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.

Cr-pyrope xenocrysts with oxide mineral inclusions from the Chompolo lamprophyres (Aldan shield): Insights into mantle processes beneath the southeastern Siberian craton

“…Initial studies classified the Chompolo mantle-derived rocks as kimberlites (Shilina and Zeitlin, 1959); but they have been re-classified subsequently as lamproites (e.g. Bogatikov et al , 1991) or lamprophyres (Kornilova, 1997; Nikolenko et al , 2020b). Here we will refer to the Chompolo intrusions as lamprophyres on the basis of the most recent and accurate petrographic descriptions by Kornilova (1997) and Nikolenko et al (2020b).…”

“…Bogatikov et al , 1991) or lamprophyres (Kornilova, 1997; Nikolenko et al , 2020b). Here we will refer to the Chompolo intrusions as lamprophyres on the basis of the most recent and accurate petrographic descriptions by Kornilova (1997) and Nikolenko et al (2020b). Within the Chompolo district, there are six pipes (Ogonek, Gornaya, Perevalnaya, Sputnik, Intrusions No.…”

“…104 exhibit massive textures (Kornilova, 1997). Abundant (30–70 vol.%) xenogenic fragments are dominated by xenoliths of metamorphic rocks and xenocrysts of upper mantle origin (pyrope, diopside, enstatite, chromium spinel, phlogopite and Mg-rich ilmenite) (Kornilova, 1997; Nikolenko et al , 2020b). The majority of mantle-derived xenoliths are extensively weathered and disintegrated.…”

“…104 was available (131 ± 4 Ma, Rb–Sr isochron ages of phlogopite; Zaitsev and Smelov, 2010). Nikolenko et al (2020b) provided additional age constraints for the Aldanskaya dyke (157.0 ± 1.6 Ma) and Ogonek diatreme (137.8 ± 1.2 Ma) on the basis of K-richterite Ar–Ar radiometric ages. For the lamprophyre sills located in the nearby Upper Amga alkaline complex, ages in the range of ca.…”

“…Although the scientific possibilities to explore these rocks have been hindered by their remoteness and inaccessibility, research of the petrology and geochemistry of lamproites, carbonatites and complex alkaline massifs has been carried out (e.g. Makhotkin et al , 1989; Bogatikov et al , 1991; Mitchell et al , 1994; Mues-Schumacher et al , 1995, 1996; Kornilova, 1997; Vladykin, 1997, 2009; Davies et al , 2006; Nikolenko et al , 2020b). The studies of lamproites, which are the dominant deep-seated rocks of mantle origin within the Aldan shield, were partly stimulated by the discovery of diamondiferous lamproites in West Kimberley, Western Australia (Jaques et al , 1984) and Prairie Creek, USA (Smith and Skinner, 1984).…”