David Sawyer - Academia.edu (original) (raw)

Papers by David Sawyer

Research paper thumbnail of Geologic map of the Montoso Peak quadrangle, Santa Fe and Sandoval Counties, New Mexico

Scientific Investigations Map

Research paper thumbnail of Geologic map of the Cochiti Dam quadrangle, Sandoval County, New Mexico

Scientific Investigations Map

Research paper thumbnail of Geologic Map of Quadrangle 3570, Tagab-E-Munjan (505) and Asmar-Kamdesh (506) Quadrangles, Afghanistan

Open-File Report

Contact Fault-Dashed where approximately located; dotted where concealed DESCRIPTION OF MAP UNITS... more Contact Fault-Dashed where approximately located; dotted where concealed DESCRIPTION OF MAP UNITS Conglomerate and sandstone (Holocene)-Alluvium: shingly and detrital sediments, gravel, sand more abundant than silt and clay Conglomerate and sandstone (Holocene and late Pleistocene)-Alluvium: shingly and detrital sediments, gravel, sand more abundant than silt and clay Conglomerate and sandstone (middle Pleistocene)-Alluvium: shingly and detrital sediments, gravel, sand more abundant than silt and clay Till (middle Pleistocene)-Till: conglomerate, shingly sediments, gravel, sand, siltstone, breccia Conglomerate and sandstone (Miocene)-Red conglomerate, sandstone more abundant than siltstone, clay; acid and mafic volcanic rocks; limestone, marl; olivine basalt, trachybasalt, andesitic basalt (Taywara Series) Granite (Oligocene)-Granite (Phase III) Granodiorite and granosyenite (Oligocene)-Granodiorite, alaskite, granosyenite more abundant than granite (Phase II) Diorite and plagiogranite (Oligocene)-Diorite and plagiogranite more abundant than granodiorite (Phase I) Gabbro and monzonite (Early Cretaceous)-Gabbro, monzonite more abundant than diorite, granodiorite Rhyolite lava (Late Triassic)-Shale more abundant than phyllite, andesite to basalt (greenstone altered), limestone (Kotagai Series) Siltstone and sandstone (Late Triassic (Rhaetian and Norian))-Siltstone, sandstone more abundant than shale, conglomerate Limestone and chert (Late Triassic (Carnian) to Permian)-Limestone, marl, chert more abundant than sandstone, shale, siltstone Sandstone and siltstone (Permian)-Red and variegated sandstone and siltstone more abundant than mudstone, conglomerate, gravelstone Sandstone and siltstone (Early Permian and Carbonifeous)-Sandstone and siltstone more abundant than slate, andesite to basalt volcanic rocks Gabbro and diorite (Early Carboniferous)-Gabbro, diorite Ultramafic intrusions (Early Carboniferous)-Dunite, peridotite, serpentinite Rhyolite to basalt (Early Carboniferous)-Rhyolite to basalt volcanic rocks more abundant than limestone, slate, sandstone, conglomerate Basalt and sandstone (Early Carboniferous (Namurian))-Basalt, sandstone, siltstone, shale Limestone (Early Carboniferous (Visean and late Tournaisian))-Limestone more abundant than slate, sandstone, mudstone, conglomerate Rhyolite to andesite (Early Carboniferous (early Tournaisian))-Rhyolite to andesite (greenstone altered) more abundant than sandstone, shale, siltstone Limestone and dolomite (Devonian and Silurian)-Limestone and dolomite more abundant than schist, sandstone Sandstone and siltstone (Ordovician)-Limestone, sandstone, siltstone, shale Gneiss and granite (Proterozoic)-Gneiss-granite, granite, plagiogranite Gneiss (Late Paleoproterozoic)-Biotite and garnet-biotite gneiss; schist, quartzite, marble, amphibolite Marble and gneiss (Middle Paleoproterozoic)-Marble, biotite gneiss, and garnetstaurolite-biotite gneiss; schist, quartzite, amphibolite

Research paper thumbnail of Caldera-related lava flows and intrusions of the south-central San Juan Mountains, Colorado; analytical data

Research paper thumbnail of Processed Landsat 7 satellite imagery of the Espanola Basin region, New Mexico

Research paper thumbnail of Processed Landsat 7 satellite imagery of the Taos Plateau-San Luis Valley region, New Mexico and Colorado

Research paper thumbnail of Geologic Map of Quadrangle 3568, Polekhomri (503) and Charikar (504) Quadrangles, Afghanistan

