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Digital geological maps of New Zealand (QMAP) have been combined with 9256 samples with rock density measurements from the national rock catalogue PETLAB and supplementary geological sources to generate a digital density model of New Zealand’s bedrock at a 1 arc-min spatial resolution. The QMAP dataset contains 123 unique main rock types spreading over more than 1800 mapping units over the three main islands of New Zealand (i.e., North, South, and Stewart Islands). Rock densities measurements from the PETLAB database and other sources have been assigned to the QMAP geological mapping units. An average surface rock density of 2440 kg/m3 for New Zealand is obtained from the analysis of the derived digital density model. The lower average density of 2336 kg/m3 in the North Island reflects the predominance of relatively young, weakly consolidated sedimentary rock, tephra and ignimbrite. This contrasts with the South Island whose average density is 2514 kg/m3 and where igneous intrusions and metamorphosed sedimentary rock, including schist and gneiss, are more common. All of these values are substantially smaller than the average density of the upper continental crust that is commonly adopted in geological, geophysical, and geodetic applications (2670 kg/m3) and typically attributed to the crystalline and granitic rock formations. The lower density has implications for the calculation of the geoid surface and gravimetric reductions through New Zealand.
Tenzer, R.; Sirguey, P.; Rattenbury, M. & Nicolson, J. (In Press, corrected proof), 'A digital bedrock density map of New Zealand', Computers & Geosciences. doi:10.1016/j.cageo.2010.07.010
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