Soldier Meadow Volcanic Centre
The Soldier Meadow peralkaline tuff and associated lavas were erupted from a linear vent area of five identified eruptive centres.
The present list of occurrences of alkaline rocks in the United States was based initially on the compilation of Barker (1974), who also discussed the distribution in space and time of North American feldspathoidal rocks (Barker, 1969). The present compilation contains not only newly discovered occurrences but also a number of peralkaline syenite and granite localities which were omitted earlier, althoughBarker himself pointed outthat a number of such occurrences had probably escaped his notice. There are probably still omissions because rocks of this type are often found in non-peralkaline environments and so easily missed during bibliographic searches. However, it is likely that coverage of the pantelleritic and comenditic rocks is relatively comprehensive, apart from as yet unknown occurrences, because of the thorough compilation of Noble and Parker (1975).
Future discoveries in the United States are likely to be in the Cordillera, and the large number of localities already known from there, when combined with the considerable numbers coming to light in British Columbia and Alaska, would suggest that western North America could become a particularly important area for exploring the relationship between alkaline igneous activity and orogenesis.
The Soldier Meadow peralkaline tuff and associated lavas were erupted from a linear vent area of five identified eruptive centres.
The type locality for the peralkaline Idaho Canyon tuff lies on the southern and southeastern sides of Big Mountain, but it outcrops extensively over northern Washow and western Humboldt Counties and extends northwards into Oregon.
This volcanic field covers some 20 000 km2 and formed by the eruption of seven ash-flow sheets having an aggregate volume of 1700 km3. All but one of the sheets are comenditic. Eruption of each sheet resulted in the formation of a large collapse caldera.
The Silent Canyon volcanic centre is located on the eastern Pahute Mesa, southern Nye County, and its dominantly pyroclastic products overlap with those that emanated from the Black Mountain centre further west.
Lying east of the Black Mountain and Silent Canyon volcanic centres Kane Springs Wash is the source of the Kane Wash tuff which covered an area of 7500-10 000 km2 and had an original volume of more than 800 km3.
Within Moon Canyon dykes, plugs and flows of lamproitic rocks are associated with andesitic pyroclastics and Palaeozoic shales and quartzites.
Dykes, sills and plugs cover an area of more than 200 km2 in the area of the San Rafael Swell. Dykes vary up to 3 m in thickness and sills up to about 35 m.
The Navajo volcanic field in the central Colorado Plateau lies within an area of about 250x180 km, but consists of a number of fields, or clusters of centres, namely Tuba, Wildcat Peak, Monument Valley, Chuska and Redrock Valleys, Lukachukai Mountains, Wheatfields, Washington Pass, Zilditloi and
Within an area of about 50x55 km are concentrated numerous volcanic necks, remnants of lava flows, now capping mesas, dykes and many craters of the maar type. Shoemaker et al. (1962, p. 329) estimate that about 300 diatremes or maar type volcanoes are present in the Hopi Buttes region.
The San Francisco volcanic field comprises numerous cones and extensive flows of basalt, latite, dacite and rhyolite, San Francisco Mountain being the largest edifice and lying towards the centre of the field.