ミクロネシア連邦ポンペイ島における火山岩の産状
と古地磁気学的性質
著者
北村 有迅
雑誌名
南太平洋海域調査研究報告=Occasional papers
巻
56
ページ
61-64
別言語のタイトル
"Occurrence of Volcanic Rocks and Their
Paleomagnetic Property in Pohnpei Island, the
Federated States of Micronesia"
࣑ࢡࣟࢿࢩ㐃㑥࣏ࣥ࣌ᓥ࠾ࡅࡿ
ⅆᒣᒾࡢ⏘≧ྂᆅ☢ẼᏛⓗᛶ㉁
ᮧ᭷㎿
Occurrence of Volcanic Rocks and Their Paleomagnetic
Property in Pohnpei Island, the Federated States of Micronesia
KITAMURAYujin
㮵ඣᓥᏛᏛ㝔⌮ᕤᏛ◊✲⛉
Graduate School of Science and Engineering, Kagoshima University
せ᪨ すኴᖹὒࡢኴᖹὒࣉ࣮ࣞࢺୖᮾす⣙3,000km ᗈࡀࡿ࢝ࣟࣜࣥᾏᕊࡣࡑࡢᡂᅉࡸᙧᡂ㐣⛬ࡀᮍヲ࡛ ࠶ࡿࠋᮏ◊✲࡛ࡣྂᆅ☢ẼᏛⓗ࡞᳨ウࡽࡇࢀࢆ᫂ࡽࡍࡿࡃࠊ࣑ࢡࣟࢿࢩ㐃㑥࣏ࣥ࣌ᓥ࠾࠸࡚ ᆅ㉁ㄪᰝ࠾ࡼࡧᒾ▼ヨᩱ᥇ྲྀࢆ⾜ࡗࡓࠋᓥෆࡢ㟢㢌࠾࠸࡚ࡣඛ⾜◊✲࡛ㄆࡵࡽࢀࡓྛ✀ᒾ▼ࡀ☜ㄆ࡛ࡁࡓࠋ ࡲࡓࠊࡇࢀࡲ࡛ⅆ○ୣࡉࢀ࡚࠸ࡓሙᡤࡣỈ୰ⅆ○ὶሁ✚≀࡛࠶ࡿࡇࡀ᫂ࡽ࡞ࡗࡓࠋࡇࢀࡽࡢヨᩱࢆ ⏝࠸ࡓྂᆅ☢ẼᏛⓗ◊✲ࡼࡾࠊ࣏ࣥ࣌ᓥⅆᒣᙧᡂࡢ㛫࣭✵㛫ⓗ⪃ᐹࡀྍ⬟࡞ࡿࡇࡀᮇᚅࡉࢀࡿࠋ ࡣࡌࡵ ࣑ࢡࣟࢿࢩ㐃㑥ࡢ࣏ࣥ࣌ᓥࡣすኴᖹὒࡢ㉥㐨ࡢ⣙ 800km ⨨ࡍࡿ࢝ࣟࣜࣥㅖᓥ ᭱ࡢᓥ࡛࠶ࡿࠋ࢝ࣟࣜࣥㅖᓥࡣ࣑ࢡࣟࢿࢩ㐃㑥ࣃࣛ࢜ඹᅜࡽᵓᡂࡉࢀࠊすኴᖹὒ ㉥㐨᪉ᮾす⣙3,000 ࢟ࣟࢃࡓࡗ࡚ศᕸࡍࡿࠋࡇࡢㅖᓥࡣ࢝ࣟࣜࣥᾏᕊࡤࢀࡿኴᖹ ὒࣉ࣮ࣞࢺୖࡢ㧗ࡲࡾ⨨ࡍࡿࠋ࢝ࣟࣜࣥᾏᕊࡢᡂᅉࡘ࠸࡚ࡣ࣍ࢵࢺࢫ࣏ࢵࢺ㉳※ 㸦DIXON et al. 1984, KEATING et al. 1984a, 1984b㸧ࡸỿࡳ㎸ࡳక࠺ᾏὒᆅẆࡢடᙧᡂ
