The laccolith-stock controversy: New results from the southern Henry Mountains, Utah

Abstract

Research Article| January 01, 1988 The laccolith-stock controversy: New results from the southern Henry Mountains, Utah MARIE D. JACKSON; MARIE D. JACKSON 1Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218 Search for other works by this author on: GSW Google Scholar DAVID D. POLLARD DAVID D. POLLARD 2Departments of Applied Earth Sciences and Geology, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Author and Article Information MARIE D. JACKSON 1Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218 DAVID D. POLLARD 2Departments of Applied Earth Sciences and Geology, Stanford University, Stanford, California 94305 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1988) 100 (1): 117–139. https://doi.org/10.1130/0016-7606(1988)100<0117:TLSCNR>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 MARIE D. JACKSON, DAVID D. POLLARD; The laccolith-stock controversy: New results from the southern Henry Mountains, Utah. GSA Bulletin 1988;; 100 (1): 117–139. doi: https://doi.org/10.1130/0016-7606(1988)100<0117:TLSCNR>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 Domes of sedimentary strata at Mount Holmes, Mount Ellsworth, and Mount Hillers in the southern Henry Mountains record successive stages in the growth of shallow (3 to 4 km deep) magma chambers. Whether the intrusions under these domes are laccoliths or stocks has been the subject of controversy. According to G. K. Gilbert, the central intrusions are direct analogues of much smaller, floored intrusions, exposed on the flanks of the domes, that grew from sills by lifting and bending of a largely concordant overburden. According to C. B. Hunt, the central intrusions are cylindrical stocks, sheathed with a zone of shattered sedimentary rocks, and the small flanking sills and laccoliths grew laterally as tongue-shaped masses from the discordant sides of these stocks. New geologic mapping demonstrates that the sedimentary overburden, now partially eroded from the domes, was uplifted about 1.2 km at Mount Holmes, 1.8 km at Mount Ellsworth, and at least 2.5 km at Mount Hillers. The radii of the domes are similar, between 5 and 7 km. The strata over the domes have a doubly hinged shape, consisting of a concave-upward lower hinge and a concave-downward upper hinge. A limb of approximately constant dip joins these two hinges and dips 20° at Mount Holmes, 50° to 55° at Mount Ellsworth, and 75° to 85° at Mount Hillers. The distal portion of each dome is composed of a gently dipping peripheral limb 3 to 4 km long, presumably underlain by sills and minor laccoliths. Although geologic cross sections and regional aeromagnetic data for the three domes are consistent with floored, laccolithic central intrusions, these data alone do not rule out the possibility of a stock at depth. At Mount Hillers, paleomagnetic vectors indicate that tongue-shaped sills and thin laccoliths overlying the central intrusion were emplaced horizontally and were rotated during doming through about 80° of dip. This sequence of events is not consistent with the emplacement of a stock and subsequent or contemporaneous lateral growth of sills and minor laccoliths. Growth in diameter of a stock from about 300 m at Mount Holmes to nearly 3 km at Mount Hillers, as Hunt suggested, should have been accompanied by considerable radial shortening of the sedimentary strata and a style of folding which is not observed. Geologic and geophysical data and mechanical models support a laccolithic origin for the central magma chambers underlying the domes. 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.