• Journal of the Korean earth science society
• /
• v.28 no.6
• /
• pp.720-732
• /
• 2007

For the Seoul metropolitan area and the eastern Kyeongsang Basin, we simultaneously calculated $Q_P^{-1}$ and $Q_S^{-1}$ by applying the extended coda-normalization method for 98 seismograms of local Earthquakes. As frequency increases from 1.5 Hz to 24 Hz, the result decreased from $(4.0{\pm}9.2){\times}10^{-3}$ to $(4.1{\pm}4.2){\times}10^{-4}$ for $Q_P^{-1}$ and $(5.5{\pm}5.6){\times}10^{-3}$ to $(3.4{\pm}1.3){\times}10^{-4}$ for $Q_S^{-1}$ in Seoul Metropolitan Area. The result of eastern Kyeongsang basin also decreased from $(5.4{\pm}8.8){\times}10^{-3}$ to $(3.7{\pm}3.4){\times}10^{-4}$ for $Q_P^{-1}$ and $(5.7{\pm}4.2){\times}10^{-3}$ to $(3.5{\pm}1.6){\times}10^{-4}$ for $Q_S^{-1}$. If we fit a frequency-dependent power law to the data, the best fits of $Q_P^{-1}$ and $Q_S^{-1}$ are $0.005f^{-0.89}$ and $0.004f^{-0.88}$ in Seoul metropolitan Area, respectively. The value of $Q_P^{-1}$ and $Q_S^{-1}$ in the eastern Kyeongsang basin are $0.007f^{-1.02}$ and $0.006f^{-0.99}$, respectively. The $Q_S^{-1}$ value of the eastern Kyeongsang basin is almost similar to Seoul metropolitan area. But the $Q_P^{-1}$ value of the eastern Kyeongsang basin is a little higher than that of Seoul metropolitan area. This may be that the crustal characteristics of the eastern Kyeongsang basin is seismologically more heterogeneous. However, these $Q_P^{-1}$ values in Korea belong to the range of seismically stable regions all over the world.

• Economic and Environmental Geology
• /
• v.28 no.1
• /
• pp.19-24
• /
• 1995

Based upon the lead isotopic compositions of the galenas collected from Pb-Zn ore deposits distributed in the eastern and southern parts of the Gyeongsang basin, we investigated what kinds of source materials were involved in the formation of these ore deposits and compared the lead isotopic characteristics of these ore deposits with those of the ore deposits in the Taebaegsan area. The isotopic compositions of the common leads from Pb-Zn ore deposits in the Gyeongsang basin show the variation with the relatively limited range ($^{206}Pb/^{204}Pb=18.156{\sim}18.377$, $^{207}Pb/^{204}Pb=15.482{\sim}15.638$, and $^{208}Pb/^{204}Pb=37.953{\sim}38.605$). They are plotted on or below ore lead growth curve(Cumming & Richards, 1975) and average crustal lead evolution curve (Stacey & Kramer, 1975). In the plumbotectonic model IV(Zartman & Haines, 1988), they are plotted between the evolution curves of mantle and orogene. But the lead isotopic compositions of the common leads in the Taebaegsan area are plotted on and above upper crust curve. Considering the above-mentioned lead isotopic characteristics, the linear trend shown in the isotopic compositions of the common leads in the Gyeongsang basin can be considered as the mixing isochron between high radiogenic crustal materials such as the Ryongnam massif and low radiogenic materials derived from depleted mantle or materials with relatively low U/Pb and Th/U ratios.

• The Journal of the Petrological Society of Korea
• /
• v.9 no.1
• /
• pp.40-50
• /
• 2000

This study is aimed at elucidating the source rocks of the Hayang strata in the northeastern part of the Gyeongsang Basin. Zircon morphology was analyzed for sandstones from the Iljig, Hupyeongdong, and Jeomgog formations of the Hayang Group and Precambrian gneisses and Jurassic granites. Generally, the composite zircon crystals extracted from the basement rocks and the Hayang Group sandstones show short prismatic to middle prismatic shapes. {110)={100) prism type is dominant and (101) pyramid is the average of the zircon morphology data. Zircon index@) and the shape trend characteristics clearly show that the zircon crystal forms of the Iljig and Hupyeongdong sandstones are dominantly similar to those of the biotite banded gneiss and granite gneiss of Precambrian age. Zircon morphology of the Jeomgog sandstones is dominantly similar to those of the Jurassic granites. Referring to the reported paleocurrent result, the source rocks of the Iljig and Hupyeongdong formations are mainly the Precambrian gneisses distributed in the southeastern and northeastern parts, respectively. And Jeomgog sandstones were mainly derived from Cheongsong granite at Cheongsong uplift region in the eastern part. At the time of completion of the Hupyeongdong sedimentation, the Precambrian basement rocks were severely eroded and formed low topography. During the Jeomgog period, the Jurassic granites which intruded the Precambrian basement began to crop out on the surface. The basin widely extended toward the east and the exposed Jurassic granite of Cheongsong uplift region actively supplied the sediments to the basin.

