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Determining the cooling history of in situ lower oceanic crust - Atlantis Bank, SW Indian Ridge

John, Barbara; Foster, David; Murphy, John; Cheadle, Michael; Baines, A Graham; Fanning, Christopher; Copeland, Peter

Description

The cooling history and therefore thermal structure of oceanic lithosphere in slow-spreading environments is, to date, poorly constrained. Application of thermochronometric techniques to rocks from the very slow spreading SW Indian Ridge provide for the first time a direct measure of the age and thermal history of in situ lower oceanic crust. Crystallization of felsic veins (∼850°C) drilled in Hole 735B is estimated at 11.93 ± 0.14 Ma, based on U-Pb analyses of zircon by ion probe. This...[Show more]

dc.contributor.authorJohn, Barbara
dc.contributor.authorFoster, David
dc.contributor.authorMurphy, John
dc.contributor.authorCheadle, Michael
dc.contributor.authorBaines, A Graham
dc.contributor.authorFanning, Christopher
dc.contributor.authorCopeland, Peter
dc.date.accessioned2015-12-13T22:48:58Z
dc.date.available2015-12-13T22:48:58Z
dc.identifier.issn0012-821X
dc.identifier.urihttp://hdl.handle.net/1885/80316
dc.description.abstractThe cooling history and therefore thermal structure of oceanic lithosphere in slow-spreading environments is, to date, poorly constrained. Application of thermochronometric techniques to rocks from the very slow spreading SW Indian Ridge provide for the first time a direct measure of the age and thermal history of in situ lower oceanic crust. Crystallization of felsic veins (∼850°C) drilled in Hole 735B is estimated at 11.93 ± 0.14 Ma, based on U-Pb analyses of zircon by ion probe. This crystallization age is older than the 'crustal age' from remanence inferred from both sea surface and near-bottom magnetic anomaly data gathered over Hole 735B which indicate magnetization between major normal polarity chrons C5n.2n and C5An.1n (10.949-11.935 Ma). 40Ar/39Ar analyses of biotite give plateau ages between 11 and 12 Ma (mean 11.42 ± 0.21 Ma), implying cooling rates of >800°C/m.y. over the first 500,00 years to temperatures below ∼330-400°C. Fission-track ages on zircon (mean 9.35 ± 1.2 Ma) and apatite reveal less rapid cooling to <110°C by ∼7 Ma, some 4-5 m.y. off axis. Comprehensive thermochronometric data from the structurally intact block of gabbro between ∼700 and 1100 m below sea floor suggest that crust traversed by ODP Hole 735B mimics conductive cooling over the temperature range ∼900-330°C, characteristic of a 2-D plate-cooling model for oceanic lithosphere. In contrast, lower temperature chronometers (fission track on zircon, titanite, and apatite; T ≤ 280°C) are not consistent with these predictions and record anomalously high temperatures for crust >700 m below sea floor at 8-10 Ma (i.e. 2-4 m.y. off axis). We offer two hypotheses for this thermal anomaly: (i) Off-axis (or asymmetric) magmatism that caused anomalous reheating of the crust preserved in Hole 735B. This postulated magmatic event might be a consequence of the transtension, which affected the Atlantis II transform from ∼ 19.5 to 7.5 Ma. (ii) Late detachment faulting, which led to significant crustal denudation (2.5-3 km removed), further from the ridge axis than conventionally thought.
dc.publisherElsevier
dc.sourceEarth and Planetary Science Letters
dc.subjectKeywords: cooling; oceanic lithosphere; spreading center; thermal structure; thermochronology; Indian Ocean; Southwest Indian Ridge Cooling; Lower oceanic crust; Ocean Drilling Program Site 735B; Thermochronometry
dc.titleDetermining the cooling history of in situ lower oceanic crust - Atlantis Bank, SW Indian Ridge
dc.typeJournal article
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.citationvolume222
dc.date.issued2004
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.ariespublicationMigratedxPub8589
local.type.statusPublished Version
local.contributor.affiliationJohn, Barbara, University of Wyoming
local.contributor.affiliationFoster, David, University of Florida
local.contributor.affiliationMurphy, John, University of Wyoming
local.contributor.affiliationCheadle, Michael, University of Wyoming
local.contributor.affiliationBaines, A Graham, University of Wyoming
local.contributor.affiliationFanning, Christopher, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationCopeland, Peter, University of Houston
local.bibliographicCitation.startpage145
local.bibliographicCitation.lastpage160
local.identifier.doi10.1016/j.epsl.2004.02.014
dc.date.updated2015-12-11T10:31:54Z
local.identifier.scopusID2-s2.0-2342463078
CollectionsANU Research Publications

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