AUTHORS: Richard Herrington, Dennis Brown
ABSTRACT : In cases of simple accretion, arc-continent collision zones preserve previously formed deposits. The obduction of ophiolites from the overlying oceanic plate is a common feature, accompanied by the accretion of all or parts of the entire volcanic arc and its mineral endowment. The subsequent ingress of continental material to the subduction channel can change the budget of contributed components from the slab to the mantle wedge and in some cases it appears that magmas enriched in metals such as gold could be generated. There is also some evidence that the physical effect of the ingress of the less dense continental crust itself could cause subduction shallowing or even stalling leading to the generation of anomalous magmas. Arc reversal is a feature of many arc-ontinent collisions, effectively turning passive continental margins into active continental arcs. This arc reversal may also result in melts being sourced from more fertile, previously metasomatised, mantle which has further implications for metallogenesis. The actual collision itself is also shown in some cases to be linked to formation of orogenic gold deposits and in rare cases post-collision extension can lead to further magmatic activity linked to mineral deposit formation.
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