[S-MP08] Micro- to macro-scale deformation: petrologic, mineralogic, geophysical and geochemical checkpoints

[SMP08-07] EBSD-measured crystal preferred orientations of Sanbagawa eclogites

*REHMAN, Hafiz UR¹, David MAINPRICE², Hiroshi YAMAMOTO¹, Kazuaki OKAMOTO³ (1.Graduate School of Science and Engineering, Kagoshima University, Japan, 2.Geosciences Montpellier, Universite Montpellier 2, France, 3.Saitama University)

Keywords:EBSD, Eclogites, crystal preferred orientations, Sanbagawa

Electron backscattered diffraction maps and crystal preferred orientations of the two types of eclogites in the subduction-related high-pressure/low-temperature type Sanbagawa metamorphic belt, central Shikoku, Japan have been reported. Type 1 eclogite (garnet: 43%, omphacite: 35%, secondary actinolite: 7% and hornblende: 5% with minor quartz, muscovite and rutile), garnet-rich and dark green, have strong crystal preferred orientations in omphacite and rutile, weak but complex fabric pattern in garnet suggesting their deformation during peak eclogite facies stage. Type 2 eclogite (omphacite: 41%, garnet: 39%, retrograde hornblende: 11% with minor quartz, epidote/zoisite, rutile and titanite), omphacite-rich and light green, also show identical fabric to that of type I. Crystal preferred orientations (CPOs) of minerals in both types show that omphacite has the strongest CPO along [001]-axes and {011}-poles, suggesting intracrystaline flow along [001]{110} and [001](100) slip systems representing subduction-related deformation rheology at mantle depth. Fabric preserved in rutile (stable at eclogite facies) is identical to omphacite with maxima along [001]-axes also indicate same deformation mechanism. Amphibolite facies minerals (e.g., hornblende and actinolite) exhibit similar CPOs to that of omphacite, indicating homotaxial crystal growth/recrystallization after the replacement of omphacite during late-stage retrogression. In both type eclogites the deformation was mainly accommodated in omphacite which developed L-type fabric, representing a constrictive stress regime. Based on jadeite content (> 0.35 in type 1 and < 0.3 in type 2) in the omphacite in both type eclogites there is no clear correlation for the development of L-type fabric in relation to the cation ordered-disordered structure despite of slightly different equilibration temperatures. Garnet, behaving as rigid body, exhibit complex CPO and do not show any clear plastic deformation.