ABSTRACT
This chapter considers processes operating at the present day, which have their own dynamics, topographic expression, seismicity, geophysical fields, etc. and can provide the maximum data about their mechanism and character. Present-day geodynamic environments and their related igneous activity are known to be continuations of geological processes initiated in the Mesozoic but associated mainly with the Late Cenozoic. In both the diversity of its rocks and its extent, magmatism at lithospheric plate boundaries vastly exceeds within-plate magmatism, accounting for about 90% of all magmatic activity. Oceanic rift zones where sea-floor spreading and accretion of the oceanic crust take place are assigned to constructive geodynamic environments. These zones are known as mid-oceanic ridges, and they form a system extending for more than 60,000 km and girdling the whole of the Earth’s surface. At present, two types of magma series: tholeiitic and moderately potassicsodic alkaline, can be recognized within mid-oceanic ridges.
