A"Preliminary"View"and"Importance"of"Metamorphic"Geology"from"Jiwo"

Hills"in"Central"Java"

Nugroho"I"SeAawan1,"Yasuhito"Osanai2,"Carolus"Prasetyadi3"

!

1Geological!Engineering,!Gadjah!Mada!University!2Division!of!Earth!Sciences,!Kyushu!University!

3Geological!Engineering,!Na@onal!Development!University!

Introduc@on!

•  Accre@onary!and!metamorphic!

complexes!expose!in!the!Central!

Java,!South!Kalimantan!and!South–

Central!Sulawesi.!

•  The!complexes!mainly!consist!of!

highLpressure!metamorphic!rocks,!

melange!and!ophiolites!!

•  NorthwesterlyLdirected!Cretaceous!subduc@on!was!suggested!

responsible!to!build!these!

forma@ons!(Hamilton,!1979;!

Parkinson,!1998).!

•  In!par@cularly!Java!Island,!the!metamorhic!compleses!expose!in!the!

Luk!Ulo!Complex,!Jiwo"Hills,"and!Ciletuh!Complex.!

Introduc@on!

•  Jiwo!Hills!s@ll!lack!of!publica@on!of!the!metamorphic!rocks!and!the!occurrence!of!highLpressure!metamorphic!rocks.!

•  This!presenta@on!explains!the!occurrence!of!various!metamorphic!rocks!in!the!Jiwo!Hills.!

•  The!occurrence!of!garnetLwollastonite!skarn!and!epidoteLglaucophane!schist!are!discussed!in!detail!on!the!petrographical!and!!mineral!chemistry!and!its!contribu@on!to!the!tectonic!evolu@on.!

!  Scale!bars!without!expression!in!each!photomicrograph!on!this!presenta@on!indicate!1!mm.!

!  Mineral!abbrevia@ons!in!this!presenta@on!are!following!Whitney!and!Evans!(2010)!!

Geological!Outline!

Modified!a\er!Surono!(1994)!and!Prasetyadi!(2007)!

[98!Ma]!

Modes!of!occurrence!(West!Jiwo)!a.!Serpen@nite!

c.!EpLGln!schist! d.!GrtLWo!skarn!

Modes!of!occurrence!(East!Jiwo)!a.!Phyllite!

c.!Gr!phyllite! d.!Marble!

b.!CalcLsilicate!schist!

Photomicrograph!a.!Serpen@nite! b.!Phyllite!

c.!CalcLsilicate!schist! d.!AbLMs!schist!

Photomicrograph!and!chemical!composi@on!of!GrtLWo!skarn!

Photomicrograph!and!chemical!composi@on!of!EpLGln!schist!

Preliminary!view!of!metamorphic!

rocks!from!Jiwo!Hills!area!

No" Rock"Type" Metamorphic"Grade" LocaAon"1! Serpen@nite! Serpen@nite! West!Jiwo!

2! Soapstone! Serpen@nite! West!Jiwo!

3! EpLGln!schist! Blueschist! West!Jiwo!

4! Phyllite! Greenschist! West!Jiwo!

5! GrtLWo!skarn! HornfelsLskarn! West!Jiwo!

6! CpxLEp!skarn! HornfelsLskarn! West!Jiwo!

7! CalcLsilicate!schist! Greenschist! East!Jiwo!

8! AbLMs!schist! Greenschist! East!Jiwo!

9! Phyllite! Greenschist! East!Jiwo!

10! Gr!phyllite! Greenschist! East!Jiwo!

11! Marble! Hornfels! East!Jiwo!

Comparison!of!geochronology!with!other!HP!metamorphic!terranes!in!Indonesia!

Rela@vely!close!synchronology!

of!available!KLAr!ages:!1.  Ban@mala!Complex!–!South!

Sulawesi:!113–137!Ma!

2.  Meratus!Complex!–!South!

Kalimantan:!110–119!Ma!

3.  Luk!Ulo!Complex!–!Central!

Java:!110–124!Ma!

4.  Jiwo!Hills!–!Central!Java:!98!Ma!

Comparison!of!whole!rock!chemistry!with!other!HP!metamorphic!terranes!in!Indonesia!

Discussion!and!Conclusion!

•  Various!metamorphic!rocks!crop!out!in!the!Jiwo!Hills!area!include!greenschist,!blueschist,!serpen@nite,!and!hornfelsLskarn.!

•  Implica@on!of!the!occurrence!of!skarn!in!the!Jiwo!Hills.!

–  Carbonate!sedimentary!rocks!should!be!considered!to!be!host!rock!of!the!contact!metamorphism.!

–  Detailed!geological!mapping!on!the!skarn!zona@on!is!needed!to!understanding!characteris@c!and!possibility!of!economic!mineral!deposits.!

–  Possibility!formed!by!contact!metamorphism!of!OligoLMiocene!local!intrusion!ac@vity!in!West!Jiwo!(G.!Kebo,!Merak,!etc?)!"!Some!of!the!metamorphic!rocks!were!not!considered!as!PreLTer@ary!Forma@on!!

Discussion!and!Conclusion!

•  Implica@on!of!the!occurrence!of!blueschistLfacies!metamorphic!rocks!in!Jiwo!Hills.!–  The!adjacent!to!the!serpen@nite!might!be!implied!that!this!rock!were!facilitate!exhuma@on!of!the!highLpressure!metamorphic!rocks.!

–  Jiwo!Hills!is!one!of!the!highLpressure!metamorphic!terranes!together!with!LukLUlo,!Ban@mala,!and!Meratus!Complexes.!

•  The!protolith!of!metamorphic!rocks!from!Jiwo!Hills!were!derived!from!sedimentary!rocks!"!Jiwo!Hills!has!con@nental!crust!signature.!

•  Detailed!study!par@cularly!on!the!occurrence!of!highLpressure!metamorphic!rocks!in!the!Jiwo!Hills!are!needed!in!order!to!determine!of!tectonic!evolu@on!in!this!region.!

Exhuma@on!mechanism!of!highLpressure!metamorphic!rocks!from!central!Indonesia!

•  The! eclogiteLfacies! metamorphic! rocks!

were! subducted! ! correspond! to! the!depth!

of! 90! km! beneath! con@nental! crust! of!

Sundaland.!

•  The! HighLpressure! metamorphic! rocks! in!

Ban@mala! and! Luk! Ulo! complexes! are!

enclosed!in!sheared!serpen@nite.!

•  The! serpen@nites! are! extremely! buoyant!

with!respect!to!the!oceanic!crust!that!have!

been! transformed! to! eclogites! during!

subduc@on!and!increasing!their!density.!

•  Serpen@nites! might! be! counterLbalancing!

the! nega@ve! buoyancy,! decouple! and!

facilitate! exhuma@on! of! the! highLpressure!

rocks! during! a! con@nued! subduc@on!

process.!

Thank"you"for"your"aLenAon"