Emanuel Mazor

Paleotemperatures and other hydrological parameters deduced from noble gases dissolved in groundwaters; Jordan Rift Valley, Israel

Abstract One cm 3 samples of thermal waters were analyzed mass spectrometrically for their dissolved He, Ne, Ar, Kr and Xe. The isotopic abundances of the four heavier gases are atmospheric and their concentrations equal those of air-equilibrated waters at 16–22°C. The waters contain up to 2700 × 10 −8 cm 3 STP radiogenic He/cm 3 STP water. The data showed: 1. (a) the thermal waters studied originated from meteoric waters that entered the ground, 2. (b) While they entered the ground (in periods up to 30,000 years ago according to C-14 dating) the average temperature in the region was rather close to the present one, i.e. around 19 ± 4° C . 3. (c) The dissolved noble gases were not lost in the ground although the waters had been heated in some cases up to 63°C for thousands of years. The present data support the reliability of the noble gas method for determining original surface paleotemperatures of ancient meteoric waters. Radiogenic He excess is a potential indicator for ancient waters along with Ra excess and low C-14 contents.

Ages of calcium-rich achondrites—I. Eucrites

The noble gases He, Ne and Ar were measured in 26 eucrites and 2 howardites, and in separated mineral fractions of 6 eucrites. The feldspar has lost nearly all its cosmogenic He3, as shown previously by Megrue (1966). Radiation ages were therefore calculated by a new method, using the He3Ar38 ratio to infer the feldspar content and hence the correction for He3 diffusion losses. Bulk samples as small as 50 mg can thus be reliably dated. Earlier measurements from the literature were recalculated in this manner. The resulting age distribution resembles that of chondrites, ranging from ≤0.1 m.y. to 62 m.y. Two distinct clusters were found at 5 and 11 m.y.; two others may be present at ~18 and ~30 m.y. Two howardites are present in the first 2 clusters. Apparently eucrites and howardites are produced in the same impacts, and hence originated from within a few kilometers of each other. K-Ar ages of eucrites lie between 2.4 and 4.4 AE; U-He ages tend to be systematically shorter, with more than one-third lying below 1 AE. The three eucrites with shortest U-He ages ( <0.2 AE) show pronounced shock effects. Presumably the short ages are due to a recent collision that heated the parent body of these meteorites. This would seem to imply that all eucrites and howardites originated in a single body. The two shergottites have virtually identical radiation ages (2.5 m.y.) and K-Ar ages (0.5–0.6 AE). Perhaps they were involved in the postulated 0.52 AE collision that fragmented the parent body of the hypersthene chondrites and produced the majority of iron meteorites now falling on Earth. Howardites and eucrites differ strikingly in the proportion of gas-rich meteorites. Not a single one of the 30 eucrites and shergottites investigated to date contains light primordial gases, while 3 out of 6 howardites do. Most of the properties of eucrites are equally consistent with a lunar or an asteroidal origin. Two factors favoring an asteroidal origin are the existence of unbrecciated eucrites and of mesosiderites with eucritic silicate inclusions.

Noble gases in unequilibrated ordinary chondrites

Abstract The rare gases were determined mass-spectrometrically in eleven unequilibrated ordinary chondrites. The amounts of primordial Ar, Kr and Xe are systematically greater than in ordinary chondrites proper. Primordial Ne was detected in only two of the meteorites. The amounts of the heavy rare gases Ar, Kr and Xe are approximately inversely proportional to the degree of equilibration of Fe in olivine, and are directly proportional to C contents. The primordial rare-gas contents of different pieces of Bishunpur, Krymka and Mezo-Madaras vary substantially, indicating that these meteorites are inhomogeneous in this respect. The heavy gases Ar, Kr and Xe are “planetary” in the sense of the model of Signer and Suess . The average primordial Ar86:Ar38 ratio of nine cases is 5.35 ± 0.16. Except for Xe129, the isotopic composition of Xe agrees with that of “average carbonaceous chondrites”. Carbonaceous chondrites, unequilibrated ordinary chondrites, and ordinary chondrites proper form a sequence of decreasing contents of primordial rare gases of the “planetary” type. This is consistent with a recent theory by Larimer and Anders on the formation of these meteorites. We infer from our results, however, that neon does not belong to the “planetary” component.

THE STABLE ISOTOPE COMPOSITION OF MINERAL WATERS IN THE JORDAN RIFT VALLEY, ISRAEL.

The stable isotopic composition (18O and 2H) of the mineral water sources in the Jordan Rift Valley suggests that these sources evolved through a two stage mixing process. It is postulated that sometime in the past waters of a slightly evaporated seawater lake had mixed with the prevailing groundwaters, to form different fossil brine pockets along the Rift Valleys floor. These brines mix nowadays with present-day local groundwaters and in some cases also with lake waters from adjacent Lake Tiberias or the Dead Sea. There is no evidence of marked changes in the isotopic content of the water concerned by exchange with rocks or by other fractionating processes.

Natural gas association with water and oil as depicted by atmospheric noble gases: case studies from the southeastern Mediterranean Coastal Plain

A model for the equilibrium distribution of atmospheric noble gases (ANG) between natural gas and water phases was extended to include the gas-oil relationship. The basic assumption is that the ANG are introduced into hydrocarbon systems via recharge or seawater. Theoretical ANG patterns of natural gas, at equilibrium with water, fall between the air pattern and that of air-saturated water. Theoretical ANG patterns of natural gas degassed from oil (which had previously equilibrated with a water phase) cover a wide range, including the range calculated for gas-water equilibration. ANG patterns in natural gas which fall outside the overlapping range may, thus, indicate association of the gas with oil. The model was tested in the case of hydrocarbon systems of the southeastern Mediterranean Coastal Plain. Other geochemical evidence indicates that the Ashdod-Sadot shallow gas wells are not related to oil. The relative ANG abundances in gas samples from these wells lie within the range predicted for gas-water association. The relative ANG abundances in samples degassed from oils of the Helez-Kokhav oilfield are similar to specific patterns predicted for the degassing of oil which was previously associated with water. Published and new analyses of methane-dominated natural gas samples from California, Japan and northern Israel also reveal ANG patterns of the type predicted by the model. The results of the case studies support our hypothesis that water is responsible for transport of atmospheric noble gases into subsurface hydrocarbon systems. This forms the basis for identification of oil-associated natural gases via ANG study.

