TMOAA/ET/EBE Threads (OT for sure but highly significant)

Origins of magnetite nanocrystals in Martian meteorite
ALH84001
K.L. Thomas-Keprta a,*, S.J. Clemett a,*, D.S. McKay b, E.K. Gibson b,
S.J. Wentworth a
aESCG at NASA/Johnson Space Center, Houston, TX 77058, USA
b KR, ARES, NASA/Johnson Space Center, Houston, TX 77058, USA
Received 20 July 2008; accepted in revised form 18 May 2009; available online 16 June 2009, published in gca journal November 24, 2009


From the actual research article:

"Abstract
The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of
microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian
epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans.
Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical
and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that
these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of magnetite
and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. For
example, the magnetites might have already been present in the aqueous fluids from which the carbonates were believed to
have been deposited. We have sought to resolve between these hypotheses through the detailed characterization of the compositional
and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in
which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation.
We then compared our observations with those from experimental thermal decomposition studies of sideritic carbonates
under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal magnetites present
in the carbonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead,
we find there is considerable evidence in support of an alternative allochthonous origin for the magnetite unrelated to any
shock or thermal processing of the carbonates.
 2009 Published by Elsevier Ltd."



"5. SUMMARY AND CONCLUSIONS
Two heating scenarios described herein provide the geological
context for the decomposition models developed
independently by Brearley (2003) and Treiman (2003).
These models are contradictory; that is, they cannot both
have occurred since application of one model negates the
applicability of the other. The first is based on carbonate
decomposition occurring under “extreme disequilibrium
conditions” in which “kinetics are the dominant controlling
factor” determining the chemical and physical nature of the
magnetites that are formed. Although never explicitly addressed,
this model is most consistent with the impact event
that ejected ALH84001 from Mars. In the second model,
carbonate decomposition occurs “at some depth beneath
the Martian surface where the pressure was greater than
the atmospheric pressure and the temperature declined
slowly.” However, based on kinetic and thermodynamic
arguments, both models proposed for the high temperature,
inorganic formation of ALH84001 magnetite would not
have produced the results observed in ALH84001 carbonate
disks. ALH84001 carbonate assemblages can be best explained
as the result of low temperature, disequilibrium precipitation
from a single fluid with variable composition or from
multiple fluids. Nanophase magnetite and Fe-sulfides were
suspended in fluids that formed the disk cores and rims.
After deposition ALH84001 carbonate disks were exposed
to multiple fluids containing amorphous silica, additional
nanophase magnetite, and S- and Fe-rich phases, some of
which were deposited in veins. While the majority of
ALH84001 magnetites were deposited in silica enriched
rims and veins, some are also distributed throughout the
cores and within the magnesite bands. Most magnetites
are chemically pure, although a few contain minor Al/Cr.
Their presence is inconsistent with formation by thermal
decomposition of their host carbonate. We suggest that
the majority of ALH84001 magnetites has an allochthonous
origin and was added to the carbonate system from
an outside source. This origin does not exclude the possibility
that a fraction is consistent with formation by biogenic
processes, as proposed in previous studies."

“The Allen Hills Martian meteorite suggests there is evidence
for life on ancient Mars. If that is true ... there could still be life –
particularly in the subsurface regions of Mars”
 Kathie Thomas-Keptra, Ph.D., NASA Johnson Space Center

“There are objects in our atmosphere which are technically
miles in advance of anything that we can deploy, that we have no means
of stopping them coming here, and that we have no defense against them,
should they be hostile.” - Lord and Admiral Peter John Hill-Norton,
former U. K. Chief of Defense Staff and Chmn., NATO Military Comm.,
2000 TV interview before his death in 2004