Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Poster

S (Solid Earth Sciences) » S-VC Volcanology

[S-VC43] Volcanic and igneous activities, and these long-term forecasting

Sun. May 20, 2018 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Teruki Oikawa(GSJ, National Institute of Advanced Industrial Science and Technology), Takeshi Hasegawa(Department of Earth Sciences, College of Science, Ibaraki University), Daisuke MIURA(一般財団法人 電力中央研究所 地球工学研究所 地圏科学領域, 共同), Nobuo Geshi(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology)

[SVC43-P09] Major element chemistry of volcanic glass from tephras around Pacayal Volcano in the eastern El Salvador, Central America

*Shigeru Kitamura1 (1.Faculty of Social Welfare, Hirosaki Gakuin University)

Keywords:tephrochronology, WDS, major element analysis

In the mountainous area of the department of Usulutan, El Salvador, Central America, stratovolcanoes are concentrated; Berlin-Tecapa, Tabulete, Usulutan, El Tigre, Chinameca-Pacayal, San Miguell-Chaparrastique. In the area, many pumice layers deposited for the last 100, 000 years are known, called Blanca Rosa, Jucuapa-1, -2, and -3, Twin/Las Gemelas, Unit/Unidad-A, Jucuapa-4, Pacayal-1, -2, -3, and -4, in ascending order, as shown in fig. 1. This study aims at revealing the charracteristics on major element chemistry of these tephras to differenciate them from other tephras and to trace them in other area. For the purpose, chemical composition of volcanic glass from these tephras was analyzed using a wave-length-dispersive electron microprobe analyzer (WDS) in the laboratory of Prof. Siba, Department of Earth and Environmental Science, Hirosaki University, resulted as follows;
1) By the difference in major element chemistry, the tephras in the area can be distinguished from other tephra originating Coatepeque Caldera in western El Salvador, or Ilopango Caldera in central El Salvador.
2) Major element chemistries of the tephras in the area were concentrated to four clusters, as shown in fig. 2. Most of the tephras belong to Cluster I that shows relatively K2O poor and FeO and CaO rich chemistry. The Twin/Las Gemelas tephra and the Unit/Unidad-A tephra compose Cluster II, slightly higher in K2O and lower in FeO and CaO than the chemistry of the Cluster I. The chemistry of the Blanca Rosa tephra and the Jucuapa-4 tephra forms Cluster III, plotted in the area where K2O is higher and FeO and CaO is lower than the Cluster II. Only the Pacayal-1 tephra belongs Cluster IV that shows clearly unique chemistry of lower FeO and higher SiO2 than other tephras while the K2O value is similar to that of the Cluster III.