Bridging the gap: 40Ar/39Ar dating of volcanic eruptions from the ‘Age of Discovery’

Preece, Katie; Mark, Darren F.; Barclay, Jenni; Cohen, B. E.; Chamberlain, Katy J.; Jowitt, Claire; Vye-Brown, Charlotte; Brown, Richard J.; Hamilton, Scott

doi:10.1130/g45415.1

Cited by 29 publications

(22 citation statements)

References 24 publications

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“…Volcanism began on the sea bed -6 Myr ago, and subaerial volcanism has occurred from ~1 Ma to present (Kar et al, 1998;Minshull et al, 2010;Paulick et al, 2010;Jicha et al, 2013;Preece et al, 2016). The most recent eruption at Ascension Island has been dated using 40 Ar-39 Ar dating to 0.51 ± 0.18 ka (Preece et al, 2018) -with no evidence for pauses in eruptive activity of greater than 130 kyr throughout the 1 million years of subaerial volcanism (Jicha et al, 2013).…”

Section: Ascension Islandmentioning

confidence: 99%

Lower Crustal Heterogeneity and Fractional Crystallization Control Evolution of Small-volume Magma Batches at Ocean Island Volcanoes (Ascension Island, South Atlantic)

Chamberlain

Barclay

Preece

et al. 2019

Journal of Petrology

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Ocean island volcanoes erupt a wide range of magmatic compositions via a diverse range of eruptive styles. Understanding where and how these melts evolve is thus an essential component in the anticipation of future volcanic activity. Here we examine the role of crustal structure and magmatic flux in controlling the location, evolution and ultimately composition of melts at Ascension Island. Located in the South Atlantic, Ascension Island is an ocean island volcano that has produced a continuum of eruptive compositions from basalt to rhyolite in its 1 Myr subaerial eruptive history. Volcanic rocks broadly follow a silica-undersaturated subalkaline evolutionary trend, and new data presented here show a continuous compositional trend from basalt through trachyte to rhyolite. Detailed petrographic observations are combined with in situ geochemical analyses of crystals and glass, and new whole-rock major and trace element data from mafic and felsic pyroclastic and effusive deposits that span the entire range in eruptive ages and compositions found on Ascension Island. These data show that extensive fractional crystallization is the main driver for the production of felsic melts for Ascension Island, a volcano built on thin, young, oceanic crust. Strong spatial variations in the compositions of erupted magmas reveal the role of a heterogeneous lower crust; differing degrees of interaction with a zone of plutonic rocks are responsible for the range in mafic lava compositions, and for the formation of the central and eastern felsic complexes. A central core of nested, small-scale plutonic, or mush-like, bodies inhibits the ascent of mafic magmas, allowing sequential fractional crystallization within the lower crust, and generating felsic magmas in the core of the island. There is no evidence for magma mixing preserved in any of the studied eruptions, suggesting that magma storage regions are transient, and material is not recycled between eruptions.

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Section: Ascension Islandmentioning

confidence: 99%

Lower Crustal Heterogeneity and Fractional Crystallization Control Evolution of Small-volume Magma Batches at Ocean Island Volcanoes (Ascension Island, South Atlantic)

Chamberlain

Barclay

Preece

et al. 2019

Journal of Petrology

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“…Volcanism began 5-6 Ma [Klingelhöfer et al 2001;Minshull et al 2010], but subaerial volcanism began only at~1 Ma (from Ar-Ar dating, [Jicha et al 2013]). Recent studies have shown that the island is still active, with the most recent eruption dated to 0.51˘0.18 ka [Preece et al 2018]. Ascension Island volcanism is the product of a transitional to mildly alkaline magmatic series of olivine basalt -hawaiite -mugearite -benmoreite -trachyte -rhyolite.…”

Section: Magmatism At Ascension Islandmentioning

confidence: 99%

Deep and disturbed: conditions for formation and eruption of a mingled rhyolite at Ascension Island, south Atlantic

et al. 2020

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The generation of felsic melts (through open or closed system processes) within ocean island volcanoes has been a key area of study since their identification. At Ascension Island in the south Atlantic, explosively erupted felsic melts have, to date, demonstrated a marked absence of signs of magma mixing and crustal assimilation. Here we present the first observations of a fall deposit from Ascension Island recording both macro-and micro-scale evidence for magma mingling. Geochemical analyses of mineral and glass phases, coupled with volatile concentrations of melt inclusions highlight the role of lower-crustal partial melting to produce rhyolitic magmas. Glass textures and the lack of zoning in major mineral phases indicate that mingling with a mafic melt occurred shortly prior to eruption. These inferences of a deep rhyolite production zone, coupled with rapid ascent rates highlight the challenges in forecasting a similar style of eruption at Ascension Island in the future.

