Geochemical and Geochronological Investigations in

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2006

Geochemical and Geochronological Investigations in the Southern Appalachians, Southern Rocky Mountains and Deccan Traps. Reshmi Das

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THE FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES

GEOCHEMICAL AND GEOCHRONOLOGICAL INVESTIGATIONS IN THE SOUTHERN APPALACHIANS, SOUTHERN ROCKY MOUNTAINS AND DECCAN TRAPS.

By RESHMI DAS

A Dissertation submitted to the Department of Geological Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy

Degree Awarded: Fall Semester, 2006

The members of the Committee approve the Dissertation of Reshmi Das defended on 1st November, 2006. ____________________________________ A. Leroy Odom Professor Directing Dissertation ____________________________________ Jeffrey Chanton Outside Committee Member ____________________________________ Stephen A. Kish Committee Member ____________________________________ Vincent J. M. Salters Committee Member ____________________________________ James F. Tull Committee Member Approved:

_____________________________________________ Professor A. Leroy Odom, Chair, Geological Sciences The Office of Graduate Studies has verified and approved the above named committee members.

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To my first geology teacher, Dr. Mohan Chand Baral, who made me fall in love with Geology.

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ACKNOWLEDGEMENTS

Many people have contributed to the making of this dissertation. First and foremost I would like to acknowledge Prof. Leroy Odom, my advisor who not only supported me academically and financially for five years but also lent personal support whenever required. This dissertation would have been impossible without him. Prof. James Tull supervised my project on the southern Appalachian and words are inadequate to express his contribution in development of this dissertation. Prof. Stephen Kish always had an answer for my most difficult question and Prof. Vincent Salters helped me with the modeling part of the chemical data. Prof. Munir Humayun, Prof. Tapas Bhattacharyya and Dr. Michael Bizimis, though not a part of my committee, supervised portions of my research. I am indebted to them for their time, technical support and patience. The field work required for this dissertation was partly funded by EDMAP component of the National Geologic Mapping Act 2002. The Isotope Geochemistry Division at the National High Magnetic Field Laboratory has been a wonderful place to work, and I would like to thank Ted Zateslo and Afi SachiKocher for their technical support. I would also like to thank all of the geochemistry graduate students for the long chats, the little favors, and camaraderie along the way. My parents made the greatest sacrifice of their life by letting their only child go ahead with her life and providing the best educational opportunity. Last but not the least is my best friend and husband Subhajit who inspired me to continue my career in academia. His extremely active academic and intellectual presence kept me going and will continue to do so.

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TABLE OF CONTENTS

List of Tables ................................................................................................ List of Figures ................................................................................................ Abstract ......................................................................................................

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1. Geochemical and Geochronological Constraints on the Origin and Evolution of the Eastern Blue Ridge, Southern Appalachians. .......................................... 1 1.1 Introduction........................................................................................... 1 1.2 Regional Overview ............................................................................... 3 1.3 Study Area and General Description of Lithotectonic Units................ 4 1.4 Purpose of the Study ............................................................................. 7 1.5 Analytical Techniques .......................................................................... 8 1.6 Results ................................................................................................ 10 1.7 Nd Model Age and Detrital Zircon Ages of the Metasediments of the Eastern Blue Ridge .......................................................................................... 14 1.8 Mulberry Rock Gneiss .......................................................................... 15 1.9 Discussion ............................................................................................. 16 2. Kilometers Scale Strontium Isotopic Homogenization During Metamorphism: A Case Study in the Tres Piedras Granite, New Mexico.................................... 62 2.1 Introduction........................................................................................... 2.2 General Geology ................................................................................... 2.3 Tres Piedras Granite.............................................................................. 2.4 Previous Work ...................................................................................... 2.5 Results ................................................................................................ 2.6 Discussion ............................................................................................. 2.7 Conclusion ............................................................................................

62 63 64 65 69 70 74

3. Trace Element and Lead Isotopic Studies of the Kutch Volcanics of Northwest India ................................................................................................ 87 3.1 Introduction........................................................................................... 3.2 Geological Setting................................................................................. 3.3 Deccan Stratigraphy..............................................................................

87 88 89

3.4 Previous Work-Sr and Nd Isotopic Data .............................................. 3.5 Analytical Technique ............................................................................ 3.6 Results ................................................................................................ 3.7 Comparison with the DVP .................................................................... 3.8 Discussion ............................................................................................. 3.9 Conclusion ............................................................................................ APPENDICES

90 91 91 93 94 95

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A Analytical Techniques .......................................................................... B Sample Locations.................................................................................. C Photomicrographs .................................................................................

107 118 120

REFERENCES

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BIOGRAPHICAL SKETCH ..............................................................................

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LIST OF TABLES Table 1.1: Major Oxide concentration in weight percent. ...................................

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Table 1.2: Trace Element and REE concentration (in ppm) of the Pumpkinvine Amphibolites (PCF) and the Galts Ferry Gneiss (GFG) ............................................................ 27 Table 1.3: Trace Element and REE concentration (in ppm) of the Hillabee Greenstones (HG) and Hillabee Dacite (dacite) ....................................................................................... 28 Table 1.4: Sr and Nd Isotopic Data......................................................................

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Table 1.5: Rb-Sr isotopic data for whole rock samples.......................................

