Showing papers by "United States Geological Survey published in 1968"

On the Maintenance of Anomalous Fluid Pressures: I. Thick Sedimentary Sequences

Abstract: Various physical and chemical processes may be envisioned which will cause anomalous pressures on an underground fluid. In order to consider the maintenance of anomalous pressure, it is necessary to consider the problem as one of nonsteady fluid flow. The time rate of pressure change and maintenance depends upon the hydrodynamics of flow through porous media and the particular boundary conditions. This paper presents a series of general solutions to hydrodynamic models which are germane to the problem of creating and maintaining excess-fluid pressures in a thick sedimentary sequence. The creation and maintenance of fluid pressures approaching lithostatic pressure through a process of continuous sedimentation was evaluated. Our results indicate that a sedimentation rate of 500 m/106 yr (reasonable for the Gulf Coast) will create fluid pressures approaching lithostatic in a sedimentary column that has a hydraulic conductivity of 10−8 cm sec−1, or lower. It is apparent that the creation of anomalous pressure and its maintenance depends, to a large degree, upon the hydraulic conductivity and, to a lesser extent, upon the specific storage of clay layers within the system.

Nutrient Loss Accelerated by Clear-Cutting of a Forest Ecosystem

Abstract: The forest of a small watershed-ecosystem was cut in order to determine the effects of removal of vegetation on nutrient cycles. Relative to undisturbed ecosystems, the cut ecosystem exhibited accelerated loss of nutrients: nitrogen lost during the first year after cutting was equivalent to the amount annually turned over in an undisturbed system, and losses of cations were 3 to 20 times greater than from comparable undisturbed systems. Possible causes of the pattern of nutrient loss from the cut ecosystem are discussed.

The Formation of Columnar Joints in the Upper Part of Kilauean Lava Lakes, Hawaii

Abstract: Cracks were observed forming at the surface of Makaopuhi lava lake during the March 1965 Kilauea eruption, and were studied by repeated mapping and observations of this lake; the 1963 Alae lava lake was similarly studied. Cracks open within a minute after molten lava is exposed at the surface, and form either random or oriented orthogonal networks which outline large plates of unjointed crust. Within a few hours, additional cracks subdivide the plates into polygons averaging 15 ft in width. The accumulation of gases trapped beneath the crust near centers of polygons, and the escape of gases from marginal parts, cause upbowing of polygon centers and downsagging of margins. As the crust cools and increases in thickness following stagnation of the lake, existing cracks extend downward and new cracks open. Some new cracks subdivide pre-existing polygons, and short cracks of shallow depth form near polygon centers. Still other cracks apparently open at depths of tens of feet within the crust, propagate upward, and finally feather out near the surface into short cracks which are concentrated in long swarms that cross several polygons. Cracks initiate at temperatures ranging from ambient to about 900°C, and propagate downward into parts of the crust near 1000°C. Cracking results from stresses induced largely by thermal contraction, but also by differential subsidence of the crust. Seismic recordings of shock vibrations due to cracking of Kilauea Iki lava lake indicate a diurnal variation in frequency, with a maximum around midnight and a minimum around noon.

Techniques for Computing Rate and Volume of Stream Depletion by Wellsa

Abstract: The effects on flow of a nearby stream from pumping a well can be calculated readily using dimensionless curves and tables. Computations can be made of: (1) the rate of stream depletion at any time during the pumping period or after the cessation of pumping; (2) the volume induced from the stream during any time, both during pumping or after the cessation of pumping; and (3) the effects, both in rate and volume of stream depletion, of any selected pattern of intermittent pumping. Sample computations illustrate the use of the curves and tables. An example shows that intermittent pumping may have a pattern of stream depletion not greatly different from a pattern for steady pumping of an equal volume. The residual effects of pumping, that is, effects after cessation of pumping, on streamflow may easily be greater than the effects during the pumping period. Adequate advance planning that includes consideration of residual effects thus is essential to effective administration of a stream-aquifer system.

