Browsing by Author "Flower, Martin F. J."
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- Magma mixing at oceanic transform fracture zonesPublication . Flower, Martin F. J.Ocean ridge eruptive chemistry reflects isochronic compositional «gradients», often attributed to the interaction of lithophile element-rich mantle plumes with the relatively depleted asthenosphere. Inspection of Atlantic and Pacific axial gradients shows lithophile-rich eruptions do not correspond exclusively to proposed loci for mantle upwelling. In contrast, transform fracture zones appear to mark the majority of lithophile-enrichment peaks, suggesting relatively superficial tectonic phenomena influence magma chemistry. A general association of lithophile and radiogenic isotope enrichment with increasingly frequent offset spreading culminates at major fracture zone ridge axis intersections (e.g., Galapagos, Iceland, Azores, Jan Mayen, and Siqueiros, Oceanographer and Romanche fracture zones). Major element and normative compositions show that enrichment also coincides with increased depth of melt segregation in the mantle. […].
- Plagioclase accumulation and phenocryst reaction in oceanic tholeiite: an indication of spreading ratePublication . Flower, Martin F. J.A comparison of basalt lithology and chemistry for different mid-ocean ridge spreading axes indicates: (1) basalt generated at slow spreading axes (< 5 cm/yr, e.g. Mid-Atlantic Ridge) reflects widespread flotation of calcic plagioclase and phenocryst-liquid reaction; (2) basalt generated at fast-spreading axes (> 5 cm/yr, e.g., Juan de Fuca Ridge, Galapagos spreading Center, East Pacific Rise) is invariably aphyric or sparsely phyric, phenocrysts if present representing low pressure Iiquidus crystallization products. Interestingly, basalt generated at intermediate spreading rates (e.g., Costa Rica Rift, Gorda Rise, Gulf of California shows incipient development of the «slow-spreading» petrographic tendencies. […].