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Medium pressure metamorphism with inverted thermal gradient associated with ophiolite nappe emplacement in Timor
Sopaheluwakan, J.; Helmers, H.; Tjokrosapoetro, S.; Surya Nila, E. (1989). Medium pressure metamorphism with inverted thermal gradient associated with ophiolite nappe emplacement in Timor. Neth. J. Sea Res. 24(2-3): 333-343
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Sopaheluwakan, J.
  • Helmers, H.
  • Tjokrosapoetro, S.
  • Surya Nila, E.

Abstract
    A study of the Mutis and Miomaffo Massifs in central Timor has revealed the common occurrence of metamorphosed pelitic and basic rocks in close association with variably serpentinized peridotites. In the metamorphites of the Mutis Complex, there is an inversion in the spatial distribution of the metamorphic zonations. A systematic decrease in grades beneath and away from the peridotites can well be seen in the metamorphites of both massifs, with the Mutis Massif showing a slightly higher-grade metamorphism than Miomaffo. The staurolite-kyanite zone in the higher structural levels gradually passes through the garnet zone and into the biotite zone in the deeper sequences. Polyphase deformation, mylonitic fabrics and partial retrogression to greenschist facies assemblages are shown by the higher-grade rocks, while the lower-grade rocks show a simpler deformation history and fewer episodes of metamorphic crystallization. P-T conditions defining the metamorphic peak are confined within the ranges of 6.4 to 8.3 kbars and 560° to 625°C based on coexisting garnet- plagioclase and garnet-biotite pairs in metapelites from the Mutis Massif. The temperature range in amphibolites from the same massif deduced from plagioclase-amphibole and garnet-amphibole thermometers overlaps with the results obtained from the metaperites, viz. 510° to 580° and 525° to 625°C, respectively. P-T-D plots of samples from Mutis yield a temperature gradient in the order of 300°C·km-1 and pressure fluctuating around 7 kbars in the 1 km thick metamorphite below the basal peridotite. The invertedly zoned metamorphites and other supporting indications in the Mutis and Miomaffo Massifs are used to suggest that they represent metamorphic aureoles below an ophiolite slab. Their presence is discussed in the light of hot ophiolite nappe emplacement.

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