Mineralogy as a function of depth in the prehistoric Makaopuhi tholeiitic lava lake, Hawaii

Abstract: The electron probe X-ray microanalyzer has been used to determine the compositional variability of the groundmass minerals and glass in 10 specimens from a complete 225-foot section of the prehistoric tholeiitic lava lake of Makaopuhi Crater, Hawaii. The order of beginning of crystallization was: (1) chromite, (2) olivine, (3) augite, (4) plagioclase, (5) pigeonite, (6) iron-titanium oxides and orthopyroxene, (7) alkali feldspar and apatite, and (8) glass. Although the lake is chemically tholeiitic throughout, the occurrence of ferromagnesian minerals is as though there were a gradation from alkali olivine basalt in the upper chill downwards to olivine tholeiite. Groundmass olivine decreases downwards and disappears at about 20 feet. Pigeonite is absent in the uppermost 5±2 feet, then increases in amount down to 20 feet, below which augite and pigeonite coexist in constant 2∶1 proportions. Strong zoning and metastable compositions characterize the pyroxenes of the chilled zones, but these features gradually disappear towards the interior of the lake to give way to equilibrium pyroxenes. Relatively homogeneous poikilitic orthopyroxene (≈ Ca4Mg70Fe26) occurs in the olivine cumulate zone, having formed partly at the expense of pre-existing olivine, augite, and pigeonite (≈ Ca8Mg66Fe26). The growth of orthopyroxene is believed to have been facilitated by the slower cooling rate and higher volatile pressure at depth, and by the rise in Mg/Fe ratio of the liquid due to the partial dissolution of settled olivine. Unlike olivine and pyroxene, feldspar is least zoned in the upper and lower chilled regions. The greatest range of compositional zoning in feldspar occurs at 160 to 190 feet, where it extends continuously from Or1.0Ab22An77 to Or64Ab33An3. The feldspar fractionation trend in the An-Ab-Or triangle gradually shifts with depth toward more “equilibrium” trends, even though the zoning becomes more extreme. The variation with depth in the initial (core) composition of the plagioclase suggests the influence of either slow nucleation and growth (undercooling) or slow diffusion in the liquid, relative to the rate of cooling. Idiomorphic opaque inclusions in olivine phenocrysts are chrome-spinels showing continuous variation from 60 percent chromite to 85 percent ulvospinel and to magnetite-rich spinel. A pre-eruption trend of increasing Al with decreasing Cr can be recognized in chromites from the upper chill. Most of the inclusions show a trend of falling Cr and Al, toward an ulvospinelmagnetite solid solution which is progressively poorer in Usp with depth. This trend was produced by solid state alteration of the chromite inclusions during cooling in the lava lake. Ilmenite (average Ilm91Hm9) coexists with variably oxidized titaniferous magnetite in the basalt groundmass. Estimated oxygen fugacities agree well with other independent determinations in tholeiitic basalt. No sulfide phase has been detected. Fractional crystallization produced a groundmass glass of granitic composition. Average, in percent, is: SiO2, 75.5; Al2O3, 12.5; K2O, 5.7; Na2O, 3.1; CaO, 0.3; MgO, 0.05; total FeO, 1.2; and TiO2, 0.8. Normative Or> Ab. Minor changes in glass composition with depth are consistent with a greater approach towards the granite minimum. Incipient devitrification precluded reliable analysis of glass from the lower half of the section. The SiO2-phase associated with devitrification contains alkalis and Al and is believed to be cristobalite. Needle-like apatite crystals in the groundmass glass are Siand Fe-bearing fluorapatites containing appreciable rare earths (predominantly Ce) and variable Cl. The grain-size and maximum An content of the cores of plagioclase grains were controlled by cooling rate and are at a maximum at the center of the section. The most homogeneous pyroxene (and olivine, Moore and Evans, 1967), most equilibrium pyroxene trends, most abundant alkali feldspar, and most equilibrium feldspar trends are found at 160 to 190 feet, which is appreciably below that part of the lake which was slowest to crystallize. Volatile pressure, increasing with depth, possibly controlled the degree of attainment of equilibrium more than cooling rate. Since they are dependent on cooling history, some of the modal criteria commonly used for recognizing basalt types, such as the absence of Ca-poor pyroxene, presence of groundmass olivine, and the presence of alkali feldspar, should be applied with caution. Petrographic comparison of basalts from one flow, volcano, or province, with another, should recognize the possible variations due to cooling history alone.

