21,003 research outputs found
The continental record and the generation of continental crust
No full textContinental crust is the archive of Earth history. The spatial and temporal distribution of Earth's record of rock units and events is heterogeneous; for example, ages of igneous crystallization, metamorphism, continental margins, mineralization, and seawater and atmospheric proxies are distributed about a series of peaks and troughs. This distribution reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. The physio-chemical resilience of zircons and their derivation largely from felsic igneous rocks means that they are important indicators of the crustal record. Furthermore, detrital zircons, which sample a range of source rocks, provide a more representative record than direct analysis of grains in igneous rocks. Analysis of detrital zircons suggests that at least ∼60%–70% of the present volume of the continental crust had been generated by 3 Ga. Such estimates seek to take account of the extent to which the old crustal material is underrepresented in the sedimentary record, and they imply that there were greater volumes of continental crust in the Archean than might be inferred from the compositions of detrital zircons and sediments. The growth of continental crust was a continuous rather than an episodic process, but there was a marked decrease in the rate of crustal growth at ca. 3 Ga, which may have been linked to the onset of significant crustal recycling, probably through subduction at convergent plate margins. The Hadean and Early Archean continental record is poorly preserved and characterized by a bimodal TTG (tonalites, trondhjemites, and granodiorites) and greenstone association that differs from the younger record that can be more directly related to a plate-tectonic regime. The paucity of this early record has led to competing and equivocal models invoking plate-tectonic– and mantle-plume–dominated processes. The 60%–70% of the present volume of the continental crust estimated to have been present at 3 Ga contrasts markedly with the <10% of crust of that age apparently still preserved and requires ongoing destruction (recycling) of crust and subcontinental mantle lithosphere back into the mantle through processes such as subduction and delamination.Peer reviewe
Assessing Model Fit: Caveats and Recommendations for Confirmatory Factor Analysis and Exploratory Structural Equation Modeling
No full textDespite the limitations of overgeneralizing cutoff values for confirmatory factor analysis (CFA; e.g., Marsh, Hau, & Wen, 2004), they are still often employed as golden rules for assessing factorial validity in sport and exercise psychology. The purpose of this study was to investigate the appropriateness of using the CFA approach with these cutoff values for typical multidimensional measures. Furthermore, we ought to examine how a model could be respecified to achieve acceptable fit and explored whether exploratory structural equation modeling (ESEM) provides a more appropriate assessment of model fit. Six multidimensional measures commonly used in sport and exercise psychology research were examined using CFA and ESEM. Despite demonstrating good validity in previous research, all eight failed to meet the cutoff values proposed by Hu and Bentler. ESEM improved model fit in all measures. In conclusion, we suggest that model misfit in this study demonstrates the problem with interpreting cutoff values rigidly. Furthermore, we recommend ESEM as a preferred approach to examining model fit in multidimensional measures
A high-resolution wide-angle seismic study of the crust beneath the Northumberland trough
No full textIn June 1987, during the BIRPS MOBIL normal-incidence seismic profiling programme, off the East coast of England, the University of Durham recorded simultaneously at several land based seismic stations in Northern England. The resulting wide-angle data, particularly from Line 1, have excellent resolution in both space and time due to the airgun source and 50 m shot spacing. The interpretation of the Line 1 wide-angle data at Durham used BEAM87, Cerveny's Gaussian beam modelling package. The main arrivals interpreted include the upper crustal refraction (Pg), the Moho wide-angle reflection (PmP), the upper mantle refraction (Pn), and a very high amplitude arrival (D) which merges into PmP. Modelling gave a crust about 30 km thick with a change in velocity gradient and a slight velocity contrast at about 20 km depth. There are several wide-angle reflections from interfaces at mid-crustal depths, between 10 and 20 km depth, and the bottom 2 km of the crust has a high velocity of about 7 kms(^-1). Two interesting results are that a lateral velocity change about 40 km offshore is required to fit the Pg travel times; also that arrival D is modelled best as the remnant of a step on the Moho at the same location. These appear to be borne out by the normal incidence data for line 1, which show a lateral decrease in the mid-crustal reflectivity above a set of strong, westerly-dipping reflections at Moho depths. These results suggest the presence of a major crustal fault about 40 km offshore. It is suggested that this fault may be the northward continuation of the Dowsing Fault Zone
Crustal accretion at the Reykjanes Ridge, 61°–62°N
No full textWe report results of a seismic, gravity, and magnetic survey of the Reykjanes Ridge spreading center at 61°–62°N, about 600 km from the center of the Iceland mantle plume. Anomalously shallow water on the ridge crest enabled us to record seismic refractions on a 2.4 km hydrophone streamer. The velocity within layer 2A is 2.4 ± 0.3 km s−1, and its mean thickness is 400 ± 100 m. The velocity at the base of layer 2A is 3.3 ± 0.3 km s−1 on the ridge axis, increasing with crustal age to ∼4.0 km s−1 at 1.5 Ma and ∼4.5 km s−1 at 5 Ma. Assuming that seismic layer 2A on the ridge axis is also the extrusive layer, i.e., the magnetic source layer, we have successfully modeled the variations in amplitude of the magnetic field. The best magnetic model includes enhanced magnetization within layer 2A at the sites of recent volcanic activity as independently recognized in side-scan sonar data. We also present a full crustal seismic model, based on wide-angle seismic recordings on digital ocean bottom hydrophones and disposable sonobuoys. The seismic model is complemented by gravity modeling, which further suggests that the ridge crest is in isostatic equilibrium. The zero age crust is 10.0 km thick, while crust of age 5 Ma is 7.8 km thick. These crustal thicknesses are greater than those of normal oceanic crust, which we attribute to the presence of anomalously hot asthenospheric mantle beneath the spreading center. We suggest that the variation in thickness between 0 Ma and 5 Ma crust is caused by temporal variation in the plume-fed asthenospheric temperature beneath the Reykjanes Ridge
Who Was Edmund Lee?
