Mull Day 5 by Cat

Day 5

Igneous centre 3

All of today was spent – mainly walking up and thankfully down Beinn a ‘ Ghraig. The majority of the hillside was rhyolite which had an intergrowth texture of quartz and feldspar.

A small intrusion had us puzzled for a while as it had a very complex formation history. Termed a hybrid quartz gabbro, it showed signs of magma mingling. The semi solidified granophyre intrusion was injected by a basic gabbro whose margins chilled to form basalt which was then incorporated as clasts.

We had lunch on part of the Loch Ba ring dyke (felsite-  58 Ma). We were informed we could walk along it in a big circle across the hills … but didn’t’ feel inclined to do so. Briefly; ring dykes are formed during caldera collapse (analogy is pushing a wine cork into the bottle and the wine is the magma). Nearer the top we examined vent agglomerates like on Arthurs Seat.

Loch Ba in the sunshine
Loch Ba

Image

 

 

 

 

 

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s