Bulletin of the Geological Society of Malaysia, Volume 31, July 1992, pp. 113 – 131
School of Physics, Universiti Sains Malaysia, Penang.
*Petroleum Research Institute, Hulu Kelang, Selangor.
**Dept. of Geology, Universiti Kebangsaan Malaysia, Bangi.
***Dept. of Earth Science, Universiti Kebangsaan Malaysia, Sabah Campus, Kota Kinabalu.
Abstract: The volcanic mountains crowned by the peaks Magdalena (1,320 m), Lucia (1,210 m), and Maria (1,090 m) consist of Quaternary pyroclastics and lava flows of dacitic, andesitic and basaltic character. Some of these products have become silicified, probably through hydrothermal action. High silica content is also evident in the “basaltic” and “andesitic” volcanic rocks that we analysed. On the other hand, nephelinite was determined among the basaltic rock of Bukit Tiger. Evidence of the most recent volcanicity consists of a 24 ka old carbonised tree trunk embedded in a lava flow. In spite of its geologic youth, the complex, including the extensive lava surfaces, is transacted by numerous long lineaments that occur either as single strands or as zones several kilometres wide. Common lineament directions are 340°, approximately north, 10-15°, 75°, and east. Several of the volcanic peaks are also aligned along three of the mentioned directions, spanning distances between 4 km and 22 km. Along a few northerly trending lineaments, normal faulting downthrowing to the west, is suggested by triangular facets (more than a hundred metres high) and scarps facing west. A major fault zone, 3 km across and traceable over almost 30 km is indicated by strongly developed lineaments trending approximately 10° across Mount Magdalena. This interpreted fault zone is transacted by many east-striking lineaments that reach lengths of 5 km.
Indications of widespread hydrothermal processes affecting the volcanic rocks of the Taman Bukit Tawau area suggest the occurrence of mineralisation and geothermal sources. The lineament map of the Lucia-Maria-Magdalena complex may prove useful for delineating mineralisation targets and geothermal centres.
Abstrak: Pergunungan volkano yang berkemuncak Magdalena (1,320 m), Lucia (1,210 m) dan Maria (1,090 m) terdiri daripada piroklas serta aliran lava dasit, andesit dan basalt yang berumur Kuaterner. Sebahagian daripada batuan tersebut telah menjadi kaya dengan silika, mungkin kerana tindakan hidrotermal. Contoh batuan yang kononnya bersifat “basalt” dan “andesit” didapati berkadar silika melebihi 60 peratus. Sebaliknya, di antara basalt Bukit Tiger telah dikenal batuan nefelinit. Petunjuk aktiviti volkano yang paling muda ialah batang pokok terkarbon dan berumur 24 ka di antara aliran lava. Walaupun batuan Taman Bukit Tawau begitu muda, namun seluruh kawasan, termasuk permukaan lava yang luas, direntasi banyak lineament panjang yang wujud sebagai utas tunggal atau sebagai zon berkelebaran beberapa kilometer. Arah lineamen yang umum adalah 340°, hampir utara, 10-15°, 75° dan timur. Sejumlah kemuncak volkano juga menunjukkan kedudukan sepanjang tiga arah lineamen yang tersebut, dan mencapai jarak antara 4 km dan 22 km. Beberapa sesar normal dengan bongkah sesar sebelah barat yang menurun, didapati berjurus mengutara dan ditandai faset segitiga menghadap ke barat dan juga oleh tubir. Sebatang zon sesar utama berkelebaran 3 km dan yang boleh dikesan sejauh hampir 30 km ditandai lineamen jelas berjurus sekitar 10° memotong tubuh Gunung Magdalena. Zon sesar ini pula dipotong oleh banyak lineamen menjurus ke timur; setiap; satu zon boleh berkepanjangan hingga 5 km. Petunjuk mengenai tindakan hidrotermal yang meluas di Taman Bukit Tawau mencadangkan kemungkinan wujudnya permineralan dan punca geotermal di sana. Peta lineamen daripada komplek Lucia-Maria-Magdalena akan berguna bagi menentukan sasaran permineralan dan pusat geotermal.
https://doi.org/10.7186/bgsm31199208
