. - o 3; f5, 5;: :igzzgzg .‘I‘. I a... u a .\ a. I k ‘ T. I. \ a...- » .0 L .. r s I. O o a i o I.. II.” J. 0 I“ .3 L A» . k . . ’— SUPPLEMENMRY 4 MATERIAL INBACKOFBOOK PETROGRAPHY AND PETROLOGY OF THE ANDALUSITE SCHISTS IN THE PORT FELIX AREA, NOVA SCOTIA, CANADA by EDWARD A. SCHILLER A THESIS Submitted to the College of Science and Arts of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Geology 1959 ACKNOWLEDGMENTS The author wishes to exnress his sincere appreciation to the members of the Geology Department of Michigan State University for their assistance in the writing of this paper. The efforts of Dr. Justin Zinn in directing this study are greatly appreciated. The criticisms and suggestions of Dr. B. T. Sandefur and Dr. H. B. Stonehouse have aided the writer considerably. He is indebted to Dr. I. M. Stevenson of the Geological Survey of Canada for providing thin sections, and maps of the area. The interest and encourgement offered by Dr. Stevenson have been instrumental in the writing of this paper. The author acknowledges the assistance of James T. Neal and fellow graduate students of Michigan State. 11 ABSTRACT The andalusite schists in the vicinity of Port Felix, ' Nova Scotia constitute a distinct belt in the regionally folded Halifax formation. Results of field observations supplemented by the petrographic study of these rocks are presented with interpretations of the origin of the anda- lusite schists and the metamorphic history of the area. The intrusion of granite into regionally folded rocks of particular chemical composition has permitted andalusite to form in a distinct horizon interbedded in the micaceous schists of the Halifax formation. Presence of two distinct metamorphic mineral assemblages, the lower ranked andalusite- muscovite sub-facies and the higher ranked cordierite-anda- lusite sub-facies, give evidence to the progressive metamor— nhic effect of contact metamorphism in the Port Felix area. It is believed, that the regional metamorphic history can be described in terms of large scale orogeny, producing isoclinal folding with subsequent granite intrusion. iii CONTENTS INTRODUCTION .... ...................................... Geology ........... ...... ... .................... ..... Purpose and Sc0pe ....... ........ .... ...... ..... ..... Definition of Zones ................................. Sampling procedure and labortory method ........... .. PETROGRAPHY .......................................... . Metamorphic zone 'one'... ........ . ............. ...... Macrosc0pic description .................. . ....... MicroscOpic description ......................... . Metamorphic zone 'two' . ............................. Macroscopic description .. ........................ Microsc0pic description .......................... MINERALOGICAL CHANGES IN METAMORPHISM ................ . METASOMATISM ... ..... ........................ .......... ’ METAMORPHISM .... ........ . ......... . ................. .. Zone 'one': Andalusite-muscovite sub-facies ....... . Zone 'two': Cordierite -andalusite sub-facies ------ METAMORPHIC PETROLOGY ..... ............ .............. .. Regional metamorphism ....... ....... . ....... ......... Contact metamorphism ................ ...... . ......... CONCLUSIONS . .......... . ......... ...... ............ .... RECOMMENDATIONS FOR FURTHER STUDY ..... . ..... . ......... REFERENCES ............................................ iv TARLE 1. Approximate mineral percentages of the and lusite scnist in zones 'one' and 'two' 2 Approximate chemical composition of the andalusite schist in zones 'ane' and 'two' FIGURE 1. Looa+10n of thesis area ..... . ............ . 2. General view, characteristic of the southeastern part of Nova Scotia . ...... ... 3. Andalusite idioblasts standing out on the weathered surface ... .................. b. An andalusite schist outcrop showing clearly defined bedding ..................... 5. Photomicrograph of sample 7 showing characteristic scnistose texture ............. 6. Photomicrograph of central portion of Figure 5c 00000000000000000000000000... 7. Photomicrograph of an andalusite idioblast 00.0.00,.....IOOOOOOOOOOOOOOOOOO S. Photomicrograph of a fractured andalusite crystal ..... ........... .................. 9. Photomicrograoh of original laminae passing through an andalusite crystal .... lO. Photomicrograph of trains of garnet, magnetite, ilmenite and graphite forced aside by an andalusite crystal ........... 11. Same as Figure 10, crossed niCOls ......... 12. Photomicrograph of a cnlorite crystal .... 13.. Photomicrograph of magnetite blobs ILLUSTRATIONS enveIOped by chlorite ..... ......... ....... ll 13 13 1h 14 17 18 18 19 l9 FIGURE _ PAGE lb. Photomicrograph of dumortierite and tourmaline .............. ............. ..... 21 15. Photomicrograph of coarse grained muscovite; also cordierite and albite ... ...... 26 16. Photomicrograoh of andalusite altering to muscovite (retrograde effect) .... .......... 28 17. Same as Figure 16, crossed nicols ...... ........ 28 18. Photomicrograph of a sub—hedral cordierite crystal ............................ 29 19. PhotomicrOgraph of cordierite grains showing pinite development (?) ..... .......... . 29 20. Photomicrograph of a staurolite idioblast OOOQOOIOOOOO,OOOOOOO.0.0....00.00000.. 33 21. Photomicrograoh of chiastolite .... ............ } 3h 22. PhotomicrOgraph of chiastolite showing crossed inclusion . .......... .......... 35 23. Map showing the regional geology in the vicinity of Port Felix, Nova Scotia ....... .. Pocket 4U. Geologic map of the Port Felix area, Nova Scotia ..................... .......... .. Pocket vi PETROGRAPEY AND PETROLOGY OF THE ANDALUSITE SCBISTS IN THE PORT FELIX AREA, NOVA SCOTIA, CANADA INTRODUCTION In the summer of 1958, the writer was employed as a Technical Officer with the Geological Survey of Canada to assist in the mapping of the Chedabucto Bay Area, Guysborough County, Nova Scotia. During the course of the summer the un- usual nature of an andalusite bearing schist in the form of a long extending belt created much interest to the writer. Dr. I. a. Stevenson, in charge of the mapping project, suggested that a detailed petrographic study of the andalusite schist . might reveal considerable information on the origin of this lrock and the metamorphic history of the area. It was decided that the study should be restricted to the portion of the and— alusite schist where a variation of metamorphic effect was apparent. Detailed sampling and mapping of the area consider- ed was undertaken at this time in preparation for petrographic study the following school year. ' The thesis area extends from the town of Port Felix, Nova Scotia to a point two and one half miles east, at approx- imately latitude 54°16', longitude 61°11'. Nova Scotia, Canada's most easterly mainland province, is bounded by the Atlantic Ocean on all sides except where the 60° 67° 4,—4.