John N Aleinikoff
John Aleinikoff is a Scientist Emeritus with the Geology, Geophysics, and Geochemistry Science Center.
Science and Products
Filter Total Items: 109
SHRIMP U-Pb and 40Ar/39Ar age constraints for relating plutonism and mineralization in the Boulder batholith region, Montana
The composite Boulder batholith, Montana, hosts a variety of mineral deposit types, including important silver-rich polymetallic quartz vein districts in the northern part of the batholith and the giant Butte porphyry copper-molybdenum pre-Main Stage system and crosscutting copper-rich Main Stage vein system in the southern part of the batholith. Previous dating studies have identified...
Authors
Karen Lund, John N. Aleinikoff, Michael J. Kunk, Daniel M. Unruh, G. D. Zeihen, W. C. Hodges, Edward A. du Bray, J. Michael O'Neill
U-Th-Pb dating of hydrothermal minerals from Carlin-type gold deposits, Nevada- Results and evaluation
No abstract available.
Authors
A. H. Hofstra, Wayne R. Premo, Poul Emsbo, J. S. Cline, John N. Aleinikoff
SHRIMP U-Pb geochronology of volcanic rocks, Belt Supergroup, western Montana: Evidence for rapid deposition of sedimentary strata
New sensitive high resolution ion microprobe (SHRIMP) U–Pb zircon analyses from two tuffs and a felsic flow in the middle and upper Belt Supergroup of northwestern Montana significantly refine the age of sedimentation for this very thick (15-20 km) Middle Proterozoic stratigraphic sequence. In ascending stratigraphic order, the results are (1) 1454 ± 9 Ma for a tuff in the upper part of...
Authors
K. V. Evans, J. N. Aleinikoff, J.D. Obradovich, C.M. Fanning
Isotopic evidence for the sources of Cretaceous and tertiary granitic rocks, east-central Alaska: Implications for the tectonic evolution of the Yukon-Tanana terrane
Magnetotelluric traverses across the southern Yukon-Tanana terrane (YTT) reveal the presence of a thick conductive layer (or layers) beneath Paleozoic crystalline rocks. These rocks have been interpreted to be flysch of probable Mesozoic age, on the basis of the occurrence of Jurassic-Cretaceous flysch in the Kahiltna assemblage and Gravina-Nutzotin belt flanking the YTT to the southwest...
Authors
J. N. Aleinikoff, G. L. Farmer, R.O. Rye, W. J. Nokleberg
U-Pb geochronology of zircon and monazite from Mesoproterozoic granitic gneisses of the northern Blue Ridge, Virginia and Maryland, USA
Mesoproterozoic granitic gneisses comprise most of the basement of the northern Blue Ridge geologic province in Virginia and Maryland. Lithology, structure, and U-Pb geochronology have been used to subdivide the gneisses into three groups. The oldest rocks, Group 1, are layered granitic gneiss (1153 ?? 6 Ma), hornblende monzonite gneiss (1149 ?? 19 Ma), porphyroblastic granite gneiss...
Authors
J. N. Aleinikoff, W.C. Burton, P. T. Lyttle, A.E. Nelson, C.S. Southworth
200,000 years of climate change recorded in eolian sediments of the High Plains of eastern Colorado and western Nebraska
Loess and eolian sand cover vast areas of the western Great Plains of Nebraska, Kansas and Colorado (Fig. 1). In recent studies of Quaternary climate change, there has been a renewed interest in loess and eolian sand. Much of the attention now given to loess stems from new studies of long loess sequences that contain detailed records of Quaternary glacial-interglacial cycles, thought to...
Authors
Daniel R. Muhs, James B. Swinehart, David B. Loope, John N. Aleinikoff, Josh Been
U-Pb zircon age of metafelsite from the Pinney Hollow formation: Implications for the development of the Vermont Appalachians
The Pinney Hollow Formation of central Vermont is part of a rift-clastic to drift-stage sequence of cover rocks deposited on the Laurentian margin during the development of the Iapetan passive margin in Late Proterozoic to Cambrian time. Conventional U-Pb zircon data indicate an age of 571+ or -5 Ma for a metafelsite from the Pinney Hollow Formation. Geochemical data indicate that the...
