Explosive summit collapse of Kīlauea Volcano in 1924 preceded by a decade of crustal contamination and anomalous Pb isotope ratios. (1st August 2019)

• Record Type: Journal Article
• Authors: Pietruszka, Aaron J.; Heaton, Daniel E.; Garcia, Michael O.; Marske, Jared P.
• Is Part Of: Geochimica et cosmochimica acta. Volume 258(2019)
• Page Start: 120
• Page End: 137
• Publication Date: 2019-08-01
• Subjects: Kīlauea -- Volcano -- Hawaiʻi -- Lead isotopes -- Mantle melting -- Source heterogeneity -- Magma chamber -- Crustal contamination; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2019.05.029
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: A geochemical time-series analysis of lavas from frequently active basaltic volcanoes has the potential to reveal the enigmatic mantle controls on volcanic behavior and hazards. In May 1924, the century-long lava lake within Halemaʻumaʻu pit crater at the summit of Kīlauea Volcano drained and the floor of Halemaʻumaʻu collapsed, triggering ∼3 weeks of phreatic explosions due to the interaction of groundwater with hot rock. For the next three decades, eruptions at Kīlauea were sporadic (the longest hiatus was from 1934 to 1952), small in volume, and short (typically <1 month long). Here, we show that the Pb isotope ratios of Kīlauea lava groundmass and tephra glass samples erupted from 1912 to 1954 are anomalous and unusually variable. Many of the samples have elevated 207 Pb/ 204 Pb ratios (at a given 206 Pb/ 204 Pb), ranging up to ∼0.05 higher than is typical for Kīlauea lavas. The variations in 206 Pb/ 204 Pb for samples from 1912–1913 (∼0.055), 1917–1921 (∼0.120), 1923 (∼0.065), and 1952–1954 (∼0.037) are larger over short time periods (∼1–4 yr) than observed during the Puʻu ʻŌʻō rift eruption (only ∼0.031 from 1986 to 2012). These Pb isotopic signatures resulted from variable amounts of crustal contamination (most likely by Pb-rich hydrothermal sulfide minerals with high 207 Pb/ 204 Pb ratios) as the parental magmas transited the ∼110 Ma Pacific oceanic crust. This crustal contamination was not directly related to the shallow volcanic events of 1924. Instead, mantle-driven processes at Kīlauea during the previous century—a factor of ∼2 decrease in the degree of partial melting of an increasingly refractory source—led to a decline in the magma supply rate, a major disruption of the magmatic plumbing system, and, for at least a decade prior to 1924, crustal contamination at or below the base of the volcanic edifice (>10 km). The Pb isotopic heterogeneity of the samples on short length (hand specimen to lava flow) and time (∼1–4 yr) scales can be explained by inefficient mixing as small batches of contaminated magma were delivered to the remnants of Kīlauea's summit magma storage reservoir. Our results confirm that the Pb isotope ratios of basalts from ocean-island volcanoes may be significantly modified by assimilation of materials from the underlying oceanic crust. In particular, the 207 Pb/ 204 Pb ratio may be a sensitive tracer of such crustal contamination at Hawaiian shield volcanoes. Mauna Loa lavas display a factor of ∼5 more scatter towards higher 207 Pb/ 204 Pb at a given 206 Pb/ 204 Pb ratio than most Kīlauea lavas (excluding the samples from 1912 to 1954). This might be caused by more pervasive crustal contamination at Mauna Loa due to its lower magma supply rate over the last ∼4 kyr.