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According to the data of comprehensive precision research, the spatial distribution and mineral composition were revealed, the petrographic and petrochemical features, and the genetic and practical significance of the Babynska effusive-pyroclastic suite tuffs of the continental flood basalts of Western Volyn were clarified in connection with the copper content. The thicknesses and hypsometry of the relief of the paleosurface of the pyroclastic formations of the Babynska suite were analyzed and the important elements of its vertical and lateral structure (by area) were clarified, the real picture of which is reflected in the constructed maps of the thicknesses and relief of the paleosurface of the pyroclastic formations of the suite, in particular, on the Ratn3--Kamin--Kashyrsk Area. The formation of the Babynska suite tuffs in the regime of gravitational deposition of pyroclastic material with the accumulation of tuff deposits at the stage of incomplete solidification of volcanic material and the formation of coarse, non-rhythmic layering, without clear signs of redeposition, i.e. of volcanomictic origin, has been proven. Differences in the mineral composition and petrochemistry of tuffs of different colors: gray-green and red-brown were found. Emphasis is placed on the enrichment of native copper in tuffs of gray-green color and possible explanations for this correlation are proposed. The obtained results from a genetic point of view provide important information for paleovolcanogenic and paleogeographical reconstructions, in practical terms they contribute to the improvement of the copper bearing prospects of volcanogenic layers of the continental flood basalts and can be proposed for use by production organizations of the geological profile. [ABSTRACT FROM AUTHOR]

A post-rift Aptian magmatism is recorded in a 500-m-thick sequence of basalts interbedded with marls in the Bacalhau oil and gas field in Santos Basin, SE Brazil. This magmatic section is within the so-called pre-salt sequence of Santos Basin that comprises the major oil and gas reserves of Brazil. This is the first publication of systematic petrological and geochronological data for the Aptian magmatism in Santos. Whole-rock Ar–Ar integrated ages obtained for these basalts are 116.93 ± 0.22 Ma, 116.16 ± 0.10 Ma, 115.21 ± 0.13 Ma and 109.95 ± 0.20 Ma and. As such, they are younger than the rift-related Camboriú basalts in Santos as well as the Paraná-Etendeka basalts and related dike swarms. The Santos basalts comprise a low-Ti tholeiitic suite with La/Nbn (2.7–4.2) and La/Ybn (4.2–5.9) ratios typical of continental flood basalt provinces. The basalts vary in MgO content but show no evidence for cogeneticity by differentiation processes. Lithogeochemical data showed that the Aptian basalts in Santos cannot be related with either the low-Ti, Esmeralda and Gramado suites in Paraná-Etendeka or the low-Ti Lumiar, Serrana, and Costa Azul suites in the Serra do Mar Dike Swarm on the basis of lithogeochemical data. No geochemical and isotopic correlation can be done with the Aptian, Alagoas basalts in Campos basin as well. Initial (115 Ma) isotope ratios (Sr: 0.705747–0.706804; εNd: −5.9 to −2.8; 206Pb/204Pb: 17.61–18.67; 207Pb/204Pb: 15.47–15.58; 208Pb/204Pb: 38.17–38.39; εHf: + 0.3 to −8.2) indicate derivation from a EM1 mantle component in the SCLM. Modal batch partial melting modelling showed that melting occurred within the garnet stability zone. We propose a geodynamic model for the Aptian in Santos in which the melting of the SCLM is related with either the presence of the Tristan da Cunha mantle plume in Aptian time below Santos or stretching of different portions of the blob-rich SCLM itself. This stretching is due to the remaining heat advected from Tristan during the voluminous Early Cretaceous magmatism that gave rise to the Paraná-Etendeka CFB. [ABSTRACT FROM AUTHOR]

• HSE data for high-3He/4He picrites formed during opening of north and south Atlantic. • Large degree partial melts from peridotite mantle with chondritic Os isotope character. • Atlantic LIP show evidence for deep mantle contributions during ocean basin formation. • Recycled components in high-3He/4He OIB consistent with lower degrees of partial melting. Osmium isotope and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance data are reported for picrites and basalts from the ∼132 Ma Etendeka large igneous province (LIP) and the ∼60 Ma North Atlantic Igneous Province (NAIP). Picrite dykes of the Etendeka LIP have HSE abundances and 187Os/188Os (0.1276 to 0.1323; γOs i = -0.5 to +3.1) consistent with derivation from high-degree partial melting (>20 %) of a peridotite source with chondritic to modestly supra-chondritic long-term Re/Os. High-3He/4He NAIP picrites from West Greenland represent large-degree partial melts with similarly elevated HSE abundances and 187Os/188Os (0.1273 to 0.1332; γOs i = -0.2 to +3.9). Broadly chondritic Os isotope ratios have also been reported for the ∼132 Ma Paraná LIP and the ∼201 Ma Central Atlantic Magmatic Province (CAMP). Consequently, LIP associated with Atlantic Ocean opening derive, at least in part, from partial melting of peridotite mantle distinct from the depleted mantle associated with mid-ocean ridge basalt volcanism. Modern locations with high-3He/4He (>25R A) include ocean island basalts (OIB) from Ofu (Samoa), Loihi (Hawaii) and Fernandina (Galapagos) in the Pacific Ocean, and from Iceland, which is considered the modern manifestation of NAIP magmatism. Unlike Etendeka and NAIP picrites, these modern OIB have Sr-Nd-Pb-Os isotopes consistent with contributions of recycled oceanic or continental crust. The lower degree of partial melting responsible for modern high-3He/4He OIB gives higher proportions of fusible recycled crustal components to the magmas, with radiogenic 187Os/188Os and low-3He/4He. The high-3He/4He, incompatible trace element-depleted mantle component in both LIP and OIB therefore also has long-term chondritic Re/Os, which is consistent with an early-formed reservoir that experienced late accretion. Atlantic LIP (CAMP; Paraná-Etendeka; NAIP) provide geochemical evidence for a prominent role for mantle plume contributions during continental break-up and formation of the Atlantic Ocean, a feature hitherto unrecognized in other ocean basin-forming events. [ABSTRACT FROM AUTHOR]

The Precordillera mafic–ultramafic belt (PMUB), located in central-western Argentina, comprises mafic and ultramafic bodies interlayered and/or in tectonic contact with marine siliciclastic units. Whole-rock, mineral geochemistry and Nd–Sr isotope analyses performed in magmatic rocks suggest a relatively different spatial and temporal evolution along the belt. The southern PMUB (south of 32° S) evolved as an intra-continental rifted margin with an enriched mid-ocean-ridge basalt (E-MORB) tholeiitic to alkaline magmatism, to a proto-ocean basin (the Cuyano proto-ocean) with tholeiitic normal-MORB geochemical signature. Based on neodymium model ages (TDM), the magmatic activity started during the late Neoproterozoic Era and continued into the early Palaeozoic Era. Instead, the northern PMUB (28–32° S) evolved as an intra-continental rifted margin with dominant tholeiitic E-MORB to continental flood basalt (CFB) magmatism during the early Palaeozoic Era. ϵNd values (+3.4 to +8.4), rare earth element trends and high-field-strength element systematics, together with an estimated potential mantle temperature of c. 50–100°C above ambient mantle, suggest the PMUB magmatism derived from an enriched mantle source related to the effect of a rising plume linked to the Iapetus Ocean opening. In particular, TDM estimations of 600–550 Ma agree with reported magmatism in central to southern Appalachians. The magmatism in the PMUB, and those registered in the Neoproterozoic Catoctin Formation and in the Southern Oklahoma Aulacogen in the conjugated Laurentian margin, seem to be contemporaneous, sharing a similar plume-enriched mantle source. In this context, the E-MORB signature identified along the PMUB can be described as a plume-distal ridge tectonic setting over an extended margin. [ABSTRACT FROM AUTHOR]

Volcanism in the western part of the Arabian plate resulted in one of the largest alkali basalt provinces in the world, where lava fields with sub-alkaline to alkaline affinity are scattered from Syria and the Dead Sea Transform Zone through western Saudi Arabia to Yemen. After the Afar plume emplacement (∼30 Ma), volcanism took place in Yemen and progressively propagated northward due to Red Sea rifting-related lithospheric thinning (initiated ∼27–25 Ma). Few lava fields were emplaced during the Mesozoic, with the oldest 200 Ma volcanic activity recorded in northern Israel. We report results from volcanic pipes in the Marthoum area, east of Harrat Uwayrid, where over a hundred pipes occupy a stratigraphic level in the early Ordovician Saq sandstones. Most of them are circular or elliptical features marked by craters aligned along NW-SE fractures in the sandstone resulting from phreatomagmatic explosions that occurred when rising magma columns came in contact with the water table in the porous sandstone host. These lavas have Sr-Pb-Nd-Hf isotopic compositions far from the Cenozoic Arabian alkaline volcanism field, being considerably more enriched in Nd-Hf and Pb isotopes than any other Arabian Plate lava ever reported. New K-Ar dating constrains their age from Late Cretaceous to Early Eocene, thus anticipating the Afar plume emplacement and the Red Sea rift. Basalt geochemistry indicates that these volcanic eruptions formed from low-degree partial melting of an enriched lithospheric mantle source triggered by local variations in the asthenosphere-lithosphere boundary. This mantle source has a composition similar to the HIMU-like enriched isotopic component reported in the East African Rift and considered to represent the lowermost lithospheric mantle of the Nubian Shield. The generated melt, mixed in different proportions with melt derived from a depleted asthenosphere, produces the HIMU-like character throughout the Cenozoic Arabian alkaline volcanism. Although apparently hidden, this enriched lithospheric component is therefore ubiquitous and widespread in the cratonic roots of the African and Arabian subcontinental mantle.

We find that Large Igneous Province (LIP) volcanism, mostly continental flood basalts (CFBs), along with the largest extraterrestrial impacts show significant correlations with mass-extinction events in the Phanerozoic geologic record. The ages of the 6 major marine mass extinctions (≥ 40% extinction of genera) of the last 541 My–the end-Ordovician (∼444 Ma), late Devonian (∼372 Ma), end-Guadalupian (∼259 Ma), end-Permian (∼252 Ma), end-Triassic (∼201 Ma), and end-Cretaceous (66 Ma) extinctions are significantly correlated with high-quality U Pb zircon and 40Ar/39Ar ages of 6 continental flood basalts (CFBs) –the Cape St. Mary's, Viluy, Emeishan, Siberian, CAMP, and the Deccan Basalts, The mass extinctions also coincide with stratigraphic Hg anomalies representing proxy evidence for the synchrony of the extinctions and the basaltic volcanism. Furthermore, ages of 6 minor extinction events (15% to 25% extinction of marine genera) at ∼ 94 Ma, 124 Ma, 134 Ma, 183 Ma, 290 Ma and 510 Ma also coincided with 6 well-dated CFB eruptions (the Madagascar, HALIP, Paranå/Etendeka, Karoo/Ferrar, Panjal and Kakarindji Basalts) and with associated Hg anomalies. At least 3 minor extinction events (at ∼ 145 Ma, 215 Ma and 227 Ma) apparently occurred close to times of oceanic plateau (OP) volcanism in the Pacific Ocean (Shatsky Rise, Angayucham and Wrangellia Basalts). Major and minor marine mass-extinction episodes at times of CFB eruptions were commonly accompanied by ocean anoxic/euxinic events, increased ocean acidity, high atmospheric p CO 2 , increases in UV-B radiation from ozone-layer destruction, and pulses of high ambient temperatures, providing potential immediate causes for the mass extinctions. The 4 most recent major marine extinctions (∼66 Ma, 201 Ma, 252 Ma, and 260 Ma) and a minor extinction (∼290 Ma) coincided with the ages of CFBs and with concurrent mass extinctions of non-marine vertebrates, indicating global-scale volcanogenic environmental crises on land and in the sea. The age of the abrupt end-Cretaceous major mass extinction (66 Ma) overlaps with the age of the Deccan eruptions, but is exactly coincident with the very large Chicxulub impact (180 km diameter crater), possibly the largest terrestrial impact of the last ∼3 By. The ages of the 3 next largest well-dated Phanerozoic terrestrial impact craters (≥100 km in diameter), the Popigai, Morokweng and Manicouagan craters, capable of causing widespread environmental effects, are concurrent with the ages of minor extinction events at ∼37 Ma, 145 Ma and 215 Ma. The significant correlations and the predicted severe environmental consequences of these major volcanic and impact events are very convincing that 12 CFB eruptions, at least 3 oceanic plateau eruptions, and the 4 largest impacts were involved with recognized biotic mass-extinction episodes of the last 541 My, and leave little room for alternate primary causes of the extinctions. • We find that the age of 15 pulses of Large Igneous Province (LIP) volcanism, mostly continental flood basalts (CFBs), and related severe climatic effects are significantly correlated with the ages of mass-extinction events in the Phanerozoic geologic record. • The four largest impact craters of the last 541 My are significantly correlated with the ages of four of the mass extinction events at ∼36, 66, 145, and 215 Ma. • Our results confirm the idea that the mass extinctions in the Phanerozoic were related to the catastrophic climatic effects of LIP volcanism and of the largest extraterrestrial impact. [ABSTRACT FROM AUTHOR]

The Gulf of Mannar and adjoining Cauvery basin to the north between India and Sri Lanka are associated with a failed rift, which initiated during the late Jurassic to early Cretaceous as a precursor to the breakup of East Gondwana. Despite the occurrence of igneous rocks that can be noted in seismic profiles, offshore, and deep seated occurrence of those have lead only to the limited understanding of igneous activity in the Mannar basin. Rock cuttings recovered in the Barracuda exploratory well in the Mannar basin shows approximately 700 m thick basalt rock sequence interlayered with sediments at a depth of 3500–4200 m below mean sea level. Here, we analyzed samples recovered from the Barracuda well for major and trace element composition. Major and trace element data suggest that the basalts were crystallized from two different degrees of partial melts from a similar source. Chondrite normalized rare earth element (REE) patterns indicate that the basalts are similar to continental flood basalt, though they show a distinct Ba positive anomaly. Importantly, supported with previously available K–Ar data, we decipher that these basalts are contemporaneous with the Deccan traps. Rifting between Seychelles and India which had occurred at ~62 Ma approximately 3.5 Ma after the main Deccan eruption is synchronous with the Barracuda volcanism suggesting coeval rifting between Seychelles–India and India–Sri Lanka. Thus, our data suggest simultaneous rifting between Seychelles–India and India–Sri Lanka. Large plate reorganizations that took place during this time period in the Indian Ocean have likely caused consequent passive rifting in the Mannar basin. [ABSTRACT FROM AUTHOR]

The temporal and spatial variations of Late Paleozoic basaltic lavas in Baoshan, the northern part of a Gondwana-derived micro-continental block called Sibumasu, are important for Gondwana reconstruction. Magmatic zircon crystals from three selected dolerite dykes in the Baoshan region yield U-Pb ages from ~295 to ~310 Ma. These new ages, together with previous zircon U-Pb ages for this type of rock, define a protracted (~30 myr) episode of basaltic magmatism from ~310 to 280 Ma in a small area of this region, which is inconsistent with the typical temporal-spatial distribution of mantle plume magmatism. The trace element compositions of the Baoshan dolerite dykes and associated lavas are similar to arc basalts as well as continental flood basalts worldwide, showing light REE enrichments and negative Nb-Ta anomalies. Mixing calculations using the Sr-Nd-Hf isotope data of the Baoshan mafic rocks indicate that their intriguing trace element characteristics can be explained by contamination of mantle-derived magmas with crustal materials. Our new data, together with the lack of Late Paleozoic are-related calcalkaline rocks and granitoids in the Sibumasu block and other contemporaneous Gondwana-derived micro-continental blocks, strongly support the premise that the 310–280 Ma basalts and dolerites in the Baoshan region are the products of continental rift-related magmatism rather than arc magmatism. Based on the temporal correlation of the 310–280 Ma rift-related magmatism in several related Gondwana-derived micro-continents (Sibumasu, South Qiangtang, Lhasa and Himalaya), plus other independent constraints such as paleoclimate biotas and paleolatitudes from the literature, we provide an improved model for the configuration of the Gondwana supercontinent in the Early Permian. Based on the results from this study, we conclude that further investment in the exploration of magmatic Ni-Cu sulfide deposits associated with the 310–280 Ma mafic-ultramafic intrusions in northern Baoshan and the other related Gondwana-derived micro-continental blocks is warranted. Unlabelled Image • The C–P basaltic magmatism in Baoshan lasted for ~30 myr (310–280 Ma). • It does not show a hot spot track related to mantle plume activity. • It provides evidence for rift-related magmatism in northern Gondwana. • It places Sibumasu in the north side of the trans-Cimmerian rift zone. • The related mafic-ultramafic intrusions have potential for Ni-Cu deposits. [ABSTRACT FROM AUTHOR]

Like many continental flood basalt (CFB) provinces in the world, the source mantle compositions (peridotites or pyroxenites) of the Emeishan CFB province in SW China are still debated. We have used the combination of olivine O isotopes determined in situ using SIMS and trace element abundances measured in situ using LA-ICP-MS to address this fundamental problem. The newly discovered picrites in the Emeishan CFB province at Yumen are used in this study. In addition, we have also analyzed primitive olivine phenocrysts with known O isotope ratios from four other picrite occurrences (Maoniuping, Tanglanghe, Wuguijing and Wulongba) in the Emeishan CFB province for trace element abundances. Based on whole rock compositions the picrite samples from Wulongba belong to the low-Ti group (Ti/Y < 500) and those from the other locations belong to the high-Ti group (Ti/Y > 500). Mineral chemical data reveal that the two different groups of picrites can be distinguished by using Ti/Al of olivine phenocrysts and Cr-spinel inclusions enclosed in olivine. Specifically, the high-Ti picrite group is characterized by 10Ti/Al (molar) >0.9 and >0.5 for olivine phenocrysts and Cr-spinel inclusions, respectively. In the mantle source discrimination diagrams based on olivine 100Mn/Fe versus 100Ni/Mg or 100Ca/Fe, both groups of picrites plot between the suggested fields of peridotite and pyroxenite mantle sources. In the same type of diagrams based on olivine Mn/Zn and 10000Zn/Fe, both groups of picrites plot exclusively in the fields for a peridotite mantle source. The mean δ18O value of olivine phenocrysts from the Yumen high-Ti picrites is 5.19 ± 0.25‰ (1σ, n = 35), which is significantly lower than that for the Wulongba low-Ti picrites (5.6 ± 0.15‰) but is similar to values (5.1 ± 0.15 to 5.3 ± 0.15‰) for the high-Ti picrites from elsewhere (Maoniuping, Talanghe and Wuguijing) in the Emeishan CFB province. The mean δ18O values of olivine phenocrysts from the Emeishan high-Ti picrites at different locations are all within the range of typical mantle olivine values (5.1 ± 0.3‰). Based on these results, we conclude that the high-Ti picrites in the Emeishan CFB province were primarily derived from a modally enriched peridotite mantle source. Our new olivine Zn-Mn-Fe data are consistent with the view that the Wulongba low-Ti picrites were derived from a lithospheric peridotite mantle source. Unlabelled Image • High-Ti and low-Ti picrites can be distinguished by 10Ti/Al in Cr-spinel and olivine. • Olivine Mn/Zn and Zn/Fe indicate a peridotite mantle source for Emeishan picrites. • Primitive olivine phenocrysts of Emeishan high-Ti picrites all have mantle-like δ18O. • No evidence from olivine to support a pyroxenite mantle source for Emeishan picrites. [ABSTRACT FROM AUTHOR]

