Geography Reference
In-Depth Information
1)
selecting typical morphological models for possible CRS of the
region;
2)
selecting diagnostic criteria to prove extraterrestrial genesis of RS;
3)
comparing the RS in point with the proven cosmogenic structures;
4)
revealing contrasts of the discovered elements with the surrounding
terrain.
To investigate the crater-related landforms, we use Google Earth satellite
images in addition to the shaded relief model. In this study we refer only to the
impact structures from EISC [1] that are in good conditions, with undisturbed
craters located in tectonically stable areas (cratons or shields), with minimum
of magmatism and sedimentary cover.
The approach was applied earlier to Rudny Altai, where the primary
cosmogenic terrain has been perfectly preserved, and led to discovery of
morphological elements of potential astroblemes (later confirmed in other
regions as well), for example
[62]:
raised rims
,
shadow
of
central cavity
,
“braces”
(called ―
bank ridge
‖, ―
central impact cone
‖, and ―
stiffening ribs
―,
respectively, in [62]),and
mini-craters
.
Post-Impact Environmental Effects on the Crater Shape
Identification of
CRSs may be problematic because post-impact
environmental effects (e.g., erosion) can distort the proportions of the crater
elements. However, according to evidence from many regions with preserved
original cosmogenic terrain [1], erosion is less destructive for large craters (D
> 1 km) than subsequent impact events or tectonic activity. For instance, the
India-Eurasia collision, which has produced the great Himalayas-Tien-Shan-
Altai-Sayan collisional system, can have ―milled" many older astroblemes.
Therefore, in identifying an impact crater one has to be aware of its possible
modification by later tectonic movements (e.g., the case of Sudbury [1, 61]).
We [62] revealed such tectonic effects on the morphology of the potential
Madagascar
1-5 impact structures discovered in 2006 by Matteo Chinellato
(Tessera, Venetia, Italy). With the above method, we have identified both the
main morphological elements and the post-impact tectonic evolution of
Madagascar 1 [1] (D = 290 km) (Figures 30 a-c). Namely, we recognized the
other half of the Madagascar-1 giant crater on the African plate [62] according
to its typical morphological elements of a depression, raised rims (Figure 30a)
and a central peak (Figure 30c), besides the elements of RS deciphering [70].
