Differentiated series
A differentiated series or magmatic series is a family of magmatic rocks formed starting from the same magma.
A magma evolves/moves by split Cristallisation, partial Fusion, change of physicochemical conditions (pressure, temperature, contribution or escape of fluids, etc). Its composition changes. An eruption at time different will give different rocks forming the differentiated series.
More the rocks are differentiated more they are rich in minerals Alcalin S, and often in Silice, and low in ferro-magnesian calcium and minerals. Differentiation is measured by the report/ratio (K+Na)/(K+Na+Ca).
There exist only two differentiated rocks: the Phonolite S, and the Rhyolite S. the term applies to the lava, but also to their hanging crystalline lenses, which are the witnesses of the tanks of this lava.
Andesitic series
An andesitic series consists of Andésite S, Dacite S, then Rhyolite S. the absence of Basalte S andesitic in an andesitic series indicates that there is no filiation basalt - > andesite.
The andesitic series are characteristic of the zones of subduction. The isotopic report/ratio 87Sr/86Sr of the andesites indicates to us that their origin is mantellic: the andesites are formed on the level of the plan of Wadati-Béniof. The andesitic magmas result from fusion partial of a hydrated olivine tholéiite. The more one moves away from the zone of subduction, the more the andesites are rich in Potassium, Rare earths, Thorium, Uranium and Césium.
An andesitic series rich in potassium is a shoshonitic series , giving viscous lava imprisoning gas, and thus a Volcan more explosive ism.
Tholeiitic series
August 1st
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