Mineralogy and physical nature of clay gouge     

Francis T. Wu 《Pure and Applied Geophysics》1978,116(4-5):655-689

Fault gouges have been observed in the surface outcrops, in shallow excavations, and in deep (300 meters below the surface) tunnels and mines in fault zones. The 2-microns fractions in these fault gouges may compose a few percent to more than fifty percent of the total mass in the outcrops, and the mineralogy of the 2-microns fractions consists of a variety of clays (the common ones are montmorillonite, illite, kaolinite, chlorite, vermiculite and mixed-layer clays) and some quartz, feldspars, etc.Although we cannot yet conclude directly from the studies of gouges that similar gouges exist at depths where many large shallow earthquakes are generated, there is a strong possibility that they do, based on (1) available equilibrium data on various clays — for example, kaolinite has been found to exist at 4 kb and 375°C (±15°C) (Thompson, 1970) and montmorillonite + kaolite has been found to exist at 450°C and 4 kb (Velde, 1969); (2) the compatibility of laboratory velocity data in gouge (Wang et al., 1977) with those in a model for central California (Healy andPeake, 1975); (3) the capability of clays to undergo sudden earthquake-like displacements (Summers andByerlee, 1977); (4) the petrology of intrafault cataclastic rocks in old fault zones (Kasza, 1977); and (5) the compatibility of gouge mineralogy with the mineralogy of hydrothermal clay deposits.If clay gouges are indeed significant components of the fault zone at depth, then the mechanical properties of clays under confining pressures up to 4 kb are important in the behavior of faults. Very few experiments have been performed under such high pressures. But from the physical makeup of clays, we can infer that (1) the range of possible behavior includes stable sliding with vermiculite and montmorillonite (asByerlee andSummers, 1977, have proven) to stick-slip-like behavior with kaolinite, chlorite, etc.; (2) the absence or presence of water will greatly affect the strengths of gouges — it is possible that water may reduce the strength of gouge to a fairly small value.  相似文献   

Uptake of radioactivity by marine sediments and implications for monitoring metal pollutants     

J.A Hetherington  B.R Harvey 《Marine pollution bulletin》1978,9(4):102-106

The value of studying artificially-produced radionuclides in the marine environment is discussed in the wider context of monitoring sediments for other metal pollutants. Differences in the dispersion of selected radionuclides discharged from the same known source are used to illustrate the sort of changes in phase or speciation which must occur with other metal pollutants, but which cannot be demonstrated directly because of the multiplicity of sources. Various chemical and physical procedures are discussed which can be applied to a study of heavy metal associations with marine sediments, as are questions such as the existence, or otherwise, of mechanisms for the slow release of adsorbed material from the buried sediment back into the water column. Suggestions are made as to how radionuclide studies may be helpful in answering questions such as these, which are considered to be vital for the meaningful interpretation of sediment analyses.  相似文献   

Biaxiality in relation to visible twinning in experimentally deformed calcite     

Francis J. Turner 《Contributions to Mineralogy and Petrology》1975,53(4):241-252

Moderate to strong biaxiality (2V = 10 °–45 °) in experimentally deformed calcite (in single crystals and in marble) is attributed to overlap between one or two thin {01¯12} twin lamellae and the enclosing host. A perfectly centered conoscopic figure (section normal to [0001]) is perceptibly asymmetric about the trace of the optic axial plane. This asymmetry is pronouned in thick sections (> 0.04 mm) and completely distrupts the biaxial configuration of the figure if the overlapping lamella exceeds about 0.0025 mm in thickness. In sections somewhat oblique to [0001] and cut at 20 ° or less to the plane of twinning the conoscopic figure may appear to be perfectly biaxial-expecially in thin sections ( 0.02 mm) enclosing thin ( 0.001 mm) but still visible twins.Similar values of 2V recorded for natural calcite likewise are attributed to twinning on a visible scale.  相似文献   

