EBSD-measured crystal preferred orientation of eclogites from the Sanbagawa metamorphic belt, central Shikoku, SW Japan

被引:10
作者
Rehman, Hafiz Ur [1 ]
Mainprice, David [2 ]
Barou, Fabrice [2 ]
Yamamoto, Hiroshi [1 ]
Okamoto, Kazuaki [3 ]
机构
[1] Kagoshima Univ, Grad Sch Sci & Engn, Kagoshima 890, Japan
[2] Univ Montpellier, UMR CNRS 5243, Geosci Montpellier, Montpellier, France
[3] Saitama Univ, Fac Educ, Dept Earth Sci, Saitama, Japan
关键词
Sanbagawa metamorphic belt; high-pressure/low-temperature eclogites; EBSD; crystal preferred orientation; CPO; omphacite; garnet; deformation; rheology; MAFIC-ULTRAMAFIC BODIES; PLASTIC-DEFORMATION; HIGH-TEMPERATURE; OMPHACITE; EVOLUTION; PRESSURE; FABRICS; GARNET; MICROSTRUCTURES; RHEOLOGY;
D O I
10.1127/ejm/2016/0028-2574
中图分类号
P57 [矿物学];
学科分类号
070901 ;
摘要
Electron back-scattered diffraction (EBSD) maps and crystal-preferred orientation (CPO) of eclogite-facies (omphacite and garnet) and amphibolite-facies (hornblende and actinolite) phases are reported for understanding the rheological behaviour of crust during subduction. Two types of eclogites from the subduction-related high-pressure/low-temperature type Sanbagawa metamorphic belt, Japan, have been investigated. Type-I eclogite (sample Sb-1) is composed of garnet, omphacite, secondary actinolite and hornblende. Type-II eclogite (samples Sb-2 and Sb-2a) are mainly composed of omphacite, garnet, and retrograde hornblende with no actinolite. Omphacite, the peak eclogite-facies phase, exhibits L-type CPO (maximum density of [001] axes parallel to and high density of 110} poles normal to the lineation) in Type-I eclogite, suggesting intra-crystalline plasticity with [001] {110} and (110) (110} active slip systems, indicating a constrictive strain regime at mantle depths. Omphacite in Type-II eclogite exhibits a similar fabric but with much weaker CPO. Using the LS-index symmetry analysis (one for the end-member L-type, zero for the end-member S-type, and intermediate values for LS-types), a progressive change in LS index of 0.80 for Type-I and 0.61 to 0.44 for Type-II eclogites is observed. These values suggest a transition from axial extension parallel to the lineation for Sb-1 and weaker CPO associated with pure or simple shear for Sb-2 and Sb-2a. Garnet, the second dominant phase in the eclogite-facies stage, exhibits weak and complex fabric patterns in all eclogite types, behaved like rigid bodies and does not show plastic deformation. Amphibolite-facies phases (e.g., hornblende and actinolite) exhibit more than two types of CPO. Hornblende and actinolite in Type-I eclogite have a strong CPO along [001] axes aligned parallel to the lineation, indicating homotactic crystal growth probably by the replacement of omphacite during the early stages of retrogression. Type-II eclogites have weak CPO in hornblende but with characteristic alignment of [001] parallel to the lineation and other poles to planes (100), (010), and (110} normal to the lineation. This fabric might have resulted from a cataclastic deformation and could be related to the late-"D1" deformation stage in the Sanbagawa metamorphic belt.
引用
收藏
页码:1155 / 1168
页数:14
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