Day 1, Locality 3
This rock face, 3.5 km S of Troodos village, sits beside the remnants of the original Troodos road before the B8 was upgraded around the mid-1930's. Nearby can be seen the old Victoria Bridge which once carried all the traffic but, having had no maintenance for 75 years, is now starting to deteriorate. Further to the right, along the old road itself, huge rocks have worked loose from high above and crashed down onto the tarmac.
Two (similar) short scene-setting videos can be viewed, either in MPG or WMV. MPG-1 or WMV-1; MPG-2 or WMV-2.
In this old roadcut, greyish-green rocks to the north (or left) are seen in sharp but apparently non-tectonic contact with rusty brown-weathering rocks to the south (or right). The grey-green rock to the north is the mantle, of harzburgitic composition, and the rust brown rock to the south is dunite, the lower layer of the crust. The contact between the two very different ultramafic rocks is the petrological Moho.
North - serpentinised grey green Harzburgite Centre - Petrological Moho South - rust brown weathered Dunite
On the right hand side of the contact the rusty brown-weathering rock is black in fresh samples, coarse grained, and is composed of olivine, around 95% or higher. Chrome spinel may also be apparent in places, seen as shiny black flecks. Some layering may also be noticeable in the faces, parallel to the sharp contact, although the exposure is not big enough to gain unequivocal evidence. These rocks are the lowest cumulates of the lower plutonic intrusives, the base of the oceanic crustal sequence, and are of dunite composition.
Watch a video of Paul touching the Moho! - MPG or WMV
Turning our attention now to the greenish rock to the left of the contact, it is the mantle harzburgite, seen as a medium to coarse grained rock with noticeable plates of orthopyroxene, now altered to bastite serpentinite. Like the dunite the surface is heavily weathered.
Mantle textures may be visible in the harzburgites, with the mantle tectonite fabric identified by parallel alignment of altered orthopyroxene crystals. The olivine in the harzburgite has been considerably altered to serpentine minerals. Relationships between this exposure and neighbouring ones are difficult to unravel due to the probable tectonic contacts which cut the mantle and the crustal units in this area.
A major phase of hydrothermal sea water circulation through the ophiolite in Pleistocene times has resulted in serpentinisation and alteration of much of the olivine and orthopyroxene.
