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• 1. [Image] Geological and Geothermal Investigation of the Lower Wind River Valley, Southwestern Washington Cascade Range

  	The Wind River Valley, on the west slope of the Cascade Range, is a northwest-trending drainage that joins the Columbia River near Carson, Washington. The region has been heavily dissected by fluvial and ...
  	Citation × Citation Citation Abstract Copy Title: Geological and Geothermal Investigation of the Lower Wind River Valley, Southwestern Washington Cascade Range Author: Berri, Dulcy A. Year: 1983 The Wind River Valley, on the west slope of the Cascade Range, is a northwest-trending drainage that joins the Columbia River near Carson, Washington. The region has been heavily dissected by fluvial and glacial erosion. Ridges have sharp crests and deep subsidiary valleys typical of a mature topography, with a total relief of as much as 900 m. The region is vegetated by fir and hemlock, as Well as dense, brushy ground-cover and undergrowth. The lower 8 km of the valley is privately owned and moderately populated. The upper reaches lies within the Gifford Pinchot National Forest, and include several campgrounds and day parks, the Carson National Fish Hatchery, and the Wind River Ranger Station and Wind River Nursery of the US Forest Service. Logging activity is light due to the rugged terrain, and consequently, most valley slopes are not accessible by vehicle. The realization that a potential for significant geothermal resources exists in the Wind River area was brought about by earlier exploration activities. Geologic mapping and interpretation was needed to facilitate further exploration of the resource by providing a knowledge of possible geologic controls on the geothermal system. This report presents the detailed geology of the lower Wind River valley with emphasis on those factors that bear significantly on development of a geothermal resource Title: Geological and Geothermal Investigation of the Lower Wind River Valley, Southwestern Washington Cascade Range Author: Berri, Dulcy A. Year: 1983 The Wind River Valley, on the west slope of the Cascade Range, is a northwest-trending drainage that joins the Columbia River near Carson, Washington. The region has been heavily dissected by fluvial and glacial erosion. Ridges have sharp crests and deep subsidiary valleys typical of a mature topography, with a total relief of as much as 900 m. The region is vegetated by fir and hemlock, as Well as dense, brushy ground-cover and undergrowth. The lower 8 km of the valley is privately owned and moderately populated. The upper reaches lies within the Gifford Pinchot National Forest, and include several campgrounds and day parks, the Carson National Fish Hatchery, and the Wind River Ranger Station and Wind River Nursery of the US Forest Service. Logging activity is light due to the rugged terrain, and consequently, most valley slopes are not accessible by vehicle. The realization that a potential for significant geothermal resources exists in the Wind River area was brought about by earlier exploration activities. Geologic mapping and interpretation was needed to facilitate further exploration of the resource by providing a knowledge of possible geologic controls on the geothermal system. This report presents the detailed geology of the lower Wind River valley with emphasis on those factors that bear significantly on development of a geothermal resource Close

• 2. [Article] A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon

  The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie ...

  Citation × Citation Citation Abstract Copy Title: A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon Author: Haas, Nina Year: 1982 The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie River along the same trend, through Columbia County, Oregon. The possibility that this lineament follows a fault or fault zone was investigated in this study. Geophysical methods were used, with seismic refraction, magnetic and gravity lines run perpendicular to the lineament. The seismic refraction models indicate the near surface basalt is broken in many places, with 15 - 30 meters (50 - 100 feet) vertical displacement, down to the west, at Bunker Hill along the Alder Creek fault. Gravity models required a faulted zone approximately two kilometers wide across the lineament. The proposed fault zone is more clearly defined in the south, becoming more diffuse and branching in the northern part of the study area. The Bouguer gravity values from this study distort the -40 milligal contour farther to the northwest than is shown on the Complete Bouguer Gravity Anomaly Map of Oregon {Berg and Thiruvathukal, 1967b). The existence of sharp topographic features and the geophysical evidence indicate fault activity along the zone. Title: A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon Author: Haas, Nina Year: 1982 The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie River along the same trend, through Columbia County, Oregon. The possibility that this lineament follows a fault or fault zone was investigated in this study. Geophysical methods were used, with seismic refraction, magnetic and gravity lines run perpendicular to the lineament. The seismic refraction models indicate the near surface basalt is broken in many places, with 15 - 30 meters (50 - 100 feet) vertical displacement, down to the west, at Bunker Hill along the Alder Creek fault. Gravity models required a faulted zone approximately two kilometers wide across the lineament. The proposed fault zone is more clearly defined in the south, becoming more diffuse and branching in the northern part of the study area. The Bouguer gravity values from this study distort the -40 milligal contour farther to the northwest than is shown on the Complete Bouguer Gravity Anomaly Map of Oregon {Berg and Thiruvathukal, 1967b). The existence of sharp topographic features and the geophysical evidence indicate fault activity along the zone. Close

