International geological congress. Report of th twenty-third session / Международный геологический конгресс. Доклады 23 сессии. Тезисы докладов

(1) Metamorphic rock complexes with a density of about 3 g/cm3 under standard atmospheric pressure are a prevailing type of petrographic associations found in that part of the earth’s crust which is available to direct observation.

(2) Presumed rock densities within the deeper parts of the earth’s crust, when based upon the values of elastic wave velocities in a sample as well as within a massif, are not sufficiently reliable for an undeniable conclusion to be drawn about the petrographic composition of geophysical “layers” in the earth’s crust.

(3) Elastic properties of various substances being experimentally investigated, a certain relationship between the elastic wave velocity and material density is stated. Yet, this dependence appears to be largely affected by the porosity and ultraporosity of the material under test.

(4) The earth’s crust differentiation along the Mohorovici£ discontinuity into mantle and crust of highly contrasting composition must be soundly grounded as well as the conclusion about the “Moho” boundary, and the fixing of changes in the physico-mechanical properties of rocks.

(5) A logical explanation for two types of the “earth’s crust” - the continental and the oceanic one - as recognized from the “Moho” boundary position could be found provided that the “Moho” interface is interpreted as a zone of changes of physico-mechanical properties of rocks constituting a mosaic crust.

(6) Experimental physico-chemical investigations supply no evidence to suggest the “Moho” boundary below the ocean floor as a possible zone of transition for isochemical eclogite and basalt (gabbro).

(7) The sum total of geological and geophysical facts gives no grounds for an “oceanization” hypothesis of a continental crust or formation of an intermediate type crust to be framed.

(8) Due to an extremely complicated geological history of our planet, a concept of a uniform earth’s crust of mosaic composition presents itself as a most possible one.

The earth’s crust does extend deep downwards, exceeding in depth the “Moho” occurrence, and its even deeper extension, down to astenosphere, is not improbable. <...>