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Simulation Of Solute Movement Through Wellbores To Characterize Public Supply Well Contaminant Vulnerability In The High Plains Aquifer, York, Nebraska, Brian R. Clark, Matthew K. Landon, Leon J. Kauffman, George Z. Hornberger Jan 2006

Simulation Of Solute Movement Through Wellbores To Characterize Public Supply Well Contaminant Vulnerability In The High Plains Aquifer, York, Nebraska, Brian R. Clark, Matthew K. Landon, Leon J. Kauffman, George Z. Hornberger

United States Geological Survey: Staff Publications

A ground-water flow and transport model simulating contaminant movement to public supply wells in the High Plains aquifer near York, Nebraska was developed as part of the U.S. Geological Survey National Water-Quality Assessment Program. Water-quality samples were collected from wells screened in unconfined and confined units. Samples collected from a public supply well and selected monitoring wells completed in the confined aquifer have chemistry and age-tracer concentrations consistent with a mix of young water from unconfined recharge areas combined with relatively older confined aquifer water. These results imply that there are preferential flow paths that permit shallow recharge water and …

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Unusual Holocene And Late Pleistocene Carbonate Sedimentation In Bear Lake, Utah And Idaho, Usa, Walter E. Dean, Joseph Rosenbaum, Gary Skipp, Steven Colman, Richard Forester, An Liu, Kathleen R. Simmons, James Bischoff Jan 2006

Unusual Holocene And Late Pleistocene Carbonate Sedimentation In Bear Lake, Utah And Idaho, Usa, Walter E. Dean, Joseph Rosenbaum, Gary Skipp, Steven Colman, Richard Forester, An Liu, Kathleen R. Simmons, James Bischoff

United States Geological Survey: Staff Publications

Bear Lake (Utah–Idaho, USA) has been producing large quantities of carbonate minerals of varying mineralogy for the past 17,000 years. The history of sedimentation in Bear Lake is documented through the study of isotopic ratios of oxygen, carbon, and strontium, percent organic carbon, percent CaCO3, X-ray diffraction mineralogy, HCl-leach inorganic geochemistry, and magnetic properties on samples from three piston cores. Historically, the Bear River, the main source of water for Great Salt Lake, did not enter Bear Lake until it was artificially diverted into the lake at the beginning of the 20th century. However, during the last glacial …

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Generalized Geologic Map For Land-Use Planning: Nicholas County, Kentucky, Daniel I. Carey, Richard A. Smath Jan 2006

Generalized Geologic Map For Land-Use Planning: Nicholas County, Kentucky, Daniel I. Carey, Richard A. Smath

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Stratigraphic Column Of The Kope And Fairview Formations, Kentucky 445, Brent, Kentucky, Steven M. Holland, Arnold I. Miller, David L. Meyer, Benjamin F. Dattilo, Sharon C. St. Louis Diekmeyer Jan 2006

Stratigraphic Column Of The Kope And Fairview Formations, Kentucky 445, Brent, Kentucky, Steven M. Holland, Arnold I. Miller, David L. Meyer, Benjamin F. Dattilo, Sharon C. St. Louis Diekmeyer

Map and Chart--KGS

The Upper Ordovician Kope Formation is exposed over a broad area of southwestern Ohio, southeastern Indiana, and northern Kentucky (Weir and others, 1984). Roadcuts along Ky. 445 near Brent (Figs. 2-3) and adjacent roadcuts along Interstate 275 expose a nearly complete section of the Kope Formation as well as the overlying Fairview Formation.

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Generalized Geologic Map For Land-Use Planning: Campbell County, Kentucky, Richard A. Smath, Daniel I. Carey, Bart Davidson, John D. Kiefer, Ken Daniels Jan 2006

Generalized Geologic Map For Land-Use Planning: Campbell County, Kentucky, Richard A. Smath, Daniel I. Carey, Bart Davidson, John D. Kiefer, Ken Daniels

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Carroll County, Kentucky, Richard A. Smath, Bart Davidson, Daniel I. Carey, John D. Kiefer Jan 2006

Generalized Geologic Map For Land-Use Planning: Carroll County, Kentucky, Richard A. Smath, Bart Davidson, Daniel I. Carey, John D. Kiefer

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Clark County, Kentucky, Daniel I. Carey, Emma Witt Jan 2006

