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Correlation of Jurassic eolian strata between the magmatic arc and the Colorado Plateau: New U-Pb geochronologic data from southern Arizona

1993; Geological Society of America; Volume: 105; Issue: 9 Linguagem: Inglês

10.1130/0016-7606(1993)105 2.3.co;2

1943-2674

Nancy R. Riggs, James M. Mattinson, Cathy J. Busby,

Geochemistry and Geologic Mapping

Research Article| September 01, 1993 Correlation of Jurassic eolian strata between the magmatic arc and the Colorado Plateau: New U-Pb geochronologic data from southern Arizona NANCY R. RIGGS; NANCY R. RIGGS 1Department of Geology, Box 4099, Northern Arizona University, Flagstaff, Arizona 86011 Search for other works by this author on: GSW Google Scholar JAMES M. MATTINSON; JAMES M. MATTINSON 2Department of Geological Sciences, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar CATHY J. BUSBY CATHY J. BUSBY 2Department of Geological Sciences, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar Author and Article Information NANCY R. RIGGS 1Department of Geology, Box 4099, Northern Arizona University, Flagstaff, Arizona 86011 JAMES M. MATTINSON 2Department of Geological Sciences, University of California, Santa Barbara, California 93106 CATHY J. BUSBY 2Department of Geological Sciences, University of California, Santa Barbara, California 93106 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1993) 105 (9): 1231–1246. https://doi.org/10.1130/0016-7606(1993)105 2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation NANCY R. RIGGS, JAMES M. MATTINSON, CATHY J. BUSBY; Correlation of Jurassic eolian strata between the magmatic arc and the Colorado Plateau: New U-Pb geochronologic data from southern Arizona. GSA Bulletin 1993;; 105 (9): 1231–1246. doi: https://doi.org/10.1130/0016-7606(1993)105 2.3.CO;2 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 SocietyGSA Bulletin Search Advanced Search Abstract Mature quartz-rich sandstone interbedded with Mesozoic magmatic-arc strata in southern Arizona has been previously considered correlative with the eolian Pleinsbachian to Toarcian Navajo Sandstone on the Colorado Plateau. New U-Pb zircon data from the Mount Wrightson Formation in the Santa Rita Mountains and from the strata of Cobre Ridge in the Pajarito Mountains and in the Arivaca area in southern Arizona support the hypothesis that sand derived from the Navajo Sandstone probably did gain access to the magmatic arc and further indicate that sands extending from younger eolian units on the Colorado Plateau are probably present as well.The Mount Wrightson Formation accumulated from ∼190 Ma to 170 Ma, corresponding to late Pleinsbachian to Aalenian time (time scale of Harland, 1990). Isotopic ratios from zircon fractions from the lower member of the Mount Wrightson Formation define a discordia line with lower intercept of 184 ± 8 Ma. The lower member is approximately coeval with the 188 ± 2 Ma Piper Gulch monzonite, dated by Asmerom and others (1990), which intrudes it. The middle and upper members of the formation yield somewhat less precise dates that indicate deposition between 183 ± 2 Ma and ≈170 Ma. Quartz-rich sandstone occurs in all three members, though most abundantly in the middle and upper members, and in many places contains sedimentary structures diagnostic of eolian sedimentation. Our results suggest that sands related to Lower Jurassic Navajo ergs and Middle Jurassic Temple Capergs gained access to the arc.The age of the strata of Cobre Ridge is ∼170 ± 5 Ma. Eighteen fractions taken from three samples of the tuff lie in a cluster near concordia. A best-fit age of 169 Ma is based on near concordance of one fraction and on model discordia trajectories using assumed upper intercepts. Sandstone horizons interbedded within the strata of Cobre Ridge in many cases contain sedimentary structures diagnostic of eolian sedimentation and, although quartz rich, in general have more volcanic detritus than sandstones in the Mount Wrightson Formation. The interval between 165-175 Ma corresponds to the Aalenian and Bajocian stages and is within the time span represented by the Temple Cap and Page sandstones of southern Utah and northern Arizona. Sandstone interstratified with the strata of Cobre Ridge may be correlative with either of those units. The possibility cannot be discounted, however, that unconsolidated or weathered Navajo-equivalent sands from the upper member of the Mount Wrightson Formation were recycled into the strata of Cobre Ridge.These results support the models (Busby-Spera, 1988; Riggs and Busby-Spera, 1990, 1991), suggesting that during Early to Middle Jurassic time the magmatic arc in southern Arizona was low standing and did not constitute an impediment to the south and southwestward movement of continental sediments. We suggest that much of the region between the Colorado Plateau and the arc was topographically low, and that tectonic and volcanic basins within the arc provided traps for windblown mature sands for as long as 35 m.y. We speculate that Early to Middle Jurassic tectonic subsidence within the magmatic arc may have been more continuous than subsidence on the Colorado Plateau, thus providing a depocenter in which major tectonically induced unconformities that characterize the Mesozoic record in the back arc are masked by ongoing volcanic activity. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.