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Geology and Arc Magmatism of the Eastern Sunda Arc

The Eastern Sunda Arc of Indonesia that consists of the islands of Java, Bali, Lombok and Sumbawa represents one of  the  most  complex  arc  magmatism  settings  in  the  world.  Cenozoic  magmatism  associated  with  a  subduction along the Java trench started since Eocene in west Java to Pacitan section, Oligocene for the easternmost Java to probably  west  Lombok,  and  Miocene  for  most  of  Lombok  and  Sumbawa.  Cenozoic  volcanoes  demonstrate common features of  island arc magmatism, such as a wide variation in SiO2 contents, high A12O3, with low TiO2, Na2O and MgO contents.

sunda-arc-imageMagma alkalinity increased towards younger volcanoes and towards the backarc-side. On the  other  hand,  the  arc  also  demonstrates  several  unique  features  that  differ  to  idealized  temporal  and  spatial schemes of subduction zone magmatism. For example, the region holds the widest range of K2O contents among all  subduction-related  magmatic  arcs  in  the  world.  Volcanic  centers  and  arc  have  also  experienced  migrations towards the backarc-side  during its Cenozoic  history, which is different from a typical trench-side migration  of a subduction zone. 

Along  the  whole  section,  there  are  at  least  two  distinctive  petrochemical  (or  lithochemical)  arc  sectors  to  be present,  i.e.  west  Java  and  east  Java  to  Sumbawa.  Such  differences  are  products  of  different  crustal  types  and source  components  for  the  magma  generation  that  may  produce  different  mineralization  styles.  West  Java  is dominated by low-sulfidation Au-Ag epithermal system associated with Neogene-Quaternary high-K to shoshonitic volcanism  at  continental  crust  setting.  Meanwhile,  eastern  Java  to  Sumbawa  sector  is  dominated  by  porphyry- related Cu-Au mineralization system associated with middle Tertiary-Neogene,  low- to moderate-K magmas with high Sr/Y affinity, suggesting immature arc magmas with minimum crustal contamination.

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