O18/O16 Ratios of Coexisting Minerals in Glaucophane-Bearing Metamorphic Rocks

Abstract: Oxygen isotope analyses have been obtained for coexisting minerals in several blue-schist-facies metamorphic rocks from California, Oregon, and New Caledonia. Detailed isotopic studies were made on a continuous exposure of schist in Ward Creek, California, previously described by Coleman and Lee (1962). The oxygen isotope fractionations among coexisting minerals in a variety of rock types, including metasediments and metabasalts, are systematic and larger than those measured in pelitic schists metamorphosed at the grade of biotite zone or higher. Therefore, these Ward Creek rocks (termed Type III) must have formed at lower temperatures than have such pelitic schists. Evidence for significant isotopic equilibration and homogenization is observed in the Ward Creek sequence. Six different metasediments and metavolcanics collected within 25 m of one another show almost identical mineral δ; -values: quartz (15.8 to 16.3), aragonite (13.1 to 13.3), glaucophane (9.8 to 10.0), muscovite (10.9 to 11.3), lawsonite (9.3 to 9.5), and garnet (8.0 to 8.4), given as per mil enrichment in O 18 relative to mean ocean water. These rocks seem to have reached equilibrium at about the same temperature in contact with abundant metamorphic pore fluids. Not all the Ward Creek rocks have completely equilibrated with the postulated metamorphic pore fluids. In particular, the metacherts seem to have been relatively impermeable to the aqueous fluids during metamorphism, as indicated by the large δ -values of quartz in such rocks (17 to 19.2) and by their appreciably higher Fe +3 /Fe +2 ratios. Gradients in O 18 /O 16 and Fe +3 /Fe +2 have been generally “smoothed out” in the rocks during metamorphism, but the process has gone to completion only locally. Cherts and limestones have apparently been lowered in O 18 content by 10 to 15 per mil, and the metabasalts are enriched by 3 to 4 per mil over their unmetamorphosed parent rocks. Using the calibrated quartz-muscovite and quartz—CaCO 3 geothermometers, the measured quartz-muscovite and quartz-aragonite fractionations indicate essentially “concordant” temperatures of formation for the Type III rocks of 270° to 315° C. Inasmuch as aragonite is part of the equilibrium assemblage, these rocks must therefore have been metamorphosed at pressures of at least 6.4 to 7.0 kb. Oxygen isotope fractionations for the mineral pairs aragonite-lawsonite, quartz-muscovite, and quartz-glaucophane progressively decrease from Type II (low-grade) through Type III to Type IV (high-grade tectonic blocks) metabasalts. The higher-grade blueschists from New Caledonia exhibit quartz-muscovite and quartz-glaucophane fractionations similar to the Type IV metabasalts at Ward Creek, indicating temperatures of formation of 400° to 550° C. Thus, glaucophane-bearing metamorphic rocks apparently form over a temperature range of 200° C to 550° C, encompassing the probable temperature range of the entire greenschist and epidote-amphibolite facies. This suggests that glaucophane schists should be separated into at least two metamorphic facies, a lower-grade, lawsonite-aragonite blueschist facies and a higher-grade, epidote-rutile blueschist facies, both representing higher pressures than are attained during ordinary low-rank and middle-rank regional metamorphism.

Argon-40: excess in submarine pillow basalts from kilauea volcano, hawaii.

Abstract: Submarine pillow basalts from Kilauea Volcano contain excess radiogenic argon-40 and give anomalously high potassium-argon ages. Glassy rims of pillows show a systematic increase in radiogenic argon-40 with depth, and a pillow from a depth of 2590 meters shows a decrease in radiogenic argon40 inward from the pillow rim. The data indicate that the amount of excess radiogenic argon-40 is a direct function of both hydrostatic pressure and rate of cooling, and that many submarine basalts are not suitable for potassium-argon dating.

Isotopic Age of the Nevadan Orogeny and Older Plutonic and Metamorphic Events in the Klamath Mountains, California

Abstract: Several metamorphic and plutonic events have been recognized in the Klamath Mountains utilizing potassium-argon and rubidium-strontium mineral and whole-rock ages. The oldest known metamorphic event in the region produced the Abrams Mica Schist and the co-extensive Salmon Hornblende Schist. Strontium evolution diagrams indicate that the age of primary metamorphism of the Abrams Mica Schist is approximately 380 m.y. (Devonian). The Stuart Fork Formation of Davis and Lipman (1962), the schists of Condrey Mountain, and related schists were produced during a Middle and Late Jurassic metamorphic event. Granitic plutonic rocks are divided into four groups that are different in age and somewhat different in chemical characteristics. The oldest pluton, the Pit River stock, has a minimum age of 246 m.y. (Permian) and is grouped with the Castle Crags pluton. The other three plutonic groups are Middle and Late Jurassic and are characterized by the following ranges in isotopic age: 165 to 167 m.y., 145 to 155 m.y., and 127 to 140 m.y. The principal lode gold deposits in the California part of the Klamath Mountains seem to be related to the youngest group of plutons. If the Nevadan orogeny in this area is restricted to a Middle and Late Jurassic deformational, metamorphic, and plutonic event, the orogeny includes the emplacement of plutons of the three younger groups and the metamorphic development of the Stuart Fork Formation, schists of Condrey Mountain, and related schists.

