Download Geology of the Kaimai Ranges

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Kaimai
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Mount Maunganui
Aongatete River
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Tauranga
Whakamarama Plateau
Tilted 3-5o
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The big picture
Papamoa Range
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Mamaku Plateau
Kaimai Dome
Making mountains
5.6 - 4 million years ago
The Kaimai Ranges are made up of a series of volcanos (mostly
Kaimai Volcanos
andesitic-dacitic cones) which erupted between 4 and 5.6 million
years ago. They are the southern end (and youngest) of a line of
Greywacke basement rocks
progressively older volcanos which extend up to the northernmost
tip of the Coromandel Peninsula.
Hauraki Fault
Covering up
3.9 - 2 million years ago
Later more explosive rhyolite eruptions in the Rotorua area (and
possibly within the Tauranga Basin) spread vast amounts of hot
rocks and ash – known as ignimbrite – out over large parts of
the land. Some ignimbrite deposits were relatively small - like the
Aongatete ignimbrite
Waiteariki ignimbrite
Aongatete Ignimbrite which covered this area. Others were much
larger, such as the Waiteariki Ignimbrite which is up to 220 metres
coast
thick. Local rhyolitic eruptions also formed hills like the Kaimai
Dome at the headwaters of the Wairoa River and Mt Maunganui
(Mauao) on the coast.
Lifting up
2 - 1.2 million years ago
Starting about 7 million years ago, massive tearing in the Earth’s
crust made what is now called the Hauraki Fault. Although it
took millions of years to form, most movement happened about
1-2 million years ago when the Kaimai volcanos on the east of the
Hauraki Fault were uplifted (in places up to 4 kilometres higher
than the west). As well as creating the mountain range, the
faulting also tilted the Waiteariki Ignimbrite to form the
gently-inclined fertile plateau of the Tauranga Basin.
Filling in
1 million years ago to present
Over the last million + years, the low land in and around what is
now Tauranga Harbour has been filled slowly with river
Deposition
Erosion
Deposition
sediments, swamp deposits, dunes and volcanic ash up to 50 m
thick in places.
The low areas west of the Hauraki Fault were also filled up with
ignimbrites and sediments to form the Hauraki Plains.
Ignimbrite rock sample
Ignimbrite
Andesite
Fact
Fact
A New Zealand geologist
The names comes from ‘The
named this type of rock –
it means ‘fiery rock dust’
Andesite rock sample
Andes’ in South America, where
this type of rock is common