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Madhusoodhan Satish-Kumar, Shizuoka University (Japan)
Tomoharu Miyamoto, Kyushu Univeristy (Japan)
Yoichi Motoyoshi, National Institute of Polar Research (Japan)
Joerg Hermann, The Australian National University (Australia)
Yasuhito Osanai, Kyushu University (Japan)
Hiroo Kagami, Niigata University (Japan)
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Marbles are common constituents in the metasedimentary sequences in mobile belts that formed during the amalgamation of Gondwana. The collision of east and west Gondwana is also manifested by the closure of the Mozambique Ocean. Thick metasedimentary supracrustal sequences exposed in southern Madagascar, southern India, Sri Lanka and East Antarctica are believed to have deposited in the Mozambique Ocean that separated the east and west Gondwana supercontinents. Based on the geochemical results, we suggest that high-grade marbles can potentially preserve pre-metamorphic signatures. This helps us to understand the chemostratigraphy of pre-existed oceans that separated continents. We present apparent depositional ages of metacarbonate lithologies for the Lzow Holm Complex, East Antarctica and try to understand the spatial and temporal extent of the Mozambique Ocean.
Dolomitic and calcitic marbles are common lithological units in the amphibolite-facies (NE) to ultrahigh-temperature (SW) metamorphosed Lzow Holm Complex, which extents about 400 km coastal stretch of East Antarctica. The marbles occur as layers with varying thickness, conformably interlayered with metapelitic and metapsammitic gneisses and granulites, especially in the SW region of the Lzow Holm Complex. Strontium, carbon and oxygen isotope geochemistry of the marbles suggest that most of the marbles were subjected to extensive alterations after deposition resulting from multiple stages of fluid-rock interaction processes during diagenesis, prograde to peak and retrograde metamorphic events. Exceptionally, some of the marble layers preserve pre-metamorphic geochemical characteristics, such as low Sr isotope ratios and sedimentary oxygen and carbon isotopic compositions. Such marble horizons are suitable for chemostratigraphic correlations with unmetamorphosed equivalents. Least altered isotopic ratios of 0.7066 and 0.7053 suggest apparent age of deposition between 730 and 830 Ma. The apparent carbonate depositional ages are consistent with existing tectonic models that can accommodate a depositional window later than 850 Ma (youngest detrital zircon age) and 650 Ma (oldest metamorphic age) reported from the Lzow Holm Complex.
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