Occurrence and source of quartz in six basaltic soils from Northland, New Zealand

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Abstract
Quartz abundance, distribution and O isotope composition was determined for 6 basaltic soils from Northland, New Zealand. Quartz > 125 .mu.m in size occurred in 2 soils, the Kiripaka and Ruatangata. .delta.18O values of 8.2.permill. for the > 250 .mu.m sized quartz in both soils and 8.1-8.4.permill. for that in the 250-125 .mu.m size fraction of the Ruatangata indicate a high temperature origin for this quartz. A probable origin is from air-fall rhyolitic tephra (particularly Kaharoa Ash) erupted from the central North Island. Another potential source is quartzose beach sand from the western (windward) coast of Northland. Quartz from these beach sands has a .delta.18O value of 8.7.permill., also indicating a high temperature origin. Quartz in the 63-20 .mu.m size fractions of the basaltic soils has a mean .delta.18O value of 12.0.permill., consistent with derivation from local sedimentary rocks as loess. Quartz in the 5-2 .mu.m fraction of the soils has a mean .delta.18O value of 13.9.permill., similar to that of aerosolic dusts prevously reported from this latitude. The Kiripaka soil had anomalously high .delta.18O values of 17.3-19.6.permill. for 5-2 .mu.m sized quartz. This quartz originated from marine shales in the vicinity of the soil profile sampled; local sources may contribute to the aerosolic size fraction of soils in addition to tropospheric aerosolic dust.

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