- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
NARROW
GeoRef Subject
-
all geography including DSDP/ODP Sites and Legs
-
Africa
-
East Africa
-
Kenya (1)
-
Tanzania
-
Olduvai Gorge (1)
-
-
Zambia (1)
-
-
-
Antarctica (1)
-
Asia
-
Far East
-
China (1)
-
Japan
-
Honshu
-
Akita Japan (1)
-
-
Kyushu
-
Nagasaki Japan (1)
-
-
-
-
Himalayas (1)
-
Middle East
-
Turkey
-
Anatolia (2)
-
-
-
-
Atlantic Ocean Islands
-
Canary Islands
-
Tenerife (1)
-
-
-
Australasia
-
New Zealand
-
Taupo volcanic zone (1)
-
-
-
Canada
-
Eastern Canada
-
Quebec
-
Noranda Quebec (1)
-
Temiscamingue County Quebec
-
Rouyn Quebec (1)
-
-
-
-
Western Canada
-
British Columbia
-
Sustut Basin (1)
-
-
-
-
Coast Ranges (1)
-
Commonwealth of Independent States
-
Caucasus
-
Greater Caucasus (1)
-
-
Georgian Republic (1)
-
Transcaucasia (1)
-
Ukraine
-
Crimea Ukraine (1)
-
-
Urals (1)
-
-
Cook Inlet (1)
-
Europe
-
Alps
-
Western Alps (1)
-
-
Carpathians
-
Eastern Carpathians (1)
-
-
Caucasus
-
Greater Caucasus (1)
-
-
Central Europe
-
Germany
-
Baden-Wurttemberg Germany
-
Kaiserstuhl (1)
-
-
Eifel (1)
-
Rhineland-Palatinate Germany (1)
-
-
Slovakia (2)
-
-
Georgian Republic (1)
-
Rhenish Schiefergebirge
-
Eifel (1)
-
-
Southern Europe
-
Bulgaria (2)
-
Greece
-
Greek Aegean Islands
-
Cyclades
-
Santorin (1)
-
Thera (1)
-
-
Samos (2)
-
-
Greek Thrace (2)
-
-
Italy
-
Campania Italy
-
Naples Italy (2)
-
-
Latium Italy
-
Alban Hills (1)
-
Rome Italy (1)
-
-
-
Romania (1)
-
Serbia (1)
-
Yugoslavia (1)
-
-
Thrace
-
Greek Thrace (2)
-
-
Transcaucasia (1)
-
Ukraine
-
Crimea Ukraine (1)
-
-
Western Europe
-
United Kingdom
-
Great Britain
-
England
-
Isle of Wight England (1)
-
-
-
Northern Ireland (1)
-
-
-
-
Great Rift Valley (1)
-
Indian Ocean Islands
-
Kerguelen Islands (1)
-
-
Mediterranean region
-
Aegean Islands
-
Greek Aegean Islands
-
Cyclades
-
Santorin (1)
-
Thera (1)
-
-
Samos (2)
-
-
-
-
Mexico
-
Guanajuato Mexico (1)
-
Sierra Madre Occidental (1)
-
Trans-Mexican volcanic belt (1)
-
-
North America
-
Appalachians
-
Piedmont (1)
-
-
Basin and Range Province (2)
-
Great Plains (1)
-
North American Cordillera (1)
-
Rocky Mountains
-
U. S. Rocky Mountains (1)
-
-
Western Interior (1)
-
-
North Island (1)
-
Pacific Ocean (1)
-
Pacific region
-
Circum-Pacific region (1)
-
-
Pasco Basin (1)
-
South America
-
Argentina
-
Chubut Argentina (1)
-
-
Chile (1)
-
Patagonia (1)
-
-
United States
-
Alaska
-
Aleutian Islands (1)
-
-
Arizona
-
Yavapai County Arizona (1)
-
-
California
-
Central California (1)
-
San Joaquin Valley (1)
-
-
Colorado (2)
-
Colorado Plateau (2)
-
Dinosaur National Monument (1)
-
Idaho
-
Snake River plain (1)
-
-
Mojave Desert (1)
-
Nebraska (1)
-
Nevada
-
Nye County Nevada
-
Yucca Mountain (1)
-
-
Pershing County Nevada
-
Lovelock Nevada (1)
-
-
-
New Mexico
-
Grant County New Mexico (1)
-
-
Oregon (1)
-
South Dakota (1)
-
Texas (1)
-
Trans-Pecos (1)
-
U. S. Rocky Mountains (1)
-
Utah (1)
-
Virginia
-
Chesterfield County Virginia (1)
-
Goochland County Virginia (1)
-
Hanover County Virginia (1)
-
Henrico County Virginia (1)
-
-
Washington
-
