3He4He ratio,noble gas abundance and K-Ar dating of diamonds—An attempt to search for the records of early terrestrial history

The ${}^3\text{He}{}^4\text{He}$ ratios measured in 27 Southern Africa diamond stones, four from Premier Mine and the rest of unidentified origin, range from 4.2 × 10^?8 to 3.2 × 10^?4, with three stones above 1 × 10^?4. We conclude that the initial helium isotopic ratio (${}^3\text{He}{}^4\text{He)}{}_0$ in the earth was significantly higher than that of the planetary helium-A (${}^3\text{He}{}^4\text{He = 1.42 × 10}{}^{\mathrm{?4}}$), but close to the solar helium (${}^3\text{He}{}^4\text{He ? 4 × 10}{}^{\mathrm{?4}}$).The apparent K-Ar ages for the twelve diamonds of unidentified origin show enormously old age, indicating excess argon-40. ${}^3\text{He}{}^4\text{He}$ evolution in diamonds suggests that the diamonds with the high ${}^3\text{He}{}^4\text{He}$ ratio (>2 × 10^?4) may be as old as the earth.Noble gas elemental abundance in the diamonds relative to the air noble gas abundance shows monotonie decrease with a decreasing mass number.This paper discusses the implications of these observations on the early solar system and the origin of diamonds.     

Sedimentary noble gases

This paper presents experimental data for the trapped noble gas contents in a variety of shales and related samples. These data, along with those previously available, indicate that the normal sedimentary rock pattern is one of progressive enrichment of the heavier gases in comparison with the proportions in air, from which sedimentary rock gases were presumably acquired. Within this normal pattern, however, variations considerably beyond an order of magnitude characterize both abundance and composition, so that multiple processes appear to be necessary to account for trapping of noble gases in sedimentary rocks. Relative to the normal pattern a number of cases of anomalous Ne enhancement occur. This unexplained phenomenon, previously thought to be exotic, must now be considered unexceptional.Noble gases in air occur in approximately the ‘planetary’ proportions characteristic of meteorites, except for more than an order of magnitude deficiency of Xe. It is commonly held that atmospheric noble gases are indeed planetary, the Xe deficiency in air being made up by the inventory in sedimentary rocks. We consider that while this hypothesis cannot be proved false the available data do not support it. At least equal weight should be given to the alternatives: either that (preferentially) Xe has failed ever to become part of the atmosphere or that the total terrestrial noble gas inventory is simply not planetary.     

Additional evidence of existence of ancient rocks in the mid-Atlantic ridge and the age of the opening of the Atlantic

A metabasalt dredged at a junction of the median valley with the Atlantis fracture zone (30°01/tN, 42°04/tW) in the Mid-Atlantic Ridge shows complete recrystallization under a metasomatic condition, though the original igneous texture of a coarse-grained basalt is still recognizable. There is strong circumstantial evidence suggesting that this rock is not an ice-rafted erratic, but an authentic Mid-Atlantic Ridge rock. The ⁴⁰Ar-³⁹Ar age of this sample is 169 m.y. (Jurassic) which should represent the time of recrystallization. The initial value (^87Sr/86Sr)_O is 0.720, far above the values previously observed in oceanfloor basalts, including both tholeiitic and alkalic rocks (0.701–0.704). Sr with such a high isotopic ratio is considered to have been introduced by metasomatism during metamorphism by a solution coming from a continental mass or masses which were then located very close to the Mid-Atlantic Ridge. The ⁴⁰Ar−³⁹Ar age of sample AM50 may approximate the time of the commencement of the opening of the Atlantic. All these data support the possible existence of ancient rock masses in the Mid-Atlantic Ridge, as was formerly claimed by Bonatti, Melson and others.     

