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Dive into the research topics where Laurence A. Coogan is active.

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Featured researches published by Laurence A. Coogan.


Earth and Planetary Science Letters | 2003

Volatile element (B, Cl, F) behaviour in the roof of an axial magma chamber from the East Pacific Rise

Kathryn M. Gillis; Laurence A. Coogan; Marc Chaussidon

Abstract Understanding the behaviour of volatile elements at mid-ocean ridges is important for reasons ranging from their influence on mantle viscosity through to their role as a food source for the deep biosphere. With the aim of constraining what processes control the distribution of volatiles in the ocean crust at fast-spreading ridges, we present a detailed study of the compositional variability in magmatic amphibole formed in the upper part of the plutonic sequence at the East Pacific Rise (EPR). These amphiboles are massively enriched in chlorine (by more than an order of magnitude), and moderately enriched in boron, with respect to magmatic amphiboles in cumulates from the Mid-Atlantic Ridge (MAR). Similar enrichments have been reported for basaltic glasses from the EPR and are interpreted as indicative of assimilation. The greater enrichments observed in the plutonic section suggest both that assimilation occurs at the roof of the axial magma chamber (AMC) and that lava compositions may record minimum amounts of exogenic contamination. Amphiboles with compositions indicative of crystallisation from a contaminated magma occur to depths of 800 m beneath the sheeted dyke complex. This is interpreted to indicate that at least this upper portion of the plutonic section forms via crystallisation within the AMC followed by subsidence of a crystal mush. Amphibole boron isotope compositions show that assimilation of altered sheeted dykes plus hydrothermal fluids drives AMC magmas to heavier δ11B values (up to +5.8‰). Subsequent degassing within a solidifying crystal mush leads to a negative trend in δ11B–B with the most degassed magma having δ11B as low as −21.2‰. This degassing was associated with hydrofracturing of the partially molten crystal mush and could have facilitated a temporal link with the overlying hydrothermal system.


Geology | 2003

Contaminating the lower crust in the Oman ophiolite

Laurence A. Coogan

Contamination of magmas, via assimilation of country rock, is widely recognized as an important process in the thermal and chemical evolution of magmas emplaced into continental crust. Its importance at mid-ocean ridges has, however, received much less consideration. Lavas from the fast-spreading East Pacific Rise show evidence for contamination through an enrichment in seawater-derived chlorine that is not observed in basalts from slow-spreading ridges. In this study magmatic amphiboles in plutonic rocks from the Oman ophiolite—an intermediate- to fast-spreading ridge analogue—have been analyzed to determine the extent of this contamination in the lower oceanic crust. These data suggest an enrichment in chlorine throughout much of the lower ocean crust. If this enrichment is representative of lower oceanic crust formed at typical intermediate- to fast-spreading ridges, assimilation may be a more important process at mid-ocean ridges than previously recognized.


Chemical Geology | 2004

A combined basalt and peridotite perspective on 14 million years of melt generation at the Atlantis Bank segment of the Southwest Indian Ridge: evidence for temporal changes in mantle dynamics?

Laurence A. Coogan; Gary M. Thompson; Christopher J. MacLeod; Henry J. B. Dick; Sj Edwards; A. Horsford Scheirer; Tiffany L. Barry


InterRidge News , 7 (2) pp. 39-43. (1998) | 1998

Geological mapping of slow-spread lower ocean crust: a deep-towed video and wireline rock drilling survey of Atlantis Bank (ODP Site 735, SW Indian Ridge)

Christopher J. MacLeod; Hjb Dick; S Allerton; Paul T. Robinson; Laurence A. Coogan; Sj Edwards; A Galley; Km Gillis; G Hirth; Ag Hunter; D Hutchinson; Aj Kvassnes; James H. Natland; Mh Salisbury; Es Schandl; T Stakes


Archive | 2009

Oxidation of ocean crust and the fate of seawater sulphate in axial hydrothermal systems

Abigail K. Barker; Laurence A. Coogan; Kathryn M. Gillis


Archive | 2008

Ti-in-quartz thermometry of hydrothermal veins in ocean crust

Abigail K. Barker; Laurence A. Coogan; Kathryn M. Gillis; Dominique Weis


Archive | 2008

Lithium isotopes provide new insights into oceanic hydrothermal systems

Cory O. Brant; Laurence A. Coogan; Kathryn M. Gillis


Archive | 2008

Assessing the role of upwelling hydrothermal fluids in altering the upper ocean crust

Kathryn M. Gillis; Laurence A. Coogan


Archive | 2004

Li Isotopes as Tracers of Fluid-Rock Interactions in Oceanic Hydrothermal Systems: Evidence From the Hess Deep Rift

Cory O. Brant; Laurence A. Coogan; Kathryn M. Gillis


Archive | 2003

Accretion of the lower crust at fast-spreading ridges: constraints from the Oman ophiolite

Christopher J. MacLeod; Richard M. Thomas; Laurence A. Coogan; G. A. Thompson

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Sj Edwards

University of Greenwich

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Aj Kvassnes

Woods Hole Oceanographic Institution

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Henry J. B. Dick

Woods Hole Oceanographic Institution

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Hjb Dick

Woods Hole Oceanographic Institution

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