Geochemical characterization of oceanic basalts using Artificial Neural Network

The geochemical discriminate diagrams help to distinguish the volcanics recovered from different tectonic settings but these diagrams tend to group the ocean floor basalts (OFB) under one class i.e., as mid-oceanic ridge basalts (MORB). Hence, a method is specifically needed to identify the OFB as normal (N-MORB), enriched (E-MORB) and ocean island basalts (OIB)

Kimberlites reveal 2.5-billion-year evolution of a deep, isolated mantle reservoir

The widely accepted paradigm of Earth's geochemical evolution states that the successive extraction of melts from the mantle over the past 4.5 billion years formed the continental crust, and produced at least one complementary melt-depleted reservoir that is now recognized as the upper-mantle source of mid-ocean-ridge basalts1. However, geochemical modelling and the occurrence of high 3He/4He (that is, primordial) signatures in some volcanic rocks suggest that volumes of relatively undifferentiated mantle may reside in deeper, isolated regions2. Some basalts from large igneous provinces may provide temporally restricted glimpses of the most primitive parts of the mantle3,4, but key questions regarding the longevity of such sources on planetary timescales—and whether any survive today—remain unresolved. Kimberlites, small-volume volcanic rocks that are the source of most diamonds, offer rare insights into aspects of the composition of the Earth’s deep mantle. The radiogenic isotope ratios of kimberlites of different ages enable us to map the evolution of this domain through time. Here we show that globally distributed kimberlites originate from a single homogeneous reservoir with an isotopic composition that is indicative of a uniform and pristine mantle source, which evolved in isolation over at least 2.5 billion years of Earth history—to our knowledge, the only such reservoir that has been identified to date. Around 200 million years ago, extensive volumes of the same source were perturbed, probably as a result of contamination by exogenic material. The distribution of affected kimberlites suggests that this event may be related to subduction along the margin of the Pangaea supercontinent. These results reveal a long-lived and globally extensive mantle reservoir that underwent subsequent disruption, possibly heralding a marked change to large-scale mantle-mixing regimes. These processes may explain why uncontaminated primordial mantle is so difficult to identify in recent mantle-derived melts

Petrology and geochemistry of Marion and Prince Edward Islands, Southern Ocean: Magma chamber processes and source region characteristics

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Bovine TB in livestock and wildlife: what's in the genes?

Please help populate SUNScholar with the full text of SU research output. Also - should you need this item urgently, please send us the details and we will try to get hold of the full text as quick possible. E-mail to [email protected]. Thank you.Journal Articles (subsidised)Geneeskunde en GesondheidswetenskappeMolekul�re Biologie & Mensgenetik

The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?

Olivine and orthopyroxene phenocrysts from picrite and picrate basalt lavas and dykes (Mg# 64-80) from the Tuli and Mwanezi (Nuanetsi) regions of the ~180 Ma Karoo Large Igneous province (LIP) have δ18O values that range from 6.0 to 6.7 ‰ (Fig. 1), suggesting that they crystallized from magmas having δ18O values about 1 to 1.5 ‰ higher than expected in an entirely mantle-derived magma. Olivines from picrite and picrite basalt dykes from the 135 Ma Etendeka LIP of Namibia and Karoo-age picrite dykes from Dronning Maud Land, Antarctica do not have such elevated δ18O values. The Etendeka picrites show good correlations between δ18O value and Sr-, Nd- and Pb-isotope ratios that are consistent with previously proposed models of crustal contamination (e.g. Thompson et al., 2007). Explanations for the high δ18O values in Tuli/Mwenezi picrites are limited to (i) alteration, (ii) crustal contamination, and (iii) derivation from mantle with an abnormally high δ18O. The lack of variation in olivine and orthopyroxene δ18O values, together with the lack of correlation between mineral and whole-rock δ18O values are not consistent with alteration being the cause of high δ18O values. The high δ18O values in selected olivine cores have been confirmed by SIMS, and aggressive cleaning of crystals with HF makes no difference to the δ18O value obtained. Average εNd and εSr values of -8 and +16, and high concentrations of incompatible elements such as K are typical of picrites from the Mwanezi (Nuanetsi) region, which have been explained by a variety of models that range from crustal contamination to derivation from the ‘enriched’ mantle lithosphere. The primitive character of the magmas combined with the lack of correlation between δ18O values and radiogenic isotope composition and MgO content or Mg# are inconsistent with crustal contamination, and lend weight to arguments in favour of an 18O-enriched mantle source having high incompatible trace element concentration and enriched radiogenic isotope composition. Although elevated initial Sr isotope ratios, εNd values of -8, and δ18O values about 1 ‰ higher than expected for mantle-derived magma are also a feature of the Bushveld mafic and ultramafic magmas, it is unlikely that a long-lived 18O-enriched mantle source would have survived for nearly 2 Ga. Incorporation of crustal material into the mantle by subduction or delamination of the lower crust are the most likely mechanisms for enriching the mantle in 18O