Pustaka Ilmiah Universitas Padjadjaran

Abstrak

Petrology And Hydrothermal Signature Of The Abangkomba Seamount, Flores Sea, East Nusa Tenggara

The Neo Volcanic Ridge-NVR- was discovered striking southeastward beneath the sea from the previously known Komba-Batu Tara- Volcano. This NVR is built by three seamounts which are; Barunakomba, Abangkomba, and Ibukomba. The Abangkomba Seamount was built by explosive volcanogenic material of pumice, tuff, breccia, and igneous volcanic rocks some of which indicate hydrothermal alteration.The abundance of explosive material suspected to have accumulated by volcanic activity, corroborate that Abangkomba is previously an active volcano. Extensional structures found are the older NW-SE striking normal faults cut by younger NE-SW striking faults, resulting in pull apart basins and some spots of hydrothermal activity. Major element compositions of the igneous volcanic rocks Indicate they are trachy andesite, trachy basalt, and shoshonite in composition. Petrographically, basaltic-andesites composed of plagioclase, pyroxene, amphibole and biotite indicate a subduction related magmatic source. Chemical compositions indicate the samples are potassium-rich and belong to a shoshonite series. The TAS diagram shows the samples mostly range between trachybasalt and trachyandesite, corresponding to increasing Si02 and alkali contents. The Abangkomba submarine volcano had undergone lower-grade differentiation with partial melting associated with extensional structures.gThe altered samples of Abangkomba indicate three alteration zones, characterized by dominant alteration minerals: a). sub-propylitic zone marked by chlorite-carbonate-illitepyrophyllite, b). phyllitic zone characterized by carbonate-sericite-illite, c). argillitic zone consisting of carbonate-smectite. Significant metal contents of Au-Ag and Cu-Zn was shown by chemical analysis. Increasing illite contents correspond to creasing Au, indicating that mineralization at Abangkomba formed in a neareutral fluid-rich environment, as also indicated by the occurrence of carbonate inerals. The chemistry and mineralogy of altered rocks strongly resembles the pithermal low sulfidation type.