[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)

キーワード：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.