Zirconium (era)

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The zirconium is the second and most recent era of the Hadaic proposed in the course of the reorganization of the Precambrian . It took 374 million years, from 4404 million years ago to 4030 million years ago.

etymology

The name zirconium, English zirconian or zirconian era , is derived from the mineral zircon , which, in the form of so-called detritic zircons, is the only substance that has been geologically transmitted from this early period. An alternative suggestion for the name of this era is Jack Hillsium ( English Jack Hillsian ), named after the Jack Hills in Western Australia , in which the very oldest detritic zircons occur.

Definition of zirconium

SEM image of various Precambrian zirconium grains. C and D are from the Jack Hills (but are not necessarily Zirconian in age).

The zirconium follows the Chaotic era and its beginning is chronometrically set at 4404 million years ago. This corresponds to the age of the first occurrence of zircons in the Jack Hills in Western Australia ( Yilgarn Craton ). Its end and thus the transition to the Archean and its first period, the Acastum , takes place with the appearance of the oldest rock at 4030 million years ago.

Geological events

While the first 163 million years of the earth's history did not leave any traces on the earth during the chaotic period, the first datable mineral substance has been handed down from zirconium with detritic zircon grains . Zircon grains crystallize primarily from magma and are extremely resistant, so that they can withstand areas of the rock cycle in which extreme conditions prevail, relatively unchanged. The oldest detritic zircons are therefore relics of the oldest earth's crust . The oldest zircon to date could be dated to an age of 4404 ± 8 million years. It was found in metasediments on Erawandoo Hill in the Jack Hills of the Narryer Gneiss Terran in Western Australia. However, zircons with this extremely old age are extremely rare there. Zircons that are 4,200-4,100 million years old are already more common. The majority of the zircons in the Narryer Gneiss Terran are much younger, with ages of 3750 and 3500 million years.

Occurrence

Finds of hadaic zircons are limited to a very few archaic cratons . In the Yilgarn Craton, in addition to the occurrences of the Narryer Gneiss Terran, zircons were discovered in quartzites of the Southern Cross Terran , which have a maximum age of 4350 million years (range 4350 to 3130 million years ago). The nuvvuagittuq greenstone belt of the superior kraton may have originated from the zirconium, but its proposed age of 4,280 million years remains controversial. The end of the zirconium is marked at 4030 million years ago by the highest recorded protolith age in the Acasta gneiss complex of the slave kraton .

Individual evidence

  1. ^ Felix M. Gradstein et al .: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45 , no. 2 , April 2012, p. 171–188 , doi : 10.1127 / 0078-0421 / 2012/0020 (English, freely available online through researchgate.net ).
  2. ^ Martin J. Van Kranendonk et al .: A Chronostratigraphic Division of the Precambrian . In: Felix M. Gradstein et al. (Ed.): The Geologic Time Scale 2012 . tape 1 . Elsevier, Oxford / Amsterdam / Waltham, MA 2012, ISBN 978-0-444-59390-0 , 16.5.1. A Hadean Eon, S. 360 (English, limited preview in Google Book Search).
  3. ↑ Simon A. Wilde et al .: Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago . In: Nature . tape 409 , no. 6817 , January 11, 2001, p. 175–178 (English, freely available online through ucsc.edu [PDF; 202 kB ]).
  4. ↑ Stephen Wyche et al .: 4350–3130 Ma detrital zircons in the Southern Cross Granite-Greenstone Terrane, Western Australia: Implications for the early evolution of the Yilgarn craton . In: Australian Journal of Earth Sciences . tape 51 , no. 1 , 2004, ISSN  0812-0099 , p. 31-45 , doi : 10.1046 / j.1400-0952.2003.01042.x (English).