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E.H. McKee

Publications and source records attributed to E.H. McKee.

At least 55 records · Page 3Linked to original sources
USGS1986

Tectonic and magmatic development of the Great Basin of western United States during the late Cenozoic time.

In the later Cainozoic, approx 18 m.y. ago, the first basin and range faulting developed in the central part of the Great Basin, this extensional tectonic system resulting from drag on the North American plate as the Pacific plate moved obliquely to the NW along the San Andreas fault. The northern boundary of the Great Basin at the Snake River plain and W across SE Oregon is the tectonic zone along which the E-W extending Basin and Range province has been moving for the past 18 m.y. In the Great Basin axis a narrow N-trending zone of basalt intruded the crust at the same time that basin and range faulting developed; this belt widens northwards as it approaches the N edge of the Great Basin and becomes diffuse and widespread in SE Oregon and SW Idaho, reaching enormous dimensions in the Columbia Plateau farther N. The basalt, which replaced andesitic igneous activity in the mid-Cainozoic, was produced by widespread partial melting in the upper mantle when the tectonic regime changed from a convergent- and subduction-related system to the extensional basin and range system. The locus of magma generated migration to the E and W margins of the Great Basin simultaneously and, as it migrated, it produced a series of eruptive centres along the N boundary of the Great Basin.-R.A.H.

Modern Geology↗
USGS1985

A reconnaissance Rb-Sr, Sm-Nd, U-Pb, and K-Ar study of some host rocks and ore minerals in the West Shasta Cu- Zn district, California

The Copley Greenstone, Balaklala Rhyolite, and Mule Mountain stock in the West Shasta Cu-Zn district, California, have Rb-Sr, Sm-Nd, U-Pb, and K-Ar systematics that indicate they are a cogenetic suite of ensimatic island-arc rocks about 400 m.y. Pervasive alteration and mineralization of these rocks, for the most part, was syngenetic and the major component of the mineralizing fluid was Devonian seawater. K-Ar ages of quartz-sericite concentrates from ore horizons and Rb-Sr systematics of a few rock and ore specimens record a later thermal and mineralizing event in the district of about 260 m.y. Contamination of some rocks with pelagic sediments is indicated by the Sm-Nd data.

Economic Geology↗
USGS1985

Demonstration of two pulses of Paleogene deformation in the Andes of Peru

New radiometric ages of about 25 m.y. on volcanic materials in a marine intercalation within clastic continental strata of the Upper Moquegua Formation near Caraveli, southern Peru, together with an age of 25.3 ± 0.4 m.y obtained by Tosdal et al. from a locality about 300 km to the ESE, show that the formation contains strata of late Oligocene as well as Miocene age, and demonstrate that the coastal region was at a low elevation during latest Oligocene time. Because the unconformities between the Upper Moquegua Formation and the underlying Lower Moquegua Formation, and between the Lower Moquegua Formation and underlying Paleocene rocks cannot both represent the same tectonic event, two discrete Paleogene events must be present in the Andes of Peru. Although the exact timing of these events is uncertain, the unconformities are likely to be of Paleocene and middle Eocene age or possibly of middle Eocene and Oligocene age.

Earth and Planetary Science Letters↗
USGS1984

RELATIONSHIP OF THE CORTEZ CALDERA TO THE CORTEZ DISSEMINATED GOLD DEPOSIT, NEVADA.

The Cortez caldera is an oval structure ten km in diameter formed by caldera collapse and is located in the northern part of the Toiyabe Range, central Nevada. The Cortez gold deposit, a carbonate-hosted disseminated gold deposit, is located three km northeast of the northern margin of the Cortez caldera. Dike within the Cortez gold deposit have a similar age and composition as the Caetano Tuff and strike N 30-40 degree W, subparallel to the caldera margin and dip up to 45 degree toward the caldera. Remnants of the outflow facies of the Caetano Tuff near the Cortez deposit indicate that the deposit formed near the Oligocene paleosurface.

