Petrogenesis of a sapphirine-bearing meta-troctolite in the Buck Creek ultramafic body Clay County, North Carolina, USA

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Petrogenesis of a sapphirine-bearing meta-troctolite in the Buck Creek ultramafic body Clay County, North Carolina, USA

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Petrogenesis of a sapphirine-bearing meta-troctolite in the Buck Creek ultramafic body Clay County, North Carolina, USA
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Tenthorey, Eric Alexandre
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Tampa, Florida
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University of South Florida
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English
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vii, 74 leaves : ill (some col.) ; 29 cm.

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Sapphirine -- North Carolina -- Clay County ( lcsh )
Metamorphic rocks -- North Carolina ( lcsh )
Dissertations, Academic -- Geology -- Masters -- USF ( FTS )

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Thesis (M.S.)--University of South Florida, 1994 Includes bibliographical references (leaves 40-44).

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University of South Florida
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Universtity of South Florida
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All applicable rights reserved by the source institution and holding location.
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020133425 ( ALEPH )
32866098 ( OCLC )
F51-00115 ( USFLDC DOI )
f51.115 ( USFLDC Handle )

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Graduate School University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL Master's Thesis This is to certify that the Master's Thesis of ERIC A. TENTHOREY with a major in Geology has been approved by the Examining Committee on July 25, 1994 as satisfactory for the thesis requirement for the Master of Science degre e Examining Committee: -----------------------Co-Major Profess: }e.fftlty(9 Ph.D Co-Major Professor : Eleanour Snow, Ph.D. Member: David Naar, Ph.D.

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DEDICATION I dedicate this work to my parents and to the taxpayers of America because they re the ones who made it possible for me to come this far.

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ACKNOWLEDGEMENTS Many thanks to Dr. Charles Prewitt and Chris Hadadiakos for allowing us access to (and for their help with) the Geophysical Laboratory microprobe. Thanks to Dr. Steve Shirey and Dave Kuentz for their assistance with the ICP at the Department of Terrestrial Magnetism. The helpful insight from Dr. Stephen Yurchovich and Dr. Jim Meen is much appreciated as is Phil Austin's able assistance in the field. Most of this study was funded, thanks to grants from the Geological Society of America and Sigma Xi. Many thanks to Chad Gunter for his contribution to the sample set. Finally, I extend my deepest gratitude to my parents (and you too Coco), whose moral and financial assistance helped make life easier

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TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES ABSTRACT 1. INTRODUCTION 2. REGIONAL GEOLOGY 3 MINERALOGY & PETROLOGY Field Relations Petrography 4 ANALYTICAL METHODS 5. RESULTS Mineral Compositions Occurrence of Sapphirine Geochemistry lll lV v 1 4 7 7 8 1 3 15 15 17 21 6 DISCUSSION 25 Thermobarometric Constraints 2 5 Sapphirine Stability 26 Geochemical Constraints on Buck Creek Petrogenesis 3 1 Metamorphic and Tectonic History 3 4 7 CONCLUSIONS 39 REFERENCES 40 APPENDICES 45 APPENDIX 1 MICROPROBE COMPOSITIONS OF MINERALS AT BUCK CREEK 46 1

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APPENDIX 2. BULK CHEMICAL AND TRACE ELEMENT ANALYSES OF BUCK CREEK ROCKS 65 APPENDIX 3. COLOUR X-RAY IMAGES OF BUCK 67 CREEK TROCTOLITES ii

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LIST OF TABLES Table 1 Electron Microprobe Analyses of Common Minerals in Corona-Bearing, Central Troctolites 16 Table 2. Average Electron Microprobe Analyses of Minerals i n Marginal Troctolites 20 Table 3. Electron Microprobe Compositions of Sapphirine and Associated Minerals as seen in Figure 4b 23 Table 4. Bulk Chemistry and Trace Element Analyses for Selected Troctolites, Dunite and Amphibolite 24 Table 5. Microprobe Compositions of Minerals at Buck Creek 46 Table 6. Bulk Chemical and Trace Element Analyses of Buck Creek Rocks 65 iii

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LIST OF FIGURES Figure 1. Map of Buck Creek Dunite and Metatroctolite Lenses 2 Figure 2. Photograph of Contact Between Troctolite and Dunite 9 Figure 3. Photomicrographs of Buck Creek Troctolites 11 Figure 4. Electron Backscatter Images of Buck Creek Troctolites 1 8 Figure 5 Elemental Co-Variation Diagrams 22 Figure 6. Proposed Model for the Metamorphic Evolution of the Buck Creek Ultramafic Body 30 Figure 7. Elemental Co-Variation Diagrams 33 Figure 8. Colour X-Ray Image of Buck Creek Troctoli te 67 Figure 9. Colour X-Ray Image of Buck Creek Troctolite 68 Figure 10 Colour X-Ray Image of Buck Creek Troctolite 69 Figure 11. Colour X-Ray Image of Buck Creek Tr octo lite 70 Figure 12. Colour X-Ray Image of Buck Creek Troctolit e 71 Figure 13. Colour X-Ray Image of Buck Creek Troctolite 72 Figure 14. Colour X-Ray Image of Buck Creek Troctolite 73 Figure 15. Colour X-Ray Image of Buck Creek Troctolite 74 iv

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PETROGENESIS OF A SAPPHIRINE-BEARING METATROCTOLITE IN THE BUCK CREEK ULTRAMAFIC BODY, CLAY COUNTY, NORTH CAROLINA, USA by ERIC ALEXANDRE TENTHOREY An Abstract Of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology University of South Florida August 1994 Major Professors: Jeffrey G. Ryan, Ph.D Eleanour Snow, Ph.D. v

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The Buck Creek ultramafic body, western North Carolina, is cross-cut by a series of aluminous lenses that have been described as metamorphosed troctolites. These lenses exhibit several distinct mineral assemblages, each recording a different stage of metamorphism. The first stage is characterized by the anhydrous reaction of primary olivine and plagioclase, r esulting i n a coronal texture consisting of orthopyroxene + clinopyroxene/ spinel symplectite. Thermobarometric calculations indicate that this assemblage formed at P= 6-7 kbar and T 825C In some of the coronal samples, sapphirine is observed, either in a symplectic relationship with clinopyroxene, or as anhedral grains within amphibole. The presence of sapphirine indicates that these assemblages formed at P = 9-10 kbar and T 8500C. The margins of the troctolite l e nses are dominated by a hydrate d mineralogy consisting of plagioclas e, zoisite margarite, amphibole and corundum, an assemblage that possibly formed during retrogressio n Bulk chemical and trace element data for the Buck Creek troctolites suggest that the protolith was an adcumulate composed of magnesia n olivine and calcic plagioclase. Trace e l ement systematics of the troctolites correlate with r esults for the adjacent Chunky Gal amphibolites, suggesting that the Buck Creek and Chunky Gal cumulates crystallized from a magma derived from an enriched mantle source. It is proposed that the Buck Creek dunite and troctolite represent basal cumulates and/ or uppermost mantle rocks formed in a marginal basin in the L a test Precambrian Eastward subduction during closure of this basin r esul ted VI

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in burial of this crust which led to the formation of pyroxene spinel coronas The onset of the Taconic orogeny in the Ordovician resulted in the emplacement of the Buck Creek ultramafic into the base of a collisional pile where conditions were appropriate for sapphirine formation. Abstract Approved: Abstract Approved: Co-Majo r l'rote'S'sor : Jeffrey G Ryan Ph. D Assistant Professor Department of Geology Date Approved: Co-Major Professor : Eleanour Snow, Ph.D Assistant Professor, Department of Geology Date Approved: vii

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1 1. INTRODUCTION The Buck Creek dunite, western North Carolina is an alpine-type ultramafic body located in the Blue Ridge Province of the southern Appalachians (figure 1) Within the ultramafic body are a series of aluminous lenses which, based on field and petrographic studies, have been described as troctolites (Hadley, 1949) Metamorphism of these troctolites occurred largely under dry conditions, during which primary olivine and plagioclase reacted to form a coronal assemblage consisting of orthopyroxene and clinopyroxene/ spinel symplectite. They also reacted in the presence of water, resulting in assemblages comprised of amphibole, zoisite, margarite and corundum. In several samples, rare sapphirine occurs in symplectic relationships with clinopyroxene, and as small, anhedral inclusions within amphibole. The observation of sapphirine in this ultramafic association provides important constraints to the metamorphic history of Buck Creek, and by extension the southern Appalachians, and has implications for the petrogenesis of the many other alpine-type ultramafic bodies in the r egio n. Although sapphirine has not been reported in the southern Appalachians, its presence in the Buck Creek troctolites is not unreasonable since lithologies containing sapphirine are necessarily Mg, Al-rich rocks metamorphosed to the upper amphibolite and granulite facies The stable coexistence of clinopyroxene and sapphirine is, however, quite rare, reported in only three other localities : an alpine ultramafic massif in Pinero Italy (Lensch, 1971; Sills et al., 1983), and in nodules from New South Wales, Australia (Griffin & O'Reilly 1986) and Stockdale Kansas (Meyer & Brookins,

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Study Area \ Georgia Buck Creek Dunite Central Meta-troctolite Meta-troctolite Indicates sample locality 50 lOOm Figure 1. Map of Buck Creek Dunite and Meta troctolite Lenses. Modified from Hadley (1949). Most contacts are inferred. Dashed lines represent minor faults. N

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3 1976) Past work at these localities and on the theoretical stability of sapphirine + clinopyroxene (Christy, 1989) indicate that this association is stable at depths corresponding to the base of the continental crust. The purpose of this study is two-fold : first, we use mineralogical evidence from the metatroctolite and thermobarometric data (where applicable) to unravel the metamorphic history of the Buck Creek massif. Second, we examine bulk rock composition and trace element geochemistry of aluminous rocks, to try and determine the geologic environment in which these troctolites crystallized and to compare their chemical signatures to those of the surrounding Buck Creek amphibolites We will then synthesize our findings to reconstruct the petrogenetic history of the Buck Creek body, beginning from a likely origin as ultramafic cumulates and upper mantle rocks.

