Home – Home – Jornals – Russian Geology and Geophysics 2003 number 11

We have studied the geologotectonic and petrochemical peculiarities of the occurrences of subalkaline ultrabasic lavas of the northern Siberian Platform. The constructed petrochemical diagrams evidence the existence of compact rock series from meymechites through porphyritic peridotites, picrite porphyries, picrites, and picrite basalts to plateau basalts. The TiO₂-MgO and K₂O/(K₂O + Na₂O)-MgO diagrams show a broad scatter of composition points. The K₂O-MgO diagram supports the existence of low-, medium-, high-, and superhigh-potassium rock series. We suggest that K serves as an indicator of the genetic relationships between the rocks from meymechites to plateau basalts (traps). Formation of K-rich magmas begins with metasomatism of the mantle substratum interacting with deep-seated K-enriched fluids. Then it gives way to potassic magma metasomatism of ultrabasic and daughter basic melts. Potassic magma metasomatism is distinguished by increased K₂O/(K₂O + Na₂O) of the melt with an increase in its Mg content.