Megacrysts and xenoliths in kimberlite,Elliott County,Kentucky: A mantle sample from beneath the Permian Appalachian Plateau

Two kimberlite pipes in Elliott County contain rare ultramafic xenoliths and abundant megacrysts of olivine (Fo_85–93), garnet (0.21–9.07% Cr₂O₃), picroilmenite, phlogopite, Cr-poor clinopyroxene (0.56–0.88% Cr₂O₃), and Cr-poor orthopyroxene (<0.03–0.34% Cr₂O₃) in a matrix of olivine (Fo_88–92), picroilmenite, Cr-spinel, magnetite, perovskite, pyrrhotite, calcite, and hydrous silicates. Rare clinopyroxene-ilmenite intergrowths also occur. Garnets show correlation of mg (0.79–0.86) and CaO (4.54–7.10%) with Cr₂O₃ content; the more Mg-rich garnets have more uvarovite in solution. Clinopyroxene megacrysts show a general decrease in Cr₂O₃ and increase in TiO₂ (0.38–0.56%) with decreasing mg (0.87–0.91). Clinopyroxene megacrysts are more Cr-rich than clinopyroxene in clinopyroxene-ilmenite intergrowths (0.06–0.38% Cr₂O₃) and less Cr-rich than peridotite clinopyroxenes (1.39–1.46% Cr₂O₃). Orthopyroxene megacrysts and orthopyroxene inclusions in olivine megacrysts form two populations: high-Ca, high-Al (1.09–1.16% CaO and 1.16–1.18% Al₂O₃) and low-Ca, low-Al (0.35–0.46% CaO and 0.67–0.74% Al₂O₃). Three orthopyroxenes belonging to a low-Ca subgroup of the high-Ca, high-Al group were also identified (0.86–0.98% CaO and 0.95–1.01% Al₂O₃). The high-Ca, high-Al group (Group I) has lower mg (0.88–0.90) than low-Ca, low-Al group (Group II) with mg=0.92–0.93; low mg orthopyroxenes (Group Ia) have lower Cr₂O₃ and higher TiO₂ than high mg orthopyroxenes (Group II). The orthopyroxene megacrysts have lower Cr₂O₃ than peridotite orthopyroxenes (0.46–0.57% Cr₂O₃). Diopside solvus temperatures indicate equilibration of clinopyroxene megacrysts at 1,165°–1,390° C and 1,295°–1,335° C for clinopyroxene in clinopyroxene-ilmenite intergrowths. P-T estimates for orthopyroxene megacrysts are bimodal: high-Ca, high-Al (Group I) orthopyroxenes equilibrated at 1,165°–1,255° C and 51–53 kb (± 5kb) and the low-Ca, low-Al (Group II) orthopyroxenes equilibrated at 970°–1,020°C and 46–56 kb (± 5kb). Garnet peridotites equilibrated at 1,240°–1,360° C and 47–49 kb. Spinel peridotites have discordant temperatures of 720°–835° C (using spinel-olivine Fe/Mg) and 865°–1,125° C (Al in orthopyroxene).Megacrysts probably precipitated from a fractionating liquid at >150 km depth. They are not disaggregated peridotite because: (1) of large crystal size (up to 1.5 cm), (2) compositions are distinctly different from peridotite phases, and (3) they display fractionation trends. The high mg, low T orthopyroxenes and the clustering of olivine rims near Fo_89–90 reflect liquid changes to higher MgO contents due to (1) assimilation of wall-rock and/or (2) an increase in Fe³⁺/Fe²⁺ and subsequently MgO/FeO as a result of an increase in f _o.     

The Laramide orogeny: Evidence from cocorp deep crustal seismic profiles in the wind river mountains, wyoming

Deep crustal reflection data that are critical for the interpretation of Laramide structure have been obtained by the Consortium for Continental Reflection Profiling (COCORP). The Laramide orogeny, which occurred from the late Cretaceous to early Eocene, is characterized in Wyoming by large uplifts of Precambrian basement, commonly flanked by reverse faults. The attitude of these faults at depth has been a major tectonic problem and is very important for deciding whether horizontal or vertical crustal movements were primarily responsible for the basement uplifts. COCORP has run 158 km of deep seismic reflection profiles (recording to 20-sec two-way travel time) across the southeastern end of the Wind River Mountains, the largest of these Laramide uplifts. Reflections from the thrust fault flanking the Wind River uplift can be clearly traced on the profiles to at least 24-km depth and possibly as deep as about 36 km with a fairly uniform apparent dip of 30°–35°. Other reflection events subparallel to the main Wind River thrust are present in the seismic profiles and may represent other faults. There is at least 21 km of crustal shortening along the thrust. There is no evidence in the reflection profiles for large-scale folding of the basement; the Wind River Mountains were formed predominantly by thrust movements. Gravity anomalies in the Wind River Mountains can be modeled by a thrust that displaces dense material in the lower crust. If the thrust ever cut the Moho, the effect is not observed in the gravity today. A proposed model for the presence of uplifted basement in Wyoming invokes a shallowly dipping, subducted Farallon plate beneath the North American continent; drag between the two plates localized compressional stresses in an area over 800 km into the North American plate causing large thrusts to develop. The earth's crust seems to have fractured as a fairly rigid plate     

Lunar magnetic anomalies detected by the Apollo substatellite magnetometers

Properties of lunar crustal magnetization thus far deduced from Apollo subsatellite magnetometer data are reviewed using two of the most accurate presently available magnetic anomaly maps — one covering a portion of the lunar near side and the other a part of the far side.

