Geneses of high chlorine and silver-lead-zinc-mineralized granitoids in Tsushima, Japan

Shunso Ishihara, Akira Imai

研究成果: ジャーナルへの寄稿記事

11 引用 (Scopus)

抄録

Miocene granitoids of the Tsushima Islands have unique characteristics that cannot be seen in other major granitic plutons in the Japanese Islands as follows: (1) They are granitic in composition but contain synplutonic mafic dikes, abundant mafic enclaves, and intermediate facies between granite and mafic enclaves. (2) They are mixture of magnetite-bearing and -free facies, but generally magnetite-free in the marginal part. (3) They are high in K2O content (K65=3.1) and intermediate in normative corundum (C65=0.1) and δ18O value (+9 ‰ at SiO2 70 %), which may be comparable with those of the Miocene Outer Zone granitoids. (4) Yet the initial Sr ratio is low as 0.7037. (5) They are high in Cl and S, which occur in fluid inclusions and as pyrrhotite>pyrite, respectively. Two genetic models are considered for the source of the unique granitoid magmas: the continental crust or the upper mantle fertilized with Si, K and 18O. The latter may be the case for the Tsushima granitoids, because of the low initial Sr ratio. The age of the granitoids (16 Ma) indicates the magmatism related to the opening of the Sea of Japan. It is suggested that both basaltic and granitic magmas were generated in the continental lithosphere under an extensional tectonic setting; the two magmas could have been partly mingled. The mingled magma was originally an oxidized type, but reduced during the emplacement by repeated inflow of S and C-bearing gases from the pelitic wall rocks. Because of the reduction, SO3 sulfur is almost nil in the rock-forming apatite, and most of sulfur remained in fluid phase of the magma as reduced species. Cl content was high in the original magma and concentrated in the fluid phase of the residual system which dissolved silver, lead and zinc metals. Such a fluid migrated into the Taishu fracture systems, as the magma crystallized, and formed the silver-lead-zinc deposits.

元の言語英語
ページ(範囲)169-178
ページ数10
ジャーナルResource Geology
50
発行部数3
DOI
出版物ステータス出版済み - 9 1 2000
外部発表Yes

Fingerprint

Chlorine
Silver
Zinc
chlorine
silver
zinc
magma
Ferrosoferric Oxide
Fluids
enclave
Sulfur
fluid
magnetite
Lead zinc deposits
Bearings (structural)
Miocene
sulfur
Wall rock
Apatites
Gas bearings

All Science Journal Classification (ASJC) codes

  • Geology
  • Geochemistry and Petrology

これを引用

Geneses of high chlorine and silver-lead-zinc-mineralized granitoids in Tsushima, Japan. / Ishihara, Shunso; Imai, Akira.

:: Resource Geology, 巻 50, 番号 3, 01.09.2000, p. 169-178.

