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Petrology of gedrite-bearing rocks in mid-crustal ductile shear zones from the Eastern Ghats Belt, India 总被引：1，自引：0，他引：1
A suite of metapelitic, basic and quartzofeldspathic rocks intruded by enderbitic gneiss from the southernmost tip of the Eastern Ghats Belt, India, and metamorphosed at c. 750–800 °C, 6 kbar, were subjected to repeated ductile shear deformation, hydration, cooling and accompanying alkali metasomatism along narrow shear zones. Gedrite-bearing assemblages developed in the shear zones traversing metapelitic rocks. Interpretation of the reaction textures in an appropriate P–T grid in the system FMASH, an isothermal–isobaric μ H2O – μ Na2O grid in the system NFMASH, and geothermobarometric data suggest a complex evolutionary history for the gedrite-bearing parageneses. Initially, gedrite-bearing assemblages were produced due to increase in μ Na2O at nearly constant but high μ H2O accompanying cooling. Gedrite was partially destabilized to orthopyroxene+albite due to progressively increasing μ Na2O . During further cooling and at increased μ H2O a second generation of gedrite appeared in the rocks. 相似文献
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Sea floor and shallow seismic data sets of terminal submarine fan lobes can provide excellent planform timeslices of distributive deep‐water systems but commonly only limited information on cross‐sectional architecture. Extensive outcrops in the Tanqua depocentre, south‐west Karoo Basin, provide these three‐dimensional constraints on lithofacies distributions, stacking patterns, depositional geometries and the stratigraphic evolution of submarine lobe deposits at a scale comparable with modern lobe systems. Detailed study (bed‐scale) of a single‐lobe complex (Fan 3) over a 15 km by 8 km area has helped to define a four‐fold hierarchy of depositional elements from bed through to lobe element, lobe and lobe complex. The Fan 3 lobe complex comprises six distinct fine‐grained sandstone packages, interpreted as lobes, which display compensational stacking patterns on a 5 km scale. Between successive lobes are thin‐bedded, very fine‐grained sandstones and siltstones that do not change lithofacies over several kilometres and therefore are identified as a different architectural element. Each lobe is built by many lobe elements, which also display compensational stacking patterns over a kilometre scale. Thickness variations of lobe elements can be extremely abrupt without erosion, particularly in distal areas where isopach maps reveal a finger‐like distal fringe to lobes. Lobe deposits, therefore, are not simple radial sheet‐dominated systems as commonly envisaged. 相似文献
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The penaeid prawns Fenneropenaeus indicus and Metapenaeus monoceros support shallow-water prawn fisheries in the south-west Indian Ocean. They are sympatric and have similar life histories, including developmental stages that depend on estuarine and marine habitats and a short dispersal duration. Nevertheless, M. monoceros juveniles display a more generalist habitat preference in estuaries and recruit to offshore habitats during a different season than F. indicus. We hypothesised that these differences would affect dispersal patterns, leading to dissimilar geographic genetic structure between the two taxa. Given their short dispersal phase, we also hypothesised that the Mozambique Channel would form a barrier to dispersal between the southeastern African mainland and Madagascar sites. Population differentiation was assessed based on analysis of mitochondrial DNA control-region sequences. Both species displayed high haplotype and low nucleotide diversity. Pairwise ?ST statistics supported the existence of admixed populations along the African mainland sites for both species, with geographic distance isolating populations at the extremes of the sampled range (Kenya and east coast of South Africa). The Madagascar population differed significantly from African mainland populations. The concordant patterns in population differentiation suggest that F. indicus and M. monoceros can be considered as single African stocks, or fisheries management units. 相似文献
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An SO2 flux of 1170±400 (1) tonnes per day was measured with a correlation spectrometer (COSPEC) in October and November 1986 from the continuous, nonfountaining, basaltic East Rift Zone eruption (episode 48A) of Kilauea volcano. This flux is 5–27 times less than those of highfountaining episodes, 3–5 times greater than those of contemporaneous summit emissions or interphase Pu'u O'o emissions, and 1.3–2 times the emissions from Pu'u O'o alone during 48A. Calculations based on the SO2 emission rate resulted in a magma supply rate of 0.44 million m3 per day and a 0.042 wt% sulfur loss from the magma upon eruption. Both of these calculated parameters agree with determinations made previously by other methods. 相似文献
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Global climatic oscillations have shaped the contemporary genetic structure of marine taxa in different ways. Previous demographic studies have indicated that various intertidal marine species display genetic signatures of demographic expansion that either pre- or postdate the Last Glacial Maximum. Such expansions and the ability of species to colonise new habitats will influence their genetic structure, but the link between scales of larval dispersal and the strength of phylogeographic structure is not always clear. We analysed a fragment of the mitochondrial COI gene of 11 sympatric species of intertidal southern African patellid limpets to investigate how ancient oceanographic dynamics have shaped and maintained their contemporary spatial genetic variation. Our data show that the patellid limpets investigated display congruent evidence of spatial expansion during the Late Pleistocene or Early Holocene, which corresponds with the establishment of the contemporary southern African shoreline. We argue that closely related and co-distributed southern African intertidal invertebrates responded to ancient climatic oscillations as a cohesive group. In contrast, contemporary oceanographic circulation has shaped the phylogeographic patterns of these limpets in different ways. We show close relationships between phylogeography and biogeography for some species, but not for others, despite the similarities in their life histories and exposure to the same climatic changes. 相似文献
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PR O'Dwyer S Berrow P López-Suárez C Oujo Lamao 《African Journal of Marine Science》2015,37(3):427-430
Despite having a worldwide distribution in tropical waters, knowledge on pygmy killer whales Feresa attenuata, including diet, is poor, with only a few studies carried out to date. The presence of otoliths and beaks in stomachs that have been examined indicate that the diet of F. attenuata includes squid, octopus and fish. In this study, the stomach contents of two F. attenuata recently stranded in Cape Verde, West Africa, were examined. A variety of fish hard parts and otoliths were recovered, in addition to the upper beak from an unidentified cephalopod and the remains of some marine arthropods. Lanternfish (Myctophidae) and deepbody boarfish Antigonia capros were identified from otoliths and comprised 95.4% of prey items. Whereas the sizes of the myctophids in the two whale stomachs were similar, those of other prey items differed. The findings provide important information on the diet of F. attenuata in the Cape Verde region. 相似文献
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North Atlantic Water (NAW) is an important source of heat and salt to the Nordic seas and the Arctic Ocean. To measure the transport and variability of one branch of NAW entering the Arctic, a transect across the entrance to the Barents Sea was occupied 13 times between July 1997 and November 1999, and hydrography and currents were measured. There is large variability between the cruises, but the mean currents and the hydrography show that the main inflow takes place in Bjørnøyrenna, with a transport of 1.6 Sv of NAW into the Barents Sea. Combining the flow field with measurements of temperature and salinity, this results in mean heat and salt transports by NAW into the Barents Sea of 3.9×1013 W and 5.7×107 kg s−1 , respectively. The NAW core increased in temperature and salinity by 0.7 °C yr−1 and 0.04 yr−1 , respectively, over the observation period. Variations in the transports of heat and salt are, however, dominated by the flow field, which did not exhibit a significant change. 相似文献
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