[1poster01-10] T1. Metamorphic rocks and tectonics

ECS

[T1-P-2] Structural evolution of the Instekleppane, Lutzow-Holm Complex: Deformation patterns in high-grade zones of east Antarctica

*Sreehari Lakshmanan¹, Tatsuro Adachi², Yuki Mori³, Tomokazu Hokada⁴ (1. Shimane U. , 2. Kyushu U., 3. JASRI, 4. NIPR)

Keywords:

East Antarctica,Structural geology,Gondwana tectonics,Continental collision

　We present comprehensive structural analysis of the Instekleppane outcrop, located in the western part of the Lützow-Holm Complex (LHC), a high-grade metamorphic terrane of Neoproterozoic to Cambrian age in East Antarctica. The approximately one-square-kilometer outcrop is situated to the southwest of Syowa Station and to the east of the Shirase Glacier and was systematically investigated as part of the 65th Japanese Antarctic Research Expedition (JARE-65). The lithological assemblage at Instekleppane comprises felsic orthopyroxene–biotite gneiss, garnet-bearing felsic granulite, magnesium–aluminium-rich gneiss, mafic hornblende–orthopyroxene–clinopyroxene granulite, ultramafic bodies, and minor granitic intrusions.Structural analysis reveals six distinct stages of deformation, designated D0 through D5, of which four (D0 to D3) represent major tectonometamorphic events. D0 corresponds to the development of primary magmatic or sedimentary layering that is locally preserved in less-deformed lithologies. D1 marks the formation of the earliest penetrative foliation, which is typically parallel to the compositional layering and may represent transposed bedding or igneous banding. The D2 event is characterized by layer-parallel stretching that led to the formation of mafic boudins and the development of two generations of folds. The first folding phase (F21) comprises recumbent, isoclinal, and intrafolial folds, while the second (F22) consists of overturned folds; both generations display axial planes that trend approximately east–west. D3 deformation is associated with the formation of upright to moderately plunging open folds (F3) with northwest–southeast trending axial planes, marking a significant change in the regional stress regime. The subsequent D4 phase is defined by reverse shear zones that locally overprint earlier structures, and the final D5 phase is represented by subvertical, high-strain zones accommodating strike-slip displacement.The deformation history documented at Instekleppane shares multiple structural and metamorphic features with those reported from other high-grade terranes in the Lützow-Holm Complex, such as Rundvågshetta and Langhovde. This suggests a regionally coherent ductile deformation history during the tectonic evolution of the LHC, reflecting large-scale crustal reworking processes associated with the assembly of East Gondwana.