Authors
Gregory J. Walsh, John Aleinikoff
Distinguishing Grenvillian basement from pre-Taconian cover rocks in the Northern Appalachians
Distinguishing Grenvillian basement rocks from pre-Taconian cover sequences in the Appalachians is a first-order problem essential for accurate structural interpretations. The Cavendish Formation in southeastern Vermont presents a classic example of this problem. Doll and others (1961) showed the Cavendish Formation as younger than the Middle Proterozoic Mount Holly Complex but older...
Authors
Paul M. Karabinos, John N. Aleinikoff, C. Mark Fanning
Late Quaternary loess in northeastern Colorado: Part I - Age and paleoclimatic significance
Loess in eastern Colorado covers an estimated 14 000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20 000 to 12 000 14C yr B.P. (ca. 20–14 ka) and correlates reasonably well with the culmination and...
Authors
D.R. Muhs, J. N. Aleinikoff, Thomas W. Stafford, R. Kihl, J. Been, S. A. Mahan, S. Cowherd
Late Quaternary loess in northeastern Colorado: Part II - Pb isotopic evidence for the variability of loess sources
Loess in eastern Colorado covers an estimated 14 000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20 000 to 12 000 14C yr B.P. (ca. 20–14 ka) and correlates reasonably well with the culmination and...
Authors
J. N. Aleinikoff, D.R. Muhs, R.R. Sauer, C.M. Fanning
Stratigraphic and structural implications of conodont and detrital zircon U-Pb ages from metamorphic rocks of the Coldfoot terrane, Brooks Range, Alaska
New paleontologic and isotopic data from the Emma Creek and Marion Creek schists of the Coldfoot terrane, Arctic Alaska superterrane, central Brooks Range, suggest Devonian and possibly younger ages of deposition for their sedimentary protoliths. Conodonts from marble of the Emma Creek schist, intruded by a roughly 392 Ma orthogneiss, are late Lochkovian (early Early Devonian, between...
Authors
Thomas E. Moore, J. N. Aleinikoff, A. G. Harris
Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia
Uranium-lead dating of zircons from the Montpelier Anorthosite confirms previous interpretations, based on equivocal evidence, that the Goochland terrane in the eastern Piedmont of Virginia contains Grenvillian basement rocks of Middle Proterozoic age. A very few prismatic, elongate, euhedral zircons, which contain 12–29 ppm uranium, are interpreted to be igneous in origin. The vast...
Authors
J. N. Aleinikoff, J. Wright Horton, M. Walters
Science and Products
Filter Total Items: 109
SHRIMP U-Pb and 40Ar/39Ar age constraints for relating plutonism and mineralization in the Boulder batholith region, Montana
The composite Boulder batholith, Montana, hosts a variety of mineral deposit types, including important silver-rich polymetallic quartz vein districts in the northern part of the batholith and the giant Butte porphyry copper-molybdenum pre-Main Stage system and crosscutting copper-rich Main Stage vein system in the southern part of the batholith. Previous dating studies have identified...
Authors
Karen Lund, John N. Aleinikoff, Michael J. Kunk, Daniel M. Unruh, G. D. Zeihen, W. C. Hodges, Edward A. du Bray, J. Michael O'Neill
U-Th-Pb dating of hydrothermal minerals from Carlin-type gold deposits, Nevada- Results and evaluation
No abstract available.
Authors
A. H. Hofstra, Wayne R. Premo, Poul Emsbo, J. S. Cline, John N. Aleinikoff
SHRIMP U-Pb geochronology of volcanic rocks, Belt Supergroup, western Montana: Evidence for rapid deposition of sedimentary strata
New sensitive high resolution ion microprobe (SHRIMP) U–Pb zircon analyses from two tuffs and a felsic flow in the middle and upper Belt Supergroup of northwestern Montana significantly refine the age of sedimentation for this very thick (15-20 km) Middle Proterozoic stratigraphic sequence. In ascending stratigraphic order, the results are (1) 1454 ± 9 Ma for a tuff in the upper part of...
Authors
K. V. Evans, J. N. Aleinikoff, J.D. Obradovich, C.M. Fanning
Isotopic evidence for the sources of Cretaceous and tertiary granitic rocks, east-central Alaska: Implications for the tectonic evolution of the Yukon-Tanana terrane
Magnetotelluric traverses across the southern Yukon-Tanana terrane (YTT) reveal the presence of a thick conductive layer (or layers) beneath Paleozoic crystalline rocks. These rocks have been interpreted to be flysch of probable Mesozoic age, on the basis of the occurrence of Jurassic-Cretaceous flysch in the Kahiltna assemblage and Gravina-Nutzotin belt flanking the YTT to the southwest...
