O.G. SHULYATIN (VNIIOkeangeologia), B.V. BELYATSKY (VSEGEI), A.A. KREMENETSKY (IMGRE)

Geochemical and geochronological studies of polychronic zircons in igneous rocks from the Mid­Atlantic Ridge and some features of its structure

Polychronic zircons in basite-­ultrabasite igneous rocks from the Mid-­Atlantic Ridge have been studied. A number of features distinguishing oceanic crust formation were discovered following the zircons’ age determination. It was found out, that along with young zircons, whose age is close to the time of Cenozoic basalt eruption, more ancient (xenogenic) zircons occur in the rocks. It was determined how young zircons differ from ancient ones in their morphological features, internal structure, crystallization temperature, and REE content. Discrete concentrations in zircon dating, coinciding in their manifestation time with tectonic-­magmatic epochs in the adjacent continents were identified. In accordance with the geological data, it appears that the present crust in the Atlantic Ocean represents a basement composed of Archean-­Paleozoic basite-­ultrabasite dislocated and metamorphosed rocks along with Pleistocene-­Holocene unmetamorphosed effusive and sedimentary rocks.
Keywords: Mid­Atlantic Ridge, age determination, polychronic zircon, protocrust.