Open-File Report

Fault-Dashed where approximately located; dotted where concealed

Research paper thumbnail of Paleomagnetism and rotation constraints for the Miocene southwestern Nevada volcanic field

Middle Miocene rocks of the southwestern Nevada volcanic field (SWNVF) lie across the projection ... more Middle Miocene rocks of the southwestern Nevada volcanic field (SWNVF) lie across the projection of the Walker Lane belt within the Basin and Range province and thus provide an interesting opportunity to test for late Cenozoic vertical-axis rotation. Palcomagnetic data from individual ash flow sheets document no significant relative vertical-axis rotation among localities within central SWNVF, an area of relatively low stratal tilts and widely spaced faults. A time-averaged mean paleomagnetic direction (D = 351.4 ø, I = 52.7 ø, ot95 = 4.5 ø) calculated from data from numerous separate rock units suggests that the central SWNVF underwent minimal counterclockwise vertical-axis rotation (R = -7.1 o ñ 6.6 o) with respect to the Noah American craton. No clockwise vertical-axis rotation is found to support projection of dextral faults of the Walker Lane beneath the central SWNVF. Clockwise rotation of variable magnitude is common at numerous sites from southern and western margins of the field. These clockwise rotations probably reflect dextral shear strain developed at the interface between the little emended central SWNVF block and more strongly extended areas to the south and southwest of the field. Negligible rotation of 11.45-Ma to 13.25-Ma tuffs relative to the central SWNVF was found at the southeast margin of the field where 90 ø clockwise rotation at the northwest termination of the Las Vegas Valley shear zone had been postulated. Any clockwise rotation in this area must predate 13.25 Ma, and thus dextral shear within this part of the Walker Lane belt was not synchronous or connected across the southern margin of the field. Small counterclockwise vertical-axis rotation relative to the craton, as found for the central SWNVF block, might be a regional feature in the western Great Basin. Hagstrum and Gans; 1989; Wells and Hillhouse, 1989; Li et al., 1990; Rosenbaum et al., 1991; Palmer et al., 1991]. The amount, areal extent, and age of such rotations are still incompletely constrained because published paleomagnetic studies pertain to small parts of the Great Basin, and because the geologic expression of vertical-axis rotations is commonly cryptic. Consequently, the structural mechanisms responsible for such rotations are not well documented. Cenozoic volcanic rocks that

Research paper thumbnail of Electromagnetic Studies and Subsurface Mapping of Electrical Resistivity in the La Bajada Constriction Area, New Mexico

Us Geological Survey Professional Paper, 2006

Research paper thumbnail of Stratigraphy of Upper Cenozoic Fluvial Deposits of the La Bajada Constriction Area, New Mexico

Us Geological Survey Professional Paper, 2006

Research paper thumbnail of Crustal and magmatic evolution in a large multicyclic caldera complex: isotopic evidence from the central San Juan volcanic field

Journal of Volcanology and Geothermal Research, Aug 1, 1995

The Sr, Nd and Pb isotope compositions of ash-flow tuffs and lavas from the central caldera clust... more The Sr, Nd and Pb isotope compositions of ash-flow tuffs and lavas from the central caldera cluster of the San Juan volcanic field, Colorado, suggest that the silicic magmas were derived by fractional crystallization of mantle-derived basalts, coupled with extensive assimilation of both lower-and upper-crustal components. Temporal trends of increasing ENd values and decreasing 87Sr/86Sr ratios of the ash-flow tuffs suggest that extensive crustal hybridization of both upper-and lower-crustal reservoirs occurred as a result of magmatism. Mantle-derived basalts are envisioned to have initially crystallized and significantly interacted with crust near the crust-mantle boundary, creating a hybrid crust that is a mixture of mantle and lower-crustal components. Evolved magmas ascended into the upper crust, where they continued to assimilate and crystallize, modifying the bulk uppercrustal composition through transfer of both lower-crustal and mantle components into the upper crust, strongly affecting the isotopic compositions of the lower and upper crust. Lower-crustal ENd values and 87Sr/86Sr ratios are calculated to have shifted * Corresponding author Elsevier Science B.V.

