Diet of albacore Thunnus alalunga from the waters of Mauritius (western Indian Ocean) inferred from stomach contents and fatty acid analysis

The diet of albacore Thunnus alalunga from their spawning ground in the waters of Mauritius was investigated. The stomach contents of 249 albacore individuals, caught by industrial longliners and artisanal fishers, was analysed, and the dominant prey taxa were selected for lipid and fatty acid (FA) analysis. The FA profiles of prey were compared with those of liver tissue of spawning-capable and post-spawning female albacore, using multivariate analysis. Whereas stomach content analysis identified cephalopods and crustaceans as the dominant prey items in number, FA-profile analysis identified crustaceans and fishes as the most-frequently consumed prey of post-spawning female albacore. In contrast, the FA profiles of spawning-capable albacore and those of prey showed very low similarity. Analysis of the prey suggests that although cephalopods, crustaceans and fishes could all provide albacore with the required lipids and FAs, cephalopod prey seem to be less desirable owing to their lower energy content (i.e. low in total lipid, triacylglycerol, 16:0, 18:0 and 18:1ω9). Instead, the most beneficial food appeared to be locally available fishes, which are more energy-rich and have a higher docosahexaenoic acid/ eicosapentaenoic acid ratio. These results provide new information on the trophic ecology of albacore, promote our understanding of the importance of prey type for successful reproduction of albacore, and highlight the advantages of FA profiling to study diet.     

Chemical Composition,U–Th–Pb Age,and Geodynamic Setting of Metavolcanic Filla Series (Rauer Islands,East Antarctica)

Geotectonics - An assemblage of mafic granulites (schists), plagiogneisses, and metasedimentary rocks, which is referred to as the Filla Series, is exposed in the Rauer Islands (opposite the...     

The Rayner tectonic Province of East Antarctica: Compositional features and geodynamic setting

Geochemical and new isotopic (U-Pb, Sm-Nd) data on the Mesoproterozoic metaigneous complexes of the Rayner Province in central East Antarctica (Enderby Land-Kemp Land and the northern Prince Charles Mountains) are presented. These territories are mainly composed of amphibolite-to-granulite-facies orthogneisses, many of which are Y-depleted tonalite gneisses and mafic schists. The igneous complexes of their protolith are largely products of anatexis of the lower crust; mantle-derived and upper crustal rocks are less abundant. The geochemical features of the mafic rocks indicate that they crystallized from high-temperature plume-related mantle melts and low-temperature lithospheric melts. As follows from the published and new Nd model ages, the Rayner Province formed and evolved over the Paleo-to-Mesoproterozoic in the regime of accretionary and collisional tectonics with predominance of accretion of the juvenile Paleoproterozoic crust between 1500–2400 Ma. New data show that in the northern Prince Charles Mountains, granite-gneiss protoliths were emplaced ca. 1040 and 930 Ma ago. The Rayner Province is considered to be a long-living mobile belt formed as a result of collision of Paleoproterozoic island-arc terranes and Archean blocks amalgamating into a continental massif 1050–1000 Ma ago in the course of the growth of the Rodinia supercontinent. In the northern Prince Charles Mountains, thermal processes related to magmatic underplating at the base of the crust were probably important.     

Charnockite composition in relation to the tectonic evolution of East Antarctica

Charnockitic suites in central Dronning Maud Land (DML), Mac.Robertson Land (MRL), and the Bunger Hills area are compositionally varied and probably include both mantle and lower-crustal components. In this paper we present new geological and geochemical data on the DML charnockitic rocks, and compare their geochemistry with that of charnockitic rocks from several other Antarctic high-grade terranes, particularly MRL and the Bunger Hills. These areas have different geological histories and one of the main aims of this study is to investigate possible links between charnockite composition and the tectonic history of their host terranes. Antarctic charnockitic rocks form two distinct compositional groups. 510 Ma DML charnockites are relatively alkalic and ferroan, with high K₂O, Zr, Ga, Fe / Mg, and Ga / Al, and very low MgO, characteristic of A-type (alkaline, commonly anorogenic) granitoids. The more mafic DML rocks, at least, were derived by fractionation of a relatively alkaline high-P–Ti ferrogabbro parent magma. Most other early Palaeozoic charnockitic rocks in Antarctica are of similar composition. In contrast, MRL (c. 980 Ma) and Bunger Hills (c. 1170 Ma) charnockites are mainly calc-alkalic or calcic and magnesian, and the associated mafic components are tholeiitic. MRL and Bunger Hills charnockites are late-orogenic, whereas DML charnockites are post-orogenic, and appear to have been emplaced after post-collision extension and decompression. These two mineralogically and geochemically distinct charnockite groups may thus reflect a compositional trend in an evolving orogen, either accretional or collisional, respectively.     