— 48° 48° “1r—* ’7 PRINCE i NEW EDWARD cape oraton BRUNSWICK I '-‘ l ATLANTIC OCEAN 44°— ‘ 44° 67° 60° 0 "Imagery / / 6'0 62° // f l / I/ e ./l ChedOWcm Bay canso 45° 45°____\ . \V/T 6l° Fig.l LOCATION OF THESIS AREA 3 peninsula is Joined by an isthmus to the province of New Brunswick on its northwest side. Guysborough County is the most easterly county on the peninsula, bounded by Chedabucto Bay on the north, and by the ocean to the east and southeast. A paved highway (Nova Scotia 16) extends from Canso (located at the extreme eastern tip of Guysborough County) to Monastery situated on the Trans-Canada highway. Port Felix can be reached by eight miles of graveled road from highway 16. From the intersection of highway 16 it is 40 miles to Monastery where the mainline of the Canadian National Railway is located. The entire southeastern part of the province may be regarded as a low lying plateau leping southeasterly to the ocean. The tOpography is one of undulating hills with few con- spicuous individual elevations. The uplands are hills and table— lands of resistant granite which lepe steeply to the lowlands of the less resistant metamorphic rocks. Recent glaciation has modified the area; glacial striae, boulder trains, and minor moraine development give indication of this. The general ice movement was from north to south. Most of Guysborough County consists of uninhabitable tracts of woodland and granite barren, resulting in limited arable land available for agriculture. Peat bogs are quite abundant in the county where individual areas permit their formation. Nova Scotia has a temperate climate, enjoying the mod- erating effects of the surrounding sea. The mean maximum temp- erature is 55 degrees, the mean minimum is 35 degrees. The precipitation is moderate but in excess of that of the inland provinces. Average precipitation is 55 inches a year. Figure 2. General view, characteristic of the southeatern part of Nova Scotia. Looking northwest from Doughboy Point up the Northwest Arm of White- haven Harbour. ' Previous to the summer of 1958, the only geological work done in Guysborough County was by Fairbault and Feltcher between the years 1882 and 1886 for the Canadian government. The work undertaken last summer by the Geological Survey of Canada was an effort to correct and to bring up to date the map and report that Fairbault and Feltcher published on this area. ‘ Geology The andalusite bearing rocks are present in the Halifax member of the Meguma series, which are believed to be Ordovician in age. Attempts to accurately date the Meguma are difficult. Woodman (1908) states: "Difficulties which lie in the way of establishing the age of the Meguma appear early to the student, for he has to deal with a group of rocks nearly 30,000 feet in thickness, apparently conformable throughout, remark- ably monotonous in texture and exhibiting neither a base beneath which is exposed an older series nor a summit above which lie any fossiliferous formation of such age as will aid much in establishing that of the Meguma. In all the 30,000 feet there has been discovered but one horizon which can be traced far, between the lower quart- zite formation and the upper slate formation." Stevenson (1959), places the Meguma in the Ordovician, on the basis of fossils found in western Nova Scotia. The Maguma series, also known as the Gold-bearing series, is made up of the Goldenville formation and the younger Halifax formation. Table of formations Period Formation & thickness Character Devonian granite Halifax, slates and Meguma 16,000 feet schists Ordovician?I Series Goldenville, quartzites and J 1n,500 feet sub-graywackes The Goldenville formation consists of grey and dark green quartzites and sub-graywackes, largely siliceous in com- position and arenaceous in texture interbedded irregularly with slates of limited thickness. The Halifax formation consists of black, lead colored, light grey and green wholly argillaceous slates and schists, in part graphitic, which are interbedded with green and grey quartzites of sizeable extent (beds up to 200 feet thick). Thicknesses of lu,500 and 16,000 feet respectively for the Goldenville and Halifax have been suggested (Malcolm, 1912). Nova Scotia forms a part of a large regional geologic unit which extends into Newfoundland and the Maritime Provinces. This unity is apparent in the general northeast southwest trend of the important geologic features of the province. Andalusite is present in a schistose rock that forms a belt 900 to 1000 feet wide and 14 miles long paralleling the re- gional folding (strike 070°). Since this belt is parallel to the folding, it appears that the andalusite bearing schist is a stratigraphic horizon in the Halifax formation. At the sur- face, granite occurs within one mile of the andalusite belt in all places except in an area between Port Felix east to the gravel road'where the distance to the nearest granite outcrOp is approximately two miles. The andalusite belt is terminated at both ends by the intruding granite. Where the granite con- tacts the belt an increase in metamorphic rank is imparted to the schist. Two similar and parallel andalusite horizons, one north and one south of the main belt and about one and one (half miles distant in each case, show similar relationships to the granite. Due to the steeply dipping beds (vary from 70 degrees north to 70 degrees south), and to the absence of other sed— imentary structures,the stratigraphic position of the andal- usite bearing beds from field studies is almost impossible to determine. The two minor andalusite belts were not studied in detailed since the author was mainly concerned with the progressive metamorphism of the main andalusite body. Structurally, three interpretations can be made of the Ithree andalusite belts: 1. They could represent three occurrences of this rock type, each existing in a synclinal trough_or an anticlinal peak. 2. They could represent three individual horizons of this rock type. 3. They could represent one horizon, tightly folded and eroded to be repeated in outcrOp as observed. It is believed that number three represents the most logical interpretation. The structural problem, though very interesting, is beyond the scOpe of this study. Purpose and ScOpe This thesis is primarily a petrographic study combined lwfoSS/J, with)? law/o / with limited detailed field mapping to invggtiggtentheflorigin’e;,-. of an unusual occurrence of the mineral andalusite that crops out in the vicinity of Port Felix, Nova Scotia. The investi- gation will be restricted to the area designated, and will in- clude a study of the change in metamorphic facies that the .andalusite belt presents in its association with the intrusive granite. Preliminary work on rocks immediately south of the andalusite belt will be presented to show that similar progress- ive metamorphic effects can be recognized in them also. An attempt to interpret the metamorphic history of the area from field and petrographic study will be made. Definition of Zones Two distinct metamorphic mineral assemblages are recog- nized in the thesis area. The area that each assemblage makes up will be referred to as either zone 'one' or 'two'. Zone - 'one' is the lowest ranked metamorphic assemblage and zone 'two' is the highest ranked assemblage. The former is located in the western half and the latter in the eastern half of the thesis area. Sampling procedure and labortory method Studies of 12 thin sections of samples obtained across the strike of the andalusite belt in zones 'one' and 'two' were made, employing standard petrographic procedures. Five thin sections of samples taken from rocks south of the andalusite belt were studied also. Numbers and locations of thin sections are plotted on Figure 2a. These sections were cut normal to the bedding—foliation. Due to the limitation of sampling and the nature of the schistose rock (irregqglar banding and fine grain), mineral percentages were determined by the use of the grid ocular, since it is doubtful whether any controlled counting method would improve the accuracy of the analysis. Identification of andalusite and cordierite was con- firmed by X-ray studies on powdered specimens, the former (‘by diffractometer, the latter by powder photograph. Attempts to positively identify the type of garnet proved futile be— cause of their minute size. PETROGRAPHY Metamorphic zone 'one'. The area comprising this metamorphic zone is located in the western half of the thesis area (Fig. 2b). From the center of this metamorphic zone, the nearest granite body is one and one-half miles to the west and two miles to the east. MacroscOpic description The andalusite schist in this zone is essentially a light grey-green to silvery grey micaceous rock containing por- phyroblasts of andalusite. The andalusite is always idioblastic, forming crystals up to four by two centimeters which are gen- erally black or grey-black in hand specimen ( a greyish pink variety was noted in one small locality). They occur in sub- parallel to non-parallel orientations in reference to the schistosity and in some cases showing the original bedding traversing the crystals. 