Benton County Washington (1)
-
-
Western U.S. (1)
-
Wyoming
-
Converse County Wyoming (1)
-
Teton County Wyoming (1)
-
-
Yellowstone National Park (1)
-
-
-
commodities
-
brines (1)
-
construction materials (1)
-
industrial minerals (1)
-
metal ores
-
gold ores (1)
-
polymetallic ores (1)
-
silver ores (1)
-
uranium ores (2)
-
vanadium ores (1)
-
-
mineral deposits, genesis (5)
-
mineral exploration (1)
-
oil and gas fields (1)
-
petroleum (2)
-
sodium carbonate (1)
-
zeolite deposits (4)
-
-
elements, isotopes
-
carbon
-
C-13/C-12 (1)
-
-
chemical elements (1)
-
isotope ratios (3)
-
isotopes
-
stable isotopes
-
Al-27 (1)
-
C-13/C-12 (1)
-
Nd-144/Nd-143 (1)
-
Si-29 (1)
-
Sr-87/Sr-86 (2)
-
-
-
large-ion lithophile elements (1)
-
metals
-
alkali metals
-
sodium (1)
-
-
alkaline earth metals
-
barium (1)
-
strontium
-
Sr-87/Sr-86 (2)
-
-
-
aluminum
-
Al-27 (1)
-
-
rare earths
-
europium (1)
-
neodymium
-
Nd-144/Nd-143 (1)
-
-
-
-
silicon
-
Si-29 (1)
-
-
-
fossils
-
Chordata
-
Vertebrata
-
Tetrapoda
-
Reptilia
-
Synapsida
-
Therapsida (1)
-
-
-
-
-
-
microfossils (1)
-
palynomorphs (1)
-
Plantae
-
algae
-
Coccolithophoraceae (1)
-
-
-
-
geochronology methods
-
Rb/Sr (1)
-
-
geologic age
-
Cenozoic
-
Quaternary
-
Holocene
-
upper Holocene
-
Roman period (1)
-
-
-
Pleistocene (1)
-
-
Tertiary
-
Neogene
-
Miocene
-
Topopah Spring Member (1)
-
-
-
Paleogene
-
Eocene
-
Bracklesham Group (1)
-
middle Eocene (1)
-
-
Oligocene (5)
-
White River Group (1)
-
-
-
-
Mesozoic
-
Cretaceous
-
Upper Cretaceous
-
Cenomanian (1)
-
Turonian (1)
-
-
-
Jurassic
-
Upper Jurassic
-
Brushy Basin Member (1)
-
Morrison Formation (2)
-
Salt Wash Sandstone Member (1)
-
-
-
-
Paleozoic
-
Permian
-
Upper Permian (1)
-
-
-
Precambrian
-
Archean (1)
-
-
-
igneous rocks
-
igneous rocks
-
feldspathoid rocks (1)
-
volcanic rocks
-
basalts (5)
-
dacites (1)
-
glasses
-
perlite (1)
-
volcanic glass (4)
-
-
latite (1)
-
phonolites (2)
-
pyroclastics
-
hyaloclastite (1)
-
ignimbrite (5)
-
pumice (1)
-
tuff (20)
-
-
rhyolites (3)
-
trachyandesites (1)
-
trachytes (1)
-
-
-
volcanic ash (1)
-
-
metamorphic rocks
-
metamorphic rocks
-
metaigneous rocks (1)
-
metavolcanic rocks (1)
-
mylonites
-
ultramylonite (1)
-
-
-
-
minerals
-
carbonates
-
calcite (1)
-
dawsonite (1)
-
-
halides
-
chlorides
-
halite (1)
-
-
-
minerals (5)
-
oxides
-
hematite (1)
-
spinel (1)
-
-
silicates
-
aluminosilicates (2)
-
chain silicates
-
pyroxene group
-
clinopyroxene
-
diopside (1)
-
-
-
tobermorite (1)
-
-
framework silicates
-
feldspar group
-
alkali feldspar
-
K-feldspar (3)
-
sanidine (1)
-
-
plagioclase
-
oligoclase (1)
-
-
-
nepheline group
-
nepheline (1)
-
-
scapolite group
-
scapolite (1)
-
-
silica minerals
-
opal
-
opal-CT (3)
-
-
quartz (1)
-
-
sodalite group
-
hauyne (1)
-
sodalite (1)
-
-
zeolite group
-
analcime (10)
-
chabazite (6)
-
clinoptilolite (14)
-
epistilbite (1)
-
ferrierite (1)
-
garronite (1)
-
heulandite (4)
-
laumontite (4)
-
mesolite (2)
-
mordenite (5)
-
natrolite (1)
-
phillipsite (7)
-
stilbite (1)
-
thomsonite (1)
-
-
-
sheet silicates
-
apophyllite (1)
