Geodynamic setting of the high-grade amphibolites and associated igneous rocks from the accretionary complex of Povorotny Cape, Taiganos Peninsula, northeastern Russia

Abstract

The petrology and geochemistry of high-grade amphibolites and associated gabbro, volcanic rocks and peridotites from Povorotny Cape (northeastern Russia) are considered with the aim to examine the geodynamic setting of different rock complexes related with the accretionary structure of this area. Geochemical and petrological evidence indicates that the following two predominant groups of igneous rocks were involved in the construction of the Povorotny Cape accretionary structure: (1) MORB and within-plate members (protolith of high-grade amphibolites, gabbro, dolerites, volcanic rocks and spinel lherzolites; (2) different products of suprasubduction magmatism, including boninites (gabbro and ultramafic cumulates, dolerites, volcanic rocks and spinel harzburgites). The P– T metamorphic conditions of the rock assemblages indicate that the Povorotny Cape rock complexes were affected by two main metamorphic events. The first corresponded to high-pressure–medium-temperature conditions and was unique to the high-grade amphibolite, and the second occurred in the form of low-temperature recrystallization under greenschist-facies conditions and manifested itself in virtually all igneous rocks of Povorotny Cape and in part of the high-grade amphibolites. The igneous and metamorphic rock complexes of Povorotny Cape were formed during the following main tectonic episodes: (1) generation of MORB and within-plate magmatic rock assemblages (gabbros, dolerites and volcanic rocks), including residual peridotites in an oceanic basin; (2) subduction of part of these rocks to a relatively shallow position within a warm subduction zone, while the remaining oceanic lithosphere was detached and tectonically incorporated into a suprasubduction complex; (3) formation of a suprasubduction magmatic complex that included a boninite series; (4) exhumation of the high-grade amphibolites and spinel lherzolites and their tectonic mixing with the oceanic and suprasubduction igneous complexes.