1 / 26

Other Tectonic Rifts: the Woodlark-D'Entrecasteaux Rift, Papua New Guinea

Other Tectonic Rifts: the Woodlark-D'Entrecasteaux Rift, Papua New Guinea. Geoffrey Abers, Boston University. Thanks to: A. Ferris (BU), S. Baldwin (Syracuse), B. Taylor (Hawaii), H. Davies (UPNG), many others. Some Recent US Projects. Marine geophysical surveys (1990s)

miron
Download Presentation

Other Tectonic Rifts: the Woodlark-D'Entrecasteaux Rift, Papua New Guinea

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Other Tectonic Rifts: the Woodlark-D'Entrecasteaux Rift, Papua New Guinea Geoffrey Abers, Boston University Thanks to:A. Ferris (BU), S. Baldwin (Syracuse), B. Taylor (Hawaii), H. Davies (UPNG), many others.

  2. Some Recent US Projects • Marine geophysical surveys (1990s) • Leg 180 Drilling: active fault system (1998) • WoodSeis2000 Passive seismic experiment • Core complex P-T-t-D thermochronology • Raised/drowned coral survey (2002-4)

  3. Regional Map

  4. Woodlark Basin Sea floor 72 mm/yr 32 mm/yr 57 mm/yr [Taylor et al., 1999 JGR] volcano • Rift follows weak, thickened continental crust • Magnetic lineations constrain past 4-6 Ma motion

  5. Sea-floor history shows stretching • 200 ± 40 km stretching before breakup (130-300% strain) • 100-200 km extension in MCC region [Taylor et al., 1999 JGR]

  6. D’Entrecasteaux MCCs GPS rate [Baldwin et al., 2004 Nature] GPS-based velocities: Wallace et al. 2004 JGR

  7. Exhumation Constraints 2.2Ma 4Ma • 2-2.4 Ma, 4-5 Kb granitoids • 4-5 Ma, 7-11 Kb gneisses • [Hill & Baldwin, 1993] • 4.3 Ma, > 70 km eclogites • [Baldwin et al., 2004] 5-20 km/Ma exhumation

  8. How can rocks be exhumed so far in extension? • requires coupling from upper crust to mantle

  9. Large events incontinentalcrust Abers et al., 1997

  10. Exhumation in upper crust: 25° dip on shear zones. Seismic? MW 6.8 (1985)

  11. Ewing 9203 MCS profile Moresby Seamount S N 5 km

  12. Earthquake Fault? 1 plane parallel to fault 4-8 km depth 3 km water depth ODP Leg 180 (1998): fault gauge

  13. Seismicity rates from global catalogs Detection complete only for M>5.3 [Abers, 2001, Geol Soc Spec Pub]

  14. WoodSeis2000 BBU Egum

  15. Receiver functions:Strong Moho arrival, varying depth P Ps [Abers et al. 2002 Nature; Ferris, 2002 MA thesis]

  16. Crustal Thickness Variations [Abers et al. 2002 Nature; Ferris, 2002 MA thesis]

  17. Flow beneath core complexes Lower crustal flow Mantle flow moho

  18. Moho cross section: Thins under MCC’s Where is missing buoyancy? [Abers et al. 2002 Nature]

  19. Velocity Anomaly is 30-100 km deep beneath thin crust... ... and isostatically compensates crust [Abers et al. 2002 Nature]

  20. Vp-T relations at 2 GPa How Hot? >4% @ 2-3 GPa 4% Vp relative to iasp91 elastic: Hacker et al. 2003 + anelasticity; no melt

  21. Crustal Velocities Joint inversion for Vp, Vs, hypocenters Vp 11.5 km 23.5 km [Ferris et al. 2006 in press GJI] resolution limit

  22. “normal” continent low Vp below Moho Velocities in the Crust [Ferris et al. 2006 in press GJI]

  23. Contin. Oceanic Possible Compositions Seismic Moho [Ferris et al. 2006 in press GJI]

  24. What is seismic Moho good for? • Marker of density boundary? probably • Structural marker indicating strain? • not clear what is below • UHP exhumation requires crust, mantle exchange

  25. Summary Up to 200 km extension in 4 Ma (how?) Exhumation of 70 (100) km in 4.3 (8) Ma Crustal unroofing on faults dipping 25°- 33° Thinned crust underneath, mantle flow Compensated by hot mantle Magmatism mostly at base of crust before rifting

  26. syn-rift volcanics: progression from andesitic to bimodal at high extension from I. Smith, multiple papers

More Related