• 3. [Article] Stratigraphy, Structure, and Petrology of the Snoqualmie Pass area, Washington

  The Snoqualmie pass area lies about 50 mi (80 km) east of Seattle, Washington, along the crest of the Cascade Range. Five stratified units, forming a composite section over 22,000 ft (6700 m) thick, are ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphy, Structure, and Petrology of the Snoqualmie Pass area, Washington Author: Chitwood, Lawrence A. Year: 1976 The Snoqualmie pass area lies about 50 mi (80 km) east of Seattle, Washington, along the crest of the Cascade Range. Five stratified units, forming a composite section over 22,000 ft (6700 m) thick, are recognized in the area. They were deformed and later intruded by granodiorite and quartz monzonite porphyry of the Snoqualmie batholith (middle Miocene). The oldest unit, the Denny Formation (Permian), 7000 ft (2100 m) thick, consists of interstratified basalt, andesite and dacite volcanic rocks and limestone and chert beds. This formation is unconformably overlain by a thick conformable sequence of early Tertiary strata which are subdivided, from oldest to youngest, into the Guye Formation, Mount Catherine Tuff, and Naches Formations (Paleocene to early Oligocene). The Guye Formation, 6500 ft (1980 m) thick, consists of carbonaceous mudstone, quartzofeldspathic siltstone and sandstone, and chert conglomerate. The Mount Catherine Tuff, 900 ft (274 m) thick, consists of interstratified dacitic and rhyolitic crystal-vitric welded tuff. The Naches Formation, more than 6000 ft (1830 m) thick, is composed of carbonaceous mudstone and quartzofeldspathic siltstone and sandstone with interstratified andesitic lava and pyroclastic rock. The Denny Mountain Formation, informally named, 1800 ft (550 m) thick,(Oligocene or early Miocene) overlies the Guye Formation along a major angular unconformity. This unit consists of interstratified dacitic and andesitic tuff, volcanic breccia, and intercalated andesitic lava. The rocks of all stratified formations except the Denny Mountain Formation were deformed at different times before emplacement of the Snoqualmie batholith. During batholithic emplacement, four stages of deformation are recognized: (1) development of an anticline in the Guye, Mount Catherine Tuff, and Naches Formations, (2) break-up of this anticline and downfaulting of limbs with displacements up to 2 mi (3.2 km), (3) uplift of blocks of the Denny Formation and juxtaposition of these with younger formational units, and (4) uplift of additional blocks of the Denny Formation along trends that cut obliquely across stratigraphic contacts and previous structural trends. Intrusion of the Snoqualmie granodiorite and quartz monzonite porphyry into limestone beds of the Denny Formation has formed local deposits of skarn containing principally magnetite and lesser amounts of chalcopyrite. Title: Stratigraphy, Structure, and Petrology of the Snoqualmie Pass area, Washington Author: Chitwood, Lawrence A. Year: 1976 The Snoqualmie pass area lies about 50 mi (80 km) east of Seattle, Washington, along the crest of the Cascade Range. Five stratified units, forming a composite section over 22,000 ft (6700 m) thick, are recognized in the area. They were deformed and later intruded by granodiorite and quartz monzonite porphyry of the Snoqualmie batholith (middle Miocene). The oldest unit, the Denny Formation (Permian), 7000 ft (2100 m) thick, consists of interstratified basalt, andesite and dacite volcanic rocks and limestone and chert beds. This formation is unconformably overlain by a thick conformable sequence of early Tertiary strata which are subdivided, from oldest to youngest, into the Guye Formation, Mount Catherine Tuff, and Naches Formations (Paleocene to early Oligocene). The Guye Formation, 6500 ft (1980 m) thick, consists of carbonaceous mudstone, quartzofeldspathic siltstone and sandstone, and chert conglomerate. The Mount Catherine Tuff, 900 ft (274 m) thick, consists of interstratified dacitic and rhyolitic crystal-vitric welded tuff. The Naches Formation, more than 6000 ft (1830 m) thick, is composed of carbonaceous mudstone and quartzofeldspathic siltstone and sandstone with interstratified andesitic lava and pyroclastic rock. The Denny Mountain Formation, informally named, 1800 ft (550 m) thick,(Oligocene or early Miocene) overlies the Guye Formation along a major angular unconformity. This unit consists of interstratified dacitic and andesitic tuff, volcanic breccia, and intercalated andesitic lava. The rocks of all stratified formations except the Denny Mountain Formation were deformed at different times before emplacement of the Snoqualmie batholith. During batholithic emplacement, four stages of deformation are recognized: (1) development of an anticline in the Guye, Mount Catherine Tuff, and Naches Formations, (2) break-up of this anticline and downfaulting of limbs with displacements up to 2 mi (3.2 km), (3) uplift of blocks of the Denny Formation and juxtaposition of these with younger formational units, and (4) uplift of additional blocks of the Denny Formation along trends that cut obliquely across stratigraphic contacts and previous structural trends. Intrusion of the Snoqualmie granodiorite and quartz monzonite porphyry into limestone beds of the Denny Formation has formed local deposits of skarn containing principally magnetite and lesser amounts of chalcopyrite. Close