研究成果: ジャーナルへの寄稿記事

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abstract = "Miocene granitoids of the Tsushima Islands have unique characteristics that cannot be seen in other major granitic plutons in the Japanese Islands as follows: (1) They are granitic in composition but contain synplutonic mafic dikes, abundant mafic enclaves, and intermediate facies between granite and mafic enclaves. (2) They are mixture of magnetite-bearing and -free facies, but generally magnetite-free in the marginal part. (3) They are high in K2O content (K65=3.1) and intermediate in normative corundum (C65=0.1) and δ18O value (+9 ‰ at SiO2 70 {\%}), which may be comparable with those of the Miocene Outer Zone granitoids. (4) Yet the initial Sr ratio is low as 0.7037. (5) They are high in Cl and S, which occur in fluid inclusions and as pyrrhotite>pyrite, respectively. Two genetic models are considered for the source of the unique granitoid magmas: the continental crust or the upper mantle fertilized with Si, K and 18O. The latter may be the case for the Tsushima granitoids, because of the low initial Sr ratio. The age of the granitoids (16 Ma) indicates the magmatism related to the opening of the Sea of Japan. It is suggested that both basaltic and granitic magmas were generated in the continental lithosphere under an extensional tectonic setting; the two magmas could have been partly mingled. The mingled magma was originally an oxidized type, but reduced during the emplacement by repeated inflow of S and C-bearing gases from the pelitic wall rocks. Because of the reduction, SO3 sulfur is almost nil in the rock-forming apatite, and most of sulfur remained in fluid phase of the magma as reduced species. Cl content was high in the original magma and concentrated in the fluid phase of the residual system which dissolved silver, lead and zinc metals. Such a fluid migrated into the Taishu fracture systems, as the magma crystallized, and formed the silver-lead-zinc deposits.",
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N2 - Miocene granitoids of the Tsushima Islands have unique characteristics that cannot be seen in other major granitic plutons in the Japanese Islands as follows: (1) They are granitic in composition but contain synplutonic mafic dikes, abundant mafic enclaves, and intermediate facies between granite and mafic enclaves. (2) They are mixture of magnetite-bearing and -free facies, but generally magnetite-free in the marginal part. (3) They are high in K2O content (K65=3.1) and intermediate in normative corundum (C65=0.1) and δ18O value (+9 ‰ at SiO2 70 %), which may be comparable with those of the Miocene Outer Zone granitoids. (4) Yet the initial Sr ratio is low as 0.7037. (5) They are high in Cl and S, which occur in fluid inclusions and as pyrrhotite>pyrite, respectively. Two genetic models are considered for the source of the unique granitoid magmas: the continental crust or the upper mantle fertilized with Si, K and 18O. The latter may be the case for the Tsushima granitoids, because of the low initial Sr ratio. The age of the granitoids (16 Ma) indicates the magmatism related to the opening of the Sea of Japan. It is suggested that both basaltic and granitic magmas were generated in the continental lithosphere under an extensional tectonic setting; the two magmas could have been partly mingled. The mingled magma was originally an oxidized type, but reduced during the emplacement by repeated inflow of S and C-bearing gases from the pelitic wall rocks. Because of the reduction, SO3 sulfur is almost nil in the rock-forming apatite, and most of sulfur remained in fluid phase of the magma as reduced species. Cl content was high in the original magma and concentrated in the fluid phase of the residual system which dissolved silver, lead and zinc metals. Such a fluid migrated into the Taishu fracture systems, as the magma crystallized, and formed the silver-lead-zinc deposits.

AB - Miocene granitoids of the Tsushima Islands have unique characteristics that cannot be seen in other major granitic plutons in the Japanese Islands as follows: (1) They are granitic in composition but contain synplutonic mafic dikes, abundant mafic enclaves, and intermediate facies between granite and mafic enclaves. (2) They are mixture of magnetite-bearing and -free facies, but generally magnetite-free in the marginal part. (3) They are high in K2O content (K65=3.1) and intermediate in normative corundum (C65=0.1) and δ18O value (+9 ‰ at SiO2 70 %), which may be comparable with those of the Miocene Outer Zone granitoids. (4) Yet the initial Sr ratio is low as 0.7037. (5) They are high in Cl and S, which occur in fluid inclusions and as pyrrhotite>pyrite, respectively. Two genetic models are considered for the source of the unique granitoid magmas: the continental crust or the upper mantle fertilized with Si, K and 18O. The latter may be the case for the Tsushima granitoids, because of the low initial Sr ratio. The age of the granitoids (16 Ma) indicates the magmatism related to the opening of the Sea of Japan. It is suggested that both basaltic and granitic magmas were generated in the continental lithosphere under an extensional tectonic setting; the two magmas could have been partly mingled. The mingled magma was originally an oxidized type, but reduced during the emplacement by repeated inflow of S and C-bearing gases from the pelitic wall rocks. Because of the reduction, SO3 sulfur is almost nil in the rock-forming apatite, and most of sulfur remained in fluid phase of the magma as reduced species. Cl content was high in the original magma and concentrated in the fluid phase of the residual system which dissolved silver, lead and zinc metals. Such a fluid migrated into the Taishu fracture systems, as the magma crystallized, and formed the silver-lead-zinc deposits.

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