Hadean zircon is the oldest-surviving crustal material from the Earth's earliest geological time period, the

Hadean The Hadean ( ) is a geologic eon of Earth history preceding the Archean. On Earth, the Hadean began with the planet's formation about 4.54 billion years ago (although the start of the Hadean is defined as the age of the oldest solid materia ...

eon, about 4 billion years ago.

Zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...

is a

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

that is commonly used for

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...

because it is highly resistant to chemical changes and appears in the form of small crystals or grains in most

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

and

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

host rocks. Hadean zircon has very low abundance around the globe because of recycling of material by

plate tectonics Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of larg ...

. When the rock at the surface is buried deep in the Earth it is heated and can recrystallise or melt. In the

Jack Hills The Jack Hills are a range of hills in Mid West Western Australia. They are best known as the source of the oldest material of terrestrial origin found to date: Hadean zircons that formed around 4.39 billion years ago. These zircons have enable ...

, 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, or during the

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Arc ...

Eon. However, the zircon crystals there are older than the rocks that contain them. Many investigations have been carried out to find the

absolute age Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy ...

and properties of zircon, for example the

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass num ...

ratios, mineral inclusions, and

geochemistry Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing th ...

of zircon. The characteristics of Hadean zircons show early Earth history and the mechanism of Earth's processes in the past. Based on the properties of these zircon crystals, many different geological models were proposed.

Background

Importance

Deeper understanding of Earth history

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 A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hou ...

or billion years).Roth, Bourdon, Mojzsis, Touboul, Sprung, Guitreau, & Blichert-Toft. (2013). Inherited 142Nd anomalies in Eoarchean protoliths. ''Earth and Planetary Science Letters,'' ''361'', 50-57. Most scientists accept that the plate recycling mechanism has melted almost all pieces of Earth's crust. 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. The examination of Hadean

detrital Detritus (; adj. ''detrital'' ) is particles of rock derived from pre-existing rock through weathering and erosion.Essentials of Geology, 3rd Ed, Stephen Marshak, p G-7 A fragment of detritus is called a clast.Essentials of Geology, 3rd Ed, Stephe ...

or inherited grains of zircon can give evidence of

geophysical Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' some ...

conditions of the early earth.

Scientific contribution

Since there is no strong evidence depicting the early Earth's true environment, many models are generated to explain early Earth history. The high value of Hadean heat production and impact

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ...

proved that continental crust did not exist, which is very different from the modern process. In the absence of large amount of undistributed data and within the constraints of analytical methods, calculation on geophysics and

planetary science Planetary science (or more rarely, planetology) is the scientific study of planets (including Earth), celestial bodies (such as moons, asteroids, comets) and planetary systems (in particular those of the Solar System) and the processes of their ...

has been rapidly developed to explore this new area of knowledge.

Abundance

Less than 1% of zircons detected around the world are over four billion years old. The probability of discovering at least a single over four billion-year-old zircon is very low. The abundance of over four billion-year-old zircon in the

is anomalously high for most Archean

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

s and thus abundances probabilities of other spots are extremely low (0.2–0.02%). By adopting uranium-lead dating (U-Pb) together with other analytical methods, more

geochemical Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...

information can be obtained. Only 3% out of over 200,000 detritial zircon grains dated by U-Pb analysis are over four billion years old.Peck, Valley, Wilde, & Graham. (2001). "Oxygen isotope ratios and rare earth elements in 3.3 to 4.4 Ga zircons: Ion microprobe evidence for high δ18O continental crust and oceans in the Early Archean". ''Geochimica Et Cosmochimica Acta,'' ''65''(22), 4215-4229. Zircon type

Types

Due to different content of uranium and trace element concentration, four clusters of zircons are identified as below Harrison, T. (2009). The Hadean Crust: Evidence from >4 Ga Zircons. ''Annual Review of Earth and Planetary Sciences,'' ''37'', 479-505. * Lunar and

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...

zircon * Detrital grains zircon *

Kimberlite Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of S ...

zircon * Ocean crust zircon Low crystallisation temperatures and trace element characteristics are the two major characteristics that differentiate mantle derived zircon or oceanic crust-derived zircon.Grimes, C., John, B., Kelemen, P., Mazdab, F., Wooden, J., Cheadle, M., . . . Schwartz, J. (2007). Trace element chemistry of zircons from oceanic crust; a method for distinguishing detrital zircon provenance. ''Geology (Boulder),'' ''35''(7), 643-646. Lunar and meteoritic zircons are unique because of their REE signature for example, lack of a

cerium Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 ...

anomaly. The crystallization temperature ranges from 900 to 1100 °C. In contrast, terrestrial Hadean zircons are restricted to 600 to 780 °C.Watson, E., & Harrison, T. (2005). Zircon thermometer reveals minimum melting conditions on earliest Earth. ''Science,'' ''308''(5723), 841-844. Hadean Jack Hills zircon has a wide range of oxygen fraction comparing to meteoritic zircons. No extraterrestrial zircons were found in any terrestrial locality. The textural characteristics like the growth

zoning Zoning is a method of urban planning in which a municipality or other tier of government divides land into areas called zones, each of which has a set of regulations for new development that differs from other zones. Zones may be defined for a si ...

and inclusion mineralogy shows that Hadean zircon from the Jack Hills all come from igneous sources.Cavosie AJ, Wilde SA, Liu D, Weiblen PW, Valley JW (2004) Internal zoning and U–Th–Pb chemistry of Jack Hills detrital zircons: a mineral record of early Archean to Mesoproterozoic (4348–1576 Ma) magmatism. Precambrian Res 135:251–279Hopkins M, Harrison TM, Manning CE (2008) Low heat flow inferred from > 4 Gyr zircons suggests Hadean plate boundary interactions. Nature 456:493–496

Properties

The unspecified samples used for analyses below were Jack Hills zircon in Australia because of the high abundances and data available.

