Publications

Rocks of the Eastern Franciscan belt, northern California, are divided into two tectonostratigraphic terranes metamorphosed to the blueschist facies, both with a distinct lithologic association and deformational history. The easternmost terrane, the Pickett Peak terrane of Early Cretaceous isotopic age, consists of crenulated mica schist and gneissic to schistose metagraywacke, with...

Small fault‐bounded slabs of low‐grade (prehnite‐pumpellyite‐bearing) slate, metagraywacke, and greenstone occur between the Coast Range ophiolite and South Fork Mountain Schist for at least 60 km south of the Klamath Mountains, northern California. The metagraywacke slabs differ from typical Franciscan Complex metagraywacke to the west by the absence of blueschist‐facies minerals and...

Tectonostratigraphic terrances in northwest California and southwest Oregon record a complex history of subduction, collision, and transform faulting. During the late Jurassic Nevadan orogeny, the Elder Creek-Snow Camp and western Klamath terranes were imbricated during collision of an island-arc system with the continental margin. Subsequent collisions are recorded in the Pickett Peak...

The Western Cascade Series (WCS) is a 3.5‐km‐thick, crudely homoclinal (east dipping) calcalkaline volcanic sequence of mid‐Oligocene to early Miocene age that crops out near the southern tip of the Cascade Range in northern California. The mean direction of remanent magnetization in the WCS is D, 4.9°; I, 57.6° (N, 53; k, 14.4; α95, 5.3°). When compared to a reference direction for the...

Using several isotopic techniques, we have determined the ages of selected metamorphic rocks in the Yukon-Tanana terrane (YTT) of east-central Alaska. U-Pb zircon data from an augen gneiss body in the Big Delta quadrangle indicate that the granitoid protolith of the gneiss was intruded 341 ± 3 m.y. ago (lower intercept age). An upper intercept age of 2,136 ± 31 m.y. indicates an...

No abstract available.

The Clarno Formation, a mostly Eocene and partly early Oligocene sequence of andesitic lavas and volcaniclastic rocks, is the oldest Tertiary formation exposed in north central Oregon. Remanent magnetization directions at 46 sites in the lavas provide a paleomagnetic pole at 84°N, 278°E with a 95% confidence cone of 7°. Comparison of this pole with the North American reference pole for...

The detailed behaviour of the geomagnetic field during reversals is documented by palaeomagnetists to constrain models of the geomagnetic dynamo. Reversals are studied by measuring the magnetic remanence preserved in rocks to obtain both the direction and intensity of the ancient magnetic field.

No abstract available.

Paleomagnetic measurements and K‐Ar age determinations on volcanic rocks from Long Valley caldera, California, have enabled further refinement of eruptive activity within this large silicic volcanic center. K‐Ar age determinations show that postcaldera volcanic eruptions began 0.73 m.y. ago and continued periodically until about 50,000 years ago. The eruptions were not temporally random...

New paleomagnetic, paleontologic, and stratigraphic data from outcrops of the Laytonville Limestone (101 to 88 million years old) support a Southern Hemisphere orgin. A paleomagnetic megaconglomerate test is statistically significant and suggests magnetization at 14?? ?? 5?? south, predating Late Cretaceous to Eocene (70 to 50 million years ago) accretion. Rapid Kula plate movement or...

Examination of grades, tonnages, and basement rocks for 88 epithermal precious- and base-metal quartz-adularia-type districts in North, Central, and South America, and Japan reveals that the type of basement rock below the mineralized veins is useful for predicting grade and size of deposits. Epithermal districts overlying basement with salt and evaporites, or rocks with trapped sea...