STRUCTURAL TRENDS AND BACK-ARC EXTENSION IN THE HAVRE TROUGH

The Havre Trough is an active back-arc ocean basin located to the west of the Kermadec trench-arc system in the southwest Pacific. Two recent cruises have provided reconnaissance swaths of Sea Beam bathymetry and GLORIA side-scan sonar data through much of the Havre Trough as well as a detailed survey at 33.5-degrees-S, allowing the overall structural character of the trough and the nature of crustal extension within the detailed survey area to be assessed. The orientation of the tectonic fabric within the Havre Trough is consistently oblique to the basin as a whole, trending 045-degrees to 060-degrees while the bounding Kermadec and Colville Ridges trend 015-degrees to 025-degrees. The oblique internal structure indicates that the Havre Trough has not opened perpendicular to its own trend. Within the detailed survey area a series of short (15-35 km long) en echelon basins are interpreted as an active spreading center; a lack of sediment cover and the dredging of fresh basalt from one of the 3500-4000 m deep basins confirms the youth of these features. No recent extensional features are observed in a GLORIA crossing of the trough at 31.5-degrees-S, suggesting that this part of the Havre Trough may currently be inactive.