Activation of the Mozambic Ocean suture zone

(1)

References

Coupling and rift geometry

Coupling and activation of weak zone

Activation of the Mozambic Ocean suture zone

Horn of Africa rift system

Anza Graben

Syncline above/ grabens parallel

to but aside the MOZS Localized deformation above the MOZS

Two layers experiments consist of a lower ductile layer made of silicone putty and an upper brittle layer consisting of feldspar sand. Extension is induced by pulling a plastic sheet from under a fixed sheet in the direction of the arrow. In this way the velocity discontinuity is stationary.

mobile sheet

static sheet static Velocity

Discountinuity (VD)

Strength ratio corresponds to ratio between the strength of the brittle and the ductile crust, thus reflects the degree of coupling Here, in the series of analogue models the strength ratio only depends of the strain rate at which the experiment has been deformed. In nature, the initial the initial thickness of the brittle and ductile crust as well as the strain rates are parameters that are a priori difficult to estimate.

Str ength of the lo w er cr ust

Strength of the upper crust

Str ength r

atio = 0,1

Strength r

atio = 0,05

Strength ratio = 0,01

Localized graben Rift/tilted blocks

Detachment

Inc rea sin g c

ou pli ng

σ1-σ3 (Pa.m)

depth (cm)

σ1-σ3 (Pa.m)

depth (cm)

σ1-σ3 (GPa.m) σ1-σ3 (GPa.m) σ1-σ3 (GPa.m) σ1-σ3 (GPa.m)

σ1-σ3 (MPa.m)

Sirte basins

Binks, R.M., Fairhead, J.D., 1992. A plate tectonic framework for the evolution of the Cretaceous rift basins in West and Central Africa. In: Ziegler, P.A. (Ed.), Geodynamics of Rifting, vol. 2, Case History studies on Rifts: North and South America, Africa–Arabia. Tectonophysics, vol. 213, 141–151.//Bosworth, W., Strecker, M.R., Blisniuk, P.M., 1992. Integration of East African paleostress and present-day stress data: implications for continental stress field dynamics. Journal of Geophysical Research 97, 11851–11865.// Brun, J.P., M.A. Gutscher & DEKORP-ECORS teams 1992 Deep crustal structure of the Rhine Graben from DEKORP-ECORS seismic reflection data: a summary - Tectonophysics 208: 139-147.// Brun and Tron 1993.Development of the North Viking Graben: inferences from laboratory modelling Sedimentary Geology, 86, p. 31-51.// Fairhead, J.D., 1988. Late Mesozoic rifting in Africa. In: Manspeizer, W., (Editor), Triassic-Jurassic Rifting. (Developments in Geotectonics, 22.1 Elsevier, Amsterdam, pp.

821-831.// Gass, I.G., 1977. The age and extent of the Red Sea oceanic crust .Nature 265, 722 - 724 ; doi:10.1038/265722a0.// Genik, G.J., 1992. Regional framework, structural and petroleum aspects of rift basins in Niger, Chad and the Central African Republic (C.A.R.): Tectonophysics, v. 213, no. 1, p. 169–185.// Guiraud, R. and Maurin, J.-C., 1991. Le rifting en Afrique au Cretace inferieur: synthese structurale, mise en evidence de deux étapes dans la génèse des bassins, relations avec les ouvertures oceaniques p & i-africaines. Bull. Sot. GCol. Fr.162:811–823.// Jolivet, L. et al., 2010. Rifting and shallow-dipping detachments, clues from the Corinth Rift and the Aegean. Tectonophysics 483 (2010) 287–304.// Kazmin, V., Shifferaw A., Balcha, T., Ababa, A., 1978. The Ethiopian Basement: Stratigraphy and Possible Manner of Evolution Band. 67, Heft 2, 1978, SeRe 531-546.// Khalil, S. M., and McClay, K.R., 2001. Extensional fault-related folding, northwestern Red Sea, Egypt. 0191-8141/02/$ -Journal of Structural Geology 24, 4, p. 743-762.// Lambiase, J.J., 1989. The framework of African rifting during the Phanerozoic. J. Afr. Earth Sci., 8: 183-190.// Rohais, S. 2007. Stratigraphic architecture of the Plio-Pleistocene infill of the Corinth Rift: Implications for its structural evolution. Tectonophysics 440, 1–4, Pages 5–28.// Russell, L.R., Snelson, S., 1994. Structure and tectonics of the Albuquerque Basin segment of the Rio Grande rift — insights from reflection seismic data Geol. Soc. Am. Spec. Pap. 291, 83–112.// Scotese, C. R., 1997. Paleogeographic Atlas, PALEOMAP Progress Report 90-0497, Department of Geology, University of Texas at Arlington, Arlington, Texas, 37 pp. // Shen W. and Ritzwoller M. H. . A 3-D Shear Velocity Model of the Crust and Uppermost Mantle Beneath the Western US from Bayesian Monte Carlo Inversion of Surface Wave Dispersion and Receiver Functions. 2012 IRIS Workshop//Shen, W., Ritzwoller, M.H., Schulte-Pelkum, V. and Lin, F.C. Joint inversion of surface wave dispersion and receiver functions: A Bayesian Monte-Carlo approach. Submitted.// Stern, R.J., 1994. Arc assembly and continental collision in the Neoproterozoic East African orogen. Annual Review of Earth and Planetary Sciences 22, 319–351.//

Neo-proterozoic Ophiolite

Archean

Basement Rifts

σ1-σ3 (Pa.m)

σ1-σ3 (Pa.m) 80

0 160

Influence of the mechanical coupling and inherited strength variations on the geometry of continental rifts.

Melody Philippon1, Pim van Delft1, Matthijs van Winden1, Dejan Zamurović1, Dimitrios Sokoutis1,², Ernst Willingshofer1, and Sierd Cloetingh1

Introduction

1. Faculty of Geosciences, Departement of Earth Sciences. Budapestlaan 4. 3584 CD Utrecht (m.m.b.philippon@uu.nl) 2. Department of Geosciences, University of Oslo, PO Box 1047 Blindern, N-0316 Oslo, Norway

Utrecht University

EGU2013-10509

The geometry of continental rifts is strongly controlled by the rheology of the lithosphere at the onset of rifting. This initial geometry will further control the de- velopment of ocean spreading centers and the structure of adjacent passive mar- gins. Therefore, understanding the influence of coupling between the different layers of the lithosphere with and without laterally variable strength in the crust is key when investigating continental rifts. In this study we infer the influence of coupling in the crust on the rift geometry by means of crustal scale analogue ex- periments, where we characterize the response of the crust to deformation in terms of the strength ratio between brittle and ductile crust. The degree of cou- pling has been varied for setups containing or not a pre-existing weak zone.

We use the concept of strength ratio to compare the models to nature. The ob- tained geometry give then a idea of the coupling conditions under which rifting developed in nature.

The velocity impacts on the strength of the ductile layer and hence the degree of brittle ductile coupling.

Increasing coupling

Red sea opening

Red Sea opening

Compilation of sutures in Eastern Africa and Arabia after Kazmin (1978) and Stern (1994); paleogeographic reconstructions from Scotese (1997).

Overview of sedimentary basins of different age after Binks and Fairhead (1992); Bosworth (1992); Genik (1992); Guiraud and Maurin (1991) Fairhead (1988); Khalil and McClay (2001) and Lambiase (1989).

Gass (1977)

Onset of the Afar mantle

plume

Qishon–Sirhan

Basin

SM ER

180,0 - 144 Ma 154,1 - 120 Ma 154,1 - 37 Ma 142,0 - 37 Ma 99,0 - 37 Ma

-

Mozambic Ocean Suture zone

East Gondwana West Gondwana

East African Orogeny

East Gondwana West Gondwana

East African Orogeny

Arabia

India Sey

Mada.

Africa

Antartica

Congo Craton

Tanzanian Craton

Kalahari Craton

PALEO TETHYS

Late Precambrian

As wa Mar mada-son

Modeified after Stern (1994)

Cretaceous Jurassic

Triassic Eo- Oligocene Present day

Strength ratio

Nature Model

FOLDING above/ grabens parallel

to but aside the weak zone FAULTING above the weak zone

Qishon–Sirhan Basin

-

500Km 500Km 500Km

Model setup

Paleo Tethys Ocean

Panthalassic Ocean

Tethys O cean spreading ridge

E. Trias 237 Ma

M. Eocene 50.2 Ma L. Jurassic

152 Ma L. Cretaceous

94 Ma

Str engh r atio

Rio G

rande Cor

in th gulf

N or th S ea gr

ab en

Cen tr al N

or th A fr ic a

U pp er R hine gr

ab en

5 cm.h -1

7.5 cm.h -1

10 cm.h

-1 20 cm.h

-1 50 cm.h

0.25 -1

0 0 2.10 2

10 20

D epth(K m) 30

0 2.102 4.102

10 20 30

D epth(K m) D epth(K m)

