Geochemical Evidence of Island-Arc Origin for Sumatra Island; A New Perspective based on Volcanic Rocks in Lampung Province, Indonesia

Iskandar Zulkarnain

Abstract


DOI: 10.17014/ijog.v6i4.128

Since decades, Sumatra Island is considered as the Eurasia continental margin where the Indian Ocean plate has been subducted oblique beneath the continental plate of Sumatra. But, the occurrences of volcanic rocks in almost all areas of Lampung Province in the southernmost of Sumatra Island, as the presence of the Quaternary Tanggamus Volcano in the western part of the province together with the Quaternary Rajabasa Volcano in the eastern area cannot be justified using the consideration. Spider diagrams of trace and rare earth elements of volcanic rocks from the western and eastern areas of the province reveal that the rocks come from three different tectonic settings, namely island-arc, active continental margin (ACM), and intra continental plate. All basalt and one dacite of western volcanic rocks show a character of island-arc origin, while the eastern volcanic rocks are reflecting characters of ACM and intra continental plate. Plot of the rocks in the diagram of Ta/Yb versus Ce/P and in Ta/Yb versus Th/Yb confirmed the tectonic environments and specifically classify the intra continental plate into Within Plate Volcanic Zone (WPVZ). The island-arc group is characterized by Ta/Yb ratio of less than 2.0 and Ce/P less than 1.8. The ACM group is recognized having Ta/Yb ratio between 2 and 4 with Ce/P more 1.8, while the WPVZ group is defined as a group having Ta/Yb more than 6 and Ce/P more than 1.0. The result indicates that the western part of Sumatra is an island-arc fragment and the eastern part belongs to the Eurasia continental margin. The concentration of volcanics having ACM character from areas around the Sumatra Fault System to the east indicates that the collision zone between the Sumatra island-arc fragments with the Eurasia continental margin is probably located along the SFS. More statistical data is still needed from other Sumatra volcanics to confirm this conclusion.


Keywords


Eurasia continental margin; volcanic rocks; Lampung Province; island-arc; active continental margin; intra continental plate; Within Plate Volcanic Zone

References


Barber, A.J., 2000. The origin of the Woyla Terranes in Sumatra and the Late Mesozoic evolution of the Sundaland margin. Journal of Asian Earth Sciences, 18, p. 713-738. doi:10.1016/S1367-9120(00)00024-9

Barber, A.J. and Crow, M.J., 2003. Evaluation of plate tectonic models for the development of Sumatra. Gondwana Research, 20, p. 1-28. doi:10.1016/S1342-937X(05)70642-0

Crow, M.J., 2005. Pre-Tertiary volcanic rocks. In: Barber, A.J., Crow, M.J., and Milsom, J.S., Sumatra: Geology, Resources and Tectonic Evolution. The Geological Society, London. doi:10.1017/S0016756806212974

Curray, J.R., 1989. The Sunda Arc: a model for oblique plate convergence. Netherlands Journal of Sea Research, 24, p. 131-140. doi:10.1016/0077-7579(89)90144-0

Gafoer, S., Amin, T.C., and Setyogroho, B., 1992. Geological Map of Indonesia, Palembang Sheet, scale 1:250.000. Geological Research and Development Centre, Bandung.

Gorton, M.P. and Schandl, E.S., 2000. From continents to Island arcs: a geochemical index of tectonic setting for arc-related and within-plate felsic to intermediate volcanic rocks. The Canadian Mineralogist, 38, p. 1065-1073. doi:10.2113/gscanmin.38.5.1065

Hamilton, W., 1979. Tectonics of the Indonesian region. U.S. Geological Survey Prof. Paper 1078.

Le Bas, M. J., Le Maitre, R. W., Streckeisen, A., and Zanettin, B., 1986. A chemical classification of volcanic rocks based on the total alkali–silica diagram. Journal of Petrology, 27, p. 745-750. doi:10.1093/petrology/27.3.745

Miyashiro, A., 1974. Volcanic rock series in island-arcs and active continental margins. American Journal of Science, 274, p. 321-355. doi:10.2475/ajs.274.4.321

Pearce, J.A., 1983. The role of sub-continental lithosphere in magma genesis at destructive plate margins. In: Hawkesworth, C.J. and Norry, M.J. (eds), Continental basalts and mantle xenoliths, Nantwich: Shiva, p. 230-249.

Sun, S.-s. and McDonough, W.F, 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D. and Norry, M.J. (eds), Magmatism in the ocean Basins, Geological Society Special Publication, 42, p. 313-345. doi:10.1144/GSL.SP.1989.042.01.19

Tatsumi, Y. and Eggins, S., 1995. Subduction zone magmatism. Blackwell Science, Frontiers in Earth Sciences, 211pp, ISBN 0-86542-361-X.

Wilson, M., 1989. Igneous Petrogenesis; a global tectonic approach. Unwin Hyman, London, 466 pp. doi:10.1017/S0016756800006658

Zulkarnain, I., 2001. Rock chemistry of quaternary volcanics around Manado and Siau island, North Sulawesi. Jurnal Teknologi Mineral, VIII(1), p. 37-52.

Zulkarnain, I., 2007. Geochemical character of Hulusimpang Formation volcanic around Kota Agung area and their genetic implication. Jurnal Teknologi Mineral, International Edition, XIV(3), p. 156-167.


Full Text: PDF

Refbacks

  • There are currently no refbacks.


Creative Commons License
Indonesian Journal on Geoscience by https://ijog.geologi.esdm.go.id/index.php/IJOG/index is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

 

Indexing Site :

 

 

 

Follow us on:


shopify visitor statistics
View My Stats