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4 2. REGIONAL GEOLOGY Alpine-type ultramafic bodies in the Blue Ridge province form a well defined chain trending NE from Alabama into southern Virginia (see review by Misra & Keller, 1978, and references therein). The majority of these units are small, variably serpentinized bodies of recrystallized dunite, though a small number of these units show evidence for more pervasive metamorphism. For the most part, they are enclosed either in basement gneisses and metasediments of the late Precambrian (Hatcher & Butler, 1979), or in the early Paleozoic Ashe Formation (Rankin, 1993). These ultramafics are widely believed to have been emplaced in the crust during the Taconic deformation event (-440-420 Ma) They have been described either as slivers of oceanic crust and lithosphere that were emplaced during collision (Hatcher 1978), ultramafic diapirs upwelled from the mantle (Stevens et al. 1974) or ophiolite blocks in a tectonic melange (Brown, 1976 ; Lacazette & Rast, 1989) The Buck Creek dunite body is in the north-central portion of the Chunky Gal Mountain mafic -ultramafic complex. This complex consists predominantly of amphibolites that have been interpreted as metamorphosed gabbroic cumulates (McElhaney & McSween, 1983; Walter, 1990) Although no one has yet shown a chemical relationship between the amphibolites and the dunite, spatial and tectonic evidence suggest an intimate association. The complex lies within the Hayesville thrust sheet, and is bounded to the west by the Chunky Gal Thrust. Most of the enclosing rocks are garnet muscovite schists and biotite gneisses which either represent Grenvillian basement, or parts of the Tallulah Formation and Coweeta Group

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5 (Hatcher & Butler, 1979) In the past, the Chunky Gal complex has been of great interest to Appalachian geologists mainly because it includes (in the Buck Creek dunite) the largest ultramafic exposure in the southern Appalachians, and because Buck Creek is one of the few ultramafic bodies in the region which possesses more than one primary lithology. Detailed information on the geology of the Buck Creek area may be found in Hadley (1949), Kuntz (1964), Sailor & Kuntz (1973) McElhaney & McSween (1983), Lacazette & Rast (1989), Meen & Lacazette (1989), Ranson et al. (1991), and Farrier & Ranson (1994) In western North Carolina, rocks of the Hayesville thrust sheet are generally upper amphibolite to lower granulite facies Thermobarometric studies on metapelites from two locations northeast of Chunky Gal Mountain indicate granulite facies metamorphic conditions. Eckert et al. (1989) suggest peak conditions of 842C 9.8 kbar in the Wayah granulite terrane while Absher & McSween (1985) suggest 775 C and 7 kbar at Winding Stair Gap, approximately 7 km east of Buck Creek along US Highway 64 Work by McElhaney & McSween (1983) on the Buck Creek amphibolites indicate temperatures of 725C and pressures up to 6 kbar, although these values may be recording retrograde conditions. Meen & Lacazette (1989) report temperatures of 800C, and pressures of 7 kbar for the enclosing metapelites at Chunky Gal. All units associated with the Hayesville thrust sheet in North Carolina are viewed to represent deep crustal rocks, and, according to isotopic evidence, attained their peak metamorphic grade during the Taconic (Ordovician) orogeny (Dallmeyer 1975a, b) Several mechanisms have been proposed specifically for the emplacement of the Chunky Gal complex McElhaney & McSween (1983) suggest two alternatives : 1) the entire complex represents the basal section of

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6 an ophiolite that was emplaced into the lower crust during the Taconic orogeny, or 2) the Chunky Gal amphibolites represent plutonic rocks that were later intruded by an ultramafic diapir. Based on structural evidence, Lacazette & Rast (1989) propose that the complex is part of a tectonic melange that formed preceding a continent-continent or island arc-continent collision of Taconic age. Since the Appalachians have undergone several deformational episodes, the development of a consensus model has been difficult

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7 3. MINERALOGY & PETROLOGY Field Relations The meta-troctolite lenses within the Buck Creek dunite are elongated bodies 30-100 m long and 30-50 m wide (figure 1). The contacts between these units and the dunite are steeply dipping at approximately 80 SE and trend NNE. A series of dip-slip faults dipping moderately to the NE have resulted in off-setting of the troctolite lenses Although the lenses are presently not exposed in most areas, trenches were previously cut and the lithologies mapped by Hadley (1949), who distinguished two major lithologies; troctoliteamphibolite near the center, and edenite-amphibolite toward their borders. In this study, our geochemical results lead us to lump these two lithologies together and call the lenses troctolites. Although the troctolit es are observed in several locations at Buck Creek, we have focussed our attention on the southern portion of the dunite, where outcrop is more prevalent. Here, the troctolites have been more resistant to erosion than the enclosing dunite and generally outcrop in elevated areas. The central portions of the troctolite lenses are composed of a weakly foliated and highly resistant lithology with a prominent bluish-gray color. These rocks include few light colored minerals, and often contain visible olivine. Intercalated within this lithology are a series of feldspar-rich bands ranging from 0.5-3.5 em, which either represent gneissic mineral segregations or primary igneous layering. Given the lack of foliation in the surrounding troctolite, the latter option may be reasonable. Toward the edges of the lenses, the troctolite becomes strongly foliated and

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8 very heterogeneous on the hand sample scale. The grain size coarsens significantly, and the lithology is hydrated, with prominent amphibole and mica along with feldspar. For the remainder of this paper, the dry, nonfoliated troctolites will be called central troctolite" while the more felsic hydrated variety will be called "marginal troctolite" Lack of outcrop precludes any resolution on the contact between the two troctolite lithologies, although compositional data from across the lenses imply this contact may be gradational. Contacts between the dunite and the troctolite are usually sharp, although in one area "wisp"-like domains of dunite encroach into the troctolite (figure 2) These contact relations resemble primary igneous features such as may result from active convection currents within a magma chamber at the time of troctolite deposition Petrography Petrographic studies of the central troctolites indicate a primary mineralogy of olivine, plagioclase and accessory chromite. The olivine and plagioclase have reacted extensively to form a mosaic of coronas, consisting of orthopyroxene closest to olivine, and clinopyroxene/ spinel symplectites nearer to the plagioclases (figure 3a). The orthopyroxene forms columnar crystals perpendicular to olivine contacts, approximately 0 2 mrn thick. The clinopyroxene/spinel symplectites average 0.3 mm wide, with individual lamellae ranging from 3-10 Jlm in width, and oriented normal to contacts with plagioclase. Electron backscatter images indicate very fine spinel coronas (SJ.l.m wide) between the orthopyroxene and the clinopyroxene/spinel symplectite (figure 4a). Although the reaction of primary olivine and plagioclase necessarily occurred under dry conditions, variable amounts of

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Figure 2. Photograph of Contact Between Troctolite and Dunite. Note the encroachment of dunite into troctolite at the left and top of photo. 9 later-stage amphibole are usually present. The central troctolites are finely and appear to have bee n nearly impermeable to infiltrating solutions. Backscatter images show amphibole replacing symplectic clinopyroxene and resorbing spinel in a few specific areas (figure 4b). Lat e stage serpentine is also observed along fractures in some cr o ss cutting olivine and sometimes orthopyroxene (figure 3b). The marginal troctolites are distinct from the central troctolites macroscopically and petrographically Plagioclase and chromi te are the only primary phases recognizable in thin section. The rock is dominated by a fine foliated matrix composed of zoisite m arga rite and euhedral corundum grains averaging 1 mm in diameter (figur e 3c )

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10 McElhaney & McSween (1983) reported kyanite in these rocks, although w e have identified none in our samples. In the marginal troctolites geochemical data together with the absence of remnant olivine indicates that corona formation was limited (if present) due to the paucity of primary olivine As a result, large clusters of plagioclase remained which probably facilitated fluid flow relative to the central troctolites. Since this lithology appears to preserve a retrograde assemblage, most of the emphasis in this paper will be given to the central troctolites

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11 a) Figure 3. Photomicrographs of Buck Creek Troctolites. a) Coronal assemblage observed in central troctolites consisting of plagioclase (plag), clinopyroxene/spinel (cpx/sp) symplectites, orthopyroxene (opx) and olivine (ol). Length of photograph : 1.3 mm. b) Same assemblage as in a), also showing late stage serpentine (serp). Length of photo : 3 mm. c) A predominantly hydrated mineral assemblage from the marginal troctolite, consisting of corundum (cor) margarite (mg) and zoisite (zo). Length of photo: 3 mm.

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12 b)

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13 4. ANAL YriCAL METHODS Mineral compositions were determined using the JEOL Superprobe at the Geophysical Laboratory of the Carnegie Institution of Washington. Beam conditions were 15 kV, with a beam current of 30 nA and spot size of 3-4 Jlm Basalt was used as a standard for Mg, Al, Si, Ca Ti Fe N a and doped diopside for Ni and Mn. Counting times varied from 40 to 120 seconds, with the longest counting times for the lowest. abundance elements. Concentrations were corrected using the ZAF correction program. All electron backscatter images were produced using the GP Lab microprobe, as were color X-ray compositional maps that were used as an aid in resolving fine-scale mineralogical variations in the symplectic samples We determined bulk chemistry and lithophile trace element abundances on our samples by plasma-emission spectrometry. The initial measurements were conducted using the J-Y 70 Type 2 IC Plasma Spectrometer at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, while later results were collected using the newly installed ARL Spectra Span 7 DC Plasma Spectrometer at the University of South Florida. Procedures for sample preparation and analysis generally follow those of Klein (1989) for mid-ocean ridge basalts (MORB) although some modifications were made to effectively dissolve ultramafic samples. LiB02 flux (0.8000 0002g) and oxidized sample powders (0.2000 0002g) were weighed into graphite crucibles homogenized, and heated in a muffle furnace at 1125 C for 15 minutes The molten fusion beads were poured into

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14 bottles containing 50. 0 ml of 2N HN03 spiked with 10 ppm Ge, and shaken until dissolved. The high fusion temperatures were necessary to prevent samples adhering to the crucibles a problem which plagued our earlier attempts to analyze these rocks At a temperature of 1125 C even dunite samples from Buck Creek were readily extractable. 2.5 ml aliquots of these initial solutions are weighed into bottles and diluted with 47.5 ml of 2N HN03 (with 10 ppm Ge), for major element analysis. The remaining concentrated solution was used to analyze for trace elements. When analyzing major elements by DCP the HN03 used in the major element dilution also contained 1000 ppm Li which acts as a peak enhancer We used Ge as an internal standard in all bulk analysis runs. We developed calibration curves for all elements using combinations of the USGS standards DTS-1, BIR-1, W-2 and DNC-1; NBS 688, and the JP-1 peridotite and JF-1 feldspar standards of the Geological Society of Japan. Sample S-16a and S-46 was run with every set of unknowns to track reproducibility The percent error for each element is shown on Table 4.