• Economic and Environmental Geology
• /
• v.39 no.4 s.179
• /
• pp.507-524
• /
• 2006

3-D seismic tomographic inversion is applied to investigation on velocity structure in and near Korean Peninsula. Firstly, it is applied to the region in southeastern Korean Peninsula. According to the results low-velocity zone seems to be clearly appeared in the so called Gyeongsang sedimentary basin and high-velocity zone is shown at the section of 7.5 km depth it implies the inclusion of plutonic rocks at the sedimentary basin. At the depth about $20{\sim}30$ km existence of low-velocity zone seems to be related with the development of Yangsan fault system. Secondly it is applied to the region not only in Korean Peninsula but also East Sea using data from both Korean Peninsula and Japan Islands. Accorging to the results, subduction zone starting from eastern part of Japan seems to be extended to the region beneath the East Sea.

• Economic and Environmental Geology
• /
• v.32 no.4
• /
• pp.353-363
• /
• 1999

The Cretaceous and the Upper Jurassic strata of the Korean Peninsula, entirely of continental facies, form a sedimentary mega-unit subdivided into three unconformity-bounded units. The lower, Upper Jurassic-early Lower Cretaceous unit (Jasong Synthem) occurs profusely in North Korea and is characterized by volcanic rocks of intermediate to acidic, calc-alkaline to alkaline compositions; but strata of this unit is very rare in South Korea. The middle, Hauterivian-Lower Albian unit occurs commonly in the Korean Peninsula, but some alkalinesubalkaline basalt and andesite occur only in South Korea. A recently obtained U-Pb isochron age about 113.6 Ma (Chang et at, 1998) from the zircon grains of the Kusandong Tuff in the uppermost part of the Haman Formation has thrown much light on the age of this unit. The stratotype of this Hauterivian-L. Albian unit is the Sindong and Hayang Groups of the Kyongsang Basin, where the unit is about twice thick and has more conglomerates than in sedimentary basins in North Korea. The unit shows various sedimentary cycles in different basins showing that the cyclicity is controlled by local crustal motion. The upper, Upper Albian-Upper Cretaceous unit is abundant in South Korea with prolific volcanic rocks which are intermediate to acidic and notably calc-alkaline. In North Korea, however, this unit occurs in only one locality without volcanic rocks and is not voluminous. The distribution of these three unconformity-bounded units shows a stepwise younging toward the Pacific Ocean: the lower unit occurs mainly in N Korea, the middle unit occurs in both N and S Korea, and the upper unit occurs mainly in the southern part of S Korea. The Cretaceous sedimentary basins of S Korea were genetically controlled by paralleling sinistral strike-slip faults parallel to the Pacific margin.

• Economic and Environmental Geology
• /
• v.40 no.3 s.184
• /
• pp.319-330
• /
• 2007

The Muposan Tuff is a stratigraphic unit which is distinguished as a cooling unit in the volcanic rocks of the northeastern Kyeongsang Basin. The Muposan Tuff commonly belongs to tuff field according to the granulometric classification and to vitric tuffs according to the constituent classification. The tuffs are mostly densely to partially welded to include very flattened and sometimes stretched pumices and shards, and involve several flow indicator and lateral gradings in maximum diameter and content of their constituents. Movement pattern from flow lineation, lithic and pumice imbrications, asymmetric flow folds, and lateral gradings in maximum diameter and content of their constituents indicate that the Muposan Tuff had a source from the southeastern part.

• The Journal of the Petrological Society of Korea
• /
• v.9 no.4
• /
• pp.238-253
• /
• 2000

In the eastern part of the Euiseong Basin acidic~intermediate volcanic rocks widely distribute on the Cretaceous sedimentary basement. Coeval granitic rocks and dyke rocks intruded into the volcanic rocks. Volcanic stratigraphy of study area are andesite lava, dacitic lapilli tuff, dacitic flow-banded lava, rhyolitic bedded tuff, rhyolitic massive tuff, dacitic massive lava, rhyolitlc welded tuff occur from the lower to the upper strata. $SiO_2$ content of the volcanic rocks range from 51 to 74 wt.%. With the increase of $SiO_2$, the contents of $TiO_2$, $Al_2$$O_3$, MgO, FeOT MnO, CaO, $P_2$$O_{5}$ decrease but those of $K_2$O increase. The contents of $Na_2$O show dispersive variation. This trend is quite sim-ilar to the major oxide variation in the volcanic rocks from the Yucheon sub-basin. The geochemical natures indicate that the volcanic rocks in the study area are discriminated to the island-arc type high K to medium K calc-alkaline rocks. The compositional variation of the volcanic rocks can be explained by the plagioclase fractionation of the volcanic magmas originated from similar source materials. The volcanic stratigraphy seems to have formed by at least two eruptive sequences of andesitic to rhyolitic and dacitic to rhyolitic magmas which underwent crystallization differentiation.

