The field trip consisted of 5 days of mapping the slopes of Ben Hiant as well as a day doing something of a guided tour of the peninsula as a whole. What follows are photos of some of the more interesting features we observed, as well as brief explanations of their geological context.

Radially Jointed Vitrophyre

Here we can see a lovely radially jointed vitrophyre outcrop on the side of a steep gulley. The jointing nicely illustrates the intrusive relationship with the surrounding Breccia.

Annotated Vitrophyre

The vitrophyre outcrops in this area are part of a group of inclined sheet intrusions which are part of the British-Irish Paleogene Igneous Province (or whatever the current politically correct name is, I favour the North-Western European Archipelago Paleogene Igneous Province personally). Other inclined sheets of varying crystal size from glass up to Dolerite abound in the area, as cone sheets emanating out from the intrusive centres.

Dolerite Sheet on Ben Hiant

Cone Sheets on the Shore at Kilchoan

Xenoliths in Dolerite Sheet

Closer to the middle of one of the intrusive centres (Centre 3) is The Great Eucrite  – a striking ring of Gabbroic ridges surrounding the inner parts of the complex.

View Northwards from the heart of Centre 3 - The Ridge is the Great Eucrite

The rocks towards the centre get steadily more silicic in composition, with Tonalites and then a Quartz Monzonite outcrop in the very centre. The current understanding of this structure is that it represents an uplifted and eroded Lopolith (not, as originally thought, a ring dyke).

Another location we visited was the Gabbros of Sanna Bay. These are a sequence of coarse grained basic rocks which show distinct mineralogical layering, both modal and phase layering.

Layered Igneous Intrusion

Layered Gabbros

Interestingly some of these units also show evidence of sedimentary structures such as normally graded bedding:

Normally Graded Bedding

Lens-Like Structures and Undulose Bedding (With my Cousin Karen for scale)

These are a classic layered intrusion similar to the grander examples found elsewhere such as Skaergaard or the Bushveld. We spent a fair bit of time studying these in the first semester of third year, so it was nice to see them in the field.

Another location visited was a delightful example of magma mixing at Eilean Carrach, opposite the Lighthouse on the point of Ardnamurchan.

Magma Mixing

For those of you who have this trip to look forward to (i.e. potential/current Glasgow Uni Earth Science Undergraduates) then expect to spend a significant amount of your evenings doing this:

Working on a Report at 3am

But also some of this as well:

Work Hard, Play Hard

The trip also provides no end of opportunities for posing dramatically on hillsides:

Ben Hiant

(and beaches)

Beach at Eilean Carrach

Further Reading

Gribble, CD (Ed). Ardnamurchan: a guide to geological excursions. 1976. Edinburgh Geological Society. – Nice book, good descriptions and a fold out map. Interpretations are a bit out of date however.

McBirney, A. Igneous Petrology. Third Edition. 2007. Jones and Bartlett. – Brilliant Section on Layered Igneous Intrusions, I highly recommend it.

]]> http://bobjamieson.net/2010/04/27/ardnamurchan-2010/feed/ 0 http://bobjamieson.net/2009/05/17/arran-2009-field-trip-day-seven/ http://bobjamieson.net/2009/05/17/arran-2009-field-trip-day-seven/#comments Sun, 17 May 2009 19:35:11 +0000 Bob http://bobjamieson.net/?p=126 Collected Tweets from April 11th. Measuring Dyke thicknesses along a section of coastline at Kildonan to calculate crustal extension. (Again; RJ is Me, HS is Hazel). The weather was truly gorgeous.

8:40 AM Apr 11th : Up and ready for a day in the field. I think we’re measuring wide dykes today. – RJ

I’d apologise for the cracks about Dykes, but to be honest it’s an accurate representation of what we were talking about while there. That’s one of the milder ones.

9:41 AM Apr 11th : It is a gorgeous day here on Arran – RJ

Looking South from Arran

11:00 AM Apr 11th : Looking at Dykes on Kildonan beach. Mainly basaltic some with phenocrysts. Glorious weather – HS

11:53 AM Apr 11th : Stopped for lunch, sunshine is glorious. – RJ

Stopping to Eat on a Dyke

1:13 PM Apr 11th : Team Faithfull Photo Opportunity – RJ

Team Faithfull

We finished early today to pack, eat a hearty meal (from the nearby Chippie) and generally get ready for the evening’s festivities.

9:07 PM Apr 11th : Last night of Arran ‘09 – we’re all chilling out after a great day of sun and dykes. – RJ

I haven’t included most of the messages we posted later in the evening; after most of a bottle of Laphroaig they got increasingly incoherent. There was definitely Karaoke. But I’ll leave you with the last one…

2:58 AM Apr 12th : Earth scientists are the best drinkers in the world. – RJ

9:34 AM Apr 10th : Pigtails are the choice of hair style for field trips! At blackwaterfoot goin to look at some ig. Rocks. – HS

9:35 AM Apr 10th : King’s Cave today as well I think. – RJ

12:24 PM Apr 10th : Stopping for lunch next to doon sill. Lots of lovely Igneous rocks. Now off to the caves. – HS

12:28 PM Apr 10th : ‘The Doon’ – a great big sill, seen from the beach and the view from halfway up. – RJ

The Doon Sill

Slightly closer View

Field Sketch

Sketch Diagram of the Base of the Sill

12:30 PM Apr 10th : The real reason we wear hard hats. – RJ

The real reason Geologists wear hard hats.

12:31 PM Apr 10th : Small intrusions with brilliant chilled margins. – RJ

Lovely Chilled Margins

2:00 PM Apr 10th : Just scrambled up a muddy waterfall, through a gorse thicket to touch John’s ‘thing’, turned out to be Triassic reptile footprints. – RJ

This innuendo probably requires an explanation. John wanted to make the Isochirotherium footprints a surprise for the groups so was referring to it as his ‘thing’. We of course took that statement and ran with it. (For more info about these check out Neil Clark’s paper in the latest volume of the Scottish Journal of Geology – Vol. 45 pt. 1)

Reptile Footprints

2:29 PM Apr 10th : Weather has turned really lovely, skimming rocks while we wait for everyone to look at the footprints. – RJ

The footprints were halfway up a waterfall and fairly inaccessible – so we went up 5 people at a time.

2:58 PM Apr 10th : A wee snake on the path. – RJ

A Snake in the Grass

3:14 PM Apr 10th : In king’s cave – a raised sandstone sea cave. – RJ

King's Cave

8:18 PM Apr 10th : Listening to John Faithful lecturing on paleogene igneous activity. – RJ