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Lawrence C. Rowan

Publications and source records attributed to Lawrence C. Rowan.

23 records · Page 2Linked to original sources
USGS1971

Relations of folded dikes and Precambrian polyphase deformation, Gardner Lake area, Beartooth Mountains, Wyoming

Two cross-cutting mafic dikes in the headwall of Gardner Lake in the eastern Beartooth Mountains, Wyoming, have structural relations with Archean migmatite and gneiss that suggest intrusion between deformational phases recognized in the eastern part of the range. Fabric data show that the older dike, an orthoamphibolite, was emplaced subsequent to the F 1 deformational event, but prior to the main episode of metamorphism, metasomatism, and folding, F 2 . The younger dike, a metanorite, was intruded after F 2 , but is folded by west-trending, open F 3 folds. The style and general trend of these F 3 folds are consistent with those observed elsewhere in the eastern part of the range. The data available and absolute age relations in other parts of the range indicate that F 2 occurred 2750 m.y. ago and F 3 1600 to 1800 m.y. ago.

Wyoming↗
USGS1971

Lunar terrain mapping and relative-roughness analysis

Terrain maps of the equatorial zone (long 70° E.-70° W. and lat 10° N-10° S.) were prepared at scales of 1:2,000,000 and 1:1,000,000 to classify lunar terrain with respect to roughness and to provide a basis for selecting sites for Surveyor and Apollo landings as well as for Ranger and Lunar Orbiter photographs. The techniques that were developed as a result of this effort can be applied to future planetary exploration. By using the best available earth-based observational data and photographs 1:1,000,000-scale and U.S. Geological Survey lunar geologic maps and U.S. Air Force Aeronautical Chart and Information Center LAC charts, lunar terrain was described by qualitative and quantitative methods and divided into four fundamental classes: maria, terrae, craters, and linear features. Some 35 subdivisions were defined and mapped throughout the equatorial zone, and, in addition, most of the map units were illustrated by photographs. The terrain types were analyzed quantitatively to characterize and order their relative-roughness characteristics. Approximately 150,000 east-west slope measurements made by a photometric technique (photoclinometry) in 51 sample areas indicate that algebraic slope-frequency distributions are Gaussian, and so arithmetic means and standard deviations accurately describe the distribution functions. The algebraic slope-component frequency distributions are particularly useful for rapidly determining relative roughness of terrain. The statistical parameters that best describe relative roughness are the absolute arithmetic mean, the algebraic standard deviation, and the percentage of slope reversal. Statistically derived relative-relief parameters are desirable supplementary measures of relative roughness in the terrae. Extrapolation of relative roughness for the maria was demonstrated using Ranger VII slope-component data and regional maria slope data, as well as the data reported here. It appears that, for some morphologically homogeneous mare areas, relative roughness can be extrapolated to the large scales from measurements at small scales.

Professional Paper↗
USGS1969

Structural geology of the Quad-Wyoming-Line Creeks area, Beartooth Mountains, Montana

The Quad-Wyoming-Line Creeks area is in the northeastern part of the Beartooth Mountains of Montana. The rocks of the area consist mainly of banded migmatite, granitic gneisses, amphibolite, quartzite, and agmatite; small amounts of biotite schist and biotite gneiss, iron-silicate rocks, ultramafic rocks, mafic dikes, and felsic porphyries are also present. Quartzite outcrops continuously around the major folds, and agmatite is especially widespread in the axial zone of a major anti-form. Two fold sets have been revealed by detailed mapping (scale 1:7200) and statistical analysis of the penetrative subfabric elements. The large later folds, F 2 , are the south-plunging Quad Creek synform and the south-southwest-plunging Wyoming Creek antiform; they are nearly upright and non-isoclinal. A metanorite intrusion is located in the axial zone of the Quad Creek synform. Small F 2 fold style varies from similar in relatively ductile rocks to open, concentric folds in non-ductile rocks. Only one large F 1 , located immediately north of the metanorite pluton, has been mapped. F 1 folds are characteristically similar in style. Refolding of small F 1 folds by small F 2 folds has been observed throughout the map area. Statistical analysis of the compositional layering, So, and the axial planes of small F 1 folds, S 1 , shows that the πS 0 - and πS 1 -axes constructed in the Wyoming Creek antiform are nearly coincident with each other and with south-southwest-plunging maxima of small F 2 fold axes, B 2 . Both B 2 and the axial planes of F 2 folds, S 2 , are dispersed, showing that the later folds are noncylindrical and nonplane. The axes of small F 1 folds, B 1 , are generally dispersed along well defined π-girdles. B 1 and B 2 maxima are generally coincident at some stations in the Wyoming Creek antiform-axial zone, suggesting that B 1 and B 2 are, at least locally, collinear. The long axes of hornblende crystals, L 1 , are also dispersed, but are not parallel to B 1 ; the L 1 -subfabric appears to indicate that L 1 developed during the F 1 folding but plunged somewhat more steeply to the south-southwest to south than Bi and that the F 2 folds are concentric rather than similar in the amphibolite. In the Quad Creek synform (F 2 ), all of the above-mentioned fabric elements diverge around the north side of the metanorite body. The Precambrian deformational history of the present map area, and probably the remainder of the eastern Beartooth Mountains, appears to be comprised of two phases of folding. During the first phase (F 1 ) south-southwest plunging, isoclinal or nearly isoclinal folds formed by passive flow during metamorphism to at least the upper amphibolite facies; these F, folds were not upright and may have been nearly recumbent. L 1 was formed during this phase. Metamorphic differentiation of a sedimentary sequence occurred at this time, but it is not clear whether any new material was added. The second phase of deformation is characterized by upright, non-isoclinal folds which also formed about south-southwest to south plunging axes. Flexural flow was the dominant mechanism in the development of the Quad Creek synform and the Wyoming Creek antiform, but passive flow was important in layers of ductile rocks. Granitization was generally synchronous with the F 2 phase; pegmatite dikes were emplaced later in a passive manner. Quartzite and amphibolite acted as resisters to granitization; their termination in granitic gneisses and migmatites is usually most adequately explained by refolding rather than granitization of the quartzite. It is possible that partial melting occurred in some areas such as the agmatized zones. Time of emplacement of the metanorite body is still questionable, but it clearly predates the F 2 folding; intrusion prior to F 1 is probable because B 1 , B 2 , and L 1 diverge in the vicinity of the body.

Montana↗