Age distribution

U-Pb dating in the U-Pb zircon system has long been viewed as the crustal geochronometer because zircon is chemically resistant and enriched in U and Th compared to the daughter product Pb.Meinhold, G., Morton, A., Fanning, C., & Whitham, A. (2011). "U–Pb SHRIMP ages of detrital granulite-facies rutiles: Further constraints on provenance of Jurassic sandstones on the Norwegian margin". ''Geological Magazine,'' ''148''(3), 473–480. Trace element and isotopic composition of zircon is important to determine the crystallisation environment. Results from detrital zircons from the Erawondoo Hill discovery site

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** ...

generally show the zircons to have a

bimodal In statistics, a multimodal distribution is a probability distribution with more than one mode. These appear as distinct peaks (local maxima) in the probability density function, as shown in Figures 1 and 2. Categorical, continuous, and d ...

age distribution with major peaks at c. 3.4 and 4.1 Ga. However, zircon is sensitive to

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

damage and can degrade into

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language, Gr ...

material. The Hadean zircon with original uranium concentrations greater than 600 ppm is challenged by the effect of post-crystallization alteration.

Isotope geochemistry

Stable

data, indicating that the original host rocks to the zircon related to a significant amount of material formed on or near the Earth's surface and subsequently transferred to a middle- to lower-crustal level where they melted to generate the host

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...

s from which zircon crystallised.

Mineral inclusions

The development of textural criteria for identifying primary inclusionsBell, Boehnke, & Harrison. (2017). "Corrigendum to 'Applications of biotite inclusion composition to zircon provenance determination' arth Planet. Sci. Lett. 473 (2017) 237–246. ''Earth and Planetary Science Letters'' 475, 267. opens up possibilities for recognising zircons' changing provenance with time and investigating their post-depositional alteration history. There are two common inclusion assemblages that are consistent with their forming in "I-type" (

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rock ...

, quartz, biotite, plagioclase,

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common ...

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...

) and "S-type" (quartz, K-feldspar, muscovite,

monazite Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the ceriu ...

) granitoids. Dominated by quartz with less abundant K-feldspar, plagioclase, muscovite, biotite, and phosphates, that are interpreted to have formed under relatively low

geothermal gradient Geothermal gradient is the rate of temperature change with respect to increasing depth in Earth's interior. As a general rule, the crust temperature rises with depth due to the heat flow from the much hotter mantle; away from tectonic plate bo ...

similar to that pertaining to modern subduction zones.

Zircon geochemistry

By analysing the content of zircon, some zircon show the presence of titanium, rare earth minerals, lithium, aluminium and carbon. Certain ratio and normal distribution give evidence of zircon's origin and the source of magma. *

Analytic method

Ion microprobe analysis

Ion microprobe (or

secondary ion mass spectrometry Secondary-ion mass spectrometry (SIMS) is a technique used to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. ...

, SIMS) and uranium-thorium-lead geochronology are two common methods to measure isotope in specific time interval. Highly precise in situ SIMS measurements of oxygen isotopes and OH/O ratios, laser-ablation inductively-coupled mass spectrometry (LA-ICP-MS) determination of

hafnium Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri M ...

isotopes, and atom-probe tomography. LA-ICP-MS is the most common method to date using isotopes but it lacks capacity to measure ²⁰⁴Pb. Therefore, there is a possibility that the occurrences of single zircons over 4 billion years old could be due to inclusion of non-radiogenic Pb. EPMA

U-Pb dating, delta ¹⁸O and Ti measurements can be tested by CAMECA ims 1270 ion microprobe. Epoxy are applied on the sample. A flat surface of sample is needed to conduct an analysis. U-Pb dating and T measurement uses a primary O⁻ beam with low intensity (10-15 nA). U-Pb age standard AS3 was used for dating studies. The concentration of Ti can be determined based on analysis of Jack Hills zircon and NIST610 glass.

Electron microprobe analysis

For inclusions investigation, JEOL 8600

electron microprobe An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It ...

analyzer (EPMA) were used to chemically analyze zircon. It is used to analyze the chemical composition of material. 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. Many isotopes can be measured at once in this analysis for example Ti and Li.

Occurrence

Proposed mechanisms for forming Hadean Jack Hills zircons

Plate tectonic theory is widely accepted for the generation of crust. With the Hadean rock record, most of the scientists concluded that the hypothesis of a hellish early Earth devoid of ocean is incorrect. Scientists have constructed different models to explain the thermal history in the early earth, such as the continental growth model, Icelandic rhyolites, intermediate igneous rocks, mafic igneous rocks, sagduction,

impact melt Impact may refer to: * Impact (mechanics), a high force or shock (mechanics) over a short time period * Impact, Texas, a town in Taylor County, Texas, US Science and technology * Impact crater, a meteor crater caused by an impact event * Impact ...

, heat pipe tectonics, terrestrial

KREEP KREEP, an acronym built from the letters K (the atomic symbol for potassium), REE (rare-earth elements) and P (for phosphorus), is a geochemical component of some lunar impact breccia and basaltic rocks. Its most significant feature is somewhat ...

and multi-stage scenarios. The most famous one is continental growth model which is similar to the modern tectonic dynamics. 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. 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. These last two sentences make no sense. Please edit accordingly.

References

{{Reflist, 30em Zircon Hadean