NEW ENGLAND APPALACHIAN SYSTEMS 



L79 



sw 



Mt. Faraway 



NE 



S.Nickerson Mtn. 



I Albany 



I quartz syenite 



Moat volcanics 



"iyZ'-tfy, Winnipesaukee 

 ?/?t'/;'4 quartz diorite 



Scale In Miles 



Scale in Kilometers 



Fig. 11.23. Section through the Ossipee Mountains, N. H. Reproduced from Billings, 1945, after 

 Kingsley. 



It is apparent that the intrusion of some ring-dikes is associated with the sub- 

 sidence of a central block. It does not follow, however, that all ring-dikes are 

 associated with central subsidence. 



Billings (1945) believes, because the ring-dikes are vertical in New 

 Hampshire, that their intrusion was controlled by an annular vertical 

 fracture zone, the width of which was comparable to the width of the 

 ring-dike. Such a fracture zone would be susceptible to piecemeal stoping. 

 Various combinations of the annular or partially annular fracture zone ■ 

 with sagging or doming are shown in Fig. 11.24. 



Stocks. For most of the stocks there are few data to indicate whether 

 they are concordant or discordant because many of them have been in- 

 truded into areas already occupied by relatively massive or weakly foli- 

 ated older plutonic rocks. The Mt. Ascutney stock has been shown to cut 

 discordantly across the steeply dipping older strata, and the lineation and 

 fold axes of the older strata have not been modified by the intrusion 

 (Chapman and Chapman, 1940). A process of underground cauldron sub- 

 sidence, whereby large blocks with outward-dipping walls approximately 

 the size of the present stocks sank, is visualized, and is illustrated in Fig. 

 11.25. The activity occurred in the last stages of the evolution of the 

 White Mountain magma series. The remarkable uniformity of the White 

 Mountain magma series through New Hampshire suggests that a single 

 reservoir underlay much of the state (Billings, 1945). 



Plutons of Forceful Injection. Many plutons belonging especially to 

 the New Hampshire magma series have been emplaced bv forceful in- 



Fig. 11.24. Origin of ring-dikes. Reproduced from Billings, 1945. Broken line is present erosion 

 surface. 



