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| Titel |
Magma sources during Gondwana breakup: chemistry and chronology of Cretaceous magmatism in Westland, New Zealand |
| VerfasserIn |
Quinten H. A. van der Meer, Tod E. Waight, James M. Scott |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074488
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| Zusammenfassung |
| Cretaceous-Paleogene rifting of the Eastern Gondwana margin thinned the continental crust
of Zealandia and culminated in the opening of the Tasman Sea between Australia
and New Zealand and the Southern Ocean, separating both from Antarctica. The
Western Province of New Zealand consists of a succession of metasedimentary
rocks intruded by Palaeozoic and Mesozoic granitoids that formed in an active
margin setting through the Phanerozoic. Upon cessation of subduction, the earliest
stages of extension (~110-100 Ma) were expressed in the formation of metamorphic
core complexes, followed by emplacement of granitoid plutons, the deposition of
terrestrial Pororari Group sediments in extensional half-grabens across on- and
offshore Westland, and the intrusion of mafic dikes from ~90 Ma. These dikes are
concentrated in the swarms of the Paparoa and Hohonu Ranges and were intruded prior
to and simultaneous with volumetrically minor A-type plutonism at 82 Ma. The
emplacement of mafic dikes and A-type plutonism at ~82 Ma is significant as it
coincides with the age of the oldest seafloor in the Tasman Sea, therefore it represents
magmatism coincident with the initiation of seafloor spreading which continued
until ~53 Ma. New 40Ar-39Ar ages indicate that the intrusion of mafic dikes in
basement lithologies both preceded and continued after the initial opening of the
Tasman Sea, including an additional population of ages at ~70 Ma. This indicates
either a prolonged period of extension-related magmatism that continued >10 Ma
after initial breakup, or two discrete episodes of magmatism during Tasman Sea
spreading.
Volumetrically minor Cenozoic within-plate magmatism continued sporadically
throughout the South Island and bears a characteristic HIMU (high time integrated U/Pb)
signature. A detailed geochemistry and chronological study of Cretaceous mafic and felsic
magmatism is currently in progress and aims to better understand the transition of magma
sources from a long lived active continental margin through breakup to a passive
setting, and to constrain the onset and evolution of the chemical characteristics of the
magmas and their sources, including the origin of the distinctive HIMU signature. |
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