LONG-TERM SURFACE UPLIFT HISTORY OF THE ACTIVE BANDA ARC-CONTINENT COLLISION: DEPTH AND AGE ANALYSIS OF FORAMINIFERA FROM ROTE AND SAVU ISLANDS, INDONESIA

Foraminifera analysis of samples from Rote and Savu Islands reveal the surface uplift history of the incipient Banda arc-continent collision. Estimates of paleodepth are provided by benthonic forams and ages by planktonic forams. These estimates are complicated by abundant reworking, yet several distinctive species are found.

Synorogenic deposits in western Rote yield forams of N21 (3.1 – 1.8 Ma) and depths from 2500-3800 meters at the base of the section, and 1200 meters at the top of the section. Eastern Rote yields forams of N21-N22 (3-1 Ma) and depths from 2000-3300 meters. Central Rote also yields N21 and depth from 2000-5000 meters. Because all of the sections are about the same elevation presently, long-term surface uplift rates are slighty higher (1.6 mm/yr) in eastern and central Rote than those in the western Rote. Forams from Savu yield ages of N21-N22 (3-1 Ma). Depth estimates range from 2500-4200 meters, which yields an uplift rate of 1.4 mm/yr.

These results indicate: 1) the Banda arc-continent collision arrived in Rote after around 3 Ma and perhaps even later in Savu, 2) long-term surface uplift rates, at a temporal scale of 10⁶ yrs., are similar to short-term rates measured using uplifted coral terraces, at temporal scales of 10⁴- 10⁵ yrs., and 3) most uplift was in a submarine setting and therefore involved minimal erosion. Uplift of Rote corresponds to its position at the boundary between the Sumba/Savu block moving mostly with Asia and the Timor block moving mostly with Australia (Nugroho, 2004). Uplift of Savu is responding to the northward propagation of the Savu thrust, which forms the near of the orogenic wedge. Uplift associated with these structures demonstrate how strain is partitioned away from the trench during the incipient stages of arc-continent collision.