Alga-Like Forms in Onverwacht Series, South Africa: Oldest Recognized Lifelike Forms on Earth

Abstract: Spheroidal and cupshaped, carbonaceous alga-like bodies, as well as filamentous structures and amorphous carbonaceous matter occur in sedimentary rocks of the Onverwacht Series (Swaziland System) in South Africa The Onverwacht sediments are older than 32 eons, and they are probably the oldest, littlealtered sedimentary rocks on Earth The basal Onverwacht sediments lie approximately 10,000 meters stratigraphically below the Fig Tree sedimentary rocks, from which similar organic microstructures have been interpreted as alga-like microfossils The Onverwacht spheroids and filaments are best preserved in black, carbonrich cherts and siliceous argillites interlayered with thick sequences of lavas These lifelike forms and the associated carbonaceous substances are probably biological in origin If so, the origins of unicellular life on Earth are buried in older rocks now obliterated by igneous and metamorphic events

Spreading of the Ocean Floor: Undeformed Sediments in the Peru-Chile Trench

Abstract: None of the expected stratigraphic and structural effects of a spreading sea floor have been imposed on the sedimentary fill of the Peru-Chile Trench. During at least the last several million years, and perhaps during much of the Cenozoic, the trench has not been affected by an oceanic crust thrusting under the continent.

On the Maintenance of Anomalous Fluid Pressures: II. Source Layer at Depth

Abstract: Physico-chemical mechanisms have been suggested to account for anomalous fluid pressures in the geologic environment which require a fluid source at depth. The persistence of anomalous pressure is a problem that involves nonsteady fluid flow. The hydrodynamics and particular boundary conditions control the time rate of pressure change and its maintenance. A series of mathematical solutions germane to the maintenance of anomalous pressure caused by the injection of fluids into the system from a source layer are presented. The phase change, gypsum to anhydrite plus water, is used as an example of a fluid source at depth. The thermodynamics of the gypsum-dehydration reaction indicates that conversion will probably occur at shallow depths and produce fluid at a constant rate. The dehydration of montmorillonite will also produce fluids at a constant rate under geologic conditions where the reaction can occur. If horizons of material of low permeability are missing or scarce, it is doubtful that anomalous pore pressures can be maintained for more than a geologic instant. The creation and continuation of anomalous pressure depend largely upon the hydraulic conductivity and, to a lesser extent, upon the specific storage of clay layers within the system.

Diatremes with Kimberlitic Affinities in North-Central Montana

Abstract: Diatremes in the Missouri River Breaks demonstrate systematic subsidence-ring structure, contain inclusions derived from far above and far below, and have been produced by gas-rich eruptions of alkalic ultramafic magmas. Similar magmas have produced diatremes in many localities in the world and are known to be closely associated with and probably parental to kimberlites.

Depth control of some concordant intrusions

Abstract: Analysis of geologic data from 54 localities, mainly in the western United States, shows that concordant igneous masses intruded zones in nearly flat-lying sedimentary rocks where the thickness of cover was 3000 to 7500 feet. The depth of intrusion was apparently affected by a well-defined parting surface (bedding plane or unconformity), static load of the overburden (lithostatic pressure), and presence of a fluid barrier above the intrusion. Most bodies intruded along well-defined bedding planes in sedimentary rocks and flow surfaces in extrusive igneous rocks; some intruded along unconformities. The range in overburden pressure is about 3000 to 7500 psi for intrusions at depths of 3000 to 7500 feet. Magma pressure for lateral injection at the lower limit of the depth range, therefore, must have exceeded 7500 psi to lift 7500 feet of overburden. A fluid barrier, such as a shale, overlies almost all intrusions studied and tended to retard upward advance of magma. At depths less than 3000 feet, the barrier shales may be brittle and easily ruptured by the fluid pressure, permitting steam and magma to escape to the surface. Below 3000 feet the shales may become ductile.

