Notices
Results 1 to 16 of 16
Like Tree5Likes
  • 2 Post By John Galt
  • 1 Post By John Galt
  • 1 Post By John Galt
  • 1 Post By John Galt

Thread: Tectonics

  1. #1 Tectonics 
    Forum Freshman
    Join Date
    Jun 2012
    Posts
    66
    Is tectonic activity observable on Mars?


    Reply With Quote  
     

  2.  
     

  3. #2  
    Forum Professor pyoko's Avatar
    Join Date
    Jun 2011
    Location
    Australia
    Posts
    1,094
    Not that I'm aware of. That is why there are places that show layers in just one place that have been undisturbed for much longer than on Earth. Not too sure, though. Maybe there is just a lot less of it.


    It is by will alone I set my mind in motion.
    Reply With Quote  
     

  4. #3  
    Forum Freshman
    Join Date
    Jun 2012
    Posts
    66
    Thanks!
    Reply With Quote  
     

  5. #4  
    Forum Freshman
    Join Date
    Jun 2012
    Posts
    66
    I believe in tectonics and its occurrence, what I wonder though, if there is a consensus in the "core" composition of other planetary objects. If so +/_ what accounts for mountain building on other planets, i.e. the earth moon, mars etc? I have to think that you are correct. What I wonder is how accurate is continental drift? I believe it is valid and true, but when I think of it in terms of other planets I am left with many queries. Thanks! Also, is the question appropriate for the Forum?
    Reply With Quote  
     

  6. #5  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Your question is a good one and you have posted it in the right forum.

    First, is there tectonic activity on Mars? There was tectonic activity on Mars. It is probably now no more, apart from minor adjustments associated with vulcanicity. Here are some notes I've previously put together on the subject.

    The Martian Dichotomy
    The Martian topography falls into two quite distinct regions. “The dichotomy is expressed three ways: as a change in elevation, a change in crustal thickness, and a change in crater density.”[1] The difference in crater density is a reflection of differing ages, a concept and dating technique established during the pre-Apollo lunar mapping[2].

    (As with all generalizations we can nitpick here if we wish. For example, topographic and gravity data determined by the Mars Global Surveyor revealed two distinct crustal types that did not exactly match the dichotomy.
    [3])

    The southern highlands are exactly that – high. They occupy about 60% of the planet. They have an uneven crust that thins progressively northwards. They are heavily cratered and they are old. The northern plains also live up to their name. They are low; they have a thin, uniform crust; they have few craters; they are young.

    Martian researchers recognize that the biggest challenge facing them is to adequately explain this dichotomy. Numerous hypotheses have been put forward, both exogenic and endogenic.

    Collisional Excavation:This is the same mechanism that created the lunar highlands and the low-lying Mare, subsequently infilled by flood basalts
    [4]. During the latter stage of major planetary accretion, possibly during the Heavy Bombardment Phase, chance (or some presently unknown mechanism) concentrated the impacts on the northern half of Mars, thinning the crust by removal of substantial volumes of crustal ejecta, either by a single giant impact[5], or multiple smaller impacts[6]. The single giant impactor hypothesis has recently been revisited[7].

    Mantle ConvectionA number of researchers have proposed that the Martian crust was originally a similar thickness over the entire planet. Thinning of the northern hemisphere occurred as a result of a) a long wave length mantle convective planform[8]; b)erosion of the base of the crust by convection[9],[10]; c) crustal subduction during an early phase of plate tectonics[11]; d) post accretion core formation[12]. Options a) and b) appear to me to remain valid possibilites. c) is discussed in more detail below. d) is rejected since it postulates a lengthy (1 billion year) core formation process which is at odds with the observed residual magnetic fields (see next section) and the U/Pb isotopic ratios of SNC meteorites[13].

    Possible Plate Tectonics on Mars

    Southern Hemisphere Plate Tectonics

    During the aero-braking maneuver to place it in orbit, Mars Global Surveyor detected linear magnetic anomalies in the southern hemisphere of Mars[14]. Researchers, using the data from two full Mars years of polar orbital data and with an improved technique to eliminate the effects of external fields, constructed a global map of remnant crustal magnetization[15]. (I note in passing that the strength of this magnetism is more than an order of magnitude greater than comparable magnetism on the Earth.)

    The similarity between these parallel patterns of magnetic reversal on Mars and those flanking mid-ocean ridges on Earth, immediately suggested a Martian equivalent to sea floor spreading. The patterns are absent from large impact basins, such as Hellas and Argyre, and from the volcanic terrain of the Tharsis bulge. This is consistent with the loss of the Martian dynamo early in history, before the final Heavy Bombardment Phase and Tharsis volcanism, but after crustal formation.

