Lutzow-Holm Complex Research Articles

UHT granulites of the Highland Complex, Sri Lanka II: Geochronological constraints and implications for Gondwana correlation

The regional ultrahigh-temperature (UHT) metamorphism of the Highland Complex, Sri Lanka is well established and has an important role in our understanding of the tectonic history of the Gondwana supercontinent. U-Pb zircon dating of sapphirine-bearing Mg-Al granulites yielded two major metamorphic age populations at approximately 620-590 and 563-525 Ma with no evidence of older zircon cores. Pelitic granulite samples with a Grt-Sil-Spl-Crd assemblage have similar metamorphic ages with concordant data clusters at similar to 602, 563, and 526 Ma and inherited zircon cores aged from 2040 to 1600 Ma. The pelitic granulites also underwent two stages of metamorphism (565-520 and 622-580 Ma). Some of these pelitic granulite samples have inherited zircon cores ranging from 3060 to 760 Ma. Zircons in mafic granulite samples have age ranges of 566-533 and 620578 Ma. A calc-silicate granulite sample also has similar age populations at 591, 541, and 524 Ma. Combining these new results with previously published ages from Sri Lanka and formerly adjacent continental fragments of Gondwana, we propose that the terranes in southern Madagascar (south of Ranotsara Shear Zone), Northern and Southern Madurai and the Trivandrum Blocks of southern India, the Highland Complex of Sri Lanka, and the Skallen Group in the Lutzow-Holm Complex of East Antarctica represent a unique metamorphic belt that regionally experienced the Ediacaran-Cambrian UHT event during the amalgamation of the Gondwana super-continent.

東南極LÜtzow-Holm Complex, Rundvågshettaに産する苦鉄質岩岩脈の産状と組成

東南極LÜtzow-Holm Complex, Rundvågshettaに産する苦鉄質岩岩脈の産状と組成

Occurrence and chemical composition of mafic dyke from Rundvagshetta, Lutzow Holm Complex, East Antarctica.

Occurrence and chemical composition of mafic dyke from Rundvagshetta, Lutzow Holm Complex, East Antarctica.

東南極Lutzow-Holm岩体に産するアルカリ～高カリウム貫入岩の産状

東南極Lutzow-Holm岩体に産するアルカリ～高カリウム貫入岩の産状

コンダライトと石灰珪質'岩脈'の境界部に出現するザクロ石と斜長石中の組成勾配について

コンダライトと石灰珪質'岩脈'の境界部に出現するザクロ石と斜長石中の組成勾配について

Linking P-T path with development of discontinuous phosphorus zoning in garnet during high-temperature metamorphism — an example from Lützow-Holm Complex, East Antarctica

Garnet porphyroblasts contained in the garnet-sillimanite gneiss from the Lutzow-Holm Complex at Skallevikshalsen, East Antarctica, have a phosphorus-poor core and phosphorus-rich rim. The core/rim boundary of the phosphorus zoning is discontinuous. The irregular shape of this core/rim boundary together with the pressure difference between the core and the rim inferred from the difference in aluminosilicate inclusions (kyanite in the core and sillimanite in the rim) suggests that this is the resorption/reprecipitation boundary. The difference between phosphorus concentrations in the garnet core and rim is accompanied by a change in phosphate inclusions in the garnet. Apatite and monazite are included in the phosphorus-poor garnet core, whereas monazite alone is included in the phosphorus-rich garnet rim. Utilizing the core/rim boundary as a contemporaneous surface when comparing different garnet grains, the timing of the discontinuous phosphorus-zoning formation (and thus, the garnet resorption) and change in the phosphate assemblage can be correlated to the pressure-temperature path of the garnet-sillimanite gneiss. The phosphorus-poor core of the garnet mainly formed during the prograde stage in the kyanite to sillimanite stability fields under which apatite probably buffered the phosphorus-content of garnet, and the phosphorus-rich garnet rim possibly crystallized from the melt at the retrograde stage near the vapor saturated solidus under which monazite alone (without apatite) probably did not buffer the phosphorus-content of garnet. Garnet resorption occurred during the decompression stage between these two garnet growth stages.

