[meteorite-list] Evidence Found For Granite on Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 19 Nov 2013 10:13:34 -0800 (PST)
Message-ID: <201311191813.rAJIDYG1007873_at_zagami.jpl.nasa.gov>

http://www.news.gatech.edu/2013/11/18/evidence-found-granite-mars

Evidence found for granite on Mars
Georgia Tech University
November 18, 2013
 
Researchers now have stronger evidence of granite on Mars and a new theory
for how the granite ? an igneous rock common on Earth -- could have formed
there, according to a new study. The findings suggest a much more geologically
complex Mars than previously believed.

Large amounts of a mineral found in granite, known as feldspar, were found
in an ancient Martian volcano. Further, minerals that are common in basalts
that are rich in iron and magnesium, ubiquitous on Mars, are nearly completely
absent at this location. The location of the feldspar also provides an
explanation for how granite could have formed on Mars. Granite, or its
eruptive equivalent, rhyolite, is often found on Earth in tectonically
active regions such as subduction zones. This is unlikely on Mars, but
the research team concluded that prolonged magmatic activity on Mars can
also produce these compositions on large scales.

"We're providing the most compelling evidence to date that Mars has granitic
rocks," said James Wray, an assistant professor in the School of Earth
and Atmospheric Sciences at the Georgia Institute of Technology and the
study's lead author.

The research was published November 17 in the Advance Online Publication
of the journal Nature Geoscience. The work was supported by the NASA Mars
Data Analysis Program.

For years Mars was considered geologically simplistic, consisting mostly
of one kind of rock, in contrast to the diverse geology of Earth. The
rocks that cover most of Mars's surface are dark-colored volcanic rocks,
called basalt, a type of rock also found throughout Hawaii for instance.

But earlier this year, the Mars Curiosity rover surprised scientists by
discovering soils with a composition similar to granite, a light-colored,
common igneous rock. No one knew what to make of the discovery because
it was limited to one site on Mars.

The new study bolsters the evidence for granite on Mars by using remote
sensing techniques with infrared spectroscopy to survey a large volcano
on Mars that was active for billions of years. The volcano is dust-free,
making it ideal for the study. Most volcanoes on Mars are blanketed with
dust, but this volcano is being sand-blasted by some of the fastest-moving
sand dunes on Mars, sweeping away any dust that might fall on the volcano.
Inside, the research team found rich deposits of feldspar, which came
as a surprise.

"Using the kind of infrared spectroscopic technique we were using, you
shouldn't really be able to detect feldspar minerals, unless there's really,
really a lot of feldspar and very little of the dark minerals that you
get in basalt," Wray said.

The location of the feldspar and absence of dark minerals inside the ancient
volcano provides an explanation for how granite could form on Mars. While
the magma slowly cools in the subsurface, low density melt separates from
dense crystals in a process called fractionation. The cycle is repeated
over and over for millennia until granite is formed. This process could
happen inside of a volcano that is active over a long period of time,
according to the computer simulations run in collaboration with Josef
Dufek, who is also an associate professor in the School of Earth and
Atmospheric Sciences at Georgia Tech.

"We think some of the volcanoes on Mars were sporadically active for billions
of years," Wray said. "It seems plausible that in a volcano you could
get enough iterations of that reprocessing that you could form something
like granite."

This process is sometimes referred to as igneous distillation. In this
case the distillation progressively enriches the melt in silica, which
makes the melt, and eventual rock, lower density and gives it the physical
properties of granite.

"These compositions are roughly similar to those comprising the plutons
at Yosemite or erupting magmas at Mount St. Helens, and are dramatically
different than the basalts that dominate the rest of the planet," Dufek
said.

Another study published in the same edition of Nature Geoscience by a
different research team offers another interpretation for the feldspar-rich
signature on Mars. That team, from the European Southern Observatory and
the University of Paris, found a similar signature elsewhere on Mars,
but likens the rocks to anorthosite, which is common on the moon. Wray
believes the context of the feldspar minerals inside of the volcano makes
a stronger argument for granite. Mars hasn't been known to contain much
of either anorthosite or granite, so either way, the findings suggest
the Red Planet is more geologically interesting than before.

"We talk about water on Mars all the time, but the history of volcanism
on Mars is another thing that we'd like to try to understand," Wray said.
"What kinds of rocks have been forming over the planet's history? We thought
that it was a pretty easy answer, but we're now joining the emerging chorus
saying things may be a little bit more diverse on Mars, as they are on
Earth."

This research is supported by the NASA Mars Data Analysis Program under
award NNX13AH80G. Any conclusions or opinions are those of the authors
and do not necessarily represent the official views of the sponsoring
agencies.

CITATION: J Wray, et al. "Prolonged magmatic activity on Mars inferred
from the detection of felsic rocks." (Nature Geoscience, 2013)
http://dx.doi.org/10.1038/NGEO1994 .

Research News
Georgia Institute of Technology
177 North Avenue
Atlanta, Georgia 30332-0181 USA

Media Contacts: Brett Israel (404-385-1933) (brett.israel at comm.gatech.edu)
or John Toon (404-8946986) (jtoon at gatech.edu)

Writer: Brett Israel
Received on Tue 19 Nov 2013 01:13:34 PM PST