Petrology and Physiographic Evolution of the Oeate Volcanic Field, North-Central New Mexico A

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Petrology and Physiographic Evolution of the Oeate Volcanic Field, North-Central New Mexico A Petrology and Physiographic Evolution of the Oeate Volcanic Field, North-Central New Mexico A. The Ocate Volcanic Field Description of Vdlcanic Vents and the Geochrondlogy, Petrography, and Whole-Rock Chemistry of Associated Flows B. Late Cenozoic Physiographic Evolution of the Ocate Volcanic Field U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1478 Petrology and Physiographic Evolution of the Ocate Volcanic Field, North-Central New Mexico A. The Ocate Volcanic Field Description of Volcanic Vents and the Geochronology, Petrography, and Whole-Rock Chemistry of Associated Flows By J. MICHAEL O'NEILL and HARALD H. MEHNERT B. Late Cenozoic Physiographic Evolution of the Ocate Volcanic Field By J. MICHAEL O'NEILL U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 147 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988 DEPARTMENT OF THE INTERIOR DONALD PAUL MODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging-in-Publication Data Petrology and physiographic evolution of the Ocate volcanic field, north-central New Mexico. (U.S. Geological Survey professional paper ; 1478-A.B) Bibliography: p. Supt. of Docs, no.: I 19.16:1778A,B Contents: Pt. A. The Ocate volcanic field description of volcanic vents and the geochronology, petrography, and whole-rock chemistry of associated flows / by J. Michael O'Neill and Harald H. Mehnert Pt. B. Late Cenozoic physiographic evolution of the Ocate volcanic field / by J. Michael O'Neill. 1. Volcanic ash, tuff, etc. Sangre de Cristo Mountains (Colo. and N.M.) 2. Volcanic ash, tuff, etc. New Mexico. 3. Geology, Stratigraphic Cenozoic. I. O'Neill, J. Michael. Ocate volcanic field description of volcanic vents and the geochronology, petrography, and whole-rock chemistry of associated flows. 1988. II. Mehnert, Harald H. Late Cenozoic physiographic evolution of the Ocate volcanic field. 1988. III. Geological Survey professional paper; 1478-A.B. IV. Title: Ocate volcanic field, north-central New Mexico. QE461.P474 1988 552'.2'09789 87-600260 For sale by the Books and Open-File Reports Section, U.S. Geological Survey Federal Center, Box 25425, Denver, CO 80225 Any use of trade, product, industry, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Sangre de Cristo Mountains 6 s a 0 r t e 9 FRONTISPIECE Ocate volcanic field. View to southwest. CONTENTS [Letters designate chapters] (A) The Ocate volcanic field Description of volcanic vents and the geochronology, petrography, and whole-rock chemistry of associated flows (B) Late Cenozoic physiographic evolution of the Ocate volcanic field The Ocate Volcanic Field Description of Volcanic Vents and the Geochronology, Petrography, and Whole-Rock Chemistry of Associated Flows By J. MICHAEL O'NEILL and HARALD H. MEHNERT PETROLOGY AND PHYSIOGRAPHIC EVOLUTION OF THE OCATE VOLCANIC FIELD, NORTH-CENTRAL NEW MEXICO U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1478-A Description of composition and age of rocks in the Ocate volcanic field, with suggestions as to their possible relationship to the Rio Grande depression CONTENTS Page Abstract ................................................................... Al Introduction ................................................................ 1 Previous work .............................................................. 1 Geochronology .............................................................. 3 Description of volcanic rocks and related features ................................ 3 Volcanic rocks older than 5 million years .................................... 3 Volcanic rocks erupted between 4 and 5 million years ago ...................... 6 Volcanic rocks younger than 4.0 million years old ............................. 13 Petrographic summary and whole-rock chemistry ................................. 20 Petrogenesis ............................................................ 25 Basaltic volcanism in and adjacent to the Rio Grande depression ............... 26 References cited ............................................................. 29 ILLUSTRATIONS Page PLATE 1. Generalized geologic map of the Ocate volcanic field, north-central New Mexico In pocket FIGURE Al. Generalized geologic map ......................................................................... A2 2-15. Photographs: 2. Sierra Montuosa and Ocate Mesas ........................................................... 4 3. Las Mesas del Conjelon .................................................................... 6 4. Olivine crystals ........................................................................... 9 5. Moreno-Guadalupita-Mora valley system ..................................................... 