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Research Article| June 01, 2017 U-Pb ages and geochemistry of zircon from Proterozoic plutons of the Sawatch and Mosquito ranges, Colorado, U.S.A.: Implications for crustal growth of the central Colorado province Richard J. Moscati; Richard J. Moscati * 1U.S. Geological Survey, MS 963, Denver Federal Center, Box 25046, Denver, Colorado 80225, U.S.A. *Correspondence should be addressed to: rmoscati@usgs.gov Search for other works by this author on: GSW Google Scholar Wayne R. Premo; Wayne R. Premo 1U.S. Geological Survey, MS 963, Denver Federal Center, Box 25046, Denver, Colorado 80225, U.S.A. Search for other works by this author on: GSW Google Scholar Ed H. DeWitt; Ed H. DeWitt 1U.S. Geological Survey, MS 963, Denver Federal Center, Box 25046, Denver, Colorado 80225, U.S.A.#deceased Search for other works by this author on: GSW Google Scholar Joseph L. Wooden Joseph L. Wooden 2U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, U.S.A.†retired Search for other works by this author on: GSW Google Scholar Author and Article Information Richard J. Moscati * 1U.S. Geological Survey, MS 963, Denver Federal Center, Box 25046, Denver, Colorado 80225, U.S.A. Wayne R. Premo 1U.S. Geological Survey, MS 963, Denver Federal Center, Box 25046, Denver, Colorado 80225, U.S.A. Ed H. DeWitt 1U.S. Geological Survey, MS 963, Denver Federal Center, Box 25046, Denver, Colorado 80225, U.S.A.#deceased Joseph L. Wooden 2U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, U.S.A.†retired *Correspondence should be addressed to: rmoscati@usgs.gov Publisher: University of Wyoming Received: 11 Nov 2016 Accepted: 12 Jun 2017 First Online: 28 Jul 2017 Online Issn: 1555-7340 Print Issn: 1555-7332 © 2017 University of WyomingUniversity of Wyoming Rocky Mountain Geology (2017) 52 (1): 17–106. https://doi.org/10.24872/rmgjournal.52.1.17 Article history Received: 11 Nov 2016 Accepted: 12 Jun 2017 First Online: 28 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Richard J. Moscati, Wayne R. Premo, Ed H. DeWitt, Joseph L. Wooden; U-Pb ages and geochemistry of zircon from Proterozoic plutons of the Sawatch and Mosquito ranges, Colorado, U.S.A.: Implications for crustal growth of the central Colorado province. Rocky Mountain Geology 2017;; 52 (1): 17–106. doi: https://doi.org/10.24872/rmgjournal.52.1.17 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyRocky Mountain Geology Search Advanced Search ABSTRACT A broad study of zircons from plutonic rocks of the Sawatch and Mosquito ranges of west-central Colorado (U.S.A.) was undertaken to significantly refine the magmatic chronology and chemistry of this under-studied region of the Colorado province. This region was chosen because it lies just to the north of the suspected arc-related Gunnison-Salida volcano-plutonic terrane, which has been the subject of many recent investigations—and whose origin is still debated. Our new results provide important insights into the processes active during Proterozoic crustal evolution in this region, and they have important ramifications for broader-scope crustal evolution models for southwestern North America.Twenty-four new U-Pb ages and sequentially acquired rare-earth element (REE), U, Th, and Hf contents of zircon have been determined using the sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG). These zircon geochemistry data, in conjunction with whole-rock major- and trace-element data, provide important insights into zircon crystallization and melt fractionation, and they help to further constrain the tectonic environment of magma generation.Our detailed zircon and whole-rock data support the following three interpretations: (1) The Roosevelt Granite in the southern Sawatch Range was the oldest rock dated at 1,766 ± 7 Ma, and it intruded various metavolcanic and metasedimentary rocks. Geochemistry of both whole-rock and zircon supports the contention that this granite was produced in a magmatic arc environment and, therefore, is likely an extension of the older Dubois Greenstone Belt of the Gunnison Igneous Complex (GIC) and the Needle Mountains (1,770–1,755 Ma). Rocks of the younger Cochetopa succession of the GIC, the Salida Greenstone Belt, and the Sangre de Cristo Mountains (1,740–1,725 Ma) were not found in the Sawatch and Mosquito ranges. This observation strongly suggests that the northern edge of the Gunnison-Salida arc terrane underlies the southern portion of the Sawatch and Mosquito ranges.(2) Calc-alkalic to alkali-calcic magmas intruded this region approximately 55 m.y. after the Roosevelt Granite with emplacement of pre-deformational plutons at ca. 1,710 Ma (e.g., Henry Mountain Granite and diorite of Denny Creek), and this continued for at least 30 m.y., ending with emplacement of post-deformational plutons at ca. 1,680 Ma (e.g., Kroenke Granodiorite, granite of Fairview Peak, and syenite of Mount Yale). The timing of deformation can be constrained to sometime after intrusion of the diorite of Denny Creek and likely before the emplacement of the undeformed granite of Fairview Peak. Geochemistry of both whole-rock and zircon indicates that the older group of ca. 1,710-Ma plutons formed at shallower depths, and then they intruded the younger group of more deeply generated, commonly peraluminous and sodic plutons. Although absent in the Sawatch and Mosquito ranges, Mazatzal-age (ca. 1,680–1,620 Ma) plutonic rocks are present regionally. Inherited zircon components of Mazatzal-age were found as cores in some 1.4-Ga Sawatch and Mosquito Range zircons, indicating the likelihood of a relatively local source. These combined data suggest the possibility that all were produced within a continental-margin magmatic arc created as a result of southward-migrating (slab rollback?), north-dipping subduction to the south of the region.(3) Widespread Mesoproterozoic plutonism—with emplacement at various depths and exhibiting bimodal geochemistry—is recognized in 16 different samples. An older group of predominantly peraluminous, yet magnesian granitoids (e.g., granodiorite of Sayers, granite of Taylor River, and the St. Kevin Granite) were emplaced between ca. 1,450 and 1,425 Ma. These geochemical parameters suggest moderate degrees of partial melting in a low-pressure environment. Three younger metaluminous, but ferroan plutons (diorite of Grottos, diorite of Mount Elbert, and granodiorite of Mount Harvard), probably represent a final magmatic pulse at ca. 1,416 Ma.A comprehensive treatment of zircon REE and whole-rock trace-element behavior from Proterozoic rocks is scarce. Discriminant U/Yb versus Y diagrams using zircon data show that the Sawatch and Mosquito plutons are of continental origin, not oceanic. Additional bivariate diagrams incorporating cation ratio combinations of Gd, Ce, Yb, U, Th, Hf, and Eu offer refined insight into differences in fractionation trends and depth of magma generation for the various plutons. These interpretations, on the basis of zircon trace-element data, are mirrored in the whole-rock geochemistry data. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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