DescriptionAN EXCEPTIONALLY RARE AND UNIQUE LUNAR METEORITE EXHIBITING 3 DISTINCT LITHOLOGIES
NWA 2727 (NWA=Northwest Africa)
Olivine Gabbro / Mare Basalt Regolith Breccia
The first indications of the scientific importance of this rare meteorite were seen in November of 2004 when an astronomy journal reported that scientists had just discovered the youngest lunar rock ever found in a new meteorite called NWA 773 or Dchira. Since that article five more stones were found that have recently been classified as paired with NWA 773 - which means that they are from the exact same source meteoroid and fell to Earth at the exact same time. Thus, this meteorite, NWA 2727, contains the youngest lunar material ever found that dates from 2.865 billion years ago. NWA 2727 is a regolith breccia which means that it is a shock-welded lunar soil composed of fragments of many different kinds of rock and minerals, including fine grains and powders that were broken away from the underlying bedrock by the repeated impact of meteorites. The shock-welding is caused by the impact of a large meteorite nearby which, much like a nuclear weapon, releases massive amounts of heat energy (thermal radiation) and shock waves. Shock-welding occurs when the impact is far enough away that no direct melting occurs, and only the massive shock wave crushes and compresses the regolith together, creating a new rock, very much like making a snowball by squeezing the snow between one's hands. The incredible pressures generated by these nuclear weapon-like impacts regularly produced very large zones of shock-welded material which, then, had to be blasted into space by an even larger impact in order to get to Earth. An important distinction in classification here is that regolith breccias only form in the first few meters of the Moon's soil because they contain high levels of implanted Hydrogen and Helium ions from the solar wind and show crystal alteration from high energy cosmic ray damage that can only occur very near the surface.
Another aspect of this meteorite's great scientific importance is that it samples two of the very rarest lithologies on the Moon:
The first is Olivine Gabbro, an intrusive igneous rock containing large amounts of olivine that formed deep under the lunar crust or in magma chambers of volcanoes. We know that gabbro crystallized deep under the crust because of the large grain/crystal size, meaning slow and steady cooling at depth. This Olivine Gabbro portion of the meteorite contained the olivine that gave the age of 2.865 billion years, proving the Moon was still volcanically active 2.865 billion years ago. This very young crystallization age shocked the scientific community when it was first reported because the Moon was previously thought to have been a "dead" planet for over 3.4 billion years. Soon after the Moon formed, approximately 4.2 billion years ago, a continual stream of meteorite impacts created an ocean of molten rock (magma) that covered the entire surface of the Moon. As this molten rock cooled, minerals and elements began crystallizing out in decreasing order of their melting points with olivine followed by pyroxene followed by plagioclase feldspar. Since olivine and pyroxene are very dense, the plagioclase feldspar floated to the top of the magmas before crystallizing creating the anorthositic crust that we see covering the lunar highlands to this day. The last things to crystallize from the magma were the rocks rich in potassium(K), phosphorus(P) and REE (rare earth elements) and metals. These "KREEP" rocks have high concentrations of radioactive elements which were the energy source for creation of these youngest magmas such as the Olivine Gabbro portion of this meteorite - Indeed, the heat engine in the molten core and semi-molten mantle of the Earth is driven by just such a mechanism involving the slow decay of radioactive elements. Very importantly, since Olivine Gabbro forms very deep under the crust, the only way that it could be brought to the surface without being melted and changed to basalt is through a gigantic meteorite or asteroid impact that excavated very deeply into the Moon's crust by at least several miles and blasted sub-crustal rock to the surface. Therefore, it is concluded that one of the very largest impacts in the Moon's history is responsible for the Olivine Gabbro being present at the surface.
The second is Mare Basalt, an extrusive or volcanic rock that formed 3-3.5 billion years ago, long after the ocean of magma that covered the infant Moon had cooled and formed the multiple layers of rock types in the Moon's crust. Huge meteorite and asteroid impacts that occurred much later broke up the crust forming weak spots. Later magma, generated by the high-radioactivity "KREEP" rock layers, penetrated the broken crust underneath these biggest impact craters and caused gigantic lava flows (molten basalt). Over time these craters became filled with the lava forming giant, very flat, basaltic plains, which early astronomers mistook for actual seas and dubbed "maria", Latin for "seas" - hence the name, Mare Basalt. These large, dark, basaltic plains delineate the face of the "Man in the Moon" that we see today. 16 % of the lunar surface is maria, but only 1% of the total volume of the lunar crust are Mare Basalts and thus, they are exceptionally rare in lunar meteorite samples as well.
This lunar meteorite, NWA 2727 and its synonymous pairs, can legitimately be called the most scientifically important lunar meteorite ever discovered and certainly the rarest yet found!
The present specimen is an end piece showing two large gray Mare Basalt clasts in a matrix of green Olivine Gabbro and regolith breccia with some fusion crust on the uncut end. The sliced face shows a single, very large area of gray Mare Basalt with green olivine phenocrysts and a smaller green Olivine Gabbro clast with very large crystal grains in a breccia with white anorthositic grains and smaller green gabbro clasts. This incredible museum piece measures 29 x27 mm by 5mm thick and weighs 6.52 grams
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