Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where David B. Stewart is active.

Publication


Featured researches published by David B. Stewart.


Geological Society of America Bulletin | 2008

The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition—Implications for the rifting of Ganderia

Klaus J. Schulz; David B. Stewart; Robert D. Tucker; Jeffrey C. Pollock; Robert A. Ayuso

The Ellsworth terrane is one of a number of fault-bounded blocks that occur along the eastern margin of Ganderia, the westernmost of the peri-Gondwanan domains in the northern Appalachians that were accreted to Laurentia in the Paleozoic. Geologic relations, detrital zircon ages, and basalt geochemistry suggest that the Ellsworth terrane is part of Ganderia and not an exotic terrane. In the Penobscot Bay area of coastal Maine, the Ellsworth terrane is dominantly composed of bimodal basalt-rhyolite volcanic sequences of the Ellsworth Schist and unconformably overlying Castine Volcanics. We use new U-Pb zircon geochronology, geochemistry, and Nd and Pb isotopes for these volcanic sequences to constrain the petrogenetic history and paleotectonic setting of the Ellsworth terrane and its relationship with Ganderia. U-Pb zircon geochronology for rhyolites indicates that both the Ellsworth Schist (508.6 ± 0.8 Ma) and overlying Castine Volcanics (503.5 ± 2.5 Ma) are Middle Cambrian in age. Two tholeiitic basalt types are recognized. Type Tb-1 basalt, present as pillowed and massive lava fl ows and as sills in both units, has depleted La and Ce ([La/Nd] N = 0.53‐0.87) values, fl at heavy rare earth element (REE) values, and no positive Th or negative Ta anomalies on primitive mantle‐ normalized diagrams. In contrast, type Tb-2 basalt, present only in the Castine Volcanics, has slightly enriched LREE ([La/Yb] N = 1.42‐ 2.92) values and no Th or Ta anomalies. Both basalt types have strongly positive e Nd (500) values (Tb-1 = +7.9‐+8.6; Tb-2 = +5.6‐+7.0) and relatively enriched Pb isotopic compositions ( 206


Geological Society of America Bulletin | 1973

Isotopic and Paleontologic Evidence for Correlating Three Volcanic Sequences in the Maine Coastal Volcanic Belt

Douglas G. Brookins; Jean M. Berdan; David B. Stewart

The correlation of the Castine Volcanics, the Thorofare Andesite–Vinalhaven Rhyolite sequence, and the Cranberry Island Series of Shaler (1889), suggested by their similar lithologies, appearance, and structural histories, is supported by the results of Rb-Sr whole-rock isotopic analyses and by the faunal assemblages from old and new fossil localities in the Castine Volcanics, Ames Knob Formation, and Thorofare Andesite. The volcanic rocks are partly Late Silurian, but mostly Early Devonian in age and yield an average radiogenic age of 390 ± 5 m.y. The use of calcite-bearing volcanic samples for whole-rock Rb-Sr dating degrades the method by greatly increasing the uncertainty of the isochron and initial Sr 87 /Sr 86 . Lower to Middle Devonian granitic plutons have initial ratios of Sr 87 and Sr 86 similar to those in the volcanic formations. The Castine Volcanics and the Lower Devonian granite of Sedgwick may be comagmatic, but the time interval between the extrusion of the Vinalhaven Rhyolite and its intrusion by the Middle Devonian granite of Vinalhaven Island is too long to support the comagmatic hypothesis.


Science | 1970

Crystallography of Some Lunar Plagioclases

David B. Stewart; Daniel E. Appleman; J. Stephen Huebner; Joan R. Clark

Crystals of calcic bytownite from type B rocks have space group I1 with c ≈ 14 angstroms. Bytownite crystals from type A rocks are more sodic and have space group C1, c ≈ 7 angstroms. Cell parameters of eight bulk feldspar separates from crystalline rocks indicate that the range of angle gamma is about 23 times the standard error of measurement, and its value might be useful for estimation of composition. Cell parameters of seven ilmenites are close to those of pure FeTiO3.


Tectonics | 1989

The extension of Grenville Basement beneath the northern Appalachians: Results from the Quebec‐Maine seismic reflection and refraction surveys

Carl Spencer; Alan G. Green; Patrick Morel-a-l'Huissier; Bernd Milkereit; James H. Luetgert; David B. Stewart; John D. Unger; Jeffrey Phillips


Reflection Seismology: The Continental Crust | 2013

The Quebec‐Western Maine Seismic Reflection Profile: Setting and First Year Results

David B. Stewart; J. D. Unger; J. D. Phillips; R. Goldsmith; W. H. Poole; C. P. Spencer; A. G. Green; M. C. Loiselle; P. St‐Julien


American Mineralogist | 1989

Crustal processes in Maine

David B. Stewart


Atlantic Geology | 1995

Silurian tectonic history of Penobscot Bay region, Maine

David B. Stewart; John D. Unger; Deborah R. Hutchinson


Archive | 1971

Studies of lunar plagioclases, tridymite, and cristobalite

Daniel E. Appleman; H.-U. Nissen; David B. Stewart; Joan R. Clark; E. Dowty; J. Stephen Huebner


Geophysical Journal International | 1987

Interpretation of migrated seismic reflection profiles across the northern Appalachians in Maine

John D. Unger; David B. Stewart; J. D. Phillips


Atlantic Geology | 2001

Minimum age of the Neoproterozoic Seven Hundred Acre Island Formation and the tectonic setting of the Islesboro Formation, Islesboro block, Maine

David B. Stewart; Robert D. Tucker; Robert A. Ayuso; Daniel R. Lux

Collaboration


Dive into the David B. Stewart's collaboration.

Top Co-Authors

Avatar

Daniel E. Appleman

United States Geological Survey

View shared research outputs
Top Co-Authors

Avatar

J. Stephen Huebner

United States Geological Survey

View shared research outputs
Top Co-Authors

Avatar

Joan R. Clark

United States Geological Survey

View shared research outputs
Top Co-Authors

Avatar

John D. Unger

United States Geological Survey

View shared research outputs
Top Co-Authors

Avatar

Robert A. Ayuso

United States Geological Survey

View shared research outputs
Top Co-Authors

Avatar

Robert D. Tucker

Washington University in St. Louis

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Arnulf Muan

Pennsylvania State University

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Deborah R. Hutchinson

United States Geological Survey

View shared research outputs
Researchain Logo
Decentralizing Knowledge