Origin and depositional environment of Archean particle-bearing sandstones in the Japanese Islands

最近的CHIME年代学研究表明，日本群岛岩石的起源可以追溯到大约3000 Ma前，即太古代晚期(例如Suzuki&Adachi，1991；Adachi和Suzuki，1993)。由于在东亚，太古宙岩石的分布仅限于中国北部的部分地区，因此，中生代砂岩中的太古宙碎屑颗粒为研究日本群岛的形成和构造演化提供了重要的关键信息。在这三年的工作中，我们对中生代砂岩进行了锆石、独居石、天青石和尿安石的钟声测年，并进行了电感耦合等离子体质谱分析。测年结果表明，米诺区、日达区和岛南区砂岩中普遍存在2000 Ma左右的重熔锆石，太古宙(2500 Ma以上)的锆石较少，3000 Ma左右的锆石非常罕见。虽然稀有，但这些稀有的锆石证明了来自中国东北部和朝鲜太古宙岩石的沉积物。文中还讨论了深水锆石、独居石等中稀土元素测定的一些基本分析问题，并结合新获得的年代学和地球化学资料、太古宙岩石分布和东亚中生代构造背景，讨论了太古宙含颗粒砂岩的成因和构造演化。

Recent CHIME geochronological studies have revealed that the origin of the rocks in the Japanese Islands was as long as ca. 3000 Ma ago, namely during late Archean time (e.g. Suzuki & Adachi, 1991; Adachi and Suzuki, 1993). Since in East Asia, the distribution of the Archean rocks is restricted to part of North China, the Archean clastic particles in Mesozoic sandstones provide important key information as to the birth and tectonic evolution of the Japanese Islands. During these three years of the project, we have carried out the CHIME dating on detrial zircon, monazite, zenotime and allanite, together with ICP mass spectrometric analysis of the Mesozoic sandstones. The dating results have shown that ca. 2000 Ma detrial zircons are common in the sandstones of the Mino, Hida and Shimanto Terrenes, while Archean (older than 2500 Ma) zircons are not common and ca. 3000 Ma zircons are very rare. Although scarce, these rare zircons demonstrate an input of sediment from Archean rocks of northeastern China and Korea. Some fundamental analytical problems with the determination of rare earth elements (REE) that are contained in detrial zircon, monazite, etc. were also addressed.The origin and tectonic evolution of the Archean particle-bearing sandstones were discussed in the light of the newly obtained chronological and geochemical data, the distribution of the Archean rocks, and the Mesozoic tectonic setting of East Asia.