Highlights • New 40Ar/39Ar age of 135.9 ± 1.2 Ma and Sr–Nd–Pb isotopes for previously undated flow of Bunbury Basalt. • >80% of Cretaceous WA magmatism synchronous with breakup of eastern Gondwana at 137–136 Ma. • Kerguelen mantle plume under Greater India at 137–136 Ma cannot be origin for Bunbury Basalt. • Breakup of eastern Gondwana not caused by a thermochemical plume. • Volatile enrichment during ca. 550–500 Ma Kuunga Orogeny instead facilitated breakup. Abstract The link between mantle plumes and continental breakup remain a topic of debate. Here, a new 40Ar/39Ar age of 135.9 ± 1.2 Ma (2 σ) and previous ages from the Bunbury Basalt – lava flows that are part of the Greater Kerguelen large igneous province (LIP) – reveal that >80% of magmatism in the southern Perth Basin was concomitant with the continental breakup of eastern Gondwana at ca. 137–136 Ma. New and existing isotope geochemical data show that only lithospheric and depleted asthenospheric sources were melted to form the Bunbury Basalt and most other early, ca. 147–124 Ma magmatic products part of the Greater Kerguelen LIP. All lines of evidence strongly point towards passive continental breakup of eastern Gondwana, including the restriction of 147–124 Ma magmatism to continental rifts, the lack of excess oceanic magmatism in this period and the >1000 km distance between the Kerguelen plume underneath Greater Indian lithosphere and the breakup nexus. It is not possible to reconcile the influence of a thermochemical plume with the observed geochemical, spatial and geochronological information. Instead, we posit that eastern Gondwana breakup occurred because it was proximal to the former suture zone associated with the ca. 550–500 Ma Kuunga Orogeny between Indo–Australia and Australo–Antarctica. Enrichment of the mantle with volatiles associated with subduction during the Kuunga Orogeny permitted partial melting when the continental crust was sufficiently attenuated in the Early Cretaceous. Repeated and protracted rifting of Greater India from Australo–Antarctic since the mid-Paleozoic eventually led to the rupture of the continental lithosphere and to mafic magmatism at ca. 137–136 Ma, approximately along the position of the former suture zone, without the influence of a mantle plume. [ABSTRACT FROM AUTHOR]

Continents influence the mantle's convective wavelength and the heat flow escaping from the planet's surface. Over the last few decades, many numerical and analytical studies have contributed to the debate about whether the continents can warm up the subcontinental mantle or not and if they do, then to what extent? However, a consensus regarding the exact nature and magnitude of this correlation between continents and elevated temperatures in the subcontinental mantle remains to be achieved. By conducting a systematic parameter study using 2‐D global mantle convection simulations with mobile continents, we provide qualitative and quantitative observations on the nature of this correlation. In our incompressible and compressible convection models, we observe the general processes of downwellings bringing cold material into the mantle along continental margins and a subsequent buildup of warm thermal anomalies underneath the continents. We compute the amplitude and degree of this correlation using spectral decomposition of the temperature and composition fields. The dominant degree of correlation evolves with time and changes with continental configuration. Using simple empirical fits, we observe that this correlation decreases with increasing core temperature, number of continents, internal heating, or decreasing reference viscosity. We also report simple regressions of the time dependence of this correlation. Additionally, we show that decompression melting as a result of a mantle upwelling or small‐scale sublithospheric convection leads to voluminous volcanism. The emplacement of this dense basalt‐eclogite material breaks the continents apart and destroys the correlation. Key Points: Correlation decreases with increasing core temperature, number of continents, internal heating, or decreasing reference viscosityDownwellings along continental margins increase thermal contrast between subcontinental and suboceanic mantleDecompression melting leads to basaltic crust production, which breaks the continents and destroys the correlation [ABSTRACT FROM AUTHOR]

The Florianópolis Dyke Swarm is located in Santa Catarina Island, comprising also the adjacent continental area, and belongs to the Paraná Magmatic Province (PMP). The dyke outcrops in the island are 0.1–70 m thick and most of them are coast-parallel (NE-SW trending), with subordinate NW-SE trending. The vast majority of the dykes has SiO 2 varying from 50 to 55 wt% and relatively high-Ti (TiO 2 > 3 wt%) contents and these rocks were divided using the criteria commonly used to distinguish the different magma-types identified in the volcanic rocks from the PMP. The Urubici dykes (Sr > 550 μg/g) are the most abundant and some of them experienced crustal contamination reaching to 10%, as evidenced by low P 2 O 5 /K 2 O (0.30–0.21), high (Rb/Ba) PM (1.0–2.2), and radiogenic Sr and Pb isotope compositions ( 87 Sr/ 86 Sr i up to 0.70716 (back to 125 Ma) and 206 Pb/ 204 Pb m up to 19.093). The Pitanga (Sr < 550 μg/g) and the basaltic trachyandesite dykes are less abundant and almost all of them were also substantially affected by at least 15% of crustal assimilation, evidenced by high (Rb/Ba) PM (up to 2.6) and Sr ( 87 Sr/ 86 Sr i = 0.70737–0.71758) and Pb ( 206 Pb/ 204 Pb m = 18.446–19.441) isotope ratios, as well as low P 2 O 5 /K 2 O values (0.30–0.18). The low-Ti (TiO 2 < 2 wt%) dykes are scarce and show a large compositional variability (SiO 2 : 50.4–64.5 wt%), with similar geochemical characteristics of the low-Ti volcanic rocks (Gramado-Palmas) from southern PMP, although the most primitive dykes show hybrid characteristics of Ribeira and Esmeralda magmas. The presence of granitic xenoliths with border reactions and dykes with diffuse contacts indicate that crustal contamination probably occurred by assimilation from re-melted the host rocks. Considering only the high-Ti Urubici dykes that were not affected by crustal contamination, the Sr, Nd and Pb isotope mixing modelling indicates the participation of a heterogeneous metasomatized (refertilized) subcontinental lithospheric mantle (SCLM). This mantle source was originated by partial melting of a depleted sublithospheric mantle (DMM – Depleted Mantle MORB), which was hybridized by addition of pyroxenite (< 5%) and carbonatite (up to 2%) melts. The isotope mixing modelling also points to a significant participation (up to 50%) of Archean SCLM, not evidenced in the mantle sources of the northern PMP high-Ti Pitanga flows (dominated by Neoproterozoic SCLM). [ABSTRACT FROM AUTHOR]

Archean and Proterozoic subcontinental lithospheric mantle (SLM) is compared using 83 similarly incompatible element ratios (SIER; minimally affected by % melting or differentiation, e.g., Rb/Ba, Nb/Pb, Ti/Y) for >3700 basalts from ten continental flood basalt (CFB) provinces representing nine large igneous provinces (LIPs). Nine transition metals (TM; Fe, Mn, Sc, V, Cr, Co, Ni, Cu, Zn) in 102 primitive basalts (Mg# = 0.69-0.72) from nine provinces yield additional SLM information. An iterative evaluation of SIER values indicates that, regardless of age, CFB transecting Archean lithosphere are enriched in Rb, K, Pb, Th and heavy REE(?); whereas P, Ti, Nb, Ta and light REE(?) are higher in Proterozoic-and-younger SLM sources. This suggests efficient transfer of alkali metals and Pb to the continental lithosphere perhaps in association with melting of subducted ocean floor to form Archean tonalite-trondhjemite-granodiorite terranes. Titanium, Nb and Ta were not efficiently transferred, perhaps due to the stabilization of oxide phases (e.g., rutile or ilmenite) in down-going Archean slabs. CFB transecting Archean lithosphere have EM1-like SIER that are more extreme than seen in oceanic island basalts (OIB) suggesting an Archean SLM origin for OIB-enriched mantle 1 (EM1). In contrast, OIB high U/Pb (HIMU) sources have more extreme SIER than seen in CFB provinces. HIMU may represent subduction-processed ocean floor recycled directly to the convecting mantle, but to avoid convective homogenization and produce its unique Pb isotopic signature may require long-term isolation and incubation in SLM. Based on all TM, CFB transecting Proterozoic lithosphere are distinct from those cutting Archean lithosphere. There is a tendency for lower Sc, Cr, Ni and Cu, and higher Zn, in the sources for Archean-cutting CFB and EM1 OIB, than Proterozoic-cutting CFB and HIMU OIB. All CFB have SiO2 (pressure proxy)-Nb/Y (% melting proxy) relationships supporting low pressure, high % melting resembling OIB tholeiites, but TM concentrations do not correlate with % melting. Thus, the association of layered intrusion (plutonic CFB) TM deposits with Archean terranes does not appear related to higher metal concentrations or higher percentages of melting in Archean SLM. Other characteristics of these EM1-like magmas (e.g., S2 or O2 fugacity) may lead to element scavenging and concentration during differentiation to form ore deposits. [ABSTRACT FROM AUTHOR]

Isotopic compositions of continental flood basalts are essential to understand their genesis and to constrain the character of their mantle sources. Because of potential crustal contamination, it needs to be evaluated if and to which degree these basalts record original isotopic signals of their mantle sources and/or crustal signatures. This study examines the Sr, Nd, Hf, and Pb isotopic compositions of the late Cenozoic Xinchang–Shengzhou (XS) flood basalts, a small-scale continental flood basalt field in eastern China. The basalts show positive correlations between 87 Sr/ 86 Sr and 143 Nd/ 144 Nd, and negative correlations between 143 Nd/ 144 Nd and 176 Hf/ 177 Hf, which deviate from compositional arrays of crustal contamination and instead highlight variations in magmatic recharge intensity and mantle source compositions. The lava samples formed by high-volume magmatic recharge recorded signals of recycled sediments in the mantle source, which are characterized by moderate Ba/Th (91.9–106.5), excess 208 Pb/ 204 Pb relative to 206 Pb/ 204 Pb, and excess 176 Hf/ 177 Hf relative to 143 Nd/ 144 Nd. Thus, we propose that magmatic recharge buffers the original isotopic compositions of magmas against crustal contamination. Identifying and utilizing the isotope systematics of continental flood basalts generated by high volumes of magmatic recharge are thus crucial to trace their mantle sources. [ABSTRACT FROM AUTHOR]

