Departmental Bulletin Paper コリア半島, 京畿地塊のCHIMEモナザイト年代

鈴木, 和博  ,  Suzuki, Kazuhiro

27pp.95 - 100 , 2016-03 , 名古屋大学宇宙地球環境研究所年代測定研究部
Metamorphic rocks in the northeastern part of the Gyeonggi massif in the Korean Peninsula include pelitic and quartzofeldspathic granulites, augen gneiss, paragneiss in the amphibolite-facies and amphibolite, and are grouped into the high-grade granulite- and the low-grade gneiss-units. The tectonically lower granulite unit is separated from the gneiss unit by an extensive mylonite zone that show a metamorphic overprint characterized by the fibrolite and K-feldspar paragenesis. Pelitic and quartzofeldspathic granulites in the granulite unit give Paleoproterozoic (1.84-1.89 Ga) CHIME monazite ages, whereas paragneisses in the gneiss unit and rocks in the mylonite zone yield unequivocal Early Triassic (240±10 Ma) ages. Augen gneiss and mylonitized pelitic granulite underlain below the mylonite zone yield Early Triassic age domains on and within predominantly Paleoproterozoic monazite grains. Augen gneiss as well as mylonite shows a consistent top-to-the-NE shear sense with gently inclined NE-SW mineral alignments. The chronological and structural data suggest that the juxtaposition of the hot gneiss unit by thrusting over the granulite unit was responsible for the Early Triassic overprint in the granulite unit and in the mylonite zone. The gneiss unit was possibly detached from the South China block during the collision between the North China and South China blocks, and was distributed as widespread allochthons on the granulite unit of the North China block. コリア半島中部,京畿地塊の変成岩は古原生代(約18.4-18.9億年)のグラニュライトユニットと三畳紀初頭(240±10 Ma)の片麻岩ユニットから構成される.境界には大規模なマイロナイト帯が発達し,マイロナイト自体が三畳紀初頭(240±10 Ma)に角閃岩相の変成作用を受けてデガッセイト組織の黒雲母を生じている. また,マイロナイト帯から2-3km以内のグラニュライトユニットの岩石も三畳紀初頭(240±10 Ma)の角閃岩相オーバープリントを受けて,ざくろ石が董青石に置換されている.片麻岩ユニットは大陸衝突時に南中国地塊から離れて北中国地塊のグラニュライトユニットに衝上した高温異地性岩体であり,その熱でマイロナイト帯や近傍のグラニュライトユニットの岩石が接触変成した.

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