東南極リュツォ・ホルム岩体ルンドボークスヘッタ，輝石片麻岩の風化過程における元素の挙動

東南極リュツォ・ホルム岩体ルンドボークスヘッタ，輝石片麻岩の風化過程における元素の挙動

東南極リュッツオホルム岩体ルンドボーグスヘッタ産グラニュライトのザクロ石斑状変晶中の大隅石，スピネル＋石英包有物

東南極リュッツオホルム岩体ルンドボーグスヘッタ産グラニュライトのザクロ石斑状変晶中の大隅石，スピネル＋石英包有物

Origins of the lower crustal reflectivity in the Lützow-Holm Complex, Enderby Land, East Antarctica

The combination of rock velocities with a seismic signature has been used as a clue to understanding the structure and evolution of the continental lithosphere. The lower crustal reflectivity beneath part of the Pan-African orogeny, the Lutzow-Holm Complex (LHC), Western Enderby Land, East Antarctica, has been imaged on single-fold seismic reflection profiles using active seismic studies on the continental ice sheet. The set of velocity layers at middle to lower crustal depths were obtained by modeling the later phases of teleseismic receiver functions observed at Syowa Station (39°E, 69°S), in the LHC. The later phases around 10–16 s from P onset in radial components are explained by assuming a layered lower crustal model with velocity changes of 0.3 km/s in shear waves for 0.5–1.0 km thick layers. The origin of lower crustal reflectivity is discussed in terms of high-pressure laboratory measurements on metamorphic rocks from Western Enderby Land. Lower crustal velocities of 6.9 km/s derived by seismic refraction surveys can be explained by a major composition of mafic pyroxene granulite, as occurs in the Archean Napier Complex. A tectonic model involving collision between the paleo East and West Gondwana blocks during the last stage of Pan-African orogeny is presented to explain the high velocities and reflectivity in the lower crust underlying the LHC. The Napier Complex is considered to have descended eastward under part of the Pan-African belt (LHC), generating a higher-pressure mafic granulite composition. The reflectivity of the lower crust of the LHC may have been enhanced subsequently by extensional stress during the breakup process.

Timing of attainment of the spinel+quartz coexistence in garnet-sillimanite leucogneiss from Skallevikshalsen, Luetzow-Holm Complex, East Antarctica

Spinel in direct contact with quartz is newly found in the Grt-Sil leucogneiss from Skallevikshalsen, Lutzow-Holm Complex, East Antarctica. It is included in the outermost core of the garnet porphyroblast and is characterized by low ZnO content (2.77-3.83 wt%) and very low Cr2O3 content (0-0.09 wt%). Incorporation of 2.77-3.39 wt% ZnO stabilized the Spl + Qtz assemblage to lower temperatures for about 50 degrees. As a result, their coexistence can be attained around the peak P-T conditions of Skallevikshalsen. The occurrence of relic staurolite, kyanite and breakdown texture of staurolite to spinel and kyanite included in the garnet core suggests that prograde stage is preserved in the garnet core and breakdown of staurolite itself was attained in the kyanite stability field. The Spl + Qtz assemblage is included at outermost part of the garnet core, suggesting that outermost core of the garnet was formed near the peak metamorphic conditions. Decrease in anorthite content of plagioclase included in the garnet core from that found in the rock matrix suggests that decompression took place during garnet formation. Attainment of these reaction sequences requires clockwise P-T path as previously proposed for the Lutzow-Holm Complex.

A Pan-African ‘Humite Epoch’ in East Gondwana: implications for Neoproterozoic Gondwana geometry

The plate geometries during Neoproterozoic time have been reconstructed using humite occurrences for the first time. These occurrences are also used to demonstrate the hitherto undocumented humite epoch dominated by extremely water-rich, fluorinated, fluid activity during the Pan-African event. Humite-bearing marbles occur in the Kerala Khondalite Belt of southernmost India, South Madagascar, Sri Lanka and the Lutzow–Holm Complex of East Antarctica. These occurrences prompt a fit of these areas with the Tanzania–Mozambique region of Africa and suggest an intercontinental humite epoch coeval with the waning stages of Pan-African activity extending from the Lutzow–Holm complex of East Antarctica upto the East African Orogen along the eastern flanks of the Mozambique Belt. The modified Smith and Hallam fit of continents finds support in this study.

