208 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



relations of the mass are unknown. A smaller satellite some 1,000 feet thick and 

 well-differentiated occurs in Lark Mountain, south of the mouth of Bay of 

 Islands. 



North of Bay of Islands, also, the basal portion of the ultrabasic rocks com- 

 posing the serpentine belt is composed of a wide zone of peridotites which dip 

 westward. 



Since no igneous rocks are known to cut the Carboniferous of western New- 

 foundland, the intrusives are referred to either the Taconic (late Ordovician) 

 or the Acadian (late Devonian) orogeny. 



The western serpentine belt extends adjacent to the west coast from 

 Port au Port Ray to Ronne Ray and forms the flat-topped Serpentine 

 Range, previously mentioned, with summit elevations around 2000 feet. 



Other areas of serpentine not included in the eastern and western belts 

 are on the east side of the northern peninsula at Hare Ray, and at Raie 

 Verte and Ming's Right. At Hare Ray considerable thicknesses of perido- 

 tites have an eastward dip and, with the enclosing sediments, form the 

 eastern limb of the northern peninsula anticline. 



At Raie Verte, the formation of that name, which consists of greenstone 

 and greenstone schist with minor amounts of graywacke, tuff, agglom- 

 erate, lava, slate, ferruginous chert, sandstone, and marble, has been in- 

 truded by large, dominantly concordant bodies of ultramafic rock and 

 gabbro (Watson, 1943). Much of the ultramafic rock has undergone in- 

 tense serpentinization and steatitization. The gabbro has suffered saus- 

 suritization, uralitization, silicification, carbonatization, and alteration to 

 zoisite-quartz and zoisite-prehnite rock. Granite, quartz-porphyry, and 

 quartz-diorite intrusions occur in the Raie Verte formation. Adjacent to 

 the latter, the greenstone and gabbro have been metamorphosed to the 

 amphibolite fades. Small sills and dikes of mafic gabbro, porphyrite, 

 diorite, and kersantite were observed in the area. 



The above areas of ultramafic rocks are shown on the map of Fig. 13.4. 

 These occurrences in Newfoundland are considered part of a major ser- 

 pentine belt from Georgia through the crystalline piedmont belt to the 

 Hudson Valley and through the Taconic system to the St. Lawrence and 

 the Gaspe Peninsula. They have been compiled by Hess, and his map is 

 reproduced in Fig. 8.29. Hess has developed the theory that serpentine 

 plutons occur in linear arrangement and mark the heart of the belts of 



great compressional deformation, especially of the volcanic arc type. If 

 the linear belt of ultramafic plutons be interpreted in this way, we have 

 to deal with additional evidence of a great orogenic belt, and can point to 

 its core of greatest deformation. 



In the St. Lawrence-Gaspe belt, most of the serpentinized plutons are 

 Taconic in age, but some may be Devonian. About the same can be said 

 of their age in Newfoundland. Their age is not known in the crystalline 

 piedmont, but it is inviting to think of the entire serpentine belt as one 

 of the manifestations of the great Taconic orogeny. 



Granitic Plutons 



Many large discordant granitic to dioritic plutons, some of batholithic 

 proportions, occur in the central part of Newfoundland between the Pre- 

 cambrian of Long Range and the Precambrian of Avalon peninsula. 

 Some lie within the Precambrian areas also. For the most part they have 

 not yet been mapped and differentiated. They are now regarded as prob- 

 ably Acadian in age, since one has been found intruding the early 

 Devonian beds of the La Poile Ray area and another one cuts the De- 

 vonian beds of the Fortune Ray area. Some may be late Silurian (Cale- 

 donian ) ; most are known to cut the Ordovician strata, and pebbles of the 

 granite are found in a Mississippian conglomerate. 



Instructive examples are the Ray du Nord granodiorite and Ackley 

 granite batholiths of the Fortune Ray and Rurin peninsula region. See 

 map, Fig. 13.5. According to White (1940): 



The (Ackley) batholith intrudes the northwest limb of a large syncline, the 

 major structure of the Fortune Bay synclinorium. The invaded rocks are largely 

 the Ordovician (?) Belle Bay volcanics, and to a lesser extent, tuffaceous slates 

 conformably overlying the volcanics, and Cambrian quartzites. The mapped 

 extent of the batholith is over 160 square miles, but this is probably less than 

 half of the total. The long axis of the intrusion is oriented approximately north- 

 east, parallel to the dominant regional structural trends. The dip of the contact, 

 where it could be determined, is 25° to 45° outward from the batholith. 



The topography of the batholith is of low relief, with elevations averaging 

 about 750 feet, in contrast to the higher elevations and considerably greater 

 local relief of the volcanics to the south. 



The intrusion consists mainly of granite ("white granite") and alaskite ("red- 

 granite"), with the latter the more abundant, in the southern part of the batho- 