The tectogenesis stages of the antarctic shield: Review of geochronological data

A review of numerous isotopic-geochronological studies is given. The major attention is paid to modern U-Pb zircon measurements using the SHRIMP method. The major tectogenesis stages recognized in the Antarctic shield are Archean (3800–3300, 3100–2800, and 2550–2450 Ma), Paleoproterozoic (2200–2000 and 1850–1700 Ma), Mesoproterozoic (1400–1250 and 1200–920 Ma), and Neoproterozoic-Early Paleozoic (600–500 Ma). Ancient Eo-and Paleoarchean processes (intrusion of tonalite gneisses protoliths, or metamorphism) took place at Enderby Land, Kemp Land, and the Prince Charles Mountains. At some localities tectonic activity ended at 1700 Ma, at other places reworking or rejuvenation occurred later. Mesoproterozoic tectogenesis was not synchronous. The completion phases of tectonic activity are known to have occurred in different places 1150, 1050, and 980–920 Ma ago. In areas of Mesoproterozoic tectogenesis, evidence of Paleoproterozoic or (rarely) Archean endogene processes is sometimes found. Most likely, this stage refers to the formation of the vast continental block. The Neoproterozoic-Early Paleozoic tectogenesis was practically synchronous over most of the Antarctic shield; on large areas it was characterized by metamorphism and pervasive schistosity, but in many other localities only various granitoids and pegmatites were intruded. Within all the areas of Neoproterozoic-Early Paleozoic tectogenesis isotopic evidence of the earlier (largely Mesoproterozoic) endogene processes are found.     

Two distinct Precambrian terranes in the Southern Prince Charles Mountains, East Antarctica: SHRIMP dating and geochemical constraints

The Southern Prince Charles Mountains (SPCM) are mostly occupied by the Archaean Ruker Terrane. The Lambert Terrane crops out in the northeastern part of the SPCM. New geochemical and zircon U–Pb SHRIMP ages for felsic orthogneisses and granitoids from both terranes are presented. Orthogneisses from the Ruker and Lambert terranes differ significantly in their major and trace-element compositions. Those from the Ruker Terrane comprise two distinct groups: rare Y-depleted and abundant Y-undepleted. U–Pb isotopic data provide evidence for tonalite−trondhjemite emplacement at 3392 ± 9 and 3377 ± 9 Ma, pre-tectonic granite emplacement at 3182 ± 9 Ma, metamorphism(?) at c. 3145 Ma, and thermal events at c. 1300(?) and 626 ± 51 Ma. The Lambert Terrane orthogneisses probably originated in a continental magmatic arc. Zircon dating shows a very different geological history: pre-tectonic granitoid emplacement at 2423 ± 18 Ma, metamorphism at 2065 ± 23 Ma, and syn-tectonic granitoid emplacement at 528 ± 6 Ma, syn-tectonic pegmatite emplacement at 495 ± 18 Ma. The Lambert Terrane can be correlated with neither the Meso- to Neoproterozoic Beaver Terrane in the Northern PCM, which differs in isotopic composition, nor with the Archaean Ruker Terrane, which differs in both granitoid chemical composition and the timing of major geological events. It represents a Palaeoproterozoic orogen which experienced strong tectonic re-activation in Pan-African times. The Lambert Terrane has some geochronological features in common with the Mawson Block, which comprises south Australia and some areas in East Antarctica.