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Geologic units containing tholeiite
A silica-oversaturated basalt, characterized by the presence of low-calcium pyroxenes in addition to clinopyroxene and calcic plagioclase. Olivine may be present in the mode, but neither olivine nor nepheline appear in the norm.
This category is also used for basalt (tholeiite).
- Holocene to middle Pliocene basaltic rocks (Middle Pliocene to Holocene)
- Mostly dark-colored basaltic lava and cinders young enough that some original volcanic landforms are still apparent. Includes a small amount of andesite, dacite, and rhyolite. Rocks of this map unit are largely restricted to six areas widely distributed in Arizona: San Francisco and Uinkaret volcanic fields in northern Arizona (0-4 Ma); Springerville (0-4 Ma) and San Carlos (0-2 Ma) volcanic fields in east-central Arizona; and San Bernardino (0-1 Ma) and Sentinel (1-4 Ma) volcanic fields in southern Arizona. Rocks of this unit are also present in the extreme southwestern part of Arizona where they were erupted at the edge of the Pinacate volcanic field (0-2 Ma) in northwestern Sonora. (0-4 Ma)
- Late to middle Miocene basaltic rocks (Middle to Late Miocene)
- Mostly dark, mesa-forming basalt deposited as lava flows. Rocks of this unit are widely exposed south of Camp Verde (Hickey Formation basalts), in the Mohon Mountains north of Bagdad, "The Mesa" east of Parker, and at other scattered locations in western Arizona. Rocks of this unit were not tilted by middle-Tertiary normal faulting except in a narrow belt from north of Phoenix to the northwest corner of the state. (8-16 Ma)
- Middle Proterozoic sedimentary rocks (Middle Proterozoic)
- Red-brown shale and sandstone, buff to orange quartzite, limestone, basalt, black shale, and sparse conglomerate. This unit includes the Grand Canyon Supergroup, Apache Group, and Troy Quartzite. These rocks were deposited in shallow marine, coastal nonmarine, and fluvial settings. (700-1300)
- Pliocene to late Miocene basaltic rocks (Late Miocene to Pliocene)
- Mostly dark, inconspicuously flat, low-lying or mesa-forming basalt deposited as lava flows. Rocks included in this unit are located almost entirely in the large volcanic fields south and west of Flagstaff, in smaller fields in northwesternmost Arizona, and in the Hopi Buttes volcanic field on the Navajo and Hopi Indian Reservations north of Holbrook. Original volcanic landforms have been obscured by erosion. (4-8 Ma)
- Basalt and gravel; Late Pleistocene basalt flows and interlayered gravel of subunit 2b; Snake River Plain (Late Pleistocene)
- Upper Pleistocene Snake Plain basaltic lava flows, unit 2.
- Basalt and silt; Late Pleistocene basalt flows and interlayered lacustrine silt beds of subunit 1b; Snake River Plain (Late Pleistocene)
- Upper Pleistocene Snake Plain basaltic lava flows, unit 1.
- Basalt, clay, and gravel; Late Pleistocene basalt flows with interlayered alluvial and lacustrine sediments; Snake River Plain and vicinity (subunits are Qpu1b, Qpu2b, Qpu3b, and Qpu4b) (Late Pleistocene)
- Upper Pleistocene Snake Plain lava flows; local stratigraphic position shown by (Qpu4b, Qpu3b, Qpu2b, Qpu1b).
- Basalt, clay, and pumice; Late Pleistocene basalt flows, volcaniclastic debris, and ponded sediments of subunit 4b; Snake River Plain; (Late Pleistocene)
- Upper Pleistocene Snake Plain basaltic lava flows, unit 4.
- Basalt flows, basaltic pyroclastic and clastic debris; Middle Pleistocene canyon-filling and plateau lava flows, pyroclastic debris, alluvium, and colluvium; Snake River Plain (Middle Pleistocene)
- Middle Pleistocene plateau and canyon-filling basalt in and near Snake Plain.
