Coromandel Volcanic Zone
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The Coromandel Volcanic Zone (CVZ) is an extinct intraplate volcanic arc stretching from
Great Barrier Island Great Barrier Island () lies in the outer Hauraki Gulf, New Zealand, north-east of central Auckland. With an area of it is the sixth-largest List of islands of New Zealand, island of New Zealand. Its highest point, Mount Hobson, Great Barrier ...
in the north, through the
Coromandel Peninsula The Coromandel Peninsula () on the North Island of New Zealand extends north from the western end of the Bay of Plenty, forming a natural barrier protecting the Hauraki Gulf and the Firth of Thames in the west from the Pacific Ocean ...
, to the
Kaimai Range The Kaimai Range (sometimes referred to as the ''Kaimai Ranges'') is a mountain range in the North Island of New Zealand. It is part of a series of ranges, with the Coromandel Range to the north and the Mamaku Ranges to the south. The Kaimai ...
in the south. The area of transition between it and the newer and still active
Taupō Volcanic Zone The Taupō Volcanic Zone (TVZ) is a volcano, volcanic area in the North Island of New Zealand. It has been active for at least the past two million years and is still highly active. Mount Ruapehu marks its south-western end and the zone runs n ...
is now usually separated and is called the
Tauranga Volcanic Centre The Tauranga Volcanic Centre is a geologic region in New Zealand's Bay of Plenty. It extends from the southern end of Waihi Beach and from the old volcanoes of the Coromandel Peninsula that make up the northern part of the Kaimai Range, towards ...
. Its volcanic activity was associated with the formation and most active period of the
Hauraki Rift The Hauraki Rift is an active NeS-to NWeSE-striking rift valley system in the North Island of New Zealand that has produced the Firth of Thames and the Hauraki Plains. It is approximately wide and long. Geology The rift valley in the north ap ...
.


Geology


Tectonics

The Coromandel Volcanic Zone is generally older than the currently still active Hauraki and
Taupō Rift The Taupō Rift is the seismically active rift valley containing the Taupō Volcanic Zone, central North Island of New Zealand. Geology The Taupō Rift (Taupo Rift) is a intra-arc continental rift resulting from an oblique convergence in the H ...
s. This has implications as the widening of the
Hauraki Rift The Hauraki Rift is an active NeS-to NWeSE-striking rift valley system in the North Island of New Zealand that has produced the Firth of Thames and the Hauraki Plains. It is approximately wide and long. Geology The rift valley in the north ap ...
was most about 5.5 million years ago, so the Kiwitahi volcanics (called by some the Kiwitahi Volcanic Zone), which occur west of the
Coromandel Peninsula The Coromandel Peninsula () on the North Island of New Zealand extends north from the western end of the Bay of Plenty, forming a natural barrier protecting the Hauraki Gulf and the Firth of Thames in the west from the Pacific Ocean ...
and the Hauraki Rift are probably best regarded as related to the Coromandel Volcanic Zone. For example, some of the volcanics are broadly contemporaneous in age, composition and orientation north south, with eruptions at 16 million years ago at
Stony Batter Stony Batter is a historic defence installation at the north-eastern end of Waiheke Island, Auckland, New Zealand. It is sited within a 50-acre (200,000 m2) scenic reserve of the same name, owned by the New Zealand Department of Conservation (D ...
,
Waiheke Island Waiheke Island is the second-largest island (after Great Barrier Island) in the Hauraki Gulf of New Zealand. Its ferry terminal in Matiatia Bay at the western end is from the central-city terminal in Auckland. It is the most populated island ...
, however Stony Batter has been active much more recently. Thus the tectonic processes involved in the formation of the
Hauraki Rift The Hauraki Rift is an active NeS-to NWeSE-striking rift valley system in the North Island of New Zealand that has produced the Firth of Thames and the Hauraki Plains. It is approximately wide and long. Geology The rift valley in the north ap ...
and Coromandel Volcanic Zone in the continent of
Zealandia Zealandia (pronounced ), also known as (Māori language, Māori) or Tasmantis (from Tasman Sea), is an almost entirely submerged continent, submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83 ...
have moved from the north to the south over the last 20 million years. The Coromandel Volcanic Zone includes back arc volcanoes that are related to historic but distinct fault structures such as the Hauraki Fault, which is along the eastern side of the zone. The undersea western side of the Coromandel Volcanic Zone has a parallel structure to the Hauraki basin and plains also of late
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
/Quaternary origin extending north, that has been called the East Coromandel Rift. The formation of the
Taupō Rift The Taupō Rift is the seismically active rift valley containing the Taupō Volcanic Zone, central North Island of New Zealand. Geology The Taupō Rift (Taupo Rift) is a intra-arc continental rift resulting from an oblique convergence in the H ...
and the old
Taupō Volcanic Zone The Taupō Volcanic Zone (TVZ) is a volcano, volcanic area in the North Island of New Zealand. It has been active for at least the past two million years and is still highly active. Mount Ruapehu marks its south-western end and the zone runs n ...
about 2 million years ago terminated significant activity in the Coromandel Volcanic Zone. However it is important to recognise that the
Tauranga Volcanic Centre The Tauranga Volcanic Centre is a geologic region in New Zealand's Bay of Plenty. It extends from the southern end of Waihi Beach and from the old volcanoes of the Coromandel Peninsula that make up the northern part of the Kaimai Range, towards ...
and its postulated Omanawa Caldera at the intersection of the two rifts, have likely relationships to the location of the more recent north eastern caldera's of the
Taupō Volcanic Zone The Taupō Volcanic Zone (TVZ) is a volcano, volcanic area in the North Island of New Zealand. It has been active for at least the past two million years and is still highly active. Mount Ruapehu marks its south-western end and the zone runs n ...
. These eruptions will have buried on land any older volcanics that were related to the southern end of the Coromandel Volcanic Zone. Offshore
tephra Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...
deposits suggest the start of a composition change, at 4.5 million years ago, about the time the Waihi Caldera was active, and well before the end of Coromandel Volcanic Zone activity if this was at Bowentown.