Research paper thumbnail of Hydrogeologic Framework of the La Bajada Constriction Area, New Mexico Integration of Subsurface and Surface Geology

Us Geological Survey Professional Paper, 2006

Research paper thumbnail of Lead isotopes in continental arc magmas and origin of porphyry Cu deposits in Arizona

Research paper thumbnail of Central San Juan caldera cluster

Research paper thumbnail of Rethinking an archetype of rift half-graben formation; a revised model of basin geometry for the Albuquerque segment of the Rio Grande Rift, New Mexico

The Albuquerque Basin, composing the Rio Grande Rift in central New Mexico, is commonly cited as ... more The Albuquerque Basin, composing the Rio Grande Rift in central New Mexico, is commonly cited as one of the archetypes of a continental rift basin that is segmented into alternating, oppositely tilted half-grabens separated by a scissor-like transfer zone. The practice originates from a structural model of the Albuquerque Basin developed primarily from oil-industry seismic-reflection data and published in the early 1990s. Key elements of this model are an east-tilted half-graben on the north separated from a west-tilted half-graben on the south by a southwest-trending transfer zone. However, this model is conceptually inconsistent with current geologic evidence and gravity modeling for the Albuquerque Basin. Problems with the earlier model probably stem from inadequate seismic and well data on the east side of the basin. A model of basin-fill thickness constructed from gravity data supports a different picture of basin geometry, primarily for the southern half of the Albuquerque Bas...

Research paper thumbnail of Geologic cross sections spanning the La Bajada Constriction and northern Cerrillos Uplift, New Mexico

Research paper thumbnail of The Silent Canyon Caldera Complex--A three-dimensional model based on drill-hole stratigraphy and gravity inversion

US Geological Survey visual mark. US Geological Survey Open-File Report 99-555 Version 1.0. The S... more US Geological Survey visual mark. US Geological Survey Open-File Report 99-555 Version 1.0. The Silent Canyon Caldera Complex— A Three-Dimensional Model Based on Drill-Hole Stratigraphy and Gravity Inversion. By. ...

Research paper thumbnail of Geophysical constraints on Rio Grande rift structure and stratigraphy from magnetotelluric models and borehole resistivity logs, northern New Mexico

Geological Society of America Special Papers, 2013

ABSTRACT

Research paper thumbnail of Geophysical interpretations west of and within the northwestern part of the Nevada Test Site

Research paper thumbnail of Day 4: Western San Juan Caldera Complex and Multii‐Stage Mineralization Around the Lake City Caldera

Research paper thumbnail of Geologic map of the Montoso Peak quadrangle, Santa Fe and Sandoval Counties, New Mexico

Scientific Investigations Map

Research paper thumbnail of Geologic map of the Cochiti Dam quadrangle, Sandoval County, New Mexico

Scientific Investigations Map

Research paper thumbnail of Geologic Map of Quadrangle 3570, Tagab-E-Munjan (505) and Asmar-Kamdesh (506) Quadrangles, Afghanistan

