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A Jurassic Granite from Southern Georgia, U.S.A.: Silicic, Extension‐Related Magmatism along the Southeastern Coastal Plain

Ann L. Heatherington, Paul A. Mueller and Allen P. Nutman
The Journal of Geology
Vol. 107, No. 3 (May 1999), pp. 375-384
DOI: 10.1086/314350
Stable URL: http://www.jstor.org/stable/10.1086/314350
Page Count: 10
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Abstract

Abstract Ion microprobe (SHRIMP) U‐Pb dating of single zircon grains extracted from granite cuttings from the subsurface of southeastern Georgia (Pierce Co.) yields a well‐defined crystallization age of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $159\pm 3$ \end{document} Ma (2σ), confirming the presence of Mesozoic silicic magmatism in the northern Suwannee terrane. Revision of Suwannee terrane subcrop age province boundaries is required by these data. The granite is 20–40 m.yr. younger than subsurface diabases in the same region. Whole‐rock isotopic and elemental data indicate that it is a high‐K, calc‐alkaline I‐type granite derived from a slightly enriched source or a mixture of mantle and crustal melts. Neodymium model ages demonstrate that lithosphere of at least Mesoproterozoic age is present beneath this part of southeastern Georgia. Because of its geochemical characteristics and proximity to the Brunswick magnetic anomaly, the granite may have been generated by partial melting of Neoproterozoic igneous crustal rocks and emplaced along a crustal discontinuity during the waning stages of Mesozoic rifting. This is the only known Mesozoic granite along the eastern coast of North America south of the White Mountain batholith in New England.

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