Geologic and Quantitative Spectral Characterization of Carbonate-Bearing Lithologies on Mars

THE GOALS OF OUR PROPOSED WORK ARE TO PERFORM QUANTITATIVE UNMIXING OF CARBONATE-BEARING LITHOLOGIES ACROSS MARS AND DETERMINE (1) CARBONATE PHYLLOSILICATE AND OTHER MINERAL ABUNDANCES AND (2)CONSTRAIN THE INVENTORY OF CO2 IN CARBONATE-BEARING ROCKS IN THE MARTIAN CRUST. CARBONATES CAN BE INDICATIVE OF NEUTRAL TO ALKALINE DEPOSITIONAL SETTINGS POTENTIALLY INDICATING HABITABLE ENVIRONMENTS. THEY ARE ALSO POTENTIAL SINKS FOR ANCIENT MARTIAN CO2 ALTHOUGH THE DEGREE TO WHICH THEY ARE RESPONSIBLE FOR LOSS OF THE ANCIENT MARTIAN ATMOSPHERE IS NOT TIGHTLY CONSTRAINED. CARBONATE OUTCROPS HAVE BEEN IDENTIFIED AND CHARACTERIZED IN SEVERAL NOACHIAN LOCALITIES ON THE MARTIAN SURFACE USING VISIBLE/NEAR- IR DATA FROM THE COMPACT RECONNAISSANCE IMAGING SPECTROMETER FOR MARS (CRISM) INSTRUMENT (E.G. EHLMANN ET AL. 2008; EDWARDS AND EHLMANN 2015; WRAY ET AL. 2016). CARBONATES TEND TO BE MG-BEARING ALTHOUGH MIXED-CATION FE- AND CA-BEARING CARBONATES ARE ALSO COMMON AND TEND TO BE OLDER (WRAY ET AL. 2016). THESE DETECTIONS ARE SEPARATE FROM THE IDENTIFICATION OF ~2-5% CARBONATE IN THE GLOBALLY HOMOGENOUS FINES BY THE MARS GLOBAL SURVEYOR THERMAL EMISSION SPECTROMETER (MGS-TES; BANDFIELD ET AL. 2003). EDWARDS AND EHLMANN (2015) USED CRISM TES AND THEMIS DATA TO CONSTRAIN THE CARBONATE ABUNDANCE IN NILLI FOSSAE TO 5-15%. IN-SITU OBSERVATIONS BY THE SPIRIT ROVER IDENTIFIED CARBONATES AT THE 16-34 WT.% LEVEL IN THE COMANCHE OUTCROP AT GUSEV CRATER. OUR OWN INITIAL ANALYSES OF CARBONATE- AND SERPENTINE-BEARING LITHOLOGIES IN MCLAUGHLIN CRATER SHOW CARBONATE ABUNDANCES OF ONLY 3-5%. THE HIGHLY VARIABLE CARBONATE ABUNDANCES DETERMINED FROM IN SITU AND REMOTE SENSING MEASUREMENTS AS WELL AS THE DIFFERENT LITHOLOGIES IN WHICH THEY OCCUR COULD BE CAUSED BY DIFFERENT FORMATION MECHANISMS RANGING FROM SURFACE/ATMOSPHERE INTERACTION TO SURFACE CHEMICAL SEDIMENTATION TO DEEP SUBSURFACE CO2 METASOMATISM AMONG OTHER PROCESSES. OUR PROPOSED WORK WILL HELP TO CONSTRAIN THE FORMATION MECHANISMS OF CARBONATES ON MARS BY DETERMINING ABUNDANCES AT EACH LOCALITY AND CORRELATING CARBONATE PHYLLOSILICATE AND PRIMARY SILICATE ABUNDANCES WITH GEOLOGIC SETTING. TO ACCOMPLISH THESE GOALS WE WILL PERFORM SEVERAL TASKS: (1) PERFORM RADIATIVE TRANSFER-BASED ATMOSPHERIC CORRECTIONS ON CRISM L SPECTROMETER DATA COVERING CARBONATE-BEARING REGIONS IDENTIFIED BY EHLMANN ET AL. (2008) BISHOP ET AL. (2013) EDWARDS AND EHLMANN (2015) AND WRAY ET AL. (2016) AMONG OTHER WORKERS (2) PERFORM FACTOR ANALYSIS AND TARGET TRANSFORMATION OF CRISM IMAGES TO ISOLATE SCENE MINERAL END-MEMBERS AND CONSTRAIN POTENTIAL END-MEMBERS FOR SPECTRAL UNMIXING (3) IN A SMALL LABORATORY STUDY CALCULATE ROBUST VNIR OPTICAL CONSTANTS OF RELEVANT CARBONATES FOR USE IN SPECTRAL MIXTURE ANALYSIS (4) PERFORM SPECTRAL MIXTURE ANALYSIS ON ATMOSPHERICALLY CORRECTED CRISM SINGLE SCATTERING ALBEDO IMAGES TO CONSTRAIN MINERAL ABUNDANCES AND PARTICLE SIZES OF CARBONATE-BEARING DEPOSITS (5) ANALYZE ATMOSPHERICALLY CORRECTED TES AND THEMIS DATA FOR THE LARGEST CARBONATE-BEARING DEPOSITS TO PROVIDE ADDITIONAL CONSTRAINTS ON CARBONATE ABUNDANCE AND THERMOPHYSICAL PROPERTIES AND (6) COORDINATE COMPOSITIONAL RESULTS WITH ANALYSES OF THEMIS CTX HIRISE AND OTHER IMAGERY TO TIE CARBONATE ABUNDANCES TO SPECIFIC GEOLOGIC SETTINGS. THIS WORK IS RELEVANT TO THE MDAP PROGRAM BECAUSE IT WOULD ENHANCE THE SCIENTIFIC DATA RETURN FROM THE MARS GLOBAL SURVEYOR MARS ODYSSEY AND MARS RECONNAISSANCE ORBITER MISSIONS. THE PROJECT IS ALSO RELEVANT TO MDAP BECAUSE IT INCLUDESANALYSIS AND COMPARISON OF MARS ORBITAL AND SURFACE DATA TO INCREASE THE PREDICTIVE ACCURACY OF SURFACE CHARACTERISTICS OF MARS FROM ORBIT. OUR PROPOSED TASKS WOULD IDENTIFY CARBONATE AND OTHER SPECTRAL END-MEMBERS WITHIN CARBONATE-BEARING REGIONS ON MARS QUANTIFY THE ABUNDANCES OF THESE PHASES AND CONSTRAIN THE GEOLOGIC SETTING(S) AND FORMATION MECHANISM(S) OF MARTIAN CARBONATE-BEARING DEPOSITS.