9 6. Augite crystals ........................................................................... 10 7. Quartz xenocryst ......................................................................... 11 8. Plagioclase phenocryst ..................................................................... 11 9. Flows of El Cerro Colorado ................................................................. 12 10. Charette Mesa and Charette Lakes .......................................................... 14 11. Older vents on Charette Mesa .............................................................. 16 12. Cerro Negro cauldron ...................................................................... 18 13. Vent east of Cerro Montoso ................................................................ 19 14. Basalt-capped terrace ...................................................................... 20 15. Cerro del Oro cinder cone .................................................................. 21 16. Normative plots of volcanic rocks .................................................................. 25 17. Plot of alumina-normative plagioclase ............................................................... 25 18. Plot of normative color index-normative plagioclase ................................................... 25 19. Plot of total alkali-silica .......................................................................... 25 20. AMF plot of volcanic rocks ....................................................................... 26 21. Plot of titania-solidification index .................................................................. 26 22. Comparison of titania-solidification index ............................................................ 27 23. Alkali-silica variation diagrams .................................................................... 28 IX CONTENTS TABLES Page TABLE Al. Late Cenozoic K-Ar ages of volcanic rocks ............................................................... A4 2. Chemical analyses and CIPW normative calculations for volcanic rocks older than 5 m.y. ....................... 22 3. Chemical analyses and CIPW normative calculations for volcanic rocks 5.0 to 4.0 m.y. old ...................... 23 4. Chemical analyses and CIPW normative calculations for volcanic rocks younger than 4 m.y. .................... 24 5. Average chemical composition of tholeiitic basalts ........................................................ 26 PETROLOGY AND PHYSIOGRAPHIC EVOLUTION OF THE OCATE VOLCANIC FIELD, NORTH-CENTRAL NEW MEXICO THE OCATE VOLCANIC FIELD DESCRIPTION OF VOLCANIC VENTS AND THE GEOCHRONOLOGY, PETROGRAPHY, AND WHOLE-ROCK CHEMISTRY OF ASSOCIATED FLOWS By J. MICHAEL O'NEILL and HARALD H. MEHNERT ABSTRACT surrounds the town of Ocate, partly within the Sangre de Cristo Mountains. Other major eruptions to the east The Ocate volcanic field is a series of flows erupted during the last of the depression are near Raton on the high plains of 8 million years. The physiographic expression of these flows reflects their ages: the oldest flows cap the highest mesas; younger flows cap northeastern New Mexico. successively lower mesas. The volcanic rocks form two groups: typical Volcanic rocks in the vicinity of Ocate (fig. Al) have flood basalts expelled from low-profile shield volcanos and fissures not previously been studied in detail. These rocks were that are classified as subalkalic, hypersthene-normative basalts rich first mentioned by Stevenson (1881), who described the in alkalies, ferric iron, and alumina; and basic rocks erupted from both physiography of the area and gave the name Ocate shield volcanos and composite cones that include alkali-rich basalt, andesite, minor dacite, and rare nepheline-normative basalt. The com­ Mesa to the lava-capped surface that extends south­ posite cones are composed of basalt, basaltic ejectamenta, and tuff ward from the Cimarron Range. This plateau almost interlayered with more viscous and silicic volcanic rocks. Flows from completely surrounds Ocate Valley and the village of composite cones are generally less extensive than the older and Ocate. Stevenson also recognized that the basalt-capped younger basalt flows. Similarities between the major-element com­ mesas in the southern part of the volcanic field were position of the Ocate volcanic rocks and basaltic rocks from the Rio Grande depression to the west suggest that these rocks may have a once continuous with Ocate Mesa. In keeping with similar origin. The composition of basalts from both localities may Stevenson's early descriptions of the region, with his be controlled in part by the intersection of two major tectonic features: naming of Ocate Mesa, and with the location of Ocate the northeast-trending Jemez line and the north-trending Rio Grande more or less central to
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