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Geology topics

Edward A. Mankinen

Publications and source records attributed to Edward A. Mankinen.

43 records · Page 3Linked to original sources
USGS1993

Latest Pleistocene and Holocene geomagnetic paleointensity on Hawaii

Geomagnetic paleointensity determinations from radiocarbon-dated lava flows on the island of Hawaii provide an estimate of broad trends in paleointensity for Holocene time and offer a glimpse of intensity variations near the end of the last glacial period. When the data from Hawaii are compared with others worldwide, the intensity of the geomagnetic field seems to have been reduced from the Holocene average by about 35 percent between 45,000 and 10,000 years ago. A long-term reduction of this magnitude is compatible with reported increases in the production rate of cosmogenic nuclides during the same interval.

Hawai'i↗
USGS1991

Concordant paleolatitudes from ophiolite sequences in the northern California Coast Ranges, U.S.A.

Paleomagnetic data have been obtained from two ophiolite sequences in the northern California Coast Ranges: from Mount Diablo in the San Francisco Bay area and from Potter Valley, north of Clear Lake. The ophiolite exposed at Mount Diablo is part of the late Middle to Late Jurassic Coast Range ophiolite, and that exposed near Potter Valley is Late Jurassic to perhaps Early Cretaceous in age and occurs within the Franciscan assemblage. Data from the sheeted-dike complex at Mount Diablo show these rocks to be strongly overprinted, probably following uplift and erosion of the ophiolite. Samples whose primary remanent magnetization seems to be recovered yield a mean paleomagnetic pole at 30.7°N, 159.5°E with α 95 = 5.6°. A comparison of this pole with the Jurassic apparent polar wander path for North America indicates that the ophiolite has rotated 45° ± 7° counterclockwise relative to the craton and has not been latitudinally displaced. The diabase and pillow basalt in Potter Valley have not been strongly overprinted and data from those rocks yield a paleomagnetic pole at 79.0°N, 61.5°E with α 95 = 6.4°. This result indicates that the ophiolite at Potter Valley has rotated approximately 29° ± 8° clockwise, and has undergone little or no latitudinal displacement. Because of the predominantly northeastward transport of oceanic plates converging with the western margin of North America since middle Mesozoic time, the absence of appreciable northward displacement of either ophiolite fragment indicates that both formed close to the continental margin.

California↗
USGS1990

Review of paleomagnetic data from the Klamath Mountains, Blue Mountains, and Sierra Nevada; Implications for paleogeographic reconstructions

Paleomagnetic studies of the Klamath Mountains, Blue Mountains, Sierra Nevada, and northwestern Nevada pertain mostly to Jurassic and Cretaceous rocks, but some data also are available for Permian and Triassic rocks of the region. Large vertical-axis rotations are indicated for rocks in many of the terranes, but few studies show statistically significant latitudinal displacements. The most complete paleomagnetic record is from the Eastern Klamath terrane, which shows large post-Triassic clockwise rotations and virtual cessation of rotation by Early Cretaceous time, when accretion to the continent was completed. Data from Permian strata of the Eastern Klamath terrane indicate no paleolatitude anomaly, in contrast to preliminary results from coeval strata of Hells Canyon in the Blue Mountains region, which are suggestive of some southward movement. If these Hells Canyon results are confirmed, some of the terranes in these two regions must have been traveling on separate plates during late Paleozoic time. Data from Triassic and younger strata in the Blue Mountains region indicate paleolatitudes that are concordant with North America. Results from Triassic rocks of the Koipato Formation in west-central Nevada also indicate southward transport, but when this movement ceased is unknown. The Nevadan orogeny may have occurred in the Sierra Nevada during Jurassic accretion of the ophiolitic and volcanic-arc terranes of that province to the continent, whereas what has been considered to be the same orogeny in the Klamath Mountains may have occurred before accretion. Using the concordance of observed and expected paleomagnetic directions as a guide, the allochthonous Sierra Nevada, Klamath Mountains, and Blue Mountains composite terranes seem to have accreted to the continent sequentially from south to north.

Blue Mountains, Klamath Mountains, Sierra Nevada↗
USGS1982

Paleomagnetic study of some Cretaceous and Tertiary sedimentary rocks of the Klamath Mountains province, California

Paleomagnetic investigation of Cretaceous outliers and Tertiary sedimentary strata of the Klamath Mountains province, and of onlapping Cretaceous strata, has shown the rocks to be largely remagnetized. Samples studied are from the Upper Jurassic to Upper Cretaceous Great Valley sequence, Upper Cretaceous Hornbrook Formation, Eocene Montgomery Creek Formation, and Oligocene(?) Weaverville Formation. Cretaceous samples that survived the remagnetization have a mean remanence direction that is very close to the expected direction of the Cretaceous magnetic field at the locality of the Klamath Mountains. Data from both primary and remagnetized samples suggest the possibility of 11.5° ± 15.8° of post-Cretaceous clockwise rotation of the Klamath Mountains province. None of the data from either the primary or remagnetized samples shows evidence of the large amounts (∼ 70°) of clockwise rotation that other workers have measured for the lower Tertiary of the Oregon Coast Range. Our data indicate that the Oregon Coast Range and Klamath Mountains province did not behave as a single rigid block during the early Tertiary. They also suggest that any post-Oligocene rotation of the Klamath Mountains province is less than the approximately 30° post-Oligocene rotation recently proposed for a combined Oregon Coast Range–Klamath Mountains–Cascade Range block.

California↗
USGS1976

Natural remanent magnetization, mag¬netic properties, and oxidation of titanomagnetite in basaltic rocks from DSDP Leg 34

We have made paleomagnetic measurements and investigated the magnetic mineralogy of 24 samples of basalt and diabase from Sites 319, 320, and 321 on the Nazca plate. Sample distributions, locations, and ages of overlying sediments are as follows: Site 319, Hole 319, lat 13°01.04'S, long 101°31.46'W, 2 samples, early Miocene (N8); Site 319, Hole 319A, (same coordinates and age), 12 samples. Site 320, Hole 320B, lat 9°00.40'S, long 83°31.8O'W, 2 samples, late Oligocene (N2); Site 321, lat 12°01.29'S, long 81°54.24'W, 8 samples, late Eocene (P16). The objectives were (1) to investigate the stability of the natural remanent magnetization (NRM), (2) to evaluate an improved method of alternating-field (AF) demagnetization, (3) to determine the directions of the magnetically stable components of NRM and the approximate in-situ intensities of NRM, (4) to identify the ferrimagnetic minerals and determine their degree of oxidation, and (5) to relate this oxidation to the magnetic characteristics of the minerals.

Initial reports of the Deep Sea Drilling Project↗
USGS1972

Paleomagnetism and potassium-argon ages of the Sonoma Volcanics, California

Paleomagnetic data and potassium-argon ages indicate that the Sonoma Volcanics was erupted during the Pliocene Gilbert reversed and Gauss normal polarity epochs. The Gilbert reversed epoch is represented in the Howell Mountains east of Napa and east of St. Helena, in the mountains immediately east of the Valley of the Moon, and on the hill just north of Santa Rosa. The Gauss normal epoch is represented by the rocks from Mount St. Helena and possibly by the flows from the upper part of Sonoma Mountain and the rhyolite flows north of Sonoma. The age of the volcanic rocks ranges from 5.3 m.y. to about 2.9 m.y. Volcanic rocks approximately 11.8 m.y. old occur at Burdell Mountain northwest of Novato. This volcanic sequence is probably part of the Tolay Volcanics of the Petaluma area.

California↗