Amazonian fluvial outflow channels in Jovis Tholus region, Mars

摘要

Outflow channels are prevalent on the surface of Mars, and they are one of the strongest lines of evidence for fluvial activity. The purported presence of some of the channel networks on the Amazonian surface provides evidence for recent surficial fluvial activity. We describe morphological evidence collectively diagnostic of fluvial origin for the channels located northwest (NW) of Jovis Tholus, within the Tharsis volcanic province. The fluvial relationships are deciphered from (1) morphological analysis of catastrophic effusion associated with the graben system superposed over the NW portion of an unnamed crater ejecta (19.85°N, 118.03°W) and (2) crater-size frequency distributions of unnamed crater ejecta revealing the tentative period of the fluvial activity. Channels, streamlined/curvilinear islands, terraces, divide crossing, crossover channels, networks of braided-like channels, and eroded ejecta are collectively suggestive of fluvial outflow that emanated from the graben. Chronological analysis revealed that the unnamed crater formed at ~3.4 Ga. Subsequently, the NW part of crater ejecta was incised by a channel network originated from the graben. Furthermore, we infer that the current channel floor has undergone volcanic and aeolian resurfacing to some extent, and the estimated modeled resurfaced channel age is ~0.2-0.5 Ga. This reveals that the fluvial activity possibly occurred after the crater formation, but before channel floor resurfacing, which is during Early to Middle Amazonian. Nevertheless, the potential source for the channel formation likely persisted under this region since the pre-Amazonian epoch. The suite of these fluvial features inferred within the Jovis Tholus region outflow channel system thus adds one another evidence for Amazonian fluvial activity.