Halogen acids in fumarolic gases of Kilauea volcano

The water-rich condensates of fumarolic gases, obtained from degassing lavas of the 1959–60 eruption of Kilauea volcano, contain unexpectedly high concentrations of hydrofluoric and hydrochloric acids, and thereby suggest that halogens are significant constituents of basaltic magmas. Vents on the pumice hill of Kilauea Iki yielded one sample that contained, in parts per million, 21,000 HF (1.1 N) with 2,920 HCl, and another sample, 20 HF with 70,500 HCl (2.0 N). Samples from vents elsewhere on the volcano had from one-fortieth to one-thousandth as much of the two acids. A rough correlation exists between the temperature of the fumaroles (range 110 to 820°C) and the total concentration of the halogen acids. This correlation is mainly due to progressive dilution of the magmatic halogen acids by water of probable meteoric origin in fumaroles of lower temperatures. Variations in the HF/HCl ratio (range 0.0003 to 7.2) may be explained by means of two different processes whose relative importance cannot be assessed with the data at hand (1). In their migration to the surface, the acid gases may have reacted with the lava to a variable extent owing to the widely different configurations of the several vents (steaming areas in glassy pumice, glowing cracks, and drillhole in lava lake). In the reaction, relatively more HF could have reacted at temperatures around 300°C with the glassy pumice (2). There is some indication that the HF/HCl ratio increases with time,suggesting that the crystallizing lava may have released HCl early, with HF concentrated in the later exhalations. The Br/Cl ratio ranges from 0.0036 down to 0.0014, as compared to 0.0034 of seawater.     

Deep geothermal brine near Salton Sea,California

A well drilled for geothermal power near Salton Sea in Imperial Valley, Calif., is 5,232 feet deep; it is the deepest well in the world (1962) in a high-temperature hot spring area. In the lower half of the hole temperatures are too high to measure with available equipment, but are at loast 270°C, and may be as much as 370°C. For comparison, maximum temperature heretofore reported at depth (1962) for hot spring areas is 295°C. The well taps a very saline brine of Na-Ca-K-Cl type (about 185,000 ppm Cl) with exceptionally high potassium, and with the highest content of minor alkali elements known for natural waters; Fe, Mn, Zn, Pb, Cu, Ag, and some other metals are also exceptionally high. This brine may be connate, but present evidence favors a source in the magma chamber at depth that supplied late Quaternary rhyolite domes of the area. If the latter is correct, the brine is an undiluted magmatic water that is residual from the separation of a more volatile phase high in CO₂, H₂S, and with some alkali halides. Elsewhere, the hypothesized volatile phase may account for near-surface hot spring activity of most thermal areas of volcanic association. The residual brine of high salinity may ordinarily remain relatively deep in the volcanic systems because of high specific gravity and low content of volatiles, seldom appearing at the surface except in a greatly diluted form. The hot springs of Arima, Japan, may be a rare example of this type of magmatic water discharging at the surface in moderate concentration (Cl as much as 42,000 ppm). Independent evidence from fluid inclusions in minerals of high-temperature base-metal deposits also favors the existence of magmatic water high in Na, Ca, and Cl, and low in CO₂ and other volatile components. During a three-month production test several tons of material precipitated in the horizontal discharge pipe from the well. Amorphous silica with iron and manganese, and bornite are the dominant recognized components. This material contains the astonishingly high contents of about 20 percent copper, 2 percent silver, and notable sulfur, arsenic, bismuth, lead, antimony, and some other minor elements. Total quantities of all elements in the original whole brine are not yet known, but calculated amounts corresponding to 1 to 3 ppm of copper and 0.1 to 0.3 ppm of silver were precipitated from the brine to form the pipe deposits. The brine, therefore, may be man’s first sample of an « active » ore solution. Equally fascinating to many geologists is the possibility that in the lower part of the hole temperatures are so high and pressures are sufficient for young sedimentary rocks to be undergoing transformation into rocks with mineral assemblages of the greenschist facies of metamorphism. Drill cores from 4,400 to 5,000 feet in depth contain chlorite, albite, K-feldspar, epidote, mica, and quartz, with some indication of increase in metamorphic grade downward. Regional geological and geophysical studies favor a depth of about 20,000 feet to pre-Tertiary basement rocks in the general area. A shallow basement or local upfaulting of old metamorphic rocks are not likely possibilities for the thermal area.     

Lateral and vertical variability in crustal velocity structure in a small area of the North Atlantic

The detailed velocity structure of a 70 by 35 km area of 6–10 Ma old crust on the flank of the mid Atlantic Ridge at 24°N was studied using 358 explosive charges and several hundred 16.4-1 airgun shots fired into an array of eight ocean bottom hydrophones. Inversion of the first arrival refracted travel times shows that the crust comprises a normal oceanic section about 5 km thick with a steep velocity gradient in the upper crust increasing from about 3.5 km/sec at the seafloor overlying a typical oceanic layer 3 and a probably anisotropic mantle. Delay time function mapping using two datasets containing arrivals from layer 3 and from the mantle show that lateral variability is generally low over most of the survey area, with a small region of high delay times in the northwest corner caused by the presence of abnormal crust probably associated with a minor fracture zone. We find that the topography of the base of layer 2 is similar to that of the top, indicating that the normal faulting which occurs along the margins of the median valley extends down at least into layer 3. Our observations from mantle arrivals are consistent with a much flatter Moho which constrains possible models of crustal formation at the spreading centre.     