0n the weathered surface the crystals stand out conspicuously against the light colored groundmass. . ‘\ . H ‘ ‘ ‘ \--Z-" 1 ”~\ ' ‘. I ’ 1"; f) ‘3 :' I~ ‘ , O ‘ . ( - -|-| V\ k Figure 3. Andalusite idioblasts standing out on the weathered surface. 10 Uniform distribution of the andalusite throughout the entire belt reflects the homogeneity of the original sediment and the constancy of the metamorphic effect. The andalusite makes up approximately lh%* of the schist in zones 'one' and 'two'. This value appears to be true for the entire andalusite belt, with the exception of the outer five feet at each edge of the belt, where the andalusite content is approximately five percent. The rocks on either side of the andalusite horizon in this zone are essentially light colored mica schistsm All the rocks in this zone possess a schistose fabric which can be related to the stresses that produced their fold- ed nature. The schistosity appears to parallel the bedding throughout the entire belt (Fig.4). Bedding is easily recog- nized by laminae of dark and light bands one to three milli- meters wide. Thin beds and lenses of a fine grained felds- pathic quartzite that average four millimeters wide are ran— domly interbedded in the schist to further accentuate the bed- ding-schistosity lineation. Fracture cleavage of a younger age than the foliation that strikes at an angle of approximately 30 degrees to it is noted throughout the thesis area. Detailed examination of the fracture cleavage system was not made, however. ‘ Reference to remaining mineral percentages will not be made in the text. A tabulated list of percentages is given in Table 1. 11 Table 1. Approximate mineral percentages of the andalusite schist in zones 'one' and 'two'. Mineral Zone '1' Zone '2' andalusite In 1“ muscovite 39_ 25 ' quartz I i 28 2h' cordierite -- 15 albite ? 10 K feldspar l ? chlorite 10 1 garnet (almandine ?) 5 l magnetite & ilmenite 2 u- staurolite —- 5 biotite <1 <1 graphite <1 <1. accessories . l ' l v—w—v— Figure H. An andalusite schist outcrop showing clearly defined bedding. Quartzite beds are very conspicuous. 12 Microsc0pic description Mineralogically, the andalusite schist is composed of the following: andalusite, muscovite, quartz, chlorite, gar- net (believed to be almandine), potassium feldspar, biotite, magnetite, ilmenite, and graphite. Accessories include tour- maline, dumortierite, spinel, apatite and rutile. The alter— ation of ilmenite to leucoxene was noted twice. The conspicuous schistosity noted in the hand specimen is equally apparent in thin section. Lineation develOped by the alignment of mica parallel to the bedding is further en- hanced by the banding of quartz and chlorite grains, trains of graphitic material and garnet crystals all paralleling the shear planes. The texture is typical of pelitic schists, except for the prolific develooment of minute garnet crystals which are found throughout the sonist (Fig. 5 and 6). Schistosity, line- ation and segregation (alternation of micaceous, mica—quartz and quartz layers) are fairly well deve10ped with the mica- quartz layers predominating. Except for the outer five feet at each edge of the belt where a finer grained texture prevails, the remainder is homogeneous. In thin section, the andalusite always exhibits an euhedral form and contains inclusions of quartz, graphite, sericite, garnet, magnetite, and ilmenite crystals (Fig. 8). Evidence of retrograde metamorphism by the alteration of and- alusite to sericite was noted on some crystals, taking place around crystals boundaries and along fractures within the l3 _ _—— ——“v‘ v Fig. 5. Characteristic schistose texture. Groundmass is muscovite and quartz. The garnet content shown is not representative of the schist. Plain light, X 21. Fig. 6. Takes in central portion of Fi . 5. Muscovite blades predominate. Quartz (Q is White, elongated in shape, believed to be secondary. Inclusions in the garnets are characteristic. Plain light, X 5h. lb -7 ‘— - _- 7—— ——. fir Fig. 7. Crystal edge of an andalusite idioblast. Groundmass is muscovite, quartz, magnetite, ilmenite and graphite. Original laminae of graphitic material bisects figure. Plain light, X 21. ( Fig. 8. A portion of a fractured andalusite crystal with sericitization (Se) taking place within the fractures. Inclusions of garnet (G), magnetite (M) and quartz (Q) are orientated with the scnistosity. Crystal frag“ ments show variable extinction. Crossed nicols, X 21. crystal (Fig. 8) Optically, the coarse prismatic form (nearly square), the high relief (d= 1.630,;3= 1.636, '5’ - 1.61m), the low interference color (K —:4- .01), biaxial negative sign and Characteristic inclusion content, distinguish the annalusite easily from any other mineral in the rock. It is apparent that the andalusite is post lineation. Evidence of this, is the lack of orientation the porphyroblasts exhibit. In thin section, where a sub-parallel alignment be- tween porphyroblast and schistosity appears evident, trains of inclusions (graphite, garnet, magnetite and ilmenite) marking the original lamination pass undisturbed through andalusite porphyroblasts (Fig. 9). Where non-parallelism exists between porphyroblasts and schistosity, the trains of inclusions curve around the porphyroblasts (Fig. 10 and 11). It appears, that when the direction of crystal growth deviated from the schist- osity beyond a certain angle, it forced aside the original laminae. The mica appears to be all muscovite; biotite forms less than one percent of the rock. The muscovite shows typical second order colors and characteristic birds-eye structure. It forms individual shreds and flakey aggregates in varying amounts with quartz (Fig. 6) and/or calorite in bands parall- eling the scnistosity. Inclusions were not found in any of the muscovite. Quartz grains, averaging .1 to .2 millimeters in diameter, with granular and mosaic texture, appear in irregu— l6 lar bands. Quartz also forms elongated aggregates and lenses in varying amounts within the micaceous material to make up the bulk of the groundmass. The grains making up these aggre- gates and lenses are elongated, generally smaller than the granular-mosaic form. The lens like quartz is thought to be secondary or non-detrital and formed as in the reaction on page 36, while the granular quartz is probably detrital. The detrital quartz exhibits minor strained shadows while the secondary quartz is free from this feature. Chlorite is found disseminated throughout the andalusite schist in this zone. The chlorite tends to occur in aggregates and patches (Fig. 12) and individual tabular plates generally aligned parallel to the schistosity. Its crystals vary from a fraction of millimeter to almost two millimeters. Due to the thickness of the thin sections (approximately .OOU mm), upper first order colors were observed. The pleochroism was as follows; a orcx, and b or 5 = green, 0 or X = yellow. An interesting occurrence of chlorite is seen in Figure 13, were it partially envelopes blobs of magnetite. 'However, this re- lationship was noted only in one thin section. Positive identification of the variety of garnet could not be made. The garnets exist as euhedral dodecahedrons .0# mm to .1 mm in diameter, averaging about .06 mm. Minute in— clusions of unknown composition appear in the central portions of the crystal. The garnets are lined up in trains and narrow bands with the lineation pre-dating the andalusite, as shown by Figures 10 and 11, where an andalusite crystal forces aside 17 w- ....— _. _——._————— |_ ,___7___,.,. ”...