Differentiation of the Tasmanian Dolerites: Red Hill Dolerite-Granophyre Association

Research Article| March 01, 1962 Differentiation of the Tasmanian Dolerites: Red Hill Dolerite-Granophyre Association IAN McDOUGALL IAN McDOUGALL Dept. Geophysics, Australian National University, Canberra, A.C.T., Australia Search for other works by this author on: GSW Google Scholar Author and Article Information IAN McDOUGALL Dept. Geophysics, Australian National University, Canberra, A.C.T., Australia Publisher: Geological Society of America Received: 09 Jan 1961 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1962, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1962) 73 (3): 279–316. https://doi.org/10.1130/0016-7606(1962)73279:DOTTDR2.0.CO;2 Article history Received: 09 Jan 1961 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation IAN McDOUGALL; Differentiation of the Tasmanian Dolerites: Red Hill Dolerite-Granophyre Association. GSA Bulletin 1962;; 73 (3): 279–316. doi: https://doi.org/10.1130/0016-7606(1962)73279:DOTTDR2.0.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 The Tasmanian dolerites were intruded during the Jurassic and form thick sheets, large transgressive bodies, and wide vertical dikes in flat-lying Permian and Triassic sedimentary rocks. The magma was tholeiitic. The Red Hill dike is up to 1 mile wide and extends vertically upward for more than 1000 feet from the roof of an extensive sheet about 1300 feet thick. Sedimentary rocks roofed the dike. Within the highest structural parts of the dike a large volume of silicic granophyre is associated with quartz dolerite. Chemical, petrographic, mineralogical, and field studies show a complete gradation between dolerite and granophyre and provide evidence that the rock series has been formed by differentiation.Magnesian pyroxene and calcic plagioclase crystallized early, and both changed progressively in composition with fractionation; the residual magma was continually enriched in less refractory components. Strong enrichment in Fe relative to Mg and moderate absolute Fe enrichment took place during the main stages of fractionation, followed by enrichment in silica and alkalies (particularly potassium) in the later stages. Differentiation resulted from fractional crystallization and relative movement of phases owing to gravity. The volume of granophyre is larger than expected; some residuum from the associated sheet probably migrated into the Red Hill dike. Differentiation is similar to that found by Edwards (1942), but it is more marked. The Red Hill study reconciles the two trends that Edwards found in sheetlike and dike-like intrusions and shows them to be part of the same sequence. 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.