The Origin and Physico-Chemical Properties of Some Unusual Earth Rock Fragments

In this paper, several researches were undertaken related to a violent phenomenon, characterized by a sonic boom, felt on an area of at least 500 km2, shortly followed by the fall of rock fragments that were then recovered from the ground. These presented different appearance characteristics from those of the materials and rocks specific to the respective area. Spectroscopic and petrographic analyses were performed to identify the composition, morphological and crystallinity characteristics in order to elucidate the nature of the collected rock samples. Using FTIR spectroscopy functional groups, as those reported in the literature for Murchison, Bells and Allende, carbonaceous chondrite meteorites were identified. The fragments evidenced topography and morphology that can be assigned to the chondrules and chondrites of carbonaceous meteorites (CMs). The material in the fragments proved to be as insoluble organic material (IOM), being insoluble in water and organic solvents. Its crystalline structure was also evidenced by XRD analysis and FTIR spectrum. These physico-chemical properties, in relation to the sonic boom perceived in the area from where they were collected, indicate the spatial origin of the fragments of rock as possible meteorite fragments.

A Model for Plate Tectonic Evolution of Mantle Layers

In plate tectonic theory, lithosphere that descends into the mantle has a largely derivative composition, because it is produced as a refractory residue by partial melting, and cannot be resorbed readily by the parent mantle. We suggest that lithosphere sinks through the asthenosphere, or outer mantle, and accumulates progressively beneath to form an accretionary mesosphere, or inner mantle. According to this model, there is an irreversible physicochemical evolution of the mantle and its layers. We make the key assumption that the rate at which mass has been transferred from the lithosphere to the mesosphere is proportional to the rate of radiogenic heat production. Calculations of mass transfer with time demonstrate that the entire mass of the present mesosphere could have been produced in geologically reasonable times (3 x 10(9) to 4.5 x 10(9) years). The model is consistent with the generation of the continental crust during the last 3 x 1O(9) years and predicts an end to plate tectonic behavior within the next 10(9) years.

Potassium, Rubidium, Strontium, Thorium, Uranium, and the Ratio of Strontium-87 to Strontium-86 in Oceanic Tholeiitic Basalt

The average concentrations of potassium, rubidium, strontium, thorium, and uranium in oceanic tholeiitic basalt are (in parts per million) K, 1400; Rb, 1.2; Sr, 120; Th, 0.2; and U, 0.1. The ratio Sr(87) to Sr(86) is about 0.702, that of K to U is 1.4 x 10(4), and of Th to U is 1.8. These amounts of K, Th, U, and radiogenic Sr(87) are less than in other common igneous rocks. The ratios of Th to U and Sr(87) to Sr(86) suggest that the source region of the oceanic tholeiites was differentiated from the original mantle material some time in the geologic past.

Fossil Particle Tracks and Uranium Distributions in Minerals of the Vaca Muerta Meteorite

Fossil tracks of charged particles have been observed in minerals separated from the Vaca Muerta mesosiderite. Irradiation of samples of the meteorite with thermal neutrons in a nuclear reactor, together with measurements of track-length distribution, indicate that some of the tracks result from the spontaneous fission of uranium impurities; others, however, are of different origin. Uranium concentrations, which ranged from about 4000 parts per million in a zircon grain to less than 10(-3) parts per million in hypersthene and anorthite, were also measured by irradiating samples with thermal neutrons.