EVOLUTION OF LOWER CRUST BENEATH THE HONSHU ARC

白垩纪至晚新生代，本州岛弧发生了长石质-镁质深部成矿作用。产于本州岛弧的新生代火山岩包含下地壳源性基性岩和上地幔源性超基性岩作为捕虏体。对这些火成岩和捕虏体进行了岩石学、石油化学（主要元素和次要元素）和年代学研究。根据这些研究，澄清了以下事实。本州弧田仓构造线西段。(1)本州岛弧西南部（良轭带，三洋带的一部分，三仁带的东部），本州岛弧东北部（石尾和筑波山脉）：这些地区的下地壳是晚古生代至早中生代由大陆岩石圈地幔形成的，具有拉斑岩化学成分。这些地区的白垩系至早新近纪火成岩是由这些下地壳和（或）上地幔形成的。(2)本州岛弧西南部（九州、三仁带西部）、本州岛弧东北部（佐渡岛、朝日山脉）：该区下地壳和上地幔与“(1)”区具有不同的特征和历史。(3)(1)与(2)中间区域：在(1)与(2)中间区域下方混合着“(1)”与“(2)”两种不同类型的下地壳与上地幔。本区出露的岩浆岩Sr、Nd同位素特征处于(1)、(2)区火成岩同位素特征的中间位置。本州弧田仓构造线东部。该区下地壳和上地幔的历史和特征可能与“I”区不同。这个地区的大部分火成岩都是由这些物质形成的。北上带最东部的花岗质岩石是洋板块俯冲的部分熔融产物。随着日本海的开闭，日本海及其周边地区的下地壳和上地幔发生了新的重构。中中新世至新近的日本海一侧火成岩来源于这些物质。少

Felsic to mafic plutonism took place in the Honshu Arc from Cretaceous to late Cenozoic. Cenozoic volcanic rocks occurring in the Honshu Arc contain lower crust-derived mafic rocks and upper mantle-derived ultramafic rocks as xenoliths. As to these igneous rocks and xenoliths, we have carried out petrological, petrochemical (major and minor elements) and geochronological studies. According to these studies, the following facts were clarified.1. Western part of Tanakura Tectonic Line of Honshu Arc. (1) Southwest Honshu Arc (Ryoke Belt, a part of San'yo Belt, eastern part of San'in Belt), Northeast Honshu Arc (Ashio & Tsukuba Mountains) : The lower crust beneath these areas was formed from continental lithospheric mantle at late Paleozoic to early Mesozoic, and has tholeiitic chemical composition. The Cretaceous to early Neogene igneous rocks occurring in these areas were formed from these lower cust and/or upper mantle. (2) Southwest Honshu Arc (Kyushu, western part of San'in Belt), Nor … More theast Honshu Arc (Sado Island, Asahi Mountains) : The lower crust and upper mantle beneath these areas have different features and history from those of area "(1)". (3) Middle area between (1) and (2) : The lower crust and upper mantle of two different types, "(1)" and "(2)", are mixed beneath the middle area between (1) and (2). Sr and Nd isotopic features of ingeous rocks occurring in this area are in the middle of those of igneous rocks from areas (1) nad (2).II.Eastern part of Tanakura Tectonic Line of Honshu Arc. History and features of the lower crust and upper mantle beneath this area are probably different from those beneath area "I". Most of the igneous rocks in this area were formed from these materials. However, granitic rocks in the most eastern part of Kitakami Belt were partial melting products of subducted oceanic plate.III.Middle Miocene to Recent. Lower crust and upper mantle beneath the Japan Sea and its surrounding area were newly reconstructed in connection with opening of the Japan Sea. Middle Miocene to Recent igneous rocks of theJapan Sea side were derived from these materials. Less