The link between the Kerguelen large igneous province and several moderately-voluminous magmatic domains emplaced on continental crust near the relict triple junction of eastern Gondwana remains tentative. In particular, linking Sr–Nd–Pb isotopic ratios of the 90,000 km 2 submerged Naturaliste Plateau at the relict triple junction of eastern Gondwana to the Kerguelen LIP were difficult due to previous age estimates of ca. 100 Ma. Sericite hydrothermal plateau ages as old as 127.6 ± 0.6 Ma indicate that the volcanism on the plateau began at or prior to ca. 128 Ma, which is > 25 m.y. older than previous estimations. These ages are closely matched by the then-nearby ca. 140–130 Ma Comei, 137–130 Ma Bunbury, 124 Ma Wallaby Plateau and 118–117 Ma Rajmahal-Bengal-Sylhet magmatic provinces. The Sr–Nd–Pb isotopic characteristics of the majority of these ca. 140–117 Ma circum-eastern Gondwana magmatic provinces display only source contributions from the depleted asthenosphere and lithosphere with negligible contribution from the Kerguelen mantle plume. The Comei Province shows a direct plume-related melt signature, probably because it sits directly in the center of the modeled plume head position at 140–130 Ma. We suggest that the Kerguelen mantle plume provided the additional heat necessary to melt the asthenosphere and lithosphere of the circum-eastern Gondwanan magmatic provinces. Only after the motion of the Kerguelen plume head into the nascent Indian Ocean at ca. 100–95 Ma does a significant melt contribution from the Kerguelen mantle plume become evident in the isotopic signature, a signal that persists until the present-day. Despite differences in source contributions over time, it is clear that the Kerguelen mantle plume is necessary for the production of all the circum-eastern Gondwana magmatic domains, which we propose should be referred to as the Greater Kerguelen Large Igneous Province. [ABSTRACT FROM AUTHOR]

North Atlantic Igneous Province (NAIP) lavas host olivine with the highest 3 He/ 4 He ever measured for terrestrial igneous rocks (up to 50 R A , or 4 He/ 3 He = ~ 15,300). The relationship of high- 3 He/ 4 He with Pb isotope compositions close to the terrestrial geochron and 143 Nd/ 144 Nd plausibly consistent with supra-chondritic mantle Sm/Nd in Baffin Island and West Greenland lavas has been interpreted to reflect an ancient ‘non-chondritic’ mantle source signature. Alternatively, assimilation of continental crustal rocks with unradiogenic Pb isotope compositions and low 143 Nd/ 144 Nd, into magmas with high- 3 He/ 4 He, and derived from variably depleted mantle sources, could impart similar geochemical signatures. Radiogenic and stable isotope data for NAIP lavas are consistent with origins as melts from upper mantle sources that contain low- 18 O/ 16 O recycled lithosphere and/or hydrothermally altered crust, or that have experienced pervasive contamination by crustal gneisses. Olivines from NAIP lavas with 3 He/ 4 He spanning from 8 to 48 R A have δ 18 O ranging from 3.5 to 5.5‰. These compositions are consistent with sources of ambient mantle and low-δ 18 O recycled lithosphere, or with concomitant crustal assimilation and He-loss during fractional crystallization. Limited assimilation (≤ 1%) of incompatible element rich crustal gneisses with low 206 Pb/ 204 Pb and 143 Nd/ 144 Nd by melts from variably depleted mantle sources can explain Nd-Pb isotope compositions of Baffin Island and West Greenland picrites. Icelandic lavas provide supporting evidence that the ancestral mantle plume responsible for generating NAIP magmatism sampled variably enriched and depleted mantle, with no evidence for ancient non-chondritic mantle sources. Pervasive crustal contamination and partial melting of heterogeneous mantle sources, generated by plate tectonic processes, can account for the compositions of continental flood basalts (CFB), without the requirement of a non-chondritic terrestrial reservoir. Combined with evidence that the 142 Nd/ 144 Nd composition of the bulk silicate Earth is due to nucleosynthetic S -process deficits in chondrite meteorites, these observations cast doubt that NAIP lavas sampled a non-chondritic mantle source with Sm/Nd higher than in chondrites. If short-lived radiogenic (e.g., 146 Sm- 142 Nd, 182 Hf- 182 W) isotope anomalies are found in CFB, they must either reflect assimilation of isotopically anomalous crustal materials, or partial melting of early-formed mantle heterogeneities produced by differentiation and late accretion. [ABSTRACT FROM AUTHOR]

Atmospheric CO 2 levels and global climate are regulated on geological timescales by the silicate weathering feedback. However, this thermostat has failed multiple times in Earth's history, most spectacularly during the Cryogenian (c. 720–635 Ma) Snowball Earth episodes. The unique middle Neoproterozoic paleogeography of a rifting, low-latitude, supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo. Under these primed conditions, the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation. Weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios ( δ 13 C ) of Neoproterozoic seawater due to their elevated P contents. In order to test these hypotheses, we have compiled new and previously published Neoproterozoic Nd isotope data from mudstones in northern Rodinia (North America, Australia, Svalbard, and South China) and Sr isotope data from carbonate rocks. The Nd isotope data are used to model the mafic detrital input into sedimentary basins in northern Rodinia. The results reveal a dominant contribution from continental flood basalt weathering during the ca. 130 m.y. preceding the onset of Cryogenian glaciation, followed by a precipitous decline afterwards. These data are mirrored by the Sr isotope record, which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early–middle Neoproterozoic ocean, including a pulse of unradiogenic Sr input into the oceans just prior to the onset of Cyrogenian glaciation. Hence, our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average δ 13 C of seawater in the Neoproterozoic and to the initiation of the first (Sturtian) Snowball Earth. [ABSTRACT FROM AUTHOR]

In this contribution, we investigate the role of a mantle plume in the genesis of the Bunbury Basalt using high-precision 40 Ar/ 39 Ar geochronology and whole-rock geochemistry, and by using crustal basement thickness of the eastern Indian Ocean and the western Australian continent. The Bunbury Basalt is a series of lava flows and deep intrusive rocks in southwestern Australia thought to be the earliest igneous products from the proto-Kerguelen mantle plume. Nine new plateau ages indicate that the Bunbury Basalt erupted in three distinct phases, at 136.96 ± 0.43 Ma , 132.71 ± 0.43 Ma and 130.45 ± 0.82 Ma . All Bunbury Basalt samples are enriched tholeiitic basalts with varying contributions from the continental lithosphere that are similar to other Kerguelen plume-products. Based on plate reconstructions and the present geochronological constraints, the eruption of the oldest Bunbury Basalt preceded the emplacement of the Kerguelen large igneous province by at least 10–20 m.y. Such age differences between a precursor and the main magmatic event are not uncommon but do require additional explanation. Low crustal stretching factors beneath the Bunbury Basalt ( β ≈ 1.4 ) indicate that decompression melting could not have been generated from asthenospheric mantle with a normal chemistry and geotherm. An elevated geotherm from the mantle plume coupled with the geochemical similarity between the Bunbury Basalt and other Kerguelen plume-products suggests a shared origin exists. However, new age constraints of the oldest Bunbury Basalt are synchronous with the breakup of eastern Gondwana and the initial opening of the Indian Ocean at ca. 137–136 Ma, which may mean an alternative explanation is possible. The enriched geochemistry can equally be explained by a patch of shallow mantle beneath the southern Perth Basin. The patch may have been enriched during Gondwana suturing at ca. 550–500 Ma, during early rifting events by magmatic underplating or by intruded melts into the subcontinental lithospheric mantle. This enriched geochemical signature would then be sufficient to trigger decompression melting from passive rifting between Greater India and Australia with no contribution from the Kerguelen hotspot. We conclude that although the proto-Kerguelen hotspot is certainly a possible explanation for the genesis of the Bunbury Basalt, decompression melting of an enriched patch of subcontinental lithospheric mantle is an alternative theory. [ABSTRACT FROM AUTHOR]

Ethiopia is a key site to investigate the interactions between mantle dynamics and surface processes because of the presence of the Main Ethiopian Rift (MER), Cenozoic continental flood basalt volcanism, and plateau uplift. The role of mantle plumes in causing Ethiopia's flood basalts and tectonics has been commonly accepted. However, the location and number of plumes and their impact on surface uplift are still uncertain. Here we present new constraints on the geological and topographic evolution of the Ethiopian Plateau (NW Ethiopia) prior to and after the emplacement of the large flood basalts (40-20 Ma). Using geological information and topographic reconstructions, we show that the large topographic dome that we see today is a long-term feature, already present prior to the emplacement of the flood basalts. We also infer that large-scale doming operated even after the emplacement of the flood basalts. Using a comparison with the present-day topographic setting, we show that an important component of the topography has been and is presently represented by a residual, nonisostatic, dynamic contribution. We conclude that the growth of the Ethiopian Plateau is a long-term, probably still active, dynamically supported process. Our arguments provide constraints on the processes leading to the formation of one of the largest igneous plateaus on Earth. [ABSTRACT FROM AUTHOR]

Continental flood basalts (CFBs) represent large-scale melting events in the Earth’s upper mantle and show considerable geochemical heterogeneity that is typically linked to substantial contribution from underlying continental lithosphere. Large-scale partial melting of the cold subcontinental lithospheric mantle and the large amounts of crustal contamination suggested by traditional binary mixing or assimilation-fractional crystallization models are difficult to reconcile with the thermal and compositional characteristics of continental lithosphere, however. The well-exposed CFBs of Vestfjella, western Dronning Maud Land, Antarctica, belong to the Jurassic Karoo large igneous province and provide a prime locality to quantify mass contributions of lithospheric and sublithospheric sources for two reasons: (1) recently discovered CFB dikes show isotopic characteristics akin to mid-ocean ridge basalts, and thus help to constrain asthenospheric parental melt compositions and (2) the well-exposed basaltic lavas have been divided into four different geochemical magma types that exhibit considerable trace element and radiogenic isotope heterogeneity (e.g., initial εNd from −16 to +2 at 180 Ma). We simulate the geochemical evolution of Vestfjella CFBs using (1) energy-constrained assimilation-fractional crystallization equations that account for heating and partial melting of crustal wall rock and (2) assimilation-fractional crystallization equations for lithospheric mantle contamination by using highly alkaline continental volcanic rocks (i.e., partial melts of mantle lithosphere) as contaminants. Calculations indicate that the different magma types can be produced by just minor (1–15 wt%) contamination of asthenospheric parental magmas by melts from variable lithospheric reservoirs. Our models imply that the role of continental lithosphere as a CFB source component or contaminant may have been overestimated in many cases. Thus, CFBs may represent major juvenile crustal growth events rather than just recycling of old lithospheric materials. [ABSTRACT FROM AUTHOR]