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15 5. RESULTS Mineral Compositions Typical microprobe analyses of minerals observed in the coronabearing, central troctolites are shown on Table 1. KzO is not tabulated since preliminary analyses indicated that none is present in any of the minerals contained within the Buck Creek troctolites. Olivine is relatively homogeneous at F039, identical to the surrounding dunite. Plagioclase is generally calcic, but compositionally variable, ranging from An87-99, and Oro. The highest An contents appear to be associated with fractured domains, where hydrated minera l assemblages have formed. Chromite is Fe and Al rich, and also is quite variable. Mg/ (Mg+Fe) and Cr/(Cr+Al) are usually 0.40.5, and 0.34-0.48, respectively. These values are similar to those for chromites in other alpine peridotites (see Haggerty, 1991, and references therein), though they may have undergone significant re-equilibration during metamorphism. Pyroxenes present in the coronas approach endmember diopside and enstatite, having Mg numbers of 0.94 and 0.88, respectively. The symplectic spinel is Mg-rich and contains minor silica, which may be a sign that the probe beam fluoresced slightly into clinopyroxene domains. Coronal phases appear compositionally uniform, except for orthopyroxene which does show a slight increase in Al away from remnant olivine grains. The amphiboles observed in all the troctolites are aluminous hornblendes which show little compositional variability.

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Tab l e 1 E l ectro n Microprobe Anal yses of Common Mi n erals in Corona-Bearing, Central Troctolites. All data s hown below a r e ave r ages of selec t e d a n alyses tabulated in Appendix 1 except for orthopyroxene data, w hic h a r e individual analyses <<<<<<<<<<<<<<<<<<<<<<< Co ronal T r a v e r se >>>>>>>>>>>>>>>>>>> o livine opx cpx spinel p lag a mph chromite S i02 4 0 49 .37 57 028 56.404 56.032 52.74.39 0.38 .48 44 66.80 44 32.89 0.00 Al203 0 00 0 778 1.809 2.281 3 16 .67 67.00 .90 35 39 63 16.37 1.03 33.30 .27 FeO 10. 80 .3 5 7.956 8 .00 8 8.254 1.93 23 9.81 67 0.05.05 3.93 .74 22.69 .89 MnO 0.15. 03 0 15 1 0.160 0.166 0.06 02 0 06.02 0.00 .01 0.05 .01 0 02.02 MgO 49.03 67 34.172 33.6 1 4 33.227 17.1 7.53 21.10 .67 0 00 17 09 63 9.46 .87 CaO 0 0 1 .01 0.140 0 177 0.168 23.96 67 0.29 19 18 85 .73 13 14.74 0.04.03 Na20 0 00 0.000 0 .001 0.0 0 9 0.32 .17 0 .01 .01 0.91 36 2 27.64 0 02 0.02 Ti02 0 .01 .0 1 0 017 0 000 0 012 0.02 03 0.01 .01 0 .01 .01 0 02.02 0.13 .01 C r203 0.01 .0 1 0.026 0 000 0.000 0 .06 .16 0.02.06 0 .01 .01 0.02 .01 33.90 .71 NiO 0 39 12 0.070 0.073 0.029 0 .03 03 0 30.08 0 .01 .01 0.05 .02 0.07.03 T o t a l 100 89 1 00.34 100 .25 100 18 99.46 99 .97 99.89 97.26 99.62 M g # 0.89 0.88 0 88 0 .88 0 .94 0.78 0.90 An# 87 65 ......

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17 Microprobe compositions of minerals observed in the marginal troctolites are shown on Table 2. Occurrence of Sapphirine Due to the fine-grained nature of sapphirine in the Buck Creek rocks many of the textural relationships could only be resolved using electron microprobe backscatter images. Backscatter images reveal that sapphirine occurs in two mineralogic associations within the central troctolites. The first, and most important occurrence is in symplectic relationships with clinopyroxene. Here, sapphirine replaces the spinel in the symplectites and results in a slight coarsening of the symplectic lamellae (figure 4b). The sapphirine domains are distinctive in that they are not resorbed when amphibolitization takes place. This association is always observed near the contact of the clinopyrox ene/ spinel symplectites and plagioclases. Sapphirine is also observed along the edges of the aforementioned anorthite layers, where it occurs both as anhedral grains and elongated domains growing along cleavage planes within amphibole (figure 4c). The direction of elongation in figure 4c may represent amphibole cleavage or cleavage planes of a previously existing mineral that has since been amphibolitized. Small spinel blebs are also present within the amphibole. Most sapphirine analyses plot very close to th e ideal 7:9:3 composition, although several anhedral grains within amphibole are more aluminous. Only three analyses of the symplectic sapphirine are reliable since the others possessed 1-3 wt% CaO, indicating that fluorescence of the probe beam encroached into the surrounding clinopyroxene. Clinopyroxene domains adjacent to sapphirine show an increase in AI relative to nearby

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18 a) Figure 4 Electron Backscatter Images of Buck Creek Troctolites. a) Image of the contact between orthopyroxene and clinopyroxene / spinel coronas All symbols as in figure 3 b) Image showing the replacement of spinel symplectites by sapphirine (sa). Surrounding amphibole (amph) resorbs spinel but does not appear to affect sapphirine. c) Anhedral sapphirine grains within amphibole. All scales are at base of images

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19 b) c)

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Table 2. Average Electron Microprobe Analyses of Mine rals in Marginal Troctolites margarite zoisite corundum amphibole Si02 32.63 67 39 .41 .33 0.00 45 17 Al203 48 62 .46 32.64.63 99 .74. 42 15 94 FeO 0 .48. 23 1.41 69 0 22 .014 4.37 MgO 1.60 73 0.03 02 0.00 16. 44 CaO 10 06 73 24.81 .11 0 .04. 02 12. 35 Na20 1.58.32 0.01 .02 0.00 2 64 Cr203 0 .16 .20 0 .01 .01 0.44 .73 0.3 5 Total 95 12 98.32 100.44 97 .26 plagioclase 43.54 .56 35 93.27 0.05 05 0 00 19.55 .33 0.44 22 0.01 .01 99.51 N 0

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21 clinopyroxene associated with spinel. Table 3 shows microprobe analyses of spinel, sapphirine and clinopyroxene such as is seen in figure 4b. Geochemistry The bulk rock and trace element chemistry of the Buck Creek troctolite is highly variable (Table 4 & Appendix 2). All samples are highly silica undersaturated, with compositions ranging from very Mg-rich to nearendmember anorthite. Na and especially K concentrations are generally low, with the highest values being found in the hydrated marginal troctolites Incompatible trace elements such as Zr Y, and P were below detection limits Figures Sa and Sb are major element plots that show the compositional variability of the troctolites. The linear correlations on these diagrams are easily interpreted as a mixing of anorthite and olivine in subequal proportions. Even if some of the mineralogical variability observed in the troctolites represents a metamorphic reorganization of phases, our geochemical data suggests a bimodal protolith. Although many primary textural features have been lost, the relict mineralogy and the geochemistry indicate a cumulate origin.

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40 -Anorthite a ..-.... s'2. 30 a ....._, 20 a ('<') 0 N 10 Olivine < \ 0 r:'l-... 0 10 20 30 40 50 MgO (wt%) 40 I':LAnorthite b a ........, [JI!IIfl .,_... 20 r:::JI:l 1!1 0 a:Jr#l co u Olivine \ 0 1':'11':'1 0 10 20 30 40 so MgO (wt%) Figure 5 Elemental Co-Variation Diagrams Element co-variation diagrams of a) Al203 vs MgO and b) CaO vs MgO for metatroctolites and dunites from Buck Creek. Error bars are within data points 22

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Table 3 Electron Microprobe Compositions of Sapphirine and Associated Minerals as seen in Figure 4b Cpx-Sa pphirine symplecti te Cpx-Spine l symplectite Surrounding cpx sap ph cpx spinel Amphibole Si02 50 928 12.429 53.090 0.043 44.194 Al203 5 010 66.105 2.349 68.127 16 .963 FeO 1.874 3.668 1.824 10.423 3.417 MnO 0.086 0.024 0.047 0 .036 0.059 MgO 16.969 18.105 16.835 21.072 17.396 CaO 23. 675 0.040 24.799 0.041 12.702 Na20 0 162 0.000 0.162 0.007 2 .378 Ti02 0 049 0.000 0.000 0.000 0.009 Cr203 0 014 0.013 0.000 0.034 0 .00 0 NiO 0.011 0.019 0 010 0.326 0.074 Total 98.778 100.403 99.116 100 109 97.192 Mg/(Mg+Fe) 0.942 0.898 0.943 0.783 0.901 N (.))

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Table 4. Bulk Chemistry and Trace Element Analyses for Selected Troctolites, Dunite and Amphibolite. central troctolite s16a bc2 Si02 43.03 44.12 Al203 15.08 16.92 Fe203 6.40 5 86 MnO 0.09 0.08 MgO 26 25 22.41 CaO 8 17 9.60 Na20 0.47 0.74 K20 0 .01 0.01 Ti02 0.01 0.05 LOI 0.22 1.03 Total 99.72 100.83 Ni 1164 1243 Cr 528 631 Sr 169 163 Ba 14 5 Cu 16 21 Zn 33 30 y n d n.d Zr n d n d ,. represents percent of amount of element present n.d.: not detectable margmal troctolite s39 s18e 35.47 41.49 24 68 24.18 12 39 4.34 0.10 0.06 13.90 16.45 10.45 10.77 2 36 1.87 0.19 0 07 0 .01 0 .01 0 89 2.35 100.45 101.58 1180 1094 1793 1599 147 120 60 40 19 6 445 30 n d n.d n.d n d anorthite amphibollte dumte layer s46 s41 d1 45.16 47.24 39.42 35 08 15.39 0.68 0.34 9.85 11.76 0.00 0.16 0.16 0.41 11.37 47.77 18.43 10.13 0.23 0.87 4.40 0.04 0.02 0.35 n.d 0.01 1.10 0.02 0.70 0.48 1.75 101.02 100.47 101.84 61 533 3532 38 586 3736 303 232 3 12 177 1 17 81 3 7 50 48 n d 30 n d n.d 78 n.d %error* 1 1 1 7 1 4 2 60 20 35 25 8 40 10 25 N ,p.

