Previous studies and recent history have shown that volcanically‐driven climate cooling can occur through reflection of sunlight by H2SO4 aerosols, while longer‐term climate warming can occur via CO2 emissions. We use the Goddard Earth Observing System Chemistry‐Climate Model to simulate a 4‐year duration volcanic SO2 emission of the scale of the Wapshilla Ridge member of the Columbia River Basalt eruption. Brief cooling from H2SO4 aerosols is outweighed by dynamically and radiatively driven warming of the climate through a three orders of magnitude increase in stratospheric H2O vapor. Plain Language Summary: Volcanic flood basalt eruptions are linked to mass extinctions and climate change through Earth's history. Using model experiments, we show that a massive release of sulfur dioxide gas, as would happen in such an eruption, can warm the climate through feedback mechanisms linked to an increase in stratospheric water vapor. Key Points: Volcanic emission of SO2 produces warming through climate feedbacksThe warming is driven by a three orders of magnitude increase in stratospheric H2O vaporClimate cooling by H2SO4 aerosols persists for less time than the eruption itself [ABSTRACT FROM AUTHOR]

Voluminous silicic (rhyolitic–dacitic) eruptive units overlie mafic lavas in many continental flood basalt (CFB) provinces of the world. These silicic units comprise lavas as well as pyroclastic deposits, including lava-like ignimbrites, and many were erupted from identified calderas. Silicic volcanic units are widespread in the northern and northwestern parts of the Deccan Traps CFB province of India, particularly the Saurashtra peninsula. In the Alech Hills in Saurashtra, whose geology is poorly known, basal mafic lavas are intruded by a ring dyke of granophyre with a diameter of 30 km. Inside this ring, silicic eruptive units are exposed. The lowest and most extensive unit is a grey, feldspar-phyric, ≥ 3.8 km3 flood rhyolite lava. This is overlain successively by rheomorphic and lava-like ignimbrites, eutaxitic ignimbrites, and non-welded tuffs and breccias. Based on a combination of geological features, such as the large granophyre ring dyke, the effusive and explosive rhyolite volcanism, fault-controlled arcuate and annular ridges of the rhyolites, possible caldera-collapse mesobreccias, and widespread hydrothermal alteration, we recognize the Alech Hills as a giant (30 km-diameter, 660 km2) effusive-explosive silicic caldera. A recently published CA-ID-TIMS 206Pb/238U date of 65.765 ± 0.018 Ma (2σ) for the granophyre ring dyke suggests that the Alech Hills caldera formed contemporaneously with the K/Pg boundary mass extinction, and may have significantly contributed to it. [ABSTRACT FROM AUTHOR]

We present a first stratigraphy of the flood basalt succession in eastern Wollo province, northern Ethiopian plateau, based on detailed field logging. This study was initiated to resolve outstanding issues in the region regarding the timing and extent of flood volcanism, assisting a wider correlation of stratigraphic sequences across the Ethiopian plateau. Our approach involved construction of stratigraphic sections from six selected gorge localities having ~ 100% exposure. Individual flow thickness, lithology, and sequence were recorded at each locality. Features common to all localities indicate a single magmatic plumbing system for the mapped area. Three formations are identified and named, and linked to published Oligocene radiometric ages from neighboring areas. These formations are from base to top: Teri Basalt, the main phase of flood basalt emission, is conformably overlain by the Wegeltena Rhyolite, composed of silicic ignimbrites dated at ~ 30.2 Ma. Upon this rests a thin bed of conglomerate, sandstone, and mudstone representing a ~ 3 Ma episode of volcanic quiescence. At the top of the sequence lies the Kon Basalt, dated at 27.8–26.7 Ma. Comparison of this new stratigraphy with other Oligocene sequences on the northern plateau reveals significant variations in lithology and age range, with implications for how the Ethiopian flood basalt province was constructed. More work is required in seeking the fissure vents and their geometry. [ABSTRACT FROM AUTHOR]