The massive outpourings of Karoo and Ferrar continental flood basalts (CFBs) ∼180 Ma ago mark the initial Jurassic rifting stages of the Gondwana supercontinent. The origin and sources of these eruptions have been debated for decades, largely due to difficulties in defining their parental melt and mantle source characteristics. Recent findings of Fe- and Mg-rich dikes (depleted ferropicrite suite) from Vestfjella, western Dronning Maud Land, Antarctica, have shed light on the composition of the deep sub-Gondwanan mantle: these magmas have been connected to upper mantle sources presently sampled by the Southwest Indian Ocean mid-ocean ridge basalts (SWIR MORBs) or to high 3 He/ 4 He plume-entrained non-chondritic primitive mantle sources formed early in Earth's history. In an attempt to determine their He isotopic composition and relative contributions from magmatic, cosmogenic, and radiogenic He sources, we performed in-vacuo stepwise crushing and melting analyses of olivine mineral separates, some of which were abraded to remove the outer layer of the grains. The best estimate for the mantle isotopic composition is given by a sample with the highest amount of He released (>50%) during the first crushing step of an abraded coarse fraction. It has a 3 He/ 4 He of 7.03 ± 0.23 (2 σ ) times the atmospheric ratio ( R a ), which is indistinguishable from those measured from SWIR MORBs (6.3–7.3 R a ; source 3 He/ 4 He ∼6.4–7.6 R a at 180 Ma) and notably lower than in the most primitive lavas from the North Atlantic Igneous Province (up to 50 R a ), considered to represent the epitome magmas from non-chondritic primitive mantle sources. Previously published trace element and isotopic (Sr, Nd, and Pb) compositions do not suggest a direct genetic link to any modern hotspot of Indian or southern Atlantic Oceans. Although influence of a mantle plume cannot be ruled out, the high magma temperatures and SWIR MORB-like geochemistry of the suite are best explained by supercontinent insulation of a precursory Indian Ocean upper mantle source. Such a model is also supported by the majority of the recent studies on the structure, geochronology, and petrology of the Karoo CFBs. [ABSTRACT FROM AUTHOR]

The Early Permian Panjal Traps of northern India are the volcanic remnants of continental rifting that led to the formation of the Neotethys Ocean and the ribbon-like continent Cimmeria. The Traps are one of at least five major mafic eruptions of flood basalts during the Late Palaeozoic however their origin and petrogenesis are poorly constrained. Basalts from the Kashmir Valley were collected and analyzed for chemical and isotopic (Sr, Nd) compositions in order to characterize their mantle source and evaluate the petrogenetic processes related to opening of the Neotethys Ocean. Samples collected from the eastern side (Guryal Ravine, Pahalgam, PJ3) of the Kashmir Valley are chemically similar to mildly alkaline to tholeiitic, within-plate flood basalts. The TiO2 contents (TiO2 = 0.8 to 3.1 wt.%), La/YbN values (La/YbN = 1.8 to 6.1) and εNd(t) values (εNd(t) = -5.3 to +1.3) along with partial melt modeling indicates that the basalts were likely derived from a spinel peridotite source. In contrast, samples collected from the western side (PJ4) of the Kashmir Valley (Buta Pathri) are more primitive in composition and show evidence for clinopyroxene fractionation. The basalts from the western side o f the Kashmir Valley have higher Mg# (Mg# = 60 to 78) values and εNd(t) values (εNd(t) = +0.3 to +4.3) suggesting they were derived by slightly higher amounts of partial melting and from a more depleted spinel peridotite source. The changing bulk composition of the basalts from 'enriched OIB-like' on the eastern side to 'depleted MORB-like' compositions on the western side is likely due to the changing nature of the Panjal rift from a nascent continental setting to one transitioning to a mature ocean basin. In comparison to Pangaean and post-Pangaean flood basalt provinces, the Panjal Traps are more chemically similar to the flood basalts from the post-Pangaean provinces that are associated with plate separation. [ABSTRACT FROM AUTHOR]

Late Pliocene to Early Pleistocene (~ 3.25–2.05 Ma), 200–400 m thick basalt lavas outcrop in the South Caucasus region, including the Kars–Erzurum Plateau (northeastern Turkey), the Javakheti Plateau (Georgia–Armenia), and the Lori Plateau (northern Armenia). These fissure-fed, rapidly erupted fluid lavas filled pre-existing river valleys over many tens of kilometres. The basalts exposed in the Debed River canyon, northern Armenia, are ~ 200 m thick and of three morphological types: (1) basal pillow basalts and hyaloclastites, overlain by (2) columnar-jointed pahoehoe sheet flows, in turn overlain by (3) slabby pahoehoe and rubbly pahoehoe flows. The lower and middle lavas show evidence for damming of river drainage, like many lavas of the Columbia River flood basalt province, Scotland, Ireland, and Iceland. There is also evidence for syn-volcanic faulting of the early lavas. Related basalts also outcrop in the Gegham Uplands and the Hrazdan River basin in Armenia. This 3.25–2.05 Ma South Caucasus basalt province, covering parts of Turkey, Georgia and Armenia, has an estimated areal extent of ~ 15,000 km 2 and volume of ~ 2250 km 3 . Because its main geological features are remarkably like those of many continental flood basalt (CFB) provinces, we consider it a true, albeit small, CFB province. It is the smallest and youngest CFB in the world. An analogue closely similar in major features is the Late Miocene Altos de Jalisco CFB province in the western Trans-Mexican Volcanic Belt. Both provinces formed during lithospheric pull-apart and transtensional faulting. Their broader significance is in showing flood basalt size distribution to be a continuum without natural breaks, with implications for geodynamic models. [ABSTRACT FROM AUTHOR]

The lavas exposed at the Rajahmundry Traps have similar ages and geochemical compositions compared to those from the Ambenali and Mahabaleshwar formations of the Deccan Traps, which is why they are believed to represent their eastern extensions. However recent geochronological data for the lavas crop out in the Rajahmundry quarries and paleontological evidence from the expanded sediment-lava sequences preserved in the Krishna-Godavari Basin indicate that the lower Rajahmundry Flow could represent a flow of the Poladpur formation. Here we present new major and trace element data for lavas of the lower (five samples) and middle (three samples) Rajahmundry Flows exposed in the Gowripatnam Quarry. To test whether the lower Rajahmundry Flow show geochemical similarities to the Poladpur formation, we applied a machine learning-based classification model which is able to predict the most probable formation affiliation for an unknown sample. The classification method we used is the Random Forest algorithm and training as well as testing our model with new and published geochemical data from the Poladpur and Ambenali formations (n = 73) by using Repeated K-Fold Cross Validation yields a prediction accuracy of ~86%. According to our model results, the lavas of the lower Rajahmundry Flow were assigned to the Poladpur formation, while those from the middle Rajahmundry Flow show geochemical similarities to the Ambenali formation. Flows of each of the voluminous Deccan formations (Poladpur, Ambenali and Mahabaleshwar) are therefore present at Rajahmundry, confirming that these are an eastward extension of the Deccan Traps. • Correlation of Deccan and Rajahmundry lava stratigraphy • Trace element-based machine learning classification model • Lava flows belonging to the Poladpur formations flowed 1000 km to Rajahmundry. [ABSTRACT FROM AUTHOR]

Since continental sediments (in addition to the marine geological record) offer important means of deciphering environmental changes, the sediments hosted by the successive flows of the continental flood basalt provinces of the world should be treasure houses in gathering the palaeoclimatic data. Palaeosols developed on top of basalt flows are potentially ideal for palaeoenvironmental reconstructions because it is easy to determine their protolith geochemistry and also they define a definite time interval. The present paper summarizes the nature of the basalt-hosted palaeosols formed on the flood basalts provinces from different parts of the globe having different ages. [ABSTRACT FROM AUTHOR]

The Early Permian Panjal Traps of northern India represent a significant eruption of volcanic rocks which occurred during the opening of the Neotethys Ocean. Basaltic, basaltic-andesites, dacitic and rhyolitic rocks collected from Guryal Ravine and Pahalgam show evidence for subaerial and subaqueous eruptions indicating that they are contemporaneous with the formation of a shallow marine basin. The major and trace element geochemistry of the basalts is consistent with a within-plate setting and there are basalts which have high-Ti (TiO2 > 2.0 wt.%) and low-Ti (TiO2 < 1.8 wt.%) compositions. The 'high-Ti' basalts are similar to OIB whereas the 'low-Ti' basalts are similar to continental tholeiites. The identification of 'high- and low-Ti' basalts within the Panjal Traps is analogous to other large igneous provinces (e.g. Karoo, Deccan, Parana, Emeishan). The Sr-Nd isotopic values (εNd(T) = - 5.3 to + 1.3; ISr = 0.70432 to 0.71168) of both types of basalts overlap indicating that the rocks may have originated from the same ancient subcontinental lithospheric (i.e. EMII-like) mantle source (TDM = ~ 2000 Ma). The two groups of basalts can be modeled by using a primitive mantle source and different degrees of partial melting where the high-Ti rocks are produced by ~ 1% partial melting of a spinel peridotite source whereas the low-Ti rocks are produced by ~ 8% partial melting. Trace elemental and isotope modeling indicates that some of the basalts assimilated ≤ 10% crustal material. In contrast, the basaltic-andesites are likely formed by mixing between basaltic magmas and crustal melts which produced rocks with higher SiO2 (~ 55 wt.%) content and enriched isotopic signatures (εNd(T) = - 6.1; ISr = 0.70992). The Panjal Trap volcanism was likely due to partial melting of the SCLM within a passive extensional setting related to the rifting of Cimmeria from Gondwana. Contemporaneous volcanic and plutonic granitic rocks throughout the Himalaya are probably not petrogenetically related but are likely part of the same regional tectonic regime. [ABSTRACT FROM AUTHOR]

