Detailed geomorphic and structural mapping of five Martian basins and preliminary study of eleven other basins reveal four characteristic styles of modification that relate to the degree and age of past tectonic activity. Within regions that exhibit no evidence for tectonic activity, the modification style can be used to distinguish areas dominated by different exogenic processes. A framework for understanding these different styles of basin modification is provided

Mcgill, G. E.

Schultz, P. M.

Stam, M.

English

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https://ntrs.nasa.gov/search.jsp?R=19850004539 2020-03-20T19:53:32+00:00Z
ZTechnical Report
1,'isitimg-Odduate Fellow at the Lunar and Planetary I stitute
6 June 1983 - 15 December 1983
MARTIAN IMPACT BASINS: MORPHOLOGY D T.FFERENCES AND TECTONIC
PROVINCES.	 Marianne Stam*, Peter H. Schultz**, and George E. McGill*
(*Dept. of Geology and Geography, Univ. of Massachisetts, Amherst, MA
01003;	 **Lunar and Planetary Institute, 3303 NASA Road 1, Houston, TX
77058)
Detailed geomorphic and structural mapping of five martian basins
and preliminary study of eleven other basins reveal four characteristic
styles	 of	 modification	 that	 relate	 to	 the	 degree	 and	 age	 of	 past	 tectonic
W activity.	 Within	 regions	 that	 exhibit	 no	 evidence	 for	 tectonic	 activity
bo ("inactive"),	 the	 modification	 style	 can	 be	 used	 to	 distinguish	 areas
(J,° dominated by different	 exogenic	 processes.	 'This	 study provides a	 framework
1	 [ for	 understanding	 these	 different	 styles	 of	 basin modificaticn 	 (1).
Basins	 in	 regions	 that	 have	 experienced	 extensive	 tectonic	 activity
("active")	 consist	 of	 two	 types	 that	 depend	 on	 whether	 the	 structures
s present	 are	 due	 to	 extension
	
or	 to	 compression.	 Al	 Qahira,	 Aram	 Chaos,
rn Chryse,	 Ladon,	 and	 Mangala
	
are	 in	 extensional	 crustal	 regimes;	 they	 are
characterized	 by	 chaotic	 terrain,	 well	 developed	 runoff	 and	 outflow chan-
aa nels,	 numerous	 floor-fractured	 craters	 (Table	 1)	 and,	 with	 the	 exception
rn
0 of	 Mangala.	 (which	 is	 largely	 obscured),	 ?ow	 ring-spacing	 values.	 These
,.	 a geomorphic	 characteristics
	
vary	 somewhat	 among	 the	 five	 basins,	 perhaps
Ln as	 a	 function	 of	 relative	 distance	 from Tharsis	 and	 Elysium.	 For example,z	 ^
H	 U Al	 Qahira	 is	 much	 closer
	 to	 the	 older	 Elysium	 province	 than	 are	 Ladon
4 ;) R and	 Aram	 Chaos,	 and	 the	 latter	 two	 have	 be ter	 preserved	 floor-fractured
z cratt-r-s,	 chaotic	 terrain,	 and	 outflow	 channels.	 From	 counts	 of	 craters
N 75ki.	 in	 diameter,	 the	 chaotic	 terrain	 associated	 with	 Al	 Qahira	 is	 older
than	 that	 associated	 with	 Ladon.	 These	 observations	 a e	 consistent	 with
modification	 of	 the	 basins	 at	 different	 times;	 earlier	 for	 basins	 closer
to	 the	 older	 center	 of	 tectonic	 activity,	 Elysium.	 As	 a	 group,	 these
A ^^
Z z five	 basins	 appear	 to	 have	 suffered	 the	 most	 endogenic	 modification	 of
m	
q
an	 on	 M rs.	 This	 is	 inferred	 to	 be	 the	 result	 of	 their	 settingsY	 s	 within^	 g
areas dominated by relatively
	