Carbon Isotope Fractionation Between Calcite and Graphite During High Temperature Metamorphism

The carbon isotope exchange thermometer between calcite and graphite have been recently widely applied to amphibolite and granulite facies marbles (e.g. Kitchen and Valley, 1995). It has been proved that the temperature dependant fractionation is reliable up to temperatures of the order of 800~ The fractionation between calcite and graphite nears unity at higher tempertures and hence is difficult to calibrate the thermometer at temperatures higher than 800~ Here we try to emperically test the high tempertaure fractionation between calcite and graphite using marble samples from the high temperature granulite facies terrains of southern India and East Antarctica. Marbles from the Trivandrum and the Madurai Block, from the southern granulite terrain were examined in this study. The Trivandrum Block comprises of granulite facies supracrustal rocks, while in the Madurai block massive charnockitic rocks predominate. Marbles bands occur in these two terrains as conformable units intercalated with quartzites. Texturally these are very coarse (up to several centimeters) and highly crystalline graphite crystals can be seen embedded within calcite. Calcite constitutes more than 80 modal % in most of the samples. The silicate mineral phases include phlogopite, forsterite, clinopyroxene and spinel; with occasional clinohumite, pargasite, and other calc-silicate mineral phases. Marbles from LutzowHolm complex, which is a granulite to amphibolite facies terrain with a regional peak granulite facies metamorphism at temperatures in the range 760830~ and pressures of 7 • kbar were also examined. Peak metamorphic temperatures were determined from fractionation of C-isotopes between calcitegraphite pairs using the recent calibration of Kitchen and Valley (1995). For example the marbles from the Trivanrum Block in Southern India gave fractionation range from 2.46%0 to 3.76%0, corresponding to a temperature range of 700 to 800~ Out of the ten calcite-graphite pairs, 6 gave similar results. These results are significant that the carbon isotope thermometer can be used to determine accurate peak metamorphic temperatures in granulite facies rocks. The marbles form the Madurai block and the Lutzow-Holm Bay gave temperatures between 800 and 900~

Cambrian Orogenic Belt in East Antarctica and Sri Lanka: Implications for Gondwana Assembly: A Discussion

The paper by Shiraishi et al. (1994) provided evidence for a Pan-African event in Lutzow-Holm Bay (LHB) of East Antarctica but dismisses evidence that Pan-African event overprints rocks with a long prior history of tectonothermal activity in both LHB and adjoining areas; thus conclusion that LHB lies in a Pan-African suture between exotic blocks may be erroneous. 1) Shiraishi et al. (1994, p. 57) state that extensive petrological study has not elucidated a polymetamorphic history in Lutzow-Holm Complex. However, amphibolite-facies metamorphism overprinting an earlier granulite facies event has been well characterized (e.g., Yoshida 1994 and references therein). For example, alteration of anhydrous minerals such as orthopyroxene by hydrous minerals such as amphibole or biotite has been widely recognized, and clear structural evidence of superposition of later upright fold over major fold which resulted in development of inclined mineral lineation and schistosity from hinges and axial surface of major fold has been documented. Earlier and later folds in Prince Olav Coast, and first (fl), second (f2) and third (f3) folds in LHB area have been recognized. Shiraishi et al. (1994, p. 49) hold that the D1 folds [referred to as earlier folds in Prince Olav Coast and fl folds in LHB] are contemporaneous with main metamorphism, since mineral lineations are parallel to D1 axes, in support of their scheme of monometamorphic history. Their view on relationship of D1 folds and main metamorphism is based totally on a few observations in Prince Olav Coast, which are neither supplemented by detailed structural elements, nor strengthened by structural comparison of folds and lineations in

Cambrian Orogenic Belt in East Antarctica and Sri Lanka: Implications for Gondwana Assembly

Ion microprobe U-Pb dating of zircons from the Lutzow-Holm Complex (LHC) and the Yamato-Belgica Complex (YBC), East Antarctica indicate high-grade regional metamorphism and associated folding of LHC occurred between $$521 \pm 9$$ and $$553 \pm 6 Ma$$. This shows, for the first time, the existence of a Cambrian orogenic belt within the East Antarctic Shield. Many zircons from the LHC contain cores that record inherited ages from ~2900 to ~1500 Ma. Components of ~1000 Ma zircon have been identified in three locations. This may indicate the maximum age of the deposition of LHC. One metasedimentary gneiss from the YBC records a well-defined age at about 600 Ma, whereas another yields a dispersion of ages interpreted as the result of varied radiogenic Pb loss in ~1000 Ma zircons at about 500-600 Ma. These gneisses have inherited ages of up to ~2500 Ma. Our work enables an improved fit to the once contiguous fragments of Gondwana. The Highland/Southwestern Complex (HSWC) of Sri Lanka has remarkable petrological...