Deep crustal anatexis, magma mixing, and the generation of epizonal plutons in the Southern Rocky Mountains, Colorado

  • Kristin H. Jacob
  • G. Lang Farmer
  • Robert Buchwaldt
  • Samuel A. Bowring
Original Paper


The Never Summer Mountains in north-central Colorado, USA, are cored by two Oligocene, epizonal granitic plutons originally emplaced in the shallow levels of a short-lived (~1 m.y.), small-volume continental magmatic system. The younger Mt. Cumulus stock (28.015 ± 0.012 Ma) is a syenogranite equivalent compositionally to topaz rhyolites. A comparison to the chemical and isotopic composition of crustal xenoliths entrained in nearby Devonian kimberlites demonstrates that the silicic melts parental to the stock were likely derived from anatexis of local Paleoproterozoic, garnet-absent, mafic lower continental crust. In contrast, the older Mt. Richthofen stock is compositionally heterogeneous and ranges from monzodiorite to monzogranite. Major and trace element abundances and Sr, Nd and Pb isotopic ratios in this stock vary regularly with increasing whole rock wt% SiO2. These data suggest that the Mt. Richthofen stock was constructed from mixed mafic and felsic magmas, the former corresponding to lithosphere-derived basaltic magmas similar isotopically to mafic enclaves entrained in the eastern portions of the stock and the latter corresponding to less differentiated versions of the silicic melts parental to the Mt. Cumulus stock. Zircon U–Pb geochronology further reveals that the Mt. Richthofen stock was incrementally emplaced over a time interval from at least 28.975 ± 0.020 to 28.742 ± 0.053 Ma. Magma mixing could have occurred either in situ in the upper crust during basaltic underplating and remelting of an antecedent, incrementally emplaced, silicic intrusive body, or at depth in the lower crust prior to periodic magma ascent and emplacement in the shallow crust. Overall, the two stocks demonstrate that magmatism associated with the Never Summer igneous complex was fundamentally bimodal in composition. Highly silicic anatectic melts of the mafic lower crust and basaltic, mantle-derived magmas were the primary melts in the magma system, with mixing of the two producing intermediate composition magmas such as those from which Mt. Richthofen stock was constructed.


Magma mixing Topaz rhyolite Mafic underplating Crustal anatexis 



Support for this study was provided by The Geological Society of America, the Colorado Scientific Society, Rocky Mountain Association of Geologists, and the University of Colorado Department of Geological Sciences. The manuscript was greatly improved in response to reviews by Eric Christiansen and Calvin Miller. We thank Timothy L. Grove for his handling of the paper as executive editor. Laboratory assistance from Emily Verplanck was extremely helpful. We thank Judy Visty at Rocky Mountain National Park for granting us access to the Grand Ditch Road which made the remote Never Summer Mountains readily accessible. Electron microprobe work was carried out with the help of Julian Allaz at the University of Colorado. U–Pb geochronology carried out at MIT was made possible by NSF EAR-0931839.

