HR: 1340h
AN: GP13A-0028    [Abstracts]
TI: Magnetic Properties and the Classification of Igneous Rocks: A Case Study of the Old Andesites from Java, Indonesia
AU: * Bijaksana, S
EM: satria@fi.itb.ac.id
AF: Department of Physics Institut Teknologi Bandung, Jalan Ganesa 10, Bandung, 40132 Indonesia
AU: Ngkoimani, L O
EM: ngkoi@sains.fisika.net
AF: Department of Physics Institut Teknologi Bandung, Jalan Ganesa 10, Bandung, 40132 Indonesia
AU: Abdullah, C I
EM: chalid@gc.itb.ac.id
AF: Department of Geology Institut Teknologi Bandung, Jalan Ganesa 10, Bandung, 40132 Indonesia
AU: The, H L
EM: the@fi.itb.ac.id
AF: Department of Physics Institut Teknologi Bandung, Jalan Ganesa 10, Bandung, 40132 Indonesia
AB: While conducting paleomagnetic and geochronological studies of the Old Andesites from Java, Indonesia, we found that magnetic parameters correlate well with certain geochemical parameters. The term Old Andesites is referred to the products of subduction zones underneath Sumatera, Java, and the Lesser Sunda Islands. Samples used in this study were taken mainly from sites that are distributed in Central and East Java. According the existing literature, the samples are referred to as andesitic lavas and intrusions. K-Ar dating by us and previous workers show that the sites are Miocene to Late Cretaceous in age. We tried to correlate rock magnetic parameters (natural remanent intensity, saturation remanence, DC susceptibility and anhysteretic susceptibility) with chemical compositions, i.e., content of SiO2, TiO2, Fe2O3, MgO and Al2O3. We found that SiO2 and MgO contents correlate well with the magnetic parameters. As SiO2 increases, saturation remanence and anhysteretic susceptibility increases but natural remanent intensity and DC susceptibility decreases. Meanwhile, as MgO increases, natural remanent intensity and DC susceptibility increases but saturation remanence and anhysteretic susceptibility decreases. Other mineral contents, however, correlate only partially with the magnetic parameters. These correlations between geochemical parameters and magnetic parameters facilitate the possibility of using magnetic parameters in classifying igneous rocks.
DE: 1512 Environmental magnetism
DE: 1518 Magnetic fabrics and anisotropy
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
DE: 1599 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005