Characterization of seaward-dipping reflectors along the South American Atlantic Margin and implications for continental breakup
File(s)
Published version
Author(s)
McDermott, C
Lonergan, L
Collier, Jenny S
McDermott, KG
Bellingham, P
Type
Journal Article
Abstract
Thick packages of lavas forming seaward‐dipping reflectors (SDRs) are diagnostic features of volcanic passive margins. Despite their significance to continental breakup studies, their formation mechanism is still debated. We use ~22,000 km of high‐quality, depth‐migrated, seismic data to document the three‐dimensional geometry of SDRs offshore South America. We find two types: Type I are planar and occur as fault‐bounded wedges. Type II are characterized by reflections that become more convex‐upward in the downdip direction and terminate against a subhorizontal base. We interpret the transition from Type I to Type II SDRs to represent a continuum from continental rifting to full plate separation with formation of new, subaerially generated, magmatic crust. Type I SDRs formed in half grabens during the stretching of continental crust, while Type II lavas infill the space produced by flexing of the crust due to the solidification of the underlying feeder dikes as the magmatic crust moved away from the spreading center. Type II SDRs vary in length and thickness along the margin. In the north, close to the Paraná flood basalts, they are long (tens of kilometers), reach thicknesses of up to 15 km, and have an across margin width of up to 600 km. To the south the Type II SDRs are thinner with lava lengths of <10 km. We propose that Type II lavas in the north erupted from a subaerial, plate spreading center above the Tristan mantle plume and that the shorter lava flows to the south indicates eruption into water, consistent with a cooler, off‐plume mantle.
Date Issued
2018-09-01
Date Acceptance
2018-08-19
Citation
Tectonics, 2018, 37 (9), pp.3303-3327
ISSN
0278-7407
Publisher
European Geosciences Union
Start Page
3303
End Page
3327
Journal / Book Title
Tectonics
Volume
37
Issue
9
Copyright Statement
©2018 American Geophysical Union. All Rights Reserved.
Identifier
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2017TC004923
Subjects
Science & Technology
Physical Sciences
Geochemistry & Geophysics
SDRs
continental breakup
South America
seismic reflection data
Tristan plume
NORTH-ATLANTIC
LAVA FLOWS
OCEANIC-CRUST
SEISMIC VOLCANOSTRATIGRAPHY
NORWEGIAN MARGIN
FLOOD VOLCANISM
MANTLE PLUME
EVOLUTION
CONSTRAINTS
EMPLACEMENT
0403 Geology
0404 Geophysics
Geochemistry & Geophysics
Publication Status
Published
Date Publish Online
2018-08-29