Zirconian
| Zirconian Era 4404–4031 million years ago | |
| view • discuss • -4500 — – -4000 — – -3500 — – -3000 — – -2500 — – -2000 — – -1500 — – -1000 — – -500 — – 0 — | |
The Zirconian is the second Era within the Hadean Eon in a proposed revision of the Precambrian time scale.[1] It lasted 373 million years from the end of the Chaotian Era 4,404 million years ago to the beginning of Eoarchean Era 4,031 million years ago. The Zirconian follows the Chaotian Era and its beginning is chronometrically set at 4.404 ± 0.008 Gya. This corresponds to the age of the first occurrence of zircons in the Jack Hills in Western Australia (Yilgarn craton). The end of the Zirconian Era and the transition to the Acastan Period (the earliest period of the Archean Eon and Eoarchean Era) occurred with the appearance of the oldest rock at 4.031 ± 0.003 Gya.
Etymology
The term Zirconian is derived from the mineral zircon, since it is the only substance that is preserved from this early period. An alternative proposal for the name of this era is "Jack Hillsian Era".
Meaning
Have the first 196 million years after the formation of Earth, it leaves except for the formation of the Moon no visible traces in the course of Chaotian Era to appear on the Zirconian Era the first datable mineral, the zircons. The oldest known crystal could be dated to 4,404 ± 8 Mya. [2] Found he was in metasedimentary on Erawandoo Hills in the Jack Hills of Narryer Gneiss Terrane in Western Australia. At 4.4 Gya ago approach reaching age but from 4.2 to 4.1 Gya are very rare, already common. The bulk of the zircons in Narryer gneiss Terran dated much later, from 3.75 to 3.5 Gya.
Occurrence
The zircons are limited only to Archean cratons. In the Yilgarn craton (range were discovered zircons in addition to the occurrence of Narryer Gneiss Terrane in quartzites of Southern Cross Terran, which provided an age 4.35-3.13 Gya).[3]
Possibly the Nuvvuagittuq greensteiner belt of the Superior Craton is of Zirconian age, its proposed age of 4.28 Gya is however still controversial. The end of the Zirconian Era is at 4.031 Gya, marked by the Acasta Gneiss of Slave craton and it is likely that its protolith is older. In 2006, a single zircon crystal in Acasta Gneiss was dated to 4.2 Gya[4]
References
- ↑ Felix M. Gradstein; et al. (2012), "On the Geologic Time Scale", Newsletters on Stratigraphy, 45/2: 171–188
- ↑ Wilde, SA; et al. (2001), "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gya ago", Nature, 409 (6817): 175–178
- ↑ Wyche, S.; et al. (2004), "4350-3130 detrital zircons in the Southern Cross Granite-Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn craton", Australian Journal of Earth Sciences, Volume 51, issue 1: 31–45
- ↑ Tsuyoshi Iizuka (2006), "4.2 Ga zircon xenocryst in to Acasta gneiss from northwestern Canada.: Evidence for early continental crust", Geology, 34, No. 4: 245–248, doi:10.1130/G22124.1