0 2.102 4.102

10 20 30

0 2.10 ²

10 20

D epth(K m) 30

0 2.102

10 20

D epth(K m) 30

500Km 500Km

Eocene

33,7- nowadays Ma

Upper Rhine graben North Central Africa basin North Sea graben Rio grande Rift Corinth gulf

5 cm.h-1 7.5 cm.h-1 10 cm.h-1 20 cm.h-1 60 cm.h 1

Modified after Genik 1992

2.10 11

4.10 11

3.10 11

1.10 11

Upper Rhine gr aben Nor th S ea gr aben

Rio gr ande R Cor inth gulf ift

Central North A frica

ε=8.10-16 ˙ ε=1,7.10-16 ˙

ε=1,16.10-15 ˙ ε=8.10-16 ˙

ε=1,15.10-15 ˙

Tanzanian craton

Nubia Arabia

Somalia

Ce nt ^r al A ^f r ^ic an ^S he ^a r zo ⁿ e

Rift

33,7- nowadays Ma 23- nowadays Ma

Rifts Basaltic traps

16- nowadays Ma 11,5- nowadays Ma

Afar

Main Ethiopian rift

Eastern branch of the African rift

Western branch of the African rift

Natural Analogues Strain rate (Est.) Crustal Thickness (km) Upper crust (km) B/D Ratio Strength Ratio

Upper Rhine graben _1,70E-16 ₃₀ ₁₇ _1,3 _0,009

Red Sea Rift _8,00E-16 ₃₀ ₂₂ _2,8 _0,010

North Sea Central graben _1,16E-15 ₂₀ ₁₃ _1,9 _0,050

Rio Grande Rift _8,00E-16 ₃₀ ₁₀ _0,5 _0,132

Corinth Rift _1,16E-15 ₃₀ ₁₀ _0,5 _0,258

East African Rift _4,00E-16 ₃₀ ₂₀ _2,0 _0,011

5 cm.h-1 7.5 cm.h-1 10 cm.h-1 20 cm.h-1 60 cm.h 1

Modified after Brun et al., 1992 Russell and Snelson, 1990; 1994; Moho depth after After Rohais et al., 2007 and Jolivet et al., 2010

Shen and Rotzwoller and Shen et al., in progress

20 km 0

10 20 30

0 10 20 30

km Modified after Brun and Tron 1993

0 10 20

30 20 km

0 20 0

20 S N

20 km

W E

W E S N WNW ESE

Pull/

assymetric extension

Pull/

symetric extension

Sand Putty

Two layers experiments consisting of a lower ductile layer made of silicone putty and an upper brittle layer consisting of feldspar sand. The model is lying on both sides on moving plastic sheets that are pulled apart. The model is

dragged from below on each side and the velocity discontinuity is therefore fixed. The models contain a weak zone located above the velocity discontinuity.

With simple analogue models at crustal scale, we demonstrate that the activation of a weak zone, such as the Mozambic Ocean Suture Zone (MOSZ), required special conditions of coupling within the crust. The evolution of the coupling whitin the Afro-arabian crust is directly linked to the arrival of the Afar mantle plume.

During the mesozoic, series of parallel NNW trending grabens develop parallel to the MOSZ. Evidences for Mesozoic sedimentation above the MOSZ is given in Kalhil and Mc Clay (2001). From the deformation ob- served in our models, these sediments were deposited in the syncline formed above the weak zone.

During Eocene, and with the arrival in the system of the Afar mantle plume, deformation started to focus and localized above the MOSZ, leading to localized stretching in the upper crust, thinning and ulti- mately the formation of the Red Sea with sea floor spreading.

Even with the presence of a weak zone, the deformation is diffuse.

In the brittle upper part, grabens develop outside of the weak

zone. A small amplitude, large wavelength syncline develop above the weak zone.

In the lower crust, extension is accommodated by flow processes in the weak zone.

When increasing the coupling, the weak zone is activated.

Faults develop inside the weak zone and in the vicinity. Extensional deformation is distributed along two decollements that are root- ing in the weak zone. A large wavelength syncline is also affecting the model.