9612113 Renne This project is to conduct a multi-disciplinary study of field, petrologic, geochemical. isotopic and geochronological study of a suite of ultrabasic-alkaline and mafic rocks of Maimecha-Kotui region of the northern Siberian platform. The volcano-plutonic complexes of this region are closely associated in time and space with the Siberian Flood Basalt Province (SFBP) of permo-Triassic age. As part of this study The P.I.s will also include the kimberlites with the alkalic and tholeiitic pulses of the SFBP mantle plume. Preliminary data on 3He/3He measurements in olivines of the alkalic rocks suggest a lower mantle source for the 3He and links the alkalic-Maimecha phase to the plume-related SFBP. More noble gas isotope ratio measurements (He, Ne, Ar and Xe) are needed for confirmation. 40Ar/39Ar age dating of kimberlites and of the ultrabasic-alkaline and mafic rocks of the 2.8 km thick Maimecha-Kotui volcanic section are proposed to determine age and duration of volcanism. Nd, Sr, Pb-isotopic and trace elemental analyses, including the rare earth elements by TCP-MS, will also be performed on these rocks during the two-year tenure of the grant period. The analytical results will be used to examine whether there is a common petrogenetic link (e.g., mantle-derived plume) for the origin of the Kharamai kimberlites, the ultrabasic-alkaline and mafic volcanic rocks of the Maimecha-Kotui section, and for the voluminous, predominantly tholeiitic SFBP. In the event that these data do not support such a hypothesis, the acquired date will still be useful in formulating and substantiating other petrogenetic models.
