Science Seminars

11/19/2015 – Discovery of alunite in Cross Crater using MRO CRISM: Evidence for Steam-Heated Hydrothermal Deposits on Mars

Speaker: Gregg Swayze (USGS)
Date: Thursday, Nov 19, 2020
Time: 4:00 PM
Location: SPSC W120

Seminar Abstract:

Cross Crater is a 65-km impact crater, formed about 3.8 Ga in the Noachian highlands of the Terra Sirenum region of Mars, and it hosts abundant Al-phyllosilicate and sulfate deposits. High spatial resolution data from MRO’s CRISM, HiRISE, and CTX instruments and from Mar Express’ OMEGA and HRSC instruments were used to examine the distribution of these minerals. A large (10 x 5 km) alunite – kaolinite deposit crops out in layered units deposited at the foot of the SW crater wall. Other kaolinite-rich areas crop out discontinuously along the foot of the crater wall, while opaline/montmorillonite deposits are exposed in topographically lower, polygonally fractured units on the crater floor. Formation of alunite requires acidic water usually with a pH < 4. For the most part, exposures of alunite encircled by kaolinite are reminiscent of alteration patterns found in relict hydrothermal deposits common in volcanic regions here on Earth. Spectrothermometry of the Cross Crater alunite suggests it formed at temperatures relatively lower (< 100°C) than those of most terrestrial hydrothermal alunite, but its formation temperature may have been influence by lower atmospheric pressures. The alunite – kaolinite deposits in Cross Crater may be evidence for a large steam-heated hydrothermal system that formed along the margin of an ephemeral crater lake that dried up during the late Noachian or early Hesperian when there was widespread volcanism and release of SO2. If these deposits are related to hydrothermal activity, then they present a tantalizing target for a future rover mission to look for evidence of past life.