New and existing geochemical and Sr-isotopic data are used to characterize the composition and time-space distribution of Laramide and younger calc-alkaline to alkaline igneous rocks in central Colorado. The study is focussed on the $\sim$36.7-31 Ma Thirtynine Mile volcanic field, a suite of shoshonitic rocks that forms the bulk of the Central Colorado alkaline province. Various petrochemical characteristics suggest generation of Thirtynine Mile mafic rocks involved melting of LIL- and HFSE-enriched lithospheric mantle, perhaps phlogopite-bearing lherzolite. Subsequent crystal fractionation appears capable of explaining diversification of the suite. The Thirtynine Mile suite is LIL- and HFSE-enriched relative to time-contemporaneous high-K calc-alkaline rocks of the San Juan volcanic field, but shares some geochemical similarities with Laramide shoshonitic rocks of the northeastern Colorado mineral belt. General petrochemistry and spatial distribution of calc-alkaline and shoshonitic volcanic rocks in the region may be consistent with a subduction origin, but no unambiguous evidence is available to confirm this. / Geochemical and Sr-isotopic evidence confirms tuff occurrences in the southern Denver basin are Wall Mountain Tuff ($\sim$36.7 Ma). Previous suggestions that the Wall Mountain Tuff is closely related to the Mount Princeton batholith are not supported by new data, and the origin of the tuff remains unknown. Combined petrologic, geochemical, and Sr-isotopic data confirm that the $\sim$33.7 Ma Badger Creek Tuff is closely related to intracauldron tuff and a resurgent(?) pluton at the Mount Aetna volcanic center. Tuff at Buffalo Peaks is probably not related to Badger Creek Tuff. Geochemical and Sr-isotopic data suggest that andesitic tuff, lahar debris, and andesite flows at Buffalo Peaks are closely related, but the source of the volcanic suite remains unknown. Tuff in the Howard paleovalley and in the southeastern Thirtynine Mile volcanic field is probably Fish Canyon Tuff derived from the San Juan volcanic field. Sparse late-Tertiary rocks within the study area include shoshonite, trachyte, latite, and siliceous rhyolite and granite. / Source: Dissertation Abstracts International, Volume: 55-08, Section: B, page: 3211. / Major Professors: Stephen A. Kish; Paul C. Ragland. / Thesis (Ph.D.)--The Florida State University, 1994.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_77220 |
| Contributors | Campbell, Steven Kent., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 648 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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