Sheared magma chamberThese rocks are part of Mount Shimansky, one of several mountain peaks found in

Sheared magma chamberThese rocks are part of Mount Shimansky, one of several mountain peaks found in Palmer Land – a name for the southern portion of the Antarctic Peninsula.The dark spots you see are known as mafic enclaves. The main rock type in this frame is a diorite – a coarse grained igneous rock consisting of mostly quartz and plagioclase, with minerals like amphibole and biotite likely making up the darker spots (papers I’ve found haven’t given precise petrography but those minerals are common in this type of rock). This coarse grained igneous rock represents magma that cooled slowly beneath the Earth’s surface, likely over a period of tens to hundreds of thousands of years. In other words, at one point this was a magma chamber.The darker rocks floating in the diorite are amphibolites. This is a common metamorphic rock type produced when basaltic igneous rocks are metamorphosed. The big blob of igneous diorite at this site forced its way up through basaltic igneous rocks and in the process it heated them, metamorphosing them and likely picking up a few chunks as it went. Some of these chunks could also have been basaltic magma that intruded into the magma chamber – available data doesn’t constrain that. What’s important – these amphibolites have a higher melting temperature than the surrounding diorite. In other words, as the diorite forced its way up, those darker rocks stayed solid and floated as clasts in the molten diorite.The rocks have been heavily sheared since they formed. The rocks of Palmer Land were a tiny sliver of a continent that accreted onto the edge of Antarctica just over 100 million years ago during the Cretaceous. This process of continental collision is violent and can stretch and strain rocks. The end result at this site is the layered pattern in these rocks that we call a foliation.-JBBImage sources:https://www.flickr.com/photos/euphro/albums/72157626952681513Reference:http://onlinelibrary.wiley.com/doi/10.1029/2011TC003006/full -- source link
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