TO: Tom Davies

FM: Jay Miller

JA Daily Science Report for Expedition 304, 17 December 2004.

LOCATION:  Site U1310 (prospectus site AMHW-01A)

Latitude: 30° 11.481'N     Longitude: 42° 03.926'W (survey position)    
Water depth: 2588 mbsl

SCIENCE UPDATE: Core 304-U1310B-1R (0.0 to 18.5 mbsf, 7% recovery) contained 1.3 m of sparsely plagioclase phyric basalt with glassy rinds on a few pieces. While coring the subsequent interval, the bit parted from the drillstring and the hole was abandoned without additional recovery. Since drilling conditions at this site were so poor, we are moving to alternate site AMHW-02A (Latitude: 30° 10.61'N, Longitude 42° 04.21' W,  2539 mbsl), a new alternate site developed during this expedition from existing site survey data. This site is along the lower eastern slope of the dome (along seismic line MEG-10), where the D-reflector (interpreted to be either a serpentinization front or a detachment fault) is interpreted to surface before diving back beneath the hanging wall. We interpret this location (Site AMHW-02A) to be a possible klippe of hanging wall material, stranded on the detachment surface (or at least the surface expression of the D-reflector). At worst (if this target is not a klippe but either the detachment surface or late volcanic cover), we should be able to address the objectives related to penetration through the D-reflector and into the footwall and this site represents the easternmost extension of our approved alternate sites along a flow line across the top of the dome (Prospectus Alternate Sites AMFW-02A to AMFW-04A). If this drilling target is a klippe, by definition it should be armoring the detachment surface so we could intersect the surface at some tens of meters below the seafloor (rather than at the seafloor where recovery is notoriously poor). Even a single bit penetration at Alternate Site AMHW-02A might define variations in the magnitude of footwall rotation by comparison to the cores we have from the central dome, possible hanging wall rotation, and potentially allow recovery of core from the fault zone.