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25 6. DISCUSSION While mineralogically complex, the troctolite lenses of the Buck Creek dunite are geochemically rather simple Our understanding of the protolith permits a relatively straight-forward interpretation of the unit's metamorphic evolution, which we can then compare to that reported for the nearby amphibolites, and to other high grade assemblages from the region Thermobarometric Constraints We have applied two-pyroxene thermobarometry to the coexisting coronal pyroxenes in order to obtain specific PT estimates for corona formation. First, temperatures were calculated using the opx-cpx thermometers of Wood & Banno (1973) and Wells (1977) These thermometers are primarily dependent on FeMg partitioning into co-e xisting pyroxenes; the Wells (1977) thermometer is theoretically better calibrated to Mg-rich compositions. Using experimental constraints for the reaction An + 01 = Opx + Cpx + Sp, we then use these calculated temperatures to estimate the minimum pressures of corona formation. Thermometry calculations were performed on six pyroxene pairs which showed no evidence for retrogression. Whenever possible, probe spots were placed very to the opx-cpx contact to minimize disequilibrium effects, but in some cases the fine-grained nature of the cpx symplectite made finding such spots difficult Our results yield temperatures of 750-900 C (825 ), using the Wells (1977) thermometer and 800-950 C (875

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26 ), using that of Wood & Banno (1973). Considering the high Mg/ Fe of all the Buck Creek rocks, the Wells geothermometer probably yields the best temperature information. The range of calculated temperatures may be a result of two factors: first the fine-grained nature of the clinopyroxene symplectites may have caused fluorescence of the probe beam to encroach into adjacent spinel domains which would increase the AI content in cpx and result in lower calculated temperatures Or the formation of coronas may have taken place over a range of temperatures. Given our available data, we estimate that the main coronal assemblage of the Buck Creek meta-troctolites formed at approximately 825C. The experimental P T curves for the dry reaction An + 01 = Opx + Cpx + Sp have been determine d by Kushiro & Yoder (1966), Green & Ringwood (1972) and Herzberg (1978). Although these curves differ at extremely low and high temperatures, in the 825C range all three curves suggest pressures of about 6 kbar. On figure 6 Herzberg's reaction curve has been included, together with the possible P-T space of Buck Creek corona formation (field (2)) Sapphirine Stability Sapphirine is generally found in Mg, Al-rich terranes that h ave undergone upper amphibolit e to granulite facies metamorphism. In some cases, it is observed in basic lithologies which are intercalated with, or are in close proximity to anorthosites. In many sapphirine-bearing granulite terranes the nature of the protolith is uncertain, though they are often interpreted to be Mg-rich metasediments (see Lal et al. 1978) The relative rarity of sapphirine is due less to a restricted PT stability field than to the

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27 narrow compositional range in which it may form. The high Mg and Mg/ Mg+Fe together with the low Si in the Buck Creek troctolites provides an ideal setting for the formation of sapphirine At Buck Creek, the most striking occurrence of sapphirine is in the magnesian central troctolit es, where it is observed as symplectites within clinopyroxene and sometimes within amphibole. In all such instances, the sapphirine forms at the expense of symplectic spinel, approximating a 1:1 replacement. These symplectites are located along the outer edge of the clinopyroxene/spinel corona and are always found in close proximity to remnant plagioclase and secondary amphibole. Unlike spinel and clinopyroxene, sapphirine is resistant to resorption during amphibole formation. The formation of sapphirine from spinel requires an influx of Si and the removal of Fe (and to a lesser extent Mg and Al see Table 2a), the sources and sinks for which are uncertain. We believe that all neede d Si was derived from plagioclase, while any excess AI and Mg was absorbed by amphibole. The solid-solution nature of most of the phases in the troctolites complicates the formulation of a balanced equation. We propose the following generalized equation for the reaction: Cpx (I) + Spin + An + H20 = Cpx (II) + Sapph + Amph (1) A problem with this proposed reaction is Fe exchange. Neither sapphirine or amphibole contain significant Fe while the spinels are Pe-rich relative to all other Mg-bearing minerals A possible explanation is that pre-existing spinel acted as a repository for Fe. The Mg number for the spinel in figure 4b is lower than for all the other minerals, indicating that such a scenario is possible. Assuming that the Fe is housed in spinel, then the amount of symplectic sapphirine that can form will be limited by diffusion rates and by Fe saturation in residual spinel. These constraints may explain why the

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28 growth of symplectic sapphirine is so limited in our samples. Another possible explanation is that during metamorphism, the troctolites were within the stability field of sapphirine + clinopyroxene for only a short period of time. Regardless of the specifics as to how symplectic sapphirine formed, its observation in stable coexistence with clinopyroxene is crucial to understanding the PT history of the Buck Creek ultramafic. Clinopyroxene-sapphirine associations have only been observed in xenoliths from two localities (Griffin & O'Reilly, 1986; Meyer & Brookins, 1976) and along a mafic-ultramafic contact at Pinero, Italy (Lensch, 1971; Sills, et al. 1983). In all three cases, the sapphirine + clinopyroxene formed at pressures corresponding to the lower crust. Christy (1989) has constructed a semi-quantitative petrogenetic grid in order to evaluate the stability of sapph + cpx in the CMAS system. He concludes that in gabbroic rocks, this association is stable at pressures in excess of 9 kbar and below temperatures of 900C, provided that Mg/Mg+Fe is high. Since the Buck Creek troctolites contain little Fe and are poor in alkalis, the CMAS system is closely approximated. We can then use the petrogenetic grid of Christy (1989) to aid in deciphering the P-T history of Buck Creek rocks. The approximate field of sapph + cpx stability is shown on figure 6. Sapphirine is also observed as anhedral or elongated grains within an amphibole matrix (figure 4c), along the edges of anorthosite bands within the central troctolites. We conducted several mass balance calculations to determine whether any proportion of sapphirine + amphibole might be generated from a reasonable troctolite composition. Our results, using the microprobe data compiled in Table 3b, indicate that 10% sapphirine and 90% amphibole, as observed in our samples, corresponds to the composition of an aluminous troctolite. Thus, the troctolitic protolith contained all the

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29 necessary components to form sapphirine As in the symplectic occurrence, the presence of amphibole suggests that fluids may have contributed to the generation of sapphirine. The associated anorthosite layers may have behaved as an access-way for this fluid The presence of amphibole in association with both sapphirine occurrences suggests that water was present as an important component in sapphirine formation However under conditions of increased pH20 and low temperatures, sapphirine will break down to form chlorite + corundum + spinel. The experimentally determined location of this reaction boundary (Seifert, 1974) is plotted on figure 6 We postulate that metamorphic conditions at Buck Creek were within the field of sapphiri ne + H20 for most of its PT history. The occurrence of these two sapphirine-bearing assemblages therefore indicate formation within field (3) on fi gure 6 The importance of water in sapphirine formation has profound implications for the tectonic history of the Buck Creek ultramafic Between the time of troctolite crystallization and corona formation the system must have been dry, as any significant hydration or alteration would have disturbed the original mineralogy so as to prevent the formation of pyroxenespinel coronas. At the peak of metamorphism however the introduction of water led to the formation of sapphirine and to partial amphibolitization of the clinopyroxene/ spinel symplectites Furthermore, the preservation of sapphirine in a hydrous assemblage suggests that tectonic uplift was quite rapid, with little time for retrogression In a later section, we will draw upon this information to synthesize a tectonic model and explore the validity of previous models.

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12 10 "i:' 8 ..0 ..,_.. :::s 6 00 00 4 2 0 600 Approximate fi e ld of sapphirine assemblage s 800 1000 Temperature (OC) Primary depo s ition o f ultramafics a s cumulate s 1200 Figure 6. Proposed Model for the Metamorphic Evolution of the Buck Creek Ultramafic Body Abbreviations as follows : An=anorthite, Chl=chlorite, Cor=corundurn, Cpx=clinopyroxene, Ky=kyanite, Mg=rnargarite, Opx= orthopyroxene, Sa=sapphirine, Sill=Sill i rnanite, Sp=spinel, V=vapour, Zo=zoisite See text for discussion. References for reaction curves : (a) Seifert, 1974 ; (b)Herzberg, 1978; (c)-Perkins et al., 1980; (d)-Holdaway, 1971. 30

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31 Geochemical Constraints on Buck Creek Petrogenesis Melts extruded in oceanic environments exhibit distinct chemical signatures depending on their geologic setting Incompatible trace elements such as Zr, Y, Pare enriched in ocean island basalts and depleted in mid-ocean r idge and island arc basalts while fluid-mobile tracers such as Sr Ba and K are enriched in island arc basalts relative to mid-ocean ridge basalts and even oceanic island arc basalts. These characteristic chemical signatures may be reflected in cumulate lithologies like those found at Buck Creek The Buck Creek troctolites and dunites were mineralogically simple, consisting essentially of olivine + anorthite chromite. Figures Sa and Sb demonstrate that all the Buck Creek troctolites plot on a mixing curve between olivine and plagioclase Due to the contrasting chemical affinities of these minerals and their close associations in mafic magmatism, it is likely that such assemblages formed as magmatic cumulates Concentrations of Zr, Y and P, all fluid immobile inc9mpatible trace elements, are at or below DCP detection limits for all our samples The virtual absence of these elements in the Buck Creek rocks indicates that the troctolites contained little or no intercumulus melt, which may imply that the protolith originally possessed an adcumulate texture. If the Buck Creek troctolites were adcumulates, the only trace elements that might be of use in characterizing magmatic parent liquids would be elements compatible in the minerals present: Ni in the olivine and Sr or Ba in the feldspar. A major problem with this approach is that Ba and Sr are susceptible to metasomatic re-equilibration This problem may be circumvented at Buck Creek by carefully selecting samples. Many of the troctolites, especially those in the center of the lenses, preserve dry, prograde pyroxene + spinel assemblages which could not be produced in the

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32 presence of a fluid, or preserved during extensive late-stage metasomatism. Using only these dry samples Sr and Ba (to a much lesser extent) form linear arrays when plotted versus Ca (figure 7), indicating that concentrations of these elements in the samples are entirely plagioclase-controlled and that later metamorphism did not significantly affect their bulk rock abundances. Figure 5 allows us to calculate the modal plagioclase contents of our samples. With this information, and bulk rock Ba and Sr contents we can determine the concentration of both elements in the primary plagioclase Partition coefficients for Ba and Sr (KdBa = 0.45, KdSr= 2 4)(Henderson 1982) can then be used to calculate concentrations of these elements in the parental melt. We performed these calculations on the three most suitable Buck Creek samples. Results for these rocks were consistent and suggest Ba and Sr concentrations of 65 ppm and 195 ppm, respectively in the parental magma. These Sr and Ba abundance estimates are higher than are usually encountered in mid-ocean ridge basalts, but much lower than observed in island arcs, though similar to magnesian lavas from Iceland The Sr /Ba ratio is also lower than in mid-ocean ridge basalts and higher than in island arcs, and thus may suggest some type of enriched mantle source The amphibolites surrounding the Buck Creek dunite have also been described as cumulates (McElhaney & McSween, 1983 ; Walter 1990). Walter (1990) has examined the trace metal chemistries of these amphibolites and attempted to quantify the concentrations of various incompatible elements in the parent gabbroic liquid Her estimated liquid abundances for the Chunky Gal amphibolites : Zr=291 ppm, Y=70 ppm, P205=0.5 wt% Ti02=4. 0 wt% Nb= 18 ppm. While these values are model-dependent and may be unrealistically high, they certainly imply parental magmas derived from an enriched source, of OIB or within plate affinity.