Geochemical characteristics of Desur-type basalt flows in the southern and southwestern part of Belgaum in Karnataka, India have been investigated to understand their petrogenesis. The basalts are compact, hard, massive, and show characteristic microporphyritic textures with abundant well-twinned and un-twinned plagioclase phenocrysts and minor clinopyroxene set in a fine-grained groundmass consisting of plagioclase, clinopyroxene, glass and Fe-Ti oxides. Thin sections show sub-ophitic, intergranular and intersertal textures. The basalts are Fe-rich tholeiites (13.4-13.8 wt %), characterized by high TiO (3.64 to 3.94 wt %); moderate MgO contents (4.79 to 5.41 wt %), low KO contents (<0.58 wt %) and low Mg# (42.4-45.9). They are enriched in large ion lithophile elements, moderately enriched in the light rare earths (chondrite-normalized La/Yb 3.37-4.24), and exhibit nearly flat heavy rare-earth patterns that lack significant Eu anomalies (Eu/Eu* 0.86-1.10). Primitive-mantle-normalized element patterns for these rocks show characteristic troughs at K and Sr, absence of a Nb anomaly, and a low Zr/Nb ratio (<15), which suggest insignificant contamination by many types of continental crust, whereas, enrichments in the large ion lithophiles, La, P and Th could suggest enriched source characteristics. Based on the geochemical characteristics of the basalts, it is inferred that the Desur basalts representing the youngest flows of the Deccan Basalt Group are derived by partial melting of a peridotite source, and subsequent fractionation gave rise to the compositions of the basalts that are found in the Belgaum region. [ABSTRACT FROM AUTHOR]

The 1.27Ga Coppermine continental flood basalt (CFB) province in northern Canada represents the extrusive manifestation of the 2.7Mkm2 Mackenzie large igneous province (LIP) that includes the Mackenzie dyke swarm and the Muskox layered intrusion. New Re–Os isotope and highly siderophile element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundance data are reported together with whole-rock major- and trace-element abundances and Nd isotopes to examine the behaviour of the HSE during magmatic differentiation and to place constraints on the extent of crustal interaction with mantle-derived melts. Mineral chemistry and petrography are also reported for an unusual andesite glass flow (CM19; 4.9wt.% MgO) found in close proximity to newly recognised picrites (>20wt.% MgO) in the lowermost stratigraphy of the Coppermine CFB. Compositions of mineral phases in CM19 are similar to the same phases found in Muskox Intrusion chromitites and the melt composition is equivalent to inclusions trapped within Muskox chromites. The apparently conflicting elevated HSE contents (e.g., 3.8ppb Os) and mantle-like initial 187Os/188Os (γOs =+2.2), versus stable isotope (δ18O=+12‰) and lithophile element evidence (εNdi=−12.8) for extensive crustal contamination, implicate an origin for CM19 as a magma mingling product formed within the Muskox Intrusion during chromitite genesis. Combined with Nd isotope data that places the feeder for lower Coppermine CFB picrites and basalts within the Muskox Intrusion, this result provides compelling evidence for direct processing of some CFB within upper-crustal magma chambers. The Coppermine CFB defines a 187Re–187Os isochron with an age of 1263 +16/−20Ma and initial γOs =+2.2±0.8. The initial Os isotope composition for the Coppermine CFB is slightly higher than the near-primitive-mantle initial 187Os/188Os for the Muskox Intrusion (γOs =+1.2±0.3). This result is interpreted to reflect greater crustal contamination in extrusive CFB and the sensitivity of Os isotopes, compared with absolute HSE concentrations, for tracking crustal contributions. Modelling of absolute and relative HSE abundances in global CFB reveals that HSE concentrations decrease with increasing fractionation for melts with <8±1wt.% MgO, with picrites (>13.5wt.% MgO) from CFB (n =98; 1.97±1.77ppb) having higher Os abundances than ocean island basalt (OIB) equivalents (n =75; 0.95±0.86ppb). The differences between CFB and OIB picrite absolute Os abundances may result from higher degrees of partial melting to form CFB but may also reflect incorporation of trace sulphide in CFB picrites from magmas that reached S-saturation in upper-crustal magma chambers. Significant inter-element fractionation of (Re+Pt+Pd)/(Os+Ir+Ru) are generated during magmatic differentiation in response to strongly contrasting partitioning of these two groups of elements into sulphides and/or HSE-rich alloys. Furthermore, fractional crystallization has a greater role on absolute and relative HSE abundances than crustal contamination under conditions of CFB petrogenesis due to the dilution effect of continental crust, which has low total abundances of the HSE. Combined data for the basaltic and intrusive portions of the Mackenzie LIP indicate a mantle source broadly within the range of the primitive upper mantle. The majority of Archaean komatiites and Phanerozoic CFB also require mantle sources with primitive upper mantle to chondritic Re/Os evolution, with exceptions typically being from analyses of highly-fractionated MgO-poor basalts. [ABSTRACT FROM AUTHOR]

Occurrence of well crystallized nontronite in a megaporphyritic basalt flow from Nighoj area, Maharashtra, India is reported. Thin section studies of the vesicles from periphery to the centre reveal the presence of greenish palagonite, probably indicating the stages of devitrification of glass and the weathering of palagonite to the formation of nontronite. The centre of the vesicles is marked by the presence of dark greenish-brown, radiating and fibrous sheets of nontronite. X-ray diffraction (XRD) analysis reveals the dominant presence of smectite (nontronite) as the major phase with traces of pyroxene. Scanning Electron Microscopy (SEM) shows well developed sheets of nontronite within the gas vesicles of the megaporphyritic basalt flows. In the present investigation, the nontronite within the gas vesicles of the megaporphyritic basalts at Nighoj was formed in-situ due to the devitrification of glass containing palagonite. Palagonite is an intermediate step in the alteration that may be accomplished by the steam generated in quenching of the lava. Weathering of palagonite under conditions of poor drainage is essential to the genesis of nontronite as has been suggested by Victor and Vernon (1946). [ABSTRACT FROM AUTHOR]

Abstract: Permian continental flood basalts (CFBs), as a main component for Tarim Large Igneous Province (TLIP), are widely distributed in the western and central parts of the Tarim Basin. Here we present a systematic study of platinum-group elements (PGEs) combined with conventional major, trace and Sr–Nd isotopic geochemistry to characterize the Tarim CFBs from the Yingan section in the Keping area, west of the Tarim Basin. The basaltic units with a total thickness of ca. 400m in the section can be divided into two basaltic sequences: the lower Kupukuziman and the upper Kaipaizileike sequences. Both of the sequences display extremely low PGE concentrations, with Os, Ir, Ru, Rh, Pt and Pd contents of 0.014–0.106, 0.007–0.072, 0.035–0.253, 0.011–0.078, 0.043–0.149 and 0.026–0.124ppb, respectively. The Keping basalts exhibit a marked increase in Cu/Pd ratios (>105) albeit with a narrow range of lower Pd/Ir ratios (<50), different from the PGE-undepleted basalts of the Siberian Traps, Emeishan Large Igneous Province (ELIP), East Greenland CFBs and Deccan Traps. Furthermore, the Tarim CFBs in Keping and elsewhere in the basin have very low Cu/Zr ratios (<0.5 commonly), indicating that their parent magmas were significantly depleted in chalcophile elements. The Tarim CFB magmas are estimated to have formed by <5% partial melting, and were probably S-saturated during partial melting, leaving residual sulfide in the mantle source. The differences in Th/Yb and (Th/Nb)N ratios between the Kupukuziman and Kaipaizileike sequences suggest that the Keping basalts incorporated variable degrees of assimilated crustal components from the Precambrian basement in the Tarim Basin. Modeling indicates that the earlier erupted Kupukuziman lavas witnessed relatively larger extent of assimilation than the later Kaipaizileike lavas. Nevertheless, the crustal assimilation did not trigger sulfur saturation and sulfide segregation for the basaltic magma in the crust. Furthermore, a magma mixing process between the relatively primitive and more evolved residual magmas of the same lineage during magma chamber replenishment is suggested according to the PGEs and Sr–Nd isotope variations in the Kaipaizileike sequence. This process might have also induced limited sulfur saturation and sulfide segregation in the late stage of the magmatic evolution. A comparison of the chalcophile element characteristics between the basalts in the Tarim Basin and the mafic–ultramafic rocks in the Eastern Tianshan and Beishan Rift areas indicates that the degree of partial melting plays an important role on the PGE geochemistry and potential PGE–(Ni–Cu) ore deposits in the TLIP. [Copyright &y& Elsevier]

Abstract: Baksi (2012) claims that a number of radiometric ages presented in Barry et al. (2010) are statistically invalid and that many of the samples were altered, thus not able to date the eruptions, and that there is no compelling evidence for a limited duration for the eruption of the Grande Ronde Basalts (GR Basalts), USA. However, Baksi (2012), has simply reiterated some of the assessment of the data presented in the paper and has used an ‘Alteration Index’, in order to assess the data. The ‘Alteration Index’ commonly shows that basaltic groundmass is altered and from this Baksi (2012) deduces that the ages are incorrect. In contrast, much work on young volcanics has shown that phenocrysts are often sources of incorrect ages. In any assessment of data, we maintain that whilst alteration is an important consideration, the best approach should include not just alteration, but also experimental reproducibility, stratigraphic order, comparison with other analyses, and analytical techniques, and that the application of an ‘Alteration Index’ is not a straightforward guide to the validity of an age. [Copyright &y& Elsevier]

