Moehau Range: Geography, Geology, and the Legacy of Coromandel Granite
The Moehau Range stands as the defining physical feature of the Colville Ecological District. Characterized by a rugged landscape, the region is defined by long ridges and steep streams that radiate toward the coast, complemented by broken hillslopes, floodplains, harbors, and estuaries. This diverse environment spans 77,201 hectares (190,770 acres), maintaining a strong connection to its natural roots with 59% of the land covered in indigenous vegetation and 8% consisting of virgin forest. To the south, the range is drained by the Waikawau River.
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Key Facts
- Total Area: 77,201 hectares within the Colville Ecological District.
- Vegetation: 59% indigenous vegetation and 8% virgin forest.
- Primary Rock Type: Metamorphic greywacke sandstones and siltstones.
- Age of Base Rock: Approximately 150 million years (Jurassic/Cretaceous).
- Notable Material: Quartz diorite, commercially known as Coromandel granite.
Geological Composition
The geological foundation of the Moehau Range is primarily composed of the Manaia Hill Group. These are metamorphic rocks—rocks that have undergone transformation by high heat and pressure—specifically prehnite-pumpellyite greywacke sandstones and siltstones belonging to the Waipapa terrane. Formed roughly 150 million years ago during the Jurassic and Cretaceous periods, these formations contain few fossils but are interbedded with mudstone, argillite, and volcanic sandstone.
The Paritu Pluton and Volcanic Activity
To the southwest, the landscape shifts with the exposure of the Paritu Pluton. A pluton is a body of intrusive igneous rock that crystallized from magma slowly cooling below the surface. This specific formation dates back 17 million years to the mid-Miocene epoch and consists of pyroxene-hornblende quartz diorite, hornblende-pyroxene granodiorite, and biotite-pyroxene. Additionally, around 15 million years ago, dikes of quartz porphyry and andesite porphyry intruded into the older Manaia Hill rocks.
The History of 'Coromandel Granite'
Despite its commercial name, the stone known as Coromandel granite is scientifically classified as a quartz diorite. First advertised in 1900, this stone was extracted from the plutonic area on the coast between Waiaro and Port Jackson at the Paritu quarry. In 1918, the Coromandel Granite Company took over operations and constructed a wharf approximately one kilometer to the south to facilitate transport.
This durable stone became a staple for prestigious New Zealand architecture. It was used in the construction of several landmark buildings, including:
- Parliament House
- Auckland Chief Post Office
- Auckland War Memorial Museum
- Auckland Ferry Terminal
- Auckland Railway Station
While commercial quarrying largely ended in the 1960s, the Moehau quarry was briefly reopened in the early 1990s specifically to provide materials for the refurbishment of Parliament House.
| Feature | Details |
|---|---|
| Ecological District | Colville |
| Total Land Area | 77,201 hectares |
| Primary Geological Group | Manaia Hill Group (Waipapa terrane) |
| Age of Primary Rocks | ~150 million years |
| Pluton Age | 17 million years (Mid-Miocene) |
| Commercial Stone Type | Quartz diorite (marketed as granite) |
Frequently Asked Questions
Is the stone from the Moehau Range actually granite?
No. Although it was commercially advertised and sold as Coromandel granite, it is geologically a quartz diorite rock.
How old are the primary rocks of the Moehau Range?
The metamorphic sandstones and siltstones of the Manaia Hill Group were formed approximately 150 million years ago during the Jurassic and Cretaceous periods.
What percentage of the Colville Ecological District is covered in native plants?
Approximately 59% of the district is covered in indigenous vegetation, with 8% specifically identified as virgin forest.
Which famous buildings used Coromandel granite?
The stone was used for Parliament House, the Auckland War Memorial Museum, the Auckland Chief Post Office, the Auckland Railway Station, and the Auckland Ferry Terminal.
What is the Paritu Pluton?
The Paritu Pluton is a mid-Miocene sub-volcanic intrusion located southwest of the range, consisting of rocks like quartz diorite and granodiorite formed about 17 million years ago.