Kapenga Caldera
Volcanic caldera in New Zealand From Wikipedia, the free encyclopedia
The Kapenga Caldera (also known as the Kapenda Volcanic Centre) in New Zealand’s Taupō Volcanic Zone lies in a low land area immediately south of Lake Rotorua through the Hemo Gap in the Rotorua Caldera rim. At some time more than 60,000 years ago Lake Rotorua drained through the Hemo Gap and some of the Kapenga Caldera floor was likely occupied by a lake, that has been called Kapenga.[2]: 360
| Kapenga Caldera | |
|---|---|
| Kapenda Volcanic Centre | |
 The Kapenga Caldera is to the south of the Rotorua Caldera and to the south-east of the Ōkataina Caldera (thick white border). Relationships to other nearby volcanic and tectonic structures is also shown. | |
| Highest point | |
| Coordinates | 38°16′S 176°16′E |
| Geography | |
.png)  Kapenga Caldera  Kapenga Caldera Kapenga Caldera (North Island) | |
| Country | New Zealand |
| Region | Waikato |
| Geology | |
| Age of rock | approximately 890,000 years |
| Mountain type | Caldera |
| Volcanic region | 275,000 ± 10,000 years ago[1] |
| Climbing | |
| Access | State Highway 5 (New Zealand) |
The Kapenga Caldera has a western boundary defined by the Horohoro cliffs and an eastern boundary by volcanic domes, including those in the Ōkareka Embayment with some buried by the younger activity of the Ōkataina Volcanic Centre. Its southern boundary of volcanic activity is ill defined but does not extend to areas of continuing low residual gravity abnormality in the Paeroa Garben.
Geology
Map centered to show selected surface volcanic deposits in area of postulated Kapenga Caldera/Volcanic Centre (light green shading). The present surface ignimbrite is various light violet shades which are identical for any single source, but other eruptions may breakup the mutual ignimbrite sheets.
Clicking on the map enlarges it, and enables panning and mouseover of volcano name/wikilink and ages before present. Key for the volcanics that are shown with panning is: basalt (shades of brown/orange), monogenetic basalts, arc basalts, arc ring basalts, andesite (shades of red), basaltic andesite, and plutonic. White shading is selected caldera features.
The Kapenda Caldera, just south of the Rotorua Caldera and between this and the Maroa Caldera, is believed to have been buried by subsequent eruptions including those of the Tarawera volcanic complex. The eastern area of the postulated caldera has had, relative to much of the rest of the central Taupō Volcanic Zone, many smaller eruptions after caldera formation.[3] Problematically to date no definite assignment of the up to seven ignimbrites attributed to it can be related to a definite caldera-forming event or documented collapse despite geology suggestive that such may have occurred.[4] It had several very large eruptive events during the ignimbrite flare-up of the Taupō Volcanic Zone between 350,000 to 240,000 years ago.[1] The boundary between the Kapenda Caldera and the Ōkataina Caldera is debated which particularly affects more recent Earthquake Flat activity. The Kapenda Caldera occupies the northern part of the Paeroa Garben between the uplift caused by the now fairly inactive Horohoro Fault and the uplift associated with the still very active Paeroa Fault. To the south of the caldera is the Ngakuru Graben. For an unknown period between the Mamaku Ignimbrite eruption of the Rotorua of 240,000 years ago and about 60,000 years ago Lake Rotorua drained via the Hemo Gorge into the Kapenga Caldera which likely contained a lake, and through the Ngakuru Graben, onwards to the Waikato River as it existed then.[2]: 358–360 Subsequent volcanic activity has buried much evidence of this phase of the caldera's history.
A large number of intra-rift faults called the Taupo Fault Belt and associated with the modern Taupō Rift exist in the Paeroa Garben and Kapenga Caldera so it is quite a tectonically active area presently.
The paired in time Rotoiti eruption and Earthquake Flat Breccia eruptions, had the later initially assigned to the Kapenga Caldera as it was within the old caldera's margins, but some have assigned to the magma mush body that underlays the magma bodies of the Ōkataina Volcanic Centre and thus to a different volcanic centre.[5]: 32, 243 The issue is unresolved.[lower-alpha 1]
There are two rhyolite domes of note. These are the Horohoro Cliffs at 817 m (2,680 ft), a rim-fracture dome associated with the Horohoro Fault that marks the northwestern edge of the Kapenda Caldera, and Haparangi a late-stage intra-caldera dome that rises above the Ngakuru Graben to 688 m (2,257 ft).[5] Haparangi Rhyolite has been a term used since 1937 to any rhyolite flows/lavas of Pliocene-Pleistocene origin in the Taupo Volcanic Zone and does not imply any origin from the Kapenda Caldera.[5]
The northern part of the caldera has amongst the highest rate of subsidence in the Taupō Rift.[9]: 4672 This is believed to be predominantly driven by cooling and subsequent contraction of an underlying magma body at about 6 km (3.7 mi) depth.[9]: 4667, 4677
Eruptions
Its known eruptions were:
- 890,000 - 680,000 years ago
- 310,000 - 275,000 years ago
- The caldera is not a source of some of the Mamaku ignimbrite as previously speculated - this all originates from Rotorua Caldera.[11]
- Neither is the caldera the source of the Ohakuri Ignimbrite as previously speculated.[5] This comes from the Ohakuri Caldera[12]
- Pokai ignimbrite (0.275 ± 0.01 Ma)[1] (previously assigned 0.23 - 0.22 Ma)[5]
- Waihou (Chimp, Chimpanzee) Ignimbrite (0.31 ± 0.1 on stratographic grounds)[1] (previously assigned 0.26 - 0.25 Ma) [5]
- (controversial)[lower-alpha 1][lower-alpha 2] about 50,000 years ago (Earthquake Flat Breccia)
- An attempt to address the controversy of which caldera was responsible for the Earthquake Flat eruption was made in 2001 by DA Bowyer with the difficulties noted.[5] Often such issues can be resolved by compositional analysis and Bowyer noted that the Earthquake Flat eruptives were distinct from the earlier Chimp erputives. Much of the compositional analysis that may help resolve this issue appears to be in the public domain and was last compiled by H. Elms using her own data on two Rotoiti samples and Earthquake flat from BLA Charlier.[6]: 42, 62, 65 Elms says "The Earthquake Flat magma was erupted from the adjacent Kāpenga caldera and was magmatically separate from the Rotoiti magmas."[6]: 105 but notes the similarity in composition of the Rotoiti and Earthquake Flat eruptives compared to other recent Ōkataina eruptives.[6]: 64 Such a similar composition would also appear to be consistent with models proposed by others where the Earthquake Flat eruptives shared the common deep magma sources that underlies the known shallower mush pockets of the Ōkataina Caldera.[6]: 123 [7] A point not apparently considered by those involved in the controversy is that it is theoretically possible by analogy to basaltic eruptions in Iceland for a Ōkataina mush pocket to erupt many kilometers away, say in an old caldera.[8]
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