- 公益社団法人 東京地学協会
- 地学雑誌 (ISSN:0022135X)
- vol.127, no.5, pp.705-721, 2018-10-25 (Released:2018-11-14)
The extensive occurrence of a felsic continental crust is one of the unique features of the Earth. The growth history of the continental crust has been a key issue in understanding the origin and evolution of the Earth. In particular, recent geological studies indicate that subduction of the continental crust into the mantle has been greater than previously imagined. The current understanding of the growth of continents and the differentiation of the crust and the mantle of the Earth is reviewed based on a detrital zircon geochronology. One of the most important achievements arises from the analysis of the age structure of individual continents and secular changes over time. The new detrital zircon geochronology suggests that the sizes of the continents have changed over time, which has been an important factor in the growth of the continents. Large continents, such as the modern examples, can preserve older crusts in their interiors, which are separated from active continental margins. Conversely, in the early Earth, continents were probably formed by the amalgamation of small fragments of crust, such as oceanic island arcs. It is speculated that the smallness of the continents was the most significant cause of the poor preservation of Hadean and Archean crusts, despite putative expected active crustal production. Consequently, the recycling of the continental crust occurred in great magnitudes during the early Earth's history. The large-scale subduction of felsic crust represents one of the most important aspects in studies of the early Earth.