continental flood basalt
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2021 ◽  
pp. SP518-2020-262
Author(s):  
R. Alex Steiner ◽  
Tyrone O. Rooney ◽  
Guillaume Girard ◽  
Nick Rogers ◽  
Cynthia Ebinger ◽  
...  

AbstractThe initial interaction between material rising from the African Large Low Shear Velocity Province and the African lithosphere manifests as the Eocene continental large igneous province (LIP), centered on southern Ethiopia and northern Kenya. Here we present a geographically well-distributed geochemical dataset comprising the flood basalt lavas of the Eocene continental LIP to refine the regional volcano-stratigraphy into three distinct magmatic units: (1) the highly-alkaline small-volume Akobo Basalts (49.4–46.6 Ma), representing the initial phase of flood basalt volcanism derived from the melting of lithospheric-mantle metasomes, (2) the primitive and spatially restricted Amaro Basalts (45.2–39.58 Ma) representing the early main phase of flood basalt volcanism derived from the melting of the upwelling thermochemical anomaly, and (3) the spatially extensive Gamo-Makonnen magmatic unit (38-28 Ma) representing the mature main phase of flood basalt volcanism that has undergone significant processing within the lithosphere resulting in relatively homogeneous compositions. The focused intrusion of these main phase magmas over 10 m.y. preconditioned the African lithosphere for the localization of strain during subsequent episodes of lithospheric stretching. The focusing of strain into the region occupied by this continental LIP may have contributed to the initial extension in SW Ethiopia associated with the East African Rift.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5557626


2021 ◽  
pp. SP518-2020-221
Author(s):  
W. R. Davis ◽  
M. A. Collins ◽  
T. O. Rooney ◽  
E. L. Brown ◽  
C. A. Stein ◽  
...  

AbstractContinental Flood Basalt Provinces (CFBPs) are large igneous features formed by the extrusion of massive amounts of lavas that require significant evolution within the lithosphere. Although sequential lava flows are effective probes of magmatic systems, CFBPs are typically poorly preserved. We focus on lava flows from the well-preserved 1.1 Ga Keweenawan CFBP that erupted within the Midcontinent Rift System. We present a new geochemical, petrographic, and stratigraphic synthesis from the Main stage Portage Lake Volcanics (PLV). Flow-by-flow analysis of the PLV reveals that major element behavior is decoupled from trace element behavior; MgO exhibits limited variability, while compatible and incompatible trace elements deviate from high to low concentrations throughout the sequence. The concentrations of incompatible trace elements slightly decrease from the base of the sequence to the top. We investigate these observations by applying a recharge, evacuation, assimilation, and fractional crystallization model to geochemical and petrographic data. Our modelling demonstrates a magmatic system experiencing increased evacuation rates while fractionation and assimilation rates decrease, indicating an increase in magmatic flux. The outcome of this modelling is a progressively more efficient magma system within the PLV. This study highlights the utility of joint petrographic and geochemical interpretation in constraining CFBP magma evolution.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5424758


2021 ◽  
Author(s):  
Xiaochuan Tian ◽  
W Buck

Abstract Temporal correlations between continental flood basalt eruptions and mass extinctions are well known 1. Massive carbon degassing from volcanism of Large Igneous Provinces can cause catastrophic global climatic and biotic perturbations 1–3. However, recent more accurate dating of the Deccan Traps 4 and Columbia River Basalts 5 challenges this causal link by showing that global warming preceded the major phase of flood basalts eruptions by several hundred thousand years. Here, we argue that major eruptions of continental flood basalts may require densification of the crust by intrusion of larger volumes of magma than are extruded. Simple models show that magma crystallization and release of CO2 from such intrusions could produce global warming before the main phase of flood basalt eruptions on the observed timescale. Being consistent with many geological, geophysical, geochemical and paleoclimate data, our model suggests that the evolving crustal density has a first order control on timing of the major phase of continental flood basalt volcanism while the preceding intrusion induced underground degassing of CO2 plays a significant role in controlling the Earth's climate and habitability.


2021 ◽  
pp. 1-22
Author(s):  
Sofía B. Pérez Luján ◽  
Florencia L. Boedo ◽  
Juan P. Ariza ◽  
Graciela I. Vujovich ◽  
Patricia Alvarado ◽  
...  

Abstract 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.


2021 ◽  
Vol 8 ◽  
Author(s):  
Stephen Self ◽  
Tushar Mittal ◽  
Anne Elizabeth Jay

Constraining the eruption rates of flood basalt lava flows remains a significant challenge despite decades of work. One potential observable proxy for eruption rates is flood basalt lava-flow lobe thicknesses, a topic that we tackle here quantitatively. In this study, we provide the first global compilation of pāhoehoe lava-lobe thicknesses from various continental flood basalt provinces (∼ 3,800 measurements) to compare characteristic thicknesses within and between provinces. We refer to thin lobes (∼ ≤5 m), characteristic of “compound” lavas, as hummocky pāhoehoe lava flows or flow-fields. Conversely, we term thicker lobes, characteristic of “simple” flows, as coming from sheet-lobe-dominated flows. Data from the Deccan Traps and Columbia River flood-basalt provinces are archetypal since they have the most consistent datasets as well as established chemo- and litho-stratigraphies. Examining Deccan lobe thicknesses, we find that previously suggested (and disputed) distinct temporal and regional distributions of hummocky pāhoehoe and sheet-lobe-dominated flow fields are not strongly supported by the data and that each geochemically defined formation displays both lobe types in varying amounts. Thin flow-lobes do not appear to indicate proximity to source. The modal lobe thickness of Deccan formations with abundant “thin” lava-lobes is 8 m, while the mode for sheet-lobe-dominated formations is only 17 m. Sheet-lobes up to 75–80 m are rare in the Deccan and Columbia River Provinces, and ones >100 m are exceptional globally. For other flood basalt provinces, modal thickness plots show a prevalence toward similar lobe thicknesses to Deccan, with many provinces having some or most lobes in the 5–8 m modal range. However, median values are generally thicker, in the 8–12 m range, suggesting that sheet-lobes dominate. By contrast, lobes from non-flood basalt flow-fields (e.g., Hawai’i, Snake River Plain) show distinctly thinner modes, sub-5 m. Our results provide a quantitative basis to ascertain variations in gross lava morphology and, perhaps, this will in future be related to emplacement dynamics of different flood basalt provinces, or parts thereof. We can also systematically distinguish outlier lobes (or regions) from typical lobes in a province, e.g., North American Central Atlantic Magmatic Province lava-lobes are anomalously thick and are closely related to feeder-intrusions, thus enabling a better understanding of conditions required to produce large-volume, thick, flood basalt lava-lobes and flows.


2020 ◽  
Vol 13 (18) ◽  
Author(s):  
Raymond A. Duraiswami ◽  
Hetu Sheth ◽  
Purva Gadpallu ◽  
Nasrrddine Youbi ◽  
El Hassane Chellai

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