Petrology and geochemistry of Tertiary volcanic rocks from inland Central and South Canterbury, South Island, New Zealand

Abstract

Three episodes of Tertiary basaltic volcanism are recognised in inland Central and South Canterbury: (1) Paleocene-Early Eocene (View Hill Volcanics); (2) Late Oligocene (Brothers Basalt, Thomas Formation, Mounseys Creek nephelinite); and (3) Miocene-Pliocene (BluffBasalt, . Harper Hills Basalt, Oxford Basalt, Timaru Basalt, Geraldine Basalt). On petrological and geochemical grounds, most rocks are classified as tholeiites. Although these rocks have been erupted in a withinplate continental setting, their trace element chemistry shows affinity to ocean island tholeiite and "plumerelated" mid-ocean ridge basalt. Early-Middle Tertiary basalts were erupted in a mildly extensional tectonic setting whereas Late Tertiary rocks were erupted in a strongly compressional setting. The chemistry and distribution of volcanism may have been influenced by crustal thickness and structure.

Temporal and geochemical evolution of the Cenozoic intraplate volcanism of Zealandia

“…Sutherland, 1995 Ar age of 56.5 ± 0.5 Ma; matrix step heat). Samples from the View Hill Volcanics in central Canterbury yielded a restricted age range with ages of 50.8 ± 0.3, 50.0 ± 1.1, 49.3 ± 0.6 and 48.9 ± 0.7 Ma (fsp and matrix step heating, within the slightly larger K/Ar age range of 48-52 Ma) (Sewell and Gibson, 1988).…”

“…The Paleocene to Lower Eocene tholeiitic basalts to basaltic andesites of the View Hill area in Central Canterbury produced K/Ar ages of 51.7 ± 2.4 (all errors are reported at the 2-sigma confidence level) and 47.9± 3.6 Ma (Sewell and Gibson, 1988), whereas the tholeiitic to alkaline Cookson Volcanics (≥100 km 3 ) (McLennan and Weaver, 1984;Morris, 1987) were erupted in the Oligocene. Based on our field studies, the stratigraphically oldest eastern Cookson units are pillow basalts and sheet flows, indicative of submarine volcanic activity, whereas the western Cookson units are characterized by stratigraphically younger conglomerates with large, well-rounded beach cobbles and heavily-oxidized lava flows with top and/or bottom breccias, indicating shallow water to subaerial conditions of emplacement.…”

“…Therefore we interpret the Cookson Volcanics to have been part of an Oligocene shield volcano, which rose above sea level and formed an island. Based on K/Ar dating, the Oxford volcanics in central Canterbury range in age from 27.1± 0.8 to 15.6 ± 1.0 Ma (Sewell and Gibson, 1988). Middle to Late Miocene alkaline to tholeiitic volcanic activity was widespread and produced the large Lyttelton (∼350 km 3 ) Fig.…”

“…Since the Otitia Basalts are, like the Arnott Basalt, on the Australian Plate, they were emplaced several hundred kilometers south of most of the South Island, which was located on the Pacific Plate. Ar ages fall at the older end of the K/Ar age range of 30-11 Ma, determined for the Oxford volcanics (McLennan and Weaver, 1984;Sewell and Gibson, 1988). Early to mid Miocene volcanic activity took place on the Central Chatham Rise, near the Chatham Islands (Charlton A Seamount, 22.0 ± 0.4 Ma; matrix step heat), western Chatham Rise (Orton/Vernon Bank, Anja Seamount and Veryan Bank, 21.8 ± 0.4, 19.9 ± 0.2 and 12.9 ± 1.1 Ma, respectively, matrix step heat ages) and at the Urry Knolls (Jordan Seamount; 14.5 ± 0.2 Ma; matrix step heat).…”

Sedimentology and structure of the Malvern Hills Coal Mine, Canterbury, New Zealand

“…Basic igneous dykes and sills of various Tertiary ages (e.g. PalaeoceneÁEocene View Hill Volcanics, Miocene Harper Hills and Bluff Basalts; Sewell and Gibson 1988) intrude the Late CretaceousÁPalaeocene succession in several places (Carlson et al 1980;Duff 1986;Duff & Barry 1989;Forsyth et al 2008). (Duff 1986).…”