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Volumetric extrusive rates of silicic supereruptions from the Afro-Arabian large igneous province.

ABSTRACT: The main phase of silicic volcanism from the Afro-Arabian large igneous province preserves some of the largest volcanic eruptions on Earth, with six units totaling >8,600 km³ dense rock equivalent (DRE). The large volumes of rapidly emplaced individual eruptions present a case study for examining the tempo of voluminous silicic magma generation and emplacement. Here were report high-precision ²⁰⁶Pb/²³⁸U zircon ages and show that the largest sequentially dated eruptions occurred within 48 ± 34 kyr (29.755 ± 0.023 Ma to 29.707 ± 0.025 Ma), yielding the highest known long-term volumetric extrusive rate of silicic volcanism on Earth. While these are the largest known sequential silicic supereruptions, they did not cause major global environmental change. We also provide a robust tie-point for calibration of the geomagnetic polarity timescale by integrating ⁴⁰Ar/³⁹Ar data with our ²⁰⁶Pb/²³⁸U ages to yield new constraints on the duration of the C11n.1r Subchron.

SUBMITTER: Thines JE

PROVIDER: S-EPMC8563981 | biostudies-literature | 2021 Nov

REPOSITORIES: biostudies-literature

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Volumetric extrusive rates of silicic supereruptions from the Afro-Arabian large igneous province.

Thines Jennifer E JE Ukstins Ingrid A IA Wall Corey C Schmitz Mark M

Nature communications 20211102 1

The main phase of silicic volcanism from the Afro-Arabian large igneous province preserves some of the largest volcanic eruptions on Earth, with six units totaling >8,600 km3 dense rock equivalent (DRE). The large volumes of rapidly emplaced individual eruptions present a case study for examining the tempo of voluminous silicic magma generation and emplacement. Here were report high-precision 206Pb/238U zircon ages and show that the largest sequentially dated eru ...[more]

PMID: 34728621

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Project description:The degree and extent of crustal hydrothermal alteration related to the eruption of large igneous provinces is poorly known and not easily recognizable in the field. We here report a new δ18O dataset for dikes and lavas from the Columbia River Basalt Group (16-15 Ma) in the western USA, and document that dikes on average are 1-2‰ more depleted in δ18O than basalt flows. We show that this observation is best explained with the involvement of heated meteoric waters during their cooling in the crust. The largest 6-8‰ depletion is found around and inside a 10 m-thick feeder dike that intruded the 125 Ma Wallowa tonalitic batholith. This dike likely operated as a magma conduit for 4-7 years, based on the extent of heating and melting its host rocks. We show that this dike also created a hydrothermal system around its contacts extending up to 100 m into the surrounding bedrock. A model that considers (a) hydrothermal circulation around the dike, (b) magma flow and (c) oxygen isotope exchange rates, suggests that the hydrothermal system operated for ~150 years after the cessation of magma flow. In agreement with a previously published (U-Th)/He thermochronology profile, our model shows that rocks 100 m away from such a dike can be hydrothermally altered. Collectively, our sample set is the first documentation of the widespread hydrothermal alteration of the shallow crust caused by the intrusion of dikes and sills of the Columbia River Basalt Province. It is estimated that heating and hydrothermal alteration of sediments rich in organic matter and carbonates around the dikes and sills releases 18 Gt of greenhouse gases (CH4 and CO2). Furthermore, hydrothermal δ18O depletion of rocks around dikes covers 500-600 km3, which, when scaled to the total CRB province constitutes 31,000 km3 of low-δ18O rocks. These volumes of crust depleted in δ18O are sufficient to explain the abundant low-δ18O magmas in eastern Oregon and western Idaho. This work also demonstrates that the width and magnitude of δ18O depletion around dikes can identify them as feeders. Given this, we here interpret Paleoproterozoic dikes in Karelia with the world's lowest δ18O depletions (-27.8‰) as feeders to the coeval large igneous province aged 2.2-2.4 Ga that operated under the Snowball Earth glaciation conditions.

Project description:AimUnderstanding diversity patterns and identifying the environmental factors that shape these patterns are essential for ecology and conservation. The Afro-Arabian region comprises one of the most important biogeographic areas connecting continents. Yet, little emphasis has been put on understanding its endemic fauna in relation to its biogeographic realms. Our objective is to fill the gaps in knowledge on diversity patterns and biogeography that are essential for prioritizing the overdue conservation efforts.LocationThe study area covers mostly the hot desert climate region in North Africa and Arabia, and includes the Mediterranean, Sahel, and Ethiopian highlands (hereafter "Afro-Arabian region").MethodsWe used distribution maps developed by IUCN and BirdLife for species endemic to the Afro-Arabian region belonging to the four tetrapod classes, amphibians, reptiles, birds, and mammals, to identify the endemic richness hotspots. We then used multivariate analyses to delineate biogeographic regions and evaluate their relationship with the environmental factors.ResultsOur study reveals a complex map of the richness hotspots for the endemic tetrapod classes. The main hotspots of endemism were concentrated at the margins of the study area, along the Mediterranean coast, Ethiopian highlands, and along the Red Sea Mountains. We propose classifying the Afro-Arabian region into three discrete biogeographic realms for endemic amphibians, four for reptiles and birds, and five discrete biogeographic realms for endemic mammals. The identified realms are defined by their environmental conditions and the historical geological processes.Main conclusionsRichness hotspots of endemic tetrapod classes were heterogeneously distributed in the Afro-Arabian region. Our results support the hypothesis that species diversity patterns and endemism have been shaped by the environmental conditions and the paleogeographic processes. Each of the identified bioregions is associated with a characteristic set of tetrapod species. Our results are a benchmark for assessing the effectiveness of the protected areas and for implementing conservation plans for biodiversity.

Dataset Information

Volumetric extrusive rates of silicic supereruptions from the Afro-Arabian large igneous province.

Publications

Volumetric extrusive rates of silicic supereruptions from the Afro-Arabian large igneous province.

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