    The researchers provisionally identified two major faults from offsets in the magnetic patterns. The character of these faults shows them to be transform faults, rather than simple strike slip faults. “The great faults in Meridiani are consistent with the properties of transform faults and define an axis of rotation (23°S and 80.5°E) describing the relative motion of two plates, north and south of the equator. The separation of the faults (1,200km) and offset of the putative ridge axis (+/-240km) in Meridiani are comparable with what is observed along ocean ridges on Earth.”

    The Sound of One Hand Clapping

    Zhong’s[16] explanation for the dichotomy is that uneven convection in a young Mars thinned the northern crust. In the south, hot mantle material rose, cooled, and then sank in the north.

    This announcement does not seem to offer anything especially new.
    · In 2001 Zhong reported that conventional models of mantle convection could not account for an internal explanation of the dichotomy. However, a thicker and weaker asthenosphere would allow a single convection cell, which in turn might allow the apparent thinning of the northern crust by mantle convection currents, or build up the crust in the southern hemisphere.
    · In 2004, working with Roberts
    [17], he is struggling to generate the required degree-1 convection cell within a stagnant lid setting. They broach the possibility that “The mobile lid regime may be appropriate if the crust and mantle are sufficiently warm as to decouple the crust and the mantle, as one may expect for the early Mars”.
    · In 2006, again with Roberts
    [18], Zhong reached the conclusion, based on further FEA modeling, that “degree-1 mantle convection induced by a layered viscosity structure may be responsible for the formation of the crustal dichotomy.”
    · Also in 2006, in another paper, they offered a description of the process “Degree-1 mantle convection develops within the first few hundred Ma. The one-plume structure drives a TPW event that places the plume near the equator. Melt associated with the plume is erupted onto the surface above it, thickening the crust in that hemisphere. This melt cools in the ancient global magnetic field and produces remnant magnetism, consistent with suggested paleopole positions near the present-day equator. As the planet cools the lithosphere thickens, reducing the dynamic topography. When Te exceeds about 30km, the geoid above the plume becomes negative and the plume rotates the planet such that it is near the south pole.”
    · Roberts and Zhong
    [19] continue this line in 2007, declaring “that the crustal thickness variations associated with the dichotomy may have driven true polar wander, establishing the north south orientation of the dichotomy very early in Martian history.” In other words, the entire crust was moving relative to the mantle.
    · Also in 2007 Zhong
    [20] argues the case for degree-1 convection, over the alternate endogenic hypotheses (magma ocean[21]; ‘conventional’ plate tectonics[22]).

    (Note: I have referenced only about half of the papers Roberts and Zhong wrote on the subject over this period. A search of the ADS data base will reveal the rest.)

    Conclusion
    These words almost sum up my thoughts: “If Mars ever had plate tectonics, it operated only briefly early in Martian history and was a very feeble mechanism quite dissimilar to Earth’s plate tectonics.”[23] I say almost because if Zhong is correct and the entire crust of Mars moved as one to achieve the current ‘balanced’ orientation – in a manner reminiscent of Hapgood’s hypothesis for the Earth[24] – then the mechanism is anything but feeble.

    Acknowledgements
    For background on the complex topic of mantle convection and for some of the earlier references on Martian convection I am indebted to a rather weighty tome by Schubert, Turcotte and Olson31.

    pyoko and ampwitch like this.
    Reply With Quote  
     

  7. #6  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    References for the above post:

    [1] McFadden. L-A, et al (eds) (2007) Encyclopedia of the Solar System Academic Press p.319

    [2] Schumaker, G. et al (1960) The Moon

    [3] Zuber, M.T. et al (2000) Internal Structure and Early Thermal Evolution of Mars from Mars Global Surveyor Topography and Gravity. Science, Volume 287, Issue 5459, pp. 1788-1793.

    [4] Basaltic Volcanism Study Project (1981) Basaltic Volcanism on the Terrestrial Planets. Lunar and Planetary Institute, p236.

    [5] Wilhelms, D.E. & Squyres, S.W. (1984). The Martian hemispheric dichotomy may be due to a giant impact. Nature 309, 138–40.

    [6] Frey, H. & Schultz, R.A. (1988). Large impact basins and the mega-impact origin for the crustal dichotomy on Mars. Geophys. Res. Lett. 15, 229–32.

    [7] Nimmo, F. et al (2008) Implications of an impact origin for the martian hemispheric dichotomy Nature, 453, Issue 7199, pp. 1220-1223.

    [8] Schubert, G. & Lingenfelter, R.E. (1973) Martian centre of mass – centre of figure offset. Nature 242, 251–2.

    [9] McGill, G.E. & Dimitriou, A.M. (1990) Origin of the Martian global dichotomy by crustal thinning in the late Noachian or early Hesperian. J.Geophys.Res. 95, 12595–605

    [10] Smith, D.E. (1999) The global topography of Mars and implications for surface evolution. Science 284, 1495 – 503.

    [11] Sleep, N.H. (1994) Martian plate tectonics. J.Geophys.Res. 99, 5639–55.

    [12] Davies, G.F. & Arvidson, R.E. (1981) Martian thermal history, core segregation, and tectonics. Icarus 45, 339–46.

    [13] Chen, J.H. & Wasserburg, G.J. (1986) Formation ages and evolution of Shergotty and its parent planet from U–Th–Pb systematics. Geochim.Cosmochim.Acta 50, 955–68.

    [14] Connerney, J.E.P., et al. (1999) Global distribution of crustal magnetization discovered by the Mars Global Surveyor MAG/ER experiment. Science 284, 794–798.

    [15] Connerney, J.E.P., et al (2005) Tectonic implications of Mars crustal magnetism. P.N.A.S. , 102, 14970–14975

    [16] Zhong, S. et al (2000) Degree-1 mantle convection and the crustal dichotomy on Mars. Earth and Planetary Science Letters, Volume 189, Issue 1-2, p. 75-84.

    [17] Roberts, J.H. & Zhong, S. (2004) Degree-1 mantle convection as a process for generating Martian hemispheric dichotomy. Workshop on Martian Hemispheres

    [18] Roberts, J.H. & Zhong, S. (2006) Degree-1 convection in the Martian mantle and the origin of the hemispheric dichotomy. Journal of Geophysical Research, Volume 111, Issue E6,

    [19] Roberts, J.H. & Zhong, S. (2007) The cause for the north south orientation of the crustal dichotomy and the equatorial location of Tharsis on Mars. Icarus, Volume 190, Issue 1, p. 24-31.

    [20] Zhong, S. (2007) Understanding the Early Evolution of Mars and the Formation of Crustal Dichotomy. Lunar and Planetary Science XXXVIII.

    [21] Elkins-Tanton et al., (2005) Earth and Planetary Science Letters, 236, 1 –12.

    [22] Sleep, N.H. (1994) Martian plate tectonics. Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. E3, p. 5,639-5,655

    [23] Kargel, J.S. (2004) Mars – A Warmer, Wetter Planet Springer-Verlag (Praxis) p.59

    [24] Hapgood, C.H. (1956) The Earth’s Shifting Crust. Museum Press
    ampwitch likes this.
    Reply With Quote  
     

  8. #7  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    You ask about core composition. We have reasonably good models the interiors of the terrestrial planets. These are constantly being improved as more and better data are retrieved from planetary probes and as modelling software becomes more sophisticated.

    Mountains on the terrstrial planets, other than the Earth are the result of both vulcanism and impact. Plate tectonics on the Earth is very well establised. As you will see from my earlier post it may have occured on Mars when the planet was very young. Venus apparently underwent a major resurfacing event about 600 million years ago. Mars has been largely quiescent for a billion years or more, though there is some evidence of volcanic activity as recently as ten million years ago. (Methane concentrations in the atmospher may indicate current activity.) The moon and Mercury have been practically dead for a very long time.
    ampwitch likes this.
    Reply With Quote  
     

  9. #8  
    Forum Junior
    Join Date
    Mar 2010
    Posts
    287
    Quote Originally Posted by John Galt View Post

    The Martian Dichotomy
    The Martian topography falls into two quite distinct regions. “The dichotomy is expressed three ways: as a change in elevation, a change in crustal thickness, and a change in crater density.”[1] The difference in crater density is a reflection of differing ages, a concept and dating technique established during the pre-Apollo lunar mapping[2].


    Do you know that this kind of dichotomy is typical of a large asymmetric expansions? Same case for Earth, the Moon, Enceladus, Ganymede.

