鈴鹿山脈北部, 美濃帯の海洋性岩石の混在  [in Japanese] Chaotically intermixed Permian oceanic rocks of Mino terrane, northern Suzuka Mountains, central Japan  [in Japanese]

鈴鹿山脈北部, 美濃帯の北鈴鹿ユニットは, 大洋域で複雑に混合されたペルム系海洋性岩石からなり, 陸源性砕屑物を全く含まない.この海洋性岩石混在岩の特徴は, 細粒の玄武岩砕屑岩からなる基質中に無秩序に様々な大きさの海洋性岩石のブロックが点在すること, ブロックが基質により支持されていること, ブロック内で海洋性岩石の層序が良く保存されていることである.ブロックとして含まれる海洋性岩石は, 玄武岩海山と, その頂部の浅海成生砕石灰岩, 斜面の砕屑性石灰岩と玄武岩質火山砕屑岩からなる重力流堆積物, 海山周辺の海洋底のチャートを起源とする.北鈴鹿ユニットのペルム系海洋性岩石の混在は, 海山での岩屑なだれにより引き起こされたと考えられる.この岩屑なだれは, 大洋域での海山の大規模な山体崩壊により発生した.

The Kitasuzuka Unit of the Mino terrane, northern Suzuka Mountains, central Japan is defined as a structurally complicated aggregate of various-sized disrupted masses of Permian oceanic rocks of limestones, cherts, and basaltic rocks, totally devoid of terrigenous sediments. The oceanic rocks masses are chaotically intermixed and set in a matrix of finely crushed basaltic rocks.By piecing together from isolated large-sized blocks, four oceanic successions were reconstructed. They include the Atodani Formation predominantly of Lower Permian shallow-water limestones, Kawachi Formation characterized by Lower Permian clastic limestone and basaltic volcaniclastic rocks, Samegai Formation composed mostly of Permian bedded cherts, and unnamed unit of basaltic rocks. These oceanic-rock assemblage is interpreted as a sedimentary cover on and around a seamount in an open ocean realm.The chaotic internal structure of the Kitasuzuka Unit is thought to have formed by debris avalanche-related intermixing of disrupted blocks, and rock-pieces and finer-pulverized basaltic particles. The debris avalanches are considered to have been triggered by a large-scale collapse of the gravitationally unstable seamount prior to its encounter with terrigenous sediments, in an open-ocean setting.