46
As a result of the new largest cycle of the expansion of the Earth,
which has begun in early Mesozoic, the supercontinent Pangea III begins to
disintegrate into modern continents, separated by oceanic depressions of
Pacific and the new formed Atlantic, Indian and Arctic oceans. The
Lavrasians and Gondwanas supercontinents were also exposed to processes
of riftogenesis and destruction, tectono-magmatic activating, transgressions
and regressions of the seas with formation of various types of mineral
deposits.
The expansion of the Earth supposes a cyclicity of core decomposition.
At the beginning of every cycle, hydrogen must have evolved rapidly. It
must later have been reduced as fast decomposition set in. Intense hydrogen
degassing should then have set off a geosynclinal
cycle of tectono-magmatic
events on the surface. The waning stage of degassing and decomposition of
the core should have resulted in the expansion of oceanic depressions.
Logically, after orogeny, continents should have quiescent tectonic regimes.
Tectonic activity at this stage is restricted mainly to the expanding the Earth
at rifts. As we correlate the causes of geological evolution with cyclic
decomposition of the earth’s core, a logical conclusion to be drawn is that
geotectonic episodes should be synchronous worldwide. This observation is
a truism of major cycles, the Alpine, Kimmeridgian, Hercynian, etc.
However, the major episodes may also have subsysles and spasms of
orogeny due to physico-mechanical properties of the crust and mantle. The
hydrogen degassing events, which replenish the water reservoirs of the
hydrosphere, and the decomposition phenomena that
responsible for ocean
expansion, should combine to give eustatic oscillations of see level.
Oscillations of this sort have caused marine transgressions and regressions
over the platforms. The increment of planetary water resources
from interior
sources at the geosynclinal stage is considered responsible for
transgressions over non-geosynclinal regions, whereas ocean basin
expansion by deepening is thought to have triggered regressions. These
interrelationships seem to tie in with the geological realities of distinct
tectonic movements in geosynclines and on platforms. Expulsion of water
to the surface must have occurred mainly at the orogenic stage, as the
asthenoliths rose (Larin, 1980).
V.1. C o n t i n e n t a l p l a t f o r m s. In Mesozoic-Cenozoic, the
deposits of siderophile elements were widely spread on the platforms of
Lavrasia, but the occurrences of chalcophile and lithophile elements are less
expanded. The sedimentary deposits of iron and manganese are dominant.
Among the diamond a rich placers and primary deposits of kimberlite,
lamproite and impactite types prevailed. The examples of the last are
Popigai and Kara ring’s structures in Russia and the meteoritic crater Devil
in state Arizona USA (Маsaitis et al., 1998). Chalcophile elements are
represented by hydrothermal and sedimentary deposits of gold and copper.
Among lithophile elements there are sedimentary and
hydrothermal deposits
of uranium, vanadium, titanium, molybdenum, salts of sodium, potassium
and barium, fluorite and icelandic spar. With carbonatites the deposits of