The Magmatic Architecture of Continental Flood Basalts: 2. A New Conceptual Model

Abstract

Continental flood basalts intruded and erupted millions of km3 of magma over ∼1–5 Ma. Previous work proposed the presence of large (>105 $ > {\mathrm{10}}^{5}$–106 km3) crustal magma reservoirs to feed these eruptions. However, in Paper I, we illustrated that this model is inconsistent with observations, by combining eruptive rate constraints with geochemical and geophysical observations from the Deccan Traps and other Continental flood basalt provinces (CFBs). Here, we use a new mechanical magma reservoir model to calculate the variation of eruptive fluxes (km3/year) and volumes for different magmatic architectures. We find that a single magma reservoir cannot explain the eruptive rate and duration constraints for CFBs. Using a 1D thermal model and characteristic timescales for magma reservoirs, we conclude that CFB eruptions were likely fed by a number of interconnected small‐medium (∼102–103 km3) magma reservoirs. It is unlikely that each individual magma reservoir participated in every eruption, thus permitting the occasional formation of large xenocrysts (e.g., megacrystic plagioclase). This magmatic architecture permits (a) large volume eruptive episodes with 10–100s of years duration, and (b) relatively short time‐periods separating eruptive episodes (1000s of years) since multiple mechanisms can trigger eruptions (via magma recharge or volatile exsolution, as opposed to long term (105–106 year) accumulation of buoyancy overpressure), and (c) lack of large upper‐crustal intrusive bodies in various geophysical datasets. Our new proposed magmatic architecture has significant implications for the tempo of CFB volatile release (CO2 and SO2), potentially helping explain the pre‐K‐Pg warming associated with Deccan Traps.

Multiscale Spatial Patterns in Giant Dike Swarms Identified Through Objective Feature Extraction

“…However, our analysis suggests that clusters generally represent multiple generations of dikes aligned along narrow axes of activity. This interpretation of large CFB dike swarms provides supporting evidence for a trans‐crustal, multi‐magma reservoir magmatic architecture model for CFBs (Mittal & Richards, 2021). The spatio‐temporal patterns in dike swarms may reflect an integrated lifecycle rather than a single time snapshot of the magmatic system (Black et al., 2021).…”

Systematic and Temporal Geochemical Changes in the Upper Deccan Lavas: Implications for the Magma Plumbing System of Flood Basalt Provinces

“… (a) Schematic sketch showing that the lavas of the MP profile were fed by multiple interconnected small‐ to medium‐sized magma reservoirs located at different crustal levels. Figure modified after Mittal and Richards (2021) (b) Early fractional crystallization (FC) within deep magma reservoirs caused the formation of Ca‐rich plagioclase crystals (gray rectangle) and volatile exsolution (white bubbles). (c) Rapid melt ascent (indicated by white arrow) caused resorption the of previously formed plagioclase and formation of sieve textures.…”

“…Alternatively, the gradual increase in Nb/Th and Ce/Pb could reflect storage in multiple and small crustal magma reservoirs where they underwent variable extents of FC and assimilation. Within these reservoirs, crustal contamination is nearly absent, because previous melts exhausted the most fusible parts and their mafic cumulates formed a compositionally boundary layer that prevented the interaction with the wall rocks (Mittal & Richards, 2021). From these reservoirs, melts periodically erupt to the surface.…”

“…Eruptions are assumed to be triggered by the interaction of these reservoirs, with primitive melts ascending from the lower ones into the upper ones, which results in pulsatory eruptions separated by volcanic hiatuses of ∼10 5 years (Black & Manga, 2017; Karlstrom & Richards, 2011). In contrast, other studies propose that LIPs are fed by interconnected small‐ to medium‐sized (10 2 –10 3 km 3 ) magma reservoirs and individual eruptions are mainly caused by recharge‐associated overpressure leading to more continuous volcanism with frequent eruptions (Mittal & Richards, 2021; Mittal et al., 2021).…”

Cryptic Magma Chamber in the Deccan Traps imaged using receiver function

“…The DVP is one of the most interesting subjects of research for three principal reasons: its enormous size, a typical area to understand the process of magmatism in the planetary system, and a unique case for solid earth-climate interaction leading to major mass extinction and rapid climate change. A series of recent papers (e.g., Krishnamurthy et al, 2000;Mittal et al, 2021;Nava et al, 2021;Self et al, 2022) provide a detailed review of the subject. indicates compound magma flow, and that marked as "S" indicates simple flow (Sen, 2001;Sen & Chandrasekharam, 2011).…”