Geo-Trips :: A Geological Field Trip to the Ballantrae Ophiolite - Day 1

Ayrshire

A walk from Girvan, Sat, 26 Sep 2020 by Anne Burgess

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The Ballantrae Ophiolite is one of the classic areas of geology, not just in Scotland but worldwide.

An ophiolite is basically a slice of oceanic crust that has been obducted, that is, uplifted by tectonic movement and is now exposed on land at the surface of the Earth. The principal components of ocean crust are peridotite, layered gabbro, sheeted dykes and pillow lavas.

Peridotite is rock from the mantle, below the crust. It is ultramafic, which means that it contains high levels of iron and magnesium, contained in minerals such as olivine and pyroxene.

When mantle rocks melt, the resulting magma preferentially contains the minerals that are less heat-resistant, and the more heat-resistant minerals, for example olivine, are left behind in the peridotite while the magma cools to form gabbro, a mafic rock type. During cooling the denser minerals in the magma sink to the floor of the magma chamber, so the chemical composition of the rock changes. New injections of melt lead to alternating layers of denser and less dense material, termed a layered gabbro.

We have all seen videos of red lava erupting in water, cooling quickly to smooth dark grey sausage shapes from which more tongues of molten lava break out and solidify in their turn. These are termed pillow lavas, and they are a sure indication that they formed in water.

The lava that forms pillows rises from the mantle in the form of dykes that exploit weaknesses in the crustal rocks. In ocean crust repeated injections of magma result in many dykes together forming a sheeted dyke complex.

When ultramafic mantle rock is obducted, its constituent minerals are generally altered by hydrothermal fluids to serpentine. Asbestos is one variety of serpentine, and talc is another. The resulting rock is called serpentinite.

Ophiolites also feature sedimentary rocks overlying the obducted rocks, for example conglomerates, sandstones and turbidites.

This is all of course a huge oversimplification of a complex subject, but may serve as background for some of the rocks seen.

I have classified this as a walk, because there is no option for a mixed driving and walking trip. We used cars to get to various locations from which we then walked to the outcrops.

Click the blue circles to see a photograph taken from that spot and read further information about the location. The blue lines indicate the direction of view. There is also a slideshow of this trip. ( )

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NS2301 : Upper Entrance by Anne Burgess
Upper Entrance
There are two tracks into Craighead Quarry, of which this is the upper one,... more

NS2301 : Hartstongue (Asplenium scolopendrium) by Anne Burgess
Hartstongue (Asplenium scolopendrium)
Formerly known as Phyllitis scolopendrium, this fern is common except in the... more

NS2301 : Reef Limestone by Anne Burgess
Reef Limestone
The limestone here is the reason for the existence of Craighead Quarry, and the... more

NS2301 : Reef Limestone by Anne Burgess
Reef Limestone
The limestone here is the reason for the existence of Craighead Quarry, and the... more

NS2301 : Quarry Buildings by Anne Burgess
Quarry Buildings
These are some of the buildings inside Craighead Quarry.

NS2301 : Lime Kilns by Anne Burgess
Lime Kilns
These are part of one of the lime kilns in Craighead Quarry.

NS2301 : Lava Pillows by Anne Burgess
Lava Pillows
As well as being the oldest reef in Britain, the limestone at Craighead is of... more

NS2301 : Quarry Access by Anne Burgess
Quarry Access
This gap was the main access from the quarry workings to the kilns where the... more

NS2301 : Lime Kilns by Anne Burgess
Lime Kilns
Two of the kilns at Craighead that were used for processing the limestone... more

NX1896 : Cow Rock by Anne Burgess
Cow Rock
Cow Rock is the outcrop or rock at the south end of Girvan beach. The building is... more

NX1896 : Cow Rock by Anne Burgess
Cow Rock
Cow Rock is one of two geologically interesting rocks at the south end of Girvan... more

NX1896 : Dramatic Erratic by Anne Burgess
Dramatic Erratic
The large boulder on the shore is an erratic, dropped by a glacier as the ice... more

NX1896 : Graded Bedding by Anne Burgess
Graded Bedding
When loose material flows down an underwater slope to settle on the sea bed, the... more

NX1896 : Sea Rocket (Cakile maritima) by Anne Burgess
Sea Rocket (Cakile maritima)
A plant of sandy shores, usually just above high tide mark.

NX1796 : Cove between the Rocks by Anne Burgess
Cove between the Rocks
This small beach is between Cow Rock on the right and Horse Rock on the left.

NX1795 : Beach at Shalloch by Anne Burgess
Beach at Shalloch
The fine sandy beach extends from Horse Rocks to the Mill of Shalloch. The more... more

NX1796 : Horse Rock by Anne Burgess
Horse Rock
The pale linear feature crossing the dark conglomerate is a bed of sandstone, laid... more

NX1796 : Horse Rock by Anne Burgess
Horse Rock
Horse Rock is one of two geologically interesting rocks at the south end of Girvan... more

NX1896 : Comfrey by Anne Burgess
Comfrey
Probably Russian Comfrey (Symphytum x uplancidum) but could be one of several... more

NX1896 : David's Snack Bar by Anne Burgess
David's Snack Bar
The snack bar was doing a roaring trade, with a long socially distanced queue... more

NX0987 : Balcreuchan Port by Anne Burgess
Balcreuchan Port
A lovely small cove reached by a precipitous and slippery path. Yet even here... more

NX1087 : Grassy Clifftop by Anne Burgess
Grassy Clifftop
A candidate for the least interesting image of the day, perhaps?

