Post-entrapment modification of residual inclusion pressure and its implications for Raman elastic thermobarometry

• Verfasst von: Zhong, Xin [VerfasserIn]
• Verfasst von: Moulas, Evangelos [VerfasserIn]
• Verfasst von: Tajcmanová, Lucie [VerfasserIn]
• Titel: Post-entrapment modification of residual inclusion pressure and its implications for Raman elastic thermobarometry
• Verf.angabe: Xin Zhong, Evangelos Moulas, and Lucie Tajčmanová
• E-Jahr: 2020
• Jahr: 25 February 2020
• Umfang: 18 S.
• Fussnoten: Gesehen am 26.03.2020
• Titel Quelle: Enthalten in: Solid earth
• Ort Quelle: Göttingen : Copernicus Publ., 2010
• Jahr Quelle: 2020
• Band/Heft Quelle: 11(2020), 1, Seite 223-240
• ISSN Quelle: 1869-9529
• DOI: doi:10.5194/se-11-223-2020
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 169336364X

Abstract

Residual pressure can be preserved in mineral inclusions, e.g. quartz-in-garnet, after exhumation due to differential expansion between inclusion and host crystals. Raman spectroscopy has been applied to infer the residual pressure and provides information on the entrapment temperature and pressure conditions. However, the amount of residual pressure relaxation cannot be directly measured. An underestimation or overestimation of residual pressure may lead to significant errors between calculated and actual entrapment pressure. This study focuses on three mechanisms responsible for the residual pressure modification: (1) viscous creep; (2) plastic yield; (3) proximity of inclusion to the thin-section surface. Criteria are provided to quantify how much of the expected residual pressure is modified due to these three mechanisms. An analytical solution is introduced to demonstrate the effect of inclusion depth on the residual pressure field when the inclusion is close to the thin-section surface. It is shown that for a quartz-in-garnet system, the distance between the thin-section surface and inclusion centre needs to be at least 3 times the inclusion radius to avoid pressure release. In terms of viscous creep, representative case studies on a quartz-in-garnet system show that viscous relaxation may occur from temperatures as low as 600-700&thinsp;<span class="inline-formula">^∘</span>C depending on the particular pressure-temperature (<span class="inline-formula"><i>P</i></span>-<span class="inline-formula"><i>T</i></span>) path and various garnet compositions. For quartz entrapped along the prograde <span class="inline-formula"><i>P</i></span>-<span class="inline-formula"><i>T</i></span> path and subject to viscous relaxation at peak <span class="inline-formula"><i>T</i></span> above 600-700&thinsp;<span class="inline-formula">^∘</span>C, its residual pressure after exhumation may be higher than predicted from its true entrapment conditions. Moreover, such a viscous resetting effect may introduce apparent overstepping of garnet nucleation that is not related to reaction affinity.</p>