Volatiles and the tempo of flood basalt magmatism

Journal Article · Wed Nov 09 00:00:00 EST 2016 · Earth and Planetary Science Letters

DOI:https://doi.org/10.1016/j.epsl.2016.09.035· OSTI ID:1479295

Black, Benjamin A.  ^[1]; Manga, Michael ^[2]

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1. University of California, Berkeley, CA (United States); City University (CUNY), NY (United States)
2. University of California, Berkeley, CA (United States)

We report that individual flood basalt lavas often exceed 10³ km³ in volume, and many such lavas erupt during emplacement of flood basalt provinces. The large volume of individual flood basalt lavas implies correspondingly large magma reservoirs within or at the base of the crust. To erupt, some fraction of this magma must become buoyant and overpressure must be sufficient to encourage failure and dike propagation. The overpressure associated with a new injection of magma is inversely proportional to the total reservoir volume, and as a large magma body heats the surrounding rocks thermally activated creep will relax isotropic overpressure more rapidly. Here, we examine the viability of buoyancy overpressure as a trigger for continental flood basalt eruptions. We employ a new one-dimensional model that combines volatile exsolution, bubble growth and rise, assimilation, and permeable fluid escape from Moho-depth and crustal chambers. We investigate the temporal evolution of degassing and the eruptibility of magmas using the Siberian Traps flood basalts as a test case. We suggest that the volatile inventory set during mantle melting and redistributed via bubble motion controls ascent of magma into and through the crust, thereby regulating the tempo of flood basalt magmatism. Volatile-rich melts from low degrees of partial melting of the mantle are buoyant and erupt to the surface with little staging or crustal interaction. Melts with moderate volatile budgets accumulate in large, mostly molten magma chambers at the Moho or in the lower crust. These large magma bodies may remain buoyant and poised to erupt—triggered by volatile-rich recharge or external stresses—for ~10⁶ yr. If and when such chambers fail, enormous volumes of magma can ascend into the upper crust, staging at shallow levels and initiating substantial assimilation that contributes to pulses of large-volume flood basalt eruption. Our model further predicts that the Siberian Traps may have released 1019–1020g of CO₂ during a number of brief (~10⁴ yr) pulses, providing a plausible trigger for warming and ocean acidification during the end-Permian mass extinction. The assimilation of carbon-rich crustal rocks strongly enhances both flood basalt eruptibility and CO₂ release, and the tempo of eruptions influences the environmental effects of CO₂, SO₂, and halogen degassing. The eruptive dynamics of flood basalts are thus inextricably linked with their environmental consequences.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC); National Science Foundation (NSF)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1479295
• Journal Information: Earth and Planetary Science Letters, Vol. 458, Issue C; ISSN 0012-821X
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
flood basalts
volcanology
eruption dynamics
Siberian traps
magmatic processes
volatiles