-
chlorite group
-
chlorite (1)
-
-
clay minerals
-
beidellite (1)
-
halloysite (1)
-
kaolinite (3)
-
montmorillonite (2)
-
saponite (1)
-
smectite (11)
-
-
mica group
-
biotite (1)
-
celadonite (1)
-
muscovite (1)
-
-
-
-
sulfates
-
alunite (1)
-
-
sulfides (1)
-
-
Primary terms
-
absolute age (1)
-
Africa
-
East Africa
-
Kenya (1)
-
Tanzania
-
Olduvai Gorge (1)
-
-
Zambia (1)
-
-
-
Antarctica (1)
-
Asia
-
Far East
-
China (1)
-
Japan
-
Honshu
-
Akita Japan (1)
-
-
Kyushu
-
Nagasaki Japan (1)
-
-
-
-
Himalayas (1)
-
Middle East
-
Turkey
-
Anatolia (2)
-
-
-
-
Atlantic Ocean Islands
-
Canary Islands
-
Tenerife (1)
-
-
-
Australasia
-
New Zealand
-
Taupo volcanic zone (1)
-
-
-
brines (1)
-
Canada
-
Eastern Canada
-
Quebec
-
Noranda Quebec (1)
-
Temiscamingue County Quebec
-
Rouyn Quebec (1)
-
-
-
-
Western Canada
-
British Columbia
-
Sustut Basin (1)
-
-
-
-
carbon
-
C-13/C-12 (1)
-
-
Cenozoic
-
Quaternary
-
Holocene
-
upper Holocene
-
Roman period (1)
-
-
-
Pleistocene (1)
-
-
Tertiary
-
Neogene
-
Miocene
-
Topopah Spring Member (1)
-
-
-
Paleogene
-
Eocene
-
Bracklesham Group (1)
-
middle Eocene (1)
-
-
Oligocene (5)
-
White River Group (1)
-
-
-
-
chemical analysis (1)
-
Chordata
-
Vertebrata
-
Tetrapoda
-
Reptilia
-
Synapsida
-
Therapsida (1)
-
-
-
-
-
-
clay mineralogy (16)
-
construction materials (1)
-
crust (1)
-
crystal chemistry (5)
-
crystal growth (3)
-
crystal structure (1)
-
deformation (4)
-
diagenesis (21)
-
economic geology (2)
-
Europe
-
Alps
-
Western Alps (1)
-
-
Carpathians
-
Eastern Carpathians (1)
-
-
Caucasus
-
Greater Caucasus (1)
-
-
Central Europe
-
Germany
-
Baden-Wurttemberg Germany
-
Kaiserstuhl (1)
-
-
Eifel (1)
-
Rhineland-Palatinate Germany (1)
-
-
Slovakia (2)
-
-
Georgian Republic (1)
-
Rhenish Schiefergebirge
-
Eifel (1)
-
-
Southern Europe
-
Bulgaria (2)
-
Greece
-
Greek Aegean Islands
-
Cyclades
-
Santorin (1)
-
Thera (1)
-
-
Samos (2)
-
-
Greek Thrace (2)
-
-
Italy
-
Campania Italy
-
Naples Italy (2)
-
-
Latium Italy
-
Alban Hills (1)
-
Rome Italy (1)
-
-
-
Romania (1)
-
Serbia (1)
-
Yugoslavia (1)
-
-
Thrace
-
Greek Thrace (2)
-
-
Transcaucasia (1)
-
Ukraine
-
Crimea Ukraine (1)
-
-
Western Europe
-
United Kingdom
-
Great Britain
-
England
-
Isle of Wight England (1)
-
-
-
Northern Ireland (1)
-
-
-
-
faults (3)
-
folds (1)
-
foliation (1)
-
fractures (2)
-
geochemistry (14)
-
geochronology (1)
-
ground water (1)
-
heat flow (2)
-
igneous rocks
-
feldspathoid rocks (1)
-
volcanic rocks
-
basalts (5)
-
dacites (1)
-
glasses
-
perlite (1)
-
volcanic glass (4)
-
-
latite (1)
-
phonolites (2)
-
pyroclastics
-
hyaloclastite (1)
-
ignimbrite (5)
-
pumice (1)
-
tuff (20)
-
-
rhyolites (3)
-
trachyandesites (1)
-
trachytes (1)
-
-
-
Indian Ocean Islands
-
Kerguelen Islands (1)
-
-
industrial minerals (1)
-
intrusions (2)
-
isotopes
-
stable isotopes
-
Al-27 (1)
-
C-13/C-12 (1)
-
Nd-144/Nd-143 (1)
-
Si-29 (1)
-
Sr-87/Sr-86 (2)
-
-
-
lava (5)
-
magmas (1)
-
Mediterranean region
-
Aegean Islands
-
Greek Aegean Islands
-
Cyclades
-
Santorin (1)
-
Thera (1)
-
-
Samos (2)
-
-
-
-
Mesozoic
-
