Azores plume

Azores plume
Name	Azores hotspot
Location	North Atlantic Ocean
Coordinates	37°N 25°W
Type	Mantle plume (hypothesized)
Tectonic setting	Triple junction of Eurasian, North American, African Plates
Notable islands	São Miguel, Terceira, Pico, Faial, São Jorge, Santa Maria, Graciosa

Azores plume is a proposed mantle upwelling beneath the North Atlantic that has been invoked to explain the volcanic islands and seamounts of the Azores archipelago and surrounding province. The feature is tied to plate interactions at the triple junction of the Eurasian Plate, North American Plate, and African Plate and to episodes of intraplate magmatism that produced the islands of São Miguel, Pico, Terceira, Faial, São Jorge, Santa Maria, and Graciosa. Interpretations balance plume-related models against alternatives invoking lithospheric extension, fracture-zone control, and shallow mantle heterogeneity explored by groups from institutions such as the Instituto Português do Mar e da Atmosfera, GEOMAR Helmholtz Centre for Ocean Research Kiel, and the United States Geological Survey.

Geology and Tectonic Setting

The region lies at the complex triple junction between the Eurasian Plate, North American Plate, and African Plate near the northern spreading axis of the Mid-Atlantic Ridge and the eastern termination of the Terceira Rift. The archipelago overlies a bathymetric high punctuated by seamount chains and fracture zones such as the Glória Fault and the Terceira Rift Fault, which interact with the ridge and transform systems like the Azores-Gibraltar Transform Fault. Seafloor morphology mapped by expeditions from the ROYAL NAVY research vessels and cruises run by institutions like IFREMER and Scripps Institution of Oceanography show crustal thickening and volcanic centers offset from the ridge axis, features used to argue for a mantle upwelling.

Volcanism and Magmatism

Volcanism across the islands ranges from subaerial stratovolcanoes and fissure-fed basaltic flows to evolved phonolitic and trachytic centres on islands such as Pico, Terceira, and São Miguel. Eruptive histories include Holocene events documented by local observatories like the Azores Seismological Observatory and historical records stretching back to early accounts from the Age of Discovery mariners. Magmatic products record alkaline to tholeiitic affinities, with eruption styles varying from effusive fissure eruptions on Faial to explosive pyroclastic activity at calderas on São Miguel and Terceira.

Geophysical and Geochemical Evidence

Geophysical surveys using seismic tomography from collaborations including IRIS and Euro-Mediterranean Seismological Centre reveal low-velocity anomalies beneath parts of the province, while gravity and magnetics data collected by NOAA and European agencies indicate crustal thickening and density variations. Geochemical studies of isotopes and trace elements—particularly helium isotopes (3He/4He), strontium, neodymium, lead, and hafnium—performed by laboratories at University of Oxford, ETH Zurich, and University of Azores show heterogeneous mantle signatures that mix enriched and depleted components reminiscent of some intraplate hotspots like Iceland and Hawaii. Petrological analyses from samples collected by submersible dives and dredging campaigns conducted by RV Knorr and RV Meteor show pyroxenite and peridotite sources, melt differentiation paths, and signatures of recycled oceanic crust.

Age, Evolution, and Mantle Dynamics

Radiometric dating (K–Ar, 40Ar/39Ar, and U–Pb on accessory minerals) constrains island and seamount ages from Miocene to Recent, with seamount chains showing age progressions inconsistent with a simple stationary hotspot track like Hawaii or Reunion yet compatible with plume-ridge interaction. Geodynamic models developed by researchers at Princeton University, University of Cambridge, and CNRS explore scenarios of a shallow asthenospheric thermal anomaly, narrow plumelets, or convective upwelling modified by plate motions and ridge suction. Mantle flow patterns inferred from seismic anisotropy and receiver-function studies by teams at ETH Zurich and GFZ German Research Centre for Geosciences suggest complex lateral flow and small-scale convection rather than a single, vertically continuous mantle stem.

Surface Expressions and Island Formation

The archipelago’s surface expressions include composite volcanic edifices, rift-related fissure systems, central volcanoes, and submerged volcanic ridges such as the North Azores Seamounts. Island construction involved repeated cycles of shield-building, intrusive activity, flank collapse, and marine erosion, producing varied geomorphologies visible on São Jorge’s fajãs and Pico’s volcanic cone. Submarine landslides, turbidite deposits recorded in cores retrieved by IODP-style expeditions, and Holocene tephra layers provide stratigraphic records used by paleovolcanologists at University of Lisbon and University of Cambridge to reconstruct eruptive sequences.

Research History and Debate

Debate over a mantle plume beneath the Azores dates to contrasting interpretations advanced in literature from the late 20th century by scholars affiliated with US Geological Survey, Universidade dos Açores, and European research centers. Early proponents compared the province to classic hotspots such as Hawaii; critics proposed fracture-zone and ridge-centered explanations inspired by work on Mid-Atlantic Ridge segmentation and transform-related volcanism examined by Woods Hole Oceanographic Institution. Ongoing multidisciplinary programs, including seismic campaigns, geochemical mapping, and numerical modeling funded by bodies like the European Research Council and national science agencies, continue to test plume versus non-plume hypotheses.

Environmental and Hazards Impacts

Volcanic hazards on the islands have included explosive eruptions, lava flows, phreatomagmatic events, seismic swarms, and flank collapses that can trigger tsunamis recorded in local archives maintained by the Azores Autonomous Government. Chronic geothermal activity produces fumaroles and hot springs exploited by regional energy initiatives and monitored by the Direção Regional do Ambiente. Impacts on biodiversity, agriculture, and maritime routes were noted historically during eruptions that affected ports used in the Age of Sail and continue to inform emergency planning coordinated with entities such as the European Civil Protection and Humanitarian Aid Operations.

Category:Geology of the Azores Category:Volcanism