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Earth of fire

Actualité volcanique, Article de fond sur étude de volcan, tectonique, récits et photos de voyage

 

South island - Banks peninsula

  NZ South Island - central portion of the island with the Banks Peninsula on the east coast - Nasa

Akaroa Volcanic Group :

It includes all volcanic eruptions products of central, flanks, and parasites vents localized in two-thirds southeast of Banks Peninsula .
A fieldwork shows that the lavas and pyroclastic which form the Akaroa volcano can be divided into two phases, described as preliminary and main .

akaroa-harbour-nature - tripadvisor
                                               Akaroa Harbour - photo Tripadvisor

Phase I / preliminary - 11 ? to 9 Ma
Rocks produced during this preliminary phase are visible on the inner coastline of Akaroa harbor. Oldest - Preliminary Phase 1 - are basaltic lava flows. The preliminary phase 2 comes in trachytic tuffs, breccias , agglomerates, flows, sills and a large dome which marks the end of the construction of the proto- Akaroa. The preliminary phase 3 includes basaltic flows, tuffs, lahar deposits, cinder cones and pyroclastic breccias

Phase II / Main - 9 - 8 Ma
A prolonged period of weathering and erosion separates the two phases . The main cone of Akaroa is built on a base of predominantly lava flows hawaiite type 
and pyroclastics, and rarer mugéarite, benmoréite and trachyte lava flows. Volcanic activity can be classified as Hawaiian to moderately Strombolian .

Elephant Rock, Akaroa Harbour, Banks Peninsula - Christchur           
Banks Peninsula , Akaroa Harbour - "Elephant Rock " - photo Christchurhnz

Onawe Peninsula, 2007 - J Oswald
                               Akaroa Volcano - the Onawe peninsula - photo J.Oswald

Akaroa harbour - Te Ara - McLinv1010The eruptive activity of Akaroa is marked by the intrusion of dykes, predominance trachytic, and building of five large domes of trachyte . Dykes radiate from a central area, S / SE of the peninsula Onawe (a plug, localized in Akaroa ), which coincides with the presumed site of the main eruption pipe.

Map of Akaroa harbor and location of the peninsula Onawe - doc . Te Ara NZ

Gravimetric analysis reveals an intrusive complex in subsurface equivalent to more than 615 km³ of intrusive materials.

akaroa-harbour-nature
                             Dyke in Akaroa Harbour - photo Tripadvisor

The Lyttelton Volcanic Complex , located north - west of Banks Peninsula , includes five overlapping cones. Centers of activity of the volcano Lyttelton arrange around Quail Island, which is considered close to the original vent .

Lyttleton-Harbour-pan5v3
                                      Lyttelton Harbour  - photo pan5v3

Lyttleton harbour - Stuff NZ
                                   Lyttelton Harbour - photo Stuff NZ

We assume that two different magmatic systems fueled the intraplate basaltic volcanism on Banks Peninsula , with simultaneous activity in the N0 and SE thereof, to form the two volcanic complexes Lyttelton and Akaroa .

New Zealand - Banks Peninsular, Arkada c1865
Old engraving of the Akaroa bay / Banks Peninsula  - 1865 c - prints of Ancient Australia & Pacific . / New Zealand - Banks Peninsular, Arkada

 

 

Sources :

- University of Canterbury / Geological sciences - The geology and geochemistry of Akaroa volcano, Banks peninsula , NZ - by C.J.Dorsey - link

- The basal beds of the Akaroa volcano - by R.Speight - link

- University of Canterbury / Geological sciences - Growth, Structure and Evolution the Lyttelton Volcanic Complex, Banks Peninsula, New Zealand - by S.J Hampton -  link

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