Open-File Report

Contact Fault-Dashed where approximately located; dotted where concealed DESCRIPTION OF MAP UNITS... more Contact Fault-Dashed where approximately located; dotted where concealed DESCRIPTION OF MAP UNITS Conglomerate and sandstone (Holocene)-Alluvium: shingly and detrital sediments, gravel, sand more abundant than silt and clay Conglomerate and sandstone (Holocene and late Pleistocene)-Alluvium: shingly and detrital sediments, gravel, sand more abundant than silt and clay Conglomerate and sandstone (middle Pleistocene)-Alluvium: shingly and detrital sediments, gravel, sand more abundant than silt and clay Till (middle Pleistocene)-Till: conglomerate, shingly sediments, gravel, sand, siltstone, breccia Conglomerate and sandstone (Miocene)-Red conglomerate, sandstone more abundant than siltstone, clay; acid and mafic volcanic rocks; limestone, marl; olivine basalt, trachybasalt, andesitic basalt (Taywara Series) Granite (Oligocene)-Granite (Phase III) Granodiorite and granosyenite (Oligocene)-Granodiorite, alaskite, granosyenite more abundant than granite (Phase II) Diorite and plagiogranite (Oligocene)-Diorite and plagiogranite more abundant than granodiorite (Phase I) Gabbro and monzonite (Early Cretaceous)-Gabbro, monzonite more abundant than diorite, granodiorite Rhyolite lava (Late Triassic)-Shale more abundant than phyllite, andesite to basalt (greenstone altered), limestone (Kotagai Series) Siltstone and sandstone (Late Triassic (Rhaetian and Norian))-Siltstone, sandstone more abundant than shale, conglomerate Limestone and chert (Late Triassic (Carnian) to Permian)-Limestone, marl, chert more abundant than sandstone, shale, siltstone Sandstone and siltstone (Permian)-Red and variegated sandstone and siltstone more abundant than mudstone, conglomerate, gravelstone Sandstone and siltstone (Early Permian and Carbonifeous)-Sandstone and siltstone more abundant than slate, andesite to basalt volcanic rocks Gabbro and diorite (Early Carboniferous)-Gabbro, diorite Ultramafic intrusions (Early Carboniferous)-Dunite, peridotite, serpentinite Rhyolite to basalt (Early Carboniferous)-Rhyolite to basalt volcanic rocks more abundant than limestone, slate, sandstone, conglomerate Basalt and sandstone (Early Carboniferous (Namurian))-Basalt, sandstone, siltstone, shale Limestone (Early Carboniferous (Visean and late Tournaisian))-Limestone more abundant than slate, sandstone, mudstone, conglomerate Rhyolite to andesite (Early Carboniferous (early Tournaisian))-Rhyolite to andesite (greenstone altered) more abundant than sandstone, shale, siltstone Limestone and dolomite (Devonian and Silurian)-Limestone and dolomite more abundant than schist, sandstone Sandstone and siltstone (Ordovician)-Limestone, sandstone, siltstone, shale Gneiss and granite (Proterozoic)-Gneiss-granite, granite, plagiogranite Gneiss (Late Paleoproterozoic)-Biotite and garnet-biotite gneiss; schist, quartzite, marble, amphibolite Marble and gneiss (Middle Paleoproterozoic)-Marble, biotite gneiss, and garnetstaurolite-biotite gneiss; schist, quartzite, amphibolite

Research paper thumbnail of Caldera-related lava flows and intrusions of the south-central San Juan Mountains, Colorado; analytical data

Research paper thumbnail of Processed Landsat 7 satellite imagery of the Espanola Basin region, New Mexico

Research paper thumbnail of Processed Landsat 7 satellite imagery of the Taos Plateau-San Luis Valley region, New Mexico and Colorado

Research paper thumbnail of Geologic Map of Quadrangle 3568, Polekhomri (503) and Charikar (504) Quadrangles, Afghanistan

Open-File Report

Fault-Dashed where approximately located; dotted where concealed

Research paper thumbnail of Paleomagnetism and rotation constraints for the Miocene southwestern Nevada volcanic field

Middle Miocene rocks of the southwestern Nevada volcanic field (SWNVF) lie across the projection ... more Middle Miocene rocks of the southwestern Nevada volcanic field (SWNVF) lie across the projection of the Walker Lane belt within the Basin and Range province and thus provide an interesting opportunity to test for late Cenozoic vertical-axis rotation. Palcomagnetic data from individual ash flow sheets document no significant relative vertical-axis rotation among localities within central SWNVF, an area of relatively low stratal tilts and widely spaced faults. A time-averaged mean paleomagnetic direction (D = 351.4 ø, I = 52.7 ø, ot95 = 4.5 ø) calculated from data from numerous separate rock units suggests that the central SWNVF underwent minimal counterclockwise vertical-axis rotation (R = -7.1 o ñ 6.6 o) with respect to the Noah American craton. No clockwise vertical-axis rotation is found to support projection of dextral faults of the Walker Lane beneath the central SWNVF. Clockwise rotation of variable magnitude is common at numerous sites from southern and western margins of the field. These clockwise rotations probably reflect dextral shear strain developed at the interface between the little emended central SWNVF block and more strongly extended areas to the south and southwest of the field. Negligible rotation of 11.45-Ma to 13.25-Ma tuffs relative to the central SWNVF was found at the southeast margin of the field where 90 ø clockwise rotation at the northwest termination of the Las Vegas Valley shear zone had been postulated. Any clockwise rotation in this area must predate 13.25 Ma, and thus dextral shear within this part of the Walker Lane belt was not synchronous or connected across the southern margin of the field. Small counterclockwise vertical-axis rotation relative to the craton, as found for the central SWNVF block, might be a regional feature in the western Great Basin. Hagstrum and Gans; 1989; Wells and Hillhouse, 1989; Li et al., 1990; Rosenbaum et al., 1991; Palmer et al., 1991]. The amount, areal extent, and age of such rotations are still incompletely constrained because published paleomagnetic studies pertain to small parts of the Great Basin, and because the geologic expression of vertical-axis rotations is commonly cryptic. Consequently, the structural mechanisms responsible for such rotations are not well documented. Cenozoic volcanic rocks that