• 4. [Article] Petrology of the Bull-of-the-Woods intrusive complex

  An area of unmapped intrusions lies within the Bull-of-the-Woods Roadless Area of Mount Hood National Forest. A variety of andesites, dacites,and diorites intruding units of tuff and andesite lava flows ...

  Citation × Citation Citation Abstract Copy Title: Petrology of the Bull-of-the-Woods intrusive complex Author: Jackson, James Streshley Year: 1978 An area of unmapped intrusions lies within the Bull-of-the-Woods Roadless Area of Mount Hood National Forest. A variety of andesites, dacites,and diorites intruding units of tuff and andesite lava flows crop out over.an area of 52 sq km. These intrusions do not appear on the Geologic Map of Oregon West of the 121st Meridian (Hells and Peck, 1961). The purpose of this investigation is to map and describe these intrusions, with attention to the following questions: What is the petrographic and geochemical nature of these intrusions? What is the order of emplacement of these intrusions? What is the probable mechanism of intrusion? What relation do these intrusions bear to a possible underlying batholith? Contact relations in the field, petrographic studies, and major and trace element trends were used to address these questions. Title: Petrology of the Bull-of-the-Woods intrusive complex Author: Jackson, James Streshley Year: 1978 An area of unmapped intrusions lies within the Bull-of-the-Woods Roadless Area of Mount Hood National Forest. A variety of andesites, dacites,and diorites intruding units of tuff and andesite lava flows crop out over.an area of 52 sq km. These intrusions do not appear on the Geologic Map of Oregon West of the 121st Meridian (Hells and Peck, 1961). The purpose of this investigation is to map and describe these intrusions, with attention to the following questions: What is the petrographic and geochemical nature of these intrusions? What is the order of emplacement of these intrusions? What is the probable mechanism of intrusion? What relation do these intrusions bear to a possible underlying batholith? Contact relations in the field, petrographic studies, and major and trace element trends were used to address these questions. Close

• 5. [Article] Geology of the Breitenbush Hot Springs area, Cascade Range, Oregon

  The Breitenbush Hot Springs area lies on the boundary of folded middle to late Tertiary Western Cascade rocks and younger High Cascade rocks. Within the mapped area the Western Cascade rocks are represented ...

