White Mountain Magma Series

The White Mountain plutonic-volcanic series, which derives its name from the White Mountains of New Hampshire, includes lavas and pyroclastic rocks but principally intrusive complexes extending in a north-south line over about 200 km. The White Mountain batholith in the central part of the province is by far the largest complex. Rock types range from gabbros, through diorites and monzonites to syenites, quartz syenites and granites. Nepheline syenites are confined to Red Hill which is described separately (No. 130). Hedenbergite and fayalite occur in many of the intermediate rock types but peralkaline rocks are confined to syenite and riebeckite granite of the Hart Lodge complex in the middle of the batholith (Creasy et al., 1979), and riebeckite granites within the body of hastingsite granite 6 km west of Chatham in the northeastern corner of the White Mountain batholith and within the Mt Osceola granite on the western margin of the batholith (Billings, 1956, p. 82). Three other areas of riebeckite granite are found (Fig. 179), being hypidiomorphic granular rocks of microperthite, quartz, riebeckite and a little biotite and pyroxene; sheaves of astrophyllite are sometimes present (Billings, 1956, p. 83). The Moat volcanics, which are preserved in a down-faulted block within one of the collapse calderas comprising the White Mountain batholith, include peralkaline rhyolites (comendites) and trachytes (Creasy and Eby, 1981).