Journal of Geochemical Exploration↗
USGS1984

Canyon-filling lavas and lava dams on the Boise River, Idaho, and their significance for evaluating downcutting during the last 2 million years

Basalts that periodically dammed the Boise River and its South Fork over the last 2 million years reveal the canyon history and illustrate how lava interacted with impounded river water. Intracanyon basalt flows record a granite canyon successively filled by lava and then recut at least five times in the last 2 million years. The most voluminous flow, Steamboat Rock Basalt, reached 60 kilometers downstream and spread out on the Snake River Plain just east of Boise. Lavas that reached the river were erupted from vents bordering the main canyon and adjacent tributaries. The river canyon was periodically flooded by basalt from these eruptions, reentrenched to a new lower level, then flooded again. This succession resulted in terraces of older flows high above the river and of younger flows lower on the canyon walls. The canyon-filling flows dammed the river and created deltas of pillow basalt and hyaloclastite overlain by massive subaerial basalt. Foreset beds in the hyaloclastite deposits and inclined pillows indicate flow into reservoirs behind the lava dams. A well-documented example of a lava dam is the one formed by the Smith Prairie Basalt, which is about 0.2 million years old. Potassium-argon ages calibrate a canyon history in which the river was lowered at a rate between 0.005 and 0.01 centimeter a year over the last 2 million years. The lava dams interrupted this lowering but were each rapidly incised in about a quarter of a million years at rates averaging 0.03 to 0.07 centimeter a year.

Idaho↗
USGS1983

K-Ar ages and the opening of the South Atlantic Ocean: Basaltic rock from the Brazilian margin

New K-Ar ages for 13 samples of basalt, gabbro, wehrlite, and trachyandesite drilled from the Brazilian continental shelf and coastline yield information about the timing of the opening of the South Atlantic and the nature of the crust seaward from the Brazil margin. The oldest basalt is 138.1 ± 3.5 m.y. "> 138.1 ± 3.5m.y. old and from offshore at 24.5°S; it represents Serra Geral flood basalt on attenuated crust in the Santos basin. Basalts from the coastline at 19.5°S are mixed with terrigenous graben sediments, and their ages confirm that rifting was underway before 130 m.y. Offshore sites in the Campos basin, ∼22°–23°S, 41°W, have basalt ranging from 124 to 112 m.y. in age and mostly continental flood basalt in composition. One 112-m.y. basalt, however, is MORB-like and could therefore represent oceanic lithosphere mixed with continental crust about 50 km from the shoreline at ∼22.5°S. Other samples reveal compositionally varied intraplate, passive-margin magmatism occurring 75-43 m.y. ago. They correlate with profuse contemporary alkalic magmatism on the southeastern Brazil coast and probably represent reactivation of zones of “weakness” (i.e., fracture zone-lineaments).

Marine Geology↗
USGS1982

Miocene volcanism and deformation in the western Cordillera and high plateaus of south-central Peru

New radiometric ages on tuffs from south-central Peru support the postulated flare-up of volcanic activity during early Miocene time. In the region of Huancavelica, Julcani, and Lircay, lower Miocene rocks lie on folded strata of pre-Cenozoic age; the absence of units of Eocene and early Oligocene age indicates that this area remained positive after Incaic deformation in Eocene time. Conglomerate beds reflecting erosion attendant on the first pulse of late Cenozoic (Quechuan) compressive deformation do not appear in the stratigraphic record until after 21.5 m.y. B.P. In one section, beds of coarse conglomerate are underlain by tuff dated at 18.3 ± 0.6 m.y. and overlain by tuff dated at 17.3 ± 0.2 m.y. At another locality, beds of conglomerate conformably overlie tuff dated at 19.6 ± 0.8 m.y. If we incorporate published data from other areas in central and southern Peru, it appears that Quechuan deformation began in early Miocene time between 19.5 and 17 m.y. ago. A firm age for the end of the first pulse of Quechuan deformation in this region is provided by an ash-flow sheet dated at 12 to 12.5 m.y. that unconformably overlies strata of Eocene to early Miocene age.

Geological Society of America Bulletin↗