Nineteenth-century observations of the Dun Mountain Ophiolite Belt, Nelson, New Zealand and trans-Tasman correlations
M. R. Johnston, 2007. "Nineteenth-century observations of the Dun Mountain Ophiolite Belt, Nelson, New Zealand and trans-Tasman correlations", Four Centuries of Geological Travel: The Search for Knowledge on Foot, Bicycle, Sledge and Camel, P. N. Wyse Jackson
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The Nelson Mineral Belt, part of the Dun Mountain Ophiolite Belt of Permian age, in the north of the South Island of New Zealand, was the subject of intense interest soon after the European settlement of New Zealand owing to the discovery of copper and chromite mineralization. The first geologist to survey the Mineral Belt in east Nelson was Thomas Ridge Hacket (c. 1830–1884), who arrived from Britain in 1857, although he was primarily interested in the mineralization. The first scientific description of the belt followed the visit in 1859 of the geologist Ferdinand von Hochstetter (1829–1884) of the Austrian Geological Survey who regarded the belt as a sill. He recognized that Dun Mountain was not serpentinite, like the rest of the belt, but an olivine-rich rock that he named dunite. von Hochstetter tentatively considered that thick mafic rocks of the Brook Street Volcanics, that were then considered to be intrusives rather than sedimentary, may have been a correlative of the Mineral Belt. Between the belt and the Brook Street rocks he mapped the Wooded Peak Limestone and Maitai Slates. von Hochstetter tentatively assigned a Mesozoic age to all of the above rocks and for nearly 100 years Mesozoic sedimentary rocks in many parts of New Zealand were regarded as a correlative of the Maitai Slates.
Both Hacket and von Hochstetter confirmed an abundance of chromite in the Mineral Belt, a finding that resulted in the building of New Zealand's first railway. Mining was short-lived but hopes were raised that gold might be found following Hacket's move to Queensland in the late 1860s. He recognized that the Gympie gold-fields had many similarities with Dun Mountain and reasoned that east Nelson might also be auriferous. This was taken up by men in Nelson such as Sir David Monro (1813–1877) and William Wells (1810–1893) who were keen geological observers, and by Monro's son in law Dr, later Sir James, Hector (1834–1907) who was director of the New Zealand Geological Survey. In 1870, Hector arranged for Edward Heydelbach Davis (1845–1871) to undertake a detailed examination of the Permo-Triassic rocks of east Nelson. Davis, like Hacket, regarded the Mineral Belt as metamorphosed Maitai rocks. As well as demonstrating that the east Nelson rocks did not contain economic concentrations of gold, copper or chromite, Davis showed that they were distinct from what had been thought to be similar rocks in the Coromandel gold-fields in North Island of New Zealand. This was the first, if not fully appreciated, step to limit the Maitai rocks. Hacket's correlation of the Gympie and Dun Mountain rocks was forgotten until the advent of plate tectonics. The various major rock units in Nelson are now recognized as terranes that accumulated as a result of convergent plate tectonics along the Mesozoic margin of Gondwanaland.
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In the last four centuries geologists have traversed the globe, searching for economically important materials or simply to satisfy their intellectual curiosity. Geologists have often been at the vanguard of scientific exploration.
The microscopist Robert Hooke explored the Isle of Wight, and Charles Darwin the Cape Verde islands and parts of South America. The volcanic wonders of Italy and central France attracted native and foreign visitors including Lyell and Murchison. The Tyrrell brothers faced great hardship in northern Canada, as did the actor and mineralogist Charles Lewis Giesecke in Greenland. The development of Sydney, Australia depended on finding limestone for building. French geologists relied on camels in the Sahara, and Grenville Cole trusted his tricycle to carry him across Europe.
Four Centuries of Geological Travel: The Search for Knowledge on Foot, Bicycle, Sledge and Camel focuses on the complexities of geological exploration and will be of particular interest to Earth scientists, historians of science and to the general reader interested in science.