예천전단대 북동부 명호지역 엽리상 화강암류와 압쇄 편마암류에 대한 지구화학및 Nd-Sr 동위원소 연구 (Geochemical and Nd-Sr Isotope Studies for Foliated Granitoids and Mylonitized Gneisses from the Myeongho Area in Northeast Yecheon Shear Zone)

서지정보

· 발행기관 : 대한자원환경지질학회
· 수록지 정보 : 자원환경지질 / 41권 / 3호 / 299 ~ 314페이지
· 저자명 : 김성원, 유인창, 이창윤

초록

The NE-trending Honam shear zone is a broad, dextral strike-slip fault zone between the southern margin of the
Okcheon Belt and the Precambrian Yeongnam Massif in South Korea and is parallel to the trend of Sinian deformation
that is conspicuous in Far East Asia. In this paper, we report geochemical and isotopic(Sr and Nd) data of
mylonitic quartz-muscovite Precambrian gneisses and surrounding foliated hornblende-biotite granitoids near the
Myeongho area in the Yecheon Shear Zone, a representative segment of the Honam Shear Zone. Foliated hornblende-
biotite granitoids commonly plot in the granodiorite field(SiO2=61.9-67.1 wt% and Na2O+K2O=5.21-
6.99 wt%) on SiO2 vs. Na2O+K2O discrimination diagram, whereas quartz-muscovite Precambrian orthogneisses
plot in the granite field. The foliated hornblende-biotite granitoids are mostly calcic and calc-alkalic and are dominantly
magnesian in a modified alkali-lime index(MALI) and Fe# [=FeOtotal/(FeOtotal+MgO)] versus SiO2 diagrams,
which correspond with geochemical characteristics of Cordilleran Mesozoic batholiths. The foliated hornblendebiotite
granitoids have molar ratios of Al2O3/(CaO+Na2O+K2O) ranging from 0.89 to 1.10 and are metaluminous to
weakly peraluminous, indicating I type. In contrast, Paleoproterozoic orthogneisses have peraluminous compositions,
with molar ratios of Al2O3/(CaO+Na2O+K2O) ranging from 1.11 to 1.22. On trace element spider diagrams
normalized to the primitive mantle, the large ion lithophile element(LILE) enrichments(Rb, Ba, Th and U) and negative
Ta-Nb-P-Ti anomalies of foliated hornblende-biotite granitoids and mylonitized quartz-muscovite gneisses in
the Yecheon Shear Zone are features common to subduction-related granitoids and are also found in granitoids from
a crustal source derived from the arc crust of active continental margin. εNd(T) and initial Sr-ratio ratios of foliated
hornblende-biotite granitoids with suggest the involvement of upper crust-derived melts in granitoid petrogenesis.
Foliated hornblende-biotite granitoids in the study area, together with the Yeongju Batholith, show not changing
contents of specific elements(Ti, P, Zr, V and Y) from shear zone to the area near the shear zone. These results
suggest that no volume changes and geochemical alterations in fluid-rich foliated hornblende-biotite granitoids may
occur during deformation, which mass transfer by fluid flow into the shear zone is equal to the mass transfer out
of the shear zone.

영어초록

The NE-trending Honam shear zone is a broad, dextral strike-slip fault zone between the southern margin of the
Okcheon Belt and the Precambrian Yeongnam Massif in South Korea and is parallel to the trend of Sinian deformation
that is conspicuous in Far East Asia. In this paper, we report geochemical and isotopic(Sr and Nd) data of
mylonitic quartz-muscovite Precambrian gneisses and surrounding foliated hornblende-biotite granitoids near the
Myeongho area in the Yecheon Shear Zone, a representative segment of the Honam Shear Zone. Foliated hornblende-
biotite granitoids commonly plot in the granodiorite field(SiO2=61.9-67.1 wt% and Na2O+K2O=5.21-
6.99 wt%) on SiO2 vs. Na2O+K2O discrimination diagram, whereas quartz-muscovite Precambrian orthogneisses
plot in the granite field. The foliated hornblende-biotite granitoids are mostly calcic and calc-alkalic and are dominantly
magnesian in a modified alkali-lime index(MALI) and Fe# [=FeOtotal/(FeOtotal+MgO)] versus SiO2 diagrams,
which correspond with geochemical characteristics of Cordilleran Mesozoic batholiths. The foliated hornblendebiotite
granitoids have molar ratios of Al2O3/(CaO+Na2O+K2O) ranging from 0.89 to 1.10 and are metaluminous to
weakly peraluminous, indicating I type. In contrast, Paleoproterozoic orthogneisses have peraluminous compositions,
with molar ratios of Al2O3/(CaO+Na2O+K2O) ranging from 1.11 to 1.22. On trace element spider diagrams
normalized to the primitive mantle, the large ion lithophile element(LILE) enrichments(Rb, Ba, Th and U) and negative
Ta-Nb-P-Ti anomalies of foliated hornblende-biotite granitoids and mylonitized quartz-muscovite gneisses in
the Yecheon Shear Zone are features common to subduction-related granitoids and are also found in granitoids from
a crustal source derived from the arc crust of active continental margin. εNd(T) and initial Sr-ratio ratios of foliated
hornblende-biotite granitoids with suggest the involvement of upper crust-derived melts in granitoid petrogenesis.
Foliated hornblende-biotite granitoids in the study area, together with the Yeongju Batholith, show not changing
contents of specific elements(Ti, P, Zr, V and Y) from shear zone to the area near the shear zone. These results
suggest that no volume changes and geochemical alterations in fluid-rich foliated hornblende-biotite granitoids may
occur during deformation, which mass transfer by fluid flow into the shear zone is equal to the mass transfer out
of the shear zone.

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