Physical volcanology of Moeraki Peninsula

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Andrews, Benjamin J. (Benjamin James)

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Abstract:

Eocene explosive submarine volcanism on the East Otago shelf is reported and discussed. Surtseyan lapilli tuff deposits with maximum stratigraphic thicknesses of at least 175 m record the existence of a volcano that built into storm wave base and may have emerged. A diverse range of large clast types, including schist xenoliths and dike fragments, show that the lapilli tuff was produced through a variety of fragmentation processes including Fuel-Coolant Interaction. Additionally, irregular shaped clasts exhibiting possible fluidal deformation indicate that magma was ejected from the vent while still molten. Stratigraphy also indicates that the volcano experienced two periods of major activity with a relatively quiescent interval between. Though widespread slumping and possible sector collapse have rendered accurate reconstruction of the volcano nearly impossible, orientations of dikes and data from two measured stratigraphic sections indicate that a large island near the centre of the field area may have been the vent.
Both basalt and clastic dikes are emplaced in lapilli tuff at Moeraki. The basalt dikes are commonly banded with alternating layers of high and low vesicularity; these textures indicate formation through repeated injection of magma. The innermost bands of the dikes are often discontinuous and pinch out in fold hinges, indicating syndeformational emplacement. Irregular intrusions of basalt also occur at Moeraki and may be large intrusive pillows. The clastic dikes at Moeraki exhibit three textures; porcelainite breccia, mudstone breccia and mudstone. Though mudstone dikes occur discretely on one beach, a progression of all three occurs in association with basalt dikes at another locality. The dikes there grade from basalt through porcelainite to mudstone and indicate formation of clastic dikes as a result of explosive brecciation of sedimentary rocks. The brecciation is generated by the phreatomagmatic interaction of hot basalt dikes with wet low permeability mudstones. Numerical modelling of this process is presented.

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141 leaves : ill. (some col.), maps ; 30 cm. + 1 CDrom.

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2001Andrews

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POLYGON ((170.845821911633834 -45.355973015372307,170.87170887119035 -45.350266282770164,170.883647607033794 -45.374304531726061,170.859848784774414 -45.37814781914598,170.845821911633834 -45.355973015372307))

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http://download.otagogeology.org.nz/temp/Abstracts/2001Andrews.pdf

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Andrews, Benjamin J. (Benjamin James), “Physical volcanology of Moeraki Peninsula ,” Otago Geology Theses, accessed December 4, 2021, http://theses.otagogeology.org.nz/items/show/375.

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