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20 I I a b.tJ. .., b. 1--+-i ._ 10 !:::. 0 fU u 0 0 100 200 300 400 Sr (ppm) 20 I b ll 6 b. ll .., !:::. 6 ._ 10 1--.t 0 II fU 6 u o ro w ro Ba (ppm) Figure 7. Elemental Co-Variation Diagrams. Element variation plots of a) CaO vs Sr and b) CaO vs Ba for the Buck Creek troctolites and dunite (filled circles : samples showing little sign of hydration ; triangles : hydrated troctolites) Error bars for CaO are within data points See text for discussion 33

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34 Our data and Walter s (1990) work are consistent with the view that the Chunky Gal Mountain mafic-ultramafic complex and other amphibolites in the region are products of an enriched mantle Late Precambrian rift -related volcanism in the Appalachians also shows an incompatible element-enriched signature characteristic of rift-related rocks (Rankin 1976; Badger, 1993 ; Hernandez et al., 1994). Whether the Buck Creek complex represents an ophiolitic fragment (McElhaney & McSween, 1983) or blocks from a tectonic melange (Lacazette & Rast, 1989) our geochemical results are consistent with the idea that the oceanic crust in question was generated during this late Precambrian rifting event. If true then those ultramafic bodies associated with the Buck Creek dunite along the strike of the Blue Ridge front may have similar origins. Metamorphic and Tectonic History The central troctolites at Buck Creek possess a predominantly dry mineralogy which records two different stages of prograde metamorphism. The dominant assemblage consists of clinopyroxene, orthopyroxene and spinel, reflecting a dry reaction between primary olivine and plagioclase. According to our work this mineral association represents the first stage of metamorphism and records temperatures of -825 C and pressures of 6-7 kbar Subsequent metamorphism up to -10 kbar and -850 C resulted in the formation of sapphirine-bearing assemblages Amphibole and sapphirine are always in close proximity, suggesting that water played a n important role in facilitating diffusive exchange of AI and Si. F igure 6 shows the prograde metamorphic path of the Buck Creek troctolite and dunite, starting from their presumed origins at the base of the oceanic lithosphere (figure 6, field (1)). If

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35 our estimates are correct, the Buck Creek ultramafic body may record higher pressures and temperatures than have previously been determined for rocks from the southern Appalachians. The hydrated mineral assemblage observed in the marginal troctolites may either represent a high pressure, wet assemblage or one which records retrograde events. The highly foliated and fine-grained nature of the marginal troctolites made it difficult to discern paragenetic relationships between corundum, zoisite, amphibole and margarite, although the latter is observed replacing most other phases. During retrogression, margarite could have formed by one of two reactions: Anorthite+ Corundum+ H20 = Margarite (2) or 3/2 Corundum+ Zoisite + Kyanite + 3/2 H20 = 2 Margarite (3) If margarite formed by reaction (3), then kyanite was most likely the limiting reactant, since we observed non e in our samples. Based on thermodynamic calculations, Perkins et al. (1980) have determined the PT trajectories of reactions (2) and (3) in the CASH system (figure 6). Regardless of which reaction occurred, the retrograde path taken by the Buck Creek troctolites is hard to constrain given the available mineralogy and textural evidence. Recent work on the Chunky Gal complex has produced two hypotheses concerning the mechanism of emplacement for the Buck Creek ultramafic. McElhaney & McSween (1983) suggest that the ultramafic and associated mafic rocks represent a fragment of an ophiolite. Classic ophiolite associations are emplaced at relatively shallow levels in collisional piles and would thus follow for part of their evolution a low P /T trajectory not recorded in the Buck Creek rocks Also since the ultramafic sections of most ophiolites are at least partially serpentinized, the primary olivine in the Buck

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36 Creek troctolite would have been obliterated early in its PT history, precluding the formation of an anhydrous corona assemblage Lacazette & Rast (1989) propose that the mafic and ultramafic rocks at Buck Creek were blocks in a tectonic melange Since most tectonic melanges are composed of lithologies derived either from the hanging wall (ie mantle wedge or accretionary prism) or from surficial parts of the slab, it is hard to envisage a scenario whereby deep seated rocks in the downgoing slab (dunites and troctolites) are scraped off and incorporated into the sedimentary pile. Furthermore, the early stages of a tectonic melange are characterized by low temperatures (<200C) and are typically associated with extremely hydrated mineralogies (e.g. Spear 1993) To better decipher the petrogenetic history of the Buck Creek ultramafic body, we confine ourselves to the known tectonic framework of the Appalachians. According to Hatcher (1978; 1989) rifting during the late Precambrian opened a marginal basin along what is now the eastern United States Within this basin a series of rift-related volcanic rocks was generated that we believe may be cogenetic with many of the southern Appalachian ultramafic bodies. This basin was probably one of many marginal seas or back-arc basins located along the edges of a larger ocean basin. During Middle to Late Cambrian time, the development of an eastward dipping subduction zone resulted in closure of the marginal basin Due to the small size of the basin, subduction quickly ceased with the collision of what Hatcher (1978) terms the Inner Piedmont-Blue Ridge fragment and the continental mainland. At this point, troctolites or other ultramafic rocks at the base of the formerly subducting ocean crust would be within the stability field of opx + cpx + sp and be isolated from any hydrous fluids, permitting extensive

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37 coronal textures to form. These conditions remained static until the Ordovician, with the onset of Taconic deformation The Taconic orogeny has historically been explained as the collision of an off-shore island arc with the east coast of North America (Drake et al. 1989). However, Drake et al. (1989) emphasize that this model may not be valid in the southern Appalachians, since no volcanic rocks of Ordovician age have been recognized. We believe that the initiation of the Hayesville thrust during the Taconic deformation (Lacazette & Rast, 1989) resulted in the emplacement of portions of Late Cambrian oceanic crust into the deep crust of the Inner Piedmont-Blue Ridge fragment. At this stage the troctolites (and o ther ultramafic lithologies) interacted with variable amounts of water, resulting in the formation of sapphirine at pressures of 9-10 kbar (figure 6, field (3)) The preservation of the high pressure assemblages in the central troctolites suggests that the Buck Creek ultramafic body was uplifted quite rapidly. The hydrous breakdown of sapphirine is strongly temperature dependent; at temperatures below -700-800 C over a range of pressures, it decomposes to chlorite+corundum+spinel. Temperatures and pressures in the Buck Creek rocks must have dropped rapidly across this reaction boundary, so as to allow sapphirine to persist metastably. A possible retrograde path is shown on figure 6, path (4). According to Ernst (1988) and Spear (1993), most collisional orogens are characterized by isothermal decompression, which occurs due to rapid erosion, and/ or extensional faulting in the collisional pile Current understanding suggests that the Appalachians are such an orogen, having uplifted and exposed deep crustal rocks, many of which are ultramafic in character. The Buck Creek ultramafic is unique among Appalachian ultramafics in that it contains lenses of

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38 troctolite, which when exposed to high pressures and temperatures produce a mineral assemblage rarely seen in other high grade metamorphic terranes

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39 7 CONCLUSIONS The conclusions of this study are as follows: 1) Bulk rock and trace element geochemistry, together with petrographic evidence indicate that the meta-troctolite lenses at Buck Creek represent adcumulate igneous rocks that originally consisted of magnesian olivine and calcic plagioclase 2) Concentrations of Ba and Sr indicate that the troctolites were products of a geochemically enriched mantle, perhaps indicative of a rift-type setting. 3) The first stage of metamorphism is characterized by the dry reaction o f primary olivine and plagiocla s e to form coronas consisting of p y ro xenes and spinel. Two pyroxene thermometry suggests that the s e coronas formed at T-825C and P= 6-7 kbar. 4) The peak of metamorphism is characterized by sapphirine-bearing assemblages, which formed in the presence of H2 0 These assemblages formed at P= 9-10 kbar and T850 C and represent some of the highest pressures reported in the southern Appalachians. 5) Based on the above data we propose the following tectonic model: The Buck Creek ultramafic represents the base of an oceanic crustal section located within a marginal basin In the late Cambrian, subduction of this crust during basin closure resulted in the formation of the dry coronal assemblage. Later thrusting during the Taconic orogeny (Ordovician) emplaced this ultramafic into the lower portion of a thickened collisional pile, where the sapphirine-bearing assemblages formed

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40 REFERENCES Absher, S. A & McSween, H. Y. (1985). Granulites at Winding Stair Gap, North Carolina : The thermal axis of Paleozoic metamorphism in the southern Appalachians. Geological Society of America 588-599. Badger, R. L. (1993) Fluid interaction and geochemical mobility in metabasalts: An example from the Central Appalachians. Journal of Geology, 101, 85-95 Brown, W. R. (1976) Tectonic melange (?) in the Arvonia Slate district of Virginia. Geological Society of America Abstracts with Programs, 142. Christy, A G. (1989) The stability of sapphirine + clinopyroxene: implications for phase relations in the CaO-MgO-Al203-Si02 system under deep-crustal and upper mantle conditions. Contributions to Mineralogy and Petrology, 102, 422-428. Dallmeyer, R. D. (1975a) Incremental 40 Ar I 39 Ar ages of biotite and hornblende from retrograded basement gneisses of the southern Blue Ridge: Their bearing' on the age of Paleozoic metamorphism. American Journal of Science, 275 444-460. Dallmeyer, R. D (1975b). 40Arj39Ar age spectra of biotite from\ basement gneisses in northwest Georgia Geological Society of America Bulletin, 1740-1744 Drake, Jr., A. A., Sinha, A. K., Laird, J & Guy, R. E (1989) The Taconic orogen. In: The Appalachian-Ouachita orogen in the United States, v.F-2 of The geology of North America : Boulder, Colo Geological Society of America, 101-177. Eckert, Jr., J 0 Hatcher, Jr., R. D. & Mohr, D W. (1989) The Wayah granulite-facies metamorphic core, southwestern North Carolina: High-grade culmination of Taconic metamorphism in the southern Blue Ridge. Geological Society of America Bulletin, 101, 1434-1447. Ernst, W. G. (1988) Tectonic history of subduction zones inferred from retrograde blueschist P-T paths Geology, 1.., 1081-1084.

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41 Farrier, K R., & Ranson, W A. (1994) Metamorphosed gabbros and troctolites from the Chunky Gal Mountain complex, North Carolina: Straddling the amphibolite-granulite facies transition? Geological Society of America Southeastern Section, Abstracts with Programs, 14. Green, D. H., & Ringwood, A. E. (1972). A comparison of recent experimental data on the gabbro-garnet granulite-eclogite transition. Journal of Geology, Q, 277-288. Griffin, W. L., & O'Reilly, S. Y. (1986) Mantle-derived sapphirine. Mineralogical 635-640. Hadley, J. B. (1949) Preliminary report on corundum deposits in the Buck Creek peridotite, Clay County, North Carolina. United States Geological Survey Bulletin, v. 948-E. Haggerty, S. E. (1991) Oxide mineralogy of the upper mantle. In: Oxide Minerals: Petrologic and Magnetic Significance (ed. D.H. Lindsley). Mineralogical Society of America, Reviews in Mineralogy, v 25, 355416. Hatcher, Jr R. D (1978) Tectonics of the western Piedmont and Blue Ridge, southern Appalachians: Review and speculation. American Journal of Science, 278, 276-304 Hatcher, Jr., R. D. (1989) Appalachians introduction. In: The AppalachianOuachita orogen in the United States, v.F-2 of The geology of North America : Boulder, Colo., Geological Society of America, 1-6 Hatcher, Jr., R. D., & Butler, J. R. (1979). Guidebook for southern Appalachian field trip in the Carolinas, Tennessee and northeastern Georgia. International Geological Correlation Program, Caledonide Orogen Program Symposium, Blacksburg, Virginia, 117p Henderson, P (1982). Inorganic Geochemistry. Pergamon Press, New York, 353 pp. Hernandez, D., Gunter, C. & Ryan, J G. (1994). Geochemical affinities of metavolcanic rocks from the Mt. Rogers Formation, SW Virginia. Geological Society of America Southeastern Section, Abstracts with Programs, 19.

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42 Herzberg, C. T (1978). Pyroxene geothermometry and geobarometry: experimental and thermodynamic evaluation of some subsolidus phase relations involving p y roxenes in the system Ca0-Mg0-Al203-Si02. Geochimica et Cosmochimica Acta 12, 945-957 Holdaway, M J (1971) Stability of andalusite and the aluminum silicate phase diagram. American Journal of Science, 271, 97-131. Klein, E. M (1989). Geochemistry of ocean ridge basalts : Mantle processes revealed by major element, trace element and isotopic variations Ph. D. Dissertation Columbia University 156p. Kuntz, M A (1964). Compos ition a l, mineralogical, and textural variation in the Buck Creek dunite, Clay County, North Carolina. Unpublished M.S. thesis Northwestern University Kushiro I. & Yoder H S (1966) : Anorthite-forsterite and anorthite-enstatite reactions and their bearing on the basalt-eclogite transformation. Journal of Petrology, Z 337362. L a cazette, Jr., A. J & Rast N. (1989). Tectonic melange at Chunky Gal Mountain, North Carolina. Geological Society of America Special Paper 228 217-227 Lal, R. K Ackermand, D., Seifert F., & Haldar, S K. (197 8 ) Chemographic relationships in sapphirine-bearing rocks from Sonapahar, Assam, India Contributions to Mineralogy and Petrology, QZ, 169-187. Lensch G. (1971) Das Vorkommen von Sapphirin im Peridotitkorper von Pinero (Zone von Ivrea It a lienische Westalpen) Contributions to Mineralogy and 145-153. McElhaney, M S & McSween, Jr ., H Y. (1983). Petrology of the Chunky Gal Mountain mafic-ultramafic complex, North Carolina. Geological Society of America Bulletin, 21, 855 87 4. Meen, J. K., & Lacazette, A. J (1989). Comparative PT histories at Chunky Gal, NC and Lake Chatuge, NCGA, Blue Ridge Province. Geological Society of America Annual Meeting, Southeastern Section, Abstracts with Programs, 50 Meyer, H 0 A. & Brookins, D G (1976) Sapphirine, sillimanite, and garnet in granulite xenoliths from Stockdale kimberlite, Kansas. American Mineralogist, L 1194-1202

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43 Misra, K C., & Keller, F. B (1978) Ultramafic bodies in the southern Appalachians: A review. American Journal of Science, 278, 389-418. Perkins III, D., Westrum, Jr., E. F., & Essene, E. J (1980). The thermodynamic properties and phase relations of some minerals in the system CaOAl203-Si02-H20. Geochimica et Cosmochimica Acta, 11, 61-84. Rankin, D. W. (1976). Appalachian salients and recesses: Late Precambrian continental breakup and the opening of the Iapetus Ocean. Journal of Geophysical Research, 5606-5619. Rankin, D. W. (1993). The volcanogenic Mount Rogers Formation and the overlying glaciogenic Konnarock Formation-two Late Proterozoic units in southwestern Virginia United States Geological Survey 2029, 26pp. Ranson, W. A., Garihan, J. M., Ulmer, K. E. (1991). Metamorphic reactions in ruby corundum amphibolite from the Chunky Gal Mountain mafic ultramafic complex, Clay County, North Carolina. Geological Society of America Annual Meeting, Abstracts with Programs, A265. Sailor, R. V., & Kuntz, M. A (1973). Petrofabric and textural evidence for syntectonic recrystallization of the Buck Creek dunite, North Carolina. Geological Society of America Abstracts with Programs, 2, 791-792 Seifert, F. (1974) Stability of sapphirine : a study of the aluminous part of the system MgO-Al203-Si02 -H20. Journal of 173-204. Sills, J. D., Ackermand, D., Herd, R. K., & Windley, B. F. (1983). Bulk composition and mineral our of 1988a rocks along a gabbro-lherzolite contact at Pinero, Ivrea Zone, Northern Italy Journal of Metamorphic Geology, .1337-351. Spear, F. S. (1993) Metamorphic Phase Equilibria and Pressure-TemperatureTime Paths. Mineralogical Society of America Monograph, 799 pp. Stevens, R. K., Strong, D F., & Kean, B. F. (1974). Do some eastern Appalachian ultramafic rocks represent mantle diapirs produced above a subduction zone? Geology,, 175-178 Walter, K A. (1990). Geochemistry and trace-element models for the petrogenesis of mafic rocks in the Hayesville thrust sheet, Georgia North Carolina Blue Ridge. Ph. D. Dissertation, University of Tennessee, Knoxville, 236p.

PAGE 54

44 Wells, P. R. A. (1977). Pyroxene thermometry in simple and complex systems. Contributions to Mineralogy and Petrology, g 129-139. Wood, B. J., & Banno, S. (1973) Garnet-orthopyroxene and orthopyroxeneclinopyroxene relationships in simple and complex systems. Contributions to Mineralogy and Petrology,!, 109-124.

PAGE 55

45 APPENDICES

PAGE 56

APPENDIX 1 MICROPROBE COMPOSITIONS OF MINERALS AT BUCK CREEK Table 5 plagioclase Si02 43.985 45.684 45.791 45.351 45.202 Al203 35.961 34 458 34.718 34.516 35.117 FeO 0.136 0.035 0 025 0.054 0.017 MnO n a 0.000 0.010 0.000 0.000 MgO 0.000 0 000 0.000 0.000 0.000 CaO 19.418 17.968 17 887 17.724 18 .6 64 Na20 0.594 1.368 1.379 1.427 1.021 Ti02 n .a. 0.000 0.000 0.000 0 005 Cr203 0.013 0.031 0.007 0.011 0.005 NiO n.a. 0 010 0.019 0.000 0.000 Total 100.107 99 554 99 836 99.083 10 0.031 45.079 34.908 0.027 0.009 0.000 18.554 1.030 0.022 0.018 0.000 99.647 44.486 35.558 0.000 0.000 0.000 1 8.995 0.897 0.000 0.025 0.023 99.984 0\

PAGE 57

APPENDIX 1. (Continued) Table 5. (Continued) plagioclase (cont'd) Si02 43 098 44.635 Al203 36.654 35 805 FeO 0 041 0.060 MnO 0.007 0.013 MgO 0 002 0.000 CaO 20.408 19 018 Na20 0.181 0.827 Ti02 0 014 0.000 Cr203 0.003 0.021 NiO 0 005 0.000 Total 100.413 100 379 43.646 44.311 44.798 36.015 35.469 35.458 0 174 0 012 0.033 0.002 0.000 0.000 0.004 0 000 0.000 19.604 18 985 18.816 0.484 0.832 0 908 0.014 0 030 0.000 0.000 0.026 0.000 0.006 0.000 0 019 99.949 99.665 100 032 43.858 35.717 0 013 0.014 0.000 19.373 0.634 0 028 0.012 0.000 99 649 45 254 35 116 0.033 0 000 0 .00 1 18.526 1.122 0.000 0 000 0.025 100 077 I '-1

PAGE 58

APPENDIX 1. (Continued) Table 5 (Continued) olivine Si02 41 .051 40.546 40.803 40 653 40.134 40 140 40 134 Al203 0.007 0.007 0.000 0 000 0 003 0 007 0 000 FeO 10.627 10.640 10.808 10.560 10.399 11. 303 11.246 MnO 0 172 0 174 0.175 0.115 0 134 0 116 0 144 MgO 50 027 49.429 49.551 48.616 48 093 48.624 48 859 CaO 0 025 0 009 0.003 0.019 0.011 0.000 0 010 Na20 0 005 0 000 0 000 0.000 0 000 0 001 0 006 Ti02 0 005 0 022 0 010 0.000 0.000 0 000 0 028 Cr203 0 000 0 000 0.009 0.007 0 000 0 000 0 037 NiO 0 301 0.309 0.297 0.594 0.524 0.317 0 357 Total 102.220 101.136 101 656 100.564 99 298 100.508 100 821

PAGE 59

APPENDIX 1 (Continued) Table 5. (Continued) orthopyroxene Si02 56.588 55 022 56.087 Al203 2.467 3.676 3.574 FeO 6.888 6.948 7.064 MnO n.a. n.a. n a. MgO 34.330 33.585 34 160 CaO 0.234 0.260 0 177 Na20 0.007 0.018 0 000 Ti02 n.a. n a n a. Cr203 0 .031 0 .000 0.002 NiO n.a n.a. n.a. Total 100.545 99.509 101.064 56.046 56.101 2 288 2.171 7 .271 7 078 n.a. n.a. 33 855 34 278 0.227 0.280 0.014 0 .001 n.a. n a. 0.000 0 029 n a n.a. 99.701 99.938 55.567 3.810 7.065 n.a 33 696 0.191 0.001 n.a. 0.000 n.a. 100.330 56.480 0 684 7.387 0 .170 33 956 0.148 0 000 0 037 0 000 0 053 98.915 ,j:>. \0

PAGE 60

APPENDIX 1. (Continued) Table 5. (Continued) orthopyroxene (cont'd) Si02 56.040 57.028 56.404 Al203 1.227 0.778 1.809 FeO 7.504 7 956 8.008 MnO 0.138 0 151 0 160 MgO 33.642 34 172 33 614 CaO 0.178 0.140 0 177 Na20 0.020 0.000 0 001 Ti02 0.000 0.017 0.000 Cr203 0.000 0.026 0.000 NiO 0.064 0 070 0.073 Total 98 813 100.338 100 246 55.964 56 .051 1.941 2.206 8.001 8.073 0.178 0 164 33 449 33.311 0 146 0.129 0 000 0 000 0 038 0.000 0.003 0 031 0 029 0.026 99.749 99.991 56.032 2.281 8 254 0 166 33.227 0.168 0.009 0.012 0.000 0 036 100 185 56.231 1.899 8.147 0 175 33.567 0 108 0.003 0.017 0 014 0 063 100 224 (.11 0

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APPENDIX 1. (Continued) Table 5 (Continued) clinopyroxene Si02 53 090 52.754 52.691 Al203 2.349 2.822 2.919 FeO 1.824 2.000 1.748 MnO 0 047 0.067 0.043 MgO 16.835 16. 727 16.567 CaO 24.799 23.071 23. 168 Na20 0 162 0.421 0.453 Ti02 0.000 0 000 0 024 Cr203 0.000 0 000 0.026 NiO 0 010 0.000 0 044 Total 99 116 97.862 97.683 50.928 49.393 5 746 5.789 2 196 2.338 0.065 0 .051 17 525 17.437 23.184 23.410 0.192 0 257 0.078 0.010 0.019 0.000 0 075 0 033 100.008 98 718 51.136 5.444 2.401 0 .091 17.410 23.336 0 262 0.014 0 .011 0.033 100.138 53.997 2.097 1 849 n.a. 17.469 24 632 0.248 n a 0 019 n a 100 .311 Ul ......

PAGE 62

APPENDIX 1. (Continued) Table 5. (Continued) clinopyroxene (cont'd) Si02 54 .191 53 228 53.668 Al203 0.917 2.116 1.729 FeO 1.756 1 918 1.709 MnO n.a. n a. n.a. MgO 17 893 17 392 17.461 CaO 24.734 24 548 24.568 Na20 0.151 0.220 0.209 Ti02 n.a. n a n.a. Cr203 0.007 0 032 0.037 NiO n.a. n.a. n.a. Total 99.649 99.454 99 .381 54.418 52.744 0.923 4.356 1.724 2.000 n.a n .a. 18 024 16.649 24.552 23.442 0.136 0.639 n.a. n.a. 0 036 0.000 n.a. n.a. 99.813 99.830 53 357 4 010 1.919 n a 16.379 23.768 0 605 n a 0 017 n.a. 100 055 52.790 3.088 1 702 n a 16. 627 24.245 0 474 n a 0 .6 04 n.a 99.530 01 N

PAGE 63

APPENDIX 1. (Continued) Tabl e 5 (Continued) spinel Si02 0 031 0.212 0 .66 0 Al203 69.059 68.969 67.992 FeO 9.070 9.041 9.029 MnO n.a. n.a. n.a. MgO 21.887 21.925 21.862 CaO 0.199 0 299 0.353 Na20 0.002 0 000 0 020 Ti02 n a n.a. n .a. Cr203 0 000 0 000 0.005 NiO n.a. n .a n.a. Total 100.248 100 446 99.921 1.508 0.107 66.036 67.468 9.611 9 782 0.039 0.078 20.251 20.272 0.717 0.214 0.000 0.000 0.020 0.026 0.010 0.000 0.229 0.248 98 421 98 195 -0 055 68.467 10.222 0 055 20.914 0.146 0.013 0 000 0 1 7 2 0.445 100.48 9 0 .251 67.959 10.834 0.065 20.621 0 269 0 003 0 010 0 000 0 230 100. 242 01 UJ

PAGE 64

APPENDIX 1. (Contin ued) T able 5. (Continued) spinel (cont'd) amphibole Si02 0 043 0.530 45 292 44.012 44.189 44 657 44 194 Al203 68 127 67 895 15 188 17.407 16.516 14.368 16.963 FeO 10 423 10 289 3 037 3 .488 3 319 3.12 7 3.417 MnO 0.036 0.076 0 035 0 029 0 060 0.041 0.059 MgO 21.072 21.099 17 992 17 .081 17.263 17.292 17 396 CaO 0.041 0 328 12.132 12.620 12.724 18.636 12. 702 Na20 0 007 0.006 2 200 2.330 2 315 0 286 2 378 Ti02 0.000 0.000 0 014 0 .041 0 000 0.000 0 009 C r203 0.034 0 000 0 0 3 5 0 000 0 000 0.015 0 000 NiO 0 326 0 342 0 057 0 045 0.034 0 06 6 0 074 Total 100 109 100.565 95.982 97.053 96.420 98.488 9 7 .192

PAGE 65

APPENDIX 1 (Continued) Table 5 (Continu ed) amphibole (cont'd) Si02 44 232 44 .5 36 41.120 Al203 17 006 16 817 19.336 FeO 3 324 5 729 8.203 MnO 0 046 0 055 0 .071 MgO 17 262 15.526 12.909 CaO 12 849 12.598 12 727 Na20 2.390 2 .131 2 258 Ti02 0 010 0 060 0.049 Cr203 0 000 0 042 0 000 NiO 0 038 0 054 0 065 Total 97.157 97 548 96 738 40 784 45 157 19.393 16.502 8 349 4 .6 88 0 098 n. a 12.745 16 350 12.708 12 345 2.313 2.585 0 022 n.a 0 031 0 079 0 074 n a 96.517 97. 706 46 6 8 3 14.4 9 0 4 447 n .a. 17.31 8 12.463 2 362 n a. 0 03 7 n .a. 97.800 44 689 16 .671 4 727 n .a. 16 158 12.417 2 639 n a 0.019 n a. 97.320 Ul Ul

PAGE 66

APPENDIX 1. (Continued) Table 5. (Continued) amphibole (cont'd) Si02 45.157 44.689 46.683 Al203 16.502 16 .671 14.490 FeO 4.688 4 727 4.447 MnO n a n a. n a MgO 16 350 16 158 17 318 CaO 12 345 12.417 12.463 Na20 2.585 2 639 2 362 Ti02 n.a. n.a. n a Cr203 0.079 0 019 0 037 NiO n.a n a. n.a. Total 97.706 97.320 97.800 44.015 43. 449 15.847 17.019 3 961 3.901 n a n a 17.659 17 322 12 682 12 646 2 538 2.558 n a n a. 0 .011 0 023 n.a. n a 96 713 96.918 44.174 15 949 3.776 n.a. 17 752 12 .691 2 539 n.a. 0.025 n a. 96 906 42.989 17 428 3.925 n a 17.059 12. 612 2 735 n a 0 007 n.a. 96 .7 55
PAGE 67

APPENDIX 1. (Continued) Tabl e 5 (Contin ued) amphi b o l e (con t'd) Si02 43.399 42.982 42.804 Al203 17 102 17.053 18 179 FeO 3 877 3 717 3 798 MnO n a n .a n a. MgO 1 7.380 17 232 18.083 CaO 1 2.666 12.549 12.006 Na20 2.713 2.731 2.008 Ti02 n.a. n.a n .a Cr203 0.023 0.006 0.006 NiO n a n.a n.a. Tota l 97.160 96 270 96 884 47.146 43.449 13.477 17. 019 3 252 3 .901 n a. n .a 18.660 17.322 12.908 12.646 1.90 1 2.558 n a. n a 0.013 0.023 n.a. n.a 97.357 96.918 45 237 15 .191 3.517 n a. 17 872 12. 787 2 172 n.a. 0.034 n.a 96 810 44 123 17.124 4.536 n.a. 15 636 12.141 2 868 n .a 0 .471 n a 96 899 (.J1 "'!

