Geology
Permanent URI for this communityhttp://hdl.handle.net/1903/2243
Browse
9 results
Search Results
Item PREDICTING THE SEISMIC SIGNATURE OF LAVA TUBES FOR THE EARTH, THE MOON, AND MARS(2024) Wike, Linden; Schmerr, Nicholas; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lava tubes are a type of volcanically-generated subsurface void structure found on Earth, the Moon, and Mars and hold the potential to serve as shelters for crew members, preservation sites of pristine geological samples, and locations of in situ resources. A key question for lava tube science is how to locate them through geophysical methods. Here, we create a workflow that locates and characterizes the geometry of subsurface voids. We build a suite of subsurface synthetic seismic wavefield models that contain lava tube structures and investigate which seismic method best images them. Our models show that the more readily detectable lava tube simulations have a geophone spacing of 0.5 m, variable diameter, and shallow ceiling depth; and reverse-time migration and phase-shift-plus-interpolation migration techniques produce more accurate lava tube reconstructions than the Kirchhoff method. The synthetic modeling serves as a benchmark for understanding seismic wave propagation around lava tubes and helps answer how voids on the Moon and Mars would be imaged through seismology.Item THE CONCENTRATION OF HYDROGEN IN INCOMPLETELY AND WHOLLY MELTED TERRESTRIAL BUILDING BLOCKS(2024) Peterson, Liam Donald; Newcombe, Megan E; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrogen (H) is the most abundant element in our solar system and exerts a primary control on the habitability, and geochemical and geodynamic evolution of rocky bodies. Therefore, constraining the source(s), timing of accretion, and abundance of H in the Earth and other bodies is of fundamental importance for understanding how planets evolve. Direct constraints on the source(s) of H and other highly volatile elements (HVEs; e.g., H, C, F, Cl, and S) to the bulk Earth can be provided by analyzing meteorites, which are the remnants of early-formed rocky bodies that were present during the accretion of the terrestrial planets. Such samples either directly sample or provide analogs for terrestrial precursor materials.Rocky solar system materials can be subdivided based upon their nucleosynthetic isotopic compositions (“genetic” tracers; e.g., 50Ti, 54Cr) into two groups, which are thought to correspond to the inner- and outer- solar system. Materials may be further subdivided by their extent of thermal processing (i.e., unmelted, incompletely melted, and wholly melted). Earths H budget is commonly accounted for by addition of unmelted (i.e., chondritic) materials, namely carbonaceous chondrite-like (CC-like) materials, thought to be derived from the outer solar system, which have high H concentrations (up to ~14 wt. % H2O; total H as H2O equivalents) and similar H isotopic compositions to the bulk Earth. Furthermore, chondrites derived from the inner solar system (e.g., ordinary and enstatite chondrites) are H-poor relative to carbonaceous chondrites. Similarly, all melted planetesimals are commonly assumed to be anhydrous. However, recent analyses of enstatite chondrites (ECs), which are formed in the inner solar system and are the closest match to the nucleosynthetic isotopic composition of the bulk Earth, suggest that ECs have a similar H isotopic composition to the bulk Earth and can account for its entire H budget. Furthermore, recent analyses suggest that melted (i.e., achondritic) bodies may retain considerable amounts of H, potentially enough to account for Earth’s H budget in the case of the enstatite achondrites (i.e., aubrites). However, achondritic materials are predominantly highly H-poor relative to chondritic materials, and it is unclear if the aubrites are an anomaly, and at which stage of planetesimal evolution H and other HVEs are lost. In chapter 2, I re-examine prior bulk analyses of H in aubrites, and by extension ECs, using in situ methods and suggest that nearly all H measured in aubrites by bulk methods reflects pervasive terrestrial contamination and alteration, a result which may extend to concurrent bulk H analyses of ECs. In chapters 3 and 4, I examine the H content of incompletely melted (i.e., primitive achondritic) planetesimals to constrain at what stage of planetesimal evolution H is lost. Chapter 3 characterizes the H contents of the ureilites, a group of C-rich primitive achondrites, and chapter 4 characterizes the H contents of the acapulcoite-lodranite clan which represents the “prototypical” primitive achondritic parent body. I find that primitive achondritic parent bodies are highly H-depleted relative to chondrites, requiring that H is efficiently lost prior to or at the onset of planetesimal melting, and that Earth’s H budget is accounted for by accretion of thermally primitive materials (e.g., chondrites). Within my primitive achondrite data sets, I observe apparent disequilibrium with respect to H between olivine, pyroxene, and feldspar. In chapter 5, I explore whether this apparent disequilibrium is the result of extrapolating high pressure experimental data to low pressures. I