Entity

Time filter

Source Type

Golden, CO, United States

Colorado School of Mines is a small public teaching and research university in Golden, Colorado, devoted to engineering and applied science, with special expertise in the development and stewardship of the Earth's natural resources. CSM placed 88th in the 2015 US News & World Report "Best National Universities" ranking. Wikipedia.


Andrews-Hanna J.C.,Colorado School of Mines
Icarus | Year: 2013

Many lunar basins are characterized by prominent positive gravity anomalies over the basin interiors, referred to as mass concentrations or mascons. While a significant fraction of some near-side mascon anomalies can be explained as a result of the flexural support of the mare basalts within the basins, a number of basins, including Orientale, exhibit mascons in excess of those that can be plausibly ascribed to the mare. Some basins exhibit mascons but lack mare altogether. Lunar gravity and topography data are used to map the isostatic anomaly, or the height of the surface above or below its isostatic level. Orientale is representative of the majority of lunar basins, in which the super-isostatic basin center is surrounded by a sub-isostatic annulus of comparable magnitude but greater area. The basin structure as a whole is found to be strongly sub-isostatic. High-resolution crustal thickness models of Orientale confirm that it is surrounded by an annulus of thickened but sub-isostatic crust. It is proposed that the flexural uplift of the annulus causes the uplift and positive gravity anomalies within the basin center. Finite element models are used to examine the flexural uplift of the sub-isostatic annulus and the basin center for a range of lithosphere thicknesses both outside the basin and in the basin interior. The uplift of the basin center can exceed 2. km, increasing the central gravity anomaly by ∼200. mGal. This annular uplift explains a significant fraction of the Orientale mascon, and is likely a dominant cause of non-mare mascons globally. © 2012 Elsevier Inc. Source


Andrews-Hanna J.C.,Colorado School of Mines
Journal of Geophysical Research E: Planets | Year: 2012

Although Valles Marineris is widely regarded as an extensional tectonic feature, the source of stress responsible for its formation remains unknown. This study argues that the tensile stresses that triggered Valles Marineris tectonism are a result of its location south of and subparallel to the buried crustal dichotomy boundary beneath Tharsis. The emplacement of the Tharsis volcanic load straddling the pre-existing topographic step of the crustal dichotomy boundary would have resulted in an abrupt change in the thickness of the load, causing differential subsidence and extension across the boundary. Thin-shell flexural models predict a narrow belt of focused tensile stresses south of the buried dichotomy boundary, coinciding with the location of present-day Valles Marineris. The interaction of these boundary-generated stresses with the competing stress fields associated with Tharsis loading can explain the formation of Noctis Labyrinthus in the west, and the deflection of the Valles Marineris troughs away from the buried boundary toward the east. Finite element models demonstrate that the magnitudes and vertical variations of stress at Valles Marineris are sensitive to the timing of loading and flexure in Tharsis. The incremental loading and flexure expected for a large volcanic rise results in the maximum tensile stress at Valles Marineris occurring at depth, with tensile stresses through the majority of the lithospheric column. Dikes forming within this tensile stress belt would propagate through the full vertical extent of the lithosphere due to the stress release associated with the dilation of the dikes, playing a crucial role in the formation of the Valles Marineris troughs. Copyright 2012 by the American Geophysical Union. Source


Andrews-Hanna J.C.,Colorado School of Mines
Journal of Geophysical Research E: Planets | Year: 2012

