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Research about Montana

Source-linked reports with geographic coverage including Montana.

At least 883 records · Page 49Linked to original sources
USGS1976

Use of thermal-infrared imagery in ground-water investigations, northwestern Montana

Thermal-infrared imagery was used to locate ground-water inflow along a 50-mile (80-kilometre) reach of the Kootenai River and Lake Koocanusa and a 55-mi (88-km) reach of the Clark Fork of the Columbia River in northwestern Montana and northeastern Idaho. The imagery confirmed that measured streamflow gains below Noxon Rapids Dam, ranging from 1,000 to 2,500 cubic feet per second (28 to 71 cubic metres per second), resulted from inflow of ground water, which was about 2.5° Celsius warmer than surface water. The thermal scanner (8.5-11 micrometres) used in May 1972 and March 1973 was mounted in a twin-engined aircraft. On the March 1973 flight, the data were recorded in an analog format on magnetic tape in flight, later were converted to digital format, and then were computer processed using an assignment of patterns to indicate differences in water temperature. Thus, subtle temperature differences are much easier to identify than they are oh conventional film-negative displays. The output data from the image-processing program can be converted to temperature maps having an isotherm spacing of 0.5°C.

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USGS1975

Garnet peridotite xenoliths in a Montana, U.S.A., kimberlite

Within a swarm of late middle Eocene subsilicic-alkalic diatremes, one diatreme 270 by 370 m and an associated dike contain common xenoliths of granulite and rare xenoliths of spinel peridotite and garnet peridotite. Six garnet lherzolite xenoliths have been found and these show a range of textures. Four are granular, and two are intensely sheared. Phlogopite is absent from the intensely sheared xenoliths and is thought to be primary in part in the granular xenoliths. Estimated temperatures and depths of equilibration of xenolith pyroxenes range from 920 ° C, 106 km (32 kbar) to 1315 ° C, 148 km (47 kbar). The xenoliths show increasing amounts of deformation with greater inferred depths of origin. The temperature-depth points suggest a segment of an Eocene geotherm for Montana which is similar in slope to the steep portion of the pyroxene-determined Lesotho geotherm (BOYD and NIXON, this volume) and is considerably steeper than typical calculated shield and continental geotherms at present. The steep trend could be a result of plate-tectonic shearing and magma ascension within an Eocene low-velocity zone. Preservation of intensely sheared textures requires rapid transport of material from about 150 km depth during active deformation of relatively dry rock. The occurrence of monticellite peridotite in this kimberlite diatreme suggests that magmas which crystallized to monticellite peridotite at relatively shallow depth could be one of the primitive types of kimberlite magma.

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USGS1975

Origin and significance of natural gases of Montana

About two years ago, I was assigned to a project to evaluate the hydrocarbon potential of the Cretaceous system of the northern Rocky Mountains; namely, in Montana, North Dakota, and South Dakota. I had no problem identifying potential traps; both structural and stratigraphic, but recognized the fact that most of the production from the Cretaceous in Montana is natural gas. More important, this production is from relatively shallow depths, often less than 2,000 feet. I realized that not only stratigraphy and structure, but also the origin, migration, and accumulation of hydrocarbons must be fully understood for effective exploration of new resources in the northern Rocky Mountains and elsewhere.

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USGS1975

Chemical analyses (raw laboratory data) and locality index maps of the Confederate Gulch area, Broadwater and Meagher Counties, Montana

Analysis of the side looking airborn radar imagery of Massachusetts, Connecticut and Rhode Island indicates that radar shows the topography in great detail. Since bedrock geologic features are frequently expressed in the topography the radar lends itself to geologic interpretation. The radar was studied by comparisons with field mapped geologic data first at a scale of approximately 1:125,000 and then at a scale of 1:500,000. The larger scale comparison revealed that faults, minor faults, joint sets, bedding and foliation attitudes, lithology and lithologic contacts all have a topographic expression interpretable on the imagery. Surficial geologic features were far less visible on the imagery over most of the area studied. The smaller scale comparisons revealed a pervasive, near orthogonal fracture set cutting all types and ages of rock and trending roughly N40?E and N30?W. In certain places the strike of bedding and foliation attitudes and some lithologic Contacts were visible in addition to the fractures. Fracturing in southern New England is apparently far more important than has been previously recognized. This new information, together with the visibility of many bedding and foliation attitudes and lithologic contacts, indicates the importance of radar imagery in improving the geologic interpretation of an area.

