Mantle in the mountains Day 2

Nice view which they were admiring when we found them

This was a very long day as we had to go right back down to the coast and along to Estepona, where Jan and I lost the rest of the convoy but with the help of Emily Satnav found them again on the road up the hill towards Stop 1 in the parking area at Puerto de Penas Blancas: this is by the junction near Km 14  at the start of the track up to Pico de los Realajes de Sierra Bermeja.
At the point where we found them we had a good view to Gibraltar and the Rif mountains, the extension of the arcuate mountain belt and, in between, the Alboran basin which has subsided 7 km.  

"How do you date a dyke?" Location 1

I'd come across the term "bermeja" before and now found that it meant "ginger coloured" - very appropriate since this is the rusty orange weathered colour of the iron rich peridotite, of which these hills are made. The peridotite sheet forms a massif in the Betic Internal Zone.

It's a complicated body with cm scale heterogeneity. There are 4 main zones but as well as the ultramafic harzburgite and lherzolite there is a suite of other rocks. The zones aren't inverted, the zone order is a function of preservation of stages in its history.
Rh-Os dating gives an age of 1.36 Ga, this is when the rock emerged from the mantle and was incorporated in continental crust.
In Jurassic the plate thinned, rifted, mantle melting with uprise, decompression. This allowed mafic veins to form.

Location 1

Close up of the leucocratic dyke material

At the back of the parking area we found the peridotite is cut by a leucocratic dyke, with brittle fracturing, sloping down to left at 30°. Presence of plagioclase indicates shallow mantle. Further up hìll (near the cyclist mirador) is annealed granular spinel peridotite. Higher still is spinel peridotite with tectonic foliation. Odd that higher pressure facies at top and lower pressure plagioclase lower down but these represent different time steps in the story. Right near top boundary are spinel peridotites with garnet.

There's serpentinisation related to the granitic dyke along a serpentinised zone. The dyke probably originated below the peridotite and a partial melt was injected upwards. Composition is quartz and feldspar and tiny black specks probably tourmaline. Also blue green diopside (chromite).

Location 2

We drove on down the hill, turning left and going about two miles on a forestry track which was level but rough. 

Leaving the granular spinel peridotite we found stripes (foliation) in rocks which were picked out by weathering. We were passing into the garnet peridotite zone where thin mafic layers contain garnets.

Peridotite with thin mafic layers dotted with garnets

This is near the contact with the overlying crust: mafic layers were formed in ultramafic mantle by partial melting, then deformed and stretched. In some places garnets are little swells in thin layers; these rocks were described by Tom as  "marginal mylonites". We also saw lineation formed by alignment of elongate cpx.

Differential weathering of layered peridotite

Back to junction where some "hippy sort" was wandering around doing some type of shaman ritual drum beating! Get all sorts on the costas!

Los Reales mirador

Location 3

A steep, winding road took us up to the refugio where we parked at Plazoleta Salvador Guerrero and walked 250 m or so to the viewpoint which was spectacular: views all way around the arcuate orogeny through the Betics, Gibraltar and round to Rif. 

Ibex

Discussed Alboran Basin, volcanics, seismics and, as we returned to the cars, saw an ibex.

Location 4

Continuing back down towards Estepona we stopped by an arroyo. Not on peridotite, because no pine trees! We are learning!
The bedrock here is migmatite breccia as seen Day 1, loose in road cut. Boulders conrain chrome diopside from higher up, sometimes in layers.

Hand specimen of peridotite from Arroyo de la Cala with green chrome diopside

Mantle in the Mountains Day 1 - Wednesday 29 April 2015

Spent the morning herding cats at Malaga Airport but by lunchtime we had 20 people and their luggage in six cars and headed west to a lunch stop at Arroyo de la Miel services on the AP7. This also served as the first geology stop as there is coarsely crystalline marble exposed in the cutting at the back.

Coarsely crystalline marble at Arroyo del Miel - part of the "Alboran Block"

On westward to San Pedro de Alcantara, then up the A 397 to Ronda, taking in a couple of stops on the way.

