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Eruption Types and Textures of Pyroclastics from the Jugam Scoria Deposits, Ulleung Island, Korea
울릉도 죽암분석층에서 나온 화성쇄설물들의 조직과 분화유형
Econ. Environ. Geol. 2019 Oct;52(5):459-69
Published online October 31, 2019;  https://doi.org/10.9719/EEG.2019.52.5.459
Copyright © 2019 the Korean society of economic and environmental gelology.

Sang Koo Hwang1,2, Ung San Ahn3*, So Jin Lee2 and Kyung Sik Oh4
황상구1.2 · 안웅산3* · 이소진2 · 오경식4

1Department of Earth and Environmental Sciences, Andong National University, Andong 36729, Korea
2Institute of Basic Sciences, Andong National University, Andong 36729, Korea
3World Heritage Office, Jeju Special Self-govering Province, Jeju 63341, Korea
4Division of New Material Engineering, Andong National University, Andong 36729, Korea
1안동대학교 자연과학대학 지구환경과학과, 2안동대학교 기초과학연구소 3제주특별자치도 세계유산본부, 4안동대학교 공과대학 신소재학부
Received September 24, 2019; Revised October 23, 2019; Accepted October 24, 2019.
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 the original work is properly cited.
 Abstract
We present a quantitative evaluation of density, vesicularity and microtextures for coarse lapilli collected from the Jugam Scoria Deposits, northeastern Ulleung Island. Lapilli from the deposits have modal vesicularities of 61% in the lower part and 67% in the upper part, and vesicle populations dominated by non-interconnected subround vesicles. Clasts of modal vesicularity have margin-parallel zonation, with subaerially quenched rims interpreted to preserve “syn-fragmentation” magmatic textures in microlite-free sideromelane rims, grading “post-fragmentation” tachylitic interiors with vesicle and microlite textures that progressively coarsen from rim to interior. Degassing scenarios are linked to syn-fragmentation vesicle textures to demonstrate that the magmas degassed in dominantly closed systems. And diffusion-controlled cooling rates of trachyandesitic pyroclasts in contact with atmosphere are linked to post-fragmentation evolution of vesicle and microlite textures to infer about transportation and dispersal of the pyroclasts in low shooting jets. These textural analyses show that the Jugam eruptions were strictly applied to the strombolian type, analogous to the hawaiian type among any classical subaerial eruption type.
Keywords : Jugam Scoria Deposits, lapilli, vesicularity, microtexture, strombolian eruption

 

December 2019, 52 (6)