Showing papers by "United States Geological Survey published in 1969"

Mesozoic California and the Underflow of Pacific Mantle

Abstract: The Mesozoic evolution of California is interpreted as dominated by the underflow of oceanic mantle beneath the continental margin. Underflow during part of Late Cretaceous time of more than 2000 km of the eastern Pacific plate seems required by the marine magnetic data. Correspondingly, varied oceanic environments—abyssal hill, island arc, trench, oceanic crust, and upper mantle, perhaps also continental rise and abyssal plain—appear to be represented in the eugeosynclinal terranes of California. The rock juxtapositions accord with the concept that these materials were scraped off against the continent as the oceanic plate slid beneath it along Mesozoic Benioff seismic zones, which are now seen as serpentine belts separating profoundly different rock assemblages. The chaotic Franciscan Formation of coastal California consists of deep-ocean Late Jurassic to Late Cretaceous sedimentary, volcanic, crustal, and mantle materials. As open-ocean abyssal oozes and the oceanic crust beneath them were swept into the Benioff-zone trench at the continental margin, they were covered by terrigenous clastic sediments, and the entire complex was carried beneath the correlative continental-shelf and continental-slope deposits (Great Valley sequence) and the older Mesozoic complexes. The other eugeosynclinal terranes of California can be interpreted, albeit with less confidence, in similar terms of underflow of Pacific mantle. In the Klamath Mountains and northern Sierra Nevada, for example, Ordovician and Silurian ocean-floor materials, overlain by or juxtaposed against an Upper Silurian to Permian island arc, were swept in first to the continent, along with a large fragment of oceanic crust and mantle and another fragment of an old orogenic belt. This debris was followed by Permian and Triassic ocean-floor deposits. Late Triassic and Jurassic volcanic products from stocks and batholiths forming in the welded complexes lapped across both landward and oceanward sides of the region. Reversal of Cenozoic extension, strike-slip faulting, and volcanic crustal growth in the western United States reveals a Cretaceous tectonic pattern strikingly like the modern pattern of the Andes, so the paleotectonic setting of North America can be inferred from the South American present. The Mesozoic batholiths of North America, like the late Cenozoic volcanic belt of the central Andes, are products of the same rapid motion of oceanic plates that carried oceanic sediments against the continent to form eugeosynclinal terranes. Magmas generated in the Benioff zones formed the batholiths and the volcanic fields which initially capped them.

Species Diversity: Benthonic Foraminifera in Western North Atlantic

Abstract: Maximum species diversity occurs at abyssal depths of greater than 2500 meters. Other diversity peaks occur at depths of 35 to 45 meters and 100 to 200 meters. The peak at 35 to 45 meters is due to species equitability, whereas the other two peaks correspond to an increase in the number of species.

The Relationship between Fluids in Some Fresh Alpine-Type Ultramafics and Possible Modern Serpentinization, Western United States

Abstract: Calcium hydroxide waters issue from four partly serpentinized Alpine-type ultramafic bodies in the western United States. The occurrence of calcium-hydroxide-type water is restricted to fresh Alpine-type ultramafic rocks. The calcium hydroxide waters are unsaturated with Mg end-member olivine and pyroxene but supersaturated with Mg end-member brucite and serpentine and thus have chemical potentials to cause Serpentinization. The calcium hydroxide waters are isotopically similar to the common magnesium bicarbonate meteoric waters peculiar to ultramafic rocks and serpentinites. Some Serpentinization is apparently a near-surface phenomenon occurring at present. The Serpentinization takes place at nearly constant composition, except for loss of CaO.

Active Metamorphism of Upper Cenozoic Sediments in the Salton Sea Geothermal Field and the Salton Trough, Southeastern California

