Geology and Volcanism of Hyeongjeseom (Islet) Volcano, Jeju Island

Jun Beom Park; Gi Won Koh; Yongmun Jeon; Won Bae Park; Soo Hyoung Moon; Deok Cheol Moon

doi:10.9719/EEG.2021.54.2.187

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Econ. Environ. Geol. 2021; 54(2): 187-197

Published online April 30, 2021

https://doi.org/10.9719/EEG.2021.54.2.187

Geology and Volcanism of Hyeongjeseom (Islet) Volcano, Jeju Island

Jun Beom Park¹, Gi Won Koh^2,*, Yongmun Jeon³, Won Bae Park⁴, Soo Hyoung Moon², Deok Cheol Moon²

Author Info. +

¹US Army Corps of Engineers Far East District, Korea
²Water Resources R&D Center, Jeju Province Development Corporation, Jeju, 63345, Korea
³Jeju World Natural Heritage Headquarters, Jeju Special Self-Governing Province, Jeju, 63341, Korea
⁴Groundwater Researh Center, Jeju Research Institute, Jeju 63147, Jeju, Korea

Correspondence to : limu50@jpdc.co.kr

Received: January 26, 2021; Revised: March 30, 2021; Accepted: March 31, 2021

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The Hyeongjeseom (Islet) is an erosional remnant of volcano which is located about 2 km northeast of sea shore of the Songaksan tuff ring, and is composed of volcaniclastic deposit, agglomerate and scoria deposit, ponded lava, aa lava flows, reworked deposit and beach deposit in ascending order from the base. The volcano is formed by volcaniclastic deposits and lava flows that recorded a transition from initial phreatomagmatic to magmatic explosions followed by lava effusion. It is interpreted that the outcropped volcaniclastic deposit may be a remaining portion of outer ring of a tuff cone. A bomb and a ponded lava yield geochemically basaltic trachyandesite compositions (SiO₂ 51.3 wt%, Na₂O+K₂O 6.0 wt%) and belong to olivine basalt with scarce (<5 %) phenocrysts of olivine, petrographically. By incremental heating Ar-Ar dating method, the plateau age of lava flow in the Heongjesom is 9.2±3.6(2σ) ka, implying that the volcanism of Heongjeseom may have occurred earlier than the Songaksan tuff ring which erupted ca. 3.7 ka. It still remains a task to find a volcano which matches with a historical record of volcanic activity that occurred a thousand years ago.

Keywords Hyengjeseom (Islet), volcanic cycle, Ar-Ar age, Jeju Island

제주도 형제섬 화산체의 지질과 화산활동

박준범¹ · 고기원^2,* · 전용문³ · 박원배⁴ · 문수형² · 문덕철²

¹미육군극동공병단 ²제주개발공사 ³제주특별자치도 세계유산본부 ⁴제주연구원

요 약

형제섬은 송악산에서 북동쪽으로 약 2 km 떨어진 해상에 위치한 침식 잔존 화산체로서, 하부로부터 화산쇄설층, 집괴암 및 분석층, 분화구 용암, 아아 용암류와 이를 피복하는 재동퇴적층과 해빈퇴적층 순으로 이루어져 있다. 형제섬 화산체는 초기 증기 마그마성에서 후기 마그마성 분출과 용암분류로 변화한 화산분화를 기록하고 있는 분출물로 이루어져 있으며, 노두로 남아있는 화산쇄설층은 응회구의 외륜 일부로 해석된다. 화산탄과 분화구 용암류는 현무암질 조면안산암의 조성(SiO₂ 51.3 wt%, Na₂O+K₂O 6.0 wt%)이며 감람석 현무암류에 해당한다. 단계별 가열에 따른 Ar-Ar 연대측정법에 의한 형제섬 용암류의 플래토연대는 9.2±3.6 ka로서, 약 3천 7백 년 전의 분화 기록을 가지고 있는 인접한 송악산 화산체보다 앞서 형성되었음을 의미한다. 여전히, 약 천 년 전 화산분화의 역사 기록에 부합되는 화산체를 찾는 숙제가 남는다.

주요어 형제섬, 화산 윤회, Ar-Ar 연대, 제주도

Article

Research Paper

Econ. Environ. Geol. 2021; 54(2): 187-197

Published online April 30, 2021 https://doi.org/10.9719/EEG.2021.54.2.187

Geology and Volcanism of Hyeongjeseom (Islet) Volcano, Jeju Island

Jun Beom Park¹, Gi Won Koh^2,*, Yongmun Jeon³, Won Bae Park⁴, Soo Hyoung Moon², Deok Cheol Moon²

Correspondence to:limu50@jpdc.co.kr

Received: January 26, 2021; Revised: March 30, 2021; Accepted: March 31, 2021

Abstract

Keywords Hyengjeseom (Islet), volcanic cycle, Ar-Ar age, Jeju Island

제주도 형제섬 화산체의 지질과 화산활동

박준범¹ · 고기원^2,* · 전용문³ · 박원배⁴ · 문수형² · 문덕철²

¹미육군극동공병단 ²제주개발공사 ³제주특별자치도 세계유산본부 ⁴제주연구원

Received: January 26, 2021; Revised: March 30, 2021; Accepted: March 31, 2021

요 약

주요어 형제섬, 화산 윤회, Ar-Ar 연대, 제주도

Fig 1.

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Figure 1.Bird‘s-eye view and general geology of Hyeongjeseom, Jeju Island. Abbreviations: Vd–volcaniclastic deposit; Ag & Sc–agglomerate (lava spatters & bombs) & scoria deposit ; Lp–ponded Lava; Lf–lava flow; Rd–reworked deposit; Bd–beach deposit.

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 2.