Generalized Geologic Map For Land-Use Planning: Clark County, Kentucky, Daniel I. Carey, Emma Witt

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Bourbon County, Kentucky, Daniel I. Carey Jan 2006

Generalized Geologic Map For Land-Use Planning: Bourbon County, Kentucky, Daniel I. Carey

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Meade County, Kentucky, Daniel I. Carey, Richard E. Sergeant, Peter Eclov Jan 2006

Generalized Geologic Map For Land-Use Planning: Meade County, Kentucky, Daniel I. Carey, Richard E. Sergeant, Peter Eclov

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Clay County, Kentucky, Oscar B. Davidson, Daniel I. Carey, John Storm Jan 2006

Generalized Geologic Map For Land-Use Planning: Clay County, Kentucky, Oscar B. Davidson, Daniel I. Carey, John Storm

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Mccreary County, Kentucky, Daniel I. Carey, Randall L. Paylor, Bethany L. Overfield Jan 2006

Generalized Geologic Map For Land-Use Planning: Mccreary County, Kentucky, Daniel I. Carey, Randall L. Paylor, Bethany L. Overfield

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Owen County, Kentucky, Daniel I. Carey, Cam Flanders Jan 2006

Generalized Geologic Map For Land-Use Planning: Owen County, Kentucky, Daniel I. Carey, Cam Flanders

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Grayson County, Kentucky, E. Glynn Beck, David A. Williams, Daniel I. Carey Jan 2006

Generalized Geologic Map For Land-Use Planning: Grayson County, Kentucky, E. Glynn Beck, David A. Williams, Daniel I. Carey

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Trimble County, Kentucky, Daniel I. Carey, Bart Davidson Jan 2006

Generalized Geologic Map For Land-Use Planning: Trimble County, Kentucky, Daniel I. Carey, Bart Davidson

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Generalized Geologic Map For Land-Use Planning: Harrison County, Kentucky, Daniel I. Carey, Richard A. Smath Jan 2006

Generalized Geologic Map For Land-Use Planning: Harrison County, Kentucky, Daniel I. Carey, Richard A. Smath

Map and Chart--KGS

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock.

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Strain Accumulation Across The Carrizo Segment Of The San Andreas Fault, California: Impact Of Laterally Varying Crustal Properties, Gina Schmalzle, Timothy H. Dixon, Rocco Malservisi, Rob Govers Jan 2006

Strain Accumulation Across The Carrizo Segment Of The San Andreas Fault, California: Impact Of Laterally Varying Crustal Properties, Gina Schmalzle, Timothy H. Dixon, Rocco Malservisi, Rob Govers

School of Geosciences Faculty and Staff Publications

Major strike slip faults juxtapose geologically dissimilar terrain which may vary in mechanical properties, leading to an asymmetric pattern of strain accumulation. We present new GPS data on the Carrizo segment of the San Andreas Fault, separating the Salinian block southwest of the fault from Franciscan terrane northeast of the fault, to better quantify asymmetric strain accumulation. We also present a series of finite element models to investigate the possible role of variable elastic layer thickness and material properties of the upper crust. The geodetic data are well fit with a simple model comprising a weak upper crustal zone 10–25 …

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Groundwater-Level Changes In Nebraska, Spring 2000 To Spring 2006/ Density Of Registered Irrigation Wells In Nebraska August 2005, Conservation Survey Division Jan 2006

Groundwater-Level Changes In Nebraska, Spring 2000 To Spring 2006/ Density Of Registered Irrigation Wells In Nebraska August 2005, Conservation Survey Division

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Pelagic Functional Group Modeling: Progress, Challenges And Prospects, Raleigh R. Hood, Edward A. Laws, Robert A. Armstrong, Nicholas R. Bates, Christopher W. Brown, Craig A. Carlson, Fei Chai, Scott C. Doney, Paul G. Falkowski, Richard A. Feely, Marjorie A. M. Friedrichs Jan 2006

Pelagic Functional Group Modeling: Progress, Challenges And Prospects, Raleigh R. Hood, Edward A. Laws, Robert A. Armstrong, Nicholas R. Bates, Christopher W. Brown, Craig A. Carlson, Fei Chai, Scott C. Doney, Paul G. Falkowski, Richard A. Feely, Marjorie A. M. Friedrichs

CCPO Publications

In this paper, we review the state of the art and major challenges in current efforts to incorporate biogeochemical functional groups into models that can be applied on basin-wide and global scales, with an emphasis on models that might ultimately be used to predict how biogeochemical cycles in the ocean will respond to global warming. We define the term "biogeochemical functional group" to refer to groups of organisms that mediate specific chemical reactions in the ocean. Thus, according to this definition, "functional groups" have no phylogenetic meaning-these are composed of many different species with common biogeochemical functions.

