• The Journal of the Petrological Society of Korea
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• v.14 no.2 s.40
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• pp.108-115
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• 2005

Gyeonggi metamorphic complex in the Gwangju area include banded biotite gneiss and quartzofeldspathic gneiss. Detailed structural analysis suggests that structural elements in the study area were formed by at least five phase of deformations. Penetrative compositional foliations(S1) formed in the banded gneiss during the first metamorphism and deformation (D1). After intrusion of plutonic rocks, the second deformation (D2) produced S2 foliations in the banded gneiss and quartzofeldspathic gneiss during the second metamorphism. D3 structures are represented by isoclinal folds (F3) whose axial surfaces are parallel to S3 foliations. The N-S oriented shortening (D4) was accommodated by closed upright F4 fold with about 100m of axial surface separation. F4 fold is refolded by regional F5 folding resulting in different orientation and fold style of F4 fold according to the position of F5 fold. The F4 fold with tight interlimb angle is subparallel to the axial surface (north-south) of F5 fold in the core of the F5 fold. In contrast the F4 fold trends northeast in the western limb and northwest in the eastern limb of F5 fold. The interlimb angle is larger in the limbs than that in the core of F5 fold. The trace of foliations is constrained by mainly F4 and F5 folds. Joint fanning around fold is developed in the limbs of F5 fold and bc joints are dominant in the hinge area of F5 fold. A strike-slip fault had developed in tile central part of the study area after F5 folding. The orientation of joint and foliation is rotated anticlockwise about $15^{\circ}$ by the landslide occurred during the Quaternary.

• Journal of the Mineralogical Society of Korea
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• v.24 no.1
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• pp.19-29
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• 2011

Clay mineral assemblages of core PC25A collected from the northern part of the Aleutian Basin in the Bering Sea were examined in order to investigate changes in sediment provenances and transport pathways. Ages of core PC25A were determined by both Last Appearance Datum of radiolaria (L. nipponica sakaii; $48.6{\pm}2\; ka$) and age control points obtained by the correlations of $a^{\ast},\; b^{\ast}$, and laminated sediment layers with the adjacent core PC23A, whose ages are well constrained. The corebottom age of core PC25A was calculated to be about 57,600 yr ago and core-top might be missing during coring execution. Average contents of smectite, illite, kaolinite, and chlorite during the last glacial period are 11% (5~24%), 47% (36~58%), 13% (9~19%), and 29% (21~40%), respectively. Clay mineral assemblages of the last glacial period are characterized by higher illite and lower smectite contents than those of core MC24 representing the modern values. Illite-rich clay sediments during the warm Early Holocene were transported from the northern part of Alaska continent (Province 1) through the ice-melt waters. During the deglacial period (B${\phi}$lling-All${\phi}$rod) of MIS 2, clay-sized particles seemed to be also transported by ice-melt waters mainly from Province 2 and Province 3 located farther south than Province 1. Higher smectite content during the Last Glacial Maximum is attributed to increased amounts of clay particles from the adjacent Alaska Peninsula (Province 4). From the early to the middle MIS 3, illite and smectite contents decreased, whereas chlorite content increased. With the low sea level standing during MIS 3 the supply of clay sediments from Province 2 and Province 3 was most likely intensified. Changes in clay mineral assemblages of core PC25A located in the northern part of the Aleutian Basin in the Bering Sea are closely related to the change of surface current system caused by sea level variation during the last glacial period.