• The Journal of the Petrological Society of Korea
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• v.12 no.3
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• pp.110-118
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• 2003

Olivine from the Layered Series (LS), Upper Border Series (UBS), and Marginal Border Series (MBS) of the Skaergaard intrusion was analyzed to examine compositional variation. In general, olivine from all three series shows similar trends in major elements with differentiation: FeO＊ (total iron as FeO＊), Ti $O_2$, and MnO in the olivine, progressively increase, MgO and $SiO_2$progressively decrease, and Na$_2$O, K$_2$O, A1$_2$ $O_3$, CaO, and P$_2$O$\_$5/ remain unchanged at low abundances. No abrupt changes in the trends of major components in Skaergaard olivine are observed. The systematic compositional variations in Skaergaard olivine during differentiation preclude the possibility of any injection of new magma into the chamber during differentiation. Abrupt change in MnO, however, is observed in Skaergaard olivine during differentiation. MnO in Skaergaard olivine steadily increases with differentiation from LZ to UZc and then decreases in UZc of the LS and its equivalents of the MBS and UBS. The decrease of MnO in Skaergaard olivine during the final stage of differentiation is attributable to the abrupt and extensive appearance of ferrobustamite as a liquidus phase.

• Economic and Environmental Geology
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• v.34 no.6
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• pp.617-625
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• 2001

The Skaergaard intrusion is widely considered a type example of a strongly fractionated, layered intrusion that has undergone extensive in situ igneous differentiation. The Intrusion, therefore, should be a good locality for modeling trace element vriation in a closed system. Previous studios (Haskin and Haskin, 1968; Faster et al., 1974), however, have suggested thats the rare earth elements in whole rocks and mineeral separates from the Intrusion did not fellow the expected trend for closed system crystatllization. Trace element modeling using published distribution coefficients, modal abundances of the coexisting minerals, and the concentration of trace elements In whole rocks and mineral separates from the Skaergaard Intrusion, reveals that the rare earth elements were significantly Influenced by the crystallization of abundant apatite in the Layered Series suring the final stages of crystallization. The results of trace element modeling also suggcsts that apatite, which appears sporadically in the UBS, is not a primary liquidus phase in these samples as previously suggested (Naslund, 1984) but an interstitial phase that (lid not directly effect trace element abundances In the evolving magma As the Skaergaard magma coaled convection, or convected as small Isolated cells during the final stages of differentiation, an elebated $P_{H2O}$ Induced by accumulation of volatile elements near the roof of the magma chamber ingibited or delayed the precipitation of primary apatite in the UBS If the Skaergaard differentiation Is modeler assuming primary apatite crystallization In the upper par of the LS where abundant modal apatite is present, and only late stage crystallization of apatite In the UBS where apatite Is less abundant, rare earth elements abundances follow a closed system variation trend. These results rule but any differentiation model for the Skaergaard Intrusion that Includesvolumetrically significant injections or discharges of magma Into or out of the chamber during the final 20% of the crystallization history.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2004.05a
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• pp.5-6
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• 2004

• Proceedings of the Petrological Society of Korea Conference
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• 2004.05a
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• pp.5-6
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• 2004

• Economic and Environmental Geology
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• v.34 no.6
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• pp.627-648
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• 2001

At least two distinct types of layering are present in the middle zone of the Skaergaard intrusion; alternating plagioclase-rich and pyroxene-rich, macro-rhythmic layers, and smaller scale, modally-graded, rhythmic layers. The macro-rhythmic layers are ubiquitous in the middle zone of the Layered Series, but are not observed in the lower and upper zone of the Layered Series or in the wall or roof tories of the intrusion. They range from 0.3 to 17.3 m in thickness, have sharp upper and lower boundaries, and can be traced laterally for over 2 ]fm in outcrop. Although individual macrorhythmic layers are not internally graded, many contain smaller-scale, modally-graded layers. Modally-graded. rhythmic layers are a common feature of the Layered Series but are not abundant in either the Upper Border Series or the Marginal Border Series. They range in thickness from 1 to 50 cm and can be traced laterally in outcrop for up to 100 m. Their lateral termination ranges from abrupt to gradational, and they are often associated with cut and fill structures and crossbedding suggestive of current activity. They are characterized by sharp lower and gradational upper contacts, and by strong intra-layer modal grading with olivine, ilmenite, and magnetite concentrated at the base, pyroxene concentrated above the base, and plagioclase concentrated at the top. The layers are also grain-size graded with the maximum size for each phase occurring at the horizon in the layer where the phase is most abundant. Modally-graded, rhythmic layers in the middle zone of the Layered Series occur within both plagioclase-rich and pyroxene-rich macro-rhythmic layers.