  Citation × Citation Citation Abstract Copy Title: Geology of the Breitenbush Hot Springs area, Cascade Range, Oregon Author: Clayton, Clifford Michael Year: 1976 The Breitenbush Hot Springs area lies on the boundary of folded middle to late Tertiary Western Cascade rocks and younger High Cascade rocks. Within the mapped area the Western Cascade rocks are represented by four formations. The Detroit Beds, a sequence of interstratified tuffaceous sandstone, mudflow breccia, and tuff, is overlain unconformably by the Breitenbush Tuff. The Breitenbush Tuff consists of three units of welded pumice-rich crystal-vitric ash-flow tuffs interbedded with tuffaceous sedimentary rocks. The Outerson Formation unconformably overlies the Breitenbush Tuff and consists primarily of basaltic lava and breccia. The Outerson Formation includes three localized members: a basal, glassy, aphanitic basalt, the Lake Leone Sediments, and the Outerson Tuff. The Outerson Formation is cut by a number of feeder dikes and plugs and is unconformably overlain by the Cheat Creek Sediments, composed of volcanic sedimentary rocks and a distinctive basaltic tuff. The Western Cascade formations total more than 1660 m {5500 ft) of strata and range from Oligocene to Pliocene in age. The High Cascade rocks are represented by two formations: the Triangulation Peak Volcanics of basalt and andesite lava and breccia, lying unconformably atop the Cheat Creek Sediments; and unconformably beneath the Collowash Volcanics, a series of thin basaltic lava flows and breccias. The Western and High Cascade rocks are covered extensively by surficial deposits, primarily glacial drift. The High Cascade formations are at least 840 m (2800 ft) thick, ranging in age from Pliocene to Pliestocene. The Western Cascade rocks have been folded and faulted in the Breitenbush Hot Springs area, and form the eastern limb of the north-trending Breitenbush Anticline. The folded rocks and the erosional unconformities between the rock units probably represent two local episodes of orogeny: one in early to middle Miocene and another in late Pliocene to Pleistocene time. The Outerson Formation represents a depositional sequence between the periods of uplift and deformation. Faulting accompanied the orogenic sequences. The primary volcanic landforms in the area have been destroyed by erosion but skeletal remains of High Cascade volcanoes are recognized. Stream erosion and glaciation are responsible for the present landforms. Breitenbush Hot Springs occurs, in part, along basaltic dikes which channel the water through impermeable Breitenbush Tuff. The dikes are believed to be associated with the Outerson basalts. The Hot Springs discharge upwards at 3400 l/min. (900 gpm) of water at temperatures up to 92°C (198°F). Title: Geology of the Breitenbush Hot Springs area, Cascade Range, Oregon Author: Clayton, Clifford Michael Year: 1976 The Breitenbush Hot Springs area lies on the boundary of folded middle to late Tertiary Western Cascade rocks and younger High Cascade rocks. Within the mapped area the Western Cascade rocks are represented by four formations. The Detroit Beds, a sequence of interstratified tuffaceous sandstone, mudflow breccia, and tuff, is overlain unconformably by the Breitenbush Tuff. The Breitenbush Tuff consists of three units of welded pumice-rich crystal-vitric ash-flow tuffs interbedded with tuffaceous sedimentary rocks. The Outerson Formation unconformably overlies the Breitenbush Tuff and consists primarily of basaltic lava and breccia. The Outerson Formation includes three localized members: a basal, glassy, aphanitic basalt, the Lake Leone Sediments, and the Outerson Tuff. The Outerson Formation is cut by a number of feeder dikes and plugs and is unconformably overlain by the Cheat Creek Sediments, composed of volcanic sedimentary rocks and a distinctive basaltic tuff. The Western Cascade formations total more than 1660 m {5500 ft) of strata and range from Oligocene to Pliocene in age. The High Cascade rocks are represented by two formations: the Triangulation Peak Volcanics of basalt and andesite lava and breccia, lying unconformably atop the Cheat Creek Sediments; and unconformably beneath the Collowash Volcanics, a series of thin basaltic lava flows and breccias. The Western and High Cascade rocks are covered extensively by surficial deposits, primarily glacial drift. The High Cascade formations are at least 840 m (2800 ft) thick, ranging in age from Pliocene to Pliestocene. The Western Cascade rocks have been folded and faulted in the Breitenbush Hot Springs area, and form the eastern limb of the north-trending Breitenbush Anticline. The folded rocks and the erosional unconformities between the rock units probably represent two local episodes of orogeny: one in early to middle Miocene and another in late Pliocene to Pleistocene time. The Outerson Formation represents a depositional sequence between the periods of uplift and deformation. Faulting accompanied the orogenic sequences. The primary volcanic landforms in the area have been destroyed by erosion but skeletal remains of High Cascade volcanoes are recognized. Stream erosion and glaciation are responsible for the present landforms. Breitenbush Hot Springs occurs, in part, along basaltic dikes which channel the water through impermeable Breitenbush Tuff. The dikes are believed to be associated with the Outerson basalts. The Hot Springs discharge upwards at 3400 l/min. (900 gpm) of water at temperatures up to 92°C (198°F). Close

• 6. [Article] The Geology of the Castle Rock Area, Grant, Harney and Malheur Counties, Oregon

  The geology of the Castle Rock area aids in the understanding of Cenozoic volcanic stratigraphy and structures in an area where these volcanic rocks thin near the margins of the pre-Tertiary basement rocks ...