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Table 1.6: Nd Model Age of metasediments from eastern Blue Ridge ...............

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Table 1.7: U-Pb analysis of Galts Ferry Gneiss zircons by LA-MS-ICPMS ......

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Table 1.8: U-Pb analysis of detrital zircons from meta-sandstone by LA-MS-ICPMS 33 Table 1.9: U-Pb analysis of Mulberry Rock Gneiss zircons by LA-MS-ICPMS

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Table 1.10: REE concentrations of eastern Blue Ridge metasediments..............

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Table 2.1: Regional Geologic history of the north-central New Mexico ............

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Table 2.2: Stratigraphic nomenclature and lithologic description of supracrustal Proterozoic rocks of New Mexico........................................................................................... 68 Table 2.3: Chemical analysis, norm and modes of the Tres Piedras Granite ......

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Table 2.4: Rb-Sr whole rock analysis of Tres Piedras Granite............................

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Table 2.5: Rb-Sr analysis of the mineral phases of the Tres Piedras Granite......

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Table 2.6: Tres Piedras Granite zircon analysis by LA-MC-ICPMS ..................

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Table 3.1: Stratigraphic nomenclature and thickness of the southwestern Deccan Formations ................................................................................................ 97 Table 3.2: Trace element and Pb-isotope results .................................................

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Table 3.3: Elemental ratios of Re'union type source at 65 Ma ............................

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LIST OF FIGURES Figure 1.1: Generalized geological map of southern Appalachians ...................

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Figure 1.1A: Generalized geologic map of eastern Alabama and western Georgia Blue Ridge terranes ................................................................................................ 38 Figure 1.2: Bimodality of Hillabee Greenstone sequence and Pumpkinvine Creek Formation ................................................................................................ 39 Figure 1.3: Total alkali vs. silica diagram for the Hillabee Greenstone sequence and Pumpkinvine Creek Formation ........................................................................... 40 Figure 1.4A: Hillabee dacite and GFG classification using Shand's index ........

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Figure 1.4B: HG and PCF amphibolite plotted on AFM diagram ......................

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Figure 1.5: Ti vs Zr plot of greenstones- dacites and PCF amphibolite - GFG ..

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Figure 1.6: Co-variation diagrams of relatively immobile elements for HG and PCF amphibolites ................................................................................................ 43 Figure 1.7: Tectonic discrimination diagrams for the PCF amphibolites and HG

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Figure 1.8: La/10-Y/15-Nb/8 diagram for the PCF amphibolite and HG ..........

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Figure 1.9: Tectonic discrimination diagram for GFG and Hillabee dacite .......

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Figure 1.10: Spider diagram plot of PCF amphibolite and HG ..........................

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Figure 1:11 CI chondrite normalized plot of PCF amphibolite and HG ............

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Figure 1.12: CI chondrite normalized plot of GFG and Hillabee dacite ............

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Figure 1.13: Initial Sr vs. epsilon Nd isotopic plot .............................................

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Figure 1.14: Rb-Sr isochron of GFG samples ....................................................

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Figure 1.15: Two chemical groups of GFG defined by REE concentrations. ....

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Figure 1.16: U-Pb ages of GFG zircons .............................................................

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Figure 1.16A: CL images of GFG zircons ..........................................................

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Figure 1.17: Nd isotopic evolution diagram of the eBR metasediments ............

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Figure 1.18: NASC normalized REE plot of the eBR metasediments ...............

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Figure 1.19: U-Pb ages of the detrital zircons of eBR ........................................

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Figure 1.20: Rb-Sr whole rock age of Mulberry Rock Gneiss ...........................

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Figure 1.21: U-Pb ages of Mulberry Rock Gneiss zircons .................................

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Figure 1.22: Epsilon Nd of Ordovician arc felsic magmas of the Appalachians.

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Figure 1.23: Model for passive mechanism of lithosphere extension ................

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Figure 1.24: Model for accretionary orogen in southern Appalachians during Ordovician ................................................................................................ 61 Figure 2.1: Map of Proterozoic basement uplifts and associated major faults in north-central New Mexico ................................................................................................ 80 Figure 2.1a: Map of Tres Piedras Granite sampling locations ...........................

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Figure 2.2: Whole rock Rb-Sr isochron of Tres Piedras Granite ........................

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Figure 2.3: Rb-Sr mineral isochron of Tres Piedras Granite ..............................

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Figure 2.4: U-Pb ages of Tres Piedras Granite zircons by LA-MC-ICPMS ......

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Figure 2.5: LA-ICPMS measurement of concentration ratios across a feldspar grain from Tres Piedras Granite ................................................................................................ 86 Figure 3.1: Structural-tectonic features of southern Asia and Indian Ocean basin

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Figure 3.2: Initial Nd vs. initial Sr isotope plot of the Kutch samples ...............

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Figure 3.3: Trace element-REE plot of the Kutch basalts .................................

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Figure 3.4: La/Nb vs Ce/Pb and La/Sm vs Sm/Yb in the Kutch basalts ............

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Figure 3.5: Pb and Sr isotopic variation in Kutch Basalts ..................................

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Figure 3.6: Melting model of garnet peridotite to produce the alkali basalts .....