—PP- -———.T«—xr -,.s m. ’ 95' Fig. 9. Original lamina ,“ ing through an andalusite (A) porphyroblast undisturbed. Groundmass (G) is muscovite and quartz, laminae are mostly graphitic material. Plain light, X 21. a train of garnets. An estimated chemical composition of the schist would allow us to say that the probable composition of the garnet approximates the iron-aluminum variety almandine, common in such rocks. Attempts to ser.rate magnetite by a magnet from a heavy mineral separation revealed the garnet to possess magnetic prOperties. One prOperty of almandine is that it is strongly magnetic relative to other garnets, which would support the probable identification. Granular potassium feldspar about .1 to .2 mm in diameter, was recognized in the quartz bands. Its negative biaxial sign and index of refraction distinguished it from quartz. Evidence of twinning could not be found. The presence of magnetite inclusions in the feldspar and the apparent absence of magne- tite inclusions in the quartz aided in distinguishing the two . 18 and groundmass of quartz and muscovite forced aside by an andalusite crystal. Plain light, X 21. ii ,_i_ ii___, _.,- Fig. 10. Trains of garnet, magnetite, ilmenite and graphite, Fig. 11. Same as Figure 10. Crossed nicols, X 21. 19 Fig. 12. A large crystal of chlorite (Ch) with a garnet train apparently swin in around it. [magnetite (M), quartz (Q), muscovite Mu . Plain light, x 54. 1 Fig. 13. Magnetite“BiobE“oEFEially'onVe opEd by ch orite (on) Plain light, x 21. minerals. Biotite is very minor in the groundmass, limited to individual flakes or blades intergrown with the muscovite. Biotite shows no relationship to the chlorite, and so is not believed to have been altered by retrograde metamorphism to form the chlorite. Magnetite snows variation from good euhedral crystals to anhedral blobs and fragments that vary from .01 mm2 to .5 by 1.0 mm. Ilmenite rods average .01 by .005 mm. The diff- iculty in differentiating ilmenite from magnetite is evident When the sizes of these minerals are considered. Ilmenite crystals are hexagonal in contrast to the cubic form of mag- netite. Ilmenite could crystallize in a rod-like halit, more so than the cubic magnetite. Other aid to this identification was the violet black tinge under reflected light which is somewhat characteristic for ilmenite but not for magnetite. The apparent parallelism between magnetite and ilmenite crys- tals and the schistosity was noted in all thin sections stud- ied. Graphite occurs in finely divided crystals or flakes that average .003 by .012 mm. Their longer dimensions always parallel the schistosity as does the clusters and bands they are present in (Fig. 7). The list of accessories in order of their abundance is as follows: tourmaline, dumortierite, apatite, spinel and rutile. The latter two.are rare and the remaining three quite common. Dumortierite occurs in prismatic crystals that average 21 Fig. lb. Dumortierite (D), and tourmaline (Tl showing no preferred orientation, set in a roundmass of mus- covite and quartz. Chlorite (Ch , garnet (0). Plain light, X 5h. about .2 by .OU mm. It is colorless to pale blue and pleo- chroic with the greatest absorption when the length of the crystal is parallel to the vibration plane of the lower nicol. Birefringence varies from orange of the first order up to blue of the second order. Tourmaline occurs in prismatic crystals that average .2 by .06 mm. It is neutral grey to pale blue, pleochroic with the greatest absorption when the length of ,the crystal is at right angles to the vibration plane of the lower nicol. The birefringence of tourmaline varies from _ lower to upper second order colors. Both dumortierite and tourmaline have no preferred orientation; their longer axes lie in all directions to the SChistosity. Figure 14 shows a 22 dumortierite crystal which grew at right angles to the schist-_ osity, and a tourmaline crystal at an angle to the schistosity. Rocks immediately south of the andalusite schist are fine grained muscovite, biotite, chlorite, quartz schists. Access— ories include garnet, magnetite, ilmenite and graphite. Texturally, these rocks are similar to the andalusite schist. The presence of biotite, which makes up five to ten percent of these mica scnists and the absence of porphyroblasts, dis- tinguishes these rocks from the andalusite schists. Since little biotite (less than one percentl is present in the andalusite schist, the occurrence of biotite in these mica schists is unusual. Metamorphic zone 'two'. The area comprising this metamorphic zone is located in the eastern half of the thesis area (Fig. 2a). Rocks of this zone come in contact with the granite along the entire eastern edge of the thesis area. Macroscopic description In this zone, the andalusite schist is a grey-blue horn- fels schistose rock that shows porphyroblasts of cordierite along with the ubiquitous andalusite idioblasts. The obvious schistosity observed in zone 'one' is much less apparent in rocks of zone 'two'. The thermal effects of granite intrusion is well illustrated by the "baked“ appearance the rocks of this zone show. W;&' The form and content of the andalusite idioblasts appear 23 to be identical with the idioblasts present in zones 'one’. Cordierite occurs in all rocks of zone 'two'. It attains its greatest develOpment in rocks south of the andalusite belt where it comprises 15 to 20 perpent of the rock. The cordierite schist is distinguished from the andalusite schist by a characteristic honeycombed or pitted surface. Ovoid grains up to 1 by .4 cm and cavities of the same dimensions are randomly dispersed throughout the groundmass of the weath- ered schist in a sub—parallel to non—parallel orientation in reference to the lineation. Cordierite is black When observ~ ed on fresh surfaces; usually a greenish brown alteration product costs the surface of the mineral giving it a shelled appearance when out in half. The peripheral weathering feature is described by Dana (p. 583) as follows: “'"” he de In lfigfi *‘~* aw'yw'w“””= “The alteration of cordierite takes place so readily by ordinary exoosure that the mineral is most commonly found in an altered state or enclosed in the altered cordierite. This change may be simply hydration; or the introduction of oxides of iron; or of alkalies, forming pinite and mica. The mineral in this state can be called hydrous cordierite." The above eXplains the honeycombed surface. The alter— ation of cordierite to mica-pinite on the weathered surface of the rock allows the grain to dislodge itself from the groundmass with subsequent removal by weathering. Proximity of the ocean which provides saline fogs plus abundant rain- fall would allow the cordierite to be easily weathered from the host rock. In the andalusite belt the cordierite is present in similar fashion but in variable amounts. The cordierite reaches its maximum amount in the vicinity of Doughboy Point where it composes about 15 percent of the rock. As one follows the andalusite belt away from this point the amount of cordierite gradually diminishes to zero in the vicinity of Muddy Lake. The diminishing amount of cordierite in rocks south of the andalusite belt cannot be observed due to the lack of outcrop. An interesting occurrence of the mineral chiastolite was found in outcrOp on the north shore of Whitehaven Harbour due south of Spear Lake (sample no. 29). Chiastolite, the noted inclusion bearing variety of andalusite, is present in a fine grained black carbonaceous slate—phyllite in crystals up to five centimeters long and one-half centimeter in cross section. The structure, composition and origin of this well known mineral type has been adequately deacribed by others. It is one of the most characteristic products of low grade metamorphism of carbonaceous bearing argillaceous rocks. The distinction between andalusite and chiastolite is purely descriptive, for when carbonaceous material has been included in the form of a cross, the name chiastolite is given, when crossed inclusions are absent (though inclusions of a diss— eminated nature are present) the mineral is called andalusite. The chiastolite is light pink, with the crossed inclusions seen plainly on the 001 face. The slate-phyllite beds in which the chiastolite occurs are about six inches thick and interbedded in a quartzose schist stratigraphically separate 25 from the main andalusite belt. Limited occurrence of this rock type is indicated by failure to trace it very far