New Mexico Bureau of Mines & Mineral Resources A DIVISION OF NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY Late Mesozoic to Cenozoic cooling histories of the flanks of the northern and central Rio Grande rift, Colorado and New Mexico Shari A. Kelley1, Charles E. Chapin2, and Jeff Corrigan3 1Department of Geological Sciences, Southern Methodist University, Dallas, Texas 75275; 2New Mexico Bureau of Mines & Mineral Resources, Socorro, New Mexico 87801; 3ARCO Oil and Gas Company, Plano, Texas 75075 SOCORRO 1992 11 NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY Laurence H. Lattman, President NEW MEXICO BUREAU OF MINES & MINERAL RESOURCES Charles E. Chapin, Director and State Geologist BOARD OF REGENTS Ex Officio Bruce King, Governor of New Mexico Alan Morgan, Superintendent of Public Instruction Appointed Lt. Gen. Leo Marquez, President, 1989-1995, Albuquerque Charles Zimmerly, Secretary/Treasurer, 1991-1997, Socorro Diane D. Denish, 1992-1997, Albuquerque J. Michael Kelly, 1992-1997, Roswell Steve Torres, 1991-1997, Albuquerque BUREAU STAFF ORIN J. ANDERSON, Senior Geologist DEBBIE GOERING, Staff Secretary VIRGINIA McLesion, Economic Geologist RUBEN ARCHULETA, Metallurgical Lab. Tech. Lois GOLLMER, Geotechnical Records Clerk NORMA J. MEEKS, Director of Publications Office Augustus K. ARMSTRONG, USGS Geologist IBRAHIM GUNDILER, Senior Metallurgist BARBARA R. Popp, Chemical lab. Tech. II GEORGE S. AusTIN, Senior Industrial Minerals Geologist STEVE HAASE, Ground-Water Geologist MARSHALL A. REITER, Senior Geophysicist AL BACA, Maintenance Carpenter II WILLIAM C. HANEBERG, Engineering Geologist JACQUES R. RENAULT, Senior Geologist JAMES M. BARKER, Senior Industrial Minerals Geologist JOHN W. HAWLEY, Senior Env. Geologist JAMES M. ROBERTSON, Senior Economic Geologist PAUL W. BAUER, Field Economic Geologist LYNNE HEMENWAY, Computer Pub./Graphics Spec. JANETTE THOMAS, Cartographic Drafter II ROBERT A. BIEBERMAN, Emeritus Sr. Petroleum Geologist CAROL A. HJELLMING, Assistant Editor SAMUEL THOMPSON III, Emeritus Senior Petrol. Geologist LYNN A. BRANDVOLD, Senior Chemist GRETCHEN K. HOFFMAN, Senior Coal Geologist REBECCA J. Titus, Cartographic Supervisor RON BROADHEAD, Senior Petroleum Geologist GLEN JONES, Computer Scientist/Geologist JUDY M. VAIZA, Executive Secretary Head, Petroleum Section FRANK E. Kottlowski, Emeritus Director/State Geologist MANUEL J. VASQUEZ, Mechanic I KATHRYN G. CAMPBELL, Cartographic Drafter II PHILLIP KYLE, Geochemist/Petrologist JEANNE M. VERPLOEGH, Chemical lab. Tech. II STEVEN M. CATHER, Field Economic Geologist ANN LANNING, Administrative Secretary ROBERT H. WEBER, Emeritus Senior Geologist RICHARD CHAMBERLIN, Field Economic Geologist ANNABELLE LOPEZ, Petroleum Records Clerk SUSAN J. WELCH, Assistant Editor RICHARD R. CHAVEZ, Assistant Head, Petroleum Section THERESA L. LOPEZ, Receptionist/Staff Secretary NEIL H. WHITEHEAD Ill, Petroleum Geologist RUBEN A. CRESPIN, Garage Supervisor DAVID W. LOVE, Senior Environmental Geologist DONALD WOLBERG, Paleontologist Lois M. DEVLIN, Business Services Coordinator JANE A. CALVERT LOVE, Editor MICHAEL W. WOOLDRIDGE, Scientific Illustrator NEliA DUNBAR, Analytical Geochemist