Abstract: Barry et al. (2010) presented 40Ar/39Ar ages to argue for a very limited duration (~ 0.4m.y.) for the eruption of the Grande Ronde lavas. Critical examination of their data sets shows (1) a number of their plateau ages are statistically invalid and (2) many of their groundmass matrix samples were altered, and did not yield valid estimates of the time of crystallization. In general, their ages err on the young side, reflecting partial 40Ar * loss, due to alteration, and there is no compelling evidence therein, to argue for very limited duration for the Grande Ronde Basalt. The Imnaha, Grande Ronde and Wanapum Basalt erupted within~0.7m.y., starting at~16.4Ma. By contrast, the “ages” of Barry et al. (2010) span the interval~16.6 to~14.7Ma and, in some instances, are out of stratigraphic sequence. [Copyright &y& Elsevier]

Abstract: Geochemical and Hf–Nd isotope studies of Neoproterozoic sedimentary and volcaniclastic rocks in the Nanhua Rift Basin, South China, demonstrate that their source provenances contained large proportions of mafic rocks and various amounts of granites. A significant proportion of the studied Neoproterozoic rift sedimentary and volcaniclastic rocks have initial εNd(t) values higher than those of Neoproterozoic granites, but fall within the range of ca. 825–750Ma basaltic rocks. Their initial εNd(t) values correlate with ratios of La/Sc, La/Cr, La/V, La/Co and La/Ni. The Nd isotope and trace element data, in combination with existing in-situ U–Pb and hafnium–oxygen isotope data from the detrital zircon grains indicate a dominant ca. 825–800Ma mafic provenance. Furthermore, the studied samples formed a linear array and plot within the field defined by the remanent of ca. 825–810Ma continental flood basalts in the Hf–Nd isotopic space. Thus, the inferred large proportions of mafic rocks in the source provenance of the Neoproterozoic rift sedimentary and volcaniclastic rocks likely signify an eroded continental flood basalt province, similar to that reported for the Neoproterozoic sedimentary rocks in Australia. This work thus provides further evidence for the possible once existence of a common large igneous province between South China and eastern Australia as adjacent parts of the supercontinent Rodinia. [Copyright &y& Elsevier]

Abstract: Turbulent volcanic plumes disperse fine ash particles and toxic gases in the atmosphere and can lead to significant temperature drops in the atmosphere. In the geological past, the emplacement of large continental flood basalts (CFB) has been associated with large changes in the global environment and extinctions of biological species. The variable intensity of environmental changes induced by otherwise similar CFB events, however, begs for a reevaluation of physical controls on the environmental impact of volcanic eruptions. The climatic impact of an eruption depends on its ability to inject gases in the stratosphere and on the eruption rate. Using integral models of turbulent plumes above line and point sources, we find that mass rate estimates for CFBs are in general not large enough for volcanic plumes to reach the stratosphere on their own. Basaltic eruptions, however, are also associated with widespread lava flows which lose large amounts of heat and generate convection in the atmosphere. This form of convection, known as penetrative convection, acts to erode the stably stratified lower atmosphere and generates a thick well-mixed heated atmospheric layer in a few hours. The added buoyancy provided by such a layer almost always ensures that volcanic gases get transported to the stratosphere. The environmental consequences of CFBs are therefore controlled not by the inputs to the atmosphere from individual volcanic plumes, but by the dynamic response of the climate system to a succession of short eruptive pulses within a longer-lasting eruption sequence. [Copyright &y& Elsevier]

Abstract: Grande Ronde Basalt (GRB) lavas represent the most voluminous eruptive pulse of the Columbia River–Snake River–Yellowstone hotspot volcanism. With an estimated eruptive volume of 150,000km3, GRB lavas form at least 66% of the total volume of the Columbia River Basalt Group. New 40Ar/39Ar dates for GRB lavas reveal they were emplaced within a maximum period of 0.42±0.18My. A well-documented stratigraphy indicates at least 110 GRB flow fields (or individual eruptions), and on this basis suggests an average inter-eruption hiatus of less than 4000years. Isotopic age-dating cannot resolve time gaps between GRB eruptions, and it is difficult to otherwise form a picture of the durations of eruptions because of non-uniform weathering in the top of flow fields and a general paucity of sediments between GR lavas. Where sediment has formed on top of GRB lavas, it varies in thickness from zero to 20–30cm of silty to fine-sandy material, with occasional diatomaceous sediment. Individual GRB eruptions varied considerably in volume but many were greater than 1000km3 in size. Most probably eruptive events were not equally spaced in time; some eruptions may have followed short periods of volcanic repose (perhaps 102 to 103 of years), whilst others could have been considerably longer (many 1000s to >104 years). Recent improvements in age-dating for other continental flood basalt (CFB) lava sequences have yielded estimates of total eruptive durations of less than 1My for high-volume pulses of lava production. The GRB appears to be a similar example, where the main pulse occupied a brief period. Even allowing for moderate to long-duration pahoehoe flow field production, the amount of time the system spends in active lava-producing mode is small — less than c. 2.6% (based on eruption durations of approximately 10,000years, compared to the duration of the entire eruptive pulse of c. 420,000years). A review of available 40Ar/39Ar data for the major voluminous phases of the Columbia River Basalt Group suggests that activity of the Steens Basalt–Imnaha Basalt–GRB may have, at times, been simultaneous, with obvious implications for climatic effects. Resolving intervals between successive eruptions during CFB province construction, and durations of main eruptive pulses, remains vital to determining the environmental impact of these huge eruptions. [Copyright &y& Elsevier]

Spatial and temporal variations in the geochemistry of an extrusive basaltic section of Deccan traps record progressive changes in mantle melting and crustal filtration and are relevant to understand continental flood basalt (CFB) magmatism. In the present work we have carried out detailed field, petrographic, density and magnetic susceptibility, and geochemical investigations on a small, semi-continuous extrusive section in the eastern Deccan Volcanic Province (DVP) to understand the role of shallow magma chambers in CFB magmatism. Four formations, Ajanta, Chikhli, Buldhana and Karanja crop out in the Gangakhed–Ambajogai area with increasing elevation. Our studies indicate that: (1) the Karanja Formation represents a major magma addition, as indicated by abrupt change in texture, increases in MgO, CaO, Ni, Cr, and Sr, and drastic decreases in Al2O3, Na2O, K2O, Rb, Ba, REE, bulk-rock density and magnetic susceptibility; (2) assimilation fractional crystallization, crystal-laden magmas, and accessory cumulus phases influence the trace element chemistry of Deccan basalts; (3) the predicted cumulate sequence of olivine gabbro–leucogabbro–oxide-apatite gabbro is supported by the observed layered series in a shallow magma chamber within the DVP; (4) the initial magma was saturated with olivine, plagioclase, and augite, and final the pressure of equilibration for the Gangakhed–Ambajogai section basalts is ~2 kbar (~6 km depth); (5) petrophysical parameters act as proxies for magmatic processes; (6) a small layer of oxide-rich basalts may represent the latest erupted pulse in a given magmatic cycle in the DVP; (7) parental basalts to some of the red boles, considered as formation boundaries, might represent small degree partial melts of the mantle; (8) SW Deccan basaltic-types continue into the eastern DVP; and (9) in addition to the magma chamber processes, dynamic melting of the mantle may have controlled DVP geochemistry. The present study underscores the importance of mapping specific stratigraphic intervals in limited areas to understand mantle and magma chamber processes relevant to CFB magmatism. [ABSTRACT FROM AUTHOR]

The voluminous succession of tholeiitic basalts, calc-alkaline andesites and minor high-K basalts that form the Late Miocene Altos de Jalisco mafic province of the western Trans-Mexican Volcanic Belt is interpreted as the magmatic manifestation of a lithospheric dripping event, which removed mantle lithosphere and lower crustal lithologies beneath the study area. During this process, the release of fluids from the foundering materials, coupled with mantle upwelling around the sinking mass, promoted abundant melting of a spinel peridotite and the production of large volumes of tholeiitic magma with low La/Yb and Gd/Yb ratios. Negative correlations of these ratios with MgO contents, Nd isotopes and Rb/Nd ratios indicate that the parental basalts subsequently experienced high-pressure fractional crystallization and contamination with a newly exposed felsic continental crust, thus producing the more evolved calc-alkaline compositions. Stronger garnet signatures and marked enrichments in highly incompatible elements in the high-K suite support derivation from a garnet- and phlogopite-bearing pyroxenitic source, presumably formed by reaction of mantle peridotites with hydrous silicic melts derived from the foundering lithologies. This new petrogenetic model for the Altos de Jalisco volcanic district suggests that the loss of mafic lower crust during lithospheric dripping might be balanced by production of abundant flood basalts within continents, and thus indicates that additional mechanisms may be required for the stabilization of andesitic crust on Earth. [ABSTRACT FROM PUBLISHER]

Many continental flood basalt provinces contain rhyolites with ‘A-type’ compositions and many studies have concluded that these higher silica rocks are crustal melts from metapelitic or tonalitic country rock. However, although many of the low-Ti continental flood basalt sequences exhibit a marked a silica gap from ∼55–65 wt. SiO2, many incompatible element ratios, and the calculated eruption temperatures (950–1100°C) are strikingly similar between the rhyolites and associated basalts. Using experimental evidence, derivation of the low-Ti rhyolites from a basaltic parent is shown to be a viable alternative to local crustal melting. Comparison of liquid compositions from experimental melting of both crustal and mantle-derived (basaltic) source materials allows the two to be distinguished on the basis of Al2O3 and FeO content. The basalt experiments are reversible, such that the same melts can be produced by melting or crystallisation. The effect of increased water content in the source is also detectable in the liquid composition. The majority of rhyolites from continental flood basalt provinces fall along the experimental trend for basalt melting/ crystallisation at relatively low water content. The onset of the silica gap in the rhyolites is accompanied by an abrupt decrease in TiO2 and FeO*, marking the start of Fe–Ti oxide crystallisation. Differentiation from 55–65 wt. SiO2 requires ∼30 fractional crystallisation in which magnetite is an important phase, sometimes accompanied by limited crustal contamination. The rapid increase in silica occurs over a small temperature interval and for relatively small changes in the amount of fractional crystallisation, thus intermediate compositions are less likely to be sampled. It is argued that the presence of a silica gap is not diagnostic of a crustal melting origin for either A-type granites or rhyolites in continental flood basalt provinces. The volume of these rhyolites erupted over the Phanerozoic is significant and models for crustal growth should take this substantial contribution from the mantle into account. [ABSTRACT FROM PUBLISHER]