Abstract: The Salton Sea geothermal system is entirely within Pliocene and Quaternary sediments of the Colorado River delta at the north end of the Gulf of California. At the time of deposition, these sediments consisted of sands, silts, and clays of uniform original mineralogic composition, but under the elevated temperatures and pressures of the geothermal system they are being transformed to low-grade metamorphic rocks of the greenschist facies. We have studied these transformations by X-ray, petrographic, and chemical analyses of cuttings and core from deep wells that penetrate the sedimentary section. Temperatures within the explored geothermal system range up to 360° C at 7100 feet. The wells produce a brine containing over 250,000 ppm dissolved solids, primarily Cl, Na, Ca, K, and Fe, plus a host of minor constituents. The original sediments consisted of detrital quartz, calcite, K-feldspar, plagioclase, montmorillonite, illite, dolomite, and kaolinite. Discrete montmorillonite is converted to illite at temperatures below 100° C, and illite-montmorillonite is completely converted to K-mica at temperatures below approximately 210° C. Ankerite forms by the conversion of calcite, dolomite, or both, at temperatures as low as 120° C, possibly as low as 80° C. Dolomite, ankerite, kaolinite, and Fe ++ (probably from the brine) react to produce chlorite, calcite, and CO 2 at temperatures as low as 180° C and possibly as low as 125° C. At temperatures greater than approximately 290° to 310° C, iron-rich epidote and K-feldspar become abundant, calcite disappears, and K-mica is sporadic. Detrital Na-Ca plagioclase persists throughout the explored system, and at depth exists out of equilibrium with metamorphic albite. The most common metamorphic assemblage at temperatures of 300° C and above is quartz + epidote + chlorite + K-feldspar + albite ± K-mica. Pyrite, sphene, and hematite are also sporadically present. Similar metamorphism occurs in the sedimentary section penetrated by the Wilson No. 1well, drilled to a depth of 13,433 feet 22 miles south-southeast of the geothermal field. The lower-temperature reactions observed in the Salton Sea geothermal field also occur in Wilson No. 1, but at much greater depths owing primarily to the lower temperature gradient. Temperatures in this well reach only 260° C, insufficient for the formation of epidote and the destruction of calcite and K-mica. The mineralogical transformations taking place in the Salton Sea geothermal field are metamorphic responses to the elevated temperatures and pressures. Some transformations such as the reaction of dolomite, ankerite, and kaolinite to produce chlorite, calcite, and CO 2 are regional in extent and pose no metasomatic requirements other than that the system be open to H2 O and CO 2 . Other relationships, such as the destruction of calcite and K-mica and the complementary formation of epidote, may involve interchange of elements with the brine. The Salton Sea geothermal system displays a continuous transition from sediments through indurated sedimentary rocks to low-grade metamorphic rocks of the greenschist facies. This transition encompasses transformations commonly considered as diagenetic, and takes place without the formation of zeolites.

Confidence Limits for the Precision Parameter k

Abstract: Summary Confidence limits are calculated for the precision parameter k used in the analysis of palaeomagnetic data and for the angular standard deviation σ. A set of tables for 95 per cent and 99 per cent confidence limits is presented.

Lithium and potassium absorption, dehydroxylation temperature, and structural water content of aluminous smectites*

Abstract: U.S. Geological Survey, Federal Center, Denver, Colo. 80225 (Received 18 December 1968) Abstract-X-ray analysis of Li +- and K~-saturated samples, differential thermal analysis (DTA), thermal gravimetric analysis (TGA), and chemical analysis of 83 samples enable a distinction to be made between Wyoming, Tatatilla, Otay, Chambers, and non-ideal types of montmorillonite, and be- tween ideal and non-ideal types of beidellite. The Greene-Kelly Li+-test differentiates between the montmorillonites and beidellites. Re-expansion with ethylene glycol after K+-saturation and heating at 300~ depends upon total net layer charge and not upon location of the charge. Wyoming-type montmorillonites characteristically have low net layer charge and re-expand to 17 A,. whereas most other montmorillonites and beidellites have a higher net layer charge and re-expand to less than 17 *. Major differences in dehydroxylation temperatures cannot be related consistently to the amount of AI :~ -for-Si ~+ substitution, nor to the amount of Mg. Fe. type of interlayer cations, or particle size. The major factor controlling temperature of dehydroxylation seems to be the amount of structural (OH). Of 19 samples analyzed by (GA. montmorillonites and the one ideal beidellite that give dehydroxyla- tion endotherms on their DTA curves between 650 ~ and 760~ all contain nearly the ideal amount of 4(OH) per unit cell, but the non-ideal montmorillonites and beidellites that give dehydroxylation peaks between 550 ~ and 600~ do not. Non-ideal beidellites contain more than the ideal amount of structural (OH) and non-ideal montmorillonites seem to contain less, although the low temperature of dehy- droxylation of the latter could also be due to other structural defects. Change in X-ray diffraction intensity of the 001 reflection during dehydroxylation suggests that the extra (OH) of beidellite occurs at the apex of SiO~ or AIO4 tetrahedrons with the H ~ of the (OH)- polarized toward vacant cation sites in the octahedral sheet.

