Gravity and seismic data obtained by the geophysical group at
Oregon State University on the R/V YAQUINA during 1969, 1971, and
1973 plus other available data over the area just west of Nicaragua
and Costa Rica indicate the tectonic complexity of the region. Gravity
measurements show negative free-air anomalies over...
A free-air gravity anomaly map of the area between 10°-17°N and
90°-101°W shows distinctive positive and negative anomalies which
parallel the Tehuatepec Ridge. The positive anomaly approximately
overlies the topographic expression of the ridge. On the wide continental
shelf southeast of the Gulf of Tehuantepec a positive gravity
anomaly with...
Magnetic, gravity and bathymetry data were collected on an extended
cruise of the R/V Yaquina in 1969. The last set of data was obtained
from those track lines leaving the Panama Basin. The area
covered is mainly the Cocos plate (Molnar and Sykes, 1969). The data
is analyzed and compared...
A zone of diffuse deformation -600 km-wide extending from northern California to Washington has developed resulting from the oblique subduction of the Juan de Fuca plate beneath North America, and the northwestward migration of the Pacific plate. This zone is marked by a change in structural style from transtension in...
Rocks south of the Main Mantle Thrust (MMT) in Swat,
Pakistan consist predominantly of Precambrian to Paleozoic
granitic gneisses and metasedimentary rocks that represent
the deformed and metamorphosed northern margin of the Indian
subcontinent. In the Karakar Pass area the rocks are divisible into three lithologic units: the Swat granite...
Ore deposits of the Butte district formed at ca. 66 to 62 Ma within a host rock of Butte Quartz Monzonite (ca. 76 Ma). Deposition of the Lowland Creek Volcanics Formation (ca. 53 to 50 Ma) on top of the Butte Quartz Monzonite and its ores, followed a period of...
Approximately 23 square miles of the east-central part
of the Tendoy Range are included in the thesis area which
lies three miles west of Dell, Montana.
Rocks ranging in age from Late Mississippian to Recent
are exposed in the study area. The upper Paleozoic section
includes approximately 4,200 feet (1,281...
The Grant Range, in east-central Nevada, is a
north-east trending range bounded on the west by a
west-dipping normal fault system. Rocks within the range
record a complex polyphase Mesozoic ductile
compressional and Cenozoic brittle extensional
deformational history. The northwestern Grant Range
exposes deformed, regionally metamorphosed and
unmetamorphosed, Cambrian to...
The Sulaiman foldbelt is an active and conspicuous tectonic
feature on the northwestern margin of the Indo-Pakistani plate.
Seismic reflection data have been combined with surface geological
mapping and drillhole data to interpret the structural style and
tectonic shortening of the eastern Sulaiman foldbelt and its adjacent
foredeep. The data...
The Whittier fault forms the central part of a fault system extending
from the East Montebello fault at Whittier Narrows to the Elsinore fault,
which is traced as far as the Mexican border. The Whittier fault forms a
restraining bend in this fault system, resulting in uplift of the Puente...
Seismic refraction data collected in 1985 by the USGS were used in
this study to derive the P and S velocity structure of the crust beneath the
Gulf of Maine. The data quality differs among instruments and is affected
by surficial lateral heterogeneities, a ringy source signature and
reverberations. Velocity...
The Corvallis fault is a 50 km long northeast-trending structure, part of which defines the boundary between the central Willamette Valley and the east-central Coast Range of Oregon. Previously the fault had been mapped as either a high-angle reverse or normal fault, with the east block down. New gravity data...
Surface geology, seismic data, petroleum exploratory well data, and water well data
have been used to analyze the structural and tectonic history of the southern Willamette
Valley. Tertiary strata beneath the southern Willamette Valley appear to have had an early
Cascade or Clarno volcanic source to the east by the...
The Whitewater River area is located directly east of Mt. Jefferson in the Cascades of central Oregon. Approximately 90 mi2 (230 km2) were mapped (scale 1/24,000) and four new K-Ar ages and 151 major element analyses were obtained in a study of the stratigraphic
and magmatic transition from the Miocene...
The Mount Polley copper-gold deposit is one of a series of porphyry copper deposits that occur in a belt of accreted Mesozoic age island arc terranes in the Canadian Cordillera. The deposit comprises three breccia-hosted Cu-Au ore zones that are associated with a series of monzodiorite to monzonite intrusions emplaced...
Both travel times and amplitudes of large offset refracted and reflected arrivals
observed during GLIMPCE (Great Lakes International Multidisciplinary Program on
Crustal Evolution) along line A in Lake Superior have been modeled using two-dimensional
ray tracing techniques. Forward modeling was used to iteratively refine an
initial velocity model that was...
Detailed subsurface structure contour maps and cross sections have shown the
northern Los Angeles basin to be underlain by a south facing monocline that is
complicated by secondary faults and folds. The monocline forms a structural shelf that
marks the northern boundary of the Los Angeles central trough. The monocline...
The intrusion-related Cerro Negro Norte Fe-oxide (Cu-Au) deposit is hosted in andesites and diorites of the early to middle Cretaceous Coastal Cordilleran arc of northern Chile. Tabular and irregularly shaped magnetite orebodies are localized on splays and fractures of the regional NINE striking Atacama Fault Zone. Production from this district...
Over 3,000 feet of nonmarine Late Cretaceous sedimentary rocks are exposed within the northern Fish Lake Plateau. The Cretaceous
strata are overlain by over 2,000 feet of Early Tertiary nonmarine sedimentary rocks and volcanics. Landslide deposits cover over one-half of the area. The Late Cretaceous Blackhawk Formation, the oldest formation...
The oldest sedimentary and metasedimentary rocks exposed
in the Himalayan foothills of Pakistan record a gradual transition
seaward from the evaporites of the Salt Range Formation to pelitic
sediments deposited in deeper water to the north. The Upper
Proterozoic Tanawal Formation was derived from erosion of a
northern highland produced...