Cretaceous
-
Upper Cretaceous
-
Cenomanian (1)
-
Turonian (1)
-
-
-
Jurassic
-
Upper Jurassic
-
Brushy Basin Member (1)
-
Morrison Formation (2)
-
Salt Wash Sandstone Member (1)
-
-
-
-
metal ores
-
gold ores (1)
-
polymetallic ores (1)
-
silver ores (1)
-
uranium ores (2)
-
vanadium ores (1)
-
-
metals
-
alkali metals
-
sodium (1)
-
-
alkaline earth metals
-
barium (1)
-
strontium
-
Sr-87/Sr-86 (2)
-
-
-
aluminum
-
Al-27 (1)
-
-
rare earths
-
europium (1)
-
neodymium
-
Nd-144/Nd-143 (1)
-
-
-
-
metamorphic rocks
-
metaigneous rocks (1)
-
metavolcanic rocks (1)
-
mylonites
-
ultramylonite (1)
-
-
-
metamorphism (6)
-
metasomatism (57)
-
Mexico
-
Guanajuato Mexico (1)
-
Sierra Madre Occidental (1)
-
Trans-Mexican volcanic belt (1)
-
-
mineral deposits, genesis (5)
-
mineral exploration (1)
-
mineralogy (1)
-
minerals (5)
-
North America
-
Appalachians
-
Piedmont (1)
-
-
Basin and Range Province (2)
-
Great Plains (1)
-
North American Cordillera (1)
-
Rocky Mountains
-
U. S. Rocky Mountains (1)
-
-
Western Interior (1)
-
-
oil and gas fields (1)
-
orogeny (1)
-
Pacific Ocean (1)
-
Pacific region
-
Circum-Pacific region (1)
-
-
paleogeography (1)
-
paleontology (1)
-
Paleozoic
-
Permian
-
Upper Permian (1)
-
-
-
palynomorphs (1)
-
paragenesis (4)
-
petroleum (2)
-
petrology (8)
-
Plantae
-
algae
-
Coccolithophoraceae (1)
-
-
-
Precambrian
-
Archean (1)
-
-
sedimentary petrology (2)
-
sedimentary rocks
-
carbonate rocks
-
travertine (1)
-
-
chemically precipitated rocks
-
siliceous sinter (2)
-
-
clastic rocks
-
arenite
-
litharenite (1)
-
-
bentonite (1)
-
mudstone (1)
-
sandstone (3)
-
-
-
sedimentary structures (1)
-
sedimentation (2)
-
sediments
-
clastic sediments
-
alluvium (1)
-
kaolin (2)
-
-
-
shorelines (1)
-
silicon
-
Si-29 (1)
-
-
sodium carbonate (1)
-
soils (2)
-
South America
-
Argentina
-
Chubut Argentina (1)
-
-
Chile (1)
-
Patagonia (1)
-
-
springs (2)
-
structural analysis (1)
-
structural geology (1)
-
tectonics (5)
-
thermal waters (1)
-
United States
-
Alaska
-
Aleutian Islands (1)
-
-
Arizona
-
Yavapai County Arizona (1)
-
-
California
-
Central California (1)
-
San Joaquin Valley (1)
-
-
Colorado (2)
-
Colorado Plateau (2)
-
Dinosaur National Monument (1)
-
Idaho
-
Snake River plain (1)
-
-
Mojave Desert (1)
-
Nebraska (1)
-
Nevada
-
Nye County Nevada
-
Yucca Mountain (1)
-
-
Pershing County Nevada
-
Lovelock Nevada (1)
-
-
-
New Mexico
-
Grant County New Mexico (1)
-
-
Oregon (1)
-
South Dakota (1)
-
Texas (1)
-
Trans-Pecos (1)
-
U. S. Rocky Mountains (1)
-
Utah (1)
-
Virginia
-
Chesterfield County Virginia (1)
-
Goochland County Virginia (1)
-
Hanover County Virginia (1)
-
Henrico County Virginia (1)
-
-
Washington
-
Benton County Washington (1)
-
-
Western U.S. (1)
-
Wyoming
-
Converse County Wyoming (1)
-
Teton County Wyoming (1)
-
-
Yellowstone National Park (1)
-
-
volcanology (1)
-
weathering (3)
-
well-logging (1)
-
-
rock formations
-
Karoo Supergroup (1)
-
-
sedimentary rocks
-
pozzolan (1)
-
sedimentary rocks
-
carbonate rocks
-
travertine (1)
-
-
chemically precipitated rocks
-
siliceous sinter (2)
