[SCG52-P09] Petrological study on the intrusive contact of a Setouchi volcanic rock dike in the Nakajima
Island, Ehime Prefecture
Keywords:Setouchi volcanic rocks, Nakajima Island, Ehime Prefecture
We performed a detailed petrological study on the intrusive contact between a Setouchi andesitic
dike and host Ryoke granitoids occurring in the Nakajima Island, Ehime Prefecture. At the
intrusive contact, the andesite contains many fragments of host granitoids. The bulk SiO2 contents
of the marginal andesite at the intrusive contact are markedly higher than those of internal
domain implying the mixing between the andesite intrusion and the host granitoids. Other bulk
chemical compositions such as MgO, CaO, Na2O, K2O, Cr and Zr also imply mixing of the host
granitoids into the andesite intrusion at the intrusive contact. However, the Al2O3 contents of the
marginal andesite can not be explained by bulk mixing of the host granitoids and the andesite
intrusion because the Al2O3 contents of the marginal andesite are higher than those of the host
granites and internal domain of the andesite intrusion. Assuming that the marginal andesite with
chilled margin texture retain original compositions of intrusive magma, we tested the major
element mass-balance modeling to explain chemical compositions of internal domain of the
andesite intrusion. The modeling reproduced the major element compositions of internal
andesites by adding ~7 % of host granite components and ~12 % of mafic phenocryst minerals
into the marginal andesite.
dike and host Ryoke granitoids occurring in the Nakajima Island, Ehime Prefecture. At the
intrusive contact, the andesite contains many fragments of host granitoids. The bulk SiO2 contents
of the marginal andesite at the intrusive contact are markedly higher than those of internal
domain implying the mixing between the andesite intrusion and the host granitoids. Other bulk
chemical compositions such as MgO, CaO, Na2O, K2O, Cr and Zr also imply mixing of the host
granitoids into the andesite intrusion at the intrusive contact. However, the Al2O3 contents of the
marginal andesite can not be explained by bulk mixing of the host granitoids and the andesite
intrusion because the Al2O3 contents of the marginal andesite are higher than those of the host
granites and internal domain of the andesite intrusion. Assuming that the marginal andesite with
chilled margin texture retain original compositions of intrusive magma, we tested the major
element mass-balance modeling to explain chemical compositions of internal domain of the
andesite intrusion. The modeling reproduced the major element compositions of internal
andesites by adding ~7 % of host granite components and ~12 % of mafic phenocryst minerals
into the marginal andesite.