    Reply With Quote  
     

  10. #9  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Warning: Florian, please do not introduce discussion of highly questionable hypotheses into mainstream discussions. This is not acceptable forum behaviour. You are free to raise these topics, as you have done, in New Hypotheses and Ideas, or in pseudoscience sub forums. Do not reply to this note. If you have an issue with this please contact me or another member of the mod/admin team by pm.
    Reply With Quote  
     

  11. #10  
    Forum Freshman
    Join Date
    Jun 2012
    Posts
    66
    Thanks for the info. A lot !
    Reply With Quote  
     

  12. #11  
    Forum Freshman
    Join Date
    Jun 2012
    Posts
    66
    Reply/question--I was wondering and thinking that Zuber, M.T. et al (2000) Internal Structure and Early Thermal Evolution of Mars from Mars Global Surveyor Topography and Gravity. Science, Volume 287, Issue 5459, pp. 1788-1793. Would be a good place to start. Much Thanks. The question I hope can be posed in this forum...Is Earth, unlike Mars or Mercury, etc. expanding do to a dynamic or more dynamic ,(I hope the right word is) 'convection', than the aforementioned in such a way, although or however minutely detectable, as to potentially change planetary positions? Here's Hoping! Thanks

    Again, Thank You for a valued response.
    Reply With Quote  
     

  13. #12  
    Comet Dust Collector Moderator
    Join Date
    Mar 2011
    Location
    New Jersey, USA
    Posts
    2,848
    Veryhard to understand your question, but if I have it right, all the rocky inner planets become less dynamic convection wise as they continue to cool.
    Reply With Quote  
     

  14. #13  
    Forum Freshman
    Join Date
    Jun 2012
    Posts
    66
    Thanks MeteorWayne for answering my question.
    Reply With Quote  
     

  15. #14  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by ampwitch View Post
    Reply/question--I was wondering and thinking that Zuber, M.T. et al (2000) Internal Structure and Early Thermal Evolution of Mars from Mars Global Surveyor Topography and Gravity. Science, Volume 287, Issue 5459, pp. 1788-1793. Would be a good place to start. Much Thanks. The question I hope can be posed in this forum...Is Earth, unlike Mars or Mercury, etc. expanding do to a dynamic or more dynamic ,(I hope the right word is) 'convection', than the aforementioned in such a way, although or however minutely detectable, as to potentially change planetary positions? Here's Hoping! Thanks

    Again, Thank You for a valued response.
    1. I believe you meant, not as Wayne interpreted, that the Earth's mantle is more active than that of Mercury or Mars. That is correct. As smaller planets their interiors have cooled more rapidly than has the Earth's.
    2. This more active mantle convection on the Earth would not cause or contribute to any expansion. There is no meanigful evidence for expansion and good counter evidence against it.
    3. Even if expansion were occuring this would not alter planetary positions - there is no significant mechanism by which an enlarged planet would alter its orbit.
    ampwitch likes this.
    Reply With Quote  
     

  16. #15  
    Forum Freshman
    Join Date
    Jun 2012
    Posts
    66
    Thank You JohnGalt!!! I had found via Google an article written titled Growing Earth Theory-XEarth. The claims seemed a little peculiar, nevertheless intriguing and perhaps factual. But as a layperson only, I wasn't sure. I did read the article you presented on Martian Dichotomy and really enjoyed it. Next time I will try to present my questions with greater precision and clarity. Again Thanks!!
    Reply With Quote  
     

  17. #16  
    Forum Freshman
    Join Date
    Jun 2012
    Posts
    66
    To John Galt, an apology if I caused a moment of embarrassment to flush over you by my last question. Nonetheless, I am confused, perhaps not new, with trying to understand land bridge from early Pangaea. what I don't understand is, well lots, continental drift. I well know it occurs, again, I have no difficulty with that. What I am trying to think is this; I want to think of the earth as these sort of "islands" floating on a fluid mosaic. But that is incorrect b/c it cannot account for the ocean basins between continents and mountain building that is occurring even at this moment. So I get confused trying to think of the expanse between continents. So here it is, why then isn't there some kind of other mechanism or "island" being sandwiched between continents as they move away from and towards each other? I recognize the sheering, tearing and other tectonic activities but it seems there may well be something else at work that I simple am overlooking. So I know the problem is with the way I am thinking about it and haven't been able to reckon my own flawed thinking. An invitation to clarity. Thanks!
    Reply With Quote  
     

Similar Threads

  1. plate tectonics
    By Steve Miller in forum Earth Sciences
    Replies: 435
    Last Post: July 7th, 2012, 06:29 AM
  2. Tectonics and gravity
    By Pong in forum Earth Sciences
    Replies: 2
    Last Post: March 21st, 2010, 04:56 PM
  3. Plate Tectonics - an on again, off again affair?
    By John Galt in forum Earth Sciences
    Replies: 11
    Last Post: February 11th, 2008, 03:39 PM
  4. Tectonics...???
    By aid in forum Earth Sciences
    Replies: 1
    Last Post: November 17th, 2007, 11:36 AM
  5. Wilson cycles in plate-tectonics
    By Pendragon in forum Earth Sciences
    Replies: 5
    Last Post: February 8th, 2005, 04:03 PM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •