Characterization of matrix material in Northwest Africa 5343: Weathering and thermal metamorphism of the least equilibrated CK chondrite     

Tasha L. Dunn  Oriana K. Battifarano  Juliane Gross  Emma J. O'Hara 《Meteoritics & planetary science》2018,53(10):2165-2180

Based on the chemical heterogeneity of chondrule and matrix olivine, Northwest Africa (NWA) 5343 is the least metamorphosed CK chondrite reported so far. To better constrain the lower limit of metamorphism in the CK chondrites, we performed a detailed analysis of matrix material in NWA 5343, including characterization of the texture and bulk composition and analyses of individual silicate minerals. Results suggest that NWA 5343 is petrologic type 3.6 or 3.7. Although silicate minerals in the matrix seem to be equilibrated to roughly the same extent throughout the sample, there are recognizable differences in grain size and shape. These textural differences may be the result of transient heating events during impacts, which would be likely on the CK chondrite parent body. The difference between the extent of chemical equilibration and texture may also suggest that grain size and shape are still sensitive to metamorphism at petrologic subtypes where silicate mineral equilibration is nearly complete (e.g., >3.7). Carbonate material present in NWA 5343 is a product of terrestrial weathering; however, infiltration of a Ca-bearing fluid did not influence the composition of silicate minerals in the matrix. To evaluate the possibility of a continuous metamorphic sequence between the CV and CK chondrites, the bulk matrix composition of NWA 5343 is compared to the CV_red chondrite, Vigarano. Although the matrix composition of NWA 5343 could be derived by secondary processing of a Vigarano-like precursor, porosity and texture of matrix olivine in NWA 5343 are hard to reconcile with a continuous metamorphic sequence.  相似文献   

Environments,Natures, and Social Theory: Toward a Critical Hybridity,by Damian F. White,Alan P. Rudy,and Brian J. Gareau,eds.     

Jeff Rose 《社会与自然资源》2018,31(4):508-510

  相似文献   

Developing and Sequencing Community Engagement and Experiential Education: A Case Study of Urban Geography Teaching and Research     

Jeff Rose 《The Professional geographer》2018,70(2):305-310

Community engagement curricula and course design can provide substantial experiences for both community members and participating students. Using a case study approach, this research focuses on four steps in this process: initial community relationship forming, engaging in community service, transitioning to civic engagement, and developing a community-based research program. Narrative examples from student course evaluations position these community-based experiences as transformative for multiple parties. Institutional structures are presented as helpful entrees to engagement for students, while noting that community relationships provide contextualized, powerful, and meaningful relationships, supporting recommendations for emerging and existing community engagement programs.  相似文献   

In Situ Chemical Treatment: A Love‐Hate Relationship          下载免费PDF全文

Suthan Suthersan  Jeff McDonough  Matt Schnobrich  Craig Divine 《Ground Water Monitoring & Remediation》2017,37(1):17-26

  相似文献   

Early-season crop area estimates for winter crops in NE Australia using MODIS satellite imagery   总被引：1，自引：0，他引：1  

A.B. Potgieter  A. Apan  G. Hammer  P. Dunn 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(4):380-387

  相似文献   

Innovation in GIS Research UK     

Dr. Christine E. Dunn 《Transactions in GIS》2010,14(3):219-221

  相似文献   

Steepland geomorphology     

Jeff Warburton 《第四纪科学杂志》1998,13(4):357-358

  相似文献   

Petrography and geochemistry of manganiferous rocks in the Mankwadzi area in the southern Kibi‐Winneba metavolcanic belt,Ghana: Implications for genesis of Mn formations in the Birimian of West Africa     

Kwabina Ibrahim  Frank K. Nyame  Thomas Armah  Johnson Manu  Jeff Baah‐Acheamfour  Jacob Tigme 《Island Arc》2020,29(1)

Manganiferous rocks in the Mankwadzi area in the southernmost portion of the Kibi‐Winneba metavolcanic belt, one of several Mn occurrences in the Paleoproterozoic Birimian of Ghana, are hosted in hornblende schist and amphibolite. These rocks are, in places, intruded by hornblende dyke. In outcrop, the manganiferous rocks appear to be conformable with the host schist and amphibolite, are macroscopically dark, fine‐grained and structurally massive to distinctly banded. Observed alternating light and dark occasionally macro‐folded bands suggest post‐depositional deformation of both light and dark bands. Microscopic observations revealed that the light bands are dominantly Si‐rich and the dark bands mainly of opaque minerals. Whole rock analyses of the manganiferous rocks show high contents of MnO (16.75–27.4 wt%) suggesting that the opaque minerals are likely rich in Mn. The analyzed rock samples show moderate to strong enrichments in light rare earth elements compared to heavy rare earth elements. Whereas the manganiferous rocks show perceptibly negative Eu anomaly, host hornblende schist and hornblende dyke do not. Eu anomaly in amphibolite samples is, however, uncertain as the three samples analyzed gave positive, negative and no Eu anomalies. Based on the field characteristics, microscopic and geochemical features, we suggest that the Mn occurrence in the Mankwadzi area originated via sedimentary deposition and was later modified by metamorphism, hydrothermal and/or supergene processes similar to manganiferous occurrences at Nsuta and Tambao in the Birimian of West Africa.  相似文献   

