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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. Plain Language Summary: Continental flood basalts represent some of the largest volcanic events in Earth's history with a significant impact on the terrestrial environment. However, the nature of the magmatic system associated with the eruption of millions of cubic km of basaltic lavas remains an open question. In this study, we developed a set of new mechanical and thermal models to analyze what sized magma chambers can feed the CFB lavas and what is the dominant physical process leading to eruptions. We find that flood basalt lavas were most likely erupted from a set of interconnected medium (∼102–103 km3) sized magma chambers. In addition, eruptions were most likely initiated by magma recharge instead of magma buoyancy associated overpressure. Using these results, we develop a new conceptual model for continental flood basalt volcanism and show that it can help explain the key observational characteristics. Our results also have implications for the CO2 flux from flood basalts and the consequent environmental impact. Key Points: Mechanical magma reservoir model demonstrates that individual continental flood basalt province (CFB) eruptive episodes cannot be fed by a single large crustal magma bodyCFB eruptions are likely fed from a number of small‐medium sized (∼102–103 km3) interconnected magma reservoirsOur new transcrustal magmatic plumbing model explains the primary geophysical and geochemical characteristics for continental flood basalts [ABSTRACT FROM AUTHOR]

Flood basalts are some of the largest magmatic events in Earth history, with intrusion and eruption of millions of km3 of basaltic magma over a short time period (∼1–5 Ma). A typical continental flood basalt (CFB) is emplaced in hundreds of individual eruptive episodes lasting decades to centuries with lava flow volumes of 103–104 km3. These large volumes have logically led to CFB models invoking large magma reservoirs (>104 $ > {\mathrm{10}}^{4}$–105 km3) within the crust or at Moho depth. Since there are currently no active CFB provinces, we must rely on observations of past CFBs with varying degrees of surface exposure to develop and test models. In the last few decades, significant improvements in geochronological, geochemical, paleomagnetic, volcanological, and paleo‐proxy measurements have provided high‐resolution constraints on CFB eruptive tempo ‐ the volume, duration, and frequency of individual eruptive episodes. Using the well‐studied Deccan Traps as an archetype for CFB systems, we compile multiple lines of evidence–geochronology, eruption tempo, dike spatial distribution, intrusive‐extrusive ratio, geochemical variations, and volcanological observations–to assess the viability of previous models. We find that the presence of just a few large crustal magma reservoirs is inconsistent with these constraints. Although observations from the Deccan Traps primarily motivate our model, we discuss constraints from other CFBs to illustrate that this conclusion may be broadly applicable for CFB magmatic systems in general. Plain Language Summary: Flood basalt eruptions are among the largest volcanic events in Earth history, erupting millions of cubic kilometers of lava over a geologically short time interval (∼1–5 Ma). Typically, continental flood basalt (CFB) eruptive sequences have hundreds of individual eruptions, each with a volume of thousands of km3 of lavas. This is significantly larger than any volcanic eruption within human history. Because of the large size of the eruptions, it is usually assumed that the magma reservoir(s) feeding the eruption are also very large (>104 $ > {\mathrm{10}}^{4}$–105 km3). In this study, we use the size, duration, and frequency of individual eruptions as known from several lines of evidence (geochronological, geochemical, paleomagnetic, volcanological, and paleo‐proxy measurements) to investigate the properties of CFB magmatic systems. We find that the dynamics of these eruptions are inconsistent with just a few large magma reservoirs and instead require a network of smaller magma bodies feeding each eruption. Key Points: We compile diverse observations from geochronology, geochemistry, volcanology for the Deccan Traps to constrain magmatic architectureThese different datasets consistently suggest large, frequent eruptions for Deccan Traps (and potentially other CFBs)Constraints from Deccan eruptive tempo, geophysics, and geochemistry are inconsistent with the large crustal magma reservoir model [ABSTRACT FROM AUTHOR]

The loss of volatiles from a magma reservoir affects the magmatic overpressure responsible for driving ground deformation and eruptions. Although the high‐temperature metamorphic aureole around a magma chamber is typically considered to have low permeability, recent theoretical, experimental, and field studies have highlighted the role of transient permeability in magmatic systems. Also, direct measurements suggest that passive degassing is a significant component of total volatile loss in both basaltic and silicic volcanoes. Consequently, the effective permeability of the crust when magma is present in the system can be many orders of magnitude larger than that of exhumed rock samples. We develop a fully coupled porothermoelastic framework to account for both the flow of volatiles as well as associated effects on the stress state of the crust and calculate an analytical solution for spherical geometry. We then combine a magma chamber box model with these solutions to analyze eruption dynamics in magmatic systems. We find that in addition to viscous relaxation, magma recharge, and cooling timescales, the pore pressure diffusion timescale exerts a first‐order control on volcanic eruptions with moderately high crustal permeabilities of order 10−17 to 10−19 m2. We describe a parameter space to identify which components dominate in different regimes for volcanic eruptions according to these different timescales. Key Points: Passive degassing of volatiles from a magma reservoir is a ubiquitous phenomenon which affects magma eruptibilityWe develop a fully coupled porothermoviscoelastic framework to analyze coupling between the magma reservoir and the surrounding crustLow crustal permeability of order 10−18 to 10−19 m2 are sufficient for pore pressure diffusion to be important [ABSTRACT FROM AUTHOR]

Frictional properties affect the propagation of high-amplitude seismic waves across rock fractures and faults. Laboratory evidence suggests that these properties can be measured in active seismic surveys, potentially offering a route to characterizing friction in situ. We present experimental results from a subresonance torsional modulus and attenuation apparatus that utilizes micron-scale sinusoidal oscillations to probe the nonlinear stress-strain relation at a range of strain amplitudes and rates. Nonlinear effects are further quantified using harmonic distortion; however, time series data best illuminate underlying physical processes. The low-frequency stress-strain hysteretic loops show stiffening at the sinusoid's static ends, but stiffening is reduced above a threshold frequency. This shape is determined by harmonic generation in the strain; the stress signal has no harmonics, confirming that the fractured sample is the source of the nonlinearity. These qualitative observations suggest the presence of rate-dependent friction and are consistent between fractures in three different rock types. We propose that static friction at the low strain rate part of the cycle, when given sufficient 'healing' time at low oscillation frequencies, causes this stiffening cusp shape in the hysteresis loop. While rate-and-state friction is commonly used to represent dynamic friction, it cannot capture static friction or negative slip velocities. So we implement another dynamic friction model, based on the work of Dahl, which describes this process and produces similar results. Since the two models have a similar form, parameterizations of field data could constraint fault model inputs, such as specific location velocity strengthening or weakening properties. [ABSTRACT FROM AUTHOR]