Possible lithospheric plate movement on Inverness Corona, Miranda

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Miranda is a small icy satellite of Uranus. Two main different types of terrain are usually distinguished in its surface: ancient cratered plains and three endogenically resurfaced areas called coronae. Inverness Corona is located close to the South Pole. It is trapezoidal in shape, and displays an inner, rectangular, dark region, adjacent to a bright chevron-shaped area (the "chevron"), also located inside the corona. It has been previously hypothesized that the two branches of the chevron may be rift arms, being the Verona Rupes graben, which joins the chevron at a common apex, the failed arm of a triple-rift junction. Crosscutting relationships indicate that the chevron is younger than the inner dark region. The northern outline of this region shows several similarities with the chevron northern outline. If the inner region is considered as a rigid lithospheric microplate, entirely surrounded by relatively stable lithosphere, both outlines can be reasonably fitted together by means of a 14° clockwise rotation of that microplate about the Euler pole (-72° Lat., 8° Lon.). In this reconstruction: 1) the hypothetic microplate is reassembled with the outer part of the corona, which has the same albedo; 2) the northern part of the chevron disappears, and the eastern part is reduced to a band running almost radially from the south pole; and 3) ridges and troughs both in the microplate and in the northern and eastern outer parts of the corona become parallel to each other, showing a possibly related origin. The anticlockwise rotation of the Inverness microplate would have implied a displacement of up to 30 km, accompanied by extension and spreading of the icy lithosphere along the eastern and northern parts of Inverness. This is in agreement with the existence of normal faults on these sides of the corona. The chevron has been previously interpreted as made up by cryovolcanic flows possibly originated from large fissures. In the global picture shown here, the chevron, at least in part, would represent material extruded during or after the microplate rotation, filling the gap created by this motion. On the other hand, this movement would have caused lithospheric convergence in the western and southern sides of the corona. The way this convergence could have been accommodated is not clear. The western side and the northwestern and southwestern corners of Inverness display subparallel convex ridges separated by narrow troughs. Some of the ridges also show semiconvex terminations ending in the cratered terrain. These morphologies might be consistent with those of folds and/or imbricate thrust sheets that could have partly accommodated this convergence. The existence of normal faults running parallel to part of the southern side of Inverness Corona may not be incongruent with the lithospheric convergence deduced here if that faults did not form contemporaneously with the microplate motion here suggested.

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