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ABSTRACT: Cenozoic evolution of the southern central range, Irian Jaya, Indonesia

Sapiie, Benyamin1, Mark P. Cloos2, Richard J. Weiland3, Paul Q. Warren4, and A. Quarles Van Ufford3
(1) Department of Geology, Institute of Technology Bandung, Bandung, Indonesia 
(2) Department of Geological Sciences, The University of Texas at Austin, Austin, TX 
(3) ARCO International, Plano, TX 
(4) P.T. MineServe International, Jakarta, Indonesia

The Gunung Bijih (Ertsberg) Mining Access road is located in the southern Central Range of Irian Jaya on the northern Australian continental margin. Along this road is exposed continuous of ~18 km-thick of Lower Paleozoic to Late Miocene of passive margin sequence. Based on detailed geologic mapping along the road, we propose a new Cenozoic tectonic evolution of the Central Range of Irian Jaya.

More than 20,000 structural data have been collected along the road. Structural analysis indicates two distinct deformation events clearly recognized. The first stage of deformation is resulted from collisional deformation occurring between ~12 and ~4 Ma. This event generated en echelon km-scale folds and minor reverse faulting which accommodate tens of km of shortening. The second stage of deformation involved hundreds of meters to a few kilometers of left-lateral strike-slip offset. Field evidence indicates that two of the major strike-slip faults were segments of older high-angle reverse faults. Therefore, the strike-slip faults are oriented sub- parallel to the regional grain generated by folding which in turn was probably controlled by pre-existing zones of weakness in the basement.

The change in deformation styles from contractional to strike-slip offset is explained as due to a change in the relative plate motion between the Pacific and Australian Plates at ~4 Ma. From ~4-2 Ma, transform motion along an ~ 270° trend caused left-lateral strike-slip offset and reactivated portions of pre-existing reverse faults.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia