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005 20240719122616.0;

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035 a| (Sirsi) o02809354;

035 a| (OCoLC)2809354;

043 a| n-mx---;

049 a| EREE;

050 4 a| QE462.I35b| G3x;

100 1 a| Gall, Daniel G.,e| author.=| ^A90666;

245 10 a| Geology of a section of ignimbrites near Sacramento, Chihuahua, Mexico /c| by Daniel G. Gall.;

264 0 c| 1977.;

300 a| 82 leaves, 13 leaves of plates :b| illustrations ;c| 28 cm;

336 a| textb| txt2| rdacontent;

337 a| unmediatedb| n2| rdamedia;

338 a| volumeb| nc2| rdacarrier;

502 b| M.S.c| East Carolina Universityd| 1977;

500 a| "A thesis presented to the faculty of the Department of Geology ... in partial fulfillment of the requirements for the Degree Master of Science in Geology.";

500 a| Advisor: Richard L. Mauger;

520 3 a| A sequence of rhyolitic ignimbrites, 150 m in thickness, is exposed along the southern edge of the Rio Sacramento flood plain approximately 25 km northwest of Chihuahua, Chihuahua, Mexico (long. 106° 12.2' W and lat. 28° 50.8' N). These rocks dip 15° NE and conform to the general low eastward dips of the late Eocene rhyolites between Majalca and Chihuahua City. The ignimbrites include welded vitric tuffs (Units 1, 2, 3, and 5) and a welded lithic tuff (Unit 4). Unit 1 is a single flow and cooling unit. Units 2, 3, and 4 comprise a multiple-flow, single cooling unit. Unit 5 is a single flow and cooling unit. Sanidine is the predominant phenocryst (0r40-70). Minor amounts of plagioclase (An29) and quartz phenocrysts are also present. The groundmass of the ignimbrites consists of sanidine and Si0₂ polymorphs. The ignimbrites are classified as alkali rhyolites because of the predominance of sanidine and Si0₂. The welded vitric tuffs are classified chemically as: 1) high silica rhyolites - Si0₂ [greater-than] 72%, and 2) subaluminous/peralkaline rhyolites - A1₂0₃/Na₂0+K₂0 + Ca0[less-than-or-equal-to]1. In the Sacramento-Majalea area, the late Eocene high silica alkali rhyolitic ignimbrites overlie the older calc-alkalic Peñas Azules volcanics and are overlain by Oligoc̈ne rhyolitic ignimbrites. The Peñas Azules volcanics were probably formed during the Laramide orogeny (late Cretaceous to early Eocene). The late Eocene high silica alkali rhyolites were erupted during Elston's (1976) active stage of extension (late Eocene to Miocene) of the western portion of the American plate. The active stage of extension was followed by the passive stage of extension during the Miocene to present (Elston, 1976). The Oligoc̈ne rhyolites of the main Sierra Madre Occidental may have been related to this period of relaxation following compression. The high silica alkali rhyolites near Sacramento are located between the calc-alkalic igneous center of western Mexico and the alkalic igneous center of western Texas. These rocks can be considered intermediate in composition between calc-alkaline and alkaline.;

504 a| Includes bibliographical references (leaves 80-82).;

650 0 a| Ignimbrite.=| ^A90667;

650 0 a| Geologyz| Mexico.=| ^A27650;

650 7 a| Geology.2| fast0| (OCoLC)fst00940627;

650 7 a| Ignimbrite.2| fast0| (OCoLC)fst00967055;

700 1 a| Mauger, Richard L.q| (Richard Leroy),d| 1936-e| degree supervisor.=| ^A1450473;

710 2 a| East Carolina University.b| Department of Geology.?| UNAUTHORIZED;

856 41 z| Access via ScholarShipu| http://hdl.handle.net/10342/11177;

949 a| Click on web addressw| asish| joyner101;

949 a| Click on web addressw| asish| hsl111;

994 a| C0b| ERE;

596 a| 1 4;

998 a| 114474;

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Geology of a section of ignimbrites near Sacramento, Chihuahua, Mexico / by Daniel G. Gall.

Author/creator	Gall, Daniel G. author.
Other author	Mauger, Richard L. (Richard Leroy), 1936- degree supervisor.
Other author	East Carolina University. Department of Geology.
Format	Theses and dissertations
Production	1977.
Description	82 leaves, 13 leaves of plates : illustrations ; 28 cm
Supplemental Content	Access via ScholarShip
Subjects	Ignimbrite. Geology--Mexico.

Summary	A sequence of rhyolitic ignimbrites, 150 m in thickness, is exposed along the southern edge of the Rio Sacramento flood plain approximately 25 km northwest of Chihuahua, Chihuahua, Mexico (long. 106° 12.2' W and lat. 28° 50.8' N). These rocks dip 15° NE and conform to the general low eastward dips of the late Eocene rhyolites between Majalca and Chihuahua City. The ignimbrites include welded vitric tuffs (Units 1, 2, 3, and 5) and a welded lithic tuff (Unit 4). Unit 1 is a single flow and cooling unit. Units 2, 3, and 4 comprise a multiple-flow, single cooling unit. Unit 5 is a single flow and cooling unit. Sanidine is the predominant phenocryst (0r40-70). Minor amounts of plagioclase (An29) and quartz phenocrysts are also present. The groundmass of the ignimbrites consists of sanidine and Si0₂ polymorphs. The ignimbrites are classified as alkali rhyolites because of the predominance of sanidine and Si0₂. The welded vitric tuffs are classified chemically as: 1) high silica rhyolites - Si0₂ [greater-than] 72%, and 2) subaluminous/peralkaline rhyolites - A1₂0₃/Na₂0+K₂0 + Ca0[less-than-or-equal-to]1. In the Sacramento-Majalea area, the late Eocene high silica alkali rhyolitic ignimbrites overlie the older calc-alkalic Peñas Azules volcanics and are overlain by Oligoc̈ne rhyolitic ignimbrites. The Peñas Azules volcanics were probably formed during the Laramide orogeny (late Cretaceous to early Eocene). The late Eocene high silica alkali rhyolites were erupted during Elston's (1976) active stage of extension (late Eocene to Miocene) of the western portion of the American plate. The active stage of extension was followed by the passive stage of extension during the Miocene to present (Elston, 1976). The Oligoc̈ne rhyolites of the main Sierra Madre Occidental may have been related to this period of relaxation following compression. The high silica alkali rhyolites near Sacramento are located between the calc-alkalic igneous center of western Mexico and the alkalic igneous center of western Texas. These rocks can be considered intermediate in composition between calc-alkaline and alkaline.
General note	"A thesis presented to the faculty of the Department of Geology ... in partial fulfillment of the requirements for the Degree Master of Science in Geology."
General note	Advisor: Richard L. Mauger
Dissertation note	M.S. East Carolina University 1977
Bibliography note	Includes bibliographical references (leaves 80-82).

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