Abstract:
Early cessation of Mars’ internal dynamo has resulted in excellent preservation of geological and geomorphological structures on its surface through time, unlike Earth where almost all the tectonic and geomorphic signatures of antiquities have been destroyed and re-organized. The present study area, Noachis Terra, in the southern highlands of Mars, is one such terrain, where the morphotectonic structures are found to be fossilized within the rocks of all timeframe. These morphotectonic features are the key to the understanding of the palaeo-tectonism and hence are the primary objects of investigations of the present study. This research identifies these features and characterizes each of these in detail. The study presents a detailed morphotectonic map of Noachis Terra in a scale of 1:12,000,000, which was unavailable till date. The entire area was subdivided into four different tectonic domains, each of which was found to have unique tectonic characteristics. These four domains were explored in detail and mapped in the scale of 1:2,500,000 to 1:5,000,000 in this study. The tectonic evolution of the four tectonic domains has been described in this study with the aid of these maps. The control of both emergent and non-emergent tectonic structures on the courses of the Martian channels observed in Domain III and IV of the study area have been statistically tested by cross-correlation methods. Palaeostress analyses done from the orientations of the tectonic structures mapped clearly shows the nature of the shift of the principal stress directions both spatially and temporally in the Noachis Terra. This is significant as it hints to the changing nature of local stress fields vis-à-vis the global stress field of Martian crust. The present study also elaborates on the chronology of the structures, seen in the area, with special emphasis on Domains III and IV. Wrinkle ridges of the western part of Noachis Terra (Domain I) were formed during the early Noachian time under the influence of Tharsis volcano-tectonic province. Large scale grabens in the eastern part of Noachis Terra (Domain II) were formed due to lithospheric stretching related to isostatic adjustment of the Hellas basin during the late Noachian time. The present study reports a set of fossae from the central part of Noachis terra (Domain IV), which was formed in late Noachian time (~3.79 Ga), after the formation of grabens in Domain II. The fossae, identified in the north-western part of the Noachis Terra (Domain III), formed in early Hesperian (~3.69 Ga), are thought to be associated with the Valles Marineris formation. It, therefore, appears that Noachis Terra is a heterogeneous terrain with diverse history of tectonic evolution; the nature of tectonism quite dissimilar to the present day plate tectonism operative on earth.