Research paper thumbnail of Electromagnetic Studies and Subsurface Mapping of Electrical Resistivity in the La Bajada Constriction Area, New Mexico

Us Geological Survey Professional Paper, 2006

Research paper thumbnail of Stratigraphy of Upper Cenozoic Fluvial Deposits of the La Bajada Constriction Area, New Mexico

Us Geological Survey Professional Paper, 2006

Research paper thumbnail of Crustal and magmatic evolution in a large multicyclic caldera complex: isotopic evidence from the central San Juan volcanic field

Journal of Volcanology and Geothermal Research, Aug 1, 1995

The Sr, Nd and Pb isotope compositions of ash-flow tuffs and lavas from the central caldera clust... more The Sr, Nd and Pb isotope compositions of ash-flow tuffs and lavas from the central caldera cluster of the San Juan volcanic field, Colorado, suggest that the silicic magmas were derived by fractional crystallization of mantle-derived basalts, coupled with extensive assimilation of both lower-and upper-crustal components. Temporal trends of increasing ENd values and decreasing 87Sr/86Sr ratios of the ash-flow tuffs suggest that extensive crustal hybridization of both upper-and lower-crustal reservoirs occurred as a result of magmatism. Mantle-derived basalts are envisioned to have initially crystallized and significantly interacted with crust near the crust-mantle boundary, creating a hybrid crust that is a mixture of mantle and lower-crustal components. Evolved magmas ascended into the upper crust, where they continued to assimilate and crystallize, modifying the bulk uppercrustal composition through transfer of both lower-crustal and mantle components into the upper crust, strongly affecting the isotopic compositions of the lower and upper crust. Lower-crustal ENd values and 87Sr/86Sr ratios are calculated to have shifted * Corresponding author Elsevier Science B.V.

Research paper thumbnail of Hydrogeologic Framework of the La Bajada Constriction Area, New Mexico Integration of Subsurface and Surface Geology

Us Geological Survey Professional Paper, 2006

Research paper thumbnail of Lead isotopes in continental arc magmas and origin of porphyry Cu deposits in Arizona

Research paper thumbnail of Central San Juan caldera cluster

Research paper thumbnail of Rethinking an archetype of rift half-graben formation; a revised model of basin geometry for the Albuquerque segment of the Rio Grande Rift, New Mexico

The Albuquerque Basin, composing the Rio Grande Rift in central New Mexico, is commonly cited as ... more The Albuquerque Basin, composing the Rio Grande Rift in central New Mexico, is commonly cited as one of the archetypes of a continental rift basin that is segmented into alternating, oppositely tilted half-grabens separated by a scissor-like transfer zone. The practice originates from a structural model of the Albuquerque Basin developed primarily from oil-industry seismic-reflection data and published in the early 1990s. Key elements of this model are an east-tilted half-graben on the north separated from a west-tilted half-graben on the south by a southwest-trending transfer zone. However, this model is conceptually inconsistent with current geologic evidence and gravity modeling for the Albuquerque Basin. Problems with the earlier model probably stem from inadequate seismic and well data on the east side of the basin. A model of basin-fill thickness constructed from gravity data supports a different picture of basin geometry, primarily for the southern half of the Albuquerque Bas...

Research paper thumbnail of Geologic cross sections spanning the La Bajada Constriction and northern Cerrillos Uplift, New Mexico

Research paper thumbnail of The Silent Canyon Caldera Complex--A three-dimensional model based on drill-hole stratigraphy and gravity inversion

US Geological Survey visual mark. US Geological Survey Open-File Report 99-555 Version 1.0. The S... more US Geological Survey visual mark. US Geological Survey Open-File Report 99-555 Version 1.0. The Silent Canyon Caldera Complex— A Three-Dimensional Model Based on Drill-Hole Stratigraphy and Gravity Inversion. By. ...

Research paper thumbnail of Geophysical constraints on Rio Grande rift structure and stratigraphy from magnetotelluric models and borehole resistivity logs, northern New Mexico

Geological Society of America Special Papers, 2013

ABSTRACT

Research paper thumbnail of Geophysical interpretations west of and within the northwestern part of the Nevada Test Site

Research paper thumbnail of Day 4: Western San Juan Caldera Complex and Multii‐Stage Mineralization Around the Lake City Caldera