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Figure 3.7: Mixing model for the Kutch tholeiites to generate the trace element-REE pattern ................................................................................................ 105 Figure 3.8: Mixing model for the Kutch tholeiites to generate the Sr and Nd isotope ratioserate the trace element-REE pattern ............................................................................ 106

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ABSTRACT In the southernmost Appalachians, bimodal volcanics of Pumpkinvine Creek Formation (PCF) and its proposed equivalent, the Hillabee Greenstone (HG) have indistinguishable ages (~460 Ma) and trace element-REE pattern similar to an arc/back-arc type setting. 143Nd values of felsic members of the HG and PCF indicate involvement of Grenville crust during petrogenesis. U-Pb dates (900-1500 Ma) of detrital zircons in PCF meta-sandstone cluster around 1100 Ma. Nd-model ages of the Ashland-Wedowee Supergroup metasediments range between 943-1439 Ma and cluster around 1000 Ma. Rb-Sr whole rock and U-Pb zircon dates of the Mulberry Rock Gneiss also demonstrate an Ordovician age (~460 Ma). It is concluded that the PCF-HG arc formed on the Laurentian continental margin on Ashland-Wedowee sediments during Ordovician and remained outboard of the continent until final closure during Alleghenian orogeny. Geochronological investigations of the Tres Piedras Granite of northcentral New Mexico have revealed a sharp discordancy between Rb-Sr whole-rock and U-Pb zircon ages. Analyses of fifty individual zircons (most concordant) by LA-MS-ICPMS yield a ~1730 Ma magmatic crystallization age. Rb-Sr whole-rock isochron ages from separate localities are 1490+/-20 Ma and 1497+/-42 Ma. Sphene/whole-rock/biotite isochron ages and initial 87Sr/86Sr ratios from separate localities are indistinguishable from those of whole-rock isochrons. In both cases feldspar plots above the isochrons and appeared to be an open system as evidenced by 4% difference in 87Sr/86Sr in the core and rim of feldspar. Taken altogether, these data are interpreted to reflect a large (kilometer) scale redistribution and rehomogenization of strontium isotopes during an independently, well-documented metamorphic event in the region. The geochemical character of the Kutch volcanics, northwest of Deccan Traps, India, have been investigated in order the magma's origin. Sr-Nd-Pb isotopic ratios and trace element patterns identifies three end members: Reunion plume-type alkali basalts, Mahabaleshwar-type alkali basalts and crustally contaminated tholeiites. The first type of alkali basalts that can be generated by very low degree of partial melting (1.6-1.8%) of Reunion plume like source at garnet stability field; the tholeiites can be explained by crustal contamination of Indian-MORB like magma. High 207Pb/204Pb (15.61-15.83) ratio of the tholeiites agrees well with the Pb-isotopes of local Archean crust.

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CHAPTER ONE GEOCHEMICAL AND GEOCHRONOLOGICAL CONSTRAINTS ON THE ORIGIN AND EVOLUTION OF THE EASTERN BLUE RIDGE, SOUTHERN APPALACHIANS. 1.1 Introduction Forty years ago Tuzo Wilson (1966) proposed the theory of the Wilson Cycle by studying the eastern margin of North America. At its simplest, the Wilson Cycle describes the opening and closing of ocean basins - plates rift into pieces and diverge away from each other and new ocean basins form in between, then there is a reversal in motion, convergence of the two rifted plates followed by a plate collision, and mountain building. The rock records of the eastern margin of North America preserves evidence of at least two complete Wilson cycles– starting with breakup of the supercontinent Rodinia and ending with the assembly of the supercontinent Pangaea and finally rifting of Pangea and opening of the modern Atlantic Ocean (Thomas, 2005). The breakup and rifting of Rodinia is well documented in the stratigraphic rock records of the eastern margin of North America that include synrift sedimentary and igneous rocks, post-rift unconformity and early post-rift sedimentary strata. Isolation of rifted Laurentia was complete by early Cambrian (ca. 530 Ma) (Thomas, 2005). The early extensions span between 760–650 Ma (e.g., Aleinikoff et al., 1995; Hogan and Gilbert, 1998; Thomas et al., 2000; Cawood and Nemchin, 2001; Owens and Tucker, 2003) followed by pervasive rifting (620–545 Ma) along the eastern margin of Laurentia and terminating with the evidence of few late stage rifting of microcontinents between 540–530 Ma. The Appalachian mountain chain was created by broadly three Paleozoic orogenies after the rifting of supercontinent Rodinia: the Ordovician-Silurian Taconic Orogeny, the Devonian Acadian orogeny and the Pennsylvanian-Permian Alleghanian orogeny. Evidence of deformation due to Taconic orogeny was first recognized in the Hudson valley of New York and the affected areas stretch from western Newfoundland south to about New York State. Deformation caused by Taconic Orogeny are also identified much farther south in Georgia and Alabama. Taconic orogeny was dominated by A-type subduction against the Laurentian margin resulting in the closure of the Proto Atlantic (also called the Iapetus Ocean). Island arcs forming due to the subduction were obducted onto the Laurentian margin. Few examples include Cowrock, Cartoogechaye and Tugaloo terranes in the southern Appalachians and the Chopawamsic, Potomac and Bultimore terranes in the central and northern Appalachians (Hatcher et al., 2006). The arc building and amalgamation produced numerous plutons (Steltenpohl et al., 2005; Bream, 2003), penetrative deformation, and as high as granulite facies metamorphism (Hatcher and Butler, 1979; Eckert et al., 1989; Moecher et al., 2004). Taconic orogeny generated a huge amount of new crust that was amalgamated along the southeastern margin of Laurentia. The Acadian Orogeny occurred during the early Devonian Period. It was a continuing collision to the island arc of the Taconic Orogeny (Hatcher, 1989). The Acadian Orogeny was primarily a continent-continent collision between Laurentia (North America) and Baltica (Europe). The 1

