“Calc-alkaline” magmatism of the Omgon Range: Evidence for Early Paleogene extension in the western Kamchatka segment of the Eurasian continental margin

The hypabyssal rocks of the Omgon Range, western Kamchatka, that intrude Upper Albian-Lower Campanian deposits of the Eurasian continental margin belong to three coeval (62.5–63.0 Ma) associations: (1) ilmenite gabbro-dolerites, (2) titanomagnetite gabbro-dolerites and quartz microdiorites, and (3) porphyritic biotite granites and granite-aplites. The Early Paleocene age of the ilmenite gabbro-dolerites and biotite granites was confirmed by zircon and apatite fission-track dating. The ilmenite and titanomagnetite gabbro-dolerites were produced by the multilevel fractional crystallization of basaltic melts with, respectively, moderate and high Fe-Ti contents and the contamination of these melts with rhyolitic melts of different compositions. The moderate-and high-Fe-Ti basaltic melts were derived from mantle spinel peridotite variably depleted and metasomatized by slab-derived fluid prior to melting. The melts were generated at variable depths and different degrees of melting. The biotite granites and granite aplites were produced by the combined fractional crystallization of a crustal rhyolitic melt and its contamination with terrigenous rocks of the Omgon Group. The rhyolitic melts were likely derived from metabasaltic rocks of suprasubduction nature. The Early Paleocene hypabyssal rocks of the Omgon Range were demonstrated to have been formed in an extensional environment, which dominated in the margin of the Eurasian continent from the Late Cretaceous throughout the Early Paleocene. Extension in the Western Kamchatka segment preceded the origin of the Western Koryakian-Kamchatka (Kinkil’) continental-margin volcanic belt in Eocene time. This research was conducted based on original geological, mineralogical, geochemical, and isotopic (Rb-Sr) data obtained by the authors for the rocks.     

Mesozoic syncollision siliciclastic sediments of the Bols’shoi Lyakhov Island (New Siberian Islands)

Graywackes and shales of the Bols’shoi Lyakhov Island originally attributed to the Mesozoic were subsequently considered based on microfossils as the Late Proterozoic in age. At present, these sediments in the greater part of the island are dated back to the Permian based on palynological assemblages. In the examined area of the island, this siliciclastic complex is intensely deformed and tectonically juxtaposed with blocks of oceanic and island-arc rocks exhumed along the South Anyui suture. The complex is largely composed of turbidites with members displaying hummocky cross-stratification. The studied mineral and geochemical characteristics of the rocks defined three provenances of clastic material: volcanic island arc, sedimentary cover and/or basement of the ancient platform, and exotic blocks of oceanic and island-arc rocks such as serpentinites and amphibolites. All the rock associations represent elements of an orogenic structure that originated by collision of the New Siberian continental block with the Anyui-Svyatoi Nos island arc. Flyschoid sediments accumulated in a foredeep in front of the latter structure in the course of collision. The Late Jurassic volcanics belonging to the Anyui-Svyatoi Nos island arc determine the lower age limit of syncollision siliciclastic rocks. Presence of Late Jurassic zircons in sandstones of the flyschoid sequence in Bols’shoi Lyakhov Island is confirmed by the fission-track dating. The upper age limit is determined by the Aptian-Albian postcollision granites and diorites intruding the siliciclastic complex. Consequently, the flyschoid sequence is within stratigraphic range from the terminal Late Jurassic to Neocomian. It appears that Permian age of sediments suggested earlier is based on redeposited organic remains. The same Late Jurassic-Neocomian age and lithology are characteristic of fossiliferous siliciclastic sequences of the Stolbovoi and Malyi Lyakhov islands, the New Siberian Archipelago, and of graywackes in the South Anyui area in Chukchi Peninsula. All these sediments accumulated in a spacious foredeep that formed in the course the late Cimmerian orogeny along the southern margin of the Arctic continental block.     

First Data on the U–Pb Isotopic Age for Zircon (LA-ICP-MS Method) from Leucocratic Granites of the Tyrnyauz Mo–W Deposit (North Caucasus,Russia)

Doklady Earth Sciences - The first data of a U–Pb isotopic study (LA-ICP-MS method) of zircon from leucocratic granites of the giant Tyrnyauz Mo–W deposit (North Caucasus) are...     

Modeling the Seismicity of the Altai–Sayan–Baikal Region

Doklady Earth Sciences - Numerical modeling of the dynamics of the block structure and the resulting seismicity of the Altai–Sayan–Baikal region has been carried out. The earthquake...