Rehydration of eclogites and garnet-replacement processes during exhumation in the amphibolite facies
Posted on 2018-03-23 - 15:34
EPMA and LA-ICP-MS trace-element maps have been acquired from amphibolitized eclogites from the Diego de Almagro Metamorphic Complex (Chile). Several garnet growth pulses and garnet resorption stages are revealed by major elements chemical zoning and by heterogeneous Y and rare earth element (REE) behaviour, associated with subduction and exhumation of these rocks. Distribution of REE in prograde garnet is texturally and chemically coupled with the breakdown of REE-bearing minerals while formation of epidote and titanite generations during amphibolitization is recorded by complex textures involving new garnet generation and overprinting phases. The latest overprint stage is characterized by fine-grained intergrowth between garnet and epidote micro-veins, phengite, hornblende, albite and titanite. Garnet cracks have been gradually re-equilibrated during this event witnessing short-scale dissolution–transport–precipitation. Pseudosection modelling shows that local variability in water content during amphibolitization controls garnet stability at the expense of epidote. Overprinting microstructures are explained by the effect of locally-derived aqueous fluids that trigger the 'unlocking' of elements from the reacting eclogite-facies paragenesis. These findings highlight the microscopic characteristics of amphibolitization processes documented in exhumed eclogite-facies terranes and shed light on the importance of thorough micro-chemical investigations while undertaking pressure–temperature (PT) estimates on rocks with strong textural disequilibrium.
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Hyppolito, Thais; Cambeses, Aitor; Angiboust, Samuel; Raimondo, Tom; García-Casco, Antonio; Juliani, Caetano (2018). Rehydration of eclogites and garnet-replacement processes during exhumation in the amphibolite facies. Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.4040798.v1
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AUTHORS (6)
TH
Thais Hyppolito
AC
Aitor Cambeses
SA
Samuel Angiboust
TR
Tom Raimondo
AG
Antonio García-Casco
CJ
Caetano Juliani
CATEGORIES
KEYWORDS
amphibolitization processesoverprint stageexhumed eclogite-facies terraneselements chemical zoningREE-bearing mineralstextural disequilibriumeclogite-facies paragenesisamphibolitized eclogitesepidote micro-veinswater contentPTGarnet cracksSeveral garnet growth pulsestitanite generationsAlmagro Metamorphic ComplexLA-ICP-MS trace-element mapsoverprinting phasesamphibolite facies EPMAmicro-chemical investigationsearth elementamphibolitization controls garnet stabilitygarnet generationgarnet resorption stagesOverprinting microstructuresgarnet-replacement processesprograde garnetGeology