Geology of the Mutis Complex, Miomaffo, West Timor

Berry, Ron1, Goemann, Karsten2, Danyushevsky, Leonid1

1CODES, University of Tasmania, Hobart, Australia, 2Central Science Laboratory, University of Tasmania, Hobart, Australia

Mesozoic accretionary assemblages are widespread across Indonesia and these can be seen in the overthrust terranes on Timor. The oldest rocks in the allochthonous Mutis Complex, West Timor are Jurassic melange containing blocks of N-MORB basalt (194 ±5 Ma), amphibolite (metamorphism at 175 Ma), garnet and actinolite bearing schists, arkosic sandstone and volcanogenic material. The sedimentary component is sourced from Mesozoic island arc along the southern margin of Indonesia (≈200 Ma based on detrital zircon). Prehnite is common as a late metamorphic mineral in the matrix. The accretionary material is complexly deformed with a dominant foliation and cataclastic zones. This sequence is intruded by calc-alkaline andesitic dykes (possibly in the Eocene). To the west of the melange is a transition to high strain greenschist facies rocks (isoclinal folding and transposition layering) where the block in matrix texture can no longer be recognised, but the range of bulk composition is the same. Further west across several faults is an amphibolite facies metamorphic province. Amphibolites have the same N-MORB composition as the basalt in the east. The peak metamorphic conditions are 600-720 C, 0.6-1.1 GPa. This area has the same bulk composition as the melange including detrital zircon ages. The metamorphic assemblages overprint low T isoclinal folds. Peak metamorphism occurs at 38 Ma reflecting an event within the active margin of Sundaland. At about 5 Ma, NW Australia collided with this margin and the Mutis Complex was thrust over Timor. A late generation of cataclastic faults zones cuts all the pre-existing lithologies but is largely a result of extensional collapse. The complex is cut by a younger fault zone that affects the underlying unconsolidated sedimentary rocks and contains evidence of both strike slip and normal fault movement. The Mutis Complex is an excellent example of the complex geological history of rocks along the boundary between Indonesia and Australia.


Ron Berry has worked on the structure and tectonics of Tasmania, Indonesia and South East Asia for 40 years. Karsten Goemann and Leonid Danyushevsky are experts in petrology, mineralogy and mineral analysis and have provide the technical expertise to make this study possible

About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.