later— ally. MicroscOpic description The increase of metamorphic rank is evident with the appearance of the minerals cordierite and the microscopically determinable staurolite. Mineralogically, the andalusite-cordierite scnist is quite similar to the andalusite schist of zone 'one‘. Except for the addition of cordierite, staurolite and albite to the rocks of zone 'two', the similarity in mineralogy is apparent. Quantitative changes include the decrease in muscovite, chlorite and garnet. The composition of the schistose rock in each zone is almost identical (see Table 2). Near the granite contact the schist loses its conspicuous foliation, and might be described as a hornfelsic schist. In thin section the original schistosity can be discerned by the alignment of muscovite, which has now become coarse grain- ed and forms lenses and irregular masses rather than cont- inous bands (compare Fig. l5 with Fig. 6). Plications or crenulations of these lenses and masses are secondary features Which may be related to structural adjustments during the .granite emplacement. Porphyroblasts of andalusite, cordierite and staurolite, and muscovite make up about 50 percent of the schist, the remaining 50 percent is groundmass which is a confusion of quartz, albite, sericite, garnet, biotite, Chlorite, Fig. 15. magnetite, 26 Coarse grained muscovite (Mu) in a lens and as individual crystals. The latter showing no pre- ferred orientation (secondary). Cordierite (Co) and albite (A1) are noted, (the former showing inclusions). Quartz (Q) shows characteristi mosaic texture. Crossed nicol, x 5h. “ ilmenite and accessories. The texture of the ground- mass is granoblastic-schistose which indicates a reorganization of the original minerals. Crenulatione and microscopic fold- ing that the groundmass reveals by linear elements as shown by the Opaques and sericite in Figure 20, combine with the lenses and masses of quartz and albite grains and the unorien- tated muscovite and sericite blades to define the granoblastic texture. Optically, the andalusite in zone 'two' is identical to the andalusite from zone 'one', except for the more retrograde effect that has altered the boundaries of the crystals in this zone. Comparison of Figures 16 and 17 with Figure 8 illustrates 27 the difference in retrograde alteration- Cordierite forms sub-hedral to anhedral prismatic cry- stals (Fig. 18) and grains (Fig. 19) containing inclusions of magnetite, ilmenite, quartz, sericite and garnet in variable amounts. Cordierite varies anywhere from less than .1 mm in diameter to large sub-hedral forms .8 by 2.0 mm. It is gen— erally colorless and non-pleochroic, though it sometimes shows diffused tints of brown. The mineral is always outlined by a light brown to brown substance, which could be the pinite re- ferred to previously. Cordierite can be either biaxial posw itive or negative. Due to the large 2V angle and the limits- tionsof the petrographic microscope, the Optic sign of the mineral is not certain. Inclusions are abundant in the cordierite, but generally less than the amount found in the andalusite idioblasts. Unusual cleavage as shown in Figure 18, is observed in sub-hedral forms of cordierite. This clea- vage whiCh is almost lamellar in appearance, extends at right angles to the prismatic face inward about one third or across the entire crystal width. Dana (p. 583) describes a lamellar structured cleavage, that parallels the 001 face for slightly altered cordierite. The cleavage noted in thin section could be this type. In cordierite grains, 90 degree cleavage is present. Characteristic pseudo-hexagonal cyclic or sector twinning could be observed when the 001 face paralleled the stage of the microsCOpe. when 010 or 110 paralleled the micros00pe stage, parallel extinction was obtained. Fig. 16. ___“___w __ f . k Andalusite alterin to muscovite (Mu) (retrograde effect). Garnet (G . Plain light, X 21. 28 Cu 29 ,__—_ _ _— - q Fig. 18. A sub-hedral cordierite (Co) crystal showing Fig. 19. lamellar cleavage. Quartz (Q). Crossed nicols, X 21. Cordierite(Co) grains outlined by a dark material believed to be pinite. Parallelism of magnetite and ilmenite (11) in both the groundmass and in the cordierite grains with the lineation is noted. Quartz (Q). Plain light x 21. 3a The distribution of staurolite is erratic. It appears to make up no more than five percent of the rocks in this zone. One perfect crystal of staurolite showing the character— istic six-sided cross section was noted in specimen number 20, 3.0 by 1.8 mm (Fig. 20). Although retrograde metamorphism had altered it considerably, its identification could be made. Staurolite, Just as cordierite,has a very large Optic angle -and can be either positive or negative. Staurolite is mildly pleochroic and varies from nearly colorless to pale yellow. Its birefringence varies from lower first order to first order yellow. In cross section, symmetrical extinction is noted. Color, pleochroism and absence of peripheral alteration (pinite develonment) distinguishes this mineral from cordierite, when idioblastic develOpment was lacking. Figure 20 shows the orientation Of quartz and magnetite inclusions in staurolite parallel to the lineation Of the groundmass. The growth of this mineral after the develOpment of foliation is therefore obvious. The muscovite occurring in zone 'two' is both fine and coarse grained. Its original parallelism is twisted and cren- ulated into a sub-parallel lineation that strikes in the gen- eral direction of the original schistosity. The effect of the granite intrusion has been to superimpose a hornfelsic texture onto the original schistose one. The majority Of the muscovite occurs in twisted lenses and masses showing a faint parallel- ism. Secondary muscovite, that occurs in individual shreds and flakes, grows in random form indicating an age later than 31 that of the foliation. The ratio of quartz to mica increases from that of zone 'one'. Quartz is essentially granular, and varies from .1 to .3 mm in diameter. When the quartz is .1 mm or less, it forms in aggregated lenses intergrown with the muscovite. When Of the order of .2 to .3 mm, quartz forms in randomly shaped masses with no apparent preferred orientation. In these masses, albite is present with the quartz intergrown in a mosaic form. Straining in quartz appears to be more common than Observed in zone 'One'. Albite was identified by its biaxial positive sign and its index of refraction which was less than balsam. It is granular in habit and contains magnetite particles about .01 mm in diameter as inclusions. The presence of magnetite inclu-' alone was the only way albite could be distinguished from quartz without resort to sign or index determination. The albite grains averaged about .2 mm in diameter. Though potassium feldspar was identified in zone 'one', it was not observed in zone 'two'. The garnet content is reduced from the five percent Ob- served in zone 'one' to about one percent in this zone.. A random distribution is apparent, with the garnet trains and bands of zone 'one' obliterated here. It appears, that the contact metamorphic action of the granite changed most of the garnet to other minerals (cordierite and staurolite). A pre- granite age for the garnet is therefore obvious. Chlorite forms a few aggregates or patches with no preferred orientation. With the mineral assemblage present in this zone, the chlorite is anomalous, and therefore prob- ably a retrograde product. Biotite is intergrown inconspicuously with the muscovite and shows no relationship to the chlorite. The quantity of magnetite and ilmenite in the rocks of zone 'two' is doubled from that of zone 'one'. Overall, these minerals appear to have better crystal form than those of zone 'one', implying that the thermal effects of the granite allowed coarser crystallization to develop. Parallelism be- tween magnetite and ilmenite crystals and the groundmass is shown in Figure 20. The only good evidence of the relict schistosity appears to be shown by this magnetite-ilmenite parallelism. Little or no graphite can be seen in the groundmass, yet it is still included in the andalusite porphyroblasts. Its absence from the groundmass is not readily eXplainable unless contact conditions were able to oxidize that graphite not held as inclusions in the porphyroblasts. The accessory minerals in the rocks of zone 'two' appear to be essentially the same in kind and distribution as those described in zone 'one'. . Since only one thin section of the chiastolite slate- phyllite was studied, the variation in its metamorphism was not evident. This rock is a fine grained, black, carbonaceous slate-phyllite that is composed of the following minerals (in order of decreasing amount), sericite, quartz, biotite, 33 .""