~90 Ma

PALEOCENE

EOCENE

EARLY CRETACEOUS

LATE CRETACEOUS

AUTHORS:

Alexander Minakov - Rolf Mjelde - Earth Sciences Dept., Univ. of Bergen, NorwayJan Inge Faleide - Dept. Geosciences, Univ. of Oslo, NorwayRitske Huismans - Earth Sciences Dept., Univ. of Bergen, NorwayAnke Dannowski - IFM Geomar, Kiel, GermanyErnst Flueh - IFM Geomar, Kiel, GermanyVladimir Glebovsky - VNIIOkeangeologia, St.Petersburg, RussiaHenk Keers - Earth Sciences Dept., Univ. of Bergen, NorwayYouri Podladchikov - Physics of Geological Processes (PGP), Univ. of Oslo, Norway

Mail to:

Earth Sciences Dept., Univ. of Bergen, Norway

Alexander.Minakov@geo.uib.no

SUMMARYWe present a systematic study of the Northern Barents Sea continental margin (see Figure above), using several types of geophysical data as well as geodynamic modeling. The results are interpreted in terms of geodynamic processes in the crust and upper mantle in the study area during various geological time periods.

METHODOLOGY- Wide angle Ocean Bottom Seismometers data acquired east of Svalbard and processed using traveltime tomography - Inversion of gravity data - Finite element thermomechanical modeling of lithospheric extension

RESULTS- The seismic velocity structure east of Svalbard contains a high-velocity anomaly. This is interpreted as early Cretaceous magmatic intrusions.- The crustal structure of both the Cenozoic and the Cretaceous N Barents Sea margin was predicted using an integrated gravity inversion method and sparse seismic reflection lines. The northern Barents Sea and Lomonosov Ridge margins are symmetric and narrow (< 150 km). The inferred Cretaceous continent-ocean transition (on the Makarov/Podvodnikov Basin side of the Lomonosov ridge) is much wider (150-400 km). On the continent, the N Barents Sea margin is underlain by Paleozoic to early Mesozoic sedimentary basins, which are separated from the oceanic crust by marginal basement uplift.- A mechanism to weaken the lithosphere is required in order to detach the Lomonosov Ridge - a narrow continental sliver. As such mechanism we propose a short-lived episode of margin-parallel shear. We simulate 2D lithospheric extension accompanied by the shear heating localization using the finite element method.

NORTHERN BARENTS SEA EVOLUTION LINKED TO THE ARCTIC OCEAN T31A-2120

L m s o R i d o o n o v g e Mak ro Basina v P

dvo

kov

odn

i

Bn

asi

na a Ca dB sia n

Men

delee

v Ridg

e

Alpha Ridge

Greenland

Franz Josef Land

B ff Ba in ay

Norwegian-Greenland

Basin

Barents Sea

Kara

Sea

A m e r a s i aB a s i n

G a k k e l R i d g e

L o n o R d g m o o s v i e

G a k k e l R i d g e

Nansen Basin

Barents Sea

Amundsen BasinNo

vaya

Zem

lya

Svalbardl rdSva ba Franz Josef Land

vSe ernaya yZeml a

Severnaya Zemlya

B n affi Bay

Greenland

Sea

Kara

Norwegian-Greenland

Basin

N en as nans B i

nd B nAmu sen asi

Canada Basin

Men

delee

v Ridg

e

Podv

odnik

ov

Basinak ro a nM a v B si

Alpha Ridge

A m e r a s i aB a s i n

Nova

ya Z

emly

a

? ?

-40

-35

-30

-25

-20

-15

-10

-5

Dep

th (k

m) NE Svalbard

LomonosovRidge (LR)

0

A A0 100 200 300

Distance (km) Distance (km)

?

-40

-35

-30

-25

-20

-15

-10

-5

0

Dep

th (k

m)

C C100 200

0 100 200 km

?

?

-40

-35

-30

-25

-20

-15

-10

-5

0

Dep

th (k

m)

D D

D D D D

GR

EE

NL

AN

DG

RE

EN

LA

ND

D D D D

C24 (53 Ma)

GR

EE

NL

AN

DG

RE

EN

LA

ND

N Barents SeaN Kara Sea

Amerasia Basin

N Barents SeaN Kara Sea

Amerasia Basin

AlphaRidge

AlphaRidge

AlphaRidge

Men

eleev

dR

dge

ienM

delee

v

Ridg

eenM

delee

v

Ridg

e

Svalbard

Svalbard

Svalbard

Franz JosefLand

Franz JosefLand

Franz JosefLand

Severnaya Zemlya

Severnaya Zemlya

Severnaya Zemlya

ACEX

Transa

rctica

89-91

Tra

sr

t ca

9n

ac

i

2

1

1

2

2

3

3

SvalbardFranz JosefLand

Severnaya Zemlya

ACEX

sTra

n arct

ica 89

-91

Tra

sarc

t ca

9n

i

2

1

1

2

2

3

3

SvalbardFranz JosefLand

Severnaya Zemlya

ACEX

sc c

89

Tran a

r ti a

-91

rTan

sarc

tica

92

1

1

2

2

3

3

BATHYMETRY

BOUGUER GRAVITY

MAGNETIC ANOMALIES

-28-15-7-14

10162551129161188232

-2953-2222-1299-336-251-187-107-58-34-161183

426

-2953-2222-1299-336-251-187-107-58-34-161183

426

-170-99-62-41-26-13-29

265090

160332

nT

mGal

m

m

o20 o30 o40

o78

o76

o78

NORDAUSTLANDET

EDGEYA

BARENTSYA

SPIT

SBER

GEN

KONG KARLS LANDPLATFORM314313 312 311310 308 307306 305 304 302 301

KONG KARLSLAND

301

Carboniferous rifts (Faleide et al., 2008)

Sills: 2 - 4 km(Grogan et al. 1998)

Sills: 1 - 2 km (Grogan et al. 1998)

Reactivated faultsOcean bottomseismometersSills/lavas: 0 - 1 km(Grogan et al. 1998)

Ray coverage

NUMERICS

PHYSICS

NorthAmerica

Eurasia

- 1 8 00

0081-

0081-

- 18 0 0

0081

-

- 18

00

00

81-

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

00

0

0

0

0081-

00

0

0

0

0

0

0

0

0

0

00

0

LR

AR

RM

Alaska

??

Greenland

CB

BarentsSea

Emergent area(Barents Sea)Magmatic province

Oceanic domain

NorthAmerica

- 1 8 00

0081-

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0081-

00

0

0

0

0

0

0

0

0

00

0

LR

aAl

ska

Greenland

BarentsSea

Eurasia

??

?

Emergent area(Barents Sea)Magmatic province

Oceanic domain

- 1 8 0 0

0081-

0081-

- 1 8 00

0081

-

- 18

00

00

81-

0

0

0

0

0

0 0

0

00

0

0

0

0

0

0

0

0

0

0

0

0081-

00

0

0

0

0

0

0

0

0

0

0

00

0

0

0

0

NA-GRErotation pole

LS

Eurasia

GreenlandBarents

Sea

LR

NorthAmerica

Emergent area(Barents Sea)Magmatic province

Oceanic domain

0081-

00

0

0

0

0

0

0

0

0

00

0

0

0

0

Eurasia

- 1 8 0 0

0081-

0081-

- 1 8 00

0081

-

- 18

00

0081-

0

0

0

0

0

0 0

0

00

0

0

0

0

0

0

0

0

0

0

0

NA-EURArotation pole

NA-GRErotation pole

Greenland

LS

NGS

EBEB

BarentsSea

NorthAmerica

LR

Emergent area(Barents Sea)Magmatic province

Oceanic domain

MARGIN EVOLUTION DATA METHOD RESULTS

25

25

25

0

0

0

75

75

75

125

125

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

4.0 m.y.

Dep

th (k

m)

Dep

th (k

m)

Dep

th (k

m)

Distance (km)

Distance (km)

Distance (km)

Effective viscosity

oC

log (Pa s)10

Temperature

125

MARGIN-PARALLEL SHEAR (~1 cm/y; 0.5 m.y.)

1 25

25

25

0

0

0

75

75

75

125

125

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

3.4 m.y.

Dep

th (k

m)

Dep

th (k

m)

Dep

th (k

m)

Distance (km)

Distance (km)

Distance (km)

125

Effective viscosity

oC

log (Pa s)10

Temperature

NO SHEAR

1

- The N Barents Sea, including Svalbard, was not affected by the major Late Jurassic to Early Cretaceous rifting which gave rise to deep basins in the SW Barents Sea. - However, the area experienced widespread Early Cretaceous (Barremian) magmatism related to the High Arctic Large Igneous Province (HALIP).- The magmatism developed without significant crustal thinning. The emplacement of mafic magmas into the crust east of Svalbard was controlled by Paleozoic rift structures which were reactivated in the Early Cretaceous.

- The Mesozoic N Barents Sea passive margin resulted from the formation of the Makarov (and Podvodnikov?) Basin. - N Barents Sea region together with the Lomonosov Ridge was standing high during most of the Late Cretaceous. - The regional uplift sourced from the Alpha Ridge area.- The extension direction in the Podvodnikov Basin is assumed to be parallel to the Mendeleev Ridge.

- The Eurasia Basin's breakup in the Paleocene preceded the opening of the Norwegian Sea, implying a connection to the Labrador Sea. - A short-lived lithosphere-scale shear zone has likely facilitated to the detachment of the Lomonosov Ridge microcontinent and the onset of seafloor spreading.

The Cenozoic N Barents Sea passive margin is characterized by the narrow symmetric rift mode and magma-poor setting of the margin development.

ARMR

- Alpha Ridge - Mendeleev Ridge

LR - Lomonosov RidgeMB - Makarov BasinCB - Canada BasinPB - Podvodnikov Basin

LR - Lomonosov RidgeLS - Labrador SeaPB - Podvodnikov BasinMB - Makarov Basin

LR - Lomonosov RidgeLS - Labrador SeaEB - Eurasia BasinNGS - Norwegian-Greenland Sea

~120 Ma

~60 Ma

~53 Ma

MB

MB

PB

PB

CB

AR

AR

MR

MR

OBSprofile

OBSprofile

OBSprofile

O rBS p ofile

B B

? ?

-40

-35

-30

-25

-20

-15

-10

-5

0

Dep

th (k

m)

A BC

C

D

DB

A

A BC

C

D

DB

A

P-wave velocitymodel fromrefraction & reflectionseismic tomography

Velocity anomaliesrelative to 1-D background model

- Conservation of momentum - Conservation of energy

- Kinematics

- Rheology

- Von Mises plasticity

- In-compressibility

- Lagrangian finite element method, thermomech. coupled- 9-node quadrilateral elements (Q P ) 2 -1- 3 dofs (u , u , T) per nodex y- P is found on the element level using static condensation- Iterative viscosity reducing to account for plasticity + Powell and Hestenes iterations - Re-meshing - 600 x 125 km model: asthenosphere, mantle lithosphere, crust, sedimentary and water layers.

Boundary conditions- top surface is stress-free- bottom is free slip- velocity 3 cm/y applied to the right side

o- T = 0, T = 1300 Ctop bot- Heat flux on the sides is zero

Initial lithosphere structure derived from gravity inversionStrike-slip related shear strain rate: = 2e-14 [1/s]

We model lithosphere extension accompanied by development of a shear zone. The problem is solved in 2-D in the plane normal to the strike-slip.

u ,u ,Tx yP

-40

-35

-30

-25

-20

-15

-10

-5

00 100 200 400 500 600-250

-200-150-100-50

050

100150200250300

Pre-Cz sedimentsCz sediments

Continental crust

? Oceanic crust

Dpt

()

eh

kmvi

yno

m(

alG

rat

aal

y m

G)

Distance (km)

Free-air gravity

Mantle residual anomaly

Observed

Calculated

3D inversionIsostasy

Barents50

S NPROFILE 1NW Barents Sea Nansen Basin

(z) = exp(-z)0

3 = 2850 kg/m

(z) = (1-T)0T = T(, t, z)

The inversion of the mantle residual gravity anomaly (MRA) was performed with the method of Oldenburg incorporating gravity effects of thermal lithosphere (Chappell & Kusznir, 2008) and sediments:

b b

1Mantle lithosphere

Asthenosphere

Crust5

25

45

65

85

105

125

Dep

th (k

m)

Distance(km)

mG

al

FAIR

MRA

Shear zone

3Mantle lithosphere

Asthenosphere

Crust5

25

45

65

85

105

125

Dep

th (k

m)

mG

al

Distance(km)

FAIRMRA

2

mG

al

Mantle lithosphere

Asthenosphere

Crust5

25

45

65

85

105

125

Dep

th (k

m)

Distance(km)

FAIR

MRA

25

25

25

0

0

0

75

75

75

125

125

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

Dep

th (k

m)

Dep

th (k

m)

Distance (km)

Distance (km)

Distance (km)

Effective viscosity

oC

log (Pa s)10

3.8 m.y.

125

Temperature

Dep

th (k

m)

225

25

25

0

0

0

75

75

75

125

125

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

Dep

th (k

m)

Dep

th (k

m)

Distance (km)

Distance (km)

Distance (km)

Effective viscosity

oC

log (Pa s)10

3.9 m.y.

125

Temperature

Dep

th (k

m)

2

N FranzJosef Land

N FranzJosef Land

NW SevernayaZemlya

C24n (53 Ma)

C24n (53 Ma)

C24n (53 Ma)

C24n (53 Ma)

LR

LRLR

Cenozoic sed.Cont. crust

Pre-Cenozoic sed.

Shear zone

Shear zone

KM

W E

400 80 120 160

Synthetic waveforms (OBS 314)

Observed waveforms (OBS 314)

0

5

10

time

- offs

et/8

(s)

11

12

9

87

6

4

3

2

1

0

5

10

time

- offs

et/8

(s)

11

12

9

8

7

6

4

3

2

1

0 20 40 60 80 100 120 140 km

MCR

Psed

Pg

PmP

KM

- Refraction & reflection travel-time tomography JIVE3D package (Hobro, 1999)- 2 layers (sediments, crust)- Layer-stripping approach- Roughness penalizing, no damping- 10 steps for the sedimentary layer- 20 steps for the crustal layer - 6 nonlinear iterations per step with constant regularization strength- Inversion stability criteria: --high and stable ray hits per cent --convergence within the step --small length of the model update vector - misfit: 55 ms (Psed) and 96 ms (Pg)- misfit: 35 ms (PgP) and 83 ms (PmP)

BATHYMETRY

BOUGUER GRAVITY

S V

A L

B A

R D

sv FJL

SV - SvalbardFJL - Franz Josef LandLR - Lomonosov Ridge

-20-510

304070100120140160190

0

mGalC24 (53 Ma)

C24 (53 Ma)

90-60 Ma

90-60 Ma

90-60 Ma

GR

AV

ITY

M

OD

ELI

NG

GE

OD

YN

AM

IC

MO

DE

LIN

GW

IDE

-AN

GLE

SE

ISM

IC

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