PAGE 68

APPENDIX 1. (Continued) Table 5. (Continued) amphibole (cont'd) chromite Si02 44.658 44.594 0.010 Al203 17.078 16 865 32.251 FeO 4.573 4.616 25. 372 MnO n a n a n.a MgO 15.986 16.137 7.119 CaO 12.281 12.521 0 073 Na20 2 820 2.557 0 038 Ti02 n.a. n a. n .a. Cr203 0 028 0.047 33 443 NiO n a n a. n.a Total 97.424 97.337 98.306 0.000 0.000 36.500 30.513 26.769 22.681 n.a. n.a. 5.954 9.285 0.033 0 .009 0.052 0.020 n a. n .a 28 .081 35 823 n.a. n a 97.389 98.331 0.000 31.196 22.673 n.a 9.190 0.000 0.004 n a. 36.149 n.a 99.212 0.005 30.467 23.121 n a 8 .733 0 .071 0 .051 n.a 37.408 n.a. 99.8 56 Ul 00

PAGE 69

APPENDIX 1. (Continued) Table 5. (Continued) chromite (cont'd) Si02 0 .000 0.000 0.004 Al203 31.900 28. 935 38 608 FeO 22.124 22.936 19. 988 MnO n.a. n.a. n a. MgO 9 395 8.904 11.653 CaO 0 067 0 .033 0.097 Na20 0.011 0.005 0.010 Ti02 n a. n.a. n.a. Cr203 36.424 39.246 29. 968 NiO n.a. n a n a Total 99.921 100.059 100.328 0.005 0.000 35 558 37.652 21.287 20.638 n.a 0 000 10.595 12.329 0.056 0.000 0 007 0.000 n .a. 0.113 32 .796 28.950 n.a. 0.089 100.304 99.771 0.000 35.530 21.556 0.037 11.650 0.000 0 000 0 137 31.091 0 047 100 048 0.005 30 467 23.121 n .a. 8.733 0.071 0 .051 n.a. 37.408 n.a. 99.856 (J1 \0

PAGE 70

APPENDIX 1 (Co n tinued) T a bl e 5 (Continued) sapphirine Si02 11.541 1 2 429 11. 970 Al203 66.825 66 105 66 768 FeO 3 567 3.668 3.618 MnO 0.024 0.024 0 014 MgO 17.468 1 8. 105 17. 709 CaO 0.252 0 0 4 0 0 077 Na20 0.065 0 000 0 000 Ti02 0.003 0 000 0.000 C r203 0.044 0 013 0 .001 NiO 0 037 0 019 0.014 To tal 99 826 100.403 100 171 11.499 12 847 67 825 65 950 3 664 2.463 0 048 0.065 17.365 18 .651 0 084 0.185 0.002 0 000 0.000 0 015 0 000 0.012 0 040 0 069 100.527 100 2 5 7 12.696 65.886 2.750 0.05 5 18.609 0 104 0 004 0 005 0 000 0 0 7 0 100 17 9 10.560 69.324 3 568 0.073 16.835 0 114 0 005 0.015 0 02 9 0.065 100 5 88 0\ 0

PAGE 71

APPENDIX 1. (Continued) Table 5. (Continued) sapphirine (cont'd) margarite Si02 12.301 12 324 33.620 Al203 65.772 65 753 47 .991 FeO 4.174 4.247 0.429 MnO 0.082 0.041 n.a MgO 17.562 17 574 1.434 CaO 0.073 0 070 9 252 Na20 0.000 0.000 2 050 Ti02 0.002 0.000 n a. Cr203 0.000 0.000 0.204 NiO 0 059 0 .051 n.a Total 100.025 100.060 94.980 32.416 32.239 49 203 50 .3 18 0.542 0.193 n a n.a 1 739 0.738 10.529 10.798 1 .33 5 1.541 n a. n .a 0.000 0.000 n.a. n.a. 95.764 95.827 32.242 46 950 0.750 n a 2 504 9.660 1.395 n.a. 0.424 n .a. 93.925 zoisite 39.115 31.913 2 281 0.051 0 .061 24. 930 0.000 0.042 0.017 0.000 98.410 ()'\ .......

PAGE 72

APPENDIX 1. (Continued) Table 5 (Continued) zoisite (cont'd) Si02 39.192 38 758 3 9. 594 Al203 31.921 31. 912 3 2.051 FeO 2 307 2 356 1.238 MnO 0.03 3 0 007 0 .061 MgO 0.059 0.055 0 026 CaO 24.857 24 886 24.760 Na20 0 000 0 000 0 062 Ti02 0.0 3 7 0 014 0 004 Cr203 0.000 0 000 0 000 NiO 0 000 0 035 0 000 Total 98.406 98 023 97. 796 3 9 687 39.836 33 249 33.172 0.901 1.092 n a. n a 0 006 0 025 24.759 24.970 0.011 0.000 n.a. n.a. 0 000 0 000 n a. n a 98 613 99.095 39.477 32 752 1.602 n a 0.040 24.702 0.004 n. a 0.023 n a 98.600 3 9.575 33 .4 3 5 0.3 72 n.a 0 0 3 3 24 666 0 012 n .a. 0.000 n .a 98 0 93 I I 0\ N

PAGE 73

APPENDIX 1 (Continued) Table 5. (Continued) zoisite (cont'd) corundum Si02 39.639 39 244 0 000 Al203 33 173 32 850 98.979 FeO 0.849 1.151 0.322 MnO n a. n.a n.a MgO 0.006 0.018 0 000 CaO 24.669 24.860 0.043 Na20 0 014 0 000 0.000 Ti02 n a n a n.a. Cr203 0.004 0 000 1.977 NiO n.a. n a. n.a. Total 98 354 98 123 101.321 0 000 0 010 100.083 99.164 0 .281 0.554 n a. n a 0 000 0.000 0 006 0.047 0 000 0.000 n a. n.a. 0.884 1.396 n a n.a. 101.254 101.171 0 000 99.651 0 115 n.a. 0 000 0.012 0 013 n.a. 0.023 n a 99 .8 14 0 000 99.508 0.085 n a 0 005 0.002 0 .001 n.a. 0 044 n .a. 99 .645 I 0\ V)

PAGE 74

APPENDIX 1. (Continued) Table 5. (Continued) corundum (cont'd) serpentine Si02 0 000 0.000 0.012 0.000 0.023 43.275 42.919 Al203 10 339 99.982 99 832 100 053 99 814 0 .3 08 0.153 FeO 0 154 0.170 0.182 0.180 0 177 2 .427 1.230 MnO n a. n.a n a n.a. n.a. 0 .001 0.019 MgO 0.000 0 000 0 000 0.000 0.000 3 8.141 42.526 CaO 0.030 0 063 0.068 0 052 0.042 0 070 1.050 Na20 0.000 0 002 0.006 0.009 0 000 0.012 0 025 Ti02 n .a. n a. n.a n.a n a 0.012 0 019 Cr203 0 000 0 006 0.000 0.012 0.014 0.184 0 000 NiO n.a n.a. n.a n .a. n a 0 159 0.242 Total 10.523 100.223 100.100 100 306 100 070 84.589 88 183

PAGE 75

APPENDIX 2. BULK CHEMICAL AND TRACE ELEM ENT ANALYSES OF BUCK CREEK ROCKS Table 6 s16a bc2 s39 s18e s46 cp1 s41 Si02 43 03 44 12 35.47 41.49 45.16 44 .23 47.24 Al203 15 08 16 92 24. 68 24. 18 3 5 08 23.07 1 5 3 9 Fe203 6.40 5 86 12.39 4.34 0 34 3 88 9 85 MnO 0.09 0.08 0 10 0 06 0 00 0.05 0 .16 MgO 26.25 22.41 13 90 16.45 0.41 15 13 11. 3 7 CaO 8 17 9.60 10.45 10.77 18.43 12 26 10.13 Na20 0.47 0 74 2 36 1.87 0 87 0.88 4.40 K20 0.01 0.01 0 19 0 07 0.02 0.01 0 35 Ti02 0.01 0.05 0 .01 0 .01 0 .01 0 .01 1.10 Total 99.50 99.80 99.56 99 .23 100 32 99.53 99 99 Ni 1164 1243 1180 1094 61 825 5 33 Cr 528 631 1793 1599 38 231 586 Sr 169 163 147 120 3 03 235 2 3 2 Ba 14 5 60 40 12 37 177 Cu 16 21 19 6 17 26 81 Zn 3 3 30 445 30 7 22 50 y n d n.d n.d n d n.d 3 0 6 Zr n.d n.d n.d n d n d 7 8 ---------d1 39.42 0.68 11. 76 0 16 47.77 0 23 0 04 n d 0 02 100.09 3 532 37 36 3 1 3 48 n d n d 0\ (J1

PAGE 76

APPENDIX 2. (Continued) Table 6. (Continued) s2 s16b s3 Si02 43 .45 43.39 44 08 Al203 31.42 16.11 25.29 Fe203 1.79 6.67 2.76 MnO 0 02 0 09 0.03 MgO 6.77 25.17 12 53 CaO 15.08 7 .25 12 38 Na20 0 94 0.32 1.14 K20 0.05 0 .01 0 05 Ti02 0 02 0 .01 0.01 Total 99.54 99.01 98.28 Ni 487 n .a. n a. Cr 3653 822 743 Sr 397 50 170 Ba 26 9 14 Cu 12 2 12 Zn 32 30 16 y n d n d n.d Zr n.d n d n.d s10 ct2 47. 78 42.91 17.43 15 27 5.40 6.35 0.09 0.09 11.89 25.67 15.15 8.49 1.11 0.43 0.08 n.d. 0.14 0.02 99.07 99 .24 531 1097 1060 516 148 158 12 15 136 28 30 36 n d n.d. n.d n d s12 48 63 20. 53 4.40 0 07 9 35 15.03 1.44 0.08 0.13 99.65 392 838 177 34 47 34 30 78 s29 40 80 0 .37 9.25 0.13 48 38 0.47 0.05 n d. n d. 99.46 4185 1860 6 2 14 33 n d n.d 0\ 0\

PAGE 77

67 APPENDIX 3. COLOUR X-RAY IMAGES OF BUCK CREEK TROCTOLITES. The following figures are colour X -ray images produced using the JEOL Superprobe Portions of the samples were scanned overnight using the EDS mode. Each figure shows the variation of a specific element (top left of each figure) according to the colour code shown at the left of each diagram. Concentrations are semi-quantitative. Figure 8

PAGE 78

68 APPENDIX 3 (Continued) Figure 9

PAGE 79

69 APPENDIX 3 (Continued) Figure 10

PAGE 80

70 APPENDIX 3 (Continued) Figure 11.

PAGE 81

71 APPENDIX 3 (Continued) Figure 12.

PAGE 82

72 APPENDIX 3. (Continued) Figure 13

PAGE 83

73 APPENDIX 3 (Continued) Figure 14.

PAGE 84

74 APPENDIX 3. (Continued) Figure 15


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