Petrogenesis and Geological Significances of Ultramafic Rocks in Hongseong Area, Gyeonggi Massif, South Korea

Department of Earth and Environmental SciencesChonbuk National University, Korea金沢大学大学院自然科学研究科Promoting Environmental Pesearch in Pan-Japan Sea Area : Young Researchers\u27 Network, Schedule: March 8-10,2006,Kanazawa Excel Hotel Tokyu, Japan, Organized by: Kanazawa University 21st-Century COE Program, Environmental Monitoring and Prediction of Long- & Short- Term Dynamics of Pan-Japan Sea Area ; IICRC(Ishikawa International Cooperation Research Centre), Sponsors : Japan Sea Research ; UNU-IAS(United Nations University Institute of Advanced Studies)+Ishikawa Prefecture Government ; City of Kanazaw

Zirconolite and baddeleyite in an ultramafic suite from southern India: Early Ordovician carbonatite-type melts associated with extensional collapse of the Gondwana crust

金沢大学理工研究域自然システム学系We report here the occurrence of rare zirconium-bearing minerals, zirconolite (CaZrTi2O7) and baddeleyite (ZrO2), from an unusual ultramafic suite within the Achankovil Shear Zone (ACSZ) in southern India. Zirconolite occurs as inclusions within spinel in phlogopite-graphite spinellite and shows characteristic development of radial cracks. Baddeleyite is commonly observed as an included phase within phlogopite from phlogopite dunite and graphite-spinel glimmerite. The mineral also occurs less commonly within spinel and graphite from graphite-spinel glimmerite. The composition of zirconolite is characterized by an enrichment of U and Th over rare earth elements. Baddeleyite shows abundance of Zr with minor Hf, Ti, and U. The mode of occurrence along with the chemical composition of these minerals implies their formation as early-stage crystallization products from a silica-undersaturated melt that was enriched in "carbonatite-phile elements" such as Ca, Zr, Ti, and volatiles CO2 and H2O. We report U-Pb chemical ages from the zirconolite that show a mean of 469 ± 11 Ma. We correlate this age with the timing of emplacement and consolidation of the ultramafic suite within ACSZ, and it is considerably younger than the late Neoproterozoic-Cambrian ages reported from this zone. Our data suggest early Ordovician carbonatite-type melts emplaced within ACSZ, which we identify as a mantle-rooted zone. We infer that deep-seated extension along the ACSZ probably triggered the generation of such melts, related to the extensional collapse of the orogen following the collisional assembly of the Gondwana supercontinent. © 2006 by The University of Chicago. All rights reserved

Neoarchean arc magmatism and Paleoproterozoic granulite-facies metamorphism in the Bhavani Suture Zone, South India

The Bhavani Suture Zone in the Southern Granulite Terrane marks the zone of amalgamation of the Neoarchean Nilgiri Block and the northwestern Madurai Block in southern India. Here, we report detailed petrological, geochemical, and geochronological data on the Mettupalayam mafic–ultramafic complex within this suture zone with a view to evaluate the tectonothermal history of the Bhavani Suture Zone and adjoining crustal blocks. The metamorphosed complex includes charnockite, hornblende‐biotite gneiss, mafic granulite, amphibolite, garnet‐bearing mafic granulite, and dioritic gneiss along with metamorphosed banded iron formation. The mafic granulite and the dioritic gneiss occur as concordant layers of varying thickness within the hornblende‐biotite gneiss. The salient geochemical features of the mafic granulite and the dioritic gneiss including the enrichment of large‐ion lithophile elements and depletion of high‐field‐strength elements suggest a subduction‐related arc magmatic setting. However, the amphibolites show MORB‐related affinity, suggesting its formation from a N‐MORB‐related source and their accretion together with the overlying banded iron formation. The peak metamorphic conditions of the garnet‐bearing mafic granulite were estimated using conventional geothermobarometers as 800–820 °C/8.5–9.2 kbar, which we further confirm through phase equilibrium modelling in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCKFMASHTO) system. Magmatic zircons with high Th/U ratio from the amphibolite display a well‐defined discordia with an upper intercept age of 2,600 ± 38 Ma. Zircon grains from the dioritic gneiss show weighted mean 206Pb/207Pb age of 2,524 ± 6 Ma from concordant zircon spots and a comparable upper intercept age of 2,562 ± 34 Ma from discordant zircon spots, indicating protolith emplacement related to Neoarchean arc magmatism as inferred from our geochemical data. The thin overgrowth rims around the magmatic zircon grains in the amphibolite yielded an upper intercept age of 2,520 ± 20 Ma, which is comparable with the protolith crystallization age of the dioritic gneiss. Slightly younger weighted mean 207Pb/208Pb ages of 2,463 ± 27 Ma (from dioritic gneiss) and 2,422 ± 30 Ma (from amphibolite) are also obtained from the metamorphic zircon rims. These ages are correlated to the timing of high‐grade metamorphism associated with final collision of the Nilgiri Block and the northwestern Madurai Block. Similar Neoarchean–Paleoproterozoic magmatism and high‐grade metamorphism were reported from many localities south of the Dharwar Craton. Our study further confirms the previous tectonic model that envisages multiple subduction and collision of magmatic arcs and continental fragments towards the Dharwar Craton during the Archean–Paleoproterozoic transition.Sam Uthup, Toshiaki Tsunogae; V.J. Rajesh, M. Santosh, Yusuke Takamura, Yukiyasu Tsutsum

