Changes

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, 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>

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">{{cite journal|last1=Cherniak|first1=D.J.|last2=Hanchar|first2=J.M.|last3=Watson|first3=E.B.|title=Diffusion of tetravalent cations in zircon|journal=Contributions to Mineralogy and Petrology|volume=127|issue=4|pages=383–390|doi=10.1007/s004100050287|accessdate=8 Oct 2014}}</ref> [[Pb]],<ref name="Pb diffusion">{{cite journal|last1=Cherniak|first1=D.J.|last2=Watson|first2=E.B.|title=Pb diffusion in zircon|journal=Chemical Geology|volume=172|issue=1-2|pages=5–24|doi=10.1016/S0009-2541(00)00233-3|accessdate=8 Oct 2014}}</ref> and Ti<ref name="Cherniak and Watson 2007">{{cite journal|last1=Cherniak|first1=D.J.|last2=Watson|first2=E.B|title=Ti diffusion in zircon|journal=Chemical Geology|date=9 May 2007|volume=242|pages=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">{{cite journal|last1=Cherniak|first1=Daniele J.|last2=Watson|first2=E. Bruce|title=Diffusion in Zircon|journal=Reviews in Mineralogy and Geochemistry|date=Jan 2003|volume=53|pages=113–133|doi=10.2113/0530113|accessdate=20 November 2014}}</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">{{cite journal|last1=Corfu|first1=Fernando|last2=Hanchar|first2=John M.|last3=Hoskin|first3=Paul W.O.|last4=Kinny|first4=Peter|title=Atlas of Zircon Textures|journal=Reviews in Mineralogy and Geochemistry|date=Jan 2003|volume=53|issue=1|page=469-500|doi=10.2113/0530469|url=http://rimg.geoscienceworld.org/content/53/1.toc|accessdate=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.; 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.

==Methods==

==Methods==

This technique is also constrained by several assumptions that, while valid, my prove inconsistent in certain situations. Laboratory studies have used constant pressures when calculating cooling temperatures and have assumed that pressure does not play a major role in Ti incorporation. When estimating cooling temperatures, increased pressure is accounted for by increased temperature estimates and thus increases the uncertainty of the estimates.<ref name="Ferry and Watson 2007 New Thermo models and revised calibrations" />

This technique is also constrained by several assumptions that, while valid, my prove inconsistent in certain situations. Laboratory studies have used constant pressures when calculating cooling temperatures and have assumed that pressure does not play a major role in Ti incorporation. When estimating cooling temperatures, increased pressure is accounted for by increased temperature estimates and thus increases the uncertainty of the estimates.<ref name="Ferry and Watson 2007 New Thermo models and revised calibrations" />

==References==

==References==