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“…The ∼ 3,800 km 3 volcanic edifice rises ∼ 4 km from the sea floor, with only 1% of its total volume exposed subaerially (Harris, 1983;Klingelhöfer et al, 2001). Submarine volcanism is believed to have begun at ∼ 6 to 7 Ma, with the edifice becoming subaerial at ∼ 1.09 Ma (Jicha et al, 2013;Preece et al, 2016Preece et al, , 2018; Figure 2). The geology of the island is well described (e.g., Daly, 1925;Darwin, 1845;Atkins et al, 1964;Nielson and Sibbett, 1996;Weaver et al, 1996;Kar et al, 1998).…”

Section: Ascensionmentioning

confidence: 99%

“…Mafic volcanic rocks are found across the island, whereas felsic eruptive products are found in two main areas; the Central Felsic Complex which forms the high ground in the island's center, and the Eastern Felsic Complex. There has been no historical volcanic activity on the island, although the youngest lava flows have recently been reliably dated at < 1 ka (Preece et al, 2018).…”

Section: Ascensionmentioning

confidence: 99%

Peralkaline Felsic Magmatism of the Atlantic Islands

Jeffery

Gertisser

2018

Front. Earth Sci.

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The oceanic-island magmatic systems of the Atlantic Ocean exhibit significant diversity in their respective sizes, ages, and the compositional ranges of their eruptive products. Nevertheless, almost all of the Atlantic islands and island groups have produced peralkaline felsic magmas, implying that similar petrogenetic regimes may be operating throughout the Atlantic Ocean, and arguably elsewhere. The origins of peralkaline magmas are frequently linked to low-degree partial melting of enriched mantle, followed by protracted differentiation in the shallow crust. However, additional petrogenetic processes such as magma mixing, crustal melting, and contamination have been identified at numerous peralkaline centers. The onset of peralkalinity leads to magma viscosities lower than those typical for metaluminous felsic magmas, which has profound implications for processes such as crystal settling. This study represents a compilation of published and original data which demonstrates trends that suggest that the peralkaline magmas of the Atlantic Ocean islands are generated primarily via extended (up to ∼ 95%), open system fractional crystallization of mantle-derived mafic magmas. Crustal assimilation is likely to become more significant as the system matures and fusible material accumulates in the crust. Magma mixing may occur between various compositional end-members and may be recognized via hybridized intermediate magmas. The peralkaline magmas are hydrous, and frequently zoned in composition, temperature, and/or water content. They are typically stored in shallow crustal magma reservoirs (∼ 2-5 km), maintained by mafic replenishment. Low melt viscosities (1 × 10 1.77 to 1 × 10 4.77 Pa s) facilitate two-phase flow, promoting the formation of alkali-feldspar crystal mush. This mush may then contribute melt to an overlying melt lens via filter pressing or partial melting. We utilize a three-stage model to account for the establishment, development, and termination of peralkaline magmatism in the ocean island magmatic systems of the Atlantic. We suggest that the overall control on peralkaline magmatism in the Atlantic is magma flux rate, which controls the stability of upper crustal magma reservoirs. The abundance of peralkaline magmas in the Atlantic suggests that their development must be a common, but not inevitable, stage in the evolution of ocean islands.

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Bridging the gap: 40Ar/39Ar dating of volcanic eruptions from the ‘Age of Discovery’

Cited by 29 publications

References 24 publications

Lower Crustal Heterogeneity and Fractional Crystallization Control Evolution of Small-volume Magma Batches at Ocean Island Volcanoes (Ascension Island, South Atlantic)

Lower Crustal Heterogeneity and Fractional Crystallization Control Evolution of Small-volume Magma Batches at Ocean Island Volcanoes (Ascension Island, South Atlantic)

Deep and disturbed: conditions for formation and eruption of a mingled rhyolite at Ascension Island, south Atlantic

Peralkaline Felsic Magmatism of the Atlantic Islands

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