Hadean zircon
Zircon is a mineral that is commonly used for radiometric dating because it is highly resistant to chemical changes and appears in the form of small crystals or grains in most igneous and metamorphic host rocks.
[1] In the Jack Hills, Australia, scientists obtained a relatively comprehensive record of Hadean zircon crystals in contrast to other locations.
The Jack Hills zircons are found in metamorphosed sediments that were initially deposited around 3 billion years ago,[1] or during the Archean Eon.
The geological history of the Hadean eon of early earth is poorly known due to the lack of rock record older than 4.02 Ga (giga-annum or billion years).
[2] However, some tiny parts of the crust have not been melted, as some rare Hadean zircon grains included in much younger host rock were discovered.
[2] The examination of Hadean detrital or inherited grains of zircon can give evidence of geophysical conditions of the early earth.
In the absence of large amount of undistributed data and within the constraints of analytical methods, calculation on geophysics and planetary science has been rapidly developed to explore this new area of knowledge.
The textural characteristics like the growth zoning and inclusion mineralogy shows that Hadean zircon from the Jack Hills all come from igneous sources.
[6][13] The development of textural criteria for identifying primary inclusions[33] opens up possibilities for recognising zircons' changing provenance with time and investigating their post-depositional alteration history.
[33] Dominated by quartz with less abundant K-feldspar, plagioclase, muscovite, biotite, and phosphates, that are interpreted to have formed under relatively low geothermal gradient similar to that pertaining to modern subduction zones.
Electron beams are emitted to the mineral's surface and blow off ions and estimate the abundance of the elements within a very small sized sample.
[1] Relatively low crystallisation temperature and some are enriched in heavy oxygen, contain inclusion similar to modern crustal processes and show evidence of silicate differentiation at ~4.5 Ga.[1] Early terrestrial hydrosphere, early felsic crust in which granitoids were produced and later weathered under high water activity conditions and even the possible existence of plate boundary interactions.
