U-Pb spot dating for detrital single zircon grains collected from the mouth of the Amazon River with help of LA-ICP-MS and continental crust growth history of the Amazon River Basin.Rino, S.*; Motoki, A.**; Hirata, T.*; Maruyama, S.*
* Tokyo Institute of Technology, Japan; ** Universidade do Estado do Rio de Janeiro, Brazil.
Short Papers of VI South American Symposium on Isotopic Geology, 1, 219-220.
August, 2003, Salvador, Bahia, Brazil.
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Alluvial sand of the mouth of large rivers is composed of the mineral grains originated from various areas within the fluvial basin, forming a general mixture of the region. They are constituted predominantly by quartz, but contain also small amount of heavy minerals, such as ilmenita, magnetite, zircon, rutile, monazite, tourmaline, and rarely micro diamond. Among them, zircon is a highly stable one against chemical and physical weathering during fluvial transportation. In this sense, detrital zircon of river outlet represents that of whole continental crust rocks of the fluvial basin.
In case of a very large river of continental extension, such as the Amazon, the La Plata, the Mississippi, and the Macknzie, river mouth detrital zircon represents a huge area, corresponding sometimes to entire craton or a half of the continent. Therefore, the geochronological studies of detrital river mouth zircon of main continental scale rivers of the world can reveal continental crust growth history of the Earth. This paper presents partial results of this worldwide research project, applied to Amazon River.