Changes

Zircon ((Zr_1–y, [[Rare earth elements|REE]]_y)(SiO₄)_1–x(OH)_4x–y)) is an [[orthosilicate]] mineral that is commonly found as an accessory mineral throughout Earth's crust.<ref name="Finch and Hanchar, structure of zircon" />

Zircon ((Zr_1–y, [[Rare earth elements|REE]]_y)(SiO₄)_1–x(OH)_4x–y)) is an [[orthosilicate]] mineral that is commonly found as an accessory mineral throughout Earth's crust.<ref name="Finch and Hanchar, structure of zircon" />

Zircon is a particularly useful mineral because of its ability to incorporate many trace elements. It is know to exchange [[Rare Earth Elements]] (REE) such as [[Uranium]], [[Thorium]], [[Yttrium]],<ref name="Bea. Residence of REE, Y, Th and U...">Bea, F. (1996). "Residence of REE, Y, Th and U in Granites and Crustal Protoliths; Implications for the Chemistry of Crustal Melts". Journal of Petrology 37 (3): 521-552. Retrieved 29 November 2014.</ref> and [[Lutetium]]. However, the chemical potential energies of these REE substitutions are not well understood, so they are not suitable for determining crystallization temperatures. Titanium is also incorporated into zircon, and its exchange rates has been studied in detail. Ti⁴⁺, a tetravalent ion, can replace Zr⁴⁺ or Si⁴⁺ in a temperature dependent mechanism. For zircons in the presence of TiO₂, i.e. the mineral [[rutile]], this substitution process is common and can be measured.<ref name="Watson Wark Thomas 2006" /> Zircon is also useful because its incorporation of other elements like Uranium, Lutetium, [[Samarium]],<ref name="Kinny and Maas Lu-Hf and Sm-Nd...">Kinny, Peter D.; Maas, Roland (Jan 2003). "Lu–Hf and Sm–Nd isotope systems in zircon". Reviews in Mineralogy and Geochemistry 53 (1): 327-341. doi:10.2113/0530327. Retrieved 29 November 2014.</ref> and [[Oxygen]]<ref name="Valley Oxygen Isotopes in Zircon">Valley, John W. (Jan 2003). "Oxygen Isotopes in Zircon". Reviews in Mineralogy and Geochemistry 53 (1): 343-385. doi:10.2113/0530343. Retrieved 29 November 2014.</ref> can be analyzed to provide further insight into the age and conditions the crystal grew under.

Zircon is a particularly useful mineral because of its ability to incorporate many trace elements. It is know to exchange [[Rare Earth Elements]] (REE) such as [[Uranium]], [[Thorium]], [[Yttrium]],<ref name="Bea. Residence of REE, Y, Th and U...">Bea, F.,1996, Residence of REE, Y, Th and U in Granites and Crustal Protoliths; Implications for the Chemistry of Crustal Melts, Journal of Petrology 37 (3): 521-552.</ref> and [[Lutetium]]. However, the chemical potential energies of these REE substitutions are not well understood, so they are not suitable for determining crystallization temperatures. Titanium is also incorporated into zircon, and its exchange rates has been studied in detail. Ti⁴⁺, a tetravalent ion, can replace Zr⁴⁺ or Si⁴⁺ in a temperature dependent mechanism. For zircons in the presence of TiO₂, i.e. the mineral [[rutile]], this substitution process is common and can be measured.<ref name="Watson Wark Thomas 2006" /> Zircon is also useful because its incorporation of other elements like Uranium, Lutetium, [[Samarium]],<ref name="Kinny and Maas Lu-Hf and Sm-Nd...">Kinny, Peter D., & R. Maas, 2003, Lu–Hf and Sm–Nd isotope systems in zircon: Reviews in Mineralogy and Geochemistry 53 (1): 327-341. doi:10.2113/0530327.</ref> and [[Oxygen]]<ref name="Valley Oxygen Isotopes in Zircon">Valley, J. W., 2003, Oxygen Isotopes in Zircon: Reviews in Mineralogy and Geochemistry 53 (1): 343-385. doi:10.2113/0530343.</ref> can be analyzed to provide further insight into the age and conditions the crystal grew under.

Thermally, zircon is resistant to temperature changes and extremes. It is stable up to 1690&nbsp;°C at ambient pressure and has a low thermal expansion rate. Zircons crystals are also some of the most incompressible silicate minerals.<ref name="Finch and Hanchar, structure of zircon">Finch, Robert J.; Hanchar, John M. "Structure and chemistry of zircon and zircon-group minerals". Reviews in Mineralogy and Geochemistry 53 (1): 1–25. doi:10.2113/0530001</ref> The high durability of zircons also allows them to crystallize around other silicate minerals, creating pockets, or inclusions, of surrounding melts that are indicative of magma at specific pressures and temperatures. This essentially forms a time-capsule giving a glimpse of past conditions in which the crystal formed.<ref name="Thomas et al. Melt Inclusions in Zircon">Thomas, J.B.; Bodnar, R.J.; Shimizu, N.; Chesner, C.A. (Jan 2003). "Melt Inclusions in Zircon". Reviews in Mineralogy and Geochemistry 53 (1): 63-87. doi:10.2113/0530063. Retrieved 29 November 2014.</ref>

