四国西部四万十帯における白亜紀後期から古第三紀初期にかけての後背地の変遷とその意義  [in Japanese] Provenance changes of the late Cretaceous to early Paleogene Shimanto Supergroup in western Shikoku, and its significance  [in Japanese]

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Abstract

四国西部の中村市東方には, 白亜紀末から古第三紀初期にかけての四万十累層群が連続的に分布している. この地域の四万十累層群の砂岩の岩石学的・地球化学的特徴を検討し, 後背地の変遷に関していくつかの新たな事実を明らかにした. また, この地域の四万十累層群の岩相や堆積年代, これと同時期の三波川変成帯における諸イベントなどを考慮して, 次のような結論を得た.<BR>i) 白亜紀後期から引き続いて前期暁新世まで珪長質火山岩類を主体とする西南日本内帯の供給源から四万十帯に砕屑物が供給された. ii) 後期暁新世には三波川帯の露出と浸食があり, ここから四万十帯に砕屑物が供給された. iii) 中期～後期始新世には西南日本内帯でunroofingが進行し, 多くの花崗岩類が供給源に出現した. iv) 三波川帯の上昇運動には, サントニアン～カンパニアン期に多量の砕屑物が四万十帯へ供給されたことと, それに伴う大量のunderplatingが関与していると推定される.

The Shimanto Supergroup in the Inomisaki- Nakamura area, western Shikoku, is favorable for the examination of geologic development around the boundary between the Cretaceous and the Paleogene, because the Maastrichtian- Paleocene strata, which are not exposed in most of the Shimanto Belt, occur as good outcrops in this area. We have studied the petrographical features and bulk chemistry of sandstones in the area, in order to clarify the geologic developments of the Shimanto accretionary complex during the late Cretaceous and early Paleogene. These data, together with chronological and geologic data of the Sanbagawa Metamorphic Belt, led to the following conclusions. <BR>1. The Shimanto Supergroup in the study area can be classified into the following three intervals on the basis of petrographic and geochemical features of sandstones: Interval 1 (Santonian-Early Paleocene), Interval 2 (Late Paleocene) and Interval 3 (Early and Middle Eocene).<BR>2. The sandstones from Interval 1 were mainly derived from felsic volcanic rocks in the Inner Belt of Southwest Japan.<BR>3. The sandstones from Interval 2 are characterized by lithic fragments of pelitic schist, siliceous schist, and weakly- to non-metamorphosed chert. An emergence and erosion of the Sanbagawa Metamorphic Belt took place in this interval along with the Mikabu Greenstones and Northern Chichibu Belt.<BR>4. Unroofing and resulting emergence of many granitic rocks in the provenance of the Inner Belt have occurred in the depositional age of the Inomisaki Formation of Interval 3.<BR>5. Voluminous and rapid underplating induced by a large amount of supply of clastic sediments to the trench area during the Santonian-Campanian in Shikoku might have resulted in an exhumation of the Sanbagawa Belt.

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 110(7), 403-416, 2004-07-15

    The Geological Society of Japan

References:  41

Cited by:  2

Codes

  • NII Article ID (NAID)
    110003009864
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    00167630
  • NDL Article ID
    7045038
  • NDL Source Classification
    ZM49(科学技術--地球科学--地質)
  • NDL Call No.
    Z15-174
  • DOI
    10.5575/geosoc.110.403
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
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