㸦REHMANet al. 2013㸧࡞ㅖㄝ࠶ࡿࡀ࠸ࡎࢀࡶỴࡵᡭࢆḞ࠸࡚࠸ࡿࠋ ࣏ࣥ࣌ᓥ࡛ࡢᆅ㉁Ꮫⓗ◊✲ࡢඛ㥑ࡅࡣࢻࢶ࠾ࡼࡧ᪥ᮏ⤫௦㐳ࡿ㸦KAISER 1903, ྜྷ 1936, ᒾ⏕ 1941㸧ࠋᓥࢆᑐ㇟ࡋࡓ᭱㏆ࡢ◊✲ࡣSPENGLERet al.㸦1992㸧ࡲࡵ ࡽࢀ࡚࠸ࡿࠋࡲࡓࠊ࣏ࣥ࣌ᓥ༡ᮾ㒊ࡢࢼ࣐ࣥࢻ࣮ࣝ㑇㊧▼ᮦࡋ࡚⏝ࡉࢀ࡚࠸ࡿᰕ≧ ⠇⌮ࡢⓎ㐩ࡋࡓ⋞Ṋᒾࡢᚤ㔞ඖ⣲ศᯒࡀ⪃ྂᏛࡢศ㔝࡛Ⓨ⾲ࡉࢀ࡚࠸ࡿ㸦MCCOYand ATHENS 2012㸧ࠋࡋࡋࠊ࢝ࣟࣜࣥᾏᕊࡢᙧᡂྐࢆ᫂ࡽࡍࡿࡣ᭦࡞ࡿᆅ㉁ࢹ࣮ࢱࡀᚲせ࡛࠶ࡿࠋ ᮏ◊✲࡛ࡣࠊ࣏ࣥ࣌ᓥᙧᡂࡢྂᆅ☢ẼᏛⓗࢹ࣮ࢱࢆᚓࡿ࡛᪂ࡓ࡞㆟ㄽࡢ➃⥴ࢆ㛤ࡃ ࡇࢆ┠ⓗࡋࠊ࣏ࣥ࣌ᓥ࡛ࡢヨᩱ᥇ྲྀࢆィ⏬ࡋࡓࠋࡇࡇ࡛ࡣࡑࡢヨᩱ᥇ྲྀ࠶ࡓࡗ࡚ ᐇࡋࡓ⌧ᆅᆅ㉁ㄪᰝࡢᴫせࢆሗ࿌ࡍࡿࠋ
ㄪᰝ᪉ἲ
࣏ࣥ࣌ᓥㄪᰝ᪑⾜ࡣ 2014 ᖺ 8 ᭶ 3 ᪥ࡽ 11 ᪥ࡢ᪥⛬࡛ᐇࡋࡓࠋ⌧ᆅ NGO ࡢ Conservation Society of Pohnpei㸦CSP㸧ࡢ㠃ⓗ࡞༠ຊࢆᚓ࡚ࠊ㛵ಀᶵ㛵ࡢᢡ⾪ࡸ⌧ᆅ࢞ ࢻࡢᡭ㓄࡞ࢆ⾜ࡗࡓࠋᓥෆࡢㄪᰝ࠾ࡼࡧヨᩱ᥇ྲྀࡘ࠸࡚ࡣࠊMinistry of Land and Natural Resources ࡽチྍࢆཷࡅࡓࠋᾏࡸἙᕝ࡛ࡢㄪᰝࢆᐃࡋ࡚Office for Fisheries ☜ㄆࢆ⾜ࡗࡓ ࡀࠊỈ⏘≀ࡢ᥇ྲྀࢆ⾜ࢃ࡞࠸ࡢ࡛≉ᡭ⥆ࡣ⾜ࢃ࡞ࡗࡓࠋᆅ㉁ㄪᰝࡣ8 ᭶5 ᪥ࡽ9 ᪥ ࡅ࡚ᐇࡋࡓࠋ⌧ᆅ࢞ࢻࡢㄏᑟࡢࡶࠊࣞࣥࢱ࣮࡛࢝ᓥෆࡢ࿘ᅇ㐨㊰ἢ࠸ࡢ㟢㢌ࡸࠊ ᒾ▼ࡢዲ㟢㢌ࡀᮇᚅࡉࢀࡿ᥇▼ሙࠊ࡞ࢆᕠᅇࡋࡓࠋ⨨ሗࡣGPS ࣮࡛ࣟ࢞ྲྀᚓࡋࡓࡀࠊ ᶵჾࡢၥ㢟୍࡛㒊ࢹ࣮ࢱࡀḞᦆࡋ࡚࠸ࡿࠋᅗ1 ほᐹ࠾ࡼࡧヨᩱ᥇ྲྀᆅⅬࢆ♧ࡋࡓࠋ Stop 1 Sokehs ᓥ㸦༙ᓥ㸧ࡢすഃᾏᓊࡢ࿘ᅇ㐨㊰ἢ࠸㟢㢌ࠋሢ≧⋞Ṋᒾࢆㄆࡵࡓࠋ Stop 2 SokehsᓥࡢすഃᾏᓊࠊRoie㞟ⴠෆࡢ࿘ᅇ㐨㊰ἢ࠸㟢㢌ࠋゅ♟ࡋࡓ⋞Ṋᒾࢆㄆࡵࡓࠋ Stop 3 Sokehs ᓥす➃Ipwal ࡢ᥇▼ሙࠋᰕ≧⠇⌮ࡀⓎ㐩ࡋࡓつᶍ࡞㟢㢌ࠋ⋞Ṋᒾ࡛࠶ࡾࠊ ࢮࣀࣜࢫࢆྵࡴࡶࡢࡀぢࡽࢀࡓࠋᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ㸦ヨᩱ␒ྕPNY01㸧ࠋ Stop 4 Sokehs ᓥࡢᮾᾏᓊPenpei ㏆ࡢ࿘ᅇ㐨㊰ἢ࠸㟢㢌ࠋὶືᵓ㐀ࡢぢࡽࢀࡿ⋞Ṋᒾࠋ Stop 5 Nett ᆅ༊ࡢKiepw ᕝᨭὶࠋゅ♟ࡋࡓ⋞Ṋᒾࠋ㢼ࡀ㐍⾜ࡋ࡚࠾ࡾࠊࢱ࢞ࢿࡀᐜ᫆
✺ࡁ่ࡉࡾᇙἐࡍࡿࠋ
Stop 6 Stop 5 ࡢ⣙ 100m ୖὶࠋᰕ≧⠇⌮ࡢⓎ㐩ࡋࡓ㟢㢌ࠋᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ 㸦PNY02㸧ࠋ
Stop 7 Stop 5㹼6 ࡢୗὶࠋỈ㐨タࡢୗὶഃ࠶ࡿẸᐙ๓ࡢ㐨㊰ἢ࠸㟢㢌ࠋሢ≧⋞Ṋᒾࠋ Stop 8 Stop 7 ࡢୗὶࠋNanpil ㏆ࠋἙᕝᩜ㟢㢌ࠋሢ≧⋞Ṋᒾࠋ
