1 st International Conference

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1 New Perspective On High Grade Metamorphic Regional In Bayah Complex, Banten Province 1 st International Conference Geoscience for Energy, Mineral Resources, and Environment applieds 2014 Aton Patonah 1, Ildrem Syafrie 1, Hero Ayasa 2,Haryadi Permana 3 1. Laboratorium of Petrology and Mineralogy, Departmen of Geologi, Faculty of Geologi, UNPAD. 2. Student of Geological Department, Faculty of Geology, UNPAD. 3. Geoteknologi LIPI. Jl. Cisitu Lama, Bandung Abstract Report of metamorphic rocks research which are exposed in Bayah Complex is still very less. Many researchers focused on their studies ophiolithic and metamorphic rock in Ciletuh as the oldest rock in West java. Some of them suggest the metamorphic rocks in Bayah complex as a product of local metamorphism because the granodiorite intrusion is present around them. Field investigation showed that the characteristic metamorphic rocks in Bayah have different from product the intrusion. We suggest that this complex is produced from regional metamorphism, it is characterized by present high grade mineral assemblage as product of high grade metamorphism in this area, that is, garnet biotite schist, biotite schist, actinolite schist and hornblend schist. With new found this rocks, probably it can change geological history, especially in this area, West Java and surrounding. Key words: Bayah complex, regional metamorphism, high grade metamorphism, garnet schist biotite, schist actinolite Introduction Tectonic setting has a role in determining potential natural resources in an area and its distributuin. The trace can be known, by identifying basement rock characteristics as one of the approaches. In Part of West Java, this basement is represented by Pre Tertiary of Ciletuh Bay (Van Bemmelen, 1949; Clemen & Hall, 2007). It is consist of Metamorphic basic and ultrabasic rock with chloritic schist and phyllite, acctered to margin of Sundaland in the Late Crestaceous (picture 1). According to Schiller et all (1991), Ciletuh Melange Complex is described as ophiolite assemblages associated with greenschist, mica schist, amphibolite schist, and quartzites which has been interpreted as a tectonic mélange (e.g. Patonah et al, 2010; Parkinson et al, 1998; Martodjojo et al, 1978; Thayyib et al, 1977). This mélange complex has Crestaceous age and it is the same age with Luk Ulo mélange complex (Parkinson et al, 1998). It has unconformity with Ciletuh Formation which deposited in shallow marine (Van Bemmelen, 1949). Bayah Formation is founded about 20 kilometres toward southeast of Ciletuh, which present as the oldest rock in Bayah area. In Bayah area, the metamorphic rock consist of Schist, Genes, and amphibolite which formed probably Early Oligocene Late Oligocene (Sujatmiko & Santosa, 1992). These rocks still unknown because lack of publication about them. This paper try to identify based on data collection field work during May September 2014.

2 Methodology For a while, this research is described by field investigation and petrography analysis. For comprehensive study, on going. We chose 40 sample represented this research. The functions are to determine kind of minerals, texture, structure and name of the rocks based on Barker classification (1994) and Robert (2000), to arrange paragenesis of the rocks and determine probably the original of the rock, also metamorphic facies and metamorphism have developed. Result and Discussion Metamorphic rock in this area distributed on Cipager and Cibaong rivers (figure 2 and 3). These dominantly have foliated, faulted and fractured, some of them weathered. As long as Cipager river, biotite schist is dominantly, grey greenish grey in colors, lgood foliated with trend dominantly west to east, some of them trend in NW-SE, commonly fine very fine grain, fractured, locally it is intruded by diorite. Microscophically, kind of mica schist are biotite schist dominantly, some garnet biotite schist and chlorite schist. Biotite schist have grey greenish grey colors, good foliated, have boudinage structure, and fractured is filled by epidote, chlorite, quartz, opaq and oxide minerals. The rock consist of plagioclase and K-feldsphare as porphyroblast, others filled as matrix, they are, biotite, muscovite, chlorite, quartz, opaq minerals, some contain garnet (picture 4). Move toward east, is founded green schist, have green colors, good foliated with trend west to east, dominantly of actinolite, some hornblend, plagioclase, quartz, biotite and chlorite minerals. Other minerals are opaq and oxide minerals. In Cibaong river, Mica schist, green schist and basalt are presents. Biotite is kind of mica that dominantly present in is Schist. It has greenish grey in colors, good foliated trends in West to East, fracture are filled by sulfide minerals, some of them are weathered. Amphibolite schist consist of actinolite schist and hornblend schist. Actinolite schist have green in colors, good foliated, some fractured, consist of actinolite dominantly, some hornblende and plagioclase present as porphyroblast, others are quartz, biotite and chlorite (figure 5). Based on mineral assemblage, protolith of biotite schist is dominantly semipelite and pelite, some of them are psammite (figure 6). Meanwhile, the protolith of amphibolite schist is volcaniclastic and mafic rock in origin. Some geothermometer has been used to temperature estimation. Biotite schist formed from 425 o C to 450 o C, is characterized by biotite, muscovite, K-feldspare, plagioclase and quartz (Deer, dkk; 1992; Barker, 1994). In some place, garnet is present, it is indicated that the rocks formed from 480 o C to 500 o C, and indicating the upper greenschist facies. The retrograde metamorphism is situated to 150 o C 200 o C, it is characterized by chlorite and muscovite replaced biotite, K-feldspare altered to sericite and muscovite.

3 Hornblende schist and actinolite schist formed from 370 o C 420 o C, is signed by actinolite, chlorite, biotite, plagioclase, quartz minerals (Deer, dkk; 1992; Barker, 1994) and included to transition of green schist amphibolite schist. The rock have retrograde traject which is characterized by hornblende altered to actinolite and actinolite to chlorite. Based on characterization of the rocks in this area, metamorphic rock in this area associated with regional metamorphism, foliated trend West to East, and boudinage structure. Some folliation have changed which is predicted by intrusion effect in some place. In this process, is predicted by accretion of Eocene Oligocene age. Conclusion Metamrphic rocks in Bayah area are dominantly by biotite schist, some chlorite schist, actinolite and hornblende schist. The rocks come from semipelite and pelite, some psammite, volcaniclastic and mafic rock. Based on mineral assemblage, we suggest that regional metamorphism happened in this area and they have retrograde traject which is produced by tectonic association in Eocene Oligocene age. Reference Barker, A. J Metamorphic Textures and Microstructures. Chapman and Hall: New York. Benyamin Clement, Robert Hall Crestaceous to Late Miocene Stratigraphic and Tectonic Evolution of West Jawa. Proceeding Indonesian Petroleum Association. Thirty first Annual Convention and Exhibitons. Deer, Howie, Zussman An Introduction to the Rock Forming Mineral. 2nd Edition. Longman Scientific and Technical. Hehuat, F.H.A An Overview of some Indonesian Melange Complexe a Contribution to the Geology of Melange. Memoir of the Geological Society of China. Martodjojo, S Evolusi Cekungan Bogor Jawa Barat. Disertasi Doktor Geologi, Fakultas Pasca Sarjana, Institut Teknologi Bandung. Tidak diterbitkan. Raymon, Loren A Petrologi; The Study of Igneous Sedimentary and Metamorphic Rock. McGraw-Hill: New York. Spear, F.S Metamorphic Pressure Temperature Time Paths. Short Course in Geology. Vol.7. American Geophysical Union. Streckeisen A To each plutonic rock its propername. Earth Sci. Rev.12. h Sujatmiko dan S. Santosa Peta Geologi Regional Lembar Leuwidamar. Pusat Penelitian dan Pengembangan Geologi: Bandung.

Van Bemmelen, R.W. 1949. The Geology of Indonesia, Volume I A.

Crestaceous Accretionary Collision Complexes in Central Indoneisa.

4 Van Bemmelen, R.W The Geology of Indonesia, Volume I A. The Hague Martinus Nijhoff: Netherland. Wakita. K Crestaceous Accretionary Collision Complexes in Central Indoneisa. Journal of Asian Earth Sciences. Daerah penelitian Picture 1. Geology of Regional the research area (Sujatmiko and Santoso, 1992) Picture 2. Biotite schist and amphibolite schist outcrop in Cipager area.

5 Picture 4. Biotite schist showed foliated and boudinage structure, consist of biotite, muscovite, K-feldspare, plagioclase, chlorite and quartz minerals.

6 Picture 5. Biotite schist is dominantly biotite altered to chlorite, some muscovite, K-feldspare, plagioclase, quartz and garnet.

7 Picture 6. Hornblend schist consist of hornblend, actinolite, plagioclase, and quartz minerals, some biotite mineral and chlorite minerals. Picture 7. Protolith of biotite schist in Bayah area are dominantly semipelite and pelite, some psammite.

Introduction to Geology Spring 2008

MIT OpenCourseWare http://ocw.mit.edu 12.001 Introduction to Geology Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms. Regional metamorphism