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  1. Acosta-Vigil A, Buick I, Hermann J et al (2010) Mechanisms of crustal anatexis: a geochemical study of partially melted metapelitic enclaves and Host Dacite, SE Spain. J Petrol 51:785–821. doi: 10.1093/petrology/egp095 CrossRefGoogle Scholar
  2. Anderson J, Smith D (1995) The effects of temperature and fO2 on the Al-in-hornblende barometer. Am Miner 80:549–559Google Scholar
  3. Annen C (2006) The genesis of intermediate and silicic magmas in deep crustal hot zones. J Petrol 47:505–539. doi: 10.1093/petrology/egi084 CrossRefGoogle Scholar
  4. Armstrong R, Ward P (1991) Evolving geographic patterns of cenozoic magmatism: the temporal and spatial association of magmatism and metamorphic core complexes. J Geophys Res 96:13201–13224Google Scholar
  5. Bachmann O, Miller CF, de Silva SL (2007) The volcanic–plutonic connection as a stage for understanding crustal magmatism. J Volcan Geotherm Res 167:1–23. doi: 10.1016/j.jvolgeores.2007.08.002 CrossRefGoogle Scholar
  6. Bailley TL (2010) A reevaluation of the origin of late Cretaceous and younger magmatism in the southern Rocky Mountain region using space-time-composition patterns in volcanic rocks and geochemical studies of mantle xenoliths. PhD Thesis: University of Colorado, Boulder, p 166Google Scholar
  7. Barnes C, Burton B, Burling T (2001) Petrology and geochemistry of the late Eocene Harrison Pass pluton, Ruby Mountains core complex, northeastern Nevada. J Petrol 42:901–929CrossRefGoogle Scholar
  8. Bédard JH (2006) A catalytic delamination-driven model for coupled genesis of Archaean crust and sub-continental lithospheric mantle. Geochim Cosmochim Acta 70:1188–1214. doi: 10.1016/j.gca.2005.11.008 CrossRefGoogle Scholar
  9. Blundy JD, Holland TJB (1990) Calcic amphibole equilibria and a new amphibole–plagioclase geothermometer. Contrib Miner Petrol 104:208–224CrossRefGoogle Scholar
  10. Bookstrom AA, Carten RB, Shannon JR, Smith RP (1988) Origins of bimodal leucogranite-lamprophyre suites, climax and Red Mountain Porphyry Molybdenum Systems, Colorado—petrologic and strontium isotopic evidence. Color Sch Mines Q 83:1–24Google Scholar
  11. Bradley S (1985) Granulite facies and related xenoloths from Colorado-Wyoming kimberlites. MSc Thesis: Colorado State University, pp 1–148Google Scholar
  12. Burgess SD, Bowring S, Shen Sz (2013) High-precision timeline for Earth’s most severe extinction. Proc Natl Acad Sci 111:3316–3321. doi: 10.1073/pnas.1317692111 CrossRefGoogle Scholar
  13. Chapin CE, Cather SM (1994) Tectonic setting of the axial basins of the northern and central Rio Grande rift. In: Keller GR, Cather SM (eds) Basins Rio Gd. Rift Struct. Stratigr. Tecton. Setting, vol 291. Geological Society of America, Boulder, pp 5–26Google Scholar
  14. Christiansen EH, McCurry M (2008) Contrasting origins of Cenozoic silicic volcanic rocks from the western Cordillera of the United States. Bull Volcan 70:251–267. doi: 10.1007/s00445-007-0138-1 CrossRefGoogle Scholar
  15. Christiansen EH, Burt DM, Sheridan MF, Wilson RT (1983) The petrogenesis of topaz rhyolites from the western United States. Contrib Miner Petrol 83:16–30. doi: 10.1007/BF00373075 CrossRefGoogle Scholar
  16. Christiansen E, Haapala I, Hart G (2007) Are Cenozoic topaz rhyolites the erupted equivalents of Proterozoic rapakivi granites? Examples from the western United States and Finland. Lithos 97:219–246. doi: 10.1016/j.lithos.2007.01.010 CrossRefGoogle Scholar