Stop 9 Uh ᆅ༊ࠋMesenpal㸦࢞ࢻࡼࡿKitttiapas㸧㞟ⴠෆࡢ࿘ᅇ㐨㊰ἢ࠸㟢㢌ࠋᾏഃ㟢 㢌࡛ࡣሢ≧⋞Ṋᒾࡢᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ㸦PNY03㸧ࠋᒣഃ㟢㢌࡛ࡣ Si ᐩࡴ ࢺࣛ࢝ࢺ㉁࡛ࡸࡸ㉥ࡃࢳࢱ࣮ࣥ࢜ࢪࣕࢺࢆྵࡴᛮࢃࢀࡿ⋞Ṋᒾࡢᐃ᪉ᒾ▼ ヨᩱࢆ᥇ྲྀ㸦PNY04㸧ࠋ Stop 10 Stop 9 ࡢᩘⓒ࣓࣮ࢺࣝᮾࡢ࿘ᅇ㐨㊰ἢ࠸㟢㢌ࠋ㈏ධࡋࡓᛮࢃࢀࡿᒾ▼ࠋᐃ᪉ ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ㸦PNY05㸧ࠋ
Stop 11 Madolenihmw ᆅ༊ࡢ Areu ༙ᓥ㏆ࠋ࿘ᅇ㐨㊰ࡽᾏ᪉ྥྥ࠺㐨㊰ࡢ㌴୧㏻⾜ 㝈⏺Ⅼ㏆ࠋ♟ᒾࠋ
Stop 12 Madolenihmw ᆅ༊ࡢMesihsou ㏆ࠋ࿘ᅇ㐨㊰ἢ࠸ࡢ㟢㢌ࠋ┤ᚄ50 cm ⛬ᗘࡢࡁ࡞ ᰕ≧⠇⌮ࡀⓎ㐩ࡋࡓ㟢㢌ࠋᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ㸦PNY06㸧ࠋ
Stop 13 Madolenihmw ᆅ༊ࡢKeproi ࠋᰕ≧⠇⌮ࡢⓎ㐩ࡋࡓ⋞Ṋᒾࠋᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀ ࡋࡓ㸦PNY07㸧ࠋ
Stop 14 Kiti ᆅ༊ࡢRohi ㏆ࡢࠋ⋞Ṋᒾ࠾ࡼࡧ㉥〓Ⰽࡢจ⅊ᒾ㉁♟ᒾࠋᐃ᪉࠾ࡼࡧ㠀ᐃ ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ㸦PNY08ࠊPNY09㸧ࠋ
Stop 15 Kiti ᆅ༊ࡢSahwartik ࠋ㉥〓Ⰽࡢจ⅊ᒾࠋ
Stop 16 Nett ᆅ༊ࡢ Sapwtik ᓥࠋ⯪╔ࡁሙࡢᒾ♋ࠋሢ≧⋞Ṋᒾ࠾ࡼࡧᒙ≧࡛⠇⌮ࡢⓎ㐩ࡋࡓ ⋞Ṋᒾࠋᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ㸦PNY10ࠊPNY11㸧ࠋ
Stop 17 Sokehs ᆅ༊Kiti ᆅ༊ࡢቃ⏺ࡢDolen Pwakorokot㸦Chicken Shit Mountain㸧ࠋẚ㧗⣙ 80m ࡢⅆᒣᒾ㢕ࠋ㡬ୖ࡛ᰕ≧⠇⌮ࡢⓎ㐩ࡋࡓ⋞Ṋᒾࡢᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ 㸦PNY12㸧ࠋ