NX0987 : Offshore Rock by Anne Burgess
Offshore Rock
The map shows that this rock is connected to the shore at low tide. It doesn't... more

NX0987 : Balcreuchan Port by Anne Burgess
Balcreuchan Port
A fine sandy cove. The headlands at either end of the cove are lava breccias, and... more

NX0299 : Firth of Clyde by Anne Burgess
Firth of Clyde
A 'panoramic' view from the top of the path up from Balcreuchan Port. In the... more

NX1087 : A77 by Anne Burgess
A77
This is the main road from Glasgow to Stranraer and ferries to Ireland. This part... more

NX0985 : Former Cliffs by Anne Burgess
Former Cliffs
In the foreground is a raised beach, left high and dry as se level fell. The braes... more

NX0986 : Folded Cherts by Anne Burgess
Folded Cherts
The rocks in the cliff face are mainly chert, which is a siliceous rock laid down... more

NX0986 : Bennan Cave by Anne Burgess
Bennan Cave
This cave was for many years the home of Henry Ewing Torbet, known as 'Snib'. He... more

NX0986 : Bloody Cranesbill (Geranium sanguineum) by Anne Burgess
Bloody Cranesbill (Geranium sanguineum)
This distinctively coloured cranesbill generally prefers limy soils, but seems to... more

NX0986 : Port Vad by Anne Burgess
Port Vad
One of the tiny coves in the cliff here, I think the more distant one, is Port... more

NX0986 : Bennane Head Lava by Anne Burgess
Bennane Head Lava
The exposed rocks on the shore are pillow lavas, erupted on the sea bed almost 500... more

NX0986 : Bennane Agglomerate by Anne Burgess
Bennane Agglomerate
Agglomerate is like conglomerate, but is specifically formed of volcanic material.... more

NX0986 : Chaotic Boulders by Anne Burgess
Chaotic Boulders
The boulders are blocks of the Bennane Agglomerate that have been eroded from the... more

NX0986 : Wild Carrot (Daucus carota) by Anne Burgess
Wild Carrot (Daucus carota)
A few late flower-heads of Wild Carrot, which seems to be very common on this... more

NX0986 : Wild Carrot (Daucus carota) by Anne Burgess
Wild Carrot (Daucus carota)
One of many seed heads of Wild Carrot found along the coast.

NX0986 : Massive Lava by Anne Burgess
Massive Lava
These rocks are part of a massive lava flow, probably a flood basalt, and have... more

NX0986 : Sea Plantain (Plantago maritima) by Anne Burgess
Sea Plantain (Plantago maritima)
A late-flowering spike of Sea Plantain, which is plentiful close to the sea here.

NX0986 : Hemp Agrimony (Eupatorium cannabinum) by Anne Burgess
Hemp Agrimony (Eupatorium cannabinum)
There was one pale stunted plant of Hemp Agrimony still in flower in a sheltered... more

NX0986 : Onion-skin Weathering? by Anne Burgess
Onion-skin Weathering?
These alternating dark and pale stripes are thought by some geologists to be the... more

NX0986 : Weathered Lava by Anne Burgess
Weathered Lava
Sea-washed rocks at the foot of Bennane Head.

NX0986 : Sandstone and Chert by Anne Burgess
Sandstone and Chert
In the foreground is an outcrop formed of pale volcaniclastic sandstone... more

NX0986 : Chert by Anne Burgess
Chert
Chert is a rock formed of the remains of tiny marine animals called radiolarians.... more

NX0986 : Rock Stacks by Anne Burgess
Rock Stacks
Mixed rocks of volcanic origin at Bennane Head.

NX0986 : Synform by Anne Burgess
Synform
A synform is a u-shaped fold in rocks, in this case chert. It was very... more

NX0986 : Chert Rocks by Anne Burgess
Chert Rocks
Chert is a rock formed of the remains of tiny marine animals called radiolarians.... more

NX0986 : Sea-spurrey by Anne Burgess
Sea-spurrey
I think it's Greater Sea-spurrey (Spergularia media) because the petals are longer... more

NX0986 : Commemorative Cairn by Anne Burgess
Commemorative Cairn
The cairn was built by local people in memory of Henry Ewing Torbet (1911-1983)... more

NX0985 : Beach at Bennane Lea by Anne Burgess
Beach at Bennane Lea
To shoreward here is an excellent example of a raised beach, left high and dry as... more

NX0986 : Beach Boulders by Anne Burgess
Beach Boulders
The pinkish and greenish rocks here are serpenitised ocean-floor rocks uplifted to... more

NX0986 : Bennane Lea by Anne Burgess
Bennane Lea
The pinkish and greenish rocks here are serpenitised ocean-floor rocks uplifted to... more

NX0986 : Serpentinised Rocks by Anne Burgess
Serpentinised Rocks
The pinkish and greenish rocks here are serpenitised ocean-floor rocks uplifted to... more

NX0985 : Borage (Borago officinalis) by Anne Burgess
Borage (Borago officinalis)
Borage isn't native, but does occur spradically as a garden escape.

NX0985 : Beach and Burn by Anne Burgess
Beach and Burn
This is the Bennane Burn where it enters the sea at Bennane Lea.

NX1391 : Roadside at Pinbane by Anne Burgess
Roadside at Pinbane
The track curving through the middle of this view is part of the Ayrshire Coastal Path.

NX1391 : Shore near Pinbain Bridge by Anne Burgess
Shore near Pinbain Bridge
A sandy beach with the Isle of Arran in the distance.

NX1897 : Sunset at Girvan by Anne Burgess
Sunset at Girvan
This view, like every view from the esplanade and park in Girvan, is dominated by... more

All images © Anne Burgess and available under a Creative Commons licence external link.

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