R-3 Repository :: Browsing by Author "Burchfiel, B. C."

Browsing by Author "Burchfiel, B. C."

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A major element geochemical study of Laramide igneous rocks of the Colorado mineral belt
(1977) Lux, Daniel R.; Burchfiel, B. C.
Major element chemical analyses for igneous rock samples from the Colorado mineral belt are presented along with chemical analyses from the literature. Petrographic data which was collected is also presented. Samples range from basaltic to granitic compositions but rocks with intermediate silica contents are most common. Data indicates that these rocks have calcalkaline characteristics, with the exception of one sample which is silica-undersaturated. Lead and strontium isotopic data taken from the literature, suggest that source materials in the lower crust are 17 to 18 m.y. old. The association in time and space suggest Laramide structural deformation and igenous activity are related. However, it appears that Precambrian structures control the emplacement of Laramide igneous rocks along the Colorado mineral belt. Distribution of ore deposits and Pb isotopic values for ores are in agreement with partial melting of Precambrian lower crust. Models involving the generation of Laramide igneous rocks by melting along a subduction zone are considered unfavorable.
Analysis of foreland basement deformation associated with the Clark Mountain thrust complex, southeastern California
(1977) Nelson, Eric; Burchfiel, B. C.
In the Sevier orogenic foreland exposed in the Clark Mountains of southeastern California, results of this study indicate that Precambrian igneous and metamorphic basement, autochthonous relative to eastward vergent Mesozoic thrusting, exhibits two different modes of postPrecambrian foreland deformation in two separate structures. In the Mesquite Mountains antiform, draping of sedimentary cover (which consists of three thrust sheets overlying thin, autochthonous sediments) has resulted from rigid rotation of basement blocks which core the antiform* This antiform, which probably formed after latest Sevier thrusting, is analogous to Larimide basement uplifts and associated drape structures studied by Stearns (197) in the Rocky Mountains. Basement in the complex, overturned Kokoweef svncline probably deformed through a combination of spaced (simple) shear and pervasive (pure) shear in response to folding of sedimentary cover associated with early thrusting in the Sevier orogen. In both structures the unconformable contact between basement and cover is unsheared. Also all foliations and folds in the basement were formed in the Precambrian, and have not been folded during Late MesozoicCenozoic formation of the Mesquite Mountains antiform or the Kokoweef syncline. However basement is more strained on a microscopic scale in the Kokoweef syncline than in the Mesquite Mountains antiform. Basement, during folding of its sedimentary cover, can adjust in three possible ways: 1) by folding, 2) by rigid rotation, or 3) by spaced or pervasive shearing. Detailed mapping of foliations presented in this study shows that the basement was not folded during formation of either structure. The unsheared basement-cover contact in the Mesquite Mountains antiform is planar indicating that rigid rotation of the basement occurred, which requires little or no basement shortening. In the Kokoweef syncline, this same contact is folded, which probably requires extensive basement shortening. Thus basement in the Kokoweef syncline adjusted by shearing along reactivated old foliation planes, although the exact mechanism is unclear and enigmatic. The ultimate cause of foreland basement deformation is dependent on local boundary conditions and not necessarily indicative of regional stresses. Involvement of basement in foreland structures, and the style of this involvement, is controlled by a number of factors including mechanical properties of basement and cover, position and timing of foreland deformation relative to tectonic elements, and scale, all being interrelated. Differences in these factors might explain the lack of pervasively developed basement uplifts in the southern Cordillera relative to the Rocky Mountain foreland.
Analytical solutions to selected boundary value problems and their application to Rocky Mountain foreland deformation
(1977) Couples, Gary Douglas; Burchfiel, B. C.
The Airy stress function is used, via the Principle of Superposition and the series summation concept, to obtain stress states in a static, self-gravitating elastic beam subjected to boundary stresses. The boundary conditions investigated are more complicated than those previously published and include cases with sawtooth-, step-, and sinusoidally-shaped lower boundary loads, with and without additional tectonic end loads. Potential shear fracture (fault) patterns derived from the calculated stress fields indicate co-existing (simultaneous) regions of lateral shortening and extension. Application of three of the cases to the study of the structural geometry of the Wind River, Owl Creek, and Beartooth Mountains of Wyoming yields a good "fit." For the case of the upthrust structures, these solution provide a possible explanation for the observed rotations and zones of shortening and extension.
