The Tectonic Significance and Origin of Kisar, Indonesia

Jonathan Major
Brigham Young University Department of Geological Sciences Provo, Utah
[email protected]

The small island of Kisar, eastern Indonesia, is found exactly where it shouldn’t be. It is located in the active arc-continent collision between the Banda Arc and the Australian continental shelf. It emerges 3 km from the sea floor between the Outer (non-volcanic) and Inner (volcanic) Banda Arcs. A recent field investigation and laboratory work are now revealing Kisar’s origin, evolution, and present location. The island is made of what are likely some of the youngest exposed metamorphic rocks in the world and is encircled by uplifted coral terraces. The metamorphic rocks record the island’s earlier geologic history, and the coral terraces are a record of recent uplift. Geothermobarometry work combined with geochrononological data will yield a long-term exhumation rate related to the rise of the island. Elevation data taken from the terraces and U-Th series age analyses on coral samples in combination with known sea-level curves will yield a short-term surface uplift rate. The uplifted terraces also allow study of fringing reef growth in response to a very active tectonic environment.

In a regional context, this study will yield insights into early orogenic processes by addressing part of a poorly-studied 400 km-wide region within the collision zone. Information gained from the island can be related to hinterland deformational processes in general, which can then be applied to the evolution of most mountain systems. Identifying and quantifying orogenic processes is also crucial in assessing seismic hazards in an area that has suffered tremendously in recent years.

AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid