B-61 Geology of the Stone Mountain-Lithonia District, Georgia
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GEORGIA STATE DIVISION OF CONSERVATION DEPARTMENT OF MINES, MINING AND GEOLOGY GARLAND PEYTON, Director THE GEOLOGICAL SURVEY Bulletin No. 61 GEOLOGY OF THE STONE MOUNTAIN-LITHONIA DISTRICT, GEORGIA By Leo Anthony Herrmann ATLANTA 1 9 5 4 LETTER OF TRANSMITTAL Department of Mines, Mining and Geology Atlanta, April 15, 1954 To His Excellency, Herman E. Talmadge, Governor Commissioner Ex-Officio of State Division of Conservation Sir: I have the honor to submit herewith Georgia Geological Survey Bulletin No. 61, "Geology of the Stone Mountain Lithonia District, Georgia". This report was prepared by Dr. Leo A. Herrmann as a Doctor's thesis in geology at The Johns Hopkins University. It represents a thorough and original investigation of one of Georgia's most important granite districts. Thus, its publica tion will be welcomed by our granite producers and by all who are interested in the science of granite. Very respectfully yours, GARLAND PEYTON Director III 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 •1 1 1 1 1 1 1 1 1 1 1 1 1 1 CONTENTS Page ABSTRACT ···----------------·-----------· ······----······-----··------XV INTRODUCTION ------------------·---------- ----------------------····· 1 Purpose of the ReporL __________ . __________________ _ 1 Location of the District .. _________ ·------------------------- __ _ 1 Physiography --------------------------------------------------------------- 2 Weathering --------------------------------------- ·--------------------- __________ _ 3 Previous Work -------------------------------------------------------------·------ 6 Present Study -----------------------··--------·----------------------···---------- 6 Acknowledgments -------------------------------------------------------------- 7 PETROGRAPHY _________________________ _ 8 Migmatite ---------------------------------·- .. ·----------------- _ 8 Lithonia gneiss ____________________ _ 8 Metamorphic Rocks ________________________ --------------------- . _ 15 General statement _____________ _ 15 Distribution ---------------------------------------------------------· 17 Garnet-mica schist and muscovite quartzite __ .___ 17 Biotite gneiss ----------------------·-· ---------------------··------·- ... 19 Muscovite-quartz schist _____ .. .. -------------· ____ ___ __ 20 Amphibolite ---------------·-----------·-- _________________ ...... _____ 20 Biotite-hornblende gneiss ...... _ ----------· 26 Porphyroblastic biotite gneiss _ ....... __ 27 Minor rock types ________________ .. ... .. __________ 28 Igneous Rocks _ ... ·--------·-- __ -·--- __ ...... ________ 29 Stone Mountain granite (quartz-monzonite) _ 29 Pegmatite dikes _____________________ ·------------- 32 Aplite dikes __________________________________ ---·------------ ... .... 33 Diabase dikes ---------------------------------------------------- ·- 33 Alluvium __________________________________ ... __ .. ..... ______ . ____ . ___ .... 33 STRUCTURAL GEOLOGY ---------------------------------- .. .. 34 Structures of the Lithonia Gneiss. ___ ·-·----------- 34 Banding _____________________________________________ . _____________ ..... _____ . __ _ 34 Garnetiferous layers ·-----------·---------------------------- __________ 34 Flow fo 1ds ________________________________________________________________ . __ __ _ 34 Ptygmatic folds ---------------------------------------------------·-- ____ . 35 Shear zones --------------------------------------------------------- ___________ 36 Mica lineation ______ ... ·----- ____ ____ ____ __ ______ ____________ __ __ __ __ __ __ __ __ _ 3 8 Joints __ .. _______________________ . _____________ .. ______________________ .. ___ ______ __ 3 9 Structures of selected exposures of the Lithonia gneiss 41 v CONTENTS Page Structures of the Metamorphic Rocks ________________________________ 43 Schistosity ---------------------------------------------------------------------- 43 Foliation -------------------------------------------------------------------------- 43 Banding -------------------------------------------------------------------------- 43 Compositional layering -------------------------------------------------- 48 Minor folds ---------------------------------------------------------------------- 48 Longitudinal folds ____________________________________________________ :_____ 50 Undulatory folds ------------------------------------------------------------ 52 Transverse folds ------------------------------------------------------------ 52 Crenulations -------------------------------------------------------------------- 52 Lineations ------------------------------------------------------------------------ 52 Faults ------------------------------------------------------------------------------ 