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Geodetic evidence for interconnectivity between Aira and Kirishima magmatic systems, Japan.

ABSTRACT: It is not known whether clustered or aligned volcanic edifices at the Earth surface have connected magmatic systems at depth. Previously suggested by geological records of paired eruptions, volcano interconnectivity still lacks proper geodetic evidence. Here we use GPS time-series and deformation modeling to show how Aira caldera and Kirishima, two adjacent volcanic centers in Kagoshima graben (southern Japan), interacted during Kirishima unrest in 2011. Whereas Aira caldera had been inflating steadily for two decades, it deflated during the eruption of Kirishima which started with a large-volume lava extrusion. This deflation, which cannot be explained by stress changes, is interpreted as the result of magma withdrawal from the Aira system during the Kirishima replenishment phase. This study highlights the behavior of connected neighboring volcanic systems before and after a large eruption, and the importance of taking into account volcano interactions in eruption probability models.

SUBMITTER: Brothelande E

PROVIDER: S-EPMC6023929 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Exploitable or potentially exploitable deposits of critical metals, such as rare-earth (REE) and high-field-strength elements (HFSE), are commonly associated with alkaline or peralkaline igneous rocks. However, the origin, transport and concentration of these metals in peralkaline systems remains poorly understood. This study presents the results of a mineralogical and geochemical investigation of the Na-metasomatism of alkali amphiboles and clinopyroxenes from a barren peralkaline granite pluton in NE China, to assess the remobilization and redistribution of REE and HFSE during magmatic-hydrothermal evolution. Alkali amphiboles and aegirine-augites from the peralkaline granites show evolutionary trends from sodic-calcic to sodic compositions, with increasing REE and HFSE concentrations as a function of increasing Na-index [Na#, defined as molar Na/(Na+Ca) ratios]. The Na-amphiboles (i.e., arfvedsonite) and aegirine-augites can be subsequently altered, or breakdown, to form hydrothermal aegirine during late- or post-magmatic alteration. Representative compositions analyzed by in-situ LA-ICPMS show that the primary aegirine-augites have high and variable REE (2194-3627 ppm) and HFSE (4194-16,862 ppm) contents, suggesting that these critical metals can be scavenged by alkali amphiboles and aegirine-augites. Compared to the primary aegirine-augites, the presentative early replacement aegirine (Aeg-I, Na# = 0.91-0.94) has notably lower REE (1484-1972) and HFSE (4351-5621) contents. In contrast, the late hydrothermal aegirine (Aeg-II, Na# = 0.92-0.96) has significantly lower REE (317-456 ppm) and HFSE (6.44-72.2 ppm) contents. Given that the increasing Na# from aegirine-augites to hydrothermal aegirines likely resulted from Na-metasomatism, a scavenging-release model can explain the remobilization of REE and HFSE in peralkaline granitic systems. The scavenging and release of REE and HFSE by Na-metasomatism provides key insights into the genesis of globally significant REE and HFSE deposits. The high Na-index of the hydrothermal aegirine might be useful as a geochemical indicator in the exploration for these critical-metals.

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Geodetic evidence for interconnectivity between Aira and Kirishima magmatic systems, Japan.

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