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Melting moments point to erratic eruptions worldwide

Discrete melt batches that move at different depths and speeds may explain the erratic spatial and temporal pattern of eruptions in the Auckland Volcanic Field (AVF).

Such behaviour may have major implications for the evolution of continental volcanic fields worldwide.

A Quaternary monogenetic basaltic field of ca. 50 volcanoes, the AVF includes Rangitoto.

The most recent volcano, Rangitoto, suggests a change in the field’s behaviour. The largest in magnitude, it erupted magmas of alkalic, then subalkalic basaltic composition in separate events.

Major and trace element geochemistry – together with Sr–Nd and U–Th–Ra isotopes – provides the basis for modelling melting conditions that have led to the eruption of the chemically different lavas.

The alkalic basalts suggest lower degrees of partial melting, higher amounts of residual garnet, a longer melting column and lower melting and upwelling rates compared with the subalkalic basalts.

Attachments

Dynamics of melting beneath a small-scale basaltic system: A U-Th–Ra study from Rangitoto volcano, Auckland volcanic field, New Zealand. Cover
Dynamics of melting beneath a small-scale basaltic system: A U-Th–Ra study from Rangitoto volcano, Auckland volcanic field, New Zealand.

Contributions to Mineralogy and Petrology · April 2012