Variations in andean andesite compositions and their petrogenetic significance     

R. S. Thorpe  P. W. Francis 《Tectonophysics》1979,57(1):53-70

Three linear zones of active andesite volcanism are present in the Andes — a northern zone (5°N–2°S) in Colombia and Ecuador, a central zone (16°S–28°S) largely in south Peru and north Chile and a southern zone (33°S–52°S) largely in south Chile. The northern zone is characterized by basaltic andesites, the central zone by andesite—dacite lavas and ignimbrites and the southern zone by high-alumina basalts, basaltic andesites and andesites. Shoshonites and volcanic rocks of the alkali basalt—trachyte association occur at scattered localities east of the active volcanic chain,The northern and central volcanic zones are 140 km above an eastward-dipping Benioff zone, while the southern zone lies only 90 km above a Benioff zone. Continental crust is ca. 70 km in thickness below the central zone, but is 30–45 km thick below northern and southern volcanic zones. The correlation between volcanic products and their structural setting is supported by trace element and isotope data. The central zone andesite lavas have higher Si, K, Rb, Sr and Ba, and higher initial Sr isotope ratios than the northern or southern zone lavas. The southern zone high-alumina basalts have lower Ce/Yb ratios than volcanics from the other zones. In addition, the central zone andesite lavas show a well-defined eastward increase in K, Rb and Ba and a decrease in Sr.Andean andesite magmas are a result of a complex interplay of partial melting, fractional crystallization and “contamination” processes at mantle depths, and contamination and fractional crystallization in the crust. Variations in andesite composition across the central Andean chain reflect a diminishing degree of partial melting or an increase in fractional crystallization or an increase in “contamination” passing eastwards. Variations along the Andean chain indicate a significant crustal contribution for andesites in the central zone, and indicate that the high-alumina basalts and basaltic andesites of the southern zone are from a shallower mantle source region than other volcanic rocks. The dacite-rhyolite ignimbrites of the central zone share a common source with the andesites and might result from fractional crystallization of andesite magma during uprise through thick continental crust. The occurrence of shoshonites and alkali basalts eat of the active volcanic chain is attributed to partial melting of mantle peridotite distant from the subduction zone.  相似文献   

A study of the Rima Sirsalis lunar magnetic anomaly     

L.J. Srnka  J.L. Hoyt  J.V.S. Harvey  J.E. McCoy 《Physics of the Earth and Planetary Interiors》1979,20(2-4):281-290

The source of the lunar magnetic anomaly associated with the Rima Sirsalis linear rille has been modelled using the vector field intensities due to arbitrary uniform magnetization in a rectangular prism. It is shown that in order to match the Apollo 16 subsatellite data, the lunar surface near the rille must have a vertical magnetization of 6–9 × 10⁻³ G if the anomaly is due to flux leakage from a gap in the crust with the dimensions of the rille. This is more than one order of magnitude larger than the magnetization of any lunar sample, but is comparable with the high magnetization recently deduced for the Reiner γ formation in Oceanus Procellarum. An alternative explanation is that Rima Sirsalis and its surroundings are the site of a vertical magnetization contrast of 10⁻⁵ – 10⁻⁴ G which is at least as wide as the rille and extends to a depth of tens of kilometers in the crust. A wider magnetic source reduces the required magnetization (or depth) proportionately, since to first order the field at high altitude is proportional to the magnetic dipole moment per unit length.  相似文献   

A proposed model for predicting trace metal composition of fly-ash leachates     

Francis H. Chapelle 《Environmental Geology》1980,3(3):117-122

A mathematical model is proposed that is designed to predict trace metal composition of leachates produced by coal fly ashes. This model is based on the assumption that the mobilization of trace metals from fly ash is primarily a surface desorption phenomenon. The validity of this model is tested using data from published sources. Good correlation is found between predicted trace metal concentrations and measured trace metal concentrations in experimentally produced leachates.  相似文献   

Note on the genesis of brucite in contact metamorphism of dolomite     

Professor Dr. Francis J. Turner 《Contributions to Mineralogy and Petrology》1965,11(4):393-397

