A study of the Mineral Breccia Member of the Deborah Volcanic Formation at Kakanui, New Zealand.

Dickey, JS(Jn)

In early Oligocene time three submarine volcanic eruptions near Kakamui, New Zealand, formed lapilli tuffs of the Deborah Volcanic Formation. The eruptions which created Tuffs I and II were of basalt or atlantite magma, the final eruption, which created the Mineral Breccia Member, was of melanophelinite magma and contained xenoliths of lherzolite, eclogite, amphibolite, pyroxenite, and granulite xenocrysts of kaerusite, anorthoclase limenite and coarse grained aggregates of pyrope and augite. Multiphase fluid inclusions probably dominated by liquid CO2 (Roedder, 1965), occur in all translucent phases of the suite of xenoliths and xenocrysts. Most of the xenoliths, except those of amphibolite, have undergone solid state deformation. Possible partial fusion zones occur along garnet-amphibole and garnet-pyroxene grain boundaries. Compound xenoliths show lherzolite in contact with amphibolite and eclogite. There are several reaction relationships between the lherzolite and the melanophelinite.
The lherzolite is believed to be either solid residue from the partial fusion of primary mantle material or the product of crystallization from a primitive liquid. The eclogite, granulite, and pyroxenite are believed to have crystallized from a basaltic liquid at various depths. the amphibolite is believed to have crystallized in the melanophelinite magma shortly before eruption. It is proposed that the nephelinite magma was created from basaltic magma chiefly by the removal of crystals of anorthoclase, pyrope, and hypershthene-normative augite.
Six chemical analyses and a large number of optical and x-ray data are presented.

iv. 113 p.; ill.; map folded.; 27cm.

1966Dickey

POLYGON ((170.874066186610406 -45.203740674443516,170.8840832803117 -45.151496646023844,170.942990678666831 -45.151382426471521,170.941895845564545 -45.205134564202034,170.874066186610406 -45.203740674443516))