Petrology and structure of the Ivanpah Mountains area, California
(1973) Weisenberg, Charles William; Burchfiel, B. C.
tn the Ivanpah Mountains area of southeastern California may be seen the intersection of the north west-southeast trend of the late Mesozoic Sevier orogenic belt of westward directed thrust faults and a similar unnamed belt of early Mesozoic age, generally found from fifty to one hundred miles apart. In the same area is found the eastern limit of Sierra Nevadan age Mesozoic plutonism in the Mojave desert. This study examines the nature of Mesozoic igneous activity in the Ivanpah Mountains area and its relation to the extensive development of at least two superimposed systems of Mesozoic thrust faulting in the area. A field and petrologic study of the Ivanpah Mountains suggests that there are three and possibly four Mesozoic plutonic episodes in the area. The Oro Wash Quartz Diorite is a small pluton petrologically similar to plutons in nearby areas that have yielded K/Ar mineral ages of 19 to 2 million years. The Striped Hills granodiorite is a relatively mafic rock which appears to be a more mafic hybrid border phase of the Teutonia Quartz Monzonite. K/Ar mineral ages suggest it is 161-167 million years in age. The Teutonia Quartz Monzonite is a tabular body, inclined west, several miles thick. it forms what is probably a gradational contact with the Striped Hills Granodiorite, and has a minimum K/Ar mineral age of 135138 million years. The Kessler Springs Quartz Monzonite is a relatively fresh, porphyritic rock which, has an isotopic age of 91-94 million years. Non-plutonic igneous rocks include the Piute Valley Plug, a small body of rhyolite which intrudes along the contact of the Teutonia Quartz Monzonite, and paleozoic carbonates. Since it is within a few miles of, and petrographically similar to, the Mesozoic Delfonte Volcanics, it may have been part of the feeder dike system of these volcanics, suggesting they are younger than the Teutonia Quartz Monzonite. The Cima Road Dikes are a group of widespread dacite dikes of probable Cenozoic age. Chemically, all the igneous rocks are calcalkaline, and most of the plutonic rocks are chemically similar to the central Sierra Nevada Batholith. Silica values for the plutonic rocks vary from 51% for the Oro Wash body to 11% for some samples of the Teutonia Quartz Monzonite. Both K2O and Na2Û vary from near 2% in the Oro Wash body to near 5% in the Teutonia Quartz Monzonite, which is chemically similar to rocks of the Eastern Sierra Nevada Batholith. The Mesozoic structures related to the plutonic rocks include cataclastic and mylonitic zones associated with Mesozoic thrusting. The tabular west-dipping form of the pluton in the Ivanpah Mountains is probably related to Mesozoic structures and may intrude the core of a large eastward overturned anticline. The pluton may be pretectonic but is probably syntectonic. Cenozoic structures include joints and numerous types of shear zones. One breccia zone appears to have incorporated alluvium along the fault zone. Tectonism appears to have occurred in this area during the Triassic prior to emplacement of the Oro Wash pluton and again after emplacement of the Teutonia Quartz Monzonite in the Jurassic-Cretaceous. Some folding may have occurred synchronously with emplacement of the Teutonia Quartz Monzonite. The last period of major thrusting (probably middle Cretaceous) does not appear to have affected the Kessler Springs Quartz Monzonite.
Stratigraphy and structure of the Late Precambrian-Early Cambrian clastic metasedimentary rocks of the Baldwin Lake area, San Bernardino Mountains, California
(1976) Tyler, David Lynn; Burchfiel, B. C.
The San Bernardino Mountains are the easternmost range of the Transverse Ranges of southern California, Precambrian crystalline rocks, and Late Precambrian and Paleozoic metasedimentary rocks are exposed in several roof pendants in the Mesozoic plutonic rocks which comprise the bulk of the range. The Late Precambrian - Early Cambrian clastic shelf sequence in chronologic order includes 1) the white quartzite of the Stirling Quartzite Equivalent; 2) the gray quartzite and phyllite of the Wood Canyon Formation; 3) the vitreous white Zabriskie Quartzite; and 4) carbonate ahd schist of the Carrara Formation. These rocks probably constitute a part of the initial deposits along the eastern margin of the Cordilleran miogeosyncline. Middle Cambrian to Permian shelf carbonates overlay the clastic sequence. The Precambrian crystalline rocks and the sedimentary rocks were deformed and metamorphosed to upper greenschist (biotite) grade, probably in Late Masozoic time. The rocks are folded into a northeast-vergent overturned anticline which is overridden by a somewhat later thrust of similar vergenz. Dominantly post-tectonic acid and intermediate plutons of the Mesozoic Sierran magmatic arc intrude the metamorphic rocks. Right-lateral strike-slip faults and gravity slides of Cenozoic age modify the Mesozoic structure. These features are related to the final uplift of the San Bernardino Mountains.