Volcanism

Activity began in the north around 18 million years ago, and was primarily andesitic in an intraplate volcanic arc until around 9–10 million years ago. The oldest volcanic rocks at the northern tip of the
Coromandel Peninsula The Coromandel Peninsula () on the North Island of New Zealand extends north from the western end of the Bay of Plenty, forming a natural barrier protecting the Hauraki Gulf and the Firth of Thames in the west from the Pacific Ocean ...
are the Port Charles andesites that are dated from about 18 million years ago. With time, the volcanism tended to move southwards at /year and eastwards at /year. After this stage it is postulated that the Kapowai Caldera, the largest in the zone, located in the centre of the
Coromandel Range The Coromandel Range is a volcanic mountain range in the Coromandel Volcanic Zone running the length of the Coromandel Peninsula in the North Island of New Zealand. It is located east of the city of Auckland, and runs north–south for approx ...
(peaks of Table mountain, The Pinnacles, Tanehua) formed. This is part of a rhyolitic transition that can be seen from
Whitianga Whitianga is a town on the Coromandel Peninsula, in the Waikato region of New Zealand's North Island. The town is located on Mercury Bay, on the northeastern coast of the peninsula. The town has a permanent population of as of making it the ...
to
Whangamatā The town of Whangamatā is on the southeast coast of the Coromandel Peninsula in the North Island of New Zealand. It is located 30 kilometres north of Waihi, to the north of the western extremity of the Bay of Plenty. In holiday times the popu ...
on the western side of the zone but it is notable that some of the eastern Whitianga rhyolites are younger than some further south. In the period 9 to 7 million years ago a bimodal basalt to basaltic andesite/rhyolite association developed with major caldera collapse, ignimbrite eruptions, and then post-caldera andesite eruption. This included the Wharepapa Ignimbrite event from the Kapowai Caldera about 8 million years ago. To the south of the large Kapowai Caldera some have located the smaller Wharekawa Caldera. The Tunaiti Caldera, immediately south of Whangamatā is believed to be about 7 million years old and has pre-caldera andesites and dacites, and later dacites and rhyolite domes and flows. Then between 6 and 5.5 million years ago bimodal eruptions of basalt to basaltic andesite as well as rhyolite and rhyolitic ignimbrite began once more. This formed the volcanic structures around
Waihi Waihi is a town in Hauraki District in the North Island of New Zealand, especially notable for its history as a gold mine town. The town is at the foot of the Coromandel Peninsula, close to the western end of the Bay of Plenty. The nearby res ...
later important in precious metal discoveries due to subsequent hydrothermal mineral deposit formation. As activity decreased between 4.7 and 4.2 million years ago it became entirely basaltic with the volcanics of the eastern
Mercury Islands The Mercury Islands are a group of seven islands off the northeast coast of New Zealand's North Island. They are located off the coast of the Coromandel Peninsula, and northeast of the town of Whitianga. History Great Mercury Island (Ahu ...
being typical before the transitioned into early activity in the Taupō Volcanic Zone. Some of the later activity in the Coromandel Volcanic Zone and its interface with the Taupō Volcanic Zone is obscured by subsequent large scale events. It was suspected to have continued in the south to at least 2.5 million years ago with the Bowentown rhyolites south of
Waihi Beach Waihī Beach is a coastal town at the western end of the Bay of Plenty in New Zealand's North Island. It lies 10 kilometres to the east of the town of Waihi, at the foot of the Coromandel Peninsula. The main beach is 10 kilometres long. The town ...
marking the transition to the
Tauranga Volcanic Centre The Tauranga Volcanic Centre is a geologic region in New Zealand's Bay of Plenty. It extends from the southern end of Waihi Beach and from the old volcanoes of the Coromandel Peninsula that make up the northern part of the Kaimai Range, towards ...
geographically. However compositional analysis suggests Bowentown rhyolites have much in common with the Minden rhyolites of the Tauranga Volcanic Centre so may belong with this centre. The extinct undersea Colville Ridge, which has been dated to 5.4 million years before present is part of the Coromandel Volcanic Zone and can be associated with the modern Taupō Volcanic Zone and Kermadec Ridge. Geothermal activity is still present in the Zone, with hot springs in several places, including at Hot Water Beach, on the central east coast between