Northern Iapetus Ocean was completely closed and the Acadian orogeny re-deformed some of the rocks previously affected by the Taconic Orogeny, and produced a mountain belt in , Nova Scotia, Newfoundland, Maine, New York, England, Ireland, Scandinavia and Greenland.that are as high as the Himalayas The Acadian Orogeny of North America is equivalent to the Caledonian Orogeny in Europe. Following the collision of Europe and North America, the newly formed Appalachian Mountains started to shed tremendous amounts of sediment westward into the foreland. The sediments were primarily conglomerates, quartz arenites, breccias, arkose sandstones etc (Harrison, 2002, Hatcher, 2005). Near the mountains, the sedimentary rocks were primarily terrestrial like river conglomerates and red shale, sands, etc. Westward, these rocks undergo facies changes into black shales and beach sands (Baranoski and Riley, 1987). In Pennsylvania and New York, the Catskill Delta represents the terrestrial-marine component (Van Tassell, 1987). In other parts of North America, sediment erosion from the Appalachian Mountains wasn’t a dominating event and the shallow marine seaways existed supporting large amounts of carbonate sedimentation and oolites and reefs formation (Drivet and Mountjoy, 1997). The Alleghenian Orogeny of the southern Appalachians was the third and last of the great orogenies that affected eastern North America during the Paleozoic. The final collision of North America with Africa, transported a huge composite crystalline thrust sheet – the Blue Ridge Piedmont megathrust sheet that included pre-Alleghanian metamorphic rocks to at least 350 Km inside the North American craton (Hatcher et al., 2006). The Alleghenian orogeny was completed by 265 Ma with the formation of Pangea and completion of the first (Paleozoic) Wilson cycle. The Alleghenian suture is marked by the boundary between the easternmost subsurface Suwannee terrane and Carolina terrane. From the fossil assemblage of the cover sequence (Gondwana basement covered by fossiliferous Ordovician to Devonian sandstones and shales) it seems likely that the Suwanee originated as part of African Gondwanaland (Mueller et al., 1994; Pojeta et al., 1976) and remained on the Laurentian side during breakup of Pangea. The three episodes of orogeny are identified in the Appalachians but they are not substantiated along the entire length of the mountain chain. (Moecher et al., 2004: Hatcher, 1978; Hatcher et al., 1989). The southern Appalachian mountain chain records protracted continental orogeny related to multiple extensional and contractional events. These events have been attributed to a range of convergent tectonic mechanisms, including subduction, arc accretion, and continental collision. Both direct and oblique convergence mechanisms have been proposed, and subduction is interpreted to have been directed both toward and away from Laurentia, the core of North America that existed at the time (Hatcher et al., 1987). The eastern Blue Ridge province was affected by all of the major events that shaped the southern Appalachian orogen and is a key link in elucidating the assembly of the Appalachian portion of the North American continent. However, important aspects of the evolution of the eastern Blue Ridge remain obscure. This work presents new data on zircon contained within the metasediments in the eastern Blue Ridge of Alabama and Georgia. The geochemical and geochronological data have bearing upon the formation, evolution and accretion of the most inboard ‘suspect’ terranes in the southern Appalachians and will compare this sequence chemically with the Hillabee Greenstone of the Talladega belt-western Blue Ridge. These data will have implication for the genesis of the

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eastern Blue Ridge in the southern Appalachians and provide the implicit constraints on the tectonic history of this region.

