- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
NARROW
Rare earth element concentrations for 52 granitoid stocks, plutons, laccoliths, and volcanic rocks, together with neodymium isotopic data for 30 of these units, indicate a dominantly crustal origin for Late Cretaceous-Tertiary magmatism in the Colorado Mineral Belt (COMB). This comprehensive data set is summarized in the table below where igneous rocks of the COMB have been grouped according to age, composition, and their REE and 143 Nd/ 144 Nd (epsilon Nd) characteristics. Rare earth element abundances in COMB granitoids are significantly higher than bulk continental crust abundances. The sources for COMB granitoids might have become enriched in rare earth elements (REE), particularly light REE, (1) early in their history, possibly by metamorphic events associated with the formation of Proterozoic batholiths, and/or (2) at a later time, possibly by degassing of metasomatized mantle or devolatilization of oceanic slab at the base of the continental crust during Laramide subduction and/or Tertiary extension. The latter requires a component of Archean detritus in Colorado Proterozoic units to accommodate distinctly negative epsilon Nd values in Laramide-Tertiary intrusions. A mixing model involving both felsic and mafic Proterozoic lower crust (± mantle) can explain COMB Late Cretaceous-Tertiary magma compositions. Older, Laramide age (Late Cretaceous-early Tertiary) alkaline monzonites probably were predominantly derived from highly metasomatized mafic crust (amphibolite to granulite) with a possible mantle component, whereas younger (Oligocene-Miocene) quartz monzonites, granodiorites, and highly evolved topaz rhyolites and Climax-type granites were probably predominantly derived from intermediate to felsic crust that underwent episode(s) of dehydration-dominated, melt-absent metamorphism (granulite). Alkali- and CO 2 -rich fluids were probably instrumental in mobilizing and concentrating REE in the lower and middle crust. The REE patterns for Laramide-Tertiary alkaline and calc-alkalic intrusions may in part reflect the history of their source rocks. The distinct U-shaped REE patterns for evolved granites and rhyolites, however, are largely the product of upper crustal mineral-melt and melt-vapor fractionation processes. Age Rock Suite Sm-Nd Model Age † Epsilon Nd (La/Yb) N Eu Anomaly (Eu/Eu*) N REE Pattern Late Cretaceous-early Tertiary (Laramide) 45 to 75 Ma MonzoniteSuite 662 to 1318 Ma (DM) 145 to 875 Ma (CHUR) −1.0 to−9.3 10 to 53 Avg = 24 La N = 117 to 382 Yb N = 2 to 15 very small to absent 0.65 to 0.95 Avg = 0.87 linear, with steep slopes Middle Tertiary 29 to 45 Ma Granodiorite-Quartz Monzonite Suite 1042 to 1377 Ma (DM) 581 to 957 Ma (CHUR) −6.7 to−10.6 11 to 24 Avg = 16 La N = 103 to 215 Yb N = 6 to 13 very small o t absent 0.73 to 0.95 Avg = 0.86 linear, with moderately steep slopes Oligocene-Miocene 10 to 29 Ma Granite Suite 1099 to 1542 Ma (DM) 715 to 1093 Ma (CHUR) −8.0 to −14.0 2 to 65 Avg = 13 La N = 46 to 207 Yb N = 3 t o 22 extremely large 0.07 to 0.65 Avg = 0.35 U-shaped † First range is calculated source age assuming depleted mantle (DM); second assumes chnodritic uniform reservoir (CHUR).