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Article
Cooling rates of hyaloclastites: applications of relaxation geospeedometry to undersea volcanic deposits
Glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits. We found that the glass fragments retain structures with a ...
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Article
Petrology of seamounts in the Central Indian Ocean Basin: Evidence for near-axis origin
Previous studies on the distribution and morphology of ancient seamount chains (> 50 Ma) in the Central Indian Ocean basin (CIOB) indicated their generation from the fast spreading Southeast Indian Ridge. Here...
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Article
Basinal seamounts and seamount chains of the Central Indian Ocean: Probable near-axis origin from a fast-spreading Ridge
Hydrosweep map** of crust in the Central Indian Ocean Basin reveals abundant volcanoes ocurring both as isolated seamounts and linear seamount chains parallel to flow lines. Their shapes, sizes and overall s...
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Article
Geochemical characteristics of Cocos Plate seamount lavas
A wide compositional continuum of basalts has been erupted from near-ridge seamounts constructed on the Cocos Plate between the Clipperton and Orozco Francture Zones. They range from highly evolved to moderate...
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Article
Off-axis volcanism at the East Pacific Rise detected by uranium-series dating of basalts
RECENT detailed surveys of the East Pacific Rise have revealed the complexity of the volcanic and magmatic processes occurring along and across fast-spreading ocean ridge crests1–7. In parallel with geological an...
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Chapter
Pacific ocean crust
The Pacific Ocean basin comprises about one third of the earth’s surface, or 49.8% by area of our planet’s oceans and seas. It includes the earth’s largest and fastest moving plate, the Pacific plate, in addit...
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Chapter
Pacific ocean crust
The Pacific Ocean basin comprises about one third of the earth’s surface, or 49.8% by area of our planet’s oceans and seas. It includes the earth’s largest and fastest moving plate, the Pacific plate, in addit...
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Article
Strontium, neodymium and lead isotope constraints on near-ridge seamount production beneath the South Atlantic
STUDIES1–7 of seamounts near the East Pacific Rise (EPR) have shown that, although most seamount lavas are petrographically and chemically identical to mid-ocean-ridge basalt, they are chemically and isotopically...
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Article
Geological and petrologic evolution of seamounts near the EPR based on submersible and camera study
Observations from 17 ALVIN dives and 14 ANGUS runs plus laboratory study of basalt samples collected with ALVIN help to constrain the morphologic, volcanic and petrologic evolution of four seamounts near the E...
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Article
New field and laboratory evidence for the origin of hyaloclastite flows on seamount summits
New field observations with the submersible ALVIN and photographic evidence from a study of the summits of seamounts near the East Pacific Rise show that hyaloclastite deposits occur commonly. Hyaloclastite ou...
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Article
Simple magma supply geometry inferred beneath a segment of the Mid-Atlantic Ridge
The petrological characteristics of axial basalts along the global mid-ocean ridge system shed light on the processes of magma supply involved in the formation of ocean crust. Several models of magma supply1–4 p...
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Article
He, Pb, Sr and Nd isotope constraints on magma genesis and mantle heterogeneity beneath young Pacific seamounts
Pb, Sr and Nd isotope variations are correlated in diverse lavas erupted at small seamounts near the East Pacific Rise. Tholeiites are isotopically indistinguishable from MORB (206Pb/204Pb=18.1–18.5; 87Sr/86Sr=0....
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Article
Small-scale heterogeneities in depleted mantle sources: near-ridge seamount lava geochemistry and implications for mid-ocean-ridge magmatic processes
The Lament seamounts form a chain of five volcanoes extending northwestward from the flanks of the East Pacific Rise (EPR) near 10° N (Fig. 1). They have been investigated using Sea MARC I and Sea Beam sonar1 ...
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Article
Helium isotope disequilibrium and geochronology of glassy submarine basalts
The (U+Th)/He dating method is the oldest method of geochronology that involves radioactivity, but historically it has not been particularly successful. Even when problems of poor helium retention and loss du...
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Article
The origin of small-scale geochemical and mineralogic variations in a granite intrusion
A post-tectonic unzoned granite intrusion in the Meatiq Dome, a Late Proterozoic metamorphic complex in the Central Eastern Desert of Egypt, shows significant chemical and mineralogic heterogeneity on the scal...
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Article
Petrological and tectonic segmentation of the East Pacific Rise, 5°30′–14°30′ N
Lavas from the fast-spreading East Pacific Rise are geochemically diverse even within a single tectonically defined spreading cell. Within such spreading cells, small offsets of the rise axis are often boundar...
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Article
Small non-overlap** offsets of the East Pacific Rise
High-resolution bathymetric surveys1,2 of the East Pacific Rise (EPR) reveal that in addition to overlap** spreading centres (OSCs), the crest of the EPR is offset tiny amounts by smaller features. Recently, La...
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Article
Inverse relationship between Sr isotope diversity and rate of oceanic volcanism has implications for mantle heterogeneity
Cohen and O'Nions1 noted that basalts from the Mid-Atlantic Ridge (MAR) display greater diversity of Pb, Nd and Sr isotopes than do basalts from the East Pacific Rise (EPR). They attributed this difference not to...
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Article
Gabbroic rocks from the Mathematician Ridge failed rift
Plutonic rocks from the ocean crust provide direct evidence on the petrological processes leading to its formation and evolution. The nature of such rocks is important for interpreting the origin of on-land op...
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Article
Miocene spreading centre south of Isla Guadalupe
The Juan de Fuca, Rivera, Cocos and Nazca plates in the eastern Pacific are small fragments remaining from the fragmentation and partial subduction of the long, narrow Farallon Plate which began as early as 55...
