Geochemistry and 40Ar/39Ar Geochronology of Basalts from ODP Leg 145 (North Pacific Transect)

Abstract

Leg 145 of the Ocean Drilling Program recovered basalts at three locations in the North Pacific. Drilling at Sites 883 and 884 on Detroit Seamount, near the northern end of the Emperor seamount chain, penetrated altered pillow basalts that may be of transitional composition (Site 883) and thick flows of tholeiitic composition (Site 884). The Site 883 basalts did not yield a reliable crystallization age, but a basalt from Site 884 yielded an age of 81 Ma. This is the first reliable radiometric age determination for the northern end of the Emperor Seamounts, and lengthens the period of known activity of the Hawaiian-Emperor seamount chain by approximately 15 million years. Published Pacific-plate-motion models predict an age for Detroit Seamount of approximately 65 to 75 Ma. Either the 81 Ma tholeiite is from very early in the history of an unusually long-lived volcano, or the velocity of the Pacific plate relative to the Hawaiian hotspot increased some time between 81 and 65 Ma.Drilling at Site 885 was expected to reach Lower? Cretaceous oceanic crust near the Chinook Trough in the central North Pacific. Basalt was contacted beneath less than one-half of the expected thickness of sediments. The basalt is altered, but appears to have a mid-ocean ridge tholeiite composition. It yielded a concordant 40 Ar/ 39 Ar plateau age of only 80 Ma, suggesting that volcanism associated with the Late Cretaceous plate reorganization and formation of the Chinook Trough affected a wider area than previously thought.Drilling at Site 887 on the Patton-Murray seamount platform in the Gulf of Alaska recovered transitional basalts overlain by two chemically distinct types of alkalic basalts. The Site 887 basalts are chemically similar to samples dredged from other seamounts in the northeast Pacific. 40 Ar/ 39 Ar dating of an alkalic basalt midway in the section yielded an age of 27 Ma. The uppermost basalt recovered is a sediment-bounded sill that yielded an 40 Ar/ 39 Ar age of 17 Ma. Thus, volcanic activity at this seamount platform spanned at least 10 million years.

Linking the Late Cretaceous to Paleogene Pacific plate and the Atlantic bordering continents using plate circuits and paleomagnetic data

“…The “Detroit” is the combined estimate from the Detroit basalts; the “Detroit‐y” denotes younger basalts collected at ODP sites 883, 1203 and 1204; the “Detroit‐o” denotes older basalts from ODP Site 884. References for radiometric ages are Tarduno et al [2003], Duncan and Keller [2004], Sharp and Clague [2006], and Keller et al [1995]. References for paleomagnetic data are Tarduno et al [2003], Kono [1980], Doubrovine and Tarduno [2004], and Tarduno and Cottrell [1997]. …”

Fossil hot spot‐ridge interaction in the Musicians Seamount Province: Geophysical investigations of hot spot volcanism at volcanic elongated ridges

“…Today, all hot spot traces on the Farallon plate have vanished since this portion of the plate has been subducted beneath North America [ Sager and Pringle , 1987; Pringle , 1993]. An additional feature of this volcanic chain which supports its interpretation as a hot spot track is its parallelity to within a few degrees to the northernmost tip of the Emperor chain (from Detroit seamount (81 Ma) to Meiji seamount (age unknown) [ Keller et al , 1995]), which is of comparable age to the Euterpe chain and thus records the same absolute plate motion.…”

Are the Pacific and Indo–Atlantic hotspots fixed? Testing the plate circuit through Antarctica

“…It is quite long (over 5000 km), therefore yielding good spatial resolution, and it is documented with many dates along track [13] extending from the present-day position of the hotspot beneath Kilauea, to about 43 Ma at the bend between the Hawaiian and Emperor chains, to about 81 Ma at the Detroit Plateau [14] in the north Pacific near the Aleutian Trench (Fig. 1).…”

“…Distances are along-track distance from Kilauea. Data are from Clague and Dalrymple [13] except Detroit Seamount [14].…”