Davy, Bryan

Gohl, Karsten

Hochmuth, Katharina

Hoernle, Kaj

Mortimer, Nick

Riefstahl, Florian

Timm, Christian

Werner, Reinhard

OceanRep

Geophysical Research AbstractsVol. 21, EGU2019-3287, 2019EGU General Assembly 2019© Author(s) 2019. CC Attribution 4.0 license.The evolution of the southern Chatham Rise margin: Cretaceous riftingand initialisation of seafloor spreading between Zealandia and AntarcticaFlorian Riefstahl (1), Karsten Gohl (1), Bryan Davy (2), Kaj Hoernle (3), Nick Mortimer (4), Reinhard Werner(3), Christian Timm (2), and Katharina Hochmuth (1)(1) Alfred Wegener Institute Helmholtz-Centre for Polar and Marine Research, Bremerhaven, Germany, (2) GNS Science,Lower Hutt, New Zealand, (3) GEOMAR Helmholtz-Centre for Ocean Research, Kiel, Germany, (4) GNS Science, Dunedin,New ZealandPassive continental margins are commonly classified as of magma-poor and magma-rich types with their ex-tensional and breakup processes are associated with far-field tectonic stresses or upwelling mantle plumes. TheChatham Rise east off New Zealand records a Cretaceous tectonic history from subduction and collision with theoceanic Hikurangi Plateau to continental extension and breakup in the Cretaceous. The mechanisms triggering thechange from lithospheric convergence to extension at the south Chatham Rise margin are poorly understood butpotentially address open questions in the formation of passive continental margins and the Wilson cycle. We ac-quired seismic wide-angle reflection/refraction, multi-channel seismic and potential field data along three profilesacross the south Chatham Rise margin and adjacent Chatham Terrace, an area of anomalously shallow seafloorand numerous seamounts, to reveal their crustal structure, define the continent-ocean transition zone, and derivebreakup mechanisms. Differences in crustal thickness along the Chatham Rise are most likely related to the pre-breakup collision with the Hikurangi Plateau. We found evidence for high-velocity lower crust, but high-volumemagmatic activity is absent. On the other hand, the southern Chatham Rise margin as well as the Chatham Terraceare strongly affected by block rotation and normal faulting, but mantle exhumation is not present. The P-wave ve-locity structure of the Chatham Terrace is close to oceanic crust, but also to hyper-extended continental crust, andwe interpreted it as hybrid crust consisting of very thin continental crust affected by magmatic activity. Accordingto our observations, the south Chatham Rise margin is neither a magma-poor nor a magma-rich passive margin. Onthe basis of our geophysical data and geochemical data from the Chatham Terrace Seamounts we propose a multi-stage evolution for the southern Chatham Rise margin. (i) Passive rifting was initiated around 105 Ma oblique tothe former subduction zone and southern Chatham Rise margin, reactivated pre-existing E-W structures along theChatham Rise and resulted in new NE-SW normal faulting. The Hikurangi Plateau in the north probably retainedfurther extension along the western Chatham Rise. (ii) Following to slab detachment after 90 Ma, hot ascendingmantle material intruded the Chatham Rise crust, formed the high-velocity lower crustal zones and triggered mag-matism of the Chatham Terrace Seamounts and Southern Volcanics on the Chatham Islands between 85 and 79 Ma.(iii) The southwestward propagation of the young Pacific-Antarctic ridge led to the formation the first oceanic crustat the eastern extremity of the Chatham Rise at 90 Ma. The ridge propagation most likely favoured pre-existingextensional structures from the former rifting episode resulting in oblique and asymmetric spreading and furthercrustal extension along Chatham Terrace. (iv) Between 85 and 79 Ma, seafloor spreading became contiguous andless oblique leading to the final separation of Zealandia from Antarctica. In conclusion, we interpret the southernChatham Rise margin as a unique hybrid rifted margin, which tectonic history was influenced by both passivecontinental rifting and plume-related magmatic activity.

The evolution of the southern Chatham Rise margin: Cretaceous rifting and initialisation of seafloor spreading between Zealandia and Antarctica

http://oceanrep.geomar.de/46525/1/EGU2019-3287.pdf

The evolution of the southern Chatham Rise margin: Cretaceous rifting and initialisation of seafloor spreading between Zealandia and Antarctica

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