See more from this Division: Topical Sessions
See more from this Session: Strengthening Links between Metamorphic Conditions and Time: New Advances in High-Temperature Geochronology and Tracing P-T-t Paths of Metamorphic Terranes
Abstract:
Monazite inclusions in garnet are depleted in Y, Sm, and Gd and linked to melt-enhanced flow of continental lower crust during fluid-absent breakdown of biotite + plagioclase + quartz at ca. 1.0-1.1 GPa. Circa 2.62-2.58 Ga Y-depleted, Th-rich domains represent peritectic growth of monazite in the presence of melt, garnet, ternary K-feldspar, and orthopyroxene at T >900°C. Low-Th rims depleted in Ca and enriched in Eu are linked to melt-absent growth of grossular-rich garnet at the expense of dynamically recrystallized orthopyroxene and plagioclase during crustal thickening at ca. 2.58-2.55 Ga to >1.5 GPa. Greater than 650 m.y. of isobaric-cooling and strengthening was followed by syn-kinematic growth of LREE-rich monazite (concurrent with dynamic recrystallization of ternary feldspar) during intra-continental dextral transpressive shear strain at ca. 1.92-1.9 Ga.
Monazite grains in this study are marked by positive Eu-anomalies relative to CI chondrite. A direct link is implied between Y, Sm, Eu, and Gd in monazite and two major phases in continental lower crust: garnet and plagioclase. Europium-anomalies in lower crustal monazite associated with modally-abundant Grt +/- Pl appear directly related to depletions of Y, Sm, and Gd during garnet-growth and loss (or removal) of plagioclase. These links permit tight constraints on the evolution of continental lower crust at depth during melting, crustal flow, isobaric-cooling, and strain-partitioning.
See more from this Division: Topical Sessions
See more from this Session: Strengthening Links between Metamorphic Conditions and Time: New Advances in High-Temperature Geochronology and Tracing P-T-t Paths of Metamorphic Terranes