#laurentia

Now the more #riebeckite facies of the #Paleozoic #Quincy #Granite

The Quincy granite was a prized architectural stone, most famously used in the #BunkerHill Monument in #Boston #Massachusetts. Current dating suggests it was intruded into #Avalonia before it glommed onto #Laurentia as #Laurasia and #Pangea were assembled. Today’s #photo set comes from a walk around the eponymous Bunker Hill Quarry. I’ll post more about the history later. Captions!
#Fujifilm #XH1 #igneous #intrusive #NewEngland

Quincy or #BlueHills #Porphyry #Granite
An alkaline, nonorogenic granite intruded into #Avalonia in the #Silurian / #Ordovician as it cruised from peri-#Gondwana to #Laurentia, before assembling #Pangea in the #Acadian #Orogeny (#Devonian). It’s coarse, with the #phenocrysts of amphiboles(?) (possibly riebeckite?)…I’m no petrologist. From@the Eaton’s Pond conservation area@at the #Braintree #Quincy border. My photos.
#geology #igneous #Massachusetts #Boston #NewEngland #Fujifilm #photo

Wilson Cycle Phase 3: Ocean Closing

“I enjoy, and have always enjoyed, disturbing scientists.”

~ John Tuzo Wilson

“From great oceans, giant mountains will form. This is the prediction of the third phase of the Wilson Cycle where we see the closure of the vast oceans like the Iapetus Ocean, and the formation of continent to continent collision mountains.”

~ Professor Dougal Jerrom, intro to Wilson Cycle Phase 3: Ocean Closing video linked below

In the 24 minute video below (a great watch), we continue our travels with Professor Dougal Jerrom of Oslo University, to look at evidence of the closing of the former Iapetus Sea in the Caledonian of Norway. The video starts with a nice recap of the other videos.

Whenever there is an ocean closure, geoscientist always look for ophiolite. Ophiolites in the geologic record provide evidence primarily of subduction zone tectonics. Although they typically lie between continental blocks, their emplacement predates the final closure of the ocean basin in which they formed by many millions of years. We have already seen the pillow basalts, sheeted dikes (gabbros) and peridotites that form ocean crust in earlier videos in this series. An ophiolite is then a bit of oceanic crust that got swept up in the continental collisions and provides the first proof of an ocean closure.

Next we learn about melange - the sediments that were scraped up, or accretionary wedge. There are also remnants of the island arc formed during subdution all sandwiched between the bits of continental crustal blocks that collided.

Last, we find evidence of of those continental crustal blocks, the paleocontinents of Laurentia and Baltica that collided to complete the closure and form high mountains on a brand new continent. The collision forms extensive faulting throughout the rocks as suture zones. There is a great labeled diagram of this portion of the Wilson Cycle here:

Enjoy the video below where you see glimpses of the geology of the beautiful Norwegian Caledonian.

Wilson Cycle Phase 3: Ocean Closing: https://youtu.be/jYlQCbDmEVw

More on the closing of the Iapetus Sea here: https://en.m.wikipedia.org/wiki/Iapetus_Ocean

Includes Step 5 and 6 of the Wilson Cycle: c.im/@vickyveritas/10962360456...

Refer to this great labeled diagram of the Wilson Cycle for the components of the ocean closure and continent to continent collision and mountain building: https://c.im/@vickyveritas/109628513962823739

Note: We will see the last step of the Wilson Cycle and the great grand finale of this series. Stay tuned.

#JohnTuzoWilson #TheWilsonCycle #Caledonides #IapetusOcean #Norway #PlateTectonics #Ophiolite #AccretionaryWedge #SutureZones #Laurentia #Baltica #geology #ScienceMastodon #NorwegianGeologyRocks @geology