GEOCHRONOLOGY OF THE CHADOBETS ALKALINE ULTRAMAFIC CARBONATITE COMPLEX (SIBERIAN CRATON): NEW U-Pb AND Ar-Ar DATA

Abstract

The Chadobets alkaline ultramafic carbonatite complex is located on the Siberian craton within the southern boundary of the Permian-Triassic plume activity. The dating of xenogenic zircons from the weathering crust of carbonatites of the Chuktukon complex yielded four clusters with ages of 1870-1820, 495-385, 290-210 and 215-162 Ma. The first two clusters correspond to the dates of activity of Paleoproterozoic granitoid magmatism and Paleozoic alkaline-mafic tectono-magmatic activity, widely occurred in the Siberian craton and its southern framing. The age of crystallization of alkaline rocks of the Chadobets complex falls within the interval of 255-240 Ma. Ar-Ar dating of damtjernite and carbonatite minerals of the Chuktukon complex falls within the intervals of 250.5±3.7 and 247.1±5.7 Ma, respectively. The crystallization ages of the mela-aillikites and damtjernites of the Terina complex, according to the Ar-Ar dating, correspond to the intervals of 257.4±3.9, 241.1±3.7, and 240±3.6 Ma. The age interval of 215-162 Ma based on zircons from the carbonatite weathering crust of the Chuktukon complex reflects the geochronology of superimposed processes and indicates the different stages of alteration of igneous rocks of the Chadobets complex. The data obtained on the age of crystallization of alkaline rocks of the Chadobets complex are consistent with the age interval of Siberian plume activity within a large igneous province (LIP).

Petrogenesis of juvenile pelletal lapilli in ultramafic lamprophyres

“…1 b). Crystallization age of rocks from the Chadobets complex lies within the range of 255–240 Ma 7 , 8 , 11 , 26 , which coincides with the Paleozoic–Mesozoic magmatic events of the Siberian large igneous province (LIP). The emplacement of the Chadobets alkaline rocks was coeval with intrusions associated with the flood basalts 27 , 28 , carbonatites and UMLs of the Maymecha–Kotuy province 29 – 32 , as well as with Siberian kimberlites from Anabar and Olenek region, and some lamproite intrusions 27 , 33 – 35 (Fig.…”

“…The last magmatic phase within the complex is represented by damtjernite dykes and pipes usually 150 × 200 m in size near the surface (Fig. 1 b) 7 , 8 , 11 , 12 , 14 , 26 .…”