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Advent of Continents: A New Hypothesis

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ABSTRACT

The straightforward but unexpected relationship presented here relates crustal thickness to magma type in the Izu-Ogasawara (Bonin) and Aleutian oceanic arcs. Volcanoes along the southern segment of the Izu-Ogasawara arc and the western Aleutian arc (west of Adak) are underlain by thin crust (10–20 km). In contrast those along the northern segment of the Izu-Ogasawara arc and eastern Aleutian arc are underlain by crust ~35 km thick. Interestingly, andesite magmas dominate eruptive products from the former volcanoes and mostly basaltic lavas erupt from the latter. According to the hypothesis presented here, rising mantle diapirs stall near the base of the oceanic crust at depths controlled by the thickness of the overlying crust. Where the crust is thin, melting occurs at relatively low pressures in the mantle wedge producing andesitic magmas. Where the crust is thick, melting pressures are higher and only basaltic magmas tend to be produced. The implications of this hypothesis are: (1) the rate of continental crust accumulation, which is andesitic in composition, would have been greatest soon after subduction initiated on Earth, when most crust was thin; and (2) most andesite magmas erupted on continental crust could be recycled from “primary” andesite originally produced in oceanic arcs.

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Number-of-analyses histograms of SiO2 content from Quaternary volcanoes along, (a) the northern segment of the Izu-Ogasawara arcs and Torishima, (b) Aleutian arc, east of Adak24, (c) the southern segment of the Izu-Ogasawara arcs, (d) Aleutian arc, west of Adak24, and (e) Oligocene lavas from the IOM system of arcs. Basalt lavas (<53 wt. % SiO2) are dominant eruptive products in the northern segment of the Izu-Ogasawara arcs, at Torishima and east of Adak, but andesites (53–63 wt. % SiO2) show major peaks in the southern segment of the Izu-Ogasawara arcs, west of Adak, and in the IOM arcs during the Oligocene.
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f3: Number-of-analyses histograms of SiO2 content from Quaternary volcanoes along, (a) the northern segment of the Izu-Ogasawara arcs and Torishima, (b) Aleutian arc, east of Adak24, (c) the southern segment of the Izu-Ogasawara arcs, (d) Aleutian arc, west of Adak24, and (e) Oligocene lavas from the IOM system of arcs. Basalt lavas (<53 wt. % SiO2) are dominant eruptive products in the northern segment of the Izu-Ogasawara arcs, at Torishima and east of Adak, but andesites (53–63 wt. % SiO2) show major peaks in the southern segment of the Izu-Ogasawara arcs, west of Adak, and in the IOM arcs during the Oligocene.

Mentions: Figure 3 shows histograms of SiO2 abundances from Quaternary volcanoes along, (a) the northern segment of the Izu-Ogasawara arcs and Torishima, (b) the Aleutian arc, east of Adak24, (c) the southern segment of the Izu-Ogasawara arcs, (d) the Aleutian arc, west of Adak24, and (e) Oligocene lavas from the IOM system of arcs. Five Quaternary volcanoes along the northern segment (Fig. 3a) of the Izu-Ogasawara arcs, eight Quaternary volcanoes along the southern segment (Fig. 3c), and Oligocene lavas from the IOM system of arcs (Fig. 3e) are based on data from references contained in Supplementary Table S1. Basalt lavas (<53 wt. % SiO2) are the dominant eruptive products in the northern segment of the Izu-Ogasawara arcs, Torishima and east of Adak, but andesites (53–63 wt. % SiO2) show major peaks in the southern segment of the Izu-Ogasawara arcs and the western Aleutian arc (west of Adak). Counter-intuitively, magmas passing through thin crust, rather than thick crust, are andesitic (Fig. 1d). Oligocene lavas from the IOM system of arcs are similar to those of the southern segment of the Izu-Ogasawara arcs and west of Adak, tending to be more SiO2-rich, and having unimodal peaks of andesitic compositions ranging from 55 to 65 wt. % SiO2 (Fig. 3e).


