Magnetic characteristics of the rock formations on Mount Kinabalu, Sabah

Abstract

Mount Kinabalu consists of granites at its core on the higher ground of the mountain, and is surrounded by sedimentary rocks of Trusmadi formations at its foot, with the occurrences of serpentinised ultrabasic rocks found between the granites and sedimentary rock at the elevation of 2000m to 2800m. The granite is subdivided into hornblende granite, biotite granite and porphyritic granite. The porphyritic granite is found in a belt between serpentinite in the lower part and hornblende granite in the upper part of the mountain. A ground magnetic data acquisition was conducted in May 2013 along the tracks from Mesilau to the summit of Mount Kinabalu and from summit down at Timpohon gate. The processed magnetic data shows distinctive magnetic characteristics that correlate very well with three different rock formations of Mount Kinabalu. Large variations of total magnetic total field from 39400nT to 41700 nT (magnetic variation range of 2300nT) were observed within the serpentinised ultrabasic rocks. It is believed that this distinctive magnetic characteristic is due to occurrence of ferromagnetic minerals, which was formed as a result of serpentinisation of ultrabasic rock with the presence of water during deep seated hydrothermal activity. The total magnetic field within the granite zone decreased gradually from the edge of serpentinite to the hornblend granite near the summit with relatively smaller variations from 40900nT to 39990nT (magnetic variation range of 910nT), probably due to small percentage of magnetite in it. The Trusmadi sedimentary formation in lower altitudes was magnetically "stable", with the small magnetic variation from 40000nT to 40385 nT (magnetic variation range of 385nT).