Florida Submergence Curve Revised: Its Relation to Coastal Sedimentation Rates

Abstract: New data substantiate as well as modify the south Florida submergence curve, which indicates that eustatic sea level has risen continuously, although at a generally decreasing rate, during the last 6500 to 7000 sidereal years (5500 standard radiocarbon years) to reach its present position. Accumulation rates of coastal deposits are similar to the rate of sea-level rise, thus supporting the generalization that submergence rates largely determine as well as limit rates of coastal sedimentation in lagoonal and estuarine areas.

Volcanic Substructure Inferred from Dredge Samples and Ocean-Bottom Photographs, Hawaii

Abstract: Ocean-bottom photographs from 18 stations and dredge hauls from 35 stations adjacent to the Island of Hawaii indicate that basaltic pillow lava and pillow fragments are the dominant rock type on the crest and flanks of the submarine rift zone ridges, whereas glassy basalt sand and scoria are the dominant type on the submarine flanks of the volcanoes directly downslope from land. These relations indicate that three major rock units comprise different levels of the volcanoes depending on the site of eruption: (1) pillow lavas and pillow fragments are dominant below sea level and are erupted from deep-water vents; (2) hyaloclastite rocks (vitric explosion debris, littoral cone ash, and flow-foot breccias) mantle the pillowed base of the volcano, and are erupted from shallow-water vents, subaerial vents in water-soaked ground, or are produced where subaerial lava flows cross the shoreline; and (3) thin subaerial lava flows make up the visible, subaerial shield volcano, are built atop the clastic layer, and are erupted from subaerial vents. This three-fold structure is similar to the table mountains of Iceland that are built by eruption beneath glacial ice. Large-scale slumping in the clastic layer may modify the submarine slopes of the volcanoes as well as produce faulting and downslope movement of parts of the overlying shield volcano. The slope change produced where the gentler shield meets the steeper pillowed pile can be recognized beneath sea level in the older volcanoes, where it has been submerged by regional subsidence.

Crustal structure of the Island of Hawaii from seismic-refraction measurements

Abstract: In August of 1964 the U. S. Geological Survey established seismic-refraction profiles along the northeast, southwest, and west coasts of the roughly triangular-shaped Island of Hawaii. Shots were fired at 10-km intervals along each coast from the U. S. Coast Guard Cutter CAPE SMALL and were recorded on shore by five refraction units spaced at approximately 25 km intervals along each coast. Most of these shots were also recorded on the 13 seismograph stations maintained on Hawaii by the U. S. Geological Survey's Hawaiian Volcano Observatory. These data were supplemented by recordings on the 13-station seismograph network and two mobile systems of three 500-ton chemical explosions deronated by the U. S. Navy on Kahoolawe as part of the SAILOR HAT program and by a re-evaluation of arrivals recorded on the seismograph network from seismic-refraction profiles shot off the northeast coast of Hawaii by Scripps Institution of Oceanography in 1962. Interpretation of the resulting seismograms suggests that the crust under Hawaii can be divided into two principal layers: (1) a basal layer 4 to 8 km thick with P-wave velocities of 7.0 to 7.2 km/sec, and (2) an upper layer 4 to 8 km thick in which P-wave velocities increase with depth from 1.8 to 3.3 km/sec at the surface to 5.1 to 6.0 km/sec at depth. The basal layer is probably the original oceanic crust under Hawaii plus the intrusive system associated with central vents and rift zones, and the upper layer is the accumulated pile of lava flows that form the bulk of the island. The crust along the northeast and southwest flanks of Kilauea is 11 to 12 km thick with P-wave velocities increasing in the upper layer from 1.8 km/sec at the surface to 5.1 km/sec at depth. The basal layer is 4 km thick and has a P-wave velocity of 7.1 km/sec. A 7.0-km/sec layer at depths of 3 to 5 km under the northeast flanks of Mauna Kea and Kohala Mountain masks first-arrival evidence for deeper structure, but secondary arrivals interpreted as reflections from the M discontinuity suggest that the underlying crust may be anywhere between 12 and 20 km thick. This shallow 7.0-km/sec layer is probably associated with the nearby rift zones of Kohala Mountain and Mauna Kea. The crust increases in thickness along the west coast of Hawaii from about 14 km under the flanks of Kohala Mountain and Hualalai to about 18 km under the flank of Mauna Loa. P-wave velocities along this coast increase with depth from 2.5 km/sec at the surface to 6.0 km/sec at about 10 km, and the lower 4 to 6 km of the crust has a P-wave velocity of about 7.2 km/sec. The upper mantle P-wave velocity under most of the island is 8.2 km/sec but may decrease to 8.1 km/sec under the southeast flank of Kilauea. Material with mantle-like P-wave velocity appears to bulge up under the summit of Kilauea to a depth as shallow as 10 or 11 km. Early P-wave arrivals associated with the summits and major rift zones of the volcanoes indicate that material with velocities as high as 7.0 km/sec approaches within 2 or 3 km of the surface under these structures and merges at depth with the 7.1- to 7.2-km/sec layer forming the base of the crust.