Evolutionary history of western Eos Chaos of Valles Marineris, Mars: Insights from morphological characteristics

The dynamics of aqueous processes within the Eos Chasma region in the trough of Valles Marineris on Mars have been attributed to a variety of Hesperian-aged landforms. We aim to improve the understanding of the geological characteristics of the western part of the Eos Chaos by investigating the morphological, topographical, and thermo-physical characteristics of the western semi-circular segment of Valles Marineris. The western Eos Chaos is characterized by remnants of an elevated crater rim, a central peak, and a circular boundary. Based on these observations, we infer that the study area is an ancient, highly degraded impact crater. Our observations indicate that numerous geological processes, such as fluvial, tectonic, and aeolian processes, have shaped the landforms. For instance, channels on the slope of the wall with a mean v-index of 0.2 indicate a fluvial origin. The chaotic mounds within the study regions are highly degraded. However, the presence of eroded inselberg peaks above the maximum ponding level of eastern Valles Marineris (–3560 m) suggests that both aeolian and fluvial processes have played a role in the denudation of the impact crater. Furthermore, both aeolian and fluvial processes also influenced the morphological evolution of inselbergs of this impact crater of Eos Chaos. The morphological, topographic, and thermal inertia characteristics of the landforms in the Eos Chaos are similar to those found elsewhere in Valles Marineris. In this study, the impact crater of Eos Chaos is considered a sub-region of Valles Marineris, in which evidence for many past geological processes is preserved. Based on possible chronological markers, we have developed a model that explains the evolution of the Eos Chaos impact crater and its incorporation into Valles Marineris

Spectral characteristics of banded iron formations in Singhbhum craton, eastern India: Implications for hematite deposits on Mars

Banded iron formations (BIFs) are major rock units having hematite layers intermittent with silica rich layers and formed by sedimentary processes during late Archean to mid Proterozoic time. In terrestrial environment, hematite deposits are mainly found associated with banded iron formations. The BIFs in Lake Superior (Canada) and Carajas (Brazil) have been studied by planetary scientists to trace the evolution of hematite deposits on Mars. Hematite deposits are extensively identified in Meridiani region on Mars. Many hypotheses have been proposed to decipher the mechanism for the formation of these deposits. On the basis of geomorphological and mineralogical studies, aqueous environment of deposition is found to be the most supportive mechanism for its secondary iron rich deposits. In the present study, we examined the spectral characteristics of banded iron formations of Joda and Daitari located in Singhbhum craton in eastern India to check its potentiality as an analog to the aqueous/marine environment on Mars. The prominent banding feature of banded iron formations is in the range of few millimeters to few centimeters in thickness. Fe rich bands are darker (gray) in color compared to the light reddish jaspilitic chert bands. Thin quartz veins (<4 mm) are occasionally observed in the hand-specimens of banded iron formations. Spectral investigations have been conducted in VIS/NIR region of electromagnetic spectrum in the laboratory conditions. Optimum absorption bands identified include 0.65, 0.86, 1.4 and 1.9 μm, in which 0.56 and 0.86 μm absorption bands are due to ferric iron and 1.4 and 1.9 μm bands are due to OH/H2O. To validate the mineralogical results obtained from VIS/NIR spectral radiometry, laser Raman and Fourier transform infrared spectroscopic techniques were utilized and the results were found to be similar. Goethite-hematite association in banded iron formation in Singhbhum craton suggests dehydration activity, which has altered the primary iron oxide phases into the secondary iron oxide phases. The optimum bands identified for the minerals using various spectroscopic techniques can be used as reference for similar mineral deposits on any remote area on Earth or on other hydrated planetary surfaces like Mars

Neoproterozoic bimodal volcanism in the Okcheon Belt, South Korea, and its comparison with the Nanhua Rift, South China: implications for rifting in Rodinia