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Figure 2.Field photographs of volcaniclastic deposit, Hyeongjeseom, Jeju Island. (a) outcrop (white arrow), (b) various change of strike-dip angle within deposit, (c) stratified unsorted lapilli tuff, (d) stratified lapilli tuff with occasional accidental clasts.

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 3.

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Figure 3.Field photographs of agglomerate, Hyeongjeseom, Jeju Island. (a) lava spatters & bombs overlying the slanted volcaniclastic deposit, (b) quenched and fragmented lava spatters & bombs, (c) quenched and fragmented scoria, (d) agglutinated volcanic bombs and lava spatters.

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 4.

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Figure 4.Field photographs of ponded lava, Hyeongjeseom, Jeju Island. (a, b) columnar jointed lava covered by agglomerate, (c) lava intrudes into agglomerate, (d) massive portion of ponded lava.

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 5.

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Figure 5.Photomicrographs of (a)(b) volcanic bomb(# HJ-01), (c)(d) ponded lava(#HJ-02). (a, c; under cross-polarized light view; b, d; under plane-polarized light view; scale bar 0.5 mm).

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 6.

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Figure 6.Field photographs of lava flows, Hyeongjeseom, Jeju Island. (a, b) aa lava flows, (c) very viscous flow surface, (d) ultramafic mantle xenolith clot (yellow arrow; much smaller than coin).

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 7.

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Figure 7.Field photographs of scoria deposit and reworked deposit, Hyeongjeseom, Jeju Island. The view covered by each image is shown in the inset. (a) black scoria overlying volcaniclastic deposit, (b) relationship between scoria deposit and reworked deposit, (c) re-deposited scoria bottom of the slope, (d) unsorted reworked deposit overlying re-deposited scoria.

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 8.

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Figure 8.(Na₂O+K₂O)(wt%) vs. SiO₂(wt%) plot of the volcanic rocks from Hyeongjeseom, Jeju Island. The fields show rock nomenclature schemes of Le Maitre et al. (2002) with thick solid line from Macdonald and Katura (1964), dividing alkalic rocks from sub-alkalic rocks. Recalculated to 100% on anhydrous basis with Fe₂O₃/FeO ratio, 0.4 (Middlemost, 1989) prior to plotting. Abbreviations: ThB-tholeiitic basalt, AB-alkali basalt; TBtrachybasalt; BTA-basaltic trachyandesite; TA-trachyandesite. Symbol: open circle from Hyeongjeseom and closed square from Songaksan (unpublished data).

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 9.

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Figure 9.Ar-Ar plateau ages of the whole rock (groundmass) samples from Hyeongjeseom, Jeju Island.

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 10.

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Figure 10.Post-glacial sea level rise. (Credit: Robert A. Rohde from Wikimedia Commons is licensed under CC BY-SA 3.0). The red line indicates absolute age of volcanic rock in Hyeongjeseom, Jeju Island.

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Fig 11.

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Figure 11.(a) bathymetry map (numbers in meter indicate depth from the sea surface; data captured from http://www.khoa.go.kr/oceanmap/main.do#) and (b) aerial orthophotography of Hyeongjeseom (dotted circle represents inferred location of crater with approximate 600 m diameter).

Economic and Environmental Geology 2021; 54: 187-197https://doi.org/10.9719/EEG.2021.54.2.187

Table 1 . Major (wt%) element abundances of volcanic rocks from Hyeongjaeseom, Jeju Island.

ID	HJ-1	HJ-2	SE02*
Rock Name	BTA	BTA	TB
SiO₂	51.25	51.31	50.10
TiO₂	2.30	2.32	2.32
Al₂O₃	16.35	16.41	15.55
FeO^t	10.53	10.64	10.47
MnO	0.15	0.15	0.15
MgO	5.48	5.44	6.82
CaO	7.34	7.40	7.92
Na₂O	4.08	4.13	3.75
K₂O	1.88	1.88	1.69
P₂O₅	0.60	0.60	0.54
Total	99.96	100.29	99.31

Analized by XRF, Oregon State University.

Total Fe as FeO^t.

Abbreviation: TB-trachybasalt, BTA-basaltic trachyandesite.

*Sample from Songaksan.

Table 2 . Result of Ar-Ar age dating of volcanic rocks from Hyeongjaeseom, Jeju Island.

ID	Weighted Plateau
ID	Age(ka)	2 s.d.	%³⁹Ar	Steps³	MSWD
HJ-01	48.9	22.1	71.0	13/19	1.15
HJ-02*	9.2	3.6	100.0	41/41	0.58
ID	Normal Isochron
ID	Age(ka)	2 s.d.	⁴⁰Ar/³⁶Ar i	2 s.d	MSWD
HJ-01
HJ-02*	1.8	6.3	301.12	1.76	0.38
ID	Inverse Isochron
ID	Age(ka)	2 s.d.	⁴⁰Ar/³⁶Ar i	2 s.d	MSWD
HJ-01
HJ-02*	1.7	0.9	301.17	1.77	0.38

Samples irradiated at OSU TRIGA reactor for 6 hours at 1MW power. Neutron flux measured using FCT-3 biotite monitor(Renne et al., 1998)..

Material-groundmass; Experiment method - incremental heating; extraction method - bulk laser heating..

Plateau age includes % ³⁹Ar and number of steps in the plateau (steps in plateau / total steps); *Two runs combined..

Dec 31, 2024 Vol.57 No.6, pp. 665~835

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Geology and Volcanism of Hyeongjeseom (Islet) Volcano, Jeju Island

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제주도 형제섬 화산체의 지질과 화산활동

요 약

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Geology and Volcanism of Hyeongjeseom (Islet) Volcano, Jeju Island

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제주도 형제섬 화산체의 지질과 화산활동

요 약

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