• The Journal of the Petrological Society of Korea
• /
• v.17 no.2
• /
• pp.83-94
• /
• 2008

The Pungcheon-myeon, Andong, consists mainly of Precambrian metamorphic rocks, Jurassic igneous rocks, Cretaceous sedimentary rocks (Hasandong, Jinju and Iljik Formations) and Cretaceous igneous rocks (gabbroic rocks, dykes), in which several major faults are developed; Andong fault of ENE trend, which is the boundary fault of the Cretaceous Gyeongsang Basin and the Precambrian-Jurassic basement (Yeongnam Massif), Namhu fault parallel to it, Maebong fault of NNW direction, bow-shaped Gwangdeok fault of ENE direction which is convex toward SSE direction, and Hahoe fault of NNE direction. This paper is researched the geological structures around these major faults by means of the detailed geometric analysis on beddings, joints, faults and drag folds. As a result, a reverse slip faulting of top-to-the SSE movement accompanied with a regional drag folding is recognized from the arrangement of bedding poles measured around the Gwangdeok and Hahoe faults at its northeastern extension, and a zone of Gwangdeok drag fold of 150-300 m width, which is wider at the central and eastern parts of Gwangdeok fault and narrower at its western part and Hahoe fault, is also defined. It indicates that the Hahoe and Gwangdeok faults are a single fault and their movements are coeval unlike the results of earlier reasearchers. And, In this area are recognized two types of faults [(E)NE${\sim}$EW(fault I), WNW${\sim}$NNW (fault II), trending faults] and four types of joints [EW (I), (N)NW (II), NNE (III), NE (IV) trending joints]. These fractures were formed at least through four different events, named as Dn to Dn+3 phases. (1) Dn phase; the formation of joint (I) (Gwangdeok joint) and the intrusion of acidic dykes of EW trend under the compression of EW direction. (2) Dn+1 phase; the formations of joint (II) (Maebong joint), lens-shaped boudinage of acidic dykes, oblique-slip reverse fault (Fault I-Gwangdeok fault) under the compression of (N)NW direction, and the formation of regional zone of Gwangdeok drag fold accompanying the Gwangdeok faulting. (3) Dn+2 phase; those of joint (III), Fault II (Maebong fault) by dextral strike-slip movement of Maebong joint under the compression of NNE direction, and the extension cutting of Dn+1 structures due to the Maebong faulting. (4) Dn+3 phase; the jointing (IV) and the reactivation of Fault II as oblique-slip type with predominant dextral motion which took place under the compression of NE direction. It also suggests that the Maebong fault is not a tear fault deveolped during thrust tectonics of the Andong and Gwangdeok faults but is a post-fault during different tectonic event.

• The Journal of the Petrological Society of Korea
• /
• v.9 no.2
• /
• pp.70-83
• /
• 2000

The purpose of this study is to identify the petrographic and geochemical characteristics of four granitic masses and clanfy for the origin and relationship among the masses. These granitic rocks are distributed in the eastern part of Yangsan fault in the Kyongsang basin, southeastern part of Korea. Based on the mineralogy and texture, the granitic rocks are divided into three facies; granodiorite, porphyritic fine-grained granite, and equigranular granite. According to the result of modal analysis, northern part and most of the southern part of Daebon granitic rocks are plotted in granodiorite field and the rest part of the xocks are plotted in granite field. These granitic rocks belong to the sub-alkaline series, and are subdivided into calc-alkaline series. The rare earth elements normalized bv chondrite show LREE is more enriched than HREE and the lowest values in O-w m- i t e and Daebon equigranular granite. The crystallization pressures and temperatures of minimum melt compositions of granitic rocks estimated from the study area are about 0.5-1 kbar and $700~820^{\circ}C$, respectively. Referring to the petrographic characteristics, geochemical data and radiogenic age data, Oyu granite was emplaced in the Paleocene, but Daebon granodiorite, Sanseo porphyritic granite, and Hoam equigranular granite are co-magmatic differentiation products, were emplaced in the Eocene.

• The Journal of the Petrological Society of Korea
• /
• v.23 no.2
• /
• pp.31-43
• /
• 2014

The Yeongdeok granite emplaced in the eastern Yeongyang subbasin is typically a medium- to coarse-grained massive biotite granite. It intruded into Precambrian schist & gneiss complex and is unconformably overlain by Cretaceous sedimentary rocks. In this study, we attempt to investigate the magma type which formed Yeongdeok granite and estimate the emplacement depth using Al-in-hornblende geobarometer to mineral composition. According to the magma fractionation, $TiO_2$, $Al_2O_3$, $Fe_2O_3{^*}$, FeO, $Fe_2O_3$, MnO, MgO, CaO, $Na_2O$ and $P_2O_5$ show positive trend but $K_2O$ indicate negative trend with $SiO_2$ contents. Those are identified as calc-alkaline series in AFM diagram and show the chemical characteristics of the I-type magma through the oxidation tendency of the iron ion and the portion of the alkaline composition. When calculated using the equation of Hollister et al. (1987), the emplacement depths of the Yeongdeok granite range from 8.98 to 17.19 km and average depth was estimated 13.03 km approximately.