PATTERNS OF HOT-SPOT VOLCANISM

The aim of this paper is to identify the characteristic features, in t erms of geophysically measured parameters, of the hot spot sites over the Earth's surface. We use a pattern recognition approach which ident ifies associations as well as single parameters, and our statistical a lgorithm allows us to work at a given significance level, avoiding any overfit. We use the following parameters: absolute plate velocity of the site, minimum distance between neighboring hot spots, minimum dist ance from a ridge, minimum distance from a trench, geoid anomaly of ha rmonic degrees 2-10 and 11-36, area of the host plate, lithospheric th ickness and stress state. The hot spots, generally defined as volcanoe s not obviously related to plate boundaries, are found to occur in sit es characterised by either one of two main significant patterns: (1) p ositive values of geoid anomalies with harmonic degree between 2 and 1 0, which is characteristic of most of the hot spots with a ''track'' o f extinct volcanoes; (2) clustered volcanoes (distance between volcano es less than approximately 900 km) in slow moving plates (velocity <2. 5 cm/yr). A third pattern, representative of isolated volcanoes (dista nce between volcanoes greater than approximately 900 km) anomalously c lose to mid-ocean ridges (distance from the ridge less than approximat ely 600 km) can also be tentatively identified. This result implies th e existence of two main types of hot spot volcanism, the first one of sublithospheric origin with dynamics which is not influenced by surfac e tectonics, and the second one mainly due to a favorably ''soft'' lit hosphere. A third type would probably consist of 'anomalous'' and magm atically very productive parts of mid-ocean ridges.