conduct olivine–melt H partitioning experiments at low pressures (10 – 200 MPa) and find that the olivine-melt H partition coefficient increases at low pressures, contrary to extrapolation from high pressure data. This observation is best explained by a control of H speciation in the melt on the partitioning of H between olivine and melt.Item Petrologic, Geochemical, and Spectral Characteristics of Oxidized Planetary Differentiation(2021) Crossley, Samuel Dean; Sunshine, Jessica M; Ash, Richard D; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Meteorites provide evidence that planetary formation occurred across a wide range of oxidation environments in the early Solar System. While the process of differentiation for many reduced, oxygen-poor assemblages has been thoroughly explored, significantly less is known about how differentiation occurred in more oxidized regions of the Solar System. Results from petrologic and geochemical investigations of oxidized chondrites (Rumurutiites) and primitive achondrites (brachinites) reveal that significant mineralogic differences occur with increasing degrees of oxidation. As a consequence, the differentiation pathways of oxidized and reduced assemblages diverge during the earliest stages of partial melting. While reduced materials differentiate to form a basaltic crust, magnesian peridotite mantle, and metallic core, oxidized materials may instead form felsic crusts, ferroan peridotite mantles, and sulfide-dominated cores. These pathways are evident in distinct siderophile trace element systematics for oxidized and reduced endmembers of the brachinite meteorite family. The compositions of olivine between oxidation endmembers are resolvable using remote sensing techniques that are applicable to asteroids. Most olivine-dominated asteroids examined in this work are consistent with having formed in oxidized environments, similar to R chondrites and brachinites, or in even more oxidizing environments not recorded among the meteoritic record. This provides strong evidence that environments capable of supporting oxidized, sulfide-dominated core formation are widespread among asteroidal materials. Several of these asteroids are likely mantle restites, based on their olivine composition and the estimated abundances of pyroxene. The predominance of oxidized over reduced environments among olivine-dominated asteroids is likely related to their respective petrogenetic histories: reduced assemblages must reach and sustain much higher temperatures to fully melt and segregate their pyroxene contents from olivine, which requires larger and earlier-accreted parent bodies. Consequently, sampling reduced mantle restites without significant pyroxene contamination would require catastrophic parent body destruction without mixing crustal and mantle materials. Oxidized materials, in contrast, have much higher initial olivine/pyroxene ratios, and thus are much more prone to producing asteroids dominated by olivine.Item A prototype miniature mass spectrometer for in situ analysis of trace elements on planetary surfaces(2021) Farcy, Benjamin Jacob; Arevalo, Ricardo D; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Interrogation of the chemical composition of rocky planets provides a deeper understanding of the history and evolution of the solar system. While laboratory studies of returned samples and remote sensing surveys of planetary surfaces can give insight into planetary history, one technique that has delivered major insights to planetary geology is in situ measurements of a planetary surface via mass spectrometry. Here, a new approach to spaceflight mass spectrometry is discussed, including an overview of the pursued scientific questions, the analytes targeted, and the prototype hardware in development. This effort constitutes the scientific and technological foundation of a landed planetary mission. This dissertation focuses on the history and evolution of the Earth-Moon system as recorded by trace elements. Specifically, the abundance and distribution of the heat producing elements (HPEs: K, Th, U) and their implications for mantle dynamics is considered. The radiogenic heat produced from K, Th, and U drives mantle convection, volcanism, and planetary dynamos. To understand better the chemical dynamics of radiogenic heat distribution in the Earth, the HPE abundance of a series of oceanic basalts was statistically analyzed. This analysis revealed the K/U ratio of the mantle and how it changes due to the enrichment or depletion of incompatible elements. The HPE abundance of the lunar interior was also discussed as a target of a future investigation, along with a series of trace element proxies meant to probe the lunar farside mantle. Further, an analysis of lunar farside craters provides a series of landing sites for an in situ mission, specifically for their surficial exposure of upper mantle material and later emplacement of lunar basalts. To access the trace element systems discussed in this dissertation, a prototype miniature inductively coupled plasma mass spectrometer (ICPMS) was developed to analyze trace elements in situ for landed planetary missions. First, the capability of the plasma to atomize and ionize input