HR: 1340h
AN: B13A-0192 [Abstracts]
TI: Formation of black and white smokers in the North Fiji Basin: Sulfur and lead isotope
constraints
AU: Kim, J
EM: jukim@kordi.re.kr
AF: Korea Ocean Research and Development Institute, Ansan P.O. Box 29, Seoul, 425-600
Korea, Republic of
AU: * Lee, I
EM: insung@snu.ac.kr
AF: School of Earth and Environmental Sciences, Seoul National University
Shinrim-dong San 56-1, Seoul, 151-742
Korea, Republic of
AU: Lee, K
EM: kylee@kordi.re.kr
AF: Korea Ocean Research and Development Institute, Ansan P.O. Box 29, Seoul, 425-600
Korea, Republic of
AU: Yoo, C
EM: cmyoo@kordi.re.kr
AF: Korea Ocean Research and Development Institute, Ansan P.O. Box 29, Seoul, 425-600
Korea, Republic of
AU: Ko, Y
EM: ytko@kordi.re.kr
AF: Korea Ocean Research and Development Institute, Ansan P.O. Box 29, Seoul, 425-600
Korea, Republic of
AB:
The hydrothermal chimneys were recovered from 16$^{o}$50_S triple junction area in the North Fiji Basin. The chimney samples
are divided into three groups according to their mineralogy and metal contents; 1) Black smoker, 2) White smoker, 3)
Transitional type. Black smoker chimneys are mainly composed of chalcopyrite and pyrite, and are enriched in high temperature
elements such as Cu, Co, Mo, and Se. White smoker chimneys consist of sphalerite and marcasite with trace of pyrite and
chalcopyrite, and are enriched in low temperature elements (Zn, Cd, Pb, As, and Ga). Transitional chimneys show intermediate
characteristics in mineralogy and composition between black and white smokers. Basaltic rocks sampled from the triple
junction show wide variation in geochemistry. Trace elements composition of basaltic rocks indicates that the magma genesis
in the triple junction area was affected by mixing between N-MORB and E-MORB sources. The sulfur and lead isotope
compositions of hydrothermal chimneys show distinct differences between the black and white smokers. Black smokers are
depleted in $^{34}$S ($^{34}$S = +0.4 to +4.8) and are low in lead isotope composition ($^{206}$Pb/$^{204}$Pb = 18.082 to
18.132; $^{207}$Pb/$^{204}$Pb = 15.440 to 15.481; $^{208}$Pb/$^{204}$Pb = 37.764 to 37.916) compared to white smoker and
transitional chimneys ($^{34}$S = +2.4 to +5.6; $^{206}$Pb/$^{204}$Pb = 18.122 to 18.193; $^{207}$Pb/$^{204}$Pb = 15.475 to
15.554; $^{208}$Pb/$^{204}$Pb = 37.882 to 38.150). The heavier sulfur isotopic fractionation in white smoker can be
explained by boiling of hydrothermal fluids and mixing with ambient seawater. The lead isotope compositions of the
hydrothermal chimneys indicate that the metal in black and white smokers come from hydrothermal reaction with N-MORB and
E-MORB, respectively. Regarding both black and white smoker are located in the same site, the condition of phase separation
of hydrothermal fluid that formed white smokers might result from P-T condition of high temperature reaction zone below the
hydrothermal venting site. Our results suggest that white smokers were formed by hydrothermal circulation closely related to
E-MORB magma intrusion at shallower depth. Meanwhile, Black smoker probably formed by deeper intrusion of N-MORB magma before
the formation of white smoker.
DE: 4832 Hydrothermal systems
DE: 3665 Mineral occurrences and deposits
DE: 3035 Midocean ridge processes
DE: 1040 Isotopic composition/chemistry
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting