Mantle Flow, Lithospheric Structure and Surface Deformation

Transcription

1 Mantle Flow, Lithospheric Structure and Surface Deformation Carolina Lithgow-Bertelloni, University College London C Conrad, J Guynn, N de Koker, JB Naliboff

2 Contributions to Topography q r h= q r /δρg Factors: Mantle Flow Isostatic balance of crust Orogenesis short λ uncompensated Epeirogeny Long λ Tectonic uplift; post-glacial rebound; dynamic topography [Mitrovica et al., 1989; Gurnis, 1993]

3 Earth s Geoid: Dynamic Topography

4 Dynamic Topography: Physical Deflection

5 Observations of Lithospheric Stress Contributions: Mantle Stresses and Lithospheric Structure Major co n=11346 Australasia European-M NAGRA, PE Fennoscan Karasu, PT Daleel Petr Adams, J. Al-Zoubi, A. Ask, M. Assumpçaõ Babyyev, G Batchelor, T Becker, A. Bell, S. Bergerat, F. Bergman, E Barr, M. Bluemling, Bohnhoff, M Bonjer, K.-P Bosworth, W Bratli, R. Brereton, R Brudy, M. 6 Chatterjee, Colmenares Connolly, P. Cornet, F. Deichmann Delvaux, D. Denham, D Doeveny, P Enever, J. Feijerskov, Finkbeiner, Fleckenstei Gay, N. Gerner, P. Gough, D.I. Gowd, T.N. Grasso, M. Gregersen, Grünthal, G Gupta, H.K Gvishiani, A Guzman, C Haimson, B Hanssen, T Heidbach, O Hergert, T. Hickman, S Hillis, R.R. Horvath, F. Jianmin, D. 6 The stress maps display the maximum horizontal compressional stress SH Method Quality focal mechanism A SH is within ± 15 Stress Regime Normal faulting breakouts B SH is within ± 2 Strike-slip faulting drill. induced frac. C SH is within ± 25 Thrust faulting We thank th Stress Map Sciences an Gabrielsen, Christoph R Unknown regime Further i overcoring SV SV hydro. fractures Advisory All stress da available fre SV Citation o geol. indicators SH Sh Referenc - SH Sh NF Data depth range -4 km Heidbach, O SS Sh This map m are from the and bathym are produce based on G SH TF Bird, P., An normal faulting regime Sv > SH > Sh strike-slip regime SH > Sv > Sh Heidbach, O thrust faulting regime SH > Sh > Sv Wessel, P., - Smith, W.H Key refer Fuchs, K. & Heidbach, O Heidbach, O Heidbach, O Sperner, B. Tingay, M., -6-6 Zoback, M. Zoback, M. Zoback, M. Projection is Mercator, Equatorial Scale is 1:46,, [Heidbach et al., 29, WSM release 28]

6 Sources of Stress Inhomogeneity Topography Edge Tractions Basal Tractions g

7 Governing Equations Momentum- Energy - t ( ρv ( ) + v i ) j X ρv i x j T t + v T i = κ 2 T x i x + H 2 i XXXXX = p x i + 2 x i 2 ( η v ij j) + f i Δρg=ραΔΤg Mass - ( ) XXXXX v = ρ t + v ρ i = ρv i x i x i Non-linear What is right Constitutive Relation? FAULTS! Large range of Time- & Length-Scales [Tackley, 1999]

8 Rheology Function of (X, P, T, σ)!8

9 Computing Mantle Flow! CitComS Finite Element code Internal density heterogeneity from S2RTSb!!! Laterally-Varying Viscosity: (T-dependence ~ age)!!! Lithospheric thickness from seismology.!! Use tractions at base of lithosphere [Conrad and Lithgow-Bertelloni, 26; Naliboff et al., 29; van Summeren et al., 212]

10 Plate Driving Forces Slab Pull from Upper Mantle Slabs Slab Suction from Lower Mantle Slabs Shallow Roots and Global Asthenosphere [van Summeren et al., 212]

11 Modeling the Lithosphere

12 Horizontal Tractions REGIME 25 2 S H (max) & S H (min) 15 Normal Strike-slip Thrust Extension 1 5 Compression Strike-Slip MPa [Naliboff et al., 29]

13 Stresses due to Basal Tractions θ (N θθ sinθ) + N θφ φ N φφcosθ + q θ Rsinθ = θ (N θφ sinθ) + N φφ φ + N θφ cosθ + q φ Rsinθ = N θθ + N φφ + q r R =

14 Radial Tractions REGIME Normal Strike-slip Thrust MPa [modified from Naliboff & Lithgow-Bertelloni, submitted]

15 Dynamic Uplift & Extension

16 Dynamic Topography from S4RTS rican Dynamic topography from S4RTS Topo (m) [Lithgow-Bertelloni and de Koker, in revision] [Forte et al., 21; Moucha and Forte, 211]

17 Model of lithospheric structure: TDL [Naliboff et al., 212; Lithgow-Bertelloni and de Koker, in revision] Procedure Divide globe into regions (4 continental + oceans(age) Crustal structure (CRUST 2.) + lithospheric mantle (depleted + undepleted) Oceans half-space cooling based on isochrons Lithospheric mantle densities at P and T[Stixrude and Lithgow-Bertelloni, 25; 211] Thicknesses determined by matching spherically averaged P at 35 km to PREM

18 Best Guess at Observed i.e. Residual [Lithgow-Bertelloni and de Koker, in revision] Figure 1. Graphical comparison between four residual topography fields calculated independently. All four models account for the flattening of old [Flament et al., 213]

19 Topography and Lithospheric Structure τ ij x j = τ zz x i Ω x i [England and McKenzie Ω = σ zz = 1 L + h h L σ zz dz = 1 L + h h L dz h z ( ) gρ z' dz'

20 Effects of Lithospheric Structure n global mean lithostatic stress ( [Naliboff et al., 212] ) and the tectonic principal stresses balancing these variations for a 1 km bas

21 Effects of Lithospheric Structure Isostasy enforced TDL MPa MPa [modified from Naliboff et al., 212]

22 Horizontal and Radial Tractions MPa MPa [Nabliboff et al. 29; Naliboff & Lithgow-Bertelloni, submitted]

23 Effect of Lateral Viscosity Variations Traction Magnitude (MPa) Most Compressional Principal Stress Magnitude (MPa) e) Ratio of Basal Horizontal Traction Magnitudes f) Ratio of Elastic Lithosphere Stress Magnitudes Ratio (Lateral Visc./Layered Visc.) [Naliboff et al., 29]

24 Effect of Weak Asthenosphere RTS1 SLB RTS1 RTS1 RTS1 SLB1 SLB1 SLB Global Distribution (%) LAB Viscosity Contrast (RTS) Change in Stress Magnitude (MPa) Dynamic Topography (meters) [Naliboff and Lithgow-Bertelloni, submitted]

25 Conclusions Mantle-Lithospheric coupling INEVITABLE but VARIABLE -horizontal mantle tractions are large..., match plate motions, but largely not stresses -radial tractions (i.e DYNAMIC TOPOGRAPHY) determine regime and transmit efficiently! -Lithospheric structure assumptions CRUCIAL both in density and rheological structure! -Choice of mantle density heterogeneity also matters What do we need to do? -Complete crustal, lithospheric structure needed -Better representations of lithospheric and mantle rheology (crustal...) -temporal evolution of stress field