Petrology and structure of Precambrian rocks, Central City quadrangle, Colorado

Sims, P.K.; Gable, Dolores J.

doi:10.3133/pp554e

Cited by 12 publications

(13 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The locations of the major rock groups are shown in Figure 1. The Precambrian rocks in the area are an interlayered, generally conformable, sequence of gneiss, migmatite, and Boulder Creek Granite and Silver Plume Quartz monzonite intrusive igneous rocks, some of which are metamorphosed (Sims and Gable 1967). The gneisses exhibit complex structural deformation including a west-northwest folding episode associated with upper amphibolite metamorphism (Taylor 1976) and a subsequent deformational event that produced large-scale north-northeast trending folds.…”

Section: Study Area Geology and Hydrologymentioning

confidence: 99%

Sequential Analysis of Hydrochemical Data for Watershed Characterization

2004

View full text Add to dashboard Cite

A methodology for characterizing the hydrogeology of watersheds using hydrochemical data that combine statistical, geochemical, and spatial techniques is presented. Surface water and ground water base flow and spring runoff samples (180 total) from a single watershed are first classified using hierarchical cluster analysis. The statistical clusters are analyzed for spatial coherence confirming that the clusters have a geological basis corresponding to topographic flowpaths and showing that the fractured rock aquifer behaves as an equivalent porous medium on the watershed scale. Then principal component analysis (PCA) is used to determine the sources of variation between parameters. PCA analysis shows that the variations within the dataset are related to variations in calcium, magnesium, SO4, and HCO3, which are derived from natural weathering reactions, and pH, NO3, and chlorine, which indicate anthropogenic impact. PHREEQC modeling is used to quantitatively describe the natural hydrochemical evolution for the watershed and aid in discrimination of samples that have an anthropogenic component. Finally, the seasonal changes in the water chemistry of individual sites were analyzed to better characterize the spatial variability of vertical hydraulic conductivity. The integrated result provides a method to characterize the hydrogeology of the watershed that fully utilizes traditional data.

show abstract

Section: Study Area Geology and Hydrologymentioning

confidence: 99%

Sequential Analysis of Hydrochemical Data for Watershed Characterization

2004

View full text Add to dashboard Cite

show abstract

“…. Geochemical data for aeolian sands, Laramie Formation sands and river sediments are from the present study; geochemical data for granitic and metamorphic rocks of the mountains are from Sims and Gable (1967), Gable (1980), Geist et al (1989), Aleinikoff et al (1993), and Houston and Marlatt (1997). Kolm, 1974, as modified by Love and Christiansen, 1985), modern sand roses, late Holocene paleowinds inferred from orientations of parabolic dunes and sample localities for the present study.…”

Section: Intermediate Mineralogical Maturity In Young Dunefields Derimentioning

confidence: 99%

Mineralogical maturity in dunefields of North America, Africa and Australia

2004

View full text Add to dashboard Cite

Studies of dunefields in central and western North America show that mineralogical maturity can provide new insights into the origin and evolution of aeolian sand bodies. Many of the world's great sand seas in Africa, Asia and Australia are quartzdominated and thus can be considered to be mineralogically mature. The Algodones (California) and Parker (Arizona) dunes in the southwestern United States are also mature, but have inherited a high degree of mineralogical maturity from quartz-rich sedimentary rocks drained by the Colorado River. In Libya, sediments of the Zallaf sand sea, which are almost pure quartz, may have originated in a similar fashion. The Fort Morgan (Colorado) and Casper (Wyoming) dunefields in the central Great Plains of North America, and the Namib sand sea of southern Africa have an intermediate degree of mineralogical maturity because their sources are large rivers that drained both unweathered plutonic and metamorphic rocks and mature sedimentary rocks. Mojave Desert dunefields in the southwestern United States are quite immature because they are in basins adjacent to plutonic rocks that were their sources. Other dunefields in the Great Plains of North America (those in Nebraska and Texas) are more mature than any possible source sediments and therefore reflect mineralogical evolution over time. Such changes in composition can occur because of either of two opposing long-term states of the dunefield. In one state, dunes are stable for long periods of time and chemical weathering depletes feldspars and other weatherable minerals in the sediment body. In the other state, which is most likely for the Great Plains, abrasion and ballistic impacts deplete the carbonate minerals and feldspars because the dunes are active for longer periods than they are stable. D

show abstract

“…Fans are present at the mouths of tributary-drainage basins in both parts of the valley. The area is underlain predominantly by Precambrian biotitic gneiss and quartz monzonite with scattered Tertiary intrusions (Spurr and others, 1908;Lovering, 1935;Sims, 1964;Braddock, 1969;Sheridan and Marsh, 1976;Bryant and others, 1981;Widmann and others, 2000;Widmann and Miersemann, 2001) with associated hydrothermal alteration and silver and gold mineralization (Harrison and Wells, 1967;Sims and Gable, 1967). The zone of mineralization that encompasses the field-trip area extends from southwestern Colorado to the Front Range northwest of Denver, and is known as the Colorado Mineral Belt (Tweto and Sims, 1963).…”

Section: Setting Physiographicmentioning

confidence: 99%