ENDOGENIC CYCLES AND THE PROBLEM OF CRUSTAL GROWTH

Abstract

The statistical analysis of geochronological data (more than 14200 dates) has been carried out by using the method of the probabilistic description of summary information on the crust and mantle and separately on both of the Earth's upper shells considered together over the whole geological history. Various lines of evidence are presented for the necessity of using the whole set of geochronological methods to reveal any systematic pattern in the evolution of crust formation and to demonstrate the uselessness of utilizing selected data obtained by any one of the methods because of the limited analytical capability of each of them. These constraints, together with compositional variations of the dated rocks and the variable amount of the initial information, lead to uncertainty in estimation of megacyclicity as a sum of contrasting dynamics of endogenic events occurring in the crust and the mantle. It has been shown that mantle processes become more intense during periods of the synchronous activation of endogenic events in both shells; mantle activity sharply decreases in the epochs when endogenic processes in these shells are waning. This difference may serve as an objective criterion for estimating the maximum duration of cycles of mantle activity, which is distinct in the Early-Middle Archean, Late Archean-Proterozoic, and Phanerozoic. These conclusions are supported by examples of geochronological systematics for cratons of northeastern Labrador, western Greenland, and western Australia. © Pleiades Publishing, Inc. 2006.