  Citation × Citation Citation Abstract Copy Title: The Geology of the Castle Rock Area, Grant, Harney and Malheur Counties, Oregon Author: Wood, John David Year: 1976 The geology of the Castle Rock area aids in the understanding of Cenozoic volcanic stratigraphy and structures in an area where these volcanic rocks thin near the margins of the pre-Tertiary basement rocks and structural trends are overlapping. The Castle Rock area is unique in several aspects and is important in understanding and interpreting the geology in adjacent regions which have all been studied, at least on a regional basis. Intrusive ash-flow bodies of the Dinner Creek Ash-Flow Tuff, well-exposed sections of complexly interstratified volcanic rocks and well-exposed faults, and of high amount of erosional relief are features which make this area a unique and important addition to the understanding of the stratigraphy of eastern Oregon. Title: The Geology of the Castle Rock Area, Grant, Harney and Malheur Counties, Oregon Author: Wood, John David Year: 1976 The geology of the Castle Rock area aids in the understanding of Cenozoic volcanic stratigraphy and structures in an area where these volcanic rocks thin near the margins of the pre-Tertiary basement rocks and structural trends are overlapping. The Castle Rock area is unique in several aspects and is important in understanding and interpreting the geology in adjacent regions which have all been studied, at least on a regional basis. Intrusive ash-flow bodies of the Dinner Creek Ash-Flow Tuff, well-exposed sections of complexly interstratified volcanic rocks and well-exposed faults, and of high amount of erosional relief are features which make this area a unique and important addition to the understanding of the stratigraphy of eastern Oregon. Close

• 7. [Article] Origins of Late- Pleistocene Coastal Dune Sheets, Magdalena and Guerrero Negro, from Continental Shelf Low-stand Supply (70-20 ka), under Conditions of Southeast Littoral- and Eolian-Sand Transport, in Baja California Sur, Mexico

  Shallow morpho-stratigraphic sections (n = 11) in each of two large coastal dune sheets including the Magdalena (7000 km2) and Guerrero Negro (8000 km2) dune sheets, from the Pacific Ocean side of Baja ...

  Citation × Citation Citation Abstract Copy Title: Origins of Late- Pleistocene Coastal Dune Sheets, Magdalena and Guerrero Negro, from Continental Shelf Low-stand Supply (70-20 ka), under Conditions of Southeast Littoral- and Eolian-Sand Transport, in Baja California Sur, Mexico Author: Peterson, Curt D., Murillo-Jiminez, Janette, Stock, Errol, Price, David M., Hostetler, Steve W., Percy, David Year: 2017 Shallow morpho-stratigraphic sections (n = 11) in each of two large coastal dune sheets including the Magdalena (7000 km2) and Guerrero Negro (8000 km2) dune sheets, from the Pacific Ocean side of Baja California Sur, Mexico, have been analyzed for dune deposit age. The shallow morpho-stratigraphic sections (∼2-10 m depth) include 11 new TL and 14C ages, and paleosol chronosequences, that differentiate cemented late Pleistocene dune deposits (20.7 ± 2.1 to 99.8 ± 9.4 ka) from uncemented Holocene dune deposits (0.7 ± 0.05 to at least 3.2 ± 0.3 ka). Large linear dune ridges (5-10 m in height) in the dune sheet interiors trend southeast and are generally of late Pleistocene age (∼70-20 ka). The late Pleistocene dune deposits reflect eolian transport of marine sand across the emerged continental shelf (30-50 km southeast distance) from low-stand paleo-shorelines (-100 ± 25 m elevation), which were locally oriented nearly orthogonal to modeled deep-water wave directions (∼300° TN). During the Holocene marine transgression, onshore and alongshore wave transport delivered remobilized shelf-sand deposits to the nearshore areas of the large dune sheets, building extensive barrier islands and sand spits. Submerged back-barrier lagoons generally precluded marine sand supply to dune sheet interiors in middle to late Holocene time, though exceptions occur along some ocean and lagoon shorelines. Reactivation of the late Pleistocene dune deposits in the dune sheet interiors lead to generally thin (1-3 m thickness), but widespread, covers of Holocene dune deposits (0.41 ± 0.05 to 10.5 ± 1.6 ka). Mechanical drilling will be required to penetrate indurated subsoil caliche layers to reach basal Pleistocene dune deposits. Title: Origins of Late- Pleistocene Coastal Dune Sheets, Magdalena and Guerrero Negro, from Continental Shelf Low-stand Supply (70-20 ka), under Conditions of Southeast Littoral- and Eolian-Sand Transport, in Baja California Sur, Mexico Author: Peterson, Curt D., Murillo-Jiminez, Janette, Stock, Errol, Price, David M., Hostetler, Steve W., Percy, David Year: 2017 Shallow morpho-stratigraphic sections (n = 11) in each of two large coastal dune sheets including the Magdalena (7000 km2) and Guerrero Negro (8000 km2) dune sheets, from the Pacific Ocean side of Baja California Sur, Mexico, have been analyzed for dune deposit age. The shallow morpho-stratigraphic sections (∼2-10 m depth) include 11 new TL and 14C ages, and paleosol chronosequences, that differentiate cemented late Pleistocene dune deposits (20.7 ± 2.1 to 99.8 ± 9.4 ka) from uncemented Holocene dune deposits (0.7 ± 0.05 to at least 3.2 ± 0.3 ka). Large linear dune ridges (5-10 m in height) in the dune sheet interiors trend southeast and are generally of late Pleistocene age (∼70-20 ka). The late Pleistocene dune deposits reflect eolian transport of marine sand across the emerged continental shelf (30-50 km southeast distance) from low-stand paleo-shorelines (-100 ± 25 m elevation), which were locally oriented nearly orthogonal to modeled deep-water wave directions (∼300° TN). During the Holocene marine transgression, onshore and alongshore wave transport delivered remobilized shelf-sand deposits to the nearshore areas of the large dune sheets, building extensive barrier islands and sand spits. Submerged back-barrier lagoons generally precluded marine sand supply to dune sheet interiors in middle to late Holocene time, though exceptions occur along some ocean and lagoon shorelines. Reactivation of the late Pleistocene dune deposits in the dune sheet interiors lead to generally thin (1-3 m thickness), but widespread, covers of Holocene dune deposits (0.41 ± 0.05 to 10.5 ± 1.6 ka). Mechanical drilling will be required to penetrate indurated subsoil caliche layers to reach basal Pleistocene dune deposits. Close