Abstract: Most of the studies on the large igneous provinces (LIPs) focus on Phanerozoic times, and in particular, those related to the disruption of Pangea (e.g. CAMP, Karoo, Parana–Etendeka) while Precambrian LIPs (e.g. Ventersdorpf, Fortescue) remain less studied. Although the investigation of Precambrian LIPs is difficult because they are relatively poorly preserved, assessment of their geochemical characteristics in parallel with younger overlapping LIP is fundamental for monitoring the evolution of the mantle composition through time. Recent 40Ar/39Ar dating of the Okavango giant dyke swarm (and related sills) in southern Africa showed that ~90% of the dykes were emplaced at 179±1 Ma and belong to the Karoo large igneous province whereas ~10% of dykes yielded Proterozoic ages (~1–1.1 Ga). Here, we provide new major, trace and rare earth elements analyses of the low-Ti Proterozoic Okavango dyke swarm (PODS) that suggest, combined with age data, a cognate origin with the 1.1 Ga Umkondo large igneous province (UIP), southern Africa. The geochemical characteristics of the PODS and UIP basalts are comparable to those of overlapping low-Ti Karoo basalts, and suggest that both LIPs were derived from similar enriched mantle sources. A mantle plume origin for these LIPs is not easily reconciled with the geochemical dataset and the coincidence of two compositionally similar mantle plumes acting 900 Myr apart is unlikely. Instead, we propose that the Umkondo and Karoo large igneous provinces monitored the slight evolution of a shallow enriched lithospheric mantle from Proterozoic to Jurassic. [Copyright &y& Elsevier]

The association between the Siberian Traps, the largest continental flood basalt province, and the largest-known mass extinction event at the end of the Permian period, has been strengthened by recently-published high-precision 40Ar/39Ar dates from widespread localities across the Siberian province[1]. We argue that the impact of the volcanism was amplified by the prevailing late Permian environmental conditions - in particular, the hothouse climate, with sluggish oceanic circulation, that was leading to widespread oceanic anoxia. Volcanism released large masses of sulphate aerosols and carbon dioxide, the former triggering short-duration volcanic winters, the latter leading to long-term warming. Whilst the mass of CO2 released from individual eruptions was small compared with the total mass of carbon in the atmosphere-ocean system, the long 'mean lifetime' of atmospheric CO2, compared with the eruption flux and duration, meant that significant accumulation could occur over periods of 105 years. Compromise of the carbon sequestration systems (by curtailment of photosynthesis, destruction of biomass, and warming and acidification of the oceans) probably led to rapid atmospheric CO2 build-up, warming, and shallow-water anoxia, leading ultimately to mass extinction. [ABSTRACT FROM AUTHOR]

Mantle plume or superplume activities have often been invoked as a cause for the breakup of the Neoproterozoic supercontinent Rodinia. However, associated Neoproterozoic continental flood basalts, a requisite product of mantle plume activities, have rarely been identified. New sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages, geochemical, and Hf-Nd isotopic data are reported here for the Bikou Group basalts, the largest Neoproterozoic volcanic units in the northwestern Yangtze block, South China. The Bikou basalts are mainly tholeiitic in composition, and they can be stratigraphically subdivided into the lower and upper groups. SHRIMP U-Pb zircon dating of intercalated rhyolites indicates that the lower and upper group basalts were erupted at 821 ± 7 Ma and 811 ± 12 Ma, respectively. The two basalt groups define two populations on most elemental and isotopic diagrams. The lower group basalts display strong subcontinental lithospheric mantle affinities and large variable εNd(t) and εHf(t) values that correlate negatively with Th/Ta and positively with MgO. The upper group basalts, on the other hand, show ocean-island basalt (OIB) affinities and highly positive εHf(t) and εNd(t) values. Numerical modeling indicates that the lower and upper group basalts were formed at melting temperatures of >1350 °C and >1450 °C and mantle potential temperatures of 1400-1488 °C and 1550 ± 30 °C, respectively. Thus, the upper group basalts were derived from an anomalously hot asthenosphere mantle, ~160 °C hotter than the contemporary ambient mid-ocean-ridge basalt (MORB) source mantle. Our results are at clear variance with the alternative tectonic model that the Bikou basalts were part of a continental magmatic arc. Our work suggests that the Bikou basalts are likely the remnants of Neoproterozoic continental flood basalts that formed in response to a mantle plume starting ca. 825 Ma during the breakup of the supercontinent Rodinia. [ABSTRACT FROM AUTHOR]

Abstract: Continental flood basalts, derived from mantle plumes that rise from the convecting mantle and possibly as deep as the core–mantle boundary, are major hosts for world-class Ni–Cu–PGE ore deposits. Each plume may have a complex history and heterogeneous composition. Therefore, some plumes may be predisposed to be favourable for large-scale Ni–PGE mineralisation (“fertile”). Geochemical data from 10 large igneous provinces (LIPs) have been collected from the literature to search for chemical signatures favourable for Ni–PGE mineralisation. The provinces include Deccan, Kerguelen, Ontong Java, Paraná, Ferrar, Karoo, Emeishan, Siberia, Midcontinent and Bushveld. Among these LIPs, Bushveld, Siberia, Midcontinent, Emei Mt and Karoo are “fertile”, hosting magmatic ore deposits or mineralisation of various type, size and grade. They most commonly intruded through, or on the edges of, Archaean–Paleoproterozoic cratonic blocks. In contrast, the “barren” LIPs have erupted through both continental and oceanic crustal terranes of various ages. Radiogenic isotopic signatures indicate that almost all parental LIP magmas are generated from deep-seated mantle plumes, and not from the more widespread depleted asthenospheric mantle source: this confirms generally accepted plume models. However, several important geochemical signatures of LIPs have been identified in this study that can discriminate between those that are “fertile” or “barren” in terms of their Ni–PGE potential. The fertile LIPs generally contain a relatively high proportion of primitive melts that are high in MgO and Ni, low in Al2O3 and Na2O, and are highly enriched in most of the strongly incompatible elements such as K, P, Ba, Sr, Pb, Th, Nb, and LREE. They have relatively high Os contents (≥0.03 to 10 ppb) and low Re/Os (<10). The fertile LIP basalts display trends of Sr–Nd–Pb isotopic variation intermediate between the depleted plume and an EM1-type mantle composition (and thus could represent a mixing of these two source types), and have elevated Ba/Th, Ba/Nb and K/Ti ratios. These elemental and isotopic signatures suggest that interaction between plume-related magmas and ancient cratonic lithospheric mantle with pre-existing Ni- and PGE-rich sulfide phases may have contributed significantly to the PGE and Ni budget of the fertile flood basalts and eventually to the mineralisation. This observation is consistent with the location of fertile LIPs adjacent to deep old lithospheric roots (as inferred from tectonic environment and also seen in global tomographic images) and has predictive implications for exploration models. Barren LIPs contain fewer high-MgO lavas. The barren LIP lavas in general have low Os contents (mostly ≤0.02 ppb) with high Re/Os (10–≥200). They show isotopic variations between plume and EM2 geochemical signatures and have high Rb/Ba ratios. These signatures may indicate involvement of deep recycled material in the mantle sources or crustal contamination for barren LIPs, but low degrees of interaction with old lithospheric-type roots. [Copyright &y& Elsevier]

Abstract: The four most recent large mass extinction events in the Phanerozoic – the Cretaceous–Tertiary (KT), the Triassic–Jurassic (TJ), and the Permo-Triassic (PT) and Guadalupian–Tatarian (GT) doublet – are associated with a major flood basalt eruption, with the timing of peak volcanic activity corresponding within measurement uncertainties to the extinction event. Three magnetic superchrons precede the four largest Phanerozoic extinctions. The Cretaceous Long Normal Superchron (duration ∼35 Myr) precedes the KT and the Permian Kiaman Long Reversed Superchron (∼50 Myr) precedes the PT–GT doublet. In addition, the newly recognized Ordovician Moyero Long Reversed Superchron (∼30 Myr) precedes the end-Ordovician extinction event. There is a 10–20 Myr delay between the end of each superchron and the subsequent mass depletion event, both of which represent distant outliers from their respective populations. We propose that deep mantle plumes link these seemingly unrelated phenomena. Long-term (∼200 Myr) variations in mantle convection possibly associated with the Wilson cycle induce temporal and spatial variations in heat flow at the core–mantle boundary. Polarity reversals are frequent when core heat flow is high and infrequent when it is low. Thermal instabilities in the D”-layer of the mantle increase core heat flow, end the magnetic superchron, and generate deep mantle plumes. The plumes ascend through the mantle on a 20 Myr time scale, producing continental flood basalt (trap) eruptions, rapid climatic change, and massive faunal depletions. [Copyright &y& Elsevier]

Continents episodically cluster together into a supercontinent, eventually breaking up with intense magmatic activity supposedly caused by mantle plumes (Morgan, 1983; Richards et al., 1989; Condie, 2004). The breakup of Pangea, the last supercontinent, was accompanied by the emplacement of the largest known continental flood basalt, the Central Atlantic Magmatic Province, which caused massive extinctions at the Triassic-Jurassic boundary (Marzoli et al., 1999). However, there is little support for a plume origin for this catastrophic event (McHone, 2000). On the basis of convection modeling in an internally heated mantle, this paper shows that continental aggregation promotes large-scale melting without requiring the involvement of plumes. When only internal heat sources in the mantle are considered, the formation of a supercontinent causes the enlargement of flow wavelength and a subcontinental increase in temperature as large as 100 °C. This temperature increase may lead to large-scale melting without the involvement of plumes. Our results suggest the existence of two distinct types of continental flood basalts, caused by plume or by mantle global warming. [ABSTRACT FROM AUTHOR]