apreliminaryviewandimportance...
TRANSCRIPT
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"