Migmatites in Aberdeenshire

Part of the Shear Zone Channel. Join Rob as he visits rocks near his home in Aberdeenshire, examining some especially strongly metamorphosed rocks (the Queen's Hill Gneiss Formation, part of the Crinan Sub-Group of the Dalradian) in the Grampian Highlands of Scotland, relating the excessive temperatures they record to syn-orogenic basic intrusions.

[@WarrenBirch-z5j]

Great video, thanks for this. Helping me to make sense of some the many varied pebbles and boulders I'm digging up from the Lochton Sand & Gravel Formation, west of Banchory...

[@briandwi2504]

Fascinating story, told beautifully. Thanks!

[@mji1967]

Liking and commenting to help the algorithm. Thanks for the great videos

[@robbutler2095]

Thanks - it all helps!

[@QuintinJDavies]

Thanks so much for these videos Rob, they are well made. I am a local geologist also (carbonate PhD Limestone) and live near Burn O' Vat) so found this one most interesting. Keep them coming. I was at Hopeman last weekend fault spotting 🙂

[@robbutler2095]

Thanks for the comments - I'm aiming to put together some more things on geology of NE Scotland.... Hopeman's great!

[@张宏远-z8t]

Your explanation through depth-temperature diagram is quite important to me. Geology is a descriptive discipline if not quantified. My question is that if the magmatite formed in an extensional environment since its thermal source is the metamorphic basic intrusions (amphibole) ? I am interested in stress regime questions.

[@robbutler2095]

The tectonics of the Grampian orogenic system (Ordovician part of the "Caledonian" in Scotland) is debatable... certainly not like "normal" continent-continent collision given the syn-tectonic basic magmatism. But the basic intrusions (and migmatisation) are seemingly emplaced into actively thickening crust... so some argue for a "back-arc" setting....

[@张宏远-z8t]

@@robbutler2095 Great! Thanks a lot!

[@grizzlymartin1]

What is key to distinguishing these from Gneiss? Thx.

[@robbutler2095]

Gneiss is a broad term - coarse-grained, commonly banded metamorphic rock. They need not (indeed generally haven't) involved melting. Migmatites are a special type generally of gneiss) - where lenses and "stringers" of quartz-feldspar veins (leucosomes) which cross-cut other fabric elements are interpreted to be frozen in situ, small fractions of partial melt.

[@grizzlymartin1]

@@robbutler2095 Very Cool. Er...”hot.” 🙂 Appreciate your detail here. By the end of the video I started to appreciate this unique chemistry/physics. Really helped me put things in the appropriate box. Slowly more geo-logic coming into focus for me. Feels good. Thanks again.

[@leesonpatton4488]

What rock types will hold gold mate they all look yummy 👌🏼

[@robbutler2095]

Good and interesting question. Most of the bedrock gold is apparently located in veins - post metamorphic peak... but that's another story....

[@leesonpatton4488]

Your good at explaining the rock type's I'm lovein your video keep up the good work mate👍🏼

[@leesonpatton4488]

Can't wait for that story heheh🤔

[@grizzlymartin1]

Something is not right about storms so readily destroying what should be well adapted forests? What gives...?

[@robbutler2095]

Well a couple of things. These storms through 2021-22 were exceptional for their wind-speeds - and the direction of the first one, from the N - was rather unusual. Increased storm strengths are expected into the future... But the forests themselves are prone to wind damage. The ones in the video are plantations, with higher tree densities than most nature ones. So the root systems are not that robust... Also the specific trees hadn't seen many storms - the forests weren't well adapted.

[@grizzlymartin1]

@@robbutler2095 I knew something wasn’t right. Thanks.