DI11A-02 Comprehensive in situ constraints on LPO fabric of fast-spreading oceanic lithosphere from seismic anisotropy Joshua B. Russell 1 , Hannah F. Mark 2,3 , James B. Gaherty 1 , Daniel Lizarralde 2 , Pei-Ying (Patty) Lin 4 , John A. Collins 2 , Greg Hirth 5 , Rob L. Evans 2 1 Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA 2 Woods Hole Oceanographic Institution, Woods Hole, MA, USA 3 MIT/WHOI Joint Program in Oceanography/Applied Ocean Science and Engineering, MA, USA 4 Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan 5 Geological Sciences Department, Brown University, Providence, Rhode Island, USA
DI11A-02 Motivation Geodynamic models simulate LPO fabric formation and evolution at mid-ocean ridge Observations: ▸ Hand-sample peridotite fabrics -3 –10 2 m length scale ▸ 10 ▸ Seismic anisotropy observations 3 –10 7 m length scale ▸ 10 Blackman et al., 2017 GJI Karato et al., 2008 Annu. Rev. 2
DI11A-02 Motivation Geodynamic models simulate LPO fabric formation and evolution at mid-ocean ridge Observations: x3’ ▸ Hand-sample peridotite fabrics x1’ -3 –10 2 m length scale [100] ▸ 10 x2’ ▸ Seismic anisotropy observations Michibayashi et al., 2016 EPSL 3 –10 7 m length scale ▸ 10 Blackman et al., 2017 GJI Karato et al., 2008 Annu. Rev. 3
DI11A-02 Motivation Geodynamic models simulate LPO fabric formation and evolution at mid-ocean ridge Observations: x3’ ▸ Hand-sample peridotite fabrics x1’ -3 –10 2 m length scale [100] ▸ 10 x2’ ▸ Seismic anisotropy observations Michibayashi et al., 2016 EPSL 3 –10 7 m length scale ▸ 10 Blackman et al., 2017 GJI Eddy et al., 2018 GJI Karato et al., 2008 Annu. Rev. 4
DI11A-02 Motivation Geodynamic models simulate LPO fabric formation and evolution at mid-ocean ridge Observations: x3’ ▸ Hand-sample peridotite fabrics x1’ -3 –10 2 m length scale [100] ▸ 10 x2’ ▸ Seismic anisotropy observations Michibayashi et al., 2016 EPSL 3 –10 7 m length scale ▸ 10 Blackman et al., 2017 GJI NoMelt (~70 Ma) 6 0 20°N 400 km 10°N Depth (m) 1000 600 km 90 −1000 80 100 −3000 110 50 −5000 70 60 −7000 Karato et al., 2008 Annu. Rev. 5 0° 160°W 150°W 140°W
DI11A-02 Olivine LPO fabric types LPO fabric development depends on stress , H 2 O content , and temperature Fast Slow Intermediate Slip systems a b c [100] [010] [001] A-type (010)[100] [100] [010] [001] D-type (0kl)[100] [100] [010] [001] E-type (001)[100] After Skemer et al., 2012 G3 6 Karato et al., 2008 Annu. Rev. ; Jung et al., 2006
2θ 2θ 2θ 2θ 2θ 2θ 2θ 2θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ 2θ DI11A-02 NoMelt anisotropy observations Love 2 θ & 4 θ (5–7.5 s) 2θ 2θ 2θ 2θ + 4θ 2θ 2θ 2θ 2θ Surface Waves: Rayleigh 2 θ (5–150 s) fossil 7.5 s spreading 2 1 c/c (%) Love = + 4θ 4θ 4θ 2θ + 4θ 2θ + 4θ b) 2θ 4θ 4θ 4θ 4θ 0 7.5 s -1 -2 -100 0 100 -100 -100 0 0 100 100 -100 0 100 Azimuth (º) Azimuth (º) Azimuth (º) Azimuth (º) Azimuth (º) 2θ 2θ 4θ 4θ 4θ 7 Russell et al. in review
2θ 2θ 2θ 2θ 2θ 2θ 2θ 2θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ 2θ DI11A-02 NoMelt anisotropy observations Love 2 θ & 4 θ (5–7.5 s) 2θ 2θ 2θ 2θ + 4θ 2θ 2θ 2θ 2θ Surface Waves: Rayleigh 2 θ (5–150 s) fossil 7.5 s spreading 2 1 c/c (%) Love = + 4θ 4θ 4θ 2θ + 4θ 2θ + 4θ b) 2θ 4θ 4θ 4θ 4θ 0 7.5 s -1 -2 -100 0 100 -100 -100 0 0 100 100 -100 0 100 Azimuth (º) Azimuth (º) Azimuth (º) Azimuth (º) Azimuth (º) 7.5 s 4 2θ 2θ 4θ 2 c/c (%) Shear Parameters Rayleigh 2θ a) 2θ 2θ 0 7.5 s G : 2 θ variation of V SV -2 E : 4 θ variation of V SH -4 -100 0 100 -100 0 100 Azimuth (º) 4θ 4θ 8 Russell et al. in review 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ 2θ 2θ 4θ 4θ 4θ