Advent of Continents: A New Hypothesis
Number-of-analyses histograms of SiO2 content from Quaternary volcanoes along, (a) the northern segment of the Izu-Ogasawara arcs and Torishima, (b) Aleutian arc, east of Adak24, (c) the southern segment of the Izu-Ogasawara arcs, (d) Aleutian arc, west of Adak24, and (e) Oligocene lavas from the IOM system of arcs. Basalt lavas (<53 wt. % SiO2) are dominant eruptive products in the northern segment of the Izu-Ogasawara arcs, at Torishima and east of Adak, but andesites (53–63 wt. % SiO2) show major peaks in the southern segment of the Izu-Ogasawara arcs, west of Adak, and in the IOM arcs during the Oligocene.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5037404&req=5

f3: Number-of-analyses histograms of SiO2 content from Quaternary volcanoes along, (a) the northern segment of the Izu-Ogasawara arcs and Torishima, (b) Aleutian arc, east of Adak24, (c) the southern segment of the Izu-Ogasawara arcs, (d) Aleutian arc, west of Adak24, and (e) Oligocene lavas from the IOM system of arcs. Basalt lavas (<53 wt. % SiO2) are dominant eruptive products in the northern segment of the Izu-Ogasawara arcs, at Torishima and east of Adak, but andesites (53–63 wt. % SiO2) show major peaks in the southern segment of the Izu-Ogasawara arcs, west of Adak, and in the IOM arcs during the Oligocene.
Mentions: Figure 3 shows histograms of SiO2 abundances from Quaternary volcanoes along, (a) the northern segment of the Izu-Ogasawara arcs and Torishima, (b) the Aleutian arc, east of Adak24, (c) the southern segment of the Izu-Ogasawara arcs, (d) the Aleutian arc, west of Adak24, and (e) Oligocene lavas from the IOM system of arcs. Five Quaternary volcanoes along the northern segment (Fig. 3a) of the Izu-Ogasawara arcs, eight Quaternary volcanoes along the southern segment (Fig. 3c), and Oligocene lavas from the IOM system of arcs (Fig. 3e) are based on data from references contained in Supplementary Table S1. Basalt lavas (<53 wt. % SiO2) are the dominant eruptive products in the northern segment of the Izu-Ogasawara arcs, Torishima and east of Adak, but andesites (53–63 wt. % SiO2) show major peaks in the southern segment of the Izu-Ogasawara arcs and the western Aleutian arc (west of Adak). Counter-intuitively, magmas passing through thin crust, rather than thick crust, are andesitic (Fig. 1d). Oligocene lavas from the IOM system of arcs are similar to those of the southern segment of the Izu-Ogasawara arcs and west of Adak, tending to be more SiO2-rich, and having unimodal peaks of andesitic compositions ranging from 55 to 65 wt. % SiO2 (Fig. 3e).

View Article: PubMed Central - PubMed

ABSTRACT

The straightforward but unexpected relationship presented here relates crustal thickness to magma type in the Izu-Ogasawara (Bonin) and Aleutian oceanic arcs. Volcanoes along the southern segment of the Izu-Ogasawara arc and the western Aleutian arc (west of Adak) are underlain by thin crust (10&ndash;20&thinsp;km). In contrast those along the northern segment of the Izu-Ogasawara arc and eastern Aleutian arc are underlain by crust ~35&thinsp;km thick. Interestingly, andesite magmas dominate eruptive products from the former volcanoes and mostly basaltic lavas erupt from the latter. According to the hypothesis presented here, rising mantle diapirs stall near the base of the oceanic crust at depths controlled by the thickness of the overlying crust. Where the crust is thin, melting occurs at relatively low pressures in the mantle wedge producing andesitic magmas. Where the crust is thick, melting pressures are higher and only basaltic magmas tend to be produced. The implications of this hypothesis are: (1) the rate of continental crust accumulation, which is andesitic in composition, would have been greatest soon after subduction initiated on Earth, when most crust was thin; and (2) most andesite magmas erupted on continental crust could be recycled from &ldquo;primary&rdquo; andesite originally produced in oceanic arcs.

No MeSH data available.


Related in: MedlinePlus