What tell us the presence of carbon in the shock-generated Martian meteorite "Tissint"
 about the genesis of the Shergottite ?
 

Unfortunately, the interpretation of the scientific investigations goes in the wrong direction, as so often. Some authors are not open to new thinking. They can not imagine that the peculiarities found (especially carbon matter) are indications that the shergottite is a rock material from the mantle-sphere of Mars that has reached explosively the surface.
A biotic origin of the carbon matter is doubtful, also the contamination by carbonaceous chondrites. The carbon matter was original enclosed in veins. The C isotopic compositions of the carbon matter are significantly different to the Martian atmospheric CO2. The exceptionally young age of some Shergottites (averaging 175 million years) proves that was still active volcanism on Mars at that time. It is possible that the material direct entered into space. The density of the Martian atmosphere at this time (Jurassic time on Earth) was already very similar to today's. Due to differences in crystallization, it is conceivable that a plug has initially formed in the crust, that was then shoot by a new explosive magma thrust from the mantle to the surface.

The shock-induced, high-pressure phases in Martian meteorites are the result of movements in the mantle magma. The high-P phases in Martian meteorites include produced glass (maskelynite from plagioclase and pyroxene-composition glass), ringwoodite (
ɣ-polymorph of olivine), akimotoite (ilmenite structure of pyroxene), lingunite (Na-hollandite structure of plagioclase), majorite (garnet structure of pyroxene), tuite (ɣ-polymorph of merrillite), stishovite (α-TiO2 structure of quartz) and silicate perovskite (perovskite structure of pyroxene). Most of the high-P phases are polymorphs (more densely packed structure) than low-P minerals. These high-P phases are typically small and were only observed in isolated occurrences in or near shock-induced melts within the meteorites.

 

NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic-bearing fluids on Mars
Yangting LIN et al. --
Meteoritics & Planetary Science 49, Nr 12, 2201–2218 (2014): doi: 10.1111/maps.12389

"Tissint has been heavily shocked, producing shock-melt veins and pockets and abundant fractures. It probably experienced multiple shock events.
Two distinct petrographic settings of carbonaceous grains were found in the adhesive-free section of Tissint. Most carbonaceous matter occurs as fine veins fully filling fractures and cleavages in olivine and pyroxene, but not in maskelynite. These fractures and cleavages terminate at the boundaries of maskelynite, a typical shock feature reported in shergottites..

The carbonaceous components are kerogen-like, based on micro-Raman spectra and multielemental ratios, and were probably deposited from fluids in shock-induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter.

Two types of carbonaceous matter were analyzed with laser micro-Raman spectroscopy. The Raman spectra exhibit a broad G-band centered at 1580 cm-1 and a smaller D-band at 1346 cm-1, similar to those reported for carbon and clearly distinct from those of ordered graphite. The kerogen-like carbon grains entrained in the shock-melt veins have the same Raman spectra as those filling the fracture space, except for the presence of a sharp band at 1327 cm-1, characteristic of the diamond T2G mode and distinguished from the D-band at 1331 cm-1 of the synthetic diamond used to polish the sections. This indicates a transformation of kerogen-like carbon to diamond at high pressure by a shock event and confirms independent observations in other samples of Tissint as well as in NWA-6162 and NWA-856 (El Goresy et al. 2013b).

We assert that the organic matter we found in Tissint is pristine and is not terrestrial contamination.
We have confirmed this by the following lines of evidence: (1) it is deuterium-enriched; (2) the presence of organic matter inclusions in shock-melt veins indicates its formation before production of the veins by shock events on Mars; (3) partial conversion of the organic carbon inclusions entrained in the shock-melt veins to diamond also points to strong pressure conditions."


Representative Raman spectra of the carbonaceous matter in the fractures (blue) and the shock-melt veins (red).
Note the sharp band at 1327-1 cm indicative of the T2G diamond band in the carbonaceous inclusion in the melt vein.

 

MULTIPLE SHOCK EVENTS AND DIAMOND FORMATION ON MARS
A. El Goresy et al
-- 44th Lunar and Planetary Science Conference (2013), 1037.pdf

"NWA-6162 and NWA-856: These shergottites enclose a unique type of broad shock-melt veins with a novel assemblage containing rosette-like objects surrounded by comb-structured net-like pattern. Each of the polygonal comb-like entities contains a small (<2μm) inclusion of carbon. Such bizarre carbon-bearing objects were never observed before in any Martian meteorite. Preliminary laser micro-Raman investigations showed that some of the carbon inclusions in NWA-6162 depict the T2G band of diamond at 1327 cm-1 that shifted 5 wave numbers below the characteristic Raman mode at 1331 cm-1 and further shifted to 1324 cm-1 upon increase of the laser power thus confirming the probable nano-sized diamond nature as previously demonstrated. This is the first report of shock-induced diamond in a Martian sample. We encountered in NWA-856 orderly arranged carbon particles also in comb-like objects in rows in a shock-melt pool. Nature of the carbon particles in Tissint, NWA 6162 and NWA 856 are under investigation and are subject of further detailed Raman study and isotopic scrutiny by NanoSIMS 50L."

A view at high magnification of a shock vein in Tissint depicting tightly packed anhedral fragmented and mobilized majorite-pyropess + magnesiowüstite grains along with fragmented carbon grains of stark variable sizes in their interstices.

A BSE-SEM view at high magnification of a 2-3 μm wide shock melt vein in Tissint depicting liquidus idiomorphic majorite-pyropess + magnesiowüstite crystals and a clot of amoeboid-shaped carbon enclosing rounded majorite grains.

BSE-SEM view of an unusual comb-like texture in Tissint containing carbon inclusion inside each polygonal comb. Some of carbon particles are confirmed to be diamond.