54 Joints ------------------------------------------------------------------------------ 55 Structures of the Stone Mountain Granite (quartz-monzonite) --------------------------------------- ____ ________ ___ 55 Flow structures -------------------------------------------------------------- 55 Xenoliths ------------------------------------------------------------------------ 57 Tourmaline clusters -------------------------------------------------------- 60 Joints ________ ------------------ ___ ___ __ ______________________ __ _______ __ __ ______ __ _ 6 0 Relationship of Structures to Deformation ________________________ 62 General statement ------------------------------------------------------- ___ 62 Coordinates of deformation____________________________________________ 62 Major axis of uplift ________________________________________________________ 62 Minor axes of uplift ________________________________________________________ 62 Mica lineation ------------------------------------------------------------- ___ 63 Shear zones -------------------------------------------------------------------- 63 Joints ___________________ ___ ____ ________ _________ ____ _________ __ ___ ______ __ ____ __ _ _ _ 63 Relationship of Igneous Intrusions to Deformation__________ 64 Petrofabric Analysis ---------------------------------------------------------- 64 Method ---------------------------------------------------------------------------- 6·1 Fabric diagrams ------------------------------------------------------------ 65 Discussion ---------------------------------------------------------------------- 65 PETROGENESIS -------------------------------------------------------------------- 68 Origin of the Lithonia Gneiss ____________________________________________ 68 General statement ---------------------------------------------------------- 68 Banding and garnetiferous layers _________ : ________________________ 68 Potash metasomatism ---------------------------------------------------- 70 Migmatization ---------------------------------------------------------------- 71 Origin of the Amphibolites____________________________________________________ 73 VI CONTENTS Page General statement ---------------------------------------------------------- 73 Igneous origin ---------------------------------------------------------------- 7 4 Sedimentary origin -------------------------------------------------------- 7-J Origin of the Biotite-Hornblende Gneiss __________________________ 75 Origin of the Stone Mountain Granite ______________________________ 75 METAMORPHISM ---------------------------------------------------------------- 76 General Statement -------------------------------------------------------------- 76 Staurolite-Kyanite Subfacies -------------------------------------------- 76 Sillimanite-almandine Subfacies -------------------------------------- 76 Mineralogical Changes During Progressive Metamorphism ---------------------------------------------------------------- 76 Causes of Metamorphism ____________________________________________________ 77 GEOLOGICAL HISTORY AND CONCLUSIONS________________ 78 THE STONE INDUSTRY ________________________________________________________ 80 History -------------------------------------------------------------------------------- 80 Types of Stone ____________________________________________________________________ 83 Stone Mountain granite (quartz-monzonite)________________ 83 Lithonia gneiss ---------------------------------------------------------------- 84 Panola granite ---------------------------------------------------------------- 85 Physical Characteristics of Granite and Gneiss________________ 85 General statement ---------------------------------------------------------- 85 Hardness ........ ---------------------------------------------------------------- 86 Crushing strength ---------------------------------------------------------- 86 Structure ------------------------------------------------------------------------ 86 Texture ---------------------------------------------------------------------------- 87 Mineral composition ------------------------------------------------------ 87 Color -------------------------------------------------------------------------------- 87 Quarrying Methods ------------------------------------------------------------ 88 Building stone --'------------------------------------------------------------- 88 Crushed stone ---------------------------------------------------------------- 89 Uses of Stone ________________________________________________________________________ 89 DESCRIPTION OF QUARRIES ____________________________________________ 90 General Statement -------------------------------------------------------------- 90 Stone Mountain Granite (quartz-monzonite)