• 8. [Article] Stratigraphic and geochemical evolution of the Glass Buttes complex, Oregon

  Glass Buttes complex lies at the northern margin of the Basin and Range province in central Oregon and is cut by the northwest-trending Brothers fault zone. An older acrystalline volcanic sequence of high-silica ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphic and geochemical evolution of the Glass Buttes complex, Oregon Author: Roche, Richard Louis Year: 1987 Glass Buttes complex lies at the northern margin of the Basin and Range province in central Oregon and is cut by the northwest-trending Brothers fault zone. An older acrystalline volcanic sequence of high-silica rhyolites (>75% SiO2) forms a broad platform composed of domes and flows with minor pyroclastic deposits. The high-silica rhyolite sequence is divided on the basis of texture into 1) zoned flows and domes, 2) obsidian flows, 3) felsite flows, and 4) biotite-phyric flows and domes. Title: Stratigraphic and geochemical evolution of the Glass Buttes complex, Oregon Author: Roche, Richard Louis Year: 1987 Glass Buttes complex lies at the northern margin of the Basin and Range province in central Oregon and is cut by the northwest-trending Brothers fault zone. An older acrystalline volcanic sequence of high-silica rhyolites (>75% SiO2) forms a broad platform composed of domes and flows with minor pyroclastic deposits. The high-silica rhyolite sequence is divided on the basis of texture into 1) zoned flows and domes, 2) obsidian flows, 3) felsite flows, and 4) biotite-phyric flows and domes. Close

• 9. [Article] Geochemical stratigraphy of the Dooley rhyolite breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon

  The Dooley Rhyolite Breccia in northeast Oregon was erupted between 12 and 16 million years ago, from central vents and linear feeder dikes within the Dooley Mountain quadrangle. The peraluminous, high-silica ...