1.2 Regional Overview The Blue Ridge province of the southern and central Appalachians includes low to high grade metamorphic rocks that have been thrust northwestward over the unmetamorphosed sedimentary rocks of the Valley and Ridge province. It is divided into eastern and western portions by the east-dipping Hayesville and related faults in the northeast and by the Allatoona fault and Hollis Line Fault in the southeast (Figs. 1.1, 1.1A). The post-metamorphic Allatoona fault and Hollis Line fault places the structurally complex eastern Blue Ridge assemblage of chemically immature clastic metasedimentary rocks, mafic to ultramafic bodies, variably deformed felsic intrusive rocks and Grenville basement (eg.Tullahh Falls Formation) over the more mature metasedimentary rocks and basement of the western Blue Ridge (Rankin, 1975; Hatcher, 1978). Regionally the eastern Blue Ridge is a composite terrane that may include parts of Laurentian outer margin cover sequence as well as accreted components of accretionary prism, ophiolitic and island arc affinity. The eastern Blue Ridge (EBR) is generally similar lithologically to the adjacent Piedmont. The Piedmont is also an exotic composite terrane that extends some 700 km southwestward from the frame of the Sauratown Mountains window in North Carolina to the Coastal Plain overlap in Alabama (Hatcher, 2002). The Brevard fault zone, that separates the eastern Blue Ridge from the Piedmont, is a major structure with a protracted, polyphase history of displacement (Hatcher, 1978). The western Blue Ridge is demonstrably part of Laurentia, but the origin of the EBR is controversial. The presence of alpine peridotite, mafic-ultramafic complexes has led some to suggest that the EBR may be an exotic, far-traveled terrane that was accreted during Paleozoic orogeny, with the mafic rocks being remnants of the closed ocean basin (for example, Horton, Drake, and Rankin, 1989; Willard and Adams, 1994; Zen, 1981; Williams and Hatcher, 1983; Shaw and Wasserburg, 1984). The Pine Mountain Window (Fig. 1.1) is exposed in the Piedmont on the Alabama promontory. It exposes 1.1 Ga Laurentian Grenvillian basement of granulite- and upper-amphibolite-facies granitic gneisses and a kyanite-sillimanite-grade platformal cover sequence (Hatcher, 2006). The easternmost accreted terrane in the central and southern Appalachians is the Carolina superterrane situated to the east of Piedmont (Fig. 1.1). During Rodinia rifting numerous microcontinents were formed in the prevailing ocean between Laurentia and Gondwana, proximal to Gondwana, loosely termed as Peri-Gondwanan terranes. The Carolina superterrane was formed by amalgamation of a series of these microcontinents of peri-Gondwana derivation and accreted to the Laurentia during the mid-Paleozoic (Rast and Skehan, 1983). The Carolina superterrane is primarily composed of Neoproterozoic mafic to felsic volcanics of volcanic arc origin and some volcaniclastic sedimentary rocks. Several plutons ranging in age between 550 to 600 Ma intrude the arc complex (Hibbard et al., 2003). This entire assemblage was metamorphosed to upper amphibolite to greenschist facies during Cambrian. This is evidenced by ~ 530 Ma plutons that intrude the metamorphic rocks (Dennis and Wright, 1997). Cambrian and Ordovician (identified from fossil assemblages) clastic sedimentary rock overlies the arc assemblage (Samson, et al., 1982; Koeppen et al., 1995). The western Carolina

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superterrane is metamorphosed to a higher grade with a 350-360 Ma metamorphic overprint and contains numerous Devonian to Carboniferous younger granitoids and gabbros (McSween et al., 1991; Hibbard et al., 2003) probably intruded during the docking of the Carolina terrane with the Laurentia during mid to late Paleozoic.

1.3 Study Area and General Description of Lithotectonic Units The study area includes the Hillabee greenstone belt, Ashland-Wedowee belt, Mulberry rock gneiss and the Pumpkinvine Creek Formation (PCF) of the southern Appalachians (Fig. 1.1A). Fresh unaltered samples were collected using several criteria including quality of mapping and documented tectonic or stratigraphic significance of individual units. Hillabee Greenstone: The Hillabee Greenstone (HG) belt structurally occurs on top of the lower greenschist facies Talladega Group in the Talladega belt. The Talladega Belt represents the most outboard Laurentian margin cover sequence and the Talladega Group is the frontal metamorphic thrust sheet of the southernmost Appalachians of Alabama and western Georgia. Like the PCF it is also a sequence of bimodal volcanics (the maximum thickness is ~2.6 Km at places ) with the mafic (~75%) and felsic members (~25%) being tholeiitic metabasalt and calcalkaline metadacite/rhyolite respectively. The metavolcanic complex is in a thrust contact with the underlying fossiliferous shallow marine Devonian to earliest Mississipian (?) metasedimentary rocks of the Talladega belt. The mafic member is primarily low-potassium tholeiitic metabasalt and basaltic meta-andesite referred to as greenstone herein and the felsic member is metadacite referred as Hillabee dacite herein (Tull et al., 2006). Unlike PCF there is not much of metasedimentary units present in the HG belt. Rare, thin layers of micaceous quartzite and sericite phyllite occur locally within the metavolcanic complex and are the only non-volcanic member of the HG belt. Textural evidences like rarely preserved ophitic, intergranular, and porphyritic textures is indicative of the extrusive nature of the mafic rocks in form of basalt flows and/or basaltic ash (Tull and Stow, 1979, 1980; Stow, 1982). The felsic volcanics that are interlayered with the mafic rocks occur in form of thick (upto 165 m) mineralogically and chemically homogeneous, laterally continuous, tabular sheet-like bodies. Compositionally they are porphyritic meta dacite/rhyolite. The metadacite shows bands of polycrystalline quartz alternating with finegrained mica and opaque minerals. The rock contains porphyroclasts of hornblende, actinolite, albitic plagioclase, and quartz (Tull et al., 1998) interpreted to be phenocrysts. Strain is evidenced by undulose extinction of quartz grains and weakly kinked lamelleae of plagioclase. Hillabee dacite extended over an area greater than 100's of sq. km. and are interpreted as largevolume pyroclastic ash flow crystal tuffs (Tull et al., 1998). Samples of the greenstone and Hillabee dacite were collected for chemical analysis. Structurally overlying the Talladega belt is the EBR allochthon.