*'W‘ " . .‘ ’—’ Fig. 20. A staurolite idioblast altering to sericite( retro- grade effect). Note abundance of quartz inclusions in the staurolite. Quartz inclusions, Opaques and groundmass show micro—folding. Magnetite (M), Ilmenite I), Staurolite (S). Crossed nicol, X 5h. chiastolite, and graphite, with accessories of ilmenite, gar- net, magnetite and chloritoid. According to Heinrich (1956), this slate-phyllite may be classified as a spotted slate, both spots (clots of min- ute graphite flakes and magnetite grains) or Fleckschiefer and chiastolite idioblasts (Fruchtschiefer) are present indi- cating a transitional phase between low and medium grade metamorphism. The characteristic feature of this rock is the combination of schistosity and cross cutting strain- slip cleavage (steeply inclined to the former, Fig. 21). The matrix is an intergrowth of sericite, quartz and biotite which parallels the schistosity. All the constituents align 34 Fig. 21. Two idioblasts of chiastolite (Ch). Peripheral alter- ation to chlorite (Cl) is}characteristic. Upper crystal shows fracturingAWT). The strain-slip clea- vage cuts the schistosity at almost 90 degrees. The crystals appear to parallel the strain-slip cleavage. Graphite (G) themselves or occur in trains parallel to the schistosity, except for chloritoid which parallels the strain-slip cleav- age. Chiastolite forms perfect euhedra (cross sectional area averages h x 2 mm) with the characteristic geometrically arr- anged included graphite grains (Fig. 22). Optically, chias- tolite is identical to the normal andalusite. Chlorite shows a peripheral develOpment about the chiastolite in a conspic- uous manner. The point of interest that this slate-phyllite provides, is the age of the chiastolite with regard to the schistosity and the strain-slip cleavage.' In cross section, the 35 anr .. ... w _7, fl Fig. 22. Chlastolite crystal-(Ch) Showing crossed inclusion (graphitic material). Same crystal as in Figure 21. Plain light, X 5N. chiastolite shows both 110 and 100 cleavage. In longitudinal section, the prismatic cleavage is apparent as is a definite near 001 parting or fracture system. Since 001 cleavage is not characteristic for chiastolite, this feature could there- fore-represent fracturing related to deformation. The orienta- tion of the chiastolite porphyroblasts appear to parallel the strain-slip cleavage, however one prismatic section occurred at right angles to the strain-slip cleavage. It is therefore apparent, that a positive statement regarding the age of the chiastolite in reference to deformation cannot be made from the study of one thin section. Though chiastolite post-dates the schistosity, it is not perfectly clear whether it pre-dates or post-dates the strain-slip cleavage. 36 MINERALOGICAL CHANGES IN METAEORPHISM The develOpment by metamorphism of andalusite in a par- ticular horizon within the Halifax formation reflects the composition of the original sediment. The high alumina con— tent of the original sediment that comprises the andalusite bearing horizon is evident when compared to the normal alumina content of the average shale (Table 2). This excessive amount manifests itself in the formation of aluminum silicates through diagenesis and subsequent metamorphism. The type of aluminum silicate formed is dependent on metamorphic condition and intensity as well as composition. An estimation of the chemical composition of the original sediment can be inferred from the present lithology of the andalusite schists, however, the origin of this sediment is doubtful. PettiJohn states: "The origin of high-alumina shales is not clear. If the material were largely of residual origin the alumina content might be high, but since most shales are a mix- ture of both residual clays and detrital silt (mainly quartz), the alumina content is depressed. If the re- sidual materials are bauxitic rather than kaolinitic, the alumina content is augmented. A high alumina shale, therefore, is either a shale containing such bauxitic materials or a shale exceptionally low in silt and hence rich in kaolin or similar clay mineral“. The obtaining of andalusite from kaolin rich sediments can be shown by the following: (CHMA1281205 a AloSioL, + 3102 + 2H20 kaolin andalusite quartz water Probably the most important prerequisite that permits 37 the above reaction to take place is potassium deficiency: If sufficient potassium was available, muscovite or a K-feldspar would form rather than andalusite under the existing conditions. Table 2 shows the approximate chemical Compositions of the andalusite in zones 'one' and 'two' compared to the composi- tion of‘an average shale. The AlZOB/KZO ratio in the shale is n.7, while the same ratio of the andalusite schists in zones 'one' and 'two' are 5.6 and 9.0 respectively. General- izations as to the significance of these figures are difficult to make since the 8102 content must also be considered. If the A1203/K20 is high and 8102 is low corundum will form in- stead of an aluminum silicate, and if any magnesium is present a spinel mineral will form also. The presence of cordierite in zone 'two' indicates the higher temperatures to which the rocks of this zone were sub- Jected. The formation of cordierite can be shown by the fol- lowing equation: 8(OH),+A1281205 + 2H8MgA12313018 4.35102 .—.-. 5Mg2A1L,515018 +2H20 kaolin chlorite quartz cordierite water The above reaction is supported by the fact that the chlorite content decreases from ten percent in zone 'one' to one percent in zone 'two'. Also, the garnet content decreases from five to one percent in similar fashion, to aid in the chemical reconstitution. It can be shown, that the mineralogical changes produced by the effects of progressive metamorphism were accomplished 38 Zone 'one' Zone 'two' Average shale $102 56.b9 ' 57.66 58.10 A1203 26.90 26.91 15.3u K20 4.78 2.96 3.2a FeO 3.55 3.99 2.45 Fe203 .62 1.2“ 4.02 MgO 3.61 3.70 2.4“ H20 3.08 1.37 5.00 T102 trace trace .65 NaZO ? 1.18 1.30 5203 trace trace —--- C trace trace .80 BaO ---- ---- .05 C02 ---— -~-- -2.63 P205 —--- ---— .17 SO3 ---— --—- .6H [5.6“ ..I :f it“ ‘I Table 2. Table Shows an approximate chemical composition of the andalusite scnist”in Zones ‘one' and 'two'. The composition of an average shale is given for comparison (Pettijohn, 1950). by chemical reconstitution of the minerals present in the original sediment. A comparison of the chemical composition of rocks in zones 'one' and 'two' (Table 2) snow that very minor additions and subtractions of materials have taken place with increase in metamorphic grade. METASOMATISK Under this heading one of the most important criterion on the origin of the andalusite porphyroblasts will be dis— cussed. By metasomatism, We imply the additions of materials into the country rocks during or shortly thereafter derived from the granite intrusion. _ The failure of the two accessory minerals dumortierite and tourmaline to align themselves with the lineation in the andalusite schists is conclusive evidence that they are post- folding in age and related to the granite intrusion. The origin of these boron bearing metamorphic minerals can be either by, the metamorphism of boron—containing sediments or the introduction of boron from an external source. If boron was a constituent of the original sediment, one would expect the minerals containing this element to be aligned with the schistosity. This is assuming that during the folding which was responsible for the schistose fabric, sufficient heat for this element to combine in mineralogical growth would be avail- able. Since a preferred orientation of crystal growth is lacking for these two minerals, it is evident then, that they deve10ped after folding and are related to contact metamorphism. If these minerals are formed as such, it is logical to assume that the andalusite formation took place in a similar ' fashion. MO METARORPHISM As the result of regional and contact metamorphism, the rocks of the thesis area show mineral assemblages characteris- tic of variable metamorphic intensity in different parts of the area. From the relative position of these mineral assem- blages, a discussion of their metamorphic history can be made in reference to the facies concept.