Sains Malaysiana 30: 13-26 (2001)                                                                                                                Sains Bumi /

    Earth Sciences  

 

Rare-earth Elements Modelling of the Langkawi Granites

 

 

Wan Fuad Wan Hassan

Geology Program

Faculty of Science and Technology

Universiti Kebangsaan Malaysia 43600 UKM Bangi

Selangor D.E Malaysia

 

Azman A. Ghani

Department of Geology

Universiti Malaya

50603 Kuala Lumpur, Malaysia

 

Syafrina Ismail

Lestari, Universiti Kebangsaan Malaysia

43600 UKM Bangi, Selangor D.E Malaysia

 

 

ABSTRAK

 

Berdasarkan pola unsur-unsur nadir bumi (REE) granit Langkawi boleh dibahagikan kepada dua kumpulan iaitu granit Gunung Raya-Dayang Bunting dan granit Kuah-Pulau Tuba. Granit Gunung Raya-Dayang Bunting mempunyai anomali Eu negatif yang lemah manakala granit Kuah-Pulau Tuba mempunyai anomali Eu negatif sederhana kuat. Nisbah-nisbah Rb/Sr juga menunjukkan perbezaan apabila nisbah Rb/Sr dalam granit Kuah-Pulau Tuba jauh lebih tinggi berbanding dengan nisbah-nisbah dalam granit Gunung Raya-Dayang Bunting. Pengamatan pola-pola REE menunjukkan granit-granit tersebut mempunyai bentuk 'sayap-burung' yang lazim dengan anomali-anomali Eu negatif dari lemah hingga sederhana kuat. Pola-pola demikian serupalah dengan granit jenis-S Pantai Barat dan berbeza daripada granit jenis-l Pantai Timur. Bahan sumber mungkin bagi granit Langkawi ialah sedimen Kambria dari Formasi Machinchang. Permodelan pola-pola REE telah dilakukan dalam dua tahap iaitu secara peleburan sebaya dan penghabluran berperingkat. Hasil permodelan menunjukkan magma Gunung Raya-Dayang Bunting memerlukan darjah pemeringkatan leburan separa sedikit lebih tinggi (0.15-0.25%) berbanding dengan magma Kuah-Pulau Tuba (0.25-0.3%). Sebaliknya magma Gunung Raya-Dayang Bunting telah melalui darjah pemeringkatan lebih tinggi (16%) berbanding dengan magma Kuah-Pulau Tuba (9%).

 

 

ABSTRACT

 

Based on the REE patterns the Langkawi granites can be divided into two groups i.e. the Gunung Raya-Dayang Bunting granite and Kuah-Pulau Tuba granite. The Gunung Raya-Dayang Bunting granite has weak negative Eu anomalies whereas the Kuah-Pulau Tuba granite has moderately strong negative Eu anomalies. Rb/Sr ratios also show similar differences with Rb/Sr ratios in Kuah-Pulau Tuba granites being much higher than those of the Gunung Raya-Dayang Bunting granite. Examination of the REE patterns shows that they have the usual 'bird-wing' shape with weak to moderately strong negative Eu anomalies. This pattern is similar to the West coast S-type granites and is different from the I-type granites of the East coast. A possible source material for the Langkawi granite is the Cambrian sediments of the Machinchang Formation. Modelling of the REE pattern has been carried out in two stages namely batch melting and fractional crystallisation. Results show that the Gunung Raya-Dayang Bunting magma requires a slightly higher degree of partial melting fraction (0.15-0.25%) compared to the Kuah-Pulau Tuba magma (0.25-0.3%). On the other hand the Gunung Raya­/Dayang Bunting magma has undergone a higher degree of fractionation (16%) compared to the Kuah-Pulau Tuba magma (9%).

 

 

RUJUKAN/REFRENCES

 

Amirulnaim bin Ahmad Dahlan. 1997. Geologi kawasan tengah Pulau Langkawi. B.Sc. dissertation, Universiti Kebangsaan Malaysia.

Arlh. J. G. 1976. Behaviour of trace elements during magmatic processes - a summary of theoretical models and their applications. J. Res. U. S. Geol. Surv. 4: 41-7.

Atherton, M. P., Mahawat, C. & Brotherton. M. S. 1992. Intergrated chemistry, textures, phase relations and modelling of a composite granodioritic - monzonitic batholith, Tak, Thailand. Jour. Southeast Asian Earth Science 7(2/3): 89-112.