The largest single anomaly found within the region of coverage on the near-side map correlates exactly with a conspicuous, light-colored marking in western Oceanus Procellarum called Reiner Gamma. This feature is interpreted as an unusual deposit of ejecta from secondary craters of the large nearby primary impact crater Cavalerius. An age for Cavalerius (and, by implication, for Reiner Gamma) of 3.2 ± 0.2 × 10⁹ y is estimated. The main (30 × 60 km) Reiner Gamma deposit is nearly uniformly magnetized in a single direction, with a minimum mean magnetization intensity of 7 × 10⁻² G cm³/g (assuming a density of 3 g/cm³), or about 700 times the stable magnetization component of the most magnetic returned samples. Additional medium-amplitude anomalies exist over the Fra Mauro Formation (Imbrium basin ejecta emplaced 3.9 × 10⁹ y ago) where it has not been flooded by mare basalt flows, but are nearly absent over the maria and over the craters Copernicus, Kepler, and Reiner and their encircling ejecta mantles.

The mean altitude of the far-side anomaly gap is much higher than that of the near-side map and the surface geology is more complex, so individual anomaly sources have not yet been identified. However, it is clear that a concentration of especially strong sources exists in the vicinity of the craters Van de Graaff and Aitken. Numerical modeling of the associated fields reveals that the source locations do not correspond with the larger primary impact craters of the region and, by analogy with Reiner Gamma, may be less conspicuous secondary crater ejecta deposits. The reason for a special concentration of strong sources in the Van de Graaff-Aitken region is unknown, but may be indirectly related to the existence of strongly modified crustal terrain which also occurs in the same region. The inferred directions of magnetization for the several sources of the largest anomalies are highly inclined with respect to one another, but are generally depleted in the north-south direction. The north-south depletion of magnetization intensity appears to continue across the far-side within the region of coverage.

The mechanism of magnetization and the origin of the magnetizing field remain unresolved, but the uniformity with which the Reiner Gamma deposit is apparently magnetized, and the north-south depletion of magnetization intensity across a substantial portion of the far side, seem to require the existence of an ambient field, perhaps of global or larger extent. The very different inferred directions of magnetization possessed by nearly adjacent sources of the Van de Graaff-Aitken anomalies, and the depletion in their north-south component of magnetization, do not favor an internally generated dipolar field oriented parallel to the present spin axis. A variably oriented interplanetary magnetizing field that was intrinsically strong or locally amplified by unknown surface processes is least inconsistent with the data.     

Analysis of the climatic signal in the South Dome,Greenland ice core

The purpose of this research was to investigate the statistical relationship between an oxygen isotope chronology from southern Greenland and climatic variables recorded at a coastal village. The response of the oxygen isotope time series to monthly temperature and precipitation data was calculated using a combination of principal components factor analysis and multiple regression analysis. Orthogonal eigenvectors extracted from 35 yr of climatic data reliably explained 59% of the temporal variance in mean annual oxygen isotope values. The response functions demonstrate an apparent seasonal reversal in the relationship between oxygen isotope values and temperature, with the response varying between a positive (direct) relationship in winter, spring, and autumn, and a negative (indirect) relationship in summer. The results, and their implications, are shown to be useful in the historical climatic reconstruction of the South Greenland region.     

Shore protection structures: Effects on recession rates and beaches from the 1870s to the 1970s along the Ohio shore of lake Erie

Shore-protection structures—largely groins and seawalls—have increased in number along the 300-km-long mainland Ohio shore of Lake Erie from about 60 in 1876–77, to about 1,400 in the late 1930s, to about 3,600 in the mid 1970s. Recession rates, on the other hand, have decreased from the early period (1876–1877 to the late 1930s) to the later period (late 1930s to 1973). Forexample, the length of shore that receded at the intermediate rate (0.3 to 0.9 m/yr) decreased from 76 to 54 km and the length of shore that receded at the lowest rate (less than 0.3 m/yr) increased from 151 to 171 km. Beach widths also have decreased; the length of shore fronted by wide (greater than 15 m) beaches decreased from 64 km to 35 km between 1876–1877 and 1968. Furthermore, the length of shore without a beach increased from 84 km in 1876–1877 to 112 km in 1968. The decreases in recession rates have been caused by the shore-protection structures, which have directly armored the shore from waves (seawalls) or reduced the wave energy reaching the shore by trapping sand (groins). Moreoever, because the shore is a major source of sand for the beaches, the decrease in recession has led to a reduced sand supply and narrower beaches. Ironically, by protecting the shore, the structures apparently have more than compensated for the loss of the best natural form of shore protection, beach sand.     

