Exploring Mt Sharp north of the dunes - Part 1: Beyond Pahrump Hills, Site 45-50, Sol 923-1147, March 12-October 28, 2015 Options

[jvandriel]

Back at Garden City.

The Navcam L view on Sol 944.

Jan van Driel

[PaulH51]

6 image mast camera mosaic of the extended veins at Garden City, images acquired after the drive during sol 944 (April 03, 2015

Contrast marginally stretched to highlight the different surface materials.

[PaulH51]

A section of the mineral filled veins at Garden City acquired on sol 946 (9 MAHLI frames) EDIT : Additional frame added (now 10 MAHLI frames) and roughly stitched and rotated to provide a little context with some earlier mast camera images (sol 929)
....

[serpens]

Nicely done Paul. A consensus seems to be forming that the veins seen here and at Sheepbed represent hydraulic fracture fill. This indicates that the mudstone must have been covered to depth certainly no less than a kilometre and probably much more. But it also implies that there would be a significant thickness of sediment below the mudstone which compacted to provide the high pressure solution necessary to fracture the mudstone cap and form the fracture fill. This means that the basal unit could be much deeper than suggested by Anderson and Bell in their outstanding landing site selection paper.

[PaulH51]

... A consensus seems to be forming that the veins seen here and at Sheepbed represent hydraulic fracture fill....

Thanks Serpens. Earlier I was studying the mineral layering in this particular part of the vein and noting the amount of separate mineral veins. I can not even begin to imagine how long these took to form, but now I can begin to appreciate why they decided to return to this location to gather more data before heading towards the mountain once again.

[serpens]

Yeah, I can see why they want more mineralogy and it will be interesting to get the take of the experts. I don't know if it is just my deranged imagination but there seems to be a couple of examples of sigmoidal fracture fill in your image at post #76 which could imply rotation of segments of mudstone. The thicker white fracture fill which I assume is the ubiquitous calcium sulphate could imply hydration of anhydrite to gypsum which gives a hefty increase in volume.

[PaulH51]

....a couple of examples of sigmoidal fracture fill in your image at post #76

This small R-MastCam mosaic may help you decide if one of those areas is a sigmoidal fracture fill, differential erosion, or something else entirely

This is certainly an interesting location, whatever these features are

[craigmcg]

While following this thread, I saw this come by my news feed. Visually similar to my non-geologist eye.

http://www.dpreview.com/galleries/30650321...um=death-valley

[serpens]

This small R-MastCam mosaic may help you decide if one of those areas is a sigmoidal fracture fill....

I was thinking more along the lines of the "S" and "C" structures here.

Attached thumbnail(s)

 

[PaulH51]

I was thinking more along the lines of the "S" and "C" structures here.

OK I'll watch out for any R-MastCam images that may help.

[eliBonora]

Some of our latest processing

sol 938 anaglyph


wheels sol 939


Kanosh anaglyph sol 940


and some more vivid MAHLI sol 942






@PaulH51 nice composition!

[Mr. Bergstrom]

craigmcg, thank you for uploading that photo. Has helped me put it into a Terran context. Have similar geological processes produced what we're seeing at Garden City?

PaulH51, 'A Puzzle For The Geologists' wow pretty impressive mosaic, how long did it take you to do? Were the images literally taken from the raw images page on NASA's site here http://marsmobile.jpl.nasa.gov/msl/multime...?s=#/?slide=946 , and then stitched together by yourself? Loved it anyway!

[tdemko]

A consensus seems to be forming that the veins seen here and at Sheepbed represent hydraulic fracture fill. This indicates that the mudstone must have been covered to depth certainly no less than a kilometre and probably much more. But it also implies that there would be a significant thickness of sediment below the mudstone which compacted to provide the high pressure solution necessary to fracture the mudstone cap and form the fracture fill.

Yes, the source of the overpressure that resulted in the brittle tensile failure of the mudstone is where my curiosity(!) lies. An authigenic or mineralogic volume increase, as you've stated, could certainly be a good candidate, especially when dealing with anhydrous and hydrated sulphate minerals. Hydrated clays also can exhibit significant volume changes as water is added and lost from their crystal lattice. Deep burial, on its own, should not cause this type of feature. Deep burial followed by quick exhumation, on the other hand, can do this, in the presence of isolated pressure cells (here the sandstone and mudstone strata). Other terrestrial causes include biogenic and thermogenic hydrocarbon generation, although when this happens at deepest burial, horizontal, rather than vertical tensile fractures can form (the famous "beef" veins of the Yorkshire, Dorset, and Somerset Jurassic exposures). It is interesting that you are seeing sigmoidal fractures and C-S features, suggesting some horizontal stress and shear in addition to the burial/vertical/lithostatic stress. In terrestrial fracture fills associated with overpressure, calcite crystallizes in veins as a distinctive cone-in-cone fabric when there is a component of horizontal stress, rather than the prismatatic, fracture-spanning "beef" fabric associated with overcoming lithostatic stress (nice review article, behind a paywall, here).

The go-to analyses to really determine the source of the overpressure involve determining the phase/PT behavior and composition of fluid inclusions in the fracture fill minerals. Certainly would be candidates for caching for a possible sample return, or reason for including such instrumentation on a future landed mission.

[tdemko]

Deep burial and exhumation could be due to filling of accommodation followed by landscape degradation via erosion, or growth and decay of a thick ice sheet.

(sorry for the additional post, but...I'm a Member!...finally!...100 posts!...it only took 11 years!)

[PaulH51]

PaulH51, 'A Puzzle For The Geologists' .... how long did it take you to do? Were the images literally taken from the raw images page and then stitched together..

Yes, less than a minute to stitch the raw images using "Microsoft Image Composite Editor" (ICE) MS ICE home page I use an older version V1.4.4.0 which I prefer to V2.0. There are many better tools, but this one works for me. PhotoScape then used to add the annotations etc. There is a thread for "MSL Images & Cameras, technical discussions of images, image processing and cameras" Kindly use that thread if you have any other queries re MS ICE, plus there is a host of great material there worth studying