The Origin of Intraplate Volcanism in New Zealand
Final Report Abstract
The Origin of intraplate volcanism has been predominately attributed to a starionary thermal anomaly beneath the lithosphere (mantle plume) or to continental rifting. Both mechanisms generally result in voluminous volcanic acrivity. However, diffusely and continuously occurring low-volume intraplate volcanism on the New Zealand micro-continent, Zealandia is inconsistent with these processes. Until the mid-Cretaceous Zealandia was part of the former super-continent Gondwana, situated at its NW margin above an active subduction zone. Subduction ended at ~ 100 Ma and volcanism changed from subduction- to rift-related as Zealandia started to separate from Gondwana, which was associated with voluminous eruptions unril ~ 90 Ma. Since the final separation of Zealandia from Gondwana, the micro-continent drifted ~ 6000 km to the NW to its recent position with respect to the upper asthenosphere. During the Cenozoic diffuse intraplate volcanism occurred randomly distributed on the continental plateau, forming two volcanic endmembers: 1) monogeneric volcanic fields and 2) composite shield volcanoes. The mafic Cenozoic volcanic rocks of these volcanic centers (MgO > 5wt %) are strongly akin to ocean island basalts and plot between three isotopic endmembers: MORB, HIMU and EMU, suggesting involvement of muhiple components in the formation of these volcanic rocks. Seismic tomography reveals a low velocity zone (most likely reflecting the presence of anomalously hot mantle) between ~ 600 and 1450 km beneath Zealandia, which can be traced to Antarctica. Since mixing of the HIMU-type source material for Cretaceous volcanic rocks with depleted upper MORB-source mantle can explain most of the isotopic compositions of the Cenozoic lavas, the deep-seated plume (which possibly contributed to the separarion of Zealandias from Gondwana) polluted the depleted upper asthenospheric mantle (MORB) with fertile (HIMU-type) domains. The EMII-type isotopic signature in some of the volcanic reflects interacrton of the asthenospheric melts with continental lithosphere (mantle, metasomarized by subducrton during the Mesozoic, and crust). A possible mechanism for triggering partial melting, however is lithospheric removal by Rayleigh-Taylor instabilities. The downwelling of a dense lower lithosphere allowed the warm and less dense upper asthenosphere to stream into the resulting cavities and form partial melts by decompression.
Publications
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(2005): Origin of long-term intraplate volcanism in the Canaries, Galapagos and New Zealand: Which are consistent with the plume hypothesis; In; AGU Chapman Conference; The Great Plume Debate, 28th August - 1st September, Fort William, Scotland; p.36
Hoernle, K.; Bogaard, P.; Hauff, F.; Werner, R.; Geldmacher, J.
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(2006) A Mantle Origin for the Enriched Signature in Basalts from Banks Peninsula, New Zealand. In: Geochimica et Cosmochimica Acta, Goldschmidt Abstracts, v. 70, August-September, p. A650
Timm, C., K. Hoernle, F. Hauff, P. van den Bogaard and S. Weaver
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(2006) Enriched Isotopic Signatures in Shield Basalts from Banks Peninsula, South Island, New Zealand, DMG Tagung, Sektion Geochemie, Kiel
Timm, C., K. Hoernle, F. Hauff, P. van den Bogaard and S. Weaver
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(2006). Cenozoic intraplate volcanism on New Zealand: Upwelling induced by lithospheric removal. Eartfi and Planetary Science Letters 248. 335-352
K. Hoernle, J.D.L. White, P. van den Bogaard, F. Hauff, D.S, Coombs, R. Werner, C. Timm, D. Garbe-Schönberg, A. Reay, A.F. Cooper
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(2006): Lithospheric removal: The cause of widespread Cenozoic intraplate volcanism on Zealandia? ; In: Goldschmldt Conference Abstracts, Melbourne, Australia, August 27 - September 1, Geochimica et Cosmochimica Acta, v. 70, p. A256-A256
Hoernle, K.; White, J.; van den Bogaard, P.; Hauff, F.; Coombs, D.; Werner, R.; Timm, C.; Garbe-Schonberg, D.; Reay, A.; Cooper, A.
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(2007): Crustal Assimilation vs. Mantle Melts in Lavas from Banks Peninsula, NZ; In: European Geosciences Union General Assembly, Vienna, April 15-20, Geophysical Research Abstracts, Vol. 9, Abstract 04990, SRef-ID: 1607-7962/gra/EGU2007-A-04990
Timm, C.; Hoernle, K.; Hauff, F.; van den Bogaard, P.; Weaver, S.
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(2007): Melting processes by Rayleigh-Taylor instabilities beneath Continents: Evidence from Cenozoic intraplate volcanism on Zealandia, SW Pacific; In: Geochimica et Cosmochimica Acta, Goldschmidt Abstracts, v. 71, p. A1022
Timm, C.; Rüpke, L.; Hoernle, K.
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(2007): The Origin of Intraplate Volcanism in New Zealand? ; In: Seminar presentation at the PGP, University of Oslo, March 22
Timm, C.; Hoernle, K.; Hauff, F.; van den Bogaard, P.; White, J.; Weaver, S.
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(2008) The origin of Intraplate Volcanism on the New Zealand microcontinent Zealandia. Doctoral Thesis, IFM-GEOMAR at the Christian Albrechts University of Kiel, 185pp
Timm C.
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(2008): The Origin of Intraplate Volcanism on Zealandia; In: European Geosciences Union General Assembly, Vienna, April 13-18, Geophysical Research Abstracts, Vol. 9, Abstract 04990
Timm, C.; Hoernle, K.; Hauff, F.; van den Bogaard, P.
