Wednesday, 3 June 2015

Packing my 'Nappe-stack'

I'm off on an adventure! Hiking in the mountains, eating knodel in wooden huts, sipping schnapps surrounded by geraniums while men in felt hats play accordions - where else could I be, but in the Alps?
As my surname suggests, although I am Scottish, my cultural background is a little more complicated than that. My family on my father's side come from the steep glacial valleys of the Alps, with a confusing interwoven fabric of Northern Italian and West Austrian blood that (we'd like to think) stretches right back to Oetzi the Ice Man. As a result, my heart two-times beautiful Scotland with it's other lover: South Tyrol.

The European Alps are a geological car crash - in fact they're a multi-car pile-up 30 million years in the making. Trying to understand the whole thing is a bit of a mind-bender, but the area of Tyrol I'll be wandering through for the next week, near Meran in Northern Italy, is made up of the crumpled margins of the Apulian or Adriatic plate, a chunk of Africa that broke off in the Cretaceous. The rest of it is still being crushed between the long boot of Italy and the coasts of Croatia to Albania, before curling round and cupping the bottom of Italy's heel.

What's left of the Apulian plate is being squeezed behind the Italian boot. To the North, beautiful Tyrol, part of the Alps mountain chain. Image: adapted from Wikipedia
One of the main tectonic boundaries in the Alps cuts West-East: the Periadriatic line, running like a seam through the mountains for 1000km. This is where the Northern edge of the Adriatic plate meets the Eurasian plate. Meran - and my family for generations - nestles right on this stunning collision zone.

As well as pieces of these continental plates, chunks of the ancient Tethys seaway have been heaved up here. The Tethys was a massive shallow sea cupped in the hands of the supercontinent of Pangea, but as the continents broke up and rearranged themselves, it was sandwiched, sub-ducted and uplifted along it's length, leaving fossils high and dry from the Alps to the Himalayas (although these fossils have often been destroyed in later metamorphic processes). 
The Alpine geology in the area I'm exploring. The Legend is at the end of this blog, or go here for the complete interactive map of the Alps.
Most of the rocks in the Alps are called 'nappes' (and when they are on top of one another, as they often are in the Alps, it's a nappe-stack!). Much of the rock I'll be thudding my boots on are the Austroalpine nappes: Adriatic plate rocks thrust up and over the Eurasian rocks. But because I'm roaming around the Periadriatic seam, I'll also get a look at some rocks from an even older collision zone. That's because the south side of the seam is made of rocks from the Variscan orogeny, when Euramerica and Gondwana got intimate during the formation of the supercontinent Pangaea, around 300 million years ago. Meanwhile even further south, the Dolomites are the result of over 200 million years of deposition at the bottom of the sea being lifted up into the air and eroded into jagged fingers by rain and ice.

Suffice to say, there's a lot going on geologically. My bag will be full of rocks by the end. On top of that, literally, is the wonderful alpine ecosystem. Although much altered by man, they valleys and mountainsides of the region are a naturalist's wonderland.
So off I go with my camera, map and ID guides, let's see what I can find.

Taken 2 years ago in the valley where my relatives live. I can't wait to return.

Legend for the geological map of the region.

No comments:

Post a Comment