- Basalt flows, pumice, and tuff; Early Pleistocene to Pliocene basaltic volcanics; Snake River Plain (Early Pleistocene)
- Lower Pleistocene to Pliocene basalts with associated tuffs and volcanic detritus.
- Basalt, gravel, and pumice; Late Pleistocene basaltic volcanics and interlayered sedimetnsof subunit 3b; Snake River Plain (Late Pleistocene)
- Upper Pleistocene Snake Plain basaltic lava flows, unit 3.
- Basalt lava flows; Early Miocene valley-filling basalt flows of subunit 1b; Columbia Plateau (Miocene)
- Miocene basalt flows of western Idaho; commonly porphyritic and exposed on lower slopes.
- Basalt, pumice; Holocene basaltic lava flows and cinder cones; Snake River Plain and vicinity (Holocene)
- Recent, relatively unweathered Snake Plain basalt flows and cinder cones.
- Rhyolitic domes, flows, pyroclastic debris, and basalt flows; Early Pleistocene subvolcanic to volcanic features; eastern Snake River Plain (Early Pleistocene)
- Lower Pleistocene to Pliocene silicic volcanic units near the Snake Plain.
- Rhyolitic tuffs, ignimbrites, and flows, basaltic flows, conglomerate and marlstone; Pliocene to Miocene volcano-sedimentary deposits; eastern Snake River Plain and southeastern Idaho (Pliocene-Miocene)
- Pliocene volcanic units, generally air-fall or pyroclastic in origin; grade into (Tpd).
- Deerfield Basalt (Lower Jurassic)
- Deerfield Basalt - Well-jointed quartz tholeiite, locally vesicular and locally pillowed near base.
- Hampden Basalt (Lower Jurassic)
- Hampden Basalt - Thin flows of quartz tholeiite, locally intimately associated with Granby Basaltic Tuff.
- Holyoke Basalt (Lower Jurassic)
- Holyoke Basalt - Thick, columnar quartz tholeiite containing local gabbroic segregations, thinks eastward; interpreted as one or more thick ponded lava flows. Assigned to Newark Supergroup (Robinson and Luttrell, 1985).
- Siletz River Volcanics and related rocks (middle and lower Eocene and Paleocene) (Paleocene to Middle Eocene)
- Aphanitic to porphyritic, vesicular pillow flows, tuff-breccias, massive lava flows and sills of tholeiitic and alkalic basalt. Upper part of sequence contains numerous interbeds of basaltic siltstone and sandstone, basaltic tuff, and locally derived basalt conglomerate. Rocks of unit pervasively zeolitized and veined with calcite. Most of these rocks are of marine origin and have been interpreted as oceanic crust and seamounts (Snavely and others, 1968). Foraminiferal assemblages referred to the Ulatisian and Penutian Stages (Snavely and others, 1969); K-Ar ages range from 50.7 +/- 3.1 to 58.1 +/- 1.5 Ma (Duncan, 1982); includes the lower part of the Roseburg Formation of Baldwin (1974), which has yielded K-Ar ages as old as 62 Ma
- Middle and lower Eocene volcanic rocks (Eocene)
- Dark-gray, course- to fine-grained, strongly chloritized basalt flows and breccia; includes pillow lava, deeply altered palagonite beds, amygdoidal and vesicular flows, and, locally, sedimentary rocks. Comprises outer volcanic belt in Olympic Peninsula, where manganese ore is associated with some submarine lavas.
- Miocene volcanic rocks (Middle Miocene)
- Dark-gray to black, dense aphanitic basalt flows; commonly columnar jointed, less commonly irregularly and platy jointed; some flows vesicular, grading to scoriaceous; includes minor pillow lava, palagonite beds, and interbedded soil profiles and sedimentary beds; contains diatomite beds locally. Maximum thickness in south-central Washington may be in excess of 10,000 feet; much thinner in western Washington, where flows are mostly associated with marine sedimentary rocks. Includes acidic and intermediate volcanic rocks in northern Cascade Mountains.