Authors
J. N. Aleinikoff, G. L. Farmer, R.O. Rye, W. J. Nokleberg
U-Pb geochronology of zircon and monazite from Mesoproterozoic granitic gneisses of the northern Blue Ridge, Virginia and Maryland, USA
Mesoproterozoic granitic gneisses comprise most of the basement of the northern Blue Ridge geologic province in Virginia and Maryland. Lithology, structure, and U-Pb geochronology have been used to subdivide the gneisses into three groups. The oldest rocks, Group 1, are layered granitic gneiss (1153 ?? 6 Ma), hornblende monzonite gneiss (1149 ?? 19 Ma), porphyroblastic granite gneiss...
Authors
J. N. Aleinikoff, W.C. Burton, P. T. Lyttle, A.E. Nelson, C.S. Southworth
200,000 years of climate change recorded in eolian sediments of the High Plains of eastern Colorado and western Nebraska
Loess and eolian sand cover vast areas of the western Great Plains of Nebraska, Kansas and Colorado (Fig. 1). In recent studies of Quaternary climate change, there has been a renewed interest in loess and eolian sand. Much of the attention now given to loess stems from new studies of long loess sequences that contain detailed records of Quaternary glacial-interglacial cycles, thought to...
Authors
Daniel R. Muhs, James B. Swinehart, David B. Loope, John N. Aleinikoff, Josh Been
U-Pb zircon age of metafelsite from the Pinney Hollow formation: Implications for the development of the Vermont Appalachians
The Pinney Hollow Formation of central Vermont is part of a rift-clastic to drift-stage sequence of cover rocks deposited on the Laurentian margin during the development of the Iapetan passive margin in Late Proterozoic to Cambrian time. Conventional U-Pb zircon data indicate an age of 571+ or -5 Ma for a metafelsite from the Pinney Hollow Formation. Geochemical data indicate that the...
Authors
Gregory J. Walsh, John Aleinikoff
Distinguishing Grenvillian basement from pre-Taconian cover rocks in the Northern Appalachians
Distinguishing Grenvillian basement rocks from pre-Taconian cover sequences in the Appalachians is a first-order problem essential for accurate structural interpretations. The Cavendish Formation in southeastern Vermont presents a classic example of this problem. Doll and others (1961) showed the Cavendish Formation as younger than the Middle Proterozoic Mount Holly Complex but older...
Authors
Paul M. Karabinos, John N. Aleinikoff, C. Mark Fanning
Late Quaternary loess in northeastern Colorado: Part I - Age and paleoclimatic significance
Loess in eastern Colorado covers an estimated 14 000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20 000 to 12 000 14C yr B.P. (ca. 20–14 ka) and correlates reasonably well with the culmination and...
Authors
D.R. Muhs, J. N. Aleinikoff, Thomas W. Stafford, R. Kihl, J. Been, S. A. Mahan, S. Cowherd
Late Quaternary loess in northeastern Colorado: Part II - Pb isotopic evidence for the variability of loess sources
Loess in eastern Colorado covers an estimated 14 000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20 000 to 12 000 14C yr B.P. (ca. 20–14 ka) and correlates reasonably well with the culmination and...
Authors
J. N. Aleinikoff, D.R. Muhs, R.R. Sauer, C.M. Fanning
Stratigraphic and structural implications of conodont and detrital zircon U-Pb ages from metamorphic rocks of the Coldfoot terrane, Brooks Range, Alaska
New paleontologic and isotopic data from the Emma Creek and Marion Creek schists of the Coldfoot terrane, Arctic Alaska superterrane, central Brooks Range, suggest Devonian and possibly younger ages of deposition for their sedimentary protoliths. Conodonts from marble of the Emma Creek schist, intruded by a roughly 392 Ma orthogneiss, are late Lochkovian (early Early Devonian, between...
Authors
Thomas E. Moore, J. N. Aleinikoff, A. G. Harris
Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia
Uranium-lead dating of zircons from the Montpelier Anorthosite confirms previous interpretations, based on equivocal evidence, that the Goochland terrane in the eastern Piedmont of Virginia contains Grenvillian basement rocks of Middle Proterozoic age. A very few prismatic, elongate, euhedral zircons, which contain 12–29 ppm uranium, are interpreted to be igneous in origin. The vast...
Authors
J. N. Aleinikoff, J. Wright Horton, M. Walters