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Clay minerals detected in ancient Martian terrains help constrain Mars’ climate and aqueous alteration history. Since Mars’ primordial origin, atmospheric redox conditions have evolved from reducing to oxidizing and clay minerals may record the effects of that transition. Ferrous trioctahedral smectites of varying iron content were synthesized and subjected to oxidation by O2 and by UV irradiation to address these as potential oxidizing agents. UV irradiation (112.77 hours with 450 W Hg lamp) of smectites equivalent to approximately four years of flux on the Martian surface caused incomplete oxidation (Fe3+/ΣFe = 16-18%). O2 experiments (two hour, twelve hour, two day, and five day) produced more oxidation in smectites with higher Fe content at the same exposure times. Photooxidation caused octahedral sheet contraction; however, chemical oxidation allowed more contraction to occur in the high Fe smectites. The mid and high Fe smectites had observable changes in their visible-near infrared (VNIR) reflectance spectra with the formation of a nontronite (Fe3+, Mg)2-OH feature at 2.3 µm, even with partial oxidation. With both oxidation experiments, the reflectance spectra lost its initial MMM-OH features (AlAl(Fe2+,Mg) and Fe2+MgMg-OH) and produced a single nontronite-like MM-OH feature. UV irradiation produced a secondary nontronite phase, possibly on the surface of the higher Fe content smectites; however there was no evidence for iron ejection. Ferrous smectites are capable of undergoing UV photooxidation under aqueous conditions and this process could have occurred during early Martian history. Distinguishing between UV and O2 oxidation in smectites cannot be completed exclusively with Martian spectra; however, the lack of secondary oxides may hint at alteration history based on the nature of mineral assemblages detected on Mars. / Geology

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1979. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 146-153. / by Kathleen Marie Parkin. / Ph.D.

Low temperature phase relations in the ice-stable field of the system NaCl-CaCl₂-H₂O were determined under 1 atm. total pressure along the NaCl-H₂O and CaCl₂-H₂O binaries and along five pseudobinaries with constant NaCl/(NaCl+CaCl₂) weight ratios. The results are in excellent agreement with published data along the NaCl-H₂O binary but show large discrepancies when compared to previous determinations of the ice liquidus along the CaCl₂-H₂O binary and in the NaCl-CaCl₂-H₂O ternary. At moderate to high salinities, isotherms cross the ice sub-field at lower total salt concentrations than previously reported. In addition, NaCl/(NaCl+CaCl₂) weight ratios estimated from hydrohalite- and ice-melting temperatures may be low by as much as 15%. Relative densities were measured for NaCl(aq) and CaCl₂(aq) solutions to 250°C and 400 bars and over the range of ionic strengths 0.2 - 5.5 and 0.2 - 19.2 mol·kg⁻¹, respectively. The results span the pressure and temperature of earlier volumetric studies and extend to higher molalities than reported previously. The relative densities have been fitted as apparent molar volumes (V_Φ) using the Pitzer ion-interaction treatment, with appropriate expressions chosen for the temperature- and pressure-dependence of the virial coefficients of the model. The results presented for NaCl(aq) are in good agreement with published results to 250°C. The results presented for CaCl₂(aq) are in good agreement with published values to approximately 125°C. Above 125°C the inter- and intralaboratory precision of the published data deteriorate and are often in very poor agreement with the data from this Study. The representation for V_Φ for CaCl₂(aq) was integrated with respect to pressure to establish the pressure dependence of excess free energies over the temperature range studied. CaCl₂ activity coefficients (γ±) have been derived to 250°C, 400 bars and 4 mol·kg⁻¹ using published fits of CaCl₂ activity coefficient data along the vapor saturation surface and the pressure dependence determined in this work. The volumetric data indicate that the mean ionic activity coefficient, γ±(CaCl₂), increases by a maximum of 32% at 400 bars, 250°C, and 4 mol·kg⁻¹ as compared with its value at saturation pressure. Relative densities were also measured for several ternary { NaCl+CaCl₂}(aq) solutions at 25 and 35°C and 1 atm. These results substantially expand the volumetric data base for ternary solutions. Based on the results of this study most of the previously reported 308.15 K density data in the ternary appear to contain large errors. / Ph. D.