-
-
clastic rocks
-
arenite
-
litharenite (1)
-
-
bentonite (1)
-
mudstone (1)
-
sandstone (3)
-
-
-
volcaniclastics (7)
-
-
sedimentary structures
-
sedimentary structures (1)
-
-
sediments
-
sediments
-
clastic sediments
-
alluvium (1)
-
kaolin (2)
-
-
-
volcaniclastics (7)
-
-
soils
-
paleosols (1)
-
soils (2)
-
zeolitization
Silica-Rich Garronite-Na From Hirado Island, Nagasaki Prefecture, Japan
ABSTRACT The deposits of Pleistocene Lake Tecopa include lacustrine, alluvial, eolian, and groundwater discharge deposits of the Tecopa basin in southeastern California. Stratigraphic sections measured in the Tecopa basin and detailed sedimentary facies analysis were used to interpret the depositional settings and track the evolution of sedimentary processes in the basin during the Pleistocene. The early Pleistocene (ca. 2.4–1.0 Ma) deposits of the Lake Tecopa beds record deposition in small saline, alkaline lakes and playas with surrounding mudflats and sandflats and adjacent alluvial fans. Ancestral Amargosa River gravels are first observed in fluvial deposits in the northern part of the basin at ca. 1.0 Ma and correspond with lake expansions (Glass Mountain [GM] lakes) during deposition of the uppermost Glass Mountain ash beds. Several oscillations in lake level followed the post-GM lake decline, culminating in the basin-filling Lava Creek (LC) lake, which reached its acme during deposition of the 0.63 Ma Lava Creek B ash bed. The post–Lava Creek B strata reflect primarily alluvial, fluvial, eolian, and groundwater discharge depositional processes, punctuated in the youngest part of the section by basin-filling lakes (high lake 1 and 2). The Lava Creek B ash bed and older lacustrine strata exhibit extensive zeolitization and clay authigenesis, characteristic of saline, alkaline lake deposits, but the post–Lava Creek B ash bed lacustrine strata have only minor zeolite and clay alteration, suggesting fresher water conditions and a change in the hydrologic state of the basin. Sedimentological observations along with shoreline elevation data provide evidence for intermittent spillover of basin-filling lakes after ca. 0.63 Ma. Subtle tectonic deformation influenced sedimentary processes in the Tecopa basin throughout its history. Episodes of uplift and tilting of Lake Tecopa strata during the middle Pleistocene in the southern part of the basin along the Tecopa Hump likely controlled the sill elevation for spillover of the lake, creating accommodation space for late Pleistocene basin-filling lakes. Ultimately, decreased uplift could not keep pace with increased discharge resulting from high effective moisture during latest middle Pleistocene pluvial periods, and Lake Tecopa drained, most likely during or immediately after marine oxygen isotope stage (MIS) 10 (ca. 0.3 Ma). The deposits of Lake Tecopa provide a detailed record of Pleistocene paleoclimate from ca. 2.4 to 0.3 Ma that demonstrates Milankovitch-scale tuning and clarifies the amplitude of Pleistocene climate change in the southern Great Basin of North America.
