Ophiolite metamorphism in northeast Borneo

The Darvel Bay ophiolite consists of a conformable sequence of mantle harzburgite, a gabbro layer of about 2 km thickness, a basalt layer and associated chert-spilite association of Late Cretaceous to Eocene age, and overlying Miocene melange and olistostrome deposits. The ophiolite is an extension into Borneo of the recently inactive Sulu Archipelago non-volcanic arc. Generally the gabbro layer has been converted to banded plagioclase-amphibole gneisses and the basalt layer to crudely foliated epidote amphibolite. Igneous relicts occur sporadically, especially in the lower gabbro horizons. They have either cumulus granular or gabbroic textures and contain diopsidic augite, bronzite, and a dark brown pargasitic hornblende. The labradorite is occasionally clouded. The partitioning of Fe/Mg between the two pyroxenes and the hornblende suggests an igneous paragenesis and the former allocation of these pyroxene-bearing rocks to the granulite facies is now rejected.The basites have undergone metamorphic re-equlibration, frequently sporadic and imperfec, through amphibolite facies, characterized by hornblende, to greenschist facies, characterized by actinolite. Igneous labradorite frequently persists to the lower grades. The partitioning of Ca/Na between amphibole and plagioclase may be correlated with metamorphic grade.Sub sea-floor retrogressive metamorphism, combined with large scale metasomatism resulting from the circulation of hot brine, appears to be the most appropriate mechanism to explain the sodium enrichment in the basalt layer and the imperfect metamorphic re-equilibration of the ophiolite generally.     

Simultaneous determinations of the sensible and latent heat transfer coefficients for tree leaves

The heat and mass transfer coefficients for exchange across the fluid dynamic boundary layer over tree leaves were simultaneously determined in a controlled environment chamber. The mass transfer coefficients were calculated from measured values of evaporation, air specific humidity and a value of leaf specific humidity at leaf temperature. The heat transfer coefficients were calculated from measured values of air temperature, leaf temperature and an estimate of the sensible heat flux density calculated as the measured net radiation at the leaf surfaces minus the latent heat flux density. The experiments described in this paper indicate that the equations based on laminar boundary-layer theory can give reasonable estimates of the transfer coefficients of real tree leaves for the velocities most commonly experienced in plant canopies, if they are adjusted by a constant multiplier greater than one. Calculations of local mass transfer coefficients based on temperature measurements at three locations at different distances from the leading edge of the leaves, indicate that the deviation from theory is probably the result of transition to turbulent boundary-layer flow at some distance from the leading edge.     

Distribution of viral and bacterial pathogens in a coastal canal community

Significant concentrations of human enteric viruses and bacteria were found to be present in the water and sediment of a coastal canal community into which secondarily treated sewage was being discharged.     

Electron microprobe analysis of glass shards from tephra assigned to set W,Mount St. Helens,Washington

We have extended the fallout areas for each of two members of tephra-set W, erupted from Mount St. Helens about 1500 ad, by several hundred kilometers beyond the limits mapped in 1975. We traced one member (We) east into Idaho, and the other (Wn) northeast into British Columbia. After using stratigraphic and petrographic observations to assign more than 100 tephra samples to set W, we found 26 of these, selected for chemical analysis, to be closely similar in content of Ca, Fe, and K in glass shards. But improved homogeneity was evident when the 26 sampling localities for tephra W were segregated geographically, east vs. northeast of the volcano. When Ca:Fe:K proportions were plotted on a ternary diagram, there was no overlap of the plotting areas for these two groups of tephra W samples. Without such data, tephra layers We and Wn are currently separable only from stratigraphic and geographic information. Partial glass analysis is also an aid, along with stratigraphic position and petrographic characteristics, in distinguishing tephra W from associated tephra layers. These include tephra layers T and Yn from Mount St. Helens, as well as older tephra layers from Mount Mazama and Glacier Peak.     

Electron microprobe data for tephra attributed to Glacier Peak,Washington

Reference samples of three prominent pumice units of Glacier Peak tephra collected east of the volcano within a distance of 100 km are similar petrographically to units described by earlier workers. Glass shards isolated from these samples were analyzed by electron microprobe to determine the content of Ca, Fe, and K. Resulting data, plus those published for two other references samples, provide a basis for attributing certain outlying tephra layers from 14 locations in eastern Washington, Idaho, Wyoming, and Montana to eruptions of Glacier Peak. Ten of the samples have properties of both Glacier Peak tephra and Mount St. Helens set J tephra, but proportions of Ca:Fe:K in glass shards indicate that 9 of the 10 outlying samples came from Glacier Peak, whereas one is assigned to Mount St. Helens set J. The remaining six outlying samples, all from southeastern Washington, contain cummingtonite phenocrysts and are chemically similar to some parts of Mount St. Helens tephra sets that are older than 12,000 BP.     

