{Geologic!} Hotspot in Eastern Australia, Bass Strait, and Tasmania

         Hotspots within continental plates are not just for Wi-Fi ;-) or for the famous Snake River Plain-Yellowstone Caldera any more. . .

      The ages of the volcanic eruptions in the northwest U.S. range from 16.1 million years on the west end (dark green) to 0.6--2.1 million years at the east end (yellow) in Yellowstone. The continental plate records the location of the underlying hotspot and possible mantle plume as the continental plate moves generally westward.

      As reported in the September, 2015, issue of "Nature", the eastern Australia south-southwestern series of extinct volcanos extends from Queensland 

at the north end of Australia 2000 kilometers through the eastern middle of the continent toward Cosgrove volcano and southward into the Bass Strait and possibly into the island of Tasmania.

     The northernmost volcanoes are 33 million years old and the Cosgrove volcano to the south is 9 million years old. The Australian plate 

      is moving north-northeastward at a very high rate of 7 centimeters per year. Currently, the Australian plate is one of the fastest moving tectonic plates as evidenced by a span of 24 million years from north to south over a distance of 2000 kilometers.

      The "Cosgrove Track," extending the entire length of Australia is more than three times the length of the Snake River Plain-Yellowstone Caldera. That Australian plate is smoking!

       The East Australia hotspot has both explosive eruptions, as well as the pahoehoe lava flows similar to the Hawaii hotspot (located within an oceanic plate). The hotspot is explosive because basaltic magma interacts with groundwater in aquifers below the surface producing violent magmatic eruptions.

     What puzzles me most is that it took so long to connect the northern and southern Australian volcano dots. . .

Your thoughts?

Steph

Adamant about Wit, Waters, (R) And Diamonds in Plate Tectonics Timing

      By using an ion probe to analyze the carbon and nitrogen isotope compositions of Witwatersrand, South African diamonds, which have been preserved for more than three billion years, researchers found that plate tectonics was likely in operation on earth as early as 3.5 billion years ago. 

      The location of the Witswatersrand Basin mines in South Africa is shown here: 

     In an article published this week, researchers at the University of Witswatersrand describe the diamonds as being like miniature time capsules recording information about the movement of the earth's tectonic plates on the earth's surface.

     Lead researcher Dr. Katie Smart noted, “The nitrogen isotope composition of the Witwatersrand diamonds indicated a sedimentary source (nitrogen derived from the Earth’s surface) and this tells us that the nitrogen incorporated in the Witwatersrand diamonds did not come from the Earth’s mantle, but that it was rather transported from Earth’s surface into the upper mantle through plate tectonics. This is important because the nitrogen trapped in the Witwatersrand diamonds indicates that plate tectonics, as we recognise it today, was operating on ancient Archaean Earth, and actively transported material at Earth’s surface deep into the mantle.”

     In other words, these carats are able to tell us "What's Up, Doc?" from at least 3.5 billion years ago.

Your thoughts on these carbon gems (or emeralds ;-)) and plate tectonics? 

Steph

P.S. Yes, I am all set with a costume as a tardigrade for Halloween 2016:

Hoo Doo, Hoo Doo You Think You're Fooling: Paint Mines Interpretive Park on the Plains of Colorado

      Hoodoo, who do you think you're fooling?! 

      A class in wild clay painting (using a mixture of native clay and wheat paste) led Maizie and me to the Paint Mines Interpretive Park, near Calhan, east of Colorado Springs, CO.

     It was a starkly beautiful, still January day in eastern Colorado. 

     We took the slightly longer, scenic route from Denver through Parker and Franktown. The Paint Mines are a wonderful surprise in the middle of miles and miles of prairie.

         The colorful clays were harvested by ancestral native people at least 9,000 years ago. The formations have been dated as 55 million years old.

The bone white clay of Paint Mines (3 minutes) is especially striking:

      Here are a few images from our clay painting class. It was great to be able to paint on a cold January day with no paint fumes, creating walls with lots of "movement" in the clay.

       Thanks to Rob Lewis of Bellingham, WA, for pointing us to the Paint Mines and for the great class on painting with all natural materials harvested in our own "backyards."

          Have you experimented with painting with clay or other natural materials? Have you heard of or been to the Paint Mines in eastern Colorado?!

Steph

Boudinage, Cactolith, Crozzle, and Slickensides: Say that Three Times Fast and with a Lith

       Enjoy this smorgasbord of fun, fun-to-say, and funny geologic terms. Be sure to dust off your best French accent for bou-di-najjj, or sausage-shaped features formed by extension in rocks.

        Boudinage is the geological term for structures formed by the aforementioned extension, where a rigid tabular body is stretched and deformed amidst less competent surroundings. The competent bed begins to break up, forming sausage-shaped boudins. Watch this 2-minute video to see boudinage forming in an ice cream sandwich.

         A cactolith is "a quasi-horizontal chonolith composed of anastomosing ductoliths, whose distal ends curl like a harpolith, thin out like a sphenolith, or bulge discordantly like an akmolith or ethmolith." This quite tongue-in-cheek definition was described by Charles B Hunt in 1953 in the Henry Mountains in Utah to describe an intrusive feature resembling a cactus. It's a long lith. . .

      Crozzle is partially burned coal. {The by-product of burned coal is called clinker.} Some underground coal seams have been burning for centuries.

     One of my favorite geologic terms is slickensides which are polished, striated rock surfaces caused by one rock mass sliding over or past another. The word describes well the result of slick features moving past each other in fault zones:

      One can almost hear the grinding and sliding of rocks past each other. . .

      It's one of the most tactile surfaces in geology:

       Have you touched slickensides? Seen a cactolith? Do you have a favorite geologic term?  Or do you have a favorite term from your profession?


What's on your lith? ;-)
Steph

Oui, and speaking of French words and mirror planes, may 2016 be filled with much "Joie!"