HR: 1340h
AN: V13E-0590    [Abstracts]
TI: Petrology of Archean greenstone in Wyoming Province -Part 2: Significance of skarn formation in Archean greenstone in Wind River Canyon-
AU: * Yuasa, T
EM: taisukeyuasa@fuji.waseda.jp
AF: Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo, 169-8050 Japan
AU: Takeuchi, Y
EM: yoh-take-21@moegi.waseda.jp
AF: Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo, 169-8050 Japan
AU: Adachi, T
EM: t-adatchi@fuji.waseda.jp
AF: Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo, 169-8050 Japan
AU: Ogasawara, Y
EM: yoshi777@waseda.jp
AF: Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo, 169-8050 Japan
AB: Wind River Canyon area is a part of the Archean greenstone belt in Wyoming Province. Amphibolites and granites crop out along the Wind River. Amphibolites occur in southern part of this area, pink granites occur in northern part. Skarn veins are developed in the limited several ten meters zone of outcrop occupied by amphibolites. Leucocratic granite dyke (1.0m width) crosscut amphibolites and skarn veins. Although Granath (1975) imply skarn veins relate to leucocratic granite, but he did not show the evidence. Pink granites crop out in 2 miles north of this skarn outcrop. Contact relation between leucocratic granite and pink granites were not determined in the field. Amphibolite in this outcrop has a mineral assemblage of Hbl + Pl (An37-43) + Qtz + Ilm Pyr Py. The ring structure suggesting pillow lava (20 to 30cm x 30 to 50cm, rim 1.0 to 3.0cm thickness) is found in amphibolite. Rim mainly consists of Hbl, with minor amount of Pl (An39-43) and Bt. Core assemblage is Hbl + Pl (An32-35) + Qtz ń Ilm. Garnet-clinopyroxene banded skarn shows the symmetric zonation from center to amphibolite; garnet zone | clinopyroxene zone | actinolite zone | amphibolite. Skarn veins sometimes lack garnet zone. Garnet zone (up to 4.0cm width) has a mineral assemblage of Grt (Grs77-86And9-17Alm2-6) + Cpx (Di49-55Hd45-51) + Ep + Ttn + Cal. Garnet includes clinopyroxene and calcite. Clinopyroxene zone (0.5 to 3.0cm width) has a mineral assemblage of Cpx (Di49-53Hd47-51) + Ep + Qtz + Py. Relict assemblage of amphibolite occurs in this zone. Actinolite zone occur with up to 2.0mm width. Gradient of ęCaO occurs from garnet zone to amphibolite. High CaO content phases do not occur in amphibolite. The source of CaO for skarn formation would be fluid. If leucocratic granite crosscut pink granites, one of the possible source of fluid is pink granites. If pink granites crosscut leucocratic granite, another igneous activity could be required to explain skarn formation. CaO component leached from other host rocks into the fluid. Significance of skarn formation are; 1) what kind of rocks contributed to make a high ęCaO condition of fluid? 2) what was the igneous activity for fluid? Conclusion at this moment is; skarn veins occurred by fluid infiltration because of ęCaO gradient along cracks. Timing of skarn formation is after amphibolite-facies metamorphism and/or before leucocratic granite intrusion.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3660 Metamorphic petrology
DE: 8400 VOLCANOLOGY
DE: 9623 Archean
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005