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Pumpkinvine Creek Formation: The Pumpkinvine Creek Formation is a linear belt of metavolcanic rock sequence extending from near the Alabama-Georgia border into northern Georgia for a length of about 100 Km. It is included as part of >220 Km long Dahlonega Gold Belt (DGB) terrane that is strike continuous and in the same structural position with the AshlandWedowee belt (Fig. 1.1, 1.1A). The importance of the PCF lies with the fact that it is structurally adjacent to the Laurentian portion of the Appalachian making it the most inboard ‘suspect’ terrane (because of uncertain affinity, lack of basement it is considered to be “suspect” with respect to Laurentia) in this portion of the southern Appalachians. Lithologically the PCF is a sequence of bimodal volcanics in the outcrop scale and mapscale containing fine grained amphibolite (referred as PCF amphibolites herein), felsic gneiss (termed as Galts Ferry Gneiss or GFG member) and minor amounts of pelitic schists (Canton Schist) and subordinate metamorphosed sandstone. The mafic and the felsic units are interlayered from centimeter scale to tens of meters. The Canton schist possibly represent background sedimentation (Holm, 2006) interpreted from its sporadic occurrence and in sharp contact with the metavolcanic rocks of the PCF. McConnell (1980) identified discontinuous but regionally mappable banded iron formation interlayered with the PCF amphibolites. Due to lack of any ordered stratigraphic occurrence of the three units of the PCF (mafic, felsic and the metasediments) they are all considered different facies of the PCF. The amphibolite is fine grained, the major mineral phases being amphibole (75-80%) and plagioclase (~20%) and the accessory mineral phases include epidote, garnet and actinolite and/or chlorite (retrograde assemblage of amphibole). Typical volcanic textures include relic amygdule filled with epidote and plagioclase phenocrysts are common. Pillow structures have also been reported by several workers (McConnell, 1980; Abrams and McConnell, 1984). The felsic metavolcanic lithology (GFG) occurs in two modes. In places it forms thin (0.1-0.5 m) layers possibly representing rhyolitic ash eruptions. The second type of occurrence is as thick, lenticular bodies up to 2 km thick extending along strike. Major mineral composition of the GFG is plagioclase and quartz and enclaves of intermediate to mafic composition rich in amphibole is common. Accessory minerals include muscovite and to a lesser degree garnet. The larger bodies of felsic gneiss are likely large felsic eruptions. The third and volumetrically least significant lithology of the PCF is the aluminous Canton Schist, composed mainly of quartz sericite/muscovite ± garnet and biotite. This likely represents background sedimentation during periods of volcanic quiescence (Holm, 2006). Presence of extremely low sediments in archetypal back-arc basins such as the Lau basin-Havre trough (portion of the Tonga-to-New Zealand back-arc system) have been reported by Gamble and Wright, 1995. In the northern portion of the study area the Chattahoochee fault (a late structure in the kinematic sequence) demarcates the upper boundary of the PCF and emplaces higher grade, migmatitic, predominantly metasedimentary units of the Sandy Springs Group (Higgins and McConnell, 1978) structurally above the PCF. The units structurally above the Pumpkinvine Creek Formation, described as the New Georgia Group (Abrams and McConnell, 1981), contain a mixture of pelitic and chemical sediments (iron-bearing quartzite), minor amphibolite and

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locally altered ultramafic pods. These units also hosts numerous intrusive bodies varying in composition from gabbroic to intermediate and felsic gneisses (eg. ~430 Ma Austell gneiss dated by Higgins et al. 1997) and many more unnamed intrusive bodies. These units likely correlate to the southwest into Alabama with part of the Ashland-Wedowee belt (Fig. 1.1). The intrusive units are similar in age and composition to the granitoids (including the 460 Ma Kowaliga and Zana granites) of Alabama as described by Russell et al. (1987) and Drummond et al. (1997). The age of the New Georgia Group and correlative units of the Ashland-Wedowee belt to the southwest is likely late-Proterozoic to earliest Paleozoic, and may represent slope-rise sediments along the eastern margin of Laurentia (Tull ,1978). The intrusives might have formed because of subduction-related slab melting beneath Laurentia (ex. Elkahatchee Quartz Diorite at 490 Ma) or later magmatic events during Taconic and Acadian orogenies (Drummond et al.,1997).

Samples were collected from both the felsic (GFG) and mafic units of the PCF and Canton Schist. Ashland Wedowee Belt: East of the Talladega belt and west of the Brevard fault zone in Alabama and west Georgia is a broad belt of medium to upper amphibolite facies schists, gneisses and amphibolites of the Ashland – Wedowee belt. These rocks are interpreted to be late Precambrian metamorphosed sedimentary rocks and minor basalts (Thomas et al., 1980). The Ashland does not continue beyond the state line but the Wedowee and Emuckfaw extend northeast into Georgia (Fig. 1.1A) Exposed over much of the northern Alabama and western Georgia Piedmont (Fig 1.1, 1.1A) is a distinctive graphite bearing metasedimentary sequence of slate, phyllite, quartzite and schist, called the Wedowee Group, interpreted as the regressive phase of a more complex sedimentary cycle involving many other rock units (Neathery, 1973). Protoliths for the metamorphic lithologies possibly are arenite, siltstone and claystone interpreted to be a deep water environment deposit. The Ashland Super Group (Tull, 1978) underlies the Wedowee Group and is characterized by metabasalts called the Poe Bridge Mountain amphibolites mostly concentrated in the lower part of the sequence and metasediments with an aggregate thickness of few thousand meters. The lower Ashland can be separated from the other units with relative ease because it is the only stratigraphic unit containing abundant metabasalts (amphibolites). Ashland Super Group is a thick sequence of metasedimentary rocks. Garnetiferous biotite schist and siliceous graphitic muscovite schist are common. Less abundant rock types include kyanite-quartz schist, sillimanite-quartz schist and quartzite (Vernon, 1973). Although arial separation and apparent lithologic differences prohibit any direct correlation, McConnell and Abrams (1984) speculated that the rocks of the new Georgia are at least in part equivalent to the Ashland Supergroup. This is based primarily on the fact that both the New Georgia Group and the Ashland Supergroup contain metavolcanic rocks and similar types of sulfide hosted ore deposits. The authors also suggested that the rocks defined as Wedowee formation in Alabama (Tull, 1978) are equivalent to the rocks of the Sandy Springs Group. This correlation is based on lithologic similarities and the association of both Sandy Springs Group