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USGS1975

Water resources data for Montana, water year 1973; Part 2. Water quality records

Water resources data for the 1973 water year for Montana include records of data for the chemical and physical characteristics of surface water. Data on the quality of surface water (chemical, temperature, and sediment) were collected from designated sampling sites at predetermined intervals such as once weekly, monthly or less frequently. Records are given for 79 sampling stations of which 69 are continuous record stations, 2 are partial-record stations, and 8 are miscellaneous sites. Locations of surface water-quality stations are shown in figure 1. A few pertinent stations (not included above) in bordering States are also included. The records were collected by the Water Resources Division of the U.S. Geological Survey under the direction of George M. Pike, district chief. These data represent that portion of the National Water Data System collected by the U.S. Geological Survey and cooperating State and Federal agencies in Montana.

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USGS1975

Andesite sills in the Red Mountain area, Scapegoat Wilderness, Lewis and Clark County, Montana

Sills 2-200 ft (0.6-60 in) thick in the Red Mountain area of the Scapegoat Wilderness in northwest Montana consist of altered andesite, basaltic andesite, and dacite and occur over a stratigraphic range of 8,000 ft (2,400 m) in the Helena and Snowslip Formations. The approximate compositional range of the sills is 50-80 percent plagioclase, 0-25 percent orthoclase, and 5-30 percent amphibole, pyroxene, and biotite; the uppermost sill contains about 15 percent quartz in the groundmass. Accessory minerals include quartz, magnetite, ilmenite, apatite, and pyrite. The petrology and alteration of the sills distinguish them from other sills in the region. Field observations and laboratory studies consisting of chemical, isotopic and X-ray analyses, and petrographic and mineralogic investigations suggest that the sills may have been emplaced in Precambrian Y time at about the same time as the extrusion of the Purcell Lava in the vicinity of Glacier National Park. Alternatively, the sills may represent a Precambrian igneous event not previously recognized in the Belt basin.

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USGS1974

Composition and time relations of plutonic and associated volcanic rocks, Boulder Batholith Region, Montana

Comparison of areally weighted bulk compositions for the Boulder batholith and prebatholith volcanic rocks (Elkhorn Mountains Volcanics) shows a close match in terms of K 2 O-Na 2 O-CaO-SiO 2 variations. Detailed examination of available chemical data suggests, however, that the constituent units of the volcanic rocks differ among themselves, as well as from many of the batholith units. Most sampled volcanic rocks are chemically and isotopically similar to the volumetrically minor mafic members of the putonic main series of Tilling (1973). The sodic-series plutonic rocks, which form about 15 percent of the exposed batholith, apparently have no compositionally similar counterparts in the Elkhorn Mountains Volcanics in terms of bulk composition. The Butte Quartz Monzonite, which makes up about three-quarters of the batholith in terms of individual samples and bulk composition, is chemically distinct from most volcanic rocks. This relation suggests that only small amounts of magma of Butte Quartz Monzonite composition erupted onto the surface. The voluminous silicic ash flows of the middle member of the volcanic rocks were probably derived from the same magma that mostly crystallized subsurface to form the Butte Quartz Monzonite. Field, chemical, K-Ar age, and paleomagnetic evidence, however, strongly suggest that a time gap separated the extrusion of the middle-member volcanic rocks from the intrusion of the Butte Quartz Monzonite and related younger silicic variants. Compositional and time relations between the plutonic and genetically associated volcanic rocks are generally compatible with the concept that the volcanic rocks are eruptive equivalents of a shallow evolving batholith but seem incompatible with some specific aspects of the “extrusive complex” or “floored sheet” hypothesis as applied to the Boulder batholith by Hamilton and Myers (1967, 1974).

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