Home – Home – Jornals – Russian Geology and Geophysics 2003 number 9

We have discovered almost unaltered porphyritic potassium-rich alkaline-ultrabasic rocks in the central Tomtor Massif and have first carried out an X-ray microanalysis of the hosted minerals (phlogopite, leucite, clinopyroxene, amphibole, K-feldspar, etc.). Using modern analytical methods (neutron activation and X-ray fluorometry), we determined the contents of 43 major, trace, and radioactive elements and CO₂ in 16 samples of differently carbonatized porphyritic rocks and estimated the content of CaO in the unaltered rocks. A correlation analysis showed that during carbonatization, the rocks received Ca, Nb, REE, Sr, and Ba and lost Si, Ti, Mg, and Na, thus transforming into rocks compositionally similar to kamafugites. The obtained structural data on concentric faults, horizontal separations, phenocryst orientation, etc. suggest that the studied potassium-rich alkaline-ultrabasic rocks are volcanics that occur in a subsidence caldera 6-10 km across. Based on the classification diagrams of Holmes, Foley et al., and La Roche, we have established that the porphyritic rocks are dominated by lamproites. The Tomtor Massif includes a unique