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" Integrated structural and geochemical studies of oceanic fault zones across the dike-pluton boundary, Troodos ophiolite, Cyprus "
L. L. Marquez
S. M. Agar
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Latin Dissertation
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English
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| Record Number
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1113240
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TLpq304442627
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| Main Entry
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L. L. Marquez
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S. M. Agar
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| Title & Author
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Integrated structural and geochemical studies of oceanic fault zones across the dike-pluton boundary, Troodos ophiolite, Cyprus\ L. L. MarquezS. M. Agar
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| College
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Northwestern University
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| Date
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1998
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1998
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| Degree
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Ph.D.
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| Page No
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344
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| Abstract
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Deformation and hydrothermal mineralization is characterized across the dike-pluton boundary in the Troodos ophiolite, Cyprus in order to constrain hydrothermal circulation at depth in the ocean crust. Six fault zones across the dike-pluton transition were mapped at scales of less than 1:50 to elucidate deformation and mineralization sequences. In the sheeted dikes, brittle failure (cataclasis and hydrothermal brecciation) localized on dike margins. Multiple hydrothermal and deformation events are evident in most fault samples indicating episodic fluid flow controlled by deformation enhanced permeability. Fault strands are mineralized with hydrothermal phases including epidote, chalcopyrite and quartz. Alteration halos in the sheeted dikes are less than 3 centimeters. In the plutonic sections, brittle failure occurs subparallel to dike margins. Plastic failure is found only along dike margins. Hydrothermal phases in fault strands are predominantly epidote and quartz. Quartz is especially prominent around a late stage pluton. Alteration haloes around brittle fault strands are wider than in the sheeted dikes and may extend 15 centimeters into the wall rock. In addition, gabbro adjacent to faults is pervasively altered by secondary minerals including actinolite, epidote, and chlorite. Zeolite facies hydrothermal phases, predominantly laumontite, commonly overprint higher temperature alteration in the plutonics. Zeolite minerals are nearly absent in the sheeted dikes. Geochemical analyses of fault strands, alteration haloes, and the footwall and hanging walls indicate that deformed samples underwent greater alteration, except for mylonites which exhibit near magmatic compositions of hornblende and feldspar. Delta O for whole rocks range from 0.2-14.4. Every structural level contains samples with depleted usd\delta\spusdO (magmatic usd\rm\delta\spO = 5.7),usd but usd\delta\spusdO enrichment increases with depth. Broad alteration haloes, extensive hydrothermal alteration, and usd\delta\spusdO enrichment of the plutonic host rocks indicate that hydrothermal fluids flowed down into and remained in the gabbros. As hydrothermal fluids cooled in the plutonics they progressively altered the gabbro at lower temperatures creating a zeolite facies overprint. Magma intrusion and faulting focused fluids out of the plutonics and through brittle faults in the sheeted dikes.
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Earth sciences
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Geochemistry
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Geology
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Geology
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hydrothermal
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