40Ar/39Ar Geochronology and New Mineralogical and Geochemical Data from Lamprophyres of Chompolo Field (South Yakutia, Russia)

Abstract

The alkaline igneous rocks of the Chompolo field (Aldan shield, Siberian craton), previously defined as kimberlites or lamproites, are more correctly classified as low-Ti lamprophyres. The emplacement age of the Ogonek pipe (137.8 ± 1.2 Ma) and the Aldanskaya dike (157.0 ± 1.6 Ma) was obtained using 40Ar/39Ar K-richterite dating. The Chompolo rocks contain abundant xenocrysts of mantle minerals (chromium-rich pyropic garnets, Cr-diopsides, spinels, etc.). The composition of the mantle xenocrysts indicates the predominance of spinel and garnet–spinel lherzolites, while the presence of garnet lherzolites, dunites, harzburgites, and eclogites is minor. The Chompolo rocks are characterized by large-ion lithophile element (LILE) and Light Rare Earth Element (LREE) enrichments, and high field strength element (HFSE) depletions. The rocks of the Ogonek pipe have radiogenic Sr (87Sr/86Sr (t) = 0.70775 and 0.70954), and highly unradiogenic εNd(t) (−20.03 and −20.44) isotopic composition. The trace element and isotopic characteristics of the Chompolo rocks are indicative of the involvement of subducted materials in their ancient enriched lithospheric mantle source. The Chompolo rocks were formed at the stage when the Mesozoic igneous activity was triggered by global tectonic events. The Chompolo field of alkaline magmatism is one of the few available geological objects, which provides the opportunity to investigate the subcontinental lithospheric mantle beneath the south part of the Siberian craton.