Nuées Ardentes of the 1968 Eruption of Mayon Volcano, Philippines

Abstract: Mayon Volcano, southeastern Luzon, began a series of explosive eruptions at 0900 April 21, 1968, and by May 15 more than 100 explosions had occurred, at least 6 people had been killed, and roughly 100 square km had been covered by more than 5 cm of airfall ash, blocky ash flows, and a lava flow. All material crupted was porphyritic augite-hypersthene andesite.

Significance of lineation and minor folds near major thrust faults in the southern Appalachians and the British and Norwegian Caledonides

Abstract: The Blue Ridge thrust sheet is one of the principal thrust masses of metamorphic rocks in the southern Appalachians. A broad zone of sheared and retrogressively metamorphosed rocks near the sole of the thrust sheet around the Grandfather Mountain window displays numerous small tight or isoclinal folds having axes subparallel to an intense penetrative cataclastic a lineation and axial planes parallel to foliation in the thrust sheet. These folds seem to have formed by tightening, flattening, and passive rotation of earlier more open folds originally formed perpendicular to the direction of transport. The style and orientation of these folds closely resemble those of analogous structures in thrust masses of crystalline rocks in the Caledonian orogenic belt in Scotland and Norway, suggesting that the structures of both regions may have similar origins.

Distribution of Oxygen and Carbon Isotopes in Fossils of Late Cretaceous Age, Western Interior Region of North America

Abstract: The oxygen isotope composition of both calcite and aragonite of the pelecypod Inoceramus is lighter than the composition of the aragonite of associated baculites and other cephalopods from the western interior region, the Gulf and Atlantic Coastal Plains, parts of Canada, and West Greenland. This difference cannot be explained by biotic and oceanographic factors or by postdepositional alteration of original isotopic compositions. Metabolic fractionation of oxygen isotopes by Inoceramus is strongly implied by the data and is not contradicted by what is known of the processes involved in the biologic deposition of shell carbonate. In addition, the oxygen isotope compositions of the inocerams and of some baculites are so light as to indicate temperatures greater than 30° C, which is too high for mollusks to tolerate. The unreasonable range of the indicated temperatures seems to be partly the result of metabolic fractionation of oxygen and partly the result of the Late Cretaceous sea in the western interior region having had a light oxygen isotope composition because of dilution with fresh water. The carbon isotope composition of the aragonite from Inoceramus is consistently heavier than that of the calcite in the same specimen by amounts ranging from 1 to 3 per mil. Metabolic fractionation of carbon isotopes within Inoceramus thus is indicated. The carbon isotope composition of the aragonite from baculites and other cephalopods is consistently lighter than that in either the aragonite or calcite in Inoceramus, indicating either that the cephalopods fractionated carbon isotopes from the dissolved carbonate in sea water differently than did inocerams or that the cephalopods utilized carbon of a different isotopic composition, probably from their food source, for their metabolic processes. While oxygen isotope data from the inocerams are not useful for paleotemperature interpretations, the oxygen isotope data from the baculites, if taken at face value, suggest either warmer temperatures for the western interior sea than around the periphery of Cretaceous North America, or water of oxygen isotope composition lighter than world oceans, or both. Data from British Columbia, southeastern Alaska, and West Greenland to the Gulf Coastal Plain do not indicate a well-developed latitudinal distribution of temperature in Late Cretaceous time. A general decline in temperatures during late Campanian and early Maestrichtian time is not evident.

Errors in Using Modern Stream-Load Data To Estimate Natural Rates of Denudation

Abstract: The practice of calculating natural rates of denudation from routinely collected data on the loads of suspended and dissolved matter in modern rivers is subject to several significant errors. The sources of these errors are demonstrated by examples from the Atlantic drainage of the United States, where their total effect has apparently doubled the natural rate of erosion. The largest error is caused by assuming that modern sediment loads in populated areas represent natural erosion, whereas in fact they mainly reflect the influence of man. Conversion of forests to croplands in the middle Atlantic states causes about a tenfold increase in sediment yield. Coal mining, urbanization, and highway construction have added extra loads of sediment to the streams. Modern sediment loads in the Atlantic-draining rivers are probably 4 to 5 times greater than they would be if the area had remained undisturbed by man. Errors in calculating the chemical denudation are caused by atmospheric contributions to the dissolved loads of streams and by pollutants that are added directly to stream waters. About one-quarter of the salts in Atlantic-draining streams were contributed from the atmosphere, either as recycled sea salts or as pollutants and soil dust that originally became airborne as a result of the activities of man. Perhaps another one-tenth of the dissolved load consists of industrial and agricultural wastes or acid mine waters that have been added directly to the streams.

