| Summary: | Jiwo Hills is an isolated hill with approximately occupied 30 km
2
in Bayat area of Central Java.
The Jiwo Hills has been considered to be composed of very low-grade metamorphic rocks. This
contribution explains a preliminary view of the metamorphic rocks from collected rocks sample in
the Jiwo Hills.
Common metamorphic rocks found in this area are phyllite, mica schist, calc-silicate schist, and
marble with the foliation trend of NE-SW. Most of the metamorphic rock exposures are strongly
weathered. Rarely epidote-glaucophane schist crop out near the exposure of serpentinite in western
part of this complex. Several carbonate sedimentary rocks are converted to garnet-wollastonite
skarn under the contact metamorphism probably caused by diabase intrusion.
Garnet-wollastonite skarn mainly consists of garnet and wollastonite embed in the quartz matrix.
The garnets are rich of grossular composition, range from Adr13–19Grs81–85Sps0–2. Those show
anisotropic, with sectorial twinning zonings. The skarn deposits might give important information
for economic resources in this area.
Epidote-glaucophane schist mainly consists of glaucophane, epidote, quartz, phengite, titanite, and
hematite. By the present of this blueschist facies of high-pressure metamorphic rock in this area, it
confirms that Jiwo Hills is one of the high-pressure metamorphic terranes together with Luk Ulo
Complex of Central Java, Meratus Complex of South Kalimantan, and Bantimala Complex of
South Sulawesi. The serpentinites might facilitate exhumation of the blueschist in the Jiwo Hills.
Detailed study of the distribution of metamorphic rocks in this area is needed in order to
understanding tectonic evolution as well as economic geology.
Keywords: Jiwo Hills, Bayat, blueschist, high-pressure metamorphic rocks, skarn
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