Substantial progress has …

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Flow Resistance Dynamics In Step-Pool Stream Channels: 1. Large Woody Debris And Controls On Total Resistance, Andrew C. Wilcox, Ellen E. Wohl Jan 2006

Flow Resistance Dynamics In Step-Pool Stream Channels: 1. Large Woody Debris And Controls On Total Resistance, Andrew C. Wilcox, Ellen E. Wohl

Geosciences Faculty Publications

Flow resistance dynamics in step-pool channels were investigated through physical modeling using a laboratory flume. Variables contributing to flow resistance in step-pool channels were manipulated in order to measure the effects of various large woody debris (LWD) configurations, steps, grains, discharge, and slope on total flow resistance. This entailed nearly 400 flume runs, organized into a series of factorial experiments. Factorial analyses of variance indicated significant two-way and three-way interaction effects between steps, grains, and LWD, illustrating the complexity of flow resistance in these channels. Interactions between steps and LWD resulted in substantially greater flow resistance for steps with LWD …

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Flow Resistance Dynamics In Step-Pool Channels: 2. Partitioning Between Grain, Spill, And Woody Debris Resistance, Andrew C. Wilcox, Jonathan M. Nelson, Ellen E. Wohl Jan 2006

Flow Resistance Dynamics In Step-Pool Channels: 2. Partitioning Between Grain, Spill, And Woody Debris Resistance, Andrew C. Wilcox, Jonathan M. Nelson, Ellen E. Wohl

Geosciences Faculty Publications

In step-pool stream channels, flow resistance is created primarily by bed sediments, spill over step-pool bed forms, and large woody debris (LWD). In order to measure resistance partitioning between grains, steps, and LWD in step-pool channels we completed laboratory flume runs in which total resistance was measured with and without grains and steps, with various LWD configurations, and at multiple slopes and discharges. Tests of additive approaches to resistance partitioning found that partitioning estimates are highly sensitive to the order in which components are calculated and that such approaches inflate the values of difficult-to-measure components that are calculated by subtraction …

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Evaluating Surface Area-Basin Volume Relationships For Prairie Potholes, Mike A. Davis Jan 2006

Evaluating Surface Area-Basin Volume Relationships For Prairie Potholes, Mike A. Davis

Theses and Dissertations

Establishing a relationship between surface area and volume of prairie potholes provides a simple method to estimate changes in water storage across the landscape. Applications include better prediction of floods and improved design for wetland restoration. Length, width, depth, surface area, and volumes were surveyed for eighty two potholes within the upper Turtle River watershed which lies sixty kilometers west of Grand Forks, ND. These data were used to determine the relationship and uncertainty between pothole surface and volume. Chi squared tests defined distributions of each variable. F and T statistical tests resolved similarities in variance and mean. The eighty …

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Wellbore Stability In Water-Sensitive Shales, Qingfeng Tao Jan 2006

Wellbore Stability In Water-Sensitive Shales, Qingfeng Tao

Theses and Dissertations

Wellbore instability is a widespread problem, especially when drilling in deep, low strength shale formations at high temperature and pressure. The instability can be caused by the high compressive effective stress or tensile stress due to the stress concentration and pore pressure increase while drilling. In addition to the in-situ stress and shale strength, shale instability is affected by drilling mud properties including mud weight, temperature and salinity. To assess wellbore stability in these situations, Diek and Ghassemi (2004) developed a non-linear coupled chemo-poro-thermoelasticity theory. The linearized version of the theory allows one to analytically investigate the coupled impacts of …

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Lithofacies, Architecture And Sequence Stratigraphic Interpretation Of The Upper Pennsylvanian Indian Cave Sandstone, Northern Midcontinent Shelf, U.S.A. (Southeastern Nebraska)., Steven A. Fischbein Jan 2006

Lithofacies, Architecture And Sequence Stratigraphic Interpretation Of The Upper Pennsylvanian Indian Cave Sandstone, Northern Midcontinent Shelf, U.S.A. (Southeastern Nebraska)., Steven A. Fischbein

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

The Virgilian “Indian Cave Sandstone” (ICS) is herein redefined as at least four incised valley fills (IVFs) of at least two different ages. These IVFs are composed of irregularly bounded, tabular-lenticular units of trough cross-bedded sandstone, grading vertically into tabular-lenticular units of mudstone-and-sandstone-dominated heterolith. Three IVFs, wider (< 2 km) than they are deep (> 30 m), are composed of multiple storeys grading upward from fluvial-to-estuarine facies to upper-estuarine facies. Storey boundaries are delineated by bounding surfaces underlying conglomerates with heterolithic clasts. One IVF (Honey Creek, NE) is smaller than the others, (> 0.5 km wide and > 25 m deep) and appears to be composed of a …

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Plant Paleoecology Of The Late Devonian Red Hill Locality, North-Central Pennsylvania, An Archaeopteris-Dominated Wetland Plant Community And Early Tetrapod Site., Walter L. Cressler Iii Jan 2006

Plant Paleoecology Of The Late Devonian Red Hill Locality, North-Central Pennsylvania, An Archaeopteris-Dominated Wetland Plant Community And Early Tetrapod Site., Walter L. Cressler Iii

Earth & Space Sciences Faculty Publications

The Late Devonian Red Hill locality in north-central Pennsylvania contains an Archaeopteris-dominated plant fossil assemblage, a diverse fossil fauna, and an extensive sedimentary sequence ideal for investigating the landscapes and biotic associations of the earliest forest ecosystems. Sedimentological analysis of the main plantfossil bearing layer at Red Hill indicates that it was a fl ood-plain pond. A seasonal wet-and-dry climate is indicated by well-developed paleovertisols. The presence of charcoal interspersed with plant fossils indicates that fi res occurred in this landscape.Fires appear to have primarily affected the fern Rhacophyton. The specifi city of the fires, the distribution profi …

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Estimating Surface Runoff In The Illinois River Basin For The Management Of Nonpoint-Source Phosphorus Loads, Adam T. Mcclymont, Mary C. Savin, Brian E. Haggard Jan 2006

Estimating Surface Runoff In The Illinois River Basin For The Management Of Nonpoint-Source Phosphorus Loads, Adam T. Mcclymont, Mary C. Savin, Brian E. Haggard

Discovery, The Student Journal of Dale Bumpers College of Agricultural, Food and Life Sciences

With the growing concern about elevated phosphorus (P) concentrations in regional lakes, rivers, and streams, it is essential to investigate factors contributing to P transport from the landscape. Phosphorus fluxes from nonpoint sources, particularly land applications of poultry litter and other animal manures, are closely related to the amount and production of surface runoff. Daily stream discharge and the software program, Base Flow Index (BFI), were used to estimate the amount and temporal patterns of surface runoff at different locations within the Illinois River Basin, including selected tributaries in northwest Arkansas and northeast Oklahoma. Daily streamflow data from nine U.S. …

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A Tool For Estimating Best Management Practice Effectiveness In Arkansas, Katherine R. Merriman, Margaret Gitau, Indrajeet Chaubey Jan 2006

A Tool For Estimating Best Management Practice Effectiveness In Arkansas, Katherine R. Merriman, Margaret Gitau, Indrajeet Chaubey

Discovery, The Student Journal of Dale Bumpers College of Agricultural, Food and Life Sciences

Increased nutrient and sediment losses from expanding agricultural practices and urban development in Arkansas are important environmental concerns. Best Management Practices (BMPs) are being implemented to lessen the effects of these developments on existing water bodies. There is, however, insufficient scientific base as to the effectiveness of these practices. A number of studies have been conducted in recent years to determine BMP effectiveness. Data from these studies can only be reliably used for the individual site from which they were obtained. When considered collectively, these data comprise quantitative effectiveness over a wide range of conditions and can thus be used …

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Stratigraphic And Palaeoenvironmental Significance Of Bartonian–Priabonian (Middle–Late Eocene) Microfossils From The Başçeşme Formation, Denizli Province, Western Anatolia, M. Serkan Akki̇raz, Funda Akgün, Sefer Örçen, Angela Bruch, Volker Mosbrugger Jan 2006

Stratigraphic And Palaeoenvironmental Significance Of Bartonian–Priabonian (Middle–Late Eocene) Microfossils From The Başçeşme Formation, Denizli Province, Western Anatolia, M. Serkan Akki̇raz, Funda Akgün, Sefer Örçen, Angela Bruch, Volker Mosbrugger

Turkish Journal of Earth Sciences

This study explains the stratigraphical and palaeoenvironmental significance of Bartonian-Priabonian (Middle-Late Eocene) fossils, the fauna and flora obtained from the Başçeşme formation of the Çardak-Tokça basin (western Anatolia). The studied sequence is an outcrop from the Başçeşme formation, deposited in a shallow-marine to coastal environment without stratigraphic breaks. Forty genera and 58 species have been recognized in the palynological assemblage of the Başçeşme formation. A well-preserved diverse palynomorph and foraminiferal assemblages yield the Middle-Late Eocene age for the Başçeşme formation. In western Anatolia, mangrove elements Nypa and Pelliciera have been first recorded in this study. The pollen of Mauritia and …

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Evaluation Of Water-Retention Ability Of Eastern Arkansas Prairie And Agricultural Soil, Maria L. Barrenechea, Kristofor R. Brye Jan 2006

Evaluation Of Water-Retention Ability Of Eastern Arkansas Prairie And Agricultural Soil, Maria L. Barrenechea, Kristofor R. Brye

Discovery, The Student Journal of Dale Bumpers College of Agricultural, Food and Life Sciences

Agricultural land use affects soil physical properties, such as bulk density, water content, organic matter content, and soil structure; all of which in turn affect ecosystem productivity. The objective of this study was to evaluate the effects of: 1) time since aboveground biomass has been removed by haying (i.e., 0 vs. 23 years), and 2) land use (i.e., undisturbed tallgrass prairie vs. cultivated agriculture) on water-retention characteristics in a silt-loam soil of the Grand Prairie region of eastern Arkansas. Soil samples were collected from the 0- to 10-cm depth and were wetted with varying amounts of distillated water to create …

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Pyritized Tube Feet In A Protasterid Ophiuroid From The Upper Ordovician Of Kentucky, U.S.A., Alexander Glass Jan 2006

Pyritized Tube Feet In A Protasterid Ophiuroid From The Upper Ordovician Of Kentucky, U.S.A., Alexander Glass

All Faculty Scholarship for the College of the Sciences

A single specimen of the protasterid ophiuroid Protasterina flexuosa from the Kope Formation (Cincinnatian, Upper Ordovician) of Kentucky exhibits three−dimensionally pyritized tube feet. This represents the first report of soft−tissue preservation in an echinoderm from the type−Cincinnatian series. The tube feet are solid and lack all internal structure. They consist of aggregated masses of small euhedral to subhedral pyrite crystals suggesting that pyritization, although decay−induced and mediated, did not necessarily replicate soft−tissues but might instead have formed inside the void−spaces left behind during the decay process. The discovery of pyritized soft−tissue as delicate as ophiuroid tube feet suggests that similar …

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Geochronology And Tectonic Significance Of Middle Proterozoic Granitic Orthogneiss, North Qaidam Hp/Uhp Terrane, Western China, Chris G. Mattinson, Joseph L. Wooden, Juhn G. Liou, D. K. Bird, C. L. Wu Jan 2006

Geochronology And Tectonic Significance Of Middle Proterozoic Granitic Orthogneiss, North Qaidam Hp/Uhp Terrane, Western China, Chris G. Mattinson, Joseph L. Wooden, Juhn G. Liou, D. K. Bird, C. L. Wu

All Faculty Scholarship for the College of the Sciences

Amphibolite-facies para- and orthogneisses near Dulan, in the southeast part of the North Qaidam terrane, enclose minor ultra-high pressure (UHP) eclogite and peridotite. Field relations and coesite inclusions in zircons from paragneiss suggest that felsic, mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. Ion microprobe U–Pb and REE analyses of zircons from two granitic orthogneisses indicate magmatic crystallization at 927 ± Ma and 921 ± 7 Ma. Zircon rims in one of these samples yield younger ages (397–618 Ma) compatible with partial zircon recrystallization during in-situ Ordovician-Silurian eclogite-facies metamorphism previously determined from eclogite and paragneiss …

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