Sedimentary Crust and Metallogeny of Granitoid Affinity: Implications from the Geotectonic Histories of the Circum‐ J apan S ea Region, Central A ndes and Southeastern A ustralia

Metallogeny of granitoid affinity was reviewed from the aspect of geotectonic history of the continental crust, particularly of the genesis of sedimentary crust involved in magmatism. The redox state of granitoids and related mineralization shows a remarkable contrast between the east and west sides of the P acific R im, but if examined closely, the reduced‐type and oxidized‐type granitoid provinces are juxtaposed in three regions: the circum‐ J apan S ea region, the central A ndes, and the L achlan F old B elt in southeastern A ustralia. Comparative study of these regions revealed that the reduced‐type magmatism associated with Sn mineralization generated in thick sedimentary crust which formed in three geotectonic environments: (i) accretionary terrane along a subduction zone (e.g. J urassic E ast A sia), (ii) continental rift (e.g. E arly P aleozoic A ndes), and (iii) mega‐fan (e.g. E arly P aleozoic southeastern A ustralia). A collisional orogen can provide large amounts of clastic sediment to these environments. The age gap between the magmatism and sedimentation varies depending on the tectonic evolution of individual regions. Thin sedimentary crust may not play an essential role for the reduced‐type magmatism. The oxidized‐type magmatism associated with porphyry Cu and other mineralization generated in the crust which was initially carbon‐free igneous crust or modified from sedimentary crust by magmatism. Subduction‐related basaltic magmas are relatively oxidized, and may enhance fO 2 conditions of granitoid activity. Repeated magmatism in a monotonous convergent margin may be favorable for porphyry Cu mineralization as exemplified in the eastern P acific R im.