Science Links Japan | SHRIMP U-Pb dating of zircons in the sedimentary rocks from the Akiyoshi and Suo zones, Southwest Japan.

SHRIMP U-Pb dating of zircons in the sedimentary rocks from the Akiyoshi and Suo zones, Southwest Japan.

Accession number;01A0565473

Title;SHRIMP U-Pb dating of zircons in the sedimentary rocks from the Akiyoshi and Suo zones, Southwest Japan.

Author; TSUTSUMI Y (Hiroshima Univ., Hiroshima, Jpn) YOKOYAMA K (National Sci. Museum, Tokyo, Jpn) TERADA K (Hiroshima Univ., Hiroshima, Jpn) SANO Y (Hiroshima Univ., Hiroshima, Jpn)

Journal Title;J Mineral Petrol Sci

Journal Code:G0150B

ISSN:1345-6296

VOL.95;NO.8;PAGE.216-227(2000)

Figure&Table&Reference;FIG.7, TBL.3, REF.14

Pub. Country;Japan

Language;English

Abstract;Radiometric ages of zircons in psammitic rocks from the Nishiki and Tsuno groups were determined from 238U/206Pb ratio and isotopic compositions of Pb which are analyzed by Sensitive High Resolution Ion Microprobe(SHRIMP II). Detrital zircons in the Nishiki sandstones show a continuous distribution from 320Ma to 240Ma, which is similar to those from the Tsuno psammitic schists; about 380-220Ma. The youngest zircons from the Nishiki and Tsuno groups are 238.7.+-.5.9Ma and 218.6.+-.11.4, respectively. It was estimated as upper limits of the depositional ages. Detrital zircon age in the psammitic rocks shows continuous variation from 380Ma to 220Ma, whereas K-Ar age of white mica corresponding to metamorphic age is around 220Ma in both the groups. Hence, it is realistic to conclude that the youngest age is close to the depositional age and clastic rocks in the Tsuno Group is Triassic in origin. Probability distributions for zircon ages in psammitic rocks from both groups, calculated by a multi-peak Gauss fitting, indicate that provenances for the clastic metarials in both the groups overlap widely and are similar to those in the Mino and Hida belts. Acidic tuff in the Nishiki group occurs in a hemi-pelagic unit different from the sandstone of trenchfill sediment. Zircons in the tuffs show apparently two distinctive U-Pb ages; about 2700-2400Ma and 320-260Ma. The former is considered to be accidental materials derived from Archean basement which will be a part of the Sino-Korean craton with 2700-2500Ma. Least squares fitting for the latter younger cluster yields a concordia intercept age of 270.3.+-.8.5Ma(2.SIGMA.) which probably represents a depositional age for the tuff. (author abst.)

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