The New Zealand Greywackes: A study of geological concepts in New Zealand

Abstract

This thesis traces changes in geological concepts associated with the New Zealand greywackes. Since mineralogists adopted the German mining term 'grauwacke' in the 1780s to refer to a type of old, hard, grey, muddy sandstone, both the name and the rock have caused confusion and controversy. English geologists in the 1830s used the term 'grauwacke' as a rock name and a formation name for their most ancient rocks. The English abandoned the name, but 'greywacke' remained useful in Scotland and began to be used in New Zealand in the 1890s. New Zealanders still refer to the association of semi-metamorphosed greywacke sandstones, argillites, minor lavas, cherts and limestone constituting the North Island ranges and the Southern Alps as 'the greywackes'. With the South Island schists, the greywackes make up 27% of the surface of the New Zealand landmass. They supply much of our road metal, but otherwise have little economic importance. Work on these basement rocks has rarely exceeded 10% of geological research in New Zealand.Leading geologists of the nineteenth and early twentieth centuries competed to construct stratigraphical models for New Zealand where the greywackes were usually classified as of Paleozoic age. Controversy was generated by insufficient data, field mistakes, wrong fossil identifications, attachment to ruling theories and the inability of European-based conventional stratigraphical methodologies to deal with these Carboniferous to Jurassic rocks formed in a very different and unsuspected geological environment. After 1945, growth of the universities, increased Geological Survey activity, and the acquisition of more reliable data led to fresh explanatory ideas about geosynclines, turbidity currents, depositional facies, low-grade metamorphism, and structural geology. New interest in the greywackes resulted in the accumulation of additional knowledge about their paleontology, petrography, sedimentology and structure. Much of this geological data is stored in visual materials including maps, photographs, and diagrams and these are essential today for the interpretation and transfer of information.The development of plate tectonic theory and the accompanying terrane concept in the seventies and eighties permitted real progress in understanding the oceanic origin of greywackes within submarine accretionary prisms and their transport to the New Zealand region. In the last half century comparatively little geological controversy about the greywackes has taken place because of the acquisition of quantities of data, technological improvements, and the use of a dependable theory of the Earth's crust. Scientific controversy takes place when data and/or background theory is inadequate.