material was investigated. A plasma operating at reduced pressure can achieve 99\% ionization efficiency of most elements on the periodic table, with as much as a 50 to 100 times reduction in gas load and forward power compared to commercial systems for both He and Ar based plasma ion sources. The plasma system was integrated with a quadrupole mass spectrometer via a series of DC ion optics and vacuum housing, with its ion current and peak resolution optimized. Quantative data for an analyte spectrum of Kr demonstrates the ability for this instrument to resolve individual mass peaks, which lead to an accuracy and precision measurement of isotope ratios. This effort represents an end-to-end prototype miniature ICPMS, successfully demonstrating a viable instrument for landed planetary missions.Item Geophysical Exploration of Terrestrial and Lunar Volcanic Fields(2021) Bell, Jr., Ernest Robert; Schmerr, Nicholas; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Planetary analogs are environments representative of current or past conditions on other planetary bodies. My research uses terrestrial volcanic fields as lunar analogs to conduct geophysical studies on the subsurface structure of cinder cones, lava flows, and lava tubes, as well as understand terrestrial field methods for application to lunar surface exploration. As part of this research, I relate the magnetic anomalies produced by lava tubes to their location and geomorphology. By comparison of magnetic anomalies against synthetic predictions, I derive a relationship between the terrestrial magnetic anomalies and underlying tube geometry. The model is shown to predict terrestrial lava tube magnetic anomalies, and adjusting for the lunar magnetic environment, anomalies resulting from tubes on the Moon. Active source seismic experiments performed by Apollo astronauts were used to determine lunar tectonic and volcanic structure at depth. Terrestrial geophysical analogs are useful for understanding the Apollo results, and for improving the quality of future lunar seismic studies. I use seismic refraction to attempt to identify subsurface continuation of locally mapped faults beneath lava flows and cinder deposits to examine their association to cinder cone vent chains. However, due to high seismic energy attenuation, my analysis was unable to resolve displacement of stratigraphic layers indicative of fault locations. The seismic attenuation properties of the field area were able to be characterized. I then analyze the Apollo 17 Lunar Seismic Profiling Experiment (LSPE) data and an Apollo LSPE equivalent terrestrial data set to provide insights into the subsurface imaging potential for a terrestrial equivalent array in the Taurus-Littrow Valley on the Moon. Finally, I insert active seismic refraction into a previously executed simulated human lunar rover mission where the traverse route and associated science station locations omitted geophysical studies. Data from these lines are used to create 1-D seismic velocity profiles to examine subsurface structural trends and geophysical features of the field area. The seismic fieldwork and analysis are related to similar activities performed by the Apollo 14 & 16 crews to highlight similarities in issues encountered with both terrestrial and lunar field operations, and discuss considerations for future human lunar surface science.Item Planetary Seismology using Single-Station and Small-Aperture Arrays: Implications for Mars and Ocean Worlds(2020) Marusiak, Angela Giuliano; Schmerr, Nicholas C; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Studying geophysical station deployment on Earth is essential preparation for future geophysical experiments elsewhere in the solar system. Here, I investigated how single-station seismometers and small-aperture seismic arrays in analog settings can quantify instrument capabilities, develop methodologies to detect and locate seismicity, and constrain internal structure. First, I used a single-station seismometer in Germany to study how the NASA InSight mission could constrain core depth. I showed that InSight could recover the Martian core within ±30 km if ≥ 3 events are located within an epicentral distance uncertainty of < ±1 degree. Increasing the number of detected events reduces core depth uncertainty, and higher signal-to-noise events will not affect core depth uncertainty or recovery rate. Next, I used environmental analogs in Earth's cryosphere to quantify how seismometer placement on a mock-lander would affect instrument performance and seismic science results for a future surface mission to an icy ocean world. If mock-lander instruments were unprotected from the wind, noise levels were 50 dB higher than those on the ground. However, once seismometers were shielded via burial, noise performances were similar to the ground-coupled seismometers, although spacecraft resonances were found at frequencies ~100 Hz. For icy ocean worlds lacking atmospheres, I showed that deck-mounted flight-candidate seismometers recorded ground motion comparably to surface-deployed instrumentation, with responses similar to terrestrial seismometers at frequencies > 0.1 Hz. Finally, I investigated seismicity detection capabilities of single-station and small-aperture seismic arrays. Small-aperture arrays were more effective at distinguishing low-frequency seismic events from noise and had fewer false positive events than a single-station. The Greenland site detected a higher percentage of teleseismic and regional tectonic events while the Gulkana Glacier, Alaska site observed more high frequency events. The high frequency seismicity was interpreted as originating from moulins, drainage events, icequakes, and rockfalls. Both sites had very high frequency events (> 100 Hz) that came from poles left in the field. These studies inform landing site selection criteria, such that there were trades between detecting local seismicity at the expense of seeing more distant events, and detecting larger teleseismic events that inform on deeper internal structure.Item Lithospheric Extension on Venus: how to form narrow rifts(2017) Martone, Alexis Ann; Montesi, Laurent G. J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Venusian rifts of Devana and Ganis Chasmata have been noted for their similar morphology to some rifts on Earth (i.e., the East African rift system). These are narrow rifts that are associated with localized deformation. This thesis aims to explore the link between lithospheric structure and rift style using a force analysis model, following previous work by Buck (1991), in order to determine under what conditions narrow rifts are predicted for Venus conditions. Results for two cases, one using a constant lithospheric thermal conductivity and another using a depth dependent thermal conductivity, are initially determined; Devana and Ganis Chasmata are predicted to be wide rifts rather than narrow rifts. Lithospheric weakening mechanisms (rheological weakening and diking) are implemented to determine their effect on localizing deformation and, thus, forming narrow rifts. Diking did not produce any effect on forming narrow rifts. Rheological weakening, likely due to a combination of melt and a transition to grain size sensitive creep, appears necessary to produce narrow rifts.Item Highly Siderophile Elements, 187Re-187Os and 182Hf-182W Isotopic Systematics of Early Solar System Materials: Constraining the Early Evolution of Chondritic and Achondritic Parent Bodies(2016) Archer, Gregory Jude; Walker, Richard J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Highly siderophile element (HSE) abundances and 187Re-187Os isotopic systematics for H chondrites and ungrouped achondrites, as well as 182Hf-182W isotopic systematics of H and CR chondrites are reported. Achondrite fractions with higher HSE abundances show little disturbance of 187Re-187Os isotopic systematics. By contrast, isotopic systematics for lower abundance fractions are consistent with minor Re mobilization. For magnetically separated H chondrite fractions, the magnitudes of disturbance for the 187Re-187Os isotopic system follow the trend coarse-metalItem TECTONICS OF ICY SATELLITES DRIVEN BY MELTING AND CRYSTALLIZATION OF WATER BODIES INSIDE THEIR ICE SHELLS(2015) Johnston, Stephanie Ann; Montési, Laurent; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Enceladus and Europa are icy satellites that currently support bodies of liquid water in the outer solar system Additionally, they show signs of being geologically active. Developing numerical models informed by observations of these icy satellites allows for the development of additional constraints and an improved understanding of the tectonics and evolution of icy satellites. The formation mechanisms for both chaos and ridges on Europa are thought to involve water as albedo changes observed in association with them imply the deposition of salt-rich water near these features. Ridges are the most ubiquitous feature on Europa and are described as central troughs flanked by two raised edifices, range in height from tens to hundreds of meters. Europan ridges can extend hundreds of km continuously along strike but are only about 2 km across. A model of a crystallizing dike–like water intrusion is able to match the overall morphology of ridges, and is consistent the long continuous strike. However, the intrusion of a large volume of water is required to match the most common heights of the ridges. Chaos on Europa is defined as a large area of disrupted ice that contain blocks of pre-existing material separated by a hummocky matrix. A proposed mechanism for the formation of Chaos is that a region of heterogeneous ice within the shell is melted and then recrystallizes. Comparing the model results with the geology of Thera Macula, a region where it has been proposed that Chaos is currently forming, suggests that additional processes may be needed to fully understand the development of Chaos. Water-rich plumes erupt from the south pole of Enceladus, suggesting the presence of a pressurized water reservoir. If a pressurized sea is located beneath the south polar terrain, its geometry and size in the ice shell would contribute to the stress state in the ice shell. The geometry and location of such an ocean, as well as the boundary conditions and thickness of an ice shell have important implications for the faulting and tectonic deformation anticipated at the surface.