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 (̉SouthernÓ
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.