Interstadial proboscidean from south-central Alaska: Implications for biogeography, geology, and archeology

In 1980 a large proboscidean femur, probably Mammuthus sp., was found in situ in a bluff exposure at the mouth of the Tyone River in the northwestern part of the Copper River Basin, Alaska. The regional setting, stratigraphy, radiocarbon chronology, flora, and implications of the fossil locality, which represents the first documented occurrence of Pleistocene terrestrial mammalian fauna in southern Alaska, are described. Radiocarbon dates and stratigraphic relations at the site indicate that the sediments containing the fossil accumulated during the transition from interstadial to glacial conditions during terminal middle Wisconsin time. During this interval the immediate vicinity was unforested and large areas of south-central Alaska may have been available for faunal and possibly human habitation. This documented find, dated at 29,450 ± 610 ¹⁴C yr B.P., extends the known range for Pleistocene mammals and possibly steppe-tundra conditions south-ward at least 150 km, and suggests that mountain passes through the Alaska Range to the north were ice free during the last part of the middle Wisconsin interstadial.     

Influence of hydropower outflow characteristics on riverbank stability: case of the lower Osage River (Missouri,USA)

ABSTRACT

This research examined the influences of outflow characteristics affecting riverbank stability. The 130-km stretch of the Lower Osage River downstream from Bagnell Dam (Missouri, USA) provided an excellent case study for this purpose. The integrated BSTEM model with the HEC-RAS model was accurately calibrated and validated with data from the US Geological Survey. Then, the outflow characteristics (peak flow duration, flow drawdown rate, and low flow duration) were investigated individually. The results of this study showed that: (1) riverbank stability is little affected by the duration time of the peak flow, especially on the reaches far from the dam; (2) sudden flow drawdown significantly reduces riverbank stability; however, the impact of the drawdown rate decreases with distance from the dam; and (3) the duration of the low flow after peak flow influences the riverbank stability value proportional to the distance from the dam. The time of low flow before failure increases as the distance from the dam increases.     

Turbulent transport within and above a maize canopy

Hot-wire anemometers were used to measure air temperature and the three velocity components of the wind within and above a maize canopy. From digitized anemometer outputs, correlation coefficients for vertical heat flux and turbulent momentum transfer were calculated. A comparison of these coefficients with profiles of mean wind speed and mean temperature indicates that the main features of the turbulence may be explained in terms of the usual mixing-length theory. Instantaneous records of heat and momentum flux, however, indicate the existence of other competing turbulent mechanisms due to the unsteady, non-equilibrium nature of the turbulent flow. Regimes of flow dominated by mechanical and/or thermal mixing are indicated. Spectral results show that high shear and turbulent intensity levels as well as the presence of the maize leaves and stalks as vortex-shedding surfaces complicate the energy transfer mechanism. An energy balance between radiation and convection reveals that the energy budget is primarily a balance between solar radiation and the flux of latent heat.Contribution of the Sibley School of Mechanical and Aerospace Engineering, Cornell University, in cooperation with the Agricultural Research Service, U.S. Department of Agriculture, Ithaca, N.Y., U.S.A. and the Cornell University Agricultural Experiment Station. Department of Agronomy Series No. 1116.Sibley School of Mechanical and Aerospace Engineering, Cornell University; U.S. Department of Agriculture, Gainesville, Florida Section for Estuary and Fjord Studies, River and Harbour Laboratory, Technical University of Norway, Trondheim, Norway; State Univ. of New York at Buffalo; and U.S. Department of Agriculture and Cornell University; respectively.     

Petrology of the Hara Lake paragneisses,northeastern Saskatchewan,Canada

Precambrian aluminous paragneisses in the Hara Lake area of northeastern Saskatchewan are characterized by the stable association of cordierite and garnet with either sillimanite or biotite; alkali feldspar is an important mineral of this association. The aluminous gneisses are interlayered with pyroxene-plagioclase gneisses that contain orthopyroxene, clinopyroxene, hornblende, and biotite. The gneisses in the study area and in the adjacent Charcoal Lake area were metamorphosed under conditions of the granulite facies. The petrologic evidence is consistent with a first metamorphic event during which the association sillimanite-biotite was stable, followed by a second event during which cordierite-garnet was stable. Consideration of mineral assemblages and mineral chemistries of the aluminous gneisses in terms of experimentally established or thermodynamically derived reactions suggests that recrystallization from the sillimanite-biotite association to cordierite-garnet took place at 680 °–750 °C and 3.2–4.4 kb.