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IODP Exp. 315: Sites C0001 and C0002

IODP Exp. 315: Sites C0001 and C0002. Jan Behrmann. Jon Lewis. Kyu Kanagawa. Vincent Famin. Expedition 315. C0001: 0~458 mbsf C0002: 0~204 mbsf, 475~1057 mbsf. Expedition 316. C0006: ASR sample from 456 mbsf. C0006. C0006. Modified after Ashi et al . (2008).

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IODP Exp. 315: Sites C0001 and C0002

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  1. IODP Exp. 315: Sites C0001 and C0002 Jan Behrmann Jon Lewis Kyu Kanagawa Vincent Famin

  2. Expedition 315 • C0001: 0~458 mbsf • C0002: 0~204 mbsf, 475~1057 mbsf Expedition 316 • C0006: ASR sample from 456 mbsf C0006 C0006 Modified after Ashi et al. (2008)

  3. Site C0001 Age VS depth 140-180 m/Ma Over pressured and/or highly fractured zone

  4. Site C0002 Age VS depth 400-800 m/My

  5. Structural Analyses • Types of structures: • Faults, shear zones, and breccia • Vein structures • Folds and kinks - rare • Distribution: • With depth, across-strike and through time • Kinematics and dynamics • Normal, thrust and strike-slip faults - Normal faults are most common

  6. Kinematics and Dynamics • Goal is to determine - σ1 and σ3 orientations and stress ratios, and possibly changes through time • Plots of incremental stain axes (P-T plots) (Marrett and Allmendinger et al., 1990) • Fitted compression (P) and extension (T) quadrants; fault plane solutions • Stress inversion - minimize angle betw resolved maximum shear stress and slickenlines (Angelier, 1984) • Multiple inverse method - subgroups of faults are inverted sequentially allowing determination of multiple stress states (Yamaji, 2000) • Anelastic strain recovery (ASR)

  7. Structural Data • Number of faults measured • 299@C0001, 185@C0002, 484 total • Number of faults with slip data and sense • 223@C0001, 101@C0002, 324 total • Number of faults reoriented with p-mag. data • 40@C0001, 47@C0002, 87 total

  8. Striation on a fault surface @C0001 Normal fault @C0001 Structural features

  9. Sample 4R 3 73-76 Macroscopic scale Anastomosing shear zone cut by thrust fault

  10. Expedition 315 • C0001: 0~458 mbsf • C0002: 0~204 mbsf, 475~1057 mbsf Expedition 316 • C0006: ASR sample from 456 mbsf C0006 C0006 Modified after Ashi et al. (2008)

  11. <936 mbsf >936 mbsf C0002: Forearc Basin Sediments N σ3 σ2 σ1 C0002 σH-max interpreted from borehole breakout data is consistent with σ2 interpreted from fault data

  12. N σ2 σ1 C0002 σ3 Anelastic Strain Recovery (ASR) Consistent with fault data and borehole breakout data

  13. C0002: Prism Sediments - Normal Faults N σ1 • Inversion yields: • σ1: subvertical cluster • σ3: two major clusters • WNW–ESE • NE–SW 1.0 σ2 –σ3 σ1 –σ3 0.5 N σ3 • Two case fo NE-trending straiations crosscutting NW trending striations • One case of NE-striations cutting thrust faults Φ= 0.0

  14. N σ2 σ3 σ1 C0002 C0002: Prism Sediments - Thrust and Strike-slip Faults • Mostly older than normal faults • Fault plane solutions • σ1: NW–SE • σ3: subvertical • Ancient subduction-related stress field

  15. N σ2 σ3 σ1 C0001 C0001: Slope Basin • Mostly normal faults • Fault plane solutions • σ1: vertical • σ3: NE–SW • Consistent with σH-max (σ2) estimated from borehole breakouts • Consistent with seismic reflection data

  16. C0001: Prism Sediments - Normal Faults N σ1 • Inversion of 21 faults • σ1: subvertical cluster • σ3: two major clusters • NNE–SSW • NW–SE 1.0 σ2 –σ3 σ1 –σ3 0.5 N σ3 Φ= 0.0

  17. N σ2 σ3 σ1 C0001 C0001: Prism Sediments - Thrust and Strike-slip Faults • Mostly older than normal faults • Fault plane solutions • σ1: NW–SE • σ3: subvertical • Ancient subduction-related stress field

  18. σ1 plunges 60° Expedition 315 • C0001: 0~458 mbsf • C0002: 0~204 mbsf, 475~1057 mbsf Expedition 316 • C0006: ASR sample from 456 mbsf C0006 C0006 Modified after Ashi et al. (2008)

  19. Summary • Thrusting and strike-slip faulting; subduction-related, NW–SE compression • appear to be inactive • Normal faulting dominates the prism, possibly even near the toe: • NW–SE extension (dominantly in forearc) followed by NE–SW extension (dominantly in slope cover) • Rare thrust faults in the slope basin sediments suggest that these sediments have experienced periods of compression

  20. NW SE σ3 σ2 σ3 σ2 Hypothesis 1 • Gravitational relaxation after underplating and duplex accretion • σ1 vertical at shallow levels everywhere • Plate convergence component (σ2) larger at C0001? and C0006?

  21. Hypothesis 2 • Seismic cycle: • Tectonic loading • Stress relaxation • Initial loading σ1 σ3 σ2 σ2 σ3

  22. Both Sites record sediment influxes at ca 2 Ma Difference in age of oldest slope sediments between C1 and C2 (2 Ma) suggests a prism growth rate of a few mm/yr 4 Ma 6 Ma

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