Changes

==Errors and Limitations==

==Errors and Limitations==

Ti-in-Zircon geothermometry is considered to be a relatively reliable and accurate method of determining crystallization temperatures of zircons, with a error of only 10-16 degrees Celsius. However, the major constraint of this process is that it is only usable in systems that contain titanium, or the mineral [[rutile]] (TiO₂). In systems that have no or very little titanium, this method is pointless, as zircons will not incorporate titanium if it is not present in the magmatic melt.<ref name="Watson and Harrison 2005" /> However, recent models have taken into account zircon's ability to replace either silicon or zirconium in the crystal with titanium by using independent activities of Si and Zr.<ref name="Ferry and Watson 2007 New Thermo models and revised calibrations">Ferry, J.M.; Watson, E.B. (Oct 2007). "New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers". Contributions to Mineralogy and Petrology 154 (4): 429-437. doi:10.1007/s00410-007-0201-0. Retrieved 29 November 2014.</ref> This has expanded the potential uses for zircons with unknown origins, due to the abundance of silicon in Earth's crust. In some zircon crystals, inclusions of the mineral [[quartz]] (SiO₂) can be used as proof that silicon was present during crystallization, thus validating the use of this geothermometer.

Ti-in-Zircon geothermometry is considered to be a relatively reliable and accurate method of determining crystallization temperatures of zircons, with a error of only 10-16 degrees Celsius. However, the major constraint of this process is that it is only usable in systems that contain titanium, or the mineral [[rutile]] (TiO₂). In systems that have no or very little titanium, this method is pointless, as zircons will not incorporate titanium if it is not present in the magmatic melt.<ref name="Watson and Harrison 2005" /> However, recent models have taken into account zircon's ability to replace either silicon or zirconium in the crystal with titanium by using independent activities of Si and Zr.<ref name="Ferry and Watson 2007 New Thermo models and revised calibrations">Ferry, J. M., & E. B. Watson, 2007, New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers: Contributions to Mineralogy and Petrology 154 (4): 429-437. doi:10.1007/s00410-007-0201-0.</ref> This has expanded the potential uses for zircons with unknown origins, due to the abundance of silicon in Earth's crust. In some zircon crystals, inclusions of the mineral [[quartz]] (SiO₂) can be used as proof that silicon was present during crystallization, thus validating the use of this geothermometer.

Due to the abundance of radioactive elements that can by incorporated into zircons, they are also susceptible to damage from radioactive decay through the process of [[Metamictization]]. As radioactive elements inside the crystal lattice decay, they bombard the interior of the crystal with radioactive particles. This weakens the crystal and leave it fractured or weakened.<ref name="hoskin and schaltegger, comp of zircon" /> This increases the chance of isotopes leaking out of the crystal and affecting titanium, or other elements, measurements.

Due to the abundance of radioactive elements that can by incorporated into zircons, they are also susceptible to damage from radioactive decay through the process of [[Metamictization]]. As radioactive elements inside the crystal lattice decay, they bombard the interior of the crystal with radioactive particles. This weakens the crystal and leave it fractured or weakened.<ref name="hoskin and schaltegger, comp of zircon" /> This increases the chance of isotopes leaking out of the crystal and affecting titanium, or other elements, measurements.

Another difficulty with this microanalysis is the contamination of Ti on external surfaces. Recent studies have expressed concern over the [[gold]] coating on the surface of the ion microprobe mounts, which contains small amounts of Ti (~1 ppm) that could provide an error during measurement. In [[detrital]] zircons found in sedimentary sources, a Ti-bearing oxide coating on the surface and in fractures of zircons can also contaminate the crystal with excess titanium.<ref name="Watson Wark Thomas 2006" />

Another difficulty with this microanalysis is the contamination of Ti on external surfaces. Recent studies have expressed concern over the [[gold]] coating on the surface of the ion microprobe mounts, which contains small amounts of Ti (~1 ppm) that could provide an error during measurement. In [[detrital]] zircons found in sedimentary sources, a Ti-bearing oxide coating on the surface and in fractures of zircons can also contaminate the crystal with excess titanium.<ref name="Watson Wark Thomas 2006" />

More recent studies have also shown that there are additional unknown factors that contribute to Ti incorporation in zircons. The chemical activity of SiO₂, pressure variance, disequilibrium crystallization from melts, late crystal growth in hydrous melts, or non-[[Henry's Law]] substitution in zircon crystals all may play a role in altering predicted crystallization temperatures.<ref name="Fu et al, applications and limitations">Fu, Bin; Page, F. Zeb; Cavosie, Aaron J.; Fournelle, John; Kita, Noriko T.; Lackey, Jade Star; Wilde, Simon A.; Valey, John W. (12 Feb 2008). "Ti-in-zircon thermometry: applications and limitations". Contributions to Mineralogy and Petrology 156: 197–215. doi:10.1007/s00410-008-0281-5.</ref>

More recent studies have also shown that there are additional unknown factors that contribute to Ti incorporation in zircons. The chemical activity of SiO₂, pressure variance, disequilibrium crystallization from melts, late crystal growth in hydrous melts, or non-[[Henry's Law]] substitution in zircon crystals all may play a role in altering predicted crystallization temperatures.<ref name="Fu et al, applications and limitations">Fu, B., F. Z. Page, A. J. Cavosie, J. Fournelle, N. T. Kita, T. Noriko, J. S. Lackey, S. A. Wilde, & J. W. Valey, 2008, Ti-in-zircon thermometry: applications and limitations: Contributions to Mineralogy and Petrology 156: 197–215. doi:10.1007/s00410-008-0281-5.</ref>

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" />