Boyle, J.F.

English

The Troodos ophiolite -includes a diverse assemblage of
metalliferous sediments which are very similar in field relations
and chemistry to those observed presently forming at modern oceanic
spreading axes. Sulphide-producing hydrothermal vents were initiated
at the axis of a narrow well-defined median valley, and persisted
off axis, almost to the limits of the volcanically active zone.
Direct oxidative erosion of the sulphide deposits led to nearby
formation of iron oxide sediments locally rich in sulphide detritus
(ochres). Iron in the discharging vent fluids became oxidised in
the water column, and was more widely dispersed. In volcanically
active regions, erupting lava disrupted the sediment, dispersing it
through cooling-fractures and pillow interstices. This local rapid
burial prevented total dissolution of pelagic carbonate, but
generally caused chemical reduction with loss of manganese oxides.
Ferromanganese sediments extremely similar to those observed at the
crest of the East Pacific Rise were preserved (umbers) in fault-hollows
within the lavas during longer quiescent periods. Individual
source vents were of limited life, ceasing abruptly after
periods of relatively stable activity. Away from the axis,
non-metalliferous sediments accumulated free of admixed hydrothermal
material.

Subsequent alteration of the sediment was promoted by two
processes. First, ageing and gradual burial of the basal sediment,
and secondly, exposure of the deeper sediments to both widespread
low temperature, and localised high temperature, hydrothermal
alteration. Temperatures did not normally exceed 100°C, but in the
vicinity of high temperature hydrothermal conduits(up to c. 350°C),
silicification has taken place (jaspers).

The chemical composition of the sediment can be described in
terms of mixing of the various sediment, sources, with modification
of some trace element abundances through diagenetic processes.

A great similarity to modern mid-ocean ridge sediments is
observed both in terms of geometric relationship to the palaeoridge,
and in chemical and mineralogical composition. Minor deviations
may be explained by the different basement composition, ocean
circulation, relative position of the carbonate compensation depth,
and aluminosilicate accumulation rates. In Cyprus the well exposed
relationships thus contribute directly to an understanding of
mid-ocean ridge processes

Boyle, John F.

Edinburgh Research Archive

The origin and geochemistry of the metalliferous sediments of the Troodos Massif, Cyprus

https://era.ed.ac.uk/bitstream/1842/7089/1/349198.pdf

The origin and geochemistry of the metalliferous sediments of the Troodos Massif, Cyprus.

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