* \ Zone 'one': Andalusite-muscovite sub-facies The mineral assemblage present in this zone consists of andalusite, muscovite, quartz and chlorite. Here in zone 'one', the andalusite schist is in its lowest metamorphic state. The mineral assemblage, andalusite-muscovite is placed by Turner (1958) in the lower region of the hornblende hornfels facies. The presence of chlorite associated with andalusite in this mineral assemblage is difficult to explain. Disequilibrium of phases is recognized since the metamorphic conditions necessary to produce andalusite are more intense and beyond the stability range of chlorite. To explain this, the fol— lowing two probabilities might be considered. 1. The chlorite is a retrograde product from a previous Fe, E The idEa of metamorphic facies and later of mineral facies was deve10ped by Eskola as a result of his work on Finnish rocks. Recent work on metamorphic principles by Turner (l9h8) and more recent by Turner, Verhoogen and Fyfe (1958) gives a complete eXposition of the subject and is followed in this study of the rocks of the Port Felix area. hl Mg mineral such as biotite or an amphibole. No evidence is noted to confirm this since the Chlorite shows no relict texture or structure.of a previous mineral. 2. The association of chlorite with andalusite is due to unusual conditions not early discovered (e.g. water content, vapor pressure or composition), allowing it to remain in dis— equilibrium with the higher ranked andalusite. The rocks immediately south of the andalusite belt are essentially fine grained mica schists containing muscovite, quartz, biotite and chlorite. This assemblage is character— istic of the greenschist facies. Yet these rocks have been subjected to essentially similar metamorphic conditions as the andalusite schists adjacent to them. Chemical variation is probably responsible since the original composition of sediment should be reflected in the metamorphic equivalent. The absence of andalusite in these rocks is probably related- to the availability of potassium. In thin sections numbers two and eight the muscovite content varies from 50 to 75 per— cent. This amount of muscovite would indicate that potassium was available, while in the andalusite horizon potassium was deficient and allowed andalusite to form rather than muscovite. The previous could be said for water, if the water content was limited the develOpment of hydrous minerals would be restricted. The assumption is made that the contact action of the intruding granite acted equally on both rock types. This assumption is supported by the observations that both #2 rock types have similar proximities to the granite, and both possess identical schistosities permitting any gaseous or solution transfer. The presence and form of andalusite would favour this zone being placed in the lower region of the hornblende horn- fels facies, while the anomalous chlorite and the lithology of the mica schists would favour this zone being placed in the upper portions of the greensChist facies. Since the assigning of facies to rock types is but a relative one, it appears that a facies, transitional between the albite-epidote hornfels or greenschist facies and the hornblende hornfels or ~ amphibolite facies is present in zone 'one'. Zone 'two': Cordierite-andalusite sub-facies. In zone ‘two', the mineral assemblage consists of cordier- ite, andalusite, staurolite, muscovite, quartz and albite. The mineralOgical changes indicative of increase in metamorphic rank are as follows: 1. The appearance of cordierite and staurolite. 2. The decrease in muscovite content, with the remaining muscovite becoming coarser grained. 3. The decrease in chlorite and garnet content. Chemically, cordierite and staurolite are Mg2A14515018 and 2(AlO.AlSi0u)Fe(.OH)2 respectively. These formulas repre- sent the ideal minerals, the substitution of Fe for Mg in cordierite and Mg for Fe in staurolite commonly occurs. The elements necessary for these minerals to form could be derived ’z3 from the previously existing chlorite and garnet. Though the existence of Chlorite in zone 'one' is difficult to ex- plain we must assume that this mineral or a chemically equiva- .lent mineral (e.g. biotite), was originally present in zone 'two'. Though the chlorite is nearly non-existent in the andalus- ite belt of zone 'two', it is present in the chiastolite slate- phyllite as an alteration product peripheral to the chiasto— lite idioblasts (Fig. 22). In the alteration of chiastolite to chlorite,‘the addition of Mg, Fe, and H20 is required. If this alteration is a retrograde effect, it is indeed an unusual one. According to Turner et al, the mineral assemblage cordier- ite-andalusite-staurolite is well within the hornblende horn- fels facies. Although andalusite is the common aluminum silicate of the hornblende hornfels facies, sillimanite usually appears instead in some pelitic hornfelses in the 21mmediate vicinity of granite bodies (Turner, 1958). Since the origin and distribution of the three polymorphs of alum- inum silicate, andalusite, sillimanite and kyanite is not- accurately known, no attempt will be made to discuss the temperature-pressure conditions that prevailed during the metamorphism of the area. b4 METAMORPHIC PETROLOGY The complex mechanisms of metamorphism and the difficul- ties in its interpretation are accepted geological facts. The history of the Port Felix andalusite belt is no exception. It is a known fact that the mineral andalusite can form from either regional or contact metamorphic effects. The problem here at Port Felix is essentially this. A discussion of each will follow and an attempt will be made to show what met- amorphic effect is responsible for the andalusites origin. Regional metamorphism By regional metamorphism we imply the application of differential crustal stresses taking the form of lateral pres- sure prOpagated through long distances in such a manner that uniformity in the direction of strike of geological structures large and small, is produced. This would imply a gradual and orderly variation in metamorphic rank on a regional scale. Ideally, a steady advance in the grade of metamorphism from the borders of the region to the central tract would be expected. * From the regional structure of the Meguma series (long north-east, south-west trending folds that extend throughout south-eastern Nova Scotia), it becomes necessary to think in terms of large scale deformation. Areas of large scale defor- mation often show evidences of high temperature conditions. If the andalusite was formed as a consequence of regional * The views of A. Harker on regional metamorphism. metamorphism, high temperature conditions could have been produced With deformation. The main schistosity that parallels the regional fold- ing is a resultant of the stresses applied. With relieving of stresses, the heat deveIOped was retained (the conductiv- ity of all rocks is extremely poor) and provided the necessary thermal conditions for andalusite formation. The equal dis— tribution of andalusite throughout the entire belt fits into the regional picture. Elevation of the andalusite schist to a cordierite, andalusite schist at the granite contact supports a / , -- I ,I'. ,r lg “'v‘bl,‘ . :..l__‘ ' p ' 1. . pre-granite age for the andalusite belt. “Wop, a I z 4 -.e ..