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Hawaiian Hotspot

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Hawaiian Hotspot V51B-0546 (AGU Fall Meeting) High precision Pb, Sr, and Nd isotope geochemistry of alkalic early Kilauea magmas from the submarine Hilina bench region, and the nature of the Hilina/Kea mantle component J-I Kimura*, TW Sisson**, N Nakano*, ML Coombs**, PW Lipman** *Department of Geoscience, Shimane University **Volcano Hazard Team, USGS JAMSTEC Shinkai 6500 81 65 Emperor Seamounts 56 42 38 27 20 12 5 0 Ma Hawaii Islands Ready to go! Hawaiian Hotspot N ' 0 3 ° 9 Haleakala 1 Kea trend Kohala Loa 5t0r6 end Mauna Kea te eii 95 ol Hualalai Th l 504 na io sit Mauna Loa Kilauea an 509 Tr Papau 208 Hilina Seamont Loihi lic ka 209 Al 505 N 98 ' 207 0 0 508 ° 93 91 9 1 98 KAIKO 99 SHINKAI 02 KAIKO Loa-type tholeiite basalt 209 Transitional basalt 95 504 208 Alkalic basalt 91 508 0 50 km 155°00'W 154°30'W Fig. 1: Samples obtained by Shinkai 6500 and Kaiko dives in 1998-2002 10 T-Alk Mauna Kea 8 Kilauea Basanite Mauna Loa -K M Hilina (low-Si tholeiite) 6 Hilina (transitional) Hilina (alkali) Kea Hilina (basanite) 4 Loa Hilina (nephelinite) Papau (Loa type tholeiite) primary 2 Nep Basaltic Basalt andesite (a) 0 35 40 45 50 55 60 SiO2 Fig. 2: TAS classification and comparison of the early Kilauea lavas to representative lavas from Hawaii Big Island. Kea-type tholeiite through transitional, alkali, basanite to nephelinite lavas were collected from Hilina bench. Loa-type tholeiite from Papau seamount 100 (a) (b) (c) OIB OIB OIB M P / e l p 10 m a S E-MORB E-MORB E-MORB Loa type tholeiite Low Si tholeiite Transitional 1 f f r r r r r r r f d y r r d b b e d o y r r r b b e d o d y h u b b b e d o a b b a h u b a b b a h u a b a a b u b u a u a m m m m m m K Y U K Y U K Y U Z Z P S H E Z L P S H E T L L P S H E T T T L L B P E D Y T T T L R N C N H B P E D Y T T G R N C N H B P E D Y G R N C N H G T S T S T S Element Element Element 100 (d) (e) (f) OIB Nep OIB M Bas P / e l p 10 m a E-MORB E-MORB S E-MORB Alkali basalt Hawaiite Basanite-Nephelinite 1 f r r r f r r d y r r r b b e d o d y b b e d o h u b a b b a h a b a b u b u f a u r a r r r d y m b b e d o m m m h a b a b u b u a m m K Y U K Y U Z Z P S H E L P S H E K Y T L L U T T T L B P E D Y T T R N C N H B P E D Y G R N C N H Z G P S H E T L S T T L S T T B P E D Y R N C N H G T S Element Element Element Fig. 3: Incompatible element spider diagrams for early Kilauea lavas Compositions range from E-MORB to OIB types and more with mid incompatible element humped and depletions in U, Th, K, and Pb 38.4 0.7042 87 86 208 204 Koolau Sr/ Sr 38.3 Pb/ Pb Loihi Kea-hi8 0.7040 Mauna Loa 38.2 Hilina 0.7038 38.1 Loihi Kilauea -mid8 38.0 Mauna 0.7036 Loa 37.9 Mauna Kea Koolau -lo8 0.7034 Hilina 37.8 Mauna Kea 0.7032 P-MORB 37.7 North Arch North arch P-MORB (a) (b) 0.7030 37.6 17.8 18.0 18.2 18.4 18.6 18.8 17.8 18.0 18.2 18.4 18.6 18.8 206Pb/204Pb 206Pb/204Pb Loa Kea Hilina(Ab) Hilina(Nep) P-MORB Loihi Kilauea Hilina(Hw) Koolau W-Hawaii Kohala Hilina (Lo-Si) Hilina(Bas) North Arch Fig.4: Figures showing isotopic characteristics of Hilina/Kea component with other endmembers (North arch, Loihi, Koolau) for Hawaiian hotspot. Four discrete components are necessary for Hawaiian hotspot. These are spatially related and classified into Loihi-Loa-Koolau and Hilina-Lea-North arch trends 100 F= F= 1 Alkali 1 Nephelinite 2 Transitional 2 Basanite 3 Kilauea 3 4 Lo-Si tholeiite 4 M 5 5 P / 10 7 7 e 8 8 l 9 9 p 10 10 m 15 3 GPa gt source 15 4 GPa gt source a S 1 Kilauea tholeiite source (a) Hilina nephelinite source (b) f f r r r r r r r i r i d d y y b e d o b e b b d o h h b a u b u a b a b a b b u u a a m m m m K Y K Y U U L L Z Z P S H E P S H E L L T L T L T T T T B P E D Y B P E D Y R N C N H R N C N H G G T T S S Element 20 Nep 1 (c) 15 2 3 Fig.5: Panels showing results of melting 4 Loihi 5 calculations for (a) tholeiite-alkali and bas 3.5 GPa gt Y gt/cpx / r 10 FC 30 10 (b) nephelinite suites with estimated Z Bas 20 15 Mauna Kea source mantle compositions. Nephelinite 10 20 Mauna Loa 1 25 2 3 10 Kilauea 5 4 5 15 20 needs distinct source from tholeiite-alkali at 3 GPa gt 25 Loihi 1 2 3 4 5 Papau melting depth deeper than other suites. 10 15 20 S2 3 GPa sp Ab Tr Lo-Si S1 Hilina Hilina (Nep) Panel (c) also shows the same story with 0 0 5 10 15 20 25 showing FC origin of basanite. Zr/Nb 19.0 .7045 Lhelzolite xenolith 206Pb/204Pb 87Sr/86Sr Kauai (rejuvenated) 18.8 Hilina Honolulu(rejuvenated) Kilauea Koolau 18.6 Kea .7040 N.Arch Hilina? Loihi 18.4 Re-juvenated Kilauea Loa 18.2 Loa Haleakala Kea .7035 Loihi 18.0 Koolau 1:2 Hilina Loihi Hilina(nep) Loa 17.8 Kilauea Koolau (a) Kea N-Arch (b) Re-juvenated 17.6 Haleakala Kauai 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 (Th/La)n 187Os/186Os Fig. 6: Mixing models of lava sources with different element-isotope pairs Hilina-Kea-North arch (Re-juvenated) and Loihi-Loa-Koolau mixing trends are again identical, which is similar with Nd-Sr-Pb isotope plots in Fig. 4. Loihi and Hilina components are generally similar but 208Pb/204Pb ratios are systematically different. Note that degree of Th depletion (Th/La)n < 1 is also important factor for Hawaiian lavas and this varies between different sources with Koolau endmember as lowest. Th depletion Pb isotope Hi-Th/La Hi-MU Os isotope Hi-Th/La Less radiogenic Os Md-Th/La Hi-MU Less radiogenic Os Md-MU Lo-Th/La Mod radiogenic Os Lo-MU Radiogenic Os PGE rich source (Loihi) (a) Less depleted in Th (b) High Th/Pb to grow HIMU source (c) High U/Pb to grow High 208Pb source Figure from Bennett et al. (2000) EPSL 183 (d) Low Re/Os or Os loss to grow radiogenic Os Fig. 7: PGE composition of Hawaiian lavas reported by Bennett et al. and its relation to Th-Pb depletions and Os isotope characteristics. Loss in Th-Pb-PGEs and Os can be caused simultaneously by sulfide melt extraction in the source. Radiogenic Os istope found in the most PGE depleted Koolau lavas shows sulfide melt depletion occurred at an ancient time. Source mantle Sulfide melt Low-degree melt Melting of metasomatized extraction extraction and mantle metasomatism 50 high U/Pb, high Re/Os 10 subdued by olivine dilution high-mu, 1 moderate time 187Os/188Os f r r r r y d b b e d o h b u growth a a b b u a m m K Y U Z P S H E L T L T T B P E D Y R N C N H G T S 50 Sulfides low-degree melt extraction separation and Tholeiite melts metasomatism Source mantle 10 Os>Pb>U>Th depletion high-mu, Metasomatized mantle sulfides high- high U/Pb, time 1 187Os/188Os high Re/Os growth f r r r r y d b b e d o h b u a a b b u a m m K Y U Z P S H E L T L T T B P E D Y R N C N H G T S Fig. 8: Figure showing sulfide melt depletion - low degree melt metasomatism two stage model for the Hilina mantle source of Hawaiian volcano Kea trend (a) Loa trend Kohala Phlogopite bearing component Mauna Kea North Arch component Hualalai Hilina component Mauna Loa Kilauea Loihi component Hilina Koolau component Plume head Loihi Kh MK KL HL (b) ML-LO MK-KL (c) Ab Thol Thol Ab-Tr Nep Thol Thol SL SL ? MOHO MOHO % melting P-MORB 10 % melting 5 10 P-MORB 2 5 2 Onset of melting ? Onset of melting ? Phl peridotite ? Phl peridotite ? Fig.
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