We found gabbro!

12/3/2016

Our camp is called Gabbro Hills, despite that we are actually in the Lillie Range, but the rock units are the same as those for Gabbro Hills. We have been collecting samples for three days and have already packed up about 1400 pounds of rock. Today we were especially victorious because we actually found gabbro! In 1400 pounds of rocks, there is only one sample of gabbro, the rock that this area is named after. It has been surprising to not see it sooner. This area is special to the Transantarctic Mountains because it might be the only place with exposed igneous rocks thought to represent intrusives for both pre-tectonic and post-tectonic Granite Harbor Intrusive activity. Finding these rocks is important because the gabbros could reveal something about the source material for all the granite that the TAM is composed of, as well as clues for the tectonic evolution of the subduction margin along the Antarctic craton. For a crude explanation, magma is generated through volatile-release from the down-moving oceanic plate subducting under the overriding continental plate. As the volatiles are released, the crust is melted, and large magma chambers form along the margin. When magma comes from melting continental crust, it tends to be mostly felsic (made up of the lighter minerals), which produces rocks like granite. Gabbro Hills, however, contains more mafic igneous rocks, possibly suggesting that the magma came from a different source. This other source is thought to represent depleted-mantle material, hence its composition of mostly mafic minerals (the darker, Mg-, Fe- and Ca-rich minerals).

The end result is that we have collected a lot of granite. So things are going well. We are surrounded by stunning granitic spires under clear sunny skies in 15-30 degree Fahrenheit temperatures on Le Couteur Glacier. This is an incredibly beautiful place. I doubt that many people have the opportunity to travel across glaciers in a terrain like this where only a few people have ever explored. We were on an outcrop yesterday and spotted about 10 paleomagnetism bore holes likely from the 1995-96 expedition season led by Anne Grunow. Incredible! I do not think I have ever found paleomagnetism. drilling evidence before. Antarctica is a rare environment where the activity of humans remains completely unaltered after years of passing time.


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