Geology of the Milton area : sheets H45BD & part I45, scale 1:50,000

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Bishop, D.G. 1994 Geology of the Milton area : sheets H45BD & part I45, scale 1:50,000. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences geological map 9 32 p. + 1 fold. map

Abstract: The Milton sheet spans the Taieri-Tokomairiro fault-angle depression, the easternmost of the northeast trending fault-angle depressions of the Otago basin-and-range province. Basement rocks consist of schistose greywacke and associated rocks in the south. Metamorphic grade increases northward, and the rocks become more strongly foliated and segregated. The highest grade rocks are biotite zone schists of the greenschist facies, present near Brighton. Metamorphism occurred during the Jurassic, with subsequent unroofing extending into the Cretaceous. The schist basement is overlain unconformably by the Upper Cretaceous Henley Breccia, a terrestrial sequence of piedmont breccias and conglomerates about 1000 m thick. The breccia was derived from a high-standing schist block immediately west of the present day Titri Fault. Henley Breccia was tilted before the formation of the Otago peneplain, which was cut across both it and schist basement prior to the deposition of a relatively thin set of transgressive Upper Cretaceous to Tertiary terrestrial and shallow marine sediments. Alkaline basaltic volcanism commenced during the Miocene, and was probably accompanied by renewal of faulting on the Titri Fault, this time with the east side being raised. The most voluminous eruptions occurred west of the Taieri-Tokomairiro depression, but numerous small bodies are aligned along or close to the major faults. Continuing uplift on the Titri Fault resulted in younger piedmont deposits being shed from the fault scarp westward into the Taieri depression. Although movement on the Titri Fault continued into the Quaternary and resulted in deformation of some of the fault scarp deposits, no Recent fault traces are known, and the locus of activity seems to have shifted further east to the Akatore Fault. Several well-preserved Recent traces are present along the Akatore Fault, movement on which probably generated the 1974 Dunedin earthquake. South of Taieri Mouth the Holocene wave cut platform has been elevated by Recent movement on the fault. The southern part of the area includes the northern portion of the Kaitangata coalfield, and lignite was formerly mined at Waronui and Elliotvale. Numerous other small pits, mainly for local domestic supply, also existed throughout the region, but no coal is mined today. Good-quality limestone was formerly quarried extensively at Milburn, and considerable reserves remain. Phosphate, which was extensively prospected around Milburn and Clarendon during World War II, is not considered to be present in economic amounts. (auth)

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