LEFT FOR DEAD? PETROLOGY OF RESURGENT DOMES, EAST DIAMANTE SUBMARINE CALDERA, MARIANAS ARC

The resurgent domes of E. Diamante caldera were explored by the JAMSTEC ROV Hyper-Dolphin in June 2009 to survey the volcanic stratigraphy and hydrothermal sulfides. Three domes were sampled and a variety of volcanic and volcaniclastic rocks were recovered with compositions that include dacite, andesite, and rhyolite. We present detailed textural and mineralogical descriptions of these samples.

On the southeast dome the lava outcrops were jointed and fractured immensely and lava pebbles and cobbles are scattered. Rock recovered from the SE dome consists of pyroxene andesite, hornblende dacite and pyroclastics. The middle dome has mostly quartz ± hornblende dacite but also some basaltic andesite. The talus piles of the middle dome consist of boulders and cobbles and even some columnar lava boulders. A rift valley is present to the north of the middle dome and contains predominantly dacite and intensely jointed lava deposits. Columnar jointed basalt overlain by breccia was discovered in the southeast flank of the northern dome.

The surrounding area has both inactive and active hydrothermal sulfide chimneys that cover at least an area of 40 by 50 meters. Two other smaller fields of chimneys were found during this dive however they were inactive, and may have recently become so. These indicate that the magmatism that produced the resurgent domes may still be active and future dome building events are possible.