Abstract
The article presents new petrologic and geochemical data on gabbroids from Shikotan Island (Lesser Kuril Chain). The results were compared with co-magmatic Late Cretaceous-Paleocene volcanics from the Zelenov Formation, as well as with the rocks from the Shikotan intrusive and Dimitrovsky dike complexes. This data confirmed that the intrusive rocks belong to the calc-alkaline series and the island-arc (suprsubduction) type. Low concentrations of high field strength and heavy rare-earth elements and their ratio in gabbroids relative to the composition of N-MORB suggest formation of primary melts from depleted or poorly enriched deep sources. As such, pyroxenites close to websterites with preserved bipyroxene paragenesis during the evolution of melts are proposed. Steeply dipping contacts of intrusive bodies and elements of their prototectonics, zones of marginal breccia and clastic dikes that sometimes over-ends by injection intrusive material field parallel dikes completion plutonic activity on Malokurilsk arc indicate «formation of Shikotan ophiolites in the setting of supersubducting intra-arc rifting» according to ideas of G.I. Govorov.
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