Whitianga Whitianga is a town on the Coromandel Peninsula, in the Waikato region of New Zealand's North Island. The town is located on Mercury Bay, on the northeastern coast of the peninsula. The town has a permanent population of as of making it the ...
and
Tairua Tairua is a beachside town located on the east coast of the Coromandel Peninsula in the North Island of New Zealand in the Thames-Coromandel District. It is located 150 kilometres (93 miles) east of Auckland and 125 kilometers (78 miles) north ...
and on the south western margins of the Zone near
Te Aroha Te Aroha is a rural town in the Waikato region of New Zealand with a population of 3,906 people in the 2013 census, an increase of 138 people since 2006. It is northeast of Hamilton, New Zealand, Hamilton and south of Thames, New Zealand, T ...
where there is only natural soda water geyser in the world. There are mineral deposits such as
gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
in quartz reefs associated with past geothermal and volcanic processes. Mount Hobson Great Barrier Island.jpg, Mount Hobson,
Great Barrier Island Great Barrier Island () lies in the outer Hauraki Gulf, New Zealand, north-east of central Auckland. With an area of it is the sixth-largest List of islands of New Zealand, island of New Zealand. Its highest point, Mount Hobson, Great Barrier ...
in the Coromandel Volcanic Zone Coastal mountains of the Coromandel (7087657167).jpg, Typical example of the rugged forested nature of the
Coromandel Range The Coromandel Range is a volcanic mountain range in the Coromandel Volcanic Zone running the length of the Coromandel Peninsula in the North Island of New Zealand. It is located east of the city of Auckland, and runs north–south for approx ...
in the Coromandel Volcanic Zone Coromandel Peninsula.jpg, Northern
Coromandel Peninsula The Coromandel Peninsula () on the North Island of New Zealand extends north from the western end of the Bay of Plenty, forming a natural barrier protecting the Hauraki Gulf and the Firth of Thames in the west from the Pacific Ocean ...
landscape in the Coromandel Volcanic Zone Cathedral Cove, Coromandel.JPG, Sea arch at Cathedral Cove, carved in
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...
Hayward, B. (2008)
Protecting NZ's Heritage Natural Arches
, ''Geological Society of New Zealand Newsletter'' 145(March), 23.
deposited by a
pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...
about 8 million years ago 00 2934 Gold and Silver Mine (Martha Mine) in New Zealand.jpg, The
Martha Mine The Martha Mine is a gold mine in the New Zealand town of Waihi. Since July 2015 it has been owned by OceanaGold. History William Nicholl marked out a claim, calling it "Martha" after a family member. Several smaller claims were later merged ...
is a large
Gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
and
Silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
mine in the middle of the Coromandel Volcanic Zone KaimaiPICT6700.jpg,
Kaimai Range The Kaimai Range (sometimes referred to as the ''Kaimai Ranges'') is a mountain range in the North Island of New Zealand. It is part of a series of ranges, with the Coromandel Range to the north and the Mamaku Ranges to the south. The Kaimai ...
with communications towers


See also

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Geology of the Auckland Region The Auckland region of New Zealand is built on a basement of greywacke rocks that form many of the islands in the Hauraki Gulf, the Hunua Ranges, and land south of Port Waikato. The Waitākere Ranges in the west are the remains of a large andesit ...
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Geology of the Waikato-King Country Region Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...
*
List of volcanoes in New Zealand This is a partial list of active, dormant, and extinct volcanoes in New Zealand. Kermadec Arc and Havre Trough North Island Taupō Volcanic Zone Elsewhere South Island Other Ross Dependency New Zealand also has ''de fact ...
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Volcanism of New Zealand The volcanism of New Zealand has been responsible for many of the country's geographical features, especially in the North Island and the country's outlying islands. While the land's volcanism dates back to before the Zealandia microcontinent ...
*
Stratigraphy of New Zealand This is a list of the geological unit, units into which the lithostratigraphy, rock succession of New Zealand is formally divided. As new geological relationships have been discovered new names have been proposed and others are made obsolete. N ...


References

{{Reflist Geography of Waikato Landforms of Waikato Volcanism of New Zealand Geology of New Zealand Volcanoes of Waikato Thames-Coromandel District Miocene volcanism Pliocene volcanism Volcanic arcs