Abstract
Zephyria Tholus has been proposed to be a composite volcano, however, detailed geomorphological study was not carried out due to limited high-resolution remote sensing data. Here we use MOLA, THEMIS, CTX and HiRISE data to conduct topographical and geomorphological analysis of Zephyria Tholus. We identify extensive valleys and troughs on the flank, which are sector collapse or glacio-fluvial in origin. The valleys and troughs indicate coexistence of different erosion resistance materials, along with the observed solid lava outcrops. There are also layered materials identified on the wall of the largest valley. In addition, perched craters are identified on the top depression and flanks of Zephyria Tholus, indicating the presence of ice-rich layer. We conducted crater size-frequency distribution of the caldera and found the absolute model age is 3.74 (+0.03, −0.04) Ga. The geomorphology evidence and chronology result support the composite volcano nature of Zephyria Tholus, and indicate the magma volatile content in the Aeolis region in Noachian is more than 0.15 wt% if the atmosphere paleo-pressure was similar to present Mars.
Highlights
Large shield volcanoes in the Tharsis and Elysium volcanic province show geomorphological characteristics of low-viscosity effusive basaltic lavas (e.g., [5]), while large ash shields lying in Circum-Hellas region are inferred to form by friable materials [4,6,7,8]
Zephyria Tholus (Figure 1a), centered at ~19.8◦ S, 172.94◦ E, lies in the Aeolis region of Mars. This cone-shaped feature is ~350 km away from the center of Gusev crater, and the adjacent has been mapped as the Early Noachian Highland unit [10]
There is a depression on the top of Zephyria Tholus with a diameter of ~8.4 km, and it slightly tilts to the north (Figure 1b)
Summary
Mars has a long history of volcanism [1,2]. Various volcanic landforms have been identified since the Mariner 9 and Viking data [3,4]. Large shield volcanoes in the Tharsis and Elysium volcanic province show geomorphological characteristics of low-viscosity effusive basaltic lavas (e.g., [5]), while large ash shields lying in Circum-Hellas region are inferred to form by friable materials [4,6,7,8]. It has been proposed that explosive eruption was dominated in early Mars geological history [9,10], and effusive eruption dominated later [11]. The transition of explosive and effusive eruption generates composite volcanoes. Extensive composite volcanoes should have existed on Mars.
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