The western Indian volcanic rifted margin, and its large-scale tectonic feature called the Panvel flexure, formed at 62.5 Ma during the late stages of Deccan Traps flood volcanism. We present a geological account of late-stage (≤ 62.5 Ma) Deccan volcanism and plutonism in the relatively poorly studied Thane–Vasai region in the Panvel flexure zone. The study area shows west-dipping basaltic sequences up to hundreds of meters thick, overlain by pyroclastic deposits of various types. The volcanic units are intruded by gabbro plutons, and all these units are in turn intruded by dykes of varied compositions (including tholeiitic basalt, lamprophyre, and granophyre). There are also early tholeiitic dykes, some of which may be feeders to the basaltic sequence. We focus on the gabbro intrusions and provide extensive petrographic and mineral chemical data on them. The gabbros are tholeiitic, and of considerable interest in commonly containing interstitial silicic melts (granophyre or silicic glass). One of the intrusions, the Chena pluton, shows clear outcrop transitions from gabbro, and gabbro with interstitial granophyre, to transitional gabbro-granophyre, and then to a distinct upper zone of granophyre and microgranite. Granophyre is common in mafic intrusions in continental flood basalt provinces of the world (e.g., the Palisades Sill and the Skaergaard Intrusion), where its genesis is ascribed to mechanisms such as fractional crystallisation, liquid immiscibility, or crustal melting, typically based on geochemical data. The Chena gabbro outcrops are valuable in providing direct evidence for a fractional crystallisation origin of the granophyres (and silicic glasses) found in the Thane–Vasai gabbro intrusions, with which the mineral chemical compositions are also consistent. [ABSTRACT FROM AUTHOR]

Abstract Deccan Traps flood basalt volcanism affected ecosystems spanning the end‐Cretaceous mass extinction, with the most significant environmental effects hypothesized to be a consequence of the largest eruptions. The Rajahmundry Traps are the farthest exposures (~1,000 km) of Deccan basalt from the putative eruptive centers in the Western Ghats and hence represent some of the largest volume Deccan eruptions. Although the three subaerial Rajahmundry lava flows have been geochemically correlated to the Wai Subgroup of the Deccan Traps, poor precision associated with previous radioisotopic age constraints has prevented detailed comparison with potential climate effects. In this study, we use new 40Ar/39Ar dates, paleomagnetic and volcanological analyses, and biostratigraphic constraints for the Rajahmundry lava flows to ascertain the timing and style of their emplacement. We find that the lower and middle flows (65.92 ± 0.25 and 65.67 ± 0.08 Ma, ±1σ systematic uncertainty) were erupted within magnetochron C29r and were a part of the Ambenali Formation of the Deccan Traps. By contrast, the uppermost flow (65.27 ± 0.08 Ma) was erupted in C29n as part of the Mahabaleshwar Formation. Given these age constraints, the Rajahmundry flows were not involved in the end‐Cretaceous extinction as previously hypothesized. To determine whether the emplacement of the Rajahmundry flows could have affected global climate, we estimated their eruptive CO2 release and corresponding climate change using scalings from the LOSCAR carbon cycle model. We find that the eruptive gas emissions of these flows were insufficient to directly cause multi‐degree warming; hence, a causal relationship with significant climate warming requires additional Earth system feedbacks.

The physical volcanology of widespread rhyolites and dacites overlying flood basalt lavas in the northwestern and northern parts of the 65.5-Ma Deccan Traps, India, is poorly known. We show that these are not lava flows but high-grade (welded and rheomorphic) to extremely high-grade (lava-like) ignimbrites deposited by pyroclastic density currents. Evidence for this interpretation includes the following: (i) flat, planar contacts with the underlying basalts and absence of basal brecciated zones; (ii) pervasive millimeter-to-centimeter-scale flow banding; (iii) parataxitic textures indicating very high degrees of compaction and welding; (iv) strong rheomorphic deformation, producing folds of diverse geometries and sizes showing overprinting relationships, with common tight-isoclinal and sheath (eye) folds that are sometimes refolded into F2 and even F3 folds; (v) curvilinear fold hinges with elongation lineations varying from transverse to subparallel to the fold axes; (vi) local boudinage and autobrecciation in flow-banded glassy tuffs; (vii) common and abundant spherulites and lithophysae; (viii) intimate association of tuff and vitrophyre at millimeter to tens-of-meter scales; and (ix) vitroclastic textures showing highly flattened and stretched glass shards and pumice fiamme wrapping around phenocrysts. Whereas rheomorphic and lava-like ignimbrites dominate, some non-welded and welded (eutaxitic) ignimbrites also occur. Voluminous rhyolites and dacites in many flood basalt provinces of the world are recognized as high-grade to extremely high-grade ignimbrites, and the Deccan is no exception. This Deccan explosive silicic volcanism may have significantly contributed to the K/Pg boundary mass extinctions, if contemporaneity can be established by future geochronological work. [ABSTRACT FROM AUTHOR]

Angria Bank, a submerged plateau with coral reefs, is located off the central-west coast of India. Biologically, the bank attracts scientific community for its coral formations. But geologically, origin and tectonic setting of this feature are not established yet due to scarcity of geological and geophysical data. Newly acquired bathymetry and magnetic data along with existing geophysical data have allowed us to determine crustal structure and tectonic evolution of the Angria Bank. The entire geological setup of the bank consists of 34 km long water plateau (average water depth ~ 20 m), and two prominent spurs extending to its western side. The area of water plateau and entire geological setup are 365 km2 and 1460 km2, respectively. The bank is characterized by two prominent magnetic low with a relative high in the middle. Integrated gravity and magnetic models revealed that flood basalt has carpeted the entire geological structure which later acted as a foundation for coral growth. The crust below the bank is continental in nature and underplated by high-density magmatic material. Moho is almost flat and lies at a depth of ~ 27 km. The results of 3D Euler deconvolution suggest that the study area is characterized by two types of linear trend viz. NE–SW to NNE–SSW and NW–SE. These trends are interpreted mostly as basement faults but at few places, they might be associated with sills/dykes. The geological setup of the bank is fault-bounded and comprised of two horst structure (interpreted as spurs) trending NE–SW to NNE–SSW. Integrated interpretation of the geophysical data revealed that the Angria Bank is an isolated feature, evolved during rifting between India and Seychelles-Laxmi Ridge in the Late Cretaceous. [ABSTRACT FROM AUTHOR]

The Quaternary Hantangang River Volcanic Field (HRVF) in the central part of the Korean Peninsula hosts unique volcanic landforms associated with fluvial topography. The volcanic field consists of a series of basaltic lava flows, ca. 0.1 to 0.6 Ma old, which originated from two source vents in DPRK (Democratic People's Republic of Korea; North Korea) and flowed along a 110 km long stretch of paleo-river channels to the terminus in the northern part of ROK (Republic of Korea; South Korea). Afterwards, the lavas were eroded by the re-established river system, producing an array of precipitous exposures of columnar-jointed lavas along the channel walls, a number of waterfalls, and other fluvial landforms. The Hantangang River National Geopark was established in 2015 based on the volcanic geoheritage values of the region. Eighteen geosites in the geopark show high geodiversity and can be divided into five major groups of geotopes, including (1) volcanic landforms, (2) fluvial landforms, (3) pre-Quaternary basement rocks, (4) Quaternary deposits associated with archeological ruins, and (5) warm spring. Several geosites are related to ecological, cultural, and historical features. Here, we provide field-based documentations of the geoheritage values of these geotopes, regarding (1) the processes of terrestrial lava flows along a river valley, (2) landform evolution through the interplay between lava flows and fluvial erosion, and (3) the relationship between geological processes and ecological, historical, cultural, and archeological values. The geoheritage values of the Quaternary HRVF may justify for a UNESCO Global Geopark status in the future. [ABSTRACT FROM AUTHOR]

Mantle melting dynamics of the Central Atlantic Magmatic Province (CAMP) is constrained from new platinum group element (PGE), gold (Au), rare earth element (REE), and high field strength element (HFSE) data and geochemical modelling of flood basalts in Morocco. The PGE are enriched similarly to flood basalts of other large igneous provinces. The magmas did not experience sulphide saturation during fractionation and were therefore fertile. The CAMP is thus prospective for PGE and gold mineralization. The Pt/Pd ratio of the Moroccan lavas indicates that they originated by partial melting of the asthenospheric mantle, not the subcontinental lithospheric mantle. Mantle melting modelling of PGE, REE and HFSE suggests the following: (1) the mantle source for all the lavas was dominated by primitive mantle and invariably included a small proportion of recycled continental crust (<8%); (2) the mantle potential temperature was moderately elevated (c. 1430°C) relative to ambient mantle; (3) intra-lava unit compositional variations are probably a combined result of variable amounts of crust in the mantle source (heterogeneous source) and fractional crystallization; (4) mantle melting initially took place at depths between c. 110 and c. 55 km and became shallower with time (c. 110 to c. 32 km depth); (5) the melting region appears to have changed from triangular to columnar with time. These results are best explained by melting of asthenospheric mantle that was mixed with continental sediments during the assembly of Pangaea, then heated and further mixed by convection while insulated under the Pangaea supercontinent, and subsequently melted in multiple continental rift systems associated with the breakup of Pangaea. Most probably the CAMP volcanism was triggered by the arrival of a mantle plume, although plume material apparently was not contributing directly (chemically) to the magmas in Morocco, nor to many other areas of CAMP. [ABSTRACT FROM AUTHOR]

Elephanta Island, located near Mumbai in the western Deccan Traps, is composed of subaerially erupted tholeiitic lava flows and dykes, with no evolved or pyroclastic rocks. In contrast, Deccan volcanism in Mumbai includes subaerial and subaqueous lava flows, intrusions, and pyroclastics, of highly varied composition. The Mumbai and Elephanta sequences, being in the Panvel flexure zone along the western Indian rifted continental margin, dip prominently seaward. The bulk of the Mumbai sequence stands dated at 62.5 Ma, contemporaneous with continental breakup between the Seychelles and Laxmi Ridge-India, voluminous offshore magmatism, and Panvel flexure formation. We have obtained whole-rock 40Ar/39Ar ages of 66–65 Ma on six Elephanta tholeiites (representing two lava flows and four dykes) and a picrite dyke. An ankaramite dyke yields a whole-rock 40Ar/39Ar age of 61.6 ± 0.4 Ma (2σ). These ages imply that the bulk of the Elephanta sequence was formed rapidly, well before continental breakup, and is contemporaneous with (and potentially a part of) the main Deccan sequence in the Western Ghats escarpment to the east. The younger age of the ankaramite dyke shows that the total duration of Elephanta magmatism was not <3.5 Myr and possibly as much as 6 Myr. Interestingly, the age of the Elephanta ankaramite dyke overlaps with that of the Powai ankaramite flow in Mumbai, suggesting the dyke to be a potential feeder of that flow. • Tholeiitic flows and dykes on Elephanta Island, on the western Indian rifted margin • Field, petrographic, whole-rock geochemical and 40Ar/39Ar age data presented • 66–65 Ma ages for seven samples indicate intense pre-breakup magmatism. • Probably stratigraphically continuous with the Western Ghats sequence • A younger ~62 Ma ankaramite dyke may have fed a lava flow in Mumbai. [ABSTRACT FROM AUTHOR]

The breakup of Africa from South America is associated with the emplacement of the Paraná-Etendeka flood basalt province from around 134 Ma and the Tristan da Cunha plume. Yet many additional volcanic events occur that are younger than the main pulse of the Paraná-Etendeka and straddle the rift to drift phases of the main breakup. This contribution reports on new geochronological constraints from the Angolan part of the African Margin. Three coastal and one inland section have been sampled stretching across some 400 Km, with 39Ar/40Ar, U-Pb and Palaeontology used to provide age constraints. Ages from the new data range from ~100 to 81 Ma, with three main events (cr. 100, 91 and 82–81 Ma). Volcanic events are occurring within the Early to Late Cretaceous, along this part of the margin with a general younging towards Namibia. With the constraints of additional age information both onshore and offshore Angola, a clear younging trend at the early stages of rift to drift is recorded in the volcanic events that unzip from North to South. Similar age volcanic events are reported from the Brazilian side of the conjugate margin, and highlight the need to fully incorporate these relatively low volume volcanic pulses into the plate tectonic breakup models of the South Atlantic Margin. [ABSTRACT FROM AUTHOR]

Abstract This paper takes its inspiration from Karl W. Butzer's course on the Human Use of Landforms at the University of Chicago. It builds upon that concept through an exploration of regional settlement patterns and landforms in the Deccan volcanic province of west-central India. The first section develops a conceptual framework for analyzing human adjustment to landforms on regional, settlement, and site scales. The second section employs that framework to analyze four major landform-settlement configurations in the Deccan from antiquity to the end of the eighteenth century. The Satavahana kingdom (ca. 100 BCE to 200 CE) had a strong southeast to northwest alignment along the Godavari River. Their capital city of Paithan was located at a navigable sacred ford across the river (tirtha), which was linked with upstream confluences (sangams), tanks (kunds), mountain passes (ghats), and port cities on the Arabian Sea. Subsequent Hindu dynasties (ca. 850–1300 CE) shifted from fluvial landforms to a north-south alignment along steep mesa escarpments and buttes in the central Deccan that provided defensive fortress and cave temple sites. Sultanate and Mughal forces expanded the urban footprint on nearby plateau lands at sites protected by surrounding mesas (ca. 1330–1700 CE). These cities were supported by local watershed runoff and long distance water channels. The final precolonial phase of Deccan settlement entailed a shift from the semiarid central plateaus to humid headwaters of the Western Ghats, whose buttes and scarps provided sites for scores of forts controlled by the founder of the Maratha empire Chhatrapati Shivaji in the seventeenth century. Maratha success led to development downstream at the capital city of Pune (1627–1803 CE), located at a river confluence flanked by mesas, which combined the strategies of previous periods. Over two millennia these four distinct, yet intersecting, patterns of human-landform relations have shaped an evolving geocultural region on the Deccan plateau that deserves comparison with other flood basalt regions. Highlights • Karl W. Butzer opened up an important line of historical geomorphology on the human use of landforms. • Human use of landforms encompasses defensive, commercial, and sacred, as well as natural resource-driven processes. • The Deccan Volcanic Plateau has supported four major precolonial landform-settlement configurations over the past 2000 years. • Collectively, these configurations have shaped the formation of a coherent geocultural region. [ABSTRACT FROM AUTHOR]