Principal Stress Directions from Plastic Flow in Crystals

Abstract: Methods for determining orientations of principal stress axes in deformed rocks involve dynamic analysis of twin-gliding and of extinction bands produced by inhomogeneous translation gliding in crystals. The methods, beginning with Turner9s (1953) technique for dynamic analysis of calcite twins, have been developed using as guides the results from experiments under controlled laboratory conditions. Structures induced by intragranular flow in calcite, dolomite, quartz, micas, orthopyroxenes, clinopyroxenes, olivine, and other common rock-forming materials, may now be used to derive orientations of principal stresses causing the deformation. The various methods, some new, are discussed in detail and examples of their application to tectonites are given. The usefulness of such studies is illustrated by evaluating the observed orientations of principal stresses around folds in light of new data from a theoretical analysis of large amplitude folding of viscous layers in a less viscous matrix. Other areas of research in structural geology in which these methods should prove useful have also been outlined.

A Seismic-Refraction Survey of Crustal Structure in Central Arizona

Abstract: The U.S. Geological Survey conducted a seismic-refraction study of the earth's crust and upper mantle near the Tonto Forest Seismological Observatory (TFO), located 10miles south of the Mogollon Rim near Payson in central Arizona. Two recording lines 400 km long intersect in the approximate form of a cross at TFO; one line trends southeast and the other northeast. The sedimentary layer at most places southwest of the rim is less than 1 km thick, but north of the rim it is 2 to 3 km thick. The velocity in this uppermost layer ranges from 2.6 to 4.7 km/sec, with the higher limit measured near or north of the rim. Arrivals refracted in the upper crust (Pg) can be attributed to two layers for all the shot points south of the rim. The velocity in the upper layer is about 5.9 km/sec with thickness ranging from 2 to 8 km; beneath the upper layer the velocity is about 6.1 km/sec. The upper layer seems to be absent northeast of the rim, where two shot points generated Pg arrivals that show only a velocity of 6.2 km/sec. A Poisson ratio of 0.22 for the upper crustal layers was measured from shear and compressional arrivals. The lower crust could not be identified from the first and later refraction arrivals; however, minimum depths to the intermediate layer were determined. An average crustal velocity of 6.2 km/sec was measured from wide-angle reflection alignments. A thin intermediate layer would explain the seismic measurements. A delay-time method was used to map the configuration of the M-discontinuity. The depth below sea level is about 36 km along the northwest-trending line. The northeast-trending line shows a shallow depth of 21 km near Gila Bend, increasing depth to about 34 km under TFO, and a flat M-discontinuity at 40 km depth under the Mogollon Mesa northeast to Sunrise Springs. There is evidence of an abrupt depth change of about 4 km on the M-discontinuity in the vicinity of TFO. The velocity in the upper mantle is 7.85 km/sec. The relation of topographic elevation to crustal thickness suggests an approach to isostatic equilibrium, which is deduced from a near-zero regional free-air gravity anomaly. However, lateral density change in the upper mantle is required to make the crustal-refraction model fit the observed gravity-anomaly values, provided that velocity and density are linearly related.

Aftershocks of the Benham nuclear explosion

Abstract: The Benham nuclear explosion, a 1.1 megaton test 1.4 km beneath Pahute Mesa at the Nevada Test Site, initiated a sequence of earthquakes lasting several months. The epicenters of these shocks were located within 13 km of ground zero in several linear zones that parallel the regional fault trends. Focal depths range from near surface to 6 km. The earthquakes are not located in the zone of the major ground breakage. The earthquake distribution and fault plane solutions together indicate that both right-lateral strike-slip fault movement and dip-slip fault movement occurred. The explosion apparently caused the release of natural tectonic strain.

Lherzolite, Anorthosite, Gabbro, and Basalt Dredged from the Mid-Indian Ocean Ridge

Abstract: The Central Indian Ridge is mantled with flows of low-potassium basalt of uniform composition. Gabbro, anorthosite, and garnet-bearing lherzolite are exposed in cross fractures, and lherzolite is the bedrock at the center of the ridge. The Iherzolites are upper-mantle rock exposed by faulting.