  17. Claiborne LL, Miller CF, Walker BA et al (2006) Tracking magmatic processes through Zr/Hf ratios in rocks and Hf and Ti zoning in zircons: an example from the Spirit Mountain batholith, Nevada. Miner Mag 70:517–543. doi: 10.1180/0026461067050348 CrossRefGoogle Scholar
  18. Cole JC, Larson E, Farmer L et al (2008) The search for Braddock's Caldera - Guidebook for Colorado Scientific Society fall 2008 field trip, Never Summer Mountains, Colorado: US Geological Survey Open-File Report 2008–1360, pp 1–30Google Scholar
  19. Cole JC, Braddock WA (2009) Geologic map of the Estes Park 30′ x 60′ quadrangle, north-central Colorado: US Geological Survey Scientific Investigations Map 3039, scale 1:100,000, p 56Google Scholar
  20. Coleman DS, Glazner AF, Miller JS et al (1995) Exposure of a Late Cretaceous layered mafic–felsic magma system in the central Sierra Nevada batholith, California. Contrib Miner Petrol 120:129–136. doi: 10.1007/BF00287110 CrossRefGoogle Scholar
  21. Condie K, Latysh N, Van Schmus W et al (1999) Geochemistry, Nd and Sr isotopes, and U-Pb Zircon ages of Granitoid and Metasedimentary Xenoliths from the Navajo Volcanic Field, Four Corners area, Southwestern United States. Chem Geol 156:95–133CrossRefGoogle Scholar
  22. Coney PJ, Reynolds S (1977) Cordilleran Benioff zones. Nature 270:403–406CrossRefGoogle Scholar
  23. DePaolo D (1981) Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Proterozoic. Nature 291:193–196CrossRefGoogle Scholar
  24. Ewart A, Griffin WL (1994) Application of proton-microprobe data to trace-element partitioning in Volcanic-rocks. Chem Geol 117:251–284CrossRefGoogle Scholar
  25. Farmer GL, Broxton DE, Warren RG, Pickthorn W (1991) Nd, Sr, and O isotopic variations in metaluminous ash-flow tuffs and related volcanic rocks at the Timber Mountain/Oasis Valley Caldera, Complex, SW Nevada: Implications for the origin and evolution of large-volume silicic magma bodies. Contrib Miner Petrol 109:53–68CrossRefGoogle Scholar
  26. Farmer GL, Bowring S, Williams M et al (2005) Constraining lower crustal evolution across an archean-proterozoic suture: physical, chemical and geochronological studies of lower Crustal Xenoliths in Southern Wyoming and Northern Colorado. In: Karlstrom KE, Keller RG (eds) The Rocky Mountain region: an evolving lithosphere, AGU Monograph, vol 154, pp 139–162Google Scholar
  27. Frost BR, Frost CD (2008) A geochemical classification for feldspathic igneous rocks. J Petrol 49:1955–1969. doi: 10.1093/petrology/egn054 CrossRefGoogle Scholar
  28. Frost BR, Barnes C, Collins WJ et al (2001) A geochemical classification for granitic rocks. J Petrol 42:2033–2048. doi: 10.1093/petrology/42.11.2033 CrossRefGoogle Scholar
  29. Gamble BM (1979) Petrography and petrology of the Mt. Cumulus stock, Never Summer Mountains, Colorado. MSc Thesis: University of Colorado at Boulder, p 75Google Scholar
  30. Geissman J, Snee L, Graaskamp G et al (1992) Deformation and age of the Red Mountain intrusive system (Urad–Henderson molybdenum deposits), Colorado: evidence from paleomagnetic and 40Ar/39Ar data. Geol Soc Am Bull 104:1031–1047. doi: 10.1130/0016-7606(1992)104<1031 CrossRefGoogle Scholar
  31. Gelman SE, Bachmann O, Deering CD et al (2014) Identifying crystal graveyards remaining after large silicic eruptions. Earth Planet Sci Lett 393:266–274CrossRefGoogle Scholar
  32. Glazner AF, Coleman DS, Bartley JM (2008) The tenuous connection between high-silica rhyolites and granodiorite plutons. Geology 36:183. doi: 10.1130/G24496A.1 CrossRefGoogle Scholar
