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The so called Maxwell’s demon is considered as a paradox of statistical thermodynamics. Velocities of molecules are distributed in a gas according to a certain rule. At every temperature, the gas is composed of fast (or hot) and slow (or cold) particles. In this medium, a closed vessel is placed. In the wall of this vessel, there is a gate (or valve), which is operated by the “demon”. When observing...
A comprehensive approach to study of the late Phanerozoic, as a time interval with common geologic evolution, is substantiated by marine Sr-isotope stratigraphy demonstrated persistently increasing 87Sr/86Sr ratios in sea water from 0.7068 to 0.7092 in the past 160 Ma. The preceding time interval of 320–210 Mawas marked by 87Sr/86Sr ratios as high as 0.7078–0.7084 with a single minimum of 0.7070 centered...
We shall not discuss the philosophical contents of the concept “time”. Geochronology deals with functional time, providing a measurement procedure not of the time itself, but of values that are included in a certain law that gives time through other parameters. For instance, the time of passage by an airplane at some distance is calculated by division of the distance of passage into speed. The time...
Comparisons of the Baikal, Rio Grande, and East African intracontinental rifts have demonstrated similarities of the rifted continental regions in terms of structural features, high heat flow, seismicity, thinned lithosphere, low-velocity sub-lithospheric mantle domains, and accompanied magmatism (Florensov 1948; Logatchev 1977; Lipman et al. 1989; Rasskazov 1993; Barry et al. 2000). We consider continental...
Rocks and minerals might occur in conditions of elevated temperatures favorable for accelerated diffusion processes. This results in accumulation of radiogenic isotopes in rocks and K–Ar isotope system in the Laplace diffusion losses. It is important to define boundary conditions of such an isotope system. As diffusion losses increase, the rate of accumulation of daughter substance approaches zero...
By U–Pb, Rb–Sr, and K–Ar methods, an age interval from 5.0 to 2.8 Gawas estimated for the oldest rocks in the Earth in the late 1950s. Model ages of 5.3–4.5 Ga were calculated from abundances of 40K (Starik 1961) and at ca. 4.6 Ga from mean concentrations of 40K in crust and 40Ar in atmosphere (Brandt 1965; Schwartzman 1973). The latter age was substantiated using more precise dating of meteorites...
At closure of a parent–daughter system some (initial) quantity of daughter substance is frequently observed. The age definition becomes impossible. To make a detour around this difficulty, an isochron model is applied.
The main advantage of the system—two series of radioactive decay: 238U→ 206Pb and 235U→ 207Pb—provides reliable results of dating (Faure 1989; Dickin 1997). The ages are calculated in the U–Pb, Pb–Pb, and mixed coordinates with simultaneous measurements of 206Pb/238U, 207Pb/235U, and 207Pb/206Pb ratios (Ludwig 2000).
Obtaining spectra of argon release from minerals and rocks by stepwise heating is at present an indispensable part of age determination by means of the 40Ar/39Ar method. A probe is subjected to heating in a vacuum vessel at temperatures increasing stepwise, for instance 700, 900, 1100Ketc. The duration of heat treating at every step is usually constant, for instance, 10 min. Argon released at every...
High precision geochronological studies require understanding of relations between apparent (measured) K–Ar ages and various episodes in a cooling history of magmatic bodies: intrusion of liquid magma, chemical closure of a magmatic system (decreasing temperature below a solidus), and closure of a parent–daughter isotope system. There arises a number of problems connected not only with distortions...
Recent decades have brought enormous progress in analytical laboratory techniques and publication of many high precision results on radioactive isotope systems. The measured isotope ratios are usually shown in data tables and graphs with standard deviations of 5 or 6 true ciphers. Often, the measured results are considered as an ultimate step for an isotope study. The precise data presume however...
A geologic time scale is conventionally considered as equivalent to a biological time scale that is based on evolution of life on the Earth. Using radiogenic isotopes is critical for understanding short-term geologic processes responsible for quick reorganizations of ecosystems at geologically important boundaries. In the Phanerozoic, significant events of mass extinctions occurred in the Early Cambrian,...
During development, the potassium–argon method was subjected to proofs of radiogenic argon safety in geologic processes. Minerals were heated to determine kinetic parameters of diffusion in them. Then, using theArrhenius equation, the diffusion parameters were extrapolated to lowtemperatures of geologic sites. Thus, the suitability of many rock-forming minerals for age determinations was established.
Radiogenic isotope dating of ore deposits is ambiguous. In many cases, different isotope systems yield inconsistent results. It remains unclear, which mineralization processes are marked in ore deposits by ages obtained and when ore substance was deposited relative to processes responsible for launch or reset of different isotope systems.
This book presents a modern approach of radiogenic isotope methods for solutions on problems in theoretical and practical geology. New approaches on thermochronology are of particular interest. Results on age measurements for timing of the Earth’s formation, main stages in evolution of biota in the Phanerozoic, and the most important tectonic and magmatic events in the Late Mesozoic through the Cenozoic...
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