Day 4, Locality 1a

1a) This first roadside section shows tectonised mantle harzburgites invaded by wehrlite, picrite, and beerbachite dykes. The wehrlites are coarse grained, with olivine and poikilitic CPX, and have an irregular, unchilled contact with the harzburgite host. Tectonite foliation in the mantle sequence does not pass into the wehrlites. Both the wehrlites and mantle harzburgites are intruded by picrite (dark) and beerbachite (white) dykes. These dykes are chilled against both the mantle sequence and the wehrlites, indicating that they had cooled before this later phase of intrusion. The ultramafic picrites are rich in olivine. The light coloured beerbachites are plagioclase rich, and represent the final phases of gabbro fractionation and differentiation, and the last pulses of waning magmatic activity. The trace element geochemistry of these later products indicates depleted boninitic affinities.

To set the scene, here is a short video of the complete section, panning from left to right (no sound):   MPG   WMV

The top, or northerly end of the section.