Stop 18 Uh ᆅ༊ࡢPahntakaiࠋᓴࡢୗ㒊ࡀᾐ㣗ࡉࢀ࡚ࡢ⫼ᚋᕧ࡞✵㛫ࡢ࠶ࡿሙᡤࠋቨ㠃 ᒙ≧ᒾ▼ࡀศᕸࡍࡿࡢࡀ☜ㄆ࡛ࡁࡓࠋୗ㒊ࡢሢ≧⋞Ṋᒾࡢᐃ᪉ᒾ▼ヨᩱࢆ ᥇ྲྀࡋࡓ㸦PNY13ࠊPNY14㸧ࠋ
Stop 19 Madolenihmw ᆅ༊ࡢ Takaiuh ࡤࢀࡿⅆᒣᒾ㢕ࠋᓥෆࡢ⋞Ṋᒾẚ࡚᫂⅊Ⰽ࡛ ᩳ㛗▼ࠊᶤḘ▼ࢆྵࡴࠋᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ㸦PNY15㸧ࠋ
Stop 20 Takaiuh ࡢ⬥ࠋ⅊Ⰽ࡛ᙅ࠸ᰕ≧⠇⌮ࡢⓎ㐩ࡋࡓ⋞Ṋᒾࠋᐃ᪉ᒾ▼ヨᩱࢆ᥇ྲྀࡋࡓ 㸦PNY16㸧ࠋ
Stop 21 Madolenihmw ᆅ༊ࡢ Temwen ᓥ➃ࠋⅆ○ὶሁ✚≀ࠋᒙ≧ᵓ㐀ࢆ࿊ࡋ࡚࠾ࡾࠊ⣭ ᒙ⌮ࡶㄆࡵࡽࢀࡿࠋ㉮ྥഴᩳࡣN75E26Nࠋ ࡲࡵ ࣏ࣥ࣌ᓥ࡛ࡢᆅ㉁ㄪᰝࡼࡾࠊᓥࢆᵓᡂࡍࡿᒾ▼ࡀඛ⾜◊✲࡛ᣦࡉࢀࡓ㏻ࡾኚ ᐩࡴࡶࡢ࡛࠶ࡿࡀ᫂ࡽ࡞ࡗࡓࠋᒣయࢆᵓᡂࡍࡿ⁐ᒾὶࡳࡽࢀࡿሢ≧࠶ࡿ࠸ࡣᰕ≧ ⠇⌮ࡢⓎ㐩ࡋࡓ⋞ṊᒾࡢࠊStop 9 ࡛ࡳࡽࢀࡓࢺࣛ࢝ࢺ㉁ᛮࢃࢀࡿᒾ▼ࠊStop 19 ࡢ Takaiuh ࡛ࡳࡽࢀࡓ᫂⅊Ⰽࡢᒾ▼࡞ࡀᣲࡆࡽࢀࡿࠋࡉࡽ㖄┤᪉ྥ㛤ࡅࡓ㟢㢌࡛ࡼࡃほᐹ ᅗ1 㟢㢌␒ྕ㸦Stop-㸧࠾ࡼࡧヨᩱ᥇ྲྀᆅⅬ㸦PNY-㸧 Stop 6 (PNY02) Stop 17 (PNY12)
ࡉࢀࡓⅆᒣ⅊㉁ࡢሁ✚≀ࠊStop 21 ࡛ほᐹࡉࢀࡓⅆ○ὶሁ✚≀࡞ⅆᒣᛶሁ✚≀ࡢᏑᅾࡶㄆࡵ ࡽࢀࡓࠋ≉ⅆ○ὶሁ✚≀ࡣỈ୰࡛ሁ✚ࡋࡓࡶࡢᛮࢃࢀࠊᅇほᐹࡉࢀࡓᒾ▼ࡢ୰࡛ࡶ ␗ᙬࢆᨺࡗ࡚࠸ࡿࠋࡇࡢỈ୰ⅆ○ὶሁ✚≀ࡣࡇࢀࡲ࡛ⅆ○ୣ㸦tuff cone㸧ࡋ࡚グ㍕ࡉࢀ࡚ ࠸ࡓࡶࡢ࡛ࠊᅇ᪂ࡓ࡞Ⓨぢ࡛࠶ࡿࠋ ᚋࠊࡇࢀࡽࡢᒾ▼ヨᩱࡢヲ⣽࡞Ꮫ⤌ᡂศᯒࡸྂᆅ☢ẼᏛⓗศᯒࢆ⾜࠺࡛ࠊᒾ▼Ꮫⓗ ᡂᅉㄽࡸ⁐ᒾࡢྠ௦ᛶࠊ⨨࡞ࡘ࠸࡚ࡢሗࢆ᳨ウࡋࠊ࣏ࣥ࣌ᓥᙧᡂࡢ㐣⛬ࠊࡦ࠸ ࡚ࡣ࢝ࣟࣜࣥㅖᓥࡢᙧᡂࡢ㐣⛬㛵ࡍࡿ▱ぢࡀᚓࡽࢀࡿࡇࡀᮇᚅࡉࢀࡿࠋ ㅰ㎡
⌧ᆅㄪᰝ࠶ࡓࡾࠊMinistry of Land and Natural Resources Conservation Society of Pohnpei ࡽࡣ㠃ⓗ࡞༠ຊࢆ㡬࠸ࡓࠋ࢞ࢻࡢRelio Ặࡣ㟢㢌ࢆෆࡋ࡚㡬ࡁࠊ⌧ᆅ࡛ࡢ౽ᐅࢆ ᅗࡗ࡚㡬࠸ࡓࠋDanny Rosenkrans Ặࡣ㈗㔜࡞㟢㢌ࡸᆅ㉁ࡢሗࢆᥦ౪ࡋ࡚㡬࠸ࡓࠋHafiz Ur Rehman ༤ኈࡣㄪᰝ࣭ヨᩱ᥇ྲྀ࡛࠾ୡヰ࡞ࡗࡓࠋᒣᮏ᐀❧༤ኈࠊἙྜ༤ኈࡣㄪᰝࡢ ⏬࣭ᡭ㓄࡛ኚ࠾ୡヰ࡞ࡗࡓࠋࡇࢀࡽࡢ᪉ࠎㅰពࢆ⾲ࡍࡿࠋ
ཧ⪃ᩥ⊩
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Composition of Alkali Basalts from Ponape Island, Western Pacific. Chemical Geology, 43: 1-28. ᒾ⏕࿘୍ 1941㸬ෆ༡ὒ࣏ࢼ࣌ᓥ㞯グ㸬ᆅᏛ㞧ㄅ㸪53㸦8㸧㸸341-350㸬
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SCHWANK, D. 1984a. Evidence for a Hot Spot Origin of the Caroline Islands. Journal of
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Atoll, Eastern Caroline Islands: Geochemical, Radiometric-Age, and Paleomagnetic Evidence. Geological Society of America Bulletin, 95: 350-356.
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of Architectural Basalt Stone from Pohnpei, Federated States of Micronesia. Journal of Pacific Archeology, 3(1): 105-114.
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SPENGLER, S. R., PETERSON, F. L. and MINK, J. F. 1992. Geology and Hydrogeology of the Island of
Pohnpei, Federated States of Micronesia. Technical Report No. 189, 79 pp., Water Resources Research Center, University of Hawai`i at Manoa, USA.
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