More on noble gases in Yellowstone National Park hot waters

Abstract Water and gas samples from research wells in hydrothermal areas of Yellowstone National Park, U.S.A., have been mass spectrometrically analyzed for their rare gas contents and isotopic composition. In agreement with previous findings, the rare gases have been found to originate from infiltrating run-off water, saturated with air at 10 to 20°C. The atmospheric rare gas retention values found for the water varied between 3 and 87 per cent. The fine structure of the Ar, Kr and Xe abundance pattern in the water reveals fraotionational enrichment of the heavier gases due to partial outgassing of the waters. Radiogenic He and Ar have been detected. No positive evidence for magmatic water contribution has been found. Nevertheless, additions of magmatic waters free of rare gas can not be excluded, but if present the proportion is significantly less than 13 to 36 per cent.

Primordial gases in the Jodzie howardite and the origin of gas-rich meteorites

Abstract The dark portion of Jodzie contains primordial gases at nearly the same levels as Kapoeta, another brecciated howardite. All five gases, He—Xe, are enriched twofold in a magnetic concentrate relative to an unfractionated sample. A similar enrichment is shown by Ni. The uniform enrichment of the gases shows that the solar and planetary components are covariant, and were presumably introduced together. Much smaller amounts of gas are found in the light portion. The dark portions of Jodzie and several gas-rich meteorites are enriched in Kr, Xe, C, Ni, Br and Bi in nearly the exact proportions in which these elements occur in carbonaceous chondrites. This supports the suggestion of Muller and Zahringer that the noble gases were introduced via a “carrier” of carbonaceous chondrite composition, admixed to a level of 1–15 %. Presumably this “carrier” consisted of interplanetary dust bombarded by the solar wind, which was accreted by the meteorite parent bodies and then incorporated in a breccia during impact. Apparently material of carbonaceous chondrite composition comprises a major part of the dust in the asteroid belt. The saturation level of He 4 in interplanetary dust is estimated as 1 × 10 18 −3 × 10 19 atoms/g, in good agreement with the He 4 content in the “carrier” inferred from the observed gas and trace element content of gas-rich meteorites.

Hydrological applications of noble gases and temperature measurements in underground water systems: Examples from Israel

The observations on the behavior of the noble gases in the hydrological cycle may provide the tools to calculate the initial noble-gas contents in recharging water. This is essential for: (a) the use of the noble gases as tracers in geothermal systems; and (b) the evaluation of initial noble-gas contents in ancient waters for paleotemperature studies. Noble-gas contents in four non-karstic and three karstic springs were repeatedly measured, along with the temperatures in the recharge and discharge points. The Ar, Kr, and Xe contents in non-karstic springs are found to reflect the temperature of the base of the aerated zone above the water table. This temperature is seen to be close to the local average annual temperature and different from the rainy season temperature. The difference between the temperature measured at a spring and the noble-gas-deduced temperature indicates the depth of circulation in the saturated aquifer and thus may enable one to recognize the recharge area (e.g., local rain or recharge from adjacent mountains). Karstic springs are found to contain substantial air excesses, revealing a negative correlation to discharge. These air excesses are attributed to air present in some parts of the karstic systems, more so in the low-discharge season than in the high one. This air is sucked in by the water when it rushes through narrow parts of the system. Excess air may provide a tracer for karstic waters.

Geochemical tracing of mineral and fresh water sources in the Lake Tiberias Basin, Israel

Some two hundred sixty analyses of K, Na, Ca, Mg, Br, Cl, SO4, HCO3, from over seventy water sources around the Lake Tiberias basin were studied. Using these analyses as a geochemical tracing tool, four compositional-geographical water subgroups were found. These are: (1) Fulya-Barbutim-Tabcha; (2) Tiberias City; (3) Zemach; (4) Ein Gev. In spite of the minor differences between these subgroups, all these waters belong to one compositional association, which includes also the Beit Shean springs and some 22 sources in the south western part in the Dead Sea basin (the Kikar-Noit subgroup1)). The name “Tiberias-Noit water association” is suggested for these waters, which are found in a segment of over 150 km of the Rift Valley. The composition and maximum concentrations of the Tiberias-Noit water association are quite close to the oceanic values.

The origin of the Tiberias-Noit mineral water association in the Tiberias-Dead Sea Rift Valley, Israel

Abstract The genesis of the mineral waters of the Tiberias-Noit water association is discussed. This water association includes some 150 wells and springs around Lake Tiberias, tens of springs in the Beit Shean Valley and 22 sources on the Dead Sea shores. It is proposed that the ocean had in the past a temporary connection to the Rift Valley. The invading waters infiltrated and impregnated porous rocks in various fissured and faulted blocks that were under tectonic tension. In this way enormous amounts of water with initial oceanic salt composition were trapped in separate reservoirs. Exchange reactions with the country rocks changed the composition of the waters slightly in the various traps. Continuous reconstitution of the tectonic structures in the Rift Valley brought part of the permeated blocks under compression and the brines are squeezed out and pushed upwards. These brines are mixed, in various degrees with local fresh waters. Other genetic models are described and discussed.