“Volcanism in the Chugoku region: a review for the first UNESCO field school on Geoenvironmental disaster reduction”

Geoenvironmental Disasters

Table 2 Igneous-tectonic associations, modified after Wilson (2007)

	Plate Margin		Intra Plate
	Convergent	Divergent	Intra Oceanic	Intra-Continental
Igneous-tectonic associations	- Island Arcs - Continental Arcs - Young (< 25 Ma) subduction zones	- Mid ocean ridge basalt (MORB) - Back-arc spreading centres	- Oceanic Islands (OIB)	- Continental rift zones - Continental Intraplate Volcanism
Magma Series	- Tholeiitic - Calk-Alkaline - Alkaline - Adakite, HMA	- Tholeiitic	- Tholeiitic - Alkaline	- Tholeiitic - Alkaline
SiO₂ range	- basalts and differentiates	- basalts	- basalts and differentiates	- basalts and differentiates

-Alkaline vs Subalkaline rocks. Distinguished within the Total Alkali vs Silica diagram (TAS) but on different discrimination functions (Irvine and Baragar 1971; Miyashiro 1978; LeBas et al. 1986).
-Subalkaline rocks are further distinguished into a Tholeiitic and a Calc-alkaline series by different criteria (Irvine and Baragar 1971; Miyashiro 1974).
-Adakites and High Magnesium Andesites (HMA). Magmas from young, hot subduction zones (e.g. SW-Japan arc) show distinct characteristics in comparison with those from old mature subduction zones (e.g. NE-Japan arc). The difference is related to the thermal structure of the subduction zone and the possibility to directly melt the subducted oceanic lithosphere (Kay 1978; Defant and Drummond 1990). Adakites and associated rock types also occur in other settings where their origin is debated. For a review see Martin et al. (2005).
-I-Type vs. S-Type intrusiva distinguished on the basis of igneous (I) and sedimentary (S) source rocks (Chappell and White 1992)