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Morphological transition during prograde olivine growth formed by high-pressure dehydration of antigorite-serpentinite to chlorite-harzburgite in a subduction setting

Nicole Dilissen, Károly Hidas Carlos J. Garrido, Vicente López Sánchez-Vizcaíno, Wolf-Achim Kahl

Lithos (2021) 382-383, 105949

https://doi.org/10.1016/j.lithos.2020.105949

Crystal morphologies are essential for deciphering the reaction history of igneous and metamorphic rocks because they often record the interplay between nucleation and growth rates controlled by the departure from equilibrium. Here, we report an exceptional record of the morphological transition of olivine formed during subduction metamorphism and high-pressure dehydration of antigorite-serpentinite to prograde chlorite-harzburgite in the Almirez ultramafic massif (Nevado–Filábride Complex, Betic Cordillera, SE Spain). In this massif, rare varied-textured chlorite-harzburgite (olivine+enstantite+chlorite+oxides) —formed after high–P dehydration of antigorite-serpentinite— exhibits large olivine porphyroblasts made up of rounded cores mantled by coronas of tabular olivine grains, similar to single tabular olivines occurring in the matrix. The correlative X-ray μ-CT and EBSD study of two varied-textured chlorite-harzburgite samples show that tabular olivine in coronas is tabular on (100)Ol with c > b >> a, and grew in nearly the same crystallographic orientation as the rounded olivine cores of the porphyroblast.

3D model of rock fabric
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