In this dissertation, we have examined mineral assemblages and geomorphologic features in the Sisyphi Planum region of Mars, as well as examined the mineral assemblage of palagonite in Iceland. Chapter 2 is focused on the mineral assemblages detected on possible glaciovolcanic edifices in the Sisyphi Planum region of Mars. Minerals were identified utilizing visible/near-infrared orbital spectra from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Analysis of eleven CRISM images located on the volcanic edifices revealed three distinct spectral classes in the region which are interpreted to be: gypsum-dominated, smectite-zeolite- iron oxide-dominated (possibly palagonite), and polyhydrated sulfate-dominated material. The possible palagonite detections on the volcanic edifices, the geomorphology of the region, and the analogous terrestrial mineralogy of subglacial eruptions strongly suggests the formation of these minerals during subglacial eruptions or associated hydrothermal systems. This implies that thick water ice sheets were present in this region in the late Noachian or early Hesperian, and that the subglacial hydrothermal systems could have supported habitable environments with excellent biosignature preservation potential. Chapter 3 is focused on evaluating the variability of the composition and crystallinity of palagonite on Earth in order to inform efforts to identify it on Mars. We hypothesized that variability in palagonite composition and crystallinity could occur due to differences in environmental conditions during formation. Palagonite samples were collected in Iceland at subglacial volcanic sites around Reykjavík in the Western Volcanic Zone, on the southern coast in the Eastern Volcanic Zone, and from the Herðubreið tuya and Askja volcano in the Northern Volcanic Zone. Visible/near-infrared reflectance spectroscopy, thermal-infrared emission spectroscopy, and quantitative XRD were used to assess the bulk mineralogy, crystallinity, and clay composition of all samples. Results show the sampled palagonites contain partially devitrified glass, unaltered glass, and secondary minerals including clay minerals, poorly crystalline ferric oxides, and zeolites. However, one sample (SCoast01) shows a vastly different mineral assemblage in all sample techniques, including well-crystalline Fe/Mg-clays as opposed to the poorly-crystalline Al-clays observed in our other samples. Based on previous studies of subaqueous palagonites and the location this sample was collected from, we hypothesize that the SCoast01 sample was formed in a submarine environment rather than subglacial. This suggests that it may be possible to differentiate submarine vs. subglacial palagonite on Earth based on composition and from remote sensing observations on Mars. Chapter 4 is a geomorphologic study of the Sisyphi Planum region of Mars where we identified and classified the tops of the Sisyphi Montes as well as geomorphologically mapped the Sisyphi Planum region. Here, we address an overarching question: What is the relationship between the Sisyphi Montes and the ice in this region? To do this, we identified 106 edifices in the region and classified them into five categories: 1) flat topped, 2) rounded tops, 3) sharp peaks, 4) cratered peaks, and 5) height less than 300 meters – a “catch-all” category for all features below the specified height, which exhibit less distinctive morphologies in MOLA topography. While many of the edifices could be sub-glacial in origin, we find that the only morphologic class that exhibits uniquely subglacial morphologies are the flat-topped edifices. These edifices are similar to terrestrial tuyas, which form when a subglacial volcano breaches an ice sheet and erupts a plateau of sub-aerial lavas. Based on the geomorphologic map and topographic data, we have shown that flat-topped edifices are all located outside of regions that we map as the Mantled Unit, which we infer to be related to the Dorsa Argentina Formation. The combination of the flat topped edifices and their location outside of the mapped ice-related regions strongly suggests that the ice in the region was once more extensive than what is currently observed. While this has been proposed in the past, it has not been documented how far the ice sheet could have extended. Here we show that the ice must have extended to at least as far as the flat topped edifices in the region. The combination of these chapters using both mineralogy and morphology suggest that the Sisyphi Planum region of Mars was subglacial in origin. <br><br>

Includes bibliographical references. / 122, [68] leaves, [7] leaves of plates : ill. (chiefly col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The aims of this thesis are to determine the provenance of the Permian sands of southern Australia, to correlate the provenance of the Permian sands with the known geology and tectonics of East Antarctica and to determine those features of light and heavy minerals that are most useful as provenance indicators. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1996

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. Includes bibliographical references.

Review of literature shows that rocks of all ages from the Archaean to the early Phanerozoic host pegmatite-based mineralisation in the central and southern region of the African continent. The greatest concentrations occur in the Archaean and late Proterozoic orogenic belts, while early to middle Proterozoic granites do not, in general, host mineralisation. Pan-African mineralisation is present, but is not widespread. Some deposits previously considered to be of Pan-African have been shown to be of Proterozoic age. In common with occurrences of other regions, the deposits are closely associated with small, late- to post-tectonic granites. Therefore, preliminary assessment of the potential of granites as sources of pegmatite mineralisation should utilise satellite data or aerial photographs. The granites also tend to be alkaline and peraluminous. Thus, in the next stage, chemical analysis for selected major and trace elements should be conducted directly on granites if they occur as small plutons. For large granitic batholiths or terranes, preliminary stream-sediment surveys may be necessary to reduce the size of the target area. Subsequently, pegmatite zonation around suitable granites should be assessed as it allows attention to be focussed on areas likely to host the specific type of mineralisation being explored for.