Epithermal Zeolite Alteration Associated with Siliceous Sinters, Hydrothermal Eruption Breccias, and Gold-Silver Mineralization, Central Taupo Volcanic Zone, New Zealand
Petrogenesis of a Large-Scale Miocene Zeolite Tuff in the Eastern Slovak Republic: The Nižný Hrabovec Open-Pit Clinoptilolite Mine
Zeolite-group minerals in phonolite-hosted deposits of the Kaiserstuhl Volcanic Complex, Germany
Reconstruction of residual melts from the zeolitized explosive products of alkaline-mafic volcanoes
Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete
The Late Jurassic (157–150 Ma) Morrison Formation of the Western Interior of the United States contains abundant altered volcanic ash. On the Colorado Plateau, this formation accumulated behind and downwind of a subduction-related volcanic arc along the western margin of North America. The ash in these distal fallout tuffs probably drifted eastward from coignimbrite ash clouds related to collapse calderas. Altered volcanic ash is particularly abundant in the Brushy Basin Member of the upper part of the Morrison Formation. In one 110-m-thick section in eastern Utah, 35 separate beds were deposited in a 2.2 m.y. period. Alteration occurred when glassy volcanic ash fell into fluvial and lacustrine environments, where it was diagenetically altered to various mineral assemblages but most commonly to smectitic clay. Periodically, ash fell into saline, alkaline lakes, and diagenetic alteration of the glassy ash produced a crudely zoned deposit on the Colorado Plateau. Altered volcanic ash beds in the outermost part of the lacustrine deposits are argillic (with smectitic clay), whereas zeolitic (clinoptilolite, analcime) and feldspathic (K-feldspar and albite) alteration dominates the interior zones. Feldspathic ash layers contain secondary silica, and consequently immobile element (e.g., Al, Ti, and high field strength elements) abundances were strongly diluted in these rocks. In contrast, the argillic ash beds experienced strong SiO 2 depletion, and, as a result, they are enriched in the relatively immobile elements. The compositions of the zeolitic ash beds are intermediate between these two extremes and experienced the least alteration. As a result of these changes, immobile element concentrations are less reliable than ratios for determining the original magmatic composition of the ash. Most of the altered ash (regardless of type) was also depleted in water-soluble elements like the alkalies, U, and V. The latter two elements were oxidized during diagenesis of the ash, became soluble, and were partially leached away by groundwater. Locally, U and V in groundwater were reduced upon contact with organic materials and formed important ore deposits. Several aspects of the mineralogy and geochemistry of the altered volcanic ash beds yield information about their original magmatic compositions. The volcanic ash beds typically have small phenoclasts of quartz, sanidine, plagioclase, biotite, zircon, apatite, and Fe-Ti oxides. Titanite is present in ∼40% of the ash beds; pyroxene and amphibole were found in less than 5%. Phenocryst assemblages, mineral compositions, inferred high f O 2 , rare earth element patterns, and immobile element ratios all suggest the parent magmas for the altered tuffs were subduction-related dacites and rhyolites. Small numbers of tuffs have Fe-rich biotite, amphibole, and/or clinopyroxene; both pyroxene and amphibole are alkali rich. These tuffs lack titanite, but some contain anorthoclase and F-rich apatite. Combined with enrichments in Nb and Y, these features show some tuffs had an A-type character and were related to some type of within-arc extension. Paleowind directions, and distribution, radiometric ages, and compositions of the volcanic ash beds and of plutons in the western United States suggest that the most likely eruption sites were in the subduction-related Jurassic magmatic arc, which extended across western Utah and central Nevada and southward into the Mojave of California and southern Arizona (present-day coordinates). Pb isotopic compositions show that at least some of the ash was erupted from magma systems (now exposed as plutons) in the Mojave Desert. We conclude that a brief ignimbrite flare-up from 157 to 150 Ma, but focused on the time period from 152 to 150 Ma, in this region may have been driven by slab steepening and conversion to a strike-slip boundary after a preceding phase of folding and thrusting. The presence of ash beds with A-type characteristics mixed with those that have more typical subduction signatures confirms that the Late Jurassic was geologically a transitional time in North America when subduction was changing to transtensional movement along the western plate boundary.