Azman A. Ghani. 1999. Western Belt granite of the Peninsular Malaysia. Proc. Dynamic Stratigraphy & Tectonics of Peninsular Malaysia, 2nd Seminar: The Western Belt & Paleozoic of Peninsular Malaysia and neighbouring areas. UKM: 26-42.

Bignell, J. D. & Snelling, N. J. 1977. Geochronology of Malayan Granites. Overseas Geology and Mineral Resources, Institute of Geological Sciences. London.

Chengyu Wu & Ishihara, S. 1994. REE geochemistry of the Southern Thailand granites. Jour. Southeast Asian Earth Sciences 10: 81-94.

Gromet, L. P. & Silver, L. T. 1983. Rare earth element distributions among accessory minerals in a granodiorite and their petrogenetic implications. Geochim. Cosmochim. Acta 47: 925 - 939.

Hutchison, C. S., & Leow, J. H. 1963. Tourmaline greisenization in Langkawi, northwest Malaya. Econ. Geol. 58: 587-592.

Jones, C. R., 1981. Geology and Mineral Resources of Perlis, North Kedah and Langkawi Islands. Geological Survey Malaysia District Memoir 17: 257 p.

Khoo, T. T. 1981. Tourmaline greisenization in Langkawi - a reinterpetation using the available composition model. Bull. Geol. Soc. Malaysia 14: 135-141.

Lee, C. P. 1983. Stratigraphy of the Turatao and Machinchang formations. Proc. Strat. Correlation of Thailand and Malaysia. Geol. Soc. Malaysia: 20-38.

Liew, T. C. 1983. Petrogenesis of the Peninsular Malaysia granitoid batholiths. Ph.D. thesis, Australian National University.

Mahawat, C., Atherton, M. P. & Brotherton, M. S. 1989. The Tak Batholith: contrasting granites types and implication for tectonic setting. Jour. Southeast Asian Earth Sci. 4: 11-27.

Mahood, G. A. & Hildreth, W. 1983. Large partition coeffients for trace elements in high silica rhyolites. Geochim. Cosmochim. Acta 47: 2537-2545.

Miller, C. F. 1985. Are strongly peraluminous magmas derived from pelitic sedimentary sources? Journal of Geology 93: 673-689.

Mitchell, A. H. G. 1977. Tectonic settings for the emplacement of Southeast Asian tin granites. Bul. Geol. Soc. Malaysia 9: 123-140.

Nash, W. P. & Crecraft, H. R. 1985. Partition coefficients for the trace elements in silicic magmas. Geochim. Cosmochim. Acta 49: 2309-2322.

Petford, & Atherton, M. P. 1996. Na-rich partial melts from newly underplated basaltic crust: the Cordillera Blanca batholith. Peru. Jour. Petrol. 37 (6): 1491 -1521.

Streckeisen, A. L. 1976. To each plutonic rock its proper name. Earth Sci. Rev. 12: 1-33.

Wakita, H., Rey, P. & Schmitt, R. A. 1971. Abundances of the 14 rare earth elements and 12 other trace elements in Apollo 12 samples and one breccia rocks and four soils. Proc. 2nd Lunar Sci. Can. Oxford: Pergamon Press, 1319-1329.

Wan Fuad Wan Hassan & Mohd Suhaimi Hamzah. 1998. Rare earth element patterns in some granitic rocks of peninsular Malaysia. GEOSEA '98- Ninth Regional Congress on Geology, Mineral and Energy Resources of Southeast Asia, Kuala Lumpur August, Abstract: 196-197.

Wan Fuad Wan Hassan. 1999. Pasir Hitam di Kepulauan Langkawi. In Ibrahim Komoo & Mohd Shafeea Leman (ed.), Warisan Geologi Malaysia: Geologi Pemuliharaan dan Pembangunan Ceotop. Bangi: Lestari, Universiti Kebangsaan Malaysia, 119-131.

Yeap, C. H. 1980. A comparative study of Peninsular Malaysian granites with special reference to tin-mineralization. Ph.D thesis. Department of Geology, Universiti Malaya.

Yeap, C. H. 1974. Some trace element analysis of West Malaysian and Singapore granites. Geol. Soc. Malaysia Newsletter 47: 1-5.

 

 

 
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