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and Wedowee Group with volcanic bearing rock groups (i.e., New Georgia Group and Ashland Supergroup, respectively) Fresh samples of quartzite, muscovite schist, garnetiferrous biotite schist from the Ashland and Wedowee Group were analyzed for Nd isotopic composition to determine the model age of the provenance. Mulberry Rock Gneiss: Holm (2001, 2001a) studied the Mulberry Rock Gneiss (MRG), that occurs as a structural window (eyelid window). The MRG occurs within a recess where the eastern Blue Ridge rocks and ‘terrane bounding Allatoona fault are tightly folded into the structural recess’ (Holm, 2001, 2001a). The unique position of the MRG (Fig. 1.1A) caused previous workers to conclude that the yet undated rocks were Grenville basement to the Talladega belt and the Talladega Group lies unconformably on the basement. Higgins et al., 1988 described them as equivalent to the nearby Grenville aged Corbin metagranite. Holm 2001, 2001a described MRG as medium grained, slightly metaluminous, two mica granite where muscovite percent dominates over biotite. The other major minerals are quartz, plagioclase and K-feldspar. Zircon, epidote and allanite occus as accessory phases. Tectono-stratigraphic models of the MRG structural recess are tested in the light of the Rb-Sr whole rock age, U/Pb zircon dates and Nd model ages of the MRG. The theories that are tested are either 1) whether MRG represents Grenville basement to the Talladega Group or 2) it is one of the numerous Paleozoic intrusion within the eastern Blue Ridge terrane. Fresh samples of MRG was collected to look at the U-Pb age of the zircon, Rb-Sr whole rock age and Nd model age to check the emplacement age as well as its connection with the Grenville basement.

1.4 Purpose of the Study This study will focus on the geochemical and geochronological constraints on the origin and evolution of different tectonic divisions of the eastern Blue Ridge, southern Appalachians. A major problem in Appalachian geology is the lack of Taconian deformation in the southern Appalachians. The eastern margin of Laurentia was curved into bays and promontories during opening and closing of the Iapetus ocean. Talladega belt (now within Alabama recess) originated as a continental promontory. During continental collision, the protruding promontories should first record the deformation. The absence of any Taconic deformation events in the Talladega belt rocks (outermost preserved portions of the Laurentian margin in the southern Appalachian) implies that a major promontory of the Laurentian margin might have escaped the effects of Taconic orogeny (Tull, 1998). As in the central Appalachians, it is difficult to appeal to subduction beneath a proven Ordovician arc as a deformation mechanism for the southern Appalachians. This study will use geochemical and geochronological data supported by detailed field maps to investigate whether or not the PCF formation can qualify for the Ordovician Arc. The PCF and Hillabee, exist only as fragments, unlike the Taconic arcs of the New England Appalachians (e.g. Bronson Hill arc) and the Ordovician northern Appalachian arcs (e.g. Chopawamsic Terrane) that commonly include typical arc related features such as voluminous arc-related sediments, accretionary wedge, and evidence of accretion in the foreland. If the PCF and Hillabee are the remnants of the Ordovician volcanic arc, the tectonic setting, timing and

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style of the Taconic orogeny in southern Appalachians and formation of the arc-related terranes took place in an environment very different from the Ordovician arcs of the northern and central Appalachians. Possibly the arc in the southern Appalachian formed during Ordovician but remained outboard of the Laurentian margin until terminal closure of the Iapetan Ocean. The goal of this research is to propose a tectonic model for the southern Appalachians during Taconic orogeny. The study will be based on new detrital/magmatic zircon ages, major and trace element analysis and Sr and Nd isotopic compositions of major tectonic units from southern Appalachians tectonic divisions west of the Brevard fault zone.