No full textLocal author Peggy Donoho discusses her pioneer ancestor, Edmund Lee, and her work to preserve their family cemetery
The Future of Canadian Climate Policy — with Marc Lee
No full textMarc Lee is a Senior Economist at the Canadian Centre for Policy Alternatives\u27 BC Office. In addition to tracking federal and provincial budgets and economic trends, Marc has published on a range of topics from poverty and inequality to globalization and international trade to public services and regulation. Marc is the Co-Director of the Climate Justice Project, a research partnership with UBC\u27s School of Community and Regional Planning that examines the links between climate change policies and social justice.Resources:Climate Justice Project: www.policyalternatives.ca/projects/cli…tice-projectMarc Lee\u27s Posts on Policy Note: www.policynote.ca/author/marclee/Canadian Centre for Policy Alternatives: www.policyalternatives.ca/Marc\u27s Twitter: twitter.com/MarcLeeCCPA International Panel on Climate Change, 2021 report: www.ipcc.ch/report/ar6/wg1
Dr. Aleksandra Sznajder Lee – Faculty Author Interview
No full textDr. Aleksandra Sznajder Lee, Associate Professor of Political Science, discusses her new book, Transnational Capitalism in East Central Europe’s Heavy Industry, published recently by the University of Michigan Press. Focusing on the steel industry during the post-communist transition from 1989 through 2009, Dr. Sznajder Lee traces the transformation of flagship state enterprises in the Czech Republic, Poland, Romania, and Slovakia into the subsidiaries of large, international corporations
Letter from K.W. Lee to Friends of Michi Weglyn, November 1, 1997
No full textA letter from K. W. (Kyung Won) Lee, an investigative journalist who wrote for the Sacramento Union, to the Friends of Michi Weglyn. Lee wrote that Weglyn was instrumental in the campaign to free Chol Soo Lee, a Korean American man was on death row, but later had his convictions overturned. Lee also wrote that other Japanese American activists were instrumental to the success of this campaign.These materials are from box 73 and 74 of the Frank Chin Papers. The Frank Chin Papers contain personal and professional correspondence between Frank Chin and Michi Weglyn relating to particular projects on which either author was working as well as files related to the Day of Remembrance Tribute to Michi Weglyn
Francis Lee Utley (interview)
No full textThis interview is included in the American Folklore Society Oral History Project held at the Archive of Folk Culture, American Folklife Center, Library of Congress, Washington, D.C. This item consists of oral history interviews with folklorist Francis Lee Utley conducted in 1973 by Patrick B. Mullen and Richard Reuss for the American Folklore Society Oral History Project. This collection consists of 2 sound tape reels : analog, 3 3/4 ips, 2 track, mono. ; 7 in. Originally recorded on July 19, 1973 by Patrick B. Mullen on a 7-inch reel, 3 3/4 ips, 2 track at an unidentified location; and on November 3, 1973 by Patrick B. Mullen and by Richard Reuss at the annual meeting of the American Folklore Society in Nashville, Tennessee on a Sony audiocassette. Sound recordings are first generation copies on two sound tape reels, 7 in. Biography/History note: Francis Lee Utley was born May 25, 1907 in Watertown, Wisconsin, and died March 8, 1974. He was a folklorist, medievalist, linguist, educator, and author who earned his M.A. in 1934 and Ph.D. in 1936 in literature at Harvard University. He taught at Ohio State University and the University of California at Berkeley, and was president of the American Folklore Society from 1951-1952
Dear SIS Seminar, Nina June Lee, Young Scholar, Fall 2020
No full textNina J. Lee is a graduating senior Comparative Women�s Studies Major from Everett, Massachusetts. After Spelman, she will pursue a Masters of Education in Community Engagement with a concentration in Community Organizations and Nonprofit Management
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