A fresh look at marine magnetic anomalies, one ofthe key datasets in the development of plate tectonics.

Ian Norton, Larry Lawver, Lisa GahaganInstitute for Geophysics

University of Texas at Austin

From Vine and Matthews, 1963:

Calculated with reversals Observed

Calculated with constant magnetization Carlsberg Ridge

Sandwell gravity

The EDSAC-2 computer used by Vine & Matthews http://en.wikipedia.org/wiki/EDSAC_2

EDSAC = Electronic Delay Storage Automatic Calculator

PLATES Database

• Plate model• Database: oceanic magnetic and tectonic (plate boundaries, paleomagnetic, hot spots, geological and geophysical data to extend the span and accuracy of global plate reconstructions)• This talk: a look at magnetic anomalies.

Crust Code

Green – Cande & Stock, 2004Black – Granot et al., 2013

Data from Global Magnetics Database http://www.soest.hawaii.edu/PT/GSFML/ML/index.html

Database run by Paul Wessel (Hawaii) & Dietmar Müller (Sydney)

Australia

Antarctica

-60

-50

-40

100 140

115˚E 120˚E

60˚S

Mismatches 5-6 km to as much as 35 km• Great dataset, needs work to use

Green – Cande & Stock, 2004Black – Granot et al., 2013

Data from Global Magnetics Database http://www.soest.hawaii.edu/PT/GSFML/ML/index.html

Example magnetic profile from Mascarene Basin

Base: Sandwell free air gravity 23.1

Base: Sandwell vertical gravity gradient 23.1

Example magnetic profile from Mascarene Basin• VGG emphasizes fracture zones and extinct ridges

ModMag model of Mascarene Basin profile• Really good match between synthetic and observed• Easy to map details of age interpretation

ModMag: Matlab program by Mendel, Munschy & Sauter, 2005. This profile is from example data files that are included with download.

Computers & Geosciences, Volume 31, Issue 5, June 2005, Pages 589–597

Young end at max +ve, old end at max -ve

ModMag GUI

Entry in magnetic anomaly database

Base: Sandwell free air gravity 23.1

M-anomalies in the Mozambique Basin

Data from König and Jokat, 2010

M-anomalies in the Mozambique Basin

Data from König and Jokat, 2010

Line 11

Line SO183-11 from Mozambique Basin• Good match over parts of profile• Need multiple lines for regional identifications• Mapping of young-old edges of anomalies not quite so accurate

Data from König and Jokat, 2010

Young end close to max –ve, old end close to max +ve

Greenland motion: Plates project database

Overlap between Greenland and Barents – Svalbard margin

Overlap

Overlap between Greenland and Barents – Svalbard margin

Next slide

Overlap between Greenland and Barents – Svalbard margin

120-130 km

Point path visualization, Greenland relative to Europe

Gaina et al. (2009) poles 100 km

The Svalbard Margin – Paleocene-Eocene foldbelt followed by some rifting (age?)

Leever et al. 2011 after Bergh et al., 1997 and Braathen et al. 1999FG = Forlandsundet Graben

Leever et al. 2011 after Faleide et al. 2008

G

E

Stylized present-day

G

E

Stylized 33 Ma(e.g. Engen et al. 2008)

GE

Stylized Oligocene(overlap to account for transtension)

G

E

Stylized Paleocene(gap to account for transpression)

Reconstructions should show (in sequence) transpression to transtension to oblique divergence with spreading

Present-day

47 Ma

Should show a gap at 47 Ma, not overlap

120-130 km overlap

47 Ma reconstruction

Europe fixed, Gaina et al. 2009 poles

47 Ma reconstruction – can Greenland be shifted to avoid overlap with Svalbard?• Check magnetic lineation identifications in Labrador Sea

Greenland

Canada

Labrador Sea magnetic data

Data from http://gdr.agg.nrcan.gc.ca/gdrdap/dap/index-eng.php?dapid=8127

Canada

Labrador Sea magnetic data – modeled profile

Data from http://gdr.agg.nrcan.gc.ca/gdrdap/dap/index-eng.php?dapid=8127

Greenland

Canada

Labrador Sea Vertical Gravity Gradient – shows extinct ridge

Sandwell 2014

Greenland

Extract topography/bathymetry

Sandwell topography

Extract sediment fill

http://www.ngdc.noaa.gov/mgg/sedthick/index.html

Get basement depth

km

Meters

Extinct ridge

ModMag model• This version provides a reasonable match

This is the currently accepted interpretation• These essentially sinusoidal anomalies are hard to identify with certainty, need

regional context to settle on interpretation

This area not modeled

Magnetic anomalies around N Atlantic triple junction

Maus et al. 2008 magnetics

120-130 km overlap

47 Ma reconstruction

Europe fixed, Gaina et al. 2009 poles

47 Ma reconstruction – can Greenland be shifted to avoid overlap with Svalbard?• Labrador Sea identifications not definitive• Triple junction provides strong constraint – can’t move Greenland• How to fix the overlap? Hopefully PhD student Bereke Karainov at UiS can figure it out!

Triple junction

It’s all in the stripes…