Convective flow and its effect on temperature logging in small‐diameter wells

Abstract: Critical thermal gradients for the onset of convection in small‐diameter wells are computed by means of an expression given by Krige (1939) and are shown graphically for water of several salinities and for glycerol. A series of field and laboratory tests in wells with diameters of 4.8 cm and 10.2 cm showed that water columns are unstable at temperature gradients as low as 0.003 °C/m. Magnitudes of thermal oscillations at higher gradients were as large as 0.49 °C, and apparent sizes of convection cells ranged up to 210 cm in height in a 10.2 cm cylinder and to 48 cm in wells 4.8 cm in diameter. Comparison of temperatures in adjacent wells showed temperature differences as great as 3 °C when thermal gradients were greater than the theoretical critical gradients. It is concluded that temperatures in the upper zone of deep wells may depart widely from ambient temperatures in the formations penetrated.

Gels Composed of Sodium-Aluminium Silicate, Lake Magadi, Kenya

Abstract: Sodium-aluminum silicate gels are found in surficial deposits as thick as 5 centimeters in the Magadi area of Kenya. Chemical data indicate they are formed by the interaction of hot alkaline springwaters (67 degrees to 82 degrees C; pH, about 9) with alkali trachyte flows and their detritus, rather than by direct precipitation. In the process, Na(2)O is added from and silica is released to the saline waters of the springs. Algal mats protect the gels from erosion and act as thermal insulators. The gels are probably yearly accumulates that are washed into the lakes during floods. Crystallization of these gels in the laboratory yields analcite; this fact suggests that some analcite beds in lacustrine deposits may have formed from gels. Textural evidence indicates that cherts of rocks of the Pleistocene chert series in the Magadi area may have formed from soft sodium silicate gels. Similar gels may have acted as substrates for the accumulation and preservation of prebiological organic matter during the Precambrian.

Summary of Regional Evidence for Right-Lateral Displacement in the Western Great Basin

Abstract: Right-lateral displacement of 80 to 120 miles across the western Great Basin is indicated by the consistent disruption of sedimentary facies and thickness trends of formations ranging in age from late Precambrian to Mesozoic. Some of this displacement occurs as fault slip and some as a more pervasive large-scale drag (oroflexural bending).

Crustal structure in Missouri by seismic-refraction methods

Abstract: Two reversed seismic-refraction profiles, each about 300 km long, were established in Missouri. One profile was in northern Missouri, oriented east-west. The other was in southern Missouri, oriented in a northeasterly direction across the Ozark uplift. Interpretation of the seismic refraction data indicates that the crust in northern Missouri may be characterized by three major layers. Approximate velocities and depths of these layers are 6.1 km/sec from near the surface to a depth of 8 km, 6.2 km/sec to 20 km, and 6.6 km/sec to 40 km. Upper-mantle velocity is 8.0 km/sec. A westward component of dip is indicated on all these layers such that the crust is a few kilometers thicker along the west portion of the profile than along the east. An alternate interpretation based upon the Herglotz-Wiechert method indicates that the velocity variation in the upper 15 km of the crust is similar to that suggested by Birch for a granitic material. The velocity of 6.6 km/sec in the lower portion of the crust is further supported by interpretation of reflected phases. The seismic data do not require the pressence of a low-velocity channel within the crust. The data from southern Missouri were more difficult to interpret, possibly because of the effect of lateral inhomogeneities within the crust. If a layered crustal model is assumed for this region, then the interpreted crustal structure does not differ greatly from that derived for northern Missouri.)

Exsolution in Clinoamphiboles

Abstract: Ten amphibole specimens from a variety of metamorphic rocks such as talc schists, eclogites, and metamorphosed iron formations contain lamellae of a second amphibole oriented parallel to ([unknown]101) or (100), or both, of the host. Tremolites, actinolites, and hornblendes commonly have lamellae of a calcium-poor clinoamphibole with P 21 /m space-group symmetry, or lamellae of cummingtonite with C 2 /m space-group symmetry. Likewise cummingtonites and P 21 /m clinoamphiboles commonly contain lamellae of calcium-rich C 2 /m amphiboles such as tremolite. Results of x-ray diffraction, electron-probe, and microscope studies indicate that most lamellae result from unmixing of a homogeneous amphibole. The P 21 /m clinoamphibole is analogous to the clinopyroxene pigeonite in agreement with the results of M. G. Bown.