# Amphibole CPO in retrograded gabbro from the Lyngen Magmatic Complex (Northern Scandinavian Caledonides, Norway).

Marina Galindos Alfarache, Holger Stünitz, Jiří Konopásek, Amicia Lee

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Marina Galindos Alfarache, Holger Stünitz, Jiří Konopásek, Amicia Lee. Amphibole CPO in retro-graded gabbro from the Lyngen Magmatic Complex (Northern Scandinavian Caledonides, Norway). vEGU21: Gather Online, Apr 2021, Online, France. 10.5194/egusphere-egu21-1303. hal-03554567

HAL Id: hal-03554567

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Submitted on 3 Feb 2022

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# Amphibole CPO in retrograded gabbro from the Lyngen Magmatic Complex (Northern Scandinavian Caledonides, Norway).

Marina Galindos Alfarache<fnref n="1" />, Holger Stünitz<fnref n="1" />,<fnref n="2" />, Jiří Konopásek<fnref n="1" />, and Amicia Lee<fnref n="1" />

Deformation of natural mafic rocks by viscous deformation mechanisms can occur even at low
temperature conditions. In such instances, crystal plastic mechanisms are not operative, as their
activity is restricted to very high temperatures for amphiboles, pyroxenes, and plagioclase.
Instead, simultaneous mineral reactions may facilitate deformation at low temperature conditions.
The gabbro from the Lyngen Magmatic Complex (LMC) constitutes a good example of such
processes, because it has experienced deformation at low temperatures of greenschist to lower
amphibolite-facies conditions, and the rock has been transformed from gabbro to greenschist.
This study focuses on detailed analysis of deformation processes, metamorphic reactions and
fabric development in the LMC gabbro. Most samples are overprinted by epidote amphibolite and
greenschist-facies mineral assemblages. Preliminary observations distinguish two different types
of amphiboles, which have been interpreted as different generations. The predominant type
defines the stretching lineation and shows long prismatic habits whereas the less abundant type
crystallized in a sub- to anhedral manner. The metamorphic conditions of growth for each
amphibole type is yet not well constrained. However, we initially interpret the former to grow
during epidote amphibolite- or greenschist facies-conditions, whereas the latter could represent
relict grains from the original magmatic assemblage or products generated at amphibolite- or
epidote amphibolite-facies conditions. Further analysis will determine the orientation,
geochemistry and metamorphic conditions during growth for both amphibole types. A recent
model proposed for eclogites suggests that simultaneous mineral growth and deformation can
result in new products growing in a preferred direction. Such preferential growth can generate a
shape preferred orientation parallel to the lineation, which results in the formation of crystal
preferred orientations (CPO). We aim to test if similar microstructural observations can be
translated to the amphiboles of the LMC gabbro. In such case, amphibole CPO's would not be the
product of crystal plasticity but of preferential growth. The large scale deformation of the LMC
emphasizes the relevance of these results, as it would demonstrate that the interaction between
mineral reactions and deformation can play a major role on regional deformation of large mafic
bodies, such as the ocean floor.

<footnote n="1">¹Dept. of Geosciences,UiT The Arctic University of Norway, Tromsø, Norway (marina.galindos@uit.no)</footnote>

<footnote n="2">²Institut des Sciences de la Terre (ISTO), Université d'Orléans, Orléans, France</footnote>