• Economic and Environmental Geology
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• v.11 no.2
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• pp.47-57
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• 1978

The study focused on the petrology and petrochemistry of the so called "Ganghwa syenitic rocks" which intruded into metasediment of basement in southeastern part of Ganghwa Island. The geologic sequence of the mapped area was shown in table 1, 10 model analyses and 7 chemical analyses on the rock samples taken from the Ganghwa syenitic rocks and Manisan granite have been used to discuss the nomenclature of the rocks and petrological relationship between rock types. The petrograpical and petrochemical features based on, the analyses are as follows: 1) Ganghwa syenitic rocks consist of Ganghwa alkali syenite and Ganghwa diorite porphyry which based on the classification of the subcommision on systematics of igneous of IGUS. Ganghwa diorite porphyry which occured as dike forms are intruded into Ganghwa alkali syenite. The rock forming minerals of Ganghwa alkali syenite are composed of perthite, plagioclase, quartz, hornblend and chlorite in major, and zircon, apatite, sericite and magnetite in minor. Ganghwa diorite porphyries consist of plagioclase, biotite, hornblend, orthoclase and chlorite, with, porphyritic texture. 2) In silica-oxides variation (Fig. 2) and AMF diagram (Fig_ 3), the Ganghwa alkali syenite is similar to the trend of Daly's average basalt-andesite-dacite-rhyolite than Skaergaard which shows the trend of the fractional crystallization of magma, and equivalent to the alkali rock series by Peacock. 3) The general trend of data points shift to plagioclase, and are superimposed on the alkali rich terminal part of the granodiorite province of SW Finland in normative Q-Kf-Pl(Fig. 4) and Or-Ab-An diagram respectively. The above-mentioned evidences suggested that the Ganghwa syenitic rocks are the differential products resulted by assimilation of intermediated magma and metasedment rock under relatively rapid cooling condition.

• Economic and Environmental Geology
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• v.12 no.3
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• pp.115-126
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• 1979

The Jecheon granite mass has turtle-shape exposure of about $190km^2$ at vicinity of Jecheon-eup, and is elongated in the direction of NEE-SWW. It discordantly intrudes the Bakdalryong metamorphic rocks and the great limestone series(Samtaesan and Hungwolri formation) which belong to the pre-Cambrian and Ordovician, respectively. The mass is composed of five facies of different grain size; texture and charecteristic minerals. The five facies are (1) coarse grained biotite granodiorite, (2) fine grained hornblende biotite granodiorite, (3) coarse grained pink feldspar granodiorite (4) leucogranite, and (5) porphyritic biotite granite. The mutual relationship between each facies is intrusion in (1)-(2) and (2)-(3), but unknown in (3)-(4) and (4)-(5). 22 modal analyses and and 10 chemical analyses on more than a hundred of representative samples taken from the mass are listed as tables. Triangular plot of modal and normative Q-Kf-Pl of this mass show a continuous differentiation products from certain common magma by change of chemical composition and anorthite contents in plagioclase. The metamorphic facies of contact aureole in surrounding rocks adjacent to the granite body are corresponded to hornblende hornfels facies with mineral assemblages of wollastonite-diopside-calcite in calcareous rocks, and of quartz-biotite-muscovite-cordierite in argillaceous rocks. Variation of silica versus oxides of major elements shows that the mass is similar to the trend of Daly's average basalt-andesite-dacite-rhyolite which shows the trend of the fractional crystallization of magma, and is equivalent to the calc-alkali rock series by Peacock. AMF diagram shows that Jecheon granite mass is equivalent to normal diffentiation products such as skaergaard intrusion. The above evidences suggest that the Jecohon granite mass is normal differentiation products formed by fractional crystallization under relatively slow cooling condition.

• Economic and Environmental Geology
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• v.7 no.3
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• pp.123-152
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• 1974

The study focused to the so called "Yangpyeong Igneous Complex" which intruded into the Gyeong Gi gneiss complex of Pre-cambrian basement of Yangpyeong area. The geologic sequence of the mapped area was shown in table 1. In laboratory work, 31 modal analyses and 7 chemical analyses on the rock samples taken from the igneous complex have been made to discuss the nomenclature of the rocks and the petrological relationship between rock types. The petrographical and petrochemical features based on the analyses are as follow; 1) The classification of this rocks based on the systematics of igneous rocks of IUGS showed that Yangpyeong Igneous complex consist of hornblende gabbro, diorite and porphyritic monzonite. The major rock forming minerals in hornblende gabbro are hornblende and plagiodase ($An_{46{\sim}55}$), in diorite, hornblende, biotite and plagioclase ($An_{23{\sim}33}$) and in porphyritic monzonite, K-feldspar, plagioclase ($An_{21{\sim}35}$), hornblende and biotite. Hornblende gabbro and diorite show coarse to medium grained hypidiomorphic granular texture and porphyritic monzonite was named by the characteristically porphyritic texture of K-feldspar phenocrysts. 2) Silica-oxides variation diagram (Fig.4) illustrate that the igneous complex is similar ttl that of Daly's average basalt-andesite-dacite-rhyolite and equivalent to the calc-alkalic rock series of Peacock's rock series. In AMF diagram (Fig. 5), the trend of the igneous complex is nearly pararell to that of the Skaergaard intrusion which shows the trend of the fractional crystalization of magma. 3) In normative Or-Ab-An diagram (Fig. 6) the general trend of the data points from gabbro to porphyritic monzonite of the igneous complex directs to a point of Or/Ab=1:1 on the side of Or-Ab. The field and laboratory evidences suggested that the Yangpyeong igneous complex was thought to be a series of comagmatic differential products.

• Economic and Environmental Geology
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• v.16 no.3
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• pp.163-221
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• 1983

Main aspects of this study are to clarify geochronology and petrogenetic processes of the so-called Hongjesa granite, which is a member of various intrusive rocks exposed in the northeastern part of the Ryongnam Massif, one of the Precambrian basements of South Korea. In this study, the Hongjesa grainte is divided into four rock units based on the geologic age, mineralogical and chemical constituents, and texture: the Precambrian Hongjesa granite gneiss (Hongjesa granite Proper) and leucogranite gneiss, the Paleozoic gnessic two mica granite, and the Jurassic muscovite granite. The Hongjesa granite gneiss is identified by its grayish color, slight foliation, and porphyroblastic texture. The leucogranite gneiss is distinct by its light gray color, sand medium to coarse grained texture. The gneissic two mica granite is distinguished from others by its strong foliation, containing gray-colored feldspar phenocrysts with biotite and muscovite in varying amounts. The muscovite granite occurs as a small stock containing feldspar phenocrysts along margin of the stock. These granitic rocks vary widely in composition, reflecting the facts that they partly include highly metamorphosed xenolith and schlierens as relics of magmatic and anatectic processes. In particular, grayish porphyroblasts of microcline perthite is characteristic of the Hongjesa granite gneiss, whereas epidote and garnet occur in both the Hongjesa granite gneiss and leucogranite gneiss. These minerals are considered to be formed by potassic metasomatism and contamination of highly metamorphosed rocks deeply buried under the level of the Hongjesa granite emplacement. The individual synchronous granitic rocks plotted on Harker diagram show mostly similar trends to the Daly's values. The plots of the Hongjesa granite gneiss and gneissic two mica granite concentrate near the end part of the calc-alkalic rock series on the AMF diagrams, whereas those of the leucogranite gneiss and muscovite granite indicate the trend of the Skaergaard pluton. These granitic rocks plotted on a Q-Ab-Or diagram (petrogeny's residua system) fall well outside the trough of the system. This can be attributed to the potassic matasomatism of these rocks. On the ACF diagram, these rocks appear to be dominantly I-type prevailing over S-type. The K-Ar ages, obtained from a total of 7 samples of the leucogranite gneiss, gneissic two mica granite, muscovite granite, porphyritic alkali granite, and rhyolitic rock, in addition to the Rb/Sr ages of the Hongjesa granite gneiss by previous workers, permit the rock units to be arranged in the following chronological order: The middle Proterozoic Hongjesa granite gneiss (1714-1825 m.y.), the upper proterozoic leucogranite gneiss (875-880 m. y.), the middle Paleozoic gneissic two mica granite (384 m. y.) the upper Jurassic muscovite granite (147 m. y.), the Eocene alkali granite (52 m. y.), and the Eocene rhyolitic rock (45 m. y.). From the facts and data mentioned above, it is concluded that the so-called Hongjesa granite is not a single granitic mass but is further subdivided into the four rock units. The Hongjesa granite gneis, leucogranite gneiss, and gneissic two mica granite are postulated to be either magmatic or parautochtonous, intrusive, and the later muscovite granite is to be magmatic in origion.