2θ 2θ 2θ 2θ 2θ 2θ 2θ 2θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ 2θ DI11A-02 NoMelt anisotropy observations Love 2 θ & 4 θ (5–7.5 s) 2θ 2θ 2θ 2θ + 4θ 2θ 2θ 2θ 2θ Surface Waves: Pn anisotropy Rayleigh 2 θ (5–150 s) fossil 7.5 s spreading 2 1 c/c (%) Love = + 4θ 4θ 4θ 2θ + 4θ 2θ + 4θ b) 2θ 4θ 4θ 4θ 4θ 0 7.5 s -1 -2 -100 0 100 -100 -100 0 0 100 100 -100 0 100 Azimuth (º) Azimuth (º) Azimuth (º) Azimuth (º) Azimuth (º) 7.5 s 4 2θ 2θ 4θ 2 c/c (%) Shear Parameters Rayleigh 2θ a) 2θ 2θ 0 7.5 s G : 2 θ variation of V SV Compressional Parameters -2 E : 4 θ variation of V SH B : 2 θ variation of V P -4 -100 0 100 -100 0 100 Azimuth (º) 4θ 4θ 9 Russell et al. in review Mark et al. in review 2θ + 4θ 2θ + 4θ 2θ + 4θ 2θ 2θ 2θ 4θ 4θ 4θ
DI11A-02 Constraining the elastic tensor (C ij ) 1 A + B c + E c A − 2 N − E c F + H c 2 B s + E s 0 0 13 elastic parameters required to constrain 13 elements of C ij 1 A − B c + E c F − H c 2 B s − E s 0 0 · C H s 0 0 · · C ij = L − G c G s 0 · · · L + G c 0 · · · · N − E c · · · · · Azimuthal Anisotropy: ρ V qP ( θ ) 2 = A + B c cos(2 θ ) + B s sin(2 θ ) + E c cos(4 θ ) + E s sin(4 θ ) ρ V qSV ( θ ) 2 = L + G c cos(2 θ ) + G s sin(2 θ ) ρ V qSH ( θ ) 2 N − E c cos(4 θ ) − E s sin(4 θ ) = 10
DI11A-02 Constraining the elastic tensor (C ij ) 1 A + B c + E c A − 2 N − E c F + H c 2 B s + E s 0 0 13 elastic parameters required to constrain 13 elements of C ij 1 A − B c + E c F − H c 2 B s − E s 0 0 · C H s 0 0 · · C ij = Rayleigh waves (2 θ ) L − G c G s 0 · · · ▸ L , G , B, H L + G c 0 (V SV ) · · · · Love waves (2 θ , 4 θ ) N − E c · · · · · 9 terms ▸ N , E , G (V SH ) 1 A + B c + E c A − 2 N − E c F + H c 2 B s + E s 0 0 Pn (2 θ , 4 θ ) 1 A − B c + E c F − H c 2 B s − E s 0 0 · ▸ A , B , E C H s 0 0 (V PH ) · · C ij = L − G c G s 0 Scaling relations · · · ▸ C, H, F 4 terms L + G c 0 · · · · (V PV ) ▸ A, B below 7 km N − E c · · · · · 11
DI11A-02 Vs, ξ , G, B, H, E, Elastic model Ψ G , Ψ B , Ψ H , Ψ E Pn-constraints Isotropic Radial Anisotropy Azimuthal anisotropy on E and B FSD FSD + 45 ° 0 0 0 0 crust H E G B V SH > V SV 5 5 5 5 V SH > V SV 10 10 10 10 15 15 15 15 20 20 20 20 25 25 25 25 30 30 30 30 35 35 35 35 50 50 50 50 Depth (km) 100 100 100 100 150 150 150 150 200 200 200 200 APM G/L 250 250 250 250 NF89 (52-110 My) B/A Pa5 H/F NoMelt E/N 300 300 300 300 3 3.5 4 4.5 5 0.95 1 1.05 1.1 1.15 0 2 4 6 8 60 90 120 150 V S (km/s) Strength (%) Azimuth ( ° ) ξ = (V SH / V SV ) 2 12
DI11A-02 Vs, ξ , G, B, H, E, Elastic model Ψ G , Ψ B , Ψ H , Ψ E Pn-constraints Isotropic Isotropic Radial Anisotropy Radial Anisotropy Azimuthal anisotropy Azimuthal anisotropy on E and B FSD FSD + 45 ° 0 0 0 0 crust H H E E G G B B Moho to V SH >V SV 5 5 5 5 35km depth V SH > V SV 10 10 10 10 15 15 15 15 20 20 20 20 25 25 25 25 30 30 30 30 35 35 35 35 50 50 50 50 Depth (km) 100 100 100 100 150 150 150 150 200 200 200 200 APM G/L 250 250 250 250 NF89 (52-110 My) B/A Pa5 H/F NoMelt E/N 300 300 300 300 3 3.5 4 4.5 5 0.95 1 1.05 1.1 1.15 0 2 4 6 8 60 90 120 150 V S (km/s) Strength (%) Azimuth ( ° ) ξ = (V SH / V SV ) 2 13
DI11A-02 Comparison to petrofabrics NoMelt NoMelt NoMelt (Moho to 35 km) V P (km/s) 5 BIM98 (fast-spreading) Fast-shear polarisation 9 5 BIM98 (fast-spreading) PN78 (Mesozoic Average) Anisotropy PN78 (Harzburgite D-type) V qP (%) 8.9 x3’ 4 V P 8.8 0 3 8.7 x1’ 2 [100] 8.6 x2’ -5 1 4 8.5 Anisotropy = 7.6% Anisotropy V qSV (%) 2 V SV 0 -2 Azimuthal Anisotropy: -4 Anisotropy 2 V qSH (%) ρ V qP ( θ ) 2 A + B c cos(2 θ ) + B s sin(2 θ ) + E c cos(4 θ ) + E s sin(4 θ ) = V SH 0 ρ V qSV ( θ ) 2 -2 = L + G c cos(2 θ ) + G s sin(2 θ ) 1.2 ( V qSH / V qSV ) 2 Anisotropy (V SH / V SV ) 2 ρ V qSH ( θ ) 2 = N − E c cos(4 θ ) − E s sin(4 θ ) Radial 1.1 1 0.9 0 50 100 150 200 250 300 350 Azimuth in x' 1 -x' 2 plane ( ° ) Azimuth in horizontal plane (º) 14
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