MESOZOIC SYSTEMS ALONG THE PACIFIC 



2&3 



tary and intrusive rocks appears to swing from a northwest strike north- 

 west of the Cleveland peninsula to a north-south strike south of the penin- 

 sula. This is not due to a change from the prevailing northwest strike of 

 the beds but to a farther west penetration of the intrusive masses at the 

 south end. The differences between the smaller intrusive masses in the 

 metamorphic belt and the quartz diorite of the western border of the 

 batholith are slight. 



West of the metamorphic belt is the Prince of Wales-Chicagof belt in 

 which intrusive masses are common but less quartzose, and the country 



'rock consists predominantly of slate, limestone, graywacke, greenstone, 



I and dynamically metamorphosed schistose rocks with locally some crystal- 

 line schist and marble. The metamorphism is much less advanced than in 



| the Wrangell-Revillagigedo belt, though locally adjacent to large igneous 

 bodies it may be intense. The belt is 40 miles wide on the north, but not 

 much more than 5 miles wide on Kupreanof Island; it widens on Etolin 

 Island, and is about 25 miles wide through Prince of Wales Island. The 

 intrusive rocks of this belt differ, in general, from those to the east in that 

 they are predominantly diorite, rather than quartz diorite, and that dif- 



| ferentiates of highly contrasted composition are more adundant. 



The Kuiu-Heceta belt is next west and is characterized by the least 

 metamorphism of any of the belts, by the fewest intrusives, and as a re- 



| suit, by the best preserved and oldest fossils in its strata. The belt includes 



i. the western fringe of the north half of Prince of Wales Island, the north 

 end of Dall Island, San Fernando, Heceta, Tuxekan, Kosciusko, and Kuiu 

 islands, Kupreanof Island with the exception of the Lindenberg peninsula, 



i and the southwestern part of Admiralty Island. 



The Dall-Baranof belt is the westernmost of the six belts of the great 



i batholith with its satellites, and is characterized again by numerous stocks 

 and batholiths. It includes Dall, Forrester, Suemez, Baker, Lulu, Noyes, 



i Warren, Coronation, and Baranof islands. The intrusive rocks on the aver- 

 age are more silicic and carry less of ferromagnesian minerals than the 

 average of the Prince of Wales-Chicagof belt. Quartz diorite and, to a 



| lesser extent, granodiorite predominate. 



In the main batholith, the rocks are prevailingly gneissoid. The banded 



i character is most accentuated near the borders of the batholith or near 



inclusions within the batholiths. Local schistose zones are found along in- 

 tensely sheared narrow bands. The gneissic structure is for the most part 

 interpreted by Buddington as primary, but still the batholith was stressed 

 considerably after its complete solidification. Yielding occurred by mash- 

 ing along local belts or zones, which may be of considerable width and 

 great length (75 miles or more), or by intensive shearing along narrow 

 zones, or by slipping along many planes of various orientation throughout 

 a zone. A belt of highly mashed rock 15 miles wide is crossed by Stikine 

 River from the head of Little Canvon to and below Flood Glacier. 



In some places west of the main batholith, extensive belts, including 

 intrusive igneous stocks, dikes, and sills, constitute a local shear zone or 

 zone of close folding; the larger masses of igneous rocks may show con- 

 siderable mashing, and the thin sills may be closely folded together with 

 the schists. 



After reviewing pertinent studies on the succession of the intrusions 

 that make up the great batholith all the way from Vancouver to Cross 

 Sound, Buddington draws the following conclusions: 



West of the main batholith a group of ultrabasic intrusive rocks is 

 present in considerable volume. These include hornblendite, pyroxenite, 

 dunite, peridotite, and intermediate variants; they are older than the 

 more silicic-alkalic types. 



Diorite and gabbro-diorite occur both as discrete stocks and batholiths, 

 and also to a minor extent as marginal variations of quartz diorite and 

 granodiorite. Locally gabbro-diorite and augite gabbro are the marginal 

 phases of diorite. The gabbro-diorite and gabbro are locally intruded by 

 diorite, quartz diorite, and more silicic-alkalic types. 



Granodiorite in stocks and small batholiths mav show marginal variants 

 of quartz diorite, gabbro-diorite, diorite, monzodlorite, and very rarely of 

 syenite. A decrease in potassic feldspar and quartz locally on the margins 

 is a common feature. 



Granite is the youngest of the major members of the plutonic complex, 

 and is uniformly found with intrusive contacts through the older mem- 

 bers. 



Buddington also point out that west of the Sierra Nevada batholith in 

 the Coast Ranges of California there is a similar older group of ultrabasic 



