ИСТИНА

The time gap between crystallization and the formation of TRM in large intrusions can reach great values. Probably the only way to directly determine the age of TRM is to date using isotope data on various minerals (the thermochronology method). Mathematical modeling of the cooling rate makes it possible to simplify the research. In a similar way was in the study of the Early Proterozoic granites of the Kodar complex in the south of the Siberian craton. Granite batholiths lie in the Olekma block of the Aldan Shield. We studied for paleomagnetic analysis 769 samples from 5 massifs – At-Bastakh, Hani, Kemen, Ikabi and Kodar. Everywhere there were rocks suitable for obtaining a paleomagnetic poles. Primary nature of the high-temperature components of the NRM is confirmed by positive reversal test and coincidence of directions in the remote intrusions. Paleomagnetic pole Plat = -21.9 Plong = 101.8 A95 = 8.2 is obtained by averaging the poles of 5 massifs. Biotites and feldspats were sampled from the granites of At-Bastakh for 40Ar/39Ar investigations. A total of 12 spectra were obtained: the apparent ages of biotites lie within a narrow interval, 1837-1859 Ma, and the age of the feldspats were strongly rejuvenated. Taking into account the U/Pb zircon age of 1873+/-3 Ma (Larin et al, 2000), we obtained an interval of about 20 Ma between crystallization of the rock and cooling down to 300 degrees. Such a value is difficult to obtain with the help of mathematical modeling. Preliminary mathematical modeling showed that at "instantaneous" intrusion the time gap between the closing temperatures of the isotope systems of zircon and biotite does not exceed 1 million years. The most likely explanation for the discrepancy is the time-stretched intrusion, because all massifs have a two- or three-phase structure.