120 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



Fig. 8.28. Serpentine belt of the Appalachians. By H. H. Hess, Princeton University; and pub- 

 lished with his permission. Circles represent known bodies of serpentine. 



at low angles; in some places the strata are flat, and the maximum in- 

 clination is 25° to 30°. Drilling is too widely spaced to permit determina- 

 tion of more than the gross structural pattern. As the rocks have been 

 encountered over an extensive area, even these low dips would be suffi- 

 cient to account for a sedimentary and volcanic sequence of considerable 

 thickness. 



These discoveries are of great interest, as they show that southeast of 

 the Appalachian system there is a foreland or shelf of little deformed 

 rocks, just as there is northwest of it. 



Ultrabasic Intrusives 



Hess ( 1937a ) has charted the serpentinized ultramafic intrusives of the 

 Appalachians and finds they form a narrow belt lengthwise of the Pied- 

 mont crystalline province through New England to Quebec City, thence 

 through the Taconic and Acadian belt of Quebec to the Gaspe Peninsula, 

 and again in a belt through Newfoundland. See the map of Fig. 8.28. In 

 his work in the Greater and Lesser Antilles, he has concluded on the basis 

 of considerable evidence (see Chapter 42) that the serpentines occur in 

 the arcuate, highly deformed, orogenic belt, and as a conclusion, that in 

 certain ancient orogenic belts, now obscured by metamorphism and 

 blanketing deposits, they can be taken to indicate the position of the 

 zone of maximum orogeny. The serpentinites are chiefly associated with 

 the Taconian orogenic belt in New England and the Maritime Provinces, 

 and they are strong evidence, it seems to Hess, that the core of the 

 Taconian orogeny stretched through the crystalline Piedmont of the 

 southern and central Appalachians. 



Resides the granite plutons, the metamorphic and plutonic belt con- 

 tains a group of intrusives of ultrabasic composition — peridotites, dunites, 

 pyroxenites, and others, now in part altered to serpentine. Unlike the 

 granites, they mostly occupy small areas, but in many places they form 

 well-defined zones, indicating that they were intruded under the in- 

 fluence of some sort of tectonic control. The most prominent zone lies 

 toward the northwest edge of the metamorphic and plutonic belt, in the 

 southeast part of the Rlue Ridge province of western North Carolina; it 

 continues northeastward into Virginia, and southwestward into Georgia. 