Thermally, zircon is resistant to temperature changes and extremes. It is stable up to 1690&nbsp;°C at ambient pressure and has a low thermal expansion rate. Zircons crystals are also some of the most incompressible silicate minerals.<ref name="Finch and Hanchar, structure of zircon">Finch, R. J., & J. M. Hanchar, 2003, Structure and chemistry of zircon and zircon-group minerals: Reviews in Mineralogy and Geochemistry 53 (1): 1–25. doi:10.2113/0530001</ref> The high durability of zircons also allows them to crystallize around other silicate minerals, creating pockets, or inclusions, of surrounding melts that are indicative of magma at specific pressures and temperatures. This essentially forms a time-capsule giving a glimpse of past conditions in which the crystal formed.<ref name="Thomas et al. Melt Inclusions in Zircon">Thomas, J.B., R. J. Bodnar, N. Shimizu, N., & C. A. Chesner, 2003, Melt Inclusions in Zircon: Reviews in Mineralogy and Geochemistry 53 (1): 63-87. doi:10.2113/0530063.</ref>

Zircons are know to be relatively retentive of their incorporated isotopes and thus very useful for microquantitative studies. Cations such as REE,<ref name="REE dif">Cherniak, D.J.; Hanchar, J.M.; Watson, E.B. "Rare earth diffusion in zircon". Chemical Geology 134 (4): 289–301. doi:10.1016/S0009-2541(96)00098-8.</ref> U, Th, Hf,<ref name="Tetravalent diffusion">Cherniak, D.J.; Hanchar, J.M.; Watson, E.B. "Diffusion of tetravalent cations in zircon". Contributions to Mineralogy and Petrology 127 (4): 383–390. doi:10.1007/s004100050287.</ref> [[Pb]],<ref name="Pb diffusion">Cherniak, D.J.; Watson, E.B. "Pb diffusion in zircon". Chemical Geology 172 (1-2): 5–24. doi:10.1016/S0009-2541(00)00233-3.</ref> and Ti<ref name="Cherniak and Watson 2007">Cherniak, D.J.; Watson, E.B (9 May 2007). "Ti diffusion in zircon". Chemical Geology 242: 470–483. doi:10.1016/j.chemgeo.2007.05.005.</ref> diffuse slowly out of zircons, and their measured quantities in the mineral are diagnostic of the melt conditions surrounding the crystal during growth. This slow rate of diffusion of many of the incorporated elements makes zircon crystals more likely to form compositional zoning, which may represent oscillatory zoning or sector zoning, as the melt composition or energy conditions change around the crystal over time.<ref name="Cherniak and Watson 2003, RMG">Cherniak, Daniele J.; Watson, E. Bruce (Jan 2003). "Diffusion in Zircon". Reviews in Mineralogy and Geochemistry 53: 113–133. doi:10.2113/0530113.</ref> These zones show compositional differences between the core and rim of the crystal, providing observable evidence of changes in melt conditions.<ref name="Corfu et al. Atlas of Zircon Textures">Corfu, Fernando; Hanchar, John M.; Hoskin, Paul W.O.; Kinny, Peter (Jan 2003). "Atlas of Zircon Textures". Reviews in Mineralogy and Geochemistry 53 (1): 469-500. doi:10.2113/0530469. Retrieved 29 November 2014.</ref> Slow diffusion rates also prevent contamination by leaking or loss of isotopes from the crystal, increasing the likelihood that chonologic and compositional measurements are accurate.

Zircons are know to be relatively retentive of their incorporated isotopes and thus very useful for microquantitative studies. Cations such as REE,<ref name="REE dif">Cherniak, D. J., J. M. Hanchar, & E. B. Watson, Rare earth diffusion in zircon: Chemical Geology 134 (4): 289–301. doi:10.1016/S0009-2541(96)00098-8.</ref> U, Th, Hf,<ref name="Tetravalent diffusion">Cherniak, D. J., J. M. Hanchar, & E. B. Watson, Diffusion of tetravalent cations in zircon: Contributions to Mineralogy and Petrology 127 (4): 383–390. doi:10.1007/s004100050287.</ref> [[Pb]],<ref name="Pb diffusion">Cherniak, D. J., & E. B. Watson, Pb diffusion in zircon: Chemical Geology 172 (1-2): 5–24. doi:10.1016/S0009-2541(00)00233-3.</ref> and Ti<ref name="Cherniak and Watson 2007">Cherniak, D. J., & E. B. Watson, 2007, Ti diffusion in zircon: Chemical Geology 242: 470–483. doi:10.1016/j.chemgeo.2007.05.005.</ref> diffuse slowly out of zircons, and their measured quantities in the mineral are diagnostic of the melt conditions surrounding the crystal during growth. This slow rate of diffusion of many of the incorporated elements makes zircon crystals more likely to form compositional zoning, which may represent oscillatory zoning or sector zoning, as the melt composition or energy conditions change around the crystal over time.<ref name="Cherniak and Watson 2003, RMG">Cherniak, D. J., & E. B. Watson, 2003, Diffusion in Zircon". Reviews in Mineralogy and Geochemistry 53: 113–133. doi:10.2113/0530113.</ref> These zones show compositional differences between the core and rim of the crystal, providing observable evidence of changes in melt conditions.<ref name="Corfu et al. Atlas of Zircon Textures">Corfu, F., J. M. Hanchar, P. W. O. Hoskin, & P. Kinny, 2003, Atlas of Zircon Textures". Reviews in Mineralogy and Geochemistry 53 (1): 469-500. doi:10.2113/0530469. Retrieved 29 November 2014.</ref> Slow diffusion rates also prevent contamination by leaking or loss of isotopes from the crystal, increasing the likelihood that chonologic and compositional measurements are accurate.

==Methods==

==Methods==