Stress distribution in the Winters Pass thrust plate
(1978) Lambert, William R.; Burchfiel, B. C.
The Winters Pass thrust plate carries a section of Precambrian basement and its sedimentary cover rocks over Precambrian and lower Paleozoic sedimentary rocks. The thrust plate has undergone two periods of movement: the first to the southeast, and the second to the northeast. The basal 3 to 4 meters of this thrust plate consists of basement rocks that are cataclastically deformed, locally blastomylonitic and contain a well-developed cataclastic foliation and mineral lineation due to feldspar and quartz streaking. In the higher parts of the thrust plate, the cataclastic rocks present in the basement are mylonitic gneisses and mylonites. Relatively undeformed gneisses are present above the mylonites and throughout the thrust plate interspersed with cataclastic rocks. Closely spaced shear fractures are present throughout the gneiss. However, they are not well-developed in the blastomylonites in the lower parts of the thrust or in the upper part where they become progressively less well developed. The shear fractures are also absent in areas of massive quartzo-feldspathic rocks. Microshear fractures, however, are found in all thin sections studied throughout the plate. Stress distribution was determined by using conjugate shear fractures present both in the field and in thin-section. The earliest stress field had with a NWSE subhorizontal orientation and varying in orientation between northeast plunging 55 degrees and southwest plunging 4 degrees. The second stress field had a subhorizontal NE-SW orientation for o oriented in a southeastern direction with plunges varying between 4 and 9 degrees. These two different stress distributions indicate two separate thrusting events. Overturned folds in the area agree with this interpretation and also give direction of movement. These folds indicate the first movement of the Winters Pass thrust plate was to the southeast and the second movement was to the northeast.
Structural and stratigraphic relationships between the Numidien formation and underlying formations in the westernmost Mogod Mountains, northern Tunisia
(1976) Miller, Elizabeth Louise; Burchfiel, B. C.
The Numidien formation in the westernmost Mogods overlies a sequence of Upper Cretaceous to Eocene limestones and marls which exhibit a shallowing event beginning prior to the lowermost Eocene. Water depths of deposition based on faunal assemblages indicate that the Upper Cretaceous limestones and marls were deposited in water depths greater than 1 meters. Middle and Upper (?) Eocene marls were deposited in water depths less than 2 meters. A probable Oligo-Miocene (?) shelf facies sandstone sequence overlies the Middle to Upper (?) Eocene marls in places. The Oligo-Miocene Numidien formation is part of a deep sea fan complex deposited further to the north and was derived from the African craton. Presence of MeIonis pompilioides (Fitchel and Moll) indicates that this sequence was deposited in water depths greater than 2 meters, and as it overlies a partially time-equivalent shelf sequence, stratigraphic considerations permit one to conclude that the Numidien is allochthonous in this area. A minimum of 15 kilometers of southeastward tectonic transport may be demonstrated. The structural style of deformation within the Numidien thrust and that within the underlying rocks indicate that the two tectonic units have been deformed and have been moved separately. Gypsiferous Triassic rocks have been tectonically injected along the detachment horizon under the Numidien. A detachment horizon also must exist in the marls beneath the Upper Cretaceous limestones and there must be one at the Upper Triassic level as well in order to allow the tectonic injection/diapirism of these rocks into higher tectonic levels. The timing of deformation is bracketed by the age of the youngest Numidien units involved in the thrusting (14-15 m.y.) and the age of a post-tectonic volcanic stock that has been dated at 8.3-.8 m.y. by Vass and others (1974) Timing of deformati onal events in this area coincides with major tectonic events occurring in the Western Mediterranean. Sardinia separated from Corsica along the straights of Bonifacio in the Early Burdigalean and continued to rotate southeastwards (Alvarez, 1974). Its subsequent collision with the North African plate caused the thrusting and deformation in the Western Mogods. The collisional event could not have been very late in the Miocene as a period of extensional faulting caused minor separation of the two continental masses previous to the Messinian salinity crisis. Later minor movement of the Numidien thrust post-dates volcanics dated at 6.6 m.y. by Glaçon and Rouvier (1972) and was presumably caused by renewed compression between the European and North African plates.
Structure and stratigraphy of the Potosi Mountain area, Southern Spring Mountains, Nevada
(1978) Cameron, Christopher Scott; Burchfiel, B. C.
