Insights from a decade of high-resolution aeromagnetic mapping

NGF-Stavanger inviterer til møte på Arkeologisk Museum torsdag 24. november kl. 18:30 (dørene åpner kl. 18:00).  

Kveldens foredragsholder er Laurent Gernigon (PhD) senior forsker på NGU i Trondheim. 

Tema er; Insights from a decade of high-resolution aeromagnetic mapping. 

Laurents foredrag handler om de geologiske resultater der har kommet ut av ca. ti års innsamling og prosessering av geofysiske, hovedsakelig aeromagnetiske data langs norskekysten. De aeromagnetiske data er innsamlet som en del av COOP Prosjektet (Crustal On-shore and Off-shore Project) som er et samarbeide mellom oljeindustrien og NGU. Målet er å forstå sammenhengen mellom geologien vi ser på land og geologien under havområdene på den norske sokkel og den tilstøtende oseanskorpe. De nye data gir nye muligheter for å forstå dyptliggende skorpestrukturer og den lange komplekse utvikling som den passive margin langs Norge har gjennomgått. (Sammendrag er tilgjengelig under "Les mer").  

Forfriskninger vil være tilgjengelige i kafèen. Velkommen!

Sammendrag:  Insights from a decade of high-resolution aeromagnetic mapping Gernigon, L., Maystrenko, Y., Nasuti, A., Olesen, O. and Continental Shelf Geophysics Team   Continental Shelf Geophysics, Geological Survey of Norway (NGU), Leiv Eirikssons vei 39, Trondheim, Norway   Over the last 10 years, the Continental Shelf Geophysics team at NGU has acquired, processed and interpreted numerous new aeromagnetic surveys over the entire Norwegian margin and the adjacent oceanic domain. Our new data allow us to understand better the onshore-offshore relationships and the controversial rift to drift evolution of this complex passive margin. The long period of rifting (and intra-thinning cooling events), the large amount of pre-breakup sedimentation and the significant amount of breakup magmatism characterised by typical Seaward Dipping Reflectors (SDR) make the Mid-Norwegian continental margin appear fundamentally different from so-called magma-poor margins. On the continental shelf, the new high-resolution data provided relevant information about the inherited structure and basement composition expected offshore. We propose a 'super-extended' and magmatic tectonic scenario where a large part of the crust observed underneath the sedimentary basin represents preserved continental basement rocks including high velocity/high density inherited material (I-LCB) recorded in various parts of the rifted margin. Combined with recent seismic data, potential field modelling suggests that the size and thickness of the continental blocks/rafts preserved beneath the distal sedimentary basins are typically larger and thicker compared to the allochthonous blocks described in distal and true "hyper-extended" domains. Some I-LCB controls the structural style of the early rift system and may explain the mullion model proposed for the Cretaceous ridge system described in the outer Vøring Basin. Closer to the SDR, the controversial crust underneath the T-Reflection most likely represents a continental crust material severely plumbed by breakup-related intrusions. Potential field data, the subsidence history before and during the onset of breakup, and the continental contamination of the lava flows recovered by ODP well 642 do not easily support the presence of a large zone of exhumed and denuded mantle material before SDR formation and final breakup. At the edge of the volcanic margins, the new aeromagnetic data also document an embryonic phase of breakup. A steady-state sea-floor spreading established slightly after magnetic chron C24r in the northern part of the Norway Basin (e.g. a few m.y before the onset of breakup expected later in the Vøring Marginal High). Further west, the spreading system is now fully covered by consistent and reliable data and reveals a more complex system of oceanic fracture zones and asymmetric oceanic segments locally affected by episodic Eocene ridge-jump instabilities. A controversial fan-shaped spreading of the Norway Basin was clearly active before the cessation of seafloor spreading and extinction of the Aegir Ridge. An important Mid Eocene kinematic event at around magnetic chron C21r is particularly recognisable thanks to the new aeromagnetic dataset. This event coincides with the onset of dyking and the increase of rifting (and possible oceanic accretion?) between the proto-JMMC and the East Greenland margin. It led to a complete and second phase of breakup and the formation of the Jan Mayen microcontinent in Late Oligocene.  

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