 |
| Titel |
Deformation mechanisms accommodating the emplacement of an igneous sill-complex in the Irish sector of the Rockall Basin, offshore NW Ireland |
| VerfasserIn |
Craig Magee, Christopher Jackson, Nick Schofield |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250073914
|
|
|
|
|
|
| Zusammenfassung |
| Magma intrusion within the subsurface is heavily influenced by the pre-existing architecture of the upper crust and, depending on the emplacement mechanisms, may modify basin structure and fluid flow pathways. Seismic reflection data reveal that intrusive networks predominantly consist of interconnected, saucer-shaped sills that are often associated with dome-shaped ‘forced’ folds generated by intrusion-induced uplift. Previous studies of intrusion-related forced folds have primarily focused on isolated sills or laccoliths and have shown that the fold amplitude is less than the intrusion thickness, suggesting that additional space-making mechanisms (e.g. grain comminution, fluidization) accompanied emplacement. Furthermore, forced folding is often considered as an instantaneous process over geological time. However, fold growth and the interplay between accompanying ductile and brittle deformation styles remains poorly understood.
Here, we use 3D seismic reflection data from the eastern margin of the Irish Rockall Basin, NE Atlantic, to quantitatively study eighty-two igneous intrusions (i.e. saucer-shaped sills and inclined sheets) in order to constrain the emplacement history of a Palaeocene–to-Middle Eocene sill-complex. Emplacement occurred across a Cretaceous clastic-to-marl dominated succession at palaeodepths of <5 km. Northwards-dipping, planar transgressive sheet intrusions are most abundant in the deeper portion of the sill-complex and magma flow indicators within them (i.e. steps and broken bridges) reveal that magma flowed upwards and outwards, feeding into shallow-level saucer-shaped sills at the peak of the transgressive limbs. The saucer-shaped sills are characterized by radial magma flow patterns, emanating from the inner sill, distinguished by mapping the long axes of magma lobes and fingers. These magma flow indictors also provide a proxy for intrusion style; i.e. where sills intrude the Lower Cretaceous sandstones, magma propagation was facilitated by brittle fracturing while non-brittle processes (e.g. fluidization) accompanied shallow-level intrusions into the Upper Cretaceous marls.
Directly overlying the sill-complex, within the Palaeocene–Mid-Eocene succession, are a series of 22 forced folds that are interpreted to have formed via intrusion-induced uplift. Onlap and truncational relationships observed throughout the folded Palaeocene–Mid-Eocene strata indicate that the folds grew progressively, likely due to the near-continuous intrusion of small magmatic pulses within the sill-complex. Importantly, individual forced folds cannot be attributed to a single intrusion and, instead, appear to have been generated from the incremental emplacement of adjacent and overlapping sills. Furthermore, where the sills are clustered, individual folds have merged together to form broad, compound folds. We show that emplacement depth below the contemporaneous seabed and vertical stacking of the sills strongly influenced forced fold development. Furthermore, magmatic activity occurred for a prolonged (~8 Ma) time period. |
|
|
|
|
|
|