• Journal of Conservation Science
• /
• v.35 no.2
• /
• pp.131-144
• /
• 2019

The Seosan Geomenyeo(black submerged rocks), once located at the Cheonsuman bay of Buseokmyeon in Seosan, Korea, is a reef rock now exposed on the land surface. The Geomenyeo can also be found in the ancient geographic maps around the area. The local geographic names, like Buseok and Buseoksa temple are derived from the Geomenyeo. It is composed of ultramafic rocks complex and intrusive felsic igneous rocks. These rocks show diverse facies with various petrographic characteristics caused by geological processes such as intrusion and alteration. Ultramafic rocks complex can be roughly categorized as coarse grained ultramafic rocks and medium grained mafic rocks. Both cases are composed of pyroxene and amphibole, showing the general rock facies of pyroxenite, diabase and lamprophyre. Felsic igneous rocks includes pinkish medium grained granite, porphyritic amphibole granite and aplite with varied mineral compositions. The Geomenyeo is the only ultramafic rocks complex in the Cheonsuman Bay; moreover, it has a distinctive geological and scenic value, as well as a symbolic property. In order to preserve the Geomenyeo, it is necessary to investigate and promote it as a designated heritage site through academic studies, and compensate for the convenience and protection facilities. Additionally, the Geomenyeo should be evaluated as a maritime heritage site, due to the unique local culture as it succeeds the recognition of forefathers which regarded it as a local scenic site with significance.

• Korean Journal of Mineralogy and Petrology
• /
• v.36 no.1
• /
• pp.73-94
• /
• 2023

We carried out the sensitive high resolution ion microprobe (SHRIMP) zircon U-Pb age dating and whole-rock geochemical analysis of granitoids and felsic porphyries in the Ssangyong Valley, Yongchu Valley, and Mungyeong Saejae geosites in the Mungyeong Geopark. The igneous rocks crop out in the western, northwestern and central parts of the Mungyeong city area, respectively, and intruded (meta)sedimentary successions of the Ogcheon Metamorphic Belt, Cambro-Ordovician Mungyeong Group and Jurrasic Daedong Group. The U-Pb isotopic compositions of zircon from two felsic porphyries and one granite samples in the Ssanyeong Valley yielded the Cretaceous intrusion ages of 93.9±3.3 Ma (tσ), 95.1±4.0 Ma (tσ) and 94.4±2.0 Ma (tσ), respectively. On the other hand, a felsic dike sample and a granite in the Yongchu Valley and a porphyritic granite in the Mungyeong Saejae had intrusion ages of 90.2±2.0 Ma (tσ), 91.0±3.0 Ma (tσ) and 88.6±1.5 Ma (tσ), respectively. Based on the average standard error calculated in combination with results of previous studies in this area (Lee et al., 2010; Yi et al., 2014; Aum et al., 2019), the geochronological results show that spatial variation in intrusion age of ~5 Myr between the Ssangyong (94.5±0.2 Ma) and Yongchu Valleys (89.7±0.4 Ma) is apparent. The geochemical compositions of major and trace elements in the samples showed an affinity of typical post-orogenic granite, indicating their petrogenesis during the late stage of Early Cretaceous magmatic activity possibly in association with subduction events of the Izanagi Plate.

• The Journal of the Petrological Society of Korea
• /
• v.13 no.2
• /
• pp.47-63
• /
• 2004

This study focuses on the petrography and petrochemical characteristics of the volcanic and plutonic rocks in Gadeog island, Busan, Korea. Based on textural and mineralogical characteristics, intermediate volcanic rocks can be divided into andesitic lava flows (porphyritic and massive andesites) and andesitic pyroclastics. Felsic volcanic rocks are composed of rhyolite, rhyolitic welded tuff, and tuff breccia. Plutonic rocks are intruded rhyolite and andesitic rocks, and composed of hornblende granodiorite which contains lots of mafic magma enclaves. Volcanic rocks are composed of andesite, dacite and rhyolite having a range in SiO$_2$ from 59 to 78wt.%. The volcanic rocks belong to the calc-alkaline rock series. Plutonic rocks have a range in SiO$_2$ from 63 to 69wt.%. This compositional variations correspond to those of Cretaceous volcanic and plutonic rocks in the southeastern Gyeongsang basin. The trace element composition and rare earth element patterns of the volcanics, which are characterized by high LREE/HFSE ratios and enrichment in LREE, suggest that they are typical of calc-alkaline volcanic rocks produced in the subduction environment around continental arc. We concluded that volcanic and plutonic rocks in Gadeog Island were evolved from orogenic andesitic magma which was produced by partial melting of the mantle wedge in the subduction environment.

• Journal of the Korean earth science society
• /
• v.25 no.4
• /
• pp.251-264
• /
• 2004

The Charnockite in Sancheong region is quarzofeldspathic rock containing orthopyroxene and garnet with a color dark than common granitic rocks. The Chamockite are mostly massive and medium to coarse-grained with K-feldspar phenocryst, but reveal weak foliation. The rock consist mainly of quartz, K-feldspar, plagioclase and orhopyroxene, with biotite, garnet, and anthophyllite. In petrochemistry, the Chamockite has 61-65% $SiO_2$ contents, varying gradually into the margin contacted with orthogneiss, which have compositions of felsic igneous rocks. Major element show almost systematical variation with those of the marginal orthogneisses, except the hornblende gneiss and anorthosite. The Charnockite and orthogneisses show the tholeiitic differentiational trend. Trace and rare earth element abundance patterns in the Charnockite show remarkable negative Sr and Eu anomalies similar to orthogneisses, but different from the hornblende gneiss and anorthosite. Eu contents of the Charnockite are richer than that of orthogneisses. The metamorphic condition of the Charnockite were tested by an orthopyroxene-garnet geotherrnorneter and a plagioclase-garnet geobarometer. Estimated P-T conditions are about $761^{\circ}C$ and 7 kbar at peak metamorphism, but $653^{\circ}C$ and 6.4 kbar at retrograde metamorphism. This suggests that the Charnockite have from an early stage of high-grade metamorphism to represent the granulite facies and then to a late stage medium-grade metamorphism belonging to the amphibolite facies.

• The Journal of Engineering Geology
• /
• v.32 no.1
• /
• pp.157-171
• /
• 2022

Electrical resistivity tomography (ERT) is a traditional and representative geophysical method for determining the resistivity distributions of surrounding soil and rock volumes. Depth resolution profiles and sensitivity distribution sections of the resistivities with respect to various electrode configurations are calculated and investigated using numerical model data. Shallow vertical resolution decreases in the order of Wenner, Schlumberger, and dipole-dipole arrays. A high investigable depth in homogeneous medium is calculated to be 0.11-0.19 times the active electrode spacing, but is counterbalanced by a low vertical resolution. For the application of ERT depth resolution profiles and sensitivity distributions, we provide subsurface structure models for two types of land-creping failure (planar and curved), subvertical fracture, and weathered layer over felsic and mafic igneous rocks. The dipole-dipole configuration appears to be most effective for mapping land-creeping failure planes (especially for curved planes), whereas the Wenner array gives the best resolution of soil horizons and shallow structures in the weathered zone.

• Journal of the Korean earth science society
• /
• v.22 no.5
• /
• pp.405-414
• /
• 2001

Jecheon granite can be divided into two types; porphyritic granite (K-feldspar megacryst bearing) and medium-grained biotite granite. Porphyritic granite, host body of feldspar deposits, is 8${\sim}$11 km in diameter and about 80 $km^{2}$ in area. It mainly contains K-feldspar, plagioclase, biotite and quartz, and magnetite, zircon, sphene and apatite are accessary minerals. Enclosed minerals in K-feldspar megacryst with 3${\sim}$10 cm in diameter are hornblende, plagioclase, quartz, magnetite, apatite, sphene and zircon. Mafic enclaves mainly consisting of hornblende, plagioclase and quartz are frequently observed in porphrytic granite. Medium-grained biotite granite consists of K-feldspar, plagioclase, biotite and hornblende as main, and hematite, muscovite, apatite and zircon as accessary minerals. Core and rim An contents of plagioclase from porphyritic granite, medium biotite granite, K-feldspar megacryst, and mafic enclave are 36 and 21, 40 and 32, 37 and 32, and 43 and 36, respectively. $X_{Fe}$ values of hornblende are 0.57 at biotite granite, 0.51 at K-feldspar mehacryst and 0.45 at mafic enclave. $X_{Fe}$ values of biotite and hornblende are homogeneous without chemical zonation. K-feldspar megacryst shows end member of pure composition with exsolved thin lamellar pure albites. Characteristics of mineral compositions and petrography indicate porphyritic granite is igneous origin and medium-grained biotite granite comes from the same source of magma; biotite granite is initiated to solidly and from residual melt porphyritic granite can be formed. Possibly K-feldspar megacrysts are formde under H$_{2}$O undersaturation condition and near K-feldspar solidus curve temperature; growth rate is faster than nucleation rate. Mafic enclaves are thought to be mingled mafic magma in felsic magma, which is formed from compositional stratigraphy. Estimated equilibrium temperature and pressure for medium-grained biotite granite are about $800^{\circ}C$ and 4.83${\sim}$5.27 Kb, respectively.