Exploring Mt Sharp north of the dunes - Part 1: Beyond Pahrump Hills, Site 45-50, Sol 923-1147, March 12-October 28, 2015 |
Exploring Mt Sharp north of the dunes - Part 1: Beyond Pahrump Hills, Site 45-50, Sol 923-1147, March 12-October 28, 2015 |
Mar 12 2015, 08:38 PM
Post
#16
|
|
Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
Finally drove away from Pahrump Hills on sol 923. Wheel tracks sure are piling up at the end of the drive -- there seems to have been quite a bit of slip.
[admin note: I was going to start a new thread for this, but realized our thread naming may be a bit out of whack because we're really not journeying to Mt Sharp anymore, are we? We'll discuss it with admins and I'll move/rename posts when we figure out our naming schema.] -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
|
|
|
Apr 6 2015, 12:10 AM
Post
#17
|
|
Senior Member Group: Members Posts: 1044 Joined: 17-February 09 Member No.: 4605 |
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.
|
|
|
Apr 6 2015, 11:11 PM
Post
#18
|
|
Member Group: Members Posts: 153 Joined: 8-February 04 From: Phoenix, AZ USA Member No.: 9 |
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. -------------------- Tim Demko
BioLink site |
|
|
Apr 6 2015, 11:25 PM
Post
#19
|
|
Member Group: Members Posts: 153 Joined: 8-February 04 From: Phoenix, AZ USA Member No.: 9 |
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!) -------------------- Tim Demko
BioLink site |
|
|
Lo-Fi Version | Time is now: 29th May 2024 - 02:41 PM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |