Subduction of the Izanagi-Pacific Ridge–transform intersection at the northeastern end of the Eurasian plate

Author:

Yamasaki Toru1,Shimoda Gen1,Tani Kenichiro2,Maeda Jinichiro3,Nanayama Futoshi11

Affiliation:

1. Research Institute of Geology and Geoinformation, Geological Survey of Japan (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan

2. Department of Geology and Paleontology, National Museum of Nature and Science, Japan, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan

3. Hokkaido Research Center of Geology, Yamanote 2-3-5-24, Nishi-ku, Sapporo, Hokkaido 063-0002, Japan

Abstract

Recent reconstructions of global plate motions suggest that the Izanagi-Pacific Ridge was subducted along the eastern margin of Eurasia at ca. 50 Ma. In the Hidaka magmatic zone (HMZ), which was located at the northeastern end of the Eurasian plate, three magmatic pulses occurred (46–45, 40–36, and 19–18 Ma). We report whole-rock geochemical and Sr-Nd-Pb isotopic data for 36 Ma high-Sr/Y (adakitic) rocks from the HMZ and show that these rocks formed by partial melting of oceanic crust and were emplaced as near-trench intrusions during ridge subduction. We reevaluate the nature of plutonic rocks in the HMZ and show that both the 46–45 and 40–36 Ma granitoids have essentially identical geochemical features. The distribution of plutons and magmatic cessation between 45 and 40 Ma are best explained by subduction of a ridge-transform intersection with a large offset of the ridge axis. The boundary between the Eocene granitoids corresponds to the position of a paleo–transform fault, and adakitic magmatism was caused by partial melting triggered by slab tearing at an overlapping spreading center. The paleoridge-transform configuration coincides with the locations of later large faults and a peridotite body.

Publisher

Geological Society of America

Subject

Geology

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