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포항(浦項) 및 장기분지(盆地)에 대한 고지자기(古地磁氣), 층서(層序) 및 구조연구(構造硏究); 화산암류(火山岩類)의 K-Ar 연대(年代)
이현구,문희수,민경덕,김인수,윤혜수,이타야 테츠마루,Lee, Hyun Koo,Moon, Hi-Soo,Min, Kyung Duck,Kim, In-Soo,Yun, Hyesu,Itaya, Tetsumaru 대한자원환경지질학회 1992 자원환경지질 Vol.25 No.3
The Tertiary basins in Korea have widely been studied by numerous researchers producing individual results in sedimentology, paleontology, stratigraphy, volcanic petrology and structural geology, but interdisciplinary studies, inter-basin analysis and basin-forming process have not been carried out yet. Major work of this study is to elucidate evidences obtained from different parts of a basin as well as different Tertiary basins (Pohang, Changgi, Eoil, Haseo and Ulsan basins) in order to build up the correlation between the basins, and an overall picture of the basin architecture and evolution in Korea. According to the paleontologic evidences the geologic age of the Pohang marine basin is dated to be late Lower Miocence to Middle Miocene, whereas other non-marine basins are older as being either Early Miocene or Oligocene(Lee, 1975, 1978: Bong, 1984: Chun, 1982: Choi et al., 1984: Yun et al., 1990: Yoon, 1982). However, detailed ages of the Tertiary sediments, and their correlations in a basin and between basins are still controversial, since the basins are separated from each other, sedimentary sequence is disturbed and intruded by voncanic rocks, and non-marine sediments are not fossiliferous to be correlated. Therefore, in this work radiometric, magnetostratigraphic, and biostratigraphic data was integrated for the refinement of chronostratigraphy and synopsis of stratigraphy of Tertiary basins of Korea. A total of 21 samples including 10 basaltic, 2 porphyritic, and 9 andesitic rocks from 4 basins were collected for the K-Ar dating of whole rock method. The obtained age can be grouped as follows: $14.8{\pm}0.4{\sim}15.2{\pm}0.4Ma$, $19.9{\pm}0.5{\sim}22.1{\pm}0.7Ma$, $18.0{\pm}1.1{\sim}20.4+0.5Ma$, and $14.6{\pm}0.7{\sim}21.1{\pm}0.5Ma$. Stratigraphically they mostly fall into the range of Lower Miocene to Mid Miocene. The oldest volcanic rock recorded is a basalt (911213-6) with the age of $22.05{\pm}0.67Ma$ near Sangjeong-ri in the Changgi (or Janggi) basin and presumed to be formed in the Early Miocene, when Changgi Conglomerate began to deposit. The youngest one (911214-9) is a basalt of $14.64{\pm}0.66Ma$ in the Haseo basin. This means the intrusive and extrusive rocks are not a product of sudden voncanic activity of short duration as previously accepted but of successive processes lasting relatively long period of 8 or 9 Ma. The radiometric age of the volcanic rocks is not randomly distributed but varies systematically with basins and localities. It becomes generlly younger to the south, namely from the Changgi basin to the Haseo basin. The rocks in the Changgi basin are dated to be from $19.92{\pm}0.47$ to $22.05{\pm}0.67Ma$. With exception of only one locality in the Geumgwangdong they all formed before 20 Ma B.P. The Eoil basalt by Tateiwa in the Eoil basin are dated to be from $20.44{\pm}0.47$ to $18.35{\pm}0.62Ma$ and they are younger than those in the Changgi basin by 2~4 Ma. Specifically, basaltic rocks in the sedimentary and voncanic sequences of the Eoil basin can be well compared to the sequence of associated sedimentary rocks. Generally they become younger to the stratigraphically upper part. Among the basin, the Haseo basin is characterized by the youngest volcanic rocks. The basalt (911214-7) which crops out in Jeongja-ri, Gangdong-myon, Ulsan-gun is $16.22{\pm}0.75Ma$ and the other one (911214-9) in coastal area, Jujon-dong, Ulsan is $14.64{\pm}0.66Ma$ old. The radiometric data are positively collaborated with the results of paleomagnetic study, pull-apart basin model and East Sea spreading theory. Especially, the successively changing age of Eoil basalts are in accordance with successively changing degree of rotation. In detail, following results are discussed. Firstly, the porphyritic rocks previously known as Cretaceous basement (911213-2, 911214-1) show the age of <TE
조규환,다카기히데오,이와무라아키라,아와지도타,장태우,손승완,이타야테츠마루,오카다도시노리 대한자원환경지질학회 2001 자원환경지질 Vol.34 No.6
단층비지의 주성분인 점토광물은 K-Ar 연대측정법으로 단층활동 시기를 구하는데 이용되어 왔다. 이 논문은 울산 단층대의 주요 단층활동에 수반된 열수변질작용 시기를 연구하기 위하여 단층비지 세 시료를 각각 5-2 $\mu$m , 2-1 $\mu$m, 1-0.35 $\mu$m, 0.35-0.05 $\mu$m 입자 크기로 분리하여 각각의 시료에 대해 X선 회절분석과 K-Ar 연대측정을 하였다. 연구결과 단층비지는 석영, 장석류로 구성되며, 점토광물은 스멕타이트, 일라이트, 녹니석, 카올리나이트가 확인된다. 운모점토광물의 일라이트 곁정도지수는 작은 입자 크기에서 큰 값(0.58-1.08)을 보이고 저온에서 안정한 일라이트(IM)가 우세하게 나타내는 것으로 보아 열수변질작용을 수반한 단층활동 동안에 생성된 운모점토광물이 작은 입자 크기에 농집되었을 가능성이 높음을 시사한다. 각 시료의 K-Ar 연령은 46-35 Ma(330-2), 45-39 Ma(16Ww) 및 32-15 Ma(102Ws)이며, 작은 입자 크기로 갈수록 연대값이 젊어진다. 이 결과는 울산단층대의 주요 단층활동에 수반된 열수변질작용이 39-35 Ma와 15 Ma에 있었던 것으로 나타난다. Clay minerals are common component of fault gouge and have been used to determine the fault activity age using K-Ar dating technique. We carried out XRD and K-Ar analyses of the mica clay minerals from the fault gouge along the Ulsan Fault Zone, southeastern Korea to estimate the timing of the major fault activity. Mica clay minerals for four grain size fractions of 5-2 Um, 2-1 $\mu$m, 1-0.35$\mu$m, and 0.35-0.05 $\mu$m were separated from the gouge samples in the three locations by the hydraulic elutriation and contrifugal separator. Fault gouges are composed of smectite, mica clay minerals, kaolinite, chlorite, quartz, and feldspar. The illite crystallinity of mica clay minerals is the highest in the finest grained fraction with lM polytype, indicating that the aulhigenic mica clay minerals have been concentrated in the fraction. K-Ar ages give some variation from 46 to 35 Ma (330-2), 45 to 39 Ma (16Ww), and 32 to 15 Ma (102Ws) and are the youngest in the finest grained fraction. These results suggest that the hydrothermal alteration associated with the major fault activities along the Ulsan fault Zone took place twice at 39-35 Ma and 15 Ma.