Magma ascent and degassing processes of the 2011 and 2017–18 eruptions of Shinmoedake in Kirishima volcano group, Japan, based on petrological characteristics and volatile content of magmas

Saito, Genji; Oikawa, Teruki; Ishizuka, Osamu

doi:10.1186/s40623-023-01836-1

Earth, Planets and Space

Table 4 Calculation of bulk volatile contents in the 2011 and 2018 magmas. Details of the calculations are given in the text and the footnotes

From: Magma ascent and degassing processes of the 2011 and 2017–18 eruptions of Shinmoedake in Kirishima volcano group, Japan, based on petrological characteristics and volatile content of magmas

	2011 eruptions
	Assumptions		Results
	End member melts ^a		2011 mixed magma^b				2011 mafic magma		2011 felsic magma
	2011 mafic melt	2011 felsic melt	2011 mixed melt of A1 magma	2011 mixed melt of A2 magma	Bulk volatile content of A1 magma	Bulk volatile content of A2 magma	Bulk volatile content of M1 magma	Bulk volatile content of M2 magma	Bulk volatile content of F1 magma	Bulk volatile content of F2 magma
SiO₂ (wt%)	56.07	74.23	62.00	62.00
H₂O (wt%)	7.0	3.7	5.9	5.9	4.0	4.0	6.2	6.2	3.7	1.9
CO₂ (wt%)	(1.5, 0.28)	0.048	1.00	0.21	0.70	0.14	1.4	0.25	0.048	0.025
S (wt%)	0.156	0.007	0.107	0.107	0.072	0.072	0.138	0.138	0.007	0.004
Cl (wt%)	0.056	0.087	0.066	0.066	0.044	0.044	0.050	0.050	0.087	0.045

	2018 eruptions
	Assumptions			Results
	End member melts^c			2018 magma^d
	2018 mafic melt	2018 felsic melt 1	2018 felsic melt 2	2018 mixed melt 1	Bulk volatile content of B1 magma	2018 mixed melt 2	Bulk volatile content of B2 magma
SiO₂ (wt%)	59.72	75.83	72.35	65.00		65.00
H₂O (wt%)	5.0	3.5	0.5	4.5	3.0	3.1	2.1
CO₂ (wt%)	–	–	–	0.15	0.10	0.13	0.087
S (wt%)	0.138	0.005	0.003	0.094	0.063	0.082	0.054
Cl (wt%)	0.072	0.129	0.094	0.091	0.060	0.081	0.054

^a"2011 mafic melt" and "2011 felsic melt" indicate melts in a mafic and a felsic magma of the 2011 eruptions. The CO₂ contents of the 2011 mafic melts shown in parenthesis, 1.5 wt% of the melt of M1 magma and 0.28 wt% of the melt of M2 magma, were estimated as below
^bThe mixing mass ratio of the mafic and felsic melts in mixed magma (mafic:felsic = 0.67:0.33) was calculated from SiO₂ contents of the mafic, felsic and mixed melts. Water, S and Cl contents of the mixed melt were calculated from the mixing mass ratio and H₂O, S and Cl contents of the mafic and felsic melts. Bulk CO₂ content of A1 magma was obtained from the bulk S content (0.072 wt%) and mass ratio of CO₂ and S in the volcanic gas (9.8). This mass ratio was calculated from mole ratio of SO₂ and H₂S (SO₂/H₂S = 8) observed on 15 March 2011 and mole ratio of CO₂ and SO₂ (CO₂/SO₂ = 8) observed on 18 May 2011 (Shinohara 2013; Additional file 11). Bulk CO₂ content of A2 magma was obtained from the bulk H₂O content (4.0 wt%) and mass ratio of CO₂ and H₂O in the volcanic gas (0.035), that was calculated from mole ratio of H₂O and CO₂ (H₂O/CO₂ = 70) of the volcanic gas (Shinohara 2013). The CO₂ contents of 2011 mixed melts were calculated to be 1.0 wt% for A1 magma and 0.21 wt% for A2 magma based on the bulk CO₂ contents and the phenocryst content in a case that the magmas had no gas phase
^c"2018 mafic melt", "2018 felsic melt 1" and "2018 felsic melt 2" indicate melts in a mafic and a felsic magma of the 2018 eruptions
^dThe mixing mass ratio of 2018 mixed melt 1 (mafic:felsic = 0.67:0.33) was calculated from SiO₂ contents of the 2018 mafic melt, the 2018 felsic melt 1 and the mixed melt. Water, S and Cl contents of the mixed melt 1 were calculated from the mixing mass ratio and H₂O, S and Cl contents of the mafic melt and the 2018 felsic melt 1. Bulk CO₂ content of B1 magma was obtained fromthe bulk S content (0.063 wt%) and mass ratio of CO₂ and S in the volcanic gas (1.6). This mass ratio was calculated from mole ratio of SO₂ and H₂S (SO₂/H₂S = 2.7) and that of CO₂ and SO₂ (CO₂/SO₂ = 1.6) observed on 12 October 2017 (GSJ/AIST 2017; Additional file 11). The mixing mass ratio of 2018 mixed melt 2 (mafic:felsic = 0.58:0.42) was calculated from SiO₂ contents of the 2018 mafic melt, the 2018 felsic melt 2 and the 2018 mixed melt 2. Water, S and Cl contents of the mixed melt 2 were calculated from the 2018 mixing mass ratio and H₂O, S and Cl contents of the mafic melt and the felsic melt 2. Bulk CO₂ content of B2 magma was obtained from the bulk S content (0.054 wt%) and the mass ratio of CO₂ and S in the volcanic gas (1.6). The CO₂ contents of 2018 mixed melts were calculated to be 0.15 wt% for B1 magma and 0.13 wt% for B2 magma based on the bulk CO₂ contents and the phenocryst content

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