  Citation × Citation Citation Abstract Copy Title: Geochemical stratigraphy of the Dooley rhyolite breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon Author: Whitson, David Neale Year: 1988 The Dooley Rhyolite Breccia in northeast Oregon was erupted between 12 and 16 million years ago, from central vents and linear feeder dikes within the Dooley Mountain quadrangle. The peraluminous, high-silica rhyolites of the formation were erupted over an irregular highland of eroded pre-Tertiary metamorphic rocks locally overlain by intracanyon, Eocene Clarno-type basalt flow(s) . The Dooley Rhyolite Braccia is exposed in a tectonically disrupted, north-south trending graben across the Elkhorn Range. The formation is variable in thickness with maximum thickness exceeding 660 meters in the south and 600 meters in the north half of the quadrangle. Volumetrically the formation is dominated by block lava flows with lessor associated volcaniclastic and pyroclastic rocks. Although initial and waning phases of eruption of the formation produced ash-flow tuffs which extend well beyond the quadrangle boundaries, volcanism within the quadrangle appears to have been primarily effusive. At least nine geochemically distinct rhyolite subunits belonging to four related chemical groups have been identified in the formation stratigraphy which appear to represent unique eruptive episodes. Chronologic geochemical patterns within the formation are consistent with a petrogenetic model of repeated partial melting and eruption from multiple silicic magma chambers in an attenuated continental crust. Basalts correlative with the Powder River Basalt and the Strawberry Volcanics overlie the Dooley Rhyolite Braccia on the north flank of Dooley Mountain. Cale-alkaline basalts correlative with the Strawberry Volcanics are overlain by thoeliitic basalts of uncertain affinity on the south flank of the mountain. These basalt flows on respective flanks of the mountain were not continuous across the quadrangle. Rhyolitic volcanism in the Dooley Mountain quadrangle is contemporary with the strawberry Volcanics and the Picture Gorge Basalt of the Columbia River Basalt Group. Title: Geochemical stratigraphy of the Dooley rhyolite breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon Author: Whitson, David Neale Year: 1988 The Dooley Rhyolite Breccia in northeast Oregon was erupted between 12 and 16 million years ago, from central vents and linear feeder dikes within the Dooley Mountain quadrangle. The peraluminous, high-silica rhyolites of the formation were erupted over an irregular highland of eroded pre-Tertiary metamorphic rocks locally overlain by intracanyon, Eocene Clarno-type basalt flow(s) . The Dooley Rhyolite Braccia is exposed in a tectonically disrupted, north-south trending graben across the Elkhorn Range. The formation is variable in thickness with maximum thickness exceeding 660 meters in the south and 600 meters in the north half of the quadrangle. Volumetrically the formation is dominated by block lava flows with lessor associated volcaniclastic and pyroclastic rocks. Although initial and waning phases of eruption of the formation produced ash-flow tuffs which extend well beyond the quadrangle boundaries, volcanism within the quadrangle appears to have been primarily effusive. At least nine geochemically distinct rhyolite subunits belonging to four related chemical groups have been identified in the formation stratigraphy which appear to represent unique eruptive episodes. Chronologic geochemical patterns within the formation are consistent with a petrogenetic model of repeated partial melting and eruption from multiple silicic magma chambers in an attenuated continental crust. Basalts correlative with the Powder River Basalt and the Strawberry Volcanics overlie the Dooley Rhyolite Braccia on the north flank of Dooley Mountain. Cale-alkaline basalts correlative with the Strawberry Volcanics are overlain by thoeliitic basalts of uncertain affinity on the south flank of the mountain. These basalt flows on respective flanks of the mountain were not continuous across the quadrangle. Rhyolitic volcanism in the Dooley Mountain quadrangle is contemporary with the strawberry Volcanics and the Picture Gorge Basalt of the Columbia River Basalt Group. Close

• 10. [Article] Soputan Volcano, Indonesia: Petrological Systematics of Volatiles and Magmas and Their Bearing on Explosive Eruptions of a Basalt Volcano

  Soputan volcano is one of the few basaltic volcanoes among 127 active volcanoes in Indonesia. It is part of the Sempu-Soputan volcanic complex located south of Tondano Caldera, North Sulawesi and commonly ...