Road cut in peridotite at Km 34 on the A397

At km 34 we were on peridotite, vegetated by pine trees and saw plenty in situ. A second rock type, stretched, flattened, and with foliation and augen that showed refolding comes from under the peridotite sheet. There were also breccias: what Tom called a magmatitic breccia, with blobs of quartz and lithic clasts; some black granular patches on faces could be chromite or spinel, a mass of small crystals.
Loose bits of carbonate are probably quarried.

Stuart with a metagranite cobble from the roadside

Metagranite with post-kinematic augen

Intricately strained and folded metabreccia

The breccia pebbles look waterworn. ? Transport, ? Reworking. One had post kinematic garnets.

This is an odd road: it was upgraded in the 1970s to serve the burgeoning tourist industry on the Costa del Sol, providing an easy route up to Ronda from the coast for the tourist excursions. It climbs steadily up through the Sierra Bermeja but doesn't go through any towns or villages! I checked an old (1966) map of Spain and the, then, C (minor) road is marked as a "slow road: tight curves and steep slopes only permit a reduced speed". I love this old map - it dates from a family holiday in Spain in that year and has so many roads marked with the red crosses that Michelin used to denote a "road in a bad state".

View NW from Km 24.5 towards the peridotite/limestone junction - where the
pine trees stop!

We stopped again at Km 24.5 where there is a view of the northern contact of the S Bermeja peridotite with a grey rock, limestone, to the north. This is the Dorsale Limestone of the Serrania de Ronda. Its steep contact with the peridotite is indicated by the straight junction at surface. 

The junction itself is by km 20: we visited this later in the week but following early starts that morning it seemed a good idea to push on into Ronda and get checked in to our hotel!

Hotel Don Javier is right in the centre, but easy enough to find as it is just off the main street, across the Puente Nuevo. Unloading (and loading up/unloading on the following days) needed some good organisation as the unloading area was the taxi rank by the bull ring, reached by going through a "no entry" sign and only 10 minutes allowed on each occasion. Then the hotel concierge had to nip down to open the underground garage, where he very kindly parked and unparked the cars for us! Probably a good thing as it was a very tight fit :(

On this first evening we identified a convenient bar, which no one but us seemed to be using, just across the alley from the hotel, and took that over on the next five evenings for our "debrief" sessions. The big G and T's they poured certainly hit the spot with some of the group!

Mantle in the Mountains - getting there - Tuesday 28 April 2015

Essential for a big trip like this - 20 people, 6 cars, multiple days and times of arrival, staying at 4 main centres plus start and end in Malaga - to be on the ground ahead of the rest. Jan and I headed down to Bristol Airport Monday evening and managed about 5 hours kip before getting up to check-in for 4am.

A pleasant flight, none of the joggling we'd had on the March ones, in one of Easyjet's lovely new A320s which, with slimmer seat backs etc seem to be roomier. Unfortunately going for the most reasonably priced hire car means the longest queue at the desk and this was no exception: it took us an hour and three-quarters to get out of the airport, but we do have a very smart, mint green car.

Coffee called and, by the time we got to Carrefour at Los Patios, our tums were rumbling too. For €4 we had a coffee each and a ham and cheese baguette before mooching round the shop for a few picnic bits to last us over the next few day's lunches.

Then onto the main business, which was getting hard hats for six (actually 5, but better safe than sorry!) of the group.  Aki at Los Patios is now something different, so we went back to Leroy Merlin and got 2 red, 2 white and 2 blue (patriotic or what?), then spent quarter of an hour struggling to fit the inserts into them!

Gone 1pm, so seemed decent to head for the hotel and siesta, get sorted out and make a cup of tea. Quick inspection of room showed that, intriguingly, the showerhead is at the open end of the walk-in shower rather than behind the screen! The soap container is down the screened end though...

Later... duh... there's an overhead shower the other end!

The airport pick ups went OK, and whilst some came back to the Malaga Nostrum with us, others had made different arrangements - just hope they all turn up in the morning LOL.

Good Friday on the South Wales coast

A field trip reccy is a good excuse for a day at the seaside!

