Compositional Variations in the Pyroxenes of the Differentiated Palisades Sill, New Jersey

Abstract

Research Article| January 01, 1973 Compositional Variations in the Pyroxenes of the Differentiated Palisades Sill, New Jersey KENNETH R. WALKER; KENNETH R. WALKER 1Bureau of Mineral Resources, Canberra, Australia Search for other works by this author on: GSW Google Scholar N. G. WARE; N. G. WARE 2Department of Geophysics and Geochemistry, Australian National University, Canberra, Australia Search for other works by this author on: GSW Google Scholar J. F. LOVERING J. F. LOVERING 3School of Geology, University of Melbourne, Victoria, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information KENNETH R. WALKER 1Bureau of Mineral Resources, Canberra, Australia N. G. WARE 2Department of Geophysics and Geochemistry, Australian National University, Canberra, Australia J. F. LOVERING 3School of Geology, University of Melbourne, Victoria, Australia Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1973) 84 (1): 89–110. https://doi.org/10.1130/0016-7606(1973)84<89:CVITPO>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation KENNETH R. WALKER, N. G. WARE, J. F. LOVERING; Compositional Variations in the Pyroxenes of the Differentiated Palisades Sill, New Jersey. GSA Bulletin 1973;; 84 (1): 89–110. doi: https://doi.org/10.1130/0016-7606(1973)84<89:CVITPO>2.0.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 Palisades Sill is a multiple intrusion of oversaturated tholeiitic magma which differentiated largely through fractional crystallization. This differentiation followed a normal course of strong iron enrichment and slight alkali enrichment, then fayalite granophyre formed as the trend changed to one of alkali and silica enrichment in the very late fractionation stages.The ferromagnesian mineral series of this fractionation sequence is augite/mauve-brown ferroaugite (Wo38 En51 Fs11 to Wo38 En10 Fs52), pale green ferroaugite (Wo44 En27 Fs29 to Wo44 En10 Fs46), pigeonite (Wo8 En54 Fs38 to Wo12 En34 Fs54), bronzite/hypersthene (Wo4.5 En75 Fs20.5 to Wo3 En58 Fs39), and ferrohypersthene (Wo3 En34 Fs63 to Wo4 En26 Fs70). Associated with these pyroxenes are olivine (Fo77 to Fo55 and Fo13 to Fo4.5), biotite whose Fe/Mg goes from 1 to 23, and hornblende whose Fe/Mg is between 5 and 10.The compositional trends of the pyroxenes in the pyroxene quadrilateral are more complete than any previously recorded from a single intrusion of Fe-rich tholeiitic magma. The normal augite/mauve-brown ferroaugite trend shows only moderate variation in Ca content (Wo33 to Wo38) without any inflection in the trend at the limit of the two-pyroxene field. The bronzite/hypersthene and pigeonite series are fairly normal, except that the pigeonite inversion is nearer En60 than the En70 found in most other tholeiitic intrusions. The most interesting aspects of pyroxene behavior are in late-middle and early-late stages of fractionation, where transformation of the mauve-brown ferroaugite in its final stages of crystallization led to the formation of a separate more Ca-rich ferroaugite series with a trend nearer the Di/Hd join than the mauve-brown ferroaugite trend, and where reactions in the Ca-poor series continued as cooling proceeded into the subsolidus, so that in the early-late stages ferriferous pigeonite inverted to ferrohypersthene while ferriferous orthopyroxene was crystallizing directly from the magma. This orthopyroxene then became unstable in the late stages, and the reaction clinopyroxene + orthopyroxene + liquid → clinopyroxene + olivine + quartz + liquid took place. With further iron enrichment in the magma, ferrohortonolite changed to fayalite, and the coexisting ferroaugites moved toward ferrohedenbergitic compositions. In the final stages, where silica and alkali enrichment became more pronounced, hornblende largely replaced the ferroaugites in the granophyric dolerite. 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.