  Citation × Citation Citation Abstract Copy Title: Soputan Volcano, Indonesia: Petrological Systematics of Volatiles and Magmas and Their Bearing on Explosive Eruptions of a Basalt Volcano Author: Kunrat, Syegi Lenarahmi Year: 2017 Soputan volcano is one of the few basaltic volcanoes among 127 active volcanoes in Indonesia. It is part of the Sempu-Soputan volcanic complex located south of Tondano Caldera, North Sulawesi and commonly produces both explosive eruptions with VEI 2-3 and effusive lava dome and flow eruptions. Over the last two decades, Soputan had thirteen eruptions, the most recent in 2016. Most eruptions started explosively, followed by dome growth and in some cases pyroclastic flows. Our study focuses on understanding the magmatic system of Soputan and what processes are responsible for its highly explosive eruptions, which are typically uncommon for a basaltic magma composition. Our study includes tephra samples predating the 1911 eruptions, lava flow samples from the 2015 eruption, and ash from a 2015 fallout deposit. Our whole rock major and trace element composition are virtually identical to lava flow and select pyroclastic deposit compositions of Kushendratno et al. (2012) for the 1911-1912 and 1991-2007 eruptions. Bulk rocks contain 49 to 51 wt.% SiO2, whereas 2015 ash samples are slightly more silicic with 53 wt.% SiO2, consistent with segregation of groundmass from phenocrysts in the eruption cloud. Mantle normalized incompatible trace elements indicate strongly depleted HFSE (High Field Strength Elements) and REE (Rare Earth Elements) signatures but with spikes at Pb and Sr and mild enrichment of Rb and Ba. In comparison of data of this study with what was reported by Kushendratno et al. (2012), Fo68-79 olivine-hosted melt inclusions range from basaltic (48-52 wt.% SiO2) to basaltic andesite (54-55 wt.%) as compared to 54 - 65 wt.% SiO2 glass in Fo68-74 olivines. The compositional range of melt inclusions is consistent with 50% fractionation of multiple minerals including observed phenocrysts of olivine, plagioclase, pyroxene and oxides. Compositional trends with an inflection point likely reflect a change in the crystallizing assemblage, where early crystallization includes clinopyroxene and plagioclase, while later crystallization is dominated by plagioclase. New volatile concentration data from melt inclusions (S max. 0.35 wt.%, Cl max. 0.17%, H2O max. 5.2 wt.% from FTIR analyses) are higher than previously reported from younger samples (S max. ~0.07 wt.%, Cl max. 0.2%, H2O max. ~1 wt.%). H2O is relatively constant (~1-4 wt.%) for individual tephra samples (data by FTIR and water by difference method). Our inclusion data suggest that more volatile-rich magmas exist at depth and this is consistent with a model whereby recharge of deep, volatile-rich magmas into a more degassed and crystal-rich magma initiates a new, highly explosive eruption. Title: Soputan Volcano, Indonesia: Petrological Systematics of Volatiles and Magmas and Their Bearing on Explosive Eruptions of a Basalt Volcano Author: Kunrat, Syegi Lenarahmi Year: 2017 Soputan volcano is one of the few basaltic volcanoes among 127 active volcanoes in Indonesia. It is part of the Sempu-Soputan volcanic complex located south of Tondano Caldera, North Sulawesi and commonly produces both explosive eruptions with VEI 2-3 and effusive lava dome and flow eruptions. Over the last two decades, Soputan had thirteen eruptions, the most recent in 2016. Most eruptions started explosively, followed by dome growth and in some cases pyroclastic flows. Our study focuses on understanding the magmatic system of Soputan and what processes are responsible for its highly explosive eruptions, which are typically uncommon for a basaltic magma composition. Our study includes tephra samples predating the 1911 eruptions, lava flow samples from the 2015 eruption, and ash from a 2015 fallout deposit. Our whole rock major and trace element composition are virtually identical to lava flow and select pyroclastic deposit compositions of Kushendratno et al. (2012) for the 1911-1912 and 1991-2007 eruptions. Bulk rocks contain 49 to 51 wt.% SiO2, whereas 2015 ash samples are slightly more silicic with 53 wt.% SiO2, consistent with segregation of groundmass from phenocrysts in the eruption cloud. Mantle normalized incompatible trace elements indicate strongly depleted HFSE (High Field Strength Elements) and REE (Rare Earth Elements) signatures but with spikes at Pb and Sr and mild enrichment of Rb and Ba. In comparison of data of this study with what was reported by Kushendratno et al. (2012), Fo68-79 olivine-hosted melt inclusions range from basaltic (48-52 wt.% SiO2) to basaltic andesite (54-55 wt.%) as compared to 54 - 65 wt.% SiO2 glass in Fo68-74 olivines. The compositional range of melt inclusions is consistent with 50% fractionation of multiple minerals including observed phenocrysts of olivine, plagioclase, pyroxene and oxides. Compositional trends with an inflection point likely reflect a change in the crystallizing assemblage, where early crystallization includes clinopyroxene and plagioclase, while later crystallization is dominated by plagioclase. New volatile concentration data from melt inclusions (S max. 0.35 wt.%, Cl max. 0.17%, H2O max. 5.2 wt.% from FTIR analyses) are higher than previously reported from younger samples (S max. ~0.07 wt.%, Cl max. 0.2%, H2O max. ~1 wt.%). H2O is relatively constant (~1-4 wt.%) for individual tephra samples (data by FTIR and water by difference method). Our inclusion data suggest that more volatile-rich magmas exist at depth and this is consistent with a model whereby recharge of deep, volatile-rich magmas into a more degassed and crystal-rich magma initiates a new, highly explosive eruption. Close