HR: 09:05h
AN: V11B-05    [PDF]
TI: Post-Hotspot Collapse Feature and Shield-Building Volcanism on Detroit Seamount
AU: * Kerr, B C
EM: bckerr@pangea.stanford.edu
AF: Stanford University, Mitchell Bldg., Stanford, CA 94305 United States
AU: Scholl, D W
EM: dscholl@pangea.stanford.edu
AF: Stanford University, Mitchell Bldg., Stanford, CA 94305 United States
AU: Klemperer, S L
EM: sklemp@pangea.stanford.edu
AF: Stanford University, Mitchell Bldg., Stanford, CA 94305 United States
AB: In July-August of 2001, ODP Leg 197 drilled Detroit Seamount of the Emperor seamount chain to obtain cores of basaltic lava flows. Prior to drilling, the JOIDES Resolution conducted high-resolution single-channel seismic surveys in the vicinity of preliminary site locations to help confirm suitability for drilling and to collect digital seismic data. At least two seismic lines (about 10 km in length) cross directly over each of the two drill sites. The seismic data provide evidence for volcanism 24-42 Myr after the main shield building event, and for collapse faults possibly coincident with that volcanism. Detroit Seamount, one of the northernmost seamounts of the Hawaiian-Emperor seamount chain, was formed at c. 76 Ma. Combined with drill core data from the summit and northeast flank of Detroit Seamount, new seismic data suggest renewed volcanism occurred during the Eocene between 52 Ma and 34 Ma, 24-42 Myr after initial seamount formation. Hence the age difference between the shield-building lavas and the post-shield edifices on Detroit is far greater than the shield/post-shield age differences observed on the Hawaiian Islands. The seismic data reveal peaks in the basement, centered c. 7-11 km north of ODP Sites 883 and 1204, and buried by the Meiji drift sediment cap. These peaks are older then the earliest Meiji sediment (34 Ma) as Meiji sediment horizons onlap onto the slopes of the peaks. Ash layers recovered in cores from ODP Sites 883, 884 and 1204 appear to be mafic in composition, and erupted locally and subaqueously. We interpret the peaks as volcanic edifices, possibly the source of the ash layers cored at ODP Sites 883, 884, and 1204. On Detroit Seamount, a significant west-northwest-striking normal fault, Summit Fault, occurs in the basement with the downthrown block to the northeast. Though we were unable to image the fault plane below the volcanic basement, the fault scarp in the basement suggests a low-angle normal fault, dipping c. $19\deg$. The apparent offset in the basement increases to the northwest from approximately 160 m to nearly 450 m over an along-strike distance of c. 10 km. Interpreted in the context of ocean bottom current deposition, sediment horizon patterns suggest that Summit Fault is much older than 34 Ma. Though Summit Fault possibly formed soon after shield building ceased at 76 Ma, it is also possible that Summit Fault's formed c. 52 Ma, concurrent with Eocene volcanism mentioned above.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 7220 Oceanic crust
DE: 8400 VOLCANOLOGY
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting