美濃-丹波帯のジュラ紀粗粒堆積物の起源(構成岩石の起源)(ジュラ紀付加体の起源と形成過程)  [in Japanese] Origin of Jurassic coarse clastic sediments in the Mino-Tanba Belt(Origin of sedimentary rocks)(Origin and evolution of Jurassic accretionary complexes in Japan)  [in Japanese]

美濃-丹波帯中のジュラ紀粗粒堆積岩の堆積相と組成の変化から砕屑物供給のテクトニクスについて議論した.ジュラ紀付加体中の粗粒堆積岩を含む陸源砕屑岩は, 復元された海洋プレート層序のうち, 遠洋性および半遠洋性堆積物の上に重なり, 層序的上位に向かって末端タービダイト相から近源タービダイト相に変化する.近源タービダイト相中には円礫岩や角礫岩が挟まれる.これらはそれぞれ浅海域に一時堆積した陸源性砕屑物や陸棚斜面を形成していたジュラ紀付加体起源の砕屑物が重力流によってより深海域に供給されたものである.粗粒堆積岩中の礫岩の礫種, 砂岩の鉱物組成, 砕屑性ザクロ石の化学組成, 砕屑性モナザイトやジルコンのCHIME年代などに基づく後背地解析の結果, 砕屑物を供給した後背地が大陸縁辺部の火山弧および接触変成帯から先カンブリア紀高度変成岩からなる大陸基盤へと変化していったことがわかった.この変化は北中国地塊と南中国地塊の衝突に起因するものであろう.

Tectonics related to sediment supply is discussed on the basis of sedimentary facies and composition of coarse clastic rocks of the Jurassic accretionary complex of the Mino-Tanba Belt.Terrigenous clastic rocks such as mudstone and sandstone occupy the upper part of reconstructed oceanic plate stratigraphy, resting on pelagic and hemipelagic rocks, and show an upward-change from distal turbidite facies to proximal turbidite facies. Conglomerates and breccias are embedded in sandstones of the proximal turbidite facies. Rounded clasts were derived from a land area and deposited in shallow marine basins, and then transported to deeper basins by gravity flow. Angular clasts were supplied from the Jurassic accretinary complex exposed on continental slope by gravity flow.Provenance analysis based on conglomerate composition, sandstone composition, chemical composition of detrital garnets and CHIME age of detrital monazites and zircons indicates that the provenance for coarse clastic rocks changed from volcanic arc and contact metamorphic terrane along continental margin to continental basement composed of Precambrian high-grade metamorphic rocks in Late Triassic to Early Jurassic time. The change is considered to have resulted from collision of the North and South China Blocks.