The Cretaceous (Cenomanian, ~96 Ma) basaltic rocks of the Strand Fiord Formation of the Sverdrup Basin of the Canadian Arctic Archipelago, Nunavut, Canada, are a part of the High Arctic large igneous province. The basaltic suite reaches a thickness of almost 1,000 m on Axel Heiberg Island in its depocentre and over 700 m at the studied section. The rocks are variably fractionated tholeiitic basalts, which are geochemically similar to many other continental flood basalts, particularly to low Ti basalts of flood basalt provinces. Geochemical as well as Sr (87Sr/86Srinitial ~ 0.7045 to 0.7067) and Nd (ƐNd(t) ~ +1.3 to +4.3) isotopic signatures of the basalts were inherited during partial melting of spinel peridotite of an ancient subcontinental lithospheric mantle, which was modified around 0.7–0.9 Ga by a metasomatic event. The melting generating the Cretaceous basalts was probably triggered by a mantle plume but was also associated with basin rifting and stretching. There is evidence of plume‐induced doming and uplift of the crust prior to and during the eruption of the basalts as documented by the progression from marine sedimentation to subaerial/lacustrine and then back to marine sedimentation in the Sverdrup Basin centre. The basalts represent parts of the Early Cretaceous igneous province that is dispersed around the Arctic Ocean due to the opening of the Canada Basin, which is inferred to be related to a mantle plume. [ABSTRACT FROM AUTHOR]

The ca. 2770–2690 Ma Fortescue Group of the Pilbara Craton in Western Australia represents one of the oldest known large igneous provinces (LIP) on Earth. Existing and new data show that the Fortescue LIP lavas have relatively evolved Nd isotopic compositions and are enriched in highly-incompatible elements. This is exemplified by mafic lavas of the 2775 Ma Mt Roe, 2740 Ma Kylena, 2715 Ma Bunjinah-Maddina and 2690 Ma Jeerinah Formations, with Th/Ti ca. 25, Th 13–5 ppm and εNd i around −4 (High-Th suite). Basalts and rare Al-depleted komatiites of the 2724–2715 Ma Pyradie Formation show more primitive compositions, with Th/Ti ca. 4, Th ca. 3–0.5 ppm and εNd i of 0 to −1 (Intermediate-Th suite). In this paper, we show that: (1) Parent magmas to all Fortescue LIP lavas were probably komatiitic; (2) Fortescue lavas contain 3.5–3.3 Ga xenocrystic zircons that correlate with the known age of Pilbara crust; and (3) the widespread enriched compositions in the Fortescue lavas require contributions to the ultramafic parent magmas from highly-enriched 3.7–3.5 Ga continental crust of the type available in the underlying Pilbara Craton. These results indicate that enriched chemical/isotopic compositions of the Fortescue mafic lavas result from large-scale crustal assimilation rather than enriched mantle/lithospheric sources. This implies that komatiite magmas were emplaced through Eo- to Paleoarchean enriched crust for ca. 90 Ma, via either (1) a long-lived source of high-temperature mantle melts such as a mantle plume; or (2) multiple mantle plumes, possibly represented by the 2775–2763 Ma Mt Roe and 2724–2715 Ma Tumbiana-Pyradie-Maddina-Bunjinah basalts. This study demonstrates that mafic magmas, with arc-like geochemical character and intermediate to felsic continental crustal compositions, can form via contamination of plume magmas by existing (local) crustal reservoirs, and the employment of modified lithospheric sources or enriched mantle is not required. [ABSTRACT FROM AUTHOR]