Cretaceous ultramafic volcanism in the Sredinnyi Range, Kamchatka

Abstract

Late Mesozoic metapicrites and metapicrobasalts occur in all apoterrigenous rock sequences in Kamchatka’s Sredinnyi crystalline massif, forming sheets, flows, and sills ranging between a few and 100 m or greater in thickness. Metapicrites possess geochemical parameters that are intermediate between mid-oceanic ridge tholeiites and island-arc tholeiites, which is typical of volcanic rock complexes in marginal basins. The host rocks are terrigenous rock sequences of the Kikhchik series and its metamorphosed analogues, viz., the Kolpakova, Kamchatka, and Malka series, which were formed in a common continental-margin sedimentary basin during the late Mesozoic sedimentation cycle with the same source, which was a province in the eastern margin of the Asian continent. The extension of continental crust in the Cretaceous sedimentary basin and intersections by faults of the same age as that of the Okhotsk-Chukotka volcanogenic belt, combined to produce basite and ultrabasite volcanism. Emplacement of mantle material (the ascent of mantle plumages) accompanied by deep hydrogen-rich fluids into the basement of the crust from volcanogenic terrigenous deposits of the marginal basin produced considerable temperature increases in the crust, as well as magmatic replacement of volcanogenic sedimentary rock sequences with the subsequent generation of magma chambers and ascent of acid volcanic and granitoid rocks into the upper crust.