WILLIAM McIntosh, Volcanologist/Geochronologist JIw ZIDEK, Chief Editor/Senior Geologist ROBERT W. Eveleth, Senior Mining Engineer CHRISTOPHER G. McKEE, X-ray Facility Manager Research Associates CHRISTINA L. BALK, NMT ALONZO D. JACKA, Texas Tech HOWARD B. NICKELSON, Carlsbad WILLIAM L. CHENOWETH, Grand Junction, CO BOB JULYAN, Albuquerque GLENN R. OSBURN, Washington Univ. RUSSELL E. CLEMONS, NMSU SHARI A. KELLEY, SMU ALLAN R. SANFORD, NMT WILLIAM A. COBBAN, USGS WILLIAM E. KING, NMSU JOHN H. SCHILliNG, Reno, NV CHARLES A. FERGUSON, Univ. Alberta MICHAEL J. KUNK, USGS WILLIAM R. SEAGER, NMSU JOHN W. GEISSMAN, UNM TIMOTHY F. LAWTON, NMSU EDWARD W. SMITH, Tesuque LELAND H. GEE, Las Cruces DAVID V. LEMONS, UTEP JOHN F. SurrER, USGS JEFFREY A. GRAMBLING, UNM GREG H. MACK, NMSU RICHARD H. TEDFORD, Amer. Mus. Nat. Hist. CAROL A. HILL, Albuquerque NANCY J. MCMILLAN, NMSU TOMMY B. THOMPSON, CSU Graduate Students WILLIAM C. BECK STEPHEN CROSS JOHN GILLENTINE JENNIFER R. BORYFA ROBERT L. FRIESEN DAVID J. SIVILS TANYA BAKER SHIRLEY WADE Plus about 30 undergraduate assistants Original Printing Published by Authority of State of New Mexico, NMSA 1953 Sec. 63-1-4 Printed by University of New Mexico Printing Services, December 1992 Available from New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801 Published as public domain, therefore reproducible without permission. Source credit requested. 111 Contents ABSTRACT 5 NORTHERN NEW MEXICO 17 INTRODUCTION 5 Sierra Nacimiento 17 INTERPRETATION OF FISSION-TRACK (FT) DATA Santa Fe Range 19 DENUDATION RATES FROM APPARENT FISSION-TRACK Sandia Mountains 20 AGES 5 CENTRAL NEW MEXICO 21 PROCEDURES 6 Manzano-Los Pinos Mountains 21 CALCULATION OF FISSION-TRACK AGES AND Joyita Hills 24 ERROR STATISTICS 6 Sierra Ladrones 24 FISSION-TRACK LENGTH MEASUREMENTS 7 Lemitar Mountains 25 MICROPROBE ANALYSES 7 Magdalena Mountains 25 TIME-TEMPERATURE ESTIMATES Gonzalez Prospect and San Lorenzo Canyon 7 Summary of FT results from the central rift RESULTS 8 DISCUSSION 29 SAWATCH RANGE 8 TECTONIC HISTORY BASED ON FT ANALYSIS 29 SANGRE DE CRISTO MOUNTAINS 11 MODELS FOR UPLIFT OF RIFT FLANKS Mosca Pass 12 30 Blanca Peak 12 ACKNOWLEDGMENTS 31 La Veta Pass 14 REFERENCES 31 Trinchera Peak 14 APPENDIX 34 Culebra Peak 17 Summary 17 Figures 1—Regional location map 6 10—Age versus elevation plots for Sierra Nacimiento and 2—Track length versus temperature, south Texas with FT Santa Fe Range 18 annealing model curves 7 11—Length distributions and thermal histories, Sierra Na- 3—Sample location map for Mt. Princeton batholith, Sa- cimiento and Santa Fe Range 19 watch Range, Colorado 10 12—Sample location map for east side of the Albuquerque 4—Age versus elevation plot from Mt. Princeton batholith Basin 22 10 13—Length distributions and thermal histories, Sandia 5—Length distributions and thermal histories, Mt. Prince- Mountains 22 ton batholith 11 14—Age versus elevation plots for central Rio Grande 6—Sample location map for Sangre de Cristo Mountains, rift 23 Colorado 13 15—Length distributions and thermal histories, Manzano 7—Age versus elevation plots for Sangre de Cristo Moun- Mountains and Sierra Ladrones 24 tains 14 16—Sample location map