Age constraints on sedimentation and metamorphism of the Taean Formation obtained by SHRIMP U-Pb and 40Ar/39Ar laser probe geochronology

Taean Formation;Gyeonggi Massif;40Ar/39Ar age;SHRIMP age;zircon;mica;titanite;태안층;경기육괴;40Ar/39Ar 연대;SHRIMP 연대;저어콘;운모;550

자연과학대학 지구환경과학부 ;

University:서울대학교 대학원

关键词: Taean Formation;    Gyeonggi Massif;    40Ar/39Ar age;    SHRIMP age;    zircon;    mica;    titanite;    태안층;    경기육괴;    40Ar/39Ar 연대;    SHRIMP 연대;    저어콘;    운모;    550;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/131391/1/000000021052.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

The middle Paleozoic Taean Formation located in the western Gyeonggi Massif, Korea represents a deep-water turbidite system. This formation has been regarded as the exotic area compared to the Precambrian gneiss complex widely distributed in the Gyeonggi Massif. In this study, geochronological data have been obtained by analyzing mica, zircon, and titanite grains from metasedimentary and post-folding intrusive rocks of the Taean Formation in Anmyeondo using the 40Ar/39Ar single grain dating and SHRIMP U-Pb dating methods. 40Ar/39Ar dating on muscovite and biotite grains from the metasediments combined with field observation revealed the middle Triassic metamorphism (~230 Ma) following the early tectonic episode at ~240 Ma. This metamorphism is also confirmed by SHRIMP titanite age (232.5 ± 3.0 Ma) of the calc-silicate rock (a metamorphosed impure sandy limestone). The SHRIMP zircon age of the syenite (229.6 ± 3.5 Ma) suggests that the metamorphism and magmatism in Anmyeondo might have a common tectonic cause. The analysis on the zircon from the gneiss xenolith taken from a mafic dike gave ages of 3.1 ~ 3.7 Ga for inherited cores and 2.34 ~2.51 Ga for rims. This suggests the possibility of existence of a different basement rock than the Paleoproterozoic Seosan Group. The detrital zircon data of the metasandstones defines 2 major age components in Silurian (426 Ma peak) and Neoproterozoic (948 Ma peak), indicating that the main source of detrital zircon grains was probably not the Gyeonggi Massif. The Jurassic zircon age of the acidic intrusive body may suggest a relation between the final phase of recrystallization of biotite and some muscovite and the intrusion. The overall geochronological data in this study give clues to reconstruct the tectonic history during the sedimentation, metamorphism and subsequent deformation of the Taean Formation.