1.5 Analytical Techniques 1.5.1 ICP MS Trace Element Analysis Trace elements for the PCF amphibolites, HG, GFG and Hillabee metadacite were determined by solution ICP-MS analysis using a ThermoFinnigan Element. Small chips of each sample were handpicked and crushed in agate mortar and pestle. Thirty mg of each sample was weighed into screw top Teflon beakers and dissolved with 2 ml of 3:1 distilled HF-HNO3. After drying on a hot plate at 120oC, the samples were allowed to reflux overnight in concentrated HNO3. Samples were then dried again and brought to a final volume of 60 ml with 2% HNO3. The sample solutions were further diluted in the ICP vials for target concentration of 100 ppm TDS. One ppb of Indium was added as internal standards and drift corrections for each analyzed mass were applied by interpolating with the internal standard. The solution ICPMS analyses of the amphibolites and greenstones were calibrated against a single solution of well-characterized Hawaiian basalt USGS standard BCR-1 prepared identically to the samples. For the felsic samples G2 was used as the USGS standard. BHVO-1 was also prepared like a sample and calibrated against the BCR-1 and G2 to check the precession of measurement. 1.5.2 Sr-Nd Isotopic Analysis Fresh whole rock samples chosen for whole rock analysis of Sr and Nd were powdered in an agate mortar and dissolved in a 3:1 mixture of 2X distilled HF: HNO3. Separation of Sr and Nd followed ion exchange procedures employing 4.5 ml of AG50W-X8 9-cm bed-length ion exchange resin. Nd was separated as a bulk REE fraction and eluted in 6 N HCl. Nd and the REE fraction was further separated on a 1.2 ml, 6 cm bed-length column of Ln resin SPS. Measurements were made on a Finnigan-MAT 262 mass spectrometer. Strontium measurements are reported relative to the measured value of the E&A Sr standard of 87Sr/86Sr = 0.708000 ± 11 (2sd, n = 15) and Nd relative to the measured LaJolla standard 143Nd/144Nd = 0.511848 ± 11 (2sd, n = 12). n= number of analysis, each analysis being the average of 100 ratios. 1.5.3 Rb/Sr Ratio Measurement in ICP MS A precise method for Rb and Sr ratio measurements for samples (GFG) with low Rb/Sr ratios ( Pb207/U235 > Pb206/U238. The Ortega Quartzite samples on the concordia diagram intersects the chord (upper intercept) at 1830 Ma (Maxon, 1976). Throughout northern New Mexico metamorphic conditions are characterized by the co-exsistence of all three aluminosilicate polymorphs. In the Rinconada Formation, garnet-biotite thermometry indicates temperatures of 530 +/- 30 °C at 4 kbar (Holdaway and Goodge, 1990). Currently, the absolute timing of peak metamorphism in northern New Mexico is debated (Bauer and Williams, 1994; Grambling, 1989). The Rb-Sr whole rock and 40Ar-39Ar muscovite and hornblende mineral ages regionally yield ages of ca. 1.4 Ga and younger, implying that much of the metamorphism may be of this age (Mawer et al. 1989; Thompson et al. 1991; Grambling and Dallmeyer, 1993). On the other hand, U-Pb zircon ages of ca. 1.65-1.7 Ga from plutons which cross-cut strongly deformed supracrustal rocks are consistent with earlier fabric development. Karlstrom et al. (1994) suggest that locally a later (1.4 Ga) 500-600 °C, 4-5 kbar metamorphism is superimposed on an earlier (1.6 Ga) 700-800 °C, 7-9 kbar metamorphic assemblage.

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Barker (1958) reported a pegmatitic hydrothermal event that produced numerous pegmatite injections, including the Harding Pegmatite in north central New Mexico. Gresens (1975) related the emplacement of the pegmatites to the regional metamorphism and associated them genetically with metasomatically altered metarhyolite. Most pegmatite bodies are quartzofeldspathic, with the exception of Li-rich Harding pegmatite. Montgomery (1953) assumed that the source for all pegmatite units is the Embudo Granite, which intrudes bedded Precambrian formations. Long (1972) dated the pegmatites of the La, Madera quadrangle to be 1425 +/- 25 Ma. His age calculation was based on Rb-Sr isotopic data from whole rocks, metamorphic muscovite and pegmatite “book muscovite”. Long (1972) concluded from low error on the age that the igneous intrusion and final stages of metamorphism appear to have ceased within a time interval too short to be resolved by the Rb-Sr method. The staurolite and garnet separates from a sample of the Rinconada Formation from the Picuris Mountains analyzed by Lanzirotti and Hanson (1997) yielded U-Pb ages of about 1461 ± 13 Ma. These data are consistent with metamorphism at 1450 Ma in northern New Mexico which results in porphyroblast growth. Table 2.1. The regional geologic history of the north-central New Mexico is summarized in the following table. AGE in Ma. GEOLOGIC EVENT ~1425

Pegmatitic event following the regional metamorphism. (Long, 1972; Gresens, 1975)

~1460

Regional metamorphism following the felsic intrusions. Peak metamorphic temperature 400-500 degrees C at 4-5 Kb pressure.(Lanzirotti and Hanson, 1997)

1480-1400

Anorogenic granitoid intrusion (Anderson, 1983, Bowring and Karlstrom, 1990)

1600

Regional metamorphism following the granite intrusion. Peak metamorphic temperature 700-800 degrees C at 7-9 Kb pressure.(Grambling and Dallmeyer, 1993) Granites and granodiorites like Maquinita granodiorite, Embudo “type” granite intruding the mafic complex and/or the metasedimentary sequence (Fullager and Shiver, 1973; Gresens, 1975). Tres Piedras Granite intrusion (Maxon, 1976) Deposition of the Hondo Group. It is thought to be a cratonic margin sedimentary sequence. (Bingler, 1974)

1650-1750