Review of paper: Interpretation of zircon corona textures from metapelitic granulites of Ivrea-Verbano Zone, Northern Italy: Two-stage decomposition of Fe-Ti oxides

Abstract. In this study, we report the occurrence of zircon coronae textures in metapelitic granulites of the Ivrea–Verbano Zone. Unusual zircon textures are spatially associated with Fe–Ti oxides and occur as (1) vermicular-shaped aggregates 50–200 µm long and 5–20 µm thick and as (2) zircon coronae and fine-grained chains, hundreds of micrometers long and ≤ 1 µm thick, spatially associated with the larger zircon grains. Formation of such textures is a result of zircon precipitation during cooling after peak metamorphic conditions, which involved: (1) decomposition of Zr-rich ilmenite to Zr-bearing rutile, and formation of the vermicular-shaped zircon during retrograde metamorphism and hydration; and (2) recrystallization of Zr-bearing rutile to Zr-depleted rutile intergrown with quartz, and precipitation of the submicron-thick zircon coronae during further exhumation and cooling. We also observed hat-shaped grains that are composed of preexisting zircon overgrown by zircon coronae during stage (2). Formation of vermicular zircon (1) preceded ductile and brittle deformation of the host rock, as vermicular zircon is found both plastically and cataclastically deformed. Formation of thin zircon coronae (2) was coeval with, or immediately after, brittle deformation as coronae are found to fill fractures in the host rock. The latter is evidence of local, fluid-aided mobility of Zr. This study demonstrates that metamorphic zircon can nucleate and grow as a result of hydration reactions and mineral breakdown during cooling after granulite-facies metamorphism. Zircon coronae textures indicate metamorphic reactions in the host rock and establish the direction of the reaction front.

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Interpretation of zircon corona textures from metapelitic granulites of the Ivrea-Verbano Zone, Northern Italy: Two-stage decomposition of Fe-Ti oxides

10.5194/se-2017-35 ◽

2017 ◽

Author(s):

Elizaveta Kovaleva ◽

Håkon O. Austrheim ◽

Urs S. Klötzli

Keyword(s):

Host Rock ◽

Granulite Facies ◽

Northern Italy ◽

Retrograde Metamorphism ◽

Brittle Deformation ◽

Granulite Facies Metamorphism ◽

Fine Grained ◽

Ti Oxides ◽

Facies Metamorphism ◽

Metapelitic Granulites

Abstract. In this study, we report the occurrence of zircon coronae textures in metapelitic granulites of the Ivrea-Verbano Zone. Unusual zircon textures are spatially associated with Fe-Ti oxides and occur as (1) vermicular-shaped aggregates 50–200 µm long and 5–20 µm thick, and as (2) zircon coronae and fine-grained chains, hundreds of µm long and ≤ 1 µm thick, spatially associated with the larger zircon grains. Formation of such textures is a result of zircon precipitation during cooling after peak metamorphic conditions, which involved: (1) decomposition of Zr-rich ilmenite to Zr-bearing rutile and vermicular-shaped zircon during retrograde metamorphism and hydration; (2) recrystallization of Zr-bearing rutile to Zr-depleted rutile intergrown with quartz and submicron-thick zircon coronae during further exhumation and cooling. We also observed hat-shaped grains that are composed of preexisting zircon overgrown by zircon coronae during stage (2). Formation of vermicular zircon (1) preceded ductile and brittle deformation of the host rock, as vermicular zircon is found both plastically- and cataclastically-deformed. Formation of thin zircon coronae (2) was coeval with, or immediately after brittle deformation, as coronae are found to fill fractures in the host rock. The latter is evidence of local, fluid-aided mobility of Zr. This study demonstrates that metamorphic zircon can nucleate and grow as a result of hydration reactions and mineral breakdown during cooling after granulite-facies metamorphism. Zircon corona textures indicate metamorphic reactions in the host rock, and establishing the direction of the reaction front.

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Interpretation of zircon corona textures from metapelitic granulites of Ivrea-Verbano Zone, Northern Italy: Two-stage decomposition of Fe-Ti oxides

10.5194/se-2016-164 ◽

2016 ◽

Author(s):

Elizaveta Kovaleva ◽

Håkon Austrheim ◽

Urs Klötzli

Keyword(s):

Host Rock ◽

Oxide Phase ◽

Granulite Facies ◽

Brittle Deformation ◽

Granulite Facies Metamorphism ◽

Cooling Stage ◽

Fine Grain ◽

Ti Oxides ◽

Two Stages ◽

Metapelitic Granulites

Abstract. In this study we report the occurrence of zircon corona textures in metapelitic granulites of the Ivrea-Verbano Zone. Unusual zircon textures are spatially associated with Fe-Ti oxides and occur as (1) vermicular-shaped aggregates 50–200 µm long and 5–20 µm thick, and as (2) zircon coronas and fine-grain chains, hundreds of µm long and ≤ 1 µm thick, spatially associated with (1). Formation of such textures is a result of mineral-fluid reactions, which occurred in two stages and involved: (1) decomposition of ilmenite to Zr-rich rutile and vermicular-shaped zircon during peak metamorphism and initial cooling stage, and (2) recrystallization of Zr-rich rutile to Zr-depleted rutile and submicron-thick zircon coronas during further exhumation and cooling. We also observed hat-shaped grains that are composed of preexisting zircon overgrown by zircon coronas during stage (2). Hat-shaped grains have a flat surface towards the oxide phase, which indicates partial dissolution of preexisting zircon grain. Formation of vermicular zircon (1) preceded ductile and brittle deformation of the host rock, as vermicular zircon is found both plastically- and cataclastically-deformed. Formation of thin zircon coronas (2) was coeval with or soon after the brittle deformation, as coronas occasionally fill fractures in the host rock. Occurrences of zircon coronas has important implications in fundamental studies regarding metamorphism, metasomatism and element transport in the Earth’s crust. We demonstrate that metamorphic zircon can nucleate and grow as a result of hydration reactions at the cooling stage after granulite-facies metamorphism, and reflects stages of rock evolution. Zircon corona textures are the tool for indicating metamorphic and metasomatic reactions in the host rock, and establish the directions of the reaction front.

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Two-stage self-seeding method for preparation of single crystals of poly(phenylene sulfide)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153816 ◽

1989 ◽

Vol 47 ◽

pp. 368-369

Author(s):

Sengshiu Chung ◽

Peggy Cebe

Keyword(s):

Single Crystals ◽

High Performance ◽

Dilute Solution ◽

Two Stage ◽

Annealing Behavior ◽

High Performance Polymers ◽

Seeding Method ◽

Phenylene Sulfide

We are studying the crystallization and annealing behavior of high performance polymers, like poly(p-pheny1ene sulfide) PPS, and poly-(etheretherketone), PEEK. Our purpose is to determine whether PPS, which is similar in many ways to PEEK, undergoes reorganization during annealing. In an effort to address the issue of reorganization, we are studying solution grown single crystals of PPS as model materials.Observation of solution grown PPS crystals has been reported. Even from dilute solution, embrionic spherulites and aggregates were formed. We observe that these morphologies result when solutions containing uncrystallized polymer are cooled. To obtain samples of uniform single crystals, we have used two-stage self seeding and solution replacement techniques.

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