10:45 AM - 11:00 AM
[SVC44-07] Magmatism in the northern Sredinny Range, Northern Kamchatka
Keywords:Kamchatka, Pacific Plate, slab edge, subduction zone, arc magma
This arc is characterized by the wide volcanic zone in the across-arc direction, which consists of three volcanic chains; the Eastern Volcanic Front (EVF), the Central Kamchatka Depression (CKD) and the Sredinny Range (SR). The volcanic front is continuous from the Kurile Arc to EVF and bent toward the Klyuchevskoy Volcanic Group (KVG) in CKD at around 55°N along the 100–180 km slab-depth contour. The offset of the volcanic front corresponds to shallowing of the slab dip angle. KVG is the world-most active and largest volcanic group. On the other hand, SR constitutes the backarc volcanic zone and a few active volcanoes are only located in the southern part of Sredinny Range (S-SR) (Pevzner, 2006). The northern Sredinny Range (N-SR) is located 100 km north beyond the northernmost active volcano in SR corresponding to the north edge of the subducting Pacific Plate (slab edge). However, we found many young volcanic features and possible magmatic products in the area. In order to characterize the magmatism in N-SR, we have conducted geochemical studies for the N-SR lavas.
The following characteristics of the magmatism in N-SR were found. The magmatism started after the Lower Pliocene and continues to the Holocene. Lava plateaus were dominant during the Neogene, while monogenetic cones and/or stratovolcanoes are dominant during the Quaternary, with different volumes, rock textures, modal mineral compositions and bulk rock major and trace element compositions between the two stages. The N-SR lavas were estimated to have derived from flux melting of water-saturated mantle under a similar genetic pressure-temperature condition. The fluids contributed to the arc magmatism were derived from the subducting Pacific Plate or derived from the subducted Bering Plate, and/or the forearc slivers beneath the northern Kamchatka. The arc lavas exhibit high HFSE concentrations (~18 ppm Nb and ~1.2 ppm Ta) compared to the lavas from KVG and are similar to the lavas of the S-SR (Volynets et al., 2010), most of which were likely caused by the deep dehydration. These results suggest that the slab-derived fluids play an important role in the arc magmatism even in N-SR which is located north beyond the slab edge.