Major-element petrochemistry of some extrusive rocks from the volcanically active Mariana Islands

Volcanic rocks from six of the currently or recently active volcances of the Mariana Island are show little variation in major element abundances. SiO₂ content averages 51.5 wt.%. The flows are high in Al₂O (mean 17.7 wt.%) and Fe oxides (mean 10.1 wt.% calculated as FeO only), and moderate in MgO content (mean 4.7 wt.%), Na₂O (mean 2.7 wt.%), and K₂O (mean 0.7 wt.%). Only the rocks from Farallon de Pajaros, the northernmost of the Mariana Islands, deviate slightly from the average of the analyses. Three analyses from this island are slightly higher in SiO₂ (about 54 wt.%) and Al₂O₃, and are lower in total Fe oxides and MgO. According to preferred classification, the lavas of the Mariana Islands can be termed mela-andesites, high-alumina basalts, or calc-alkaline (orogenic) basalts. The K₂O values (mean 0.7 wt.%) obtained from lavas of the Mariana Islands are significantly higher than the K₂O values (about 0.33 wt.%) from volcanics of the Izu chain to the north. Inasmuch as the substantial scatter in location of earthquake foci beneath both arcs prevents accurate delineation of the upper boundary of the Benioff zone, it presently cannot be determined whether this discrepancy in K₂O values reflects a difference in depth from the volcanic are to the dipping seismic zone or relates to other phenomena. The older volcanic islands within the Mariana-Bonin island chain apparently defined an island arc system during Eocene to Miocene time. This indicates that the present plane of convergence between the Pacific plate and the Philippine Sea plate has defined the convergence between these plates since Eocene time.     

Effects of a plastic deformation on the remanent magnetization of a Cu-Co alloy

Compressional plastic deformation of a Cu-Co alloy in which Co particles (submicron to a few tens of microns in diameter) were precipitated in a Cu matrix resulted in a systematic rotation of remanent magnetization (IRM atH = 1000Oe) away from the axis of compression with increasing degree of the deformation.     

Experimental studies of He and Ar degassing during rock fracturing

We studied degassing of He and Ar from granite, basalt and volcanic tuff samples which were subjected to uniaxial compression. From the samples which were fractured in the dilatant region He was always degassed, while degassing of Ar dependent not only on the dilatancy, but also on the type of rock and the compressional conditions such as wet, room dry or vacuum conditions. It is concluded that degassing of rare gases from the compressed samples depends primarily on the generation of new surface area by dilatancy.     

Deuterium abundance of natural waters

The deuterium abundance of natural water of various sources has been determined by the use of a deuterium mass spectrometer. The absolute deuterium contents of the reference sample nos. 1 and 1a of the U.S. National Bureau of Standards were found to be 0·0149 and 0·0128 mole % D₂O, respectively, by the comparison of the samples with the standard samples of known deuterium content. Relative enrichment of no. la to no. 1 (R_1a−R₁)/R₁×100 was 14·13 ± 0·23, which agrees perfectly to the value reported by . The variation of deuterium contents of tap waters of Tokyo and Osaka during last 2 years were within ± 1 per cent and any seasonal regularities could not be detected. Marine waters of the West Pacific have almost the same deuterium content as those of the Pacific coast of the United States. Marine waters at various depths of the Antarctic showed relatively large variation of deuterium content (from +0·84 to −1·16 per cent on the SMOW-scale), whereas the samples of Black Current of the Pacific showed little variation. It was found that the deuterium content of spring water suggests the origin of springs in some cases.     

Orphan radiogenic noble gases in lunar breccias: evidence for planet pollution of the Sun?

Surface-correlated noble gases in lunar soils are primarily implanted SW (solar wind) noble gases. However, they also include apparently orphan radiogenic ⁴⁰Ar, ¹²⁹Xe, and ²⁴⁴Pu-derived fission Xe in excess of plausible primordial solar origin. These orphan radiogenic components are usually assigned a lunar origin, in a scenario in which radiogenic noble gases produced in the lunar interior were degassed into the transient atmosphere and then re-implanted to the lunar surface together with SW. There are some quantitative difficulties with this scenario, however, and it requires special constraints on the degassing history of the Moon that have not emerged from more general thermal history models. We therefore urge consideration of alternative hypotheses. As a possible source for the orphan radiogenic noble gases, we have examined planetary pollution of the Sun, as suggested by studies of extrasolar planetary systems (e.g., Murray et al., 2001, Astrophys. J. 555, 801-815; Israelian et al., 2001, Nature 411, 163-166). Pollution of the Sun by 2M_⊕ (two Earth mass) planetary materials (Murray et al., 2001, Astrophys. J. 555, 801-815) is likely not significant for Ar but could be important to account for orphan Xe in the Moon.