for the south end of the Albu- 8—Length distributions and thermal histories, Sangre de querque Basin 25 Cristo Mountains 15 17—Summary map of FT results 30 9—Sample location map for Sierra Nacimiento and Santa 18—FT age histogram 30 Fe Range 17 Tables 1—Estimated cooling rates 8 5—Apatite fission-track ages and lengths, Sierra Naci- 2—Chlorine concentrations, Rio Grande rift apatite 9 miento, New Mexico 20 3—Apatite fission-track ages and lengths, Sawatch Range, 6—Apatite fission-track ages and lengths, Kelley and Dun- Colorado 12 can (1986) 21 4—Apatite fission-track ages and lengths, Sangre de Cristo 7—Apatite fission-track ages and lengths, central Rio Grande Mountains, Colorado 16 rift 26 5 Abstract Apatite fission-track (FT) data collected in the northern and central Rio Grande rift of New Mexico and Colorado indicate that rocks now exposed in the eastern and western margins of the rift cooled during uplift and erosion in a complex spatial and temporal pattern. FT data from the Santa Fe Range, Los Pinos Mountains, and northern Nacimiento Mountains indicate that these mountain blocks cooled during the early stage of the Laramide orogenic event. Other mountain blocks (south- ern Nacimiento and Manzano Mountains, high elevation portions of the Sangre de Cristo Mountains and Magdalena Mountains) began cooling during the late stage of the Laramide event and subse- quent Eocene erosion. The Sandia Mountains, Blanca Peak, Joyita Hills, Sierra Ladrones, the high- elevation portion of the Sawatch Range, and the lower-elevation samples in the Sangre de Cristo Mountains began cooling during early extension of the Rio Grande rift and/or waning of regional volcanism in the late Oligocene and early Miocene. The eastern front of the Sawatch Range, the Sangre de Cristo Mountains north of Blanca Peak, the low-elevation portion of the Sangre de Cristo Mountains near San Luis, Colorado, and the Lemitar Mountains cooled during late-stage rifting in middle to late Miocene. Generally, the youngest FT ages are found in the rift flanks adjacent to large normal faults along the deep margins of the en-echelon half-grabens that make up the present Rio Grande rift. Two of the blocks with Miocene FT ages, the Sierra Ladrones and Blanca Peak, are promontories that project into rift basins at the junction of arcuate normal faults bounding the deep side of half-grabens. Tectonic denudation of three sides has allowed unusually rapid isostatic uplift in these blocks. Similarly, the Sangre de Cristo Mountains north of Blanca Peak are bounded on two sides by active late Cenozoic faults that have allowed the rapid isostatic rise of these mountains. Cooling rates increased from the Laramide orogenic event (1 to 4°C/Ma) to the development of the Rio Grande rift (7 to 20°C/Ma). Introduction from all the mountain ranges into a discussion of the tec- The Southern Rocky Mountains in Colorado and New tonic development of this region during Laramide com- Mexico have had a long and complex geologic history, cul- pression, mid-Tertiary magmatism, and Rio Grande rift minating in the Late Cretaceous (Campanian and Maas- extension; (4) to use the FT results to qualitatively assess trichtian)