A STUDY OF DEEP FLUID CIRCULATION IN THE TROODOS OPHIOLITE, CYPRUS

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" A STUDY OF DEEP FLUID CIRCULATION IN THE TROODOS OPHIOLITE, CYPRUS "
N. J. Vibetti

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112382
Doc. No	:	TLpq303654207
Main Entry	:	N. J. Vibetti
Title & Author	:	A STUDY OF DEEP FLUID CIRCULATION IN THE TROODOS OPHIOLITE, CYPRUS\ N. J. Vibetti
College	:	The University of Western Ontario (Canada)
Date	:	1987
student score	:	1987
Degree	:	Ph.D.
Page No	:	1
Abstract	:	Submarine upwelling of magma at a constructive plate margin took place at Troodos 85 M.a. B.P. forming oceanic lithosphere which proceeded to cool both by conductive heat transfer as well as by convective mass transfer of seawater. The convection of seawater through the newly formed crust initiated complex and highly variable hydrothermal alteration which in places culminated in the complete recrystallization of parts of the oceanic crust. The circulation of seawater through the uppermost layers of the newly formed crust caused major changes in the chemistry of the oceanic lithosphere and ultimately led to the formation of the base and precious metal deposits of Cyprus, originally in excess of forty million tonnes of ore. Drawing on samples collected from sites far removed from mineralized areas, the current study, utilizing petrological and geochemical methods, reports extensive hydrothermal alteration attributable to sub-oceanic processes throughout the ophiolite sequence. It also indicates that the overall spilitic composition of the ophiolite is the result of prolonged seawater-basalt interaction at continuously variable water/rock ratios at low pressures and low to high temperatures, up to 600C. Metamorphic mineral assemblages and microthermometric data from fluid inclusions point to the local evolution of seawater into a hot hypersaline brine which appears to have been an ideal agent for the leaching of a host of major elements, transition metals, and trace elements from oceanic lithosphere. Observations on fracture distribution and alteration indicates that fluids infiltrated a great depth, apparently beyond the oceanic moho. Oxygen and strontium isotope analyses positively identify the alteration fluids as being seawater derived, with the oxygen isotope pattern indicating that the fluid/rock interaction was complex and depth related. The metamorphic mineral assemblages reflect an evolving cycle from high to low temperatures, and water/rock ratios involving fluids of continuously evolving composition. Current models of oceanic lithosphere cooling that involve the dissipation of heat by mass transfer in the sub-seafloor environment adequately explain the nature and pattern of observed postmagmatic alteration with the additional observations that locally, the process of seawater infiltration extends to depths in the oceanic crust beyond the moho and that it also appears to be responsible for the development of at least two chemically distinct types of hydrothermal fluids.
Subject	:	Earth sciences
	:	Paleobotany