Monte Carlo simulation of small air-mass showers

The present model permits simulation of any geographic region and the symmetrical or random positioning of any number of rain gauges. The operator has the option of entering precipitation parameters: rain cell diameter, duration, rain swath length, vector angle, and precipitation amount for any number of discrete showers. In a series of computations the model generates (1) a random first echo location and resulting rain swath, which is superimposed on a specific grid of rain gauges; (2) the number of rain gauge receiving a hit; and (3) the number of undetected rain events within an area.By use of a portion of the Iowa climatological rain gauge network and parameters derived from radar and rain gauge observations the model shows that only 7% of single cell showers are detected by the existing sampling grid.Journal Paper No. J-10378 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011. Project 2449.A portion of this paper was presented at the 93rd Annual Meeting of the Iowa Academy of Science, April 1981.     

Heat flow and age of the Gulf of Oman

We present the results of twenty heat flow stations in the Gulf of Oman which are used to infer the first reliable age estimates for the basin. A mean surface heat flux of 42.6±3.6 mW m^?2 exhibits no significant regional variation. After correction for thick and rapidly deposited sediments this yields an age of 70 to 100 Ma according to oceanic thermal models. This age is also consistent with the sediment corrected basement depths of 5.5–6.0 km and with formation during the Cretaceous quiet zone. The latter can explain the absence of magnetic sea-floor spreading lineations. Heat flow measurements are also used to confirm the presence of gas hyrdate layers. The measured thermal gradient yields a depth for the solid to free gas phase transition which is the same as that deduced from “bright spots” seen on seismic reflection profiles.     

Neodymium isotopic composition of Quaternary island arc lavas from Indonesia

${}^{143}\text{Nd}{}^{144}\text{Nd}$ ratios measured in Quaternary lavas from Java and the Banda arc of Indonesia range from 0.51242 to 0.51280 and exhibit an inverse correlation with ${}^{87}\text{Sr}{}^{86}\text{Sr}$. Isotopically, the Indonesian samples resemble Andean rather than island arc lavas. The samples from Java plot either within, or adjacent to the mantle array, towards higher ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios. Samples from the Banda arc and the anomalous calc-alkaline volcano Papandajan are characterized by relatively low ${}^{143}\text{Nd}{}^{144}\text{Nd}$ and high ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios. These characteristics are consistent with the interpretation that subducted terrigenous material was involved in the genesis of these lavas. Furthermore the Banda arc samples appear to lie on a mixing line between isotopic compositions characteristic of the mantle and upper continental crust. A high-K trachyte from the alkaline volcano Muriah, Java, has isotopic characteristics of the mantle (${}^{143}\text{Nd}{}^{144}\text{Nd}\text{= 0.51270}$, ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.70424}$), which implies that the extreme enrichment in large-ion-lithophile elements in its source must have occurred only shortly before its formation. The inferred ${}^{143}\text{Nd}{}^{144}\text{Nd}$ ratio of the unmodified mantle beneath Java and the Banda arc is lower than that observed in mid-ocean ridge basalt, which may have important implications for a better understanding of the geochemical structure of the mantle.     

A history of neotectonic studies in Ontario

First observations of geologically young rock faults and folds in New York in the late nineteenth century were shortly followed by others in Ontario. Remapping of the Paleozoic rocks began in the 1930s, and Quaternary geology mapping became organized in the 1950s, leading to further discoveries of faults and folds in the bedrock. Engineering works in the Niagara and Hamilton areas from the 1890s to the 1970s encountered repeated problems of rock squeeze. The separate geological and engineering experiences were linked in the 1970s, and with heightened awareness, discoveries of rock disturbances (mainly popups) greatly increased in the 1970s and 1980s. Understanding centered on high horizontal stress in the bedrock, which became quantified through rock testing and modeling. The creation of the Multi-Agency Group for Neotectonics in Eastern Canada (MAGNEC) in 1986 brought together a diverse group interested in all aspects of neotectonics, including the distribution and causes of rock stress and the potential implications for seismic risk. The existence of nuclear power plants sensitive to variations in the stress environment and high population densities near the Great Lakes provided motivation for further attention, and Prince Edward County was designated for special study. Recent suggestions of reduced seismic activity under ice sheets and increased activity associated with isostatic uplift during their retreat lead to the question whether seismic risk is slowly decreasing as uplift rates decline.     

Climate Change,Extreme Events and the Canadian Insurance Industry

Natural Hazards - At the same time that a scientific consensus has arisen that the world will most likely experience a changing climate in the near future, with more frequent extreme events of some...     

40Ar/39Ar and U-Pb dating in the eastern Pilbara,Australia; temporal constraints on structural and metamorphic events between 3.5 and 2.8 Ga (extended abstract)

Geologie en Mijnbouw -