Despite the enormous size of the Valles Marineris chasmata on Mars, the mechanism responsible for the formation of these unique troughs remains unknown. Previous studies proposed mechanisms of trough formation through extensional tectonism, vertical collapse into subsurface voids, or some combination of the two. Recent work in a pair of companion papers demonstrated that the troughs must have formed dominantly by vertical subsidence with little net horizontal extension, and that the modest extension required likely arose from the effect of the buried dichotomy boundary beneath Tharsis. This study now proposes a new mechanism of Valles Marineris formation, with a focus on the large-scale geodynamic and tectonic processes. Prior to the formation of Valles Marineris, the lithosphere within Tharsis was maintained in a super-isostatic state by the membrane-flexural support of the rise. Local moderate extension at Valles Marineris controlled subsequent intrusive activity, resulting in the emplacement of long parallel dikes. This intrusive activity weakened the lithosphere, effectively removing the flexural support from long lithospheric blocks. Left unsupported, these blocks would have subsided approximately 0.49 ± 0.32 km to their isostatic level. The total subsidence would have been increased to 8.6 ± 5.6 km by the effects of contemporaneous sedimentary loading within the troughs and viscous deformation at the base of the crust. This mechanism successfully predicts the observed depths of the Valles Marineris chasmata, and is consistent with all geological and geophysical observations. The unique nature of Valles Marineris is explained as a result of the unique geodynamic and tectonic environment of Tharsis. © 2012 American Geophysical Union. All Rights Reserved. Source


Andrews-Hanna J.C.,Colorado School of Mines
Journal of Geophysical Research E: Planets | Year: 2012

The formation of the Valles Marineris troughs on Mars is widely held to involve some combination of horizontal extension and vertical subsidence or collapse, but the specific tectonic mechanism is poorly understood. This study uses boundary element models of Valles Marineris formation to evaluate a range of fault dip angles for two end-member models of trough formation: simple extensional tectonism, and extension together with vertical accommodation at the base of the lithosphere representing either viscous lower crustal flow or some other form of deep-seated collapse. The models are constrained by the lack of footwall uplift on the plateau surface outside the troughs, and the lack of significant tectonic failure of the plateau in response to the stress changes induced by Valles Marineris formation. The results demonstrate that trough formation by extensional tectonism alone generates large surface uplifts in the surrounding plateau and enormous stresses in the lithosphere, in conflict with the observations. The only mechanism that is compatible with both the observed topography and the limitations imposed by the finite strength of the lithosphere is trough formation through displacement along steeply dipping to subvertical border faults, together with vertical accommodation at the base of the subsiding fault block. Fault dips are constrained to be greater than or equal to 85, leading to a ratio of vertical subsidence to horizontal extension exceeding 5.7 and a maximum extension of less than 4.6 km. These results confirm earlier studies suggesting that trough formation involved a substantial component of vertical subsidence or collapse, with only modest amounts of total extension. Copyright 2012 by the American Geophysical Union. Source


Klusman R.W.,Colorado School of Mines
International Journal of Greenhouse Gas Control | Year: 2011

A summary of geochemical techniques for purposes of determination of a baseline condition and subsequent monitoring of potential gas microseepage from CO2-EOR or geologic sequestration is presented. The methods include; above ground open-atmosphere techniques, measurements at the land surface-atmosphere interface, and shallow subsurface sampling and measurements. The advantages and disadvantages are presented based on previously published measurements utilizing these techniques. The monitoring for seepage from a CO2-EOR or geologic sequestration project might logically focus on measurements of CO2. Carbon dioxide measurements, particularly in the atmosphere will suffer some quantifiable disadvantages; relatively high atmospheric concentration for a tracer, high environmental variance, multiple natural sources, and solubility/reactivity with water. These factors combine to suggest that CO2 may not effectively serve as an early warning tracer or surface indicator of seepage. Other methods and tracers that are discussed focus on gas exchange measured at the surface and shallow soil gas measurements utilizing a variety of tracers. These parameters include; CO2, CH4 and light hydrocarbons, stable carbon isotopic measurements of carbon-containing gases, carbon-14 content of CO2, inert gases, and artificial tracers entrained in the injected CO2. Use of secondary carbonates in the soil or upper portion of the sedimentary column and their readily measured stable isotopic ratios, and composition of shallow groundwater are included. These materials can be useful in the baseline characterization and provide evidence for fossil gas leakage from depth. © 2011 Elsevier Ltd. Source

Discover hidden collaborations