Permo-Triassic hypabyssal mafic intrusions and associated tholeiitic basalts of the Kolyuchinskaya Bay, Chukotka (NE Russia): Links to the Siberian LIPстатья
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Аннотация:In order to test tectonic hypotheses regarding the evolution of the Arctic Alaska–Chukotka microplate
prior to the opening of the Amerasian basin, we investigated rocks exposed near Kolyuchinskaya Bay,
eastern Chukotka. Hypabyssal mafic rocks and associated basaltic flows enclose terrigenous sediments,
minor cherts and limestones in pillow interstices. The hypabyssal mafic rock yields a U–Pb zircon age
of 252 ± 4 Ma and indicates intrusion of basic magma at the Permo-Triassic boundary, contemporaneous
with voluminous magmatism of the Siberian large igneous province (LIP). The lava flows and hypabyssal
mafic rocks of the Kolyuchinskaya Bay region have trace elements, Sm–Nd and Rb–Sr isotope compositions
identical to the tholeiitic flood basalts of the main plateau stage of the Siberian LIP, but differ from
the latter in the major-element variations. We conclude that compositional variations in the hypabyssal
rocks studied reflect their generation in an extensional environment that might be related to the Siberian
super-plume activity at the time. Although the genetic and temporal links between intrusive mafic rocks
and lavas are not well proved, compositional variations of the eruptive rocks still indicate their generation
in an extensional environment.