Oblique-Impact Complex on Mars including Syria and Sinai Planum Rev. 2016-03
Syria Planum and Sinai Planum lie at the center of a complex crustal
to be the result of a multiple, hypervelocity (> 6 km/sec) impact event on Mars. Syria
Planum is shown to be a composite, asymmetric crater formed by impact of at least two
bolides whereas Sinai Planum is the result of a chain of tightly-clustered impacts (fig. 1),
perhaps from a frgameted cluster of bolides or partly the result of spalled projectiles
(Schultz and Gault, 1990). The impact complex is portrayed below as having tectonic
elements including a circumferential crustal welt, a compressed foreland wedge and an
extensional strain regime in it's wake where Olympus Mons and Tharsus Montes
volcanisim lie (fig. 1).
Figure 1. Part of the Topographic Map of Mars (2002) centered on the Syria,
and Solis Planums. Click on the central part of the image for a more detailed view.
A set of craters located between longitudea 20o
to 60o W and 0o to 30oS latitude are
centered in a crustal welt having about 135o surface span. Other tectonic features include
near-crater fracturing and symmetric topographic ridges fanning outward from the wedge
apex toward a prominent foreland scarp. Solis Planum and Thaumasia Planum are probably
plateaus along with other foreland fault scarps forming the toe of the crustal wedge.
Details of the proposed craters are capture in figure 2. Figures 2a (uninterpreted), 2b
(interpreted), and 2c show a series of faint outer rims within Syria Planum that probably
result from multiple, overlapping oblique impacts. Figure 2d covers the Tharsis Montes
region and the symmetry of the volcanisim with respect to the crater complex. The
horizontal component of the bolide trajectories as modeled in figures 3 and 4 are based on
Figure 2. NASA photographs showing details of the crater region.
Figures 3 and 4 include primitive and rendered views of the impact complex
kilometers using AutoCad software. Map sectors are defined relative to the impact
center that include compressional (C), extensional (E), and marginal (M) regions. The
compressional region of crustal wedging lies foreland of the craters in the direction
of the inferred flight trajectories. The model shows a set of three overlapping wedges
having structural components including lateral shear fracture systems, topographic
ridges, and crustal scarps associated with crustal thickening and uplift. Valley Marineris
flanks the compressional wede to one side and coocides with a fault zone of intense
crustal fracturing, although this well known crustal feature has a complex structutal
history including other impact overprints.
The volcanic center of Olympic Mons and Tharsis Montes occupy the crater
where the crust and mantle were extended with steeply-dipping extension fractures
that needed to penetrating to mantle depths in order to initiate decompression melting
and generation of mantle melts that subsequently ascended along these fracture that
fed the volcanoes. The inferred fractures are now buried beneath volcanic flows. Even
the alignment of Tharsis Montes belies the strike angle and concomminant extension
directions lying approximatley normal to the bolide flight trajectory (fig. 3).
Figure 3. AutoCADR14 model of the impact complex. Click on any image for more details.
Marginal regions have the lowest topographic elevations in the circumferential
crustal welt and correlate to areas that probably contain near-impact ejecta and
crustal fractures having a different trend from those in the compressional region.
The diameter of the circumferential welt roughly corresponds to the diameter of
the Martian core (1700 km) as detailed in profile (fig. 4). The crustal welt is also
cut by arcuate lineations assumed to parallel fracture dispersed in front of the
impacts, as ripple marks cast in front of a stone splash. The bolide angle of descent
is modeled below as being about 30o from horizontal, although this is highly
Figure 4. Profile diagram of Mars showing the geometric relations
associated with the proposed impact structure.
Two global perspectives of the impact complex are shown in figure 5 using
Global Surveyor, orbital laser altimetry (fig. 5a) and gravity (5b) data. Digital traces
of geological structures from the Viking Orbiter-based geologic maps of Mars are
superimposed on the geophysical coverage that include undifferentiated grabens,
calderas, wrinkle ridges, channels, crustal scarps, depressions, and crater rims (Skinner
and others, 2006).
Figure 5. Mars Global Surveyor altimetry (left) and gravity (right) data rendered
using ESRI ArcGlobe. Click on any image for more details.
The composite set of tectonic features are proposed to result from impact
and mantle fracturing and upheaval, and perhaps relaxation. Here, the impact tectonic
features are frozen in time due to the lack of active orogenic processes that would
otherwise mask such effects.
Figure 6. NASA Viking Orbiter image showing global view of Sinai Planum and Valley
Marineris and other components of the proposed impact complex. Click on the image
for a more-detailed view.
This impact event created a huge energy flux and solid-body disturbance on
that genrated body waves that reflecting and refracting off major phase boundaries
in the planet's interior while leaving telltales scars of brittle deformation at the surface.
The nature of the mantle deformation necessary to produce such a crustal signature
is only speculative but may originate from primary reflections of compression waves
gnerated by impact and resounding off the core-mantle boundary back to the surface
to produce giant concentric welts welts in the planetary lithopshere. Similar geometric
relationships are seen on Earth for known (Herman, 2006) and suspected (Cuvette Central
of Rajmon, 2007) impacts, among other supsected ones. The relative timing and
development of the various ductile and brittle strains and associated volcanic activity
are also unknown. However, most of the brittle crustal disturbance must have been
relatively instantaneous with both ductile flow and igneous activity ensuing. It's
possible that tectonic activity in the form of mantle plumes, perhaps even mantle
dynamics with associated crustal stains persist today, thereby reflecting long-lasting
regional strain effects from this catastrophic event.
Herman, G. C, 2006, Neotectonic setting of the North American Plate in relation
Chicxulub impact: Geological Society America Abstracts with Programs, Vol. 38, No. 7, p. 415
Rajmon, David , 2007, Suspected Earth Impact Sites database, April 13, 2007:
Houston, TX, USA. http://eps.utk.edu/ifsg_files/SEIS/SEIS_database9.xls (Excel 708KB).
Schultz, P. H. and Gault, D. E., 1990, Prolonged global catastophes from
impacts in Sharpton V.L., and Ward, P.D., eds., Global catastrophes in Earth history;
An interdisciplinary conference on impacts, volcanism, and mass mortality: Geological
Society of America Special Paper 247, p. 239-261.
Skinner, J. A., Jr, T. M. Hare, and K. L. Tanaka 2006, Lunar and Planetary
Conference XXXVII, abstract #2331
G.C. Herman, www.impacttectonics.org Rev. 2016-03-05 / 2007-10