Hoping to do a repeat of last summer's field skills day, but in South Wales rather than North Cornwall, I'd been looking at some potential locations and thought the strip of coast south of Cardiff between Lavernock Point and St Mary's Well Bay  might just fit the bill. There's a cliff section which could be good for field sketching, and a faulted syncline which would give mapping practice, strike and dip measurements etc plus an opportunity to test a hypothesis about fault movement. So, having done the homework, off we went.

Finding St Mary's Well Bay

My plan was to find somewhere to park at St Mary's Well Bay, walk eastwards along the cliff to Lavernock Point (Wales has a complete coastal path, right?) descend to the beach and work back to the start point. Following signs to ST MWB (can't keep typing it out in full!) took us past a holiday park, and down to the coast.... double yellow lines both sides all the way ... then onwards past the headland to Swanbridge, opposite Sully Island. Here the road ended abruptly! It looks as though there has been some erosion here in the past - though whether natural or anthropogenic isn't clear! 

Anyway we took the opportunity to take a look across at Sully Island: I'd only seen this, and it's famous unconformity, from the sea before on the way to Flatholm.

Sully Island from Swanbridge - we could actually have walked across as the
tide was far enough out, and going down, but it is extremely slippery so a "No"!

The unconformity is between dipping Carboniferous limestone, which has been
eroded before Triassic breccia was deposited on top

The unconformity isn't as clear at the eastern end of Sully Island

There were good views from here up the Channel to Flatholm and Steepholm, as well as similar rock exposures at the eastern end of Swanbridge foreshore. However, not a lot of point exploring them as nowhere to park!

Flatholm and Steepholm (the thing in between is a container ship, not a
new island!)

Back to Lavernock

Since SMWB was obviously no use as a parking/start point, we headed back round to Lavernock Point - there's a bit of parking here, maybe enough for 8 cars if we pack in - can't count on using the church CP as the trip will be on a Sunday! They might want it themselves....

Two paths start from here, one heads north up the coast towards Penarth and the other, currently appropriated by a small stream, down a gully to the beach. Jan went on down while I slipped and slid my way, ending up on my seat for safety, onto the foreshore. 

The wrong size cobbles :(

This is the problem here - they are deuced uncomfortable to walk on and I'm afraid that I just couldn't see myself prancing around from one group to another checking their field sketching etc. Jan clambered over an algae covered concreted pipe (sewer?) to look round the headland and reported more of the same, loose, wobbly cobbles with ridges of rock to clamber over in between. It just isn't a place where you could potter comfortably learning how to use a clino, draw exposures etc so, what with that and the lack of parking and loos, we decided it was no go.

Had a good view of Coltsfoot on the way down to the beach!

Where next?

Sifting through what places were nearby, we thought we might take a look at Ogmore by Sea and headed round there - lunchtime by now so we parked up, (at least there's plenty of parking here) and ate our sandwiches before taking a look.

As the tide was well out (low springs) we were able to make our way down onto
the sand and walk along there. 

I'd not appreciated before just how much of the rock exposed below the car park and for quite a way to the east, is Triassic breccia! The tide has always been at least halfway up, and covered the sand, on my previous visits. We had to walk quite a way before we came to the Carboniferous limestone and in the end we went up a slipway to the cliff path and walked along there instead.

Triassic breccia on the left, plastered over the eroded surface of Carboniferous
limestone - the horizontal beds on the right

This entire area is covered with breccia

View across to Porthcawl

However, interesting as Ogmore has been for a field trip looking at the rocks exposed here, the lack of structure means that it has less potential for a mapping/field skills/graphic logging type exercise. Its strengths are the beautiful coral fossils, and the unconformity and that is just not enough to build a day around. 

Walking back to the car park we were treated to some beautiful skies as we looked across the Channel towards the North Somerset coast, and we had had a good day out at the seaside even if we didn't achieve the object of finding a field skills locality.

Skies look threatening but we were lucky and the rain held off all day!

It looks as though it could be a bit damp and misty on Exmoor though!