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Eagle Mountains caldera volcanic rocks

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Eagle Mountains caldera volcanic rocks
State Texas
Name Eagle Mountains caldera volcanic rocks
Geologic age Phanerozoic | Cenozoic | Tertiary | Oligocene
Comments Total of about 3,000-4,000 ft of eruptive rocks: lower rhyolite, a sequence of tuff, flow breccia, volcanic breccia, extrusive and intrusive rhyolite, with sedimentary rocks at base, thickness more than 1,000 ft. Trachyte porphyry--hard, compact, weathers to angular blocks, thickness as much as approximately 750 ft. Upper rhyolite--rhyolite including an upper volcanic breccia, flow breccia, and patches of basal conglo.; volc. breccia fragments of volc. rock, quartzite, and limestone in aphanitic matrix, white to lt. gray; rhyolite, aphanitic, comapct, brittle, intensely fractured, thickness 1,500 to 2,000 ft at Eagle Bluff.
Primary rock type rhyolite
Secondary rock type trachyte
Other rock types conglomerate; tuff; volcanic breccia (agglomerate)
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)
Minor
Igneous > Volcanic > Felsic-volcanic > Trachyte (Pyroclastic, tuff)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Pyroclastic, tuff)
Map references
Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000
Unit references
Bureau of Economic Geology, 1979, Marfa Sheet, Geologic Atlas of Texas: Bureau of Economic Geology and The University of Texas at Austin, scale 1:250,000.
Counties Culberson - Hudspeth - Jeff Davis