Consideration of available thermodynamic data and the published results of direct experiments relating to (1) formation. of periclase from dolomite and (2) hydration of periclase to brucite, permits the following conclusions to be drawn: (1) At very low partial pressures of CO₂ (perhaps of the order of 1 bar) and relatively high partial pressures of water (up to 2000 bars), dolomite can break down directly to brucite and calcite at temperatures above about 400° C, and below temperatures on the brucite dehydration curve. (2) The reaction dolomite calcite + periclase + CO₂ in contact metamorphism near granitic bodies is likely to occur only at low partial pressures of CO₂ (perhaps 10 or 20 bars); this can be achieved without direct formation of brucite, by maintaining a partial pressure of water of the order of 1000 bars or more. (3) At low CO₂ pressures dolomite may re-form in the cooling stages of metamorphism by reaction between calcite, brucite, and CO₂ at temperatures below about 400° C.  相似文献   

Stranded tar on Florida beaches: September 1979–October 1980     

G.C. Romero  G.R. Harvey  D.K. Atwood 《Marine pollution bulletin》1981,12(8):280-284

Amounts of tar stranded on Florida beaches were determined periodically over one year (September 1979–October 1980). Results show that tar fouling of southeast Florida beaches is an order of magnitude greater than the rest of the state. This may result from the extensive ship traffic in the Straits of Florida. There is no evidence that any Florida beaches received increased amounts of tar as a result of the 1979 Ixtoc-1 blowout in the southern Bay of Campeche. There is also no evidence that the amounts of tar on southeast Florida beaches have increased over amounts measured in API studies conducted in 1958 and 1971.  相似文献   

Crystal bending in metamorphic calcite,and its relations to associated twinning     

Francis J. Turner  Miguel Orozco 《Contributions to Mineralogy and Petrology》1976,57(1):83-97

This paper deals with the incidence and geometry of lattice bending in calcite of naturally strained marble and possible relations in time to associated {01¯12} twinning, as revealed by microscopic examination with a universal stage. Microscopic technique and graphic treatment of data with a view to identifying the relation in time of bending to twinning, and possible glide mechanisms involved in the bending process are reviewed as a basis for present and subsequent investigation of this general topic.In most instances development of surviving thin e twins postdates bending of the host crystal (such twins everywhere are rationally oriented). Rarely (in contrast with experimental experience) some thin twins are slightly irrational (L_e lamellae) and apparently developed in the final stages of bending. Thick twins (a few tens of microns wide) on the other hand rather commonly predate or are synchronous with bending.The geometry of bending (external rotation) — especially for rotation less than 25° —commonly is compatible with models (based on experimental experience) of simple translation in the strained domains. The commonest translation system so identified is on {10¯11}, with sense of shear, where recognizable, either negative or positive. Translation on {02¯21} is relatively rare. Unexpectedly there is rather strong but not conclusive evidence of translation on {0001} parallel to an a axis. This mechanism, hitherto never identified with certainty, is now here documented unequivocally in a crystal of calcite experimentally strained at 300° C, 5 kb.  相似文献   

Amphibole pyroxenite xenoliths: Cumulate or replacement phenomena from the upper mantle,Nunivak Island,Alaska     

Donald M. Francis 《Contributions to Mineralogy and Petrology》1976,58(1):51-61

Interstitial to poikilitic amphibole found in garnet pyroxenite xenoliths has been interpreted, in the past, to represent a critically silica undersaturated, residual intercumulus melt trapped by its cumulate assemblage of anhydrous phases. The textural features of such amphibole in pyroxenite xenoliths from Nunivak Island, Alaska, however, are more compatible with an origin by replacement of the anhydrous phases of the pyroxenite, following a period of cooling and sub-solidus recrystallization in the upper mantle. The reaction of amphibole and olivine to give orthopyroxene, observed in two specimens, requires that the associated fluid phase was not critically silica undersaturated. The amphibole is therefore thought to reflect the interaction of an alkali-bearing, migratory, aqueous fluid and an upper mantle consisting of spinel lherzolite cut by veins of spinel and garnet pyroxenite.  相似文献