recent
	 extensional	 tectonics.
tiu I Sirenum	 basin	 is	 located	 in	 an	 "active"	 crustal	 region	 with	 NW-SE
14 trending	 ridges	 believed	 due	 to	 compressional	 tectonics.	 Sire p um	 is
w V degraded,	 with	 many	 heavily	 and	 lightly	 furrowed	 areas	 and	 furrowedIJ,-..1a
-I ^ N
craters.	 A	 large	 compressional	 ridge
	
system	 collars	 the	 western	 portion
o y 7 — of	 its	 innermost ring	 (2).	 Chaotic terrain and outflow and runoff channels
are	 absent,	 and	 floor-fractured
	 craters	 are	 rare,	 in	 contrast	 to	 the
r- ^+ rejuvenated basins of the extensional regions near Tharsis and 	 Elysium.
i4	w ,^ South	 of	 Lyot	 and	 Deuteronilus
	
A	 and	 B	 ("active/inactive"),	 found
U	
c v on	 the	 martian	 crustal	 dichotomy	 boundary,	 are	 characterized	 by	 planated
-+ or	 inverted	 topography,	 fretted	 terrain,	 and	 "fretted	 channels"	 (3).
:14 _ e They appear	 to have undergone complete planation, 	 or were	 filled completely
;a
'`^ and	 later	 exhumed	 by	 mass	 wasting	 processes	 (1).	 Their	 complex	 history
suggests
	
extensive
	 endogenic	 modification	 in	 thw-' past	 but	 relatively
"inactive"	 conditions	 now.	 Presently,	 the	 morphologies	 of	 these	 basins
are dominated by exogenic
	 (periglacial?)	 processes.	 ­
Basins	 in	 "inactive"	 crustal	 regions	 are	 characterized	 by	 a	 mantled
appearance	 or	 by	 heavily	 furrowed	 and	 channelled	 basic	 rims." (Table	 1).
Cassini	 and	 Cassini	 A	 are	 heavily	 mantled	 basins,N Wth	 rings expressed
by	 furrowe-'	 scarps	 rather	 than massifs or knobs. 	 Thg-;f^rt• owing	 is	 inferred
to	 result	 from	 a	 mass-wasting	 process	 that	 "pasgiVe ""	 re}ji'venates	 the
mantled	 rings	 (1).	 In	 other	 "inactive"	 crustal	 zones,	 basins	 are	 charac-
terized	 by	 heavily	 furrowed	 and	 channelled	 rims,	 and	 4-hIgh	 ring-spacing
R.
averages. Examples include: Schiaparelli, Huygens, Overlapped by Newcomb
Crater, Overlapped by Schiaparelli, and West of Le Verrier (Table 1).
Unlike the Cassini basins, these structures are mostly modified by
erosional processes. Fu:cowing and channelling preserve the identy of
their ring s:arp forms while, at the same time, these processes are back-
wasting the scarps.	 These basins are located in an "inactive" crustal
r4,gion that is relatively old and is or was volatile rich.
In conclusion, martian impact basins express at least four major
styles of modification. 	 These styles of rejuvenation and degradation
are important indicators of: 1) the intensit: r and age of past tectonic
activity, 2) whether the tectonic activity was extensile or compressive,
and 3) the types of exogeni(. processes that dominate in different stable
crustal regions on Mars.
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(1) Schultz, P.H., Schultz, R.A. and Rogers, J. (1982)_."Jour.• Geophys.
Research, p. 9803-9820. (2) Chicarro, A.F. Schultz, P.H., and Masson,
P. (1983) Lunar and Planetary Science XIV, p. 88-999 -_Lunar and Planetary
Institute, Houston.	 (3) Sharp, R.P. and Malin, M.C. (1975) Geol.	 Soc.
Amer. Bull., 86, p. 593-609.	 (4) Croft, S.K. (1979) UCLA Ph.D.	 Disser-
tation.	 (5) Pike, R.J. (1981) Rpts. of Planetary Geology Program, NASA
TM 84211, p. 123-125.
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Martian impact basins: Morphology differences and tectonic provinces

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