A systematic geochemical examination and zircon U-Pb dating of Neoproterozoic bimodal volcanic rocks from the Chungju area in the northeast segment of the Okcheon Metamorphic Belt (OMB), South Korea, allow a comparison with similar rocks from the Nanhua Rift, South China. The bimodal metavolcanics of the Chungju area comprise the subalkaline to alkaline basalts (hereafter "mafic metavolcanic rocks") and trachytes (hereafter "felsic metavolcanic rocks"). The mafic metavolcanic rocks are characterized by light rare earth element (LREE)-enriched and "humped" trace-element patterns with moderate depletions in Sr and Ti and variable but reasonably low εNd(T) values between +0.83 and +2.99. These geochemical features are consistent with the area's origin in an ocean island basalt (OIB) mantle source with minor crustal contamination. The felsic metavolcanic rocks are characterized by LREE-enriched patterns with a remarkable negative Eu anomaly. They display an overall enriched trace-element pattern with significant depletions of Sr, P, Eu, and Ti. They have the geochemical characteristics typical of A1-type granites and εNd(T) values between +1.30 and +2.54. The incompatible element versus incompatible element diagrams for both rocks exhibit nearly smooth positive trends. In the Y/Nb versus Yb/Ta diagram, all the felsic rocks plot within the OIB field. Hence, our data imply a genetic linkage between the mafic and the felsic rocks. The felsic rocks were most likely generated from basaltic protoliths through extensive fractional crystallization plus minor crustal contamination/assimilation. Igneous zircon from a felsic metavolcanic rock from the Munjuri Formation in the OMB gives a SHRIMP U-Pb age of 762 ± 7 Ma, providing a temporal link to the Neoproterozoic rift-related volcanism in South China. Rare detrital zircons extracted from a felsic sample from the Gyemyeongsan Formation yield a mixture of ages: ∼1.9 Ga, ∼870 Ma, and ∼250 Ma. The presence of some Triassic metamorphic overgrowths reflects a high-grade metamorphic event coeval with that recently identified in the Gyeonggi and Yeongnam massifs and linked to an Early Triassic collision event in South Korea. The lithological and geochemical data from the Neoproterozoic metavolcanic rocks in the OMB of South Korea show similarities with th Nanhua Rift in South China, pointing to a North Asian connection associated with the disruption of Rodinia

Petrology, geochronology and tectonic implications of Mesozoic high Ba-Sr granites in the Haemi area, Hongseong Belt, South Korea

Collision between the North and South China continental blocks began in the Korean peninsula during the Permian (290-260 Ma). The Haemi area in the Hongseong collision belt (proposed as the eastern extension in South Korea of the Dabie-Sulu collision zone of China) within the Gyeonggi Massif comprises post-collisional high Ba-Sr granite with intermediate enclaves that intruded into the Precambrian rocks. The intermediate enclaves have a shoshonitic affinity whereas the granite is a high-K calc-alkaline variety. The chondrite-normalized rare earth element (REE) pattern with relative enrichment of LREE over HREE and absence of a significant negative Eu anomaly typifies both enclaves and granite. Geochemical similarities of enclaves and granite are attributed to the involvement of enriched mantle sources in their genesis. However, dominant crustal components were involved in the formation of high Ba-Sr granites. A granite crystallization age of 233 ± 2 Ma was obtained from SHRIMP U-Pb zircon dating. This age is slightly younger than the Triassic collision event in the Hongseong Belt. Geochemical data, U-Pb zircon age, and regional tectonics indicate that the Haemi high Ba-Sr granite formed in a post-collisional tectonic environment. A Mesozoic post-collisional lithospheric delamination model can account for the genesis of high Ba-Sr granite in the Haemi area

Petrology, geochronology and tectonic implications of Mesozoic high Ba-Sr granites in the Haemi area, Hongseong Belt, South Korea

Collision between the North and South China continental blocks began in the Korean peninsula during the Permian (290-260 Ma). The Haemi area in the Hongseong collision belt (proposed as the eastern extension in South Korea of the Dabie-Sulu collision zone of China) within the Gyeonggi Massif comprises post-collisional high Ba-Sr granite with intermediate enclaves that intruded into the Precambrian rocks. The intermediate enclaves have a shoshonitic affinity whereas the granite is a high-K calc-alkaline variety. The chondrite-normalized rare earth element (REE) pattern with relative enrichment of LREE over HREE and absence of a significant negative Eu anomaly typifies both enclaves and granite. Geochemical similarities of enclaves and granite are attributed to the involvement of enriched mantle sources in their genesis. However, dominant crustal components were involved in the formation of high Ba-Sr granites. A granite crystallization age of 233 ± 2 Ma was obtained from SHRIMP U-Pb zircon dating. This age is slightly younger than the Triassic collision event in the Hongseong Belt. Geochemical data, U-Pb zircon age, and regional tectonics indicate that the Haemi high Ba-Sr granite formed in a post-collisional tectonic environment. A Mesozoic post-collisional lithospheric delamination model can account for the genesis of high Ba-Sr granite in the Haemi area