‘ . /. /.’. II' - 'P . ( ".E" (x . /"‘45P W‘Il I" . C-(.~.'(44("L,-F.,; ~' " - 9 ‘1‘ 0 Though the evidences brought out in this study point clearly to a contact metamorphic origin, the above discussion deserves some merit. The writer believes that only through a detailed study could a regional metamorphic origin be proven untenable. Contact metamorphism The main orogenic movement that folded the Meguma series was compressional and produced the long almost.east-west folds. The time interval between folding and later granite intrusion is not certain. The areal distribution of granite plutons in Meguma sediments goes beyond the map area and the prOportion of these rocks in the present erosion surface is approximately 'one to one. Though this ratio does not imply anything definite, it is felt that in mountain building orogenies an amount of igneous material of this order would not be abnormal. The b6 common occurrence of mountain building followed by igneous intrusion is noted throughout the world. It is therefore felt that the metamorphic history of the effected rocks can __be described in terms of large scale orogeny, producing 150- clinal folding with subsequent granite intrusion. The Acadian disturbance which took place during Devonian time was accompanied by much igneous activity. The deformation and granite intrusion shown in south-eastern Nova Scotia is probably related to this disturbance. A recapitulation of the events leading to the present metamorphic state of the Meguma might be: 1. The develOpment of the main schistosity during stress conditions at the time of folding. 2. With the cessation of stress conditions the granite intrusion followed providing the necessary heat re— quirements for porphyroblast deve10pment. #7 CONCLUSIONS The evidences cited appear to favour the contact metamor- phic origin of the andalusite schists in the Port Felix area, Nova Scotia. Though the distribution of cordierite leaves no doubt as to its contact metamorphic origin, the homogeneous distribution of andalusite into a belt paralleling the region- al folding leaves some doubt as to its exact metamorphic origin. The superimposing of a contact metamorphic effect on rocks dynamically deformed produces controversy in the recognition and interpretation of such a metamorphic history. In any event, the results of this study support a contact metamor- phic origin; the following evidences are Cited. 1. The andalusite porphyrohlasts show a random orientation in reference to the schistosity. 2.. The failure of the boron bearing minerals, dumortierite and tourmaline to orientate themselves with the schistosity. 3. In the Port Felix area, the granite is everywhere within one mile of the andalusite belt, and in the subsurface is ' 5 i r I ' - . . . .~-' (T .> J ,. " 120' 9 flu ( l b " "1:", I .’--’ f ‘- ‘ ‘, ' d. L at -' "x‘e. probably even closer. U. Porphyroblastic bearing metamorphic rocks of the Meguma series always occur associated with granite intrusions in the entire Province of Nova Scotia. 5. The aureole develOpment of cordierite about the granite _intrusion defines its contact metamorphic origin. Probably, the most important point brought out in this study is the role played by sedimentation in determining the ultimate product this rock has reached. A particular chem- ical composition related to sedimentation combined with large scale orogenic forces consisting of folding with subsequent granite intrusion are the gross geological mechanisms resoon— sible for the metamorphic history history of the area. RECOMRENDATIUN FOR FYRTFER STUDY The need for greater field study combined with concen~ trated petrographic and petrofebric investigations would aid much in the interpretation of the metamorphic history of the Meguma series. Knowledge of the structure of the folded keguma would be of great value. Chemical analyses of rock types studied would assist the student considerably. The relationship of structural deformation, regional metamorphism and granite intrusion is difficult to differen— tiate in textural differences or mineral relationsnips. Even if foliation is rresent, it leaves uncertain whether the metamorphic agent for andalusite formation was one of con- tact or regional extent. It is therefore apparent, that a detailed investigation of all three andalusite belts and adjacent rocks would permit greater Opportunity for important data to be discoverd. REFERENCES Faribault, E. R., and F1etcp er, H. (1336) deport on the L: :r Cambrian rocks of Guysbor'bgh and Halifax *ouniie;, no' Scotia, Geol., Natural History, C::n;;1:, Ann. Pep., Vol. 11, Part P, p. 129~163. Ford, W. E. and Dana, E. S. (1953) A Text book of Mineralogy, \v John Wiley & Sons, Inc. lew York. a? Fyfe, W. 3., Turner, F. J. and Verhoogen, J. (1958) Letamorpih ic , Reactions and Metamorphic Facies, hem.-73, Geol. Soc. Am. a Harker, A. (1939) Metamorphism, E. P. Button & Co., Inc. New York. ( Heinrich, E. W. (1956) Microscopic PetrOgraphy, thraw—Eill Book Co., Inc., New York, p. 173. Malcolm, W. (1912) Gold Fields of Nova Scotia, Geol. Sur., Canada, Eem. ZO-E, (compiled largely from the results of investigations by E. R. Faribault). Pettijohn, F. J. (1956) Sedimentary Rocks, Harper & DTOthLIS, New York, p. 365. Stevenson, I. M. (1959) Personal communication. Tilley, C. E. (192“) Contact Metamorphism in the-Comrie area, Geol. Soc. London Quart. Jour., Vol. 80, p. 22-71. Turner, F. J. (l9h8) Mineralogical and structural evolution of the metamorphic rocks, Geol. Soc. Am. Hem. 30. 9~l) Ii; leous an1 metamorphic / ———————————— , and Verhoogen, J. petrology, thraw—Hill, New York. Woodman, J. E. (1908) Probable age of the heguma series, bull. Geol. Soc. Am., vol. 19, p. 99-112. Ref-m Mia 45° (9‘ F, I Mcgumo Series (Unduvnded) 1 - ‘O _o v V v‘: I 'v v v v v v v v v v 45 w , v v v v v v v v v v v , LEGEND .v v v v v v v v v v V Iv v v v v v v v v v v DEVONIAN v o- .. __ V V V V V V V V V V V lv v? Gromte v v v v v v v v v v v v -- — v v v v v v v v v v v v v v P oaoovscmN . v v v v v v v v v v v v _ p g 1 : ANDALUSITE SCHIST v v v v v v v v v v v v v v ' ‘ v v v v v v v v v v v v v v v v v v v v v v v v v V v v v v v v v v v v v v v v v v v v v v v v v v V {I v v v v v v v v v - v v v i v v v v v v v v v ' 1' v "9' v v v v v v v ~V~- , "g V v v v vx/i E p30,, Whitehoven V ; A), - "' , ; ) 1 ) 1 Felix... _H.arbs2u_r : g ' l l I l 1 ' Gravel Road - 9 V | I . ' : Q) I . : i ‘3 J I ‘ / v Stole ‘ 1 i ' I I IINCH TOI MILE 1/1 ’ l ‘ / ’ Tor Bay (3!"m Fig. 23.Regionol Geology in the Vicinity of Port Felix, Nova Scotia ——- ...— “. _. ...__._ .. ...... .— E.A.S. 6|° 12' 6l°lll0' Muddy Lake ///' \TQ‘ “ [a L.E:C§E:hJ[) [)9/5 "4v \5 / \ w} ' l / Zone One // / / H X . . . ? -' \ , o - \ ‘ Andoiumte—Muscovute Subfocue \' ,/ _ / // ,i a 0 .. ‘ \K - / _ / . / ,./— v,— .\ w 7;. Northwest ' | / /:/8/‘5 .- I /\//N Arm ZOne TWO ,/ / X / /’/ // .- ,, / \ . . _ . . -./~. /, / 7/ / / - N Cordierite Andolusnte Subfome \ //// . f _ / 4/ \ X \ ° . . / / / O k ”7 7V 3 DEVONlAN . / ' ) / //// ? Z \\‘ \7.» VV V V Granite 45°|6 —- .. ./ / \ {m —— 45° le' / ’/° \c oaoovzcmN _7 / _ / Z \\ V Andalus.te Scn:sl /’/ / m —-t-— fifi—u—fi Holifox Formation ; / / 08 Doughboy MIG/E If m \ POM? ol‘ 6 03 './‘ ‘1" /o s‘ / OI’L .- 9 / M/‘Cfi/ ° 8:); ,, / 5 [R t t; as \ 7 oz. __ Location 8 Specimen Number M .. X . ‘7‘ —.~— 027 of thin section A 80 '80 _ \ ”1.3: Strike 8 Dip of Beds 0 ——+—— Strike of vertical Beds é ~+~~ Schistosity g9 z—i——7 Fracture Cleavage -1-- Z 0 ’° »— ‘ ? Gravel Road Whitehcven Harbour ? Scale of Feet 50 50° o 600 l200 y l l l l l Molasses Harbour v V V l | v eI°II2' el°iIO° E.A.S. Scoho Fig. 24. Geological Map of the Port Felix Area, Novo V V V V V V V V V V V V V V V V V ,V V V V V V l I V 9% V o ... n v k. W D m Gloce' "Ilflilllllllllligllllllllllillil ES 29603