Chemical compositions and K-Ar ages of Pliocene volcanic rocks along Aimagawa river, western Gunma, central Japan

Tetsumaru Itaya, Satoshi Nomura, Mitsuru Ebihara

Research output: Contribution to journalArticle

Abstract

From the area along the Aimagawa river in western Gunma, central Japan, 12 samples were collected for the determination of K-Ar ages and chemical compositions. X-ray fluorescence and instrumental neutron activation analysis methods were applied to determine major and trace elements, respectively. Based on the K-Ar ages, the rock samples were divided into two groups having 4.5Ma and 2.0Ma. Although transformation of magnetite to maghemite, possibly due to high temperature oxidation, was observed among the samples, there is no apparent inconsistency between stratigraphic relation and the K-Ar ages, suggesting that such oxidation gave no effect on the K-Ar ages. No large variation is observed in chemical compositions for both major and trace elements. Among the trace elements, lithophile elements such as rare earth elements and Zn show small variations in their abundances. The samples with K-Ar ages of 4.5Ma yield La/Yb ratios larger than 2.5 as chondrite-normalized values, while the remaining samples (ca. 2.0Ma) give values smaller than 2.0, suggesting a difference in the degree of partial melting between the two stages of magmatism. In contrast to the lithophiles, Cr, Ni, and Co show relatively large variations. Chromium shows a positive correlation with 36Ar. Non-radiogenic Ar must have been trapped in some Cr-bearing mineral(s) (chromite and/or clinopyroxene?).

Original languageEnglish
Pages (from-to)149-160
Number of pages12
JournalGeochemical Journal
Volume23
Issue number4
DOIs
Publication statusPublished - 1989 Jan 1
Externally publishedYes

Fingerprint

Volcanic rocks
Trace Elements
rivers
volcanology
Japan
volcanic rock
Pliocene
chemical composition
Rivers
rocks
trace elements
trace element
Bearings (structural)
Chemical analysis
river
Ferrosoferric Oxide
Chromite
Neutron activation analysis
Thermooxidation
Chromium

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Chemical compositions and K-Ar ages of Pliocene volcanic rocks along Aimagawa river, western Gunma, central Japan. / Itaya, Tetsumaru; Nomura, Satoshi; Ebihara, Mitsuru.

In: Geochemical Journal, Vol. 23, No. 4, 01.01.1989, p. 149-160.

Research output: Contribution to journalArticle

@article{c378a30602fd4306aeaa64313db17e77,
title = "Chemical compositions and K-Ar ages of Pliocene volcanic rocks along Aimagawa river, western Gunma, central Japan",
abstract = "From the area along the Aimagawa river in western Gunma, central Japan, 12 samples were collected for the determination of K-Ar ages and chemical compositions. X-ray fluorescence and instrumental neutron activation analysis methods were applied to determine major and trace elements, respectively. Based on the K-Ar ages, the rock samples were divided into two groups having 4.5Ma and 2.0Ma. Although transformation of magnetite to maghemite, possibly due to high temperature oxidation, was observed among the samples, there is no apparent inconsistency between stratigraphic relation and the K-Ar ages, suggesting that such oxidation gave no effect on the K-Ar ages. No large variation is observed in chemical compositions for both major and trace elements. Among the trace elements, lithophile elements such as rare earth elements and Zn show small variations in their abundances. The samples with K-Ar ages of 4.5Ma yield La/Yb ratios larger than 2.5 as chondrite-normalized values, while the remaining samples (ca. 2.0Ma) give values smaller than 2.0, suggesting a difference in the degree of partial melting between the two stages of magmatism. In contrast to the lithophiles, Cr, Ni, and Co show relatively large variations. Chromium shows a positive correlation with 36Ar. Non-radiogenic Ar must have been trapped in some Cr-bearing mineral(s) (chromite and/or clinopyroxene?).",
author = "Tetsumaru Itaya and Satoshi Nomura and Mitsuru Ebihara",
year = "1989",
month = "1",
day = "1",
doi = "10.2343/geochemj.23.149",
language = "English",
volume = "23",
pages = "149--160",
journal = "Geochemical Journal",
issn = "0016-7002",
publisher = "The Physiological Society of Japan",
number = "4",

}

TY - JOUR

T1 - Chemical compositions and K-Ar ages of Pliocene volcanic rocks along Aimagawa river, western Gunma, central Japan

AU - Itaya, Tetsumaru

AU - Nomura, Satoshi

AU - Ebihara, Mitsuru

PY - 1989/1/1

Y1 - 1989/1/1

N2 - From the area along the Aimagawa river in western Gunma, central Japan, 12 samples were collected for the determination of K-Ar ages and chemical compositions. X-ray fluorescence and instrumental neutron activation analysis methods were applied to determine major and trace elements, respectively. Based on the K-Ar ages, the rock samples were divided into two groups having 4.5Ma and 2.0Ma. Although transformation of magnetite to maghemite, possibly due to high temperature oxidation, was observed among the samples, there is no apparent inconsistency between stratigraphic relation and the K-Ar ages, suggesting that such oxidation gave no effect on the K-Ar ages. No large variation is observed in chemical compositions for both major and trace elements. Among the trace elements, lithophile elements such as rare earth elements and Zn show small variations in their abundances. The samples with K-Ar ages of 4.5Ma yield La/Yb ratios larger than 2.5 as chondrite-normalized values, while the remaining samples (ca. 2.0Ma) give values smaller than 2.0, suggesting a difference in the degree of partial melting between the two stages of magmatism. In contrast to the lithophiles, Cr, Ni, and Co show relatively large variations. Chromium shows a positive correlation with 36Ar. Non-radiogenic Ar must have been trapped in some Cr-bearing mineral(s) (chromite and/or clinopyroxene?).

AB - From the area along the Aimagawa river in western Gunma, central Japan, 12 samples were collected for the determination of K-Ar ages and chemical compositions. X-ray fluorescence and instrumental neutron activation analysis methods were applied to determine major and trace elements, respectively. Based on the K-Ar ages, the rock samples were divided into two groups having 4.5Ma and 2.0Ma. Although transformation of magnetite to maghemite, possibly due to high temperature oxidation, was observed among the samples, there is no apparent inconsistency between stratigraphic relation and the K-Ar ages, suggesting that such oxidation gave no effect on the K-Ar ages. No large variation is observed in chemical compositions for both major and trace elements. Among the trace elements, lithophile elements such as rare earth elements and Zn show small variations in their abundances. The samples with K-Ar ages of 4.5Ma yield La/Yb ratios larger than 2.5 as chondrite-normalized values, while the remaining samples (ca. 2.0Ma) give values smaller than 2.0, suggesting a difference in the degree of partial melting between the two stages of magmatism. In contrast to the lithophiles, Cr, Ni, and Co show relatively large variations. Chromium shows a positive correlation with 36Ar. Non-radiogenic Ar must have been trapped in some Cr-bearing mineral(s) (chromite and/or clinopyroxene?).

UR - http://www.scopus.com/inward/record.url?scp=85010119098&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85010119098&partnerID=8YFLogxK

U2 - 10.2343/geochemj.23.149

DO - 10.2343/geochemj.23.149

M3 - Article

VL - 23

SP - 149

EP - 160

JO - Geochemical Journal

JF - Geochemical Journal

SN - 0016-7002

IS - 4

ER -