A. Wandke — Study of Cape Neddick Gabbro. 295 



Art. XXVIII. — A Petrologic Study of the Cape Neddick 

 Gabbro; by Alfred Wandke. 



Location and Associated Rocks. 



The Cape Neddick gabbro, an elliptical stock, elongated 

 northwest, measuring three fourth's by half a mile, forms 

 the major portion of Cape Neddick, York County, Maine. 

 The stock invades the Kittery quartzite, a fine-grained 

 thinly bedded and vari-colored formation of steeply 

 inclined sediments which strike about 45 degrees north- 

 east, dip 60 degrees northwest and are presumably of 

 Upper Carboniferous 1 age. The intrusive may then be 

 dated tentatively as post Upper Carboniferous. 



In addition to this intrusive of gabbro the shoreline 

 portion of this part of Southwestern Maine offers a vast 

 assemblage of dike rocks which not only illustrate most 

 of the features associated with dike intrusion but also 

 show contrasted types as diabases, diorites, quartz dio- 

 rites, granite porphyries, tinguaites, camptonites and 

 aplites. Within half a mile of the stock is a batholith of 

 alkaline granite, but one of the rock varieties that make 

 up the composite mass known as the Agamenticus com- 

 plex. This complex shows in addition to a normal biotite 

 granite, alkaline rocks such as alkaline granite, syenite 

 and nordmarkite. 



The stock rising 45 feet above tide is well exposed. A 

 small portion of the landward half of its surface is drift- 

 covered, whereas the seaward half is almost swept clean 

 of debris. Excellent exposures are thus to be had not 

 only of the contacts permitting the contact phenomena to 

 be studied in detail, but also of the igneous mass itself 

 which is seen to be -composed of contrasting rock types 

 in rather complex relationships. 



Method of Emplacement. 



The debris-free contact zone, which in places is 

 exposed two hundred feet away from the intrusive, 

 enables one to study the mechanism of intrusion as well 

 as the details of contact metamorphism. As is shown in 

 fig. 1 the stock is clearly cross cutting. Although the out- 



1 U. S. Geol. Survey, Prof. Paper 108, p. 165, 1917. 