  33. Gualda GAR, Ghiorso MS (2013) Low-pressure origin of high-silica rhyolites and granites. J Geol 121:537–545. doi: 10.1086/671395 CrossRefGoogle Scholar
  34. Harper BE, Miller CF, Koteas GC et al (2004) Granites, dynamic magma chamber processes and pluton construction: the Aztec Wash. Trans R Soc Edinb Earth Sci 95:277–295CrossRefGoogle Scholar
  35. Hermann J (2002) Allanite: thorium and light rare earth element carrier in subducted crust. Chem Geol 192:289–330CrossRefGoogle Scholar
  36. Hofmann AW (1997) Mantle geochemistry: the message from oceanic magmatism. Nature 385:219–229CrossRefGoogle Scholar
  37. Holden P, Halliday AN, Stephens WE, Henney PJ (1991) Chemical and isotopic evidence for major mass transfer between mafic enclaves and felsic magma. Chem Geol 92:135–152CrossRefGoogle Scholar
  38. Holland T, Blundy J (1994) Non-ideal interactions in calcic amphiboles and their bearing on amphibole–plagioclase thermometry. Contrib Miner Petrol 116:433–447. doi: 10.1007/BF00310910 CrossRefGoogle Scholar
  39. Holland T, Powell R (2001) Calculation of phase relations involving haplogranitic melts using an internally consistent thermodynamic dataset. J Petrol 42:673–683CrossRefGoogle Scholar
  40. Kelley S, Chapin C (2004) Denudation history and internal structure of the Front Range and Wet Mountains, Colorado, based on apatite-fission-track thermochronology. N M Bur Geol Miner Resour 160:41–77Google Scholar
  41. Kellogg KS (1999) Neogene basins of the northern Rio Grande rift: partitioning and asymmetry inherited from Laramide and older uplifts. Tectonophysics 305:141–152. doi: 10.1016/S0040-1951(99)00013-X CrossRefGoogle Scholar
  42. Knox K (2005) The Never Summer igneous complex. MSc Thesis: Universiry of Colorado, pp 1–58Google Scholar
  43. Lange RA (2002) Constraints on the preeruptive volatile concentrations in the Columbia River flood basalts. Geology 30:179–182CrossRefGoogle Scholar
  44. Leake B (1997) Nomenclature of amphiboles. Can Miner 61:295–321Google Scholar
  45. Lipman PW (2007) Incremental assembly and prolonged consolidation of Cordilleran magma chambers: evidence from the Southern Rocky Mountain volcanic field. Geosphere 3:42. doi: 10.1130/GES00061.1 CrossRefGoogle Scholar
  46. Ludington S, Plumlee G (2009) Climax-type porphyry molybdenum deposits. US Geol Surv Open File Rep 2009-1215:1–16Google Scholar
  47. McBirney A, Taylor H, Armstrong R (1987) Paricutin re-examined: a classic example of crustal assimilation in calc-alkaline magma. Contrib Miner Petrol 95:4–20CrossRefGoogle Scholar
  48. McDonough WF, Sun S (1995) The composition of the Earth. Chem Geol 120:223–253CrossRefGoogle Scholar
  49. Nash WP, Crecraft HR (1985) Partition-coefficients for trace-elements in silicic magmas. Geochim Cosmochim Acta 49:2309–2322CrossRefGoogle Scholar
  50. Nehring F, Foley SF, Hölttä P (2009) Trace element partitioning in the granulite facies. Contrib Miner Petrol 159:493–519. doi: 10.1007/s00410-009-0437-y CrossRefGoogle Scholar
  51. O’Neill JM (1976) The geologyof the Mt. Richthofen Quadrangle and adjacent Kawuneeche Valley, North-central Colorado. PhD Thesis: University of Colorado, p 178Google Scholar
  52. O’Neill JM (1981) Geologic map of the Mt. Richthofen Quadrangle and the western part of the Fall River Pass Quadrangle, Grand and Jackson Counties, ColoradoGoogle Scholar
  53. Prowatke S, Klemme S (2006) Trace element partitioning between apatite and silicate melts. Geochim Cosmochim Acta 70:4513–4527CrossRefGoogle Scholar
  54. Putirka KD (2008) Thermometers and barometers for Volcanic systems. Rev Miner Geochem 69:61–120. doi: 10.2138/rmg.2008.69.3 CrossRefGoogle Scholar
  55. Sisson TW, Bacon CR (1992) Garnet high-silica rhyolite trace-element partition-coefficients measured by ion microprobe. Geochim Cosmochim Acta 56:2133–2136CrossRefGoogle Scholar
  56. Sisson TW, Grove TL, Coleman DS (1996) Hornblende gabbro sill complex at Onion Valley, California, and a mixing origin for the Sierra Nevada batholith. Contrib Miner Petrol 126:81–108. doi: 10.1007/s004100050237 CrossRefGoogle Scholar
  57. Slaby E, Martin H (2008) Mafic and felsic magma interaction in granites: the Hercynian Karkonosze Pluton (Sudetes, Bohemian Massif). J Petrol 49:353–391. doi: 10.1093/petrology/egm085 CrossRefGoogle Scholar
  58. Snelson CM, Keller GR, Miller KC et al (2005) Regional crustal structure derived from the CD-ROM 99 seismic refraction/wide-angle reflection profile: the lower crust and upper mantle: Rocky Mountain region. An Evol Lithosph 154:271–291Google Scholar
  59. Stein HJ, Crock JG (1990) Late Cretaceous-Tertiary magmatism in the Colorado Mineral Belt; rare earth element and samarium–neodymium isotopic studies. In: Anderson JL (ed) Nat. Orig. Cordilleran Magmat, vol 174. Geol. Soc. Am., Boulder, p 19Google Scholar
  60. Stein HJ, Hannah JL (1985) Movement and origin of ore fluids in climax-type systems. Geology 13:469–474CrossRefGoogle Scholar
  61. Stepanov AS, Hermann J, Rubatto D, Rapp RP (2012) Experimental study of monazite/melt partitioning with implications for the REE, Th and U geochemistry of crustal rocks. Chem Geol 300:200–220CrossRefGoogle Scholar
  62. Stolper E, Walker D (1980) Melt density and the average composition of Basalt. Contrib Miner Petrol 74:7–12CrossRefGoogle Scholar
  63. Streckeisen A (1978) Classification and nomenclature of plutonic rocks. Recommendations of the IUGS subcommission on the systematics of igneous rocks. Geol Rundschau Int Zeitschrift für Geol Stuttgart 63:773–785CrossRefGoogle Scholar
  64. Thompson AB, Connolly JAD (1995) Melting of the continental-crust—some thermal and petrological constraints on anatexis in continental collision zones and other tectonic settings. J Geophys Res Earth 100:15565–15579CrossRefGoogle Scholar
  65. Van der Laan SR, Wyllie PJ (1993) Experimental interaction of granitic and basaltic magmas and implications for mafic enclaves. J Petrol 34:491–517CrossRefGoogle Scholar
  66. Wendlandt E, Depaolo D, Baldrige W (1993) Nd and Sr isotope chronostratigraphy of Colorado Plateau lithosphere: implications for magmatic and tectonic underplating of the continental crust. Earth Planet Sci Lett 116:23–43CrossRefGoogle Scholar
  67. Wenner JM, Coleman DS (2004) Magma mixing and cretaceous crustal growth: geology and geochemistry of granites in the Central Sierra Nevada Batholith, California magma mixing and cretaceous crustal growth: geology and geochemistry of granites in the Central Sierra Nevada Batholith. Int Geol Rev 46:880–903CrossRefGoogle Scholar
  68. Wiebe R, Blair K, Hawkins D, Sabine C (2002) Mafic injections, in situ hybridization, and crystal accumulation in the Pyramid Peak granite, California. Geol Soc Am Bull 114:909–920. doi: 10.1130/0016-7606(2002)114<0909 CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Kristin H. Jacob
    • 1
  • G. Lang Farmer
    • 1
  • Robert Buchwaldt
    • 2
  • Samuel A. Bowring
    • 2
  1. 1.Department of Geological Sciences, CIRESUniversity of ColoradoBoulderUSA
  2. 2.Department of Earth, Atmospheric, and Planetary SciencesMassachusetts Institute of TechnologyCambridgeUSA

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