2. 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.

3. 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)

4. Regional Map

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

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

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

8. Exhumation Constraints 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] 2.2Ma 4Ma 5-20 km/Ma exhumation

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

10. Large events in continental crust Abers et al., 1997

11. Exhumation in upper crust: 25° dip on shear zones. Seismic? M W 6.8 (1985)

12. Ewing 9203 MCS profile Moresby Seamount SN 5 km

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

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

15. Egum BBU WoodSeis2000

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

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

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

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

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

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

22. Crustal Velocities Joint inversion for Vp, Vs, hypocenters 11.5 km23.5 km resolution limit Vp [Ferris et al. 2006 in press GJI]

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

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

25. 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

26. 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

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