ALKALINE  PICRITE

 

I’ve only got four rocks from Antarctica.  Antarctica is a big place, but it's almost entirely covered in glacial ice.  Some of the peripheral areas of the continent are decently exposed during austral summers, and some of the mountain ranges have peaks that top out above ice level.  What few rocks are exposed in Antarctica have been visited & collected & studied by geologists from various countries.

 

The rock shown below was collected by Russians in the 1980s from exposures along the western side of Lambert Glacier, the largest valley glacier on Earth.  Many of the rocks in the area are intrusive igneous rocks emplaced in a late Mesozoic rift complex (the Lambert-Amery Rift System).

 

This sample is a alkaline picrite (a.k.a. alkaline ultramafite/ultrabasite) from the Yuzhnoe Intrusion (“Southern” Intrusion), a stock that intruded at about Jurassic-Cretaceous boundary time (145 m.y.).  The groundmass consists of augite pyroxene, olivine, phlogopite mica, perovskite, and glass.  Larger grains in the rock include olivine phenocrysts & xenocrysts, plus chromian diopside xenocrysts.  Some small mantle-derived rocks also occur in this intrusion as xenoliths.

 

Alkaline picrite (a.k.a. alkaline ultramafite) (wet, cut surface; field of view ~4.3 cm across) from the Yuzhnoe Intrusion, Jetty Peninsula, East Antarctica.

 


 

Synthesized from info. in:

 

Egorov & Andronikov (1989) - Novye dannye o shtokoobrznykh telakh shchelochno-ultraosnovnykh porod oazisa Dzhetti (zemlya Mak-Robertsona, Vostochnaya Antarktida), polychennye v sezone 1986/87 g.  Informatsionnyy Byulleten Sovetskoy Antarkticheskoy Ekspeditsii 111: 5-13. [in Russian]

 

Andronikov (1994) - Glass in lherzolite inclusions from Jetty Peninsula (East Antarctica).  Mineralogical Magazine 58A: 19-20.

 


 

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