Constraints from Monazite Petrochronology on the Assembly of the Ivrea-Verbano Zone
Open Access
- Author:
- Wyatt, Damaris Christine
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- September 06, 2019
- Committee Members:
- Andrew James Smye, Thesis Advisor/Co-Advisor
Kevin Patrick Furlong, Committee Member
Tanya Furman, Committee Member
Mark E Patzkowsky, Program Head/Chair - Keywords:
- Lower Crust
Metamorphism
Lower Continental Crust
Monazite
U-Pb Geochronology
Metamorphic Petrology
Tectonics
Trace Element Geochemistry
Thermobarometry
Pseudosection Modeling - Abstract:
- The Ivrea-Verbano Zone (IVZ) in northwest Italy is an archetypal section of lower continental crust. This section is dominated by metasedimentary rocks, in contrast to constraints from geochemical data, seismic wave speeds, and heat flow estimates interpreted to reflect a mafic lower continental crustal composition. How, then, are sediments incorporated into lower continental crust? Burial, crustal underthrusting, and relamination are three tectonic mechanisms that could emplace sediments at lower crustal depths. This investigation seeks to constrain the prograde pressure-temperature-time (P-T-t) path of IVZ metapelites and compare it to the expected prograde P-T-t path for each mechanism to determine which is responsible for the assembly of the lower crustal section. The tectonic mechanisms are further assessed by comparing their predicted petrological and field scale characteristics with features observed in IVZ rocks. Laser ablation split stream (LASS) ICP-MS measurements of U-Pb dates and trace element concentrations in monazite grains found in two suites of amphibolite to granulite facies metapelitic rocks from Val Strona di Omegna, IVZ, provide a record of the Permian-to-Jurassic metamorphic history of the lower crust of the Southern Alpine basement. Monazite dates are quantitatively linked to P-T conditions through phase equilibria calculations and the yttrium-in-garnet and monazite (Y-MG) thermometer applied to the pre-300 Ma monazite population. These constraints on the prograde P-T-t evolution of the Ivrea Zone, combined with field and petrographic observations of IVZ metapelites, indicate that the IVZ lower crustal section likely formed through crustal underthrusting.