Hydraulic Performance of the Horizontal Reactive Media Treatment Well: Pilot and Numerical Study     

Blossom N. Nzeribe  Wen Li  Michelle Crimi  Guangming Yao  Craig E. Divine  Jeff McDonough  Jack Wang 《Ground Water Monitoring & Remediation》2020,40(3):30-41

This study is focused on a passive treatment system known as the horizontal reactive treatment well (HRX Well®) installed parallel to groundwater flow, which operates on the principle of flow focusing that results from the hydraulic conductivity (K) ratio of the well and aquifer media. Passive flow and capture in the HRX Well are described by simplified equations adapted from Darcy's Law. A field pilot-scale study (PSS) and numerical simulations using a finite element method (FEM) were conducted to verify the HRX Well concept and test the validity of the HRX Well-simplified equations. The hydraulic performance results from both studies were observed to be within a close agreement to the simplified equations and their hydraulic capture width approximately five times greater than the well diameter (0.20 m). Key parameters affecting capture included the aquifer thickness, well diameter, and permeability ratio of the HRX Well treatment media and aquifer material. During pilot testing, the HRX Well captured 39% of flow while representing 0.5% of the test pit cross-sectional volume, indicating that the well captures a substantial amount of surrounding groundwater. While uncertainty in the aquifer and well properties (porosity, K, well losses), including the effects of boundary conditions, may have caused minor differences in the results, data from this study indicate that the simplified equations are valid for the conceptual design of a field study. A full-scale HRX Well was installed at Site SS003 at Vanderberg Air Force Base, California, in July/August 2018 based on outcomes from this study.  相似文献   

Field Demonstration of the Horizontal Treatment Well (HRX Well®) for Passive In Situ Remediation     

Craig E. Divine  Jesse Wright  Michelle Crimi  J.F. Devlin  Michael Lubrecht  Jack Wang  Jeff McDonough  Michael Kladias  Jesse Hinkle  Allison Cormican  Trevor Osorno  Blossom N. Nzeribe  Fiona Laramay  Daniel Ombalski  Kathleen Gerber  Hunter Anderson 《Ground Water Monitoring & Remediation》2020,40(3):42-54

The horizontal reactive media treatment well (HRX Well®) uses directionally drilled horizontal wells filled with a treatment media to induce flow-focusing behavior created by the well-to-aquifer permeability contrast to passively capture proportionally large volumes of groundwater. Groundwater is treated in situ as it flows through the HRX Well and downgradient portions of the aquifer are cleaned via elution as these zones are flushed with clean water discharging from the HRX Well. The HRX Well concept is particularly well suited for sites where long-term mass discharge control is a primary performance objective. This concept is appropriate for recalcitrant and difficult-to-treat constituents, including chlorinated solvents, per- and polyfluoroalkyl substances (PFAS), 1,4-dioxane, and metals. A full-scale HRX Well was installed and operated to treat trichloroethene (TCE) with zero valent iron (ZVI). The model-predicted enhanced flow through the HRX Well (compared to the flow in and equivalent cross-sectional area orthogonal to flow in the natural formation before HRX Well installation) and treatment zone width was consistent with flows and widths estimated independently by point velocity probe (PVP) testing, HRX Well tracer testing, and observed treatment in downgradient monitoring wells. The actual average capture zone width was estimated to be between 45 and 69 feet. Total TCE mass discharge reduction was maintained through the duration of the performance monitoring period and exceeded 99.99% (%). Decreases in TCE concentrations were observed at all four downgradient monitoring wells within the treatment zone (ranging from 50 to 74% at day 436), and the first arrival of treated water was consistent with model predictions. The field demonstration confirmed the HRX Well technology is best suited for long-term mass discharge control, can be installed under active infrastructure, requires limited ongoing operation and maintenance, and has low life cycle energy and water requirements.  相似文献