SOME PECULIARITIES OF THE PRECAMBRIAN EARTH EVOLUTION

Some latest researches show that the Archean Greenstone Belts are not related to the ocean crust (Bickle et. Al., 1994), and peridotite component in rocks of those belts is less than 1 %. Absence of clear evidence of oceanic sediments older than Proterozoic age is also well known (Condie et. al. 2000), as well as absence of peridotites, ophiolites, and serpentinites older than the Early Proterosoic. Incompatibility of olivine with quartz, and wide spread of Early Precambrian Iron formations could be the result of unsuccessful attempt of olivine (and peridotite) formation during that period. These facts point at absence of present type ocean crust (with main peridotite layer in it) before the Proterozoic and possible absence of present type oceans. On the other hand our research show that present type of ocean crust was formed not earlier than in the Early Proterozoic. The main periods of ocean crust activity and ophiolite belts formation during the Precambrian are the end of Early Proterozoic – beginning of Middle Proterozoic, Grenvillian, and the end of Late Proterozoic. These periods are also the main periods of most powerful orogenic processes in the Precambrian. Periods of olivine and peridotite formation in continental regions coincide with carbonatite activity in those regions with following development of kimberlites. Periods of serpentinization, and ophiolite formation in the ocean regions coincide with formation of thick evaporitic layers, carbonate layers (even carbonate platforms, mostly in the Phanerozoic), and periods of C13 excursions. In the Phanerozoic these processes coincide with periods of climate warming, sea level transgressions, and mass extinctions. Latest most powerful earthquakes also coincide with regions of serpentinization and/or ophiolite formation.