Sangun Metamorphic Research Articles

砕屑性ジルコン年代分布およびＫ－Ｓ検定を用いた三郡変成帯・蓮華変成岩類の後背地推定の試み

砕屑性ジルコン年代分布およびＫ－Ｓ検定を用いた三郡変成帯・蓮華変成岩類の後背地推定の試み

Protolith-age constraints and two-phase folding of Sangun Metamorphic Rocks in northern Kyushu

Protolith-age constraints and two-phase folding of Sangun Metamorphic Rocks in northern Kyushu

CHEMICAL AND PHYSICAL PROPERTIES OF WEATHERED SOILS OF SANGUN METAMORPHIC ROCKS IN YAMAGUCHI PREFECTURE AND ITS APPLICABILITY FOR FILLING MATERIALS

CHEMICAL AND PHYSICAL PROPERTIES OF WEATHERED SOILS OF SANGUN METAMORPHIC ROCKS IN YAMAGUCHI PREFECTURE AND ITS APPLICABILITY FOR FILLING MATERIALS

Landslide at the Sangun Metamorphic Region

A landslide occurred on a slope consisting of the Sangun metamorphic rock in Ube-shi, Yamaguchi Prefecture. The slope of the surface was 10-20 degrees. The area of the landslide itself was 25m wide and 80m long.We examined the slope from a geological, a petrological, and a soil engineering perspectives to identify the characteristics of this landslide. This research resulted in the following findings.The geological features of the slope included tremolite rock and serpentinite hornfels produced by the action of contact metamorphism caused by granite. The landslide occurred as a result of cutting at the end of the slope and heavy rainfalls. The base of the slope may have been easily weakend by the heavy rainfalls because the base primarily consisted of alternating strata of massive rock that had been finely ruptured, and weathered, sandy to silty soils with a relativily high permeability. The residual strength of the clay (chlorite) at the slide surface was almost the same as that obtained by the simple inverse analysis. The analysis of Skempton's residual factors for the three slide surfaces showed that the slide near the end of the slope occurred due to a reactivity movement of an older landslide, while the other two slides occurred first.

U-Pb dating of detrital zircons from the Sangun metamorphic rocks, Kyushu, Southwest Japan: An evidence for 1.9-2.0 Ga granite emplacement in the provenance.

U-Pb and Rb-Sr radiometric dating has been done on zircon samples and mineral concentrates, respectively, separated from psammitic schists of the Sangun metamorphic rocks in central Kyushu, Japan. Based on their shapes and colors, zircon grains were grouped into six. Rounded and short prismatic zircons define, independently of their colors, a common discordia with an upper intercept at 1.91 ± 0.04 Ga. Elongated zircons define another discordia with an upper intercept at 0.93 ± 0.06 Ga. A Rb-Sr internal isochron defined by the mineral concentrates gives an age of 197.7 ± 6.5 Ma, which represents the time of the Sangun metamorphism in central Kyushu. The U-Pb age of 1.91 Ga coincides with that of zircons from the Oki metamorphic rocks (1.96 ± 0.04 Ga: Yamashita and Yanagi, 1994). This and the great abundance of 1.91 Ga grains in the zircon populations seem to indicate a prominent plutonic activity at 1.9–2.0 Ga in the provenance common for the Sangun and Oki metamorphic rocks. The U-Pb ages of zircon from the Sangun metamorphic rocks indicate the episodic growth at 1.91 and 0.93 Ga of the East Asian continent close to the Japanese Islands.

K-Ar ages of hornblendes from gabbroic rocks in Southwest Japan.

K-Ar age determinations have been carried out on 15 hornblendes from the Yakuno Basic Rocks and their affinities in the Inner Zone of Southwest Japan. Gabbroic rocks from the Yakuno Basic Rocks and those from the Sangun Metamorphic Terrane in eastern Chugoku gave ages ranging from 228 to 275 m.y.; more than half of them are concordant with the geologically estimated age of the rocks. Remaining older ages may indicate either the time of plutonism in Early Permian, which might have been contemporaneous and comagmatic with the basic volcanic activity in the same areas, or the existence of inherited argon in hornblendes. Ages of gabbroic rocks from the Sangun Metamorphic Terrane in northern Kyushu are 296-372m.y., all older than those from eastern Chugoku. Hornblendes from gabbroic rocks in the Nagasaki Metamorphic Terrane gave still older ages of 449-472m.y., suggesting that these rocks may be a part of old basement rocks in the Japanese Islands. Graphical presentation of argon and potassium data indicates that most of the hornblende samples contain no significant amount of excess argon.

Geological Relations of the "Non-metamorphic Palaeozoic Formations" to the Sangun Metamorphic Rocks in the Nishiki-cho Area, Yamaguchi Prefecture

Geological Relations of the "Non-metamorphic Palaeozoic Formations" to the Sangun Metamorphic Rocks in the Nishiki-cho Area, Yamaguchi Prefecture

Structural Petrology of a Thrust Shear-Zone Developed between the Sangun Metamorphic Zone and the Ryoke Zone in the Eastern Part of Yamaguchi Prefecture

Structural Petrology of a Thrust Shear-Zone Developed between the Sangun Metamorphic Zone and the Ryoke Zone in the Eastern Part of Yamaguchi Prefecture

On the Crystalline-schist-pebble-bearing Phyllitic Conglomerate found in the Sangun Metamorphic Rocks

On the Crystalline-schist-pebble-bearing Phyllitic Conglomerate found in the Sangun Metamorphic Rocks

Sangun Metamorphic Rocks in the Wakasa Area, Tottori Prefecture (Preliminary Report)

Sangun Metamorphic Rocks in the Wakasa Area, Tottori Prefecture (Preliminary Report)

The Type of Kieslager in the Sangun Metamorphic Zone of Eastern Chugoku

The Type of Kieslager in the Sangun Metamorphic Zone of Eastern Chugoku

Outline of the Sangun Metamorphic Zone of the Eastern Chugoku District

Outline of the Sangun Metamorphic Zone of the Eastern Chugoku District

On the Age of the Original Rock of the Sangun Metamorphic Rocks Distributed in the Area South of Nariwa-machi, Okayama Prefecture

On the Age of the Original Rock of the Sangun Metamorphic Rocks Distributed in the Area South of Nariwa-machi, Okayama Prefecture