⁴⁰Ar-³⁹Ar incremental heating experiments were performed on volcanic rocks recovered by drilling during Ocean Drilling Program Leg 152, southeast Greenland Margin (63°N), and Deep Sea Drilling Project Leg 81, southwest Rockall Plateau (56°N). Both of these legs drilled into thick sections of submerged lava flows, known as seaward-dipping reflector sequences,...
Paleomagnetic directions from the Eocene Tillamook Volcanic Series of the Oregon Coast Range
point 460 clockwise from the expected Eocene field direction. Potassium argon dating of six dikes and
flows from this formation yields a mean age of 44.3 ± 0.6 m.y. These results establish that the Oregon
coastal block...
Radiometric ages (K-Ar and ⁴⁰Ar-
³⁹Ar methods) have been determined on dredged
volcanic rocks from seven of the New England
Seamounts, a prominent northwest-southeast trending
volcanic lineament in the northwestern
Atlantic Ocean. The ⁴⁰Ar-³⁹Ar total fusion and
incremental heating ages show an increase in
seamount construction age from southeast to...
The island of Tahiti, the largest in French Polynesia, comprises two major volcanoes aligned NW-SE, parallel with the general trend of the Society Islands hotspot track. Rocks form this volcanic system are basalts transitional to tholeiites, alkali basalts, basanites, picrites, and evolved lavas. Through K-Ar radiometric dating we have established...
A succession of basaltic lavas, volcaniclastic sediments, and lignite beds in the Holmatindur region of eastern Iceland provides the means for tying magnetic reversal stratigraphy and a record of major North Atlantic cooling to a precise radiometric timescale. A prominent part of the section is the Holmatindur classic bed, which...
Satellite altimeter measurements of marine gravity reveal 100 to 200-km
wavelength lineations over a wide area of the Pacific plate oriented roughly in the direction of
absolute plate motion. At least three mechanisms have been proposed for their origin: smallscale
convective rolls aligned in the direction of absolute plate motion...
The Marquesas archipelago is a short. NW-SE trending cluster of islands and seamounts that formed as a result of volcanic activity over a weak hotspot. This volcanic chain lies at the northern margin of a broad region of warm and compositionally diverse mantle that melts to build several other subparallel...
We report new major element, trace element, isotope ratio, and geochronological data on the Galapagos
Archipelago. Magmas erupted from the large western volcanos are generally moderately fractionated tholeiites of
uniform composition; those erupted on other islands are compositionally diverse, ranging from tholeiites to picritic
basanitoids. While these volcanoes do not...
Within the Australian-Antarctic Discordance (AAD), a boundary exists between isotopically defined “Pacific-type” and “Indian-type” mid-ocean ridge basalt (MORB) erupted along the Southeast Indian Ridge (SEIR). This boundary has migrated westward beneath the easternmost AAD spreading segment at a minimum rate of 25 mm/yr since 4 Ma; however, its long-term history...
Lavas from seamounts of the central Galápagos Platform and the Carnegie Ridge increase in age with distance from the western edge of the platform, consistent with a hotspot model for the generation of these features. The areal distribution of seamount ages suggests that the pattern of dispersed volcanism seen on...