The Potosi Mountain area is located 25 miles southwest of Las Vegas, Nevada, along the eastern margin of the Cordilleran foreland thrust belt. Three structural blocks are exposed, including, from lowest to highest, the autochthon, the Contact thrust plate and the Keystone thrust plate. Both thrust plates contain a similar sequence of Middle Cambrian through Permian shelf carbonates. The presence of the Upper Ordovician (?) Mountain Springs Formation in both indicates a similar marginal miogeoclinal paleogeographic affinity. Triassic to Latest Jurassic (?) strata of cratonic facies are exposed in the autochthonous block. The Contact thrust, exposed east of Potosi Mountain, carries Paleozoic carbonate rocks east-northeastward over autochthonous Jurassic Aztec Sandstone, or locally, Latest Jurassic (?) synorogenic conglomerates. The Contact thrust plate is truncated north of Potosi Mountain by the northwest trending Cottonwood fault. The Keystone thrust plate overrides the Contact thrust plate south of this fault, and the autochthon to the north. The Cottonwood fault downdrops the Keystone thrust only 2 feet. The following sequence of structural events was deduced: 1) inferred high angle faulting of the autochthon; 2) east vergent folding within the future Contact thrust plate; 3) emplacement of the Contact and intraplate Potosi thrusts; 4) high angle faulting of the autochthon and Contact thrust plates (development of Cottonwood fault and Ninetynine fault zone); 5) emplacement of the Keystone thrust; 6) minor high angle faulting; and 7) minor gravity sliding. Event 1 probably predates Latest Jurassic (?) synorogenic conglomerates. Event 3 postdates these deposits and probably correlates with a folding and thrusting event dated at 135±5 M.Y.B.P. in the Clark Mountains (Burchfiel and Davis, 1971). Event 5 predates a 95±5 M.Y.B.P. post-tectonic pluton in the Clark Mountains (Burchfiel and Davis, 1971). The Keystone thrust is localized near the base of the Banded Mountain Member of the Middle Cambrian Bonanza King Formation, and similar stratigraphic control is inferred for the Contact thrust in subsurface. Cross sections indicate thrust faulting has produced a minimum 1 miles of shortening of miogeoclinal rocks in the Potosi Mountain area. The occurrence of synorogenic chert and quartzite pebble conglomerate restricted to a zone below the Contact thrust and unconformably overlying Aztec Sandstone is interpreted as evidence that the Contact thrust plate moved over an erosional surface.
The geology of the Qued Sedjenane Area, Northern Tunisia and its bearing on the Numidian Flysch problem
(1976) Carr, Michael D.; Burchfiel, B. C.
Evidence from the Oued Sedjenane area, northern Tunisia, indicates that the Numidian Flysch Complex is allochthonous in the western Mogod Mountains. The complex consists of interlayered quartzose conglomerate, sandstone, and shale which were deposited by turbidity currents in the mid-fan region of a submarine fan complex on the northern margin of the African continent during Oligocène and lower Miocene times. The depth of deposition of the flysch was greater than 2 meters. Data support the hypothesis of Wezel (197b) that the source area for the Numidian sediments was to the south on the African craton. During middle Miocene time, the Numidian Complex was detached from its substratum and thrust southward over the Maestrichtian to Eocene limestone-marl sequence which underlay the thin, locally-preserved veneer of clastic rocks on the Miocene African shelf. Only the lower Miocene portion of the Numidian Complex was involved in the frontal part of the thrust sheet exposed in the map area. The displacement of the Numidian thrust sheet is a minimum of 25 kilometers. During and following the emplacement of the thrust sheet, diapiars of Triassic evaporite rising from the main decollment surface beneath the Tellian Atlas were injected along the thrust plane. A middle Miocene time of thrusting and contemporaneous internal deformation
The stratigraphy of the Noonday Dolomite in the Clark Mountain thrust complex, San Bernardino County, California
(1975) Wilson, William McLennan; Burchfiel, B. C.
Three exposures of the Noonday Dolomite in the Clark Mountain thrust complex were studied extensively. Several sections were measured. Local accumulations of orthoquartzite within the dolomite were examined and described. The Noonday in the dark Mountain area is divided into four units and correlated withtthe units originally described by Hazzard (1937) from the southern Nopah Range. The Noonday in the study area represents the eastern feather edge of the formation and defines the eastern end of the Late Precambrian Amargosa Aulacogen, The Noonday represents a short period of quiet shallow subtidal to intertidal stromatolitic sedimentation. The quartzite bodies are interpreted as the filling of a young karst topography by the initial transgression of the overlying Johnnie Formation.

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