Saponite and celadonite in layer 2 basalts,DSDP Leg 37

Detailed examination of igneous core recovered during Leg 37 of the DSDP, has revealed that basalt diagenesis, an alteration effect resulting from low temperature interaction with seawater, is pervasive to depths of greater than 600 meters in layer 2. Phyllosilicates are among the main components of this low grade alteration effect and occur exclusively as saponite, celadonite and interlayered mixtures of these two phases. Saponites fall into two chemical groups as (a) Mg rich-Fe poor types characteristic of oxidative diagenesis and (b) Fe rich-Mg poor types characteristic of non-oxidative diagenesis. Celadonite is entirely restricted in occurrence to the oxidative diagenetic environment (oxidation halos) and rarely, if ever, occurs as a pure phase. In this respect, X-ray and electron microprobe analyses suggest the presence of interlayered smectite in some cases and iron-oxide contamination in others.Phyllosilicates generated during oxidative diagenesis of basalt occur in discrete mineralogical zones, typically arranged in the sequence Fe³⁺-oxide, celadonite, saponite proceeding outwards from a vein. The generation of these zones are modelled in terms of an infiltration dominated metasomatic process and their occurrence reflects a gradual extraction of oxygen from inflowing seawater during progressive reaction with the massive crystalline basalt.Mass balance calculations applied to the oxidative diagenetic process suggest that a source external to the immediate environment of the massive crystalline rock is required for Si, Fe, K, Mg, Ca, and Al, in order to account for the observed secondary minerals. While Mg, K, and Ca are indigenous to seawater, Si, Fe, and Al were probably enriched in the fluid during wall rock reactions in the fracture system.It is suggested that diagenesis of layer 2 basalts results in the extraction of Mg and K from seawater, in enough quantity to contribute significantly to the chemical mass balance of the oceans.     

The effect of intrinsic model noise upon resistivity inversion

Model uncertainty is introduced into direct-current resistivity data by adding random changes to layer thicknesses in a ten-layer model. The resulting information is then aliased by generating a sounding curve which contains less information than the ten resistivities and nine thicknesses. These sounding curves are then inverted via the Backus-Gilbert algorithm using singular value decomposition to obtain solutions in terms of simpler two-or three-layer models. Quantitative results confirm what has been known qualitatively for many years as the principle of equivalence. An interesting result is that the geometric average of a given suite of noisy models is virtually identical to the best-fit model for the average of the noisy curves. The results show that the inversion of resistivity data by nonlinear least-squares parameter fitting is stable in the sense that noise in the data inverts to the same magnitude of noise in the model.     

Morphometric analysis of cinder cone degradation

Measurements of Vie geometry of cinder cones can be used to determine the morphological effects and rates of degradation. Cinder cones in the San Francisco volcanic field, Arizona (where radiometric dates and stratigraphic studies have determined cone ages) decrease in height, height/width ratio and slope through time. The ratio of crater diameter to cone basal diameter does not appear to change with degradation, nor, as suggested previously, with chemical composition or particle size. Similar results obtained for cinder cones in Nevada, Oregon, Manchuria, Italy and Reunion suggest that the morphometric patterns of degradation are similar for all cinder-cones. The rates of degradation vary tremendously however, with rainfall and temperature being perhaps the most important factors. Since the initial geometries of cinder cones are remarkably similar, degraded cones may be ideal gauges of long-term climatic change.Degradation can be readily modelled for two cases: burial of cinder cone flanks by subsequent lava flows, and erosion and mass wasting. Although the former is locally important, degradation appears to occur principally by the second process: cinders weather to clay, which is gullied by rainfall, with the debris sliding downslope. Such erosion and mass wasting produces a degradation curve in general agreement with observations. Erosion rates can be accelerated orders of magnitude, however, by the mantling of old cones with easily eroded ash deposited during nearby eruptions. Comparison of cinder zone isopach radii and cone separation distances suggests it to be a common effect.     

Radioelements,radiogenic helium and age relationships for groundwaters from the granites at Stripa,Sweden

The solution of radioelements and radiogenic ⁴He by groundwaters in fractured rocks is dependent upon the radioelement distribution in the rock matrix and the extent of the rock-water interface. The ${}^{234}\text{U}{}^{238}\text{U}$ activity ratio and the dissolved U, Rn and He contents of such groundwaters respond to changes in the flow regime with time. Although ${}^{234}\text{U}{}^{238}\text{U}$ activity ratios change with groundwater residence time as a consequence of ²³⁴Th-recoil induced solution of ²³⁴U, the activity ratio is strongly influenced by the U distribution within fractures, by the extent of the rock-water interface and by the amount of ²³⁸U in solution. A model for the quantitative evaluation of these effects is presented.Groundwaters from depths up to 880 m in the Stripa granite have variable dissolved uranium contents and ${}^{234}\text{U}{}^{238}\text{U}$ activity ratios. The uranium geochemistry is primarily determined by variations in flow path rather than by groundwater age.Dissolved radiogenic ⁴He in the groundwaters increases with their depth of origin, and is dependent upon the U content of the granite and upon its fracture porosity. It increases with groundwater residence time but movement of ⁴He by diffusion and transport processes make the actual groundwater age indeterminate.     

Conversion of profile difference quotients to true gradients at the geometric mean height in the surface layer

Theoretical profiles of wind speed and air temperature can provide synthetic measurements at discrete levels which may be compared with actual field measurements. In addition to wind and temperature gradients at any height, profile theory permits us to determine the difference quotients from measurements at discrete levels. It is shown that corrections are required to obtain the gradients at the geometric mean height of the two discrete levels of measurement. The correction factor depends on the measurement height and spacing, profile structure, surface roughness and the measured Richardson number. The correction can be reduced by close spacing of the measurement levels.