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A Geology Bullseye: The Black Hills of South Dakota

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Manage episode 322390607 series 2784864
内容由Chris and Jesse提供。所有播客内容(包括剧集、图形和播客描述)均由 Chris and Jesse 或其播客平台合作伙伴直接上传和提供。如果您认为有人在未经您许可的情况下使用您的受版权保护的作品,您可以按照此处概述的流程进行操作https://zh.player.fm/legal

The Black Hills happens to be one of our favorite places. We thought it was the right time to talk about them as people are getting the itch for summer to arrive so we can play in the mountains. The Black Hills is the perfect area to orient a young family to a life of adventure and respect for the outdoors. You can't get into too much trouble here and these mountains and the surrounding area offers so much to do. The Black Hills of South Dakota are a destination - not a speed bump on your way out West. Sit back and enjoy!
Geology of the Hills

  • The geology is complex but there are 3 basic suites of rock formations. The igneous and metamorphic core in the southern part of the Hills (Black Elk Peak, Mount Rushmore), some intrusive and extrusive igneous activity in the northern part of the hills (Bear butte and Devils Tower), and the sedimentary rocks that rim and surround the entire area (Racetrack and Wind Cave). From a 30,000 foot perspective, everythings looks like a huge oval shaped bullseye.
  • The granite core, that has tons of awesome pegmatite was formed between 2 by and 1.8 by ago in the Trans-Hudson Orogeny. This is ancient mountain building event that formed the Canadian shield and the North American Craton (Jesse, you probably know a lot about this). The pegmatite makes for a climbing meca.
  • Surrounding the Granite, is a diverse group of metamorphic rocks. These are the oldest in the area, because they were formerly sedimentary rocks that were metamorphosed into schists and gneisses by the THO. These rocks were intensely heated and squeezed enormously. In some areas of the hills, the metamorphic rocks are tilted 90 degrees (upended) and have been heavily eroded since. (Jesse, we love this stuff because we LOVE schist - garnet, staurolite, etc)
  • The PreC core was eventually brought to the surface. How did this happen and How do we know?
    • It was relatively flat, and then covered by a shallow sea and eventually the Western Interior Seaway.
    • The sedimentary rocks that circle the BH are oldest near the core and get progressively younger further out. You can always tell where you are in the BH by the types of rocks around you - core vs. unaltered sed. rx.
  • Over 7500 feet of vertically accumulated rocks here

Then the Laramide Orogeny began to influence this area. This is the famous event that formed the Rocky Mountains far to the West. But a stray blob of magma rose way to the East under the Black Hills - pushing up the PreC core and the sedimentary strata covering them.

  • The highest parts of the BH are 7200 feet above sea level. The sed rx were 7500 feet thick so the total uplift is near 15,000 feet, but they were not likely ever that tall. As uplift was going on, so was erosion.
  • The blob of magma was like a piston, shoving up the rocks from below. As the PreC core poked through, the sedimenta

We now have a live Mobile App for iOS and Android. There you can learn all the basics of geoscience with our CampGeo content, purchase a visual audiobook on the Geology of Yellowstone National Park, and listen to past PlanetGeo episodes!
Download now
at this link
Like, Subscribe, and leave us a Rating!
——————————————————
Instagram: @planetgeocast
Twitter: @planetgeocast
Facebook: @planetgeocast
Support us: https://planetgeocast.com/support-us
Email: planetgeocast@gmail.com
Website: https://planetgeocast.com/

  continue reading

186集单集

Artwork
icon分享
 
Manage episode 322390607 series 2784864
内容由Chris and Jesse提供。所有播客内容(包括剧集、图形和播客描述)均由 Chris and Jesse 或其播客平台合作伙伴直接上传和提供。如果您认为有人在未经您许可的情况下使用您的受版权保护的作品,您可以按照此处概述的流程进行操作https://zh.player.fm/legal

The Black Hills happens to be one of our favorite places. We thought it was the right time to talk about them as people are getting the itch for summer to arrive so we can play in the mountains. The Black Hills is the perfect area to orient a young family to a life of adventure and respect for the outdoors. You can't get into too much trouble here and these mountains and the surrounding area offers so much to do. The Black Hills of South Dakota are a destination - not a speed bump on your way out West. Sit back and enjoy!
Geology of the Hills

  • The geology is complex but there are 3 basic suites of rock formations. The igneous and metamorphic core in the southern part of the Hills (Black Elk Peak, Mount Rushmore), some intrusive and extrusive igneous activity in the northern part of the hills (Bear butte and Devils Tower), and the sedimentary rocks that rim and surround the entire area (Racetrack and Wind Cave). From a 30,000 foot perspective, everythings looks like a huge oval shaped bullseye.
  • The granite core, that has tons of awesome pegmatite was formed between 2 by and 1.8 by ago in the Trans-Hudson Orogeny. This is ancient mountain building event that formed the Canadian shield and the North American Craton (Jesse, you probably know a lot about this). The pegmatite makes for a climbing meca.
  • Surrounding the Granite, is a diverse group of metamorphic rocks. These are the oldest in the area, because they were formerly sedimentary rocks that were metamorphosed into schists and gneisses by the THO. These rocks were intensely heated and squeezed enormously. In some areas of the hills, the metamorphic rocks are tilted 90 degrees (upended) and have been heavily eroded since. (Jesse, we love this stuff because we LOVE schist - garnet, staurolite, etc)
  • The PreC core was eventually brought to the surface. How did this happen and How do we know?
    • It was relatively flat, and then covered by a shallow sea and eventually the Western Interior Seaway.
    • The sedimentary rocks that circle the BH are oldest near the core and get progressively younger further out. You can always tell where you are in the BH by the types of rocks around you - core vs. unaltered sed. rx.
  • Over 7500 feet of vertically accumulated rocks here

Then the Laramide Orogeny began to influence this area. This is the famous event that formed the Rocky Mountains far to the West. But a stray blob of magma rose way to the East under the Black Hills - pushing up the PreC core and the sedimentary strata covering them.

  • The highest parts of the BH are 7200 feet above sea level. The sed rx were 7500 feet thick so the total uplift is near 15,000 feet, but they were not likely ever that tall. As uplift was going on, so was erosion.
  • The blob of magma was like a piston, shoving up the rocks from below. As the PreC core poked through, the sedimenta

We now have a live Mobile App for iOS and Android. There you can learn all the basics of geoscience with our CampGeo content, purchase a visual audiobook on the Geology of Yellowstone National Park, and listen to past PlanetGeo episodes!
Download now
at this link
Like, Subscribe, and leave us a Rating!
——————————————————
Instagram: @planetgeocast
Twitter: @planetgeocast
Facebook: @planetgeocast
Support us: https://planetgeocast.com/support-us
Email: planetgeocast@gmail.com
Website: https://planetgeocast.com/

  continue reading

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